Oxidative Responses Induced by Pharmacologic Vitreolysis and/or Long-term Hyperoxia Treatment in Rat Lenses

Abstract

Purpose The aim of the study was to investigate the protective effects of intact vitreous gel on the lens after pharmacologic vitreolysis and hyperoxia exposure in rats in vivo. Methods Eyes of Sprague-Dawley rats were induced to posterior vitreous detachment (PVD) by pharmacologic vitreolysis, and the rats with and without PVD were treated with hyperoxia 3 h per day for 5 months. Lens transparency was monitored by a slit-lamp biomicroscope. A series of biochemical measurements were made in extracts of the lens cortex and nucleus. Ascorbate levels were measured in the aqueous and vitreous humors. Results No significant differences in lens transparency or morphology were observed in all groups, and no significant biochemical changes were observed in the cortex or nucleus of lenses of the PVD group. In the lens nucleus, the values of water-soluble protein concentration in PVD + hyperoxia group were lower than that of the PVD group. The levels of water-soluble proteins, glutathione (GSH) and ascorbate decreased in the hyperoxia group with an intact vitreous body. Vitreolysis enhanced the effect of hyperoxia, decreasing soluble protein, GSH and ascorbate below the levels seen in eyes with vitreolysis alone. The levels of antioxidants and soluble proteins were lower in the lens nucleus, and the effects of vitreolysis plus hyperoxia were more significant in the nucleus. Hyperoxia and hyperoxia plus vitreolysis reduced catalase activity and increased oxidized GSH to a greater extent in the lens cortex, although these treatments increased protein-GSH mixed disulfides in both regions. Long-term hyperoxia also lowered ascorbate levels in the vitreous and aqueous humors, an effect that was enhanced by vitreolysis. Conclusions Exposure to excess molecular oxygen produces significant oxidative damage to the lens, especially the lens nucleus. These effects were enhanced by pharmacologic vitreolysis, indicating that intact vitreous gel protects the lens from oxidative damage.

Quantitative Imaging of Enzymatic Vitreolysis-Induced Fiber Remodeling

“…Sebag et al 48 showed enhanced nanosphere diffusion in the vitreous after treatment with microplasmin (a shorter version of plasmin with the same proteolytic domain; now called ocriplasmin). Moreover, increased oxygen content in the vitreous body and in the lens after plasmin or microplasmin treatment has been reported by a number of investigators, [49][50][51] Enzyme-Induced Vitreous Remodeling IOVS j December 2014 j Vol. 55 j No.…”

Preserve the (intraocular) environment: the importance of maintaining normal oxygen gradients in the eye

“…Similar treatment in rats increased oxygen levels in the lens [12]. When rats were exposed to HBO, vitreolysis lowered ascorbate levels in the vitreous and aqueous humors, decreased levels of protective enzymes in the lens, and increased levels of Glutathione (GSH)-protein mixed disulfides in the lens compared to animals with the vitreous intact [13].…”

Lens glutathione homeostasis: Discrepancies and gaps in knowledge standing in the way of novel therapeutic approaches

“…While one could argue that nothing new was to be expected concerning the protective role of GSH in the lens, our interest in GSH homeostasis in the lens was rekindled with the unexpected finding that lenticular GSH levels were not completely suppressed in the LEGSKO mouse in spite of complete absence of γ-glutamylcysteine ligase(Fan et al, 2012). This issue, which is the subject of intense investigation in our laboratory, is closely linked to lenticular ascorbate metabolism and cataractogenesis and the work of David Beebe who has pioneered the importance of the vitreous as a source of oxidative stress to the lens(Beebe et al, 2014; Holekamp et al, 2005; Li et al, 2013b; Shui et al, 2009). These paradigm shifting studies inspired us to study lens biology in connection not only to the aqueous humor but also to the vitreous humor.…”