Activation of AMP-activated protein kinase by metformin ablates angiotensin II-induced endoplasmic reticulum stress and hypertension in mice in vivo

Metformin Impedes Oxidation of LDL In Vitro

Metformin is the most commonly prescribed glucose-lowering drug for the treatment of type 2 diabetes. The aim of this study was to investigate whether metformin is capable of impeding the oxidation of LDL, a crucial step in the development of endothelial dysfunction and atherosclerosis. LDL was oxidized by addition of CuCl2 in the presence of increasing concentrations of metformin. The extent of LDL oxidation was assessed by measuring lipid hydroperoxide and malondialdehyde concentrations, relative electrophoretic mobilities, and oxidation-specific immune epitopes. Cytotoxicity of oxLDL in the vascular endothelial cell line EA.hy926 was assessed using the alamarBlue viability test. Quantum chemical calculations were performed to determine free energies of reactions between metformin and radicals typical for lipid oxidation. Metformin concentration-dependently impeded the formation of lipid hydroperoxides, malondialdehyde, and oxidation-specific immune epitopes when oxidation of LDL was initiated by addition of Cu2+. The cytotoxicity of oxLDL was reduced when it was obtained under increasing concentrations of metformin. The quantum chemical calculations revealed that only the reaction of metformin with hydroxyl radicals is exergonic, whereas the reactions with hydroperoxyl radicals or superoxide radical anions are endergonic. Metformin, beside its glucose-lowering effect, might be a suitable agent to impede the development of atherosclerosis and associated CVD. This is due to its capability to impede LDL oxidation, most likely by scavenging hydroxyl radicals.

Endoplasmic reticulum as a target in cardiovascular diseases: Is there a role for flavonoids?

Flavonoids are found in natural health products and plant-based foods. The flavonoid molecules contain a 15-carbon skeleton with the particular structural construction of subclasses. The most flavonoid's critical subclasses with improved health properties are the catechins or flavonols (e.g., epigallocatechin 3-gallate from green tea), the flavones (e.g., apigenin from celery), the flavanones (e.g., naringenin from citrus), the flavanols (e.g., quercetin glycosides from berries, onion, and apples), the isoflavones (e.g., genistein from soya beans) and the anthocyanins (e.g., cyanidin-3-O-glucoside from berries). Scientific data conclusively demonstrates that frequent intake of efficient amounts of dietary flavonoids decreases chronic inflammation and the chance of oxidative stress expressing the pathogenesis of human diseases like cardiovascular diseases (CVDs). The endoplasmic reticulum (ER) is a critical organelle that plays a role in protein folding, post-transcriptional conversion, and transportation, which plays a critical part in maintaining cell homeostasis. Various stimuli can lead to the creation of unfolded or misfolded proteins in the endoplasmic reticulum and then arise in endoplasmic reticulum stress. Constant endoplasmic reticulum stress triggers unfolded protein response (UPR), which ultimately causes apoptosis. Research has shown that endoplasmic reticulum stress plays a critical part in the pathogenesis of several cardiovascular diseases, including diabetic cardiomyopathy, ischemic heart disease, heart failure, aortic aneurysm, and hypertension. Endoplasmic reticulum stress could be one of the crucial points in treating multiple cardiovascular diseases. In this review, we summarized findings on flavonoids' effects on the endoplasmic reticulum and their role in the prevention and treatment of cardiovascular diseases.

A positive feedback loop between AMPK and GDF15 promotes metformin antidiabetic effects

BACKGROUND AND AIMS

Metformin, the most prescribed drug for the treatment of type 2 diabetes mellitus, has been recently reported to promote weight loss by upregulating the anorectic cytokine growth differentiation factor 15 (GDF15). Since the antidiabetic effects of metformin are mostly mediated by the activation of AMPK, a key metabolic sensor in energy homeostasis, we examined whether the activation of this kinase by metformin was dependent on GDF15.

METHODS

Cultured hepatocytes and myotubes, and wild-type and Gdf15^-/- mice were utilized in a series of studies to investigate the involvement of GDF15 in the activation of AMPK by metformin.

RESULTS

A low dose of metformin increased GDF15 levels without significantly reducing body weight or food intake, but it ameliorated glucose intolerance and activated AMPK in the liver and skeletal muscle of wild-type mice but not Gdf15^-/- mice fed a high-fat diet. Cultured hepatocytes and myotubes treated with metformin showed AMPK-mediated increases in GDF15 levels independently of its central receptor GFRAL, while Gdf15 knockdown blunted the effect of metformin on AMPK activation, suggesting that AMPK is required for the metformin-mediated increase in GDF15, which in turn is needed to sustain the full activation of this kinase independently of the CNS.

CONCLUSION

Overall, these findings uncover a novel mechanism through which GDF15 upregulation by metformin is involved in achieving and sustaining full AMPK activation by this drug independently of the CNS.

Endoplasmic Reticulum Stress and Renin-Angiotensin System Crosstalk in Endothelial Dysfunction

BACKGROUND

Vascular endothelial dysfunction (VED) significantly results in catastrophic cardiovascular diseases with multiple aetiologies. Variations in vasoactive peptides, including angiotensin II and endothelin 1, and metabolic perturbations like hyperglycaemia, altered insulin signalling, and homocysteine levels result in pathogenic signalling cascades, which ultimately lead to VED. Endoplasmic reticulum (ER) stress reduces nitric oxide availability, causes aberrant angiogenesis, and enhances oxidative stress pathways, consequently promoting endothelial dysfunction. Moreover, the renin-angiotensin system (RAS) has widely been acknowledged to impact angiogenesis, endothelial repair and inflammation. Interestingly, experimental studies at the preclinical level indicate a possible pathological link between the two pathways in the development of VED. Furthermore, pharmacological modulation of ER stress ameliorates angiotensin-II mediated VED as well as RAS intervention either through inhibition of the pressor arm or enhancement of the depressor arm of RAS, mitigating ER stress-induced endothelial dysfunction and thus emphasizing a vital crosstalk.

CONCLUSION

Deciphering the pathway overlap between RAS and ER stress may open potential therapeutic avenues to combat endothelial dysfunction and associated diseases. Several studies suggest that alteration in a component of RAS may induce ER stress or induction of ER stress may modulate the RAS components. In this review, we intend to elaborate on the crosstalk of ER stress and RAS in the pathophysiology of VED.

Comparison between aerobic exercise training and enalapril treatment as tools to improve diet-induced metabolic-associated fatty liver disease: Effects on endoplasmic reticulum stress markers

AIMS

Endoplasmic reticulum (ER) stress poses a new pathological mechanism for metabolic-associated fatty liver disease (MAFLD). MAFLD treatment has encompassed renin-angiotensin system (RAS) blockers and aerobic exercise training, but their association with hepatic ER stress is not well known. Therefore, we aimed to compare the effects of hepatic RAS modulation by enalapril and/or aerobic exercise training over ER stress in MAFLD caused by a diet-induced obesity model.

