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

The cannabinoid antagonist, AM251 attenuates ataxia related deficiencies in a cerebellar ataxic model

Aim: Disruption in cerebellar inputs, as well as dysfunction of Purkinje cells (PCs), causes a change in the timing of electrical signaling in the cerebellum resulting in disorders such as cerebellar ataxia. Although much clinical and molecular genetics research has been conducted to understand this disorder, there is no specific treatment for cerebellar ataxia. As cannabinoid type 1 receptors (CB1Rs) are highly expressed in the cerebellum and have been suggested as a therapeutic strategy, we determined whether AM251, a cannabinoid receptor antagonist, was neuroprotective of PCs in a rat cerebellar ataxic model.Materials and methods: To this end, we conducted behavioral and histological tests in the 3-acetylpyridine (3AP) rat cerebellar ataxia model, to explore whether AM251 was protective against induction of ataxia and cell death.Results: Rats with chemical degeneration of the inferior olive induced by 3AP (55 mg/kg, i.p.) clearly showed cerebellar ataxic symptoms. The locomotor activity and motor coordination of the ataxic animals were clearly disrupted compared to the control group. Further, histological analysis showed cell death and PCs degenerated with loss of cell membrane integrity associated with 3AP. Pre-treatment by AM251 improved the locomotor activity of the ataxic animals, and AM251 almost prevented PCs neuronal degeneration.Conclusion: Our data which show protection of cerebellar PCs and motor improvement in the ataxic rat model by treatment with AM251 suggests that targeting cannabinoid receptors should be considered for therapeutic intervention in cerebellar ataxia.HIGHLIGHTS:AM251 was protective against induction of ataxia and cell death.CBR antagonist typically ameliorated 3AP induced Ataxia.AM251 affected explorative and gait disturbances induced by 3AP.CBR antagonist improved impairments of anxiety-like behaviors following 3AP.

Pharmacologic antagonism of CB1 receptors improves electrophysiological alterations in Purkinje cells exposed to 3-AP

INTRODUCTION

Although ataxia is associated with cerebellar dysfunction, little is known about the effects of 3-AP exposure on Purkinje cell electrophysiological properties. Here, we evaluated these parameters in cerebellar vermis brain slices.

METHODS

Purkinje cells were exposed to artificial cerebrospinal fluid (aCSF) (control) or to 1 mM 3-acetylpyridine (3-AP) in the recording chamber. The effects of a cannabinoid agonist (WIN; 7.5 nmol) and a cannabinoid antagonist (AM; 20 nmol) were evaluated under both conditions.

RESULTS

Exposure to 3-AP induced dramatic changes in cellular excitability that likely would affect Purkinje cell output. In whole-cell current clamp recordings, 3-AP-exposed Purkinje cells demonstrated a significantly higher frequency of action potentials, a larger afterhyperpolarization (AHP), and a larger rebound of action potentials. In addition, 3-AP caused a significant decrease in the interspike interval (ISI), half-width, and first spike latency. Remarkably, the action potential frequency, AHP amplitude, rebound, ISI, action potential halfwidth, and first spike latency were no longer different from controls in 3-AP cells treated with AM. Sag percentage, on the other hand, showed no significant difference under any treatment condition, indicating that cannabinoids' actions on 3-AP-mediated Purkinje cell changes may not include effects on neuronal excitability through changes of Ih.

CONCLUSIONS

These data show that cannabinoid antagonists reduce the excitability of Purkinje cells following exposure to 3-AP and suggest their potential as therapeutics in cerebellar dysfunctions.

