Synthesis, characterization, and biological study of new synthetic opioid hemorphin-4 peptides containing sterically restricted nonnatural amino acids.

Some new hemorphin-4 analogs with structures of Xxx-Pro-Trp-Thr-NH2 and Tyr-Yyy-Trp-Thr-NH2, where Xxx is 2-amino-3-(4-hydroxy-2,6-dimethylphenyl)propanoic acid or 2-amino-3-(4-dibenzylamino-2,6-dimethylphenyl)propanoic acid, and Yyy is (2S,4S)-4-amino-pyrrolidine-2-carboxylic acid, were synthesized and characterized by electrochemical and spectral analyses. In vivo anticonvulsant and antinociceptive activities of peptide derivatives were studied after intracerebroventricular injection in mice. The therapeutic effects of the modified peptides on seizures and pain in mice were evaluated to provide valuable insights into the potential applications of the novel compounds. Electrochemical characterization showed that the compounds behave as weak protolytes and that they are in a soluble, stable molecular form at physiological pH values. The antioxidant activity of the peptides was evaluated with voltammetric analyses, which were confirmed by applying the 2,2-Diphenyl-1-picrylhydrazyl method. The compounds showed satisfactory results regarding their structural stability, reaching the desired centers for the manifestation of biological activity without hydrolysis processes at 37°C and physiological pH. Dm-H4 and H4-P1 exhibited 100% and 83% potency to suppress the psychomotor seizures in the 6-Hz test compared to 67% activity of H4. Notably, only the H4-P1 had efficacy in blocking the tonic component in the maximal electroshock test with a potency comparable to H4. All investigated peptides containing unnatural conformationally restricted amino acids showed antinociceptive effects. The analogs Db-H4 and H4-P1 showed the most pronounced and long-lasting effect in both experimental models of pain induced by thermal and chemical stimuli. Dm-H4 produced a dose-dependent thermal antinociception and H4-P2 inhibited only formalin-induced pain behavior.

Evaluation of Habenaria aitchisonii Reichb. for antioxidant, anti-inflammatory, and antinociceptive effects with in vivo and in silico approaches.

Habenaria aitchisonii Reichb was analyzed in this research, including its chemical composition and its in vitro antioxidant, anti-inflammatory, acute oral toxicity, and antinociceptive activity. The chloroform and ethyl acetate fractions were found to be the most powerful based on in vitro antioxidant, anti-inflammatory, and analgesic assays. The acute oral toxicity of the crude methanolic extract was determined before in vivo studies. The acetic acid and formalin tests were used to measure the antinociceptive effect, and the potential mechanisms involved in antinociception were explored. The carrageenan-induced paw edema test was used to examine the immediate anti-inflammatory effect, and many phlogistic agents were used to determine the specific mechanism. Furthermore, for ex vivo activities, the mice were sacrificed, the forebrain was isolated, and the antioxidant levels of glutathione (GSH), superoxide dismutase (SOD), thiobarbituric acid reactive substances (TBARS) and catalase (CAT) were estimated using a UV spectrophotometer. No toxicity was seen at oral dosages up to 3,000 mg/kg. The antinociceptive impact was much higher than the standard drug. Both the inflammatory and neurogenic phases of the formalin experiment revealed an analgesic effect in the chloroform and ethyl acetate fractions. In carrageenan anti-inflammatory assays, the chloroform fraction (Ha.Chf) was the most potent fraction. We further studied the GC-MS of crude plant extract and found a total of 18 compounds. In the anti-inflammatory mechanism, it was observed that the Ha.Chf inhibits the COX-2 as well as 5-LOX pathways. The results exhibited that this species is a good source of phytocomponents like germacrone, which can be employed as a sustainable and natural therapeutic agent, supporting its traditional use in folk medicine for inflammatory conditions and pain.

In Vitro and In Vivo Pharmacological Profiles of LENART01, a Dermorphin-Ranatensin Hybrid Peptide.

