Hyperlipidemia attenuates the infarct size-limiting effect of ischemic preconditioning: role of matrix metalloproteinase-2 inhibition

Association between MMP2 gene polymorphisms and dilated cardiomyopathy in a Chinese Han population

AIMS

Dilated cardiomyopathy (DCM) belongs to the common types of cardiomyopathies. The pathogenesis remains unclear despite the fact that various genes have been found associated with DCM. MMP2 is a zinc-dependent and calcium-containing secreted endoproteinases, which could cleave a broad spectrum of substrates including extracellular matrix components and cytokines. It has proved to play an important role in the cardiovascular diseases. This study aimed to investigate the potential role of MMP2 gene polymorphisms in DCM susceptibility and prognosis in a Chinese Han population.

METHODS AND RESULTS

A total of 600 idiopathic DCM patients and 700 healthy controls were enrolled. Patients with contact information were followed up for a median period of 28 months. Three tagged single nucleotide polymorphisms (rs243865, rs2285052, and rs2285053) in the promoter of MMP2 gene were genotyped. A series of function analysis were conducted to illuminate the underlying mechanism. The frequency of rs243865-C allele was increased in DCM patients when compared with healthy controls (P = 0.001). Genotypic frequencies of rs243865 were associated with the susceptibility of DCM in the codominant, dominant, and overdominant models (P < 0.05). Besides, rs243865-C allele presented a correlation with the poor prognosis of DCM patients in both dominant (HR = 2.0, 95% confidence interval [CI] = 1.14-3.57, P = 0.017) and additive (HR = 1.85, 95% CI = 1.09-3.13, P = 0.02) model. The statistical significance remained after adjustment for sex, age, hypertension, diabetes, hyperlipidaemia, and smoking status. There were significant differences in left ventricular end-diastolic diameter and left ventricular ejection fraction between rs243865-CC and CT genotypes. Functional analysis indicated that rs243865-C allele increased luciferase activity and the mRNA expression level of MMP2 by facilitating ZNF354C binding.

CONCLUSIONS

Our study suggested that MMP2 gene polymorphisms were associated with DCM susceptibility and prognosis in the Chinese Han population.

Interaction of Cardiovascular Nonmodifiable Risk Factors, Comorbidities and Comedications With Ischemia/Reperfusion Injury and Cardioprotection by Pharmacological Treatments and Ischemic Conditioning

Preconditioning, postconditioning, and remote conditioning of the myocardium enhance the ability of the heart to withstand a prolonged ischemia/reperfusion insult and the potential to provide novel therapeutic paradigms for cardioprotection. While many signaling pathways leading to endogenous cardioprotection have been elucidated in experimental studies over the past 30 years, no cardioprotective drug is on the market yet for that indication. One likely major reason for this failure to translate cardioprotection into patient benefit is the lack of rigorous and systematic preclinical evaluation of promising cardioprotective therapies prior to their clinical evaluation, since ischemic heart disease in humans is a complex disorder caused by or associated with cardiovascular risk factors and comorbidities. These risk factors and comorbidities induce fundamental alterations in cellular signaling cascades that affect the development of ischemia/reperfusion injury and responses to cardioprotective interventions. Moreover, some of the medications used to treat these comorbidities may impact on cardioprotection by again modifying cellular signaling pathways. The aim of this article is to review the recent evidence that cardiovascular risk factors as well as comorbidities and their medications may modify the response to cardioprotective interventions. We emphasize the critical need for taking into account the presence of cardiovascular risk factors as well as comorbidities and their concomitant medications when designing preclinical studies for the identification and validation of cardioprotective drug targets and clinical studies. This will hopefully maximize the success rate of developing rational approaches to effective cardioprotective therapies for the majority of patients with multiple comorbidities. SIGNIFICANCE STATEMENT: Ischemic heart disease is a major cause of mortality; however, there are still no cardioprotective drugs on the market. Most studies on cardioprotection have been undertaken in animal models of ischemia/reperfusion in the absence of comorbidities; however, ischemic heart disease develops with other systemic disorders (e.g., hypertension, hyperlipidemia, diabetes, atherosclerosis). Here we focus on the preclinical and clinical evidence showing how these comorbidities and their routine medications affect ischemia/reperfusion injury and interfere with cardioprotective strategies.

Reperfusion Cardiac Injury: Receptors and the Signaling Mechanisms

It has been documented that Ca2+ overload and increased production of reactive oxygen species play a significant role in reperfusion injury (RI) of cardiomyocytes. Ischemia/reperfusion induces cell death as a result of necrosis, necroptosis, apoptosis, and possibly autophagy, pyroptosis and ferroptosis. It has also been demonstrated that the NLRP3 inflammasome is involved in RI of the heart. An increase in adrenergic system activity during the restoration of coronary perfusion negatively affected cardiac resistance to RI. Toll-like receptors are involved in RI of the heart. Angiotensin II and endothelin-1 aggravated ischemic/reperfusion injury of the heart. Activation of neutrophils, monocytes, CD4+ T-cells and platelets contributes to cardiac ischemia/reperfusion injury. Our review outlines the role of these factors in reperfusion cardiac injury.

Influence of cardiometabolic comorbidities on myocardial function, infarction, and cardioprotection: Role of cardiac redox signaling

The morbidity and mortality from cardiovascular diseases (CVD) remain high. Metabolic diseases such as obesity, hyperlipidemia, diabetes mellitus (DM), non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) as well as hypertension are the most common comorbidities in patients with CVD. These comorbidities result in increased myocardial oxidative stress, mainly from increased activity of nicotinamide adenine dinucleotide phosphate oxidases, uncoupled endothelial nitric oxide synthase, mitochondria as well as downregulation of antioxidant defense systems. Oxidative and nitrosative stress play an important role in ischemia/reperfusion injury and may account for increased susceptibility of the myocardium to infarction and myocardial dysfunction in the presence of the comorbidities. Thus, while early reperfusion represents the most favorable therapeutic strategy to prevent ischemia/reperfusion injury, redox therapeutic strategies may provide additive benefits, especially in patients with heart failure. While oxidative and nitrosative stress are harmful, controlled release of reactive oxygen species is however important for cardioprotective signaling. In this review we summarize the current data on the effect of hypertension and major cardiometabolic comorbidities such as obesity, hyperlipidemia, DM, NAFLD/NASH on cardiac redox homeostasis as well as on ischemia/reperfusion injury and cardioprotection. We also review and discuss the therapeutic interventions that may restore the redox imbalance in the diseased myocardium in the presence of these comorbidities.

Zinc homeostasis plays an important role in the prevention of obesity-induced cardiac inflammation, remodeling and dysfunction

Obesity often leads to cardiovascular diseases, such as obesity-related cardiac hypertrophy (ORCH), due to chronic cardiac inflammation. Zinc is structurally and functionally essential for many transcription factors, therefore it not only has anti-inflammatory and anti-oxidative stress functions, but also has insulin-like function, however, its role in the development of obesity-associated cardiac pathogenesis and the potentially underlying mechanism(s) remains unclear. This review aims to summarize the available evidence on the role of zinc homeostasis in the prevention of ORCH. It was recently reported that when four-week old mice were fed either high fat diet (HFD) or normal diet containing deficient, adequate or supplemented zinc, HFD induced obesity and ORCH along with increased phosphorylation of p38 MAPK and increased expression of B-cell lymphoma/ leukemia 10 (BCL10) and caspase recruitment domain family member 9 (CARD9). These effects were further aggravated by zinc deficiency and significantly alleviated by zinc supplementation. Mechanistically administration of a p38 MAPK specific inhibitor in HFD-fed mice for 3 months did not affect HFD-induced obesity and increased expression of BCL10 and CARD9, but completely abolished HFD/obesity-induced cardiac hypertrophy and inflammation. In cultured cardiomyocytes, inhibition of BCL10 expression by siRNA prevented palmitate-induced increased p38 MAPK activation and atrial natriuretic peptide expression. Deletion of metallothionein abolished the protective effect of zinc on palmitate-induced up-regulation of BCL10 and phospho-p38 MAPK. Taken together with other recent studies, we concluded that HFD and zinc deficiency synergistically induce ORCH by increasing oxidative stress-mediated activation of BCL10/CARD9/p38 MAPK signaling. Zinc supplementation ameliorates ORCH through activation of metallothionein to repress oxidative stress-activated BCL10 expression and p38 MAPK activation.

