Estrogen has a neuroprotective effect on axotomized RGCs through ERK signal transduction pathway

A two sample Mendelian randomized study of the association of sex hormones and behavioral and clinical risk factors with macular hole

Macular hole (MH) is a disease of the vitreoretinal interface that develops in relation to age and gender, and is 3.3 times more prevalent in females than in males. However, it remains inconclusive whether gender plays a role in the pathogenesis of MH. We adopted a two-sample Mendelian randomisation (MR) analysis to explore the relationship between free testosterone, bioavailable testosterone, oestradiol, menopause, smoking, alcohol consumption, type 2 diabetes, diastolic blood pressure, and systolic blood pressure and the risk of MH. We found that genetically predicted free testosterone levels in males were significantly associated with an increased risk of MH (IVW model: OR = 1.642; 95% CI, 1.162-2.322; P = 0.005), while genetically predicted oestradiol levels in females were significantly associated with a reduced risk of MH (IVW model: OR = 0.711; 95% CI, 0.517-0.978; P = 0.036). A sensitivity analysis verified the robustness of the causal relationship. MVMR results indicate that oestradiol in females is associated with MH risk using the IVW method (OR = 0.66; 95% CI, 0.47-0.88; P = 0.011). Our study demonstrates that the genetic risk of free testosterone in males and oestradiol in females may be correlated with MH risk.

Systemic oxidative stress levels and their associations with the risk of neovascular age-related macular degeneration and treatment response

PURPOSE

To investigate the association between oxidative stress (OS) and both the risk of neovascular age-related macular degeneration (nAMD) and the treatment response to intravitreal anti-vascular endothelial growth factor injections (anti-VEGF IVIs).

METHODS

This retrospective study included 46 treatment-naïve nAMD eyes of 46 patients (26 male and 20 female) who received anti-VEGF IVIs with a "treat-and-extend" regimen following an initial loading phase for one year. The patients were divided into two groups according to the total number of anti-VEGF IVIs administered during the year: the "effective" group and the "resistant" group. OS was evaluated by diacron reactive oxygen metabolites (d-ROMs), biological antioxidant potential (BAP), and skin autofluorescence (SAF) at baseline. For comparison, 54 control subjects were recruited.

RESULTS

There were no significant differences in d-ROM or BAP levels between control subjects and nAMD patients, regardless of sex, whereas SAF levels were higher in nAMD patients overall and in male nAMD patients than in controls (P < 0.001 for both). The effective and resistant groups included 30 and 16 eyes, respectively. Among the male nAMD patients, the effective and resistant groups had similar baseline characteristics, including age, smoking history, visual acuity, and central macular thickness; however, the resistant group had higher SAF levels (effective vs. resistant: 2.3 vs. 2.6 arbitrary units [AU]; P = 0.02). This finding was further supported by a multiple logistic regression analysis, which showed that the odds ratio for SAF was 1.57 per 0.1 AU increase (P = 0.01).

CONCLUSION

SAF levels were significantly higher in nAMD patients than in controls. The total number of anti-VEGF IVIs required over one year in male nAMD patients depended on SAF levels, suggesting that the SAF levels may serve as a potential biomarker for the response to anti-VEGF IVIs in nAMD.

Ovariectomy drives increase of an ECM transcription signature in the posterior eye and retina

Increased risk of developing glaucoma has recently been associated with early age of menopause. Here, we examined how age and surgically-induced menopause via ovariectomy (OVX) impacted gene expression in gene pathways previously linked to glaucoma, such as extracellular matrix (ECM) remodeling and TGF-β signaling. Using bulk RNA sequencing, we analyzed changes in young (3-4 months) and middle-aged (9-10 months) Long-Evans rats. We focused on posterior pole tissues (sclera and optic nerve head) but also examined the retina to compare observed changes across different tissue regions. Our results demonstrated that aging and OVX significantly alter gene expression in the sclera and optic nerve head. Generally, OVX triggered the enrichment of immune-related processes. However, OVX in young rats also led to significant enrichment of ECM and TGF-β gene sets. At the same time, these effects were diminished in middle-aged rats, indicating an age dependency of the effects of OVX on matrix-related pathways. Notably, the transcriptional factor Fos was downregulated in the posterior eye and retina in aged and OVX animals. Fos is a major regulator of cell proliferation and survival, and its dysregulation may play an important role in aging and menopause for women. These findings underscore the important role of menopause timing in modulating molecular pathways associated with glaucoma, which is consistent with clinical studies showing that early menopause may heighten the risk of developing this condition. This study also highlights the importance of considering women's health factors, such as menopause, in understanding and managing glaucoma risk.

Estrogen, via ESR2 receptor, prevents oxidative stress-induced Müller cell death and stimulates FGF2 production independently of NRF2, attenuating retinal degeneration

In this study, we aimed to investigate the effects of the deficient antioxidative gene, nuclear factor-erythroid 2-related factor 2 (Nrf2), on 17β-estradiol (E2)-mediated oxidative stress response, with a specific focus on growth factor production and cell death in Müller cells and retinal tissue. Administration of hydrogen peroxide (H2O2) reduced the viability of Müller cells derived from Nrf2 wild-type (WT) and knockout (KO) mice. However, this effect was more significant in the KO cells than in the WT cells. Pretreatment with E2 inhibited H2O2-induced cell death in both Nrf2 WT and KO Müller cell genotypes. Small interfering RNA-mediated gene silencing of estrogen receptor 2 (Esr2) attenuated the cell survival-promoting activity of E2 in Nrf2 KO Müller cells, while other identified estrogen receptors, Esr1 or G protein-coupled estrogen receptor 1 (Gper1), had no effect. Western blotting revealed higher ESR2 expression levels in Nrf2 KO cells than in WT Müller cells. Conditioned media from E2-and H2O2-treated Nrf2 WT or KO Müller cells enhanced the dissociated retinal cell viability compared with H2O2-treated cells. Both quantitative reverse-transcription polymerase chain reaction assay (qRT-PCR) and enzyme-linked immunosorbent assay exhibited a significant increase in fibroblast growth factor 2 (FGF2) expression levels in E2-and H2O2-treated Nrf2 WT and KO Müller cells compared to those in E2-treated cells. In vivo, administration of N-methyl-N-nitrosourea (MNU) reduced the thickness and cell density of the outer nuclear layer (ONL) in Nrf2 KO mice and enhanced the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells in the ONL. However, E2 administration attenuated these defects in MNU-treated mice. Concomitant administration of MNU and E2 enhanced FGF2 protein levels in retinal lysates of Nrf2 KO mice. In conclusion, E2 demonstrated a significant role in preventing oxidative stress-induced retinal cell death by stimulating FGF2 production in Müller cells, independent of the Nrf2 gene. Based on these findings, we anticipate that exogenous administration of estrogens or ESR2-selective agonists could aid in treating patients with oxidative stress-related retinal degenerative diseases such as age-related macular degeneration and retinitis pigmentosa.

Association of Age of Menopause and Glaucoma Diagnosis in Female Veterans

Purpose

Age of menopause has been associated with the risk of developing glaucoma; however, it is unclear if the onset of menopause is directly associated with the development of glaucoma. Our objective was to determine if there is an association between the age at diagnosis of menopause and glaucoma.

Methods

This retrospective, case-only analysis was performed using the Veterans Affairs (VA) Corporate Data Warehouse of female veterans from 2000 to 2019. Women with both menopause and glaucoma diagnoses were matched based on covariates. The two matched cohorts were early menopause-early comparative (EM-EC; n = 1075) and late menopause-late comparative (LM-LC; n = 1050) women. We used a Pearson correlation to examine the linear relationship between age at diagnosis of menopause and glaucoma. Afterward, we used a multivariate linear regression model with age at diagnosis of glaucoma serving as the outcome variable to account for the covariates.

