Histochemical assessment of early myocardial infarction using 2,3,5-triphenyltetrazolium chloride in blood-perfused porcine hearts

β-Caryophyllene, a natural bicyclic sesquiterpene attenuates β-adrenergic agonist-induced myocardial injury in a cannabinoid receptor-2 dependent and independent manner

The downregulation of cannabinoid type-2 receptors (CB2R) have been reported in numerous diseases including cardiovascular diseases (CVDs). The activation of CB2R has recently emerged as an important therapeutic target to mitigate myocardial injury. We examined whether CB2R activation can protect against isoproterenol (ISO)-induced myocardial injury (MI) in rats. In the present study, we investigated the cardioprotective effect of β-caryophyllene (BCP), a naturally occurring dietary cannabinoid in rat model of MI. Rats were pre- and co-treated with BCP (50 mg/kg, orally) twice daily for 10 days along with subcutaneous injection of ISO (85 mg/kg) at an interval of 24 h for two days (9th and 10th days). AM630 (1 mg/kg), a CB2 receptor antagonist, was injected intraperitoneal as a pharmacological challenge prior to BCP treatment to reveal CB2R-mediated cardioprotective mechanisms of BCP. Desensitization of beta-adrenergic receptor (β-AR) signaling, receptor phosphorylation and recruitment of adapter β-arrestins were observed in ISO-induced MI in rats. ISO injections caused impaired cardiac function, elevated the levels of serum cardiac marker enzymes, and enhanced oxidative stress markers along with altered PI3K/Akt and NrF2/Keap1/HO-1 signaling pathways. ISO also promoted lysosomal dysfunction along with activation of NLRP3 inflammasomes and TLR4-NFκB/MAPK signaling and triggered rise in proinflammatory cytokines. There was a concomitant mitochondrial dysfunction followed by the activation of endoplasmic reticulum (ER) stress-mediated Hippo signaling and intrinsic pathway of apoptosis as well as altered autophagic flux/mTOR signaling in ISO-induced MI. Furthermore, ISO also triggered dyslipidemia evidenced by altered lipids, lipoproteins and lipid marker enzymes along with ionic homeostasis malfunction. However, treatment with BCP resulted in significant protective effects on all biochemical and molecular parameters analyzed. The cardioprotective effects were further strengthened by preservation of cardiomyocytes and cell organelles as observed in histopathological and ultrastructural studies. Interestingly, treatment with AM630, a CB2R antagonist was observed to abrogate the protective effects of BCP on the biochemical and molecular parameters except hyperlipidemia and ionic homeostasis in ISO-induced MI in rats. The present study findings demonstrate that BCP possess the potential to protect myocardium against ISO-induced MI in a CB2-dependent and independent manner.

Oxidized cholesterol exacerbates toll-like receptor 4 expression and activity in the hearts of rats with myocardial infarction

Introduction: The present study examined the effects of high cholesterol and high oxidized-cholesterol diets on the myocardial expression of TLR4 and pro-inflammatory cytokine in rats.

Methods: Male Wistar rats were allocated into 6 groups and fed with a normal diet, cholesterol, and oxidized-cholesterol rich diets with or without isoproterenol-induced myocardial infarction. TLR4 and MyD 88 expression and levels tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) were measured in the heart and serum.

Results: Oxidized cholesterol-fed animals had higher serum levels of oxidized low-density lipoprotein (LDL) (263 ± 13 ng/dL) than the cholesterol-fed animals (98 ± 8 ng/dL; P < 0.001). A high level of oxidized-LDL caused fibrotic cell formation and enhanced neutrophil infiltration in the absence of MI. Both cholesterol and oxidized-cholesterol upregulated TLR4 mRNA expression and increased TNF-α and IL-6 production in the hearts of rats with MI. In rats fed with oxidized-cholesterol the serum and myocardial levels of TNF-α (653 ± 42 pg/mL, 1375 ± 121 pg/100 mg, respectively) were higher than MI group (358±24 pg/mL, P < 0.001 and 885 ± 56 pg/100 mg, P < 0.01). A significant correlation was seen between TLR4 expression and infarct size.

Conclusion: These findings suggest that cardiac TLR4 is preferentially upregulated by oxidized cholesterol in rats. Oxidized cholesterol may have a critical role in cardiac toxicity in the absence of pathological conditions.

α-Bisabolol protects against β-adrenergic agonist-induced myocardial infarction in rats by attenuating inflammation, lysosomal dysfunction, NLRP3 inflammasome activation and modulating autophagic flux

Emerging evidence demonstrates that NLRP3 inflammasome activation, lysosomal dysfunction, and impaired autophagic flux play a crucial role in the pathophysiology of myocardial infarction (MI).

