Taurine provides neuroprotection against retinal ganglion cell degeneration

Therapeutic Effects of Anti-Inflammatory and Anti-Oxidant Nutritional Supplementation in Retinal Ischemic Diseases

Appropriate nutrients are essential for cellular function. Dietary components can alter the risk of systemic metabolic diseases, including cardiovascular diseases, cancer, diabetes, and obesity, and can also affect retinal diseases, including age-related macular degeneration, diabetic retinopathy, and glaucoma. Dietary nutrients have been assessed for the prevention or treatment of retinal ischemic diseases and the diseases of aging. In this article, we review clinical and experimental evidence concerning the potential of some nutritional supplements to prevent or treat retinal ischemic diseases and provide further insights into the therapeutic effects of nutritional supplementation on retinopathies. We will review the roles of nutrients in preventing or protecting against retinal ischemic diseases.

Taurine induces hormesis in multiple biological models: May have transformative implications for overall societal health

This paper represents the first integrative assessment and documentation of taurine-induced hormetic effects in the biological and biomedical areas, their dose response features, mechanistic frameworks, and possible public health, therapeutic and commercial applications. Taurine-induced hormetic effects are documented in a wide range of experimental models, cell types and for numerous biological endpoints, with most of these experimental findings being reported within the past five years. It is suggested that the concept of hormesis may have a transformative effect on taurine research and its public health and therapeutic applications.

Taurine: a promising nutraceutic in the prevention of retinal degeneration

Taurine is considered a non-essential amino acid because it is synthesized by most mammals. However, dietary intake of taurine may be necessary to achieve the physiological levels required for the development, maintenance, and function of certain tissues. Taurine may be especially important for the retina. The concentration of taurine in the retina is higher than that in any other tissue in the body and taurine deficiency causes retinal oxidative stress, apoptosis, and degeneration of photoreceptors and retinal ganglion cells. Low plasma taurine levels may also underlie retinal degeneration in humans and therefore, taurine administration could exert retinal neuroprotective effects. Taurine has antioxidant, anti-apoptotic, immunomodulatory, and calcium homeostasis-regulatory properties. This review summarizes the role of taurine in retinal health and disease, where it appears that taurine may be a promising nutraceutical.

Visual fatigue a comprehensive review of mechanisms of occurrence, animal model design and nutritional intervention strategies

When the eyes work intensively, it is easy to have eye discomfort such as blurred vision, soreness, dryness, and tearing, that is, visual fatigue. Visual fatigue not only affects work and study efficiency, but long-term visual fatigue can also easily affect physical and mental health. In recent years, with the popularization of electronic products, although it has brought convenience to the office and study, it has also caused more frequent visual fatigue among people who use electronic devices. Moreover, studies have reported that the number of people with visual fatigue is showing a trend of increasing year by year. The range of people involved is also extensive, especially students, people who have been engaged in computer work and fine instruments (such as microscopes) for a long time, and older adults with aging eye function. More and more studies have proposed that supplementation with the proper nutrients can effectively relieve visual fatigue and promote eye health. This review discusses the physiological mechanisms of visual fatigue and the design ideas of animal experiments from the perspective of modern nutritional science. Functional food ingredients with the ability to alleviate visual fatigue are discussed in detail.

Taurine: A Source and Application for the Relief of Visual Fatigue

According to reports, supplementation with appropriate doses of taurine may help to reduce visual fatigue. Presently, some progress has been made in research related to taurine in eye health, but the lack of systematic summaries has led to the neglect of its application in the relief of visual fatigue. This paper, therefore, provides a systematic review of the sources of taurine, including the endogenous metabolic and exogenous dietary pathways, as well as a detailed review of the distribution and production of exogenous taurine. The physiological mechanisms underlying the production of visual fatigue are summarized and the research progress of taurine in relieving visual fatigue is reviewed, including the safety of consumption and the mechanism of action in relieving visual fatigue, in order to provide some reference basis and inspiration for the development and application of taurine in functional foods for relieving visual fatigue.

Development of an AAV-based model of tauopathy targeting retinal ganglion cells and the mouse visual pathway to study the role of microglia in Tau pathology

Tauopathy is a typical feature of Alzheimer's disease of major importance because it strongly correlates with the severity of cognitive deficits experienced by patients. During the pathology, it follows a characteristic spatiotemporal course which takes its origin in the transentorhinal cortex, and then gradually invades the entire forebrain. To study the mechanisms of tauopathy, and test new therapeutic strategies, it is necessary to set-up relevant and versatile in vivo models allowing to recapitulate tauopathy. With this in mind, we have developed a model of tauopathy by overexpression of the human wild-type Tau protein in retinal ganglion cells in mice (RGCs). This overexpression led to the presence of hyperphosphorylated forms of the protein in the transduced cells as well as to their progressive degeneration. The application of this model to mice deficient in TREM2 (Triggering Receptor Expressed on Myeloid cells-2, an important genetic risk factor for AD) as well as to 15-month-old mice showed that microglia actively participate in the degeneration of RGCs. Surprisingly, although we were able to detect the transgenic Tau protein up to the terminal arborization of RGCs at the level of the superior colliculi, spreading of the transgenic Tau protein to post-synaptic neurons was detected only in aged animals. This suggests that there may be neuron-intrinsic- or microenvironment mediators facilitating this spreading that appear with aging.

New insight of metabolomics in ocular diseases in the context of 3P medicine

Metabolomics refers to the high-through untargeted or targeted screening of metabolites in biofluids, cells, and tissues. Metabolome reflects the functional states of cells and organs of an individual, influenced by genes, RNA, proteins, and environment. Metabolomic analyses help to understand the interaction between metabolism and phenotype and reveal biomarkers for diseases. Advanced ocular diseases can lead to vision loss and blindness, reducing patients' quality of life and aggravating socio-economic burden. Contextually, the transition from reactive medicine to the predictive, preventive, and personalized (PPPM / 3P) medicine is needed. Clinicians and researchers dedicate a lot of efforts to explore effective ways for disease prevention, biomarkers for disease prediction, and personalized treatments, by taking advantages of metabolomics. In this way, metabolomics has great clinical utility in the primary and secondary care. In this review, we summarized much progress achieved by applying metabolomics to ocular diseases and pointed out potential biomarkers and metabolic pathways involved to promote 3P medicine approach in healthcare.

Systemic taurine treatment affords functional and morphological neuroprotection of photoreceptors and restores retinal pigment epithelium function in RCS rats

The aim of our work was to study whether taurine administration has neuroprotective effects in dystrophic Royal College of Surgeons (RCS) rats, suffering retinal degeneration secondary to impaired retinal pigment epithelium phagocytosis caused by a MERTK mutation. Dystrophic RCS-p + female rats (n = 36) were divided into a non-treated group (n = 16) and a treated group (n = 20) that received taurine (0.2 M) in drinking water from postnatal day (P)21 to P45, when they were processed. Retinal function was assessed with electroretinogram. Retinal morphology was assessed in cross-sections using immunohistochemical techniques to label photoreceptors, retinal microglial and macroglial cells, active zones of conventional and ribbon synaptic connections, and oxidative stress. Retinal pigment epithelium function was examined using intraocular fluorogold injections. Our results document that taurine treatment increases taurine plasma levels and photoreceptor survival in dystrophic rats. The number of photoreceptor nuclei rows at P45 was 3-5 and 6-11 in untreated and treated animals, respectively. Electroretinograms showed increases of 70% in the rod response, 400% in the a-wave amplitude, 30% in the b-wave amplitude and 75% in the photopic b-wave response in treated animals. Treated animals also showed decreased numbers of microglial cells in the outer retinal layers, decreased glial fibrillary acidic protein (GFAP) expression in Müller cells, decreased oxidative stress in the outer and inner nuclear layers and improved maintenance of synaptic connections. Treated animals showed increased FG phagocytosis in the retinal pigment epithelium cells. In conclusion, systemic taurine treatment decreases photoreceptor degeneration and increases electroretinographic responses in dystrophic RCS rats and these effects may be mediated through various neuroprotective mechanisms.