Results

We found that EM women developed glaucoma 6.0 years (interquartile range [IQR], 5.1-6.5) earlier than the EC group (P < 0.001), and LM women developed glaucoma an average of 5.2 years (IQR, 4.8-5.7) later than the LC group (P < 0.001). There was a modest linear relationship between the age of menopause and glaucoma diagnoses in the EM-EC (r = 0.40) and LM-LC (r = 0.46) cohorts. In our multivariate analysis, age at diagnosis of menopause was the largest factor related to age at diagnosis of glaucoma while accounting for our covariates. Our models predicted a 0.67-year delay in age at diagnosis of glaucoma with each additional premenopausal year.

Conclusions

This case-only analysis elucidates a temporal association between menopause and glaucoma, highlighting the need to characterize the role of menopause in the onset of glaucoma for women.

The relationship between equol production status and normal tension glaucoma

PURPOSE

Equol is metabolized by intestinal bacteria from soy isoflavones and is chemically similar to estrogen. Dietary habits, such as consumption of soy products, influence equol production. A relationship between glaucoma and estrogen has been identified; here, we investigated the relationship between equol production status and glaucoma in Japan.

METHODS

We recruited 68 normal-tension glaucoma (NTG) patients (male to female ratio 26:42, average age 63.0 ± 7.6 years) and 31 controls (male to female ratio 13:18, average age 66.0 ± 6.3 years) from our hospital. All women included were postmenopausal. Urinary equol concentration was quantified with the ELISA method. MD was calculated based on the Humphrey visual field. The association between MD and equol was analyzed with Spearman's rank correlation coefficient. The Mann-Whitney U test was used to compare the equol-producing (> 1 μM) and non-producing (< 1 μM) subjects. We also investigated the association between equol and glaucoma with a logistic regression analysis.

RESULTS

There was a significant association between equol and MD (r = 0.36, P < 0.01) in the NTG patients. Glaucoma, represented by MD, was significantly milder in the equol-producing subjects than the non-equol producing subjects (P = 0.03). A multivariate analysis revealed the independent contributions of equol, cpRNFLT, and IOP to MD (P = 0.03, P = 0.04, and P < 0.01, respectively).

CONCLUSION

Our results suggest that equol, acting through estrogen receptor-mediated neuroprotective effects, might be involved in suppressing the progression of NTG. This result also adds to evidence that glaucoma may be influenced by lifestyle.

G protein-coupled estrogen receptor expression in postnatal developing mouse retina

Introduction

Estrogen has emerged as a multifaceted signaling molecule in the retina, playing an important role in neural development and providing neuroprotection in adults. It interacts with two receptor types: classical estrogen receptors (ERs) alpha and beta, and G protein-coupled estrogen receptor (Gper). Gper differs from classical ERs in structure, localization, and signaling. Here we provide the first report of the temporal and spatial properties of Gper transcript and protein expression in the developing and mature mouse retina.

Methods

We applied qRT-PCR to determine Gper transcript expression in wild type mouse retina from P0-P21. Immunohistochemistry and Western blot were used to determine Gper protein expression and localization at the same time points.

Results

Gper expression showed a 6-fold increase during postnatal development, peaking at P14. Relative total Gper expression exhibited a significant decrease during retinal development, although variations emerged in the timing of changes among different forms of the protein. Gper immunoreactivity was seen in retinal ganglion cells (RGCs) throughout development and also in somas in the position of horizontal cells at early time points. Immunoreactivity was observed in the cytoplasm and Golgi at all time points, in the nucleus at early time points, and in RGC axons as the retina matured.

Discussion

In conclusion, our study illuminates the spatial and temporal expression patterns of Gper in the developing mouse retina and provides a vital foundation for further investigations into the role of Gper in retinal development and degeneration.

Influence of sex on chronic steroid-induced glaucoma: 24-Weeks follow-up study in rats

The objective was to evaluate ocular changes based on sex in steroid-induced glaucoma models in rats comparing healthy controls, over 24 weeks follow-up. Eighty-nine Long-Evans rats (38 males and 51 females) with steroid-induced glaucoma were analysed. Two steroid-induced glaucoma models were generated by injecting poly-co-lactic-glycolic acid microspheres loaded with dexamethasone (MMDEX model) and dexamethasone-fibronectin (MMDEXAFIBRO model) into the ocular anterior chamber. Intraocular pressure was measured by rebound tonometer Tonolab®. Neuroretinal function was analysed using dark- and light-adapted electroretinography (Roland consult® RETIanimal ERG), and structure was analysed using optical coherence tomography (OCT Spectralis, Heidelberg® Engineering) using Retina Posterior Pole, Retinal Nerve Fibre Layer and Ganglion Cell Layer protocols over 24 weeks. Males showed statistically (p < 0.05) higher intraocular pressure measurements. In both sexes and models neuroretinal thickness tended to decrease over time. In the MMDEX model, males showed higher IOP values and greatest percentage thickness loss in the Ganglion Cell Layer (p = 0.015). Females receiving MMDEXAFIBRO experienced large fluctuations in thickness, a higher percentage loss (on average) in Retina Posterior Pole (p = 0.035), Retinal Nerve Fibre Layer and Ganglion Cell Layer than aged-matched males, and the highest thickness loss rate by mmHg. Although no difference was found by sex in dark- and light-adapted electroretinography, increased amplitude in photopic negative response was found in MMDEX males and MMDEXAFIBRO females at 12 weeks. Although both glaucoma models used dexamethasone, different intraocular pressure and neuroretinal changes were observed depending on sex and other influential cofactors (fibronectin). Both sex and the induced glaucoma model influenced neuroretinal degeneration.

Estrogen dysregulation, intraocular pressure, and glaucoma risk

Characterized by optic nerve atrophy due to retinal ganglion cell (RGC) death, glaucoma is the leading cause of irreversible blindness worldwide. Of the major risk factors for glaucoma (age, ocular hypertension, and genetics), only elevated intraocular pressure (IOP) is modifiable, which is largely regulated by aqueous humor outflow through the trabecular meshwork. Glucocorticoids such as dexamethasone have long been known to elevate IOP and lead to glaucoma. However, several recent studies have reported that steroid hormone estrogen levels inversely correlate with glaucoma risk, and that variants in estrogen signaling genes have been associated with glaucoma. As a result, estrogen dysregulation may contribute to glaucoma pathogenesis, and estrogen signaling may protect against glaucoma. The mechanism for estrogen-related protection against glaucoma is not completely understood but likely involves both regulation of IOP homeostasis and neuroprotection of RGCs. Based upon its known activities, estrogen signaling may promote IOP homeostasis by affecting extracellular matrix turnover, focal adhesion assembly, actin stress fiber formation, mechanosensation, and nitric oxide production. In addition, estrogen receptors in the RGCs may mediate neuroprotective functions. As a result, the estrogen signaling pathway may offer a therapeutic target for both IOP control and neuroprotection. This review examines the evidence for a relationship between estrogen and IOP and explores the possible mechanisms by which estrogen maintains IOP homeostasis.

Mitochondrial network adaptations of microglia reveal sex-specific stress response after injury and UCP2 knockout

Mitochondrial networks remodel their connectivity, content, and subcellular localization to support optimized energy production in conditions of increased environmental or cellular stress. Microglia rely on mitochondria to respond to these stressors, however our knowledge about mitochondrial networks and their adaptations in microglia in vivo is limited. Here, we generate a mouse model that selectively labels mitochondria in microglia. We identify that mitochondrial networks are more fragmented with increased content and perinuclear localization in vitro vs. in vivo. Mitochondrial networks adapt similarly in microglia closest to the injury site after optic nerve crush. Preventing microglial UCP2 increase after injury by selective knockout induces cellular stress. This results in mitochondrial hyperfusion in male microglia, a phenotype absent in females due to circulating estrogens. Our results establish the foundation for mitochondrial network analysis of microglia in vivo, emphasizing the importance of mitochondrial-based sex effects of microglia in other pathologies.

