Neuroprotective effects of erythropoietin on rat retinas subjected to oligemia

OBJECTIVES: Erythropoietin may have neuroprotective potential after ischemia of the central nervous system. Here, we conducted a study to characterize the protective effects of erythropoietin on retinal ganglion cells and gliotic reactions in an experimentally induced oligemia model. METHODS: Rats were subjected to global oligemia by bilateral common carotid artery occlusion and then received either vehicle or erythropoietin via intravitreal injection after 48 h; they were euthanized one week after the injection. The densities of retinal ganglion cells and contents of glial fibrillary acidic protein (astrocytes/Müller cells) and cluster of differentiation 68 clone ED1 (microglia/macrophages), assessed by fluorescence intensity, were evaluated in frozen retinal sections by immunofluorescence and epifluorescence microscopy. RESULTS: Retinal ganglion cells were nearly undetectable one week after oligemia compared with the sham controls; however, these cells were partially preserved in erythropoietin-treated retinas. The contents of glial fibrillary acidic protein and cluster of differentiation 68 clone ED1, markers for reactive gliosis, were significantly higher in retinas after bilateral common carotid artery occlusion than those in both sham and erythropoietin-treated retinas. CONCLUSIONS: The number of partially preserved retinal ganglion cells in the erythropoietin-treated group suggests that erythropoietin exerts a neuroprotective effect on oligemic/ischemic retinas. This effect could be related to the down-modulation of glial reactivity, usually observed in hypoxic conditions, clinically observed during glaucoma or retinal artery occlusion conditions. Therefore, glial reactivity may enhance neurodegeneration in hypoxic conditions, like normal-tension glaucoma and retinal ischemia, and erythropoietin is thus a candidate to be clinically applied after the detection of decreased retinal blood flow.

Rescuing axons from degeneration does not affect retinal ganglion cell death

After a traumatic injury to the central nervous system, the distal stumps of axons undergo Wallerian degeneration (WD), an event that comprises cytoskeleton and myelin breakdown, astrocytic gliosis, and overexpression of proteins that inhibit axonal regrowth. By contrast, injured neuronal cell bodies show features characteristic of attempts to initiate the regenerative process of elongating their axons. The main molecular event that leads to WD is an increase in the intracellular calcium concentration, which activates calpains, calcium-dependent proteases that degrade cytoskeleton proteins. The aim of our study was to investigate whether preventing axonal degeneration would impact the survival of retinal ganglion cells (RGCs) after crushing the optic nerve. We observed that male Wistar rats (weighing 200-400 g; n=18) treated with an exogenous calpain inhibitor (20 mM) administered via direct application of the inhibitor embedded within the copolymer resin Evlax immediately following optic nerve crush showed a delay in the onset of WD. This delayed onset was characterized by a decrease in the number of degenerated fibers (P<0.05) and an increase in the number of preserved fibers (P<0.05) 4 days after injury. Additionally, most preserved fibers showed a normal G-ratio. These results indicated that calpain inhibition prevented the degeneration of optic nerve fibers, rescuing axons from the process of axonal degeneration. However, analysis of retinal ganglion cell survival demonstrated no difference between the calpain inhibitor- and vehicle-treated groups, suggesting that although the calpain inhibitor prevented axonal degeneration, it had no effect on RGC survival after optic nerve damage.

The Neuroprotective Effect of Maltol against Oxidative Stress on Rat Retinal Neuronal Cells

