Impact of hyperglycemia on myocardial ischemia-reperfusion susceptibility and ischemic preconditioning in hearts from rats with type 2 diabetes

Effects of Canagliflozin Preconditioning on Post-resuscitation Myocardial Function in a Diabetic Rat Model of Cardiac Arrest and Cardiopulmonary Resuscitation

BACKGROUND

Canagliflozin can reduce the risk of cardiovascular disease in patients except for its targeted antidiabetic effects. However, it remains unknown whether canagliflozin alleviates the post-resuscitation myocardial dysfunction (PRMD) in type 2 diabetes mellitus.

OBJECTIVE

To explore the effects and potential mechanisms of canagliflozin on myocardial function after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) in a type 2 diabetic rat model.

METHODS

Twenty-four type 2 diabetic rats were randomized into four groups: (1) sham+canagliflozin, (2) sham+placebo, (3) CPR+placebo, and (4) CPR+canagliflozin. Except for the sham+canagliflozin and placebo groups, both the CPR+placebo and canagliflozin groups underwent 8 minutes of CPR after the induction of ventricular fibrillation for 6 minutes. Myocardial function and hemodynamics were assessed at baseline and within 6 hours after autonomous circulation (ROSC) return. Left ventricular tissues were sampled to determine the expressions of relevant proteins in the NLRP3 inflammasome pathway.

RESULTS

The results demonstrated that the mean arterial pressure (MAP) was significantly improved in the CPR+canagliflozin group after ROSC compared with the CPR+placebo group (p <0.05). Meanwhile, both ejection fraction (EF) and fraction shortening (FS) were dramatically increased in the CPR+canagliflozin group when compared with the CPR+placebo group at 2h, 4h, and 6h after ROSC (p <0.05). In addition, the levels of NT-proBNP, cTn-I, and NLRP3 inflammatory inflammasome-associated proteins were significantly decreased in the CPR+canagliflozin group compared with the CPR+placebo group.

CONCLUSIONS

In type 2 diabetic rats, pretreatment of canagliflozin alleviates PRMD. The potential mechanisms may include inhibition of the NLRP3/caspase-1 signaling pathway.

Mechanisms and Therapeutic Strategies for Myocardial Ischemia-Reperfusion Injury in Diabetic States

In patients with myocardial infarction, one of the complications that may occur after revascularization is myocardial ischemia-reperfusion injury (IRI), characterized by a depleted myocardial oxygen supply and absence of blood flow recovery after reperfusion, leading to expansion of myocardial infarction, poor healing of myocardial infarction and reversal of left ventricular remodeling, and an increase in the risk for major adverse cardiovascular events such as heart failure, arrhythmia, and cardiac cell death. As a risk factor for cardiovascular disease, diabetes mellitus increases myocardial susceptibility to myocardial IRI through various mechanisms, increases acute myocardial infarction and myocardial IRI incidence, decreases myocardial responsiveness to protective strategies and efficacy of myocardial IRI protective methods, and increases diabetes mellitus mortality through myocardial infarction. This Review summarizes the mechanisms, existing therapeutic strategies, and potential therapeutic targets of myocardial IRI in diabetic states, which has very compelling clinical significance.

Inhibition of Caspase-1-dependent pyroptosis alleviates myocardial ischemia/reperfusion injury during cardiopulmonary bypass (CPB) in type 2 diabetic rats

Cardiovascular complications pose a significant burden in type 2 diabetes mellitus (T2DM), driven by the intricate interplay of chronic hyperglycemia, insulin resistance, and lipid metabolism disturbances. Myocardial ischemia/reperfusion (MI/R) injury during cardiopulmonary bypass (CPB) exacerbates cardiac vulnerability. This study aims to probe the role of Caspase-1-dependent pyroptosis in global ischemia/reperfusion injury among T2DM rats undergoing CPB, elucidating the mechanisms underlying heightened myocardial injury in T2DM. This study established a rat model of T2DM and compared Mean arterial pressure (MAP), heart rate (HR), and hematocrit (Hct) between T2DM and normal rats. Myocardial cell morphology, infarction area, mitochondrial ROS and caspase-1 levels, NLRP3, pro-caspase-1, caspase-1 p10, GSDMD expressions, plasma CK-MB, cTnI, IL-1β, and IL-18 levels were assessed after reperfusion in both T2DM and normal rats. The role of Caspase-1-dependent pyroptosis in myocardial ischemia/reperfusion injury during CPB in T2DM rats was examined using the caspase-1 inhibitor VX-765 and the ROS scavenger NAC. T2DM rats demonstrated impaired glucose tolerance but stable hemodynamics during CPB, while showing heightened vulnerability to MI/R injury. This was marked by substantial lipid deposition, disrupted myocardial fibers, and intensified cellular apoptosis. The activation of caspase-1-mediated pyroptosis and increased reactive oxygen species (ROS) production further contributed to tissue damage and the ensuing inflammatory response. Notably, myocardial injury was mitigated by inhibiting caspase-1 through VX-765, which also attenuated the inflammatory cascade. Likewise, NAC treatment reduced oxidative stress and partially suppressed ROS-mediated caspase-1 activation, resulting in diminished myocardial injury. This study proved that Caspase-1-dependent pyroptosis significantly contributes to the inflammation and injury stemming from global MI/R in T2DM rats under CPB, which correlate with the surplus ROS generated by oxidative stress during reperfusion.

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.

