Regulation of immunological and inflammatory functions by biotin.

Biotin is a water-soluble B-complex vitamin and is well-known as a co-factor for 5 indispensable carboxylases. Holocarboxylase synthetase (HLCS) catalyzes the biotinylation of carboxylases and other proteins, whereas biotinidase catalyzes the release of biotin from biotinylated peptides. Previous studies have reported that nutritional biotin deficiency and genetic defects in either HLCS or biotinidase induces cutaneous inflammation and immunological disorders. Since biotin-dependent carboxylases involve various cellular metabolic pathways including gluconeogenesis, fatty acid synthesis, and the metabolism of branched-chain amino acids and odd-chain fatty acids, metabolic abnormalities may play important roles in immunological and inflammatory disorders caused by biotin deficiency. Transcriptional factors, including NF-κB and Sp1/3, are also affected by the status of biotin, indicating that biotin regulates immunological and inflammatory functions independently of biotin-dependent carboxylases. An in-vivo analysis with a murine model revealed the therapeutic effects of biotin supplementation on metal allergies. The novel roles of biotinylated proteins and their related enzymes have recently been reported. Non-carboxylase biotinylated proteins induce chemokine production. HLCS is a nuclear protein involved in epigenetic and chromatin regulation. In this review, comprehensive knowledge on the regulation of immunological and inflammatory functions by biotin and its potential as a therapeutic agent is discussed.