Vitamins – Vitamin B3 (Niacin) – part 13

Niacin (also known as vitamin B3, nicotinic acid and vitamin PP) is an organic compound with the formula C6H5NO2 and, depending on the definition used, one of the 40 to 80 essential human nutrients.

Niacin is one of five vitamins (when lacking in human diet) associated with a pandemic deficiency disease: niacin deficiency (pellagra), vitamin C deficiency (scurvy), thiamin deficiency (beriberi), vitamin D deficiency (rickets), vitamin A deficiency (night blindness and other symptoms). Niacin has been used for over 50 years to increase levels of HDL in the blood and has been found to modestly decrease the risk of cardiovascular events in a number of controlled human trials.

This colorless, water-soluble solid is a derivative of pyridine, with a carboxyl group (COOH) at the 3-position. Other forms of vitamin B3 include the corresponding amide, nicotinamide (“niacinamide”), where the carboxyl group has been replaced by a carboxamide group (CONH2), as well as more complex amides and a variety of esters.

Niacin cannot be directly converted to nicotinamide, but both compounds could be converted to NAD and NADP in vivo. Although the two are identical in their vitamin activity, nicotinamide does not have the same pharmacological effects (lipid modifying effects) as niacin. Nicotinamide does not reduce cholesterol or cause flushing. Nicotinamide may be toxic to the liver at doses exceeding 3 g/day for adults. Niacin is a precursor to NAD+/NADH and NADP+/NADPH, which play essential metabolic roles in living cells.Niacin is involved in both DNA repair, and the production of steroid hormones in the adrenal gland.


Niacin
Identifiers
CAS number 59-67-6 
PubChem 938
ChemSpider 913 
UNII 2679MF687A 
EC number 200-441-0
DrugBank DB00627
KEGG D00049 
MeSH Niacin
ChEBI CHEBI:15940 
ChEMBL CHEMBL573 
IUPHAR ligand 1588
RTECS number QT0525000
ATC code C04AC01,C10AD02
Beilstein Reference 109591
Gmelin Reference 3340
3DMet B00073
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C6NH5O2
Molar mass 123.1094 g mol-1
Appearance White, translucent crystals
Density 1.473 g cm-3
Melting point 237 °C, 510 K, 458 °F
Solubility in water 18 g L-1
log P 0.219
Acidity (pKa) 2.201
Basicity (pKb) 11.796
Isoelectric point 4.75
Refractive index (nD) 1.4936
Dipole moment 0.1271305813 D
Thermochemistry
Std enthalpy of
formation
ΔfHo298
-344.9 kJ mol-1
Std enthalpy of
combustion
ΔcHo298
-2.73083 MJ mol-1
Pharmacology
Routes of
administration
Intramuscular, Oral
Elimination
half-life
20-45 min
Hazards
EU classification Irritant Xi
R-phrases R36/37/38
S-phrases S26, S36
NFPA 704
NFPA 704.svg
1
1
0
Flash point 193 °C
Autoignition
temperature
365 °C

Dietary needs

One recommended daily allowance of niacin is 2–12 mg/day for children, 14 mg/day for women, 16 mg/day for men, and 18 mg/day for pregnant or breast-feeding women. Tolerable upper intake levels (UL) for adult men and women is considered to be 35 mg/day by the Dietary Reference Intake system to avoid flushing. In general, niacin status is tested through urinary biomarkers, which are believed to be more reliable than plasma levels.

Deficiency(Pellagra)

A man with pellagra, which is caused by a chronic lack of vitamin B3 in the diet

At present, niacin deficiency is sometimes seen in developed countries, and it is usually apparent in conditions of poverty, malnutrition, and chronic alcoholism. It also tends to occur in areas where people eat maize (corn, the only grain low in digestible niacin) as a staple food. A special cooking technique called nixtamalization is needed to increase the bioavailability of niacin during maize meal/flour production.

Mild niacin deficiency has been shown to slow metabolism, causing decreased tolerance to cold.

Severe deficiency of niacin in the diet causes the disease pellagra, which is characterized by diarrhea, dermatitis, and dementia, as well as “necklace” lesions on the lower neck, hyperpigmentation, thickening of the skin, inflammation of the mouth and tongue, digestive disturbances, amnesia, delirium, and eventually death, if left untreated. Common psychiatric symptoms of niacin deficiency include irritability, poor concentration, anxiety, fatigue, restlessness, apathy, and depression. Studies have indicated that, in patients with alcoholic pellagra, niacin deficiency may be an important factor influencing both the onset and severity of this condition. Patients with alcoholism typically experience increased intestinal permeability, leading to negative health outcomes.

Hartnup’s disease is a hereditary nutritional disorder resulting in niacin deficiency. This condition was first identified in the 1950s by the Hartnup family in London. It is due to a deficit in the intestines and kidneys, making it difficult for the body to break down and absorb dietary tryptophan. The resulting condition is similar to pellagra, including symptoms of red, scaly rash, and sensitivity to sunlight. Oral niacin is given as a treatment for this condition in doses ranging from 40–200 mg, with a good prognosis if identified and treated early. Niacin synthesis is also deficient in carcinoid syndrome, because of metabolic diversion of its precursor tryptophan to form serotonin.

Lipid-modifying effects

Niacin binds to and stimulates a G-protein-coupled receptor, GPR109A, which causes the inhibition of fat breakdown in adipose tissue. Nicotinamide does not bind this receptor which explains why it does not affect blood lipid levels. Lipids that are liberated from adipose tissue are normally used to build very-low-density lipoproteins (VLDL) in the liver, which are precursors of low-density lipoprotein (LDL) or “bad” cholesterol. Because niacin blocks the breakdown of fats, it causes a decrease in free fatty acids in the blood and, as a consequence, decreases the secretion of VLDL and cholesterol by the liver.

By lowering VLDL levels, niacin also increases the level of high-density lipoprotein (HDL) or “good” cholesterol in blood, and therefore it is sometimes prescribed for people with low HDL, who are also at high risk of a heart attack.

The ARBITER 6-HALTS study, reported at the 2009 annual meeting of the American Heart Association and in the New England Journal of Medicine concluded that, when added to statins, 2000 mg/day of extended-release niacin was more effective than ezetimibe (Zetia) in reducing carotid intima-media thickness, a marker of atherosclerosis. Additionally, a recent meta-analysis covering 11 randomized controlled clinical trials found positive effects of niacin alone or in combination on all cardiovascular events and on atherosclerosis evolution.

However, a 2011 study (AIM-HIGH) was halted early because patients showed no decrease in cardiovascular events, but did experience an increase in the risk of stroke. These patients already had LDL levels well controlled by a statin drug, and the aim of the study was to evaluate extended-release niacin (2000 mg per day) to see if raising HDL levels had an additional positive effect on risk. In this study, it did not have such an effect, and appeared to increase stroke risk. The role of niacin in patients whose LDL is not well-controlled (as in the majority of previous studies with niacin) is still under study and debate. However, it does not seem to offer benefits via raising HDL, in patients already lowering LDL by taking a statin.

Toxicity

Pharmacological doses of niacin (1.5 – 6 g per day) lead to side effects that can include dermatological conditions such as skin flushing and itching, dry skin, and skin rashes including eczema exacerbation and acanthosis nigricans. Some of these symptoms are generally related to niacin’s role as the rate limiting cofactor in the histidine decarboxylase enzyme which converts l-histidine into histamine. H1 and H2 receptor mediated histamine is metabolized via a sequence of mono (or di-) amine oxidase and COMT into methylhistamine which is then conjugated through the liver’s CYP450 pathways. Persistent flushing and other symptoms may indicate deficiencies in one or more of the cofactors responsible for this enzymatic cascade. Gastrointestinal complaints, such as dyspepsia (indigestion), nausea and liver toxicity fulminant hepatic failure, have also been reported. Side effects of hyperglycemia, cardiac arrhythmias and “birth defects in experimental animals” have also been reported.

Flushing lasts for about 15 to 30 minutes, and is sometimes accompanied by a prickly or itching sensation, in particular, in areas covered by clothing. This effect is mediated by GPR109A-mediated prostaglandin release from the Langerhans cells of the skin and can be blocked by taking 300 mg of aspirin half an hour before taking niacin, by taking one tablet of ibuprofen per day or by co-administering the prostaglandin receptor antagonist laropiprant. Taking the niacin with meals also helps reduce this side effect. After several weeks of a consistent dose, most patients no longer flush. Slow- or “sustained”-release forms of niacin have been developed to lessen these side effects. One study showed the incidence of flushing was significantly lower with a sustained release formulation though doses above 2 g per day have been associated with liver damage, in particular, with slow-release formulations. Flushing is often thought to involve histamine, but histamine has been shown not to be involved in the reaction.Prostaglandin (PGD2) is the primary cause of the flushing reaction, with serotonin appearing to have a secondary role in this reaction.

Although high doses of niacin may elevate blood sugar, thereby worsening diabetes mellitus, recent studies show the actual effect on blood sugar to be only 5–10%. Patients with diabetes who continued to take anti-diabetes drugs containing niacin did not experience major blood glucose changes. Thus looking at the big picture, niacin continues to be recommended as a drug for preventing cardiovascular disease in patients with diabetes.