MAIN METHODS

C57BL/6 mice were fed a standard-chow (CON, n = 10) or a high-fat (HF, n = 40) diet for 8 weeks. HF group was then randomly divided into: HF (n = 10), HF + Enalapril (EN, n = 10), HF + Aerobic exercise training (AET, n = 10), and HF + Enalapril+Aerobic exercise training (EN + AET, n = 10) for 8 more weeks. Body mass (BM) and glucose profile were evaluated. In the liver, ACE and ACE2 activity, morphology, lipid profile, and protein expression of ER stress and metabolic markers were assessed.

KEY FINDINGS

Both enalapril and aerobic exercise training provided comparable efficacy in improving diet-induced MAFLD through modulation of RAS and ER stress, but the latter was more efficient in improving ER stress, liver damage and metabolism.

SIGNIFICANCE

This is the first study to evaluate pharmacological (enalapril) and non-pharmacological (aerobic exercise training) RAS modulators associated with ER stress in a diet-induced MAFLD model.

Molecular Mechanism Underlying Role of the XBP1s in Cardiovascular Diseases

Spliced X-box binding protein-1 (XBP1s) is a protein that belongs to the cAMP-response element-binding (CREB)/activating transcription factor (ATF) b-ZIP family with a basic-region leucine zipper (bZIP). There is mounting evidence to suggest that XBP1s performs a critical function in a range of different cardiovascular diseases (CVDs), indicating that it is necessary to gain a comprehensive knowledge of the processes involved in XBP1s in various disorders to make progress in research and clinical therapy. In this research, we provide a summary of the functions that XBP1s performs in the onset and advancement of CVDs such as atherosclerosis, hypertension, cardiac hypertrophy, and heart failure. Furthermore, we discuss XBP1s as a novel therapeutic target for CVDs.

Roles of ATP and SERCA in the Regulation of Calcium Turnover in Unloaded Skeletal Muscles: Current View and Future Directions

A decrease in skeletal muscle contractile activity or its complete cessation (muscle unloading or disuse) leads to muscle fibers’ atrophy and to alterations in muscle performance. These changes negatively affect the quality of life of people who, for one reason or another, are forced to face a limitation of physical activity. One of the key regulatory events leading to the muscle disuse-induced changes is an impairment of calcium homeostasis, which leads to the excessive accumulation of calcium ions in the sarcoplasm. This review aimed to analyze the triggering mechanisms of calcium homeostasis impairment (including those associated with the accumulation of high-energy phosphates) under various types of muscle unloading. Here we proposed a hypothesis about the regulatory mechanisms of SERCA and IP3 receptors activity during muscle unloading, and about the contribution of these mechanisms to the excessive calcium ion myoplasmic accumulation and gene transcription regulation via excitation–transcription coupling.

Protection by metformin against severe Covid-19: an in-depth mechanistic analysis

Since the outbreak of Covid-19, several observational studies on diabetes and Covid-19 have reported a favourable association between metformin and Covid-19-related outcomes in patients with type 2 diabetes mellitus (T2DM). This is not surprising since metformin affects many of the pathophysiological mechanisms implicated in SARS-CoV-2 immune response, systemic spread and sequelae. A comparison of the multifactorial pathophysiological mechanisms of Covid-19 progression with metformin's well-known pleiotropic properties suggests that the treatment of patients with this drug might be particularly beneficial. Indeed, metformin could alleviate the cytokine storm, diminish virus entry into cells, protect against microvascular damage as well as prevent secondary fibrosis. Although our in-depth analysis covers many potential metformin mechanisms of action, we want to highlight more particularly its unique microcirculatory protective effects since worsening of Covid-19 disease clearly appears as largely due to severe defects in the structure and functioning of microvessels. Overall, these observations confirm that metformin is a unique, pleiotropic drug that targets many of Covid-19′s pathophysiology processes in a diabetes-independent manner.

Functional ACE2 deficiency leading to angiotensin imbalance in the pathophysiology of COVID-19

SARS-CoV-2, the virus responsible for COVID-19, uses angiotensin converting enzyme 2 (ACE2) as its primary cell-surface receptor. ACE2 is a key enzyme in the counter-regulatory pathway of the broader renin-angiotensin system (RAS) that has been implicated in a broad array of human pathology. The RAS is composed of two competing pathways that work in opposition to each other: the "conventional" arm involving angiotensin converting enzyme (ACE) generating angiotensin-2 and the more recently identified ACE2 pathway that generates angiotensin (1-7). Following the original SARS pandemic, additional studies suggested that coronaviral binding to ACE2 resulted in downregulation of the membrane-bound enzyme. Given the similarities between the two viruses, many have posited a similar process with SARS-CoV-2. Proponents of this ACE2 deficiency model argue that downregulation of ACE2 limits its enzymatic function, thereby skewing the delicate balance between the two competing arms of the RAS. In this review we critically examine this model. The available data remain incomplete but are consistent with the possibility that the broad multisystem dysfunction of COVID-19 is due in large part to functional ACE2 deficiency leading to angiotensin imbalance with consequent immune dysregulation and endothelial cell dysfunction.

Effect of Propionic Acid on Diabetes-Induced Impairment of Unfolded Protein Response Signaling and Astrocyte/Microglia Crosstalk in Rat Ventromedial Nucleus of the Hypothalamus

Background

The aim was to investigate the influence of propionic acid (PA) on the endoplasmic reticulum (ER), unfolded protein response (UPR) state, and astrocyte/microglia markers in rat ventromedial hypothalamus (VMH) after type 2 diabetes mellitus (T2DM).

Methods

Male Wistar rats were divided: (1) control, (2) T2DM, and groups that received the following (14 days, orally): (3) metformin (60 mg/kg), (4) PA (60 mg/kg), and (5) PA+metformin. Western blotting, RT-PCR, transmission electron microscopy, and immunohistochemical staining were performed.

Results

We found T2DM-associated enlargement of ER cisterns, while drug administration slightly improved VMH ultrastructural signs of damage. GRP78 level was 2.1-fold lower in T2DM vs. control. Metformin restored GRP78 to control, while PA increased it by 2.56-fold and metformin+PA—by 3.28-fold vs. T2DM. PERK was elevated by 3.61-fold in T2DM, after metformin—by 4.98-fold, PA—5.64-fold, and metformin+PA—3.01-fold vs. control. A 2.45-fold increase in ATF6 was observed in T2DM. Metformin decreased ATF6 content vs. T2DM. Interestingly, PA exerted a more pronounced lowering effect on ATF6, while combined treatment restored ATF6 to control. IRE1 increased in T2DM (2.4-fold), metformin (1.99-fold), and PA (1.45-fold) groups vs. control, while metformin+PA fully normalized its content. The Iba1 level was upregulated in T2DM (5.44-fold) and metformin groups (6.88-fold). Despite PA treatment leading to a further 8.9-fold Iba1 elevation, PA+metformin caused the Iba1 decline vs. metformin and PA treatment. GFAP level did not change in T2DM but rose in metformin and PA groups vs. control. PA+metformin administration diminished GFAP vs. PA. T2DM-induced changes were associated with dramatically decreased ZO-1 levels, while PA treatment increased it almost to control values.

