Metformin improves cardiac function in mice with heart failure after myocardial infarction by regulating mitochondrial energy metabolism

Mitochondria-Targeted Natural Antioxidant Nanosystem for Diabetic Vascular Calcification Therapy

The development of nanotherapy targeting mitochondria to alleviate oxidative stress is a critical therapeutic strategy for vascular calcification (VC) in diabetes. In this study, we engineered mitochondria-targeted nanodrugs (T4O@TPP/PEG-PLGA) utilizing terpinen-4-ol (T4O) as a natural antioxidant and mitochondrial protector, PEG-PLGA as the nanocarrier, and triphenylphosphine (TPP) as the mitochondrial targeting ligand. In vitro assessments demonstrated enhanced cellular uptake of T4O@TPP/PEG-PLGA, with effective mitochondrial targeting. This nanodrug successfully reduced oxidative stress induced by high glucose levels in vascular smooth muscle cells. In vivo studies showed prolonged retention of the nanomaterials in the thoracic aorta for up to 24 h. Importantly, experiments in diabetic VC models underscored the potent antioxidant properties of T4O@TPP/PEG-PLGA, as evidenced by its ability to mitigate VC and restore mitochondrial morphology. These results suggest that these nanodrugs could be a promising strategy for managing diabetic VC.

Repurposing Metformin for the Treatment of Atrial Fibrillation: Current Insights

Metformin is an orally effective anti-hyperglycemic drug that despite being introduced over 60 years ago is still utilized by an estimated 120 to 150 million people worldwide for the treatment of type 2 diabetes (T2D). Metformin is used off-label for the treatment of polycystic ovary syndrome (PCOS) and for pre-diabetes and weight loss. Metformin is a safe, inexpensive drug with side effects mostly limited to gastrointestinal issues. Prospective clinical data from the United Kingdom Prospective Diabetes Study (UKPDS), completed in 1998, demonstrated that metformin not only has excellent therapeutic efficacy as an anti-diabetes drug but also that good glycemic control reduced the risk of micro- and macro-vascular complications, especially in obese patients and thereby reduced the risk of diabetes-associated cardiovascular disease (CVD). Based on a long history of clinical use and an excellent safety record metformin has been investigated to be repurposed for numerous other diseases including as an anti-aging agent, Alzheimer's disease and other dementias, cancer, COVID-19 and also atrial fibrillation (AF). AF is the most frequently diagnosed cardiac arrythmia and its prevalence is increasing globally as the population ages. The argument for repurposing metformin for AF is based on a combination of retrospective clinical data and in vivo and in vitro pre-clinical laboratory studies. In this review, we critically evaluate the evidence that metformin has cardioprotective actions and assess whether the clinical and pre-clinical evidence support the use of metformin to reduce the risk and treat AF.

2-APQC, a small-molecule activator of Sirtuin-3 (SIRT3), alleviates myocardial hypertrophy and fibrosis by regulating mitochondrial homeostasis

Sirtuin 3 (SIRT3) is well known as a conserved nicotinamide adenine dinucleotide+ (NAD+)-dependent deacetylase located in the mitochondria that may regulate oxidative stress, catabolism and ATP production. Accumulating evidence has recently revealed that SIRT3 plays its critical roles in cardiac fibrosis, myocardial fibrosis and even heart failure (HF), through its deacetylation modifications. Accordingly, discovery of SIRT3 activators and elucidating their underlying mechanisms of HF should be urgently needed. Herein, we identified a new small-molecule activator of SIRT3 (named 2-APQC) by the structure-based drug designing strategy. 2-APQC was shown to alleviate isoproterenol (ISO)-induced cardiac hypertrophy and myocardial fibrosis in vitro and in vivo rat models. Importantly, in SIRT3 knockout mice, 2-APQC could not relieve HF, suggesting that 2-APQC is dependent on SIRT3 for its protective role. Mechanically, 2-APQC was found to inhibit the mammalian target of rapamycin (mTOR)-p70 ribosomal protein S6 kinase (p70S6K), c-jun N-terminal kinase (JNK) and transforming growth factor-β (TGF-β)/ small mother against decapentaplegic 3 (Smad3) pathways to improve ISO-induced cardiac hypertrophy and myocardial fibrosis. Based upon RNA-seq analyses, we demonstrated that SIRT3-pyrroline-5-carboxylate reductase 1 (PYCR1) axis was closely assoiated with HF. By activating PYCR1, 2-APQC was shown to enhance mitochondrial proline metabolism, inhibited reactive oxygen species (ROS)-p38 mitogen activated protein kinase (p38MAPK) pathway and thereby protecting against ISO-induced mitochondrialoxidative damage. Moreover, activation of SIRT3 by 2-APQC could facilitate AMP-activated protein kinase (AMPK)-Parkin axis to inhibit ISO-induced necrosis. Together, our results demonstrate that 2-APQC is a targeted SIRT3 activator that alleviates myocardial hypertrophy and fibrosis by regulating mitochondrial homeostasis, which may provide a new clue on exploiting a promising drug candidate for the future HF therapeutics.

Met-Exo attenuates mitochondrial dysfunction after hepatic ischemia-reperfusion injury in rats by modulating AMPK/SIRT1 signaling pathway

Hepatic ischemia-reperfusion injury (IRI) results in significant postoperative liver dysfunction, and the intricate mechanism of IRI poses challenges in developing effective therapeutic drugs. Mitigating the damage caused by hepatic IRI and promoting the repair of postoperative liver injury have become focal points in recent years, holding crucial clinical significance. Adipose mesenchymal stem cell derived exosomes (ADSCs-Exo) and metformin (Met) can play a mitochondrial protective role in the treatment of hepatic IRI, but whether there is a synergistic mechanism for their intervention is not yet known. Combining the unique advantages of exosomes as drug carriers, the aim of this study was to investigate the protective effects and mechanisms of the constructed Met and ADSCs-Exo complex (Met-Exo) on the liver IRI combined with partial resection injury in rat and hypoxic reoxygenation injury of rat primary hepatocytes (HCs). In this study, firstly, we detected that mitochondrial morphology and function were severely affected in hepatic tissues after hepatic IRI combined with partial resection, and then verified by in vitro experiments that Met-Exo could promote mitochondrial biosynthesis and fusion-associated protein expression and inhibit mitochondrial fission-related protein expression by modulating the AMPK/SIRT1 signalling pathway. This indicates that ADSCs-Exo can not only play a targeting role as a drug carrier but also has a great potential to act as a vehicle to act synergistically with drugs in the treatment of tissue and organ damage, which provides a new therapeutic strategy and experimental basis for the treatment of liver injury in medical science and clinical veterinary.

Peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family in physiological and pathophysiological process and diseases

Peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family (PGC-1s), consisting of three members encompassing PGC-1α, PGC-1β, and PGC-1-related coactivator (PRC), was discovered more than a quarter-century ago. PGC-1s are essential coordinators of many vital cellular events, including mitochondrial functions, oxidative stress, endoplasmic reticulum homeostasis, and inflammation. Accumulating evidence has shown that PGC-1s are implicated in many diseases, such as cancers, cardiac diseases and cardiovascular diseases, neurological disorders, kidney diseases, motor system diseases, and metabolic disorders. Examining the upstream modulators and co-activated partners of PGC-1s and identifying critical biological events modulated by downstream effectors of PGC-1s contribute to the presentation of the elaborate network of PGC-1s. Furthermore, discussing the correlation between PGC-1s and diseases as well as summarizing the therapy targeting PGC-1s helps make individualized and precise intervention methods. In this review, we summarize basic knowledge regarding the PGC-1s family as well as the molecular regulatory network, discuss the physio-pathological roles of PGC-1s in human diseases, review the application of PGC-1s, including the diagnostic and prognostic value of PGC-1s and several therapies in pre-clinical studies, and suggest several directions for future investigations. This review presents the immense potential of targeting PGC-1s in the treatment of diseases and hopefully facilitates the promotion of PGC-1s as new therapeutic targets.

