White and colored grapefruit juice produce similar pharmacokinetic interactions

Colored (pink and red) grapefruit pulp contains lower amounts of the furanocoumarin derivatives that cause pharmacokinetic interactions than white grapefruit pulp. However, few studies have examined interactions with colored juice products. Therefore, we examined the potential interactions of both white and colored grapefruit products by measuring the concentrations of furanocoumarin derivatives and inhibition of the metabolizing cytochrome P450 (CYP) 3A enzymes, the target of the furanocoumarins. We measured concentrations of three major furanocoumarin derivatives, bergaptol, bergamottin, and 6',7'-dihydroxybergamottin, with high-performance liquid chromatography in 21 brands of grapefruit juice sold in Japan, including 14 white and 7 colored brands. The mean difference in bergaptol, bergamottin, and 6',7'-dihydroxybergamottin concentrations in white grapefruit juice samples was 1.59, 0.902, and 1.03 times, respectively, the amounts in colored samples. White samples inhibited CYP3A-mediated testosterone-6beta oxidation in human liver microsomes by 1.04 and 0.922 times (whole juice and furanocoumarin, respectively) the inhibition by colored juice. Thus, colored grapefruit juice may produce drug interactions at the same rate as white grapefruit juice.