Diabetes and hyperglycemia impair activation of mitochondrial K(ATP) channels

Acute Hyperglycemia-Induced Injury in Myocardial Infarction

Acute hyperglycemia is a transient increase in plasma glucose level (PGL) frequently observed in patients with ST-elevation myocardial infarction (STEMI). The aim of this review is to clarify the molecular mechanisms whereby acute hyperglycemia impacts coronary flow and myocardial perfusion in patients with acute myocardial infarction (AMI) and to discuss the consequent clinical and prognostic implications. We conducted a comprehensive literature review on the molecular causes of myocardial damage driven by acute hyperglycemia in the context of AMI. The negative impact of high PGL on admission recognizes a multifactorial etiology involving endothelial function, oxidative stress, production of leukocyte adhesion molecules, platelet aggregation, and activation of the coagulation cascade. The current evidence suggests that all these pathophysiological mechanisms compromise myocardial perfusion as a whole and not only in the culprit coronary artery. Acute hyperglycemia on admission, regardless of whether or not in the context of a diabetes mellitus history, could be, thus, identified as a predictor of worse myocardial reperfusion and poorer prognosis in patients with AMI. In order to reduce hyperglycemia-related complications, it seems rational to pursue in these patients an adequate and quick control of PGL, despite the best pharmacological treatment for acute hyperglycemia still remaining a matter of debate.

Nitric Oxide/Glucose Transporter Type 4 Pathway Mediates Cardioprotection against Ischemia/Reperfusion Injury under Hyperglycemic and Diabetic Conditions in Rats

INTRODUCTION

The comorbidities of ischemic heart disease (IHD) and diabetes mellitus (DM) compromise the protection of the diabetic heart from ischemia/reperfusion (I/R) injury. We hypothesized that manipulation of reperfusion injury salvage kinase (RISK) and survivor activating factor enhancement (SAFE) pathways might protect the diabetic heart, and intervention of these pathways could be a new avenue for potentially protecting the diabetic heart.

METHODS

All hearts were subjected to 30-min ischemia and 30-min reperfusion. During reperfusion, hearts were exposed to molecules proven to protect the heart from I/R injury. The hemodynamic data were collected using suitable software. The infarct size, troponin T levels, and protein levels in hearts were evaluated.

RESULTS

Both cyclosporine-A and nitric oxide donor (SNAP) infusion at reperfusion protected 4-week diabetic hearts from I/R injury. However, 6-week diabetic hearts were protected only by SNAP, but not cyclosporin-A. These treatments significantly (p < 0.05) improved cardiac hemodynamics and decreased infarct size.

CONCLUSIONS

The administration of SNAP to diabetic hearts protected both 4- and 6-week diabetic hearts; however, cyclosporine-A protected only the 4-week diabetic hearts. The eNOS/GLUT-4 pathway executed the SNAP-mediated cardioprotection.

KATP channels are regulators of programmed cell death and targets for the creation of novel drugs against ischemia/reperfusion cardiac injury

BACKGROUND

The use of percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI) is associated with a mortality rate of 5%-7%. It is clear that there is an urgent need to develop new drugs that can effectively prevent cardiac reperfusion injury. ATP-sensitive K+ (KATP ) channel openers (KCOs) can be classified as such drugs.

RESULTS

KCOs prevent irreversible ischemia and reperfusion injury of the heart. KATP channel opening promotes inhibition of apoptosis, necroptosis, pyroptosis, and stimulation of autophagy. KCOs prevent the development of cardiac adverse remodeling and improve cardiac contractility in reperfusion. KCOs exhibit antiarrhythmic properties and prevent the appearance of the no-reflow phenomenon in animals with coronary artery occlusion and reperfusion. Diabetes mellitus and a cholesterol-enriched diet abolish the cardioprotective effect of KCOs. Nicorandil, a KCO, attenuates major adverse cardiovascular event and the no-reflow phenomenon, reduces infarct size, and decreases the incidence of ventricular arrhythmias in patients with acute myocardial infarction.

CONCLUSION

The cardioprotective effect of KCOs is mediated by the opening of mitochondrial KATP (mitoKATP ) and sarcolemmal KATP (sarcKATP ) channels, triggered free radicals' production, and kinase activation.

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.

Risk Factors for No-Reflow in Patients with ST-Elevation Myocardial Infarction Who Underwent Percutaneous Coronary Intervention: A Case-Control Study

Methods

This case-control study retrospectively reviewed the medical data of patients treated with primary percutaneous coronary intervention within 12 h after STEMI onset between January 2010 and January 2013 at the Department of Cardiology of the Beijing Anzhen Hospital.

Results

A total of 902 patients were included in the analysis. The basic characteristics between the reflow and no-reflow groups were similar, except for time-to-hospital admission, heart rate, plasma glucose, high-sensitivity C-reactive protein (hsCRP)/prealbumin (PAB), neutrophil count, intraaortic balloon pump, and aspiration thrombectomy. The multivariable analysis showed that hsCRP/PAB (OR = 1.003, 95% CI: 1.000–1.006, P=0.022), neutrophil count (OR = 1.085, 95% CI: 1.028–1.146, P=0.003), plasma glucose levels (OR = 1.086, 95% CI: 1.036–1.138, P=0.001), diabetes mellitus (OR = 0.596, 95% CI: 0.371–0.958, P=0.033), Killip classification >1 (OR = 2.002, 95% CI: 1.273–3.148, P=0.003), intraoperative intraaortic balloon pump (IABP) use (OR = 3.257, 95% CI: 1.954–5.428, P=0.001), and aspiration thrombectomy (OR = 3.412, 95% CI: 2.259–5.152, P=0.001) were independently associated with no-reflow.

Conclusion

hsCRP/PAB, neutrophil count, plasma glucose levels, diabetes mellitus, Killip classification, intraoperative IABP use, and aspiration thrombectomy were independent risk factors for no-reflow in patients with STEMI.

Cardioprotective Properties of Humoral Factors Released after Remote Ischemic Preconditioning in CABG Patients with Propofol-Free Anesthesia-A Translational Approach from Bedside to Bench

The cardioprotective effect of remote ischemic preconditioning (RIPC) is well detectable in experimental studies but not in clinical trials. Propofol, a commonly used sedative, is discussed to negatively influence the release of humoral factors after RIPC. Further, results from experimental and clinical trials suggest various comorbidities interact with inducible cardioprotective properties of RIPC. In the present study, we went back from bedside to bench to investigate, in male patients undergoing CABG surgery, whether (1) humoral factors are released after RIPC during propofol-free anesthesia and/or (2) DM interacts with plasma factor release. Blood samples were taken from male patients with and without DM undergoing CABG surgery before (control) and after RIPC (RIPC). To investigate the release of cardioprotective humoral factors into the plasma, isolated perfused hearts of young rats (n = 5 per group) were used as a bioassay. The hearts were perfused with patients’ plasma without (Con) and with RIPC (RIPC) for 10 min (1% of coronary flow) before global ischemia and reperfusion. In additional groups, the plasma of patients with DM was administered (Con DM, RIPC DM). Infarct size was determined by TTC staining. Propofol-free RIPC plasma of male patients without DM showed an infarct size of 59 ± 5% compared to 61 ± 13% with Con plasma (p = 0.973). Infarct sizes from patients with DM showed similar results (RIPC DM: 55 ± 3% vs. Con DM: 56 ± 4%; p = 0.995). The release of humoral factors into the blood after RIPC in patients receiving propofol-free anesthesia undergoing CABG surgery did not show any cardioprotective properties independent of a pre-existing diabetes mellitus.

