Neuroprotection of quercetin on central neurons against chronic high glucose through enhancement of Nrf2/ARE/glyoxalase-1 pathway mediated by phosphorylation regulation
Although dietary flavonoid quercetin alleviates diabetes-associated cognitive decline in rodents, the mechanisms are not clearly clarified. This study was designed to investigate whether quercetin showed neuroprotection on central neurons against chronic high glucose through the enhancement of Nrf2/ARE/glyoxalase 1 (Glo-1) pathway. SH-SY5Y cells were divided into 8 groups: normal glucose, high glucose (HG), osmotic pressure control, solvent control, HG plus low, middle, high concentrations of quercetin, or Nrf2 activator (sulforaphane). After treatment for 72 h, the associated parameters were measured. We found quercetin and sulforaphane increased cell viability, and enhanced Glo-1 functions (Glo-1 activity, the reduced glutathione and advanced glycation end-products levels) as well as Glo-1 protein and mRNA levels in SH-SY5Y cells cultured with HG. Meanwhile, quercetin and sulforaphane activated Nrf2/ARE pathway, reflected by the raised Nrf2 and p-Nrf2 levels, and the elevated protein and mRNA levels of γ-glutamycysteine synthase (γ-GCS), a known target gene of Nrf2/ARE signaling. Moreover, Nrf2/ARE pathway was activated after pretreatment with a PKC activator, p38 MAPK inhibitor, or GSK-3β inhibitor under the condition of HG, and quercetin addition further strengthened this pathway; however, PKC inhibition or GSK-3β activation pretreatment reversed the effects of quercetin on the protein expression of γ-GCS in the HG condition. In summary, quercetin exerts the neuroprotection by enhancing Glo-1 functions in central neurons under chronic HG condition, which may be mediated by activation of Nrf2/ARE pathway; furthermore, the increased Nrf2 phosphorylation mediated by PKC activation and/or GSK-3β inhibition may involve in the activation of Nrf2/ARE pathway.
Curcumin augments the cardioprotective effect of metformin in an experimental model of type I diabetes mellitus; Impact of Nrf2/HO-1 and JAK/STAT pathways
Metformin is one of the most commonly prescribed antidiabetic drugs. A recent clinical study has highlighted the protective role of metformin against cardiac complications in type I diabetes. Curcumin is a natural compound with well-known antioxidant and anti-inflammatory properties. The present study was designed to investigate the possible role of curcumin in potentiating metformin`s putative effects. Rats received single injection of 52.5 mg/kg streptozocin and the diabetic rats were treated with metformin (200 mg/kg/day), curcumin (100 mg/kg/day) and their combination for 6 weeks. Diabetic rats showed degenerated myocardium as well as significant increase in Creatine Kinase-MB (CK-MB), troponin I and TGF-β levels. In addition, cardiac levels of lipid peroxidation, IL-6, and NF-κB were significantly elevated. Although treatment with metformin restored most of the measured parameters, it showed insignificant improvement in histopathological architecture accompanied by absence of antioxidant effect. Interestingly, concomitant administration of curcumin along with metformin revealed more protection than metformin alone. Inhibition of JAK/STAT pathway and activation of Nrf2/HO-1 pathway seems to be among the mechanisms mediating the effects of curcumin and metformin. The findings of this study highlight the benefits of metformin/curcumin combination in preventing diabetic cardiomyopathy.
Protective effects of sulforaphane on diabetic retinopathy: activation of the Nrf2 pathway and inhibition of NLRP3 inflammasome formation
Sulforaphane (SFN) is abundant in cruciferous plants, providing significant protection against many chronic diseases. With the aim of clarifying the efficacy of sulforaphane in diabetic retinopathy (DR), a series of systematic studies were carried out in the present study. Male Sprague Dawley rats were intraperitoneally injected with streptozotocin (STZ, 65 mg/kg), and those with confirmed diabetes mellitus were given different doses of SFN (0.5 and 1 mg/kg/d) for 12 weeks. In vitro, Müller cells exposed to 25 mM glucose were treated with 2.5 μM SFN. The results indicated that SFN significantly reduced the generation of pro-inflammatory cytokines (TNF-α,IL-6, and IL-1β) and enhanced the activity of antioxidant enzymes (GSH, SOD, and CAT) in the retina of STZ rats. Further, SFN enhanced the nuclear accumulation of Nrf2 and increased the expression of HO-1 and NQO1, two major antioxidants downstream to Nrf2, in the injured retina. In addition, retinal expression levels of NLRP3, cleaved caspase-1 p20, IL-1β p17, and ASC were dramatically increased in STZ-induced DR, and this was abolished by SFN intervention. In vitro, high glucose-induced inflammation and oxidative stress damage in Müller cells were attenuated by SFN. SFN also exerted antioxidant effects, activated the Nrf2 pathway, and inhibited the NLRP3 inflammasome in Müller cells. In conclusion, our work demonstrates that SFN attenuates retinal inflammation and oxidative stress induced by high glucose and activates the antioxidative Nrf2 pathway and inhibits the formation of the NLRP3 inflammasome in vivo and in vitro.
