Associations of Particulate Matter Exposures With Brain Gray Matter Thickness and White Matter Hyperintensities: Effect Modification by Low-Grade Chronic Inflammation

Association between air pollution exposure and brain cortical thickness throughout the lifespan: A systematic review

Increasing research has focused on the impact of air pollution on brain health. As the prevalence of air pollution is increasing alongside other environmental harms, the importance of studying the effects of these changes on human health has become more significant. Additionally, gaining insight into how air pollution exposure, measured at different points in the lifespan, can affect brain structure is critical, as this could be a precursor to cognitive decline later in life. The purpose of this review was to synthesize the literature on the association between air pollutant exposure and cortical thickness, a structural change with known associations with later cognition and neurodegenerative disease. After screening, twelve studies were included in this systematic review. Across a majority of studies, results suggest significant associations between increasing air pollution exposure and decreases in cortical thickness, primarily in areas such as prefrontal cortex, precuneus, and temporal regions of the brain. These results did differ somewhat between age groups and different air pollutants, with the most prominent results being found with exposure to PM2.5, the smallest particulate matter size included in the review. In the future, it is important to continue studying cortical thickness as it is essential to brain functioning and can be influential in disease progression. Furthermore, conducting more longitudinal studies in which air pollution is measured as a cumulation throughout the lifespan would help elucidate when exposure is most impactful and when brain structural changes become observable.

Correlation of Disease Severity, Proinflammatory Cytokines, and Reduced Brain Gray Matter Volumes in Patients with Atopic Dermatitis

Background: Atopic dermatitis (AD) is a chronic inflammatory skin disease. However, few studies have investigated brain changes associated with chronic inflammation. We hypothesized that chronic inflammation might be related to brain structural alterations in patients with AD. Objectives: To investigate the association between disease severity (Eczema Area and Severity Index [EASI]), proinflammatory cytokines, and differences in brain gray matter (GM) volume in patients with AD. Methods: Nineteen patients with AD and 19 age- and sex-matched healthy subjects were enrolled. All participants underwent clinical assessment and brain magnetic resonance imaging. Voxel-based morphometry was performed to analyze GM volume differences. Results: Patients with AD exhibited significantly decreased GM volume in many brain regions, such as bilateral precentral gyrus, right frontal pole, and right middle temporal gyrus (P < 0.001), compared with healthy subjects. Notably, in patients with AD, the GM volume in right middle temporal gyrus was negatively associated with both EASI score and proinflammatory cytokines (sIL-2R [soluble interleukin 2 receptor] and TNF-α receptor-1), whereas the GM volume in left precentral gyrus was negatively associated with both EASI score and proinflammatory cytokines (sIL-2R and CRP). Conclusion: Patients with AD demonstrated significant brain GM volume reduction in many brain regions, which is related to disease severity and proinflammatory cytokines.

Associations of long-term exposure to low-level PM2.5 and brain disorders in 260,922 middle-aged and older adults

Long-term exposure to high-level ambient PM2.5 was associated with increased risks of brain disorders, while the associations remain uncertain when the exposure is lower than current air quality standards in numerous countries. This study aimed to assess the effects of PM2.5 exposure on the brain system in the population with annual mean concentrations ≤15 μg/m3. We analyzed data from 260,922 participants without preexisting brain diseases at baseline in the UK Biobank. The geographical distribution of PM2.5 in 2010 was estimated by a land use regression model and linked with individual residential address. We investigated associations of ambient PM2.5 with incident neurological (dementia, Parkinson's diseases [PD], epilepsy, and migraine) and psychiatric (major depressive disorder [MDD] and anxiety disorder) diseases through Cox proportional hazard models. We further estimated the links with brain imaging phenotypes by neuroimaging analysis. Results showed that in the population with PM2.5 concentrations ≤15 μg/m3, each interquartile range (IQR, 1.28 μg/m3) increment in PM2.5 was related to incidence risks of dementia, epilepsy, migraine, MDD, and anxiety disorder with hazard ratios of 1.08 (95% confidence interval [CI]: 1.03, 1.13), 1.12 (1.05, 1.20), 1.07 (1.00, 1.13), 1.06 (1.03, 1.09), and 1.05 (1.02, 1.08), respectively. We did not observe a significant association with PD. The association with dementia was stronger among the population with poor cardiovascular health (measured by Life's Essential 8) than the counterpart (P for interaction = 0.037). Likewise, per IQR increase was associated with specific brain imaging phenotypes, including volumes of total brain (β = -0.036; 95% CI: -0.050, -0.022), white matter (-0.030; -0.046, -0.014), grey matter (-0.030; -0.042, -0.017), respectively. The findings suggest long-term exposure to ambient PM2.5 at low-level still has an adverse impact on the neuro-psychiatric systems. The brain-relevant epidemiological assessment suggests that each country should update the standard for ambient PM2.5 following the World Health Organization Air Quality Guidelines 2021.