Endocannabinoids in cerebrovascular regulation

Cardiovascular effects of marijuana and synthetic cannabinoids: the good, the bad, and the ugly

Dysregulation of the endogenous lipid mediators endocannabinoids and their G-protein-coupled cannabinoid receptors 1 and 2 (CB1R and CB2R) has been implicated in a variety of cardiovascular pathologies. Activation of CB1R facilitates the development of cardiometabolic disease, whereas activation of CB2R (expressed primarily in immune cells) exerts anti-inflammatory effects. The psychoactive constituent of marijuana, Δ9-tetrahydrocannabinol (THC), is an agonist of both CB1R and CB2R, and exerts its psychoactive and adverse cardiovascular effects through the activation of CB1R in the central nervous and cardiovascular systems. The past decade has seen a nearly tenfold increase in the THC content of marijuana as well as the increased availability of highly potent synthetic cannabinoids for recreational use. These changes have been accompanied by the emergence of serious adverse cardiovascular events, including myocardial infarction, cardiomyopathy, arrhythmias, stroke, and cardiac arrest. In this Review, we summarize the role of the endocannabinoid system in cardiovascular disease, and critically discuss the cardiovascular consequences of marijuana and synthetic cannabinoid use. With the legalization of marijuana for medicinal purposes and/or recreational use in many countries, physicians should be alert to the possibility that the use of marijuana or its potent synthetic analogues might be the underlying cause of severe cardiovascular events and pathologies.

Neuroprotective Effects of MAGL (Monoacylglycerol Lipase) Inhibitors in Experimental Ischemic Stroke

BACKGROUND AND PURPOSE

MAGL (monoacylglycerol lipase) is an enzyme that hydrolyzes the endocannabinoid 2-arachidonoylglycerol and regulates the production of arachidonic acid and prostaglandins-substances that mediate tissue inflammatory response. Here, we have studied the effects of the selective MAGL inhibitors JZL184 and MJN110 and their underlying molecular mechanisms on 3 different experimental models of focal cerebral ischemia.

METHODS

SHR (spontaneously hypertensive rats) and normotensive WKY (Wistar Kyoto) rats were subject to an intracortical injection of the potent vasoconstrictor endothelin-1, permanent occlusion of a distal segment of the middle cerebral artery via craniectomy, or transient occlusion of the middle cerebral artery by the intraluminal suture method. JZL184 or MJN110 was administered 60 minutes after focal cerebral ischemia. Infarct volumes, hemispheric swelling, and functional outcomes were assessed between days 1 to 28 by magnetic resonance imaging, histology, and behavioral tests.

RESULTS

Pharmacological inhibition of MAGL significantly attenuated infarct volume and hemispheric swelling. MAGL inhibition also ameliorated sensorimotor deficits, suppressed inflammatory response, and decreased the number of degenerating neurons. These beneficial effects of MAGL inhibition were not fully abrogated by selective antagonists of cannabinoid receptors, indicating that the anti-inflammatory effects are caused by inhibition of eicosanoid production rather than by activation of cannabinoid receptors.

CONCLUSIONS

Our results suggest that MAGL may contribute to the pathophysiology of focal cerebral ischemia and is thus a promising therapeutic target for the treatment of ischemic stroke.

Role of the endogenous cannabinoid receptor 1 in brain injury induced by chronic intermittent hypoxia in rats

PURPOSE

This study investigated the effect of rimonabant, a cannabinoid receptor type 1 antagonist, on calcium/calmodulin- dependent protein kinase II and cannabinoid receptor type 1 in chronic intermittent hypoxia.

MATERIALS AND METHODS

Healthy male rats were divided into control group, intermittent hypoxia group for 4 or 6 weeks, hypoxic intervention group that received rimonabant (1 mg/kg/d) before exposure to hypoxia for 4 or 6 weeks (n = 10/group). Morphological changes and expressions of the two indexes in the cerebral hippocampus cells were determined by haematoxylin-eosin staining and immunohistochemistry, respectively.

