Mechanisms of endothelium-dependent relaxation evoked by anandamide in isolated human pulmonary arteries

GPR18-Mediated Relaxation of Human Isolated Pulmonary Arteries

GPR18 receptor protein was detected in the heart and vasculature and appears to play a functional role in the cardiovascular system. We investigated the effects of the new GPR18 agonists PSB-MZ-1415 and PSB-MZ-1440 and the new GPR18 antagonist PSB-CB-27 on isolated human pulmonary arteries (hPAs) and compared their effects with the previously proposed, but unconfirmed, GPR18 ligands NAGly, Abn-CBD (agonists) and O-1918 (antagonist). GPR18 expression in hPAs was shown at the mRNA level. PSB-MZ-1415, PSB-MZ-1440, NAGly and Abn-CBD fully relaxed endothelium-intact hPAs precontracted with the thromboxane A₂ analog U46619. PSB-CB-27 shifted the concentration-response curves (CRCs) of PSB-MZ-1415, PSB-MZ-1440, NAGly and Abn-CBD to the right; O-1918 caused rightward shifts of the CRCs of PSB-MZ-1415 and NAGly. Endothelium removal diminished the potency and the maximum effect of PSB-MZ-1415. The potency of PSB-MZ-1415 or NAGly was reduced in male patients, smokers and patients with hypercholesterolemia. In conclusion, the novel GPR18 agonists, PSB-MZ-1415 and PSB-MZ-1440, relax hPAs and the effect is inhibited by the new GPR18 antagonist PSB-CB-27. GPR18, which appears to exhibit lower activity in hPAs from male, smoking or hypercholesterolemic patients, may become a new target for the treatment of pulmonary arterial hypertension.

Cannabinoids-A New Perspective in Adjuvant Therapy for Pulmonary Hypertension

Currently, no treatment can completely cure pulmonary hypertension (PH), which can lead to right ventricular failure and, consequently, death. Therefore, searching for new therapies remains important. Increased resistance in pulmonary circulation is mainly caused by the excessive contraction and proliferation of small pulmonary arteries. Cannabinoids, a group of lipophilic compounds that all interact with cannabinoid receptors, exert a pulmonary vasodilatory effect through several different mechanisms, including mechanisms that depend on vascular endothelium and/or receptor-based mechanisms, and may also have anti-proliferative and anti-inflammatory properties. The vasodilatory effect is important in regulating pulmonary resistance, which can improve patients’ quality of life. Moreover, experimental studies on the effects of cannabidiol (plant-derived, non-psychoactive cannabinoid) in animal PH models have shown that cannabidiol reduces right ventricular systolic pressure and excessive remodelling and decreases pulmonary vascular hypertrophy and pulmonary vascular resistance. Due to the potentially beneficial effects of cannabinoids on pulmonary circulation and PH, in this work, we review whether cannabinoids can be used as an adjunctive therapy for PH. However, clinical trials are still needed to recommend the use of cannabinoids in the treatment of PH.

Multifactorial Basis and Therapeutic Strategies in Metabolism-Related Diseases

Throughout the 20th and 21st centuries, the incidence of non-communicable diseases (NCDs), also known as chronic diseases, has been increasing worldwide. Changes in dietary and physical activity patterns, along with genetic conditions, are the main factors that modulate the metabolism of individuals, leading to the development of NCDs. Obesity, diabetes, metabolic associated fatty liver disease (MAFLD), and cardiovascular diseases (CVDs) are classified in this group of chronic diseases. Therefore, understanding the underlying molecular mechanisms of these diseases leads us to develop more accurate and effective treatments to reduce or mitigate their prevalence in the population. Given the global relevance of NCDs and ongoing research progress, this article reviews the current understanding about NCDs and their related risk factors, with a focus on obesity, diabetes, MAFLD, and CVDs, summarizing the knowledge about their pathophysiology and highlighting the currently available and emerging therapeutic strategies, especially pharmacological interventions. All of these diseases play an important role in the contamination by the SARS-CoV-2 virus, as well as in the progression and severity of the symptoms of the coronavirus disease 2019 (COVID-19). Therefore, we briefly explore the relationship between NCDs and COVID-19.

