anandamide and 1-2-oleoylphosphatidylcholine

Endocannabinoids are amphiphilic molecules that play crucial neurophysiological functions acting as lipid messengers. Antagonists and knockdown of the classical CB1 and CB2 cannabinoid receptors do not completely abolish many endocannabinoid activities, supporting the idea of a mechanism independent of receptors whose mode of action remains unclear. Here we combine gramicidin A (gA) single channel recordings and membrane capacitance measurements to investigate the lipid bilayer-modifying activity of endocannabinoids. Single channel recordings show that the incorporation of endocannabinoids into lipid bilayers reduces the free energy necessary for gramicidin channels to transit from the monomeric to the dimeric conformation. Membrane capacitance demonstrates that the endocannabinoid anandamide has limited effects on the overall structure of the lipid bilayers. Our results associated with the theory of membrane elastic deformation reveal that the action of endocannabinoids on membrane proteins can involve local adjustments of the lipid/protein hydrophobic interface. The current findings shed new light on the receptor-independent mode of action of endocannabinoids on membrane proteins, with important implications towards their neurobiological function.

Topics: Arachidonic Acids; Cell Membrane; Endocannabinoids; Gramicidin; Lipid Bilayers; Membrane Proteins; Phosphatidylcholines; Polyunsaturated Alkamides; Receptor, Cannabinoid, CB1; Receptor, Cannabinoid, CB2

The phospholipid bilayer plays a central role in the lifecycle of the endogenous cannabinoid N-arachidonoylethanolamine (anandamide, 1). Compound 1 has been shown to be synthesized from lipids, to interact with the membrane-embedded cannabinoid CB1 receptor, to be transported to intracellular compartments, possibly via caveolae-related endocytosis, and finally, to be degraded by fatty acid amide hydrolase (FAAH), an integral membrane protein which has an active site that is accessed by 1 possibly via the bilayer. Because the anandamide system is intimately associated with the lipid milieu, information concerning the location of 1 in the phospholipid bilayer and the conformations it can adopt is important to our understanding of the mechanism of cannabinoid action at the molecular level. We report here an exploration of the properties of 1 in a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) phospholipid bilayer via multi-nanosecond molecular dynamics simulations. Our results suggest that the polar headgroup of 1 resides at the lipid-water interface, specifically in the polar phospholipid headgroup region, whereas the nonpolar acyl chain of 1 extends into the hydrocarbon core of the membrane. Our analysis also indicates that (i) an elongated conformation of 1 is preferred in the DOPC bilayer environment; however, many other conformations of 1 are observed; (ii) hydrogen-bonding between the lipid (DOPC) and the headgroup of 1, although extensive, is quite short-lived; and (iii) the C-H bond order parameters for the acyl chain of 1 are low compared to order parameters typically seen for saturated acyl chains of fatty acids, and these order parameters decrease toward the bilayer center. The bilayer location for 1 revealed by these studies may be important for the interaction of 1 with membrane-embedded proteins such as the cannabinoid CB1 receptor and membrane-associated proteins such as FAAH.

Topics: Arachidonic Acids; Cannabinoid Receptor Modulators; Computer Simulation; Endocannabinoids; Hydrogen Bonding; Lipid Bilayers; Models, Molecular; Molecular Conformation; Phosphatidylcholines; Phospholipids; Polyunsaturated Alkamides