Fenofibrate ameliorates diabetic retinopathy by modulating Nrf2 signaling and NLRP3 inflammasome activation

Resveratrol Ameliorates Retinal Ischemia-Reperfusion Injury by Modulating the NLRP3 Inflammasome and Keap1/Nrf2/HO-1 Signaling Pathway

Glaucoma, as an ischemia-reperfusion (I/R) injury disease, leading irreversible blindness through the loss of retinal ganglion cells (RGCs), mediated by various pathways. Resveratrol (Res) is a polyphenolic compound that exerts protective effects against I/R injury in many tissues. This article aimed to expound the underlying mechanisms through which Res protects RGCs and reduces visual dysfunction in vivo. An experimental glaucoma model was created using 6-8-week wild-type male C57BL/6J mice. Res was injected intraperitoneally for 5 days. The mice were then grouped according to the number of days after surgery and whether Res treatment was administered. We applied the Brn3a-labeled immunofluorescence staining and flash electroretinography (ERG) to assess the survival of RGCs and visual function. The expression of components of the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome, the interleukin-1-beta (IL-1β), and vital indicators of kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2)/heme-oxygenase 1 (HO-1) pathway at the protein and RNA levels were detected respectively. The survival of RGCs was reduced after surgery compared to controls, whereas Res application rescued RGCs and improved visual dysfunction. In conclusion, our results discovered that Res administration showed neuroprotective effects through inhibition of the NLRP3 inflammasome pathway and activation of Keap1/Nrf2/HO-1 pathway. Thus, we further elucidated the potential of Res in glaucoma therapy.

The Pleiotropic Effects of Lipid-Modifying Interventions: Exploring Traditional and Emerging Hypolipidemic Therapies

Atherosclerotic cardiovascular disease poses a significant global health issue, with dyslipidemia standing out as a major risk factor. In recent decades, lipid-lowering therapies have evolved significantly, with statins emerging as the cornerstone treatment. These interventions play a crucial role in both primary and secondary prevention by effectively reducing cardiovascular risk through lipid profile enhancements. Beyond their primary lipid-lowering effects, extensive research indicates that these therapies exhibit pleiotropic actions, offering additional health benefits. These include anti-inflammatory properties, improvements in vascular health and glucose metabolism, and potential implications in cancer management. While statins and ezetimibe have been extensively studied, newer lipid-lowering agents also demonstrate similar pleiotropic effects, even in the absence of direct cardiovascular benefits. This narrative review explores the diverse pleiotropic properties of lipid-modifying therapies, emphasizing their non-lipid effects that contribute to reducing cardiovascular burden and exploring emerging benefits for non-cardiovascular conditions. Mechanistic insights into these actions are discussed alongside their potential therapeutic implications.

Diabetic Retinopathy: New Treatment Approaches Targeting Redox and Immune Mechanisms

Diabetic retinopathy (DR) represents a severe complication of diabetes mellitus, characterized by irreversible visual impairment resulting from microvascular abnormalities. Since the global prevalence of diabetes continues to escalate, DR has emerged as a prominent area of research interest. The development and progression of DR encompass a complex interplay of pathological and physiological mechanisms, such as high glucose-induced oxidative stress, immune responses, vascular endothelial dysfunction, as well as damage to retinal neurons. Recent years have unveiled the involvement of genomic and epigenetic factors in the formation of DR mechanisms. At present, extensive research explores the potential of biomarkers such as cytokines, molecular and cell therapies, antioxidant interventions, and gene therapy for DR treatment. Notably, certain drugs, such as anti-VEGF agents, antioxidants, inhibitors of inflammatory responses, and protein kinase C (PKC)-β inhibitors, have demonstrated promising outcomes in clinical trials. Within this context, this review article aims to introduce the recent molecular research on DR and highlight the current progress in the field, with a particular focus on the emerging and experimental treatment strategies targeting the immune and redox signaling pathways.

NLRP3 Inflammasome Priming in the Retina of Diabetic Mice Requires REDD1-Dependent Activation of GSK3β

Purpose

Inflammasome activation has been implicated in the development of retinal complications caused by diabetes. This study was designed to identify signaling events that promote retinal NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activation in response to diabetes.

Methods

Diabetes was induced in mice by streptozotocin administration. Retinas were examined after 16 weeks of diabetes. Human MIO-M1 Müller cells were exposed to hyperglycemic culture conditions. Genetic and pharmacological interventions were used to interrogate signaling pathways. Visual function was assessed in mice using a virtual optomotor system.

Results

In the retina of diabetic mice and in Müller cell cultures, NLRP3 and interleukin-1β (IL-1β) were increased in response to hyperglycemic conditions and the stress response protein Regulated in Development and DNA damage 1 (REDD1) was required for the effect. REDD1 deletion prevented caspase-1 activation in Müller cells exposed to hyperglycemic conditions and reduced IL-1β release. REDD1 promoted nuclear factor κB signaling in cells exposed to hyperglycemic conditions, which was necessary for an increase in NLRP3. Expression of a constitutively active GSK3β variant restored NLRP3 expression in REDD1-deficient cells exposed to hyperglycemic conditions. GSK3 activity was necessary for increased NLRP3 expression in the retina of diabetic mice and in cells exposed to hyperglycemic conditions. Müller glia-specific REDD1 deletion prevented increased retinal NLRP3 levels and deficits in contrast sensitivity in diabetic mice.

Conclusions

The data support a role for REDD1-dependent activation of GSK3β in NLRP3 inflammasome transcriptional priming and in the production of IL-1β by Müller glia in response to diabetes.

Recent advances in the treatment and delivery system of diabetic retinopathy

Diabetic retinopathy (DR) is a highly tissue-specific neurovascular complication of type 1 and type 2 diabetes mellitus and is among the leading causes of blindness worldwide. Pathophysiological changes in DR encompass neurodegeneration, inflammation, and oxidative stress. Current treatments for DR, including anti-vascular endothelial growth factor, steroids, laser photocoagulation, and vitrectomy have limitations and adverse reactions, necessitating the exploration of novel treatment strategies. This review aims to summarize the current pathophysiology, therapeutic approaches, and available drug-delivery methods for treating DR, and discuss their respective development potentials. Recent research indicates the efficacy of novel receptor inhibitors and agonists, such as aldose reductase inhibitors, angiotensin-converting enzyme inhibitors, peroxisome proliferator-activated receptor alpha agonists, and novel drugs in delaying DR. Furthermore, with continuous advancements in nanotechnology, a new form of drug delivery has been developed that can address certain limitations of clinical drug therapy, such as low solubility and poor penetration. This review serves as a theoretical foundation for future research on DR treatment. While highlighting promising therapeutic targets, it underscores the need for continuous exploration to enhance our understanding of DR pathogenesis. The limitations of current treatments and the potential for future advancements emphasize the importance of ongoing research in this field.

NOD1 deficiency ameliorates the progression of diabetic retinopathy by modulating bone marrow-retina crosstalk

BACKGROUND

Nucleotide-binding oligomerization domain-containing protein 1 (NOD1) plays a pivotal role in inducing metabolic inflammation in diabetes. Additionally, the NOD1 ligand disrupts the equilibrium of bone marrow-derived hematopoietic stem/progenitor cells, a process that has immense significance in the development of diabetic retinopathy (DR). We hypothesized that NOD1 depletion impedes the advancement of DR by resolving bone marrow dysfunction.

METHODS

We generated NOD1-/--Akita double-mutant mice and chimeric mice with hematopoietic-specific NOD1 depletion to study the role of NOD1 in the bone marrow-retina axis.

RESULTS

Elevated circulating NOD1 activators were observed in Akita mice after 6 months of diabetes. NOD1 depletion partially restored diabetes-induced structural changes and retinal electrical responses in NOD1-/--Akita mice. Loss of NOD1 significantly ameliorated the progression of diabetic retinal vascular degeneration, as determined by acellular capillary quantification. The preventive effect of NOD1 depletion on DR is linked to bone marrow phenotype alterations, including a restored HSC pool and a shift in hematopoiesis toward myelopoiesis. We also generated chimeric mice with hematopoietic-specific NOD1 ablation, and the results further indicated that NOD1 had a protective effect against DR. Mechanistically, loss of hematopoietic NOD1 resulted in reduced bone marrow-derived macrophage infiltration and decreased CXCL1 and CXCL2 secretion within the retina, subsequently leading to diminished neutrophil chemoattraction and NETosis.

