Fewer Functional Deficits and Reduced Cell Death after Ranibizumab Treatment in a Retinal Ischemia Model

[Cell loss in retinal ischemia is associated with increased necroptosis]

BACKGROUND

Retinal ischemia plays a central pathophysiological role in numerous eye diseases, such as glaucoma. In addition to apoptosis, autophagy, necroptosis and ferroptosis are among the cell death mechanisms of ischemia; however, their role is not clearly understood and controversially discussed.

OBJECTIVE

The aim of this study is to gain an improved understanding of the role of alternative cell death mechanisms such as autophagy and necroptosis after retinal ischemia. Based on this, future autophagy-based or necroptosis-based therapeutic approaches could be developed.

MATERIAL AND METHODS

Retinal ischemia reperfusion was induced in one eye of 6 to 8‑week-old rats by temporarily increasing the intraocular pressure to 140 mm Hg (60 min), followed by reperfusion. The untreated contralateral eye served as a control. Retinas after ischemia and control retinas were examined 7 days after ischemia immunohistochemically with markers for retinal ganglion cells (RGC), astrocytes (GFAP) as well as an autophagy (LAMP1) and a necroptosis marker (RIPK3) (n = 6/group).

RESULTS

Ischemia reperfusion resulted in both significant RGC loss (p ≤ 0.001) and a significant increase of astrocyte area (p = 0.026) after 7 days. Interestingly, the number of autophagic LAMP1 positive cells was unchanged 7 days after ischemia (p = 0.272), whereas the number of necroptotic RIPK3 positive cells was significantly increased (p ≤ 0.001).

CONCLUSION

Necroptotic processes appear to be activated 7 days after ischemia reperfusion, contributing to retinal cell death and activation of astrocytes. Late autophagic processes are not activated 7 days after ischemia. Necroptosis-associated parameters could therefore be targeted as an early therapeutic approach after ischemia in the future.

Microglia in retinal angiogenesis and diabetic retinopathy

Diabetic retinopathy has a high probability of causing visual impairment or blindness throughout the disease progression and is characterized by the growth of new blood vessels in the retina at an advanced, proliferative stage. Microglia are a resident immune population in the central nervous system, known to play a crucial role in regulating retinal angiogenesis in both physiological and pathological conditions, including diabetic retinopathy. Physiologically, they are located close to blood vessels and are essential for forming new blood vessels (neovascularization). In diabetic retinopathy, microglia become widely activated, showing a distinct polarization phenotype that leads to their accumulation around neovascular tufts. These activated microglia induce pathogenic angiogenesis through the secretion of various angiogenic factors and by regulating the status of endothelial cells. Interestingly, some subtypes of microglia simultaneously promote the regression of neovascularization tufts and normal angiogenesis in neovascularization lesions. Modulating the state of microglial activation to ameliorate neovascularization thus appears as a promising potential therapeutic approach for managing diabetic retinopathy.

Dose-Related Side Effects of Intravitreal Injections of Humanized Anti-Vascular Endothelial Growth Factor in Rats: Glial Cell Reactivity and Retinal Ganglion Cell Loss

Purpose

In a previous study, we documented that the Intravitreal injections (IVIs) of bevacizumab in rats caused a retinal inflammatory response. We now study whether the IVI of other humanized anti-VEGF: ranibizumab and aflibercept also cause an inflammatory reaction in the rat retina and if it depends on the dose administered. Finally, we study whether this reaction affects retinal ganglion cell (RGC) survival.

Methods

Albino Sprague-Dawley rats received a single IVI of 5 µL of PBS or ranibizumab or aflibercept at the concentration used in clinical practice (10 µg/µL or 40 µg/µL) or at a lower concentration (0.38 µg/µL and 1.5 µg/µL) calculated to obtain within the rat eye the same concentration as in the human eye in clinical practice. Others received a single 5 µL IVI of a polyclonal goat anti-rat VEGF (0.015 µg/µL) or of vehicle (PBS). Animals were processed 7 days or 1 month later. Retinal whole mounts were immunolabeled for the detection of microglial, macroglial, RGCs, and intrinsically photosensitive RGCs (ipRGCs). Fluorescence and confocal microscopy were used to examine retinal changes, and RGCs and ipRGCs were quantified automatically or semiautomatically, respectively.

Results

All the injected substances including the PBS induced detectable side effects, namely, retinal microglial cell activation and retinal astrocyte hypertrophy. However, there was a greater microglial and macroglial response when the higher concentrations of ranibizumab and aflibercept were injected than when PBS, the antibody anti-rat VEGF and the lower concentrations of ranibizumab or aflibercept were injected. The higher concentration of ranibizumab and aflibercept resulted also in significant RGC death, but did not cause appreciable ipRGC death.

Conclusions

The IVI of all the substances had some retinal inflammatory effects. The IVI of humanized anti-VEGF to rats at high doses cause important side effects: severe inflammation and RGC death, but not ipRGC death.

