TY - JOUR T1 - Inhibition of Glutathione Conjugation by Glutathione Analogues in the Perfused Rat Liver JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 1137 LP - 1143 VL - 25 IS - 10 AU - Sivi Ouwerkerk-Mahadevan AU - Rommel G. Tirona AU - Richard A. Ripping AU - Jan H. T. M. Ploemen AU - Peter J. van Bladeren AU - K. Sandy Pang AU - Jacques H. van Boom AU - Gerard J. Mulder Y1 - 1997/10/01 UR - http://dmd.aspetjournals.org/content/25/10/1137.abstract N2 - To assess the role of GST’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- (1–1 and 2–2) more effectively than Mu (3–3 and 4–4) class GSTs; Pi-(5–5) and Theta (7–7) classes were minimally inhibited. The unesterified R-Hep was the most effective inhibitor towards purified isoenzymes; its Ki value towards GST 3–3 (S-BIU as substrate) was 27 μM. The mono ethyl ester derivative, Et-R-Hep (Ki 270 μM for 3–3), 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 ER -