Identifying, Understanding, and Addressing Disparities in Glaucoma Care in the United States

Glaucoma is the leading cause of irreversible blindness worldwide, currently affecting around 80 million people. Glaucoma prevalence is rapidly rising in the United States due to an aging population. Despite recent advances in the diagnosis and treatment of glaucoma, significant disparities persist in disease detection, management, and outcomes among the diverse patient populations of the United States. Research on disparities is critical to identifying, understanding, and addressing societal and healthcare inequalities. Disparities research is especially important and impactful in the context of irreversible diseases such as glaucoma, where earlier detection and intervention are the primary approach to improving patient outcomes. In this article, we first review recent studies identifying disparities in glaucoma care that affect patient populations based on race, age, and gender. We then review studies elucidating and furthering our understanding of modifiable factors that contribute to these inequities, including socioeconomic status (particularly age and education), insurance product, and geographic region. Finally, we present work proposing potential strategies addressing disparities in glaucoma care, including teleophthalmology and artificial intelligence. We also discuss the presence of non-modifiable factors that contribute to differences in glaucoma burden and can confound the detection of glaucoma disparities.

Translational Relevance

By recognizing underlying causes and proposing potential solutions, healthcare providers, policymakers, and other stakeholders can work collaboratively to reduce the burden of glaucoma and improve visual health and clinical outcomes in vulnerable patient populations.

Etiology of Idiopathic Macular Holes in the Light of Estrogen Hormone

The aim of this review was to identify a new potential explanation for the development of macular holes in relation to the female sex and to explain the possible underlying pathways. This approach was based on the evaluation of anatomical, physiological, and morphological analyses currently available in the literature. The findings showed that estrogen exerts a protective effect on the neuroretina and may influence Müller and cone cells. Both cell types are responsible for the building of the fovea structure. However, this protection may be lost due to the sudden decrease in estrogen levels during menopause. In conclusion, the fovea cones, through its sensitivity to estrogen and high energy consumption, may be very vulnerable to damage caused by a sudden changes in the concentration of estrogen in menopausal females. Such changes may result in cone degeneration, and thus a destroyed structure of the fovea, and may lead to the development of a hole in the fovea, as in the case of macular holes. This review revealed that under the decreasing influence of estrogen may cones play a key role with regard to the etiology of the development of macular holes. This aspect may be of strategic importance in prophylactic therapy for the prevention of the development of macular holes in premenopausal females or after ocular trauma.

Bifidobacterium promotes retinal ganglion cell survival by regulating the balance of retinal glial cells

INTRODUCTION

Optic nerve injury is a leading cause of irreversible blindness worldwide. The retinal ganglion cells (RGCs) and their axons cannot be regenerated once damaged. Therefore, reducing RGC damage is crucial to prevent blindness. Accordingly, we aimed to investigate the potential influence of the gut microbiota on RGC survival, as well as the associated action mechanisms.

METHODS

We evaluated the effects of microbiota, specifically Bifidobacterium, on RGC. Optic nerve crush (ONC) was used as a model of optic nerve injury. Vancomycin and Bifidobacterium were orally administered to specific pathogen-free (SPF) mice.

RESULTS

Bifidobacterium promoted RGC survival and optic nerve regeneration. The administration of Bifidobacterium inhibited microglia activation but promoted Müller cell activation, which was accompanied by the downregulation of inflammatory cytokines and upregulation of neurotrophic factors and retinal ERK/Fos signaling pathway activation.

CONCLUSIONS

Our study demonstrates that Bifidobacterium-induced changes in intestinal flora promote RGC survival. The protective effect of Bifidobacterium on RGC can be attributed to the inhibition of microglia activation and promotion of Müller cell activation and the secondary regulation of inflammatory and neurotrophic factors.

Evidence for Menopause as a Sex-Specific Risk Factor for Glaucoma

Glaucoma is a leading cause of irreversible blindness worldwide and is characterized by progressive loss of visual function and retinal ganglion cells (RGC). Current epidemiological, clinical, and basic science evidence suggest that estrogen plays a role in the aging of the optic nerve. Menopause, a major biological life event affecting all women, coincides with a decrease in circulating sex hormones, such as estrogen. While 59% of the glaucomatous population are females, sex is not considered a risk factor for developing glaucoma. In this review, we explore whether menopause is a sex-specific risk factor for glaucoma. First, we investigate how menopause is defined as a sex-specific risk factor for other pathologies, including cardiovascular disease, osteoarthritis, and bone health. Next, we discuss clinical evidence that highlights the potential role of menopause in glaucoma. We also highlight preclinical studies that demonstrate larger vision and RGC loss following surgical menopause and how estrogen is protective in models of RGC injury. Lastly, we explore how surgical menopause and estrogen signaling are related to risk factors associated with developing glaucoma (e.g., intraocular pressure, aqueous outflow resistance, and ocular biomechanics). We hypothesize that menopause potentially sets the stage to develop glaucoma and therefore is a sex-specific risk factor for this disease.

Surgical Menopause Impairs Retinal Conductivity and Worsens Prognosis in an Acute Model of Rat Optic Neuropathy

Deficiency of estradiol during the menopausal period is an important risk factor for neurodegenerative diseases, including various optic neuropathies. The aim of this study was to evaluate the impact of surgical menopause on the function and survival ratio of RGCs in the rat model of ONC (optic nerve crush). We used eight-week-old female Long Evans rats, divided into two main groups depending on the time between ovariectomy procedure (OVA) and euthanasia (two weeks vs. seven weeks), and subgroups—OVA, OVA + ONC, or ONC. Retinal function was assessed with electroretinography (ERG). RGC loss ratio was evaluated using immunolabelling and counting of RGCs. Seven weeks after OVA, the menopause morphologically affected interneurons but not RGC; however, when the ONC procedure was applied, RGCs appeared to be more susceptible to damage in case of deprivation of estrogens. In our analysis, PhNR (photopic negative responses) were severely diminished in the OVA + ONC group. A deprivation of estrogens in menopause results in accelerated retinal neurodegeneration that firstly involves retinal interneurons. The lack of estrogens increases the susceptibility of RGCs to insults.

Association Between Sex Hormones and Visual Field Progression in Women With Primary Open Angle Glaucoma: A Cross-Sectional and Prospective Cohort Study

Purpose: We evaluated the level of sex hormones in female patients with primary open angle glaucoma (POAG) to determine whether they are associated with the onset and/or progression of POAG.

Methods: The cross-sectional study enrolled 63 women with POAG and 56 healthy women as normal control subjects. Furthermore, 57 women with POAG were included and followed-up for at least 2 years in the cohort study. All subjects were evaluated for serum concentration of sex hormones [prolactin (PRL), luteinizing hormone (LH), testosterone (TESTO), follicle-stimulating hormone (FSH), progesterone (PROG), and estrogen (E2)] and underwent visual field (VF) examination. In the cross-sectional study, Spearman analysis, linear regression analysis, and logistic regression analysis were performed to assess risk factors for POAG in women. In the cohort study, Cox regression analyses and Kaplan–Meier survival analysis were performed to identify factors associated with VF progression in women with POAG.

Results: In the cross-sectional study, the level of E2 was significantly lower in the POAG group than in the normal group (p < 0.05). Multiple logistic regression showed that the decreased level of E2 was a risk factor of POAG (OR = 0.27, 95% CI = 0.09–0.78, p < 0.05), especially in premenopausal subjects. In the cohort study, there were 29 non-progression subjects and 28 progression subjects. Patients in the progression group had significantly lower levels of E2 than those in the no progression group (p < 0.01). The decreased level of E2 at baseline was associated with POAG progression (HR = 0.08, 95% CI = 0.02–0.46, p < 0.05), especially in premenopausal subjects. Patients with POAG and with lower baseline E2 levels had significantly lower VF non-progression rates than patients with higher E2 levels (log-rank test p < 0.001), especially premenopausal subjects (log-rank test p < 0.05). Additionally, logistic regression analyses, Cox regression analyses, and Kaplan–Meier survival analysis showed that PROG, LH, FSH, and TESTO were risk factors of POAG and/or significantly associated with POAG progression.

