Metformin prevents the development of chronic heart failure in the SHHF rat model

Effect of metformin (vs. placebo or sulfonylurea) on all-cause and cardiovascular mortality and incident cardiovascular events in patients with diabetes: an umbrella review of systematic reviews with meta-analysis

Purpose

The current umbrella review aimed to evaluate the effect of metformin on all-cause mortality (ACM), cardiovascular mortality, and cardiovascular disease (CVD) incidence in DM patients.

Methods

PubMed, Scopus, Cochrane, Google Scholar, and Web of Science databases were searched with special keywords. Related studies were included after screening by two independent investigators based on title and full texts. The AMSTAR2 checklist was used to assess the quality of studies, and Cochran tests were used to assess the heterogeneity between studies. Overall, seventeen systematic reviews and meta-analysis studies were included. The results revealed that the risk of ACM in patients who received metformin was lower than in patients who did not receive metformin. (OR: 0.80, 95% CI:0.744,0.855); also, the risk of CVD mortality in metformin patients was lower than in the other two groups (placebo and other anti-diabetic drugs) (OR: 0.771, 95% CI:0.688,0.853, P:0.001). The risk of CVD in metformin users was also lower than in the other two groups (OR: 0.828, 95% CI:0.781,0.785).

Summary

This comprehensive review showed that the risk of ACM, death due to CVD, and incidents of CVD in DM who use metformin was lower than the patients who received a placebo only or other diabetic drugs, which can guide clinicians in medical decision-making.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-023-01309-y.

Metformin induction of heat shock factor 1 activation and the mitochondrial unfolded protein response alleviate cardiac remodeling in spontaneously hypertensive rats

Heart failure and cardiac remodeling are both characterized by mitochondrial dysfunction. Healthy mitochondria are required for adequate contractile activity and appropriate regulation of cell survival. In the mammalian heart, enhancement of the mitochondrial unfolded protein response (UPRmt) is cardioprotective under pressure overload conditions. We explored the UPRmt and the underlying regulatory mechanism in terms of hypertension-induced cardiac remodeling and the cardioprotective effect of metformin. Male spontaneously hypertensive rats and angiotensin II-treated neonatal rat cardiomyocytes were used to induce cardiac hypertrophy. The results showed that hypertension induced the formation of aberrant mitochondria, characterized by a reduced mtDNA/nDNA ratio and swelling, as well as lower levels of mitochondrial complexes I to V and inhibition of the expression of one protein subunit of each of complexes I to IV. Such changes eventually enlarged cardiomyocytes and increased cardiac fibrosis. Metformin treatment increased the mtDNA/nDNA ratio and regulated the UPRmt, as indicated by increased expression of activating transcription factor 5, Lon protease 1, and heat shock protein 60, and decreased expression of C/EBP homologous protein. Thus, metformin improved mitochondrial ultrastructure and function in spontaneously hypertensive rats. In vitro analyses revealed that metformin reduced the high levels of angiotensin II-induced mitochondrial reactive oxygen species in such animals and stimulated nuclear translocation of heat shock factor 1 (HSF1). Moreover, HSF1 small-interfering RNA reduced the metformin-mediated improvements in mitochondrial morphology and the UPRmt by suppressing hypertrophic signals and cardiomyocyte apoptosis. These results suggest that HSF1/UPRmt signaling contributes to the beneficial effects of metformin. Metformin-mediated targeting of mitochondrial protein homeostasis and modulation of HSF1 levels have potential therapeutic implications in terms of cardiac remodeling.

Effect of Metformin on Oxidative Stress and Left Ventricular Geometry in Nondiabetic Heart Failure Patients: A Randomized Controlled Trial

Introduction: There is an increasing interest in using metformin in cardiovascular diseases and its potential new roles. Only two randomized controlled trials investigated the effect of metformin in nondiabetic heart failure (HF) patients. However, none of these studies assess the role of metformin in reducing oxidative stress. We hypothesized that metformin might improve oxidative stress and left ventricular remodeling in nondiabetic HF patients with reduced ejection fraction (HFrEF). Methods and Methods: Seventy HFrEF patients (EF 37% ± 8%; median age 66 years) were randomized to metformin (n = 35) or standard of care (SOC) for HF (n = 35) for 6 months in addition to standard therapy. Outcomes included the difference in the change (Δ) in total antioxidant capacity (TAC) and malondialdehyde (MDA), both assessed colorimetrically and left ventricular mass index (LVMI) assessed through transthoracic echocardiography. Results: Compared with the SOC, metformin treatment increased TAC [Δ = 0.12 mmol/L, confidence intervals (95% CIs): 0.03-0.21; P = 0.007]. TAC increased significantly only in the metformin group (0.90 ± 0.08 mmol/L at baseline vs. 1.04 ± 0.99 mmol/L at 6 months, P < 0.05). Metformin therapy preserved LVMI (Δ = -23 g/m2, 95% CI: -42.91 to -4.92; P = 0.014) and reduced fasting plasma glucose (Δ = -6.16, 95% CI: -12.31 to -0.02, P = 0.047) compared with the SOC. Results did not change after adjusting for baseline values. Changes in MDA left ventricular ejection fraction (LVEF) and blood pressure were not significantly different between groups. Conclusion: Metformin treatment in HF patients with reduced LVEF improved TAC and prevented the increase in LVMI compared with the SOC. These effects of metformin warrant further research in HF patients without diabetes to explore the potential benefits of metformin. Trial Registration Number: This protocol was registered in ClinicalTrials.gov under the number NCT05177588.

Beneficial effects of metformin on mice female fertility after a high-fat diet intake

Female fertility is highly dependent on energy balance. High fat diet (HFD) intake entails a risk of infertility and ovulatory disorders. Considering the increase in the prevalence of overweight and obesity over the last decades, it is crucial to understand the mechanisms involved in overweight-associated infertility. In this study, we evaluated the reproductive performance of female mice fed with a HFD and the effects of metformin administration on ovarian function in these mice. We hypothesized that one of the mechanisms involved in subfertility due to a HFD intake is the alteration of ovarian blood vessel formation. We found that mice fed with HFD had altered estrous cycles and steroidogenesis, increased ovarian fibrosis, fewer pups per litter and require more time to achieve pregnancy. HFD-fed mice also presented dysregulated ovarian angiogenesis and an increase in nuclear DNA damage in ovarian cells. Ovulation rates were lower in these animals, as evidenced both in natural mating and after ovulation induction with gonadotropins. Metformin ameliorated ovarian angiogenesis, improved steroidogenesis, fibrosis, and ovulation, decreased the time to pregnancy and increased litter sizes in HFD-fed mice. We conclude that ovarian angiogenesis is one of the mechanisms detrimentally affected by HFD intake. Since metformin could improve ovarian microvasculature, it may be an interesting strategy to study in women to shed light on new targets for patients with metabolic disturbances.

Amino acid homeostasis is a target of metformin therapy

OBJECTIVE

Unexplained changes in regulation of branched chain amino acids (BCAA) during diabetes therapy with metformin have been known for years. Here we have investigated mechanisms underlying this effect.

METHODS

We used cellular approaches, including single gene/protein measurements, as well as systems-level proteomics. Findings were then cross-validated with electronic health records and other data from human material.

RESULTS

In cell studies, we observed diminished uptake/incorporation of amino acids following metformin treatment of liver cells and cardiac myocytes. Supplementation of media with amino acids attenuated known effects of the drug, including on glucose production, providing a possible explanation for discrepancies between effective doses in vivo and in vitro observed in most studies. Data-Independent Acquisition proteomics identified that SNAT2, which mediates tertiary control of BCAA uptake, was the most strongly suppressed amino acid transporter in liver cells following metformin treatment. Other transporters were affected to a lesser extent. In humans, metformin attenuated increased risk of left ventricular hypertrophy due to the AA allele of KLF15, which is an inducer of BCAA catabolism. In plasma from a double-blind placebo-controlled trial in nondiabetic heart failure (trial registration: NCT00473876), metformin caused selective accumulation of plasma BCAA and glutamine, consistent with the effects in cells.

CONCLUSIONS

Metformin restricts tertiary control of BCAA cellular uptake. We conclude that modulation of amino acid homeostasis contributes to therapeutic actions of the drug.

Improving mitochondrial function in preclinical models of heart failure: therapeutic targets for future clinical therapies?

