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

Dyslipidemia and Efficacy of Remote Ischemic Conditioning in Acute Moderate Ischemic Stroke: A Post Hoc Analysis of the RICAMIS Study

BACKGROUND

Ischemic conditioning-induced cardioprotection was attenuated by dyslipidemia in some animal and clinical studies, which is not investigated in patients with stroke. We conducted a post hoc analysis of the RICAMIS (Remote Ischemic Conditioning for Acute Moderate Ischemic Stroke) trial to investigate the association of dyslipidemia on admission with the efficacy of remote ischemic conditioning (RIC).

METHODS AND RESULTS

In this analysis, eligible patients were divided into dyslipidemia and normal-lipid groups according to the levels of 4 blood lipid profiles (total cholesterol, triglycerides, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol), which were further subdivided into RIC and control subgroups. We analyzed the differences in functional outcome between RIC and control subgroups in dyslipidemia and normal-lipid patients, respectively, and the interaction effects of RIC treatment with blood lipid levels were evaluated. Among 1776 patients from intention-to-treat analysis, 1419 patients with data of blood lipid profiles were included in the final analysis. A significantly higher proportion of modified Rankin Scale score 0 to 1 was identified in the RIC versus control subgroup across the normal-total cholesterol group (69.9% versus 63.5%; P=0.04), normal-triglycerides group (68.1% versus 60.5%; P=0.016), high-low-density lipoprotein cholesterol group (65.7% versus 57.7%; P=0.025), and normal-high-density lipoprotein cholesterol group (68.3% versus 60.5%; P=0.005). Similar statistical trends were found in the high-total cholesterol group (62.8% versus 55.5%; P=0.059), high-triglycerides group (67.8% versus 60.1%; P=0.099), normal-low-density lipoprotein cholesterol group (69.8% versus 63.7%; P=0.105), but no statistical significance was found in the low-high-density lipoprotein cholesterol group (63.4% versus 61%; P=0.705). Furthermore, no significant interaction effect of RIC intervention by blood lipid profiles was found. Similar results were obtained for lipids as continuous variables.

CONCLUSIONS

Blood lipids on admission was not associated with the neuroprotective effect of RIC.

Preclinical multi-target strategies for myocardial ischemia-reperfusion injury

Despite promising breakthroughs in diagnosing and treating acute coronary syndromes, cardiovascular disease’s high global mortality rate remains indisputable. Nearly half of these patients died of ischemic heart disease. Primary percutaneous coronary intervention (PCI) and coronary artery bypass grafting can rapidly restore interrupted blood flow and become the most effective method for salvaging viable myocardium. However, restoring blood flow could increase the risk of other complications and myocardial cell death attributed to myocardial ischemia-reperfusion injury (IRI). How to reduce the damage of blood reperfusion to ischemic myocardium has become an urgent problem to be solved. In preclinical experiments, many treatments have substantial cardioprotective effects against myocardial IRI. However, the transition from these cardioprotective therapies to clinically beneficial therapies for patients with acute myocardial infarction remains elusive. The reasons for the failure of the clinical translation may be multi-faceted, and three points are summarized here: (1) Our understanding of the complex pathophysiological mechanisms of myocardial IRI is far from enough, and the classification of specific therapeutic targets is not rigorous, and not clear enough; (2) Most of the clinical patients have comorbidities, and single cardioprotective strategies including ischemia regulation strategies cannot exert their due cardioprotective effects under conditions of hyperglycemia, hypertension, hyperlipidemia, and aging; (3) Most preclinical experimental results are based on adult, healthy animal models. However, most clinical patients had comorbidities and received multiple drug treatments before reperfusion therapy. In 2019, COST Action proposed a multi-target drug combination initiative for prospective myocardial IRI; the optimal cardioprotective strategy may be a combination of additive or synergistic multi-target therapy, which we support. By establishing more reasonable preclinical models, screening multi-target drug combinations more in line with clinical practice will benefit the translation of clinical treatment strategies.

