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Background and Purpose: MicroRNA (miRNA) therapy is a promising approach to induce cardioprotection. We have previously identified cardiac microRNA-125b* (microRNA-125b-2-3p; miR-125b*) as a potential cardioprotective miRNA, termed ProtectomiR. We aimed to characterize the pharmacokinetics and pharmacodynamics, and the effect of miR-125b* mimic on infarct size using an in vivo mouse model., Experimental Approach: To characterize the pharmacokinetics properties of miR-125b* mimic, a single injection of 10-μg miR-125b* mimic or its scramble miRNA control, or vehicle i.v. was given to C57BL/6 mice. MiR-125b* expression was measured from plasma, heart, kidney and liver samples. Effect of miR-125b* on area at risk and infarct size was assessed after 45-min coronary occlusion, followed by 24-h reperfusion; 10-μg miR-125b* mimic or 10-μg non-targeting miRNA mimic control or vehicle were administered via the right jugular vein at 10th mins of coronary occlusion. To assess molecular mechanism involved in cardioprotection, expression of mRNA targets of miR-125b* were measured from ventricular myocardium at 1, 2, 4, 8 or 24 h post-treatment using quantitative real time polymerase chain reaction., Key Results: MiR-125b* expression was markedly increased in plasma and myocardium 1 h, and in the liver 2h after treatment. Infarct size was significantly reduced after miR-125b* mimic treatment when compared to the vehicle. The expression of Ccna2, Eef2k and Cacnb2 target mRNAs was significantly reduced 8 h after injection of miR-125b* mimic., Conclusion and Implications: This is the first demonstration of pharmacokinetic and molecular pharmacodynamic properties as well as the cardioprotective effect of miR-125b* mimic in vivo., Linked Articles: This article is part of a themed issue Non-coding RNA Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v182.2/issuetoc., (© 2024 The Author(s). British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

The cardiomyocyte-specific knockout (KO) of monoamine oxidase (MAO)-B, an enzyme involved in the formation of reactive oxygen species (ROS), reduced myocardial ischemia/reperfusion (I/R) injury in vitro. Because sex hormones have a strong impact on MAO metabolic pathways, we analyzed the myocardial infarct size (IS) following I/R in female and male MAO-B KO mice in vivo., Method and Results: To induce the deletion of MAO-B, MAO-B KO mice (Myh6 Cre+/MAO-B fl/fl ) and wild-type (WT, Cre-negative MAO-B fl/fl littermates) were fed with tamoxifen for 2 weeks followed by 10 weeks of normal mice chow. Myocardial infarction (assessed by TTC staining and expressed as a percentage of the area at risk as determined by Evans blue staining)) was induced by 45 min coronary occlusion followed by 120 min of reperfusion., Results: The mortality following I/R was higher in male compared to female mice, with the lowest mortality found in MAO-B KO female mice. IS was significantly higher in male WT mice compared to female WT mice. MAO-B KO reduced IS in male mice but had no further impact on IS in female MAO-B KO mice. Interestingly, there was no difference in the plasma estradiol levels among the groups., Conclusion: The cardiomyocyte-specific knockout of MAO-B protects male mice against acute myocardial infarction but had no effect on the infarct size in female mice.

During the last decades, mortality from acute myocardial infarction has been dramatically reduced. However, the incidence of post-infarction heart failure is still increasing. Cardioprotection by ischaemic conditioning had been discovered more than three decades ago. Its clinical translation, however, is still an unmet need. This is mainly due to the disrupted cardioprotective signalling pathways in the presence of different cardiovascular risk factors, co-morbidities and the medication being taken. Sensory neuropathy is one of the co-morbidities that has been shown to interfere with cardioprotection. In the present review, we summarize the diverse aetiology of sensory neuropathies and the mechanisms by which these neuropathies may interfere with ischaemic heart disease and cardioprotective signalling. Finally, we suggest future therapeutic options targeting both ischaemic heart and sensory neuropathy simultaneously. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc., (© 2020 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

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.

