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Opioid tolerance remains a challenging problem, which limits prolonged drug usage in clinics. Previous studies have shown a fundamental role of platelet-derived growth factor receptor β submit (PDGFRβ) in morphine tolerance. The aim of this study was to investigate the mechanisms of spinal PDGFRβ activation in morphine tolerance.
In the lumbar spinal cord dorsal horn, release of afferent nerve glutamate activates the neurons that relay information about injury pain. Here, we examined the effects of protein tyrosine kinase (PTK) inhibition on NMDA receptor NR1 subunit protein expression and subcellular localization in an acute experimental arthritis model. PTK inhibitors genistein and lavendustin A reduced cellular histological translocation of NMDA NR1 in the spinal cord occurring after the inflammatory insult and the nociceptive behavioral responses to heat. The PTK inhibitors were administered into lumbar spinal cord by microdialysis, and secondary heat hyperalgesia was determined using the Hargreaves test. NMDA NR1 cellular protein expression and nuclear translocation were determined by immunocytochemical localization with light and electron microscopy, as well as with Western blot analysis utilizing both C- and N-terminal antibodies. Genistein and lavendustin A (but not inactive lavendustin B or diadzein) effectively reduced (i) pain related behavior, (ii) NMDA NR1 subunit expression increases in spinal cord, and (iii) the shift of NR1 from a cell membrane to a nuclear localization. Genistein pre-treatment reduced these events that occur within 4 h after inflammatory insult to the knee joint with kaolin and carrageenan (k/c). Cycloheximide reduced glutamate activated upregulation of NR1 content confirming synthesis of new protein in response to the inflammatory insult. In addition to this data, genistein or staurosporin inhibited upregulation of NMDA NR1 protein and nuclear translocation after treatment of human neuroblastoma clonal cell cultures (SH-SY5Y) with glutamate or NMDA (4 h). These studies provide evidence that inflammatory activation of peripheral nerves initiates increase in NMDA NR1 in the spinal cord coincident with development of pain related behaviors through glutamate non-receptor, PTK dependent cascades.
Calcitonin gene related peptide (CGRP) monoclonal antibodies (mAbs) have been the first class of specifically developed preventive treatments for migraine. Clinical trials data suggest superiority of the CGRP mAbs to placebo in terms of prevention of migraine symptoms, migraine-specific quality of life and headache related disability. Treatment-related side effects overall did not differ significantly from placebo and discontinuation rate due to side effects has been low across the clinical trials, perhaps in view of their peripheral mode of action. Along with their route and frequency of administration, these novel class of drugs may constitute an improvement compared with the established arsenal of migraine treatments. Erenumab is a fully human antibody and the only mAb acting on the CGRP pathway by blocking its receptor. It is the first of the CGRP mAb class approved by the US Food and Drug Administration (May 2018) and the European Medicines Agency (July 2018). Erenumab exists in two different doses (70 mg and 140 mg) and it is administered with monthly subcutaneous injections. This review summarises erenumab pharmacological characteristics, clinical trials data, focusing on the potential role of this treatment in clinical practice.
It is thought that endogenous cannabinoids have a role in the analgesia induced by specific forms of stress. We examined if the role of endogenous cannabinoids is also dependent upon the mode of nociception, and whether this could be altered by drugs which block their enzymatic degradation. In C57BL/6 mice, restraint stress produced analgesia in the hot plate and plantar tests, two thermal pain assays that engage distinct supraspinal and spinal nociceptive pathways. Stress-induced analgesia in the hot plate test was abolished by pre-treatment with the opioid receptor antagonist naltrexone but was unaffected by the cannabinoid receptor antagonist AM281. By contrast, stress-induced analgesia in the plantar test was abolished by pre-treatment with naltrexone plus AM281, but not by either antagonist individually. Remarkably, inhibiting the breakdown of endocannabinoids, with the dual fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) inhibitor JZL195, rescued stress-induced analgesia in the hotplate test when endogenous opioid signalling was blocked by naltrexone. Furthermore, JZL195 recruited analgesia induced by sub-threshold restraint stress in both thermal pain assays. These findings indicate the role of endocannabinoids in stress-induced analgesia differs with the type of thermal pain behaviour. However, by inhibiting their breakdown, endocannabinoids can be recruited to substitute for endogenous opioid signalling when their activity is blocked, indicating a degree of redundancy between opioid and cannabinoid systems. Together these data suggest targeting endocannabinoid breakdown could provide an alternative, or adjuvant to mainstream analgesics such as opioids.
