Formation and protein binding of the acyl glucuronide of a leukotriene B4 antagonist (SB-209247):: Relation to species differences in hepatotoxicity

SB-209247 [(E)-3-[6-[[(2,6-dichlorophenyl)-thio] methyl]-3-(2-phenylethoxy)2- pyridinyl]-2-propenoic acid], an anti-inflammatory leukotriene B-4 receptor antagonist, was associated in beagle dogs but not male rats with an inflammatory hepatopathy. It also produced a concentration-dependent ( 10 - 1000 muM) but equal leakage of enzymes from dog and rat precision-cut liver slices. The hepatic metabolism of SB-209247 was investigated with reference to the formation of reactive acyl glucuronides. [C-14] SB-209247 (100 mumol/ kg) administered i.v. to anesthetized male rats was eliminated by biliary excretion of the acyl glucuronides of the drug and its sulfoxide. After 5 h, 1.03 +/- 0.14% ( mean +/- S. E. M., n = 4) of the dose was bound irreversibly to liver tissue. The sulfoxide glucuronide underwent pH-dependent rearrangement in bile more rapidly than did the SB-209247 conjugate. [C-14] SB-209247 was metabolized by sulfoxidation and glucuronidation in rat and dog hepatocytes, and approximately 1 to 2% of [C-14] SB-209247 (100 muM) became irreversibly bound to cellular material. [C-14] SB-209247 sulfoxide and glucuronide were the only metabolites produced by dog, rat, and human liver microsomes in the presence of NADPH and UDP-glucuronic acid (UDPGA), respectively. V-max values for [C-14] SB-209247 glucuronidation by dog, rat, and human microsomes were 2.6 +/- 0.1, 1.2 +/- 0.1, and 0.4 +/- 0.0 nmol/min/mg protein, respectively. Hepatic microsomes from all three species catalyzed UD-PGA-dependent but not NADPH-dependent irreversible binding of [C-14] SB-209247 (100 - 250 muM) to microsomal protein. Although a reactive acyl glucuronide was formed by microsomes from every species, the binding did not differ between species. Therefore, neither the acute cellular injury nor glucuronidation-driven irreversible protein binding in vitro is predictive of the drug-induced hepatopathy.