Cardioprotective Effect of Novel Matrix Metalloproteinase Inhibitors

Background: We recently developed novel matrix metalloproteinase-2 (MMP-2) inhibitor small molecules for cardioprotection against ischemia/reperfusion injury and validated their efficacy in ischemia/reperfusion injury in cardiac myocytes. The aim of the present study was to test our lead compounds for cardioprotection in vivo in a rat model of acute myocardial infarction (AMI) in the presence or absence of hypercholesterolemia, one of the major comorbidities affecting cardioprotection. Methods: Normocholesterolemic adult male Wistar rats were subjected to 30 min of coronary occlusion followed by 120 min of reperfusion to induce AMI. MMP inhibitors (MMPI)-1154 and -1260 at 0.3, 1, and 3 µmol/kg, MMPI-1248 at 1, 3, and 10 µmol/kg were administered at the 25th min of ischemia intravenously. In separate groups, hypercholesterolemia was induced by a 12-week diet (2% cholesterol, 0.25% cholic acid), then the rats were subjected to the same AMI protocol and single doses of the MMPIs that showed the most efficacy in normocholesterolemic animals were tested in the hypercholesterolemic animals. Infarct size/area at risk was assessed at the end of reperfusion in all groups by standard Evans blue and 2,3,5-triphenyltetrazolium chloride (TTC) staining, and myocardial microvascular obstruction (MVO) was determined by thioflavine-S staining. Results: MMPI-1154 at 1 µmol/kg, MMPI-1260 at 3 µmol/kg and ischemic preconditioning (IPC) as the positive control reduced infarct size significantly; however, this effect was not seen in hypercholesterolemic animals. MVO in hypercholesterolemic animals decreased by IPC only. Conclusions: This is the first demonstration that MMPI-1154 and MMPI-1260 showed a dose-dependent infarct size reduction in an in vivo rat AMI model; however, single doses that showed the most efficacy in normocholesterolemic animals were abolished by hypercholesterolemia. The further development of these promising cardioprotective MMPIs should be continued with different dose ranges in the study of hypercholesterolemia and other comorbidities.

Hypercholesterolemia Interferes with Induction of miR-125b-1-3p in Preconditioned Hearts

Ischemic preconditioning (IPre) reduces ischemia/reperfusion (I/R) injury in the heart. The non-coding microRNA miR-125b-1-3p has been demonstrated to play a role in the mechanism of IPre. Hypercholesterolemia is known to attenuate the cardioprotective effect of preconditioning; nevertheless, the exact underlying mechanisms are not clear. Here we investigated, whether hypercholesterolemia influences the induction of miR-125b-1-3p by IPre. Male Wistar rats were fed with a rodent chow supplemented with 2% cholesterol and 0.25% sodium-cholate hydrate for 8 weeks to induce high blood cholesterol levels. The hearts of normo- and hypercholesterolemic animals were then isolated and perfused according to Langendorff, and were subjected to 35 min global ischemia and 120 min reperfusion with or without IPre (3 × 5 min I/R cycles applied before index ischemia). IPre significantly reduced infarct size in the hearts of normocholesterolemic rats; however, IPre was ineffective in the hearts of hypercholesterolemic animals. Similarly, miR-125b-1-3p was upregulated by IPre in hearts of normocholesterolemic rats, while in the hearts of hypercholesterolemic animals IPre failed to increase miR-125b-1-3p significantly. Phosphorylation of cardiac Akt, ERK, and STAT3 was not significantly different in any of the groups at the end of reperfusion. Based on these results we propose here that hypercholesterolemia attenuates the upregulation of miR-125b-1-3p by IPre, which seems to be associated with the loss of cardioprotection.

Circulating mediators of remote ischemic preconditioning: search for the missing link between non-lethal ischemia and cardioprotection

Acute myocardial infarction (AMI) is one of the leading causes of mortality and morbidity worldwide. There has been an extensive search for cardioprotective therapies to reduce myocardial ischemia-reperfusion (I/R) injury. Remote ischemic preconditioning (RIPC) is a phenomenon that relies on the body's endogenous protective modalities against I/R injury. In RIPC, non-lethal brief I/R of one organ or tissue confers protection against subsequent lethal I/R injury in an organ remote to the briefly ischemic organ or tissue. Initially it was believed to be limited to direct myocardial protection, however it soon became apparent that RIPC applied to other organs such as kidney, liver, intestine, skeletal muscle can reduce myocardial infarct size. Intriguing discoveries have been made in extending the concept of RIPC to other organs than the heart. Over the years, the underlying mechanisms of RIPC have been widely sought and discussed. The involvement of blood-borne factors as mediators of RIPC has been suggested by a number of research groups. The main purpose of this review article is to summarize the possible circulating mediators of RIPC, and recent studies to establish the clinical efficacy of these mediators in cardioprotection from lethal I/R injury.

Development of Matrix Metalloproteinase-2 Inhibitors for Cardioprotection

The objective of our present study is to develop novel inhibitors for MMP-2 for acute cardioprotection. In a series of pilot studies, novel substituted carboxylic acid derivatives were synthesized based on imidazole and thiazole scaffolds and then tested in a screeening cascade for MMP inhibition. We found that the MMP-inhibiting effects of imidazole and thiazole carboxylic acid-based compounds are superior in efficacy in comparison to the conventional hydroxamic acid derivatives of the same molecules. Based on these results, a 568-membered focused library of imidazole and thiazole compounds was generated in silico and then the library members were docked to the 3D model of MMP-2 followed by an in vitro medium throughput screening (MTS) based on a fluorescent assay employing MMP-2 catalytic domain. Altogether 45 compounds showed a docking score of >70, from which 30 compounds were successfully synthesized. Based on the MMP-2 inhibitory tests using gelatin zymography, 7 compounds were then selected and tested in neonatal rat cardiac myocytes subjected to simulated I/R injury. Six compounds showed significant cardio-cytoprotecion and the most effective compound (MMPI-1154) significantly decreased infarct size when applied at 1 μM in an ex vivo model for acute myocardial infarction. This is the first demonstration that imidazole and thiazole carboxylic acid-based compounds are more efficacious MMP-2 inhibitor than their hydroxamic acid derivatives. MMPI-1154 is a promising novel cardio-cytoprotective imidazole-carboxylic acid MMP-2 inhibitor lead candidate for the treatment of acute myocardial infarction.

Gualou Xiebai Decoction, a Traditional Chinese Medicine, Prevents Cardiac Reperfusion Injury of Hyperlipidemia Rat via Energy Modulation

Background: Gualou Xiebai Decoction (GLXB) is a classic prescription of Chinese medicine used for the treatment of cardiac problems. The present study was designed to explore the effect and mechanism of GLXB on ischemia/reperfusion (I/R) induced disorders in myocardial structure and function, focusing on the regulation of energy metabolism and the RhoA/ROCK pathway.

Methods: After hyperlipidemic rat model was established by oral administration of high fat diet, the rats were treated with GLXB for 6 weeks and subjected to 30 min occlusion of the left anterior descending coronary artery (LADCA) followed by 90 min reperfusion to elicit I/R challenge. Myocardial infarct size was assessed by Evans blue-TTC staining. Myocardial blood flow (MBF) and cardiac function were evaluated. Enzyme-linked immunosorbent assay was performed to examine the content of ATP, ADP, AMP, CK, CK-MB, LDH, cTnT, cTnI, and IL-6. Double staining of F-actin and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling was conducted to assess myocardial apoptosis. Expressions of ATP synthase subunit δ (ATP 5D), and RhoA and ROCK were determined by Western blotting.

Results: Administration with GLXB at high dose for 6 weeks protected heart against I/R-induced MBF decrease, myocardial infarction and apoptosis, ameliorated I/R-caused impairment of cardiac function and myocardial structure, restored the decrease in the ratio of ADP/ATP and AMP/ATP, and the expression of ATP 5D with inhibiting the expression of RhoA and ROCK.

Conclusions: Treatment with GLXB effectively protects myocardial structure and function from I/R challenge, possibly via regulating energy metabolism involving inactivation of RhoA/ROCK signaling pathway.

Matrix Metalloproteinase-2 Impairs Homing of Intracoronary Delivered Mesenchymal Stem Cells in a Porcine Reperfused Myocardial Infarction: Comparison With Intramyocardial Cell Delivery

Background

Intracoronary (IC) injection of mesenchymal stem cells (MSCs) results in a prompt decrease of absolute myocardial blood flow (AMF) with late and incomplete recovery of myocardial tissue perfusion. Here, we investigated the effect of decreased AMF on oxidative stress marker matrix metalloproteinase-2 (MMP-2) and its influence on the fate and homing and paracrine character of MSCs after IC or intramyocardial cell delivery in a closed-chest reperfused myocardial infarction (MI) model in pigs.

