Mirogabalin Decreases Pain-like Behaviours and Improves Opioid and Ketamine Antinociception in a Mouse Model of Neuropathic Pain

Neuropathic pain remains a difficult clinical challenge due to its diverse aetiology and complex pathomechanisms, which are yet to be fully understood. Despite the variety of available therapies, many patients suffer from ineffective pain relief; hence, the search for more efficacious treatments continues. The new gabapentinoid, mirogabalin has recently been approved for clinical use. Although its main mechanism of action occurs at the α2σ-1 and α2σ-2 subunits of calcium channels and is well documented, how the drug affects the disturbed neuropathic interactions at the spinal cord level has not been clarified, which is crucial information from a clinical perspective. The findings of our study suggest that several indirect mechanisms may be responsible for the beneficial analgesic effect of mirogabalin. This is the first study to report that mirogabalin enhances the mRNA expression of spinal antinociceptive factors, such as IL-10 and IL-18BP, and reduces the concentration of the pronociceptive substance P. Importantly, mirogabalin improves the morphine-, buprenorphine-, oxycodone-, and ketamine-induced antinociceptive effects in a neuropathic pain model. Our findings support the hypothesis that enhancing opioid and ketamine analgesia by combining these drugs with mirogabalin may represent a new strategy for the effective pharmacotherapy of neuropathic pain.

Bifunctional Opioid/Melanocortin Peptidomimetics for Use in Neuropathic Pain: Variation in the Type and Length of the Linker Connecting the Two Pharmacophores

Based on the mechanism of neuropathic pain induction, a new type of bifunctional hybrid peptidomimetics was obtained for potential use in this type of pain. Hybrids consist of two types of pharmacophores that are connected by different types of linkers. The first pharmacophore is an opioid agonist, and the second pharmacophore is an antagonist of the pronociceptive system, i.e., an antagonist of the melanocortin-4 receptor. The results of tests in acute and neuropathic pain models of the obtained compounds have shown that the type of linker used to connect pharmacophores had an effect on antinociceptive activity. Peptidomimetics containing longer flexible linkers were very effective at low doses in the neuropathic pain model. To elucidate the effect of linker lengths, two hybrids showing very high activity and two hybrids with lower activity were further tested for affinity for opioid (mu, delta) and melanocortin-4 receptors. Their complexes with the target receptors were also studied by molecular modelling. Our results do not show a simple relationship between linker length and affinity for particular receptor types but suggest that activity in neuropathic pain is related to a proper balance of receptor affinity rather than maximum binding to any or all of the target receptors.

Antinociceptive Investigations of Niranthin in Complete Freund’s Adjuvant-induced Chronic Pain in Mice

The main objectives of the present work are to determine the clinical effect of niranthin on visceral or somatic inflammatory pain. The study was performed to determine the effects of niranthin on visceral or somatic inflammatory hypersensitivity of adult Swiss albino mice by using complete Freund’s adjuvant (CFA) induced pain model. The effect of CFA injection was determined after 24 hours of injection by using an aesthesiometer such as Von Frey filaments to evaluate tactile acetone-evoked cooling and thermal sensitivity. We used a digital Plethysmometer to measure paw edema. Single dose of niranthin intraperitoneal injection (5 & 10 mg/kg) was injected into mice having CFA-induced mechanical hypersensitivity and after 30 minutes of administration, reduced mechanical hypersensitivity was observed. In addition, niranthin also reduced acetone-evoked hypersensitivity within 4 hours. Compared to DMSO, niranthin was most highly active to reduce CFA-induced paw edema. To reduce mechanical hypersensitivity, multiple doses of niranthin (bis in die (b.i.d.)) from 1st - 5th day and b.i.d. day 9th and 10th) were given and remarkable results were observed such as did not cause tolerance in multiple dosing and significantly reduced in CFA induced hypersensitivity. This work reported niranthin having antinociceptive activity and indicated that niranthin is conventionally active in the management of persistent pain.

