Cyclooxygenase metabolism mediates vasorelaxation to 2-arachidonoylglycerol (2-AG) in human mesenteric arteries

Hormetic effects of a cannabinoid system component, 2-arachidonoyl glycerol, on cell viability and expression profile of growth factors in cultured mouse Sertoli cells: Friend or foe of male fertility?

The generally undesired effects of exocannabinoids on male reproduction include alterations in testicular cell proliferation and function, as well as apoptosis induction. However, this paradigm has been challenged by the ability of endocannabinoids to regulate reproductive function. The present study addresses these paradoxical facts by investigating the effects of the endocannabinoid 2-arachidonoyl glycerol (2-AG) on mouse Sertoli cells' survival and apoptosis, with a mechanistic insight into Sertoli cell-based growth factors' production. The Mus musculus Sertoli cell line (TM4) was exposed to different concentrations of 2-AG, and cell viability was evaluated using MTT assay. Growth factors' gene and protein expressions were analyzed through RT-PCR and western blotting. 2-AG concentration dependently increased TM4 viability, with a slight increase starting at 0.0001 µM, a peak of 190% of the control level at 1 µM, and a decrease at 3 µM. Moreover, 2-AG paradoxically altered mRNA expression of caspase-3 and growth factors. Caspase-3 mRNA expression was down-regulated, and growth factors mRNA and protein expression were up-regulated when using a low concentration of 2-AG (1 μM). Opposite effects were observed by a higher concentration of 2-AG (3 μM). These paradoxical effects of 2-AG can be explained through the concept of hormesis. The results indicate the pivotal role of 2-AG in mediating Sertoli cell viability and apoptosis, at least in part, through altering growth factors secretion. Furthermore, they suggest the involvement of endocannabinoids in Sertoli cell-based physiological and pathological conditions and reflect the ability of abnormally elevated 2-AG to mimic the actions of exocannabinoids in reproductive dysfunction.

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.

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.

Functional Interaction among KCa and TRP Channels for Cardiovascular Physiology: Modern Perspectives on Aging and Chronic Disease

Effective delivery of oxygen and essential nutrients to vital organs and tissues throughout the body requires adequate blood flow supplied through resistance vessels. The intimate relationship between intracellular calcium ([Ca²⁺]_i) and regulation of membrane potential (V_m) is indispensable for maintaining blood flow regulation. In particular, Ca²⁺-activated K⁺ (K_Ca) channels were ascertained as transducers of elevated [Ca²⁺]_i signals into hyperpolarization of V_m as a pathway for decreasing vascular resistance, thereby enhancing blood flow. Recent evidence also supports the reverse role for K_Ca channels, in which they facilitate Ca²⁺ influx into the cell interior through open non-selective cation (e.g., transient receptor potential; TRP) channels in accord with robust electrical (hyperpolarization) and concentration (~20,000-fold) transmembrane gradients for Ca²⁺. Such an arrangement supports a feed-forward activation of V_m hyperpolarization while potentially boosting production of nitric oxide. Furthermore, in vascular types expressing TRP channels but deficient in functional K_Ca channels (e.g., collecting lymphatic endothelium), there are profound alterations such as downstream depolarizing ionic fluxes and the absence of dynamic hyperpolarizing events. Altogether, this review is a refined set of evidence-based perspectives focused on the role of the endothelial K_Ca and TRP channels throughout multiple experimental animal models and vascular types. We discuss the diverse interactions among K_Ca and TRP channels to integrate Ca²⁺, oxidative, and electrical signaling in the context of cardiovascular physiology and pathology. Building from a foundation of cellular biophysical data throughout a wide and diverse compilation of significant discoveries, a translational narrative is provided for readers toward the treatment and prevention of chronic, age-related cardiovascular disease.

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.

