Alterations in glutamate cysteine ligase content in the retina of two retinitis pigmentosa animal models

Inhibition of altered Orai1 channels in Müller cells protects photoreceptors in retinal degeneration

The expressions of ion channels by Müller glial cells (MGCs) may change in response to various retinal pathophysiological conditions. There remains a gap in our understanding of MGCs' responses to photoreceptor degeneration towards finding therapies. The study explores how an inhibition of store-operated Ca2+ entry (SOCE) and its major component, Orai1 channel, in MGCs protects photoreceptors from degeneration. The study revealed increased Orai1 expression in the MGCs of retinal degeneration 10 (rd10) mice. Enhanced expression of oxidative stress markers was confirmed as a crucial pathological mechanism in rd10 retina. Inducing oxidative stress in rat MGCs resulted in increasing SOCE and Ca2+ release-activated Ca2+ (CRAC) currents. SOCE inhibition by 2-Aminoethoxydiphenyl borate (2-APB) protected photoreceptors in degenerated retinas. Finally, molecular simulations proved the structural and dynamical features of 2-APB to the target structure Orai1. Our results provide new insights into the physiology of MGCs regarding retinal degeneration and shed a light on SOCE and Orai1 as new therapeutic targets.

Mechanism of Cone Degeneration in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a group of genetic disorders resulting in inherited blindness due to the degeneration of rod and cone photoreceptors. The various mechanisms underlying rod degeneration primarily rely on genetic mutations, leading to night blindness initially. Cones gradually degenerate after rods are almost eliminated, resulting in varying degrees of visual disability and blindness. The mechanism of cone degeneration remains unclear. An understanding of the mechanisms underlying cone degeneration in RP, a highly heterogeneous disease, is essential to develop novel treatments of RP. Herein, we review recent advancements in the five hypotheses of cone degeneration, including oxidative stress, trophic factors, metabolic stress, light damage, and inflammation activation. We also discuss the connection among these theories to provide a better understanding of secondary cone degeneration in RP. Five current mechanisms of cone degenerations in RP Interactions among different pathways are involved in RP.

Modulating antioxidant systems as a therapeutic approach to retinal degeneration

The human retina is facing a big challenge of reactive oxygen species (ROS) from endogenous and exogenous sources. Excessive ROS can cause damage to DNA, lipids, and proteins, triggering abnormal redox signaling, and ultimately lead to cell death. Thus, oxidative stress has been observed in inherited retinal diseases as a common hallmark. To counteract the detrimental effect of ROS, cells are equipped with various antioxidant defenses. In this review, we will focus on the antioxidant systems in the retina and how they can protect retina from oxidative stress. Both small antioxidants and antioxidant enzymes play a role in ROS removal. Particularly, the thioredoxin and glutaredoxin systems, as the major antioxidant systems in mammalian cells, exert functions in redox signaling regulation via modifying cysteines in proteins. In addition, the thioredoxin-like rod-derived cone viability factor (RdCVFL) and thioredoxin interacting protein (TXNIP) can modulate metabolism in photoreceptors and promote their survival. In conclusion, elevating the antioxidant capacity in retina is a promising therapy to curb the progress of inherited retinal degeneration.

Impact of Plasma Oxidative Stress Markers on Post-race Recovery in Ultramarathon Runners: A Sex and Age Perspective Overview

Oxidative stress has been widely studied in association to ultra-endurance sports. Although it is clearly demonstrated the increase in reactive oxygen species and free radicals after these extreme endurance exercises, the effects on the antioxidant defenses and the oxidative damage to macromolecules, remain to be fully clarified. Therefore, the aim of this study was to elucidate the impact of an ultramarathon race on the plasma markers of oxidative stress of 32 runners and their post-race recovery, with especial focused on sex and age effect. For this purpose, the antioxidant enzymes glutathione peroxidase (GPx) and glutathione reductase (GR) activity, as well as the lipid peroxidation product malondialdehyde (MDA) and the carbonyl groups (CG) content were measured before the race, in the finish line and 24 and 48 h after the race. We have reported an increase of the oxidative damage to lipids and proteins (MDA and CG) after the race and 48 h later. Moreover, there was an increase of the GR activity after the race. No changes were observed in runners' plasma GPx activity throughout the study. Finally, we have observed sex and age differences regarding damage to macromolecules, but no differences were found regarding the antioxidant enzymes measured. Our results suggest that several basal plasma markers of oxidative stress might be related to the extent of muscle damage after an ultraendurance race and also might affect the muscle strength evolution.

