Attenuation of increased myocardial ischaemia-reperfusion injury conferred by hypercholesterolaemia through pharmacological inhibition of the caspase-1 cascade

GSDMD contributes to myocardial reperfusion injury by regulating pyroptosis

Background

Gasdermin D (GSDMD) plays an essential role in the pathway of pyroptosis. However, whether GSDMD participates in myocardial ischaemia/reperfusion injury (MI/RI) remains poorly understood.

Methods

Serum levels of GSDMD and IL-18 in ST-segment elevation myocardial infarction (STEMI) patients were measured by ELISA. The expression of GSDMD and GSDMD N-terminal (GSDMD-NT) in vivo and in vitro was assessed by western blot and immunofluorescence staining. GSDMD-/- mice and wild type (WT) mice were induced MI/RI, followed by cardiac ultrasound and histological analysis.

Results

Clinically, patients suffering from STEMI after percutaneous coronary intervention (PCI) exhibited higher levels of GSDMD and IL-18 than that in the controls. In vitro, the cleavage of GSDMD was significantly upregulated in macrophages exposed to hypoxia/reoxygenation or H2O2. In vivo, the levels of GSDMD and GSDMD-NT increased notably after MI/RI, especially in macrophages infiltrating in the infarct area. Moreover, compared with WT mice, GSDMD-/- mice showed reduced infarct size (25.45 ± 3.07% versus 36.47 ± 3.72%), improved left ventricular ejection fraction (37.71 ± 1.81% versus 29.44 ± 2.28%) and left ventricular fractional shortening (18.01 ± 0.97% versus 13.62 ± 1.15%) as well as attenuated pathological damage after I/R injury, along with reduced levels of proinflammatory cytokines and decreased infiltration of neutrophils.

Conclusions

Our study revealed that GSDMD deficiency significantly alleviated the inflammatory response by regulating pyroptosis, reduced the infarct size and preserved cardiac function after MI/RI, thus providing a potential strategy for the treatment of myocardial reperfusion injury.

Clopidogrel or prasugrel reduces mortality and lessens cardiovascular damage from acute myocardial infarction in hypercholesterolemic male rats

AIMS

Hypercholesterolemia is a hazard for increasing susceptibility of the heart to myocardial infarction (MI) by inducing platelet hyperaggregability. Clopidogrel and prasugrel have documented cardioprotective effects in clinical studies. Herein, we investigated whether clopidogrel and prasugrel could protect against isoproterenol-induced acute MI (A-MI) under hypercholesterolemic conditions in rats.

MAIN METHODS

Dietary hypercholesterolemic rats were subjected to acute doses of isoproterenol. Serum lipids, inflammatory markers, aortic endothelin1 and endothelial nitric oxide synthase (eNOS) mRNAs expression and immunexpression of BCL2 were determined.

KEY FINDINGS

Hypercholesterolemic rats showed infiltration of inflammatory cells and reduction in aortic wall thickness, deposition of fibrous tissue between cardiac muscle fibers. Protective doses of prasugrel or clopidogrel for 28 days before A-MI increased survival, amended the ECG parameters -including ST segment elevation- and improved the histopathological picture in hypercholesterolemic rats. This was coupled with reductions in platelet aggregation, creatine kinase-MB activity, endothelin 1, systemic inflammation and cardiac lipid peroxidation and increment in aortic eNOS expression. Clopidogrel and prasugrel groups showed enhanced BCL2 expression in cardiac fibers and aortic wall.

SIGNIFICANCE

Prasugrel and clopidogrel protected against A-MI via anti-aggregatory and anti-inflammatory effects. These results add to the value of these drugs in correcting cardiovascular dysfunction in patients vulnerable to A-MI after confirmation by appropriate human studies.

Calpain silencing alleviates myocardial ischemia-reperfusion injury through the NLRP3/ASC/Caspase-1 axis in mice

AIMS

Prior to reperfusion, Calpains remain inactive due to the acidic pH and elevated ionic strength in the ischemic myocardium; but Calpain is activated during myocardial reperfusion. The underlying mechanism of Calpain activation in the ischemia-reperfusion (I/R) is yet to be determined. Therefore, the present study aims to investigate the mechanism of Calpain in I/R-induced mice.

MAIN METHODS

In order to detect the function of Calpain and the NLRP3/ASC/Caspase-1 axis in cardiomyocyte pyroptosis, endoplasmic reticulum (ER) stress and myocardial function, the cardiomyocytes were treated with hypoxia-reoxygenation (H/R), and NLRP3 were silenced, Calpain was overexpressed and Caspase-1 inhibitors were used to determine cardiomyocyte pyroptosis. The results obtained from the cell experiments were then verified with an animal experiment in I/R mice.