Mitochondria-loaded alginate-based hydrogel accelerated angiogenesis in a rat model of acute myocardial infarction

Here, mitochondria were isolated from mesenchymal stem cells (MSCs) after being treated with mitochondria-stimulating substrates, 50 μM metformin (Met), and 40 μM dichloroacetic acid (DCA). The isolated mitochondria (2 × 107 particles) were characterized and encapsulated inside 100 μl hydrogel composed of alginate (3 % w/v; Alg)/gelatin (Gel; 1 % w/v) enriched with 1 μM pyrrole (Pyr) solidified in the presence of 0.2 M FeCl3. The physicochemical properties and cytocompatibility of prepared hydrogels were assessed using FTIR, swelling, biodegradation, porosity assays, and scanning electron microscopy (SEM). The mitochondria-bearing hydrogel was injected into the ischemic area of rat hearts. FTIR absorption bands represented that the addition of FeCl3 led to polypyrrole (PPy) formation, polysaccharide oxidation, and interaction between Alg and Gel. SEM images exhibited porous structure and the size of pores was reduced in Alg/Gel + PPy group compared to Alg + PPy hydrogel. Based on the data, both Alg + PPy and Alg/Gel + PPy hydrogels can preserve the integrity and morphology of loaded mitochondria. It was noted that Alg/Gel + PPy hydrogel possessed a higher swelling ratio, degradation, and porosity compared to Alg + PPy group. Data confirmed that Alg/Gel + PPy hydrogel containing 1 μM Pyr yielded the highest survival rate compared to groups with 2 and 4 μM Pyr (p < 0.05). Injection of mitochondria-loaded Alg/Gel + PPy hydrogel yielded significant restoration of left ventricle thickness compared to the infarction, mitochondria, and Alg/Gel + PPy hydrogel groups 14 days post-injection (p < 0.05). Histological analyses revealed a significant increase of vWF+ capillaries and α-SMA+ arterioles in the mitochondria-loaded Alg/Gel + PPy hydrogel group (p < 0.05). Immunofluorescence imaging revealed the ability of rat cardiomyocytes to uptake mitochondria alone or after being loaded into Alg/Gel + PPy hydrogel. These effects were evident in the Alg/Gel + PPy group. Taken together, electroconductive Alg-based hydrogels are suitable platforms for the transplantation of cells and organelles and the regeneration of ischemic heart changes.

Prognostic implication of heart failure stage and left ventricular ejection fraction for patients with in-hospital cardiac arrest: a 16-year retrospective cohort study

BACKGROUND

The 2022 AHA/ACC/HFSA guidelines for the management of heart failure (HF) makes therapeutic recommendations based on HF status. We investigated whether the prognosis of in-hospital cardiac arrest (IHCA) could be stratified by HF stage and left ventricular ejection fraction (LVEF).

METHODS

This single-center retrospective study analyzed the data of patients who experienced IHCA between 2005 and 2020. Based on admission diagnosis, past medical records, and pre-arrest echocardiography, patients were classified into general IHCA, at-risk for HF, pre-HF, HF with preserved ejection fraction (HFpEF), and HF with mildly reduced ejection fraction or HF with reduced ejection fraction (HFmrEF-or-HFrEF) groups.

RESULTS

This study included 2,466 patients, including 485 (19.7%), 546 (22.1%), 863 (35.0%), 342 (13.9%), and 230 (9.3%) patients with general IHCA, at-risk for HF, pre-HF, HFpEF, and HFmrEF-or-HFrEF, respectively. A total of 405 (16.4%) patients survived to hospital discharge, with 228 (9.2%) patients achieving favorable neurological recovery. Multivariable logistic regression analysis indicated that pre-HF and HFpEF were associated with better neurological (pre-HF, OR: 2.11, 95% confidence interval [CI]: 1.23-3.61, p = 0.006; HFpEF, OR: 1.90, 95% CI: 1.00-3.61, p = 0.05) and survival outcomes (pre-HF, OR: 2.00, 95% CI: 1.34-2.97, p < 0.001; HFpEF, OR: 1.91, 95% CI: 1.20-3.05, p = 0.007), compared with general IHCA.

CONCLUSION

HF stage and LVEF could stratify patients with IHCA into different prognoses. Pre-HF and HFpEF were significantly associated with favorable neurological and survival outcomes after IHCA. Further studies are warranted to investigate whether HF status-directed management could improve IHCA outcomes.

Oxidative Stress, Inflammation, and Mitochondrial Dysfunction: A Link between Obesity and Atrial Fibrillation

The adipose tissue has long been thought to represent a passive source of triglycerides and fatty acids. However, extensive data have demonstrated that the adipose tissue is also a major endocrine organ that directly or indirectly affects the physiological functions of almost all cell types. Obesity is recognized as a risk factor for multiple systemic conditions, including metabolic syndrome, type 2 diabetes mellitus, sleep apnea, cardiovascular disorders, and many others. Obesity-related changes in the adipose tissue induce functional and structural changes in cardiac myocytes, promoting a wide range of cardiovascular disorders, including atrial fibrillation (AF). Due to the wealth of epidemiologic data linking AF to obesity, the mechanisms underlying AF occurrence in obese patients are an area of rich ongoing investigation. However, progress has been somewhat slowed by the complex phenotypes of both obesity and AF. The triad inflammation, oxidative stress, and mitochondrial dysfunction are critical for AF pathogenesis in the setting of obesity via multiple structural and functional proarrhythmic changes at the level of the atria. The aim of this paper is to provide a comprehensive view of the close relationship between obesity-induced oxidative stress, inflammation, and mitochondrial dysfunction and the pathogenesis of AF. The clinical implications of these mechanistic insights are also discussed.

Autophagy Behavior under Local Hypothermia in Myocardiocytes Injury

Hypothermia and autophagy are critical regulators of cell homeostasis by regulating intra and intercellular cell communication. Myocardiocyte cryotherapy poses multiple cellular and subcellular effects on the injured cell, including upregulation of autophagy. Autophagy plays a crucial role in modifying cell metabolism by regulating downregulation, reducing reactive oxygen species production, and improving the natural cellular antioxidant defense system. Reduction of reactive oxygen species production and improving natural cellular antioxidant defense system. Therapeutic hypothermia ranges from 32-34°C in terms of local myocardiocyte cooling. Hypothermia induces autophagy by phosphorylating the Akt signaling pathway. Hypothermia has a more therapeutic effect when applied at the beginning of reperfusion rather than in the beginning of ischemia. Moderate hypothermia with 33°C poses most therapeutic effect by viability maintaining and reduction of reactive oxygen species release. Application of local hypothermia to myocardiocytes can be applied to infarcted myocardiocytes, anginal and to the cardiomyopathies.

Identification of Key Immune-Related Genes in the Treatment of Heart Failure After Myocardial Infarction with Empagliflozin Based on RNA-Seq

Purpose

Heart failure is a serious complication after acute myocardial infarction (AMI). It is crucial to investigate the mechanism of action of empagliflozin in the treatment of heart failure.

Methods

A total of 20 wild type (WT) male C57BL6/J mice were used to establish a model of heart failure after myocardial infarction and randomly divided into 2 groups: treatment group and control group. The treatment group was treated with empagliflozin, and the control group was treated with placebo. After 8 weeks of treatment, mouse heart tissues were collected for next generation sequencing. Bioinformatics methods were used to screen the key genes. Finally, the correlation between clinical data and gene expression was analyzed. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to verify the expression of key genes.

Results

A mouse model of heart failure was successfully constructed. By DEG analysis, a total of 740 DEGs in the treatment group vs the control group were obtained. Dendritic cells, granulocytes, follicular B, plasma cell, cDC1, cDC2, pDC and neutrophils were 8 different immune cells identified by immunoinfiltration analysis. Through WGCNA, the turquoise module with the highest correlation with the above differential immune cells was selected. One hundred and forty-two immune-related DEGs were obtained by taking intersection of the DEGs and the genes of the turquoise module. Col17a1 and Gria4 were finally screened out as key immune-related genes via PPI analysis and machine learning. Col17a1 was significantly up-regulated, while Gria4 was significantly down-regulated in the treatment group. At the same time, the expression level of Col17a1 was significantly correlated with left ventricular ejection fraction (LVEF), left ventricular fraction shortening (LVFS) and left ventricular internal dimension systole (LVIDs).

Conclusion

Col17a1 and Gria4 are key immune-related genes of empagliflozin in the treatment of heart failure after myocardial infarction. This study provides a scientific basis for elucidating the mechanism of action of empagliflozin in treating heart failure after myocardial infarction.