Swiprosin-1 (EFhD2) is a molecule that triggers structural adaptation of isolated adult rat cardiomyocytes to cell culture conditions by initiating a process known as cell spreading. This process mimics central aspects of cardiac remodeling, as it occurs subsequent to myocardial infarction. However, expression of swiprosin-1 in cardiac tissue and its regulation in vivo has not yet been addressed. The expression of swiprosin-1 was analyzed in mice, rat, and pig hearts undergoing myocardial infarction or ischemia/reperfusion with or without cardiac protection by ischemic pre- and postconditioning. In mouse hearts, swiprosin-1 protein expression was increased after 4 and 7 days in myocardial infarct areas specifically in cardiomyocytes as verified by immunoblotting and histology. In rat hearts, swiprosin-1 mRNA expression was induced within 7 days after ischemia/reperfusion but this induction was abrogated by conditioning. As in cultured cardiomyocytes, the expression of swiprosin-1 was associated with a coinduction of arrestin-2, suggesting a common mechanism of regulation. Rno-miR-32-3p and rno-miR-34c-3p were associated with the regulation pattern of both molecules. Moreover, induction of swiprosin-1 and ssc-miR-34c was also confirmed in the infarct zone of pigs. In summary, our data show that up-regulation of swiprosin-1 appears in the postischemic heart during cardiac remodeling and repair in different species.

The aim of this study was to describe the potential associations of the expression of matricellular components in adverse post-infarction remodeling of the geriatric heart. In male geriatric (OM, age: 18 months) and young (YM, age: 11 weeks) OF1 mice myocardial infarction (MI) was induced by permanent ligation of the left anterior descending coronary artery. Cardiac function was evaluated by MRI. Plasma and myocardial tissue samples were collected 3d, 7d, and 32d post-MI. Age and MI were associated with impaired cardiac function accompanied by left-ventricular (LV) dilatation. mRNA expression of MMP-2 (7d: p < 0.05), TIMP-1 (7d: p < 0.05), TIMP-2 (7d: p < 0.05), Collagen-1 (3d and 7d: p < 0.05) and Collagen-3 (7d: p < 0.05) in LV non-infarcted myocardium was significantly higher in YM than in OM after MI. MMP-9 activity in plasma was increased in OM after MI (3d: p < 0.01). Tenascin-C protein levels assessed by ELISA were decreased in OM as compared to YM after MI in plasma (3d: p < 0.001, 7d: p < 0.05) and LV non-infarcted myocardium (7d: p < 0.01). Dysregulation in ECM components in non-infarcted LV might be associated and contribute to adverse LV remodeling and impaired cardiac function. Thus, targeting ECM might be a potential therapeutic approach to enhance cardiac function in geriatric patients following MI., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The transcriptional regulator JDP2 (Jun dimerization protein 2) has been identified as a prognostic marker for patients to develop heart failure after myocardial infarction. We now performed in vivo studies on JDP2-overexpressing mice, to clarify the impact of JDP2 on heart failure progression. Therefore, during birth up to the age of 4 weeks cardiac-specific JDP2 overexpression was prevented by doxycycline feeding in transgenic mice. Then, JDP2 overexpression was started. Already after 1 week, cardiac function, determined by echocardiography, decreased which was also resembled on the cardiomyocyte level. After 5 weeks blood pressure declined, ejection fraction and cardiac output was reduced and left ventricular dilatation developed. Heart weight/body weight, and mRNA expression of ANP, inflammatory marker genes, collagen and fibronectin increased. Collagen 1 protein expression increased, and fibrosis developed. As an additional sign of elevated extracellular matrix remodeling, matrix metalloproteinase 2 activity increased in JDP2 mice. Thus, JDP2 overexpression is deleterious to heart function in vivo. It can be concluded that JDP2 overexpression provokes cardiac dysfunction in adult mice that is accompanied by hypertrophy and fibrosis. Thus, induction of JDP2 is a maladaptive response contributing to heart failure development.

