Enhanced and complementary benefits of a nalfurafine and fingolimod combination to treat immune-driven demyelination

OBJECTIVES

Multiple sclerosis (MS) is a neurodegenerative disease characterised by inflammation and damage to myelin sheaths. While all current disease-modifying treatments (DMTs) are very effective at reducing relapses, they do not slow the progression of the disease, and there is little evidence that these treatments are able to repair or remyelinate damaged axons. Recent evidence suggests that activating kappa opioid receptors (KORs) has a beneficial effect on the progression of MS, and this study investigates the effects of KOR agonists treatment in combination with two current DMTs.

METHODS

Using the well-established murine model for immune-driven demyelination of MS, experimental autoimmune encephalomyelitis, the effect of KOR agonists in combination with DMTs fingolimod or dimethyl fumarate on disease progression, immune cell infiltration and activation as well as myelination were analysed.

RESULTS

Fingolimod in combination with the KOR agonist, nalfurafine, significantly increased each individual beneficial effect as measured by increased recovery of mice and reduced relapses. These beneficial effects correlated with a reduction in immune cell infiltration into the CNS as well as peripheral immune cell alterations including a reduction in autoreactive CD4+ T-cell cytokine production as well as increased myelination in the spinal cords of co-treated animals. In contrast, while the use of dimethyl fumarate in combination with nalfurafine did not adversely affect the benefits of nalfurafine, the combination did not significantly enhance those benefits.

CONCLUSION

This study indicates that KOR agonists can be used in combination with fingolimod and dimethyl fumarate with the nalfurafine-fingolimod combination providing enhanced benefits.

The Kappa Opioid Receptor Agonist 16-Bromo Salvinorin A Has Anti-Cocaine Effects without Significant Effects on Locomotion, Food Reward, Learning and Memory, or Anxiety and Depressive-like Behaviors

Kappa opioid receptor (KOR) agonists have preclinical antipsychostimulant effects; however, adverse side effects have limited their therapeutic development. In this preclinical study, conducted in Sprague Dawley rats, B6-SJL mice, and non-human primates (NHPs), we evaluated the G-protein-biased analogue of salvinorin A (SalA), 16-bromo salvinorin A (16-BrSalA), for its anticocaine effects, side effects, and activation of cellular signaling pathways. 16-BrSalA dose-dependently decreased the cocaine-primed reinstatement of drug-seeking behavior in a KOR-dependent manner. It also decreased cocaine-induced hyperactivity, but had no effect on responding for cocaine on a progressive ratio schedule. Compared to SalA, 16-BrSalA had an improved side effect profile, with no significant effects in the elevated plus maze, light-dark test, forced swim test, sucrose self-administration, or novel object recognition; however, it did exhibit conditioned aversive effects. 16-BrSalA increased dopamine transporter (DAT) activity in HEK-293 cells coexpressing DAT and KOR, as well as in rat nucleus accumbens and dorsal striatal tissue. 16-BrSalA also increased the early phase activation of extracellular-signal-regulated kinases 1 and 2, as well as p38 in a KOR-dependent manner. In NHPs, 16-BrSalA caused dose-dependent increases in the neuroendocrine biomarker prolactin, similar to other KOR agonists, at doses without robust sedative effects. These findings highlight that G-protein-biased structural analogues of SalA can have improved pharmacokinetic profiles and fewer side effects while maintaining their anticocaine effects.

The Kappa Opioid Receptor: A Promising Therapeutic Target for Multiple Pathologies

Kappa-opioid receptors (KOR) are widely expressed throughout the central nervous system, where they modulate a range of physiological processes depending on their location, including stress, mood, reward, pain, inflammation, and remyelination. However, clinical use of KOR agonists is limited by adverse effects such as dysphoria, aversion, and sedation. Within the drug-development field KOR agonists have been extensively investigated for the treatment of many centrally mediated nociceptive disorders including pruritis and pain. KOR agonists are potential alternatives to mu-opioid receptor (MOR) agonists for the treatment of pain due to their anti-nociceptive effects, lack of abuse potential, and reduced respiratory depressive effects, however, dysphoric side-effects have limited their widespread clinical use. Other diseases for which KOR agonists hold promising therapeutic potential include pruritis, multiple sclerosis, Alzheimer’s disease, inflammatory diseases, gastrointestinal diseases, cancer, and ischemia. This review highlights recent drug-development efforts targeting KOR, including the development of G-protein–biased ligands, mixed opioid agonists, and peripherally restricted ligands to reduce side-effects. We also highlight the current KOR agonists that are in preclinical development or undergoing clinical trials.

Sex Differences in Kappa Opioid Receptor Agonist Mediated Attenuation of Chemotherapy-Induced Neuropathic Pain in Mice

Chemotherapy-induced neuropathic pain is a common side effect for cancer patients which has limited effective treatment options. Kappa opioid receptor (KOR) agonists are a promising alternative to currently available opioid drugs due to their low abuse potential. In the current study, we have investigated the effects of Salvinorin A (SalA) analogues, 16-Ethynyl SalA, 16-Bromo SalA and ethyoxymethyl ether (EOM) SalB, and in a preclinical model of paclitaxel-induced neuropathic pain in male and female C57BL/6J mice. Using an acute dose-response procedure, we showed that compared to morphine, 16-Ethynyl SalA was more potent at reducing mechanical allodynia; and SalA, 16-Ethynyl SalA, and EOM SalB were more potent at reducing cold allodynia. In the mechanical allodynia testing, U50,488 was more potent in males and SalA was more potent in females. There were no sex differences in the acute cold allodynia testing. In the chronic administration model, treatment with U50,488 (10 mg/kg) reduced the mechanical and cold allodynia responses to healthy levels over 23 days of treatment. Overall, we have shown that KOR agonists are effective in a model of chemotherapy-induced neuropathic pain, indicating that KOR agonists could be further developed to treat this debilitating condition.

