DNA repair synthesis following irradiation with 254-nm and 312-nm ultraviolet light is not diminished in fibroblasts from patients with dysplastic nevus syndrome

The DNA excision repair capacity of 23 primary fibroblast lines from patients with dysplastic nevus syndrome was investigated and DNA repair synthesis (unscheduled DNA synthesis) was determined after UV exposure. Seventeen fibroblast lines from normal donors served as controls. The dose/response experiments included up to ten dose levels and two wavelength ranges: UV-C (using a low-pressure mercury lamp emitting predominantly 254-nm light) and UV-B (artificial sunlamp radiation centering around 312-nm light). For each dose level, silver grains over fibroblast nuclei were counted by visual inspection. Twelve cell lines were also evaluated for both UV wavelength ranges using a new semi-automatic image analyzing system. This system included components for rapid sequential identification of both fibroblast nuclei and silver grains sited above them. Silver grains over 100 nuclei were determined for each UV dose level. Dose/response curves were established and analyzed by linear regression. As a quantitative term for assessing DNA excision repair capacity of a cell line we calculated the linear increase (G₀) in the number of grains per nucleus, when the UV dose was multiplied by the factor e (i.e. 2.72). The sensitivity of grain detection and resolution ofoverlapping grains was approximately threefold better in visual than in automatic counting, especially when there were more than 70 grains over nuclei. The time recired for visual conting, however, was tenfold that of automatic counting. The varianceweighted meanG₀^v,w of all fibroblast lines from patients with dysplastic nevus syndrome was found to be 79.1 (±1.8-grains/nucleus, that of fibroblast lines from normal donors was 74.2 (±1.7) grains/nucleus. This difference revealed a slightly better repair capability for cell lines from patients but was at the borderline of detection and, therefore, should not be overinterpreted. From the experimental accuracy achieved by determination of the varianceweighted means of the two groups, we would have been able to detect a difference of 7 and more grains [> 2 x (_normal + _patients)]. The variance-weighted meanG_o^v,w of all fibroblast lines from patients with dysplastic nevus syndrome was found to be 76.4 (±1.4) grains/nucleus, whereas that of fibroblast lines from normal donors was only 66.6 (±1.8) grains/nucleus. This difference was statistically significant and, contrary to expectation, revealed better, not worse post-UV DNA repair capability in cell lines from patients that in those from normal donors. From the experimental accuracy achieved by determination of the variance-weighted means of the two groups, we would have been able to detect a difference of 6.4 or more grains [> 2 x (_normal + _patients)]. Variation between cell lines belonging to the same group was expressed by the standard deviation. On average, the standard deviation was in the range 18.2–21.1 grains/nucleus. This variation did not reflect experimental inaccuracy but different responses of individual cell lines to UV irradiation. On the basis of our data, we consider the hypothesis that patients with dysplastic nevus syndrome are prone to melanoma development because of a general defect in post-UV DNA repair to be improbable.This work was supported by the Deutsche Forschungsgemeinschaft, SFB 136