Abnormal Ca2+ Signals in Reactive Astrocytes as a Common Cause of Brain Diseases

In pathological brain conditions, glial cells become reactive and show a variety of responses. We examined Ca2+ signals in pathological brains and found that reactive astrocytes share abnormal Ca2+ signals, even in different types of diseases. In a neuropathic pain model, astrocytes in the primary sensory cortex became reactive and showed frequent Ca2+ signals, resulting in the production of synaptogenic molecules, which led to misconnections of tactile and pain networks in the sensory cortex, thus causing neuropathic pain. In an epileptogenic model, hippocampal astrocytes also became reactive and showed frequent Ca2+ signals. In an Alexander disease (AxD) model, hGFAP-R239H knock-in mice showed accumulation of Rosenthal fibers, a typical pathological marker of AxD, and excessively large Ca2+ signals. Because the abnormal astrocytic Ca2+ signals observed in the above three disease models are dependent on type II inositol 1,4,5-trisphosphate receptors (IP3RII), we reanalyzed these pathological events using IP3RII-deficient mice and found that all abnormal Ca2+ signals and pathologies were markedly reduced. These findings indicate that abnormal Ca2+ signaling is not only a consequence but may also be greatly involved in the cause of these diseases. Abnormal Ca2+ signals in reactive astrocytes may represent an underlying pathology common to multiple diseases.

Investigating the anti-cocaine, anti-nociceptive properties and side effects of MP1104, a novel mixed opioid receptor agonist

<p>Rationale: Drug addiction is a chronic, relapsing disease with great socioeconomic and morbidity costs. There are limited treatments, with no Food and Drug Administration approved pharmacotherapies available for psychostimulant addiction. In addition, the use of prescription opioid medications has reached epidemic proportions in the world. More than 40,000 deaths from prescription opioid overdose was reported in USA alone in the year 2017. There is an urgent need for the development of effective, non-addictive pain medications and addiction treatments. The opioid receptors play an important role in the modulation of pain and addiction. Mu opioid receptor (MOPr) agonists are widely used to treat pain, however, can also induce respiratory depression, tolerance and addiction. In contrast, drugs activating the kappa opioid receptor (KOPr) attenuate the rewarding properties of drugs, hence are promising non-addictive analgesics. However, side effects like aversion, sedation, anxiety and depression limit their clinical utility. Delta opioid receptor (DOPr) agonists have rewarding, anti-nociceptive and anti-depressive properties, but can also cause seizures. We hypothesise that development of mixed opioid receptor ligands may have therapeutic properties with reduced side effects. Therefore, this thesis evaluated MP1104, a potent mixed opioid receptor agonist, with full efficacy at all three receptors and 3- and 13-fold higher binding affinity for KOPr compared to MOPr and DOPr, respectively. MP1104 was evaluated for the ability to modulate cocaine-induced behaviours, the anti-nociceptive effects and side effects. Methods: Male Sprague-Dawley rats were used to investigate the effects of acute MP1104 treatment on cocaine self-administration and drug seeking behaviour. To determine the mechanism, the modulatory effect of MP1104 on dopamine transporter (DAT) function was assessed using rotating disk electrode voltammetry to measure dopamine uptake in rat dorsal striatum (dStr) and nucleus accumbens (NAc) tissue. Evaluation of side effects included sedation (spontaneous locomotor activity), anxiety (elevated plus maze (EPM)), aversion (conditioned place aversion (CPA)) and depression (forced swim tests (FST)) in rats. The anti-nociceptive effects were measured in the warm-water tail withdrawal assay in rats and male C57BL/6 mice. Acute and chronic administration of MP1104 were evaluated in the paclitaxel-induced neuropathic pain model in mice. Results: In rats trained to self-administer cocaine, acute MP1104 (0.3 and 1 mg/kg, i.p.) administration reduced cocaine-primed reinstatement of drug seeking behaviour and caused a significant downward shift in the cocaine dose-response curve. The anti-cocaine effects exerted by MP1104 are in part due to increased dopamine uptake by DAT in the NAc, which was KOPr-mediated. In the warm-water tail withdrawal assay in rats, acute administration of MP1104 (0.3 and 0.6 mg/kg, i.p.) was 4 times longer acting (8 h) than morphine (2 h). These effects were both KOPr and DOPr dependent. In the dose-response tail withdrawal assay, MP1104 was found to be potent in both rats (ED₅₀ = 0.58 mg/kg, s.c.) and mice (ED₅₀ = 0.35 mg/kg, s.c.). In the paclitaxel-induced neuropathic pain model, mice treated with MP1104 showed potent reductions in both mechanical (ED₅₀ = 0.449 mg/kg, s.c.) and cold (ED₅₀ = 0.479 mg/kg, s.c.) allodynia compared to morphine. Following chronic daily administration of the ED₈₀ dose, MP1104 (1.2 mg/kg, i.p.) was more potent than morphine in reducing mechanical and cold allodynia. Surprisingly, MP1104 reversed responding back to baseline (non-disease) levels. The most remarkable finding was that MP1104, unlike morphine did not produce tolerance when administered chronically. When the side effects of MP1104 were evaluated in rats, no significant anxiogenic effects were seen in the EPM, nor pro-depressive effects in the FST, nor aversion in CPA tests in rats. Furthermore, pre-treatment with a DOPr antagonist, led to MP1104 producing aversive effects. This data suggests that the DOPr agonist actions of MP1104 attenuate the KOPr-mediated aversive effects of MP1104. However, at higher doses, MP1104 (1 mg/kg, i.p.) was found to be sedative. Conclusions: MP1104 exerts potent anti-cocaine properties in self-administration tests. The reduced cocaine reward is at least in part due to the ability of MP1104 to modulate DAT function by increasing dopamine uptake in the NAc. MP1104 is also a potent and long-lasting anti-nociceptive agent in rats. Significantly, when evaluated in a chronic neuropathic pain model, MP1104 was potent with no tolerance to the anti-nociceptive effects observed. Moreover, MP1104 showed fewer side effects with reduced sedative effects and no observed anxiety, aversive, nor pro-depressive effects, unlike pure KOPr agonists. This data supports the therapeutic development of mixed opioid receptor agonists, particularly mixed KOPr/DOPr agonists as non-addictive pain medications and anti-cocaine pharmacotherapies with fewer side effects.</p>

