Metformin Protects H9C2 Cardiomyocytes from High-Glucose and Hypoxia/Reoxygenation Injury via Inhibition of Reactive Oxygen Species Generation and Inflammatory Responses: Role of AMPK and JNK

Molecular Basis of Cardiomyopathies in Type 2 Diabetes

Diabetic cardiomyopathy (DbCM) is a common complication in individuals with type 2 diabetes mellitus (T2DM), and its exact pathogenesis is still debated. It was hypothesized that chronic hyperglycemia and insulin resistance activate critical cellular pathways that are responsible for numerous functional and anatomical perturbations in the heart. Interstitial inflammation, oxidative stress, myocardial apoptosis, mitochondria dysfunction, defective cardiac metabolism, cardiac remodeling, hypertrophy and fibrosis with consequent impaired contractility are the most common mechanisms implicated. Epigenetic changes also have an emerging role in the regulation of these crucial pathways. The aim of this review was to highlight the increasing knowledge on the molecular mechanisms of DbCM and the new therapies targeting specific pathways.

Pterostilbene Reverses Epigenetic Silencing of Nrf2 and Enhances Antioxidant Response in Endothelial Cells in Hyperglycemic Microenvironment

The epigenetic regulation of nuclear factor erythroid 2-related factor 2 (Nrf2), a pivotal redox transcription factor, plays a crucial role in maintaining cellular homeostasis. Recent research has underscored the significance of epigenetic modifications of Nrf2 in the pathogenesis of diabetic foot ulcers (DFUs). This study investigates the epigenetic reversal of Nrf2 by pterostilbene (PTS) in human endothelial cells in a hyperglycemic microenvironment (HGM). The activation potential of PTS on Nrf2 was evaluated through ARE-Luciferase reporter assays and nuclear translocation studies. Following 72 h of exposure to an HGM, mRNA expression and protein levels of Nrf2 and its downstream targets NAD(P)H quinone oxidoreductase 1 (NQO1), heme-oxygenase 1(HO-1), superoxide dismutase (SOD), and catalase (CAT) exhibited a decrease, which was mitigated in PTS-pretreated endothelial cells. Epigenetic markers, including histone deacetylases (HDACs class I-IV) and DNA methyltransferases (DNMTs 1/3A and 3B), were found to be downregulated under diabetic conditions. Specifically, Nrf2-associated HDACs, including HDAC1, HDAC2, HDAC3, and HDAC4, were upregulated in HGM-induced endothelial cells. This upregulation was reversed in PTS-pretreated cells, except for HDAC2, which exhibited elevated expression in endothelial cells treated with PTS in a hyperglycemic microenvironment. Additionally, PTS was observed to reverse the activity of the methyltransferase enzyme DNMT. Furthermore, CpG islands in the Nrf2 promoter were hypermethylated in cells exposed to an HGM, a phenomenon potentially counteracted by PTS pretreatment, as shown by methyl-sensitive restriction enzyme PCR (MSRE-qPCR) analysis. Collectively, our findings highlight the ability of PTS to epigenetically regulate Nrf2 expression under hyperglycemic conditions, suggesting its therapeutic potential in managing diabetic complications.

Low-level Nd:YAG laser inhibiting inflammation and oxidative stress in human gingival fibroblasts via AMPK/SIRT3 axis

OBJECTIVE

Photobiomodulation is extensively employed in the management of chronic inflammatory diseases such as periodontitis because of its anti-inflammatory and antioxidant effects. This study used low-level Nd:YAG laser to investigate the mechanism of photobiomodulation as well as the role of adenosine monophosphate-activated protein kinase (AMPK) and Sirtuins (SIRT) 3 in it, providing new clues for the treatment of periodontitis.

METHODS

Human gingival fibroblasts (HGFs) were extracted from gingiva and stimulated with LPS. The suitable parameters of Nd:YAG laser were chosen for subsequent experiments by detecting cell viability. We assessed the level of inflammation and oxidative stress as well as AMPK and SIRT3. The mechanism for AMPK targeting SIRT3 modulating the anti-inflammatory and antioxidant effects of photobiomodulation was explored by the AMPK inhibitor (Compound C) test, cell transfection, western blot, and immunofluorescence.

RESULTS

HGFs were isolated and identified, followed by the identification of optimal Nd:YAG laser parameters (60 mJ, 15 Hz, 10s) for subsequent experimentation. With this laser, inflammatory factors (IL-6, TNF-α, COX2, and iNOS) decreased as well as the phosphorylation and nuclear translocation of NFκB-P65. SOD2 was up-regulated but reactive oxygen species (ROS) was down-regulated. The laser treatment exhibited enhancements in AMPK phosphorylation and SIRT3 expression. The above effects could all be reversed by Compound C. Silencing AMPK or SIRT3 by siRNA, the down-regulation of COX2, iNOS, and ROS by laser was inhibited. SIRT3 was down-regulated when the AMPK was silenced.

CONCLUSION

Low-level Nd:YAG laser activated AMPK-SIRT3 signaling pathway, facilitating the anti-inflammatory and antioxidative activity.

Role of gibberellins, neem leaf extract, and serine in improving wheat growth and grain yield under drought-triggered oxidative stress

The foliar application of gibberellins (GA3), neem leaf extract (NLE) and serine can be proven as effective growth regulating agents to counter drought stress-related deleterious effects. The literature about the collaborative role of these substances in foliar spray application under drought stress is not available to this date. No single report is available in literature on combine foliar application of GA3, NLE, and serine in improving wheat growth and yield under drought-triggered oxidative stress. The objective of this study was to induct tolerance against drought stress in order to sustain maximum growth and yield of wheat varieties (Anaj-2017 and Galaxy-2013) with foliar applications of GA3, NLE, and serine. The current field trial was designed to disclose the protective role of these substances in wheat varieties (Anaj-2017 and Galaxy-2013) under water-deficit stress. Two irrigation levels, i.e., control (normal irrigation) and water stress (water deficit irrigation), and 5 levels of GA3, NLE and serine i.e., control (water spray), GA3 (10.0 ppm), NLE (10.0%), serine (9.5 mM), and mixture (GA3 + NLE + serine) in a 1:1:1 ratio was applied. Application of these substances improved the pigments (Chlorophyll a, b), carotenoids, growth, biomass, and grain yield traits of both wheat varieties under water-deficit stress. Activities of antioxidant enzymes (POD, CAT and SOD), and non-enzymatic antioxidants (proline, total phenolic contents, anthocyanin and free amino acids) were up-regulated under drought stress and with foliar spray treatments. The foliar applications of these substances reduced the drought triggered overproduction of lipid peroxidation (MDA) and H2O2. The study found that Galaxy-2013 variety is more tolerant to drought stress than Anaj-2017, while co-applied treatments (GA3 + NLE + serine) were shown to be the most effective among all applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01402-9.

Novel insights into the role of mitochondria in diabetic cardiomyopathy: molecular mechanisms and potential treatments

Diabetic cardiomyopathy describes decreased myocardial function in diabetic patients in the absence of other heart diseases such as myocardial ischemia and hypertension. Recent studies have defined numerous molecular interactions and signaling events that may account for deleterious changes in mitochondrial dynamics and functions influenced by hyperglycemic stress. A metabolic switch from glucose to fatty acid oxidation to fuel ATP synthesis, mitochondrial oxidative injury resulting from increased mitochondrial ROS production and decreased antioxidant capacity, enhanced mitochondrial fission and defective mitochondrial fusion, impaired mitophagy, and blunted mitochondrial biogenesis are major signatures of mitochondrial pathologies during diabetic cardiomyopathy. This review describes the molecular alterations underlying mitochondrial abnormalities associated with hyperglycemia and discusses their influence on cardiomyocyte viability and function. Based on basic research findings and clinical evidence, diabetic treatment standards and their impact on mitochondrial function, as well as mitochondria-targeted therapies of potential benefit for diabetic cardiomyopathy patients, are also summarized.

Dapagliflozin attenuates high glucose-and hypoxia/reoxygenation-induced injury via activating AMPK/mTOR-OPA1-mediated mitochondrial autophagy in H9c2 cardiomyocytes

This study investigated the protective effect of dapagliflozin on H9c2 cardiomyocyte function under high glucose and hypoxia/reoxygenation (HG-H/R) conditions and identified the underlying molecular mechanisms. Dapagliflozin reduced the level of lactate dehydrogenase and reactive oxygen species in cardiomyocytes under HG-H/R conditions and was accompanied by a decrease in caspase-3/9 activity. In addition, Dapagliflozin significantly reduced mitochondrial permeability transition pore opening and increased ATP content, accompanied by upregulation of OPA1 with autophagy-related protein molecules and activation of the AMPK/mTOR signalling pathway in HG-H/R treated cardiomyocytes. OPA1 knockdown or compound C treatment attenuated the protective effects of dapagliflozin on the cardiomyocytes under HG-H/R conditions. Downregulation of OPA1 expression increased mitochondrial intolerance in cardiomyocytes during HG-H/R injury and the AMPK-mTOR-autophagy signalling is a key mechanism for protecting mitochondrial function and reducing cardiomyocyte apoptosis. Collectively, dapagliflozin exerted protective effects on the cardiomyocytes under HG-H/R conditions. Dapagliflozin attenuated myocardial HG-H/R injury by activating AMPK/mTOR-OPA1-mediated mitochondrial autophagy.

