The Endocannabinoid System

Genetics, Biochemistry, Brain Disorders, and Therapy

Eric Murillo-Rodriguez

• Publisher: Academic Press
• Year: 2017
• Print ISBN: 9780128096666
• eBook ISBN: 9780128096673
• Topic: Technology & Engineering
• Subtopic: Animal Husbandry
• Index: Technology & Engineering

The Endocannabinoid System: Genetics, Biochemistry, Brain Disorders, and Therapy examines the cellular, biochemical, genetic, and therapeutic aspects of the endocannabinoid system. The chapters cover significant conceptual advances in the endocannabinoid field and shed light on the many brain disorders in which this biological system is involved.Written by world-leading experts in the field, the topics covered in this book will have a positive impact on the area of molecular biology, including, but not limited to, cell biology, neuroscience, pharmacology, signaling, disease mechanisms, and therapeutics.- Provides an introduction to endocannabinoids in the central nervous system and an overview to their functions in the brain- Presents information on neurobiological and cellular studies on the role of the cannabinoid signaling system and its implications in human diseases- Includes well-written overviews of the basics of endocannabinoid system structure and function- Contains well-illustrated material, with diagrams, charts, and tables- Explores compelling case studies and their application to chapters written by experts

Chapter 1

Basic Mechanisms of Synthesis and Hydrolysis of Major Endocannabinoids

Natalia Battista¹, and Mauro Maccarrone^{2,3 1}University of Teramo, Teramo, Italy ²Campus Bio-Medico University of Rome, Rome, Italy ³European Center for Brain Research/IRCCS Santa Lucia Foundation, Rome, Italy

Abstract

Twenty-five years after the discovery of the first cannabinoid receptor, several efforts have been made to identify the biochemical routes potentially used by cells to produce its endogenous ligands anandamide and 2-arachidonoylglycerol. These endocannabinoids (eCBs) are key molecules engaged in multiple biological processes that, together with their molecular targets, biosynthetic and catabolic enzymes, form the so-called “endocannabinoid system.” Despite the development of selective pharmacological and genetic tools to target eCB metabolic enzymes, there are still some missing pieces that prevent a full understanding of eCB biosynthesis and hydrolysis. In this chapter, we will review the latest advances on the metabolic pathways that account for production and degradation of eCBs.

Keywords

2-Arachidonoylglycerol; Anandamide; Biosynthesis; Catabolism; Endocannabinoids metabolic routes

Endocannabinoids and Their Analogs

The isolation of the psychoactive ingredient of cannabis (Cannabis sativa), Δ⁹-tetrahydrocannabinol, back in 1964 led almost 30 years later to the discovery of the endogenous lipophilic molecules, collectively termed endocannabinoids (eCBs), able to activate the same two G-protein-coupled receptors, type 1 (CB₁) and type 2 (CB₂) cannabinoid receptors (Maccarrone et al., 2015).

On the basis of their main role in controlling biological processes both in human health and disease, N-arachidonoylethanolamine (anandamide) (AEA) and 2-arachidonoylglycerol (2-AG) are presently recognized as the two main members of this family (Fig. 1.1). Other important ω-6 (n-6) fatty acid compounds with cannabimimetic properties, such as N-arachidonoyldopamine (NADA), 2-arachidonoylglycerylether (noladin ether), and O-arachidonoylethanolamine (virodhamine), have also been listed among these bioactive lipids, although their pharmacology and biological relevance remain to be clarified (Fezza et al., 2014). In addition, in the past 5 years it has been demonstrated that eCBs are closely interconnected to docosahexaenoic acid (DHA) throughout the eicosanoid pathway. Indeed, N-docosahexaenoylethanolamine, a derivative of DHA that is thought to be produced by the same pathway that generates AEA, acts as an eCB not only in its ability to activate CB receptors, but also in its susceptibility to be metabolized by the catabolic enzyme fatty acid amide hydrolase (FAAH) (Brown et al., 2010; Cascio, 2013). eCB congeners [i.e., N-palmitoylethanolamine (PEA), N-oleoylethanolamine (OEA), and N-stearoylethanolamine] that exert their effects independently of CB receptors are commonly classified as “endocannabinoid-like” compounds (Ben-Shabat et al., 1998; Costa, Comelli, Bettoni, Colleoni, & Giagnoni, 2008; Fezza et al., 2014; Ho, Barrett, & Randall, 2008). Indeed, these molecules might significantly contribute to an entourage effect that prevents true eCBs from being degraded by specific metabolic enzymes, or from allosterically modulating receptor binding (Fezza et al., 2014).