Conclusion: A decreased E2 level is a POAG risk factor and is associated with VF progression in women with POAG, especially in premenopausal subjects. Additionally, other sex hormones (PROG, LH, FSH, and TESTO) might also play a role in POAG pathogenesis.

Genetic variation reveals the influence of steroid hormones on the risk of retinal neurodegenerative diseases

It is difficult to get evidence from randomized trials of a causal relationship between steroid hormones produced by the adrenal gland and gonad and retinal neurodegenerative disorders (RND). In this study, genetic variations of aldosterone (Aldo), androstenedione (A4), progesterone (P4), hydroxyprogesterone (17-OHP), and testosterone/17β-estradiol (T/E2) were obtained from genome-wide association studies as instrumental variables. Mendelian randomization (MR) analysis was used to assess the impact on the risk of RND, including glaucoma (8,591 cases and 210,201 controls), diabetic retinopathy (DR, 14,584 cases and 202,082 controls) and age-related macular degeneration (AMD, 14,034 cases and 91,214 controls). As the main method, inverse variance weighted results suggest that the increased glaucoma risk was affected by T/E2 (OR = 1.11, 95% CI, 1.01-1.22, P = 0.03), which was further validated by other methods (P_WM = 0.03, P_MLE = 0.03, P_{MR-RAPS =} 0.03). In the replicated stage, the causal relationship between T/E2 and glaucoma was verified based on the MRC-IEU consortium (P = 0.04). No impact of Aldo, A4, P4, 17-OHP, and T/E2 was observed for the risk of DR (P > 0.05) and AMD (P > 0.05). The heterogeneity test (P > 0.05) and pleiotropy test (P > 0.05) verified the robustness of the results. Our results suggest that T/E2 has a suggestive effect on the glaucoma risk. However, the genetic evidence based on a large sample does not support the effect of steroid hormones on DR and AMD risk. Further studies are vital to assess the possibility of steroid hormones as targets for prevention and treatment.

Girl Power in Glaucoma: The Role of Estrogen in Primary Open Angle Glaucoma

Estrogen is essential in maintaining various physiological features in women, and a decline in estrogen levels are known to give rise to numerous unfortunate symptoms associated with menopause. To alleviate these symptoms hormone replacement therapy with estrogen is often used, and has been shown to be fruitful in improving quality of life in women suffering from postmenopausal discomforts. An often forgotten condition associated with menopause is the optic nerve disorder, glaucoma. Thus, estrogen may also have an impact in maintaining the retinal ganglion cells (RGCs), which make up the optic nerve, thereby preventing glaucomatous neurodegeneration. This review aims to provide an overview of possible associations of estrogen and the glaucoma subtype, primary open-angle glaucoma (POAG), by evaluating the current literature through a PubMed-based literature search. Multiple in vitro and in vivo studies of RGC protection, as well as clinical and epidemiological data concerning the well-defined retinal neurodegenerative disorder POAG have been reviewed. Over all, deficiencies in retinal estrogen may potentially instigate RGC loss, visual disability, and eventual blindness. Estrogen replacement therapy may therefore be a beneficial future treatment. However, more studies are needed to confirm the relevance of estrogen in glaucoma prevention.

Influence of Sex on Neuroretinal Degeneration: Six-Month Follow-Up in Rats With Chronic Glaucoma

Purpose

To evaluate differences by sex in the neuroretina of rats with chronic glaucoma over 24 weeks of follow-up, and to assess by sex the influence on neurodegeneration of different methods of inducing ocular hypertension.

Methods

Forty-six Long-Evans rats-18 males and 28 females-with induced chronic glaucoma were analyzed. Glaucoma was achieved via 2 models: repeatedly sclerosing the episcleral veins (9 male/14 female) or by injecting poly(lactic-co-glycolic acid) microspheres measuring 20 to 10 µm (Ms20/10) into the anterior chamber (9 male/14 female). The IOP was measured weekly by tonometer; neuroretinal function was recorded by dark/light-adapted electroretinography at baseline and weeks 12 and 24; and structure was analyzed by optical coherence tomography using the retina posterior pole, retinal nerve fiber layer and ganglion cell layer protocols at baseline and weeks 8, 12, 18, and 24.

Results

Males showed statistically significant (P < 0.05) higher IOP in both chronic glaucoma models, and greater differences were found in the episcleral model at earlier stages. Males with episclerally induced glaucoma showed a statistically higher increase in retinal thickness in optical coherence tomography recordings than females and also when comparing Ms20/10 at 12 weeks. Males showed a higher percentage of retinal nerve fiber layer thickness loss in both models. Ganglion cell layer thickness loss was only detected in the Ms20/10 model. Males exhibited worse dark/light-adapted functionality in chronic glaucoma models, which worsened in the episcleral sclerosis model at 12 weeks, than females.

Conclusions

Female rats with chronic glaucoma experienced lower IOP and structural loss and better neuroretinal functionality than males. Sex and the ocular hypertension-inducing method influenced neuroretinal degeneration.

Effects of testosterone on intraocular pressure, thicknesses of retinal nerve fiber layer, ganglion cell complex, macula and on ocular blood flow in female-to-male transgender persons

PURPOSE

To compare the effects of testosterone on intraocular pressure (IOP), thicknesses of retinal nerve fiber layer (RNFL), ganglion cell complex (GCC), macula and on ocular blood flow between female-to-male transgender (FMT) persons who use testosterone and healthy women and healthy men.

METHOD

The study included 39 eyes of 20 FMT(Group 1), 40 eyes of 20 healthy women (Group 2), and 42 eyes of 21 healthy men (Group 3). In all subjects, RNFL, GCC and, macular thicknesses (MT) were measured by optical coherence tomography (OCT). Ocular blood flow was measured by Color Doppler Ultrasonography in all subjects.

RESULTS

IOP levels in FMT were significantly higher than men (p = 0.025). Superior (Sup), inferior (Inf) thicknesses of parafovea, and nasal thickness of perifovea in FMT were significantly higher than the Group 2 (p = 0.024, p = 0.037, p = 0.018). Sup thickness of perifovea in FMT was significantly higher than Group 3 (p = 0.011). Inf thickness of perifovea in FMT was significantly higher than Group 2 and 3 (p = 0.038, p = 0.002). Mean thickness of RNFL Inf in FMT was significantly higher than the Group 2 and 3 (p = 0.039, p = 0.032). Avg and Inf thicknesses of GCC in FMT were significantly higher than group 2 (p = 0.02, p = 0.005). In correlation test, systole/diastole ratio(S/D) in ophthalmic artery (OA) (r = 0.504, p = 0.028) and Inf thickness of perifovea (r = 0.485, p = 0.035) were positively correlated with the serum levels of testosterone in FMT.

CONCLUSIONS

We found that the use of supraphysiologic testosterone dose increased IOP and the thicknesses of macula, RNFL, and GCC in FMT. Serum testosterone level was positively correlated with S/D ratio in the OA.