Conclusions

T2DM-induced UPR imbalance, activation of microglia, and impairments in cell integrity may trigger VMH dysfunction. Drug administration slightly improved ultrastructural changes in VMH, normalized UPR, and caused an astrocyte activation. PA and metformin exerted beneficial effects for counteracting diabetes-induced ER stress in VMH.

Uncovering antiobesity-related hypertension targets and mechanisms of metformin, an antidiabetic medication

Metformin, a common clinical drug used to treat diabetes mellitus, is found with potential antiobese actions as reported in increasing evidences. However, the detailed mechanisms of metformin-antiobesity-related hypertension remain unrevealed. We have utilized the bioinformatics strategy, including network pharmacology and molecular docking analyses, to uncover pharmacological targets and molecular pathways of bioactive compounds against clinical disorders, such as cancers, coronavirus disease 2019. In this report, the in-silico approaches using network pharmacology and molecular docking was utilized to identify the core targets, pharmacological functions and mechanisms of metformin against obesity-related hypertension. The networking analysis identified 154 differentially expressed genes of obesity and hypertension, and 21 interaction genes, 6 core genes of metformin treating obesity-related hypertension. As results, molecular docking findings indicated the binding capability of metformin with key proteins, including interleukin 6 (IL-6) and chemokine (C-C motif) Ligand 2 (CCL2) expressed in obesity- and hypertension-dependent tissues. Metformin-exerted antihypertension/obesity actions involved in metabolic regulation, inflammatory suppression. And antihypertension/obesity mechanisms of metformin were revealed, including regulation of inflammatory and immunological signaling pathways for ameliorating microenvironmental homeostasis in targeting tissues. In conclusion, our current bioinformatics findings have uncovered all pharmacological targets, biological functions and signaling pathways of metformin treating obesity-related hypertension, thus promoting its clinical application in future.

Crosstalk between the renin-angiotensin system and the endoplasmic reticulum stress in the cardiovascular system: Lessons learned so far

The renin-angiotensin (Ang) system (RAS) is a complex hormonal system present locally in several tissues such as cardiovascular organs. RAS deregulation through overactivation of the classical arm [Ang-converting enzyme (ACE)/Ang-II/Ang type 1 receptor (AT1R)] has been linked to the development of cardiovascular diseases and activation of endoplasmic reticulum (ER) stress pathways. The ER stress is a condition that, if unresolved, might lead to heart failure, atherosclerosis, hypertension, and endothelial dysfunction. Accumulated evidence has shown that the RAS modulates the UPR activation. Several studies reported increased ER stress markers in response to Ang-II treatment, in both in vivo and in vitro models. Evidence has also pointed that targeting the RAS classical arm through RAS blockers, gene silencing or genetic models leads to lower levels of ER stress markers. Few studies demonstrated protective effects of the counter-regulatory arm (ACE-2/Ang-(1-7)/Mas receptor) over ER stress. However, the crosstalk mechanisms between the arms of the RAS and ER stress remain unclear. In this review, we sought to explore the classical arm of the RAS as a key mechanism in UPR activation and to suggest a possible protective role of the counter-regulatory arm in mitigating ER stress.

Down-regulation of AMPK/PPARδ signalling promotes endoplasmic reticulum stress-induced endothelial dysfunction in adult rat offspring exposed to maternal diabetes

AIMS

Exposure to maternal diabetes is associated with increased prevalence of hypertension in the offspring. The mechanisms underlying the prenatal programming of hypertension remain unclear. Because endoplasmic reticulum (ER) stress plays a key role in vascular endothelial dysfunction in hypertension, we investigated whether aberrant ER stress causes endothelial dysfunction and high blood pressure in the offspring of dams with diabetes.

METHODS AND RESULTS

Pregnant Sprague-Dawley rats were intraperitoneally injected with streptozotocin (35 mg/kg) or citrate buffer at Day 0 of gestation. Compared with control mother offspring (CMO), the diabetic mother offspring (DMO) had higher blood pressure and impaired endothelium-dependent relaxation in mesenteric arteries, accompanied by decreased AMPK phosphorylation and PPARδ expression, increased ER stress markers, and reactive oxygen species (ROS) levels. The inhibition of ER stress reversed these aberrant changes in DMO. Ex vivo treatment of mesenteric arteries with an AMPK agonist (A769662) or a PPARδ agonist (GW1516) improved the impaired EDR in DMO and reversed the tunicamycin-induced ER stress, ROS production, and EDR impairment in mesenteric arteries from CMO. The effects of A769662 were abolished by co-treatment with GSK0660 (PPARδ antagonist), whereas the effects of GW1516 were unaffected by Compound C (AMPK inhibitor).

CONCLUSION

These results suggest an abnormal foetal programming of vascular endothelial function in offspring of rats with maternal diabetes that is associated with increased ER stress, which can be ascribed to down-regulation of AMPK/PPARδ signalling cascade.

Association between Three Variants in the PRKAA2 gene, rs2796498, rs9803799, and rs2746342, with 10-year ASCVD Risk on Newly Diagnosed T2DM in Yogyakarta, Indonesia

BACKGROUND: AMPK has pivotal roles in glucose and lipid metabolism, including  AMPKa2, which PRKAA2 encodes. Metformin as an anti-hyperglycemia agent acts through AMPK. Poor glycemia control among patients with type 2 diabetes mellitus (T2DM) could increase atherosclerosis cardiovascular disease (ASCVD) risk. Therefore, PRKAA2 genetic variation might contribute to 10-year ASCVD risk in patients with newly diagnosed T2DM receiving monotherapy metformin. AIM: The study aimed to detect an association between PRKAA2 genetic variation with 10 year-ASCVD risk among newly diagnosed T2DM patients prescribed monotherapy metformin. METHODS: This present study was a case-control study involving 107 participants. Analysis of PRKAA2 genetic variation was performed using the TaqMan assay. RESULTS: A total of 91 participants who fulfilled our criteria enrolled in this study. Most of the participants were female, with mean age 54.40±7.75 years old, mean HbA1c level of 8.35±1.31%, and the lipid profile indicated normal conditions. There was a significant difference in age (p<0.01), HbA1c level (p=0.04), sex (p<0.01), and smoking status (p<0.01) between low-risk and high-risk groups. The GT genotype of rs9803799 had 187.86 times higher possibility for high-risk of 10-year ASCVD risk than TT genotype (OR=187.86, 95%CI:2.98–11863.51). The dominant model of rs9803799 showed that GT+GG had 94.33 times higher possibility for high-risk of 10-year ASCVD risk than TT genotype (OR=94.33; 95%CI:2.32–3841.21). Other results showed that G allele of rs980377 had 20.48 times higher possibility for high-risk of 10-year ASCVD risk than T allele (OR = 20.48; 95%CI:1.48–283.30). These associations were found after multivariate analysis. CONCLUSION: Our findings indicated that rs9803799 as one of PRKAA2 genetic variations might impact the 10-year ASCVD risk among newly diagnosed T2DM patients receiving monotherapy metformin. After considering non-genetic factors, patient assessment should include potential genetic factors in cases with hyperglycemia involving treatment affecting glucose and lipid metabolism such as monotherapy metformin.   Keywords: PRKAA2, genetic variation, atherosclerosis cardiovascular disease, type 2 diabetes mellitus, metformin, Indonesia

