Sustained neuroprotection from a single intravitreal injection of PGJ2 in a rodent model of anterior ischemic optic neuropathy

Neuroprotective Strategies for Nonarteritic Anterior Ischemic Optic Neuropathy: A Systematic Review

PURPOSE

Nonarteritic anterior ischemic optic neuropathy (NAION) is the second most common form of optic neuropathy. Most patients show no improvement over time. Until now, there is still no definitive therapy for NAION. The available literatures on the possible treatment of NAION are quite diverse and controversial. Neuroprotection strategies have been suggested as one of the potential treatments for NAION. This review aims to critically evaluate the literature on neuroprotective strategy for NAION.

METHODS

This report was written in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines. We performed a systematic literature search in Pubmed, Science Direct, Proquest, and Cochrane databases. Only neuroprotective agents that directly work in protecting neurons were included. The outcome of interest in this review is retinal ganglion cell density and apoptosis for animal studies and retinal nerve fiber layer thickness for human studies.

RESULTS

The systematic search identified 591 studies of which 24 met the eligibility criteria, including 21 animal studies and three human studies. Only a few of the studies evaluated the same treatments, showing how diverse neuroprotector treatments are currently being evaluated as NAION treatment. From 21 animal studies, 14 studies showed significantly higher retinal ganglion cell density (1.49- to 2.81-fold) with neuroprotective treatment compared to control group. Two of three human studies in this review had also found a beneficial effect of preserving retinal nerve fiber layer thickness in NAION patients.

CONCLUSIONS

This review suggests the potential of neuroprotection as a viable option in the quest for an effective treatment strategy for NAION. Further studies, particularly clinical studies, are necessary to establish its efficacy in NAION patients.

Anti-NOGO Antibody Neuroprotection in a Rat Model of NAION

Purpose

To evaluate the efficacy and mechanisms of anti-NOGO receptor monoclonal antibody 11C7mAb in a rat model of nonarteritic anterior ischemic optic neuropathy (rNAION).

Methods

The rNAION was induced in one eye of 20 Long-Evans rats, which were studied in 10 groups of two rats, each group containing a sham rat receiving intravitreal injections of vehicle and a treatment rat receiving intravitreal injections of 11C7mAb. Fellow eyes served as naïve controls. The rats were tested using flash electroretinograms (ERGs), flash visual evoked potentials (VEPs), and optical coherence tomography (OCT). Thirty days after induction, they were euthanized, and the eyes were prepared for immunohistochemistry (two groups), hematoxylin and eosin staining (two groups) or transmission electron microscopy (TEM; six groups).

Results

Ninety-five percent of the VEP amplitude was preserved in eyes treated with 11C7mAb, versus 69% in the control eyes. Immunohistochemistry revealed a large reduction in microglia and extrinsic macrophages with axon sparing. In addition to axon preservation, TEM also showed reduced extracellular debris and only slight myelin damage compared with the vehicle-treated animals. There were no significant differences in retinal ganglion cell counts, nor was there a difference in optic nerve swelling as measured by OCT. ERGs were used to exclude eyes with retinal vascular occlusions, an occasional complication of the induction technique.

Conclusions

The 11C7mAb preserves optic nerve integrity and reduces inflammation in rNAION.

Translational Relevance

This study evaluates the efficacy of an anti-NOGO receptor antibody in a rat model of NAION, a disorder that currently has no universally-acknowledged treatment.

Approaches to Potentiated Neuroprotective Treatment in the Rodent Model of Ischemic Optic Neuropathy

