Delta opioid receptors and low temperature myocardial protection

Delta Opioid Receptors and Cardioprotection

The opioid receptor family, with associated endogenous ligands, has numerous roles throughout the body. Moreover, the delta opioid receptor (DORs) has various integrated roles within the physiological systems, including the cardiovascular system. While DORs are important modulators of cardiovascular autonomic balance, they are well-established contributors to cardioprotective mechanisms. Both endogenous and exogenous opioids acting upon DORs have roles in myocardial hibernation and protection against ischaemia-reperfusion (I-R) injury. Downstream signalling mechanisms governing protective responses alternate, depending on the timing and duration of DOR activation. The following review describes models and mechanisms of DOR-mediated cardioprotection, the impact of co-morbidities and challenges for clinical translation.

Combination treatment of hypothermia and mesenchymal stromal cells amplifies neuroprotection in primary rat neurons exposed to hypoxic-ischemic-like injury in vitro: role of the opioid system

This study was designed to reveal the therapeutic regimen and mechanism of action underlying hypothermia treatment in combination with stem cell transplantation for ameliorating neonatal hypoxic-ischemic-like injury. Primary rat neurons were exposed to oxygen-glucose deprivation (OGD), which produced hypoxic-ischemic-like injury in vitro, then incubated at 25°C (severe hypothermia), 34°C (moderate hypothermia), and 37°C (normothermia) with or without subsequent co-culture with mesenchymal stromal cells (MSCs). Combination treatment of moderate hypothermia and MSCs significantly improved cell survival and mitochondrial activity after OGD exposure. The exposure of delta opioid human embryonic kidney cells (HEK293) to moderate hypothermia attenuated OGD-mediated cell alterations, which were much more pronounced in HEK293 cells overexpressing the delta opioid receptor. Further, the addition of delta opioid peptide to 34°C hypothermia and stem cell treatment in primary rat neurons showed synergistic neuroprotective effects against OGD which were significantly more robust than the dual combination of moderate hypothermia and MSCs, and were significantly reduced, but not completely abolished, by the opioid receptor antagonist naltrexone altogether implicating a ligand-receptor mechanism of neuroprotection. Further investigations into non-opioid therapeutic signaling pathways revealed growth factor mediation and anti-apoptotic function accompanying the observed therapeutic benefits. These results support combination therapy of hypothermia and stem cells for hypoxic-ischemic-like injury in vitro, which may have a direct impact on current clinical trials using stand-alone hypothermia or stem cells for treating neonatal encephalopathy.

The myocardial protection of polarizing cardioplegia combined with delta-opioid receptor agonist in swine

BACKGROUND

The purpose of this study was to determine whether polarized arrest using adenosine/lidocaine cold crystalloid cardioplegia in combination with the hibernation inductor δ-opioid receptor agonist pentazocine would give satisfactory myocardial protection rather than using depolarized supranormal potassium cardioplegia, supranormal potassium cardioplegia with pentazocine, or adenosine/lidocaine cardioplegia.

METHODS

Twenty pigs were randomly divided into four groups (n=5 each) to receive the four types of cold crystalloid cardioplegia with an aortic cross-clamp time of 1 hour. Hemodynamic data were continuously measured, as was the left ventricular end-diastolic pressure (LVEDP), left ventricular end-systolic pressure (LVESP), plus or minus derivative of change in diastolic pressure over time (±dp/dt), cardiac output, pulmonary artery pressure, pulmonary capillary wedge pressure, cardiac troponin I, and left ventricular ultrastructure.

RESULTS

Both the adenosine/lidocaine/pentazocine group and the adenosine/lidocaine group got significantly better results than the hyperkalemic and hyperkalemic pentazocine groups in improving hemodynamic values, pulmonary capillary wedge pressure, LVEDP, LVESP, ±dp/dt, cardiac output, cardiac troponin I values, and left ventricular ultrastructure. There were no statistical differences between the adenosine/lidocaine/pentazocine group and the adenosine/lidocaine group at 1 hour after cross-clamp removal; but at 2 hours after cross-clamp removal, the adenosine/lidocaine/pentazocine group stands out (LVEDP 3.3±0.5, LVESP 122.5±18.9, +dp/dt 2.9±0.1, -dp/dt 2.0±0.6, cardiac output 2.6±0.4, and troponin I 4.9±0.5), with significant differences from the adenosine/lidocaine group (LVEDP 5.8±1.0, LVESP 98.5±10.1, +dp/dt 2.5±0.2, -dp/dt 1.0±0.2, cardiac output 2.2±0.2, troponin I 8.2±0.8; p<0.05). The defibrillation rate was largely decreased after the cross-clamp was released in the group containing pentazocine in cardioplegia.

CONCLUSIONS

Adenosine/lidocaine/pentazocine cold crystalloid cardioplegia gave satisfactory cardiac arrest and better myocardial protection than the other three groups, especially with regard to improving prolonged postoperative cardiac function.

Myocardial Protection During Minimally Invasive Cardiac Surgery

Minimally invasive cardiac surgery or beating heart surgery requires very precise observation, explanation, diagnosis, and proper treatment of all changes in the cardiovascular system that occur during the procedure. A major concern in beating heart surgery is the risk of inducing myocardial ischemia without the circulatory support of cardiopulmonary bypass. Protection of myocardium in different stages of the perioperative period is crucial. The following issues should be taken into consideration: preoperative preparation of the myocardium, providing anesthesia techniques that may help to protect the myocardium, and the use of surgical techniques for myocardial protection. Hemodynamic alterations during dislocations of the heart require understanding of these changes and the effects they have on the myocardium. Proper monitoring during the whole procedure, correlation of all findings with the treatment and therapeutic maneuvers, and excellent cooperation between anesthesiologist and surgeon are essential for myocardial protection. New pharmacologic methods, some experimental, should be considered in near future for myocardial protection during beating heart surgery.