Influence of Hyperglycemia and Diabetes on Cardioprotection by Humoral Factors Released after Remote Ischemic Preconditioning (RIPC)

Remote ischemic preconditioning (RIPC) protects hearts from ischemia-reperfusion (I/R) injury in experimental studies; however, clinical RIPC trials were unsatisfactory. This discrepancy could be caused by a loss of cardioprotection due to comorbidities in patients, including diabetes mellitus (DM) and hyperglycemia (HG). RIPC is discussed to confer protective properties by release of different humoral factors activating cardioprotective signaling cascades. Therefore, we investigated whether DM type 1 and/or HG (1) inhibit the release of humoral factors after RIPC and/or (2) block the cardioprotective effect directly at the myocardium. Experiments were performed on male Wistar rats. Animals in part 1 of the study were either healthy normoglycemic (NG), type 1 diabetic (DM1), or hyperglycemic (HG). RIPC was implemented by four cycles of 5 min bilateral hind-limb ischemia/reperfusion. Control (Con) animals were not treated. Blood plasma taken in vivo was further investigated in isolated rat hearts in vitro. Plasma from diseased animals (DM1 or HG) was administered onto healthy (NG) hearts for 10 min before 33 min of global ischemia and 60 min of reperfusion. Part 2 of the study was performed vice versa-plasma taken in vivo, with or without RIPC, from healthy rats was transferred to DM1 and HG hearts in vitro. Infarct size was determined by TTC staining. Part 1: RIPC plasma from NG (NG Con: 49 ± 8% vs. NG RIPC 29 ± 6%; p < 0.05) and DM1 animals (DM1 Con: 47 ± 7% vs. DM1 RIPC: 38 ± 7%; p < 0.05) reduced infarct size. Interestingly, transfer of HG plasma showed comparable infarct sizes independent of prior treatment (HG Con: 34 ± 9% vs. HG RIPC 35 ± 9%; ns). Part 2: No infarct size reduction was detectable when transferring RIPC plasma from healthy rats to DM1 (DM1 Con: 54 ± 13% vs. DM1 RIPC 53 ± 10%; ns) or HG hearts (HG Con: 60 ± 16% vs. HG RIPC 53 ± 14%; ns). These results suggest that: (1) RIPC under NG and DM1 induces the release of humoral factors with cardioprotective impact, (2) HG plasma might own cardioprotective properties, and (3) RIPC does not confer cardioprotection in DM1 and HG myocardium.

Comparative evaluation of cardioprotective activity of Gala and Fuji apple juice against isoprenaline-induced cardiotoxicity in rats

OBJECTIVES

Comparative evaluation of cardioprotective activity of Gala and Fuji apple juice against isoprenaline induced cardiotoxicity in rats.

METHODS

Rats (125-150 g) were orally administered Gala (GA) and Fuji (FA) apple juice (3 mL/day, per oral) for 13 days. Myocardial injury was inducted on 14th and 15th day by the administration of Isoprenaline (85 mg/kg/day, subcutaneous).

RESULTS

In treated group i.e. GA and FA, aspartate aminotransferase (AST), alanine transaminase (ALT), lactate dehydrogenase (LDH), creatine kinase (CK), Troponin-I level and malondialdehyde (MDA) content was reduced while glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) level was significantly increased. Marked reduction in cholesterol, triglyceride, phospholipids, low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) was observed while high-density lipoprotein (HDL) level increased significantly. In tissue and serum total serum protein (TSP) level, Albumin, Globulin and A/G ratio increased very significantly in the treated group while the level of white blood corpuscles (WBC), haemoglobin (Hb), erythrocyte sedimentation rate (ESR), total fibrinogen (TF), bleeding time (BT), c-reactive protein (C-rP), red blood corpuscles (RBC), clotting time (CT) and prothrombin time (PT) showed a significant rise in the level. The level of Sialic acid, hexose, fucose and hexosamine was highly significantly increased, there was an increase in the level of K⁺ and glycogen while a significant reduction in electrolyte and glucose level was observed when all these parameters were compared to Isoprenaline (ISO) group. The above findings were supported by histopathological examination of hearts. Cardioprotective activity was compared with standard drug, metoprolol. On comparative analysis of both juices, GA juices have found more effective when compared to FA juice.

CONCLUSIONS

The study was concluded that Gala and Fuji apple possessed significant prophylactic and protective effects against Isoprenaline-induced cardiotoxicity in rats through maintaining inhibiting lipid peroxidation, endogenous antioxidant enzyme activities and cytokine levels.

Combination of Cyclosporine A and Levosimendan Induces Cardioprotection under Acute Hyperglycemia

Prognosis of patients with myocardial infarction is detrimentally affected by comorbidities like diabetes mellitus. In the experimental setting, not only diabetes mellitus but also acute hyperglycemia is shown to hamper cardioprotective properties by multiple pharmacological agents. For Levosimendan-induced postconditioning, a strong infarct size reducing effect is demonstrated in healthy myocardium. However, acute hyperglycemia is suggested to block this protective effect. In the present study, we investigated whether (1) Levosimendan-induced postconditioning exerts a concentration-dependent effect under hyperglycemic conditions and (2) whether a combination with the mitochondrial permeability transition pore (mPTP) blocker cyclosporine A (CsA) restores the cardioprotective properties of Levosimendan under hyperglycemia. For this experimental investigation, hearts of male Wistar rats were randomized and mounted onto a Langendorff system, perfused with Krebs-Henseleit buffer with a constant pressure of 80 mmHg. All isolated hearts were subjected to 33 min of global ischemia and 60 min of reperfusion under hyperglycemic conditions. (1) Hearts were perfused with various concentrations of Levosimendan (Lev) (0.3–10 μM) for 10 min at the onset of reperfusion, in order to investigate a concentration–response relationship. In the second set of experiments (2), 0.3 μM Levosimendan was administered in combination with the mPTP blocker CsA, to elucidate the underlying mechanism of blocked cardioprotection under hyperglycemia. Infarct size was determined by tetrazolium chloride (TTC) staining. (1) Control (Con) hearts showed an infarct size of 52 ± 12%. None of the administered Levosimendan concentrations reduced the infarct size (Lev0.3: 49 ± 9%; Lev1: 57 ± 9%; Lev3: 47 ± 11%; Lev10: 50 ± 7%; all ns vs. Con). (2) Infarct size of Con and Lev0.3 hearts were 53 ± 4% and 56 ± 2%, respectively. CsA alone had no effect on infarct size (CsA: 50 ± 10%; ns vs. Con). The combination of Lev0.3 and CsA (Lev0.3 ± CsA) induced a significant infarct size reduction compared to Lev0.3 (Lev0.3+CsA: 35 ± 4%; p < 0.05 vs. Lev0.3). We demonstrated that (1) hyperglycemia blocks the infarct size reducing effects of Levosimendan-induced postconditioning and cannot be overcome by an increased concentration. (2) Furthermore, cardioprotection under hyperglycemia can be restored by combining Levosimendan and the mPTP blocker CsA.

Effect of hyperglycaemia and diabetes on acute myocardial ischaemia-reperfusion injury and cardioprotection by ischaemic conditioning protocols

Diabetic patients are at increased risk of developing coronary artery disease and experience worse clinical outcomes following acute myocardial infarction. Novel therapeutic strategies are required to protect the myocardium against the effects of acute ischaemia-reperfusion injury (IRI). These include one or more brief cycles of non-lethal ischaemia and reperfusion prior to the ischaemic event (ischaemic preconditioning [IPC]) or at the onset of reperfusion (ischaemic postconditioning [IPost]) either to the heart or to extracardiac organs (remote ischaemic conditioning [RIC]). Studies suggest that the diabetic heart is resistant to cardioprotective strategies, although clinical evidence is lacking. We overview the available animal models of diabetes, investigating acute myocardial IRI and cardioprotection, experiments investigating the effects of hyperglycaemia on susceptibility to acute myocardial IRI, the response of the diabetic heart to cardioprotective strategies e.g. IPC, IPost and RIC. Finally we highlight the effects of anti-hyperglycaemic agents on susceptibility to acute myocardial IRI and cardioprotection. 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.