Hyperuricemia is another side effect of taking high-dose niacin, and may exacerbate gout.

Niacin in doses used to lower cholesterol levels has been associated with birth defects in laboratory animals, with possible consequences for infant development in pregnant women.

Niacin, particularly the time-release variety, at extremely high doses can cause acute toxic reactions. Extremely high doses of niacin can also cause niacin maculopathy, a thickening of the macula and retina, which leads to blurred vision and blindness. This maculopathy is reversible after niacin intake ceases.

Nicotinamide

Nicotinamide may be obtained from the diet where it is present primarily as NAD+ and NADP+. These are hydrolysed in the intestine and the resulting nicotinamide is absorbed either as such, or following its hydrolysis to nicotinic acid. Nicotinamide is present in nature in only small amounts. In unprepared foods, niacin is present mainly in the form of the cellular pyridine nucleotides NAD and NADP. Enzymatic hydrolysis of the co-enzymes can occur during the course of food preparation. Boiling releases most of the total niacin present in sweet corn as nicotinamide (up to 55 mg/kg).

Inositol hexanicotinate

One form of dietary supplement is inositol hexanicotinate (IHN), which is inositol that has been esterified with niacin on all six of inositol’s alcohol groups. IHN is usually sold as “flush-free” or “no-flush” niacin in units of 250, 500, or 1000 mg/tablets or capsules. It is sold as an over-the-counter formulation, and often is marketed and labeled as niacin, thus misleading consumers into thinking they are getting the active form of the medication. While this form of niacin does not cause the flushing associated with the immediate-release products, the evidence that it has lipid-modifying functions is contradictory, at best. As the clinical trials date from the early 1960s (Dorner, Welsh) or the late 1970s (Ziliotto, Kruse, Agusti), it is difficult to assess them by today’s standards. One of the last of those studies affirmed the superiority of inositol and xantinol esters of nicotinic acid for reducing serum free fatty acid, but other studies conducted during the same period found no benefit. Studies explain that this is primarily because “flush-free” preparations do not contain any free nicotinic acid. A more recent placebo-controlled trial was small (n=11/group), but results after three months at 1500 mg/day showed no trend for improvements in total cholesterol, LDL-C, HDL-C or triglycerides. Thus, so far there is not enough evidence to recommend IHN to treat dyslipidemia. Furthermore, the American Heart Association and the National Cholesterol Education Program both take the position that only prescription niacin should be used to treat dyslipidemias, and only under the management of a physician. The reason given is that niacin at effective intakes of 1500–3000 mg/day can also potentially have severe adverse effects. Thus liver function tests to monitor liver enzymes are necessary when taking therapeutic doses of niacin, including alkaline phosphatase (ALP), aspartate transaminase (AST), and alanine transaminase (ALT).

Biosynthesis and chemical synthesis

Biosynthesis

The liver can synthesize niacin from the essential amino acid tryptophan, requiring 60 mg of tryptophan to make one mg of niacin.The 5-membered aromatic heterocycle of tryptophan is cleaved and rearranged with the alpha amino group of tryptophan into the 6-membered aromatic heterocycle of niacin. Riboflavin, vitamin B6 and iron are required in some of the reactions involved in the conversion of tryptophan to NAD.

Several million kilograms of niacin are manufactured each year, starting from 3-methylpyridine.

Receptor

In addition to its effects as NAD and NADP, niacin may have additional effects by receptor activation. The receptor for niacin is a G protein-coupled receptor called HM74A. It couples to the Gi alpha subunit.

Food sources

Niacin is found in variety of foods, including liver, chicken, beef, fish, cereal, peanuts and legumes, and is also synthesized from tryptophan, an essential amino acid found in most forms of protein.

Animal products:

Fruits and vegetables:

Seeds:

Fungi:

Other:

History

Niacin was first described by chemist Hugo Weidel in 1873 in his studies of nicotine. The original preparation remains useful: The oxidation of nicotine using nitric acid. Niacin was extracted from livers by biochemist Conrad Elvehjem in 1937, who later identified the active ingredient, then referred to as the “pellagra-preventing factor” and the “anti-blacktongue factor.” Soon after, in studies conducted in Alabama and Cincinnati, Dr. Tom Spies found that nicotinic acid cured the sufferers of pellagra.

When the biological significance of nicotinic acid was realized, it was thought appropriate to choose a name to dissociate it from nicotine, to avoid the perception that vitamins or niacin-rich food contains nicotine, or that cigarettes contain vitamins. The resulting name ‘niacin’ was derived from nicotinic acid + vitamin.

Carpenter found in 1951 that niacin in corn is biologically unavailable, and can be released only in very alkaline lime water of pH 11. This process, known as nixtamalization, was discovered by the prehistoric civilizations of Mesoamerica.

Niacin is referred to as vitamin B3 because it was the third of the B vitamins to be discovered. It has historically been referred to as “vitamin PP” or “vitamin P-P”.

Research

As of August 2008, a combination of niacin with laropiprant is being tested in a clinical trial. Laropiprant reduces facial flushes induced by niacin.

source: http://en.wikipedia.org/wiki/Niacin

Vitamins – Vitamin B9 (Folic Acid) – part 14

Folic acid (also known as folate, vitamin M, vitamin B9, vitamin Bc (or folacin), pteroyl-L-glutamic acid, pteroyl-L-glutamate, and pteroylmonoglutamic acid) are forms of the water-soluble vitamin B9. Folic acid is itself not biologically active, but its biological importance is due to tetrahydrofolate and other derivatives after its conversion to dihydrofolic acid in the liver.

Vitamin B9 (folic acid and folate) is essential to numerous bodily functions. The human body needs folate to synthesize DNA, repair DNA, and methylate DNA as well as to act as a cofactor in certain biological reactions. It is especially important in aiding rapid cell division and growth, such as in infancy and pregnancy. Children and adults both require folic acid to produce healthy red blood cells and prevent anemia.

Folate and folic acid derive their names from the Latin word folium (which means “leaf”). Leafy vegetables are principal sources of folic acid, although in Western diets fortified cereals and bread may be a larger dietary source.

A lack of dietary folates leads to folate deficiency, which is uncommon in normal Western diets. A complete lack of dietary folate takes months before deficiency develops as normal individuals have about 500–20,000 µg of folate in body stores.This deficiency can result in many health problems, the most notable one being neural tube defects in developing embryos. Common symptoms of folate deficiency include diarrhea, macrocytic anemia with weakness or shortness of breath, nerve damage with weakness and limb numbness (peripheral neuropathy), pregnancy complications, mental confusion, forgetfulness or other cognitive declines, mental depression, sore or swollen tongue, peptic or mouth ulcers, headaches, heart palpitations, irritability, and behavioral disorders. Low levels of folate can also lead to homocysteine accumulation. DNA synthesis and repair are impaired and this could lead to cancer development.

Folic acid
Skeletal formula
Ball-and-stick model
Space-filling model
Folic acid as an orange powder
Identifiers
CAS number 59-30-3 
PubChem 6037
ChemSpider 5815 
UNII 935E97BOY8 
DrugBank DB00158
KEGG C00504 
ChEBI CHEBI:27470 
ChEMBL CHEMBL1622 
RTECS number LP5425000
ATC code B03BB01
Jmol-3D images Image 1
Properties
Molecular formula C19H19N7O6
Molar mass 441.4 g mol−1
Appearance yellow-orange crystalline powder
Melting point 250 °C (523 K), decomp.
Solubility in water 1.6 mg/L (25 °C)
Acidity (pKa) 1st: 4.65, 2nd: 6.75, 3rd: 9.00

Health benefits and risks

Pregnancy

Adequate folate intake during the preconception period (which is the time right before and just after a woman becomes pregnant) helps protect against a number of congenital malformations, including neural tube defects (which are the most notable birth defects that occur from folate deficiency). Neural tube defects produce malformations of the spine, skull, and brain including spina bifida and anencephaly. The risk of neural tube defects is significantly reduced when supplemental folic acid is consumed in addition to a healthy diet before conception and during the first month after conception. Supplementation with folic acid has also been shown to reduce the risk of congenital heart defects, cleft lips, limb defects, and urinary tract anomalies. Folate deficiency during pregnancy may also increase the risk of preterm delivery, infant low birth weight and fetal growth retardation, as well as increasing homocysteine level in the blood, which may lead to spontaneous abortion and pregnancy complications, such as placental abruption and pre-eclampsia. Women who could become pregnant are advised to eat foods fortified with folic acid or take supplements in addition to eating folate-rich foods to reduce the risk of serious birth defects. Taking 400 micrograms of synthetic folic acid daily from fortified foods and/or supplements has been suggested for all non-pregnant women, in order to have adequate folic acid intake even in case of unplanned pregnancies. The RDA for folate equivalents for pregnant women vary widely, from 400 micrograms up to 4 milligrams (4000 micrograms) in an old U.S. Public Health Service guideline that is still followed by many health care providers, despite evidence that such high dose is as effective as 400 micrograms. The mechanisms and reasons why folic acid prevents birth defects is unknown. It is hypothesized that the insulin-like growth factor 2 gene is differentially methylated and these changes in IGF2 result in improved intrauterine growth and development. Approximately 85% of women in an urban Irish study reported using folic acid supplements before they become pregnant, but only 18% used enough folic acid supplements to meet the current folic acid requirements due, it is reported, to socio-economic challenges. Folic acid supplements may also protect the fetus against disease when the mother is battling a disease or taking medications or smoking during pregnancy.

