Céline Dreyfuss

Acute Exposure to Diesel Exhaust Impairs Nitric Oxide–Mediated Endothelial Vasomotor Function by Increasing Endothelial Oxidative Stress

Exposure to diesel exhaust was recently identified as an important cardiovascular risk factor, but whether it impairs nitric oxide (NO)–mediated endothelial function and increases production of reactive oxygen species (ROS) in endothelial cells is not known. We tested these hypotheses in a randomized, controlled, crossover study in healthy male volunteers exposed to ambient and polluted air (n=12). The effects of skin microvascular hyperemic provocative tests, including local heating and iontophoresis of acetylcholine and sodium nitroprusside, were assessed using a laser Doppler imager. Before local heating, skin was pretreated by iontophoresis of either a specific NO–synthase inhibitor (L-N-arginine-methyl-ester) or a saline solution (Control). ROS production was measured by chemiluminescence using the lucigenin technique in human umbilical vein endothelial cells preincubated with serum from 5 of the subjects. Exposure to diesel exhaust reduced acetylcholine-induced vasodilation (P<0.01) but did not affect vasodilation with sodium nitroprusside. Moreover, the acetylcholine/sodium nitroprusside vasodilation ratio decreased from 1.51±0.1 to 1.06±0.07 (P<0.01) and was correlated to inhaled particulate matter 2.5 (r=−0.55; P<0.01). NO–mediated skin thermal vasodilatation decreased from 466±264% to 29±123% (P<0.05). ROS production was increased after polluted air exposure (P<0.01) and was correlated with the total amount of inhaled particulate matter <2.5 &mgr;m (PM2.5). In healthy subjects, acute experimental exposure to diesel exhaust impaired NO–mediated endothelial vasomotor function and promoted ROS generation in endothelial cells. Increased PM2.5 inhalation enhances microvascular dysfunction and ROS production.

Nicotine increases chemoreflex sensitivity to hypoxia in non-smokers.

Background The peripheral chemoreflex contributes to cardiovascular regulation and represents the first line of defence against hypoxia. The effects of nicotine on chemoreflex regulation in non-smoking humans are unknown. Method We conducted a prospective, randomized, crossover, and placebo-controlled study in 20 male non-smokers to test the hypothesis that nicotine increases chemoreflex sensitivity. The effects of two intakes of 2 mg nicotine tabs and placebo on sympathetic nerve activity to muscle circulation (muscle sympathetic nerve activity; MSNA), minute ventilation (Ve), blood pressure and heart rate were assessed during normoxia, moderate isocapnic hypoxia, hyperoxic hypercapnia and an isometric handgrip in 10 subjects. Maximal end-expiratory apnoeas were performed at baseline and at the end of the fifth minute of hypoxia. In a second experimental setting, we studied the ventilatory response to a more marked isocapnic hypoxia in 10 other volunteers. Results Mean MSNA and Ve were not modified by nicotine during the 5 min of normoxia or moderate hypoxia. In the presence of nicotine MSNA was related to oxygen desaturation (P < 0.01). The sympathoexcitatory effects of nicotine became especially evident when apnoeas achieved oxygen saturations less than 85% (511 ± 44% increase in MSNA after the first intake, and 436 ± 43% increase after the second intake versus 387 ± 56% and 338 ± 31% with placebo, respectively, P < 0.05). Nicotine also increased the ventilatory response compared with placebo when oxygen saturation decreased to less than 85% (P < 0.05). Conclusion This is the first study to demonstrate that nicotine increases peripheral chemoreflex sensitivity to large reductions in arterial oxygen content in healthy non-smokers.

Facial cooling and peripheral chemoreflex mechanisms in humans

Aim:  Reductions in arterial oxygen partial pressure activate the peripheral chemoreceptors which increase ventilation, and, after cessation of breathing, reduce heart rate. We tested the hypothesis that facial cooling facilitates these peripheral chemoreflex mechanisms.

Vascular oxidative stress induced by diesel exhaust microparticles: synergism with hypertension.