Mitochondrial Calcium Overload Plays a Causal Role in Oxidative Stress in the Failing Heart

Heart failure is a serious global health challenge, affecting more than 6.2 million people in the United States and is projected to reach over 8 million by 2030. Independent of etiology, failing hearts share common features, including defective calcium (Ca2+) handling, mitochondrial Ca2+ overload, and oxidative stress. In cardiomyocytes, Ca2+ not only regulates excitation-contraction coupling, but also mitochondrial metabolism and oxidative stress signaling, thereby controlling the function and actual destiny of the cell. Understanding the mechanisms of mitochondrial Ca2+ uptake and the molecular pathways involved in the regulation of increased mitochondrial Ca2+ influx is an ongoing challenge in order to identify novel therapeutic targets to alleviate the burden of heart failure. In this review, we discuss the mechanisms underlying altered mitochondrial Ca2+ handling in heart failure and the potential therapeutic strategies.

Energy metabolism: A critical target of cardiovascular injury

Cardiovascular diseases are the main killers threatening human health. Many studies have shown that abnormal energy metabolism plays a key role in the occurrence and development of acute and chronic cardiovascular diseases. Regulating cardiac energy metabolism is a frontier topic in the treatment of cardiovascular diseases. However, we are not very clear about the choice of different substrates, the specific mechanism of energy metabolism participating in the course of cardiovascular disease, and how to develop appropriate drugs to regulate energy metabolism to treat cardiovascular disease. Therefore, this paper reviews how energy metabolism participates in cardiovascular pathophysiological processes and potential drugs aimed at interfering energy metabolism.It is expected to provide good suggestions for promoting the clinical prevention and treatment of cardiovascular diseases from the perspective of energy metabolism.

MircroRNA-145 Attenuates Cardiac Fibrosis Via Regulating Mitogen-Activated Protein Kinase Kinase Kinase 3

PURPOSE

This study aimed to explore the effect of microRNA (miR)-145 on cardiac fibrosis in heart failure mice and its target.

METHODS

Experiments were carried out in mice receiving left coronary artery ligation, transverse aortic constriction (TAC), or angiotensin (Ang) II to trigger heart failure, and in cardiac fibroblasts (CFs) with Ang II-induced fibrosis.

RESULTS

The miR-145 levels were decreased in the mice hearts of heart failure induced by myocardial infarction (MI), TAC or Ang II infusion, and in the Ang II-treated CFs. The impaired cardiac function was ameliorated by miR-145 agomiR in MI mice. The increased fibrosis and the levels of collagen I, collagen III, and transforming growth factor-beta (TGF-β) in MI mice were inhibited by miR-145 agomiR or miR-145 transgene (TG). The agomiR of miR-145 also attenuated the increases of collagen I, collagen III, and TGF-β in Ang II-treated CFs. Bioinformatics analysis and luciferase reporter assays indicated that mitogen-activated protein kinase kinase kinase 3 (MAP3K3) was a direct target gene of miR-145. MAP3K3 expression was suppressed by MiR-145 in CFs, while the MAP3K3 over-expression reversed the inhibiting effects of miR-145 agomiR on the Ang II-induced increases of collagen I, collagen III, and TGF-β in CFs.

CONCLUSION

These results indicated that miR-145 upregulation could improve cardiac dysfunction and cardiac fibrosis by inhibiting MAP3K3 in heart failure. Thus, upregulating miR-145 or blocking MAP3K3 can be used to treat heart failure and cardiac fibrosis.

Administration of metformin rescues age-related vulnerability to ischemic insults through mitochondrial energy metabolism

Ischemic heart disease (IHD) is the leading cause of death on a global scale. Despite significant advances in the reperfusion treatment of acute myocardial infarction, there is still a significant early mortality rate among the elderly, as angioplasty-achieved reperfusion can exacerbate myocardial damage, leading to severe ischemia/reperfusion (I/R) injury and induce fatal arrhythmias. Mitochondria are a key mediator of ischemic insults; a transient blockade of the electron transport chain (ETC) at complex I during reperfusion can reduce myocardial infarct caused by ischemic insults. The reversible, transient modulation of complex I during early reperfusion is limited by the available of clinically tractable agents. We employed the novel use of acute, high dose metformin to modulate complex I activity during early reperfusion to decrease cardiac injury in the high-risk aged heart. Young (3-6 months) and aged (22-24 months) male and female C57BL/6 J mice were subjected to in vivo regional ischemia for 45 min, followed by metformin (2 mM, i. v.) injection 5 min prior to reperfusion for 24 h. The cardiac functions were measured with echocardiography. A Seahorse XF24 Analyzer was used to ascertain mitochondrial function. Cardiomyocyte sarcomere shortening and calcium transients were measured using the IonOptix Calcium and Contractility System. The results demonstrated that administration of acute, high dose metformin at the onset of reperfusion significantly limited cardiac damage and rescued cardiac dysfunction caused by I/R in both young and aged mice. Importantly, metformin treatment improves contractile functions of isolated cardiomyocytes and maintains mitochondrial integrity under I/R stress conditions. Thus, acute metformin administration at the onset of reperfusion has potential as a mitochondrial-based therapeutic to mitigate reperfusion injury and reduce infarct size in the elderly heart attack patient who remains at greater mortality risk despite reperfusion alone.

Effect of Sirolimus/Metformin Co-Treatment on Hyperglycemia and Cellular Respiration in BALB/c Mice

Sirolimus (SRL) is widely used as an immunosuppressant to prevent graft rejection, despite the risk of impairing glucose metabolism. Metformin (MET) can reduce the detrimental effects of SRL in many patients, including diabetes and renal transplant recipients. Limited in vivo studies have reported on SRL and MET therapy, particularly in relation to cellular bioenergetics, glucose metabolism, and insulin resistance. Herein, we investigated the efficacy of SRL and MET co-treatment in BALB/c mice over 4 weeks. Balb/c mice (4-6 weeks old) were divided into four groups and injected intraperitoneally (i.p.) with water (control, CTRL), MET (200 µg/g), SRL (5 µg/g), or MET (200 µg/g) +SRL (5 µg/g) over a period of one month. We evaluated the body weight, food consumption rate, random blood glucose (BG), insulin levels, serum biochemistry parameters (ALT, Albumin, BUN, Creatinine), and histomorphology in all groups using standardized techniques and assays. All drug-treated groups showed a statistically significant decrease in weight gain compared to the CTRL group, despite normal food intake. Treatment with SRL caused elevated BG and insulin levels, which were restored with SRL + MET combination. Serum biochemical parameters were within the normal range in all the studied groups. SRL+ MET co-treatment decreased liver cellular respiration and increased cellular ATP levels in the liver. In the pancreas, co-treatment resulted in increased cellular respiration and decreased cellular ATP levels. Liver and pancreatic histology were unchanged in all groups. This study showed that co-treatment of SRL with MET alleviates hyperglycemia induced by SRL without any deleterious effects. These results provide initial insights into the potential use of SRL + MET therapy in various settings.

Effect of metformin on left ventricular mass and functional parameters in non-diabetic patients: a meta-analysis of randomized clinical trials

Background

Left ventricular hypertrophy is a common finding in patients with ischemic heart disease and is associated with mortality in patients with cardiovascular disease (CVD). Metformin, an antidiabetic drug, has been shown to reduce oxidative stress and left ventricular mass index (LVMI) in animal hypertrophy models. We summarized evidence regarding the effect of metformin on LVMI and LVEF.

Methods

Electronic databases were searched for randomized clinical trials (RCTs) that used metformin in non-diabetic patients with or without pre-existing CVD. The standardized mean change using change score standardization (SMCC) was calculated for each study. The random-effects model was used to pool the SMCC across studies. Meta-regression analysis was used to assess the association of heart failure (HF), metformin dose, and duration with the SMCC.

Results

Data synthesis from nine RCTs (754 patients) showed that metformin use resulted in higher reduction in LVMI after 12 months (SMCC = −0.63, 95% CI − 1.23; − 0.04, p = 0.04) and an overall higher reduction in LVMI (SMCC = −0.5, 95% CI − 0.84; − 0.16, p < 0.01). These values equate to absolute values of 11.3 (95% CI 22.1–0.72) and 8.97 (95% CI 15.06–2.87) g/m², respectively. The overall improvement in LVEF was also higher in metformin users after excluding one outlier (SMCC = 0.26, 95% CI 0.03–0.49, P = 0.03) which translates to a higher absolute improvement of 2.99% (95% CI 0.34; 5.63). Subgroup analysis revealed a favorable effect for metformin on LVEF in patients who received > 1000 mg/day (SMCC = 0.28, 95% CI 0.04; 0.52, P = 0.04), and patients with HF (SMCC = 0.23; 95% CI 0.1; 0.36; P = 0.004). These values translate to a higher increase of 2.64% and 3.21%, respectively.

