Pharmacological Actions of Cannabinoids

R.G. Pertwee

School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen,

Foresterhill, Aberdeen AB25 2ZD, UK

1 Introduction 2

2 Bioassays for Characterizing CBj and CB2 Receptor Ligands 6

2.1 In Vitro Binding Assays 6

2.2 In Vitro Functional Bioassays 9

2.2.1 Assays Using Whole Cells or Cell Membranes 9

2.2.2 Isolated Nerve-Smooth Muscle Preparations 11

2.3 In Vivo Bioassays 11

2.4 Cannabinoid Receptor Knockout Mice 12

3 CBj and CB2 Cannabinoid Receptor Ligands 13

3.1 Cannabinoid Receptor Agonists 13

3.2 Cannabinoid CBi and CB2 Receptor Antagonists 20

3.2.1 Selective CB 1 Receptor Antagonists 20

3.2.2 Selective CB2 Receptor Antagonists 22

3.3 Inverse Agonism at Cannabinoid Receptors 22

3.4 Neutral Antagonism at Cannabinoid Receptors 24

4 Other Pharmacological Targets for Cannabinoids in Mammalian Tissues ... 26

4.1 Receptors 26

4.1.1 Vanilloid Receptors 26

4.1.2 CB1 Receptor Subtypes 27

4.1.3 CB2-Like Receptors 27

4.1.4 Neuronal Non-CB1, Non-CB2, Non-TRPV1 Receptors 28

4.1.5 Receptors for Abnormal-Cannabidiol 33

4.2 Allosteric Sites 35

4.3 Some CB1- and CB2-Independent Actions of Cannabidiol, HU-211

and Other Phenol-Containing Cannabinoids 36

4.3.1 Neuroprotective Actions 36

4.3.2 Other Actions of Cannabidiol 37

5 CBj Receptor Oligomerization 38

6 Future Directions 38

References 39

Abstract Mammalian tissues express at least two types of cannabinoid receptor, CB1 and CB2, both G protein coupled. CB1 receptors are expressed predominantly at nerve terminals where they mediate inhibition of transmitter release. CB2 receptors are found mainly on immune cells, one of their roles being to modulate cytokine release. Endogenous ligands for these receptors (endocannabinoids) also exist. These are all eicosanoids; prominent examples include arachidonoylethanolamide (anandamide) and 2-arachidonoyl glycerol. These discoveries have led to the development of CBi- and CB2-selective agonists and antagonists and of bioassays for characterizing such ligands. Cannabinoid receptor antagonists include the CBi-selective SR141716A, AM251, AM281 and LY320135, and the CB2-selective SR144528 and AM630. These all behave as inverse agonists, one indication that CB1 and CB2 receptors can exist in a constitutively active state. Neutral cannabinoid receptor antagonists that seem to lack inverse agonist properties have recently also been developed. As well as acting on CB1 and CB2 receptors, there is convincing evidence that anandamide can activate transient receptor potential vanilloid type 1 (TRPV1) receptors. Certain cannabinoids also appear to have non-CB1; non-CB2, non-TRPV1 targets, for example CB2-like receptors that can mediate antinociception and "abnormal-cannabidiol" receptors that mediate vasorelaxation and promote microglial cell migration. There is evidence too for TRPV1-like receptors on glutamatergic neurons, for a2-adrenoceptor-like (imidazoline) receptors at sympathetic nerve terminals, for novel G protein-coupled receptors for £-(+)-WIN55212 and anandamide in the brain and spinal cord, for novel receptors for ^-tetrahydrocannabinol and cannabinol on perivascular sensory nerves and for novel anandamide receptors in the gastro-intestinal tract. The presence of allosteric sites for cannabinoids on various ion channels and non-cannabinoid receptors has also been proposed. In addition, more information is beginning to emerge about the pharmacological actions of the non-psychoactive plant cannabi-noid, cannabidiol. These recent advances in cannabinoid pharmacology are all discussed in this review.

Keywords Cannabinoid receptors ■ Cannabinoid receptor agonists and antagonists ■ Abnormal-cannabidiol ■ Cannabidiol ■ Inverse agonism

0 0

Post a comment