Brassica vegetables increase and apiaceous vegetables decrease cytochrome P450 1A2 activity in humans: changes in caffeine metabolite ratios in response to controlled vegetable diets

Induction or inhibition of biotransformation enzymes, enzymes that activate or detoxify numerous xenobiotics, is one mechanism by which vegetables may alter cancer risk, Using a randomized crossover design, we examined the ef fect of various vegetable diets on cytochrome P450 (CYP) 1A2, N-acetyltrans ferase 2 (NAT2) and xanthine oxidase activity in humans. Men and women, non -smokers, on no medication and 20-40 years of age ate four 6-day controlled diets: basal (vegetable-free) and basal with three botanically defined veg etable groups. Enzyme activities were determined by measuring urinary caffe ine metabolite ratios after a 200 mg caffeine dose on the last day of each feeding period. Mean CYP1A2 activity for 19 men and 17 women (least squares means adjusted for sex, GSTM1 genotype, urine volume and feeding period) w ith basal, brassica, allium and apiaceous vegetable diets differed signific antly (P less than or equal to 0.0005) by diet, irrespective of the caffein e metabolite molar ratio used to describe CYP1A2 activity; brassica vegetab les increased (P < 0.04) and apiaceous vegetables decreased (P less than or equal to 0.02) activity compared with the basal and allium diets. There wa s no effect of diet on NAT2 and xanthine oxidase activities and none of the subjects differed by GSTM1 genotype. These results demonstrate that while one vegetable subgroup induces human CYP1A2 activity, another subgroup inhi bits it. This points to a complex association between consumption of a typi cal diet of various vegetables and biotransformation enzyme activities in h umans, an association that may be difficult to interpret in observational s tudies.