Roles of O-GlcNAcylation in Mitochondrial Homeostasis and Cardiovascular Diseases

Protein posttranslational modifications are important factors that mediate the fine regulation of signaling molecules. O-linked β-N-acetylglucosamine-modification (O-GlcNAcylation) is a monosaccharide modification on N-acetylglucosamine linked to the hydroxyl terminus of serine and threonine of proteins. O-GlcNAcylation is responsive to cellular stress as a reversible and posttranslational modification of nuclear, mitochondrial and cytoplasmic proteins. Mitochondrial proteins are the main targets of O-GlcNAcylation and O-GlcNAcylation is a key regulator of mitochondrial homeostasis by directly regulating the mitochondrial proteome or protein activity and function. Disruption of O-GlcNAcylation is closely related to mitochondrial dysfunction. More importantly, the O-GlcNAcylation of cardiac proteins has been proven to be protective or harmful to cardiac function. Mitochondrial homeostasis is crucial for cardiac contractile function and myocardial cell metabolism, and the imbalance of mitochondrial homeostasis plays a crucial role in the pathogenesis of cardiovascular diseases (CVDs). In this review, we will focus on the interactions between protein O-GlcNAcylation and mitochondrial homeostasis and provide insights on the role of mitochondrial protein O-GlcNAcylation in CVDs.

Effect of Dexmedetomidine Preconditioning on Hepatic Ischemia-Reperfusion Injury in Acute Hyperglycemic Rats

BACKGROUND

Acute hyperglycemia frequently occurs in stressful situations, including liver transplantation or hepatic surgery, which may affect the protective effects of dexmedetomidine preconditioning and increase postoperative mortality. Therefore, this study aimed to investigate the effects of dexmedetomidine on hepatic ischemia-reperfusion injury in acute hyperglycemia.

METHODS

Thirty-six Sprague-Dawley rats were randomly assigned to 6 groups, including a combination between 2 glycemic (normo- and hyperglycemia) and 3 ischemia-reperfusion conditions (sham, ischemia-reperfusion only, and dexmedetomidine plus ischemia-reperfusion). Dexmedetomidine 70 μg/kg was preconditioned 30 minutes before ischemic injury. After 6 hours of reperfusion, serum aminotransferase levels were measured to confirm the hepatic tissue injury. Furthermore, inflammatory (nuclear factor-κb, tumor necrosis factor-α, and interleukin-6) and oxidative stress markers (malondialdehyde and superoxide dismutase) were detected.

RESULTS

Ischemia-reperfusion injury significantly increased the serum levels of aminotransferase and inflammatory and oxidative stress markers. These ischemia-reperfusion-induced changes were further exacerbated in hyperglycemia and were significantly attenuated by dexmedetomidine preconditioning. However, the effects of dexmedetomidine in hyperglycemia were lesser than those in normoglycemia (P < .05 for aminotransferases, inflammatory markers, malondialdehyde, and superoxide dismutase).

CONCLUSIONS

These findings suggest that the protective effects of dexmedetomidine preconditioning may be intact against hepatic ischemia-reperfusion injury in acute hyperglycemia. Although its effects appeared to be relatively reduced, this may be because of the increase in oxidative stress and inflammatory response caused by acute hyperglycemia. To determine whether the effects of dexmedetomidine itself would be impaired in hyperglycemia, further study is needed.

Organ-specific model of simulated ischemia/reperfusion and hyperglycemia based on engineered heart tissue

Here we aimed to establish an in vitro engineered heart tissue (EHT) co-morbidity mimicking model of ischemia-reperfusion injury and diabetes. EHTs were generated from primary neonatal rat cardiomyocytes. Hyperglycemic conditions or hyperosmolar controls were applied for one day to model acute hyperglycemia and for seven days to model chronic hyperglycemia. 120 min' simulated ischemia (SI) was followed by 120 min' reperfusion (R) and 1-day follow-up reperfusion (FR). Normoxic controls (N) were not subjected to SI/R. Half of the EHTs was paced, the other half was left unpaced. To assess cell injury, lactate-dehydrogenase (LDH) concentration was measured. Beating force and activity (frequency) were monitored as cardiomyocyte functional parameters. LDH-release indicated relevant cell injury after SI/N in each experimental condition, with much higher effects in the chronically hyperglycemic/hyperosmolar groups. SI stopped beating of EHTs in each condition, which returned during reperfusion, with weaker recovery in chronic conditions than in acute conditions. Acutely treated EHTs showed small LDH-release and ∼80% recovery of force during reperfusion and follow-up, while chronically treated EHTs showed a marked LDH-release, only ∼30% recovery with reperfusion and complete loss of beating activity during 24 h follow-up reperfusion. We conclude that EHTs respond differently to SI/R injury in acute and chronic hyperglycemia/hyperosmolarity, and that our EHT model is a novel in vitro combination of diabetes and ischemia-reperfusion.

Nobiletin alleviates myocardial ischemia-reperfusion injury via ferroptosis in rats with type-2 diabetes mellitus

Susceptibility to myocardial ischemia-reperfusion (IR) injury in type-2 diabetes (T2DM) remains disputed, although studies have reported that ferroptosis is associated with myocardial IR injury. Nobiletin, a flavonoid isolated from citrus peels, is an antioxidant that possesses anti-inflammatory and anti-diabetic activities. However, it remains unknown whether nobiletin has any protective effects on susceptibility to myocardial IR injury during T2DM in rats via ferroptosis. To investigate the effects and underlying mechanisms of nobiletin on myocardial IR injury during T2DM, we induced myocardial IR model in rats at T2DM onset vs mature disease. We also established a high-fat high-glucose (HFHG) and hypoxia-reoxygenation (H/R) model in H9c2 cells to imitate abnormal glycolipid metabolism during T2DM. Myocardial injury, oxidative stress and ferroptosis towards myocardial IR in rats with mature T2DM but not at T2DM onset were increased. These changes were restored under treatment with ferrostain-1 or nobiletin. Both ferrostain-1 and nobiletin decreased the expression of ferroptosis-related proteins including Acyl-CoA synthetase long chain family member 4 (ACSL4) and nuclear receptor coactivator 4 (NCOA4) but not glutathione peroxidase 4 (GPX4) in rats with mature T2DM and cells with HFHG and H/R injury. Nobiletin strengthened the effect of si-ACSL4 on inhibiting ACSL4 expression, and also inhibited the effect of Erastin or oe-ACSL4 on increasing ACSL4 expression. Taken together, our data indicates that ferroptosis involves in susceptibility to myocardial IR injury in rats during T2DM. Nobiletin has therapeutic potential for alleviating myocardial IR injury associated with ACSL4- and NCOA4-related ferroptosis.

