Myeloid differentiation factor 2 inhibitor and N-acetyl cysteine synergistically reduced left ventricular dysfunction in rats with cardiac ischemia/reperfusion injury

Background

Myeloid differentiation factor 2 inhibitor (MD2i) is a novel anti-inflammatory agent that exerts favorable outcomes in various diseases including cardiac ischemia/reperfusion (I/R) injury. However, whether a potent antioxidant N-acetyl cysteine (NAC) can augment the beneficial effects of MD2i in rats with cardiac I/R injury have never been investigated.

Purpose

We tested the hypothesis that NAC increases the beneficial effects of MD2i against cardiac I/R injury in rats.

Methods

Rats were divided into either a sham (n=6) or cardiac I/R group (n=72). Rats in the I/R group received one of the following 6 treatments (n=12 each) at the onset of reperfusion: vehicle, MD2i at 20 and 40 mg/kg, NAC at 75 and 150 mg/kg, and combined MD2i 20 mg/kg with NAC 150 mg/kg. Left ventricular (LV) function, infarct size, arrhythmia score, and cardiac mitochondrial function and dynamics were determined.

Results

Myocardial infarction, LV dysfunction, and cardiac arrhythmias were observed in rats with cardiac I/R injury, along with mitochondrial dysfunction (Fig. 1). Treatment with MD2i at either 20 or 40 mg/kg effectively reduced LV dysfunction but failed to reduce the infarct size (Fig. 1). NAC at 150 mg/kg, but not at 75 mg/kg, significantly decreased both LV dysfunction and infarct size following cardiac I/R injury (Fig. 1). However, combined treatment exerted even greater efficacy in reducing cardiac I/R injury than monotherapy, through a greater reduction of cardiac mitochondrial dysfunction and mitochondrial fission (Fig. 1). However, no benefit on reducing the arrhythmia score in all groups.

Conclusion

Combined MD2i and NAC treatment exerted a superior cardioprotective effect against cardiac I/R injury than either monotherapy regimen via an improved cardiac mitochondrial function.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): 1. NSTDA Research Chair Grant from the National Science and Technology Development Agency Thailand2. National Research Council of Thailand

Inhibition of myeloid differentiation factor 2 by MAC28 suppresses reactive oxygen species, inflammation and improves mitochondrial function, leading to improved cardiac function in prediabetic rats

Background

Chronic inflammation involves in the left ventricular (LV) dysfunction in high-fat diet (HFD)-induced prediabetes, along with cardiac mitochondrial dysfunction. This involved an activation of myeloid differentiation factor 2 (MD2)/toll-like receptor 4 (TLR4) by lipopolysaccharide, leading to inflammatory cytokines production in the heart. MAC28 is a novel MD2 inhibitor, which had been shown to provide effects against LPS-induced cytokine secretion from macrophages. However, the potential benefits of MAC28 on the LV function and its underlying mechanisms in HFD-induced prediabetic rats are unknown.

Purpose

We tested the hypothesis that MAC28 improves LV function in prediabetic rats by reducing cardiac oxidative stress, inflammation, and cardiac mitochondrial dysfunction.

Methods

Male Wistar rats were fed either a normal diet (ND, n=8) or HFD (n=24) for 16 weeks. At week 12, HFD-fed rats developed prediabetes and LV dysfunction. At this time, these HFD-fed rats were divided into 3 treatment groups (n=8/group): 1) vehicle (HFDV; 1% Na-carboxymethyl cellulose; p.o.); 2) MAC28 (40 mg/kg; p.o.); 3) metformin (300 mg/kg; p.o.; a positive control), the ND-fed rats received a vehicle (NDV). Rats were received their treatment for 4 weeks. Then, LV function and heart rate variability (HRV) were examined, and the heart was removed to determinecardiac malondialdehyde (MDA), cardiac inflammation (TNF-α) and mitochondrial function.

Results

HFD-induced prediabetes, together with depressed HRV and %LV ejection fraction (LVEF) (Fig. 1A). Moreover, cardiac oxidative stress and inflammation overproduction, and cardiac mitochondrial dysfunction was also observed, shown by elevated cardiac MDA, cardiac TNF-α protein levels, and mitochondrial ROS levels, mitochondrial depolarization and swelling (Fig. 1B). Notably, treatment with MAC28 effectively improved HRV and %LVEF and HRV (Fig. 1A), compared to HFDV group. Moreover, MAC28 significantly reduced cardiac MDA levels, cardiac TNF-α protein levels and cardiac mitochondrial dysfunction in HFD-induced prediabetic rats (Fig. 1B). These beneficial effects were also observed in metformin-treated rats (Fig. 1A, B).

