Aim: 

The endocannabinoids 2-arachidonoylglycerol (2-AG) and 2-arachidonyl glyceryl ether (noladin ether [NE]) are derivatives of arachidonic acid. These compounds exert most of their biological activities throught interactions with cannabinoid receptors (CB₁ and CB₂), which belong to the G-protein-coupled receptor family. However, the chemical features of 2-AG and NE suggest that some of their biological effects could be related to physical interactions with the lipidic part of the membrane. The aim of this work is to study the effect of different concentrations of 2-AG and NE on the structural and physicochemical properties of dipalmitoylphosphatidylcholine (DPPC) bilayer and on phospholipase A₂ (PLA₂) activity, which is strictly dependent on lipid bilayer features.

Methods: 

PLA₂ hydrolytic activity was triggered by 5 mM Ca²⁺ on DPPC large unilamellar vesicles (LUVs), containing the fluorescent probe Laurdan, at 38.8°C, in the presence of increasing concentrations of 2-AG and NE (molar ratio 0.013, 0.04, 0.1). Lipid hydrolysis was followed by measuring the time course of Laurdan GP (generalized polarization) changes in DPPC LUVs. Samples for X-ray diffraction studies were prepared by a freeze-thaw method.

Results: 

PLA₂ activity is characterized by a latency period [identified as lag time (t)] of slow rate followed by an abrupt increase of the hydrolytic rate. The time course of vesicle hydrolysis in DPPC LUVs showed that different concentrations of both 2-AG and NE affect PLA₂ activity. In particular we observed a faster PLA₂ lag time by decreasing endocannabinoids concentrations. These findings are discussed with the X-ray diffraction results in order to analyze possible changes of the bilayer phase structure induced by the arachidonyl derivatives.

Conclusion: 

We suggest that endocannabinoids induce the formation of membrane microenvironments with particular structural and physicochemical features affecting PLA₂ activity.