Contribution of calpains to photoreceptor cell death in N-methyl-N-nitrosourea-treated rats

The purpose of the present study was to determine if proteolysis by the calcium-dependent enzyme calpains (EC 3.4.22.17) contributed to retinal cell death in a rat model of photoreceptor degeneration induced by intraperitoneal injection of N-methyl-N-nitrosourea (MNU). Retinal degeneration was evaluated by H&E staining, and cell death was determined by TUNEL assay. Total calcium in retina was measured by atomic absorption spectrophotometry. Activation of calpains was determined by casein zymography and immunoblotting. Proteolysis of alpha-spectrin and p35 (regulator of Cdk5) were evaluated by immunoblotting. Calpain inhibitor SNJ-1945 was orally administrated to MNU-treated rats to test drug efficacy. MNU decreased the thickness of photoreceptor cell layer, composed of the outer nuclear layer (ONL) and outer segment (OS). Numerous cells in the ONL showed positive TUNEL staining. Total calcium was increased in retina after MNU. Activation of calpains and calpain-specific proteolysis of alpha-spectrin were observed after MNU injection. Oral administration of SNJ-1945 to MNU-treated rats showed a significant protective effect against photoreceptor cell loss, confirming involvement of calpains in photoreceptor degeneration. Conversion of p35 to p25 was well correlated with calpain activation, suggesting prolonged activation of Cdk5/p25 as a possible downstream mechanism for MNU-induced photoreceptor cell death. SNJ-1945 reduced photoreceptor cells death, even though MNU is one of the most severe models of photoreceptor cell degeneration. Oral calpain inhibitor SNJ-1945 may be a candidate for testing as a medication against retinal degeneration in retinitis pigmentosa.     

Orally administered epigallocatechin gallate attenuates light-induced photoreceptor damage

EGCG, a major component of green tea, has a number of properties which includes it being a powerful antioxidant. The purpose of this investigation was to deduce whether inclusion of EGCG in the drinking water of albino rats attenuates the effect of a light insult (2200 lx, for 24 h) to the retina. TUNEL-positive cells were detected in the outer nuclear layer of the retina, indicating the efficacy of the light insult in inducing photoreceptor degeneration. Moreover, Ret-P1 and the mRNA for rhodopsin located at photoreceptors were also significantly reduced as well as the amplitude of both the a- and b-waves of the electroretinogram was also reduced showing that photoreceptors in particular are affected by light. An increase in protein/mRNA of GFAP located primarily to Müller cells caused by light shows that other retinal components are also influenced by the light insult. However, antigens associated with bipolar (α-PKC), ganglion (Thy-1) and amacrine (GABA) cells, in contrast, appeared unaffected. The light insult also caused a change in the content of various proteins (caspase-3, caspase-8, PARP, Bad, and Bcl-2) involved in apoptosis. A number of the changes to the retina caused by a light insult were significantly attenuated when EGCG was in the drinking water. The reduction of the a- and b-waves and photoreceptor specific mRNAs/protein caused by light were significantly less. In addition, EGCG attenuated the changes caused by light to certain apoptotic proteins (especially at after 2 days) but did not appear to significantly influence the light-induced up-regulation of GFAP protein/mRNA. It is concluded that orally administered EGCG blunts the detrimental effect of light to the retina of albino rats where the photoreceptors are primarily affected.     

Rat retinal ganglion cells upregulate the pro-apoptotic BH3-only protein Bim after optic nerve transection

Increased expression of Bim, a pro-apoptotic member of the Bcl-2 family, has been shown to be critical for neuronal apoptosis. To study the involvement of Bim in injury-induced cell death in retina, Bim expression was studied in normal rat retina and in retina after optic nerve transection using quantitative RT-PCR and immunohistochemistry. As a complement to this, the apoptotic regulators Bax, Bcl-2, caspase-3 and phosphorylated c-jun were studied. The relative levels of Bim mRNA in retina were significantly higher 4 days after optic nerve transection and below normal levels at 14 days after transection. A parallel increase in the number of Bim-immunoreactive cells in the retinal ganglion cell layer could be seen. Bim-immunoreactivity localized to retrogradely True Blue-labeled retinal ganglion cells. The relative mRNA levels for both Bax and Bcl-2 were higher at 4 days after transection when compared to normal. Immunoreactivity for Bax, Bcl-2 as well as for caspase-3 and phosphorylated c-jun, indicative of cell death, localized to True Blue-identified retinal ganglion cells 4 days after injury. Bcl-2 immunoreactivity was also seen on other cells, most likely Müller glia cells. In addition, optic nerve transection caused an increase in Bim, Bax, and Bcl-2 mRNA levels in optic nerve and superior colliculus. Our results suggest that Bim is involved in injury-induced retinal ganglion cell death and indicate that the increase in Bim and Bax expression promote cell death of axotomized retinal ganglion cells whereas the elevation in Bcl-2 in retina may contribute to the control of the extent of apoptosis after the optic nerve transection.     

