Low doses of UVB or UVA induce chromosomal aberrations in cultured human skin cells

Chromosomal defects are frequently present in malignant and premalignant sk in disorders; however, it is not known whether ultraviolet radiation from s unlight plays a role in their induction. To obtain information on the abili ty of ultraviolet A and ultraviolet B to induce chromosomal aberrations, cu ltured melanocytes and fibroblasts were exposed to physiologic doses of ult raviolet A or ultraviolet B and, for comparison, to gamma rays. As a measur e of chromosomal aberrations, the formation of micronuclei was determined. To obtain sufficient statistical data on induced micronuclei and cell kinet ics, a flow cytometry method has been modified and applied. The flow cytome try method analysis is based on staining the DNA with ethidium bromide and the cell membranes with 1,6-diphenyl-1,3,5,-hexatriene, We observed dose-de pendent micronuclei formation after gamma or ultraviolet B irradiation in b oth cell types and also for ultraviolet A in fibroblasts. The yield of micr onuclei induced in fibroblasts by ultraviolet A was only a factor 15 smalle r than that induced by ultraviolet B (313 nm). The results indicate that 10 kJ per m(2) (equivalent to 1 minimal erythema dose) of ultraviolet B and 1 50 kJ per m(2) of ultraviolet A (0.2 minimal erythema dose) can induce 1% o f micronuclei in fibroblasts, equivalent to the induction due to 0.6 Gy of gamma radiation. In conclusion, physiologic doses of sunlight can induce ch romosomal aberrations at a level comparable with that observed after exposu re to approximately 1 Gy of ionizing radiation. Therefore, sunlight can be considered a potential inducer of chromosomal aberrations in skin cells, wh ich may contribute to skin carcinogenesis.