Modulation of mean arterial pressure and diuresis by renomedullary infusion of a selective inhibitor of fatty acid amide hydrolase

The kidneys contribute to the control of body fluid and electrolytes and the long-term regulation of blood pressure through various systems, including the endocannabinoid system. Previously, we showed that inhibition of the two major endocannabinoid-hydrolyzing enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase, in the renal medulla increased the rate of urine excretion (UV) and salt excretion without affecting mean arterial pressure (MAP). The present study evaluated the effects of a selective FAAH inhibitor, N-3-pyridinyl-4-[[3-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenyl]methyl]-1-piperidine carboxamide (PF-3845) on MAP and renal functions. Infusion of PF-3845 into the renal medulla of C57BL/6J mice reduced MAP during the posttreatment phases and increased UV at 15 and 30 nmol/min per gram kidney weight (g kwt), relative to the pretreatment control phase. Intravenous PF-3845 administration reduced MAP at the 7.5, 15, and 30 doses and increased UV at the 15 and 30 nmol⋅min^-1⋅g^-1 kwt doses. PF-3845 treatment elevated sodium and potassium urinary excretion and medullary blood flow. Homozygous FAAH knockout mice were refractory to intramedullary PF-3845-induced changes in MAP, but UV was increased. Both MAP and UV responses to intramedullary PF-3845 in C57BL/6J mice were diminished by pretreatment with the cannabinoid type 1 receptor-selective antagonist, rimonabant (3 mg/kg, ip) but not the cyclooxygenase 2-selective inhibitor, celecoxib (15 mg/kg, iv). Liquid chromatography-tandem mass spectrometry analyses showed increased anandamide in kidney tissue and 2-arachidonoyl glycerol in plasma after intramedullary PF-3845. These data suggest that inhibition of FAAH in the renal medulla leads to both a diuretic and blood pressure-lowering response mediated by elevated anandamide in kidney tissue or 2-arachidonoyl glycerol in plasma.

Sex differences in the role of phospholipase A2 -dependent arachidonic acid pathway in the perivascular adipose tissue function in pigs

KEY POINTS

The fat surrounding blood vessels (perivascular adipose tissue or PVAT) releases vasoactive compounds that regulate vascular smooth muscle tone. There are sex differences in the regulation of vascular tone, but, to date, no study has investigated whether there are sex differences in the regulation of blood vessel tone by PVAT. This study has identified that the cyclooxygenase products thromboxane and PGF_2α are released from coronary artery PVAT from pigs. Thromboxane appears to mediate the PVAT-induced contraction in arteries from females, whereas PGF_2α appears to mediate the contraction in arteries from males. These sex differences in the role of these prostanoids in the PVAT-induced contraction can be explained by a greater release of thromboxane from PVAT from female animals and greater sensitivity to PGF_2α in the porcine coronary artery from males.

ABSTRACT

Previous studies have demonstrated that perivascular adipose tissue (PVAT) causes vasoconstriction. In this present study, we determined the role of cyclooxygenase-derived prostanoids in this contractile response and determined whether there were any sex differences in the regulation of vascular tone by PVAT. Contractions in isolated segments of coronary arteries were determined using isolated tissue baths and isometric tension recording. Segments were initially cleaned of PVAT, which was then re-added to the tissue bath and changes in tone measured over 1 h. Levels of PGF_2α and thromboxane B₂ (TXB₂ ) were quantified by ELISA, and PGF_2α (FP) and thromboxane A₂ (TP) receptor expression determined by Western blotting. In arteries from both male and female pigs, re-addition of PVAT caused a contraction, which was partially inhibited by the cyclooxygenase inhibitors indomethacin and flurbiprofen. The FP receptor antagonist AL8810 attenuated the PVAT-induced contraction in arteries from males, whereas the TP receptor antagonist GR32191B inhibited the PVAT-induced contraction in arteries from females. Although there was no difference in PGF_2α levels in PVAT between females and males, PGF_2α produced a larger contraction in arteries from males, correlating with a higher FP receptor expression. In contrast, release of TXB₂ from PVAT from females was greater than from males, but there was no difference in the contraction by the TXA₂ agonist U46619, or TP receptor expression in arteries from different sexes. These findings demonstrate clear sex differences in PVAT function in which PGF_2α and TXA₂ antagonists can inhibit the PVAT-induced vasoconstriction in male and female PCAs, respectively.

