Fatty acid amide hydrolase inhibitor URB597 prevented tolerance and cognitive deficits induced by chronic morphine administration in rats

The Effect of Antinociceptive Dose of Morphine on Cell Therapy in Rats with Spinal Cord Injury

Spinal cord injury (SCI) is a sensory-motor injury. Today, combined treatments such as cell therapy along with drug therapy and their interactions are of interest. Morphine is an opioid drug used to relieve intolerable pain. This study aims to evaluate the impact of an antinociceptive dose of morphine (with minimal tolerance/dependence but effective pain relief) on cell therapy in SCI. The antinociceptive dose of morphine was determined in rats with SCI through the Hargreaves and naloxone-induced morphine withdrawal tests. The rats were then allocated to 5 groups: laminectomy, SCI, SCI + Morphine, SCI + cell therapy, SCI + Morphine + cell therapy. The antinociceptive dose (5 mg/kg) was administered on days 1, 4, 10, and 13 (i.p.) post-SCI. On day 7, Neural-like stem cells derived from adipose tissue were transplanted intraspinally into the injured animals, and they were monitored for 12 weeks. The outcomes were assessed using the BBB test, somatosensory evoked potential (SSEP), and histology. The BBB test indicated that morphine significantly hindered functional recovery post-cell transplantation compared to animals receiving only cell therapy (p < 0.05). In the SSEP test, the analysis of amplitude and latency of waves did not reveal a significant difference (p > 0.05). The histological results showed that cell therapy reduced the cavity size post-SCI, while morphine had no significant impact on it. Morphine at the antinociceptive dose significantly impairs motor recovery despite cell therapy. Nonetheless, there was no significant difference between groups in terms of sensory pathway outcomes.

Alternative pain management via endocannabinoids in the time of the opioid epidemic: Peripheral neuromodulation and pharmacological interventions

The use of opioids in pain management is hampered by the emergence of analgesic tolerance, which leads to increased dosing and side effects, both of which have contributed to the opioid epidemic. One promising potential approach to limit opioid analgesic tolerance is activating the endocannabinoid system in the CNS, via activation of CB1 receptors in the descending pain inhibitory pathway. In this review, we first discuss preclinical and clinical evidence revealing the potential of pharmacological activation of CB1 receptors in modulating opioid tolerance, including activation by phytocannabinoids, synthetic CB1 receptor agonists, endocannabinoid degradation enzyme inhibitors, and recently discovered positive allosteric modulators of CB1 receptors. On the other hand, as non-pharmacological pain relief is advocated by the US-NIH to combat the opioid epidemic, we also discuss contributions of peripheral neuromodulation, involving the electrostimulation of peripheral nerves, in addressing chronic pain and opioid tolerance. The involvement of supraspinal endocannabinoid systems in peripheral neuromodulation-induced analgesia is also discussed. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Alterations and interactions of subcortical modulatory systems in Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) is not fully understood. Here we summarize current knowledge on the involvement of the serotonergic, noradrenergic, dopaminergic, cholinergic, and opioid systems in AD, emphasizing the importance of interactions between the serotonergic and the other subcortical modulatory systems during the progression of AD. In physiological conditions, all neurotransmitter systems function in concert and are interdependent at both the neuroanatomical and molecular levels. Through their early involvement in AD, cognitive and behavioral abilities that rely on their interactions also become disrupted. Considering that serotonin (5HT) regulates the release of noradrenaline (NA), dopamine (DA) and acetylcholine (ACh), any alteration in 5HT levels leads to disturbance of NA, DA, and ACh homeostasis in the brain. One of the earliest pathological changes during the prodromal phase of AD is a decrease of serotonergic transmission throughout the brain, with serotonergic receptors being also affected. Additionally, serotonergic and noradrenergic as well as serotonergic and dopaminergic nuclei are reciprocally interconnected. As the serotonergic dorsal raphe nucleus (DRN) is affected by pathological changes early in AD, and the noradrenergic locus coeruleus (LC) and dopaminergic ventral tegmental area (VTA) exhibit AD-related pathological changes, their connectivity also becomes altered in AD. Such disrupted interactions among neurotransmitter systems in AD can be used in the development of multi-target drugs. Some of the potential AD therapeutics (such as ASS234, RS67333, tropisetron) target multiple neurotransmitter systems to achieve the best possible improvement of cognitive and behavioral deficits observed in AD. Here, we review how serotonergic system interacts with other subcortical modulatory systems (noradrenergic, dopaminergic, cholinergic, and opioid systems) during AD.