KEY FINDINGS

There was an overexpression in Calpain, ASC, NLRP3, GRP78 and C/EBP homologous protein (CHOP) in cardiomyocytes following H/R. A significant increase was witnessed in lactic acid dehydrogenase (LDH) activity, cardiomyocyte pyroptosis rate, Calpain activity, reactive oxygen species (ROS) concentration, as well as activation of ER stress in cardiomyocytes after H/R. However, opposing results were observed in H/R cardiomyocytes that received siRNA Calpain, siRNA NLRP3 or Caspase-1 inhibitor treatment. Overall, the results obtained from the animal experiment were consistent with the results from the cell experiment.

SIGNIFICANCE

The silencing of Calpain suppresses the activation of the NLRP3/ASC/Caspase-1 axis, thus inhibiting ER stress in mice and improving myocardial dysfunction induced by I/R, providing a novel therapeutic pathway for I/R.

Cardioprotective and Anti-Aggregatory Effects of Levosimendan on Isoproterenol-Induced Myocardial Injury in High-Fat-Fed Rats Involves Modulation of PI3K/Akt/mTOR Signaling Pathway and Inhibition of Apoptosis

Hyperlipidemia and hypercoagulability states are linked with the increased risks of myocardial infarction (MI). Levosimendan has vasorelaxant and anti-aggregatory properties. The present study evaluated the anti-aggregatory and cardioprotective effects of levosimendan versus cilostazol in high-fat diet (HFD)-fed rats subjected to isoproterenol-induced MI. Rats were assigned to normal, HFD, HFD + isoproterenol, HFD + isoproterenol + cilostazol, and HFD + isoproterenol + levosimendan. The present study investigated the anti-aggregatory effect of both levosimendan and cilostazol and revealed that both drugs attenuated the severity of platelet aggregation. Moreover, both levosimendan and cilostazol revealed effectiveness in attenuating the severity of HFD/isoproterenol-induced myocardial injury as revealed by electrocardiogram signs, apoptotic markers, and histopathological score via counteracting the oxidative stress burden, increments in the expression of inflammatory mediators, and modulating nuclear factor kappa-B (NF-κB) and phosphatidylinositide 3-kinases (PI3K)/protein kinase B (Akt)/ mechanistic target of rapamycin (mTOR) pathway. It was obvious that levosimendan offered more cardioprotective properties than cilostazol. The study showed the relations between hyperlipedemia, hyperaggregability state, and myocardial injury with the modulation of NF-κB and PI3K/Akt/mTOR pathway.

The NLRP3 and CASP1 gene polymorphisms are associated with developing of acute coronary syndrome: a case-control study

The protein products of NLRP3 and CASP1 genes are involved in the cleavage of pro-IL-1B and pro-IL-18 leading to the active cytokines, which play an important role in the development of the acute coronary syndrome (ACS). The aim of the present study was to evaluate whether NLRP3 and CASP1 gene polymorphisms are biomarkers of ACS susceptibility in Mexican population. Two polymorphisms of the CASP1 gene [G+7/in6A (rs501192) and A10370-G Exon-6 (rs580253)] and one of the NLRP3 gene [UTR'3 G37562-C (rs10754558)] were genotyped by 5' exonuclease TaqMan assays in a group of 617 patients with ACS and 609 control individuals. Under recessive model, the CASP1 G+7/in6A polymorphism was associated with an increased risk of developing ACS when compared to healthy controls (OR = 1.76, 95% CI 1.08-2.86, P _Res  = 0.022). In the same way, under recessive model, the CASP1 A10370-G was associated with increased risk of ACS (OR = 1.75, 95% CI 1.07-2.85, P _Res  = 0.025). Moreover, under co-dominant, dominant, over-dominant, and additive models, the NLRP3 UTR'3 G37562-C was associated with a decreased risk of ACS (OR = 0.45, 95%CI 0.22-0.92, P _Co-dom  = 0.006; OR = 0.61, 95%CI 0.44-0.84, P _Dom  = 0.002; OR = 0.67, 95%CI 0.48-0.94, P _Over-dom  = 0.02; and OR = 0.65, 95%CI 0.50-0.94, P _Add  = 0.02, respectively). In summary, this study demonstrates that the G+7/in6A and A10370-G polymorphisms of the CASP1 gene are associated with increased risk of developing ACS, whereas the UTR'3 G37562-C polymorphism of the NLRP3 gene is associated with a decreased risk of developing ACS in Mexican population.

