A dual nociceptin and mu opioid receptor agonist exhibited robust antinociceptive effect with decreased side effects.

The compelling demand of a consummate analgesic medication without addiction is rising due to the clinical mistreatment. Additionally, the series of severe untoward effects usually deterred the utilization while coping with serious pain. As a possible turning point, we revealed that compound 14 is a dual agonist of mu opioid receptor (MOR) and nociceptin-orphanin FQ opioid peptide (NOP) receptor in this study. More importantly, compound 14 achieves pain relieving at very small doses, meanwhile, reduces several unwanted side effects such as constipation, reward, tolerance and withdrawal effects. Here, we evaluated the antinociception and side effects of this novel compound from wild type and humanized mice to further develop a safer prescription analgesic drug.

Evidence for Endogenous Opioid Dependence Related to Latent Sensitization in a Rat Model of Chronic Inflammatory Pain.

Studies performed in a mouse model of chronic inflammatory pain induced by intraplantar injection of complete Freund's adjuvant (CFA) have shown that constitutive activation of the endogenous opioid signaling, besides serving as a mechanism of endogenous analgesia that tonically represses pain sensitization, also generates a state of endogenous opioid dependence. Since species-related differences concerning pain biology and addictive behaviors occur between mice and rats, the present study explored whether the coexistence of endogenous opioid analgesia and endogenous opioid dependence also characterizes a homologous rat model. To this aim, CFA-injured Wistar rats were treated with either 3 mg/kg or 10 mg/kg of the opioid receptor inverse agonist naltrexone (NTX) during the pain remission phase and monitored for 60 min for possible withdrawal behaviors. At 3 mg/kg, NTX, besides inducing the reinstatement of mechanical allodynia, also caused a distinct appearance of ptosis, with slight but nonsignificant changes to the occurrence of teeth chatters and rearing. On the other hand, 10 mg/kg of NTX failed to unmask pain sensitization and induced significantly lower levels of ptosis than 3 mg/kg. Such an NTX-related response pattern observed in the rat CFA model seems to differ substantially from the pattern previously described in the mouse CFA model. This supports the knowledge that mice and rats are not identical in terms of pharmacological response and stresses the importance of choosing the appropriate species for preclinical pain research purposes depending on the scientific question being asked.

Peptidomimetics and Their Applications for Opioid Peptide Drug Discovery.

Despite various advantages, opioid peptides have been limited in their therapeutic uses due to the main drawbacks in metabolic stability, blood-brain barrier permeability, and bioavailability. Therefore, extensive studies have focused on overcoming the problems and optimizing the therapeutic potential. Currently, numerous peptide-based drugs are being marketed thanks to new synthetic strategies for optimizing metabolism and alternative routes of administration. This tutorial review briefly introduces the history and role of natural opioid peptides and highlights the key findings on their structure-activity relationships for the opioid receptors. It discusses details on opioid peptidomimetics applied to develop therapeutic candidates for the treatment of pain from the pharmacological and structural points of view. The main focus is the current status of various mimetic tools and the successful applications summarized in tables and figures.

Current and Future Therapeutic Options in Pain Management: Multi-mechanistic Opioids Involving Both MOR and NOP Receptor Activation.

Opioids are widely used in chronic pain management, despite major concerns about their risk of adverse events, particularly abuse, misuse, and respiratory depression from overdose. Multi-mechanistic opioids, such as tapentadol and buprenorphine, have been widely studied as a valid alternative to traditional opioids for their safer profile. Special interest was focused on the role of the nociceptin opioid peptide (NOP) receptor in terms of analgesia and improved tolerability. Nociceptin opioid peptide receptor agonists were shown to reinforce the antinociceptive effect of mu opioid receptor (MOR) agonists and modulate some of their adverse effects. Therefore, multi-mechanistic opioids involving both MOR and NOP receptor activation became a major field of pharmaceutical and clinical investigations. Buprenorphine was re-discovered in a new perspective, as an atypical analgesic and as a substitution therapy for opioid use disorders; and buprenorphine derivatives have been tested in animal models of nociceptive and neuropathic pain. Similarly, cebranopadol, a full MOR/NOP receptor agonist, has been clinically evaluated for its potent analgesic efficacy and better tolerability profile, compared with traditional opioids. This review overviews pharmacological mechanisms of the NOP receptor system, including its role in pain management and in the development of opioid tolerance. Clinical data on buprenorphine suggest its role as a safer alternative to traditional opioids, particularly in patients with non-cancer pain; while data on cebranopadol still require phase III study results to approve its introduction on the market. Other bifunctional MOR/NOP receptor ligands, such as BU08028, BU10038, and AT-121, are currently under pharmacological investigations and could represent promising analgesic agents for the future.

