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

Fibroblast growth factor 21 is independently associated with long term mortality in metabolic syndrome

Background

Metabolic syndrome (MetS), a cluster of interrelated cardiovascular risk factors, is associated with increased risk of cardiovascular and non-cardiovascular disease. Fibroblast growth factor 21 (FGF21) plays an important role in metabolic regulation and has been shown to be elevated in MetS. However, role of FGF21 in pathogenesis of cardiovascular disease is still controversial.

Objective

We aimed to identify the association between plasma FGF21 level and long-term mortality in MetS patients.

Methods

Patients with MetS were enrolled in this study during 2015–2017. Blood samples for FGF21 were collected after 12-hour fasting and plasma FGF21 levels were determined using a human FGF21 enzyme-linked immunosorbent assay (ELISA) at the first time of the enrollment. Clinical parameters, and all-cause mortality were recorded. Cox-proportional hazard regression was used for the analysis of association between plasma FGF21 level and all-cause mortality.

Results

A total of 202 Mets patients (male 44.6%) with mean age of 64.3±8.3 years and BMI of 27.3±5.4 kg/m2 were enrolled. After a median follow up of 80 months, 32 (15.8%) patients died. Multivariable Cox proportional hazard regression showed that FGF21 level was independently associated with all-cause mortality after adjustment for age, established cardiovascular disease, estimated glomerular filtration rate and left ventricular ejection fraction. Patients with FGF21 level above median (240 pg/ml) had higher risk of all-cause death compared to patients with FGF21 ≤240 pg/ml (hazard ratio [HR], 3.66; 95% confidence interval [CI], 1.24–10.82; p=0.019) (Figure 1).

Conclusion

FGF21 level is independently associated with long term mortality in metabolic syndrome.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Thailand research fund

Chronic mitochondrial fusion promotor as a novel pharmacological intervention to alleviate left ventricular dysfunction in rats with chronic myocardial infarction

Background

Decreased cardiac mitochondrial fusion associated with increased mitochondrial dysfunction has been demonstrated in acute myocardial infarction pathology. However, whether this pathophysiologic process is associated with myocardial injury in chronic myocardial infarction (CMI) is still unclear. Recently, a novel pharmacological intervention to promote mitochondrial fusion using mitochondrial fusion promotor-M1 (M1) has been shown to exert cardioprotection against myocardial ischemia and reperfusion injury. However, the roles of M1 in CMI has never been investigated.

Purpose

We investigated the potential cardioprotective benefits of chronic treatment with mitochondrial fusion promotor-M1 in rats with chronic MI model.

Methods

Adult male Wistar rats were assigned to the sham group (n=5) and the CMI group (n=15), which was induced by a permanent left anterior descending coronary occlusion. After 1 week of operation, rats in the CMI group were randomly divided into 3 subgroups which was treated with one of the followings: 1) vehicle (3% DMSO/day, ip, CON, n=5), 2) enalapril (10 mg/kg/day, po, ENA, n=5), or 3) mitochondrial fusion promotor-M1 (2 mg/kg/day, ip, M1, n=5) once daily for 4 weeks. In the end, echocardiography for the left ventricular (LV) function was performed, and the heart was removed to determine the mitochondrial function and malondialdehyde (MDA) level for oxidative stress.

Results

CMI rats that received vehicle showed significantly impaired LV function and cardiac mitochondrial function as evidenced by a 60% reduction in LV ejection fraction (LVEF) along with increased mitochondrial reactive oxygen species (ROS) production, mitochondrial depolarization and mitochondrial swelling, respectively, when compared with the sham rats (Fig. 1A–D). The CMI rats also exhibited a higher cardiac tissue MDA level than those of sham rats, further indicating cardiac oxidative stress (Fig. 1E). Interestingly, chronic treatment with either enalapril or M1 effectively attenuated CMI-induced mitochondrial dysfunction and oxidative stress upregulation, thus increasing LVEF (27% improvement for both ENA and M1), when compared with the vehicle group (Fig. 1A).

Conclusion

Long-term promotion of mitochondrial fusion mitigated cardiac mitochondrial dysfunction and oxidative stress, eventually culminating in improved LV function in rats with CMI. These findings suggest that chronic modulation of mitochondrial fusion could be a promising pharmacological intervention to improve LV function in CMI.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): 1. The National Science and Technology Development Agency Thailand2. The Thailand Research Fund (RGJ)

Cardiac autonomic modulation with donepezil attenuates pyroptosis and mitochondrial dysfunction, leading to improved left ventricular function in trastuzumab-induced cardiotoxicity in rats

Background

Trastuzumab (Trz)-induced cardiotoxicity (TIC) is one of the most common cardiovascular complications of targeted anticancer agents. Cardiac inflammation, cardiac mitochondrial dysfunction, oxidative stress, and cardiac autonomic dysfunction have been identified as potential mechanisms underlying the adverse effects of TIC. Although cardiac inflammation is one of the key mechanisms triggering “pyroptosis”, i.e. a new inflammatory form of programmed cell death, the association between TIC and pyroptosis is still largely unknown. Moreover, the modulation of cardiac autonomic activity using an acetylcholinesterase inhibitor (AChE) has been shown to exert cardioprotection in various heart diseases. However, the role of donepezil (DPZ), an AChE, in treating TIC has never been investigated.

Purpose

We evaluated the cardioprotective effects of DPZ on left ventricular (LV) function, cardiac mitochondrial function, and pyroptosis in rats with TIC. We hypothesised that DPZ reduces mitochondrial dysfunction and pyroptosis, leading to a reduction of LV dysfunction in TIC rats.

Methods

Fifteen male Wistar rats were randomly divided into the control group (n=5, 0.9% normal saline solution, ip) and the Trz group (n=10, 4 mg/kg/day for 7 days, ip). Trz-treated rats were subdivided into the vehicle group (n=5, drinking water, po) and the DPZ group (n=5, 5 mg/kg/day for 7 days, po). At the end of the experiment, echocardiography was performed, and the heart was removed to determine the cardiac mitochondrial function and pyroptosis.

Results

Compared with the control group, %LV ejection fraction (%LVEF) was significantly decreased in the Trz group (Fig. 1A). Trz treatment also markedly increased cardiac mitochondrial reactive oxygen species (ROS) production and mitochondrial depolarisation, as indicated by a lower red/green fluorescence intensity ratio (Fig. 1B and C, respectively). Furthermore, Trz induced pyroptosis by increasing NLR family pyrin domain containing 3 (NLRP3) expression and cleaved Gasdermin D/Gasdermin D ratio, compared to the control group (Fig, 1D–F). Notably, DPZ co-treatment potentially reduced mitochondrial ROS production, mitochondrial depolarisation, and pyroptosis (NLRP3 and cleaved Gasdermin D/Gasdermin D ratio), leading to improved %LVEF (Figure 1).