CONCLUSIONS

The results of our study unveil, for the first time, the critical role of NOD1 as a trigger for a hematopoietic imbalance toward myelopoiesis and local retinal inflammation, culminating in DR progression. Targeting NOD1 in bone marrow may be a potential strategy for the prevention and treatment of DR.

Role of fenofibrate in multiple sclerosis

Multiple sclerosis (MS) is the most frequent inflammatory and demyelinating disease of the central nervous system (CNS). The underlying pathophysiology of MS is the destruction of myelin sheath by immune cells. The formation of myelin plaques, inflammation, and injury of neuronal myelin sheath characterizes its neuropathology. MS plaques are multiple focal regions of demyelination disseminated in the brain's white matter, spinal cords, deep grey matter, and cerebral cortex. Fenofibrate is a peroxisome proliferative activated receptor alpha (PPAR-α) that attenuates the inflammatory reactions in MS. Fenofibrate inhibits differentiation of Th17 by inhibiting the expression of pro-inflammatory signaling. According to these findings, this review intended to illuminate the mechanistic immunoinflammatory role of fenofibrate in mitigating MS neuropathology. In conclusion, fenofibrate can attenuate MS neuropathology by modulating different pathways, including oxidative stress, autophagy, mitochondrial dysfunction, inflammatory-signaling pathways, and neuroinflammation.

Manifestation of Pathology in Animal Models of Diabetic Retinopathy Is Delayed from the Onset of Diabetes

Diabetic retinopathy (DR) is the most common complication that develops in patients with diabetes mellitus (DM) and is the leading cause of blindness worldwide. Fortunately, sight-threatening forms of DR develop only after several decades of DM. This well-documented resilience to DR suggests that the retina is capable of protecting itself from DM-related damage and also that accumulation of such damage occurs only after deterioration of this resilience. Despite the enormous translational significance of this phenomenon, very little is known regarding the nature of resilience to DR. Rodent models of DR have been used extensively to study the nature of the DM-induced damage, i.e., cardinal features of DR. Many of these same animal models can be used to investigate resilience because DR is delayed from the onset of DM by several weeks or months. The purpose of this review is to provide a comprehensive overview of the literature describing the use of rodent models of DR in type-1 and type-2 diabetic animals, which most clearly document the delay between the onset of DM and the appearance of DR. These readily available experimental settings can be used to advance our current understanding of resilience to DR and thereby identify biomarkers and targets for novel, prevention-based approaches to manage patients at risk for developing DR.

Crosstalk between inflammasomes, inflammation, and Nrf2: Implications for gestational diabetes mellitus pathogenesis and therapeutics

The role of inflammasomes in gestational diabetes mellitus (GDM) has emerged as a critical area of research in recent years. Inflammasomes, key components of the innate immune system, are now recognized for their involvement in the pathogenesis of GDM. Activation of inflammasomes in response to various triggers during pregnancy can produce pro-inflammatory cytokines, such as interleukin-1β (IL-1β) and interleukin-18 (IL-18), contributing to systemic inflammation and insulin resistance. This dysregulation not only impacts maternal health but also poses significant risks to fetal development and long-term health outcomes. Understanding the intricate interplay between inflammasomes and GDM holds promise for developing novel therapeutic strategies and interventions to mitigate the adverse effects of this condition on both mothers and their offspring. Researchers have elucidated that targeting inflammasomes using anti-inflammatory drugs and compounds can effectively reduce inflammation in GDM. Furthermore, the addition of nuclear factor erythroid 2-related factor 2 (Nrf2) to this complex mechanism opens novel avenues for therapeutics. The antioxidant properties of Nrf2 may potentially suppress inflammasome activation in GDM. This comprehensive review investigates the intricate relationship between inflammasomes and GDM, emphasizing the pivotal role of inflammation in its pathogenesis. It also sheds light on potential therapeutic strategies targeting inflammasome activation and explores the role of Nrf2 in mitigating inflammation in GDM.

Molecular pathways of NF-ĸB and NLRP3 inflammasome as potential targets in the treatment of inflammation in diabetic wounds: A review

Diabetic wounds are slow healing wounds characterized by disordered healing processes and frequently take longer than three months to heal. One of the defining characteristics of impaired diabetic wound healing is an abnormal and unresolved inflammatory response, which is primarily brought on by abnormal macrophage innate immune signaling activation. The persistent inflammatory state in a diabetic wound may be attributed to inflammatory pathways such as nuclear factor kappa B (NF-ĸB) and nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, which have long been associated with inflammatory diseases. Despite the available treatments for diabetic foot ulcers (DFUs) that include debridement, growth factor therapy, and topical anti-bacterial agents, successful wound healing is still hampered. Further understanding of the molecular mechanism of these pathways could be useful in designing potential therapeutic targets for diabetic wound healing. This review provides an update and novel insights into the roles of NF-ĸB and NLRP3 pathways in the molecular mechanism of diabetic wound inflammation and their potential as therapeutic targets in diabetic wound healing.

Human Carboxylesterase 1A Plays a Predominant Role in Hydrolysis of the Anti-Dyslipidemia Agent Fenofibrate in Humans

Fenofibrate, a marketed peroxisome proliferator-activated receptor-α (PPARα) agonist, has been widely used for treating severe hypertriglyceridemia and mixed dyslipidemia. As a canonical prodrug, fenofibrate can be rapidly hydrolyzed to release the active metabolite (fenofibric acid) in vivo, but the crucial enzyme(s) responsible for fenofibrate hydrolysis and the related hydrolytic kinetics have not been well-investigated. This study aimed to assign the key organs and crucial enzymes involved in fenofibrate hydrolysis in humans, as well as reveal the impact of fenofibrate hydrolysis on its non-PPAR-mediated biologic activities. Our results demonstrated that fenofibrate could be rapidly hydrolyzed in the preparations from both human liver and lung to release fenofibric acid. Reaction phenotyping assays coupling with chemical inhibition assays showed that human carboxylesterase 1A (hCES1A) played a predominant role in fenofibrate hydrolysis in human liver and lung, while human carboxylesterase 2A (hCES2A) and human monoacylglycerol esterase (hMAGL) contributed to a very lesser extent. Kinetic analyses showed that fenofibrate could be rapidly hydrolyzed by hCES1A in human liver preparations, while the inherent clearance of hCES1A-catalyzed fenofibrate hydrolysis is much higher (>200-fold) than than that of hCES2A or hMAGL. Biologic assays demonstrated that both fenofibrate and fenofibric acid showed very closed Nrf2 agonist effects, but fenofibrate hydrolysis strongly weakens its inhibitory effects against both hCES2A and hNtoum. Collectively, our findings reveal that the liver is the major organ and hCES1A is the predominant enzyme-catalyzing fenofibrate hydrolysis in humans, while fenofibrate hydrolysis significantly reduces inhibitory effects of fenofibrate against serine hydrolases. SIGNIFICANCE STATEMENT: Fenofibrate can be completely converted to fenofibric acid in humans and subsequently exert its pharmacological effects, but the hydrolytic pathways of fenofibrate in humans have not been well-investigated. This study reported that the liver was the predominant organ and human carboxylesterase 1A was the crucial enzyme involved in fenofibrate hydrolysis in humans.

Pathogenic Role of Fibrinogen in the Neuropathology of Multiple Sclerosis: A Tale of Sorrows and Fears

Multiple sclerosis (MS) is an autoimmune demyelinating neurodegenerative disease of the central nervous system (CNS) due to injury of the myelin sheath by immune cells. The clotting factor fibrinogen is involved in the pathogenesis of MS by triggering microglia and the progress of neuroinflammation. Fibrinogen level is correlated with MS severity; consequently, inhibition of the fibrinogen cascade may reduce MS neuropathology. Thus, this review aimed to clarify the potential role of fibrinogen in the pathogenesis of MS and how targeting of fibrinogen affects MS neuropathology. Accumulation of fibrinogen in the CNS may occur independently or due to disruption of blood-brain barrier (BBB) integrity in MS. Fibrinogen acts as transduction and increases microglia activation which induces the progression of inflammation, oxidative stress, and neuronal injury. Besides, brain fibrinogen impairs the remyelination process by inhibiting the differentiation of oligodendrocyte precursor cells. These findings proposed that fibrinogen is associated with MS neuropathology through interruption of BBB integrity, induction of neuroinflammation, and demyelination with inhibition of the remyelination process by suppressing oligodendrocytes. Therefore, targeting of fibrinogen and/or CD11b/CD18 receptors by metformin and statins might decrease MS neuropathology. In conclusion, inhibiting the expression of CD11b/CD18 receptors by metformin and statins may decrease the pro-inflammatory effect of fibrinogen on microglia which is involved in the progression of MS.

