Induction and excretion of ultraviolet-induced 8-oxo-2 '-deoxyguanosine and thymine dimers in vivo: Implications for PUVA

Molecular epidemiology has linked ultraviolet-induced DNA damage with mutag enesis and skin carcinogenesis. Ultraviolet radiation may damage DNA in one of two ways: either directly, leading to lesions such as cyclobutane thymi ne dimers (T<>T), or indirectly, via photosensitizers that generate free ra dical species that may ultimately produce such oxidative lesions as 8-oxo-2 '-deoxyguanosine. We report the results of a pilot, case control study in w hich seven, healthy, human volunteers (skin type II; aged 23-56 y; three ma le, four female) received a suberythemal dose of whole body irradiation fro m ultraviolet-A-emitting fluorescent tubes used in psoralen plus ultraviole t A therapy. First void, mid-stream urine samples were collected pre-exposu re and daily postexposure, for up to 13 d. Analysis of urinary 8-oxo-2'-deo xyguanosine and cyclobutane thymine dimers was by competitive enzyme-linked immunosorbent assay (interassay coefficient of variation less than or equa l to 10%) and compared with a matched, control group of unirradiated indivi duals. A maximal increase in levels of urinary 8-oxo-2'-deoxyguanosine was seen 4 d post-ultraviolet exposure. A subsequent reduction was noted, befor e finally returning to baseline. Similarly, cyclobutane thymine dimer level s peaked 3 d postexposure, before returning to baseline. In contrast to the 8-oxo-2'-deoxyguanosine analysis, however, a second peak was noted at days 9-11, before again returning to baseline. This is the first report examini ng urinary 8-oxo-2'-deoxyguanosine and cyclobutane thymine dimers following ultraviolet exposure of healthy human subjects. This work illustrates the induction and time course for excretion of ultraviolet-induced lesions, per haps alluding to repair and ultimately offering the potential to define pso ralen plus ultraviolet A dosage regimes in terms of minimizing DNA damage a nd hence cancer risk.