Minutes Of Coronary Artery Occlusion Research Articles

Cardioprotective Effects of Sodium-Glucose Cotransporter Subtype Inhibition on Ischemic and Pharmacological Preconditioning.

Sodium-glucose cotransporter (SGLT) 2 inhibitors partially inhibit SGLT1 expression; however, whether a clinical dose of SGLT2 inhibitor abrogates ischemic preconditioning (IPC) is unknown, and the pharmacological cardioprotective effect under SGLT1 inhibition has not been examined. In this study, we investigated whether a clinical dose of tofogliflozin abrogates IPC and whether pharmacological preconditioning with olprinone has cardioprotective effects under SGLT1 inhibition. Male Wistar rats were divided into seven groups (seven rats per group) and subjected to the following treatments before inducing ischemia/reperfusion (I/R; 30 minutes of coronary artery occlusion followed by 120 minutes of reperfusion): saline infusion control treatment (Con); ischemic preconditioning(IPC); IPC after phlorizin infusion (IPC+Phl); IPC after low-dose tofogliflozin infusion (IPC+L-Tof); IPC after high-dose tofogliflozin infusion (IPC+H-Tof); olprinone infusion (Olp); and Olp infusion after phlorizin infusion (Olp+Phl). The infarct size was significantly decreased in the IPC group, but not in the IPC+Phl group. In contrast, the infarct size decreased in the IPC+L-Tof and IPC+H-Tof groups. Additionally, Olp reduced the infarct size, and the effect was preserved in Olp+Phl groups. Phosphorylated AMP-activated protein kinase (AMPK) expression was lower in the IPC+Phl group compared to that in the IPC group. The cardioprotective effect of IPC was attenuated by strong SGLT1 inhibition, but the effect was preserved under a clinical dose of highly selective SGLT2 inhibitor. Olprinone exerts a cardioprotective effect even under strong SGLT1 inhibition.

Remote and Anesthetic-Induced Myocardial Preconditioning Is Preserved in Atherosclerotic LDL Receptor-/- Mice In Vivo

Introduction In the animal model, preconditioning is a powerful weapon against ischemic damage. The reason why the human heart cannot be protected from ischemic damage by preconditioning remains unclear. There are assumptions that the lack of preconditioning in humans is caused by concomitant diseases such as dyslipoproteinemia and arteriosclerosis. This study investigates whether dyslipoproteinemia and the resulting arteriosclerosis can be a cause of a reduced precondition effect of heart in mice. Methods LDL receptor-deficient mice were fed a long-term (14-16 weeks) high-fat atherogenic diet to induce arteriosclerosis. Arteriosclerosis was identified by histological examination and vessel contraction tests. LDLR-/- and wild-type mice were randomly assigned to anesthetic-induced, remote ischemic, or no preconditioning. All mice were subjected to 45 minutes of coronary artery occlusion and 180 minutes of reperfusion. The area at risk and infarct size were determined by Evans Blue and triphenyltetrazolium chloride staining. Results Histopathological examination showed atherosclerosis in high-fat atherogenic fed LDLR-/- mice, and the vessel relaxation capacity was significantly reduced compared to wild-type mice. In the wild type, as expected, infarct size was significantly reduced by preconditioning compared to the control. In LDLR-/- mice, infarct size was significantly reduced by preconditioning compared to the control. Surprisingly, the LDLR-/- control group also had a significantly reduced infarct size compared to the wild-type control group. Conclusion We were able to demonstrate that a high-fat diet morphologically and functionally triggered atherosclerosis in LDLR-/- mice. Interestingly, LDLR-/- mice with an atherogenic diet had smaller infarct sizes compared to wild-type mice. Moreover, preconditioning additionally reduced myocardial infarct size in LDLR-/- mice. A long-term high-fat atherogenic diet and preconditioning seem to result in additive cardioprotection in LDLR-/- mice.

