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2021 ◽  
Vol 8 (12) ◽  
pp. 689-691
Author(s):  
H. Reid Zweifel ◽  
Jonathan Browne ◽  
Jeffrey M Levine

Objective: Drug overdose deaths have risen precipitously over the past two years in the United States. Polysubstance overdose with opiates and amphetamines have been of particular concern. Kratom (Mitragyna speciosa) is an unregulated widely available herb with both stimulant and opiate μ-receptor activity. Studies suggest that its use is quickly increasing. Case: We describe a patient who presented to a psychiatric hospital with a mixed toxic syndrome due to chronic kratom and prescribed SSRI use compounded by acute intake of methamphetamine. The patient displayed psychosis, tremulousness, myoclonus, and extreme anxiety. Her clinical picture was consistent with both serotonin syndrome and opiate withdrawal. Conclusion: We call attention to this case because polysubstance overdoses are common, and kratom is widely available. Complex toxic presentations that involve kratom are likely to be increasingly encountered.


Molecules ◽  
2021 ◽  
Vol 26 (18) ◽  
pp. 5448
Author(s):  
Sandra Piras ◽  
Gabriele Murineddu ◽  
Giovanni Loriga ◽  
Antonio Carta ◽  
Enrica Battistello ◽  
...  

Opioid analgesics are clinically used to relieve severe pain in acute postoperative and cancer pain, and also in the long term in chronic pain. The analgesic action is mediated by μ-, δ-, and κ-receptors, but currently, with few exceptions for k-agonists, μ-agonists are the only ones used in therapy. Previously synthesized compounds with diazotricyclodecane cores (DTDs) have shown their effectiveness in binding opioid receptors. Fourteen novel diazatricyclodecanes belonging to the 9-propionyl-10-substituted-9,10-diazatricyclo[4.2.1.12,5]decane (compounds 20–23, 53, 57 and 59) and 2-propionyl-7-substituted-2,7-diazatricyclo[4.4.0.03,8]decane (compounds 24–27, 54, 58 and 60) series, respectively, have been synthesized and their ability to bind to the opioid μ-, δ- and κ-receptors was evaluated. Five of these derivatives, compounds 20, 21, 24, 26 and 53, showed μ-affinity in the nanomolar range with a negligible affinity towards δ- and κ-receptors and high μ-receptor selectivity. The synthesized compounds showed μ-receptor selectivity higher than those of previously reported methylarylcinnamyl analogs.


2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Anna Borsodi ◽  
Michael Bruchas ◽  
Girolamo Caló ◽  
Charles Chavkin ◽  
MacDonald J. Christie ◽  
...  

Opioid and opioid-like receptors are activated by a variety of endogenous peptides including [Met]enkephalin (met), [Leu]enkephalin (leu), β-endorphin (β-end), α-neodynorphin, dynorphin A (dynA), dynorphin B (dynB), big dynorphin (Big dyn), nociceptin/orphanin FQ (N/OFQ); endomorphin-1 and endomorphin-2 are also potential endogenous peptides. The Greek letter nomenclature for the opioid receptors, μ, δ and κ, is well established, and NC-IUPHAR considers this nomenclature appropriate, along with the symbols spelled out (mu, delta, and kappa), and the acronyms, MOP, DOP, and KOP. [121, 100, 91]. The human N/OFQ receptor, NOP, is considered 'opioid-related' rather than opioid because, while it exhibits a high degree of structural homology with the conventional opioid receptors [294], it displays a distinct pharmacology. Currently there are numerous clinically used drugs, such as morphine and many other opioid analgesics, as well as antagonists such as naloxone, however only for the μ receptor.


2021 ◽  
Author(s):  
Huiping Ding ◽  
Claudio Trapella ◽  
Norikazu Kiguchi ◽  
Fang-Chi Hsu ◽  
Girolamo Caló ◽  
...  