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 Ratio of 2-AG to Its Isomer 1-AG as an Intrinsic Fine Tuning Mechanism of CB1 Receptor Activation

Endocannabinoids are pleiotropic lipid messengers that play pro-homeostatic role in cellular physiology by strongly influencing intracellular Ca²⁺ concentration through the activation of cannabinoid receptors. One of the best-known endocannabinoid ‘2-AG’ is chemically unstable in aqueous solutions, thus its molecular rearrangement, resulting in the formation of 1-AG, may influence 2-AG-mediated signaling depending on the relative concentration and potency of the two isomers. To predict whether this molecular rearrangement may be relevant in physiological processes and in experiments with 2-AG, here we studied if isomerization of 2-AG has an impact on 2-AG-induced, CB1-mediated Ca²⁺ signaling in vitro. We found that the isomerization-dependent drop in effective 2-AG concentration caused only a weak diminution of Ca²⁺ signaling in CB1 transfected COS7 cells. We also found that 1-AG induces Ca²⁺ transients through the activation of CB1, but its working concentration is threefold higher than that of 2-AG. Decreasing the concentration of 2-AG in parallel to the prevention of 1-AG formation by rapid preparation of 2-AG solutions, caused a significant diminution of Ca²⁺ signals. However, various mixtures of the two isomers in a fix total concentration – mimicking the process of isomerization over time – attenuated the drop in 2-AG potency, resulting in a minor decrease in CB1 mediated Ca²⁺ transients. Our results indicate that release of 2-AG into aqueous medium is accompanied by its isomerization, resulting in a drop of 2-AG concentration and simultaneous formation of the similarly bioactive isomer 1-AG. Thus, the relative concentration of the two isomers with different potency and efficacy may influence CB1 activation and the consequent biological responses. In addition, our results suggest that 1-AG may play role in stabilizing the strength of cannabinoid signal in case of prolonged 2-AG dependent cannabinoid mechanisms.

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.

Increased Renal 2-Arachidonoylglycerol Level Is Associated with Improved Renal Function in a Mouse Model of Acute Kidney Injury

Background: Acute kidney injury (AKI) is associated with a significantly increased risk of morbidity and mortality. Ischemia-reperfusion injury (IRI) is a major cause of AKI. In this study, we investigated the role of the endocannabinoid (EC) system in renal IRI using a well-established mouse model. Materials and Methods: Renal ischemia was induced in male C57BL/6 mice by clamping both kidney pedicles for 30 min followed by 24 h of reperfusion. To increase renal 2-arachidonoylglycerol (2-AG) levels, mice were pretreated with JZL184 (16 mg/kg), 30 min before IRI. Serum creatinine and blood urea nitrogen (BUN), renal tubular damage, renal content of ECs and renal expression of markers of inflammation and oxidative stress were measured. Results: Renal IRI was associated with significantly increased serum BUN and creatinine, increased tubular damage score, increased expression of renal markers of inflammation and oxidative stress and elevated renal 2-AG content. Pretreatment with JZL184 was associated with a significant increase in renal 2-AG content and there was also improved serum BUN, creatinine and tubular damage score. However, renal expression of inflammation and oxidative stress markers remained unchanged. Conclusions: This is the first report documenting that renal IRI is associated with an increase in kidney 2-AG content. Further enhancement of 2-AG levels using JZL184 improved indices of renal function and histology, but did not lower renal expression of markers of inflammation and oxidative stress. Further studies are needed to determine the mechanisms responsible for the effects observed and the potential value of 2-AG as a therapeutic target in renal IRI.