Metabolic Analysis of Vitreous/Lens and Retina in Wild Type and Retinal Degeneration Mice

Photoreceptors are the light-sensing cells of the retina and the major cell type affected in most inherited retinal degenerations. Different metabolic pathways sustain their high energetic demand in physiological conditions, particularly aerobic glycolysis. The principal metabolome of the mature retina has been studied, but only limited information is available on metabolic adaptations in response to key developmental events, such as eye opening. Moreover, dynamic metabolic changes due to retinal degeneration are not well understood. Here, we aimed to explore and map the ocular metabolic dynamics induced by eye opening in healthy (wild type) or Pde6b-mutant (retinal degeneration 1, Rd1) mice, in which photoreceptors degenerate shortly after eye opening. To unravel metabolic differences emerging before and after eye opening under physiological and pathophysiological conditions, we performed nuclear magnetic resonance (NMR) spectroscopy-based metabolome analysis of wild type and Rd1 retina and vitreous/lens. We show that eye opening is accompanied by changes in the concentration of selected metabolites in the retina and by alterations in the vitreous/lens composition only in the retinal degeneration context. As such, we identify NAcetylaspartate as a potential novel vitreous/lens marker reflecting progressive retinal degeneration. Thus, our data can help elucidating mechanisms underlying key events in retinal physiology and reveal changes occurring in pathology, while highlighting the importance of the vitreous/lens in the characterization of retinal diseases.

Biochemical and Behavioral Consequences of Ethanol Intake in a Mouse Model of Metabolic Syndrome

Ethanol abuse is a common issue in individuals with sedentary lifestyles, unbalanced diets, and metabolic syndrome. Both ethanol abuse and metabolic syndrome have negative impacts on the central nervous system, with effects including cognitive impairment and brain oxidative status deterioration. The combined effects of ethanol abuse and metabolic syndrome at a central level have not yet been elucidated in detail. Thus, this work aims to determine the effects of ethanol intake on a mouse model of metabolic syndrome at the behavioral and biochemical levels. Seven-week-old male control (B6.V-Lep ob/+JRj) and leptin-deficient (metabolic syndrome) (B6.V-Lep ob/obJRj) mice were used in the study. Animals were divided into four groups: control, ethanol, obese, and obese-ethanol. Ethanol consumption was monitored for 6 weeks. Basal glycemia, insulin, and glucose overload tests were performed. To assess short- and long-term memory, an object recognition test was used. In order to assess oxidative status in mouse brain samples, antioxidant enzyme activity was analyzed with regard to glutathione peroxidase, glutathione reductase, glutathione, glutathione disulfide, lipid peroxidation products, and malondialdehyde. Ethanol intake modulated the insulin response and impaired the oxidative status in the ob mouse brain.

Ex-Vivo Trans-Corneal and Trans-Scleral Diffusion Studies with Ocular Formulations of Glutathione as an Antioxidant Treatment for Ocular Diseases

