Drinking Water Supplementation With Ascorbate Is Not Protective Against Ultraviolet Radiation–B (UVR–B)–Induced Cataract In the Pigmented Guinea Pig

Abstract

Abstract: : Purpose: To determine if drinking water supplementation with ascorbate increases lens ascorbate concentration. To study if ascorbate supplementation decreases UVR–B–induced cataract development in the guinea pig. Methods: Sixty six–to–nine–week–old pigmented guinea pigs, two groups, received drinking water supplemented with 0 mM or 5.5 mM L–ascorbate for four weeks. Chow fed to animals contained 0.125 mol L–ascorbate/kg. UVR–B exposure: After supplementation, forty animals were exposed unilaterally in vivo under anesthesia to 80 kJ/m² UVR–B. One day after UVR–B exposure, animals were sacrificed and lenses were extracted. Degree of cataract was quantified by measurement of intensity of forward lens light scattering. Lens ascorbate concentration was measured. No UVR–B exposure: After supplementation, twenty animals were sacrificed. The animals served as controls. Lens ascorbate concentration was measured. Ascorbate measurement: The lens was processed in metaphosphoric acid and ultrafiltered. High performance liquid chromatography with ultraviolet radiation detection at =254 nm was used for ascorbate measurement. Results: Lens ascorbate concentration: Supplementation increased lens ascorbate concentration significantly (t–test). Control animals: 95% confidence intervals (CIs) for mean for animal–averaged lens ascorbate concentration (µmol/g wet weight lens) were: 0.721 ±0.120 [0 mM ascorbate] and 0.900 ±0.152 [5.5 mM ascorbate](p=0.046). UVR–B–exposed animals: 95% CIs for mean for animal–averaged lens ascorbate concentration (µmol/g wet weight lens) were: 0.544 ±0.073 [0 mM ascorbate] and 0.825 ±0.051 [5.5 mM ascorbate](p=3.55x10^–5). Cataract development: Control animals: All lenses were devoid of cataract. UVR–B–exposed animals: Anterior subcapsular cataract developed in all exposed lenses. 95% CIs for mean difference in forward light scattering between exposed and non–exposed lenses were: 39.2 ±14.1 mtEDC [0 mM ascorbate] and 35.9 ±14.0 mtEDC [5.5 mM ascorbate]. Group difference was non–significant (t–test; p=0.72). Conclusions: Drinking water supplementation with ascorbate increases lens ascorbate concentration. Cortical cataract develops in lenses exposed to UVR–B. Ascorbate supplementation is non–toxic to UVR–B–exposed lenses and control lenses. Ascorbate supplementation does not decrease in vivo UVR–B cataract development in the guinea pig.

Keywords: cataract • radiation damage: light/UV • antioxidants