Effect of age and sex on neurodevelopment and neurodegeneration in the healthy eye: Longitudinal functional and structural study in the Long-Evans rat

The processes involved in neurodevelopment and aging have not yet been fully discovered. This is especially challenging in premorbid or borderline situations of neurodegenerative diseases such as Alzheimer's or glaucoma. The retina, as part of the central nervous system, can be considered the easiest and most accessible neural structure that can be analyzed using non-invasive methods. Animal studies of neuroretinal tissue in situations of health and under controlled conditions allow the earliest sex- and aging-induced changes to be analyzed so as to differentiate them from the first signs occurring in manifested disease. This study evaluates differences by age and sex based on intraocular pressure (IOP) and neuroretinal function and structure in healthy young and adult rats before decline due to senescence. For this purpose, eighty-five healthy Long-Evans rats (31 males and 54 females) were analyzed in this 6-month longitudinal study running from childhood to adulthood. IOP was measured by tonometer (Tonolab; Tiolat Oy Helsinki, Finland), neuroretinal function was recorded by flash scotopic and light-adapted photopic negative response electroretinography (ERG) (Roland consult® RETIanimal ERG, Germany) at 4, 16 and 28 weeks of age; and structure was evaluated by in vivo optical coherence tomography (OCT) (Spectralis, Heidelberg® Engineering, Germany). Analyzing both sexes together, IOP was below 20 mmHg throughout the study; retina (R), retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL) thicknesses measured by OCT decreased over time; an increase in ERG signal was recorded at week 16; and no differences were found between right and left eyes. However, analyzing differences by sex revealed that males had higher IOP (even reaching ocular hypertension [>20 mmHg] by the end of the study [7 months of age]), exhibited greater neuroretinal thickness but higher structural percentage loss, and had worse dark- and light-adapted function as measured by ERG than females. This study concludes that age and sex influenced neurodevelopment and neurodegeneration. Different structural and functional degenerative patterns were observed by sex; these occurred earlier and more intensely in males than in age-matched females.

Retina-Targeted Delivery of 17β-Estradiol by the Topically Applied DHED Prodrug

The purpose of this study was to explore retina-targeted delivery of 17β-estradiol (E2), a powerful neuroprotectant, by its bioprecursor prodrug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED) administered as eye drops in animal models. Compared to the parent hormone, DHED displayed increased transcorneal flux ex vivo both with and without the presence of 2-hydroxypropyl-β-cyclodextrin used as a penetration-enhancing excipient in rat, rabbit, and pig. In vitro, the prodrug also showed facile bioactivation to E2 in the retina but not in the cornea. After topical administration to rats and rabbits, peak DHED-derived E2 concentrations reached 13 ± 5 ng/g and 18 ± 7 ng/g in the retina of female rats and rabbits, respectively. However, the prodrug remained inert in the rest of the body and, therefore, did not cause increase in circulating hormone concentration, as well as wet uterine and anterior pituitary weights as typical markers of E2′s endocrine impact. Altogether, our studies presented here have demonstrated the premise of topical retina-selective estrogen therapy by the DHED prodrug approach for the first time and provide compelling support for further investigation into the full potential of DHED for an efficacious and safe ocular neurotherapy.

17β-Estradiol Delivered in Eye Drops: Evidence of Impact on Protein Networks and Associated Biological Processes in the Rat Retina through Quantitative Proteomics

To facilitate the development of broad-spectrum retina neuroprotectants that can be delivered through topical dosage forms, this proteomics study focused on analyzing target engagements through the identification of functional protein networks impacted after delivery of 17β-estradiol in eye drops. Specifically, the retinae of ovariectomized Brown Norway rats treated with daily eye drops of 17β-estradiol for three weeks were compared to those of vehicle-treated ovariectomized control animals. We searched the acquired raw data against a composite protein sequence database by using Mascot, as well as employed label-free quantification to detect changes in protein abundances. Our investigation using rigorous validation criteria revealed 331 estrogen-regulated proteins in the rat retina (158 were up-regulated, while 173 were down-regulated by 17β-estradiol delivered in eye drops). Comprehensive pathway analyses indicate that these proteins are relevant overall to nervous system development and function, tissue development, organ development, as well as visual system development and function. We also present 18 protein networks with associated canonical pathways showing the effects of treatments for the detailed analyses of target engagements regarding potential application of estrogens as topically delivered broad-spectrum retina neuroprotectants. Profound impact on crystallins is discussed as one of the plausible neuroprotective mechanisms.

Sex hormone levels and risk of primary open-angle glaucoma in postmenopausal women

OBJECTIVE

We evaluated the relation of prediagnostic sex hormone levels in postmenopausal women with primary open-angle glaucoma (POAG) and intraocular pressure (IOP).

METHODS

Among postmenopausal participants of the Nurses' Health Study, POAG cases (n = 189; diagnosed 1990-2008) and controls (n = 189) were matched on age, fasting status, and postmenopausal hormone use at blood draw (1989-1990). Plasma concentrations of estrone sulfate, estradiol, testosterone, sex hormone binding globulin, and dehydroepiandrosterone sulfate were assessed. The primary outcome was POAG; in secondary analyses, among cases only, we evaluated maximum untreated IOP at diagnosis. Multivariable-adjusted logistic/multiple linear regression models were used to evaluate tertiles (Ts) of biomarker levels and the two outcomes, adjusting for various potential confounders.

RESULTS

We observed no significant associations of estrone, estradiol, sex hormone binding globulin, or dehydroepiandrosterone sulfate with POAG risk or with maximum IOP at glaucoma diagnosis among cases. Suggestive significant associations were observed with highest testosterone and POAG risk (T3 vs T1 multivariable-adjusted odds ratio 1.84; 95% confidence interval 1.02, 3.33; P trend 0.10). Similarly, for maximum IOP at diagnosis among cases only (mean 8 years after blood draw), higher testosterone was significantly associated with higher IOP (multivariable-adjusted difference in IOP T3 vs T1 2.17 mm Hg; 95% confidence interval 0.34, 3.99; P trend 0.02).

CONCLUSIONS

Overall, plasma sex hormone levels in postmenopausal women were not associated with POAG risk; however, a trend of higher testosterone levels being associated with higher POAG risk and higher IOP at diagnosis was observed and needs confirmation.

Progesterone anti-inflammatory properties in hereditary retinal degeneration

The interactions between steroid gonadal hormones and the retina (a part of the visual system and the central nervous system (CNS)) have received limited attention and beneficial effects of these hormones in retinal diseases is controversial. Retinitis pigmentosa (RP) is the most common cause of retinal hereditary blindness and to date no treatment is available. However, results regarding the effects of progesterone on the progression of RP are promising. With the idea of demonstrating if the progesterone retinal protection in RP is related to its possible anti-inflammatory properties, we have administered orally progesterone to rd10 mice, an animal model of RP. We observed that progesterone decreased photoreceptors cell death, reactive gliosis and the increase in microglial cells caused by RP. We also examined the expression of neuronal and inducible nitric oxide synthase (nNOS and iNOS), the enzyme responsible for NO production. The results demonstrated a decrease in nNOS expression only in control mice treated with progesterone. Inflammation has been related with an increase in lipid peroxidation. Noticeably progesterone administration was able to diminish retinal malondialdehyde (MDA, a lipid peroxidation product) concentrations in rd10 mice. Altogether, we can conclude that progesterone could be a good therapeutic option not only in RP but also for other retinal diseases that have been associated with inflammation and lipid peroxidation.

Sex Hormones and Optic Nerve Disorders: A Review

Aim: This review article presents a comprehensive overview of the literature on sex hormones (estrogens, androgens, progesterone) and optic nerve disorders, with a discussion of the implications for therapy and prevention.

Methods: Epidemiological, pre-clinical and clinical studies were reviewed.

Results: Analysis of the biological basis for a relationship between eye diseases and sex hormones showed that some types of hormones can exert a protective effect either directly on the retina and optic nerve or indirectly by modulating ocular blood flow. For example, it seems that estrogen exposure has a protective effect against glaucoma, whereas its deficit may lead to early onset of the disease. If further studies confirm the data in the literature, estrogen therapy, because of its antioxidant action, may be effective in the treatment of Leber's hereditary optic neuropathy, whereas, in the light of current studies, there does not seem to be an influence of estrogen on non-arteritic anterior ischemic optic neuritis (NAION).