The Salvinorin Analogue, Ethoxymethyl Ether Salvinorin B, Promotes Remyelination in Preclinical Models of Multiple Sclerosis

Multiple sclerosis is a neurodegenerative disease associated with demyelination and neuroinflammation in the central nervous system. There is an urgent need to develop remyelinating therapies to better treat multiple sclerosis and other demyelinating diseases. The kappa opioid receptor (KOR) has been identified as a potential target for the development of remyelinating therapies; however, prototypical KOR agonists, such as U50,488 have side effects, which limit clinical use. In the current study, we investigated a Salvinorin A analog, ethoxymethyl ether Salvinorin B (EOM SalB) in two preclinical models of demyelination in C57BL/6J mice. We showed that in cellular assays EOM SalB was G-protein biased, an effect often correlated with fewer KOR-mediated side effects. In the experimental autoimmune encephalomyelitis model, we found that EOM SalB (0.1-0.3 mg/kg) effectively decreased disease severity in a KOR-dependent manner and led to a greater number of animals in recovery compared to U50,488 treatment. Furthermore, EOM SalB treatment decreased immune cell infiltration and increased myelin levels in the central nervous system. In the cuprizone-induced demyelination model, we showed that EOM SalB (0.3 mg/kg) administration led to an increase in the number of mature oligodendrocytes, the number of myelinated axons and the myelin thickness in the corpus callosum. Overall, EOM SalB was effective in two preclinical models of multiple sclerosis and demyelination, adding further evidence to show KOR agonists are a promising target for remyelinating therapies.

Oxidative Metabolism as a Modulator of Kratom's Biological Actions

The leaves of Mitragyna speciosa (kratom), a plant native to Southeast Asia, are increasingly used as a pain reliever and for attenuation of opioid withdrawal symptoms. Using the tools of natural products chemistry, chemical synthesis, and pharmacology, we provide a detailed in vitro and in vivo pharmacological characterization of the alkaloids in kratom. We report that metabolism of kratom's major alkaloid, mitragynine, in mice leads to formation of (a) a potent mu opioid receptor agonist antinociceptive agent, 7-hydroxymitragynine, through a CYP3A-mediated pathway, which exhibits reinforcing properties, inhibition of gastrointestinal (GI) transit and reduced hyperlocomotion, (b) a multifunctional mu agonist/delta-kappa antagonist, mitragynine pseudoindoxyl, through a CYP3A-mediated skeletal rearrangement, displaying reduced hyperlocomotion, inhibition of GI transit and reinforcing properties, and (c) a potentially toxic metabolite, 3-dehydromitragynine, through a non-CYP oxidation pathway. Our results indicate that the oxidative metabolism of the mitragynine template beyond 7-hydroxymitragynine may have implications in its overall pharmacology in vivo.

Nalfurafine reduces neuroinflammation and drives remyelination in models of CNS demyelinating disease

Objectives

Multiple sclerosis (MS) is a neurodegenerative disease characterised by inflammation and damage to the myelin sheath, resulting in physical and cognitive disability. There is currently no cure for MS, and finding effective treatments to prevent disease progression has been challenging. Recent evidence suggests that activating kappa opioid receptors (KOR) has a beneficial effect on the progression of MS. Although many KOR agonists like U50,488 are not suitable for clinical use because of a poor side‐effect profile, nalfurafine is a potent, clinically used KOR agonist with a favorable side‐effect profile.

Methods

Using the experimental autoimmune encephalomyelitis (EAE) model, the effect of therapeutically administered nalfurafine or U50,488 on remyelination, CNS infiltration and peripheral immune responses were compared. Additionally, the cuprizone model was used to compare the effects on non‐immune demyelination.

Results

Nalfurafine enabled recovery and remyelination during EAE. Additionally, it was more effective than U50,488 and promoted disease reduction when administered after chronic demyelination. Blocking KOR with the antagonist, nor‐BNI, impaired full recovery by nalfurafine, indicating that nalfurafine mediates recovery from EAE in a KOR‐dependent fashion. Furthermore, nalfurafine treatment reduced CNS infiltration (especially CD4⁺ and CD8⁺ T cells) and promoted a more immunoregulatory environment by decreasing Th17 responses. Finally, nalfurafine was able to promote remyelination in the cuprizone demyelination model, supporting the direct effect on remyelination in the absence of peripheral immune cell invasion.

Conclusions

Overall, our findings support the potential of nalfurafine to promote recovery and remyelination and highlight its promise for clinical use in MS.

N-docosahexaenoyl ethanolamine (synaptamide) has antinociceptive effects in male mice

BACKGROUND

N-docosahexaenoyl ethanolamine (DHEA; also known as synaptamide) binds to both the cannabinoid-1 and 2 (CB1 and CB2) cannabinoid receptors and has anti-inflammatory properties in vitro. However, the in vivo effects of DHEA remain unknown. Therefore, this study was designed to understand the effects of DHEA in models of pain and inflammation in mice.

