Heteromer formation between cannabinoid type 1 and dopamine type 2 receptors is altered by combination cannabinoid and antipsychotic treatments.

The cannabinoid type 1 (CB1 ) receptor and the dopamine type 2 (D2 ) receptor are co-localized on medium spiny neuron terminals in the globus pallidus where they modulate neural circuits involved in voluntary movement. Physical interactions between the two receptors have been shown to alter receptor signaling in cell culture. The objectives of the current study were to identify the presence of CB1 /D2 heteromers in the globus pallidus of C57BL/6J male mice, define how CB1 /D2 heteromer levels are altered following treatment with cannabinoids and/or antipsychotics, and determine if fluctuating levels of CB1 /D2 heteromers have functional consequences. Using in situ proximity ligation assays, we observed CB1 /D2 heteromers in the globus pallidus of C57BL/6J mice. The abundance of the heteromers increased following treatment with the nonselective cannabinoid receptor agonist, CP55,940. In contrast, treatment with the typical antipsychotic haloperidol reduced the number of CB1 /D2 heteromers, whereas the atypical antipsychotic olanzapine treatment had no effect. Co-treatment with CP55,940 and haloperidol had similar effects to haloperidol alone, whereas co-treatment with CP55,940 and olanzapine had similar effects to CP55,940. The observed changes were found to have functional consequences as the differential effects of haloperidol and olanzapine also applied to γ-aminobutyric acid release in STHdhQ7/Q7 cells and motor function in C57BL/6J male mice. This work highlights the clinical relevance of co-exposure to cannabinoids and different antipsychotics over acute and prolonged time periods.

Effects of intravitreal bevacizumab in Gram-positive and Gram-negative models of ocular inflammation.

BACKGROUND: Exogenous endophthalmitis is a potential complication of intraocular surgery and frequently results in visual impairment. Current treatment involves administration of intravitreal (IVT) antibiotics with or without vitrectomy surgery. Evidence for the use of adjunctive anti-inflammatory agents is conflicting. We set out to determine if bevacizumab, a humanized monoclonal IgG1 antibody targeted against vascular endothelial growth factor (VEGF), has anti-inflammatory properties in experimental models of Gram-positive and Gram-negative inflammation. METHODS: BALB/c mice were subjected to lipopolysaccharide- (LPS) or peptidoglycan- (PGN) induced ocular inflammation and treated with IVT bevacizumab. Iris microvasculature was imaged 6 hours following irritant/treatment using intravital microscopy (IVM) before the mice were euthanized and the eyes were enucleated immediately post-mortem. Following enucleation, levels of VEGF and 23 cytokines and chemokines (IL-1α, IL-1ß, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10, IL-12 (p40), IL-12 (p70), IL-13, IL-17, TNF, KC, G-CSF, GM-CSF, Eotaxin, INF-γ, MCP-1, MIP-1α, MIP-1ß, RANTES) were quantified using a multiplex assay. RESULTS: Levels of VEGF were significantly increased during the inflammatory response, triggered by either PGN or LPS. Both the adherence of leukocytes to the iris vascular endothelium and the levels of pro-inflammatory cytokines and chemokines were significantly increased following administration of either irritant. Treatment with bevacizumab decreased levels of leukocyte adherence in LPS-treated eyes, however, not in PGN-treated eyes. Conversely, bevacizumab treatment decreased levels of cytokines and chemokines (TNF, IL-6, MCP-1, MIP-1α, MIP-1ß, RANTES, KC) in PGN-treated eyes, however, not in LPS-treated eyes. CONCLUSIONS: Within a 6-hour window bevacizumab had anti-inflammatory actions that were distinct in both Gram-positive (PIU) and Gram-negative (EIU) models, respectively. Given our findings, this would suggest that bevacizumab may have utility as an adjunctive therapy to IVT antibiotics and vitrectomy in the management of exogenous endophthalmitis.

The Cannabinoids Δ8THC, CBD, and HU-308 Act via Distinct Receptors to Reduce Corneal Pain and Inflammation.

