Ascorbate Consumption in Ultraviolet Radiation–B (UVR–B)–Induced Cataract in Albino Rats

Abstract

Abstract: : Purpose: To study the effect of UVR–B eye exposure on lens ascorbate content. Methods: Fifty albino Sprague Dawley rats, ten rats per group, were unilaterally exposed in vivo to 300 nm UVR–B under anesthesia, receiving 0, 0.25, 3.5, 4.3, and 4.9 kJ/m² over a duration of 15 minutes. Each rat was sacrificed one week after exposure. Intensity of forward light scattering was measured in vitro for each lens. Ascorbate concentration in the processed lens was determined using HPLC with UVR detection. Data were fit to non–linear regression. Results: Rats exposed to UVR–B dose greater than or equal to 3.5 kJ/m² developed cortical cataracts in anterior subcapsular and equatorial regions. Estimated 95% confidence interval (CI) for mean difference in intensity of forward lens light scattering between exposed and non–exposed lenses was for 0 kJ/m² –7 ±14, for 0.25 kJ/m² –23 ±30, for 3.5 kJ/m² 119 ±70, for 4.3 kJ/m² 200 ±78, and for 4.9 kJ/m² 238 ±104 mtEDC. Estimated 95% CI for mean difference of lens ascorbate concentration between exposed and contralateral non–exposed lens was for 0 kJ/m² –0.004± 0.004, for 0.25 kJ/m² –0.027± 0.010, for 3.5 kJ/m² –0.104± 0.013, for 4.3 kJ/m² –0.103± 0.013, and for 4.9 kJ/m² –0.111± 0.009 µmol/g wet weight lens. UVR–B exposure decreased the difference of lens ascorbate concentration between exposed and contralateral non–exposed lenses following an exponentially declining model. Total lens ascorbate, C, consumable lens ascorbate, C_Co, non–consumable lens ascorbate, C_NonCo, lens ascorbate difference between exposed and non–exposed lenses, C_d, rate constant, k, and UVR–B dose, H_e, fit to the exponential models: 1) C = C_NonCo+ C_Co e^{–kH_{e for exposed lenses}} 2) C = C_NonCo+ C_{Co ^{for non–exposed lenses 3)}} C_d = C_{Co ⁽}e^–kH_e –1). Parameters were estimated to C_NonCo=0.04 µmol/g wet weight of lens and C_Co=0.11 µmol/g wet weight of lens. For lens ascorbate difference, k=1.16 m²/kJ, τ=1/k=0.86 kJ/m². 63% of UVR–B–consumable ascorbate has been consumed after only τ=0.86 kJ/m², indicating that the ascorbate decrease is on the order of 3.5 times more sensitive to detect UVR–B damage in the lens than forward light scattering. Conclusions: In vivo UVR–B exposure of the rat eye decreases lens ascorbate concentration following an exponentially declining model, with a supra–threshold dose having a greater effect than a sub–threshold dose.

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