METHODS

The intraplantar formaldehyde assay, hot water tail withdrawal assay and hotplate model were used to assess the antinociceptive properties of DHEA in mice. The mechanism of action was studied by antagonising the cannabinoid receptors, transient receptor potential vanilloid 1 (TRPV1) ion channel, peroxisome proliferator-activated receptors (PPARs) and G-protein receptor 55 (GPR55).

RESULTS

N-docosahexaenoyl ethanolamine (2-10 mg/kg) reduced the levels of nociceptive and inflammatory pain-related behaviour over 60 min in the intraplantar formaldehyde assay via both intraperitoneal and local intraplantar administration. The area under the curve analysis showed the overall antinociceptive effects of DHEA (10 mg/kg) were not modulated by pre-treatment with antagonists for the cannabinoid receptors, TRPV1ion channel, PPARα, PPARγ or GPR55. However, the time-course analysis showed that within the early inflammatory phase, antagonism of the CB2 receptor, PPARα and PPARγ led to a partial reversal of the antinociceptive effects of DHEA. In the hot water tail withdrawal and hotplate models of thermal nociception, DHEA (2-10 mg/kg) did not have any antinociceptive effects.

CONCLUSIONS

N-docosahexaenoyl ethanolamine reduced the level of formaldehyde-induced nociceptive and inflammatory pain-related behaviour; however, was not active in thermal nociceptive models. This study highlights the potential of DHEA for the treatment of acute inflammatory pain.

SIGNIFICANCE

This study shows that both intraperitoneal and intraplantar administration of DHEA reduces the level of formaldehyde-induced nociceptive and inflammatory pain.

Strategies for Developing κ Opioid Receptor Agonists for the Treatment of Pain with Fewer Side Effects

There is significant need to find effective, nonaddictive pain medications. κ Opioid receptor (KOPr) agonists have been studied for decades but have recently received increased attention because of their analgesic effects and lack of abuse potential. However, a range of side effects have limited the clinical development of these drugs. There are several strategies currently used to develop safer and more effective KOPr agonists. These strategies include identifying G-protein-biased agonists, developing peripherally restricted KOPr agonists without centrally mediated side effects, and developing mixed opioid agonists, which target multiple receptors at specific ratios to balance side-effect profiles and reduce tolerance. Here, we review the latest developments in research related to KOPr agonists for the treatment of pain. SIGNIFICANCE STATEMENT: This review discusses strategies for developing safer κ opioid receptor (KOPr) agonists with therapeutic potential for the treatment of pain. Although one strategy is to modify selective KOPr agonists to create peripherally restricted or G-protein-biased structures, another approach is to combine KOPr agonists with μ, δ, or nociceptin opioid receptor activation to obtain mixed opioid receptor agonists, therefore negating the adverse effects and retaining the therapeutic effect.

Evaluation of Biased and Balanced Salvinorin A Analogs in Preclinical Models of Pain

In the search for safer, non-addictive analgesics, kappa opioid receptor (KOPr) agonists are a potential target, as unlike mu-opioid analgesics, they do not have abuse potential. Salvinorin A (SalA) is a potent and selective KOPr agonist, however, clinical utility is limited by the short duration of action and aversive side effects. Biasing KOPr signaling toward G-protein activation has been highlighted as a key cellular mechanism to reduce the side effects of KOPr agonists. The present study investigated KOPr signaling bias and the acute antinociceptive effects and side effects of two novel analogs of SalA, 16-Bromo SalA and 16-Ethynyl SalA. 16-Bromo SalA showed G-protein signaling bias, whereas 16-Ethynyl SalA displayed balanced signaling properties. In the dose-response tail-withdrawal assay, SalA, 16-Ethynyl SalA and 16-Bromo SalA were more potent than the traditional KOPr agonist U50,488, and 16-Ethynyl SalA was more efficacious. 16-Ethynyl SalA and 16-Bromo SalA both had a longer duration of action in the warm water tail-withdrawal assay, and 16-Ethynyl had greater antinociceptive effect in the hot-plate assay, compared to SalA. In the intraplantar 2% formaldehyde test, 16-Ethynyl SalA and 16-Bromo SalA significantly reduced both nociceptive and inflammatory pain-related behaviors. Moreover, 16-Ethynyl SalA and 16-Bromo SalA had no anxiogenic effects in the marble burying task, and 16-Bromo SalA did not alter behavior in the elevated zero maze. Overall, 16-Ethynyl SalA significantly attenuated acute pain-related behaviors in multiple preclinical models, while the biased KOPr agonist, 16-Bromo SalA, displayed modest antinociceptive effects, and lacked anxiogenic effects.

Synthetic Studies of Neoclerodane Diterpenes from Salvia divinorum: Design, Synthesis, and Evaluation of Analogues with Improved Potency and G-protein Activation Bias at the μ-Opioid Receptor

Previous structure-activity relationship (SAR) studies identified the first centrally acting, non-nitrogenous μ-opioid receptor (MOR) agonist, kurkinorin (1), derived from salvinorin A. In an effort to further probe the physiological effects induced upon activation of MORs with this nonmorphine scaffold, a variety of analogues were synthesized and evaluated in vitro for their ability to activate G-proteins and recruit β-arrestin-2 upon MOR activation. Through these studies, compounds that are potent agonists at MORs and either biased toward β-arrestin-2 recruitment or biased toward G-protein activation have been identified. One such compound, 25, has potent activity and selectivity at the MOR over KOR with bias for G-protein activation. Impressively, 25 is over 100× more potent than morphine and over 5× more potent than fentanyl in vitro and elicits antinociception with limited tolerance development in vivo. This is especially significant given that 25 lacks a basic nitrogen and other ionizable groups present in other opioid ligand classes.