Exposure to sunlight and contact with atmospheric oxygen makes the eye particularly susceptible to oxidative stress, which can potentially produce cellular damage. In physiological conditions, there are several antioxidant defense mechanisms within the eye. Glutathione (GSH) is the most important antioxidant in the eye; GSH deficit has been linked to several ocular pathologies. The aim of this study was to explore the potential for newly developed formulations allowing controlled delivery of antioxidants such as GSH and vitamin C (Vit C) directly to the eye. We have investigated the stability of antioxidants in aqueous solution and assessed ex-vivo the diffusion of GSH through two ocular membranes, namely cornea and sclera, either in solution or included in a semisolid insert. We have also carried out the hen’s egg-chlorioallantoic membrane test (HET-CAM) to evaluate the ocular irritancy of the different antioxidant solutions. Our results showed that GSH is stable for up to 30 days at 4 °C in darkness and it is not an irritant to the eye. The diffusion studies revealed that the manufactured formulation, a semisolid insert containing GSH, could deliver this tripeptide directly to the eye in a sustained manner.

Drug repurposing studies of PARP inhibitors as a new therapy for inherited retinal degeneration

The enzyme poly-ADP-ribose-polymerase (PARP) has important roles for many forms of DNA repair and it also participates in transcription, chromatin remodeling and cell death signaling. Currently, some PARP inhibitors are approved for cancer therapy, by means of canceling DNA repair processes and cell division. Drug repurposing is a new and attractive aspect of therapy development that could offer low-cost and accelerated establishment of new treatment options. Excessive PARP activity is also involved in neurodegenerative diseases including the currently untreatable and blinding retinitis pigmentosa group of inherited retinal photoreceptor degenerations. Hence, repurposing of known PARP inhibitors for patients with non-oncological diseases might provide a facilitated route for a novel retinitis pigmentosa therapy. Here, we demonstrate and compare the efficacy of two different PARP inhibitors, BMN-673 and 3-aminobenzamide, by using a well-established retinitis pigmentosa model, the rd1 mouse. Moreover, the mechanistic aspects of the PARP inhibitor-induced protection were also investigated in the present study. Our results showed that rd1 rod photoreceptor cell death was decreased by about 25-40% together with the application of these two PARP inhibitors. The wealth of human clinical data available for BMN-673 highlights a strong potential for a rapid clinical translation into novel retinitis pigmentosa treatments. Remarkably, we have found that the efficacy of 3 aminobenzamide was able to decrease PARylation at the nanomolar level. Our data also provide a link between PARP activity with the Wnt/β-catenin pathway and the major intracellular antioxidant concentrations behind the PARP-dependent retinal degeneration. In addition, molecular modeling studies were integrated with experimental studies for better understanding of the role of PARP1 inhibitors in retinal degeneration.

Nitrosative Stress in Retinal Pathologies: Review

Nitric oxide (NO) is a gas molecule with diverse physiological and cellular functions. In the eye, NO is used to maintain normal visual function as it is involved in photoreceptor light transduction. In addition, NO acts as a rapid vascular endothelial relaxant, is involved in the control of retinal blood flow under basal conditions and mediates the vasodilator responses of different substances such as acetylcholine, bradykinin, histamine, substance P or insulin. However, the retina is rich in polyunsaturated lipid membranes and is sensitive to the action of reactive oxygen and nitrogen species. Products generated from NO (i.e., dinitrogen trioxide (N₂O₃) and peroxynitrite) have great oxidative damaging effects. Oxygen and nitrogen species can react with biomolecules (lipids, proteins and DNA), potentially leading to cell death, and this is particularly important in the retina. This review focuses on the role of NO in several ocular diseases, including diabetic retinopathy, retinitis pigmentosa, glaucoma or age-related macular degeneration (AMD).

Effects of Acute Ethanol Administration on Brain Oxidative Status: The Role of Acetaldehyde

BACKGROUND

Ethanol (EtOH), one of the most widely consumed substances of abuse, can induce brain damage and neurodegeneration. EtOH is centrally metabolized into acetaldehyde, which has been shown to be responsible for some of the neurophysiological and cellular effects of EtOH. Although some of the consequences of chronic EtOH administration on cell oxidative status have been described, the mechanisms by which acute EtOH administration affects the brain's cellular oxidative status and the role of acetaldehyde remain to be elucidated in detail.