Impact of the Cannabinoid System in Alzheimer's Disease

Cannabinoids are compounds isolated from cannabis and are also widely present in both nervous and immune systems of animals. In recent years, with in-depth research on cannabinoids, their clinical medicinal value has been evaluated, and many exciting achievements have been continuously accumulating, especially in the field of neurodegenerative disease. Alzheimer's disease is the most common type of neurodegenerative disease that causes dementia and has become a global health problem that seriously impacts human health today. In this review, we discuss the therapeutic potential of cannabinoids for the treatment of Alzheimer's disease. How cannabinoids act on different endocannabinoid receptor subtypes to regulate Alzheimer's disease and the roles of the endocannabinoid system in Alzheimer's disease are outlined, and the underlying mechanisms are discussed. Finally, we summarize the most relevant opportunities of cannabinoid pharmacology related to Alzheimer's disease and discuss the potential usefulness of cannabinoids in the clinical treatment of Alzheimer's disease.

Modulation of the CB1 cannabinoid receptor has potential therapeutic utility in the 3-acetylpyridine cerebellar ataxia rat model

Cerebellar ataxia is a neurodegenerative disorder leading to severe motor incoordination. Recently, it has been suggested that cannabinoids play a role in modulating ataxic symptoms. To understand the possible therapeutic effect of cannabinoids for the management of cerebellar ataxia, we used cannabinoid agonist/antagonists to target the cannabinoid type 1 receptor (CB1R) in the 3 acetyl pyridine (3AP) rat model of ataxia. The role of the CB1R was examined using three different doses of the CB1R agonist, WIN-55,212-2 (WIN; 0.1, 0.5, 1 mg/kg) administrated 30 min prior to 3AP (55 mg/kg, i.p.) which leads to motor impairment through destruction of the inferior olive. In some groups, the CB1R antagonist AM251 (1 mg/kg) was given in combination with WIN. Locomotor activity and motor coordination were impaired by 3AP, and the application of WIN did not ameliorate this effect. However, the abnormal gait, rearing and grooming caused by 3AP were prevented by co-administration of AM251 with WIN. While the addition of the CB1R antagonist improved some ataxic symptoms, there was no effect of AM251 on balance or locomotor activity when co-administrated with WIN. Behavioral testing indicated that not only did WIN fail to exert any protective effect on ataxic symptoms; it exacerbated ataxic symptoms, suggesting that CB1R agonists may not be the ideal therapeutic drug in this disorder. When taken together, the findings from the present study indicate that cannabinoid modulation of ataxia symptoms may not act solely through CB1Rs and other cannabinoid receptors should be considered in future studies.

Cannabis use in patients with Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay

Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) is an early-onset cerebellar ataxia with often presence of peripheral sensorimotor neuropathy and lower limb spasticity. Recently, the presence of pain has been associated with ARSACS in a quarter of the population in relation to spasms and neuropathic pain. However, limited therapeutic options available to patients and the occurrence of persistent symptoms despite treatment with the usual pharmacologic agents have led to exploring cannabis as a potential alternative. The aim of this study was to characterize the profile of cannabis use among patients with ARSACS. Phone interviews were conducted to document current or former cannabis use. Reasons of cannabis use and the characteristics of use were also investigated. Among the 50 study participants, 18% currently used cannabis, 40% reported at least one occurrence of cannabis use and 42% reported having never used cannabis. A greater proportion of patients with regular cannabis use reported chronic pain in comparison to those who never used. Although less frequent than ataxia, spasticity, muscle cramps or muscle spasms, which were independently reported by more than half of the studied sample, chronic pain was notably present in 30% of participants. While our study did not assess the therapeutic effects of cannabis, our results highlight that there is a potential role for cannabis and cannabinoids in the management of multiple ARSACS-associated symptoms and that agents modulating the endocannabinoid system need to be properly investigated.