An Overview on the Considerations for the Planning of Nonclinical Necropsies for Medical Device Studies

The terminal collection and histological processing of medical devices is an expensive, labor-, and material-intensive endeavor, which requires adequate experience, innovation, and preparation for success. It is also an exciting endeavor that continually challenges, intellectually engages, and improves the skills and knowledge of the pathologist. Awareness of the importance of the medical device pathologist's involvement, communication, and oversight throughout the development, implementation, and execution of a nonclinical assessment of a medical device is in the best interest of the test facility, the histopathology laboratory, the pathologist, the sponsor, and, ultimately, the patients. This article serves to present as a primer of key considerations for the approach and conduct of "nontoxicological" studies, defined as studies involving animal models of deployment or implantation of medical devices as well as surgical animal models.

Pitavastatin ameliorates myocardial damage by preventing inflammation and collagen deposition via reduced free radical generation in isoproterenol-induced cardiomyopathy

Pitavastatin inhibits 3 hydroxy 3 methyl glutaryl coenzyme A (HMGCoA) reductase enzyme, preventing cholesterol synthesis along with elevating high density apolipoprotein A1 (Apo-A1). The present study was designed to evaluate cardioprotective potential of pitavastatin at 1 mg/kg/day and 3 mg/kg/day dose for 14 days in low dose isoproterenol (ISO) (5 mg/kg/day for 7 consecutive days) induced myocardial damage. ISO administration induced significant reduction in endogenous antioxidant enzymes like reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and raised thiobarbituric acid reactive substances (TBARS) indicating activated lipid peroxidation. Along with this, a significant increase in level of cardiac injury biomarkers vie, creatine kinase (CK-MB), lactate dehydrogenase (LDH), aspartate amino transferase (AST), tumor necrosis factor (TNF-α) and transforming growth factor (TGF-β) as well as brain natriuretic peptide (BNP). Histological examination also revealed marked myocardial tissue damage in ISO treated rats. However, pretreatment with pitavastatin (3 mg/kg/day) significantly maintained nearly normal levels of cardiac biomarkers and oxidant antioxidant status as well as lipid peroxidation in ISO induced MI rats. Cardiac histological assessment and infarct size assessment also showed marked reduction in myocardial architecture alteration including infarct size as well as collagen deposition by pitavastatin that strongly supported biochemical findings. These observations strongly corroborate that pitavastatin prevents myocardial damages via up regulation of endogenous oxidants along with its hypocholesterolemic activity.

Nepeta deflersiana attenuates isoproterenol-induced myocardial injuries in rats: Possible involvement of oxidative stress, apoptosis, inflammation through nuclear factor (NF)-κB downregulation

BACKGROUND

Nepeta deflersiana (Lamiaceae) is a perennial herb used in the Saudi and Yemeni folk medicine as an anti-inflammatory, carminative, and antirheumatic agent.

PURPOSE

This study explores the phytochemistry of the plant and the cardioprotective effect of N. deflersiana ethanolic extract (NDEE) against isoproterenol (ISP)-induced myocardial injury in rats.

DESIGN/METHODS

Cardiac function, serum cardiac enzymes, myocardial antioxidants, inflammatory, and apoptotic biomarkers, and histopathological parameters were studied in ISP-injured Wistar rat heart tissues.

RESULTS

To the best of our knowledge, this is the first study to report the isolation of nine secondary metabolites from this plant: 1α-hydroxy-7α,14α,18-triacetoxy-isopimara-8,15-diene (1), β-sitosterol (2), lupeol (3), ursolic acid (4), 2,3-dihydroxy ursolic acid (5), caffeic acid (6), methyl rosmarinate (7), rosmarinic acid (8), and an irridoid glucoside 8-epi-7-deoxyloganic acid (9). To explain the mechanisms underlying the cardioprotective effect of NDEE, we evaluated the redox-sensitivity of NDEE in ISP-induced cardiac injury. The oral administration of NDEE (50 and 100 mg/kg b.w) prevented the depletion of endogenous antioxidants (CAT, SOD, NP-SH, and NO) and myocyte injury marker enzymes and inhibited lipid peroxidation (MDA, MPO). Moreover, NDEE downregulated the expression of pro-inflammatory cytokines (TNFα, IL-6, and IL-10) and apoptotic markers (caspase-3 and Bax) and upregulated the anti-apoptotic protein Bcl2. Furthermore, NDEE pretreatment significantly downregulated cardiac NF-κB (p65) expression, NF-κB-DNA binding activity, and MPO activity. Histological data showed that NDEE pretreatment reduced myonecrosis, edema, and infiltration of inflammatory cells and restored the architecture of cardiomyocytes.