Diverse chemical and pharmacological strategies are currently being explored to minimize the unwanted side effects of currently used opioid analgesics while achieving effective pain relief. The use of multitarget ligands with activity at more than one receptor represents a promising therapeutic approach. We recently reported a bifunctional peptide-based hybrid LENART01 combining dermorphin and ranatensin pharmacophores, which displays activity to the mu-opioid receptor (MOR) and dopamine D2 receptor (D2R) in rat brains and spinal cords. In this study, we investigated the in vitro binding and functional activities to the human MOR and the in vivo pharmacology of LENART01 in mice after subcutaneous administration. In vitro binding assays showed LENART01 to bind and be selective to the human MOR over the other opioid receptor subtypes and delta, kappa and nociceptin receptors. In the [35S]GTPγS binding assay, LENART01 acted as a potent and full agonist to the human MOR. In mice, LENART01 produced dose-dependent antinociceptive effects in formalin-induced inflammatory pain, with increased potency than morphine. Antinociceptive effects were reversed by naloxone, indicating MOR activation in vivo. Behavioral studies also demonstrated LENART01's properties to induce less adverse effects without locomotor dysfunction and withdrawal syndrome compared to conventional opioid analgesics, such as morphine. LENART01 is the first peptide-based MOR-D2R ligand known to date and the first dual MOR-dopamine D2R ligand for which in vivo pharmacology is reported with antinociceptive efficacy and reduced opioid-related side effects. Our current findings may pave the way to new pain therapeutics with limited side effects in acute and chronic use.

Low-Efficacy Mu Opioid Agonists as Candidate Analgesics: Effects of Novel C-9 Substituted Phenylmorphans on Pain-Depressed Behavior in Mice.

Low efficacy mu opioid receptor (MOR) agonists may serve as novel candidate analgesics with improved safety relative to high-efficacy opioids. This study used a recently validated assay of pain-depressed behavior in mice to evaluate a novel series of MOR-selective C9-substituted phenylmorphan opioids with graded MOR efficacies. Intraperitoneal injection of dilute lactic acid (IP acid) served as a noxious stimulus to depress locomotor activity by mice in an activity chamber composed of two compartments connected by an obstructed door. Behavioral measures included (1) crosses between compartments (vertical activity over the obstruction) and (2) movement counts quantified as photobeam breaks summed across compartments (horizontal activity). Each drug was tested alone and as a pretreatment to IP acid. A charcoal-meal test and whole-body-plethysmography assessment of breathing in 5% CO2 were also used to assess gastrointestinal (GI) inhibition and respiratory depression, respectively. IP acid produced a concentration-dependent depression in crosses and movement that was optimally alleviated by intermediate- to low-efficacy phenylmorphans with sufficient efficacy to produce analgesia with minimal locomotor disruption. Follow-up studies with two low-efficacy phenylmorphans (JL-2-39 and DC-1-76.1) indicated that both drugs produced naltrexone-reversible antinociception with a rapid onset and a duration of ~1hr. Potency of both drugs increased when behavior was depressed by a lower IP-acid concentration, and neither drug alleviated behavioral depression by a non-pain stimulus (IP lithium chloride). Both drugs produced weaker GI inhibition and respiratory depression than fentanyl and attenuated fentanyl-induced GI inhibition and respiratory depression. Results support further consideration of selective, low-efficacy MOR agonists as candidate analgesics. Significance Statement This study used a novel set of mu opioid receptor (MOR)-selective opioids with graded MOR efficacies to examine the lower boundary of MOR efficacy sufficient to relieve pain-related behavioral depression in mice. Two novel low-efficacy opioids (JL-2-39, DC-1-76.1) produced effective antinociception with improved safety relative to higher- or lower-efficacy opioids, and results support further consideration of these and other low-efficacy opioids as candidate analgesics.

Evaluation of physical variables, thermal nociceptive threshold testing and pharmacokinetics during placement of transdermal buprenorphine matrix-type patch in healthy adult horses.

