Epigallocatechin gallate upregulates NRF2 to prevent diabetic nephropathy via disabling KEAP1

The Keap1-Nrf2 System: A Mediator between Oxidative Stress and Aging

Oxidative stress, a term that describes the imbalance between oxidants and antioxidants, leads to the disruption of redox signals and causes molecular damage. Increased oxidative stress from diverse sources has been implicated in most senescence-related diseases and in aging itself. The Kelch-like ECH-associated protein 1- (Keap1-) nuclear factor-erythroid 2-related factor 2 (Nrf2) system can be used to monitor oxidative stress; Keap1-Nrf2 is closely associated with aging and controls the transcription of multiple antioxidant enzymes. Simultaneously, Keap1-Nrf2 signaling is also modulated by a more complex regulatory network, including phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), protein kinase C, and mitogen-activated protein kinase. This review presents more information on aging-related molecular mechanisms involving Keap1-Nrf2. Furthermore, we highlight several major signals involved in Nrf2 unbinding from Keap1, including cysteine modification of Keap1 and phosphorylation of Nrf2, PI3K/Akt/glycogen synthase kinase 3β, sequestosome 1, Bach1, and c-Myc. Additionally, we discuss the direct interaction between Keap1-Nrf2 and the mammalian target of rapamycin pathway. In summary, we focus on recent progress in research on the Keap1-Nrf2 system involving oxidative stress and aging, providing an empirical basis for the development of antiaging drugs.

The Anti-Inflammatory Properties of Phytochemicals and Their Effects on Epigenetic Mechanisms Involved in TLR4/NF-κB-Mediated Inflammation

Innate immune response induces positive inflammatory transducers and regulators in order to attack pathogens, while simultaneously negative signaling regulators are transcribed to maintain innate immune homeostasis and to avoid persistent inflammatory immune responses. The gene expression of many of these regulators is controlled by different epigenetic modifications. The remarkable impact of epigenetic changes in inducing or suppressing inflammatory signaling is being increasingly recognized. Several studies have highlighted the interplay of histone modification, DNA methylation, and post-transcriptional miRNA-mediated modifications in inflammatory diseases, and inflammation-mediated tumorigenesis. Targeting these epigenetic alterations affords the opportunity of attenuating different inflammatory dysregulations. In this regard, many studies have identified the significant anti-inflammatory properties of distinct naturally-derived phytochemicals, and revealed their regulatory capacity. In the current review, we demonstrate the signaling cascade during the immune response and the epigenetic modifications that take place during inflammation. Moreover, we also provide an updated overview of phytochemicals that target these mechanisms in macrophages and other experimental models, and go on to illustrate the effects of these phytochemicals in regulating epigenetic mechanisms and attenuating aberrant inflammation.

Dihydroactinidiolide regulates Nrf2/HO-1 expression and inhibits caspase-3/Bax pathway to protect SH-SY5Y human neuroblastoma cells from oxidative stress induced neuronal apoptosis

Alzheimer's disease (AD) etiology has been studied for a long time and it is found to be multifaceted involving the accumulation of amyloid β and tau protein. Oxidative stress is an early event in AD associated neurodegeneration provoking neuronal death through mitochondrial dysfunction and activation of caspase-3. Therefore we tested the efficacy of dihydroactinidiolide (DHAc), a monoterpene lactone against the oxidative load involved in AD like pathological conditions induced by sodium dithionite, glutamate, amyloid β and colchicine in SH-SY5Y cells. Some of the indicators of neurotoxicity like acetylcholinesterase activity, intracellular reactive oxygen species (ROS), nitrite content, lipid peroxidation, protein carbonylation, nuclear and membrane damage were found to be significantly high in the toxicant treated cells when compared to the control cells while DHAc pretreatment significantly restored the toxicant induced neuronal damage signatures. Caspase-3 activity was found to be increased in the toxicant treated cells while DHAc significantly reduced it. Western blotting and RT-PCR revealed that DHAc significantly increased anti-apoptotic Bcl-2 expression and mRNA levels of Nrf2 and HO-1. Therefore DHAc was found to protect SH-SY5Y cells from neurotoxicant induced oxidative stress and apoptosis by regulating cellular antioxidant defenses and apoptosis related genes.

New insights into the role of the Nrf2 signaling pathway in green tea catechin applications

Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a transcriptional signaling pathway that plays a crucial role in numerous clinical complications. Pivotal roles of Nrf2 have been proved in cancer, autoimmune diseases, neurodegeneration, cardiovascular diseases, diabetes mellitus, renal injuries, respiratory conditions, gastrointestinal disturbances, and general disorders related to oxidative stress, inflammation, apoptosis, gelatinolysis, autophagy, and fibrogenesis processes. Green tea catechins as a rich source of phenolic compounds can deal with various clinical problems and manifestations. In this review, we attempted to focus on intervention between green tea catechins and Nrf2. Green tea catechins especially epigallocatechin gallate (EGCG) elucidated the protective role of Nrf2 and its downstream molecules in various disorders through Keap-1, HO-1, NQO-1, GPx, GCLc, GCLm, NF-kB cross-link, kinases, and apoptotic proteins. Subsequently, we compiled an updated expansions of the Nrf2 role as a gate to manage and protect different disorders and feasible indications of green tea catechins through this signaling pathway. The present review highlighted recent evidence-based data in silico, in vitro, and in vivo studies on an outline for future clinical trials.

Pharmacotherapy against Oxidative Stress in Chronic Kidney Disease: Promising Small Molecule Natural Products Targeting Nrf2-HO-1 Signaling

The global burden of chronic kidney disease (CKD) intertwined with cardiovascular disease has become a major health problem. Oxidative stress (OS) plays an important role in the pathophysiology of CKD. The nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant responsive element (ARE) antioxidant system plays a critical role in kidney protection by regulating antioxidants during OS. Heme oxygenase-1 (HO-1), one of the targets of Nrf2-ARE, plays an important role in regulating OS and is protective in a variety of human and animal models of kidney disease. Thus, activation of Nrf2-HO-1 signaling may offer a potential approach to the design of novel therapeutic agents for kidney diseases. In this review, we have discussed the association between OS and the pathogenesis of CKD. We propose Nrf2-HO-1 signaling-mediated cell survival systems be explored as pharmacological targets for the treatment of CKD and have reviewed the literature on the beneficial effects of small molecule natural products that may provide protection against CKD.

Epigallocatechin Gallate Ameliorates the Effects of Prenatal Alcohol Exposure in a Fetal Alcohol Spectrum Disorder-Like Mouse Model

Fetal alcohol spectrum disorder is the main preventable cause of intellectual disability in the Western world. Although binge drinking is the most studied prenatal alcohol exposure pattern, other types of exposure, such as the Mediterranean, are common in specific geographic areas. In this study, we analyze the effects of prenatal alcohol exposure in binge and Mediterranean human drinking patterns on placenta and brain development in C57BL/6J mice. We also assess the impact of prenatal treatment with the epigallocatechin-3-gallate antioxidant in both groups. Study experimental groups for Mediterranean or binge patterns: (1) control; (2) ethanol; (3) ethanol + epigallocatechin-3-gallate. Brain and placental tissue were collected on gestational Day 19. The molecular pathways studied were fetal and placental growth, placental angiogenesis (VEGF-A, PLGF, VEGF-R), oxidative stress (Nrf2), and neurodevelopmental processes including maturation (NeuN, DCX), differentiation (GFAP) and neural plasticity (BDNF). Prenatal alcohol exposure resulted in fetal growth restriction and produced imbalances of placental angiogenic factors. Moreover, prenatal alcohol exposure increased oxidative stress and caused significant alterations in neuronal maturation and astrocyte differentiation. Epigallocatechin-3-gallate therapy ameliorated fetal growth restriction, attenuated alcohol-induced changes in placental angiogenic factors, and partially rescued neuronal nuclear antigen (NeuN), (doublecortin) DCX, and (glial fibrillary acidic protein) GFAP levels. Any alcohol consumption (Mediterranean or binge) during pregnancy may generate a fetal alcohol spectrum disorder phenotype and the consequences may be partially attenuated by a prenatal treatment with epigallocatechin-3-gallate.