INTRODUCTION

Heart failure is a complex clinical syndrome resulting from the unsuccessful compensation of symptoms of myocardial damage. Mitochondrial dysfunction is a process that occurs because of an attempt to adapt to the disruption of metabolic and energetic pathways occurring in the myocardium. This, in turn, leads to further dysfunction in cardiomyocyte processes. Currently, many therapeutic strategies have been implemented to improve mitochondrial function, but their effectiveness varies widely.

AREAS COVERED

This review focuses on new models of therapeutic strategies targeting mitochondrial function in the treatment of heart failure.

EXPERT OPINION

Therapeutic strategies targeting mitochondria appear to be a valuable option for treating heart failure. Currently, the greatest challenge is to develop new research models that could restore the disrupted metabolic processes in mitochondria as comprehensively as possible. Only the development of therapies that focus on improving as many dysregulated mitochondrial processes as possible in patients with heart failure will be able to bring the expected clinical improvement, along with inhibition of disease progression. Combined strategies involving the reduction of the effects of oxidative stress and mitochondrial dysfunction, appear to be a promising possibility for developing new therapies for a complex and multifactorial disease such as heart failure.

Metformin: A Review of Potential Mechanism and Therapeutic Utility Beyond Diabetes

Metformin has been designated as one of the most crucial first-line therapeutic agents in the management of type 2 diabetes mellitus. Primarily being an antihyperglycemic agent, metformin also has a plethora of pleiotropic effects on various systems and processes. It acts majorly by activating AMPK (Adenosine Monophosphate-Activated Protein Kinase) in the cells and reducing glucose output from the liver. It also decreases advanced glycation end products and reactive oxygen species production in the endothelium apart from regulating the glucose and lipid metabolism in the cardiomyocytes, hence minimizing the cardiovascular risks. Its anticancer, antiproliferative and apoptosis-inducing effects on malignant cells might prove instrumental in the malignancy of organs like the breast, kidney, brain, ovary, lung, and endometrium. Preclinical studies have also shown some evidence of metformin's neuroprotective role in Parkinson's disease, Alzheimer's disease, multiple sclerosis and Huntington's disease. Metformin exerts its pleiotropic effects through varied pathways of intracellular signalling and exact mechanism in the majority of them remains yet to be clearly defined. This article has extensively reviewed the therapeutic benefits of metformin and the details of its mechanism for a molecule of boon in various conditions like diabetes, prediabetes, obesity, polycystic ovarian disease, metabolic derangement in HIV, various cancers and aging.

Positive regulation of endothelial Tom70 by metformin as a new mechanism against cardiac microvascular injury in diabetes

Microvascular protection is the main mechanism of metformin against diabetic complications. Cardiac microvascular endothelial cells (CMECs) are the basic component of cardiac microvessels, and they suffer from oxidative stress and mitochondrial dysfunction under type 2 diabetes mellitus (T2DM). Translocase of the outer mitochondrial membrane 70 (Tom70) improves mitochondrial dysfunction, but its role in the hearts of T2DM patients remains unclear. The purpose of this study was to demonstrate the protective effect of metformin on diabetic cardiac microvascular injury and to identify the role of Tom70 in this effect. T2DM mice were established by multiple intraperitoneal injections of low-dose streptozotocin and 12-week high-fat feeding. CMECs were isolated and cultured with normal glucose (NG), high glucose (HG), and HG plus high fat (HG-HF) media. The results indicated that long-term metformin treatment partly reversed cardiovascular complication and mitigated cardiac microvascular injury in T2DM. In addition, exposure to HG-HF led to CMEC damage, aggravated oxidative stress, aggravated mitochondrial dysfunction, and reduced mitochondrial Tom70 expression, whereas upregulation of Tom70 significantly ameliorated these injuries. Furthermore, metformin treatment promoted Tom70 expression and effectively reversed CMEC injury induced by HG-HF. However, all of these effects were interrupted after Tom70 was knocked down. In conclusion, T2DM damages microvascular integrity by activating a cycle of decreased Tom70 expression, mitochondrial dysfunction, and reactive oxygen species (ROS) overload in CMECs. However, metformin suppresses oxidative stress, relieves mitochondrial dysfunction, and promotes the expression of Tom70, ultimately ameliorating diabetic microvascular injury and heart complications.

Metformin and the heart: Update on mechanisms of cardiovascular protection with special reference to comorbid type 2 diabetes and heart failure

Metformin has been in clinical use for the management of type 2 diabetes for more than 60 years and is supported by a vast database of clinical experience: this includes evidence for cardioprotection from randomised trials and real-world studies. Recently, the position of metformin as first choice glucose-lowering agent has been supplanted to some extent by the emergence of newer classes of antidiabetic therapy, namely the sodium-glucose co-transporter-2 (SGLT2) inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists. These agents have benefitted through support from large cardiovascular outcomes trials with more modern trial designs than earlier studies conducted to assess metformin. Nevertheless, clinical research on metformin continues to further assess its many potentially advantageous effects. Here, we review the evidence for improved cardiovascular outcomes with metformin in the context of the current era of diabetes outcomes trials. Focus is directed towards the potentially cardioprotective actions of metformin in patients with type 2 diabetes and heart failure (HF), now recognised as the most common complication of diabetes.

CAQK modification enhances the targeted accumulation of metformin-loaded nanoparticles in rats with spinal cord injury

Spinal cord injury (SCI) often causes neuronal membrane rupture and immediate death of neurons, followed by complicated secondary injuries. Treatment of SCI still remains a major challenge in clinical practice; thus, a great advance is urgently needed in this field. Metformin (MET) has anti-oxidant, anti-inflammatory, anti-apoptotic and neuroprotective properties, which may exert a potential therapeutic effect on SCI. In this study, we established a zein-based MET-loaded nanodrug system (CAQK-MET-NPs) for the targeted drug delivery for SCI. The results showed that MET could be effectively encapsulated into zein to obtain the zein-based spherical nanoparticles. Pharmacokinetic analysis indicated that CAQK-MET-NPs exhibited sustained-release and long-term therapeutic effects. The fluorescence imaging and tissue distribution experiments showed that CAQK-MET-NPs could efficiently accumulate at the lesion site of SCI rats. In conclusion, CAQK-MET-NPs may be a promising nanodrug for the treatment of SCI.

The role of metabolic syndrome in sudden cardiac death risk: Recent evidence and future directions

Metabolic syndrome (MetS) is a frequent condition whose deleterious effects on the cardiovascular system are often underestimated. MetS is nowadays considered a real pandemic with an estimated prevalence of 25% in general population. Individuals with MetS are at high risk of sudden cardiac death (SCD) as this condition accounts for 50% of all cardiac deaths in such a population. Of interest, recent studies demonstrated that individuals with MetS show 70% increased risk of SCD even without previous history of coronary heart disease (CHD). However, little is known about the interplay between the two conditions. MetS is a complex disease determined by genetic predisposition, unhealthy lifestyle and ageing with deleterious effects on different organs. MetS components trigger a systemic chronic low-grade pro-inflammatory state, associated with excess of sympathetic activity, cardiac hypertrophy, arrhythmias and atherosclerosis. Thus, MetS has an important burden on the cardiovascular system as demonstrated by both preclinical and clinical evidence. The aim of this review is to summarize recent evidence concerning the association between MetS and SCD, showing possible common aetiological processes, and to indicate prospective for future studies and therapeutic targets.

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.

Metformin Prevents Low-dose Isoproterenol-induced Cardiac Dilatation and Systolic Dysfunction in Male Sprague-Dawley Rats

ABSTRACT

Myocardial metabolic abnormalities are well recognized alterations in chronic heart failure, effects that may contribute to progressive cardiac dysfunction. However, whether metabolic alterations in-part mediate their deleterious effects by modifying the chronic impact of excess low dose sympathetic stimulation on cardiac chamber dilatation, is uncertain. We therefore aimed to determine the effect of metformin administration on cardiac function and mitochondrial architectural changes in a rat model of chronic sympathetic-induced left ventricular (LV) remodeling and systolic dysfunction (daily subcutaneous isoproterenol [ISO] injection at a low-dose of 0.02 mg/kg for 7 months). Echocardiography was used to assess in vivo LV dimensions and function, and mitochondrial and myofibril arrangement was assessed using transmission electron microscopy. 7 months of low-dose ISO administration increased left ventricular diastolic diameter (in mm) (CONT: 7.29±0.19 vs. ISO: 8.76±0.21; p=0.001), an effect that was attenuated by metformin (ISO+MET: 7.63±0.29 vs ISO: p=0.001) administration. Similarly, ISO increased LV end systolic diameter (CONT: 4.43±0.16 vs ISO: 5.49±0.16: p<0.0001) an effect prevented by metformin (ISO+MET: 4.04±0.25 vs. ISO: p<0.0001). Moreover, chronic ISO administration reduced LV endocardial fractional shortening (p=0.0001), midwall fractional shortening (p=0.0001) and ejection fraction (p=0.0001), effects similarly prevented by metformin administration. Furthermore, changes in mitochondrial arrangement and relative mitochondrial area (CONT: 37.7±2.2 vs. ISO: 28.1±2.9; p=0.05) were produced by ISO administration, effects prevented by metformin. In conclusion, metformin offers cardiac protection against chronic sympathetic-induced LV dilatation and systolic dysfunction. These data support a role for myocardial metabolic changes in mediating LV dilatation and LV dysfunction produced by chronic neurohumoral activation in cardiac disease.