Methods

Porcine MSCs were transiently transfected with Ad-Luc and Ad-green fluorescent protein (GFP). One week after MI, the GFP-Luc-MSCs were injected either IC (group IC, 11.00 ± 1.07 × 10⁶) or intramyocardially (group IM, 9.88 ± 1.44 × 10⁶). AMF was measured before, immediately after, and 24 h post GFP-Luc-MSC delivery. In vitro bioluminescence signal was used to identify tissue samples containing GFP-Luc-MSCs. Myocardial tissue MMP-2 and CXCR4 receptor expression (index of homing signal) were measured in bioluminescence positive and negative infarcted and border, and non-ischemic myocardial areas 1-day post cell transfer. At 7-day follow-up, myocardial homing (cadherin, CXCR4, and stromal derived factor-1alpha) and angiogenic [fibroblast growth factor 2 (FGF2) and VEGF] were quantified by ELISA of homogenized myocardial tissues from the bioluminescence positive and negative infarcted and border, and non-ischemic myocardium. Biodistribution of the implanted cells was quantified by using Luciferase assay and confirmed by fluorescence immunochemistry. Global left ventricular ejection fraction (LVEF) was measured at baseline and 1-month post cell therapy using magnet resonance image.

Results

AMF decreased immediately after IC cell delivery, while no change in tissue perfusion was found in the IM group (42.6 ± 11.7 vs. 56.9 ± 16.7 ml/min, p = 0.018). IC delivery led to a significant increase in myocardial MMP-2 64 kD expression (448 ± 88 vs. 315 ± 54 intensity × mm², p = 0.021), and decreased expression of CXCR4 (592 ± 50 vs. 714 ± 54 pg/tissue/ml, p = 0.006), with significant exponential decay between MMP-2 and CXCR4 (r = 0.679, p < 0.001). FGF2 and VEGF of the bioluminescence infarcted and border zone of homogenized tissues were significantly elevated in the IM goups as compared to IC group. LVEF increase was significantly higher in IM group (0.8 ± 8.4 vs 5.3 ± 5.2%, p = 0.046) at the 1-month follow up.

Conclusion

Intracoronary stem cell delivery decreased AMF, with consequent increase in myocardial expression of MMP-2 and reduced CXCR4 expression with lower level of myocardial homing and angiogenic factor release as compared to IM cell delivery.

Hypercholesterolemia Abrogates Remote Ischemic Preconditioning-Induced Cardioprotection: Role of Reperfusion Injury Salvage Kinase Signals

Remote ischemic preconditioning (RIPC) is one of the most powerful intrinsic cardioprotective strategies discovered so far and experimental data indicate that comorbidity may interfere with the protection by RIPC. Therefore, we investigate whether RIPC-induced cardioprotection was intact in hypercholesterolemic rat hearts exposed to ischemia reperfusion in vivo. Normal or hypercholesterolemic rat hearts were exposed to 30 min of ischemia and 2 h of reperfusion, with or without RIPC, PI3K inhibitor wortmannin, MEK-ERK1/2 inhibitor PD98059, GSK3β inhibitor SB216763. Infarct size, apoptosis, MG53, PI3K-p85, p-Akt, p-ERK1/2, p-GSK3β, and cleaved Caspase-3 were determined. RIPC reduced infarct size, limited cardiomyocyte apoptosis following IR that was blocked by wortmannin but not PD98059. RIPC triggered unique cardioprotective signaling including MG53, phosphorylation of Akt, and glycogen synthase kinase-3ß (GSK3β) in concert with reduced proapoptotic active caspase-3. In contrast, RIPC failed to reduce myocardial necrosis and apoptosis as well as to increase the phosphorylated Akt and GSK3β in hypercholestorolemic myocardium. Importantly, we found that inhibition of GSK with SB216763 reduced myocardial infarct size in healthy and hypercholesterolemic hearts, but no additional cardioprotective effect was achieved when combined with RIPC. Our results suggest that acute GSK3β inhibition may provide a novel therapeutic strategy for hypercholesterolemic patients during acute myocardial infarction, whereas RIPC is less effective due to signaling events that adversely affect GSK3β.

Ischemic preconditioning: Interruption of various disorders

Ischemic heart diseases are the leading cause of morbidity and mortality worldwide. Reperfusion of an ischemic heart is necessary to regain the normal functioning of the heart. However, abrupt reperfusion of an ischemic heart elicits a cascade of adverse events that leads to injury of the myocardium, i.e., ischemia-reperfusion injury. An endogenous powerful strategy to protect the ischemic heart is ischemic preconditioning, in which the myocardium is subjected to short periods of sublethal ischemia and reperfusion before the prolonged ischemic insult. However, it should be noted that the cardioprotective effect of preconditioning is attenuated in some pathological conditions. The aim of this article is to review present knowledge on how menopause and some metabolic disorders such as diabetes and hyperlipidemia affect myocardial ischemic preconditioning and the mechanisms involved.

Hypercholesterolemia downregulates autophagy in the rat heart

BACKGROUND

We have previously shown that efficiency of ischemic conditioning is diminished in hypercholesterolemia and that autophagy is necessary for cardioprotection. However, it is unknown whether isolated hypercholesterolemia disturbs autophagy or the mammalian target of rapamycin (mTOR) pathways. Therefore, we investigated whether isolated hypercholesterolemia modulates cardiac autophagy-related pathways or programmed cell death mechanisms such as apoptosis and necroptosis in rat heart.

METHODS

Male Wistar rats were fed either normal chow (NORM; n = 9) or with 2% cholesterol and 0.25% cholic acid-enriched diet (CHOL; n = 9) for 12 weeks. CHOL rats exhibited a 41% increase in plasma total cholesterol level over that of NORM rats (4.09 mmol/L vs. 2.89 mmol/L) at the end of diet period. Animals were sacrificed, hearts were excised and briefly washed out. Left ventricles were snap-frozen for determination of markers of autophagy, mTOR pathway, apoptosis, and necroptosis by Western blot.

RESULTS

Isolated hypercholesterolemia was associated with a significant reduction in expression of cardiac autophagy markers such as LC3-II, Beclin-1, Rubicon and RAB7 as compared to controls. Phosphorylation of ribosomal S6, a surrogate marker for mTOR activity, was increased in CHOL samples. Cleaved caspase-3, a marker of apoptosis, increased in CHOL hearts, while no difference in the expression of necroptotic marker RIP1, RIP3 and MLKL was detected between treatments.

CONCLUSIONS

This is the first comprehensive analysis of autophagy and programmed cell death pathways of apoptosis and necroptosis in hearts of hypercholesterolemic rats. Our data show that isolated hypercholesterolemia suppresses basal cardiac autophagy and that the decrease in autophagy may be a result of an activated mTOR pathway. Reduced autophagy was accompanied by increased apoptosis, while cardiac necroptosis was not modulated by isolated hypercholesterolemia. Decreased basal autophagy and elevated apoptosis may be responsible for the loss of cardioprotection reported in hypercholesterolemic animals.

Targeting chronic cardiac remodeling with cardiac progenitor cells in a murine model of ischemia/reperfusion injury

BACKGROUND

Translational failure for cardiovascular disease is a substantial problem involving both high research costs and an ongoing lack of novel treatment modalities. Despite the progress already made, cell therapy for chronic heart failure in the clinical setting is still hampered by poor translation. We used a murine model of chronic ischemia/reperfusion injury to examine the effect of minimally invasive application of cardiac progenitor cells (CPC) in cardiac remodeling and to improve clinical translation.

METHODS

28 days after the induction of I/R injury, mice were randomized to receive either CPC (0.5 million) or vehicle by echo-guided intra-myocardial injection. To determine retention, CPC were localized in vivo by bioluminescence imaging (BLI) two days after injection. Cardiac function was assessed by 3D echocardiography and speckle tracking analysis to quantify left ventricular geometry and regional myocardial deformation.

RESULTS

BLI demonstrated successful injection of CPC (18/23), which were mainly located along the needle track in the anterior/septal wall. Although CPC treatment did not result in overall restoration of cardiac function, a relative preservation of the left ventricular end-diastolic volume was observed at 4 weeks follow-up compared to vehicle control (+5.3 ± 2.1 μl vs. +10.8 ± 1.5 μl). This difference was reflected in an increased strain rate (+16%) in CPC treated mice.

CONCLUSIONS

CPC transplantation can be adequately studied in chronic cardiac remodeling using this study set-up and by that provide a translatable murine model facilitating advances in research for new therapeutic approaches to ultimately improve therapy for chronic heart failure.

