Abstract 13659: Transition in Mechanism of Flow-Mediated Dilation During Stress in Humans: Role of Ceramide
Flow-mediated dilation, (FMD; the ability of the vasculature to dilate to increased shear stress in an endothelium-dependent manner), maintains vascular homeostasis and is inversely related to future cardiovascular events. Our laboratory has discovered that risk factors for, or the presence of CAD, causes a transition in the mediator of FMD from NO to mitochondrial-derived H2O2. Ceramide, a signaling lipid product of sphingomyelinase, stimulates mitochondrial H2O2 formation and is increased in CAD. We tested the hypothesis that ceramide is critical for this transition of FMD from NO to H2O2. Small adipose arterioles (100-200µm) from patients with or without CAD were prepared for videomicroscopy. Vessels were preconstricted with endothelin-1, and changes in internal diameter to flow were recorded. In non-CAD arterioles, L-NAME inhibited FMD (17.8±13.7 of maximal dilator capacity, n=4, p<0.01, one-way ANOVA*) versus vehicle (72.2±11.3, n=3), whereas FMD was unaffected by PEG-Catalase (500 Units) (76.6±5.5, n=6). In non-CAD vessels pretreated with C2 ceramide (10µM, 15-20hrs), L-NAME no longer inhibited FMD (78.3±7.3, n=4), however dilation was blocked by catalase (19.0±7.4, n=5, p<0.01*). To determine if inhibition of ceramide production can restore NO as the main dilator of FMD in CAD, arterioles from subjects with CAD were pretreated with the specific neutral sphingomyelinase inhibitor GW4869 (4µM). Catalase inhibited FMD in CAD arterioles (5.7±38.2, n=2) compared to vehicle (81.7±3.0, n=4) but had no effect in arterioles pre-treated with GW4869 (76.6±2.7, n=3). L-NAME had minimal effect on FMD in CAD vessels (67.7±15.6, n=3), but reduced FMD in arterioles incubated with GW4869 (26.9±9.3, n=4, p<0.01*). These data suggest that exposure to ceramide is sufficient to change the mediator of FMD from NO to H2O2 in arterioles from patients without CAD. Moreover, inhibition of sphingomyelinase restores NO as the mediator of dilation to FMD in arterioles from patients with chronic CAD. We conclude that ceramide is a novel and critical mechanistic component of the dilator mechanism of FMD in the human heart with onset of disease. This may provide a novel therapeutic target for maintaining or restoring normal mechanisms of tissue perfusion.
- © 2012 by American Heart Association, Inc.