Repurposing metformin for covid-19 complications in patients with type 2 diabetes and insulin resistance

Understanding the exact role of current drugs in Covid-19 disease is essential in the era of global pandemics. Metformin which prescribed as the first-line treatment of type 2 diabetes has beneficial effects on Sars-cov2 infection. These effects are including regulation of immune system, Renin-Angiotensin System and Dipeptidyl Peptidase 4 function in Covid-19 infection. It also activates ACE2, the main receptor of Sars-cov2, in the epithelial cells of respiratory tissue through AMPK signaling and subsequently decreases the rate of viral adhesion. Metformin also declines the adherence of Sars-cov2 to DPP4 (the other receptor of the virus) on T cells. Hence, regulatory effects of metformin on membranous ACE2, and DPP4 can modulate immune reaction against Sars-cov2. Also, immunometabolic effects of metformin on inflammatory cells impair hyper-reactive immune response against the virus through reduction of glycolysis and propagation of mitochondrial oxidation. Metformin also decreases platelet aggravation and risk of thrombosis. In this article, we argue that metformin has beneficial effects on Covid-19 infection in patients with type 2 diabetes and insulin resistance. This opinion should be investigated in future clinical trials.

Chronic metformin treatment decreases cardiac injury during ischemia-reperfusion by attenuating endoplasmic reticulum stress with improved mitochondrial function

Aging impairs mitochondrial function that leads to greater cardiac injury during ischemia and reperfusion. Cardiac endoplasm reticulum (ER) stress increases with age and contributes to mitochondrial dysfunction. Metformin is an anti-diabetic drug that protects cardiac mitochondria during acute ER stress. We hypothesized that metformin treatment would improve preexisting mitochondrial dysfunction in aged hearts by attenuating ER stress, followed by a decrease in cardiac injury during subsequent ischemia and reperfusion.

Male young (3 mo.) and aged mice (24 mo.) received metformin (300 mg/kg/day) dissolved in drinking water with sucrose (0.2 g/100 ml) as sweetener for two weeks versus sucrose vehicle alone. Cytosol, subsarcolemmal (SSM), and interfibrillar mitochondria (IFM) were isolated. In separate groups, cardioprotection was evaluated using ex vivo isolated heart perfusion with 25 min. global ischemia and 60 min. reperfusion. Infarct size was measured.

The contents of CHOP and cleaved ATF6 were decreased in metformin-treated 24 mo. mice compared to vehicle, supporting a decrease in ER stress. Metformin treatment improved OXPHOS in IFM in 24 mo. using a complex I substrate. Metformin treatment decreased infarct size following ischemia-reperfusion. Thus, metformin feeding decreased cardiac injury in aged mice during ischemia-reperfusion by improving pre-ischemic mitochondrial function via inhibition of ER stress.

Role of AMP-activated protein kinase on cardio-metabolic abnormalities in the development of diabetic cardiomyopathy: A molecular landscape

Cardiovascular complications associated with diabetes mellitus remains a leading cause of morbidity and mortality across the world. Diabetic cardiomyopathy is a descriptive pathology that in absence of co-morbidities such as hypertension, dyslipidemia initially characterized by cardiac stiffness, myocardial fibrosis, ventricular hypertrophy, and remodeling. These abnormalities further contribute to diastolic dysfunctions followed by systolic dysfunctions and eventually results in clinical heart failure (HF). The clinical outcomes associated with HF are considerably worse in patients with diabetes. The complexity of the pathogenesis and clinical features of diabetic cardiomyopathy raises serious questions in developing a therapeutic strategy to manage cardio-metabolic abnormalities. Despite extensive research in the past decade the compelling approaches to manage and treat diabetic cardiomyopathy are limited. AMP-Activated Protein Kinase (AMPK), a serine-threonine kinase, often referred to as cellular "metabolic master switch". During the development and progression of diabetic cardiomyopathy, a plethora of evidence demonstrate the beneficial role of AMPK on cardio-metabolic abnormalities including altered substrate utilization, impaired cardiac insulin metabolic signaling, mitochondrial dysfunction and oxidative stress, myocardial inflammation, increased accumulation of advanced glycation end-products, impaired cardiac calcium handling, maladaptive activation of the renin-angiotensin-aldosterone system, endoplasmic reticulum stress, myocardial fibrosis, ventricular hypertrophy, cardiac apoptosis, and impaired autophagy. Therefore, in this review, we have summarized the findings from pre-clinical and clinical studies and provided a collective overview of the pathophysiological mechanism and the regulatory role of AMPK on cardio-metabolic abnormalities during the development of diabetic cardiomyopathy.

Smyd3-PARP16 axis accelerates unfolded protein response and vascular aging

Vascular endothelial cell senescence and endoplasmic reticulum (ER) stress induced unfolded protein response (UPR) are two critical contributors to individual aging. However, whether these two biological events have crosstalk and are controlled by shared upstream regulators are largely unknown. Here, we found PARP16, a member of the Poly (ADP-ribose) polymerases family that tail-anchored ER transmembrane, was upregulated in angiotensin II (Ang II)-induced vascular aging and promoted UPR. Further, PARP16 was epigenetically upregulated by Smyd3, a histone H3 lysine 4 methyltransferase that bound to the promotor region of Parp16 gene and increased H3K4me3 level to activate its host gene’s transcription. Intervention of either Smyd3 or PARP16 ameliorated vascular aging associated phenotypes in both cell and mice models. This study identified Smyd3-PARP16 as a novel signal axis in regulating UPR and endothelial senescence, and targeting this axis has implications in preventing vascular aging and related diseases.

Curcumin attenuates angiotensin II-induced podocyte injury and apoptosis by inhibiting endoplasmic reticulum stress

Podocytes are an important component of the glomerular filtration barrier in the kidneys. The dysfunction and apoptosis of podocytes are important factors that can lead to the progression of chronic kidney disease (CKD). In CKD, angiotensin II is continuously elevated in circulation and is considered to have key roles in inducing podocyte injury and apoptosis. Curcumin is a hydrophobic polyphenolic compound extracted from turmeric. Increasing evidence demonstrates that curcumin has a protective effect on the kidneys in CKD. However, the mechanisms mediating this protective effect remain unclear. The aim of this study was to explore whether curcumin could protect against angiotensin II‐induced injury and apoptosis of podocytes. We performed western blotting, immunofluorescence, phalloidin staining, and terminal deoxynucleotidyl transferase nick‐end labeling staining to observe the expression level of podocyte‐specific proteins, apoptosis‐related proteins, and the arrangement of F‐actin. We found that curcumin could reverse angiotensin II‐induced podocyte injury and apoptosis in a dose‐dependent manner. In addition, curcumin dose‐dependently attenuated a pro‐apoptotic pathway, activated by angiotensin II‐induced endoplasmic reticulum stress. Conversely, the protective effects of curcumin were impaired upon addition of tunicamycin, an activator of endoplasmic reticulum stress. Thus, we speculate that curcumin protects against angiotensin II‐induced podocyte injury and apoptosis, at least partly by inhibiting endoplasmic reticulum stress.