MP1104, a mixed kappa-delta opioid receptor agonist has anti-cocaine properties with reduced side-effects in rats

Kappa opioid receptor (KOPr) agonists have preclinical anti-cocaine and antinociceptive effects. However, adverse effects including dysphoria, aversion, sedation, anxiety and depression limit their clinical development. MP1104, an analogue of 3-iodobenzoyl naltrexamine, is a potent dual agonist at KOPr and delta opioid receptor (DOPr), with full agonist efficacy at both these receptors. In this study, we evaluate the ability of MP1104 to modulate cocaine-induced behaviors and side-effects preclinically. In male Sprague-Dawley rats trained to self-administer cocaine, MP1104 (0.3 and 1 mg/kg) reduced cocaine-primed reinstatement of drug-seeking behavior and caused significant downward shift of the dose-response curve in cocaine self-administration tests (0.3 and 0.6 mg/kg). The anti-cocaine effects exerted by MP1104 are in part due to increased dopamine (DA) uptake by the dopamine transporter (DAT) in the dorsal striatum (dStr) and nucleus accumbens (NAc). MP1104 (0.3 and 0.6 mg/kg) showed no significant anxiogenic effects in the elevated plus maze, pro-depressive effects in the forced swim test, or conditioned place aversion. 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. The overall results from this study show that MP1104, modulates DA uptake in the dStr and NAc, and exerts potent anti-cocaine properties in self-administration tests with reduced side-effects compared to pure KOPr agonists. This data supports the therapeutic development of dual KOPr/DOPr agonists to reduce the side-effects of selective KOPr agonists. This article is part of the Special Issue entitled 'Opioid Neuropharmacology: Advances in treating pain and opioid addiction'.

Addressing Structural Flexibility at the A-Ring on Salvinorin A: Discovery of a Potent Kappa-Opioid Agonist with Enhanced Metabolic Stability

Previous structure-activity studies on the neoclerodane diterpenoid salvinorin A have demonstrated the importance of the acetoxy functionality on the A-ring in its activity as a κ-opioid receptor agonist. Few studies have focused on understanding the role of conformation in these interactions. Herein we describe the synthesis and evaluation of both flexible and conformationally restricted compounds derived from salvinorin A. One such compound, spirobutyrolactone 14, was synthesized in a single step from salvinorin B and had similar potency and selectivity to salvinorin A (EC₅₀ = 0.6 ± 0.2 nM at κ; >10000 nM at μ and δ). Microsomal stability studies demonstrated that 14 was more metabolically resistant than salvinorin A. Evaluation of analgesic and anti-inflammatory properties revealed similar in vivo effects between 14 and salvinorin A. To our knowledge, this study represents the first example of bioisosteric replacement of an acetate group by a spirobutyrolactone to produce a metabolically resistant derivative.

The analgesic and anti-inflammatory effects of Salvinorin A analogue β-tetrahydropyran Salvinorin B in mice

BACKGROUND

Drugs activating the mu opioid receptor are routinely used to treat severe acute and chronic pain. Unfortunately, side effects including nausea, constipation, respiratory depression, addiction and tolerance can limit clinical utility. In contrast, kappa opioid receptor (KOPr) agonists, such as Salvinorin A (SalA), have analgesic properties with little potential for abuse.

METHODS

We evaluated SalA and the novel analogue β-tetrahydropyran Salvinorin B (β-THP SalB) for the ability to modulate pain and inflammation in vivo. The hot water tail-withdrawal assay, intradermal formalin-induced inflammatory pain and paclitaxel-induced neuropathic pain models were used to evaluate analgesic properties in mice. Tissue infiltration of inflammatory cells was measured by histology and flow cytometry.

RESULTS

β-tetrahydropyran Salvinorin B produced a longer duration of action in the tail-withdrawal assay compared to the parent compound SalA, and, like SalA and U50,488, β-THP SalB is a full agonist at the KOPr. In the formalin-induced inflammatory pain model, β-THP SalB and SalA significantly reduced pain score, paw oedema and limited the infiltration of neutrophils into the inflamed tissue. β-THP SalB and SalA supressed both mechanical and cold allodynia in the paclitaxel-induced neuropathic pain model, in a dose-dependent manner.

CONCLUSIONS

Structural modification of SalA at the C-2 position alters its analgesic potency and efficacy in vivo. Substitution with a tetrahydropyran group at C-2 produced potent analgesic and anti-inflammatory effects, including a reduction in paclitaxel-induced neuropathic pain. This study highlights the potential for KOPr agonists as analgesics with anti-inflammatory action and little risk of abuse.

SIGNIFICANCE

Salvinorin A and the novel analogue β-THP Salvinorin B show analgesic effects in the tail-withdrawal and formalin assays. They reduce oedema and decrease neutrophil infiltration into inflamed tissue, and suppress mechanical and cold allodynia in paclitaxel-induced neuropathic pain.

Synthetic Studies of Neoclerodane Diterpenes from Salvia divinorum: Identification of a Potent and Centrally Acting μ Opioid Analgesic with Reduced Abuse Liability

Opioids are widely used to treat millions suffering from pain, but their analgesic utility is limited due to associated side effects. Herein we report the development and evaluation of a chemical probe exhibiting analgesia and reduced opioid-induced side effects. This compound, kurkinorin (5), is a potent and selective μ-opioid receptor (MOR) agonist (EC₅₀ = 1.2 nM, >8000 μ/κ selectivity). 5 is a biased activator of MOR-induced G-protein signaling over β-arrestin-2 recruitment. Metadynamics simulations of 5's binding to a MOR crystal structure suggest energetically preferred binding modes that differ from crystallographic ligands. In vivo studies with 5 demonstrate centrally mediated antinociception, significantly reduced rewarding effects, tolerance, and sedation. We propose that this novel MOR agonist may represent a valuable tool in distinguishing the pathways involved in MOR-induced analgesia from its side effects.