Abstract 13764: Chronic Electronic Cigarette Vapor Exposure Leads to Impaired Cardiac Function in Experimental Rat Myocardial Ischemia/reperfusion Model

Background: We investigated the effects of long-term electronic cigarettes with nicotine (eC) vaping on cardiac function and structure in rats subjected to myocardial infarction (MI). Methods: After 8 weeks of exposure to either pure air (n=20) or eC (n=20), rats were anesthetized, and were subjected to 30 minutes of coronary artery occlusion followed by 3 hours of reperfusion. Cardiac function was assessed by echocardiogram and pressure measurements of the aorta and left ventricle (LV). Cardiac output (CO) was measured using a thermodilution catheter. At 3 hours of reperfusion, ischemic risk zone, no-reflow and infarct areas were determined. Results: Prior to coronary artery occlusion, chronic eC exposure was associated with a lower CO (45 ± 2 ml/min ) compared to air (55 ± 4 ml/min; p<0.05)) and a decrease in +dP/dt (5226 ± 294 mmHg/s versus 6062 ± 271 mmHg/s; p=0.05). After 30 minutes of coronary occlusion and 2.5 hours of reperfusion, CO and LV + dp/dt fell in both groups, but remained significantly lower in eC compared to the pure air group (Table). LV systolic and diastolic dimensions were significantly smaller in the E-Cig group compared to the air group. Systolic and diastolic anterior LV wall thickness were significantly thicker in the eC group after reperfusion. The ischemic risk size was comparable between the 2 groups. MI size was 48.8 ± 4.8% of the ischemic risk zone in the air group and 45.4 ± 4.4 % in the eC group (p=0.603). The area of no reflow was 26.7 ± 4.0% of the ischemic risk zone in the air group and 21.1 ± 3.5% in the E-C group (p=0.298). Chronic eC exposure did not change heart rate and blood pressure, but the significantly increased the systemic arterial resistance. Conclusions: Chronic exposure to eC significantly impaired cardiac function in rats prior to and during ischemia/reperfusion, increased arterial resistance, but did not increase infarct size or no-reflow zone. Increased LV wall thickness of the risk zone suggested that eC may have increased edema.

Inhibition of the Let-7 Family MicroRNAs Induces Cardioprotection Against Ischemia-Reperfusion Injury in Diabetic Rats

The expression of the let-7 family microRNAs in the myocardium of streptozotocin-induced diabetic rats was measured, and the cardioprotection of inhibition of let-7 microRNAs against ischemia-reperfusion injury was investigated. The diabetic rats and nondiabetic rats were subjected to 30 minutes of coronary artery occlusion followed by 120 minutes of reperfusion. The infarct size was determined by triphenyltetrazolium chloride staining. The expression of let-7 was measured by quantitative real-time polymerase chain reaction, and expressions of insulin receptor (InsR), insulin-like growth factor-1 receptor (IGF-1R), glucose transporter type 4 (GLUT4), and the phosphorylation states of Akt and the mammalian target of rapamycin (mTOR) were analyzed using Western blot. Inhibition of let-7 was performed by local transfection of lentivirus gene transfer vectors containing let-7 antimiR. Compared with nondiabetic rats, the expression of let-7 was enhanced in the myocardium of diabetic rats (p= 0.029), whereas expressions of InsR, IGF-1R, and GLUT4 were decreased after ischemia-reperfusion (p < 0.01). Local transfection of the let-7 antimiR markedly inhibited the expression of let-7 (p= 0.038) and improved expressions of InsR, IGF-1R, and GLUT4 in the myocardium of diabetic rats (p < 0.01). The infarct size of diabetic rats was much higher than that of nondiabetic rats (p < 0.0001). Transfection of the let-7 antimiR significantly reduced the infarct size of diabetic rats (p < 0.0001), and such an antiinfarct effect was abolished completely by pretreatment of Akt inhibitor LY294002 or mTOR inhibitor rapamycin. Inhibition of the let-7 family microRNAs improves glucose uptake and insulin resistance in the diabetic myocardium and induces cardioprotection against ischemia-reperfusion injury through Akt and mTOR pathways.

Statin (Mevalotin) preconditioning decreases infarct size in senile rat myocardial infarction model