PURPOSE: Maltol (3-hydroxy-2-methyl-4-pyrone), formed by the thermal degradation of starch, is found in coffee, caramelized foods, and Korean ginseng root. This study investigated whether maltol could rescue neuroretinal cells from oxidative injury in vitro. METHODS: R28 cells, which are rat embryonic precursor neuroretinal cells, were exposed to hydrogen peroxide (H2O2, 0.0 to 1.5 mM) as an oxidative stress with or without maltol (0.0 to 1.0 mM). Cell viability was monitored with the lactate dehydrogenase assay and apoptosis was examined by the terminal deoxynucleotide transferase-mediated terminal uridine deoxynucleotidyl transferase nick end-labeling (TUNEL) method. To investigate the neuroprotective mechanism of maltol, the expression and phosphorylation of nuclear factor-kappa B (NF-kappaB), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 were evaluated by Western immunoblot analysis. RESULTS: R28 cells exposed to H2O2 were found to have decreased viability in a dose- and time-dependent manner. However, H2O2-induced cytotoxicity was decreased with the addition of maltol. When R28 cells were exposed to 1.0 mM H2O2 for 24 hours, the cytotoxicity was 60.69 ± 5.71%. However, the cytotoxicity was reduced in the presence of 1.0 mM maltol. This H2O2-induced cytotoxicity caused apoptosis of R28 cells, characterized by DNA fragmentation. Apoptosis of oxidatively-stressed R28 cells with 1.0 mM H2O2 was decreased with 1.0 mM maltol, as determined by the TUNEL method. Western blot analysis showed that treatment with maltol reduced phosphorylation of NF-kappaB, ERK, and JNK, but not p38. The neuroprotective effects of maltol seemed to be related to attenuated expression of NF-kappaB, ERK, and JNK. CONCLUSIONS: Maltol not only increased cell viability but also attenuated DNA fragmentation. The results obtained here show that maltol has neuroprotective effects against hypoxia-induced neuroretinal cell damage in R28 cells, and its effects may act through the NF-kappaB and mitogen-activated protein kinase signaling pathways.

Effect of Heat Shock Protein 72 Expression on Etoposide-induced Cell Death of Rat Retinal Ganglion Cells

PURPOSE: To assess whether the expression of heat shock protein 72 (Hsp72) protects rat retinal ganglion cells (RGC-5) from apoptotic cell death. METHODS: Hsp72 expression in RGC-5 cells transduced with replication-deficient recombinant adenovirus was analyzed by Western blot analysis and immunofluorescence. The effect of Hsp72 expression on etoposide-induced apoptotic cell death was examined by microscopic analysis and confirmed by cell proliferation assay. RESULTS: Western blot analysis and immunofluorescence clearly showed adenovirus-mediated Hsp72 expression in RGC-5 cells. Treatment with etoposide resulted in the death of a proportion of the cells by apoptosis. However, this apoptotic cell death was significantly reduced in cells expressing Hsp72, with the reduction in cell death correlating to the level of Hsp72 expression. CONCLUSIONS: Over-expression of Hsp72 alone is sufficient to rescue neuronal cells from apoptotic cell death, suggesting that fine-tuning its expression may be an effective neuroprotective approach in retinal degenerative disease.

Glaucomatous neurodegeneration An eye on tumor necrosis factor-alpha.

Glaucoma, a neurodegenerative disease, is currently being treated by modulation of one of its primary risk factors, the elevated intraocular pressure. Newer therapies that can provide direct neuroprotection to retinal ganglion cells are being extensively investigated. Tumor necrosis factor-α, a cytokine, has been recognized to play an important role in pro and antiapoptotic cellular events. In this paper we review the relevant literature to understand (1) The association of increased expression of tumor necrosis factor-α with glaucomatous neurodegeneraion, (2) Modulation of tumor necrosis factor-α expression by exposure to various risk factors of glaucoma, (3) Downstream cellular signaling mechanisms following interaction of tumor necrosis factor-α with its receptors and (4) Role of tumor necrosis factor-α as a possible target for therapeutic intervention in glaucoma. Literature was reviewed using PubMed search engine with relevant key words and a total of 82 English language papers published from 1990 to 2010 are included in this review.