Conclusion

Results suggest a favorable effect for metformin on LVMI and LVEF in patients with or without pre-existing CVD. Additional trials are needed to address the long-term effect of metformin.

Registration The study was registered on the PROSPERO database with the registration number CRD42021239368 (https://www.crd.york.ac.uk/prospero).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02845-w.

Metformin therapy regresses LVH by approximately 10 g/m² in non-diabetic patients after 12 months of use (SMCC = −0.63, 95% CI − 1.23; − 0.04, p = 0.04).

Metformin therapy was associated with a modest (2–3%) but greater overall improvement in LVEF.

Higher dose (> 1000 mg/day) and longer treatment duration were associated with a significant effect for metformin on LVMI and LVEF.

Metformin use in HF patients was associated with an absolute increase of 3.21% in LVEF (SMCC = 0.23; 95% CI 0.1; 0.36, P = 0.004).

LKB1: An emerging therapeutic target for cardiovascular diseases

Cardiovascular diseases (CVDs) are currently the most common cause of morbidity and mortality worldwide. Experimental studies suggest that liver kinase B1 (LKB1) plays an important role in the heart. Several studies have shown that cardiomyocyte-specific LKB1 deletion leads to hypertrophic cardiomyopathy, left ventricular contractile dysfunction, and an increased risk of atrial fibrillation. In addition, the cardioprotective effects of several medicines and natural compounds, including metformin, empagliflozin, bexarotene, and resveratrol, have been reported to be associated with LKB1 activity. LKB1 limits the size of the damaged myocardial area by modifying cellular metabolism, enhancing the antioxidant system, suppressing hypertrophic signals, and inducing mild autophagy, which are all primarily mediated by the AMP-activated protein kinase (AMPK) energy sensor. LKB1 also improves myocardial efficiency by modulating the function of contractile proteins, regulating the expression of electrical channels, and increasing vascular dilatation. Considering these properties, stimulation of LKB1 signaling offers a promising approach in the prevention and treatment of heart diseases.

Emerging Roles of SIRT3 in Cardiac Metabolism

The heart is a highly metabolically active organ that predominantly utilizes fatty acids as an energy substrate. The heart also derives some part of its energy by oxidation of other substrates, including glucose, lactose, amino acids and ketones. The critical feature of cardiac pathology is metabolic remodeling and loss of metabolic flexibility. Sirtuin 3 (SIRT3) is one of the seven mammalian sirtuins (SIRT1 to SIRT7), with NAD⁺ dependent deacetylase activity. SIRT3 is expressed in high levels in healthy hearts but downregulated in the aged or diseased hearts. Experimental evidence shows that increasing SIRT3 levels or activity can ameliorate several cardiac pathologies. The primary deacetylation targets of SIRT3 are mitochondrial proteins, most of which are involved in energy metabolism. Thus, SIRT3 improves cardiac health by modulating cardiac energetics. In this review, we discuss the essential role of SIRT3 in regulating cardiac metabolism in the context of physiology and pathology. Specifically, we summarize the recent advancements that emphasize the critical role of SIRT3 as a master regulator of cardiac metabolism. We also present a comprehensive view of all known activators of SIRT3, and elaborate on their therapeutic potential to ameliorate energetic abnormalities in various cardiac pathologies.

Metformin for Cardiovascular Protection, Inflammatory Bowel Disease, Osteoporosis, Periodontitis, Polycystic Ovarian Syndrome, Neurodegeneration, Cancer, Inflammation and Senescence: What Is Next?

Diabetes is accompanied by several complications. Higher prevalence of cancers, cardiovascular diseases, chronic kidney disease (CKD), obesity, osteoporosis, and neurodegenerative diseases has been reported among patients with diabetes. Metformin is the oldest oral antidiabetic drug and can improve coexisting complications of diabetes. Clinical trials and observational studies uncovered that metformin can remarkably prevent or alleviate cardiovascular diseases, obesity, polycystic ovarian syndrome (PCOS), osteoporosis, cancer, periodontitis, neuronal damage and neurodegenerative diseases, inflammation, inflammatory bowel disease (IBD), tuberculosis, and COVID-19. In addition, metformin has been proposed as an antiaging agent. Numerous mechanisms were shown to be involved in the protective effects of metformin. Metformin activates the LKB1/AMPK pathway to interact with several intracellular signaling pathways and molecular mechanisms. The drug modifies the biologic function of NF-κB, PI3K/AKT/mTOR, SIRT1/PGC-1α, NLRP3, ERK, P38 MAPK, Wnt/β-catenin, Nrf2, JNK, and other major molecules in the intracellular signaling network. It also regulates the expression of noncoding RNAs. Thereby, metformin can regulate metabolism, growth, proliferation, inflammation, tumorigenesis, and senescence. Additionally, metformin modulates immune response, autophagy, mitophagy, endoplasmic reticulum (ER) stress, and apoptosis and exerts epigenetic effects. Furthermore, metformin protects against oxidative stress and genomic instability, preserves telomere length, and prevents stem cell exhaustion. In this review, the protective effects of metformin on each disease will be discussed using the results of recent meta-analyses, clinical trials, and observational studies. Thereafter, it will be meticulously explained how metformin reprograms intracellular signaling pathways and alters molecular and cellular interactions to modify the clinical presentations of several diseases.

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.

LncRNA LncHrt preserves cardiac metabolic homeostasis and heart function by modulating the LKB1-AMPK signaling pathway

Metabolic modulation is a promising therapeutic approach to prevent adverse remodeling of the ischemic heart. Because little is known about the involvement of long non-coding RNAs (lncRNAs) in regulating cardiac metabolism, we used unbiased transcriptome profiling in a mouse model of myocardial infarction (MI). We identified a novel cardiomyocyte-enriched lncRNA, called LncHrt, which regulates metabolism and the pathophysiological processes that lead to heart failure. AAV-based LncHrt overexpression protects the heart from MI as demonstrated by improved contractile function, preserved metabolic homeostasis, and attenuated maladaptive remodeling responses. RNA-pull down followed by mass spectrometry and RNA immunoprecipitation (RIP) identified SIRT2 as a LncHrt-interacting protein involved in cardiac metabolic regulation. Mechanistically, we established that LncHrt interacts with SIRT2 to preserve SIRT2 deacetylase activity by interfering with the CDK5 and SIRT2 interaction. This increases downstream LKB1-AMPK kinase signaling, which ameliorates functional and metabolic deficits. Importantly, we found the expression of the human homolog of mouse LncHrt was decreased in patients with dilated cardiomyopathy. Together, these studies identify LncHrt as a cardiac metabolic regulator that plays an essential role in preserving heart function by regulating downstream metabolic signaling pathways. Consequently, LncHrt is a potentially novel RNA-based therapeutic target for ischemic heart disease.

Mitochondrial proteins in heart failure: The role of deacetylation by SIRT3

Heart failure (HF) is still the leading cause of death worldwide, occurring with a variety of complex mechanisms. However, most intervention for HF do not directly target the pathological mechanisms underlying cell damage in failing cardiomyocytes. Mitochondria are involved in many physiological processes, which is an important guarantee for normal heart function. Mitochondrial dysfunction is considered to be the critical node of the development of HF. Strict modulation of the mitochondrial function can ameliorate the myocardial injury and protect cardiac function. Acetylation plays an important role in mitochondrial protein homeostasis, and SIRT3, the most important deacetylation protein in mitochondria, is involved in the maintenance of mitochondrial function. SIRT3 can delay the progression of HF by improving mitochondrial function. Herein we summarize the interaction between SIRT3 and proteins related to mitochondrial function including oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO), mitochondrial biosynthesis, mitochondrial quality control. In addition, we also sum up the effects of this interaction on HF and the research progress of treatments targeting SIRT3, so as to find potential HF therapeutic for clinical use in the future.

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.

