The diabetic heart: too sweet for its own good?

Risk factors for postoperative myocardial injury-related cardiogenic shock in patients undergoing cardiac surgery

BACKGROUND

Myocardial injury-related cardiogenic shock (MICS) is significantly associated with poor outcomes in patients after cardiac surgery. Herein, we aimed to investigate the risk factor for postoperative MICS.

METHODS

We performed a case-control study on 792 patients undergoing cardiac surgery from 2016 to 2019, including 172 patients with postoperative MICS and 620 age- and sex-matched controls. MICS was defined as composite criteria: a cardiac index of < 2.2 L/m²/min, arterial lactate levels of > 5 mmol/L at the end of the surgery, a vasoactive-inotropic score of > 40 at the end of the surgery, and a cardiac troponin T (cTnT) level of > 0.8 µg/L on postoperative day 1 (POD1) with an increase of > 10% on POD 2.

RESULTS

A total of 4671 patients who underwent cardiac surgery in our hospital between 2016 and 2019 were included; of these, 172 (3.68%) had MICS and the remaining 4499 did not. For investigating the risk factors, we selected 620 age- and sex-matched controls. In the univariate analysis, MICS was significantly associated with death (P < 0.05), extracorporeal membrane oxygenation (P < 0.05), continuous renal replacement therapy (P < 0.01), and ventricular arrhythmias (P < 0.05). Multivariable logistic regression analysis revealed that diabetes mellitus (OR:8.11, 95% CI: 3.52-18.66, P < 0.05) and a cardiopulmonary bypass (CPB) time of > 2 h (OR: 3.16, 95% CI: 1.94-5.15, P < 0.05) were associated with postoperative MICS. Moreover, long-time administration of preoperative calcium channel blocker (CCB) was associated with a less incidence of MICS (OR: 0.11, 95% CI: 0.05-0.27, P < 0.05).

CONCLUSIONS

Postoperative MICS is significantly associated with poor outcomes. Diabetes mellitus and long CPB time are associated with MICS. Preoperative CCB administration is associated with less incidence of MICS.

Remote ischaemic conditioning: defining critical criteria for success-report from the 11th Hatter Cardiovascular Workshop

The Hatter Cardiovascular Institute biennial workshop, originally scheduled for April 2020 but postponed for 2 years due to the Covid pandemic, was organised to debate and discuss the future of Remote Ischaemic Conditioning (RIC). This evolved from the large multicentre CONDI-2-ERIC-PPCI outcome study which demonstrated no additional benefit when using RIC in the setting of ST-elevation myocardial infarction (STEMI). The workshop discussed how conditioning has led to a significant and fundamental understanding of the mechanisms preventing cell death following ischaemia and reperfusion, and the key target cyto-protective pathways recruited by protective interventions, such as RIC. However, the obvious need to translate this protection to the clinical setting has not materialised largely due to the disconnect between preclinical and clinical studies. Discussion points included how to adapt preclinical animal studies to mirror the patient presenting with an acute myocardial infarction, as well as how to refine patient selection in clinical studies to account for co-morbidities and ongoing therapy. These latter scenarios can modify cytoprotective signalling and need to be taken into account to allow for a more robust outcome when powered appropriately. The workshop also discussed the potential for RIC in other disease settings including ischaemic stroke, cardio-oncology and COVID-19. The workshop, therefore, put forward specific classifications which could help identify so-called responders vs. non-responders in both the preclinical and clinical settings.

Cordycepin Decreases Ischemia/Reperfusion Injury in Diabetic Hearts via Upregulating AMPK/Mfn2-dependent Mitochondrial Fusion

Diabetes mellitus is considered to be a major risk factor for cardiovascular disease, the most common cause of death in diabetes. However, therapeutic strategies for myocardial protection in patients with diabetes are still limited. Cordycepin is a traditional Tibetan medicine with a long history of widespread use, and exerts a wide range of anti-tumor, anti-inflammatory, and anti-oxidative effects. In recent years, although the therapeutic potential of cordycepin has attracted the attention of researchers, it remains unknown whether cordycepin plays a protective role in myocardial ischemia/reperfusion (MI/R) injury in diabetic patients. Here, using a diabetic mouse model, we found that cordycepin protected diabetic hearts from MI/R injury by promoting mitochondrial fusion and Mfn2 expression. Our in vitro results showed that cordycepin enhanced Mfn2-medicated mitochondrial fusion, improved mitochondrial function, and reduced cardiomyocyte apoptosis in high-glucose/high-fat cultured simulated ischemia/reperfusion cardiomyocytes. Furthermore, we found that knockout of Mfn2 significantly blocked the cardioprotective effects of cordycepin in diabetic mice. Finally, an AMPK-dependent pathway was found to upregulate Mfn2 expression upon cordycepin treatment, indicating that cordycepin protected diabetic hearts via AMPK/Mfn2-dependent mitochondrial fusion. Collectively, our study firstly demonstrated that cordycepin could be a potential cardioprotective agent for MI/R injury, and we established a novel mechanism by which upregulated AMPK/Mfn2-dependent mitochondrial fusion contributes to the cardioprotective role of cordycepin.

Naringenin alleviates myocardial ischemia reperfusion injury by enhancing the myocardial miR-126-PI3K/AKT axis in streptozotocin-induced diabetic rats

Ischemic heart disease (IHD) is a leading cause of death in patients with type 1 diabetes. The key to treating IHD is to restore blood supply to the ischemic myocardium, which inevitably causes myocardial ischemia reperfusion (MI/R) injury. Although naringenin (Nar) prevents MI/R injury, the role of Nar in diabetic MI/R (D-MI/R) injury remains to be elucidated. The PI3K/AKT signaling pathway and microRNA (miR)-126 have previously been shown to serve anti-MI/R injury roles. The present study aimed to investigate the protection of Nar against D-MI/R injury and the role of the miR-126-PI3K/AKT axis. Diabetic rats were treated distilled water or Nar (25 or 50 mg/kg, orally) for 30 days and then exposed to MI/R. The present results revealed that Nar alleviated MI/R injury in streptozotocin (STZ)-induced diabetic rats, as shown below: the reduction myocardial enzymes levels was measured using spectrophotometry, the increase of cardiac viability was detected by MTT assay, the inhibition of myocardial oxidative stress was measured using spectrophotometry and the enhancement of cardiac function were recorded using a hemodynamic monitoring system. Furthermore, Nar upregulated the myocardial miR-126-PI3K/AKT axis in D-MI/R rats. These results indicated that Nar alleviated MI/R injury through upregulating the myocardial miR-126-PI3K/AKT axis in STZ-induced diabetic rats. The current findings revealed that Nar, as an effective agent against D-MI/R injury, may provide an effective approach in the management of diabetic IHD.

Extracellular vesicles - mediating and delivering cardioprotection in acute myocardial infarction and heart failure

New treatments are urgently needed to reduce myocardial infarct size and prevent adverse post-infarct left ventricular remodeling, in order to preserve cardiac function, and prevent the onset of heart failure in patients presenting with acute myocardial infarction (AMI). In this regard, extracellular vesicles (EVs) have emerged as key mediators of cardioprotection. Endogenously produced EVs are known to play crucial roles in maintaining normal cardiac homeostasis and function, by acting as mediators of intercellular communication between different types of cardiac cells. Endogenous EVs have also been shown to contribute to innate cardioprotective strategies such as remote ischemic conditioning. In terms of EV-based therapeutics, stem cell-derived EVs have been shown to confer cardioprotection in a large number of small and large animal AMI models, and have the therapeutic potential to be applied in the clinical setting for the benefit of AMI patients, although several challenges need to be overcome. Finally, EVs may be used as vehicles to deliver therapeutics to the infarcted heart, providing a potential synergist approach to cardioprotection. In this review article, we highlight the various roles that EVs play as mediators and deliverers of cardioprotection, and discuss their therapeutic potential for improving clinical outcomes following AMI.