AMPK protects against alcohol-induced liver injury through UQCRC2 to up-regulate mitophagy

Recent reports indicated that mitophagy protects against alcohol-induced liver injury, which helps remove damaged mitochondria to reduce the accumulation of reactive oxygen species (ROS). AMP-activated protein kinase (AMPK) has been recently used in ALD (alcoholic liver disease) and mitochondrial dysfunction research. However, the inner mechanism, whether AMPK can regulate mitophagy in ALD, remains unknown. Here we found that AMPK can significantly reduce alcohol-induced liver injury and enhances hepatocytes' mitophagy level. Next, we identified that AMPK rescued alcohol-induced low expression of UQCRC2 (ubiquinol-cytochrome c reductase core protein 2). Interestingly, UQCRC2 knockdown (KD) treatment causes impaired mitophagy, whereas UQCRC2 overexpression (OE) can significantly increase mitophagy to attenuate liver injury. Also, we identified that AMPK indirectly upregulates UQCRC2 protein level, and RNA-seq, chromatin immunoprecipitation (ChIP) assay, bioinformatics, and luciferase assays helped us understand that AMPK enhanced UQCRC2 gene transcription through activating NFE2L2/NRF2 (nuclear factor, erythroid 2 like 2). Our results demonstrate that AMPK regulating UQCRC2 is a significant mitochondrial event in mitophagy. It identifies a new signaling axis, AMPK-NFE2L2-UQCRC2, in the regulation of mitophagy levels in the liver, suggesting a possible therapeutic strategy to treat ALD.Abbreviations: AAV: AENO-associated virus; ALD: alcoholic liver disease; AMPK: AMP-activated protein kinase; BUN: blood urea nitrogen; H&E: hematoxylin and eosin; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; ChIP: chromatin immunoprecipitation assay; CO-IP: co-immunoprecipitation; COPD: chronic obstructive pulmonary disease; EM: electron microscope; GOT1/AST: glutamic-oxaloacetic transaminase 1; GPT/ALT: glutamic-pyruvic transaminase; IF: immunofluorescence; IHC: immunohistochemistry; KD: knockdown; MAP1LC3/LC3: microtubule associated protein 1 light chain protein 3; MTDR: MitoTracker Deep Red; NFE2L2/NRF2: nuclear factor, erythroid 2 like 2; mtDNA: mitochondrial DNA; MTRC: MitoTracker Red CMXRos; OCR: Oxygen consumption rate; OE: overexpress; PINK1: PTEN induced kinase 1; qRT-PCR: quantitative real-time PCR; ROS: reactive oxygen species; SD: standard deviation; SOD2: superoxide dismutase 2; UQCRC2: ubiquinol-cytochrome c reductase core protein 2; WB: western blot; ΔΨ: mitochondrial membrane potential.

Fibrosis of the diabetic heart: Clinical significance, molecular mechanisms, and therapeutic opportunities

In patients with diabetes, myocardial fibrosis may contribute to the pathogenesis of heart failure and arrhythmogenesis, increasing ventricular stiffness and delaying conduction. Diabetic myocardial fibrosis involves effects of hyperglycemia, lipotoxicity and insulin resistance on cardiac fibroblasts, directly resulting in increased matrix secretion, and activation of paracrine signaling in cardiomyocytes, immune and vascular cells, that release fibroblast-activating mediators. Neurohumoral pathways, cytokines, growth factors, oxidative stress, advanced glycation end-products (AGEs), and matricellular proteins have been implicated in diabetic fibrosis; however, the molecular links between the metabolic perturbations and activation of a fibrogenic program remain poorly understood. Although existing therapies using glucose- and lipid-lowering agents and neurohumoral inhibition may act in part by attenuating myocardial collagen deposition, specific therapies targeting the fibrotic response are lacking. This review manuscript discusses the clinical significance, molecular mechanisms and cell biology of diabetic cardiac fibrosis and proposes therapeutic targets that may attenuate the fibrotic response, preventing heart failure progression.

The Hormetic Effect of Metformin: "Less Is More"?

Metformin (MTF) is the first-line therapy for type 2 diabetes (T2DM). The euglycemic effect of MTF is due to the inhibition of hepatic glucose production. Literature reports that the principal molecular mechanism of MTF is the activation of 5′-AMP-activated protein kinase (AMPK) due to the decrement of ATP intracellular content consequent to the inhibition of Complex I, although this effect is obtained only at millimolar concentrations. Conversely, micromolar MTF seems to activate the mitochondrial electron transport chain, increasing ATP production and limiting oxidative stress. This evidence sustains the idea that MTF exerts a hormetic effect based on its concentration in the target tissue. Therefore, in this review we describe the effects of MTF on T2DM on the principal target organs, such as liver, gut, adipose tissue, endothelium, heart, and skeletal muscle. In particular, data indicate that all organs, except the gut, accumulate MTF in the micromolar range when administered in therapeutic doses, unmasking molecular mechanisms that do not depend on Complex I inhibition.

Normalizing glucose levels reconfigures the mammary tumor immune and metabolic microenvironment and decreases metastatic seeding

Obesity and diabetes cumulatively create a distinct systemic metabolic pathophysiological syndrome that predisposes patients to several diseases including breast cancer. Moreover, diabetic and obese women with breast cancer show a significant increase in mortality compared to non-obese and/or non-diabetic women. We hypothesized that these metabolic conditions incite an aggressive tumor phenotype by way of impacting tumor cell-autonomous and tumor cell non-autonomous events. In this study, we established a type 2 diabetic mouse model of triple-negative mammary carcinoma and investigated the effect of a glucose lowering therapy, metformin, on the overall tumor characteristics and immune/metabolic microenvironment. Diabetic mice exhibited larger mammary tumors that had increased adiposity with high levels of O-GlcNAc protein post-translational modification. These tumors also presented with a distinct stromal profile characterized by altered collagen architecture, increased infiltration by tumor-permissive M2 macrophages, and early metastatic seeding compared to non-diabetic/lean mice. Metformin treatment of the diabetic/obese mice effectively normalized glucose levels, reconfigured the mammary tumor milieu, and decreased metastatic seeding. Our results highlight the impact of two metabolic complications of obesity and diabetes on tumor cell attributes and showcase metformin's ability to revert tumor cell and stromal changes induced by an obese and diabetic host environment.

Metformin Reduces Vascular Assembly in High Glucose-Treated Human Microvascular Endothelial Cells in An AMPK-Independent Manner

Objective

The aim is to examine the effect of metformin in human microvascular endothelial cells exposed to high glucose (HG) concentration and compare them with the effects of other 5' adenosine monophosphate-activated protein kinase (AMPK) modulators under the same condition.

Materials and Methods

In this experimental study, human microvascular endothelial cells (HMECs) were treated with 15 mM metformin, 1 mM 5-aminoimidazol-4-carboxamideribonucleotide (AICAR) and 10 mM compound C in the presence of 20 mM glucose (hyperglycemic condition). Migration, invasion and proliferation were evaluated as well as the capillary-like structures formation. Moreover, the expression of angiogenic genes was assessed.

Results

Metformin significantly inhibited vessel formation and migration, although it did not change HMECs proliferation and invasion. In addition, metformin significantly reduced collagen formation as evidenced by histological staining. Concomitantly, expression of several genes implicated in angiogenesis and fibrosis, namely TGFß2, VEGFR2, ALK1, JAG1, TIMP2, SMAD5, SMAD6 and SMAD7, was slightly upregulated. Immunostaining for proteins involved in ALK5 receptor signaling, the alternative TGFß signaling pathway, revealed significant differences in SMAD2/3 expression.

Conclusion

Our data showed that metformin prevents vessel assembly in HMECs, probably through an AMPK- independent mechanism. Understanding the molecular mechanisms by which this pharmacological agent affects endothelial dysfunction is of paramount importance and paves the way to its particular use in preventing development of diabetic retinopathy and nephropathy, two processes where angiogenesis is exacerbated.

