Effects of selenium compounds on induction of DNA damage by broadband ultraviolet radiation in human keratinocytes.

Background Ultraviolet radiation (UVR), a ubiquitous environmental genotoxin for the skin, produces DNA damage. The trace element selenium induces synthesis of the glutathione peroxidase and thioredoxin reductase enzyme families. These selenoenzymes detoxify a range of toxic compounds generated by free radicals. Objectives To assess the effects of pretreatment of primary human keratinocytes with selenium on UVR-induced DNA damage. Methods Cells were irradiated with UVR from FS-20 lamps and were subjected to comet assay. Results Comet tail length due to UVR-induced T4 endonuclease V-sensitive sites (caused by cyclopyrimidine dimers, CPDs) increased to 35 +/- 4.5 microm (mean +/- SD) immediately after irradiation (time 0 h, 100%). After 4 h, 68% of the damage remained and after 24 h, 23% of the damage was still present. Treatment with up to 200 nmol L-1 selenomethionine or 50 nmol L-1 sodium selenite had no effect on CPD formation or rates of repair, or on the number of excision repair sites as measured by cytosine arabino furanoside and hydroxyurea treatment. However, selenite and selenomethionine protected against oxidative damage to DNA as measured by formation of formamidopyrimidine (FaPy) glycosylase-sensitive sites, which are indicative of 8-hydroxy-2-deoxyguanosine photoproduct formation. In this assay, irradiation of keratinocytes increased mean +/- SD glycosylase-specific comet tail length from 5 +/- 1.5 microm to 19 +/- 3.3 microm. Preincubation for 18 h with 50 nmol L-1 selenite abolished the UVR-induced increase in comet length. Preincubation with 200 nmol L-1 selenomethionine was similarly protective. Conclusions Selenite and selenomethionine protect keratinocytes from UVR-induced oxidative damage, but not from formation of UVR-induced excision repair sites.