Influence of Hyperglycemia on Dexmedetomidine-Induced Cardioprotection in the Isolated Perfused Rat Heart

Pharmacological preconditioning (PC) and postconditioning (PoC), for example, by treatment with the α2-adrenoreceptor agonist Dexmedetomidine (Dex), protects hearts from ischemia-reperfusion (I/R) injury in experimental studies, however, translation into the clinical setting has been challenging. Acute hyperglycemia adversely affects the outcome of patients with myocardial infarction. Additionally, it also blocks cardioprotection by multiple pharmacological agents. Therefore, we investigated the possible influence of acute hyperglycemia on Dexmedetomidine-induced pre- and postconditioning. Experiments were performed on the hearts of male Wistar rats, which were randomized into 7 groups, placed in an isolated Langendorff system and perfused with Krebs-Henseleit buffer. All hearts underwent 33 min of global ischemia, followed by 60 min of reperfusion. Control (Con) hearts received Krebs-Henseleit buffer (Con KHB), glucose (Con HG) or mannitol (Con NG) as vehicle only. Hearts exposed to hyperglycemia (HG) received KHB, containing 11 mmol/L glucose (an elevated, but commonly used glucose concentration for Langendorff perfused hearts) resulting in a total concentration of 22 mmol/L glucose throughout the whole experiment. To ensure comparable osmolarity with HG conditions, normoglycemic (NG) hearts received mannitol in addition to KHB. Hearts were treated with 3 nM Dexmedetomidine (Dex) before (DexPC) or after ischemia (DexPoC), under hyperglycemic or normoglycemic conditions. Infarct size was determined by triphenyltetrazoliumchloride staining. Acute hyperglycemia had no impact on infarct size compared to the control group with KHB (Con HG: 56 ± 9% ns vs. Con KHB: 56 ± 7%). DexPC reduced infarct size despite elevated glucose levels (DexPC HG: 35 ± 3%, p < 0.05 vs. Con HG). However, treatment with Dex during reperfusion showed no infarct size reduction under hyperglycemic conditions (DexPoC HG: 57 ± 9%, ns vs. Con HG). In contrast, hearts treated with mannitol demonstrated a significant decrease in infarct size compared to the control group (Con NG: 37 ± 3%, p < 0.05 vs. Con KHB). The combination of Dex and mannitol presents exactly opposite results to hearts treated with hyperglycemia. While DexPC completely abrogates infarct reduction through mannitol treatment (DexPC NG: 55 ± 7%, p < 0.05 vs. Con NG), DexPoC had no impact on mannitol-induced infarct size reduction (DexPoC NG: 38 ± 4%, ns vs. Con NG). Acute hyperglycemia inhibits DexPoC, while it has no impact on DexPC. Treatment with mannitol induces cardioprotection. Application of Dex during reperfusion does not influence mannitol-induced infarct size reduction, however, administering Dex before ischemia interferes with mannitol-induced cardioprotection.

New advances in perioperative cardioprotection

With the increasing age of the general population, medical conditions necessitating a surgical intervention will increase. Concomitant with advanced age, the prevalence of type 2 diabetes mellitus will also increase. These patients have a two- to three-fold higher risk of occurrence of cardiovascular events and are at higher risk of perioperative myocardial ischemia. This review will discuss recent advances in the field of perioperative cardioprotection and focus specifically on strategies that have aimed to protect the diabetic and the aged myocardium. This review will not deal with potential putative cardioprotective effects of opioids and anesthetic agents, as this is a very broad area that would necessitate a dedicated overview.

Sevoflurane postconditioning is not mediated by ferritin accumulation and cannot be rescued by simvastatin in isolated streptozotocin-induced diabetic rat hearts

Sevoflurane postconditioning (sevo postC) is an attractive and amenable approach that can protect the myocardium against ischemia/reperfusion (I/R)-injury. Unlike ischemic preconditioning (IPC), sevo postC does not require additional induced ischemic periods to a heart that is already at risk. IPC was previously shown to generate myocardial protection against I/R-injury through regulation of iron homeostasis and de novo ferritin synthesis, a process found to be impaired in the diabetic state. The current study investigated whether alterations in iron homeostasis and ferritin mRNA and protein accumulation are also involved in the cardioprotective effects generated by sevo postC. It was also investigated whether the protective effects of sevo postC in the diabetic state can be salvaged by simvastatin, through inducing nitric oxide (NO) bioavailability/activity, in isolated streptozotocin (STZ)-induced diabetic hearts (DH). Isolated rat hearts from healthy Controls and diabetic animals were retrogradely perfused using the Langendorff configuration and subjected to prolonged ischemia and reperfusion, with and without (2.4 and 3.6%) sevo postC and/or pre-treatment with simvastatin (0.5 mg/kg). Sevo postC significantly reduced infarct size and improved myocardial function in healthy Controls but not in isolated DH. The sevo postC mediated myocardial protection against I/R-injury was not associated with de novo ferrtin synthesis. Furthermore, simvastatin aggravated myocardial injury after sevo postC in STZ-induced DHs, likely due to increasing NO levels. Despite the known mechanistic overlaps between PC and postC stimuli, distinct differences underlie the cardioprotective interventions against myocardial I/R-injury and are impaired in the DH. Sevo postC mediated cardioprotection, unlike IPC, does not involve de novo ferritin accumulation and cannot be rescued by simvastatin in STZ-induced DHs.

Glycemic variability is associated with myocardial damage in nondiabetic patients with ST-elevation myocardial infarction

Background

Glycemic variability (GV) induces coronary microcirculatory disturbance and myocardial damage in diabetic patients with acute myocardial infarction. However, in nondiabetic acute myocardial infarction patients, the relationship between GV and myocardial damage remains unclear.

Patients and methods

We investigated GV with a continuous glucose monitoring system in nondiabetic ST-segment elevation myocardial infarction patients treated with emergent percutaneous coronary intervention. GV was expressed as the mean amplitude of glycemic excursions (MAGE). Myocardial damage was estimated by myocardial blush grade and ST-segment resolution (STRes). STRes was defined as complete (>70%), partial (30–70%), or none (<30%).

Results

Consecutive patients (n=73) were enrolled and classified into a lower or higher MAGE group on the basis of the median MAGE. The higher MAGE group showed lower levels of myocardial blush grade (2.41±0.76 vs. 1.72±0.85, P=0.001) and STRes (complete: 56.8 vs. 33.3%, P=0.044; partial: 32.4 vs. 36.1%, P=0.741; none: 10.8 vs. 30.6%, P=0.037).

Conclusion

GV was associated with myocardial damage after percutaneous coronary intervention in nondiabetic ST-segment elevation myocardial infarction patients.

Investigation of the Protective Effect of Kefir against Isoproterenol Induced Myocardial Infarction in Rats

This study aims to investigate the protective effects of kefir against myocardial infarction induced by isoproterenol (ISO). The rats were randomly divided into 4 groups, each group consisting of 8 rats. The control group, the kefir group (5 mL/kg/d kefir administered to rats as intra-gastric gavage for 60 d), the ISO group (100 mg/kg ISO was administered to rats, s.c. on 61. and 62. d), and kefir+ISO group (5 mL/kg/d kefir was administered to rats intra gastric gavage for 60 days prior to ISO, 100 mg/kg in two doses on day 61 and 62). 12 h after the last ISO dose, all rats were decapitated and their blood samples were collected. Cardiac tissue was reserved for histopathological examination. creatine kinase (CK), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), triglycerides, total cholesterol,very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL) and glucose were measured by autoanalyzer, whole blood malondialdehyde (MDA), glutathione (GSH) and plasma advanced oxidation protein products (AOPP) levels were measured spectrophotometrically. It was determined that in the group of kefir+ISO, the levels of AST (p<0.001), CK (p<0.001), LDH (p<0.001), MDA (p<0.001) and AOPP (p<0.001) were decreased, while the GSH (p<0.05) increased, compared to ISO group. There were no significant changes in lipid profile and glucose levels between these two groups. In conclusion, by examining cardiac enzymes and histopathological changes in cardiac tissue, it can be concluded that the administration of kefir in myocardial infarction induced by ISO can protect the heart with its antioxidant characteristic and minimize the toxic damage created by ISO.

Ethyl pyruvate attenuates myocardial ischemia-reperfusion injury exacerbated by hyperglycemia via retained inhibitory effect on HMGB1

BACKGROUND

Hyperglycemia (HG) exacerbates myocardial ischemia/reperfusion (I/R) injury and renders protective strategies ineffective by amplified inflammatory response via enhanced high-mobility group box-1 (HMGB1) release. This study investigated the role of ethyl pyruvate (EP) against myocardial I/R injury under a clinically relevant HG condition.

METHODS

Sprague-Dawley rats (n=76) were randomly assigned to 6 groups: normoglycemia (NG)-Sham, NG-I/R-control (C, saline), NG-I/R-EP treatment (50mg/kg) upon reperfusion, HG-Sham, HG-I/R-C, and HG-I/R-EP treatment upon reperfusion. HG was induced by 1.2g/kg dextrose. I/R was induced by ligation of the left anterior descending artery for 30min followed by 4h of reperfusion.

RESULTS

HG resulted in exacerbation of myocardial infarct size by 19% with amplified activation of HMGB1-receptors of advanced glycation end products/toll like receptors-NF-κB pathway compared to NG following I/R, which all could be attenuated by EP. EP treatment was associated with diminished tumor necrosis factor-α, interleukin-1β, and interleukin-6 expressions. It also served to normalize the increase in pro-apoptotic Bax and the decrease in anti-apoptotic Bcl-2 protein levels. These effects were associated with decreased myocardial apoptosis and infarct size (by 30% and 36% in the NG and HG groups, respectively) regardless of the glycemic condition.