Background: Matrix type transdermal buprenorphine patches have not been investigated in horses and may provide an effective means of providing continuous pain control for extended period and eliminating venous catheterization. Objective: Assessment of the physiological variables (heart rate, respiratory rate, body temperature) and thermal nociceptive threshold testing, and describing the pharmacokinetic profile of transdermal buprenorphine matrix-type patch (20 µg h-1 and 40 µg h-1 dosing) in healthy adult horses. Study design: Randomised experimental study with a Latin-square design. Methods: Six adult healthy horses received each of the three treatments with a minimum 10 day washout period. BUP0 horses did not receive a patch (control). BUP20 horses received one patch (20 µg h-1) applied on the ventral aspect of the tail base resulting in a dose of 0.03-0.04 µg kg-1 h-1. BUP40 horses received two patches placed alongside each other (40 µg h-1) on the tail base resulting in a dose of 0.07-0.09 µg kg-1 h-1. Whole blood samples (for determination of buprenorphine concentration), physiological variables and thermal threshold testing were performed before (0 h) and at 2, 4, 8, 12, 16, 24, 32, 40, 48, 56, 64, 72, and 96 h after patch application. The patches were removed 72 h following placement and were analyzed for residual buprenorphine content. Results: Between the three groups, there was no change in physiological variables across timepoints as compared to baseline (p > 0.1). With the higher dose, there was a significant increase in thermal thresholds from baseline values from 2 h until 48 h and these values were significantly higher than the group receiving the lower patch dose for multiple timepoints up to 40 h. 40 µg h-1 patch led to consistent measurable plasma concentrations starting at 2 h up to 96 h, with the mean plasma concentrations of > 0.1 ng/ml from 4 h to 40 h. Conclusions: 20 µg h-1 and 40 µg h-1 patch doses were well tolerated by all horses. At higher dose, plasma buprenorphine concentrations were more consistently measurable and blunted thermal thresholds for 48 h vs. 32 h with 20 µg h-1 dosing as compared to control.

Effects of acute cannabidiol on behavior and the endocannabinoid system in HIV-1 Tat transgenic female and male mice.

Background: Some evidence suggests that cannabidiol (CBD) has potential to help alleviate HIV symptoms due to its antioxidant and anti-inflammatory properties. Here we examined acute CBD effects on various behaviors and the endocannabinoid system in HIV Tat transgenic mice. Methods: Tat transgenic mice (female/male) were injected with CBD (3, 10, 30 mg/kg) and assessed for antinociception, activity, coordination, anxiety-like behavior, and recognition memory. Brains were taken to quantify endocannabinoids, cannabinoid receptors, and cannabinoid catabolic enzymes. Additionally, CBD and metabolite 7-hydroxy-CBD were quantified in the plasma and cortex. Results: Tat decreased supraspinal-related nociception and locomotion. CBD and sex had little to no effects on any of the behavioral measures. For the endocannabinoid system male sex was associated with elevated concentration of the proinflammatory metabolite arachidonic acid in various CNS regions, including the cerebellum that also showed higher FAAH expression levels for Tat(+) males. GPR55 expression levels in the striatum and cerebellum were higher for females compared to males. CBD metabolism was altered by sex and Tat expression. Conclusion: Findings indicate that acute CBD effects are not altered by HIV Tat, and acute CBD has no to minimal effects on behavior and the endocannabinoid system.

Differential Effect of Chronic Morphine on Neuronal Degeneration in Male vs. Female Mice.

Opioid abuse in the United States has been increasing at an alarming rate over the past 20 years. Sex differences are documented for the rates of opioid-related overdoses, abuse patterns, and drug-induced physiological effects. In our previous study, we demonstrated that chronic oxycodone administration in young female rats is associated with neurodegeneration in the brain. Males and females are susceptible to neurodegenerative diseases via differing mechanisms. To investigate whether opioid exposure affects males and females differently, we treated young mice with chronic morphine. We observed that females had stronger antinociceptive responses to acute morphine and showed a delayed development of tolerance. Males had a higher basal Bax level in the brain that correlated with a higher number of apoptotic cells. Morphine increased Bax levels in both males and females without affecting the numbers of apoptotic cells. Morphine increased activated caspase 3 in axons and increased the MBP level in plasma only in females, suggesting a demyelination process. Our data suggest that males are protected from demyelination by having a higher basal BDNF level. Altogether, our results suggest that males and females have different molecular signaling underlying their patterns in the development of morphine tolerance and drug-induced neuronal degeneration.

A conjugate vaccine strategy that induces protective immunity against arecoline.

Betel-quid chewing addiction is the leading cause of oral submucous fibrosis and oral cancer, resulting in significant socio-economic burdens. Vaccination may serve as a promising potential remedy to mitigate the abuse and combat accidental overdose of betel nut. Hapten design is the crucial factor to the development of arecoline vaccine that determines the efficacy of a candidate vaccine. Herein, we reported that two kinds of novel arecoline-based haptens were synthesized and conjugated to Bovine Serum Albumin (BSA) to generate immunogens, which generated antibodies with high affinity for arecoline but reduced binding for guvacoline and no affinity for arecaidine or guvacine. Notably, vaccination with Arec-N-BSA, which via the N-position on the tetrahydropyridine ring (tertiary amine group), led to a higher antibody affinity compared to Arec-CONH-BSA, blunted analgesia and attenuated hypothermia for arecoline.