In a novel autoimmune and high-pressure glaucoma model a complex immune response is induced

Background

The neurodegenerative processes leading to glaucoma are complex. In addition to elevated intraocular pressure (IOP), an involvement of immunological mechanisms is most likely. In the new multifactorial glaucoma model, a combination of high IOP and optic nerve antigen (ONA) immunization leads to an enhanced loss of retinal ganglion cells accompanied by a higher number of microglia/macrophages in the inner retina. Here, we aimed to evaluate the immune response in this new model, especially the complement activation and the number of T-cells, for the first time. Further, the microglia/macrophage response was examined in more detail.

Methods

Six-week-old wildtype (WT+ONA) and βB1-connective tissue growth factor high-pressure mice (CTGF+ONA) were immunized with 1 mg ONA. A wildtype control (WT) and a CTGF group (CTGF) received NaCl instead. Six weeks after immunization, retinae from all four groups were processed for immunohistology, RT-qPCR, and flow cytometry, while serum was used for microarray analyses.

Results

We noticed elevated numbers of C1q+ cells (classical complement pathway) in CTGF and CTGF+ONA retinae as well as an upregulation of C1qa, C1qb, and C1qc mRNA levels in these groups. While the complement C3 was only increased in CTGF and CTGF+ONA retinae, enhanced numbers of the terminal membrane attack complex were noted in all three glaucoma groups. Flow cytometry and RT-qPCR analyses revealed an enhancement of different microglia/macrophages markers, including CD11b, especially in CTGF and CTGF+ONA retinae. Interestingly, increased retinal mRNA as well as serum levels of the tumor necrosis factor α were found throughout the different glaucoma groups. Lastly, more T-cells could be observed in the ganglion cell layer of the new CTGF+ONA model.

Conclusion

These results emphasize an involvement of the complement system, microglia/macrophages, and T-cells in glaucomatous disease. Moreover, in the new multifactorial glaucoma model, increased IOP in combination with autoimmune processes seem to enforce an additional T-cell response, leading to a more persistent pathology. Hence, this new model mimics the pathomechanisms occurring in human glaucoma more accurately and could therefore be a helpful tool to find new therapeutic approaches for patients in the future.

Retinal stroke: research models, targets and experimental drugs

INTRODUCTION

Retinal artery occlusion (RAO), often caused by a microembolus and resulting in inner retinal ischemia, could be considered as the retinal analog to cerebral stroke. Although several therapeutic targets have been suggested in animal models of retinal ischemia and several potential treatments have been evaluated on small series of patients, central retinal artery occlusion (CRAO) is still rarely treatable in clinical practice.

AREAS COVERED

Here, we review several animal models of RAO, including increased intraocular pressure, laser, vasoconstriction, embolization and clamp. We also review the pathogenic mechanisms that contribute to cell death cascades during ischemia, and the therapeutic strategies targeting these events. These strategies aim to restore blood flow by fibrinolysis, increase the oxygen or glucose supply, decrease the energy demands, restrict ionic leak fluxes or reduce the detrimental effects of glutamate, calcium and free radicals. The current literature suggests that tPA treatment could be effective for CRAO.

EXPERT OPINION

Eye care professionals must make a rapid and accurate diagnosis and immediately refer patients with acute retinal stroke to specialized centers. CRAO management should also be facilitated by developing local networks to encourage collaboration among ophthalmologists, retina specialists and stroke neurologists.

Enhanced glaucomatous damage accompanied by glial response in a new multifactorial mouse model

Introduction

Glaucoma is a complex, multifactorial neurodegenerative disease, which can lead to blindness if left untreated. It seems that, among others, immune processes, elevated intraocular pressure (IOP), or a combination of these factors are responsible for glaucomatous damage. Here, we combined two glaucoma models to examine if a combination of risk factors (IOP and immune response) results in a more severe damage of retinal ganglion cells (RGCs) and the optic nerves as well as an additional glia activation.

Methods

Six-week-old wildtype (WT+ONA) and βB1-Connective Tissue Growth Factor (CTGF) mice (CTGF+ONA) were immunized with 1 mg ONA (optic nerve antigen). A WT and a CTGF control group (CTGF) received sodium chloride instead. IOP was measured before and every two weeks after immunization. After six weeks, electroretinogram (ERG) measurements were performed. Then, retinae and optic nerves were processed for (immuno-) histology. Further, mRNA levels of corresponding genes in optic nerve and retina were analyzed via RT-qPCR.

Results

Six weeks after immunization, the IOP in CTGF and CTGF+ONA mice was increased. The optic nerve of CTGF+ONA animals displayed the most severe cell inflammation, demyelination, and macroglia activation. Fewer numbers of oligodendrocytes were only observed in WT+ONA optic nerves, while more apoptotic cells triggered by the extrinsic pathway could be revealed in all three glaucoma groups. The number of microglia/macrophages was not altered within the optic nerves of all groups. The loss of neuronal cells, especially RGCs was most pronounced in CTGF+ONA retinae in the central part and this was accompanied by an enhanced activation of microglia/macrophages. Also, Müller cell activation could be noted in CTGF and CTGF+ONA retinae.

Discussion

In this new model, an additive degeneration could be noted in optic nerves as well as in the number of RGCs. These results suggest a potential additive role of high IOP and immune factors in glaucoma development, which will aid for understanding this multifactorial disease more precisely in the future.

