Modulation by phytochemicals of cytochrome P450-linked enzyme activity

Abstract

Compounds derived from plant sources with putative anticancer properties were studied for their effects on alkoxyresorufin O-dealkylase activity, a measure of cytochrome P450 activity. The phytochemicals investigated included benzyl isothiocyanate, caffeic acid, chlorogenic acid, diosmin, ferulic acid, indole-3-carbinol, phenethyl isothiocyanate and resveratrol. Each phytochemical at concentrations of 0.25 and 0.5 μM was incubated with 0.2 mg hamster liver microsomal protein and 0.5 μM concentrations of benzyloxyresorufin, ethoxyresorufin and methoxyresorufin. Three of the phytochemicals tested, namely benzyl isothiocyanate, phenethyl isothiocyanate and resveratrol, exhibited potent inhibition of alkoxyresorufin O-dealkylase activity. Benzyl isothiocyanate inhibited benzyloxyresorufin O-dealkylase (BROD) activity, ethoxyresorufin O-deethylase (EROD) activity and methoxyresorufin O-demethylase (MROD) activity by 90% at both the 0.25 and 0.5 μM concentrations. Phenethyl isothiocyanate inhibited BROD activity by 69%, EROD activity by 90% and MROD activity by 94% at both concentrations tested. Resveratrol inhibited BROD activity by 69% at the 0.25 μM concentration and by 78% at the 0.5 μM concentration. It inhibited EROD activity by 60% at the 0.25 μM concentration and by 80% at the 0.5 μM concentration. Resveratrol exhibited the greatest inhibitory action toward MROD, i.e. 76% and 84% at the two concentrations tested. Chlorogenic acid significantly affected BROD, EROD and MROD activity only at the 0.5 μM concentration inhibiting by 51%, 47% and 54%, respectively. Caffeic acid affected BROD and MROD activity at 0.5 μM only inhibiting BROD activity by 46% and MROD activity by 40%. Diosmin inhibited EROD activity by 11% at the 0.25 μM concentration and by 61% at 0.5 μM. It inhibited MROD by 47% and 54% at the two concentrations tested but did not significantly alter BROD activity. Ferulic acid significantly inhibited EROD and MROD activity at the 0.5 μM concentration by 28% and 32%, respectively. Indole-3-carbinol significantly inhibited BROD activity by 26% at 0.25 μM and by 42% at 0.5 μM. It inhibited EROD and MROD activity by 28% and 29% at 0.5 μM, respectively. The alkoxyresorufin O-dealkylase reactions are selective for various isoforms of cytochrome P450. Our results suggest that the phytochemicals we tested have varied effects on the enzymatic activity of isoforms of cytochrome P450 that dealkylate benzyloxyresorufin, methoxyresorufin and ethoxyresorufin and therefore may have varied effects on the metabolism of substrates for these isoforms.