Search

Background Nirmatrelvir/ritonavir, the first severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protease inhibitor, reduces the risk of hospitalization and death by coronavirus disease 2019 (COVID-19) but has been associated with symptomatic rebound after therapy completion. Methods Six individuals with relapse of COVID-19 symptoms after treatment with nirmatrelvir/ritonavir, 2 individuals with rebound symptoms without prior antiviral therapy and 7 patients with acute Omicron infection (controls) were studied. Soluble biomarkers and serum SARS-CoV-2 nucleocapsid protein were measured. Nasal swabs positive for SARS-CoV-2 underwent viral isolation and targeted viral sequencing. SARS-CoV-2 anti-spike, anti–receptor-binding domain, and anti-nucleocapsid antibodies were measured. Surrogate viral neutralization tests against wild-type and Omicron spike protein, as well as T-cell stimulation assays, were performed. Results High levels of SARS-CoV-2 anti-spike immunoglobulin G (IgG) antibodies were found in all participants. Anti-nucleocapsid IgG and Omicron-specific neutralizing antibodies increased in patients with rebound. Robust SARS-CoV-2–specific T-cell responses were observed, higher in rebound compared with early acute COVID-19 patients. Inflammatory markers mostly decreased during rebound. Two patients sampled longitudinally demonstrated an increase in activated cytokine-producing CD4+ T cells against viral proteins. No characteristic resistance mutations were identified. SARS-CoV-2 was isolated by culture from 1 of 8 rebound patients; Polybrene addition increased this to 5 of 8. Conclusions Nirmatrelvir/ritonavir treatment does not impede adaptive immune responses to SARS-CoV-2. Clinical rebound corresponds to development of a robust antibody and T-cell immune response, arguing against a high risk of disease progression. The presence of infectious virus supports the need for isolation and assessment of longer treatment courses. Clinical trials registration NCT04401436.

Aims Long-term or recreational use of ketamine affects the urinary system and can result in ketamine-induced cystitis (KIC). Rodent models of KIC are important to study KIC pathophysiology and are paramount to the future development of therapies for this painful condition. This review aims to provide a summary of rodent models of KIC, focusing on disease induction, experimental methods, and pathological features of the model. Method A literature search was performed using the National Center for Biotechnology Information (NCBI) Pubmed database up to March 2021. 20 articles met the inclusion criteria and were finally selected. Results There are considerable variations in the rodent models used for studying KIC in terms of the strain of the animal being used; dose, duration, and route of ketamine administration to induce KIC, and assessment of pathological features. Conclusion KIC remains difficult to fully recapitulate in humans. Improved characterization of KIC models and the experimental parameters and meticulous discussion on translational limitations are required to improve the translational value of research using rodent models of KIC.

Clinical rebound of COVID-19 after nirmatrelvir/ritonavir treatment has been reported. We performed clinical, virologic, and immune measurements in seven patients with symptomatic rebound, six after nirmatrelvir/ritonavir treatment and one without previous treatment. There was no evidence of severe disease or impaired antibody and T-cell responses in people with rebound symptoms.

The human brain requires adequate cerebral blood flow to meet the high demand for nutrients and to clear waste products. With age, there is a chronic reduction in cerebral blood flow in small resistance arteries that can eventually limit proper brain function. The endothelin system is a key mediator in the regulation of cerebral blood flow, but the contributions of its constituent receptors in the endothelial and vascular smooth muscle layers of cerebral arteries have not been well defined in the context of aging. We isolated posterior cerebral arteries from young and aged Fischer 344 rats, as well as ETB receptor knock-out rats and mounted the vessels in plexiglass pressure myograph chambers to measure myogenic tone in response to increasing pressure and targeted pharmacological treatments. We used an ETA receptor antagonist (BQ-123), an ETB receptor antagonist (BQ-788), endothelin-1, an endothelin-1 synthesis inhibitor (phosphoramidon), and vessel denudation to dissect the roles of each receptor in aging vasculature. Aged rats exhibited a higher myogenic tone than young rats, and the tone was sensitive to the ETA antagonist, BQ-123, but insensitive to the ETB antagonist, BQ-788. By contrast, the tone in the vessels from young rats was raised by BQ-788 but unaffected by BQ-123. When the endothelial layer that is normally enriched with ETB1 receptors was removed from young vessels, myogenic tone increased. However, denudation of the endothelial layer did not influence vessels from aged animals. This indicated that endothelial ETB1 receptors were not functional in the vessels from aged rats. There was also an increase in ETA receptor expression with age, whereas ETB receptor expression remained constant between young and aged animals. These results demonstrate that in young vessels, ETB1 receptors maintain a lower myogenic tone, but in aged vessels, a loss of ETB receptor activity allows ETA receptors in vascular smooth muscle cells to raise myogenic tone. Our findings have potentially important clinical implications for treatments to improve cerebral perfusion in older adults with diseases characterized by reduced cerebral blood flow.

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.

Huntington’s disease (HD) is an inherited progressive neurodegenerative disease characterized by motor, cognitive, and behavioural changes. One of the earliest changes to occur in HD is a reduction in cannabinoid 1 receptor (CB(1)) levels in the striatum, which is strongly correlated with HD pathogenesis. CB(1) positive allosteric modulators (PAM) enhance receptor affinity for, and efficacy of activation by, orthosteric ligands, including the endocannabinoids anandamide and 2-arachidonoylglycerol. The goal of this study was to determine whether the recently characterized CB(1) allosteric modulators GAT211 (racemic), GAT228 (R-enantiomer), and GAT229 (S-enantiomer), affected the signs and symptoms of HD. GAT211, GAT228, and GAT229 were evaluated in normal and HD cell models, and in a transgenic mouse model of HD (7-week-old male R6/2 mice, 10 mg/kg/d, 21 d, i.p.). GAT229 was a CB(1) PAM that improved cell viability in HD cells and improved motor coordination, delayed symptom onset, and normalized gene expression in R6/2 HD mice. GAT228 was an allosteric agonist that did not enhance endocannabinoid signaling or change symptom progression in R6/2 mice. GAT211 displayed intermediate effects between its enantiomers. The compounds used here are not drugs, but probe compounds used to determine the potential utility of CB(1) PAMs in HD. Changes in gene expression, and not protein, were quantified in R6/2 HD mice because HD pathogenesis is associated with dysregulation of mRNA levels. The data presented here provide the first proof of principle for the use of CB(1) PAMs to treat the signs and symptoms of HD.

