Negative interaction between nitrates and remote ischemic preconditioning in patients undergoing cardiac surgery: the ERIC-GTN and ERICCA studies.

Remote ischaemic preconditioning (RIPC) using transient limb ischaemia failed to improve clinical outcomes following cardiac surgery and the reasons for this remain unclear. In the ERIC-GTN study, we evaluated whether concomitant nitrate therapy abrogated RIPC cardioprotection. We also undertook a post-hoc analysis of the ERICCA study, to investigate a potential negative interaction between RIPC and nitrates on clinical outcomes following cardiac surgery. In ERIC-GTN, 185 patients undergoing cardiac surgery were randomized to: (1) Control (no RIPC or nitrates); (2) RIPC alone; (3); Nitrates alone; and (4) RIPC + Nitrates. An intravenous infusion of nitrates (glyceryl trinitrate 1 mg/mL solution) was commenced on arrival at the operating theatre at a rate of 2-5 mL/h to maintain a mean arterial pressure between 60 and 70 mmHg and was stopped when the patient was taken off cardiopulmonary bypass. The primary endpoint was peri-operative myocardial injury (PMI) quantified by a 48-h area-under-the-curve high-sensitivity Troponin-T (48 h-AUC-hs-cTnT). In ERICCA, we analysed data for 1502 patients undergoing cardiac surgery to investigate for a potential negative interaction between RIPC and nitrates on clinical outcomes at 12-months. In ERIC-GTN, RIPC alone reduced 48 h-AUC-hs-cTnT by 37.1%, when compared to control (ratio of AUC 0.629 [95% CI 0.413-0.957], p = 0.031), and this cardioprotective effect was abrogated in the presence of nitrates. Treatment with nitrates alone did not reduce 48 h-AUC-hs-cTnT, when compared to control. In ERICCA there was a negative interaction between nitrate use and RIPC for all-cause and cardiovascular mortality at 12-months, and for risk of peri-operative myocardial infarction. RIPC alone reduced the risk of peri-operative myocardial infarction, compared to control, but no significant effect of RIPC was demonstrated for the other outcomes. When RIPC and nitrates were used together they had an adverse impact in patients undergoing cardiac surgery with the presence of nitrates abrogating RIPC-induced cardioprotection and increasing the risk of mortality at 12-months post-cardiac surgery in patients receiving RIPC.

Reply to Sanfilippo et al. Caution Is Warranted When Assessing Diastolic Function Using Transesophageal Echocardiography. Comment on "Kyle et al. Consensus Defined Diastolic Dysfunction and Cardiac Postoperative Morbidity Score: A Prospective Observational Study. J. Clin. Med. 2021, 10, 5198".

We thank Sanfilippo and colleagues for their insightful comments about the assessment of diastolic function with transesophageal echocardiography (TEE) [...].

Consensus Defined Diastolic Dysfunction and Cardiac Postoperative Morbidity Score: A Prospective Observational Study.

Diastolic dysfunction is associated with major adverse outcomes following cardiac surgery. We hypothesized that multisystem endpoints of morbidity would be higher in patients with diastolic dysfunction. A total of 142 patients undergoing cardiac surgical procedures with cardiopulmonary bypass were included in the study. Intraoperative assessments of diastolic function according to the 2016 American Society of Echocardiography and European Association of Cardiovascular Imaging guidelines using transesophageal echocardiography were performed. Cardiac Postoperative Morbidity Score (CPOMS) on days 3, 5, 8, and 15; length of stay in ICU and hospital; duration of intubation; incidence of new atrial fibrillation; 30-day major adverse cardiac and cerebrovascular events were recorded. Diastolic function was determinable in 96.7% of the dataset pre and poststernotomy assessment (n = 240). Diastolic dysfunction was present in 70.9% (n = 88) of measurements before sternotomy and 75% (n = 93) after sternal closure. Diastolic dysfunction at either stage was associated with greater CPOMS on D5 (p = 0.009) and D8 (p = 0.009), with CPOMS scores 1.24 (p = 0.01) higher than in patients with normal function. Diastolic dysfunction was also associated with longer durations of intubation (p = 0.001), ICU length of stay (p = 0.019), and new postoperative atrial fibrillation (p = 0.016, OR (95% CI) = 4.50 (1.22-25.17)). We were able to apply the updated ASE/EACVI guidelines and grade diastolic dysfunction in the majority of patients. Any grade of diastolic dysfunction was associated with greater all-cause morbidity, compared with patients with normal diastolic function.

