Remote ischemic conditioning provides humoural cross-species cardioprotection through glycine receptor activation

Vago-splenic signal transduction of cardioprotection in humans

BACKGROUND AND AIMS

The spleen serves as an important relay organ that releases cardioprotective factor(s) upon vagal activation during remote ischaemic conditioning (RIC) in rats and pigs. The translation of these findings to humans was attempted.

METHODS

Remote ischaemic conditioning or electrical auricular tragus stimulation (ATS) were performed in 10 healthy young volunteers, 10 volunteers with splenectomy, and 20 matched controls. Venous blood samples were taken before and after RIC/ATS or placebo, and a plasma dialysate was infused into isolated perfused rat hearts subjected to global ischaemia/reperfusion.

RESULTS

Neither left nor right RIC or ATS altered heart rate and heart rate variability in the study cohorts. With the plasma dialysate prepared before RIC or ATS, respectively, infarct size (% ventricular mass) in the recipient rat heart was 36 ± 6% (left RIC), 34 ± 3% (right RIC) or 31 ± 5% (left ATS), 35 ± 5% (right ATS), and decreased with the plasma dialysate from healthy volunteers after RIC or ATS to 20 ± 4% (left RIC), 23 ± 6% (right RIC) or to 19 ± 4% (left ATS), 26 ± 9% (right ATS); infarct size was still reduced with plasma dialysate 4 days after ATS and 9 days after RIC. In a subgroup of six healthy volunteers, such infarct size reduction was abrogated by intravenous atropine. Infarct size reduction by RIC or ATS was also abrogated in 10 volunteers with splenectomy, but not in their 20 matched controls.

CONCLUSIONS

In humans, vagal innervation and the spleen as a relay organ are decisive for the cardioprotective signal transduction of RIC and ATS.

Holter ECG monitoring and platelets characteristics in patients with coronary artery disease and atrial fibrillation

OBJECTIVE

Aim: To check the relationships between platelet characteristics and Holter ECG monitoring results in patients with atrial fibrillation (AF) and coronary artery disease (CAD).

PATIENTS AND METHODS

Materials and Methods: 300 investigated patients were separated into three groups: I (CAD) - 149 patients with CAD without arrhythmias, II (CAD and AF) - 124 patients with CAD and AF paroxysm, and the control group (CG) - 27 patients without CAD and arrhythmias.

RESULTS

Results: In the II group was detected an increase in mean platelet volume (MPV) (9.30%) and platelet-to-leucocyte ratio (PLR) (41.12%) and a decrease in platelet count (PC) (12.20%) in comparison with the I group, P<0.05. Also, in the II group was found an increase in platelet leucine (12.63%), isoleucine (10.73%), and a decrease in serine (5.06%), threonine (23.05%), valine (30.83%), glycine (32.21%) levels in comparison with the I group, P<0.05. PC, MPV, and PLR ratios were correlated with supraventricular extrasystoles per hour (r=-0.352, r=0.308, and r=0.359, consequently), P<0.05. Platelets distribution width (PDW) was correlated with ST-segment changes (r=0.371), P<0.05. Platelet threonine, serine, glycine, alanine, and valine levels were correlated with total supraventricular extrasystoles (r=-0.374, r=-0.358, r=-0.402, r=-0.307, r=-0.312, consequently) and supraventricular extrasystoles per hour (r=-0.374, r=-0.358, r=-0.402, r=-0.307, r=-0.312, consequently), P<0.05. Platelet lysine, taurine, cysteine, and phenylalanine levels were correlated with ST-segment changes (r=-0.319, r=-0.344, r=-0.376, and r=0.317, consequently), P<0.05.

CONCLUSION

Conclusions: Platelet features (PC, MPV, PDW, PLR, and amino acid spectrum) are significantly correlated with supraventricular arrhythmias and ST-segment episodes, which shows their role in AF and CAD pathogenesis.

Myocardial remote ischemic preconditioning: from cell biology to clinical application

Remote ischemic preconditioning (rIPC) is a cardioprotective phenomenon where brief periods of ischemia followed by reperfusion of one organ/tissue can confer subsequent protection against ischemia/reperfusion injury in other organs, such as the heart. It involves activation of humoral, neural or systemic communication pathways inducing different intracellular signals in the heart. The main purpose of this review is to summarize the possible mechanisms involved in the rIPC cardioprotection, and to describe recent clinical trials to establish the efficacy of these strategies in cardioprotection from lethal ischemia/reperfusion injury. In this sense, certain factors weaken the subcellular mechanisms of rIPC in patients, such as age, comorbidities, medication, and anesthetic protocol, which could explain the heterogeneity of results in some clinical trials. For these reasons, further studies, carefully designed, are necessary to develop a clearer understanding of the pathways and mechanism of early and late rIPC. An understanding of the pathways is important for translation to patients.