Conclusions: Although there is some evidence that in some optic nerve pathologies the sex hormones seem to play an important role there are still too few studies providing evidence for its wider use in clinical practice.

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.

Association between mitochondrial DNA damage and ocular blood flow in patients with glaucoma

Background/Aims

We determined the relationship between tissue mean blur rate (MT) and mitochondrial dysfunction, represented by the mitochondrial/nuclear DNA (mtDNA/nDNA) ratio. We also investigated the usefulness of these biomarkers.

Methods

We assessed ocular blood flow in 123 eyes of 123 patients with open-angle glaucoma (OAG) and 37 control eyes of 37 healthy subjects by measuring MT in the optic nerve head with laser speckle flowgraphy. We measured mtDNA and nDNA with PCR, calculated the mtDNA/nDNA ratio and compared this ratio with MT using Spearman’s rank test. We used multiple regression analysis to further investigate the association between MT and glaucoma in the most severe group.

Results

The control and the patients with glaucoma had significant differences in the mtDNA/nDNA ratio, circumpapillary retinal nerve fibre layer thickness and MT. There was no significant relationship between the mtDNA/nDNA ratio and MT in patients with OAG overall or the female patients with OAG, but there was a significant relationship between the mtDNA/nDNA ratio and MT, temporal-MT and superior-MT in male patients with severe OAG (r=−0.46, p=0.03; r=−0.51, p=0.02; r=−0.61, p<0.01, respectively). Furthermore, we found that the mtDNA/nDNA ratio was an independent contributor to temporal-MT and superior-MT in these patients (p<0.01 and p=0.03, respectively).

Conclusion

We found that there was a significant relationship between the mtDNA/nDNA ratio and MT in male patients with severe OAG, suggesting that the mtDNA/nDNA ratio may be a new biomarker in glaucoma and may help research on the vulnerability of these patients to mitochondrial dysfunction.

Neuroprotective strategies for retinal disease

Diseases that affect the eye, including photoreceptor degeneration, diabetic retinopathy, and glaucoma, affect 11.8 million people in the US, resulting in vision loss and blindness. Loss of sight affects patient quality of life and puts an economic burden both on individuals and the greater healthcare system. Despite the urgent need for treatments, few effective options currently exist in the clinic. Here, we review research on promising neuroprotective strategies that promote neuronal survival with the potential to protect against vision loss and retinal cell death. Due to the large number of neuroprotective strategies, we restricted our review to approaches that we had direct experience with in the laboratory. We focus on drugs that target survival pathways, including bile acids like UDCA and TUDCA, steroid hormones like progesterone, therapies that target retinal dopamine, and neurotrophic factors. In addition, we review rehabilitative methods that increase endogenous repair mechanisms, including exercise and electrical stimulation therapies. For each approach, we provide background on the neuroprotective strategy, including history of use in other diseases; describe potential mechanisms of action; review the body of research performed in the retina thus far, both in animals and in humans; and discuss considerations when translating each treatment to the clinic and to the retina, including which therapies show the most promise for each retinal disease. Despite the high incidence of retinal diseases and the complexity of mechanisms involved, several promising neuroprotective treatments provide hope to prevent blindness. We discuss attractive candidates here with the goal of furthering retinal research in critical areas to rapidly translate neuroprotective strategies into the clinic.

Gonadal Hormones and Retinal Disorders: A Review

AIM

Gonadal hormones are essential for reproductive function, but can act on neural and other organ systems, and are probably the cause of the large majority of known sex differences in function and disease. The aim of this review is to provide evidence for this hypothesis in relation to eye disorders and to retinopathies in particular.

METHODS

Epidemiological studies and research articles were reviewed.

RESULTS

Analysis of the biological basis for a relationship between eye diseases and hormones showed that estrogen, androgen, and progesterone receptors are present throughout the eye and that these steroids are locally produced in ocular tissues. Sex hormones can have a neuroprotective action on the retina and modulate ocular blood flow. There are differences between the male and the female retina; moreover, sex hormones can influence the development (or not) of certain disorders. For example, exposure to endogenous estrogens, depending on age at menarche and menopause and number of pregnancies, and exposure to exogenous estrogens, as in hormone replacement therapy and use of oral contraceptives, appear to protect against age-related macular degeneration (both drusenoid and neurovascular types), whereas exogenous testosterone therapy is a risk factor for central serous chorioretinopathy. Macular hole is more common among women than men, particularly in postmenopausal women probably owing to the sudden drop in estrogen production in later middle age. Progestin therapy appears to ameliorate the course of retinitis pigmentosa. Diabetic retinopathy, a complication of diabetes, may be more common among men than women.

CONCLUSION

We observed a correlation between many retinopathies and sex, probably as a result of the protective effect some gonadal hormones may exert against the development of certain disorders. This may have ramifications for the use of hormone therapy in the treatment of eye disease and of retinal disorders in particular.

Novel Therapeutics in Glaucoma Management

BACKGROUND

Glaucoma is a progressive optic neuropathy characterized by retinal ganglion cell death and alterations of visual field. Elevated intraocular pressure (IOP) is considered the main risk factor of glaucoma, even though other factors cannot be ruled out, such as epigenetic mechanisms.

OBJECTIVE

An overview of the ultimate promising experimental drugs to manage glaucoma has been provided.

RESULTS

In particular, we have focused on purinergic ligands, KATP channel activators, gases (nitric oxide, carbon monoxide and hydrogen sulfide), non-glucocorticoid steroidal compounds, neurotrophic factors, PI3K/Akt activators, citicoline, histone deacetylase inhibitors, cannabinoids, dopamine and serotonin receptors ligands, small interference RNA, and Rho kinase inhibitors.

CONCLUSIONS

The review has been also endowed of a brief chapter on last reports about potential neuroprotective benefits of anti-glaucoma drugs already present in the market.

Age- and sex-dependency of the association between systemic antioxidant potential and glaucomatous damage

Systemic oxidative stress is thought to be an important factor in the pathogenesis of glaucoma. In particular, low systemic antioxidative capacity, which normally counters oxidative stress, may contribute to glaucoma. Thus, we investigated the association between biological antioxidant potential (BAP), a biomarker of systemic antioxidative capacity, and glaucoma severity in patients with open-angle glaucoma (OAG). This study included 480 eyes of 240 patients with OAG and 66 healthy control eyes. We measured the BAP serum level with a free radical analyzer and compared it with a weighted estimate of the number of retinal ganglion cells (wrgc), derived from circumpapillary retinal nerve fiber layer thickness and visual field mean deviation. We found that wrgc was uncorrelated with BAP in the overall, male, and female OAG patients, but was correlated in young (aged ≤ 65 years) male OAG patients (better eye: r = 0.33, P = 0.02; worse eye: r = 0.27, P = 0.047). Furthermore, a mixed-effects regression analysis revealed that BAP was an independent contributing factor to wrgc in young male OAG patients (P = 0.02). Thus, systemic antioxidant capacity was associated with glaucomatous damage in relatively young male patients, suggesting that anti-oxidant therapy might be more effective in these patients.