Mechanism of the hypoxia inducible factor 1/hypoxic response element pathway in rat myocardial ischemia/diazoxide post‑conditioning

Ischemic post-conditioning (IPO) and diazoxide post-conditioning (DPO) has been proven to reduce myocardial ischemia reperfusion injury (MIRI); however, the mechanisms of IPO/DPO are still not clear. The present study aimed to investigate whether mitochondrial ATP-sensitive potassium channels (mitoK_ATP) channels are activated by IPO/DPO, which may further activate the hypoxia inducible factor 1/hypoxic response element (HIF-1/HRE) pathway to mitigate MIRI. Using a Langendorff perfusion device, healthy male (250–300 g) Sprague Dawley rat hearts were randomly divided into the following groups. Group N was aerobically perfused with K-H solution for 120 min. Group ischaemia/reperfusion (I/R) was aerobically perfused for 20 min, then subjected to 40 min hypoxia plus 60 min reperfusion. Group IPO was treated like the I/R group, but with 10 sec of hypoxia plus 10 sec of reperfusion for six rounds before reperfusion. Group DPO was exposed to 50 µM diazoxide for 5 min before reperfusion and otherwise treated the same as group I/R. In groups IPO+5-hydroxydecanoic acid (5HD), DPO+5HD and I/R+5HD, exposure to 100 µM 5HD (a mitoK_ATP channel specific blocker) for 5 min before reperfusion as described for groups IPO, DPO and I/R, respectively. In groups IPO+2-methoxyestradiol (2ME2), DPO+2ME2 and I/R+2ME2, exposure to 2 µM 2ME2 (a HIF-1α specific blocker) for 10 min before reperfusion as described for groups IPO, DPO and I/R respectively. Cardiac hemodynamics, myocardial injury and the expression of HIF-1/HRE pathway [HIF-1α, heme oxygenase (HO-1), inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor (VEGF)] were detected in each group. The infarct size and mitochondrial Flameng scores of groups IPO/DPO were significantly decreased compared with the I/R group (P<0.05), but the myocardial protective effects of IPO/DPO could be eliminated by 5HD or 2ME2 (P<0.05). In addition, IPO/DPO could increase the mRNA expression of HIF-1α and the downstream factors of the HIF-1/HRE pathway (the mRNA and protein expression of HO-1, iNOS and VEGF; P<0.05). However, the myocardial protective effects and the activation the HIF-1/HRE pathway mediated by IPO/DPO could be eliminated by 5HD or 2ME2 (P<0.05). Therefore, the activation of the HIF-1/HRE pathway by opening mitoK_ATP channels may work with the mechanism of IPO/DPO in reducing MIRI.

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.

Signaling mediators modulated by cardioprotective interventions in healthy and diabetic myocardium with ischaemia-reperfusion injury

Ischaemic heart diseases are one of the major causes of death in the world. In most patients, ischaemic heart disease is coincident with other risk factors such as diabetes. Patients with diabetes are more prone to cardiac ischaemic dysfunctions including ischaemia-reperfusion injury. Ischaemic preconditioning, postconditioning and remote conditionings are reliable interventions to protect the myocardium against ischaemia-reperfusion injuries through activating various signaling pathways and intracellular mediators. Diabetes can disrupt the intracellular signaling cascades involved in these myocardial protections, and studies have revealed that cardioprotective effects of the conditioning interventions are diminished in the diabetic condition. The complex pathophysiology and poor prognosis of ischaemic heart disease among people with diabetes necessitate the investigation of the interaction of diabetes with ischaemia-reperfusion injury and cardioprotective mechanisms. Reducing the outcomes of ischaemia-reperfusion injury using targeted strategies would be particularly helpful in this population. In this study, we review the protective interventional signaling pathways and mediators which are activated by ischaemic conditioning strategies in healthy and diabetic myocardium with ischaemia-reperfusion injury.

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.

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.

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.

Effect of Ambrex (a herbal formulation) on hematological variables in hyperlipidemic rats