Conclusion

DPZ alleviated cardiac dysfunction in TIC rats by improving mitochondrial function and reducing pyroptosis. These findings suggested that DZP could be a novel effective pharmacological intervention against TIC.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): 1. The National Science and Technology Development Agency Thailand2. The Thailand Research Fund (RGJ)

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

Ranolazine exerted cardioprotection against doxorubicin-induced cardiotoxicity through inhibiting excessive autophagy in rats

Background

Doxorubicin (Dox) is a highly effective chemotherapeutic agent for several malignancies. However, its cardiotoxicity and progressive heart failure are the most serious adverse effects that compromised its clinical use. Recently, ranolazine, the late sodium (Na+) current inhibitor for patients with chronic angina, has been suggested as a potential agent to treat early cardiotoxicity induced by antitumor drugs. In that single report, pretreatment with ranolazine improved cardiac function and decreased mortality rates in the Dox-treated rats, by decreasing oxidative stress and apoptosis. Nevertheless, its protective mechanisms on autophagy in the Dox-treated rats have never been elucidated.

Purpose

We hypothesized that ranolazine exerts cardioprotection in the Dox-treated rats by improving left ventricular (LV) function and reducing cardiac injury though suppressing excessive autophagy.

Methods

Male Wistar rats (n=24) received either normal saline solution (NSS, n=8) or Dox (3 mg/kg/day, i.p.) for 6 doses. Then, the Dox-treated rats were assigned to orally administered with either saline (n=8) or ranolazine (305 mg/kg/day, n=8) for 30 consecutive days. Following the treatment, the LV function, cardiac injury, and autophagy were determined.

Results

Dox caused LV dysfunction as indicated by the decreased %LV ejection fraction (LVEF) and the increased serum cardiac troponin-I (cTn-I) levels (Fig. 1A). In addition, Dox induced excessive autophagy by increasing Beclin-1, p62, and light chain 3-II/I (LC3II/I) protein expressions (Fig. 1B). Treatment with ranolazine attenuated autophagic-related proteins (Beclin-1, p62, and LC3II/I), and improved LV function (Fig. 1A-B).

Conclusion

Ranolazine exerted cardioprotection in the Dox-treated rats through suppressing autophagic-regulatory proteins, suggesting its potential cardioprotective roles as a concomitant therapy for cancer patients receiving Dox.

Funding Acknowledgement

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

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)

Hyperbaric oxygen therapy attenuates D-galactose-induced-age-related cardiac dysfunction through mitigating cardiac mitochondrial dysfunction in pre-diabetic rats

Background

D-galactose (D-gal) induced ageing has been shown to exacerbate left ventricular (LV) dysfunction via worsening of apoptosis and mitochondrial dysfunction in the heart of obese rats. Hyperbaric oxygen therapy (HBOT) has been demonstrated to exert anti-inflammatory and anti-apoptotic effects in multiple neurological disorders. However, the cardioprotective effect of HBOT on inflammation, apoptosis, LV and mitochondrial functions in D-gal induced ageing rats in the presence of obese-insulin resistant condition has never been investigated.

Purpose

We sought to determine the effect of HBOT on inflammation, apoptosis, mitochondrial functions and LV function in pre-diabetic rats with D-gal induced ageing. We hypothesized that HBOT attenuates D-gal induced cardiac mitochondrial dysfunctions and reduces inflammation and apoptosis, leading to improved LV function in pre-diabetic rats.

Methods

Forty-eight male Wistar rats were fed with either normal diet or high-fat diet for 12 weeks. Then, rats were treated with either vehicle groups (0.9% NSS, subcutaneous injection (SC)) or D-gal groups (150 mg/kg/day, SC) for 8 weeks. At week 21, rats in each group were equally divided into 6 sub-groups: normal diet fed rats treated with vehicle (NDV) sham, normal diet fed rats treated with D-gal (NDDg) sham, high fat diet fed rats treated with D-gal (HFDg) sham, high fat diet fed rats treated with vehicle (HFV) + HBOT, NDDg + HBOT and HFDg + HBOT. Sham treated rats were given normal concentration of O2 (flow rate of 80 L/min, 1 ATA for 60 minutes), whereas HBOT treated rats were subjected to 100% O2 (flow rate of 250 L/min, 2 ATA for 60 minutes), given once daily for 2 weeks.

Results

Under obese-insulin resistant condition, D-gal-induced ageing aggravated LV dysfunction (Fig 1A) and impaired cardiac mitochondrial function, increased cardiac inflammatory and apoptotic markers (Fig 1B). HBOT markedly reduced cardiac TNF-α level and TUNEL positive apoptotic cells, and improved cardiac mitochondrial function as indicated by decreased mitochondrial ROS production, mitochondrial depolarization and mitochondrial swelling, resulting in the restoration of the normal LV function in HFV and NDDg rats, compared to sham NDDg rats. In addition, in HFDg treated rats, HBOT attenuated cardiac TNF-α level, TUNEL positive apoptotic cells and cardiac mitochondrial dysfunction, compared to sham HFDg rats, leading to improved cardiac function as indicated by increased %LV ejection fraction (LVEF) (Figure 1).

Conclusion

HBOT efficiently alleviates D-gal-induced-age-related LV dysfunction through mitigating inflammation, apoptosis and mitochondrial dysfunction in pre-diabetic rats.

Figure 1

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): 1. The National Science and Technology Development Agency Thailand, 2. Thailand Research Fund Grants

Silencing of lipocalin-2 and its receptor improved cardiomyocytes viability via decreasing iron uptake, mitochondrial fission, mitophagy and apoptosis under iron overload condition

Background

Iron overload cardiomyopathy is a common cause of death in iron overload patients. L-type calcium channels (LTCC) and T-type calcium channels (TTCC) have been shown to play important roles for iron uptake into the heart under iron overload condition. Recently, cardiomyocytes which exposed to lipocalin-2 (LCN-2) have been shown to increase apoptosis due to excessive intracellular iron accumulation. However, the mechanistic roles of LCN-2 and LCN-2 receptor (LCN-2R) as iron transporters in cardiomyocytes under iron overload condition have never been investigated.

Purpose

We hypothesized that the LCN-2 and LCN-2R are alternate iron uptake pathways into cardiomyocytes under iron overload condition.

