Cannabinoid Receptor Type 1 in Parkinson's Disease: A Positron Emission Tomography Study with [18 F]FMPEP-d2

The Expression and Functionality of CB1R-NMDAR Complexes Are Decreased in A Parkinson's Disease Model

One of the hallmarks of Parkinson's disease (PD) is the alteration in the expression and function of NMDA receptor (NMDAR) and cannabinoid receptor 1 (CB1R). The presence of CB1R-NMDAR complexes has been described in neuronal primary cultures. The activation of CB1R in CB1R-NMDAR complexes was suggested to counteract the detrimental NMDAR overactivation in an AD mice model. Thus, we aimed to explore the role of this receptor complex in PD. By using Bioluminescence Resonance Energy Transfer (BRET) assay, it was demonstrated that α-synuclein induces a reorganization of the CB1R-NMDAR complex in transfected HEK-293T cells. Moreover, α-synuclein treatment induced a decrease in the cAMP and MAP kinase (MAPK) signaling of both CB1R and NMDAR not only in transfected cells but also in neuronal primary cultures. Finally, the interaction between CB1R and NMDAR was studied by Proximity Ligation Assay (PLA) in neuronal primary cultures, where it was observed that the expression of CB1R-NMDAR complexes was decreased upon α-synuclein treatment. These results point to a role of CB1R-NMDAR complexes as a new therapeutic target in Parkinson's disease.

A Robust and Efficient FRET-Based Assay for Cannabinoid Receptor Ligands Discovery

The identification of new modulators for Cannabinoid Receptors (CBRs) has garnered significant attention in drug discovery over recent years, owing to their manifold pathophysiological implications. In the context of hit identification, the availability of robust and sensitive high-throughput screening assays is essential to enhance the likelihood of success. In this study, we present the development and validation of a Tag-lite® binding assay designed for screening hCB1/hCB2 binding, employing a dual fluorescent ligand, CELT-335. Representative ligands for CBRs, exhibiting diverse affinity and functional profiles, were utilized as reference compounds to validate the robustness and efficiency of the newly developed Tag-lite® binding assay protocol. The homogeneous format, coupled with the sensitivity and optimal performance of the fluorescent ligand CELT-335, establishes this assay as a viable and reliable method for screening in hit and lead identification campaigns.

Treadmill exercise modulates nigral and hippocampal cannabinoid receptor type 1 in the 6-OHDA model of Parkinson's disease

Physical exercise benefits Parkinson's disease (PD) patients but the mechanism is unclear. Cannabinoid receptor type 1 (CB1R) is known to be reduced in PD patients and animal models. We test the hypothesis that binding of the CB1R inverse agonist, [3H]SR141716A, is normalized by treadmill exercise in the toxin-induced 6-hydroxydopamine (6-OHDA) model of PD. Male rats had unilateral striatal injections of 6-OHDA or saline. After 15 days, half were submitted to treadmill exercise and half remained sedentary. [3H]SR141716A autoradiography was performed in postmortem tissue from striatum, substantia nigra (SN) and hippocampus. There was a 41% decrease of [3H]SR141716A specific binding in the ipsilateral SN of 6-OHDA-injected sedentary animals which was attenuated to 15% by exercise, when compared to saline-injected animals. No striatal differences were observed. A 30% bilateral hippocampal increase was observed in both healthy and 6-OHDA exercised groups. In addition, a positive correlation between nigral [3H]SR141716A binding and nociceptive threshold was observed in PD-exercised animals (p = 0.0008), suggesting a beneficial effect of exercise in the pain associated with the model. Chronic exercise can reduce the detrimental effects of PD on nigral [3H]SR141716A binding, similar to the reported reduction after dopamine replacement therapy, so should be considered as an adjunct therapy for PD.

Neuroinflammation and Mitochondrial Dysfunction in Parkinson's Disease: Connecting Neuroimaging with Pathophysiology

There is a pressing need for disease-modifying therapies in patients suffering from neurodegenerative diseases, including Parkinson's disease (PD). However, these disorders face unique challenges in clinical trial designs to assess the neuroprotective properties of potential drug candidates. One of these challenges relates to the often unknown individual disease mechanisms that would, however, be relevant for targeted treatment strategies. Neuroinflammation and mitochondrial dysfunction are two proposed pathophysiological hallmarks and are considered to be highly interconnected in PD. Innovative neuroimaging methods can potentially help to gain deeper insights into one's predominant disease mechanisms, can facilitate patient stratification in clinical trials, and could potentially map treatment responses. This review aims to highlight the role of neuroinflammation and mitochondrial dysfunction in patients with PD (PwPD). We will specifically introduce different neuroimaging modalities, their respective technical hurdles and challenges, and their implementation into clinical practice. We will gather preliminary evidence for their potential use in PD research and discuss opportunities for future clinical trials.