Protective effects of Purendan superfine powder on retinal neuron apoptosis in a rat model of type 2 diabetes mellitus

This study sought to investigate the effects of Purendan superfine powder comprised of Momordica charantia, Radix Ginseng, and Radix Salviae Miltiorrhiae on neuronal apoptosis and expression of bcl-2, bax, and caspase-3, which are retinal apoptosis-associated factors in rats with diabetes mellitus induced by continuous intraperitoneal injection of streptozotocin. The results showed that Purendan superfine powder could upregulate the expression of bcl-2 protein and mRNA, and downregulate the expression of bax and caspase-3 in the retina of diabetes mellitus rats. In addition, Purendan superfine powder was shown to reduce the number of apoptotic neurons. Our experimental findings indicate that Purendan superfine powder can inhibit neuronal apoptosis in the retina of diabetes mellitus rats and has protective effects on diabetic retinopathy.     

糖尿病大鼠蛛网膜下腔出血后海马组织中caspase-3、Bax和Bcl-2的表达及醒脑静干预的研究

目的探讨醒脑静对糖尿病大鼠蛛网膜下腔出血（sAH）后海马组织凋亡相关因子天冬氨酸特异性半胱氨酸蛋白酶（casDase-3）、Bax和Bcl-2表达的影响。方法成年雄性Wistar大鼠28只,按随机数字表法随机分为空白对照组（n=7）、糖尿病对照组（n=7）、糖尿病SAH组（n=7）和醒脑静治疗组（n=7）;采用链脲佐菌素（STZ）腹腔注射方法建立糖尿病大鼠模型,然后采用枕大池两次注血法建立糖尿病大鼠SAH模型。SAH后48h取海马组织,用实时聚合酶链式反应检测caspase-3、Bax及Bcl-2的mRNA的表达,并用免疫印迹法测定它们蛋白表达,进行验证。结果空白对照组和糖尿病对照组大鼠海马组织中的caspase-3、Bax和Bcl-2的mRNA表达量均无显著差异（P〉0．05）;与空白对照组和糖尿病对照组相比,糖尿病SAH组和醒脑静治疗组其mRNA表达量均显著升高（P〈0．05）;醒脑静治疗组caspase-3和BaxmRNA表达水平均显著低于糖尿病SAH组大鼠（P〈0．05）,而Bcl-2mRNA表达水平却明显高于糖尿病SAH组（P〈0．05）。它们蛋白表达变化与mRNA表达基本相符。结论醒脑静抑制糖尿病SAH大鼠海马组织促凋亡相关因子表达,而促进抗凋亡相关因子表达,从而发挥保护作用。     

Phototoxic-induced photoreceptor degeneration causes retinal ganglion cell degeneration in pigmented rats

Human retinitis pigmentosa results eventually in retinal ganglion cell (RGC) death, but how this occurs remains obscure. We have previously documented that in pigmented dystrophic Royal College of Surgeons (RCS) rats, photoreceptor degeneration is followed by retinal pigment epithelial (RPE) migration, formation of RPE-vascular complexes, and vascular displacement that causes RGC axonal compression and death. To investigate if phototoxic-induced photoreceptor degeneration is capable of causing similar pathologic events, we dilated the left pupil of pigmented nondystrophic RCS and Lister-Hooded rats and exposed them to light (3000 lux) for 72 hours. After various survival periods ranging between 0 hours and 21 months, the retinas were processed as whole mounts or in cross-sections. Two separate retinal degenerative events that may relate to differential light exposure across the retina were observed: an early arciform area of degeneration in the superotemporal retina and a delayed degeneration in the central and ventral retina. Although degeneration in the arciform area was always more severe and developed earlier (sensitive region), both of them showed quite comparable pathologic events to those described for dystrophic RCS rats. RGC axonal compression was seen as soon as 21 days after light exposure and RGC loss was seen 9 months after light exposure, mainly in the superotemporal retina, but also in the ventral retina. The results show that RGC loss in induced photoreceptor degeneration results from a similar series of events to those occurring as a consequence of inherited degeneration and therefore is not uniquely a property of inherited photoreceptor degeneration.     

