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 necessa ry to induce apoptosis in human T-lymphocytic and monocytic cell lines . In order to assess apoptosis, we used fluorescent microscopy to exam ine changes in light scattering as well as internucleosomal DNA fragme ntation. Generation of a dose response curve showed that the minimum c ombination 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/cm(2 ) UVA and 12.5 ng/mL of 8-MOP. A striking observation was that UVA alo ne at doses greater than or equal to 1.0 J/cm(2), but not 8-MOP alone (0-300 ng/mL), induced significant apoptosis in the Sup-T1 cell line w ithin 24 h. Although the percentage of apoptotic 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 concentra tion of 8-MOP (ng/mL) times the dose of UVA (J/cm(2)) and the percenta ge of apoptotic cells was observed. This correlation provides an impor tant tool for studying the relationship of UVA-induced DNA damage to a poptosis induction. Moreover, it will provide a means by which early e vents in the apoptotic pathway can be dissected.