We report the effect of UVA irradiation on collagen metabolism of fibroblasts, including both synthesis of the collagen degrading enzyme collagenase and de novo synthesis of type I collagen as the major structural component of the dermis. For this purpose confluent fibroblast monolayers were irradiated under standardized conditions (5, 15, 35, 60 J/cm2 using UVASUN 3000, Mutzhas, Munich, FRG, and UV source Sellas sunlight type 2.001, Sellas, Gevelsberg, FRG). Subsequently, total RNA was isolated and subjected to dot blot and northern blot analysis using oligolabelled cDNA clones for human type I collagen, collagenase and beta-actin. Collagen type I and beta-actin mRNA levels remained unaltered following irradiation, suggesting that the synthetic pathway of collagen metabolism at the pretranslational level is not affected by short-term UVA irradiation. However, collagenase mRNA was found to be dose-dependently induced in fibroblasts after irradiation, thus probably contributing to the actinic damage to the dermis. These in vitro data were confirmed in vivo using in situ hybridization on frozen sections of biopsy material obtained from UVA irradiated patients.
We report the results of a long-term (12.8 years) follow-up study of the detection of malignant and benign skin tumours in patients with psoriasis, who were treated with PUVA according to the European, 'high single-dose' regimen. A total of 13 squamous cell carcinomas (SCC) and 24 basal cell carcinomas (BCC) were diagnosed in 11 of 260 patients. The incidence of both SCC and BCC was increased in comparison with the general Dutch population. The ratio of SCC to BCC in the general population was 1:8 but was 1:2.5 in our study group. A positive correlation was observed between the development of SCC and the total UVA dosage, the age of the patient at the start of the PUVA treatment and a history of arsenic use. This dose-related increase in the incidence of SCC, reported in studies from the U.S.A., has not been found in earlier European studies. The average time period between the start of PUVA therapy and the diagnosis of the first malignant skin tumour was 6.0 years for SCC and 4.7 years for BCC. Among the 49 benign skin tumours were actinic keratoses, a keratoacanthoma and 'PUVA keratoses', a newly described hyperkeratotic lesion, especially found in PUVA-treated patients.
The influence of tap-water (TW) and salt solutions on the minimal erythema dose (MED) was investigated for normal human skin and uninvolved skin of psoriasis patients. MED (UVB) determinations on the forearm revealed that: (1) the MED definitely decreases whenever the arm is immersed in TW or NaCl solutions with a low concentration (4%) prior to UVB exposure, whereas almost saturated NaCl solution (26%), as well as locum Dead Sea water (LDSW), do not produce a change in the MED, and (2) the decrease in MED obtained by wetting the skin with TW was no longer present when the skin was allowed to dry for 20 min. A decrease in water uptake by skin (in vivo) and by callus (in vitro) was found as the salt concentration of the external solution increased. It is proposed that water taken up by the skin plays an important role in the sensitivity of the skin to UVB exposure. Bathing in TW or 4% NaCl prior to UVB exposure offered a slight to moderate improvement in psoriasis over UVB irradiation alone. Finally, it was shown that there is no obvious difference in clearance of the psoriatic skin between a bath in TW, 4% NaCl, or LDSW prior to UVB exposure.
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.
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