Research progress on the effects of novel hypoglycemic drugs in diabetes combined with myocardial ischemia/reperfusion injury

Acute myocardial infarction (AMI) reperfusion is associated with ischemia/reperfusion (I/R) injury, which leads to enlarged myocardial infarction size, poor healing of the infarcted myocardium, and poor left ventricular remodeling, thus increasing the risk of major adverse cardiovascular events (MACEs). Diabetes increases myocardial susceptibility to I/R injury, decreases myocardial responsiveness to cardioprotective strategies, exacerbates myocardial I/R injury, and expands the infarct size of AMI, thereby increasing the incidence of malignant arrhythmias and heart failure. Currently, evidence regarding pharmacological interventions for diabetes combined with AMI and I/R injury is lacking. Traditional hypoglycemic drugs have a limited role in the prevention and treatment of diabetes combined with I/R injury. Current evidence suggests that novel hypoglycemic drugs may exert a preventive effect on diabetes combined with myocardial I/R injury, especially glucagon-like peptide-1 receptor agonists (GLP-1 RA) and sodium-dependent glucose transporter protein 2 inhibitors (SGLT2i), which may increase coronary blood flow, reduce acute thrombosis, attenuate I/R injury, decrease myocardial infarction size, inhibit structural and functional remodeling of the ischemic heart, improve cardiac function, and reduce the occurrence of MACEs of diabetes patients combined with AMI via mechanisms such as reduction of inflammatory response, inhibition of oxidative stress, and improvement of vascular endothelial function. This paper will systematically elaborate the protective role and molecular mechanisms of GLP-1 RA and SGLT2i in diabetes combined with myocardial I/R injury, aiming to provide clinical assistance.

Influence of cigarettes on myocardial injury in healthy population after exposure to high altitude over 5000 m

BACKGROUND

Myocardial injury (MI) is a severe complication once subjected to hypoxic condition at high altitude. Little evidence exists about the association of cigarettes and MI at high altitude, especially over 5000 m. In the present study, we intend to explore the influence of cigarettes on MI in healthy population after travelling to this extreme environment.

METHODS

Physical examination was performed in population at Pamirs plateau during November and December 2020. All participants were divided into cigarette group or control group. MI was diagnosed based on lactate dehydrogenase (LDH), creatine kinase (CK), creatine kinase isoenzymes (CK-MB) and aspartate amino transferase (AST).

RESULTS

311 people were included, 58 of whom developed MI, accounting for 18.6 %. Participants in cigarette group were all male, and younger than those in control group. There was longer exposure time in cigarette group. Compared with control group, red blood cell counting, hemoglobin (HGB) and hematocrit in cigarette group were significantly increased, while heart rate was significantly decreased. Cigarettes were found to significantly upregulate the level of CK-MB and LDH. After adjustment with age, sex, body mass index, altitude and exposure time as covariables, 108 male participants remained in each group, showing that none of clinical indexes had significant difference between the two groups. Logistic regression analysis revealed that female sex and oxygen saturation (SO₂) were independent risk factors for MI in non-smokers while HGB was independent risk factor in smokers. By using Spearman correlation analysis, four myocardial enzymes were not relevant with the level of SO₂ in non-smokers. For smokers, HGB was found to be in significant positive correlation with LDH.

CONCLUSION

Our study suggested that exposure to high altitude over 5000 m could abrogate the impact of cigarettes on MI in healthy population. The independent factors affecting the occurrence of MI were distinctive depending on current smoking status.

Remote ischemic preconditioning-induced late cardioprotection: possible role of melatonin-mitoKATP-H2S signaling pathway

PURPOSE

Remote ischemic preconditioning (RIPC) confers cardioprotection against ischemia reperfusion (IR) injury. However, the precise mechanisms involved in RIPC-induced cardioprotection are not fully explored. The present study was aimed to identify the role of melatonin in RIPC-induced late cardioprotective effects in rats and to explore the role of H2S, TNF-α and mitoKATP in melatonin-mediated effects in RIPC.

METHODS

Wistar rats were subjected to RIPC in which hind limb was subjected to four alternate cycles of ischemia and reperfusion of 5 min duration by using a neonatal blood pressure cuff. After 24 h of RIPC or ramelteon-induced pharmacological preconditioning, hearts were isolated and subjected to IR injury on the Langendorff apparatus.

RESULTS

RIPC and ramelteon preconditioning protected the hearts from IR injury and it was assessed by a decrease in LDH-1, cTnT and increase in left ventricular developed pressure (LVDP). RIPC increased the melatonin levels (in plasma), H2S (in heart) and decreased TNF-α levels. The effects of RIPC were abolished in the presence of melatonin receptor blocker (luzindole), ganglionic blocker (hexamethonium) and mitochondrial KATP blocker (5-hydroxydecanoic acid).

CONCLUSIONS

RIPC produce delayed cardioprotection against IR injury through the activation of neuronal pathway, which may increase the plasma melatonin levels to activate the cardioprotective signaling pathway involving the opening of mitochondrial KATP channels, decrease in TNF-α production and increase in H2S levels. Ramelteon-induced pharmacological preconditioning may also activate the cardioprotective signaling pathway involving the opening of mitochondrial KATP channels, decrease in TNF-α production and increase in H2S levels.

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.

Diabetes mellitus — metabolic preconditioning in protecting the heart from ischemic damage?

