Endogenous Cannabinoid-Like Arachidonoyl Serine Protects Against LPS-Induced Endothelial Apoptosis.

The endocannabinoid system is involved in several physiological processes, and has been reported to have neuroprotective and vasoprotective effects. N-Arachidonoyl Serine (ARA-S), a recently identified endocannabinoid, possesses vasodilatory properties and shows protective effects on the endothelium. ARA-S does not bind to the CB1, CB2, or vanilloid TRPV1 receptors, and most likely binds to an endothelial-specific cannabinoid receptor. This receptor has not yet been identified. We previously found that ARA-S can enhance endothelial wound healing in vitro. Now, we demonstrate that ARA-S can protect endothelial cells from lipopolysaccharide (LPS)-mediated apoptosis, a pathological process which commonly occurs during infection and inflammation. Human primary dermal microvascular endothelial cells (HMVEC) expressing both CB1 and CB2 receptors were used in our functional and biochemical assays. Upon pretreatment of HMVEC with ARA-S (1 μM), LPS-induced apoptosis was significantly diminished by 25–30% compared to treatment with the vehicle control, as shown by in situ TUNEL staining and Annexin V/Propidium Iodide (PI) co-staining assays in live cells. This ARA-S-mediated protection was dose-dependent and could be partially blocked by specific CB1 and CB2 antagonists (AM251 and AM630), either individually or in combination. Other receptors besides CB1 and CB2 appeared to be involved in this process, since O-1918, a blocker of the putative third cannabinoid receptor, also inhibited the activity of ARA-S by 80%. To decipher how ARA-S changes the fate of these cells, we compared LPS-induced signaling cascades in HMVEC in the presence or absence of ARA-S. ARA-S activated both Akt and eNOS in the LPS-treated HMVEC, two important molecules for endothelial survival. In contrast, ARA-S inhibited the activities of Caspase 9 and Cytochrome C, which were induced by LPS and cause cell apoptosis. Our findings support a role for novel endocannabinoids like ARA-S that may interact with putative cannabinoid receptors in protecting the cardiovascular system from toxic stimuli like LPS.