Antinociceptive and Cardiorespiratory Effects of a Single Dose of Dexmedetomidine in Laboratory Mice Subjected to Craniotomy under General Anaesthesia with Isoflurane and Carprofen or Meloxicam.

Pain refinement represents an important aspect of animal welfare in laboratory animals. Refining analgesia regimens in mice undergoing craniotomy has been sparsely investigated. Here, we sought to investigate the effect of dexmedetomidine in combination with other analgesic drugs on intraoperative anti-nociceptive effects and cardiorespiratory stability. All mice were anaesthetised with isoflurane and received local lidocaine infiltration at the surgical site. Mice were randomised into treatment groups consisting of either carprofen 5 mg kg-1 or meloxicam 5 mg kg-1 with or without dexmedetomidine 0.1 mg kg-1 administered subcutaneously. Intra-anaesthetic heart rates, breathing rates, isoflurane requirements, and arterial oxygen saturations were continuously monitored. We found that administration of dexmedetomidine significantly improved heart and breathing rate stability during two of four noxious stimuli (skin incision and whisker stimulation) compared to non-dexmedetomidine-treated mice and lowered isoflurane requirements throughout anaesthesia by 5-6%. No significant differences were found between carprofen and meloxicam. These results demonstrate that dexmedetomidine reduces nociception and provides intra-anaesthetic haemodynamic and respiratory stability in mice. In conclusion, the addition of dexmedetomidine to anaesthetic regimes for craniotomy offers a refinement over current practice for laboratory mice.

Comparison of the µ-opioid receptor antagonists methocinnamox (MCAM) and naloxone to reverse and prevent the ventilatory depressant effects of fentanyl, carfentanil, 3-methylfentanyl, and heroin in male rats.

The number of opioid overdose deaths has increased significantly over the past decade. The life-threatening effect of opioids is hypoventilation that can be reversed by the µ-opioid receptor (MOR) antagonist naloxone; however, because of the very short duration of action of naloxone, re-emergence of MOR agonist-induced hypoventilation can occur, requiring additional doses of naloxone. The MOR antagonist methocinnamox (MCAM) antagonizes hypoventilation by the non-morphinan fentanyl and the morphinan heroin in laboratory animals with an unusually long duration of action. Whole-body plethysmography was used to compare the potency and effectiveness of MCAM and naloxone for preventing and reversing hypoventilation by fentanyl, heroin, and the ultra-potent and longer-acting fentanyl analogs carfentanil and 3-methylfentanyl in male rats breathing normal air. Sessions comprised a 45-minute habituation period followed by intravenous (i.v.) administration of saline or an acute dose of MOR agonist. The rank order of potency to decrease ventilation was 3-methylfentanyl > carfentanil > fentanyl > heroin. MCAM (0.0001-0.1 mg/kg) and naloxone (0.0001-0.01 mg/kg) dose-dependently reversed hypoventilation by 3-methylfentanyl (0.01 mg/kg), carfentanil (0.01 mg/kg), fentanyl (0.1 mg/kg), or heroin (3.2 mg/kg). For prevention studies, MCAM, naloxone, or vehicle was administered i.v. 22, 46, or 70 hours prior to a MOR agonist. When administered 22 hours earlier, MCAM (0.1-1.0 mg/kg) but not naloxone (1.0 mg/kg) prevented hypoventilation by each MOR agonist. This study demonstrates the effectiveness of MCAM to reverse and prevent hypoventilation by MOR agonists including ultra-potent fentanyl analogs that have a long duration of action. Significance Statement The number of opioid overdose deaths increased over the past decade despite the availability of antagonists that can prevent and reverse the effects of opioids. This study demonstrates the effectiveness and long duration of action of the µ-opioid receptor (MOR) antagonist methocinnamox (MCAM) for reversing and preventing hypoventilation by MOR agonists including ultra-potent fentanyl analogs. These results provide support for the notion that MCAM has the potential to positively impact the ongoing opioid crisis by reversing and preventing opioid overdose.

Subcutaneous hydromorphone hydrochloride provides antinociception with transient adverse effects in four-toed hedgehogs (Atelerix albiventris).