Metabolism of Anandamide by Human Cytochrome P450 2J2 in the Reconstituted System and Human Intestinal Microsomes

According to the Centers for Disease Control and Prevention, the incidence of inflammatory bowel diseases (IBD) is about 1 in 250 people in the United States. The disease is characterized by chronic or recurring inflammation of the gut. Because of the localization of the endocannabinoid system in the gastrointestinal tract, it may be a potential pharmacologic target for the treatment of IBD and other diseases. Fatty acid amide hydrolase (FAAH) is a potential candidate because it is upregulated in IBD. FAAH hydrolyzes and, as a consequence, inactivates anandamide (AEA), a prominent endocannabinoid. Inhibition of FAAH would lead to increases in the amount of AEA oxidized by cytochrome P450s (P450s). CYP2J2, the major P450 epoxygenase expressed in the heart, is also expressed in the intestine and has previously been reported to oxidize AEA. We have investigated the possibility that it may play a role in AEA metabolism in the gut and have demonstrated that purified human CYP2J2 metabolizes AEA to form the 20-hydroxyeicosatetraenoic acid ethanolamide (HETE-EA) and several epoxygenated products, including the 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acid ethanolamides (EET-EAs), in the reconstituted system. Kinetic studies suggest that the KM values for these products range from approximately 10 to 468 μM and the kcat values from 0.2 to 23.3 pmol/min per picomole of P450. Human intestinal microsomes, which express CYP2J2, metabolize AEA to give the 5,6-, 8,9-, and 11,12-EET-EAs, as well as 20-HETE-EA. Studies using specific P450 inhibitors suggest that although CYP2J2 metabolizes AEA, it is not the primary P450 responsible for AEA metabolism in human intestines.

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.

Translational value of mechanical and vasomotor properties of mouse isolated mesenteric resistance-sized arteries

Mice are increasingly used in vascular research for studying perturbations and responses to vasoactive agents in small artery preparations. Historically, small artery function has preferably been studied in rat isolated mesenteric resistance-sized arteries (MRA) using the wire myograph technique. Although different mouse arteries have been studied using the wire myograph no establishment of optimal settings has yet been performed. Therefore, the purposes of this study were firstly to establish the optimal settings for wire myograph studies of mouse MRA and compare them to those of rat MRA. Second, by surveying the literature, we aimed to evaluate the overall translatability of observed pharmacological vasomotor responses of mouse MRA to those obtained in rat MRA as well as corresponding and different arteries in terms of vessel size and species origin. Our results showed that the optimal conditions for maximal active force development in mouse MRA were not significantly different to those determined in rat MRA. Furthermore, we found that the observed concentration-dependent vasomotor responses of mouse MRA to noradrenaline, phenylephrine, angiotensin II, sarafotoxin 6c, 5-hydroxytryptamine, carbachol, sodium nitroprusside, and retigabine were generally similar to those described in rat MRA as well as arteries of different sizes and species origin. In summary, the results of this study provide a framework for evidence-based optimization of the isometric wire myograph setup to mouse MRA. Additionally, in terms of translational value, our study suggests that mouse MRA can be applied as a useful model for studying vascular reactivity.

Role of endothelial TRPV4 channels in vascular actions of the endocannabinoid, 2-arachidonoylglycerol

BACKGROUND AND PURPOSE

Metabolites of the endocannabinoid, 2-arachidonoylglycerol (2-AG) have been postulated to act as endogenous activators of TRPV4, a Ca(2+) -permeable cation channel that plays a critical role in endothelium-dependent relaxation. However, it is unclear if TRPV4 contributes to the vascular actions of 2-AG.

EXPERIMENTAL APPROACH

Isometric tension recording of rat small mesenteric arteries and aortae were used to assess the effect of 2-AG and the synthetic TRPV4 activator, GSK1016790A (GSK) on vascular reactivity. Changes in intracellular Ca(2+) concentration and single-channel currents were measured in TRPV4-expressing human coronary endothelial cells.

