Activation of Neutral Sphingomyelinase Contributes to Nitric Oxide‐Mediated Flow‐Induced Dilation in the Human Microvasculature

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Flow induced dilation (FID) is a critical physiological mechanism to maintain tissue perfusion and modulate vascular homeostasis. Recently our laboratory has shown that sphingolipids can influence the endothelial‐derived mediator that is generated in response to flow. Exposure to elevated levels of ceramide, or, inhibition of ceramide metabolism, induces a transition in endothelial‐derived FID mediator from nitric oxide (NO) to hydrogen peroxide (H2O2), the same change in mechanism that occurs with presence of CAD. Interestingly, studies have suggested that endothelial nitric oxide synthase (eNOS) is regulated by ceramide metabolites, such as sphingosine‐1‐phosphate (S1P), suggesting that ceramide is necessary for NO formation due to shear stress. We therefore hypothesized that activation of the shear sensitive, ceramide‐producing enzyme, neutral sphingomyelinase (NSmase) is required for NO‐dependent FID. Resistance arterioles (100–200μm) were dissected from adipose tissue collected from healthy patients and were prepared for videomicroscopy. Following equilibration and preconstriction with endothelin‐1, changes in internal diameter to flow were recorded. L‐NAME (100mM) did not affect FID in healthy arterioles pre‐treated with the NSmase inhibitor, GW4869 (4mM, 16–20hrs), (69.1%±4.9 of maximal dilator capacity, n=4), however dilation was decreased in the presence of PEG‐Catalase (500 Units/ml) (15.2%±9.4, n=3). A similar effect was observed with acute inhibition (30 min) of NSmase. Vasodilation due to increased flow was maintained in the presence of L‐NAME (88.0%±3.5, n=3), however was impaired when exposed to PEG‐Catalase (−5.3%±1.3, n=3). GW4869 alone did not impair the overall magnitude of dilation due to flow (86.1%±3.9, n=2). These findings suggest that while elevated levels of ceramide promote H2O2‐dependent FID, NSmase‐derived products of ceramide are a key component of NO‐mediated signaling in the human microvasculature.Support or Funding InformationK08HL141562