Background Cebranopadol, a mixed nociceptin/opioid receptor full agonist, can effectively relieve pain in rodents and humans. However, it is unclear to what degree different opioid receptor subtypes contribute to its antinociception and whether cebranopadol lacks acute opioid-associated side effects in primates. The authors hypothesized that coactivation of nociceptin receptors and μ receptors produces analgesia with reduced side effects in nonhuman primates. Methods The antinociceptive, reinforcing, respiratory-depressant, and pruritic effects of cebranopadol in adult rhesus monkeys (n = 22) were compared with μ receptor agonists fentanyl and morphine using assays, including acute thermal nociception, IV drug self-administration, telemetric measurement of respiratory function, and itch-scratching responses. Results Subcutaneous cebranopadol (ED50, 2.9 [95% CI, 1.8 to 4.6] μg/kg) potently produced antinociception compared to fentanyl (15.8 [14.6 to 17.1] μg/kg). Pretreatment with antagonists selective for nociceptin and μ receptors, but not δ and κ receptor antagonists, caused rightward shifts of the antinociceptive dose–response curve of cebranopadol with dose ratios of 2 and 9, respectively. Cebranopadol produced reinforcing effects comparable to fentanyl, but with decreased reinforcing strength, i.e., cebranopadol (mean ± SD, 7 ± 3 injections) versus fentanyl (12 ± 3 injections) determined by a progressive-ratio schedule of reinforcement. Unlike fentanyl (8 ± 2 breaths/min), systemic cebranopadol at higher doses did not decrease the respiratory rate (17 ± 2 breaths/min). Intrathecal cebranopadol (1 μg) exerted full antinociception with minimal scratching responses (231 ± 137 scratches) in contrast to intrathecal morphine (30 μg; 3,009 ± 1,474 scratches). Conclusions In nonhuman primates, the μ receptor mainly contributed to cebranopadol-induced antinociception. Similar to nociceptin/μ receptor partial agonists, cebranopadol displayed reduced side effects, such as a lack of respiratory depression and pruritus. Although cebranopadol showed reduced reinforcing strength, its detectable reinforcing effects and strength warrant caution, which is critical for the development and clinical use of cebranopadol. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New


2021 ◽  
Vol 10 (8) ◽  
pp. 1735
Author(s):  
Basavana Goudra ◽  
Keira P. Mason

Successful pharmacological innovations that have made a difference in daily practice are rare in the world of anesthesia and sedation. After many years of research, it seems that we finally have two new drug innovations that are likely to change the paradigm of moderate and deep sedation. These are oliceridine and remimazolam. Both have been in development for over a decade. Oliceridine was synthesized in a lab as an entirely new molecule. It is a biased μ- receptor agonist that acts preferentially on the G-protein pathway (which is responsible for analgesia). At least in lower doses, it has minimal effect on the beta-arrestin pathway, which is responsible for unwanted effects of μ-opioid receptor activation such as respiratory depression and gastrointestinal dysfunction. Like any other μ- receptor agonist, it produces appropriate dose-dependent analgesia. Remimazolam is structurally similar to midazolam; however, it has an additional ester linkage that delivers the kinetics of remifentanil. As a result, while pharmacodynamically identical to midazolam, remimazolam is metabolized by ester hydrolysis and subsequently its elimination is rapid and predictable. The present review discusses the two drugs in detail with a particular emphasis on their potential role in moderate and deep sedation.


PeerJ ◽  
2021 ◽  
Vol 9 ◽  
pp. e11175
Author(s):  
Preeti Manandhar ◽  
Bridin Patricia Murnion ◽  
Natasha L. Grimsey ◽  
Mark Connor ◽  
Marina Santiago

Background Pregabalin and gabapentin improve neuropathic pain symptoms but there are emerging concerns regarding their misuse. This is more pronounced among patients with substance use disorder, particularly involving opioids. Co-ingestion of gabapentinoids with opioids is increasingly identified in opioid related deaths, however, the molecular mechanism behind this is still unclear. We have sought to determine whether pregabalin or gabapentin directly modulates acute μ receptor signaling, or μ receptor activation by morphine. Methods The effects of pregabalin and gabapentin were assessed in HEK 293 cells stably transfected with the human μ receptor. Their effect on morphine induced hyperpolarization, cAMP production and ERK phosphorylation were studied using fluorescent-based membrane potential assay, bioluminescence based CAMYEL assay and ELISA assay, respectively. Pregabalin/gabapentin effects on morphine-induced hyperpolarization were also investigated in AtT20 cells. Results Pregabalin or gabapentin (1 µM, 100 µM each) did not activate the µ receptor or affect K channel activation or ERK phosphorylation produced by morphine. Neither drug affected the desensitization of K channel activation produced by prolonged (30 min) application of morphine. Gabapentin (1 µM, 100 µM) and pregabalin (1 µM) did not affect inhibition of forskolin-stimulated cAMP production by morphine. However, pregabalin (100 µM) potentiated forskolin mediated cAMP production, although morphine still inhibited cAMP levels with a similar potency to control. Discussion Pregabalin or gabapentin did not activate or modulate µ receptor signaling in three different assays. Our data do not support the hypothesis that gabapentin or pregabalin augment opioid effects through direct or allosteric modulation of the µ receptor. Pregabalin at a high concentration increases cAMP production independent of morphine. The mechanism of enhanced opioid-related harms from co-ingestion of pregabalin or gabapentin with opioids needs further investigation.