Nonarteritic anterior ischemic optic neuropathy (NAION) commonly causes sudden optic nerve (ON)-related vision loss. The rodent NAION model (rAION) closely resembles NAION in presentation and physiological responses. We identified early rAION-associated optic nerve head (ONH) inflammatory gene expression responses and the anti-inflammatory prostaglandin PGJ₂’s effects on those responses. We hypothesized that blocking pro-inflammatory prostaglandin (PGE₂) production by inhibiting monoacylglycerol lipase or cyclooxygenase activity and co-administering PGJ₂ would potentiate RGC survival following ischemic neuropathy. Deep sequencing was performed on vehicle- and PGJ₂-treated ONHs 3d post-rAION induction. Results were compared against responses from a retinal ischemia model. Animals were treated with PGJ₂ and MAGL inhibitor KML29, or PGJ₂ + COX inhibitor meloxicam. RGC survival was quantified by stereology. Tissue PG levels were quantified by ELISA. Gene expression was confirmed by qPCR. PGJ₂ treatment nonselectively reduced inflammatory gene expression post-rAION. KML29 did not reduce PGE₂ 1d post-induction and KML29 alone increased RGC loss after rAION. Combined treatments did not improve ONH edema and RGC survival better than reported with PGJ₂ alone. KML29′s failure to suppress PGE₂ ocular synthesis, despite its purported effects in other CNS tissues may result from alternative PG synthesis pathways. Neither KML29 nor meloxicam treatment significantly improved RGC survival compared with vehicle. While exogenous PGJ₂ has been shown to be neuroprotective, treatments combining PGJ₂ with these PG synthesis inhibitors do not enhance PGJ₂’s neuroprotection.

Protective Effects of Intravitreal Injection of the Rho-Kinase Inhibitor Y-27632 in a Rodent Model of Nonarteritic Anterior Ischemic Optic Neuropathy (rAION)

Purpose

We sought to explore the effects of intravitreal injection of the Rho-kinase inhibitor Y-27632 in a rodent model of nonarteritic anterior ischemic optic neuropathy (rAION).

Methods

The rAION model was established by using laser-induced photoactivation of intravenously administered Rose Bengal in rats. The rats received intravitreal injections of Y-27632 or PBS 1, 3, and 6 days after rAION induction. Optical coherence tomography (OCT) was performed at 2 days and 4 weeks after induction. Visual evoked potential (VEP) was used to evaluate the visual function at 4 weeks. Brn3a immunofluorescence staining of surviving RGCs and apoptosis assays of RGCs were performed at 4 weeks.

Results

Optic nerve head (ONH) width was significantly reduced in the Y-27632 group compared with that in the PBS group at 2 days after induction (p < 0.05). At 4 weeks, the P1 amplitude of flash-VEP (FVEP) in the Y-27632 group was significantly higher than that of the PBS group (p < 0.05). The RGC densities in the central and midperipheral retinas in the Y-27632 group were significantly higher than those in the PBS group (p < 0.05). Furthermore, there was a significant decrease in apoptotic RGCs in the Y-27632 group than in the PBS group (p < 0.05).

Conclusions

Intravitreal injection of Y-27632 had neuroprotective effects on ONH edema, RGC survival, and visual function preservation in rAION.

Intravitreal Triamcinolone Acetonide Injection in a Rodent Model of Anterior Ischemic Optic Neuropathy

INTRODUCTION

The management of nonarteritic anterior ischemic optic neuropathy centers around prevention of second eye involvement, without a uniformly accepted therapy for the involved eye. Several researchers have assessed the benefit of steroids with conflicting results. This experimental study was designed to evaluate the efficacy of a single intravitreal triamcinolone acetonide injection (IVTA) in preserving retinal ganglion cells (RGCs) in a rodent model of anterior ischemic optic neuropathy (rAION).

METHODS

The rAION was induced in female Wistar rats. Animals were randomized into 3 groups: 1) untreated, 2) treated with 56 μg IVTA, and 3) intravitreal saline (placebo). Procedures were performed in the left eye, with the right eye serving as control. After 30 days, animals were sacrificed and eyes were assessed histologically for RGC number.

RESULTS

The average number of RGC was significantly lower in rAION subgroups when compared with the control group (P < 0.001). No significant difference was seen between rAION eyes treated with IVTA, placebo, and untreated eyes (P > 0.05%).

CONCLUSIONS

In this rodent model for AION, no therapeutic benefit of intravitreal steroid injection was identified.

