Effects of nitrite and nitrate on DNA damage induced by ultraviolet light.

UV light is a major cause of human skin cancers. Nitrite and nitrate are well-known potential risk factors for gastric cancer. Little attention has been paid to the relationship between UV light and nitrite or nitrate on cancer. We examined the effects of nitrite and nitrate on the damage to nucleosides and DNA induced by UV light from a mercury lamp and by sunlight at neutral pH. A biologically relevant dose of nitrite and nitrate increased the generation of nucleobases and malondialdehyde on the reaction of nucleosides and DNA with UV light. The efficiency of nitrite enhancing the reaction was higher than that of nitrate at low doses. The contribution of the hydroxyl radical as the reactive species was suggested from the results of the inhibitory effects of hydroxyl radical scavengers. Nitrite and nitrate also enhanced the formation of nucleobases and malondialdehyde from DNA induced by sunlight. In the presence of 5 muM nitrite, the concentration in human skin cells, the product yields by sunlight were 5-10-fold greater than those in the absence of nitrite. The addition of 80 muM NO(3)(-), a concentration in human skin cells, also increased the yields significantly. Nitrite and nitrate may play a role in enhancing the genotoxic effects of UV light in humans.