We apply the magic methyl effect to improve the potency/efficacy of GAT211, the prototypic 2-phenylindole-based cannabinoid type-1 receptor (CB1R) agonist-positive allosteric modulator (ago-PAM). Introducing a methyl group at the α-position of nitro group generated two diastereomers, the greater potency and efficacy of erythro, (±)-9 vs threo, (±)-10 constitutes the first demonstration of diastereoselective CB1R-allosteric modulator interaction. Of the (±)-9 enantiomers, (-)-(S,R)-13 evidenced improved potency over GAT211 as a CB1R ago-PAM, whereas (+)-(R,S)-14 was a CB1R allosteric agonist biased toward G protein- vs β-arrestin1/2-dependent signaling. (-)-(S,R)-13 and (+)-(R,S)-14 were devoid of undesirable side effects (triad test), and (+)-(R,S)-14 reduced intraocular pressure with an unprecedentedly long duration of action in a murine glaucoma model. (-)-(S,R)-13 docked into both a CB1R extracellular PAM and intracellular allosteric-agonist site(s), whereas (+)-(R,S)-14 preferentially engaged only the latter. Exploiting G-protein biased CB1R-allosteric modulation can offer safer therapeutic candidates for glaucoma and, potentially, other diseases.

The human brain requires adequate cerebral blood flow to meet the high demand for nutrients and to clear waste products. With age, there is a chronic reduction in cerebral blood flow in small resistance arteries that can eventually limit proper brain function. The endothelin system is a key mediator in the regulation of cerebral blood flow, but the contributions of its constituent receptors in the endothelial and vascular smooth muscle layers of cerebral arteries have not been well defined in the context of aging. We isolated posterior cerebral arteries from young and aged Fischer 344 rats, as well as ET

The endothelin receptor A (ETA) and endothelin receptor B (ETB) are G protein-coupled receptors that are co-expressed in vascular smooth muscle cells. Endothelin-1 (ET-1) activates endothelin receptors to cause microvascular vasoconstriction. Previous studies have shown that heteromerization between ETA and ETB prolongs Ca2+ transients, leading to prolongation of Gαq-dependent signaling and sustained vasoconstriction. We hypothesized that these effects are in part mediated by the resistance of ETA/ETB heteromers to β-arrestin recruitment and subsequent desensitization. Using bioluminescence resonance energy transfer 2 (BRET2), we found that ETB has a relatively equal affinity to form either homomers or heteromers with ETA when co-expressed in the human embryonic kidney 293 (HEK293) cells. When co-expressed, activation of ETA and ETB by ET-1 caused a heteromer-specific reduction and delay in β-arrestin-2 recruitment with a corresponding reduction and delay in ET-1-induced ETA/ETB co-internalization. Furthermore, the co-expression of ETA and ETB inhibited ET-1-induced β-arrestin-1-dependent extracellular signal-regulated kinase (ERK) phosphorylation while prolonging ET-1-induced Gαq-dependent ERK phosphorylation. ETA/ETB heteromerization mediates the long-lasting vasoconstrictor response to ET-1 by the prolongation of Gαq-dependent signaling and inhibition of β-arrestin function.

Background Proton pump inhibitors (PPI) are commonly prescribed medications which are indicated in various different gastrointestinal (GI) diseases, including peptic ulcer disease, gastroesophageal reflux disorder and upper GI bleeding. There is some evidence to suggest that PPI use in cirrhosis may predispose to the development of hepatic encephalopathy (HE) and spontaneous bacterial peritonitis (SBP), albeit with some controversy. Aims We aim to conduct a retrospective epidemiological analysis of the association between PPI use in hospitalized patients with cirrhosis, and prevalence of HE and SBP. Methods This was a retrospective cohort study of 600 adult patients (mean age 61.4 (SD=12.2)) admitted the Ottawa Hospital between January 1, 2011 and December 31, 2015 with cirrhosis. A chart review was conducted and relevant information extracted. Results Average MELD-Na on admission was 16.2 (sd=6.7). 14.8% of patients had a history of HE, 5.0% SBP, 7.8% with history of hepatocellular carcinoma and 1.0% with history of hepatorenal syndrome. 28.5% of patients had a history of varices, of which 11.0% had previous variceal bleeding. 69.3% of patients were on a PPI during their hospitalization. Not surprisingly, patients admitted with variceal bleeding were more likely to be exposed to PPI in hospital (97.2% vs 63.2%, p Conclusions We did not observe a significant difference in HE and SBP among this cohort of cirrhotic patients by in-hospital PPI use. We did however note significantly higher PPI use in patients with previous diagnosis of cirrhosis as compared to those who were newly diagnosed, as well as those whose admissions were related to bleeding. Patients with ascites had lower prevalence of PPI use. Prescribing patterns for PPIs in patients with cirrhosis warrant further attention, including clinical utility and longer-term risks and benefits of this therapy. Funding Agencies None

