Prevention by sulforaphane of diabetic cardiomyopathy is associated with up-regulation of Nrf2 expression and transcription activation

Thioredoxin plays a key role in retinal neuropathy prior to endothelial damage in diabetic mice

Diabetes is a chronic metabolic syndrome that results in changes in carbohydrate, lipid and protein metabolism. With diabetes for a long time, it increases the risk of diabetic retinopathy (DR) and long-term morbidity and mortality. Moreover, emerging evidence suggests that neuron damage occurs earlier than microvascular complications in DR patients, but the underlying mechanism is unclear. We investigated diabetes-induced retinal neuropathy and elucidated key molecular events to identify new therapeutic targets for the clinical treatment and prevention of DR. For in vivo studies, a high-fat diet and streptozotocin (STZ) injection were used to generate the diabetes model. Hematoxylin-eosin staining was used for morphological observations and measurements of the outer nuclear layer thickness. Electroretinography (ERG) was used to assess retinal function. For in vitro studies, Neuro2a cells were incubated in normal (5.5 mM) and high-glucose (30 mM) conditions. Flow cytometry assays were performed to analyze apoptosis. Additionally, real-time PCR and Western blotting analyses were carried out to determine gene and protein expression in vitro and in vivo. Taken together, the results indicated that retinal neuropathy occurred prior to endothelial damage induced by diabetes, and thioredoxin (Trx) plays a key role in this process. This underlying mechanism may be related to activation of the Trx/ASK1/p-p38/Trx-interacting protein pathway.

Cardioprotective potential of N-acetyl cysteine against hyperglycaemia-induced oxidative damage: a protocol for a systematic review

BACKGROUND

Hyperglycaemia-induced oxidative damage is a well-established factor implicated in the development of diabetic cardiomyopathy (DCM) in diabetic individuals. Some of the well-known characteristics of DCM include increased myocardial left ventricular wall thickness and remodelling that result in reduced cardiac efficiency. To prevent this, an increasing number of pharmacological compounds such as N-acetyl cysteine (NAC) are explored for their antioxidant properties. A few studies have shown that NAC can ameliorate hyperglycaemia-induced oxidative damage within the heart. Hence, the objective of this review is to synthesise the available evidence pertaining to the cardioprotective role of NAC against hyperglycaemia-induced oxidative damage and thus prevent DCM.

METHODS

This systematic review protocol will be reported in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) 2015 statement. We will perform a comprehensive search on major databases such as EMBASE, Cochrane Library, PubMed and Google scholar for original research articles published from January 1960 to March 2017. We will only report on literature that is available in English. Two authors will independently screen for eligible studies using pre-defined criteria, and data extraction will be done in duplicate. All discrepancies will be resolved by consensus or consultation of a third reviewer. The quality of studies will be checked using Cochrane Risk of Bias Assessment Tool and The Joanna Briggs Institute (JBI) Critical Appraisal tools for non-randomised experimental studies. Heterogeneity across studies will be assessed using the Cochrane Q statistic and the inconsistency index (I ²). We will use the random effects model to calculate a pooled estimate.

DISCUSSION

Although several studies have shown that NAC can ameliorate hyperglycaemia-induced oxidative damage within the heart, this systematic review will be the first pre-registered synthesis of data to identify the cardioprotective potential of NAC against hyperglycaemia-induced oxidative damage. This result will help guide future research evaluating the cardioprotective role of NAC against DCM and better identify possible mechanisms of action for NAC to prevent oxidative damage with a diabetic heart.

SYSTEMIC REVIEW REGISTRATION

PROSPERO CRD42017055851 .

Sulforaphane prevents bleomycin‑induced pulmonary fibrosis in mice by inhibiting oxidative stress via nuclear factor erythroid 2‑related factor‑2 activation

Lung fibrosis is associated with inflammation, apoptosis and oxidative damage. The transcription factor nuclear factor erythroid 2-related factor-2 (Nrf2) prevents damage to cells from oxidative stress by regulating the expression of antioxidant proteins. Sulforaphane (SFN), an Nrf2 activator, additionally regulates excessive oxidative stress by promoting the expression of endogenous antioxidants. The present study investigated if SFN protects against lung injury induced by bleomycin (BLM). The secondary aim of the present study was to assess if this protection mechanism involves upregulation of Nrf2 and its downstream antioxidants. Pulmonary fibrosis was induced in C57/BL6 mice by intratracheal instillation of BLM. BLM and age-matched control mice were treated with or without a daily dose of 0.5 mg/kg SFN until sacrifice. On days 7 and 28, mice were assessed for induction of apoptosis, inflammation, fibrosis, oxidative damage and Nrf2 expression in the lungs. The lungs were investigated with histological techniques including haematoxylin and eosin staining, Masson's trichrome staining and terminal deoxynucleotidyl transferase UTP nick end labeling. Inflammatory, fibrotic and apoptotic processes were confirmed by western blot analysis for interleukin-1β, tumor necrosis factor-α, transforming growth factor-β and caspase-3 protein expressions. Furthermore, protein levels of 3-nitro-tyrosine, 4-hydroxynonenal, superoxide dismutase 1 and catalase were investigated by western blot analysis. It was demonstrated that pulmonary fibrosis induced by BLM significantly increased apoptosis, inflammation, fibrosis and oxidative stress in the lungs at days 7 and 28. Notably, SFN treatment significantly attenuated the infiltration of the inflammatory cells, collagen accumulation, epithelial cell apoptosis and oxidative stress in the lungs. In addition, SFN treatment increased expression of the Nrf2 gene and its downstream targets. In conclusion, these results suggested that SFN treatment of pulmonary fibrosis mouse models may attenuate alveolitis, fibrosis, apoptosis and lung oxidative stress by increasing the expression of antioxidant enzymes, including NAPDH quinone oxidoreductase, heme oxygenase-1, superoxide dismutase and catalase, via upregulation of Nrf2 gene expression. Thus, the results from the present study may facilitate the development of therapies for BLM-toxicity and pulmonary fibrosis.

Oxidative stress and diabetic retinopathy: development and treatment

Diabetic retinopathy (DR) is the most common microvascular complication in diabetic patients and one of the main causes of acquired blindness in the world. From the 90s until date, the incidence of this complication has increased. Reactive oxygen species (ROS) is a free radical with impaired electron that usually participates in the redox mechanisms of some body molecules such as enzymes, proteins, and so on. In normal biological conditions, ROS is maintained in equilibrium, however its overproduction can lead to biological process called oxidative stress and this is considered the main pathogenesis of DR. The retina is susceptible to ROS because of high-energy demands and exposure to light. When the balance is broken, ROS produces retinal cell injury by interacting with the cellular components. This article describes the possible role of oxidative stress in the development of DR and proposes some treatment options based on its stages. The review of the topic shows that blindness caused by DR can be avoided by early detection and timely treatment.

Pathophysiological Fundamentals of Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) was first recognized more than four decades ago and occurred independent of cardiovascular diseases or hypertension in both type 1 and type 2 diabetic patients. The exact mechanisms underlying this disease remain incompletely understood. Several pathophysiological bases responsible for DCM have been proposed, including the presence of hyperglycemia, nonenzymatic glycosylation of large molecules (e.g., proteins), energy metabolic disturbance, mitochondrial damage and dysfunction, impaired calcium handling, reactive oxygen species formation, inflammation, cardiac cell death, and cardiac hypertrophy and fibrosis, leading to impairment of cardiac contractile functions. Increasing evidence also indicates the phenomenon called "metabolic memory" for diabetes-induced cardiovascular complications, for which epigenetic modulation seemed to play an important role, suggesting that the aforementioned pathogenic bases may be regulated by epigenetic modification. Therefore, this review aims at briefly summarizing the current understanding of the pathophysiological bases for DCM. Although how epigenetic mechanisms play a role remains incompletely understood now, extensive clinical and experimental studies have implicated its importance in regulating the cardiac responses to diabetes, which are believed to shed insight into understanding of the pathophysiological and epigenetic mechanisms for the development of DCM and its possible prevention and/or therapy. © 2017 American Physiological Society. Compr Physiol 7:693-711, 2017.