Therapeutic potential of nociceptin/orphanin FQ peptide (NOP) receptor modulators for treatment of traumatic brain injury, traumatic stress, and their co-morbidities.

The nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor is a member of the opioid receptor superfamily with N/OFQ as its endogenous agonist. Wide expression of the NOP receptor and N/OFQ, both centrally and peripherally, and their ability to modulate several biological functions has led to development of NOP receptor modulators by pharmaceutical companies as therapeutics, based upon their efficacy in preclinical models of pain, anxiety, depression, Parkinson's disease, and substance abuse. Both posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) are debilitating conditions that significantly affect the quality of life of millions of people around the world. PTSD is often a consequence of TBI, and, especially for those deployed to, working and/or living in a war zone or are first responders, they are comorbid. PTSD and TBI share common symptoms, and negatively influence outcomes as comorbidities of the other. Unfortunately, a lack of effective therapies or therapeutic agents limits the long term quality of life for either TBI or PTSD patients. Ours, and other groups, demonstrated that PTSD and TBI preclinical models elicit changes in the N/OFQ-NOP receptor system, and that administration of NOP receptor ligands alleviated some of the neurobiological and behavioral changes induced by brain injury and/or traumatic stress exposure. Here we review the past and most recent progress on understanding the role of the N/OFQ-NOP receptor system in PTSD and TBI neurological and behavioral sequelae. There is still more to understand about this neuropeptide system in both PTSD and TBI, but current findings warrant further examination of the potential utility of NOP modulators as therapeutics for these disorders and their co-morbidities. We advocate the development of standards for common data elements (CDE) reporting for preclinical PTSD studies, similar to current preclinical TBI CDEs. That would provide for more standardized data collection and reporting to improve reproducibility, interpretation and data sharing across studies.

Non-Opioid Peptides Targeting Opioid Effects.

Opioids are the most potent widely used analgesics, primarily, but not exclusively, in palliative care. However, they are associated with numerous side effects, such as tolerance, addiction, respiratory depression, and cardiovascular events. This, in turn, can result in their overuse in cases of addiction, the need for dose escalation in cases of developing tolerance, and the emergence of dose-related opioid toxicity, resulting in respiratory depression or cardiovascular problems that can even lead to unintentional death. Therefore, a very important challenge for researchers is to look for ways to counteract the side effects of opioids. The use of peptides and their related compounds, which have been shown to modulate the effects of opioids, may provide such an opportunity. This short review is a compendium of knowledge about the most important and recent findings regarding selected peptides and their modulatory effects on various opioid actions, including cardiovascular and respiratory responses. In addition to the peptides more commonly reported in the literature in the context of their pro- and/or anti-opioid activity-such as neuropeptide FF (NPFF), cholecystokinin (CCK), and melanocyte inhibiting factor (MIF)-we also included in the review nociceptin/orphanin (N/OFQ), ghrelin, oxytocin, endothelin, and venom peptides.

[Therapeutic potentials of safe opioid analgesics targeting nociceptin/orphanin FQ peptide receptor].

