Valproate attenuates the development of morphine antinociceptive tolerance

Xenon gas as a potential treatment for opioid use disorder, alcohol use disorder, and related disorders

Xenon gas is considered to be a safe anesthetic and imaging agent. Research on its other potentially beneficial effects suggests that xenon may have broad efficacy for treating health disorders. A number of reviews on xenon applications have been published, but none have focused on substance use disorders. Accordingly, we review xenon effects and targets relevant to the treatment of substance use disorders, with a focus on opioid use disorder and alcohol use disorder. We report that xenon inhaled at subsedative concentrations inhibits conditioned memory reconsolidation and opioid withdrawal symptoms. We review work by others reporting on the antidepressant, anxiolytic, and analgesic properties of xenon, which could diminish negative affective states and pain. We discuss research supporting the possibility that xenon could prevent analgesic- or stress-induced opioid tolerance and, by so doing could reduce the risk of developing opioid use disorder. The rapid kinetics, favorable safety and side effect profiles, and multitargeting capability of xenon suggest that it could be used as an ambulatory on-demand treatment to rapidly attenuate maladaptive memory, physical and affective withdrawal symptoms, and pain drivers of substance use disorders when they occur. Xenon may also have human immunodeficiency virus and oncology applications because its effects relevant to substance use disorders could be exploited to target human immunodeficiency virus reservoirs, human immunodeficiency virus protein-induced abnormalities, and cancers. Although xenon is expensive, low concentrations exert beneficial effects, and gas separation, recovery, and recycling advancements will lower xenon costs, increasing the economic feasibility of its therapeutic use. More research is needed to better understand the remarkable repertoire of effects of xenon and its potential therapeutic applications.

A Selective GSK3β Inhibitor, Tideglusib, Decreases Intermittent Access and Binge Ethanol Self-Administration in C57BL/6J Mice

Over 10% of the US population over 12 years old meets criteria for alcohol use disorder (AUD), yet few effective, long-term treatments are currently available. Glycogen synthase kinase 3-beta (GSK3β) has been implicated in ethanol behaviours and poses as a potential therapeutic target in the treatment of AUD. Here, we investigated the preclinical evidence for tideglusib, a clinically available selective GSK3β inhibitor, in modulating chronic and binge ethanol consumption. Tideglusib decreased ethanol consumption in both a model of daily, progressive ethanol intake (two-bottle choice, intermittent ethanol access) and binge-like drinking behaviour (drinking in the dark) without effecting water intake. With drinking in the dark, tideglusib was more potent in males (ED50 = 64.6, CI = 58.9-70.8) than females (ED50 = 79.4, CI = 70.8-93.3). Further, we found tideglusib had no effect on ethanol pharmacokinetics, taste preference or anxiety-like behaviour, although there was a transient increase in total locomotion following treatment. Additionally, tideglusib treatment did not alter liver function as measured by serum activity of alanine aminotransferase and aspartate aminotransferase but did cause a decrease in serum alkaline phosphatase activity. RNA sequencing analysis of tideglusib actions on ethanol consumption revealed alterations in genes involved in synaptic plasticity and transmission, as well as genes downstream of the canonical Wnt signalling pathway, suggesting tideglusib may modulate ethanol consumption via β-catenin binding to the transcription factors TCF3 and LEF1. The data presented here further implicate GSK3β in alcohol consumption and support the use of tideglusib as a potential therapeutic in the treatment of AUD.

Susceptibility to Pentylenetetrazole-Induced Seizures in Mice with Distinct Activity of the Endogenous Opioid System

Currently, pharmacotherapy provides successful seizure control in around 70% of patients with epilepsy; however, around 30% of cases are still resistant to available treatment. Therefore, effective anti-epileptic therapy still remains a challenge. In our study, we utilized two mouse lines selected for low (LA) and high (HA) endogenous opioid system activity to investigate the relationship between down- or upregulation of the opioid system and susceptibility to seizures. Pentylenetetrazole (PTZ) is a compound commonly used for kindling of generalized tonic-clonic convulsions in animal models. Our experiments revealed that in the LA mice, PTZ produced seizures of greater intensity and shorter latency than in HA mice. This observation suggests that proper opioid system tone is crucial for preventing the onset of generalized tonic-clonic seizures. Moreover, a combination of an opioid receptor antagonist-naloxone-and a GABA receptor agonist-diazepam (DZP)-facilitates a significant DZP-sparing effect. This is particularly important for the pharmacotherapy of neurological patients, since benzodiazepines display high addiction risk. In conclusion, our study shows a meaningful, protective role of the endogenous opioid system in the prevention of epileptic seizures and that disturbances in that balance may facilitate seizure occurrence.