Investigating the Vascular Toxicity Outcomes of the Irreversible Proteasome Inhibitor Carfilzomib

Background: Carfilzomib’s (Cfz) adverse events in myeloma patients include cardiovascular toxicity. Since carfilzomib’s vascular effects are elusive, we investigated the vascular outcomes of carfilzomib and metformin (Met) coadministration. Methods: Mice received: (i) saline; (ii) Cfz; (iii) Met; (iv) Cfz+Met for two consecutive (acute) or six alternate days (subacute protocol). Leucocyte-derived reactive oxygen species (ROS) and serum NO_x levels were determined and aortas underwent vascular and molecular analyses. Mechanistic experiments were recapitulated in aged mice who received similar treatment to young animals. Primary murine (prmVSMCs) and aged human aortic smooth muscle cells (HAoSMCs) underwent Cfz, Met and Cfz+Met treatment and viability, metabolic flux and p53-LC3-B expression were measured. Experiments were recapitulated in AngII, CoCl₂ and high-glucose stimulated HAoSMCs. Results: Acutely, carfilzomib alone led to vascular hypo-contraction and increased ROS release. Subacutely, carfilzomib increased ROS release without vascular manifestations. Cfz+Met increased PGF2α-vasoconstriction and LC3-B-dependent autophagy in both young and aged mice. In vitro, Cfz+Met led to cytotoxicity and autophagy, while Met and Cfz+Met shifted cellular metabolism. Conclusion: Carfilzomib induces a transient vascular impairment and oxidative burst. Cfz+Met increased vascular contractility and synergistically induced autophagy in all settings. Therefore, carfilzomib cannot be accredited for a permanent vascular dysfunction, while Cfz+Met exert vasoprotective potency.

Endoplasmic reticulum stress and focused drug discovery in cardiovascular disease

Endoplasmic reticulum (ER) is an intracellular membranous organelle involved in the synthesis, folding, maturation and post-translation modification of secretory and transmembrane proteins. Therefore, ER is closely related to the maintenance of intracellular homeostasis and the good balance between health and diseases. Endoplasmic reticulum stress (ERS) occurs when unfolded/misfolded proteins accumulate after disturbance of ER environment. In response to ERS, cells trigger an adaptive response called the Unfolded protein response (UPR), which helps cells cope with the stress. In recent years, a large number of studies show that ERS can aggravate cardiovascular diseases. ERS-related proteins expression in cardiovascular diseases is on the rise. Therefore, down-regulation of ERS is critical for alleviating symptoms of cardiovascular diseases, which may be used in the near future to treat cardiovascular diseases. This article reviews the relationship between ERS and cardiovascular diseases and drugs that inhibit ERS. Furthermore, we detail the role of ERS inhibitors in the treatment of cardiovascular disease. Drugs that inhibit ERS are considered as promising strategies for the treatment of cardiovascular diseases.

An investigation into the pleiotropic activity of metformin. A glimpse of haemostasis

The most characteristic features of type 2 diabetes mellitus (T2DM) are hyperglycaemia and insulin resistance, however, patients with T2DM are at higher risk of cardiovascular disease (CVD) and atherosclerosis. Diabetes, frequently related to metabolic and vascular impairments, is also associated with thrombosis, increased blood coagulation and an imbalance between coagulation and fibrinolysis. Metformin is the most often used oral glucose-lowering agent; its beneficial properties include lowering insulin resistance, weight reduction and cardioprotection. Available data suggest that the advantageous properties of metformin stem from its favourable effects on endothelium, and anti-oxidative and anti-inflammatory properties. This paper reviews the favourable impact of metformin on endothelial function, with particular emphasis on the release of endogenous molecules modulating the state of the vascular endothelium and coagulation. It also summarizes the present knowledge on the influence of metformin on platelet activity and plasma haemostasis, including clot formation, stabilization and fibrinolysis. Its findings confirm that metformin should constitute first line therapy of T2DM subjects; however, more comprehensive methodical studies are required to discover the full potential of this drug.

Amelioration of metabolic syndrome by metformin associates with reduced indices of low-grade inflammation independently of the gut microbiota

Metformin beneficially impacts several aspects of metabolic syndrome including dysglycemia, obesity, and liver dysfunction, thus making it a widely used frontline treatment for early-stage type 2 diabetes, which is associated with these disorders. Several mechanisms of action for metformin have been proposed, including that it acts as an anti-inflammatory agent, possibly as a result of its impact on intestinal microbiota. In accord with this possibility, we observed herein that, in mice with diet-induced metabolic syndrome, metformin impacts the gut microbiota by preventing its encroachment upon the host, a feature of metabolic syndrome in mice and humans. However, the ability of metformin to beneficially impact metabolic syndrome in mice was not markedly altered by reduction or elimination of gut microbiota, achieved by the use of antibiotics or germfree mice. Although reducing or eliminating microbiota by itself suppressed diet-induced dysglycemia, other features of metabolic syndrome including obesity, hepatic steatosis, and low-grade inflammation remained suppressed by metformin in the presence or absence of gut microbiota. These results support a role for anti-inflammatory activity of metformin, irrespective of gut microbiota, in driving some of the beneficial impacts of this drug on metabolic syndrome.

Vascular adenosine monophosphate-activated protein kinase: Enhancer, brake or both?

Adenosine monophosphate-activated protein kinase (AMPK), expressed/present ubiquitously in the body, contributes to metabolic regulation. In the vasculature, activation of AMPK is associated with several beneficial biological effects including enhancement of vasodilatation, reduction of oxidative stress and inhibition of inflammatory reactions. The vascular protective effects of certain anti-diabetic (metformin and sitagliptin) or lipid-lowering (simvastatin and fenofibrate) therapeutic agents, of active components of Chinese medicinal herbs (resveratrol and berberine) and of pharmacological agents (AICAR, A769662 and PT1) have been attributed to the activation of AMPK (in endothelial cells, vascular smooth muscle cells and/or perivascular adipocytes), independently of changes in the metabolic profile (eg glucose tolerance and/or plasma lipoprotein levels), leading to improved endothelium-derived nitric oxide-mediated vasodilatation and attenuated endothelium-derived cyclooxygenase-dependent vasoconstriction. By contrast, endothelial AMPK activation with pharmacological agents or by genetic modification is associated with reduced endothelium-dependent relaxations in small blood vessels and elevated systolic blood pressure. Indeed, AMPK activators inhibit endothelium-dependent hyperpolarization (EDH)-type relaxations in superior mesenteric arteries, partly by inhibiting endothelial calcium-activated potassium channel signalling. Therefore, AMPK activation is not necessarily beneficial in terms of endothelial function. The contribution of endothelial AMPK in the regulation of vascular tone, in particular in the microvasculature where EDH plays a more important role, remains to be characterized.