Methods

H9c2 cardiomyocytes were treated with either LCN-2 siRNA or LCN-2R siRNA for 72 hr or LTCC blocker (verapamil), TTCC blocker (TTA-P2), or iron chelator deferiprone (DFP) for 1 hr. After treatment, cells were exposed to ferric ammonium citrate (FAC, Fe3+) or FAC + 1mM ascorbic acid (Fe2+) at 200 μM for 48 hr. Intracellular iron level, cell viability, mitochondrial dynamics, mitophagy and apoptosis were determined.

Results

Both Fe2+ and Fe3+ treated groups showed significantly increased intracellular iron uptake, decreased cell viability, increased mitochondrial fission, mitophagy and apoptotic protein expression in cardiomyocytes. Under Fe2+ overload condition, treatments with LTCC blocker, TTCC blocker, and DFP could significantly decrease intracellular iron accumulation and increase cell viability via decreasing mitochondrial fission, mitophagy and cleaved caspase-3 (Figure), whereas both LCN-2 and LCN-2R siRNA treatment had no beneficial effects on these parameters. Under Fe3+ overload condition, treatment with LCN-2 siRNA, LCN-2R siRNA, and DFP showed beneficial effects on those parameters, whereas neither LTCC nor TTCC blocker provided these benefits (Figure 1).

Conclusion

Silencing of LCN-2 and LCN-2R increased cardiomyocyte viability via decreasing iron uptake, mitochondrial fission, mitophagy and apoptosis under Fe3+ iron overload condition. Meanwhile, treatment with calcium channel blockers improved cardiomyocytes viability via decreasing iron uptake, mitochondrial fission, mitophagy and apoptosis under Fe2+ iron overload condition. All of these findings suggested that LTCC and TTCC played important roles for Fe2+ uptake, whereas LCN-2 and LCN-2R were essential for Fe3+ uptake into the cardiomyocytes under iron overload conditions.

Figure 1. Cell viability and apoptosis

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Thailand Research Fund and NSTDA Research Chair Grant (NC)

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)

Cardiopreventive effects of mitochondrial dynamics modulators in pre-diabetic rats subjected to cardiac ischaemia-reperfusion injury

Background

Chronic exposure to a high-fat diet (HFD) consumption causes alteration of cardiac mitochondrial dynamics and function, leading to the abnormal left ventricular (LV) function. Since excessive mitochondrial fission and reduced mitochondrial fusion are correlated with both obesity and myocardial ischaemia, targeting mitochondrial fission and fusion could be an effective cardioprotective strategy. We previously showed that acute inhibition of mitochondrial fission and promotion of mitochondrial fusion exerted cardioprotection in obese rats. However, the chronic treatment with mitochondrial fission inhibitor (Mdivi-1) and mitochondrial fusion promoter (M1) in pre-diabetic rats subjected to cardiac ischaemia-reperfusion (I/R) injury has never been investigated.

Purpose

We investigated the cardiopreventive effects of chronic Mdivi-1 and M1 treatment in pre-diabetic rats with cardiac I/R injury on infarct size, mitochondrial function, and LV contractility.

Methods

Wistar rats (n=32, male) were fed with HFD for 12 weeks, then randomly divided into: 1) HFV (Vehicle, 0.1% DMSO), 2) HFMdivi1 (Mdivi-1, 1.2 mg/kg), and 3) HFM1 (M1, 2 mg/kg) with intraperitoneal injection. After 2 weeks of drugs administration, all rats underwent 30 min of left anterior descending coronary artery occlusion followed by reperfusion for 120 min. LV function was monitored throughout the experiment. At the end, the heart was removed to determine infarct size and mitochondrial function.

Results

Chronic treatment with Mdivi-1 and M1 similarly showed a decrease in mitochondrial reactive oxygen species and infarct size, leading to an improvement in LV function in HFD rats, as indicated by increased ejection fraction, when compared to HFV rats (Figure).

Conclusion

Mitochondrial fission inhibitor and fusion promoter exerted similar efficacy in protecting pre-diabetic rat hearts against cardiac I/R injury through attenuating mitochondrial dysfunction, reducing infarct size and increasing LV contractility.

Figure 1

Funding Acknowledgement

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

Acetylcholinesterase inhibitor protects against cardiac ischaemia/reperfusion injury via enhancing mitophagy and rebalancing mitochondrial dynamics

Background

Ischaemic heart disease is the most common cause of death globally. Although reperfusion therapy is essential to restore myocardial blood flow, it can also damage heart tissues, this process is known as ischaemia/reperfusion (I/R) injury. Cardiac autonomic imbalance including sympathetic overactivity and diminished parasympathetic activity plays an important role in cardiac I/R injury, resulting in left ventricular (LV) dysfunction. Increased vagus nerve activity by an electrical stimulation from an implantable medical device has been shown to be cardioprotective in cardiac I/R injury. However, the role of pharmacological intervention that increases parasympathetic activity on the heart during I/R is not clear.

Purpose

We investigated the effects of a parasympathomimetic drug, donepezil, on the heart with I/R injury. We hypothesized that donepezil exerts cardioprotective effects in rats with cardiac I/R injury by attenuating the impairment of cardiac mitochondrial function, mitochondrial dynamics and mitophagy, resulting in improved LV function.

Methods

Forty male Wistar rats were randomly divided into sham and I/R groups. In I/R group, rats were subjected to acute cardiac I/R injury by ligating left anterior descending coronary artery (LAD) for 30 mins followed by reperfusion for 120 mins, while sham group had similar operation but did not have LAD ligation. Moreover, rats in the I/R group were randomly assigned to be treated with either saline (vehicle group) or donepezil 3 mg/kg by intravenous injection. In donepezil-treated rats, they were divided into 3 subgroups to receive the drug at one of the following time-points; before ischaemia, or during ischaemia, or at the onset of reperfusion. During I/R protocol, LV function was recorded. At the end of protocol, the heart was removed to determine infarct size, cardiac mitochondrial function, mitochondrial dynamics, and mitophagy.

Results

Rats with cardiac I/R injury showed increased infarct size when compared to sham group (Fig. 1A). Rats in all donepezil-treated groups showed reduction of infarct size compared to the vehicle group. This accounts for ∼63%, ∼47%, and ∼44% reduction for the treatment before ischaemia, during ischaemia and onset of reperfusion, respectively. In addition, all donepezil-treated rats had improved LV function by attenuating the reduction of LV ejection fraction (Fig. 1B). The reduction in cardiac mitochondrial ROS production (Fig. 1C), increased mitophagy as indicated by increased PINK-1 expression (Fig. 1D), and rebalancing mitochondrial dynamics were also found in all donepezil-treated rats.