Although statins have been proved to have cardioprotective effects, it remains to be investigated whether “statin-induced preconditioning (PC)” can reduce the infarct size for senile animals. Senile Wistar rats (weighing 350–450 g) were randomly assigned to one of 14 experiment groups ( n ≥ 5 for each group). All hearts underwent 30 minutes of coronary artery occlusion and 2 hours of reperfusion (control procedure). Ischemic PC was elicited by three cycles of 5-minute occlusion and 5-minute reperfusion. Statin PC was performed by administering Mevalotin (1 mg/kg, the optimal dose being determined by a dose–effect study) 30 minutes prior to the control procedure. In addition, pretreatment with glibenclamide, 5-hydroxydecanoic acid, chelerythrine, genistein, and N G -nitro-4-arginine methyl ester, or their combination, was also performed to test possible signaling mechanisms. Statin PC decreased the infarct size significantly compared with the control group (22 ± 4% vs. 53 ± 4%, p < 0.01). Pretreatment with N G -nitro-4-arginine methyl ester completely blocked the effects of Mevalotin (infarct size: 48 ± 4% vs. 22 ± 4%, p < 0.01). The cardioprotective effects of statin PC could be blunted by antagonism of mitochondrial adenosine triphosphate (ATP)-sensitive potassium and sarcolemmal ATP-sensitive potassium channels (glibenclamide: 50 ± 4% vs. 22 ± 4%, p < 0.01; 5-hydroxydecanoic acid: 50 ± 4% vs. 22 ± 4%, p < 0.01). In addition, protein kinase C antagonist (chelerythrine) and tyrosine kinase antagonist (genisteine) also have similar effects (chelerythrine: 48 ± 4% vs. 22 ± 4%, p < 0.01; genistein: 45 ± 4% vs. 22 ± 4%, p < 0.01). It is established in this study the myocardial PC caused by statins, that is involved cellular mechanisms including mainly the pathway of endothelial nitrous oxide synthase (eNOS)–nitrous oxide donation–ATP-sensitive potassium channels. Protein kinase C and tyrosine kinase have regulatory effects.

Repeated Non‐invasive Remote ischemic Preconditioning Confers Cardioprotection in Diabetic Rats (LB559)

Non‐invasive Remote ischemic preconditioning (NRIPC) has a cardioprotective effect in normal rats, but its effect in rats with diabetes is controversial. This study was mainly to determine the cardioprotective effect of NRIPC on ischemia reperfusion injury (IRI) in diabetic rats. Diabetes was induced in Sprague‐Dawley rats with streptozotocin. NRIPC was implemented by applying 3 cycles of 5‐min occlusion/5‐min reperfusion in a unilateral hindlimb once per day for three days. The animals were then subjected to 30 minutes of coronary artery occlusion followed by two hours of reperfusion. A control group had no NRIPC. The results showed that NRIPC significantly reduced post‐ischemic myocardial infarct size,lactate dehydrogenase (LDH) and troponin‐1 release during reperfusion in both control and diabetic rats. Protein PKC‐ε, phosphorylation of AKT and signal transducer and activator of transcription 3(STAT3) were all significantly increased after NRIPC and their enhancement after reperfusion was correlated with reductions of post‐ischemic myocardial infarction and cellular injury. In conclusion, cardioprotection can be achieved in diabetes by NRIPC applied repeatedly for three days prior to inducing myocardial infarction and activation of PKC‐ε and STAT3 might be a major mechanism of NRIPC protection.Grant Funding Source: RGC/GRF grant (768211M) and a HKU seeding grant

Acute testosterone infusion does not exacerbate arrhythmias in the rat model of ischemia/reperfusion (547.15)

Introduction: With increasing direct‐to‐consumer marketing, testosterone (T) prescriptions have tripled over the past decade. Clinical literature suggests that exogenous T use may increase various arrhythmias. Therefore, we examined the effect of exogenous T in an acute rat model of arrhythmias.Methods and Results: Anesthetized female Sprague Dawley rats (250g) were given T (2.5 mg/kg, n=9) or vehicle (n=10) intravenously 15 minutes before 5 minutes of coronary artery occlusion. Rats were then reperfused for 5 minutes and arrhythmias were examined. T levels were measured one minute before occlusion. T levels were different between groups (5.4 ± 1 ng/mL control; 206.9 ± 35 ng/mL T, P &lt; 0.001). The ischemic risk zone as a percentage of the left ventricle did not differ between groups (33 ± 2% control; 29 ± 3% T, P = 0.48). The number of episodes of ventricular tachycardia did not differ between groups (11.7 ± 3.2 control; 8.8 ± 3.0 T, P = 0.3). There was a non‐significant trend toward fewer ventricular premature beats with T (37.8 ± 10.3 control; 16.9 ± 8.9 T, P = 0.06) Conclusion: Despite large differences in T levels between groups, T had little effect on the incidence of arrhythmias, suggesting that T supplementation does not increase risk of arrhythmias.

