On-road exposure to highway aerosols. 2. Exposures of aged, compromised rats

Air pollution, glymphatic impairment, and Alzheimer's disease

Epidemiological evidence demonstrates a link between air pollution exposure and the onset and progression of cognitive impairment and Alzheimer's disease (AD). However, current understanding of the underlying pathophysiological mechanisms is limited. This opinion article examines the hypothesis that air pollution-induced impairment of glymphatic clearance represents a crucial etiological event in the development of AD. Exposure to airborne particulate matter (PM) leads to systemic inflammation and neuroinflammation, increased metal load, respiratory and cardiovascular dysfunction, and sleep abnormalities. All these factors are known to reduce the efficiency of glymphatic clearance. Rescuing glymphatic function by restricting the impact of causative agents, and improving sleep and cardiovascular system health, may increase the efficiency of waste metabolite clearance and subsequently slow the progression of AD. In sum, we introduce air pollution-mediated glymphatic impairment as an important mechanistic factor to be considered when interpreting the etiology and progression of AD as well as its responsiveness to therapeutic interventions.

Ozone-induced acute phase response in lung versus liver: the role of adrenal-derived stress hormones

Acute-phase response (APR) is an innate stress reaction to tissue trauma or injury, infection, and environmental insults like ozone (O₃). Regardless of the location of stress, the liver has been considered the primary contributor to circulating acute-phase proteins (APPs); however, the mechanisms underlying APR induction are unknown. Male Wistar-Kyoto rats were exposed to air or O₃ (1 ppm, 6-hr/day, 1 or 2 days) and examined immediately after each exposure and after 18-hr recovery for APR proteins and gene expression. To assess the contribution of adrenal-derived stress hormones, lung and liver global gene expression data from sham and adrenalectomized rats exposed to air or O₃ were compared for APR transcriptional changes. Data demonstrated serum protein alterations for selected circulating positive and negative APPs following 2 days of O₃ exposure and during recovery. At baseline, APP gene expression was several folds higher in the liver relative to the lung. O₃-induced increases were significant for lung but not liver for some genes including orosomucoid-1. Further, comparative assessment of mRNA seq data for known APPs in sham rats exhibited marked elevation in the lung but not liver, and a near-complete abolishment of APP mRNA levels in lung tissue of adrenalectomized rats. Thus, the lung appears to play a critical role in O₃-induced APP synthesis and requires the presence of circulating adrenal-derived stress hormones. The relative contribution of lung versus liver and the role of neuroendocrine stress hormones need to be considered in future APR studies involving inhaled pollutants.

Associations of Long-Term Exposure to Ultrafine Particles and Nitrogen Dioxide With Increased Incidence of Congestive Heart Failure and Acute Myocardial Infarction

Although long-term exposure to traffic-related air pollutants such as nitrogen dioxide has been linked to cardiovascular disease (CVD) mortality, little is known about the association between ultrafine particles (UFPs), defined as particles less than or equal to 0.1 μm in diameter, and incidence of major CVD events. We conducted a population-based cohort study to assess the associations of chronic exposure to UFPs and nitrogen dioxide with incident congestive heart failure (CHF) and acute myocardial infarction. Our study population comprised all long-term Canadian residents aged 30-100 years who lived in Toronto, Ontario, Canada, during the years 1996-2012. We estimated annual concentrations of UFPs and nitrogen dioxide by means of land-use regression models and assigned these estimates to participants' postal-code addresses in each year during the follow-up period. We estimated hazard ratios for the associations of UFPs and nitrogen dioxide with incident CVD using random-effects Cox proportional hazards models. We controlled for smoking and obesity using an indirect adjustment method. Our cohorts comprised approximately 1.1 million individuals at baseline. In single-pollutant models, each interquartile-range increase in UFP exposure was associated with increased incidence of CHF (hazard ratio for an interquartile-range increase (HRIQR) = 1.03, 95% confidence interval (CI): 1.02, 1.05) and acute myocardial infarction (HRIQR = 1.05, 95% CI: 1.02, 1.07). Adjustment for fine particles and nitrogen dioxide did not materially change these estimated associations. Exposure to nitrogen dioxide was also independently associated with higher CHF incidence (HRIQR = 1.04, 95% CI: 1.03, 1.06).

