Role of nociceptin/orphanin FQ and nociceptin opioid peptide receptor in depression and antidepressant effects of nociceptin opioid peptide receptor antagonists

Perioperative changes of serum orphanin in diabetic patients and its relationship with sympathetic nervous system

The occurrence of cardiovascular events in diabetic patients during the perioperative period is related to the activation of sympathetic nerves. Basic research shows that serum nociceptin/orphanin FQ (N/OFQ) levels in diabetic neuropathy rats increased, and N/OFQ reduces the release of norepinephrine (NE). We hypothesize that N/OFQ will affect the sympathetic nervous system during perioperative myocardium of diabetic patients. 66 patients with unilateral knee arthroplasty were divided into diabetes group (D group) and non-diabetes group (N group). Measured blood glucose, serum NE, N/OFQ concentrations at the 30 min before anesthesia (T0), 1 h after surgery (T1), 24 h after surgery (T2) and the cardiac troponinI (cTnI) concentration at T0 and T2. Compared with N group, the concentration of blood glucose, N/OFQ and cTnI in D group was higher and the NE was lower at T0 (P < 0.05). At T1, the blood glucose, N/OFQ, NE concentrations of D group increased, only the blood glucose increased in N group (P < 0.05). Serum N/OFQ of D group from T0 to T1 was correlated with the change trend of blood glucose, NE concentration from T0 to T1 and cTnI from T0 to T2(r = 0.386, P = 0.027; r = 0.350, P = 0.046; r = 0.363, P = 0.038). The outcomes demonstrated that the preoperative serum N/OFQ concentration in diabetic patients was increased, and the increase in N/OFQ concentration during the operation was related to the increase in NE and cTnI concentrations, perioperative N/OFQ may mediate myocardial injury through sympathetic nervous system.

Contribution of the opioid system to depression and to the therapeutic effects of classical antidepressants and ketamine

Major depressive disorder (MDD) afflicts approximately 5 % of the world population, and about 30-50 % of patients who receive classical antidepressant medications do not achieve complete remission (treatment resistant depressive patients). Emerging evidence suggests that targeting opioid receptors mu (MOP), kappa (KOP), delta (DOP), and the nociceptin/orphanin FQ receptor (NOP) may yield effective therapeutics for stress-related psychiatric disorders. As depression and pain exhibit significant overlap in their clinical manifestations and molecular mechanisms involved, it is not a surprise that opioids, historically used to alleviate pain, emerged as promising and effective therapeutic options in the treatment of depression. The opioid signaling is dysregulated in depression and numerous preclinical studies and clinical trials strongly suggest that opioid modulation can serve as either an adjuvant or even an alternative to classical monoaminergic antidepressants. Importantly, some classical antidepressants require the opioid receptor modulation to exert their antidepressant effects. Finally, ketamine, a well-known anesthetic whose extremely efficient antidepressant effects were recently discovered, was shown to mediate its antidepressant effects via the endogenous opioid system. Thus, although opioid system modulation is a promising therapeutical venue in the treatment of depression further research is warranted to fully understand the benefits and weaknesses of such approach.

Regulation of N-type calcium channels by nociceptin receptors and its possible role in neurological disorders

Activation of nociceptin opioid peptide receptors (NOP, a.k.a. opioid-like receptor-1, ORL-1) by the ligand nociceptin/orphanin FQ, leads to G protein-dependent regulation of Cav2.2 (N-type) voltage-gated calcium channels (VGCCs). This typically causes a reduction in calcium currents, triggering changes in presynaptic calcium levels and thus neurotransmission. Because of the widespread expression patterns of NOP and VGCCs across multiple brain regions, the dorsal horn of the spinal cord, and the dorsal root ganglia, this results in the alteration of numerous neurophysiological features. Here we review the regulation of N-type calcium channels by the NOP-nociceptin system in the context of neurological conditions such as anxiety, addiction, and pain.

Antidepressant-like effect of tofisopam in mice: A behavioural, molecular docking and MD simulation study

BACKGROUND

Depression is a disease that affects millions of people worldwide, and the discovery and development of effective and safe antidepressant drugs is one of the important topics of psychopharmacology.

OBJECTIVES

In this study, it was aimed to investigate the antidepressant-like activity potential of tofisopam, an anxiolytic drug with 2,3-benzodiazepine structure, and to elucidate the pharmacological mechanisms mediating this effect.

METHODS

The antidepressant-like activity of tofisopam was investigated using tail suspension and modified forced swimming tests. Possible interactions of tofisopam with µ- and δ-opioid receptor subtypes were clarified by pharmacological antagonism, molecular docking and molecular dynamics simulation studies.

RESULTS

Tofisopam (50 and 100 mg/kg) significantly shortened the immobility time of mice in both the tail suspension and the modified forced swimming tests. The drug, at the same doses, prolonged the duration of swimming and climbing behaviours measured in modified forced swimming tests. A dosage of 25 mg/kg was ineffective. Mechanistic studies showed that the pretreatment with p-chlorophenylalanine methyl ester (serotonin synthesis inhibitor; 4 consecutive days, 100 mg/kg), α-methyl-para-tyrosine methyl ester (catecholamine synthesis inhibitor; 100 mg/kg), naloxonazine (selective µ-opioid receptor blocker, 7 mg/kg) and naltrindole (a selective δ-opioid receptor blocker, 0.99 mg/kg) abolished the anti-immobility effect induced by the 50 mg/kg dose of tofisopam in the tail suspension tests. Our in silico studies supported the behavioural findings that the antidepressant-like effect of tofisopam is mediated by μ- and δ-opioid receptors.