CONCLUSION

NDEE demonstrated strong antioxidant, cardioprotective, anti-inflammatory, and anti-apoptotic potential against myocardial damage. This further endorses the use of N. deflersiana in Yemeni folk medicine against cardiovascular diseases.

Primary Outcome Assessment in a Pig Model of Acute Myocardial Infarction

Mortality after acute myocardial infarction remains substantial and is associated with significant morbidity, like heart failure. Novel therapeutics are therefore required to confine cardiac damage, promote survival and reduce the disease burden of heart failure. Large animal experiments are an essential part in the translational process from experimental to clinical therapies. To optimize clinical translation, robust and representative outcome measures are mandatory. The present manuscript aims to address this need by describing the assessment of three clinically relevant outcome modalities in a pig acute myocardial infarction (AMI) model: infarct size in relation to area at risk (IS/AAR) staining, 3-dimensional transesophageal echocardiography (TEE) and admittance-based pressure-volume (PV) loops. Infarct size is the main determinant driving the transition from AMI to heart failure and can be quantified by IS/AAR staining. Echocardiography is a reliable and robust tool in the assessment of global and regional cardiac function in clinical cardiology. Here, a method for three-dimensional transesophageal echocardiography (3D-TEE) in pigs is provided. Extensive insight into cardiac performance can be obtained by admittance-based pressure-volume (PV) loops, including intrinsic parameters of myocardial function that are pre- and afterload independent. Combined with a clinically feasible experimental study protocol, these outcome measures provide researchers with essential information to determine whether novel therapeutic strategies could yield promising targets for future testing in clinical studies.

Effect of intravenous administration of antioxidants alone and in combination on myocardial reperfusion injury in an experimental pig model

BACKGROUND

Several antioxidants have been found to have conflicting results in attenuating myocardial reperfusion injury. These studies were done primarily in experimental protocols that did not approximate clinical situations.

OBJECTIVE

The aim of this study was to test the efficacy of 3 different antioxidants (ascorbic acid [AA], desferrioxamine, and N-acetylcysteine [NAC]) administered IV alone and in combination in a closed-chest pig model.

METHODS

Farm-raised domestic male pigs (aged 3-5 months, weight of 30-35 kg) were assigned to 1 of 5 groups to receive treatment as follows: group A, AA 100 mg/kg; group B, desferrioxamine 60 mg/kg; group C, a loading dose of NAC 100 mg/kg for 20 minutes and a 20-mg/kg maintenance dose; group D, all 3 drugs in combination; and group E, normal saline (control group). The infusion of all drugs was started 15 minutes before and completed 5 minutes after reperfusion, except for the administration of NAC, which was terminated 60 minutes postreperfusion. Myocardial ischemia (45 minutes) and reperfusion (210 minutes) were achieved percutaneously by circumflex artery balloon occlusion. Ejection fraction, left ventricular end-diastolic pressure (LVEDP), flow in the infarcted artery, and all ventricular arrhythmias were recorded. Oxidative stress was estimated by serial measurements of thiobarbituric acid reactive substance (TBARS) concentration in coronary sinus blood. Infarct size was assessed as a percentage of the area at risk (I/R ratio) using the tetrazolium red staining method.

RESULTS

The 25 pigs were divided into 5 groups of 5 pigs each. No significant between-group differences were found in I/R ratio or in oxidative stress (as measured by TBARS concentration). Group C developed significantly more ventricular atrhythmias than the control group (80% vs 0%, P = 0.02). No other differences among groups were found. LVEDP was significantly elevated in all treatment groups (mean LVEDP difference [SD] for group A, 6.0 [1.6] mm Hg; group B, 17.6 [1.9] mm Hg; group C, 3.6 [1.7] mm Hg; group D, 6.8 [3.2] and group E, 5.4 [3.4] mm Hg). LVEDP elevation was found to be significantly higher in group B compared with all the other groups (all, P < 0.001). No significant between-group differences were found in the other parameters measured.

CONCLUSION

In this experimental pig model, the antioxidants AA, desferrioxamine, and NAC administered alone or in combination did not reduce the deleterious effects of reperfusion injury and specifically the extent of myocardial necrosis.

Towards stratifying ischemic components by cardiac MRI and multifunctional stainings in a rabbit model of myocardial infarction

OBJECTIVES

We sought to identify critical components of myocardial infarction (MI) including area at risk (AAR), MI-core and salvageable zone (SZ) by using cardiac magnetic resonance imaging (cMRI) and multifunctional stainings in rabbits.