Cardiovascular and related disorders are one of the most common disease prevailing all over the world. Hyperlipidemic condition have been largely considered in the treatment of cardiovascular diseases. The present study was carried out to investigate the effect of Ambrex on hematological factors in hyperlipidemic rats and untreated hyperlipidemic rats. In this study, eighteen rats were randomly divided into three groups of six animals each. The groups received normal diet (Control Group A) high fat diet (HFD group B) and Ambrex treatment (Group C). After the study period, White Blood Cell (WBC), Red Blood Cell (RBC), hematocrit (HCT), Hemoglobin, platelet (PLT), lymphocytes, monocytes, granulocytes, Mean Corpuscular Hemoglobin Concentration (MCHC), plateletcrit (PCT), Mean Corpuscular Volume (MCV), Platelet Distribution Width (PDW), red cell distribution-standard deviation (RDW-SD), red cell distribution-correlation variance (RDW-CV), micro red blood cell (pRBC), macroRBC were measured using digital cell counter (MS9-3s). Hyperlipidemia increases markedly the PLT count. Administration of Ambrex appeared to significantly increase WBC, Lymphocytes, granulocytes. However, erythrocyte indices does not show statistically significant variations among the test groups and control groups. The findings demonstrated that Ambrex does not cause any significant undesirable alterations in hematological factors in male rats. Ambrex also enhances white blood cell concentration and lymphocytes which probably stimulate the immune defense mechanism.

Protective effect of olmesartan against cardiac ischemia/reperfusion injury in spontaneously hypertensive rats

Olmesartan, as a new angiotensin II receptor blocker, has shown beneficial effects on cardiovascular diseases. Nevertheless, the effect of olmesartan on ischemia/reperfusion (I/R) injury in the hypertensive heart has not been investigated. Therefore, the present study aimed to investigate the effect of olmesartan on I/R injury in spontaneously hypertensive rats (SHRs). Experimental groups were designed with a 2×2 factorial design for olmesartan and I/R effects. In the I/R group, the left anterior descending coronary artery (LAD) was ligated for 40 min followed by a 180-min reperfusion. In the sham group, SHRs underwent the same surgical procedure as the I/R group, with the exception that the suture passed under the LAD without being tightened. In the Olm-I/R group, the SHRs received olmesartan (5 mg/kg) for 4 weeks prior to surgery and other procedures were the same as for the I/R group. In the Olm-sham group, the SHRs received olmesartan (5 mg/kg) for 4 weeks prior to surgery and other procedures were the same as for the sham group. Infarct size was measured for the I/R and Olm-I/R groups. Blood pressure (BP), serum creatine kinase (CK), left ventricular mass index (LVMI), high mobility group box 1 (HMGB1) protein expression levels and hypoxia-inducible factor-1α (HIF-1α) mRNA expression levels were measured for all four groups. Olmesartan significantly reduced BP and LVMI in the olmesartan-treated SHRs compared with those in the SHRs that were not treated with olmesartan. HMGB1 and HIF-1α expression levels were significantly decreased in the Olm-sham and Olm-I/R groups compared with those in the sham and I/R groups, respectively. The proportional increase in HIF-1α expression due to I/R was greater in the olmesartan-treated rats than in the untreated rats. Serum CK levels were significantly reduced in the Olm-I/R group compared with those in the I/R group. In conclusion, olmesartan ameliorates left ventricular hypotrophy and protects the heart against I/R injury in addition to lowing BP in SHRs. The protective effect of olmesartan may be partly due to its antioxidative and anti-inflammatory properties.

Inhibition of Rho-kinase by fasudil restores the cardioprotection of ischemic postconditioninng in hypercholesterolemic rat heart

Ischemic postconditioning (IPoC) reduces lethal reperfusion injury under normal conditions, but its effectiveness is blocked by hypercholesterolemia. The present study aimed to determine whether the inhibition of Rho‑kinase by fasudil restores the cardioprotection of IPoC in the hypercholesterolemic rat heart, and to elucidate the potential mechanisms underlying this process. The isolated rat hearts underwent 30 min global ischemia and 120 min reperfusion. IPoC was induced by six cycles of 10 sec ischemia and 10 sec reperfusion at the onset of the reperfusion. Fasudil was administered 15 min prior to ischemia, and wortmannin and L‑NAME were administered following IPoC. The myocardial infarct size, apoptosis, myocardial nitric oxide (NO) content and Rho‑kinase activity, as well as the activation of the phosphatidylinositol 3‑kinase/Akt/endothelial nitric oxide synthase (PI3K/Akt/eNOS) pathway, were examined. The results revealed that IPoC and 1 µM fasudil treatment alone failed to reduce the infarct size and apoptosis rate. However, IPoC combined with 1 µM fasudil treatment or 10 µM fasudil treatment alone restored the cardioprotection as evidenced by the decreasing in infarct size and apoptosis rate, whereas it was blocked by the administration of wortmannin or L‑NAME. Furthermore, IPoC combined with 1 µM fasudil treatment also enhanced the phosphorylation of Akt and eNOS and conferred a significant increase in the content of NO. By contrast, no significant improvements were demonstrated in the phosphorylation of Akt and eNOS, as well as myocardial NO content when treated with 1 µM fasudil and IPoC alone. The inhibition of Rho‑kinase by fasudil was able to restore the cardioprotection of IPoC in the hypercholesterolemic rat heart. The underlying mechanisms involved in this process appear to be mediated by the activation of the PI3K/Akt/eNOS signal pathway and an increase in the myocardial NO content.

