Metformin and myocardial ischemia and reperfusion injury: Moving toward "prime time" human use?

The benefits of oral glucose-lowering agents: GLP-1 receptor agonists, DPP-4 and SGLT-2 inhibitors on myocardial ischaemia/reperfusion injury

Myocardial infarction (MI) is a life-threatening cardiovascular disease that, on average, results in 8.5 million deaths worldwide each year. Timely revascularization of occluded vessels is a critical method of myocardial salvage. However, reperfusion paradoxically leads to the worsening of myocardial damage known as myocardial ischaemia/reperfusion injury (MI/RI). Therefore, reducing the size of myocardial infarction after reperfusion is critical and remains an important therapeutic goal. The susceptibility of the myocardium to MI/RI may be increased by diabetes. Currently, some traditional antidiabetic agents such as metformin reduce MI/RI by decreasing inflammation, inhibiting oxidative stress, and improving vascular endothelial function. This appears to be a new direction for the treatment of MI/RI. Recent cardiovascular outcome trials have shown that several oral antidiabetic agents, including glucagon-like peptide-1 receptor agonists (GLP-1RAs), dipeptidyl peptidase-4 inhibitors (DPP-4is), and sodium-glucose-linked transporter-2 inhibitors (SGLT-2is), not only have good antidiabetic effects but also have a protective effect on myocardial protection. This article aims to discuss the mechanisms and effects of oral antidiabetic agents, including GLP-1RAs, DPP-4is, and SGLT-2is, on MI/RI to facilitate their clinical application.

Platelet Membrane-Encapsulated Nanocomplexes Based on Profundity Scavenging ROS Strategy for Myocardial Infarction Therapy

Ischemia-induced myocardial injury has become a serious threat to human health, and its treatment remains a challenge. The occurrence of ischemic events leads to a burst release of reactive oxygen species (ROS), which triggers extensive oxidative damage and leads to dysfunctional autophagy, making it difficult for cells to maintain homeostasis. Antioxidants and modulation of autophagy have thus become promising strategies for the treatment of ischemic myocardial injury. This study proposes an antioxidant-activated autophagy therapeutic regimen based on combining melanin (Mel), an excellent antioxidant with metformin mimetic ploymetformin via electrostatic interactions, to obtain a nanocomplex (Met-Mel). The nanocomplex is finally encapsulated with platelet membranes (PMN) to construct a biomimetic nanoparticle (PMN@Met-Mel) capable of targeting injured myocardium. The prepared PMN@Met-Mel has good Mel loading capacity and optimal biosafety. It exhibits excellent antioxidant activity and autophagy activation, rapidly restoring mitochondrial function. Moreover, RNA sequencing (RNA-seq) analysis reveals that PMN@Met-Mel operates mechanistically by triggering the activation of the autophagy pathway. Subsequent in vivo experiments showcase promising cardioprotective effects of these nanoparticles. These discoveries present a newly devised nanoplatform with promising potential for the effective treatment of myocardial infarction.

Endoplasmic reticulum stress and alterations of peroxiredoxins in aged hearts

Aging-related cardiovascular disease is influenced by multiple factors, with oxidative stress being a key contributor. Aging-induced endoplasmic reticulum (ER) stress exacerbates oxidative stress by impairing mitochondrial function. Furthermore, a decline in antioxidants, including peroxiredoxins (PRDXs), augments the oxidative stress during aging. To explore if ER stress leads to PRDX degradation during aging, young adult (3 mo.) and aged (24 mo.) male mice were studied. Treatment with 4-phenylbutyrate (4-PBA) was used to alleviate ER stress in young adult and aged mice. Aged hearts showed elevated oxidative stress levels compared to young hearts. However, treatment with 4-PBA to attenuate ER stress reduced oxidative stress in aged hearts, indicating that ER stress contributes to increased oxidative stress in aging. Moreover, aging resulted in reduced levels of peroxiredoxin 3 (PRDX3) in mitochondria and peroxiredoxin 4 (PRDX4) in myocardium. While 4-PBA treatment improved PRDX3 content in aged hearts, it did not restore PRDX4 content in aged mice. These findings suggest that ER stress not only leads to mitochondrial dysfunction and increased oxidant stress but also impairs a vital antioxidant defense through decreased PRDX3 content. Additionally, the results suggest that PRDX4 may contribute an upstream role in inducing ER stress during aging.