METHODS

Swiss CD-I mice were pretreated with the acetaldehyde-sequestering agent d-penicillamine (DP; 75 mg/kg, i.p.) or the antioxidant lipoic acid (LA; 50 mg/kg, i.p.) 30 minutes before EtOH (2.5 g/kg, i.p.) administration. Animals were sacrificed 30 minutes after EtOH injection. Glutathione peroxidase (GPx) mRNA levels; GPx and glutathione reductase (GR) enzymatic activities; reduced glutathione (GSH), glutathione disulfide (GSSG), glutamate, g-L-glutamyl-L-cysteine (Glut-Cys), and malondialdehyde (MDA) concentrations; and protein carbonyl group (CG) content were determined in whole-brain samples.

RESULTS

Acute EtOH administration enhanced GPx activity and the GSH/GSSG ratio, while it decreased GR activity and GSSG concentration. Pretreatment with DP or LA only prevented GPx activity changes induced by EtOH.

CONCLUSIONS

Altogether, these results show the capacity of a single dose of EtOH to unbalance cellular oxidative homeostasis.

Rescue of Retinal Degeneration in rd1 Mice by Intravitreally Injected Metformin

Retinitis pigmentosa (RP) is a progressive hereditary retinal degenerative disease in which photoreceptor cells undergo degeneration and apoptosis, eventually resulting in irreversible loss of visual function. Currently, no effective treatment exists for this disease. Neuroprotection and inflammation suppression have been reported to delay the development of RP. Metformin is a well-tested drug used to treat type 2 diabetes, and it has been reported to exert beneficial effects in neurodegenerative diseases, such as Parkinson’s disease and Alzheimer’s disease. In the present study, we used immunofluorescence staining, electroretinogram (ERG) recordings and RNA-Seq to explore the effects of metformin on photoreceptor degeneration and its mechanism in rd1 mice. We found that metformin significantly reduced apoptosis in photoreceptors and delayed the degeneration of photoreceptors and rod bipolar cells in rd1 mice, thus markedly improving the visual function of rd1 mice at P14, P18, and P22 when tested with a light/dark transition test and ERG. Microglial activation in the outer nuclear layer (ONL) of the retina of rd1 mice was significantly suppressed by metformin. RNA-Seq showed that metformin markedly downregulated inflammatory genes and upregulated the expression of crystallin proteins, which have been demonstrated to be important neuroprotective molecules in the retina, revealing the therapeutic potential of metformin for RP treatment. αA-crystallin proteins were further confirmed to be involved in the neuroprotective effects of metformin in a Ca²⁺ ionophore-damaged 661W photoreceptor-like cell line. These data suggest that metformin exerts a protective effect in rd1 mice via both immunoregulatory and new neuroprotective mechanisms.

Progesterone, Lipoic Acid, and Sulforaphane as Promising Antioxidants for Retinal Diseases: A Review

Oxidative stress has been documented to be a key factor in the cause and progression of different retinal diseases. Oxidative cellular unbalance triggers a sequence of reactions which prompt cell degeneration and retinal dysfunction, both hallmarks of several retinal pathologies. There is no effective treatment, yet, for many retinal diseases. Antioxidant treatment have been pointed out to be an encouraging palliative treatment; the beneficial effects documented involve slowing the progression of the disease, a reduction of cell degeneration, and improvement of retinal functions. There is a vast information corpus on antioxidant candidates. In this review, we expose three of the main antioxidant treatments, selected for their promising results that has been reported to date. Recently, the sulforaphane, an isothiocyanate molecule, has been unveiled as a neuroprotective candidate, by its antioxidant properties. Progesterone, a neurosteroid has been proposed to be a solid and effective neuroprotective agent. Finally, the lipoic acid, an organosulfur compound, is a well-recognized antioxidant. All of them, have been tested and studied on different retinal disease models. In this review, we summarized the published results of these works, to offer a general view of the current antioxidant treatment advances, including the main effects and mechanisms described.