Neurodegenerative Diseases: Implications of Environmental and Climatic Influences on Neurotransmitters and Neuronal Hormones Activities

Neurodegenerative and neuronal-related diseases are major public health concerns. Human vulnerability to neurodegenerative diseases (NDDs) increases with age. Neuronal hormones and neurotransmitters are major determinant factors regulating brain structure and functions. The implications of environmental and climatic changes emerged recently as influence factors on numerous diseases. However, the complex interaction of neurotransmitters and neuronal hormones and their depletion under environmental and climatic influences on NDDs are not well established in the literature. In this review, we aim to explore the connection between the environmental and climatic factors to NDDs and to highlight the available and potential therapeutic interventions that could use to improve the quality of life and reduce susceptibility to NDDs.

Taurine protects R28 cells from hypoxia/re-oxygenation-induced damage via regulation of mitochondrial energy metabolism

Oxidative-induced damage and hypoxia/re-oxygenation (H/R) injury are common causes of irreversible visual impairment. The goals of this study were to explore the effects of taurine on R28 cells under the two damage models and the underlying mechanisms. Low doses of taurine supplementation promoted cell viability, mitochondrial membrane potential (MMP), SOD levels, ATP contents and attenuated cytotoxicity and intracellular ROS generation of the R28 cells under the two kinds of damage. The expression level of GTPBP3, a mitochondrial-tRNA (mt-tRNA) modification enzyme that catalyzes the taurine involved modification, was decreased under the two damage and taurine could reverse the reduction. After knocking down GTPBP3, the R28 cells become vulnerable to damage. The viability, cytotoxicity, MMP and intracellular ROS level of knockdown cells changed more obviously under the H/R injury than those of control cell. We also found that knockdown of GTPBP3 significantly decreased mitochondrial energy metabolism by measuring the oxidative respiration rate by the Seahorse XFe24 extracellular flux analyzer. The protection of low doses of taurine disappeared on knockdown R28 cells, indicating that GTPBP3 is crucial in the protection mechanisms of taurine. However, the impacts of the reduction of GTPBP3 level can be reversed by relatively high doses of taurine, implying the protection effects of taurine were dose-dependent, and there were more complicated mechanisms remain to be explored. This study explored a new mechanism of the neuroprotective effects of taurine, which depend on the GTPBP3-mediated taurine modification of mt-tRNAs and the promotion of mitochondrial energy metabolism.

Effects of Hydrostatic Pressure on Electrical Retinal Activity in a Multielectrode Array-Based ex vivo Glaucoma Acute Model

Glaucoma is a heterogeneous eye disease causing atrophy of the optic nerve head (ONH). The optic nerve is formed by the axons of the retinal ganglion cells (RGCs) that transmit visual input to the brain. The progressive RGC loss during glaucoma leads to irreversible vision loss. An elevated intraocular pressure (IOP) is described as main risk factor in glaucoma. In this study, a multielectrode array (MEA)-based ex vivo glaucoma acute model was established and the effects of hydrostatic pressure (10, 30, 60, and 90 mmHg) on the functionality and survival of adult male and female wild-type mouse (C57BL/6) retinae were investigated. Spontaneous activity, response rate to electrical and light stimulation, and bursting behavior of RGCs was analyzed prior, during, and after pressure stress. No pressure related effects on spontaneous firing and on the response rate of the RGCs were observed. Even a high pressure level (90 mmHg for 2 h) did not disturb the RGC functionality. However, the cells’ bursting behavior significantly changed under 90 mmHg. The number of spikes in bursts doubled during pressure application and stayed on a high level after pressure stress. Addition of the amino sulfonic acid taurine (1 mM) showed a counteracting effect. OFF ganglion cells did not reveal an increase in bursts under pressure stress. Live/dead staining after pressure application showed no significant changes in RGC survival. The findings of our ex vivo model suggest that RGCs are tolerant toward high, short-time pressure stress.

A multielectrode array-based hypoxia model for the analysis of electrical activity in murine retinae

Several eye diseases, for example, retinal artery occlusion, diabetic retinopathy, and glaucoma, are associated with retinal hypoxia. The lack of oxygen in the retina, especially in retinal ganglion cells (RGCs), causes cell damage up to cell degeneration and leads to blindness. Using multielectrode array recordings, an ex vivo hypoxia acute model was established to analyze the electrical activity of murine wild-type retinae under hypoxic stress conditions. Hypoxia was induced by exchanging the perfusion with oxygen-saturated medium by nitrogen-saturated medium. Hypoxic periods of 0 min (control) up to 60 min were tested on the retinae of adult female C57BL/6J mice. The electrical RGC activity vanished during hypoxia, but conditionally returned after the reestablishment of conventional test conditions. With increasing duration of hypoxia, the returning RGC activity decreased. After a hypoxic period of 30 min and a subsequent recovery time of 30 min, 59.43 ± 11.35% of the initially active channels showed a restored RGC activity. The survival rate of retinal cells after hypoxic stress was analyzed by a live/dead staining assay using two-photon laser scanning microscopy. For detailed information about molecular changes caused by hypoxia, a microarray gene expression analysis was performed. Furthermore, the effect of 2-aminoethanesulfonic acid (taurine, 1 mM) on retinae under hypoxic stress was tested. Treatment with taurine resulted in an increase in the RGC response rate after hypoxia and also increased the survival rate of retinal cells under hypoxic stress, confirming its potential as promising candidate for neuroprotective therapies of eye diseases.

Effect of a TSPO ligand on retinal pigment epithelial cholesterol homeostasis in high-fat fed mice, implication for age-related macular degeneration

Age-related Macular Degeneration (AMD) is a major cause of sight impairment in the elderly with complex aetiology involving genetics and environment and with limited therapeutic options which have limited efficacy. We have previously shown in a mouse-model of the condition, induced by feeding a high fat diet, that adverse effects of the diet can be reversed by co-administration of the TSPO activator, etifoxine. We extend those observations showing improvements in retinal pigment epithelial (RPE) cells with decreased lipids and enhanced expression of cholesterol metabolism and transport enzymes. Further, etifoxine decreased levels of reactive oxygen species (ROS) in RPE and inflammatory cytokines in RPE and serum. With respect to gut microbiome, we found that organisms abundant in the high fat condition (e.g. in the genus Anaerotruncus and Oscillospira) and implicated in AMD, were much less abundant after etifoxine treatment. The changes in gut flora were associated with the predicted production of metabolites of benefit to the retina including tryptophan and other amino acids and taurine, an essential component of the retina necessary to counteract ROS. These novel observations strengthen earlier conclusions that the mechanisms behind improvements in etifoxine-induced retinal physiology involve an interaction between effects on the host and the gut microbiome.

Taurine and oxidative stress in retinal health and disease

Retinal disorders are leading causes of blindness and are due to an imbalance between reactive oxygen species and antioxidant scavenger (in favor of pro‐oxidant species) or a disruption of redox signaling and control. Indeed, it is well known that oxidative stress is one of the leading causes of retinal degenerative diseases. Different approaches using nutraceuticals resulted in protective effects in these disorders. This review will discuss the impact of oxidative stress in retinal neurodegenerative diseases and the potential strategies for avoiding or counteracting oxidative damage in retinal tissues, with a specific focus on taurine. Increasing data indicate that taurine may be effective in slowing down the progression of degenerative retinal diseases, thus suggesting that taurine can be a promising candidate for the prevention or as adjuvant treatment of these diseases. The mechanism by which taurine supplementation acts is mainly related to the reduction of oxidative stress. In particular, it has been demonstrated to improve retinal reduced glutathione, malondialdehyde, superoxide dismutase, and catalase activities. Antiapoptotic effects are also involved; however, the protective mechanisms exerted by taurine against retinal damage remain to be further investigated.