Anti-inflammatory phytochemicals for the treatment of diabetes and its complications: Lessons learned and future promise

Diabetes mellitus (type 1 and type 2) and its various complications continue to place a huge burden on global medical resources, despite the availability of numerous drugs that successfully lower blood glucose levels. The major challenging issue in diabetes management is the prevention of various complications that remain the leading cause of diabetes-related mortality. Moreover, the limited long-term durability of monotherapy and undesirable side effects of currently used anti-diabetic drugs underlie the urgent need for novel therapeutic approaches. Phytochemicals represent a rich source of plant-derived molecules that are of pivotal importance to the identification of compounds with therapeutic potential. In this review, we aim to discuss recent advances in the identification of a large array of phytochemicals with immense potential in the management of diabetes and its complications. Given that metabolic inflammation has been established as a key pathophysiological event that drives the progression of diabetes, we focus on the protective effects of representative phytochemicals in metabolic inflammation. This paper also discusses the potential of phytochemicals in the development of new drugs that target the inflammation in the management of diabetes and its complications.

Interindividual Differences in Human In Vitro Intestinal Microbial Conversion of Green Tea (‐)‐Epigallocatechin‐3‐ O ‐Gallate and Consequences for Activation of Nrf2 Mediated Gene Expression

Scope

An in vitro faecal incubation model combined with reporter gene assay based testing strategy is developed to characterize interindividual differences in the gut microbial conversion of (‐)‐epigallocatechin‐3‐O‐gallate (EGCG) and its consequences for potential activation of Nrf2‐mediated gene expression.

Method & Results

Anaerobic human faecal incubations are performed to characterize the microbial metabolism of EGCG including interindividual variability. EGCG derived intestinal microbial metabolite patterns show substantial interindividual differences that are correlated to relative microbial abundances determined by 16S rRNA sequencing. Results obtained show the time‐dependent formation of gallic acid, pyrogallol, phenylpropane‐2‐ols, phenyl‐γ‐valerolactones, and 5‐(3′,5′‐dihydroxyphenyl)valeric acid as the major metabolites, with substantial interindividual differences. The activity of the formed metabolites in the activation of EpRE‐mediated gene expression is tested by EpRE‐LUX reporter gene assay. In contrast to EGCG, at low micromolar concentrations, especially gallic acid, pyrogallol, and catechol induce significant activity in the EpRE‐LUX assay.

Conclusions

Given these results and taking the level of formation into account, it is concluded that especially gallic acid and pyrogallol contribute to the EpRE‐mediated beneficial effects of EGCG. The interindividual differences in the formation may result in interindividual differences in the beneficial effects of EGCG and green tea consumption.

An Overview of Nrf2 Signaling Pathway and Its Role in Inflammation

Inflammation is a key driver in many pathological conditions such as allergy, cancer, Alzheimer’s disease, and many others, and the current state of available drugs prompted researchers to explore new therapeutic targets. In this context, accumulating evidence indicates that the transcription factor Nrf2 plays a pivotal role controlling the expression of antioxidant genes that ultimately exert anti-inflammatory functions. Nrf2 and its principal negative regulator, the E3 ligase adaptor Kelch-like ECH- associated protein 1 (Keap1), play a central role in the maintenance of intracellular redox homeostasis and regulation of inflammation. Interestingly, Nrf2 is proved to contribute to the regulation of the heme oxygenase-1 (HO-1) axis, which is a potent anti-inflammatory target. Recent studies showed a connection between the Nrf2/antioxidant response element (ARE) system and the expression of inflammatory mediators, NF-κB pathway and macrophage metabolism. This suggests a new strategy for designing chemical agents as modulators of Nrf2 dependent pathways to target the immune response. Therefore, the present review will examine the relationship between Nrf2 signaling and the inflammation as well as possible approaches for the therapeutic modulation of this pathway.

Role of Nrf2 dysfunction in the pathogenesis of diabetic nephropathy: Therapeutic prospect of epigallocatechin-3-gallate

Diabetic nephropathy (DN), a progressive kidney disease afflicts more than 20 and up to 40% of the diabetic population and it is characterized by persistent microalbuminuria declined glomerular filtration rate. The interesting feature associated with DN is that, even though the progression of the disease correlates with oxidative stress, Nrf2, the master regulator of antioxidant defense system involved in counteracting oxidative stress is also upregulated in the diabetic kidneys of both human as well as experimental animals in early stages of DN. Despite the increased expression, the ability of this protein to get translocated into the nucleus is diminished signifying the functional impairment of Nrf2, implying redox imbalance. Hence, it is understood that agents that boost the translocation of Nrf2 might be beneficial rather than those that quantitatively overexpress Nrf2 in treating DN. The deleterious effects of synthetic Nrf2 activators have instigated the researchers to search for phytochemicals that have ambient Nrf2 boosting ability with no side effects, one such phytochemical is Epigallocatechin-3-gallate (EGCG) and it has shown beneficial effects by preventing the progression of DN via influencing Nrf2/ARE pathway, however, the modus operandi is unclear, despite speculations. This study was designed to find out whether supplementation of Nrf2 booster like EGCG at the crucial time of Nrf2 dysfunction can mitigate the progression of DN. Based on the findings of the present study, it might be concluded that the beneficial effect of EGCG in mitigating DN is mediated mainly through its ability to activate the Nrf2/ARE signaling pathway at multiple stages i.e., by downregulating Keap1 and boosting the nuclear Nrf2 level by disrupting Nrf2-Keap1 interaction. These results emphasize that supplementation of EGCG might be more beneficial at an early stage of DN, where dysfunctional Nrf2 accumulation occurs, which should be further validated.

Protective Effects of Epigallocatechin Gallate (EGCG) on Endometrial, Breast, and Ovarian Cancers

Green tea and its major bioactive component, (-)-epigallocatechin gallate (EGCG), possess diverse biological properties, particularly antiproliferation, antimetastasis, and apoptosis induction. Many studies have widely investigated the anticancer and synergistic effects of EGCG due to the side effects of conventional cytotoxic agents. This review summarizes recent knowledge of underlying mechanisms of EGCG on protective roles for endometrial, breast, and ovarian cancers based on both in vitro and in vivo animal studies. EGCG has the ability to regulate many pathways, including the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), inhibition of nuclear factor-κB (NF-κB), and protection against epithelial-mesenchymal transition (EMT). EGCG has also been found to interact with DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), which affect epigenetic modifications. Finally, the action of EGCG may exert a suppressive effect on gynecological cancers and have beneficial effects on auxiliary therapies for known drugs. Thus, future clinical intervention studies with EGCG will be necessary to more and clear evidence for the benefit to these cancers.

(-)-Epicatechin and the colonic metabolite 2,3-dihydroxybenzoic acid protect against high glucose and lipopolysaccharide-induced inflammation in renal proximal tubular cells through NOX-4/p38 signalling

Chronic hyperglycaemia and inflammation are present in diabetes and both processes have been related to the pathogenesis of diabetic kidney disease. Epicatechin (EC) and main colonic phenolic acids derived from flavonoid intake, such as 2,3-dihydroxybenzoic acid (DHBA), 3,4-dihydroxyphenylacetic acid (DHPAA) and 3-hydroxyphenylpropionic acid (HPPA), have been suggested to exert beneficial effects in diabetes. This study was aimed at investigating whether the mentioned compounds could prevent inflammation in renal proximal tubular NRK-52E cells induced by high glucose and lipopolysaccharide (LPS). Pre-treatment of cells with EC and DHBA (5 μM) reverted the enhanced levels of pro-inflammatory cytokines, such as tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6) and monocyte chemoattractant protein 1 (MCP-1), activated by high glucose and LPS. Additionally, EC and DHBA pre-incubation reduced the increased values of adhesion molecules, namely, intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), as well as those of mitogen-activated protein kinases (MAPKs) [extracellular signal-regulated kinase (ERK), -c-jun N-terminal kinase (JNK) and -p38 protein kinase (p38)] activated by the high glucose and LPS challenge. Thus, in EC and DHBA pre-treated cells ICAM-1, p-ERK and p-JNK were returned to control values, and VCAM-1 and p-p38 levels were reduced by ∼20 and 25%, respectively, when compared to high glucose plus LPS-stimulated cells. Likewise, pre-treatment with EC and DHBA protected against high glucose plus LPS-triggered oxidative stress by preventing increased ROS and NADPH oxidase 4 (NOX-4) levels (∼25 and 45% reduction, respectively). By using specific inhibitors of p38 and NOX-4, the participation of both proteins in EC- and DHBA-mediated protection against inflammation and associated oxidative stress was shown. Taken together, EC and DHBA exert beneficial effects in renal proximal tubular cells, as they contribute to preventing the inflammatory-induced milieu and the accompanying redox imbalance, playing NOX-4/p38 a crucial role.