The negative impact of diabetes mellitus (DM) on the cardiovascular system has been confirmed by numerous clinical studies. However, there are experimental studies that show an increase in the resistance of the heart to ischemic and reperfusion damage in animals with DM. This phenomenon is characterized by a smaller size of the infarct zone, better preservation of the contractile function of the myocardium, and a lower incidence of ischemic and reperfusion arrhythmias. It is assumed that at a certain stage in the development of DM, a “metabolic window” is formed, in which metabolic alterations at the cellular level trigger adaptive mechanisms that increase the viability of cardiomyocytes. Published data confirm that the magnitude of the protective effect induced by DM is comparable to, and in some cases even exceeds, the effect of the preconditioning phenomenon. It is recognized that the mechanisms that protect the heart from ischemic and reperfusion damage against the background of DM are universal and are associated with the modulation of the antioxidant system, apoptosis factors, pro-inflammatory cytokines, and signaling systems that ensure cell survival. The one of the main pathogenic factor in DM is hyperglycemia, but under stress it plays the role of an adaptive mechanism aimed at meeting the increased energy demand in pathological conditions. Probably, at a certain stage of DM, hyperglycemia becomes a trigger for the development of protective effects and activates not only signaling pathways, but also the restructuring of energy metabolism, which makes it possible to maintain ATP production at a sufficient level to maintain the vital activity of heart cells under ischemia/reperfusion conditions. It is possible that an increased level of glucose, accompanied by the activation of insulin-independent mechanisms of its entry into cells, as well as the availability of this energy substrate, will contribute to a better restoration of energy production in heart cells after a infarction, which, in turn, will significantly reduce the degree of myocardial damage and will help preserve the contractile function of the heart. Identification of the conditions and mechanisms of the cardioprotective phenomenon induced by DM will make it possible to simulate the metabolic state in which the protection of cardiomyocytes from damaging factors is realized.

Rev-erbs agonist SR9009 alleviates ischemia-reperfusion injury by heightening endogenous cardioprotection at onset of type-2 diabetes in rats: Down-regulating ferritinophagy/ferroptosis signaling

The complex progression of type-2 diabetes (T2DM) results in inconsistent findings on myocardial susceptibility to ischemia-reperfusion (IR). IR injuries in multiple organs interconnect with ferroptosis. Targeting Rev-erbs might limit ferroptosis, with increasing attention turning to the application of circadian medicine against IR injuries. However, whether the Rev-erbs agonist SR9009 could mitigate diabetic IR injury remains unknown. Here, we investigated the susceptibility to IR at onset of T2DM in rats and its potential association between SR9009 and ferritinophagy/ferroptosis signaling. Onset of T2DM model was induced with a high-fat diet and the intraperitoneal injection of a low dose of streptozotocin. Myocardial IR model was established as well. Rats' general characteristics, cardiac function, glycolipid profiles, serum biochemistry, apoptosis index (AI) and morphological histology were observed and analyzed. Western blot and immunofluorescence (IF) were employed to evaluate the expression of ferritinophagy/ferroptosis signaling and its co-localization. Glycolipid profiles and cardiac diastolic function were significantly impaired in diabetic rats. CK-MB, AI levels and ferritinophagy/ferroptosis-related proteins expression decreased towards myocardial IR in diabetic rats compared to non-diabetic rats'. The ferroptosis inducer Erastin up-regulated SOD, MDA, and AI levels, as well as the expression of ferritinophagy/ferroptosis-related proteins in diabetic rats towards IR. Treatment with SR9009 down-regulated the degree of myocardial injury and ferritinophagy/ferroptosis-related proteins expression compared to diabetic rats treated with or without Erastin. Onset of T2DM activated endogenous cardioprotection against the susceptibility to myocardial IR injury, and SR9009 exogenously enhanced this endogenous mechanism and alleviated myocardial IR injury at onset of T2DM by down-regulating ferritinophagy/ferroptosis signaling.

Short and long-term prognosis of admission hyperglycemia in patients with and without diabetes after acute myocardial infarction: a retrospective cohort study

OBJECTIVE

Admission hyperglycemia is associated with poor prognosis in patients with acute myocardial infarction (AMI), but the effects of baseline diabetes status on this association remain elusive. We aim to investigate the impact of admission hyperglycemia on short and long-term outcomes in diabetic and non-diabetic AMI patients.

METHODS

In this retrospective cohort study, 3330 patients with regard to first-time AMI between July 2012 and July 2020 were identified. Participants were divided into two groups according to diabetes status (1060 diabetic patients and 2270 non-diabetic patients). Thereafter, they were divided into four groups according to diabetes status-specific cutoff values of fasting blood glucose (FBG) identified by restricted cubic spline. Short-term outcomes included in-hospital death and cardiac complications. Long-term outcomes were all-cause mortality and major adverse cardiovascular events (MACE). Inverse probability of treatment weighting (IPTW) was conducted to adjust for baseline differences among the groups, followed by a weighted Cox proportional hazards regression analysis to calculate hazard ratios and 95% confidence intervals for all-cause mortality associated with each FBG category. Subgroup analysis and sensitivity analysis were performed to test the robustness of our findings.

RESULTS

During a median follow-up of 3.2 years, 837 patients died. There was a significant interaction between diabetes status and FBG levels for all-cause mortality during long-term follow-up (p-interaction < 0.001). Moreover, restricted cubic spline curves for the association between FBG and all-cause mortality followed a J shape in patients with diabetes and a non-linear in patients without diabetes. Kaplan-Meier analysis demonstrated greater survival in non-hyperglycemia patients compared to hyperglycemia patients for both diabetic and non-diabetic patients groups. Survival of hyperglycemia patients without diabetes greater than in hyperglycemia patients with diabetes. In the weighted Multivariable cox analysis, admission hyperglycemia predicted higher short and long-term mortality. Subgroup analysis and sensitivity analysis showed the robustness of the results.