Growth Factors as Tools in Photoreceptor Cell Regeneration and Vision Recovery

Photoreceptor loss is a major cause of blindness around the world. Stem cell therapy offers a new strategy in retina degenerative disease. Retinal progenitors can be derived from embryonic stem cells (ESC) in vitro, but cannot be processed to a mature state. In addition, the adult recipient retina presents a very different environment than the photoreceptor precursor donor. It seems that modulation of the recipient environment by ectopic development regulated growth factors for transplanted cells could generate efficient putative photoreceptors. The purpose of this review article was to investigate the signaling pathway of growth factors including: insulin-like growth factors (IGFs), fibroblast growth factors (FGF), Nerve growth factor (NGF), Brain-derived neurotrophic factor (BDNF), Taurin and Retinoic acid (RA) involved in the differentiation of neuroretina cell, like; photoreceptor and retinal progenitor cells. Given the results available in the related literature, the differentiation efficacy of ESCs toward the photoreceptor and retinal neurons and the important role of growth factors in activating signaling pathways such as Akt, Ras/Raf1/ and ERKs also inhibit the ASK1/JNK apoptosis pathway. Manipulating differentiated culture, growth factors can influence photoreceptor transplantation efficiency in retinal degenerative disease.

New solutions for old challenges in glaucoma treatment: is taurine an option to consider?

Glaucoma is a range of progressive optic neuropathies characterized by progressive retinal ganglion cell loss and visual field defects. It is recognized as a leading cause of irreversible blindness affecting more than 70 million people worldwide. Currently, reduction of intraocular pressure, a widely recognized risk factor for glaucoma development, is the only pharmacological strategy for slowing down retinal ganglion cell loss and disease progression. However, retinal ganglion cell death and visual field loss have been observed in normotensive glaucoma, suggesting that the disease process is partially independent of intraocular pressure. Taurine is one of the agents that have attracted attention of researchers recently. Taurine has been shown to be involved in multiple cellular functions, including a central role as a neurotransmitter, as a trophic factor in the central nervous system development, as an osmolyte, as a neuromodulator, and as a neuroprotectant. It also plays a role in the maintenance of the structural integrity of the membranes and in the regulation of calcium transport and homeostasis. Taurine is known to prevent N-methyl-D-aspartic acid-induced excitotoxic injury to retinal ganglion cells. A recently published study clearly demonstrated that taurine prevents retinal neuronal apoptosis both in vivo and in vitro. Protective effect of taurine may be attributed to direct inhibition of apoptosis, an activation of brain derived neurotrophic factor-related neuroprotective mechanisms and reduction of retinal oxidative and nitrosative stresses. Further studies are needed to fully explore the potential of taurine as a neuroprotective agent, so that it can be applied in clinical practice, particularly for the treatment of glaucoma. The objective of current review was to summarize recent evidence on neuroprotective properties of taurine in glaucoma.

Natural Products: Evidence for Neuroprotection to Be Exploited in Glaucoma

Glaucoma, a leading cause of irreversible blindness worldwide, is an optic neuropathy characterized by the progressive death of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is recognized as the main risk factor. Despite effective IOP-lowering therapies, the disease progresses in a significant number of patients. Therefore, alternative IOP-independent strategies aiming at halting or delaying RGC degeneration is the current therapeutic challenge for glaucoma management. Here, we review the literature on the neuroprotective activities, and the underlying mechanisms, of natural compounds and dietary supplements in experimental and clinical glaucoma.

Metabolomic profiling of aqueous humor from glaucoma patients - The metabolomics in surgical ophthalmological patients (MISO) study

Glaucoma is still a poorly understood disease with a clear need for new biomarkers to help in diagnosis and potentially offer new therapeutic targets. We aimed to determine if the metabolic profile of aqueous humor (AH) as determined by nuclear magnetic resonance (NMR) spectroscopy allows the distinction between primary open-angle glaucoma patients and control subjects, and to distinguish between high-tension (POAG) and normal-tension glaucoma (NTG). We analysed the AH of patients with POAG, NTG and control subjects (n = 30/group). ¹H NMR spectra were acquired using a 400 MHz spectrometer. Principle component analysis (PCA), machine learning algorithms and descriptive statistics were applied to analyse the metabolic variance between groups, identify the spectral regions, and hereby potential metabolites that can act as biomarkers for glaucoma. According to PCA, fourteen regions of the NMR spectra were significant in explaining the metabolic variance between the glaucoma and control groups, with no differences found between POAG and NTG groups. These regions were further used in building a classifier for separating glaucoma from control patients, which achieved an AUC of 0.93. Peak integration was performed on these regions and a statistical analysis, after false discovery rate correction and adjustment for the different perioperative topical drug regimen, revealed that five of them were significantly different between groups. The glaucoma group showed a higher content in regions typical for betaine and taurine, possibly linked to neuroprotective mechanisms, and also a higher content in regions that are typical for glutamate, which can indicate damaged neurons and oxidative stress. These results show how aqueous humor metabolomics based on NMR spectroscopy can distinguish glaucoma patients from controls with a high accuracy. Further studies are needed to validate these results in order to incorporate them in clinical practice.

Atherosclerosis Linked to Aberrant Amino Acid Metabolism and Immunosuppressive Amino Acid Catabolizing Enzymes

Cardiovascular disease is the leading global health concern and responsible for more deaths worldwide than any other type of disorder. Atherosclerosis is a chronic inflammatory disease in the arterial wall, which underpins several types of cardiovascular disease. It has emerged that a strong relationship exists between alterations in amino acid (AA) metabolism and the development of atherosclerosis. Recent studies have reported positive correlations between levels of branched-chain amino acids (BCAAs) such as leucine, valine, and isoleucine in plasma and the occurrence of metabolic disturbances. Elevated serum levels of BCAAs indicate a high cardiometabolic risk. Thus, BCAAs may also impact atherosclerosis prevention and offer a novel therapeutic strategy for specific individuals at risk of coronary events. The metabolism of AAs, such as L-arginine, homoarginine, and L-tryptophan, is recognized as a critical regulator of vascular homeostasis. Dietary intake of homoarginine, taurine, and glycine can improve atherosclerosis by endothelium remodeling. Available data also suggest that the regulation of AA metabolism by indoleamine 2,3-dioxygenase (IDO) and arginases 1 and 2 are mediated through various immunological signals and that immunosuppressive AA metabolizing enzymes are promising therapeutic targets against atherosclerosis. Further clinical studies and basic studies that make use of animal models are required. Here we review recent data examining links between AA metabolism and the development of atherosclerosis.

