Inhibition of glutathione conjugation in the rat in vivo by analogues of glutathione conjugates.

Glutathione (GSH) conjugation plays an important role in (de-)toxification of its substrates in vivo. We have developed inhibitors of GSH conjugation that are active in the rat in vivo which are derived from the structure of GSH conjugates: they contain a backbone of gamma-L-Glu-D-2-aminoadipic acid that is virtually isosteric with the gamma-L-Glu-L-Cys-Gly structure of GSH. In addition, a hydrophobic alkyl group is attached such that it may interact with the H-site of the enzyme. Finally, the carboxyl groups were esterified with alcohols of varying chain length. The results show that all these compounds preferentially inhibit alpha-GST's 1-1 and 2-2, have less effect on mu isoenzymes 3-3 and 4-4, and finally, have little effect on rat theta (G.J. Mulder, S. Ouwerkerk-Mahadevan, Modulation of glutathione conjugation in vivo: How to decrease glutathione conjugation in vivo or in intact cellular systems in vitro, Chem. Biol. Interact. 105 (1997) 17-34) and pi (S. Ouwerkerk-Mahadevan, J.H. van Boom, M.C. Dreef-Tromp, J.H.T.M. Ploemen, D.J. Meyer, G.J. Mulder, Glutathione analogues as novel inhibitors of rat and human glutathione S-transferase isoenzymes, as well as of glutathione conjugation in isolated rat hepatocytes and the rat in vivo, Bioche. J., 308 (1995) 283-290). Several of the compounds inhibit the GSH conjugation of bromsulfophthalein and (S)-2-bromisovalerylurea in hepatocytes, in the situ recirculating rat liver perfusion and in the rat in vivo (after i.v. administration). The most effective compound contains a 2-heptylamine group linked as an amide to the 1-carboxyl group of the aminoadipic acid moiety at the H-site, and an ethyl ester at the 5-carboxylic acid group of aminoadipic acid.