Conclusion

MAC28 exerts cardioprotection in prediabetic rats by reducing cardiac oxidative stress, inflammation, and mitochondrial dysfunction, leading to restoring LV function.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This work was supported by the Thailand Science Research and Innovation

Melatonin membrane receptor 2 activation is a key determinant for melatonin-mediated cardioprotection in cardiac ischaemia-reperfusion injury

Background

Cardiac ischaemia/reperfusion (I/R) injury has been an economic and health burden worldwide. Previous studies have reported the beneficial effects of melatonin when given prior to cardiac ischaemia in animals with cardiac I/R injury. However, the effects of melatonin on the hearts when it is given after ischaemia or at the onset of reperfusion, which is more relevant to the clinical setting, is not known. Moreover, the mechanisms responsible for the potential benefits of melatonin and the roles of melatonin receptors on the heart during cardiac I/R injury have not been fully investigated.

Purpose

We tested the hypothesis that in rats with cardiac I/R injury, melatonin exerts cardioprotective effects even when it is given after ischaemia via an activation of both melatonin receptors 1 (MT1) and 2 (MT2), leading to decreased mitochondrial dysfunction, mitochondrial dynamics imbalance, excessive mitophagy, cardiomyocyte death and finally resulting in decreased infarct size and improved left ventricular (LV) function.

Methods

Male Wistar rats were subjected to cardiac I/R (30 min of LAD ligation and 120 min of reperfusion). These rats were divided into 4 interventions (n=12/group) including vehicle, pretreatment with melatonin, melatonin treatment during ischaemia, or at the onset of reperfusion. Melatonin was given to the rats at the dose of 10 mg/kg via intravenous injection. In addition, either a non-specific melatonin receptor blocker (Luzindole) or specific MT2 blocker (4-PPDOT) at 1 mg/kg was given intravenously to 2 additional sets of rats (n=12/set) prior to melatonin and cardiac I/R induction. At the end of cardiac I/R, infarct size, LV function, and molecular mechanisms were determined. Furthermore, in vitro experiment was conducted in MT1 or MT2 silenced H9C2 cell with hypoxia/reoxygenation (H/R) to investigate the mechanism underlying cardioprotective effects of melatonin during cardiac I/R.

Results

Rats in all melatonin-treated groups had similarly reduced cardiac I/R injury as indicated by reduced infarct size (Fig. 1A), arrhythmia score. Melatonin-treated rats also had decreased mitochondrial ROS production, mitochondrial depolarization and swelling, decreased p-Drp1/Drp1 ratio (Fig. 1B) and increased Mfn1, Mfn2, and OPA1, and decreased apoptosis, leading to increased %LVEF. Luzindole and 4-PPDOT abolished these protective effects of melatonin (Fig. 1A). In in vitro study, melatonin increased %cell viability (Fig. 1C), reduced mitochondrial dynamics imbalance and cardiomyocyte apoptosis in H9C2 cells with H/R. However, these beneficial effects of melatonin were abrogated only in MT2 silenced H9C2 cell with H/R.

Conclusion

Melatonin exerted both preventive and treatment effects in reducing cardiac I/R injury. Its cardioprotective effects were dependent upon the activation of MT2 receptor.

Figure 1

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): National Science and Technology Development Agency of Thailand

Necroptosis inhibitor directly reduced left ventricular dysfunction in obese-insulin resistant rats, independent of the metabolic status

Background

The number of obese people is increasing globally. Our previous studies showed that chronic high-fat diet (HFD) consumption led to obesity with peripheral insulin resistance, which was associated with left ventricular (LV) dysfunction. Mechanistically, cardiac mitochondrial dysfunction and cell death are proposed as an underlying mechanism for LV dysfunction in obese subjects. Recently, necroptosis was defined as a novel cell death pathway, which can be found in various types of cardiac diseases such as myocardial ischaemia and heart failure. Pharmacological inhibition of necroptosis by necrostatin 1 (nec-1) provided the favorable outcomes to those cardiac diseases. However, the roles of necroptosis and the effects of nec-1 on the heart of obese-insulin resistant rats have never been investigated.

Purpose

We hypothesized that nec-1 attenuates LV dysfunction by reducing cardiac mitochondrial dysfunction, necroptosis, and apoptosis in obese-insulin resistant rats.