Metformin mitigates SASP secretion and LPS-triggered hyper-inflammation in Doxorubicin-induced senescent endothelial cells

Introduction: Doxorubicin (DOX), a chemotherapeutic drug, induces senescence and increases the secretion of senescence-associated secretory phenotype (SASP) in endothelial cells (ECs), which contributes to DOX-induced inflammaging. Metformin, an anti-diabetic drug, demonstrates senomorphic effects on different models of senescence. However, the effects of metformin on DOX-induced endothelial senescence have not been reported before. Senescent ECs exhibit a hyper-inflammatory response to lipopolysachharide (LPS). Therefore, in our current work, we identified the effects of metformin on DOX-induced endothelial senescence and LPS-induced hyper-inflammation in senescent ECs. Methods: ECs were treated with DOX ± metformin for 24 h followed by 72 h incubation without DOX to establish senescence. Effects of metformin on senescence markers expression, SA-β-gal activity, and SASP secretion were assessed. To delineate the molecular mechanisms, the effects of metformin on major signaling pathways were determined. The effect of LPS ± metformin was determined by stimulating both senescent and non-senescent ECs with LPS for an additional 24 h. Results: Metformin corrected DOX-induced upregulation of senescence markers and decreased the secretion of SASP factors and adhesion molecules. These effects were associated with a significant inhibition of the JNK and NF-κB pathway. A significant hyper-inflammatory response to LPS was observed in DOX-induced senescent ECs compared to non-senescent ECs. Metformin blunted LPS-induced upregulation of pro-inflammatory SASP factors. Conclusion: Our study demonstrates that metformin mitigates DOX-induced endothelial senescence phenotype and ameliorates the hyper-inflammatory response to LPS. These findings suggest that metformin may protect against DOX-induced vascular aging and endothelial dysfunction and ameliorate infection-induced hyper-inflammation in DOX-treated cancer survivors.

Metformin Acutely Mitigates Oxidative Stress in Human Atrial Tissue: A Pilot Study in Overweight Non-Diabetic Cardiac Patients

Metformin, the first-line drug in type 2 diabetes mellitus, elicits cardiovascular protection also in obese patients via pleiotropic effects, among which the anti-oxidant is one of the most investigated. The aim of the present study was to assess whether metformin can acutely mitigate oxidative stress in atrial tissue harvested from overweight non-diabetic patients. Right atrial appendage samples were harvested during open-heart surgery and used for the evaluation of reactive oxygen species (ROS) production by means of confocal microscopy (superoxide anion) and spectrophotometry (hydrogen peroxide). Experiments were performed after acute incubation with metformin (10 µM) in the presence vs. absence of angiotensin II (AII, 100 nM), lipopolysaccharide (LPS, 1 μg/mL), and high glucose (Gluc, 400 mg/dL). Stimulation with AII, LPS, and high Gluc increased ROS production. The magnitude of oxidative stress correlated with several echocardiographic parameters. Metformin applied in the lowest therapeutic concentration (10 µM) was able to decrease ROS generation in stimulated but also non-stimulated atrial samples. In conclusion, in a pilot group of overweight non-diabetic cardiac patients, acute incubation with metformin at a clinically relevant dose alleviated oxidative stress both in basal conditions and conditions that mimicked the activation of the renin-angiotensin-aldosterone system, acute inflammation, and uncontrolled hyperglycemia.

Bioactive Peptides and Exercise Modulate the AMPK/SIRT1/PGC-1α/FOXO3 Pathway as a Therapeutic Approach for Hypertensive Rats

Peptides are fragments of fundamental protein sequences that may have health benefits in addition to basic dietary benefits. Recently, we have reported on the pharmacological benefits of alcalase potato protein hydrolysate (APPH) and bioactive peptides isolated from APPH. The aim was to evaluate the synergistic effect of exercise along with DIKTNKPVIF (DF) peptides in ameliorating hypertension in spontaneously hypertensive rat (SHR) rats. We examined ECG parameters, lipid profiles, cardiac markers, and histology, and quantified the proteins associated with fibrosis, hypertrophy, apoptosis, mitochondrial biogenesis, and longevity pathways. DF peptide administration, along with exercise, reduced the blood pressure and cardiac marker levels in serum. Furthermore, it also suppressed the expression of fibrosis markers COL1A1, CTGF, and uPA and downregulated cardiac-hypertrophy-associated markers such as calcineurin, NFATC3, GATA4, pGATA4 and BNP. Exercise synergistically increases the expression of IFG1, PI3K, and AKT cell-survival pathway proteins, along with DF administration. Moreover, AMPK/SIRT1/PGC-1α/FOXO3 pathway protein expression was increased with the combinatorial administration of DF and exercise. Our data suggest that exercise, along with DF peptides, act synergistically in alleviating hypertension by activating the mitochondrial biogenesis pathway.

Ginkgolide B Protects Against Ischemic Stroke via Targeting AMPK/PINK1

Introduction: Ginkgolide B (GB), which is an active constituent derived from Ginkgo biloba leaves, has been reported to ameliorate Alzheimer’s disease (AD), ischemic stroke, as well as other neurodegenerative diseases due to its viable immunosuppressive and anti-inflammatory functions. However, it has yet to be proven whether GB inhibits neuronal apoptosis in ischemic stroke.

Methods: In the present research, the inhibition function of GB on neuronal apoptosis and its underpinning process(s) after cerebral ischemia were studied through transient middle cerebral artery occlusion (t-MCAO) in an in vivo rat model as well as in cultured SH-SY5Y cells subjected to oxygen and glucose deprivation (OGD)/reoxygenation in vitro. The neurological score was calculated and Nissl and TUNEL staining were performed to evaluate the stroke outcome, neuronal loss, and neuronal apoptosis. Subsequently, the western blot was utilized to detect Bcl2 and p-AMPK/AMPK expression.

Results: Compared to t-MCAO rats, rats receiving GB treatment showed a significant reduction of neuronal loss and apoptosis and improved neurological behavior at 72 h after MCAO. GB treatment also upregulated the expression of Bcl2 and p-AMPK. In vitro, GB suppressed the apoptosis in OGD/reoxygenation-challenged neuronal SH-SY5Y cells through AMPK activation.

Conclusions: Our observations suggest that GB enhanced AMPK activation in neural cells, reducing neuronal apoptosis, thus eventually preventing ischemic stroke.

Metformin: A Narrative Review of Its Potential Benefits for Cardiovascular Disease, Cancer and Dementia

The biguanide metformin has been used as first-line therapy in type 2 diabetes mellitus (T2DM) treatment for several decades. In addition to its glucose-lowering properties and its prevention of weight gain, the landmark UK Prospective Diabetes Study (UKPDS) demonstrated cardioprotective properties in obese T2DM patients. Coupled with a favorable side effect profile and low cost, metformin has become the cornerstone in the treatment of T2DM worldwide. In addition, metformin is increasingly being investigated for its potential anticancer and neuroprotective properties both in T2DM patients and non-diabetic individuals. In the meantime, new drugs with powerful cardioprotective properties have been introduced and compete with metformin for its place in the treatment of T2DM. In this review we will discuss actual insights in the various working mechanisms of metformin and the evidence for its beneficial effects on (the prevention of) cardiovascular disease, cancer and dementia. In addition to observational evidence, emphasis is placed on randomized trials and recent meta-analyses to obtain an up-to-date overview of the use of metformin in clinical practice.