OBJECTIVE: To evaluate the efficacy and safety of hydromorphone administered SC in four-toed hedgehogs (Atelerix albiventris). ANIMALS: 12 healthy adult hedgehogs. METHODS: Hedgehogs underwent 2 randomized, blinded, placebo-controlled, complete crossover studies. Hind limb withdrawal latencies in response to an acute thermal noxious stimulus were measured to evaluate the antinociceptive efficacy of hydromorphone. Baseline latencies were obtained prior to injection and collected again at 0.5, 1, 2, 4, and 6 hours following injection. Based on pilot studies, single doses of SC hydromorphone at 0.15 and 0.3 mg/kg were evaluated for efficacy in crossover trials. Safety of single (0.15 and 0.3 mg/kg) and multiple doses of hydromorphone (0.3 mg/kg, SC, q 4 h, for 3 doses) was also assessed. In addition to monitoring behavior during latency measurements, animals were evaluated for overt sedation and daily changes in food intake, body weight, and running wheel activity for 6 days after injection to evaluate for adverse effects. RESULTS: Hydromorphone at 0.15 mg/kg provided antinociception lasting < 4 hours, and 0.3 mg/kg provided antinociception lasting < 6 hours. Hydromorphone produced transient abnormal behaviors at both doses, including vocalization, chewing motions of the jaw, and paw raising. There were no statistically significant differences in body weight or running wheel activity between treatments for single or multiple doses of hydromorphone. Three doses of 0.3 mg/kg hydromorphone (q 4 h) produced a statistically significant decrease (median, -9.7%; range, -64% to 10%) in 6-day total food intake. CLINICAL RELEVANCE: Subcutaneous hydromorphone (0.15 to 0.3 mg/kg) can be used for short-term antinociception with transient adverse effects in hedgehogs.

Investigation of anti-nociceptive, anti-inflammatory potential and ADMET studies of pure compounds isolated from Isodon rugosus Wall. ex Benth.

The strong ethnopharmacological utilization of Isodon rugosus Wall. Ex. Benth is evident in the treatment of several types of pain and inflammation, including toothache, earache, abdominal pain, gastric pain, and generalized body pain and inflammation. Based on this background, the antinociceptive effects of the crude extract, various fractions, and essential oil have been reported previously. In this research work, we isolate and characterize pure bioactive compounds from I. rugosus and evaluate possible mechanisms using various in vivo and in vitro models. The pure compounds were analyzed for analgesic and anti-inflammatory activities through various assays. The column chromatography of the chloroform fraction of I. rugosus led to the identification of two pure compounds, i.e., 1 and 2. Compound 1 demonstrated notable inhibition (62% writhing inhibition, 72.77% COX-2 inhibition, and 76.97% 5-LOX inhibition) and anti-inflammatory potential (>50% paw edema inhibition at various intervals). The possible mechanism involved in antinociception was considered primarily, a concept that has already been elucidated through the application of naloxone (an antagonist of opioid receptors). The involvement of adrenergic receptors was investigated using a hot plate model (an adrenergic receptor antagonist). The strong ethnomedicinal analgesic background of I. rugosus, supported by previous reports and current observations, leads to the conclusion that I. rugosus is a potential source of antinociceptive and anti-inflammatory bioactive compounds. It may be concluded from the results that the isolated analgesic compounds of I. rugosus may be a possible alternative remedy for pain and inflammation management with admirable efficacy and safety profiles.

Effects of Repeated Treatment with the Monoacylglycerol Lipase Inhibitor MJN110 on Pain-Related Depression of Nesting and Cannabinoid 1 Receptor Function in Male and Female Mice.

