Mitochondria-targeted antioxidant peptide SS-31 mediates neuroprotection in a rat experimental glaucoma model

Synergistic effects of PS-NPs and Cd on ovarian toxicity in adolescent rats: Ferroptosis by induction of mitochondrial redox imbalance via the SIRT3-SOD2/Gpx4 pathway

Nanoplastics (NPs) are an emerging class of pollutants. They can act as a"Trojan horse" to change the bioavailability and toxicity of heavy metals in the environment. However, research on the combined toxicity of heavy metals and NPs is scarce, especially during the critical developmental period of adolescence. In this study, polystyrene nanoplastics (PS-NPs) and/or cadmium (Cd) were exposed to 4-week-old female rats for 28 days, with the aim of exploring the potential effects of combined exposure to PS-NPs and Cd on the ovaries of adolescence rats. Results showed that co-exposure to PS-NPs and Cd exacerbated ovarian toxicity in rats, primarily through increased atretic follicle numbers and endocrine disruption. Further studies revealed that PS-NPs and Cd synergistically repressed the SIRT3-SOD2/Gpx4 pathway, inducing mitochondrial oxidative stress and ferroptosis, resulting in damage to ovarian structure and function. However, the addition of the mitochondrion-targeted antioxidant SS-31 and the ferroptosis inhibitor Fer-1 reversed the harm to the ovaries from co-exposure to PS-NPs and Cd, the aberrant expression of genes related to the SIRT3-SOD2/Gpx4 pathway was also improved. Our results suggested that co-exposure to PS-NPs and Cd may trigger ferroptosis by inhibiting the SIRT3-SOD2/Gpx4 pathway, leading to mitochondrial redox imbalance, which provided novel insights into reproductive toxicity due to the interaction of PS-NPs and Cd during adolescence.

Protective effects of different exercise modalities on oxidative stress in animal models of high intraocular pressure and diabetes

High intraocular pressure (HIOP) and high glucose levels are associated with oxidative stress. Although physical exercise protects against oxidative damage, its specific impact on eye health remains unclear. Thus, this study aimed to assess the impact of physical exercise on the oxidative status of whole eyes in male Swiss mice subjected to HIOP model and cafeteria diet (CD). In experiment one, mice were divided into sedentary, aerobic, and strength (four-week physical exercise) groups and subjected to an HIOP/ischemia model. In experiment two, mice were submitted to CD and voluntary physical exercise for 18 weeks, according to the following groups: sedentary control, sedentary CD, exercise control, and exercise CD. Experiment one revealed elevated 2',7'-dichlorodihydrofluorescein (DCFH) levels in aerobic group, which decreased in all groups after ischemia. Nitrite levels were decreased on strength than in sedentary group. The superoxide dismutase (SOD) activity did not change in all treatments. Although catalase (CAT) activity increased in aerobic and strength groups, and after ischemia in all groups. In experiment two, the sedentary CD group presented higher body weight than the other groups. DCFH levels were increased in the exercise control and reduced in the exercise CD compared with the other groups. CAT activity and sulfhydryl groups were decreased, while protein carbonylation was increased in the sedentary CD group compared with the other groups. Thus, these results suggested that physical exercise promoted antioxidant effects on eyes exposed to an HIOP model and CD.

Effect of elamipretide and methylprednisolone treatment on optic nerve, retina and brain damage in a methanol poisoning model: biochemical and histopathological evaluation

PURPOSE

This study aimed to biochemically and histopathologically evaluate the protective and therapeutic effects of elamipretide and methylprednisolone on methanol poisoning-induced brain, optic nerve, and retinal toxicity.

METHOD

In this study, 40 male Wistar Albino rats were divided into six groups: healthy control (HC), methotrexate (MTX, 0.3 mg/kg/d for 7 d), methotrexate + methanol (MTX-M, 0.3 mg/kg/d for 7 d + methanol 3 g/kg on Day 8), methotrexate + methanol + methylprednisolone (MTX-M-MPZ, 0.3 mg/kg/d for 7 d + methanol 3 g/kg on Day 8 + MPZ 1 mg/kg/d for 3 d), methotrexate + methanol + elamipretide (MTX-M-E, 0.3 mg/kg/d for 7 d + methanol 3 g/kg on Day 8 + elamipretide 5 mg/kg/d for 3 d), and methotrexate + methanol + methylprednisolone + elamipretide (MTX-M-MPZ-E, 0.3 mg/kg/d for 7 d + methanol 3 g/kg on Day 8 + MPZ 1 mg/kg/d + Elamipretide 5 mg/kg/d for 3 d). The rats were euthanized 8 h after the last drug administration. Histopathological and biochemical evaluations were performed on serum, caudatoputamen, and ocular tissues. Retinal degeneration was assessed using a scoring system where higher scores indicate less degeneration, with a score of 5 representing normal structure and 1 reflecting severe degeneration.

