Mark J. Utell

Ultrafine Particle Deposition in Humans During Rest and Exercise

Ultrafine particles (diameter < 100 nm) may be important in the health effects of air pollution, in part because of their predicted high respiratory deposition. However, there are few measurements of ultrafine particle deposition during spontaneous breathing. The fractional deposition for the total respiratory tract of ultrafine carbon particles (count median diameter = 26 nm, geometric standard deviation = 1.6) was measured in 12 healthy subjects (6 female, 6 male) at rest (minute ventilation 9.0 ± 1.3 L/min) using a mouthpiece exposure system. The mean ± SD fractional deposition was 0.66 ± 0.11 by particle number and 0.58 ± 0.13 by particle mass concentration, similar to model predictions. The number deposition fraction increased as particle size decreased, reaching 0.80 ± 0.09 for the smallest particles (midpoint count median diameter = 8.7 nm). No gender differences were observed. In an additional 7 subjects (2 female, 5 male) alternating rest with moderate exercise (minute ventilation 38.1 ± 9.5 L/min), the deposition fraction during exercise increased to 0.83 ± 0.04 and 0.76 ± 0.06 by particle number and mass concentration, respectively, and reached 0.94 ± 0.02 for the smallest particles. Experimental deposition data exceeded model predictions during exercise. The total number of deposited particles was more than 4.5-fold higher during exercise than at rest because of the combined increase in deposition fraction and minute ventilation. Fractional deposition of ultrafine particles during mouth breathing is high in healthy subjects, and increases further with exercise.

Ultrafine particles in the urban air: to the respiratory tract--and beyond?

fine particle hypothesis stating that ambient ultrafine particles (UFP; < 0.1 μm in aerodynamic diameter) may cause adverse health effects at the first Colloquium for Particulate Air Pollution and Human Mortality and Morbidity in Irvine, California, it was met with friendly skepticism as well as out-right dismissal. Arguments were that UFP are very short-lived and disappear through heterogeneous and homogeneous aggregation within seconds or minutes and therefore are toxicologically irrelevant. These arguments did not recognize that UFP are continuously generated or that ambient UFP contribute very little, if any, mass to ambient PM10 (particles < 10 μm in aerodynamic diameter) or PM2.5 (particles < 2.5 μm in aerodynamic diameter). Indeed, the mass distribution of a typical urban aerosol among the different particle sizes may support this point (Figure 1). This attitude of skepticism has changed considerably. Research teams across the world are working now on UFP, forming multidisciplinary alliances between atmospheric scientists, engineers, epidemiologists, clinicians, and toxicologists. They investigate UFP sources, generation, physicochemical characteristics, behavior in ambient air, and potential effects and underlying mechanisms following their inhalation. Still, sound skepticism lingers, as demonstrated by the title of a presentation at the 2002 meeting of the Health Effects Institute: “Nanoparticles: Are They Real?” Obviously, there is no question that UFP are real, but it is also clear that we still do not know enough about them, despite significant progress in our understanding since 1994. Atmospheric UFP derived from gas-to-particle conversions have many sources, natural and anthropogenic, the latter being mostly derived from internal combustion processes. Diesel fuel, gasoline, and even compressed natural gas—considered to be “clean”—powered engines all emit high numbers of UFP. If these anthropogenic UFP cause significant health effects, is the conversion of dieselpowered buses to compressed natural gas—as practiced now in several cities—really a good idea? We should be more cautious about introducing technologies based on the assumption that they result in cleaner air with fewer and less toxic contaminants. The experience with methyl tert-butyl ether as a fuel additive should serve as a reminder of the potential unintended health and environmental consequences of altering fuels and resulting emissions on a large scale without an adequate understanding of toxicity. Since vehicular emissions are regulated by mass output, modern technologies for internal combustion engines favor the generation and formation of UFP because they contribute minimally to the mass output of fine particles (Figure 1). It should come as no surprise that “clean” engines are built to conform to present standards of mass output, despite emitting high numbers of UFP. A standard based on particle number would be more appropriate to reduce UFP emissions. A standard based on particle surface area—as is also proposed—may not be helpful to control UFP because fine particles comprise most of the total particle surface area (Figure 1). In recent measurements made during road-chase studies in Minnesota, UFP concentrations were as high as 1 × 107 particles/cm3 (Kittelson et al. 2001). A short distance from the highways, these high UFP concentrations are lower, but individuals in automobiles on the highways are directly exposed to the high concentrations. Moreover, these UFP are freshly generated, and if results of earlier toxicologic studies with UFP generated from thermodegradation products of polymers are an indication of a general principle of UFP toxicity, freshness and proximity to the source are key requirements for inducing acute adverse effects of UFP. Do UFP emitted from internal combustion engines cause adverse health effects? We still need to know more, but results from our controlled clinical and animal studies using ultrafine elemental carbon particles permit some preliminary conclusions: The high deposition of inhaled UFP (0.007–0.1 μm) in the human respiratory tract as predicted by ICRP (1994) could be confirmed; moreover, deposition was even higher during exercise and in asthmatics. Unlike larger fine particles, UFP seem to escape phagocytosis by alveolar macrophages and are translocated to extrapulmonary organs, as was determined in rodents using ultrafine 13C particles, although such translocation was only minimal with ultrafine iridium particles. Cardiovascular effects in humans and animals and mild pulmonary inflammation in animals were also found following ultrafine carbon particle exposures. Although health effects data and understanding of mechanisms are still limited, there are intriguing data from other disciplines, in particular the field of drug delivery: Intravenously administered UFP were found to cross the blood–brain barrier (Kreuter, 2001), and a transport function of caveolae for macromolecules with molecular radii of several