Inhibition of fatty acid amide hydrolase in the CNS prevents and reverses morphine tolerance in male and female mice

BACKGROUND AND PURPOSE

Fatty acid amide hydrolase (FAAH) is an intracellular serine amidase that terminates the signalling of various lipid messengers involved in pain regulation, including anandamide and palmitoylethanolamide. Here, we investigated the effects of pharmacological or genetic FAAH removal on tolerance to the anti-nociceptive effects of morphine.

EXPERIMENTAL APPROACH

We induced tolerance in male and female mice by administering twice-daily morphine for 7 days while monitoring nociceptive thresholds by the tail immersion test. The globally active FAAH inhibitor URB597 (1 and 3 mg·kg^-1 , i.p.) or the peripherally restricted FAAH inhibitor URB937 (3 mg·kg^-1 , i.p.) were administered daily 30 min prior to morphine, alone or in combination with the cannabinoid CB₁ receptor antagonist AM251 (3 mg·kg^-1 , i.p.), the CB₂ receptor antagonist AM630 (3 mg·kg^-1 , i.p.), or the PPAR-α antagonist GW6471 (4 mg·kg^-1 , i.p.). Spinal levels of FAAH-regulated lipids were quantified by LC/MS-MS. Gene transcription was assessed by RT-qPCR.

KEY RESULTS

URB597 prevented and reversed morphine tolerance in both male and female mice. This effect was mimicked by genetic FAAH deletion, but not by URB937. Treatment with AM630 suppressed, whereas treatment with AM251 or GW6471, attenuated the effects of URB597. Anandamide mobilization was enhanced in the spinal cord of morphine-tolerant mice. mRNA levels of the anandamide-producing enzyme N-acyl-phosphatidylethanolamine PLD (NAPE-PLD) and the palmitoylethanolamide receptor PPAR-α, but not those for CB₂ , CB₁ receptors or FAAH, were elevated in spinal cord CONCLUSION AND IMPLICATIONS: FAAH-regulated lipid signalling in the CNS modulated opiate tolerance, suggesting FAAH as a potential target for opiate-sparing medications.

Brain-Permeant and -Impermeant Inhibitors of Fatty Acid Amide Hydrolase Synergize with the Opioid Analgesic Morphine to Suppress Chemotherapy-Induced Neuropathic Nociception Without Enhancing Effects of Morphine on Gastrointestinal Transit