MJN110 inhibits the enzyme monoacylglycerol lipase (MAGL) to increase levels of the endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG), an endogenous high-efficacy agonist of cannabinoid 1 and 2 receptors (CB1/2R). MAGL inhibitors are under consideration as candidate analgesics, and we reported previously that acute MJN110 produced partial antinociception in an assay of pain-related behavioral depression in mice. Given the need for repeated analgesic administration in many pain patients and the potential for analgesic tolerance during repeated treatment, this study examined antinociceptive effects of repeated MJN110 on pain-related behavioral depression and CB1R-mediated G-protein function. Male and female ICR mice were treated daily for 7 days in a 2x2 design with (a) 1.0 mg/kg/day MJN110or its vehicle followed by (b) intraperitoneal injection of dilute lactic acid (IP acid) or its vehicle as a visceral noxious stimulus to depress nesting behavior. After behavioral testing, G-protein activity was assessed in lumbar spinal cord andfive brain regions using an assay of CP55,940-stimulated [35S]GTPÉ£S activation. As reported previously, acute MJN110 produced partial but significant relief of IP acid-induced nesting depression on Day 1. After 7 days, MJN110 continued to produce significant but partial antinociception in males, while antinociceptive tolerance developed in females. Repeated MJN110 also produced modest decreases in maximum levels of CP55,940-induced [35S]GTPÉ£S binding in spinal cord and most brain regions. These results indicate that repeated treatment with a relatively low antinociceptive MJN110 dose produces only partial and sex-dependent transient antinociception associated with the emergence of CB1R desensitization in this model of IP acid-induced nesting depression. Significance Statement The drug MJN110 inhibits monoacylglycerol lipase (MAGL) to increase levels of the endogenous cannabinoid 2-arachidonoylglycerol and produce potentially useful therapeutic effects including analgesia. This study used an assay of pain-related behavioral depression in mice to show that repeated MJN110 treatment produced (1) weak but sustained antinociception in male mice, (2) antinociceptive tolerance in females, and (3) modest cannabinoid-receptor desensitization that varied by region and sex. Antinociceptive tolerance may limit the utility of MJN110 for treatment of pain.

Effect of the Location of Tetanic Stimulation on Autonomic Responses: A Randomized Cross-Over Pilot Study.

Background: Tetanic stimuli are used as standardized noxious inputs to investigate nociception. Previous studies have applied tetanic stimuli to various anatomical locations without validating that the resulting physiological responses were independent of the location where tetanic stimuli were applied. Our aim was to investigate the effects of three anatomical tetanic stimulus application sites on physiological variables reflecting autonomic nervous system responses as measured by photoplethysmography (PPG). Methods: Under general anesthesia, a five second, 100 hertz, 70 milliamp tetanic stimulus was applied to the ulnar nerve, medial side of the tibia, and thorax (T5 dermatome) (N=12). The effect of tetanic stimuli on PPG-derived variables (AC, DC, and ACDC) and pulse rate at each stimulus location was determined using repeated-measures analysis of variance (ANOVA) followed by Dunnett's post hoc test. Maximum tetanic stimulus-induced changes in PPG-derived variables and pulse rates were compared among the three stimulus locations using ANOVA. Results: AC and ACDC values of PPG decreased, and the DC values of PPG increased in response to tetanic stimuli-induced vasoconstriction at each location (p<0.001 for all). The maximum changes in the AC, ACDC, and DC values did not differ between locations (p=NS). There were no significant changes in pulse rate (p=NS). Conclusion: The results showed that tetanic stimulation at either of these three locations provides the same autonomic nervous system responses, as measured by PPG. Clinical Trial Registration: ClinicalTrials.gov; NCT03648853.

Efficacy and safety of subcutaneous methadone hydrochloride in four-toed hedgehogs (Atelerix albiventris).

OBJECTIVE: To evaluate the efficacy and safety of SC methadone in four-toed hedgehogs. ANIMALS: 9 to 12 healthy adult four-toed hedgehogs (7 to 9 males and 3 females). METHODS: Hedgehogs underwent 3 randomized, blinded, placebo-controlled, complete crossover studies. Hind limb withdrawal latencies in response to an acute thermal noxious stimulus were measured to evaluate the antinociceptive efficacy of methadone. Single doses of SC methadone were evaluated at 0.5 and 1 mg/kg for dose-dependent effects. Additionally, methadone (1.5 mg/kg) was administered at different concentrations to assess the effect of injection volume on antinociceptive efficacy. Finally, the safety of multiple doses of methadone (1.5 mg/kg, SC, q 2 h, for 3 doses) was also evaluated. In addition to monitoring behavior during latency measurements, animals were assessed for overt sedation. Food intake, body weight, and running wheel activity were assessed daily for 6 days following methadone administration to evaluate for adverse effects. RESULTS: Methadone at 1 and 1.5 mg/kg provided antinociception lasting < 2 hours, and injection volume had no significant effect on efficacy. Methadone at 0.5 mg/kg did not induce antinociception. Methadone produced transient abnormal behaviors in all hedgehogs, with more animals affected at the 1.5-mg/kg dose. Behaviors included periods of standing motionless, vocalization, chewing motions, and paw raising. Single- or multiple-dose administration of methadone had no significant effect on total food intake, body weight, or running wheel activity. CLINICAL RELEVANCE: The results of this study provide additional information on providing analgesia to hedgehogs. Subcutaneous methadone (1 to 1.5 mg/kg) can be used for short-term antinociception in hedgehogs.

