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Biotin

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Biotin[1]
File:Biotin 3D Molecule.png
Names
IUPAC name
5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoic acid
Other names
Vitamin B7; Vitamin H; Coenzyme R; Biopeiderm
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.000.363 Edit this at Wikidata
  • InChI=1/C10H16N2O3S/c13-8(14)4-2-1-3-7-9-6(5-16-7)11-10(15)12-9/h6-7,9H,1-5H2,(H,13,14)(H2,11,12,15)/t6-,7-,9-/m0/s1
  • O=C1N[C@@H]2[C@H](CCCCC(=O)O)SC[C@@H]2N1
Properties
C10H16N2O3S
Molar mass 244.31 g·mol−1
Appearance White crystalline needles
Melting point 232-233 °C
22 mg/100 mL
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Biotin, also known as vitamin H or B7, is a water-soluble B-complex vitamin which is composed of an 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 cofactor in the metabolism of fatty acids and leucine, and it plays a role in gluconeogenesis.

General overview

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. Biotin is also helpful in maintaining a steady blood sugar level. Biotin is often recommended for strengthening hair and nails. Consequently, it is found in many cosmetic and health products for the hair and skin.

Deficiency is extremely rare, as intestinal bacteria generally produce an excess of the body's daily requirement. For that reason, statutory agencies in many countries (e.g., the Australian Department of Health and Aging) do not prescribe a recommended daily intake.

Sources

Dietary

Biotin is widely distributed in a variety of foods, but most often at low concentrations. Estimates are that the typical U.S. diet provides roughly 40 ug/day. There are only a couple of foods which contain biotin in large amounts, including royal jelly and brewer's yeast. The best natural sources of biotin in human nutrition are liver, legume, soybeans, Swiss chard, tomatoes, romaine lettuce, and carrots. This includes almonds, eggs, onions, cabbage, cucumber, cauliflower, goat's milk, cow's milk, raspberries, strawberries, halibut, oats, and walnuts. The most important natural sources in feeding nonruminant animals are oilseed meals, alfalfa, and dried yeasts. The biotin content of food varies and can be influenced by factors such as plant variety, season, and yield (endosperm-to-pericarp ratio).[2]

Recommended Adequate Intake* for Biotin
Age Biotin (ug/day)
Infants 0–6 months 5
7–12 months 6
Children 1–3 years 8
4–8 years 12
Males and Females 9–13 years 20
14-18 years 25
19–70 years 30
70+ years 30
Pregnant <18-50 30
Lactating <18-50 35
  • Adequate intake are determined for nutrients when there is insufficient scientific evidence to establish a Recommended Dietary Allowance (RDA). These values are set as goals for individuals to support adequate nutritional status. NOTE: U.S. Food and supplement labels show 30 ug of biotin as providing only 10% DV (Daily Value) because DVs are based on older and in some instances outdated RDAs for nutrients. Thus, the DV for biotin is 300 ug even though there is now consensus that 30 ug is adequate. There is no current Tolerable Upper Limit (UL) set for biotin as research has indicated that high levels of intake by humans has no detrimental effects.[3]

Bioavailability

Studies on the bioavailability of biotin have been conducted in rats and in chicks. From these studies, it was concluded that 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 [4]. Proteolysis by protease is required prior absorption. This process assists free biotin release from biocytin and protein bound biotin.The biotin present in corn is readily available; however, most grain have about a 20-40% bioavailability of biotin.[2]

A possible explanation for the wide variability in biotin bioavailability is that it is due to ability of an organism to break various biotin-protein bonds from food. Whether an organism has an enzyme with the ability to break that bond will determine the bioavailability of biotin from the foodstuff.[2]

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 partial gastrectomy or who have other causes of achlorhydria, burn patients, epileptics, elderly individuals and athletes.[2] 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 that 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.[5]

Uses

Hair problems

Biotin supplements are often recommended as a natural product to counteract the problem of hair loss in both children and adults. The signs and symptoms of biotin deficiency include hair loss which progresses in severity to include loss of eye lashes and eye brows in severely deficient subjects. Some shampoos are available that contain biotin, but it is doubtful whether they would have any useful effect, as biotin is not absorbed well through the skin.

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 [citation needed] in these cases.

Deficiency

Biotin deficiency is relatively rare and mild, and can be addressed with supplementation. Such deficiency can be caused by the excessive consumption of raw egg whites (20 eggs/day would be required to induce it), which contain high levels of the protein avidin, which binds biotin strongly. Avidin is deactivated by cooking, while the biotin remains intact.

¨Symptoms of overt biotin deficiency include hair loss and a scaly red rash around the eyes, nose, mouth, and genital area. Neurological symptoms in adults have included 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.¨[6]

Biotinidase deficiency is not due to inadequate biotin, but rather to a deficiency in the enzymes that process it.