RESULTS

In the intermittent hypoxia group at 4 weeks, the hippocampal cells were damaged with sparse cytoplasm and unclear boundaries, which are even worse at 6 weeks. In contrast, the hippocampal cells of the hypoxic intervention group were neatly arranged at 4 weeks. At 6 weeks, cells were larger with scarce cytoplasm and nuclear changes indicative of cell death. Calcium/calmodulin-dependent protein kinase II and cannabinoid receptor type 1 expression in the cerebral hippocampus was elevated in the intermittent hypoxia group at 4 weeks with even greater at 6 weeks. Cannabinoid receptor type 1 expression was reduced in the hypoxic intervention group compared to the intermittent hypoxia group. Correlation analysis revealed significant positive correlation of them in the intermittent hypoxia group.

CONCLUSIONS

Chronic intermittent hypoxia induced structural damage in the hippocampus and increased cannabinoid receptor type 1 and calcium/calmodulin-dependent protein kinase II expression, which may mediate cognitive impairment associated with chronic intermittent hypoxia. Rimonabant had a protective effect against chronic intermittent hypoxia.

Detrimental effects of 2-arachidonoylglycerol on whole blood platelet aggregation and on cerebral blood flow after a focal ischemic insult in rats

2-Arachidonoylglycerol (2-AG) is a major modulator of blood flow and platelet aggregation and a potential neuroprotectant. The present study investigated, for the first time, the effects of 2-AG on cerebral blood flow (CBF) in the first critical hours during middle cerebral artery occlusion (MCAO) and on platelet aggregation in rats. Adult male Sprague-Dawley rats ( n = 30) underwent permanent MCAO under isoflurane anesthesia and were randomly assigned to receive either 2-AG (6 mg/kg iv), monoacylglycerol lipase inhibitor JZL-184 (10 mg/kg iv), or vehicle ( n = 6 rats/group) treatment. CBF and cardiovascular responses were measured, by a blinded investigator, for up to 4 h. In separate experiments, platelet aggregation by 2-AG (19-300 µM) was assessed by whole blood aggregometry ( n = 40). 2-AG and JZL-184 significantly increased the severity of the CBF deficit versus vehicle (20.2 ± 8.8% and 22.7 ± 6.4% vs. 56.4 ± 12.1% of pre-MCAO baseline, respectively, P < 0.05) but had no effect on blood pressure or heart rate. While JZL-184 significantly increased the number of thrombi after MCAO, this did not reach significance by 2-AG. 2-AG induced platelet aggregation in rat whole blood in a similar manner to arachidonic acid and was significantly reduced by the cyclooxygenase inhibitors indomethacin and flurbiprofen and the thromboxane receptor antagonist ICI 192,605 ( P < 0.05). This is the first study showing that 2-AG increases the severity of the CBF deficit during MCAO, and further interrogation confirmed 2-AG-induced platelet aggregation in rats. These findings are important because 2-AG had previously been shown to exert neuroprotective actions and therefore force us to reevaluate the circumstances under which 2-AG is beneficial. NEW & NOTEWORTHY 2-Arachidonoylglycerol (2-AG) has neuroprotective properties; however, the present study revealed that 2-AG increases the severity of the cerebral blood flow deficit during middle cerebral artery occlusion in rats. Further interrogation showed that 2-AG induces platelet aggregation in rats. These findings force us to reevaluate the circumstances under which 2-AG is beneficial.

Activation of Endocannabinoid Receptor 2 as a Mechanism of Propofol Pretreatment-Induced Cardioprotection against Ischemia-Reperfusion Injury in Rats

Propofol pretreatment before reperfusion, or propofol conditioning, has been shown to be cardioprotective, while its mechanism is unclear. The current study investigated the roles of endocannabinoid signaling in propofol cardioprotection in an in vivo model of myocardial ischemia/reperfusion (I/R) injury and in in vitro primary cardiomyocyte hypoxia/reoxygenation (H/R) injury. The results showed that propofol conditioning increased both serum and cell culture media concentrations of endocannabinoids including anandamide (AEA) and 2-arachidonoylglycerol (2-AG) detected by LC-MS/MS. The reductions of myocardial infarct size in vivo and cardiomyocyte apoptosis and death in vitro were accompanied with attenuations of oxidative injuries manifested as decreased reactive oxygen species (ROS), malonaldehyde (MDA), and MPO (myeloperoxidase) and increased superoxide dismutase (SOD) production. These effects were mimicked by either URB597, a selective endocannabinoids degradation inhibitor, or VDM11, a selective endocannabinoids reuptake inhibitor. In vivo study further validated that the cardioprotective and antioxidative effects of propofol were reversed by selective CB2 receptor antagonist AM630 but not CB1 receptor antagonist AM251. We concluded that enhancing endogenous endocannabinoid release and subsequent activation of CB2 receptor signaling represent a major mechanism whereby propofol conditioning confers antioxidative and cardioprotective effects against myocardial I/R injury.