Figure 1.1 Chemical structures of AEA and 2-AG.

The knowledge of metabolic pathways that regulate the endogenous tone of eCBs, as well as the discovery of the proteins that bind them, shed light on the critical functions of these molecules at central (Maccarrone, Guzmán, Mackie, Doherty, & Harkany, 2014) and peripheral levels (Maccarrone et al., 2015). The most relevant proteins identified to date in controlling eCB tone will be described in the following sections.

N-Arachidonoylethanolamine Metabolism: Synthesis

The classical dogma that eCBs are synthesized and released “on demand” via hydrolysis of cell membrane phospholipid precursors has been revisited on the basis of unexpected evidence for intracellular reservoirs and transporters of eCBs. These new entities have been shown to drive intracellular trafficking of eCBs, adding a new dimension to the regulation of their biological activity (Maccarrone, Dainese, & Oddi, 2010). However, several routes have been proposed to explain the metabolic pathways of AEA biosynthesis (Ueda, Tsuboi, & Uyama, 2013).

The possibility to synthesize AEA in vitro by a simple condensation of arachidonic acid (AA) and ethanolamine catalyzed by a reverse FAAH or an AEA hydrolase “working in reverse” was not feasible in vivo (Kurahashi, Ueda, Suzuki, Suzuki, & Yamamoto, 1997; Ueda, Kurahashi, Yamamoto, Yamamoto, & Tokunaga, 1996). Indeed, the substrate concentrations required to form AEA are much higher than those actually detected in cells, and, nowadays, it is accepted that the generation of AEA in cells and tissues occurs mainly as a result of the hydrolysis of a minor membrane phospholipid, N-arachidonoylphosphatidylethanolamine (NArPE) (Di Marzo et al., 1994). Although an ever-growing number of enzymes have been ascribed to AEA biosynthesis (Cascio & Marini, 2015), the orchestrated and sequential action of N-acyltransferase (NAT) and N-acyl-phosphatidylethanolamine (NAPE)-specific phospholipase D (NAPE-PLD) is believed to be the most relevant pathway to generate AEA. Indeed, NAT acts by transferring AA from the sn-1 position of 1,2-sn-di-arachidonoylphosphatidylcholine (PC) to phosphatidylethanolamine (PE), thus generating NArPE.

The latter compound is next cleaved to yield AEA and phosphatidic acid (PA) by NAPE-PLD. The enzyme is encoded by the Nape-pld gene on chromosome 5, position 9.97 cM (21662901–21701396 bp, —strand) (Zimmer, 2015). The transcript has five exons. Exons 2–5 contain the open reading frame of the 396-amino acid NAPE-PLD protein. This 46-kDA protein belongs to the zinc metallohydrolase family of the metallo-β-lactamase fold, is characterized by a highly conserved residues involved in the binding of substrates, is stimulated by divalent cations such as Mg²⁺ and Ca²⁺, and is involved in the formation of other cannabinoid-receptor-inactive, N-acylethanolamines (NAE) (Liu, Tonai, & Ueda, 2002; Okamoto, Morishita, Tsuboi, Tonai, & Ueda, 2004; Petersen & Hansen, 1999; Ueda, Liu, & Yamanaka, 2001). Thanks to the generation of NAPE-PLD-deficient mice, alternative pathways to for...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Acknowledgments
• Introduction
• Chapter 1. Basic Mechanisms of Synthesis and Hydrolysis of Major Endocannabinoids
• Chapter 2. Cannabinoid Receptors and Their Signaling Mechanisms
• Chapter 3. The Endocannabinoid System and Parkinson Disease
• Chapter 4. Putative Role of Endocannabinoids in Schizophrenia
• Chapter 5. The Endocannabinoid System and Human Brain Functions: Insight From Memory, Motor, and Mood Pathologies
• Chapter 6. The Role of the Endocannabinoid System in Addiction
• Index