Monoclonal antibodies in diabetic retinopathy

INTRODUCTION

Diabetic retinopathy (DR), as one of the main complications of diabetes, is among the leading causes of blindness and visual impairment worldwide.

AREAS COVERED

Current clinical therapies include photocoagulation, vitrectomy, and anti-vascular endothelial growth factor (VEGF) therapies. Bevacizumab and ranibizumab are two monoclonal antibodies (mAbs) inhibiting angiogenesis. Intravitreal ranibizumab and bevacizumab can decrease the rate of blindness and retinal thickness, and improve visual acuity whether as monotherapy or combined with other treatments. They can increase the efficacy of other treatments and decrease their adverse events. Although administered intravitreally, they also might enter the circulation and cause systemic effects. This study is aimed to review our current knowledge about mAbs, bevacizumab and ranibizumab, in DR including superiorities, challenges, and limitations. Meanwhile, we tried to shed light on new ideas to overcome these limitations. Our latest search was done in April 2021 mainly through PubMed and Google Scholar. Relevant clinical studies were imported.

EXPERT OPINION

Future direction includes detection of more therapeutic targets considering other components of DR pathophysiology and shared pathogenesis of DR and neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease, the treat-and-extend regimen, and new ways of drug delivery and other routes of ocular drug administration.

Synthesis, Characterization, and in vivo Evaluation of a Novel Potent Autotaxin-Inhibitor

The autotaxin-lysophosphatidic acid (ATX-LPA) signaling pathway plays a role in a variety of autoimmune diseases, such as rheumatoid arthritis or neurodegeneration. A link to the pathogenesis of glaucoma is suggested by an overactive ATX-LPA axis in aqueous humor samples of glaucoma patients. Analysis of such samples suggests that the ATX-LPA axis contributes to the fibrogenic activity and resistance to aqueous humor outflow through the trabecular meshwork. In order to inhibit or modulate this pathway, we developed a new series of ATX-inhibitors containing novel bicyclic and spirocyclic structural motifs. A potent lead compound (IC50 against ATX: 6 nM) with good in vivo PK, favorable in vitro property, and safety profile was generated. This compound leads to lowered LPA levels in vivo after oral administration. Hence, it was suitable for chronic oral treatment in two rodent models of glaucoma, the experimental autoimmune glaucoma (EAG) and the ischemia/reperfusion models. In the EAG model, rats were immunized with an optic nerve antigen homogenate, while controls received sodium chloride. Retinal ischemia/reperfusion (I/R) was induced by elevating the intraocular pressure (IOP) in one eye to 140 mmHg for 60 min, followed by reperfusion, while the other untreated eye served as control. Retinae and optic nerves were evaluated 28 days after EAG or 7 and 14 days after I/R induction. Oral treatment with the optimized ATX-inhibitor lead to reduced retinal ganglion cell (RGC) loss in both glaucoma models. In the optic nerve, the protective effect of ATX inhibition was less effective compared to the retina and only a trend to a weakened neurofilament distortion was detectable. Taken together, these results provide evidence that the dysregulation of the ATX-LPA axis in the aqueous humor of glaucoma patients, in addition to the postulated outflow impairment, might also contribute to RGC loss. The observation that ATX-inhibitor treatment in both glaucoma models did not result in significant IOP increases or decreases after oral treatment indicates that protection from RGC loss due to inhibition of the ATX-LPA axis is independent of an IOP lowering effect.

Microvascular Structure Changes After Intravitreal Ranibizumab Injection in Retinal Vein Occlusion Patients With and Without Macular Ischemia

Purpose: To investigate the changes in the macular microvascular structure after anti-vascular endothelial growth factor (anti-VEGF) treatment in retinal vein occlusion (RVO) patients with and without macular ischemia.

Methods: A total of 39 patients were divided into the macular ischemia group (n = 22) and the nonischemia group (n = 17) at baseline. All the patients received an intravitreal injection of ranibizumab with a 3+ pro re nata (PRN) regimen. The foveal avascular zone (FAZ) areas, macular vessel density (VD), and macular ischemic index (ISI) were evaluated at baseline and 3 and 6 months after treatment.

Results: After treatment, some patients in the macular ischemia group achieved obvious reperfusion in macular nonperfusion areas. The VD and macular ISI improved in RVO patients, but the changes in VD and macular ISI were different in the two groups. The improvement of best corrected visual acuity (BCVA) was positively correlated with the improvement of macular perfusion status. Macular perfusion remained stable in most patients in RVO and only one patient had macular ischemia aggravation.

Conclusion: The macular microvascular structures were stable in most RVO patients after anti-VEGF treatment. At the same time, some patients with macular ischemia presented reperfusion in macular nonperfusion areas, and still a few patients presented aggravated macular ischemia. Macular ISI is a good way to evaluate macular perfusion status in RVO compared to VD.