CONCLUSION

HG exacerbated myocardial I/R injury through amplified inflammatory response via increased HMGB1 level. EP treatment upon reperfusion conveyed significant myocardial protection against the I/R injury under both NG and HG conditions. Common to both glycemic conditions, associated mechanisms involved attenuated increase in HMGB1 level and suppression of its down-stream pathways.

Platelets, diabetes and myocardial ischemia/reperfusion injury

Mechanisms underlying the pathogenesis of ischemia/reperfusion injury are particularly complex, multifactorial and highly interconnected. A complex and entangled interaction is also emerging between platelet function, antiplatelet drugs, coronary diseases and ischemia/reperfusion injury, especially in diabetic conditions. Here we briefly summarize features of antiplatelet therapy in type 2 diabetes (T2DM). We also treat the influence of T2DM on ischemia/reperfusion injury and how anti-platelet therapies affect post-ischemic myocardial damage through pleiotropic properties not related to their anti-aggregating effects. miRNA-based signature associated with T2DM and its cardiovascular disease complications are also briefly considered. Influence of anti-platelet therapies and different effects of healthy and diabetic platelets on ischemia/reperfusion injury need to be further clarified in order to enhance patient benefits from antiplatelet therapy and revascularization. Here we provide insight on the difficulty to reduce the cardiovascular risk in diabetic patients and report novel information on the cardioprotective role of widely used anti-aggregant drugs.

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.

Aleglitazar, a Balanced Dual PPARα and -γ Agonist, Protects the Heart Against Ischemia-Reperfusion Injury

PURPOSE

To evaluate whether aleglitazar (Ale), a dual PPARα/γ agonist, has additive effects on myocardial protection against ischemia-reperfusion injury.

METHODS

Human cardiomyocytes (HCMs), cardiomyocytes from cardiac-specific PPARγ knockout (MCM-PPARγ (CKO) ) or wild type (MCM-WT) mice were incubated with different concentrations of Ale, and subjected to simulated ischemia-reperfusion (SIR) or normoxic conditions (NSIR). Cell viability, apoptosis and caspase-3 activity were determined. HCMs were transfected with siRNA against PPARα (siPPARα) or PPARγ (siPPARγ) followed by incubation with Ale. PPARα/γ DNA binding capacity was measured. Cell viability, apoptosis and levels of P-AKT and P-eNOS were assessed. Infarct size following 30 min coronary artery occlusion and 24 h reperfusion were assessed in WT and db/db diabetic mice following 3-day pretreatment with vehicle, Ale or glimeperide.

RESULTS

Ale (at concentrations of 150-600 nM) increased cell viability and reduced apoptosis in HCMs, MCM-WT and MCM-PPAR (CKO) exposed to SIR. In HCM, the protective effect was partially blocked by siPPARα alone or siPPARγ alone, and completely blocked by siPPARα+siPPARγ. Ale increased P-Akt/P-eNOS in HCMs. P-Akt or P-eNOS levels were decreased when PPARα alone, PPARγ alone and especially when both were knocked down. Peritoneal GTTs revealed that db/db mice had developed impaired glucose tolerance and insulin sensitivity, which were normalized by Ale or glimepiride treatment. Ale, but not glimepiride, limited infarct size in both WT and diabetic mice after ischemia-reperfusion.

CONCLUSIONS

Ale protects against myocardial apoptosis caused by hypoxia-reoxygenation in vitro and reduces infarct size in vivo.

Remote ischaemic conditioning in the context of type 2 diabetes and neuropathy: the case for repeat application as a novel therapy for lower extremity ulceration

An emerging treatment modality for reducing damage caused by ischaemia–reperfusion injury is ischaemic conditioning. This technique induces short periods of ischaemia that have been found to protect against a more significant ischaemic insult. Remote ischaemic conditioning (RIC) can be administered more conveniently and safely, by inflation of a pneumatic blood pressure cuff to a suprasystolic pressure on a limb. Protection is then transferred to a remote organ via humoral and neural pathways. The diabetic state is particularly vulnerable to ischaemia–reperfusion injury, and ischaemia is a significant cause of many diabetic complications, including the diabetic foot. Despite this, studies utilising ischaemic conditioning and RIC in type 2 diabetes have often been disappointing. A newer strategy, repeat RIC, involves the repeated application of short periods of limb ischaemia over days or weeks. It has been demonstrated that this improves endothelial function, skin microcirculation, and modulates the systemic inflammatory response. Repeat RIC was recently shown to be beneficial for healing in lower extremity diabetic ulcers. This article summarises the mechanisms of RIC, and the impact that type 2 diabetes may have upon these, with the role of neural mechanisms in the context of diabetic neuropathy a focus. Repeat RIC may show more promise than RIC in type 2 diabetes, and its potential mechanisms and applications will also be explored. Considering the high costs, rates of chronicity and serious complications resulting from diabetic lower extremity ulceration, repeat RIC has the potential to be an effective novel advanced therapy for this condition.

High Glucose Attenuates Anesthetic Cardioprotection in Stem-Cell-Derived Cardiomyocytes: The Role of Reactive Oxygen Species and Mitochondrial Fission

BACKGROUND

Hyperglycemia can blunt the cardioprotective effects of isoflurane in the setting of ischemia-reperfusion injury. Previous studies suggest that reactive oxygen species (ROS) and increased mitochondrial fission play a role in cardiomyocyte death during ischemia-reperfusion injury. To investigate the role of glucose concentration in ROS production and mitochondrial fission during ischemia-reperfusion (with and without anesthetic protection), we used the novel platform of human-induced pluripotent stem-cell (iPSC)-derived cardiomyocytes (CMs).

METHODS

Cardiomyocyte differentiation from iPSC was characterized by the expression of CM-specific markers using immunohistochemistry and by measuring contractility. iPSC-CMs were exposed to varying glucose conditions (5, 11, and 25 mM) for 24 hours. Mitochondrial permeability transition pore opening, cell viability, and ROS generation endpoints were used to assess the effects of various treatment conditions. Mitochondrial fission was monitored by the visualization of fragmented mitochondria using confocal microscopy. Expression of activated dynamin-related protein 1, a key protein responsible for mitochondrial fission, was assessed by Western blot.

RESULTS

Cardiomyocytes were successfully differentiated from iPSC. Elevated glucose conditions (11 and 25 mM) significantly increased ROS generation, whereas only the 25-mM high glucose condition induced mitochondrial fission and increased the expression of activated dynamin-related protein 1 in iPSC-CMs. Isoflurane delayed mitochondrial permeability transition pore opening and protected iPSC-CMs from oxidative stress in 5- and 11-mM glucose conditions to a similar level as previously observed in various isolated animal cardiomyocytes. Scavenging ROS with Trolox or inhibiting mitochondrial fission with mdivi-1 restored the anesthetic cardioprotective effects in iPSC-CMs in 25-mM glucose conditions.

CONCLUSIONS

Human iPSC-CM is a useful, relevant model for studying isoflurane cardioprotection and can be manipulated to recapitulate complex clinical perturbations. We demonstrate that the cardioprotective effects of isoflurane in elevated glucose conditions can be restored by scavenging ROS or inhibiting mitochondrial fission. These findings may contribute to further understanding and guidance for restoring pharmacological cardioprotection in hyperglycemic patients.

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.

Decreased effectiveness of ischemic heart preconditioning in the state of chronic inflammation

There is growing evidence, that beneficial effects of ischemic heart preconditioning (IPC) may be lost or limited due to diabetes, hyperlipidemia, hypertension, atherosclerosis, heart failure and senility. It is plausible, that these conditions interfere with the biochemical pathways underlying the IPC response, but the detailed explanation is not clear. Pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), monocyte chemotactic protein-1 (MCP-1), histamine and many other agents used in a single dose before prolonged ischemia mimic IPC. However prolonged exposure to preconditioning mimetics leads to tolerance (tachyphylaxis). In the state of such tolerance ischemic preconditioning is no longer protective. Studies suggest that diabetes, hyperlipidemia, hypertension, atherosclerosis, heart failure and older age are accompanied by increased plasma levels of pro-inflammatory cytokines, MCP-1 and other inflammatory mediators. Therefore, we raised the hypothesis, that the reported lack of benefits of IPC in the listed states may be due to tolerance to IPC developed during prolonged exposure of the myocardium to preconditioning mimetics.