1H NMR serum metabolomic profiling of patients at risk of cardiovascular diseases performing stress test

Cardiovascular diseases are the leading cause of death worldwide. Changes in lifestyle and/or pharmacological treatment are able to reduce the burden of coronary artery diseases (CAD) and early diagnosis is crucial for the timely and optimal management of the disease. Stress testing is a good method to measure the burden of CAD but it is time consuming and pharmacological testing may not fully mimic exercise test. The objectives of the present project were to characterize the metabolic profile of the population undergoing pharmacological and exercise stress testing to evaluate possible differences between them, and to assess the capacity of ¹H NMR spectroscopy to predict positive stress testing. Pattern recognition was applied to ¹H NMR spectra from serum of patients undergoing stress test and metabolites were quantified. The effects of the stress test, confounding variables and the ability to predict ischemia were evaluated using OPLS-DA. There was an increase in lactate and alanine concentrations in post-test samples in patients undergoing exercise test, but not in those submitted to pharmacological testing. However, when considering only pharmacological patients, those with a positive test result, showed increased serum lactate, that was masked by the much larger amount of lactate associated to exercise testing. In conclusion, we have established that pharmacological stress test does not reproduce the dynamic changes observed in exercise stress. Although there is promising evidence suggesting that ¹H NMR based metabolomics could predict stress test results, further studies with much larger populations will be required in order to obtain a definitive answer.

Cardioprotective effect of succinate dehydrogenase inhibition in rat hearts and human myocardium with and without diabetes mellitus

Ischemia reperfusion (IR) injury may be attenuated through succinate dehydrogenase (SDH) inhibition by dimethyl malonate (DiMAL). Whether SDH inhibition yields protection in diabetic individuals and translates into human cardiac tissue remain unknown. In isolated perfused hearts from 24 weeks old male Zucker diabetic fatty (ZDF) and age matched non-diabetic control rats and atrial trabeculae from patients with and without diabetes, we compared infarct size, contractile force recovery and mitochondrial function. The cardioprotective effect of a 10 minutes DiMAL administration prior to global ischemia and ischemic preconditioning (IPC) was evaluated. In non-diabetic hearts exposed to IR, DiMAL 0.1 mM reduced infarct size compared to IR (55 ± 7% vs. 69 ± 6%, p < 0.05). Mitochondrial respiration was reduced by DiMAL 0.6 mM compared to sham and DiMAL 0.1 mM (p < 0.05). In diabetic hearts an increased concentration of DiMAL (0.6 mM) was required for protection compared to IR (64 ± 13% vs. 79 ± 8%, p < 0.05). Mitochondrial function remained unchanged. In trabeculae from humans without diabetes, IPC and DiMAL improved contractile force recovery compared to IR (43 ± 12% and 43 ± 13% vs. 23 ± 13%, p < 0.05) but in patients with diabetes only IPC provided protection compared to IR (51 ± 15% vs. 21 ± 8%, p < 0.05). Neither IPC nor DiMAL modulated mitochondrial respiration in patients. Cardioprotection by SDH inhibition is possible in human tissue, but depends on diabetes status. The narrow therapeutic range and discrepancy in respiration between experimental and human studies may limit clinical translation.

Tryptophane-kynurenine pathway in the remote ischemic conditioning mechanism

The actual protective mechanisms underlying cardioprotection with remote ischemic conditioning (RIC) remain unclear. Recent data suggest that RIC induces kynurenine (KYN) and kynurenic acid synthesis, two metabolites derived from tryptophan (TRP), yet a causal relation between TRP pathway and RIC remains to be established. We sought to study the impact of RIC on the levels of TRP and its main metabolites within tissues, and to assess whether blocking kynurenine (KYN) synthesis from TRP would inhibit RIC-induced cardioprotection. In rats exposed to 40-min coronary occlusion and 2-h reperfusion, infarct size was significantly smaller in RIC-treated animals (35.7 ± 3.0% vs. 46.5 ± 2.2%, p = 0.01). This protection was lost in rats that received 1-methyl-tryptophan (1-MT) pretreatment, an inhibitor of KYN synthesis from TRP (infarct size = 46.2 ± 5.0%). Levels of TRP and nine compounds spanning its metabolism through the serotonin and KYN pathways were measured by reversed-phase liquid chromatography-tandem mass spectrometry in the liver, heart, and limb skeletal muscle, either exposed or not to RIC. In the liver, RIC induced a significant increase in xanthurenic acid, nicotinic acid, and TRP. Likewise, RIC increased NAD-dependent deacetylase sirtuin activity in the liver. Pretreatment with 1-MT suppressed the RIC-induced increases in NAD-dependent deacetylase sirtuin activity. Altogether, these findings indicate that RIC mechanism is dependent on TRP-KYN pathway activation.