Background and purpose We sought to understand why (-)-cannabidiol (CBD) and (-)-cannabidiol-dimethylheptyl (CBD-DMH) exhibit distinct pharmacology, despite near identical structures. Experimental approach HEK293A cells expressing either human type 1 cannabinoid (CB1 ) receptors or CB2 receptors were treated with CBD or CBD-DMH with or without the CB1 and CB2 receptor agonist CP55,940, CB1 receptor allosteric modulator Org27569 or CB2 receptor inverse agonist SR144528. Ligand binding, cAMP levels and βarrestin1 recruitment were measured. CBD and CBD-DMH binding was simulated with models of human CB1 or CB2 receptors, based on the recently published crystal structures of agonist-bound (5XRA) or antagonist-bound (5TGZ) human CB1 receptors. Key results At CB1 receptors, CBD was a negative allosteric modulator (NAM), and CBD-DMH was a mixed agonist/positive allosteric modulator. CBD and Org27569 shared multiple interacting residues in the antagonist-bound model of CB1 receptors (5TGZ) but shared a binding site with CP55,940 in the agonist-bound model of CB1 receptors (5XRA). The binding site for CBD-DMH in the CB1 receptor models overlapped with CP55,940 and Org27569. At CB2 receptors, CBD was a partial agonist, and CBD-DMH was a positive allosteric modulator of cAMP modulation but a NAM of βarrestin1 recruitment. CBD, CP55,940 and SR144528 shared a binding site in the CB2 receptor models that was separate from CBD-DMH. Conclusion and implications The pharmacological activity of CBD and CBD-DMH in HEK293A cells and their modelled binding sites at CB1 and CB2 receptors may explain their in vivo effects and illuminates the difficulties associated with the development of allosteric modulators for CB1 and CB2 receptors. Linked articles This article is part of a themed section on 8th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Background Portal vein thrombosis (PVT) has a reported prevalence ranging from 0.6 to 26% in cirrhotic patients and yet optimal management in these patients remains unclear [1]. PVT can lead to poor outcomes including increased risk of bleeding, intestinal injury, and deterioration in liver function. Conversely, treatment of PVT in cirrhotic patients increases their risk of bleeding complications, particularly in patients with known varices. Aims The aim of this study is to better characterize the prevalence and impact of PVT in cirrhotic inpatients. Methods We conducted a retrospective cohort study based on data collected on adult patients admitted to the Ottawa Hospital between January 1, 2011 and December 31, 2015. We included patients with a diagnosis of cirrhosis either before or during index admission. Patients with a radiology report indicating a PVT were compared to those without PVT. Non-Ontario residents were excluded and where there were multiple admissions per patient one admission was randomly selected to be used. Ethics approval was obtained from the Research Ethics Board at the University of Ottawa. Results This study found 34 patients with cirrhosis diagnosed with PVT during their hospitalization (3.73%). Of the patients with PVT, 23 were acute and 11 were chronic based on radiologic appearance. Mean age was similar between groups (PVT: 61.7, SD=9.8; No PVT: 62.3, SD=12.3). The mean Na-MELD was also similar (PVT: 17.6, no PVT: 17.3, p=0.82). Among patients with PVT, 11 patients presented with ascites, 10 with hepatic encephalopathy (HE), 5 with abdominal pain and 5 with an upper GI bleed. Spontaneous bacterial peritonitis (SBP) occurred in 11.76% of patients with PVT as compared to 3% of patients without PVT (p value= 0.006). There also seemed to be a trend towards more HE in the cohort with PVT (20.6% vs 10.7%, p value= 0.07). With regards to screening for varices, 2 patients had an EGD in the 6 months prior to admission, 11 had an EGD on admission, 1 after anticoagulation due to bleeding, and 18 had no screening in the 6 months prior to admission. Twelve patients were treated for PVT, 17 were untreated and 5 did not have documentation about treatment. Of the patients that were not treated, 9 were due to palliative goals of care, 1 due to bleeding, 1 due to thrombocytopenia, 2 due to chronicity on imaging and 4 did not have reasons documented. Conclusions PVT is a known complication of cirrhosis, however the clinical significance and optimal management of patients with PVT is poorly understood. Although prevalence of PVT was low in this cohort, our data suggests some possible association between liver related complications and PVT, including SBP and HE. Further research is needed to determine how to best manage patients with PVT. 1. Garcia-Pagan JC, Valla DC. Portal vein thrombosis: a predictable milestone in cirrhosis? Journal of hepatology. 2009 Oct 1;51(4):632–4. Funding Agencies None

Type 1 cannabinoid (CB1) and dopamine 2 long form (D2L) receptors can physically interact to form heteromers that display unique pharmacology in vitro compared to homomeric complexes. Co-expression of CB1 and D2L and co-application of CB1 and D2 agonists increases cAMP levels while administration of either agonist alone decreases cAMP levels. To understand the observed co-agonist response, our first goal of the current study was to define the stoichiometry of CB1/D2L/Gα protein complexes. Using bioluminescence resonance energy transfer 2 (BRET2), we confirmed that, CB1 homodimers, D2L homodimers, and CB1/D2L heteromers are formed. By using sequential resonance energy transfer 2 (SRET2) combined with bimolecular fluorescence complementation (BiFC), we were able to demonstrate that CB1/D2L form heterotetramers consisting of CB1 and D2L homodimers. We demonstrated that CB1/D2L heterotetramers are coupled to at least two Gα proteins. The second aim of the study was to investigate allosteric effects of a D2L agonist (quinpirole) on CB1 receptor function and to investigate the effects of a CB1 agonist [arachidonyl-2-chloroethylamide (ACEA)] on D2L receptor function within CB1/D2L heterotetramers. Treating cells co-expressing CB1 and D2L with both ACEA and quinpirole switched CB1 and D2L receptor coupling and signaling from Gαi to Gαs proteins, enhanced β-arrestin1 recruitment and receptor co-internalization. The concept of bidirectional allosteric interaction within CB1/D2 heterotetramers has important implications for understanding the activity of receptor complexes in native tissues and under pathological conditions.

