Biotin

Biotin[1]
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
CAS number	58-85-5 Y
PubChem	171548
ChemSpider	149962 Y
UNII	6SO6U10H04 Y
DrugBank	DB00121
KEGG	D00029 Y
ChEBI	CHEBI:15956 Y
ChEMBL	CHEMBL857 Y
Jmol-3D images	Image 1 Image 2
SMILES O=C1N[C@@H]2[C@@H](SC[C@@H]2N1)CCCCC(=O)O C1[C@H]2[C@@H]([C@@H](S1)CCCCC(=O)O)NC(=O)N2
InChI InChI=1S/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 Y Key: YBJHBAHKTGYVGT-ZKWXMUAHSA-N Y 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 Key: YBJHBAHKTGYVGT-ZKWXMUAHBB
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
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Biotin, also known as Vitamin H or Coenzyme R^[2], is a water-soluble B-complex vitamin (vitamin B₇) discovered by Bateman in 1916^{[chronology citation needed]}. 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 in the metabolism of fatty acids, isoleucine, and valine, 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 may also be helpful in maintaining a steady blood sugar level.^[3] Biotin is often recommended for strengthening hair and nails.^{[citation needed]} As a consequence, it is found in many cosmetics and health products for the hair and skin, though it cannot be absorbed through the hair or skin itself.

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^[4] and Australia,^[5] do not prescribe a recommended daily intake of biotin. However, a number of metabolic disorders in which an individual's metabolism of biotin is abnormal exist.^{[citation needed]}

Biosynthesis

The Empirical formula of Biotin is (C10 H16 O3 N2 S). Biotin has an unusual structure. It has two side rings fused together. The two side rings are imidazole and thiophene. Biotin is a heterocyclic S-containing (mono-)carboxylic acid. Biotin 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. 7,8-Diaminopelargonic acid (DAPA) aminotransferase, is unsual in using S-adenosylmethionine (AdoMet) as the NH2 donor. Dethiobiotin synthethase catalyzes the formation of the ureido ring via a DAPA carbamate activated with ATP. Biotin synthase reductively cleaves AdoMet 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.^[6]

Cofactor Biochemistry

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

• Acetyl-CoA carboxylase alpha
• Acetyl-CoA carboxylase beta
• Methylcrotonyl-CoA carboxylase
• Propionyl-CoA carboxylase
• Pyruvate carboxylase

and, so, is important in fatty acid synthesis, branched-chain amino acid catabolism, and gluconeogenesis. Biotin 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.^[7] The attachment of biotin to various chemical sites 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 histone proteins,^[8] 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 K_d in the order of 10⁻¹⁵, which is one of the strongest known protein-ligand interactions, approaching the covalent bond in strength.^[9] This is often used in different biotechnological applications. Until 2005, very harsh conditions were thought to be required to break the biotin-streptavidin bond.^[10]

Sources of biotin

Biotin is consumed from a wide range of food sources in the diet, however there are few particularly rich sources. Foods with a relatively high biotin content include Swiss chard, raw egg yolk (however, the consumption of egg whites with egg yolks minimizes the effectiveness of egg yolk's biotin in one's body), liver, some vegetables^{[citation needed][vague]}, and peanuts. The dietary biotin intake in Western populations has been estimated to be 35 to 70 μg/d (143–287 nmol/d).^[11]

Biotin is also available from supplements. The synthetic process developed by Leo Sternbach and Moses Wolf Goldberg in the 1940s uses fumaric acid as a starting material. ^[12]

Bioavailability

Biotin is also called vitamin H (the H represents "Haar und Haut”, German words for “hair and skin”) or vitamin B₇. 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.^[13] 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.^[14]

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.^[14]

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 that have had partial gastrectomy or that have other causes of achlorhydria, burn patients, epileptics, elderly individuals, and athletes.^[14] 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.^[15]

Deficiency

Biotin deficiency is relatively rare and mild, and can be addressed with supplementation. Such deficiency can be caused by the consumption of raw egg whites (eating two or more uncooked egg whites daily for several months has caused biotin deficiency that is serious enough to produce symptoms [1]), which contain high levels of the protein avidin, which binds biotin strongly.

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, hair loss, alopecia,^[16] and neuromuscular dysfunction. This syndrome was called egg white injury and was discovered to be caused by a glycoprotein found in egg white called avidin.^{[citation needed]}

Avidin denaturates 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.^[4]

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.^[17]

Pregnant women tend to have a high risk of biotin deficiency. Research has shown that nearly half of pregnant women have an abnormal increase of 3-hydroxyisovaleric acid, which reflects reduced status of biotin.^[17] 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 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.^[18] Biochemical and clinical manifestation includes: 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.^[18] General symptoms include decreased appetite and growth. Dermatologic symptoms include dermatitis, alopecia (hair loss) and achromotrichia (absence or loss of pigment in the hair).^[19] Perosis (a shortening and thickening of bones) is seen in the skeleton. Fatty liver and kidney syndrome (FLKS) and hepatic steatosis also can occur.^[14]

Uses

Diabetes

Diabetics may benefit from biotin supplementation. In both insulin-dependent and non-insulin-dependent diabetics, supplementation with biotin can improve blood sugar control and help lower fasting blood glucose levels, in some studies the reduction in fasting glucose exceeded 50 percent. 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.^[20][21]

Hair & 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. Biotin supplements are available in most pharmacies. The recommended dose is about 5000mcg to 7500mcg per day. Thicker and stronger hair and healthier nails may be seen within several months, depending on rate of growth.^{[citation needed]} 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.^{[citation needed]}

Palmo Plantar 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 that 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, and so the biotin treatment provided beneficial effects in the therapy of the diseases, as in the case of palmoplantar pustulosis.^{[citation needed]}

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^[22] in these cases.