A rodent model of anterior ischemic optic neuropathy (AION) based on laser photoactivation of verteporfin

Background

A rodent model of photodynamic AION resulting from intravenous verteporfin is presented. The analysis of the morphological function, the pathological changes and the potential mechanism of action were further investigated.

Methods

Photodynamic treatment was conducted on the optic nerve head (ONH) following administration of the photosensitizer. The fellow eye was considered as sham control. Fundus Fluorescein angiography (FFA), spectral domain optical coherence tomography (SD-OCT) and Flash-visual evoked potential (F-VEP) recordings were conducted at different time points. Immunohistochemistry was used to observe apoptotic cell death (TUNEL) and macrophage infiltration (ED-1/Iba-1). Retrograde labeling of retinal ganglion cells (RGCs) was used to evaluate the loss of RGCs.

Results

After laser treatment, SD-OCT indicated optic nerve edema, while FFA indicated late leakage of the ONH. F-VEPs were distinctly reduced compared to control eyes. The number of apoptotic RGCs peaked on day 14 (5.71 ± 0.76, p < 0.01). The infiltration of ED-1 and Iba-1 increased on the 3rd day following PDT, while it peaked on day 14 (67.5 ± 9.57 and 77.5 ± 12.58 respectively, p < 0.01). Following 3 weeks of AION, the densities of RGCs in the central retinas of the normal and AION eyes were 3075 ± 298/mm² and 2078 ± 141/mm² (p < 0.01), respectively.

Conclusions

Verteporfin photodynamic treatment on rodents ONH can lead to functional, histological, and pathological changes. This type of animal model of AION is easy to establish and stable. It can be used for studying the mechanism and neuroprotective medicine of AION injury.

Spectral-Domain Optical Coherence Tomography of the Vitreopapillary Interface in Acute Nonarteritic Anterior Ischemic Optic Neuropathy

PURPOSE

To use spectral-domain optical coherence tomography (SD-OCT) to assess whether epipapillary vitreous traction from evolving posterior vitreous detachment (PVD) is mechanistically involved in the pathogenesis of nonarteritic anterior ischemic optic neuropathy (NAION).

DESIGN

Retrospective cohort study.

METHODS

Setting: Single academic center. Patient or Study Population: Eighty eyes in 74 subjects presenting within 2 weeks of symptom onset of NAION. Intervention or Observation Procedures: SD-OCT imaging of the optic nerve head, macula, and peripapillary retinal nerve fiber layer (pRNFL) were reviewed for PVD and vitreopapillary traction (VPT).

MAIN OUTCOME MEASURES

Prevalence and incidence of PVD and VPT, logMAR best-corrected visual acuity (BCVA), mean deviation (MD) on automated perimetry, and pRNFL thickness at presentation and final follow-up.

RESULTS

The co-prevalence of PVD at the time of acute presentation for NAION was 30% (n = 24/80). This was similar to the prevalence of PVD in contralateral uninvolved eyes (34.5%, n = 19/55). In 8 NAION eyes, PVD had been documented prior to the onset of NAION. No eyes had SD-OCT evidence of VPT on presentation or final follow-up. Only 5 eyes developed a PVD following the development of NAION, and this typically occurred months after resolution of optic disc edema. When comparing eyes with PVD and without PVD, there was no significant difference in BCVA, MD, and pRNFL thickness at baseline, final follow-up, or the change from baseline to final follow-up (all P > .10).

CONCLUSIONS

VPT was not mechanistically related to the development of classic NAION. Preexisting PVD did not preclude the future development of NAION. The co-prevalence of PVD with acute NAION had no impact on final visual outcome.