AMPK: a balancer of the renin-angiotensin system

The renin-angiotensin system (RAS) is undisputedly well-studied as one of the oldest and most critical regulators for arterial blood pressure, fluid volume, as well as renal function. In recent studies, RAS has also been implicated in the development of obesity, diabetes, hyperlipidemia, and other diseases, and also involved in the regulation of several signaling pathways such as proliferation, apoptosis and autophagy, and insulin resistance. AMP-activated protein kinase (AMPK), an essential cellular energy sensor, has also been discovered to be involved in these diseases and cellular pathways. This would imply a connection between the RAS and AMPK. Therefore, this review serves to draw attention to the cross-talk between RAS and AMPK, then summering the most recent literature which highlights AMPK as a point of balance between physiological and pathological functions of the RAS.

Stimulation of Na+/K+-ATPase with an Antibody against Its 4th Extracellular Region Attenuates Angiotensin II-Induced H9c2 Cardiomyocyte Hypertrophy via an AMPK/SIRT3/PPARγ Signaling Pathway

Activation of the renin-angiotensin system (RAS) contributes to the pathogenesis of cardiovascular diseases. Sodium potassium ATPase (NKA) expression and activity are often regulated by angiotensin II (Ang II). This study is aimed at investigating whether DR-Ab, an antibody against 4^th extracellular region of NKA, can protect Ang II-induced cardiomyocyte hypertrophy. Our results showed that Ang II treatment significantly reduced NKA activity and membrane expression. Pretreatment with DR-Ab preserved cell size in Ang II-induced cardiomyopathy by stabilizing the plasma membrane expression of NKA and restoring its activity. DR-Ab reduced intracellular ROS generation through inhibition of NADPH oxidase activity and protection of mitochondrial functions in Ang II-treated H9c2 cardiomyocytes. Pharmacological manipulation and Western blotting analysis demonstrated the cardioprotective effects were mediated by the activation of the AMPK/Sirt-3/PPARγ signaling pathway. Taken together, our results suggest that dysfunction of NKA is an important mechanism for Ang II-induced cardiomyopathy and DR-Ab may be a novel and promising therapeutic approach to treat cardiomyocyte hypertrophy.

Sulfenamide and Sulfonamide Derivatives of Metformin - A New Option to Improve Endothelial Function and Plasma Haemostasis

Type 2 diabetes mellitus (T2DM) is a multi-factorial disease which can cause multiple organ dysfunction, including that of the vascular endothelium. The aim of the present study was to evaluate the effects of metformin, and its sulfenamide and sulfonamide derivatives (compounds 1–8) on the selected markers of endothelial function and blood coagulation. The integrity of endothelial cells(ECs) was examined using the real-time cell electric impedance system. Tissue Factor(TF) production, the release of von Willebrand Factor (vWF) and tissue plasminogen activator(t-PA) from ECs were determined using immunoenzymatic assays, while the process of platelet thrombus formation using the Total Thrombus-Formation Analysis System. Sulfenamide with n-butyl alkyl chain(3) does not interfere with ECs integrity, and viability (nCI_(24h) = 1.03 ± 0.03 vs. 1.06 ± 0.11 for control), but possesses anticoagulation properties manifested by prolonged platelet-dependent thrombus formation (Occlusion Time 370.3 ± 77.0 s vs. 286.7 ± 65.5 s for control) in semi-physiological conditions. Both p- and o-nitro-benzenesulfonamides (compounds7,8) exhibit anti-coagulant properties demonstrated by decreased vWF release and prolonged parameters of platelet thrombus formation and total blood thrombogenicity. In conclusion, chemical modification of metformin scaffold into sulfenamides or sulfonamides might be regarded as a good starting point for the design and synthesis of novel biguanide-based compounds with anticoagulant properties and valuable features regarding endothelial function.

Metformin prevents vascular damage in hypertension through the AMPK/ER stress pathway

Metformin is an antidiabetic drug. However, the pleiotropic beneficial effects of metformin in nondiabetic models still need to be defined. The objective of this study is to investigate the effect of metformin on angiotensin II (Ang II)-induced hypertension and cardiovascular diseases. Mice were infused with Ang II (400 ng/kg per min) with or without metformin for 2 weeks. Mice infused with angiotensin II displayed an increase in blood pressure associated with enhanced vascular endoplasmic reticulum (ER) stress markers, which were blunted after metformin treatment. Moreover, hypertension-induced reduction in phosphorylated AMPK, endothelial nitric oxide synthase (eNOs) phosphorylation, and endothelium-dependent relaxation (EDR) in mesenteric resistance arteries (MRA) were rescued after metformin treatment. Infusion of ER stress inducer (tunicamycin, Tun) in control mice induced ER stress in MRA and reduced phosphorylation of AMPK, eNOS synthase phosphorylation, and EDR in MRA without affecting systolic blood pressure (SBP). All these factors were reversed subsequently with metformin treatment. ER stress inhibition by metformin improves vascular function in hypertension. Therefore, metformin could be a potential therapy for cardiovascular diseases in hypertension independent of its effects on diabetes.

Metformin Promotes Regeneration of the Injured Endometrium Via Inhibition of Endoplasmic Reticulum Stress-Induced Apoptosis

Intrauterine adhesion (IUA) is now recognized as one of the most common diseases in reproductive-age women. Metformin, a well-known frontline oral antidiabetic drug, has been found effective in numerous different diseases. The aim of this study was to determine the effect of metformin on reducing adhesions in an animal model of IUA. Sprague-Dawley rats were randomized into 4 groups: sham operation, control, metformin-treated for 7 days, and metformin-treated for 14 days. To establish the IUA model, mechanical injury to the endometria of rats was induced with a mini curette. Metformin was injected intraperitoneally after surgery. A significant amelioration in both the number of glands and the fibrotic area, compared to those of the control group, was detected 14 days after metformin intervention. The expression levels of antigen KI-67 and vascular endothelial growth factor were increased at 7 and 14 days after treatment. However, the transforming growth factor-β expression was decreased at 14 days after treatment. Endoplasmic reticulum stress-related apoptosis proteins (glucose-regulated protein 78, caspase-12, and CCAAT/enhancer binding protein (EBP) homologous protein) were downregulated after metformin treatment. Moreover, we determined that the effect of metformin was related to the inhibition of endoplasmic reticulum stress-induced apoptosis via the Phosphatidylinositol 3 kinase (PI3K)/Protein kinase B (AKT) and Extracellular regulated protein kinases1/2 pathways. In conclusion, metformin can attenuate the adhesion and promote the regeneration of the endometrium of the IUA rat, and metformin may serve as a novel therapeutic strategy for IUA patients.