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.^[23]

Laboratory uses

In the laboratory, biotin is often chemically linked to proteins for biochemical assays. Its 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 (K_d of ~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 primary antibodies against the antigen of interest, followed by a detection step using streptavidin conjugated to a reporter molecule, such as Horseradish peroxidase.

See also

• Avidin
• Biotinylation
• Multiple carboxylase deficiency
• NeutrAvidin
• Photobiotin
• Strep-tag
• Streptavidin

References

1. ^ Merck Index, 11th Edition, 1244.
2. ^ "Biotin". The Free Medical Dictionary. http://medical-dictionary.thefreedictionary.com/biotin. Retrieved 2011-10-10. 
3. ^ Supplementinfo.org
4. ^ ^{a b} Otten, JJ, Hellwig, JP and Meyers, LD., ed (2006). Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. The National Academies Press. ISBN 0-309-10091-7. 
5. ^ National Health and Medical Research Council: Nutrient Reference Values for Australia and New Zealand
6. ^ Marquet A, Bui BT, Florentin D (2001). "Biosynthesis of biotin and lipoic acid". Vitam. Horm. 61: 51-101. PMID 11153271. 
7. ^ Zempleni J, Wijeratne SS, Hassan YI. (2009). "Biotin". Biofactors 35 (1): 36–46. doi:10.1002/biof.8. PMID 19319844. 
8. ^ 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. 
9. ^ 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. 
10. ^ Holmberg A, Blomstergren A, Nord O et al. (2005). "The biotin-streptavidin interaction can be reversibly broken using water at ALL BS BS BS BS elevated temperatures". Electrophoresis 26 (3): 501–10. doi:10.1002/elps.200410070. PMID 15690449. 
11. ^ Zempleni J, Mock DM. (1999). "Biotin biochemistry and human requirements". J Nutr Biochem. 10 (3): 128–138. doi:10.1016/S0955-2863(98)00095-3. PMID 15539280. 
12. ^ "Biotin". DSM Nutritional Products. 2009-08-31. http://www.dsm.com/en_US/html/dnp/prod_vit_biotin.htm. Retrieved 2010-02-19. ^{[dead link]}
13. ^ Gropper S.S., Smith, J.L.,Groff, J.L. (2005). Advanced nutrition and human metabolism. Belmont. ISBN 0534559867. 
14. ^ ^{a b c d} Combs, Gerald F. Jr. (2008). The Vitamins: Fundamental Aspects in Nutrition and Health. San Diego: Elsevier, Inc. ISBN 9780121834937. 
15. ^ Bowman, BA and Russell, RM., ed (2006). "Biotin". Present Knowledge in Nutrition, Ninth Edition, Vol 1. Washington, DC: Internation Life Sciences Institute. ISBN 9781578811984. 
16. ^ "Biotin deficiency craft hair loss and alopecia citation of Bible". Healthy Hair Highlights News. 22 July 2011. http://www.healthyhairhighlights.com/hair_loss_and_hair_growth_in_bible.html. Retrieved 2011-11-09. 
17. ^ ^{a b} Higdon, Jane (2003). "Biotin". An evidence-based approach to vitamins and minerals. Thieme. ISBN 9781588901248. 
18. ^ ^{a b} Wolf B, Grier RE, Secor McVoy JR, Heard GS. (1985). "Biotinidase deficiency: a novel vitamin recycling defect". J Inherit Metab Dis. 8 (1): 53–8. doi:10.1007/BF01800660. PMID 3930841. 
19. ^ biology-online.org
20. ^ Howstuffworks.com
21. ^ Oregon State University, Linus Pauling Institute, Micronutrient Research
22. ^ Murray, Michael; Pizzorno, Joseph (1997). "Encyclopedia of Natural Medicine" (Revised 2nd Edition) Three Rivers Press. ISBN 0761511571
23. ^ Combs, Gerald F. Jr. (1998). The Vitamins: Fundamental Aspects in Nutrition and Health. Ithaca: Elsevier Academic Press. ISBN 0121834921. pg. 360

External links

• Jane Higdon, "Biotin", Micronutrient Information Center, Linus Pauling Institute, Oregon State University
• Clercq, Pierre J. De (1997). "Biotin: A Timeless Challenge for Total Synthesis". Chemical Reviews 97 (6): 1755–1792. doi:10.1021/cr950073e. PMID 11848892. 
• "Biotin". DSM Nutritional Products. 2009-10-29. http://www.vitamin-basics.com/index.php?id=52. Retrieved 2010-05-14.