The Effect of Remote Ischemic Conditioning and Glyceryl Trinitrate on Perioperative Myocardial Injury in Cardiac Bypass Surgery Patients: Rationale and Design of the ERIC-GTN Study.

Remote ischemic conditioning (RIC) using transient limb ischemia/reperfusion has been reported to reduce perioperative myocardial injury in patients undergoing coronary artery bypass grafting and/or valve surgery. The role of intravenous glyceryl trinitrate (GTN) therapy administered during cardiac surgery as a cardioprotective agent and whether it interferes with RIC cardioprotection is not clear and is investigated in the ERIC-GTN trial ( http://www.clinicaltrials.gov: NCT01864252). The ERIC-GTN trial is a single-site, double-blind, randomized, placebo-controlled study. Consenting adult patients (age > 18 years) undergoing elective coronary artery bypass grafting ± valve surgery with blood cardioplegia will be eligible for inclusion. Two hundred sixty patients will be randomized to 1 of 4 treatment groups following anesthetic induction: (1) RIC alone, a RIC protocol comprising three 5-minute cycles of simultaneous upper-arm and thigh cuff inflation/deflation followed by an intravenous (IV) placebo infusion; (2) GTN alone, a simulated sham RIC protocol followed by an IV GTN infusion; (3) RIC + GTN, a RIC protocol followed by an IV GTN infusion; and (4) neither RIC nor GTN, a sham RIC protocol followed by IV placebo infusion. The primary endpoint will be perioperative myocardial injury as quantified by the 72-hour area-under-the-curve serum high-sensitivity troponin T. The ERIC-GTN trial will determine whether intraoperative GTN therapy is cardioprotective during cardiac surgery and whether it affects RIC cardioprotection.

Plasma exosomes protect the myocardium from ischemia-reperfusion injury.

BACKGROUND: Exosomes are nanometer-sized vesicles released from cells into the blood, where they can transmit signals throughout the body. Shown to act on the heart, exosomes' composition and the signaling pathways they activate have not been explored. We hypothesized that endogenous plasma exosomes can communicate signals to the heart and provide protection against ischemia and reperfusion injury. OBJECTIVES: This study sought to isolate and characterize exosomes from rats and healthy volunteers, evaluate their cardioprotective actions, and identify the molecular mechanisms involved. METHODS: The exosome-rich fraction was isolated from the blood of adult rats and human volunteers and was analyzed by protein marker expression, transmission electron microscopy, and nanoparticle tracking analysis. This was then used in ex vivo, in vivo, and in vitro settings of ischemia-reperfusion, with the protective signaling pathways activated on cardiomyocytes identified using Western blot analyses and chemical inhibitors. RESULTS: Exosomes exhibited the expected size and expressed marker proteins CD63, CD81, and heat shock protein (HSP) 70. The exosome-rich fraction was powerfully cardioprotective in all tested models of cardiac ischemia-reperfusion injury. We identified a pro-survival signaling pathway activated in cardiomyocytes involving toll-like receptor (TLR) 4 and various kinases, leading to activation of the cardioprotective HSP27. Cardioprotection was prevented by a neutralizing antibody against a conserved HSP70 epitope expressed on the exosome surface and by blocking TLR4 in cardiomyocytes, identifying the HSP70/TLR4 communication axis as a critical component in exosome-mediated cardioprotection. CONCLUSIONS: Exosomes deliver endogenous protective signals to the myocardium by a pathway involving TLR4 and classic cardioprotective HSPs.

Pharmacologic therapy that simulates conditioning for cardiac ischemic/reperfusion injury.