CONCLUSIONS

The inflection points of FBG level for poor prognosis were 5.60 mmol/L for patients without diabetes and 10.60 mmol/L for patients with diabetes. Admission hyperglycemia was identified as an independent predictor of worse short and long-term outcomes in AMI patients, with or without diabetes. These findings should be explored further.

Risk Factors of Ischemia Reperfusion Injury After PCI in Patients with Acute ST-Segment Elevation Myocardial Infarction and its Influence on Prognosis

Purpose

To explore the risk factors of ischemia reperfusion injury (IRI) after percutaneous coronary intervention (PCI) in patients with acute ST-segment elevation myocardial infarction (STEMI) and its influence on prognosis.

Methods

The clinical data of 80 patients with STMEI undergoing PCI in our hospital from June 2020 to June 2021 were collected. According to whether IRI occurred after PCI, STMEI patients were divided into IRI group and non-IRI group. The basic information, clinical characteristics, examination parameters and other data of all patients were collected, and the prognosis of the two groups was observed. Risk factors were analyzed by fitting binary Logistic regression model. The survival prognosis was analyzed by Kaplan-Meier survival curve.

Results

Logistic regression analysis showed that type 2 diabetes mellitus (T2DM), pre-hospital delay time (PHD) and door-to-balloon expansion time (DTB) were the influencing factors of IRI in patients with STMEI (p < 0.05). MACE occurred in 11 cases (32.35%) in the IRI group and 13 cases (28.26%) in the non-IRI group. Log-rank test showed p = 0.503, indicating no statistically significant difference.

Conclusion

T2DM, PHD and DTB were the influencing factors of IRI in patients with STMEI, and IRI will not reduce the prognosis of patients.

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.

The dual role of the hexosamine biosynthetic pathway in cardiac physiology and pathophysiology

The heart is a highly metabolic organ with extensive energy demands and hence relies on numerous fuel substrates including fatty acids and glucose. However, oxidative stress is a natural by-product of metabolism that, in excess, can contribute towards DNA damage and poly-ADP-ribose polymerase activation. This activation inhibits key glycolytic enzymes, subsequently shunting glycolytic intermediates into non-oxidative glucose pathways such as the hexosamine biosynthetic pathway (HBP). In this review we provide evidence supporting the dual role of the HBP, i.e. playing a unique role in cardiac physiology and pathophysiology where acute upregulation confers cardioprotection while chronic activation contributes to the onset and progression of cardio-metabolic diseases such as diabetes, hypertrophy, ischemic heart disease, and heart failure. Thus although the HBP has emerged as a novel therapeutic target for such conditions, proposed interventions need to be applied in a context- and pathology-specific manner to avoid any potential drawbacks of relatively low cardiac HBP activity.

Effect of sleeve gastrectomy, Roux-en-Y gastric bypass, and ileal transposition on myocardial ischaemia-reperfusion injury in non-obese non-diabetic rats

Bariatric surgery (BS) improves outcomes in patients with myocardial infarction (MI). Here we tested the hypothesis that BS-mediated reduction in fatal MI could be attributed to its infarct-limiting effect. Wistar rats were randomized into five groups: control (CON), sham (SHAM), Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy (SG), and ileotransposition (IT). Ten weeks later, animals were subjected to 30-min myocardial ischemia plus 120-min reperfusion. Infarct size (IS) and no-reflow area were determined histochemically. Fasting plasma levels of glucagon-like peptide-1 (GLP-1), leptin, ghrelin, and insulin were measured using ELISA. Compared with SHAM, RYGB and SG reduced IS by 22% (p = 0.011) and 10% (p = 0.027), and no-reflow by 38% (p = 0.01) and 32% (p = 0.004), respectively. IT failed to reduce IS and no-reflow. GLP-1 level was increased in the SG and RYGB groups compared with CON. In both the SG and RYGB, leptin level was decreased compared with CON and SHAM. In the SG group, ghrelin level was lower than that in the CON and SHAM. Insulin levels were not different between groups. In conclusion, RYGB and SG increased myocardial tolerance to ischemia-reperfusion injury of non-obese, non-diabetic rats, and their infarct-limiting effect is associated with decreased leptin and ghrelin levels and increased GLP-1 level.

Protein O-GlcNAcylation in the heart

O-GlcNAcylation is a ubiquitous post-translational modification that is extremely labile and plays a significant role in physiology, including the heart. Sustained activation of cardiac O-GlcNAcylation is frequently associated with alterations in cellular metabolism, leading to detrimental effects on cardiovascular function. This is particularly true during conditions such as diabetes, hypertension, cardiac remodelling, heart failure and arrhythmogenesis. Paradoxically, transient elevation of cardiac protein O-GlcNAcylation can also exert beneficial effects in the heart. There is compelling evidence to suggest that a complex interaction between O-GlcNAcylation and phosphorylation also exists in the heart. Beyond direct functional consequences on cardiomyocytes, O-GlcNAcylation also acts indirectly by altering the function of transcription factors that affect downstream signalling. This review focuses on the potential cardioprotective role of protein O-GlcNAcylation during ischaemia-reperfusion injury, the deleterious consequences of chronically elevated O-GlcNAc levels, the interplay between O-GlcNAcylation and phosphorylation in the cardiomyocytes and the effects of O-GlcNAcylation on other major non-myocyte cell types in the heart.

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.

Effects of three types of bariatric interventions on myocardial infarct size and vascular function in rats with type 2 diabetes mellitus

AIMS

The effects of three types of bariatric interventions on myocardial infarct size were tested in the rat model of type 2 diabetes mellitus (T2DM). We also evaluated the effects of bariatric surgery on no-reflow phenomenon and vascular dysfunction caused by T2DM.

