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

Chromosomal defects are frequently present in malignant and premalignant skin disorders; however, it is not known whether ultraviolet radiation from sunlight plays a role in their induction. To obtain information on the ability of ultraviolet A and ultraviolet B to induce chromosomal aberrations, cultured melanocytes and fibroblasts were exposed to physiologic doses of ultraviolet A or ultraviolet B and, for comparison, to gamma rays. As a measure of chromosomal aberrations, the formation of micronuclei was determined. To obtain sufficient statistical data on induced micronuclei and cell kinetics, a flow cytometry method has been modified and applied. The flow cytometry 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-dependent micronuclei formation after gamma or ultraviolet B irradiation in both cell types and also for ultraviolet A in fibroblasts. The yield of micronuclei induced in fibroblasts by ultraviolet A was only a factor 15 smaller than that induced by ultraviolet B (313 nm). The results indicate that 10 kJ per m2 (equivalent to 1 minimal erythema dose) of ultraviolet B and 150 kJ per m2 of ultraviolet A (0.2 minimal erythema dose) can induce 1% of micronuclei in fibroblasts, equivalent to the induction due to 0.6 Gy of gamma radiation. In conclusion, physiologic doses of sunlight can induce chromosomal aberrations at a level comparable with that observed after exposure to approximately 1 Gy of ionizing radiation. Therefore, sunlight can be considered a potential inducer of chromosomal aberrations in skin cells, which may contribute to skin carcinogenesis.

(Pheo)melanin photosensitizes UVA-induced DNA damage in cultured human melanocytes.

The question of whether melanins are photoprotecting and/or photosensitizing in human skin cells continues to be debated. To evaluate the role of melanin upon UVA irradiation, DNA single-strand breaks (ssb) were measured in human melanocytes differing only in the amount of pigment produced by culturing at two different concentrations, basic (0.01 mM) or high (0.2 mM), of L-tyrosine, the main precursor of melanin. In parallel, pheo- and total melanin contents of the cells were determined. Identical experiments were performed with two melanocyte cultures derived from a skin type I and a skin type VI individual. For the first time the correlation between UVA-induced genotoxicity and pheo-/total melanin content has been investigated. We observed that cultured in basic medium, the skin type VI melanocytes contained 10 times more total melanin and about seven times more pheomelanin than the skin type I melanocytes. Elevation of tyrosine level in the culture medium resulted in an increase of both pheo- and total melanin levels in both melanocyte cultures; however, the melanin composition of skin type I melanocytes became more pheomelanogenic, whereas that of skin type VI melanocytes remained the same. The skin type VI melanocytes cultured in basic medium demonstrated a very high sensitivity (1.18 ssb per 10(10) Da per kJ per m2) toward UVA that is probably related to their high pheo- and total melanin content. Their UVA sensitivity, however, did not change after increasing their melanin content by culturing at high tyrosine concentration. In contrast, the skin type I melanocytes demonstrated a low sensitivity (0.04 ssb per 10(10) Da per kJ per m2) toward UVA when cultured in basic medium, but increasing their melanin content resulted in a 3-fold increase in their UVA sensitivity (0.13 ssb per 10(10) Da per kJ per m2). These results demonstrate that UVA-irradiated cultured human melanocytes are photosensitized by their own synthesized chromophores, most likely pheomelanin and/or melanin intermediates.

Physiological doses of ultraviolet irradiation induce DNA strand breaks in cultured human melanocytes, as detected by means of an immunochemical assay.

An immunochemical assay, i.e. sandwich enzyme-linked immunosorbent assay, has been modified to detect UV-induced damage in cellular DNA of monolayer-grown human melanocytes. The method is based on the binding of a monoclonal antibody to single-stranded DNA. The melanocytes derived from human foreskin of skin type II individuals were suspended and exposed to UVA, UVB, solar-simulated light or gamma-rays. Following physiological doses of UVA, UVB or solar-simulated light, a dose-related DNA unwinding comprising a considerable number of single-strand breaks (ssb) was observed. No correlation was found between different seeded cell densities or different culturing periods and the UVA sensitivity of the cells. After UVA irradiation, 0.07 ssb/10(10) Da/kJ/m2 were detected and after UVB irradiation 1.9 ssb/10(10) Da/kJ/m2 were seen. One minimal erythema dose of solar-simulated light induced 2.25 ssb/10(10) Da. Our results from melanocytes expressed in ssb/Da DNA are comparable and have the same sensitivity toward UVA as well as toward UVB as nonpigmented skin cells. As low doses of UVA have already been shown to induce detectable numbers of ssb, this assay is of great interest for further investigations about the photoprotecting and/or photosensitizing effects of melanins in human melanocytes derived from different skin types.

[Position taken by the profession of dermatology on the use of the solarium]. / A börgyógyász állásfoglalása a szolárium használatáról.

This article is to summarize the potential adverse effects of exposure to ultraviolet radiation from sunbeds and to provide recommendations from the British Photodermatology Group that, if followed, will minimize the risks of such effects. The recommendations in this document apply only to the use of sunbeds for cosmetic purposes.