Background: The endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG) is a known modulator of inflammation and ligand to both, pro-inflammatory cannabinoid receptor 1 (CB1) and anti-inflammatory CB2. While both receptors have been studied extensively, the role of 2-AG in atherogenesis and endothelial repair is less well characterised.

Methods: The impact of 2-AG on atherogenesis was studied in two treatment groups of ApoE−/− mice. One group received the monoacylglycerol lipase (MAGL)-inhibitor JZL184 [5 mg/kg i.p.], which impairs 2-AG degradation and thus causes elevated 2-AG levels, the other group received vehicle for four weeks. Simultaneously, both groups were fed a high-cholesterol diet. The atherosclerotic plaque burden was assessed in frozen sections through the aortic sinus following oil red O staining and infiltrating macrophages were detected by immunofluorescence targeting CD68. In vitro, the effect of 2-AG on B6-MCL macrophage migration was assessed by Boyden chamber experiments. Finally, endothelial repair was studied in wildtype mice receiving either JZL184 [5 mg/kg i.p.] or vehicle following electrical denudation of the common carotid artery.

Results: As expected, application of the MAGL-inhibitor JZL184 resulted in a significant increase in 2-AG levels in vascular tissue (98.2±16.1 nmol/g vs. 27.3±4.5 nmol/g; n=14–16; p<0.001). ApoE−/− mice treated with JZL184 displayed a significantly increased plaque burden compared to vehicle treated controls (0.46±0.03 vs. 0.36±0.03; n=11–12; p<0.05). This was accompanied by a significant increase in infiltrating macrophages within the atherosclerotic vessel wall (0.32±0.02 vs. 0.26±0.01; n=11; p<0.05). Consistently, 2-AG enhanced macrophage migration in vitro by 1.7±0.2 -fold (n=4; p<0.05) compared to vehicle, which was completely abolished by co-administration of the CB1-receptor-antagonist AM281. Finally, elevated 2-AG levels significantly impaired reendothelialisation in wildtype mice following electrical injury of the common carotid artery, resulting in a residual denudation at 5 days of 2291±286 μm vs. 1505±223 μm (n=18–19; p<0.05).

Conclusion: Taken together, elevated 2-AG levels appear to hamper endothelial repair and to promote atherogenesis in vivo. Our data suggest that 2-AG promotes macrophage migration via a CB1-dpendent pathway and thereby potentially contributes to vascular inflammation. Thus, decreasing vascular 2-AG levels might represent a promising therapeutic strategy in patients suffering from atherosclerosis and coronary heart disease.