Long-chain free fatty acids inhibit ischaemic preconditioning of the isolated rat heart

We recently reported that non-preconditioned hearts from diet-induced obese rats showed, compared to controls, a significant reduction in infarct size after ischaemia/reperfusion, whilst ischaemic preconditioning was without effect. In view of the high circulating FFA concentration in diet rats, the aims of the present study were to: (i) compare the effect of palmitate on the preconditioning potential of hearts from age-matched controls and diet rats (ii) elucidate the effects of substrate manipulation on ischaemic preconditioning. Substrate manipulation was done with dichloroacetate (DCA), which enhances glucose oxidation and decreases fatty acid oxidation. Isolated hearts from diet rats, age-matched controls or young rats, were perfused in the working mode using the following substrates: glucose (10 mM); palmitate (1.2 mM)/3% albumin) + glucose (10 mM) (HiFA + G); palmitate (1.2 mM/3% albumin) (HiFA); palmitate (0.4 mM/3% albumin) + glucose(10 mM) (LoFA + G); palmitate (0.4 mM/3% albumin) (LoFA). Hearts were preconditioned with 3 × 5 min ischaemia/reperfusion, followed by 35 min coronary ligation and 60 min reperfusion for infarct size determination (tetrazolium method) or 20 min global ischaemia/10 or 30 min reperfusion for Western blotting (ERKp44/42, PKB/Akt). Preconditioning of glucose-perfused hearts from age-matched control (but not diet) rats reduced infarct size, activated ERKp44/42 and PKB/Akt and improved functional recovery during reperfusion (ii) perfusion with HiFA + G abolished preconditioning and activation of ERKp44/42 (iii) DCA pretreatment largely reversed the harmful effects of HiFA. Hearts from non-preconditioned diet rats exhibited smaller infarcts, but could not be preconditioned, regardless of the substrate. Similar results were obtained upon substrate manipulation of hearts from young rats. Abolishment of preconditioning in diet rats may be due to altered myocardial metabolic patterns resulting from changes in circulating FA. The harmful effects of HiFA were attenuated by stimulation of glycolysis and inhibition of FA oxidation.

Aggravated intestinal ischemia‑reperfusion injury is associated with activated mitochondrial autophagy in a mouse model of diabetes

Numerous studies have reported that diabetes is associated with an increased susceptibility to cardiac ischemia- reperfusion injury; however, the mechanism underlying the role of diabetes during intestinal ischemia-reperfusion (IIR) has yet to be elucidated. The present study evaluated the intestinal pathological alterations and possible underlying mechanisms in a mouse model of type 1 diabetes mellitus with IIR. The effects of diabetes were investigated by assessing the histopathology, oxidative stress, inflammatory cytokine levels in intestine tissues and blood plasma, and protein expression levels of phosphatase and tensin homolog-induced putative kinase (PINK1), Parkin and the ratio of light chain 3B (LC3B) II/I. The results demonstrated that diabetes increased the Chiu's intestinal injury score, concentration of interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α, and levels of oxidative stress. Furthermore, the alterations were more pronounced in the diabetes with IIR group. The expression levels of PINK1 and Parkin, as well as the ratio of LC3BII/I, were significantly upregulated in the IIR group compared with the Sham group. Diabetes activated PINK1 and Parkin, and increased the expression of LC3BII. Furthermore, transmission electron microscopy revealed that mitochondrial destruction and the number of autophagosomes was increased in the diabetic groups compared with the non-diabetic groups. Collectively, the results of the present study suggest that diabetes increased intestinal vulnerability to IIR by enhancing inflammation and oxidative stress. Furthermore, IIR was associated with overactivation of mitochondrial autophagy; therefore, the increased vulnerability to IIR-induced intestine damage due to diabetes may be associated with PINK1/Parkin-regulated mitochondrial autophagy.

Protective effect of intermediate doses of hydrogen sulfide against myocardial ischemia-reperfusion injury in obese type 2 diabetic rats

OBJECTIVE

Subjects with type 2 diabetes (T2D) have lower circulating hydrogen sulfide (H₂S) levels following myocardial ischemia and a higher risk of mortality. The aim of this study was to determine the dose-dependent favorable effects of sodium hydrosulfide (NaSH) on myocardial ischemia-reperfusion (IR) injury in rats with T2D.

METHODS

T2D was induced using a high-fat diet (HFD) and low-dose of streptozotocin. Rats were divided into control, T2D, and T2D + NaSH groups. NaSH (0.28, 0.56, 1.6, 2.8, and 5.6 mg/kg) was administered intraperitoneally for 9 weeks. At the end of the study, heart from all rats were isolated and left ventricular developed pressure (LVDP) and the peak rates of positive and negative changes in LV pressure (±dp/dt) were recorded during baseline and following myocardial IR injury. In addition, infarct size as well as mRNA expression of H₂S- and nitric oxide (NO)-producing enzymes were measured.

RESULTS

In diabetic rats, NaSH only at doses of 0.56 and 1.6 mg/kg increased recovery of LVDP (16% and 42%), +dp/dt (25% and 35%) and -dp/dt (23% and 32%) as well as decreased infarct size (44% and 35%). At these doses, NaSH increased expressions of cystathionine γ-lyase (CSE) (440% and 271%) and endothelial NO synthase (eNOS) (232% and 148%) but it decreased the expressions of inducible NOS (iNOS) (55% and 71%). NaSH at 0.28, 2.8 and 5.6 mg/kg had no significant effects on these parameters.

CONCLUSION

NaSH had a bell-shaped cardioprotective effect against myocardial IR injury in rats with T2D. Higher tolerance to IR injury in heart isolated from type 2 diabetic rats treated with intermediate doses of NaSH is associated with higher CSE-derived H₂S and eNOS-derived NO as well as lower iNOS-derived NO.

Cardiac innervation in acute myocardial ischaemia/reperfusion injury and cardioprotection

Acute myocardial infarction (AMI) and the heart failure (HF) that often complicates this condition, are among the leading causes of death and disability worldwide. To reduce myocardial infarct (MI) size and prevent heart failure, novel therapies are required to protect the heart against the detrimental effects of acute ischaemia/reperfusion injury (IRI). In this regard, targeting cardiac innervation may provide a novel therapeutic strategy for cardioprotection. A number of cardiac neural pathways mediate the beneficial effects of cardioprotective strategies such as ischaemic preconditioning and remote ischaemic conditioning, and nerve stimulation may therefore provide a novel therapeutic strategy for cardioprotection. In this article, we provide an overview of cardiac innervation and its impact on acute myocardial IRI, the role of extrinsic and intrinsic cardiac neural pathways in cardioprotection, and highlight peripheral and central nerve stimulation as a cardioprotective strategy with therapeutic potential for reducing MI size and preventing HF following AMI. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Myocardial ischaemia reperfusion injury and cardioprotection in the presence of sensory neuropathy: Therapeutic options

During the last decades, mortality from acute myocardial infarction has been dramatically reduced. However, the incidence of post‐infarction heart failure is still increasing. Cardioprotection by ischaemic conditioning had been discovered more than three decades ago. Its clinical translation, however, is still an unmet need. This is mainly due to the disrupted cardioprotective signalling pathways in the presence of different cardiovascular risk factors, co‐morbidities and the medication being taken. Sensory neuropathy is one of the co‐morbidities that has been shown to interfere with cardioprotection. In the present review, we summarize the diverse aetiology of sensory neuropathies and the mechanisms by which these neuropathies may interfere with ischaemic heart disease and cardioprotective signalling. Finally, we suggest future therapeutic options targeting both ischaemic heart and sensory neuropathy simultaneously.