Conclusion

Donepezil protects against cardiac I/R injury by reducing mitochondrial ROS production, enhancing mitophagy, and improving mitochondrial dynamics, leading to decreased infarct size and improved cardiac function.

Figure 1. The effects of donepezil in cardiac I/R

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Thailand Research Fund grants TRF-Royal Golden Jubilee Program (TK and NC), RTA6180003 (SCC), RSA6180056 (SP); The NSTDA Research Chair grant from the National Science and Technology Development Agency Thailand (NC)

Metformin exerts cardioprotection via attenuating mitochondrial fission in cardiac ischaemia-reperfusion injury in rats

Background

Cardiac ischemia/reperfusion (I/R) injury following myocardial infarction reperfusion therapy is a phenomenon that results in further cardiomyocytes death and impaired cardiac contractility. Although metformin has been shown to exert cardioprotection in addition to glycemic control, its effect on cardiac I/R injury are still controversy, and the comparative doses of metformin in cardiac I/R injury have never been investigated.

Purpose

We hypothesized that metformin given acutely prior to cardiac ischaemia exerts cardioprotection in rats with cardiac I/R injury via attenuating cardiac mitochondrial dysfunction, leading to improved left ventricular (LV) function.

Methods

Forty Male Wistar rats were subjected to cardiac I/R injury. Four treatment groups were investigated. The first group received saline as a control group. The second to the fourth groups received metformin at 100, 200, and 400 mg/kg intravenously, respectively. During the I/R protocols, the LV function, arrhythmia score, and mortality rate were determined. At the end, the hearts were rapidly removed to determine infarct size, cardiac mitochondrial function, cardiac mitochondrial dynamics, and cardiac apoptosis.

Results

Metformin 200 mg/kg exerted the highest level of cardioprotection through the attenuated incidence of arrhythmia, decreased infarct size (Fig. 1), improved cardiac mitochondrial function, and decreased mitochondrial fission (Fig. 1) and cardiac apoptotic markers, leading to improved cardiac function during I/R injury. Although Metformin at all doses effectively decreased infarct size, improved cardiac mitochondrial function and LV function, Metformin at 200 mg/kg exerted the best efficacy (Fig. 1).

Conclusions

Metformin exerts cardioprotection by attenuating mitochondrial dysfunction and decreased mitochondrial fission, leading to decreased infarct size and ultimately improved LV function after acute cardiac I/R injury in rats. These findings also indicate the potential biphasic effects of metformin on infarct size which are dose-dependent.

Figure 1

Funding Acknowledgement

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

Plasma humanin as a prognostic biomarker for canine myxomatous mitral valve disease: a comparison with plasma NT-roBNP

Myxomatous mitral valve disease (MMVD) is a cardiac condition commonly found in older dogs. The disease process can lead to heart failure (HF). In HF, an increase of reactive oxygen species (ROS) and abnormal mitochondrial activity, as well as apoptosis, have been reported. Humanin (HN) is a polypeptide that has a cardioprotective effect against apoptosis and oxidative stress. The purposes of this study were (1) to investigate the potential role of plasma HN as a cardiac biomarker to predict disease progression of MMVD, and (2) to compare plasma HN concentrations with plasma NT-pro BNP concentrations. Thirty-one dogs were included in the study. The dogs were separated into four groups: Group 1 was healthy dogs (n = 8), Group 2 was MMVD class B (n = 8), Group 3 was MMVD class C (n = 8), and Group 4 was MMVD class D (n = 7). All dogs were given a physical examination, thoracic radiography, echocardiography, and samples of their blood were collected for hematology and blood chemistry analysis. Levels of plasma HN and plasma NT-proBNP were also investigated. The results showed that plasma HN levels were lower in the dogs with MMVD and that lower plasma HN levels were associated with greater severity of MMVD-induced HF. It was possible to observe changes in plasma HN levels at a less severe disease stage than plasma NT-proBNP in dogs with MMVD. These findings sug- gest that a decreased plasma HN level can be used as a biomarker to identify dogs with MMVD-induced HF.

Fibroblast growth factor 21 (FGF21) therapy attenuates left ventricular dysfunction and metabolic disturbance by improving FGF21 sensitivity, cardiac mitochondrial redox homoeostasis and structural changes in pre-diabetic rats

AIMS

Fibroblast growth factor 21 (FGF21) acts as a metabolic regulator and exerts cardioprotective effects. However, the effects of long-term FGF21 administration on the heart under the FGF21-resistant condition in obese, insulin-resistant rats have not been investigated. We hypothesized that long-term FGF21 administration reduces FGF21 resistance and insulin resistance and attenuates cardiac dysfunction in obese, insulin-resistant rats.

METHODS

Eighteen rats were fed on either a normal diet (n = 6) or a high-fat diet (HFD; n = 12) for 12 weeks. Then, rats in the HFD group were divided into two subgroups (n = 6 per subgroup) and received either the vehicle (HFV) or recombinant human FGF21 (rhFGF21, 0.1 mg kg(-1)  day(-1) ; HFF) injected intraperitoneally for 28 days. The metabolic parameters, inflammation, malondialdehyde (MDA), heart rate variability (HRV), left ventricular (LV) function, cardiac mitochondrial redox homoeostasis, cardiac mitochondrial fatty acid β-oxidation (FAO) and anti-apoptotic signalling pathways were determined.

RESULTS

HFV rats had increased dyslipidaemia, insulin resistance, plasma FGF21 levels, TNF-α, adiponectin and MDA, depressed HRV, and impaired LV and mitochondrial function. HFV rats also had decreased cardiac Bcl-2, cardiac PGC-1α and CPT-1 protein expression. However, FGF21 restored metabolic parameters, decreased TNF-α and MDA, increased serum adiponectin, and improved HRV, cardiac mitochondrial and LV function in HFF rats. Moreover, HFF rats had increased cardiac Bcl-2, cardiac PGC-1α and CPT-1 protein expression.

CONCLUSION

Long-term FGF21 therapy attenuates FGF21 resistance and insulin resistance and exerts cardioprotection by improving cardiometabolic regulation via activating anti-apoptotic and cardiac mitochondrial FAO signalling pathways in obese, insulin-resistant rats.