RESULTS

In the MTX-M-MPZ-E group, the retinal degeneration score was higher than in MTX-M group (p = 0.002). The apoptosis index in the retina was highest in MTX-M group, while it was lower in MTX-M-MPZ-E group compared to MTX-M group (p = 0.018). In addition, the apoptosis index in the caudatoputamen was lower in MTX-M-MPZ-E group compared to MTX-M group (p = 0.009).

CONCLUSION

Combined elamipretide and methylprednisolone treatment improved optic nerve and retinal degeneration, reduced neuronal degeneration in the caudatoputamen, decreased oxidative stress and lipid peroxidation, and reduced apoptosis in the retina and caudatoputamen.

Remyelination-oriented clemastine treatment attenuates neuropathies of optic nerve and retina in glaucoma

As one of the top causes of blindness worldwide, glaucoma leads to diverse optic neuropathies such as degeneration of retinal ganglion cells (RGCs). It is widely accepted that the level of intraocular pressure (IOP) is a major risk factor in human glaucoma, and reduction of IOP level is the principally most well-known method to prevent cell death of RGCs. However, clinical studies show that lowering IOP fails to prevent RGC degeneration in the progression of glaucoma. Thus, a comprehensive understanding of glaucoma pathological process is required for developing new therapeutic strategies. In this study, we provide functional and histological evidence showing that optic nerve defects occurred before retina damage in an ocular hypertension glaucoma mouse model, in which oligodendroglial lineage cells were responsible for the subsequent neuropathology. By treatment with clemastine, an Food and Drug Administration (FDA)-approved first-generation antihistamine medicine, we demonstrate that the optic nerve and retina damages were attenuated via promoting oligodendrocyte precursor cell (OPC) differentiation and enhancing remyelination. Taken together, our results reveal the timeline of the optic neuropathies in glaucoma and highlight the potential role of oligodendroglial lineage cells playing in its treatment. Clemastine may be used in future clinical applications for demyelination-associated glaucoma.

NAD+ supplementation improves mitochondrial functions and normalizes glaucomatous trabecular meshwork features

Glaucoma is characterized by pathological elevation of intraocular pressure (IOP) due to dysfunctional trabecular meshwork (TM), which is the primary cause of irreversible vision loss. There are currently no effective treatment strategies for glaucoma. Mitochondrial function plays a crucial role in regulating IOP within the TM. In this study, primary TM cells treated with dexamethasone were used to simulate glaucomatous changes, showing abnormal cellular cytoskeleton, increased expression of extracellular matrix, and disrupted mitochondrial fusion and fission dynamics. Furthermore, glaucomatous TM cell line GTM3 exhibited impaired mitochondrial membrane potential and phagocytic function, accompanied by decreased oxidative respiratory levels as compared to normal TM cells iHTM. Mechanistically, lower NAD + levels in GTM3, possibly associated with increased expression of key enzymes CD38 and PARP1 related to NAD + consumption, were observed. Supplementation of NAD + restored mitochondrial function and cellular viability in GTM3 cells. Therefore, we propose that the aberrant mitochondrial function in glaucomatous TM cells may be attributed to increased NAD + consumption dependent on CD38 and PARP1, and NAD + supplementation could effectively ameliorate mitochondrial function and improve TM function, providing a novel alternative approach for glaucoma treatment.

Application research of novel peptide mitochondrial-targeted antioxidant SS-31 in mitigating mitochondrial dysfunction

Due to the pivotal role of mitochondria in the generation of adenosine triphosphate (ATP) and the regulation of cellular homeostasis, mitochondrial dysfunction may exert a profound impact on various physiological systems, potentially precipitating a spectrum of distinct diseases. Consequently, research pertaining to mitochondrial therapeutics has assumed increasing significance, warranting heightened scrutiny. In recent years, the field of mitochondrial therapy has witnessed noteworthy advancements, with active exploration into diverse pharmacological agents aimed at ameliorating mitochondrial function. Elamipretide (SS-31), a novel synthetic mitochondrial-targeted antioxidant, has emerged as a promising candidate with extensive therapeutic potential. Its notable attributes encompass the mitigation of oxidative stress, the suppression of inflammatory processes, the maintenance of mitochondrial dynamics, and the prevention of cellular apoptosis. As such, SS-31 may emerge as a viable choice for the treatment of mitochondrial dysfunction-related ailments in the foreseeable future. This article extensively expounds upon the superiority of SS-31 over natural antioxidants and traditional mitochondrial-targeted antioxidants, delves into its mechanisms of modulating mitochondrial function, and comprehensively summarizes its applications in alleviating mitochondrial dysfunction-associated disorders. Furthermore, we offer a comprehensive outlook on the expansive prospects of SS-31's future development and application.