MATERIALS AND METHODS

Fifteen rabbits received 90-min coronary artery (CA) ligation and reopening to induce reperfused MI. First-pass perfusion weighted imaging (PWI(90')) was performed immediately before CA reperfusion. Necrosis avid dye Evans blue (EB) was intravenously injected for later MI-core detection. One-day later, cMRI with T2-weighted imaging (T2WI), PWI(24h) and delayed enhancement (DE) T1WI was performed at a 3.0T clinical scanner. The heart was excised and CA was re-ligated with aorta infused by red-iodized-oil (RIO). The heart was sliced into 3-mm sections for digital radiography (DR), histology and planimetry with myocardial salvage index (MSI) and perfusion density rate (PDR) calculated.

RESULTS

There was no significant difference between MI-cores defined by DE-T1WI and EB-staining (31.13±8.55% vs 29.80±7.97%; p=0.74). The AAR was defined similarly by PWI90' (39.93±9.51%), RIO (38.82±14.41%) and DR (38.17±15.98%), underestimated by PWI(24h) (36.44±5.31%), but overestimated (p<0.01) by T2WI (56.93±8.87%). Corresponding MSI turned out to be 24.17±9.5% (PWI(90')), 21.97±9.41% (DR) and 22.68±9.65% (RIO), which were significantly (p<0.01) higher and lower than that with PWI(24h) (15.15±7.34%) and T2WI (45.52±7.5%) respectively. The PDR differed significantly (p<0.001) between normal myocardium (350.6±33.1%) and the AAR (31.2±15%), suggesting 11-times greater blood perfusion in normal myocardium over the AAR.

CONCLUSION

The introduced rabbit platform and new staining techniques together with the use of a 3.0T clinical scanner for cMRI enabled visualization of MI components and may contribute to translational cardiac imaging research for improved theranostic management of ischemic heart disease.

Bifunctional staining for ex vivo determination of area at risk in rabbits with reperfused myocardial infarction

AIM: To develop a method for studying myocardial area at risk (AAR) in ischemic heart disease in correlation with cardiac magnetic resonance imaging (cMRI).

METHODS: Nine rabbits were anesthetized, intubated and subjected to occlusion and reperfusion of the left circumflex coronary artery (LCx) to induce myocardial infarction (MI). ECG-triggered cMRI with delayed enhancement was performed at 3.0 T. After euthanasia, the heart was excised with the LCx re-ligated. Bifunctional staining was performed by perfusing the aorta with a homemade red-iodized-oil (RIO) dye. The heart was then agar-embedded for ex vivo magnetic resonance imaging and sliced into 3 mm-sections. The AAR was defined by RIO-staining and digital radiography (DR). The perfusion density rate (PDR) was derived from DR for the AAR and normal myocardium. The MI was measured by in vivo delayed enhancement (iDE) and ex vivo delayed enhancement (eDE) cMRI. The AAR and MI were compared to validate the bifunctional straining for cardiac imaging research. Linear regression with Bland-Altman agreement, one way-ANOVA with Bonferroni’s multiple comparison, and paired t tests were applied for statistics.

RESULTS: All rabbits tolerated well the surgical procedure and subsequent cMRI sessions. The open-chest occlusion and close-chest reperfusion of the LCx, double suture method and bifunctional staining were successfully applied in all animals. The percentage MI volumes globally (n = 6) and by slice (n = 25) were 36.59% ± 13.68% and 32.88% ± 12.38% on iDE, and 35.41% ± 12.25% and 32.40% ± 12.34% on eDE. There were no significant differences for MI determination with excellent linear regression correspondence (r_global = 0.89; r_slice = 0.9) between iDE and eDE. The percentage AAR volumes globally (n = 6) and by slice (n = 25) were 44.82% ± 15.18% and 40.04% ± 13.64% with RIO-staining, and 44.74% ± 15.98% and 40.48% ± 13.26% by DR showing high correlation in linear regression analysis (r_global = 0.99; r_slice = 1.0). The mean differences of the two AAR measurements on Bland-Altman were almost zero, indicating RIO-staining and DR were essentially equivalent or inter-replaceable. The AAR was significantly larger than MI both globally and slice-by-slice (P < 0.01). After correction with the background and the blank heart without bifunctional staining (n = 3), the PDR for the AAR and normal myocardium was 32% ± 15% and 35.5% ± 35%, respectively, which is significantly different (P < 0.001), suggesting that blood perfusion to the AAR probably by collateral circulation was only less than 10% of that in the normal myocardium.