After the identification of nociceptin/orphanin FQ (N/OFQ) peptide (NOP) and its cognate receptor, the unique functional profiles of the N/OFQ-NOP receptor system have been uncovered. NOP receptors are distributed in the key regions that regulate pain and reward processing in the central nervous system. In non-human primates (NHPs), activation of the NOP receptor causes antinociception and anti-hypersensitivity via spinal and supraspinal effects. Moreover, activation of the NOP receptor attenuates dopaminergic transmission and potentiates mu-opioid peptide (MOP) receptor-mediated analgesia. Here, we highlight the functional profiles of bifunctional NOP and MOP receptor agonists based on their promising effects for the treatment of pain and drug abuse. Bifunctional NOP/MOP receptor "partial" agonists, such as AT-121, BU08028, and BU10038, exert potent analgesic effects without MOP receptor-related side effects such as abuse liability, respiratory depression, physical dependence, and itching in NHPs. These novel NOP/MOP receptor agonists reduce rewarding and the reinforcing effects of abused drugs. Furthermore, a mixed NOP/opioid receptor "full" agonist, cebranopadol, is undergoing several clinical trials, and the therapeutic advantage of the coactivation of NOP and MOP receptors has also been confirmed in humans. Therefore, this class of drugs that coactivate NOP and MOP receptors proposes a wide therapeutic range with fewer side effects, indicating a greater potential for the development of novel safer opioid analgesics.

Novel Natural-based Biomolecules Discovery for Tackling Chronic Diseases.

In the last decade, natural-derived/-based biomolecules have continuously played an important role in novel drug discovery (as a prototype drug template) for potential chronic disease treatment [...].

Food-Derived Opioid Peptides in Human Health: A Review.

World Health Organization data suggest that stress, depression, and anxiety have a noticeable prevalence and are becoming some of the most common causes of disability in the Western world. Stress-related disorders are considered to be a challenge for the healthcare system with their great economic and social impact. The knowledge on these conditions is not very clear among many people, as a high proportion of patients do not respond to the currently available medications for targeting the monoaminergic system. In addition, the use of clinical drugs is also associated with various side effects such as vomiting, dizziness, sedation, nausea, constipation, and many more, which prevents their effective use. Therefore, opioid peptides derived from food sources are becoming one of the safe and natural alternatives because of their production from natural sources such as animals and plant proteins. The requirement for screening and considering dietary proteins as a source of bioactive peptides is highlighted to understand their potential roles in stress-related disorders as a part of a diet or as a drug complementing therapeutic prescription. In this review, we discussed current knowledge on opioid endogenous and exogenous peptides concentrating on their production, purification, and related studies. To fully understand their potential in stress-related conditions, either as a drug or as a therapeutic part of a diet prescription, the need to screen more dietary proteins as a source of novel opioid peptides is emphasized.

Molecular basis of the therapeutic properties of hemorphins.

Hemorphins are endogenous peptides, 4-10 amino acids long, belonging to the family of atypical opioid peptides released during the sequential cleavage of hemoglobin protein. Hemorphins have been shown to exhibit diverse therapeutic effects in both human and animal models. However, the precise cellular and molecular mechanisms involved in such effects remain elusive. In this review, we summarize and propose potential mechanisms based on studies that investigated the biological activity of hemorphins of different lengths on multiple therapeutic targets. Special emphasis is given to molecular events related to renin-angiotensin system (RAS), opioid receptors and insulin-regulated aminopeptidase receptor (IRAP). This review provides a comprehensive coverage of the molecular mechanisms that underpin the therapeutic potential of hemorphins. Furthermore, it highlights the role of various hemorphin residues in pathological conditions, which could be explored further for therapeutic purposes.

Replacement of current opioid drugs focusing on MOR-related strategies.

The scarcity and limited risk/benefit ratio of painkillers available on the market, in addition to the opioid crisis, warrant reflection on new innovation strategies. The pharmacopoeia of analgesics is based on products that are often old and derived from clinical empiricism, with limited efficacy or spectrum of action, or resulting in an unsatisfactory tolerability profile. Although they are reference analgesics for nociceptive pain, opioids are subject to the same criticism. The use of opium as an analgesic is historical. Morphine was synthesized at the beginning of the 19th century. The efficacy of opioids is limited in certain painful contexts and these drugs can induce potentially serious and fatal adverse effects. The current North American opioid crisis, with an ever-rising number of deaths by opioid overdose, is a tragic illustration of this. It is therefore legitimate to develop research into molecules likely to maintain or increase opioid efficacy while improving their tolerability. Several avenues are being explored including targeting of the mu opioid receptor (MOR) splice variants, developing biased agonists or targeting of other receptors such as heteromers with MOR. Ion channels acting as MOR effectors, are also targeted in order to offer compounds without MOR-dependent adverse effects. Another route is to develop opioid analgesics with peripheral action or limited central nervous system (CNS) access. Finally, endogenous opioids used as drugs or compounds that modify the metabolism of endogenous opioids (Dual ENKephalinase Inhibitors) are being developed. The aim of the present review is to present these various targets/strategies with reference to current indications for opioids, concerns about their widespread use, particularly in chronic non-cancer pains, and ways of limiting the risk of opioid abuse and misuse.