Sulforaphane suppresses cell growth and collagen expression of keloid fibroblasts

Keloids are fibroproliferative diseases characterized by the accumulation of an extracellular matrix including collagen. Various growth factors, or cytokines, and their receptors are overexpressed in keloids, and they are expected to be therapy targets. Sulforaphane, a dietary isothiocyanate, has recently shown anti-tumor, anti-inflammatory, and anti-fibrotic properties. In this study, we found that sulforaphane inhibited cell growth and reduced collagen at the mRNA and protein levels in keloid fibroblasts. Moreover, sulforaphane markedly suppressed the expression of IL-6 and α-SMA and inhibited Stat3 and Smad3 signaling pathways in keloid fibroblast KF112 cells. Sulforaphane induced G2/M cell-cycle arrest with the induction of p21 in KF112 cells. In addition, sulforaphane inhibited cell growth and suppressed the expression of collagen in keloid fibroblasts under a coculture with peripheral blood mononuclear cells. Furthermore, sulforaphane suppressed IL-6, Stat3, and Smad3 signaling in the coculture system. This study suggests that sulforaphane may be a novel keloid treatment.

Sulforaphane Protects against Brain Diseases: Roles of Cytoprotective Enzymes

Sulforaphane (SFN) is a kind of isothiocyanate derived from broccoli and other cruciferous vegetables. Because of its roles of antioxidant, anti-inflammatory, and anti-tumor through multiple targets and various mechanisms, SFN has drawn broad attention of the researchers. One of the most important target of SFN is nuclear factor erythroid 2 related factor 2 (Nrf2), wildly known for its ability to regulate the expression of a series of cytoprotective enzymes with antioxidative, prosurvival, and detoxification effects. Multiple researches have shown that SFN protects against central nervous system diseases through Nrf2pathway. In this article, we list SFN contents in common cruciferous vegetables, and summarize recent advances in the protective effects of SFN against acute brain injuries and neurodegenerative diseases through activating Nrf2 signaling pathway.

Apigenin alleviates STZ-induced diabetic cardiomyopathy

Apigenin is an important component of fruits and vegetables in human daily diets. Several cellular and animal models have been performed to demonstrate its anti-oxidant and anti-inflammatory bioactivities. However, the cardioprotective effects of apigenin in diabetic cardiomyopathy (DCM) remain unclear. In this study, we intended to explore the roles of apigenin in cardiac remodeling of DCM. Male C57BL/6 J mice were treated with streptozotocin (STZ, 50 mg/kg) for 5 consecutive days to induce DCM. The echocardiography and catheter-based measurements of hemodynamic parameters were performed to evaluate the cardiac function. Paraffin slices of harvested hearts were prepared for histological pathological analysis and TUNEL assay. Oxidative assay kits were used to detect Glutathione Peroxidase (GPx), Lipid Peroxidation Malondialdehyde (MDA), and Superoxide Dismutase (SOD). Western blot and real-time PCR were used for accessing the expressions of protein and mRNA. Diabetes mellitus exacerbated the cardiac dysfunction, fibrosis, and overaccumulation of 4-hydroxynonenal accompanying with down-regulation of Bcl2, GPx, and SOD, up-regulation of MDA, cleaved caspase3, and pro-apoptotic protein Bax, and contribution to the translocation of NF-κB. All these pathological changes could be effectively blunted by treatment of apigenin in vivo. Finally, H9c2 treated with high glucose or apigenin was used for further investigation of these effects in vitro; what is more, we also compared the effects between apigenin and Resveratrol in in vitro experiments. Our experiments have demonstrated that apigenin may be a potential drug for diabetic patients suffering from DCM.

Metallothionein Is Downstream of Nrf2 and Partially Mediates Sulforaphane Prevention of Diabetic Cardiomyopathy

We have reported that sulforaphane (SFN) prevented diabetic cardiomyopathy in both type 1 and type 2 diabetes (T2DM) animal models via the upregulation of nuclear transcription factor erythroid 2-related factor 2 (Nrf2) and metallothionein (MT). In this study, we tested whether SFN protects the heart from T2DM directly through Nrf2, MT, or both. Using Nrf2-knockout (KO), MT-KO, and wild-type (WT) mice, T2DM was induced by feeding a high-fat diet for 3 months followed by a small dose of streptozotocin. Age-matched controls were given a normal diet. Both T2DM and control mice were then treated with or without SFN for 4 months by continually feeding a high-fat or normal diet. SFN prevented diabetes-induced cardiac dysfunction as well as diabetes-associated cardiac oxidative damage, inflammation, fibrosis, and hypertrophy, with increases in Nrf2 and MT expressions in the WT mice. Both Nrf2-KO and MT-KO diabetic mice exhibited greater cardiac damage than WT diabetic mice. SFN did not provide cardiac protection in Nrf2-KO mice, but partially or completely protected the heart from diabetes in MT-KO mice. SFN did not induce MT expression in Nrf2-KO mice, but stimulated Nrf2 function in MT-KO mice. These results suggest that Nrf2 plays the indispensable role for SFN cardiac protection from T2DM with significant induction of MT and other antioxidants. MT expression induced by SFN is Nrf2 dependent, but is not indispensable for SFN-induced cardiac protection from T2DM.

Sulforaphane Prevents Angiotensin II-Induced Testicular Cell Death via Activation of NRF2

Although angiotensin II (Ang II) was reported to facilitate sperm motility and intratesticular sperm transport, recent findings shed light on the efficacy of Ang II in stimulating inflammatory events in testicular peritubular cells, effect of which may play a role in male infertility. It is still unknown whether Ang II can induce testicular apoptotic cell death, which may be a more direct action of Ang II in male infertility. Therefore, the present study aims to determine whether Ang II can induce testicular apoptotic cell death and whether this action can be prevented by sulforaphane (SFN) via activating nuclear factor (erythroid-derived 2)-like 2 (NRF2), the governor of antioxidant-redox signalling. Eight-week-old male C57BL/6J wild type (WT) and Nrf2 gene knockout mice were treated with Ang II, in the presence or absence of SFN. In WT mice, SFN activated testicular NRF2 expression and function, along with a marked attenuation in Ang II-induced testicular oxidative stress, inflammation, endoplasmic reticulum stress, and apoptotic cell death. Deletion of the Nrf2 gene led to a complete abolishment of these efficacies of SFN. The present study indicated that Ang II may result in testicular apoptotic cell death, which can be prevented by SFN via the activation of NRF2.

Aspalathin Protects the Heart against Hyperglycemia-Induced Oxidative Damage by Up-Regulating Nrf2 Expression

Aspalathin (ASP) can protect H9c2 cardiomyocytes against high glucose (HG)-induced shifts in myocardial substrate preference, oxidative stress, and apoptosis. The protective mechanism of ASP remains unknown. However, as one of possible, it is well known that phytochemical flavonoids reduce oxidative stress via nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activation resulting in up-regulation of antioxidant genes and enzymes. Therefore, we hypothesized that ASP protects the myocardium against HG- and hyperglycemia-induced oxidative damage by up-regulating Nrf2 expression in H9c2 cardiomyocytes and diabetic (db/db) mice, respectively. Using an oxidative stress RT² Profiler PCR array, ASP at a dose of 1 µM was demonstrated to protect H9c2 cardiomyocytes against HG-induced oxidative stress, but silencing of Nrf2 abolished this protective response of ASP and exacerbated cardiomyocyte apoptosis. Db/db mice and their non-diabetic (db/+) littermate controls were subsequently treated daily for six weeks with either a low (13 mg/kg) or high (130 mg/kg) ASP dose. Compared to nondiabetic mice the db/db mice presented increased cardiac remodeling and enlarged left ventricular wall that occurred concomitant to enhanced oxidative stress. Daily treatment of mice with ASP at a dose of 130 mg/kg for six weeks was more effective at reversing complications than both a low dose ASP or metformin, eliciting enhanced expression of Nrf2 and its downstream antioxidant genes. These results indicate that ASP maintains cellular homeostasis and protects the myocardium against hyperglycemia-induced oxidative stress through activation of Nrf2 and its downstream target genes.

Antioxidative Effects of Natural Products on Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) is a common and severe complication of diabetes and results in high mortality. It is therefore imperative to develop novel therapeutics for the prevention or inhibition of the progression of DCM. Oxidative stress is a key mechanism by which diabetes induces DCM. Hence, targeting of oxidative stress-related processes in DCM could be a promising therapeutic strategy. To date, a number of studies have shown beneficial effects of several natural products on the attenuation of DCM via an antioxidative mechanism of action. The aim of the present review is to provide a comprehensive and concise overview of the previously reported antioxidant natural products in the inhibition of DCM progression. Clinical trials of the antioxidative natural products in the management of DCM are included. In addition, discussion and perspectives are further provided in the present review.