Nanometer-sized emissions from municipal waste incinerators: A qualitative risk assessment

Municipal waste incinerators (MWI) are beneficial alternatives to landfills for waste management. A recent constituent of concern in emissions from these facilities is incidental nanometer-sized particles (INP_MWI), i.e., particles smaller than 1 micrometer in size that may deposit in the deepest parts of the lungs, cross into the bloodstream, and affect different regions of the body. With limited data, the public may fear INP_MWI due to uncertainty, which may affect public acceptance, regulatory permitting, and the increased lowering of air quality standards. Despite limited data, a qualitative risk assessment paradigm can be applied to determine the relative risk due to INP_MWI emissions. This review compiles existing data on nanometer-sized particle generation by MWIs, emissions control technologies used at MWIs, emission releases into the atmosphere, human population exposure, and adverse health effects of nanometer-sized particles to generate a qualitative risk assessment and identify data gaps. The qualitative risk assessment conservatively concludes that INP_MWI pose a low to moderate risk to individuals, primarily due to the lack of relevant toxicological data on INP_MWI mixtures in ambient particulate matter.

The biological effects upon the cardiovascular system consequent to exposure to particulates of less than 500 nm in size

CONTEXT

Ultrafine particulate matter contribution to cardiovascular disease is not known and not regulated. PM up to 500 nm are abundant in urban air and alveolar deposition is significant.

OBJECTIVE

Effects beyond the alveolar barrier within the body or in vitro tissues exposed to particles <500 nm.

METHODS AND RESULTS

DATABASES

MEDLINE; Ovid-MEDLINE PREM; Web of Science; PubMed (SciGlobe). 127 articles. Results in tables: "subject type exposed", "exposure type", "technique".

CONCLUSION

Heart rate, vasoactivity, atherosclerotic advancement, oxidative stress, coagulability, inflammatory changes are affected. Production of reactive oxygen species is a useful target to limit outcomes associated with UFP exposure.

Particulate matter beyond mass: recent health evidence on the role of fractions, chemical constituents and sources of emission

Particulate matter (PM) is regulated in various parts of the world based on specific size cut offs, often expressed as 10 or 2.5 µm mass median aerodynamic diameter. This pollutant is deemed one of the most dangerous to health and moreover, problems persist with high ambient concentrations. Continuing pressure to re-evaluate ambient air quality standards stems from research that not only has identified effects at low levels of PM but which also has revealed that reductions in certain components, sources and size fractions may best protect public health. Considerable amount of published information have emerged from toxicological research in recent years. Accumulating evidence has identified additional air quality metrics (e.g. black carbon, secondary organic and inorganic aerosols) that may be valuable in evaluating the health risks of, for example, primary combustion particles from traffic emissions, which are not fully taken into account with PM2.5 mass. Most of the evidence accumulated so far is for an adverse effect on health of carbonaceous material from traffic. Traffic-generated dust, including road, brake and tire wear, also contribute to the adverse effects on health. Exposure durations from a few minutes up to a year have been linked with adverse effects. The new evidence collected supports the scientific conclusions of the World Health Organization Air Quality Guidelines and also provides scientific arguments for taking decisive actions to improve air quality and reduce the global burden of disease associated with air pollution.

Evaluation of potential for toxicity from subacute inhalation of tire and road wear particles in rats

Tire and road wear particles (TRWP) are a component of ambient particulate matter (PM) produced from the interaction of tires with the roadway. Inhalation of PM has been associated with cardiopulmonary morbidities and mortalities thought to stem from pulmonary inflammation. To determine whether TRWP may contribute to these events, the effects of subacute inhalation of TRWP were evaluated in rats. TRWP were collected at a road simulator laboratory, aerosolized, and used to expose male and female Sprague-Dawley rats (n = 10/treatment group) at ~10, 40, or 100 μg/m³ TRWP via nose-only inhalation for 6 h/day for 28 days. Particle size distribution of the aerosolized TRWP was found to be within the respirable range for rats. Toxicity was assessed following OECD guidelines (TG 412). No TRWP-related effects were observed on survival, clinical observations, body or organ weights, gross pathology, food consumption, immune system endpoints, serum chemistry, or biochemical markers of inflammation or cytotoxicity. Rare to few focal areas of subacute inflammatory cell infiltration associated with TWRP exposure were observed in the lungs of one mid and four high exposure animals, but not the low-exposure animals. These alterations were minimal, widely scattered and considered insufficient in extent or severity to have an impact on pulmonary function. Furthermore, it is expected that these focal lesions would remain limited and may undergo resolution without long-term or progressive pulmonary alterations. Therefore, from this study we identified a no-observable-adverse-effect-level (NOAEL) of 112 μg/m³ of TRWP in rats for future use in risk assessment of TRWP.

