Revisiting the role of erythropoietin for treatment of ocular disorders

Cognitive Impairment in Multiple Sclerosis

Almost three million individuals suffer from multiple sclerosis (MS) throughout the world, a demyelinating disease in the nervous system with increased prevalence over the last five decades, and is now being recognized as one significant etiology of cognitive loss and dementia. Presently, disease modifying therapies can limit the rate of relapse and potentially reduce brain volume loss in patients with MS, but unfortunately cannot prevent disease progression or the onset of cognitive disability. Innovative strategies are therefore required to address areas of inflammation, immune cell activation, and cell survival that involve novel pathways of programmed cell death, mammalian forkhead transcription factors (FoxOs), the mechanistic target of rapamycin (mTOR), AMP activated protein kinase (AMPK), the silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), and associated pathways with the apolipoprotein E (APOE-ε4) gene and severe acute respiratory syndrome coronavirus (SARS-CoV-2). These pathways are intertwined at multiple levels and can involve metabolic oversight with cellular metabolism dependent upon nicotinamide adenine dinucleotide (NAD+). Insight into the mechanisms of these pathways can provide new avenues of discovery for the therapeutic treatment of dementia and loss in cognition that occurs during MS.

Use of Poly Lactic-co-glycolic Acid Nano and Micro Particles in the Delivery of Drugs Modulating Different Phases of Inflammation

Chronic inflammation contributes to the pathogenesis of many diseases, including apparently unrelated conditions such as metabolic disorders, cardiovascular diseases, neurodegenerative diseases, osteoporosis, and tumors, but the use of conventional anti-inflammatory drugs to treat these diseases is generally not very effective given their adverse effects. In addition, some alternative anti-inflammatory medications, such as many natural compounds, have scarce solubility and stability, which are associated with low bioavailability. Therefore, encapsulation within nanoparticles (NPs) may represent an effective strategy to enhance the pharmacological properties of these bioactive molecules, and poly lactic-co-glycolic acid (PLGA) NPs have been widely used because of their high biocompatibility and biodegradability and possibility to finely tune erosion time, hydrophilic/hydrophobic nature, and mechanical properties by acting on the polymer's composition and preparation technique. Many studies have been focused on the use of PLGA-NPs to deliver immunosuppressive treatments for autoimmune and allergic diseases or to elicit protective immune responses, such as in vaccination and cancer immunotherapy. By contrast, this review is focused on the use of PLGA NPs in preclinical in vivo models of other diseases in which a key role is played by chronic inflammation or unbalance between the protective and reparative phases of inflammation, with a particular focus on intestinal bowel disease; cardiovascular, neurodegenerative, osteoarticular, and ocular diseases; and wound healing.

Intraocular Sustained Release of EPO-R76E Mitigates Glaucoma Pathogenesis by Activating the NRF2/ARE Pathway

Erythropoietin (EPO) is neuroprotective in multiple models of neurodegenerative diseases, including glaucoma. EPO-R76E retains the neuroprotective effects of EPO but diminishes the effects on hematocrit. Treatment with EPO-R76E in a glaucoma model increases expression of antioxidant proteins and is neuroprotective. A major pathway that controls the expression of antioxidant proteins is the NRF2/ARE pathway. This pathway is activated endogenously after elevation of intraocular pressure (IOP) and contributes to the slow onset of pathology in glaucoma. In this study, we explored if sustained release of EPO-R76E in the eye would activate the NRF2/ARE pathway and if this pathway was key to its neuroprotective activity. Treatment with PLGA.EPO-E76E prevented increases in retinal superoxide levels in vivo, and caused phosphorylation of NRF2 and upregulation of antioxidants. Further, EPO-R76E activates NRF2 via phosphorylation by the MAPK pathway rather than the PI3K/Akt pathway, used by the endogenous antioxidant response to elevated IOP.

The Association of Erythropoietin and Age-Related Macular Degeneration in Hemodialysis Patients: A Nationwide Population-Based Cohort Study

This population-based retrospective cohort study investigated the effectiveness of erythropoietin (EPO) treatment in reducing the risk of age-related macular degeneration (AMD) in hemodialysis patients, using the National Health Insurance Research Data of Taiwan. From the database, we identified 147,318 end-stage renal disease (ESRD) patients on hemodialysis who had been diagnosed in 2000−2014 to establish the propensity-score-matched EPO user cohort and non-EPO user cohort with equal sample size of 15,992. By the end of 2016, the cumulative incidence of AMD in EPO users was about 3.29% lower than that in non-EPO users (Kaplan−Meier survival p < 0.0001). The risk of AMD was 43% lower in EPO users than in non-EPO users, with an adjusted hazard ratio (aHR) of 0.57 (95% confidence interval (CI) = 0.51−0.64) estimated in the multivariate Cox model. A significant negative dose−response relationship was identified between the EPO dosage and the risk of AMD (p < 0.0001). Another beneficial effect of EPO treatment was a reduced risk of both exudative AMD (aHR = 0.48, 95% CI = 0.40−0.61) and non-exudative AMD (aHR = 0.61, 95% CI = 0.53−0.69), also in similar dose−response relationships (p < 0.0001). Our findings suggest that EPO treatment for hemodialysis patients could reduce AMD risk in a dose−response relationship.

Role of Erythropoietin Receptor Signaling in Macrophages or Choroidal Endothelial Cells in Choroidal Neovascularization

Erythropoietin (EPO) has been proposed to reduce the progression of atrophic age-related macular degeneration (AMD) due to its potential role in neuroprotection. However, overactive EPO receptor (EPOR) signaling increased laser-induced choroidal neovascularization (CNV) and choroidal macrophage number in non-lasered mice, which raised the question of whether EPOR signaling increased CNV through the recruitment of macrophages to the choroid that released pro-angiogenic factors or through direct angiogenic effects on endothelial cells. In this study, we addressed the hypothesis that EPOR signaling increased CNV by direct effects on macrophages or endothelial cells. We used tamoxifen-inducible macrophage-specific or endothelial cell-specific EPOR knockout mice in the laser-induced CNV model, and cultured choroidal endothelial cells isolated from adult human donors. We found that macrophage-specific knockout of EPOR influenced laser-induced CNV in females only, whereas endothelial-specific knockout of EPOR reduced laser-induced CNV in male mice only. In cultured human choroidal endothelial cells, knockdown of EPOR reduced EPO-induced signal transducer and activator of transcription 3 (STAT3) activation. Taken together, our findings suggest that EPOR signaling in macrophages or choroidal endothelial cells regulates the development of CNV in a sex-dependent manner. Further studies regarding the role of EPO-induced signaling are required to assess EPO safety and to select or develop appropriate therapeutic approaches.