Cannabinoids in the Cardiovascular System

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 CB₁ and CB₂ receptors or non-CB_1/2 receptor targets. Preclinical and some clinical studies have suggested that targeting the endocannabinoid system can improve cardiovascular functions in a number of pathophysiological conditions, including hypertension, metabolic syndrome, sepsis, and atherosclerosis. In this chapter, we summarize the local and systemic cardiovascular effects of cannabinoids and highlight our current knowledge regarding the therapeutic potential of endocannabinoid signaling and modulation.

Maternal alcohol exposure during mid-pregnancy dilates fetal cerebral arteries via endocannabinoid receptors

Prenatal alcohol exposure often results in fetal alcohol syndrome and fetal alcohol spectrum disorders. Mechanisms of fetal brain damage by alcohol remain unclear. We used baboons (Papio spp.) to study alcohol-driven changes in the fetal cerebral artery endocannabinoid system. Pregnant baboons were subjected to binge alcohol exposure via gastric infusion three times during a period equivalent to the second trimester of human pregnancy. A control group was infused with orange-flavored drink that was isocaloric to the alcohol-containing solution. Cesarean sections were performed at a time equivalent to the end of the second trimester of human pregnancy. Fetal cerebral arteries were harvested and subjected to in vitro pressurization followed by pharmacological profiling. During each alcohol-infusion episode, maternal blood alcohol concentrations (BAC) reached 80 mg/dL, that is, equivalent to the BAC considered legal intoxication in humans. Circulating anandamide (AEA) and 2-arachidonoylglycerol (2-AG) remained unchanged. Ultrasound studies on pregnant mothers revealed that fetal alcohol exposure decreased peak systolic blood velocity in middle cerebral arteries when compared to pre-alcohol levels. Moreover, ethanol-induced dilation was observed in fetal cerebral arteries pressurized in vitro. This dilation was abolished by the mixture of AM251 and AM630, which block cannabinoid receptors 1 and 2, respectively. In the presence of AM251, the cannabinoid receptor agonist AEA evoked a higher, concentration-dependent dilation of cerebral arteries from alcohol-exposed fetuses. The difference in AEA-induced cerebral artery dilation vanished in the presence of AM630. CB1 and CB2 receptor mRNA and protein levels were similar in cerebral arteries from alcohol-exposed and control-exposed fetuses. In summary, alcohol exposure dilates fetal cerebral arteries via endocannabinoid receptors and results in an increased function of CB2.

Metabolism of the Endocannabinoid Anandamide: Open Questions after 25 Years

Cannabis extracts have been used for centuries, but its main active principle ∆⁹-tetrahydrocannabinol (THC) was identified about 50 years ago. Yet, it is only 25 years ago that the first endogenous ligand of the same receptors engaged by the cannabis agents was discovered. This “endocannabinoid (eCB)” was identified as N-arachidonoylethanolamine (or anandamide (AEA)), and was shown to have several receptors, metabolic enzymes and transporters that altogether drive its biological activity. Here I report on the latest advances about AEA metabolism, with the aim of focusing open questions still awaiting an answer for a deeper understanding of AEA activity, and for translating AEA-based drugs into novel therapeutics for human diseases.