2021 ◽  
Author(s):  
Amy Alder

<b>Chronic pain is a major problem worldwide, affecting 1 in 5 New Zealanders resulting in a decreased quality of life for the patient and a large socioeconomic problem costing an estimated $13-$14.5 billion a year. Current therapeutics target the mu opioid receptor (μ receptor) and include drugs such as morphine and fentanyl. While these drugs are highly effective in the treatment of strong acute pain, their long-term use is associated with tolerance to the analgesic effects and increasing rates of side effects such as respiratory depression and constipation. Due to their high abuse liability, they are also known to cause dependence and addiction when prescribed for extended periods. This is believed to have played a role in the opioid crisis in the United States and highlights the need for improved therapeutics for the treatment of chronic pain. </b><p><br></p><p>One mechanism that has been proposed to generate μ receptor agonists for the treatment of chronic pain with reduced analgesic tolerance and safer side effects is the development of G-protein biased agonists. Such agonists selectively activate the canonical G-protein signalling to a greater extent than the non-canonical β-arrestin2 pathway. This is based on previous work in β-arrestin2 knockout mice where the antinociceptive effects were increased, while side effects, including respiratory depression, tolerance, and constipation are reduced, increasing the therapeutic window. In this thesis, we aimed to assess the anti-nociceptive and side effect behavioural profiles of two novel μ receptor agonists, kurkinol (bias = 0.14) and kurkinorin (bias = 0.57), with a varying bias for the G-protein pathway to assess the role of this paradigm. </p><p><br></p> Evaluation of the behavioural profile of kurkinol and kurkinorin revealed that G-protein bias was correlated to increased anti-nociceptive potency and reduced tolerance in wildtype C57BL/6J mice. Furthermore, the anti-nociceptive potency of morphine was increased, and tolerance decreased in in β-arrestin2 knockout mice. While the level of tolerance was reduced for kurkinorin. However, in the chemotherapy-induced model of neuropathic pain, tolerance to kurkinol and kurkinorin developed at the same rate as morphine. Overall this work showed a poor correlation between G-protein bias and therapeutic window. With the G-protein selective kurkinol inducing worse respiratory depression, constipation, and motor coordination impairment compared to kurkinorin. Interestingly, respiratory depressive and constipation effects of kurkinol were not prevented in the β-arrestin2 knockout mice indicating that they are induced through the G-protein pathway. <p><br></p><p>These results highlight the change that has occurred in the biased agonism field over the last 4 years, with the lack of reproducibility of key experiments and poor translation of G-protein biased μ receptor agonists resulting in improved therapeutic windows both clinically and pre-clinically. Moreover, recent research has shown that pathway efficacy (i.e. partial agonism) and not G-protein bias is responsible for the behavioural profiles of compounds previously identified as G-protein biased. We, therefore, decided to further investigate the cell signalling profiles of our two novel agonists to assess them for partial agonism and to assess downstream signalling molecules activated by G-protein and β-arrestin2. </p><div><br></div> This revealed cell-specific inhibition of membrane hyperpolarisation in Hek293 and CHO cells stably expressing the human μ receptor, with kurkinol found to be the most potent in both cell lines, followed by kurkinorin, morphine, and [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO). However, no differences were identified between the μ receptor agonists in the activation of the inwardly rectifying channels in the CHO cell line. The assessment of pCREB (phosphorylated cAMP response-element binding protein) as a β-arrestin2 dependent pathway revealed poor activation by kurkinorin while kurkinol was a potent activator. Bias factors generated from this data showed poor correlations to therapeutic windows. While the differences om CREB phosphorylation was shown to have a stronger correlation to therapeutic windows generated from the behavioural data. <p><br></p><p>Overall this thesis has identified kurkinorin as a μ receptor agonist that induces potent anti-nociception with reduced side effects, without strong-G-protein bias. We also show that the highly selective μ receptor agonist kurkinol has improved anti-nociception with a worse side effect profile adding to the growing body of literature showing bias is not a good predictor in its current state. Furthermore, the discrepancies between cell lines, differential activation of subcellular pathways, and lack of reproducibility between bias equations indicate that the field has massively oversimplified a complex system. Which has, most likely, resulted in the poor translation of in vitro bias factors to clinically available μ receptor agonists for chronic pain. </p>


