[D-Ala2,D-Leu5]-enkephalin (DADLE) and morphine-induced postconditioning by inhibition of mitochondrial permeability transition pore, in human myocardium

[D-Ala2, D-Leu5]-enkephalin (DADLE) provides protection against myocardial ischemia reperfusion injury by inhibiting Wnt/β-Catenin pathway

BACKGROUND

Acute myocardial infarction is one of the leading causes of death worldwide. Myocardial ischemia reperfusion (MI/R) injury occurs immediately after the coronary reperfusion and aggravates myocardial ischemia. Whether the Wnt/β-Catenin pathway is involved in the protection against MI/R injury by DADLE has not been evaluated. Therefore, the present study aimed to investigate the protective effect of DADLE against MI/R injury in a mouse model and to further explore the association between DADLE and the Wnt/β-Catenin pathway.

METHODS

Forty-four mice were randomly allocated to four groups: Group Control (PBS Control), Group D 0.25 (DADLE 0.25 mg/kg), Group D 0.5 (DADLE 0.5 mg/kg), and Group Sham. In the control and DADLE groups, myocardial ischemia injury was induced by occluding the left anterior descending coronary artery (LAD) for 45 min. PBS and DADLE were administrated, respectively, 5 min before reperfusion. The sham group did not go through LAD occlusion. 24 h after reperfusion, functions of the left ventricle were assessed through echocardiography. Myocardial injury was evaluated using TTC double-staining and HE staining. Levels of myocardial enzymes, including CK-MB and LDH, in the serum were determined using ELISA kits. Expression of caspase-3, TCF4, Wnt3a, and β-Catenin was evaluated using the Western blot assay.

RESULTS

The infarct area was significantly smaller in the DADLE groups than in the control group (P < 0.01). The histopathology score and serum levels of myocardial enzymes were significantly lower in the DADLE groups than in the control group (P < 0.01). DADLE significantly improved functions of the left ventricle (P < 0.01), decreased expression of caspase-3 (P < 0.01), TCF4 (P < 0.01), Wnt3a (P < 0.05), and β-Catenin (P < 0.01) compared with PBS.

CONCLUSIONS

The present study showed that DADLE protected the myocardium from MI/R through suppressing the expression of caspase-3, TCF4, Wnt3a, and β-Catenin and consequently improving functions of the left ventricle in I/R model mice. The TCF4/Wnt/β-Catenin signaling pathway might become a therapeutic target for MI/R treatment.

Effects of delta-opioid receptor agonist pretreatment on the cardiotoxicity of bupivacaine in rats

Background

Delta-opioid receptor is widely expressed in human and rodent hearts, and has been proved to protect cardiomyocytes against ischemia/reperfusion and heart failure. The antagonist of delta-opioid receptor could block the rescue effect of lipid emulsion against local anesthetic cardiotoxicity. However, no evidence is available for the direct effect of delta-opioid-receptor agonists on the cardiotoxicity of local anesthetics.

Methods

Anesthetized Sprague Dawley rats were divided into five groups. Group NS received 2 ml·kg⁻¹·min⁻¹ normal saline, group LE received 2 ml·kg⁻¹·min⁻¹ 30% lipid emulsion and group BW received 0.1, 1.0, or 5.0 mg/kg BW373U86, a delta-opioid-receptor agonist, for 5 min. Then 0.5% bupivacaine was infused intravenously at a rate of 3.0 mg·kg⁻¹·min⁻¹ until asystole. The time of arrhythmia, 50% mean arterial pressure-, 50% heart rate-reduction and asystole were recorded, and the dose of bupivacaine at each time point was calculated.

Results

All three different doses of BW373U86 did not affect the arrhythmia, 50% mean arterial pressure-reduction, 50% heart rate-reduction and asystole dose of bupivacaine compared with group NS. 30% LE significantly increased the bupivacaine threshold of 50% mean arterial pressure-reduction (17.9 [15.4–20.7] versus 7.2 [5.9–8.7], p = 0.018), 50% heart rate-reduction (18.7 ± 4.2 versus 8.8 ± 1.7, p < 0.001) and asystole (26.5 [21.0–29.1] versus 11.3 [10.7–13.4], p = 0.008) compared with group NS. There was no difference between group LE and group NS in the arrhythmia dose of bupivacaine (9.9 [8.9–11.7] versus 5.6 [4.5–7.0], p = 0.060).

Conclusions

Our data show that BW373U86 does not affect the cardiotoxicity of bupivacaine compared with NS control in rats. 30% LE pretreatment protects the myocardium against bupivacaine-induced cardiotoxicity.

[D-Ala2, D-Leu5] Enkephalin Inhibits TLR4/NF-κB Signaling Pathway and Protects Rat Brains against Focal Ischemia-Reperfusion Injury

Background

Cerebral ischemia-reperfusion (I/R) injury is the main cause of acute brain injury, which is a life-threatening disease due to the lack of effective treatments. [D-Ala², D-Leu⁵] enkephalin (DADLE) is a synthetic delta-opioid receptor agonist that is reported to confer neuroprotective effect; however, the underlying mechanism is still being explored. The purpose of the present study is to determine whether DADLE administrated intracerebroventricularly could attenuate the cerebral I/R injury, to determine if this is through inhibiting the toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signaling pathway and therefore inhibiting neuroinflammation in an ischemic stroke model.