Inhibition of SENP3 by URB597 ameliorates neurovascular unit dysfunction in rats with chronic cerebral hypoperfusion

Disruption of the neurovascular unit (NVU), induced by chronic cerebral hypoperfusion (CCH), has been broadly found in various neurological disorders. SUMO-specific protease 3 (SENP3) is expressed in neurons, astrocytes, and microglia, and regulates a variety of cell events. However, whether SENP3 is involved in neurovascular injury under the condition of CCH is still elusive. To address this issue, we investigated the effect of the fatty acid amide hydrolase (FAAH) inhibitor URB597 on NVU and the role of SENP3 in this process, as well as the underling mechanisms. The expression of SENP3 was detected by immunochemistry. The function and structure of the NVU was assessed by Western blot analysis and transmission electron microscopy. CCH caused the upregulation of SENP3, the disruption of cell and non-cell components at the protein level within the NVU, and ultrastructural deterioration. The NVU impairment as well as overexpression of SENP3 were reversed by treatment with URB597. These results reveal a novel neuroprotective role in URB597, which implicates URB597 in the amelioration of CCH-induced NVU impairment by inhibiting SENP3.

A Pulsed Electromagnetic Field Protects against Glutamate-Induced Excitotoxicity by Modulating the Endocannabinoid System in HT22 Cells

Glutamate-induced excitotoxicity is common in the pathogenesis of many neurological diseases. A pulsed electromagnetic field (PEMF) exerts therapeutic effects on the nervous system, but its specific mechanism associated with excitotoxicity is still unknown. We investigated the role of PEMF exposure in regulating glutamate-induced excitotoxicity through the endocannabinoid (eCB) system. PEMF exposure improved viability of HT22 cells after excitotoxicity and reduced lactate dehydrogenase release and cell death. An eCB receptor 1 (CB1R) specific inhibitor suppressed the protective effects of PEMF exposure, even though changes in CB1R expression were not observed. Elevation of N-arachidonylethanolamide (AEA) and 2-arachidonylglycerol (2-AG) following PEMF exposure indicated that the neuroprotective effects of PEMF were related to modulation of the eCB metabolic system. Furthermore, CB1R/ERK signaling was shown to be an important downstream pathway of PEMF in regulating excitotoxicity. These results suggest that PEMF exposure leads to neuroprotective effects against excitotoxicity by facilitating the eCB/CB1R/ERK signaling pathway. Therefore, PEMF may be a potential physical therapeutic technique for preventing and treating neurological diseases.

URB597 improves cognitive impairment induced by chronic cerebral hypoperfusion by inhibiting mTOR-dependent autophagy

Chronic cerebral hypoperfusion (CCH) is associated with various ischemic cerebrovascular diseases that are characterized by cognitive impairment. The role of autophagy in cognitive dysfunction under conditions of CCH is poorly understood. To address this issue, the present study investigated the effect of the fatty acid amide hydrolase (FAAH) inhibitor URB597 on autophagy and cognition in a CCH model as well as the underlying mechanisms. Cognitive function was evaluated with the Morris water maze and by assessing long-term potentiation (LTP). The expression of autophagy-related proteins and mammalian target of rapamycin (mTOR) signaling pathway components was evaluated by immunofluorescence and western blot analyses, and ultrastructural changes were examined by transmission electron microscopy (EM). URB597 improved cognitive impairment by inhibiting CCH-induced autophagy, which was associated with mTOR signaling. Moreover, the ultrastructural deterioration resulting from CCH was improved by chronic treatment with URB597. These findings indicate that URB597 modulates autophagy in an mTOR-dependent manner, and mitigates neuronal damage and cognitive deterioration caused by CCH.

Selective Estrogen Receptor Modulators: Cannabinoid Receptor Inverse Agonists with Differential CB1 and CB2 Selectivity