Glycine Protects Muscle Cells From Wasting in vitro via mTORC1 Signaling

Glycine supplementation can protect skeletal muscles of mice from cancer-induced wasting, but the mechanisms underlying this protection are not well-understood. The aim of this study was to determine whether exogenous glycine directly protects skeletal muscle cells from wasting. C2C12 muscle cells were exposed to non-inflammatory catabolic stimuli via two models: serum withdrawal (SF) for 48 h; or incubation in HEPES buffered saline (HBS) for up to 5 h. Cells were supplemented with glycine or equimolar concentrations of L-alanine. SF- and HBS-treated myotubes (with or without L-alanine) were ~20% and ~30% smaller than control myotubes. Glycine-treated myotubes were up to 20% larger (P < 0.01) compared to cells treated with L-alanine in both models of muscle cell atrophy. The mTORC1 inhibitor rapamycin prevented the glycine-stimulated protection of myotube diameter, and glycine-stimulated S6 phosphorylation, suggesting that mTORC1 signaling may be necessary for glycine's protective effects in vitro. Increasing glycine availability may be beneficial for muscle wasting conditions associated with inadequate nutrient intake.

A Review of Humoral Factors in Remote Preconditioning of the Heart

A humoral mechanism of cardioprotection by remote ischemic preconditioning (RIP) has been clearly demonstrated in various models of ischemia-reperfusion including upper and lower extremities, liver, and the mesenteric and renal arteries. A wide range of humoral factors for RIP have been proposed including hydrophobic peptides, opioid peptides, adenosine, prostanoids, endovanilloids, endocannabinoids, calcitonin gene-related peptide, leukotrienes, noradrenaline, adrenomedullin, erythropoietin, apolipoprotein, A-I glucagon-like peptide-1, interleukin 10, stromal cell-derived factor 1, and microRNAs. Virtually, all of the components of ischemic preconditioning's signaling pathway such as nitric oxide synthase, protein kinase C, redox signaling, PI3-kinase/Akt, glycogen synthase kinase β, ERK1/2, mitoK_ATP channels, Connexin 43, and STAT were all found to play a role. The signaling pattern also depends on which remote vascular bed was subjected to ischemia and on the time between applying the rip and myocardial ischemia occurs. Because there is convincing evidence for many seemingly diverse humoral components in RIP, the most likely explanation is that the overall mechanism is complex like that seen in ischemic preconditioning where multiple components are both in series and in parallel and interact with each other. Inhibition of any single component in the right circumstance may block the resulting protective effect, and selectively activating that component may trigger the protection. Identifying the humoral factors responsible for RIP might be useful in developing drugs that confer RIP's protection in a more comfortable and reliable manner.

Circulating mediators of remote ischemic preconditioning: search for the missing link between non-lethal ischemia and cardioprotection

Acute myocardial infarction (AMI) is one of the leading causes of mortality and morbidity worldwide. There has been an extensive search for cardioprotective therapies to reduce myocardial ischemia-reperfusion (I/R) injury. Remote ischemic preconditioning (RIPC) is a phenomenon that relies on the body's endogenous protective modalities against I/R injury. In RIPC, non-lethal brief I/R of one organ or tissue confers protection against subsequent lethal I/R injury in an organ remote to the briefly ischemic organ or tissue. Initially it was believed to be limited to direct myocardial protection, however it soon became apparent that RIPC applied to other organs such as kidney, liver, intestine, skeletal muscle can reduce myocardial infarct size. Intriguing discoveries have been made in extending the concept of RIPC to other organs than the heart. Over the years, the underlying mechanisms of RIPC have been widely sought and discussed. The involvement of blood-borne factors as mediators of RIPC has been suggested by a number of research groups. The main purpose of this review article is to summarize the possible circulating mediators of RIPC, and recent studies to establish the clinical efficacy of these mediators in cardioprotection from lethal I/R injury.

