ABSTRACT
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.
Subject(s)
Chromosome Aberrations , Lymphocytes/drug effects , Methoxsalen/analogs & derivatives , Methoxsalen/toxicity , Mutagens/toxicity , PUVA Therapy , Reactive Oxygen Species , Ultraviolet Rays , 5-Methoxypsoralen , Cells, Cultured , Ethanol/toxicity , Humans , Kinetics , Lymphocytes/cytology , Lymphocytes/radiation effects , Time FactorsABSTRACT
The repair of DNA interstrand cross-links (CL) induced by 8-methoxypsoralen (8-MOP) plus UVA irradiation was analyzed by the alkaline step elution technique. A double-exposure protocol was used with 8-MOP, starting with exposure to monochromatic 405-nm radiation inducing only DNA monoadducts (MA), followed, after washing out of unbound 8-MOP molecules, by a second exposure to 365-nm radiation inducing varying relative amounts of CL at a constant level of total photoadducts. In the range of doses used for the second exposure, repair of CL took place; however, in the presence of increased relative amounts of CL induced non-specific incision of DNA occurred. This endonucleolytic cleavage appears to be related to the increased mutagenic and recombinogenic effects observed at increased levels of CL.
