Effect of inhaled carbon ultrafine particles on reactive hyperemia in healthy human subjects.

BACKGROUND: Ultrafine particles (UFP) may contribute to the cardiovascular effects of exposure to particulate air pollution, partly because of their relatively efficient alveolar deposition and potential to enter the pulmonary vascular space. OBJECTIVES: This study tested the hypothesis that inhalation of elemental carbon UFP alters systemic vascular function. METHODS: Sixteen healthy subjects (mean age, 26.9 +/- 6.5 years) inhaled air or 50 microg/m3 elemental carbon UFP by mouthpiece for 2 hr, while exercising intermittently. Measurements at preexposure baseline, 0 hr (immediately after exposure), 3.5 hr, 21 hr, and 45 hr included vital signs, venous occlusion plethysmography and reactive hyperemia of the forearm, and venous plasma nitrate and nitrite levels. RESULTS: Peak forearm blood flow after ischemia increased 3.5 hr after exposure to air but not UFP (change from preexposure baseline, air: 9.31 +/- 3.41; UFP: 1.09 +/- 2.55 mL/min/100 mL; t-test, p = 0.03). Blood pressure did not change, so minimal resistance after ischemia (mean blood pressure divided by forearm blood flow) decreased with air, but not UFP [change from preexposure baseline, air: -0.48 +/- 0.21; UFP: 0.07 +/- 0.19 mmHg/mL/min; analysis of variance (ANOVA), p = 0.024]. There was no UFP effect on pre-ischemia forearm blood flow or resistance, or on total forearm blood flow after ischemia. Venous nitrate levels were significantly lower after exposure to carbon UFP compared with air (ANOVA, p = 0.038). There were no differences in venous nitrite levels. CONCLUSIONS: Inhalation of 50 microg/m3 carbon UFP during intermittent exercise impairs peak forearm blood flow during reactive hyperemia in healthy human subjects.

Smokers have reduced nitric oxide production by conducting airways but normal levels in the alveoli.

Air exhaled by cigarette smokers contains reduced amounts of nitric oxide (NO). Measurement of NO at different expiratory flow rates permits calculation of NO production by the conducting airways (Vaw(NO)) and alveolar concentration of NO (P(ALV)). An independent measurement of diffusing capacity of the alveolar compartment (D(LNO)) multiplied by P(ALV) allows calculation of NO production by the alveoli (V(LNO)). Twelve asymptomatic cigarette smokers and 22 age-matched nonsmokers had measurements of D(LNO) and expired NO at constant expiratory flow rates varying from 60 to 1500 ml/s. Vaw(NO) in smokers was only 22 +/- 11 nl/min (mean +/- standard deviation, SD) compared to 70 +/- 37 nl/min in nonsmokers (p < .0001). In contrast, V(LNO) showed no significant difference (smokers: 203 +/- 104 nl/min, nonsmokers: 209 +/- 74 nl/min, p = .86). These data show that the diminished NO expired by smokers results from diminished NO production by the tissues of the conducting airways but normal values produced by the alveoli.

Inhalation of ultrafine particles alters blood leukocyte expression of adhesion molecules in humans.

Ultrafine particles (UFPs; aerodynamic diameter < 100 nm) may contribute to the respiratory and cardiovascular morbidity and mortality associated with particulate air pollution. We tested the hypothesis that inhalation of carbon UFPs has vascular effects in healthy and asthmatic subjects, detectable as alterations in blood leukocyte expression of adhesion molecules. Healthy subjects inhaled filtered air and freshly generated elemental carbon particles (count median diameter approximately 25nm, geometric standard deviation approximately 1.6), for 2 hr, in three separate protocols: 10 microg/m3 at rest, 10 and 25 microg/m3 with exercise, and 50 microg/m3 with exercise. In a fourth protocol, subjects with asthma inhaled air and 10 microg/m3 UFPs with exercise. Peripheral venous blood was obtained before and at intervals after exposure, and leukocyte expression of surface markers was quantitated using multiparameter flow cytometry. In healthy subjects, particle exposure with exercise reduced expression of adhesion molecules CD54 and CD18 on monocytes and CD18 and CD49d on granulocytes. There were also concentration-related reductions in blood monocytes, basophils, and eosinophils and increased lymphocyte expression of the activation marker CD25. In subjects with asthma, exposure with exercise to 10 microg/m3 UFPs reduced expression of CD11b on monocytes and eosinophils and CD54 on granulocytes. Particle exposure also reduced the percentage of CD4+ T cells, basophils, and eosinophils. Inhalation of elemental carbon UFPs alters peripheral blood leukocyte distribution and expression of adhesion molecules, in a pattern consistent with increased retention of leukocytes in the pulmonary vascular bed.