Novel Targets of Metformin in Cardioprotection: Beyond the Effects Mediated by AMPK

Ischemic heart disease is the main cause of death globally. In the heart, the ischemia/reperfusion injury gives rise to a complex cascade of molecular signals, called cardiac remodeling, which generates harmful consequences for the contractile function of the myocardium and consequently heart failure. Metformin is the drug of choice in the treatment of type 2 diabetes mellitus. Clinical data suggest the direct effects of this drug on cardiac metabolism and studies in animal models showed that metformin activates the classical pathway of AMP-activated protein kinase (AMPK), generating cardioprotective effects during cardiac remodeling, hypertrophy and fibrosis. Furthermore, new studies have emerged about other targets of metformin with a potential role in cardioprotection. This state of the art review shows the available scientific evidence of the cardioprotective potential of metformin and its possible effects beyond AMPK. Targeting of autophagy, mitochondrial function and miRNAs are also explored as cardioprotective approaches along with a therapeutic potential. Further advances related to the biological effects of metformin and cardioprotective approaches may provide new therapies to protect the heart and prevent cardiac remodeling and heart failure.

Cardiometabolism as an Interlocking Puzzle between the Healthy and Diseased Heart: New Frontiers in Therapeutic Applications

Cardiac metabolism represents a crucial and essential connecting bridge between the healthy and diseased heart. The cardiac muscle, which may be considered an omnivore organ with regard to the energy substrate utilization, under physiological conditions mainly draws energy by fatty acids oxidation. Within cardiomyocytes and their mitochondria, through well-concerted enzymatic reactions, substrates converge on the production of ATP, the basic chemical energy that cardiac muscle converts into mechanical energy, i.e., contraction. When a perturbation of homeostasis occurs, such as an ischemic event, the heart is forced to switch its fatty acid-based metabolism to the carbohydrate utilization as a protective mechanism that allows the maintenance of its key role within the whole organism. Consequently, the flexibility of the cardiac metabolic networks deeply influences the ability of the heart to respond, by adapting to pathophysiological changes. The aim of the present review is to summarize the main metabolic changes detectable in the heart under acute and chronic cardiac pathologies, analyzing possible therapeutic targets to be used. On this basis, cardiometabolism can be described as a crucial mechanism in keeping the physiological structure and function of the heart; furthermore, it can be considered a promising goal for future pharmacological agents able to appropriately modulate the rate-limiting steps of heart metabolic pathways.

Differential epigenetic factors in the prediction of cardiovascular risk in diabetic patients

Hyperglycaemia can strongly alter the epigenetic signatures in many types of human vascular cells providing persistent perturbations of protein–protein interactions both in micro- and macro-domains. The establishment of these epigenetic changes may precede cardiovascular (CV) complications and help us to predict vascular lesions in diabetic patients. Importantly, these epigenetic marks may be transmitted across several generations (transgenerational effect) and increase the individual risk of disease. Aberrant DNA methylation and imbalance of histone modifications, mainly acetylation and methylation of H3, represent key determinants of vascular lesions and, thus, putative useful biomarkers for prevention and diagnosis of CV risk in diabetics. Moreover, a differential expression of some micro-RNAs (miRNAs), mainly miR-126, may be a useful prognostic biomarker for atherosclerosis development in asymptomatic subjects. Recently, also environmental-induced chemical perturbations in mRNA (epitranscriptome), mainly the N⁶-methyladenosine, have been associated with obesity and diabetes. Importantly, reversal of epigenetic changes by modulation of lifestyle and use of metformin, statins, fenofibrate, and apabetalone may offer useful therapeutic options to prevent or delay CV events in diabetics increasing the opportunity for personalized therapy. Network medicine is a promising molecular-bioinformatic approach to identify the signalling pathways underlying the pathogenesis of CV lesions in diabetic patients. Moreover, machine learning tools combined with tomography are advancing the individualized assessment of CV risk in these patients. We remark the need for combining epigenetics and advanced bioinformatic platforms to improve the prediction of vascular lesions in diabetics increasing the opportunity for CV precision medicine.

Metformin in Pulmonary Hypertension in Left Heart Disease

Metformin is ubiquitously used in the management of Type II Diabetes Mellitus (DMII). Over the years, our growing knowledge of its therapeutic potential has broadened its use to the treatment of infertility in polycystic ovarian syndrome, gestational diabetes, and even obesity. Recently, it has been suggested as a novel therapy in cardiovascular disease (CVD). Given that CVD is the leading cause of death in patients with DMII, with ~ 75% dying from a cardiovascular event, the intersection of DMII and CVD provides a unique therapeutic target. In particular, pulmonary hypertension (PH) related to CVD (Group II PH) may be an optimal target for metformin therapy. The objective of this review article is to provide an overview of the pathophysiology of PH related to left heart disease (PH-LHD), outline the proposed pathophysiologic mechanism of insulin resistance in heart failure and PH-LHD, and evaluate the role metformin may have in heart failure and PH-LHD.

Metformin Lowers Body Weight But Fails to Increase Insulin Sensitivity in Chronic Heart Failure Patients without Diabetes: a Randomized, Double-Blind, Placebo-Controlled Study

PURPOSE

The glucose-lowering drug metformin has recently been shown to reduce myocardial oxygen consumption and increase myocardial efficiency in chronic heart failure (HF) patients without diabetes. However, it remains to be established whether these beneficial myocardial effects are associated with metformin-induced alterations in whole-body insulin sensitivity and substrate metabolism.

METHODS

Eighteen HF patients with reduced ejection fraction and without diabetes (median age, 65 (interquartile range 55-68); ejection fraction 39 ± 6%; HbA1c 5.5 to 6.4%) were randomized to receive metformin (n = 10) or placebo (n = 8) for 3 months. We studied the effects of metformin on whole-body insulin sensitivity using a two-step hyperinsulinemic euglycemic clamp incorporating isotope-labeled tracers of glucose, palmitate, and urea. Substrate metabolism and skeletal muscle mitochondrial respiratory capacity were determined by indirect calorimetry and high-resolution respirometry, and body composition was assessed by bioelectrical impedance analysis. The primary outcome measure was change in insulin sensitivity.

RESULTS

Compared with placebo, metformin treatment lowered mean glycated hemoglobin levels (absolute mean difference, - 0.2%; 95% CI - 0.3 to 0.0; p = 0.03), reduced body weight (- 2.8 kg; 95% CI - 5.0 to - 0.6; p = 0.02), and increased fasting glucagon levels (3.2 pmol L^-1; 95% CI 0.4 to 6.0; p = 0.03). No changes were observed in whole-body insulin sensitivity, endogenous glucose production, and peripheral glucose disposal or oxidation with metformin. Equally, resting energy expenditure, lipid and urea turnover, and skeletal muscle mitochondrial respiratory capacity remained unaltered.

CONCLUSION

Increased myocardial efficiency during metformin treatment is not mediated through improvements in insulin action in HF patients without diabetes.

CLINICAL TRIAL REGISTRATION

URL: https://clinicaltrials.gov . Unique identifier: NCT02810132. Date of registration: June 22, 2016.

Targeting perivascular and epicardial adipose tissue inflammation: therapeutic opportunities for cardiovascular disease

Major shifts in human lifestyle and dietary habits toward sedentary behavior and refined food intake triggered steep increase in the incidence of metabolic disorders including obesity and Type 2 diabetes. Patients with metabolic disease are at a high risk of cardiovascular complications ranging from microvascular dysfunction to cardiometabolic syndromes including heart failure. Despite significant advances in the standards of care for obese and diabetic patients, current therapeutic approaches are not always successful in averting the accompanying cardiovascular deterioration. There is a strong relationship between adipose inflammation seen in metabolic disorders and detrimental changes in cardiovascular structure and function. The particular importance of epicardial and perivascular adipose pools emerged as main modulators of the physiology or pathology of heart and blood vessels. Here, we review the peculiarities of these two fat depots in terms of their origin, function, and pathological changes during metabolic deterioration. We highlight the rationale for pharmacological targeting of the perivascular and epicardial adipose tissue or associated signaling pathways as potential disease modifying approaches in cardiometabolic syndromes.

