Isobolographic analysis of the opioid-opioid interactions in a tonic and a phasic mouse model of induced nociceptive pain

Synthesis, biological, and structural explorations of a series of μ-opioid receptor (MOR) agonists with high G protein signaling bias

Biased agonism refers to the ability of compounds to drive preferred signaling pathways and avoid adverse signaling pathways in a ligand-dependent manner for some G-protein-coupled receptors. It is thought that the separation of therapeutic efficacy (e.g., analgesia) from adverse effects (e.g., respiration depression) can be achieved through the design of biased MOR agonists and one example is the recently approved MOR biased agonist oliceridine (TRV130). However, oliceridine only demonstrates modest beneficial effects as compared to other opioids in terms of therapeutic/adverse effect balance. One possibility attributable to the modest success of oliceridine is its limited bias, and as such developing MOR ligands with a more biased agonism profile could in theory further improve the beneficial effects of the ligands. Here, we rationally designed and synthesized a series of derivatives as potent highly biased MOR agonists (19a-v) through the modification and structure-activity relationship study of TRV130. This novel synthetic molecule, LPM3480392 (19m), demonstrated improved in vitro biased agonism (EC₅₀ = 0.35 nM, Emax = 91.4%) with no measured β-arrestin recruitment (EC₅₀ > 30000 nM, Emax = 1.6%), good brain penetration (B/P ratio = 4.61, 0.25 h post-IV dosing 2.0 mg/kg), a favorable pharmacokinetic profile (distribution volume = 10766 mL/kg, t_1/2 = 1.9 h) and produced potent antinociceptive effect with reduced respiratory suppression (sO₂(%) = 92.17, 0.32 mg/kg, SC) as compared to TRV130. LPM3480392 has completed preclinical studies and is currently under clinical development (CTR20210370) as an analgesic for the treatment of moderate to severe pain.

Antinociception and less gastric injury with the dexketoprofen-tapentadol combination in mice

The purpose of this study was to evaluate the antinociceptive interaction between dexketoprofen and tapentadol in three different dose ratios, as well as the ulcerogenic activity of this combination. Dose-response curves were carried out for dexketoprofen, tapentadol, and dexketoprofen-tapentadol combinations in the acetic acid-induced writhing test in mice. On the other hand, the gastric damage of all treatments was assessed after the surgical extraction of the stomachs. Intraperitoneal administration of dexketoprofen and tapentadol induced a dose-dependent antinociceptive effect, reaching a maximal effect of about 58% and 99%, respectively. Isobolographic analysis and the interaction index showed that the three proportions produced an analgesic potentiation (synergistic interaction). Interestingly, the 1:1 and 1:3 ratios of the drugs combination produced minor gastric injury in comparison with the 3:1 proportion. Our data suggest that all proportions of the dexketoprofen-tapentadol combination produced a synergistic interaction in the acetic acid-induced visceral pain model in mice with a low incidence of gastric injury.

Analgesia additive interaction between tadalafil and morphine in an experimental animal model

Since both morphine and tadalafil have been proven to exert some of their analgesic activity through modulation of the NO-cGMP pathway, the aim of the current study is to evaluate the pharmacologic interaction between tadalafil and morphine to decrease the dose of morphine and subsequently its side effects. The assessment was carried out through isobolographic analysis relative to ED₅₀s of both morphine and tadalafil obtained by tail-flick test on BALB/c mice. Morphine and tadalafil ED₅₀s calculated from the dose-response curves were 8303 and 2080 μg/kg, respectively. The experimental ED₅₀ values of morphine and tadalafil in their mixture were 4800 and 1210 μg/kg, respectively. Those results showed an additive interaction between morphine and tadalafil presented by a total fraction value for the mixture of 1160 μg/kg. This outcome can be interpreted by the fact that both drugs share common pathways, namely, NO-cGMP and opioid receptors. As a conclusion, the morphine and tadalafil combination showed an additive effect against acute pain, which is mediated through the central nervous system, thus providing a rationale for combining them to decrease morphine dose and thus minimizing its side effects.

