@article {Ouwerkerk-Mahadevan1137, author = {Sivi Ouwerkerk-Mahadevan and Rommel G. Tirona and Richard A. Ripping and Jan H. T. M. Ploemen and Peter J. van Bladeren and K. Sandy Pang and Jacques H. van Boom and Gerard J. Mulder}, title = {Inhibition of Glutathione Conjugation by Glutathione Analogues in the Perfused Rat Liver}, volume = {25}, number = {10}, pages = {1137--1143}, year = {1997}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {To assess the role of GST{\textquoteright}s (glutathione S-transferases) in the (de)toxification of their substrates, an in vivo active inhibitor based on the structure of glutathione (GSH), γ-L-glutamyl-α-(D-2-aminoadipyl)-N-2-heptylamine monoethyl ester (Et-R-Hep), was developed. To increase its effectivity, analogues esterified with alkyl chains of varying lengths and one diesterified derivative (DiEt-R-Hep) were synthesized. The unesterified analogue, R-Hep, was also tested. Their isoenzyme selectivity was characterized using purified rat GST isoenzymes. Furthermore, the extent of inhibition of the GSH conjugation of (RS)-2-bromoisovalerylurea (BIU) was evaluated in rat liver cytosol, isolated hepatocytes, and in liver perfusions. All compounds inhibited Alpha- (1{\textendash}1 and 2{\textendash}2) more effectively than Mu (3{\textendash}3 and 4{\textendash}4) class GSTs; Pi-(5{\textendash}5) and Theta (7{\textendash}7) classes were minimally inhibited. The unesterified R-Hep was the most effective inhibitor towards purified isoenzymes; its Ki value towards GST 3{\textendash}3 (S-BIU as substrate) was 27 μM. The mono ethyl ester derivative, Et-R-Hep (Ki 270 μM for 3{\textendash}3), was the most potent inhibitor in hepatocytes and in the perfused liver: 50 μM inhibited the conjugation of (S)-BIU by 50\%. Longer ester chains or diesterification did not increase the inhibitory potency; R-Hep had less inhibitory activity. In all systems, only the (S)-enantiomer of BIU, which is conjugated mainly by Alpha class GSTs, was inhibited, confirming Alpha isoenzyme selective inhibition. The American Society for Pharmacology and Experimental Therapeutics}, issn = {0090-9556}, URL = {https://dmd.aspetjournals.org/content/25/10/1137}, eprint = {https://dmd.aspetjournals.org/content/25/10/1137.full.pdf}, journal = {Drug Metabolism and Disposition} }