Tea Drinking Alleviates Diabetic Symptoms via Upregulating Renal Water Reabsorption Proteins and Downregulating Renal Gluconeogenic Enzymes in db/db Mice

SCOPE

Tea, made from the plant Camellia sinensis, is known to have anti-diabetes effects and different mechanisms of action are proposed. Kidney is a vital organ in managing water reabsorption and glucose metabolism, and is greatly influenced by diabetes. The present study investigates the effects of tea administration on water reabsorption and gluconeogenesis in the kidney of diabetic mice.

METHODS AND RESULTS

Db/db mice are given tea infusion as drinking fluid when they begin to exhibit hyperglycemia. It is found that green tea or black tea infusion potently elevates renal proteins vital for water reabsorption, including protein kinase C-α, aquaporin 2, and urea transporter-A1, as well as increases trafficking of these proteins to apical plasma membrane where they exert water reabsorption function. The treatment also downregulates renal gluconeogenic enzymes, including glucose-6-phosphatase-α and phosphoenolpyruvate carboxykinase. Associated with these biochemical changes are the rectified polyuria, polydipsia, polyphagia, and hyperglycemia, all symptoms of diabetes.

CONCLUSIONS

For the first time, the present study demonstrates that tea has robust effects in enhancing kidney water reabsorption proteins and downregulating gluconeogenic enzymes in db/db mice. It remains to be investigated whether such beneficial effects of tea occur in humans.

Shenyan Kangfu tablet alleviates diabetic kidney disease through attenuating inflammation and modulating the gut microbiota

Inflammation plays a predominant role in the pathogenesis of diabetic kidney disease (DKD). The Shenyan Kangfu tablet (SYKFT) is a prescription of traditional Chinese medicine for treating chronic kidney disease. However, the concrete mechanism is still unclear. According to previous clinical trial, we explored the effects and potential mechanism on DKD in db/db model supplemented with SYKFT. As a result, SYKFT reduced stimulated blood glucose and HbA1c levels, alleviated renal dysfunction, glomerular and tubular damage, and renal inflammation (TNF-α and IL-1β) in db/db mice. The primary mechanistic study illustrated that SYKFT improved renal injury mainly associated with inhibition of NF-κB in vivo and in vitro. This study further observed that SYKFT increased relative abundance of Firmicutes and decreased Bacteroidetes, showing direct correlation between representative microbiota relative abundance and renal function parameters. SYKFT effectively decreased the relative abundance of Bacteroides, and positive correlation between the relative abundance and protein expression of NF-κB, TNF-α and IL-1β predicted that anti-inflammatory activity of SYKFT was associated with modulating the gut microbiota. Therefore, we first demonstrated SYKFT alleviated DKD through regulating renal inflammatory signaling cascades and intestinal microbiota and also pointed out the role of specific gut microbiota in the development of DKD.

Protective Effects of Grape Seed Proanthocyanidins on the Kidneys of Diabetic Rats through the Nrf2 Signalling Pathway

Background

Diabetic nephropathy (DN) is the most common cause of end-stage renal failure. Grape seed proanthocyanidin extract (GSPE) is a powerful antioxidant that is believed to protect the kidney through antioxidant action. However, the underlying mechanism of GSPE protection against DN remains unclear.

Objective

To explore if GSPE can improve DN by activating nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant response element signalling and to clarify its possible mechanism. Materials and methods. Ten healthy Sprague-Dawley rats were randomly selected as controls. Rats with streptozotocin-induced diabetes were randomly divided into three groups (10 animals/group): type 2 diabetes mellitus (T2DM) group (untreated), L-GSPE group (treated with 125-mg/kg/day GSPE for 8 weeks), and H-GSPE group (treated with 250 mg/kg/day GSPE for 8 weeks).

Results

Renal histopathological results indicated limited pathological damage in GSPE-treated groups. Compared with the T2DM group, the H-GSPE group had significantly reduced kidney weight and renal index. Similarly, the levels of fasting blood glucose, serum creatinine, blood urea nitrogen, uric acid, urinary albumin, and renal malondialdehyde (p < 0.05) were also significantly decreased. In addition, GSPE significantly increased the levels of superoxide dismutase, total antioxidative capability, and glutathione (p < 0.05) as well as the protein levels of Nrf2, HO-1, glutathione S-transferase, and NAD (P)H quinone oxidoreductase 1 (p < 0.05).

Conclusion

The results indicate that GSPE reduced renal damage in rats with diabetes by activating the Nrf2 signalling pathway, which consequently increased the antioxidant capacity of the tissue. Therefore, GSPE is a potential natural agent for the treatment of diabetic nephropathy.

Epigallocatechin Gallate Slows Retinal Degeneration, Reduces Oxidative Damage, and Modifies Circadian Rhythms in P23H Rats

Retinitis pigmentosa (RP) includes a group of genetic disorders that involve the loss of visual function due to mutations mainly in photoreceptors but also in other retinal cells. Apoptosis, retinal disorganization, and inflammation are common in the progression of the disease. Epigallocatechin gallate (EGCG) has been proved as beneficial in different eye diseases. Pigmented heterozygous P23H rat was used as an animal model of RP. Visual function was assessed by optomotor and electroretinogram (ERG) and circadian rhythms were evaluated by telemetry. Hepatic oxidative damage and antioxidant defenses were assessed using biochemical tests. The visual function of the EGCG P23H group was preserved, with a deterioration in the activity period and lower values in the interdaily stability parameter. Control rats treated with EGCG were less active than the sham group. EGCG increased antioxidant levels in P23H rats but reduced total hepatic antioxidant capacity by almost 42% in control rats compared to the sham group. We conclude that treatment with EGCG improves visual function and antioxidant status in P23H rats but diminishes antioxidant defenses in wild-type control animals, and slightly worsens activity circadian rhythms. Further studies are necessary to clarify the beneficial effects in disease conditions and in healthy organisms.

Epigallocatechin-3-gallate (EGCG) inhibits myofibroblast transformation of human Tenon's fibroblasts

Myofibroblast transformation of human Tenon's fibroblasts severely challenges the outcome of glaucoma filtration surgery. epigallocatechin-3-gallate (EGCG) is considered as a potential reagent to overcome this issue for its anti-fibrosis effect on various human diseases, but it is unclear on the fibrosis of Tenon's fibroblasts. This study was conducted to investigate the effect of EGCG on TGF-β1-induced myofibroblast transformation of human Tenon's fibroblasts. The human Tenon's fibroblasts were incubated in the medium containing 10 ng/mL TGF-β1, and subsequently treated with EGCG or mitomycin C (MMC). The cell proliferation and migration were analyzed. The expression of alpha-smooth muscle actin (α-SMA), type I collagen (Col-I), and p-Smad2/3 were also evaluated. It showed that EGCG and MMC strongly inhibited the elevation in cell number in tissue explants compared to the tissues treated with TGF-β1 alone. Scratch-Wound assay showed that 48 h after TGF-β1 induction, only 10% of the wound width remained. But cells treated with EGCG still showed over 93% wound width. Further, EGCG effectively inhibited TGF-β1-induced expression of α-SMA and Col-I as well as phosphorylation of Smad2/3 in Tenon's fibroblasts. Altogether, we concluded that EGCG suppressed the myofibroblast transformation in Tenon's fibroblasts through inactivating TGF-β1/Smad signaling. These findings demonstrate that EGCG can be considered as one of the possible antifibrotic reagents for preventing postoperative scarring in glaucoma filtration surgery.