An interaction between glucagon-like peptide-1 and adenosine contributes to cardioprotection of a dipeptidyl peptidase 4 inhibitor from myocardial ischemia-reperfusion injury

Dipeptidyl peptidase 4 (DPP4) inhibitors suppress the metabolism of the potent antihyperglycemic hormone glucagon-like peptide-1 (GLP-1). DPP4 was recently shown to provide cardioprotection through a reduction of infarct size, but the mechanism for this remains elusive. Known interactions between DPP4 and adenosine deaminase (ADA) suggest an involvement of adenosine signaling in DPP4 inhibitor-mediated cardioprotection. We tested whether the protective mechanism of the DPP4 inhibitor alogliptin against myocardial ischemia-reperfusion injury involves GLP-1- and/or adenosine-dependent signaling in canine hearts. In anesthetized dogs, the coronary artery was occluded for 90 min followed by reperfusion for 6 h. A 4-day pretreatment with alogliptin reduced the infarct size from 43.1 ± 2.5% to 17.1 ± 5.0% without affecting collateral flow and hemodynamic parameters, indicating a potent antinecrotic effect. Alogliptin also suppressed apoptosis as demonstrated by the following analysis: 1) reduction in the Bax-to-Bcl2 ratio; 2) cytochrome c release, 3) an increase in Bad phosphorylation in the cytosolic fraction; and 4) terminal deoxynucleotidyl transferase dUTP nick end labeling assay. This DPP4 inhibitor did not affect blood ADA activity or adenosine concentrations. In contrast, the nonselective adenosine receptor blocker 8-(p-sulfophenyl)theophylline (8SPT) completely blunted the effect of alogliptin. Alogliptin did not affect Erk1/2 phosphorylation, but it did stimulate phosphorylation of Akt, glycogen synthase kinase-3β, and cAMP response element-binding protein (CREB). Only 8SPT prevented alogliptin-induced CREB phosphorylation. In conclusion, the DPP4 inhibitor alogliptin suppresses ischemia-reperfusion injury via adenosine receptor- and CREB-dependent signaling pathways.

Up-regulation of hypoxia-inducible factor-1α enhanced the cardioprotective effects of ischemic postconditioning in hyperlipidemic rats

Hyperlipidemia is an independent risk factor in the development of ischemic heart disease, which can increase myocardial susceptibility to ischemia/reperfusion (I/R) injury. Ischemic postconditioning (PostC) has now been demonstrated as a novel strategy to harness nature's protection against myocardial I/R injury in normal conditions. However, the effect of PostC on hyperlipidemic animals remains elusive. It has been shown in our previous study that PostC reduces the myocardial I/R injury, and hypoxia-inducible factor-1α (HIF-1α) may play an important role in the cardioprotective mechanisms of PostC on normal rats. Here, we tested the hypothesis that the cardioprotection of PostC on hyperlipidemic rats is associated with the up-regulated HIF-1α expression. Male Wistar rats were fed with a high-fat diet for 8 weeks, and then randomly divided into five groups: sham, I/R, dimethyloxalylglycine (DMOG) + I/R, PostC, and DMOG + PostC group. The detrimental indices induced by I/R injury included infarct size, plasma creatine kinase (CK) activity and caspase-3 activity. The results showed that PostC could reduce the infarct size, when compared with the I/R group, which was consistent with the significant lower levels of plasma CK activity and caspase-3 activity, and that it increased the expression of HIF-1α in hyperlipidemic rats. When DMOG was given before PostC to up-regulate HIF-1α protein level, the degree of I/R injury was attenuated. In conclusion, these data suggested that the up-regulation of HIF-1α may be one of the cardioprotective mechanisms of PostC against I/R injury in hyperlipidemic rats.

Hyperlipidemia does not prevent the cardioprotection by postconditioning against myocardial ischemia/reperfusion injury and the involvement of hypoxia inducible factor-1alpha upregulation

Hyperlipidemia is regarded as an independent risk factor in the development of ischemic heart disease, and it can increase the myocardial susceptibility to ischemia/reperfusion (I/R) injury. Ischemic postconditioning (Postcon) has been demonstrated to attenuate the myocardial injury induced by I/R in normal conditions. But the effect of ischemic Postcon on hyperlipidemic animals is unknown. Hypoxia inducible factor-1 (HIF-1) has been demonstrated to play a central role in the cardioprotection by preconditioning, which is one of the protective strategies except for Postcon. The aim of this study was to determine whether Postcon could reduce myocardial injury in hyperlipidemic animals and to assess whether HIF-1 was involved in Postcon mechanisms. Male Wistar rats underwent the left anterior descending coronary occlusion for 30 min followed by 180 min of reperfusion with or without Postcon after fed with high fat diet or normal diet for 8 weeks. The detrimental indices induced by the I/R insult included infarct size, plasma creatine kinase activity and caspase-3 activity. Results showed that hyperlipidemia remarkably enhanced the myocardial injury induced by I/R, while Postcon significantly decreased the myocardial injury in both normolipidemic and hyperlipidemic rats. Moreover, both hyperlipidemia and I/R promoted the HIF-1alpha expression. Most importantly, we have for the first time demonstrated that Postcon further induced a significant increase in HIF-1alpha protein level not only in normolipidemic but also in hyperlipidemic conditions. Thus, Postcon reduces the myocardial injury induced by I/R in normal and hyperlipidemic animals, and HIF-1alpha upregulation may involve in the Postcon-mediated cardioprotective mechanisms.