The cannabinoid 1 receptor (CB1R) is one of the most widely expressed metabotropic G protein-coupled receptors in brain, and its participation in various (patho)physiological processes has made CB1R activation a viable therapeutic modality. Adverse psychotropic effects limit the clinical utility of CB1R orthosteric agonists and have promoted the search for CB1R positive allosteric modulators (PAMs) with the promise of improved drug-like pharmacology and enhanced safety over typical CB1R agonists. In this study, we describe the synthesis and in vitro and ex vivo pharmacology of the novel allosteric CB1R modulator GAT211 (racemic) and its resolved enantiomers, GAT228 (R) and GAT229 (S). GAT211 engages CB1R allosteric site(s), enhances the binding of the orthosteric full agonist [3H]CP55,490, and reduces the binding of the orthosteric antagonist/inverse agonist [3H]SR141716A. GAT211 displayed both PAM and agonist activity in HEK293A and Neuro2a cells expressing human recombinant CB1R (hCB1R) and in mouse-bra...

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’.

Cannabinoid receptor 1 (CB1) activation has been reported to reduce transient receptor potential cation channel subfamily V member 1 (TRPV1)-induced inflammatory responses and is anti-nociceptive and anti-inflammatory in corneal injury. We examined whether allosteric ligands, can modulate CB1 signaling to reduce pain and inflammation in corneal hyperalgesia. Corneal hyperalgesia was generated by chemical cauterization of cornea in wildtype and CB2 knockout (CB2&minus, /&minus, ) mice. The novel racemic CB1 allosteric ligand GAT211 and its enantiomers GAT228 and GAT229 were examined alone or in combination with the orthosteric CB1 agonist &Delta, 8-tetrahydrocannabinol (&Delta, 8-THC). Pain responses were assessed following capsaicin (1 &micro, M) stimulation of injured corneas at 6 h post-cauterization. Corneal neutrophil infiltration was also analyzed. GAT228, but not GAT229 or GAT211, reduced pain scores in response to capsaicin stimulation. Combination treatments of 0.5% GAT229 or 1% GAT211 with subthreshold &Delta, 8-THC (0.4%) significantly reduced pain scores following capsaicin stimulation. The anti-nociceptive effects of both GAT229 and GAT228 were blocked with CB1 antagonist AM251, but remained unaffected in CB2&minus, mice. Two percent GAT228, or the combination of 0.2% &Delta, 8-THC with 0.5% GAT229 also significantly reduced corneal inflammation. CB1 allosteric ligands could offer a novel approach for treating corneal pain and inflammation.

(1) Background: The cannabinoid 2 receptor (CB2R) is a promising anti-inflammatory drug target and development of selective CB2R ligands may be useful for treating sight-threatening ocular inflammation. (2) Methods: This study examined the pharmacology of three novel chemically-diverse selective CB2R ligands: CB2R agonists, RO6871304, and RO6871085, as well as a CB2R inverse agonist, RO6851228. In silico molecular modelling and in vitro cell-based receptor assays were used to verify CB2R interactions, binding, cell signaling (&szlig, arrestin and cAMP) and early absorption, distribution, metabolism, excretion, and toxicology (ADMET) profiling of these receptor ligands. All ligands were evaluated for their efficacy to modulate leukocyte-neutrophil activity, in comparison to the reported CB2R ligand, HU910, using an in vivo mouse model of endotoxin-induced uveitis (EIU) in wild-type (WT) and CB2R-/- mice. The actions of RO6871304 on neutrophil migration and adhesion were examined in vitro using isolated neutrophils from WT and CB2R-/- mice, and in vivo in WT mice with EIU using adoptive transfer of WT and CB2R-/- neutrophils, respectively. (3) Results: Molecular docking studies indicated that RO6871304 and RO6871085 bind to the orthosteric site of CB2R. Binding studies and cell signaling assays for RO6871304 and RO6871085 confirmed high-affinity binding to CB2R and selectivity for CB2R &gt, CB1R, with both ligands acting as full agonists in cAMP and &szlig, arrestin assays (EC50s in low nM range). When tested in EIU, topical application of RO6871304 and RO6871085 decreased leukocyte-endothelial adhesion and this effect was antagonized by the inverse agonist, RO6851228. The CB2R agonist, RO6871304, decreased in vitro neutrophil migration of WT neutrophils but not neutrophils from CB2R-/-, and attenuated adhesion of adoptively-transferred leukocytes in EIU. (4) Conclusions: These unique ligands are potent and selective for CB2R and have good immunomodulating actions in the eye. RO6871304 and RO6871085, as well as HU910, decreased leukocyte adhesion in EIU through inhibition of resident ocular immune cells. The data generated with these three structurally-diverse and highly-selective CB2R agonists support selective targeting of CB2R for treating ocular inflammatory diseases.

G protein-coupled receptors (GPCRs) are the target for many drugs. Evidence continues to accumulate demonstrating that multiple receptors form homo- and heteromeric complexes, which in turn dynamically couple with G proteins, and other interacting proteins. Here, we describe a method to simultaneously determine the identity of up to four distinct constituents of GPCR complexes using a combination of sequential bioluminescence resonance energy transfer 2-fluorescence resonance energy transfer (SRET