Acute, High Dose Metformin Therapy at Reperfusion Decreases Infarct Size in the High-Risk Aging Heart

Elderly patients (age > 75) sustain larger infarcts with greater mortality from ST elevation myocardial infarcts (STEMI) despite successful reperfusion treatment. Elderly age remains an independent risk despite correction for clinical and angiographic variables. The elderly represent a high-risk population and may benefit from treatment in addition to reperfusion alone. We hypothesized that modulation of cardiac signaling and metabolism with acute, high dose metformin given at reperfusion would exhibit additional cardioprotection. Using a translational aging murine model (22-24-month C57BL/6J mice) of in vivo STEMI (45 min artery occlusion with reperfusion for 24 hours); treatment acutely at reperfusion by high dose metformin decreased infarct size and enhanced contractile recovery, demonstrating cardioprotection in the high-risk aging heart.

Metformin preconditioning protects against myocardial stunning and preserves protein translation in a mouse model of cardiac arrest

Cardiac arrest (CA) causes high mortality due to multi-system organ damage attributable to ischemia-reperfusion injury. Recent work in our group found that among diabetic patients who experienced cardiac arrest, those taking metformin had less evidence of cardiac and renal damage after cardiac arrest when compared to those not taking metformin. Based on these observations, we hypothesized that metformin's protective effects in the heart were mediated by AMPK signaling, and that AMPK signaling could be targeted as a therapeutic strategy following resuscitation from CA. The current study investigates metformin interventions on cardiac and renal outcomes in a non-diabetic CA mouse model. We found that two weeks of metformin pretreatment protects against reduced ejection fraction and reduces kidney ischemia-reperfusion injury at 24 h post-arrest. This cardiac and renal protection depends on AMPK signaling, as demonstrated by outcomes in mice pretreated with the AMPK activator AICAR or metformin plus the AMPK inhibitor compound C. At this 24-h time point, heart gene expression analysis showed that metformin pretreatment caused changes supporting autophagy, antioxidant response, and protein translation. Further investigation found associated improvements in mitochondrial structure and markers of autophagy. Notably, Western analysis indicated that protein synthesis was preserved in arrest hearts of animals pretreated with metformin. The AMPK activation-mediated preservation of protein synthesis was also observed in a hypoxia/reoxygenation cell culture model. Despite the positive impacts of pretreatment in vivo and in vitro, metformin did not preserve ejection fraction when deployed at resuscitation. Taken together, we propose that metformin's in vivo cardiac preservation occurs through AMPK activation, requires adaptation before arrest, and is associated with preserved protein translation.

Metformin Protects Against Cardiac and Renal Damage in Diabetic Cardiac Arrest Patients

INTRODUCTION

Metformin is a first-line diabetic therapy that improves survival in a wide number of ischemic pathologies. We tested the association of metformin with markers of cardiac and renal injury in diabetic post-arrest patients.

METHODS

We performed a retrospective analysis of clinical outcomes in diabetic cardiac arrest patients with and without metformin therapy at a single academic medical center. We used generalized linear models to test the independent association of metformin, insulin, and other hypoglycemic agents with peak 24-hour serum creatinine and peak 24-hour serum troponin.

RESULTS

Metformin prescription at the time of SCA was independently associated with lower 24-hour peak serum troponin and lower 24-hour peak serum creatinine when compared to non-metformin patients.

CONCLUSION

Metformin pretreatment may offer cardiac and renal protection for diabetic patients during sudden cardiac arrest.

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

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

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

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