The role of antioxidants in the hydrogen peroxide-induced opacification of sheep lens

Abstract

The lens of the eye needs to be transparent with a high refractive index to focus images on the retina. In cataracts the lens becomes opaque, eventually leading to blindness. There are many possible causes of cataract but a lot of evidence implicates oxidative damage as contributing to opacification. This includes epidemiological studies showing that diets rich in antioxidants lowered the prevalence of cataract. This research tested the hypothesis that if cataracts were at least partially caused by oxidative damage then their progression would be slowed by application of antioxidants. The antioxidants used were two plant compounds found in the diet, resveratrol and quercetin. The system used was sheep lenses cultured in Eagles Minimal Essential Medium (EMEM). Lenses remained transparent for up to 7 days in EMEM but became opaque within 24 h when exposed to 1 mM hydrogen peroxide (H₂O₂). The lens is exposed to H₂O₂ in vivo as it is found in the aqueous humor. Prior Lenses pre-treated with quercetin reduced but did not prevent opacification. Lens cell death, as determined by measurement of leakage of lactate dehydrogenase, was found to increase with H₂O₂ and the increase was prevented by pre-treatment with antioxidants. The role of the endogenous antioxidant glutathione was also investigated. It was found that H₂O₂ decreased the amount of reduced glutathione in the lens cortex and increased the levels of oxidised glutathione but only at levels of 2 mM and above. Thus the results of this research indicate that H₂O₂ at low concentration (1 mM) is able to damage lens cells and cause opacification without affecting the reduced glutathione levels and that the exogenous antioxidants have some ability to protect the lens.