Potent, Efficacious, and Stable Cyclic Opioid Peptides with Long Lasting Antinociceptive Effect after Peripheral Administration.

Four novel fluorinated cyclic analogues of biphalin with excellent to modest binding affinity for µ-, δ-, and κ-receptors were synthesized. The cyclic peptides have a combination of piperazine or hydrazine linker with or without a xylene bridge. Among the ligands, MACE3 demonstrated a better activity than biphalin after intravenous administration, and its corresponding analogue incorporating the hydrazine linker (MACE2) was able to induce longer lasting analgesia following subcutaneous administration. An analogue of MACE2 containing 2,6-dimethyl-l-tyrosine (MACE4) showed the best potency and in vivo antinociceptive activity of this series.

Hyperactivity, dopaminergic abnormalities, iron deficiency and anemia in an in vivo opioid receptors knockout mouse: Implications for the restless legs syndrome.

Previous studies have uncovered a potential role of the opioid system in iron hemostasis and dopamine metabolism. Abnormalities in both of these systems have been noted in human RLS. Autopsy studies of human RLS have shown an endogenous opioid deficiency in the thalamus. Opioids, particularly prolonged-release oxycodone/naloxone, have been approved in Europe to be a second-line therapy for severe restless legs syndrome (RLS). To study the role of opioid receptors in the pathogenesis of RLS, we used a triple knockout (KO) mouse strain that lack mu, delta, and kappa opioid receptors and explored the behavioral and biochemical parameters relevant to RLS. The triple KO mice showed hyperactivity and a trend of increased probability of waking during the rest period (day) akin to that in human RLS (night). Surprisingly, triple KO mice also exhibit decreased serum iron concentration, evidence of anemia, a significant dysfunction in dopamine metabolism akin to that noted in human RLS, as well as an increased latency in response to thermal stimuli. To our knowledge, this is the first study to demonstrate that the endogenous opioid system may play a role in iron metabolism and subsequently in the pathogenesis of anemia. It is also the first study showing that opioid receptors are involved in the production of motor restlessness with a circadian predominance. Our findings support the role of endogenous opioids in the pathogenesis of RLS, and the triple KO mice can be used to understand the relationship between iron deficiency, anemia, dopaminergic dysfunction, and RLS.

Dermorphin [D-Arg2, Lys4] (1-4) amide inhibits below-level heat hypersensitivity in mice after contusive thoracic spinal cord injury.

Opioid use for chronic pain is limited by severe central adverse effects. We examined whether activating mu-opioid receptors (MORs) in the peripheral nervous system attenuates spinal cord injury (SCI) pain-like behavior in mice. We produced a contusive SCI at the T10 vertebral level and examined motor and sensory dysfunction for 6 weeks. At 6 weeks, we tested the effect of subcutaneous (s.c.) injection of dermorphin [D-Arg2, Lys4] (1-4) amide (DALDA), a peripherally acting MOR-preferring agonist, on mechanical and heat hypersensitivity. Basso mouse scale score was significantly decreased after SCI, and mice showed hypersensitivity to mechanical and heat stimulation at the hind paw beginning at 2 weeks, as indicated by increased paw withdrawal frequency to mechanical stimulation and decreased paw withdrawal latency to heat stimulation. In wild-type SCI mice, DALDA (1 mg/kg, s.c.) attenuated heat but not mechanical hypersensitivity. The effect was blocked by pretreatment with an intraperitoneal injection of methylnaltrexone (5 mg/kg), a peripherally restricted opioid receptor antagonist, and was also diminished in Pirt-MOR conditional knockout mice. DALDA did not adversely affect exploratory activity or induced preference to drug treatment in SCI mice. In vivo calcium imaging showed that DALDA (1, 10 mg/kg, s.c.) inhibited responses of small dorsal root ganglion neurons to noxious heat stimulation in Pirt-GCaMP6s mice after SCI. Western blot analysis showed upregulation of MOR in the lumbar spinal cord and sciatic nerves at 6 weeks after SCI. Our findings suggest that peripherally acting MOR agonist may inhibit heat hypersensitivity below the injury level with minimal adverse effects.

