Kinetic Analysis of Apoptosis Induction in Human Cell Lines by UVA and 8‐MOP

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Abstract
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 mono‐cytic cell lines. In order to assess 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 1.0 J/cm2, but not 8‐MOP alone (6300 ng/mL), induced significant apoptosis in the Sup‐T1 cell line within 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 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.