From Innate Immunity to Metabolic Disorder: A Review of the NLRP3 Inflammasome in Diabetes Mellitus

The role of the NLRP3 inflammasome is pivotal in the pathophysiology and progression of diabetes mellitus (DM), encompassing both type 1 (T1D), or type 2 (T2D). As part of the innate immune system, NLRP3 is also responsible for the chronic inflammation triggered by hyperglycemia. In both conditions, NLRP3 facilitates the release of interleukin-1β and interleukin-18. For T1D, NLRP3 perpetuates the autoimmune cascade, leading to the destruction of pancreatic islet cells. In T2D, its activation is associated with the presence of insulin resistance. NLRP3 activation is also instrumental for the presence of numerous complications associated with DM, microvascular and macrovascular. A considerable number of anti-diabetic drugs have demonstrated the ability to inhibit the NLRP3 inflammasome.

Research progress of diabetic retinopathy and gut microecology

According to the prediction of the International Diabetes Federation, global diabetes mellitus (DM) patients will reach 783.2 million in 2045. The increasing incidence of DM has led to a global epidemic of diabetic retinopathy (DR). DR is a common microvascular complication of DM, which has a significant impact on the vision of working-age people and is one of the main causes of blindness worldwide. Substantial research has highlighted that microangiopathy and chronic low-grade inflammation are widespread in the retina of DR. Meanwhile, with the introduction of the gut-retina axis, it has also been found that DR is associated with gut microecological disorders. The disordered structure of the GM and the destruction of the gut barrier result in the release of abnormal GM flora metabolites into the blood circulation. In addition, this process induced alterations in the expression of various cytokines and proteins, which further modulate the inflammatory microenvironment, vascular damage, oxidative stress, and immune levels within the retina. Such alterations led to the development of DR. In this review, we discuss the corresponding alterations in the structure of the GM flora and its metabolites in DR, with a more detailed focus on the mechanism of gut microecology in DR. Finally, we summarize the potential therapeutic approaches of DM/DR, mainly regulating the disturbed gut microecology to restore the homeostatic level, to provide a new perspective on the prevention, monitoring, and treatment of DR.

Fenofibrate for diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) remains a major cause of sight loss worldwide, despite new therapies and improvements in the metabolic control of people living with diabetes. Therefore, DR creates a physical and psychological burden for people, and an economic burden for society. Preventing the development and progression of DR, or avoiding the occurrence of its sight-threatening complications is essential, and must be pursued to save sight. Fenofibrate may be a useful strategy to achieve this goal, by reversing diabetes' effects and reducing inflammation in the retina, as well as improving dyslipidaemia and hypertriglyceridaemia.  OBJECTIVES: To investigate the benefits and harms of fenofibrate for preventing the development and progression of diabetic retinopathy in people with type 1 (T1D) or type 2 diabetes (T2D), compared with placebo or observation.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, and three trials registers (February 2022).

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that included people with T1D or T2D, when these compared fenofibrate with placebo or with observation, and assessed the effect of fenofibrate on the development or progression of DR (or both).

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods for data extraction and analysis. Our primary outcome was progression of DR, a composite outcome of 1) incidence of overt retinopathy for participants who did not have DR at baseline, or 2) advancing two or more steps on the Early Treatment Diabetic Retinopathy Study (ETDRS) severity scale for participants who had any DR at baseline (or both), based on the evaluation of stereoscopic or non-stereoscopic fundus photographs, during the follow-up period. Overt retinopathy was defined as the presence of any DR observed on stereoscopic or non-stereoscopic colour fundus photographs. Secondary outcomes included the incidence of overt retinopathy, reduction in visual acuity of participants with a reduction in visual acuity of 10 ETDRS letters or more, proliferative diabetic retinopathy, and diabetic macular oedema; mean vision-related quality of life, and serious adverse events of fenofibrate. We used GRADE to assess the certainty of evidence.

MAIN RESULTS

We included two studies and their eye sub-studies (15,313 participants) in people with T2D. The studies were conducted in the US, Canada, Australia, Finland, and New Zealand; follow-up period was four to five years. One was funded by the government, the other by industry. Compared to placebo or observation, fenofibrate likely results in little to no difference in progression of DR (risk ratio (RR) 0.86; 95% confidence interval (CI) 0.60 to 1.25; 1 study, 1012 participants; moderate-certainty evidence) in a population with and without overt retinopathy at baseline. Those without overt retinopathy at baseline showed little or no progression (RR 1.00, 95% CI 0.68 to 1.47; 1 study, 804 participants); those with overt retinopathy at baseline found that their DR progressed slowly (RR 0.21, 95% CI 0.06 to 0.71; 1 study, 208 people; test for interaction P = 0.02). Compared to placebo or observation, fenofibrate likely resulted in little to no difference in either the incidence of overt retinopathy (RR 0.91; 95% CI 0.76 to 1.09; 2 studies, 1631 participants; moderate-certainty evidence); or the incidence of diabetic macular oedema (RR 0.39; 95% CI 0.12 to 1.24; 1 study, 1012 participants; moderate-certainty evidence). The use of fenofibrate increased severe adverse effects (RR 1.55; 95% CI 1.05 to 2.27; 2 studies, 15,313 participants; high-certainty evidence). The studies did not report on incidence of a reduction in visual acuity of 10 ETDRS letters or more, incidence of proliferative diabetic retinopathy, or mean vision-related quality of life.

AUTHORS' CONCLUSIONS

Current, moderate-certainty evidence suggests that in a mixed group of people with and without overt retinopathy, who live with T2D, fenofibrate likely results in little to no difference in progression of diabetic retinopathy. However, in people with overt retinopathy who live with T2D, fenofibrate likely reduces the progression. Serious adverse events were rare, but the risk of their occurrence was increased by the use of fenofibrate. There is no evidence on the effect of fenofibrate in people with T1D. More studies, with larger sample sizes, and participants with T1D are needed. They should measure outcomes that are important to people with diabetes, e.g. change in vision, reduction in visual acuity of 10 ETDRS letters or more, developing proliferative diabetic retinopathy; and evaluating the requirement of other treatments, e.g. injections of anti-vascular endothelial growth factor therapies, steroids.

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

Targeting the NLRP3 inflammasome in diabetic retinopathy: From Pathogenesis to Therapeutic Strategies

Diabetic retinopathy (DR) is a common diabetic microvascular complication and the main cause of vision loss in working-aged people. The NLRP3 inflammasome is a cytosolic multimeric complex that plays a significant role in innate immunity. After sensing injury, the NLRP3 inflammasome induces inflammatory mediator secretion and triggers a form of inflammatory cell death known as pyroptosis. Studies over the past five years have shown increased expression of NLRP3 and related inflammatory mediators in vitreous samples from DR patients at different clinical stages. Many NLRP3-targeted inhibitors have shown great antiangiogenic and anti-inflammatory effects in diabetes mellitus models, suggesting that the NLRP3 inflammasome is involved in the progression of DR. This review covers the molecular mechanisms of NLRP3 inflammasome activation. Furthermore, we discuss the implications of the NLRP3 inflammasome in DR, including the induction of pyroptosis and inflammation and the promotion of microangiopathy and retinal neurodegeneration. We also summarize the research progress on targeting the NLRP3 inflammasome in DR therapeutics with the expectation of providing new insights into DR progression and treatment.

Inhibition of the pyroptosis-associated inflammasome pathway: The important potential mechanism of ginsenosides in ameliorating diabetes and its complications

Diabetes mellitus (DM) and its complications have become an important global public health issue, affecting human health and negatively impacting life and lifespan. Pyroptosis is a recently discovered form of pro-inflammatory programmed cell death (PCD). To date, pyroptosis-associated inflammasome pathways have been identified primarily in the canonical and non-canonical inflammasome pathway, apoptotic caspase-mediated pathway, granzyme-mediated pathway, and streptococcal pyrogenic exotoxin B (SpeB)-mediated pathway. The activation of diabetes-mediated pyroptosis-associated factors play an important role in the pathophysiology of DM and its complications. Studies have shown that ginsenosides exert significant protective effects on DM and its complications. Through inhibiting the activation of pyroptosis-associated inflammasome pathways, and then the DM and its complications are improved. This review summarizes the subtypes of ginsenosides and their chemical characteristics, pharmacokinetics and side effects, the main pyroptosis-associated inflammasome pathways that have been discovered to date, and the potential mechanism of different subtypes of ginsenosides in the treatment of DM and its complications (such as diabetic cardiomyopathy, diabetic nephropathy, diabetic liver injury, diabetic retinopathy, and diabetic ischemic stroke) via anti-pyroptosis-associated inflammasome pathways. These findings may provide ideas for further research to explore ginsenoside mechanism in improving DM and its complications. However, many pyroptosis-associated inflammasome pathways and targets involved in the occurrence and development of DM and its complications are still unknown. In the future, further studies using in vitro cell models, in vivo animal models, and human disease models can be used to further elucidate the mechanism of ginsenosides in the treatment of DM and its complications.

