Abstract 12364: Exogenous Sphingosine-1-Phosphate Restores Nitric Oxide-Mediated Flow-Induced Dilation During Acute Inhibition of Ceramide Formation

Abstract

Our previous work has shown that chronic exposure to ceramide, a sphingolipid that when elevated in plasma is an independent risk factor major adverse cardiac events, causes microvascular endothelial dysfunction in arterioles collected from healthy adult patients. This presents as a change in the mediator of flow-induced dilation (FID) from the vasoprotective nitric oxide (NO) to the pro-atherosclerotic hydrogen peroxide (H 2 O 2 ). Despite the known detrimental effects of ceramide, its metabolite sphingosine-1-phosphate (S1P) can promote NO formation. However, shear-induced ceramide formation is also necessary for maintaining NO-mediated FID, as arterioles from healthy individuals transition to H 2 O 2 -mediated FID during inhibition of the ceramide-forming enzyme neutral sphingomyelinase (NSmase). We hypothesize that the transition in mediator is due to the loss of acute S1P production, and thus addition of exogenous S1P can prevent microvascular endothelial dysfunction during inhibition of NSmase. Human arterioles (100-250μm) were dissected from otherwise discarded adipose tissue from healthy patients undergoing surgery. Videomicroscopy was used to assess vascular function in vitro . Microvessels were pre-constricted with endothelin-1, and changes in internal diameter were measured following exposure to increased levels of flow. Dilation to flow was significantly impaired in the presence of the NO-synthase inhibitor L-NAME (100μM, 30 min) when healthy human arterioles were treated acutely with S1P (1μM, 30 min) in the presence of the NSmase inhibitor, GW4869 (10μM, 30 min), compared to GW4859 alone (% maximal diameter±SEM, 5.1±8.7, n=4 vs 70.1±5.3, n=4; p=0.001, 2-way ANOVA). Whereas, the presence of PEG-catalase, an enzyme that breaks down H 2 O 2 , had no effect (85.0±4.3; n=3). These data highlight the importance of S1P in maintaining NO signaling during exposure to shear and strengthens the concept that the conversion of ceramide to S1P is critical in promoting a quiescent endothelium.