1-, 2- and 3-AG as substrates of the endocannabinoid enzymes and endogenous ligands of the cannabinoid receptor 1

2-Arachidonoylglycerol (2-AG) is the most potent and abundant endocannabinoid that acts as a full agonist at the cannabinoid 1 (CB1) and 2 (CB2) receptors. It serves as a substrate for several serine hydrolases, including monoacylglycerol lipase (MGL), α/β hydrolase domain 6 (ABHD6) and fatty acid amide hydrolase (FAAH). However, 2-AG's rapid conversion to 1-AG (the S stereoisomer) and 3-AG (the R stereoisomer) complicates in vivo signaling. Here, we present the interaction profiles of 2-AG and its isomerization products, 1- and 3-AG, with the endocannabinoid MGL, ABHD6 and FAAH enzymes as well as the CB1 receptor. The 1- and 3-AG enantiomers are less prone to isomerization, and their affinities to endocannabinoid enzymes and potencies at CB1 receptor are quite different compared to 2-AG. Although MGL is the principal hydrolytic enzyme of 2-AG, 3-AG (the R isomer) appears to be the best substrate for hMGL. Contrarily, 1-AG (the S isomer) demonstrates the worst substrate profile, indicating that the stereochemistry of 1(3)-monoacylglycerols is very important for MGL enzyme. On the other hand, both 1- and 3-AG (the sn1 monoacylglycerols) are efficiently hydrolyzed by hABHD6 without preference, while 2-AG (the sn2 monoacylglycerol) has the lowest rate of hydrolysis. FAAH, the principal hydrolytic enzyme for arachidonoylethanolamide (anandamide, AEA), catalyzes the hydrolysis of all three isomers with similar efficiencies. In a functional cAMP assay at CB1 receptor, all three isomers behaved as agonists, with 2-AG being the most potent, followed by 3-AG then 1-AG. The presented data provides stereochemical insights to design chemically stable AG analogs with preferential stability against enzymes of interest.

Endocannabinoids regulate cerebellar GABAergic transmission in a synapse type-dependent manner

Endocannabinoids (eCBs) act as ubiquitous modulators of synaptic transmission via the activation of cannabinoid receptors (CBRs). Cerebellar Purkinje cells (PCs) make strong inhibitory synaptic contacts not only with neurons in the deep cerebellar nuclei (DCN) but also with Lugaro cells and globular cells, whose cell bodies are located underneath the PC layer. However, little is known about the modulatory actions of eCBs on GABA release from PC axon terminals. Here, we examined the effects of eCBs on the GABAergic transmission at PC-globular cell synapses and PC-large DCN neuron synapses electrophysiologically using mouse cerebellar slices. We showed that the types 1 and 2 CBR agonist WIN55212 did not affect either spontaneous or miniature inhibitory postsynaptic currents (IPSCs) in globular cells under control conditions and in a state of enhanced synaptic activity. By contrast, another G_i/o protein-coupled receptor agonist, baclofen, significantly reduced the miniature IPSC frequency in globular cells. WIN55212 had no effects on IPSCs in large DCN neurons. A type 2 CBR agonist, HU308, also had no effects on IPSCs in either globular cells or large DCN neurons. Moreover, the PCs' target neurons did not elicit depolarization-induced suppression of inhibition. These results suggest the lack of a functional role of CBRs at PCs' axon terminals. This is in sharp contrast to the fact that PCs receive abundant excitatory and inhibitory inputs that are under eCB-mediated presynaptic inhibitory modulation. The actions of eCBs are selective to distinct synapses and possibly contribute to information processes and rigorous signal transmission in the cerebellum.

The endocannabinoid system is affected by cholesterol dyshomeostasis: Insights from a murine model of Niemann Pick type C disease

The dyshomeostasis of intracellular cholesterol trafficking is typical of the Niemann-Pick type C (NPC) disease, a fatal inherited lysosomal storage disorder presenting with progressive neurodegeneration and visceral organ involvement. In light of the well-established relevance of cholesterol in regulating the endocannabinoid (eCB) system expression and activity, this study was aimed at elucidating whether NPC disease-related cholesterol dyshomeostasis affects the functional status of the brain eCB system. To this end, we exploited a murine model of NPC deficiency for determining changes in the expression and activity of the major molecular components of the eCB signaling, including cannabinoid type-1 and type-2 (CB₁ and CB₂) receptors, their ligands, N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), along with their main synthesizing/inactivating enzymes. We found a robust alteration of distinct components of the eCB system in various brain regions, including the cortex, hippocampus, striatum and cerebellum, of Npc1-deficient compared to wild-type pre-symptomatic mice. Changes of the eCB component expression and activity differ from one brain structure to another, although 2-AG and AEA are consistently found to decrease and increase in each structure, respectively. The thorough biochemical characterization of the eCB system was accompanied by a behavioral characterization of Npc1-deficient mice using a number of paradigms evaluating anxiety, locomotor activity, spatial learning/memory abilities, and coping response to stressful experience. Our findings provide the first description of an early and region-specific alteration of the brain eCB system in NPC and suggest that defective eCB signaling could contribute at producing and/or worsening the neurological symptoms of this disorder.