CARDIOVASCULAR EFFECTS ASSOCIATED WITH AIR POLLUTION: POTENTIAL MECHANISMS AND METHODS OF TESTING

A recent series of epidemiologic reports have shown associations between fine particulate matter (PM) levels and increased cardiovascular morbidity and mortality. Elevated PM levels have been linked with cardiac events, including serious ventricular arrhythmias and myocardial infarction. A workshop brought together epidemiologists, cardiologists, and toxicologists from academia, government, and industry to examine plausible mechanisms that could be responsible for such effects, and to consider the armamentarium of noninvasive tests available to examine these relationships. Possible mechanisms considered by the participants include: (a) effects on the autonomic nervous system; (b) alterations on ion channel function in myocardial cells; (c) ischemic responses in the myocardium; and (d) inflammatory responses triggering endothelial dysfunction, atherosclerosis, and thrombosis. A large number of tests were identified to assess specific mechanistic pathways underlying the cardiovascular effects of air pollution and include: (a) autonomic control of the cardiovascular system assessed primarily by heart-rate variability; (b) myocardial substrate and vulnerability assessed by the electrocardiogram and estimations of ejection fraction and wall motion abnormalities in imaging studies; and (c) endothelial function, atherosclerosis, and thrombosis assessed by clotting parameters, cytokines, lipid profiles, and forearm blood flow. A variety of approaches ranging from molecular and genetic investigations to human clinical studies were recommended to further investigate the important epidemiologic associations.

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 ~ 25 nm, geometric standard deviation ~ 1.6), for 2 hr, in three separate protocols: 10 μg/m3 at rest, 10 and 25 μg/m3 with exercise, and 50 μg/m3 with exercise. In a fourth protocol, subjects with asthma inhaled air and 10 μg/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 μg/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.

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 μ m 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 μ g/m3, while asthmatics were exposed to 10 μ g/m3. 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 μ g/m3. However, exposing 16 normal subjects to the higher concentration of 50 μ g/m3 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.

Nitrogen dioxide exposure in vivo and human alveolar macrophage inactivation of influenza virus in vitro

Epidemiologic studies have reported an increased incidence of respiratory infections and illness in association with elevated indoor levels of nitrogen dioxide (NO2). Animal exposure studies have found that brief exposures to peak levels of NO2 produce greater morbidity than continuous lower level exposure. In order to examine the effect of NO2 inhalation on human alveolar macrophages, normal volunteers were exposed sequentially to air or NO2, by double-blind randomization, in an environmental chamber. Two exposure protocols with comparable concentration x time products were used: (a) continuous 0.60 ppm NO2 (n = 9), and (b) background 0.05 ppm NO2 with three 15-min peaks of 2.0 ppm (n = 15). Inhalation of NO2 caused no significant changes in pulmonary function or airway reactivity in either exposure protocol. Alveolar macrophages obtained by bronchoalveolar lavage 3 1/2 hr after exposure to continuous 0.60 ppm NO2 tended to inactivate influenza virus in vitro less effectively than cells collected after air exposure (1.96 vs 1.25 log10 plaque-forming units on Day 2 of incubation, P less than 0.07). Four of nine subjects accounted for the observed impairment in virus inactivation; cells from these four subjects demonstrated an increase in interleukin-1 (IL-1) production after NO2 vs air, whereas the five remaining subjects decreased IL-1 production after NO2. In contrast, intermittent peak exposure did not alter the rate of viral inactivation or IL-1 production. This methodology has the potential to identify pollutant effects on mechanisms of respiratory defense in humans.