Sinapic Acid Ameliorates the Progression of Streptozotocin (STZ)-Induced Diabetic Nephropathy in Rats via NRF2/HO-1 Mediated Pathways

Diabetic neuropathy (DN) is a complicated inauspicious outcome of diabetes, like other abnormalities of diabetes the cause of DN is still vague and it may be the result of various pathological conditions leading up to end-stage renal failure. The present study examines the efficacy of sinapic acid (SA) in streptozotocin (STZ)-induced DN nephropathy and the linked pathway. Twenty-four rats were equally divided randomly into four categories: Normal control (NC), STZ, STZ + SA 20 mg/kg bw, and STZ + SA 40 mg/kg bw. After 8 weeks they were evaluated for ratio of renal index, the fasting blood glucose (FBG), blood urea nitrogen (BUN), 24 h urea protein, serum creatinine (SCr), reduced glutathione peroxidase (GPx), superoxide dismutase (SOD), lipid peroxidation (MDA), tumor necrosis factor α (TNFα), interleukin (IL)-6, as well as lipid profile total cholesterol (TC), total triglycerides (TG), very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL) levels. Additionally, histomorphology and ultrastructure of the kidneys were also assessed. Protein expression levels of transforming growth factor-β1 (TGF-β1), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), IκBα protein (IkBα), anti-apoptotic protein BCl2, nuclear factor kappa B (NF-kB), and Bax were examined. We observed that SA 20 mg/kg bw and 40 mg/kg bw pretreatment significantly and dose-dependently upregulated the protein expression of HO-1, Nrf2, IKBα, and Bcl-2 but downregulated the protein expression of NF-κB, proposing that the nephroprotective mechanism of SA is due to its antioxidant and anti-inflammatory activity; SA prevents the release of cytokines and inflammatory markers (TNFα and IL-6), upregulates antioxidant defense enzymes, and reduces lipid peroxidation, as well as nitric oxide, and anti-apoptotic activity, which may be influenced by the regulation of TNF-α, IL-6, Bcl-2, NF-kB, and BaX via the Nrf2/HO-1 pathway in STZ induced DN. Thus, our results suggest that SA ameliorates the development of STZ-induced DN in rats via NRF2/HO-1 mediated pathways. Further comprehensive studies are required for complete elucidation of the fundamental mechanisms.

Protective role of NRF2 in macrovascular complications of diabetes

Macrovascular complications develop in over a half of the diabetic individuals, resulting in high morbidity and mortality. This poses a severe threat to public health and a heavy burden to social economy. It is therefore important to develop effective approaches to prevent or slow down the pathogenesis and progression of macrovascular complications of diabetes (MCD). Oxidative stress is a major contributor to MCD. Nuclear factor (erythroid‐derived 2)‐like 2 (NRF2) governs cellular antioxidant defence system by activating the transcription of various antioxidant genes, combating diabetes‐induced oxidative stress. Accumulating experimental evidence has demonstrated that NRF2 activation protects against MCD. Structural inhibition of Kelch‐like ECH‐associated protein 1 (KEAP1) is a canonical way to activate NRF2. More recently, novel approaches, such as activation of the Nfe2l2 gene transcription, decreasing KEAP1 protein level by microRNA‐induced degradation of Keap1 mRNA, prevention of proteasomal degradation of NRF2 protein and modulation of other upstream regulators of NRF2, have emerged in prevention of MCD. This review provides a brief introduction of the pathophysiology of MCD and the role of oxidative stress in the pathogenesis of MCD. By reviewing previous work on the activation of NRF2 in MCD, we summarize strategies to activate NRF2, providing clues for future intervention of MCD. Controversies over NRF2 activation and future perspectives are also provided in this review.

The Potential for Reducing Lynch Syndrome Cancer Risk with Nutritional Nrf2 Activators

Lynch syndrome (LS), is an autosomal dominant disorder predisposing patients to multiple cancers, predominantly colorectal (CRC) and endometrial, and is implicated in 2-4% of all CRC cases. LS is characterized by mutations of four mismatch repair (MMR) genes which code for proteins responsible for recognizing and repairing DNA lesions occurring through multiple mechanisms including oxidative stress (OS). Increased OS can cause DNA mutations and is considered carcinogenic. Due to reduced MMR activity, LS patients have an increased risk of cancer as a result of a decreased ability to recognize and repair DNA lesions caused by OS. Due to its carcinogenic properties, reducing the level of OS may reduce the risk of cancer. Nutritional Nrf2 activators have been shown to reduce the risk of carcinogenesis in the general population through activation of the endogenous antioxidant system. Common nutritional Nrf2 activators include sulforaphane, curcumin, DATS, quercetin, resveratrol, and EGCG. Since LS patients are more susceptible to carcinogenesis caused by OS, it is hypothesized that nutritional Nrf2 activators may have the potential to reduce the risk of cancer in those with LS by modulating OS and inflammation. The purpose of this paper is to review the available evidence in support of this statement.

(-)-Epigallocatechin-3-gallate (EGCG) attenuates salt-induced hypertension and renal injury in Dahl salt-sensitive rats

Epigallocatechin-3-gallate (EGCG), a main active catechin in green tea, was reported to attenuate renal injury and hypertension. However, its effects on salt-induced hypertension and renal injury remain unclear. In the present study, we explored its effects on hypertension and renal damage in Dahl rats with salt-sensitive hypertension. We found that EGCG could lower blood pressure after 6 weeks of oral administration, reduce 24 h urine protein levels and decrease creatinine clearance, and attenuate renal fibrosis, indicating that it could attenuate hypertension by protecting against renal damage. Furthermore, we studied the renal protective mechanisms of EGCG, revealing that it could lower malondialdehyde levels, reduce the numbers of infiltrated macrophages and T cells, and induce the apoptosis of NRK-49F cells. Considering that the 67 kD laminin receptor (67LR) binds to EGCG, its role in EGCG-induced fibroblast apoptosis was also investigated. The results showed that an anti-67LR antibody partially abrogated the apoptosis-inducing effects of EGCG on NRK-49F cells. In summary, EGCG may attenuate renal damage and salt-sensitive hypertension via exerting anti-oxidant, anti-inflammatory, and apoptosis-inducing effects on fibroblasts; the last effect is partially mediated by 67LR, suggesting that EGCG represents a potential strategy for treating salt-sensitive hypertension.

Potential Applications of NRF2 Modulators in Cancer Therapy

The nuclear factor erythroid 2-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 (KEAP1) regulatory pathway plays an essential role in protecting cells and tissues from oxidative, electrophilic, and xenobiotic stress. By controlling the transactivation of over 500 cytoprotective genes, the NRF2 transcription factor has been implicated in the physiopathology of several human diseases, including cancer. In this respect, accumulating evidence indicates that NRF2 can act as a double-edged sword, being able to mediate tumor suppressive or pro-oncogenic functions, depending on the specific biological context of its activation. Thus, a better understanding of the mechanisms that control NRF2 functions and the most appropriate context of its activation is a prerequisite for the development of effective therapeutic strategies based on NRF2 modulation. In line of principle, the controlled activation of NRF2 might reduce the risk of cancer initiation and development in normal cells by scavenging reactive-oxygen species (ROS) and by preventing genomic instability through decreased DNA damage. In contrast however, already transformed cells with constitutive or prolonged activation of NRF2 signaling might represent a major clinical hurdle and exhibit an aggressive phenotype characterized by therapy resistance and unfavorable prognosis, requiring the use of NRF2 inhibitors. In this review, we will focus on the dual roles of the NRF2-KEAP1 pathway in cancer promotion and inhibition, describing the mechanisms of its activation and potential therapeutic strategies based on the use of context-specific modulation of NRF2.

The Regulation of Host Intestinal Microbiota by Polyphenols in the Development and Prevention of Chronic Kidney Disease

Polyphenols are essential antioxidants in our regular diet, and have shown potential antibacterial effects. Other important biological effects, such as anticancer or antibacterial activities, have been demonstrated by some polyphenols. In recent years, the benefits of polyphenols to human health have attracted increasing attention from the scientific community. Recent studies have shown that polyphenols such as anthocyanin, catechin, chlorogenic acid, and resveratrol can inhibit pathogenic bacteria such as Escherichia coli and Salmonella to help regulate intestinal microflora. An imbalance of intestinal microflora and the destruction of intestinal barrier function have been found to have a potential relationship with the occurrence of chronic kidney disease (CKD). Specifically, they can aberrantly trigger the immune system to cause inflammation, increase the production of uremic toxins, and further worsen the condition of CKD. Therefore, the maintenance of intestinal microflora and the intestinal tract in a stable and healthy state may be able to "immunize" patients against CKD, and treat pre-existing disease. The use of common antibiotics may lead to drug resistance in pathogens, and thus beneficial polyphenols may be suitable natural substitutes for antibiotics. Herein we review the ability of different polyphenols, such as anthocyanin, catechin, chlorogenic acid, and resveratrol, to regulate intestinal microorganisms, inhibit pathogenic bacteria, and improve inflammation. In addition, we review the ability of different polyphenols to reduce kidney injury, as described in recent studies.