Blockade of mitochondrial calcium uniporter prevents cardiac mitochondrial dysfunction caused by iron overload

AIM

Iron overload in the heart can lead to iron-overload cardiomyopathy and cardiac arrhythmia. In the past decades, growing evidence has suggested that cardiac mitochondrial dysfunction is associated with the development of cardiac dysfunction and lethal arrhythmias. Despite these facts, the effect of iron overload on cardiac mitochondrial function is still unclear. In this study, we determined the effects of iron overload on the cardiac mitochondrial function and the routes of cardiac mitochondrial iron uptake. We tested the hypothesis that iron overload can lead to cardiac mitochondrial dysfunction and that mitochondrial calcium uniporter (MCU) plays a major role for cardiac mitochondrial iron uptake under iron-overload condition. Cardiac mitochondrial function was assessed via the determination of mitochondrial swelling, mitochondrial reactive oxygen species (ROS) production and mitochondrial membrane potential changes.

METHODS

Isolated cardiac mitochondria from male Wistar rats were used in this study. To determine the routes for cardiac mitochondrial iron uptake, isolated mitochondria were exposed to MCU blocker (Ru360), mitochondrial permeability transition pore (mPTP) blocker (cyclosporin A) and an iron chelator (deferoxamine).

RESULTS

We found that (i) iron overload caused cardiac mitochondrial dysfunction, indicated by increased ROS production, mitochondrial membrane depolarization and mitochondrial swelling; and (ii) only MCU blocker completely protected cardiac mitochondrial dysfunction caused by iron overload.

CONCLUSIONS

These findings strongly suggest that MCU could be the major route for iron uptake into cardiac mitochondria. The inhibition of MCU could be the novel pharmacological intervention for preventing iron-overload cardiomyopathy.

Decreased jaw bone density and osteoblastic insulin signaling in a model of obesity

Previous studies have demonstrated that decreased bone mass results from either the impairment of osteoblastic insulin signaling or obesity. Our previous study revealed that 12-week high-fat-diet (HFD) consumption caused obesity as well as peripheral and brain insulin resistance. However, the osteoblastic insulin resistance induced by HFD has not been elucidated. Therefore, we hypothesized that 12-week HFD rats exhibited not only peripheral insulin resistance but also osteoblastic insulin resistance, which leads to decreased jawbone quality. We found that the jawbones of rats fed a 12-week HFD exhibited increased osteoporosis. The osteoblastic cells isolated from HFD-fed rats exhibited the impairment of osteoblastic insulin signaling as well as reduction of cell proliferation and survival. In conclusion, this study demonstrated that insulin resistance induced by 12-week HFD impaired osteoblastic insulin signaling, osteoblast proliferation, and osteoblast survival and resulted in osteoporosis in the jawbone.

NaV 1.8, but not NaV 1.9, is upregulated in the inflamed dental pulp tissue of human primary teeth

AIM

To investigate alterations in Na(V) 1.8 and Na(V) 1.9 expression within inflamed dental pulp tissue of human primary teeth.

METHODOLOGY

Dental pulp tissue obtained from both normal and inflamed pulps in primary teeth as well as pulps from normal and inflamed permanent teeth was used. The quantity of Na(V) 1.8 and Na(V) 1.9 expression in the dental pulp tissue was investigated using Western blot analysis. General neuron marker (PGP9.5) was used to quantify for neural density, and an increase in metalloproteinase-9 was used to indicate pulpal inflammation in inflamed teeth. Statistically significant differences for each determined parameter between normal and inflamed teeth of both primary and permanent teeth were tested using the Mann-Whitney rank sum test.

RESULTS

There was no significant difference in neural density of normal and inflamed dental pulp tissue, although degrees of inflammation were increased in the inflamed dental pulp of both permanent and primary teeth (P < 0.05). Na(V) 1.8 and Na(V) 1.9 expression in inflamed pulps of permanent teeth increased significantly compared with normal permanent teeth (P < 0.05). However, only Na(V) 1.8 expression was increased significantly in the inflamed dental pulp of primary teeth (P < 0.05).

CONCLUSIONS

Na(V) 1.8 alone may be the therapeutic target for treatment of painful pulpitis in primary teeth.

Reversal of cardiac iron loading and dysfunction in thalassemic mice by curcuminoids

Non-transferrin bound iron (NTBI) is found in plasma of β-thalassemia patients and causes oxidative tissue damage. Cardiac siderosis and complications are the secondary cause of death in β-thalassemia major patients. Desferrioxamine (DFO), deferiprone (DFP) and deferasirox (DFX) are promising chelators used to get negative iron balance and improve life quality. DFP has been shown to remove myocardial iron effectively. Curcuminoids (CUR) can chelate plasma NTBI, inhibit lipid peroxidation and alleviate cardiac autonomic imbalance. Effects of CUR on cardiac iron deposition and function were investigated in iron-loaded mice. Wild type ((mu)β(+/+) WT) and heterozygous β-knockout ((mu)β(th-3/+) BKO) mice (C57BL/6) were fed with ferrocene-supplemented diet (Fe diet) and coincidently intervened with CUR and DFP for 2 months. Concentrations of plasma NTBI and malondialdehyde (MDA) were measured using HPLC techniques. Heart iron concentration was determined based on atomic absorption spectrophotometry and Perl's staining methods. Short-term electrocardiogram (ECG) was recorded with AD Instruments Power Lab, and heart rate variability (HRV) was evaluated using MATLAB 7.0 program. Fe diet increased levels of NTBI and MDA in plasma, nonheme iron and iron deposit in heart tissue significantly, and depressed the HRV, which the levels were higher in the BKO mice than the WT mice. CUR and DFP treatments lowered plasma NTBI as well as MDA concentrations (p <0.05), heart iron accumulation effectively, and also improved the HRV in the treated mice. The results imply that CUR would be effective in decreasing plasma NTBI and myocardial iron, alleviating lipid peroxidation and improving cardiac function in iron-loaded thalassemic mice.

Granulocyte colony-stimulating factor stabilizes cardiac electrophysiology and decreases infarct size during cardiac ischaemic/reperfusion in swine

AIM

Effects of granulocyte colony-stimulating factor (G-CSF) on cardiac electrophysiology during ischaemic/reperfusion (I/R) period are unclear. We hypothesized that G-CSF stabilizes cardiac electrophysiology during I/R injury by prolonging the effective refractory period (ERP), increasing the ventricular fibrillation threshold (VFT) and decreasing the defibrillation threshold (DFT), and that the cardioprotection of G-CSF is via preventing cardiac mitochondrial dysfunction.