Effect of anti-VEGF treatment on nonperfusion areas in ischemic retinopathy

In recent years, retinal ischemia such as that which occurs in diabetic retinopathy (DR) and retinal vein occlusion (RVO) has become a hotspot of ischemic retinopathy research. High levels of vascular endothelial growth factor (VEGF) are recognized as a major cause of macular edema (ME) in DR and RVO. High concentrations of VEGF in the vitreous can lead to serious retinal ischemia and hypoxia and form retinal nonperfusion areas (NPAs). Different levels of retinal ischemia can represent disease severity and progression. Anti-VEGF therapy as the first-line treatment for ME has been found to be effective in improving vision, but there are still disputes about whether anti-VEGF therapy could improve retinal ischemia and achieve reperfusion of previously developed retinal NPAs. Here, we review and summarize studies of the effects of anti-VEGF drugs on retinal ischemia, especially NPAs.

Cytokine and Complement Response in the Glaucomatous βB1-CTGF Mouse Model

Glaucoma is a complex neurodegenerative disease leading to a loss of retinal ganglion cells (RGCs) and optic nerve axons. An activation of the complement system seems to contribute to cell loss in this disease. Hence, we investigated a possible initiation of the complement system and the cytokine response in the βB1-CTGF glaucoma model. In these mice, intraocular pressure is elevated, which is the main glaucoma risk factor in patients, and RGC loss occurs at 15 weeks of age. Therefore, quantitative real-time PCR and immunohistological experiments were performed in 5-, 10-, and 15-week-old βB1-CTGF animals and their corresponding wildtypes (WT) to analyze the expression of several complement system factors. We could show that mRNA levels of the terminal complement pathway components C3 and C5 (Hc) were upregulated at 10 weeks. In accordance, more C3+ and membrane attack complex+ cells were observed in transgenic retinae. Further, the C5a receptor anaphylatoxin receptor (C5ar) and the complement component C5a receptor 1 (C5ar1; CD88) mRNA levels were upregulated in 10- and 15-week-old βB1-CTGF mice. Interestingly, all three activation routes of the complement system were elevated in βB1-CTGF mice at some age. Especially C1q, as a marker of the classical pathway, was significantly increased at all investigated ages. Furthermore, mRNA expression levels of interferon-γ (Infg) were upregulated at 5 weeks, while Cxcl1 and Cxcl2 mRNA levels were upregulated at 10 and 15 weeks. The mRNA levels of the chemokines Cxcl10 were increased at all ages in βB1-CTGF mice. These results lead to the assumption that in these transgenic mice, a complement activation mainly through the classical pathway as well as a cytokine response plays a major role in cell death.

Activation of Apoptosis in a βB1-CTGF Transgenic Mouse Model

To reveal the pathomechanisms of glaucoma, a common cause of blindness, suitable animal models are needed. As previously shown, retinal ganglion cell and optic nerve degeneration occur in βB1-CTGF mice. Here, we aimed to determine possible apoptotic mechanisms and degeneration of different retinal cells. Hence, retinae were processed for immunohistology (n = 5–9/group) and quantitative real-time PCR analysis (n = 5–7/group) in 5- and 10-week-old βB1-CTGF and wildtype controls. We noted significantly more cleaved caspase 3⁺ cells in βB1-CTGF retinae at 5 (p = 0.005) and 10 weeks (p = 0.02), and a significant upregulation of Casp3 and Bax/Bcl2 mRNA levels (p < 0.05). Furthermore, more terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL⁺) cells were detected in transgenic mice at 5 (p = 0.03) and 10 weeks (p = 0.02). Neurofilament H staining (p = 0.01) as well as Nefh (p = 0.02) and Tubb3 (p = 0.009) mRNA levels were significantly decreased at 10 weeks. GABAergic synapse intensity was lower at 5 weeks, while no alterations were noted at 10 weeks. The glutamatergic synapse intensity was decreased at 5 (p = 0.007) and 10 weeks (p = 0.01). No changes were observed for bipolar cells, photoreceptors, and macroglia. We conclude that apoptotic processes and synapse loss precede neuronal death in this model. This slow progression rate makes the βB1-CTGF mice a suitable model to study primary open-angle glaucoma.

Minocycline reduces inflammatory response and cell death in a S100B retina degeneration model

BACKGROUND

Previous studies noted that intravitreal injection of S100B triggered a glaucoma-like degeneration of retina and optic nerve as well as microglia activation after 14 days. The precise role of microglia in our intravitreal S100B model is still unclear. Hence, microglia were inhibited through minocycline. The aim is to investigate whether microglia have a significant influence on the degeneration process or whether they are only a side effect in the model studied here.

METHODS

Minocycline was applied daily in rats by intraperitoneal injection using two different concentrations (13.5 mg/kg body weight, 25 mg/kg body weight). One day after treatment start, S100B or PBS was intravitreally injected in one eye per rat. The naïve groups received no injections. This resulted in a total of five groups (naïve n = 14, PBS n = 14, S100B n = 13, 13.5 mg/kg mino n = 15, 25 mg/kg mino n = 15). At day 14, electroretinogram measurements were performed, followed by immunofluorescence and label-free quantitative proteomics analysis. The focus of these investigations was on the survival of RGCs as well as their axons, the response of the microglia, and the identification of further pathological modes of action of S100B.