Epigallocatechin-3-gallate preconditioned Adipose-derived Stem Cells confer Neuroprotection in aging rat brain

Aging is the most important current issue and is usually accompanied by complications, such as cardiovascular disorders and neurodegenerative diseases, which are the leading causes of death worldwide and the second major cause of death in Taiwan. In this study, we have investigated the protective effect of adipose-derived mesenchymal stem cells (ADSCs) and the role of epigallocatechin gallate (EGCG) in enhancing this effect in aging cerebral cortex of rats. Further, we attempted to elucidate the molecular mechanism through which EGCG influences the protective effects of ADSC. ADSCs, co-cultured with EGCG, were injected into 20-month-old Wistar rats. Hematoxylin and eosin staining of the cerebral cortex revealed noticeable neurogenic activity and visible improvements in the integrity of the pre-frontal cortex tissue, compared to that in rats treated with ADSCs alone. Western blot analysis confirmed that ADSC, co-cultured with EGCG, enhanced cell survival via the p-Akt pathway and improved mitochondrial biogenesis via the SIRT-1 pathway. Moreover, it increased the available brain-derived neurotrophic factor to a higher degree than that in the ADSC group. Furthermore, western blotting showed that EGCG improved the antioxidant activity of the ADSCs in the cortex tissues via the Nrf-2 and HO-1 pathway. Based on these findings, we propose that this variation in stem cell treatment may facilitate functional recovery and enhanced neuroprotection in aged brains.

Dietary antioxidants remodel DNA methylation patterns in chronic disease

Chronic diseases account for over 60% of all deaths worldwide according to the World Health Organization reports. Majority of cases are triggered by environmental exposures that lead to aberrant changes in the epigenome, specifically, the DNA methylation patterns. These changes result in altered expression of gene networks and activity of signalling pathways. Dietary antioxidants, including catechins, flavonoids, anthocyanins, stilbenes and carotenoids, demonstrate benefits in the prevention and/or support of therapy in chronic diseases. This review provides a comprehensive discussion of potential epigenetic mechanisms of antioxidant compounds in reversing altered patterns of DNA methylation in chronic disease. Antioxidants remodel the DNA methylation patterns through multiple mechanisms, including regulation of epigenetic enzymes and chromatin remodelling complexes. These effects can further contribute to antioxidant properties of the compounds. On the other hand, decrease in oxidative stress itself can impact DNA methylation delivering additional link between antioxidant mechanisms and epigenetic effects of the compounds. LINKED ARTICLES: This article is part of a themed section on The Pharmacology of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.6/issuetoc.

Redox signaling in aging kidney and opportunity for therapeutic intervention through natural products

Kidney diseases are serious public problems with high morbidity and mortality in the general population and heavily retard renal function with aging regardless of the cause. Although myriad strategies have been assigned to prevent or harness disease progression, unfortunately, thus far, there is a paucity of effective therapies partly due to an insufficient knowledge of underlying pathological mechanisms, indicating deeper studies are urgently needed. Additionally, natural products are increasingly recognized as an alternative source for disease intervention owing to the potent safety and efficacy, which might be exploited for novel drug discovery. In this review, we primarily expatiate the new advances on mediators that might be amenable to targeting aging kidney and kidney diseases, including nicotinamide adenine dinucleotide phosphate oxidase (NOX), transforming growth factor-β (TGF-β), renin-angiotensin system (RAS), nuclear factor-erythroid 2 related factor 2 (Nrf2), peroxisome proliferator-activated γ receptor (PPARγ), advanced glycation endproducts (AGEs) as well as microRNAs and vitagenes. Of note, we conclude by highlighting some natural products which have the potential to facilitate the development of novel treatment for patients with myriad renal diseases.

Molecular Mechanisms of Epigallocatechin-3-Gallate for Prevention of Chronic Kidney Disease and Renal Fibrosis: Preclinical Evidence

Chronic kidney disease (CKD) is a common public health problem worldwide characterized by gradual decline of renal function over months/years accompanied by renal fibrosis and failure in tissue wound healing after sustained injury. Patients with CKD frequently present with profound signs/symptoms that require medical treatment, mostly culminating in hemodialysis and renal transplantation. To prevent CKD more efficiently, there is an urgent need for better understanding of the pathogenic mechanisms and molecular pathways of the disease pathogenesis and progression, and for developing novel therapeutic targets. Recently, several lines of evidence have shown that epigallocatechin-3-gallate (EGCG), an abundant phytochemical polyphenol derived from Camellia sinensis, might be a promising bioactive compound for prevention of CKD development/progression. This review summarizes current knowledge of molecular mechanisms underlying renoprotective roles of EGCG in CKD based on available preclinical evidence (from both in vitro and in vivo animal studies), particularly its antioxidant property through preservation of mitochondrial function and activation of Nrf2 (nuclear factor erythroid 2-related factor 2)/HO-1 (heme oxygenase-1) signaling, anti-inflammatory activity, and protective effect against epithelial mesenchymal transition. Finally, future perspectives, challenges, and concerns regarding its clinical use in CKD and renal fibrosis are discussed.

Retracted: Epigallocatechin gallate ameliorates morphological changes of pancreatic islets in diabetic mice and downregulates blood sugar level by inhibiting the accumulation of AGE-RAGE

This study aimed to elucidate the key mechanisms and effects of the functional component of green tea, epigallocatechin gallate (EGCG) on a diabetic mouse model. The detected relationship between compounds and genes recorded in the STITCH database highlighted an interaction network between the direct target genes of EGCG and the known diabetes-related genes, which was made apparent through the analysis of gene-gene interactions and signaling pathways, revealing that a key AGE-RAGE signaling pathway in diabetes was enriched in the network. By means of systematic supplementary analyses on diabetic mice, provided evidence suggested that EGCG could significantly enhance the morphology of pancreatic tissues in diabetic mice and downregulate the blood glucose level in a clear dose effect manner, and increased insulin receptor (IR), insulin receptor substrate (IRS1 and IRS2) expression in the liver. Through the detection of protein expression, EGCG was observed to possess the ability to downregulate the accumulation of AGE-RAGE in pancreatic tissues as well as in the transcription factor nuclear factor-κB (NF-κB), which represents a potentially significant method by which EGCG influences diabetes. The results of this study provided evidence indicating that EGCG can effectively improve the morphology of pancreatic tissues, but notably reduce blood glucose levels in diabetic mice, which may be related to its inhibition of AGE-RAGE signaling pathway and activation of transcription factor NF-κB pathway.

P53/NRF2 mediates SIRT1's protective effect on diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end stage renal disease, posing a severe threat to public health. Previous studies reported the protective role of sirtuin 1 (SIRT1) in DN, encouraging the investigation of more potent and specific SIRT1 activators. SRT2104 is a novel, first-in-class, highly selective small-molecule activator of SIRT1, with its effect and mechanism unknown on DN. To this end, streptozotocin-induced C57BL/6 wild-type (WT) diabetic mice were treated with SRT2104, for 24 weeks. To determine whether SRT2104 acted through inhibition of P53 - a substrate of SIRT1, the P53 activator nutlin3a was administered to the WT diabetic mice in the presence of SRT2104. In order to test whether nuclear factor erythroid 2-related factor 2 (NRF2) - the master of cellular antioxidants - mediated SIRT1 and P53's actions, WT and Nrf2 gene knockout (KO) diabetic mice were treated with SRT2104 or the P53 inhibitor pifithrin-α (PFT-α). In the WT mice, SRT2104 enhanced renal SIRT1 expression and activity, deacetylated P53, and activated NRF2 antioxidant signaling, providing remarkable protection against the DM-induced renal oxidative stress, inflammation, fibrosis, glomerular remodeling and albuminuria. These effects were completely abolished in the presence of nutlin3a. Deletion of the Nrf2 gene completely abrogated the efficacies of SRT2104 and PFT-α in elevating antioxidants and ameliorating DN, despite their abilities to activate SIRT1 and inhibit P53 in the Nrf2 KO mice. The present study reports the beneficial effects of SRT2104 on DN, uncovering a SIRT1/P53/NRF2 pathway that modulates the pathogenesis of DN.