It also contributes to oocyte maturation, implantation, placentation, in addition to the general effects of folic acid and pregnancy. Therefore, it is necessary to receive sufficient amounts through the diet to avoid subfertility.

There is growing concern worldwide that prenatal high folic acid in the presence of low vitamin b12 causes epigenetic changes in the unborn predisposing them to metabolic syndromes, central adiposity and adult diseases such as Type 2 diabetes. Another active area of research and concern is that excess folic acid in utero causes epigenetic changes to the brain leading to autism spectrum disorders.

Sperm quality

Folic acid may also reduce chromosomal defects in sperm. A benefit is indicated even for more than 700 µg folate per day, which, though below the tolerable upper intake levels of 1,000 µg/day, was 1.8 times the recommended dietary allowance. Folate is necessary for fertility in both men and women. It contributes to spermatogenesis. Therefore, it is necessary to receive sufficient amounts through the diet to avoid subfertility. Also, polymorphisms in genes of enzymes involved in folate metabolism could be one reason for fertility complications in some women with unexplained infertility.

Heart disease

Taking folic acid does not reduce cardiovascular disease even though it reduces homocysteine levels.

Folic acid supplements consumed before and during pregnancy may reduce the risk of heart defects in infants, and may reduce the risk for children to develop metabolic syndrome. That may, however, worsen the outcomes in people with cardiovascular disease such as angina and myocardial infarction.

Stroke

Folic acid appears to reduce the risk of stroke. The reviews indicate the risk of stroke appears to be reduced only in some individuals, but a definite recommendation regarding supplementation beyond the current RDA has not been established for stroke prevention.Observed stroke reduction is consistent with the reduction in pulse pressure produced by folate supplementation of 5 mg per day, since hypertension is a key risk factor for stroke. Folic supplements are inexpensive and relatively safe to use, which is why stroke or hyperhomocysteinemia patients are encouraged to consume daily B vitamins including folic acid.

Cancer

Many cancer cells have a high requirement for folic acid and overexpress the folic acid receptor. This finding has led to the development of anti-cancer drugs that target the folic acid receptor.

A meta-analysis published in 2010 failed to find a statistically significant cancer risk due to folic acid supplements.

Some investigations have proposed good levels of folic acid may be related to lower risk of esophageal, stomach, and ovarian cancers, but the benefits of folic acid against cancer may depend on when it is taken and on individual conditions. In addition, folic acid may not be helpful, and could even be damaging, in people already suffering from cancer or from a precancerous condition. Likewise, it has been suggested excess folate may promote tumor initiation. Folate has shown to play a dual role in cancer development; low folate intake protects against early carcinogenesis, and high folate intake promotes advanced carcinogenesis. Therefore, public health recommendations should be careful not to encourage too much folate intake.

Diets high in folate are associated with decreased risk of colorectal cancer; some studies show the association is stronger for folate from foods alone than for folate from foods and supplements, Colorectal cancer is the most studied type of cancer in relation to folate and one carbon metabolism. One study concluded that there was not strong support for an association between prostate cancer risk and circulating concentrations of folate or vitamin B12. The researchers noted that while elevated concentrations of vitamin B12 may be associated with an increased risk for advanced stage prostate cancer, that this was not true of folic acid and that the association between B12 and cancer risk required examination in other large prospective studies.

Most epidemiologic studies suggest diets high in folate are associated with decreased risk of breast cancer, but results are not uniformly consistent. One broad cancer screening trial reported a potential harmful effect of much folate intake on breast cancer risk, suggesting routine folate supplementation should not be recommended as a breast cancer preventive, but a 2007 Swedish prospective study found much folate intake was associated with a lower incidence of postmenopausal breast cancer. A 2008 study has shown no significant effect of folic acid on overall risk of total invasive cancer or breast cancer among women. Folate intake may not have any effect on the risk of breast cancer but may have an effect for women who consume at least 15 g/d of alcohol. Folate intake of more than 300 µg/d may reduce the risk of breast cancer in women who consume alcohol.

Most research studies associate high dietary folate intake with a reduced risk of prostate cancer.Recently, a clinical trial showed daily supplementation of 1 mg of folic acid increased the risk of prostate cancer, while dietary and plasma folate levels among vitamin nonusers actually decreased the risk of prostate cancer. A Finnish study consisting of 29,133 older male smokers observed prostate cancer risk had no relationship with serum folate levels.

A 2013 study suggested that folate intake might be beneficial in the prevention of alcohol-associated hepatocellular carcinoma.

Antifolates

Folate is important for cells and tissues that rapidly divide. Cancer cells divide rapidly, and drugs that interfere with folate metabolism are used to treat cancer. The antifolate methotrexate is a drug often used to treat cancer because it inhibits the production of the active form of THF from the inactive dihydrofolate (DHF). However, methotrexate can be toxic, producing side effects, such as inflammation in the digestive tract that make it difficult to eat normally. Also, bone marrow depression (inducing leukopenia and thrombocytopenia), and acute renal and hepatic failure have been reported.

Folinic acid, under the drug name leucovorin, a form of folate (formyl-THF), can help “rescue” or reverse the toxic effects of methotrexate. Folinic acid is not the same as folic acid. Folic acid supplements have little established role in cancer chemotherapy. There have been cases of severe adverse effects of accidental substitution of folic acid for folinic acid in patients receiving methotrexate cancer chemotherapy. It is important for anyone receiving methotrexate to follow medical advice on the use of folic or folinic acid supplements. The supplement of folinic acid in patients undergoing methotrexate treatment is to give cells dividing less rapidly enough folate to maintain normal cell functions. The amount of folate given will be depleted by rapidly dividing cells (cancer) very fast and so will not negate the effects of methotrexate.

Psychological

Some evidence links a shortage of folate with depression. Limited evidence from randomised controlled trials showed using folic acid in addition to antidepressants, to be specific SSRIs, may have benefits. Research at the University of York and Hull York Medical School has found a link between depression and low levels of folate. One study by the same team involved 15,315 subjects. However, the evidence is probably too limited at present for this to be a routine treatment recommendation. Folic acid supplementation affects noradrenaline and serotonin receptors within the brain, which could be the cause of folic acid’s possible ability to act as an antidepressant.

The exact mechanisms involved in the development of schizophrenia are not entirely clear, but may have something to do with DNA methylation and one carbon metabolism, and these are the precise roles of folate in the body.

Macular degeneration

A substudy of the Women’s Antioxidant and Folic Acid Cardiovascular Study published in 2009 reported use of a nutritional supplement containing folic acid, pyridoxine, and cyanocobalamin decreased the risk of developing age-related macular degeneration by 34.7%.

Folic Acid, B12 and Iron

There is a complex interaction between folic acid, vitamin B12 and iron. A deficiency of one may be “masked” by excess of another so the three must be in balance.

Toxicity

The risk of toxicity from folic acid is low, because folate is a water-soluble vitamin and is regularly removed from the body through urine. One potential issue associated with high dosages of folic acid is that is has a masking effect on the diagnosis of pernicious anaemia (vitamin B12 deficiency), and a variety of concerns of potential negative impacts on health.

Folate deficiency (Folate deficiency)

Folate deficiency may lead to glossitis, diarrhea, depression, confusion, anemia, and fetal neural tube defects and brain defects (during pregnancy). Folate deficiency is accelerated by alcohol consumption. Folate deficiency is diagnosed by analyzing CBC and plasma vitamin B12 and folate levels. CBC may indicate megaloblastic anemia but this could also be a sign of vitamin B12 deficiency. A serum folate of 3 μg/L or lower indicates deficiency. Serum folate level reflects folate status but erythrocyte folate level better reflects tissue stores after intake. An erythrocyte folate level of 140 μg/L or lower indicates inadequate folate status. Increased homocysteine level suggests tissue folate deficiency but homocysteine is also affected by vitamin B12 and vitamin B6, renal function, and genetics. One way to differentiate between folate deficiency from vitamin B12 deficiency is by testing for methylmalonic acid levels. Normal MMA levels indicate folate deficiency and elevated MMA levels indicate vitamin B12 deficiency. Folate deficiency is treated with supplemental oral folate of 400 to 1000 μg per day. This treatment is very successful in replenishing tissues, even if deficiency was caused by malabsorption. Patients with megaloblastic anemia need to be tested for vitamin B12 deficiency before folate treatment, because if the patient has vitamin B12 deficiency, folate supplementation can remove the anemia, but can also worsen neurologic problems. Morbidly obese patients with BMIs of greater than 50 are more likely to develop folate deficiency Patients with celiac disease have a higher chance of developing folate deficiency. Cobalamin deficiency may lead to folate deficiency, which, in turn, increases homocysteine levels and may result in the development of cardiovascular disease or birth defects.

