Light-induced damage to ocular lens cation pump: prevention by vitamin C.

Abstract

The cation pump activity of the ocular lens was damaged by exposure to light in the presence of riboflavin phosphate. The intensit of ight was similar to that used for reading purposes. The observed light-induced damage was due to superoxide or its derivatives, the superoxide being produced photochemically. Such damage was attenuated by vitamin C in amounts comparable to that in the aqueous humor. Thus, a new role for the high ascorbate level present in the anterior chamber fluid and the lens has been suggested. Ascorbate in other tissues also might have this novel physiological function of protecting against damage due to superoxide and its derivatives produced during normal cellular oxidation. The concentration of ascorbic acid (vitamin C) in the aqueous humor of man, monkey, and many other animals is one of the highest among the various body fluids (1). The prevalence of this high level of ascorbate has been attributed to the ability of the ciliary epithelium to transport this compound actively from the plasma to the posterior chamber through the blood aqueous barrier (2). For reasons undefined at the present time, the concentration of ascorbate is also high in tissues surrounding the aqueous humor-namely, the cornea and the lens. The concentration in the latter tissue in many instances is second only to that in adrenals (1). Although the importance of ascorbic acid in hydroxylation reactions is known in many tissues, the relevance of a high ascorbate level in the aqueous humor and the lens is not precisely known, although it has been suggested that photochemical oxidation of ascorbic acid in the anterior chamber serves to provide hydrogen peroxide to the lens. The peroxide, in turn, may regulate the tissue hexose monophosphate shunt through the following series of interlinked reactions

Effect of Sorbinil and Ascorbic Acid on myo‐Inositol Transport in Cultured Rat Schwann Cells Exposed to Elevated Extracellular Glucose

“…NAD~and NADPH!NADP~redox couples linked to AR and sorbitol dehydrogenase, respectively (Carroll et al, 1986;Williamson et al, 1993;Thomas et al, 1994). AA is a well documented physiological antioxidant (Varma et a!., 1979;Organisciak et a!., 1985). Therefore, AA could have a dual effect, i.e., as an ARI-like agent and also as an antioxidant, and thus ameliorate the deleterious effects of long-term exposure to elevated glucose levels on MI metabolism.…”

Influence Dietary Riboflavin Deficiency on Lenticular Glutathione Redox Cycle, Lipid Peroxidation, and Free Radical Scavengers in the Rat

“…PHAT lens and is present in very high concentrations in lens and aqueous humour [41]. Ascorbic acid has been demonstrated to be a potent scavenging agent of singlet oxygen [42] and superoxide [43]. Lowered ascorbic acid levels are commonly associated with cataract formation [6,25,41].…”

A possible role for vitamin C in age-related cataract

“…Laboratory studies have shown that high levels of the oxygen radicals superoxide and H202 are generated in the lens of photochemically-induced cataracts (Varma et al 1979;Spector et al 1993). Hz02 is also called a 'mobile time bomb' as it can react in a Fenton reaction to form the highly-damaging hydroxyl radical (Gutteridge & Halliwell,1 994).…”