Melatonin attenuates acute kidney ischemia/reperfusion injury in diabetic rats by activation of the SIRT1/Nrf2/HO-1 signaling pathway
Diabetic kidney is more sensitive to ischemia/reperfusion (I/R) injury, which is associated with increased oxidative stress and impaired nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling. Melatonin, a hormone that is secreted with the rhythm of the light/dark cycle, has antioxidative effects in reducing acute kidney injury (AKI). However, the molecular mechanism of melatonin protection against kidney I/R injury in the state of diabetes is still unknown. In the present study, we hypothesized that melatonin attenuates renal I/R injury in diabetes by activating silent information regulator 2 associated protein 1 (SIRT1) expression and Nrf2/HO-1 signaling. Control or streptozotocin (STZ)-induced Type 1 diabetic rats were treated with or without melatonin for 4 weeks. Renal I/R injury was achieved by clamping both left and right renal pedicles for 30 min followed by reperfusion for 48 h. Diabetic rats that were treated with melatonin undergoing I/R injury prevented renal injury from I/R, in aspects of the histopathological score, cell apoptosis, and oxidative stress in kidney, accompanied with decreased expressions of SIRT1, Nrf2, and HO-1 as compared with those in control rats. All these alterations were attenuated or prevented by melatonin treatment; but these beneficial effects of melatonin were abolished by selective inhibition of SIRT1 with EX527. These findings suggest melatonin could attenuate renal I/R injury in diabetes, possibly through improving SIRT1/Nrf2/HO-1 signaling.
Testicular injury attenuated by rapamycin through induction of autophagy and inhibition of endoplasmic reticulum stress in streptozotocin-induced diabetic rats
This study investigated whether rapamycin has the protective effect on the testis of diabetic rats by regulating autophagy, endoplasmic reticulum stress, and oxidative stress.
Nrf2 represses the onset of type 1 diabetes in non-obese diabetic mice
The transcription factor Nrf2 (NF-E2-related factor 2) plays a critical role in oxidative stress responses. While activation of Nrf2 signaling is known to exert anti-inflammatory effects, Nrf2 function in inflammation-mediated autoimmune disorders, such as type 1 diabetes, is not well established. To address the roles of Nrf2 in protection against autoreactive T-cell-induced type 1 diabetes, we used non-obese diabetic (NOD) mice, a polygenic model of human type 1 diabetes, to generate a genetic model that allowed us to assess the contribution of Nrf2 activation to preventing and/or treating type 1 diabetes. As Keap1 negatively regulates Nrf2, we used Keap1 gene knockdown driven by either hypomorphic or knockout alleles of Keap1,which enhances Nrf2 signaling to moderate and excess levels, respectively. We found that Nrf2 activation in NOD::Keap1FA/- mice inhibited T-cell infiltration within or near the islets, ameliorated impairment of insulin secretion, and prevented development of diabetes mellitus in the NOD mice. Notably, Nrf2 activation decreased both plasma interferon-γ (IFN-γ) levels and IFN-γ-positive cell numbers in the pancreatic islets. These findings were also observed in mice with two hypomorphic Keap1 alleles (Keap1FA/FA). Both NOD::Keap1FA/- and NOD::Keap1FA/FA mice had decreased incidence of diabetes mellitus, demonstrating that the activation of Nrf2 signaling prevents the onset of type 1 diabetes mellitus in NOD mice. Thus, Nrf2 appears to be a potential target for preventing and treating type 1 diabetes.