METHODS

In intact-heart protocol, pigs were infused with either G-CSF or vehicle (n = 7 each group) without I/R induction. In I/R protocol, pigs were infused with G-CSF (0.33 μg kg(-1 ) min(-1) ) or vehicle (n = 8 each group) for 30 min prior to a 45-min left anterior descending artery occlusion and at reperfusion. Diastolic pacing threshold (DPT), ERP, VFT and DFT were determined in all pigs before and during I/R period. Rat's isolated cardiac mitochondria were used to test the protective effect of G-CSF (100 nm) in H(2) O(2) -induced mitochondrial oxidative damage.

RESULTS

Neither G-CSF nor vehicle altered any parameter in intact-heart pigs. During ischaemic period, G-CSF significantly increased the DPT, ERP and VFT without altering the DFT. During reperfusion, G-CSF continued to increase the DPT without altering other parameters. The infarct size was significantly decreased in the G-CSF group, compared to the vehicle. G-CSF could also prevent cardiac mitochondrial swelling, decrease ROS production, and prevent mitochondrial membrane depolarization.

CONCLUSION

G-CSF increases the DPT, ERP and VFT and reduces the infarct size, thus stabilizing the myocardial electrophysiology, and preventing fatal arrhythmia during I/R. The protective mechanism could be via its effect in preventing cardiac mitochondrial dysfunction.

Effect of sildenafil citrate on the cardiovascular system

Sildenafil citrate is a drug commonly used to manage erectile dysfunction. It is designated chemically as 1-[[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H -pyrazolo[4,3-d]pyrimidin-5-yl)-4 ethoxyphenyl] sulfonyl]-4-methylpiperazine citrate (C22H30N6(O4)S). It is a highly selective inhibitor of cyclic guanine monophosphate-specific phosphodiesterase type 5. In late March through mid-November 1998, the US Food and Drug Administration (FDA) published a report on 130 confirmed deaths among men (mean age, 64 years) who received prescriptions for sildenafil citrate, a period during which >6 million outpatient prescriptions (representing about 50 million tablets) were dispensed. The US FDA recently reported that significant cardiovascular events, including sudden cardiac death, have occurred in men with erectile dysfunction who were taking sildenafil citrate. These reports have raised concerns that sildenafil citrate may increase the risk of cardiovascular events, particularly fatal arrhythmias, in patients with cardiovascular disease. In the past few years, the cardiac electrophysiological effects of sildenafil citrate have been investigated extensively in both animal and clinical studies. According to extensive data available to date, sildenafil citrate has been shown to pose minimal cardiovascular risks to healthy people taking this drug. Some precautions are needed for patients with cardiovascular diseases. However, the only absolute contraindication for sildenafil citrate is the concurrent use of nitrates. This article is intended to review sildenafil citrate's cardiovascular effects, as well as current debates about its arrhythmogenic effects.

Mechanism of ventricular defibrillation for near-defibrillation threshold shocks: a whole-heart optical mapping study in swine

BACKGROUND

To study the mechanism by which shocks succeed (SDF) or fail (FDF) to defibrillate, global cardiac activation and recovery and their relationship to defibrillation outcome were investigated for shock strengths with approximately equal SDF and FDF outcomes (DFT(50)).

METHODS AND RESULTS

In 6 isolated pig hearts, dual-camera video imaging was used to record optically from approximately 8000 sites on the anterior and posterior ventricular surfaces before and after 10 DFT(50) biphasic shocks. The interval between the shock and the last ventricular fibrillation activation preceding the shock (coupling interval, CI) and the time from shock onset to 90% repolarization of the immediate postshock action potential (RT(90)) were determined at all sites. Of 60 shocks, 31 were SDF. The CI (59+/-7 versus 52+/-6 ms) and RT(90) (108+/-19 versus 88+/-8 ms) were significantly longer for SDF than FDF episodes. Spatial dispersions of CI (36+/-5 versus 34+/-3 ms) and RT(90) (40+/-16 versus 40+/-8 ms) were not significantly different for SDF versus FDF episodes. The first global activation cycle appeared focally on the left ventricular apical epicardium 78+/-32 ms after the shock.

CONCLUSIONS

For near-threshold shocks, defibrillation outcome correlates with the electrical state of the heart at the time of the shock and on RT. Global dispersion of RT was similar in both SDF and FDF episodes, suggesting that it is not crucial in determining defibrillation outcome after DFT(50) shocks.

Reduction in atrial defibrillation threshold by a single linear ablation lesion

INTRODUCTION

This study investigated a hybrid approach to reduce the atrial defibrillation threshold (ADFT) by determining the effect of a single linear radiofrequency ablation (RFA) lesion on both the ADFT and activation patterns during atrial fibrillation (AF).

METHODS AND RESULTS

In 18 open chest sheep (45 to 57 kg), coil defibrillation electrodes were placed in a superior vena cava/right ventricular configuration. AF was induced by burst pacing and maintained with acetyl beta-methylcholine (2 to 42 microL/min). ADFTs were obtained before and after a linear RFA lesion was created in the left atrium (LAL; n = 6), right atrium (RAL; n = 6), or neither atrium as a control (n = 6). In animals receiving an LAL, a 504-unipolar-electrode plaque was sutured to the LA. For animals receiving an RAL, two 504-electrode plaques were placed, one each on the LA and RA. From each plaque, activations were recorded before and after ADFT shocks, and organizational characteristics of activations were analyzed using algorithms that track individual wavefronts. In sham-treated controls, the ADFT did not change. In contrast, LAL reduced ADFT energy 29%, from 4.5 +/- 2.3 J to 3.2 +/- 2.0 J (P < 0.05). RAL reduced ADFT energy 25%, from 2.0 +/- 0.9 J to 1.5 +/- 0.7 J (P < 0.05). AF activation was substantially more organized after RFA than before RFA for both the RAL- and LAL-treated animals.

CONCLUSION

A single RFA lesion in either the RA or LA reduces the ADFT in this sheep model. This decrease is associated with an increase in fibrillatory organization.

Effect of altering the left ventricular pressure on epicardial activation time in dogs with and without pacing-induced heart failure

BACKGROUND

The influence of an increased left ventricular end-diastolic pressure (LVEDP) on the development of lethal arrhythmias in chronic heart failure is unclear. We investigated the effect of chronic and acute LVEDP increase on the epicardial activation time of sinus (SB) and paced (PB) beats.