2021 ◽  
Author(s):  
Amy Alder

<b>Chronic pain is a major problem worldwide, affecting 1 in 5 New Zealanders resulting in a decreased quality of life for the patient and a large socioeconomic problem costing an estimated $13-$14.5 billion a year. Current therapeutics target the mu opioid receptor (μ receptor) and include drugs such as morphine and fentanyl. While these drugs are highly effective in the treatment of strong acute pain, their long-term use is associated with tolerance to the analgesic effects and increasing rates of side effects such as respiratory depression and constipation. Due to their high abuse liability, they are also known to cause dependence and addiction when prescribed for extended periods. This is believed to have played a role in the opioid crisis in the United States and highlights the need for improved therapeutics for the treatment of chronic pain. </b><p><br></p><p>One mechanism that has been proposed to generate μ receptor agonists for the treatment of chronic pain with reduced analgesic tolerance and safer side effects is the development of G-protein biased agonists. Such agonists selectively activate the canonical G-protein signalling to a greater extent than the non-canonical β-arrestin2 pathway. This is based on previous work in β-arrestin2 knockout mice where the antinociceptive effects were increased, while side effects, including respiratory depression, tolerance, and constipation are reduced, increasing the therapeutic window. In this thesis, we aimed to assess the anti-nociceptive and side effect behavioural profiles of two novel μ receptor agonists, kurkinol (bias = 0.14) and kurkinorin (bias = 0.57), with a varying bias for the G-protein pathway to assess the role of this paradigm. </p><p><br></p> Evaluation of the behavioural profile of kurkinol and kurkinorin revealed that G-protein bias was correlated to increased anti-nociceptive potency and reduced tolerance in wildtype C57BL/6J mice. Furthermore, the anti-nociceptive potency of morphine was increased, and tolerance decreased in in β-arrestin2 knockout mice. While the level of tolerance was reduced for kurkinorin. However, in the chemotherapy-induced model of neuropathic pain, tolerance to kurkinol and kurkinorin developed at the same rate as morphine. Overall this work showed a poor correlation between G-protein bias and therapeutic window. With the G-protein selective kurkinol inducing worse respiratory depression, constipation, and motor coordination impairment compared to kurkinorin. Interestingly, respiratory depressive and constipation effects of kurkinol were not prevented in the β-arrestin2 knockout mice indicating that they are induced through the G-protein pathway. <p><br></p><p>These results highlight the change that has occurred in the biased agonism field over the last 4 years, with the lack of reproducibility of key experiments and poor translation of G-protein biased μ receptor agonists resulting in improved therapeutic windows both clinically and pre-clinically. Moreover, recent research has shown that pathway efficacy (i.e. partial agonism) and not G-protein bias is responsible for the behavioural profiles of compounds previously identified as G-protein biased. We, therefore, decided to further investigate the cell signalling profiles of our two novel agonists to assess them for partial agonism and to assess downstream signalling molecules activated by G-protein and β-arrestin2. </p><div><br></div> This revealed cell-specific inhibition of membrane hyperpolarisation in Hek293 and CHO cells stably expressing the human μ receptor, with kurkinol found to be the most potent in both cell lines, followed by kurkinorin, morphine, and [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO). However, no differences were identified between the μ receptor agonists in the activation of the inwardly rectifying channels in the CHO cell line. The assessment of pCREB (phosphorylated cAMP response-element binding protein) as a β-arrestin2 dependent pathway revealed poor activation by kurkinorin while kurkinol was a potent activator. Bias factors generated from this data showed poor correlations to therapeutic windows. While the differences om CREB phosphorylation was shown to have a stronger correlation to therapeutic windows generated from the behavioural data. <p><br></p><p>Overall this thesis has identified kurkinorin as a μ receptor agonist that induces potent anti-nociception with reduced side effects, without strong-G-protein bias. We also show that the highly selective μ receptor agonist kurkinol has improved anti-nociception with a worse side effect profile adding to the growing body of literature showing bias is not a good predictor in its current state. Furthermore, the discrepancies between cell lines, differential activation of subcellular pathways, and lack of reproducibility between bias equations indicate that the field has massively oversimplified a complex system. Which has, most likely, resulted in the poor translation of in vitro bias factors to clinically available μ receptor agonists for chronic pain. </p>