Activation of Adenosine Triphosphate-regulated Potassium Channels during Reperfusion Restores Isoflurane Postconditioning-induced Cardiac Protection in Acutely Hyperglycemic Rabbits

BACKGROUND

Hyperglycemia is known to inhibit myocardial anesthetic postconditioning. The authors tested whether activation of adenosine triphosphate-regulated potassium (KATP) channels would restore anesthetic postconditioning during acute hyperglycemia.

METHODS

Rabbits subjected to 40-min myocardial ischemia and 3-h reperfusion (ischemia-reperfusion [I/R]) were assigned to groups (n = 10 in each group) with or without isoflurane postconditioning (2.1% for 5 min) in the presence or absence of hyperglycemia and/or the KATP channel agonist diazoxide. Creatine kinase MB fraction and infarct size were measured. Phosphorylated protein kinase B (Akt) and endothelial nitric oxide synthase (eNOS) were assessed. Oxidative stress was evaluated by measuring malondialdehyde, and apoptosis was assessed by dUTP nick-end labeling and activated caspase-3.

RESULTS

Postconditioning significantly reduced myocardial infarct size (26 ± 4% in the isoflurane [ISO] group vs. 53 ± 2% in the I/R group; P = 0.007); whereas, hyperglycemia inhibited this effect (infarct size: 47 ± 2%, P = 0.02 vs. the ISO group). Phosphorylated and eNOS levels increased, whereas malondialdehyde and myocardial apoptosis were significantly lower after isoflurane postconditioning compared with I/R. These effects were inhibited by acute hyperglycemia. Diazoxide restored the protective effect of isoflurane in the hyperglycemic animals (infarct size: 29 ± 2%; P = 0.01 vs. the I/R group), reduced malondialdehyde levels and myocardial apoptosis, but did not affect the expression of phosphorylated Akt or eNOS.

CONCLUSIONS

KATP channel activation restored anesthetic postconditioning-induced myocardial protection under acute hyperglycemia. This effect occurred without increasing Akt or eNOS phosphorylation, suggesting that KATP channels are located downstream to Akt and eNOS in the pathway of isoflurane-induced myocardial postconditioning.

Myocardial potency of Bio-tea against Isoproterenol induced myocardial damage in rats

Kombucha (Bio-tea) is a beverage produced by the fermentation of sugared black tea using a symbiotic association of bacteria and yeasts. Traditional claims about Kombucha report beneficial effects such as antibiotic properties, gastric regulation, relief from joint rheumatism and positive influence on the cholesterol level, arteriosclerosis, diabetes, and aging problems. The present investigation was carried out to understand the preventive effect of Kombucha on heart weight, blood glucose, total protein, lipid profile and cardiac markers in rats with myocardial damage induced using Isoproterenol. As Bio-tea is produced by fermenting tea, the parameters were compared in rats pre-treated with normal black tea and Bio-tea for 30 days followed by subcutaneous injection of Isoproterenol (85 mg/kg body weight). Normal rats as well as Isoproterenol induced myocardial infarcted rats were also used, which served as controls. Isoproterenol induced myocardial infarcted control rats showed a significant increase in heart weight, blood glucose and cardiac markers and a decrease in plasma protein. Increased levels of cholesterol, triglycerides, low density lipids (LDL) and very low density lipids (VLDL) were also observed, while the high density lipid (HDL) content decreased. Bio-tea showed a higher preventive effect against myocardial infarction when compared to tea, as was observed by the significant reduction in heart weight, and blood glucose and increase in plasma albumin levels. Bio-tea significantly decreased cholesterol, triglycerides, LDL and VLDL while simultaneously increasing the levels of HDL. Similarly a decrease in leakage of cardiac markers from the myocardium was also observed.

Inhibition of mammalian target of rapamycin protects against reperfusion injury in diabetic heart through STAT3 signaling

Diabetic patients suffer augmented severity of myocardial infarction. Excessive activation of the mammalian target of rapamycin (mTOR) and decreased activation of STAT3 are implicated in diabetic complications. Considering the potent cardioprotective effect of mTOR inhibitor, rapamycin, we hypothesized that reperfusion therapy with rapamycin would reduce infarct size in the diabetic hearts through STAT3 signaling. Hearts from adult male db/db or wild type (WT) C57 mice were isolated and subjected to 30 min of normothermic global ischemia and 60 min of reperfusion in Langendorff mode. Rapamycin (100 nM) was infused at the onset of reperfusion. Myocardial infarct size (IS) was significantly reduced in rapamycin-treated mice (13.3 ± 2.4 %) compared to DMSO vehicle control (35.9 ± 0.9 %) or WT mice (27.7 ± 1.1 %). Rapamycin treatment restored phosphorylation of STAT3 and enhanced AKT phosphorylation (target of mTORC2), but significantly reduced ribosomal protein S6 phosphorylation (target of mTORC1) in the diabetic heart. To determine the cause and effect relationship of STAT3 in cardioprotection, inducible cardiac-specific STAT3-deficient (MCM TG:STAT3(flox/flox)) and WT mice (MCM TG:STAT3(flox/flox)) were made diabetic by feeding high fat diet (HFD). Rapamycin given at reperfusion reduced IS in WT mice but not in STAT3-deficient mice following I/R. Moreover, cardiomyocytes isolated from HFD-fed WT mice showed resistance against necrosis (trypan blue staining) and apoptosis (TUNEL assay) when treated with rapamycin during reoxygenation following simulated ischemia. Such protection was absent in cardiomyocytes from HFD-fed STAT3-deficient mice. STAT3 signaling plays critical role in reducing IS and attenuates cardiomyocyte death following reperfusion therapy with rapamycin in diabetic heart.

Gating behavior of endoplasmic reticulum potassium channels of rat hepatocytes in diabetes

BACKGROUND

Defects in endoplasmic reticulum homeostasis are common occurrences in different diseases, such as diabetes, in which the function of endoplasmic reticulum is disrupted. It is now well established that ion channels of endoplasmic reticulum membrane have a critical role in endoplasmic reticulum luminal homeostasis. Our previous studies showed the presence of an ATP-sensitive cationic channel in endoplasmic reticulum. Therefore, in this study, we examined and compared the activities of this channel in control and diabetic rats using single-channel recording techniques.

METHOD

Male Wistar rats were made diabetic for 2 weeks with a single dose injection of streptozotocin (45 mg/kg). Ion channel incorporation of rough endoplasmic reticulum of diabetic hepatocytes into the bilayer lipid membrane allowed the characterization of K+ channel.

RESULTS

Ion channel incorporation of rough endoplasmic reticulum vesicles into the bilayer lipid revealed that the channel current-voltage (I-V) relation with a mean slope conductance of 520 ± 19 pS was unaffected in diabetes. Interestingly, the channel Po-voltage relation was significantly lower in diabetic rats at voltages above +30 mV.

CONCLUSION

We concluded that the endoplasmic reticulum cationic channel is involved in diabetes. Also, this finding could be considered as a goal for further therapeutic plans.

Erythropoietin protects myocardium against ischemia-reperfusion injury under moderate hyperglycemia

Erythropoietin (EPO), an essential hormone for erythropoiesis, provides protection against myocardial ischemia/reperfusion (I/R) injury. Hyperglycemia during acute myocardial infarction aggravates organ damage and attenuates the efficacies of various protective measures. This study aimed to investigate the protective role of EPO against myocardial I/R injury under a clinically relevant moderate hyperglycemic condition and its associated mechanisms. Eighty-two Sprague-Dawley rats were randomly assigned to six groups: normoglycemia-Sham, normoglycemia-I/R-control-saline (IRC), normoglycemia-I/R-EPO (IRE), hyperglycemia-Sham, hyperglycemia-IRC, and hyperglycemia-IRE. The rats received 1.2 g/kg dextrose or same volume of normal saline depending on the group. I/R was induced by a 30 min period of ischemia followed by reperfusion for 4 h. For 1 h before I/R injury, intravenous 4000 IU/kg of EPO was administered. EPO pretreatment significantly reduced the number of apoptotic cells and the infarct size compared with those of the control groups. EPO increased GATA-4 phosphorylation and acetylation against I/R in hyperglycemic myocardium. It also enhanced ERK induced GATA-4 post-translational modifications such as increased GATA-4 phosphorylation and acetylation, and decreased GATA-4 ubiquitination following hypoxia-reoxygenation in H9c2 cells in hyperglycemic medium. Increased GATA-4 stability by EPO diminished I/R-related down-regulation of Bcl-2 and reduction of caspase-3 activities in hyperglycemic myocardium. In conclusion, EPO pretreatment before I/R injury conveyed significant myocardial protection under moderate hyperglycemic condition through mechanisms involved in reduction of caspase-3 activity and up-regulation of Bcl-2 in association with enhanced ERK-induced GATA-4 stability.