A Drug-Tunable Gene Therapy for Broad-Spectrum Protection against Retinal Degeneration

Retinal degenerations are a large cluster of diseases characterized by the irreversible loss of light-sensitive photoreceptors that impairs the vision of 9.1 million people in the US. An attractive treatment option is to use gene therapy to deliver broad-spectrum neuroprotective factors. However, this approach has had limited clinical translation because of the inability to control transgene expression. To address this problem, we generated an adeno-associated virus vector named RPF2 that was engineered to express domains of leukemia inhibitory factor fused to the destabilization domain of bacterial dihydrofolate reductase. Fusion proteins containing the destabilization domain are degraded in mammalian cells but can be stabilized with the binding of the drug trimethoprim. Our data show that expression levels of RPF2 are tightly regulated by the dose of trimethoprim and can be reversed by trimethoprim withdrawal. We further show that stabilized RPF2 can protect photoreceptors and prevent blindness in treated mice.

Oxidative stress and autophagy-related changes during retinal degeneration and development

Retinitis pigmentosa (RP) is an inherited retinopathy that leads to photoreceptor loss. RP has been related to oxidative stress, autophagy, and inflammation. This study aimed to identify changes in the levels of oxidative stress and autophagy markers in the retina of control and rd10 mice during different phases of retinal development. Changes in the retinal oxidation system were investigated by measuring the levels of oxidized and reduced glutathione (GSH/GSSG), retinal avidin-positive cells, and 4-hydroxynonenal (4-HNE) staining intensity. Autophagy characterization was explored by measuring the levels of microtubule-associated protein 1 light chain 3 (LC3), beclin, autophagy-related proteins 5 and 7 (Atg5 and Atg7), and lysosomal associated membrane protein-2A (LAMP-2A). At P28 retinal GSH concentrations decreased in rd10 mice compared to the controls. No differences were found in retinal GSSG concentrations between the control and rd10 mice. There was an increase in retinal GSSG concentrations and a decrease in the GSH/GSSG ratio in the control and rd10 mice at P21 and P28 compared to P13. We observed an increase in avidin-positive cells in rd10 retinas. 4-HNE was increased in rd10 retinas at P13, and it also increased in control mice with age. We did not observe any differences in the retinal levels of LC3II/I ratio, Beclin, Atg5, or Atg7 in the rd10 mice compared to the controls. There was an increase in the LAMP-2A concentrations in the control and rd10 mice with development age (P28 concentrations vs. P13). Although only slight differences were found in the oxidative stress and autophagy markers between the control and rd10 mice, there were increases in the GSSG, 4-HNE, and LAMP-2A with age. This increase in the oxidative stress and chaperone-mediated autophagy has not been described before and occurred just after the mice opened their eyes, potentially indicating a retinal response to light exposure.

Lipoic Acid and Progesterone Alone or in Combination Ameliorate Retinal Degeneration in an Experimental Model of Hereditary Retinal Degeneration

Retinitis pigmentosa (RP) is a group of inherited retinopathies characterized by photoreceptors death. Our group has shown the positive progesterone (P4) actions on cell death progression in an experimental model of RP. In an effort to enhance the beneficial effects of P4, the aim of this study was to combine P4 treatment with an antioxidant [lipoic acid (LA)] in the rd1 mice. rd1 and control mice were treated with 100 mg/kg body weight of P4, LA, or a combination of both on postnatal day 7 (PN7), 9, and 11, and were sacrificed at PN11. The administration of LA and/or P4 diminishes cell death in rd1 retinas. The effect obtained after the combined administration of LA and P4 is higher than the one obtained with LA or P4 alone. The three treatments decreased GFAP staining, however, in the far peripheral retina, and the two treatments that offered better results were LA and LA plus P4. LA or LA plus P4 increased retinal glutathione (GSH) concentration in the rd1 mice. Although LA and P4 are able to protect photoreceptors from death in rd1 mice retinas, a better effectiveness is achieved when administering LA and P4 at the same time.