Lovastatin enhances the photocytotoxicity of UVA radiation towards cultured N.C.T.C. 2544 human keratinocytes: prevention by cholesterol supplementation and by a cathepsin inhibitor.

The effect of the hydroxymethylglutaryl-CoA (HMG-CoA) inhibitor lovastatin on the UVA-induced photocytotoxicity has been investigated in cultured human N.C.T.C. 2544 keratinocytes. In the absence of irradiation, 5 x 10(-7) M lovastatin did not exhibit any significant cytotoxic effect towards this cell line. Although the drug cannot act as a photosensitizer, because it does not absorb in the UVA range, it markedly increased the UVA-induced cellular damage (about 70% reduction in cell viability at 5 x 10(-7) M). This effect was not accompanied by an increase in the lipid peroxidation product content of cells as compared with treatment with UVA alone. Medium supplementation with 0.01 mg/ml free cholesterol totally prevented the enhancement of UVA photocytotoxicity induced by lovastatin. A protective effect was also observed when cells were supplemented with an amount of low-density lipoprotein giving the same cholesterol concentration in the culture medium. Finally, E64 [L-trans-epoxysuccinyl-leucylamido-(4-guanidino)-butane], a lysosomal cathepsin inhibitor, also prevents the cell death induced by UVA in cells treated with lovastatin. These results suggest that HMG-CoA reductase inhibitors could increase the sensitivity of skin cells to UVA radiation, and that this phenomenon is related to lysosomal enzyme release.