Protective Effect of Ascorbate Against Oxidative Stress in Mouse Lens

Abstract

Abstract: : Purpose: The ascorbate level remains relatively high in the aqueous of man and some other species. In view of the uncertainties over the possibility of its pro- and anti-oxidant physiological effects, further studies aimed at determining its effect on the lens was desirable. The primary objective of this study was, therefore, to assess its possible effectiveness against oxidative damage to mouse lens in culture. The selection of the mouse lens was based on its similarity to human lens, contrary to rat lens, in terms of its lower activity of aldose reductase which is involved in maintaining tissue redox status. Methods: Lenses isolated from CD-1 mice were contralaterally transferred to culture tubes containing medium 199 at 37°C gassed with air:CO₂(95:5) or O₂-CO₂(95:5). ⁸⁶RbCl, xanthine oxidase and uricase were also added. Ascorbate (2mM) and NaCl (2mM) were added to experimentals and controls respectively. Xanthine (0.5mM) was then added to all the tubes. At the end (5 or 17 hours), lenses were taken out and rinsed with saline and their radioactivity determined. ⁸⁶Rb⁺ uptake was expressed as the ratio of the counts in the lens water (CL) and the medium (CM). ATP and GSH were also determined using standard techniques. Basal controls were run without xanthine. Results: The transport of ⁸⁶Rb⁺ in the control lenses incubated without ascorbate was 50% of that in presence of ascorbate, either in air-CO₂ or O₂-CO₂. ATP levels in presence of asorbate were 2.5 times higher. GSH in the ascorbate group was also about 3 times greater. The values in presence of ascorbate were also closer to the basal controls. Conclusions: The membrane transport activity was better preserved in the presence of ascorbate, evident by the greater CL/CM ratio. The ROS-induced intracellular stress was also prevented, as reflected by the GSH levels. The overall metabolic status of the tissue, indexed by ATP, was also significantly better. The results, therefore, suggest that ascorbate is effective in protecting the lens against oxidative insult even in a low lens AR situation. Evidence of lens damage by ascorbate could not be obtained. Hence, in conformity with our previous studies, the overall effect of ascorbate at physiological levels is primarily antioxidative; the possibility of any pro-oxidant effect being remote.

Keywords: oxidation/oxidative or free radical damage • cataract • antioxidants