One of the most abundant G-protein coupled receptors (GPCRs) in brain, the cannabinoid 1 receptor (CB1R), is a tractable therapeutic target for treating diverse psychobehavioral and somatic disorders. Adverse on-target effects associated with small-molecule CB1R orthosteric agonists and inverse agonists/antagonists have plagued their translational potential. Allosteric CB1R modulators offer a potentially safer modality through which CB1R signaling may be directed for therapeutic benefit. Rational design of candidate, druglike CB1R allosteric modulators requires greater understanding of the architecture of the CB1R allosteric endodomain(s) and the capacity of CB1R allosteric ligands to tune the receptor's information output. We have recently reported the synthesis of a focused library of rationally designed, covalent analogues of Org27569 and PSNCBAM-1, two prototypic CB1R negative allosteric modulators (NAMs). Among the novel, pharmacologically active CB1R NAMs reported, the isothiocyanate GAT100 emerged as the lead by virtue of its exceptional potency in the [(35)S]GTPγS and β-arrestin signaling assays and its ability to label CB1R as a covalent allosteric probe with significantly reduced inverse agonism in the [(35)S]GTPγS assay as compared to Org27569. We report here a comprehensive functional profiling of GAT100 across an array of important downstream cell-signaling pathways and analysis of its potential orthosteric probe-dependence and signaling bias. The results demonstrate that GAT100 is a NAM of the orthosteric CB1R agonist CP55,940 and the endocannabinoids 2-arachidonoylglycerol and anandamide for β-arrestin1 recruitment, PLCβ3 and ERK1/2 phosphorylation, cAMP accumulation, and CB1R internalization in HEK293A cells overexpressing CB1R and in Neuro2a and STHdh(Q7/Q7) cells endogenously expressing CB1R. Distinctively, GAT100 was a more potent and efficacious CB1R NAM than Org27569 and PSNCBAM-1 in all signaling assays and did not exhibit the inverse agonism associated with Org27569 and PSNCBAM-1. Computational docking studies implicate C7.38(382) as a key feature of GAT100 ligand-binding motif. These data help inform the engineering of newer-generation, druggable CB1R allosteric modulators and demonstrate the utility of GAT100 as a covalent probe for mapping structure-function correlates characteristic of the druggable CB1R allosteric space.

G protein-coupled receptors (GPCRs) are the target for many drugs. Evidence continues to accumulate demonstrating that multiple receptors form homo- and heteromeric complexes, which in turn dynamically couple with G proteins, and other interacting proteins. Here, we describe a method to simultaneously determine the identity of up to four distinct constituents of GPCR complexes using a combination of sequential bioluminescence resonance energy transfer 2-fluorescence resonance energy transfer (SRET2) with bimolecular fluorescence complementation (BiFC). The method is amenable to moderate throughput screening of changes in response to ligands and time-course analysis of protein-protein oligomerization.

Central nervous system (CNS) injury, such as stroke or trauma, is known to increase susceptibility to various infections that adversely affect patient outcomes (CNS injury-induced immunodepression—CIDS). The endocannabinoid system (ECS) has been shown to have immunoregulatory properties. Therefore, the ECS might represent a druggable target to overcome CIDS. Evidence suggests that cannabinoid type 2 receptor (CB2R) activation can be protective during the early pro-inflammatory phase after CNS injury, as it limits neuro-inflammation and, therefore, attenuates CIDS severity. In the later phase post CNS injury, CB2R inhibition is suggested as a promising pharmacologic strategy to restore immune function in order to prevent infection.

Challenges in the management of ocular pain are an underappreciated topic. Currently available therapeutics lack both efficacy and clear guidelines for their use, with many also possessing unacceptable side effects. Promising novel agents would offer analgesic, anti-inflammatory, and possibly neuroprotective actions; have favorable ocular safety profiles; and show potential in managing neuropathic pain. Growing evidence supports a link between the endocannabinoid system (ECS) and a range of physiological and disease processes, notably those involving inflammation and pain. Both preclinical and clinical data suggest analgesic and anti-inflammatory actions of cannabinoids and ECS-modifying drugs in chronic pain conditions, including those of neuropathic origin. This review will examine existing evidence for the anatomical and physiological basis of ocular pain, specifically, ocular surface disease and the development of chronic ocular pain. The mechanism of action, efficacy, and limitations of currently available treatments will be discussed, and current knowledge related to ECS-modulation of ocular pain and inflammatory disease will be summarized. A perspective will be provided on the future directions of ECS research in terms of developing cannabinoid therapeutics for ocular pain.

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-1β, 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-1β, 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-1β, 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 cannabinoid receptor CB2 plays a significant role in the regulation of immune function whereas neuronal expression remains a subject of contention. Multiple studies have described CB2 in retina and a recent study showed that CB2 deletion altered retinal visual processing. We revisited CB2 expression using immunohistochemistry and a recently developed CB2-eGFP reporter mouse. We examined the consequence of acute vs. prolonged CB2 deactivation on the electroretinogram (ERG) responses. We also examined lipidomics in CB2 knockout mice and potential changes in microglia using Scholl analysis. Consistent with a published report, in CB2 receptor knockout mice see an increased ERG scotopic a-wave, as well as stronger responses in dark adapted cone-driven ON bipolar cells and, to a lesser extent cone-driven ON bipolar cells early in light adaptation. Significantly, however, acute block with CB2 antagonist, AM630, did not mimic the results observed in the CB2 knockout mice whereas chronic (7 days) block did. Immunohistochemical studies show no CB2 in retina under non-pathological conditions, even with published antibodies. Retinal CB2–eGFP reporter signal is minimal under baseline conditions but upregulated by intraocular injection of either LPS or carrageenan. CB2 knockout mice see modest declines in a broad spectrum of cannabinoid-related lipids. The numbers and morphology of microglia were unaltered. In summary minimal CB2 expression is seen in healthy retina. CB2 appears to be upregulated under pathological conditions. Previously reported functional consequences of CB2 deletion are an adaptive response to prolonged blockade of these receptors. CB2 therefore impacts retinal signaling but perhaps in an indirect, potentially extra-ocular fashion. post-print 8285 KB

G protein-coupled receptors (GPCRs) interact with multiple intracellular effector proteins such that different ligands may preferentially activate one signal pathway over others, a phenomenon known as signaling bias. Signaling bias can be quantified to optimize drug selection for preclinical research. Here, we describe moderate-throughput methods to quantify signaling bias of known and novel compounds. In the example provided, we describe a method to define cannabinoid-signaling bias in a cell culture model of Huntington's disease (HD). Decreasing type 1 cannabinoid receptor (CB

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.