The Role of Cyclooxygenase-1 and -2 in Sevoflurane-Induced Postconditioning Against Myocardial Infarction

Cyclooxygenase (COX)-2 mediates ischemic pre- and postconditioning as well as anesthetic-induced preconditioning. However, the role of COX-1 and -2 in anesthetic-induced postconditioning has not been investigated. We evaluated the role of COX-1 and -2 in sevoflurane-induced postconditioning in vivo. Pentobarbital-anaesthetized male C57BL/6 mice were subjected to 45 minutes of coronary artery occlusion and 3 hours of reperfusion. Animals received either no intervention, the vehicle dimethyl sulfoxide (DMSO, 10 µL/g intraperitoneally), acetylsalicylic acid (ASA, 5 µg/g intraperitoneally), the selective COX-1 inhibitor SC-560 (10 µg/g intraperitoneally), or the selective COX-2 inhibitor NS-398 (5 µg/g intraperitoneally). 1.0 MAC (minimum alveolar concentration) sevoflurane was administered for 18 minutes during early reperfusion either alone or in combination with ASA, SC-560, and NS-398. Infarct size was determined with triphenyltetrazolium chloride. Statistical analysis was performed using 1-way and 2-way analyses of variance with post hoc Duncan testing. The infarct size in the control group was 44% ± 9%. DMSO (42% ± 7%), ASA (36% ± 6%), and NS-398 (44% ± 18%) had no effect on infarct size. Sevoflurane (17% ± 4%; P < .05) and SC-560 (26% ± 10%; P < .05) significantly reduced the infarct size compared with control condition. Sevoflurane-induced postconditioning was not abolished by ASA (16% ± 5%) and SC-560 (22% ± 4%). NS-398 abolished sevoflurane-induced postconditioning (33% ± 14%). It was concluded that sevoflurane induces postconditioning in mice. Inhibition of COX-1 elicits a myocardial infarct size reduction and does not abolish sevoflurane-induced postconditioning. Blockade of COX-2 abolishes sevoflurane-induced postconditioning. These results indicate that sevoflurane-induced postconditioning is mediated by COX-2.

Role of Extracellular RNA and TLR3‐Trif Signaling in Myocardial Ischemia–Reperfusion Injury

BackgroundToll‐like receptor 3 (TLR3) was originally identified as the receptor for viral RNA and represents a major host antiviral defense mechanism. TLR3 may also recognize extracellular RNA (exRNA) released from injured tissues under certain stress conditions. However, a role for exRNA and TLR3 in the pathogenesis of myocardial ischemic injury has not been tested. This study examined the role of exRNA and TLR3 signaling in myocardial infarction (MI), apoptosis, inflammation, and cardiac dysfunction during ischemia‐reperfusion (I/R) injury.Methods and ResultsWild‐type (WT), TLR3−/−, Trif−/−, and interferon (IFN) α/β receptor‐1 deficient (IFNAR1−/−) mice were subjected to 45 minutes of coronary artery occlusion and 24 hours of reperfusion. Compared with WT, TLR3−/− or Trif−/− mice had smaller MI and better preserved cardiac function. Surprisingly, unlike TLR(2/4)‐MyD88 signaling, lack of TLR3‐Trif signaling had no impact on myocardial cytokines or neutrophil recruitment after I/R, but myocardial apoptosis was significantly attenuated in Trif−/− mice. Deletion of the downstream IFNAR1 had no effect on infarct size. Importantly, hypoxia and I/R led to release of RNA including microRNA from injured cardiomyocytes and ischemic heart, respectively. Necrotic cardiomyocytes induced a robust and dose‐dependent cytokine response in cultured cardiomyocytes, which was markedly reduced by RNase but not DNase, and partially blocked in TLR3‐deficient cardiomyocytes. In vivo, RNase administration reduced serum RNA level, attenuated myocardial cytokine production, leukocytes infiltration and apoptosis, and conferred cardiac protection against I/R injury.ConclusionTLR3‐Trif signaling represents an injurious pathway during I/R. Extracellular RNA released during I/R may contribute to myocardial inflammation and infarction.