Association of polymorphisms in the erythropoietin gene with diabetic retinopathy: a case–control study and systematic review with meta-analysis

Background

Diabetic retinopathy (DR) is characterized by ischemia, hypoxia, and angiogenesis. Erythropoietin (EPO), an angiogenic hormone, is upregulated in DR, and the association of EPO genetic variants with DR is still uncertain, as conflicting results have been reported. Therefore, we performed a case–control study followed by a meta-analysis to investigate whether the rs1617640, rs507392, and rs551238 polymorphisms in EPO gene are associated with DR.

Methods

The case–control study included 1042 Southern Brazilians with type 2 diabetes (488 without DR and 554 with DR). Eligible studies for the meta-analysis were searched from electronic databases up to June 1, 2021. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were estimated for five genetic inheritance models.

Results

The minor alleles of the EPO polymorphisms had nearly the same frequency in all groups of patients (35%), and no association was detected with DR in the case–control study. The meta-analysis included 14 independent sets of cases and controls with 9117 subjects for the rs1617640 polymorphism and nine independent sets with more than 5000 subjects for the rs507392 and rs551238 polymorphisms. The G allele of the rs1617640 polymorphism was suggestively associated with DR under the dominant (OR = 0.82, 95% CI: 0.68–0.98), heterozygous additive (OR = 0.82, 95% CI: 0.69–0.97), and overdominant (OR = 0.88, 95% CI: 0.79–0.97) models. In the subgroup analyses, the G allele was also suggestively associated with proliferative DR (PDR), non-proliferative DR (NPDR), and DR (PDR + NPDR) among patients with type 1 diabetes (T1DM) or non-Asian ancestry. After considering the Bonferroni correction for multiple comparisons, the G allele remained associated with NPDR and DR in T1DM. Regarding the rs507392 and rs551238 polymorphisms, no association was found between these variants and DR.

Conclusion

Our findings provide additional support to EPO as a susceptibility gene for DR, with the rs1617640 polymorphism deserving further investigation.

The GG genotype of erythropoietin rs1617640 polymorphism affects the risk of proliferative diabetic retinopathy in Slovenian subjects with type 2 diabetes mellitus: enemy or ally?

PURPOSE

The aim of this study was to investigate the relationship between erythropoietin rs1617640 polymorphism and proliferative diabetic retinopathy (PDR) in Slovenian subjects with type 2 diabetes mellitus. The second aim was to find whether erythropoietin expression in fibrovascular membranes varies among individuals carrying different genotypes of the rs1617640.

METHODS

This was a retrospective cross-sectional study based on 797 unrelated Slovenian (Caucasian) participants with type 2 diabetes mellitus. The study group consisted of 217 cases with PDR and 580 controls without clinical signs of diabetic retinopathy. Each subject was genotyped for rs1617640 polymorphism. Fibrovascular membranes from 27 subjects who underwent vitreoretinal surgery were analysed with immunohistochemistry. We searched for expression of erythropoietin, its cognate receptor and for a pan-endothelial marker CD-34.

RESULTS

Our results show that subjects carrying a minor GG genotype had significantly higher risk for PDR in both unadjusted (p = 0.02) and adjusted (p = 0.04) recessive genetic models. Subjects with the GG genotype had a 1.6-fold increased risk of developing PDR compared to subjects carrying the major T allele. In fibrovascular membranes from subjects with PDR, the mean number of cells expressing EPO was significantly higher in G allele carriers compared to the homozygotes for the common T allele.

CONCLUSION

In Slovenian subjects with type 2 diabetes mellitus, a significant increased risk of PDR was found in GG carriers of the erythropoietin gene rs1617640 polymorphism.

Potential effects of angiogenesis-related factors on the severity of APAC and surgical outcomes of trabeculectomy

Background

EPO (erythropoietin) and PDGF (platelet derived growth factor) families are thought to be associated with angiogenesis under hypoxic condition. The sharp rise of intraocular pressure in acute primary angle closure (APAC) results in an inefficient supply of oxygen and nutrients. We aimed to measure the expression of EPO and PDGF family members in APAC eyes and demonstrate their associations with APAC’s surgical success rate.

Methods

Concentrations of EPO, PDGF-AA, -BB, -CC and -DD collected in aqueous humor samples of 55 patients recruited were measured. Before operations, correlations between target proteins and IOP (intraocular pressure) were detected between APAC (acute primary angle closure) and cataract patients. Based on the post-operative follow-up, the effects of EPO and PDGF family members on the successful rate of trabeculectomy were tested.

Results

The levels of EPO, PDGF-CC and -DD were significantly elevated in the APAC group compared to the cataract group. During the post-operative follow-up, EPO, PDGF-CC and -DD showed significant differences between the success and failure groups. In multivariable linear regression analyses, failed filtration surgery was more likely in APAC eyes with higher EPO level. The Kaplan-Meier survival plot suggested that the success rate in eyes with low EPO level was significantly higher than that in eyes with high EPO level.

Conclusion

The levels of EPO, PDGF-CC and -DD were significantly elevated in failure group. EPO level correlated with preoperative IOP and numbers of eyedrops, and higher EPO level in aqueous humor is a risk factor for trabeculectomy failure. It can be a biomarker to estimate the severity of APAC and the success rate of surgery. The investigation of mechanism of EPO in APAC a may have potential clinical applications for the surgical treatment of APAC.

