IN-VITRO INHIBITION OF RAT AND HUMAN GLUTATHIONE-S-TRANSFERASE ISOENZYMES BY DISULFIRAM AND DIETHYLDITHIOCARBAMATE

The drug disulfiram (DSF, Antabuse(R)) has been used in the therapy of alcohol abuse. It is a potent inhibitor of aldehyde dehydrogenase. It s reduced form, diethyldithiocarbamate (DDTC), and further metabolites show similar activities. DSF and DDTC have also been widely used to i nhibit mixed-function oxidases. In this study, the reversible inhibiti on and time-dependent inactivation of the major rat and human glutathi one S-transferase (GST) isoenzymes by DSF and DDTC was investigated. R eversible inhibition, using 1-chloro-2,4-dinitrobenzene as substrate f or the GST alpha-, mu-, and pi-class, expressed as I-50 (in mu M), ran ged from 5-18 (human Al-1), 43-57 (rat 4-4) and 66-83 (rat 1-1), for b oth DSF and DDTC. The I-50 for rat GST theta, using 1,2-epoxy-3-(p-nit rophenoxy)-propane as substrate, was 350 mu M for DDTC. The other GSTs were significantly less sensitive to inhibition. The major part of re versible inhibition by DSF was shown to be due to DDTC, formed rapidly upon reduction of DSF by the glutathione (GSH) present in the assay t o measure GST activity. The oxidized GSH formed upon reduction of DSF might also have made a minor contribution to reversible inhibition. Th e rat and human pi-class was, by far, the most: sensitive class for ti me dependent inactivation by DSF, but no such inactivation was observe d for any of the GSTs by DDTC. Moderate susceptibility to inactivation by DSF of all the other GSTs was observed, except for human A2-2, whi ch does not possess a cysteine residue. Consistent with the assumption that a thiol residue is involved in this inactivation, a significant part of the activity could be restored by treatment of the inactivated GST with GSH or dithiotreitol.