A review for the pharmacological effect of lycopene in central nervous system disorders
Lycopene is an aliphatic hydrocarbon carotenoid extracted from plants like tomatoes, papayas, and watermelons. Previous studies have shown that lycopene can exert prophylactic and/or therapeutic effects in different disorders, such as heart failure and neoplasm via anti-oxidative, anti-inflammatory, and anti-proliferative activities. In the central nervous system (CNS), lycopene also has prophylactic and/or therapeutic effects in different type of disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), cerebral ischemia, epilepsy, and depression. Lycopene also improves cognition and memory ability of rodents in different pathological conditions, such as diabetes, colchicine exposure, high-fat diet (HFD), and aging. Further, lycopene can prevent neuro-toxicities induced by monosodium glutamate (MSG), trimethyltin (TMT), methylmercury (MeHg), tert-butyl hydroperoxide (t-BHP), and cadmium (Cd). In some special conditions such as ethanol addiction and haloperidol-induced orofacial dyskinesia, lycopene administration displays special therapeutic effects. Mechanisms including inhibition of oxidative stress and neuroinflammation, inhibition of neuronal apoptosis, and restoration of mitochondrial function have been shown to mediate the neuroprotective effects of lycopene. Other mechanisms, such as inhibition of nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK), activation of the nuclear factor erythroid 2-related factor (Nrf2) and brain-derived neurotrophic factor (BDNF) signaling, and restoration of intracellular Ca homeostasis, may be also involved in the neuroprotective effect of lycopene. In hope of get a clear impression about the role of lycopene in the CNS, we summarize and discuss the pharmacological effects of lycopene as well as its possible mechanisms in CNS disorder prevention and/or therapy.
Notoginsenoside R1 Protects db/db Mice against Diabetic Nephropathy via Upregulation of Nrf2-Mediated HO-1 Expression
Diabetic nephropathy (DN) is a leading cause of end-stage renal failure, and no effective treatment is available. Notoginsenoside R1 (NGR1) is a novel saponin that is derived from , and our previous studies showed the cardioprotective and neuroprotective effects of NGR1. However, its role in protecting against DN remains unexplored. Herein, we established an experimental model in / mice and HK-2 cells exposed to advanced glycation end products (AGEs). The in vivo investigation showed that NGR1 treatment increased serum lipid, β2-microglobulin, serum creatinine, and blood urea nitrogen levels of / mice. NGR1 attenuated histological abnormalities of kidney, as evidenced by reducing the glomerular volume and fibrosis in diabetic kidneys. In vitro, NGR1 treatment was further found to decrease AGE-induced mitochondria injury, limit an increase in reactive oxygen species (ROS), and reduce apoptosis in HK-2 cells. Mechanistically, NGR1 promoted nucleus nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) expressions to eliminate ROS that induced apoptosis and transforming growth factor beta (TGF-β) signaling. In summary, these observations demonstrate that NGR1 exerts renoprotective effects against DN through the inhibition of apoptosis and renal fibrosis caused by oxidative stress. NGR1 might be a potential therapeutic medicine for the treatment of DN.
Exendin-4 prevented pancreatic beta cells from apoptosis in (Type I) diabetic mouse via keap1-Nrf2 signaling
Nrf2 is an essential part of the defense mechanism of vertebrates and protects them from surrounding stress via participation in stimulated expression of detoxification as well as antioxidant enzymes. It also exerts a role in defending hosts from different stress in the environment, including reactive oxygen species. Our study investigates the role of exendin-4 on Nrf2 pathway as well as cell death in pancreatic β-cell and in non-obese diabetic mice. Result of study indicates exendin-4 mediates activation of Keap1-Nrf2-ARE pathway and may serve as a potential agent to treat type I diabetes mellitus. In our research, we observed excessive reactive oxygen species production, low level of cell death, and PKC phosphorylation on exendine-4 treatment. Nrf2 knockdown led to suppression of reactive oxygen species generation as well as increasing apoptosis. Moreover, siRNA-mediated Nrf2 down-regulation attenuated the suppressive effect of exendin-4 in pancreatic β-cell viability, via modulating apoptosis promoting- and counteracting-proteins, Bax, and Bcl-2.
