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Effect of light on the hydrocarbon‐DNA adducts formed in hamster embryo cells

Polycyclic aromatic hydrocarbons are metabolically activated and bind to DNA in hamster embryo cell cultures. The effect of light exposure on the DNA adducts formed from two hydrocarbons of different photosensitivities was investigated by exposing cells to light during hydrocarbon treatment and by exposing DNA to light after isolation from cells treated with hydrocarbon in darkness. The total hydrocarbon‐DNA adducts formed per mg DNA in cells treated with the highly photosensitive hydrocarbon 7,12‐dimethylbenz(a)anthracene (DMBA) in the presence of light was less than in cells treated in darkness. No appreciable amounts of hydrocarbon‐DNA adducts were formed in cells treated with a major photo‐oxidation product of DMBA, the 7,12‐endoperoxide, in either the presence or absence of light. DMBA‐deoxyribonucleoside adducts were analyzed by chromatography on Sephadex LH20 columns. Exposure to light of the DMBA‐deoxyribonucleoside adducts obtained by enzymatic degradation of DNA isolated from cells treated with DMBA in darkness converted more than half to photoproducts. DNA that was exposed to light prior to degradation contained less than half as many photoproducts and had an elution profile similar to that obtained from DNA isolated from cells treated with DMBA in the presence of light. With the less photosensitive hydrocarbon benzo(a)pyrene, benzo(a)pyrene‐DNA adducts were identical for DNA from cells treated with benzo(a)pyrene in darkness, DNA from cells treated in the presence of light, and DNA exposed to light after isolation. These results indicate that exposure to light does not alter the mechanism of binding of hydrocarbons to DNA in hamster embryo cells, but does affect the DNA adducts of the photosensitive hydrocarbon DMBA in a similar manner in cells and in isolated DNA.