Malaria

Some studies show iron-folic acid supplementation in children under 5 may result in increased mortality due to malaria; this has prompted the World Health Organization to alter their iron-folic acid supplementation policies for children in malaria-prone areas, such as India.

Aging

A study published in 2010 showed that folic acid has an effect on glycation in E. coli, which affords the cultures protection against higher sugar levels that normally lead to the death of the culture. The same study also showed that too much folic acid is toxic to cells. Because of this, the authors theorized that folic acid could potentially have an effect on aging since glycation tends to increase with age.

Dietary reference intake

Because of the difference in bioavailability between supplemented folic acid and the different forms of folate found in food, the dietary folate equivalent (DFE) system was established. One DFE is defined as 1 μg (microgram) of dietary folate, or 0.6 μg of folic acid supplement.

National Institutes of Health Nutritional Requirements (µg per day)
Age Infants (RDI) Infants (UL) Adults (RDI) Adults (UL) Pregnant women (RDI) Pregnant women (UL) Lactating women (RDI) Lactating women (UL)
0–6 months 65 None set
7–12 months 80 None set
1–3 years 150 300
4–8 years 200 400
9–13 years 300 600
14–18 400 800 600 800 500 800
19+ 400 1000 600 1000 500 1000

The Dietary Reference Intake (DRIs) were developed by the United States National Academy of Sciences to set reference values for planning and assessing nutrient intake for healthy people. DRIs incorporate two reference values, the Reference Daily Intake (RDI, the daily intake level that is adequate for 97–98% of the population in the United States where the standards were set) and tolerable upper intake levels (UL, the highest level of intake that is known to avoid toxicity). The UL for folate refers to only synthetic folate, as no health risks have been associated with high intake of folate from food sources.

Sources

Certain foods are very high in folate:

Moderate amounts:

A table of selected food sources of folate and folic acid can be found at the USDA National Nutrient Database for Standard Reference. Folic acid is added to grain products in many countries, and, in these countries, fortified products make up a significant source of the population’s folic acid intake. Because of the difference in bioavailability between supplemented folic acid and the different forms of folate found in food, the dietary folate equivalent (DFE) system was established. 1 DFE is defined as 1 μg of dietary folate, or 0.6 μg of folic acid supplement. This is reduced to 0.5 μg of folic acid if the supplement is taken on an empty stomach.

Folate naturally found in food is susceptible to high heat and ultraviolet light, and is soluble in water. It is heat-labile in acidic environments and may also be subject to oxidation.

Some meal replacement products do not meet the folate requirements as specified by the RDAs.

History

In the 1920s, scientists believed folate deficiency and anemia were the same condition. A key observation by researcher Lucy Wills in 1931 led to the identification of folate as the nutrient needed to prevent anemia during pregnancy. Dr. Wills demonstrated anemia could be reversed with brewer’s yeast. Folate was identified as the corrective substance in brewer’s yeast in the late 1930s, and was first isolated in and extracted from spinach leaves by Mitchell and others in 1941. Bob Stokstad isolated the pure crystalline form in 1943, and was able to determine its chemical structure while working at the Lederle Laboratories of the American Cyanamid Company. This historical research project, of obtaining folic acid in a pure crystalline form in 1945, was done by the team called the “folic acid boys,” under the supervision and guidance of Director of Research Dr. Yellapragada Subbarao, at the Lederle Lab, Pearl River, NY. This research subsequently led to the synthesis of the antifolate aminopterin, the first-ever anticancer drug, the clinical efficacy was proven by Sidney Farber in 1948. In the 1950s and 1960s, scientists began to discover the biochemical mechanisms of action for folate.In 1960, experts first linked folate deficiency to neural tube defects. In the late 1990s, US scientists realized, despite the availability of folate in foods and in supplements, there was still a challenge for people to meet their daily folate requirements, which is when the US implemented the folate fortification program.

Biological roles

A diagram of the chemical structure of folate

DNA and cell division

Folate is necessary for the production and maintenance of new cells, for DNA synthesis and RNA synthesis, and for preventing changes to DNA, and, thus, for preventing cancer. It is especially important during periods of frequent cell division and growth, such as infancy and pregnancy. Folate is needed to carry one-carbon groups for methylation reactions and nucleic acid synthesis (the most notable one being thymine, but also purine bases). Thus, folate deficiency hinders DNA synthesis and cell division, affecting hematopoietic cells and neoplasms the most because of their greater frequency of cell division. RNA transcription, and subsequent protein synthesis, are less affected by folate deficiency, as the mRNA can be recycled and used again (as opposed to DNA synthesis, where a new genomic copy must be created). Since folate deficiency limits cell division, erythropoiesis, production of red blood cells, is hindered and leads to megaloblastic anemia, which is characterized by large immature red blood cells. This pathology results from persistently thwarted attempts at normal DNA replication, DNA repair, and cell division, and produces abnormally large red cells called megaloblasts (and hypersegmented neutrophils) with abundant cytoplasm capable of RNA and protein synthesis, but with clumping and fragmentation of nuclear chromatin. Some of these large cells, although immature (reticulocytes), are released early from the marrow in an attempt to compensate for the anemia. Both adults and children need folate to make normal red and white blood cells and prevent anemia. Deficiency of folate in pregnant women has been implicated in neural tube defects (NTD); therefore, many developed countries have implemented mandatory folic acid fortification in cereals, etc. NTDs occur early in pregnancy (first month), therefore women must have abundant folate upon conception. Folate is required to make red blood cells and white blood cells and folate deficiency may lead to anemia, which further leads to fatigue and weakness and inability to concentrate.

Biochemistry of DNA base and amino acid production

Metabolism of folic acid to produce methyl-vitamin B12

In the form of a series of tetrahydrofolate (THF) compounds, folate derivatives are substrates in a number of single-carbon-transfer reactions, and also are involved in the synthesis of dTMP (2′-deoxythymidine-5′-phosphate) from dUMP (2′-deoxyuridine-5′-phosphate). It is a substrate for an important reaction that involves vitamin B12 and it is necessary for the synthesis of DNA, and so required for all dividing cells.

The pathway leading to the formation of tetrahydrofolate (FH4) begins when folate (F) is reduced to dihydrofolate (DHF) (FH2), which is then reduced to THF. Dihydrofolate reductase catalyses the last step. Vitamin B3 in the form of NADPH is a necessary cofactor for both steps of the synthesis.

Methylene-THF (CH2FH4) is formed from THF by the addition of a methylene bridge from one of three carbon donors: formate, serine, or glycine. Methyl tetrahydrofolate (CH3-THF, or methyl-THF) can be made from methylene-THF by reduction of the methylene group with NADPH.

Another form of THF, 10-formyl-THF, results from oxidation of methylene-THF or is formed from formate donating formyl group to THF. Also, histidine can donate a single carbon to THF to form methenyl-THF.

Vitamin B12 is the only acceptor of methyl-THF, and this reaction produces methyl-B12 (methylcobalamin). There is also only one acceptor for methyl-B12, homocysteine, in a reaction catalyzed by homocysteine methyltransferase. These reactions are of importance because a defect in homocysteine methyltransferase or a deficiency of B12 may lead to a so-called “methyl-trap” of THF, in which THF is converted to a reservoir of methyl-THF which thereafter has no way of being metabolized, and serves as a sink of THF that causes a subsequent deficiency in folate. Thus, a deficiency in B12 can generate a large pool of methyl-THF that is unable to undergo reactions and will mimic folate deficiency.

The reactions that lead to the methyl-THF reservoir can be shown in chain form:

folate → dihydrofolate → tetrahydrofolate ↔ methylene-THF → methyl-THF
Folate metabolism

Conversion to biologically active derivatives

All the biological functions of folic acid are performed by tetrahydrofolate and other derivatives. Their biological availability to the body depends upon dihydrofolate reductase action in the liver. This action is unusually slow in humans, being less than 2% of that in rats. Moreover, in contrast to rats, an almost-5-fold variation in the activity of this enzyme exists between humans. Due to this low activity, it has been suggested this limits the conversion of folic acid into its biologically active forms “when folic acid is consumed at levels higher than the Tolerable Upper Intake Level (1 mg/d for adults).”

Overview of drugs that interfere with folate reactions

A number of drugs interfere with the biosynthesis of folic acid and THF. Among them are the dihydrofolate reductase inhibitors such as trimethoprim, pyrimethamine, and methotrexate; the sulfonamides (competitive inhibitors of 4-aminobenzoic acid in the reactions of dihydropteroate synthetase).

Valproic acid, one of the most commonly prescribed anticonvulsants that is also used to treat certain psychological conditions, is a known inhibitor of folic acid, and as such, has been shown to cause neural tube defects and cases of spina bifida and cognitive impairment in the newborn. Because of this considerable risk, those mothers who must continue to use valproic acid or its derivatives during pregnancy to control their condition (as opposed to stopping the drug or switching to another drug or to a lesser dose) should take folic acid supplements under the direction and guidance of their health care providers.

The National Health and Nutrition Examination Survey (NHANES III 1988–91) and the Continuing Survey of Food Intakes by Individuals (1994–96 CSFII) indicated most adults did not consume adequate folate. However, the folic acid fortification program in the United States has increased folic acid content of commonly eaten foods such as cereals and grains, and as a result, diets of most adults now provide recommended amounts of folate equivalents.