LINKED ARTICLES

This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc

Irisin and troponin I expression in dialysis patients submitted to remote ischemic preconditioning: a pilot study

Background:

Renal replacement therapy continues to be related to high hospitalization rates and poor quality of life. All-cause morbidity and mortality in renal replacement therapy in greater than 20% per year, being 44 times greater when diabetes is present, and over 10 times that of the general population. Regardless of treatment, the 5-year survival is 40%, surpassing many types of cancers. Irisin is a hormone that converts white adipose tissue into beige adipose tissue, aggregating positive effects like fat mass control, glucose tolerance, insulin resistance, prevention of muscle loss, and reduction in systemic inflammation.

Objectives:

To determine the serum levels of troponin I in hemodialysis patients submitted to remote ischemic preconditioning (RIPC) associated with irisin expression.

Methods:

This was a prospective, randomized, double-blind clinical trial with patients with chronic kidney disease submitted to hemodialysis for a 6-month period. Troponin I, IL-6, urea, TNF-α, and creatinine levels were determined from blood samples. The expressions of irisin, thioredoxin, Nf-kb, GPX4, selenoprotein and GADPH were also evaluated by RT-PCR.

Results:

Samples from 14 hypertensive patients were analyzed, 9 (64.3%) of whom were type 2 diabetics, aged 44-64 years, and 50% of each sex. The difference between pre- and post-intervention levels of troponin I was not significant. No differences were verified between the RIPC and control groups, except for IL-6, although a significant correlation was observed between irisin and troponin I.

Conclusion:

Remote ischemic preconditioning did not modify irisin or troponin I expression, independent of the time of collection.

Co-morbidities and co-medications as confounders of cardioprotection-Does it matter in the clinical setting?

The translation of cardioprotection from robust experimental evidence to beneficial clinical outcome for patients suffering acute myocardial infarction or undergoing cardiovascular surgery has been largely disappointing. The present review attempts to critically analyse the evidence for confounders of cardioprotection in patients with acute myocardial infarction and in patients undergoing cardiovascular surgery. One reason that has been proposed to be responsible for such lack of translation is the confounding of cardioprotection by co-morbidities and co-medications. Whereas there is solid experimental evidence for such confounding of cardioprotection by single co-morbidities and co-medications, the clinical evidence from retrospective analyses of the limited number of clinical data is less robust. The best evidence for interference of co-medications is that for platelet inhibitors to recruit cardioprotection per se and thus limit the potential for further protection from myocardial infarction and for propofol anaesthesia to negate the protection from remote ischaemic conditioning in cardiovascular surgery. 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.

Mesenchymal stem cells improve survival in ischemic diabetic random skin flap via increased angiogenesis and VEGF expression

Random skin flaps (RSFs) are cutaneous flaps. Despite the negative impact of diabetes mellitus (DM) on RSF viability, they are commonly used in diabetic patients. In this study, we have assessed bone marrow mesenchymal stem cell (BMMSC) treatment on RSF survival, tensiometrical parameters, angiogenesis, and mast cells (MCs) count in an ischemic RSF model in rats with type 1 DM (T1DM). We induced T1DM in 30 Wistar adult male rats. The animals were assigned to three groups of 10 rats per group as follows: group 1 (control); group 2 (placebo), and group 3 (BMMSCs). A 30  ×  80  mm RSF was created in each rat. On day 7, we measured the viable portion of each RSF. A sample was taken for histological and immunohistochemistry studies, fibroblasts, MCs, angiogenesis, collagen bundle density, and the presence of vascular endothelial growth factor (VEGF)+ cells. An additional sample was taken to evaluate the flap's incision strength. Treatment with BMMSCs (17.8  ±  0.37) significantly increased RSF survival compared with the control (13.3  ±  0.35) and placebo (16.1  ±  0.27) groups (one-way analysis of variance, P  =  .000; least significant difference, P  =  .000, P  =  .002). There was a significant improvement in angiogenesis, as confirmed by stereologic examination. Assessment of VEGF+ cells showed prominent neovascularization in BMMSC-treated RSFs compared with the control and placebo groups. Subdermal injection of BMMSC significantly increased ischemic RSF survival as a result of stimulated neovascularization in T1DM rats. Treatment of diabetic RSF with BMMSCs showed no beneficial effects in the fibroblast number and biomechanical parameters for the repair of ischemic wounds in the rat model. Treatment with BMMSCs significantly increased collagen bundle density.

SGLT2 Inhibitor, Canagliflozin, Attenuates Myocardial Infarction in the Diabetic and Nondiabetic Heart

•

Long-term SGLT2 inhibition with dietary canagliflozinin diabetic and nondiabetic rats attenuates myocardial ischemia/reperfusion injury ex vivo.

•

This suggests that the improvement in myocardial infarct size by SGLT2 inhibition may occur independent of the glycemic status.

•

Canagliflozin improved hyperglycemia in diabetic rats but importantly did not cause hypoglycemia in nondiabetic rats.

•

Short-term perfusion of the nondiabetic heart with canagliflozin, solubilized in the Langendorff perfusion buffer, had no impact on the myocardial infarct size.

The authors hypothesized that despite similar cardiovascular event rates, the improved cardiovascular survival from sodium glucose transporter 2 (SGLT2) inhibition, seen clinically, could be via a direct cytoprotective effect, including protection against myocardial ischemia/reperfusion injury. Langendorff-perfused hearts, from diabetic and nondiabetic rats, fed long-term for 4 weeks with canagliflozin, had lower infarct sizes; this being the first demonstration of canagliflozin’s cardioprotective effect against ischemia/reperfusion injury in both diabetic and nondiabetic animals. By contrast, direct treatment of isolated nondiabetic rat hearts with canagliflozin, solubilized in the isolated Langendorff perfusion buffer, had no impact on infarct size. This latter study demonstrates that the infarct-sparing effect of long-term treatment with canagliflozin results from either a glucose-independent effect or up-regulation of cardiac prosurvival pathways. These results further suggest that SGLT2 inhibitors could be repurposed as novel cardioprotective interventions in high-risk cardiovascular patients irrespective of diabetic status.

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.

Effect of Autophagy Inhibition on the Protection of Ischemia Preconditioning against Myocardial Ischemia/Reperfusion Injury in Diabetic Rats

BACKGROUND

Ischemia preconditioning (IPC) remains the most powerful intervention of protection against myocardial ischemia/reperfusion injury (IRI), but diabetes can weaken or eliminate its cardioprotective effect and detailed mechanisms remain unclear. In this study, we aimed to explore whether changes of autophagy in the diabetic condition are attributable to the decreased cardioprotective effect of IPC.

METHODS

Sixty diabetic male Sprague-Dawley rats were randomly divided into the control (C), IRI, rapamycin (R), wortmannin (W), rapamycin + IPC (R + IPC), and wortmannin + IPC (W + IPC) groups. The in vivo rat model of myocardial IRI was established by ligaturing and opening the left anterior descending coronary artery via the left thoracotomy. Durations of ischemia and reperfusion are 30 min and 120 min, respectively. Blood samples were taken at 120 min of reperfusion for measuring serum concentrations of troponin I (TnI) and creatine kinase isoenzyme MB (CK-MB) using the enzyme-linked immunosorbent assay. The infarct size was assessed by Evans blue and triphenyltetrazolium chloride staining. The expressions of LC3-II, beclin-1, phosphoinositide 3-kinase (PI3K), mammalian target of rapamycin (mTOR), and P-Akt/Akt ratio in the ischemic myocardium were assessed by Western blotting.

