Eribis peptide 94 reduces infarct size in rat hearts via activation of centrally located μ opioid receptors

Intra-operative anesthetic induced myocardial protection during cardiothoracic surgery: a literature review

Background and Objective

Myocardial protection involves limiting the metabolic activity and oxygen consumption of the heart, thus enabling surgery to proceed with minimal blood loss while reducing the level of ischemic injury. It was this concept that allowed for the development of the open-heart surgical technique. We know myocardial ischemia and reperfusion injury are both detrimental, thus developing strategies to mitigate this can help reduce peri-operative morbidity and mortality. In this review, we will mainly be addressing the anesthetic considerations for myocardial protection, along with discussing potential future research which can help expand the field.

Methods

We searched the PubMed database for relevant studies dating from 2004-2022. In total, 18 studies were deemed suitable for this literature review.

Key Content and Findings

Studies have demonstrated cardioprotective effects with use of the volatile agents and propofol, mainly with respect to lower levels of inflammatory markers such as creatine kinase (CK)-MB and troponin I (TnI)/troponin T (TnT). The data is lacking regarding protective effects of dexmedetomidine and lidocaine, hence we cannot recommend either agent at present.

Conclusions

Myocardial protection with respect to the anesthetic agents have been extensively studied over the past two decades, some routinely used drugs such as the volatile agents, propofol and opiates have demonstrated a cardioprotective role. The ideal dosing regimen and duration are areas of research that can be studied further. The data for the other anesthetic adjuncts such as lidocaine, dexmedetomidine along with use of regional anesthesia is still equivocal. Alongside advances in anesthesia, we believe surgical research looking into optimal cardioplegia solutions will also help improve myocardial protection in the future.

Effects of the Delta Opioid Receptor Agonist DADLE in a Novel Hypoxia-Reoxygenation Model on Human and Rat-Engineered Heart Tissue: A Pilot Study

Intermittent hypoxia and various pharmacological compounds protect the heart from ischemia reperfusion injury in experimental approaches, but the translation into clinical trials has largely failed. One reason may lie in species differences and the lack of suitable human in vitro models to test for ischemia/reperfusion. We aimed to develop a novel hypoxia-reoxygenation model based on three-dimensional, spontaneously beating and work performing engineered heart tissue (EHT) from rat and human cardiomyocytes. Contractile force, the most important cardiac performance parameter, served as an integrated outcome measure. EHTs from neonatal rat cardiomyocytes were subjected to 90 min of hypoxia which led to cardiomyocyte apoptosis as revealed by caspase 3-staining, increased troponin I release (time control vs. 24 h after hypoxia: cTnI 2.7 vs. 6.3 ng/mL, ** p = 0.002) and decreased contractile force (64 ± 6% of baseline) in the long-term follow-up. The detrimental effects were attenuated by preceding the long-term hypoxia with three cycles of 10 min hypoxia (i.e., hypoxic preconditioning). Similarly, [d-Ala2, d-Leu5]-enkephalin (DADLE) reduced the effect of hypoxia on force (recovery to 78 ± 5% of baseline with DADLE preconditioning vs. 57 ± 5% without, p = 0.012), apoptosis and cardiomyocyte stress. Human EHTs presented a comparable hypoxia-induced reduction in force (55 ± 5% of baseline), but DADLE failed to precondition them, likely due to the absence of δ-opioid receptors. In summary, this hypoxia-reoxygenation in vitro model displays cellular damage and the decline of contractile function after hypoxia allows the investigation of preconditioning strategies and will therefore help us to understand the discrepancy between successful conditioning in vitro experiments and its failure in clinical trials.

Impact of Morphine Treatment on Infarct Size and Reperfusion Injury in Acute Reperfused ST-Elevation Myocardial Infarction

