US EPA

7432028 

Journal Article 

Effect of carbamate thioester derivatives of methyl- and 2-chloroethyl isocyanate on glutathione levels and glutathione reductase activity in isolated rat hepatocytes 

Kassahun, K; Jochheim, CM; Baillie, TA; , 

1994 

Yes 

Biochemical Pharmacology
ISSN: 0006-2952
EISSN: 1873-2968 

PERGAMON-ELSEVIER SCIENCE LTD 

OXFORD 

48 

3 

587-594 

English 

8068046 

10.1016/0006-2952(94)90290-9 

WOS:A1994PC35400019 

https://linkinghub.elsevier.com/retrieve/pii/0006295294902909
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The present study examined the effects of S-(N-methylcarbamoyl)glutathione (SMG), S-(N-methylcarbamoyl)-L-cysteine (L-SMC) and some analogs of these S-linked conjugates of methyl isocyanate (MIC) on the activity of glutathione reductase (GR) in freshly isolated rat hepatocytes and on the levels of reduced and oxidized glutathione (GSH and GSSG) in exposed cells. Both SMG and its monoethyl ester (0.5 mM) were found to inhibit GR weakly, although L-SMC proved to be an effective inhibitor of the enzyme (60 +/- 4% activity remaining after a 4-hr incubation at 0.5 mM). The cysteine adduct (SCC) of 2-chloroethyl isocyanate (CEIC) was a strong inhibitor of GR (27 +/- 1% activity remaining after a 1-hr incubation at 0.1 mM) and was essentially equipotent with the antitumor agent N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU). L-SMC depleted intracellular GSH in a time- and concentration-dependent manner up to 2 hr of incubation, beyond which time GSH levels began to recover. Exposure of cells to the enantiomeric conjugate, D-SMC, led to a similar concentration- and time-dependent inhibition of GR and fall in intracellular GSH, but in this case the depletion of GSH was extensive and was sustained throughout the 5-hr incubation period. Only a small amount (less than 10%) of the GSH that was lost from cells exposed to SMC was recovered in the medium, indicating that SMC did not cause efflux of GSH (most of the free cysteine released during breakdown of SMC was recovered in the medium). Experiments with hepatocytes exposed for 5 hr to SCC (0.1 mM) demonstrated that GSSG levels were elevated by 32 +/- 5% relative to controls. Collectively, these results indicate that carbamate thioester conjugates of MIC and CEIC inhibit GR, probably via release of the free isocyanate at the cell surface, which then penetrates the hepatocyte. The inhibitory effects of the isocyanates on GR, coupled with their propensity to react spontaneously with GSH, combine to deplete significantly intracellular stores of GSH. 

carbamate thioesters; enzyme inhibition; glutathione; glutathione reductase; isolated rat hepatocytes; 2 chloroethyl isocyanate; carbamic acid ester; carmustine; glutathione; glutathione disulfide; glutathione reductase; isocyanic acid derivative; methyl isocyanate; s (n methylcarbamoyl)cysteine; s (n methylcarbamoyl)glutathione; unclassified drug; animal cell; article; controlled study; cytotoxicity; drug activity; drug effect; drug screening; enzyme inhibition; liver cell culture; nonhuman; priority journal; rat; Animal; Cells, Cultured; Cysteine; Glutathione; Glutathione Disulfide; Glutathione Reductase; Hydrogen-Ion Concentration; Liver; Male; Rats; Rats, Sprague-Dawley; Support, Non-U.S. Gov't; Support, U.S. Gov't, P.H.S.