Dietary fortification

In the USA many grain products are fortified with folic acid.

Folic acid fortification is a process in which where folic acid is added to flour with the intention of promoting a public health through increasing blood folate levels in the public. In the USA, food is fortified with folic acid, only one of the many naturally-occurring forms of folate, and a substance contributing only a minor amount to the folates in natural foods.

Since the discovery of the link between insufficient folic acid and neural tube defects, governments and health organizations worldwide have made recommendations concerning folic acid supplementation for women intending to become pregnant.

Fortification is controversial, with issues having been raised concerning individual liberty, as well as the health concerns described in the Toxicity section above. In the USA, there is concern that the federal government mandates fortification, but does not provide any monitoring of any potential undesirable effects of fortification.

Several western countries now fortify their flour, along with a number of Middle Eastern countries and Indonesia. Mongolia and a number of former Soviet republics are among those having widespread voluntary fortification; about five more countries (including Morocco, the first African country) have agreed, but not yet implemented, fortification. To date, no EU country has yet mandated fortification. It was raised again however at the Gastein Health Forum meeting in Bad Gastein, Austria, in October 2012 when health policymakers were shown a study that claimed fortifying bread sold to the general public with folic acid could reduce the number of birth defects by up to 60 per cent.

Australia

There has been previous debate in Australia regarding the inclusion of folic acid in products such as bread and flour.

Australia and New Zealand have jointly agreed to fortification though the Food Standards Australia New Zealand. Australia will fortify all flour from 18 September 2009. Although the food standard covers both Australia and New Zealand, an Australian government official has stated it is up to New Zealand to decide whether to implement it there, and they will watch with interest.

The requirement is 0.135 mg of folate per 100g of bread.

Canada

In 2003, a Hospital for Sick Children, University of Toronto research group published findings showing the fortification of flour with folic acid in Canada has resulted in a dramatic decrease in neuroblastoma, an early and very dangerous cancer in young children.In 2009, further evidence from McGill University showed a 6.2% decrease per year in the birth prevalence of severe congenital heart defects.

Folic acid used in fortified foods is a synthetic form called pteroylmonoglutamate.[103] It is in its oxidized state and contains only one conjugated glutamate residue. Folic acid therefore enters via a different carrier system from naturally occurring folate, and this may have different effects on folate binding proteins and its transporters. Folic acid has a higher bioavailability than natural folates and are rapidly absorbed across the intestine, therefore it is important to consider the Dietary Folate Equivalent (DFE) when calculating one’s intake. Natural occurring folate is equal to 1 DFE, however 0.6 µg of folic acid is equal to 1 DFE.

Folic acid food fortification became mandatory in Canada in 1998, with the fortification of 150 µg of folic acid per 100 grams of enriched flour and uncooked cereal grains. The purpose of fortification was to decrease the risk of neural tube defects in newborns.It is important to fortify grains because it is a widely eaten food and the neural tube closes in the first four weeks of gestation, often before many women even know they are pregnant. Canada’s fortification program has been successful with a decrease of neural tube defects by 19% since its introduction. A seven-province study from 1993 to 2002 showed a reduction of 46% in the overall rate of neural tube defects after folic acid fortification was introduced in Canada. The fortification program was estimated to raise a person’s folic acid intake level by 70–130 µg/day, however an increase of almost double that amount was actually observed. This could be from the fact that many foods are over fortified by 160–175% the predicted value. In addition, much of the elder population take supplements that adds 400 µg to their daily folic acid intake. This is a concern because 70–80% of the population have detectable levels of unmetabolized folic acid in their blood and high intakes can accelerate the growth of preneoplasmic lesions. It is still unknown the amount of folic acid supplementation that might cause harm

Supplementation promotion

According to a Canadian survey, 58% of women said they took a folic acid containing multivitamin or a folic acid supplement as early as three months before becoming pregnant. Women in higher income households and with more years of school education are using more folic acid supplements before pregnancy. Women with planned pregnancies and who are over the age of 25 are more likely to use folic acid supplement. Canadian public health efforts are focused on promoting awareness of the importance of folic acid supplementation for all women of childbearing age and decreasing socio-economic inequalities by providing practical folic acid support to vulnerable groups of women.

New Zealand

New Zealand was planning to fortify bread (excluding organic and unleavened varieties) from 18 September 2009, but has opted to wait until more research is done.

The Association of Bakers  and the Green Party  have opposed mandatory fortification, describing it as “mass medication”. Food Safety Minister Kate Wilkinson reviewed the decision to fortify in July 2009, citing links between overconsumption of folate with cancer . The New Zealand Government is reviewing whether it will continue with the mandatory introduction of folic acid to bread.

United Kingdom

There has been previous debate in the United Kingdom regarding the inclusion of folic acid in products such as bread and flour.

The Food Standards Agency has recommended fortification.

United States

The United States Public Health Service recommends an extra 0.4 mg/day for newly pregnant women, which can be taken as a pill. However, many researchers believe supplementation in this way can never work effectively enough, since about half of all pregnancies in the U.S. are unplanned, and not all women will comply with the recommendation. Approximately 53% of the US population uses dietary supplements and 35% uses dietary supplements containing folic acid. Men consume more folate (in dietary folate equivalents) than women, and non-Hispanic whites have higher folate intakes than Mexican Americans and non-Hispanic blacks. Twenty nine percent of black women have inadequate intakes of folate. The age group consuming the most folate and folic acid is the >50 group. 5% of the population exceeds the Tolerable Upper Intake Level.

In 1996, the United States Food and Drug Administration (FDA) published regulations requiring the addition of folic acid to enriched breads, cereals, flours, corn meals, pastas, rice, and other grain products. This ruling took effect on January 1, 1998, and was specifically targeted to reduce the risk of neural tube birth defects in newborns. There are concerns that the amount of folate added is insufficient . In October 2006, the Australian press claimed that U.S. regulations requiring fortification of grain products were being interpreted as disallowing fortification in non-grain products, specifically Vegemite (an Australian yeast extract containing folate). The FDA later said the report was inaccurate, and no ban or other action was being taken against Vegemite.

As a result of the folic acid fortification program, fortified foods have become a major source of folic acid in the American diet. The Centers for Disease Control and Prevention in Atlanta, Georgia used data from 23 birth defect registries covering about half of United States births, and extrapolated their findings to the rest of the country. These data indicate since the addition of folic acid in grain-based foods as mandated by the FDA, the rate of neural tube defects dropped by 25% in the United States  The results of folic acid fortification on the rate of neural tube defects in Canada have also been positive, showing a 46% reduction in prevalence of NTDs;the magnitude of reduction was proportional to the prefortification rate of NTDs, essentially removing geographical variations in rates of NTDs seen in Canada before fortification.

When the U.S. Food and Drug Administration set the folic acid fortification regulation in 1996, the projected increase in folic acid intake was 100 µg/d. Data from a study with 1480 subjects showed that folic acid intake increased by 190 µg/d and total folate intake increased by 323 µg dietary folate equivalents (DFE)/d. Folic acid intake above the upper tolerable intake level (1000 µg folic acid/d) increased only among those individuals consuming folic acid supplements as well as folic acid found in fortified grain products. Taken together, folic acid fortification has led to a bigger increase in folic acid intake than first projected.

source: http://en.wikipedia.org/wiki/Folic_acid

Vitamins – Vitamin B6 (Pyridoxine) – part 12

Pyridoxine is one of the compounds that can be called vitamin B6, along with pyridoxal and pyridoxamine. It differs from pyridoxamine by the substituent at the ‘4’ position. Its hydrochloride salt pyridoxine hydrochloride is often used.

Pyridoxine
Identifiers
CAS number 65-23-6,
58-56-0 (HCl)
PubChem 1054
ChemSpider 1025 
DrugBank DB00165
KEGG D08454 
ChEBI CHEBI:16709 
ChEMBL CHEMBL1364 
ATC code A11HA02
Jmol-3D images Image 1
Properties
Molecular formula C8H11NO3
Molar mass 169.18 g mol−1
Melting point 159-162 °C

Chemistry

It is based on a pyridine ring, with hydroxyl, methyl, and hydroxymethyl substituents. It is converted to the biologically active form pyridoxal 5-phosphate.

Function in the body

Pyridoxine assists in the balancing of sodium and potassium as well as promoting red blood cell production. It is linked to cardiovascular health by decreasing the formation of homocysteine. Pyridoxine may help balance hormonal changes in women and aid the immune system. Lack of pyridoxine may cause anemia, nerve damage, seizures, skin problems, and sores in the mouth.

It is required for the production of the monoamine neurotransmitters serotonin, dopamine, norepinephrine and epinephrine, as it is the precursor to pyridoxal phosphate: cofactor for the enzyme aromatic amino acid decarboxylase. This enzyme is responsible for converting the precursors 5-hydroxytryptophan (5-HTP) into serotonin and levodopa (L-DOPA) into dopamine, noradrenaline and adrenaline. As such it has been implicated in the treatment of depression and anxiety.