VEGF is an autocrine/paracrine neuroprotective factor for injured retinal ganglion neurons

Vascular endothelial growth factor-A (VEGF) is the angiogenic factor promoting the pathological neovascularization in age-related macular degeneration (AMD) or diabetic macular edema (DME). Evidences have suggested a neurotrophic and neuroprotective role of VEGF, albeit in retina, cellular mechanisms underlying the VEGF neuroprotection remain elusive. Using purified adult retinal ganglion cells (RGCs) in culture, we demonstrated here that VEGF is released by RGCs themselves to promote their own survival, while VEGF neutralization by specific antibodies or traps drastically reduced the RGC survival. These results indicate an autocrine VEGF neuroprotection on RGCs. In parallel, VEGF produced by mixed retinal cells or by mesenchymal stem cells exerted a paracrine neuroprotection on RGCs. Such neuroprotective effect was obtained using the recombinant VEGF-B, suggesting the involvement of VEGF-R1 pathway in VEGF-elicited RGC survival. Finally, glaucomatous patients injected with VEGF traps (ranibizumab or aflibercept) due to either AMD or DME comorbidity, showed a significant reduction of RGC axon fiber layer thickness, consistent with the plausible reduction of the VEGF autocrine stimulation of RGCs. Our results provide evidence of the autocrine neuroprotective function of VEGF on RGCs is crucially involved to preserve injured RGCs such as in glaucomatous patients.

Role of Taurine Transporter in the Retinal Uptake of Vigabatrin

Vigabatrin (VGB) is a first-line drug used for treatment of infantile spasms. On therapeutic dose, VGB accumulates in the retina causing permanent peripheral visual field constriction. The mechanism involved in retinal accumulation of VGB is ambiguous. In the present study, mechanism of VGB transport into retina was evaluated. VGB uptake into retina was studied in vitro using human adult retinal pigment epithelial (ARPE-19) cells as a model for outer blood retinal barrier. The VGB cell uptake studies demonstrated saturation kinetics with K_m value of 13.1 mM and uptake was significantly increased at pH 7.4 and hyperosmolar conditions indicating involvement of carrier-mediated Na⁺-Cl^--dependent transporter. In the presence of taurine transporter (TauT) substrates (taurine and GABA) and inhibitor guanidinoethyl sulfonate (GES), the uptake of VGB decreased significantly demonstrating contribution of TauT. The VGB retinal levels in rats were decreased by 1.5- and 1.3-folds on chronic administration of GES and taurine, respectively. In conclusion, this study demonstrated the TauT involvement in VGB uptake and accumulation in retina.

Taurocholic acid inhibits features of age-related macular degeneration in vitro

Previous metabolomics studies from our lab found altered plasma levels of bile acids in patients with age-related macular degeneration (AMD) compared to controls. In this study, we investigated the ability of the bile acid taurocholic acid (TCA) to inhibit features of AMD modeled in vitro. Paraquat was used to induce oxidative stress in HRPEpiC primary retinal pigment epithelial (RPE) cells. Cells were treated with 300 μM paraquat alone or with TCA (10, 50, 100, 200, or 500 μM). RPE tight junction integrity was assessed via ZO-1 immunofluorescence and transepithelial electrical resistance (TEER) measurements. RF/6A macaque choroidal endothelial cells were treated with 100 ng/mL vascular endothelial growth factor (VEGF) to induce angiogenesis. The effect of TCA on VEGF-induced angiogenesis was evaluated with cell proliferation, cell migration, and tube formation assays. Addition of TCA at 100 (P = 8.6 × 10^-4), 200 (P = 0.0035), and 500 (P = 2.1 × 10^-4) μM resulted in significant preservation of TEER in paraquat treated cells. In RF/6A cells, TCA did not significantly affect VEGF-induced cell proliferation. VEGF-induced migration of RF/6A cells was significantly inhibited at TCA concentrations of 100 (P = 0.010), 200 (P = 0.023) and 500 (P = 0.0049) μM. VEGF-induced tube formation was significantly inhibited when treated with 200 (P = 0.014) and 500 (P = 7.1 × 10^-4) μM TCA. In vitro, TCA promoted RPE cell integrity and diminished VEGF-induced choroidal endothelial cell migration and tube formation. This suggests that TCA may have protective effects against both degenerative and neovascular AMD.

Effect of an oral supplementation with a formula containing R-lipoic acid in glaucoma patients

OBJECTIVE

To analyse the safety and effectiveness of the oral administration of a commercialised supplement containing R-alpha lipoic acid, taurine, vitamins C and E, lutein, zeaxanthin, zinc, copper and docosahexaenoic acid, in patients with primary open angle glaucoma (POAG), and in control subjects.

MATERIAL AND METHODS

A prospective study of cases and controls was carried out, including 30 participants of both genders that were divided into: POAG Group (n=15) and a control group (CG; n=15), assigned to the oral intake of NuaDHA preparations Vision® (1 pill/day)+NuaDHA 1000 (2 pills/day) for 6 months. Participants were interviewed, ophthalmologically examined, and peripheral blood was taken for routine analysis and the determination of the pro-oxidant (malondialdehyde) and total antioxidant status. Statistical analysis was performed using the SPSS 22.0 program.

RESULTS

After 6 months of supplementation, there was a significant increase in the plasma total antioxidant status (1.073±0.090mM vs 1.276±0.107mM, P=.028), along with a parallel decrease in malondialdehyde (7.066±1.070μM vs 2.771±0.462μM, P=.005) in the POAG group. The malondialdehyde also decreased in the control group (6.17±1.336 vs. 2.51±0.391, P=.028). The Schirmer test improved (20-30%) and the subjective dry eye signs/symptoms noticeably decreased in the POAG group versus the CG.

CONCLUSIONS

Formulations containing antioxidant vitamins, R-alpha lipoic acid and docosahexaenoic acid, administered for 6 consecutive months, counteracted the oxidative stress by further stabilising the morphological/functional parameters of both the ocular surface and the glaucoma, without presenting with adverse effects or intolerances.

Taurine Protects Retinal Cells and Improves Synaptic Connections in Early Diabetic Rats

Purpose: Taurine has long been thought to be involved in retinal protection from retinal degenerative diseases, but the underlying molecular mechanisms remain unclear. Retinal neurodegeneration is an early event in the pathogenesis of diabetic retinopathy (DR) that precedes and participates in the microcirculatory abnormalities that occur in DR. Our objective was to investigate the role and mechanisms of taurine in early diabetic retinas.Methods: Eight-week-old STZ-induced diabetic rats and control animals were randomly assigned to receive taurine or vehicle by intraperitoneal injection or by intragastric administration. The retinal function and retinal cell counts were evaluated using an electroretinography (ERG) and immunofluorescence microscopy. Plasma amino acids were measured by ion-exchange chromatography (IEC). The expression levels of retinal taurine transporter (Tau-T), mitochondria-dependent apoptosis-associated genes and reactive gliosis markers were studied by western blotting and immunofluorescence. Pre- and post-synaptic markers (PSD95 and mGluR6) in outer plexiform layer (OPL), and the bipolar cell marker protein kinase C alpha (PKCα) were localized by immunofluorescence. Levels of PSD95 and mGluR6 were determined by quantitative western blot.Results: Taurine significantly prevented the reduction of photopic b-wave amplitude and retinal cone cells and ganglion cells loss and maintained the Bcl-2/Bax ratio balance in diabetic rats. Taurine also prevented the upregulation of glial fibrillary acidic protein (GFAP) and reduced retinal reactive gliosis. Taurine reduced plasma glutamate and tyrosine levels, which were elevated in diabetic rats. Moreover, mGluR6 levels reduction detected by western blot and immunofluorescence in diabetic retinas was inhibited and the displacement of mGluR6 in OPL into the inner nuclear layer (INL) detected by immunofluorescence was reduced by Taurine treatment.Conclusion: Taurine may protect retinal cells from diabetic attacks by activating Tau-T, reducing retinal reactive gliosis, improving retinal synaptic connections and decreasing retinal cell apoptosis. Thus, taurine treatment may be a novel approach for early DR.