Omega 3 rich diet modulates energy metabolism via GPR120-Nrf2 crosstalk in a novel antioxidant mouse model
With obesity rates reaching epidemic proportions, more studies concentrated on reducing the risk and treating this epidemic are vital. Redox stress is an important metabolic regulator involved in the pathophysiology of cardiovascular disease, Type 2 diabetes, and obesity. Oxygen and nitrogen-derived free radicals alter glucose and lipid homeostasis in key metabolic tissues, leading to increases in risk of developing metabolic syndrome. Oxidants derived from dietary fat differ in their metabolic regulation, with numerous studies showing benefits from a high omega 3 rich diet compared to the frequently consumed "western diet" rich in saturated fat. Omega 3 (OM3) fatty acids improve lipid profile, lower inflammation, and ameliorate insulin resistance, possibly through maintaining redox homeostasis. This study is based on the hypothesis that altering endogenous antioxidant production and/or increasing OM3 rich diet consumption will improve energy metabolism and maintain insulin sensitivity. We tested the comparative metabolic effects of a diet rich in saturated fat (HFD) and an omega 3-enriched diet (OM3) in the newly developed 'stress-less' mice model that overexpresses the endogenous antioxidant catalase. Eight weeks of dietary intervention showed that mice overexpressing endogenous catalase compared to their wild-type controls when fed an OM3 enriched diet, in contrast to HFD, activated GPR120-Nrf2 cross-talk to maintain balanced energy metabolism, normal circadian rhythm, and insulin sensitivity. These findings suggest that redox regulation of GPR120/FFAR4 might be an important target in reducing risk of metabolic syndrome and associated diseases.
D3T acts as a pro-oxidant in a cell culture model of diabetes-induced peripheral neuropathy
Diabetes mellitus is one of the most common chronic diseases in the United States and peripheral neuropathy (PN) affects at least 50% of diabetic patients. Medications available for patients ameliorate symptoms (pain), but do not protect against cellular damage and come with severe side effects, leading to discontinued use. Our research group uses differentiated SH-SY5Y cells treated with advanced glycation end products (AGE) as a model to mimic diabetic conditions and to study the mechanisms of oxidative stress mediated cell damage and antioxidant protection. N-acetylcysteine (NAC), a common antioxidant supplement, was previously shown by our group to fully protect against AGE-induced damage. We have also shown that 3H-1,2-dithiole-3-thione (D3T), a cruciferous vegetable constituent and potent inducer of nuclear factor (erythroid-derived 2)- like 2 (Nrf2), can significantly increase cellular GSH concentrations and protect against oxidant species-induced cell death. Paradoxically, D3T conferred no protection against AGE-induced cell death or neurite degeneration. In the present study we establish a mechanism for this paradox by showing that D3T in combination with AGE increased oxidant species generation and depleted GSH via inhibition of glutathione reductase (GR) activity and increased expression of the NADPH generating enzyme glucose-6-phosphate dehydrogenase (G6PD). Blocking NADPH generation with the G6PD inhibitor dehydroepiandrosterone was found to protect against AGE-induced oxidant species generation, loss of viability, and neurite degeneration. It further reversed the D3T potentiation effect under AGE-treated conditions. Collectively, these results suggest that strategies aimed at combating oxidative stress that rely on upregulation of the endogenous antioxidant defense system via Nrf2 may backfire and promote further damage in diabetic PN.
Ischemic and hypoxic conditioning: Potential for protection of vital organs
What is the topic of this review? Paradoxically, ischemic and hypoxic conditioning paradigms protect vital organs from ischemic and hypoxic injury. In this Symposium Report, we focus on remote ischemic preconditioning (RIPC) and hypoxic preconditioning as novel therapeutic approaches for cardiac- and neuro-protection. What advances does it highlight? Growing interest in ischemic and hypoxic preconditioning has facilitated improved understanding of associated mechanisms and signaling pathways, and identified potential pitfalls with application of these therapies to clinical trials. Novel adaptations of preconditioning paradigms have also been developed, including intermittent hypoxia training, RIPC training, and RIPC-exercise, extending their utility to chronic settings.
