DNA repair synthesis in human skin exposed to ultraviolet radiation used in PUVA (psoralen and UV-A) 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).

Mass spectrometry-based metabolite profiling in the mouse liver following exposure to ultraviolet B radiation

Although many studies have been performed on the effects of ultraviolet (UV) radiation on the skin, only a limited number of reports have investigated these effects on non-skin tissue. This study aimed to describe the metabolite changes in the liver of hairless mice following chronic exposure to UVB radiation. We did not observe significant macroscopic changes or alterations in hepatic cholesterol and triglyceride levels in the liver of UVB-irradiated mice, compared with those for normal mice. In this study, we detected hepatic metabolite changes by UVB exposure and identified several amino acids, fatty acids, nucleosides, carbohydrates, phospholipids, lysophospholipids, and taurine-conjugated cholic acids as candidate biomarkers in response to UVB radiation in the mouse liver by using various mass spectrometry (MS)-based metabolite profiling including ultra-performance liquid chromatography-quadrupole time-of-flight (TOF)-MS, gas chromatography-TOF-MS and nanomate LTQ-MS. Glutamine exhibited the most dramatic change with a 5-fold increase in quantity. The results from altering several types of metabolites suggest that chronic UVB irradiation may impact significantly on major hepatic metabolism processes, despite the fact that the liver is not directly exposed to UVB radiation. MS-based metabolomic approach for determining regulatory hepatic metabolites following UV irradiation will provide a better understanding of the relationship between internal organs and UV light.

Mutagenic risk in psoriatic patients before and after 8-methoxypsoralen and long-wave ultraviolet radiation

Sister-chromatid exchange (SCE) analysis was carried out in different age groups prior to and after therapy with 8-Methoxypsoralen (8-MOP) followed by exposure of the patient to long-wave UV-A (PUVA) and compared to control. The SCE frequencies were increased significantly in PUVA-treated patients as compared to their pre-treatment SCE levels and to controls. A significant increase in SCEs was found in smoking PUVA-treated patients as compared to non-smoking PUVA-treated patients. This study indicates a detectable chromosome-damaging effect of PUVA therapy on its human users.

Scheduled and unscheduled DNA synthesis in epidermal cells of hairless mice treated with immunosuppressive drugs and UVB-UVA irradiation

The effects of the immunosuppressive drugs azathioprine, prednisolone and cyclosporin A, and UV irradiation on scheduled DNA synthesis, representing mitotic activity, and unscheduled DNA synthesis, representing DNA repair activity, in the skin of hairless mice were determined autoradiographically following intradermal administration of [3H]-thymidine. Azathioprine and prednisolone, and, to a lesser extent, cyclosporin A, were found to impair normal repair of UVR-induced DNA lesions in epidermal keratinocytes. Prednisolone, but not the other two drugs, further suppressed the normal delayed mitotic response in the skin following UVR. The depressive effects of these drugs, particularly the combined azathioprine/prednisolone regime, on scheduled and unscheduled DNA synthesis are considered likely to predispose skin to mutagenic and carcinogenic processes.

DNA repair elicited by UVB during PUVA therapy for psoriasis

The skin of patients receiving psoralen and UVA (PUVA) therapy for psoriasis is exposed to trace amounts of UVB radiation emitted by PUVA irradiators in addition to UVA. DNA repair activity was measured using autoradiography in the uninvolved skin of PUVA-treated patients in order to determine whether 8-methoxypsoralen (8-MOP) plus UVA elicits repair, inhibits the skin repair response to UVB, or protects epidermal-cell DNA from UVB damage by promoting a tan. Epidermal-DNA repair activity was observed in 27 out of 37 patients following the first PUVA treatment. Phototesting with multiples of the initial UV dose elicited a linear increase in repair activity. Glass-filtered radiation failed to stimulate repair, indicating that the reaction was due to UVB, not to 8-MOP plus UVA. The same amount of repair activity was observed in the skin of patients irradiated either before or after 8-MOP ingestion, demonstrating that the drug did not interfere with the response of the skin to UVB. At clearing, however, the repair activity was never greater than that elicited at the initial treatment and was often undetectable despite a tenfold increase in UV exposure. It is proposed that DNA damage should be measured to determine whether epidermal cells are entirely protected from UVB radiation at the completion of therapy.

The carcinogenic effect of UVA irradiation

The carcinogenic effect of UVA radiation (from Philips black light tubes filtered through a 2 mm-thick glass plate to eliminate the radiation below 320 nm) was studied in 7 groups of 25 lightly pigmented hairless mice. Irradiation with a moderate daily dose of combined UVB and UVA for 3 months induced a tumor incidence of 0.22 after 58 weeks. When the combined UVB and UVA irradiation was followed by filtered UVA for 2, 4, or 6 months, the tumor incidence was marginally significantly increased to 0.42, 0.48, and 0.50 (p less than 0.05), respectively. However, irradiation with the moderate dose of combined UVB and UVA induced a slight but not significantly lower tumor incidence as compared to UVB alone (0.22 vs 0.30, p greater than 0.1). UVA alone induced no tumors. It thus appears that in hairless mice initially exposed to a combination of UVB and UVA, subsequent continued irradiation with UVA increases tumor incidence. While only marginally statistically significant, tumor incidence in these animals seems to increase with duration and hence total UVA exposure. Furthermore, it is suggested that the photoaugmentative carcinogenic effect of UVA irradiation from unfiltered UVA bulbs can be reduced by attenuating the shorter wavelengths of the radiation.

Unscheduled DNA synthesis in normal human skin after single and combined doses of UV-A, UV-B and UV-A with methoxsalen (PUVA)

The aim of this study was to measure unscheduled DNA synthesis (UDS) by autoradiography in normal human skin (I) after high dose UV-A, (2) after low dose UV-A applied before or after erythemogenic doses of UV-B, (3) after high dose PUVA and (4) after therapeutic doses of PUVA applied before and after erythemogenic doses of UV-B. Single high dose UV-A exposure induced roughly 60% of the amount of UDS induced by equally erythemogenic doses of UV-B. Single low dose UV-A exposure did not induce UDS, nor did it significantly alter the amount of UV-B induced UDS when combined with UV-B exposure. Single high dose PUVA did not lead to UDS and had no influence on UV-B induced UDS when combined with UV-B exposure. Our findings indicate: (I) erythemogenic doses of UV-A induce a considerable DNA excision repair; (2) low dose UV-A neither augments UV-B induced DNA repair nor does it inhibit the repair process; (3) no UDS was shown to occur after eight high or therapeutic doses of PUVA. This was unexpected since psoralen-DNA monoadducts have been shown to be repairable by a mechanism similar to excision repair of pyrimidine dimers. It is therefore assumed that PUVA as performed for therapeutic purposes either preferentially induced interstrand crosslinks not repairable via the classical repair mechanism or the repair of monoadducts was below resolution in this study; (4) therapeutic PUVA doses apparently do not interfere with excision repair of UV-B induced DNA lesions.