Effect of hypercholesterolaemia on myocardial function, ischaemia-reperfusion injury and cardioprotection by preconditioning, postconditioning and remote conditioning

Hypercholesterolaemia is considered to be a principle risk factor for cardiovascular disease, having direct negative effects on the myocardium itself, in addition to the development of atherosclerosis. Since hypercholesterolaemia affects the global cardiac gene expression profile, among many other factors, it results in increased myocardial oxidative stress, mitochondrial dysfunction and inflammation triggered apoptosis, all of which may account for myocardial dysfunction and increased susceptibility of the myocardium to infarction. In addition, numerous experimental and clinical studies have revealed that hyperlcholesterolaemia may interfere with the cardioprotective potential of conditioning mechanisms. Although not fully elucidated, the underlying mechanisms for the lost cardioprotection in hypercholesterolaemic animals have been reported to involve dysregulation of the endothelial NOS-cGMP, reperfusion injury salvage kinase, peroxynitrite-MMP2 signalling pathways, modulation of ATP-sensitive potassium channels and apoptotic pathways. In this review article, we summarize the current knowledge on the effect of hypercholesterolaemia on the non-ischaemic and ischaemic heart as well as on the cardioprotection induced by drugs or ischaemic preconditioning, postconditioning and remote conditioning. Future perspectives concerning the mechanisms and the design of preclinical and clinical trials are highlighted.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Effect of pioglitazone on the abrogated cardioprotective effect of ischemic preconditioning in hyperlipidemic rat heart

Objectives:

The signaling pathways upstream of glycogen synthase kinase-3β (GSK-3β) get reduced during ischemic preconditioning (IPC) in hyperlipidemic rat heart. Pioglitazone, an insulin sensitizer, exerts cardioprotection through GSK-3β. The objective of the study is to investigate the role of pioglitazone on the attenuated cardioprotective effect of IPC in hyperlipidemic rat heart.

Materials and Methods:

The rats were administered high-fat diet for 8 weeks to induce experimental hyperlipidemia (HL). After mounting on a Langendorff apparatus, isolated perfused hearts were given four cycles of IPC; each consists of 5 min of both ischemia and reperfusion followed by 30 min of ischemia and 120 min of reperfusion. Insulin (50 mU/ml) was perfused alone and in combination with pioglitazone (2 μM), while in other groups, this combination was repeated with wortmannin (100 nM), a selective PI3K inhibitor and rapamycin (1 nM), a selective mammalian target of rapamycin (mTOR) inhibitor, separately, and in combination. Myocardial injury was assessed by measuring infarct size and the levels of creatinine kinase-myocardial band (CK-MB) and lactate dehydrogenase (LDH) in the coronary effluent.

Results:

IPC significantly decreased the infarct size and levels of LDH and CK-MB in normal but not in HL rat heart. Perfusion of insulin along with pioglitazone significantly reduced the infarct size and release of CK-MB and LDH in IPC-treated HL rat hearts. Perfusion of wortmannin or rapamycin alone significantly and in combination almost completely abolished the pioglitazone-induced restored cardioprotection (P < 0.05).

Conclusion:

Cardioprotective effect of IPC gets lost in hyperlipidemic rat heart. The results suggest that perfusion of pioglitazone restored the cardioprotective effect of IPC in hyperlipidemic rat heart, an effect that may be via PI3K and mTOR.

"Pistacia lentiscus L." reduces the infarct size in normal fed anesthetized rabbits and possess antiatheromatic and hypolipidemic activity in cholesterol fed rabbits

HYPOTHESIS/PURPOSE

The aim of the present study was to evaluate in vivo the potential anti-ischemic and antiatheromatic activity of Chios Mastic gum, the resin of the trunk and branches of "Pistacia lentiscus var. chia", used since antiquity in traditional Greek medicine. The main compounds of mastic are triterpenes, possessing phytosterol-like structures. This led to the hypothesis that mastic and particularly its neutral fraction, enriched in phytosterol-like compounds, possess antiatheromatic activities.

METHODS

Total Mastic Extract without Polymer (TMEWP) and the neutral mastic fraction (NMF) were administered orally for 6 weeks to normal fed and to cholesterol fed rabbits in the form of sunflower oil solution. All the animals were randomly divided into 6 groups, anesthetized and subjected to 30min ischemia of the heart, followed by 3h reperfusion: At the end of the experiment the area at risk and the infarct zone were determined with the aid of fluorescent particles and triphenyl tetrazolium chloride staining, and small segments of the ascending and descending aorta and the heart were taken for histologic examination. Blood samples were collected at different time points of ischemia and reperfusion, for malondialdehyde (MDA) evaluation as an index of lipid peroxidation, for total and LDL cholesterol determination and for evaluation of oxidized LDL.

RESULTS

In the normal fed animals the NMF and the TMEWP reduced significantly the infarct size, while in the hypercholesterolemic rabbits both treatments were ineffective. Atherosclerosis was detected in all the animals fed cholesterol enriched diet in the form of subintimal accumulation of lipids and foamy macrophages. There was no detection of atherosclerosis in Groups treated with TMEWP and NMF, which both reduced the total cholesterol levels by 47 and 88% respectively, whilst had not effect on LDL oxidation. TMEWP and NMF reduced the MDA concentration in normal fed rabbits, but had no effect on MDA levels in cholesterol fed animals. TMEWP and NMPF reduce the infarct size in normal animals and possess significant antiatheromatic and hypolipidemic activities in rabbits fed cholesterol enriched diet.

Acute hyperglycemia abolishes cardioprotection by remote ischemic perconditioning

Background

Remote ischemic perconditioning (RIPerC) has a promising therapeutic insight to improve the prognosis of acute myocardial infarction. Chronic comorbidities such as diabetes are known to interfere with conditioning interventions by modulating cardioprotective signaling pathways, such as e.g., mTOR pathway and autophagy. However, the effect of acute hyperglycemia on RIPerC has not been studied so far. Therefore, here we investigated the effect of acute hyperglycemia on cardioprotection by RIPerC.

Methods

Wistar rats were divided into normoglycemic (NG) and acute hyperglycemic (AHG) groups. Acute hyperglycemia was induced by glucose infusion to maintain a serum glucose concentration of 15–20 mM throughout the experimental protocol. NG rats received mannitol infusion of an equal osmolarity. Both groups were subdivided into an ischemic (Isch) and a RIPerC group. Each group underwent reversible occlusion of the left anterior descending coronary artery (LAD) for 40 min in the presence or absence of acute hyperglycemia. After the 10-min LAD occlusion, RIPerC was induced by 3 cycles of 5-min unilateral femoral artery and vein occlusion and 5-min reperfusion. After 120 min of reperfusion, infarct size was measured by triphenyltetrazolium chloride staining. To study underlying signaling mechanisms, hearts were harvested for immunoblotting after 35 min in both the NG and AHG groups.

Results

Infarct size was significantly reduced by RIPerC in NG, but not in the AHG group (NG + Isch: 46.27 ± 5.31 % vs. NG + RIPerC: 24.65 ± 7.45 %, p < 0.05; AHG + Isch: 54.19 ± 4.07 % vs. 52.76 ± 3.80 %). Acute hyperglycemia per se did not influence infarct size, but significantly increased the incidence and duration of arrhythmias. Acute hyperglycemia activated mechanistic target of rapamycine (mTOR) pathway, as it significantly increased the phosphorylation of mTOR and S6 proteins and the phosphorylation of AKT. In spite of a decreased LC3II/LC3I ratio, other markers of autophagy, such as ATG7, ULK1 phopsphorylation, Beclin 1 and SQSTM1/p62, were not modulated by acute hyperglycemia. Furthermore, acute hyperglycemia significantly elevated nitrative stress in the heart (0.87 ± 0.01 vs. 0.50 ± 0.04 µg 3-nitrotyrosine/mg protein, p < 0.05).

Conclusions

This is the first demonstration that acute hypreglycemia deteriorates cardioprotection by RIPerC. The mechanism of this phenomenon may involve an acute hyperglycemia-induced increase in nitrative stress and activation of the mTOR pathway.

Role of atrial natriuretic peptide in ischemic preconditioning-induced cardioprotection in the diabetic rat heart

BACKGROUND

It has been noted that nitric oxide (NO) is involved in the ischemic preconditioning (IPC)-mediated cardioprotection. Diabetes is a downregulator of atrial natriuretic peptide (ANP), resulting in low expression of endothelial nitric oxide synthase (eNOS) by which NO level get reduced. The purpose of the present study was to investigate the role of ANP in attenuated cardioprotective effect of IPC in the diabetic rat heart.

METHODS

The heart was isolated from the diabetic rat and mounted on Langendorff's apparatus, subjected to 30-min ischemia and 120-min reperfusion. IPC was mediated by four cycles of 5-min ischemia and 5-min reperfusion. The infarct size was estimated using triphenyltetrazolium chloride stain, and coronary effluent was analyzed for lactate dehydrogenase and creatinine kinase-MB release to assess the degree of myocardial injury. The cardiac release of NO was estimated indirectly by measuring the release of nitrite in coronary effluent.