Erythropoietin (EPO) has been shown to protect the heart against acute myocardial infarction in pre-clinical studies, however, EPO failed to reduce infarct size in clinical trials and showed significant safety problems. Here, we investigated cardioprotective effects of two selective non-erythropoietic EPO receptor ligand dimeric peptides (AF41676 and AF43136) lacking erythropoietic activity, EPO, and the prolonged half-life EPO analogue, darbepoetin in acute myocardial infarction (AMI) in rats. In a pilot study, EPO at 100U/mL significantly decreased cell death compared to vehicle (33.8±2.3% vs. 40.3±1.5%, p<0.05) in rat neonatal cardiomyocytes subjected to simulated ischemia/reperfusion. In further studies (studies 1-4), in vivo AMI was induced by 30min coronary occlusion and 120min reperfusion in male Wistar rats. Test compounds and positive controls for model validation (B-type natriuretic peptide, BNP or cyclosporine A, CsA) were administered iv. before the onset of reperfusion. Infarct size (IS) was measured by standard TTC staining. In study 1, 5000U/kg EPO reduced infarct size significantly compared to vehicle (45.3±4.8% vs. 59.8±4.5%, p<0.05). In study 2, darbepoetin showed a U-shaped dose-response curve with maximal infarct size-reducing effect at 5μg/kg compared to the vehicle (44.4±5.7% vs. 65.9±2.7%, p<0.01). In study 3, AF41676 showed a U-shaped dose-response curve, where 3mg/kg was the most effective dose compared to the vehicle (24.1±3.9% vs. 44.3±2.5%, p<0.001). The positive control BNP significantly decreased infarct size in studies 1-3 by approximately 35%. In study 4, AF43136 at 10mg/kg decreased infarct size, similarly to the positive control CsA compared to the appropriate vehicle (39.4±5.9% vs. 58.1±5.4% and 45.9±2.4% vs. 63.8±4.1%, p<0.05, respectively). This is the first demonstration that selective, non-erythropoietic EPO receptor ligand dimeric peptides AF41676 and AF43136 administered before reperfusion are able to reduce infarct size in a rat model of AMI. Therefore, non-erythropoietic EPO receptor peptide ligands may be promising cardioprotective agents., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Context: The activation of the renin-angiotensin-aldosterone system (RAAS) plays an important role in the pathophysiology of congestive heart failure, which is the reason that angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin 2 receptor blockers (ARBs) have become established therapies for heart failure. However, it is still not known whether preventive treatment with losartan or enalapril can reduce symptoms of infarction-induced heart failure. Ultra-low dose (ULD) drug therapy is thought to exert specific activity, with a lower chance of side effects. OBJECTIVES • The research team had hypothesized that preventive treatment with inhibitors of RAAS signaling-losartan, enalapril, and a preparation of a ULD antibody (ie, cardosten), which target the angiotensin type 1 (AT1) receptor-might alleviate pathological hypertrophy and/or functional decline in infarction-induced heart failure., Methods: The research team treated male Wistar rats orally for 30 d with 20 mg/kg of losartan, 10 mg/kg enalapril, 5 or 7.5 mL/kg of cardosten, or a control solution, started 1 d prior to permanent coronary occlusion. A sham-operated group functioned as a second control group., Settings: The study was conducted at the Department of Biochemistry of the Faculty of Medicine at the University of Szeged in Szeged, Hungary, in cooperation with the Pharmahungary Group, also in Szeged, Hungary, and with OOO "NPF" Materia Medica Holding Ltd in Moscow, Russia., Outcome Measures: To determine cardiac functional parameters in vivo, the research team inserted a catheter into the left ventricle of the rats and measured the parameters of ventricular pressure, and cardiac output was determined by thermodilution. Morphological parameters were measured after heart isolation in transverse sections by a digital caliper., Results: A total of 30 d after permanent coronary ligation, both losartan and enalapril, significantly decreased mean arterial blood pressure (MABP), attenuated the development of the left-ventricular anterior-wall and septum hypertrophy, and reduced scar thickness compared with the vehicle control group. The deterioration of cardiac output and the increase in total peripheral resistance (TPR) due to coronary ligation were significantly inhibited by both losartan and enalapril. The effects of cardosten were comparable with those of losartan and enalapril on cardiac morphology, left ventricular function, and TPR; however, it did not influence MABP. Moreover, in contrast to losartan and enalapril, cardosten did not decrease the rate of survival., Conclusions: The study was the first to have demonstrated that preventive treatment with losartan, enalapril, or cardosten can attenuate pathological hypertrophy in infarction-induced heart failure in rats.