Metformin ameliorates cardiac conduction delay by regulating microRNA-1 in mice

Cardiac conduction delay may occur as a common complication of several cardiac diseases. A few therapies and drugs have a good effect on cardiac conduction delay. Metformin (Met) has a protective effect on the heart. This study's aim was to investigate whether Met could ameliorate cardiac conduction delay and its potential mechanism. Cardiac-specific microRNA-1 (miR-1) transgenic (TG) and myocardial infarction (MI) mouse models were used. Mice were administered with Met in an intragastric manner. We found that the expression of miR-1 was significantly up-regulated in H₂O₂ treated cardiomyocytes as well as in TG and MI mice. The protein levels of inwardly rectifying potassium channel 2.1 (Kir2.1) and Connexin43 (CX43) were down-regulated both in cardiomyocytes treated with H₂O₂ as well as cardiac tissues of TG and MI mice, as compared to their controls. Furthermore, the PR and QT intervals were prolonged, action potential duration (APD) was delayed, and conduction velocity (CV) was reduced, with upregulation of miR-1 in the hearts. In the meanwhile, intercalated disc injuries were found in the hearts of MI mice. Interestingly, Met can noticeably inhibit miR-1 upregulation and attenuate the changes mentioned above. Taken together, this suggested that Met could play an important role in improving cardiac conduction delay through inhibition of miR-1 expression. Our study proposes that Met is a potential candidate for the treatment of cardiac conduction delay and provides a new idea of treating arrhythmia with a drug.

Histomorphological, VEGF and TGF-β immunoexpression changes in the diabetic rats' ovary and the potential amelioration following treatment with metformin and insulin

Diabetes mellitus (DM) affects the ovary by reducing the number and diameters of ovarian follicles and increasing atretic follicles. Follicular growth and diameters depend on VEGF production. Hyperglycemia causes ovarian stromal and follicular degeneration then fibrosis by activating TGF-β. Insulin and metformin promote development of ovarian follicles and reduce atretic follicles. Therefore, the present study investigates the ovarian VEGF and TGF-β immune-expression and its variations in diabetic, insulin and metformin-treated rats. Forty adult female albino rats were divided equally into four groups: control, diabetic (STZ-induced diabetes), diabetic metformin-treated group (100 mg/kg/day orally/eight weeks) and diabetic insulin-treated group (5 U insulin /day). Ovarian sections were stained with hematoxylin and eosin, Masson's trichrome, immunohistochemistry for VEGF and TGF-β. The diabetic group showed noticeable atrophic and degenerative changes in cortex and medulla as well as increased density and distribution of the collagenous fibers. The number and diameter of primary, secondary and tertiary follicles were decreased. However, the number of atretic follicles and corpus luteum was increased. Significant decrease in the surface area percentage of VEGF immuno-expression and significant increase in TGF-β immuno-expression surface area percentage were detected. By treating animals with metformin and insulin, there was restoration of the ovarian histological structure more or less as in control. DM negatively affects the histological and morphometric parameters of ovaries. Furthermore, insulin showed more beneficial effects than metformin in hindering these complications by modifying the expression of VEGF and TGF-β.

Metformin Improves Cardiac Metabolism and Function, and Prevents Left Ventricular Hypertrophy in Spontaneously Hypertensive Rats

Background

In spontaneously hypertensive rats (SHR) we observed profound myocardial metabolic changes during early hypertension before development of cardiac dysfunction and left ventricular hypertrophy. In this study, we evaluated whether metformin improved myocardial metabolic abnormalities and simultaneously prevented contractile dysfunction and left ventricular hypertrophy in SHR.

Methods and Results

SHR and control Wistar–Kyoto rats were treated with metformin from 2 to 5 months of age, when SHR hearts exhibit metabolic abnormalities and develop cardiac dysfunction and left ventricular hypertrophy. We evaluated the effect of metformin on myocardial glucose uptake rates with dynamic 2‐[¹⁸F] fluoro‐2‐deoxy‐D‐glucose positron emission tomography. We used cardiac MRI in vivo to assess the effect of metformin on ejection fraction, left ventricular mass, and end‐diastolic wall thickness, and also analyzed metabolites, AMP‐activated protein kinase and mammalian target‐of‐rapamycin activities, and mean arterial blood pressure. Metformin‐treated SHR had lower mean arterial blood pressure but remained hypertensive. Cardiac glucose uptake rates, left ventricular mass/tibia length, wall thickness, and circulating free fatty acid levels decreased to normal, and ejection fraction improved in treated SHR. Hearts of treated SHR exhibited increased AMP‐activated protein kinase phosphorylation and reduced mammalian target‐of‐rapamycin activity. Cardiac metabolite profiling demonstrated that metformin decreased fatty acyl carnitines and markers of oxidative stress in SHR.

Conclusions

Metformin reduced blood pressure, normalized myocardial glucose uptake, prevented left ventricular hypertrophy, and improved cardiac function in SHR. Metformin may exert its effects by normalizing myocardial AMPK and mammalian target‐of‐rapamycin activities, improving fatty acid oxidation, and reducing oxidative stress. Thus, metformin may be a new treatment to prevent or ameliorate chronic hypertension–induced left ventricular hypertrophy.

Metformin use and cardiovascular outcomes after acute myocardial infarction in patients with type 2 diabetes: a cohort study

Background

The use of metformin after acute myocardial infarction (AMI) has been associated with reduced mortality in people with type 2 diabetes mellitus (T2DM). However, it is not known if it is acutely cardioprotective in patients taking metformin at the time of AMI. We compared patient outcomes according to metformin status at the time of admission for fatal and non-fatal AMI in a large cohort of patients in England.

Methods

This study used linked data from primary care, hospital admissions and death registry from 4.7 million inhabitants in England, as part of the CALIBER resource. The primary endpoint was a composite of acute myocardial infarction requiring hospitalisation, stroke and cardiovascular death. The secondary endpoints were heart failure (HF) hospitalisation and all-cause mortality.

Results

4,030 patients with T2DM and incident AMI recorded between January 1998 and October 2010 were included. At AMI admission, 63.9% of patients were receiving metformin and 36.1% another oral hypoglycaemic drug. Median follow-up was 343 (IQR: 1–1436) days. Adjusted analyses showed an increased hazard of the composite endpoint in metformin users compared to non-users (HR 1.09 [1.01–1.19]), but not of the secondary endpoints. The higher risk of the composite endpoint in metformin users was only observed in people taking metformin at AMI admission, whereas metformin use post-AMI was associated with a reduction in risk of all-cause mortality (0.76 [0.62–0.93], P = 0.009).

Conclusions

Our study suggests that metformin use at the time of first AMI is associated with increased risk of cardiovascular disease and death in patients with T2DM, while its use post-AMI might be beneficial. Further investigation in well-designed randomised controlled trials is indicated, especially in view of emerging evidence of cardioprotection from sodium-glucose co-transporter-2 (SGLT2) inhibitors.

From Molecular Mechanisms to Clinical Management of Antineoplastic Drug-Induced Cardiovascular Toxicity: A Translational Overview

Significance: Antineoplastic therapies have significantly improved the prognosis of oncology patients. However, these treatments can bring to a higher incidence of side-effects, including the worrying cardiovascular toxicity (CTX). Recent Advances: Substantial evidence indicates multiple mechanisms of CTX, with redox mechanisms playing a key role. Recent data singled out mitochondria as key targets for antineoplastic drug-induced CTX; understanding the underlying mechanisms is, therefore, crucial for effective cardioprotection, without compromising the efficacy of anti-cancer treatments. Critical Issues: CTX can occur within a few days or many years after treatment. Type I CTX is associated with irreversible cardiac cell injury, and it is typically caused by anthracyclines and traditional chemotherapeutics. Type II CTX is generally caused by novel biologics and more targeted drugs, and it is associated with reversible myocardial dysfunction. Therefore, patients undergoing anti-cancer treatments should be closely monitored, and patients at risk of CTX should be identified before beginning treatment to reduce CTX-related morbidity. Future Directions: Genetic profiling of clinical risk factors and an integrated approach using molecular, imaging, and clinical data may allow the recognition of patients who are at a high risk of developing chemotherapy-related CTX, and it may suggest methodologies to limit damage in a wider range of patients. The involvement of redox mechanisms in cancer biology and anticancer treatments is a very active field of research. Further investigations will be necessary to uncover the hallmarks of cancer from a redox perspective and to develop more efficacious antineoplastic therapies that also spare the cardiovascular system.