Mitochondrial Dysfunction in Atrial Fibrillation-Mechanisms and Pharmacological Interventions

Despite the enormous progress in the treatment of atrial fibrillation, mainly with the use of invasive techniques, many questions remain unanswered regarding the pathomechanism of the arrhythmia and its prevention methods. The development of atrial fibrillation requires functional changes in the myocardium that result from disturbed ionic fluxes and altered electrophysiology of the cardiomyocyte. Electrical instability and electrical remodeling underlying the arrhythmia may result from a cellular energy deficit and oxidative stress, which are caused by mitochondrial dysfunction. The significance of mitochondrial dysfunction in the pathogenesis of atrial fibrillation remains not fully elucidated; however, it is emphasized by the reduction of atrial fibrillation burden after therapeutic interventions improving the mitochondrial welfare. This review summarizes the mechanisms of mitochondrial dysfunction related to atrial fibrillation and current pharmacological treatment options targeting mitochondria to prevent or improve the outcome of atrial fibrillation.

Longevity genes, cardiac ageing, and the pathogenesis of cardiomyopathy: implications for understanding the effects of current and future treatments for heart failure

The two primary molecular regulators of lifespan are sirtuin-1 (SIRT1) and mammalian target of rapamycin complex 1 (mTORC1). Each plays a central role in two highly interconnected pathways that modulate the balance between cellular growth and survival. The activation of SIRT1 [along with peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α) and adenosine monophosphate-activated protein kinase (AMPK)] and the suppression of mTORC1 (along with its upstream regulator, Akt) act to prolong organismal longevity and retard cardiac ageing. Both activation of SIRT1/PGC-1α and inhibition of mTORC1 shifts the balance of cellular priorities so as to promote cardiomyocyte survival over growth, leading to cardioprotective effects in experimental models. These benefits may be related to direct actions to modulate oxidative stress, organellar function, proinflammatory pathways, and maladaptive hypertrophy. In addition, a primary shared benefit of both SIRT1/PGC-1α/AMPK activation and Akt/mTORC1 inhibition is the enhancement of autophagy, a lysosome-dependent degradative pathway, which clears the cytosol of dysfunctional organelles and misfolded proteins that drive the ageing process by increasing oxidative and endoplasmic reticulum stress. Autophagy underlies the ability of SIRT1/PGC-1α/AMPK activation and Akt/mTORC1 suppression to extend lifespan, mitigate cardiac ageing, alleviate cellular stress, and ameliorate the development and progression of cardiomyopathy; silencing of autophagy genes abolishes these benefits. Loss of SIRT1/PGC-1α/AMPK function or hyperactivation of Akt/mTORC1 is a consistent feature of experimental cardiomyopathy, and reversal of these abnormalities mitigates the development of heart failure. Interestingly, most treatments that have been shown to be clinically effective in the treatment of chronic heart failure with a reduced ejection fraction have been reported experimentally to exert favourable effects to activate SIRT1/PGC-1α/AMPK and/or suppress Akt/mTORC1, and thereby, to promote autophagic flux. Therefore, the impairment of autophagy resulting from derangements in longevity gene signalling is likely to represent a seminal event in the evolution and progression of cardiomyopathy.

Energy metabolism disorders and potential therapeutic drugs in heart failure

Heart failure (HF) is a global public health problem with high morbidity and mortality. A large number of studies have shown that HF is caused by severe energy metabolism disorders, which result in an insufficient heart energy supply. This deficiency causes cardiac pump dysfunction and systemic energy metabolism failure, which determine the development of HF and recovery of heart. Current HF therapy acts by reducing heart rate and cardiac preload and afterload, treating the HF symptomatically or delaying development of the disease. Drugs aimed at cardiac energy metabolism have not yet been developed. In this review, we outline the main characteristics of cardiac energy metabolism in healthy hearts, changes in metabolism during HF, and related pathways and targets of energy metabolism. Finally, we discuss drugs that improve cardiac function via energy metabolism to provide new research ideas for the development and application of drugs for treating HF.

Predictive Value of Sirtuins in Acute Myocardial Infarction - Bridging the Bench to the Clinical Practice

Acute myocardial infarction (AMI) is a non-transmissible condition with high prevalence, morbidity, and mortality. Different strategies for the management of AMI are employed worldwide, but its early diagnosis remains a major challenge. Many molecules have been proposed in recent years as predictive agents in the early detection of AMI, including troponin (C, T, and I), creatine kinase MB isoenzyme, myoglobin, heart-type fatty acid-binding protein, and a family of histone deacetylases with enzymatic activities named sirtuins. Sirtuins may be used as predictive or complementary treatment strategies and the results of recent preclinical studies are promising. However, human clinical trials and data are scarce, and many issues have been raised regarding the predictive values of sirtuins. The present review summarizes research on the predictive value of sirtuins in AMI. We also briefly summarize relevant clinical trials and discuss future perspectives and possible clinical applications.

MicroRNA-132 attenuated cardiac fibrosis in myocardial infarction-induced heart failure rats

The aim of the present study was to determine the effect of microRNA (miR)-132 on cardiac fibrosis in myocardial infarction (MI)-induced heart failure and angiotensin (Ang) II-treated cardiac fibroblasts (CFs). Experiments were carried out in Sprague-Dawley rat treatment with ligation of left coronary artery to induce heart failure, and in CFs administration of Ang II to induce fibrosis. The level of miR-132 was increased in the heart of rats with MI-induced heart failure and the Ang II-treated CFs. In MI rats, left ventricle (LV) ejection fraction, fractional shortening, the maximum of the first differentiation of LV pressure (LV +dp/dtmax) and decline (LV -dp/dtmax) and LV systolic pressure (LVSP) were reduced, and LV end-systolic diameter (LVESD), LV end-diastolic diameter (LVEDD), LV volumes in systole (LVVS) and LV volumes in diastole (LVVD) were increased, which were reversed by miR-132 agomiR but deteriorated by miR-132 antagomiR. The expression levels of collagen I, collagen III, transforming growth factor-β (TGF-β), and α-smooth muscle actin (α-SMA) were increased in the heart of rat with MI-induced heart failure and CFs administration of Ang II. These increases were inhibited by miR-132 agomiR but enhanced by miR-132 antagomiR treatment. MiR-132 inhibited PTEN expression, and attenuated PI3K/Akt signal pathway in CFs. These results indicated that the up-regulation of miR-132 improved the cardiac dysfunction, attenuated cardiac fibrosis in heart failure via inhibiting PTEN expression, and attenuating PI3K/Akt signal pathway. Up-regulation of miR-132 may be a strategy for the treatment of heart failure and cardiac fibrosis.

The Role of Posttranslational Modification and Mitochondrial Quality Control in Cardiovascular Diseases

Cardiovascular disease (CVD) is the leading cause of death in the world. The mechanism behind CVDs has been studied for decades; however, the pathogenesis is still controversial. Mitochondrial homeostasis plays an essential role in maintaining the normal function of the cardiovascular system. The alterations of any protein function in mitochondria may induce abnormal mitochondrial quality control and unexpected mitochondrial dysfunction, leading to CVDs. Posttranslational modifications (PTMs) affect protein function by reversibly changing their conformation. This review summarizes how common and novel PTMs influence the development of CVDs by regulating mitochondrial quality control. It provides not only ideas for future research on the mechanism of some types of CVDs but also ideas for CVD treatments with therapeutic potential.

The Current and Potential Therapeutic Use of Metformin-The Good Old Drug

Metformin, one of the oldest oral antidiabetic agents and still recommended by almost all current guidelines as the first-line treatment for type 2 diabetes mellitus (T2DM), has become the medication with steadily increasing potential therapeutic indications. A broad spectrum of experimental and clinical studies showed that metformin has a pleiotropic activity and favorable effect in different pathological conditions, including prediabetes, type 1 diabetes mellitus (T1DM) and gestational diabetes mellitus (GDM). Moreover, there are numerous studies, meta-analyses and population studies indicating that metformin is safe and well tolerated and may be associated with cardioprotective and nephroprotective effect. Recently, it has also been reported in some studies, but not all, that metformin, besides improvement of glucose homeostasis, may possibly reduce the risk of cancer development, inhibit the incidence of neurodegenerative disease and prolong the lifespan. This paper presents some arguments supporting the initiation of metformin in patients with newly diagnosed T2DM, especially those without cardiovascular risk factors or without established cardiovascular disease or advanced kidney insufficiency at the time of new guidelines favoring new drugs with pleotropic effects complimentary to glucose control. Moreover, it focuses on the potential beneficial effects of metformin in patients with T2DM and coexisting chronic diseases.