SUR1-Associated Mechanisms Are Not Involved in Ischemic Optic Neuropathy 1 Day Post-Injury

Ischemia-reperfusion injury after central nervous system (CNS) injury presents a major health care challenge with few promising treatments. Recently, it has become possible to reduce edema after CNS injury by antagonizing a sulfonylurea receptor 1 (SUR1) regulated ion channel expressed after injury. SUR1 upregulation after injury is a necessary precondition for the formation of this channel, and has been implicated in white matter injury after clinical spinal cord trauma. Glibenclamide, an SUR1 antagonist, appears to have neuroprotective effect against cerebral stroke in an open-label small clinical trial and great effectiveness in reducing damage after varied experimental CNS injury models. Despite its importance in CNS injuries, SUR1 upregulation appears to play no part in rodent anterior ischemic optic neuropathy (rAION) injury as tested by real-time PCR and immunohistochemical staining of rAION-injured rat optic nerve (ON). Furthermore, the SUR1 antagonist glibenclamide administered immediately after rAION injury provided no protection to proximal ON microvasculature 1 day post-injury but may reduce optic nerve head edema in a manner unrelated to ON SUR1 expression. Our results suggest that there may be fundamental differences between rAION optic nerve ischemia and other CNS white matter injuries where SUR1 appears to play a role.

Early applications of granulocyte colony-stimulating factor (G-CSF) can stabilize the blood-optic-nerve barrier and ameliorate inflammation in a rat model of anterior ischemic optic neuropathy (rAION)

Granulocyte colony-stimulating factor (G-CSF) was reported to have a neuroprotective effect in a rat model of anterior ischemic optic neuropathy (rAION model). However, the therapeutic window and anti-inflammatory effects of G-CSF in a rAION model have yet to be elucidated. Thus, this study aimed to determine the therapeutic window of G-CSF and investigate the mechanisms of G-CSF via regulation of optic nerve (ON) inflammation in a rAION model. Rats were treated with G-CSF on day 0, 1, 2 or 7 post-rAION induction for 5 consecutive days, and a control group were treated with phosphate-buffered saline (PBS). Visual function was assessed by flash visual evoked potentials at 4 weeks post-rAION induction. The survival rate and apoptosis of retinal ganglion cells were determined by FluoroGold labeling and TUNEL assay, respectively. ON inflammation was evaluated by staining of ED1 and Iba1, and ON vascular permeability was determined by Evans Blue extravasation. The type of macrophage polarization was evaluated using quantitative real-time PCR (qRT-PCR). The protein levels of TNF-α and IL-1β were analyzed by western blotting. A therapeutic window during which G-CSF could rescue visual function and retinal ganglion cell survival was demonstrated at day 0 and day 1 post-infarct. Macrophage infiltration was reduced by 3.1- and 1.6-fold by G-CSF treatment starting on day 0 and 1 post-rAION induction, respectively, compared with the PBS-treated group (P<0.05). This was compatible with 3.3- and 1.7-fold reductions in ON vascular permeability after G-CSF treatment compared with PBS treatment (P<0.05). Microglial activation was increased by 3.8- and 3.2-fold in the early (beginning treatment at day 0 or 1) G-CSF-treated group compared with the PBS-treated group (P<0.05). Immediate (within 30 mins of infarct) treatment with G-CSF also induced M2 microglia/macrophage activation. The cytokine levels were lower in the group that received immediate G-CSF treatment compared to those in the later G-CSF treatment group (P<0.05). Early treatment with G-CSF stabilized the blood-ON barrier to reduce macrophage infiltration and induced M2 microglia/macrophage polarization to decrease the expressions of pro-inflammatory cytokines in this rAION model.

An Experimental Animal Model of Photodynamic Optic Nerve Head Injury (PONHI)

PURPOSE

Anterior ischemic optic neuropathy (AION) is the most common cause of non-glaucomatous optic nerve head (ONH) injury among older adults. AION results from a sudden ischemic insult to the proximal portion of the optic nerve, typically leading to visual impairment. Here, we present an experimental model of photodynamically induced ONH injury that can be used to study neuroprotective modalities.

