Alterations in intracellular thiol homeostasis during the metabolism of menadione by isolated rat hepatocytes.
The effects of menadione (2-methyl-1,4-naphthoquinone) metabolism on intracellular soluble and protein-bound thiols were investigated in freshly isolated rat hepatocytes. Menadione was found to cause a dose-dependent decrease in intracellular glutathione (GSH) level by three different mechanisms: (a) Oxidation of GSH to glutathione disulfide (GSSG) accounted for 75% of the total GSH loss; (b) About 15% of the cellular GSH reacted directly with menadione to produce a GSH-menadione conjugate which, once formed, was excreted by the cells into the medium; (c) A small amount of GSH (approximately 10%) was recovered by reductive treatment of cell protein with NaBH4, indicating that GSH-protein mixed disulfides were also formed as a result of menadione metabolism. Incubation of hepatocytes with high concentrations of menadione (greater than 200 microM) also induced a marked decrease in protein sulfhydryl groups; this was due to arylation as well as oxidation. Binding of menadione represented, however, a relatively small fraction of the total loss of cellular sulfhydryl groups, since it was possible to recover about 80% of the protein thiols by reductive treatments which did not affect protein binding. This suggests that the loss of protein sulfhydryl groups, like that of GSH, was mainly a result of oxidative processes occurring within the cell during the metabolism of menadione.
D000818:Animals; D005978:Glutathione / Q000378:metabolism; D006706:Homeostasis; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction; D011506:Proteins / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012995:Solubility; D013347:Subcellular Fractions / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism; D014812:Vitamin K / Q000378:metabolism* / Q000494:pharmacology
D011506:Proteins; D013438:Sulfhydryl Compounds; D013481:Superoxides; D014812:Vitamin K; D005978:Glutathione