Clinical cardioprotection and the value of conditioning responses

Adjunctive cardioprotective strategies for ameliorating the reversible and irreversible injuries with ischemia-reperfusion (I/R) are highly desirable. However, after decades of research, the promise of clinical cardioprotection from I/R injury remains poorly realized. This may arise from the challenges of trialing and effectively translating experimental findings from laboratory models to patients. One can additionally consider whether features of the more heavily focused upon candidates could limit or preclude therapeutic utility and thus whether we might shift attention to alternate strategies. The phenomena of preconditioning and postconditioning have proven fertile in identification of experimental means of cardioprotection and are the most intensely interrogated responses in the field. However, there is evidence these processes, which share common molecular signaling elements and end effectors, may be poor choices for clinical exploitation. This includes evidence of age dependence, limiting efficacy in target aged or senescent hearts; refractoriness to conditioning stimuli in diseased myocardium; interference from a variety of relevant pharmaceuticals; inadvertent induction of these responses by prior ischemia or commonly used drugs, precluding further benefit; and sex dependence of protective signaling. This review focuses on these features, raising questions about current research strategies, and the suitability of these widely studied phenomena as rational candidates for clinical translation.

Experimental hyperlipidaemia does not prevent preconditioning and it reduces ischemia-induced apoptosis

BACKGROUND

Although ischemic preconditioning (PC) is known to confer cardioprotection in healthy subjects, it is unclear whether this phenomenon exists in the presence of hyperlipidaemia. The goal of this study was to determine whether the cardioprotective effect of PC is affected by hyperlipidaemia in a guinea pig model.

METHODS

We investigated the influence of preconditioning in normo- and hyperlipidaemic animals on papillary muscle contractility and myocardial damage as expressed by the percentage of apoptotic cells. Guinea pigs were fed a normal diet or a hyperlipidaemic diet for 5 weeks. Experiments were performed on papillary muscles subjected to experimental ischemia-reperfusion with or without prior PC.

RESULTS

The dietary treatment resulted in significant changes in lipid parameters, which had not affected the functionality of the right ventricle papillary muscle, both at basal conditions and in response to ischemia-reperfusion injury. However, it was found that the hyperlipidaemic diet had an effect on ischemia-induced apoptosis. Papillary muscles of hyperlipidaemic animals with higher HDL plasma concentrations were less susceptible to ischemia-reperfusion injury.

CONCLUSIONS

This study demonstrates that hyperlipidaemia does not alter the benefits of ischemic preconditioning such as a reduction of apoptosis and preservation of myocardial contractility. Additionally, it has been shown that plasma HDL may protect cardiomyocytes against ischemia-induced apoptosis.

Interaction of cardiovascular risk factors with myocardial ischemia/reperfusion injury, preconditioning, and postconditioning

Therapeutic strategies to protect the ischemic myocardium have been studied extensively. Reperfusion is the definitive treatment for acute coronary syndromes, especially acute myocardial infarction; however, reperfusion has the potential to exacerbate lethal tissue injury, a process termed "reperfusion injury." Ischemia/reperfusion injury may lead to myocardial infarction, cardiac arrhythmias, and contractile dysfunction. Ischemic preconditioning of myocardium is a well described adaptive response in which brief exposure to ischemia/reperfusion before sustained ischemia markedly enhances the ability of the heart to withstand a subsequent ischemic insult. Additionally, the application of brief repetitive episodes of ischemia/reperfusion at the immediate onset of reperfusion, which has been termed "postconditioning," reduces the extent of reperfusion injury. Ischemic pre- and postconditioning share some but not all parts of the proposed signal transduction cascade, including the activation of survival protein kinase pathways. Most experimental studies on cardioprotection have been undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of other disease processes. However, ischemic heart disease in humans is a complex disorder caused by or associated with known cardiovascular risk factors including hypertension, hyperlipidemia, diabetes, insulin resistance, atherosclerosis, and heart failure; additionally, aging is an important modifying condition. In these diseases and aging, the pathological processes are associated with fundamental molecular alterations that can potentially affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Among many other possible mechanisms, for example, in hyperlipidemia and diabetes, the pathological increase in reactive oxygen and nitrogen species and the use of the ATP-sensitive potassium channel inhibitor insulin secretagogue antidiabetic drugs and, in aging, the reduced expression of connexin-43 and signal transducer and activator of transcription 3 may disrupt major cytoprotective signaling pathways thereby significantly interfering with the cardioprotective effect of pre- and postconditioning. The aim of this review is to show the potential for developing cardioprotective drugs on the basis of endogenous cardioprotection by pre- and postconditioning (i.e., drug applied as trigger or to activate signaling pathways associated with endogenous cardioprotection) and to review the evidence that comorbidities and aging accompanying coronary disease modify responses to ischemia/reperfusion and the cardioprotection conferred by preconditioning and postconditioning. We emphasize the critical need for more detailed and mechanistic preclinical studies that examine car-dioprotection specifically in relation to complicating disease states. These are now essential to maximize the likelihood of successful development of rational approaches to therapeutic protection for the majority of patients with ischemic heart disease who are aged and/or have modifying comorbid conditions.