A Review on Mesenchymal Stem Cells for Treatment of Retinal Diseases

Mesenchymal Stem Cells (MSCs) have been studied extensively for the treatment of several retinal diseases. The therapeutic potential of MSCs lies in its ability to differentiate into multiple lineages and secretome enriched with immunomodulatory, anti-angiogenic and neurotrophic factors. Several studies have reported the role of MSCs in repair and regeneration of the damaged retina where the secreted factors from MSCs prevent retinal degeneration, improve retinal morphology and function. MSCs also donate mitochondria to rescue the function of retinal cells and exosomes secreted by MSCs were found to have anti-apoptotic and anti-inflammatory effects. Based on several promising results obtained from the preclinical studies, several clinical trials were initiated to explore the potential advantages of MSCs for the treatment of retinal diseases. This review summarizes the various properties of MSCs that help to repair and restore the damaged retinal cells and its potential for the treatment of retinal degenerative diseases.

Retinal oxidative stress activates the NRF2/ARE pathway: An early endogenous protective response to ocular hypertension

Oxidative stress contributes to degeneration of retinal ganglion cells and their axons in glaucoma, a leading cause of irreversible blindness worldwide, through sensitivity to intraocular pressure (IOP). Here, we investigated early elevations in reactive oxygen species (ROS) and a role for the NRF2-KEAP1-ARE endogenous antioxidant response pathway using microbead occlusion to elevate IOP in mice. ROS levels peaked in the retina at 1- and 2-wks following IOP elevation and remained elevated out to 5-wks. Phosphorylation of NRF2 and antioxidant gene transcription and protein levels increased concomitantly at 2-wks after IOP elevation, along with phosphorylation of PI3K and AKT. Inhibiting PI3K or AKT signaling prevented NRF2 phosphorylation and reduced transcription of antioxidant-regulated genes. Ocular hypertensive mice lacking Nrf2 had elevated ROS and a diminished increase in antioxidant gene expression. They also exhibited earlier axon degeneration and loss of visual function. In conclusion, the NRF2-KEAP1-ARE pathway is endogenously activated early in ocular hypertension due to phosphorylation of NRF2 by the PI3K/AKT pathway and serves to slow the onset of axon degeneration and vision loss in glaucoma. These data suggest that exogenous activation of this pathway might further slow glaucomatous neurodegeneration.

Transplanted Erythropoietin-Expressing Mesenchymal Stem Cells Promote Pro-survival Gene Expression and Protect Photoreceptors From Sodium Iodate-Induced Cytotoxicity in a Retinal Degeneration Model

Mesenchymal stem cells (MSC) are highly regarded as a potential treatment for retinal degenerative disorders like retinitis pigmentosa and age-related macular degeneration. However, donor cell heterogeneity and inconsistent protocols for transplantation have led to varied outcomes in clinical trials. We previously showed that genetically-modifying MSCs to express erythropoietin (MSC^EPO) improved its regenerative capabilities in vitro. Hence, in this study, we sought to prove its potential in vivo by transplanting MSCs^EPO in a rat retinal degeneration model and analyzing its retinal transcriptome using RNA-Seq. Firstly, MSCs^EPO were cultured and expanded before being intravitreally transplanted into the sodium iodate-induced model. After the procedure, electroretinography (ERG) was performed bi-weekly for 30 days. Histological analyses were performed after the ERG assessment. The retina was then harvested for RNA extraction. After mRNA-enrichment and library preparation, paired-end RNA-Seq was performed. Salmon and DESeq2 were used to process the output files. The generated dataset was then analyzed using over-representation (ORA), functional enrichment (GSEA), and pathway topology analysis tools (SPIA) to identify enrichment of key pathways in the experimental groups. The results showed that the MSC^EPO-treated group had detectable ERG waves (P <0.05), which were indicative of successful phototransduction. The stem cells were also successfully detected by immunohistochemistry 30 days after intravitreal transplantation. An initial over-representation analysis revealed a snapshot of immune-related pathways in all the groups but was mainly overexpressed in the MSC group. A subsequent GSEA and SPIA analysis later revealed enrichment in a large number of biological processes including phototransduction, regeneration, and cell death (P_adj <0.05). Based on these pathways, a set of pro-survival gene expressions were extracted and tabulated. This study provided an in-depth transcriptomic analysis on the MSC^EPO-treated retinal degeneration model as well as a profile of pro-survival genes that can be used as candidates for further genetic enhancement studies on stem cells.

Mitigation of Sodium Iodate-Induced Cytotoxicity in Retinal Pigment Epithelial Cells in vitro by Transgenic Erythropoietin-Expressing Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) have shown promise in restoring the vision of patients in clinical trials. However, this therapeutic effect is not observed in every treated patient and is possibly due to the inefficacies of cell delivery and high cell death following transplantation. Utilizing erythropoietin can significantly enhance the regenerative properties of MSCs and hence improve retinal neuron survivability in oxidative stress. Hence, this study aimed to investigate the efficacy of conditioned medium (CM) obtained from transgenic human erythropoietin-expressing MSCs (MSC _EPO ) in protecting human retinal pigment epithelial cells from sodium iodate (NaIO₃)-induced cell death. Human MSC and MSC _EPO were first cultured to obtain conditioned media (CM). The IC₅₀ of NaIO₃ in the ARPE-19 culture was then determined by an MTT assay. After that, the efficacy of both MSC-CM and MSC-CM _EPO in ARPE-19 cell survival were compared at 24 and 48 h after NaIO₃ treatment with MTT. The treatment effects on mitochondrial membrane potential was then measured by a JC-1 flow cytometric assay. The MTT results indicated a corresponding increase in cell survivability (5-58%) in the ARPE-19 cell cultures. In comparison to MSC-CM, the use of conditioned medium collected from the MSC-CM _EPO further enhanced the rate of ARPE-19 survivability at 24 h (P < 0.05) and 48 h (P < 0.05) in the presence of NaIO₃. Furthermore, more than 90% were found viable with the JC-1 assay after MSC-CM _EPO treatment, showing a positive implication on the mitochondrial dynamics of ARPE-19. The MSC-CM _EPO provided an enhanced mitigating effect against NaIO₃-induced ARPE-19 cell death over that of MSC-CM alone during the early phase of the treatment, and it may act as a future therapy in treating retinal degenerative diseases.