LncAABR07025387.1 Enhances Myocardial Ischemia/Reperfusion Injury Via miR-205/ACSL4-Mediated Ferroptosis

Ferroptosis is associated with the pathology of myocardial ischemia/reperfusion (MI/R) injury following myocardial infarction, which is a leading cause of death worldwide. Although long noncoding RNAs (lncRNAs) are known to regulate gene expression, their roles in MI/R-induced ferroptosis remain unclear. In this study, we explored the lncRNA expression profiles in a rat model of MI/R injury and found that the novel lncRNA, lncAABR07025387.1, was highly expressed in MI/R-injured myocardial tissues and hypoxia/reoxygenation (H/R)-challenged myocardial cells. Silencing lncAABR07025387.1 improved MI/R injury in vivo and inhibited myocardial cell ferroptosis under H/R conditions. Bioinformatics analyses and luciferase, pull-down, and RNA-binding immunoprecipitation assays further revealed that lncAABR07025387.1 interacted with miR-205, which directly targeted ACSL4, a known contributor to ferroptosis. Furthermore, downregulating miR-205 reversed the ACSL4 inhibition induced by silencing lncAABR07025387.1. These findings suggest that, mechanistically, lncAABR07025387.1 negatively regulates miR-205 expression and subsequently upregulates ACSL4-mediated ferroptosis. In conclusion, this study demonstrates that lncAABR07025387.1 acts as a competing endogenous RNA during MI/R injury and highlights the therapeutic potential of lncRNAs for treating myocardial injury.

Effects of Metformin in Heart Failure: From Pathophysiological Rationale to Clinical Evidence

Type 2 diabetes mellitus (T2DM) is a worldwide major health burden and heart failure (HF) is the most common cardiovascular (CV) complication in affected patients. Therefore, identifying the best pharmacological approach for glycemic control, which is also useful to prevent and ameliorate the prognosis of HF, represents a crucial issue. Currently, the choice is between the new drugs sodium/glucose co-transporter 2 inhibitors that have consistently shown in large CV outcome trials (CVOTs) to reduce the risk of HF-related outcomes in T2DM, and metformin, an old medicament that might end up relegated to the background while exerting interesting protective effects on multiple organs among which include heart failure. When compared with other antihyperglycemic medications, metformin has been demonstrated to be safe and to lower morbidity and mortality for HF, even if these results are difficult to interpret as they emerged mainly from observational studies. Meta-analyses of randomized controlled clinical trials have not produced positive results on the risk or clinical course of HF and sadly, large CV outcome trials are lacking. The point of force of metformin with respect to new diabetic drugs is the amount of data from experimental investigations that, for more than twenty years, still continues to provide mechanistic explanations of the several favorable actions in heart failure such as, the improvement of the myocardial energy metabolic status by modulation of glucose and lipid metabolism, the attenuation of oxidative stress and inflammation, and the inhibition of myocardial cell apoptosis, leading to reduced cardiac remodeling and preserved left ventricular function. In the hope that specific large-scale trials will be carried out to definitively establish the metformin benefit in terms of HF failure outcomes, we reviewed the literature in this field, summarizing the available evidence from experimental and clinical studies reporting on effects in heart metabolism, function, and structure, and the prominent pathophysiological mechanisms involved.

Dexmedetomidine Attenuates Hypoxia/Reoxygenation Injury of H9C2 Myocardial Cells by Upregulating miR-146a Expression via the MAPK Signal Pathway

INTRODUCTION AND OBJECTIVE

Dexmedetomidine (Dex) and a number of miRNAs contribute to ischemia/reperfusion injury. We aimed to explore the role of Dex and miR-146a on myocardial cells injured by hypoxia/reoxygenation (H/R).

METHOD

H9C2 cells were injured by H/R. Cell viability was tested using the cell counting kit-8. Lactate dehydrogenase (LDH) activity, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) levels were determined using commercial kits. Flow cytometry was performed to determine apoptosis rate and reactive oxygen species (ROS) level. Protein and mRNA levels were assessed using Western blot and qPCR.

RESULTS

miR-146a expression and cell viability of H9C2 cells were downregulated under the circumstance of H/R injury. The tendency could be reversed by Dex, which could also upregulate SOD activity and decrease apoptosis, LDH activity, MDA, 78-kDa glucose-regulated protein (GRP78), and C/EBP homologous protein (CHOP) levels of H9C2 cells. GRP78, CHOP levels, and cell viability were negatively modulated by miR-146a. Dex elevated cell viability, catalase, MnSOD, and NAD(P)H dehydrogenase (NQO1) levels but suppressed apoptosis rate, GRP78, and CHOP levels by increasing miR-146a expression and downregulating ROS, phosphorylation of p38, and extracellular signal-regulated kinases 1/2 levels. By using SB203580 (SB), the p38 mitogen-activated protein kinase (MAPK) inhibitor, Dex or the inhibition of miR-146 upregulated cell viability but downregulated GRP78 and CHOP levels.

CONCLUSION

Dex might regulate miR-146a expression, which could further modulate the endoplasmic reticulum stress and oxidative stress and eventually affect the cell viability and apoptosis of myocardial cells injured by H/R via the MAPK signal pathway.

Period 2-Induced Activation of Autophagy Improves Cardiac Remodeling After Myocardial Infarction

Accumulating evidence indicates that the onset of myocardial infarction (MI) shows obvious circadian rhythmicity. Clinical studies have shown that MIs that occur in the early morning have a poor prognosis, but the mechanisms involved are still unknown. In this study, we showed that the expression level of Period 2 (per2) in the heart of mice is lower in the early morning than at noon and that increasing the expression of per2 in H9C2 cells and rat cardiomyocytes increases autophagy levels. Further studies indicated that overexpression of per2 after an MI improved cardiac function by increasing autophagy. In summary, this study has shown that the circadian clock protein, per2, may be a regulator of MI.

LncRNA-Fendrr protects against the ubiquitination and degradation of NLRC4 protein through HERC2 to regulate the pyroptosis of microglia

OBJECTIVES

Targeted inhibition of inflammatory response can reduce diabetic cerebral ischemia-reperfusion (I/R) injure. Pyroptosis is characterized by caspase-1 dependence and the release of a large number of pro-inflammatory factors. LncRNA-Fendrr is associated with a variety of diseases, but Fendrr has not been studied in diabetic cerebral I/R. NLR-family CARD-containing protein 4 (NLRC4) regulate the pyroptosis of microglia cells. This study was designed to investigate whether Fendrr is involved in the effects of diabetic cerebral I/R injury.

METHODS

The diabetic brain I/R model in mice was constructed. Mouse microglia cell line BV-2 cells were exposed to high glucose followed by hypoxia/reoxygenation (H/R). Fendrr and some pyroptosis-associated proteins were detected by qRT-PCR, western blot or ELISA. HE staining was used to detect pathological changes. Microglia pyroptosis was detected by TUNEL staining. RNA pull-down and RNA Immunoprecipitation were used to detect binding of Fendrr to HERC2 (E3 ubiquitin ligase), and CO-IP detected binding of HERC2 to NLRC4. The ubiquitination of NLRC4 was detected by ubiquitination experiments.

RESULTS

Fendrr was significantly increased in the diabetic cerebral I/R model, and NLRC4 inflammatory complex and pyroptosis mediated inflammatory factors were increased. NLRC4 and inflammatory cytokines associated with pyroptosis were decreased in the high glucose-treated hypoxia/reoxygenation (H/R)-induced microglia after Fendrr knockdown. Fendrr bound to HERC2 protein, and HERC2 bound to NLRC4. Meanwhile, Fendrr could inhibit the ubiquitination of NLRC4, HERC2 promoted the ubiquitination of NLRC4 protein. Moreover, the effect of Fendrr overexpression in the diabetic cerebral I/R model of microglia can be reversed by HERC2 overexpression.

CONCLUSION

Fendrr can protect against the ubiquitination and degradation of NLRC4 protein through E3 ubiquitin ligase HERC2, thereby accelerating the pyroptosis of microglia.

Metformin protects cardiomyocytes against oxygen-glucose deprivation injury by promoting autophagic flux through AMPK pathway

Metformin has been shown to protect myocardial ischaemia/reperfusion or hypoxia/reoxygenation injury. In our current study, we investigated the effects of metformin on autophagy and its possible underlying mechanisms in in vivo myocardial infarction (MI) model and in vitro oxygen-glucose deprivation (OGD) model. A rat model of MI was made by ligating coronary artery in vivo study. Metformin (200 mg/kg/day) could improve cardiac function, prevent rats from MI-induced injury by reducing myocardial infarct size and apoptosis. Moreover, metformin furtherly promoted autophagy by increasing the protein expression of LC3-II, ATG5, ATG7 and Beclin1, and by involving AMPK pathway during MI. H9c2 cells were treated with metformin (4 mM) in vitro study to assess its effects after exposure to OGD. Metformin increased cell viability and inhibited OGD-induced LDH synthesis and cell apoptosis. Furthermore, metformin increased autophagosome formations as well as expression of autophagy-related proteins, promoted autophagic flux. In addition, metformin augmented the protein level of Bcl-2 and diminished the protein levels of Bax and cleaved caspase-3. Metformin also upregulated p-AMPK expression. Nevertheless, the above-mentioned effects of metformin on H9c2 cells were remarkably eliminated by compound C (an AMPK inhibitor). In summary, we displayed that metformin protected cardiomyocytes against OGD-induced injury and apoptosis by promoting autophagic flux through the AMPK pathway.