Metformin mitigates renal dysfunction in obese insulin-resistant rats via activation of the AMPK/PPARα pathway

Insulin signaling and lipid metabolism are disrupted by long-term consumption of a high-fat diet (HFD). This disruption can lead to insulin resistance, dyslipidemia and subsequently renal dysfunction as a consequence of the inactivation of the AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-α (PPARα) or AMPK/PPARα pathways. We investigated the impact of metformin on the prevention of renal dysfunction through the modulation of AMPK-regulated PPARα-dependent pathways in insulin-resistant rats induced by a HFD. Male Wistar rats were fed a HFD for 16 weeks to induce insulin resistance. After insulin resistance had been confirmed, metformin (30 mg/kg) or gemfibrozil (50 mg/kg) was given orally for 8 weeks. Evidence of insulin resistance, dyslipidemia, lipid accumulation and kidney injury were observed in HF rats. Impairment of lipid oxidation, energy metabolism and renal organic anion transporter 3 (Oat3) expression and function were demonstrated in HF rats. Metformin can stimulate the AMPK/PPARα pathways and suppress sterol regulatory element-binding transcription factor 1 (SREBP1) and fatty acid synthase (FAS) signaling (SREBP1/FAS) to enable the regulation of lipid metabolism. Renal inflammatory markers and renal fibrosis expression induced by a HFD were more effectively reduced after metformin treatment than after gemfibrozil treatment. Interestingly, renal Oat3 function and expression and kidney injury were improved following metformin and gemfibrozil treatment. Renal cluster of differentiation 36 (CD36) or sodium glucose cotransporter type 2 (SGLT2) expression did not differ after treatment with metformin or gemfibrozil. Metformin and gemfibrozil could reduce the impairment of renal injury in obese conditions induced by a HFD through the AMPK/PPARα-dependent pathway. Interestingly, metformin demonstrated greater efficacy than gemfibrozil in attenuating renal lipotoxicity through the AMPK-regulated SREBP1/FAS signaling pathway.

Role of the inflammasome in insulin resistance and type 2 diabetes mellitus

The inflammasome is a protein complex composed of a variety of proteins in cells and which participates in the innate immune response of the body. It can be activated by upstream signal regulation and plays an important role in pyroptosis, apoptosis, inflammation, tumor regulation, etc. In recent years, the number of metabolic syndrome patients with insulin resistance (IR) has increased year by year, and the inflammasome is closely related to the occurrence and development of metabolic diseases. The inflammasome can directly or indirectly affect conduction of the insulin signaling pathway, involvement the occurrence of IR and type 2 diabetes mellitus (T2DM). Moreover, various therapeutic agents also work through the inflammasome to treat with diabetes. This review focuses on the role of inflammasome on IR and T2DM, pointing out the association and utility value. Briefly, we have discussed the main inflammasomes, including NLRP1, NLRP3, NLRC4, NLRP6 and AIM2, as well as their structure, activation and regulation in IR were described in detail. Finally, we discussed the current therapeutic options-associated with inflammasome for the treatment of T2DM. Specially, the NLRP3-related therapeutic agents and options are widely developed. In summary, this article reviews the role of and research progress on the inflammasome in IR and T2DM.

Fenofibrate for COVID-19 and related complications as an approach to improve treatment outcomes: the missed key for Holy Grail

INTRODUCTION

Fenofibrate is an agonist of peroxisome proliferator activated receptor alpha (PPAR-α), that possesses anti-inflammatory, antioxidant, and anti-thrombotic properties. Fenofibrate is effective against a variety of viral infections and different inflammatory disorders. Therefore, the aim of critical review was to overview the potential role of fenofibrate in the pathogenesis of SARS-CoV-2 and related complications.

RESULTS

By destabilizing SARS-CoV-2 spike protein and preventing it from binding angiotensin-converting enzyme 2 (ACE2), a receptor for SARS-CoV-2 entry, fenofibrate can reduce SARS-CoV-2 entry in human cells Fenofibrate also suppresses inflammatory signaling pathways, which decreases SARS-CoV-2 infection-related inflammatory alterations. In conclusion, fenofibrate anti-inflammatory, antioxidant, and antithrombotic capabilities may help to minimize the inflammatory and thrombotic consequences associated with SARSCoV-2 infection. Through attenuating the interaction between SARS-CoV-2 and ACE2, fenofibrate can directly reduce the risk of SARS-CoV-2 infection.

CONCLUSIONS

As a result, fenofibrate could be a potential treatment approach for COVID-19 control.

Role of Oxidative Stress in Retinal Disease and the Early Intervention Strategies: A Review

The retina, owing to its cellular anatomy and physical location, is susceptible to generating reactive oxygen species (ROS), which are associated with several major retinal diseases. When ROS exceeds the body's natural antioxidants, the retina is in a state of oxidative stress, which is recognized as the pathogenesis of retinal diseases. The early stage of the pathogenic process is an adaptive change in which oxidative stress and endogenous defense mechanisms occur. If no treatment is applied, the retinal diseases will progress to the pathological stage with neuronal and vascular dysfunction or damage and even blindness. This review summarizes the role of oxidative stress in several common retinal diseases, including retinitis pigmentosa, age-related macular degeneration, diabetic retinopathy, glaucoma, and retinopathy of prematurity. In addition, we discuss the early intervention strategies for these diseases. An outline is provided to identify potential intervention targets for further research. Early intervention for retinal diseases is necessary and urgent and may offer hope to improve patients' quality of life through functional vision.

Urolithin A ameliorates diabetic retinopathy via activation of the Nrf2/HO-1 pathway

Diabetic retinopathy (DR) is a progressive microvascular complication of diabetes mellitus and is characterised by excessive inflammation and oxidative stress. Urolithin A (UA), a major metabolite of ellagic acid, exerts anti-inflammatory and antioxidant functions in various human diseases. This study, for the first time, uncovered the role of UA in DR pathogenesis. Streptozotocin-induced diabetic rats were used to determine the effects of UA on blood glucose levels, retinal structures, inflammation, and oxidative stress. High glucose (HG)-induced human retinal endothelial cells (HRECs) were used to elucidate the anti-inflammatory and antioxidant mechanisms of UA in DR in vitro. The in vivo experiments demonstrated that UA injection reduced blood glucose levels, decreased albumin and vascular endothelial growth factor concentrations, and ameliorated the injured retinal structures caused by DR. UA administration also inhibited inflammation and oxidative damage in the retinal tissues of diabetic rats. Similar anti-inflammatory and antioxidant effects of UA were observed in HRECs induced by HG. Furthermore, we found that UA elevated the levels of nuclear Nrf2 and HO-1 both in vivo and in vitro. Nrf2 silencing reversed the inhibitory effects of UA on inflammation and oxidative stress during DR progression. Together, our findings indicate that UA can ameliorate DR by repressing inflammation and oxidative stress via the Nrf2/HO-1 pathway, which suggests that UA could be an effective drug for clinical DR treatment.

Potential diabetic cardiomyopathy therapies targeting pyroptosis: A mini review

Pyroptosis is primarily considered a pro-inflammatory class of caspase-1- and gasdermin D (GSDMD)-dependent programmed cell death. Inflammasome activation promotes the maturation and release of interleukin (IL)-1β and IL-18, cleavage of GSDMD, and development of pyroptosis. Recent studies have reported that NLRP3 inflammasome activation-mediated pyroptosis aggravates the formation and development of diabetes cardiomyopathy (DCM). These studies provide theoretical mechanisms for exploring a novel approach to treat DCM-associated cardiac dysfunction. Accordingly, this review aims to summarize studies that investigated possible DCM therapies targeting pyroptosis and elucidate the molecular mechanisms underlying NLRP3 inflammasome-mediated pyroptosis, and its potential association with the pathogenesis of DCM. This review may serve as a basis for the development of potential pharmacological agents as novel and effective treatments for managing and treating DCM.