Inhibition of GSK-3β Activation Protects SD Rat Retina Against N-Methyl-N-Nitrosourea-Induced Degeneration by Modulating the Wnt/β-Catenin Signaling Pathway

Retinal degenerative diseases are characterized by photoreceptor cell loss. Photoreceptor cell loss leading to retinal degeneration can be induced by N-methyl-N-nitrosourea (MNU), which was widely used to mimic the pathology. However, the mechanism by which MNU induces photoreceptor cell loss is still largely unknown. The purpose of the present study was to investigate whether phosphorylation of glycogen synthase kinase-3β (p-GSK-3β) is a potent mediator of MNU-induced retinal degeneration and how p-GSK-3β affects the process. MNU-induced photoreceptor cell loss was evaluated in Sprague-Dawley (SD) rat retinas. GSK-3β and Akt expression levels did not change during MNU-induced retinal degeneration but the phosphorylation of GSK-3β and Akt was decreased by MNU treatment. Lithium chloride (LiCl), which increases p-GSK-3β level and active-β-catenin level, reversed retinal degeneration induced by MNU treatment. These results suggest that GSK-3β activation is closely related to photoreceptor cell loss and that the application of the GSK-3β inhibitor LiCl could activate Wnt/β-catenin signaling pathway and reduce photoreceptor cell loss induced by MNU. Our findings indicate that inhibition of GSK-3β activation may be a potential therapeutic target for retinal degeneration induced by photoreceptor cell loss.     

间歇低氧大鼠淋巴细胞促进脑血管内皮细胞凋亡的机制

目的 探讨间歇低氧大鼠淋巴细胞促进脑血管内皮细胞内质网应激凋亡作用及机制。方法 取SD雄性大鼠30只,分为正常对照组、间歇低氧组、抗低氧组,每组各10只; 抗低氧组、间歇低氧组建立间歇低氧大鼠模型,并分别于间歇低氧前半小时腹腔注射100 mg/kg超氧阴离子清除剂和等量生理盐水,1次/d,然后间歇低氧干预8 h/d; 正常对照组维持常氧量,干预6周; 各组干预后分离淋巴细胞,测定CD4⁺、CD8⁺ T细胞凋亡率; 取对数期内皮细胞RBE4,与各组分离淋巴细胞共培养,命名为正常对照RBE4组、间歇低氧RBE4组、抗低氧RBE4组; 4 h后测定培养基上清液中超氧化物歧化酶(Superoxide dismutase,SOD)及丙二醛(Malonaldehyde,MDA)水平、内皮细胞凋亡率、内皮细胞中C增强子结合蛋白同源蛋白(Cenhancer binding protein homologous protein,CHOP)、葡萄糖调节蛋白78(Glucose regulatory protein 78,GRP78)、半胱氨酸天冬氨酸蛋白水解酶-3(Cysteine containing aspartate-specific proteases-3,Caspase-3)mRNA及蛋白水平。结果 与正常对照组比较,间歇低氧组、抗低氧组CD4⁺、CD8⁺ T细胞凋亡率降低,且间歇低氧组低于抗低氧组(P<0.05); 与正常对照RBE4组比较,间歇低氧RBE4组、抗低氧RBE4组上清液中SOD水平降低、MDA水平增高、RBE4凋亡率增高、CHOP,Caspase-3 mRNA及蛋白水平升高、GRP78 mRNA及蛋白水平降低(P均<0.05); 与抗低氧RBE4组比较,间歇低氧组SOD水平降低、MDA水平增高、RBE4凋亡率增高、CHOP,Caspase-3 mRNA及蛋白水平升高、GRP78 mRNA及蛋白水平降低(P均<0.05)。结论 间歇低氧大鼠淋巴细胞促进脑血管内皮细胞凋亡可能通过激发内质网应激而发挥作用。     

