The mechanisms by which exposure to particulate matter increases the risk of cardiovascular events are not known. Recent human and animal data suggest that particulate matter may induce alterations in hemostatic factors. In this study we determined the mechanisms by which particulate matter might accelerate thrombosis. We found that mice treated with a dose of well characterized particulate matter of less than 10 μM in diameter exhibited a shortened bleeding time, decreased prothrombin and partial thromboplastin times (decreased plasma clotting times), increased levels of fibrinogen, and increased activity of factor II, VIII, and X. This prothrombotic tendency was associated with increased generation of intravascular thrombin, an acceleration of arterial thrombosis, and an increase in bronchoalveolar fluid concentration of the prothrombotic cytokine IL-6. Knockout mice lacking IL-6 were protected against particulate matter-induced intravascular thrombin formation and the acceleration of arterial thrombosis. Depletion of macrophages by the intratracheal administration of liposomal clodronate attenuated particulate matter-induced IL-6 production and the resultant prothrombotic tendency. Our findings suggest that exposure to particulate matter triggers IL-6 production by alveolar macrophages, resulting in reduced clotting times, intravascular thrombin formation, and accelerated arterial thrombosis. These results provide a potential mechanism linking ambient particulate matter exposure and thrombotic events.

BackgroundExposure of human populations to ambient particulate matter (PM) air pollution significantly contributes to the mortality attributable to ischemic cardiovascular events. We reported that mice treated with intratracheally instilled PM develop a prothrombotic state that requires the release of IL-6 by alveolar macrophages. We sought to determine whether exposure of mice to PM increases the levels of PAI-1, a major regulator of thrombolysis, via a similar or distinct mechanism.Methods and Principal FindingsAdult, male C57BL/6 and IL-6 knock out (IL-6−/−) mice were exposed to either concentrated ambient PM less than 2.5 µm (CAPs) or filtered air 8 hours daily for 3 days or were exposed to either urban particulate matter or PBS via intratracheal instillation and examined 24 hours later. Exposure to CAPs or urban PM resulted in the IL-6 dependent activation of coagulation in the lung and systemically. PAI-1 mRNA and protein levels were higher in the lung and adipose tissue of mice treated with CAPs or PM compared with filtered air or PBS controls. The increase in PAI-1 was similar in wild-type and IL-6−/− mice but was absent in mice treated with etanercept, a TNF-α inhibitor. Treatment with etanercept did not prevent the PM-induced tendency toward thrombus formation.ConclusionsMice exposed to inhaled PM exhibited a TNF-α-dependent increase in PAI-1 and an IL-6-dependent activation of coagulation. These results suggest that multiple mechanisms link PM-induced lung inflammation with the development of a prothrombotic state.

Objective To determine whether elevated levels of hemostatic factors are associated with the subsequent development of subclinical cardiovascular disease. Methods Fibrinogen, factors VII (FVII) and VIII (FVIII), and von Willebrand factor (vWF) were measured in 1396 participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study. Coronary artery calcification (CAC) and carotid intimal/medial thickness (CIMT) were determined 13 years later. The adjusted prevalence of CAC and mean CIMT across the quartiles of each hemostatic factor was computed for the total sample and for each race and gender group. Results The age, race, and gender-adjusted prevalences of CAC with increasing quartiles of fibrinogen were 14.4%, 15.2%, 20.0%, and 29.1% (p<0.001 for trend). This trend persisted after further adjustment for body mass index (BMI), smoking, educational level, center, systolic blood pressure (BP), diabetes, antihypertensive medication use, total and high density lipoprotein (HDL) cholesterol, and CRP. A similar trend was observed for CIMT (age, race and gender-adjusted, p<0.001; multivariable-adjusted, p=0.014). Further analyses of race and gender subgroups showed that increasing quartiles of fibrinogen were associated with CAC and CIMT in all subgroups except black men. The prevalence of CAC was not associated with increasing quartiles of FVII, FVIII or vWF, suggesting they may be less involved in plaque progression. Conclusion An elevated fibrinogen concentration in persons aged 25 to 37 is independently associated with subclinical cardiovascular disease in the subsequent decade.

This study determined whether immunoassays of factors VII (FVII) and VIII (FVIII) and von Willebrand factor (vWF) in EDTA-anticoagulated plasma samples are comparable to bioassays and immunoassays of these factors in citrate-anticoagulated plasma. Blood from 40 healthy volunteers was collected in EDTA- and citrate-anticoagulant tubes and assayed using immunoassays (EDTA and citrate) and clotting assays (citrate). Linear regression analyses were performed and Pearson correlation coefficients recorded. The correlation coefficients (95% confidence intervals [CIs]) between levels in EDTA- and citrate-anticoagulated plasma samples were 0.893 (0.806–0.943) for FVII antigen (ag), 0.930 (0.870–0.962) for FVIIIag, 0.990 (0.981–0.995) for vWFag, and 0.949 (0.906–0.973) for vWF activity. Coefficients (CIs) were 0.811(0.668–0.896) for FVII coagulant activity (c) in citrate and FVIIag in EDTA and 0.608 (0.366–0.774) for FVIIIc in citrate and FVIIIag in EDTA. Measurements of FVII, FVIII, and vWF antigens in EDTA-anticoagulated plasma samples give values comparable to similar measurements in citrate-anticoagulated samples. Clotting activity, especially of FVIII, is less well correlated. Although antigen assays using EDTA are not recommended for patients with coagulopathies, they may be suitable for population-based studies.

Background and Purpose-To investigate associations of procoagulants (factor VII [FVII], FVIII, von Willebrand factor) with subclinical atherosclerosis, we examined participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study. Methods-Clotting factor assays were performed in 1254 participants 23 to 37 years of age (baseline) and repeated at ages 38 through 50 (follow-up). Carotid intima-media thickness (IMT) was measured at follow-up. Results-Baseline levels of procoagulants (%), mean (SD) were: FVII, 76 (18) Baseline FVIII was associated with greater internal carotid IMT in the total group, in whites, and in women after age adjustment but not multivariable adjustment. No associations were seen for von Willebrand factor. Conclusions-FVII is associated with common carotid IMT in young adults, but the strength of the association is modified by other cardiovascular disease risk factors, such as body mass index. FVIII is associated with internal carotid IMT only in age-adjusted analyses, and no associations were observed for von Willebrand factor. (Stroke.