Magnesium Salt, a Simple Strategy to Improve Methadone Analgesia in Chronic Pain: An Isobolographic Preclinical Study in Neuropathic Mice

Analgesic efficacy of methadone in cancer and chronic non-cancer pains is greater than that of other opioids, probably because of its unique pharmacokinetics properties and also because it targets glutamatergic receptors in addition to µ-opioid receptors. However, methadone has drawbacks which are clearly related to dosing and treatment duration. The authors hypothesized that the antinociceptive efficacy of methadone could be synergistically potentiated by magnesium and copper salts in a preclinical mouse model of chronic pain, using the intraplantar formalin test as algesimetric tool. The spared nerve injury mice model was used to generate mononeuropathy. A low dose (0.25%) formalin was injected in the neuropathic limb in order to give rise only to Phase I response, resulting from direct activation by formalin of nociceptive primary afferents. Licking/biting of the formalin-injected limb was evaluated as nociceptive behavior during a 35-min observation period. Dose-response curves for intraperitoneal magnesium sulfate (10, 30, 100, and 300 mg/kg i.p.), copper sulfate (0.1, 0.3, 1, and 3 mg/kg i.p.) and methadone (0.1, 0.3, 1, and 3 mg/kg i.p.) allowed to combine them in equieffective doses and to determine their interaction by isobolographic analysis. Magnesium sulfate, copper sulfate and methadone dose-dependently decreased the nociceptive response evoked by formalin injection, the respective ED₅₀ being 76.38, 1.18, and 0.50 mg/kg i.p. Isobolographic analysis showed a superadditive interaction for magnesium and methadone. Indeed, despite that both ED₅₀ are obviously equieffective, the ED₅₀ for the MgSO4/methadone combination contained less than one third of the methadone having the ED₅₀ for methadone alone. For the CuSO₄/methadone combination, the interaction was only additive. Extrapolated to clinical settings, the results suggest that magnesium salts might be used to improve synergistically the efficacy of methadone in neuropathy, which would allow to reduce the dose of methadone and its associated side effects.

Antihyperalgesic Activity of Quillaic Acid Obtained from Quillaja Saponaria Mol

BACKGROUND

Quillaja saponaria Mol. bark contains a high concentration of triterpene saponins that have been used for centuries as a cleansing, antiinflammatory and analgesic agent in Chilean folk medicine. In earlier studies, in mice, both the anti-inflammatory as well as the antinociceptive effect of the major sapogenin, quillaic acid have been demonstrated (QA).

OBJECTIVE

To determine the antihyperalgesic effect of QA one and seven days after itpl administration of complete Freund's adjuvant (CFA) in male mice using the hot plate test in the presence of complete Freund's adjuvant (HP/CFA) as an acute and chronic skeletal muscle pain model.

METHODS

The present study evaluated the antihyperalgesic activity of QA against acute and chronic skeletal muscle pain models in mice using the hot plate test in the presence of complete Freund's adjuvant (HP/CFA), at 24 h (acute assay) and 7 days (chronic assay) , with dexketoprofen (DEX) as the reference drug.

RESULTS

In acute and chronic skeletal muscle pain assays, QA at 30 mg/kg ip elicited its maximal antihyperalgesic effects (65.0% and 53.4%) at 24 h and 7 days, respectively. The maximal effect of DEX (99.0 and 94.1 at 24 h and 7 days, respectively) was induced at 100 mg/kg.

CONCLUSION

QA and DEX elicit dose-dependent antihyperalgesic effects against acute and chronic skeletal muscle pain, but QA is more potent than DEX in the early and late periods of inflammatory pain induced by CFA.

The analgesic interaction of tramadol and morphine in rats: An isobolographic study

In order to assess possible synergistic antinociceptive interactions, the analgesic effects of intra-peritoneal tramadol and morphine administered either separately or in combination were determined using tail-flick latency test following exposure to radiant heat in rats. Groups of eight male Sprague-Dawley rats received either tramadol (3.90, 7.00, 12.50, and 22.20 mg kg^-1) and morphine (1.26, 2.25, 4.00 and 7.10 mg kg^-1) or a combination of tramadol and morphine (4 different combinations). The baseline latency was obtained before drug injection for each rat, then at 15, 30, 45, 60 and 75 min after injection. The effective dose (ED)₅₀ for either tramadol or morphine individually was 11.70 mgkg^-1 and 2.26 mg kg^-1, respectively. Based on isobolographic analysis, the ED₅₀ values obtained by drug combination were significantly less than the calculated additive values; which indicates that the co-administration of tramadol and morphine produces synergistic antinociception in the radiant heat tail-flick assay. Combination of morphine and tramadol administered intra-peritoneally can be used for the control of acute pain in rats.

The Effect of Alpha-Tocopherol on Morphine Tolerance-induced Expression of c-fos Proto-oncogene from a Biotechnological Perspective

BACKGROUND

The increase of oxidant compounds is the most well-known reasons for the tolerance to the analgesic properties of Morphine. Additionally, the production of proxy-nitrite impairs receptors, proteins and enzymes involved in the signaling pathways of analgesia, apoptosis and necrosis. Also, we revised all patents relating to opioid tolerance control methods.