A Novel Leu-Enkephalin Prodrug Produces Pain-Relieving and Antidepressant Effects.

Persistent pain is a significant healthcare problem with limited treatment options. The high incidence of comorbid chronic pain and depression significantly reduces life quality and complicates the treatment of both conditions. Antidepressants are less effective for pain and depression than for depression alone and they induce severe side effects. Opioids are highly efficacious analgesics, but rapid development of tolerance, dependence, and debilitating side effects limit their efficacy and safe use. Leucine-enkephalin (Leu-ENK), the endogenous delta opioid receptor agonist, controls pain and mood and produces potent analgesia with reduced adverse effects compared to conventional opioids. High proteolytic instability, however, makes Leu-ENK ineffective after systemic administration and limits its clinical usefulness. KK-103, a Leu-ENK prodrug, was developed to overcome these limitations of Leu-ENK via markedly increased plasma stability in mice. We showed rapid and substantially increased systemic adsorption and blood plasma exposure of KK-103 compared to Leu-ENK. We also observed brain uptake of radiolabeled KK-103 after systemic administration, indicating a central effect of KK-103. We then established KK-103's prolonged antinociceptive efficacy in the ramped hot plate and formalin test. In both models, KK-103 produced a comparable dose to the maximum antinociceptive-effect relationship. The pain-alleviating effect of KK-103 primarily resulted from activating the delta opioid receptor after the likely conversion of KK-103 to Leu-ENK in vivo. Finally, KK-103 produced an antidepressant-like activity comparable to the antidepressant desipramine, but with minimal gastrointestinal inhibition and no incidence of sedation.

Endomorphin-2 analogs with C-terminal esterification display potent antinociceptive effects in the formalin pain test in mice.

Previously, we have investigated three C-terminal esterified endomorphin-2 (EM-2) analogs EM-2-Me, EM-2-Et and EM-2-Bu with methyl, ethyl and tert-butyl ester modifications, respectively. These analogs produced significant antinociception in acute pain at the spinal and supraspinal levels, with reduced tolerance and gastrointestinal side effects. The present study was undertaken to determine the analgesic effects and opioid mechanisms of these three analogs in the formalin pain test. Our results demonstrated that intracerebroventricular (i.c.v.) administration of 0.67-20 nmol EM-2 analogs EM-2-Me, EM-2-Et and EM-2-Bu produced dose-dependent antinociceptive effects in both phase Ⅰ and phase Ⅱ of formalin pain. EM-2-Me and EM-2-Bu displayed more potent antinociception than morphine. Especially, EM-2-Bu exhibited the highest antinociception in phase Ⅱ of formalin pain, with the ED50 value being 2.1 nmol. Naloxone (80 nmol, i.c.v.) completely antagonized the antinociceptive effects of EM-2-Me, EM-2-Et and EM-2-Bu (20 nmol, i.c.v.) in both phase I and phase Ⅱ of formalin pain, suggesting a central opioid mechanism. Nevertheless, the antinociception induced by EM-2-Me might be involved in the release of dynorphin A, which subsequently acted on κ- opioid receptor. EM-2-Bu produced the antinociception probably by the direct activation of both µ- and δ-opioid receptors. EM-2-Me, EM-2-Et and EM-2-Bu also produced significant analgesic effects after peripheral administration, and the central opioid receptors were involved. Furthermore, EM-2-Bu had no influence on the locomotor activity after i.c.v. injection. The present investigation demonstrated that C-terminal esterified modifications of EM-2 will be beneficial for developing novel therapeutics in formalin pain.

Antinociceptive action of cannabidiol on thermal sensitivity and post-operative pain in male and female rats.