Signs of Biotin Deficiency: In general, appetite and growth are decreased. Dermatologic symptoms include dermatitis, alopecia (hair loss) and achromotrichia (absence or loss of pigment in the hair.[7]) Perosis (a shortening and thickening of bones) is seen in the skeleton. Fatty Liver and Kidney Syndrome (FLKS) and hepatic steatosis also can occur.[2] Genetic defect could also cause biotin deficiency. Holocarboxylase synthetase deficiency is a genetic mutation. It is a severe metabolic disorder. Biochemical and clinical manifestation includes: ketolactic acidosis, organic aciduria, hyperammonemia, skin rash, feeding problems, hypotonie, seizures, development delay, alopecia, and coma. This disease is lethal, however, mentioned manifestation can be reversed by pharmacologic doses of biotin (10-100 mg per day).[citation needed]

Pregnant women tend to have high risk of biotin deficiency. Research as shown nearly half of pregnant women have an abnormal increase of 3-hydroxyisovaleric acid which reflects reduced status of biotin.[6]

Numbers of studies reported that 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 mother's biotin deficiency which does not reach the appearance of physiological deficiency signs may cause a serious consequence in the infants.

Toxicity

Animal studies have indicated few, if any, effects due to toxic 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, particularly when used in the treatment of metabolic disorders causing sebhorrheic dermatitis in infants.[8]

Biochemistry

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

The attachment of biotin to various chemical sites, called biotinylation, can be 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 histones,[9] but little biotin is found naturally attached to chromatin. Holocarboxylase synthetase is the mammalian enzyme that covalently attaches biotin to carboxylases.

Biotin binds very tightly to the tetrameric protein avidin (also streptavidin and neutravidin), with a dissociation constant Kd in the order of 10-15 mol/L which is one of the strongest known protein-ligand interactions, approaching the covalent bond in strength.[10] This is often used in different biotechnological applications. Until 2005, very harsh conditions were required to break the biotin-streptavidin bond.[11]

Laboratory uses

In the biology laboratory, biotin is often chemically linked, or tagged, to a molecule or protein for biochemical assays. This process is called biotinylation. Since avidins bind preferentially to biotin, biotin-tagged molecules can be extracted from a sample by mixing them with beads with covalently-attached avidin, and washing away anything unbound to the beads.

For example, biotin can be attached to a molecule of interest (e.g. a protein), and this modified molecule will be mixed with a complex mixture of proteins. Avidin or streptavidin beads are added to the mixture, and the biotinylated molecule will bind to the beads. Any other proteins binding to the biotinylated molecule will also stay with the beads. All other unbound proteins can be washed away, and the scientist can use a variety of methods to determine which proteins have bound to the biotinylated molecule.

Biotinylated antibodies are used to capture avidin or streptavidin in both the ELISPOT and ELISA techniques.

Ruminant nutrition

Ruminal bacteria normally synthesize biotin. Biotin is not extensively metabolized in the rumen and increased intake of dietary biotin results in elevated concentrations of biotin in serum and milk.[12] Unpublished epidemiologic data suggest a negative relationship between serum concentrations of biotin and the incidence of clinical lameness in dairy cattle. Feeding approximately 20 mg/day of supplemental biotin statistically improved measures of hoof health. Currently, insufficient data are available at this time to quantify the requirement for biotin of dairy cattle.

See also

References

  1. ^ Merck Index, 11th Edition, 1244.
  2. ^ a b c d e Combs, Gerald F. Jr. (2008). The Vitamins: Fundamental Aspects in Nutrition and Health. San Diego: Elsevier, Inc. ISBN 9780121834937.
  3. ^ McGuire M, Beerman KA. Nutritional sciences: from fundamentals to food. California: Thomson Wadsworth, 2007.
  4. ^ Gropper S.S., Smith, J.L.,Groff, J.L. (2005). Advanced nutrition and human metabolism. Belmont.{{cite book}}: CS1 maint: multiple names: authors list (link)
  5. ^ Bowman, BA and Russell, RM., ed. (2006). "Biotin". Present Knowledge in Nutrition, Ninth Edition, Vol 1. Washington, DC: Internation Life Sciences Institute. ISBN 9781578811984.{{cite book}}: CS1 maint: multiple names: editors list (link)
  6. ^ a b Higdon, Jane (2003). "Biotin". An evidence-based approach to vitamins and minerals. Thieme. ISBN 9781588901248.
  7. ^ biology-online.org
  8. ^ Combs, Gerald F. Jr. (1998). The Vitamins: Fundamental Aspects in Nutrition and Health. Ithaca: Elsevier Academic Press. ISBN 0121834921.pg. 360
  9. ^ Hymes, J; Fleischhauer, K; Wolf, B. (1995). "Biotinylation of histones by human serum biotinidase: assessment of biotinyl-transferase activity in sera from normal individuals and children with biotinidase deficiency". Biochem Mol Med. 56 (1): 76–83. doi:10.1006/bmme.1995.1059. PMID 8593541.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ Laitinen OH, Hytonen VP, Nordlund HR, Kulomaa MS. (2006). "Genetically engineered avidins and streptavidins". Cell Mol Life Sci. 63 (24): 2992–3017. doi:10.1007/s00018-006-6288-z. PMID 17086379.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ Holmberg A, Blomstergren A, Nord O; et al. (2005). "The biotin-streptavidin interaction can be reversibly broken using water at elevated temperatures". Electrophoresis. 26 (3): 501–10. doi:10.1002/elps.200410070. PMID 15690449. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
  12. ^ National Research Council (2001). Nutrient Requirements of Dairy Cattle. 7th rev. ed. Natl. Acad. Sci., Washington, DC. ISBN 0309069971.
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