Myocardial protection by remote ischaemic pre-conditioning is abolished in sulphonylurea-treated diabetics undergoing coronary revascularisation

BACKGROUND

Remote ischaemic pre-conditioning attenuates myocardial injury. Because sulphonylurea drugs interfere with ischaemic and anaesthetic pre-conditioning, we assessed whether remote ischaemic pre-conditioning effects are altered in sulphonylurea-treated diabetics.

METHODS

Using the database of our ongoing randomised, placebo-controlled study (ClinicalTrials.gov NCT01406678), we assessed the troponin I concentration area under curve (measurements: baseline, 1, 6, 12, 24, 48, and 72 h post-operatively) in sulphonylurea-treated diabetics (n = 27) and non-diabetics (n = 230) without and with remote ischaemic pre-conditioning (three 5-min periods of left upper arm ischaemia with 5-min reperfusion each) during isoflurane anaesthesia before two- to three-vessel coronary artery surgery.

RESULTS

Remote ischaemic pre-conditioning in non-diabetic patients evoked a 41% decrease in the troponin I concentration area under curve (514 ng/ml × 72 h ± 600 vs. 302 ± 190, P = 0.001) but no change (404 ng/ml × 72 h ± 224 vs. 471 ± 383, P = 0.62) in sulphonylurea-treated diabetics. There was no significant correlation between the troponin I concentration area under curve and arterial glucose concentrations, and the latter was not an independent confounder.

CONCLUSION

Cardioprotection by remote ischaemic pre-conditioning during isoflurane anaesthesia is abolished in sulphonylurea-treated diabetics.

Increased protein aggregation in Zucker diabetic fatty rat brain: identification of key mechanistic targets and the therapeutic application of hydrogen sulfide

BACKGROUND

Diabetes and particularly high blood glucose levels are implicated in neurodegeneration. One of the hallmarks of neurodegeneration is protein aggregation. We investigated the presence of protein aggregation in the frontal brain of Zucker diabetic fatty (ZDF) rats, an animal model for diabetes. Further, the effect of NaHS in suppressing protein aggregation in cultured brain slices from ZDF was assessed.

RESULTS

The levels of protein synthesis, protein/gene expression, autophagy and anti-oxidant defense were evaluated in ZDF and control (Lean) brains.Compared to Lean, ZDF brains displayed a significant increase in protein aggregates, p-tau, fibronectin expression and protein glycosylation. Increased phosphorylation of mTOR and S6 ribosomal protein in ZDF indicated higher protein synthesis, while the increase in ubiquitinated proteins and LC3-I in ZDF brains accompanied by lower LC3-II expression and LC3-II/LC3-I levels indicated the blockage of proteolytic pathways. CBS (cystathionine beta synthase) protein and mRNA expression and thiol group levels in ZDF brains were lower compared to Lean. ZDF brains show a higher level of reactive oxygen species. In vitro NaHS treatment normalized proteostasis while counteracting oxidative stress.

CONCLUSION

Our data demonstrate increased protein synthesis and aggregation in the diabetic ZDF rat brain, which was reversible by NaHS treatment.This is the first report on the potential use of NaHS as a novel strategy against protein aggregation in diabetic brain.

Acute hyperglycemia abolishes ischemic preconditioning by inhibiting Akt phosphorylation: normalizing blood glucose before ischemia restores ischemic preconditioning

This study examined the hypothesis that acute hyperglycemia (HG) blocks ischemic preconditioning (IPC) by inhibiting Akt phosphorylation. Brief HG of approximately 400 mg/dL was induced in C57BL/6 mice via intraperitoneal injection of 20% dextrose (2 g/kg). All mice underwent 40 min LAD occlusion and 60 min reperfusion. The IPC protocol was 2 cycles of 5 min ischemia and 5 min reperfusion prior to index ischemia.

RESULTS

In control mice, infarct size (IF) was 51.7 ± 2.0 (% risk region). Preconditioning reduced IF by 50% to 25.8 ± 3.2 (P < 0.05 versus control). In HG mice, IF was significantly exacerbated to 58.1 ± 2.3. However, the effect of IPC completely disappeared in HG mice. Normalization of blood glucose with insulin 5 min before IPC recovered the cardioprotective effect. Administration of CCPA before index ischemia mimicked IPC effect. The cardioprotective effect of CCPA, not its chronotropic effect, completely disappeared in HG mice. Phosphorylation of cardiac tissue Akt before index ischemia was enhanced by IPC or CCPA but was significantly inhibited by HG in both groups. Normalization of glucose with insulin reversed the inhibition of Akt phosphorylation by HG.

CONCLUSION

HG abolishes the cardioprotective effect of preconditioning by inhibiting Akt phosphorylation. Normalization of blood glucose with insulin suffices to recover the cardioprotective effect of preconditioning.

Diabetic cardiomyopathy: pathophysiology and clinical features

Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.

Decreased brain K(ATP) channel contributes to exacerbating ischemic brain injury and the failure of neuroprotection by sevoflurane post-conditioning in diabetic rats

Diabetes leads to exacerbating brain injury after ischemic stroke, but the underlying mechanisms and whether therapeutic intervention with anesthetic post-conditioning can induce neuroprotection in this population are not known. We tested the hypothesis that alteration of brain mitochondrial (mito) K_ATP channels might cause exacerbating brain injury after ischemic stroke and attenuate anesthetic post-conditioning induced neuroprotection in diabetes. We also examined whether hyperglycemic correction with insulin would restore anesthetic post-conditioning in diabetes. Non-diabetic rats and diabetic rats treated with or without insulin were subjected to focal cerebral ischemia for 2 h followed by 24 h of reperfusion. Post-conditioning was performed by exposure to sevoflurane for 15 min, immediately at the onset of reperfusion. The role of the mitoK_ATP channel was assessed by administration of a selective blocker 5-hydroxydecanoate (5-HD) before sevoflurane post-conditioning or by diazoxide (DZX), a mitoK_ATP channel opener, given in place of sevoflurane. Compared with non-diabetic rats, diabetic rats had larger infarct volume and worse neurological outcome at 24 h after ischemia. Sevoflurane or DZX reduced the infarct volume and improved neurological outcome in non-diabetic rats but not in diabetic rats, and the protective effects of sevoflurane in non-diabetic rats were inhibited by pretreatment with 5-HD. Molecular studies revealed that expression of Kir6.2, an important mitoK_ATP channel component, was decreased in the brain of diabetic rats as compared to non-diabetic rats. In contrast, hyperglycemic correction with insulin in diabetic rats normalized expression of brain Kir6.2, reduced ischemic brain damage and restored neuroprotective effects of sevoflurane post-conditioning. Our findings suggest that decreased brain mitoK_ATP channel contributes to exacerbating ischemic brain injury and the failure of neuroprotection by anesthetic post-conditioning in diabetes. Insulin glycemic control in diabetes may restore the neuroprotective effects of anesthetic post-conditioning by modulation of brain mitoK_ATP channel.

Diabetes mellitus reduces the function and expression of ATP-dependent K⁺ channels in cardiac mitochondria

AIM

Our goal was to determine the effects of type I diabetes mellitus on the function and expression of ATP-dependent K(+) channels in cardiac mitochondria (mitoKATP), composed of a pore-forming subunit (Kir6.1) and a diazoxide-sensitive sulphonylurea receptor (SUR1). We tested the hypothesis that diabetes reduces Kir6.1 and SUR1 expression as well as diazoxide-induced depolarization of mitochondrial membrane potential (ΔΨm).

MAIN METHODS

Male FVB mice were made diabetic for 5weeks with multiple low dose injections of streptozotocin. Cardiac mitochondria were separated into two populations: subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). mitoKATP expression was determined via Western blot analysis of Kir6.1 and SUR1 proteins. mitoKATP function was determined by measuring ΔΨm with the potentiometric dye rhodamine 123.

KEY FINDINGS

Diabetes reduced Kir6.1 and SUR1 expression in IFM by over 40% (p<0.05 for both). Similarly, diabetes reduced Kir6.1 expression in SSM by approximately 40% (p<0.05); however, SUR1 expression was unaffected. Opening mitoKATP with diazoxide (100μM) depolarized control IFM ΔΨm by 80% of the valinomycin maximum; diabetic IFM depolarized only 30% (p<0.05). Diazoxide-induced depolarization was much less in SSM (20-30%) and unaffected by diabetes.