A comparison of sex steroid concentration levels in the vitreous and serum of patients with vitreoretinal diseases

The purpose of this study was to compare steroid hormone concentration levels in the vitreous and serum of vitreoretinal disease patients to elucidate the possibility of neurosteroid production in the retina. Serum and vitreous samples were collected from vitrectomy patients, and estradiol (E2) and testosterone (T) concentrations were measured using electro-chemiluminescence immunoassay. We measured E2 in epiretinal membrane (ERM, n = 14), macular hole (MH, n = 18), proliferative diabetic retinopathy (PDR, n = 20), and retinal detachment (RD, n = 19) cases, and T in ERM (n = 14), MH (n = 17), PDR (n = 13), and RD (n = 17) cases. No statistically significant age differences existed among the groups. Mean respective E2 concentrations (pg/ml) in the male/female vitreous were ERM: 6.67±4.04/18.82±7.10, MH: 10.3±7.02/17.00±4.8, PDR: 4.2±3.05/15.83±3.46, and RD: 10.00±4.58/16.06±4.57, while those in serum were ERM: 31.67±5.51/5.82±1.08, MH: 21.00±8.89/7.53±3.2, PDR: 29.20±7.07/12.75±10.62, and RD: 24.33±6.51/7.5±4.42. E2 concentrations were significantly higher (P<0.001) in the male serum than vitreous, yet significantly higher in the female vitreous than serum. Mean respective T concentrations (ng/ml) in the male/female vitreous were ERM: 0.15±0.03/0.15±0.01, MH: 0.15±0.01/0.15±0.01, PDR: 0.15±0.03/0.16±0.12, and RD: 0.14±0.01/0.17±0.08, while those in serum were ERM: 4.54±1.46/0.16±0.01, MH: 8.04±2.29/0.16±0.10, PDR: 5.14±1.54/0.22±0.11, and RD: 3.24±0.75/0.17±0.10. T concentrations were high in the male serum, yet extremely low in the male and female vitreous and female serum. High concentrations of E2 were found in the vitreous, and women, in particular, exhibited significantly higher concentrations in the vitreous than in the serum. This finding suggests the possibility that in vitreoretinal disease cases, the synthesis of E2 is increased locally only in female eyes.

Contribution of the Nurses' Health Study to the Epidemiology of Cataract, Age-Related Macular Degeneration, and Glaucoma

OBJECTIVES

To review the contribution of the Nurses' Health Study (NHS) to understanding the genetic and lifestyle factors that influence the risk of cataract, age-related macular degeneration, and glaucoma.

METHODS

We performed a narrative review of the publications of the NHS between 1976 and 2016.

RESULTS

The NHS has helped to elucidate the roles of genetics, lifestyle factors (e.g., cigarette smoking associated with cataract extraction and age-related macular degeneration), medical conditions (e.g., diabetes associated with cataract extraction and glaucoma), and dietary factors (e.g., greater carotenoid intake and lower glycemic diet associated with lower risk of age-related macular degeneration) in the etiology of degree and progression of lens opacities, cataract extraction, age-related macular degeneration, primary open-angle glaucoma, and exfoliation glaucoma.

CONCLUSIONS

The findings from the NHS, combined with those of other studies, have provided compelling evidence to support public health recommendations for helping to prevent age-related eye diseases: abstinence from cigarette smoking, maintenance of healthy weight and diabetes prevention, and a healthy diet rich in fruits and vegetables.

Neuroprotective actions of progesterone in an in vivo model of retinitis pigmentosa

Progesterone has been shown to have neuroprotective effects in experimental acute brain injury models, but little is known about the effects of steroid sex hormones in models of retinitis pigmentosa (RP). The aim of this study was to asses whether progesterone had a protective effect in one animal model of RP (the rd1 mice), and whether its action was due at least in part, to its ability to reduce free radical damage or to increase antioxidant defences. Rd1 and wild type (wt) mice received an oral administration of 100 mg/kg body/weight of progesterone on alternate days starting at postnatal day 7 (PN7) and were sacrificed at different postnatal days. Our results show that progesterone decreases cell death, as the number of TUNEL-positive cells were decreased in the ONL of the retina from treated rd1 mice. At PN15, treatment with progesterone increased values of ERG b-wave amplitude (p<0,5) when compared with untreated mice. Progesterone also decreased the observed gliosis in RP, though this effect was transient. Treatment with progesterone significantly reduced retinal glutamate concentrations at PN15 and PN17. To clarify the mechanism by which progesterone is able to decrease retinal glutamate concentration, we examined expression levels of glutamine synthase (GS). Our results showed a significant increase in GS in rd1 treated retinas at PN13. Treatment with progesterone, significantly increase not only GSH but also oxidized glutathione retinal concentrations, probably because progesterone is able to partially increase glutamate cysteine ligase c subunit (GCLC) at PN15 and PN17 (p<0,05). In summary, our results demonstrate that oral administration of progesterone appears to act on multiple levels to delay photoreceptor death in this model of RP.

Natural compounds and retinal ganglion cell neuroprotection

Glaucoma, the second leading cause of blindness in the world, is a chronic optic neuropathy often associated with increased intraocular pressure and characterized by progressive retinal ganglion cell (RGC) axons degeneration and death leading to typical optic nerve head damage and distinctive visual field defects. Although the pathogenesis of glaucoma is still largely unknown, it is hypothesized that RCGs become damaged through various insults/mechanisms, including ischemia, oxidative stress, excitotoxicity, defective axonal transport, trophic factor withdrawal, and neuroinflammation. In this review, we summarize the potential benefits of several natural compounds for RGCs neuroprotection.

Oestrogen, ocular function and low-level vision: a review

Over the past 10 years, a literature has emerged concerning the sex steroid hormone oestrogen and its role in human vision. Herein, we review evidence that oestrogen (oestradiol) levels may significantly affect ocular function and low-level vision, particularly in older females. In doing so, we have examined a number of vision-related disorders including dry eye, cataract, increased intraocular pressure, glaucoma, age-related macular degeneration and Leber's hereditary optic neuropathy. In each case, we have found oestrogen, or lack thereof, to have a role. We have also included discussion of how oestrogen-related pharmacological treatments for menopause and breast cancer can impact the pathology of the eye and a number of psychophysical aspects of vision. Finally, we have reviewed oestrogen's pharmacology and suggest potential mechanisms underlying its beneficial effects, with particular emphasis on anti-apoptotic and vascular effects.

Mechanisms of secondary degeneration after partial optic nerve transection

Secondary degeneration occurs commonly in the central nervous system after traumatic injuries and following acute and chronic diseases, including glaucoma. A constellation of mechanisms have been shown to be associated with secondary degeneration including apoptosis, necrosis, autophagy, oxidative stress, excitotoxicity, derangements in ionic homeostasis and calcium influx. Glial cells, such as microglia, astrocytes and oligodendrocytes, have also been demonstrated to take part in the process of secondary injury. Partial optic nerve transection is a useful model which was established about 13 years ago. The merit of this model compared with other optic nerve injury models used for glaucoma study, including complete optic nerve transection model and optic nerve crush model, is the possibility to separate primary degeneration from secondary degeneration in location. Therefore, it provides a good tool for the study of secondary degeneration. This review will focus on the research progress of the mechanisms of secondary degeneration using partial optic nerve transection model.

Neuroprotective effects of nonfeminizing estrogens in retinal photoreceptor neurons

PURPOSE

Retinal diseases such as macular degeneration and glaucoma are disorders that target specific retinal neurons that can ultimately lead to vision loss. Under these conditions and pathologies, retinal neurons can die via apoptosis that may be due to increased oxidative stress. The neuroprotective effects of 17β-estradiol (E2) and three synthetic nonfeminizing estrogen analogs (ZYC-26, ZYC-23, and ZYC-3) were investigated to examine their abilities to protect retinal neurons against glutamate toxicity.

METHODS

Using an in vitro model of glutamate-induced cell death in 661W cells, a mouse cone photoreceptor cell line, shown to express both estrogen receptors (ERs) via immunoblotting, was pretreated with E2 and its analogs and cell viability were assessed.