The Nrf2/Keap1/ARE Pathway and Oxidative Stress as a Therapeutic Target in Type II Diabetes Mellitus

Despite improvements in awareness and treatment of type II diabetes mellitus (TIIDM), this disease remains a major source of morbidity and mortality worldwide, and prevalence continues to rise. Oxidative damage caused by free radicals has long been known to contribute to the pathogenesis and progression of TIIDM and its complications. Only recently, however, has the role of the Nrf2/Keap1/ARE master antioxidant pathway in diabetic dysfunction begun to be elucidated. There is accumulating evidence that this pathway is implicated in diabetic damage to the pancreas, heart, and skin, among other cell types and tissues. Animal studies and clinical trials have shown promising results suggesting that activation of this pathway can delay or reverse some of these impairments in TIIDM. In this review, we outline the role of oxidative damage and the Nrf2/Keap1/ARE pathway in TIIDM, focusing on current and future efforts to utilize this relationship as a therapeutic target for prevention, prognosis, and treatment of TIID.

Sulforaphane ameliorates the insulin responsiveness and the lipid profile but does not alter the antioxidant response in diabetic rats

Diabetes is one of the most prevalent chronic non-communicable diseases and is characterized by hyperglycemia and increased oxidative stress. These two alterations are also responsible for the main diabetic complications: cardiovascular disease, retinopathy, nephropathy and peripheral neuropathy. Diabetes progression is governed by pancreatic β-cell failure, and recent studies showed that sulforaphane (SFN) might be able to prevent this change, preserving insulin production. Consequently, our goal was to test the effects of SFN on metabolic parameters related to diabetic complications and antioxidant defenses (superoxide dismutase, catalase and sulfhydryl groups) in the pancreas, liver and kidney of non-diabetic and diabetic rats. Male Wistar rats were treated with water or 0.5 mg kg(-1) SFN i.p. for 21 days after diabetes induction. In diabetic animals treated with SFN, the serum levels of total cholesterol, non-HDL cholesterol and triacylglycerols were similar to those of non-diabetic animals, and the insulin responsiveness was higher than that of the diabetic animals that did not receive the compound. No effect of SFN on the superoxide dismutase and catalase activity or sulfhydryl groups was observed in the pancreas, liver or kidney of the treated animals. We conclude that SFN ameliorates some features of clinical diabetic complications particularly the lipid profile and insulin responsiveness, but it does not modulate the antioxidant response induced by superoxide dismutase, catalase and sulfhydryl groups in the evaluated organs.

An overview of the mechanisms and novel roles of Nrf2 in cardiovascular diseases

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a basic leucine zipper (bZIP) transcription factor of the cap'n'collar (CNC) family that is present in various organs. The cardiovascular system (CVS) is susceptible to a spectrum of diseases that are strongly associated with increased risks of mortality and morbidity, and studies have demonstrated that Nrf2 has a pivotal role in protection against cardiovascular diseases (CVDs). Areas covered: Nrf2 is a basic protective molecule that guards against CVD by attenuating oxidative stress, mitochondrial dysfunction, and inflammation. Initially, we briefly introduce the biological characteristics of Nrf2 and the newly discovered Neh7 domain. Next, we discuss the concrete roles of Nrf2 in the CVS and enumerate some related upstream molecules and downstream targets. Lastly, we expand our focus to the behaviors of Nrf2 in CVDs and discuss potential research directions. Expert opinion: Although certain studies have cast doubt on the positive actions of Nrf2 in the CVS, Nrf2 is a pivotal endogenous molecule for defense against CVD. The review compiled here may serve as a broad and comprehensive reference for the roles of Nrf2 in the CVS, with the aim of facilitating the design of new drugs and clinical therapies for CVDs.

Genetic variants of nuclear factor erythroid-derived 2-like 2 associated with the complications in Han descents with type 2 diabetes mellitus of Northeast China

The transcription factor nuclear factor erythroid 2-like 2 (NFE2L2) is essential for preventing type 2 diabetes mellitus (T2DM)-induced complications in animal models. This case and control study assessed genetic variants of NFE2L2 for associations with T2DM and its complications in Han Chinese volunteers. T2DM patients with (n = 214) or without (n = 236) complications, or healthy controls (n = 359), were genotyped for six NFE2L2 single nucleotide polymorphisms (SNPs: rs2364723, rs13001694, rs10497511, rs1806649, rs1962142 and rs6726395) with TaqMan Pre-Designed SNP Genotyping and Sequence System. Serum levels of heme oxygenase-1 (HMOX1) were determined through enzyme-linked immunosorbent assay. Informative data were obtained for 341 cases and 266 controls. Between T2DM patients and controls, the genotypic and allelic frequencies and haplotypes of the SNPs were similar. However, there was a significant difference in genotypic and allelic frequencies of rs2364723, rs10497511, rs1962142 and rs6726395 between T2DM patients with and without complications, including peripheral neuropathy, nephropathy, retinopathy, foot ulcers and microangiopathy. Furthermore, HMOX1 levels were significantly higher in T2DM patients with complications than in controls. Multiple logistic regression analysis, however, showed that only rs2364723 significantly reduced levels of serum HMOX1 in T2DM patients for the GG genotype carriers compared with participants with CG+CC genotype. The data suggest that although NFE2L2 rs2364723, rs10497511, rs1962142 and rs6726395 were not associated with T2DM risk, they were significantly associated with complications of T2DM. In addition, only for rs2364723 higher serum HMOX1 levels were found in the T2DM patients with CG+CC than those with GG genotype.

Sulforaphane Prevents Testicular Damage in Kunming Mice Exposed to Cadmium via Activation of Nrf2/ARE Signaling Pathways

Sulforaphane (SFN) is a natural and highly effective antioxidant. Studies suggest that SFN protects cells and tissues against cadmium (Cd) toxicity. This study investigated the protective effect of SFN against oxidative damage in the testes of Kunming mice exposed to cadmium, and explored the possible molecular mechanisms involved. Cadmium greatly reduced the serum testosterone levels in mice, reduced sperm motility, total sperm count, and increased the sperm deformity rate. Cadmium also reduces superoxide dismutase (T-SOD) and glutathione (GSH) levels and increases malondialdehyde (MDA) concentrations. SFN intervention improved sperm quality, serum testosterone, and antioxidant levels. Both mRNA and protein expression of mouse testicular nuclear factor-erythroid 2-related factor 2 (Nrf2) was reduced in cadmium-treated group. Furthermore, the downstream genes of Nrf2, glutathione peroxidase (GSH-Px), γ-glutamyl cysteine synthetase (γ-GCS), heme oxygenase-1 (HO-1), and NAD(P)H:quinone oxidoreductase-1 (NQO1) were also decreased in cadmium-treated group. SFN intervention increases the expression of these genes. Sulforaphane prevents cadmium-induced testicular damage, probably via activation of Nrf2/ARE signaling.

Protective role of sulphoraphane against vascular complications in diabetes

Context Diabetes is a global health challenge. Although large prospective clinical trials have shown that intensive control of blood glucose or blood pressure reduces the risk for development and progression of vascular complications in diabetes, a substantial number of diabetic patients still experience renal failure and cardiovascular events, which could account for disabilities and high mortality rate in these subjects. Objective Sulphoraphane is a naturally occurring isothiocyanate found in widely consumed cruciferous vegetables, such as broccoli, cabbage and Brussels sprouts, and an inducer of phase II antioxidant and detoxification enzymes with anticancer properties. We reviewed here the protective role of sulphoraphane against diabetic vascular complications. Methods In this review, literature searches were undertaken in Medline and in CrossRef. Non-English language articles were excluded. Keywords [sulphoraphane and (diabetes, diabetic nephropathy, diabetic retinopathy, diabetic neuropathy, diabetic complications, vascular, cardiomyocytes, heart or glycation)] have been used to select the articles. Results There is accumulating evidence that sulphoraphane exerts beneficial effects on vascular damage in both cell culture and diabetic animal models via antioxidative properties. Furthermore, we have recently found that sulphoraphane inhibits in vitro formation of advanced glycation end products (AGEs), suppresses the AGE-induced inflammatory reactions in rat aorta by reducing receptor for AGEs (RAGE) expression and decreases serum levels of AGEs in humans. Conclusion These findings suggest that blockade of oxidative stress and/or the AGE-RAGE axis by sulphoraphane may be a novel therapeutic strategy for preventing vascular complications in diabetes.

Differential mechanistic investigation of protective effects from imperatorin and sec-O-glucosylhamaudol against arsenic trioxide-induced cytotoxicity in vitro

BACKGROUND AND PURPOSE

The clinical use of arsenic trioxide (As₂O₃) for treating acute promyelocytic leukemia (APL) is limited due to its severe cardiotoxicity. The possible mechanisms of As₂O₃-induced cardiotoxicity include DNA fragmentation, reactive oxygen species (ROS) generation, cardiac ion channel changes and apoptosis. The present study is designed to investigate the protective effects of imperatorin and sec-O-glucosylhamaudol and to explore their mechanistic involvement in As₂O₃-induced cytotoxicity.