Stem cell therapies for retinal diseases: from bench to bedside

As the human retina has no regenerative ability, stem cell interventions represent potential therapies for various blinding retinal diseases. This type of therapy has been extensively studied in the human eyes through decades of preclinical studies. The safety profiles shown in clinical trials thus far have indicated that these strategies should be further explored. There are still challenges with regard to cell source, cell delivery, immuno-related adverse events and long-term maintenance of the therapeutic effects. Retinal stem cell therapy is likely to be most successful with a combination of multiple technologies, such as gene therapy. The purpose of this review is to present a synthetical and systematic coverage of stem cell therapies that target retinal diseases from bench to bedside, intending to appeal to both junior specialists and the broader community of clinical investigators alike. This review will only focus on therapies that have already been studied in clinical trials. This review summarizes key concepts, highlights the main studies in human patients and discusses the current challenges and potential methods to reduce safety concerns while enhancing the therapeutic effects.

Screening Medications for Association with Progression to Wet Age-Related Macular Degeneration

PURPOSE

There is an urgent need for treatments that prevent or delay development to advanced age-related macular degeneration (AMD). Drugs already on the market for other conditions could affect progression to neovascular AMD (nAMD). If identified, these drugs could provide insights for drug development targets. The objective of this study was to use a novel data mining method that can simultaneously evaluate thousands of correlated hypotheses, while adjusting for multiple testing, to screen for associations between drugs and delayed progression to nAMD.

DESIGN

We applied a nested case-control study to administrative insurance claims data to identify cases with nAMD and risk-set sampled controls that were 1:4 variable ratio matched on age, gender, and recent healthcare use.

PARTICIPANTS

The study population included cases with nAMD and risk set matched controls.

METHODS

We used a tree-based scanning method to evaluate associations between hierarchical classifications of drugs that patients were exposed to within 6 months, 7 to 24 months, or ever before their index date. The index date was the date of first nAMD diagnosis in cases. Risk-set sampled controls were assigned the same index date as the case to which they were matched. The study was implemented using Medicare data from New Jersey and Pennsylvania, and national data from IBM MarketScan Research Database. We set an a priori threshold for statistical alerting at P ≤ 0.01 and focused on associations with large magnitude (relative risks ≥ 2.0).

MAIN OUTCOME MEASURES

Progression to nAMD.

RESULTS

Of approximately 4000 generic drugs and drug classes evaluated, the method detected 19 distinct drug exposures with statistically significant, large relative risks indicating that cases were less frequently exposed than controls. These included (1) drugs with prior evidence for a causal relationship (e.g., megestrol); (2) drugs without prior evidence for a causal relationship, but potentially worth further exploration (e.g., donepezil, epoetin alfa); (3) drugs with alternative biologic explanations for the association (e.g., sevelamer); and (4) drugs that may have resulted in statistical alerts due to their correlation with drugs that alerted for other reasons.

CONCLUSIONS

This exploratory drug-screening study identified several potential targets for follow-up studies to further evaluate and determine if they may prevent or delay progression to advanced AMD.

Sensitized heat shock protein 27 induces retinal ganglion cells apoptosis in rat glaucoma model

AIM

To investigate the relationships between the changes of heat shock protein 27 antibody (anti-HSP27) in serum/cerebrospinal fluid (CSF), intraocular pressure (IOP), retinal ganglion cell (RGC) apoptosis in a rat glaucoma model and disclose the underlying pathogenesis of glaucoma.

METHODS

A total of 115 Wistar rats were randomly divided into 4 groups. Group 1 was the ocular hypertension group by condensing 3 episcleral & limbal veins or episcleral area of right eye (HP group, n=25) and sham operation group with conjunctiva incision without coagulation (n=25). Group 2: HSP27 or dose-matched PBS was injected into the vitreous (V-HSP27 group, n=15; V-PBS group, n=15). Group 3: HSP27 and complete Freund's adjuvant or dose-matched PBS was injected subcutaneously into the hind limb accompanied intraperitoneal injection of pertussis toxin [sensitized group (I-HSP27 group), n=15; I-PBS group, n=15)]. Group 4 was normal group without any treatment (n=5). IOPs of the rats were measured before, day 3, weeks 1, 2, 4, 6, and 8 after treatment. Paraffin-embedded sections were prepared for HE staining and RGCs apoptosis were detected by TUNEL. Anti-HSP27 level in serum and CSF were examined by ELISA.

RESULTS

IOPs were elevated significantly in HP and V-HSP27, V-PBS groups (P<0.01) and positively related to anti-HSP27 levels in serum and CSFs. Anti-HSP27 levels in serum and CSF were elevated significantly in I-HSP27 group compared to other groups (P<0.05). However, the IOPs did not show any relationship with the high-level anti-HSP27 in serum and CSFs. RGC apoptosis were all elevated significantly in the HP, V-HSP27, V-PBS and I-HSP27 groups and also positively relative with anti-HSP27 level in serum and CSFs except that high-level of anti-HSP27 in the serum of I-HSP group.

CONCLUSION

The increases of anti-HSP27 levels in serum and CSFs both promote IOP escalation and the increase of RGC apoptosis in retina when anti-HSP27 is at low level. The case of high-level anti-HSP27 is opposite and shows protective function in preventing IOP increase and RGC apoptosis.

