Kinetic analysis of apoptosis induction in human cell lines by UVA and 8-MOP.

Whereas previous studies have indicated that DNA damage as a result of 8-methoxypsoralen (8-MOP) and UVA treatment leads to cell death, this study establishes the minimum concentrations of 8-MOP and UVA necessary to induce apoptosis in human T-lymphocytic and monocytic cell lines. In order to asses apoptosis, we used fluorescent microscopy to examine changes in light scattering as well as internucleosomal DNA fragmentation. Generation of a dose response curve showed that the minimum combination of UVA and 8-MOP that was necessary to induce greater than background levels of apoptosis within 24 h of treatment was 0.5 J/cm2 UVA and 12.5 ng/mL of 8-MOP. A striking observation was that UVA alone at doses > or = 1.0 J/cm2, but not 8-MOP alone (0-300 ng/mL), induced significant apoptosis in the Sup-T1 cells induced by UVA alone was not as great as that of 8-MOP and UVA in combination, a highly significant correlation between the product of the concentration of 8-MOP (ng/mL) times the dose of UVA (J/cm2) and the percentage of apoptotic cells was observed. This correlation provides an important tool for studying the relationship of UVA-induced DNA damage to apoptosis induction. moreover, it will provide a means by which early events in the apoptotic pathway can be dissected.