Current evidence regarding the effect of intravenous morphine administration on reperfusion injury and/or cardioprotection in patients with myocardial infarction is conflicting. The aim of this study was to evaluate the impact of morphine administration, on infarct size and reperfusion injury assessed by cardiac magnetic resonance imaging (CMR) in a large multicenter ST-elevation myocardial infarction (STEMI) population. In total, 734 STEMI patients reperfused by primary percutaneous coronary intervention <12 h after symptom onset underwent CMR imaging at eight centers for assessment of myocardial damage. Intravenous morphine administration was recorded in all patients. CMR was completed within one week after infarction using a standardized protocol. The clinical endpoint of the study was the occurrence of major adverse cardiac events (MACE) within 12 months after infarction. Intravenous morphine was administered in 61.8% (n = 454) of all patients. There were no differences in infarct size (17%LV, interquartile range [IQR] 8–25%LV versus 16%LV, IQR 8–26%LV, p = 0.67) and microvascular obstruction (p = 0.92) in patients with versus without morphine administration. In the subgroup of patients with early reperfusion within 120 min and reduced flow of the infarcted vessel (TIMI-flow ≤2 before PCI) morphine administration resulted in significantly smaller infarcts (12%LV, IQR 12–19 versus 19%LV, IQR 10–29, p = 0.035) and reduced microvascular obstruction (p = 0.003). Morphine administration had no effect on hard clinical endpoints (log-rank test p = 0.74) and was not an independent predictor of clinical outcome in Cox regression analysis. In our large multicenter CMR study, morphine administration did not have a negative effect on myocardial damage or clinical prognosis in acute reperfused STEMI. In patients, presenting early ( ≤120 min) morphine may have a cardioprotective effect as reflected by smaller infarcts; but this finding has to be assessed in further well-designed clinical studies

Effect of Chronic Continuous Normobaric Hypoxia on Functional State of Cardiac Mitochondria and Tolerance of Isolated Rat Heart to Ischemia and Reperfusion: Role of µ and δ2 Opioid Receptors

Chronic continuous normobaric hypoxia (CNH) increases cardiac tolerance to ischemia/reperfusion injury in vivo and this effect is mediated via µ and δ2 opioid receptors (ORs) activation. CNH has also been shown to be cardioprotective in isolated rat heart. In this study, we hypothesize that this cardioprotective effect of CNH is mediated by activation of µ and δ2 ORs and preservation of mitochondrial function. Hearts from rats adapted to CNH (12 % oxygen) for 3 weeks were extracted, perfused in the Langendorff mode and subjected to 45 min of global ischemia and 30 min of reperfusion. Intervention groups were pretreated for 10 min with antagonists for different OR types: naloxone (300 nmol/l), the selective δ OR antagonist TIPP(ψ) (30 nmol/l), the selective δ1 OR antagonist BNTX (1 nmol/l), the selective δ2 OR antagonist naltriben (1 nmol/l), the selective peptide μ OR antagonist CTAP (100 nmol/l) and the selective κ OR antagonist nor-binaltorphimine (3 nmol/l). Creatine kinase activity in coronary effluent and cardiac contractile function were monitored to assess cardiac injury and functional impairment. Additionally, cardiac tissue was collected to measure ATP and to isolate mitochondria to measure respiration rate and calcium retention capacity. Adaptation to CNH decreased myocardial creatine kinase release during reperfusion and improved the postischemic recovery of contractile function. Additionally, CNH improved mitochondrial state 3 and uncoupled respiration rates, ADP/O, mitochondrial transmembrane potential and calcium retention capacity and myocardial ATP level during reperfusion compared to the normoxic group. These protective effects were completely abolished by naloxone, TIPP(ψ), naltriben, CTAP but not BNTX or nor-binaltorphimine. These results suggest that cardioprotection associated with adaptation to CNH is mediated by µ and δ2 opioid receptors activation and preservation of mitochondrial function.

Participation of opioid receptors in the cytoprotective effect of chronic normobaric hypoxia

We studied the role of the delta, micro, and kappa opioid receptor (OR) subtypes in the cardioprotective effect of chronic continuous normobaric hypoxia (CNH) in the model of acuteanoxia-reoxygenation of isolated cardiomyocytes. Adaptation of rats to CNH was performed by their exposure to atmosphere containing 12% of O(2) for 21 days. Anoxia-reoxygenation of cardiomyocytes isolated from normoxiccontrol rats caused the death of 51 % of cells and lactate dehydrogenase (LDH) release. Adaptation of rats to CNH resulted in the anoxia/reoxygenation-induced cardiomyocyte death of only 38 %, and reduced the LDH release by 25 %. Pre-incubation of the cells with either the non-selective OR (opioid receptor) blocker naloxone (300 nM/l), the delta OR antagonist TIPP(psi) (30 nM/l), the selective delta(2) OR antagonist naltriben (1 nM/l) or the micro OR antagonist CTAP (100 nM/l) for 25 minutes before anoxia abolished the reduction of cell death and LDH release afforded by CNH. The antagonist of delta(1) OR BNTX (1 nM/l) or the kappa OR antagonist nor-binaltorphimine (3 nM/l) did not influence the cytoprotective effects of CNH. Taken together, the cytoprotective effect of CNH is associated with the activation of the delta(2) and micro OR localized on cardiomyocytes.