A selective GSK3β inhibitor, tideglusib, decreases intermittent access and binge ethanol self-administration in C57BL/6J mice

Over 10% of the US population over 12 years old meets criteria for Alcohol Use Disorder (AUD), yet few effective, long-term treatments are currently available. Glycogen synthase kinase 3 beta (GSK3β) has been implicated in ethanol behaviors and poses as a potential therapeutic target in the treatment of AUD. Here we investigate the role of tideglusib, a selective GSK3β inhibitor, in ethanol consumption and other behaviors. We have shown tideglusib decreases ethanol consumption in both a model of daily, progressive ethanol intake (two-bottle choice, intermittent ethanol access) and binge-like drinking behavior (drinking-in-the-dark) without effecting water intake. Further, we have shown tideglusib to have no effect on ethanol pharmacokinetics, taste preference, or anxiety-like behavior, though there was a transient increase in total locomotion following treatment. Additionally, we assessed liver health following treatment via serum levels of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase and showed no effect on aminotransferase levels though there was a decrease in alkaline phosphatase. RNA sequencing studies revealed a role of GSK3β inhibition via tideglusib on the canonical Wnt signaling pathway, suggesting tideglusib may carry out its effects on ethanol consumption through effects on β-catenin binding to the transcription factors TCF3 and LEF1. The data presented here further implicate GSK3β in alcohol consumption and support the use of tideglusib as a potential therapeutic in the treatment of AUD.

Influence of methadone on the anticonvulsant efficacy of valproate sodium gabapentin against maximal electroshock seizure in mice by regulation of brain MDA TNF-α

Methadone is the most frequently used opioid therapy worldwide, with controversial effects on oxidative stress homeostasis. This study investigated the effects of intraperitoneal (i.p.) co-administration of methadone (0.1, 0.3, 1, and 3 mg/kg) and valproate sodium (300 mg/kg) or gabapentin (50 mg/kg) in the mice maximal electroshock (MES)-induced seizure model. The adverse effect of drugs was assessed using the chimney test. The levels of tumor necrosis factor-alpha (TNF-α) and malondialdehyde (MDA) contents were measured in mice brains after a single seizure. Administration of methadone alone resulted in a significant reduction in the duration of hind limb extension (HLE) than that in the control group. Methadone pretreatment at doses of 0.1 and 0.3 mg/kg i.p. decreased, and at doses of 1 and 3 mg/kg i.p. had an increasing effect on anticonvulsant efficacy of gabapentin. Pretreatment with all doses of methadone significantly decreased the valproate anticonvulsive efficacy. At doses of 1 and 3 mg/kg i.p. methadone per se increased brain MDA levels after MES-induced seizure. Administration of methadone (0.3 mg/kg i.p.) enhanced and at 3 mg/kg decreased gabapentin effect on brain MDA level, but their co-treatment did not lead to further increase in MDA. Methadone at 0.3–3 mg/kg enhanced the effect of sodium valproate on MDA levels in the brain, but at all doses significantly potentiated its effect on brain TNF-α levels. The drugs did not produce any side effects on motor coordination in experimental animals. In conclusion, methadone showed different effects on anticonvulsant actions of gabapentin and valproate through regulation of brain levels of MDA and TNF-α.

Suppression of histone deacetylases by SAHA relieves bone cancer pain in rats via inhibiting activation of glial cells in spinal dorsal horn and dorsal root ganglia

BACKGROUND

Robust activation of glial cells has been reported to occur particularly during the pathogenesis of bone cancer pain (BCP). Researchers from our group and others have shown that histone deacetylases (HDACs) play a significant role in modulating glia-mediated immune responses; however, it still remains unclear whether HDACs are involved in the activation of glial cells during the development of BCP.

