An investigation of ultraviolet and ionizing radiation on the eye-lens of rainbow trout

Abstract

The lens of the eye is one of the most radiosensitive tissues in the body, and the effects of radiation on the eye-lens are not fully understood. Dose limit and tissue effect threshold recommendations have been lowered due to cataracts occurring at unexpected doses, and there is therefore a need for biological experiments on the early stages of cataractogenesis. There is also a need for radiobiological evidence in the context of environmental radioprotection, since the current recommendations for dose limits to non-human biota are based on assumptions rather than evidence of radiation response. In this work, the effects of ionizing and ultraviolet radiation on the eye-lens of rainbow trout have been investigated in vitro. Eye-lenses were excised and maintained in culture, then irradiated with either X-rays or ultraviolet (UV) radiation and assessed for several types of damage response. Optical quality was quantified using laser focal analysis; the structural integrity of cell membranes was assessed by measuring protein leakage from eye-lenses; and the response of lens cells to the radiation was characterized using proteomics analysis. A dose of 0.2 J/cm² of UVB radiation was shown to produce no changes in the optical quality of intact rainbow trout eye-lenses over 30 days post-irradiation. However, there is evidence of a damage-response process that triggers cellular 'housekeeping' and results in irradiated lenses maintaining transparency longer than control lenses. Comparative studies with groups of lenses being exposed to either 1 J/cm² of UVB radiation or 2 Gy of X-rays has shown that this dose of ionizing radiation produces significant changes in the expression of proteins related to cell membranes, DNA repair, and removal of damaged proteins. The UVB dose led to elevated expression of the same types of proteins, but not in significant amounts. Combining results across damage assays and experiments has revealed trends which support the concepts of individual variation in radiosensitivity, membrane damage and bystander effect as factors in early cataractogenesis, and the relationship between stress response and lens transparency. Overall, this characterization of specific aspects of damage response in the eye-lens to ionizing and ultraviolet radiation has contributed to the understanding of cataractogenesis as well as environmental radioprotection.