RESULTS

IPC-mediated cardioprotection was significantly attenuated in the diabetic rat as compared with the normal rat. Perfusion of ANP (0.1 μM/L) in the diabetic rat heart significantly restored the attenuated cardioprotective effect of IPC and also increased the release of NO. However, this observed cardioprotection was significantly attenuated by perfusion of N-nitro L-arginine methyl ester, an eNOS inhibitor (100 μM/L) noted in terms of increase in myocardial infarct size, release of lactate dehydrogenase and creatinine kinase-MB, and also decreases in release of NO.

CONCLUSIONS

Thus, it is suggested that ANP restores the attenuated cardioprotective effect in the diabetic heart which may be due to increase in the expression of eNOS and subsequent increase in the activity of NO.

Interaction of risk factors, comorbidities, and comedications with ischemia/reperfusion injury and cardioprotection by preconditioning, postconditioning, and remote conditioning

Pre-, post-, and remote conditioning of the myocardium are well described adaptive responses that markedly enhance the ability of the heart to withstand a prolonged ischemia/reperfusion insult and provide therapeutic paradigms for cardioprotection. Nevertheless, more than 25 years after the discovery of ischemic preconditioning, we still do not have established cardioprotective drugs on the market. Most experimental studies on cardioprotection are still undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of cardiovascular risk factors. However, ischemic heart disease in humans is a complex disorder caused by, or associated with, cardiovascular risk factors and comorbidities, including hypertension, hyperlipidemia, diabetes, insulin resistance, heart failure, altered coronary circulation, and aging. These risk factors induce fundamental alterations in cellular signaling cascades that affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Moreover, some of the medications used to treat these risk factors, including statins, nitrates, and antidiabetic drugs, may impact cardioprotection by modifying cellular signaling. The aim of this article is to review the recent evidence that cardiovascular risk factors and their medication may modify the response to cardioprotective interventions. We emphasize the critical need to take into account the presence of cardiovascular risk factors and concomitant medications when designing preclinical studies for the identification and validation of cardioprotective drug targets and clinical studies. This will hopefully maximize the success rate of developing rational approaches to effective cardioprotective therapies for the majority of patients with multiple risk factors.

The challenge of translating ischemic conditioning from animal models to humans: the role of comorbidities

Following a period of ischemia (local restriction of blood supply to a tissue), the restoration of blood supply to the affected area causes significant tissue damage. This is known as ischemia-reperfusion injury (IRI) and is a central pathological mechanism contributing to many common disease states. The medical complications caused by IRI in individuals with cerebrovascular or heart disease are a leading cause of death in developed countries. IRI is also of crucial importance in fields as diverse as solid organ transplantation, acute kidney injury and following major surgery, where post-operative organ dysfunction is a major cause of morbidity and mortality. Given its clinical impact, novel interventions are urgently needed to minimize the effects of IRI, not least to save lives but also to reduce healthcare costs. In this Review, we examine the experimental technique of ischemic conditioning, which entails exposing organs or tissues to brief sub-lethal episodes of ischemia and reperfusion, before, during or after a lethal ischemic insult. This approach has been found to confer profound tissue protection against IRI. We discuss the translation of ischemic conditioning strategies from bench to bedside, and highlight where transition into human clinical studies has been less successful than in animal models, reviewing potential reasons for this. We explore the challenges that preclude more extensive clinical translation of these strategies and emphasize the role that underlying comorbidities have in altering the efficacy of these strategies in improving patient outcomes.

Orally active epoxyeicosatrienoic acid analog does not exhibit antihypertensive and reno- or cardioprotective actions in two-kidney, one-clip Goldblatt hypertensive rats

This study examined the effects of a novel orally active 14,15-epoxyeicosatrienoic acid analog (EET-A) on blood pressure (BP) and myocardial infarct size (IS) in two-kidney, one-clip (2K1C) Goldblatt hypertensive rats during sustained phase of hypertension. Between days 31 and 35 after clip placement the rats were treated with EET-A and BP was monitored by radiotelemetry; sham-operated normotensive rats were used as controls. Tissue concentrations of epoxyeicosatrienoic acids served as a marker of production of epoxygenase metabolites. The rats were subjected to acute myocardial ischemia/reperfusion (I/R) injury and IS was determined. We found that EET-A treatment did not lower BP in 2K1C rats and did not alter availability of biologically active epoxygenase metabolites in 2K1C or in sham-operated rats. The myocardial IS was significantly smaller in untreated 2K1C rats as compared with normotensive controls and EET-A reduced it in controls but not in 2K1C rats. Our findings suggest that during the phase of sustained hypertension 2K1C Goldblatt hypertensive rats exhibit increased cardiac tolerance to I/R injury as compared with normotensive controls, and that in this animal model of human renovascular hypertension short-term treatment with EET-A does not induce any antihypertensive and cardioprotective actions.

Preconditioning offers cardioprotection in hyperlipidemic rat hearts: possible role of Dopamine (D2) signaling

BACKGROUND

Ischemic preconditioning (IPC) induced cardioprotection has been reported to be blunted in hyperlipidemic subjects. Dopamine, via its D2 receptor signaling, appears to mimic the signaling cascade involved in myocardial preconditioning and is also involved in the inhibition of hyperlipidemia induced mediators. The present study was designed to investigate the possible involvement of D2 receptors in IPC and to see whether dopamine preconditioning can offer cardioprotection in hyperlipidemic rat hearts.

METHODS

Wistar albino rats were divided into 8 groups and fed on normal or high fat diet for 4 weeks. Hyperlipidemia was confirmed after 4 weeks by serum lipid estimations. Isolated perfused hearts were subjected to ischemic preconditioning or dopamine induced pharmacological preconditioning followed by 30-min ischemic insult and 60-min reperfusion. Clozapine was administered as D2 antagonist. Coronary perfusate (basal and post-ischemic) was collected for the estimations of LDH (Lactate dehydrogenase) and CKMB (Creatine kinase MB). Hearts were then removed and frozen for infarct size measurement.

RESULTS

A significant increase body weight, serum lipids except HDL was noted in high fat diet fed rats, as compared to normal rats. The level of LDH, CKMB in coronary effluent and infarct size were found to be decreased in preconditioned normal hearts, as compared to hearts treated with ischemia reperfusion. This effect was found to be blunted in hyperlipidemic animals. Dopamine (10 μM) alone and in combination with ischemic preconditioning significantly reduced the levels of LDH, CKMB and infarct size in hyperlipidemic hearts, as compared to preconditioned and non-preconditioned hyperlipidemic hearts. This effect was abolished significantly by Clozapine (D2 antagonist).

CONCLUSION

The present study reveals possible involvement of D2 receptors in ischemic preconditioning and suggests that dopamine preconditioning may offer significant cardioprotection in hyperlipidemic rat hearts.

Pleiotropic preconditioning-like cardioprotective effects of hypolipidemic drugs in acute ischemia–reperfusion in normal and hypertensive rats

Although pleiotropy, which is defined as multiple effects derived from a single gene, was recognized many years ago, and considerable progress has since been achieved in this field, it is not very clear how much this feature of a drug is clinically relevant. During the last decade, beneficial pleiotropic effects from hypolipidemic drugs (as in, effects that are different from the primary ones) have been associated with reduction of cardiovascular risk. As with statins, the agonists of peroxisome proliferator-activated receptors (PPARs), niacin and fibrates, have been suggested to exhibit pleiotropic activity that could significantly modify the outcome of a cardiovascular ailment. This review examines findings demonstrating the impacts of treatment with hypolipidemic drugs on cardiac response to ischemia in a setting of acute ischemia–reperfusion, in relation to PPAR activation. Specifically, it addresses the issue of susceptibility to ischemia, with particular regard to the preconditioning-like cardioprotection conferred by hypolipidemic drugs, as well as the potential molecular mechanisms behind this cardioprotection. Finally, the involvement of PPAR activation in the mechanisms of non-metabolic cardioprotective effects from hypolipidemic drugs, and their effects on normal and pathologically altered myocardium (in the hearts of hypertensive rats) is also discussed.

Matrix metalloproteinases and their tissue inhibitor after reperfused ST-elevation myocardial infarction treated with doxycycline. Insights from the TIPTOP trial

BACKGROUND

The TIPTOP (Early Short-term Doxycycline Therapy In Patients with Acute Myocardial Infarction and Left Ventricular Dysfunction to Prevent The Ominous Progression to Adverse Remodelling) trial demonstrated that a timely, short-term therapy with doxycycline is able to reduce LV dilation, and both infarct size and severity in patients treated with primary percutaneous intervention (pPCI) for a first ST-elevation myocardial infarction (STEMI) and left ventricular (LV) dysfunction. In this secondary, pre-defined analysis of the TIPTOP trial we evaluated the relationship between doxycycline and plasma levels of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs).