RESULTS

The best signal transmission was detected via ERG in the 13.5 mg/kg mino group. The inhibition of the microglia protected optic nerve neurofilaments and decreased the negative impact of S100B on RGCs. However, the minocycline treatment could not trigger complete protection of RGCs. Furthermore, in retina and optic nerve, the minocycline treatment reduced the number and activity of S100B-triggered microglia in a concentration-dependent manner. Proteomics analysis showed that S100B application led to numerous metabolic functions and cellular stress, mainly an increased inflammatory response, glycolysis, and mitochondrial dysfunction, which caused oxidative stress in the retina. Importantly, the protective capability of lower dose of minocycline was unraveled by suppressing the apoptotic, inflammatory, and the altered metabolic processes caused by S100B insult in the retina.

CONCLUSION

Intravitreally injected S100B not only led to a pro-inflammatory microglial reaction, but also a mitochondrial and metabolic dysfunction. Also, these results suggest that an excessive microglial response may be a significant degenerative factor, but not the only trigger for increased cell death.

Clinical effect of conbercept on improving diabetic macular ischemia by OCT angiography

BACKGROUND

Varying degrees of macular ischemia generally occur in diabetic retinopathy (DR). This study aims to evaluate the effect of conbercept with 3+ pro re nata (PRN) on macular perfusion status in patients with diabetic macular edema (DME) and quantitatively assess changes in foveal avascular zone (FAZ) areas and capillary density in macular regions by applying optical coherence tomography angiography (OCTA).

METHODS

Fifty patients were divided into ischemic (n = 31) and non-ischemic (n = 19) groups according to the presence of ischemia on OCTA at baseline. All patients received intravitreal injections of 0.5 mg of conbercept with 3+ PRN principle. The FAZ areas and macular vessel density measured using OCTA were evaluated at baseline, 3 months, and 6 months after treatment in both groups.

RESULTS

At months 3 and 6, the FAZ area in the ischemic group changed from 0.510 ± 0.171 mm2 to 0.441 ± 0.158 mm2 then to 0.427 ± 0.153 mm2 (p = 0.003, p = 0.296); in the non-ischemic group, it remained stable (p = 0.269, p = 0.926). The superficial vessel density changed from 41.1 ± 4.1 to 42.5% ± 4.7% then to 42.6% ± 4.6% (p = 0.043, p = 0.812), and the deep vessel density changed from 40.7 ± 4.4 to 42.3% ± 3.6% then to 42.3% ± 4.7% (p = 0.072, p = 0.961) in the ischemic group. In the non-ischemic group, the superficial vessel density changed from 44.8 ± 3.2 to 46.0% ± 3.5% then to 45.7% ± 3.3% (p = 0.108, p = 0.666), whereas the deep vessel density changed from 43.6 ± 3.6 to 43.8% ± 3.2% then to 43.5% ± 4.5% (p = 0.882, p = 0.736). Reperfusion in macular nonperfusion areas was observed.

CONCLUSION

Anti-vascular endothelial growth factor treatment may have a positive effect on macular perfusion status. Furthermore, OCTA had advantages in quantifying and calculating blood flow index in the study of macular perfusion status.

Microglia Activation in Retinal Ischemia Triggers Cytokine and Toll-Like Receptor Response

Mechanisms and progression of ischemic injuries in the retina are still incompletely clarified. Therefore, the time course of microglia activation as well as resulting cytokine expression and downstream signaling were investigated. Ischemia was induced in one eye by transiently elevated intraocular pressure (60 min) followed by reperfusion; the other eye served as a control. Eyes were processed for RT-qPCR and immunohistochemistry analyses at 2, 6, 12, and 24 h as well as at 3 and 7 days. Already 2 h after ischemia, more microglia/macrophages were in an active state in the ischemia group. This was accompanied by an upregulation of pro-inflammatory cytokines, like IL-1β, IL-6, TNFα, and TGFβ. Activation of TLR3, TLR2, and the adaptor molecule Myd88 was also observed after 2 h. NFκB revealed a wave-like activation pattern. In addition, an extrinsic caspase pathway activation was noted at early time points, while enhanced numbers of cleaved caspase 3⁺ cells could be observed in ischemic retinae throughout the study. Retinal ischemia induced an early and strong microglia/macrophage response as well as cytokine and apoptotic activation processes. Moreover, in early and late ischemic damaging processes, TLR expression and downstream signaling were involved, suggesting an involvement in neuronal death in ischemic retinae. Graphical Abstract.

Retinal ischemia triggers early microglia activation in the optic nerve followed by neurofilament degeneration

Retinal ischemia leads to an early severe damage of the retina and thus plays an important role in eye diseases such as angle-closure glaucoma or retinal vascular occlusion. In retinal diseases, there is common sense about the affection of the optic nerve by ischemic injury. However, the exact dynamic processes of this optic nerve degeneration are mainly unclear. In this study, retinal ischemia was induced in one eye of Brown-Norway rats by raising the intraocular pressure 60 min to 140 mmHg followed by natural reperfusion. Optic nerves were analyzed at six different points in time: 2, 6, 12, and 24 h as well as 3 and 7 days after ischemic injury. Cell infiltration and moreover signs of tissue demyelination and dissolution were noticed in optic nerves 7 days after ischemia (hematoxylin & eosin: p < 0.001, luxol fast blue: p = 0.04). Although microglial activation was verified already from 12 h on after ischemia (p = 0.030), the beginning of a structural degeneration of the neurofilament was seen at 3 days (p = 0.02). Interestingly, proliferative microglia were present later on (7 days: p = 0.017). At this point, the number of total microglia was also increased in ischemic nerves (p = 0.003). Concluding, our data indicate that not only retinal tissue is affected by an ischemia, the optic nerve also demonstrates progressive damage. Interestingly, a microglia activation was noted days before structural damage became visible.