降纤酶对大鼠局灶脑缺血／再灌后caspase—3 mRNA表达和细胞凋亡的影响

目的:通过观察降纤酶对大鼠脑缺血损伤后半胱氨酸蛋白酶-3(caspase-3)的表达和细胞凋亡的影响,研究其对脑保护机制。方法:采用大鼠线栓法栓塞一侧大脑中动脉(MCAO)制作局灶脑缺血/再灌注模型,健康雄性Wistar大鼠144只,分为生理盐水组和降纤酶两组,用原位杂交和原位末端标记(TUNEL)方法,观察缺血0、1、3、6和24 h;缺血3 h再灌注3、6和24 h;缺血 6 h再灌注3、6和 24 h的caspase-3 mRNA的表达和 TUNEL染色阳性细胞数。结果:降纤酶保护组caspase-3 mRNA的表达和TUNEL染色阳性细胞数明显少于生理盐水组。结论:降纤酶可抑制大鼠脑缺血/再灌注后caspase-3 mRNA的表达和细胞凋亡。     

Induction of heat shock (stress) protein 70 and its mRNA in the normal and light-damaged rat retina after whole body hyperthermia

In situ hybridization and immunocytochemistry were used to investigate the distribution of the 70 kDa heat shock or stress protein (hsp70) and its mRNA in specific layers of the retina of adult rats at 0, 4, 18, and 48 or 50 hr after a brief whole body hyperthermic treatment. Induction of hsp70 mRNA was noted in the photoreceptor layer of the retina within 4 hr after hyperthermia. Pronounced accumulation of inducible hsp70 immunoreactivity was observed in cytoplasmic extensions of the photoreceptor cells, especially the inner segment zone which attained peak levels at the 18 hr time point. Selective destruction of photoreceptors by light damage prior to hyperthermia inhibited the post-hyperthermic rise in newly synthesized retinal hsp70. Our results suggest that the photoreceptor cell layer is the primary site of synthesis of hsp70 in the rat retina and that the greatest increase in hsp70 immunoreactivity following such a hyperthermic stress occurs in that layer. This stress response of the photoreceptors is discussed in relation to their location and function in the retina. © 1994 Wiley-Liss, Inc.     

Neuroprotective Effect of Magnesium Acetyltaurate Against NMDA-Induced Excitotoxicity in Rat Retina

Glutamate excitotoxicity plays a major role in the loss of retinal ganglion cells (RGCs) in glaucoma. The toxic effects of glutamate on RGCs are mediated by the overstimulation of N-methyl-d-aspartate (NMDA) receptors. Accordingly, NMDA receptor antagonists have been suggested to inhibit excitotoxicity in RGCs and delay the progression and visual loss in glaucoma patients. The purpose of the present study was to examine the potential neuroprotective effect of Mg acetyltaurate (MgAT) on RGC death induced by NMDA. MgAT was proposed mainly due to the combination of magnesium (Mg) and taurine which may provide neuroprotection by dual mechanisms of action, i.e., inhibition of NMDA receptors and antioxidant effects. Rats were divided into 5 groups and were given intravitreal injections. Group 1 (PBS group) was injected with vehicle; group 2 (NMDA group) was injected with NMDA while groups 3 (pre-), 4 (co-), and 5 (post-) treatments were injected with MgAT, 24 h before, in combination or 24 h after NMDA injection respectively. NMDA and MgAT were injected in PBS at doses 160 and 320 nmol, respectively. Seven days after intravitreal injection, the histological changes in the retina were evaluated using hematoxylin & eosin (H&E) staining. Optic nerves were dissected and stained in Toluidine blue for grading on morphological neurodegenerative changes. The extent of apoptosis in retinal tissue was assessed by TUNEL assay and caspase-3 immunohistochemistry staining. The estimation of neurotrophic factor, oxidative stress, pro/anti-apoptotic factors and caspase-3 activity in retina was done using enzyme-linked immunosorbent assay (ELISA) technique. The retinal morphometry showed reduced thickness of ganglion cell layer (GCL) and reduction in the number of retinal cells in GCL in NMDA group compared to the MgAT-treated groups. TUNEL and caspase-3 staining showed increased number of apoptotic cells in inner retina. The results were further corroborated by the estimation of neurotrophic factor, oxidative stress, pro/anti-apoptotic factors, and caspase-3 activity in retina. In conclusion, current study revealed that intravitreal MgAT prevents retinal and optic nerve damage induced by NMDA. Overall, our data demonstrated that the pretreatment with MgAT was more effective than co- and posttreatment. This protective effect of MgAT against NMDA-induced retinal cell apoptosis could be attributed to the reduction of retinal oxidative stress and activation of BDNF-related neuroprotective mechanisms.     