METHODS

In 106 of the 110 (96%) patients enrolled in the TIPTOP trial, plasma MMPs and TIMPs were measured at baseline, and at post-STEMI days 1, 7, 30 and 180. To evaluate the remodeling process, 2D-Echo studies were performed at baseline and at 6months. A (99m)Tc-SPECT was performed to evaluate the 6-month infarct size and severity.

RESULTS

Doxycycline therapy was independently related to higher plasma TIMP-2 levels at day 7 (p<0.05). Plasma TIMP-2 levels above the median value at day 7 were correlated with the 6-month smaller infarct size (3% [0%-16%] vs. 12% [0%-30%], p=0.002) and severity (0.55 [0.44-0.64] vs. 0.45 [0.29-0.60], p=0.002), and LV dilation (-1ml/m(2) [from -7ml/m(2) to 9ml/m(2)] vs. 3ml/m(2) [from -2ml/m(2) to 19ml/m(2)], p=0.04), compared to their counterpart.

CONCLUSIONS

In this clinical setting, doxycycline therapy results in higher plasma levels of TIMP-2 which, in turn, inversely correlate with 6month infarct size and severity as well as LV dilation.

Cardioprotective effects of voluntary exercise in a rat model: role of matrix metalloproteinase-2

Background. Regular exercise at moderate intensity reduces cardiovascular risks. Matrix metalloproteinases (MMPs) play a major role in cardiac remodeling, facilitating physiological adaptation to exercise. The aim of this study was to examine the influence of voluntary physical exercise on the MMP-2 enzyme activity and to investigate the cardiac performance by measurement of angina susceptibility of the heart, the basal blood pressure, the surviving aorta ring contraction, and the cardiac infarct size after I/R-induced injury. Methods. Male Wistar rats were divided into control and exercising groups. After a 6-week period, the serum level of MMP-2, basal blood pressure, cardiac angina susceptibility (the ST segment depression provoked by epinephrine and 30 s later phentolamine), AVP-induced heart perfusion and aorta ring contraction, infarct size following 30 min ischemia and 120 min reperfusion, and coronary effluent MMP-2 activity were measured. Results. Voluntary wheel-running exercise decreased both the sera (64 kDa and 72 kDa) and the coronary effluent (64 kDa) MMP-2 level, reduced the development of ST depression, improved the isolated heart perfusion, and decreased the ratio of infarct size. Conclusion. 6 weeks of voluntary exercise training preserved the heart against cardiac injury. This protective mechanism might be associated with the decreased activity of MMP-2.

Effect of zinc supplements in the attenuated cardioprotective effect of ischemic preconditioning in hyperlipidemic rat heart

Hyperlipidemia is regarded as independent risk factor in the development of ischemic heart disease, and it can increase the myocardial susceptibility to ischemia-/reperfusion (I/R)-induced injury. Hyperlipidemia attenuates the cardioprotective response of ischemic preconditioning (IPC). The present study investigated the effect of zinc supplements in the attenuated cardioprotective effect of ischemic preconditioning in hyperlipidemic rat hearts. Hyperlipidemia was induced in rat by feeding high-fat diet (HFD) for 6 weeks then the serum lipid profile was observed. In experiment, the isolated Langendorff rat heart preparation was subjected to 4 cycles of ischemic preconditioning (IPC), then 30 min of ischemia followed by 120 min of reperfusion. Myocardial infarct size was elaborated morphologically by triphenyltetrazolium chloride (TTC) staining and biochemically by lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) release from coronary effluent and left ventricular collagen content. However, the effect of zinc supplement, i.e., zinc pyrithione (10 μM) perfused during reperfusion for 120 min, significantly abrogated the attenuated cardioprotective effect of ischemic preconditioning in hyperlipidemic rat heart whereas administration of chelator of this zinc ionophore, i.e., N,N,N',N'-tetrakis(2-pyridylmethyl)ethylene diamine (TPEN; 10 μM), perfused during reperfusion 2 min before the perfusion of zinc pyrithione abrogated the cardioprotective effect of zinc supplement during experiment in hyperlipidemic rat heart. Thus, the administration of zinc supplements limits the infarct size, LDH, and CK-MB and enhanced the collagen level which suggests that the attenuated cardioprotective effect of IPC in hyperlipidemic rat is due to zinc loss during reperfusion caused by ischemia/reperfusion.

Redox signalling and cardioprotection: translatability and mechanism

The morbidity and mortality from coronary artery disease (CAD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of culprit coronary arteries. Although it is mandatory to reperfuse the ischaemic territory as soon as possible, paradoxically this leads to additional myocardial injury, namely ischaemia/reperfusion (I/R) injury, in which redox stress plays a pivotal role and for which no effective therapy is currently available. In this review, we report evidence that the redox environment plays a pivotal role not only in I/R injury but also in cardioprotection. In fact, cardioprotective strategies, such as pre- and post-conditioning, result in a robust reduction in infarct size in animals and the role of redox signalling is of paramount importance in these conditioning strategies. Nitrosative signalling and cysteine redox modifications, such as S-nitrosation/S-nitrosylation, are also emerging as very important mechanisms in conditioning cardioprotection. The reasons for the switch from protective oxidative/nitrosative signalling to deleterious oxidative/nitrosative/nitrative stress are not fully understood. The complex regulation of this switch is, at least in part, responsible for the diminished or lack of cardioprotection induced by conditioning protocols observed in ageing animals and with co-morbidities as well as in humans. Therefore, it is important to understand at a mechanistic level the reasons for these differences before proposing a safe and useful transition of ischaemic or pharmacological conditioning. Indeed, more mechanistic novel therapeutic strategies are required to protect the heart from I/R injury and to improve clinical outcomes in patients with CAD.

Targeting MMP-2 to treat ischemic heart injury

Matrix metalloproteinase (MMPs) are long understood to be involved in remodeling of the extracellular matrix. However, over the past decade, it has become clear that one of the most ubiquitous MMPs, MMP-2, has numerous intracellular targets in cardiac myocytes. Notably, MMP-2 proteolyzes components of the sarcomere, and its intracellular activity contributes to ischemia-reperfusion injury of the heart. Together with the well documented role played by MMPs in the myocardial remodeling that occurs following myocardial infarction, this has led to great interest in targeting MMPs to treat cardiac ischemic injury. In this review we will describe the expanding understanding of intracellular MMP-2 biology, and how this knowledge may lead to improved treatments for ischemic heart injury. We also critically review the numerous preclinical studies investigating the effects of MMP inhibition in animal models of myocardial infarction and ischemia-reperfusion injury, as well as the recent clinical trials that are part of the effort to translate these results into clinical practice. Acknowledging the disappointing results of past clinical trials of MMP inhibitors for other diseases, we discuss the need for carefully designed preclinical and clinical studies to avoid mistakes that have been previously made. We conclude that inhibition of MMPs, and in particular MMP-2, shows promise as a therapy to prevent the progression from ischemic injury to heart failure. However, it is critical that the full breadth of MMP-2 biology be taken into account as such therapies are developed.

Mechanisms involved in attenuated cardio-protective role of ischemic preconditioning in metabolic disorders

Myocardial infarction is a pathological state which occurs due to severe abrogation of the blood supply (ischemia) to a part of heart, which can cause myocardial damage. The short intermittent cycles of sub-lethal ischemia and reperfusion has shown to improve the tolerance of the myocardium against subsequent prolonged ischemia/reperfusion (I/R)-induced injury, which is known as ischemic preconditioning (IPC). Although, IPC-induced cardioprotection is well demonstrated in various species, including human beings, accumulated evidence clearly suggests critical abrogation of the beneficial effects of IPC in diabetes mellitus, hyperlipidemia and hyperhomocysteinemia. Various factors are involved in the attenuation of the cardioprotective effect of preconditioning, such as the reduced release of calcitonin gene-related peptide (CGRP), the over-expression of glycogen synthase kinase-3β (GSK-3β) and phosphatase and tensin homolog (PTEN), impairment of mito-KATP channels, the consequent opening of mitochondrial permeability transition pore (MPTP), etc. In this review, we have critically discussed the various signaling pathways involved in abrogated preconditioning in chronic diabetes mellitus, hyperlipidemia and hyperhomocysteinemia. We have also focused on the involvement of PTEN in abrogated preconditioning and the significance of PTEN inhibitors.