This study investigated the antinociceptive potential of cannabidiol (CBD) in male and female Wistar rats. The assessment and analysis included tail withdrawal to thermal stimulation (tail flick test) and mechanical allodynia induced by plantar incision injury (von Frey test). CBD reduced acute thermal sensitivity in uninjured animals and post-operative mechanical allodynia in males and females. In the tail flick test, CBD 30 mg/kg i.p. was required to induce antinociception in males. During the proestrus phase, females did not show a statistically significant antinociceptive response to CBD treatment despite a noticeable trend. In contrast, in a separate group of rats tested during the late diestrus phase, antinociception varied with CBD dosage and time. In the post-operative pain model, CBD at 3 mg/kg decreased mechanical allodynia in males. Similarly, this dose reduced allodynia in females during proestrus. However, in females during late diestrus, the lower dose of CBD (0.3 mg/kg) reduced mechanical allodynia, although the latency to onset of the effect was slower (90 min). The effectiveness of a 10-fold lower dose of CBD during the late diestrus stage in females suggests that ovarian hormones can influence the action of CBD. While CBD has potential for alleviating pain in humans, personalized dosing regimens may need to be developed to treat pain in women.

Synthesis, molecular docking, electrochemical and fluorimetric analysis of new caffeic and cinnamic acid-conjugated hemorphin derivatives designed as potential anticonvulsant and antinociceptive agents.

Based on the pharmacophore model of opioid receptors, our team recently synthesized a series of short-chain hemorphin peptide analogs containing non-natural amino acids. They demonstrated anticonvulsant and antinociceptive activity with low neurotoxicity. In the present study, a series of novel bioconjugates of N-modified hemorphin analogs containing second pharmacophore cinnamic acids (CA) or caffeic (KA) were synthesized by a traditional solid-phase Fmoc chemistry method for peptide synthesis. Electrochemical and fluorimetric analysis, in vivo anticonvulsant and antinociceptive activity in mice were conducted on the compounds. The three CA acid- (H4-CA, H5-CA, and H7-CA) and three KA acid- (H4-KA, H5-KA, and H7-KA) conjugated hemorphin derivatives exhibited potency at the highest doses of 2 µg/5 µl, administered by intracerebroventricular (icv) mode, against seizure spread in the maximal electroshock test (MES) in mice. The KA-conjugated H5-KA derivate, at the lowest dose, was the only compound that suppressed clonic seizures in the subcutaneous pentylenetetrazol (scPTZ) test. Except for the H5-CA, all tested CA acid- and KA acid-conjugated peptide derivates had the potency to increase the latency for clonic seizures in a dose-dependent mode. The activity against the psychomotor seizures in the 6-Hz test was detected only for the H4-CA (0.5 µg) and H4-KA (0.5 µg and 1 µg), respectively. All investigated peptides showed a more pronounced antinociceptive effect in the "intraplantar formalin" test compared to the "hot plate" test. Shorter chain analogs showed a better antinociceptive profile against tonic pain. The data suggest a DOR and KOR-mediated mechanism of action. According to the docking analysis, H7-CA showed a different antinociceptive profile than other investigated peptides. The novel peptide derivates did not exhibit neurotoxicity in the rotarod test. Our findings suggest that conjugated CA and KA morphine peptides can be used to develop novel morphine-related analogs with anticonvulsant and antinociceptive activity.

Bromelain regulates TRP channels to induce orofacial nociception relief in adult zebrafish.

Bromelain, the main protease enzyme found in the pineapple plant (Ananas comosus), has had its antinociceptive effect previously demonstrated. This investigation aimed to appraise the role of TRP (Transient Receptor Potential) channels in the nociception-relieving effects of bromelain in the orofacial region of adult zebrafish. The animals were pretreated with bromelain (3.0, 10.0 or 30.0 mg/mL; gavage) and submitted to open field and acute orofacial (capsaicin - TRPV1 agonist, cinnamaldehyde - TRPA1 agonist or menthol - TRPM8 agonist) nociception tests. The investigation also explored the contribution of central afferent C-fibers. Naive groups were included for comparison. Bromelain did not independently affect the zebrafish movement patterns. However, bromelain decreased the nociceptive responses elicited by all three TRP channel activators. Capsazepine (TRPV1 inhibitor) and AMTB (TRPM8 inhibitor), but not HC-030031 (TRPA1 inhibitor), prevented the antinociceptive effect of bromelain. Moreover, capsaicin-induced desensitization effectively nullified the antinociceptive effect of bromelain. Collectively, these findings corroborate the therapeutic relevance of bromelain as a suppressor of orofacial nociception, which seems to be intricately connected to the modulation of TRP channels.