Mechanisms of action of metformin and its regulatory effect on microRNAs related to angiogenesis

Angiogenesis is rapidly initiated in response to pathological conditions and is a key target for pharmaceutical intervention in various malignancies. Anti-angiogenic therapy has emerged as a potential and effective therapeutic strategy for treating cancer and cardiovascular-related diseases. Metformin, a first-line oral antidiabetic agent for type 2 diabetes mellitus (T2DM), not only reduces blood glucose levels and improves insulin sensitivity and exerts cardioprotective effects but also shows benefits against cancers, cardiovascular diseases, and other diverse diseases and regulates angiogenesis. MicroRNAs (miRNAs) are endogenous noncoding RNA molecules with a length of approximately 19-25 bases that are widely involved in controlling various human biological processes. A large number of miRNAs are involved in the regulation of cardiovascular cell function and angiogenesis, of which miR-21 not only regulates vascular cell proliferation, migration and apoptosis but also plays an important role in angiogenesis. The relationship between metformin and abnormal miRNA expression has gradually been revealed in the context of numerous diseases and has received increasing attention. This paper reviews the drug-target interactions and drug repositioning events of metformin that influences vascular cells and has benefits on angiogenesis-mediated effects. Furthermore, we use miR-21 as an example to explain the specific molecular mechanism underlying metformin-mediated regulation of the miRNA signaling pathway controlling angiogenesis and vascular protective effects. These findings may provide a new therapeutic target and theoretical basis for the clinical prevention and treatment of cardiovascular diseases.

Inhibitory Action of Antidiabetic Drugs on the Free Radical Production by the Rod Outer Segment Ectopic Aerobic Metabolism

Rod outer segments (OS) express the FoF1-ATP synthase and the respiratory chain, conducting an ectopic aerobic metabolism that produces free radicals in vitro. Diabetic retinopathy, a leading cause of vision loss, is associated with oxidative stress in the outer retina. Since metformin and glibenclamide, two anti-type 2 diabetes drugs, target the respiratory complexes, we studied the effect of these two drugs, individually or in association, on the free radical production in purified bovine rod OS. ATP synthesis, oxygen consumption, and oxidative stress production were assayed by luminometry, oximetry and flow cytometry, respectively. The expression of FoF1-ATP synthase was studied by immunogold electron microscopy. Metformin had a hormetic effect on the OS complex I and ATP synthetic activities, being stimulatory at concentrations below 1 mM, and inhibitory above. Glibenclamide inhibited complexes I and III, as well as ATP production in a concentration-dependent manner. Maximal concentrations of both drugs inhibited the ROI production by the light-exposed OS. Data, consistent with the delaying effect of these drugs on the onset of diabetic retinopathy, suggest that a combination of the two drugs at the beginning of the treatment might reduce the oxidative stress production helping the endogenous antioxidant defences in avoiding retinal damage.

Metformin protects high glucose‑cultured cardiomyocytes from oxidative stress by promoting NDUFA13 expression and mitochondrial biogenesis via the AMPK signaling pathway

Tissue damage in diabetes is at least partly due to elevated reactive oxygen species production by the mitochondrial respiratory chain during hyperglycemia. Sustained hyperglycemia results in mitochondrial dysfunction and the abnormal expression of mitochondrial genes, such as NADH: Ubiquinone oxidoreductase subunit A13 (NDUFA13). Metformin, an AMP-activated protein kinase (AMPK) activator, protects cardiomyocytes from oxidative stress by improving mitochondrial function; however, the exact underlying mechanisms are not completely understood. The aim of the present study was to investigated the molecular changes and related regulatory mechanisms in the response of H9C2 cardiomyocytes to metformin under high glucose conditions. H9C2 cells were subjected to CCK-8 assay to assess cell viability. Reactive oxygen species generation was measured with DCFH-DA assay. Western blotting was used to analyze the expression levels of NDUFA13, AMPK, p-AMPK and GAPDH. Reverse transcription-quantitative PCR was used to evaluate the expression levels of mitochondrial genes and transcription factors. It was observed that metformin protected H9C2 cardiomyocytes by suppressing high glucose (HG)-induced elevated oxidative stress. In addition, metformin stimulated mitochondrial biogenesis, as indicated by increased expression levels of mitochondrial genes (NDUFA1, NDUFA2, NDUFA13 and manganese superoxide dismutase) and mitochondrial biogenesis-related transcription factors [peroxisome proliferator-activated receptor-gamma coactivator-1α, nuclear respiratory factor (NRF)-1, and NRF-2] in the metformin + HG group compared with the HG group. Moreover, metformin promoted mitochondrial NDUFA13 protein expression via the AMPK signaling pathway, which was abolished by pretreatment with the AMPK inhibitor, Compound C. The results suggested that metformin protected cardiomyocytes against HG-induced oxidative stress via a mechanism involving AMPK, NDUFA13 and mitochondrial biogenesis.

Circ_0010729 regulates hypoxia-induced cardiomyocyte injuries by activating TRAF5 via sponging miR-27a-3p

Ischemic cardiomyopathy is a severe cardiovascular disease with high mortality. Circular RNAs (circRNAs) are widely regulated in diverse human diseases, including Ischemic cardiomyopathy. This study aimed to investigate a novel functional mechanism of circRNA circ_0010729 in hypoxia-induced cardiomyocyte injuries. Human cardiomyocytes (AC16) were exposed to hypoxia to mimic ischemic cardiomyopathy in vitro. Cell viability, apoptosis/necrosis and glycolysis progress, were determined using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, flow cytometry assay and glycolysis stress test, respectively. Cell apoptosis was also assessed by the activity of cleaved caspase-3/7. The levels of glycolysis-related proteins and tumor necrosis factor receptor-associated factor 5 (TRAF5) were examined by western blot. The expression of circ_0010729 and miR-27a-3p was measured by real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The prediction about the targeted relationship was verified by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay. As a result, hypoxia treatment inhibited cell viability, induced cell apoptosis and blocked glycolysis, however, these injuries were alleviated by circ_0010729 knockdown. MiR-27a-3p was targeted by circ_0010729, and miR-27a-3p inhibition reversed the role of circ_0010729 knockdown, leading to the deterioration of cell injuries. Further, TRAF5 was a target of miR-27a-3p, and circ_0010729 upregulated the expression of TRAF5 by sponging miR-27a-3p. MiR-27a-3p restoration enhanced cell viability, depleted cell apoptosis and promoted glycolysis of hypoxia-induced AC16 cells, while these effects were abolished by TRAF5 overexpression. In conclusion, circ_0010729 knockdown alleviated hypoxia-induced AC16 cell injuries by mediating the miR-27a-3p/TRAF5 axis.

miR‑155 modulates high glucose‑induced cardiac fibrosis via the Nrf2/HO‑1 signaling pathway

Cardiac fibrosis is a major pathological manifestation of diabetic cardiomyopathy, which is a leading cause of mortality in patients with diabetes. MicroRNA (miR)‑155 is upregulated in cardiomyocytes in cardiac fibrosis, and the aim of the present study was to investigate if the inhibition of miR‑155 was able to ameliorate cardiac fibrosis by targeting the nuclear factor erythroid‑2‑related factor 2 (Nrf2)/heme oxygenase‑1 (HO‑1) signaling pathway. H9C2 rat cardiomyocytes were cultured with high glucose (HG; 30 mM) to establish an in vitro cardiac fibrosis model that mimicked diabetic conditions; a miR‑155 inhibitor and a miR‑155 mimic were transfected into H9C2 cells. Following HG treatment, H9C2 cells exhibited increased expression levels of miR‑155 and the fibrosis markers collagen I and α‑smooth muscle actin (α‑SMA). In addition, the expression levels of endonuclear Nrf2 and HO‑1 were decreased, but the expression level of cytoplasmic Nrf2 was increased. Moreover, oxidative stress, mitochondrial damage and cell apoptosis were significantly increased, as indicated by elevated reactive oxygen species, malonaldehyde and monomeric JC‑1 expression levels. In addition, superoxide dismutase expression was attenuated and there was an increased expression level of released cytochrome‑c following HG treatment. Furthermore, it was demonstrated that expression levels of Bcl‑2 and uncleaved Poly (ADP‑ribose) polymerase were downregulated, whereas Bax, cleaved caspase‑3 and caspase‑9 were upregulated after HG treatment. However, the miR‑155 inhibitor significantly restored Nrf2 and HO‑1 expression levels, and reduced oxidative stress levels, the extent of mitochondrial damage and the number of cells undergoing apoptosis. Additionally, the miR‑155 inhibitor significantly reversed the expression levels of collagen I and α‑SMA, thus ameliorating fibrosis. Furthermore, the knockdown of Nrf2 reversed the above effects induced by the miR‑155 inhibitor. In conclusion, the miR‑155 inhibitor may ameliorate diabetic cardiac fibrosis by reducing the accumulation of oxidative stress‑related molecules, and preventing mitochondrial damage and cardiomyocyte apoptosis by enhancing the Nrf2/HO‑1 signaling pathway. This mechanism may facilitate the development of novel targets to prevent cardiac fibrosis in patients with diabetes.