Sulforaphane Delays Fibroblast Senescence by Curbing Cellular Glucose Uptake, Increased Glycolysis, and Oxidative Damage
Increased cell senescence contributes to the pathogenesis of aging and aging-related disease. Senescence of human fibroblasts may be delayed by culture in low glucose concentration. There is also accumulating evidence of senescence delay by exposure to dietary bioactive compounds that activate transcription factor Nrf2. The mechanism of cell senescence delay and connection between these responses is unknown. We describe herein that the cruciferous vegetable-derived metabolite, sulforaphane (SFN), activates Nrf2 and delays senescence of human MRC-5 and BJ fibroblasts . Cell senescence is associated with a progressive and marked increased rate of glucose metabolism through glycolysis. This increases mitochondrial dysfunction and overwhelms defences against reactive metabolites, leading to increasing proteomic and genomic oxidative damage. Increased glucose entry into glycolysis in fibroblast senescence is mainly mediated by increased hexokinase-2. SFN delayed senescence by decreasing glucose metabolism on the approach to senescence, exhibiting a caloric restriction mimetic-like activity and thereby decreased oxidative damage to cell protein and DNA. This was associated with increased expression of thioredoxin-interacting protein, curbing entry of glucose into cells; decreased hexokinase-2, curbing entry of glucose into cellular metabolism; decreased 6-phosphofructo-2-kinase, downregulating formation of allosteric enhancer of glycolysis fructose-2,6-bisphosphate; and increased glucose-6-phosphate dehydrogenase, downregulating carbohydrate response element- (ChRE-) mediated transcriptional enhancement of glycolysis by Mondo/Mlx. SFN also enhanced clearance of proteins cross-linked by transglutaminase which otherwise increased in senescence. This suggests that screening of compounds to counter senescence-associated glycolytic overload may be an effective strategy to identify compounds with antisenescence activity and health beneficial effects of SFN in longevity may involve delay of senescence through glucose and glycolytic restriction response.
Novel Curcumin C66 That Protects Diabetes-Induced Aortic Damage Was Associated with Suppressing JNK2 and Upregulating Nrf2 Expression and Function
Diabetes-related cardiovascular diseases are leading causes of the mortality worldwide. Our previous study has explored the protective effect of curcumin analogue C66 on diabetes-induced pathogenic changes of the aorta. In the present study, we sought to reveal the underlying protective mechanisms of C66. Diabetes was induced in male WT and JNK2 mice with a single intraperitoneal injection of streptozotocin. Diabetic mice and age-matched nondiabetic mice were randomly treated with either vehicle (WT, WT DM, JNK2, and JNK2DM) or C66 (WT + C66, WT DM + C66, JNK2 + C66, and JNK2DM + C66) for three months. Aortic oxidative stress, cell apoptosis, inflammatory changes, fibrosis, and Nrf2 expression and function were assessed by immunohistochemical staining for the protein level and real-time PCR method for mRNA level. The results suggested that either C66 treatment or JNK2 deletion can reverse diabetes-induced aortic oxidative stress, cell apoptosis, inflammation, and fibrosis. Nrf2 was also found to be activated either by C66 or JNK2 deletion. However, C66 had no extra effect on diabetic aortic damage or Nrf2 activation without JNK2. These results suggest that diabetes-induced pathological changes in the aorta can be protected by C66 mainly via inhibition of JNK2 and accompanied by the upregulation of Nrf2 expression and function.
Enhanced Oxidative Damage and Nrf2 Downregulation Contribute to the Aggravation of Periodontitis by Diabetes Mellitus
Diabetes mellitus is a well-recognized risk factor for periodontitis. The goal of the present study was to elucidate whether oxidative stress and nuclear factor erythroid 2-related factor 2 (Nrf2) participate in the aggravation of periodontitis by diabetes. For this purpose, we assigned Wistar rats to control, periodontitis, diabetes, and diabetic periodontitis groups. Two weeks after induction of diabetes by streptozotocin, periodontitis was induced by ligation. Two weeks later, periodontal tissues and blood were harvested and analyzed by stereomicroscopy, immunohistochemistry, and real-time polymerase chain reaction. We found that ligation induced more severe bone loss and periodontal cell apoptosis in diabetic rats than in normal rats ( < 0.05). Compared with the control group, periodontitis significantly enhanced local oxidative damage (elevated expression of 3-nitrotyrosine, 4-hydroxy-2-nonenal, and 8-hydroxy-deoxyguanosine), whereas diabetes significantly increased systemic oxidative damage and suppressed antioxidant capacity (increased malondialdehyde expression and decreased superoxide dismutase activity) ( < 0.05). Simultaneous periodontitis and diabetes synergistically aggravated both local and systemic oxidative damage ( < 0.05); this finding was strongly correlated with the more severe periodontal destruction in diabetic periodontitis. Furthermore, gene and protein expression of Nrf2 was significantly downregulated in diabetic periodontitis ( < 0.05). Multiple regression analysis indicated that the reduced Nrf2 expression was strongly correlated with the aggravated periodontal destruction and oxidative damage in diabetic periodontitis. We conclude that enhanced local and systemic oxidative damage and Nrf2 downregulation contribute to the development and progression of diabetic periodontitis.