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In vitro and in vivo effects of beta-carotene on rat epidermal lipoxygenases.

The in vitro and in vivo interaction between beta-carotene (BC) and lipoxygenase (LOX) was studied in rat skin. Significant in vitro inhibitory effects of BC on epidermal LOX activity were observed with both linoleic acid or arachidonic acid as substrate. Lineweaver-Burk plots for the inhibition of epidermal purified LOX indicated mixed competitive/non-competitive inhibition. In vivo effects of BC were examined in an ultraviolet A (UVA) irradiation model. Following UVA irradiation (200 Kjoule/m2) significant increases in LOX activity and malondialdehyde (MDA) values were found, whereas catalase activity was significantly decreased. Topical pretreatment of skin with BC prevented increases in LOX activity and MDA values 4 hr post-irradiation. Catalase activity was not affected by BC treatment. BC was more effective at preventing UVA induced lipid peroxidation at low then at high concentrations. Our present results indicate the protective potential of BC on in vivo UVA induced skin damage by reduction of non-enzymatic and enzymatic lipid peroxidation.