Dysregulation of the endocannabinoid signaling system in the cerebellum and brainstem in a transgenic mouse model of spinocerebellar ataxia type-3

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“Spinocerebellar ataxia type-3 (SCA-3) is a rare disease but it is the most frequent type within the autosomal dominant inherited ataxias. The disease lacks an effective treatment to alleviate major symptoms and to modify disease progression.

Our recent findings that endocannabinoid receptors and enzymes are significantly altered in the post-mortemcerebellum of patients affected by autosomal-dominant hereditary ataxias suggest that targeting the endocannabinoid signaling system may be a promising therapeutic option.

Our goal was to investigate the status of the endocannabinoid signaling system in a transgenic mouse model of SCA-3, in the two CNS structures most affected in this disease –cerebellum and brainstem-.

These animals exhibited progressive motor incoordination, imbalance, abnormal gait, muscle weakness, and dystonia, in parallel to reduced in vivobrain glucose metabolism, deterioration of specific neuron subsets located in the dentate nucleus and pontine nuclei, small changes in microglial morphology, and reduction in glial glutamate transporters.

Concerning the endocannabinoid signaling, our data indicated no changes in CB2 receptors. By contrast, CB1 receptors increased in the Purkinje cell layer, in particular in terminals of basket cells, but they were reduced in the dentate nucleus.

We also measured the levels of endocannabinoid lipids and found reductions in anandamide and oleanolamideoyleth in the brainstem. These changes correlated with an increase in the FAAH enzyme in the brainstem, which also occurred in some cerebellar areas, whereas other endocannabinoid-related enzymes were not altered.

Collectively, our results in SCA-3 mutant mice confirm a possible dysregulation in the endocannabinoid system in the most important brain structures affected in this type of ataxia, suggesting that a pharmacological manipulation addressed to correct these changes could be a promising option in SCA-3.”

http://www.sciencedirect.com/science/article/pii/S0306452216305012

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ENDOCANNABINOID SYSTEM: A multi-facet therapeutic target.

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“Cannabis sativa is also popularly known as marijuana. It is being cultivated and used by man for recreational and medicinal purposes from many centuries.

Study of cannabinoids was at bay for very long time and its therapeutic value could not be adequately harnessed due to its legal status as proscribed drug in most of the countries.

The research of drugs acting on endocannabinoid system has seen many ups and down in recent past. Presently, it is known that endocannabinoids has role in pathology of many disorders and they also serve “protective role” in many medical conditions.

Several diseases like emesis, pain, inflammation, multiple sclerosis, anorexia, epilepsy, glaucoma, schizophrenia, cardiovascular disorders, cancer, obesity, metabolic syndrome related diseases, Parkinson’s disease, Huntington’s disease, Alzheimer’s disease and Tourette’s syndrome could possibly be treated by drugs modulating endocannabinoid system.

Presently, cannabinoid receptor agonists like nabilone and dronabinol are used for reducing the chemotherapy induced vomiting. Sativex (cannabidiol and THC combination) is approved in the UK, Spain and New Zealand to treat spasticity due to multiple sclerosis. In US it is under investigation for cancer pain, another drug Epidiolex (cannabidiol) is also under investigation in US for childhood seizures. Rimonabant, CB1 receptor antagonist appeared as a promising anti-obesity drug during clinical trials but it also exhibited remarkable psychiatric side effect profile. Due to which the US Food and Drug Administration did not approve Rimonabant in US. It sale was also suspended across the EU in 2008.

Recent discontinuation of clinical trial related to FAAH inhibitor due to occurrence of serious adverse events in the participating subjects could be discouraging for the research fraternity. Despite of some mishaps in clinical trials related to drugs acting on endocannabinoid system, still lot of research is being carried out to explore and establish the therapeutic targets for both cannabinoid receptor agonists and antagonists.

One challenge is to develop drugs that target only cannabinoid receptors in a particular tissue and another is to invent drugs that acts selectively on cannabinoid receptors located outside the blood brain barrier. Besides this, development of the suitable dosage forms with maximum efficacy and minimum adverse effects is also warranted.

Another angle to be introspected for therapeutic abilities of this group of drugs is non-CB1 and non-CB2 receptor targets for cannabinoids.

In order to successfully exploit the therapeutic potential of endocannabinoid system, it is imperative to further characterize the endocannabinoid system in terms of identification of the exact cellular location of cannabinoid receptors and their role as “protective” and “disease inducing substance”, time-dependent changes in the expression of cannabinoid receptors.”

http://www.ncbi.nlm.nih.gov/pubmed/27086601

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Does modulation of the endocannabinoid system have potential therapeutic utility in cerebellar ataxia?