Metformin Inhibits the Expression of Biomarkers of Fibrosis of EPCs In Vitro

Endothelial progenitor cells (EPCs) are a group of circulating cells with important functions in vascular repair and treatment of cardiovascular diseases. However, in patients with atrial fibrillation (AF), the number and function of EPCs reportedly are decreased. TGF-β is highly expressed in AF patients. In this study, we examined the effect of TGF-β1 on EPCs and the therapeutic outcome of metformin treatment on TGF-β1-induced EPCs. EPCs were induced with TGF-β1 at different concentrations (5 ng/ml, 10 ng/ml, and 20 ng/ml) for 48 h followed by western blot, qPCR, and immunofluorescence analyses to investigate changes in the levels of the fibrosis-related proteins, α-SMA, Col I, Col III, CTGF, and MMP-1. Live-dead cell staining was used to evaluate cell apoptosis. Compared with the control, TGF-β1 treatment significantly (p < 0.05) enhanced the levels of α-SMA, Col I, Col III, CTGF, and MMP-1 in a dose-dependent manner. The most effective concentration of TGF-β1 (20 ng/ml) was then used to induce fibrosis biomarker expression in EPCs, followed by treatment with metformin at different concentrations (0.5, 1, and 2 mmol/l). Metformin treatment suppressed TGF-β-induced expression of all above factors, with the effect at 2 mmol/l being significant (p < 0.05). Live-dead cell staining showed no difference among the control, TGF-β1-treated, and metformin-treated groups. In conclusion, our study showed that TGF-β1 induces the expression of fibrosis biomarkers in EPCs, which is attenuated by treatment with metformin. Thus, metformin may have therapeutic potential for improving EPC function in cardiovascular diseases.

miR-26a Limits Muscle Wasting and Cardiac Fibrosis through Exosome-Mediated microRNA Transfer in Chronic Kidney Disease

Uremic cardiomyopathy and muscle atrophy are associated with insulin resistance and contribute to chronic kidney disease (CKD)-induced morbidity and mortality. We hypothesized that restoration of miR-26a levels would enhance exosome-mediated microRNA transfer to improve muscle wasting and cardiomyopathy that occur in CKD.

Methods: Using next generation sequencing and qPCR, we found that CKD mice had a decreased level of miR-26a in heart and skeletal muscle. We engineered an exosome vector that contained Lamp2b, an exosomal membrane protein gene fused with a muscle-specific surface peptide that targets muscle delivery. We transfected this vector into muscle satellite cells and then transduced these cells with adenovirus that expresses miR-26a to produce exosomes encapsulated miR-26a (Exo/miR-26a). Exo/miR-26a was injected once per week for 8 weeks into the tibialis anterior (TA) muscle of 5/6 nephrectomized CKD mice.

Results: Treatment with Exo/miR-26a resulted in increased expression of miR-26a in skeletal muscle and heart. Overexpression of miR-26a increased the skeletal muscle cross-sectional area, decreased the upregulation of FBXO32/atrogin-1 and TRIM63/MuRF1 and depressed cardiac fibrosis lesions. In the hearts of CKD mice, FoxO1 was activated, and connective tissue growth factor, fibronectin and collagen type I alpha 1 were increased. These responses were blunted by injection of Exo/miR-26a. Echocardiograms showed that cardiac function was improved in CKD mice treated with Exo/miR-26a.

Conclusion: Overexpression of miR-26a in muscle prevented CKD-induced muscle wasting and attenuated cardiomyopathy via exosome-mediated miR-26a transfer. These results suggest possible therapeutic strategies for using exosome delivery of miR-26a to treat complications of CKD.

Metformin alleviates hyperglycemia-induced endothelial impairment by downregulating autophagy via the Hedgehog pathway

Studies regarding macroautophagic/autophagic regulation in endothelial cells (ECs) under diabetic conditions are very limited. Clinical evidence establishes an endothelial protective effect of metformin, but the underlying mechanisms remain unclear. We aimed to investigate whether metformin exerts its protective role against hyperglycemia-induced endothelial impairment through the autophagy machinery. db/db mice were treated with intravitreal metformin injections. Human umbilical vein endothelial cells (HUVECs) were cultured either in normal glucose (NG, 5.5 mM) or high glucose (HG, 33 mM) medium in the presence or absence of metformin for 72 h. We observed an obvious inhibition of hyperglycemia-triggered autophagosome synthesis in both the diabetic retinal vasculature and cultured HUVECs by metformin, along with restoration of hyperglycemia-impaired Hedgehog (Hh) pathway activity. Specifically, deletion of ATG7 in retinal vascular ECs of db/db mice and cultured HUVECs indicated a detrimental role of autophagy in hyperglycemia-induced endothelial dysfunction. Pretreatment with GANT61, a Hh pathway inhibitor, abolished the metformin-mediated downregulation of autophagy and endothelial protective action. Furthermore, GLI-family (transcription factors of the Hh pathway) knockdown in HUVECs and retinal vasculature revealed that downregulation of hyperglycemia-activated autophagy by the metformin-mediated Hh pathway activation was GLI1 dependent. Mechanistically, GLI1 knockdown-triggered autophagy was related to upregulation of BNIP3, which subsequently disrupted the association of BECN1/Beclin 1 and BCL2. The role of BNIP3 in BECN1 dissociation from BCL2 was further confirmed by BNIP3 overexpression or BNIP3 RNAi. Taken together, the endothelial protective effect of metformin under hyperglycemia conditions could be partly attributed to its role in downregulating autophagy via Hh pathway activation. Abbreviations: 3-MA = 3-methyladenine; 8×GLI BS-FL = 8×GLI-binding site firefly luciferase; AAV = adeno-associated virus; AAV-Cdh5-sh-Atg7 = AAV vectors carrying shRNA against murine Atg7 under control of murine Cdh5 promoter; AAV-Cdh5-sh-Gli1 = AAV vectors carrying shRNA against murine Gli1 under control of murine Cdh5 promoter; AAV-Cdh5-Gli1 = AAV vectors carrying murine Gli1 cDNA under the control of murine Cdh5 core promoter; ACAC = acetyl-CoA carboxylase; Ad-BNIP3 = adenoviruses harboring human BNIP3`; Ad-GLI1 = adenoviruses harboring human GLI1; Ad-sh-ATG7 = adenoviruses harboring shRNA against human ATG7; Ad-sh-BNIP3 = adenoviruses harboring shRNA against human BNIP3; Ad-sh-GLI = adenoviruses harboring shRNA against human GLI; AGEs = advanced glycation end products; ATG = autophagy-related; atg7^flox/flox mice = mice bearing an Atg7^flox allele, in which exon 14 of the Atg7 gene is flanked by 2 loxP sites; BafA1 = bafilomycin A₁; BECN1 = beclin 1; CDH5/VE-cadherin = cadherin 5; CASP3 = caspase 3; CASP8 = caspase 8; CASP9 = caspase 9; ECs = endothelial cells; GAPDH = glyceraldehyde-3-phosphate dehydrogenase; GCL = ganglion cell layer; GFP-LC3B = green fluorescent protein labelled LC3B; HG = high glucose; Hh = Hedgehog; HHIP = hedgehog interacting protein; HUVECs = human umbilical vein endothelial cells; IB4 = isolectin B4; INL = inner nuclear layer; i.p. = intraperitoneal; MAP1LC3/LC3 = microtubule-associated protein 1 light chain 3; MAN = mannitol; MET = metformin; NG = normal glucose; ONL = outer nuclear layer; p-ACAC = phosphorylated acetyl-CoA carboxylase; PECAM1/CD31= platelet/endothelial cell adhesion molecule 1; PRKAA1/2 = protein kinase AMP-activated catalytic subunits alpha 1/2; p-PRKAA1/2 = phosphorylated PRKAA1/2; PTCH1 = patched 1; RAPA = rapamycin; RL = Renilla luciferase; SHH = sonic hedgehog; shRNA = short hairpin RNA; sh-PRKAA1/2 = short hairpin RNA against human PRKAA1/2; scrambled shRNA = the scrambled short hairpin RNA serves as a negative control for the target-specific short hairpin RNA, which has the same nucleotide composition as the input sequence and has no match with any mRNA of the selected organism database; SMO = smoothened, frizzled class receptor; sqRT-PCR = semi-quantitative RT-PCR; TEK/Tie2 = TEK receptor tyrosine kinase; Tek-Cre (+) mice = a mouse strain expressing Cre recombinase under the control of the promoter/enhancer of Tek, in a pan-endothelial fashion; TUNEL = terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling.

Metformin added to bosentan therapy in patients with pulmonary arterial hypertension associated with congenital heart defects: a pilot study

Pulmonary arterial hypertension (PAH) is a common complication of a congenital heart defect (CHD). Recent studies suggest metformin may be a potential drug to improve cardiac function in PAH. A pilot study was conducted to investigate the efficacy of short-term treatment with a combination regimen consisting of bosentan and metformin in PAH-CHD patients as compared with bosentan monotherapy in a prospective, randomised study.