Changes to smoking habits and addiction following tobacco excise tax increases: a comparison of Māori, Pacific and New Zealand European smokers

OBJECTIVE

To compare changes in smoking habit and psychological addiction in Māori/Pacific and NZ European smokers in response to two annual excise tax increases from 2012 to 2014.

METHODS

Smokers from New Zealand cities completed questionnaires at three time points before and after two excise tax increases.

RESULTS

There were no significant differences in cigarettes per day or psychological addiction at baseline, but a linear decline in both measures was observed in Māori/Pacific and NZ European smokers. Cigarettes per day reduced at a greater rate for Māori/Pacific than NZ European smokers but dependence did not.

CONCLUSION

Results indicated that Māori/Pacific smokers' demand for cigarettes may be more price sensitive than NZ European smokers. Implications for Public Health: Tobacco excise tax may be particularly effective for Māori/Pacific smokers and may contribute to reductions in smoking-related health inequalities in NZ.

Gender differences in satisfaction ratings for nicotine electronic cigarettes by first-time users

INTRODUCTION

Nicotine electronic cigarettes (NECs) are becoming increasingly popular as a potentially safer alternative to tobacco but little is known regarding their subjective effects, including possible gender differences.

METHOD

Participants were New Zealand smokers with no intention to quit (N = 357) and whom had never used an NEC. During an interview in November-December 2012, participants sampled an NEC and rated it and their own-brand tobacco for satisfaction on a 10-point visual analogue scale. Participants were contacted again in February-March 2013 after a 10% increase in the tobacco excise tax on 1 January 2013.

RESULTS

Overall participants rated NECs 83.3% as satisfying as own-brand tobacco. Females rated NECs more highly than males. Of those who agreed to be re-interviewed (n = 227), 37.8% said they had cut back or made a change in their smoking habit and 7% had quit in February-March 2013. NEC satisfaction ratings predicted changes in smoking habit and reductions in nicotine dependence after controlling for covariates including demographic variables, factory-made vs. roll-your-own tobacco preference, and addiction scores.

CONCLUSION

Smokers' first impressions of NECs were very favourable, and were correlated with readiness to change after a tobacco tax increase. NECs appear to be particularly attractive for female smokers, and their use may help to improve the efficacy of nicotine replacement therapy for women.

Proteomics Analysis of Dorsal Striatum Reveals Changes in Synaptosomal Proteins following Methamphetamine Self-Administration in Rats

Methamphetamine is a widely abused, highly addictive drug. Regulation of synaptic proteins within the brain’s reward pathway modulates addiction behaviours, the progression of drug addiction and long-term changes in brain structure and function that result from drug use. Therefore, using large scale proteomics studies we aim to identify global protein expression changes within the dorsal striatum, a key brain region involved in the modulation of addiction. We performed LC-MS/MS analyses on rat striatal synaptosomes following 30 days of methamphetamine self-administration (2 hours/day) and 14 days abstinence. We identified a total of 84 differentially-expressed proteins with known roles in neuroprotection, neuroplasticity, cell cytoskeleton, energy regulation and synaptic vesicles. We identify significant expression changes in stress-induced phosphoprotein and tubulin polymerisation-promoting protein, which have not previously been associated with addiction. In addition, we confirm the role of amphiphysin and phosphatidylethanolamine binding protein in addiction. This approach has provided new insight into the effects of methamphetamine self-administration on synaptic protein expression in a key brain region associated with addiction, showing a large set of differentially-expressed proteins that persist into abstinence. The mass spectrometry proteomics data are available via ProteomeXchange with identifier PXD001443.

mRNA and microRNA analysis reveals modulation of biochemical pathways related to addiction in the ventral tegmental area of methamphetamine self-administering rats

BACKGROUND

Methamphetamine is a highly addictive central nervous system stimulant with increasing levels of abuse worldwide. Alterations to mRNA and miRNA expression within the mesolimbic system can affect addiction-like behaviors and thus play a role in the development of drug addiction. While many studies have investigated the effects of high-dose methamphetamine, and identified neurotoxic effects, few have looked at the role that persistent changes in gene regulation play following methamphetamine self-administration. Therefore, the aim of this study was to identify RNA changes in the ventral tegmental area following methamphetamine self-administration. We performed microarray analyses on RNA extracted from the ventral tegmental area of Sprague-Dawley rats following methamphetamine self-administration training (2 h/day) and 14 days of abstinence.

RESULTS

We identified 78 miRNA and 150 mRNA transcripts that were differentially expressed (fdr adjusted p < 0.05, absolute log2 fold change >0.5); these included genes not previously associated with addiction (miR-125a-5p, miR-145 and Foxa1), loci encoding receptors related to drug addiction behaviors and genes with previously recognized roles in addiction such as miR-124, miR-181a, DAT and Ret.

CONCLUSION

This study provides insight into the effects of methamphetamine on RNA expression in a key brain region associated with addiction, highlighting the possibility that persistent changes in the expression of genes with both known and previously unknown roles in addiction occur.