Alteration of peripheral blood monocyte gene expression in humans following diesel exhaust inhalation

CONTEXT

Epidemiologic associations between acutely increased cardiorespiratory morbidity and mortality and particulate air pollution are well established, but the effects of acute pollution exposure on human gene expression changes are not well understood.

OBJECTIVE

In order to identify potential mechanisms underlying epidemiologic associations between air pollution and morbidity, we explored changes in gene expression in humans following inhalation of fresh diesel exhaust (DE), a model for particulate air pollution.

MATERIALS AND METHODS

Fourteen ethnically homogeneous (white males), young, healthy subjects underwent 60-min inhalation exposures on 2 separate days with clean filtered air (CA) or freshly generated and diluted DE at a concentration of 300 μg/m(3) PM(2.5). Prior to and 24 h following each session, whole blood was sampled and fractionated for peripheral blood mononuclear cell (PBMC) isolation, RNA extraction, and generation of cDNA, followed by hybridization with Agilent Whole Human Genome (4X44K) arrays.

RESULTS

Oxidative stress and the ubiquitin proteasome pathway, as well as the coagulation system, were among hypothesized pathways identified by analysis of differentially expressed genes. Nine genes from these pathways were validated using real-time polymerase chain reaction (PCR) to compare fold change in expression between DE exposed and CA days. Quantitative gene fold changes generated by real-time PCR were directionally consistent with the fold changes from the microarray analysis.

DISCUSSION AND CONCLUSION

Changes in gene expression connected with key oxidative stress, protein degradation, and coagulation pathways are likely to underlie observed physiologic and clinical outcomes and suggest specific avenues and sensitive time points for further physiologic exploration.

Whole and particle-free diesel exhausts differentially affect cardiac electrophysiology, blood pressure, and autonomic balance in heart failure-prone rats

Epidemiological studies strongly link short-term exposures to vehicular traffic and particulate matter (PM) air pollution with adverse cardiovascular (CV) events, especially in those with preexisting CV disease. Diesel engine exhaust is a key contributor to urban ambient PM and gaseous pollutants. To determine the role of gaseous and particulate components in diesel exhaust (DE) cardiotoxicity, we examined the effects of a 4-h inhalation of whole DE (wDE) (target PM concentration: 500 µg/m(3)) or particle-free filtered DE (fDE) on CV physiology and a range of markers of cardiopulmonary injury in hypertensive heart failure-prone rats. Arterial blood pressure (BP), electrocardiography, and heart rate variability (HRV), an index of autonomic balance, were monitored. Both fDE and wDE decreased BP and prolonged PR interval during exposure, with more effects from fDE, which additionally increased HRV triangular index and decreased T-wave amplitude. fDE increased QTc interval immediately after exposure, increased atrioventricular (AV) block Mobitz II arrhythmias shortly thereafter, and increased serum high-density lipoprotein 1 day later. wDE increased BP and decreased HRV root mean square of successive differences immediately postexposure. fDE and wDE decreased heart rate during the 4th hour of postexposure. Thus, DE gases slowed AV conduction and ventricular repolarization, decreased BP, increased HRV, and subsequently provoked arrhythmias, collectively suggesting parasympathetic activation; conversely, brief BP and HRV changes after exposure to particle-containing DE indicated a transient sympathetic excitation. Our findings suggest that whole- and particle-free DE differentially alter CV and autonomic physiology and may potentially increase risk through divergent pathways.

