Isoenzyme-selective inhibition of glutathione conjugation in vivo: selective inhibition of the conjugation of S-2-Bromoisovalerylurea in the rat.
Glutathione S-transferases (GSTs) play a major role in the (de-)toxification of many endogenous and xenobiotic substrates. To assess their contribution in (de-)toxification, specific in vivo inhibitors that ideally are selective for a single isoenzyme of GST are required. In the present study, selective inhibition of the alpha class GST by the glutathione analog (R)-5-ethyloxycarbonyl-2-gamma-(S)-glutamylamino-N-2-hept ylpentamide (Et-R-Hep) was studied. In rat liver cytosol and in isolated rat hepatocytes, only the conjugation of the (S)-enantiomer of (RS)-2-bromoisovalerylurea (BIU), which is conjugated mainly by alpha class GST 2-2 (Te Koppele et al., Biochem. J. 252:137-142, 1988), was inhibited by Et-R-hep. The conjugation of (R)-BIU, which is mainly catalyzed by mu class GSTs 3-3 and 4-4, was unaffected. In anesthetized rats to which an infusion of (RS)-BIU was administered, the biliary excretion of the glutathione conjugate of (S)-BIU was inhibited by up to 67% after administration of Et-R-hep (an i.v. bolus dose of 200 mu mol/kg followed by an infusion of 6.7 mu mol/min/kg for 30 min). The extent of inhibition decreased gradually to reach 40% at the end of the experiment (4 hr after administration of the inhibitor). The conjugation of (R)-BIU was unaffected. Thus, the inhibitor Et-R-Hep shows preferential inhibition of the alpha-GST substrate (S)-BIU. Although Et-R-Hep is not specific for alpha class GST, it may be used to assess the role of this class of GST in (de)-toxification and conjugation in vivo.
Ouwerkerk-Mahadevan
S
S
Division of Toxicoloy, Leiden/Amsterdam Center for Drug Research, The Netherlands.
van Boom
J H
JH
Mulder
G J
GJ
D000818:Animals; D001968:Bromisovalum / Q000494:pharmacology*; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000494:pharmacology*; D007527:Isoenzymes / Q000378:metabolism*; D008099:Liver / Q000187:drug effects*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014508:Urea / Q000378:metabolism*; D014554:Urination / Q000187:drug effects
D007527:Isoenzymes; D001968:Bromisovalum; D014508:Urea; D005982:Glutathione Transferase; D005978:Glutathione