KEY RESULTS

In mesenteric arteries, endothelium-dependent relaxation to both 2-AG and GSK was attenuated by structurally distinct TRPV4 antagonists, HC067047, RN1734 and ruthenium red. The responses were inhibited by KCa inhibitors (apamin + charybdotoxin) and a gap junction inhibitor (18α-glycyrrhetinic acid). In contrast to GSK, 2-AG elicited considerable relaxation independently of the endothelium or TRPV4. Inhibition of 2-AG metabolism via monoacylglycerol lipase and COX (by MAFP and indomethacin) caused potentiation, while cytochrome P450 and lipoxygenase inhibitors had no effect on 2-AG relaxation. In coronary endothelial cells, 2-AG (with and without MAFP) induced HC067047-sensitive increases in intracellular Ca(2+) concentration. 2-AG also increased TRPV4 channel opening in inside-out patches. However, in aortae, GSK induced a relaxation sensitive to HC067047 and ruthenium red, whereas 2-AG induced contractions.

CONCLUSIONS AND IMPLICATIONS

These data suggest that 2-AG can directly activate endothelial TRPV4, which partly contributes to the relaxant response to 2-AG. However, the functional role of TRPV4 is highly dependent on the vascular region.

Cannabidiol causes endothelium-dependent vasorelaxation of human mesenteric arteries via CB1 activation

Aims

The protective effects of cannabidiol (CBD) have been widely shown in preclinical models and have translated into medicines for the treatment of multiple sclerosis and epilepsy. However, the direct vascular effects of CBD in humans are unknown.

Methods and results

Using wire myography, the vascular effects of CBD were assessed in human mesenteric arteries, and the mechanisms of action probed pharmacologically. CBD-induced intracellular signalling was characterized using human aortic endothelial cells (HAECs). CBD caused acute, non-recoverable vasorelaxation of human mesenteric arteries with an R_max of ∼40%. This was inhibited by cannabinoid receptor 1 (CB₁) receptor antagonists, desensitization of transient receptor potential channels using capsaicin, removal of the endothelium, and inhibition of potassium efflux. There was no role for cannabinoid receptor-2 (CB₂) receptor, peroxisome proliferator activated receptor (PPAR)γ, the novel endothelial cannabinoid receptor (CB_e), or cyclooxygenase. CBD-induced vasorelaxation was blunted in males, and in patients with type 2 diabetes or hypercholesterolemia. In HAECs, CBD significantly reduced phosphorylated JNK, NFκB, p70s6 K and STAT5, and significantly increased phosphorylated CREB, ERK1/2, and Akt levels. CBD also increased phosphorylated eNOS (ser1177), which was correlated with increased levels of ERK1/2 and Akt levels. CB₁ receptor antagonism prevented the increase in eNOS phosphorylation.

Conclusion

This study shows, for the first time, that CBD causes vasorelaxation of human mesenteric arteries via activation of CB₁ and TRP channels, and is endothelium- and nitric oxide-dependent.

Endocannabinoid-mediated modulation of Gq/11 protein-coupled receptor signaling-induced vasoconstriction and hypertension

Activation of G protein-coupled receptors (GPCRs) can induce vasoconstriction via calcium signal-mediated and Rho-dependent pathways. Earlier reports have shown that diacylglycerol produced during calcium signal generation can be converted to an endocannabinoid, 2-arachidonoylglycerol (2-AG). Our aim was to provide evidence that GPCR signaling-induced 2-AG production and activation of vascular type1 cannabinoid receptors (CB1R) is capable of reducing agonist-induced vasoconstriction and hypertension. Rat and mouse aortic rings were examined by myography. Vascular expression of CB1R was demonstrated with immunohistochemistry. Rat aortic vascular smooth muscle cells (VSMCs) were cultured for calcium measurements and 2-AG-determination. Inhibition or genetic loss of CB1Rs enhanced vasoconstriction induced by angiotensin II (AngII) or phenylephrine (Phe), but not by prostaglandin(PG)F2α. AngII-induced vasoconstriction was augmented by inhibition of diacylglycerol lipase (tetrahydrolipstatin) and was attenuated by inhibition of monoacylglycerol lipase (JZL184) suggesting a functionally relevant role for endogenously produced 2-AG. In Gαq/11-deficient mice vasoconstriction was absent to AngII or Phe, which activate Gq/11-coupled receptors, but was maintained in response to PGF2α. In VSMCs, AngII-stimulated 2-AG-formation was inhibited by tetrahydrolipstatin and potentiated by JZL184. CB1R inhibition increased the sustained phase of AngII-induced calcium signal. Pharmacological or genetic loss of CB1R function augmented AngII-induced blood pressure rise in mice. These data demonstrate that vasoconstrictor effect of GPCR agonists is attenuated via Gq/11-mediated vascular endocannabinoid formation. Agonist-induced endocannabinoid-mediated CB1R activation is a significant physiological modulator of vascular tone. Thus, the selective modulation of GPCR signaling-induced endocannabinoid release has a therapeutic potential in case of increased vascular tone and hypertension.