OBJECTIVE

The aim of this study was to assess the effects of Alpha-tocopherol as an anti-oxidant agent to reduce Morphine tolerance.

METHOD

Forty male rats randomly divided into four groups. 10 mg/kg of morphine was injected subcutaneously to create the desired level of tolerance. After modeling, 70 mg/kg Alpha- Tocopherol was injected intraperitoneal. Also, the hot plate recorded pain threshold alterations was used to evaluate the behavioral test. All tissue samples were extracted from the spinal cord, thalamus and frontal cortex for molecular and gene expression evaluations. Also, the effect of Alpha- Tocopherol on the apoptosis and necrosis parameters was analyzed using nissl staining and tunel test.

RESULTS

The time latency results showed that there were no significant differences in the different days in groups treated with Morphine plus Alpha-Tocopherol. However, our data highlighted that the pain threshold and their time latency in respond to it had substantially increased in comparison with the control group. Furthermore, we found that the Alpha-Tocopherol obviously decreased c-fos gene expression, especially in the spinal cord.

CONCLUSION

Thus, co-administration of Alpha-Tocopherol with Morphine can decrease the adverse effects of nitrite proxy, which is released due to repeated injections of Morphine.

Outpatient intravenous multimodal elastomeric pump with methadone in ambulatory surgery

BACKGROUND AND OBJECTIVE

Analgesia in Ambulatory Surgery (AS) needs to evolve in parallel with surgical complexity. We designed a study to try to improve analgesia in painful surgery using an intravenous elastomeric pump. As a novelty, methadone was included.

PATIENTS AND METHODS

An observational study, physical status ASA I-II, underwent ambulatory surgeries with moderate-severe postoperative pain. Analgesia was administered for 48h by an intravenous multimodal elastomeric pump (methadone, tramadol, dexketoprofen and ondansetron at low doses). Visual Analogue Scale (VAS) at rest and movement were evaluated at 24 and 48h. Andersen Scale, Lattinen Test, rescue analgesia and side-effects were recorded at 24h after surgery.

RESULTS

We included 73 patients: 37% abdominal wall surgery, 30% hemorrhoidectomies and 33% perineal surgery. Median VAS score at rest and movement were 0 and 3 at 24h, and 0 and 2 at 48h. At 24h, Andersen's Scale score was ≤1 in 89%, and Lattinen Test ≤6 in 90% of patients. Rescue medication was administered in 30% of patients. Two patients had vomiting at 24 and 48h. Minor catheter and pump dysfunctions were observed in 8% of patients.

CONCLUSIONS

Multimodal analgesia with intravenous methadone administered by elastomeric perfusion at home is effective and safe. However, monitoring is needed to diagnosis dysfunction of devices.

Prevention of morphine dependence and tolerance by Nepeta menthoides was accompanied by attenuation of Nitric oxide overproduction in male mice

ETHNOPHARMACOLOGICAL RELEVANCE

Repeated administration of morphine for chronic pain leads to dependence and tolerance that limits clinical usage. Nepeta menthoides is commonly known as Iranian Ustukhuddoos and are administered in traditional medicine for gastrodynia, bone pain, blood depurative and restlessness.

AIMS OF STUDY

To investigate the effects of Nepeta menthoides on expression and acquisition of morphine dependence and tolerance in mice with regard to oxidative stress.

MATERIALS AND METHODS

Morphine dependence in mice was developed by administration of gradually increasing doses of morphine twice daily for 7 consecutive days. In experimental groups, administration of Nepeta menthoides (200 and 400mg/kg), methadone and their combination were performed 60min prior to each morphine injection (for acquisition) or the last injection of morphine on test day (for expression). Morphine tolerance was measured by the tail-immersion test before and after the administration of a single dose of morphine (100mg/kg; i.p.) on the test day (8th day). Morphine dependence was also evaluated by counting the number of jumps after the injection of naloxone (5mg/kg; i.p.).

RESULTS

Nepeta menthoides, similar to methadone, significantly prevented the development (but not the expression) of morphine dependence, tolerance, and potentiated morphine antinociception and also reduced (23.23±1.15) Nitric oxide (NO) overproduction (35.23±3.36) (in compared with naloxone group (6.3±0.52)). However, single and repeated application of the extract could not change high single-dose morphine analgesia.

CONCLUSION

It appears that Nepeta menthoides and methadone prevented morphine dependence and tolerance, partly through inhibition of the NO overproduction.

Broccoli sprouts in analgesia – preclinical in vivo studies

Broccoli sprouts produce significant and dose-dependent antinociceptive activity involving an opioid mechanism without sedative or gastric damage.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 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 (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 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 (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).