Vasodilatory effects of cannabidiol in human pulmonary and rat small mesenteric arteries: modification by hypertension and the potential pharmacological opportunities

Objective:

Cannabidiol (CBD) has been suggested as a potential antihypertensive drug. The aim of our study was to investigate its vasodilatory effect in isolated human pulmonary arteries (hPAs) and rat small mesenteric arteries (sMAs).

Methods:

Vascular effects of CBD were examined in hPAs obtained from patients during resection of lung carcinoma and sMAs isolated from spontaneously hypertensive (SHR); 11-deoxycorticosterone acetate (DOCA-salt) hypertensive rats or their appropriate normotensive controls using organ bath and wire myography, respectively.

Results:

CBD induced almost full concentration-dependent vasorelaxation in hPAs and rat sMAs. In hPAs, it was insensitive to antagonists of CB₁ (AM251) and CB₂ (AM630) receptors but it was reduced by endothelium denudation, cyclooxygenase inhibitors (indomethacin and nimesulide), antagonists of prostanoid EP₄ (L161982), IP (Cay10441), vanilloid TRPV1 (capsazepine) receptors and was less potent under KCl-induced tone and calcium-activated potassium channel (K_Ca) inhibitors (iberiotoxin, UCL1684 and TRAM-34) and in hypertensive, overweight and hypercholesteremic patients. The time-dependent effect of CBD was sensitive to the PPARγ receptor antagonist GW9662. In rats, the CBD potency was enhanced in DOCA-salt and attenuated in SHR. The CBD-induced relaxation was inhibited in SHR and DOCA-salt by AM251 and only in DOCA-salt by AM630 and endothelium denudation.

Conclusion:

The CBD-induced relaxation in hPAs that was reduced in hypertensive, obese and hypercholesteremic patients was endothelium-dependent and mediated via K_Ca and IP, EP₄, TRPV1 receptors. The CBD effect in rats was CB₁-sensitive and dependent on the hypertension model. Thus, modification of CBD-mediated responses in disease should be considered when CBD is used for therapeutic purposes.

Cannabidiol Ameliorates Monocrotaline-Induced Pulmonary Hypertension in Rats

Cannabidiol (CBD) is known for its vasorelaxant (including in the human pulmonary artery), anti-proliferative and anti-inflammatory properties. The aim of our study was to examine the potential preventive effect of chronic CBD administration (10 mg/kg/day for three weeks) on monocrotaline (MCT)-induced pulmonary hypertension (PH) rats. PH was connected with elevation of right ventricular systolic pressure; right ventricle hypertrophy; lung edema; pulmonary artery remodeling; enhancement of the vasoconstrictor and decreasing vasodilatory responses; increases in plasma concentrations of tissue plasminogen activator, plasminogen activator inhibitor type 1 and leukocyte count; and a decrease in blood oxygen saturation. CBD improved all abovementioned changes induced by PH except right ventricle hypertrophy and lung edema. In addition, CBD increased lung levels of some endocannabinoids (anandamide, N-arachidonoyl glycine, linolenoyl ethanolamide, palmitoleoyl ethanolamide and eicosapentaenoyl ethanolamide but not 2-arachidonoylglycerol). CBD did not affect the cardiopulmonary system of control rats or other parameters of blood morphology in PH. Our data suggest that CBD ameliorates MCT-induced PH in rats by improving endothelial efficiency and function, normalization of hemostatic alterations and reduction of enhanced leukocyte count determined in PH. In conclusion, CBD may be a safe, promising therapeutic or adjuvant therapy agent for the treatment of human pulmonary artery hypertension.

Reduction of the serotonin 5-HT1B and 5-HT2A receptor-mediated contraction of human pulmonary artery by the combined 5-HT1B receptor antagonist and serotonin transporter inhibitor LY393558

Background

LY393558 is a combined antagonist of serotonin (5-HT) 5-HT_1B receptors and inhibitor of serotonin transporter (SERT). LY393558 reduces 5-HT-induced vasoconstriction and remodelling of rat and/or mouse pulmonary arteries. The aim of our study was to examine the effect of LY393558 on the 5-HT-stimulated vasoconstriction of human pulmonary arteries (hPAs) and to determine the underlying mechanism(s).

Methods

Vascular effects of 5-HT receptor agonists, antagonists and a SERT inhibitor were examined in organ bath studies on intralobar hPAs obtained from patients during resection of lung carcinoma.