骨髓间充质干细胞旁分泌途径与阿霉素损伤心肌细胞凋亡：怎样证明其抑制效应？

背景：近来研究发现骨髓间充质干细胞移植后短期心功能受益主要是因为其可分泌多种细胞因子,促进了内生性修复过程,而不是心肌细胞的再生。 目的：观察骨髓间充质干细胞旁分泌途径对阿霉素损伤心肌细胞凋亡的影响。 方法：体外培养的乳鼠心肌细胞按3×108 L-1浓度加入6孔培养板,3 mL/孔,培养72 h后分为3组：阿霉素损伤组、共培养组加入1 mg/L阿霉素作用4 h建立心肌细胞损伤模型,正常对照组不进行任何干预。共培养组取培养至第3代大鼠骨髓间充质干细胞,调整细胞浓度为3×108 L-1,以3 mL/孔加入共培养插件Millicell装置中,预培养24 h,在造模后将Millicell装置插入到预先培养心肌细胞的6孔培养板中,建立共培养体系。检测条件培养基内细胞因子的质量浓度变化,骨髓间充质干细胞对阿霉素损伤心肌细胞Caspase-9和Caspase-3活性、细胞凋亡、Bcl-2和Bax蛋白表达的影响。 结果与结论：与正常对照组比较,阿霉素损伤组胰岛素样生长因子1及肝细胞生长因子的质量浓度、心肌细胞Caspase-3及Caspase-9活性、心肌细胞凋亡率、心肌细胞Bax蛋白表达均明显升高(P < 0.05),Bcl-2蛋白表达明显降低(P < 0.05)。与阿霉素损伤组比较,共培养组胰岛素样生长因子1及肝细胞生长因子的质量浓度、心肌细胞Bcl-2蛋白表达均明显升高 (P < 0.05),心肌细胞Caspase-3及Caspase-9活性、心肌细胞凋亡率、心肌细胞Bax蛋白表达均明显降低(P < 0.05)。结果证实骨髓间充质干细胞在损伤环境下细胞因子分泌增加,并可通过旁分泌途径抑制阿霉素诱导的心肌细胞凋亡。     

caspase-3/8 mRNA在增殖期病理性瘢痕组织中的表达

背景：细胞凋亡参与了肉芽组织向瘢痕组织转化过程中多种细胞成分大量减少的动态过程,而Caspase家族介导的细胞凋亡是细胞凋亡的主要途径。 目的：从基因水平探讨caspase-3 mRNA及caspase-8 mRNA在增生性瘢痕组织中的作用。 方法：实验所用病理性瘢痕组织及正常皮肤组织均取自本院烧伤整形外科住院、伤口愈合6个月以后的增殖期病理性瘢痕组织18例。以正常皮肤组织18例做对照。利用RT-PCT技术分别检测半年以上增生性瘢痕组织中成纤维细胞caspase-3 mRNA及caspase-8 mRNA的表达情况。 结果与结论：在增生性瘢痕组织中,caspase-3 mRNA及caspase-8 mRNA表达的相对值分别为8.31±1.47和7.12±1.24,均明显低于正常皮肤组织(P < 0.05)。提示caspase-3/8在瘢痕形成过程中起着得要的作用,增生性瘢痕的形成可能与组织中caspase-3/8表达低下有关。     