Protection of the abnormal heart

Myocardial ischemia and reperfusion injury have been extensively investigated in the laboratory mainly in healthy tissues. However, in clinical settings, ischemic heart disease coexists with certain illnesses, which could potentially influence the response of the myocardium to ischemia and reperfusion. Recent research has revealed that the abnormal heart may not be always vulnerable to ischemic injury. Furthermore, the effect of powerful means of protection, such as ischemic preconditioning, may not be in operation under certain pathological conditions. With this evidence in mind, the present review will focus on the response of the abnormal heart to ischemia and reperfusion, the possible underlying mechanisms, and potential cardioprotective strategies.

Targeting caspase-1 by inhalation-therapy: effects of Ac-YVAD-CHO on IL-1 beta, IL-18 and downstream proinflammatory parameters as detected in rat endotoxaemia

OBJECTIVE

We set out to investigate whether the nebulized and inhaled specific caspase-1 inhibitor Ac-YVAD-CHO has the potential to attenuate the pulmonary and systemic release of the caspase-1-dependent cytokines interleukin-1 beta (IL-1 beta) and interleukin-18 (IL-18) as well as their downstream enzymes iNOS and COX-2 in rat experimental endotoxaemia.

DESIGN AND SETTING

Controlled, randomized animal study in a university research facility.

SUBJECT

Male Sprague-Dawley rats (n=32) were randomly treated as follows: Inhaled Ac-YVAD-CHO was administered in eight rats at a inhaled total dosage of 5 mg and in eight rats at a inhaled total dose of 0.5 mg before infusion of lipopolysaccharide (LPS; 5 mg/kg, i.v.). Eight animals received LPS only. Eight animals served as controls without endotoxaemia.

MEASUREMENTS AND RESULTS

After 4h of endotoxaemia, levels of IL-1 beta, IL-18 and TNF-alpha in plasma and bronchoalveolar fluid (BALF) were analyzed. Nitric oxide (NO) release from alveolar macrophages was measured by Griess assay. Amounts of iNOS protein in alveolar macrophages and COX-2 protein in lung homogenates were determined by Western blotting. Significant reductions in release of IL-1 beta (-58%, p<0.05) and IL-18 (-51%, p<0.05) in plasma and IL-1 beta (-59%, p<0.05) in BALF were found in animals pretreated with inhaled caspase-1 inhibitor compared with animals without therapy. Expression of iNOS in alveolar macrophages and COX-2 in lung tissue was concurrently decreased in the treatment groups compared with control animals.

CONCLUSIONS

Our data demonstrate that administration of the caspase-1 inhibitor Ac-YVAD-CHO by inhalation is able to reduce the pulmonary and systemic release of proinflammatory mediators in rat endotoxaemia. These results further underscore that inhalation may constitute an effective route of anti-inflammatory drug administration, beneficial in the clinical setting of ARDS.

Hypercholesterolemia exacerbates ventricular remodeling in the rat model of myocardial infarction

BACKGROUND

Detrimental left ventricular (LV) remodeling is exacerbated in hypercholesterolemic patients with myocardial infarction; however, this could result from either larger infarcts or more extensive remodeling itself in this population. Therefore, we sought to investigate whether high cholesterol feeding exacerbates LV remodeling and heart failure in rats with myocardial infarction independently from its influence on infarct size.