Results

Serotonin and agonists of the 5-HT_1B receptor (5-carboxamidotryptamine, 5-CT) and 5-HT_2A receptor (α-methyl-5-HT) contracted endothelium-intact hPAs in a concentration-dependent fashion. The 5-HT_1B antagonists SB224289 and GR55562 reduced responses induced by 5-HT and 5-CT and the 5-HT_2A antagonist ketanserin inhibited the effects of 5-HT and α-methyl-5-HT. Administration of the SERT inhibitor citalopram (at a concentration that failed to modify the 5-HT-induced vasoconstriction) in combination with SB224289 or GR55562 was more effective in inhibiting the response to 5-HT than the 5-HT_1B antagonists alone. LY393558 showed the greatest antagonistic effect against the vasoconstriction elicited by 5-HT, 5-CT and α-methyl-5-HT.

Conclusions

LY393558 reduces the 5-HT-induced contraction antagonizing 5-HT_1B and 5-HT_2A receptors probably due to synergic interaction between SERT inhibition and 5-HT_1B receptor antagonism. Thus, it might represent a valuable future option in the pulmonary arterial hypertension therapy.

Synthesis, physicochemical characterisation and biological activity of anandamide/ɛ-polycaprolactone nanoparticles obtained by electrospraying

Drug encapsulation in nanocarriers such as polymeric nanoparticles (Nps) may help to overcome the limitations associated with cannabinoids. In this study, the authors' work aimed to highlight the use of electrospraying techniques for the development of carrier Nps of anandamide (AEA), an endocannabinoid with attractive pharmacological effects but underestimated due to its unfavourable physicochemical and pharmacokinetic properties added to its undesirable effects at the level of the central nervous system. The authors characterised physicochemically and evaluated in vitro biological activity of anandamide/ɛ-polycaprolactone nanoparticles (Nps-AEA/PCL) obtained by electrospraying in epithelial cells of the human proximal tubule (HK2), to prove the utility of this method and to validate the biological effect of Nps-AEA/PCL. They obtained particles from 100 to 900 nm of diameter with a predominance of 200-400 nm. Their zeta potential was -20 ± 1.86 mV. They demonstrated the stable encapsulation of AEA in Nps-AEA/PCL, as well as its dose-dependent capacity to induce the expression of iNOS and NO levels and to decrease the Na+/K+ ATPase activity in HK2 cells. Obtaining Nps-AEA/PCL by electrospraying would represent a promising methodology for a novel AEA pharmaceutical formulation development with optimal physicochemical properties, physical stability and biological activity on HK2 cells.

Chronic dosing with metformin plus bosentan decreases in vitro pulmonary artery contraction from isolated arteries in adults with pulmonary hypertension

Introduction: Pulmonary arterial hypertension (PAH) specific drug therapy using bosentan has significantly improved quality of life and survival, although PAH is still an incurable disease. Recent studies suggest metformin may have additional treatment benefits in PAH. We therefore investigated in vitro pulmonary artery reactivity after combination therapy of bosentan and metformin in PAH patients as compared with bosentan monotherapy in a prospective, randomized study.

Methods: Adult patients with PAH associated with congenital heart defects (PAH-CHD) were randomised to receive bosentan (initially at 62.5 mg twice daily for 4 weeks and then 125 mg twice daily) for 3 months with or without the combination treatment of metformin (500 mg twice daily). Vessel reactivity of isolated pulmonary arteries was examined using a wire myograph.

Results: Phenylephrine (PE)-induced contractions of arteries in patients received combination therapy were significantly attenuated at concentrations of 3 × 10^-7 M, 10^-6 M and 3 × 10^-6 M, compared to those received bosentan monotherapy. After denudation, PE-induced contractions at concentrations of 3 × 10^-6 M and 10^-5 M were significantly decreased in the combination therapy group. AMP-activated protein kinase (AMPK) inhibitor compound C abrogated the inhibitory effects of metformin on PE-induced contractility. AMPK and eNOS phosphorylation in the pulmonary arteries of patients treated with combination therapy was increased compared to monotherapy (P < 0.05).

Conclusion: Adding metformin to bosentan therapy in patients with PAH-CHD decreased in vitro pulmonary artery contraction induced by PE, which is possibly related to increased AMPK phosphorylation.