Uveitis is inflammation of the uvea which consists of the iris, ciliary body and the choroid of the eye. Uveitis can lead to impaired vision and is responsible for 10% of all cases of blindness globally. Using an endotoxin-induced uveitis (EIU) rodent model, our previous data implicated the endogenous cannabinoid system (ECS) in the amelioration of many of the components of the inflammatory response. Here, we test the hypothesis that the reduction in inflammatory mediators in the EIU model by the CB

Huntington disease (HD) is an inherited, autosomal dominant, neurodegenerative disorder with limited treatment options. Prior to motor symptom onset or neuronal cell loss in HD, levels of the type 1 cannabinoid receptor (CB1) decrease in the basal ganglia. Decreasing CB1 levels are strongly correlated with chorea and cognitive deficit. CB1 agonists are functionally selective (biased) for divergent signaling pathways. In this study, six cannabinoids were tested for signaling bias in in vitro models of medium spiny projection neurons expressing wild-type (STHdh(Q7/Q7)) or mutant huntingtin protein (STHdh(Q111/Q111)). Signaling bias was assessed using the Black and Leff operational model. Relative activity [ΔlogR (τ/KA)] and system bias (ΔΔlogR) were calculated relative to the reference compound WIN55,212-2 for Gαi/o, Gαs, Gαq, Gβγ, and β-arrestin1 signaling following treatment with 2-arachidonoylglycerol (2-AG), anandamide (AEA), CP55,940, Δ(9)-tetrahydrocannabinol (THC), cannabidiol (CBD), and THC+CBD (1:1), and compared between wild-type and HD cells. The Emax of Gαi/o-dependent extracellular signal-regulated kinase (ERK) signaling was 50% lower in HD cells compared with wild-type cells. 2-AG and AEA displayed Gαi/o/Gβγ bias and normalized CB1 protein levels and improved cell viability, whereas CP55,940 and THC displayed β-arrestin1 bias and reduced CB1 protein levels and cell viability in HD cells. CBD was not a CB1 agonist but inhibited THC-dependent signaling (THC+CBD). Therefore, enhancing Gαi/o-biased endocannabinoid signaling may be therapeutically beneficial in HD. In contrast, cannabinoids that are β-arrestin-biased--such as THC found at high levels in modern varieties of marijuana--may be detrimental to CB1 signaling, particularly in HD where CB1 levels are already reduced.

G protein-coupled receptors (GPCRs) interact with multiple intracellular effector proteins such that different ligands may preferentially activate one signal pathway over others, a phenomenon known as signaling bias. Signaling bias can be quantified to optimize drug selection for preclinical research. Here, we describe moderate-throughput methods to quantify signaling bias of known and novel compounds. In the example provided, we describe a method to define cannabinoid-signaling bias in a cell culture model of Huntington's disease (HD). Decreasing type 1 cannabinoid receptor (CB1) levels is correlated with chorea and cognitive deficits in HD. There is evidence that elevating CB1 levels and/or signaling may be beneficial for HD patients while decreasing CB1 levels and/or signaling may be detrimental. Recent studies have found that Gαi/o-biased CB1 agonists activate extracellular signal-regulated kinase (ERK), increase CB1 protein levels, and improve viability of cells expressing mutant huntingtin. In contrast, CB1 agonists that are β-arrestin1-biased were found to reduce CB1 protein levels and cell viability. Measuring agonist bias of known and novel CB1 agonists will provide important data that predict CB1-specific agonists that might be beneficial in animal models of HD and, following animal testing, in HD patients. This method can also be applied to study signaling bias for other GPCRs.

BACKGROUND AND PURPOSE: We sought to understand why (−)‐cannabidiol (CBD) and (−)‐cannabidiol‐dimethylheptyl (CBD‐DMH) exhibit distinct pharmacology, despite near identical structures. EXPERIMENTAL APPROACH: HEK293A cells expressing either human type 1 cannabinoid (CB(1)) receptors or CB(2) receptors were treated with CBD or CBD‐DMH with or without the CB(1) and CB(2) receptor agonist CP55,940, CB(1) receptor allosteric modulator Org27569 or CB(2) receptor inverse agonist SR144528. Ligand binding, cAMP levels and βarrestin1 recruitment were measured. CBD and CBD‐DMH binding was simulated with models of human CB(1) or CB(2) receptors, based on the recently published crystal structures of agonist‐bound (5XRA) or antagonist‐bound (5TGZ) human CB(1) receptors. KEY RESULTS: At CB(1) receptors, CBD was a negative allosteric modulator (NAM), and CBD‐DMH was a mixed agonist/positive allosteric modulator. CBD and Org27569 shared multiple interacting residues in the antagonist‐bound model of CB(1) receptors (5TGZ) but shared a binding site with CP55,940 in the agonist‐bound model of CB(1) receptors (5XRA). The binding site for CBD‐DMH in the CB(1) receptor models overlapped with CP55,940 and Org27569. At CB(2) receptors, CBD was a partial agonist, and CBD‐DMH was a positive allosteric modulator of cAMP modulation but a NAM of βarrestin1 recruitment. CBD, CP55,940 and SR144528 shared a binding site in the CB(2) receptor models that was separate from CBD‐DMH. CONCLUSION AND IMPLICATIONS: The pharmacological activity of CBD and CBD‐DMH in HEK293A cells and their modelled binding sites at CB(1) and CB(2) receptors may explain their in vivo effects and illuminates the difficulties associated with the development of allosteric modulators for CB(1) and CB(2) receptors. LINKED ARTICLES: This article is part of a themed section on 8(th) European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc

Cannabinoids are known to modulate cardiovascular functions including heart rate, vascular tone, and blood pressure in humans and animal models. Essential components of the endocannabinoid system, namely, the production, degradation, and signaling pathways of endocannabinoids have been described not only in the central and peripheral nervous system but also in myocardium, vasculature, platelets, and immune cells. The mechanisms of cardiovascular responses to endocannabinoids are often complex and may involve cannabinoid CB

Medical access to cannabis was first granted in Canada in 1999, with several amendments leading to the current Access to Cannabis for Medical Purposes Regulations .[1][1] Patients have the right to access cannabis for medical purposes if they have the support of a health care practitioner. Three

Type 1 cannabinoid (CB

Modulation of type 1 cannabinoid receptor (CB1) activity has been touted as a potential means of treating addiction, anxiety, depression, and neurodegeneration. Different agonists of CB1 are known to evoke varied responses in vivo. Functional selectivity is the ligand-specific activation of certain signal transduction pathways at a receptor that can signal through multiple pathways. To understand cannabinoid-specific functional selectivity, different groups have examined the effect of individual cannabinoids on various signaling pathways in heterologous expression systems. In the current study, we compared the functional selectivity of six cannabinoids, including two endocannabinoids (2-arachidonyl glycerol (2-AG) and anandamide (AEA)), two synthetic cannabinoids (WIN55,212-2 and CP55,940), and two phytocannabinoids (cannabidiol (CBD) and Δ(9)-tetrahydrocannabinol (THC)) on arrestin2-, Gα(i/o)-, Gβγ-, Gα(s)-, and Gα(q)-mediated intracellular signaling in the mouse STHdh(Q7/Q7) cell culture model of striatal medium spiny projection neurons that endogenously express CB1. In this system, 2-AG, THC, and CP55,940 were more potent mediators of arrestin2 recruitment than other cannabinoids tested. 2-AG, AEA, and WIN55,212-2, enhanced Gα(i/o) and Gβγ signaling, with 2-AG and AEA treatment leading to increased total CB1 levels. 2-AG, AEA, THC, and WIN55,212-2 also activated Gα(q)-dependent pathways. CP55,940 and CBD both signaled through Gα(s). CP55,940, but not CBD, activated downstream Gα(s) pathways via CB1 targets. THC and CP55,940 promoted CB1 internalization and decreased CB1 protein levels over an 18-h period. These data demonstrate that individual cannabinoids display functional selectivity at CB1 leading to activation of distinct signaling pathways. To effectively match cannabinoids with therapeutic goals, these compounds must be screened for their signaling bias.

Interstitial cystitis (IC) is a chronic bladder disorder with unclear etiology. The endocannabinoid system has been identified as a key regulator of immune function, with experimental evidence for the involvement of cannabinoid receptors in bladder inflammation. This study used intravital microscopy (IVM) and behavioral testing in lipopolysaccharide-induced IC, to investigate the anti-inflammatory analgesic effects of a natural dietary sesquiterpenoid, beta-caryophyllene (BCP), which is present in cannabis among other plants, and has reported agonist actions at the cannabinoid 2 receptor (CB2R). BCP&rsquo, s anti-inflammatory actions were compared to the synthetic CB2R-selective cannabinoid, HU308, and to an FDA-approved clinical treatment (dimethyl sulfoxide: DMSO). IVM data revealed that intravesical instillation of BCP and/or HU308 significantly reduces the number of adhering leukocytes in submucosal bladder venules and improves bladder capillary perfusion. The effects of BCP were found to be comparable to that of the selective CB2R synthetic cannabinoid, HU308, and superior to intravesical DMSO treatment. Oral treatment with BCP was also able to reduce bladder inflammation and significantly reduced mechanical allodynia in experimental IC. Based on our findings, we believe that CB2R activation may represent a viable therapeutic target for IC, and that drugs that activate CB2R, such as the generally regarded as safe (GRAS) dietary sesquiterpenoid, BCP, may serve as an adjunct and/or alternative treatment option for alleviating symptoms of inflammation and pain in the management of IC.

INTRODUCTION Impairment of the intestinal microcirculation in endotoxemia may cause a deterioration of the mucosal barrier function thus releasing intraluminal bacteria and their toxins into the systemic circulation. In clinical sepsis this mechanism may influence disease severity and outcome. The aim of the study was to investigate the impact of cannabinoid receptor 1 (CB1R) modulation within the intestinal microcirculation with regard to leukocyte activation and capillary perfusion, and on intestinal histology in experimental endotoxemia in rats. METHODS Endotoxemia was induced by intravenous lipopolysaccharide (LPS) administration. We studied 5 groups of animals: controls (CON), LPS, LPS + CB1R agonist (ACEA, 2.5 mg/kg), LPS + CB1R antagonist (AM281, 2 mg/kg) and LPS + CB1R agonist (ACEA, 2.5 mg/kg) + CB1R antagonist (AM281, 2 mg/kg). Intestinal intravital microscopy (IVM) was performed two hours following LPS/placebo administration. Intestinal leukocyte adhesion in submucosal venules and functional capillary density (FCD) of the intestinal wall was quantified using IVM. Histological changes were assessed using a standardized injury score. RESULTS After two hours of endotoxemia, we observed a significant increase of leukocyte adhesion in intestinal submucosal venules. Administration of the CB1R antagonist in endotoxemic animals significantly reduced the number of adhering leukocytes (p < 0.05). The CB1R agonist did not further increase leukocyte adhesion. FCD was significantly improved by the CB1R antagonist (p < 0.05). Administration of the CB1R agonist, ACEA, reversed the beneficial effect of the CB1R antagonist, AM281. CONCLUSIONS CB1R inhibition significantly improved intestinal microcirculation by reducing leukocyte adhesion and increasing FCD in acute endotoxemia in rats. The data supports the involvement of the CB1R signaling in leukocyte activation during sepsis. Drugs targeting the CB1R may have therapeutic potential in systemic inflammation, such as sepsis.