Very good sources of pyridoxine are grains and nuts.

Medicinal uses

Pyridoxine is given to patients taking isoniazid to combat the toxic side effects of the drug. It is given 10–50 mg/day to patients on to prevent peripheral neuropathy and CNS effects that are associated with the use of INH.

It is also essential for patients with extremely rare pyridoxine-dependent epilepsy, thought to be caused by mutations in the ALDH7A1 gene.

In one form of homocystinuria, activity of the deficient enzyme can be enhanced by the administration of large doses of pyridoxine (100-1000 mg/day).

Vitamin B6 can be compounded into a variety of different dosage forms. It can be used orally as a tablet, capsule, or solution. It can also be used as a nasal spray or for injection when in its solution form.

Vitamin B6 is usually safe, at regular intakes up to 200 mg per day in adults. However, vitamin B6 can cause neurological disorders, such as loss of sensation in legs and imbalance, when taken in high doses (200 mg or more per day – 10,000% of US RDA) over a long period of time. Vitamin B6 toxicity can damage sensory nerves, leading to numbness in the hands and feet as well as difficulty walking. Symptoms of a pyridoxine overdose may include poor coordination, staggering, numbness, decreased sensation to touch, temperature, and vibration, and tiredness for up to six months. One study reported that over a 6 month period or longer, 21% of women taking doses greater than 50 mg daily experienced neurological toxicity. The effect of doses below 50 mg was not reported. Pyridoxine’s fetal safety is “A” in Briggs’ Reference Guide to Fetal and Neonatal Risk.

source: http://en.wikipedia.org/wiki/Pyridoxine

Vitamins – Vitamin B7 (Biotin) – part 11

Biotin, also known as vitamin H or coenzyme R, is a water-soluble B-vitamin (vitamin B7).

It is composed of a ureido (tetrahydroimidizalone) ring fused with a tetrahydrothiophene ring. A valeric acid substituent is attached to one of the carbon atoms of the tetrahydrothiophene ring. Biotin is a coenzyme for carboxylase enzymes, involved in the synthesis of fatty acids, isoleucine, and valine, and in gluconeogenesis.

Biotin
Identifiers
CAS number 58-85-5 
PubChem 171548
ChemSpider 149962 
UNII 6SO6U10H04 
DrugBank DB00121
KEGG D00029 
ChEBI CHEBI:15956 
ChEMBL CHEMBL857 
ATC code A11HA05
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C10H16N2O3S
Molar mass 244.31 g mol−1
Appearance White crystalline needles
Melting point 232-233 °C
Solubility in water 22 mg/100 mL
Hazards
NFPA 704
NFPA 704.svg
1
1
0

General overview

Dean Burk, American biochemist who co-discovered biotin.

Biotin is necessary for cell growth, the production of fatty acids, and the metabolism of fats and amino acids. It plays a role in the citric acid cycle, which is the process by which biochemical energy is generated during aerobic respiration. Biotin not only assists in various metabolic reactions, but also helps to transfer carbon dioxide. It may also be helpful in maintaining a steady blood sugar level.Biotin is often recommended as a dietary supplement for strengthening hair and nails, though scientific data supporting this usage are weak. Nevertheless, biotin is found in many cosmetics and health products for the hair and skin.

Biotin deficiency is rare because, in general, intestinal bacteria produce biotin in excess of the body’s daily requirements. For that reason, statutory agencies in many countries, for example the USA and Australia, do not prescribe a recommended daily intake of biotin. However, a number of metabolic disorders exist in which an individual’s metabolism of biotin is abnormal, such as deficiency in the holocarboxylase synthetase enzyme which covalently links biotin onto the carboxylase, where the biotin acts as a cofactor.

Biosynthesis

Biotin has an unusual structure (see above figure), with two rings fused together via one of their sides. The two rings are ureido and thiophene moieties. Biotin is a heterocyclic, S-containing monocarboxylic acid. It is made from two precursors, alanine and pimeloyl-CoA via three enzymes. 8-Amino-7-oxopelargonic acid synthase is a pyridoxal 5′-phosphate enzyme. The pimeloyl-CoA, could be produced by a modified fatty acid pathway involving a malonyl thioester as the starter. 7,8Diaminopelargonic acid (DAPA) aminotransferase is unusual in using S-adenosyl methionine (SAM) as the NH2 donor. Dethiobiotin synthethase catalyzes the formation of the ureido ring via a DAPA carbamate activated with ATP. Biotin synthase reductively cleaves SAM into a deoxyadenosyl radical—a first radical formed on dethiobiotin is trapped by the sulfur donor, which was found to be the iron-sulfur (Fe-S) center contained in the enzyme.

Cofactor biochemistry

D-(+)-Biotin is a cofactor responsible for carbon dioxide transfer in several carboxylase enzymes:

Biotin is important in fatty acid synthesis, branched-chain amino acid catabolism, and gluconeogenesis. It covalently attaches to the epsilon-amino group of specific lysine residues in these carboxylases. This biotinylation reaction requires ATP and is catalyzed by holocarboxylase synthetase. In bacteria, biotin is attached to biotin carboxyl carrier protein (BCCP) by biotin protein ligase (BirA in E. coli). The attachment of biotin to various chemical sites, biotinylation, is used as an important laboratory technique to study various processes, including protein localization, protein interactions, DNA transcription, and replication. Biotinidase itself is known to be able to biotinylate histone proteins, but little biotin is found naturally attached to chromatin.

Biotin binds very tightly to the tetrameric protein avidin (also streptavidin and neutravidin), with a dissociation constant Kd on the order of 10−15 M, which is one of the strongest known protein-ligand interactions. This is often used in different biotechnological applications. Until 2005, very harsh conditions were thought to be required to break the biotin-streptavidin bond.

Sources of biotin

Biotin is consumed from a wide range of food sources in the diet, but few are particularly rich sources. Foods with a relatively high biotin content include Swiss chard, raw egg yolk (however, the consumption of avidin-containing egg whites with egg yolks minimizes the effectiveness of egg yolk’s biotin in one’s body), liver, Saskatoon berries, leafy green vegetables, and peanuts. The dietary biotin intake in Western populations has been estimated to be 35 to 70 μg/d (143–287 nmol/d).

Biotin is also available in supplement form and can be found in most pharmacies. The synthetic process developed by Leo Sternbach and Moses Wolf Goldberg in the 1940s uses fumaric acid as a starting material.

Bioavailability

Biotin is also called vitamin H (the H represents Haar und Haut, German words for “hair and skin”) or vitamin B7. Studies on its bioavailability have been conducted in rats and in chicks. Based on these studies, biotin bioavailability may be low or variable, depending on the type of food being consumed. In general, biotin exists in food as protein-bound form or biocytin. Proteolysis by protease is required prior to absorption. This process assists free biotin release from biocytin and protein-bound biotin. The biotin present in corn is readily available; however, most grains have about a 20-40% bioavailability of biotin.

The wide variability in biotin bioavailability may be due to the ability of an organism to break various biotin-protein bonds from food. Whether an organism has an enzyme with that ability will determine the bioavailability of biotin from the foodstuff.

Factors that affect biotin requirements

The frequency of marginal biotin status is not known, but the incidence of low circulating biotin levels in alcoholics has been found to be much greater than in the general population. Also, relatively low levels of biotin have been reported in the urine or plasma of patients who have had a partial gastrectomy or have other causes of achlorhydria, burn patients, epileptics, elderly individuals, and athletes. Pregnancy and lactation may be associated with an increased demand for biotin. In pregnancy, this may be due to a possible acceleration of biotin catabolism, whereas, in lactation, the higher demand has yet to be elucidated. Recent studies have shown marginal biotin deficiency can be present in human gestation, as evidenced by increased urinary excretion of 3-hydroxyisovaleric acid, decreased urinary excretion of biotin and bisnorbiotin, and decreased plasma concentration of biotin. Additionally, smoking may further accelerate biotin catabolism in women.

Deficiency

Biotin deficiency is rare and mild, and can be addressed with supplementation. It is caused by the consumption of raw egg whites (two or more daily for several months) due the avidin they contain, a protein which binds extremely strongly with biotin, making it unavailable. Such regimens have produced the only examples of biotin deficiency serious enough to produce symptoms.

The first demonstration of biotin deficiency in animals was observed in animals fed raw egg white. Rats fed egg white protein were found to develop dermatitis, alopecia, and neuromuscular dysfunction. This syndrome, called egg white injury, was discovered to be caused by a glycoprotein found in egg white, avidin. Avidin denatures upon heating (cooking), while the biotin remains intact.

Symptoms of biotin deficiency include:

  • Hair loss (alopecia)
  • Conjunctivitis
  • Dermatitis in the form of a scaly, red rash around the eyes, nose, mouth, and genital area.
  • Neurological symptoms in adults, such as depression, lethargy, hallucination, and numbness and tingling of the extremities

The characteristic facial rash, together with an unusual facial fat distribution, has been termed the “biotin-deficient face” by some experts. Individuals with hereditary disorders of biotin deficiency have evidence of impaired immune system function, including increased susceptibility to bacterial and fungal infections.