N-Acetylcysteine and Allopurinol Confer Synergy in Attenuating Myocardial Ischemia Injury via Restoring HIF-1α/HO-1 Signaling in Diabetic Rats

ObjectivesTo determine whether or not the antioxidants N-acetylcysteine (NAC) and allopurinol (ALP) confer synergistic cardioprotection against myocardial ischemia/reperfusion (MI/R) injury by stabilizing hypoxia inducible factor 1α (HIF-1α)/heme oxygenase 1 (HO-1) signaling in diabetic myocardium.MethodsControl or diabetic [streptozotocin (STZ)-induced] Sprague Dawley rats received vehicle or NAC, ALP or their combination for four weeks starting one week after STZ injection. The animals were then subjected to thirty minutes of coronary artery occlusion followed by two hours reperfusion in the absence or presence of the selective HO-1 inhibitor, tin protoporphyrin-IX (SnPP-IX) or the HIF-1α inhibitor 2-Methoxyestradiol (2ME2). Cardiomyocytes exposed to high glucose were subjected to hypoxia/re-oxygenation in the presence or absence of HIF-1α and HO-1 achieved by gene knock-down with related siRNAs.ResultsMyocardial and plasma levels of 15-F2t-isoprostane, an index of oxidative stress, were significantly increased in diabetic rats while cardiac HO-1 protein and activity were reduced; this was accompanied with reduced cardiac protein levels of HIF-1α, and increased post-ischemic myocardial infarct size and cellular injury. NAC and ALP given alone and in particular their combination normalized cardiac levels of HO-1 and HIF-1α protein expression and prevented the increase in 15-F2t-isoprostane, resulting in significantly attenuated post-ischemic myocardial infarction. NAC and ALP also attenuated high glucose-induced post-hypoxic cardiomyocyte death in vitro. However, all the above protective effects of NAC and ALP were cancelled either by inhibition of HO-1 or HIF-1α with SnPP-IX and 2ME2 in vivo or by HO-1 or HIF-1α gene knock-down in vitro.ConclusionNAC and ALP confer synergistic cardioprotection in diabetes via restoration of cardiac HIF-1α and HO-1 signaling.

A Model of Hypoxia-Reoxygenation on Isolated Adult Mouse Cardiomyocytes

The use of in vitro experimental models of hypoxia-reoxygenation (H/R) that mimic in vivo ischemia-reperfusion represents a powerful tool to investigate cardioprotective strategies against myocardial infarction. Most in vitro studies are performed using neonatal cardiac cells or immortalized embryonic cardiac cell lines which may limit the extrapolation of the results. We developed an H/R model using adult cardiomyocytes freshly isolated from mice and compared its characteristics to the in vivo ischemia-reperfusion conditions. First, cell death was assessed at different values of pH medium during hypoxia (6.2 vs 7.4) to simulate extracellular pH during in vivo ischemia. Cardiomyocyte mortality was aggravated with hypoxia under acidic pH. We next evaluated the relationship between the duration of hypoxia and cell death. Hypoxia time-dependently reduced myocyte viability (-24%, -36%, -53%, and -74% with 1, 1.5, 2, and 3 hours of hypoxia followed by 17 hours of reoxygenation, respectively). We then focused on the duration of reoxygenation as cardioprotective strategies have been reported to have different effects with short and long durations of reperfusion. We observed that cardiomyocyte mortality was increased when the duration of reoxygenation was increased from 2 h to 17 hours. Finally, we used our characterized model to investigate the cardioprotective effect of regular treadmill exercise. Myocyte viability was significantly greater in exercised when compared to sedentary mice (44% and 26%, respectively). Similarly, mice submitted to in vivo ischemia-reperfusion elicited infarct sizes reaching 27%, 43%, and 55% with 20, 30, and 45 minutes of coronary artery occlusion. In addition, infarct size was significantly reduced by exercise. In conclusion, this H/R model of cardiomyocytes freshly isolated from adult mice shows similar characteristics to the in vivo ischemia-reperfusion conditions. The comparison of in vivo and in vitro settings represents a powerful approach to investigate cardioprotective strategies and to distinguish between direct and indirect cardiomyocyte-dependent mechanisms.

