| Objective:1. To determine whether the biochemical effects of vitrectomy can be studied in rabbit lenses.2. To assess the possible protective effects of N-acetylcysteine on the lens following vitrectomy.Methods:1. Twenty-four New-Zealand rabbits (2.3-2.4 kg) were randomly divided into A, B, C three groups of eight each. Single vitrectomy group, left eyes of group A undergoing single vitrectomy surgery; 20 mM NAC treated group, equal numbers of treated eyes were injected with 20 mM N-acetylcysteine; 100 mM NAC treated group, equal numbers of treated eyes were injected with 100 mM N-acetylcysteine. Left eyes underwent vitrectomy surgery. The contralateral right eyes of group A served as the control. The animals were anesthetized with an intramuscular injection of Xylazine (5 mg·kg-1) and Ketamine (45 mg·kg-1). The surgical technique involved standard three port pars plana vitrectomy with removal of all visible vitreous gel. Vitreous was removed using the Megatron (Germany) vitrector for 10 min. Eyes with surgical complications, such as retinal detachment or cataract due to a'lens touch'were excluded from the study.2. Single vitrectomy group, left eyes of group A undergoing single vitrectomy surgery; 20 mM NAC treated group, left eyes of group B injected with 0.5 ml NAC into the vitreous cavity immediately after vitrectomy to achieve a final concentration of 20 mM; 100 mM NAC treated group, left eyes of group C injected with 0.5 ml NAC into the vitreous cavity immediately after vitrectomy to achieve a final concentration of 100 mM.3. After dilation of the pupils with a drop of 1% tropicamide, the rabbits were anaesthetized with an intramuscular injection of Xylazine (1 mg·kg-1) and Ketamine (9 mg·kg-1). Progression of cataract formation in both eye lenses from all rabbits was monitored and photographed once a week by a slit lamp (Haag-Streit BQ 900). The grading of lens opacification was performed according to the Oxford University system.4. After five months, animals selected randomly from each group were sacrificed by air embolism and their eyeballs were removed for biochemical and morphological evaluation. Eyeballs were soaked in 0.9% neutral normal saline, and the lenses were dissected by the posterior approach. One lens from each group was fixed in 10% formalin and embedded in paraffin. Paraffin sections (5μm-thicks) were subjected to hematoxylineosin (H&E) staining. Six lenses were placed into pre-weighed Eppendorf tubes and frozen at–70 oC until further analysis. The levels of reduced glutathione (GSH), the water-soluble protein concentration, and the activites of Na~+-K~+-ATPase, catalase (CAT) and glutathione reductase (GR) were measured in both of the left and right lenses.Results:1. After five months, the mean weight of the lenses from the vitrectomized eyes was 0.525±0.018 g, and the weight of the lenses from the contralateral controls was 0.537±0.019 g. There was no statistically significant difference. No significant morphological change or opacification of the lenses was detected by slit lamp examination after vitrectomy, whether lenses were treated with NAC or not.2. Mean water-soluble protein concentration and the level of GSH were decreased at the 5th month after vitrectomy, although these changes did not reach statistical significance. There was a significant reduction in Na~+-K~+-ATPase and CAT activity (by 56% and 17%) in the lenses of the eyes that underwent vitrectomy, compared to the contralateral unoperated eyes. The activity of GR was not significantly decreased after vitrectomy.3. No significant differences were detected between the NAC-treated groups and the untreated group in the water-soluble protein concentration at the 5th month after vitrectomy. The activities of GR were higher in the two NAC treated groups compared with that of the untreated group, although these differences were also not statistically significant. Treatment with 20 mM NAC enhanced the GSH level by about 18% compared with the untreated group, though this difference was not statistically significant. Treatment with NAC restored Na~+-K~+-ATPase activity toward normal levels. The 20 mM and 100 mM NAC treatment resulted in an increase in Na~+-K~+-ATPase activity by 30% and 16% compared with the untreated group. CAT activity was increased significantly in the 20 mM NAC treated group by 13%, but the group treated with 100 mM NAC increased CAT activity by only a minimal amount, compared with the eyes that received vitrectomy, but no NAC.Conclusions:This study is the first to report a biochemical effect of vitrectomy on the rabbit lens. Post-vitrectomy lens changes are associated with long-term decreases in enzymes activities in the lens. Injection of N-acetylcysteine into the vitreous cavity protects against some of these changes. Antioxidants like N-acetylcysteine may slow or prevent post-vitrectomy cataract. |
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