We aimed to characterize early changes in microRNA expression in acute cardioprotection by ischemic pre- and postconditioning in rat hearts. Hearts isolated from male Wistar rats were subjected to 1) time-matched nonischemic perfusion, 2) ischemia-reperfusion (30 min of coronary occlusion and 120 min of reperfusion), 3) preconditioning (3 × 5 min of coronary occlusion) followed by ischemia-reperfusion, or 4) ischemia-reperfusion with postconditioning (6 × 10 s of global ischemia-reperfusion at the onset of reperfusion). Infarct size was significantly reduced by both interventions. Of 350 different microRNAs assessed by microarray analysis, 147-160 microRNAs showed detectable expression levels. Compared with microRNA alterations induced by ischemia-reperfusion versus time-matched nonischemic controls, five microRNAs were significantly affected by both pre- and postconditioning (microRNA-125b*, microRNA-139-3p, microRNA-320, microRNA-532-3p, and microRNA-188), four microRNAs were significantly affected by preconditioning (microRNA-487b, microRNA-139-5p, microRNA-192, and microRNA-212), and nine microRNAs were significantly affected by postconditioning (microRNA-1, microRNA let-7i, microRNA let-7e, microRNA let-7b, microRNA-181a, microRNA-208, microRNA-328, microRNA-335, and microRNA-503). Expression of randomly selected microRNAs was validated by quantitative real-time PCR. By a systematic comparison of the direction of microRNA expression changes in all groups, we identified microRNAs, specific mimics, or antagomiRs that may have pre- and postconditioning-like cardioprotective effects (protectomiRs). Transfection of selected protectomiRs (mimics of microRNA-139-5p, microRNA-125b*, microRNA let-7b, and inhibitor of microRNA-487b) into cardiac myocytes subjected to simulated ischemia-reperfusion showed a significant cytoprotective effect. This is the first demonstration that the ischemia-reperfusion-induced microRNA expression profile is significantly influenced by both pre- and postconditioning, which shows the involvement of microRNAs in cardioprotective signaling. Moreover, by analysis of microRNA expression patterns in cardioprotection by pre- and postconditioning, specific protectomiRs can be revealed as potential therapeutic tools for the treatment of ischemia-reperfusion injury., (Copyright © 2014 the American Physiological Society.)

Background: Although complex multivitamin products are widely used as dietary supplements to maintain health or as special medical food in certain diseases, the effects of these products were not investigated in hyperlipidemia which is a major risk factor for cardiovascular diseases. Therefore, here we investigated if a preparation developed for human use containing different vitamins, minerals and trace elements enriched with phytosterol (VMTP) affects the severity of experimental hyperlipidemia as well as myocardial ischemia/reperfusion injury., Methods: Male Wistar rats were fed a normal or cholesterol-enriched (2% cholesterol + 0.25% cholate) diet for 12 weeks to induce hyperlipidemia. From week 8, rats in both groups were fed with a VMTP preparation or placebo for 4 weeks. Serum triglyceride and cholesterol levels were measured at week 0, 8 and 12. At week 12, hearts were isolated, perfused according to Langendorff and subjected to a 30-min coronary occlusion followed by 120 min reperfusion to measure infarct size., Results: At week 8, cholesterol-fed rats showed significantly higher serum cholesterol level as compared to normal animals, however, serum triglyceride level did not change. VMTP treatment significantly decreased serum cholesterol level in the hyperlipidemic group by week 12 without affecting triglyceride levels. However, VMTP did not show beneficial effect on infarct size. The inflammatory marker hs-CRP and the antioxidant uric acid were also not significantly different., Conclusions: This is the first demonstration that treatment of hyperlipidemic subjects with a VMTP preparation reduces serum cholesterol, the major risk factor for cardiovascular disease; however, it does not provide cardioprotection.

