Chronic treatment with rofecoxib but not ischemic preconditioning of the myocardium ameliorates early intestinal damage following cardiac ischemia/reperfusion injury in rats

There is some recent evidence that cardiac ischemia/reperfusion (I/R) injury induces intestinal damage within days, which contributes to adverse cardiovascular outcomes after myocardial infarction. However, it is not clear whether remote gut injury has any detectable early signs, and whether different interventions aiming to reduce cardiac damage are also effective at protecting the intestine. Previously, we found that chronic treatment with rofecoxib, a selective inhibitor of cyclooxygenase-2 (COX-2), limited myocardial infarct size to a comparable extent as cardiac ischemic preconditioning (IPC) in rats subjected to 30-min coronary artery occlusion and 120-min reperfusion. In the present study, we aimed to analyse the early intestinal alterations caused by cardiac I/R injury, with or without the above-mentioned infart size-limiting interventions. We found that cardiac I/R injury induced histological changes in the small intestine within 2 h, which were accompanied by elevated tissue level of COX-2 and showed positive correlation with the activity of matrix metalloproteinase-2 (MMP-2), but not of MMP-9 in the plasma. All these changes were prevented by rofecoxib treatment. By contrast, cardiac IPC failed to reduce intestinal injury and plasma MMP-2 activity, although it prevented the transient reduction in jejunal blood flow in response to cardiac I/R. Our results demonstrate for the first time that rapid development of intestinal damage follows cardiac I/R, and that two similarly effective infarct size-limiting interventions, rofecoxib treatment and cardiac IPC, have different impacts on cardiac I/R-induced gut injury. Furthermore, intestinal damage correlates with plasma MMP-2 activity, which may be a biomarker for its early diagnosis

Hidden Cardiotoxicity of Rofecoxib Can be Revealed in Experimental Models of Ischemia/Reperfusion

Cardiac adverse effects are among the leading causes of the discontinuation of clinical trials and the withdrawal of drugs from the market. The novel concept of 'hidden cardiotoxicity' is defined as cardiotoxicity of a drug that manifests in the diseased (e.g. ischemic/reperfused), but not in the healthy heart or as a drug-induced deterioration of cardiac stress adaptation (e.g. ischemic conditioning). Here, we aimed to test if the cardiotoxicity of a selective COX-2 inhibitor rofecoxib that was revealed during its clinical use, i.e., increased occurrence of proarrhythmic and thrombotic events, could have been revealed in early phases of drug development by using preclinical models of ischemia/reperfusion (I/R) injury. Rats that were treated with rofecoxib or vehicle for four weeks were subjected to 30 min. coronary artery occlusion and 120 min. reperfusion with or without cardioprotection that is induced by ischemic preconditioning (IPC). Rofecoxib increased overall the arrhythmias including ventricular fibrillation (VF) during I/R. The proarrhythmic effect of rofecoxib during I/R was not observed in the IPC group. Rofecoxib prolonged the action potential duration (APD) in isolated papillary muscles, which was not seen in the simulated IPC group. Interestingly, while showing hidden cardiotoxicity manifested as a proarrhythmic effect during I/R, rofecoxib decreased the infarct size and increased the survival of adult rat cardiac myocytes that were subjected to simulated I/R injury. This is the first demonstration that rofecoxib increased acute mortality due to its proarrhythmic effect via increased APD during I/R. Rofecoxib did not interfere with the cardiprotective effect of IPC; moreover, IPC was able to protect against rofecoxib-induced hidden cardiotoxicity. These results show that cardiac safety testing with simple preclinical models of I/R injury uncovers hidden cardiotoxicity of rofecoxib and might reveal the hidden cardiotoxicity of other drugs

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 microg 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

Protection of neonatal rat cardiac myocytes against radiation-induced damage with agonists of growth hormone-releasing hormone

[Display omitted] Despite the great clinical significance of radiation-induced cardiac damage, experimental investigation of its mechanisms is an unmet need in medicine. Beneficial effects of growth hormone-releasing hormone (GHRH) agonists in regeneration of the heart have been demonstrated. The aim of this study was the evaluation of the potential of modern GHRH agonistic analogs in prevention of radiation damage in an in vitro cardiac myocyte-based model. Cultures of cardiac myocytes isolated from newborn rats (NRVM) were exposed to a radiation dose of 10Gy. The effects of the agonistic analogs, JI-34 and MR-356, of human GHRH on cell viability, proliferation, their mechanism of action and the protein expression of the GHRH/SV1 receptors were studied. JI-34 and MR-356, had no effect on cell viability or proliferation in unirradiated cultures. However, in irradiated cells JI-34 showed protective effects on cell viability at concentrations of 10 and 100nM, and MR-356 at 500nM; but no such protective effect was detected on cell proliferation. Both agonistic analogs decreased radiation-induced ROS level and JI-34 interfered with the activation of SAFE/RISK pathways. Using Western blot analysis, a 52kDa protein isoform of GHRHR was detected in the samples in both irradiated and unirradiated cells. Since GHRH agonistic analogs, JI-34 and MR-356 alleviated radiation-induced damage of cardiac myocytes, they should be tested in vivo as potential protective agents against radiogenic heart damage