Diabetic retinopathy: Involved cells, biomarkers, and treatments

Diabetic retinopathy (DR), a leading cause of vision loss and blindness worldwide, is caused by retinal neurovascular unit dysfunction, and its cellular pathology involves at least nine kinds of retinal cells, including photoreceptors, horizontal and bipolar cells, amacrine cells, retinal ganglion cells, glial cells (Müller cells, astrocytes, and microglia), endothelial cells, pericytes, and retinal pigment epithelial cells. Its mechanism is complicated and involves loss of cells, inflammatory factor production, neovascularization, and BRB impairment. However, the mechanism has not been completely elucidated. Drug treatment for DR has been gradually advancing recently. Research on potential drug targets relies upon clear information on pathogenesis and effective biomarkers. Therefore, we reviewed the recent literature on the cellular pathology and the diagnostic and prognostic biomarkers of DR in terms of blood, protein, and clinical and preclinical drug therapy (including synthesized molecules and natural molecules). This review may provide a theoretical basis for further DR research.

Transcription factor nuclear factor erythroid 2 p45-related factor 2 (NRF2) ameliorates sepsis-associated acute kidney injury by maintaining mitochondrial homeostasis and improving the mitochondrial function

Mitochondrial dysfunction has a role in sepsis-associated acute kidney injury (S-AKI), so the restoration of normal mitochondrial homeostasis may be an effective treatment strategy. Transcription factor nuclear factor erythroid 2 p45-related factor 2 (NRF2) is a main regulator of cell-redox homeostasis, and recent studies reported that NRF2 activation helped to preserve mitochondrial morphology and function under conditions of stress. However, the role of NRF2 in the process of S-AKI is still not well understood. The present study investigated whether NRF2 regulates mitochondrial homeostasis and influences mitochondrial function in S-AKI. We demonstrated activation of NRF2 in an in vitro model: lipopolysaccharide (LPS) challenge of ductal epithelial cells of rat renal tubules (NRK-52e cells), and an in vivo model: cecal ligation and puncture (CLP) of rats. Over-expression of NRF2 attenuated oxidative stress, apoptosis, and the inflammatory response; enhanced mitophagy and mitochondrial biogenesis; and mitigated mitochondrial damage in the in vitro model. In vivo experiments showed that rats treated with an NRF2 agonist had higher adenosine triphosphate (ATP) levels, lower blood urea nitrogen and creatinine levels, fewer renal histopathological changes, and higher expression of mitophagy-related proteins [PTEN-induced putative kinase 1 (PINK1), parkin RBR E3 ubiquitin protein ligase (PRKN), microtubule-associated protein 1 light chain 3 II (LC3 II)] and mitochondrial biogenesis-related proteins [peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1α) and mitochondrial transcription factor A (TFAM)]. Electron microscopy of kidney tissues showed that mitochondrial damage was alleviated by treatment with an NRF2 agonist, and the opposite response occurred upon treatment with an NRF2 antagonist. Overall, our findings suggest that mitochondria have an important role in the pathogenesis of S-AKI, and that NRF2 activation restored mitochondrial homeostasis and function in the presence of this disease. This mitochondrial pathway has the potential to be a novel therapeutic target for the treatment of S-AKI.

A Potential Target for Diabetic Vascular Damage: High Glucose-Induced Monocyte Extracellular Vesicles Impair Endothelial Cells by Delivering miR-142-5p

Endothelial dysfunction is a key accessory to diabetic cardiovascular complications, and the regulatory role of the extracellular vesicles (EVs) from the innate immune system is growing. We tested whether EVs derived from high glucose-induced monocytes could shuttle microRNAs and impair endothelial cells. EVs from high glucose- and basal glucose-treated THP-1 cells (^HG-THP-1 EVs and ^BG-THP-1 EVs) were isolated and identified. After coculture with THP-1 EVs, human umbilical vein endothelial cells (HUVECs) were tested by proliferation, migration, reactive oxygen species (ROS) detection assays, and western blot for Nrf2/NLRP3 signaling. MiR-142-5p was predicted by miRNAs databases and further verified by RT–qPCR and dual-luciferase reporter gene assays that inhibit Nrf2 expression. The regulation of miR-142-5p in HUVECs was further evaluated. A type 1 diabetes mellitus (T1DM) mouse model was developed for miR-142-5p inhibition. Aorta tissue was harvested for hematoxylin-eosin staining and immunohistochemistry of interleukin-1β (IL-1β). Compared to ^BG-THP-1 EVs, ^HG-THP-1 EVs significantly reduced migration and increased ROS production in HUVECs but did not affect proliferation. ^HG-THP-1 EVs induced suppression of Nrf2 signaling and NLRP3 signaling activation. RT–qPCR results showed that ^HG-THP-1 EVs overexpressed miR-142-5p in HUVECs. The transfection of miR-142-5p mimics into HUVECs exhibited consistent regulatory effects on ^HG-THP-1 EVs, whereas miR-142-5p inhibitors demonstrated protective effects. The miR-142-5p antagomir significantly reduced the IL-1β level in T1DM aortas despite morphological changes. To conclude, miR-142-5p transferred by high glucose-induced monocyte EVs participates in diabetic endothelial damage. The inhibition of miR-142-5p could be a potential adjuvant to diabetic cardiovascular protection.

NLRP3 Inflammasome Activation: A Therapeutic Target for Cerebral Ischemia–Reperfusion Injury

Millions of patients are suffering from ischemic stroke, it is urgent to figure out the pathogenesis of cerebral ischemia–reperfusion (I/R) injury in order to find an effective cure. After I/R injury, pro-inflammatory cytokines especially interleukin-1β (IL-1β) upregulates in ischemic brain cells, such as microglia and neuron. To ameliorate the inflammation after cerebral I/R injury, nucleotide-binding oligomerization domain (NOD), leucine-rich repeat (LRR), and pyrin domain-containing protein 3 (NLRP3) inflammasome is well-investigated. NLRP3 inflammasomes are complicated protein complexes that are activated by endogenous and exogenous danger signals to participate in the inflammatory response. The assembly and activation of the NLRP3 inflammasome lead to the caspase-1-dependent release of pro-inflammatory cytokines, such as interleukin (IL)-1β and IL-18. Furthermore, pyroptosis is a pro-inflammatory cell death that occurs in a dependent manner on NLRP3 inflammasomes after cerebral I/R injury. In this review, we summarized the assembly and activation of NLRP3 inflammasome; moreover, we also concluded the pivotal role of NLRP3 inflammasome and inhibitors, targeting the NLRP3 inflammasome in cerebral I/R injury.

Müller Glial Expression of REDD1 Is Required for Retinal Neurodegeneration and Visual Dysfunction in Diabetic Mice

Clinical studies support a role for the protein regulated in development and DNA damage response 1 (REDD1) in ischemic retinal complications. To better understand how REDD1 contributes to retinal pathology, we examined human single-cell sequencing data sets and found specificity of REDD1 expression that was consistent with markers of retinal Müller glia. Thus, we investigated the hypothesis that REDD1 expression specifically in Müller glia contributes to diabetes-induced retinal pathology. The retina of Müller glia-specific REDD1 knockout (REDD1-mgKO) mice exhibited dramatic attenuation of REDD1 transcript and protein expression. In the retina of streptozotocin-induced diabetic control mice, REDD1 protein expression was enhanced coincident with an increase in oxidative stress. In the retina of diabetic REDD1-mgKO mice, there was no increase in REDD1 protein expression, and oxidative stress was reduced compared with diabetic control mice. In both Müller glia within the retina of diabetic mice and human Müller cell cultures exposed to hyperglycemic conditions, REDD1 was necessary for increased expression of the gliosis marker glial fibrillary acidic protein. The effect of REDD1 deletion in preventing gliosis was associated with suppression of oxidative stress and required the antioxidant transcription factor nuclear factor erythroid-2-related factor 2 (Nrf2). In contrast to diabetic control mice, diabetic REDD1-mgKO mice did not exhibit retinal thinning, increased markers of neurodegeneration within the retinal ganglion cell layer, or deficits in visual function. Overall, the findings support a key role for Müller glial REDD1 in the failed adaptive response of the retina to diabetes that includes gliosis, neurodegeneration, and impaired vision.

