Mechanisms of Diesel-Induced Endothelial Nitric Oxide Synthase Dysfunction in Coronary Arterioles

Abstract

Background and objectiveIncreased air pollutants correlate with increased incidence of cardiovascular disease potentially due to vascular dysfunction. We have reported that acute diesel engine exhaust (DE) exposure enhances vasoconstriction and diminishes acetylcholine (ACh)-induced dilation in coronary arteries in a nitric oxide synthase (NOS)-dependent manner. We hypothesize that acute DE inhalation leads to endothelial dysfunction by uncoupling NOS.MethodsRats inhaled fresh DE (300 μg particulate matter/m3) or filtered air for 5 hr. After off-gassing, intraseptal coronary arteries were isolated and dilation to ACh recorded using videomicroscopy.ResultsArteries from DE-exposed animals dilated less to ACh than arteries from air-exposed animals. NOS inhibition did not affect ACh dilation in control arteries but increased dilation in the DE group, suggesting NOS does not normally contribute to ACh-induced dilation in coronary arteries but does contribute to endothelial dysfunction after DE inhalation. Cyclooxygenase (COX) inhibition did not affect ACh dilation in the DE group, but combined inhibition of NOS and COX diminished dilation in both groups and eliminated intergroup differences, suggesting that the two pathways interact. Superoxide scavenging increased ACh dilation in DE arteries, eliminating differences between groups. Tetrahydrobiopterin (BH4) supplementation with sepiapterin restored ACh-mediated dilation in the DE group in a NOS-dependent manner. Superoxide generation (dihydroethidium staining) was greater in DE arteries, and superoxide scavenging, BH4 supplementation, or NOS inhibition reduced the signal in DE but not air arteries.ConclusionAcute DE exposure appears to uncouple NOS, increasing reactive oxygen species generation and causing endothelial dysfunction, potentially because of depletion of BH4 limiting its bioavailability.

Vascular Oxidative Stress Induced by Diesel Exhaust Microparticles

“…33 This mechanism of endothelial nitric oxide synthase uncoupling was already investigated in previous studies. 34,35 The plasma DEP concentration reached after the in vivo exposures is nevertheless unknown. It might be lower than those used in our in vitro experiments; indeed, in our normotensive group, the muscarinic relaxations of the aortas were not impaired after in vivo exposures.…”

NFAT is required for spontaneous pulmonary hypertension in superoxide dismutase 1 knockout mice

“…Lung cryostat sections were stained with the superoxide-sensitive fluorescent dye dihydroethidium (DHE) as previously described (20,95,104). Specific DHE fluorescence intensity was analyzed in the arterial wall using Image J software.…”

The Effect of High Salt Intake on Endothelial Function: Reduced Vascular Nitric Oxide in the Absence of Hypertension

“…Elevated steady-state O 2 - levels in these vessels, as well as the ability of agonists to further increase these levels, is prevented by NOS inhibition with an L -arginine analog [23]. Reduced availability of tetrahydrobiopterin (BH 4 ), an essential cofactor for eNOS, is one of the primary causes of NOS uncoupling [35,36], and this has been documented at the level of the arterioles in various pathological settings [37,38,39]. In a follow-up study on mouse spinotrapezius muscle, arteriolar wall BH 4 levels were found to be almost 50% lower in animals with high salt intake than in those fed a normal diet [24].…”