METHODS

Six dogs underwent rapid ventricular pacing at 220-280[emsp4 ]beats/min for 6-14 weeks for induction of heart failure. On the study day, baseline (ba) LVEDP was determined for the surviving heart failure animals (HF-ba), and for seven control animals (C-ba). The epicardial activation time (EAT, time between the earliest and latest epicardial activation) for five consecutive SB and five ventricular PB during the baseline hemodynamic state were recorded using a 504 electrode mapping-sock. In the control animals a 2-litre volume (vl) was infused over 10[emsp4 ]min to acutely increase the LVEDP (C-vl) to a level comparable to the chronic increased LVEDP of the HF-ba. The same volume challenge was performed in two HF animals (HF-vl) and the EAT for SB and PB was redetermined.

RESULTS

Three of six HF animals died during induction of heart failure. In the three remaining HF animals, chronic LVEDP increased from 6+/-1 to 17+/-10.8[emsp4 ]mmHg (P=0.07), EAT for SB increased by 68 % compared to control animals (HF-ba vs. C-ba, P<0.05). In contrast, in the control animals the acute rise in LVEDP from 6.8+/-4.5 to 14.7+/-6.2 mmHg P<0.05), shortened the EAT for SB (C-ba vs. C-vl, P<0.05). A similar decrease in EAT for SB caused by acute volume load was seen in the HF animals, but did not reach significance due to the small sample size (one of the three remaining HF animals died of spontaneous ventricular fibrillation before the volume load). Chronic LVEDP elevation significantly prolonged the EAT for PB from 72+/-11 to 120+/-31[emsp4 ]ms (C-ba vs. HF-ba) while acute LVEDP increase had no significant effect on EAT for PB.

CONCLUSION

Chronic HF increases LVEDP and prolongs EAT, while an acute increase in LVEDP shortens the EAT for sinus beats. A prolongation of EAT in heart failure may make the heart more susceptible to ventricular arrhythmias and electromechanical dissociation.

Pacing following shocks stronger than the defibrillation threshold: impact on defibrillation outcome

INTRODUCTION

A recent study of shocks near defibrillation threshold (DFT) strength demonstrated that at least three rapid cycles always occur after failed shocks but not after successful shocks, suggesting that the number and rapidity of postshock cycles are important in determining defibrillation success. To test this hypothesis, rapid pacing was performed following a shock stronger than the DFT that by itself did not induce rapid cycles and ventricular fibrillation (VF).

METHODS AND RESULTS

Epicardial activation was mapped in six pigs using a 504-electrode sock. The DFT was determined by an up/down protocol with S1 shocks (right ventricle-superior vena cava, biphasic). Ten shocks that were 100 to 200 V above the DFT (aDFT) were delivered after 10 seconds of VF to confirm they always defibrillated. Then, S2, S3, etc., pacing at 5 to 10 times diastolic threshold was performed from the left ventricular apex after aDFT shocks during VF. First, the postshock interval after aDFT shocks was scanned with an S2 stimulus to find the shortest S1-S2 coupling interval (CI) that captured. This was repeated for S3, S4, etc., until VF was induced. To induce VF after aDFT shocks, three pacing stimuli (S2, S3, S4) with progressively shorter CIs were always required; S2 or S2,S3 never induced VF. For the S2-S4 cycles, the intercycle interval was shorter (P < 0.01), and the wavefront conduction time was longer (P < 0.01) for episodes in which VF was induced (n = 57) than for episodes in which it was not (n = 60). Following the S4 cycle that induced VF, two types of spontaneous activation patterns appeared: focal (88%) and reentrant (12%).

CONCLUSION

VF induction after aDFT shocks always required at least three rapid successive paced-induced cycles. Thus, the number and rapidity of the first several postshock cycles rather than just the first postshock cycle may be determining factors for defibrillation outcome.

Prediction of defibrillation outcome by epicardial activation patterns following shocks near the defibrillation threshold

INTRODUCTION

Ventricular defibrillation is probabilistic and shock strength dependent. We investigated the relationship between defibrillation outcome and postshock activation patterns for shocks of the same strength (approximately 50% probability of success for defibrillation [ED50] to yield an equal number of successful and failed shocks).

METHODS AND RESULTS

In five pigs, 10 shocks of approximately ED50 strength (right ventricle-superior vena cava, biphasic, 6/4 msec) were delivered after 10 seconds of ventricular fibrillation (VF). Epicardial activation sequences following shocks were mapped with a 504-electrode shock and analyzed by animating dV/dt of the electrograms. Intercycle interval (ICI, time between the onset of successive postshock cycles), wavefront conduction time (WCT, time between the earliest and latest activation of a cycle), and overlapping index (WCT of cycle[n]/ICI of cycle[n+1]) were determined for the first five postshock cycles. An overlapping index >1 indicates overlap between successive cycles. Of 50 defibrillation attempts, 25 were successes. There was no difference between successful and failed episodes for both ICI (68 +/- 9 msec vs 62 +/- 10 msec) and WCT (97 +/- 24 msec vs 100 +/- 14 msec) of cycle 1. However, starting at cycle 2, the ICI was longer, and the WCT was shorter for successful than failed episodes (P < 0.01). Overlapping cycles (index > 1) were found during the transition from cycles 2 through 5 in all failed (index >1) and in no successful episodes.

CONCLUSIONS

(1) Defibrillation outcome cannot be determined during the first postshock cycle. (2) At least three rapid successive cycles with overlap of cycles 2 and 3 are present in all failed and in no successful episodes. (3) The overlapping index is a marker to predict defibrillation outcome.

Left ventricular apex ablation decreases the upper limit of vulnerability

BACKGROUND

After shocks with an approximately 50% probability of success for the upper limit of vulnerability (ULV(50)) of strength, the first few activations appear focally on the epicardium at almost the same site at the left ventricular (LV) apex in both successful and failed induction of ventricular fibrillation (VF). We tested the hypothesis that subendocardial ablation at this early site would decrease the shock strength required for the ULV(50).

METHODS AND RESULTS

Ten S1 stimuli were delivered from the right ventricular apex at a 300-ms coupling interval in 5 pigs. Biphasic shocks were delivered from right ventricular-superior vena cava electrodes after the last S1 stimulus. The ULV(50) was determined using an up/down protocol with T-wave scanning. Radiofrequency ablation was performed endocardially at the apical LV. The ULV(50) was determined again 30 minutes after ablation. To determine the importance of the ablation region, this protocol was repeated in another 5 pigs with ablation at the LV base. Delivered voltage (401+/-60 versus 323+/-50 V) and energy (11+/-3 versus 7+/-2 J) for the ULV(50) were significantly decreased after LV apex ablation by 19% and 34%, respectively. However, no difference existed in ULV(50) before and after LV base ablation. Lesions at both the LV apex and base were subendocardial and ranged from 0.8 to 1.1 cm in diameter.

