Studies on the interaction of furan with hepatic cytochrome P‐450

Abstract

In vitro incubation of rat liver microsomes with [14C]-furan in the presence of NADPH resulted in the covalent incorporation of furan-derived radioactivity in microsomal protein. Compared to microsomes from untreated rats a two- to threefold increase in binding was observed with microsomes from phenobarbital-treated rats and a four- to five-fold increase was observed with microsomes from rats pretreated with imidazole or pyrazole. Covalent binding was reduced with microsomes from rats pretreated with beta-naphthoflavone. Chemicals containing an amine group (semi-carbazide), those in which the amine group is blocked but have a free thiol group (N-acetylcysteine), and those which have both an amine and a thiol group (glutathione) effectively blocked binding of [14C]-furan to microsomal protein. A decrease in cytochrome P-450 (P-450) content and decreases in the activities of P-450-dependent aniline hydroxylase, 7-ethoxycoumarin-O-deethylase (ECD), and 7-ethoxyresorufin-O-deethylase (ERD) was observed 24 hours after a single oral administration of 8 or 25 mg/kg of furan, suggesting that the reactive intermediate formed during P-450 catalyzed metabolism could be binding with nucleophilic groups within the P-450. In vitro studies indicated a significant decrease in the activity of aniline hydroxylase in pyrazole microsomes and ECD in phenobarbital microsomes without any significant change in the CO-binding spectrum of P-450 or in the total microsomal heme content, suggesting that furan inhibits the P-450s induced by PB and pyrazole.(ABSTRACT TRUNCATED AT 250 WORDS)

GLUTATHIONE TRAPPING TO MEASURE MICROSOMAL OXIDATION OF FURAN TOCIS-2-BUTENE-1,4-DIAL

“…14 C]furan to microsomal proteins (Parmar and Burka, 1993). The presence of the complete microsomal system did not seem to alter the relative ratio of the mono-versus bis-GSH-reaction products.…”

“…Furan is transformed into a protein binding intermediate via a cytochrome P450-dependent process both in vivo and in vitro (Burka et al, 1991;Parmar and Burka, 1993). The reactive metabolite is efficiently trapped with glutathione (GSH), reducing protein binding by Ͼ85% (Parmar and Burka, 1993).…”

“…The use of semicarbazide was not explored since it is a potential inhibitor of the cytochrome P450-mediated oxidation of furan. GSH was chosen as the trapping agent since it protects against the majority of cytochrome P450-catalyzed protein binding of [ 14 C]furan (Parmar and Burka, 1993) and will not inhibit cytochrome P450. Trapping reactive metabolites with GSH or other sulfhydryl reagents has been used as a method to estimate the extent of metabolic activation for a number of drugs and environmental compounds (Tang et al, 1999;Smith et al, 2003;Alvarez-Diez and Zheng, 2004;Baer et al, 2005;Gan et al, 2005).…”

Trapping of cis-2-Butene-1,4-dial to Measure Furan Metabolism in Human Liver Microsomes by Cytochrome P450 Enzymes

“…Microsomally generated BDA has been successfully captured with either semicarbazide or glutathione (Chen et al, 1995;Peterson et al, 2005). However, semicarbazide does not completely block the protein binding of furan's reactive metabolite (Parmar and Burka, 1993), and reaction with glutathione yielded multiple products (Peterson et al, 2005). A simpler trapping method for reactive furanyl intermediates was reported by Baer et al (2005) in which the reactive enedial intermediate of 4-ipomeanol was quenched with NAC and NAL, forming a single substituted pyrrole conjugate in which NAC was cross-linked to NAL.…”

Comparative Metabolism of Furan in Rodent and Human Cryopreserved Hepatocytes

“…Furan's toxic effects in model systems require metabolism (Burka et al, 1991;Carfagna et al, 1993;Kedderis et al, 1993;Parmar and Burka, 1993;Fransson-Steen et al, 1997;Mugford et al, 1997). The initial product of CYP-catalyzed oxidation of furan is cis-2-butene-1,4-dial (BDA; Fig.…”