METHODS

BCP model was established by intra-tibia tumor cell inoculation (TCI). The expression levels and distribution sites of histone deacetylases (HDACs) in the spinal dorsal horn and dorsal root ganglia were evaluated by Western blot and immunofluorescent staining, respectively. Suberoylanilide hydroxamic acid (SAHA), a clinically used HDAC inhibitor, was then intraperitoneally and intrathecally injected to rescue the increased expression levels of HDAC1 and HDAC2. The analgesic effects of SAHA administration on BCP were then evaluated by measuring the paw withdrawal thresholds (PWTs). The effects of SAHA on activation of glial cells and expression of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) in the spinal dorsal horn and dorsal root ganglia of TCI rats were further evaluated by immunofluorescent staining and Western blot analysis. Subsequently, the effects of SAHA administration on tumor growth and cancer cell-induced bone destruction were analyzed by hematoxylin and eosin (HE) staining and micro-CT scanning.

RESULTS

TCI caused rapid and long-lasting increased expression of HDAC1/HDAC2 in glial cells of the spinal dorsal horn and dorsal root ganglia. Inhibiting HDACs by SAHA not only reversed TCI-induced upregulation of HDACs but also inhibited the activation of glial cells in the spinal dorsal horn and dorsal root ganglia, and relieved TCI-induced mechanical allodynia. Further, we found that SAHA administration could not prevent cancer infiltration or bone destruction in the tibia, which indicated that the analgesic effects of SAHA were not due to its anti-tumor effects. Moreover, we found that SAHA administration could inhibit GSK3β activity in the spinal dorsal horn and dorsal root ganglia, which might contributed to the relief of BCP.

CONCLUSION

Our findings suggest that HDAC1 and HDAC2 are involved in the glia-mediated neuroinflammation in the spinal dorsal horn and dorsal root ganglia underlying the pathogenesis of BCP, which indicated that inhibiting HDACs by SAHA might be a potential strategy for pain relief of BCP.

Valproate reverses stress-induced somatic hyperalgesia and visceral hypersensitivity by up-regulating spinal 5-HT2C receptor expression in female rats

Sodium valproate (VPA) has analgesic effects in clinical and experimental studies, but the mechanisms are still unclear. The present study examined the effects of VPA on stress-induced somatic hyperalgesia and visceral hypersensitivity and the role of 5-HT_2C receptors in the spinal cord. Repeated 3 day forced swim (FS) significantly reduced the thermal withdrawal latency and mechanical withdrawal threshold, and increased the magnitude of the visceromotor response to colorectal distention compared to the baseline values in rats. The somatic hyperalgesia and visceral hypersensitivity were accompanied by significant down-regulation of 5-HT_2C receptor expression in the L4-L5 and L6-S1 dorsal spinal cord. Intraperitoneal administration of VPA (300 mg/kg) before each FS and 1 day post FS prevented the development of somatic hyperalgesia and visceral hypersensitivity induced by FS stress, as well as down-regulation of 5-HT_2C receptors in the spinal cord. The reversal of somatic hyperalgesia and visceral hypersensitivity by VPA in FS rats was blocked by intrathecal administration of the selective 5-HT_2C receptor antagonist RS-102221 (30 μg/10 μL) 30 min after each VPA injection. The results suggest that VPA attenuates FS-induced somatic hyperalgesia and visceral hypersensitivity by restoring down-regulated function of 5-HT_2C receptors in the spinal cord.

Glycogen Synthase Kinase 3β in the Ventral Hippocampus is Important for Cocaine Reward and Object Location Memory

The ventral hippocampus is a component of the neural circuitry involved with context-associated memory for reward and generation of appropriate behavioral responses to context. Glycogen synthase kinase 3 beta (GSK3β) has been linked to the maintenance of synaptic plasticity, contextual memory retrieval, and is involved in the reconsolidation of cocaine-associated contextual memory. In this study, the effects of targeted downregulation of GSK3β in the ventral hippocampus were examined on a series of behavioral tests for assessing drug reward-context association and non-reward related memory. The Cre/loxP site-specific recombination system was used to knockdown GSK3β through bilateral stereotaxic delivery of an adeno-associated virus expressing Cre-recombinase (AAV-Cre) into the ventral hippocampus of adult mice homozygous for a floxed GSK3β allele. GSK3β floxed mice injected with AAV-Cre had a loss of 56-75% of GSK3β in the ventral hippocampus and displayed diminished development of cocaine conditioned place preference, but not morphine place preference as compared with wild-type mice injected with AAV-Cre or GSK3β floxed mice injected with a control virus, AAV-GFP. Impaired object location memory was observed in mice with GSK3β downregulation in the ventral hippocampus, but novel object recognition remained intact. These results indicate that GSK3β signaling in the ventral hippocampus is differentially involved in the formation of place-drug reward association dependent upon drug class. Additionally, ventral hippocampal GSK3β signaling is important in detection of discrete spatial cues, but not recognition memory for objects.