Lycopene attenuates AFB1-induced renal injury with the activation of the Nrf2 antioxidant signaling pathway in mice

Oxidative stress is an important molecular mechanism for kidney injury in aflatoxin B1 (AFB1) nephrotoxicity. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master transcription factor for regulating the cellular oxidative stress response, which has been confirmed in animal models. Lycopene (LYC), a natural carotenoid, has received extensive attention due to its antioxidant effect with the activation of Nrf2. However, the role of LYC in protecting against AFB1-induced renal injury is unknown. To evaluate the chemoprotective effect of LYC on AFB1-induced renal injury, forty-eight male mice were randomly divided into 4 groups and treated with LYC (5 mg per kg of bodyweight) and/or AFB1 (0.75 mg per kg of bodyweight) by intragastric administration for 30 days. AFB1 and LYC were respectively dissolved in olive oil. We found that AFB1 exposure significantly increased the serum concentrations of blood urea nitrogen (BUN) and serum creatinine (SCR), and caused damage to the renal structure. Notably, LYC potentially alleviated AFB1-induced kidney lesions through attenuating AFB1-induced oxidative stress. Renal nuclear factor-erythroid 2-related factor 2 (Nrf2) and its downstream target gene (CAT, NQO1, SOD1, GSS, GCLM and GCLC) translation and protein expression were ameliorated by pretreatment with LYC in AFB1-exposed mice. These results suggested that LYC potentially alleviates AFB1-induced renal injury. This effect may be attributed to the enhancement of renal antioxidant capacity with the activation of the Nrf2 antioxidant signaling pathway.

Antioxidant and nephroprotection activities of Combretum micranthum: A phytochemical, in-vitro and ex-vivo studies

Management of chronic renal failure is exceedingly expensive. Despite of encouraging experimental outcomes, there is a lack of potent nephroprotective drugable molecules in a clinics or market. To develop a nephroprotective phytomedicine, the present study was designed to do a literature survey on reported phytochemical and biological analysis of Combretum micranthum and to carry out chemoprofiling, in-vitro antioxidant and ex-vivo nephroprotective capacity of the title plant. The phytochemical and biological activity survey of C. micranthum has reveals the presence of many bioactive compounds such as flavonoids, terpenoids, steroids and alkaloids with many biological activities. Phytochemical investigation re-confirmed the presence of these compounds. Hydroalcoholic extract of C. micranthum (CM extract) showed a strong antioxidant activity by scavenging AAPH, DPPH, nitric oxide, hydrogen peroxide and chelating metal ions. CM extract exhibited significant (P < 0.001) dose dependent inhibition of ferric chloride-ascorbic acid induced lipid peroxidation. Diabetic nephropathy is a serious and common complication leading to end stage renal disease. Therefore, in the present study, glucose-induced toxicity was also studied in human embryonic kidney cells (HEK-293) as an in vitro model for diabetic nephropathy. The results showed that exposure of cells to high glucose (100 mM) for 72 h significantly reduced the cell viability resulting in morphological changes such as cell shrinkage, rounded cell shape and cytoplasmic vacuolation. Treatment with CM extract at 10 and 25 μg/mL resulted in significant improvement in cell viability from 10 to 23% compared to the high glucose control. This study demonstrated the potential antioxidant and nephroprotective properties of C. micranthum, justifying its traditional use in the treatment of various diseases.

Tannins and vascular complications of Diabetes: An update

BACKGROUND

Diabetes mellitus is a chronic metabolic disorder associated with persistent increased level of glucose in the blood. According to a report by World Health Organisation (WHO), prevalence of diabetes among adults over 18 years of age had reached to 8.5% in year 2014 which was 4.7% in 1980s. The Prolong increased level of glucose in blood leads to development of microvascular (blindness, nephropathy and neuropathy) and macrovascular (cardiovascular and stroke) degenerative complications because of uncontrolled level of glucose in blood. This also leads to the progression of oxidative stress and affecting metabolic, genetic and haemodynamic system by activation of polyol pathway, protein kinase C pathway, hexosamine pathway and increases advanced glycation end products (AGEs) formation. Diabetes mellitus and its associated complications are one of the major leading causes of mortality worldwide. Various natural products like alkaloids, glycosides, flavonoids, terpenoids and polyphenols are reported for their activity in management of diabetes and its associated diabetic complications. Tannins are systematically studied by many researchers in past few decades for their effect in diabetes and its complications.

AIM

The present review was designed to compile the data of tannins and their beneficial effects in the management of diabetic complications.

METHOD

Literature search was performed using various dataset like pubmed, EBSCO, proQuest Scopus and selected websites including the National Institutes of Health (NIH) and the World Health Organization (WHO).

RESULTS

Globally, more than 400 natural products have been investigated in diabetes and its complications. Tannins are the polyphenolic compounds present in many medicinal plants and various dietary sources like fruits, nuts, grains, spices and beverages. Various reports have shown that compounds like gallic acid, ellagic acid, catechin, epicatechin and procynidins from medicinal plants play major role in controlling progression of diabetes and its related complications by acting on molecular pathways and key targets involved in progression. Many chemists used above mentioned phyto-constituents as a pharmacophore for the developing new chemical entities having higher therapeutic benefits in management of diabetic complications.

CONCLUSION

This review focuses on the role of various tannins in prevention and management of diabetic complications like diabetic nephropathy, diabetic neuropathy, diabetic retinopathy and diabetic cardiomyopathy. It will help researchers to find some leads for the development of new cost effective therapy using dietary source for the management of diabetic complications.

Inhibition of P53/miR-34a improves diabetic endothelial dysfunction via activation of SIRT1

Endothelial dysfunction contributes to diabetic macrovascular complications, resulting in high mortality. Recent findings demonstrate a pathogenic role of P53 in endothelial dysfunction, encouraging the investigation of the effect of P53 inhibition on diabetic endothelial dysfunction. Thus, high glucose (HG)‐treated endothelial cells (ECs) were subjected to pifithrin‐α (PFT‐α)—a specific inhibitor of P53, or P53‐small interfering RNA (siRNA), both of which attenuated the HG‐induced endothelial inflammation and oxidative stress. Moreover, inhibition of P53 by PFT‐α or P53‐siRNA prohibited P53 acetylation, decreased microRNA‐34a (miR‐34a) level, leading to a dramatic increase in sirtuin 1 (SIRT1) protein level. Interestingly, the miR‐34a inhibitor (miR‐34a‐I) and PFT‐α increased SIRT1 protein level and alleviated the HG‐induced endothelial inflammation and oxidative stress to a similar extent; however, these effects of PFT‐α were completely abrogated by the miR‐34a mimic. In addition, SIRT1 inhibition by EX‐527 or Sirt1‐siRNA completely abolished miR‐34a‐I's protection against HG‐induced endothelial inflammation and oxidative stress. Furthermore, in the aortas of streptozotocin‐induced diabetic mice, both PFT‐α and miR‐34a‐I rescued the inflammation, oxidative stress and endothelial dysfunction caused by hyperglycaemia. Hence, the present study has uncovered a P53/miR‐34a/SIRT1 pathway that leads to endothelial dysfunction, suggesting that P53/miR‐34a inhibition could be a viable strategy in the management of diabetic macrovascular diseases.

The Role of Natural Products in Targeting Cardiovascular Diseases via Nrf2 Pathway: Novel Molecular Mechanisms and Therapeutic Approaches

Cardiovascular diseases (CVDs) are closely linked to cellular oxidative stress and inflammation. This may be resulted from the imbalance generation of reactive oxygen species and its role in promoting inflammation, thereby contributing to endothelial dysfunction and cardiovascular complications. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that plays a significant role in regulating expression of antioxidant and cytoprotective enzymes in response to oxidative stress. Natural products have emerged as a potential source of bioactive compounds which have shown to protect against atherogenesis development by activating Nrf2 signaling. This review aims to provide a comprehensive summary of the published data on the function, regulation and activation of Nrf2 as well as the molecular mechanisms of natural products in regulating Nrf2 signaling. The beneficial effects of using natural bioactive compounds as a promising therapeutic approach for the prevention and treatment of CVDs are reviewed.