MAIN METHODS

Rats with T2DM were assigned into groups: without surgery, sham-operated, ileal transposition, Roux-en-Y gastric bypass, and sleeve gastrectomy. Oral glucose tolerance, glucagon-like peptide-1, and insulin levels were measured. Six weeks after surgery, the animals were subjected to myocardial ischemia-reperfusion followed by histochemical determination of infarct size (IS), no-reflow zone, and blood stasis area size. Vascular dysfunction was characterized using wire myography.

KEY FINDINGS

All bariatric surgery types caused significant reductions in animal body weight and resulted in T2DM compensation. All bariatric interventions partially normalized glucagon-like peptide-1 responses attenuated by T2DM. IS was significantly smaller in animals with T2DM. Bariatric surgery provided no additional IS limitation compared with T2DM alone. Bariatric surgeries reversed T2DM-induced enhanced contractile responses of the mesenteric artery to 5-hydroxytryptamine. Sleeve gastrectomy normalized decreased nitric oxide synthase contribution to the endothelium-dependent vasodilatation in T2DM.

SIGNIFICANCE

T2DM resulted in a reduction of infarct size and no-reflow zone size. Bariatric surgery provided no additional infarct-limiting effect, but it normalized T2DM-induced augmented vascular contractility and reversed decreased contribution of nitric oxide to endothelium-dependent vasodilatation typical of T2DM. All taken together, we suggest that this type of surgery may have a beneficial effect on T2DM-induced cardiovascular diseases.

Matrix Metalloproteinases and Their Role in Mechanisms Underlying Effects of Quercetin on Heart Function in Aged Zucker Diabetic Fatty Rats

Several mechanisms may contribute to cardiovascular pathology associated with diabetes, including dysregulation of matrix metalloproteinases (MMPs). Quercetin (QCT) is a substance with preventive effects in treatment of cardiovascular diseases and diabetes. The aim of the present study was to explore effects of chronic QCT administration on changes in heart function in aged lean and obese Zucker Diabetic Fatty (ZDF) rats and that in association with MMPs. Signaling underlying effects of diabetes and QCT were also investigated. In the study, we used one-year-old lean and obese ZDF rats treated for 6 weeks with QCT. Results showed that obesity worsened heart function and this was associated with MMP-2 upregulation, MMP-28 downregulation, and inhibition of superoxide dismutases (SODs). Treatment with QCT did not modulate diabetes-induced changes in heart function and MMPs. However, QCT activated Akt kinase and reversed effects of diabetes on SODs inhibition. In conclusion, worsened heart function due to obesity involved changes in MMP-2 and MMP-28 and attenuation of antioxidant defense by SOD. QCT did not have positive effects on improvement of heart function or modulation of MMPs. Nevertheless, its application mediated activation of adaptive responses against oxidative stress through Akt kinase and prevention of diabetes-induced negative effects on antioxidant defense by SODs.

Involvement of amylin B-H2S-connexin 43 signaling pathway in vascular dysfunction and enhanced ischemia-reperfusion-induced myocardial injury in diabetic rats

The present study was designed to investigate the role of amylin, H₂S, and connexin 43 in vascular dysfunction and enhanced ischemia–reperfusion (I/R)-induced myocardial injury in diabetic rats. A single dose of streptozotocin (65 mg/kg) was employed to induce diabetes mellitus. After 8 weeks, there was a significant decrease in the plasma levels of amylin, an increase in I/R injury to isolated hearts (increase in CK-MB and cardiac troponin release) on the Langendorff apparatus. Moreover, there was a significant impairment in vascular endothelium function as assessed by quantifying acetylcholine-induced relaxation in norepinephrine-precontracted mesenteric arteries. There was also a marked decrease in the expression of H₂S and connexin 43 in the hearts following I/R injury in diabetic rats. Treatment with amylin agonist, pramlintide (100 and 200 µg/kg), and H₂S donor, NaHS (10 and 20 μmol/kg) for 2 weeks improved the vascular endothelium function, abolished enhanced myocardial injury and restored the levels of H₂S along with connexin 43 in diabetic animals. However, pramlintide and NaHS failed to produce these effects the presence of gap junction blocker, carbenoxolone (20 and 40 mg/kg). Carbenoxolone also abolished the myocardial levels of connexin 43 without affecting the plasma levels of amylin and myocardial levels of H₂S. The decrease in the amylin levels with a consequent reduction in H₂S and connexin 43 may contribute to inducing vascular dysfunction and enhancing I/R-induced myocardial injury in diabetic rats.

The disappearance of IPO in myocardium of diabetes mellitus rats is associated with the increase of succinate dehydrogenase-flavin protein

BACKGROUND

The aim of the present study was to investigate whether the disappearance of ischemic post-processing (IPO) in the myocardium of diabetes mellitus (DM) is associated with the increase of succinate dehydrogenase-flavin protein (SDHA).

METHODS

A total of 50 Sprague Dawley rats, weighing 300-400 g, were divided into 5 groups according to the random number table method, each with 10 rats. After DM rats were fed a high-fat and -sugar diet for 4 weeks, they were injected with Streptozotocin to establish the diabetic rat model. Normal rats were fed the same regular diet for the same number of weeks. Next, the above rats were taken to establish a cardiopulmonary bypass (CPB) model. Intraperitoneal glucose tolerance test (IPGTT) and oral glucose tolerance test (OGTT) were used to detect whether the DM rat model was established successfully. Taking blood from the femoral artery to collect the blood-gas analysis indicators, and judged whether the CPB model is established. After perfusion was performed according to the experimental strategy, the area of myocardial infarction (MI), and serum creatine kinase isoenzyme (CK-MB) and cardiac troponin (CTnI) levels were measured. Finally, the relative mRNA and protein expression of SDHA was detected.

