Melanocytes, moles and melanoma--a study on UV effects

To investigate the UV effect on epidermal melanocytes, 21 volunteers and 11 patients with dysplastic nevus syndrome (DNS) received UVB irradiation three times weekly during 17 days. Skin biopsies were taken before and three weeks after the last irradiation (on day 37) from exposed and covered buttock skin. The epidermal melanocyte population density was estimated in dopa-stained split skin preparations. The biopsies taken on day 37 revealed that repeated UVB irradiation induces an increase in the number of melanocytes not only in exposed but also in covered skin. This increased mitotic activity might be a link between sun exposure and melanoma development in covered skin. The size of the proliferative response was inversely correlated to the basal melanocyte number. The larger population increase in skin with few melanocytes might amplify the propagation of DNA damage and increase the likelihood of tumor development. The pigment metabolite 5-S-cysteinyldopa (5-S-CD) was measured in urine before the irradiation and twice weekly until day 38. No correlation was found between the basal 5-S-CD excretion and the size or activity of the melanocyte organ, suggesting that the basal 5-S-CD excretion is mainly of non-melanocytic origin. Despite numerous nevi, DNS-patients did not differ from controls in their 5-S-CD excretion. The normal upper range for the tumor maker 5-S-CD is therefore valid in these melanoma-prone subjects. During the irradiation, subjects with a low tanning ability developed a more pronounced erythema and excreted more 5-S-CD than those with a good tanning ability. This suggests that the UVB-induced 5-S-CD excretion is rather due to melanocyte damage than to an increased melanin synthesis. To investigate the influence of sun exposure on the development of nevi and melanoma (CMM), the distribution over the body surface of CMM, common nevi (CN) greater than or equal to 2 mm and dysplastic nevi (DN) was registered in 121 melanoma patients and 310 controls. Four times as many nevi were found in a sun-exposed area than in a comparable sun-protected area, demonstrating that sun exposure plays an important role in nevus development. Subjects with DNA had a larger difference in nevus counts between the two areas than subjects without DN, indicating a different UV-dose and/or a higher sensitivity to the "nevogenic" effect of UV-light than subjects without DN.(ABSTRACT TRUNCATED AT 400 WORDS)