EXPERIMENTAL METHODS

Cell viability assay, Lactate dehydrogenase (LDH) release, Acridine orange/ethidium bromide (AO/EB) double staining, Caspase-3 activity assay, ROS generation, cellular calcium levels, mRNA expression levels by qRT-PCR and protein expression levels by Western blotting were measured in H9c2 cells in combination with As₂O₃ and imperatorin or sec-O-glucosylhamaudol.

KEY RESULTS

We observed that H9c2 cells treated with imperatorin or sec-O-glucosylhamaudol were more resistant to As₂O₃-induced cell death. Both imperatorin and sec-O-glucosylhamaudol reduced H9c2 cell apoptosis, but both imperatorin and sec-O-glucosylhamaudol had no effects on Caspase-3 activity and intracellular calcium accumulation. Furthermore, imperatorin was capable of suppressing ROS generation, while sec-O-glucosylhamaudol did not show this effect. Moreover, imperatorin and sec-O-glucosylhamaudol triggered Nrf2 activation, which resulted in upregulation of downstream phase II metabolic enzymes and antioxidant protein/enzyme, probably offering cellular protection to As₂O₃-induced cardiotoxicity via the Nrf2 signal pathway.

CONCLUSIONS AND IMPLICATIONS

Imperatorin and sec-O-glucosylhamaudol can ameliorate As₂O₃-induced cytotoxicity and apoptosis in H9c2 cells, the mechanisms probably related to antioxidation. As₂O₃ in combination with imperatorin or sec-O-glucosylhamaudol could be considered as a novel strategy to expand the clinical application of As₂O₃.

From the Cover: Zinc Deficiency Worsens and Supplementation Prevents High-Fat Diet Induced Vascular Inflammation, Oxidative Stress, and Pathological Remodeling

Obesity has become a common public health problem in the world and raises the risk of various cardiovascular diseases. Zinc is essential for multiple organs in terms of normal structure and function. The present study investigated the effects of high fat diet (HFD) induced obesity on the aorta in mice, and evaluated whether it can be affected by zinc deficiency or supplementation. Four-week-old male C57BL/6J mice were fed HFD with varied amounts of zinc (deficiency, adequate and supplementation) for 3 and 6 months. Results showed that HFD feeding induced a time-dependent aortic remodeling, demonstrated by increased vessel wall thickness, tunica cell proliferation and fibrotic responses, and inflammatory response, reflected by increased expression of inflammatory cytokines (tumor necrosis factor-α and vascular cell adhesion molecule 1). HFD feeding also caused aortic oxidative damage, reflected by 3-nitrotyrosine and 4-hydroxy-2-nonenal accumulation, and down-regulated nuclear factor (erythroid-derived 2)-like 2 (Nrf2) expression and function, shown by down-regulation of its downstream antioxidants, catalase, NAD(P)H dehydrogenase (quinone 1), and metallothionein expression. The vascular effects of obesity-induced by HFD was exacerbated by zinc deficiency but significantly improved by zinc supplementation. In addition, down-regulation of Nrf2 function and associated antioxidants expression were also worsened by zinc deficiency but improved by zinc supplementation. These results suggest that HFD induces aortic remodeling, which can be exacerbated by zinc deficiency and improved by zinc supplementation.

Myocardial redox status, mitophagy and cardioprotection: a potential way to amend diabetic heart?

Diabetic cardiomyopathy (DCM) is one of the major cardiovascular complications in diabetes that increase the mortality of diabetic patients. Mechanisms underlying DCM have not been fully elucidated, hindering targeted design of effective strategies to delay or treat DCM. Mitochondrial dysfunction is recognized as the driving force for the pathogenesis of DCM; therefore, maintaining cardiac mitochondrial quality is crucial for DCM prevention. Mitophagy is the process by which cells degrade abnormal or superfluous mitochondria in order to correct mitochondrial dysfunction, improve mitochondrial quality and maintain cardiac homoeostasis. Although the roles of mitophagy in various cardiomyopathies have been suggested, it remains largely unknown how the process is regulated and whether it is altered in the diabetic heart. In this review, we summarize currently available studies that investigate mitophagy in the heart, including its pathways, features and protective roles in several situations, including DCM. Due to limited data about mitophagy in diabetic hearts, future studies are required to gain a deeper understanding of the regulatory mechanisms of mitophagy in the heart and to develop mitophagy-based strategies for protecting the heart from diabetic injury.

Broccoli sprout extract prevents diabetic cardiomyopathy via Nrf2 activation in db/db T2DM mice

To develop a clinic-relevant protocol for systemic up-regulation of NFE2-related factor 2 (Nrf2) to prevent diabetic cardiomyopathy (DCM), male db/db and age-matched wild-type (WT) mice were given sulforaphane (SFN, an Nrf2 activator) and its natural source, broccoli sprout extract (BSE) by gavage every other day for 3 months, with four groups: vehicle (0.1 ml/10 g), BSE-low dose (estimated SFN availability at 0.5 mg/kg), BSE-high dose (estimated SFN availability at 1.0 mg/kg), and SFN (0.5 mg/kg). Cardiac function and pathological changes (hypertrophy, fibrosis, inflammation and oxidative damage) were assessed by echocardiography and histopathological examination along with Western blot and real-time PCR, respectively. Both BSE and SFN significantly prevented diabetes-induced cardiac dysfunction, hypertrophy and fibrosis. Mechanistically, BSE, like SFN, significantly up-regulated Nrf2 transcriptional activity, evidenced by the increased Nrf2 nuclear accumulation and its downstream gene expression. This resulted in a significant prevention of cardiac oxidative damage and inflammation. For all these preventive effects, BSE at high dose provided a similar effect as did SFN. These results indicated that BSE at high dose prevents DCM in a manner congruent with SFN treatment. Therefore, it suggests that BSE could potentially be used as a natural and safe treatment against DCM via Nrf2 activation.

Sulforaphane induces neurovascular protection against a systemic inflammatory challenge via both Nrf2-dependent and independent pathways

Sepsis is often characterized by an acute brain inflammation and dysfunction, which is associated with increased morbidity and mortality worldwide. Preventing cerebral leukocyte recruitment may provide the key to halt progression of systemic inflammation to the brain. Here we investigated the influence of the anti-inflammatory and anti-oxidant compound, sulforaphane (SFN) on lipopolysaccharide (LPS)-induced cellular interactions in the brain. The inflammatory response elicited by LPS was blunted by SFN administration (5 and 50mg/kg i.p.) 24h prior to LPS treatment in WT animals, as visualized and quantified using intravital microscopy. This protective effect of SFN was lost in Nrf2-KO mice at the lower dose tested, however 50mg/kg SFN revealed a partial effect, suggesting SFN works in part independently of Nrf2 activity. In vitro, SFN reduced neutrophil recruitment to human brain endothelial cells via a down regulation of E-selectin and vascular cell adhesion molecule 1 (VCAM-1). Our data confirm a fundamental dose-dependent role of SFN in limiting cerebral inflammation. Furthermore, our data demonstrate that not only is Nrf2 in part essential in mediating these neuroprotective effects, but they occur via down-regulation of E-selectin and VCAM-1. In conclusion, SFN may provide a useful therapeutic drug to reduce cerebral inflammation in sepsis.

The Role of p38 MAPK in the Development of Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) is a major complication of diabetes that contributes to an increase in mortality. A number of mechanisms potentially explain the development of DCM including oxidative stress, inflammation and extracellular fibrosis. Mitogen-activated protein kinase (MAPK)-mediated signaling pathways are common among these pathogenic responses. Among the diverse array of kinases, extensive attention has been given to p38 MAPK due to its capacity for promoting or inhibiting the translation of target genes. Growing evidence has indicated that p38 MAPK is aberrantly expressed in the cardiovascular system, including the heart, under both experimental and clinical diabetic conditions and, furthermore, inhibition of p38 MAPK activation in transgenic animal model or with its pharmacologic inhibitor significantly prevents the development of DCM, implicating p38 MAPK as a novel diagnostic indicator and therapeutic target for DCM. This review summarizes our current knowledge base to provide an overview of the impact of p38 MAPK signaling in diabetes-induced cardiac remodeling and dysfunction.