Signalling pathways and cell death mechanisms in glaucoma: Insights into the molecular pathophysiology

Glaucoma is a complex multifactorial eye disease manifesting in retinal ganglion cell (RGC) death and optic nerve degeneration, ultimately causing irreversible vision loss. Research in recent years has significantly enhanced our understanding of RGC degenerative mechanisms in glaucoma. It is evident that high intraocular pressure (IOP) is not the only contributing factor to glaucoma pathogenesis. The equilibrium of pro-survival and pro-death signalling pathways in the retina strongly influences the function and survival of RGCs and optic nerve axons in glaucoma. Molecular evidence from human retinal tissue analysis and a range of experimental models of glaucoma have significantly contributed to unravelling these mechanisms. Accumulating evidence reveals a wide range of molecular signalling pathways that can operate -either alone or via intricate networks - to induce neurodegeneration. The roles of several molecules, including neurotrophins, interplay of intracellular kinases and phosphates, caveolae and adapter proteins, serine proteases and their inhibitors, nuclear receptors, amyloid beta and tau, and how their dysfunction affects retinal neurons are discussed in this review. We further underscore how anatomical alterations in various animal models exhibiting RGC degeneration and susceptibility to glaucoma-related neuronal damage have helped to characterise molecular mechanisms in glaucoma. In addition, we also present different regulated cell death pathways that play a critical role in RGC degeneration in glaucoma.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

SS31 Confers Cerebral Protection by Reversing Mitochondrial Dysfunction in Early Brain Injury Following Subarachnoid Hemorrhage, via the Nrf2- and PGC-1α-Dependent Pathways

In early brain injury (EBI), oxidative stress occurs following subarachnoid hemorrhage (SAH), and mitochondria are intricately linked to this process. SS31, a mitochondria-targeting antioxidative peptide, has been demonstrated to be beneficial for multiple diseases because of its powerful antioxidant and neuroprotective properties. Although our previous study revealed that SS31 was involved in the powerful antioxidant effect following SAH, the underlying molecular mechanisms remained unclear. Thus, our study aimed to investigate the neuroprotective effects of SS31 by reversing mitochondrial dysfunction in EBI following SAH, via activating the Nrf2 signaling and PGC-1α pathways. Our findings confirmed that SS31 ameliorated SAH-triggered oxidative insult. SS31 administration decreased redundant reactive oxygen species, alleviated lipid peroxidation, and elevated the activities of antioxidant enzymes. Concomitant with the inhibited oxidative insult, SS31 dramatically attenuated neurological deficits, cerebral edema, neural apoptosis, and blood-brain barrier disruption following SAH. Moreover, SS31 remarkably promoted nuclear factor-erythroid 2 related factor 2 (Nrf2) nuclear shuttle and upregulated the expression levels of heme oxygenase-1 and NADPH: quinine oxidoreductase1. Additionally, SS31 enhanced the expression levels of PGC-1α and its target genes, and increased the mtDNA copy number, promoting mitochondrial function. However, PGC-1α-specific inhibitor SR-18292 pretreatment dramatically suppressed SS31-induced Nrf2 expression and PGC-1α activation. Furthermore, pretreatment with SR-18292 reversed the neuroprotective and antioxidant roles of SS31. These significant beneficial effects were associated with the activation of the Nrf2 signaling and PGC-1α pathways and were antagonized by SR-18292 administration. Our findings reveal that SS31 exhibits its neuroprotective activity by reversing mitochondrial dysfunction via activating the Nrf2 signaling pathway, which could be mediated through PGC-1α activation.

