Figure 1.

(A) Biosynthesis of cysteamine and intersection with cysteine catabolism. Cysteamine is generated in mammals by the degradation of coenzyme A, which is required for the metabolism of fatty acids, carbohydrates, amino acids and ketone bodies. When coenzyme A is cleaved (cleavage at the dotted line), pantetheine is generated, which is acted on by pantetheinase or vanin to form cysteamine. Cysteamine is converted to hypotaurine by cysteamine decarboxylase. Cysteine, a component of coenzyme A, is acted on by cysteine dioxygenase to form cysteine sulfonate which is decarboxylated by cysteine sulfonate decarboxylase to form hypotaurine. Hypotaurine generated is further metabolized to taurine by hypotaurine decarboxylase. (B) Effects of cysteamine/cystamine. Both cysteamine and its oxidized form cystamine have protective effects in cells and tissues. Originally identified as radioprotective molecules, subsequently these aminothiols have been reported to mitigate cystinosis, a condition characterized by accumulation of cystine crystals in the body. Cystamine and cysteamine have a variety of other effects which include antioxidant effects (by increasing cysteine and glutathione levels), inhibition of transglutaminase 2 and caspase 3 (possibly by modifying reactive cysteine residues or cysteaminylation), modulation of mitochondrial function, immunomodulation. These molecules have also been reported to increase levels of brain derived neurotrophic factor (BDNF) and heat shock proteins, which affords neuroprotective benefits.