Lipids, hyperreflective crystalline deposits and diabetic retinopathy: potential systemic and retinal-specific effect of lipid-lowering therapies

The metabolically active retina obtains essential lipids by endogenous biosynthesis and from the systemic circulation. Clinical studies provide limited and sometimes conflicting evidence as to the relationships between circulating lipid levels and the development and progression of diabetic retinopathy in people with diabetes. Cardiovascular-system-focused clinical trials that also evaluated some retinal outcomes demonstrate the potential protective power of lipid-lowering therapies in diabetic retinopathy and some trials with ocular primary endpoints are in progress. Although triacylglycerol-lowering therapies with fibrates afforded some protection against diabetic retinopathy, the effect was independent of changes in traditional blood lipid classes. While systemic LDL-cholesterol lowering with statins did not afford protection against diabetic retinopathy in most clinical trials, and none of the trials focused on retinopathy as the main outcome, data from very large database studies suggest the possible effectiveness of statins. Potential challenges in these studies are discussed, including lipid-independent effects of fibrates and statins, modified lipoproteins and retinal-specific effects of lipid-lowering drugs. Dysregulation of retinal-specific cholesterol metabolism leading to retinal cholesterol accumulation and potential formation of cholesterol crystals are also addressed.

Contribution of Müller Cells in the Diabetic Retinopathy Development: Focus on Oxidative Stress and Inflammation

Diabetic retinopathy is a neurovascular complication of diabetes and the main cause of vision loss in adults. Glial cells have a key role in maintenance of central nervous system homeostasis. In the retina, the predominant element is the Müller cell, a specialized cell with radial morphology that spans all retinal layers and influences the function of the entire retinal circuitry. Müller cells provide metabolic support, regulation of extracellular composition, synaptic activity control, structural organization of the blood-retina barrier, antioxidant activity, and trophic support, among other roles. Therefore, impairments of Müller actions lead to retinal malfunctions. Accordingly, increasing evidence indicates that Müller cells are affected in diabetic retinopathy and may contribute to the severity of the disease. Here, we will survey recently described alterations in Müller cell functions and cellular events that contribute to diabetic retinopathy, especially related to oxidative stress and inflammation. This review sheds light on Müller cells as potential therapeutic targets of this disease.

Obstructive Sleep Apnea Affects Lacrimal Gland Function

Purpose

To determine the effect of obstructive sleep apnea syndrome (OSA) on lacrimal gland function and its mechanism.

Methods

Male mice aged seven to eight weeks were housed in cages with cyclic intermittent hypoxia to mimic OSA, and the control group was kept in a normal environment. Slit-lamp observation, fluorescein staining, and corneal sensitivity detection are used to assess cornea changes. Tear secretion was detected by phenol red cotton thread, and the pathological changes of lacrimal gland were observed by hematoxylin and eosin staining, oil red O staining, cholesterol and triglyceride kits, immunofluorescence staining, immunohistochemical staining, real-time polymerase chain reaction, transmission electron microscopy, and Western blot.

Results

Studies revealed a decreased tear secretion, corneal epithelial defects and corneal hypersensitivity. Myoepithelial cell damage, abnormal lipid accumulation, reduced cell proliferation, increased apoptosis and inflammatory cell infiltration in the lacrimal gland were also seen. Hifα and NF-κB signaling pathways, moreover, were activated, while Pparα was downregulated, in the lacrimal glands of OSA mice. Fenofibrate treatment significantly alleviated pathological changes of the lacrimal gland induced by OSA.

Conclusion

OSA disturbs the Hifα/Pparα/NF-κB signaling axis, which affects lacrimal gland structure and function and induces dry eye.

Down-expression of the NLRP3 inflammasome delays the progression of diabetic retinopathy

The investigation aimed to evaluate the effects of Mcc950, an inhibitor of the NLRP3 inflammasome, on diabetic retinopathy (DR) mice. The general physiological condition of each group of mice was recorded. Retinal blood vessels were stained for observation of the density of blood vessels, and retinas were used for further morphological examination and fluorescent staining after the intravitreal injection of Mcc950. Mcc950 partially reversed hyperglycemia-induced vascular damage and had reduced histological changes compared to DR mice. IL-1β production in mice retinas in the diabetic model (DM) group increased, but pretreatment with Mcc950 significantly reversed these changes. Additionally, Mcc950 engineered reduced FITC dextran extravasation and vascular leakage. Therefore, it played an apparent protective role in DR and could be a new treatment strategy for DR.

Curcumin is a Potential Adjuvant to Alleviates Diabetic Retinal Injury via Reducing Oxidative Stress and Maintaining Nrf2 Pathway Homeostasis

Curcumin is a natural polyphenol compound with anti-diabetic, anti-oxidative, and anti-inflammatory effects. Although many studies have reported the protective effect of curcumin in diabetes mellitus or diabetic nephropathy, there is a lack of research on curcumin in diabetic retinopathy. The purpose of this study was to investigate the therapeutic effects of curcumin on the diabetic retinal injury. Streptozotocin (STZ)-induced diabetic rats (60, n = 12 each) were respectively given curcumin orally (200 mg/kg/day), insulin subcutaneously (4–6 IU/day), and combined therapy with curcumin and insulin for 4 weeks. Retinal histopathological changes, oxidative stress markers, and transcriptome profiles from each group were observed. Curcumin, insulin, or combination therapy significantly reduced blood glucose, alleviated oxidative stress, and improved pathological damage in diabetic rats. Curcumin not only significantly reduced retinal edema but also had a better anti-photoreceptor apoptosis effect than insulin. In the early stage of diabetes, the enhancement of oxidative stress in the retina induced the adaptive activation of the nuclear factor E2-associated factor 2 (Nrf2) pathway. Treatment of curcumin alleviated the compensatory activation of the Nrf2 pathway induced by oxidative stress, by virtue of its antioxidant ability to transfer hydrogen atoms to free radicals. When curcumin combined with insulin, the effect of maintaining Nrf2 pathway homeostasis in diabetic rats was better than that of insulin alone. Transcriptomic analyses revealed that curcumin either alone, or combined with insulin, inhibited the AGE-RAGE signaling pathway and the extracellular matrix (ECM)-receptor interaction in the diabetic retina. Thus, at the early stage of diabetes, curcumin can be used to alleviate diabetic retinal injury through its anti-oxidative effect. If taking curcumin as a potential complementary therapeutic option in combination with antihyperglycemic agents, which would lead to more effective therapeutic outcomes against diabetic complications.

Recent Insights into the Role of Gut Microbiota in Diabetic Retinopathy

The microbiome has become a hot issue in recent years. The composition, modification, alteration, and disturbance of gut microbiota were found to influence important physiological processes, including energy metabolism and microenvironmental homeostasis, and lead to various diseases, including obesity, type 2 diabetes mellitus and chronic kidney disease. Diabetic retinopathy (DR) is a major microvascular complication of diabetes mellitus and one of the leading causes of blindness and vision impairment. The underlying mechanisms in DR pathogenesis remain limited. Recently, important insights have been made regarding possible connections between gut microbiome dysbiosis and ocular disease including DR, uveitis, glaucoma, and age-related macular degeneration, and the concept of a "microbiota-gut-retina axis" has been put forward. Hence, we reviewed current understanding of the relationship between DR and gut microbiota. We summarized potential pathophysiological mechanisms that contribute to the role of the gut microbiota on DR, including hyperglycemia, anti-diabetes drugs, microbial metabolites, and inflammatory properties. We aimed to find novel effective therapeutic options to prevent the onset and development of DR.

