DNA repair elicited by UVB during PUVA therapy for psoriasis

Molecular markers of the risk of development of skin cancer in psoriasis patients receiving a phototherapy

State Research Center of Dermatovenereology and Cosmetology, Ministry of Healthcare of the Russian Federation Korolenko str., 3, bldg 6, Moscow, 107076, Russia Goal. To study potential molecular and genetic markers of an increased risk of development of malignant skin melanomas on the basis of the assessment of nucleotide replacements of genes in the excision system of DNA repair in psoriasis patients receiving a phototherapy. Materials and methods. Biological blood samples taken from 47 psoriasis patients, 24 patients with malignant skin melanomas and 20 healthy subjects. The following methods were used in the study: clinical, molecular and biological (DNA extraction, amplification, PcR, sequencing). Results. The study revealed molecular markers of an increased risk of development of malignant skin melanomas in psoriasis patients: CC genotype of the XPD gene at the 35931 locus (p = 0.00001); TC genotype of the XPF gene at the 27945 locus (p = 0.0067). It also revealed a molecular marker of an increased risk of development of malignant skin melanomas in healthy people: CC genotype of the XPD gene at the 35931 locus (p = 0.0042).

Induction of unscheduled DNA synthesis in hairless mouse epidermis by 8-methoxypsoralen plus ultraviolet A (PUVA)

Induction of unscheduled DNA synthesis (UDS) by 8-methoxypsoralen (8-MOP) plus ultraviolet A (UV-A) (PUVA) was investigated in the epidermis of female hairless mice by means of an in vivo--in vitro assay using a liquid scintillation counting method. Groups of three to five 8-week-old female hairless mice had 8-MOP applied once onto two areas of the back after stripping of the stratum corneum with adhesive tape to enhance skin penetration, and were irradiated with UV-A. Skin samples were taken and cultured in a medium containing [3H]thymidine with or without hydroxyurea (HU) for 2 hr. DNA of the epidermis was extracted, and the incorporation of [3H]thymidine into DNA and the DNA content were determined with a liquid scintillation counter and a fluorescence spectrophotometer, respectively. Induction of UDS was judged in terms of the UDS index [(the ratio of DNA synthesis in the presence of HU to that in its absence) x 100]. In a time-course study, the UDS index was increased at 1, 2 and 24 hr after 1 x 10(5) J/m2 UV-A irradiation with 0.001% 8-MOP, reaching the maximum level at 24 hr. In a dose-response study, it was significantly increased at the dose of 1 x 10(5) J/m2 of UV-A at 24 hr with 0.001% 8-MOP, but showed no significant change at the doses of 0.5 x 10(5), 2 x 10(5) and 4 x 10(5) J/m2. In a further study on the effect of varying the dose of 8-MOP, the UDS index was significantly increased at 0.001 and 0.002% 8-MOP at 24 hr after 1 x 10(5) J/m2 UV-A irradiation, reaching the maximum level with 0.002% 8-MOP. The increase of the UDS index in these studies was less than 3-fold. These results show that PUVA causes a small induction of UDS, which might be due to slow DNA excision repair over a long period.