Cardiovascular disease remains a leading cause of deaths due to noncommunicable diseases, of which ischemic heart disease forms a large percentage. The main therapeutic strategy to treat ischemic heart disease is reperfusion that could either be medical or surgical. However, reperfusion following ischemia is known to increase the infarct size further. Newer strategies such as ischemic preconditioning (IPC), ischemic postconditioning, and remote IPC have been shown to condition the myocardium to ischemia-reperfusion injury and thus reduce the final infarct size. Research over the past 3 decades has deepened our understanding of cellular and subcellular pathways that mediate ischemia-reperfusion injury. This in turn has resulted in the development of several pharmacological agents that act as conditioning agents, which reduce the final myocardial infarct size following ischemia-reperfusion. This review discusses many of these agents, their mechanisms of action, and the animal and clinical evidence behind them.

Failure of the adipocytokine, resistin, to protect the heart from ischemia-reperfusion injury.

Experimental studies have linked the adipocytokines with acute cardioprotection. Whether the adipocytokine, resistin, confers protection is, however, debatable. In the current study, the actions of resistin, administered at reperfusion, were investigated in in vivo and in vitro rodent and in vitro human models of myocardial ischemia-reperfusion (I/R) injury. Resistin did not reduce infarct size in Langendorff-perfused rat hearts or murine hearts perfused in vivo. Resistin also did not protect human atrial muscle subjected to hypoxia-reoxygenation. Although cyclosporin A delayed mitochondrial permeability transition pore (MPTP) opening in murine cardiomyocytes, resistin was ineffective. Western blot analysis revealed that resistin treatment was associated with enhanced phosphorylation of Akt, at both the serine-473 (+ 51.9%, P = .01) and threonine-308 (+107%, P < .01) phosphorylation sites, although not to the extent seen with ischemic preconditioning (+132.5%, P = .002 and +389.1%, P < .01, respectively). We conclude that resistin administered at reperfusion at concentrations/doses equivalent to normal (upper end) and pathological serum levels does not protect against I/R injury or inhibit MPTP opening.

Preconditioning the diabetic human myocardium.

Our objective was to determine whether human diabetic myocardium is amenable to the cardioprotective actions of ischaemic preconditioning. Human right atrial appendages were harvested from diabetic and non-diabetic patients undergoing elective coronary artery bypass graft surgery. The atrial trabeculae were isolated and subjected to 90 min. of hypoxia followed by 120 min. of reoxygenation, following which the percentage recovery of baseline contractile function was determined. The atrial trabeculae were randomized to: (i) controls (groups 1 and 3); (ii) standard hypoxic preconditioning (HPC) protocol consisting of 4 min. of hypoxia/16 min. of reoxygenation before the 90 min. index hypoxic period (groups 2 and 4); (iii) Prolonged HPC protocol consisting of: 7 min. of hypoxia /16 min. of reoxygenation before the index hypoxic period (group 5). In addition, basal levels of Akt phosphorylation were determined in right atrial appendages harvested from non-diabetic patients and diabetic patients to determine whether PI3K-Akt signalling is down-regulated in the diabetic heart. Standard HPC improved baseline contractile function in human atrial trabeculae harvested from non-diabetic patients (52.4 +/- 3.8% with HPC versus 30.0 +/- 3.2% in control: P = 0.001; N = 6/group), but not in atrial trabeculae isolated from diabetic patients (22.6 +/- 3.3% with HPC versus 28.5 +/- 1.9% in control: P > 0.05; N = 6/group). However, the prolonged HPC protocol did improve baseline contractile function in atrial trabeculae harvested from diabetic patients (42.0 +/- 2.4% with HPC versus 28.5 +/- 1.9% in control: P= 0.001; N > or = 6/group). Western blot analysis demonstrated lower levels of phosphorylated Akt in diabetic myocardium compared to non-diabetic myocardium (0.13 +/- 0.03 arbitrary units versus 0.39 +/- 0.11 arbitrary units: P= 0.047; N > or = 4/group). From the data obtained it appears that the threshold for preconditioning the diabetic myocardium is elevated which may be related to the down-regulation of the PI3K-Akt pathway.

The divergent roles of protein kinase C epsilon and delta in simulated ischaemia-reperfusion injury in human myocardium.

