Assessment of nociceptin/orphanin FQ and micro-opioid receptor mRNA in the human right atrium

The activated caveolin-3/μ-opioid receptor complex drives morphine-induced rescue therapy in failing hearts

BACKGROUND AND PURPOSE

Opioid analgesics can alleviate ischaemia/reperfusion (I/R) injury in chronic heart failure. However, the underlying mechanisms and targets remain unknown. Here, we investigate if caveolin-3 (Cav3) interacts with μ opioid receptors and if Cav3-μ receptor interactions play a role in morphine-induced cardioprotection in failing hearts.

EXPERIMENTAL APPROACH

Cav3 and μ receptor proteins in human and rat heart tissue were determined by western blot, immunofluorescence and co-immunoprecipitation. Methyl-β-cyclodextrin (MβCD), a destroyer of caveolae, and AAV-Cav3 shRNA were used to reduce Cav3 expression in failing rat hearts. CTOP, a specific μ antagonist, was administrated before morphine preconditioning in perfused failing heart models of myocardial I/R injury.

KEY RESULTS

Levels of Cav3 and μ receptor proteins were significantly higher in human and rat myocardial tissues with heart failure than in control tissues. Cav3 and μ receptor expression levels were positively correlated with disease severity. The signal of the cardiac Cav3 protein was colocalized with μ receptor in both the human and rat heart sections. Disruption of caveolae in the failing heart by either MβCD or AAV-Cav3 shRNA significantly inhibits morphine-induced phosphorylation of ERK1/2 and cardioprotection. Administration of CTOP substantially reduced Cav3 expression and morphine-induced cardioprotective effect in heart failure.

CONCLUSION AND IMPLICATIONS

Our data suggest that up-regulation of the Cav3/μ receptor complex is critical for morphine protection of the failing heart against I/R injury by regulating the ERK1/2 pathway. The activated Cav3/μ receptor complex is an understudied therapeutic target for opioid treatment of heart failure and ischaemic insult.

Human OPRM1 and murine Oprm1 promoter driven viral constructs for genetic access to μ-opioidergic cell types

With concurrent global epidemics of chronic pain and opioid use disorders, there is a critical need to identify, target and manipulate specific cell populations expressing the mu-opioid receptor (MOR). However, available tools and transgenic models for gaining long-term genetic access to MOR+ neural cell types and circuits involved in modulating pain, analgesia and addiction across species are limited. To address this, we developed a catalog of MOR promoter (MORp) based constructs packaged into adeno-associated viral vectors that drive transgene expression in MOR+ cells. MORp constructs designed from promoter regions upstream of the mouse Oprm1 gene (mMORp) were validated for transduction efficiency and selectivity in endogenous MOR+ neurons in the brain, spinal cord, and periphery of mice, with additional studies revealing robust expression in rats, shrews, and human induced pluripotent stem cell (iPSC)-derived nociceptors. The use of mMORp for in vivo fiber photometry, behavioral chemogenetics, and intersectional genetic strategies is also demonstrated. Lastly, a human designed MORp (hMORp) efficiently transduced macaque cortical OPRM1+ cells. Together, our MORp toolkit provides researchers cell type specific genetic access to target and functionally manipulate mu-opioidergic neurons across a range of vertebrate species and translational models for pain, addiction, and neuropsychiatric disorders.

Long-acting opioids and cardiovascular diseases: Help or hindrance!

Opioids are widely being used for chronic pain management, cough and diarrhea suppressants, anesthetic agents, and opioid de-addiction therapy. Opioid receptors, present in the central nervous system and peripheral tissues, are documented to regulate several cardiac functions through different signaling pathways. Long-acting opioids (LAO) have been successfully evaluated for their beneficial effects in various cardiovascular diseases viz. myocardial infarction, ischemic reperfusion injuries, atherosclerosis etc. However, on the other hand, several research studies pointed towards the harmful effects of LAOs which are mainly associated with QTc prolongation, torsade de pointes, ventricular arrhythmias, and cardiac arrest. This review shall familiarize readers with the benefits as well as the harmful effects of long-acting opioids in cardiovascular diseases. We have also provided an overview of cardiac opioid receptors, endogenous cardiac opioid peptides, and regulation of cardiovascular functions by central and cardiac opioid receptors.