Non-addictive orally-active kappa opioid agonists for the treatment of peripheral pain in rats.

Addiction to conventional opioid pain analgesics is a major societal problem that is increasing at an alarming rate. New drugs to combat the effects of opioid abuse are desperately needed. Kappa-opioid agonists are efficacious in peripheral pain models but suffer from centrally-mediated effects. In this article, we discuss our efforts in developing peripheral kappa-based opioid receptor agonists that have the potential analgesic activity of opioids but do not manifest the negative side-effects of opioid use and abuse. Further, derivatives of the tetra-peptide D-Phe-D-Phe-D-Nle-D-Arg-NH2, such as CR665, exhibit high peripheral to central selectivity in analgesic models when administered intravenously (i.v.); however, they are inactive when administered orally. Application of our laboratory's proprietary non-natural amino acid technology to CR665 produced derivatives that exhibit peripheral analgesic activity when dosed orally but do not promote CNS-based effects. Lead compound JT09 activates the kappa-opioid receptor with EC50s in the low nM range, while agonist selectivity for kappa over other peripheral opioid receptors was >33,400 fold. Results indicate that JT09 is approximately as efficacious as morphine in alleviating peripheral pain, while failing to produce undesired CNS-mediated activity. Additionally, JT09 did not promote other CNS-mediated effects associated with morphine (addiction, sedation, dysphoria, tolerance, addiction). Thus, we propose that JT09 has potential for development as a novel analgesic. PERSPECTIVE: This article presents data supporting the analgesic properties of an orally available, peripherally-restricted, kappa-opioid agonist for peripheral pain. A potential out-patient pharmaceutical that acts as efficacious as morphine in alleviating peripheral pain, while failing to produce undesired CNS-mediated effects, could help reduce the current health care burden associated with prescription opioids.

Multivalent peptide and peptidomimetic ligands for the treatment of pain without toxicities and addiction.

The current opioid crisis has created a tragic problem in medicine and society. Pain is the most ubiquitous and costly disease in society and yet all of our "treatments" have toxicities, especially for prolonged use. However, there are several alternatives that have been discovered in the past fifteen years that have been demonstrated in animals to have none of the toxicities of current drugs. Many of the compounds are multivalent and have novel biological activity profiles. Unfortunately, none of these have been in clinical trials in humans, perhaps because they were discovered in academic laboratories. A review of these novel chemicals are given in this paper.

Role of mu-opioid agonist efficacy on antinociceptive interactions between mu agonists and the nociceptin opioid peptide agonist Ro 64-6198 in rhesus monkeys.