Raynaud's phenomenon of the lung☆

To determine if pulmonary vessels develop vasospasm during Raynauds phenomenon, digital vasospasm was induced by hand immersion in 15 degrees C water (cold pressor test) in 17 subjects, and pulmonary function was measured during the subsequent 120 minutes. Five healthy persons were control subjects, seven subjects had well documented systemic disorders associated with Raynauds phenomenon (secondary Raynauds), and five subjects had a history of Raynauds phenomenon but no evidence of an associated disorder (primary Raynauds). The only measure of pulmonary function that changed significantly following cold pressor testing was carbon monoxide diffusing capacity. Subjects with primary Raynauds phenomenon had normal baseline carbon monoxide diffusing capacity (23.7 +/- 4.6 ml/minute/mm Hg) but demonstrated significant decreases (p less than 0.05) at 15 minutes (21.2 +/- 3.5 ml/minute/mm Hg), 45 minutes (19.5 +/- 3.7 ml/minute/mm Hg), and 120 minutes (17.1 +/- 2.1 ml/minute/mm Hg) after cold pressor testing. Subjects with secondary Raynauds phenomenon had low baseline carbon monoxide diffusing capacity (71 percent predicted) and showed no significant change following cold pressor testing. These findings indicate that digital vasospasm in patients with primary Raynauds phenomenon is part of a systemic vascular response that includes a decrease in the size of the pulmonary capillary bed.

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 μg/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 μg/m3 carbon UFP during intermittent exercise impairs peak forearm blood flow during reactive hyperemia in healthy human subjects.

Effects of on-road highway aerosol exposures on autonomic responses in aged, spontaneously hypertensive rats.

Epidemiological studies associate ambient particulate pollution with adverse health outcomes in elderly individuals with cardiopulmonary diseases. We hypothesized that freshly generated ultrafine particles (UFP) contribute to these effects, as they are present in high number concentrations on highways and vehicle passengers are exposed directly to them. Aged spontaneously hypertensive rats (9–12 mo) with implanted radiotelemetry devices were exposed to highway aerosol or filtered, gas-denuded (clean) air using an on-road exposure system to examine effects on heart rate (HR) and heart-rate variability (HRV). On the day of exposure, rats were pretreated with low-dose inhaled or injected lipopolysaccharide (LPS) to simulate respiratory tract or systemic inflammation, respectively. Exposures (6 h) in compartmentalized whole-body chambers were performed in an air conditioned compartment of a mobile laboratory on I-90 between Rochester and Buffalo, NY. HRV parameters were calculated from telemetric blood pressure signals and analyzed for the baseline period and for the first 32 h postexposure. The aerosol size (count median diameter = 15–20 nm; geometric standard deviation = 1.4–4.3) and number concentration (1.95–5.62 × 105/cm3) indicated the predominance of UFP. Intraperitoneal LPS significantly affected all of the parameters in a time-dependent manner; response patterns after inhaled or injected LPS pretreatment were similar, but more prolonged and greater in LPS-injected rats. A significant effect of highway aerosol was found, irrespective of pretreatment, which resulted in decreased HR in comparison to clean air-exposed rats. This effect was more persistent (∼ 14 h) in those rats that received ip LPS as compared to saline. The highway aerosol also significantly affected short-term alterations in autonomic control of HR, as evidenced by elevations in normalized high frequency power and decreased vagosympathetic balance. These findings show that environmental exposure concentrations of mixed traffic-related UFP/gas-phase emissions can affect the autonomic nervous system.

Characterization of Residential Wood Combustion Particles Using the Two-Wavelength Aethalometer

In the United States, residential wood combustion (RWC) is responsible for 7.0% of the national primary PM(2.5) emissions. Exposure to RWC smoke represents a potential human health hazard. Organic components of wood smoke particles absorb light at 370 nm more effectively than 880 nm in two-wavelength aethalometer measurements. This enhanced absorption (Delta-C = BC(370 nm) - BC(880 nm)) can serve as an indicator of RWC particles. In this study, aethalometer Delta-C data along with measurements of molecular markers and potassium in PM(2.5) were used to identify the presence of airborne RWC particles in Rochester, NY. The aethalometer data were corrected for the loading effect. Delta-C was found to strongly correlate with wood smoke markers (levoglucosan and potassium) during the heating season. No statistically significant correlation was found between Delta-C and vehicle exhaust markers. The Delta-C values were substantially higher during winter compared to summer. The winter diurnal pattern showed an evening peak around 21:00 that was particularly enhanced on weekends. A relationship between Delta-C and PM(2.5) was found that permits the estimation of the contribution of RWC particles to the PM mass. RWC contributed 17.3% to the PM(2.5) concentration during the winter. Exponential decay was a good estimator for predicting Delta-C concentrations at different winter precipitation rates and different wind speeds. Delta-C was also sensitive to remote forest fire smoke.