Patients with PAH-CHD were randomised to receive bosentan (initially at 62.5 mg twice daily for 4 weeks and then 125 mg twice daily) for 3 months with or without the combination treatment of metformin (500 mg twice daily).

93 patients were enrolled to bosentan monotherapy (n=48) or bosentan/metformin combination treatment (n=45). After 3 months, both treatments significantly improved World Health Organization functional class, 6-min walking distance (6MWD), N-terminal pro-brain natriuretic peptide and right heart haemodynamic parameters. The improvements in 6MWD and pulmonary vascular resistance index were significantly greater in patients treated with combination therapy than in those who received monotherapy (mean±sd 95±136 versus 48±119 m (p=0.017) and −1.8±1.2 versus −1.2±1.3 Wood units per m² (p<0.001), respectively). Pulmonary endothelin (EDN)1 was significantly decreased after combination therapy (p=0.006). However, plasma EDN1 levels were not affected.

Combination therapy with bosentan and metformin in PAH-CHD patients provides improvements in important outcomes such as exercise capacity and pulmonary haemodynamics, compared with bosentan alone.

This study investigated, for the first time, the efficacy of a combination regimen consisting of bosentan and metformin in patients with pulmonary arterial hypertension associated with congenital heart defect as compared with bosentan monotherapyhttp://ow.ly/n4nJ30kT98d

Multiple hormonal and metabolic deficiency syndrome in chronic heart failure: rationale, design, and demographic characteristics of the T.O.S.CA. Registry

Recent evidence supports the concept that progression of chronic heart failure (CHF) depends upon an imbalance of catabolic forces over the anabolic drive. In this regard, multiple hormonal deficiency syndrome (MHDS) significantly has impacts upon CHF progression, and is associated with a worse clinical status and increased mortality. The T.O.S.CA. (Trattamento Ormonale nello Scompenso CArdiaco; Hormone Therapy in Heart Failure) Registry (clinicaltrial.gov = NCT02335801) tests the hypothesis that anabolic deficiencies reduce survival in a large population of mild-to-moderate CHF patients. The T.O.S.CA. Registry is a prospective multicenter observational study coordinated by "Federico II" University of Naples, and involves 19 centers situated throughout Italy. Thyroid hormones, insulin-like growth factor-1, total testosterone, dehydroepiandrosterone , and insulin are measured at baseline and every year for a patient-average follow-up of 3 years. Subjects with CHF are divided into two groups: patients with one or no anabolic deficiency, and patients with two or more anabolic deficiencies at baseline. The primary endpoint is the composite of all-cause mortality and cardiovascular hospitalization. Secondary endpoints include the composite of all-cause mortality and hospitalization, the composite of cardiovascular mortality and cardiovascular hospitalization, and change of VO₂ peak. Patient enrollment started in April 2013, and was completed in July 2017. Demographics and main clinical characteristics of enrolled patients are provided in this article. Detailed cross-sectional results will be available in late 2018. The T.O.S.CA. Registry represents the most robust prospective observational trial on MHDS in the field of CHF. The study findings will advance our knowledge with regard to the intimate mechanisms of CHF progression and hopefully pave the way for future randomized clinical trials of single or multiple hormonal replacement therapies in CHF.

Negative regulation of TGF-β by AMPK and implications in the treatment of associated disorders

Transforming growth factor beta (TGF-β) regulates a large number of biological processes, including proliferation, differentiation, immune response, and development. In addition, TGF-β plays important roles in some pathological processes, for instance, it is upregulated and activated in fibrosis and advanced cancer. Adenosine monophosphate-activated protein kinase (AMPK) acts as a fuel gauge that is activated when cells sense shortage of ATP and increase in AMP or AMP:ATP ratio. Activation of AMPK slows down anabolic processes and stimulates catabolic processes, leading to increased production of ATP. Furthermore, the functions of AMPK have been extended beyond energy homeostasis. In fact, AMPK has been shown to exert a tumor suppressive effect. Recent studies have demonstrated negative impacts of AMPK on TGF-β function. Therefore, in this review, we will discuss the differences in the biological functions of TGF-β and AMPK, and some pathological processes such as fibrosis, epithelial-mesenchymal transition (EMT) and cancer metastasis, as well as angiogenesis and heterotopic ossifications where TGF-β and AMPK exert opposite effects.

Cardioprotection by Metformin: Beneficial Effects Beyond Glucose Reduction

Metformin is a biguanide that is widely used as an insulin-sparing agent to treat diabetes. When compared with the general population, diabetics are twice as likely to die from fatal myocardial infarction and congestive heart failure (CHF). There has been a significant concern regarding the use of metformin in patients with CHF because of their higher tendency to develop lactic acidosis. However, large epidemiological trials have reported better cardiovascular prognosis with metformin compared to other glucose-lowering agents among diabetics. Additionally, metformin has reduced the risk of reinfarction and all-cause mortality in patients with coronary artery disease and CHF, respectively. The protection against cardiovascular diseases appears to be independent of the anti-hyperglycemic effects of metformin. These effects are mediated through an increase in 5' adenosine monophosphate-activated protein kinase (AMPK) phosphorylation and by increased phosphorylation of endothelial nitric oxide synthase (eNOS) in cardiomyocytes with an increased production of nitric oxide (NO). Metformin preconditions the heart against ischemia-reperfusion injury and may improve myocardial remodeling after an ischemic insult. The preponderance of evidence currently suggests that metformin is safe in patients with CHF, prompting the Food and Drug Administration to remove CHF as a contraindication from the package insert of all generic metformin preparations. In this narrative, along with a limited meta-analysis of available studies, we have reviewed the pleiotropic (non-glucose-lowering) effects of metformin that potentially contribute to its cardioprotective properties. Additionally, we have reviewed issues surrounding the safety of metformin in patients with cardiac diseases.

Intrauterine exposure to metformin: Evaluation of endothelial and perivascular adipose tissue function in abdominal aorta of adult offspring

The biguanide metformin (MET) has been used during pregnancy for treatment of polycystic ovary syndrome and gestational diabetes. MET crosses the placenta and maternal treatment can expose the progeny to this drug during important phases of body development. Direct vascular protective effects have been described with the treatment of metformin. Nevertheless, it is unclear whether intrauterine exposure to metformin is safe for the vascular system of offspring. Thus, the present study aimed to investigate the intrinsic effects of metformin exposure in utero in the offspring abdominal aorta reactivity, in the presence and absence of perivascular adipose tissue (PVAT) and endothelium. For this, Wistar rats were treated with metformin 293 mg/kg/day (MET) or water (CTR) by gavage during the gestational period. The abdominal aorta reactivity to phenylephrine, acetylcholine, and sodium nitroprusside was evaluated in male adult offspring. It was observed that abdominal aorta relaxation was similar between MET and CTR groups in the presence or absence of PVAT. In addition, the contraction to phenylephrine was similar between MET and CTR groups in the presence and absence of PVAT and endothelium. Therefore, metformin exposure during pregnancy had no intrinsic effect on the offspring abdominal aorta PVAT and endothelial function, demonstrating it to be safe to the vascular system of the offspring.

Epicardial Adipose Tissue May Mediate Deleterious Effects of Obesity and Inflammation on the Myocardium

Epicardial adipose tissue has unique properties that distinguish it from other depots of visceral fat. Rather than having distinct boundaries, the epicardium shares an unobstructed microcirculation with the underlying myocardium, and in healthy conditions, produces cytokines that nourish the heart. However, in chronic inflammatory disorders (especially those leading to heart failure with preserved ejection fraction), the epicardium becomes a site of deranged adipogenesis, leading to the secretion of proinflammatory adipokines that can cause atrial and ventricular fibrosis. Accordingly, in patients at risk of heart failure with preserved ejection fraction, drugs that promote the accumulation or inflammation of epicardial adipocytes may lead to heart failure, whereas treatments that ameliorate the proinflammatory characteristics of epicardial fat may reduce the risk of heart failure. These observations suggest that epicardial adipose tissue is a transducer of the adverse effects of systemic inflammation and metabolic disorders on the heart, and thus, represents an important target for therapeutic interventions.