Chemotherapy-induced neuropathic pain (CINP) in both sexes compromises many current chemotherapeutics and lacks a FDA-approved therapy. We recently identified the sphingosine-1-phosphate receptor subtype 1 (S1PR1) and A3 adenosine receptor subtype (A3AR) as novel targets for therapeutic intervention. Our work in male rodents using paclitaxel, oxaliplatin and bortezomib showed robust inhibition of CINP with either S1PR1 antagonists or A3AR agonists. The S1PR1 functional antagonist FTY720 (Gilenya®) is FDA approved for treating multiple sclerosis and selective A3AR agonists are in advanced clinical trials for cancer and inflammatory disorders, underscoring the need for their expedited trials in CINP patients as chemotherapy adjuncts. Our findings reveal that S1PR1 antagonists and A3AR agonists mitigate paclitaxel and oxaliplatin CINP in female and male rodents, but failed to block or reverse bortezomib-induced neuropathic pain (BINP) in females. Although numerous mechanisms likely underlie these differences, we focused on receptor levels. We found that BINP in male rats, but not female rats, was associated with increased expression of A3AR in spinal cord dorsal horn, while S1PR1 levels were similar in both sexes. Thus, alternative mechanisms beyond receptor expression may account for sex differences in response to S1PR1 antagonists. Morphine and duloxetine, both clinical analgesics, reversed BINP in female mice, demonstrating that the lack of response is specific to S1PR1 and A3AR agents. Our findings suggest that A3AR- and S1PR1-based therapies are not viable approaches in preventing and treating BINP in females and should inform future clinical trials of these drugs as adjuncts to chemotherapy. SUMMARY:: We have found that there are sexually dimorphic responses to S1PR1 antagonists and A3AR agonists for the treatment of bortezomib-induced neuropathic pain.
Pain in response to various types of acute injury can be a protective stimulus to prevent the organism from using the injured part and allow tissue repair and healing. On the other hand, neuropathic pain, defined as 'pain caused by a lesion or disease of the somatosensory nervous system', is a debilitating pathology. The TRPA1 neurons in the Dorsal Root Ganglion (DRG) respond to reactive oxygen species (ROS) and induce pain. In acute nerve injury and inflammation, macrophages infiltrating the site of injury undergo an oxidative burst, and generate ROS that promote tissue repair and induce pain via TRPA1. The latter discourages using the injured limb, with a lack of movement helping wound healing. In chronic inflammation caused by diabetes, cancer etc., ROS levels increase systemically and modulate TRPA1 neuronal functions and cause debilitating neuropathic pain. It is important to distinguish between drug targets that elicit protective vs. debilitating pain when developing effective drugs for neuropathic pain. In this context, the connection of the Angiotensin type 2 receptor (ATR) to neuropathic pain presents an interesting dilemma. Several lines of evidence show that ATR activation promotes anti-inflammatory and anti-nociceptive signaling, tissue repair, and suppresses ROS in chronic inflammatory models. Conversely, some studies suggest that ATR antagonists are anti-nociceptive and therefore ATR is a drug target for neuropathic pain. However, ATR expression in nociceptive neurons is lacking, indicating that neuronal ATR is not involved in neuropathic pain. It is also important to consider that Novartis terminated their phase II clinical trial (EMPHENE) to validate that ATR antagonist EMA401 mitigates post-herpetic neuralgia. This trial, conducted in Australia, United Kingdom, and a number of European and Asian countries in 2019, was discontinued due to pre-clinical drug toxicity data. Moreover, early data from the trial did not show statistically significant positive outcomes. These facts suggest that may ATR not be the proper drug target for neuropathic pain in humans and its inhibition can be harmful.