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.

Cardioprotection by ischemic preconditioning (IP) was abolished in connexin 43 (Cx43)-deficient mice due to loss of Cx43 located in mitochondria rather than at the sarcolemma. IP is lost in hyperlipidemic rat hearts as well. Since changes in mitochondrial Cx43 in hyperlipidemia have not yet been analyzed, we determined total and mitochondrial Cx43 levels in male Wistar rats fed a laboratory chow enriched with 2% cholesterol or normal chow for 12 wk. Hearts were isolated and perfused according to Langendorff. After a 10-min perfusion, myocardial tissue cholesterol, superoxide, and nitrotyrosine contents were measured and Cx43 content in whole heart homogenate and a mitochondrial fraction determined. In the cholesterol-fed group, tissue cholesterol and superoxide formation was increased (P < 0.05), while total Cx43 content remained unchanged. Mitochondrial total and dephosphorylated Cx43 content decreased. Hearts were subjected to an IP protocol (3 × 5 min ischemia-reperfusion) or time-matched aerobic perfusion followed by 30-min global ischemia and 5-min reperfusion. IP reduced infarct size in normal but not in cholesterol-fed rats. At 5-min reperfusion following 30-min global ischemia, the total and dephosphorylated mitochondrial Cx43 content was increased, which was abolished by IP in both normal and high-cholesterol diet. In conclusion, loss of cardioprotection by IP in hyperlipidemia is associated with a redistribution of both sarcolemmal and mitochondrial Cx43.

We have previously shown that the inhibition of myocardial nitric oxide (NO) and peroxynitrite-matrix metalloproteinase (MMP) signaling by early preconditioning (PC) is involved in its cardioprotective effect. Therefore, in the present study, we investigated the role of NO and peroxynitrite-MMP signaling in the development of late PC. PC was performed by five consecutive cycles of 4-min coronary occlusion and 4-min reperfusion in anesthetized rats in vivo. Twenty-four hours later, hearts were subjected to a 30-min coronary occlusion followed by 180-min reperfusion to measure infarct size. In separate experiments, heart tissue was sampled to measure biochemical parameters before and 3, 6, 12, or 24 h after the PC protocol, respectively. Late PC decreased infarct size, increased cardiac inducible NO synthase (iNOS) activity and gene expression, and decreased SOD activity at 24 h significantly compared with sham-operated controls. Late PC increased cardiac superoxide levels significantly at 24 h; however, it did not change cardiac NO levels. Cardiac peroxynitrite levels were significantly decreased. Downstream cellular targets of peroxynitrite, MMP-2 and MMP-9 activities were decreased in the late PC group at 24 h compared with the sham-operated group. To verify if PC-induced inhibition of MMPs had a causative role in the reduction of infarct size, in separate experiments, we measured infarct size after the pharmacological inhibition of MMPs by ilomastat and found a significant reduction of infarct size compared with the vehicle-treated group. In conclusion, this is the first demonstration that the inhibition of cardiac peroxynitrite-MMP signaling contributes to cardioprotection by late PC and that pharmacological inhibition of MMPs is able to reduce infarct size in vivo. Furthermore, increased expression of iNOS may play a role in the development of late PC; however, increased iNOS activity does not lead to increased NO production in late PC.