RESULTS

Compared to the IRI group, infarct size (56.1% ± 6.1% vs. 75.4 ± 7.1%, P < 0.05), serum cTnI (0.61 ± 0.21 vs. 0.95 ± 0.26 ng/ml, P < 0.05), and CK-MB levels (6.70 ± 1.25 vs. 11.51 ± 2.35 ng/ml, P < 0.05) obviously decreased in the W + IPC group. Compared with the C group, myocardial expressions of LC3-II (0.46 ± 0.04 and 0.56 ± 0.04 vs. 0.36 ± 0.04, P < 0.05) and beclin-1 (0.34 ± 0.08 and 0.38 ± 0.07 vs. 0.24 ± 0.03, P < 0.05) evidently increased, and myocardial expressions of mTOR (0.26 ± 0.08 and 0.25 ± 0.07 vs. 0.38 ± 0.06, P < 0.05), PI3K (0.29 ± 0.04 and 0.30 ± 0.03 vs. 0.38 ± 0.02, P < 0.05), and P-Akt/Akt ratio (0.49 ± 0.10 and 0.48 ± 0.06 vs. 0.72 ± 0.07, P < 0.05) markedly decreased in the IRI and R groups, indicating an increased autophagy. Compared with the IRI group, myocardial expression of beclin-1 (0.26 ± 0.03 vs. 0.34 ± 0.08, P < 0.05) significantly decreased, and myocardial expressions of mTOR (0.36 ± 0.04 vs. 0.26 ± 0.08, P < 0.05), PI3K (0.37 ± 0.03 vs. 0.29 ± 0.04, P < 0.05), and P-Akt/Akt ratio (0.68 ± 0.05 vs. 0.49 ± 0.10, P < 0.05) increased obviously in the W + IPC group, indicating a decreased autophagy.

CONCLUSIONS

Increased autophagy in the diabetic myocardium is attributable to decreased cardioprotection of IPC, and autophagy inhibited by activating the PI3K-Akt-mTOR signaling pathway can result in an improved protection of IPC against diabetic myocardial IRI.

Diabetes Worsens Skeletal Muscle Mitochondrial Function, Oxidative Stress, and Apoptosis After Lower-Limb Ischemia-Reperfusion: Implication of the RISK and SAFE Pathways?

Objectives: Diabetic patients respond poorly to revascularization for peripheral arterial disease (PAD) but the underlying mechanisms are not well understood. We aimed to determine whether diabetes worsens ischemia-reperfusion (IR)-induced muscle dysfunction and the involvement of endogenous protective kinases in this process.

Materials and Methods: Streptozotocin-induced diabetic and non-diabetic rats were randomized to control or to IR injury (3 h of aortic cross-clamping and 2 h of reperfusion). Mitochondrial respiration, reactive oxygen species (ROS) production, protein levels of superoxide dismutase (SOD2) and endogenous protective kinases (RISK and SAFE pathways) were investigated in rat gastrocnemius, together with upstream (GSK-3β) and downstream (cleaved caspase-3) effectors of apoptosis.

Results: Although already impaired when compared to non-diabetic controls at baseline, the decline in mitochondrial respiration after IR was more severe in diabetic rats. In diabetic animals, IR-triggered oxidative stress (increased ROS production and reduced SOD2 levels) and effectors of apoptosis (reduced GSK-3β inactivation and higher cleaved caspase-3 levels) were increased to a higher level than in the non-diabetics. IR had no effect on the RISK pathway in non-diabetics and diabetic rats, but increased STAT 3 only in the latter.

Conclusion: Type 1 diabetes worsens IR-induced skeletal muscle injury, endogenous protective pathways not being efficiently stimulated.

Influence of diabetes mellitus duration on the efficacy of ischemic preconditioning in a Zucker diabetic fatty rat model

Augmented mortality and morbidity following an acute myocardial infarction in patients with diabetes mellitus Type 2 (T2DM) may be caused by increased sensitivity to ischemia reperfusion (IR) injury or altered activation of endogenous cardioprotective pathways modified by T2DM per se or ischemic preconditioning (IPC). We aimed to investigate, whether the duration of T2DM influences sensitivity against IR injury and the efficacy of IPC, and how myocardial glucose oxidation rate was involved. Male Zucker diabetic fatty rats (homozygote (fa/fa)) at ages 6-(prediabetic), 12- (onset diabetes) and 24-weeks of age (late diabetes) and their age-matched non-diabetic controls (heterozygote (fa/+) were subjected to IR injury in the Langendorff model and randomised to IPC stimulus or control. T2DM rats were endogenously protected at onset of diabetes, as infarct size was lower in 12-weeks T2DM animals than in 6- (35±2% vs 53±4%; P = 0.006) and 24-weeks animals (35±2% vs 72±4%; P<0.0001). IPC reduced infarct size in all groups irrespective of the presence of T2DM and its duration (32±3%; 20±2%; 36±4% respectively; (ANOVA P<0.0001). Compared to prediabetic rats, myocardial glucose oxidation rates were reduced during stabilisation and early reperfusion at onset of T2DM, but these animals retained the ability to increase oxidation rate in late reperfusion. Late diabetic rats had low glucose oxidation rates throughout stabilisation and reperfusion. Despite inherent differences in sensitivity to IR injury, the cardioprotective effect of IPC was preserved in our animal model of pre-, early and late stage T2DM and associated with adaptations to myocardial glucose oxidation capacity.

GYY4137 protects against myocardial ischemia/reperfusion injury via activation of the PHLPP-1/Akt/Nrf2 signaling pathway in diabetic mice

BACKGROUND

This study explores the protective effects of a hydrogen sulfide donor, morpholin-4-ium 4-methoxyphenyl-morpholino-phosphinodithioate (GYY4137), in the hearts of diabetic mice that had been subjected to myocardial ischemia/reperfusion injury. Diabetes impairs the Akt pathway, in which the Akt protein is dephosphorylated and inactivated by PH domain leucine-rich repeat protein phosphatase-1 (PHLPP-1). However, the function of PHLPP-1 and molecular mechanism that underlies the cardiac protection exerted by GYY4137 remains unknown.

METHODS

Diabetic or nondiabetic mice were subjected to 45 min of coronary artery occlusion followed by 2 h of reperfusion. H9c2 cells were cultured with normal or high glucose and then subjected to 3 h of hypoxia followed by 6 h of reoxygenation. Pretreatment with GYY4137 was performed in a randomized manner before ischemia/reperfusion or hypoxia/reoxygenation. The infarct size, cardiomyocyte apoptosis, and oxidative stress were measured. Western blotting was conducted to elucidate the protective mechanism.

RESULTS

Diabetic mice or H9c2 cells exposed to high glucose displayed a larger infarct size, more severe cardiomyocyte apoptosis, lower cell viability, and increased oxidative stress, which were associated with increased levels of PHLPP-1 and reduced levels of p-Akt and nuclear factor-erythroid-2-related factor 2 (Nrf2) protein expression. These changes were prevented/reversed by GYYG4137 pretreatment. At the cellular level, PHLPP-1 siRNA attenuated cellular injury, and this was associated with increased p-Akt and nuclear Nrf2 protein, whereas the decrement of Akt phosphorylation induced by LY294002 augmented cellular injury and decreased nuclear Nrf2.