Retinoprotective Effect of 2-Ethyl-3-hydroxy-6-methylpyridine Nicotinate

An important task of pharmacology is to find effective agents to improve retinal microcirculation and resistance to ischemia. The purpose of the study is to pharmacologically evaluate the retinoprotective effect of 2-ethyl-3-hydroxy-6-methylpyridine nicotinate in a rat model of retinal ischemia–reperfusion. A retinal ischemia–reperfusion model was used, in which an increase in intraocular pressure (IOP) to 110 mmHg was carried out within 30 min. The retinoprotective effect of 2-ethyl-3-hydroxy-6-methylpyridine nicotinate at a dose of 3.8 mg/kg, in comparison with nicotinic acid at a dose of 2 mg/kg and emoxipine at a dose of 2 mg/kg, was estimated by the changes in the eye fundus during ophthalmoscopy, the retinal microcirculation level with laser Doppler flowmetry (LDF), and electroretinography (ERG) after 72 h of reperfusion. The use of 2-ethyl-3-hydroxy-6-methylpyridine nicotinate prevented the development of ischemic injuries in the fundus and led to an increase in the retinal microcirculation level to 747 (median) (lower and upper quartiles: 693;760) perfusion units (p = 0.0002) in comparison with the group that underwent no treatment. In the group with the studied substance, the b-wave amplitude increased significantly (p = 0.0022), and the b/a coefficient increased reliably (p = 0.0002) in comparison with the group with no treatment. Thus, 2-ethyl-3-hydroxy-6-methylpyridine nicotinate has established itself as a potential retinoprotector.

Role of the PGE2 receptor in ischemia-reperfusion injury of the rat retina

Purpose

To investigate the function and expression of the PGE2 receptors EP1-4 in rat retinal ischemia-reperfusion (I/R) injury and to determine the regulatory role of resveratrol (RES) in this process.

Methods

In vitro, we stimulated primary astrocytes extracted from the optic disc of rats with epidermal growth factor (EGF) and RES, and detected the location of EP1-4 expression with immunofluorescence. The expression of antiglial fibrillary acidic protein (GFAP), EGF receptor (EGFR), inducible NOS (iNOS), and EP1-4 in astrocytes was detected with western blotting. In vivo, we established an I/R injury model and RES treatment model with Sprague-Dawley rats. Changes in the thickness of the inner retina were observed with hematoxylin and eosin (H&E) staining. EP1-4 localization in the retina was observed with immunohistochemistry. The expression of COX-2, iNOS, and EP1-4 in the control and model groups was detected with western blotting.

Results

In this study, immunofluorescence and immunohistochemistry showed that EP1-4 are expressed in astrocytes and the rat retina. EGF stimulation increased the expression of EGFR, iNOS, EP1, EP2, and EP4 in astrocytes. The expression of EP1-4 was statistically significantly increased on the third day after model induction, and EP1-4 expression decreased to normal levels on day 7. EGF and RES mediated the decrease in the expression of EP2. RES treatment significantly reduced retinal damage and RGC loss, as demonstrated by the relatively intact tissue structure on day 7 observed with H&E staining. Moreover, inflammation was associated with this I/R injury model, as demonstrated by the early induction of proinflammatory mediators, and this inflammation was significantly attenuated after RES treatment.

Conclusions

These results indicate that the COX-2/PGE2/EPs pathway is involved in retinal damage and astrocyte inflammation. In addition, the results suggest that the neuroprotective effects of RES may be associated with decreased production of inflammatory mediators. These results suggest that the PGE2 receptor may be a key factor in the treatment of neurodegenerative diseases, and that RES may be used as a possible therapeutic strategy for glaucoma.

Correction of retinal ischemic injuries by using non-selective imidazoline receptor agonists in the experiment

Introduction: Retinoprotective effects of non-selective imidazoline receptor agonists: potassium salt of С7070; sodium salt of С7070; С7070 processed with CO2 – were investigated in comparison with C7070 on the retinal ischemia-reperfusion model in rats.

Materials and methods: The protective effects of the substances were evaluated by using ophthalmoscopy, laser Doppler flowmetry, electroretinography, histological and morphometric studies of retinal layers.

Results and discussion: The most pronounced retinoprotective effect was observed in potassium salt of C7070 at a dose of 10 mg/kg, which expresses in approaching the normal eye fundus image, achieving the target values of the retinal blood flow, b/a coefficient, and reaching the norm values of morphometric indicators. A less pronounced protective effect was found in sodium salt of C7070 at a dose of 10 mg/kg, which expresses in a 71% decrease (p &lt; 0.05) in semi-quantitative assessment of the eye fundus changes, an increase in the retinal blood flow level by 70.4% (p &lt; 0.05), in b/a by 94% (p &lt; 0.05) in comparison with the group without correction, and reaching the norm of the morphometric indicators. A retinoprotective effect of the substance C7070 processed with CO2 at a dose of 10 mg/kg is inferior to that of the sodium salt of C7070.