Sulforaphane Ameliorates Bladder Dysfunction through Activation of the Nrf2-ARE Pathway in a Rat Model of Partial Bladder Outlet Obstruction

Purpose. We evaluated the effect of sulforaphane (SFN) treatment on the function and changes of expression of Nrf2-ARE pathway in the bladder of rats with bladder outlet obstruction (BOO). Materials and Methods. A total of 18 male Sprague-Dawley rats at age of 8 weeks were divided into 3 groups (6 of each): the sham operated group, the BOO group, and the BOO+SFN group. We examined histological alterations and the changes of oxidative stress markers and the protein expression of the Nrf2-ARE pathway. Results. We found that SFN treatment could prolong micturition interval and increase bladder capacity and bladder compliance. However, the peak voiding pressure was lower than BOO group. SFN treatment can ameliorate the increase of collagen fibers induced by obstruction. SFN treatment also increased the activity of SOD, GSH-Px, and CAT compared to the other groups. The level of bladder cell apoptosis was decreased in BOO rats with SFN treatment. Moreover, SFN could reduce the ratio of Bax/Bcl-2 expression. Furthermore, SFN could activate the Nrf2 expression with elevation of its target antioxidant proteins. Conclusions. The sulforaphane-mediated decrease of oxidative stress and activation of the Nrf2-ARE pathway may ameliorate bladder dysfunction caused by bladder outlet obstruction.

Mangiferin Upregulates Glyoxalase 1 Through Activation of Nrf2/ARE Signaling in Central Neurons Cultured with High Glucose

Mangiferin, a natural C-glucoside xanthone, has anti-inflammatory, anti-oxidative, neuroprotective actions. Our previous study showed that mangiferin could attenuate diabetes-associated cognitive impairment of rats by enhancing the function of glyoxalase 1 (Glo-1) in brain. The aim of this study was to investigate whether Glo-1 upregulation by mangiferin in central neurons exposed to chronic high glucose may be related to activation of Nrf2/ARE pathway. Compared with normal glucose (25 mmol/L) culture, Glo-1 protein, mRNA, and activity levels were markedly decreased in primary hippocampal and cerebral cortical neurons cultured with high glucose (50 mmol/L) for 72 h, accompanied by the declined Nrf2 nuclear translocation and protein expression of Nrf2 in cell nucleus, as well as protein expression and mRNA level of γ-glutamylcysteine synthetase (γ-GCS) and superoxide dismutase activity, target genes of Nrf2/ARE signaling. Nonetheless, high glucose cotreating with mangiferin or sulforaphane, a typical inducer of Nrf2 activation, attenuated the above changes in both central neurons. In addition, mangiferin and sulforaphane significantly prevented the formation of advanced glycation end-products (AGEs) reflecting Glo-1 activity, while elevated the level of glutathione, a cofactor of Glo-1 activity and production of γ-GCS, in high glucose cultured central neurons. These findings demonstrated that Glo-1 was greatly downregulated in central neurons exposed to chronic high glucose, which is expected to lead the formation of AGEs and oxidative stress damages. We also proved that mangiferin enhanced the function of Glo-1 under high glucose condition by inducing activation of Nrf2/ARE signaling pathway.

Wogonin attenuates diabetic cardiomyopathy through its anti-inflammatory and anti-oxidative properties

Among diabetic cardiovascular complications cardiomyopathy is major event which if not well controlled culminates in cardiac failure. Wogonin from the root of Scutellaria baicalensis Georgi has shown specific anti-diabetes bioactivity. However, its effect on diabetic complications remains unclear. The main purpose of this study is to investigate the potential effects of wogonin on diabetic cardiomyopathy and to figure out its underlying mechanism. We found that wogonin administration suppressed hyperglycemia, improved cardiac function, and mitigated cardiac fibrosis in STZ-induced diabetic mice. Wogonin supplementation also attenuated diabetic-induced cardiomyocyte apoptosis and necrosis. In addition, wogonin treatment exhibited the properties of anti-oxidative stress and anti-inflammation in STZ diabetic mice, evidenced by improved activities of anti-oxidases including SOD1/2 and CAT, decreased ROS and MDA production, suppressed expression of inflammation factors such as IL-1β, IL-6, TNFα, and PAI-1, and inhibited NF-κB signaling. These results suggested that wogonin potentially mitigate hyperglycemia-related cardiomyocyte impairment through inhibiting inflammation and oxidative stress.

Sulforaphane improves oxidative status without attenuating the inflammatory response or cardiac impairment induced by ischemia–reperfusion in rats

Sulforaphane, a natural isothiocyanate, demonstrates cardioprotection associated with its capacity to stimulate endogenous antioxidants and to inhibit inflammation. The aim of this study was to investigate whether sulforaphane is capable of attenuating oxidative stress and inflammatory responses through the TLR4/MyD88/NFκB pathway, and thereby could modulate post-ischemic ventricular function in isolated rat hearts submitted to ischemia and reperfusion. Male Wistar rats received sulforaphane (10 mg·kg−1·day−1) or vehicle i.p. for 3 days. Global ischemia was performed using isolated hearts, 24 h after the last injection, by interruption of the perfusion flow. The protocol included a 20 min pre-ischemic period followed by 20 min of ischemia and a 20 min reperfusion. Although no changes in mechanical function were observed, sulforaphane induced a significant increase in superoxide dismutase and heme oxygenase-1 expression (both 66%) and significantly reduced reactive oxygen species levels (7%). No differences were observed for catalase and glutathione peroxidase expression or their activities, nor for thioredoxin reductase, glutaredoxin reductase and glutathione-S-transferase. No differences were found in lipid peroxidation or TLR4, MyD88, and NF-κB expression. In conclusion, although sulforaphane was able to stimulate endogenous antioxidants modestly, this result did not impact inflammatory signaling or cardiac function of hearts submitted to ischemia and reperfusion.

Diabetic cardiomyopathy: role of the E3 ubiquitin ligase

Diabetic cardiomyopathy (DCM) is the leading cause of mortality in diabetes. As the number of cases of diabetes continues to rise, it is urgent to develop new strategies to protect against DCM, which is characterized by cardiac hypertrophy, increased apoptosis, fibrosis, and altered insulin metabolism. The E3 ubiquitin ligases (E3s), one component of the ubiquitin-proteasome system, play vital roles in all of the features of DCM listed above. They also modulate the activity of several transcription factors involved in the pathogenesis of DCM. In addition, the E3s degrade both insulin receptor and insulin receptor substrates and also regulate insulin gene transcription, leading to insulin resistance and insulin deficiency. Therefore, the E3s may be a driving force for DCM. This review summarizes currently available studies to analyze the roles of the E3s in DCM, enriches our knowledge of how DCM develops, and provides a novel strategy to protect heart from diabetes.

Low-dose radiation prevents type 1 diabetes-induced cardiomyopathy via activation of AKT mediated anti-apoptotic and anti-oxidant effects

We investigated whether low-dose radiation (LDR) can prevent late-stage diabetic cardiomyopathy and whether this protection is because of the induction of anti-apoptotic and anti-oxidant pathways. Streptozotocin-induced diabetic C57BL/6J mice were treated with/without whole-body LDR (12.5, 25, or 50 mGy) every 2 days. Twelve weeks after onset of diabetes, cardiomyopathy was diagnosed characterized by significant cardiac dysfunction, hypertrophy and histopathological abnormalities associated with increased oxidative stress and apoptosis, which was prevented by LDR (25 or 50 mGy only). Low-dose radiation-induced cardiac protection also associated with P53 inactivation, enhanced Nrf2 function and improved Akt activation. Next, for the mechanistic study, mouse primary cardiomyocytes were treated with high glucose (33 mmol/l) for 24 hrs and during the last 15 hrs bovine serum albumin-conjugated palmitate (62.5 μmol/l) was added into the medium to mimic diabetes, and cells were treated with LDR (25 mGy) every 6 hrs during the whole process of HG/Pal treatment. Data show that blocking Akt/MDM2/P53 or Akt/Nrf2 pathways with small interfering RNA of akt, mdm2 and nrf2 not only prevented LDR-induced anti-apoptotic and anti-oxidant effects but also prevented LDR-induced suppression on cardiomyocyte hypertrophy and fibrosis against HG/Pal. Low-dose radiation prevented diabetic cardiomyopathy by improving cardiac function and hypertrophic remodelling attributed to Akt/MDM2/P53-mediated anti-apoptotic and Akt/Nrf2-mediated anti-oxidant pathways simultaneously.