The primate model for understanding and restoring vision

Retinal degenerative diseases caused by photoreceptor cell death are major causes of irreversible vision loss. As only primates have a macula, the nonhuman primate (NHP) models have a crucial role not only in revealing biological mechanisms underlying high-acuity vision but also in the development of therapies. Successful translation of basic research findings into clinical trials and, moreover, approval of the first therapies for blinding inherited and age-related retinal dystrophies has been reported in recent years. This article explores the value of the NHP models in understanding human vision and reviews their contribution to the development of innovative therapeutic strategies to save and restore vision.

Retinal Ganglion Cell Death as a Late Remodeling Effect of Photoreceptor Degeneration

Inherited or acquired photoreceptor degenerations, one of the leading causes of irreversible blindness in the world, are a group of retinal disorders that initially affect rods and cones, situated in the outer retina. For many years it was assumed that these diseases did not spread to the inner retina. However, it is now known that photoreceptor loss leads to an unavoidable chain of events that cause neurovascular changes in the retina including migration of retinal pigment epithelium cells, formation of “subretinal vascular complexes”, vessel displacement, retinal ganglion cell (RGC) axonal strangulation by retinal vessels, axonal transport alteration and, ultimately, RGC death. These events are common to all photoreceptor degenerations regardless of the initial trigger and thus threaten the outcome of photoreceptor substitution as a therapeutic approach, because with a degenerating inner retina, the photoreceptor signal will not reach the brain. In conclusion, therapies should be applied early in the course of photoreceptor degeneration, before the remodeling process reaches the inner retina.

Taurine administration ablates sepsis induced diaphragm weakness

Infection induced diaphragm weakness is a major contributor to death and prolonged mechanical ventilation in critically ill patients. Infection induced muscle dysfunction is associated with activation of muscle proteolytic enzymes, and taurine is known to suppress proteolysis. We therefore postulated that taurine administration may prevent infection induced diaphragm dysfunction. The purpose of this study was to test this hypothesis using a clinically relevant animal model of infection, i.e. cecal ligation puncture induced sepsis (CLP). Studies were performed on (n = 5-7 mice/group): (a) sham operated controls, (b) animals with sepsis induced by CLP, (c) sham operated animals given taurine (75 mg/kg/d, intraperitoneally), and (d) CLP animals given taurine. At intervals after surgery animals were euthanized, diaphragm force generation measured in vitro, and diaphragm calpain, caspase and proteasomal activity determined. CLP elicited a large reduction in diaphragm specific force generation at 24 h (1-150 Hz, p < 0.001) and taurine significantly attenuated CLP induced diaphragm weakness at all stimulation frequencies (p < 0.001). CLP induced significant increases in diaphragm calpain, caspase and proteasomal activity; taurine administration prevented increases in the activity of all three pathways. In additional time course experiments, diaphragm force generation remained at control levels over 72 h in CLP animals treated with daily taurine administration, while CLP animals demonstrated severe, sustained reductions in diaphragm strength (p < 0.01 for all time points). Our results indicate that taurine administration prevents infection induced diaphragm weakness and reduces activation of three major proteolytic pathways. Because this agent is has been shown to be safe, non-toxic when administered to humans, taurine may have a role in treating infection induced diaphragm weakness. Future clinical studies will be needed to assess this possibility.

Systemic taurine treatment provides neuroprotection against retinal photoreceptor degeneration and visual function impairments

Objective

Retinitis pigmentosa causes progressive photoreceptor degeneration in the subjects while no clinical therapy exists. The present study sought to evaluate the potential protective effects of taurine on a pharmacologically induced RP animal model.

Methods

Photoreceptor degeneration in mice was induced by an intraperitoneal injection of N-methyl-N-nitrosourea (MNU). The MNU-administrated mouse received taurine treatment and then they were examined by electroretinography, spectral-domain optical coherence tomography, optokinetic test, and histological and immunohistochemistry assay.

Results

Prominent taurine deficiency was found in the retinas of MNU-administered mice. Intravenous taurine treatment increased significantly the retinal taurine level. Morphological studies showed that taurine could alleviate the retinal disorganizations in the MNU-induced mice. Taurine also ameliorated the visual impairments in the MNU-induced mice as evidenced by functional examinations. Immunostaining experiments demonstrated that both the M-cone and S-cone populations in the degenerative retinas are rescued by taurine. In particular, the M-cone photoreceptors in superior-temporal quadrant and the S-cone photoreceptors in inferior-nasal quadrant were preferentially rescued. Mechanism study showed that the photoreceptor apoptosis and oxidative stress in the degenerative retina were effectively alleviated by taurine treatment.

Conclusion

Taurine is protective against the MNU-induced photoreceptor degeneration. Systemic taurine administration may act as a promising therapeutic potion for retinopathies with chronic cycle.

Biodegradable Thermosensitive PLGA-PEG-PLGA Polymer for Non-irritating and Sustained Ophthalmic Drug Delivery

Challenges of ophthalmic drug delivery arise from not only the limited solubility of hydrophobic therapeutics, but also the restricted permeability and fast clearance of drugs due to the complex anatomy and physiology of the eyes. Biodegradable thermosensitive polymer, poly(dl-lactide-co-glycolide-b-ethylene glycol-b-dl-lactide-co-glycolide) (PLGA-PEG-PLGA) is a desirable ophthalmic drug delivery system because it can be formulated into injectable solution which forms gel in situ to provide prolonged drug release. In this study, excellent biocompatibility of blank PLGA-PEG-PLGA (1800-1500-1800) thermogel was demonstrated with insignificant difference from saline noted in rat eye enucleation test, in vivo inflammation test upon topical instillation, and subconjunctival injection. After subconjunctival injection, thermogel formulations loaded with hydrophilic (rhodamine B) or hydrophobic (coumarin 6) fluorescent dyes were retained up to 4 weeks in eye tissues and significantly higher level was detected than rhodamine B solution or coumarin 6 suspension in weeks 3 and 4. Moreover, in vivo whole body imaging showed that dye-loaded (sulfo-cyanine 7 NHS ester, Cy7; or cyanine 7.5 alkyne, Cy7.5) thermogels had longer retention at the injection site and retarded release to other body parts than dye solutions. Generally, the release rate of hydrophobic dyes (coumarin 6 and Cy7.5) was much slower than that of the hydrophilic dyes (rhodamine B and Cy7) from the thermogel. In summary, the thermogel was safe for ophthalmic drug delivery and could deliver both hydrophobic and hydrophilic compounds for sustained drug release into eye tissues with single subconjunctival injection for better patient compliance and reduced risks on repeated injection.

Genetically-modified human mesenchymal stem cells to express erythropoietin enhances differentiation into retinal photoreceptors: An in-vitro study

Dysfunctional or death of retinal photoreceptors is an irreversible phenomenon that is closely associated with a broad range of retinal degenerative diseases, such as retinitis pigmentosa and age-related macular degeneration (AMD), resulting in successive loss of visual function and blindness. In search for viable treatment for retinal degenerative diseases, mesenchymal stem cells (MSCs) has demonstrated promising therapeutic capabilities to repair and replace damaged photoreceptor cells in both in vitro and in vivo conditions. Nevertheless, the dearth of MSC differentiation capacity into photoreceptors has limited its use in cell replacement therapy. Erythropoietin (EPO) has vital role in early neural retinal cell differentiation and demonstrated rescue potential on dying photoreceptor cells. Hence, we aimed to evaluate the differentiation capacity of MSCs into photoreceptor cells in the presence of human EPO protein. We derived the MSC from human Wharton's jelly of umbilical cord and transduced the cells with lentivirus particles encoding EPO and green fluorescent protein (GFP) as reporter gene. The transduced cells were selectively cultured and induced to differentiate into photoreceptors by exposing to photoreceptor differentiation cocktail. Our preliminary results showed that transduced cells exposed to induction medium had an enhanced differentiation capacity when compared to non-transduced cells. Our results demonstrated a novel strategy to increase the yield of in vitro photoreceptor differentiation and may be potentially useful in improving the efficiency of stem cell transplantation for ocular disorders.