RESULTS

It was observed that E2 and estrogen analogs, ZYC-26 and ZYC-3, were protective against a 5 mM glutamate insult in 661W cells. The neuroprotective abilities of ZYC-26 and ZYC-3 were autonomous of estrogen receptor-α (ERα) and ERβ demonstrated by their ability to protect in the presence of ICI 182780, a pan-ER antagonist with a high affinity for the estrogen receptor. Treatment with PPT and DPN, ERα- and ERβ-specific agonists, respectively, did not protect the 661W cells from the glutamate insult. Studying the membrane ER (mER) or GPR30 did show that activation of the receptor by G1 protected the retinal neuron from insult, whereas G15, an antagonist of the mER was not able to antagonize the protection previously seen.

CONCLUSIONS

These data demonstrate that nonfeminizing estrogens may emerge as useful compounds for neuroprotection of retinal cells.

Axonal protection by 17β-estradiol through thioredoxin-1 in tumor necrosis factor-induced optic neuropathy

Axonal degeneration often leads to the death of neuronal cell bodies. Previous studies demonstrated the substantial protective role of 17β-estradiol (E2) in several types of neuron. However, most studies examined cell body protection, and the role of 17β-E2 in axonal degeneration of retinal ganglion cells (RGC) remains unclear. In this study, we showed the presence of thioredoxin-1 (Trx1) in the optic nerve axons and found that the levels of Trx1 protein were significantly decreased in isolated RGC and the optic nerve after intravitreal injection of TNF, which was shown previously to induce optic nerve degeneration and subsequent loss of RGC. These changes were concomitant with disorganization of the microtubules with neurofilament accumulation, which were blocked by 17β-E2 implantation. 17β-E2 treatment also totally abolished TNF-induced decreases in Trx1 protein levels in isolated RGC and the optic nerve. The induction of Trx1 by 17β-E2 in the optic nerve was significantly inhibited by simultaneous injection of Trx1 small interfering RNA (siRNA) with TNF. Up-regulation of Trx1 by 17β-E2 in RGC-5 cells was prevented by Trx1 siRNA treatment. 17β-E2 significantly prevented TNF-induced axonal loss, and this axonal-protective effect was inhibited by intravitreal injection of Trx1 siRNA. This finding was also supported by the quantification of microtubules and neurofilaments. These results suggest that a Trx1 decrease in RGC bodies and their axons may be associated with TNF-induced optic nerve axonal degeneration. Axonal protection by 17β-E2 may be related to its regulatory effect on Trx1 induction.

Functional and morphological effects of β-estradiol in eyes with N-methyl-D-Aspartate-induced retinal neurotoxicity in rats

Glutamate-mediated excitotoxicity, mainly induced by N-methyl-d-aspartate (NMDA) receptors, is known to cause retinal ganglion cell death in retinal ischemia, glaucoma, and several other retinal diseases. We evaluated the effects of β-estradiol (E2) against a single intravitreal injection of NMDA using a functional and morphological approach. Male rats were randomly divided into 3 treatment groups: (1) Control; (2) NMDA (intravitreal injection of 5 mM NMDA); and (3) NMDA + E2 (intravitreal injection of 5 mM NMDA and pretreatment with subcutaneous E2 implantation). Seven days after NMDA injection, full-field electroretinograms (ERGs) and quantitative morphological analyses using transverse sections of the retina were conducted. In the NMDA group, full-field ERGs showed reductions in the amplitudes of the negative-scotopic threshold response, rod response b-wave, oscillatory potentials, flicker response second b-wave and cone response b-wave. Morphological evaluations of transverse sections of the retina demonstrated a reduction in the thickness of the inner plexiform layer, increases in the thickness of the outer plexiform and outer nuclear layers, and a loss of cells in the ganglion cell layer. In the NMDA + E2 group, pretreatment with E2 prevented the aggravations in the amplitudes of the ERGs except for oscillatory potential 2 (OP2); however, no morphological differences between the NMDA and NMDA + E2 groups were seen. These findings indicate that E2 can protect retinal function against NMDA-induced neurotoxicity. In addition, these indications suggested that the effect of E2 may have therapeutic benefits in NMDA related diseases, such as retinal ischemia and glaucoma.

Neuroprotection in glaucoma - Is there a future role?

In glaucoma, the major cause of global irreversible blindness, there is an urgent need for treatment modalities that directly target the RGCs. The discovery of an alternative therapeutic approach, independent of IOP reduction, is highly sought after, due to the indirect nature and limited effectiveness of IOP lowering therapy in preventing RGC loss. Several mechanisms have been implicated in initiating the apoptotic cascade in glaucomatous retinopathy and numerous drugs have been shown to be neuroprotective in animal models of glaucoma. These mechanisms and their potential treatment include excitotoxicity, protein misfolding, mitochondrial dysfunction, oxidative stress, inflammation and neurotrophin deprivation. All of these mechanisms ultimately lead to programmed cell death with loss of RGCs. In this article we summarize the mechanisms involved in glaucomatous disease, highlight the rationale for neuroprotection in glaucoma management and review current potential neuroprotective strategies targeting RGCs from the laboratory to the clinic.

Effect of estrogen on electroretinographic responses in streptozotocin-induced diabetic female rats

The aim of this study is to investigate the effects of estrogen on functional changes in the retinas of streptozotocin (STZ)-induced diabetic rats by using an electroretinography. Female rats were randomly divided into four treatment groups: (1) Control (sham operation and vehicle administration); (2) STZ (sham operation and STZ administration); (3) OVX (ovariectomy and vehicle administration); and (4) OVX + STZ (ovariectomy and STZ administration). Full-field electroretinograms (ERGs) were recorded before OVX and STZ administration and 4 and 12 weeks after STZ administration. At 4 weeks after STZ administration, although there were no differences in the STZ and OVX groups compared with the Control group, the amplitude of the cone-response was significantly lower in the OVX + STZ group than in the Control group (P = 0.013). At 12 weeks after STZ administration, this response showed a similar tendency in the STZ and the OVX + STZ groups. At 12 weeks after STZ administration, the implicit times of OP3 and OP4 and of the cone-response were significantly delayed in the STZ and OVX + STZ groups (OP3: P = 0.030 and 0.050, OP4: P = 0.0060 and 0.0053, cone-response: P = 0.014 and 0.039), compared with in the Control group. Thus, the retinal functions in STZ-induced diabetic female rats were aggravated by OVX. OVX-induced estrogen deficiency resulted in earlier changes in the amplitudes of cone-response, especially in the diabetes, although this is a transient effect and it is difficult to explain. Recognizing the early neurosensory change would enable a better understanding of the effect of estrogen in the retina.

Effects of epigallocatechin-3-gallate on rat retinal ganglion cells after optic nerve axotomy

The purpose of this study was to investigate the effects of epigallocatechin-3-gallate (EGCG) in axotomized eyes and the pathways related to its action. Wistar rats received intracranial optic nerve (ON) axotomy 2 mm behind the globe in left eyes, whereas right eyes received sham operations. EGCG was administrated via intraperitoneal injection 30 min before and 4 days after axotomy. The density of retinal ganglion cell (RGC) was examined by a retrograde labeling technique. Western blot analysis was used to assess the expression of neuronal nitric oxide synthase (nNOS), Bax, Bcl-2, ERK and Akt. Optic nerve axotomy caused 54% RGC loss 7 days following surgery, and EGCG treatment reduced RGC loss by 12% (P = 0.017). The expression of the nNOS and pro-apoptotic Bax proteins were increased 5 days after axotomy, while EGCG treatment significantly blunted the up-regulation of the above two proteins (P = 0.04 and 0.02, respectively). Axotomy-induced p-ERK 1/2 and p-Akt proteins expression 5 days and 3 days following injury, respectively. Treatment with EGCG further enhanced p-ERK 1/2 and p-Akt expressions after axotomy. Inhibition of ERK and Akt pathways attenuated the protection of EGCG on RGC against axotomy damage. Thus, we demonstrated that administration of EGCG prior to axotomy promotes RGC survival. The neuroprotective capacity of EGCG appears to act through mediating nitric oxide, anti-apoptotic, and cell survival signaling pathways.