Ranjini M. Krishnan

Vascular Responses to Long- and Short-Term Exposure to Fine Particulate Matter : MESA Air (Multi-Ethnic Study of Atherosclerosis and Air Pollution)

OBJECTIVES This study evaluated the association of long- and short-term air pollutant exposures with flow-mediated dilation (FMD) and baseline arterial diameter (BAD) of the brachial artery using ultrasound in a large multicity cohort. BACKGROUND Exposures to ambient air pollution, especially long-term exposure to particulate matter <2.5 μm in aerodynamic diameter (PM(2.5)), are linked with cardiovascular mortality. Short-term exposure to PM(2.5) has been associated with decreased FMD and vasoconstriction, suggesting that adverse effects of PM(2.5) may involve endothelial dysfunction. However, long-term effects of PM(2.5) on endothelial dysfunction have not been investigated. METHODS FMD and BAD were measured by brachial artery ultrasound at the initial examination of the Multi-Ethnic Study of Atherosclerosis. Long-term PM(2.5) concentrations were estimated for the year 2000 at each participants residence (n = 3,040) using a spatio-temporal model informed by cohort-specific monitoring. Short-term PM(2.5) concentrations were based on daily central-site monitoring in each of the 6 cities. RESULTS An interquartile increase in long-term PM(2.5) concentration (3 μg/m(3)) was associated with a 0.3% decrease in FMD (95% confidence interval [CI] of difference: -0.6 to -0.03; p = 0.03), adjusting for demographic characteristics, traditional risk factors, sonographers, and 1/BAD. Women, nonsmokers, younger participants, and those with hypertension seemed to show a greater association of PM(2.5) with FMD. FMD was not significantly associated with short-term variation in PM(2.5) (-0.1% per 12 μg/m(3) daily increase [95% CI: -0.2 to 0.04] on the day before examination). CONCLUSIONS Long-term PM(2.5) exposure was significantly associated with decreased endothelial function according to brachial ultrasound results. These findings may elucidate an important pathway linking air pollution and cardiovascular mortality.

Blood Pressure Response to Controlled Diesel Exhaust Exposure in Human Subjects

Exposure to traffic-related air pollution is associated with risk of cardiovascular disease and mortality. We examined whether exposure to diesel exhaust increased blood pressure (BP) in human subjects. We analyzed data from 45 nonsmoking subjects, 18 to 49 years of age in double-blinded, crossover exposure studies, randomized to order. Each subject was exposed to diesel exhaust, maintained at 200 &mgr;g/m3 of fine particulate matter, and filtered air for 120 minutes on days separated by ≥2 weeks. We measured BP pre-exposure, at 30-minute intervals during exposure, and 3, 5, 7, and 24 hours from exposure initiation and analyzed changes from pre-exposure values. Compared with filtered air, systolic BP increased at all of the points measured during and after diesel exhaust exposure; the mean effect peaked between 30 and 60 minutes after exposure initiation (3.8 mm Hg [95% CI: −0.4 to 8.0 mm Hg] and 5.1 mm Hg [95% CI: 0.7–9.5 mm Hg], respectively). Sex and metabolic syndrome did not modify this effect. Combining readings between 30 and 90 minutes, diesel exhaust exposure resulted in a 4.4-mm Hg increase in systolic BP, adjusted for participant characteristics and exposure perception (95% CI: 1.1–7.7 mm Hg; P=0.0009). There was no significant effect on heart rate or diastolic pressure. Diesel exhaust inhalation was associated with a rapid, measurable increase in systolic but not diastolic BP in young nonsmokers, independent of perception of exposure. This controlled trial in humans confirms findings from observational studies. The effect may be important on a population basis given the worldwide prevalence of exposure to traffic-related air pollution.