Comparing inhaled ultrafine versus fine zinc oxide particles in healthy adults: a human inhalation study.

RATIONALE: Zinc oxide is a common, biologically active constituent of particulate air pollution as well as a workplace toxin. Ultrafine particles (< 0.1 microm diameter) are believed to be more potent than an equal mass of inhaled accumulation mode particles (0.1-1.0 microm diameter). OBJECTIVES: We compared exposure-response relationships for respiratory, hematologic, and cardiovascular endpoints between ultrafine and accumulation mode zinc oxide particles. METHODS: In a human inhalation study, 12 healthy adults inhaled 500 microg/m3 of ultrafine zinc oxide, the same mass of fine zinc oxide, and filtered air while at rest for 2 hours. MEASUREMENTS AND MAIN RESULTS: Preexposure and follow-up studies of symptoms, leukocyte surface markers, hemostasis, and cardiac electrophysiology were conducted to 24 hours post-exposure. Induced sputum was sampled 24 hours after exposure. No differences were detected between any of the three exposure conditions at this level of exposure. CONCLUSIONS: Freshly generated zinc oxide in the fine or ultrafine fractions inhaled by healthy subjects at rest at a concentration of 500 microg/m3 for 2 hours is below the threshold for acute systemic effects as detected by these endpoints.

Pulmonary function, diffusing capacity, and inflammation in healthy and asthmatic subjects exposed to ultrafine particles.

Particulate air pollution is associated with asthma exacerbations and increased morbidity and mortality from respiratory causes. Ultrafine particles (particles less than 0.1 microm in diameter) may contribute to these adverse effects because they have a higher predicted pulmonary deposition, greater potential to induce pulmonary inflammation, larger surface area, and enhanced oxidant capacity when compared with larger particles on a mass basis. We hypothesized that ultrafine particle exposure would induce airway inflammation in susceptible humans. This hypothesis was tested in a series of randomized, double-blind studies by exposing healthy subjects and mild asthmatic subjects to carbon ultrafine particles versus filtered air. Both exposures were delivered via a mouthpiece system during rest and moderate exercise. Healthy subjects were exposed to particle concentrations of 10, 25, and 50 microg/m(3), while asthmatics were exposed to 10 microg/m(3). Lung function and airway inflammation were assessed by symptom scores, pulmonary function tests, and airway nitric oxide parameters. Airway inflammatory cells were measured via induced sputum analysis in several of the protocols. There were no differences in any of these measurements in normal or asthmatic subjects when exposed to ultrafine particles at concentrations of 10 or 25 microg/m(3). However, exposing 16 normal subjects to the higher concentration of 50 microg/m(3) caused a reduction in maximal midexpiratory flow rate (-4.34 +/- 1.78% [ultrafine particles] vs. +1.08 +/- 1.86% [air], p =.042) and carbon monoxide diffusing capacity (-1.76 +/- 0.66 ml/min/mm Hg [ultrafine particles] vs. -0.18 +/- 0.41 ml/min/mm Hg [air], p =.040) at 21 h after exposure. There were no consistent differences in symptoms, induced sputum, or exhaled nitric oxide parameters in any of these studies. These results suggest that exposure to carbon ultrafine particles results in mild small-airways dysfunction together with impaired alveolar gas exchange in normal subjects. These effects do not appear related to airway inflammation. Additional studies are required to confirm these findings in normal subjects, compare them with additional susceptible patient populations, and determine their pathophysiologic mechanisms.

Effects of exposure to ultrafine carbon particles in healthy subjects and subjects with asthma.

