P53 expression and single strand DNA breakage as a measure of 8-methoxypsoralen and ultraviolet-a radiation [PUVA] induced genotoxicity

ABSTRACT

The use of Psoralen combined with exposure to ultraviolet - A radiation [PUVA] is a long-term major treatment for a number of skin diseases as well as for controlling graft versus host reaction. Although PUVA treatment is highly effective, careful follow-up cohort studies have shown that it greatly increases the risk for the development of hepatotoxicity, immunotoxicity and cutaneous squamous cell carcinoma. Strategies to reduce the risk of these toxic effects particularly cancer development in PUVA treated population is highly desirable. Because of the complexity of the processes involved in photocarcinogenesis, it is clear that more information particularly regarding its genotoxic effects is needed at cellular and molecular levels in order to develop optimal protection against photocarcinogenic risks related to UVA exposure. In the present study we used single cell gel electrophoresis assay [comet assay] to determine DNA damage, mainly strand breaks and alkali labile sites in the DNA molecule of lymphocytes of 3 groups of persons. Group [1] consisted of 30 patients treated with oral Psoralen while group [2] consisted of 30 patients treated with bath PUVA therapy, each group was then subdivided according to the number of sessions into less than and more than 30 PUVA sessions treated subgroups. Group [3] consisted of 15 healthy individuals served as control. The results indicated that patients treated by oral PUVA for more than 30 sessions have shown significant increase in the percentage of damaged and strongly damaged DNA spots of lymphocytes measured by comet assay as compared to their corresponding values in bath PUVA treated group, while there was insignificant increase in the percentage of damaged DNA spots of lymphocytes from patients treated by less than 30 sessions of oral PUVA therapy as compared to its corresponding percentages in the group of patients treated by bath PUVA therapy. P53 started to accumulate after at least 18 sessions of oral PUVA therapy while in patients under bath PUVA therapy it was not detected until they reached 25 sessions. The intensity of P53 bands increased as the number of sessions increased. The present study documented that, oral PUVA therapy is more genotoxic than bath PUVA therapy especially with cumulative doses. In conclusion, early detection of the genotoxic effects of PUVA therapy could be achieved by detection of DNA damage using comet assay together with the analysis of P53 expression status