Capsaicin as an in vitro inhibitor of benzo(a)pyrene metabolism and its DNA binding in human and murine keratinocytes.

Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide), the active principle of capsicum fruits, such as hot peppers, is a known inhibitor of substance P. This substance was also found to be a potent in vitro inhibitor of human and murine epidermal metabolism of benzo(a)pyrene (BP) and the enzyme-mediated binding of BP metabolites to DNA. In both untreated and 3-methylcholanthrene-treated neonatal rat epidermal microsomes, capsaicin resulted in a dose-dependent inhibition of aryl hydrocarbon hydroxylase activity with an I50 value of 3.0 X 10(-4)-3.6 X 10(-4) M. A Lineweaver-Burk plot of the inhibition of aryl hydrocarbon hydroxylase activity suggested that the inhibition is of the noncompetitive type with Ki value of 50 microM. Capsaicin also inhibited BP metabolism and the binding of 3H-BP to DNA in BALB/c mouse and human keratinocytes. The formation of BP-7,8-diol was also substantially diminished in both systems in the presence of capsaicin (180-300 microM). Our results indicate that the substance P inhibitor, capsaicin, is also an inhibitor of epidermal BP metabolism and DNA binding of its metabolites. Therefore, in addition to its neurological effects, capsaicin may represent a new category of compound with anti-carcinogenic effects.