RT Journal Article
SR Electronic
T1 Identification of the Thiophene Ring of Methapyrilene as a Novel Bioactivation-Dependent Hepatic Toxicophore
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 657
OP 671
DO 10.1124/jpet.107.135483
VO 326
IS 2
A1 Emma E. Graham
A1 Rachel J. Walsh
A1 Charlotte M. Hirst
A1 James L. Maggs
A1 Scott Martin
A1 Martin J. Wild
A1 Ian D. Wilson
A1 John R. Harding
A1 J. Gerald Kenna
A1 Raimund M. Peter
A1 Dominic P. Williams
A1 B. Kevin Park
YR 2008
UL http://jpet.aspetjournals.org/content/326/2/657.abstract
AB Methapyrilene (MP), a 2-thiophene H1-receptor antagonist, is a model toxicant in the genomic and proteomic analyses of hepatotoxicity. In rats, it causes an unusual periportal necrosis that is hypothetically attributed to chemically reactive and cytotoxic metabolites. We have characterized the bioactivation of MP by hepatic microsomes and primary rat hepatocytes, and we established a possible causal linkage with cytotoxicity. Methapyrilene tritiated at C-2 of the diaminoethane moiety ([3H]MP) was metabolized via an NADPH-dependent pathway to intermediates that combined irreversibly with microsomes (rat > mouse ≈ human). This binding was attenuated by the cytochrome P450 (P450) inhibitor 1-aminobenzotriazole and thiols but not by trapping agents for iminium ions and aldehydes. Reactive intermediates were trapped as thioether adducts of monooxygenated MP. Mass spectrometric and hydrogen/deuterium exchange analysis of the glutathione adduct produced by rat liver microsomes indicated that the metabolite was most probably a thioether of MP S-oxide substituted in the thiophene ring. The glutathione adduct was formed by rat hepatocytes and eliminated in bile by rats administered [3H]MP intravenously. MP produced concentration- and time-dependent cytotoxicity, depleted glutathione, and underwent irreversible binding to the hepatocytes before a significant increase in cell damage was observed. P450 inhibitors reduced turnover of the drug, production of the glutathione adduct, irreversible binding, and cytotoxicity but inhibited glutathione depletion selectively. MP underwent lesser turnover and bioactivation in mouse hepatocytes and was not cytotoxic. Analogs with phenyl and p-methoxyphenyl rings were much less hepatocytotoxic than MP. Hepatotoxicity in rats was diminished by predosing with 1-aminobenzotriazole. For the first time, a thiophene ring substituent is identified as a bioactivation-dependent toxicophore in hepatocytes. The American Society for Pharmacology and Experimental Therapeutics