Glutathione S-conjugate formation and metabolism in HepG2 cells: a cell model of mercapturic acid biosynthesis.
Mercapturic acid biosynthesis is mediated by a series of at least four enzymatic steps and three cell membrane transport events, and is believed to require the interorgan shuttling of the various metabolic intermediates. To identify a single cell type that can carry out all of these metabolic and transport steps, the present study examined whether HepG2 cells, a human hepatoma-derived cell line, can convert an electrophilic chemical (1-chloro-2,4-dinitrobenzene, CDNB) to its corresponding mercapturic acid (S-dinitrophenyl-N-acetylcysteine, DNP-NAC). The results demonstrate that HepG2 cells are able to convert CDNB to DNP-NAC in a dose- and time-dependent fashion. Intracellular conjugation with glutathione occurred rapidly, and the resulting glutathione S-conjugate was promptly transported into the culture medium, where it was sequentially degraded to the cysteinylglycine and cysteine S-conjugates. The cysteine conjugate was then presumably reabsorbed, and N-acetylated intracellularly to form the mercapturic acid. The mercapturic acid was found to accumulate slowly in the culture medium, such that after 4 h of incubation, 4-10% of the CDNB dose was recovered as the mercapturic acid. These data provide the first demonstration that a single cell type can carry out all of the transport and enzymatic steps required for mercapturic acid biosynthesis. HepG2 cells may provide a useful model system for studying this important detoxification pathway.
Rebbeor
J F
JF
Department of Environmental Medicine, University of Rochester School of Medicine, New York 14642, USA. rebbeor@envmed.rochester.edu
Wang
W
W
Clifton
D
D
Ballatori
N
N
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics*; D001692:Biological Transport; D006528:Carcinoma, Hepatocellular; D003545:Cysteine / Q000737:chemistry; D004137:Dinitrochlorobenzene / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D008658:Inactivation, Metabolic; D008113:Liver Neoplasms; D008954:Models, Biological; D014407:Tumor Cells, Cultured
C098267:2,4-dinitrophenyl-S-(N-acetylcysteine); D004137:Dinitrochlorobenzene; D005978:Glutathione; D003545:Cysteine; D000111:Acetylcysteine