Cannabinoids and Cardiovascular System

Cannabinoids influence cardiovascular variables in health and disease via multiple mechanisms. The chapter covers the impact of cannabinoids on cardiovascular function in physiology and pathology and presents a critical analysis of the proposed signalling pathways governing regulation of cardiovascular function by endogenously produced and exogenous cannabinoids. We know that endocannabinoid system is overactivated under pathological conditions and plays both a protective compensatory role, such as in some forms of hypertension, atherosclerosis and other inflammatory conditions, and a pathophysiological role, such as in disease states associated with excessive hypotension. This chapter focuses on the mechanisms affecting hemodynamics and vasomotor effects of cannabinoids in health and disease states, highlighting mismatches between some studies. The chapter will first review the effects of marijuana smoking on cardiovascular system and then describe the impact of exogenous cannabinoids on cardiovascular parameters in humans and experimental animals. This will be followed by analysis of the impact of cannabinoids on reactivity of isolated vessels. The article critically reviews current knowledge on cannabinoid induction of vascular relaxation by cannabinoid receptor-dependent and -independent mechanisms and dysregulation of vascular endocannabinoid signaling in disease states.

CB2-deficiency is associated with a stronger hypertrophy and remodeling of the right ventricle in a murine model of left pulmonary artery occlusion

AIMS

Pulmonary hypertension (PH) leads to right ventricular (RV) adaptation and remodeling and has deleterious long-term effects on RV function. The endocannabinoid receptor CB2 has been associated with protective effects in adaptation and remodeling of the left ventricle after ischemia. Therefore, we investigated the role of CB2 receptor in RV adaptation after occlusion of the left pulmonary artery (LPA) in a murine model.

MAIN METHODS

C57/Bl6 (WT)- and CB2 receptor-deficient (Cnr2^-/^-)-mice underwent paramedian sternotomy and LPA was occluded using a metal clip. Right heart hemodynamic study (Millar®) preceded organ harvesting for immunohistochemistry and mRNA analysis 7 and 21 days (d) post-occlusion.

KEY FINDINGS

LPA occlusion led to higher RV systolic pressure in Cnr2^-/^--hearts, while hemodynamics were comparable with WT-hearts after 21d. Cnr2^-/^--hearts showed higher macrophage infiltration and lower interleukin-10 expression after 7 d, but otherwise a comparable inflammatory mediator expression profile. Cardiomyocyte-hypertrophy was stronger in Cnr2^-/^--mice, presenting with higher tenascin-C expression than WT-hearts. Planimetry revealed higher collagen area in Cnr2^-/^--hearts and small areas of cardiomyocyte-loss. Surrounding cardiomyocytes were cleaved caspase-3- and TUNEL positive in Cnr2^-/^--hearts. This was associated by maladaptation of myosin heavy-chain isoforms and lower reactive oxygen scavenger enzymes induction in Cnr2^-/^--hearts. We found comparable morphological changes in both lungs between the two genotypes.

SIGNIFICANCE

LPA occlusion led to increased systolic pressure and adaptation of RV in CB2-deficient mice. CB2 receptor seems to modulate RV adaptation through expression of contractile elements, reactive oxygen scavenger enzymes, and inflammatory response in order to prevent cardiomyocyte apoptosis.

Anandamide and endocannabinoid system: an attractive therapeutic approach for cardiovascular disease

Cardiovascular disease is currently not adequately managed and has become one of the main causes of morbidity and mortality worldwide. Current therapies are inadequate in terms of preventing its progression. There are several limitations, such as poor oral bioavailability, side effects, low adherence to treatment, and high dosage frequency of formulations due to the short half-life of the active ingredients used, among others. This review aims to highlight the most relevant aspects of the relationship between the cardiovascular system and the endocannabinoid system, with special attention to the possible translational effect of the use of anandamide in cardiovascular health. The deep and detailed knowledge of this interaction, not always beneficial, and that for years has gone unnoticed, is essential for the development of new therapies. We discuss the most recent and representative results obtained in the field of basic research, referring to the aforementioned subject, emphasizing fundamentally the main role of nitric oxide, renal physiology and its deregulation in pathological processes.