Pregnant women tend to have a high risk of biotin deficiency. Nearly half of pregnant women have abnormal increases of 3-hydroxyisovaleric acid, which reflects reduced status of biotin. Several studies have reported this possible biotin deficiency during the pregnancy may cause infants’ congenital malformations, such as cleft palate. Mice fed with dried raw egg to induce biotin deficiency during the gestation resulted in up to 100% incidence of the infants’ malnourishment. Infants and embryos are more sensitive to the biotin deficiency. Therefore, even a mild level of the mother’s biotin deficiency that does not reach the appearance of physiological deficiency signs may cause a serious consequence in the infants.

Metabolic disorders

Inherited metabolic disorders characterized by deficient activities of biotin-dependent carboxylases are termed multiple carboxylase deficiency. These include deficiencies in the enzymes holocarboxylase synthetase or biotinidase. Holocarboxylase synthetase deficiency prevents the body’s cells from using biotin effectively, and thus interferes with multiple carboxylase reactions.Biochemical and clinical manifestations include: ketolactic acidosis, organic aciduria, hyperammonemia, skin rash, feeding problems, hypotonia, seizures, developmental delay, alopecia, and coma.

Biotinidase deficiency is not due to inadequate biotin, but rather to a deficiency in the enzymes that process it. Biotinidase catalyzes the cleavage of biotin from biocytin and biotinyl-peptides (the proteolytic degradation products of each holocarboxylase) and thereby recycles biotin. It is also important in freeing biotin from dietary protein-bound biotin. General symptoms include decreased appetite and growth. Dermatologic symptoms include dermatitis, alopecia, and achromotrichia (absence or loss of pigment in the hair). Perosis (a shortening and thickening of bones) is seen in the skeleton. Fatty liver and kidney syndrome and hepatic steatosis also can occur.

Uses

Health and diet

Diabetes

Diabetics may benefit from biotin supplementation. In both insulin-dependent and insulin-independent diabetics deficient in biotin, supplementation with biotin can improve blood sugar control and help lower fasting blood glucose levels; in one study, the reduction in fasting glucose approached 50%. Biotin can also play a role in preventing the neuropathy often associated with diabetes, reducing both the numbness and tingling associated with poor glucose control.

Hair and nail problems

The signs and symptoms of biotin deficiency include hair loss, which progresses in severity to include loss of eyelashes and eyebrows in severely deficient subjects, as well as nails that break, chip, or flake easily. The recommended dose to treat deficiency for adults varies from 3,000 mcg per day for brittle fingernails up to 7,000 to 15,000 mcg per day for diabetics.

Palmoplantar pustulosis

Patients with palmoplantar pustulosis had metabolic derangements of glucose and fatty acids, as well as immune dysfunction derived from biotin deficiency, which led to abnormal manifestations of skin, bone and other tissues and organs. All of the clinical, metabolic and immune disorders were improved by biotin administration. These findings indicate biotin deficiency was implicated in the outbreak and exacerbation of the disease and its complications. Supplementary addition of a probiotic agent to the biotin treatment intensified the therapeutic effect of the vitamin. Additionally, patients with psoriasis vulgaris, systemic lupus erythematosus, atopic dermatitis or rheumatoid arthritis also had biotin deficiency with the subsequent metabolic abnormalities and immune dysfunction, so the biotin treatment provided beneficial effects in the therapy of the diseases, as in the case of palmoplantar pustulosis.

Cradle cap (seborrheic dermatitis)

Children with a rare inherited metabolic disorder called phenylketonuria (PKU; in which one is unable to break down the amino acid phenylalanine) often develop skin conditions such as eczema and seborrheic dermatitis in areas of the body other than the scalp. The scaly skin changes that occur in people with PKU may be related to poor ability to use biotin. Increasing dietary biotin has been known to improve seborrheic dermatitis in these cases.

Biotechnology

Biotin is widely used throughout the biotechnology industry to conjugate proteins for biochemical assays. Biotin’s small size means the biological activity of the protein will most likely be unaffected. This process is called biotinylation. Because both streptavidin and avidin bind biotin with high affinity (Kd of 10−14 mol/l to 10−15 mol/l) and specificity, biotinylated proteins of interest can be isolated from a sample by exploiting this highly stable interaction. The sample is incubated with streptavidin/avidin beads, allowing capture of the biotinylated protein of interest. Any other proteins binding to the biotinylated molecule will also stay with the bead and all other unbound proteins can be washed away. However, due to the extremely strong streptavidin-biotin interaction, very harsh conditions are needed to elute the biotinylated protein from the beads (typically 6M guanidine HCl at pH 1.5), which often will denature the protein of interest. To circumvent this problem, beads conjugated to monomeric avidin can be used, which has a decreased biotin-binding affinity of ~10−8 mol/l, allowing the biotinylated protein of interest to be eluted with excess free biotin.

ELISAs often make use of biotinylated secondary antibodies against the antigen of interest, followed by a detection step using streptavidin conjugated to a reporter molecule, such as horseradish peroxidase or alkaline phosphatase.

Toxicity

Animal studies have indicated few, if any, effects due to high level doses of biotin. This may provide evidence that both animals and humans could tolerate doses of at least an order of magnitude greater than each of their nutritional requirements. There are no reported cases of adverse effects from receiving high doses of the vitamin, in particular, when used in the treatment of metabolic disorders causing sebhorrheic dermatitis in infants.

source: http://en.wikipedia.org/wiki/Biotin

Vitamins – Vitamin B5 (Phantotenic Acid) – part 10

Pantothenic acid, also called pantothenate or vitamin B5 (a B vitamin), is a water-soluble vitamin discovered by Roger J. Williams in 1919. For many animals, pantothenic acid is an essential nutrient. Animals require pantothenic acid to synthesize coenzyme-A (CoA), as well as to synthesize and metabolize proteins, carbohydrates, and fats.

Pantothenic acid is the amide between pantoic acid and β-alanine. Its name derives from the Greek pantothen (πάντοθεν) meaning “from everywhere” and small quantities of pantothenic acid are found in nearly every food, with high amounts in whole-grain cereals, legumes, eggs, meat, royal jelly, avocado, and yogurt. It is commonly found as its alcohol analog, the provitamin panthenol, and as calcium pantothenate. Pantothenic acid is an ingredient in some hair and skin care products.

Pantothenic acid
Identifiers
CAS number 599-54-2, 79-83-4 R 
PubChem 988, 6613 R, 5748353 S
ChemSpider 963 , 6361 R , 4677898 S 
UNII 568ET80C3D 
EC number 209-965-4
DrugBank DB01783
KEGG D07413 
MeSH Pantothenic+Acid
ChEBI CHEBI:7916 
ChEMBL CHEMBL1594 
Beilstein Reference 1727062, 1727064 R
3DMet B00193
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C9H17NO5
Molar mass 219.23 g mol−1
Density 1.266 g mL−1
Melting point 183.83 °C, 457 K, 363 °F
Boiling point 551.5 °C, 825 K, 1025 °F
log P −0.856
Acidity (pKa) 4.299
Basicity (pKb) 9.698
Related compounds
Related alkanoic acids
Related compounds Panthenol

Biological role

Only the dextrorotatory (D) isomer of pantothenic acid possesses biologic activity. The levorotatory (L) form may antagonize the effects of the dextrorotatory isomer.

Pantothenic acid is used in the synthesis of coenzyme A (CoA). Coenzyme A may act as an acyl group carrier to form acetyl-CoA and other related compounds; this is a way to transport carbon atoms within the cell. CoA is important in energy metabolism for pyruvate to enter the tricarboxylic acid cycle (TCA cycle) as acetyl-CoA, and for α-ketoglutarate to be transformed to succinyl-CoA in the cycle. CoA is also important in the biosynthesis of many important compounds such as fatty acids, cholesterol, and acetylcholine. CoA is incidentally also required in the formation of ACP, which is also required for fatty acid synthesis in addition to CoA.

Pantothenic acid in the form of CoA is also required for acylation and acetylation, which, for example, are involved in signal transduction and enzyme activation and deactivation, respectively.

Since pantothenic acid participates in a wide array of key biological roles, it is essential to all forms of life. As such, deficiencies in pantothenic acid may have numerous wide-ranging effects, as discussed below.

Sources

Dietary

Small quantities of pantothenic acid are found in most foods. The major food source of pantothenic acid is meat. The concentration found in animal muscle is about half that in human muscle.  Whole grains are another good source of the vitamin, but milling removes much of the pantothenic acid, as it is found in the outer layers of whole grains. Vegetables, such as broccoli and avocados, also have an abundance. In animal feeds, the most important sources are rice, wheat bran, cereal, alfalfa, peanut meal, molasses, yeasts, and condensed fish solutions. The most significant sources of pantothenic acid in nature are coldwater fish ovaries and royal jelly.

Supplementation

The derivative of pantothenic acid, pantothenol, is a more stable form of the vitamin and is often used as a source of the vitamin in multivitamin supplements. Another common supplemental form of the vitamin is calcium pantothenate. Calcium pantothenate is often used in dietary supplements because, as a salt, it is more stable than pantothenic acid in the digestive tract, allowing for better absorption.