Diabetes blocks the cardioprotective effects of sevoflurane postconditioning by impairing Nrf2/Brg1/HO-1 signaling

Sevofluane postconditioning (SPostC) protects heart against ischemia/reperfusion injury. However, SPostC cardioprotection is lost in diabetes whose cardiac heme oxygenase-1 (HO-1) is reduced. Brahma-related gene 1 (Brg1) facilitates nuclear factor-erythroid-2-related factor-2 (Nrf2) to activate HO-1 to increase myocardial antioxidant capacity in response to oxidative stress. However, cardiac Brg1 is reduced in diabetes. We hypothesized that SPostC confers cardioprotection by activating HO-1 through Nrf2/Brg1 and that impaired Nrf2/Brg1/HO-1 in diabetes is responsible for the loss of SPostC. Control and streptozotocin-induced diabetic mice were subjected to 45min coronary artery occlusion followed by 2h reperfusion with or without SPostC achieved by exposing the mice to 2% sevoflurane for 15min at the onset of reperfusion. In invitro study, H9c2 cells were exposed to normal or high glucose and subjected to 3h hypoxia followed by 6h reoxygenation. Diabetic mice displayed larger post-ischemic infarct size, severer cardiomyocytes apoptosis, and increased oxidative stress concomitant with reduced HO-1, nuclear Nrf2 and Brg1 protein expression. These changes were prevented/reversed by SPostC in control but not in diabetic mice, and these beneficial effects of SPostC were abolished by HO-1 inhibition. In H9c2 cells exposed to normal glucose but not high glucose, SPostC significantly attenuated hypoxia/reoxygenation-induced cellular injury and oxidative stress with increased HO-1 and nuclear Nrf2. These SPostC beneficial effects were canceled by HO-1 inhibition. In conclusion, SPostC protects against myocardial ischemia/reperfusion injury through activation of Nrf2/Brg1/HO-1 signaling and impairment of this signaling may be responsible for the loss of SPostC cardioprotection in diabetes.

Restoration of Nrf2 Signaling Normalizes the Regenerative Niche

Chronic hyperglycemia impairs intracellular redox homeostasis and contributes to impaired diabetic tissue regeneration. The Keap1/Nrf2 pathway is a critical regulator of the endogenous antioxidant response system, and its dysfunction has been implicated in numerous pathologies. Here we characterize the effect of chronic hyperglycemia on Nrf2 signaling within a diabetic cutaneous regeneration model. We characterized the effects of chronic hyperglycemia on the Keap1/Nrf2 pathway within models of diabetic cutaneous wound regeneration. We assessed reactive oxygen species (ROS) production and antioxidant gene expression following alterations in the Nrf2 suppressor Keap1 and the subsequent changes in Nrf2 signaling. We also developed a topical small interfering RNA (siRNA)-based therapy to restore redox homeostasis within diabetic wounds. Western blotting demonstrated that chronic hyperglycemia-associated oxidative stress inhibits nuclear translocation of Nrf2 and impairs activation of antioxidant genes, thus contributing to ROS accumulation. Keap1 inhibition increased Nrf2 nuclear translocation, increased antioxidant gene expression, and reduced ROS production to normoglycemic levels, both in vitro and in vivo. Topical siKeap1 therapy resulted in improved regenerative capacity of diabetic wounds and accelerated closure. We report that chronic hyperglycemia weakens the endogenous antioxidant response, and the consequences of this defect are manifested by intracellular redox dysregulation, which can be restored by Keap1 inhibition. Targeted siRNA-based therapy represents a novel, efficacious strategy to reestablish redox homeostasis and accelerate diabetic cutaneous tissue regeneration.

Metallothionein plays a prominent role in the prevention of diabetic nephropathy by sulforaphane via up-regulation of Nrf2

Sulforaphane (SFN) prevents diabetic nephropathy (DN) in type 1 diabetes via up-regulation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2). However, it has not been addressed whether SFN also prevents DN from type 2 diabetes or which Nrf2 downstream gene(s) play(s) the key role in SFN renal protection. Here we investigated whether Nrf2 is required for SFN protection against type 2 diabetes-induced DN and whether metallothionein (MT) is an Nrf2 downstream antioxidant using Nrf2 knockout (Nrf2-null) mice. In addition, MT knockout mice were used to further verify if MT is indispensable for SFN protection against DN. Diabetes-increased albuminuria, renal fibrosis, and inflammation were significantly prevented by SFN, and Nrf2 and MT expression was increased. However, SFN renal protection was completely lost in Nrf2-null diabetic mice, confirming the pivotal role of Nrf2 in SFN protection from type 2 diabetes-induced DN. Moreover, SFN failed to up-regulate MT in the absence of Nrf2, suggesting that MT is an Nrf2 downstream antioxidant. MT deletion resulted in a partial, but significant attenuation of SFN renal protection from type 2 diabetes, demonstrating a partial requirement for MT for SFN renal protection. Therefore, the present study demonstrates for the first time that as an Nrf2 downstream antioxidant, MT plays an important, though partial, role in mediating SFN renal protection from type 2 diabetes.

Mechanisms of activation of the transcription factor Nrf2 by redox stressors, nutrient cues, and energy status and the pathways through which it attenuates degenerative disease

Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) regulates the basal and stress-inducible expression of a battery of genes encoding key components of the glutathione-based and thioredoxin-based antioxidant systems, as well as aldo-keto reductase, glutathione S-transferase, and

NAD(P)H

quinone oxidoreductase-1 drug-metabolizing isoenzymes along with multidrug-resistance-associated efflux pumps. It therefore plays a pivotal role in both intrinsic resistance and cellular adaptation to reactive oxygen species (ROS) and xenobiotics. Activation of Nrf2 can, however, serve as a double-edged sword because some of the genes it induces may contribute to chemical carcinogenesis by promoting futile redox cycling of polycyclic aromatic hydrocarbon metabolites or confer resistance to chemotherapeutic drugs by increasing the expression of efflux pumps, suggesting its cytoprotective effects will vary in a context-specific fashion. In addition to cytoprotection, Nrf2 also controls genes involved in intermediary metabolism, positively regulating those involved in NADPH generation, purine biosynthesis, and the β-oxidation of fatty acids, while suppressing those involved in lipogenesis and gluconeogenesis. Nrf2 is subject to regulation at multiple levels. Its ability to orchestrate adaptation to oxidants and electrophiles is due principally to stress-stimulated modification of thiols within one of its repressors, the Kelch-like ECH-associated protein 1 (Keap1), which is present in the cullin-3 RING ubiquitin ligase (CRL) complex CRLKeap1. Thus modification of Cys residues in Keap1 blocks CRLKeap1 activity, allowing newly translated Nrf2 to accumulate rapidly and induce its target genes. The ability of Keap1 to repress Nrf2 can be attenuated by p62/sequestosome-1 in a mechanistic target of rapamycin complex 1 (mTORC1)-dependent manner, thereby allowing refeeding after fasting to increase Nrf2-target gene expression. In parallel with repression by Keap1, Nrf2 is also repressed by β-transducin repeat-containing protein (β-TrCP), present in the Skp1-cullin-1-F-box protein (SCF) ubiquitin ligase complex SCFβ-TrCP. The ability of SCFβ-TrCP to suppress Nrf2 activity is itself enhanced by prior phosphorylation of the transcription factor by glycogen synthase kinase-3 (GSK-3) through formation of a DSGIS-containing phosphodegron. However, formation of the phosphodegron in Nrf2 by GSK-3 is inhibited by stimuli that activate protein kinase B (PKB)/Akt. In particular, PKB/Akt activity can be increased by phosphoinositide 3-kinase and mTORC2, thereby providing an explanation of why antioxidant-responsive element-driven genes are induced by growth factors and nutrients. Thus Nrf2 activity is tightly controlled via CRLKeap1 and SCFβ-TrCP by oxidative stress and energy-based signals, allowing it to mediate adaptive responses that restore redox homeostasis and modulate intermediary metabolism. Based on the fact that Nrf2 influences multiple biochemical pathways in both positive and negative ways, it is likely its dose-response curve, in terms of susceptibility to certain degenerative disease, is U-shaped. Specifically, too little Nrf2 activity will lead to loss of cytoprotection, diminished antioxidant capacity, and lowered β-oxidation of fatty acids, while conversely also exhibiting heightened sensitivity to ROS-based signaling that involves receptor tyrosine kinases and apoptosis signal-regulating kinase-1. By contrast, too much Nrf2 activity disturbs the homeostatic balance in favor of reduction, and so may have deleterious consequences including overproduction of reduced glutathione and NADPH, the blunting of ROS-based signal transduction, epithelial cell hyperplasia, and failure of certain cell types to differentiate correctly. We discuss the basis of a putative U-shaped Nrf2 dose-response curve in terms of potentially competing processes relevant to different stages of tumorigenesis.

