The clastogenic effect of 5-methoxypsoralen plus UV-A in human lymphocytes in vitro and its modification by the anticlastogen beta-aminoethylisothiouronium

Chromosome damage in PUVA-treated human lymphocytes is related to active oxygen species and clastogenic factors

Besides the direct interaction of psoralens with DNA and other macromolecules, the role of reactive oxygen species in the PUVA-induced cellular injury has been stressed. The present study shows that treatment of human blood cultures with 5-methoxypsoralen or 8-methoxypsoralen, followed by UVA exposure, results in chromosome damage. The supernatant of these cultures contains secondarily formed chromosome damaging material, called clastogenic factor (CFs). Not only CF formation, but also CF action is inhibited by superoxide dismutase (SOD), suggesting that superoxide is formed on the pathway to chromosome aberration. CF is detectable in the cell culture supernatants after a minimal delay of 18 h, and reaches a plateau at 24 h of cultivation. SOD is no longer protective if added after 24 h, i.e., the enzyme can prevent, but not repair the oxyradical-induced damage.

Synergistic effects of azathioprine and ultraviolet light detected by sister chromatid exchange analysis

The immunosuppressant azathioprine and longwave ultraviolet (UV) light have been postulated to have a synergistic effect on DNA resulting in carcinogenic change. This study investigated the in vitro effect of UV light on renal transplant recipients (RTRs) immunosuppressed with azathioprine and prednisolone to prevent rejection and patients on azathioprine for skin conditions and normal controls on no drug therapy. The results show clearly that there is an increase in sister chromatid exchanges (SCEs) in both patient groups in response to UV light with the greatest increase shown by the RTRs. Both patient groups without exposure to UV also showed a significant increase, as compared with normal controls, with the RTRs again showing the highest level. Both patient groups also showed disruption of the cell cycle in response to UV light as measured by the proliferative rate index (PRI) but the controls did not. These findings support the hypothesis of a synergistic effect between azathioprine and UV light and correlate well with the clinical pattern of carcinogenesis observed in these patients, with RTRs having a well-documented increased risk of neoplasia, particularly skin carcinomas in light-exposed areas.