Neuroprotection of Rodent and Human Retinal Ganglion Cells In Vitro/Ex Vivo by the Hybrid Small Molecule SA-2

The mechanisms underlying the neuroprotective effects of the hybrid antioxidant-nitric oxide donating compound SA-2 in retinal ganglion cell (RGC) degeneration models were evaluated. The in vitro trophic factor (TF) deprivation model in primary rat RGCs and ex vivo human retinal explants were used to mimic glaucomatous neurodegeneration. Cell survival was assessed after treatment with vehicle or SA-2. In separate experiments, tert-Butyl hydroperoxide (TBHP) and endothelin-3 (ET-3) were used in ex vivo rat retinal explants and primary rat RGCs, respectively, to induce oxidative damage. Mitochondrial and intracellular reactive oxygen species (ROS) were assessed following treatments. In the TF deprivation model, SA-2 treatment produced a significant decrease in apoptotic and dead cell counts in primary RGCs and a significant increase in RGC survival in ex vivo human retinal explants. In the oxidative stress-induced models, a significant decrease in the production of ROS was observed in the SA-2-treated group compared to the vehicle-treated group. Compound SA-2 was neuroprotective against various glaucomatous insults in the rat and human RGCs by reducing apoptosis and decreasing ROS levels. Amelioration of mitochondrial and cellular oxidative stress by SA-2 may be a potential therapeutic strategy for preventing neurodegeneration in glaucomatous RGCs.

Influences of Glaucoma on the Structure and Function of Synapses in the Visual System

Significance: Glaucoma is an age-related neurodegenerative disorder of the visual system associated with sensitivity to intraocular pressure (IOP). It is the leading irreversible cause of vision loss worldwide, and vision loss results from damage and dysfunction of the retinal output neurons known as retinal ganglion cells (RGCs). Recent Advances: Elevated IOP and optic nerve injury triggers pruning of RGC dendrites, altered morphology of excitatory inputs from presynaptic bipolar cells, and disrupted RGC synaptic function. Less is known about RGC outputs, although evidence to date indicates that glaucoma is associated with altered mitochondrial and synaptic structure and function in RGC-projection targets in the brain. These early functional changes likely contribute to vision loss and might be a window into early diagnosis and treatment. Critical Issues: Glaucoma affects different RGC populations to varying extents and along distinct time courses. The influence of glaucoma on RGC synaptic function as well as the mechanisms underlying these effects remain to be determined. Since RGCs are an especially energetically demanding population of neurons, altered intracellular axon transport of mitochondria and mitochondrial function might contribute to RGC synaptic dysfunction in the retina and brain as well as RGC vulnerability in glaucoma. Future Directions: The mechanisms underlying differential RGC vulnerability remain to be determined. Moreover, the timing and mechanisms of RGCs synaptic dysfunction and degeneration will provide valuable insight into the disease process in glaucoma. Future work will be able to capitalize on these findings to better design diagnostic and therapeutic approaches to detect disease and prevent vision loss. Antioxid. Redox Signal. 37, 842-861.

Subcellular delivery of lipid nanoparticles to endoplasmic reticulum and mitochondria

Primarily responsible for the biogenesis and metabolism of biomolecules, endoplasmic reticulum (ER) and mitochondria are gradually becoming the targets of therapeutic modulation, whose physiological activities and pathological manifestations determine the functional capacity and even the survival of cells. Drug delivery systems with specific physicochemical properties (passive targeting), or modified by small molecular compounds, polypeptides, and biomembranes demonstrating tropism for ER and mitochondria (active targeting) are able to reduce the nonselective accumulation of drugs, enhancing efficacy while reducing side effects. Lipid nanoparticles feature high biocompatibility, diverse cargo loading, and flexible structure modification, which are frequently used for subcellular organelle-targeted delivery of therapeutics. However, there is still a lack of systematic understanding of lipid nanoparticle-based ER and mitochondria targeting. Herein, we review the pathological significance of drug selectively delivered to the ER and mitochondria. We also summarize the molecular basis and application prospects of lipid nanoparticle-based ER and mitochondria targeting strategies, which may provide guidance for the prevention and treatment of associated diseases and disorders. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Lipid-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Retinal Glutamate Neurotransmission: From Physiology to Pathophysiological Mechanisms of Retinal Ganglion Cell Degeneration

Glutamate neurotransmission and metabolism are finely modulated by the retinal network, where the efficient processing of visual information is shaped by the differential distribution and composition of glutamate receptors and transporters. However, disturbances in glutamate homeostasis can result in glutamate excitotoxicity, a major initiating factor of common neurodegenerative diseases. Within the retina, glutamate excitotoxicity can impair visual transmission by initiating degeneration of neuronal populations, including retinal ganglion cells (RGCs). The vulnerability of RGCs is observed not just as a result of retinal diseases but has also been ascribed to other common neurodegenerative and peripheral diseases. In this review, we describe the vulnerability of RGCs to glutamate excitotoxicity and the contribution of different glutamate receptors and transporters to this. In particular, we focus on the N-methyl-d-aspartate (NMDA) receptor as the major effector of glutamate-induced mechanisms of neurodegeneration, including impairment of calcium homeostasis, changes in gene expression and signalling, and mitochondrial dysfunction, as well as the role of endoplasmic reticular stress. Due to recent developments in the search for modulators of NMDA receptor signalling, novel neuroprotective strategies may be on the horizon.