CONCLUSION: The myocardial area at risk in ischemic heart disease could be accurately determined postmortem by this novel bifunctional staining, which may substantially contribute to translational cardiac imaging research.

9-Phenanthrol, a TRPM4 inhibitor, protects isolated rat hearts from ischemia-reperfusion injury

Despite efforts to elucidate its pathophysiology, ischemia-reperfusion injury lacks an effective preventative intervention. Because transient receptor potential cation channel subfamily M member 4 (TRPM4) is functionally expressed by many cell types in the cardiovascular system and is involved in the pathogenesis of various cardiovascular diseases, we decided to assess its suitability as a target of therapy. Thus, the aim of this study was to examine the possible cardioprotective effect of 9-phenanthrol, a specific inhibitor of TRPM4. Isolated Langendorff-perfused rat hearts were pretreated with Krebs-Henseleit (K-H) solution (control), 9-phenanthrol, or 5-hydroxydecanoate (5-HD, a blocker of the ATP-sensitive potassium channel) and then subjected to global ischemia followed by reperfusion with the K-H solution. To evaluate the extent of heart damage, lactate dehydrogenase (LDH) activity in the effluent solution was measured, and the size of infarcted area of the heart was measured by 2,3,5-triphenyltetrazolium chloride staining. In controls, cardiac contractility decreased, and LDH activity and the infarcted area size increased. In contrast, in hearts pretreated with 9-phenanthrol, contractile function recovered dramatically, and the infarcted area size significantly decreased. The cardioprotective effects of 9-phenanthrol was not completely blocked by 5-HD. These findings show that 9-phenanthrol exerts a cardioprotective effect against ischemia in the isolated rat heart and suggest that its mechanism of action is largely independent of ATP-sensitive potassium channels.

Matrix metalloproteinase-2 is activated during ischemia/reperfusion in a model of myocardial infarction

BACKGROUND

The degradation of myosin light chain 1 (MLC1) by matrix metalloproteinase-2 (MMP-2) during ischemia/reperfusion has been implicated in the development of cardiac dysfunction. Our objective was to elucidate the role of MMP-2 and MLC1 in the development of cardiac injury and dysfunction in a model of left anterior descending (LAD) coronary artery occlusion.

METHODS

Adult rats (300-350 g) were anaesthetized, and the isolated hearts were retrogradely perfused in a Langendorff apparatus. The LAD was stabilized for 25 minutes and occluded for either 45 or 90 minutes and then reperfused. Cardiac function (evaluated as rate-pressure product) was significantly decreased in the reperfused hearts subjected to 90 minutes of LAD occlusion in comparison with hearts subjected to either sham or 45 minutes of occlusion. Ninety minutes of occlusion resulted in 60% of infarct.

RESULTS

MMP-2 activity, measured by gelatin zymography, was significantly increased following occlusion as well as reperfusion. An increased degradation of MLC1 was observed at the end of reperfusion, but not at the end of occlusion, which most likely was because of the compensatory increase in tissue inhibitor of matrix metalloproteinases-4 (TIMP-4) during occlusion, but not reperfusion.

CONCLUSION

We demonstrate that MMP-2 activation is an ischemic event that extends into the reperfusion phase, while MLC1 degradation in response to ischemia/reperfusion is strictly a reperfusion event. MLC1 degradation during occlusion is prevented by a compensatory increase in the levels of TIMP-4.

Inhalation of NO during myocardial ischemia reduces infarct size and improves cardiac function

PURPOSE

Bioactive NO carriers in circulating blood formed during NO inhalation selectively distribute blood flow to areas in need, and may thus improve collateral perfusion to the area-at-risk in acute myocardial infarction (AMI). Here, we tested the hypothesis that NO inhalation during the ischemic phase of AMI may improve left ventricular function and reduce infarct size in rats.

METHODS

Following left anterior descending coronary artery (LAD) occlusion, rats received 50 ppm NO for 2 h of ischemia, during subsequent 3 h of reperfusion, or for 5 h of ischemia and reperfusion. Effects of inhaled NO were compared to those of intravenous nitrite as a putative carrier formed during NO inhalation. Downstream signaling via soluble guanylate cyclase was tested by inhibition with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ).

RESULTS

NO inhalation during myocardial ischemia increased left ventricular systolic pressure, contractility, relaxation, and cardiac output, and reduced myocardial infarction size and area-at-risk as compared to untreated controls. NO inhalation during the reperfusion phase caused a comparable protective effect. Combined inhalation during ischemia and reperfusion did not further improve left ventricular hemodynamics, but had an additive protective effect on the myocardial area-at-risk. NO inhalation increased circulating nitrite levels, and mimicking of this effect by intravenous nitrite infusion achieved similar protection as NO inhalation during myocardial ischemia, while ODQ blocked the protective NO effect.

