Associations of particulate matter exposures with brain cortical thickness and white matter hyperintensities: effect modification by c-reactive protein

Abstract

Background and aim: Numerous studies have shown the effect of particulate matter exposure on brain imaging markers. However, little evidence exists about whether the effect differs by the level of systemic inflammation, a mechanism of neurotoxicity of particulate matter. We investigated whether the level of c-reactive protein (CRP; a marker of systemic inflammation) modifies the associations of particulate matter exposures with brain cortical thickness and white matter hyperintensities (WMH). Methods: Adults with no dementia or stroke were recruited. Concentrations of particulate matter ≤10 µm in diameter (PM10) and ≤2.5 µm (PM2.5) at each participant’s home address were estimated. Mean cortical thickness (n=874) and WMH volumes (n=397) were estimated from brain magnetic resonance images. We built generalized linear and logistic regression models for mean cortical thickness and WMH volumes (higher versus lower than median), respectively. Significance of the CRP group (higher versus lower than median) difference in the association was expressed as p for interaction. Results: Particulate matter exposures were significantly associated with a reduced mean cortical thickness only in the higher CRP group among men (p for interaction=0.012 for PM10 and 0.006 for PM2.5). A 10 μg/m3 increase in PM10 was associated with having higher volumes of total WMH (odds ratio, 1.67; 95% confidence interval, 1.01–2.76) and periventricular WMH (1.81; 1.10–2.98). A 1 μg/m3 increase in PM2.5 was associated with having a higher volume of periventricular WMH (odds ratio, 1.53; 95% confidence interval, 1.01–2.33). These associations did not significantly differ by the level of CRP. Conclusions: Particulate matter exposures were associated with a reduced mean cortical thickness in men with a high level of systemic inflammation. Particulate matter exposures were associated with having a high volume of WMH, with no evidence of effect modification by the level of systemic inflammation. Keywords: air pollution; neuroimaging; inflammation