Metformin attenuates ischemia/reperfusion-induced apoptosis of cardiac cells by downregulation of p53/microRNA-34a via activation of SIRT1

Metformin has been demonstrated to be beneficial for the treatment of an impaired myocardium as a result of ischemia/reperfusion (I/R) injury, and miR-34a may be involved in this process. The aim of the present study was to determine the mechanisms by which metformin attenuated myocardial I/R injury-induced apoptosis. In the in vivo I/R model using Sprague-Dawley rats, metformin reduced the area of damaged myocardium and serum creatine MB isoform (CKMB) activity resulting in protection of the myocardium. Metformin also reduced apoptosis and the expression of apoptosis associated proteins, including caspase 3 and cleaved caspase, and decreased the expression of miR-34a, which is upregulated during I/R injury, which in turn resulted in corresponding changes in expression of Bcl-2, a direct target of miR-34a both in vitro and in vivo. To further examine the role of miR-34a in this process, H9C2 cells were transfected by a miR-34a mimic and inhibitor. Overexpression of miR-34a increased apoptosis in H9C2 cells induced by oxygen-glucose deprivation/recovery and knockdown of miR-34a expression-reduced apoptosis under the same conditions. Therefore, the effect of metformin on miR-34a in vitro were assessed. Metformin decreased the deacetylation activity of silent information regulator 1 resulting in reduced Ac-p53 levels, which reduced the levels of pri-miR-34a, and thus in turn reduced miR-34a levels. To confirm these results clinically, 90 patients with ST-segment elevation myocardial infarction following percutaneous coronary intervention were recruited. Patients who took metformin regularly before infarction had lower miR-34a levels and lower serum CKMB activity. Metformin also improved the sum ST-segment recovery following I/R injury. In conclusion, metformin may be helpful in the treatment of myocardial I/R.

Natural Antioxidants Improve the Vulnerability of Cardiomyocytes and Vascular Endothelial Cells under Stress Conditions: A Focus on Mitochondrial Quality Control

Cardiovascular disease has become one of the main causes of human death. In addition, many cardiovascular diseases are accompanied by a series of irreversible damages that lead to organ and vascular complications. In recent years, the potential therapeutic strategy of natural antioxidants in the treatment of cardiovascular diseases through mitochondrial quality control has received extensive attention. Mitochondria are the main site of energy metabolism in eukaryotic cells, including myocardial and vascular endothelial cells. Mitochondrial quality control processes ensure normal activities of mitochondria and cells by maintaining stable mitochondrial quantity and quality, thus protecting myocardial and endothelial cells against stress. Various stresses can affect mitochondrial morphology and function. Natural antioxidants extracted from plants and natural medicines are becoming increasingly common in the clinical treatment of diseases, especially in the treatment of cardiovascular diseases. Natural antioxidants can effectively protect myocardial and endothelial cells from stress-induced injury by regulating mitochondrial quality control, and their safety and effectiveness have been preliminarily verified. This review summarises the damage mechanisms of various stresses in cardiomyocytes and vascular endothelial cells and the mechanisms of natural antioxidants in improving the vulnerability of these cell types to stress by regulating mitochondrial quality control. This review is aimed at paving the way for novel treatments for cardiovascular diseases and the development of natural antioxidant drugs.

Regulation of Mitochondrial Quality Control by Natural Drugs in the Treatment of Cardiovascular Diseases: Potential and Advantages

Mitochondria are double-membraned cellular organelles that provide the required energy and metabolic intermediates to cardiomyocytes. Mitochondrial respiratory chain defects, structure abnormalities, and DNA mutations can affect the normal function of cardiomyocytes, causing an imbalance in intracellular calcium ion homeostasis, production of reactive oxygen species, and apoptosis. Mitochondrial quality control (MQC) is an important process that maintains mitochondrial homeostasis in cardiomyocytes and involves multi-level regulatory mechanisms, such as mitophagy, mitochondrial fission and fusion, mitochondrial energy metabolism, mitochondrial antioxidant system, and mitochondrial respiratory chain. Furthermore, MQC plays a role in the pathological mechanisms of various cardiovascular diseases (CVDs). In recent years, the regulatory effects of natural plants, drugs, and active ingredients on MQC in the context of CVDs have received significant attention. Effective active ingredients in natural drugs can influence the production of energy-supplying substances in the mitochondria, interfere with the expression of genes associated with mitochondrial energy requirements, and regulate various mechanisms of MQC modulation. Thus, these ingredients have therapeutic effects against CVDs. This review provides useful information about novel treatment options for CVDs and development of novel drugs targeting MQC.

Metformin decreased myocardial fibrosis and apoptosis in hyperhomocysteinemia -induced cardiac hypertrophy

BACKGROUND

Hyperhomocysteinemia (HHcy) is one of the major risk factors of cardiovascular diseases. Metformin acts as a cardioprotective role in several cardiovascular diseases, including ischemia/reperfusion, atherosclerosis, and myocardial infarction. However, whether metformin protects against HHcy-induced cardiac hypertrophy is unclear.

METHODS AND RESULTS

HHcy model was established in C57BL/6 mice with high L-methionine (L-MET) diet for 12 weeks. AC16 cells were exposed to homocysteine (Hcy) and then intervened with different concentrations of metformin in in vitro studies. The results showed that HHcy was able to induce cardiac hypertrophy, and metformin could abrogate this effect. HHcy increased the fibrosis area and induced apoptosis in the myocardium, whereas metformin could reverse the detrimental effects above. TUNEL assay showed that metformin was able to decrease Hcy-induced apoptosis in AC16 cells. Moreover, western blotting assay revealed that metformin could decrease Hcy-induced expression of Bax and cleaved caspase3, and increase the expression of Bcl-2.

CONCLUSIONS

This study demonstrates that metformin is able to attenuate HHcy-induced cardiac hypertrophy by decreasing myocardial fibrosis and apoptosis.

Metformin Shortens Prolonged QT Interval in Diabetic Mice by Inhibiting L-Type Calcium Current: A Possible Therapeutic Approach

The incidence and mortality of cardiovascular disease in diabetic patients are 2-3 times higher than those in non-diabetic patients. Abnormal function of the L-type calcium channel in myocardial tissue might result in multiple cardiac disorders such as a prolonged QT interval. Therefore, QT prolongation is an independent risk factor of cardiovascular disease in patients with diabetes mellitus. Metformin, a hypoglycemic agent, is widely known to effectively reduce the occurrence of macrovascular diseases. The aim of the present study was to evaluate the effect of metformin on prolonged QT interval and to explore potential ionic mechanisms induced by diabetes. Diabetic mouse models were established with streptozotocin and an electrocardiogram was used to monitor the QT interval after 4 weeks of metformin treatment in each group. Action potential duration (APD) and L-type calcium current (I_Ca-L) were detected by patch-clamp in isolated mice ventricular cardiomyocytes and neonatal cardiomyocytes of mice. The expression levels of CACNA1C mRNA and Cav1.2 were measured by real-time PCR, western blot and immunofluorescence. A shortened QT interval was observed after 4 weeks of metformin treatment in diabetic mice. Patch-clamp results revealed that both APD and I_Ca-L were shortened in mouse cardiomyocytes. Furthermore, the expression levels of CACNA1C mRNA and Cav1.2 were decreased in the metformin group. The same results were also obtained in cultured neonatal mice cardiomyocytes. Overall, these results verify that metformin could shorten a prolonged QT interval by inhibiting the calcium current, suggesting that metformin may play a role in the electrophysiology underlying diabetic cardiopathy.

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.

Metformin mediates cardioprotection against aging-induced ischemic necroptosis

Necroptosis is crucially involved in severe cardiac pathological conditions. However, whether necroptosis contributes to age‐related intolerance to ischemia/reperfusion (I/R) injury remains elusive. In addition, metformin as a potential anti‐aging related injury drug, how it interacts with myocardial necroptosis is not yet clear. Male C57BL/6 mice at 3–4‐ (young) and 22–24 months of age (aged) and RIPK3‐deficient (Ripk3^−/−) mice were used to investigate aging‐related I/R injury in vivo. Metformin (125 μg/kg, i.p.), necrostatin‐1 (3.5 mg/kg), and adenovirus vector encoding p62‐shRNAs (Ad‐sh‐p62) were used to treat aging mice. I/R‐induced myocardial necroptosis was exaggerated in aged mice, which correlated with autophagy defects characterized by p62 accumulation in aged hearts or aged human myocardium. Functionally, blocking autophagic flux promoted H/R‐evoked cardiomyocyte necroptosis in vitro. We further revealed that p62 forms a complex with RIP1‐RIP3 (necrosome) and promotes the binding of RIP1 and RIP3. In mice, necrostatin‐1 treatment (a RIP1 inhibitor), RIP3 deficiency, and cardiac p62 knockdown in vivo demonstrated that p62‐RIP1‐RIP3‐dependent myocardial necroptosis contributes to aging‐related myocardial vulnerability to I/R injury. Notably, metformin treatment disrupted p62‐RIP1‐RIP3 complexes and effectively repressed I/R‐induced necroptosis in aged hearts, ultimately reducing mortality in this model. These findings highlight previously unknown mechanisms of aging‐related myocardial ischemic vulnerability: p62‐necrosome‐dependent necroptosis. Metformin acts as a cardioprotective agent that inhibits this unfavorable chain mechanism of aging‐related I/R susceptibility.

