Interaction of ultraviolet-B-rich and ultraviolet-A-rich radiation in ketoprofen-induced photohemolysis

Interactions between different wavelengths can cause inhibition or enhancement of various biological reactions. We evaluated in vitro the effect of UVB-rich irradiation on UVA-induced phototoxicity. Suspensions of human erythrocytes were incubated with ketoprofen, a phototoxic nonsteroidal anti-inflammatory drug. These samples were exposed to 0, 20, 40, 80, 160 or 320 mJ/cm² UVB followed by irradiation with 0 or 6 J/cm² UVA. Photo-induced hemolysis was calculated as a percentage of complete hemolysis. Ketoprofen-dependent hemolysis due to UVA alone was 63% (median). UVB did not induce ketoprofen-dependent photohemolysis at doses <80 mJ/cm². Exposure to UVB at all doses enhanced significantly (P<0.01) UVA-induced ketoprofen-dependent hemolysis in samples from 9 of 15 donors. However, with erythrocytes from the other 6 donors, 20 or 40 mJ/cm² UVB reduced the median of UVA-induced photohemolysis by 69% (P<0.05) or 47% (not significant), respectively. Co-incubation of samples with ascorbic acid resulted in a profound inhibition of ketoprofen-dependent photohemolysis. These results indicate that the effect of low UVB doses on UVA-induced phototoxicity depends on individual, yet unknown characteristics of the target cells.