Inhibition of Histone Deacetylases Attenuates Morphine Tolerance and Restores MOR Expression in the DRG of BCP Rats

The easily developed morphine tolerance in bone cancer pain (BCP) significantly hindered its clinical use. Increasing evidence suggests that histone deacetylases (HDACs) regulate analgesic tolerance subsequent to continuous opioid exposure. However, whether HDACs contribute to morphine tolerance in the pathogenesis of BCP is still unknown. In the current study, we explored the possible engagement of HDACs in morphine tolerance during the pathogenesis of BCP. After intra-tibia tumor cell inoculation (TCI), we found that the increased expression of HDACs was negatively correlated with the decreased expression of MOR in the DRG following TCI. The paw withdrawal threshold (PWT) and percentage maximum possible effects (MPEs) decreased rapidly in TCI rats when morphine was used alone. In contrast, the concomitant use of SAHA and morphine significantly elevated the PWT and MPEs of TCI rats compared to morphine alone. Additionally, we found that SAHA administration significantly elevated MOR expression in the DRG of TCI rats with or without morphine treatment. Moreover, the TCI-induced increase in the co-expression of MOR and HDAC1 in neurons was significantly decreased after SAHA administration. These results suggest that HDACs are correlated with the downregulation of MOR in the DRG during the pathogenesis of BCP. Inhibition of HDACs using SAHA can be used to attenuate morphine tolerance in BCP.

Morphine-Mediated Brain Region-Specific Astrocytosis Involves the ER Stress-Autophagy Axis

A recent study from our lab has revealed a link between morphine-mediated autophagy and synaptic impairment. The current study was aimed at investigating whether morphine-mediated activation of astrocytes involved the ER stress/autophagy axis. Our in vitro findings demonstrated upregulation of GFAP indicating astrocyte activation with a concomitant increase in the production of proinflammatory cytokines in morphine-exposed human astrocytes. Using both pharmacological and gene-silencing approaches, it was demonstrated that morphine-mediated defective autophagy involved upstream activation of ER stress with subsequent downstream astrocyte activation via the μ-opioid receptor (MOR). In vivo validation demonstrated preferential activation of ER stress/autophagy axis in the areas of the brain not associated with pain such as the basal ganglia, frontal cortex, occipital cortex, and the cerebellum of morphine-dependent rhesus macaques, and this correlated with increased astrocyte activation and neuroinflammation. Interventions aimed at blocking either the MOR or ER stress could thus likely be developed as promising therapeutic targets for abrogating morphine-mediated astrocytosis.

[Altered expression of transporter and analgesic of morphine in neuropathic pain mice]

It is known that morphine is less effective for patients with neuropathic pain, accounting for approximately 70% of cancer patients with severe pain. One of the causes of the decline is reported as a decreased function of the μ-opioid receptor, which binds to the active metabolites of morphine in the mesencephalic ventral tegmental area. However, the details of this mechanism are not understood. We hypothesized that a decrease in the concentration of morphine in the brain reduces its analgesic effect on neuropathic pain, and found that the analgesic effect of morphine was correlated with its concentration in the brain. We examined the reason for the decreased concentration of morphine in the brain in case of neuropathic pain. We discovered increased P-glycoprotein (P-gp) expression in the small intestine, increased expression and activity of UGT2B in the liver, and increased P-gp expression in the brain under conditions of neuropathic pain. In this symposium, we argue that low brain morphine concentration is considered one of the causes of lower sensitivity to morphine in neuropathic pain patients.