Aqueous Inflammation and Ischemia-Related Biomarkers in Neovascular Glaucoma with Stable Iris Neovascularization

Purpose: To characterize the aqueous levels of inflammation and ischemia-related biomarkers in a spectrum of retinal ischemic conditions, including neovascular glaucoma (NVG) with stable iris neovascularization after pan retinal photocoagulation (PRP) and anti-VEGF treatment. Methods: Aqueous samples were collected from 139 eyes including NVG (n = 12), stable NVG (n = 26), CRVO (n = 11), NPDR (n = 18), PACG (n = 18), PDR (n = 25), BRVO (n = 7) and cataract (n = 22). The levels of VEGF-A, IL-8 and EPO were measured with ELISA. Results: Aqueous VEGF-A significantly decreased after anti-VEGF and PRP, from 983.79 ± 821.16 pg/ml in the NVG group (n = 11) to 256.50 ± 51.14 pg/ml in the stable NVG group (n = 24) (P = .015). Aqueous VEGF-A in stable NVG group (256.50 ± 51.14 pg/ml, n = 24) was significantly higher (ANOVA, P < .001) than in CRVO (212.10 ± 19.84 pg/ml, n = 7, P = .017), NPDR (221.18 ± 38.21 pg/ml, n = 14, P = .015), BRVO (213.14 ± 48.50 pg/ml, n = 6, P = .028) and cataract group (185.30 ± 34.35 pg/ml, n = 22, P < .001). Aqueous IL-8 in stable NVG group (74.82 ± 10.78 pg/ml, n = 24) was significantly higher (ANOVA, P < .001) than in CRVO (65.19 ± 15.34 pg/ml, n = 11, P = .032) and cataract group (54.11 ± 12.28 pg/ml, n = 22, P < .001). Aqueous EPO in stable NVG group (17.48 ± 3.02 pg/ml, n = 24) was significantly higher (ANOVA, P < .001) than in BRVO (14.98 ± 2.57 pg/ml, n = 7, P = .034) and cataract group (13.50 ± 2.65 pg/ml, n = 22, P < .001). Aqueous concentrations of VEGF-A and IL-8 correlated positively with IOP (r = 0.413, P < .001, r = 0.349, P < .001, respectively, r = correlation coefficient). VEGF-A correlated positively with IL-8 and EPO (P < .001, P = .002, respectively). IL-8 correlated positively with EPO (P < .001). Conclusions: The aqueous levels of VEGF-A, IL-8 and EPO in NVG patients with stable iris neovascularization, who had received PRP and anti-VEGF, were still significantly higher than in control groups with some retinal ischemic conditions.

Erythropoietin Receptor Signaling Supports Retinal Function after Vascular Injury

The investigation of erythropoietin (EPO) has expanded to include potential nonhematopoietic roles in neural and retinal diseases, including diabetic retinopathy. However, it remains unclear how EPO functions to support the neural retina. Transgenic mice with hypoactive EPO receptor (EPOR) signaling (hWtEPOR) were compared with littermate control mice (WT) to test the role of EPOR signaling under normal conditions and after vascular injury and regrowth into the retina. Although retinal function tested with OptoMotry and electroretinography was comparable to adult (8-week-old) littermate WT mice, hWtEPOR mice had thinner inner and outer plexiform layers and a greater number of amacrine cells. Injury and repair caused by the oxygen-induced retinopathy model reduced visual acuity thresholds, reduced electroretinography amplitudes, and thinned the outer plexiform and inner nuclear layers of both WT and hWtEPOR 8-week-old mice. In hWtEPOR compared with WT mice, scotopic a-wave amplitudes were reduced by injury, despite no change in outer nuclear layer thickness; and peripheral rod, but not cone number, was reduced. Scotopic b-waves were reduced in injured hWtEPOR mice compared with WT, and rod bipolar cell ectopic neurites were increased in both genotypes after injury, suggesting a potential reparative process to preserve connectivity and the b-wave. Normal EPOR signaling appeared important because ectopic neurites and b-waves were lower in the hWtEPOR than WT injured mice.

Identifying Genetic Risk Factors for Diabetic Macular Edema and the Response to Treatment

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes mellitus (DM). DR is complex and the term encompasses several clinical subtypes of diabetic eye disease, including diabetic macular edema (DME), the most frequent cause of central vision loss in DR patients. Both genetic and environmental factors contribute to the pathophysiology of DR and its subtypes. While numerous studies have identified several susceptibility genes for DR, few have investigated the impact of genetics on DME susceptibility. This review will focus on the current literature surrounding genetic risk factors associated with DME. We will also highlight the small number of studies investigating the genetics of response to antivascular endothelial growth factor (anti-VEGF) injection, which is used to treat DME.

Angiogenic and inflammatory biomarker levels in aqueous humor and vitreous of neovascular glaucoma and proliferative diabetic retinopathy

PURPOSE

To explore the relationships between the aqueous and vitreous levels of vascular endothelial growth factor-A (VEGF-A), interleukin-8 (IL-8), placental growth factor (PlGF) and erythropoietin (EPO) in proliferative diabetic retinopathy (PDR) and neovascular glaucoma (NVG).

METHODS

Aqueous and vitreous samples were obtained from patients with PDR and NVG during surgery. Aqueous and vitreous concentrations of VEGF-A, IL-8, PlGF and EPO were measured via enzyme-linked immunosorbent assay.

RESULTS

No correlation between the aqueous and vitreous levels of VEGF-A, IL-8, PlGF or EPO was found in both the PDR and the NVG eyes. Aqueous VEGF-A was significantly higher in the NVG group (317.55 ± 36.25 pg/ml, n = 15) than that in the PDR group (256.23 ± 46.11 pg/ml, n = 17, P < 0.001). The level of VEGF-A in aqueous (317.55 ± 36.25 pg/ml, n = 15) was significantly higher than that in vitreous (224.74 ± 60.32 pg/ml, n = 15, P < 0.001) in NVG patients. The level of IL-8 in aqueous (76.55 ± 10.88 pg/ml, n = 17) was significantly higher than that in vitreous (63.55 ± 10.74 pg/ml, n = 17, P = 0.001) in PDR patients. The level of EPO in aqueous (18.62 ± 2.87 mIU/ml, n = 15) was significantly higher than that in vitreous (15.97 ± 3.11 mIU/ml, n = 15, P = 0.022) in NVG patients. The ratio of aqueous versus vitreous for VEGF-A was significantly higher in the NVG group (1.475 ± 0.289, n = 15) than that in the PDR group (0.996 ± 0.227, n = 17, P < 0.001).

CONCLUSION

Aqueous levels of VEGF-A, IL-8, PlGF and EPO do not correlate with vitreous levels of those proteins. The relationship between protein levels in aqueous humor and vitreous might be dependent on different disease status or protein types investigated.