Air pollutants: the key stages in the pathway towards the development of cardiovascular disorders

Air pollution has been one of the significant risks to human health. Various studies indicate that ambient particulate matter in air pollution is most strongly allied to increased morbidity and mortality due to their link with cardiovascular adverse events. The mechanisms leading to these harmful effects on the cardiovascular system have not been defined clearly but several hypotheses have been proposed that elucidate the direct and indirect effects of air pollution. Adverse cardiovascular events such as thrombosis, vascular dysfunction, atherosclerosis, myocardial infarction and disturbance in cardiac autonomic control are thought to be linked with air pollution. Recently, an association has also been found between cardiac hypertrophy and air pollution. The present review focuses on highlighting the implications of air pollution in deteriorating cardiac health.

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 x 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 ( approximately 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.

Platelet adhesion and fibrinogen deposition in murine microvessels upon inhalation of nanosized carbon particles

SUMMARY BACKGROUND

The translocation of nanoparticles in the lung toward effector organs via the circulation is considered an important direct pathway for systemic effects of nanoparticles after inhalation. Recently, we have reported that a moderate dose of systemically administered nanosized carbon black particles exerted thrombogenic effects in hepatic microvessels of healthy mice.

OBJECTIVES

This study addresses the questions of whether similar thrombogenic effects are also evoked upon inhalation of nanosized carbon particles (NCP) and whether NCP-induced hepatic platelet accumulation is associated with pulmonary or systemic inflammation.

METHODS

Two and 8 h after a 24-h exposure to either filtered air or to NCP, intravital fluorescence microscopy of the hepatic microcirculation was performed in C57Bl/6 mice. Parameters of pulmonary or systemic inflammatory response were determined in bronchoalveolar lavage and blood/plasma samples.

RESULTS

Inhalative exposure to NCP caused platelet accumulation in the hepatic microvasculature, whereas leukocyte recruitment and sinusoidal perfusion did not differ from controls. Fibrinogen deposition was detected by immunohistochemistry in both hepatic and cardiac microvessels from NCP-exposed mice. In contrast, inhalation of NCP affected neither the plasma levels of proinflammatory cytokines nor blood cell counts. Moreover, the bronchoalveolar lavage data indicate that no significant inflammatory response occurred in the lung.

CONCLUSIONS

Thus, exposure to NCP exerts thrombogenic effects in the microcirculation of healthy mice independent of the route of administration (i.e. inhalation or systemic intra-arterial administration). The NCP-induced thrombogenic effects are not liver specific, are associated with neither a local nor a systemic inflammatory response, and seem to be independent of pulmonary inflammation.

Physicochemical factors that affect metal and metal oxide nanoparticle passage across epithelial barriers

The diversity of nanomaterials in terms of size, shape, and surface chemistry poses a challenge to those who are trying to characterize the human health and environmental risks associated with incidental and unintentional exposures. There are numerous products that are already commercially available that contain solid metal and metal oxide nanoparticles, either embedded in a matrix or in solution. Exposure assessments for these products are often incomplete or difficult due to technological challenges associated with detection and quantitation of nanoparticles in gaseous or liquid carriers. The main focus of recent research has been on hazard identification. However, risk is a product of hazard and exposure, and one significant knowledge gap is that of the target organ dose following in vivo exposures. In order to reach target organs, nanoparticles must first breach the protective barriers of the respiratory tract, gastrointestinal tract, or skin. The fate of those nanoparticles that reach physiological barriers is in large part determined by the properties of the particles and the barriers themselves. This article reviews the physiological properties of the lung, gut, and skin epithelia, the physicochemical properties of metal and metal oxide nanoparticles that are likely to affect their ability to breach epithelial barriers, and what is known about their fate following in vivo exposures.

Particulate matter (PM) research centers (1999-2005) and the role of interdisciplinary center-based research

OBJECTIVE

The U.S. Environmental Protection Agency funded five academic centers in 1999 to address the uncertainties in exposure, toxicity, and health effects of airborne particulate matter (PM) identified in the "Research Priorities for Airborne Particulate Matter" of the National Research Council (NRC). The centers were structured to promote interdisciplinary approaches to address research priorities of the NRC. In this report, we present selected accomplishments from the first 6 years of the PM Centers, with a focus on the advantages afforded by the interdisciplinary, center-based research approach. The review highlights advances in the area of ultrafine particles and traffic-related health effects as well as cardiovascular and respiratory effects, mechanisms, susceptibility, and PM exposure and characterization issues.