Remote ischemic conditioning protects against endothelial ischemia-reperfusion injury via a glucagon-like peptide-1 receptor-mediated mechanism in humans

BACKGROUND

Remote ischemic conditioning (RIC), i.e. short cycles of ischemia and reperfusion in remote tissue, is a novel approach to protect against myocardial ischemia-reperfusion injury in ST-elevation myocardial infarction. The nature of the factors transmitting the protective effect of RIC remains unknown, and both neuronal and hormonal mechanisms appear to be involved. A recent study indicated involvement of glucagon-like peptide-1 (GLP-1) regulated by the vagal nerve in RIC in rats. In the present study we aimed to investigate whether the protective effect of RIC is mediated by a GLP-1 receptor-dependent mechanism in humans.

METHODS

Endothelial function was determined from flow-mediated dilatation (FMD) of the brachial artery before and after 20 min of forearm ischemia and 20 min of reperfusion in twelve healthy subjects on three occasions: (A) ischemia-reperfusion without intervention, (B) ischemia-reperfusion + RIC and (C) iv administration of the GLP-1 receptor antagonist exendin(9-39) + ischemia-reperfusion + RIC.

RESULTS

Ischemia-reperfusion reduced FMD from 4.7 ± 0.8% at baseline to 1.5 ± 0.4% (p < 0.01). RIC protected from the impairment in FMD induced by ischemia-reperfusion (4.6 ± 1.1% at baseline vs. 5.0 ± 1.1% following ischemia-reperfusion). Exendin(9-39) abolished the protection induced by RIC (FMD 4.9 ± 0.9% at baseline vs. 1.4 ± 1.3% following ischemia-reperfusion; p < 0.01) but did not affect basal FMD. Plasma GLP-1 levels did not change significantly between examinations.

CONCLUSION

The present study is the first to suggest that RIC protects against endothelial ischemia-reperfusion injury via a GLP-1 receptor-mediated mechanism in humans.

Neural mechanisms in remote ischaemic conditioning in the heart and brain: mechanistic and translational aspects

Remote ischaemic conditioning (RIC) is a promising method of cardioprotection, with numerous clinical studies having demonstrated its ability to reduce myocardial infarct size and improve prognosis. On the other hand, there are several clinical trials, in particular those conducted in the setting of elective cardiac surgery, that have failed to show any benefit of RIC. These contradictory data indicate that there is insufficient understanding of the mechanisms underlying RIC. RIC is now known to signal indiscriminately, protecting not only the heart, but also other organs. In particular, experimental studies have demonstrated that it is able to reduce infarct size in an acute ischaemic stroke model. However, the mechanisms underlying RIC-induced neuroprotection are even less well understood than for cardioprotection. The existence of bidirectional feedback interactions between the heart and the brain suggests that the mechanisms of RIC-induced neuroprotection and cardioprotection should be studied as a whole. This review, therefore, addresses the topic of the neural component of the RIC mechanism.

Potential humoral mediators of remote ischemic preconditioning in patients undergoing surgical coronary revascularization

Remote ischemic preconditioning (RIPC) by repeated brief cycles of limb ischemia/reperfusion may reduce myocardial ischemia/reperfusion injury and improve patients‘ prognosis after elective coronary artery bypass graft (CABG) surgery. The signal transducer and activator of transcription (STAT)5 activation in left ventricular myocardium is associated with RIPC´s cardioprotection. Cytokines and growth hormones typically activate STATs and could therefore act as humoral transfer factors of RIPC´s cardioprotection. We here determined arterial plasma concentrations of 25 different cytokines, growth hormones, and other factors which have previously been associated with cardioprotection, before (baseline)/after RIPC or placebo (n = 23/23), respectively, and before/after ischemic cardioplegic arrest in CABG patients. RIPC-induced protection was reflected by a 35% reduction of serum troponin I release. With the exception of interleukin-1α, none of the humoral factors changed in their concentrations after RIPC or placebo, respectively. Interleukin-1α, when normalized to baseline, increased after RIPC (280 ± 56%) but not with placebo (97 ± 15%). The interleukin-1α concentration remained increased until after ischemic cardioplegic arrest and was also higher than with placebo in absolute concentrations (25 ± 6 versus 16 ± 3 pg/mL). Only interleukin-1α possibly fulfills the criteria which would be expected from a substance to be released in response to RIPC and to protect the myocardium during ischemic cardioplegic arrest.