CONCLUSIONS

Inhalation of NO during myocardial ischemia improves left ventricular function and reduces infarct size by mechanisms that increase levels of circulating nitrite and involve soluble guanylate cyclase. NO inhalation may represent a promising early intervention in AMI.

Peak longitudinal strain most accurately reflects myocardial segmental viability following acute myocardial infarction - an experimental study in open-chest pigs

Background

The extension and the transmurality of the myocardial infarction are of high predictive value for clinical outcome. The aim of the study was to characterize the ability of longitudinal, circumferential and radial strain measured by 2-dimensional speckle tracking echocardiography (2D-STE) to predict the extent of necrosis in myocardial segments following acute myocardial infarction and to separate transmural necrotic segments from non-transmural necrotic segments in a full 18-segment porcine model.

Methods

2D-STE strain was assessed in long- and short-axis following myocardial infarction in ten open-chest anesthetized pigs. Strain was defined according to systolic peak values. In segments displaying both negative and positive peaks, only the peak with the highest absolute value was utilized. Necrosis was measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining and expressed as percent of each myocardial segment.

Results

Significant correlations were found between the extension of necrosis and all measured parameters of myocardial deformation (p < 0.001), but was stronger for longitudinal strain (r² = 0.52) than circumferential strain (r² = 0.38) and radial strain (r² = 0.23). The area under the receiver operator characteristic curve (AUC) for separating transmural necrotic segments (>50% necrosis) from predominantly viable segments (0–50% necrosis) was significantly larger for longitudinal strain (AUC = 0.98, CI = 0.97–1.00) when compared with circumferential strain (AUC = 0.91, CI = 0.84–0.97, p < 0.05) and radial strain (AUC = 0.90, CI = 0.83 – 0.96, p < 0.01), indicating a stronger ability of longitudinal strain to identify segments with transmural necrosis.

Conclusion

Peak strain values derived from 2D-STE correlate well with the extent of necrosis in myocardial segments following acute myocardial infarction. Longitudinal strain most accurately reflects myocardial segmental viability in this setting.

Cardioprotective potential of Punica granatum extract in isoproterenol-induced myocardial infarction in Wistar rats

OBJECTIVE

To determine the protective role of Punica granatum L. (Punicaceae) seed juice extract and its butanolic fraction on heart rate, electrocardiographic patterns, vascular reactivity to catecholamines, cardiac marker enzymes, antioxidant enzymes together with morphologic and histopathological changes in isoproterenol-induced myocardial infarction in male Wistar rats.

MATERIALS AND METHODS

The effects of Punica granatum seed juice extract (100 mg/kg, p.o. and 300 mg/kg, p.o.) and butanolic fraction of Punica granatum seed juice extract (100 mg/kg., p.o.) on cardiac parameters were studied. Isoproterenol hydrochloride was used to induce myocardial infarction in Wistar rats. At the end of the experiment, heart rate, ECG, pressure rate index and cardiac marker enzyme levels were assessed.

RESULTS

Rats treated with isoproterenol (85 mg/kg, administered subcutaneously twice at an interval of 24 h) showed a significant increase in heart rate, ST elevation in ECG, pressure rate index and a significant increase in the levels of cardiac marker enzymes- lactate dehydrogenase, and creatine kinase in serum. Isoproterenol significantly reduced superoxide dismutase and catalase activity and increased vascular reactivity to various catecholamines. Pretreatment with PJ (100 mg/kg, p.o. and 300 mg/kg, p.o.) and B-PJ (100 mg/kg., p.o.) for a period of 21 days significantly inhibited the effects of ISO on heart rate, PRI, ECG patterns, levels of LDH, CK, SOD, CAT, and vascular reactivity changes. Treatment with PJ (100 mg/kg and 300 mg/kg) and B-PJ (100 mg/kg., p.o.) alone did not alter any of the parameters as compared to vehicle-treated Wistar rats. Punica granatum-treated animals showed a lesser degree of cellular infiltration in histopathological studies.

CONCLUSION

Punica granatum ameliorates cardiotoxic effects of isoproterenol and may be of value in the treatment of MI.

Adenosine A(2A)R modulates cardiovascular function by activating ERK1/2 signal in the rostral ventrolateral medulla of acute myocardial ischemic rats

AIMS

To investigate the cardiovascular regulatory mechanism of adenosine A(2A) receptor (A(2A)R) in the rostral ventrolateral medulla (RVLM) in acute myocardial ischemic (AMI) rats.