Exercise-induced cardiac opioid system activation attenuates apoptosis pathway in obese rats

AIM

To compare the effect of 150 min vs. 300 min of weekly moderate intensity exercise training on the activation of the opioid system and apoptosis in the hearts of a diet-induced obesity model.

METHODS

Male Wistar rats were fed with either control (CON) or high fat (HF) diet for 32 weeks. At the 20th week, HF group was subdivided into sedentary, low (LEV, 150 min·week^-1) or high (HEV, 300 min·week^-1) exercise volume. After 12 weeks of exercise, body mass gain, adiposity index, systolic blood pressure, cardiac morphometry, apoptosis biomarkers and opioid system expression were evaluated.

RESULTS

Sedentary animals fed with HF presented pathological cardiac hypertrophy and higher body mass gain, systolic blood pressure and adiposity index than control group. Both exercise volumes induced physiological cardiac hypertrophy, restored systolic blood pressure and improved adiposity index, but only 300 min·week^-1 reduced body mass gain. HF group exhibited lower proenkephalin, PI3K, ERK and GSK-3β expression, and greater activated caspase-3 expression than control group. Compared to HF, no changes in the cardiac opioid system were observed in the 150 min·week^-1 of exercise training, while 300 min·week^-1 showed greater proenkephalin, DOR, KOR, MOR, Akt, ERK and GSK-3β expression, and lower activated caspase-3 expression.

CONCLUSION

300 min·week^-1 of exercise training triggered opioid system activation and provided greater cardioprotection against obesity than 150 min·week^-1. Our findings provide translational aspect with clinical relevance about the critical dose of exercise training necessary to reduce cardiovascular risk factors caused by obesity.

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.

Antagonism of endogenous nociceptin/orphanin FQ inhibits infarction-associated ventricular arrhythmias via PKC-dependent mechanism in rats

BACKGROUND AND PURPOSE

Evidence indicates nociceptin/orphanin FQ (N/OFQ) may participate in the pathology of cardiac arrhythmias associated with myocardial infarction. But the role of N/OFQ in the arrhythmogenesis in acute myocardial infarction is unclear. The aim of this study was to investigate the effects of endogenous N/OFQ on infarction-associated arrhythmias.

EXPERIMENTAL APPROACH

The expression of N/OFQ, PKC activity and ventricular arrhythmias in presence and absence of UFP-101, a specific antagonist of N/OFQ receptor, were examined following permanent coronary artery occlusion in anaesthetized rats. The effect of N/OFQ on action potential duration was examined in isolated rat cardiomyocytes.

KEY RESULTS

It was observed that N/OFQ was increased by 41% in the myocardium after coronary artery occlusion (P < 0.01 vs. control). Pretreatment with UFP-101 (10(-7)  mol·kg(-1) , i.v.) reduced the incidence of ventricular ectopic beats by 70% and ventricular tachycardia by 51% respectively (all P < 0.05 vs. control). Meanwhile, PKC activity was elevated in the rats treated with UFP-101 (by 35%, P < 0.05 vs. control). A selective PKC inhibitor, calphostin C, completely abolished the anti-arrhythmic effects of UFP-101 (P < 0.01). N/OFQ (at 10(-11) , 10(-9) and 1 × 10(-7)  mol·L(-1) ) shortened the action potential duration by 3% (P > 0.05), 10% (P < 0.05) and 22% (P < 0.01), respectively, via N/OFQ receptor.

CONCLUSIONS AND IMPLICATIONS

Antagonism of endogenous N/OFQ produces anti-arrhythmic effects on ventricular arrhythmias in acute myocardial infarction, possibly via modulating PKC activity and action potential of myocytes.

Detection and distribution of opioid peptide receptors in porcine myocardial tissue

There is growing evidence that opioid peptide receptors (OPRs) play an important role in cardiovascular function. Many studies have been conducted in swine, in view of their anatomic and physiologic similarities to humans. Until now, the presence and particularly distribution of OPRs has been unclear. Porcine myocardial tissue was obtained from both the left and right atria and ventricles. Expression of mRNA for μ-, δ- and κ-OPR was determined by reverse transcription PCR. OPR proteins were detected by Western blot, distribution and cellular location were identified using immunohistochemistry. Homogenous expression of mRNA and protein for δ- and κ-OPRs were demonstrated in all porcine myocardial tissue tested, whereas expression of μ-OPR mRNA was not demonstrated in any of the tissues tested. This study demonstrates the expression of δ- and κ-OPRs in porcine myocardial tissue. No differences in distribution of δ- and κ-OPRs were found between the four heart cavities. Modulation of cardiac function by δ- and κ-OPR agonists or antagonists is therefore possible, while μ-OPR-mediated direct cardiac effects appear unlikely, due to nonexpression of the receptor. This study demonstrates that porcine studies can further elucidate the role of OPRs in cardiac (patho-)physiology.