Update of inflammatory proliferative retinopathy: Ischemia, hypoxia and angiogenesis

Diabetic retinopathy (DR) and retinopathy of prematurity (ROP) present two examples of proliferative retinopathy, characterized by the same stages of progression; ischemia of the retinal vessels, leads to hypoxia and to correct the problem there is the setting up of uncontrolled angiogenesis, which subsequently causes blindness or even detachment of the retina. The difference is the following; that DR initiated by the metabolic complications that are due to hyperglycemia, and ROP is induced by overexposure of the neonatal retina to oxygen. In this review, we will demonstrate the physiopathological mechanism of the two forms of proliferative retinopathy DR and ROP, in particular the role of the CD40/CD40L axis and IL-1 on vascular complications and onset of inflammation of the retina, the implications of their effects on the onset of pathogenic angiogenesis, thus understanding the link between platelets and retinal ischemia. In addition, what are the therapeutic targets that could slow its progression?

Diabetic Retinopathy-An Underdiagnosed and Undertreated Inflammatory, Neuro-Vascular Complication of Diabetes

Diabetes mellitus is a world-wide epidemic and diabetic retinopathy, a devastating, vision-threatening condition, is one of the most common diabetes-specific complications. Diabetic retinopathy is now recognized to be an inflammatory, neuro-vascular complication with neuronal injury/dysfunction preceding clinical microvascular damage. Importantly, the same pathophysiologic mechanisms that damage the pancreatic β-cell (e.g., inflammation, epigenetic changes, insulin resistance, fuel excess, and abnormal metabolic environment), also lead to cell and tissue damage causing organ dysfunction, elevating the risk of all complications, including diabetic retinopathy. Viewing diabetic retinopathy within the context whereby diabetes and all its complications arise from common pathophysiologic factors allows for the consideration of a wider array of potential ocular as well as systemic treatments for this common and devastating complication. Moreover, it also raises the importance of the need for methods that will provide more timely detection and prediction of the course in order to address early damage to the neurovascular unit prior to the clinical observation of microangiopathy. Currently, treatment success is limited as it is often initiated far too late and after significant neurodegeneration has occurred. This forward-thinking approach of earlier detection and treatment with a wider array of possible therapies broadens the physician's armamentarium and increases the opportunity for prevention and early treatment of diabetic retinopathy with preservation of good vision, as well the prevention of similar destructive processes occurring among other organs.

Visual-Evoked-Response-Supported Outcome of Intravitreal Erythropoietin in Management of Indirect Traumatic Optic Neuropathy

PURPOSE

Investigating the efficacy of intravitreal injection of erythropoietin (EPO) in managing indirect traumatic optic neuropathy (ITON) of different durations.

METHODS

A case series that included two groups of ITON patients: recent ITON group (<3 months trauma duration; 7 eyes) and old duration ITON group (3-36 months; 7 eyes). Diagnostic computerized tomography (CT) and baseline flash visual evoked response (VER) were performed at the presentation time. At the initial visit and each follow-up, all patients had undergone assessment of best-corrected visual acuity (BCVA), pupil reaction, and anterior and posterior segments. VER was repeated 1 and 3 months after injection. All patients received an intravitreal injection of 2000 IU EPO in 0.2 ml of commercially available sterile EPREX 4000 solution, Jansen Cilag, Zug, Switzerland. Five patients had received a second injection 3 months later.

RESULTS

Significant improvement was found in BCVA, VER amplitude, and latency (P < 0.0001, 0.0154, and 0.0291, respectively). Initial values of BCVA, VER amplitude, and latency correlated significantly to the final values. Differences between recent and old trauma groups were insignificant in the three parameters. In patients who received second injection, further clinical but statistically insignificant improvement was noted in BCVA in 60% of patients, VER amplitude in 50% of patients, and in VER latency in 100% of patients. No complications were recorded.

CONCLUSION

Intravitreal injection of EPO may be effective and safe in treatment of recent and old indirect traumatic optic neuropathy.

The Role of Endogenous Neuroprotective Mechanisms in the Prevention of Retinal Ganglion Cells Degeneration

Retinal neurons are not able to undergo spontaneous regeneration in response to damage. A variety of stressors, i.e., UV radiation, high temperature, ischemia, allergens, and others, induce reactive oxygen species production, resulting in consecutive alteration of stress-response gene expression and finally can lead to cell apoptosis. Neurons have developed their own endogenous cellular protective systems. Some of them are preventing cell death and others are allowing functional recovery after injury. The high efficiency of these mechanisms is crucial for cell survival. In this review we focus on the contribution of the most recently studied endogenous neuroprotective factors involved in retinal ganglion cell (RGC) survival, among which, neurotrophic factors and their signaling pathways, processes regulating the redox status, and different pathways regulating cell death are the most important. Additionally, we summarize currently ongoing clinical trials for therapies for RGC degeneration and optic neuropathies, including glaucoma. Knowledge of the endogenous cellular protective mechanisms may help in the development of effective therapies and potential novel therapeutic targets in order to achieve progress in the treatment of retinal and optic nerve diseases.

Human Mesenchymal Stem Cells Expressing Erythropoietin Enhance Survivability of Retinal Neurons Against Oxidative Stress: An In Vitro Study

Retinal degeneration is a prominent feature in ocular disorders. In exploring possible treatments, Mesenchymal Stem Cells (MSCs) have been recognized to yield therapeutic role for retinal degenerative diseases. Studies have also displayed that erythropoietin (EPO) administration into degenerative retina models confers significant neuroprotective actions in limiting pathological cell death. In this study, we aimed to use MSCs to deliver EPO and to evaluate the ability of EPO to rescue retinal neurons from dying upon reactive oxidative stress induction. We derived human MSCs from Wharton's jelly (hWJMSCs) of the umbilical cord and cells were transduced with lentivirus particles encoding EPO and a reporter gene of green fluorescent protein (GFP). The supernatants of both transduced and non-transduced cells were collected and used as a pre-conditioning medium for Y79 retinoblastoma cells (retinal neuron cell line) following exposure to glutamate induction. Retinal cells exposed to glutamate showed reduced mitochondrial depolarization and enhanced improvement in cell viability when incubated with pre-conditioned media of transduced cells. Our results established a proof-of-concept that MSCs could be used as a candidate for the delivery of EPO therapeutic gene in the treatment of retinal degenerations.

