COMET ASSAY DEMONSTRATES A HIGHER ULTRAVIOLET-B SENSITIVITY TO DNA-DAMAGE IN DYSPLASTIC NEVUS CELLS THAN IN COMMON MELANOCYTIC NEVUS CELLS AND FORESKIN MELANOCYTES

We used the single cell gel electrophoresis assay (comet assay) to stu dy ultraviolet B (UVB)-induced DNA damage in pigment cells, This assay detects DNA damage, mainly DNA strand breaks and alkali labile sites in the DNA molecule, We studied the effect of biologically relevant do ses (comparable to 2-3 MED (minimal erythemal dose) for in vivo irradi ated full-thickness skin) of monochromatic UVB light of 302 nm on cult ured melanocytes derived from foreskin, common melanocytic nevi, and d ysplastic nevi. We were able to demonstrate a linear dose-response rel ationship between UV dose and the migration coefficient of the comet t ail in all three types of pigment cells, Nevus cells originating from dysplastic nevi showed the highest sensitivity to UVB irradiation: 65% higher induction of DNA damage compared to the induction in foreskin melanocytes. Common melanocytic nevus cells were most resistant and sh owed a 30% lower induction of DNA damage in comparison to foreskin mel anocytes. Differences in chromatin structure and cell cycle profile ma y influence the results of the comet assay, Control experiments with x -ray irradiation, which is well known to produce direct DNA strand bre aks via radical formation, revealed only small differences between the three types of melanocytic cells, It is unlikely, therefore, that int rinsic nuclear characteristics may account for the observed difference s.