Meta-Biol

• Pathways

Cyanide is a potent metabolic poison, a major component of which is binding to and inhibition of cytochrome c oxidase (cytochrome a3), resulting in the rapid inhibition of oxidative phosphorylation (Hall & Rumack 1986). As a result, cells can't utilise oxygen, giving rise to central nervous system, cardiovascular and respiratory dysfunction that can result in permanent neurological defects and, in severe cases, death. At body's pH, cyanide exists mainly in the undissociated form hydrogen cyanide (HCN) which can cross cellular and subcellular membranes such as the blood brain barrier and mitochondrial membranes. Cyanide intoxication can occur after smoke inhalation, industrial exposure, ingestion of cyanogenic substances and cyanogenic food sources such as cassava. Antidotes for HCN poisoning cases include HCN binders, sulfur donors that convert HCN to the less toxic thiosulfate and competitors for HCN enzymatic binding sites such as NO (Petrikovics et al. 2015).

Two pathways in mammals are able to detoxify cyanide as thiocyanate via transfer of a sulfur atom: thiosulfate sulfurtransferase (TST aka rhodanese) in mitochondria and 3-mercaptopyruvate sulfurtransferase (MPST aka 3MST) in cytosol and mitochondria. TST can act to detoxify HCN by transsulfuration, that is mediating the transfer of a sulfur atom from thiosulfate (S2O3(2-)) to HCN to form the less toxic thiocyanic acid (HSCN) (Himwich & Saunders 1948, Aita et al. 1997, Zottola 2009). HSCN can be excreted in urine via the kidneys (Hamel 2011).