METHODS AND RESULTS

Myocardial infarction was induced by permanent ligation of left coronary artery in rats fed normal and high-cholesterol diet and the animals were followed for 8 weeks. Hypercholesterolemic rats were matched with normocholesterolemic animals for infarct size 24 hours after infarction and exhibited more pronounced LV dilation at 8 weeks after infarction (LV systolic/diastolic diameter 8.1 +/- 0.2/10.2 +/- 0.3 versus 6.7 +/- 0.2/8.9 +/- 0.2, respectively, measured by echocardiography, P < .05 each). Pressure-volume curves obtained in isolated Langendorff-perfused hearts revealed higher diastolic LV volumes (1677 +/- 102 versus 1385 +/- 46 muL/kg body weight, P < .05) and hemodynamic examination demonstrated higher LV end-diastolic pressure (21.8 +/- 0.7 versus 18.7 +/- 1.0 mm Hg, P < .05) in hypercholesterolemic rats compared with normocholesterolemic animals.

CONCLUSION

In a rat model of myocardial infarction, LV remodeling and heart failure are more pronounced in rats fed high-cholesterol diet in comparison to animals fed normal chow. This effect is independent from effect of hypercholesterolemia on infarct size.

Haplotypes of the Caspase-1 Gene, Plasma Caspase-1 Levels, and Cardiovascular Risk

Caspase-1 processes the interleukin (IL)-1beta and IL-18 inactive precursors to the biologically active cytokines that are known to have proatherogenic effects. The present study investigated the genetic variability of the CASP1 gene and plasma levels of caspase-1 in relation to cardiovascular risk. In Europeans, 3 tag SNPs captured 4 common haplotypes of the CASP1 gene. Among these, the A(in6) allele of the G+7/in6A polymorphism was less frequent in 246 cases with myocardial infarction and a parental history of disease than in 253 controls free of familial history of disease (0.13+/-0.02 versus 0.20+/-0.02; P=0.005). However, in a larger case/control study (n=1774), these effects are borderline restricted to the UK population. In a prospective cohort of 1168 patients with coronary artery disease followed up during a median period of 6.0 years, the A(in6) allele exhibited a borderline association with future cardiovascular death (hazard ratio [HR]: 0.64, 0.41 to 1.01; P=0.053) and was associated with lower serum IL-18 levels (P=0.014). Baseline caspase-1 levels in the top quartile of the distribution were predictive of cardiovascular deaths (HR=3.62, 1.81 to 7.27; P=0.0003 compared with the bottom quartile). Finally, in vitro assays of allelic imbalance showed that the CASP1 haplotype carrying the A(in6) allele was associated with a lower mRNA expression. These results indicate that caspase-1 levels are predictive of future cardiovascular death in patients with coronary artery disease. The role of CASP1 genetic variations in the susceptibility to myocardial infarction requires further investigation.

Gene expression profiles in hypoxic preconditioning using cDNA microarray analysis: altered expression of an angiogenic factor, carcinoembryonic antigen-related cell adhesion molecule 1

Hypoxic preconditioning has been shown to exhibit cardioprotective effects on myocardium from ischemic or reperfusion injury. The specific regulated gene involved in the hypoxia-induced cardioprotective effects is profiled in this study. Young male Wistar rats and ICR mice were exposed to sea level (as normal control) or simulated high altitude for 15 h/day for 2, 4, or 8 weeks, or for 4 weeks at high altitude after 2 weeks at sea level. The left ventricles of the animals were isolated for mRNA isolation and cDNA microarray analysis. Our data demonstrated that hypoxic preconditioning significantly ameliorated cardiac ischemic injury by minimizing the infarct size. After cluster analysis of expression profiles after different courses of hypoxic preconditioning (0, 2, 4, and 8 weeks), 386 genes showed an ascending pattern, whereas 301 genes showed a descending pattern. The ascending genes include several angiogenic factors: FGF receptor 4, vascular endothelial growth factor (vEGF), and carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM-1). The microvessel density was also significantly increased in hypoxic hearts. Using Western blotting and immunohistochemical analysis, the protein expression level and localization of CEACAM-1 were observed in hypoxic myocardium. The results also indicated that CEACAM-1 was upregulated as with other hypoxic angiogenic factors, heme oxygenase 1 (HO-1) and hypoxia inducible factor-1alpha (HIF-1alpha), in in vitro cultured cardiomyocytes (H9c2) after hypoxia treatment and in vivo hypoxic preconditioning. Furthermore, incubation with recombinant vEGF could also increase the expression level of CEACAM-1 in H9c2 cells. These results demonstrated that hypoxic preconditioning resulted in transcriptional changes, and some of these genes have been correlated with angiogenesis. The HIF-1/vEGF/CEACAM-1 pathway might be important for hypoxia-induced angiogenesis in the heart during hypoxic preconditioning.