Methods

Rats were subjected to 120 minutes of ischemia by transient middle cerebral artery occlusion (MCAO). At 45 minutes after ischemia, DADLE or control vehicle (artificial cerebrospinal fluid, ACSF) was given to the rats intracerebroventricularly. Neurological deficit, cerebral infarct volume, and histopathological changes were assessed at 24 hours after reperfusion. Brain inflammation was assessed by measuring tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the ischemic penumbra by ELISA. The expression of TLR4 was determined by immunohistochemistry staining and western blotting. The expression of NF-κB was investigated by western blotting.

Results

Compared with the vehicle-treatment (ACSF), DADEL improved neurological deficit (9.6 ± 2.1 versus 13.8 ± 1.9), reduced cerebral infarct volume (18.74 ± 3.30% versus 10.57 ± 2.50%), and increased the number of normal neurons (29.72 ± 8.53% versus 51.37 ± 9.18%) after cerebral I/R injury in rats (all P < 0.05). Expressions of inflammatory molecules including TNF-α and IL-6 were highly expressed in the vehicle-treated rats, whereas treatment with DADLE downregulated these expressions (P < 0.05). Additionally, cerebral I/R injury significantly increased the TLR4 and NF-κB expression in vehicle-control group, which was markedly inhibited by DADLE (P < 0.05).

Conclusions

DADLE, administrated intracerebroventricularly at 45 minutes after cerebral ischemia, significantly ameliorated I/R-induced brain damage in rats. This kind of neuroprotective effect appears to be related to the downregulation of TLR4-mediated inflammatory responses.

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.

Effects of D‑Ala2, D‑Leu5‑Enkephalin pre‑ and post‑conditioning in a rabbit model of spinal cord ischemia and reperfusion injury

It has recently been revealed that during the aorta-clamped period, D-Ala², D-Leu⁵-Enkephalin (DADLE) infusion can protect the spinal cord against ischemia and reperfusion (I/R) injury. However, the protective effects of DADLE administration prior to ischemia or at the time of early reperfusion have not yet been investigated. Drug pre- or post-conditioning can serve as a more valuable clinical strategy. Therefore, the present study was designed to investigate the neuroprotective effect of DADLE infusion at different time intervals in order to determine the optimum time point for ischemic spinal cord protection. A total of 40 New Zealand white rabbits were randomly divided into 5 groups: Sham-operated (Sham), normal saline pre-conditioning (NS), DADLE per-conditioning (D_per), DADLE pre-conditioning (D_pre) and DADLE post-conditioning (D_post). All animals were subjected to spinal cord ischemia for 30 min followed by 48 h reperfusion. Hind limb motor functions were assessed according to the Tarlov criterion when the animals regained consciousness, 6, 24 and 48 h after reperfusion. Histological analysis and the number of viable α-motor neurons were also used to assess the extent of spinal cord injury. Compared with the NS group, the Tarlov scores and the number of normal neurons were significantly higher in the D_per group (P<0.05), which were consistent with the results of a previous study. In addition, the paraplegia rate and loss of normal motor neurons were lower in the DADLE per- and post-conditioning groups compared with the DADLE pre-conditioning; however, these were not statistically significant. DADLE 0.05 mg/kg administration at three time points all mitigated normal motor neuron injury in the anterior horn and decreased the paraplegia rates in rabbits. The therapeutic benefits appeared best in the post-conditioning group with DADLE, and worst in the pre-conditioning group.

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.

Sufentanil attenuates impairment of the endothelium-dependent vasodilation induced by hypoxia-reoxygenation in the rat coronary artery

Sufentanil has been used broadly in cardiac surgery, but the mechanisms by which it modulates coronary vascular tone after ischemia-reperfusion injury are largely unknown. Effects of sufentanil on coronary tone and on the relaxation of rat coronary arteries (CAs) in response to endothelium-dependent (acetylcholine) and endothelium-independent (sodium nitroprusside) relaxing agents in the presence of hypoxia-reoxygenation (H/R) was studied in an in vitro organ chamber setup. Sufentanil (10^-7-10^-4 mol/L) relaxed rat CA rings in endothelium-dependent and endothelium-independent manners. In endothelium-intact rings, preincubation of H/R-treated CAs with sufentanil (10^-5 mol/L) significantly increased the acetylcholine response, but did not augment sodium nitroprusside-induced relaxation. Sufentanil-mediated potentiation of acetylcholine-induced relaxation was not affected by a nitric oxide synthase inhibitor or by intermediate- or small-conductance Ca²⁺-activated K⁺ channel blockers. However, potentiation was abolished by iberiotoxin (100 nmol/L), a selective inhibitor of large-conductance Ca²⁺-activated K⁺ channels, as well as Rp-cAMPS (30 μmol/L), a cyclic AMP-dependent protein kinase (PKA) inhibitor. Sufentanil induced endothelium-dependent and endothelium-independent relaxation and attenuated H/R-induced impairment of endothelium-dependent vasodilation in the rat CAs. The potentiating effect of sufentanil may involve activation of large-conductance Ca²⁺-activated K⁺ channels via cAMP-dependent mechanisms.

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.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.