Effect of ambrex (a herbal formulation) on oxidative stress in hyperlipidemic rats and differentiation of 3T3-L1 preadipocytes

Background:

Ambrex is a polyherbal formulation which consists of Withania somnifera, Orchis mascula, Cycas circirnalis, Shorea robusta with amber.

Objective:

The present study was designed to explore the potential effects of ambrex on the antioxidant status in high fat diet fed rats and to investigate the possible mechanisms focusing on the gene expression involved in adipogenesis and inflammation in 3T3-L1 cell line.

Materials and Methods:

Male Wistar rats were divided into four groups (n = 6); Group A received normal diet, Group B received high fat diet for 30 days, Group C and D received high fat diet for 30 days and treated with ambrex (40 mg/kg b.w) and atorvastatin (10 mg/kg b.w) for successive 15 days respectively. This study also assesses the effect of ambrex on adipogenesis in 3T3-L1 adipocytes.

Results:

The serum total cholesterol and triglycerides were significantly decreased in ambrex treated hyperlipidemic animals when compared to untreated animals. The activities of catalase, superoxide dismutase and reduced glutathione were significantly augmented in the serum, liver, and heart of hyperlipidemic rats treated with ambrex when compared to control. Ambrex treated rats had significant reductions in malondiadehyde levels in the serum, liver and heart compared to untreated rats. In addition, we observed that treatment with ambrex resulted in a major inhibition of pre-adipocyte differentiation of 3T3-L1 cells in vitro by suppression of peroxisome proliferator activated receptor gamma, sterol regulatory binding proteins, tumor necrosis factor-α, inducible nitricoxide synthase, leptin, and upregulation of thioredoxin 1 (TRX1) and TRX2 mRNA expression.

Conclusion:

Therefore, ambrex may be a potential drug for treatment of hyperlipidemia and related disorders.

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

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

High‑dose fasudil preconditioning and postconditioning attenuate myocardial ischemia‑reperfusion injury in hypercholesterolemic rats

Fasudil may induce preconditioning and postconditioning against myocardial ischemia‑reperfusion injury in normal rats, however, their effectivenesses in hypercholesterolemia remains to be determined. The study aimed to investigate whether fasudil induces preconditioning and postconditioning in hypercholesterolemic rats and to determine the roles of the phosphoinositol 3‑kinase (PI3K)/Akt/endothelial nitric oxide synthase (eNOS) pathway and mitochondrial KATP (m‑KATP) channels in this process. Isolated rat hearts underwent 30 min global ischemia and 120 min reperfusion. Low‑ (1 mg/kg) or high‑dose (10 mg/kg) fasudil was administered 15 min prior to ischemia and at the initial onset of reperfusion. 5‑Hydroxydecanoic acid (5HD), an m‑KATP channel blocker, at 10 mg/kg was administered 5 min prior to reperfusion. Myocardial infarct size was estimated by 2,3,5‑triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) and creatine kinase‑MB (CK‑MB) were analyzed from coronary effluents. Phosphorylation of Akt and eNOS was measured by immunoblotting. High‑dose fasudil‑induced preconditioning and postconditioning significantly reduced infarct size and the release of LDH and CK‑MB and increased the phosphorylation of Akt and eNOS compared with the control group, whereas low‑dose fasudil did not exert these beneficial effects. In addition, the cardioprotection of high‑dose fasudil‑induced preconditioning and postconditioning are blocked by 5HD. Low‑dose fasudil‑induced preconditioning and postconditioning are abrogated by hypercholesterolemia, while high‑dose fasudil restores the cardioprotection, which is involved in upregulation of the PI3K/Akt/eNOS pathway and inducing the opening of the m‑KATP channel.