Endoplasmic reticulum stress and Nrf2 signaling in cardiovascular diseases

Various cellular perturbations implicated in the pathophysiology of human diseases, including cardiovascular and neurodegenerative diseases, diabetes mellitus, obesity, and liver diseases, can alter endoplasmic reticulum (ER) function and lead to the abnormal accumulation of misfolded proteins. This situation configures the so-called ER stress, a form of intracellular stress that occurs whenever the protein-folding capacity of the ER is overwhelmed. Reduction in blood flow as a result of atherosclerotic coronary artery disease causes tissue hypoxia, a condition that induces protein misfolding and ER stress. In addition, ER stress has an important role in cardiac hypertrophy mainly in the transition to heart failure (HF). ER transmembrane sensors detect the accumulation of unfolded proteins and activate transcriptional and translational pathways that deal with unfolded and misfolded proteins, known as the unfolded protein response (UPR). Once the UPR fails to control the level of unfolded and misfolded proteins in the ER, ER-initiated apoptotic signaling is induced. Furthermore, there is considerable evidence that implicates the presence of oxidative stress and subsequent related cellular damage as an initial cause of injury to the myocardium after ischemia/reperfusion (I/R) and in cardiac hypertrophy secondary to pressure overload. Oxidative stress is counterbalanced by complex antioxidant defense systems regulated by a series of multiple pathways, including the UPR, to ensure that the response to oxidants is adequate. Nuclear factor-E2-related factor (Nrf2) is an emerging regulator of cellular resistance to oxidants; Nrf2 is strictly interrelated with the UPR sensor called pancreatic endoplasmic reticulum kinase. A series of studies has shown that interventions against ER stress and Nrf2 activation reduce myocardial infarct size and cardiac hypertrophy in the transition to HF in animals exposed to I/R injury and pressure overload, respectively. Finally, recent data showed that Nrf2/antioxidant-response element pathway activation may be of importance also in ischemic preconditioning, a phenomenon in which the heart is subjected to one or more episodes of nonlethal myocardial I/R before the sustained coronary artery occlusion.

Sulforaphane Protects against Cardiovascular Disease via Nrf2 Activation

Cardiovascular disease (CVD) causes an unparalleled proportion of the global burden of disease and will remain the main cause of mortality for the near future. Oxidative stress plays a major role in the pathophysiology of cardiac disorders. Several studies have highlighted the cardinal role played by the overproduction of reactive oxygen or nitrogen species in the pathogenesis of ischemic myocardial damage and consequent cardiac dysfunction. Isothiocyanates (ITC) are sulfur-containing compounds that are broadly distributed among cruciferous vegetables. Sulforaphane (SFN) is an ITC shown to possess anticancer activities by both in vivo and epidemiological studies. Recent data have indicated that the beneficial effects of SFN in CVD are due to its antioxidant and anti-inflammatory properties. SFN activates NF-E2-related factor 2 (Nrf2), a basic leucine zipper transcription factor that serves as a defense mechanism against oxidative stress and electrophilic toxicants by inducing more than a hundred cytoprotective proteins, including antioxidants and phase II detoxifying enzymes. This review will summarize the evidence from clinical studies and animal experiments relating to the potential mechanisms by which SFN modulates Nrf2 activation and protects against CVD.

Sulforaphane protects the heart from doxorubicin-induced toxicity

Cardiotoxicity is one of the major side effects encountered during cancer chemotherapy with doxorubicin (DOX) and other anthracyclines. Previous studies have shown that oxidative stress caused by DOX is one of the primary mechanisms for its toxic effects on the heart. Since the redox-sensitive transcription factor, Nrf2, plays a major role in protecting cells from the toxic metabolites generated during oxidative stress, we examined the effects of the phytochemical sulforaphane (SFN), a potent Nrf2-activating agent, on DOX-induced cardiotoxicity. These studies were carried out both in vitro and in vivo using rat H9c2 cardiomyoblast cells and wild type 129/sv mice, and involved SFN pretreatment followed by SFN administration during DOX exposure. SFN treatment protected H9c2 cells from DOX cytotoxicity and also resulted in restored cardiac function and a significant reduction in DOX-induced cardiomyopathy and mortality in mice. Specificity of SFN induction of Nrf2 and protection of H9c2 cells was demonstrated in Nrf2 knockdown experiments. Cardiac accumulation of 4-hydroxynonenal (4-HNE) protein adducts, due to lipid peroxidation following DOX-induced oxidative stress, was significantly attenuated by SFN treatment. The respiratory function of cardiac mitochondria isolated from mice exposed to DOX alone was repressed, while SFN treatment with DOX significantly elevated mitochondrial respiratory complex activities. Co-administration of SFN reversed the DOX-associated reduction in nuclear Nrf2 binding activity and restored cardiac expression of Nrf2-regulated genes at both the RNA and protein levels. Together, our results demonstrate for the first time that the Nrf2 inducer, SFN, has the potential to provide protection against DOX-mediated cardiotoxicity.

Wogonin suppresses osteopontin expression in adipocytes by activating PPARα

AIM

Wogonin (5,7-dihydroxy-8-methoxyflavone), a major bioactive compound of the flavonoid family, is commonly extracted from the traditional Chinese medicine Scutellaria baicalensis and possesses antioxidant and anti-inflammatory activities and is assumed to have anti-diabetes function. Indeed, a current study has shown that it can possibly treat metabolic disorders such as those found in db/db mice. However, the underlying molecular mechanism remains largely unclear. The aim of this study was to investigate the impact of wogonin on osteopontin (OPN) expression in adipose tissue from type 1 diabetic mice and in 3T3-L1 adipocytes.

METHODS

Type 1 diabetes was induced by streptozotocin (STZ) injection. 3T3-L1 preadipocytes were converted to 3T3-L1 adipocytes through treatment with insulin, dexamethasone, and 3-isobutyl-1-methylxanthine (IBMX). Western blot analysis and RT-PCR were performed to detect protein expression and mRNA levels, respectively.

RESULTS

Wogonin treatment suppressed the increase in serum OPN levels and reduced OPN expression in adipose tissue from STZ-induced type 1 diabetic mice. Administration of wogonin enhanced PPARα expression and activity. Silencing of PPARα diminished the inhibitory effects of wogonin on OPN expression in 3T3-L1 adipocytes. Furthermore, the levels of c-Fos and phosphorylated c-Jun were reduced in wogonin-treated adipose tissue and 3T3-L1 adipocytes. In addition, wogonin treatment dramatically mitigated p38 MAPK phosphorylation. Pharmacological inhibition of p38 MAPK by its specific inhibitor SB203580 increased PPARα activity and decreased OPN expression.

CONCLUSION

Our results suggest that wogonin downregulated OPN expression in adipocytes through the inhibition of p38 MAPK and the sequential activation of the PPARα pathway. Given the adverse effects of high OPN levels on metabolism, our results provide evidence for the potential administration of wogonin as a treatment for diabetes.

Potential drugs which activate nuclear factor E2-related factor 2 signaling to prevent diabetic cardiovascular complications: A focus on fumaric acid esters

Diabetes and its cardiovascular complications have been a major public health issue. These complications are mainly attributable to a severe imbalance between free radical and reactive oxygen species production and the antioxidant defense systems. Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that controls the basal and inducible expression of a battery of antioxidant enzyme genes and other cyto-protective phase II detoxifying enzymes. As a result, Nrf2 has gained great attention as a promising drug target for preventing diabetic cardiovascular complications. And while animal studies have shown that several Nrf2 activators manifest a potential to efficiently prevent the diabetic complications, their use in humans has not been approved due to the lack of substantial evidence regarding safety and efficacy of the Nrf2 activation. We provide here a brief review of a few clinically-used drugs that can up-regulate Nrf2 with the potential of extending their usage to diabetic patients for the prevention of cardiovascular complications and conclude with a closer inspection of dimethyl fumarate and its mimic members.

