Academic journal article Environmental Health Perspectives

Medium-Term Exposure to Traffic-Related Air Pollution and Markers of Inflammation and Endothelial Function

Academic journal article Environmental Health Perspectives

Medium-Term Exposure to Traffic-Related Air Pollution and Markers of Inflammation and Endothelial Function

Article excerpt

BACKGROUND: Exposure to traffic-related air pollution (TRAP) contributes to increased cardiovascular risk. Land-use regression models can improve exposure assessment for TRAP.

OBJECTIVES: We examined the association between medium-term concentrations of black carbon (BC) estimated by land-use regression and levels of soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular cell adhesion molecule-1 (sVCAM-1), both markers of inflammatory and endothelial response.

METHODS: We studied 642 elderly men participating in the Veterans Administration (VA) Normative Aging Study with repeated measurements of sICAM-1 and sVCAM-1 during 1999-2008. Daily estimates of BC exposure at each geocoded participant address were derived using a validated spatio-temporal model and averaged to form 4-, 8-, and 12-week exposures. We used linear mixed models to estimate associations, controlling for confounders. We examined effect modification by statin use, obesity, and diabetes.

RESULTS: We found statistically significant positive associations between BC and sICAM-1 for averages of 4, 8, and 12 weeks. An interquartile-range increase in 8-week BC exposure (0.30 [micro]g/[m.sup.3]) was associated with a 1.58% increase in sICAM-1 (95% confidence interval, 0.18-3.00%). Overall associations between sVCAM-1 and BC exposures were suggestive but not statistically significant. We found a significant interaction with diabetes--where diabetics were more susceptible to the effect of BC--for both sICAM-1 and sVCAM-1. We also observed an interaction with statin use, which was statistically significant for sVCAM-1 and suggestive for sICAM-1. We found no evidence of an interaction with obesity.

CONCLUSION: Our results suggest that medium-term exposure to TRAP may induce an increased inflammatory/endothelial response, especially among diabetics and those not using statins.

KEY WORDS: adhesion molecules, air, cardiovascular, environmental, outdoor air, roadway proximity. Environ Health Perspect 119:481-486 (2011). doi:10.1289/ehp.1002560 [Online 24 February 2011]

There is strong epidemiological evidence that short-term air pollution exposure (i.e., < 24 hr to 3 weeks) is related to mortality and other cardiovascular events (Brook et al. 2010). Much of this evidence involves exposure to ambient particulate matter (PM) with aerodynamic diameter [less than or equal to] 2.5 [micro]m ([PM.sub.2.5]), which comprises many components and varies regionally. Contributions of specific components and sources to these effects are not well understood but are critical for informing the development of regulations.

Short-term exposure studies often use stationary monitors to estimate exposure in a nearby region. However, specific components of traffic-related air pollution (TRAP) vary substantially within cities, and traffic variables may contribute to this variation (Brauer et al. 2003; Clougherty et al. 2008; Kinney et al. 2000). This suggests that a geographically based approach could substantially improve assessment of black carbon (BC) exposure.

Long-term exposure to TRAP (i.e., averages [greater than or equal to] 1 year) has also been associated with cardiovascular mortality, often based on studies using nitrogen dioxide as a surrogate for traffic pollutants and spatial modeling of exposures (Brunekreef et al. 2009; Gehring et al. 2006; Yorifuji et al. 2010). In a Boston, Massachusetts-area case-crossover analysis, we reported an association between mortality and BC exposure on the day before death, using spatiotemporally modeled BC exposure estimates as a marker of TRAP (Maynard et al. 2007).

Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) are markers of inflammation and endothelial function that are expressed on cell surfaces and are also found in soluble form in the plasma (sICAM-1 and sVCAM-1). These markers are independently and jointly associated with increased risk of cardiovascular disease (Albert and Ridker 1999; Pradhan et al. …

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