Hypercholesterolemic myocardium is vulnerable to ischemia-reperfusion injury and refractory to sevoflurane-induced protection

Recent studies have demonstrated that volatile anesthetic postconditioning confers myocardial protection against ischemia-reperfusion (IR) injury through activation of the reperfusion injury salvage kinase (RISK) pathway. As RISK has been shown to be impaired in hypercholesterolemia. Therefore, we investigate whether anesthetic-induced cardiac protection was maintained in hypercholesterolemic rats. In the present study, normocholesteolemic or hypercholesterolemic rat hearts were subjected to 30 min of ischemia and 2 h of reperfusion. Animals received 2.4% sevoflurane for 5 min or 3 cycles of 10-s ischemia/10-s reperfusion. The hemodynamic parameters, including left ventricular developed pressure, left ventricular end-diastolic pressure and heart rate, were continuously monitored. The infarct size, apoptosis, p-Akt, p-ERK1/2, p-GSK3β were determined. We found that both sevoflurane and ischemic postconditioning significantly improved heart pump function, reduced infarct size and increased the phosphorylation of Akt, ERK1/2 and their downstream target of GSK3β in the healthy rats. In the hypercholesterolemic rats, neither sevoflurane nor ischemic postconditioning improved left ventricular hemodynamics, reduced infarct size and increased the phosphorylated Akt, ERK1/2 and GSK3β. In contrast, GSK inhibitor SB216763 conferred cardioprotection against IR injury in healthy and hypercholesterolemic hearts. In conclusions, hyperchoesterolemia abrogated sevoflurane-induced cardioprotection against IR injury by alteration of upstream signaling of GSK3β and acute GSK inhibition may provide a novel therapeutic strategy to protect hypercholesterolemic hearts against IR injury.

Hypercholesterolemia blocked sevoflurane-induced cardioprotection against ischemia-reperfusion injury by alteration of the MG53/RISK/GSK3β signaling

BACKGROUND

Recent studies have demonstrated that volatile anesthetic preconditioning confers myocardial protection against ischemia-reperfusion (IR) injury through activation of the reperfusion injury salvage kinase (RISK) pathway. As RISK has been shown to be impaired in hypercholesterolemia, we investigate whether anesthetic-induced cardiac protection was maintained in hypercholesterolemic rats.

METHODS

Normocholesteolemic or hypercholesterolemic rat hearts were subjected to 30 min of ischemia and 2 h of reperfusion. Animals received 2.4% sevoflurane during three 5 min periods with and without PI3K antagonist wortmannin (10 μg/kg, Wort) or the ERK inhibitor PD 98059 (1 mg/kg, PD). The infarct size, apoptosis, p-Akt, p-ERK1/2, p-GSK3β were determined.

RESULTS

Two hundred and six rats were analyzed in the study. In the healthy rats, sevoflurane significantly reduced infarct size by 42%, a phenomenon completely reversed by wortmannin and PD98059 and increased the phosphorylation of Akt, ERK1/2 and their downstream target of GSK3β. In the hypercholesterolemic rats, sevoflurane failed to reduce infarct size and increase the phosphorylated Akt, ERK1/2 and GSK3β. In contrast, GSK inhibitor SB216763 conferred cardioprotection against IR injury in healthy and hypercholesterolemic hearts.

CONCLUSIONS

Hyperchoesterolemia abrogated sevoflurane-induced cardioprotection against IR injury by alteration of upstream signaling of GSK3β and acute GSK inhibition may provide a novel therapeutic strategy to protect hypercholesterolemic hearts against IR injury.

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.

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.

Hypoxia-inducible factor as a therapeutic target for cardioprotection

Hypoxia inducible factor (HIF) is an oxygen-sensitive transcription factor that enables aerobic organisms to adapt to hypoxia. This is achieved through the transcriptional activation of up to 200 genes, many of which are critical to cell survival. Under conditions of normoxia, the hydroxylation of HIF by prolyl hydroxylase domain-containing (PHD) enzymes targets it for polyubiquitination and proteosomal degradation by the von Hippel-Lindau protein (VHL). However, under hypoxic conditions, PHD activity is inhibited, thereby allowing HIF to accumulate and translocate to the nucleus, where it binds to the hypoxia-responsive element sequences of target gene promoters. Experimental studies suggest that HIF may act as a mediator of ischemic preconditioning, and that the genetic or pharmacological stabilization of HIF under normoxic conditions, may protect the heart against the detrimental effects of acute ischemia-reperfusion injury. The mechanisms underlying the cardioprotective effect of HIF are unclear, but it may be attributed to the transcriptional activation of genes associated with cardioprotection such as erythropoietin, heme oxygenase-1, and inducible nitric oxide synthase or it may be due to reprogramming of cell metabolism. In this review article, we highlight the role of HIF in mediating both adaptive and pathological processes in the heart, as well as focusing on the therapeutic potential of the HIF-signaling pathway as a target for cardioprotection.

