The Role of Endocannabinoids in Atherosclerosis

Cardiovascular disease leads in morbidity and mortality in Western societies with no known cure. NADPH oxidase (Nox) contributes to atherosclerosis through the indirect activation of macrophages leading to the internalization of oxidized low density lipoproteins (oxLDL). Chronic inflammation in activated macrophages contributes to atherosclerosis. Because macrophages are positioned at the cross-roads of lipid metabolism in vessel walls, they are important in the cellular pathology of atherosclerosis. Components of the endocannabinoid (eCB) system are vital to atherosclerotic development, since the eCB system has been found to play an important role in the amelioration of atherosclerosis. The eCB system has several components, including the G-protein-coupled cannabinoid receptors (CB1 and CB2); their endogenous ligands, 2-arachidonoylglycerol (2-AG) and anandamide (AEA); and biosynthetic enzymes that produce and degrading these compounds. CB2 signaling has been shown to upregulate immunoprotective and anti-oxidative pathways, whereas CB1 signaling has opposite effects. We hypothesized a mechanistic link between scavenger receptor activation and Nox activity, which leads to enhanced 2-AG biosynthesis via a signaling pathway that activates diacylglycerol lipase beta (DAGLB). Activation of CB2-mediated signaling by enhanced “eCB tone” can potentially reduce oxidative stress in macrophages. The released 2-AG is subsequently catabolized hydrolytic enzymes, leading to enhanced 2-AGbiosynthesis via activated DAGLB. We first proved that macrophage treated with oxLDL can activate Nox and increase reactive oxygen species production. We used human and mouse macrophages to demonstrate cause and effect. Secondly, we demonstrated that increased levels of superoxide causes enhanced 2-AG biosynthesis within the macrophage, and that upregulation in eCB production is an adaptive response to oxidative stress. Finally, we identified and quantified the serine hydrolases found in smooth muscle cells (SMCs) using an activity-based protein profiling (ABPP)-MudPIT approach that our laboratory has previously done using human macrophages. Additionally, the catabolism of 2-AG by primary SMCs was explored to demonstrate SMCs can hydrolyze 2-AG to its metabolites arachidonic acid and glycerol by the known hydrolytic enzymes. We demonstrated that enhancing endocannabinoid tone within the vessel wall is a valuable strategy to reduce the occurrence of inflammation that leads to atherosclerosis