Metformin protects against PM2.5-induced lung injury and cardiac dysfunction independent of AMP-activated protein kinase α2

Fine particulate matter (PM2.5) airborne pollution increases the risk of respiratory and cardiovascular diseases. Although metformin is a well-known antidiabetic drug, it also confers protection against a series of diseases through the activation of AMP-activated protein kinase (AMPK). However, whether metformin affects PM2.5-induced adverse health effects has not been investigated. In this study, we exposed wild-type (WT) and AMPKα2-/- mice to PM2.5 every other day via intratracheal instillation for 4 weeks. After PM2.5 exposure, the AMPKα2-/- mice developed more severe lung injury and cardiac dysfunction than were developed in the WT mice; however the administration of metformin was effective in attenuating PM2.5-induced lung injury and cardiac dysfunction in both the WT and AMPKα2-/- mice. In the PM2.5-exposed mice, metformin treatment resulted in reduced systemic and pulmonary inflammation, preserved left ventricular ejection fraction, suppressed induction of pulmonary and myocardial fibrosis and oxidative stress, and increased levels of mitochondrial antioxidant enzymes. Moreover, pretreatment with metformin significantly attenuated PM2.5-induced cell death and oxidative stress in control and AMPKα2-depleted BEAS-2B and H9C2 cells, and was associated with preserved expression of mitochondrial antioxidant enzymes. These data support the notion that metformin protects against PM2.5-induced adverse health effects through a pathway that appears independent of AMPKα2. Our findings suggest that metformin may also be a novel drug for therapies that treat air pollution associated disease.

Mechanisms of action of metformin with special reference to cardiovascular protection

Management guidelines continue to identify metformin as initial pharmacologic antidiabetic therapy of choice for people with type 2 diabetes without contraindications, despite recent randomized trials that have demonstrated significant improvements in cardiovascular outcomes with newer classes of antidiabetic therapies. The purpose of this review is to summarize the current state of knowledge of metformin's therapeutic actions on blood glucose and cardiovascular clinical evidence and to consider the mechanisms that underlie them. The effects of metformin on glycaemia occur mainly in the liver, but metformin-stimulated glucose disposal by the gut has emerged as an increasingly import site of action of metformin. Additionally, metformin induces increased secretion of GLP-1 from intestinal L-cells. Clinical cardiovascular protection with metformin is supported by three randomized outcomes trials (in newly diagnosed and late stage insulin-treated type 2 diabetes patients) and a wealth of observational data. Initial evidence suggests that cotreatment with metformin may enhance the impact of newer incretin-based therapies on cardiovascular outcomes, an important observation as metformin can be combined with any other antidiabetic agent. Multiple potential mechanisms support the concept of cardiovascular protection with metformin beyond those provided by reduced blood glucose, including weight loss, improvements in haemostatic function, reduced inflammation, and oxidative stress, and inhibition of key steps in the process of atherosclerosis. Accordingly, metformin remains well placed to support improvements in cardiovascular outcomes, from diagnosis and throughout the course of type 2 diabetes, even in this new age of improved outcomes in type 2 diabetes.

Spermidine-enhanced autophagic flux improves cardiac dysfunction following myocardial infarction by targeting the AMPK/mTOR signalling pathway

BACKGROUND AND PURPOSE

Spermidine, a natural polyamine, is abundant in mammalian cells and is involved in cell growth, proliferation, and regeneration. Recently, oral spermidine supplements were cardioprotective in age-related cardiac dysfunction, through enhancing autophagic flux. However, the effect of spermidine on myocardial injury and cardiac dysfunction following myocardial infarction (MI) remains unknown.

EXPERIMENTAL APPROACH

We determined the effects of spermidine in a model of MI, Sprague-Dawley rats with permanent ligation of the left anterior descending artery, and in cultured neonatal rat cardiomyocytes (NRCs) exposed to angiotensin II (Ang II). Cardiac function in vivo was assessed with echocardiography. In vivo and in vitro studies used histological and immunohistochemical techniques, along with western blots.

KEY RESULTS

Spermidine improved cardiomyocyte viability and decreased cell necrosis in NRCs treated with angiotensin II. In rats post-MI, spermidine reduced infarct size, improved cardiac function, and attenuated myocardial hypertrophy. Spermidine also suppressed the oxidative damage and inflammatory cytokines induced by MI. Moreover, spermidine enhanced autophagic flux and decreased apoptosis both in vitro and in vivo. The protective effects of spermidine on cardiomyocyte apoptosis and cardiac dysfunction were abolished by the autophagy inhibitor chloroquine, indicating that spermidine exerted cardioprotective effects at least partly through promoting autophagic flux, by activating the AMPK/mTOR signalling pathway.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that spermidine improved MI-induced cardiac dysfunction by promoting AMPK/mTOR-mediated autophagic flux.

Pro-neurocognitive and anti-sarcopenic benefits of one-year metformin therapy in ovariectomized aged mice

Health promotion and healthy nutrition significantly increased life expectancy around the world. Aging is associated with an increase in age-related diseases. The use of metformin (Met) as an anti-aging drug has recently been proposed based on its widespread use in clinical practice. Reports have shown that Met acts as an anti-aging agent. In this study, the effects of long-term, 1 year, Met administration on aging-related behaviors and longevity in ovariectomized mice was studied. Met (1 and 10 mg/kg, daily) was administered orally in ovariectomized mice. The anxiety-like behavior, working memory, and physical strength were measured through elevated plus maze, Y-maze, vertical grid holding, and the obligatory swimming capacity tests. Brains were harvested to measure brain-derived neurotrophic factor (BDNF) level. Also, the Kaplan-Meier survival curves were used to show differences and similarities in survival patterns. Met (10 mg/kg) decreased anxiety-like behaviors as well as increased muscle strength and working memory in the ovariectomized mice. Moreover, Met increased the physical strength and longevity as well as the level of BDNF in the ovariectomized mice. Our results indicate that Met administration can be an effective strategy for having a healthy aging in the absence of female gonadal hormones and reverses deleterious effects of ovariectomy-induced aging possibly through BDNF.

Depletion of β3-adrenergic receptor induces left ventricular diastolic dysfunction via potential regulation of energy metabolism and cardiac contraction

Left ventricular diastolic dysfunction (LVDD) is a central perturbation in heart failure with preserved ejection fraction, and there are currently no effective remedies to improve LVDD in clinical practice. The β3-adrenergic receptor (ADRB3) was reported to play protective effects on inhibiting myocardial fibrosis in response to hemodynamic stress. However, the effects of ADRB3 on LVDD and its underlying mechanisms are still undefined. In the current study, the role of ADRB3 in LVDD was identified in ADRB3-knockout mice. Echocardiography parameters showed that depletion of ADRB3 had little effect on cardiac systolic function but obviously led to cardiac diastolic dysfunction in vivo. Proteomics (including the global proteome, phosphorylated and acetylated proteome) and bioinformatics analysis (including GO analysis, KEGG pathway analysis, GO-Tree network, Pathway-Act network, and protein-protein interaction network) were performed on cardiac specimens of ADRB3-KO mice and wild-type mice. The results showed that the cardiac energy metabolism (especially the citrate cycle), actin cytoskeleton organization, and cardiac muscle contraction (related to mitogen-activated protein kinase, toll-like receptor, and ErbB signalling pathway) were potential core mechanisms underlying ADRB3-KO-induced LVDD. In addition, the protein-protein interaction network indicated that the core proteins associated with ADRB3-KO-induced LVDD were FGG, ALDH1A1, FGA, APOC3, SLC4A1, SERPINF2, HP, CTNNB1, and TKT. In conclusion, the absence of ADRB3 leads to LVDD, which is potentially associated with the regulation of cardiac energy metabolism, actin cytoskeleton organization, and cardiac muscle contraction.