MAIN METHODS

The animal model of AMI was established by ligating the left anterior descending coronary artery (LAD). The A(2A)R expression was examined by immunohistochemistry, western blot and real-time PCR. CGS21680 and SCH58261 (an agonist and antagonist of A(2A)R) were respectively microinjected into the RVLM. In a subgroup of rats, PD98059 (an antagonist of extracellular signal-regulated kinase (ERK1/2)) was microinjected prior to CGS21680 administration. Phosphorylation of ERK1/2 was examined by western blot.

KEY FINDINGS

Our results demonstrated that A(2A)R immunoreactive positive neurons, the expressions of protein and mRNA of A(2A)R in the RVLM of AMI group were increased compared with the sham group. Microinjection CGS21680 into the RVLM inhibited mean arterial pressure (MAP) and heart rate (HR) in both AMI and sham groups. The inhibition was significantly greater in AMI group than in sham group. The cardiovascular effects of CGS21680 mentioned above were almost abolished by prior administration of PD98059. The increase of ERK1/2 in the RVLM with the cardiovascular responses was induced by CGS21680 in AMI rats; this effect was also blocked by SCH58261.

SIGNIFICANCE

This study reveals that the activated A(2A)R in the RVLM underlies the depressor and bradycardiac responses in AMI rats via phosphorylation of ERK1/2 increasing.

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.

Ischemic postconditioning inhibits apoptosis after acute myocardial infarction in pigs

OBJECTIVES

Recent studies have shown that ischemic postconditioning reduces myocardial ischemia-reperfusion (I/R) injury; however, the effects of inhibiting apoptosis on cardioprotection induced by ischemic postconditioning remain to be determined. The objective of this study was to investigate whether ischemic postconditioning attenuates myocardial I/R injury by reduced apoptosis in a closed-chest pig model of acute myocardial infarction.

METHODS

Diannan small-ear pigs were randomly divided into 3 groups (5/group): (1) The sham group underwent a sham operation without ischemia; (2) the I/R group received 60 minutes of ischemia and 72 hours of reperfusion; and (3) the ischemic postconditioning (Postcond) group was treated the same as the I/R group except that the pigs received 8 cycles of 30 seconds of reperfusion and 30 seconds of ischemia at the onset of reperfusion. After 72 hours of reperfusion, infarct size was measured by 2,3,5-triphenyltetrazolium chloride staining. Apoptotic cells in the peri-infarct myocardium were evaluated with the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method, and apoptosis-related molecules were studied with western blotting analysis.

RESULTS

After 72 hours of reperfusion, mean (±SEM) infarct size was significantly smaller in the Postcond group than in the I/R group (23.26% ± 3.13% versus 10.89% ± 2.02%, P < .05). Apoptotic myocytes in the peri-infarct region were lower in the Postcond group than in the I/R group (15.31% ± 4.58% versus 33.83% ± 4.44%, P < .05). This decrease in the extent of apoptosis was accompanied by a significant decrease in Bax expression (0.306 ± 0.075 versus 0.433 ± 0.102 for the I/R group; P < .05) and a significant increase in Bcl-2 expression (1.801 ± 0.227 versus 1.267 ± 0.308 for the I/R group; P < .05).

CONCLUSIONS

In a clinically relevant closed-chest pig model of myocardial infarction, these data suggest the following: (1) Ischemic postconditioning reduces infarct size following prolonged reperfusion, and (2) this cardioprotective effect is likely achieved via antiapoptotic mechanisms.