Experimental studies suggest that cardioprotection can be achieved through either the activation of PKC-epsilon prior to the index ischaemic episode or the inhibition of PKC-delta at the onset of reperfusion. However, whether these PKC isoforms exert such divergent roles in human myocardium, subjected to simulated ischaemia-reperfusion injury, is unclear. Human atrial trabeculae were isolated from right atrial appendages harvested from patients undergoing elective cardiac surgery. These were subjected to 90 min of hypoxia followed by 120 min of reoxygenation, at the end of which the recovery of baseline contractile function was determined. Atrial trabeculae were randomised to receive various treatment protocols comprising a peptide activator of PKC-epsilon, a peptide inhibitor of PKC-delta and their respective inactive control peptides. Administering the PKC-delta peptide inhibitor at reoxygenation improved the recovery of function at all the concentrations tested (39.3+/-1.4% at 5 nM, 52.4+/-2.9% at 50 nM and 46.8+/-2.9% at 500 nM versus the control group, 27.5+/-1.4%: N > or = 6/group: P<0.02). Preconditioning with the PKC-epsilon peptide activator improved the recovery of function (40.0+/-0.8% at 50 nM and 49.7+/-3.1% at 500 nM versus the control group 27.5+/-1.4%: N > or = 6/group: P<0.02). This cardioprotective effect was comparable to that achieved by a standard hypoxic preconditioning protocol (52.3+/-3.2%). Interestingly, administering the PKC-epsilon activator (500 nM) at the onset of reperfusion also improved the recovery of contractile function (40.7+/-2.1% versus 27.5+/-1.5%: N > or = 6/group: P < 0.05). In human myocardium, cardioprotection can be achieved by either inhibiting PKC-delta or activating PKC-epsilon at the onset of reperfusion. In addition, PKC-epsilon activation offers cardioprotection when administered as a preconditioning strategy.

Postconditioning protects human atrial muscle through the activation of the RISK pathway.

Ischemic postconditioning (IPost) has been demonstrated to reduce myocardial injury in patients undergoing primary coronary angioplasty for an acute myocardial infarction.Pre-clinical animal studies suggest that pro-survival protein kinases of the Reperfusion Injury Salvage Kinase (RISK) pathway such as Akt and Erk1/2 mediate the cardioprotective effect of IPost. Whether IPost can protect human myocardial tissue ex vivo and whether it recruits the RISK pathway in human myocardium are both not known. To investigate this, atrial appendages were harvested from patients undergoing cardiac surgery. From these samples atrial trabeculae were isolated and mounted on a superperfusion apparatus and subjected to 90 min of hypoxia followed by 120 min of reoxygenation at the end of which function expressed as a percentage of the recovery of baseline contractile function was determined. Atrial trabeculae were randomized to control, hypoxic preconditioning (HPre), hypoxic postconditioning comprising either four 30-s (HPost-30) or 60-s (HPost-60) episodes of alternating hypoxia and reoxygenation, and HPost in the presence or absence of UO126 (a MEK1/2 inhibitor) or LY294002 (a PI3K inhibitor). HPre and HPost-60 improved the recovery of baseline contractile function (45.4+/-3.2% with HPre and 45.2+/-2.2% with HPost-60 vs 26.7+/-2.1 % in control: N>or=6/group: P<0.05), whereas HPost-30 failed to cardioprotect (28.3+/-3.4% with HPost-30 vs 26.7+/-2.1 % in control: N>or=6/group: P>0.05). The cardioprotective effect of HPost-60 was abolished in the presence of either LY (28.1+/-2.5% with HPost-60+LY vs 45.2+/-2.2% with HPost-60: N>or=6/group: P<0.05) or UO (32.7+/-1.8% with HPost-60+UO vs 45.2+/-2.2% with HPost-60:N=7/group: P<0.05). The kinase inhibitors alone had no effect on functional recovery (28.2+/-3.6% with LY and 30.1+/-4.8% with UO vs 26.7+/-2.1 % in control: N>or=5/group: P>0.05). In conclusion, we demonstrate for the first time that postconditioning protects human myocardium ex vivo and that this effect is dependent on the activation of the RISK pathway.