Hypercholesterolemia abrogates late preconditioning via a tetrahydrobiopterin-dependent mechanism in conscious rabbits

BACKGROUND

Although the late phase of ischemic preconditioning (PC) is known to confer cardioprotection in healthy animal models, it is unknown whether this phenomenon exists in the presence of hypercholesterolemia. The goal of this study was to determine whether the infarct-sparing effect of late PC is affected by hypercholesterolemia and, if so, whether a tetrahydrobiopterin (BH4)-dependent mechanism is responsible for the loss of late PC.

METHODS AND RESULTS

Conscious rabbits fed a normal diet or a 1% cholesterol diet for 6 weeks were subjected to ischemic PC (six 4-minute coronary occlusion/4-minute reperfusion cycles) and, 24 hours later, underwent a 30-minute occlusion followed by 3 days of reperfusion. A total of 125 rabbits were used. In normocholesterolemic rabbits, ischemic PC reduced infarct size, an effect that was abrogated by administration of the BH4 synthesis inhibitor N-acetylserotonin (15 mg/kg IV) before the 30-minute occlusion. In hypercholesterolemic rabbits, however, ischemic PC failed to reduce infarct size. Myocardial BH4 levels in the ischemic zone increased 24 hours after ischemic PC in normocholesterolemic rabbits but not in hypercholesterolemic rabbits. In addition, in normocholesterolemic rabbits, pretreatment with N-acetylserotonin completely abolished the ischemic PC-induced increase in myocardial BH4 levels.

CONCLUSIONS

This study demonstrates that (1) hypercholesterolemia abrogates both the infarct-sparing effect of late PC and the concomitant upregulation of myocardial BH4, and (2) inhibition of myocardial BH4 synthesis in the absence of hypercholesterolemia is sufficient to abolish the infarct-sparing effect of late PC. The results support the concept that hypercholesterolemia abrogates late PC by preventing the upregulation of BH4, an essential cofactor for inducible nitric oxide synthase.

Plasma interleukin-18 concentration: a novel marker of myocardial ischemia rather than necrosis in humans

OBJECTIVE

Myocardial ischemia contributes to cytokine expression in the myocardium in animals; therefore, plasma interleukin-18 concentration may be a good marker of myocardial ischemia/injury in patients with possible acute coronary syndrome. We sought to determine whether increases in plasma interleukin-18 concentrations might be indicative of myocardial ischemia in patients with acute coronary syndrome.

METHODS

Plasma interleukin-18 concentrations were assessed in 27 acute coronary syndrome patients in whom creatine kinase activity was within normal range on admission, in addition to 10 controls. Myocardial infarction was retrospectively evidenced in 15 of the 27 patients. All patients with acute coronary syndrome were treated by emergent coronary interventions just after admission. Blood sampling was done immediately after admission to determine plasma IL-18 concentration and biochemical markers of myocardial infarction.

RESULTS

An increase in plasma interleukin-18 concentration was observed in acute coronary syndrome patients on admission, regardless of the retrospective evidence of myocardial necrosis. Plasma interleukin-18 elevation preceded creatine kinase-MB elevation in myocardial infarction patients. Plasma interleukin-18 concentrations on admission did not correlate with peak creatine kinase-MB (r=0.38, P=n.s.) or with left ventricular ejection fraction (r=-0.14, P=n.s.).

CONCLUSIONS

Plasma interleukin-18 concentration elevates quickly after severe myocardial ischemic event regardless of evolving myocardial necrosis. Thus, plasma interleukin-18 concentration may be a good and early marker to identify whether the symptom is due to myocardial ischemia, and therefore, may be used in deciding the therapeutic strategy in individual patients with possible acute coronary syndrome.

Proapoptotic Effects of Caspase-1/Interleukin-Converting Enzyme Dominate in Myocardial Ischemia

Caspase-1/interleukin-converting enzyme (ICE) is a cysteine protease traditionally considered to have importance as an inflammatory mediator, but not as an apoptotic effector. Because of the dual functions of this caspase, the pathophysiological impact of its reported upregulation in hypertrophy and heart failure is not known. Here, the consequences of increased myocardial expression of procaspase-1 were examined on the normal and ischemically injured heart. In unstressed mouse hearts with a 30-fold increase in procaspase-1 content, unprocessed procaspase-1 was well tolerated, without detectable pathology. Cardiomyocyte processing and activation of caspase-1 and caspase-3 occurred after administration of endotoxin or with transient myocardial ischemia. In post-ischemic hearts, procaspase-1 overexpression was associated with strikingly increased cardiac myocyte apoptosis in the peri- and noninfarct regions and with 50% larger myocardial infarctions. Tissue culture studies revealed that procaspase-1 processing/activation is stimulated by hypoxia, and that caspase-1 acts in synergy with hypoxia to stimulate caspase-3 mediated apoptosis without activating upstream caspases. These data demonstrate that the proapoptotic effects of caspase-1 can significantly impact the myocardial response to ischemia and suggest that conditions in which procaspase-1 in the heart is increased may predispose to apoptotic myocardial injury under conditions of physiological stress.