Endocannabinoids modulate Gq/11 protein-coupled receptor agonist-induced vasoconstriction via a negative feedback mechanism

OBJECTIVES

The endocannabinoid (eCB) system centrally and peripherally regulates cardiovascular parameters, including blood pressure, in health and disease. The relationship between G_q/11 protein-coupled receptor activation, regulation of eCBs release (mainly 2-arachidonoylglycerol) and subsequent CB₁ receptor activation was initially observed in the central nervous system. Here, we review the latest findings from systemic physiological studies which include for the first time data from pulmonary arteries. We present evidence for direct CB₁ -dependent cannabinoid ligand-induced vasorelaxation, vascular expression of eCBs along with their degradation enzymes, and indicate the location of the described interaction.

KEY FINDINGS

Endocannabinoids (mainly 2-arachidonoylglycerol), acting via CB₁ receptors, evoke vasodilatory effects and may modulate responses of vasoconstrictors for G_q/11 protein-coupled receptors including angiotensin II, thromboxane A₂ , phenylephrine, noradrenaline in systemic or pulmonary arteries. However, the role of the endothelium in this interaction is not well-established, and the precise vascular location of eCB system components remains unclear, which contributes to discrepancies in the interpretation of results when describing the above-mentioned relationship.

SUMMARY

Endocannabinoid's negative feedback is responsible for diminishing agonist-induced vasoconstriction, which may be clinically important in the treatment of arterial and pulmonary hypertension. Further research is required to establish the importance of the eCB system and its downstream signalling pathways.

Mechanisms of l-alpha-lysophosphatidylinositol-induced relaxation in human pulmonary arteries

AIMS

l-Alpha-lysophosphatidylinositol (LPI) is an endogenous agonist of G protein-coupled receptor 55 (GPR55) which relaxes mesenteric arteries on activation. The aim of the present study was to determine the influence and underlying mechanisms of LPI-induced relaxation in human pulmonary arteries (hPAs).

MAIN METHODS

Functional studies were performed in isolated hPAs using organ bath technique. The expression of GPR55 in hPAs and bronchioles was determined by real-time qPCR, Western blot analysis, and immunohistochemistry.

KEY FINDINGS

LPI induced a concentration-dependent vasorelaxation in endothelium-intact hPAs. This effect was attenuated by the GPR55 antagonist CID16020046, the peroxisome proliferator-activated receptor-γ (PPARγ) antagonist GW9662, the putative endothelial cannabinoid receptor (CB_e) antagonist O-1918 and the inhibitor of nitric oxide (NO) synthase (L-NAME). In addition, vasorelaxation was also attenuated by the presence of a high KCl concentration, selective blockers of small (K_Ca2.3; UCL1684), intermediate (K_Ca3.1; TRAM-34) and large conductance (K_Ca1.1; iberiotoxin) calcium-activated potassium channels and by endothelium denudation. However, vasorelaxation was not attenuated by the cannabinoid CB₁ receptor antagonist AM251 or by the cyclooxygenase inhibitor indomethacin.

SIGNIFICANCE

The study showed that the LPI-induced vasorelaxation was endothelium-dependent and mediated by GPR55, PPARγ and CB_e receptors, occurred in a NO- and calcium-activated potassium channel-dependent manner in isolated hPAs. LPI seems to possess positive, hypotensive properties in pulmonary vascular bed.

Recent advances in oxygen sensing and signal transduction in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is a physiological reaction, which adapts lung perfusion to regional ventilation and optimizes gas exchange. Impaired HPV may cause systemic hypoxemia, while generalized HPV contributes to the development of pulmonary hypertension. The triggering mechanisms underlying HPV are still not fully elucidated. Several hypotheses are currently under debate, including a possible decrease as well as an increase in reactive oxygen species as a triggering event. Recent findings suggest an increase in the production of reactive oxygen species in pulmonary artery smooth muscle cells by complex III of the mitochondrial electron transport chain and occurrence of oxygen sensing at complex IV. Other essential components are voltage-dependent potassium and possibly L-type, transient receptor potential channel 6, and transient receptor potential vanilloid 4 channels. The release of arachidonic acid metabolites appears also to be involved in HPV regulation. Further investigation of the HPV mechanisms will facilitate the development of novel therapeutic strategies for the treatment of HPV-related disorders.

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.