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.

Brain and whole-body imaging of nociceptin/orphanin FQ peptide receptor in humans using the PET ligand 11C-NOP-1A

Nociceptin/orphanin FQ peptide (NOP) receptor is a new class of opioid receptor that may play a pathophysiologic role in anxiety and drug abuse and is a potential therapeutic target in these disorders. We previously developed a high-affinity PET ligand, (11)C-NOP-1A, which yielded promising results in monkey brain. Here, we assessed the ability of (11)C-NOP-1A to quantify NOP receptors in human brain and estimated its radiation safety profile.

METHODS

After intravenous injection of (11)C-NOP-1A, 7 healthy subjects underwent brain PET for 2 h and serial sampling of radial arterial blood to measure parent radioligand concentrations. Distribution volume (V(T); a measure of receptor density) was determined by compartmental (1- and 2-tissue) and noncompartmental (Logan analysis and Ichise's bilinear analysis [MA1]) methods. A separate group of 9 healthy subjects underwent whole-body PET to estimate whole-body radiation exposure (effective dose).

RESULTS

After (11)C-NOP-1A injection, the peak concentration of radioactivity in brain was high (∼5-7 standardized uptake values), occurred early (∼10 min), and then washed out quickly. The unconstrained 2-tissue-compartment model gave excellent V(T) identifiability (∼1.1% SE) and fitted the data better than a 1-tissue-compartment model. Regional V(T) values (mL·cm(-3)) ranged from 10.1 in temporal cortex to 5.6 in cerebellum. V(T) was well identified in the initial 70 min of imaging and remained stable for the remaining 50 min, suggesting that brain radioactivity was most likely parent radioligand, as supported by the fact that all plasma radiometabolites of (11)C-NOP-1A were less lipophilic than the parent radioligand. Voxel-based MA1 V(T) values correlated well with results from the 2-tissue-compartment model, showing that parametric methods can be used to compare populations. Whole-body scans showed radioactivity in brain and in peripheral organs expressing NOP receptors, such as heart, pancreas, and spleen. (11)C-NOP-1A was significantly metabolized and excreted via the hepatobiliary route. Gallbladder had the highest radiation exposure (21 μSv/MBq), and the effective dose was 4.3 μSv/MBq.

CONCLUSION

(11)C-NOP-1A is a promising radioligand that reliably quantifies NOP receptors in human brain. The effective dose in humans is low and similar to that of other (11)C-labeled radioligands, allowing multiple scans in 1 subject.

Endogenous opiates and behavior: 2010

This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 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 (Section 16); and immunological responses (Section 17).

Nociceptin/orphanin FQ in inflammation and sepsis

Nociceptin/orphanin FQ, N/OFQ, and its receptor NOP represent a non-opioid branch of the opioid superfamily that were first studied for their effects on pain responses. Both N/OFQ and NOP are involved in a wide range of 'non-pain' responses including immunomodulation and cardiovascular control. There is now growing interest in this system in inflammation and sepsis, which is the focus of this review article. The N/OFQ-NOP system is present in immune cells and N/OFQ modifies immunocyte function. On the basis of various in vitro and in vivo studies, N/OFQ increases the inflammatory response in healthy anaesthetized animals and in those with a septic or inflammatory process. It affects tissue perfusion, increases capillary leakage and inflammatory markers, and leads to immune cell chemotaxis. Moreover, NOP activation produces bradycardia and hypotension. Systemic N/OFQ administration also increased mortality in an animal model of sepsis, and there is limited evidence for increased plasma N/OFQ concentrations in patients with sepsis who died compared with those who survived. There is a need for further observational and mechanistic studies in patients with established inflammatory processes or sepsis. These studies may facilitate the design of appropriate clinical studies to evaluate NOP ligands as modifiers of the inflammatory response.