The
protoberberine alkaloid berberine carries methylenedioxy moiety and exerts a variety of pharmacological effects, such as anti-
inflammation and
lipid-lowering effects.
Berberine causes potent CYP1B1 inhibition, whereas
CYP1A2 shows resistance to the inhibition. To reveal the influence of oxidative metabolism on CYP1 inhibition by
berberine,
berberine oxidation and the metabolite-mediated inhibition were determined. After
NADPH-fortified preincubation of
berberine with P450, the inhibition of
CYP1A1 and CYP1B1 variants (CYP1B1.1, CYP1B1.3, and CYP1B1.4) by
berberine was not enhanced, and
CYP1A2 remained resistant.
Demethyleneberberine was identified as the most abundant metabolite of CYP1A1- and CYP1B1-catalyzed oxidations, and
thalifendine was generated at a relatively low rate. CYP1A1-catalyzed
berberine oxidation had the highest maximal velocity (V max) and exhibited positive cooperativity, suggesting the assistance of substrate binding when the first substrate was present. In contrast, the demethylenation by CYP1B1 showed the property of substrate inhibition. CYP1B1-catalyzed
berberine oxidation had low K m values, but it had V max values less than 8% of those of
CYP1A1. The dissociation constants generated from the binding spectrum and fluorescence quenching suggested that the low K m values of CYP1B1-catalyzed oxidation might include more than the rate constants describing
berberine binding. The natural
protoberberine/
berberine fmetabolites with methylenedioxy ring-opening (
palmatine,
jatrorrhizine, and
demethyleneberberine) and the demethylation (
thalifendine and
berberrubine) caused weak CYP1 inhibition. These results demonstrated that
berberine was not efficiently oxidized by CYP1B1, and metabolism-dependent irreversible inactivation was minimal. Metabolites of
berberine caused a relatively weak inhibition of CYP1.