Vascular targets for cannabinoids: animal and human studies

Application of cannabinoids and endocannabinoids to perfused vascular beds or individual isolated arteries results in changes in vascular resistance. In most cases, the result is vasorelaxation, although vasoconstrictor responses are also observed. Cannabinoids also modulate the actions of vasoactive compounds including acetylcholine, methoxamine, angiotensin II and U46619 (thromboxane mimetic). Numerous mechanisms of action have been proposed including receptor activation, potassium channel activation, calcium channel inhibition and the production of vasoactive mediators such as calcitonin gene-related peptide, prostanoids, NO, endothelial-derived hyperpolarizing factor and hydrogen peroxide. The purpose of this review is to examine the evidence for the range of receptors now known to be activated by cannabinoids. Direct activation by cannabinoids of CB1 , CBe , TRPV1 (and potentially other TRP channels) and PPARs in the vasculature has been observed. A potential role for CB2, GPR55 and 5-HT1 A has also been identified in some studies. Indirectly, activation of prostanoid receptors (TP, IP, EP1 and EP4 ) and the CGRP receptor is involved in the vascular responses to cannabinoids. The majority of this evidence has been obtained through animal research, but recent work has confirmed some of these targets in human arteries. Vascular responses to cannabinoids are enhanced in hypertension and cirrhosis, but are reduced in obesity and diabetes, both due to changes in the target sites of action. Much further work is required to establish the extent of vascular actions of cannabinoids and the application of this research in physiological and pathophysiological situations.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Cannabidiol improves vasorelaxation in Zucker diabetic fatty rats through cyclooxygenase activation

Cannabidiol (CBD) decreases insulitis, inflammation, neuropathic pain, and myocardial dysfunction in preclinical models of diabetes. We recently showed that CBD also improves vasorelaxation in the Zucker diabetic fatty (ZDF) rat, and the objective of the present study was to establish the mechanisms underlying this effect. Femoral arteries from ZDF rats and ZDF lean controls were isolated, mounted on a myograph, and incubated with CBD (10 μM) or vehicle for 2 hours. Subsequent vasorelaxant responses were measured in combination with various interventions. Prostaglandin metabolites were detected using enzyme immunoassay. Direct effects of CBD on cyclooxygenase (COX) enzyme activity were measured by oxygraph assay. CBD enhanced the maximum vasorelaxation to acetylcholine (ACh) in femoral arteries from ZDF lean rats (P < 0.01) and especially ZDF rats (P < 0.0001). In ZDF arteries, this enhancement persisted after cannabinoid receptor (CB) type 1, endothelial CB, or peroxisome proliferator-activated receptor-γ antagonism but was inhibited by CB2 receptor antagonism. CBD also uncovered a vasorelaxant response to a CB2 agonist not previously observed. The CBD-enhanced ACh response was endothelium-, nitric oxide-, and hydrogen peroxide-independent. It was, however, COX-1/2- and superoxide dismutase-dependent, and CBD enhanced the activity of both purified COX-1 and COX-2. The CBD-enhanced ACh response in the arteries was inhibited by a prostanoid EP4 receptor antagonist. Prostaglandin E2 metabolite levels were below the limits of detection, but 6-keto prostaglandin F1 α was decreased after CBD incubation. These data show that CBD exposure enhances the ability of arteries to relax via enhanced production of vasodilator COX-1/2-derived products acting at EP4 receptors.