Prospects for Creation of Cardioprotective and Antiarrhythmic Drugs Based on Opioid Receptor Agonists

It has now been demonstrated that the μ, δ1 , δ2 , and κ1 opioid receptor (OR) agonists represent the most promising group of opioids for the creation of drugs enhancing cardiac tolerance to the detrimental effects of ischemia/reperfusion (I/R). Opioids are able to prevent necrosis and apoptosis of cardiomyocytes during I/R and improve cardiac contractility in the reperfusion period. The OR agonists exert an infarct-reducing effect with prophylactic administration and prevent reperfusion-induced cardiomyocyte death when ischemic injury of heart has already occurred; that is, opioids can mimic preconditioning and postconditioning phenomena. Furthermore, opioids are also effective in preventing ischemia-induced arrhythmias.

Role of Opioid Receptors Signaling in Remote Electrostimulation--Induced Protection against Ischemia/Reperfusion Injury in Rat Hearts

Aims

Our previous studies demonstrated that remote electro-stimulation (RES) increased myocardial GSK3 phosphorylation and attenuated ischemia/ reperfusion (I/R) injury in rat hearts. However, the role of various opioid receptors (OR) subtypes in preconditioned RES-induced myocardial protection remains unknown. We investigated the role of OR subtype signaling in RES-induced cardioprotection against I/R injury of the rat heart.

Methods & Results

Male Spraque-Dawley rats were used. RES was performed on median nerves area with/without pretreatment with various receptors antagonists such as opioid receptor (OR) subtype receptors (KOR, DOR, and MOR). The expressions of Akt, GSK3, and PKCε expression were analyzed by Western blotting. When RES was preconditioned before the I/R model, the rat's hemodynamic index, infarction size, mortality and serum CK-MB were evaluated. Our results showed that Akt, GSK3 and PKCε expression levels were significantly increased in the RES group compared to the sham group, which were blocked by pretreatment with specific antagonists targeting KOR and DOR, but not MOR subtype. Using the I/R model, the duration of arrhythmia and infarct size were both significantly attenuated in RES group. The mortality rates of the sham RES group, the RES group, RES group + KOR antagonist, RES group + DOR/MOR antagonists (KOR left), RES group + DOR antagonist, and RES group + KOR/MOR antagonists (DOR left) were 50%, 20%, 67%, 13%, 50% and 55%, respectively.

Conclusion

The mechanism of RES-induced myocardial protection against I/R injury seems to involve multiple target pathways such as Akt, KOR and/or DOR signaling.

Opioid receptors and cardioprotection - 'opioidergic conditioning' of the heart

Ischaemic heart disease (IHD) remains a major cause of morbidity/mortality globally, firmly established in Westernized or 'developed' countries and rising in prevalence in developing nations. Thus, cardioprotective therapies to limit myocardial damage with associated ischaemia-reperfusion (I-R), during infarction or surgical ischaemia, is a very important, although still elusive, clinical goal. The opioid receptor system, encompassing the δ (vas deferens), κ (ketocyclazocine) and μ (morphine) opioid receptors and their endogenous opioid ligands (endorphins, dynorphins, enkephalins), appears as a logical candidate for such exploitation. This regulatory system may orchestrate organism and organ responses to stress, induces mammalian hibernation and associated metabolic protection, triggers powerful adaptive stress resistance in response to ischaemia/hypoxia (preconditioning), and mediates cardiac benefit stemming from physical activity. In addition to direct myocardial actions, central opioid receptor signalling may also enhance the ability of the heart to withstand I-R injury. The δ- and κ-opioid receptors are strongly implicated in cardioprotection across models and species (including anti-infarct and anti-arrhythmic actions), with mixed evidence for μ opioid receptor-dependent protection in animal and human tissues. A small number of clinical trials have provided evidence of cardiac benefit from morphine or remifentanil in cardiopulmonary bypass or coronary angioplasty patients, although further trials of subtype-specific opioid receptor agonists are needed. The precise roles and utility of this GPCR family in healthy and diseased human myocardium, and in mediating central and peripheral survival responses, warrant further investigation, as do the putative negative influences of ageing, IHD co-morbidities, and relevant drugs on opioid receptor signalling and protective responses.