CONCLUSIONS

GYY4137 activates the PHLPP-1/Akt/Nrf2 pathway to protect against diabetic myocardial ischemia/reperfusion injury.

Effects of hypoglycemia on myocardial susceptibility to ischemia-reperfusion injury and preconditioning in hearts from rats with and without type 2 diabetes

BACKGROUND

Hypoglycemia is associated with increased mortality rate in patients with diabetes. The underlying mechanisms may involve reduced myocardial tolerance to ischemia and reperfusion (IR) or reduced capacity for ischemic preconditioning (IPC). As IPC is associated with increased myocardial glucose uptake (MGU) during reperfusion, cardioprotection is linked to glucose metabolism possibly by O-linked β-N-acetylglucosamine (O-GlcNAc). We aimed to investigate the impact of hypoglycemia in hearts from animals with diabetes on myocardial IR tolerance, on the efficacy of IPC and whether modulations of MGU and O-GlcNAc levels are involved in the underlying mechanisms.

METHODS

In a Langendorff model using diabetic ZDF (fa/fa) and non-diabetic (fa/+) rats (n = 6-7 in each group) infarct size (IS) was evaluated after 40 min of global ischemia and 120 min reperfusion during hypoglycemia [(glucose) = 3 mmol/l] and normoglycemia [(glucose) = 11 mmol/l]. Myocardial glucose uptake and O-GlcNAc levels were evaluated during reperfusion. IPC was induced by 2 × 5 min of global ischemia prior to index ischemia.

RESULTS

IS increased in hearts from animals with (p < 0.01) and without (p < 0.01) diabetes during hypoglycemia compared to normoglycemia. IPC reduced IS during normoglycemia in both animals with (p < 0.01) and without (p < 0.01) diabetes. During hypoglycemia, however, IPC only reduced IS in hearts from animals with diabetes (p < 0.05). IPC increased MGU during reperfusion and O-GlcNAc levels in animals with diabetes during hypo- (MGU: p < 0.05, O-GlcNAc: p < 0.05) and normoglycemia (MGU: p < 0.01, O-GlcNAc: p < 0.05) and in animals without diabetes only during normoglycemia (MGU: p < 0.05, O-GlcNAc: p < 0.01).

CONCLUSIONS

Hypoglycemia increases myocardial susceptibility to IR injury in hearts from animals with and without diabetes. In contrast to hearts from animals without diabetes, the hearts from animals with diabetes are amenable to cardioprotection during hypoglycemia. In parallel with IPC induced cardioprotection, MGU and O-GlcNAc levels increase suggesting that increased MGU and O-GlcNAc levels are involved in the mechanisms of IPC.

Arrhythmia Vulnerability in Diabetic Cardiac Tissue is Species-Dependent: Effects of I KATP, Uncoupling, and Connexin Lateralization

Amongst the complications of diabetes is arrhythmia, the risk of which depends on multiple factors. This study was designed to investigate several factors, including the effects of ATP-sensitive potassium current, lateralized connexins, and gap junction uncoupling. ATP-sensitive potassium channel (I _KATP) opening is caused by ischemia, which can occur in diabetic or non-diabetic hearts. I _KATP opening was simulated in this work to determine if the risk of ischemia-induced arrhythmias is affected by diabetes. Simulations were performed using healthy and diabetic models of rat and rabbit ventricle. Results showed that the diabetic rat model is less vulnerable to reentrant arrhythmia than the healthy rat model. The diabetic rabbit model was more vulnerable to reentrant arrhythmia than the healthy rabbit model. In both rabbit models, the vulnerability increased as the gap junctional coupling decreased. Opening of I _KATP resulted in larger window of vulnerability. Conduction reserve was simulated based on 1D simulations for both rat and rabbit models. There was no difference between rat and rabbit conduction reserve. Our results showed that the simulation results are model-dependent, i.e., results from the rabbit model are similar to human clinical data, while the results from the rat model contradict human clinical observations, suggesting a significant species-dependence in arrhythmia vulnerability in the diabetic heart.

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.

N-Acetylcysteine Attenuates Diabetic Myocardial Ischemia Reperfusion Injury through Inhibiting Excessive Autophagy

Background. Excessive autophagy is a major mechanism of myocardial ischemia reperfusion injury (I/RI) in diabetes with enhanced oxidative stress. Antioxidant N-acetylcysteine (NAC) reduces myocardial I/RI. It is unknown if inhibition of autophagy may represent a mechanism whereby NAC confers cardioprotection in diabetes. Methods and Results. Diabetes was induced in Sprague-Dawley rats with streptozotocin and they were treated without or with NAC (1.5 g/kg/day) for four weeks before being subjected to 30-minute coronary occlusion and 2-hour reperfusion. The results showed that cardiac levels of 15-F2t-Isoprostane were increased and that autophagy was evidenced as increases in ratio of LC3 II/I and protein P62 and AMPK and mTOR expressions were significantly increased in diabetic compared to nondiabetic rats, concomitant with increased postischemic myocardial infarct size and CK-MB release but decreased Akt and eNOS activation. Diabetes was also associated with increased postischemic apoptotic cell death manifested as increases in TUNEL positive cells, cleaved-caspase-3, and ratio of Bax/Bcl-2 protein expression. NAC significantly attenuated I/RI-induced increases in oxidative stress and cardiac apoptosis, prevented postischemic autophagy formation in diabetes, and reduced postischemic myocardial infarction (all p < 0.05). Conclusions. NAC confers cardioprotection against diabetic heart I/RI primarily through inhibiting excessive autophagy which might be a major mechanism why diabetic hearts are less tolerant to I/RI.

Remote ischaemic pre-conditioning for the prevention of acute kidney injury

Acute kidney injury (AKI) is a common complication associated with high morbidity and mortality in hospitalized patients. One potential mechanism underlying renal injury is ischaemia/reperfusion injury (IRI), which attributed the organ damage to the inflammatory and oxidative stress responses induced by a period of renal ischaemia and subsequent reperfusion. Therapeutic strategies that aim at minimizing the effect of IRI on the kidneys may prevent AKI and improve clinical outcomes significantly. In this review, we examine the technique of remote ischaemic preconditioning (rIPC), which has been shown by several trials to confer organ protection by applying transient, brief episodes of ischaemia at a distant site before a larger ischaemic insult. We provide an overview of the current clinical evidence regarding the renoprotective effect of rIPC in the key clinical settings of cardiac or vascular surgery, contrast-induced AKI, pre-existing chronic kidney disease (CKD) and renal transplantation, and discuss key areas for future research.

Ischaemic conditioning and targeting reperfusion injury: a 30 year voyage of discovery

To commemorate the auspicious occasion of the 30th anniversary of IPC, leading pioneers in the field of cardioprotection gathered in Barcelona in May 2016 to review and discuss the history of IPC, its evolution to IPost and RIC, myocardial reperfusion injury as a therapeutic target, and future targets and strategies for cardioprotection. This article provides an overview of the major topics discussed at this special meeting and underscores the huge importance and impact, the discovery of IPC has made in the field of cardiovascular research.

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.