Treatment of age-related visual impairment with a peptide acting on mitochondria

Age-related visual decline and disease due to neural dysfunction are major sources of disability that have resisted effective treatment. In light of evidence that visual impairment and mitochondrial dysfunction advance with age, we characterized age-related decline of spatial visual function in mice and investigated whether treatment of aged mice with the mitochondrion-penetrating peptide elamipretide that has been reported to improve mitochondrial function, would improve it. Impaired photopic acuity measured by using a virtual optokinetic system emerged near 18 months and declined to ∼40% below normal by 34 months. Daily application of the synthetic peptide elamipretide, which has high selectivity for mitochondrial membranes that contain cardiolipin and promotes efficient electron transfer, was able to mitigate visual decline from 18 months onwards. Daily application from 24 months onwards, i.e. when acuity had reduced by ∼16%, reversed visual decline and normalized function within 2 months. Recovered function persisted for at least 3 months after treatment was withdrawn and a single treatment at 24 months delayed subsequent visual decline. Elamipretide applied daily from 32 months onwards took longer to take effect, but substantial improvement was found within 2 months. The effects of age and elamipretide treatment on contrast sensitivity were similar to those on acuity, systemic and eye drop applications of elamipretide had comparable effects, scotopic spatial visual function was largely unaffected by age or treatment, and altered function was independent of variation in optical clarity. These data indicate that elamipretide treatment adaptively alters the aging visual system. They also provide a rationale to investigate whether mitochondrial dysfunction is a treatable pathophysiology of human visual aging and age-related visual disease.

SS-31 efficacy in a mouse model of Friedreich ataxia by upregulation of frataxin expression

Friedreich ataxia (FRDA) is a serious hereditary neurodegenerative disease, mostly accompanied with hypertrophic cardiomyopathy, caused by the reduced expression of frataxin (FXN). However, there is still no effective treatment. Our previous studies have shown that SS-31, a mitochondrion-targeted peptide, is capable to upregulate the expression of FXN and improve the mitochondrial function in cells derived from FRDA patients. To further explore the potential of SS-31, we used the GAA expansion-based models, including Y47 and YG8R (Fxn KIKO) mice, primary neurons and macrophages from the mice and cells derived from FRDA patients. After once-daily intraperitoneal injection of 1 mg/kg SS-31 for 1 month, we observed the significant improvement of motor function. The vacuolation in dorsal root ganglia, lesions in dentate nuclei and the lost thickness of myelin sheath of spinal cord were all repaired after SS-31 treatment. In addition, the hypertrophic cardiomyocytes and disarrayed abnormal Purkinje cells were dramatically reduced. Interestingly, we found that SS-31 treatment upregulated FXN expression not only at the translational levels as observed in cell culture but also at mRNA levels in vivo. Consequently, mitochondrial morphology and function were greatly improved in all tested tissues. Importantly, our data provided additional evidence that the maintenance of the therapeutic benefits needed continuous drug administration. Taken together, our findings have demonstrated the effectiveness of SS-31 treatment through the upregulation of FXN in vivo and offer guidance of the potential usage in the clinical application for FRDA.

Potential Therapeutic Candidates for Age-Related Macular Degeneration (AMD)

Aging contributes to the risk of development of ocular diseases including, but not limited to, Age-related Macular Degeneration (AMD) that is a leading cause of blindness in the United States as well as worldwide. Retinal aging, that contributes to AMD pathogenesis, is characterized by accumulation of drusen deposits, alteration in the composition of Bruch’s membrane and extracellular matrix, vascular inflammation and dysregulation, mitochondrial dysfunction, and accumulation of reactive oxygen species (ROS), and subsequent retinal pigment epithelium (RPE) cell senescence. Since there are limited options available for the prophylaxis and treatment of AMD, new therapeutic interventions are constantly being looked into to identify new therapeutic targets for AMD. This review article discusses the potential candidates for AMD therapy and their known mechanisms of cytoprotection in AMD. These target therapeutic candidates include APE/REF-1, MRZ-99030, Ciliary NeuroTrophic Factor (CNTF), RAP1 GTPase, Celecoxib, and SS-31/Elamipretide.

