Interactions of selenium compounds with other antioxidants in DNA damage and apoptosis in human normal keratinocytes

Selenite (SeL) or selenomethionine (SeM) are the most common selenium (Se) compounds taken as dietary antioxidants to reduce oxidative stress. Because the public may frequently supplement Se compounds at high doses, the possi ble pro-oxidant effect of Se becomes a concern. Set and SeM have entirely d ifferent pharmacokinetic effects based on dose-related cytotoxicity. Our la boratory has shown previously that high doses of Set resulted in cytotoxici ty and induction of 8-hydroxydeoxyguanosine (8-OHdG) in DNA of primary huma n keratinocytes (NHK), compared with those treated with the same doses of S eM. Besides Se compounds, other dietary antioxidants, such as vitamin (Vit) C or Vit E, are often supplemented and taken together with Se compounds. H owever, the cellular effects of these interactions of Se with antioxidants are still unknown. In addition, copper is commonly present in drinking wate r, food, soil, or the environment to increase the possibility of subchronic toxicity. Copper has been shown to inhibit SeL-induced cytotoxicity and ap optosis in human colonic carcinoma cells. The present study was designed to investigate the interactive effects of SeL or SeM plus Vit C, trolox (a wa ter-soluble Vit E), or copper sulfate (CuSO4) on cell viability and inducti on of 8-OHdG adduct formation in DNA of NHK. NHK cells were treated with no Se, SeL (126.6 muM Se), or SeM (316.6 muM Se) plus two doses each of Vit C (2.27 and 4.45 muM), trolox (40 and 80 muM), or CuSO4 (7.85 and 15.7 muM) for 24 h. Coincubation of Vit C or CuSO4 with SeL appeared to protect NHK a gainst SeL-induced cytotoxicity. However, synergistic effects were observed between SeL and trolox resulting in enhanced cytotoxicity. On the other ha nd, SeM + Vit C, SeM + trolox, and SeM + CuSO4 did not affect cell viabilit y. In the absence of Se supplementation, Vit C, trolox, or CuSO4 alone did not induce 8-OHdG adduct formation, regardless of dose. When NHK cells were coincubated with SeL (126.6 muM Se) and Vit C or CuSO4, they protected NHK from SeL-induced DNA damage with a reduction in 8-OHdG generation. In cont rast, treatment of SeL C trolox elevated generation of 8-OHdG. Furthermore, treatments of SeM plus trolox or CuSO4 elevated 8-OHdG adduct formation. I n terms of apoptosis measured as internucleosomal DNA fragmentation, copper protected NHK against SeL-induced apoptosis in cultured NHK. These data su ggest that the use of CuSO4 may play a protective role in SeL-induced cytot oxicity, DNA oxidative damage, and apoptosis and that there may be potentia lly deleterious interactions among common high-dose antioxidant supplements taken by the public.