Objective

N-methyl-D-aspartate (NMDA) excitotoxicity has been proposed to mediate apoptosis of retinal ganglion cells (RGCs) in glaucoma. Taurine (TAU) has been shown to have neuroprotective properties, thus we examined anti-apoptotic effect of TAU against retinal damage after NMDA exposure.

Methodology

Sprague-Dawley rats were divided into 5 groups of 33 each. Group 1 was administered intravitreally with PBS and group 2 was similarly injected with NMDA (160 nmol). Groups 3, 4 and 5 were injected with TAU (320 nmol) 24 hours before (pre-treatment), in combination (co-treatment) and 24 hours after (post-treatment) NMDA exposure respectively. Seven days after injection, rats were sacrificed; eyes were enucleated, fixed and processed for morphometric analysis, TUNEL and caspase-3 staining. Optic nerve morphology assessment was done using toluidine blue staining. The estimation of BDNF, pro/anti-apoptotic factors (Bax/Bcl-2) and caspase-3 activity in retina was done using ELISA technique.

Results

Severe degenerative changes were observed in retinae after intravitreal NMDA exposure. The retinal morphology in the TAU pre-treated group appeared more similar to the control retinae and demonstrated a higher number of nuclei than the NMDA group both per 100 μm length (by 1.5-fold, p < 0.001) and per 100 μm² area (by 1.41-fold, p < 0.05) of the GCL. After NMDA exposure, visible axonal swelling was observed in optic nerve sections. In comparison with the changes observed in the NMDA treated group, the TAU treated group showed fewer prominent changes; axonal swelling was less frequent and less marked. Additionally, no marked glial cell changes were observed in the TAU-pretreated group. All TAU treated groups, particularly the pre-treated group, showed a significant decrease in the NMDA-induced optic nerve damage, with a 50% reduction (p < 0.001) in the mean grading compared to NMDA group. For the same, there was 25% decrease in co- and post-treatment groups, as compared with the NMDA group. Pre-treatment with TAU abolished apoptotic response to NMDA as indicated by decrease in the number of TUNEL- and caspase-3-positive cells. TAU pre-treatment also increased the Bcl-2 level (by 2.80-fold, p < 0.001) and decreased the level of Bax (by 34%, p < 0.01), and activity of caspase-3 (by 36%, p < 0.001) compared to NMDA group.

In conclusion

our study revealed that pre-treatment with TAU prevents NMDA-induced retinal cell apoptosis more effectively than co- and post-treatment with TAU.

中文翻译：

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牛磺酸对大鼠NMDA引起的视网膜兴奋性毒性的抗凋亡作用

客观的

已经提出了N-甲基-D-天冬氨酸（NMDA）兴奋性毒性来介导青光眼中的视网膜神经节细胞（RGC）的凋亡。牛磺酸（TAU）具有神经保护作用，因此我们研究了NMDA暴露后TAU对视网膜损伤的抗凋亡作用。

方法

将Sprague-Dawley大鼠分为5组，每组33只。第1组玻璃体内注射PBS，第2组类似地注射NMDA（160 nmol）。在第3组，第4组和第5组分别在NMDA暴露前（治疗前）24小时，联合治疗（共同治疗）和24小时后（治疗后）注射TAU（320 nmol）。注射后7天，处死大鼠。摘除眼球，固定并处理以进行形态分析，TUNEL和caspase-3染色。使用甲苯胺蓝染色进行视神经形态评估。使用ELISA技术估算视网膜中BDNF，促凋亡/抗凋亡因子（Bax / Bcl-2）和caspase-3的活性。

结果

玻璃体内NMDA暴露后，视网膜中出现严重的变性变化。预处理过的TAU组中的视网膜形态似乎更类似于对照视网膜和表现出较高数量的核比NMDA基团的两每100μm长度（1.5倍，P <0.001）和每100μm ²GCL的面积（降低1.41倍，p <0.05）。NMDA暴露后，在视神经切片中观察到可见的轴突肿胀。与在NMDA治疗组中观察到的变化相比，TAU治疗组显示出较少的显着变化。轴突肿胀的频率较低，症状也较轻。此外，在经TAU预处理的组中未观察到明显的神经胶质细胞变化。与NMDA组相比，所有TAU治疗组，特别是预处理组，均显示NMDA引起的视神经损伤显着减少，平均分级降低了50％（p <0.001）。与此同时，与NMDA组相比，联合治疗组和治疗后组减少了25％。TAU预处理消除了对NMDA的凋亡反应，这由TUNEL和caspase-3阳性细胞数量的减少所表明。

综上所述

我们的研究表明，与TAU联合治疗和后处理相比，TAU预处理可以更有效地防止NMDA诱导的视网膜细胞凋亡。