Intraocular Redox Regulation in Mice

Abstract

Purpose: : A decrease of plasma glutathione (GSH) levels occurs in aging human and may be involved in the pathogenesis of many age-related diseases including primary open angle glaucoma. The purpose of this study is to determine whether a glutathione synthesis inhibitor, buthionine sulfoximine (BSO), can modulate the intraocular redox status and affect retinal function in mice.

Methods: : BSO was administrated to C57/BL mice via drinking water for 20 days or via drinking water and intraperitoneal injections twice daily for 7 days. At the end of the studies, retinal functions were assessed in the dark-adapted mice using electroretinogram. The plasma, retina, optic nerve, and anterior segment excluding cornea and lens (i.e. anterior chamber angle) were collected. GSH and GSH disulfide (GSSG) were measured from HPLC. Apoptosis was determined in the tissue sections by TUNEL.

Results: : The intracellular GSH in the retina was 6 times higher than that in the anterior chamber angle. This resulted in more reduced intracellular GSH redox status in the retina. Optic nerve had twice the GSH concentration as in the retina but the GSH redox status was the same. In the mice given BSO by water for 20 days, there was a 20% reduction of GSH in the plasma, 69% in the anterior chamber angle, 34% in the optic nerve but only 3% in the retina. Mice given BSO by water plus injection for 7 days had greater decrease in GSH, 48% in the plasma, 74% in the anterior chamber angle, 77% in the optic nerve, and 20% in the retina. A slight decrease of retinal function was observed only in mice given BSO by water and injection. Histological study showed that there was no structural change in the eyes from either group of mice. No apoptosis was detected in the eyes of mice treated with BSO.

Conclusions: : The retina has a more reduced redox status and is resistant to GSH depletion. This may serve as an important defense mechanism to protect visually critical retinal cells from injury. This experimental model may also provide insight into whether the observed shift in blood plasma redox state in aging human could stimulate a similar shift in the intracellular redox state in the anterior chamber angle and optic nerve and whether this could contribute to pathogenesis of glaucoma.

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