2021 ◽  
Author(s):  
Amy Alder

<b>Chronic pain is a major problem worldwide, affecting 1 in 5 New Zealanders resulting in a decreased quality of life for the patient and a large socioeconomic problem costing an estimated $13-$14.5 billion a year. Current therapeutics target the mu opioid receptor (μ receptor) and include drugs such as morphine and fentanyl. While these drugs are highly effective in the treatment of strong acute pain, their long-term use is associated with tolerance to the analgesic effects and increasing rates of side effects such as respiratory depression and constipation. Due to their high abuse liability, they are also known to cause dependence and addiction when prescribed for extended periods. This is believed to have played a role in the opioid crisis in the United States and highlights the need for improved therapeutics for the treatment of chronic pain. </b><p><br></p><p>One mechanism that has been proposed to generate μ receptor agonists for the treatment of chronic pain with reduced analgesic tolerance and safer side effects is the development of G-protein biased agonists. Such agonists selectively activate the canonical G-protein signalling to a greater extent than the non-canonical β-arrestin2 pathway. This is based on previous work in β-arrestin2 knockout mice where the antinociceptive effects were increased, while side effects, including respiratory depression, tolerance, and constipation are reduced, increasing the therapeutic window. In this thesis, we aimed to assess the anti-nociceptive and side effect behavioural profiles of two novel μ receptor agonists, kurkinol (bias = 0.14) and kurkinorin (bias = 0.57), with a varying bias for the G-protein pathway to assess the role of this paradigm. </p><p><br></p> Evaluation of the behavioural profile of kurkinol and kurkinorin revealed that G-protein bias was correlated to increased anti-nociceptive potency and reduced tolerance in wildtype C57BL/6J mice. Furthermore, the anti-nociceptive potency of morphine was increased, and tolerance decreased in in β-arrestin2 knockout mice. While the level of tolerance was reduced for kurkinorin. However, in the chemotherapy-induced model of neuropathic pain, tolerance to kurkinol and kurkinorin developed at the same rate as morphine. Overall this work showed a poor correlation between G-protein bias and therapeutic window. With the G-protein selective kurkinol inducing worse respiratory depression, constipation, and motor coordination impairment compared to kurkinorin. Interestingly, respiratory depressive and constipation effects of kurkinol were not prevented in the β-arrestin2 knockout mice indicating that they are induced through the G-protein pathway. <p><br></p><p>These results highlight the change that has occurred in the biased agonism field over the last 4 years, with the lack of reproducibility of key experiments and poor translation of G-protein biased μ receptor agonists resulting in improved therapeutic windows both clinically and pre-clinically. Moreover, recent research has shown that pathway efficacy (i.e. partial agonism) and not G-protein bias is responsible for the behavioural profiles of compounds previously identified as G-protein biased. We, therefore, decided to further investigate the cell signalling profiles of our two novel agonists to assess them for partial agonism and to assess downstream signalling molecules activated by G-protein and β-arrestin2. </p><div><br></div> This revealed cell-specific inhibition of membrane hyperpolarisation in Hek293 and CHO cells stably expressing the human μ receptor, with kurkinol found to be the most potent in both cell lines, followed by kurkinorin, morphine, and [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO). However, no differences were identified between the μ receptor agonists in the activation of the inwardly rectifying channels in the CHO cell line. The assessment of pCREB (phosphorylated cAMP response-element binding protein) as a β-arrestin2 dependent pathway revealed poor activation by kurkinorin while kurkinol was a potent activator. Bias factors generated from this data showed poor correlations to therapeutic windows. While the differences om CREB phosphorylation was shown to have a stronger correlation to therapeutic windows generated from the behavioural data. <p><br></p><p>Overall this thesis has identified kurkinorin as a μ receptor agonist that induces potent anti-nociception with reduced side effects, without strong-G-protein bias. We also show that the highly selective μ receptor agonist kurkinol has improved anti-nociception with a worse side effect profile adding to the growing body of literature showing bias is not a good predictor in its current state. Furthermore, the discrepancies between cell lines, differential activation of subcellular pathways, and lack of reproducibility between bias equations indicate that the field has massively oversimplified a complex system. Which has, most likely, resulted in the poor translation of in vitro bias factors to clinically available μ receptor agonists for chronic pain. </p>


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