Endocannabinoids And The Control Of Cardiovascular Funct

Alcohol Abuse And Alcoholism

Investigators

Linked publications & trials

Abstract

Our earlier studies, confirmed by others, have indicated that the endothelium-dependent vasodilator effect of the endocannabinoid anandamide and of some atypical cannabinoid ligands, such as abnormal cannabidiol (abn-cbd) is mediated by a pertussis toxin-sensitive, G protein-coupled receptor distinct from CB1 or CB2. In a recent collaboration with Raphael Mechoulam's group a novel, endocannabinoid-like brain constituent, arachidonoyl L-serine (ARA-S) has been identified and characterized. Contrary to anandamide, ARA-S has very low or no affinity for CB1, CB2 or vanilloid TRPV1 receptors. However, ARA-s produces endothelium-dependent vasodilation in rat isolated mesenteric artery and aorta preparations and stimulates p44/42 MAP kinase and protein kinase B/Akt phosphorylation in human umbilical vein endothelial cells (HUVEC). ARA-S also suppresses LPS-induced formation of TNFalpha in a murine macrophage cell line and in wild-type mice, as well as in mice deficient in CB1 or CB2 receptors. Many of these effects parallel those reported for abn-cbd. These findings, published this year, suggest that ARA-S may be an endogenous ligand for the putative abn-cbd sensitive receptor. [unreadable] [unreadable] In an effort to identify this receptor, we set up a collaboration with a European biotech company that provides us with cells stably transfected with different orphan GPCR. These cells are screened by testing the ability of ARA-S and abn-cbd to induce p44/42 MAP kinase and Akt phosphorylation and stimulate GTPgammaS binding in a dose-dependent, pertussis toxin sensitive manner. Once a positive clone is identified, the results are verified in Dr. Stephen Ikeda's laboratory by generating a fusion construct of the cDNA of the given GPCR and of green fluorescent protein, transfecting this construct into primary cultured rat sympathetic ganglion neurons, in which Gi/Go-coupled receptors have been shown to inhibit calcium currents carried by an N type calcium channel. Once proper expression and membrane localization of the receptor is verified, such cells are then tested by patch clamp recording of the ability of ARA-S and abn-cbd to inhibit this calcium current.[unreadable] [unreadable] We have earlier established that the vasodilated state in advanced liver cirrhosis is mediated by endocannabinoids acting at vascular CB1 receptors (Nat Med 7:827, 2001). Cirrhosis is also known to be associated with altered cardiac function characterized by reduced contractility and contractile response to catecholamines. The cirrhotic 'cardiomyopathy' was recently proposed to be also due to stimulation of CB1 receptors by an endocannabinoids, based on a study using isolated papillary muscles from control and cirrhotic rats. We are testing this hypothesis by testing the cardiovascular effects of CB1 antagonists in an in vivo model of CCl4-induced cirrhosis in rats, in which cardiac hemodynamics are analyzed directly by using the Millar pressure/volume system, and by post-mortem quantification of cardiac endocannabinoid and CB1 receptor content in cirrhotic rats and their non-cirrhotic controls.[unreadable] [unreadable] In a fourth study, we have been investigating the role of the endocannabinoid system in cardiovascular regulation and as a potential therapeuic target in hypertension. We have earlier reported (Batkai et al., Circulation, 2004) that the endocannabinoid/CB1 receptor system becomes tonically active as a compensatory mechanism in 3 different rat models of hypertension. In these models using anesthetized, instrumented animals, blocking CB1 receptors was found to cause a further increase in blood pressure due to both increased cardiac contractility and peripheral vasoconstriction. In contrast, treatment of the animals with a commercially available inhibitor of fatty acid amidohydrolase (FAAH), the enzyme responsible for the in vivo degradation of anandamide, normalized blood pressure and the inappropriately increased cardiac contractility. These findings suggested that inhibition of FAAH may be a novel approach to treat hypertension and also to possibly prevent/reverse the associated cardiac hypertrophy. We have now developed (in collaboration with Dr. Alex Makriyannis) a novel, in vivo effective FAAH inhibitor which is both more potent and has a much longer lasting effect than URB597, the inhibitor we used before. This inhibitor is now tested in a chronic model using unanesthetized hypertensive rats implanted with telemetric recording probes for the non-invasive monitoring of blood pressure and heart rate. In addition, cardiac wall thickness is monitored by ultrasound to test the effect of chronic treatment with the novel FAAH inhibitor on the development of cardiac hypertrophy.