Antioxidants N‐acetylcysterine and Allopurinol synergistically enhance cardiac HIF‐1α and heme oxygenase‐1 and attenuate Postischemic Myocardial Injury in Diabetic Rats

Hypoxia inducible factor 1(HIF) α can reduce myocardial ischemia‐reperfusion injury(MIRI). However, hyperglycemia‐induced oxidative stress may reduce cardiac HIF‐1α and subsequently inhibit heme oxygenase 1 (HO‐1), a down‐stream protein of HIF‐1α that has anti‐ischemic properties. N‐acetylcysteine (NAC) and allopurinol (ALP) synergistically reduce MIRI in diabetes (PLoS One. 2011;6:e23967), but the role of HIF‐1α/HO‐1 in this process in unknown. Control or streptozotocin (STZ)‐induced diabetic rats were untreated (C, D) or treated with NAC (1.5g/kg/day) or ALP (100 mg/kg/day) or their combination (NAC+ALP) for four weeks starting one week after STZ injection. Cardiac and plasma 15‐F2t‐isoprostane (IsoP) were increased in D rats while cardiac HO‐1 and protein expression and activity were reduced, accompanied with reduced cardiac HIF‐1α, and increased post‐ischemic myocardial infarct size (IS) and cellular injury in D rats subjected to 30 minutes of coronary artery occlusion and 2 hours of reperfusion (all P&lt;0.05 D vs. C). NAC+ALP normalized cardiac levels of HO‐1 and HIF‐1α protein expression, prevented the increase in IsoP, and reduced myocardial IS, but these effects of NAC+ALP were cancelled by either the HO‐1 blocker protoporphyrin or the HIF‐1α blocker 2‐Methoxyestradiol. It is concluded that HIF‐1α and HO‐1 activation play an important role in NAC and ALP mediated cardioprotection in diabetes.

Antioxidants N‐Acetylcysteine and Allopurinol attenuation of postischemic myocardial injury in diabetic rats involve Akt and STAT3 mediated eNOS activation

Hyperglycemia‐induced oxidative stress exacerbates myocardial ischemic reperfusion (MI/R) injury. N‐acetylcysteine (NAC) and allopurinol (ALP) reduced MI/R injury in streptozotocin (STZ)‐induced diabetes (PLoS One. 2011;6:e23967), but the mechanism is unclear. We postulated that NAC and ALP attenuate MI/R injury via PI3k/Akt and Jak2/STAT3 mediated eNOS activation in diabetes. Control (C) or STZ‐induced diabetic (D) rats were untreated or treated with NAC (1.5g/kg/day) or ALP (100 mg/kg/day) or their combination for four weeks starting one week after STZ injection. NAC and ALP synergistically decreased myocardial infarct size in D rats subjected to 30 minutes of coronary artery occlusion and 2 hours reperfusion, and restored phosphorylations of cardiac Akt, STAT3 and eNOS (P&lt;0.05 NAC+ALP vs. D). Exposure of rat cardiomyocytes to high glucose and 45 min hypoxia and 2 hours reoxygenation induced post‐hypoxic cell death reflected as increase of lactate dehydrogenase leakage and reduced cell viability. NAC and ALP synergistically reduced post‐hypoxic cell death and enhanced phosphorylations of Akt, STAT3 and eNOS. The PI3K inhibitor wortmannin and Jak2 inhibitor AG490, respectively attenuated NAC and ALP's protective effects in vivo and in vitro. We conclude that activation of both the PI3K/Akt and the Jak2/STAT3 signaling are involved in NAC and ALP mediated attenuation of MI/R injury in diabetes.

Adenosine and Opioid Receptors Do Not Trigger the Cardioprotective Effect of Mild Hypothermia

Mild hypothermia (32°C-34°C) exerts a potent cardioprotection in animal models of myocardial infarction. Recently, it has been proposed that this beneficial effect is related to survival signaling. We, therefore, hypothesized that the well-known cardioprotective pathways dependent on adenosine and/or opioid receptors could be the trigger of hypothermia-induced salvage. Open-chest rabbits were accordingly exposed to 30 minutes of coronary artery occlusion (CAO) under normothermic (NT) or hypothermic ([HT] 32°C) conditions. In the latter, hypothermia was induced by total liquid ventilation with temperature-controlled perfluorocarbons in order to effect ultrafast cooling and to accurately control cardiac temperature. After 4 hours of reperfusion, infarct and no-reflow zone sizes were assessed and quantified as a percentage of the risk zone. In animals experiencing HT ischemia, the infarct size was dramatically reduced as compared to NT animals (9% ± 3% vs 55% ± 2% of the risk zone, respectively). Importantly, administration of opioid and adenosine receptor antagonists (naloxone [6 mg/kg iv] and 8-(p-sulfophenyl) theophylline [20 mg/kg iv], respectively) did not alter the infarct size or affect the cardioprotective effect of hypothermia. Doses of these 2 antagonists were appropriately chosen since they blunted infarct size reduction induced by selective opioid or adenosine receptor stimulation with morphine (0.3 mg/kg iv) or N (6)-cyclopentyladenosine ([CPA] 100 μg/kg iv), respectively. Therefore, the cardioprotective effect of mild hypothermia is not triggered by either opioid or adenosine receptor activation, suggesting the involvement of other cardioprotective pathways.