Reduced occurrence of programmed cell death and gliosis in the retinas of juvenile rabbits after shortterm treatment with intravitreous bevacizumab

OBJECTIVE: Bevacizumab has been widely used as a vascular endothelial growth factor antagonist in the treatment of retinal vasoproliferative disorders in adults and, more recently, in infants with retinopathy of prematurity. Recently, it has been proposed that vascular endothelial growth factor acts as a protective factor for neurons and glial cells, particularly in developing nervous tissue. The purpose of this study was to investigate the effects of bevacizumab on the developing retinas of juvenile rabbits. METHODS: Juvenile rabbits received bevacizumab intravitreously in one eye; the other eye acted as an untreated control. Slit-lamp and fundoscopic examinations were performed both prior to and seven days after treatment. At the same time, retina samples were analyzed using immunohistochemistry to detect autophagy and apoptosis as well as proliferation and glial reactivity. Morphometric analyses were performed, and the data were analyzed using the Mann-Whitney U test. RESULTS: No clinical abnormalities were observed in either treated or untreated eyes. However, immunohistochemical analyses revealed a reduction in the occurrence of programmed cell death and increases in both proliferation and reactivity in the bevacizumab-treated group compared with the untreated group. CONCLUSIONS: Bevacizumab appears to alter programmed cell death patterns and promote gliosis in the developing retinas of rabbits; therefore, it should be used with caution in developing eyes.

Protective mechanism of agmatine pretreatment on RGC-5 cells injured by oxidative stress

Agmatine has neuroprotective effects on retinal ganglion cells (RGCs) as well as cortical and spinal neurons. It protects RGCs from oxidative stress even when it is not present at the time of injury. As agmatine has high affinity for various cellular receptors, we assessed protective mechanisms of agmatine using transformed RGCs (RGC-5 cell line). Differentiated RGC-5 cells were pretreated with 100 ìM agmatine and consecutively exposed to 1.0 mM hydrogen peroxide (H2O2). Cell viability was determined by measuring lactate dehydrogenase (LDH), and the effects of selective alpha 2-adrenergic receptor antagonist yohimbine (0-500 nM) and N-methyl-D-aspartic acid (NMDA) receptor agonist NMDA (0-100 µM) were evaluated. Agmatine’s protective effect was compared to a selective NMDA receptor antagonist MK-801. After a 16-h exposure to H2O2, the LDH assay showed cell loss greater than 50 percent, which was reduced to about 30 percent when agmatine was pretreated before injury. Yohimbine almost completely inhibited agmatine’s protective effect, but NMDA did not. In addition, MK-801 (0-100 µM) did not significantly attenuate the H2O2-induced cytotoxicity. Our results suggest that neuroprotective effects of agmatine on RGCs under oxidative stress may be mainly attributed to the alpha 2-adrenergic receptor signaling pathway.

Tomografia de coerência óptica na avaliação da camada de fibras nervosas peripapilar nos usuários de cloroquina / Optical coherence tomography to evaluate peripapillary retinal nerve fiber layer in chloroquine patients

OBJETIVO: Analisar a camada de fibras nervosas nos usuários de cloroquina com a tomografia de coerência óptica (OCT). MÉTODOS: A espessura da camada de fibras nervosas foi mensurada pelo Stratus OCT® através do protocolo scan rápido da camada de fibras nervosas em 94 olhos de 48 pacientes usuários de cloroquina a pelo menos um ano e sem alteração macular aparente. A dose cumulativa e dose diária máxima (mg/kg/dia) e o tempo de uso da cloroquina foram correlacionadas com a espessura da camada de fibras nervosas. Os dados formam comparados com um grupo controle de 30 pacientes não usuários de cloroquina. Todos os pacientes foram submetidos a um exame oftalmológico completo incluindo medida da acuidade visual, refração, pressão intraocular, fundoscopia, retinografia e medida da escavação de papila. RESULTADOS: Comparação entre a média da espessura da camada de fibras nervosas entre usuários do antimalárico (107,60 ± 13,25 µm) e o grupo controle (99,05 ± 13,08 µm) teve uma associação estatisticamente significativa (p=0,0137). Também foi encontrada essa associação entre os quadrantes temporal, superior e inferior da camada de fibras nervosas peripapilar dos dois grupos. Ao analisar a camada de fibras nervosas através das 12 h do relógio detectou-se pelo menos um defeito focal em mais de 50 por cento dos usuários da medicação. Nos pacientes com o defeito focal foi observado uma relação com a dose diária máxima (p=0,0120). CONCLUSÃO: A tomografia de coerência óptica demonstrouse eficaz na detecção da diminuição da camada de fibras nervosas em usuários de cloroquina sem alterações fundoscópicas aparentes. Dessa forma, a tomografia de coerência óptica pode contribuir para o diagnóstico mais precoce da retinopatia por cloroquina.