The human type 1 cannabinoid (hCB1) receptor is expressed at high levels in the central nervous system. mRNA variants of the coding region of this receptor, human cannabinoid hCB1a and hCB1b receptors, have been identified, their biological function remains unclear. The present study demonstrated that the three human cannabinoid hCB1 coding region variants are expressed in the human and monkey (Macaca fascicularis) brain. Western blot analyses of homogenates from different regions of the monkey brain demonstrated that proteins with the expected molecular weights of the cannabinoid CB1, CB1a and CB1b receptors were co-expressed throughout the brain. Given the co-localization of these receptors, we hypothesized that physical interactions between the three splice variants may affect cannabinoid pharmacology. The human cannabinoid hCB1, hCB1a, and hCB1b receptors formed homodimers and heterodimers, as determined by BRET in transiently transfected HEK 293A cells. We found that the co-expression of the human cannabinoid hCB1 and each of the splice variants increased cell surface expression of the human cannabinoid hCB1 receptor and increased Gi/o-dependent ERK phosphorylation in response to cannabinoid agonists. Therefore, the human cannabinoid hCB1 coding region splice variants play an important physiological role in the activity of the endocannabinoid system.

Free fatty acids (FFAs) are metabolic intermediates that may be obtained through the diet, synthesized endogenously, or produced via fermentation of carbohydrates by gut microbiota. In addition to serving as an important source of energy, FFAs are known to produce a variety of both beneficial and detrimental effects on metabolic and inflammatory processes. While historically, FFAs were believed to produce these effects only through intracellular targets such as peroxisome proliferator-activated receptors, it has now become clear that FFAs are also agonists for several GPCRs, including a family of four receptors now termed FFA1-4. Increasing evidence suggests that FFA1-4 mediate many of the beneficial properties of FFAs and not surprisingly, this has generated significant interest in the potential of these receptors as therapeutic targets for the treatment of a variety of metabolic and inflammatory disorders. In addition to the traditional strategy of developing small-molecule therapeutics targeting these receptors, there has also been some consideration given to alternate therapeutic approaches, specifically by manipulating endogenous FFA concentrations through alteration of either dietary intake, or production by gut microbiota. In this review, the current state of knowledge for FFA1-4 will be discussed, together with their potential as therapeutic targets in the treatment of metabolic and inflammatory disorders. In particular, the evidence in support of small molecule versus dietary and microbiota-based therapeutic approaches will be considered to provide insight into the development of novel multifaceted strategies targeting the FFA receptors for the treatment of metabolic and inflammatory disorders.

The type 1 cannabinoid receptor (CB1) is a G protein-coupled receptor that is expressed at high levels in the striatum. Activation of CB1 increases expression of neuronal trophic factors and inhibits neurotransmitter release from GABA-ergic striatal neurons. CB1 mRNA levels can be elevated by treatment with cannabinoids in non-neuronal cells. We wanted to determine whether cannabinoid treatment could induce CB1 expression in a cell culture model of striatal neurons and, if possible, determine the molecular mechanism by which this occurred. We found that treatment of STHdh(7/7) cells with the cannabinoids ACEA, mAEA, and AEA produced a CB1receptor-dependent increase in CB1 promoter activity, mRNA, and protein expression. This response was Akt- and NF-κB-dependent. Because decreased CB1 expression is thought to contribute to the pathogenesis of Huntington's disease (HD), we wanted to determine whether cannabinoids could increase CB1 expression in STHdh(7/111) and (111/111) cells expressing the mutant huntingtin protein. We observed that cannabinoid treatment increased CB1 mRNA levels approximately 10-fold in STHdh(7/111) and (111/111) cells, compared to vehicle treatment. Importantly, cannabinoid treatment improved ATP production, increased the expression of the trophic factor BDNF-2, and the mitochondrial regulator PGC1α, and reduced spontaneous GABA release, in HD cells. Therefore, cannabinoid-mediated increases in CB1 levels could reduce the severity of some molecular pathologies observed in HD.

The endocannabinoid, N-arachidonoylethanolamine (AEA), is degraded by the enzyme fatty acid amide hydrolase (FAAH). This study examined whether the FAAH inhibitor, URB597, increases retinal ganglion cell (RGC) survival following optic nerve axotomy in young and aged animals. URB597 alone, or together with either a CB1 or CB2 receptor antagonist, was administered daily for 1 or 2 weeks post-axotomy. Histological assessment of retinas indicated that URB597 increased RGC survival in young retina at 1 and 2 weeks post-axotomy. The increase in RGC survival at 2 weeks was accompanied by a reduction in phagocytic microglia. The CB1 antagonist, AM281, but not the CB2 antagonist, AM630, ablated URB597-mediated RGC neuroprotection. CB1 or CB2 antagonism increased phagocytic microglia in URB597 and vehicle-treated animals. In aged animals, URB597 increased RGC survival at 1 week, but not at 2 weeks post-axotomy and had no effect on microglia. Retinal Iba-1 positive microglia were also decreased in URB597-treated axotomized young animals and this decrease was mitigated by CB1 but not CB2 antagonism. As seen with phagocytotic microglia, the CB2 antagonist, AM630, increased Iba-1 positive microglia in the absence of URB597 treatment. Measurement of retinal endocannabinoid levels in URB597-treated animals at 2 weeks post-axotomy revealed a significant increase in AEA levels, accompanied by a decrease in the AEA metabolite, N-arachidonoyl glycine, in young animals but not aged animals. 2-arachidonoylglycerol levels were similar across all experimental groups. These data demonstrate that URB597-mediated retinal neuroprotective effects are mediated primarily through CB1 receptors and that URB597 neuroprotective efficacy declines with age.