Endogenous cardioprotection by ischaemic postconditioning and remote conditioning

Persistent myocardial ischaemia causes cell death if not rescued by early reperfusion. Millions of years in nature's laboratory have evolved protective responses that 'condition' the heart (and other tissues) to adapt to stressors, and these responses are applicable to the relatively new societal stress of myocardial ischaemia and reperfusion injury. Conditioning can be applied before (preconditioning), during (perconditioning), or after (postconditioning) the ischaemic stressor by imposing short periods of non-lethal ischaemia separated by brief periods of reperfusion. This conditioning protects multiple cell types and induces or rebalances a number of physiological and molecular pathways that ultimately attenuate necrosis and apoptosis. The seemingly disparate pathways may converge directly or indirectly on the mitochondria as a final effector, but other pathways not affecting mitochondria broaden the mechanisms of cardioprotection. The potential downsides of imposing even brief ischaemia directly on the heart somewhat tempered the enthusiasm for applying conditioning stimuli to the heart, but this hurdle was surmounted by applying ischaemia to remote organs and tissues in pre-, per-, and postconditioning. Although the clinical translation of remote per- and postconditioning has been rapid compared with classical preconditioning, there are numerous basic questions that require further investigation, and wider adoption awaits large-scale randomized clinical trials. Pharmacological mimetics may provide another important therapeutic approach by which to treat evolving myocardial infarction.

The multidimensional physiological responses to postconditioning

Reperfusion is the definitive treatment to reduce infarct size and other manifestations of postischemic injury. However, reperfusion contributes to postischemic injury, and, therefore, reperfusion therapies do not achieve the optimal salvage of myocardium. Other tissues as well undergo injury after reperfusion, notably, the coronary vascular endothelium. Postconditioning has been shown to have salubrious effects on different tissue types within the heart (cardiomyocytes, endothelium) and to protect against various pathologic processes, including necrosis, apoptosis, contractile dysfunction, arrhythmias, and microvascular injury or "no-reflow." The mechanisms by which postconditioning alters the pathophysiology of reperfusion injury is exceedingly complex and involves physiological mechanisms (e.g., delaying re-alkalinization of tissue pH, triggering release of autacoids, and opening and closing of various channels) and molecular mechanisms (activation of kinases) that affect cellular and subcellular targets or effectors. The physiologic responses to postconditioning are not isolated or mutually exclusive, but are interactive, with one response affecting another in an integrated manner. This integrated response on multiple targets differs from the monotherapy approach by drugs that have failed to reduce reperfusion injury on a consistent basis and may underlie the efficacy of this therapeutic approach across species and in human trials.

Hypoxia inducible factor 1 (HIF-1) and cardioprotection

Since its discovery in early 1990s, hypoxia inducible factor 1 (HIF-1) has been increasingly recognized for its key role in transcriptional control of more than a hundred genes that regulate a wide-spectrum of cellular functional events, including angiogenesis, vasomotor control, glucose and energy metabolism, erythropoiesis, iron homeostasis, pH regulation, cell proliferation and viability. Evidence accumulated during the past 7 years suggests a critical role for HIF-1alpha in mediating cardioprotection. The purpose of our present article is to provide an updated overview on this important regulator of gene expression in the cellular stress-responsive and adaptive process. We have particularly emphasized the involvement of HIF-1 in the induction of cardioprotective molecules, such as inducible nitric oxide synthase (iNOS), hemeoxygenase 1 (HO-1), and erythropoietin (EPO), which in turn alleviate myocardial damages caused by harmful events such as ischemia-reperfusion injury. Despite these advances, further in-depth studies are needed to elucidate the possible coordination or interaction between HIF-1alpha and other key transcription factors in regulating protein expression that leads to cardioprotection.