Methods

Male rats (n=32) were fed with normal diet (ND) or HFD for 12 weeks to induce obese-insulin resistance. At weeks 13, HFD-fed rats were assigned into 3 interventional groups (n=8/group) as follows: 1) HFD-fed rats treated with saline, 2) HFD-fed rats treated with nec-1 (1.65 mg/kg/day, subcutaneous injection), 3) HFD-fed rats treated with metformin (300 mg/kg/day, oral gavage feeding, served as a positive control). ND rats were treated with saline. Rats received their assigned interventions for additional 7 weeks. Blood pressure (BP), cardiac sympathovagal balance, and LV function were determined. At the end, the heart was excised to determine cardiac mitochondrial function including mitochondrial respiration, reactive oxygen species (ROS) levels, membrane potential changes, swelling, as well as apoptosis and necroptosis protein levels.

Results

HFD-fed rats had increased body weight, visceral fat deposition, hyperinsulinemia with euglycemia, and dyslipidemia. Moreover, HFD-fed rats had increased systolic and diastolic BP, reduced cardiac sympathovagal balance, and %LV ejection fraction (LVEF) (Fig. 1A). For mitochondrial function, respiratory control ratio was decreased, ROS levels were increased, along with mitochondrial membrane depolarization and swelling (Fig. 1B). Both necroptosis and apoptosis were observed in HFD-fed rats. Treatment with nec-1 reduced systolic and diastolic BP, cardiac sympathovagal imbalance, and increased %LVEF (Fig. 1A). Necroptosis and apoptosis were reduced, and all mitochondrial function parameters were improved in nec-1 treated rats (Fig. 1B). However, the metabolic parameters were not modified by nec-1. Treatment with metformin had similar benefits as nec-1 (Fig. 1), with additional improvement in metabolic parameters in HFD-fed rats.

Conclusion

Nec-1 directly improves LV function in obese-insulin resistant rats via attenuating cardiac mitochondrial dysfunction and cell death, independent of metabolic parameters.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): National Science and Technology Development Agency, Thailand Research Fund (TRF)

Pretreatment with metformin reduced dendritic spine loss following cardiac ischaemia/reperfusion injury by preventing amyloid beta aggregation, brain inflammation and mitochondrial dysfunction

Background

Cognitive impairment is a major complication following acute myocardial infarction (AMI). Although reperfusion therapy is a standard treatment for AMI, it leads to additional damage to the heart, known as cardiac ischaemia/reperfusion (I/R) injury. In addition to cardiac damage, brain damage was observed following cardiac I/R including brain mitochondrial dysfunction, brain inflammation, amyloid beta aggregation, resulting in dendritic spine loss. Metformin has been reported as an effective neuroprotective agent in several brain pathologies such as stroke, diabetes-related cognitive decline, and cerebral I/R injury. However, the effects of metformin on the brain pathology after cardiac I/R have not been investigated.

Purpose

We hypothesized that metformin attenuates brain damages and increases dendritic spine density by preventing brain mitochondrial dysfunction, brain inflammation, and amyloid beta aggregation in non-diabetic rats.

Methods

Male Wistar rats (n=30) were received either sham operation (n=6) or cardiac I/R operation (n=24). Cardiac I/R was done by left anterior descending coronary artery ligation for 30 min followed by a reperfusion for 120 min. In cardiac I/R group, rats were randomly divided into 4 interventions (n=6/group) as follows; 1) vehicle (a normal saline solution), 2) 100 mg/kg of metformin (Met 100), 3) 200 mg/kg of metformin (Met 200), and 4) 400 mg/kg of metformin (Met 400). Sham operated rats were received normal saline solution. Metformin or vehicle was given to the rats at 15 min prior to cardiac ischemia via intravenous injection. At the end of reperfusion, rats were sacrificed, and the brain was rapidly removed to determine brain mitochondrial function, microglial morphology, Alzheimer's related protein, and dendritic spine density.

Results

Cardiac I/R led to brain mitochondrial dysfunction as indicated by increasing reactive oxygen species (ROS) levels, mitochondrial membrane depolarization, and mitochondrial swelling, compared with sham. Moreover, microglial hyperactivity was observed, together with tau hyperphosphorylation and amyloid beta aggregation, compared with sham (Fig. 1). All dosages of metformin successfully activated AMPK at the similar levels, compared with vehicle group. Mitochondrial ROS and membrane potential changes were equally improved in all groups of metformin, compared with vehicle. Although mitochondrial swelling was reduced in all groups of metformin, it was markedly reduced in Met 400 group (Fig. 1). Furthermore, microglial hyperactivity, amyloid beta aggregation, and tau hyperphosphorylation were equally reduced in all groups of metformin. For dendritic spine density, metformin significantly increased dendritic spine density, and the density was highest in Met400 group, compared with other groups (Fig. 1).

Conclusion

Pretreatment with metformin offers neuroprotection against the brain damages following cardiac I/R injury in a dose-dependent manner.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Thailand Research Fund (SCC), and National Science and Technology Development Agency Thailand (NC)