Metabolomic Profiling of Aqueous Humor in Glaucoma Points to Taurine and Spermine Deficiency: Findings from the Eye-D Study

We compared the metabolomic profile of aqueous humor from patients with primary open-angle glaucoma (POAG; n = 26) with that of a group of age- and sex-matched non-POAG controls (n = 26), all participants undergoing cataract surgery. Supervised paired partial least-squares discriminant analysis showed good predictive performance for test sets with a median area under the receiver operating characteristic of 0.89 and a p-value of 0.0087. Twenty-three metabolites allowed discrimination between the two groups. Univariate analysis after the Benjamini-Hochberg correction showed significant differences for 13 of these metabolites. The POAG metabolomic signature indicated reduced concentrations of taurine and spermine and increased concentrations of creatinine, carnitine, three short-chain acylcarnitines, 7 amino acids (glutamine, glycine, alanine, leucine, isoleucine, hydroxyl-proline, and acetyl-ornithine), 7 phosphatidylcholines, one lysophosphatidylcholine, and one sphingomyelin. This suggests an alteration of metabolites involved in osmoprotection (taurine and creatinine), neuroprotection (spermine, taurine, and carnitine), amino acid metabolism (7 amino acids and three acylcarnitines), and the remodeling of cell membranes drained by the aqueous humor (hydroxyproline and phospholipids). Five of these metabolic alterations, already reported in POAG plasma, concern spermine, C3 and C4 acylcarnitines, PC aa 34:2, and PC aa 36:4, thus highlighting their importance in the pathogenesis of glaucoma.

Disorganization of Retinal Inner Layers and Ellipsoid Zone Disruption Predict Visual Outcomes in Central Retinal Vein Occlusion

PURPOSE

To assess the associations and predictive value of spectral-domain (SD) OCT inner and outer retinal structural parameters and visual acuity (VA) outcomes in macular edema (ME) secondary to central retinal vein occlusion (CRVO).

DESIGN

Retrospective, longitudinal cohort study.

PARTICIPANTS

Eighty-four patients with ME secondary to CRVO receiving pro re nata anti-vascular endothelial growth factor (VEGF) therapy at 3 tertiary-level retina referral centers.

METHODS

In all participants, VA, demographic and clinical parameters, and SD OCT images from baseline, 3 months, and 12 months were reviewed. Spectral-domain OCT-based morphologic features in the 1500-μm foveal zone were analyzed by masked graders for disorganization of the retinal inner layers (DRIL), ellipsoid zone (EZ) and external limiting membrane disruption, cone outer segment tip (COST) visibility, cysts, subretinal and intraretinal fluid, and epiretinal membranes.

MAIN OUTCOME MEASURES

Spectral-domain OCT-based retinal structural parameters and VA outcomes.

RESULTS

In multivariate analyses adjusting for baseline VA, worsening VA over 1 year was associated with 1-year increases in DRIL (point estimate, 0.06 per 100 μm; P < 0.001) and EZ disruption (0.07 per 100 μm; P = 0.023), but decreased COST visibility (-0.09 per 100 μm; P = 0.018). A 3-month increase in DRIL (0.05 per 100 μm; P = 0.003) and EZ disruption (0.10 per 100 μm; P < 0.001) were the only factors predicting VA worsening over 1 year, after controlling for baseline VA. A multivariate model including 3-month evolution in DRIL, EZ disruption, and VA accounted for 86.3% of variability in 1-year VA change. Absolute differences between predicted and actual 1-year VA were within 2 lines in 80.9%. When DRIL increased by 250 μm or more over 3 months, no eyes showed VA improvement of 1 line or more in 1 year. When EZ disruption decreased by 250 μm or more over 3 months, no eyes worsened by 1 line or more over 1 year.

CONCLUSIONS

Early recovery over 3 months in both DRIL and EZ parameters are key drivers of 1-year VA outcomes. Predictive models incorporating 3-month changes in DRIL and EZ disruption support their usefulness as potential robust determinants of future VA.

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.

Antiapoptotic effect of taurine against NMDA-induced retinal excitotoxicity in rats

OBJECTIVE

N-methyl-D-aspartate (NMDA) excitotoxicity has been proposed to mediate apoptosis of retinal ganglion cells (RGCs) in glaucoma. Taurine (TAU) has been shown to have neuroprotective properties, thus we examined anti-apoptotic effect of TAU against retinal damage after NMDA exposure.

METHODOLOGY

Sprague-Dawley rats were divided into 5 groups of 33 each. Group 1 was administered intravitreally with PBS and group 2 was similarly injected with NMDA (160 nmol). Groups 3, 4 and 5 were injected with TAU (320 nmol) 24 hours before (pre-treatment), in combination (co-treatment) and 24 hours after (post-treatment) NMDA exposure respectively. Seven days after injection, rats were sacrificed; eyes were enucleated, fixed and processed for morphometric analysis, TUNEL and caspase-3 staining. Optic nerve morphology assessment was done using toluidine blue staining. The estimation of BDNF, pro/anti-apoptotic factors (Bax/Bcl-2) and caspase-3 activity in retina was done using ELISA technique.

RESULTS

Severe degenerative changes were observed in retinae after intravitreal NMDA exposure. The retinal morphology in the TAU pre-treated group appeared more similar to the control retinae and demonstrated a higher number of nuclei than the NMDA group both per 100 μm length (by 1.5-fold, p < 0.001) and per 100 μm² area (by 1.41-fold, p < 0.05) of the GCL. After NMDA exposure, visible axonal swelling was observed in optic nerve sections. In comparison with the changes observed in the NMDA treated group, the TAU treated group showed fewer prominent changes; axonal swelling was less frequent and less marked. Additionally, no marked glial cell changes were observed in the TAU-pretreated group. All TAU treated groups, particularly the pre-treated group, showed a significant decrease in the NMDA-induced optic nerve damage, with a 50% reduction (p < 0.001) in the mean grading compared to NMDA group. For the same, there was 25% decrease in co- and post-treatment groups, as compared with the NMDA group. Pre-treatment with TAU abolished apoptotic response to NMDA as indicated by decrease in the number of TUNEL- and caspase-3-positive cells. TAU pre-treatment also increased the Bcl-2 level (by 2.80-fold, p < 0.001) and decreased the level of Bax (by 34%, p < 0.01), and activity of caspase-3 (by 36%, p < 0.001) compared to NMDA group.

IN CONCLUSION

our study revealed that pre-treatment with TAU prevents NMDA-induced retinal cell apoptosis more effectively than co- and post-treatment with TAU.

Taurine Promotes Retinal Ganglion Cell Survival Through GABAB Receptor Activation

Retinal ganglion cell (RGC) degeneration occurs in numerous retinal diseases, either as a primary process like in glaucoma, or secondary to photoreceptor loss and no efficient compound targeting directly RGC neuroprotection is yet available. We previously described that taurine exerts a direct protective effect on RGCs cultured under serum-deprived conditions. Because taurine was known to have an agonist-like activity for GABA/glycine receptors, we investigated here if the taurine-elicited neuroprotective effect may be mediated through the activation of these receptors using selective antagonist ligands. RGCs were purified, seeded in 96-well plate and maintained in culture during 6 days in vitro. Viable cells were labelled with calcein and densities in full-well area were then automatically counted. Here we show that the protective effect of taurine against RGC loss observed under serum deprivation can be mediated through the GABAB receptor stimulation. Hence, two selective agonists, including baclofen, at this metabotropic GABAB receptor were found to reproduce taurine action by enhancing RGC survival in culture. This study suggests that GABAB receptor stimulation provides direct neuroprotection for RGCs. Accordingly, drugs targeting GABAB receptor may represent a new way for the prevention of RGC degeneration.