Possible benefits of supplementation: Doses of 2 g/day of calcium pantothenate may reduce the duration of morning stiffness, degree of disability, and pain severity in rheumatoid arthritis patients. Although the results are inconsistent, supplementation may improve oxygen utilization efficiency and reduce lactic acid accumulation in athletes.

Daily requirement

Pantothenate in the form of 4’phosphopantetheine is considered to be the more active form of the vitamin in the body; however, any derivative must be broken down to pantothenic acid before absorption. 10 mg of calcium pantothenate is equivalent to 9.2 mg of pantothenic acid.

Age group Age Requirements
Infants 0–6 months 1.7 mg
Infants 7–12 months 1.8 mg
Children 1–3 years 2 mg
Children 4–8 years 3 mg
Children 9–13 years 4 mg
Adult men and women 14+ years 5 mg
Pregnant women (vs. 5) 6 mg
Breastfeeding women (vs. 5) 7 mg
  • United Kingdom RDA: 6 mg/day

Absorption

When found in foods, most pantothenic acid is in the form of CoA or acyl carrier protein (ACP). For the intestinal cells to absorb this vitamin, it must be converted into free pantothenic acid. Within the lumen of the intestine, CoA and ACP are hydrolyzed into 4′-phosphopantetheine. The 4′-phosphopantetheine is then dephosphorylated into pantetheine. Pantetheinase, an intestinal enzyme, then hydrolyzes pantetheine into free pantothenic acid.

Free pantothenic acid is absorbed into intestinal cells via a saturable, sodium-dependent active transport system. At high levels of intake, when this mechanism is saturated, some pantothenic acid may also be absorbed via passive diffusion. As intake increases 10-fold, however, absorption rate decreases to 10%.

Deficiency

Pantothenic acid deficiency is exceptionally rare and has not been thoroughly studied. In the few cases where deficiency has been seen (victims of starvation and limited volunteer trials), nearly all symptoms can be reversed with the return of pantothenic acid.

Symptoms of deficiency are similar to other vitamin B deficiencies. There is impaired energy production, due to low CoA levels, which could cause symptoms of irritability, fatigue, and apathy. Acetylcholine synthesis is also impaired; therefore, neurological symptoms can also appear in deficiency; they include numbness, paresthesia, and muscle cramps. Deficiency in pantothenic acid can also cause hypoglycemia, or an increased sensitivity to insulin. Insulin receptors are acylated with palmitic acid when they do not want to bind with insulin. Therefore, more insulin will bind to receptors when acylation decreases, causing hypoglycemia Additional symptoms could include restlessness, malaise, sleep disturbances, nausea, vomiting, and abdominal cramps. In a few rare circumstances, more serious (but reversible) conditions have been seen, such as adrenal insufficiency and hepatic encephalopathy.

One study noted painful burning sensations of the feet were reported in tests conducted on volunteers. Deficiency of pantothenic acid may explain similar sensations reported in malnourished prisoners of war.

Deficiency symptoms in other nonruminant animals include disorders of the nervous, gastrointestinal, and immune systems, reduced growth rate, decreased food intake, skin lesions and changes in hair coat, and alterations in lipid and carbohydrate metabolism.

Toxicity

Toxicity of pantothenic acid is unlikely. In fact, no Tolerable Upper Level Intake (UL) has been established for the vitamin. Large doses of the vitamin, when ingested, have no reported side effects and massive doses (e.g., 10 g/day) may only yield mild intestinal distress, and diarrhea at worst. It has been suggested, however, that high doses of pantothenic acid might worsen panic attacks in those with panic disorder by prolonging the duration until adrenal exhaustion.

There are also no adverse reactions known following parenteral or topical application of the vitamin.

Uses

Given pantothenic acid’s prevalence among living things and the limited body of studies in deficiency, many uses of pantothenic acid have been the subject of research.

Testicular torsion

Testicular torsion can severely affect fertility if it occurs. One study on a rat model indicated a treatment of 500 mg of dexpanthenol/kg body weight 30 minutes prior to detorsion can greatly decrease the risk of infertility after torsion. Pantothenic acid has the ability to spare reduced glutathione levels. Reactive oxygen species play a role in testicular atrophy, which glutathione counteracts.

Diabetic ulceration

Foot ulceration is a problem commonly associated with diabetes, which often leads to amputation.A preliminary study completed by Abdelatif, Yakoot and Etmaan indicated that perhaps a royal jelly and panthenol ointment can help cure the ulceration. People with foot ulceration or deep tissue infection in the study had a 96% and 92% success rate of recovery. While these results appear promising, they need to be validated, as this was a pilot study; it was not a randomized, placebo-controlled, double-blind study.

Hypolipidemic effects

Pantothenic acid derivatives, panthenol, phosphopantethine and pantethine, have also been seen to improve the lipid profile in the blood and liver. In this mouse model, they injected 150 mg of the derivative/kg body weight. All three derivatives were able to effectively lower low-density lipoprotein (LDL), as well as triglyceride (TG) levels; panthenol was able to lower total cholesterol, and pantethine was able to lower LDL-cholesterol in the serum. The decrease in LDL is significant, as it is related to a decrease the risk of myocardial infarction and stroke. In the liver, panthenol was the most effective, as it lowered TG, total cholesterol, free cholesterol and cholesterol-ester levels.

Wound healing

A study in 1999 showed pantothenic acid has an effect on wound healing in vitro. Wiemann and Hermann found cell cultures with a concentration of 100 μg/mL calcium D-pantothenate increased migration, and the fibers ran directionally with several layers, whereas the cell cultures without pantothenic acid healed in no orderly motion, and with fewer layers. Cell proliferation or cell multiplication was found to increase with pantothenic acid supplementation. Finally, increased concentrations of two proteins, both of which have yet to be identified, were found in the supplemented culture, but not in the control. Further studies are needed to determine whether these effects will stand in vivo.

Hair care

Mouse models identified skin irritation and loss of hair color as possible results of severe pantothenic acid deficiency. As a result, the cosmetic industry began adding pantothenic acid to various cosmetic products, including shampoo. These products, however, showed no benefits in human trials. Despite this, many cosmetic products still advertise pantothenic acid additives.

Acne

Following from discoveries in mouse trials, in the late 1990s, a small study was published promoting the use of pantothenic acid to treat acne vulgaris.

According to a study published in 1995 by Dr. Lit-Hung Leung, high doses of vitamin B5 resolved acne and decreased pore size. Dr. Leung also proposed a mechanism, stating that CoA regulates both hormones and fatty acids, and without sufficient quantities of pantothenic acid, CoA will preferentially produce androgens. This causes fatty acids to build up and be excreted through sebaceous glands, causing acne. Leung’s study gave 45 Asian males and 55 Asian females varying doses of 10–20g of pantothenic acid (100000% of the US Daily Value), 80% orally and 20% through topical cream. Leung noted improvement of acne within one week to one month of the start of the treatment.

Obesity

In a report published in 1997 by Lit-Hung Leung, it was hypothesized that pantothenic acid also has an effect on weight management. Leung proposed that those who were deficient in pantothenic acid would feel the effects of hunger and weakness more strongly. To access fat storages in the body in times of fasting or dieting requires CoA. Diets high in pantothenic acid produce more CoA. In a study done on 100 Chinese individuals from age range 15–55 it was observed that on a diet of 1000 calories a day and 10 g pantothenic acid, the dieters could lose on average 1.2 kg/week with lessened effects from hunger or weakness. Ketone bodies in urine indicated that some dieters required more than 10 g of pantothenic acid a day. The possibilities of pantothenic acid in weight management have not been fully explored, but remain an area of research.

Diabetic peripheral polyneuropathy

Twenty-eight out of 33 patients (84.8%) previously treated with alpha-lipoic acid for peripheral polyneuropathy reported further improvement after combination with pantothenic acid. The theoretical basis for this is that both substances intervene at different sites in pyruvate metabolism and are, thus, more effective than one substance alone. Additional clinical findings indicated diabetic neuropathy may occur in association with a latent prediabetic metabolic disturbance, and that the symptoms of neuropathy can be favorably influenced by the described combination therapy, even in poorly controlled diabetes.

Cholesterol and Triglyceride

Pantothenic acid was originally studied on rats. Studies showed that those fed a diet with less pantothenic acid were more likely to have higher cholesterol. Pantethine, a more active form of pantothenic acid, has been used to lower cholesterol and triglyceride levels. Clinical trials have shown that taking pantethine can lower cholesterol by 19% and triglyceride levels by 32%. Although not all studies agree, pantethine has also been shown to raise high-density lipoprotein cholesterol (often referred to as “good” cholesterol).

Ruminant nutrition

No dietary requirement for pantothenic acid has been established as synthesis of pantothenic acid by ruminal microorganisms appears to be 20 to 30 times more than dietary amounts. Net microbial synthesis of pantothenic acid in the rumen of steer calves has been estimated to be 2.2 mg/kg of digestible organic matter consumed per day. The degradation of dietary intake of pantothenic acid is considered to be 78 percent. Supplementation of pantothenic acid at 5 to 10 times theoretic requirements did not improve performance of feedlot cattle.

source: http://en.wikipedia.org/wiki/Pantothenic_acid