Vigabatrin, the GABA-transaminase inhibitor, damages cone photoreceptors in rats

Epileptic patients experienced an irreversible loss of their peripheral visual field upon treatment with vigabatrin (gamma-vinyl GABA), an inhibitor of the GABA degrading enzyme, GABA transaminase. Subsequently, central visual function was reported to also be irreversibly altered. This visual loss is associated with a decrease in the electroretinogram measurement localizing the deficit to the retina. To investigate its cellular origin, we treated rats daily with vigabatrin for 45 days. Two days after arresting this treatment, rats exhibited an irreversible decrease in the photopic electroretinogram, the flicker response, and the oscillatory potentials. These functional alterations were associated with a peripheral disorganization of the outer retina. However, photoreceptor damage was not limited to these disorganized areas, but cone inner and outer segments were severely injured in more central areas and their numbers were irreversibly decreased by 17 to 20%. Ultrastructural examination of the retina confirmed the presence of major photoreceptor damages, which were further supported by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) and caspase-3 activation both indicative of photoreceptor apoptosis. This study suggests that the visual field loss in vigabatrin-treated epileptic patients may result from a sequence of events starting from cone cell injury to a more severe disorganization of the photoreceptor layer.     

细胞凋亡在热打击致大鼠大脑皮质神经元损害中的作用及机制

目的探讨热打击后大鼠大脑皮质神经元凋亡及caspase-3的表达变化。方法将Wistar大鼠随机分为正常对照组和热打击组,正常对照组大鼠始终置于(25±0.5)℃,相对湿度(35±5)%环境下;热打击组置于人工智能气候舱内100 min,舱内温度(40±0.5)℃,相对湿度(60±5)%。TUNEL染色观察大鼠大脑皮质神经元的凋亡情况;免疫组织化学方法及荧光定量PCR检测大鼠大脑皮质神经元caspase-3的表达。结果热打击1 d后大脑皮质神经元出现凋亡,第3天达高峰。caspase-3于热打击2 d后开始表达,于第3天表达最明显。荧光定量PCR检测结果显示,caspase-3在1 d、2 d、3 d和7 d各时间点含量与正常对照组比较差异均有统计学意义(P0.05),3 d时caspase-3含量最高。结论热打击可激活caspase-3表达,诱导皮质神经元凋亡。     

大鼠局灶性脑缺血再灌流后Caspase-3激活与神经元凋亡的关系

目的探讨Caspase-3与局灶性脑缺血后神经元凋亡的关系。方法局灶性脑缺血再灌流大鼠模型,按再灌流时间不同随机分为5组。用半定量RT-PCR观察了脑缺血后不同时程Caspase-3mRNA表达及四肽荧光底物法检测Caspase-3蛋白酶活性;用TUNEL方法检测不同时程细胞凋亡。结果脑缺血2h再灌流2h组Caspase-3mRNA水干即已升高(P＜0.05)),蛋白酶活性轻度升高,再灌流6h后两者均明显升高(P＜0.05);脑缺血再灌流后不同时程细胞凋亡具有与Caspase-3相似的变化趋势。结论提示脑缺血后细胞凋亡的发生与Caspase-3的激活有关。     

Pinacidil抑制线粒体和死亡受体通路减少大鼠脑缺血再灌注后神经元凋亡

目的探讨ATP敏感性钾通道开放剂pinacidil对大鼠脑缺血再灌注后神经元凋亡的保护作用及信号转导机制。方法100只Wistar雄性大鼠随机分为四组：A组（假手术组）、B组（缺血组）、C组（KATP开放剂处理组）及D组（KATP 开放剂和阻断剂处理组）。用线栓法制备大鼠大脑中动脉缺血（middle cerebral artery occlusion,MCAO）模型,用DNA断端末端标记法（tenninal-deoxynucleotidytransferase-mediated dUTP—biotin nick end labeling,TUNEL）检测神经元凋亡,用原位杂交方法检测caspase-3、caspase-8及caspase-9mRNA的表达。结果（1）C组12h、24h、48h、72h时间点的凋亡细胞数较B、D组显著减少（P〈0．05或P〈0．01）;B组和D组之间无显著性差异fP〉0．05）。（2）C组caspase-3mRNA和caspase-8mRNA在各时间点及caspase-9mRNA在12h、24h、48h、72h时间点的表达显著少于B组和D组（P〈0．01或P〈0．05）,B组和D组之间无显著性差异（P〉0．05）。结论K通道开放剂能显著减少大鼠脑缺血再灌注后的细胞凋亡及caspase-3、caspase-8及caspase-9 mRNA的表达。K通道开放剂可能通过抑制线粒体通路和死亡受体通路降低神经元凋亡,保护缺血再灌注损伤后的脑组织。     

Antiapoptotic effect of taurine against NMDA-induced retinal excitotoxicity in rats

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