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Herbal supplements are not governed by the same regulations as prescription drugs, we hypothesize that the content of their active ingredients may vary largely among different manufacturers. This may produce variable therapeutic outcomes. This study aims to examine this hypothesis on commonly used herbal supplements among cancer patients. CYP1A2 has been implicated in the activation of many carcinogens and alteration in its activity may be a mechanism associated with the protective effect of herbal products. Activity of human CYP1A2 was used to determine the effect of four herbal supplements of different brands, namely, black cohosh (BC), ginseng, grape seed extract (GSE) and green tea extract (GTE). The herbal content was extracted with methanol, and extract aliquots were used to determine their effect on CYP1A2. Human liver microsomes, the CYP1A2 probe (7-ethoxyresorufin) and NADPH in buffer were incubated with and without herbal extract. Metabolite (resorufin) formation was monitored by HPLC. Seven BC products caused a mild inhibition of CYP1A2, ranging from 2.4 % by GNC Plus to 21.9 % by Nature's Resource. Among nine ginseng products tested, the inhibitory effect varied from 4.2 % by Imperial to 44.6 % by Solarays. The effect of nine GSE brands also varied, ranging from 1.7 % (Country Life) to 26.5 % (Veg Life). Of twelve GTE products, the inhibitory effect varied from 2.9 % by Henry's to 46.6 % by GNC Plus. It appears that the inhibition of selected herbal supplements on CYP1A2 activity varies considerably among different brands of the products. This may be due to variations in the herbal products' active ingredients content.

Variable inhibitory effect of herbal supplements of different brands on human P450 CYP1A2