A randomized cross-over study of inhalation of diesel exhaust, hematological indices, and endothelial markers in humans

BackgroundExposure to traffic-related air pollution (TRAP) is considered a trigger for acute cardiovascular events. Diesel Exhaust (DE) is a major contributor to TRAP in the world. We evaluated the effect of DE inhalation on circulating blood cell populations, hematological indices, and systemic inflammatory cytokines in humans using a specialized facility.MethodsIn a randomized double-blind crossover study balanced to order, 17 metabolic syndrome (MetS) and 15 healthy subjects inhaled filtered air (FA) or DE exposure in two-hour sessions on different days with a minimum 2-week washout period. We collected blood pre-exposure, 7, and 22 hours after exposure initiation and measured the complete blood count and differential. We performed multiplex cytokine assay to measure the changes in the systemic inflammatory cytokines, and endothelial adhesion molecules (n=15). A paired analysis compared the effect of DE and FA exposures for the change from pre-exposure to the subsequent time points.ResultsA significant increase in the hematocrit was noted 7 hrs after DE [1.4% (95% CI: 0.9 to 1.9%)] compared to FA exposure [0.5% (95% CI: -0.09 to 1.0%); p=0.008. The hemoglobin levels increased non-significantly at 7 hrs post DE [0.3 gm/dL (95% CI: 0.2 to 0.5 gm/dL)] versus FA exposure [0.2 gm/dL (95% CI: 0 to 0.3 gm/dL)]; p=0.06. Furthermore, the platelet count increased 22 hrs after DE exposure in healthy, but not in MetS subjects [DE: 16.6 (95% CI: 10.2 to 23) thousand platelets/mL versus [FA: 3.4 (95% CI: -9.5 to 16.3) thousand platelets/mL)]; p=0.04. No DE effect was observed for WBC, neutrophils, lymphocytes or erythrocytes. Using the multiplex assay, small borderline significant increases in matrix metalloproteinase-9, interleukins (IL)-1beta, 6 and 10 occurred 7 hrs post exposure initiation, whereas E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule -1, and myeloperoxidase 22 hrs post exposure.ConclusionsOur results suggest that short-term DE exposure results in hemoconcentration and thrombocytosis, which are important determinants of acute cardiovascular events. Multiplex assay showed a non-significant increase in IL-1β and IL-6 immediately post exposure followed by myeloperoxidase and endothelial activation molecules. Further specific assays in a larger population will improve our understanding of the systemic inflammatory mechanisms following acute exposure to TRAP.Clinical trials registration numberStudy was conducted between 2004 to 2006, prior to expectation for registration.

Mechanisms of Urokinase Plasminogen Activator (uPA)-mediated Atherosclerosis ROLE OF THE uPA RECEPTOR AND S100A8/A9 PROTEINS

Data from clinical studies, cell culture, and animal models implicate the urokinase plasminogen activator (uPA)/uPA receptor (uPAR)/plasminogen system in the development of atherosclerosis and aneurysms. However, the mechanisms through which uPA/uPAR/plasminogen stimulate these diseases are not yet defined. We used genetically modified, atherosclerosis-prone mice, including mice with macrophage-specific uPA overexpression and mice genetically deficient in uPAR to elucidate mechanisms of uPA/uPAR/plasminogen-accelerated atherosclerosis and aneurysm formation. We found that macrophage-specific uPA overexpression accelerates atherosclerosis and causes aortic root dilation in fat-fed Ldlr−/− mice (as we previously reported in Apoe−/− mice). Macrophage-expressed uPA accelerates atherosclerosis by stimulation of lesion progression rather than initiation and causes disproportionate lipid accumulation in early lesions. uPA-accelerated atherosclerosis and aortic dilation are largely, if not completely, independent of uPAR. In the absence of uPA overexpression, however, uPAR contributes modestly to both atherosclerosis and aortic dilation. Microarray studies identified S100A8 and S100A9 mRNA as the most highly up-regulated transcripts in uPA-overexpressing macrophages; up-regulation of S100A9 protein in uPA-overexpressing macrophages was confirmed by Western blotting. S100A8/A9, which are atherogenic in mice and are expressed in human atherosclerotic plaques, are also up-regulated in the aortae of mice with uPA-overexpressing macrophages, and macrophage S100A9 mRNA is up-regulated by exposure of wild-type macrophages to medium from uPA-overexpressing macrophages. Macrophage microarray data suggest significant effects of uPA overexpression on cell migration and cell-matrix interactions. Our results confirm in a second animal model that macrophage-expressed uPA stimulates atherosclerosis and aortic dilation. They also reveal uPAR independence of these actions and implicate specific pathways in uPA/Plg-accelerated atherosclerosis and aneurysmal disease.