Selective estrogen receptor modulators (SERMs) are used to treat estrogen receptor (ER)-positive breast cancer and osteoporosis. Interestingly, tamoxifen and newer classes of SERMs also exhibit cytotoxic effects in cancers devoid of ERs, indicating a non-estrogenic mechanism of action. Indicative of a potential ER-independent target, reports demonstrate that tamoxifen binds to cannabinoid receptors (CBRs) with affinity in the low μM range and acts as an inverse agonist. To identify cannabinoids with improved pharmacological properties relative to tamoxifen, and further investigate the use of different SERM scaffolds for future cannabinoid drug development, this study characterized the affinity and activity of SERMs in newer structural classes at CBRs. Fourteen SERMs from five structurally distinct classes were screened for binding to human CBRs. Compounds from four of five SERM classes examined bound to CBRs. Subsequent studies fully characterized CBR affinity and activity of one compound from each class. Ospemifine (a triphenylethylene) selectively bound to CB1Rs, while bazedoxifine (an indole) bound to CB2Rs with highest affinity. Nafoxidine (a tetrahydronaphthalene) and raloxifene (RAL; a benzothiaphene) bound to CB1 and CB2Rs non-selectively. All four compounds acted as inverse agonists at CB1 and CB2Rs, reducing basal G-protein activity with IC₅₀ values in the nM to low μM range. Ospemifine, bazedoxifene and RAL also acted as inverse agonists to elevate basal intracellular cAMP levels in intact CHO-hCB2 cells. The four SERMs examined also acted as CB1 and CB2R antagonists in the cAMP assay, producing rightward shifts in the concentration-effect curve of the CBR agonist CP-55,940. In conclusion, newer classes of SERMs exhibit improved pharmacological characteristics (e.g., in CBR affinity and selectivity) relative to initial studies with tamoxifen, and thus suggest that different SERM scaffolds may be useful for development of safe and selective drugs acting via CBRs.

Leveraging allostery to improve G protein-coupled receptor (GPCR)-directed therapeutics: cannabinoid receptor 1 as discovery target

INTRODUCTION

Allosteric modulators of G-protein coupled receptors (GPCRs) hold the promise of improved pharmacology and safety over typical orthosteric GPCR ligands. These features are particularly relevant to the cannabinoid receptor 1 (CB1R) GPCR, since typical orthosteric CB1R ligands are associated with adverse events that limit their translational potential. Areas covered: The contextual basis for applying allostery to CB1R is considered from pharmacological, drug-discovery, and medicinal standpoints. Rational design of small-molecule CB1R allosteric modulators as potential pharmacotherapeutics would be greatly facilitated by direct experimental characterization of structure-function correlates underlying the biological activity of chemically-diverse CB1R allosteric modulators, CB1R allosteric ligand-binding binding pockets, and amino acid contact residues critical to allosteric ligand engagement and activity. In these regards, designer covalent probes exhibiting well-characterized molecular pharmacology as CB1R allosteric modulators are emerging as valuable molecular reporters enabling experimental interrogation of CB1R allosteric site(s) and informing the design of new CB1R agents as drugs. Expert opinion: Synthesis and pharmacological profiling of CB1R allosteric ligands will continue to provide valuable insights into CB1R structure-function correlates. The resulting data should expand the repertoire of novel agents capable of exerting therapeutic benefit by modulating CB1R-dependent signaling.

Adaptation of the cerebrocortical circulation to carotid artery occlusion involves blood flow redistribution between cortical regions and is independent of eNOS

Cerebral circulation is secured by feed-forward and feed-back control pathways to maintain and eventually reestablish the optimal oxygen and nutrient supply of neurons in case of disturbances of the cardiovascular system. Using the high temporal and spatial resolution of laser-speckle imaging we aimed to analyze the pattern of cerebrocortical blood flow (CoBF) changes after unilateral (left) carotid artery occlusion (CAO) in anesthetized mice to evaluate the contribution of macrovascular (circle of Willis) vs. pial collateral vessels as well as that of endothelial nitric oxide synthase (eNOS) to the cerebrovascular adaptation to CAO. In wild-type mice CoBF reduction in the left temporal cortex started immediately after CAO, reaching its maximum (-26%) at 5-10 s. Thereafter, CoBF recovered close to the preocclusion level within 30 s indicating the activation of feed-back pathway(s). Interestingly, the frontoparietal cerebrocortical regions also showed CoBF reduction in the left (-17-19%) but not in the right hemisphere, although these brain areas receive their blood supply from the common azygos anterior cerebral artery in mice. In eNOS-deficient animals the acute CoBF reduction after CAO was unaltered, and the recovery was even accelerated compared with controls. These results indicate that 1) the Willis circle alone is not sufficient to provide an immediate compensation for the loss of one carotid artery, 2) pial collaterals attenuate the ischemia of the temporal cortex ipsilateral to CAO at the expense of the blood supply of the frontoparietal region, and 3) eNOS, surprisingly, does not play an important role in this CoBF redistribution.