Interaction of risk factors, comorbidities, and comedications with ischemia/reperfusion injury and cardioprotection by preconditioning, postconditioning, and remote conditioning

Pre-, post-, and remote conditioning of the myocardium are well described adaptive responses that markedly enhance the ability of the heart to withstand a prolonged ischemia/reperfusion insult and provide therapeutic paradigms for cardioprotection. Nevertheless, more than 25 years after the discovery of ischemic preconditioning, we still do not have established cardioprotective drugs on the market. Most experimental studies on cardioprotection are still undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of cardiovascular risk factors. However, ischemic heart disease in humans is a complex disorder caused by, or associated with, cardiovascular risk factors and comorbidities, including hypertension, hyperlipidemia, diabetes, insulin resistance, heart failure, altered coronary circulation, and aging. These risk factors induce fundamental alterations in cellular signaling cascades that affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Moreover, some of the medications used to treat these risk factors, including statins, nitrates, and antidiabetic drugs, may impact cardioprotection by modifying cellular signaling. The aim of this article is to review the recent evidence that cardiovascular risk factors and their medication may modify the response to cardioprotective interventions. We emphasize the critical need to take into account the presence of cardiovascular risk factors and concomitant medications when designing preclinical studies for the identification and validation of cardioprotective drug targets and clinical studies. This will hopefully maximize the success rate of developing rational approaches to effective cardioprotective therapies for the majority of patients with multiple risk factors.

Involvement of Glycogen Synthase Kinase-3β and Oxidation Status in the Loss of Cardioprotection by Postconditioning in Chronic Diabetic Male Rats

PURPOSE

Diabetes mellitus as a main risk-factor of ischemic heart disease may interfere with postconditioning'scardioprotective effects. This study aimed to investigate the involvement of glycogen synthase kinase-3β (GSK-3β) and oxidation status in chronic diabetes-induced loss of cardioprotective effect of ischemic-postconditioning (IPostC) in Wistar rats.

METHODS

After 8 weeks of induction of diabetes by streptozotocin (50mg/kg), hearts of control and diabetic rats were isolated and mounted on a constant-pressure Langendorff system. All hearts were subjected to 30min regional ischemia followed by 60min reperfusion (by occluding and re-opening of left anterior descending coronary artery, respectively). IPostC was applied immediately at the onset of reperfusion. At the end of reperfusion, the infarct size of myocardium was measured via computerized planimetry. Myocardial contents of malondealdehyde and glutathione as indices of oxidative status were assayed spectrophotometrically and the total and phosphorylated forms of myocardial GSK-3β were quantified through western blotting.

RESULTS

IPostC reduced the infarct size of control hearts from 41±2.9% to 28±1.9% (P<0.05), whereas it could not induce significant changes in infarct size of diabetic animals (35±1.8% vs. 39±3.1%). IPostC-induced reduction in malondealdehyde and elevation in glutathione contents were significant only in control not in diabetic hearts. The total forms of GSK-3β were similar in all groups; however, the phosphorylation of GSK-3β (at Ser9) by IPostC was greater in control hearts than diabetics (P<0.01).

CONCLUSION

The failure of cardioprotection by IPostC in diabetic hearts may be attributed to the loss of phosphorylation of GSK-3β and thereby increase in oxidative stress in diabetic states.

The science of reperfusion injury post cardiac arrest--Implications for emergency nurses

Survival following cardiac arrest in the developed world remains below 10%. In those who survive the initial cardiac arrest, prognosis remains poor due to the onset of multi-organ failure with both significant cardiac and neurological dysfunction. Nurses have demonstrated good understanding of cardiac arrest/post arrest guidelines and have good technical skills but deficits remain in their understanding of pathophysiological processes involved in post cardiac arrest syndromes. This article aims to provide an overview of these pathophysiological processes involved in the post cardiac arrest phase, potential treatment options and the nursing interventions that may be required within the emergency department setting. This article will focus emergency nurses to become more involved in patient management at this critical phase of treatment and highlight potential early signs of deterioration. Although return of spontaneous circulation (ROSC) is crucial in the process of recovery from cardiac arrest, it is only the first of many complex stages. Given the complexity of post cardiac arrest syndrome and its impact on the patient, healthcare professionals need to understand the cellular changes associated with reperfusion injuries in order to improve outcomes. It is only through effective nursing care and medical management that improved outcomes will become more common in the future.

Effect of metformin pretreatment on myocardial injury during coronary artery bypass surgery in patients without diabetes (MetCAB): a double-blind, randomised controlled trial

BACKGROUND

During coronary artery bypass graft (CABG) surgery, ischaemia and reperfusion damage myocardial tissue, and increased postoperative plasma troponin concentration is associated with a worse outcome. We investigated whether metformin pretreatment limits cardiac injury, assessed by troponin concentrations, during CABG surgery in patients without diabetes.

METHODS

We did a placebo-controlled, double-blind, single-centre study in an academic hospital in Nijmegen (Netherlands) in adult patients without diabetes undergoing an elective on-pump CABG procedure. We randomly assigned patients (1:1) in blocks of ten via a computer-generated randomisation sequence to either metformin hydrochloride (500 mg three times per day) or placebo (three times per day) for 3 days before surgery. The last dose was given roughly 3 h before surgery. Patients, investigators, trial staff, and the statistician were all masked to treatment allocation. The primary endpoint was the plasma concentration of high-sensitive troponin I at 6, 12, and 24 h postreperfusion after surgery, analysed in the per-protocol population with a mixed-model analysis using all these timepoints. Secondary endpoints included the occurrence of clinically relevant arrhythmias within 24 hours after reperfusion, the need for inotropic support, time to detubation, duration of stay in the intensive-care unit, and postoperative use of insulin. This study is registered with ClinicalTrials.gov, number NCT01438723.

FINDINGS

Between Nov 8, 2011, and Nov 22, 2013, we randomly assigned 111 patients to treatment (57 to metformin and 54 to placebo). Five patients dropped out from the metformin group, and six from the placebo group. 52 patients in the metformin group and 48 patients in the placebo group were included in the per-protocol analysis. Geometric mean high-sensitivity troponin I increased from 0 μg/L to 3·67 μg/L (95% CI 3·06-4·41) with metformin and to 3·32 μg/L (2·75-4·01) with placebo at 6 h after reperfusion; 2·84 μg/L (2·37-3·41) and 2·45 μg/L (2·02-2·96), respectively, at 12 h; and to 1·77 μg/L (1·47-2·12) and 1·60 μg/L (1·32-1·94) at 24 h. The concentrations did not differ significantly between the groups (difference 12·3% for all timepoints [95% CI -12·4 to 44·1] p=0·35). Occurrence of arrhythmias did not differ between groups (three [5·8%] of 52 patients who received metformin vs three [6·3%] of 48 patients who received placebo; p=1·00). There was no difference between groups in the need for inotropic support, time to detubation, duration of stay in the intensive-care unit, or postoperative use of insulin. No patients died within 30 days after surgery. Occurrence of gastrointestinal discomfort (mostly diarrhoea) was significantly higher with metformin than with placebo (11 [21·2%] of 52 vs two [4·2%] of 48 patients; p=0·01).

INTERPRETATION

Short-term metformin pretreatment, although safe, does not seem to be an effective strategy to reduce periprocedural myocardial injury in patients without diabetes undergoing CABG surgery.

FUNDING

Netherlands Organisation for Health Research and Development and Netherlands Heart Foundation.

Remote ischemic conditioning

In remote ischemic conditioning (RIC), brief, reversible episodes of ischemia with reperfusion in one vascular bed, tissue, or organ confer a global protective phenotype and render remote tissues and organs resistant to ischemia/reperfusion injury. The peripheral stimulus can be chemical, mechanical, or electrical and involves activation of peripheral sensory nerves. The signal transfer to the heart or other organs is through neuronal and humoral communications. Protection can be transferred, even across species, with plasma-derived dialysate and involves nitric oxide, stromal derived factor-1α, microribonucleic acid-144, but also other, not yet identified factors. Intracardiac signal transduction involves: adenosine, bradykinin, cytokines, and chemokines, which activate specific receptors; intracellular kinases; and mitochondrial function. RIC by repeated brief inflation/deflation of a blood pressure cuff protects against endothelial dysfunction and myocardial injury in percutaneous coronary interventions, coronary artery bypass grafting, and reperfused acute myocardial infarction. RIC is safe and effective, noninvasive, easily feasible, and inexpensive.