Investigating the anti-cocaine, anti-nociceptive properties and side effects of MP1104, a novel mixed opioid receptor agonist

<p>Rationale: Drug addiction is a chronic, relapsing disease with great socioeconomic and morbidity costs. There are limited treatments, with no Food and Drug Administration approved pharmacotherapies available for psychostimulant addiction. In addition, the use of prescription opioid medications has reached epidemic proportions in the world. More than 40,000 deaths from prescription opioid overdose was reported in USA alone in the year 2017. There is an urgent need for the development of effective, non-addictive pain medications and addiction treatments. The opioid receptors play an important role in the modulation of pain and addiction. Mu opioid receptor (MOPr) agonists are widely used to treat pain, however, can also induce respiratory depression, tolerance and addiction. In contrast, drugs activating the kappa opioid receptor (KOPr) attenuate the rewarding properties of drugs, hence are promising non-addictive analgesics. However, side effects like aversion, sedation, anxiety and depression limit their clinical utility. Delta opioid receptor (DOPr) agonists have rewarding, anti-nociceptive and anti-depressive properties, but can also cause seizures. We hypothesise that development of mixed opioid receptor ligands may have therapeutic properties with reduced side effects. Therefore, this thesis evaluated MP1104, a potent mixed opioid receptor agonist, with full efficacy at all three receptors and 3- and 13-fold higher binding affinity for KOPr compared to MOPr and DOPr, respectively. MP1104 was evaluated for the ability to modulate cocaine-induced behaviours, the anti-nociceptive effects and side effects. Methods: Male Sprague-Dawley rats were used to investigate the effects of acute MP1104 treatment on cocaine self-administration and drug seeking behaviour. To determine the mechanism, the modulatory effect of MP1104 on dopamine transporter (DAT) function was assessed using rotating disk electrode voltammetry to measure dopamine uptake in rat dorsal striatum (dStr) and nucleus accumbens (NAc) tissue. Evaluation of side effects included sedation (spontaneous locomotor activity), anxiety (elevated plus maze (EPM)), aversion (conditioned place aversion (CPA)) and depression (forced swim tests (FST)) in rats. The anti-nociceptive effects were measured in the warm-water tail withdrawal assay in rats and male C57BL/6 mice. Acute and chronic administration of MP1104 were evaluated in the paclitaxel-induced neuropathic pain model in mice. Results: In rats trained to self-administer cocaine, acute MP1104 (0.3 and 1 mg/kg, i.p.) administration reduced cocaine-primed reinstatement of drug seeking behaviour and caused a significant downward shift in the cocaine dose-response curve. The anti-cocaine effects exerted by MP1104 are in part due to increased dopamine uptake by DAT in the NAc, which was KOPr-mediated. In the warm-water tail withdrawal assay in rats, acute administration of MP1104 (0.3 and 0.6 mg/kg, i.p.) was 4 times longer acting (8 h) than morphine (2 h). These effects were both KOPr and DOPr dependent. In the dose-response tail withdrawal assay, MP1104 was found to be potent in both rats (ED₅₀ = 0.58 mg/kg, s.c.) and mice (ED₅₀ = 0.35 mg/kg, s.c.). In the paclitaxel-induced neuropathic pain model, mice treated with MP1104 showed potent reductions in both mechanical (ED₅₀ = 0.449 mg/kg, s.c.) and cold (ED₅₀ = 0.479 mg/kg, s.c.) allodynia compared to morphine. Following chronic daily administration of the ED₈₀ dose, MP1104 (1.2 mg/kg, i.p.) was more potent than morphine in reducing mechanical and cold allodynia. Surprisingly, MP1104 reversed responding back to baseline (non-disease) levels. The most remarkable finding was that MP1104, unlike morphine did not produce tolerance when administered chronically. When the side effects of MP1104 were evaluated in rats, no significant anxiogenic effects were seen in the EPM, nor pro-depressive effects in the FST, nor aversion in CPA tests in rats. Furthermore, pre-treatment with a DOPr antagonist, led to MP1104 producing aversive effects. This data suggests that the DOPr agonist actions of MP1104 attenuate the KOPr-mediated aversive effects of MP1104. However, at higher doses, MP1104 (1 mg/kg, i.p.) was found to be sedative. Conclusions: MP1104 exerts potent anti-cocaine properties in self-administration tests. The reduced cocaine reward is at least in part due to the ability of MP1104 to modulate DAT function by increasing dopamine uptake in the NAc. MP1104 is also a potent and long-lasting anti-nociceptive agent in rats. Significantly, when evaluated in a chronic neuropathic pain model, MP1104 was potent with no tolerance to the anti-nociceptive effects observed. Moreover, MP1104 showed fewer side effects with reduced sedative effects and no observed anxiety, aversive, nor pro-depressive effects, unlike pure KOPr agonists. This data supports the therapeutic development of mixed opioid receptor agonists, particularly mixed KOPr/DOPr agonists as non-addictive pain medications and anti-cocaine pharmacotherapies with fewer side effects.</p>