Structural Alteration of Gut Microbiota during the Amelioration of Human Type 2 Diabetes with Hyperlipidemia by Metformin and a Traditional Chinese Herbal Formula: a Multicenter, Randomized, Open Label Clinical Trial

Accumulating evidence implicates gut microbiota as promising targets for the treatment of type 2 diabetes mellitus (T2DM). With a randomized clinical trial, we tested the hypothesis that alteration of gut microbiota may be involved in the alleviation of T2DM with hyperlipidemia by metformin and a specifically designed herbal formula (AMC). Four hundred fifty patients with T2DM and hyperlipidemia were randomly assigned to either the metformin- or AMC-treated group. After 12 weeks of treatment, 100 patients were randomly selected from each group and assessed for clinical improvement. The effects of the two drugs on the intestinal microbiota were evaluated by analyzing the V3 and V4 regions of the 16S rRNA gene by Illumina sequencing and multivariate statistical methods. Both metformin and AMC significantly alleviated hyperglycemia and hyperlipidemia and shifted gut microbiota structure in diabetic patients. They significantly increased a coabundant group represented by Blautia spp., which significantly correlated with the improvements in glucose and lipid homeostasis. However, AMC showed better efficacies in improving homeostasis model assessment of insulin resistance (HOMA-IR) and plasma triglyceride and also exerted a larger effect on gut microbiota. Furthermore, only AMC increased the coabundant group represented by Faecalibacterium spp., which was previously reported to be associated with the alleviation of T2DM in a randomized clinical trial. Metformin and the Chinese herbal formula may ameliorate type 2 diabetes with hyperlipidemia via enriching beneficial bacteria, such as Blautia and Faecalibacterium spp.IMPORTANCE Metabolic diseases such as T2DM and obesity have become a worldwide public health threat. Accumulating evidence indicates that gut microbiota can causatively arouse metabolic diseases, and thus the gut microbiota serves as a promising target for disease control. In this study, we evaluated the role of gut microbiota during improvements in hyperglycemia and hyperlipidemia by two drugs: metformin and a specifically designed Chinese herbal formula (AMC) for diabetic patients with hyperlipidemia. Both drugs significantly ameliorated blood glucose and lipid levels and shifted the gut microbiota. Blautia spp. were identified as being associated with improvements in glucose and lipid homeostasis for both drugs. AMC exerted larger effects on the gut microbiota together with better efficacies in improving HOMA-IR and plasma triglyceride levels, which were associated with the enrichment of Faecalibacterium spp. In brief, these data suggest that gut microbiota might be involved in the alleviation of diabetes with hyperlipidemia by metformin and the AMC herbal formula.

Metformin improves ovarian follicle dynamics by reducing theca cell proliferation and CYP-17 expression in an androgenized rat model

Background

Metformin influences insulin receptor signaling, which might interfere with the proliferation of ovarian follicular structures and steroidogenesis. We hypothesize that reductions in glucose and insulin levels might interfere with CYP-17 expression and histomorphological changes in an androgenized rat model. The aim of this study was to analyze the effect of metformin on CYP-17 expression, follicular dynamics, and proliferative parameters in neonatally androgenized female rats.

Methods

Thirty-six newborn rats were randomly allocated to the following three groups on the third day of life: control (CG, n = 12), androgenized (GA, n = 12), and androgenized + metformin (GAmet, n = 12). The GA and GAmet animals were administered 0.1 mL of testosterone propionate (1.25 mg/animal) diluted in castor oil (vehicle) in a single dose; the CG rats received a subcutaneous injection of the vehicle in the dorsum. After 90 days, gavage treatment was initiated, distilled water was administered to the CG and GA rats, and metformin (150 mg/kg) was administered to the GAmet animals. The treatment was administered daily for six weeks. Following anesthesia, blood was drawn for biochemical measurements, and the ovaries were removed for histological and immunohistochemical analyses of Ki67, VEGFA and CYP17 expression. The glucose and insulin levels were also measured.

Results

The comparison of the GA and GAmet animals revealed that metformin decreased the weight as well as the glucose and insulin levels, slowed the proliferation of the theca interna and interstitial cells, as evidenced by Ki-67 and VEGF-A expression, and diminished CYP17 expression in the analyzed ovarian structures. In addition, metformin reduced the number of degenerating follicles and interstitial cells and improved angiogenesis.

Conclusion

Metformin improves the carbohydrate metabolism, reduces proliferation, and decreases CYP-17 expression in the follicular structures of androgenized rats.

SIRT2 Acts as a Cardioprotective Deacetylase in Pathological Cardiac Hypertrophy

BACKGROUND

Pathological cardiac hypertrophy induced by stresses such as aging and neurohumoral activation is an independent risk factor for heart failure and is considered a target for the treatment of heart failure. However, the mechanisms underlying pathological cardiac hypertrophy remain largely unknown. We aimed to investigate the roles of SIRT2 in aging-related and angiotensin II (Ang II)-induced pathological cardiac hypertrophy.

METHODS

Male C57BL/6J wild-type and Sirt2 knockout mice were subjected to the investigation of aging-related cardiac hypertrophy. Cardiac hypertrophy was also induced by Ang II (1.3 mg/kg/d for 4 weeks) in male C57BL/6J Sirt2 knockout mice, cardiac-specific SIRT2 transgenic (SIRT2-Tg) mice, and their respective littermates (8 to ≈12 weeks old). Metformin (200 mg/kg/d) was used to treat wild-type and Sirt2 knockout mice infused with Ang II. Cardiac hypertrophy, fibrosis, and cardiac function were examined in these mice.

RESULTS

SIRT2 protein expression levels were downregulated in hypertrophic hearts from mice. Sirt2 knockout markedly exaggerated cardiac hypertrophy and fibrosis and decreased cardiac ejection fraction and fractional shortening in aged (24-month-old) mice and Ang II-infused mice. Conversely, cardiac-specific SIRT2 overexpression protected the hearts against Ang II-induced cardiac hypertrophy and fibrosis and rescued cardiac function. Mechanistically, SIRT2 maintained the activity of AMP-activated protein kinase (AMPK) in aged and Ang II-induced hypertrophic hearts in vivo as well as in cardiomyocytes in vitro. We identified the liver kinase B1 (LKB1), the major upstream kinase of AMPK, as the direct target of SIRT2. SIRT2 bound to LKB1 and deacetylated it at lysine 48, which promoted the phosphorylation of LKB1 and the subsequent activation of LKB1-AMPK signaling. Remarkably, the loss of SIRT2 blunted the response of AMPK to metformin treatment in mice infused with Ang II and repressed the metformin-mediated reduction of cardiac hypertrophy and protection of cardiac function.

CONCLUSIONS

SIRT2 promotes AMPK activation by deacetylating the kinase LKB1. Loss of SIRT2 reduces AMPK activation, promotes aging-related and Ang II-induced cardiac hypertrophy, and blunts metformin-mediated cardioprotective effects. These findings indicate that SIRT2 will be a potential target for therapeutic interventions in aging- and stress-induced cardiac hypertrophy.

Metformin effects on the heart and the cardiovascular system: A review of experimental and clinical data

BACKGROUND

Metformin, the eldest and most widely used glucose lowering drug, is likely to be effective also on cardiac and vascular disease prevention. Nonetheless, uncertainty still exists with regard to its effects on the cardiovascular system as a whole and specifically on the myocardium, both at the organ and cellular levels.

METHODS

We reviewed the available data on the cardiac and vascular effects of metformin, encompassing both in vitro, either tissue or isolated organ, and in vivo studies in experimental animals and humans, as well as the evidence generated by major clinical trials.

RESULTS

At the cellular level metformin's produces both AMP-activated kinase (AMPK) dependent and independent effects. At the systemic level, possibly also through other pathways, this drug improves endothelial function, protects from oxidative stress and inflammation, and from the negative effects of angiotensin II. On the myocardium it attenuates ischemia-reperfusion injury and prevents adverse remodeling induced by humoral and hemodynamic factors. The effects on myocardial cell metabolism and contractile function being not evident at rest or in more advanced stages of cardiac dysfunction, could be relevant during transient ischemia, during an acute increase in workload and in the early stages of diabetic/hypertensive cardiomyopathy as confirmed by few small clinical trials and some observational studies. The overall evidence emerging from both clinical trials and real world registry is in favor of a protective effect of metformin with respect to both coronary events and progression to heart failure.

CONCLUSIONS

Given this potential, its efficacy and its safety (and also its low cost) metformin remains the central pillar of the therapy of diabetes.

Metformin in heart failure patients

The use of metformin was considered a contraindication in heart failure patients because of the potential risk of lactic acidosis; however, more recent evidence has shown that this should no longer be the case. We reviewed the current literature and the recent guideline to correct the misconception.