Mild Type 2 Diabetes Mellitus Reduces the Susceptibility of the Heart to Ischemia/Reperfusion Injury: Identification of Underlying Gene Expression Changes

Despite clinical studies indicating that diabetic hearts are more sensitive to ischemia/reperfusion injury, experimental data is contradictory. Although mild diabetes prior to ischemia/reperfusion may induce a myocardial adaptation, further research is still needed. Nondiabetic Wistar (W) and type 2 diabetic Goto-Kakizaki (GK) rats (16-week-old) underwent 45 min occlusion of the left anterior descending coronary artery and 24 h reperfusion. The plasma glucose level was significantly higher in diabetic rats compared to the nondiabetics. Diabetes mellitus was associated with ventricular hypertrophy and increased interstitial fibrosis. Inducing myocardial infarction increased the glucose levels in diabetic compared to nondiabetic rats. Furthermore, the infarct size was smaller in GK rats than in the control group. Systolic and diastolic functions were impaired in W + MI and did not reach statistical significance in GK + MI animals compared to the corresponding controls. Among the 125 genes surveyed, 35 genes showed a significant change in expression in GK + MI compared to W + MI rats. Short-term diabetes promotes compensatory mechanisms that may provide cardioprotection against ischemia/reperfusion injury, at least in part, by increased antioxidants and the upregulation of the prosurvival PI3K/Akt pathway, by the downregulation of apoptotic genes, proinflammatory cytokine TNF-α, profibrogenic TGF-β, and hypertrophic marker α-actin-1.

Chronic metformin treatment is associated with reduced myocardial infarct size in diabetic patients with ST-segment elevation myocardial infarction

PURPOSE

Increased myocardial infarct (MI) size is associated with higher risk of developing left ventricular dysfunction, heart failure and mortality. Experimental studies have suggested that metformin treatment reduces MI size after induced ischaemia but human data is lacking. We aimed to investigate the effect of metformin on MI size in patients presenting with an acute MI.

METHODS

All consecutive patients (n = 3,288) presenting to our hospital with ST-segment elevation myocardial infarction (STEMI) undergoing primary PCI between January 2004 and December 2010 were included in this retrospective analysis. Patients with diabetes were divided according to metformin versus non-metformin based pharmacotherapy. MI size was estimated using peak values of serum creatine kinase (CK), myocardial band of CK (CK-MB), and troponin-T.

RESULTS

We identified 677 (20.6 %) patients with diabetes, of whom 189 (27.9 %) were treated with metformin. Chronic metformin treatment was associated with lower peak levels of CK (1,101 vs. 1,422 U/L, P = 0.005), CK-MB (152 vs. 182 U/L, P = 0.018) and troponin-T (2.5 vs. 4.0 ng/L, P = 0.021) compared to non-metformin using diabetics. After adjustment for age, sex, TIMI flow post PCI, and previous MI, the use of metformin treatment remained an independent predictor of smaller MI size. Patient with diabetes treated with metformin had even smaller MI size than patients without diabetes.

CONCLUSIONS

Chronic metformin treatment is associated with reduced MI size compared to non-metformin based strategies in diabetic patients presenting with STEMI. Metformin might have additional beneficial effects beyond glucose lowering efficacy.

Short-term melatonin consumption protects the heart of obese rats independent of body weight change and visceral adiposity

Chronic melatonin treatment has been shown to prevent the harmful effects of diet-induced obesity and reduce myocardial susceptibility to ischaemia-reperfusion injury (IRI). However, the exact mechanism whereby it exerts its beneficial actions on the heart in obesity/insulin resistance remains unknown. Herein, we investigated the effects of relatively short-term melatonin treatment on the heart in a rat model of diet-induced obesity. Control and diet-induced obese Wistar rats (fed a high calorie diet for 20 wk) were each subdivided into three groups receiving drinking water with or without melatonin (4 mg/kg/day) for the last 6 or 3 wk of experimentation. A number of isolated hearts were perfused in the working mode, subjected to regional or global ischaemia-reperfusion; others were nonperfused. Metabolic parameters, myocardial infarct sizes (IFS), baseline and postischaemic activation of PKB/Akt, ERK42/44, GSK-3β and STAT-3 were determined. Diet-induced obesity caused increases in body weight gain, visceral adiposity, fasting blood glucose, serum insulin and triglyceride (TG) levels with a concomitant cardiac hypertrophy, large postischaemic myocardial IFSs and a reduced cardiac output. Melatonin treatment (3 and 6 wk) decreased serum insulin levels and the HOMA index (P < 0.05) with no effect on weight gain (after 3 wk), visceral adiposity, serum TG and glucose levels. It increased serum adiponectin levels, reduced myocardial IFSs in both groups and activated baseline myocardial STAT-3 and PKB/Akt, ERK42/44 and GSK-3β during reperfusion. Overall, short-term melatonin administration to obese/insulin resistant rats reduced insulin resistance and protected the heart against ex vivo myocardial IRI independently of body weight change and visceral adiposity.

Cardioprotective effects of oral nicorandil use in diabetic patients undergoing elective percutaneous coronary intervention

OBJECTIVE

This study sought to evaluate the cardioprotective role of oral nicorandil (a hybrid between the nitrates and adenosine triphosphate [ATP] sensitive potassium channel activators) in diabetic patients undergoing elective percutaneous coronary intervention (PCI).

BACKGROUND

Myocardial injury commonly occurs during PCI. Several agents that mimic ischemic preconditioning could help minimize this phenomenon.

METHODS

One hundred diabetic patients with stable angina were prospectively enrolled, then randomly assigned to receive oral nicorandil: 20 mg once daily (group A, 50 patients) or placebo (group B, 50 patients) 1 week before and 6 months after PCI. Cardiac troponin I (cTnI) and creatine kinase-MB (CK-MB) levels were measured before and 6, 12, and 24 hours post-PCI.

RESULTS

Mean age of the study cohort was 59.8 ± 5.8 years (males = 68%). cTnI level was significantly lower in group A (6 hours: 7.3 ± 0.3 vs. 14.5 ± 0.4 pg/mL; 12 hours: 12.7 ± 0.7 vs. 25.3 ± 0.5 pg/mL; and 24 hours: 7.7 ± 0.5 vs. 15.0 ± 0.4 pg/mL, P < 0.001). After 6 months, the same group showed significantly higher left ventricle ejection fraction (LVEF%), that is, 63.5 ± 7.7% versus 56.5 ± 8.3% (P < 0.05), with a trend toward lower incidence of major adverse cardiac events (MACE).

CONCLUSION

In diabetic patients undergoing elective PCI, nicorandil intake was associated with decreased incidence of PCI-related myocardial injury and improvement of LVEF% after 6 months.

High carbohydrate and high fat diets protect the heart against ischaemia/reperfusion injury

Background

Although obesity is still considered a risk factor in the development of cardiovascular disorders, recent studies suggested that it may also be associated with reduced morbidity and mortality, the so-called “obesity paradox”. Experimental data on the impact of diabetes, obesity and insulin resistance on myocardial ischaemia/reperfusion injury are controversial. Similar conflicting data have been reported regarding the effects of ischaemic preconditioning on ischaemia/reperfusion injury in hearts from such animals. The aim of the present study was to evaluate the susceptibility to myocardial ischaemia/reperfusion damage in two models of diet-induced obesity as well as the effect of ischaemic and pharmacological preconditioning on such hearts.