Identification of potentially painful disc fissures in magnetic resonance images using machine-learning modelling

Purpose It is suggested that non-specific low back pain (LBP) can be related to nerve ingrowth along granulation tissue in disc fissures, extending into the outer layers of the annulus fibrosus. Present study aimed to investigate if machine-learning modelling of magnetic resonance imaging (MRI) data can classify such fissures as well as pain, provoked by discography, with plausible accuracy and precision. Methods The study was based on previously collected data from 30 LBP patients (age = 26–64 years, 11 males). Pressure-controlled discography was performed in 86 discs with pain-positive discograms, categorized as concordant pain-response at a pressure ≤ 50 psi and for each patient one negative control disc. The CT-discograms were used for categorization of fissures. MRI values and standard deviations were extracted from the midsagittal part and from 5 different sub-regions of the discs. Machine-learning algorithms were trained on the extracted MRI markers to classify discs with fissures extending into the outer annulus or not, as well as to classify discs as painful or non-painful. Results Discs with outer annular fissures were classified in MRI with very high precision (mean of 10 repeated testings: 99%) and accuracy (mean: 97%) using machine-learning modelling, but the pain model only demonstrated moderate diagnostic accuracy (mean accuracy: 69%; precision: 71%). Conclusion The present study showed that machine-learning modelling based on MRI can classify outer annular fissures with very high diagnostic accuracy and, hence, enable individualized diagnostics. However, the model only demonstrated moderate diagnostic accuracy regarding pain that could be assigned to either a non-sufficient model or the used pain reference.

Understanding the Mechanism of Action of NAI-112, a Lanthipeptide with Potent Antinociceptive Activity

NAI-112, a glycosylated, labionine-containing lanthipeptide with weak antibacterial activity, has demonstrated analgesic activity in relevant mouse models of nociceptive and neuropathic pain. However, the mechanism(s) through which NAI-112 exerts its analgesic and antibacterial activities is not known. In this study, we analyzed changes in the spinal cord lipidome resulting from treatment with NAI-112 of naive and in-pain mice. Notably, NAI-112 led to an increase in phosphatidic acid levels in both no-pain and pain models and to a decrease in lysophosphatidic acid levels in the pain model only. We also showed that NAI-112 can form complexes with dipalmitoyl-phosphatidic acid and that Staphylococcus aureus can become resistant to NAI-112 through serial passages at sub-inhibitory concentrations of the compound. The resulting resistant mutants were phenotypically and genotypically related to vancomycin-insensitive S. aureus strains, suggesting that NAI-112 binds to the peptidoglycan intermediate lipid II. Altogether, our results suggest that NAI-112 binds to phosphate-containing lipids and blocks pain sensation by decreasing levels of lysophosphatidic acid in the TRPV1 pathway.