Effects and Mechanisms of Taurine as a Therapeutic Agent

Taurine is an abundant, β-amino acid with diverse cytoprotective activity. In some species, taurine is an essential nutrient but in man it is considered a semi-essential nutrient, although cells lacking taurine show major pathology. These findings have spurred interest in the potential use of taurine as a therapeutic agent. The discovery that taurine is an effective therapy against congestive heart failure led to the study of taurine as a therapeutic agent against other disease conditions. Today, taurine has been approved for the treatment of congestive heart failure in Japan and shows promise in the treatment of several other diseases. The present review summarizes studies supporting a role of taurine in the treatment of diseases of muscle, the central nervous system, and the cardiovascular system. In addition, taurine is extremely effective in the treatment of the mitochondrial disease, mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), and offers a new approach for the treatment of metabolic diseases, such as diabetes, and inflammatory diseases, such as arthritis. The review also addresses the functions of taurine (regulation of antioxidation, energy metabolism, gene expression, ER stress, neuromodulation, quality control and calcium homeostasis) underlying these therapeutic actions.

Phenotypic characterization of P23H and S334ter rhodopsin transgenic rat models of inherited retinal degeneration

We produced 8 lines of transgenic (Tg) rats expressing one of two different rhodopsin mutations in albino Sprague-Dawley (SD) rats. Three lines were generated with a proline to histidine substitution at codon 23 (P23H), the most common autosomal dominant form of retinitis pigmentosa in the United States. Five lines were generated with a termination codon at position 334 (S334ter), resulting in a C-terminal truncated opsin protein lacking the last 15 amino acid residues and containing all of the phosphorylation sites involved in rhodopsin deactivation, as well as the terminal QVAPA residues important for rhodopsin deactivation and trafficking. The rates of photoreceptor (PR) degeneration in these models vary in proportion to the ratio of mutant to wild-type rhodopsin. The models have been widely studied, but many aspects of their phenotypes have not been described. Here we present a comprehensive study of the 8 Tg lines, including the time course of PR degeneration from the onset to one year of age, retinal structure by light and electron microscopy (EM), hemispheric asymmetry and gradients of rod and cone degeneration, rhodopsin content, gene dosage effect, rapid activation and invasion of the outer retina by presumptive microglia, rod outer segment disc shedding and phagocytosis by the retinal pigmented epithelium (RPE), and retinal function by the electroretinogram (ERG). The biphasic nature of PR cell death was noted, as was the lack of an injury-induced protective response in the rat models. EM analysis revealed the accumulation of submicron vesicular structures in the interphotoreceptor space during the peak period of PR outer segment degeneration in the S334ter lines. This is likely due to the elimination of the trafficking consensus domain as seen before as with other rhodopsin mutants lacking the C-terminal QVAPA. The 8 rhodopsin Tg lines have been, and will continue to be, extremely useful models for the experimental study of inherited retinal degenerations.

Rational Basis for Nutraceuticals in the Treatment of Glaucoma

BACKGROUND

Glaucoma, the second leading cause of blindness worldwide, is a chronic optic neuropathy characterized by progressive retinal ganglion cell (RGC) axons degeneration and death. Primary open-angle glaucoma (OAG), the most common type, is often associated with increased intraocular pressure (IOP), however other factors have been recognized to partecipate to the patogenesis of the optic neuropathy. IOP-independent mechanisms that contribute to the glaucoma-related neurodegeneration include oxidative stress, excitotoxicity, neuroinflammation, and impaired ocular blood flow. The involvement of several and diverse factors is one of the reasons for the progression of glaucoma observed even under efficient IOP control with the currently available drugs.

METHODS

Current research and online content related to the potential of nutritional supplements for limiting retinal damage and improving RGC survival is reviewed.

RESULTS

Recent studies have suggested a link between dietary factors and glaucoma risk. Particularly, some nutrients have proven capable of lowering IOP, increase circulation to the optic nerve, modulate excitotoxicity and promote RGC survival. However, the lack of clinical trials limit their current therapeutic use. The appropriate use of nutraceuticals that may be able to modify the risk of glaucoma may provide insight into glaucoma pathogenesis and decrease the need for, and therefore the side effects from, conventional therapies.

CONCLUSION

The effects of nutrients with anti-oxidant and neuroprotective properties are of great interest and nutraceuticals may offer some therapeutic potential although a further rigorous evaluation of nutraceuticals in the treatment of glaucoma is needed to determine their safety and efficacy.

Taurine protects against retinal and optic nerve damage induced by endothelin-1 in rats via antioxidant effects

Endothelin-1 (ET-1), a potent vasoconstrictor, is involved in retinal vascular dysregulation and oxidative stress in glaucomatous eyes. Taurine (TAU), a naturally occurring free amino acid, is known for its neuroprotective and antioxidant properties. Hence, we evaluated its neuroprotective properties against ET-1 induced retinal and optic nerve damage. ET-1 was administered intravitreally to Sprague-Dawley rats and TAU was injected as pre-, co- or post-treatment. Animals were euthanized seven days post TAU injection. Retinae and optic nerve were examined for morphology, and were also processed for caspase-3 immunostaining. Retinal redox status was estimated by measuring retinal superoxide dismutase, catalase, glutathione, and malondialdehyde levels using enzyme-linked immuosorbent assay. Histopathological examination showed significantly improved retinal and optic nerve morphology in TAU-treated groups. Morphometric examination showed that TAU pre-treatment provided marked protection against ET-1 induced damage to retina and optic nerve. In accordance with the morphological observations, immunostaining for caspase showed a significantly lesser number of apoptotic retinal cells in the TAU pre-treatment group. The retinal oxidative stress was reduced in all TAU-treated groups, and particularly in the pre-treatment group. The findings suggest that treatment with TAU, particularly pre-treatment, prevents apoptosis of retinal cells induced by ET-1 and hence prevents the changes in the morphology of retina and optic nerve. The protective effect of TAU against ET-1 induced retinal and optic nerve damage is associated with reduced retinal oxidative stress.

Inhibition of Starvation-Triggered Endoplasmic Reticulum Stress, Autophagy, and Apoptosis in ARPE-19 Cells by Taurine through Modulating the Expression of Calpain-1 and Calpain-2

Age-related macular degeneration (AMD) is a complex disease with multiple initiators and pathways that converge on death for retinal pigment epithelial (RPE) cells. In this study, effects of taurine on calpains, autophagy, endoplasmic reticulum (ER) stress, and apoptosis in ARPE-19 cells (a human RPE cell line) were investigated. We first confirmed that autophagy, ER stress and apoptosis in ARPE-19 cells were induced by Earle’s balanced salt solution (EBSS) through starvation to induce RPE metabolic stress. Secondly, inhibition of ER stress by 4-phenyl butyric acid (4-PBA) alleviated autophagy and apoptosis, and suppression of autophagy by 3-methyl adenine (3-MA) reduced the cell apoptosis, but the ER stress was minimally affected. Thirdly, the apoptosis, ER stress and autophagy were inhibited by gene silencing of calpain-2 and overexpression of calpain-1, respectively. Finally, taurine suppressed both the changes of the important upstream regulators (calpain-1 and calpain-2) and the activation of ER stress, autophagy and apoptosis, and taurine had protective effects on the survival of ARPE-19 cells. Collectively, this data indicate that taurine inhibits starvation-triggered endoplasmic reticulum stress, autophagy, and apoptosis in ARPE-19 cells by modulating the expression of calpain-1 and calpain-2.

