Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced tumor promotion and ornithine decarboxylase activity by quercetin: possible involvement of lipoxygenase inhibition

Abstract

Quercetin (30 μ mol/mouse) markedly suppressed the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA, 20 nmol/mouse) on skin tumor formation in the CD-1 mice initiated by 7,12-dimethylbenz[a]anthracene (200 nmol/mouse). TPA (20 nmol/mouse)-induced epidermal ornithine decarboxylase (ODC) activity was also inhibited by quercetin (10–30 μ mol/mouse), but it failed to inhibit the stimulation, of epidermal DNA synthesis by TPA. In addition, quercetin potently inhibited lipoxygenase from 105 000 g supernatant of epidermal homogenate of mice. The 50% inhibition of lipoxygenase was observed by quercetin at 1.3 μ M. These results suggest that the inhibition of lipoxygenase by quercetin is one of the major actions of the above agent to inhibit tumor promotion and TPA-induced ODC activity.