Biotin
TRADE NAMES
D-Biotin (Numerous manufacturers), Biotin Forte (Vitaline Corporation), Meribin (Mericon Industries).
DESCRIPTION
Biotin, a member of the B-vitamin family, is an essential nutrient in human nutrition. It is involved in the biosynthesis of fatty acids, gluconeogenesis, energy production, the metabolism of the branched-chain amino acids (L-leucine, L-isoleucine, L-valine) and the de novo synthesis of purine nucleotides. Recent research indicates that biotin plays a role in gene expression, both at the transcriptional and translational levels, and that it may also play a role in DNA replication.
Biotin is widely distributed in natural foodstuffs. However, the absolute amounts of biotin in foodstuffs is relatively low when compared with the other B vitamins. Some of the better food sources of biotin, are egg yolk, liver, kidney, pancreas, milk, soya and barley. Brewer's yeast or Saccharomyces cerevisiae (see Brewer's Yeast), which is used as a nutritional supplement, is one of the richest sources of biotin, as well as the other B vitamins. Royal jelly, also used as a nutritional supplement (see Royal Jelly), is another rich source of biotin. Mammals and many plant species are unable to synthesize biotin. Biotin is synthesized by bacteria, yeast and other fungi, algae and certain plant species. In fact, the microflora of the human large intestine appear to contribute to the biotin requirements of the body.
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 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. It was subsequently found that egg white injury could be cured by a liver factor which was first called protective factor X and later determined to be biotin. Because biotin cured the skin disorder of egg white injury it was called vitamin H. H is for haut, the German word for skin. Avidin causes egg white injury because it binds very tightly to biotin, preventing its absorption. This is only true for native avidin, which is resistant to hydrolysis by proteolytic enzymes. When egg white is cooked, avidin is denatured and denatured avidin is digested by proteolytic enzymes.
Although clinical biotin deficiency in humans is rare, it does occur. Prolonged consumption of raw egg white, long-term total parenteral nutrition without biotin supplementation and malabsorption syndromes, such as short-gut syndrome, have resulted in biotin-deficiency states. The symptoms and signs of biotin-deficiency, include a generalized erythematous scaly skin eruption, alopecia, conjunctivitis and neurological abnormalities. The rash may be distributed around the eyes, nose, mouth, ears and perineal orifices. The facial appearance associated with the deficiency, with the rash around the eyes, nose and mouth along with an unusual distribution of facial fat, is called biotin deficiency facies. In biotin deficient infants, the neurological findings are hypotonia, lethargy and developmental delay. In adults, the neurological findings are lethargy, depression, hallucinations and paresthesias of the extremities. Marginal biotin status may occur under certain conditions, e.g., during the first trimester of pregnancy, and it is thought that this situation may be teratogenic. Functional biotin deficiency occurs in certain genetic disorders. These will be discussed below.