Activation of α1B-adrenoceptors contributes to intermittent hypobaric hypoxia-improved postischemic myocardial performance via inhibiting MMP-2 activation

Inhibition of matrix metalloproteinases-2 (MMP-2) activation renders cardioprotection from ischemia/reperfusion (I/R) injury; however, the signaling pathways involved have not been fully understood. Intermittent hypobaric hypoxia (IHH) has been shown to enhance myocardial tolerance to I/R injury via triggering intrinsic adaptive responses. Here we investigated whether IHH protects the heart against I/R injury via the regulation of MMP-2 and how the MMP-2 is regulated. IHH (Po2 = 84 mmHg, 4-h/day, 4 wk) improved postischemic myocardial contractile performance, lactate dehydrogenase (LDH) release, and infarct size in isolated perfused rat hearts. Moreover, IHH reversed I/R-induced MMP-2 activation and release, disorders in the levels of MMP-2 regulators, peroxynitrite (ONOO(-)) and tissue inhibitor of metalloproteinase-4 (TIMP-4), and loss of the MMP-2 targets α-actinin and troponin I. This protection was mimicked, but not augmented, by a MMP inhibitor doxycycline and lost by the α1-adrenoceptor (AR) antagonist prazosin. Furthermore, IHH increased myocardial α1A-AR and α1B-AR density but not α1D-AR after I/R. Concomitantly, IHH further enhanced the translocation of PKC epsilon (PKCε) and decreased the release of mitochondrial cytochrome c due to I/R via the activation of α1B-AR but not α1A-AR or α1D-AR. IHH-conferred cardioprotection in the postischemic contractile function, LDH release, MMP-2 activation, and nitrotyrosine as well as TIMP-4 contents were mimicked but not additive by α1-AR stimulation with phenylephrine and were abolished by an α1B-AR antagonist chloroethylclonidine and a PKCε inhibitor PKCε V1-2. These findings demonstrate that IHH exerts cardioprotection through attenuating excess ONOO(-) biosynthesis and TIMP-4 loss and sequential MMP-2 activation via the activation of α1B-AR/PKCε pathway.

Cholesterol-enriched diet inhibits cardioprotection by ATP-sensitive K+ channel activators cromakalim and diazoxide

It has been previously shown that hyperlipidemia interferes with cardioprotective mechanisms. Here, we investigated the interaction of hyperlipidemia with cardioprotection induced by pharmacological activators of ATP-sensitive K(+) (KATP) channels. Hearts isolated from rats fed a 2% cholesterol-enriched diet or normal diet for 8 wk were subjected to 30 min of global ischemia and 120 min of reperfusion in the presence or absence of KATP modulators. In normal diet-fed rats, either the nonselective KATP activator cromakalim at 10(-5) M or the selective mitochondrial (mito)KATP opener diazoxide at 3 × 10(-5) M significantly decreased infarct size compared with vehicle-treated control rats. Their cardioprotective effect was abolished by coadministration of the nonselective KATP blocker glibenclamide or the selective mitoKATP blocker 5-hydroxydecanoate, respectively. However, in cholesterol-fed rats, the cardioprotective effect of cromakalim or diazoxide was not observed. Therefore, we further investigated how cholesterol-enriched diet influences cardiac KATP channels. Cardiac expression of a KATP subunit gene (Kir6.1) was significantly downregulated in cholesterol-fed rats; however, protein levels of Kir6.1 and Kir6.2 were not changed. The cholesterol diet significantly decreased cardiac ATP, increased lactate content, and enhanced myocardial oxidative stress, as shown by increased cardiac superoxide and dityrosine formation. This is the first demonstration that cardioprotection by KATP channel activators is impaired in cholesterol-enriched diet-induced hyperlipidemia. The background mechanism may include hyperlipidemia-induced attenuation of mitoKATP function by altered energy metabolism and increased oxidative stress in the heart.

Delayed cardioprotective effects of WY-14643 are associated with inhibition of MMP-2 and modulation of Bcl-2 family proteins through PPAR-α activation in rat hearts subjected to global ischaemia–reperfusion

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors regulating cardiac lipid metabolism and energy homeostasis. Although the activation of PPARs has been implicated in cardioprotection, the molecular mechanisms are largely unexplored. In this study, we aimed to investigate the effect of the PPAR-α agonist WY-14643 (WY), mimicking a delayed effect of preconditioning in rat hearts exposed to acute ischaemia–reperfusion (I/R) 24 h later, and to define whether antioxidative and antiapoptotic mechanisms are involved. Treatment with WY markedly attenuated post-ischaemic contractile dysfunction (as evidenced by the reduced infarct size), the higher left ventricular developed pressure (LVDP) recovery, and the decreased occurrence of arrhythmias. These effects were abolished in the presence of the PPAR-α antagonist MK886. Heme oxygenase-1, a key antioxidative enzyme implicated in cytoprotection, was upregulated in response to WY at baseline, but was markedly reduced after I/R, indicating reduced oxidative stress. WY treatment was also associated with decreased mRNA levels and enzymatic activity of matrix metalloproteinase-2, and increased ratios of Bcl-2:Bax proteins. These results indicate that PPAR-α activation by its selective ligand WY may confer delayed preconditioning-like protection in rat hearts subjected to I/R by modulating oxidative stress, activation of matrix metalloproteinase-2, and expression of Bcl-2 and Bax.

Matrix metalloproteinase inhibition protects CyPD knockout mice independently of RISK/mPTP signalling: a parallel pathway to protection

The mitochondrial permeability transition pore (mPTP) is widely accepted as an end-effector mechanism of conditioning protection against injurious ischaemia/reperfusion. However, death can be initiated in cells without pre-requisite mPTP opening, implicating alternate targets for ischaemia/reperfusion injury amelioration. Matrix metalloproteinases (MMP) are known to activate extrinsic apoptotic cascades and therefore we hypothesised that MMP activity represents an mPTP-independent target for augmented attenuation of ischaemia/reperfusion injury. In ex vivo and in vivo mouse hearts, we investigated whether the MMP inhibitor, ilomastat (0.25 μmol/l), administered upon reperfusion could engender protection in the absence of cyclophilin-D (CyPD), a modulator of mPTP opening, against injurious ischaemia/reperfusion. Ilomastat attenuated infarct size in wild-type (WT) animals [37 ± 2.8 to 22 ± 4.3 %, equivalent to ischaemic postconditioning (iPostC), used as positive control, 27 ± 2.1 %, p < 0.05]. Control CyPD knockout (KO) hearts had smaller infarcts than control WT (28 ± 4.2 %) and iPostC failed to confer additional protection, yet ilomastat significantly attenuated infarct size in KO hearts (11 ± 3.0 %, p < 0.001), and similar protection was also seen in isolated cardiomyocytes. Moreover, ilomastat, unlike the cyclophilin inhibitor cyclosporine-A, had no impact upon reactive oxygen species-mediated mPTP opening. While MMP inhibition was associated with increased Akt and ERK phosphorylation, neither Wortmannin nor PD98059 abrogated ilomastat-mediated protection. We demonstrate that MMP inhibition is cardioprotective, independent of Akt/ERK/CyPD/mPTP activity and is additive to the protection observed following inhibition of mPTP opening, indicative of a parallel pathway to protection in ischaemic/reperfused heart that may have clinical applicability in attenuating injury in acute coronary syndromes and deserve further investigation.

Self-cross-linkable hydrogels composed of partially oxidized alginate and gelatin for myocardial infarction repair

Calcium cross-linked alginate hydrogel has shown positive results for the treatment of myocardial infarction in both acute and chronic rat models. However, cross-linked alginate hydrogels possess poor mechanical properties, uncontrollable degradation, and poor cell adhesion and infiltration. In this study, covalent cross-linking of partially oxidized alginate and gelatin hydrogel was developed for myocardial infarction treatment, as compared to cross-linked alginate hydrogel and saline. Specifically, the gelation process, mechanical properties, and biodegradation of both cross-linked alginate hydrogel and oxidized alginate and gelatin hydrogel were examined in vitro and in vivo; and a rat myocardial infarction model was developed by injecting hydrogel into hearts, and postinjection, echocardiography was performed at 2, 4, and 6 weeks, respectively. Matrix metalloprotease-2/9 activity was also examined by in situ zymography on frozen slices of the treated hearts. Based on the results, that both hydrogels enhanced scar thickness and attenuated heart remodeling compared with the saline control group and that, compared to cross-linked alginate hydrogel, oxidized alginate and gelatin hydrogel exhibited the increased mechanical strength, enhanced angiogenesis, and stronger cell-recruiting capacity. It has also been illustrated that oxidized alginate and gelatin hydrogel–treated hearts have much weaker cardiac remodeling, enhanced extracellular matrix accumulation, and reduced matrix metalloprotease activity than cross-linked alginate hydrogel–treated ones. All results suggest oxidized alginate and gelatin hydrogel may be more suitable for the myocardial infarction treatment.