Conclusion: The retinoprotective activity of the substances is expressed in descending order: potassium salt of С7070 (10 mg/kg) ≈ С7070 (50 mg/kg) &gt; sodium salt of С7070 (10 mg/kg) &gt; С7070 processed with CO2 (10 mg/kg) ≈ С7070 (10 mg/kg). Injections of glibenclamide leveled the neuroretinoprotective effects of the substances to varying degrees, which confirmed the participation of ATP-dependent potassium channels in the implementation of these effects.

Intravitreal Therapy Against the Complement Factor C5 Prevents Retinal Degeneration in an Experimental Autoimmune Glaucoma Model

In glaucoma, studies revealed an involvement of the complement system. In an experimental autoimmune glaucoma model, immunization with an optic nerve homogenate antigen (ONA) led to retinal ganglion cell (RGC) loss, while intraocular pressure (IOP) remained unchanged. Here, we investigated the therapeutic effect of a complement system inhibition in this model. Hence, rats were immunized with ONA and compared to controls. In one eye of the ONA animals, an antibody against complement factor C5 was intravitreally injected (15 μmol: ONA+C5-I or 25 μmol: ONA+C5-II) before immunization and then every two weeks. IOP was measured weekly. After 6 weeks, spectral-domain optical coherence tomographies (SD-OCT), electroretinograms (ERG), immunohistochemistry, and quantitative real-time PCR analyses were performed. IOP and retinal thickness remained unchanged within all groups. The a-wave amplitudes were not altered in the ONA and ONA+C5-I groups, whereas a decrease was noted in ONA+C5-II animals (p < 0.05). ONA immunization provoked a significant decrease of the b-wave amplitude (p < 0.05), which could be preserved in ONA+C5-I, but not in ONA+C5-II animals. ONA animals showed a loss of RGCs (p = 0.001), while ONA+C5-I and ONA+C5-II retinae had similar cell counts as controls. A significant downregulation of apoptotic Bax/Bcl2 mRNA was noted in ONA+C5-I retinae (p = 0.02). Significantly more C3⁺ and MAC⁺ cells were observed in ONA animals (p < 0.001). The amount of C3⁺ cells in both treatment groups was significantly increased (p < 0.01), while the number of MAC⁺ cells in the treated retinas did not differ from controls. The number of activated microglia cells remained unchanged in ONA animals, but was increased in the treatment groups (p < 0.05). Recoverin⁺ cells were diminished in ONA animals (p = 0.049), but not in treated ones. Rho mRNA was downregulated in ONA and in ONA+C5-II retinas (both p = 0.014). Less opsin⁺ cones were observed in ONA animals (p = 0.009), but not in the treated groups. Our results indicate that the C5 antibody inhibits activation of the complement system, preventing the loss of retinal function as well as RGC, cone bipolar, and photoreceptor loss. Therefore, this approach might be a suitable new treatment for glaucoma patients, in which immune dysregulation plays an important factor for the development and progression of glaucoma.

Loss of retinal ganglion cells in a new genetic mouse model for primary open-angle glaucoma

Primary open‐angle glaucoma (POAG) is one of the most common causes for blindness worldwide. Although an elevated intraocular pressure (IOP) is the main risk factor, the exact pathology remained indistinguishable. Therefore, it is necessary to have appropriate models to investigate these mechanisms. Here, we analysed a transgenic glaucoma mouse model (βB1‐CTGF) to elucidate new possible mechanisms of the disease. Therefore, IOP was measured in βB1‐CTGF and wildtype mice at 5, 10 and 15 weeks of age. At 5 and 10 weeks, the IOP in both groups were comparable (P > 0.05). After 15 weeks, a significant elevated IOP was measured in βB1‐CTGF mice (P < 0.001). At 15 weeks, electroretinogram measurements were performed and both the a‐ and b‐wave amplitudes were significantly decreased in βB1‐CTGF retinae (both P < 0.01). Significantly fewer Brn‐3a⁺ retinal ganglion cells (RGCs) were observed in the βB1‐CTGF group on flatmounts (P = 0.02), cross‐sections (P < 0.001) and also via quantitative real‐time PCR (P = 0.02). Additionally, significantly more cleaved caspase 3⁺ RGCs were seen in the βB1‐CTGF group (P = 0.002). Furthermore, a decrease in recoverin⁺ cells was observable in the βB1‐CTGF animals (P = 0.004). Accordingly, a significant down‐regulation of Recoverin mRNA levels were noted (P < 0.001). Gfap expression, on the other hand, was higher in βB1‐CTGF retinae (P = 0.023). Additionally, more glutamine synthetase signal was noted (P = 0.04). Although no alterations were observed regarding photoreceptors via immunohistology, a significant decrease of Rhodopsin (P = 0.003) and Opsin mRNA (P = 0.03) was noted. We therefore assume that the βB1‐CTGF mouse could serve as an excellent model for better understanding the pathomechanisms in POAG.