RESULTS

The OGTT and IPGTT suggested that the DM rat model was successfully established. The arterial blood gas analysis indicated that the CPB model was successfully established. As compared with the N group, the heart function of the IR group was significantly reduced, the levels of myocardial enzyme markers, the area of MI, as well as the relative mRNA and protein expression of SDHA, were all increased. As compared with the IR group, the CK-MB and CTnI levels in the IPO group, the MI area, relative mRNA and protein expression of SDHA decreased. As compared with the IPO group, the myocardial enzyme content in the DM + IPO group, the MI area and the relative mRNA and protein expression of SDHA increased. As compared with the DM + IPO group, in the DM + IPO + dme group, the myocardial enzyme content, area of MI and relative mRNA and protein expression were all decreased.

CONCLUSION

IPO can inhibit the expression of SDHA, reduce MIRI and exert a cardioprotective effect in the normal rats. However, the protective effect of IPO disappears in the diabetic rats. The inhibitor dme combined with IPO can increase the expression of SDHA and restore the protective effect of IPO in DM myocardia.

Myocardial salvage by succinate dehydrogenase inhibition in ischemia-reperfusion injury depends on diabetes stage in rats

Inhibition of succinate dehydrogenase (SDH) by Dimethyl Malonate (DiMal) reduces cardiac ischemia-reperfusion (IR) injury. We investigated the cardioprotective effect of DiMal in a rat model during advancing type 2 diabetes. Zucker Diabetic Fatty rats and lean controls were investigated corresponding to prediabetes, onset and mature diabetes. Hearts were mounted in an isolated perfused model, and subjected to IR for investigation of infarct size (IS) and mitochondrial respiratory control ratio (RCR). DiMal was administered for 10 min before ischemia. Compared with age-matched non-diabetic rats, prediabetic rats had larger IS (49 ± 4% vs. 36 ± 2%, p = 0.007), rats with onset diabetes smaller IS (51 ± 3% vs. 62 ± 3%, p = 0.05) and rats with mature diabetes had larger IS (79 ± 3% vs. 69 ± 2%, p = 0.06). At the prediabetic stage DiMal did not alter IS. At onset of diabetes DiMal 0.6 mM increased IS in diabetic but not in non-diabetic control rats (72 ± 4% vs. 51 ± 3%, p = 0.003). At mature diabetes DiMal 0.1 and 0.6 mM reduced IS (68 ± 3% vs. 79 ± 3% and 64 ± 5% vs. 79 ± 3%, p  = 0.1 and p = 0.01), respectively. DiMal 0.1 mM alone reduced IS in age-matched non-diabetic animals (55 ± 3% vs. 69 ± 2% p = 0.01). RCR was reduced at mature diabetes but not modulated by DiMal. Modulation of SDH activity results in variable infarct size reduction depending on presence and the stage of diabetes. Modulation of SDH activity may be an unpredictable cardioprotective approach.

Hyperglycemia, inflammatory response and infarct size in obstructive acute myocardial infarction and MINOCA

BACKGROUND

Hyperglycemia has been associated with increased inflammatory indexes and larger infarct sizes in patients with obstructive acute myocardial infarction (obs-AMI). In contrast, no studies have explored these correlations in non-obstructive acute myocardial infarction (MINOCA). We investigated the relationship between hyperglycemia, inflammation and infarct size in a cohort of AMI patients that included MINOCA.

METHODS

Patients with AMI undergoing coronary angiography between 2016 and 2020 were enrolled. The following inflammatory markers were evaluated: C-reactive protein, neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and neutrophil-to-platelet ratio (NPR). Myocardial infarct size was measured by peak high sensitivity troponin I (Hs-TnI) levels, left-ventricular-end-diastolic-volume (LVEDV) and left ventricular ejection fraction (LVEF).

RESULTS

The final study population consisted of 2450 patients with obs-AMI and 239 with MINOCA. Hyperglycemia was more prevalent among obs-AMI cases. In all hyperglycemic patients-obs-AMI and MINOCA-NLR, NPR, and LPR were markedly altered. Hyperglycemic obs-AMI subjects exhibited a higher Hs-TnI (p < 0.001), a larger LVEDV (p = 0.003) and a lower LVEF (p < 0.001) compared to normoglycemic ones. Conversely, MINOCA patients showed a trivial myocardial damage, irrespective of admission glucose levels.

CONCLUSIONS

Our data confirm the association of hyperglycemic obs-AMI with elevated inflammatory markers and larger infarct sizes. MINOCA patients exhibited modest myocardial damage, regardless of admission glucose levels.

[Perioperative cardioprotection - From bench to bedside : Current experimental evidence and possible reasons for the limited translation into the clinical setting]

Hintergrund

Ziel der perioperativen Kardioprotektion ist es, die Auswirkungen eines Ischämie- und Reperfusionsschadens zu minimieren. Aus anästhesiologischer Sicht spielt dieser Aspekt insbesondere in der Herzchirurgie bei Patienten mit Einsatz der Herz-Lungen-Maschine, aber auch allgemein bei längerfristigen hypotensiven Phasen oder perioperativen ischämischen Ereignissen im nichtkardiochirurgischen Setting eine wichtige Rolle. Im Laufe der letzten Jahre konnten diverse pharmakologische sowie nichtpharmakologische Strategien der Kardioprotektion identifiziert werden. Die Ergebnisse von Studien an isoliertem Gewebe sowie von tierexperimentellen In-vivo-Studien sind vielversprechend. Eine Translation dieser kardioprotektiven Strategien in die klinische Praxis ist bislang jedoch nicht gelungen. Große klinische Studien konnten keine signifikante Verbesserung des Outcome der Patienten zeigen.