Updates on the Current Treatments for Diabetic Retinopathy and Possibility of Future Oral Therapy

Diabetic retinopathy (DR) is a complication of diabetes and one of the leading causes of vision loss worldwide. Despite extensive efforts to reduce visual impairment, the prevalence of DR is still increasing. The initial pathophysiology of DR includes damage to vascular endothelial cells and loss of pericytes. Ensuing hypoxic responses trigger the expression of vascular endothelial growth factor (VEGF) and other pro-angiogenic factors. At present, the most effective treatment for DR and diabetic macular edema (DME) is the control of blood glucose levels. More advanced cases require laser, anti-VEGF therapy, steroid, and vitrectomy. Pan-retinal photocoagulation for non-proliferative diabetic retinopathy (NPDR) is well established and has demonstrated promising outcomes for preventing the progressive stage of DR. Furthermore, the efficacy of laser therapies such as grid and subthreshold diode laser micropulse photocoagulation (SDM) for DME has been reported. Vitrectomy has been performed for vitreous hemorrhage and tractional retinal detachment for patients with PDR. In addition, anti-VEGF treatment has been widely used for DME, and recently its potential to prevent the progression of PDR has been remarked. Even with these treatments, many patients with DR lose their vision and suffer from potential side effects. Thus, we need alternative treatments to address these limitations. In recent years, the relationship between DR, lipid metabolism, and inflammation has been featured. Research in diabetic animal models points to peroxisome proliferator-activated receptor alpha (PPARα) activation in cellular metabolism and inflammation by oral fenofibrate and/or pemafibrate as a promising target for DR. In this paper, we review the status of existing therapies, summarize PPARα activation therapies for DR, and discuss their potentials as promising DR treatments.

Sinomenine activation of Nrf2 signaling prevents inflammation and cerebral injury in a mouse model of ischemic stroke

Sinomenine (SINO), which is used clinically to treat rheumatoid arthritis and neuralgia, is derived from the root and stems of Sinomenium acutum. SINO has been reported to exert analgesic, sedative and anti-inflammatory effects, and provides a protective role against shock and organ damage. Studies have suggested that SINO primarily exerts it anti-inflammatory function by inhibiting NF-κB signaling. There is also evidence to indicate that SINO may regulate inflammation Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling. The present study aimed to investigate whether the anti-inflammatory and cerebral protective effects of SINO were induced through Nrf2 both in vitro and in vivo. The results revealed that SINO significantly upregulated Nrf2 protein expression levels, increased Nrf2 nuclear translocation and the upregulated the protein expression levels of downstream factors. The treatment of a middle cerebral artery occlusion model mice with SINO effectively reduced cerebral damage and inflammation, and restored the balance in cerebral oxidative stress. In addition, SINO treatment also promoted Nrf2-dependent microglia M1/M2 polarization and inhibited the phosphorylation of IκBα as well as NF-κB nuclear translocation. This revealed an important upstream event that contributed to its anti-inflammatory and cerebral tissue protective effects. In conclusion, the findings of the present study identified a novel pathway through which SINO may exert its anti-inflammatory and cerebral protective functions, and provided a molecular basis for the potential applications of SINO in the treatment of cerebral inflammatory disorders.

Nuclear Receptors in the Control of the NLRP3 Inflammasome Pathway

The innate immune system is the first line of defense specialized in the clearing of invaders whether foreign elements like microbes or self-elements that accumulate abnormally including cellular debris. Inflammasomes are master regulators of the innate immune system, especially in macrophages, and are key sensors involved in maintaining cellular health in response to cytolytic pathogens or stress signals. Inflammasomes are cytoplasmic complexes typically composed of a sensor molecule such as NOD-Like Receptors (NLRs), an adaptor protein including ASC and an effector protein such as caspase 1. Upon stimulation, inflammasome complex components associate to promote the cleavage of the pro-caspase 1 into active caspase-1 and the subsequent activation of pro-inflammatory cytokines including IL-18 and IL-1β. Deficiency or overactivation of such important sensors leads to critical diseases including Alzheimer diseases, chronic inflammatory diseases, cancers, acute liver diseases, and cardiometabolic diseases. Inflammasomes are tightly controlled by a two-step activation regulatory process consisting in a priming step, which activates the transcription of inflammasome components, and an activation step which leads to the inflammasome complex formation and the subsequent cleavage of pro-IL1 cytokines. Apart from the NF-κB pathway, nuclear receptors have recently been proposed as additional regulators of this pathway. This review will discuss the role of nuclear receptors in the control of the NLRP3 inflammasome and the putative beneficial effect of new modulators of inflammasomes in the treatment of inflammatory diseases including colitis, fulminant hepatitis, cardiac ischemia-reperfusion and brain diseases.

Fenofibrate Reduces the Severity of Neuroretinopathy in a Type 2 Model of Diabetes without Inducing Peroxisome Proliferator-Activated Receptor Alpha-Dependent Retinal Gene Expression

Fenofibrate slows the progression of clinical diabetic retinopathy (DR), but its mechanism of action in the retina remains unclear. Fenofibrate is a known agonist of peroxisome proliferator-activated receptor alpha (PPARα), a transcription factor critical for regulating metabolism, inflammation and oxidative stress. Using a DR mouse model, db/db, we tested the hypothesis that fenofibrate slows early DR progression by activating PPARα in the retina. Relative to healthy littermates, six-month-old db/db mice exhibited elevated serum triglycerides and cholesterol, retinal gliosis, and electroretinography (ERG) changes including reduced b-wave amplitudes and delayed oscillatory potentials. These pathologic changes in the retina were improved by oral fenofibrate. However, fenofibrate did not induce PPARα target gene expression in whole retina or isolated Müller glia. The capacity of the retina to respond to PPARα was further tested by delivering the PPARα agonist GW590735 to the intraperitoneal or intravitreous space in mice carrying the peroxisome proliferator response element (PPRE)-luciferase reporter. We observed strong induction of the reporter in the liver, but no induction in the retina. In summary, fenofibrate treatment of db/db mice prevents the development of early DR but is not associated with induction of PPARα in the retina.

Pemafibrate prevents retinal neuronal cell death in NMDA-induced excitotoxicity via inhibition of p-c-Jun expression

Excitotoxicity is involved in the retinal neuronal cell death in diabetic retinopathy. Although fenofibrate has been shown to ameliorate the progression of diabetic retinopathy, the effect of pemafibrate, which is highly selective for peroxisome proliferator-activated receptor α on retinal neuronal cell death has not been documented. Here, we investigated whether pemafibrate exerts a beneficial effect against retinal ganglion cell (RGC) death induced by N-methyl-D-aspartate (NMDA) in rats. Experiments were performed on adult male Wistar rats that received an intravitreal injection of 20 nmol NMDA. Fluoro-Gold labeled RGC morphometry showed that oral intake of pemafibrate once a day for 7 days resulted in significant protection on RGC death induced by NMDA. Phosphorylated c-Jun protein, which is involved in apoptosis, was upregulated after NMDA exposure, and this increase was significantly lessened by the systemic pemafibrate treatment. Phosphorylated c-Jun immunopositive cells were colocalized with Thy-1 immunopositive cells, and the increased these cells were ameliorated by the pemafibrate treatment. An increase in TUNEL-positive cells was significantly suppressed by the pemafibrate treatment. Phosphorylated c-Jun immunopositive cells were colocalized with TUNEL-positive cells, and they were decreased by pemafibrate treatment. These results suggest that the RGC protection achieved with pemafibrate appears to be associated with inhibition of phosphorylated c-Jun and its anti-apoptotic effect.

Dysregulation of the NLRP3 Inflammasome in Diabetic Retinopathy and Potential Therapeutic Targets

Diabetic Retinopathy (DR) is an insidious neurovascular disorder secondary to chronic glycemic dysregulation in elderly diabetic patients. In the later stages of DR, the disease manifests as fluid infiltrating the macula, culminating in the leading cause of irreversible visual impairment in working age adults. With the current mainstay treatments preoccupied with slowing down the progression of DR, this presents an unsustainable solution from both an economic and quality of life perspective. Although the exact mechanisms by which hyperglycemia leads to retinal tissue insult are unknown, the evidence suggests that chronic low-grade inflammation in diabetic eye is in part driving the constellation of symptoms present in DR. Of the innate immune system within the eye, the NLR Family Pyrin Domain Containing 3 Inflammasome (NLRP3) has been identified in retinal cells as a causal factor in the pathogenesis of DR. Multiple pathways appear to be present in the diabetic eye that instigate prolonged activation of the NLRP3 which subsequently exerts its deleterious effects by upregulating the release of Interleukin-1Beta and Interleukin-18. In this review, we highlight the current understanding of the pathophysiology of DR, the dysregulation of the NLRP3 secondary to hyperglycemic stress in retinal cells, and novel therapeutic targets to alleviate overactivation of the inflammasome.

The role of reactive oxygen species in the pathogenesis and treatment of retinal diseases

Reactive oxygen species (ROS) normally play an important physiological role in health regulating cellular processes and signal transduction. The amount of ROS is usually kept in fine balance with the generation of ROS largely being offset by the body's antioxidants. A tipping of this balance has increasingly been recognised as a contributor to human disease. The retina, as a result of its cellular anatomy and physical location, is a potent generator of ROS that has been linked to several major retinal diseases. This review will provide a summary of the role of oxidative stress in the pathogenesis of diabetic retinopathy, age-related macular degeneration, myopia, retinal vein occlusion, retinitis pigmentosa and retinopathy of prematurity. Therapies aimed at controlling oxidative stress in these diseases are also examined.