METHODS

Intraperitoneal injection of mesoporphyrin IX was followed by photodynamic treatment of the ONH in one eye of Brown-Norway rats; the fellow eye received the reverse sequence as a sham control. Fluorescein angiography (FA), spectral domain optical coherence tomography (SD-OCT), and visual evoked potential (VEP) recordings were performed at different time points following laser treatment. Immunohistochemistry was used to monitor apoptotic cell death (TUNEL) and macrophage infiltration (CD68). Cytokine levels were evaluated using enzyme-linked immunosorbent assay (ELISA).

RESULTS

FA showed early hyperfluorescence and late leakage of the ONH, while SD-OCT revealed optic nerve edema. No leakage or other abnormalities were detected in control eyes. VEPs were significantly reduced in amplitude and showed prolonged responses compared to sham eyes. The number of apoptotic retinal ganglion cells was elevated one day after laser treatment (13.77 ± 4.49, p < 0.01) and peaked on day 7 (57.22 ± 11.34, p < 0.01). ONH macrophage infiltration also peaked on day 7 (101.8 ± 9.8, p < 0.05). ELISAs performed showed upregulation of macrophage chemoattractant protein-1 and macrophage inflammatory protein-2 on days 3 and 1, respectively.

CONCLUSIONS

Photodynamic treatment of the ONH after administration of mesoporphyrin IX leads to macroscopic, histologic, and physiologic evidence of ONH injury. Given the long half-life of mesoporphyrin IX and the ease of intraperitoneal injections, this new model of photodynamically induced ONH injury may be a useful tool for studying optic nerve injury and possible neuroprotective treatments.

Dendrimers Target the Ischemic Lesion in Rodent and Primate Models of Nonarteritic Anterior Ischemic Optic Neuropathy

Introduction

Polyamidoamine dendrimer nanoparticles (~ 4 nanometers) are inert polymers that can be linked to biologically active compounds. These dendrimers selectively target and accumulate in inflammatory cells upon systemic administration. Dendrimer-linked compounds enable sustained release of therapeutic compounds directly at the site of damage. The purpose of this study was to determine if dendrimers can be used to target the optic nerve (ON) ischemic lesion in our rodent and nonhuman primate models of nonarteritic anterior ischemic optic neuropathy (NAION), a disease affecting >10,000 individuals in the US annually, and for which there currently is no effective treatment.

Methods

NAION was induced in male Long-Evans rats (rNAION) and in one adult male rhesus monkey (pNAION) using previously described procedures. Dendrimers were covalently linked to near-infrared cyanine-5 fluorescent dye (D-Cy5) and injected both intravitreally and systemically (in the rats) or just systemically (in the monkey) to evaluate D-Cy5 tissue accumulation in the eye and optic nerve following induction of NAION.

Results

Following NAION induction, Cy-5 dendrimers selectively accumulated in astrocytes and circulating macrophages. Systemic dendrimer administration provided the best penetration of the ON lesion site when injected shortly after induction. Systemic administration 1 day post-induction in the pNAION model gave localization similar to that seen in the rats.

Conclusions

Dendrimers selectively target the ischemic ON lesion after induction of both rNAION and pNAION. Systemic nanoparticle-linked therapeutics thus may provide a powerful, targeted and safe approach to NAION treatment by providing sustained and focused treatment of the cells directly affected by ischemia.

Ischemic optic neuropathies and their models: disease comparisons, model strengths and weaknesses

Ischemic optic neuropathies (IONs) describe a group of diseases that specifically target the optic nerve and result in sudden vision loss. These include nonarteritic and arteritic anterior ischemic optic neuropathy (NAION and AAION) and posterior ischemic optic neuropathy (NPION, APION). Until recently, little was known of the mechanisms involved in ION damage, due to a lack of information about the mechanisms associated with these diseases. This review discusses the new models that closely mimic these diseases (rodent NAION, primate NAION, rodent PION). These models have enabled closer dissection of the mechanisms involved with the pathophysiology of these disorders and enable identification of relevant mechanisms and potential pathways for effective therapeutic intervention. Descriptions of the different models are included, and comparisons between the models, their relative similarities with the clinical disease, as well as differences are discussed.