Compounds that extend longevity are protective in neurodegenerative diseases and provide a novel treatment strategy for these devastating disorders

While aging is the greatest risk factor for the development of neurodegenerative disease, the role of aging in these diseases is poorly understood. In the inherited forms of these diseases, the disease-causing mutation is present from birth but symptoms appear decades later. This indicates that these mutations are well tolerated in younger individuals but not in older adults. Based on this observation, we hypothesized that changes taking place during normal aging make the cells in the brain (and elsewhere) susceptible to the disease-causing mutations. If so, then delaying some of these age-related changes may be beneficial in the treatment of neurodegenerative disease. In this review, we examine the effects of five compounds that have been shown to extend longevity (metformin, rapamycin, resveratrol, N-acetyl-l-cysteine, curcumin) in four of the most common neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis). While not all investigations observe a beneficial effect of these compounds, there are multiple studies that show a protective effect of each of these lifespan-extending compounds in animal models of neurodegenerative disease. Combined with genetic studies, this suggests the possibility that targeting the aging process may be an effective strategy to treat neurodegenerative disease.

Metformin preferentially provides neuroprotection following cardiac ischemia/reperfusion in non-diabetic rats

Following acute myocardial infarction, re-establishment of coronary perfusion aggravates further injuries in the heart and remote organs including the brain as a consequence of ischemia/reperfusion (I/R) injury. Since pretreatment with metformin attenuated both cardiac and cerebral I/R injury via AMP-activated protein kinase (AMPK) pathways, we hypothesized that metformin given after ischemia mitigates both cardiac and brain pathologies following cardiac I/R. Male Wistar rats were subjected to either cardiac I/R (30 min-ischemia/120 min-reperfusion; n = 30) or sham operation (n = 5). Metformin 200 mg/kg was given intravenously to the cardiac I/R group (n = 10/group), either during ischemia (D-MET) or at the onset of reperfusion (R-MET). Left ventricular ejection fraction (LVEF) and arrhythmia scores were determined. The heart and brain tissues were collected to determine the extent of injury, mitochondrial function, and apoptosis. Additionally, microglial morphology, Alzheimer's proteins, and dendritic spine density were determined in the brain. Cardiac I/R led to not only reduced LVEF, cardiac mitochondrial dysfunction, and arrhythmias, but also brain mitochondrial dysfunction, apoptosis, Alzheimer's protein aggregation, microglial activation, and dendritic spine loss. A single dose of metformin did not alter p-AMPK/AMPK in both organs. In the heart, impaired LVEF, arrhythmias, infarct size expansion, mitochondrial dysfunction, and apoptosis were not alleviated. On the contrary, metformin attenuated brain mitochondrial dysfunction, apoptosis, and Alzheimer's protein levels. Microglial morphology and dendritic spine density were additionally preserved in D-MET group. In conclusion, metformin given during ischemia preferentially provides neuroprotection against brain mitochondrial dysfunction, apoptosis, microglial activation, and dendritic spine loss in an AMPK-independent manner following cardiac I/R injury.

Glycyrrhizic acid exerts protective effects against hypoxia/reoxygenation-induced human coronary artery endothelial cell damage by regulating mitochondria

Hypoxia/reoxygenation (H/R) is one of the main causes of coronary artery disease (CAD), which is primarily induced by damage to coronary artery endothelial cells (CAECs). Glycyrrhizic acid (GA) is a natural and abundant pentacyclic triterpenoid glycoside of the licorice root extract, and it has been reported to elicit protective effects against hypoxia, inflammation and apoptosis in ischemic myocardium; therefore, GA may serve as a promising therapeutic agent for ischemia-associated CAD. In the present study, the protective effects of GA against H/R-induced injury in CAECs were investigated. Treatment with GA during H/R maintained cell viability and decreased H/R-induced cell apoptosis in human CAECs. In addition, H/R-mediated induction of intracellular and mitochondrial reactive oxygen species (ROS) was significantly decreased by GA exposure. Similar to ROS scavengers, GA treatment not only exhibited protective effects, but also maintained the mitochondrial membrane potential after H/R and inhibited H/R-induced mitochondrial dysfunction, including deficits in ATP synthesis, mitochondrial DNA copy number and mitochondrial transcriptional activity. Furthermore, GA decreased autophagy/mitophagy, and its protective effect against H/R was abolished by autophagy promotion. Collectively, the results suggested that GA exhibited protective effects against H/R-induced CAEC injury by decreasing ROS accumulation and maintaining mitochondrial homeostasis. Further investigation into the precise mechanisms underlying the decrease in ROS accumulation induced by GA is required.

Role of MicroRNA-34a in Anti-Apoptotic Effects of Granulocyte-Colony Stimulating Factor in Diabetic Cardiomyopathy

BACKGROUND

Recent studies have shown that microRNAs (miRNAs) are involved in the process of cardiomyocyte apoptosis. We have previously reported that granulocyte-colony stimulating factor (G-CSF) ameliorated diastolic dysfunction and attenuated cardiomyocyte apoptosis in a rat model of diabetic cardiomyopathy. In this study, we hypothesized a regulatory role of cardiac miRNAs in the mechanism of the anti-apoptotic effect of G-CSF in a diabetic cardiomyopathy rat model.

METHODS

Rats were given a high-fat diet and low-dose streptozotocin injection and then randomly allocated to receive treatment with either G-CSF or saline. H9c2 rat cardiomyocytes were cultured under a high glucose (HG) condition to induce diabetic cardiomyopathy in vitro. We examined the extent of apoptosis, miRNA expression, and miRNA target genes in the myocardium and H9c2 cells.

RESULTS

G-CSF treatment significantly decreased apoptosis and reduced miR-34a expression in diabetic myocardium and H9c2 cells under the HG condition. G-CSF treatment also significantly increased B-cell lymphoma 2 (Bcl-2) protein expression as a target for miR-34a. In addition, transfection with an miR-34a mimic significantly increased apoptosis and decreased Bcl-2 luciferase activity in H9c2 cells.

CONCLUSION

Our results indicate that G-CSF might have an anti-apoptotic effect through down-regulation of miR-34a in a diabetic cardiomyopathy rat model.

Tetramethylpyrazine reverses high-glucose induced hypoxic effects by negatively regulating HIF-1α induced BNIP3 expression to ameliorate H9c2 cardiomyoblast apoptosis

Background

Diabetic patients are highly vulnerable to hypoxic injury, which is associated with hypoxia induced BNIP3 expression that subsequently activate apoptosis. Our previous research show that Tetramethylpyrazine (TMP), a food flavoring agent, represses the hypoxia induced BNIP3 expression attenuate myocardial apoptosis. In this study, we evaluate the effect of TMP to provide protection against hypoxia aggravated high-glucose associated cellular apoptosis.

Methods

The cytoprotective effect of TMP against high glucose induced cellular damages was determined on embryo derived H9c2 cardiomyoblast cells that were subjected to 5% hypoxia for 24 h and subjected to different duration of 33 mM high glucose challenge. Further, the involvement of HIF-1α and BNIP3 in cellular damage and the mechanism of protection of TMP were determined by overexpression and silencing HIF-1α and BNIP3 protein expression.

Results

The results show that hypoxic effects on cell viability aggravates with high glucose challenge and this augmentative effect is mediated through BNIP3 in H9c2 cardiomyoblast cells. However, TMP administration effectively reversed the augmented HIF-1α levels and BNIP3 elevation. TMP improved the survival of H9c2 cells and effectively suppressed apoptosis in H9c2 cells. Further comparison on the effects of TMP on H9c2 cells challenged with high glucose and those challenged with hypoxia show that TMP precisely regulated the hypoxic intensified apoptotic effects in high-glucose condition.

Conclusion

The results clearly show that flavoring agent-TMP attenuates cytotoxicity amplified by hypoxia challenge in high glucose condition by destabilizing HIF-1α.

Treatment with metformin prevents myocardial ischemia-reperfusion injury via STEAP4 signaling pathway

Objective:

The aim of the present study was to investigate the underlying mechanism of metformin in reducing myocardial apoptosis and improving mitochondrial function in rats and H9c2 cells subjected to myocardial ischemia–reperfusion (I/R) or hypoxia–reoxygenation (H/R) injuries, respectively.