Astaxanthin Protects Retinal Photoreceptor Cells against High Glucose-Induced Oxidative Stress by Induction of Antioxidant Enzymes via the PI3K/Akt/Nrf2 Pathway

Diabetic retinopathy (DR) is a major microvascular complication that can lead to severe visual impairment in patients with diabetes. The elevated oxidative stress and increased reactive oxygen species (ROS) production induced by hyperglycemia have been reported to play an important role in the complex pathogenesis of DR. Astaxanthin (AST), a natural carotenoid derivative, has been recently recognized as a strong free radical scavenger and might, therefore, be beneficial in different diseases, including DR. In this study, we evaluated the potential role of AST as an antioxidative and antiapoptotic agent in protecting retinal cells and also investigated the involvement of the PI3K/Akt/Nrf2 pathway in AST-mediated effects. We treated high glucose-cultured mouse photoreceptor cells (661W) with different concentrations of AST and analyzed ROS production and cell apoptosis in the different regimens. Moreover, we also analyzed the expression of PI3K, Akt, Nrf2, and Phase II enzymes after AST treatment. Our results showed that AST dose-dependently reduced ROS production and attenuated 661W cell apoptosis in a high glucose environment. Importantly, its protective effect was abolished by treatment with PI3K or Nrf2 inhibitors, indicating the involvement of the PI3K/Akt/Nrf2 pathway. These results suggest AST as a nutritional supplement that could benefit patients with DR.

The Inflammasome in Chronic Complications of Diabetes and Related Metabolic Disorders

Diabetes mellitus (DM) ranks seventh as a cause of death worldwide. Chronic complications, including cardiovascular, renal, and eye disease, as well as DM-associated non-alcoholic fatty liver disease (NAFLD) account for most of the morbidity and premature mortality in DM. Despite continuous improvements in the management of late complications of DM, significant gaps remain. Therefore, searching for additional strategies to prevent these serious DM-related conditions is of the utmost importance. DM is characterized by a state of low-grade chronic inflammation, which is critical in the progression of complications. Recent clinical trials indicate that targeting the prototypic pro-inflammatory cytokine interleukin-1β (IL-1 β) improves the outcomes of cardiovascular disease, which is the first cause of death in DM patients. Together with IL-18, IL-1β is processed and secreted by the inflammasomes, a class of multiprotein complexes that coordinate inflammatory responses. Several DM-related metabolic factors, including reactive oxygen species, glyco/lipoxidation end products, and cholesterol crystals, have been involved in the pathogenesis of diabetic kidney disease, and diabetic retinopathy, and in the promoting effect of DM on the onset and progression of atherosclerosis and NAFLD. These metabolic factors are also well-established danger signals capable of regulating inflammasome activity. In addition to presenting the current state of knowledge, this review discusses how the mechanistic understanding of inflammasome regulation by metabolic danger signals may hopefully lead to novel therapeutic strategies targeting inflammation for a more effective treatment of diabetic complications.

Oxidative stress in the retina and retinal pigment epithelium (RPE): Role of aging, and DJ-1

High levels of oxidative radicals generated by daily light exposure and high metabolic rate suggest that the antioxidant machinery of the retina and retinal pigment epithelium (RPE) is crucial for their survival. DJ-1 is a redox-sensitive protein that has been shown to have neuroprotective function in the brain in Parkinson's disease and other neurodegenerative diseases. Here, we analyzed the role of DJ-1 in the retina during oxidative stress and aging. We induced low-level oxidative stress in young (3-month-old) and old (15-month-old) C57BL/6J (WT) and DJ-1 knockout (KO) mice and evaluated effects in the RPE and retina. Absence of DJ-1 resulted in increased retinal dysfunction in response to low levels of oxidative stress. Our findings suggest that loss of DJ-1 affects the RPE antioxidant machinery, rendering it unable to combat and neutralize low-level oxidative stress, irrespective of age. Moreover, they draw a parallel to the retinal degeneration observed in AMD, where the occurrence of genetic variants may leave the retina and RPE unable to fight sustained, low-levels of oxidative stress.

•

Antioxidants are upregulated in young DJ-1 KO RPE but downregulated in the retina.

•

DJ-1 KO retinas are degenerated under low-level oxidative stress, regardless of age.

•

Retinas of both young C57BL and DJ-1 KO were able to regulate antioxidant genes upon low-level oxidative stress.

•

Retinas of both aged C57BL and DJ-1 KO were unable to regulate antioxidant genes upon low-level oxidative stress.

•

RPE of aged C57BLl mice upregulated some antioxidant genes.

Effects of rhaponticin on retinal oxidative stress and inflammation in diabetes through NRF2/HO-1/NF-κB signalling

Oxidative stress and inflammation have long been considered to be responsible for the development and progression of diabetic retinopathy. On the other hand, rhaponticin (RN) has received scientific attention due to its various pharmacological properties. Keeping all these in view, the present study was performed to investigate the potential protective effects of RN on the retina in diabetic rats. Rats were randomly divided into three groups: control group rats, diabetic group rats, diabetic + RN (20 mg/kg body weight for 28 days through oral route) group rats. RN supplementation to diabetic rats significantly prevent the reduction of final body weight loss, reduced weekly fasting blood glucose levels and HbA1c levels with a significant increase in serum insulin levels. quantitative polymerase chain reaction and immunohistochemical analysis found upregulation of Nrf2, NQO-1, HO-1 and upregulation of Keap1 genes and protein distribution along with significantly reduced levels of malondialdehyde and increased activity of superoxide dismutase, catalase and glutathione peroxidase in RN-treated diabetic rats as compared to diabetic rats. Furthermore, treatment of diabetic rats with RN showed downregulated expression of tumour necrosis factor-α, matrix metalloproteinase-2 and upregulated expression of interleukin-10 (IL-10) and TIMP-1 in the retina. RN treatment decreased nuclear factor kappa-light-chain-enhancer of activated B cells distribution and increased IL-10 protein distribution in the retinae of diabetic rats. In addition, RN treatment ameliorated morphological changes observed in retinae of diabetic rats. Altogether, these results provided clear evidence that treatment of diabetic rats with RN attenuated diabetic retinal changes through its hypoglycaemic, antioxidant and anti-inflammatory effects.

Fenofibrate ameliorates testicular damage in rats with streptozotocin-induced type 1 diabetes: role of HO-1 and p38 MAPK

BACKGROUND

Since diabetes mellitus type-1 (DM-1) induces testicular oxidative and inflammatory damage with finally an ultimate male infertility, and as fenofibrate (FEN) plays an important antioxidant and anti-inflammatory role, the aim of the present study was to investigate the effects of FEN on diabetes-induced reproductive damage and clarifying the underlying related mechanisms.

METHODS

DM-1 was induced in male Wistar rats by a single intraperitoneal injection of streptozotocin (50 mg/kg). FEN (100 mg/kg/day, orally) was administrated to diabetic rats for 4 weeks. Testicular damage was detected by estimation of both testicular and body weights, assessment of serum testosterone, testicular oxidative stress parameters (malondialdehyde and nitric oxide levels) and testicular oxidant defenses (reduced glutathione, superoxide dismutase and hemeoxygenase-1). Expressions of the inflammatory markers (inducible nitric oxide synthase, p38 mitogen-activated protein kinase (MAPK), tumor necrosis factor alpha, interleukin-6 and apoptotic marker (caspase-3) were evaluated in testicular tissue. Our results were confirmed by histopathological examination of testicular tissues.

RESULTS

Diabetic testicular damage was proved by both biochemical and histopathological examinations. FEN treatment reversed diabetic testicular damage; normalized the serum testosterone level, improved anti-oxidative capacity, ameliorated the pro-inflammatory cytokine expression in testicular tissue with the down regulation of p38 MAPK mediated-testicular apoptosis.

CONCLUSION

FEN treatment exerted a protective effect against streptozotocin-induced diabetic reproductive dysfunction not only through its powerful antioxidant and hypoglycemic effects, but also through its anti-inflammatory and anti-apoptotic effect via down-regulation of testicular p38 MAPK expression in diabetic rats.