Pathophysiology
Clinical meaning
Cyanide is one of the most rapidly lethal poisons known, capable of causing death within minutes at sufficient doses. It exists in multiple forms: hydrogen cyanide (HCN, a volatile gas), cyanide salts (potassium cyanide/KCN, sodium cyanide/NaCN), cyanogenic glycosides (amygdalin in bitter almonds, cassava, apple seeds), and cyanide-releasing compounds (sodium nitroprusside, acetonitrile in artificial nail remover). The most common cause of cyanide poisoning in developed countries is smoke inhalation from structural fires -- combustion of synthetic materials (polyurethane, nylon, wool, silk, plastics) releases hydrogen cyanide gas, and fire victims often have combined cyanide and carbon monoxide (CO) poisoning, which is synergistically lethal. Industrial exposure in mining, electroplating, chemical manufacturing, and photography is another important source. The mechanism of cyanide toxicity centers on the inhibition of cytochrome c oxidase (Complex IV), the terminal enzyme of the mitochondrial electron transport chain (ETC). Under normal aerobic metabolism, cells generate ATP through oxidative phosphorylation: electrons from NADH and FADH2 are passed through Complexes I, II, III, and IV of the ETC embedded in the inner mitochondrial membrane, with molecular oxygen (O2) serving as the final...