Functional and Structural Effects of Erythropoietin Subconjunctival Administration in Glaucomatous Animals

Purpose

The present study aimed to assess functional and structural benefits of erythropoietin (EPO) when administered subconjunctivally in the retina of glaucomatous rats using electroretinography (ERG) and retinal thickness (RT) measurements.

Methods

Glaucoma was experimentally induced in 26 Wistar Hannover albino rats. Animals were divided into 2 groups of 13 animals each: a treated group receiving a unique subconjunctival injection of 1,000 IU of EPO and a control group receiving a saline solution. In each group, 7 animals were used for retinal function evaluation (ERG) and 6 animals were used for retinal structural evaluation (histology). RT was measured, dorsally and ventrally, at 500 μm (RT1) and at 1,500 μm (RT2) from the optic nerve.

Results

Retinal function evaluation: for both scotopic and photopic conditions, ERG wave amplitudes increased in the treated group. This increase was statistically significant (p < 0.05) in photopic conditions. Structural evaluation: for both locations RT1 and RT2, the retinas were significantly (p < 0.05) thicker in the treated group.

Conclusion

Subconjunctival EPO administration showed beneficial effects both on retinal structure and on retinal function in induced glaucoma in albino rats. This neuroprotective effect should be applied in other animal species.

Pharmacotherapy and ROP: Going Back to the Basics

Retinopathy of prematurity (ROP) is a leading cause of blindness in preterm infants around the world. Through the development of animal models and clinical trials our understanding of the pathophysiology of this disease and approach to therapy has evolved significantly since ROP was first described in the 1940s in the United States. The mainstay of treatment in ROP remains ablative laser therapy to the avascular retina but pharmacologic agents are being more and more commonly used with new targets for pharmacotherapy emerging. This paper summarizes our current understanding of the pathophysiology of ROP based on the data gleaned from animal models and discusses current approaches to pharmacotherapy.

Recent Updates on Treatment of Ocular Microbial Infections by Stem Cell Therapy: A Review

Ocular microbial infection has emerged as a major public health crisis during the past two decades. A variety of causative agents can cause ocular microbial infections; which are characterized by persistent and destructive inflammation of the ocular tissue; progressive visual disturbance; and may result in loss of visual function in patients if early and effective treatments are not received. The conventional therapeutic approaches to treat vision impairment and blindness resulting from microbial infections involve antimicrobial therapy to eliminate the offending pathogens or in severe cases; by surgical methods and retinal prosthesis replacing of the infected area. In cases where there is concurrent inflammation, once infection is controlled, anti-inflammatory agents are indicated to reduce ocular damage from inflammation which ensues. Despite advances in medical research; progress in the control of ocular microbial infections remains slow. The varying level of ocular tissue recovery in individuals and the incomplete visual functional restoration indicate the chief limitations of current strategies. The development of a more extensive therapy is needed to help in healing to regain vision in patients. Stem cells are multipotent stromal cells that can give rise to a vast variety of cell types following proper differentiation protocol. Stem cell therapy shows promise in reducing inflammation and repairing tissue damage on the eye caused by microbial infections by its ability to modulate immune response and promote tissue regeneration. This article reviews a selected list of common infectious agents affecting the eye; which include fungi; viruses; parasites and bacteria with the aim of discussing the current antimicrobial treatments and the associated therapeutic challenges. We also provide recent updates of the advances in stem cells studies on sepsis therapy as a suggestion of optimum treatment regime for ocular microbial infections.

Erythropoietin Signaling Increases Choroidal Macrophages and Cytokine Expression, and Exacerbates Choroidal Neovascularization

Erythropoietin (EPO) is recognized for neuroprotective and angiogenic effects and has been associated with aging and neovascular age-related macular degeneration (AMD). We hypothesized that systemic EPO facilitates the development of choroidal neovascularization (CNV). Wild type mice expressed murine EPOR (mWtEPOR) in RPE/choroids at baseline and had significantly increased serum EPO after laser treatment. To test the role of EPO signaling, we used human EPOR knock-in mice with the mWtEPOR gene replaced by either the human EPOR gene (hWtEPOR) or a mutated human EPOR gene (hMtEPOR) in a laser-induced choroidal neovascularization (LCNV) model. Loss-of-function hWtEPOR mice have reduced downstream activation, whereas gain-of-function hMtEPOR mice have increased EPOR signaling. Compared to littermate controls (mWtEPOR), hMtEPOR with increased EPOR signaling developed larger CNV lesions. At baseline, hMtEPOR mice had increased numbers of macrophages, greater expression of macrophage markers F4/80 and CD206, and following laser injury, had greater expression of cytokines CCL2, CXCL10, CCL22, IL-6, and IL-10 than mWtEPOR controls. These data support a hypothesis that injury from age- and AMD-related changes in the RPE/choroid leads to choroidal neovascularization through EPOR-mediated cytokine production.