“Cerebellar ataxias represent a spectrum of disorders which are, however, linked by common symptoms of motor incoordination and are typically associated with deficient in Purkinje cell firing activity and, often, degeneration. Cerebellar ataxias currently lack a curative agent.

The endocannabinoid (eCB) system includes eCB compounds and their associated metabolic enzymes, together with cannabinoid receptors, predominantly the cannabinoid CB1 receptor (CB1 R) in the cerebellum; activation of this system in the cerebellar cortex is associated with deficits in motor coordination characteristic of ataxia, effects which can be prevented by CB1 R antagonists.

Of further interest are various findings that CB1 R deficits may also induce a progressive ataxic phenotype.

Together these studies suggest that motor coordination is reliant on maintaining the correct balance in eCB system signalling.

Recent work also demonstrates deficient cannabinoid signalling in the mouse ‘ducky2J ‘ model of ataxia.

In light of these points, the potential mechanisms whereby cannabinoids may modulate the eCB system to ameliorate dysfunction associated with cerebellar ataxias are considered.”

http://www.ncbi.nlm.nih.gov/pubmed/26970080

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The endocannabinoid system and its therapeutic exploitation.

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“The term ‘endocannabinoid’ – originally coined in the mid-1990s after the discovery of membrane receptors for the psychoactive principle in Cannabis, Delta9-tetrahydrocannabinol and their endogenous ligands – now indicates a whole signalling system that comprises cannabinoid receptors, endogenous ligands and enzymes for ligand biosynthesis and inactivation. This system seems to be involved in an ever-increasing number of pathological conditions. With novel products already being aimed at the pharmaceutical market little more than a decade since the discovery of cannabinoid receptors, the endocannabinoid system seems to hold even more promise for the future development of therapeutic drugs. We explore the conditions under which the potential of targeting the endocannabinoid system might be realized in the years to come.”  http://www.ncbi.nlm.nih.gov/pubmed/15340387

http://www.nature.com/nrd/journal/v3/n9/full/nrd1495.html

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Pharmacological and pharmacokinetic characterization of the cannabinoid receptor 2 agonist, GW405833, utilizing rodent models of acute and chronic pain, anxiety, ataxia and catalepsy.

“To date, two cannabinoid receptors have been identified, CB1 and CB2. Activation of these receptors with non-selective cannabinoid receptor agonists reduces pain sensitivity in animals and humans. However, activation of CB1 receptors is also associated with central side effects… More recently, a role for selective CB2 agonists in pain modification has been demonstrated…a selective CB2 agonist, was recently reported to partially reverse the inflammation and hyperalgesia in a rat model of acute inflammation. In the current report, we extend the characterization and therapeutic potential of this compound…

 These data support the tenet that selective CB2 receptor agonists have the potential to treat pain without eliciting the centrally-mediated side effects associated with non-selective cannabinoid agonists…”

http://www.ncbi.nlm.nih.gov/pubmed/15814101

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Nabilone. A preliminary review of its pharmacological properties and therapeutic use.

Abstract

“Nabilone is a new orally active cannabinoid for the treatment of severe gastrointestinal toxicity associated with cancer chemotherapy. The pharmacological profile of nabilone suggests that it acts primarily by preventing emesis controlled by the medulla oblongata, although its secondary mild anxiolytic activity may contribute to the overall efficacy. Nabilone 2mg twice daily starting 12 hours prior to, and continued for the duration of, chemotherapy produces significant reduction in the severity and duration of nausea and the frequency of vomiting in about 50 to 70% of patients with severe symptoms refractory to conventional therapy. Nabilone has proven to be more effective in controlling symptoms and preferred by more patients than prochlorperazine 10mg 2 to 4 times daily in a limited number of studies, despite a higher incidence of side effects. Comparative trials against other new antiemetic agents, such as high dose metoclopramide, and use of nabilone in combination with other antiemetics remain to be undertaken. The incidence of side effects is high with nabilone; drowsiness, dizziness and/or vertigo occur in 60 to 70% of patients, but rarely lead to drug withdrawal, although more troublesome effects, such as postural hypotension, ataxia, vision disturbance and toxic psychoses, may cause discontinuation of therapy. Thus, nabilone offers an effective alternative to the treatment options available in a difficult therapeutic area – those patients with severe gastrointestinal side effects from cancer chemotherapy who are refractory to conventional therapy.”

http://www.ncbi.nlm.nih.gov/pubmed/2863127

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