Do We Really Need Another Biomarker to Diagnose Myocardial Infarction After Coronary Artery Bypass Graft Surgery?

Do We Really Need Another Biomarker to Diagnose Myocardial Infarction After Coronary Artery Bypass Graft Surgery?

Hold Me Tight

Hold Me Tight

Propofol Inhibits Desflurane-Induced Preconditioning in Rabbits

The authors tested the hypothesis that ischemic and desflurane-induced preconditioning are blocked by propofol. A prospective, randomized, vehicle-controlled study. A university research laboratory. New Zealand white rabbits (n = 52). Pentobarbital-anesthetized rabbits were subjected to 30 minutes of coronary artery occlusion followed by 3 hours of reperfusion. Rabbits received 0.0 (control) or 1.0 minimum alveolar concentration of desflurane (30 minutes' duration and a 30-minute memory period) or ischemic preconditioning (5 minutes of ischemia and a 30-minute memory period) in the absence or presence of propofol (10 mg/kg/h intravenously) or its vehicle (10% Intralipid emulsion; B Braun, Melsungen, Germany). The myocardial infarct size was measured with triphenyltetrazolium staining. Statistical analysis was performed with 1-way and 2-way analysis of variance when appropriate, followed by a post hoc Duncan test. Data are mean ± standard deviation. Myocardial infarct size was 56% ± 8% in control animals (n = 7). Desflurane significantly (p < 0.05) reduced the infarct size to 37% ± 6% (n = 7). Desflurane-induced preconditioning was blocked by propofol (65% ± 10%, n = 7) but not by its vehicle (45% ± 11%, n = 5). Propofol and its vehicle alone had no effect on the infarct size (62% ± 8% [n = 6] and 58% ± 3% [n=5], respectively). Ischemic preconditioning reduced infarct size in the absence or presence of propofol to 24% ± 7% (n = 7) and 29% ± 12% (n = 6). Desflurane-induced preconditioning markedly reduced infarct size and was blocked by propofol, whereas ischemic preconditioning was not blocked by propofol. The results suggest an important interference between propofol and anesthetic-induced preconditioning and might explain some contradictory findings in studies in humans.

Profound Cardioprotection With Chloramphenicol Succinate in the Swine Model of Myocardial Ischemia-Reperfusion Injury

Emerging evidence suggests that "adaptive" induction of autophagy (the cellular process responsible for the degradation and recycling of proteins and organelles) may confer a cardioprotective phenotype and represent a novel strategy to limit ischemia-reperfusion injury. Our aim was to test this paradigm in a clinically relevant, large animal model of acute myocardial infarction. Anesthetized pigs underwent 45 minutes of coronary artery occlusion and 3 hours of reperfusion. In the first component of the study, pigs received chloramphenicol succinate (CAPS) (an agent that purportedly upregulates autophagy; 20 mg/kg) or saline at 10 minutes before ischemia. Infarct size was delineated by tetrazolium staining and expressed as a % of the at-risk myocardium. In separate animals, myocardial samples were harvested at baseline and 10 minutes following CAPS treatment and assayed (by immunoblotting) for 2 proteins involved in autophagosome formation: Beclin-1 and microtubule-associated protein light chain 3-II. To investigate whether the efficacy of CAPS was maintained with "delayed" treatment, additional pigs received CAPS (20 mg/kg) at 30 minutes after occlusion. Expression of Beclin-1 and microtubule-associated protein light chain 3-II, as well as infarct size, were assessed at end-reperfusion. CAPS was cardioprotective: infarct size was 25±5 and 41±4%, respectively, in the CAPS-pretreated and CAPS-delayed treatment groups versus 56±5% in saline controls (P<0.01 and P<0.05 versus control). Moreover, administration of CAPS was associated with increased expression of both proteins. Our results demonstrate attenuation of ischemia-reperfusion injury with CAPS and are consistent with the concept that induction of autophagy may provide a novel strategy to confer cardioprotection.