Background: Epidemiological and clinical studies have shown that traffic-related air pollution and, particularly, diesel exhaust particles (DEP) are strongly linked to cardiovascular mortality. Methods: Vascular toxicity was studied by assessing vasomotor responses of aortas isolated from normotensive Wistar rats exposed in vitro to DEP (DEP suspension and aqueous DEP extract). In vivo experiments were performed on Wistar rats and spontaneously hypertensive rats (SHRs) exposed for 4 weeks via intratracheal instillation to either DEP or saline vehicle. After killing, vascular responses to acetylcholine (ACh) or sodium nitroprusside were assessed in vitro and the expression of p22phox, a major nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit, was studied by real-time quantitative polymerase chain reaction. Results: In aortas from Wistar rats, in vitro DEP incubation (both preparations) markedly inhibited the relaxations to ACh and slightly to sodium nitroprusside; this effect was reversed in the presence of superoxide dismutase. In contrast, in aortas from in vivo–exposed animals, ACh-induced relaxations were only significantly impaired in the SHR group, accompanied with a significant upregulation of p22phox and no change in systolic blood pressure. Conclusions: Although in vitro exposure to DEP produces a vascular oxidative stress, repeated in vivo exposures to DEP only impair vascular function in SHR, via an upregulation of p22phox. This suggests a synergistic effect on endothelial dysfunction between particulate air pollution and hypertension.

L-NAME iontophoresis: a tool to assess NO-mediated vasoreactivity during thermal hyperemic vasodilation in humans.

Background: Decreased endothelial Nitric oxide (NO) bioavailability is one of the earliest events of endothelial dysfunction. Assessment of microvascular blood flow using a Laser Doppler Imager during local noninvasive administration of L-N-Arginine-Methyl-Ester (L-NAME) by skin iontophoresis may help discriminate the relative contributions of NO and non-NO pathways during a skin thermal hyperemic test. Methods: In healthy nonsmokers, the effects of thermal vasodilation and sodium nitroprusside–mediated vasodilation were tested on skin pretreated with 0.9% saline solution, 2% L-NAME iontophoresis (n = 12), or intradermal injection of 25 nmol L-NAME (n = 10). The effects of L-NAME iontophoresis were also measured in a group of smokers (n = 10). Results: L-NAME iontophoresis and intradermal injection of L-NAME decreased the skin response to local heating to a similar degree (−41% ± 4% vs. −44% ± 6%). L-NAME iontophoresis site-to-site and day-to-day coefficients of correlation were 0.83 and 0.76, respectively (P < 0.01). The site-to-site and day-to-day coefficients of correlation of L-NAME injection were lower than those of iontophoresis at 0.66 (P < 0.05) and 0.12, respectively (P = not significant). Sodium nitroprusside–induced skin hyperemia was not affected by L-NAME administration. L-NAME iontophoresis–mediated inhibition of skin thermal hyperemia was greater in smokers than in nonsmokers (P < 0.05). Conclusions: Laser Doppler Imager assessment of skin thermal hyperemia after L-NAME iontophoresis provides a reproducible and selective bedside method of qualitatively analyzing the contribution of the NO pathway to microvascular vasomotor function.

A STUDY OF THE FEASIBILITY OF L NAME IONTOPHORESIS: EFFECTS OF L NAME CONCENTRATION AND SMOKING: PP.6.224

Introduction: Early detection of endothelial dysfunction, characterized by a reduced bioavailability of NO, is essential as it is a key phenomenon in the genesis of cardiovascular diseases. Heat-induced vasodilatation is mediated mainly by NO, as shown by L Name (L) microdialysis. L Name is a competitive inhibitor of cNOS, produced by the vascular endothelium, and is polarized negatively. The application of a microcurrent on the skin allows polarized molecules, such as sodium nitroprusside and acetylcholine, to penetrate into the dermis. Whether L Name iontophoresis is feasible, and will reduce skin blood flow measured by a laser Doppler imager (LDI) in response to heating, is not known. We also assessed whether this response is dose-dependent. Last, we compared this response between habitual smokers and non smokers. Methods: In a population of 17 healthy male smokers and 17 matched healthy male non-smokers (aged 28 years ± 5 yrs, BMI 22 ± 3 kg/m2), we conducted an iontophoresis of L Name and placebo on the two arms on Day 0. This was repeated with the same dose, and a double dose of L, on Day 4, on both arms. After iontophoresis, the sites were heated to 44°C to induce vasodilation, and scanned to measure blood flow in the microcirculation. We also determined pulse wave velocity in both groups. Smoking was forbidden 12 hours before the experiments. Results: L Name decreased equally blood flow during heating in the non smokers and smokers (p < 0.01, table 1). Both concentrations of 20 and 40 mM of L Name were equally effective. Pulse wave velocity was normal at 9 m/s, and did not differ between groups. Figure 1. No caption available. Conclusion: L Name iontophoresis is feasible and is able to inhibit vascular endothelial NOS. Higher concentrations of L Name than 20 mM do not provide further vasodilatation. NO-mediated skin blood flow vasodilatation is not altered in healthy young sportive smokers investigated after 12 hours of smoking cessation.