Protocols and Good Operating Practices in the Study of Cannabinoid Receptors.

With the approach of the 30th year since the pioneering discovery of a cannabinoid receptor in rat brain (Devane et al., 1988), the field of cannabinoid pharmacology and physiology has impacted human physiology at multiple levels. The development of highly specific and potent orthosteric ligands, as well as the blossoming field of allosteric ligand development, has placed the endocannabinoid system in the forefront as a modulator of a multitude of physiologic processes. Reproducibility among laboratories is especially important due to the development of novel tools to investigate the role(s) of the endocannabinoid system in human physiology, and to clarify the roles for medicinal marijuana. Any definitive role in normal, or diseased states, must be satisfied through the demonstration of a specific receptor-mediated event. This chapter provides working protocols for the study of cannabinoid receptor-ligand binding, as well as immediate and downstream G protein-dependent signaling assays to assess receptor function.

Structural analysis of the human cannabinoid receptor one carboxyl-terminus identifies two amphipathic helices.

Recent research has implicated the C-terminus of G-protein coupled receptors in key events such as receptor activation and subsequent intracellular sorting, yet obtaining structural information of the entire C-tail has proven a formidable task. Here, a peptide corresponding to the full-length C-tail of the human CB1 receptor (residues 400-472) was expressed in E.coli and purified in a soluble form. Circular dichroism (CD) spectroscopy revealed that the peptide adopts an alpha-helical conformation in negatively charged and zwitterionic detergents (48-51% and 36-38%, respectively), whereas it exhibited the CD signature of unordered structure at low concentration in aqueous solution. Interestingly, 27% helicity was displayed at high peptide concentration suggesting that self-association induces helix formation in the absence of a membrane mimetic. NMR spectroscopy of the doubly labeled ((15)N- and (13)C-) C-terminus in dodecylphosphocholine (DPC) identified two amphipathic alpha-helical domains. The first domain, S401-F412, corresponds to the helix 8 common to G protein-coupled receptors while the second domain, A440-M461, is a newly identified structural motif in the distal region of the carboxyl-terminus of the receptor. Molecular modeling of the C-tail in DPC indicates that both helices lie parallel to the plane of the membrane with their hydrophobic and hydrophilic faces poised for critical interactions.

The search for the palmitoylethanolamide receptor.

Palmitoylethanolamide (PEA), the naturally occurring amide of ethanolamine and palmitic acid, is an endogenous lipid that modulates pain and inflammation. Although the anti-inflammatory effects of PEA were first characterized nearly 50 years ago, the identity of the receptor mediating these actions has long remained elusive. We recently identified the ligand-activated transcription factor, peroxisome proliferator-activated receptor-alpha (PPAR-alpha), as the receptor mediating the anti-inflammatory actions of this lipid amide. Here we outline the history of PEA, starting with its initial discovery in the 1950s, and discuss the pharmacological properties of this compound, particularly in regards to its ability to activate PPAR-alpha.