Ischemic heart disease is a major cause of morbidity and mortality worldwide. Myocardial ischemia followed by reperfusion results in tissue injury termed ischemia/reperfusion injury which is characterized by decreased myocardial contractile function, occurrence of arrhythmias, and development of tissue necrosis (infarction). These pathologies are all relevant as clinical consequences of myocardial ischemia/reperfusion injury and they are also important as experimental correlates and endpoints. The most critical determinant of acute and long-term mortality after myocardial infarction is the volume of the infarcted tissue. Therefore, development of cardioprotective therapies aims at reducing the size of the infarct developing due to myocardial ischemia/reperfusion injury. Different techniques are available to measure myocardial infarct size in humans and in experimental settings, however, accurate determination of the extent of infarction is necessary to evaluate interventions that may delay the onset of necrosis and/or limit the total extent of infarct size during ischemia/reperfusion. This paper highlights recent advances of the different techniques to measure infarct size., (Copyright 2010 Elsevier Inc. All rights reserved.)

Hyperlipidemia attenuates the cardioprotective effect of preconditioning via unknown mechanisms. We have reported previously that in normolipidemic rats, preconditioning decreased ischemia-induced activation and release of myocardial matrix metalloproteinase (MMP)-2 into the coronary perfusate. Here, we investigated whether hyperlipidemia interferes with the cardioprotective effect of preconditioning through modulation of MMP-2. Hearts isolated from male Wistar rats fed 2% cholesterol-enriched or control chow for 9 weeks were subjected to a preconditioning protocol (three intermittent periods of ischemia/reperfusion of 5-min duration each) or a time-matched nonpreconditioning protocol. This was followed by a test ischemia/reperfusion (30-min ischemia and 120-min reperfusion) in both groups. Preconditioning decreased infarct size in the control but not the cholesterol-fed group. Cardioprotection in the preconditioned control group but not in the cholesterol-fed group was associated with an 18 +/- 3% (p < 0.05) inhibition of test ischemia/reperfusion-induced activation and release of myocardial MMP-2 into the perfusate. Myocardial protein levels of tissue inhibitors of MMPs [tissue inhibitor of metalloproteinases (TIMP)-2 and TIMP-4] were not changed in either group. A reduction of infarct size in nonpreconditioned hearts from both control and cholesterol-fed group was produced by the MMP inhibitor ilomastat at 0.25 microM, a concentration producing MMP-2 inhibition comparable with that of preconditioning in the control group. We conclude that hyperlipidemia blocks preconditioning-induced cardioprotection, hyperlipidemia abolishes preconditioning-induced inhibition of myocardial MMP-2 activation and release, preconditioning-induced inhibition of MMP-2 activation and release is not mediated by TIMPs, and pharmacological inhibition of MMPs produces cardioprotection in both normal and hyperlipidemic rats.

BackgroundIschemic preconditioning (IPC) and ischemic postconditioning (IPoC) are currently among the most efficient strategies protecting the heart against ischemia/reperfusion injury. However, the effect of IPC and IPoC on functional recovery following ischemia/reperfusion is less clear, particularly with regard to the specific receptor‐mediated signaling of the postischemic heart. The current article examines the effect of IPC or IPoC on the regulation and coupling of β‐adrenergic receptors and their effects on postischemic left ventricular function. Methods and ResultsThe β‐adrenergic signal transduction was analyzed in 3‐month‐old Wistar rats for each of the intervention strategies (Sham, ischemia/reperfusion, IPC, IPoC) immediately and 7 days after myocardial infarction. Directly after the infarction a cardioprotective potential was demonstrated for both IPC and IPoC: the infarct size was reduced, apoptosis and production of reactive oxygen species were lowered, and the myocardial tissue was preserved. Seven days after myocardial ischemia, only IPC hearts showed significant functional improvement. Along with a deterioration in fractional shortening, IPoC hearts no longer responded adequately to β‐adrenergic stimulation. The stabilization of β‐adrenergic receptor kinase‐2 via increased phosphorylation of Mdm2 (an E3‐ubiquitin ligase) was responsible for desensitization of β‐adrenergic receptors and identified as a characteristic specific to IPoC hearts. ConclusionsImmediately after myocardial infarction, rapid and transient activation of β‐adrenergic receptor kinase‐2 may be an appropriate means to protect the injured heart from excessive stress. In the long term, however, induction and stabilization of β‐adrenergic receptor kinase‐2, with the resultant loss of positive inotropic function, leads to the functional picture of heart failure.