Dimethyl fumarate accelerates wound healing under diabetic condition

Impaired wound healing is a common complication among patients with diabetes mellitus (DM), resulting in high rates of disability and mortality. Recent findings highlighted the critical role of nuclear factor erythroid 2-related factor 2 (NRF2) - a master of cellular antioxidants scavenging excessive DM-induced free radicals - in accelerating diabetic wound healing. Dimethyl fumarate (DMF) is a potent NRF2 activator used for the treatment of multiple sclerosis. However, the effect of DMF on wound healing has not been determined. The present study investigated the effect of DMF on the diabetic and the non-diabetic wound healing in streptozotocin-induced diabetic mice and non-diabetic control mice. DMF activated NRF2 signaling under both conditions. Interestingly, DMF attenuated oxidative damage and inflammation, and accelerated wound closure in the diabetic mice. However, this effect was not observed in non-diabetic mice. Keratinocytes were treated with normal glucose (NG), high glucose (HG), or hydrogen peroxide (H2O2), in the presence or absence of DMF to assess the role of reactive oxygen species (ROS) - inducible in DM - in mediating DMF-induced protection. Both HG and H2O2 elevated ROS, oxidative damage, and inflammation, the effects of which were similarly blunted by DMF. However, in spite of the activation of NRF2, DMF lost this capability under the NG condition. The findings of this study demonstrate that ROS activate the protective effect of DMF on the diabetic wound healing.

Sodium butyrate attenuates diabetes-induced aortic endothelial dysfunction via P300-mediated transcriptional activation of Nrf2

Oxidative stress and inflammation are major contributors to diabetes-induced endothelial dysfunction which is the critical first step to the development of diabetic macrovascular complications. Nuclear factor erythroid 2-related factor 2 (NRF2) plays a key role in combating diabetes-induced oxidative stress and inflammation. Sodium butyrate (NaB) is an inhibitor of histone deacetylase (HDAC) and an activator of NRF2. However, NaB's effect on diabetes-induced aortic injury was unknown. It was also not known whether or to what extent NRF2 is required for both self-defense and NaB's protection in the diabetic aorta. Additionally, the mechanism by which NaB activates NRF2 was unclear. Therefore, C57BL/6 Nrf2 knockout (KO) and wild type (WT) mice were induced to diabetes by streptozotocin, and were treated in the presence or absence of NaB, for 20 weeks. The KO diabetic mice developed more severe aortic endothelial oxidative stress, inflammation and dysfunction, as compared with the WT diabetic mice. NaB significantly attenuated these effects in the WT, but not the KO, mice. In high glucose-treated aortic endothelial cells, NaB elevated Nrf2 mRNA and protein without facilitating NRF2 nuclear translocation, an effect distinct from that of sulforaphane. NaB inhibited HDAC activity, and increased occupancy of the transcription factor aryl hydrocarbon receptor and the co-activator P300 at the Nrf2 gene promoter. Further, the P300 inhibitor C646 completely abolished NaB's efficacies. Thus, NRF2 is required for both self-defense and NaB's protection against diabetes-induced aortic endothelial dysfunction. Other findings suggest that P300 mediates the transcriptional activation of Nrf2 by NaB.

NRF2 Activation Inhibits Both TGF-β1- and IL-13-Mediated Periostin Expression in Fibroblasts: Benefit of Cinnamaldehyde for Antifibrotic Treatment

Systemic fibrosing or sclerotic disorders are life-threatening, but only very limited treatment modalities are available for them. In recent years, periostin (POSTN), a major extracellular matrix component, was established by several studies as a novel key player in the progression of systemic fibrotic disease. In this research, we revealed the involvement of oxidative stress in the expression of POSTN induced by TGF-β1 and IL-13 in dermal fibroblasts. We found that the antioxidant cinnamaldehyde activated the NRF2/HMOX1 pathway. Cinnamaldehyde also alleviated TGF-β1- and IL-13-mediated production of reactive oxygen species and subsequent POSTN upregulation in dermal fibroblasts. In contrast, NRF2 silencing abolished the cinnamaldehyde-mediated downregulation of POSTN. These results suggest that cinnamaldehyde is a broad inhibitor of POSTN expression covering both TGF-β1 and IL-13 signaling. Cinnamaldehyde may thus be beneficial for the treatment of systemic fibrotic diseases.

Nutrients, Nutraceuticals, and Xenobiotics Affecting Renal Health

Chronic kidney disease (CKD) affects 8–16% of the population worldwide. In developed countries, the most important risk factors for CKD are diabetes, hypertension, and obesity, calling into question the importance of educating and acting on lifestyles and nutrition. A balanced diet and supplementation can indeed support the maintenance of a general health status, including preservation of renal function, and can help to manage and curb the main risk factors for renal damage. While the concept of protein and salt restriction in nephrology is historically acknowledged, the role of some nutrients in renal health and the importance of nutrition as a preventative measure for renal care are less known. In this narrative review, we provide an overview of the demonstrated and potential actions of some selected nutrients, nutraceuticals, and xenobiotics on renal health and function. The direct and indirect effects of fiber, protein, fatty acids, curcumin, steviol glycosides, green tea, coffee, nitrates, nitrites, and alcohol on kidney health are reviewed here. In view of functional and personalized nutrition, understanding the renal and systemic effects of dietary components is essential since many chronic conditions, including CKD, are related to systemic dysfunctions such as chronic low-grade inflammation.

Hordenine protects against hyperglycemia-associated renal complications in streptozotocin-induced diabetic mice

The worldwide prevalence of diabetes and associated metabolic diseases has dramatically increased. Pharmacological treatment of diabetes is still limited. Hordenine (HOR), a phenethylamine alkaloid, is a natural constituent in many plants. The present study was designed to explore the possible anti-diabetic effect of HOR in streptozotocin (STZ)-induced diabetic mice. Combined treatment of HOR and insulin significantly reduced fasting and postprandial blood glucose level in diabetic mice. HOR and insulin did not show evident protective effect against structural and functional injuries of pancreas. Renal histological and functional injuries were significantly improved by HOR or insulin treatment. Moreover, combined treatment of HOR and insulin resulted in a more significant amelioration of renal histological and functional injuries in diabetic mice. HOR induced a decrease of renal IL-1α/β and IL-6 expression, and a reduction of Col1α1 and MMP9 expression and PAS-stained mesangial expansion in glomeruli of diabetic mice. In diabetic mice, HOR significantly decreased Nrf2 expression and increased hnRNPF and hnRNPK expression in kidney. Moreover, HOR showed a synergistic effect with insulin on the expression of these regulators. Renal ROS level and TBARS content in diabetic mice were decreased by HOR. The reduction of renal expression of antioxidant enzymes in diabetic mice was inhibited by HOR and insulin. Furthermore, HOR and insulin function synergistically to play an antioxidant role against oxidative injury in diabetic nephropathy. In conclusion, to the best of our knowledge, we, for the first time, found the anti-diabetic, anti-inflammatory, and anti-fibrotic role of HOR in combination with insulin. HOR functions synergistically with insulin and prevents diabetic nephropathy. However, the molecular mechanism of the synergistic effect of HOR and insulin needs to be elucidated.

Role of NRF2 in protection of the gastrointestinal tract against oxidative stress

The gastrointestinal tract is exposed to a variety of noxious factors, such as Helicobacter pylori, nonsteroidal anti-inflammatory drugs, gastric acid, ischemia-reperfusion, and mental stresses. Theses stressors generate free radicals within gastrointestinal tissues, causing organ injury and functional disturbance. Although the gastrointestinal tract can withstand such oxidative stresses to some extent by enhancing its antioxidant system via nuclear factor erythroid 2-related factor 2-Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1-mediated pathways, acute or chronic exposure to oxidative stress can cause several gastrointestinal tract disorders, such as inflammation, ulcers, cancers, and various functional disturbances. Recent studies have demonstrated that some natural compounds and drugs can upregulate the nuclear factor erythroid 2-related factor 2-mediated antioxidant system, ameliorating or preventing these disorders. Although these compounds may be useful as chemopreventive agents, sufficient evidence for their clinical efficacy has not yet been provided. In addition, it is important to note that excessive nuclear factor erythroid 2-related factor 2 stimulation can be harmful to human health, especially from the standpoint of tumor biology.

