Solar UV radiation: differential effectiveness of UVB subcomponents in causing cell death, micronucleus induction and delayed expression of heritable damage in human hybrid cells

Purpose: To determine the effectiveness of two UV spectra with different UVB components for cell kill and micronucleus induction in irradiated human HeLa x skin fibroblast (CGL1) hybrid cells and their progeny. To determine the presence of reactive oxygen species (ROS) in the progeny of the irradiated cells at various post-irradiation times and their relationship with induced delayed biological effects. Material and methods: A commercial solar ultraviolet simulator was used. Two different filters were employed: the first transmitted radiation with lambda >284 nm and the second radiation with lambda >293 nm. The resulting spectra have different UVB components (lambda between 284 and 320 nm, 19 W/m(2), and between 293 and 320 nm, 13 W/m(2)) and the same UVA component (lambda between 320 and 400 nm, 135 W/m(2)). CGL1 cells were irradiated with various doses. Clonogenic survival and micronucleus formation were scored in the irradiated cells and their progeny. ROS were detected by incubation of cultures at various post-irradiation times with dichlorodihydrofluorescein diacetate followed by flow cytometric measurement of the final product, dichlorofluorescein. Results: The biological effectiveness of the lambda >284 nm spectrum was higher by a factor of 3 compared to the lambda >293 nm spectrum for cell kill, and by a factor of 5 for micronucleus induction. No delayed cell death or micronucleus formation was found in the progeny of cells exposed to lambda >294 nm, while a large and dose-dependent effect was found in the progeny of cells exposed to lambda >284 nm for both of these endpoints. ROS levels above those in unirradiated controls were found only in the progeny of cells exposed to the lambda >284 nm spectrum. Conclusions: The spectrum with lambda >284 nm was more effective than that with lambda >293 nm for induction of cell kill and micronucleus formation in the directly irradiated cells as well as induction of delayed effects in the progeny in the form of delayed reproductive death and micronucleus formation. The presence of ROS in the progeny of the irradiated cells may be the cause of the delayed effects.