Endocannabinoid System in Spinocerebellar Ataxia Type-3 and Other Autosomal-Dominant Cerebellar Ataxias: Potential Role in Pathogenesis and Expected Relevance as Neuroprotective Targets

Spinocerebellar ataxias (SCAs) are a group of hereditary and progressive neurological disorders characterized by a loss of balance and motor coordination typically associated with cerebellar atrophy. The most prevalent SCA types are all polyQ disorders like Huntington’s disease, sharing the most relevant events in pathogenesis with this basal ganglia disorder, but with most of the damage concentrated in cerebellar neurons, and in their afferent and efferent connections (e.g., brainstem nuclei). SCAs have no cure and effective symptom-alleviating and disease-modifying therapies are not currently available. However, based on results obtained in studies conducted in murine models and information derived from analyses in post-mortem tissue samples from patients, which show notably higher levels of CB₁ receptors found in different cerebellar neuronal subpopulations, the blockade of these receptors has been proposed for acutely modulating motor incoordination in cerebellar ataxias, whereas their chronic activation has been proposed for preserving specific neuronal losses. Additional studies in post-mortem tissues from SCA patients have also demonstrated elevated levels of CB₂ receptors in Purkinje neurons as well as in glial elements in the granular layer and in the cerebellar white matter, with a similar profile found for endocannabinoid hydrolyzing enzymes, then suggesting that activating CB₂ receptors and/or inhibiting these enzymes may also serve to develop cannabinoid-based neuroprotective therapies. The present review will address both aspects. On one hand, the endocannabinoid system becomes dysregulated in the cerebellum and also in other CNS structures (e.g., brainstem, basal ganglia) in SCAs, which may contribute to the progression of pathogenic events in these diseases. On the other hand, these endocannabinoid alterations may be pharmacologically corrected or enhanced, and this may have therapeutic consequences, either alleviating specific symptoms or eliciting neuroprotective effects, an objective presently under investigation.

Cerebellar ataxia

The cerebellum plays an integral role in the control of limb and ocular movements, balance, and walking. Cerebellar disorders may be classified as sporadic or hereditary with clinical presentation varying with the extent and site of cerebellar damage and extracerebellar signs. Deficits in balance and walking reflect the cerebellum's proposed role in coordination, sensory integration, coordinate transformation, motor learning, and adaptation. Cerebellar dysfunction results in increased postural sway, hypermetric postural responses to perturbations and optokinetic stimuli, and postural responses that are poorly coordinated with volitional movement. Gait variability is characteristic and may arise from a combination of balance impairments, interlimb incoordination, and incoordination between postural activity and leg movement. Intrinsic problems with balance lead to a high prevalence of injurious falls. Evidence for pharmacologic management is limited, although aminopyridines reduce attacks in episodic ataxias and may have a role in improving gait ataxia in other conditions. Intensive exercises targeting balance and coordination lead to improvements in balance and walking but require ongoing training to maintain/maximize any effects. Noninvasive brain stimulation of the cerebellum may become a useful adjunct to therapy in the future. Walking aids, orthoses, specialized footwear and seating may be required for more severe cases of cerebellar ataxia.

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

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-mortem cerebellum 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 vivo brain 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 oleoylethanolamide 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.