Electronic Cigarette Exposure Induces Vascular Endothelial Dysfunction with NADPH Oxidase Activation and eNOS Uncoupling

Abstract

BackgroundWe recently reported a mouse model of chronic electronic cigarette (e‐cig) exposure‐induced cardiovascular pathology, where long‐term exposure to e‐cig vape (ECV) induces cardiac abnormalities, impairment of endothelial function, and systemic hypertension. Using this model, we performed studies to delineate the underlying mechanisms of ECV‐induced vascular endothelial dysfunction (VED), which is a central trigger of cardiovascular disease.MethodsC57/BL6 male mice were exposed 2 hours/day, 5 days/week to ECV generated from e‐cig liquid containing 0, 6, or 24 mg/ml nicotine for 16 and 60 weeks. Blood pressure was measured by tail cuff and endothelial‐dependent and independent relaxation was measured on aortic segments using wire myography. Western blotting, immunofluorescence and ELISA were used to analyze the pathways involved in the mechanism of ECV‐induced VED.ResultsTime‐dependent elevation in blood pressure and systemic vascular resistance were observed, along with an impairment of acetylcholine‐induced aortic relaxation in ECV‐exposed mice, compared to air‐exposed control. Decreased intravascular nitric oxide (NO) levels and increased superoxide generation with elevated 3‐nitrotyrosine levels in the aorta of ECV‐exposed mice were observed, indicating that ECV‐induced superoxide reacts with NO to generate cytotoxic peroxynitrite. Exposure increased NADPH oxidase expression, supporting its role in ECV‐induced superoxide generation. Downregulation of endothelial nitric oxide synthase (eNOS) expression and Akt‐dependent eNOS phosphorylation occurred in the aorta of ECV‐exposed mice, indicating that exposure inhibited de novo NO synthesis. Following ECV exposure, the critical NOS cofactor tetrahydrobiopterin was decreased, with a concomitant loss of its salvage enzyme, dihydrofolate reductase. NADPH oxidase and NOS inhibitors abrogated ECV‐induced superoxide generation in the aorta of ECV exposed mice.ConclusionOur data demonstrate that ECV exposure activates NADPH oxidase and uncouples eNOS, causing a vicious cycle of superoxide generation and vascular oxidant stress that triggers VED and hypertension with predisposition to other cardiovascular disease.