DATA SOURCES AND SYNTHESIS

The collective publications of the centers served as the data source. To provide a concise synthesis of overall findings, authors representing each of the five centers identified a limited number of topic areas that serve to illustrate the key accomplishments of the PM Centers program, and a consensus statement was developed.

CONCLUSIONS

The PM Centers program has effectively applied interdisciplinary research approaches to advance PM science.

Adverse cardiovascular effects of air pollution

Air pollution is increasingly recognized as an important and modifiable determinant of cardiovascular disease in urban communities. Acute exposure has been linked to a range of adverse cardiovascular events including hospital admissions with angina, myocardial infarction, and heart failure. Long-term exposure increases an individual's lifetime risk of death from coronary heart disease. The main arbiter of these adverse health effects seems to be combustion-derived nanoparticles that incorporate reactive organic and transition metal components. Inhalation of this particulate matter leads to pulmonary inflammation with secondary systemic effects or, after translocation from the lung into the circulation, to direct toxic cardiovascular effects. Through the induction of cellular oxidative stress and proinflammatory pathways, particulate matter augments the development and progression of atherosclerosis via detrimental effects on platelets, vascular tissue, and the myocardium. These effects seem to underpin the atherothrombotic consequences of acute and chronic exposure to air pollution. An increased understanding of the mediators and mechanisms of these processes is necessary if we are to develop strategies to protect individuals at risk and reduce the effect of air pollution on cardiovascular disease.

On-Road Exposure to Highway Aerosols. 1. Aerosol and Gas Measurements

On-road experiments were conducted to determine the sensitivities of rats to real-world aerosol. This article summarizes the on-road aerosol and gas measurements and provides background information for the companion paper on the rat exposures. Measurements were carried out over 10 days, 6 h/day, driving a route from Rochester to Buffalo. Aerosol instrumentation used in this study included two scanning mobility particle sizers (SMPS) to determine the aerosol size distribution from 10 to 300 nm, 2 stand-alone condensation particle counters to determine the total aerosol number concentration, and an electrical aerosol detector to determine the aerosol length concentration. A thermal denuder (TD) was used with one of the SMPS instruments to determine the size distribution of the non-volatile fraction. Filter samples were collected and analyzed for elemental carbon, and gas analyzers measured ambient levels of CO, CO(2), and NO. Average daily total aerosol number concentration ranged from 200,000 to 560,000 particles/cm(3). Past studies on urban highways have measured total number concentrations ranging between 10(4) and 10(6) particles/cm(3). The average daily NO concentration ranged from 0.10 to 0.24 ppm and the corresponding CO(2) concentration ranged from 400 to 420 ppm. The average daily geometric number mean particle size determined by the SMPS ranged from 15 to 20 nm. The TD reduced the average SMPS number concentration between 87 and 95% and the SMPS volume between 54 and 83%, suggesting that most of the particles consisted of volatile material. The TD also increased the geometric number mean diameter from 15 to 20 nm to 30 to 40 nm.

Report: Combustion Byproducts and Their Health Effects: Summary of the 10th International Congress

The 10th International Congress on Combustion Byproducts and their Health Effects was held in Ischia, Italy, from June 17-20, 2007. It is sponsored by the US NIEHS, NSF, Coalition for Responsible Waste Incineration (CRWI), and Electric Power Research Institute (EPRI). The congress focused on: the origin, characterization, and health impacts of combustion-generated fine and ultrafine particles; emissions of mercury and dioxins, and the development/application of novel analytical/diagnostic tools. The consensus of the discussion was that particle-associated organics, metals, and persistent free radicals (PFRs) produced by combustion sources are the likely source of the observed health impacts of airborne PM rather than simple physical irritation of the particles. Ultrafine particle-induced oxidative stress is a likely progenitor of the observed health impacts, but important biological and chemical details and possible catalytic cycles remain unresolved. Other key conclusions were: (1) In urban settings, 70% of airborne fine particles are a result of combustion emissions and 50% are due to primary emissions from combustion sources, (2) In addition to soot, combustion produces one, possibly two, classes of nanoparticles with mean diameters of ~10 nm and ~1 nm. (3) The most common metrics used to describe particle toxicity, viz. surface area, sulfate concentration, total carbon, and organic carbon, cannot fully explain observed health impacts, (4) Metals contained in combustion-generated ultrafine and fine particles mediate formation of toxic air pollutants such as PCDD/F and PFRs. (5) The combination of metal-containing nanoparticles, organic carbon compounds, and PFRs can lead to a cycle generating oxidative stress in exposed organisms.