Methods:

Following pretreatment with metformin, male Sprague–Dawley rats were used to establish an I/R model in vivo. Serum creatinine kinase-MB and cardiac troponin T levels were examined by enzyme-linked immunosorbent assay. Infarct size and apoptosis were measured by triphenyl tetrazolium chloride staining and terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Pathological changes were evaluated by hematoxylin and eosin staining. H9c2 cells were used to establish an H/R model in vitro. Cell apoptosis and mitochondrial membrane potential (MMP) were examined by flow cytometry and Rhodamine 123. The expression levels of six-transmembrane epithelial antigen of prostate 4 (STEAP4), B-cell lymphoma 2, Bcl-2-associated X protein, and glyceraldehyde 3-phosphate dehydrogenase in both myocardial tissues and H9c2 cells were determined by western blotting.

Results:

We found that metformin decreased infarct size, increased STEAP4 expression, mitigated myocardial apoptosis, and increased MMP when the models were subjected to H/R or I/R injuries. However, STEAP4 knockdown significantly abrogated the beneficial effect of metformin.

Conclusion:

We further demonstrated the protective effect of metformin on cardiomyocytes, which might be at least partly attributable to the upregulation of STEAP4. Therefore, STEAP4 might be a new target to decrease apoptosis and rescue mitochondrial function in myocardial I/R injury.

Metformin decreases LPS-induced inflammatory response in rabbit annulus fibrosus stem/progenitor cells by blocking HMGB1 release

The present study aimed to investigate the mechanism of intervertebral disc degeneration (IVDD) and identify an efficient treatment for low back pain. Rabbit annulus fibrosus stem cells (AFSCs) were treated with metformin and lipopolysaccharide (LPS). The results indicated that LPS induced HMGB1 release from the nuclei of AFSCs and caused cell senescence in a concentration-dependent manner. The production of PGE2 and HMGB1 was increased in the medium of the LPS-treated AFSCs. Certain inflammation-associated genes (IL-β1, IL-6, COX-2 and TNF-α) and proteins (IL-β1, COX-2 and TNF-α) and specific catabolic genes (MMP-3 and MMP-13) exhibited increased expression in LPS-treated AFSCs. However, the expression levels of other anabolic genes, such as collagen I and collagen II were decreased in LPS-treated AFSCs. Following addition of metformin to LPS-containing medium, HMGB1 was retained in the nuclei of AFSCs and the production of PGE2 and HMGB1 was reduced. The expression levels of the catabolic genes and proteins were decreased and those of the anabolic genes were increased. The findings indicated that metformin exerted an anti-inflammatory effect by blocking the HMGB1 translocation and by inhibiting catabolic production and cell senescence in AFSCs. Therefore, metformin may be used as an efficient treatment for the disc degenerative disease.

An In Vitro Study on the Combination Effect of Metformin and N-Acetyl Cysteine against Hyperglycaemia-Induced Cardiac Damage

Chronic hyperglycaemia is a major risk factor for diabetes-induced cardiovascular dysfunction. In a hyperglycaemic state, excess production of reactive oxygen species (ROS), coupled with decreased levels of glutathione, contribute to increased lipid peroxidation and subsequent myocardial apoptosis. N-acetylcysteine (NAC) is a thiol-containing antioxidant known to protect against hyperglycaemic-induced oxidative stress by promoting the production of glutathione. While the role of NAC against oxidative stress-related cardiac dysfunction has been documented, to date data is lacking on its beneficial effect when used with glucose lowering therapies, such as metformin (MET). Thus, the aim of the study was to better understand the cardioprotective effect of NAC plus MET against hyperglycaemia-induced cardiac damage in an H9c2 cardiomyoblast model. H9c2 cardiomyoblasts were exposed to chronic high glucose concentrations for 24 h. Thereafter, cells were treated with MET, NAC or a combination of MET and NAC for an additional 24 h. The combination treatment mitigated high glucose-induced oxidative stress by improving metabolic activity i.e. ATP activity, glucose uptake (GU) and reducing lipid accumulation. The combination treatment was as effective as MET in diminishing oxidative stress, lipid peroxidation and apoptosis. We observed that the combination treatment prevented hyperglycaemic-induced cardiac damage by increasing GLUT4 expression and mitigating lipid accumulation via phosphorylation of both AMPK and AKT, while decreasing nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), as well as protein kinase C (PKC), a known activator of insulin receptor substrate-1 (IRS-1), via phosphorylation at Ser307. On this basis, the current results support the notion that the combination of NAC and MET can shield the diabetic heart against impaired glucose utilization and therefore its long-term protective effect warrants further investigation.

Combination of metformin and p38 MAPK inhibitor, SB203580, reduced myocardial ischemia/reperfusion injury in non-obese type 2 diabetic Goto-Kakizaki rats

Diabetic cardiomyopathy, especially myocardial ischemia reperfusion (I/R) injury, is a major cause of morbidity and mortality in type 2 diabetic patients. The increasing of basal p38 MAP Kinase (p38 MAPK) activation is a major factor that aggravates cardiac death on diabetic cardiomyopathy. In addition, metformin also shows cardio-protective effects on myocardial ischemia/reperfusion injury. In this study, we investigated the effect of the combination between metformin and p38 MAPK inhibitor (SB203580) in diabetic rats subjected to I/R injury. H9c2 cells were induced into a hyperglycemic condition and treated with metformin, SB203580 or the combination of metformin and SB203580. In addition, cells in both the presence and absence of drug treatment were subjected to simulated ischemia/reperfusion injury. Cell viability and cellular reactive oxygen species (ROS) were determined. Moreover, the Goto-Kakizaki (GK) rats were treated with metformin, SB203580, and the combination of metformin and SB203580 for 4 weeks. Diabetic parameters and cardiac functions were assessed. Finally, rat hearts were induced ischemia/reperfusion injury for the purpose of infarct size analysis and determination of signal transduction. A high-glucose condition did not reduce cell viability but significantly increased ROS production and significantly decreased cell viability after induced sI/R. Treatment using drugs was shown to reduce ROS generation and cardiac cell death. The GK rats displayed diabetic phenotype by increasing diabetic parameters and these parameters were significantly decreased when treated with drugs. Treatment with metformin or SB203580 could significantly reduce the infarct size. Interestingly, the combination of metformin and SB203580 could enhance cardio-protective ability. Myocardial I/R injury significantly increased p38 MAPK phosphorylation, Bax/Bcl-2 ratio and caspase-3 level. Treatment with drugs significantly decreased the p38 MAPK phosphorylation, Bax/Bcl-2 ratio, caspase-3 level and increased Akt phosphorylation. In conclusion, using the combination of metformin and SB203580 shows positive cardio-protective effects on diabetic ischemic cardiomyopathy.

Effects of metformin on the heart with ischaemia-reperfusion injury: Evidence of its benefits from in vitro, in vivo and clinical reports

Ischaemia reperfusion (I/R) injury following myocardial infarction reperfusion therapy is a phenomenon that results in further loss of cardiomyocytes and cardiac contractility. Among the potential therapeutics to counter cardiac I/R injury, the antidiabetic drug metformin has shown promising experimental results. This review encompasses evidence available from studies of metformin's protective effects on the heart following cardiac I/R in vitro, ex vivo and in vivo, alongside clinical trials. Experimental data describes potential mechanisms of metformin, including activation of AMPK, an energy sensing kinase with many downstream effects. Suggested effects include upregulation of superoxide dismutases (SODs), which reduce oxidative stress and improve mitochondrial function. Additionally, metformin demonstrates anti-apoptotic effects, most likely by inhibiting mitochondrial permeability transition pore (mPTP) opening, and anti-inflammatory effects, by JNK inhibition. Recent reports of metformin's role in modulating complex I activity of the electron transport chain following cardiac I/R are also presented and discussed. Furthermore, clinical reports present mixed findings, suggesting that beneficial effects may depend on dosage, timing and condition of patients receiving metformin treatment. Conclusively there is an increased need for prospective, placebo-controlled clinical studies to confirm the mechanisms and to demonstrate that metformin is a suitable and safe drug for treatment of cardiac I/R injury.