Caspase Inhibition Modulates Left Ventricular Remodeling Following Myocardial Infarction Through Cellular and Extracellular Mechanisms

Myocyte death occurs by necrosis and caspase-mediated apoptosis in myocardial infarction (MI). In vitro studies suggest caspase activation causes myocardial contractile protein degradation without inducing apoptosis. Thus, caspase activation may evoke left ventricular (LV) remodeling through independent processes post-MI. The effects of caspase activation on LV geometry post-MI remain unclear. This project applied pharmacologic caspase inhibition (CASPI) to a porcine model of MI. Pigs (34 kg) were instrumented to induce 60 minutes of coronary artery occlusion followed by reperfusion and a 7-day follow-up period. Upon reperfusion, the pigs were randomized to saline (n = 12) or CASPI (n = 10, IDN6734, 6 mg/kg i.v., then 6 mg/kg/h for 24 hours). Plasma troponin-I values were reduced with CASPI compared with saline at 24 hours post-MI (133 +/- 15 vs. 189 +/- 20 ng/mL, respectively, P < 0.05). LV end-diastolic area (echocardiography) and interregional length (sonomicrometry) increased from baseline in both groups but were attenuated with CASPI by 40% and 90%, respectively (P < 0.05). Myocyte length was reduced with CASPI compared with saline (128 +/- 3 vs. 141 +/- 4 microm, respectively, P < 0.05). Plasma-free pro-matrix metalloproteinase-2 values increased from baseline with CASPI (27% +/- 6%, P < 0.05) indicative of reduced conversion to active MMP-2. Separate in vitro studies demonstrated that activated caspase species cleaved pro-MMP-2 yielding active MMP-2 forms and that MMP activity was increased in the presence of activated caspase-3. CASPI attenuated regional and global LV remodeling post-MI and altered viable myocyte geometry. Caspases increased MMP activity in vitro, whereas CASPI modified conversion of MMP-2 to the active form in vivo. Taken together, the results of the present study suggest that the elaboration of caspases post-MI likely contribute to LV remodeling through both cellular and extracellular mechanisms.

Desflurane-Induced Preconditioning Has a Threshold That Is Lowered by Repetitive Application and Is Mediated by β 2-Adrenergic Receptors

An optimal administration protocol to induce a maximal effect of anesthetic preconditioning has not been evaluated to date. In this study, desflurane preconditioning was characterized with respect to its threshold, dose dependency, and continuous versus repetitive application. Furthermore, the role of beta(2)-adrenergic receptors in anesthetic preconditioning was tested. A randomized controlled study. Laboratory study in a University hospital. New Zealand white rabbits in vivo. Systemic hemodynamics were continuously measured. Rabbits were subjected to 30 minutes of coronary artery occlusion and 3 hours of reperfusion. Animals received desflurane continuously for 30 minutes at 0.5, 1.0, or 1.5; desflurane for 90 minutes at 0.5 or 1.5 MAC; or repetitively for three 10-minute periods at 0.5, 1.0, or 1.5 MAC before coronary occlusion. The beta(2)-adrenergic receptor blocker ICI 118,551 (0.2 mg/kg) or saline placebo was given in the absence or presence of 1.0 MAC desflurane. Myocardial infarct size was measured with triphenyltetrazolium staining. Myocardial infarct size was 61% +/- 5% in control experiments. Desflurane, administered continuously at 0.5 MAC for 30 minutes (52% +/- 4%) or 90 minutes (56% +/- 8%) had no effect, whereas 0.5 MAC of desflurane given repetitively reduced infarct size to 36% +/- 7%. Desflurane administered continuously for 30 minutes at 1.0 or 1.5 MAC reduced infarct size to 35% +/- 5% and 39% +/- 4%, respectively. Repetitive application at 1.0 MAC (37% +/- 6%) or 1.5 MAC (29% +/- 4%) and continuous administration of 1.5 MAC for 90 minutes (32% +/- 6%) did not result in further infarct size reduction. ICI 118,551 did not affect infarct size (53% +/- 2%) but abolished desflurane preconditioning (51% +/- 5%). beta(2)-Adrenergic receptors mediate desflurane-induced preconditioning. Desflurane-induced preconditioning has a threshold that can be lowered by repetitive administration.