Diesel exhaust inhalation elicits acute vasoconstriction in vivo

BACKGROUND

Traffic-related air pollution is consistently associated with cardiovascular morbidity and mortality. Recent human and animal studies suggest that exposure to air pollutants affects vascular function. Diesel exhaust (DE) is a major source of traffic-related air pollution.

OBJECTIVES

Our goal was to study the effects of short-term exposure to DE on vascular reactivity and on mediators of vascular tone.

METHODS

In a double-blind, crossover, controlled exposure study, 27 adult volunteers (10 healthy and 17 with metabolic syndrome) were exposed in randomized order to filtered air (FA) and each of two levels of diluted DE (100 or 200 microg/m(3) of fine particulate matter) in 2-hr sessions. Before and after each exposure, we assessed the brachial artery diameter (BAd) by B-mode ultrasound and collected blood samples for endothelin-1 (ET-1) and catecholamines. Postexposure we also assessed endothelium-dependent flow-mediated dilation (FMD).

RESULTS

Compared with FA, DE at 200 microg/m(3) elicited a decrease in BAd (0.11 mm; 95% confidence interval, 0.02-0.18), and the effect appeared linearly dose related with a smaller effect at 100 microg/m(3). Plasma levels of ET-1 increased after 200 microg/m(3) DE but not after FA (p = 0.01). There was no consistent impact of DE on plasma catecholamines or FMD.

CONCLUSIONS

These results demonstrate that short-term exposure to DE is associated with acute endothelial response and vasoconstriction of a conductance artery. Elucidation of the signaling pathways controlling vascular tone that underlie this observation requires further study.

Air pollution and atherothrombosis

Observational studies have consistently demonstrated an association between exposure to air pollution and increased cardiovascular morbidity and mortality. This association is strongest for particulate matter (PM), of which combustion-derived particulate is an important component. Studies assessing the effects of PM exposure in vitro and in vivo have provided insight into the biological mechanisms underlying these observations. In this review we discuss the potential for inhaled particles to impact on the development and progression of atherosclerosis. Oxidative stress and inflammation are central to both the toxicology of PM and the pathogenesis of atherosclerosis. It is possible that nanoparticulates or soluble components of PM may translocate into the bloodstream, resulting in direct effects on atherosclerotic plaque stability, the vascular endothelium, platelet function, and thrombosis. We summarize the latest experimental research and relate this to current understanding of the role of inflammation and vascular dysfunction in the pathogenesis of atherothrombosis. Ongoing research in this area will continue to provide insight into the adverse vascular effects of PM, with the possibility of therapeutic interventions to reduce the impact of environmental air pollution on cardiovascular disease a realistic goal.

Nanoparticles-a thoracic toxicology perspective

A substantial literature demonstrates that the main ultrafine particles found in ambient urban air are combustion-derived nanoparticles (CDNP) which originate from a number of sources and pose a hazard to the lungs. For CDNP, three properties appear important-surface area, organics and metals. All of these can generate free radicals and so induce oxidative stress and inflammation. Inflammation is a process involved in the diseases exhibited by the individuals susceptible to the effects of PM- development and exacerbations of airways disease and cardiovascular disease. It is therefore possible to implicate CDNP in the common adverse effects of increased PM. The adverse effects of increases in PM on the cardiovascular system are well-documented in the epidemiological literature and, as argued above, these effects are likely to be driven by the combustion-derived NP. The epidemiological findings can be explained in a number of hypotheses regarding the action of NP:-1) Inflammation in the lungs caused by NP causes atheromatous plaque development and destabilization; 2) The inflammation in the lungs causes alteration in the clotting status or fibrinolytic balance favouring thrombogenesis; 3) The NP themselves or metals/organics released by the particles enter the circulation and have direct effects on the endothelium, plaques, the clotting system or the autonomic nervous system/ heart rhythm. Environmental nanoparticles are accidentally produced but they provide a toxicological model for a new class of purposely 'engineered' NP arising from the nanotechnology industry, whose effects are much less understood. Bridging our toxicological knowledge between the environmental nanoparticles and the new engineered nanoparticles is a considerable challenge.

