“It is now clear that, in contrast to traditional descriptions of G protein-coupled receptor signaling, agonists can activate or inhibit characteristic patterns of downstream effector pathways depending on their structures and the conformational changes induced in the receptor. This is referred to as functional selectivity (also known as agonist-directed trafficking, ligand-induced differential signaling, or biased agonism). It is important because even small structural differences can result in significant variations in overall agonist effects (wanted and unwanted) depending on which postreceptor signaling systems are engaged by each agonist/receptor pairing. In addition to the canonical signaling pathways mediated by Gi/o proteins, CB1 and CB2 receptor agonists can have effects via differential activation not only of Gi subtypes but also of Gs and Gq/11 proteins. For example, the classical cannabinoid HU-210 produces maximal activation of both Gi and Go proteins, while the endocannabinoid anandamide and aminoalkylindole WIN 55,212 both produce maximal activation of Gi, but submaximal activation of Go. Cannabinoid agonists can also signal differentially via β-arrestins coupled to mitogen-activated protein kinases, subsequently promoting varying degrees of receptor internalization and agonist desensitization. A recent extensive characterization of the molecular pharmacology of CB2 agonists (Soethoudt et al., 2017) identified marked differences (bias) in the ability of certain agonists to activate distinct signaling pathways (cAMP accumulation, ERK phosphorylation, GIRK activation, GTPγS binding, and β-arrestin recruitment) and to cause off-target effects, exemplifying the need to evaluate functional selectivity in agonist drug development.” https://www.ncbi.nlm.nih.gov/pubmed/28826535 http://www.sciencedirect.com/science/article/pii/S1054358917300285?via%3Dihub]]>
Tag Archives: antagonists
CB1 and CB2 Receptor Pharmacology.
“The CB1 and CB2 cannabinoid receptors (CB1R, CB2R) are members of the G protein-coupled receptor (GPCR) family that were identified over 20 years ago. CB1Rs and CB2Rs mediate the effects of Δ9-tetrahydrocannabinol (Δ9-THC), the principal psychoactive constituent of marijuana, and subsequently identified endogenous cannabinoids (endocannabinoids) anandamide and 2-arachidonoyl glycerol. CB1Rs and CB2Rs have both similarities and differences in their pharmacology. Both receptors recognize multiple classes of agonist and antagonist compounds and produce an array of distinct downstream effects. Natural polymorphisms and alternative splice variants may also contribute to their pharmacological diversity. As our knowledge of the distinct differences grows, we may be able to target select receptor conformations and their corresponding pharmacological responses. This chapter will discuss their pharmacological characterization, distribution, phylogeny, and signaling pathways. In addition, the effects of extended agonist exposure and how that affects signaling and expression patterns of the receptors are considered.” https://www.ncbi.nlm.nih.gov/pubmed/28826534 http://www.sciencedirect.com/science/article/pii/S1054358917300340?via%3Dihub]]>
Antidote to cannabinoid intoxication: Inverse cannabinoid receptor one (CB1) agonism by N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidse (AM251) reverses the hypothermic effects of cannabinoid receptor one agonism by 1-Naphthalenyl [4-(pentyloxy)-1-naphthalenyl] methanone (CB13) in mice.
“Cannabis is a recreational drug leading to intoxication, due to cannabinoid receptor one (CB1 ) stimulation. The aim of the study was to determine whether CB1 antagonism could reverse physical cannabimimetic effects. In this study, the pre-existing, central nervous system-related cannabimimetic effects, measured via the hypothermic effect, induced by CB1 receptor agonism where therapeutically treated and were rapidly reversed by CB1 receptor antagonism/inverse agonism. There was also a subjective reversal of visually-evident sedation.
CONCLUSIONS & IMPLICATIONS:
Cannabinoid receptor antagonists have been used in thousands of people and so may provide a single-dose antidote to cannabinoid intoxication, which may save human life,” https://www.ncbi.nlm.nih.gov/pubmed/28800377]]>Cannabinoid receptor 2-63 RR variant is independently associated with severe necroinflammation in HIV/HCV coinfected patients.
“This is the first study to analyze the impact of the rs35761398 variant of the CNR2 gene leading to the substitution of GLN (Q) of codon 63 of the cannabinoid receptor 2 (CB2) with ARG (R) on the clinical presentation of chronic hepatitis in HIV/HCV coinfected patients.
This study shows interesting interplay between the CB2-RR variant and liver necroinflammation in chronic hepatitis patients with HIV/HCV coinfection, an observation of clinical value that coincides with the interest in the use of the CB2 agonists and antagonists in clinical practice emerging from the literature.”
CB₁ receptor antagonism in the bed nucleus of the stria terminalis interferes with affective opioid withdrawal in rats.
“The bed nucleus of the stria terminalis (BNST) is a region of the extended amygdala that is implicated in addiction, anxiety, and stress related behaviors. This region has been identified in mediating the aversive state of naloxone-precipitated morphine withdrawal (MWD) and cannabinoid Type I (CB1) receptors have been found to modulate neurotransmission within this region. Previous findings suggest that the CB1 antagonist/inverse agonist, AM251, administered systemically or by infusion into the central nucleus of the amygdala (CeA) prevented the aversive affective properties of MWD as measured by conditioned place aversion learning. The current findings emphasize an important role for the BNST in opioid withdrawal and suggest that the ameliorative effects of systemically administered CB1 antagonists are mediated, in part, by their actions within this region.” https://www.ncbi.nlm.nih.gov/pubmed/28714716]]>
The cannabinoid ligand LH-21 reduces anxiety and improves glucose handling in diet-induced obese pre-diabetic mice.
“LH-21 is a triazol derivative that has been described as a low-permeant neutral CB1 antagonist, though its pharmacology is still unclear. It has been associated with anti-obesity actions in obese rats. However, its role in preventing type 2 diabetes (T2D) onset have not been studied yet. Given CB1 receptors remain as potential pharmacological targets to fight against obesity and T2D, we wanted to explore the metabolic impact of this compound in an animal model of obesity and pre-diabetes as well as the lack of relevant actions in related central processes such as anxiety. These results suggest that LH-21 can be a new candidate to fight against diabetes onset. Indeed, this compound shows potential in counteracting obesity-related anxiety.” https://www.ncbi.nlm.nih.gov/pubmed/28638091 https://www.nature.com/articles/s41598-017-03292-w