Risk Factors for Retinal Ganglion Cell Distress in Glaucoma and Neuroprotective Potential Intervention

Retinal ganglion cells (RGCs) are a population of neurons of the central nervous system (CNS) extending with their soma to the inner retina and with their axons to the optic nerve. Glaucoma represents a group of neurodegenerative diseases where the slow progressive death of RGCs results in a permanent loss of vision. To date, although Intra Ocular Pressure (IOP) is considered the main therapeutic target, the precise mechanisms by which RGCs die in glaucoma have not yet been clarified. In fact, Primary Open Angle Glaucoma (POAG), which is the most common glaucoma form, also occurs without elevated IOP. This present review provides a summary of some pathological conditions, i.e., axonal transport blockade, glutamate excitotoxicity and changes in pro-inflammatory cytokines along the RGC projection, all involved in the glaucoma cascade. Moreover, neuro-protective therapeutic approaches, which aim to improve RGC degeneration, have also been taken into consideration.

Mitochondrial dysfunction and beneficial effects of mitochondria-targeted small peptide SS-31 in Diabetes Mellitus and Alzheimer's disease

Diabetes and Alzheimer's disease are common chronic illnesses in the United States and lack clearly demonstrated therapeutics. Mitochondria, the "powerhouse of the cell", is involved in the homeostatic regulation of glucose, energy, and reduction/oxidation reactions. The mitochondria has been associated with the etiology of metabolic and neurological disorders through a dysfunction of regulation of reactive oxygen species. Mitochondria-targeted chemicals, such as the Szeto-Schiller-31 peptide, have advanced therapeutic potential through the inhibition of oxidative stress and the restoration of normal mitochondrial function as compared to traditional antioxidants, such as vitamin E. In this article, we summarize the pathophysiological relevance of the mitochondria and the beneficial effects of Szeto-Schiller-31 peptide in the treatment of Diabetes and Alzheimer's disease.

The Influence of Mitochondrial Dynamics and Function on Retinal Ganglion Cell Susceptibility in Optic Nerve Disease

The important roles of mitochondrial function and dysfunction in the process of neurodegeneration are widely acknowledged. Retinal ganglion cells (RGCs) appear to be a highly vulnerable neuronal cell type in the central nervous system with respect to mitochondrial dysfunction but the actual reasons for this are still incompletely understood. These cells have a unique circumstance where unmyelinated axons must bend nearly 90° to exit the eye and then cross a translaminar pressure gradient before becoming myelinated in the optic nerve. This region, the optic nerve head, contains some of the highest density of mitochondria present in these cells. Glaucoma represents a perfect storm of events occurring at this location, with a combination of changes in the translaminar pressure gradient and reassignment of the metabolic support functions of supporting glia, which appears to apply increased metabolic stress to the RGC axons leading to a failure of axonal transport mechanisms. However, RGCs themselves are also extremely sensitive to genetic mutations, particularly in genes affecting mitochondrial dynamics and mitochondrial clearance. These mutations, which systemically affect the mitochondria in every cell, often lead to an optic neuropathy as the sole pathologic defect in affected patients. This review summarizes knowledge of mitochondrial structure and function, the known energy demands of neurons in general, and places these in the context of normal and pathological characteristics of mitochondria attributed to RGCs.

Whether short peptides are good candidates for future neuroprotective therapeutics?

Neurodegenerative diseases are a broad group of largely debilitating, and ultimately terminal conditions resulting in progressive degeneration of different brain regions. The observed damages are associated with cell death, structural and functional deficits of neurons, or demyelination. The concept of neuroprotection concerns the administration of the agent, which should reverse some of the damage or prevent further adverse changes. A growing body of evidence suggested that among many classes of compounds considered as neuroprotective agents, peptides derived from natural materials or their synthetic analogs are good candidates. They presented a broad spectrum of activities and abilities to act through diverse mechanisms of action. Biologically active peptides have many properties, including antioxidant, antimicrobial, antiinflammatory, and immunomodulatory effects. Peptides with pro-survival and neuroprotective activities, associated with inhibition of oxidative stress, apoptosis, inflammation and are able to improve cell viability or mitochondrial functions, are also promising molecules of particular interest to the pharmaceutical industries. Peptide multiple activities open the way for broad application potential as therapeutic agents or ingredients of health-promoting functional foods. Significantly, synthetic peptides can be remodeled in numerous ways to have desired features, such as increased solubility or biological stability, as well as selectivity towards a specific receptor, and finally better membrane penetration. This review summarized the most common features of major neurodegenerative disorders, their causes, consequences, and reported new neuroprotective drug development approaches. The author focused on the unique perspectives in neuroprotection and provided a concise survey of short peptides proposed as novel therapeutic agents against various neurodegenerative diseases.