Enhanced phosphorylation of AMPK by lutein and oxidised lutein that lead to mitochondrial biogenesis in hyperglycemic HepG2 cells

The stimulation of adenosine monophosphate-activated protein kinase (AMPK) is a prime target to decrease the hyperglycemic condition, hence it is a lutein (L) and oxidised lutein (OXL) is a target molecule for the treatment of type II diabetes. In the current study, a plausible interaction of L and OXL with AMPK was investigated by molecular docking. In addition, the effect of L and OXL for the activation of AMPK that triggers the downstream regulator peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), TFAM expression, mitochondrial DNA (mtDNA), mitochondrial biogenesis and superoxide dismutase 2 (SOD2) in high glucose treated HepG2 cells were investigated by quantitative polymerase chain reaction and Western blot analysis. Molecular docking reveals higher binding affinity of L (ΔG = -6.3 kcal/mol) and OXL (ΔG = -15.5 kcal/mol) with AMPK, compared with metformin (ΔG = -5.0 kcal/mol). The phosphorylation of AMPK increased by 1.3- and 1.5-fold with L and OXL treatment, respectively, in high glucose induced HepG2 cells. The activation of PGC-1α is significant (P < 0.05) in OXL group than L. Similarly, TFAM expression is increased with L and OXL compared with the high glucose group. Further increase in SOD2 and mtDNA, confirms the efficacy of L and OXL in restoring the mitochondrial biogenesis in high glucose induced cells through AMPK, PGC-1α, and TFAM.

AMPK is associated with the beneficial effects of antidiabetic agents on cardiovascular diseases

Diabetics have higher morbidity and mortality in cardiovascular disease (CVD). A variety of antidiabetic agents are available for clinical choice. Cardiovascular (CV) safety assessment of these agents is crucial in addition to hypoglycemic effect before clinical prescription. Adenosine 5'-monophosphate-activated protein kinase (AMPK) is an important cell energy sensor, which plays an important role in regulating myocardial energy metabolism, reducing ischemia and ischemia/reperfusion (I/R) injury, improving heart failure (HF) and ventricular remodeling, ameliorating vascular endothelial dysfunction, antichronic inflammation, anti-apoptosis, and regulating autophagy. In this review, we summarized the effects of antidiabetic agents to CVD according to basic and clinical research evidence and put emphasis on whether these agents can play roles in CV system through AMPK-dependent signaling pathways. Metformin has displayed definite CV benefits related to AMPK. Sodium-glucose cotransporter 2 inhibitors also demonstrate sufficient clinical evidence for CV protection, but the mechanisms need further exploration. Glucagon-likepeptide1 analogs, dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors and thiazolidinediones also show some AMPK-dependent CV benefits. Sulfonylureas and meglitinides may be unfavorable to CV system. AMPK is becoming a promising target for the treatment of diabetes, metabolic syndrome and CVD. But there are still some questions to be answered.

Scutellarin Exerts Hypoglycemic and Renal Protective Effects in db/db Mice via the Nrf2/HO-1 Signaling Pathway

This study investigated the hypoglycemic and renal protective effects of scutellarin (SCU) in db/db mice and elucidated the underlying mechanisms. The oral administration of metformin hydrochloride (Met) at 120 mg/kg and SCU at 25, 50, and 100 mg/kg over an eight-week period had hypoglycemic effects, demonstrated by decreases in body weight, blood glucose, food and water intake, and glycated hemoglobin activity and by augmented insulin levels and pyruvate kinase activity in the serum of db/db mice. SCU alleviated dyslipidemia by decreasing the levels of triglycerides and total cholesterol and enhancing the levels of high-density lipoprotein cholesterol in the serum of db/db mice. SCU reversed the overexpression of mRNA of renal damage markers (receptor for advanced glycation end products, neutrophil gelatinase-associated lipocalin, and kidney injury molecule 1), macrophage marker CD11b, and T cell marker CD3 in kidney of db/db mice. Pathological examination confirmed that SCU improved the organ structures of hyperglycemia-damaged livers, kidneys, and pancreas islets. Antibody array assay and enzyme-linked immunosorbent assay were combined to screen and analyze the regulatory effects of SCU on inflammatory factors and oxidative enzymes. SCU exerted anti-inflammatory effects by inhibiting the levels of proinflammatory cytokines (glycogen synthase kinase, intercellular adhesion molecule 2, and interleukin 1β and 2) and promoting anti-inflammatory cytokines (interleukin 4). SCU decreased the reactive oxygen species and malondialdehyde concentrations and increased the activity levels of antioxidative enzymes (superoxide dismutase, glutathione peroxidase, and catalase) in serum and kidneys. Furthermore, SCU upregulated the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), which in turn improved heme oxygenase 1 (HO-1), superoxide dismutase 1 and 2, and catalase expression levels in kidneys. The study showed that SCU has at least partial hypoglycemic and renal protective effects in db/db mice, and the mechanism is the modulation of the Nrf2/HO-1 signaling pathway.

B-type natriuretic peptide attenuates endoplasmic reticulum stress in H9c2 cardiomyocytes underwent hypoxia/reoxygenation injury under high glucose/high fat conditions

Exogenously administered B-type natriuretic peptide (BNP) has been shown to provide cardioprotection against various heart diseases. However, the underlying mechanisms remain elusive. This study explores whether BNP exerts its cardioprotection against hypoxia/reoxygenation (H/R) injury under high glucose/high fat (HG/HF) conditions in cardiac H9c2 cells and uncovers the underlying mechanisms. Our data revealed that BNP significantly increased the cell viability and decreased the release of lactate dehydrogenase (LDH) and creatine kinase (CK), with a maximal effect at the BNP concentration of 10^-7 mol/L. In addition, by analyzing the activation of cleaved caspase-3 and by Annexin V-FITC/PI staining, we showed that BNP attenuated H/R-induced cell apoptosis in HG/HF conditions. Western blot analysis showed enhanced phosphorylation of protein kinase RNA (PKR)-like endoplastmic reticulum (ER) kinase (PERK) and eukaryotic initiation factor 2α (eIF2α)(one of the three main signaling pathways in endoplastmic reticulum (ER) stress), and increased expression of GRP78 and CHOP proteins (ER stress-related proteins) in H9c2 cells which underwent H/R in HG/HF conditions. Treatment with BNP or 8-Br-cGMP (an analog of cGMP) reversed this activation. However, this effect was significantly weakened by KT-5823, a selective cGMP-dependent protein kinase G (PKG) inhibitor. In addition, similar to BNP, treatment with a specific inhibitor of ER stress tauroursodeoxycholic acid (TUDCA) protected the cells against H/R injury exposed to HG/HF conditions. In conclusion, these findings demonstrated that BNP effectively protected cells against H/R injury under HG/HF conditions by inhibiting the ER stress via activation of the cGMP-PKG signaling pathway.

The regulatory effects of metformin on the [SNAIL/miR-34]:[ZEB/miR-200] system in the epithelial-mesenchymal transition(EMT) for colorectal cancer(CRC)

The epithelial-mesenchymal transition (EMT) plays a critical role in cancer progression, metastasis and drug resistance. The transcription factor(TF) and microRNA (miR) chimeric [SNAIL/miR-34]:[ZEB/miR-200] unit is the core regulatory system for the EMT process. Here, we proposed to assess the anti-EMT abilities and explore the inherent pharmacological mechanisms of the classic hypoglycaemic agent metformin for colorectal cancer(CRC). For the EMT model, the TGF-β-induced CRC cell lines SW480 and HCT116 were treated with metformin. The viability, migration and invasion abilities of the cells were evaluated with the Cell Counting Kit-8, wound-healing and trans-well assay. The alterations of the [SNAIL/miR-34]:[ZEB/miR-200] system and the EMT markers E-cadherin and vimentin were detected by western blot, qPCR and immunofluorescent staining. Metformin exhibited inhibitory effects on the proliferation, migration and invasion of the CRC SW480 cells. The up-regulation of E-cadherin and the down-regulation of vimentin for both SW480 and HCT116 cells revealed the anti-EMT abilities of metformin. For the [SNAIL/miR-34]:[ZEB/miR-200] system, metformin increased miR-200a, miR-200c and miR-429 levels and decreased miR-34a, SNAIL1 and ZEB1 levels in the TGF-β-induced EMT. From immunofluorescence, we observed increased E-cadherin and ZEB1 co-expression in metformin-treated cells. Metformin may perform bidirectional regulations of the [SNAIL/miR-34]:[ZEB/miR-200] system in the EMT process for colorectal cancer. Such regulation is expressed as the inhibition of EMT in general as well as an increased higher proportion of E/M hybrid cells in the total population.

c-Jun N-Terminal Kinases (JNKs) in Myocardial and Cerebral Ischemia/Reperfusion Injury

In this article, we review the literature regarding the role of c-Jun N-terminal kinases (JNKs) in cerebral and myocardial ischemia/reperfusion injury. Numerous studies demonstrate that JNK-mediated signaling pathways play an essential role in cerebral and myocardial ischemia/reperfusion injury. JNK-associated mechanisms are involved in preconditioning and post-conditioning of the heart and the brain. The literature and our own studies suggest that JNK inhibitors may exert cardioprotective and neuroprotective properties. The effects of modulating the JNK-depending pathways in the brain and the heart are reviewed. Cardioprotective and neuroprotective mechanisms of JNK inhibitors are discussed in detail including synthetic small molecule inhibitors (AS601245, SP600125, IQ-1S, and SR-3306), ion channel inhibitor GsMTx4, JNK-interacting proteins, inhibitors of mixed-lineage kinase (MLK) and MLK-interacting proteins, inhibitors of glutamate receptors, nitric oxide (NO) donors, and anesthetics. The role of JNKs in ischemia/reperfusion injury of the heart in diabetes mellitus is discussed in the context of comorbidities. According to reviewed literature, JNKs represent promising therapeutic targets for protection of the brain and the heart against ischemic stroke and myocardial infarction, respectively. However, different members of the JNK family exert diverse physiological properties which may not allow for systemic administration of non-specific JNK inhibitors for therapeutic purposes. Currently available candidate JNK inhibitors with high therapeutic potential are identified. The further search for selective JNK3 inhibitors remains an important task.