Protective effects of systemic treatment with methylprednisolone in a rodent model of non-arteritic anterior ischemic optic neuropathy (rAION)

This study investigated the protective effects of the administration of steroids on optic nerves (ON) and retinal ganglion cells (RGCs) in a rodent model of non-arteritic anterior ischemic optic neuropathy (rAION). We induced rAION using rose bengal and argon laser irradiation in a photodynamic procedure on the optic discs of rats. The treated groups received methylprednisolone (MP) via peritoneal injection for 2 weeks. The control group received intraperitoneal injections of phosphate-buffered saline (PBS) post-rAION. At the 4th week post-infarct, MP treatments significantly rescued the RGCs (mm(2)) in the central retinas (1920 ± 210, p < 0.001) and mid-peripheral retinas (950 ± 240, respectively, p = 0.018) compared with those of the PBS-treated rats (central: 900 ± 210 and mid-peripheral: 440 ± 180). Functional assessment with flash visual-evoked potentials demonstrated that P1 latency (ms) was shortened in the MP group compared to the PBS group (108 ± 14 and 147 ± 9, respectively, p < 0.001). In addition, the P1 amplitude (uV) was enhanced in the MP group compared to the PBS group (55 ± 12 and 41 ± 13, respectively, p < 0.05). TUNEL assays showed a decrease in the number of apoptotic cells in the RGC layers of MP-treated retinas compared to the PBS-treated group (p < 0.05). ED1 positive cells (/HPF) were significantly decreased in the ONs of the MP group compared to the PBS group (p < 0.001). In conclusion, systemic administration of MP had neuroprotective effects on RGC survival and ON function in the rAION animal model.

Sustained neuroprotection from a single intravitreal injection of PGJ₂ in a nonhuman primate model of nonarteritic anterior ischemic optic neuropathy

PURPOSE

Prostaglandin J₂ (PGJ₂) is neuroprotective in a murine model of nonarteritic anterior ischemic optic neuropathy (NAION). After assessing for potential toxicity, we evaluated the efficacy of a single intravitreal (IVT) injection of PGJ₂ in a nonhuman primate model of NAION (pNAION).

METHODS

We assessed PGJ₂ toxicity by administering it as a single high-dose intravenous (IV) injection, consecutive daily high-dose IV injections, or a single IVT injection in one eye of five adult rhesus monkeys. To assess efficacy, we induced pNAION in one eye of five adult male rhesus monkeys using a laser-activated rose bengal induction method. We then injected the eye with either PGJ₂ or phosphate-buffered saline (PBS) intravitreally immediately or 5 hours post induction. We performed a clinical assessment, optical coherence tomography, electrophysiological testing, fundus photography, and fluorescein angiography in all animals prior to induction and at 1 day, 1 week, 2 weeks, and 4 weeks after induction. Following analysis of the first eye, we induced pNAION in the contralateral eye and then injected either PGJ₂ or PBS. We euthanized all animals 5 weeks after final assessment of the fellow eye and performed both immunohistochemical and light and electron microscopic analyses of the retina and optic nerves.

RESULTS

TOXICITY

PGJ₂ caused no permanent systemic toxicity regardless of the amount injected or route of delivery, and there was no evidence of any ocular toxicity with the dose of PGJ₂ used in efficacy studies. Transient reduction in the amplitudes of the visual evoked potentials and the N95 component of the pattern electroretinogram (PERG) occurred after both IV and IVT administration of high doses of PGJ₂; however, the amplitudes returned to normal in all animals within 1 week.

EFFICACY

In all eyes, a single IVT dose of PGJ₂ administered immediately or shortly after induction of pNAION resulted in a significant reduction of clinical, electrophysiological, and histological damage compared with vehicle-injected eyes (P = 0.03 for both VEP and PERG; P = 0.05 for axon counts).

CONCLUSIONS

In nonhuman primates, PGJ₂ administered either intravenously or intravitreally produces no permanent toxicity at even four times the dose given for neuroprotection. Additionally, a single IVT dose of PGJ₂ is neuroprotective when administered up to 5 hours after induction of pNAION.