Oxidation of hydrogen sulfide and methanethiol to thiosulfate by rat tissues: A specialized function of the colonic mucosa

Colonic bacteria release large quantities of the highly toxic thiols hydrogen sulfide (H₂S) and methanethiol (CH₃SH). These gases rapidly permeate the colonic mucosa, and tissue damage would be expected if the mucosa could not detoxify these compounds rapidly. We previously showed that rat cecal mucosa metabolizes these thiols via conversion to thiosulfate. The purpose of the present study in rats was to determine if this conversion of thiols to thiosulfate is (a) a generalized function of many tissues, or (b) a specialized function of the colonic mucosa. The tissues studied were mucosa from the cecum, right colon, mid-colon, ileum, and stomach; liver; muscle; erythrocytes; and plasma. The metabolic rate was determined by incubating homogenates of the various tissues with H₂³⁵S and CH₃³⁵SH and measuring the rate of incorporation of ³⁵S into thiosulfate and sulfate. The detoxification activity of H₂S (expressed as nmol/mg per min) that resulted in thiosulfate production was at least eight times greater for cecal and right colonic mucosa than for the non-colonic tissues. Thiosulfate production from CH₃SH was at least five times more rapid for cecal and right colonic mucosa than for the non-colonic tissues. We conclude that colonic mucosa possesses a specialized detoxification system that allows this tissue to rapidly metabolize H₂S and CH₃SH to thiosulfate. Presumably, this highly developed system protects the colon from what otherwise might be injurious concentrations of H₂S and CH₃SH. Defects in this detoxification pathway possibly could play a role in the pathogenesis of various forms of colitis.