PURPOSE: To evaluated the retinal nerve fiber layer in chloroquine patients with optical coherence tomography (OCT). METHODS: Nerve fibers layer thickness was measured by a proprietary OCT Stratus® through the fast retinal nerve fiber layer protocol in ninety-four eyes of 48 patients exposed to chloroquine for at least one year with no apparent macular disorder. Cumulative dose, maximum daily dose (mg/kg/day) and time of chloroquine use were correlated with the retinal nerve fiber layer thickness. Data were compared with a control group of 30 patients who did not use chloroquine. All patients underwent a complete ophthalmologic examination including visual acuity, refraction, intraocular pressure, fundoscopy, angiography and measurement of cup-to-disc ratio. RESULTS: The average thickness of retinal nerve fiber layer between antimalaric users (107.60 ± 13.25 µm) and the control group (99.05 ± 13.08 µm) had a statistically significant difference (p=0.0137). Furthermore, a positive association of the peripapillary thickness measurements between temporal, upper and lower quadrants of both groups was found. Twelve clock hours retinal nerve fiber layer analysis detected at least one focal defect in more than 50 percent of the medication users. Particularly, a statistical correlation with the maximum daily dose was found in patients with focal defects (p=0.0120). CONCLUSION: Optical coherence tomography is effective in detecting nerve fiber layer loss in chloroquine patients without apparent fundus changes. Thus, optical coherence tomography may contribute to the early diagnosis of chloroquine retinopathy.

Neuroprotection in glaucoma.

Currently, glaucoma is recognised as an optic neuropathy. Selective death of retinal ganglion cells (RGC) is the hallmark of glaucoma, which is also associated with structural changes in the optic nerve head. The process of RGC death is thought to be biphasic: a primary injury responsible for initiation of damage that is followed by a slower secondary degeneration related to noxious environment surrounding the degenerating cells. For example, retinal ishaemia may establish a cascade of changes that ultimately result in cell death: hypoxia leads to excitotoxic levels of glutamate, which cause a rise in intra-cellular calcium, which in turn, leads to neuronal death due to apoptosis or necrosis. Neuroprotection is a process that attempts to preserve the cells that were spared during the initial insult, but are still vulnerable to damage. Although not yet available, a neuroprotective agent would be of great use in arresting the progression of glaucoma. There is evidence that neuroprotection can be achieved both pharmacologically and immunologically. Pharmacological intervention aims at neutralising some of the effects of the nerve-derived toxic factors, thereby increasing the ability of the spared neurons to cope with stressful conditions. On the other hand, immunological interventions boost the body's own repair mechanisms for counteracting the toxic effects of various chemicals generated during the cascade. This review, based on a literature search using MEDLINE, focuses on diverse cellular events associated with glaucomatous neurodegeneration, and discusses some pharmacological agents believed to have a neuroprotective role in glaucoma.

Veratridine increases the survival of retinal ganglion cells in vitro

Neuronal cell death is an important phenomenon involving many biochemical pathways. This degenerative event has been studied to understand how the cells activate the mechanisms that lead to self-destruction. Target cells and afferent cells play a relevant role in the regulation of natural cell death. We studied the effect of veratridine (1.5, 3.0, 4.5 and 6.0 muM) on the survival of neonatal rat retinal ganglion cells in vitro. Veratridine (3.0 muM), a well-known depolarizing agent that opens the Na+ channel, promoted a two-fold increase in the survival of retinal ganglion cells kept in culture for 48 h. This effect was dose-dependent and was blocked by 1.0 muM tetrodotoxin (a classical voltage-dependent Na+ channel blocker) and 3.0 muM flunarizine (a Na+ and Ca2+ channel blocker). These results indicate that electrical activity is also important for the maintenance of retinal ganglion cell survival in vitro.