J Toxicol Environ Health A

Glutathione S-conjugate formation and metabolism in HepG2 cells: a cell model of mercapturic acid biosynthesis.

Year 1998
Rebbeor JF. Wang W. Clifton D. Ballatori N.
Department of Environmental Medicine, University of Rochester School of Medicine, New York 14642, USA. rebbeor@envmed.rochester.edu
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.