Estimating cross-price elasticity of e-cigarettes using a simulated demand procedure

INTRODUCTION

Our goal was to measure the cross-price elasticity of electronic cigarettes (e-cigarettes) and simulated demand for tobacco cigarettes both in the presence and absence of e-cigarette availability.

METHOD

A sample of New Zealand smokers (N = 210) completed a Cigarette Purchase Task to indicate their demand for tobacco at a range of prices. They sampled an e-cigarette and rated it and their own-brand tobacco for favorability, and indicated how many e-cigarettes and regular cigarettes they would purchase at 0.5×, 1×, and 2× the current market price for regular cigarettes, assuming that the price of e-cigarettes remained constant.

RESULTS

Cross-price elasticity for e-cigarettes was estimated as 0.16, and was significantly positive, indicating that e-cigarettes were partially substitutable for regular cigarettes. Simulated demand for regular cigarettes at current market prices decreased by 42.8% when e-cigarettes were available, and e-cigarettes were rated 81% as favorably as own-brand tobacco. However when cigarettes cost 2× the current market price, significantly more smokers said they would quit (50.2%) if e-cigarettes were not available than if they were available (30.0%).

CONCLUSION

Results show that e-cigarettes are potentially substitutable for regular cigarettes and their availability will reduce tobacco consumption. However, e-cigarettes may discourage smokers from quitting entirely as cigarette price increases, so policy makers should consider maintaining a constant relative price differential between e-cigarettes and tobacco cigarettes.

Assessing the Temporal Stability of a Cigarette Purchase Task After an Excise Tax Increase for Factory-Made and Roll-Your-Own Smokers

INTRODUCTION

Cigarette purchase tasks (CPTs) are used increasingly to measure simulated demand curves for tobacco. However, there is currently limited information about the temporal stability of demand curves obtained from these tasks.

METHOD

We interviewed a sample (N = 210) of smokers in New Zealand both before and after a 10% increase in the tobacco excise tax that took effect on January 1, 2013. Participants were interviewed in November-December 2012 (wave 1) and February-March 2013 (wave 2). At each interview, participants completed a high-resolution CPT with 64 prices ranging from NZ $0.00 to NZ $5.00/cigarette, and questionnaires regarding their smoking habit.

RESULTS

Roll-your-own smokers had higher levels of nicotine dependence and tobacco demand based on CPT responses than factory-made smokers. Although demand curves for waves 1 and 2 were similar, intentions to purchase cigarettes were significantly less at wave 2 for three prices (NZ $0.85, NZ $0.90, and NZ $0.95) that were just higher than the actual price after the tax increase, for both roll-your-own and factory-made smokers. Measures of elasticity (α) derived from Hursh and Silberberg's model were significantly greater at wave 2 than wave 1, and there was a significant reduction in smoking habit as measured by cigarettes/day and the Fagerström Test for Nicotine Dependence at wave 2.

CONCLUSIONS

Purchase tasks can discriminate between smokers based on their tobacco preference, and although results are relatively stable over time, they depend on contextual factors such as the current real price for tobacco.

Synthesis and κ-opioid receptor activity of furan-substituted salvinorin A analogues

The neoclerodane diterpene salvinorin A, found in the leaves of Salvia divinorum, is a potent κ-opioid receptor agonist, making it an attractive scaffold for development into a treatment for substance abuse. Although several successful semisynthetic studies have been performed to elucidate structure-activity relationships, the lack of analogues with substitutions to the furan ring of salvinorin A has prevented a thorough understanding of its role in binding to the κ-opioid receptor. Herein we report the synthesis of several salvinorin A derivatives with modified furan rings. Evaluation of these compounds in a functional assay indicated that sterically less demanding substitutions are preferred, suggesting the furan ring is bound in a congested portion of the binding pocket. The most potent of the analogues successfully reduced drug-seeking behavior in an animal model of drug-relapse without producing the sedation observed with other κ-opioid agonists.

Predicting decreases in smoking with a cigarette purchase task: evidence from an excise tax rise in New Zealand

BACKGROUND

Tobacco excise taxes are known to be effective in reducing smoking at the population level, but less research has examined how individual smokers respond to changes in tax policy. We ask whether price elasticities for individual smokers, derived from simulated demand curves obtained with a cigarette purchase task (CPT), can predict changes in smoking after a tax increase.

METHOD

Smokers (N=357) were recruited from four New Zealand cities and interviewed before and after a 10% tobacco excise tax increase.

RESULTS

Simulated demand curves from the CPT were curvilinear and well described by an exponential model. Smokers reported significant reductions in cigarettes/day and addiction scores at Wave 2 (n=226). Local elasticities derived from the demand curves significantly predicted decreases in cigarettes/day after controlling for covariates.

CONCLUSIONS

Elasticities from simulated demand curves can predict decreases in consumption for individual smokers after an excise tax increase. Understanding individual differences in tobacco demand curves may help to predict how different groups of smokers will respond to price increases.

Pharmacology and anti-addiction effects of the novel κ opioid receptor agonist Mesyl Sal B, a potent and long-acting analogue of salvinorin A

BACKGROUND AND PURPOSE

Acute activation of κ opioid (KOP) receptors results in anticocaine-like effects, but adverse effects, such as dysphoria, aversion, sedation and depression, limit their clinical development. Salvinorin A, isolated from the plant Salvia divinorum, and its semi-synthetic analogues have been shown to have potent KOP receptor agonist activity and may induce a unique response with similar anticocaine addiction effects as the classic KOP receptor agonists, but with a different side effect profile.