Chronic Intracerebroventricular Infusion of Metformin Inhibits Salt-Sensitive Hypertension via Attenuation of Oxidative Stress and Neurohormonal Excitation in Rat Paraventricular Nucleus

Metformin (MET), an antidiabetic agent, also has antioxidative effects in metabolic-related hypertension. This study was designed to determine whether MET has anti-hypertensive effects in salt-sensitive hypertensive rats by inhibiting oxidative stress in the hypothalamic paraventricular nucleus (PVN). Salt-sensitive rats received a high-salt (HS) diet to induce hypertension, or a normal-salt (NS) diet as control. At the same time, they received intracerebroventricular (ICV) infusion of MET or vehicle for 6 weeks. We found that HS rats had higher oxidative stress levels and mean arterial pressure (MAP) than NS rats. ICV infusion of MET attenuated MAP and reduced plasma norepinephrine levels in HS rats. It also decreased reactive oxygen species and the expression of subunits of NAD(P)H oxidase, improved the superoxide dismutase activity, reduced components of the renin-angiotensin system, and altered neurotransmitters in the PVN. Our findings suggest that central MET administration lowers MAP in salt-sensitive hypertension via attenuating oxidative stress, inhibiting the renin-angiotensin system, and restoring the balance between excitatory and inhibitory neurotransmitters in the PVN.

Metformin: An Old Drug with New Applications

Metformin is a biguanide drug that has been used to treat type 2 diabetes mellitus for more than 60 years. The United Kingdom Prospective Diabetic Study (UKPDS) has shown metformin to improve mortality rates in diabetes patients, and recent studies suggest metformin has additional effects in treating cancer, obesity, nonalcoholic fatty liver disease (NAFLD), polycystic ovary syndrome (PCOS), and metabolic syndrome. Metformin has also been shown to alleviate weight gain associated with antipsychotic medication. Metformin has recently been extensively studied and emerging evidence suggests metformin decreases hepatocyte triglyceride accumulation in NAFLD and prevents liver tumorigenesis. Interestingly, studies have also shown metformin reduces visceral fat, suppresses white-adipose-tissue (WAT) extracellular matrix remodeling, and inhibits obesity-induced inflammation. However, clinical evidence for using metformin to treat NAFLD, cancer, metabolic syndrome, or to prevent hepatocellular carcinoma in NAFLD patients is lacking. This review therefore addresses the potential beneficial effects of metformin on NAFLD, its role in protecting against cardiac ischemia–reperfusion (I/R) injury, atherosclerosis, glucotoxicity, and lipotoxicity induced oxidative and ER stress in pancreatic β-cell dysfunction, as well as its underlying molecular mechanisms of action.

Metformin attenuates diabetes-induced tau hyperphosphorylation in vitro and in vivo by enhancing autophagic clearance

Diabetes mellitus (DM) can increase the risk of Alzheimer's disease (AD) in patients. However, no effective approaches are available to prevent its progression and development. Recently, autophagy dysfunction was identified to be involved in the pathogenesis of neurodegenerative diseases. This study was designed to investigate the effect of metformin on hyperphosphorylated tau proteins in diabetic encephalopathy (DE) by regulating autophagy clearance. db/db mice were randomly divided into four groups, db/+ mice were used as control group. Twelve-week old male db/db mice received consecutive intraperitoneal injection of 200 mg/kg/d metformin or (and) 10 mg/kg/d chloroquine for eight weeks. Morris water maze (MWM) tests were performed to test cognitive functions before the mice were euthanized. Metformin attenuated cognitive impairment in db/db mice, reduced hyperphosphorylated tau proteins, restored the impaired autophagy in diabetic mice, all of which were reversed by inhibiting of autophagy activity. In high glucose-cultured HT22 cells, metformin increased autophagy in a dose-dependent manner. Besides, metformin enhanced autophagy activity in an AMPK dependent manner. These data show that metformin may reduce tauopathy and improve cognitive impairment in db/db mice by modulating autophagy through the AMPK dependent pathway. These findings highlight metformin as a new therapeutic strategy for the treatment of DE.

Paeoniflorin attenuates atRAL-induced oxidative stress, mitochondrial dysfunction and endoplasmic reticulum stress in retinal pigment epithelial cells via triggering Ca2+/CaMKII-dependent activation of AMPK

Abnormal accumulation of the free-form all-trans-retinal (atRAL), a major intermediate of human visual cycle, is considered to be a key cause of retinal pigment epithelial (RPE) dysfunction in the pathogenesis of retinal degenerative diseases such as age-related macular degeneration (AMD). Paeoniflorin (PF), a monoterpene glucoside isolated from Paeonia lactiflora Pall., has been used in clinical treatment of retinal degenerative diseases in China for several years; however, the underlying mechanism remains unclear. The aim of this study is to investigate the protective effect of PF against atRAL toxicity in human ARPE-19 cells and its molecular mechanism. The results of our study showed that the pre-treatment of PF dose-dependently attenuated atRAL-induced cell injury by the reduction of Nox1/ROS-associated oxidative stress, mitochondrial dysfunction and GRP78-PERK-eIF2α-ATF4-CHOP-regulated endoplasmic reticulum (ER) stress in ARPE-19 cells. Additionally, our data showed that PF mainly exerted its activity via triggering calcium-calmodulin dependent protein kinase II (CaMKII)-mediated activation of AMP-activated protein kinase (AMPK). AMPK inhibition significantly reversed the protective effect of PF against atRAL toxicity in ARPE-19 cells. Overall, our findings provided the novel mechanism of PF protecting human RPE cells, which may prevent the progression of retinal degenerative diseases.

Apigenin-7-O-β-d-(-6″-p-coumaroyl)-glucopyranoside pretreatment attenuates myocardial ischemia/reperfusion injury via activating AMPK signaling

AIMS

Apigenin-7-O-β-d-(-6″-p-coumaroyl)-glucopyranoside (APG) was considered as the major active compound derived from Clematis tangutica. Though we have demonstrated that APG exerts cardioprotective effects, the mechanism of APG-mediated cardioprotection remains largely unknown. Numerous studies indicate that endoplasmic reticulum stress (ERS) is a vital injury factor in myocardial ischemia reperfusion (MI/R). In this study, we mainly investigated whether modulation of the ERS and AMPK were involved in the cardioprotective action of APG during MI/R injury.

MAIN METHODS

The perfused isolated rat heart or primary neonatal rat cardiomyocytes which exposed to APG with or else without the AMPK inhibitor Compound C was then subject to MI/R. After reperfusion, the degree of myocardial injury was assessed by using lactate dehydrogenase (LDH) release, creatine kinase (CK) release, histological examination, and TTC staining. The protein expressions of p-AMPK, AMPK, p-PERK, PERK, p-eIF2α, eIF2α, CHOP, Bax, Bcl2 and Cleaved Caspase 3 were analyzed by western blot. The cell viability was assessed by CCK-8 kit while apoptosis assessed by using TUNEL assay.

KEY FINDINGS

Pretreatment of APG significantly improved cardiac function and suppressed ERS through activating the AMPK signaling pathway, which could simultaneously improve cardiac function, alleviate myocardial injury, increase the cell viability and decrease apoptosis.

SIGNIFICANCE

To conclude, APG ameliorates MI/R injury by activating the AMPK signaling pathway and relieving endoplasmic reticulum stress. APG may be a natural product with pharmacological preconditioning activity, which could do us a favor to develop more novel therapy methods to against MI/R injury in the future.