Myocardial protection by anesthetic agents against ischemia-reperfusion injury: an update for anesthesiologists

PURPOSE

The aim of this review of the literature was to evaluate the effectiveness of anesthetics in protecting the heart against myocardial ischemia-reperfusion injury.

SOURCE

Articles were obtained from the Medline database (1980-, search terms included heart, myocardium, coronary, ischemia, reperfusion injury, infarction, stunning, halothane, enflurane, desflurane, isoflurane, sevoflurane, opioid, morphine, fentanyl, alfentanil sufentanil, pentazocine, buprenorphine, barbiturate, thiopental, ketamine, propofol, preconditioning, neutrophil adhesion, free radical, antioxidant and calcium).

PRINCIPAL FINDINGS

Protection by volatile anesthetics, morphine and propofol is relatively well investigated. It is generally agreed that these agents reduce the myocardial damage caused by ischemia and reperfusion. Other anesthetics which are often used in clinical practice, such as fentanyl, ketamine, barbiturates and benzodiazepines have been much less studied, and their potential as cardioprotectors is currently unknown. There are some proposed mechanisms for protection by anesthetic agents: ischemic preconditioning-like effect, interference in the neutrophil/platelet-endothelium interaction, blockade of Ca2+ overload to the cytosolic space and antioxidant-like effect. Different anesthetics appear to have different mechanisms by which protection is exerted. Clinical applicability of anesthetic agent-induced protection has yet to be explored.

CONCLUSION

There is increasing evidence of anesthetic agent-induced protection. At present, isoflurane, sevoflurane and morphine appear to be most promising as preconditioning-inducing agents. After the onset of ischemia, propofol could be selected to reduce ischemia-reperfusion injury. Future clinical application depends on the full elucidation of the underlying mechanisms and on clinical outcome trials.

Myocardial protection by ischemic preconditioning and delta-opioid receptor activation in the isolated working rat heart

OBJECTIVE

delta-Opioid receptors are involved in the cardioprotective effect of ischemic preconditioning. This study was designed (1) to assess the protective capacities of ischemic preconditioning and the synthetic delta-opioid receptor agonist D-Ala(2)-D-Leu(5) enkephalin (DADLE) in a functionally oriented experimental model of ischemia and reperfusion and (2) to assess whether the effects of both protective measures are similarly blocked by naloxone, a nonspecific delta-opioid receptor antagonist.

METHODS

Sixty-four isolated working rat hearts were subjected to 45 minutes of hypothermic ischemia at 30 degrees C followed by 25 minutes of normothermic reperfusion. Rats were pretreated with DADLE (1 mg/kg body weight intravenously), naloxone (3 mg/kg body weight intravenously), or a combination thereof within 60 minutes before onset of isolated heart perfusion. During the preischemic perfusion period, 8 hearts per group were preconditioned by one cycle of 5 minutes of normothermic global ischemia and subsequent reperfusion whereas another 8 served as nonpreconditioned controls. The postischemic functional recovery of hearts and their creatine kinase leakage were determined.

RESULTS

Pretreatment with DADLE and ischemic preconditioning improved the postischemic recovery of aortic flow when compared with nonpreconditioning (57.7% +/- 4.0% and 60.8% +/- 4.3% vs 40.0% +/- 4.2% of preischemic baseline value, P <.001). Combined pretreatment with DADLE before ischemic preconditioning afforded additional aortic flow recovery compared with pretreatment with DADLE alone (68.6% +/- 3.3% vs 57.7% +/- 4.0% of preischemic baseline value; P =.038). With combined pretreatment, early postischemic creatine kinase release was lower than control in hearts without pretreatment (0.48 +/- 0.11 vs 0.80 +/- 0.12 IU/5 minutes per heart; P =.001). Naloxone abolished the beneficial functional effects of pretreatment with DADLE and ischemic preconditioning.

CONCLUSIONS

Pharmacologic activation of delta-opioid receptors affords improvement of functional protection in isolated working rat hearts similar to that conferred by classic ischemic preconditioning. The combination of both pretreatments reduces ischemic cellular damage and further adds to postischemic functional recovery. These changes are reversed by naloxone, an observation providing evidence that ischemic preconditioning involves signaling through opioid receptors.

Opioid preconditioning: myocardial function and energy metabolism

BACKGROUND

Opioid receptor agonists are involved in ischemic preconditioning and natural hibernation. The aim of this study was to determine whether pretreatment with D-Ala2-Leu5-enkephalin or morphine confers cardioprotection in large mammalian hearts. We assessed myocardial functional recovery and global energy metabolism after ischemic cold storage.

METHODS

After pretreatment with D-Ala2-Leu5-enkephalin, morphine sulfate, or saline (n = 6 each), swine hearts were excised and stored for 75 minutes at 4 degrees C, then reperfused in a four-chamber isolated working heart apparatus. Serial myocardial biopsies were performed to assess cellular energy metabolism.

RESULTS

Improved systolic (cardiac output, contractility) and diastolic (tau) left ventricular functions were observed in hearts pretreated with D-Ala2-Leu5-enkephalin or morphine. These benefits were not correlated with changes in high-energy phosphate levels. Cardiac enzyme leakage (creatine kinase, troponin-I) was similar among treated and control groups. Lactate efflux increased significantly in controls, but not in opioid-pretreated hearts (p < 0.01) at 75 minutes of reperfusion.

CONCLUSIONS

D-Ala2-Leu5-enkephalin and morphine pretreatments improve postischemic function after cold storage of swine hearts. Postischemic lactate reduction, but not high-energy phosphate levels, may account for the observed cardioprotective effects.