EXPERIMENTAL APPROACH

We evaluated the duration of effects of Mesyl Sal B in vivo utilizing antinociception assays and screened for cocaine-prime induced cocaine-seeking behaviour in self-administering rats to predict anti-addiction effects. Cellular transporter uptake assays and in vitro voltammetry were used to assess modulation of dopamine transporter (DAT) function and to investigate transporter trafficking and kinase signalling pathways modulated by KOP receptor agonists.

KEY RESULTS

Mesyl Sal B had a longer duration of action than SalA, had anti-addiction properties and increased DAT function in vitro in a KOP receptor-dependent and Pertussis toxin-sensitive manner. These effects on DAT function required ERK1/2 activation. We identified differences between Mesyl Sal B and SalA, with Mesyl Sal B increasing the Vmax of dopamine uptake without altering cell-surface expression of DAT.

CONCLUSIONS AND IMPLICATIONS

SalA analogues, such as Mesyl Sal B, have potential for development as anticocaine agents. Further tests are warranted to elucidate the mechanisms by which the novel salvinorin-based neoclerodane diterpene KOP receptor ligands produce both anti-addiction and adverse side effects.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

The effects of nicotine and tobacco particulate matter on dopamine uptake in the rat brain

Cigarette smoking is the leading cause of preventable death worldwide. Recently, tobacco extracts have been shown to have a different pharmacological profile to nicotine alone and there is increasing evidence of a role for non-nicotinic components of cigarette smoke in smoking addiction. Nicotine is known to affect the uptake of dopamine in the brain of laboratory animals, but studies in the literature are often contradictory and little is known of the effects on non-nicotinic tobacco components on dopamine uptake. This study has examined the acute and chronic effects of nicotine and a tobacco extract (TPM) on dopamine uptake by the dopamine and norepinephrine transporters (DAT and NET) ex vivo using rotating disk electrode voltammetry, and quantified DAT and NET protein and mRNA expression in key brain regions. Nicotine (0.35 mg/kg) significantly decreased DAT function in the nucleus accumbens (NAc) at 30 min with no change in protein expression. This effect was sensitive to mecamylamine and DHβE but not MLA, indicating that it is dependent on α4 subunit containing nicotinic receptors. Furthermore, TPM, but not nicotine, increased DAT function in the dorsal striatum at 1 h in a nicotinic receptor independent manner with no change in DAT protein expression. At 1 h DAT mRNA in the ventral tegmental area was decreased by both acute and chronic TPM treatments.

Salvinorin A analogs and other κ-opioid receptor compounds as treatments for cocaine abuse

Acute activation of kappa-opioid receptors produces anti-addictive effects by regulating dopamine levels in the brain. Unfortunately, classic kappa-opioid agonists have undesired side effects such as sedation, aversion, and depression, which restrict their clinical use. Salvinorin A (Sal A), a novel kappa-opioid receptor agonist extracted from the plant Salvia divinorum, has been identified as a potential therapy for drug abuse and addiction. Here, we review the preclinical effects of Sal A in comparison with traditional kappa-opioid agonists and several new analogs. Sal A retains the anti-addictive properties of traditional kappa-opioid receptor agonists with several improvements including reduced side effects. However, the rapid metabolism of Sal A makes it undesirable for clinical development. In an effort to improve the pharmacokinetics and tolerability of this compound, kappa-opioid receptor agonists based on the structure of Sal A have been synthesized. While work in this field is still in progress, several analogs with improved pharmacokinetic profiles have been shown to have anti-addictive effects. While in its infancy, it is clear that these compounds hold promise for the future development of anti-addictive therapeutics.

The 2-methoxy methyl analogue of salvinorin A attenuates cocaine-induced drug seeking and sucrose reinforcements in rats

κ Opioid receptor activation by traditional arylacetamide agonists and the novel neoclerodane diterpene κ opioid receptor agonist Salvinorin A (Sal A) results in attenuation of cocaine-seeking behavior in pre-clinical models of addiction. However, adverse effects such as sedation, depression and aversion limit their clinical utility. The Sal A analogue, 2-methoxy-methyl salvinorin B (MOM Sal B) is a longer acting Sal A analogue with high affinity for κ opioid receptors. In this study, we tested MOM Sal B for its ability to modulate cocaine-seeking behavior in rats. MOM Sal B (0.3mg/kg) successfully attenuated cocaine-seeking but also attenuated sucrose reinforcement. No change in activity was observed in either cocaine-induced hyperactivity or spontaneous open field activity tests but increased immobility and decreased swimming times in the forced swim test were observed. This study indicates that κ opioid receptor activation by more potent Sal A analogues modulates cocaine-seeking behavior non-selectively without causing sedation, suggesting an improved side effects profile. However, pro-depressive effects are seen, which may limit the therapeutic potential of this compound. Future studies with Sal A analogues having affinities at other opioid receptors are warranted as they have the potential to identify compounds having effective anti-addiction properties.