Opioid receptors and cardioprotection - 'opioidergic conditioning' of the heart

Ischaemic heart disease (IHD) remains a major cause of morbidity/mortality globally, firmly established in Westernized or 'developed' countries and rising in prevalence in developing nations. Thus, cardioprotective therapies to limit myocardial damage with associated ischaemia-reperfusion (I-R), during infarction or surgical ischaemia, is a very important, although still elusive, clinical goal. The opioid receptor system, encompassing the δ (vas deferens), κ (ketocyclazocine) and μ (morphine) opioid receptors and their endogenous opioid ligands (endorphins, dynorphins, enkephalins), appears as a logical candidate for such exploitation. This regulatory system may orchestrate organism and organ responses to stress, induces mammalian hibernation and associated metabolic protection, triggers powerful adaptive stress resistance in response to ischaemia/hypoxia (preconditioning), and mediates cardiac benefit stemming from physical activity. In addition to direct myocardial actions, central opioid receptor signalling may also enhance the ability of the heart to withstand I-R injury. The δ- and κ-opioid receptors are strongly implicated in cardioprotection across models and species (including anti-infarct and anti-arrhythmic actions), with mixed evidence for μ opioid receptor-dependent protection in animal and human tissues. A small number of clinical trials have provided evidence of cardiac benefit from morphine or remifentanil in cardiopulmonary bypass or coronary angioplasty patients, although further trials of subtype-specific opioid receptor agonists are needed. The precise roles and utility of this GPCR family in healthy and diseased human myocardium, and in mediating central and peripheral survival responses, warrant further investigation, as do the putative negative influences of ageing, IHD co-morbidities, and relevant drugs on opioid receptor signalling and protective responses.

Opioid-induced cardioprotection

Ischemic heart disease and myocardial infarction continue to be leading causes of cardiovascular morbidity and mortality. Activation of opioid, adenosine, bradykinin, adrenergic and other G-protein coupled receptors has been found to be cardioprotective. κ- and/or δ-opioid receptor activation is involved in direct myocardial protection, while the role of µ-opioid receptors seems less clear. In addition, differential affinities to the three opioid-receptor subtypes by various agonists and cross-talk among different G-protein coupled receptors render conclusions regarding opioid-mediated cardioprotection challenging. The present review will focus on the protective effects of endogenously released opioid peptides as well as exogenously administered opioids such as morphine, fentanyl, remifentanil, butorphanol, and methadone against myocardial ischemia/reperfusion injury. Receptor heterodimerization and cross-talk as well as interactions with other cardioprotective techniques will be discussed. Implications for opioid-induced cardioprotection in humans and for future drug development to improve myocardial salvage will be provided.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Role of endogenous opioid peptides in the infarct size-limiting effect of adaptation to chronic continuous hypoxia

AIMS

The objective of this study was to examine the involvement of endogenous opioid peptides and opioid receptor (OR) subtypes in the cardioprotective effect of adaptation to chronic hypoxia in rats.

MAIN METHODS

Rats were exposed to continuous normobaric hypoxia (CNH; 12% oxygen) for 3 weeks. Myocardial ischemia was induced by 20-min coronary artery occlusion followed by 3-h reperfusion in anesthetized open-chest animals. Various OR antagonists were administered to rats prior to ischemia. The size of myocardial infarction and the incidence of ischemic ventricular arrhythmias were assessed. Myocardial and plasma concentrations of opioid peptides (met-enkephalin, β-endorphin, and endomorphins) were determined.