Plasminogen mediates the atherogenic effects of macrophage-expressed urokinase and accelerates atherosclerosis in apoE-knockout mice.

Urokinase-type plasminogen activator (uPA) is expressed at elevated levels in atherosclerotic human arteries, primarily in macrophages. Plasminogen (Plg), the primary physiologic substrate of uPA, is present at significant levels in blood and interstitial fluid. Both uPA and Plg have activities that could affect atherosclerosis progression. Moreover, correlations between increased Plg activation and accelerated atherosclerosis are reported in several human studies. However, a coherent picture of the role of the uPA/Plg system in atherogenesis has not yet emerged, with at least one animal study suggesting that Plg is atheroprotective. We used a transgenic mouse model of macrophage-targeted uPA overexpression in apolipoprotein E-deficient mice to investigate the roles of uPA and Plg in atherosclerosis. We found that macrophage-expressed uPA accelerated atherosclerotic plaque growth and promoted aortic root dilation through Plg-dependent pathways. These pathways appeared to affect lesion progression rather than initiation and to include actions that disproportionately increase lipid accumulation in the artery wall. In addition, loss of Plg was protective against atherosclerosis both in the presence and absence of uPA overexpression. Transgenic mice with macrophage-targeted uPA overexpression reveal atherogenic roles for both uPA and Plg and are a useful experimental setting for investigating the molecular mechanisms that underlie clinically established relationships between uPA expression, Plg activation, and atherosclerosis progression.

Level of Macrophage uPA Expression Is an Important Determinant of Atherosclerotic Lesion Growth in Apoe −/− Mice

Objective—Enhanced plasminogen activation, mediated by overexpression of urokinase-type plasminogen activator (uPA), accelerates atherosclerosis in apolipoprotein E–null mice. However, the mechanisms through which uPA acts remain unclear. In addition, although elevated uPA expression can accelerate murine atherosclerosis, there is not yet any evidence that decreased uPA expression would retard atherosclerosis. Methods and Results—We used a bone marrow transplant (BMT) approach and apolipoprotein E–deficient (Apoe−/−) mice to investigate cellular mechanisms of uPA-accelerated atherosclerosis, aortic dilation, and sudden death. We also used BMT to determine whether postnatal loss of uPA expression in macrophages retards atherosclerosis. BMT from uPA-overexpressing mice yielded recipients with macrophage-specific uPA overexpression; whereas BMT from uPA knockout mice yielded recipients with macrophage-specific loss of uPA expression. Recipients of uPA-overexpressing BM acquired all the vascular phenotypes (accelerated atherosclerosis, aortic medial destruction and dilation, severe coronary stenoses) as well as the sudden death phenotype of uPA-overexpressing mice. Moreover, fat-fed 37-week-old recipients of uPA-null BM had significantly less atherosclerosis than recipients of uPA wild-type marrow (40% less aortic surface lesion area; P=0.03). Conclusions—The level of uPA expression by macrophages—over a broad range—is an important determinant of atherosclerotic lesion growth in Apoe−/− mice.

LONG-TERM EXPOSURE TO TRAFFIC RELATED AIR POLLUTION AND ENDOTHELIAL DYSFUNCTION: MULTIETHNIC STUDY OF ATHEROSCLEROSIS AND AIR POLLUTION (MESA AIR)

Traffic related air pollution (TRAP) has been associated with increased atherosclerosis, left ventricular mass, myocardial infarction; endothelial dysfunction may mediate these effects. In the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air), an interquartile (25th to 75th