Abstract
Purpose :
Cannabinoid (CB) receptors are G-coupled protein receptors, and two CB receptors have been identified so far, CB1 and CB2. There is abundant data suggesting that epoxyeicosatrienoic ethanolamides (EET-EAs) and epoxydocosahexaenoic ethanolamides (EDP-EAs), which are derived from ω-6 and -3 fatty acids, respectively, may inhibit retinal inflammation through CB2 activation. In this study, we aim to provide a comprehensive in-silico comparison of the regioisomers of EET-EA and EDP-EA on their affinities to CB1 and CB2.
Methods :
CB1 (PDB:5TGZ) and CB2 (PDB:5ZTY) have been used for molecular docking of 5,6-, 8,9-, 11,12-, and 14,15-EET-EA as well as 4,5-, 7,8-, 10,11-, 13,14-, 16,17-, and 19,20-EDP-EA. Additionally, arachidonoyl ethanolamide (AEA), docosahexaenoyl ethanolamide (DHA-EA), CB1-selective AM-6538 (PubChem CID: 46912833), and CB2-selective AM-10257 (PubChem CID: 137321161) have also been investigated. Docking was carried out with AutoDock Vina (Scripps Research, USA) and scored by their binding free energy, ΔG in kcal/mol. Their protein-ligand interactions were visualized with PyMOL (Schrödinger, Inc., USA).
Results :
AM-6538 and AM-10257 displayed CB1- and CB2-selectivity, respectively, and their predicted binding modes were consistent with their crystallographies in the literature. AEA and DHA-EA displayed preference for CB2 over CB1, and their metabolites, EET-EA and EDP-EA, shared a similar pattern but showed more CB2-selectivity. This is consistent with the literature in that the epoxygenation step of AEA and DHA-EA serves as a “bioactivation” event, since the products exhibit enhanced selectivity for CB2. Among EET-EAs, 11,12-EET-EA had the highest affinity to CB2 (ΔG of -8.3 kcal/mol). Among EDP-EAs, 19,20-EDP-EA had the highest affinity to CB2 (ΔG of -9.0 kcal/mol). The PyMOL visualization predicted that the intracellular region of CB receptors most likely contains the binding site, where phenylalanine at position 183 in CB2 associates with hydrophobic tails of EET-EA and EDP-EA.
Conclusions :
The results predict that EET-EA and EDP-EA bind to the intracellular region of cannabinoid receptors and are more CB2-selective than their parent compounds, AEA and DHA-EA. Considering the rising interest in CB2 agonism to inhibit retinal inflammation, these epoxygenated fatty acids, specifically 11,12-EET-EA and 19,20-EDP-EA, can be potentially useful in inhibiting inflammation in DR.
This is a 2021 ARVO Annual Meeting abstract.