SIGNIFICANCE

Our data indicate that diabetes reduces mitoKATP expression and function in IFM. These changes in mitoKATP may provide an opportunity to understand mechanisms leading to diabetic cardiomyopathy and loss of cardioprotective mechanisms in the diabetic heart.

Marked hyperglycemia attenuates anesthetic preconditioning in human-induced pluripotent stem cell-derived cardiomyocytes

INTRODUCTION

Anesthetic preconditioning protects cardiomyocytes from oxidative stress-induced injury, but it is ineffective in patients with diabetes mellitus. To address the role of hyperglycemia in the inability of diabetic individuals to be preconditioned, we used human cardiomyocytes differentiated from induced pluripotent stem cells generated from patients with or without type 2 diabetes mellitus (DM-iPSC- and N-iPSC-CMs, respectively) to investigate the efficacy of preconditioning in varying glucose conditions (5, 11, and 25 mM).

METHODS

Induced pluripotent stem cells were induced to generate cardiomyocytes by directed differentiation. For subsequent studies, cardiomyocytes were identified by genetic labeling with enhanced green fluorescent protein driven by a cardiac-specific promoter. Cell viability was analyzed by lactate dehydrogenase assay. Confocal microscopy was utilized to measure opening of the mitochondrial permeability transition pore and the mitochondrial adenosine 5'-triphosphate-sensitive potassium channels.

RESULTS

Isoflurane (0.5 mM) preconditioning protected N-iPSC- and DM-iPSC-CMs from oxidative stress-induced lactate dehydrogenase release and mitochondrial permeability transition pore opening in 5 mM and 11 mM glucose. Isoflurane triggered mitochondrial adenosine-5'-triphosphate-sensitive potassium channel opening in N-iPSC-CMs in 5 mM and 11 mM glucose and in DM-iPSC-CMs in 5 mM glucose; 25 mM glucose disrupted anesthetic preconditioning-mediated protection in DM-iPSC- and N-iPSC-CMs.

CONCLUSIONS

The opening of mitochondrial adenosine 5'-triphosphate-sensitive potassium channels are disrupted in DM-iPSC-CMs in 11 mM and 25 mM glucose and in N-iPSC-CMs in 25 mM glucose. Cardiomyocytes derived from healthy donors and patients with a specific disease, such as diabetes in this study, open possibilities in studying genotype- and phenotype-related pathologies in a human-relevant model.

Improved resistance to ischemia and reperfusion, but impaired protection by ischemic preconditioning in patients with type 1 diabetes mellitus: a pilot study

Background

In patients with type 1 diabetes mellitus (T1DM), cardiovascular events are more common, and the outcome following a myocardial infarction is worse than in nondiabetic subjects. Ischemic or pharmacological preconditioning are powerful interventions to reduce ischemia reperfusion (IR)-injury. However, animal studies have shown that the presence of T1DM can limit these protective effects. Therefore, we aimed to study the protective effect of ischemic preconditioning in patients with T1DM, and to explore the role of plasma insulin and glucose on this effect.

Methods

^99mTechnetium-annexin A5 scintigraphy was used to detect IR-injury. IR-injury was induced by unilateral forearm ischemic exercise. At reperfusion, Tc-annexin A5 was administered, and IR-injury was expressed as the percentage difference in radioactivity in the thenar muscle between the experimental and control arm 4 hours after reperfusion. 15 patients with T1DM were compared to 21 nondiabetic controls. The patients were studied twice, with or without ischemic preconditioning (10 minutes of forearm ischemia and reperfusion). Patients were studied in either normoglycemic hyperinsulinemic conditions (n = 8) or during hyperglycemic normoinsulinemia (n = 7). The controls were studied once either with (n = 8) or without (n = 13) ischemic preconditioning.

Results

Patients with diabetes were less vulnerable to IR-injury than nondiabetic healthy controls (12.8 ± 2.4 and 11.0 ± 5.1% versus 27.5 ± 4.5% in controls; p < 0.05). The efficacy of ischemic preconditioning to reduce IR-injury, however, was lower in the patients and was even completely abolished during hyperglycemia.

Conclusions

Patients with T1DM are more tolerant to forearm IR than healthy controls in our experimental model. The efficacy of ischemic preconditioning to limit IR-injury, however, is reduced by acute hyperglycemia.

Trial Registration

The study is registered at www.clinicaltrials.gov (NCT00184821)

The effect of statins on the no-reflow phenomenon: an observational study in patients with hyperglycemia before primary angioplasty

BACKGROUND

An association between admission plasma glucose levels and an increased risk of no-reflow has been well documented. Although HMG-CoA reductase inhibitor (statin) therapy can reduce no-reflow, little is known about its effect on no-reflow in patients with hyperglycemia. In the present study, we investigated whether pretreatment with a statin could reduce no-reflow in patients with hyperglycemia, who underwent primary coronary intervention for acute myocardial infarction (AMI).

METHODS

A total of 259 consecutive patients who underwent primary angioplasty for a first AMI were studied. Blood glucose and creatinine kinase levels were measured on admission. All patients underwent 2-dimensional echocardiography and electrocardiographic analysis just after admission. No-reflow was defined as a Thrombolysis in Myocardial Infarction (TIMI) flow grade <3. Hyperglycemia was defined as a blood glucose level >or=10 mmol/L. Statin administration prior to admission was determined by detailed interview or information in the medical records.

RESULTS

Hyperglycemia was diagnosed in 154 patients on admission. The no-reflow phenomenon was found in 31 of the 154 patients with hyperglycemia. The incidence of no-reflow was significantly greater in patients with hyperglycemia compared with no hyperglycemia. A multivariable logistic regression analysis showed that hyperglycemia on admission was an independent predictor of no-reflow. Among the 154 patients with hyperglycemia, there were no significant differences in baseline clinical characteristics between patients who received statin pretreatment and those who did not; however, hyperlipidemia occurred in a greater number of the patients who did not receive statin pretreatment. The 40 patients with hyperglycemia who received statins before admission had a lower incidence of no-reflow than those who did not receive statin pretreatment (5% and 25.4%; p < 0.05). Multivariable logistic regression analysis revealed that absence of statin pretreatment was a significant predictor of no-reflow in patients with hyperglycemia, along with ejection fraction on admission, initial TIMI 0 flow, number of Q waves, and anterior AMI.

CONCLUSION

The results of our study show that pretreatment with statins could attenuate no-reflow after AMI in patients with acute hyperglycemia.

Effects of diabetes on myocardial infarct size and cardioprotection by preconditioning and postconditioning

In spite of the current optimal therapy, the mortality of patients with ischemic heart disease (IHD) remains high, particularly in cases with diabetes mellitus (DM) as a co-morbidity. Myocardial infarct size is a major determinant of prognosis in IHD patients, and development of a novel strategy to limit infarction is of great clinical importance. Ischemic preconditioning (PC), postconditioning (PostC) and their mimetic agents have been shown to reduce infarct size in experiments using healthy animals. However, a variety of pharmacological agents have failed to demonstrate infarct size limitation in clinical trials. One of the possible reasons for the discrepancy between the results of animal experiments and clinical trials is that co-morbidities, including DM, modified myocardial responses to ischemia/reperfusion and to cardioprotective agents. Here we summarize observations of the effects of DM on myocardial infarct size and ischemic PC and PostC and discuss perspectives for protection of DM hearts.

Acute hyperglycemia causes microvascular damage, leading to poor functional recovery and remodeling in patients with reperfused ST-segment elevation myocardial infarction

BACKGROUND

Although acute hyperglycemia (AHG) is associated with poor outcomes in ST-segment elevation myocardial infarction (STEMI) patients, underlying mechanisms have not been fully elucidated. We investigated the influence of AHG on myocardial microcirculation in reperfused STEMI patients.

