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(PP276) A positive and negative bystander effect influences cataractogenesis in lenses exposed to low doses of x-rays.
Worgul, Basil*,1, Kleiman, Norman2, David, Janice1, 1 Eye Radiation & Environmental Reseach, Dept. Ophthalmology, New York, NY, US2 Environmental Health Sciences, New York, NY, US
ABSTRACT- Introduction: Previously, we confirmed early reports that partial shielding of an irradiated lens reduces cataract development in the exposed portion, a rare example of a positive bystander effect in a tissue. We speculated that using appropriate dose regimes, with more extensive follow-up, a concomitant, negative effect might be discernible. This would be expressed by the irradiated portion having a cataractogenic influence on its non-exposed neighbors. An appreciation of this possibility is important not only to radiation risk assessment but also the understanding of lens biology and cataractogenesis. Results: Partially shielded and unshielded eyes of Brown Norway rats, in groups of ten were exposed to 10 mGy and 50 mGy doses of 250 kVp X-rays. As was found previously, at significantly higher doses, protecting a section of the lens from exposure resulted in an ameliorating influence on cataractogenesis in the unprotected portion when compared to lenses irradiated in toto. There was a clear dose response in that changes appeared in the irradiated lenses earlier in the 50 mGy rats than in the 10 mGy exposed animals (Stage 1 CD50′s were 10.25 ± 0.5 and 13.0 ± 0.75 months respectively). Onset time was not affected by shielding. Of moment, and heretofore never reported, was the finding that the unexposed portions of the partially shielded lenses manifested vacuoles and small discrete opacities with greater frequency than those of unirradiated or fully shielded control eyes. Conclusions: A positive bystander effect for cataract development occurs in the mammalian lens even at very low radiation doses. In concert with the protective effect is a negative bystander influence on the unirradiated lens regions. Because the overall cataractogenicity of a given radiation dose is reduced, it appears that the positive bystander influence outweighs the converse negative bystander expression at the tissue level.
Key words: Radiation Cataract, Bystander Effect, Low Dose, Tissue
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