Activation of AMPK inhibits inflammatory response during hypoxia and reoxygenation through modulating JNK-mediated NF-κB pathway

BACKGROUND

AMP-activated Protein Kinase (AMPK) is a stress-activated kinase that protects against cardiomyocyte injury during ischemia and reperfusion. c-Jun N-terminal kinase (JNK), a mitogen activated protein kinase, is activated by ischemia and reperfusion. NF-κB is an important transcription factor involved in ischemia and reperfusion injury.

METHODS AND RESULTS

The intrinsic activation of AMPK attenuates the inflammation which occurred during ischemia/reperfusion through the modulation of the JNK mediated NF-κB signaling pathway. Rat cardiac myoblast H9c2 cells were subjected to hypoxia and/or reoxygenation to investigate the signal transduction that occurred during myocardial ischemia/reperfusion. Mitochondrial function was measured by the Seahorse XF24 V7 PS system. Hypoxia treatment triggered AMPK activation in H9c2 cells in a time dependent manner. The inhibition of hypoxic AMPK activation through a pharmacological approach (Compound C) or siRNA knockdown of AMPK α catalytic subunits caused dramatic augmentation in JNK activation, inflammatory NF-κB phosphorylation, and apoptosis during hypoxia and reoxygenation. Inhibition of AMPK activation significantly impaired mitochondrial function and increased the generation of reactive oxygen species (ROS) during hypoxia and reoxygenation. In contrast, pharmacological activation of AMPK by metformin significantly inhibited mitochondrial permeability transition pore (mPTP) opening and ROS generation. Moreover, AMPK activation significantly attenuated the JNK-NF-κB signaling cascade and inhibited mRNA and protein levels of pro-inflammatory cytokines, such as TNF-α and IL-6, during hyopoxia/reoxygenation in H9c2 cells. Intriguingly, both pharmacologic inhibition of JNK by JNK-IN-8 and siRNA knockdown of JNK signaling pathway attenuated NF-κB phosphorylation and apoptosis but did not affect AMPK activation in response to hypoxia and reoxygenation.

CONCLUSIONS

AMPK activation modulates JNK-NF-κB signaling cascade during hypoxia and reoxygenation stress conditions. Cardiac AMPK activation plays a critical role in maintaining mitochondrial function and inhibiting the inflammatory response caused by ischemic insults.

How AMPK and PKA Interplay to Regulate Mitochondrial Function and Survival in Models of Ischemia and Diabetes

Adenosine monophosphate-activated protein kinase (AMPK) is a conserved, redox-activated master regulator of cell metabolism. In the presence of oxidative stress, AMPK promotes cytoprotection by enhancing the conservation of energy by suppressing protein translation and by stimulating autophagy. AMPK interplays with protein kinase A (PKA) to regulate oxidative stress, mitochondrial function, and cell survival. AMPK and dual-specificity A-kinase anchoring protein 1 (D-AKAP1), a mitochondrial-directed scaffold of PKA, interact to regulate mitochondrial function and oxidative stress in cardiac and endothelial cells. Ischemia and diabetes, a chronic disease that increases the onset of cardiovascular diseases, suppress the cardioprotective effects of AMPK and PKA. Here, we review the molecular mechanisms by which AMPK and D-AKAP1/PKA interplay to regulate mitochondrial function, oxidative stress, and signaling pathways that prime endothelial cells, cardiac cells, and neurons for cytoprotection against oxidative stress. We discuss recent literature showing how temporal dynamics and localization of activated AMPK and PKA holoenzymes play a crucial role in governing cellular bioenergetics and cell survival in models of ischemia, cardiovascular diseases, and diabetes. Finally, we propose therapeutic strategies that tout localized PKA and AMPK signaling to reverse mitochondrial dysfunction, oxidative stress, and death of neurons and cardiac and endothelial cells during ischemia and diabetes.

Insulin Therapy Increases Cardiovascular Risk in Type 2 Diabetes

Insulin therapy increased cardiovascular (CV) risk and mortality among type 2 diabetes (T2D) patients in several recently reported clinical outcomes trials. To assess whether this association is causative or coincidental, PubMed searches were used to query the effects of insulin therapy for T2D on CV health and longevity from large-scale outcomes trials, meta-analyses, and patient registry studies, as well as basic research on insulin's direct and pleiotropic actions. Although several old studies provided conflicting results, the majority of large observational studies show strong dose-dependent associations for injected insulin with increased CV risk and worsened mortality. Insulin clearly causes weight gain, recurrent hypoglycemia, and, other potential adverse effects, including iatrogenic hyperinsulinemia. This over-insulinization with use of injected insulin predisposes to inflammation, atherosclerosis, hypertension, dyslipidemia, heart failure (HF), and arrhythmias. These associations support the findings of large-scale evaluations that strongly suggest that insulin therapy has a poorer short- and long-term safety profile than that found to many other anti-T2D therapies. The potential adverse effects of insulin therapy should be weighed against proven CV benefits noted for select other therapies for T2D as reported in recent large randomized controlled trials.

The Effects of Metformin on Obesity-Induced Dysfunctional Retinas

Purpose

The purpose of this study was to determine the effects of metformin on dysfunctional retinas in obesity-induced type 2 diabetic mice.

Methods

A high-fat diet (HFD)-induced diabetic mouse model (C57BL/6J) was used in this study. After 2 months of the HFD regimen, HFD mice were given daily metformin through oral gavage. Body weights, glucose tolerance, and retinal light responses were monitored regularly. Fluorescein angiography (FA) was used to assess changes in retinal vasculature. Ocular tissues (retina, vitreous, and lens) were harvested and analyzed for molecular changes as determined by immunofluorescent staining, Western blot analysis, and cytokine profiling.

Results

Starting 1 month after the diet regimen, mice fed the HFD had mildly compromised retinal light responses as measured by electroretinography (ERG), which worsened over time compared to that in the control. In HFD mice treated with metformin, systemic glucose levels reverted back to normal, and their weight gain slowed. Metformin reversed HFD-induced changes in phosphorylated protein kinase B (pAKT), extracellular signal-regulated kinase (pERK), and 5′AMP-activated protein kinase (pAMPK) in the retina. However, metformin treatments for 3 months did not restore the retinal light responses nor lessen the HFD-induced retinal neovascularization, even though it did reduce intraocular inflammation.

Conclusions

Although metformin was able to reverse systemic changes induced by HFD, it was not able to restore HFD-caused retinal light responses or deter neovascularization.

Insights for Oxidative Stress and mTOR Signaling in Myocardial Ischemia/Reperfusion Injury under Diabetes

Diabetes mellitus (DM) displays a high morbidity. The diabetic heart is susceptible to myocardial ischemia/reperfusion (MI/R) injury. Impaired activation of prosurvival pathways, endoplasmic reticulum (ER) stress, increased basal oxidative state, and decreased antioxidant defense and autophagy may render diabetic hearts more vulnerable to MI/R injury. Oxidative stress and mTOR signaling crucially regulate cardiometabolism, affecting MI/R injury under diabetes. Producing reactive oxygen species (ROS) and reactive nitrogen species (RNS), uncoupling nitric oxide synthase (NOS), and disturbing the mitochondrial quality control may be three major mechanisms of oxidative stress. mTOR signaling presents both cardioprotective and cardiotoxic effects on the diabetic heart, which interplays with oxidative stress directly or indirectly. Antihyperglycemic agent metformin and newly found free radicals scavengers, Sirt1 and CTRP9, may serve as promising pharmacological therapeutic targets. In this review, we will focus on the role of oxidative stress and mTOR signaling in the pathophysiology of MI/R injury in diabetes and discuss potential mechanisms and their interactions in an effort to provide some evidence for cardiometabolic targeted therapies for ischemic heart disease (IHD).