CONCLUSION

This study is the first to show that tofisopam has antidepressant-like activity mediated by the serotonergic, catecholaminergic and opioidergic systems.

Novel Pharmacological Approaches to the Treatment of Depression

Major depressive disorder is one of the most prevalent mental health disorders. Monoamine-based antidepressants were the first drugs developed to treat major depressive disorder. More recently, ketamine and other analogues were introduced as fast-acting antidepressants. Unfortunately, currently available therapeutics are inadequate; lack of efficacy, adverse effects, and risks leave patients with limited treatment options. Efforts are now focused on understanding the etiology of depression and identifying novel targets for pharmacological treatment. In this review, we discuss promising novel pharmacological targets for the treatment of major depressive disorder. Targeting receptors including N-methyl-D-aspartate receptors, peroxisome proliferator-activated receptors, G-protein-coupled receptor 39, metabotropic glutamate receptors, galanin and opioid receptors has potential antidepressant effects. Compounds targeting biological processes: inflammation, the hypothalamic-pituitary-adrenal axis, the cholesterol biosynthesis pathway, and gut microbiota have also shown therapeutic potential. Additionally, natural products including plants, herbs, and fatty acids improved depressive symptoms and behaviors. In this review, a brief history of clinically available antidepressants will be provided, with a primary focus on novel pharmaceutical approaches with promising antidepressant effects in preclinical and clinical studies.

Neuropeptides: Potential neuroprotective agents in ischemic injury

AIM

Ischemic damage to the brain is linked to an increased rate of morbidity and mortality worldwide. In certain parts of the world, it remains a leading cause of mortality and the primary cause of long-term impairment. Ischemic injury is exacerbated when particular neuropeptides are removed, or their function in the brain is blocked, whereas supplying such neuropeptides lowers ischemic harm. Here, we have discussed the role of neuropeptides in ischemic injury.

MATERIALS & METHODS

Numerous neuropeptides had their overexpression following cerebral ischemia. Neuropeptides such as NPY, CGRP, CART, SP, BK, PACAP, oxytocin, nociception, neurotensin and opioid peptides act as transmitters, documented in several "in vivo" and "in vitro" studies. Neuropeptides provide neuroprotection by activating the survival pathways or inhibiting the death pathways, i.e., MAPK, BDNF, Nitric Oxide, PI3k/Akt and NF-κB.

KEY FINDINGS

Neuropeptides have numerous beneficial effects in ischemic models, including antiapoptotic, anti-inflammatory, and antioxidant actions that provide a powerful protective impact in neurons when combined. These innovative therapeutic substances have the potential to treat ischemia injury due to their pleiotropic modes of action.

SIGNIFICANCE

This review emphasizes the neuroprotective role of neuropeptides in ischemic injury via modulation of various signalling pathways i.e., MAPK, BDNF, Nitric Oxide, PI3k/Akt and NF-κB.

Role of Nociceptin/Orphanin FQ-NOP Receptor System in the Regulation of Stress-Related Disorders

Nociceptin/orphanin FQ (N/OFQ) is a 17-residue neuropeptide that binds the nociceptin opioid-like receptor (NOP). N/OFQ exhibits nucleotidic and aminoacidics sequence homology with the precursors of other opioid neuropeptides but it does not activate either MOP, KOP or DOP receptors. Furthermore, opioid neuropeptides do not activate the NOP receptor. Generally, activation of N/OFQ system exerts anti-opioids effects, for instance toward opioid-induced reward and analgesia. The NOP receptor is widely expressed throughout the brain, whereas N/OFQ localization is confined to brain nuclei that are involved in stress response such as amygdala, BNST and hypothalamus. Decades of studies have delineated the biological role of this system demonstrating its involvement in significant physiological processes such as pain, learning and memory, anxiety, depression, feeding, drug and alcohol dependence. This review discusses the role of this peptidergic system in the modulation of stress and stress-associated psychiatric disorders in particular drug addiction, mood, anxiety and food-related associated-disorders. Emerging preclinical evidence suggests that both NOP agonists and antagonists may represent a effective therapeutic approaches for substances use disorder. Moreover, the current literature suggests that NOP antagonists can be useful to treat depression and feeding-related diseases, such as obesity and binge eating behavior, whereas the activation of NOP receptor by agonists could be a promising tool for anxiety.

Endogenous opiates and behavior: 2019

This paper is the forty-second consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2019 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

[The role of nociceptin in opioid regulation of brain functions]

This review discusses our current knowledge on the nociceptin/orphanin (N/OFQ) system regarding its role in regulation of brain functions. Nociceptin receptor (NOPr) was identified in 1994 [Bunzow et al., 1994; Mollereau et al., 1994]. In 1995 a 17 amino acid endogenous peptide was found to be the high-affinity ligand for the NOPr [Reinscheid et al., 1995]. N/OFQ has a broad spectrum of activity and can act as on opioid-like as well as an anti-opioid peptide. Considering high level of N/OFQ and NOPr mRNA expression in the limbic brain regions, the N/OFQ/NOP system is suggested to be involved in regulation of emotions, resward, pain sensitivity, stress responsibility, sexual behavior, aggression, drug abuse and addiction. However it is still not well understood whether an increased vulnerability to drugs of abuse may be associated with dysregulation of N/OFQ/NOP system. Current review further highlights a need for further research on N/OFQ/NOP system as it could have clinical utility for substance abuse, depression, and anxiety pharmacotherapy.