Induction of inflammation in vascular endothelial cells by metal oxide nanoparticles: effect of particle composition

BACKGROUND

The mechanisms governing the correlation between exposure to ultrafine particles and the increased incidence of cardiovascular disease remain unknown. Ultrafine particles appear to cross the pulmonary epithelial barrier into the bloodstream, raising the possibility of direct contact with the vascular endothelium.

OBJECTIVES

Because endothelial inflammation is critical for the development of cardiovascular pathology, we hypothesized that direct exposure of human aortic endothelial cells (HAECs) to ultrafine particles induces an inflammatory response and that this response depends on particle composition.

METHODS

To test the hypothesis, we incubated HAECs for 1-8 hr with different concentrations (0.001-50 mug/mL) of iron oxide (Fe(2)O(3)), yttrium oxide (Y(2)O(3)), and zinc oxide (ZnO) nanoparticles and subsequently measured mRNA and protein levels of the three inflammatory markers intra-cellular cell adhesion molecule-1, interleukin-8, and monocyte chemotactic protein-1. We also determined nanoparticle interactions with HAECs using inductively coupled plasma mass spectrometry and transmission electron microscopy.

RESULTS

Our data indicate that nanoparticle delivery to the HAEC surface and uptake within the cells correlate directly with particle concentration in the cell culture medium. All three types of nanoparticles are internalized into HAECs and are often found within intracellular vesicles. Fe(2)O(3) nanoparticles fail to provoke an inflammatory response in HAECs at any of the concentrations tested; however, Y(2)O(3) and ZnO nanoparticles elicit a pronounced inflammatory response above a threshold concentration of 10 mug/mL. At the highest concentration, ZnO nanoparticles are cytotoxic and lead to considerable cell death.

CONCLUSIONS

These results demonstrate that inflammation in HAECs following acute exposure to metal oxide nanoparticles depends on particle composition.

Inhalation of ultrafine and fine particulate matter disrupts systemic vascular function

This study investigated the effects of particulate matter (PM) with aerodynamic diameter 0.02-1 microm (noted as PM1) inhalation during exercise on conduit artery and microvascular function. Inhalation of internal combustion-derived PM is associated with cardiovascular mortality and morbidity. Direct action of PM on the vascular endothelium is likely, as a substantial fraction of ultrafine PM translocates from the alveoli to the circulatory system. Sixteen intercollegiate athletes performed 30 min of exercise while inhaling low or high PM1. Flow-mediated brachial artery dilation (FMD) using high-resolution ultrasonography with simultaneous measurements of forearm oxygen kinetics using near infrared spectrophotometry (NIRS) was done before and after exercise. Basal brachial artery vasoconstriction was found after high PM1 exercise (4.0%, 4.66 +/- 0.609 to 4.47 +/- 0.625 mm diameter; p = .0002), but not after low PM1 exercise (-0.3%, 4.66 +/- 0.626 to 4.68 +/- 0.613 mm diameter). FMD was impaired after high PM1 exercise (6.8 +/- 3.58% for preexercise FMD and 0.30 +/- 2.74% for postexercise FMD, p = .0001), but not after low PM1 exercise (6.6 +/- 4.04% for preexercise FMD and 4.89 +/- 4.42% for postexercise FMD). Reduction in forearm muscle reperfusion estimated by reoxygenation slope-to-baseline after 4 min cuff ischemia was observed for high PM1 exercise (55% vs. 3%, p = .0006); no difference was noted for low PM1 exercise. Brachial artery FMD was significantly correlated to muscle reoxygenation slope-to-baseline (r = .50, p = .005). Acute inhalation of high [PM1] typical of urban environments impairs both systemic conduit artery function and microcirculation. The observed decrease reoxygenation slope-to-baseline after cuff release is consistent with reduced blood flow in the muscle microvasculature.