Increased levels of particulate air pollution are associated with increased respiratory and cardiovascular mortality and morbidity as well as worsening of asthma. Ultrafine particles (UFP; less than 0.1 microm in aerodynamic diameter) may contribute to the health effects of particulate matter (PM) for a number of reasons. Compared with larger particles on a mass basis, UFP have a higher predicted pulmonary deposition, greater potential to induce pulmonary inflammation, larger surface area, and enhanced oxidant capacity. UFP also have the potential to cross the epithelium and enter the systemic circulation. We hypothesized that exposure to UFP causes airway inflammation in susceptible humans with activation of circulating leukocytes and vascular endothelium, a systemic acute phase response, and transient hypercoagulability. We further hypothesized that in people with asthma, UFP deposition would be increased and underlying airway inflammation enhanced. Our objectives were: to develop a system for controlled exposures of humans to UFP; to measure the pulmonary fractional deposition of UFP; to assess the effects of UFP exposure on blood leukocyte and endothelial adhesion molecule expression and activation, on airway nitric oxide (NO) production, on the systemic acute phase response, on blood coagulability, and on cardiac electrical activity and repolarization; and to evaluate these responses in both healthy subjects and people with asthma. We developed and validated a mouthpiece exposure system for human studies of carbon UFP and then conducted three clinical exposure studies: healthy subjects breathing filtered air and UFP (10 microg/m3) at rest (UPREST); healthy subjects breathing air and UFP (10 and 25 microg/m3) with intermittent exercise (UPDOSE); and subjects with mild asthma breathing air and UFP (10 microg/m3) with intermittent exercise (UPASTHMA). All exposures were for 2 hours on the mouthpiece system. Exposures were separated by at least 2 (UPREST and UPDOSE) or 3 (UPASTHMA) weeks. Prior to and at intervals after each exposure, we assessed symptoms, pulmonary function, blood markers of inflammation and coagulation, and airway NO production. Sputum inflammatory cells were assessed 21 hours after exposure. Continuous 12-lead electrocardiography (ECG) recordings were analyzed for changes in heart rate variability, repolarization, and arrhythmias. For healthy subjects, the fractional deposition of UFP at rest was 0.66 +/- 0.11 (mean +/- SD) by particle number, confirming the high deposition for UFP predicted by models. Deposition further increased during exercise (0.83 +/- 0.04). Asthmatic subjects showed higher UFP deposition than did healthy subjects when breathing at rest (0.76 +/- 0.05). During the UPREST protocol, there were no convincing effects for any outcome measures. Breathing 25 microg/m3 UFP with exercise (UPDOSE) was associated with reductions in blood monocytes and activation of T lymphocytes in healthy females. In asthmatic subjects (UPASTHMA), breathing 10 microg/m3 UFP was associated with reduced numbers of blood eosinophils and CD4+ T lymphocytes. In the UPDOSE group, monocyte expression of intercellular adhesion molecule-1 (ICAM-1) was reduced in a concentration-related manner (P = 0.001). In the UPASTHMA group, CD11b expression was reduced on monocytes and eosinophils, and ICAM-1 expression was reduced on polymorphonuclear leukocytes (PMNs). ECG analyses of UPDOSE subjects showed transient reductions in parasympathetic influence on heart rate variability and a reduced repolarization (QT) interval. In UPASTHMA subjects, ECG analyses showed decreased QT variability, but no effect on the QT interval. There were no significant effects in any of the studies on symptoms, pulmonary function, or markers of airway inflammation. We found no increases in soluble markers of systemic inflammation or coagulation. Our hypothesis that inhalation of carbon UFP causes pulmonary inflammation and an acute phase response was not confirmed. However, the observed subtle changes in leukocyte subsets and adhesion molecule expression are consistent with effects on vascular endothelial function. We also found effects on heart rate variability and on cardiac repolarization in healthy subjects. If confirmed, the finding that very low mass concentrations of particles have cardiovascular effects would have important implications for future PM regulatory strategies.

Nitrogen dioxide exposure: effects on airway and blood cells.

This study examined the effects of nitrogen dioxide (NO(2)) exposure on airway inflammation, blood cells, and antiviral respiratory defense. Twenty-one healthy volunteers were exposed on separate occasions to air and 0.6 and 1.5 ppm NO(2) for 3 h with intermittent moderate exercise. Phlebotomy and bronchoscopy were performed 3.5 h after each exposure, and recovered cells were challenged with respiratory viruses in vitro. Blood studies revealed a 4.1% NO(2) dose-related decrease in hematocrit (P = 0.003). Circulating total lymphocytes (P = 0.024) and T lymphocytes (P = 0.049) decreased with NO(2) exposure. Exposure to NO(2) increased the blood lymphocyte CD4(+)-to-CD8(+) ratio from 1.74 +/- 0.11 to 1.85 +/- 0.12 in males but decreased it from 1.88 +/- 0.19 to 1.78 +/- 0.19 in females (P < 0.001 for gender difference). Polymorphonuclear leukocytes in bronchial lavage increased with NO(2) exposure (P = 0.003). Bronchial epithelial cells obtained after exposure to 1.5 ppm NO(2) released 40% more lactate dehydrogenase after challenge with respiratory syncytial virus than with air exposure (P = 0.024). In healthy subjects, exposures to NO(2) at levels found indoors cause mild airway inflammation, effects on blood cells, and increased susceptibility of airway epithelial cells to injury from respiratory viruses.