Hypercholesterolemia blunts NO donor-induced late preconditioning against myocardial infarction in conscious rabbits

Although NO donors have been shown to confer late preconditioning (PC) against myocardial ischemia/reperfusion injury in healthy rabbits, it is unknown whether concurrent systemic disorders affect NO donor-induced cardioprotection. Since many patients with coronary artery disease have hypercholesterolemia (HC), we examined the effect of this condition on late PC induced by the NO donor diethylenetriamine/nitric oxide (DETA/ NO). Chronically instrumented rabbits were fed a normal diet (normocholesterolemia, NC) or a diet enriched with 1% cholesterol (HC) for 4 weeks. Plasma cholesterol levels were significantly elevated and the arterial pressure response to the endothelium-dependent vasodilator bradykinin was blunted in cholesterol diet-fed rabbits. Conscious rabbits underwent a 30-minute coronary occlusion followed by 3 days of reperfusion. When NC rabbits were pretreated with DETA/NO (0.1 mg/kg, i. v. x 4, group II, n = 7) 24 hours before the 30-minute occlusion, infarct size was reduced by 52% (29.7 +/- 3.4% versus 62.4 +/- 4.0% of the region at risk in NC controls [group I, n = 5], P < 0.05), indicating that DETA/NO induced a late PC effect against myocardial infarction. In contrast, when HC rabbits were pretreated with the same dose of DETA/NO (group IV, n = 6), infarct size was not significantly reduced (61.0 +/- 5.7% versus 68.1 +/- 4.5% of the region at risk in HC [group III, n = 5], P = NS), suggesting that DETA/NO failed to induce a delayed cardioprotective effect. These data demonstrate, for the first time, that HC blunts NO donor-induced late PC against myocardial infarction, implying that the inhibitory effects of HC on ischemia-induced and NO donor-induced late PC are caused by disruption of biochemical pathways distal to the generation of NO that triggers these adaptations.

Caspase-dependent cytochrome c release and cell death in chick cardiomyocytes after simulated ischemia-reperfusion

We recently demonstrated that reperfusion rapidly induces the mitochondrial pathway of apoptosis in chick cardiomyocytes after 1 h of simulated ischemia. Here we tested whether ischemia-reperfusion (I/R)-induced apoptosis could be initiated by caspase-dependent cytochrome c release in this model of cardiomyocyte injury. Fluorometric assays of caspase activity showed little, if any, activation of caspases above baseline levels induced by 1 h of ischemia alone. However, these assays revealed rapid activation of caspase-2, yielding a 2.95 ± 0.52-fold increase (over ischemia only) within the 1st h of reperfusion, whereas activities of caspases-3, -8, and -9 increased only slightly from their baseline levels. The rapid and prominent activation of caspase-2 suggested that it could be an important initiator caspase in this model, and using specific caspase inhibitors given only at the point of reperfusion, we tested this hypothesis. The caspase-2 inhibitor benzyloxycarbonyl-Val-Asp(Ome)-Val-Ala-Asp(Ome)-CH2F was the only caspase inhibitor that significantly inhibited cytochrome c release from mitochondria. This inhibitor also completely blocked activation of caspases-3, -8, and -9. The caspase-3/7 inhibitor transiently and only partially blocked caspase-2 activity and was less effective in blocking the activities of caspases-8 and -9. The caspase-8 inhibitor failed to significantly block caspase-2 or -3, and the caspase-9 inhibitor blocked only caspase-9. Furthermore, the caspase-2 inhibitor protected against I/R-induced cell death, but the caspase-8 inhibitor failed to do so. These data suggest that active caspase-2 initiates cytochrome c release after reperfusion and that it is critical for the I/R-induced apoptosis in this model.

Apoptosis as a therapeutic target in acutely ischemic myocardium

In addition to necrosis, apoptosis makes a significant contribution to cell death following acute myocardial ischemia; apoptosis is particularly enhanced during reperfusion. Several studies are beginning to indicate that the cell death by apoptosis may be preventable. A boost in the research in this direction has been provided by noninvasive means of detection of apoptosis, such as that achieved by technetium-99m labeled Annexin-A5 scintigraphy. Various levels within the apoptotic cascade are being investigated as therapeutic targets. Caspase inhibitors, mitochondrial stabilizers, and Na+-H+ exchanger inhibitors reduce cell death by apoptosis and infarct size. Although most of the evidence at present is limited to the laboratory animals, this approach seems to hold a promise for the future.