Prenatal Metformin Therapy Attenuates Hypertension of Developmental Origin in Male Adult Offspring Exposed to Maternal High-Fructose and Post-Weaning High-Fat Diets

Widespread consumption of a Western diet, comprised of highly refined carbohydrates and fat, may play a role in the epidemic of hypertension. Hypertension can take origin from early life. Metformin is the preferred treatment for type 2 diabetes. We examined whether prenatal metformin therapy can prevent maternal high-fructose plus post-weaning high-fat diets-induced hypertension of developmental origins via regulation of nutrient sensing signals, uric acid, oxidative stress, and the nitric oxide (NO) pathway. Gestating Sprague–Dawley rats received regular chow (ND) or chow supplemented with 60% fructose diet (HFR) throughout pregnancy and lactation. Male offspring were onto either the ND or high-fat diet (HFA) from weaning to 12 weeks of age. A total of 40 male offspring were assigned to five groups (n = 8/group): ND/ND, HFR/ND, ND/HFA, HFR/HFA, and HFR/HFA+metformin. Metformin (500 mg/kg/day) was administered via gastric gavage for three weeks during the pregnancy period. Combined maternal HFR plus post-weaning HFA induced hypertension in male adult offspring, which prenatal metformin therapy prevented. The protective effects of prenatal metformin therapy on HFR/HFA-induced hypertension, including downregulation of the renin-angiotensin system, decrease in uric acid level, and reduction of oxidative stress. Our results highlighted that the programming effects of metformin administered prenatally might be different from those reported in adults, and that deserves further elucidation.

Metformin attenuates ER stress-induced mitochondrial dysfunction

Endoplasmic reticulum (ER) stress, a disturbance of the ER function, contributes to cardiac injury. ER and mitochondria are closely connected organelles within cells. ER stress contributes to mitochondrial dysfunction, which is a key factor to increase cardiac injury. Metformin, a traditional anti-diabetic drug, decreases cardiac injury during ischemia-reperfusion. Metformin also inhibits ER stress in cultured cells. We hypothesized that metformin can attenuate the ER stress-induced mitochondrial dysfunction and subsequent cardiac injury. Thapsigargin (THAP, 3 mg/kg) was used to induce ER stress in C57BL/6 mice. Cell injury and mitochondrial function were evaluated in the mouse heart 48 hours after 1-time THAP treatment. Metformin was dissolved in drinking water (0.5 g/250 ml) and fed to mice for 7 days before THAP injection. Metformin feeding continued after THAP treatment. THAP treatment increased apoptosis in mouse myocardium compared to control. THAP also led to decreased oxidative phosphorylation in heart mitochondria-oxidizing complex I substrates. THAP decreased the calcium retention capacity, indicating that ER stress sensitizes mitochondria to mitochondrial permeability transition pore opening. The cytosolic C/EBP homologous protein (CHOP) content was markedly increased in THAP-treated hearts compared to control, particularly in the nucleus. Metformin prevented the THAP-induced mitochondrial dysfunction and reduced CHOP content in cytosol and nucleus. Thus, metformin reduces cardiac injury during ER stress through the protection of cardiac mitochondria and attenuation of CHOP expression.

The sirtuin 6 prevents angiotensin II-mediated myocardial fibrosis and injury by targeting AMPK-ACE2 signaling

Sirtuin 6 (SIRT6) is an important modulator of cardiovascular functions in health and diseases. However, the exact role of SIRT6 in heart disease is poorly defined. We hypothesized that SIRT6 is a negative regulator of angiotensin II (Ang II)-mediated myocardial remodeling, fibrosis and injury. The male Sprague-Dawley rats were randomized to Ang II (200 ng/kg/min) infusion with an osmotic minipump and pretreated with recombinant plasmids adeno-associated viral vector (AAV)-SIRT6 (pAAV-SIRT6) or pAAV-GFP for 4 weeks. Ang II triggered downregulated levels of SIRT6 and angiotensin-converting enzyme 2 (ACE2) and upregulated expression of connective tissue growth factor (CTGF) and proinflammatory chemokine fractalkine (FKN), contributing to enhanced cardiac fibrosis and ultrastructural injury. Reduced levels of phosphorylated pAMPK-α, increased myocardial hypertrophy and impaired heart dysfunction were observed in both Ang II-induced hypertensive rats and ACE2 knockout rats, characterized with increases in heart weight and left ventricular (LV) posterior wall thickness and decreases in LV ejection fraction and LV fractional shortening. More importantly, pAAV-SIRT6 treatment strikingly potentiated cardiac levels of pAMPKα and ACE2 as well as decreased levels of CTGF, FKN, TGFβ1, collagen I and collagen III, resulting in alleviation of Ang II-induced pathological hypertrophy, myocardial fibrosis, cardiac dysfunction and ultrastructural injury in hypertensive rats. In conclusion, our findings confirmed cardioprotective effects of SIRT6 on pathological remodeling, fibrosis and myocardial injury through activation of AMPK-ACE2 signaling and suppression of CTGF-FKN pathway, indicating that SIRT6 functions as a partial agonist of ACE2 and targeting SIRT6 has potential therapeutic importance for cardiac fibrosis and heart disease.

Activation of AMP-activated protein kinase by metformin ablates angiotensin II-induced endoplasmic reticulum stress and hypertension in mice in vivo

BACKGROUND AND PURPOSE

Metformin, one of the most frequently prescribed medications for type 2 diabetes, reportedly exerts BP-lowering effects in patients with diabetes. However, the effects and underlying mechanisms of metformin on BP in non-diabetic conditions remain to be determined. The aim of the present study was to determine the effects of metformin on angiotensin II (Ang II) infusion-induced hypertension in vivo.

EXPERIMENTAL APPROACH

The effects of metformin on BP were investigated in wild-type (WT) C57BL/6J mice and in mice lacking AMP-activated protein kinase α2 (AMPKα2) mice with or without Ang II infusion. Also, the effect of metformin on Ang II-induced endoplasmic reticulum (ER) stress was explored in cultured human vascular smooth muscle cells (hVSMCs).

KEY RESULTS

Metformin markedly reduced BP in Ang II-infused WT mice but not in AMPKα2-deficient mice. In cultured hVSMCs, Ang II treatment resulted in inactivation of AMPK, as well as the subsequent induction of spliced X-box binding protein-1, phosphorylation of eukaryotic translation initiation factor 2α and expression of glucose-regulated protein 78 kDa, representing three well-characterized ER stress biomarkers. Moreover, AMPK activation by metformin ablated Ang II-induced ER stress in hVSMCs. Mechanistically, metformin-activated AMPKα2 suppressed ER stress by increasing phospholamban phosphorylation.

CONCLUSION AND IMPLICATIONS

Metformin alleviates Ang II-triggered hypertension in mice by activating AMPKα2, which mediates phospholamban phosphorylation and inhibits Ang II-induced ER stress in vascular smooth muscle cells.