Pyrimidine dimer induction and repair in cultured human skin keratinocytes or melanocytes after irradiation with monochromatic ultraviolet radiation.

We compared the susceptibilities of cultured melanocytes and keratinocytes to dimer induction in DNA by monochromatic ultraviolet (UV) radiation. Keratinocytes as well as melanocytes were derived from human foreskin, grown as a monolayer in petri dishes, covered with phosphate-buffered saline containing 0.1% glucose, and irradiated. UV irradiation was carried out at 254, 297, and 302 nm as well as with a light source emitting predominantly 312 nm. The induction of pyrmidine dimers was assessed by determination of the number of T4 endonuclease V-sensitive sites (ESS). We found a slightly higher response for dimer induction in melanocytes at 254, 297, and 302 nm; this difference was only significant at the 297-nm wavelength. Action spectra for pyrimidine dimer induction were derived from the exposure-response data obtained. The action spectra mimic to a large degree the action spectra for dimer induction in other cultured mammalian cells. The repair rate during a post-irradiation period lasting up to 24 h was substantially the same for the two cell types. The percentage of T4 endonuclease V-sensitive sites (ESS) remaining 9 and 24 h after irradiation was 45% and 30%, respectively.

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 study 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 doses (comparable to 2-3 MED (minimal erythemal dose) for in vivo irradiated full-thickness skin) of monochromatic UVB light of 302 nm on cultured melanocytes derived from foreskin, common melanocytic nevi, and dysplastic nevi. We were able to demonstrate a linear dose-response relationship between UV dose and the migration coefficient of the comet tail 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 showed a 30% lower induction of DNA damage in comparison to foreskin melanocytes. Differences in chromatin structure and cell cycle profile may influence the results of the comet assay. Control experiments with x-ray irradiation, which is well known to produce direct DNA strand breaks via radical formation, revealed only small differences between the three types of melanocytic cells. It is unlikely, therefore, that intrinsic nuclear characteristics may account for the observed differences.

UV induction of cyclobutane thymine dimers in the DNA of cultured melanocytes from foreskin, common melanocytic nevi and dysplastic nevi.

We compared the induction of cyclobutane thymine dimers after exposure to 302 nm UV in foreskin-derived melanocytes and melanocytes from nevocellular nevi, as well as in melanocytes cultured from dysplastic nevi, precursor lesions of melanoma, derived from four, three and four individuals, respectively. Cyclobutane thymine dimers were quantified in situ by means of an immunofluorescence assay with a specific monoclonal antibody. A method was developed to compare separately performed experiments in a standardized manner. For melanocytes from each source, we demonstrated a linear relationship between UV dose and immunofluorescence. In nevocellular and dysplastic nevi, two subpopulations could be detected, distinguished by their nuclear size. Large nucleated nevocellular nevus cells were most susceptible to the induction of thymine dimers (49% higher induction compared to induction in foreskin melanocytes), while in normal-sized nuclei of these nevus cells the same induction of thymine dimers was found as in nuclei from foreskin melanocytes. In contrast, large nucleated dysplastic nevus melanocytes did not differ from the foreskin melanocytes, while normal-sized nuclei of dysplastic nevus cells showed a lower induction (32% lower induction than in foreskin melanocytes).

Variations in melanin formation by cultured melanocytes from different skin types.

In many laboratories, culturing skin melanocytes has become a routine research activity. However, recent investigations have revealed that the quality and quantity of the pigment formed in the cultured cells may differ significantly from those of the original skin pigment cells. To shed more light on this issue, we examined the influence of different culture media on pigment production. We showed that there were notable passage-to-passage variations in the synthesis of melanin. This was particularly true for phaeomelanin. It is therefore advisable to analyse the melanin in the cells before the start of experiments. In spite of the variations, basic differences in the pigmentation pattern between melanocytes isolated from light-skinned and dark-skinned individuals remained preserved in the corresponding cultures as observed by electron microscopy. Also, the total melanin content was higher in a skin type VI melanocyte culture than in skin type I and II melanocyte cultures. In contrast to total melanin, the phaeomelanin concentration of skin type VI cells was similar to that of the skin type I melanocytes. With higher L-tyrosine concentrations in the medium, as well as increased eumelanin synthesis, phaeomelanogenesis was also stimulated in all cultures tested. This stimulation was particularly prominent in skin type I melanocytes. Our preliminary experiments also showed that a melanocyte culture from atypical naevus cells exhibited a similar preference for phaeomelanogenesis when pigmentation was stimulated.

Ulcerating necrobiosis lipoidica effectively treated with pentoxifylline.

A 30-year-old man had suffered from persistent ulceration within an area of necrobiosis lipoidica diabeticorum for 13 months. The ulcerating necrobiosis lipoidica was resistant to topical therapy and oral therapy with acetylsalicylic acid. However, the ulcers healed completely within 8 weeks of administration of 400 mg pentoxifylline twice daily.

Beneficial effects of fumarate therapy in psoriasis vulgaris patients coincide with downregulation of type 1 cytokines.

BACKGROUND: Fumarates have been shown to be effective in psoriasis vulgaris. OBJECTIVES: To find out whether successful therapy is associated with modulation of cytokines. METHODS: We determined interferon (IFN)-gamma, interleukin (IL)-4 and IL-10 secretion capacities of peripheral blood mononuclear cells (PBMC) after phytohaemagglutinin stimulation, and IL-12p70 and IL-10 secretion capacities of PBMC after endotoxin stimulation in psoriasis vulgaris patients during treatment with fumarates. In a cohort study, 12 patients (five men, median age 50 years; seven women, median age 46 years) with psoriasis vulgaris were followed during 24 months of fumarate treatment. In addition, we followed 14 healthy controls (six men, median age 31 years; eight women, median age 29 years) without skin diseases during 12 months to investigate possible changes in the cytokine secretion capacity of PBMC as a result of seasonal changes. Disease activity in patients was determined by Psoriasis Area and Severity Index (PASI) score. Blood was collected for measurement by enzyme-linked immunosorbent assay of cytokine levels after stimulation of PBMC. RESULTS: Within 6 months of fumarate treatment, the mean +/- SD PASI score had decreased to 22 +/- 9% of its initial value. These beneficial effects coincided with lymphocytopenia and a significant (P < 0.05) downregulation of IFN-gamma expression by circulating blood cells, followed by a significant downregulation of IL-4 expression. Notably, production of the cytokine synthesis inhibitor IL-10 by PBMC was unchanged. CONCLUSIONS: The beneficial effects of fumarates may be attributed to their downregulatory action on type 1 cytokines.