Targeted Knockdown of Overexpressed VEGFA or VEGF164 in Müller cells maintains retinal function by triggering different signaling mechanisms

Oxygen-induced retinopathy (OIR) upregulates Müller cell vascular endothelial growth factor A (VEGFA) that causes intravitreal neovascularization similar to severe retinopathy of prematurity (ROP). Safety concerns exist with anti-VEGF treatment for ROP. We evaluated long-term knockdown of Müller cell-VEGFA with short-hairpin RNAs to VEGFA or VEGF164 via subretinal lentivirus delivery (L-VEGFAshRNA, L-VEGF164shRNA) on retinal structure and function in a rat OIR model. Lectin-stained retinal flat mounts analyzed for areas of avascular/total retina (AVA) and intravitreal neovascular/total retina (IVNV) showed initial significantly reduced IVNV by L-VEGFAshRNA and L-VEGF164shRNA compared to control, luciferase-shRNA lentivirus, without late recurrence. Spectral-domain optical coherence tomography (OCT) and immunohistochemical sections (IHC) demonstrated changes in retinal layer thicknesses in L-VEGFAshRNA or L-VEGF164shRNA  compared to control. Ganzfeld electroretinograms were increased in L-VEGFAshRNA or L-VEGF164shRNA compared to control. Erythropoietin (EPO), brain-derived neurotrophic factor, glial-derived neurotrophic factor, nerve growth factor, neurotrophin-3 (NT-3) mRNAs were increased in L-VEGFAshRNA, but not L-VEGF164shRNA retinas. In cultured rat Müller cells, knockdown of VEGF upregulated NT-3 and EPO, whereas treatment with EPO activated neuroprotective signaling. Methods to reduce IVNV by selective knockdown of VEGFA, and particularly VEGF164, in Müller cells may have fewer deleterious effects than nonselective VEGFA inhibition to all cells in the retina.

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.

Erythropoietin in diabetic retinopathy

Over the past years, knowledge has expanded with regards to the multiple roles played by erythropoietin (EPO) in the body. Once believed to be a hormone synthesised in the kidney and involved only in the modulation of erythrocyte production, it is recognised now that EPO can be produced in many tissues, including the retina, and by many cells. In these tissues EPO is released in response to "tissue injury" and appears to have protective functions. Despite the extensive research conducted to date, the cues leading to release of EPO and its effects in the normal and diseased retina have not been fully elucidated. In vitro and in vivo experimental studies as well as small interventional clinical studies suggest a potential beneficial effect of externally administered EPO in early diabetic retinopathy and diabetic macular oedema. In contrast, controversy exists with regards to the possible use of EPO in proliferative diabetic retinopathy. Non-erythropoietic EPO-derived peptides, produced with the aim of increasing effectiveness and reducing side effects of EPO, are currently under investigation in early phase clinical trials.

Cellular Reparative Mechanisms of Mesenchymal Stem Cells for Retinal Diseases

The use of multipotent mesenchymal stem cells (MSCs) has been reported as promising for the treatment of numerous degenerative disorders including the eye. In retinal degenerative diseases, MSCs exhibit the potential to regenerate into retinal neurons and retinal pigmented epithelial cells in both in vitro and in vivo studies. Delivery of MSCs was found to improve retinal morphology and function and delay retinal degeneration. In this review, we revisit the therapeutic role of MSCs in the diseased eye. Furthermore, we reveal the possible cellular mechanisms and identify the associated signaling pathways of MSCs in reversing the pathological conditions of various ocular disorders such as age-related macular degeneration (AMD), retinitis pigmentosa, diabetic retinopathy, and glaucoma. Current stem cell treatment can be dispensed as an independent cell treatment format or with the combination of other approaches. Hence, the improvement of the treatment strategy is largely subjected by our understanding of MSCs mechanism of action.

Retinal pigment epithelium-secretome: A diabetic retinopathy perspective

Diabetic retinopathy is a major complication of diabetes mellitus that can lead to retinal vascular abnormalities and visual impairment. While retinal endothelial pathology is well studied, retinal pigment epithelium (RPE) layer modifications and the patho-physiological regulations are not widely understood. The RPE is a highly specialized pigmented layer regulating not only physiological functions such as transport of nutrients, ions, absorption of light, phagocytosis of photoreceptor membranes, but also secretion of a number of cytokines, chemokines, angiogenic and anti-angiogenic factors. The RPE secretome, though crucial in health and disease, remains elusive in diabetic retinopathy. A knowledge of these secreted factors would help explain and correlate the clinical phase of the disease aiding in improved disease management. A comprehensive knowledge of the secreted factors of the RPE is a potential tool for understanding the differential treatment regime of early diabetic retinopathy, diabetic proliferative retinopathy and diabetic macular edema. In this review, we have delineated the importance of factors secreted by the retinal pigment epithelium and its regulation in the pathogenesis of diabetic retinopathy.

Association between macular degeneration and mild to moderate chronic kidney disease: A nationwide population-based study

Chronic kidney disease (CKD) and macular degeneration (MD) are 2 grave diseases leading to significant disability secondary to renal failure and blindness. The 2 diseases share not only common risk factors but also similar pathogenic mechanisms to renal and retinal injuries. Previous epidemiological studies indicated association between these 2 diseases. However, this concept is challenged by recent investigations. Patients with mild to moderate CKD (n = 30,696) between January 1, 1995 and December 31, 2005 were selected from the Taiwan National Health Insurance Database. Controls (n = 122,784) were matched by age, gender, diabetes mellitus type 2, and hypertension status (1:4 ratios). The risk of MD was compared between the 2 groups. The mean age of patients was 54.9 ± 15.7 years. The proportion of MD was 2.7% in mild to moderate CKD patients and 1.9% in normal controls (P < 0.001); and, 0.39% and 0.26% (P < 0.001) in advanced MD. Mild to moderate CKD patients had higher risk for MD [adjusted odds ratio (OR), 1.301; 95% confidence interval (CI), 1.200-1.411; P < 0.001] than normal renal function subjects. The association was more pronounced for advanced MD. From all age strata (10 years increase), the presence of CKD in those patients aged less than 40 years had highest OR for all MD (OR = 2.125, 95% CI: 1.417-3.186, P < 0.001). The results were consistent in interaction terms, highlighting the importance of CKD in young age patient for risk of MD. The high risk for MD in mild to moderate CKD patients remains significant after adjustment for personal habits (alcohol drinking and smoking, model 1; OR: 1.371; 95% CI: 1.265-1.486; P < 0.001), comorbidities (dyslipidemia, cerebrovascular disease, and peripheral vascular disease, model 2; OR: 1.369; 95% CI: 1.264-1.484; P < 0.001) and all these factors (model 3; OR: 1.320, 95% CI: 1.218-1.431, P < 0.001). This association was consistent in the subanalysis, excluding those patients with diabetic retinopathy. Proper diagnosis and timely intervention should be warranted to retard visual loss of these patients.