The effects of a mitochondrial targeted peptide (elamipretide/SS31) on BAX recruitment and activation during apoptosis

OBJECTIVE

Elamipretide (SS31) is a mitochondria-targeted peptide that has reported functions of stabilizing mitochondrial cristae structure and improving mitochondrial bioenergetics. Several studies have documented cell protective features of this peptide, including impairment of intrinsic apoptosis by inhibiting the recruitment and activation of the pro-apoptotic BAX protein. We used live-cell imaging of ARPE-19 cells expressing fluorescently labeled BAX, cytochrome c, and a mitochondrial marker to investigate the effect of elamipretide on the kinetics of BAX recruitment, mitochondrial outer membrane permeabilization (as a function of cytochrome c release), and mitochondrial fragmentation, respectively.

RESULT

In nucleofected and plated ARPE-19 cells, elamipretide accelerated the formation of larger mitochondria. In the presence of the apoptotic stimulator, staurosporine, cells treated with elamipretide exhibited moderately slower rates of BAX recruitment. Peptide treatment, however, did not significantly delay the onset of BAX recruitment or the final total amount of BAX that was recruited. Additionally, elamipretide showed no impairment or delay of cytochrome c release or mitochondrial fragmentation, two events associated with normal BAX activation during cell death. These results indicate that the protective effect of elamipretide is not at the level of BAX activity to induce pro-apoptotic mitochondrial dysfunction after the initiation of staurosporine-induced apoptosis.

Synthesis, Characterization, and Specific Localization of Mitochondrial-Targeted Antioxidant Peptide SS31 Probe

The aim of this study is to investigate the targeting efficiency of FITC-SS31 to mitochondria in both normal and H2O2-induced oxidative damaged 661W cells, characterizing the properties of FITC-SS31 in the biological assays. The purity and molecular weight of FITC-SS31 were identified using HPLC and MS. MTT and LDH assays were used to evaluate the cytotoxicity and cell permeability. The binding ability of FITC-SS31 to cells was demonstrated by flow cytometry. The colocalization of FITC-SS31 and MitoTracker both in normal and oxidative cells was analyzed by a laser confocal microscope. We detected the DEGs between SS31+H2O2 and H2O2-alone-treated cells by RNA seq. GO and KEGG analyses were performed to predict the functional gene of SS31. The molecular weight of FITC-SS31 was 1142.2 with the 97.76% purity. The flow cytometry results showed that the MFI (mean fluorescence intensity) of FITC-SS31 in normal cells in the 4 h probe treatment group was higher than that in the 2 h and the 0 h group. The MFI in the 2 h probe treatment group was much higher than that in the 4 h and 0 h groups in damaged cells. The positive rate of 10 μM FITC-SS31 was higher than that of 1 μM and 5 μM. Fluorescein imaging analysis confirmed that FITC-SS31 was overlapped with MitoTracker. Through the analysis, DEGs were highly expressed in "localization, organelle, antioxidant activity, binding" functions and enriched in "AMPK signaling pathway, MAPK targets/nuclear events mediated by MAP kinase pathway and PI3K-Akt signaling pathway." It is speculated that SS31 exerts an antioxidant effect through one of these pathways. We hypothesized that SS31 could play a more efficient role in the pathological cells in the half-life period to avoid cell death due to oxidative damage. The functions of the DEGs in SS31+H2O2 and H2O2-alone samples are related to the localization and antioxidant activity of SS31. DEGs are mostly enriched in the AMPK signaling pathway, which needs further studies.

Glaucoma and Antioxidants: Review and Update

Glaucoma is a neurodegenerative disease characterised by the progressive degeneration of retinal ganglion cells. Oxidative stress has been related to the cell death in this disease. Theoretically, this deleterious consequence can be reduced by antioxidants substances. The aim of this review is to assemble the studies published in relation to antioxidant supplementation and its effects on glaucoma and to offer the reader an update on this field. With this purpose, we have included studies in animal models of glaucoma and clinical trials. Although there are variable results, supplementation with antioxidants in glaucoma may be a promising therapy in glaucoma.