Opioid-based therapies remain a mainstay for chronic pain management, but unwanted side effects limit therapeutic use. We compared efficacies of brain-permeant and -impermeant inhibitors of fatty acid amide hydrolase (FAAH) in suppressing neuropathic pain induced by the chemotherapeutic agent paclitaxel. Paclitaxel produced mechanical and cold allodynia without altering nestlet shredding or marble burying behaviors. We compared FAAH inhibitors that differ in their ability to penetrate the central nervous system for antiallodynic efficacy, pharmacological specificity, and synergism with the opioid analgesic morphine. (3'-(aminocarbonyl)[1,1'-biphenyl]- 3-yl)-cyclohexylcarbamate (URB597), a brain-permeant FAAH inhibitor, attenuated paclitaxel-induced allodynia via cannabinoid receptor 1 (CB₁) and cannabinoid receptor 2 (CB₂) mechanisms. URB937, a brain-impermeant FAAH inhibitor, suppressed paclitaxel-induced allodynia through a CB₁ mechanism only. 5-[4-(4-cyano-1-butyn-1-yl)phenyl]-1-(2,4-dichlorophenyl)-N-(1,1-dioxido-4-thiomorpholinyl)-4-methyl-1H-pyrazole-3-carboxamide (AM6545), a peripherally restricted CB₁ antagonist, fully reversed the antiallodynic efficacy of N-cyclohexyl-carbamic acid, 3'-(aminocarbonyl)-6-hydroxy[1,1'- biphenyl]-3-yl ester (URB937) but only partially reversed that of URB597. Thus, URB937 suppressed paclitaxel-induced allodynia through a mechanism that was dependent upon peripheral CB₁ receptor activation only. Antiallodynic effects of both FAAH inhibitors were reversed by N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251). Antiallodynic effects of URB597, but not URB937, were reversed by 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl](4-methoxyphenyl)methanone (AM630). Isobolographic analysis revealed synergistic interactions between morphine and either URB597 or URB937 in reducing paclitaxel-induced allodynia. A leftward shift in the dose-response curve of morphine antinociception was observed when morphine was coadministered with either URB597 or URB937, consistent with morphine sparing. However, neither URB937 nor URB597 enhanced morphine-induced deficits in colonic transit. Thus, our findings suggest that FAAH inhibition may represent a therapeutic avenue to reduce the overall amount of opioid needed for treating neuropathic pain with potential to reduce unwanted side effects that accompany opioid administration.

URB597 improves cognitive impairment induced by chronic cerebral hypoperfusion by inhibiting mTOR-dependent autophagy

Chronic cerebral hypoperfusion (CCH) is associated with various ischemic cerebrovascular diseases that are characterized by cognitive impairment. The role of autophagy in cognitive dysfunction under conditions of CCH is poorly understood. To address this issue, the present study investigated the effect of the fatty acid amide hydrolase (FAAH) inhibitor URB597 on autophagy and cognition in a CCH model as well as the underlying mechanisms. Cognitive function was evaluated with the Morris water maze and by assessing long-term potentiation (LTP). The expression of autophagy-related proteins and mammalian target of rapamycin (mTOR) signaling pathway components was evaluated by immunofluorescence and western blot analyses, and ultrastructural changes were examined by transmission electron microscopy (EM). URB597 improved cognitive impairment by inhibiting CCH-induced autophagy, which was associated with mTOR signaling. Moreover, the ultrastructural deterioration resulting from CCH was improved by chronic treatment with URB597. These findings indicate that URB597 modulates autophagy in an mTOR-dependent manner, and mitigates neuronal damage and cognitive deterioration caused by CCH.

Effect of forced treadmill exercise and blocking of opioid receptors with naloxone on memory in male rats

Background:

The forced treadmill running can influence the opioid contents of the brain, through both effects of exercise and the effects of stress caused by coercion. Since opioids can cause negative effects on brain functions, this study aimed to evaluate the effect of forced treadmill exercise and blocking of opioid receptors with naloxone on memory in male rats.

Materials and Methods:

Experimental groups were the control, the exercise, the naloxone, and the naloxone exercise. The exercise program was treadmill running at 22 m/min at 0° inclination for 50 min/day, 6 days/week, for 4 weeks. Naloxone (1 mg/kg) was injected 5 min before the treadmill running. Morris water maze and passive avoidance learning tests were used for evaluation of memory. Acquisition phase of both tests was performed before interventions, and memory was evaluated 1-day and 1-week after the last session of exercise and treatments.

Results:

Our data showed that forced exercise impaired performance in passive avoidance learning test (P < 0.05 and P <0.01, 1-day, and 1-week after the last session of exercise and treatments, respectively). Spatial memory was only impaired after 1-week in the exercise group. Naloxone had no significant effect on memory in the control group. However, it improved memory in the exercise group, as there was no significant difference between the control and the naloxone exercise in both tests.

Conclusion:

The data correspond to the possibility that opioidergic system may have mediatory roles in exercise-induced responses in forced exercise. These roles are likely harmful for memory.