In vivo study of myocardial elastography under graded ischemia conditions

The capability of currently available echocardiography-based strain estimation techniques to fully map myocardial abnormality at early stages of myocardial ischemia is yet to be investigated. In this study, myocardial elastography (ME), a radio-frequency (RF)-based strain imaging technique that maps the full 2D transmural angle-independent strain tensor in standard echocardiographic views at both high spatial and temporal resolution is presented. The objectives were to (1) evaluate the performance of ME on mapping the onset, extent and progression of myocardial ischemia at graded coronary constriction levels (from partial to complete coronary flow reduction), and (2) validate the accuracy of the strain estimates against sonomicrometry (SM) measurements. A non-survival canine ischemic model (n = 5) was performed by gradually constricting the left anterior descending (LAD) coronary blood flow from 0% (baseline blood flow) to 100% (zero blood flow) at 20% increments. An open-architecture ultrasound system was used to acquire RF echocardiograms in a standard full short-axis view at the frame rate of 211 fps, at least twice higher than what is typically used in conventional echocardiographic systems, using a previously developed, fully automated composite technique. Myocardial deformation was estimated by ME and validated against sonomicrometry. ME estimates and maps transmural (1) 2D displacements using RF cross-correlation and recorrelation; and (2) 2D polar (radial and circumferential) strains, derived from 2D (i.e. both lateral and axial) displacement components, at high accuracy. Full-view strain images were shown and found to reliably depict decreased myocardial function in the region at risk at increased levels of coronary flow reduction. The ME radial strain was deemed to be a more sensitive, quantitative, regional measure of myocardial ischemia as a result of coronary flow reduction when compared to the conventional wall motion score index and ejection fraction. Good agreement (0.22% strain bias, 95% limits of agreement) using Bland-Altman analysis and good correlation (r = 0.84) were found between the ME and SM measurements. These findings demonstrate for the first time that ME could map angle-independent strains to non-invasively detect, localize and characterize the early onset of myocardial ischemia, i.e. at 40%, and possibly as low as 20%, LAD flow reduction, which could be further associated with the severity of coronary stenosis.

Visualization and quantification of NAD(H) in brain sections by a novel histo-enzymatic nitrotetrazolium blue staining technique

A histo-enzymatic technique for visualizing and quantifying endogenous NAD(H) in brain tissue was developed, based on coupled enzymatic cycling reactions that reduce nitrotetrazolium blue chloride to produce formazan. Conditions were used where the endogenous level of nicotinamide adenine dinucleotides (NAD(H)) was the rate limiting factor for formazan production. Spontaneous degradation of NAD(+) that occurs during incubation of thawed tissue was minimized by the addition of nicotinamide mononucleotide, an inhibitor of NAD(+) glycohydrolases. Cryostat sections of brains obtained from rats immediately after decapitation and 30 min later were used to determine the effects of ischemia alone on brain NAD(H) levels and neuroanatomic distribution. The ischemic insult resulted in a greater than 50% decline in the rate of formazan generation in the CA1 pyramidal neuronal layer of the hippocampus and in the parietal cortex and striatum, but not in the CA3 and dentate gyrus (DG) subregions of the hippocampus. The ischemia-induced changes in NAD(H) levels were confirmed by utilizing spectrofluorimetric measurements of NAD(H) present in perchloric acid extracts of brain samples. This new histo-enzymatic technique is suitable for visualizing and quantifying relative NAD(H) levels in the brain. This assay could prove useful in identifying region-selective NAD(H) catabolism that may contribute to neurodegeneration.

Comparison of cumulative planimetry versus manual dissection to assess experimental infarct size in isolated hearts

INTRODUCTION

Infarct size (IS) is an important variable to estimate cardiac ischemia/reperfusion injury in animal models. Triphenyltetrazolium chloride (TTC) stains viable cells red while leaving infarcted cells unstained. To quantify IS, infarcted and non-infarcted tissue is often manually dissected and weighed (IS-DW). An alternative is to measure infarcted areas by cumulative planimetry (IS-CP).

METHODS

We prospectively compared these two methods in 141 Langendorff-prepared guinea pig hearts (1.44+/-0.02 g) that were part of different studies on mechanisms of cardioprotection. Hearts were perfused with Krebs-Ringer's and subjected to 30 min global ischemia after various cardioprotective treatments. Two hours after reperfusion hearts were cut into 6-7 transverse sections (3mm) and stained for 5 min in 1% TTC and 0.1M KH2PO4 buffer (pH 7.4, 38 degrees C). Each slice was first scanned and its infarcted area measured with Image 1.62 software (NIH). Infarctions in individual slices of each heart were averaged (IS-CP) on the basis of their weight. After scanning, IS-DW was determined by careful manual dissection of infarcted from non-infarcted tissue and measuring their respective total weight.

RESULTS

We found limited tissue permeation of TTC in relation to the slice thickness leaving tissue in the center unstained, as well as significant cross-contamination of stained vs. unstained tissue after manual dissection. IS-CP and IS-DW ranged from 6.0 to 73.1% and 19.4 to 70.5%, respectively, and correlated as follows: IS-DW=(27.6+/-1.4)+(0.518+/-0.038) * IS-CP; r=0.75 (Pearson), p<0.001. In addition, IS-CP correlated better with return of function after reperfusion like developed left ventricular pressure, contractility and relaxation, and myocardial oxygen consumption.

DISCUSSION

Despite a good correlation between both methods, limited tissue permeation by TTC diffusion and limited precision in the ability to manually dissect stained from unstained tissue leads to an overestimation of infarct size by dissection and weighing compared to cumulative planimetry.