GSK3β-activation is a point of convergence for HIV-1 and opiate-mediated interactive neurotoxicity

Infection of the CNS with HIV-1 occurs rapidly after primary peripheral infection. HIV-1 can induce a wide range of neurological deficits, collectively known as HIV-1-associated neurocognitive disorders. Our previous work has shown that the selected neurotoxic effects induced by individual viral proteins, Tat and gp120, and by HIV(+) supernatant are enhanced by co-exposure to morphine. This mimics co-morbid neurological effects observed in opiate-abusing HIV(+) patients. Although there is a correlation between opiate drug abuse and progression of HIV-1-associated neurocognitive disorders, the mechanisms underlying interactions between HIV-1 and opiates remain obscure. Previous studies have shown that HIV-1 induces neurotoxic effects through abnormal activation of GSK3β. Interestingly, expression of GSK3β has shown to be elevated in brains of young opiate abusers indicating that GSK3β is also linked to neuropathology seen with opiate-abusing patients. Thus, we hypothesize that GSK3β activation is a point of convergence for HIV- and opiate-mediated interactive neurotoxic effects. Neuronal cultures were treated with supernatant from HIV-1SF162-infected THP-1 cells, in the presence or absence of morphine and GSK3β inhibitors. Our results show that GSK3β inhibitors, including valproate and small molecule inhibitors, significantly reduce HIV-1-mediated neurotoxic outcomes, and also negate interactions with morphine that result in cell death, suggesting that GSK3β-activation is an important point of convergence and a potential therapeutic target for HIV- and opiate-mediated neurocognitive deficits.

Psychiatric agents and implications for perioperative analgesia

The use of antidepressants, anxiolytics, mood stabilizers, anticonvulsants, and major tranquilizers introduces neurochemical, behavioral, cognitive, and emotional factors that increase the complexity of medical and surgical tasks. Increasingly, various classes of psychotropic medications are being prescribed in the perioperative setting for their analgesic properties in patients with or without a psychiatric diagnosis. In many cases, the precise mechanisms of action and dose-response relationships by which these agents mediate analgesia are largely unclear. An appreciation of the side effects and adverse-effect profiles of such medications and familiarity with the clinically relevant drug interactions that may occur in the perioperative setting are imperative to ensure the best possible outcome in dealing with patients on these medications. This review focuses on various classes of psychotropic agents, which are addressed individually, with particular focus on their analgesic properties. The latest published research is summarized, deficiencies in our current collective knowledge are discussed, and evidence-based recommendations are made for clinical practice.

Inhibition of glycogen synthase kinase-3β prevents remifentanil-induced hyperalgesia via regulating the expression and function of spinal N-methyl-D-aspartate receptors in vivo and vitro

A large number of experimental and clinical studies have confirmed that brief remifentanil exposure can enhance pain sensitivity presenting as opioid-induced hyperalgesia (OIH). N-methyl-D-aspartate (NMDA) receptor antagonists have been reported to inhibit morphine analgesic tolerance in many studies. Recently, we found that glycogen synthase kinase-3β (GSK-3β) modulated NMDA receptor trafficking in a rat model of remifentanil-induced postoperative hyperalgesia. In the current study, it was demonstrated that GSK-3β inhibition prevented remifentanil-induced hyperalgesia via regulating the expression and function of spinal NMDA receptors in vivo and in vitro. We firstly investigated the effects of TDZD-8, a selective GSK-3β inhibitor, on thermal and mechanical hyperalgesia using a rat model of remifentanil-induced hyperalgesia. GSK-3β activity as well as NMDA receptor subunits (NR1, NR2A and NR2B) expression and trafficking in spinal cord L4-L5 segments were measured by Western blot analysis. Furthermore, the effects of GSK-3β inhibition on NMDA-induced current amplitude and frequency were studied in spinal cord slices by whole-cell patch-clamp recording. We found that remifentanil infusion at 1 μg·kg(-1)·min(-1) and 2 μg·kg(-1)·min(-1) caused mechanical and thermal hyperalgesia, up-regulated NMDA receptor subunits NR1 and NR2B expression in both membrane fraction and total lysate of the spinal cord dorsal horn and increased GSK-3β activity in spinal cord dorsal horn. GSK-3β inhibitor TDZD-8 significantly attenuated remifentanil-induced mechanical and thermal hyperalgesia from 2 h to 48 h after infusion, and this was associated with reversal of up-regulated NR1 and NR2B subunits in both membrane fraction and total lysate. Furthermore, remifentanil incubation increased amplitude and frequency of NMDA receptor-induced current in dorsal horn neurons, which was prevented with the application of TDZD-8. These results suggest that inhibition of GSK-3β can significantly ameliorate remifentanil-induced hyperalgesia via modulating the expression and function of NMDA receptors, which present useful insights into the mechanistic action of GSK-3β inhibitor as potential anti-hyperalgesic agents for treating OIH.

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).