Ziel der Arbeit

Dieser Übersichtsartikel gibt einen Überblick über die aktuelle experimentelle Evidenz pharmakologischer und nichtpharmakologischer Kardioprotektion. Außerdem sollen mögliche Gründe für die limitierte Translation diskutiert werden. Schließlich werden Möglichkeiten aufgezeigt, wie der Schritt „from bench to bedside“ in Zukunft doch noch gelingen könnte.

Material und Methoden

Narrative Übersichtsarbeit.

Ergebnisse und Diskussion

Trotz der vielversprechenden präklinischen experimentellen Ansätze zum Thema Kardioprotektion besteht nach wie vor eine große Diskrepanz zu den Ergebnissen aus großen klinischen Studien in der perioperativen Phase. Mögliche Gründe für die limitierte Translation könnten insbesondere Komorbiditäten und Komedikationen, die Wahl des Anästhesieverfahrens, aber auch die Wahl des Studiendesigns sein. Eine sorgfältige Studienplanung mit Berücksichtigung der genannten Probleme sowie ein simultaner Einsatz mehrerer kardioprotektiver Strategien mit dem Ziel eines additiven bzw. synergistischen Effekts stellen mögliche Ansätze für die Zukunft dar.

Remote ischemic conditioning: A potential therapeutic strategy of type 2 diabetes

Type 2 diabetes (T2D) is one of the major public diseases which is characterized by peripheral insulin resistance (IR) and progressive pancreatic β-cell failure. While in the past few years, some new factors, such as inflammation, oxidative stress, immune responses and other potential pathways, have been identified to play critical roles in T2D, and thereby provide novel promising targets for the treatment of T2D. Remote ischemic conditioning (RIC) is a non-invasive and convenient operation performed by transient, repeated ischemia in distant place. Nowadays, RIC has been established as a potentially powerful therapeutic tool for many diseases, especially in I/R injuries. Through activating a series of neural, humoral and immune pathways, it can release multiple protective signals, which then regulating inflammation, oxidative stress, immune response and so on. Interestingly, several recent studies have discovered that the beneficial effects of RIC on I/R injuries might be abolished by T2D, wherein the higher basal levels of inflammation and oxidative stress, dysregulation of immune system and some potential pathways secondary to hyperglycemia may play critical roles. In contrast, a higher intensity of conditioning could restore the protective effects. Based on the overlapped mechanisms RIC and T2D performs, we provide a hypothesis that RIC may also play a protective role in T2D via targeting these signaling pathways.

Differences in intrinsic aerobic capacity alters sensitivity to ischemia-reperfusion injury but not cardioprotective capacity by ischemic preconditioning in rats

INTRODUCTION

Aerobic capacity is a strong predictor of cardiovascular mortality. Whether aerobic capacity influences myocardial ischemia and reperfusion (IR) injury is unknown.

PURPOSE

To investigate the impact of intrinsic differences in aerobic capacity and the cardioprotective potential on IR injury.

METHODS

We studied hearts from rats developed by selective breeding for high (HCR) or low (LCR) capacity for treadmill running. The rats were randomized to: (1) control, (2) local ischemic preconditioning (IPC) or (3) remote ischemic preconditioning (RIC) followed by 30 minutes of ischemia and 120 minutes of reperfusion in an isolated perfused heart model. The primary endpoint was infarct size. Secondary endpoints included uptake of labelled glucose, content of selected mitochondrial proteins in skeletal and cardiac muscle, and activation of AMP-activated kinase (AMPK).

RESULTS

At baseline, running distance was 203±7 m in LCR vs 1905±51 m in HCR rats (p<0.01). Infarct size was significantly lower in LCR than in HCR controls (49±5% vs 68±5%, p = 0.04). IPC reduced infarct size by 47% in LCR (p<0.01) and by 31% in HCR rats (p = 0.01). RIC did not modulate infarct size (LCR: 52±5, p>0.99; HCR: 69±6%, p>0.99, respectively). Phosphorylaion of AMPK did not differ between LCR and HCR controls. IPC did not modulate cardiac phosphorylation of AMPK. Glucose uptake during reperfusion was similar in LCR and HCR rats. IPC increased glucose uptake during reperfusion in LCR animals (p = 0.02). Mitochondrial protein content in skeletal muscle was lower in LCR than in HCR (0.77±0.10 arbitrary units (AU) vs 1.09±0.07 AU, p = 0.02), but not in cardiac muscle.

CONCLUSION

Aerobic capacity is associated with altered myocardial sensitivity to IR injury, but the cardioprotective effect of IPC is not. Glucose uptake, AMPK activation immediately prior to ischemia and basal mitochondrial protein content in the heart seem to be of minor importance as underlying mechanisms for the cardioprotective effects.

Prognostic value of fasting glucose on the risk of heart failure and left ventricular systolic dysfunction in non-diabetic patients with ST-segment elevation myocardial infarction

Recent studies have shown that acute blood glucose elevation in patients with ST-segment elevation myocardial infarction (STEMI) suggests a poor prognosis. To investigate the effect of fasting blood glucose (FBG) on the risk of heart failure (HF) and left ventricular systolic dysfunction (LVSD) in non-diabetic patients undergoing primary percutaneous coronary intervention (PCI) for acute STEMI, we retrospectively recruited consecutive non-diabetic patients who underwent primary PCI for STEMI in our hospital from February 2003 to March 2015. The patients were divided into two groups according to the FBG level. A total of 623 patients were recruited with an age of 61.3 ± 12.9 years, of whom 514 (82.5%) were male. The HF risk (odds ratio 3.401, 95% confidence interval (CI) 2.144-5.395, P < 0.001) was significantly increased in patients with elevated FBG than those with normal FBG. Elevated FBG was also independently related to LVSD (β 1.513, 95%CI 1.282-1.785, P < 0.001) in a multiple logistics regression analysis. In conclusion, elevated FBG was independently associated with 30-day HF and LVSD risk in non-diabetic patients undergoing primary PCI for STEMI.

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.