Apelin is an endogenous neuropeptide, which has wide distribution in central nervous system and peripheral tissues. Pyroglutamyl apelin-13 [(pyr)apelin-13] is the major apelin isoform in human plasma. However, the role of peripheral (pyr)apelin-13 in pain regulation is unknown. The aim of this study was to investigate the effect of the peripheral injection of (pyr)apelin-13 on inflammatory pain using the formalin test as well as to evaluate the mechanistic basis for the effect. Results showed intravenous (i.v.) injection of (pyr)apelin-13 (10, 20 mg/kg) to significantly decrease licking/biting time during the second phase of the mouse formalin test. In contrast, i.v. injection of apelin-13 had no influence on such effect. Intramuscular injection of (pyr)apelin-13 reduced licking/biting time during the second phase only at a dose of 20 mg/kg. The antinociception of i.v. (pyr)apelin-13 was antagonized by the apelin receptor (APJ, angiotensin II receptor-like 1) antagonist, apelin-13(F13A). (pyr)apelin-13 (i.v. 20 mg/kg) markedly upregulated and gene expression in the prefrontal cortex, whereas gene expression was downregulated. The antinociception of i.v. (pyr)apelin-13 was blocked by the opioid receptor antagonist naloxone and the specific kappa opioid receptor (KOR) antagonist nor-binaltorphimine (nor-BNI). (pyr)Apelin-13 upregulated the dynorphin and KOR gene expression and protein levels in the mouse prefrontal cortex, not in striatum. (pyr)Apelin-13 did not influence the motor behavior. Our results demonstrate that i.v. injection of (pyr)apelin-13 induces antinociception via the KOR in the inflammatory pain mouse model.
Legalization of cannabis encourages the development of specific cultivars to treat disease such as neuropathic pain. Because of the large number of cultivars, it is necessary to prioritize extracts before proceeding to clinical trials.
Migraine is the most common acute primary headache in children and adolescents. In 2014, topiramate became the first preventive drug for migraine, approved by the Food and Drug Administration (FDA) for adolescents. This meta-analysis was aimed to evaluate the efficacy and safety of topiramate in the prevention of pediatric migraine. We searched the PubMed, EMBASE, Cochrane Library, and Chinese National Knowledge Infrastructure (CNKI) databases up to June 2019 for eligible randomized controlled trials (RCTs). The primary outcomes were mean migraine days per month, ≥50% reduction rate, and Pediatric Migraine Disability Assessment Scale (PedMIDAS) scores. RevMan5.3 software was performed for statistical analysis. Overall, 5 RCTs recruiting 531 patients (6-17 years of age) were included in the meta-analysis. The target dose of topiramate was 2 mg/kg (the maintenance phase was 12 weeks), 2-3 mg/kg, 50 mg/day, and 100 mg/day (maintaining for 16 weeks), respectively, in the included studies. Our results demonstrate that participants receiving topiramate had a significant advantage in remitting the monthly migraine days than those receiving placebo, with a mean difference (MD) of -0.78 ( = 531; 95% CI, -1.23 to -0.32; = 3.37; = 0.0008). Topiramate could also reduce the mean PedMIDAS scores ( = 238; 95% CI, -16.53 to -0.49; = 2.43; = 0.04). However, there was no significant difference in the percentage of patients experiencing a ≥50% reduction in monthly headache days between topiramate and placebo groups ( = 531; 95% CI, 0.94-1.77; = 1.58; = 0.11). Topiramate was associated with higher rates of side effects such as weight decrease ( = 395; 95% CI, 2.73-22.98; = 3.81; < 0.01) and paresthesia ( = 531; 95% CI, 3.05-13.18; = 4.94; < 0.01). Topiramate can significantly decrease monthly headache days and migraine-related burden in migraine patients <18 years old. However, it failed to increase 50% response rate. Adverse events seem to be more frequent in topiramate-treated children.
Opioid-induced hyperalgesia is a state of nociceptive sensitization secondary to opioid administration. The objective of this meta-analysis was to test the hypothesis that high-dose intraoperative opioids contribute to increased postoperative pain and hyperalgesia when compared with a low-dose regimen in patients under general anaesthesia.