Adiponectin ameliorates hyperglycemia-induced cardiac hypertrophy and dysfunction by concomitantly activating Nrf2 and Brg1

Hyperglycemia-induced oxidative stress is implicated in the development of cardiomyopathy in diabetes that is associated with reduced adiponectin (APN) and heme oxygenase-1 (HO-1). Brahma-related gene 1 (Brg1) assists nuclear factor-erythroid-2-related factor-2 (Nrf2) to activate HO-1 to increase myocardial antioxidant capacity in response to oxidative stress. We hypothesized that reduced adiponectin (APN) impairs HO-1 induction which contributes to the development of diabetic cardiomyopathy, and that supplementation of APN may ameliorate diabetic cardiomyopathy by activating HO-1 through Nrf2 and Brg1 in diabetes. Control (C) and streptozotocin-induced diabetic (D) rats were untreated or treated with APN adenovirus (1×10(9) pfu) 3 weeks after diabetes induction and examined and terminated 1 week afterward. Rat left ventricular functions were assessed by a pressure-volume conductance system, before the rat hearts were removed to perform histological and biochemical assays. Four weeks after diabetes induction, D rats developed cardiac hypertrophy evidenced as increased ratio of heart weight to body weight, elevated myocardial collagen I content, and larger cardiomyocyte cross-sectional area (all P<0.05 vs C). Diabetes elevated cardiac oxidative stress (increased 15-F2t-isoprostane, 4-hydroxynonenal generation, 8-hydroxy-2'-deoxyguanosine, and superoxide anion generation), increased myocardial apoptosis, and impaired cardiac function (all P<0.05 vs C). In D rats, myocardial HO-1 mRNA and protein expression were reduced which was associated with reduced Brg1 and nuclear Nrf2 protein expression. All these changes were either attenuated or prevented by APN. In primarily cultured cardiomyocytes (CMs) isolated from D rats or in the embryonic rat cardiomyocytes cell line H9C2 cells incubated with high glucose (HG, 25 mM), supplementation of recombined globular APN (gAd, 2μg/mL) reversed HG-induced reductions of HO-1, Brg1, and nuclear Nrf2 protein expression and attenuated cellular oxidative stress, myocyte size, and apoptotic cells. Inhibition of HO-1 by ZnPP (10μM) or small interfering RNA (siRNA) canceled all the above gAd beneficial effects. Moreover, inhibition of Nrf2 (either by the Nrf2 inhibitor luteolin or siRNA) or Brg1 (by siRNA) canceled gAd-induced HO-1 induction and cellular protection in CMs and in H9C2 cells incubated with HG. In summary, our present study demonstrated that APN reduced cardiac oxidative stress, ameliorated cardiomyocyte hypertrophy, and prevented left ventricular dysfunction in diabetes by concomitantly activating Nrf2 and Brg1 to facilitate HO-1 induction.

Discovery of direct inhibitors of Keap1-Nrf2 protein-protein interaction as potential therapeutic and preventive agents

The Keap1–Nrf2–ARE pathway is an important antioxidant defense mechanism that protects cells from oxidative stress and the Keap1–Nrf2 protein–protein interaction (PPI) has become an important drug target to upregulate the expression of ARE-controlled cytoprotective oxidative stress response enzymes in the development of therapeutic and preventive agents for a number of diseases and conditions. However, most known Nrf2 activators/ARE inducers are indirect inhibitors of Keap1–Nrf2 PPI and they are electrophilic species that act by modifying the sulfhydryl groups of Keap1׳s cysteine residues. The electrophilicity of these indirect inhibitors may cause "off-target" side effects by reacting with cysteine residues of other important cellular proteins. Efforts have recently been focused on the development of direct inhibitors of Keap1–Nrf2 PPI. This article reviews these recent research efforts including the development of high throughput screening assays, the discovery of peptide and small molecule direct inhibitors, and the biophysical characterization of the binding of these inhibitors to the target Keap1 Kelch domain protein. These non-covalent direct inhibitors of Keap1–Nrf2 PPI could potentially be developed into effective therapeutic or preventive agents for a variety of diseases and conditions.

CB1 cannabinoid receptor antagonist attenuates left ventricular hypertrophy and Akt-mediated cardiac fibrosis in experimental uremia

Cannabinoid receptor type 1 (CB1R) plays an important role in the development of myocardial hypertrophy and fibrosis-2 pathological features of uremic cardiomyopathy. However, it remains unknown whether CB1R is involved in the pathogenesis of uremic cardiomyopathy. Here, we aimed to elucidate the role of CB1R in the development of uremic cardiomyopathy via modulation of Akt signalling. The heart size and myocardial fibrosis were evaluated by echocardiography and immunohistochemical staining, respectively, in 5/6 nephrectomy chronic kidney disease (CKD) mice treated with a CB1R antagonist. CB1R and fibrosis marker expression levels were determined by immunoblotting in H9c2 cells exposed to the uremic toxin indoxyl sulfate (IS), with an organic anion transporter 1 inhibitor or a CB1R antagonist or agonist. Akt phosphorylation was also assessed to examine the signaling pathways downstream of CB1R activation induced by IS in H9c2 cells. CKD mice exhibited marked left ventricular hypertrophy and myocardial fibrosis, which were reversed by treatment with the CB1R antagonist. CB1R, collagen I, transforming growth factor (TGF)-β, and α-smooth muscle actin (SMA) expression showed time- and dose-dependent upregulation in H9c2 cells treated with IS. The inhibition of CB1R by either CB1R antagonist or small interfering RNA-mediated knockdown attenuated the expression of collagen I, TGF-β, and α-SMA in IS-treated H9c2 cells, while Akt phosphorylation was enhanced by CB1R agonist and abrogated by CB1R antagonist in these cells. In summary, we conclude that CB1R blockade attenuates LVH and Akt-mediated cardiac fibrosis in a CKD mouse model. Uremic toxin IS stimulates the expression of CB1R and fibrotic markers and CB1R inhibition exerts anti-fibrotic effects via modulation of Akt signaling in H9c2 myofibroblasts. Therefore, the development of drugs targeting CB1R may have therapeutic potential in the treatment of uremic cardiomyopathy.

Magnolia bioactive constituent 4-O-methylhonokiol prevents the impairment of cardiac insulin signaling and the cardiac pathogenesis in high-fat diet-induced obese mice

In obesity, cardiac insulin resistance is a putative cause of cardiac hypertrophy and dysfunction. In our previous study, we observed that Magnolia extract BL153 attenuated high-fat-diet (HFD)-induced cardiac pathogenic changes. In this study, we further investigated the protective effects of the BL153 bioactive constituent, 4-O-methylhonokiol (MH), against HFD-induced cardiac pathogenesis and its possible mechanisms. C57BL/6J mice were fed a normal diet or a HFD with gavage administration of vehicle, BL153, or MH (low or high dose) daily for 24 weeks. Treatment with MH attenuated HFD-induced obesity, as evidenced by body weight gain, and cardiac pathogenesis, as assessed by the heart weight and echocardiography. Mechanistically, MH treatment significantly reduced HFD-induced impairment of cardiac insulin signaling by preferentially augmenting Akt2 signaling. MH also inhibited cardiac expression of the inflammatory factors tumor necrosis factor-α and plasminogen activator inhibitor-1 and increased the phosphorylation of nuclear factor erythroid-derived 2-like 2 (Nrf2) as well as the expression of a Nrf2 downstream target gene heme oxygenase-1. The increased Nrf2 signaling was associated with decreased oxidative stress and damage, as reflected by lowered malondialdehyde and 3-nitrotyrosine levels. Furthermore, MH reduced HFD-induced cardiac lipid accumulation along with lowering expression of cardiac fatty acid translocase/CD36 protein. These results suggest that MH, a bioactive constituent of Magnolia, prevents HFD-induced cardiac pathogenesis by attenuating the impairment of cardiac insulin signaling, perhaps via activation of Nrf2 and Akt2 signaling to attenuate CD36-mediated lipid accumulation and lipotoxicity.

Earlier onset of diabesity-Induced adverse cardiac remodeling in female compared to male mice

OBJECTIVE

Emerging evidence suggests female type 2 diabetes (T2DM) patients may fare worse than males with respect to cardiovascular complications. Hence the impact of sex on relative progression of left ventricular (LV) remodeling in obese db/db mice was characterized.

METHODS

The changes in parameters of LV hypertrophy (heart weight, pro-hypertrophic gene expression, cardiomyocyte size) and fibrosis (LV collagen deposition and oxidative stress), in parallel with body weight and blood glucose and lipid profiles, in male and female db/db T2DM mice, at 10, 14, and 18 weeks of age, were determined.

RESULTS

Diabesity-induced cardiac remodeling was at least comparable in female (compared to male) mice. Females exhibited enhanced systemic oxidative stress and nonesterified fatty acid levels. Progression of LV pro-hypertrophic (β-myosin heavy chain, B-type natriuretic peptide) and pro-oxidant gene expression (NADPH oxidase subunit Nox2, plasminogen activator inhibitor-1 PAI-I) was, however, exaggerated in females when expressed relative to 10-week-old db/db mice. Increased cardiomyocyte width was also evident earlier in db/db females than males. No other gender differences were observed.

CONCLUSIONS

Progressive, age-dependent development of cardiac remodeling in db/db mice parallels impairments in glucose handling and oxidative stress. Certain aspects of the T2DM-induced LV remodeling response may have an earlier and/or exaggerated onset in diabetic females.