Background and Purpose: Corneal injury can result in dysfunction of corneal nociceptive signaling and corneal sensitization. Activation of the endocannabinoid system has been reported to be analgesic and anti-inflammatory. The purpose of this research was to investigate the antinociceptive and anti-inflammatory effects of cannabinoids with reported actions at cannabinoid 1 (CB1R) and cannabinoid 2 (CB2R) receptors and/or noncannabinoid receptors in an experimental model of corneal hyperalgesia. Methods: Corneal hyperalgesia (increased pain response) was generated using chemical cauterization of the corneal epithelium in wild-type (WT) and CB2R knockout (CB2R-/-) mice. Cauterized eyes were treated topically with the phytocannabinoids Δ8-tetrahydrocannabinol (Δ8THC) or cannabidiol (CBD), or the CBD derivative HU-308, in the presence or absence of the CB1R antagonist AM251 (2.0 mg/kg i.p.), or the 5-HT1A receptor antagonist WAY100635 (1 mg/kg i.p.). Behavioral pain responses to a topical capsaicin challenge at 6 h postinjury were quantified from video recordings. Mice were euthanized at 6 and 12 h postcorneal injury for immunohistochemical analysis to quantify corneal neutrophil infiltration. Results: Corneal cauterization resulted in hyperalgesia to capsaicin at 6 h postinjury compared to sham control eyes. Neutrophil infiltration, indicative of inflammation, was apparent at 6 and 12 h postinjury in WT mice. Application of Δ8THC, CBD, and HU-308 reduced the pain score and neutrophil infiltration in WT mice. The antinociceptive and anti-inflammatory actions of Δ8THC, but not CBD, were blocked by the CB1R antagonist AM251, but were still apparent, for both cannabinoids, in CB2R-/- mice. However, the antinociceptive and anti-inflammatory actions of HU-308 were absent in the CB2R-/- mice. The antinociceptive and anti-inflammatory effects of CBD were blocked by the 5-HT1A antagonist WAY100635. Conclusion: Topical cannabinoids reduce corneal hyperalgesia and inflammation. The antinociceptive and anti-inflammatory effects of Δ8THC are mediated primarily via CB1R, whereas that of the cannabinoids CBD and HU-308, involve activation of 5-HT1A receptors and CB2Rs, respectively. Cannabinoids could be a novel clinical therapy for corneal pain and inflammation resulting from ocular surface injury.

Cannabinoid 2 receptor is a novel anti-inflammatory target in experimental proliferative vitreoretinopathy.

Proliferative vitreoretinopathy (PVR) can develop after ocular trauma or inflammation and is a common complication of surgery to correct retinal detachment. Currently, there are no pharmacological treatments for PVR. Cannabinoids acting at cannabinoid 2 receptor (CB2R) can decrease inflammation and fibrosis. The objective of this study was to examine the anti-inflammatory actions of CB2R as a candidate novel therapeutic target in experimental PVR. PVR was induced by intravitreal injection of dispase in wild-type (WT) and CB2R genetic knockout (CB2R-/-) mice. Ocular pathology was studied at 24 h or one week after dispase injection. CB2R modulation was examined in WT mice, using the CB2R agonist, HU308, and the CB2R antagonist, AM630. Histopathological scoring and quantification of microglia was used to evaluate tissue pathology. Quantitative PCR and multiplex assays were used to assess changes in proinflammatory cytokines. Intravital microscopy (IVM) was used to visualize and quantify leukocyte-endothelial adhesion to the iridial microcirculation. Activation of CB2R with HU308 in WT mice with PVR decreased mean histopathological scores, the number of microglia, and leukocyte adhesion compared to vehicle-treated animals. Conversely, an increase in histopathological scores and activated microglia was observed in PVR animals after treatment with AM630. CB2R-/- mice with PVR exhibited exacerbated ocular histopathology, increased microglia numbers, and elevated protein levels of cytokines as compared to WT mice. In conclusion, our results indicate that intervention at early stage PVR with CB2R agonists reduces ocular inflammation and disease severity. CB2R may represent a therapeutic target to prevent PVR progression and vision loss. This article is part of the Special Issue entitled 'Lipid Sensing G Protein-Coupled Receptors in the CNS'.

Turning Down the Thermostat: Modulating the Endocannabinoid System in Ocular Inflammation and Pain.

The endocannabinoid system (ECS) has emerged as an important regulator of both physiological and pathological processes. Notably, this endogenous system plays a key role in the modulation of pain and inflammation in a number of tissues. The components of the ECS, including endocannabinoids, their cognate enzymes and cannabinoid receptors, are localized in the eye, and evidence indicates that ECS modulation plays a role in ocular disease states. Of these diseases, ocular inflammation presents a significant medical problem, given that current clinical treatments can be ineffective or are associated with intolerable side-effects. Furthermore, a prominent comorbidity of ocular inflammation is pain, including neuropathic pain, for which therapeutic options remain limited. Recent evidence supports the use of drugs targeting the ECS for the treatment of ocular inflammation and pain in animal models; however, the potential for therapeutic use of cannabinoid drugs in the eye has not been thoroughly investigated at this time. This review will highlight evidence from experimental studies identifying components of the ocular ECS and discuss the functional role of the ECS during different ocular inflammatory disease states, including uveitis and corneal keratitis. Candidate ECS targeted therapies will be discussed, drawing on experimental results obtained from both ocular and non-ocular tissue(s), together with their potential application for the treatment of ocular inflammation and pain.