Cannabinoids alleviate experimentally induced intestinal inflammation by acting at central and peripheral receptors

Molecular-interaction and signaling profiles of AM3677, a novel covalent agonist selective for the cannabinoid 1 receptor

The cannabinoid 1 receptor (CB1R) is one of the most abundant G protein-coupled receptors (GPCRs) in the central nervous system. CB1R involvement in multiple physiological processes, especially neurotransmitter release and synaptic function, has made this GPCR a prime drug discovery target, and pharmacological CB1R activation has been demonstrated to be a tenable therapeutic modality. Accordingly, the design and profiling of novel, drug-like CB1R modulators to inform the receptor's ligand-interaction landscape and molecular pharmacology constitute a prime contemporary research focus. For this purpose, we report utilization of AM3677, a designer endocannabinoid (anandamide) analogue derivatized with a reactive electrophilic isothiocyanate functionality, as a covalent, CB1R-selective chemical probe. The data demonstrate that reaction of AM3677 with a cysteine residue in transmembrane helix 6 of human CB1R (hCB1R), C6.47(355), is a key feature of AM3677's ligand-binding motif. Pharmacologically, AM3677 acts as a high-affinity, low-efficacy CB1R agonist that inhibits forskolin-stimulated cellular cAMP formation and stimulates CB1R coupling to G protein. AM3677 also induces CB1R endocytosis and irreversible receptor internalization. Computational docking suggests the importance of discrete hydrogen bonding and aromatic interactions as determinants of AM3677's topology within the ligand-binding pocket of active-state hCB1R. These results constitute the initial identification and characterization of a potent, high-affinity, hCB1R-selective covalent agonist with utility as a pharmacologically active, orthosteric-site probe for providing insight into structure-function correlates of ligand-induced CB1R activation and the molecular features of that activation by the native ligand, anandamide.

Endocannabinoid signaling at the periphery: 50 years after THC

In 1964, the psychoactive ingredient of Cannabis sativa, Δ(9)-tetrahydrocannabinol (THC), was isolated. Nearly 30 years later the endogenous counterparts of THC, collectively termed endocannabinoids (eCBs), were discovered: N-arachidonoylethanolamine (anandamide) (AEA) in 1992 and 2-arachidonoylglycerol (2-AG) in 1995. Since then, considerable research has shed light on the impact of eCBs on human health and disease, identifying an ensemble of proteins that bind, synthesize, and degrade them and that together form the eCB system (ECS). eCBs control basic biological processes including cell choice between survival and death and progenitor/stem cell proliferation and differentiation. Unsurprisingly, in the past two decades eCBs have been recognized as key mediators of several aspects of human pathophysiology and thus have emerged to be among the most widespread and versatile signaling molecules ever discovered. Here some of the pioneers of this research field review the state of the art of critical eCB functions in peripheral organs. Our community effort is aimed at establishing consensus views on the relevance of the peripheral ECS for human health and disease pathogenesis, as well as highlighting emerging challenges and therapeutic hopes.

AM841, a covalent cannabinoid ligand, powerfully slows gastrointestinal motility in normal and stressed mice in a peripherally restricted manner

BACKGROUND AND PURPOSE

Cannabinoid (CB) ligands have been demonstrated to have utility as novel therapeutic agents for the treatment of pain, metabolic conditions and gastrointestinal (GI) disorders. However, many of these ligands are centrally active, which limits their usefulness. Here, we examine a unique novel covalent CB receptor ligand, AM841, to assess its potential for use in physiological and pathophysiological in vivo studies.

EXPERIMENTAL APPROACH

The covalent nature of AM841 was determined in vitro using electrophysiological and receptor internalization studies on isolated cultured hippocampal neurons. Mouse models were used for behavioural analysis of analgesia, hypothermia and hypolocomotion. The motility of the small and large intestine was assessed in vivo under normal conditions and after acute stress. The brain penetration of AM841 was also determined.

KEY RESULTS

AM841 behaved as an irreversible CB1 receptor agonist in vitro. AM841 potently reduced GI motility through an action on CB1 receptors in the small and large intestine under physiological conditions. AM841 was even more potent under conditions of acute stress and was shown to normalize accelerated GI motility under these conditions. This compound behaved as a peripherally restricted ligand, showing very little brain penetration and no characteristic centrally mediated CB1 receptor-mediated effects (analgesia, hypothermia or hypolocomotion).

CONCLUSIONS AND IMPLICATIONS

AM841, a novel peripherally restricted covalent CB1 receptor ligand that was shown to be remarkably potent, represents a new class of potential therapeutic agents for the treatment of functional GI disorders.

Genetic Manipulation of the Endocannabinoid System

The physiological and pathophysiological functions of the endocannabinoid system have been studied extensively using transgenic and targeted knockout mouse models. The first gene deletions of the cannabinoid CB(1) receptor were described in the late 1990s, soon followed by CB(2) and FAAH mutations in early 2000. These mouse models helped to elucidate the fundamental role of endocannabinoids as retrograde transmitters in the CNS and in the discovery of many unexpected endocannabinoid functions, for example, in the skin, bone and liver. We now have knockout mouse models for almost every receptor and enzyme of the endocannabinoid system. Conditional mutant mice were mostly developed for the CB(1) receptor, which is widely expressed on many different neurons, astrocytes and microglia, as well as on many cells outside the CNS. These mouse strains include "floxed" CB(1) alleles and mice with a conditional re-expression of CB(1). The availability of these mice made it possible to decipher the function of CB(1) in specific neuronal circuits and cell populations or to discriminate between central and peripheral effects. Many of the genetic mouse models were also used in combination with viral expression systems. The purpose of this review is to provide a comprehensive overview of the existing genetic models and to summarize some of the most important discoveries that were made with these animals.