KEY FINDINGS

Adaptation to CNH significantly increased myocardial and plasma concentrations of opioids, potentiated their further elevation by ischemia/reperfusion, and reduced myocardial infarct size, but it did not affect the incidence of ischemic arrhythmias. The infarct size-limiting effect of CNH was abolished by OR antagonists naltrexone (non-selective), naloxone methiodide (non-selective peripherally acting), TIPP[ψ] (δ-OR), naltriben (δ2-OR), or CTAP (μ-OR), while BNTX (δ1-OR) and nor-binaltorphimine (κ-OR) had no effect.

SIGNIFICANCE

The results suggest that the infarct size-limiting effect afforded by adaptation to CNH is mediated by activation of peripheral δ2- and μ-ORs by elevated levels of endogenous opioid peptides.

In vivo and in vitro inhibition of human liver cancer progress by downregulation of the μ-opioid receptor and relevant mechanisms

Opiates have long been used as analgesics to relieve pain associated with various medical conditions. μ-opioid receptor (MOR) is the main member of the opioid receptor super-family and the excitation or overexpression of MOR promotes the proliferation of many kinds of tumor cells. It was found in our previous studies that MOR was highly expressed in the tissue and cells of human liver cancer. However, the impact of MOR on the progress of human liver cancer remains unknown. The purpose of this study is to investigate the impact of MOR downregulation on the progress of human liver cancer and the mechanisms involved. RNA interfering or specific inhibitor was administered to downregulate the MOR in human hepato-cellular carcinoma cells and it was found that the proliferation of hepatocellular carcinoma cells was significantly inhibited with the increase of the apoptotic rate, while the cell cycle was blocked in G0/G1 phase and the tumor growth in the mice was retarded. In addition, downregulation of MOR resulted in the increase of phosphorylation of the MKK7 expression and JNK activation. On the contrary, blockade of MKK7 pathway can reverse the antitumor role of MOR. In summary, downregulation of MOR is able to inhibit both in vivo and in vitro human liver cancer progress and it shows potential to be used in cancer therapy.

Cardioprotection from remote preconditioning involves spinal opioid receptor activation

AIMS

Remote preconditioning is a powerful and potentially clinically viable mode of cardioprotection. The mechanisms underlying its transmission process have not been extensively studied. The aim of this study was to test the hypothesis that spinal opioid receptors are involved with signal transmission of remote cardiac preconditioning.

MAIN METHODS

Two established models of remote preconditioning were used, one using intermittent ischaemia of the lower limb (remote ischaemic preconditioning, RIPC) and the other by stimulation of cutaneous pain fibres via an abdominal incision (remote preconditioning of trauma, RPOT). Classic ischaemic preconditioning (IPC) was used as positive control. Selective blockade of spinal opioid receptors was achieved through intrathecal injection of naloxone methiodide, a compound not known to cross the blood-brain barrier.

KEY FINDINGS

The prior introduction of naloxone methiodide abolished the cardioprotective effects of RIPC, RPOT but not IPC, as assessed by infarct size as a percentage of area at risk following 30min of ischaemia and 120min reperfusion. Of the specific receptor antagonists, only that specific for the mu receptor subtype, and not delta or kappa receptor, block the protective response.

SIGNIFICANCE

These results suggest that the central nervous system at the spinal cord level is involved with the relaying of signals between the afferent and efferent arms of remote preconditioning.

Acute and chronic cardioprotection by the enkephalin analogue, Eribis peptide 94, is mediated via activation of nitric oxide synthase and adenosine triphosphate-regulated potassium channels

BACKGROUND/AIMS

Eribis peptide 94 (EP 94) is a new enkephalin derivative which potently binds to the µ- and δ-opioid receptor. In this study, we determined the effects of EP 94 and potential mechanism(s) involved in cardioprotection of the rat heart.

METHODS AND RESULTS

An acute (5 and10 min into ischemia) and a chronic (24 h prior to ischemia) EP 94 administration produced a similar 30-40% reduction in infarct size/area at risk and the effects were blocked by the K(ATP) channel antagonists, HMR 1098 and 5-HD. The cardioprotective effects were blocked by a nonselective nitric oxide synthase (NOS) inhibitor (L-NAME) following acute administration and by a selective iNOS inhibitor (1400W) following chronic administration.

CONCLUSION

These results suggest that EP 94 may have potential for the treatment of ischemic heart disease via a nitric oxide (NO)-K(ATP)-mediated mechanism.