Methods

Three groups of rats were fed with: (i) normal rat chow (controls) (ii) a sucrose-supplemented diet (DIO) (iii) a high fat diet (HFD). After 16 weeks, rats were sacrificed and isolated hearts perfused in the working mode and subjected to 35 min regional ischaemia/60 min reperfusion. Endpoints were infarct size and functional recovery. Infarct size was determined, using tetrazolium staining. Activation of PKB/Akt and ERKp44/p42 (RISK pathway) during early reperfusion was determined using Western blot. Statistical evaluation was done using ANOVA and the Bonferroni correction.

Results

Infarct sizes of non-preconditioned hearts from the two obese groups were significantly smaller than those of the age-matched controls. Ischaemic as well as pharmacological (beta-adrenergic) preconditioning with a beta2-adrenergic receptor agonist, formoterol, caused a significant reduction in infarct size of the controls, but were without effect on infarct size of hearts from the obese groups. However, ischaemic as well as beta-preconditioning caused an improvement in functional performance during reperfusion in all three groups. A clear-cut correlation between the reduction in infarct size and activation of ERKp44/p42 and PKB/Akt was not observed: The reduction in infarct size observed in the non-preconditioned hearts from the obese groups was not associated with activation of the RISK pathway. However, beta-adrenergic preconditioning caused a significant activation of ERKp44/p42, but not PKB/Akt, in all three groups.

Conclusions

Relatively long-term administration of the two obesity-inducing diets resulted in cardioprotection against ischaemia/reperfusion damage. Further protection by preconditioning was, however, without effect on infarct size, while an improvement in functional recovery was observed.

Impact of conditioning hyperglycemic on myocardial infarction rats: Cardiac cell survival factors

While clinical data have suggested that the diabetic heart is more susceptible to ischemic heart disease (IHD), animal data have so far pointed to a lower probability of IHD. Thus, the aim of this present review is to look at these conflicting results and discuss the protective mechanisms that conditioned hyperglycemia may confer to the heart against ischemic injury. Several mechanisms have been proposed to explain the cardioprotective action of high glucose exposure, namely, up-regulation of anti-apoptotic factor Bcl-2, inactivation of pro-apoptotic factor bad, and activation of pro-survival factors such as protein kinase B (Akt), vascular endothelial growth factor (VEGF), hypoxia inducible factor-1α and protein kinase C-ε. Indeed, cytosolic increase in Ca²⁺ concentration, the mitochondrial permeability transition pore, plays a key role in the genesis of ischemic injury. Previous studies have shown that the diabetic heart decreased Na⁺/Ca²⁺ and Na⁺/H⁺ exchanger activity and as such it accumulates less Ca²⁺ in cardiomyocyte, thus preventing cardiac injury and the associated heart dysfunctions. In addition, the expression of VEGF in diabetic animals leads to increased capillary density before myocardial infarction. Despite poor prognostic in the long-term, all these results suggest that diabetes mellitus and consequently hyperglycemia may indeed play a cardioprotective role against myocardial infarction in the short term.

Cardioprotection in the aging, diabetic heart: the loss of protective Akt signalling

AIMS

Old age and diabetes are risk factors that often coexist increasing the vulnerability of the heart to the lethal effects of ischaemia-reperfusion injury (IRI). However, to our knowledge, no investigations have examined IRI and cardioprotective signalling in animal models bearing these co-morbidities concomitantly. The ability of the heart to recover following IRI is greatly dependent on its innate cardioprotective potential, in which a central role is played by Akt. We aimed to investigate in an aging diabetic rat model, the susceptibility of the heart to IRI, the achievability of ischaemic preconditioning (IPC) against this lethal event, and the changes in Akt signalling, as the main prosurvival intracellular pathway.

METHODS AND RESULTS

Our data showed that the isolated hearts of aged, diabetic Goto-Kakizaki rats were more susceptible to sub-lethal injury and not amenable to cardioprotection via IPC, compared with younger diabetic rat hearts. Western blot analysis of the heart tissue suggested a chronic up-regulation of Akt phosphorylation, and reduced expression of the mitochondrial regulator PGC-1α and of the anti-oxidant enzyme catalase, potentially due to the Akt up-regulation. Moreover, no further activation of Akt could be achieved following IPC.

CONCLUSION

An increased susceptibility to IRI in the aged, diabetic heart could be a consequence of impaired Akt signalling due to chronic Akt phosphorylation. Additional Akt phosphorylation required for IPC protection may therefore not be possible in the aged, diabetic rat heart and may explain why this cardioprotective manoeuvre cannot be achieved in these hearts.

Oxidative stress and myocardial injury in the diabetic heart

Reactive oxygen or nitrogen species play an integral role in both myocardial injury and repair. This dichotomy is differentiated at the level of species type, amount and duration of free radical generated. Homeostatic mechanisms designed to prevent free radical generation in the first instance, scavenge, or enzymatically convert them to less toxic forms and water, playing crucial roles in the maintenance of cellular structure and function. The outcome between functional recovery and dysfunction is dependent upon the inherent ability of these homeostatic antioxidant defences to withstand acute free radical generation, in the order of seconds to minutes. Alternatively, pre-existent antioxidant capacity (from intracellular and extracellular sources) may regulate the degree of free radical generation. This converts reactive oxygen and nitrogen species to the role of second messenger involved in cell signalling. The adaptive capacity of the cell is altered by the balance between death or survival signal converging at the level of the mitochondria, with distinct pathophysiological consequences that extends the period of injury from hours to days and weeks. Hyperglycaemia, hyperlipidaemia and insulin resistance enhance oxidative stress in the diabetic myocardium that cannot adapt to ischaemia-reperfusion. Altered glucose flux, mitochondrial derangements and nitric oxide synthase uncoupling in the presence of decreased antioxidant defence and impaired prosurvival cell signalling may render the diabetic myocardium more vulnerable to injury, remodelling and heart failure.

RU28318, an aldosterone antagonist, in combination with an ACE inhibitor and angiotensin receptor blocker attenuates cardiac dysfunction in diabetes

AIMS

We evaluated the effects of RU28318 (RU), a selective mineralocorticoid receptor (MR) antagonist, Captopril (Capt), an angiotensin converting enzyme inhibitor, and Losartan (Los), an angiotensin receptor blocker, alone or in combination with ischemia/reperfusion- (I/R-) induced cardiac dysfunction in hearts obtained from normal and diabetic rats.

METHODS

Isolated hearts were perfused for 30 min and then subjected to 30 min of global ischemia (I) followed by a period of 30 min of reperfusion (R). Drugs were administered for 30 min either before or after ischemia. Drug regimens tested were RU, Capt, Los, RU + Capt, RU + Los, Capt + Los, and RU + Capt + Los (Triple). Recovery of cardiac hemodynamics was evaluated.

RESULTS

Recovery of cardiac function was up to 5-fold worse in hearts obtained from diabetic animals compared to controls. Treatment with RU was generally better in preventing or reversing ischemia-induced cardiac dysfunction in normal hearts compared to treatment with Capt or Los alone. In diabetic hearts, RU was generally similarly effective as Capt or Los treatment.

CONCLUSIONS

RU treatment locally might be considered as an effective therapy or preventative measure in cardiac I/R injury. Importantly, RU was the most effective at improving -dP/dt (a measure of diastolic function) when administered to diabetic hearts after ischemia.

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)