Mu-opioid receptor agonists are clinically effective analgesics, but also produce undesirable effects that limit their clinical utility. The nociceptin opioid peptide (NOP) receptor system also modulates nociception, and NOP agonists might be useful adjuncts to enhance the analgesic effects or attenuate the undesirable effects of mu-opioid agonists. The present study determined behavioral interactions between the NOP agonist (-)-Ro 64-6198 and mu-opioid ligands that vary in mu-opioid receptor efficacy (17-cyclopropylmethyl-3,14ß-dihyroxy-4,5α-epoxy-6α-[(3 ́-isoquinolyl)acetamindo]morphinan (NAQ) < buprenorphine < nalbuphine < morphine = oxycodone < methadone) in male rhesus monkeys. For comparison, Ro 64-6198 interactions were also examined with the kappa-opioid receptor agonist nalfurafine. Each opioid ligand was examined alone and following fixed-dose Ro 64-6198 pretreatments in assays of thermal nociception (n = 3-4) and schedule-controlled responding (n = 3). Ro 64-6198 alone failed to produce significant antinociception up to doses (0.32 mg/kg, IM) that significantly decreased rates of responding. All opioid ligands, except NAQ and nalfurafine, produced dose- and thermal intensity-dependent antinociception. Ro 64-6198 enhanced the antinociceptive potency of buprenorphine, nalbuphine, methadone, and nalfurafine. Ro 64-6198 enhancement of nalbuphine antinociception was NOP antagonist SB-612111 reversible and occurred under a narrow range of dose and time conditions. All opioid ligands, except NAQ and buprenorphine, produced dose-dependent decreases in rates of responding. Ro 64-6198 did not significantly alter mu-opioid ligand rate-decreasing effects. Although these results suggest that NOP agonists may selectively enhance the antinociceptive vs. rate-suppressant effects of some mu-opioid agonists, this small enhancement occurred under a narrow range of conditions dampening enthusiasm for NOP agonists as candidate "opioid-sparing" adjuncts.

Intra-hippocampal administration of orexin receptor antagonists dose-dependently attenuates reinstatement of morphine seeking behavior in extinguished rats.

It has been shown that the hippocampus plays an essential role in the regulation of reward and memory as indicated by the conditioned place preference (CPP) paradigm. Morphine-induced CPP is a common method to consider motivational properties of morphine in animals. Recently, this model has been used in many laboratories to investigate neuronal mechanisms underlying reinstatement of morphine seeking induced by drug re-exposure. Our previous studies indicate that the hippocampus especially CA1 region is involved in reinstatement of drug-seeking behaviors. Also, several studies have shown that orexin attenuates key functional and behavioral effects of its co-transmitter dynorphin. The present study evaluates the role of orexinergic receptors within the CA1 region of the hippocampus in the reinstatement of morphine-induced CPP. Therefore, after the extinction period, the different doses (SB 334867; 0.3, 3, and 30 nM/0.5 µl DMSO) of either orexin-1 or -2 receptor antagonists were bilaterally microinjected into the CA1, 15 min before receiving an effective priming dose of morphine (1 mg/kg). The results revealed that administration of both SB 334867 and TCS OX2 29 prior to injection of the priming dose of morphine significantly reduced the reinstatement of morphine-induced CPP without altering the animal's locomotor activity. Also, the 50% effective dose value of SB 334867 on the reinstatement of morphine seeking behavior was close three times more than that in TCS OX2 29 treatment group. Therefore, the consequences suggested that both orexin receptors in the CA1 play a considerable role in the reinstatement of morphine-induced CPP.

Nociceptin/Orphanin Fq in inflammation and remodeling of the small airways in experimental model of airway hyperresponsiveness.

It is widely recognized that airway inflammation and remodeling play a key role not only in the central airway but also small airway pathology during asthma. Nociceptin/Orphanin FQ (N/OFQ), an endogenous peptide, and its receptor N/OFQ peptide (NOP) are involved in airway hyperresponsiveness (AHR). We studied a murine model of AHR in order to understand the role of N/OFQ in the inflammation and remodeling of the small airways. Balb/c mice were sensitized to ovalbumin (OVA). At days 0 and 7 (pre-OVA sensitization) or from day 21 to 23 (post-OVA sensitization), the mice were treated intraperitoneally with N/OFQ or saline solution. After the last OVA challenge, all OVA-sensitized mice were aerosol-challenged with 1% OVA in PBS for 48 h, and then euthanized. Small airway compliance (sCaw ) was measured and lung samples were collected for histological and molecular evaluations such as perimeter and diameter of small airway, total wall area, airway smooth muscle (ASM) thickness and number of alveolar attachments. Both pre- and post-OVA sensitization N/OFQ treatments induced: (1) increases in sCaw ; (2) reduction of the bronchial wall thickness; (3) attenuation of the hyperplastic phase of airway smooth muscle mass; and (4) protection against loss of alveolar attachments compared with saline solution treatments. These results suggest that N/OFQ protects against inflammation, and mechanical damage and remodeling of small airways caused by OVA sensitization, suggesting a new potential therapeutic target for asthma.