MDM2 controls NRF2 antioxidant activity in prevention of diabetic kidney disease

Oxidative stress and P53 contribute to the pathogenesis of diabetic kidney disease (DKD). Nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of cellular antioxidant defense system, is negatively regulated by P53 and prevents DKD. Recent findings revealed an important role of mouse double minute 2 (MDM2) in protection against DKD. However, the mechanism remained unclear. We hypothesized that MDM2 enhances NRF2 antioxidant signaling in DKD given that MDM2 is a key negative regulator of P53. The MDM2 inhibitor nutlin3a elevated renal P53, inhibited NRF2 signaling and induced oxidative stress, inflammation, fibrosis, DKD-like renal pathology and albuminuria in the wild-type (WT) non-diabetic mice. These effects exhibited more prominently in nutlin3a-treated WT diabetic mice. Interestingly, nutlin3a failed to induce greater renal injuries in the Nrf2 knockout (KO) mice under both the diabetic and non-diabetic conditions, indicating that NRF2 predominantly mediates MDM2's action. On the contrary, P53 inhibition by pifithrin-α activated renal NRF2 signaling and the expression of Mdm2, and attenuated DKD in the WT diabetic mice, but not in the Nrf2 KO diabetic mice. In high glucose-treated mouse mesangial cells, P53 gene silencing completely abolished nutlin3a's inhibitory effect on NRF2 signaling. The present study demonstrates for the first time that MDM2 controls renal NRF2 antioxidant activity in DKD via inhibition of P53, providing MDM2 activation and P53 inhibition as novel strategies in the management of DKD.

SRT2104 attenuates diabetes-induced aortic endothelial dysfunction via inhibition of P53

Endothelial dysfunction contributes to diabetic macrovascular complications. Sirtuin 1 (SIRT1) protects against diabetic vasculopathy. SRT2104 is a novel SIRT1 activator and was not previously studied for its effects on diabetes-induced aortic endothelial dysfunction. Additionally, whether or to what extent deacetylation of P53, a substrate of SIRT1, is required for the effects of SIRT1 activation was unclear, given the fact that SIRT1 has multiple targets. Moreover, little was known about the pathogenic role of P53 in diabetes-induced aortic injury. To these ends, diabetes was induced by streptozotocin in C57BL/6 mice. The diabetic mice developed enhanced aortic contractility, oxidative stress, inflammation, P53 hyperacetylation and a remarkable decrease in SIRT1 protein, the effects of which were rescued by SRT2104. In HG-treated endothelial cells (ECs), P53 siRNA and SRT2104 produced similar effects on the induction of SIRT1 and the inhibition of P53 acetylation, oxidative stress and inflammation. Interestingly, SRT2104 failed to further enhance these effects in the presence of P53 siRNA. Moreover, P53 activation by nutlin3a completely abolished SRT2104's protection against HG-induced oxidative stress and inflammation. Further, forced activation of P53 by nutlin3a increased aortic contractility in the healthy mice and generated endothelial oxidative stress and inflammation in both the normal glucose-cultured ECs and the aortas of the healthy mice. Collectively, the present study demonstrates that P53 deacetylation predominantly mediates SRT2104's protection against diabetes-induced aortic endothelial dysfunction and highlights the pathogenic role of P53 in aortic endothelial dysfunction.

The critical role of epigallocatechin gallate in regulating mitochondrial metabolism

Epigallocatechin gallate (EGCG), one of polyphenols isolated from green tea, exhibits biology-benefiting effects with minimum severe adverse. EGCG is known to be a mitochondrion-targeting medicinal agent, regulating mitochondrial metabolism, including mitochondrial biogenesis, mitochondrial bioenergetics, and mitochondria-mediated cell cycle and apoptosis. EGCG might exhibit either antioxidative activity to prevent against oxidative stress or pro-oxidative activity to counteract cancer cells, which depends on the cellular stress situations, cell types and the concentration of EGCG. Recent research has gained positive and promising data. This review will discuss the interaction between EGCG and mitochondrion.

The critical role of epigallocatechin gallate in regulating mitochondrial metabolism

Epigallocatechin gallate (EGCG), one of polyphenols isolated from green tea, exhibits biology-benefiting effects with minimum severe adverse. EGCG is known to be a mitochondrion-targeting medicinal agent, regulating mitochondrial metabolism, including mitochondrial biogenesis, mitochondrial bioenergetics, and mitochondria-mediated cell cycle and apoptosis. EGCG might exhibit either antioxidative activity to prevent against oxidative stress or pro-oxidative activity to counteract cancer cells, which depends on the cellular stress situations, cell types and the concentration of EGCG. Recent research has gained positive and promising data. This review will discuss the interaction between EGCG and mitochondrion.

Preservation of renal function in chronic diabetes by enhancing glomerular glucose metabolism

Diabetic nephropathy (DN) affects approximately 30-40% of patients with type 1 (T1DM) and type 2 diabetes (T2DM). It is a major cause of end-stage renal disease (ESRD) for the developed world. Hyperglycemia and genetics are major causal factors for the initiation and progression of DN. Multiple abnormalities in glucose and mitochondrial metabolism induced by diabetes likely contribute to the severity of DN. Recent clinical studies in people with extreme duration of T1DM (> 50 years, Joslin Medalist Study) have supported the importance of endogenous protective factors to neutralize the toxic effects of hyperglycemia on renal and other vascular tissues. Using renal glomeruli from these patients (namely Medalists) with and without DN, we have shown the importance of increased glycolytic flux in decreasing the accumulation of glucose toxic metabolites, improving mitochondrial function, survival of glomerular podocytes, and reducing glomerular pathology. Activation of a key glycolytic enzyme, pyruvate kinase M2 (PKM2), resulted in the normalization of renal hemodynamics and mitochondrial and glomerular dysfunction, leading to the mitigation of glomerular pathologies in several mouse models of DN.

SP600125 suppresses Keap1 expression and results in NRF2-mediated prevention of diabetic nephropathy

c-Jun N-terminal kinase (JNK) contributes to the pathogenesis of diabetic nephropathy (DN). The JNK inhibitor SP600125 was reported to ameliorate DN. However, the mechanism remained unclear. We previously reported that SP600125 activated nuclear factor erythroid 2-related factor 2 (NRF2), a governor of the cellular antioxidant defense system, in the aortas of the diabetic mice. Given the critical role of NRF2 in preventing DN, the present study aimed to test whether or not NRF2 is required for SP600125's protection against DN. To test the role of NRF2 in SP600125's effect, streptozotocin-induced C57BL/6 wild-type (WT) and Nrf2-knockout (KO) diabetic mice were treated in the presence or absence of SP600125, for 24 weeks. To explore the mechanism by which SP600125 activates NRF2, mouse mesangial cells (MMCs) were treated with high glucose (HG), in the presence or absence of either SP600125 or JNK siRNA. SP600125 significantly attenuated the diabetes-induced renal oxidative stress, inflammation, fibrosis, pathological change and dysfunction in the WT, but not the Nrf2 KO mice. SP600125 inactivated JNK, inhibited kelch-like ECH-associated protein 1 expression, preserved NRF2 protein and facilitated its nuclear translocation in the kidneys of the WT mice, the effects of which were similarly produced by either SP600125 or JNK siRNA in HG-treated MMCs. Further, both SP600125 and JNK siRNA alleviated HG-induced mesangial oxidative stress and expression of inflammatory and fibrotic genes. The present study demonstrates that NRF2 is required for SP600125's protection against DN. SP600125 activates NRF2 possibly via inhibition of JNK-induced Keap1 expression.

Early Growth Response 1 (Egr1) Is a Transcriptional Activator of NOX4 in Oxidative Stress of Diabetic Kidney Disease

BACKGROUND

NADPH oxidase 4 (NOX4) plays a major role in renal oxidative stress of diabetic kidney disease (DKD). NOX4 was significantly increased in Egr1-expressing fibroblasts, but the relationship between Egr1 and NOX4 in DKD is unclear.

METHODS

For the evaluation of the potential relationship between Egr1 and NOX4, both were detected in HFD/STZ-induced mice and HK-2 cells treated with TGF-β1. Then, changes in NOX4 expression were detected in HK-2 cells and mice with overexpression and knockdown of Egr1. The direct relationship between Egr1 and NOX4 was explored via chromatin immunoprecipitation (ChIP).

RESULTS

We found increased levels of Egr1, NOX4, and α-SMA in the kidney cortices of diabetic mice and in TGF-β1-treated HK-2 cells. Overexpression or silencing of Egr1 in HK-2 cells could upregulate or downregulate NOX4 and α-SMA. ChIP assays revealed that TGF-β1 induced Egr1 to bind to the NOX4 promoter. Finally, Egr1 overexpression or knockdown in diabetic mice could upregulate or downregulate the expression of NOX4 and ROS, and α-SMA was also changed.

CONCLUSION

Our study provides strong evidence that Egr1 is a transcriptional activator of NOX4 in oxidative stress of DKD. Egr1 contributes to DKD by enhancing EMT, in part by targeting NOX4.