Mu and delta opioid receptor immunoreactivity and mu receptor regulation in brainstem cells cultured from late fetal and early postnatal rats

Cultured cells from the rat brainstem were used to study opioid receptor (OpR) expression during late fetal and early postnatal development. Mu and delta opioid receptor (MOR and DOR) expression was investigated from embryonic day 16 (E16) to 6 days postnatal (P6). Postnatal neurons showed more intense MOR immunoreactivity (IR) than neurons cultured from fetal brainstem (P < 0.006). DOR IR showed a similar pattern, but the differences between fetal and neonatal animals were not statistically significant. Using confocal microscopy, MOR and DOR IR were shown to be present on both the cell membrane and within the cytoplasm, in a similar pattern to the IR seen in SH-SY5Y neuroblastoma cells that endogenously express both MOR and DOR. Double-labeling experiments demonstrated colocalization of MOR and DOR in the same brainstem neurons; however, not all MOR IR regions of a single neuron were also positively stained for DOR, and not all DOR IR regions were also positive for MOR. MOR was down-regulated after a 1- or 2-h treatment with 1 microM DAMGO, a potent mu opioid agonist, in both non-transfected and MOR-transfected SH-SY5Y cells and in primary cell cultures. It was concluded that many brainstem neurons express functional MOR or DOR or coexpress both receptors, although intracellular distributions of the receptors are unique for each receptor type.

Abundant expression of mu and delta opioid receptor mRNA and protein in the cerebellum of the fetal, neonatal, and adult rat

Opioid receptor proteins and mRNAs have been localized to a variety of regions within the rat brain. It is generally accepted that within the lobes of the rat cerebellum, only delta opioid receptor (DOR) is expressed. This is in contrast to that observed in humans and rabbits which express both mu opioid receptor (MOR) and DOR. In this study, we report detection of MOR as well as DOR protein by immunohistochemical localization, and mRNA by fluorescent in situ hybridization (FISH) within Purkinje cells (PK) and the granular layer of neonatal (P6) and adult rat cerebellum. Expression of MOR mRNA was also detected within cells of the molecular layer, but at lower levels than those seen within the PK cells. Abundant expression of MOR and DOR mRNA was detected in the external germinal layer of the immature cerebellum of the fetal (E16) rat, supporting a role for MOR and DOR in regulating neurogenesis of the cerebellum. In addition, using exon-specific cRNA probes, exons 1 and 4, which are both found in the MOR-1 splice variant mRNA, were detected in PK cells in the cerebellum and also within deep cerebellar nuclei in the adult.

Developmental expression of mu and delta opioid receptors in the rat brainstem: evidence for a postnatal switch in mu isoform expression

Opioid receptors are expressed in the brain during fetal and postnatal development, and the expression patterns vary with developmental age. To investigate the role of opioids in brain development, immunoblotting and immunohistochemical techniques were used to determine mu (MOR) and delta (DOR) opioid receptor expression levels and regional distributions in fetal, early postnatal and adult rat brainstem. Two immunoreactive bands were seen on Western blots of brainstem lysates for both MOR (50 and 70 kDa) and DOR (30 and 60 kDa). The expression levels of the isoforms changed dramatically between 6 and 15 days after birth. Total MOR protein was expressed at low levels in fetal and early postnatal animals with the 50-kDa band predominating. MOR expression then increased in the older animals and the 70-kDa isoform became dominant. Total DOR protein showed the opposite pattern, being high in the fetal and neonatal brainstem and low in the juvenile and adult. A postnatal switch in isoform expression for DOR was not evident in our study. In general, regional brainstem distributions in developing and adult animals were comparable to those reported in the literature, and both receptors were localized in the same areas where opioid receptor expression was high. It was concluded that MOR and DOR are developmentally regulated in the brainstem of the rat, that the isoform ratio switches postnatally from a fetal-neonatal pattern to a juvenile-adult pattern and that both receptors are generally expressed in the same brainstem regions from E16 to adult.

Method for serum-free culture of late fetal and early postnatal rat brainstem neurons

Primary culture of postnatal brainstem neurons in defined medium has not been described in the literature. Successful primary culture of brainstem neurons is typically restricted to embryonic ages E14-E18. This study describes a method for culture of late fetal and early postnatal brainstem neurons using a serum-free culture medium. The culture system is based on Neurobasal medium supplemented with antioxidant-rich B27 (Life Technologies). Neuron survival was optimized by replacing glutamine with GlutaMaxI, by matching osmolality with neuronal age, and by using Hibernate medium to increase neuron survival during tissue dissociation. This paper describes the first reliable method for culturing brainstem neurons from late fetal and early postnatal stages of the rat for up to 6 days postpartum.

Serum-free culture of rat post-natal and fetal brainstem neurons

Serum-free medium is essential for cell culture studies in which complete control of the environment is required. Primary culture of post-natal brainstem neurons in defined medium has not been described in the literature, and successful culture of primary brainstem neurons is typically restricted to embryonic ages E14-E18. This study describes a method for culture of fetal and post-natal brainstem neurons using a serum-free culture medium. The culture system is based on Neurobasal medium supplemented with antioxidant-rich B27. Media and supplements are commercially available products from Life Technologies. Neuron survival was optimized by replacing glutamine with GlutaMaxI, by matching osmolality with neuronal age, and by using Hibernate medium to increase neuron survival during tissue dissociation. Fetal E14, E16, E20, and post-natal P3 and P6 cultures were examined after 4, 7, and 9 days in culture. Neuron and glial cells present in the cultures were identified using immunocytochemistry with antibodies raised against microtubule-associated protein 2 (MAP2) and glial fibrillary acidic protein (GFAP), respectively. Fetal E14 cultures had more bipolar neurons than multipolar neurons compared with developmentally older P6 cultures. Early fetal cultures had a higher percentage of neurons than late fetal and early post-natal cultures. Neuron survival was similar between 4 and 9 days in culture for all age groups tested. This is the first reliable, defined culture medium that supports brainstem neurons from late fetal and early post-natal stages of the rat for up to 6 days post-partum.