CONCLUSIONS

Subendocardial ablation at the apical LV markedly decreases ULV(50), which suggests that the activation originating from this postshock early site is responsible for VF initiation and that interventions to electrically silence this site can influence the outcome of VF induction by ULV shocks.

Influence of postshock epicardial activation patterns on initiation of ventricular fibrillation by upper limit of vulnerability shocks

BACKGROUND

Shocks of identical strength and timing sometimes induce ventricular fibrillation (VFI) and other times do not (NoVFI). To investigate this probabilistic behavior, a shock strength near the upper limit of vulnerability, ULV(50), was delivered to yield equal numbers of VFI and NoVFI episodes.

METHODS AND RESULTS

In 6 pigs, a 504-electrode sock was pulled over the ventricles. ULV(50) was determined by scanning the T wave. S(1) pacing was from the right ventricular apex. Ten S(2) shocks of approximate ULV(50) strength were delivered at the same S(1)-S(2) coupling interval. Intercycle interval (ICI) and wave front conduction time (WCT) were determined for the first 5 postshock cycles. ICI and the WCT of cycle 1 were not different for VFI versus NoVFI episodes (P=0.3). Beginning at cycle 2, ICI was shorter and WCT was longer for VFI than NoVFI episodes (P<0.05).

CONCLUSIONS

The first cycle after shocks of the same strength (ULV(50)) delivered at the same time has the same activation pattern regardless of shock outcome. During successive cycles, however, a progressive decrease in ICI and increase in WCT occur during VFI but not NoVFI episodes. These findings suggest shock outcome is (1) deterministic but exquisitely sensitive to differences in electrophysiological state at the time of the shock that are too small to detect or (2) probabilistic and not determined until after the first postshock cycle.

Pacing after shocks stronger than the upper limit of vulnerability: impact on fibrillation induction

BACKGROUND

After upper-limit-of-vulnerability (ULV) shocks of the same strength and coupling interval (CI) during the T wave, (1) the epicardial activation pattern (EAP) for the first postshock cycle is indistinguishable between shocks that do (VF) and do not (NoVF) induce ventricular fibrillation (VF) and (2) >/=3 cycles in rapid succession always occur during VF but not during NoVF episodes. To study the role of these rapid cycles, rapid pacing was performed after a shock stronger than the ULV that by itself did not induce rapid cycles and VF.

METHODS AND RESULTS

A 504-electrode sock was sutured to the heart in 6 pigs to map EAPs. The S2 shock strength and S1-S2 CI at the ULV were determined by T-wave scanning with an up/down protocol. Ten shocks 50 to 100 V above the ULV (aULV) were delivered at the same S1-S2 CI to confirm that VF was not induced. Then, the postshock interval after aULV shocks was scanned with an S3 pacing stimulus from the LV apex until the shortest S2-S3 CI that captured was reached. This was repeated for S4, S5, etc, until VF was induced. To induce VF, 3 pacing stimuli (S3-S5) with progressively shorter CIs were required; S3 or S3, S4 never induced VF. After cycle S5, which induced VF, 2 EAP types occurred: focal (74%) and reentrant (26%).

CONCLUSIONS

At least 3 cycles with short CIs are necessary for VF induction after aULV shocks. Cycles S3-S4 may create the substrate for cycle S5 to initiate VF.

Relationship between oversizing of self-expanding stents and late loss index in carotid stenting

Stenting of the internal carotid artery is facilitated by stenting across the carotid bifurcation and sizing the diameter of a self-expanding stent to the large common carotid segment. This usually results in marked oversizing of the self-expanding stent in the internal carotid segment. This study was done to determine the relationship between stent oversizing and late luminal loss index after stenting of the internal carotid artery. Between September 1995 and March 1997, there were 165 patients (189 vessels) who underwent successful carotid stenting with self-expanding stents. Fifty-nine patients (63 vessels) had six-month follow-up carotid angiograms and on-line quantitative angiographic analysis. The mean reference diameter of the internal carotid arteries was 4.93+/-1.31 mm. Nominal stent size was 5 mm in 4 patients, 6 mm in 6 patients, 8 mm in 106 patients, 10 mm in 77 patients, and 12 mm in 1 patient. The average stent/patient was 1.03+/-0.16. There were three patients who had more than 50% diameter renarrowing at follow-up. The mean late loss index was 0.25+/-0.41. By linear regression analysis, there was no clear linear relationship between stent oversizing and late loss index after stenting (correlation coefficient = -0.21, P = 0.09). When analysis of variance with linear contrast was used to analyze six groups of different stent/artery ratios (from 1.4 to > or = 2), late loss indexes are significantly lower in the groups of high stent/artery ratio than the groups of low stent/artery ratio (P = 0.01). The process of oversizing of self-expanding stents deployed in the internal carotid artery does not appear to be associated with late restenosis and high stent/artery ratio seems to be associated with low late loss index.

Locally propagated activation immediately after internal defibrillation

BACKGROUND

Electrical mapping studies indicate an interval of 40 to 100 ms between a defibrillation shock and the earliest activation that propagates globally over the ventricles (globally propagated activation, GPA). This study determined whether activation occurs during this interval but propagates only locally before being blocked (locally propagated activation, LPA).

METHODS AND RESULTS

In five anesthetized pigs, the heart was exposed and a 504-electrode sock with 4-mm interelectrode spacing was pulled over the ventricles. Ten biphasic shocks of a strength near the defibrillation threshold (DFT) were delivered via intracardiac catheter electrodes, and epicardial activation sequences were mapped before and after attempted defibrillation. Local activation was defined as dV/dt < or =-0.5 V/s. Postshock activation times and wave-front interaction patterns were determined with an animated display of dV/dt at each electrode in a computer representation of the ventricular epicardium. LPAs were observed after 40 of the 50 shocks. A total of 173 LPA regions were observed, each of which involved 2+/-2 (mean+/-SD) electrodes. LPAs were observed after both successful and failed shocks but occurred earlier (P<.0001) after failed (35+/-8 ms) than successful (41+/-16 ms) shocks, although the times at which the GPA appeared were not significantly different. On reaching the LPA region, the GPA front either propagated through it (n=135) or was blocked (n=38). The time from the onset of the LPA until the GPA front propagated to reach the LPA region was shorter (P<.01) when the GPA front was blocked (32+/-12 ms) than when it propagated through the LPA region (63+/-20 ms).

CONCLUSIONS

LPAs exist after successful and failed shocks near the DFT. Thus, the time from the shock to the GPA is not totally electrically silent.