Mitochondrial Dysfunction and Diabetes: Is Mitochondrial Transfer a Friend or Foe?

Obesity, insulin resistance and type 2 diabetes are accompanied by a variety of systemic and tissue-specific metabolic defects, including inflammation, oxidative and endoplasmic reticulum stress, lipotoxicity, and mitochondrial dysfunction. Over the past 30 years, association studies and genetic manipulations, as well as lifestyle and pharmacological invention studies, have reported contrasting findings on the presence or physiological importance of mitochondrial dysfunction in the context of obesity and insulin resistance. It is still unclear if targeting mitochondrial function is a feasible therapeutic approach for the treatment of insulin resistance and glucose homeostasis. Interestingly, recent studies suggest that intact mitochondria, mitochondrial DNA, or other mitochondrial factors (proteins, lipids, miRNA) are found in the circulation, and that metabolic tissues secrete exosomes containing mitochondrial cargo. While this phenomenon has been investigated primarily in the context of cancer and a variety of inflammatory states, little is known about the importance of exosomal mitochondrial transfer in obesity and diabetes. We will discuss recent evidence suggesting that (1) tissues with mitochondrial dysfunction shed their mitochondria within exosomes, and that these exosomes impair the recipient's cell metabolic status, and that on the other hand, (2) physiologically healthy tissues can shed mitochondria to improve the metabolic status of recipient cells. In this context the determination of whether mitochondrial transfer in obesity and diabetes is a friend or foe requires further studies.

Isobaric tags for relative and absolute quantitation‑based proteomics reveals potential novel biomarkers for the early diagnosis of acute myocardial infarction within 3 h

Acute myocardial infarction (AMI) is one of the most common and life-threatening cardiovascular diseases. However, the ability to diagnose AMI within 3 h is currently lacking. The present study aimed to identify the differentially expressed proteins of AMI within 3 h and to investigate novel biomarkers using isobaric tags for relative and absolute quantitation (ITRAQ) technology. A total of 30 beagle dogs were used for establishing the MI models successfully by injecting thrombin powder and a polyethylene microsphere suspension. Serum samples were collected prior to (0 h) and following MI (1, 2 and 3 h). ITRAQ-coupled liquid chromatography-mass spectrometry (LC-MS) technology was used to identify the differentially expressed proteins. The bioinformatics analysis selected several key proteins in the initiation of MI. Further analysis was performed using STRING software. Finally, western blot analysis was used to evaluate the results obtained from ITRAQ. In total, 28 proteins were upregulated and 23 were downregulated in the 1 h/0 h group, 28 proteins were upregulated and 26 were downregulated in the 2 h/0 h group, and 24 proteins were upregulated and 19 were downregulated in the 3 h/0 h group. The Gene Ontology (GO) annotation and functional enrichment analysis identified 19 key proteins. Protein-protein interactions (PPIs) were investigated using the STRING database. GO enrichment analysis revealed that a number of key proteins, including ATP synthase F1 subunit β (ATP5B), cytochrome c oxidase subunit 2 and cytochrome c, were components of the electron transport chain and were involved in energy metabolism. The western blot analysis demonstrated that the expression of ATP5B decreased significantly at all three time points (P<0.01), which was consistent with the ITRAQ results, whereas the expression of fibrinogen γ chain increased at 2 and 3 h (P<0.01) and the expression of integrator complex subunit 4 increased at all three time points (P<0.01), which differed from the ITRAQ results. According to the proteomics of the beagle dog MI model, ATP5B may serve as the potential biomarkers of AMI. Mitochondrial dysfunction and disruption of the electron transport chain may be critical indicators of early MI within 3 h. These finding may provide a novel direction for the diagnosis of AMI.

Metformin intervention prevents cardiac dysfunction in a murine model of adult congenital heart disease

OBJECTIVE

Congenital heart disease (CHD) is the most frequent birth defect worldwide. The number of adult patients with CHD, now referred to as ACHD, is increasing with improved surgical and treatment interventions. However the mechanisms whereby ACHD predisposes patients to heart dysfunction are still unclear. ACHD is strongly associated with metabolic syndrome, but how ACHD interacts with poor modern lifestyle choices and other comorbidities, such as hypertension, obesity, and diabetes, is mostly unknown.

METHODS

We used a newly characterized mouse genetic model of ACHD to investigate the consequences and the mechanisms associated with combined obesity and ACHD predisposition. Metformin intervention was used to further evaluate potential therapeutic amelioration of cardiac dysfunction in this model.

RESULTS

ACHD mice placed under metabolic stress (high fat diet) displayed decreased left ventricular ejection fraction. Comprehensive physiological, biochemical, and molecular analysis showed that ACHD hearts exhibited early changes in energy metabolism with increased glucose dependence as main cardiac energy source. These changes preceded cardiac dysfunction mediated by exposure to high fat diet and were associated with increased disease severity. Restoration of metabolic balance by metformin administration prevented the development of heart dysfunction in ACHD predisposed mice.

CONCLUSIONS

This study reveals that early metabolic impairment reinforces heart dysfunction in ACHD predisposed individuals and diet or pharmacological interventions can be used to modulate heart function and attenuate heart failure. Our study suggests that interactions between genetic and metabolic disturbances ultimately lead to the clinical presentation of heart failure in patients with ACHD. Early manipulation of energy metabolism may be an important avenue for intervention in ACHD patients to prevent or delay onset of heart failure and secondary comorbidities. These interactions raise the prospect for a translational reassessment of ACHD presentation in the clinic.

Metformin improves diastolic function in an HFpEF-like mouse model by increasing titin compliance

Heart failure with preserved ejection fraction (HFpEF) is a syndrome characterized by increased diastolic stiffness, for which effective therapies are lacking. Slater et al. show that metformin lowers titin-based passive stiffness in an HFpEF mouse model and may therefore be of therapeutic benefit.

Heart failure with preserved ejection fraction (HFpEF) is a complex syndrome characterized by a preserved ejection fraction but increased diastolic stiffness and abnormalities of filling. Although the prevalence of HFpEF is high and continues to rise, no effective therapies exist; however, the diabetic drug metformin has been associated with improved diastolic function in diabetic patients. Here we determine the therapeutic potential of metformin for improving diastolic function in a mouse model with HFpEF-like symptoms. We combine transverse aortic constriction (TAC) surgery with deoxycorticosterone acetate (DOCA) supplementation to obtain a mouse model with increased diastolic stiffness and exercise intolerance. Echocardiography and pressure–volume analysis reveal that providing metformin to TAC/DOCA mice improves diastolic function in the left ventricular (LV) chamber. Muscle mechanics show that metformin lowers passive stiffness of the LV wall muscle. Concomitant with this improvement in diastolic function, metformin-treated TAC/DOCA mice also demonstrate preserved exercise capacity. No metformin effects are seen in sham operated mice. Extraction experiments on skinned ventricular muscle strips show that the metformin-induced reduction of passive stiffness in TAC/DOCA mice is due to an increase in titin compliance. Using phospho-site-specific antibodies, we assay the phosphorylation of titin’s PEVK and N2B spring elements. Metformin-treated mice have unaltered PEVK phosphorylation but increased phosphorylation of PKA sites in the N2B element, a change which has previously been shown to lower titin’s stiffness. Consistent with this result, experiments with a mouse model deficient in the N2B element reveal that the beneficial effect of metformin on LV chamber and muscle stiffness requires the presence of the N2B element. We conclude that metformin offers therapeutic benefit during HFpEF by lowering titin-based passive stiffness.

Targeting mitochondrial dysfunction and oxidative stress in heart failure: Challenges and opportunities

Mitochondrial dysfunction characterized by impaired bioenergetics, oxidative stress and aldehydic load is a hallmark of heart failure. Recently, different research groups have provided evidence that selective activation of mitochondrial detoxifying systems that counteract excessive accumulation of ROS, RNS and reactive aldehydes is sufficient to stop cardiac degeneration upon chronic stress, such as heart failure. Therefore, pharmacological and non-pharmacological approaches targeting mitochondria detoxification may play a critical role in the prevention or treatment of heart failure. In this review we discuss the most recent findings on the central role of mitochondrial dysfunction, oxidative stress and aldehydic load in heart failure, highlighting the most recent preclinical and clinical studies using mitochondria-targeted molecules and exercise training as effective tools against heart failure.