METHODS AND RESULTS

Thirty-four STEMI patients were divided into 2 groups according to the presence (Group H, n 5 11) or the absence (Group L, n 5 23) of AHG. Myocardial blood flow (MBF) and myocardial flow reserve (MFR) in the infarct-related area were compared between 2 groups, using ¹³N-ammonia positron emission tomography. Wall motion abnormality scores (WMASs) and end-diastolic volume indices (EDVI) were also assessed at 1 and 6 months after the onset. Although resting MBF was similar, MFR was lower in Group H than in Group L (1.69 ± 0.37 vs 2.39 ± 0.56, P = .001). WMAS was greater in Group H than in Group L at both 1 month (7.4 ± 3.7 vs 3.7 ± 3.0, P = .011) and 6 months (7.3 ± 3.9 vs 3.1 ± 3.4, P = .015). EDVI tended to be greater in Group H than in Group L at 6 months (103.8 ± 42.9 vs 73.9 ± 16.0 mL/m2, P = .071). Multivariate analysis showed AHG to be independently associated with low MFR.

CONCLUSIONS

In STEMI patients, AHG impaired myocardial microcirculation, leading to poor functional recovery and remodeling despite successful reperfusion.

High-dose fasudil preserves postconditioning against myocardial infarction under hyperglycemia in rats: role of mitochondrial KATP channels

BACKGROUND

The current study was carried out to determine whether fasudil hydrochloride (fasudil), a Rho-kinase inhibitor, has myocardial postconditioning (PostC) activity under hyperglycemia as well as normoglycemia, and if so, whether the effects could be mediated by mitochondrial ATP-sensitive potassium (m-KATP) channels.

METHODS

Male Sprague-Dawley rats were anesthetized with sodium pentobarbital. After opening the chest, all rats underwent 30-min coronary artery occlusion followed by 2-h reperfusion. The rats received low-dose (0.15 mg/kg) or high-dose (0.5 mg/kg) fasudil or diazoxide, an m-KATP channel opener, at 10 mg/kg, just before reperfusion under normoglycemic or hyperglycemic conditions. In another group, rats received 5-hydroxydecanoic acid (5HD), an m-KATP channel blocker, at 10 mg/kg, before high-dose fasudil. Myocardial infarct size was expressed as a percentage of area at risk (AAR).

RESULTS

Under normoglycemia, low-dose and high-dose fasudil and diazoxide reduced myocardial infarct size (23 ± 8%, 21 ± 9% and 21 ± 10% of AAR, respectively) compared with that in the control (42 ± 7%). Under hyperglycemia, low-dose fasudil (40 ± 11%) and diazoxide (44 ± 14%) could not exert this beneficial effect, but high-dose fasudil reduced myocardial infarct size in the same manner as under normoglycemia (21 ± 13%). 5HD prevented fasudil-induced reduction of myocardial infarct size (42 ± 13%).

CONCLUSION

Fasudil induces PostC against myocardial infarction via activation of m-KATP channels in the rat. Although hyperglycemia attenuates the PostC, high-dose fasudil can restore cardioprotection.

Insulin therapy for the management of hyperglycemia in hospitalized patients

It has long been established that hyperglycemia with or without a prior diagnosis of diabetes increases both mortality and disease-specific morbidity in hospitalized patients and that goal-directed insulin therapy can improve outcomes. This article reviews the pathophysiology of hyperglycemia during illness, the mechanisms for increased complications and mortality due to hyperglycemia and hypoglycemia, and beneficial mechanistic effects of insulin therapy and provides updated recommendations for the inpatient management of diabetes in the critical care setting and in the general medicine and surgical settings.

The diabetic heart: too sweet for its own good?

Diabetes mellitus is a major risk factor for ischemic heart disease (IHD). Patients with diabetes and IHD experience worse clinical outcomes, suggesting that the diabetic heart may be more susceptible to ischemia-reperfusion injury (IRI). In contrast, the animal data suggests that the diabetic heart may be either more, equally, or even less susceptible to IRI. The conflicting animal data may be due to the choice of diabetic and/or IRI animal model. Ischemic conditioning, a phenomenon in which the heart is protected against IRI by one or more brief nonlethal periods of ischemia and reperfusion, may provide a novel cardioprotective strategy for the diabetic heart. Whether the diabetic heart is amenable to ischemic conditioning remains to be determined using relevant animal models of IRI and/or diabetes. In this paper, we review the limitations of the current experimental models used to investigate IRI and cardioprotection in the diabetic heart.

Acute hyperglycemia in patients with acute myocardial infarction

Acute hyperglycemia is a common feature during the early phase after acute myocardial infarction (AMI), regardless of diabetes status. Numerous studies have demonstrated that patients with AMI and hyperglycemia on admission have high rates of mortality. It has been reported that there is a linear positive relation between admission blood glucose levels and mortality after AMI. However, recent studies showed that the relationship is U-shaped in patients with a history of diabetes. Diabetic patients with moderate hyperglycemia (glucose 9-11 mmol/L) had the lowest mortality and not only severe hyperglycemia (glucose ≥ 11 mmol/L) but also euglycemia (glucose < 7 mmol/L) was associated with higher mortality. Although it has been debated whether acute hyperglycemia is causally related to adverse outcomes after AMI or is simply an epiphenomenon of severely damaged myocardium, multiple physiological studies have demonstrated that hyperglycemia has a direct detrimental effect on ischemic myocardium through several mechanisms, including oxidative stress, inflammation, apoptosis, endothelial dysfunction, hypercoagulation, platelet aggregation and impairment of ischemic preconditioning. Current guidelines recommend the use of an insulin-based regimen to achieve and maintain glucose levels < 10.0 mmol/dl, and emphasize the avoidance of hypoglycemia. However, the optimal management goal of glucose levels for patients with acute hyperglycemia remains uncertain. Further studies are warranted into the appropriate management in patients with AMI and acute hyperglycemia.

Hyperglycemia raises the threshold of levosimendan- but not milrinone-induced postconditioning in rat hearts

Background

The authors examined whether milrinone and levosimendan could exert cardiac postconditioning effects in rats under normoglycemia and hyperglycemia, and whether the effects could be mediated by mitochondrial permeability transition pore (mPTP).

Methods

Wistar rats underwent 30-min coronary artery occlusion followed by 2-h reperfusion. The rats received milrinone or levosimendan just before reperfusion under normoglycemic or hyperglycemic conditions with or without atractyloside, an mPTP opener.

Results

Under normoglycemia, both 30 μg/kg milrinone (29 ± 12%) and 10 μg/kg levosimendan (33 ± 13%) reduced infarct size compared with that in the control (58 ± 7%). Under hyperglycemia, milrinone (34 ± 13%) reduced infarct size at the same dose as under normoglycemia. In contrast, neither 10 nor 30 μg/kg levosimendan protected hyperglycemic hearts, and only 100 μg/kg levosimendan (32 ± 9%) reduced infarct size compared with that in the hyperglycemic control (58 ± 13%). All of these cardioprotective effects under normoglycemia and hyperglycemia are abolished by atractyloside.

Conclusion

Milrinone and levosimendan exert postconditioning effects via inhibition of mPTP opening. Hyperglycemia raises the threshold of levosimendan-induced postconditioning, while milrinone-induced postconditioning is not influenced by hyperglycemia.

The potential effects of anti-diabetic medications on myocardial ischemia-reperfusion injury

Heart disease and stroke account for 65% of the deaths in people with diabetes mellitus (DM). DM and hyperglycemia cause systemic inflammation, endothelial dysfunction, a hypercoagulable state with impaired fibrinolysis and increased platelet degranulation, and reduced coronary collateral blood flow. DM also interferes with myocardial protection afforded by preconditioning and postconditioning. Newer anti-diabetic agents should not only reduce serum glucose and HbA1c levels, but also improve cardiovascular outcomes. The older sulfonylurea agent, glyburide, abolishes the benefits of ischemic and pharmacologic preconditioning, but newer sulfonylurea agents, such as glimepiride, may not interfere with preconditioning. GLP-1 analogs and sitagliptin, an oral dipeptidyl peptidase IV inhibitor, limit myocardial infarct size in animal models by increasing intracellular cAMP levels and activating protein kinase A, whereas metformin protects the heart by activating AMP-activated protein kinase. Both thiazolidinediones (rosiglitazone and pioglitazone) limit infarct size in animal models. The protective effect of pioglitazone is dependent on downstream activation of cytosolic phospholipase A(2) and cyclooxygenase-2 with subsequent increased production of 15-epi-lipoxin A(4), prostacyclin and 15-d-PGJ(2). We conclude that agents used to treat DM have additional actions that have been shown to affect the ability of the heart to protect itself against ischemia-reperfusion injury in preclinical models. However, the effects of these agents in doses used in the clinical setting to minimize ischemia-reperfusion injury and to affect clinical outcomes in patients with DM have yet to be shown. The clinical implications as well as the mechanisms of protection should be further studied.