Neuroprotective Effect of Magnesium Acetyltaurate Against NMDA-Induced Excitotoxicity in Rat Retina

Glutamate excitotoxicity plays a major role in the loss of retinal ganglion cells (RGCs) in glaucoma. The toxic effects of glutamate on RGCs are mediated by the overstimulation of N-methyl-D-aspartate (NMDA) receptors. Accordingly, NMDA receptor antagonists have been suggested to inhibit excitotoxicity in RGCs and delay the progression and visual loss in glaucoma patients. The purpose of the present study was to examine the potential neuroprotective effect of Mg acetyltaurate (MgAT) on RGC death induced by NMDA. MgAT was proposed mainly due to the combination of magnesium (Mg) and taurine which may provide neuroprotection by dual mechanisms of action, i.e., inhibition of NMDA receptors and antioxidant effects. Rats were divided into 5 groups and were given intravitreal injections. Group 1 (PBS group) was injected with vehicle; group 2 (NMDA group) was injected with NMDA while groups 3 (pre-), 4 (co-), and 5 (post-) treatments were injected with MgAT, 24 h before, in combination or 24 h after NMDA injection respectively. NMDA and MgAT were injected in PBS at doses 160 and 320 nmol, respectively. Seven days after intravitreal injection, the histological changes in the retina were evaluated using hematoxylin & eosin (H&E) staining. Optic nerves were dissected and stained in Toluidine blue for grading on morphological neurodegenerative changes. The extent of apoptosis in retinal tissue was assessed by TUNEL assay and caspase-3 immunohistochemistry staining. The estimation of neurotrophic factor, oxidative stress, pro/anti-apoptotic factors and caspase-3 activity in retina was done using enzyme-linked immunosorbent assay (ELISA) technique. The retinal morphometry showed reduced thickness of ganglion cell layer (GCL) and reduction in the number of retinal cells in GCL in NMDA group compared to the MgAT-treated groups. TUNEL and caspase-3 staining showed increased number of apoptotic cells in inner retina. The results were further corroborated by the estimation of neurotrophic factor, oxidative stress, pro/anti-apoptotic factors, and caspase-3 activity in retina. In conclusion, current study revealed that intravitreal MgAT prevents retinal and optic nerve damage induced by NMDA. Overall, our data demonstrated that the pretreatment with MgAT was more effective than co- and posttreatment. This protective effect of MgAT against NMDA-induced retinal cell apoptosis could be attributed to the reduction of retinal oxidative stress and activation of BDNF-related neuroprotective mechanisms.

Protective effect of magnesium acetyltaurate against endothelin-induced retinal and optic nerve injury

Vascular dysregulation has long been recognized as an important pathophysiological factor underlying the development of glaucomatous neuropathy. Endothelin-1 (ET1) has been shown to be a key player due to its potent vasoconstrictive properties that result in retinal ischemia and oxidative stress leading to retinal ganglion cell (RGC) apoptosis and optic nerve (ON) damage. In this study we investigated the protective effects of magnesium acetyltaurate (MgAT) against retinal cell apoptosis and ON damage. MgAT was administered intravitreally prior to, along with or after administration of ET1. Seven days post-injection, animals were euthanized and retinae were subjected to morphometric analysis, TUNEL and caspase-3 staining. ON sections were stained with toluidine blue and were graded for neurodegenerative effects. Oxidative stress was also estimated in isolated retinae. Pre-treatment with MgAT significantly lowered ET1-induced retinal cell apoptosis as measured by retinal morphometry and TUNEL staining. This group of animals also showed significantly lesser caspase-3 activation and significantly reduced retinal oxidative stress compared to the animals that received intravitreal injection of only ET1. Additionally, the axonal degeneration in ON was markedly reduced in MgAT pretreated animals. The animals that received MgAT co- or post-treatment with ET1 also showed improvement in all parameters; however, the effects were not as significant as observed in MgAT pretreated animals. The current study showed that the intravitreal pre-treatment with MgAT reduces caspase-3 activation and prevents retinal cell apoptosis and axon loss in ON induced by ET1. This protective effect of ET1 was associated with reduced retinal oxidative stress.

Effect of Antiglaucoma Medicine on Intraocular Pressure in DBA/2J Mice

BACKGROUND

The DBA/2J mouse strain is known to develop glaucomatous changes. Intraocular pressure (IOP) fluctuations affected by age or antiglaucoma drug administration were compared among three mouse strains, DBA/2J, C57BL/6, and BALB/c.

METHODS

IOP was measured using the TonoLab tonometer under systemic anesthesia. For each mouse strain, the effects of age and topical administration of antiglaucoma medications (timolol maleate, dorzolamide, brimonidine tartrate, and travoprost) were assessed, and results were compared among the three strains.

RESULTS

IOP started to rise in DBA/2J mice at 21 weeks of age. The highest values of IOP were distributed from 18 to 51 mm Hg. Eighty percent of DBA/2J mice showed maximum IOP at either 35 or 46 weeks. IOP of C57BL/6 ranged from 9 to 14 mm Hg as the mice aged. Treatment with any of the antiglaucoma medications resulted in IOP-lowering effects in all three strains. The difference in levels before and after administration ranged from 6 to 10 mm Hg on average in DBA/2J.

CONCLUSION

DBA/2J mice are a useful animal model to study the effects of antiglaucoma therapy.

Towards axonal regeneration and neuroprotection in glaucoma: Rho kinase inhibitors as promising therapeutics

Due to a prolonged life expectancy worldwide, the incidence of age-related neurodegenerative disorders such as glaucoma is increasing. Glaucoma is the second cause of blindness, resulting from a slow and progressive loss of retinal ganglion cells (RGCs) and their axons. Up to now, intraocular pressure (IOP) reduction is the only treatment modality by which ophthalmologists attempt to control disease progression. However, not all patients benefit from this therapy, and the pathophysiology of glaucoma is not always associated with an elevated IOP. These limitations, together with the multifactorial etiology of glaucoma, urge the pressing medical need for novel and alternative treatment strategies. Such new therapies should focus on preventing or retarding RGC death, but also on repair of injured axons, to ultimately preserve or improve structural and functional connectivity. In this respect, Rho-associated coiled-coil forming protein kinase (ROCK) inhibitors hold a promising potential to become very prominent drugs for future glaucoma treatment. Their field of action in the eye does not seem to be restricted to IOP reduction by targeting the trabecular meshwork or improving filtration surgery outcome. Indeed, over the past years, important progress has been made in elucidating their ability to improve ocular blood flow, to prevent RGC death/increase RGC survival and to retard axonal degeneration or induce proper axonal regeneration. Within this review, we aim to highlight the currently known capacity of ROCK inhibition to promote neuroprotection and regeneration in several in vitro, ex vivo and in vivo experimental glaucoma models.

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.

Primary retinal cultures as a tool for modeling diabetic retinopathy: an overview

Experimental models of diabetic retinopathy (DR) have had a crucial role in the comprehension of the pathophysiology of the disease and the identification of new therapeutic strategies. Most of these studies have been conducted in vivo, in animal models. However, a significant contribution has also been provided by studies on retinal cultures, especially regarding the effects of the potentially toxic components of the diabetic milieu on retinal cell homeostasis, the characterization of the mechanisms on the basis of retinal damage, and the identification of potentially protective molecules. In this review, we highlight the contribution given by primary retinal cultures to the study of DR, focusing on early neuroglial impairment. We also speculate on possible themes into which studies based on retinal cell cultures could provide deeper insight.