Mitochondrial targeted therapy with elamipretide (MTP-131) as an adjunct to tumor necrosis factor inhibition for traumatic optic neuropathy in the acute setting

Traumatic optic neuropathy (TON) can occur following blunt trauma to the orbit and can lead to permanent vision loss. In this study, we investigated the effectiveness of elamipretide (MTP-131), a small mitochondrially-targeted tetrapeptide, in conjunction with etanercept, a tumor necrosis factor (TNF) inhibitor, as neuroprotective agents of retinal ganglion cells (RGCs) after optic nerve trauma with sonication-induced TON (SI-TON) in mice. Treatment with intravitreal MTP-131 and subcutaneous etanercept and MTP-131 showed a 21% increase (p < 0.01) in RGC survival rate compared to PBS-treated control eyes. Subcutaneous etanercept and MTP-131 had an 11% increase (p < 0.05) in RGC survival compared to controls. Subcutaneous etanercept only group showed 20% increase (p < 0.01) in RGC survival compared to controls, while subcutaneous MTP-131 alone showed a 17% increase (p < 0.01). Surprisingly, we did not observe a synergistic effect between the two drugs in the group receiving both etanercept and MTP-131. One possible explanation for the absence of a synergistic effect is that MTP-131 and etanercept may be acting on different portions of the same pathway.

A novel rat model of ocular hypertension by a single intracameral injection of cross-linked hyaluronic acid hydrogel (Healaflow® )

To create a novel animal model of ocular hypertension via the intracameral injection of Healaflow. Unilateral chronic ocular hypertension model of rats was created by the intracameral injection of 3 μL Healaflow. The IOP of subjects was monitored. Dynamic morphological changes were evaluated by fundus imaging, OCT and histological examination. Visual function changes were measured by electroretinography and flash visual-evoked potentials. 24 and 72 hours after injection, the retinal tissue was collected for transcriptome analysis. The expression levels of related genes and proteins were further evaluated by qRT-PCR and Western blotting. The IOP peaked within 1 day after a single intracameral injection of Healaflow and then decreased gradually within 4 weeks. Furthermore, the persistently degenerating retinal ganglion cells occurred within 4 weeks. The visual function of these rats was also impaired. The results of transcriptome analyses, qRT-PCR and Western blotting showed that the expression levels of B2m, Ikzf1 and Stat3 were up-regulated, while the expression levels of Six3 and Prss56 were down-regulated in the retinal tissues. Intracameral injection of Healaflow is an effective approach to induce glaucomatous neurodegeneration in rats. Six3 and Prss56 may be involved in the pathogenesis of progressive glaucomatous damage.

A Dietary Combination of Forskolin with Homotaurine, Spearmint and B Vitamins Protects Injured Retinal Ganglion Cells in a Rodent Model of Hypertensive Glaucoma

There is indication that nutritional supplements protect retinal cells from degeneration. In a previous study, we demonstrated that dietary supplementation with an association of forskolin, homotaurine, spearmint extract and B vitamins efficiently counteracts retinal dysfunction associated with retinal ganglion cell (RGC) death caused by optic nerve crush. We extended our investigation on the efficacy of dietary supplementation with the use of a mouse model in which RGC degeneration depends as closely as possible on intraocular pressure (IOP) elevation. In this model, injecting the anterior chamber of the eye with methylcellulose (MCE) causes IOP elevation leading to RGC dysfunction. The MCE model was characterized in terms of IOP elevation, retinal dysfunction as determined by electrophysiological recordings, RGC loss as determined by brain-specific homeobox/POU domain protein 3A immunoreactivity and dysregulated levels of inflammatory and apoptotic markers. Except for IOP elevation, dysfunctional retinal parameters were all recovered by dietary supplementation indicating the involvement of non-IOP-related neuroprotective mechanisms of action. Our hypothesis is that the diet supplement may be used to counteract the inflammatory processes triggered by glial cell activation, thus leading to spared RGC loss and the preservation of visual dysfunction. In this respect, the present compound may be viewed as a potential remedy to be added to the currently approved drug therapies for improving RGC protection.

Inducible rodent models of glaucoma

Glaucoma is one of the leading causes of vision impairment worldwide. In order to further understand the molecular pathobiology of this disease and to develop better therapies, clinically relevant animal models are necessary. In recent years, both the rat and mouse have become popular models in glaucoma research. Key reasons are: many important biological similarities shared among rodent eyes and the human eye; development of improved methods to induce glaucoma and to evaluate glaucomatous damage; availability of genetic tools in the mouse; as well as the relatively low cost of rodent studies. Commonly studied rat and mouse glaucoma models include intraocular pressure (IOP)-dependent and pressure-independent models. The pressure-dependent models address the most important risk factor of elevated IOP, whereas the pressure-independent models assess "normal tension" glaucoma and other "non-IOP" related factors associated with glaucomatous damage. The current article provides descriptions of these models, their characterizations, specific techniques to induce glaucoma, mechanisms of injury, advantages, and limitations.