Abstract
Sodium dodecyl sulphate polyacrylamide disc gel electrophoresis has been used to evaluate the induction of hepatic microsomal cytochrome P-450 in the rat by isosafrole and related compounds. Many of the benzodioxole compounds examined formed metabolite-cytochrome P-450 complexes in vitro but few were capable of forming an isolable metabolite complex in vivo. The formation of a stable metabolite complex in vivo is apparently associated with induction of cytochrome P-450 and induction of a polypeptide of molecular weight 53,000. The induction of cytochrome P-450 by benzodioxole compounds displays a high degree of structural specificity, requiring a dioxole ring and a lipophilic side chain for optimal induction. Isosafrole interacts with phenobarbitone to produce additive induction, but with methylcholanthrene it produces a synergistic induction of cytochrome P-450. Treatment of genetically "responsive" C57BL/10 and "nonresponsive"DBA/2 mice produced metabolite-cytochrome P-450 complexes and increases in monooxygenase activities in both strains. Following treatment with isosafrole the induction of a microsomal polypeptide of mol. wt. 54,000 was demonstrated in both strains on gel electrophoresis. Addition of isosafrole to isolated rat hepatocytes resulted in the initial formation of a Type I spectrum, and subsequent formation of peaks at 427 and 458 nm. The mechanism of induction by benzodioxole compounds is discussed in the light of this and evidence for the instability of the metabolite-cytochrome P-450 complex formed initially in vivo. Variation in the rate of diplacement of metabolite complexes formed in vivo with alkenyl-substituted benzodioxole compounds suggests a role for lipophilic stabilization of the metabolite-complex in the oxidized state. Benzofuran showed differing inducing characteristics compared to benzodioxole compounds, and caused induction of epoxide hydratase and glutathione S-transferases. Benzofuran administration also caused decreases in cytochrome P-450 levels and aminopyrine N-demethylase activities.