Activation of CB1 receptors by 2-arachidonoylglycerol attenuates vasoconstriction induced by U46619 and angiotensin II in human and rat pulmonary arteries

Recent evidence suggests that endocannabinoids acting via cannabinoid CB₁ receptors may modulate vascular responses of various vasoconstrictors in the rodent systemic vasculature. The aim of the study was to investigate whether endocannabinoids modulate the contractile responses evoked by a thromboxane A₂ analog (U46619), angiotensin II (ANG II), serotonin (5-HT), and phenylephrine, which stimulate distinct G_q/11 protein-coupled receptors (thromboxane, ANG II type 1, 5-HT₂, and α₁-adrenergic receptors) in isolated endothelium-intact human and rat pulmonary arteries (hPAs and rPAs, respectively). The CB₁ receptor antagonist AM251 (1 μM) and diacylglycerol lipase (2-arachidonoylglycerol synthesis enzyme) inhibitor RHC80267 (40 μM) enhanced contractions induced by U46619 in hPAs and rPAs and by ANG II in rPAs in an endothelium-dependent manner. AM251 did not influence vasoconstrictions induced by 5-HT or phenylephrine in rPAs. The monoacylglycerol lipase (2-arachidonoylglycerol degradation enzyme) inhibitor JZL184 (1 μM), but not the fatty acid amide hydrolase (anandamide degradation enzyme) inhibitor URB597 (1 μM), attenuated contractions evoked by U46619 in hPAs and rPAs and ANG II in rPAs. 2-Arachidonoylglycerol concentration-dependently induced relaxation of hPAs, which was inhibited by endothelium denudation or AM251 and enhanced by JZL184. Expression of CB₁ receptors was confirmed in hPAs and rPAs using Western blotting and immunohistochemistry. The present study shows the protective interaction between the endocannabinoid system and vasoconstriction in response to U46619 and ANG II in the human and rat pulmonary circulation. U46619 and ANG II may stimulate rapid endothelial release of endocannabinoids (mainly 2-arachidonoylglycerol), leading to CB₁ receptor-dependent and/or CB₁ receptor-independent vasorelaxation, which in the negative feedback mechanism reduces later agonist-induced vasoconstriction.

The endocannabinoid anandamide causes endothelium-dependent vasorelaxation in human mesenteric arteries

The endocannabinoid anandamide (AEA) causes vasorelaxation in animal studies. Although circulating AEA levels are increased in many pathologies, little is known about its vascular effects in humans. The aim of this work was to characterise the effects of AEA in human arteries. Ethical approval was granted to obtain mesenteric arteries from patients (n = 31) undergoing bowel resection. Wire myography was used to probe the effects and mechanisms of action of AEA. RT‐PCR was used to confirm the presence of receptor mRNA in human aortic endothelial cells (HAECs) and intracellular signalling proteins were measured using multiplex technology. AEA caused vasorelaxation of precontracted human mesenteric arteries with an R_max of ∼30%. A synthetic CB₁ agonist (CP55940) caused greater vasorelaxation (R_max ∼60%) while a CB₂ receptor agonist (HU308) had no effect on vascular tone. AEA-induced vasorelaxation was inhibited by removing the endothelium, inhibition of nitric oxide (NO) synthase, antagonising the CB₁ receptor and antagonising the proposed novel endothelial cannabinoid receptor (CB_e). AEA‐induced vasorelaxation was not affected by CB₂ antagonism, by depleting sensory neurotransmitters, or inhibiting cyclooxygenase activity. RT‐PCR showed CB₁ but not CB₂ receptors were present in HAECs, and AEA and CP55940 had similar profiles in HAECs (increased phosphorylation of JNK, NFκB, ERK, Akt, p70s6K, STAT3 and STAT5). Post hoc analysis of the data set showed that overweight patients and those taking paracetamol had reduced vasorelaxant responses to AEA. These data show that AEA causes moderate endothelium-dependent, NO-dependent vasorelaxation in human mesenteric arteries via activation of CB₁ receptors.

Protective role of cannabinoid CB1 receptors and vascular effects of chronic administration of FAAH inhibitor URB597 in DOCA-salt hypertensive rats

AIMS

This study examined whether the fall in blood pressure (BP) induced by the chronic inhibition of fatty acid amide hydrolase (FAAH) by URB597 in deoxycorticosterone acetate (DOCA-salt) hypertensive rats correlates with endocannabinoid-mediated vascular changes.