Autophagy, myocardial protection, and the metabolic syndrome

Autophagy is a housekeeping process that helps to maintain cellular energy homeostasis and remove damaged organelles. In the heart, autophagy is an adaptive process that is activated in response to stress including acute and chronic ischemia. Given the evidence that autophagy is suppressed in energy-rich conditions, the objective of this review is to examine autophagy and cardioprotection in the setting of the metabolic syndrome. Clinical approaches that involve the induction of cardiac autophagy pharmacologically to enhance the heart's tolerance to ischemia are also discussed.

Preconditioning protects the heart in a prolonged uremic condition

Metabolic diseases such as hyperlipidemia and diabetes attenuate the cardioprotective effect of ischemic preconditioning. In the present study, we examined whether another metabolic disease, prolonged uremia, affects ischemia/reperfusion injury and cardioprotection by ischemic preconditioning. Uremia was induced by partial nephrectomy in male Wistar rats. The development of uremia was verified 29 wk after surgery. Transthoracic echocardiography was performed to monitor cardiac function. At week 30, hearts of nephrectomized and sham-operated rats were isolated and subjected to a 30-min coronary occlusion followed by 120 min reperfusion with or without preceding preconditioning induced by three intermittent cycles of brief ischemia and reperfusion. In nephrectomized rats, plasma uric acid, carbamide, and creatinine as well as urine protein levels were increased as compared with sham-operated controls. Systolic anterior and septal wall thicknesses were increased in nephrectomized rats, suggesting the development of a minimal cardiac hypertrophy. Ejection fraction was decreased and isovolumic relaxation time was shortened in nephrectomized rats demonstrating a mild systolic and diastolic dysfunction. Infarct size was not affected significantly by nephrectomy itself. Ischemic preconditioning significantly decreased infarct size from 24.8 ± 5.2% to 6.6 ± 1.3% in the sham-operated group and also in the uremic group from 35.4 ± 9.5% to 11.9 ± 3.1% of the area at risk. Plasma ANG II and nitrotyrosine were significantly increased in the uremic rats. We conclude that although prolonged experimental uremia leads to severe metabolic changes and the development of a mild myocardial dysfunction, the cardioprotective effect of ischemic preconditioning is still preserved.

Reactive oxygen species are not a required trigger for exercise-induced late preconditioning in the rat heart

Reactive oxygen species (ROS) have been reported to play a primary role in triggering the cardioprotective adaptations by some preconditioning procedures, but whether they are required for exercise-induced preconditioning is unclear. Thus in this study we used the free radical scavenger N-(2-mercaptopropionyl)glycine (MPG) to test the hypothesis that ROS is the trigger for exercise-induced preconditioning of the heart against ischemia-reperfusion injury. Male F344 rats were assigned to four groups: sedentary (SED, n = 7), SED/MPG (100 mg/kg ip daily for 2 days, n = 12), exercised on a treadmill for 2 days at 20 m/min, 6° grade, for 60 min (RUN, n = 7), and RUN/MPG with 100 mg/kg MPG injected 15 min before exercise (n = 10). Preliminary experiments verified that MPG administration maintained myocardial redox status during the exercise bout. Twenty-four hours postexercise or MPG treatment isolated perfused working hearts were subjected to global ischemia for 22.5 min followed by reperfusion for 30 min. Recovery of myocardial external work (percentage of preischemic systolic pressure times cardiac output) for SED (50.4 ± 4.5) and SED/RUN (54.7 ± 6.6) was similar and improved in both exercise groups (P < 0.05) to 77.9 ± 3.0 in RUN and 76.7 ± 4.5 in RUN/MPG. A 2 × 2 ANOVA also revealed that exercise decreased lactate dehydrogenase release from the heart during reperfusion (marker of cell damage) without MPG effects or interactions. Expression of the cytoprotective protein inducible heat shock protein 70 increased by similar amounts in the left ventricles of RUN and RUN/MPG compared with sedentary groups (P < 0.05). We conclude that ROS are not a necessary trigger for exercise-induced preconditioning in rats.

Hypercholesterolemia abrogates sevoflurane-induced delayed preconditioning against myocardial infarct in rats by alteration of nitric oxide synthase signaling

The aim of the current study was to determine whether hypercholesterolemia affects the delayed sevoflurane preconditioning against myocardial ischemia-reperfusion (IR) injury and, if so, the underlying mechanism. Male Sprague-Dawley rats fed 2% cholesterol-enriched chow for 8 weeks were subjected to sevoflurane preconditioning (2.4% vol/vol, 1 h) 24 h before myocardial ischemia was induced by occluding the left anterior descending coronary artery for 30 min followed by reperfusion for 120 min. The hemodynamic parameters left ventricular developed pressure, left ventricular end-diastolic pressure, and maximal rise/fall rate of left ventricular pressure were continuously monitored, and myocardial infarct size was determined at the end of reperfusion. The protein expression of myocardial nitric oxide synthase (NOS), Bcl-2, and Bad was assessed before ischemia. We found that the left ventricular hemodynamic parameters during the whole IR procedure and the myocardial infarct size did not significantly differ between the normocholesterolemic and hypercholesterolemic control groups. The hemodynamic parameters were all markedly improved during the reperfusion period, and the myocardial infarct size was significantly reduced by delayed sevoflurane preconditioning in normocholesterolemic rats, but all of these improvements were reversed by N-(3-(aminomethyl)benzyl) acetamidine (1400W, 1 mg/kg; i.v., 10 min before ischemia), a selective inducible NOS (iNOS) inhibitor, and 5-hydroxy decanoate sodium (5 mg/kg, i.v., 10 min before ischemia), a mitochondrial ATP-dependent K⁺ channel blocker. Such cardiac improvement induced by delayed sevoflurane preconditioning did not occur in hypercholesterolemic rats and was not exacerbated by 1400W or 5-hydroxy decanoate sodium. The expression of myocardial iNOS was markedly enhanced by delayed sevoflurane preconditioning in normocholesterolemic, but not in hypercholesterolemic rats. The expression of endothelial NOS and Bad did not differ among all groups. The expression of myocardial phosphorylated endothelial NOS, Bcl-2, and phosphorylated Bad in normocholesterolemic rats was not affected by delayed sevoflurane preconditioning but was decreased in the hypercholesterolemic control group, and this was not reversed by sevoflurane, compared with the normocholesterolemic control group. Taken together, these results indicate that sevoflurane preconditioning exerts delayed cardioprotection against IR injury in normocholesterolemic rats, which is blocked by hypercholesterolemia potentially via interference with the iNOS/mitochondrial ATP-dependent K⁺ channel pathway.

Ischemic conditioning protects the uremic heart in a rodent model of myocardial infarction

BACKGROUND

Outcomes after acute myocardial infarction in patients with chronic kidney disease are extremely poor. Ischemic conditioning techniques are among the most powerful cytoprotective strategies discovered to date. However, experimental data suggest that comorbidity may attenuate the protective effects of ischemic conditioning.

METHODS AND RESULTS

We conducted investigations into the effects of chronic uremia on myocardial infarct size and the protective effects of ischemic preconditioning (IPC), remote ischemic preconditioning, and ischemic postconditioning in 2 rodent models of chronic uremia. In addition, a limited investigation into the signaling mechanisms involved in cardioprotection after IPC was performed in both uremic and nonuremic animals. Myocardial infarct size was increased in uremic animals, but all 3 conditioning strategies (IPC, remote IPC, ischemic postconditioning) proved highly efficacious in reducing myocardial infarct size (relative reduction, 86%, 39%, and 65% [P<0.005, P<0.05, and P<0.05], respectively). Moreover, some protocols (IPC and ischemic postconditioning) appeared to be more effective in uremic than in sham (nonuremic) animals. Analysis of the signaling mechanisms revealed that components of both the reperfusion injury salvage kinase and survivor activating factor enhancement pathways were similarly upregulated in both uremic and nonuremic animals after an IPC stimulus.

CONCLUSION

Conditioning strategies may present the best opportunity to improve outcomes for patients with chronic kidney disease after an acute coronary syndrome.

Novel effects of macrolide antibiotics on cardiovascular diseases

Macrolide antibiotics are broadly used for the treatment of various microbial infections. However, they are also known to have multiple biologic effects, such as alteration of inflammatory factors and matrix metalloproteinases (MMPs). Because of controversial results in clinical trials, the effects of macrolides on cardiovascular diseases are still to be elucidated. It has been reported that MMP activity is upregulated in various cardiovascular diseases, such as myocarditis, cardiac transplant rejection and myocardial infarction. However, little is known about the effects of macrolides on cardiovascular diseases. We have reported that clarithromycin suppressed the development of myocarditis, cardiac rejection and myocardial ischemia using animal models. In this article, we reviewed the roles of MMPs in cardiovascular diseases and the effects of macrolides on the prevention of adverse tissue remodeling.