Transfer of the Experimental Autoimmune Glaucoma Model from Rats to Mice-New Options to Study Glaucoma Disease

Studies have suggested an involvement of the immune system in glaucoma. Hence, a rat experimental autoimmune glaucoma model (EAG) was developed to investigate the role of the immune response. Here, we transferred this model into mice. Either 0.8 mg/mL of the optic nerve antigen homogenate (ONA; ONA 0.8) or 1.0 mg/mL ONA (ONA 1.0) were injected in 129/Sv mice. Controls received sodium chloride. Before and 6 weeks after immunization, the intraocular pressure (IOP) was measured. At 6 weeks, retinal neurons, glia cells, and synapses were analyzed via immunohistology and quantitative real-time PCR (RT-qPCR). Additionally, optic nerves were examined. The IOP stayed in the normal physiological range throughout the study (p > 0.05). A significant reduction of retinal ganglion cells (RGCs) was noted in both immunized groups (p < 0.001). Remodeling of glutamatergic and GABAergic synapses was seen in ONA 1.0 retinas. Furthermore, both ONA groups revealed optic nerve degeneration and macrogliosis (all: p < 0.001). An increase of activated microglia was noted in ONA retinas and optic nerves (p < 0.05). Both ONA concentrations led to RGC loss and optic nerve degeneration. Therefore, the EAG model was successfully transferred from rats to mice. In further studies, transgenic knockout mice can be used to investigate the pathomechanisms of glaucoma more precisely.

From Ganglion Cell to Photoreceptor Layer: Timeline of Deterioration in a Rat Ischemia/Reperfusion Model

Neuronal damage and impaired vision in different retinal disorders are induced, among other factors, by ischemia/reperfusion (I/R). Since the mechanisms and the progression of ischemic injury are still not completely clarified, a timeline of this retinal degeneration is needed. In this study, we investigated protein and mRNA alterations at 2, 6, 12, and 24 h as well as 3 and 7 days after ischemia to determine the course of an ischemic insult through the whole retina. Moreover, functional analyses were performed at later stages. We detected a significant functional loss of cells in the inner nuclear layer and photoreceptors at 3 and 7 days. Additionally, the thickness of the whole retina was decreased at these points in time, indicating a severe degradation of all retinal layers. Immunohistological and qRT-PCR analyses of retinal ganglion cells (RGCs), glial cells, AII amacrine, cone and rod bipolar as well as cone and rod photoreceptor cells confirmed this first assumption. Our results show that all investigated cell types were damaged by ischemia induction. Especially RGCs, cone bipolar cells, and photoreceptor cones are very sensitive to I/R. These cells were lost shortly after ischemia induction with a progressive course up to 7 days. In addition, Müller cell gliosis was observed over the entire period of time. These results provide evidence, that I/R induces damage of the whole retina at early stages and increases over time. In conclusion, our study could demonstrate the intense impact of an ischemic injury. The ischemic defect spreads across the whole retina right up to the outer layers in the long-term and thus seems to impair the visual perception already during the stimulus processing. In addition, our findings indicate that the cone pathway seems to be particularly affected by this damage.

Vagal Nerve Stimulation Attenuates Ischemia-Reperfusion Induced Retina Dysfunction in Acute Ocular Hypertension

Purpose: The present study aimed to investigate whether cervical vagal nerve stimulation (VNS) could prevent retinal ganglion cell (RGC) loss and retinal dysfunction after ischemia/reperfusion (I/R) injury.

Methods: First, rats were randomly divided into sham group (n = 4) and VNS group (n = 12). Activation of the nodose ganglia (NOG), nucleus of the solitary tract (NTS), superior salivatory nucleus (SSN), and pterygopalatine ganglion (PPG) neural circuit were evaluated by c-fos expression at 0 h after sham VNS and at 0 h (n = 4), 6 h (n = 4), 72 h (n = 4) after VNS. Secondly, rats were randomly assigned to I/R group (pressure-induced retinal ischemia for 1 h and reperfusion for 1 h in the right eye, n = 16) and I/R+VNS group (right cervical VNS for 2 h during the I/R period, n = 16). The left eye of each rat served as a control. Electroretinogram (ERG), RGC numbers, tumor necrosis factor-α (TNF-α) and vasoactive intestinal polypeptide (VIP) levels in retina were determined. Additionally, the level of VIP in PPG was evaluated.

Results: In the first part of the study, compared with the sham group, the VNS group exhibited significantly increased expression of c-fos in NOG, NTS, SSN, and PPG tissues at 0, 6, and 72 h. In the second part of the study, compared with left eyes, retinal function in right eyes (as assessed by the a-wave, b-wave and the oscillatory potential amplitudes of ERG and RGC data) was significantly decreased by I/R. The decreased retinal function was attenuated by VNS. In addition, I/R induced an increase in inflammation, which was reflected by elevated TNF-α expression in the retina. VNS significantly attenuated the increase in I/R-induced inflammation. Moreover, VIP expression in the retina and PPG, which may contribute to the inhibition of the inflammatory response, was significantly increased after VNS.

Conclusion: VNS could protect against retinal I/R injury by downregulating TNF-α. Upregulation of VIP expression due to activation of the NOG-NTS-SSN-PPG neural circuit may underlie to the protective effects of VNS.