MAIN METHODS

Functional studies were performed in isolated endothelium-intact aortas and small mesenteric arteries (sMAs) using organ bath technique and wire myography, respectively.

KEY FINDINGS

In the DOCA-salt rats, methanandamide-stimulated relaxation was enhanced in sMAs or diminished in aortas. Its vasorelaxant effect in sMAs was sensitive to the antagonist of the Transient Receptor Potential Vanilloid type 1 (TRPV1), capsazepine, in normo- and hypertensive animals and to the antagonist of the cannabinoid CB1 receptors, AM6545, only in DOCA-salt rats. Cannabinoid CB1 receptors were up-regulated merely in DOCA-salt sMAs. URB597 decreased elevated BP in DOCA-salt rats, medial hypertrophy in DOCA-salt aortas. In sMAs it reduced FAAH expression and restored the augmented phenylephrine-induced contraction in the DOCA-salt rats to the level obtained in normotensive controls. In normotensive rats it diminished endothelium-dependent relaxation and increased phenylephrine-induced contraction.

SIGNIFICANCE

The study showed the protective role of cannabinoid CB1 receptors in DOCA-salt sMAs. Reduction in BP after chronic administration of the FAAH inhibitor URB597 in DOCA-salt hypertensive rats only partially correlates with structural and functional changes in conductance and resistance vessels, respectively. Caution should be taken in studying cannabinoids and FAAH inhibitors as potential therapeutics, because of their vessel- and model-specific activities, and side effects connected with off-target response and activation of alternative pathways of anandamide metabolism.

Endocannabinoids and the Cardiovascular System in Health and Disease

The endocannabinoid system is widely distributed throughout the cardiovascular system. Endocannabinoids play a minimal role in the regulation of cardiovascular function in normal conditions, but are altered in most cardiovascular disorders. In shock, endocannabinoids released within blood mediate the associated hypotension through CB(1) activation. In hypertension, there is evidence for changes in the expression of CB(1), and CB(1) antagonism reduces blood pressure in obese hypertensive and diabetic patients. The endocannabinoid system is also upregulated in cardiac pathologies. This is likely to be cardioprotective, via CB(2) and CB(1) (lesser extent). In the vasculature, endocannabinoids cause vasorelaxation through activation of multiple target sites, inhibition of calcium channels, activation of potassium channels, NO production and the release of vasoactive substances. Changes in the expression or function of any of these pathways alter the vascular effect of endocannabinoids. Endocannabinoids have positive (CB(2)) and negative effects (CB(1)) on the progression of atherosclerosis. However, any negative effects of CB(1) may not be consequential, as chronic CB(1) antagonism in large scale human trials was not associated with significant reductions in atheroma. In neurovascular disorders such as stroke, endocannabinoids are upregulated and protective, involving activation of CB(1), CB(2), TRPV1 and PPARα. Although most of this evidence is from preclinical studies, it seems likely that cannabinoid-based therapies could be beneficial in a range of cardiovascular disorders.

G protein coupled receptor 18: A potential role for endocannabinoid signaling in metabolic dysfunction

Endocannabinoids are products of dietary fatty acids that are modulated by an alteration in food intake levels. Overweight and obese individuals have substantially higher circulating levels of the arachidonic acid derived endocannabinoids, anandamide and 2-arachidonoyl glycerol, and show an altered pattern of cannabinoid receptor expression. These cannabinoid receptors are part of a large family of G protein coupled receptors (GPCRs). GPCRs are major therapeutic targets for various diseases within the cardiovascular, neurological, gastrointestinal, and endocrine systems, as well as metabolic disorders such as obesity and type 2 diabetes mellitus. Obesity is considered a state of chronic low-grade inflammation elicited by an immunological response. Interestingly, the newly deorphanized GPCR (GPR18), which is considered to be a putative cannabinoid receptor, is proposed to have an immunological function. In this review, the current scientific knowledge on GPR18 is explored including its localization, signaling pathways, and pharmacology. Importantly, the involvement of nutritional factors and potential dietary regulation of GPR18 and its (patho)physiological roles are described. Further research on this receptor and its regulation will enable a better understanding of the complex mechanisms of GPR18 and its potential as a novel therapeutic target for treating metabolic disorders.