Concentration-dependent alterations in the human plasma proteome following controlled exposure to diesel exhaust.

Traffic-related air pollution (TRAP) exposure is associated with systemic health effects, which can be studied using blood-based markers. Although we have previously shown that high TRAP concentrations alter the plasma proteome, the concentration-response relationship between blood proteins and TRAP is unexplored in controlled human exposure studies. We aimed to identify concentration-dependent plasma markers of diesel exhaust (DE), a model of TRAP. Fifteen healthy non-smokers were enrolled into a double-blinded, crossover study where they were exposed to filtered air (FA) and DE at 20, 50 and 150 µg/m3 PM2.5 for 4h, separated by ≥ 4-week washouts. We collected blood at 24h post-exposure and used label-free mass spectrometry to quantify proteins in plasma. Proteins exhibiting a concentration-response, as determined by linear mixed effects models (LMEMs), were assessed for pathway enrichment using WebGestalt. Top candidates, identified by sparse partial least squares discriminant analysis and LMEMs, were confirmed using enzyme-linked immunoassays. Thereafter, we assessed correlations between proteins that showed a DE concentration-response and acute inflammatory endpoints, forced expiratory volume in 1 s (FEV1) and methacholine provocation concentration causing a 20% drop in FEV1 (PC20). DE exposure was associated with concentration-dependent alterations in 45 proteins, which were enriched in complement pathways. Of the 9 proteins selected for confirmatory immunoassays, based on complementary bioinformatic approaches to narrow targets and availability of high-quality assays, complement factor I (CFI) exhibited a significant concentration-dependent decrease (-0.02 µg/mL per µg/m3 of PM2.5, p = 0.04). Comparing to FA at discrete concentrations, CFI trended downward at 50 (-2.14 ± 1.18, p = 0.08) and significantly decreased at 150 µg/m3 PM2.5 (-2.93 ± 1.18, p = 0.02). CFI levels were correlated with FEV1, PC20 and nasal interleukin (IL)-6 and IL-1ß. This study details concentration-dependent alterations in the plasma proteome following DE exposure at concentrations relevant to occupational and community settings. CFI shows a robust concentration-response and association with established measures of airway function and inflammation.

Exposure to diesel exhaust alters the functional metagenomic composition of the airway microbiome in former smokers.

The lung microbiome plays a crucial role in airway homeostasis, yet we know little about the effects of exposures such as air pollution therein. We conducted a controlled human exposure study to assess the impact of diesel exhaust (DE) on the human airway microbiome. Twenty-four participants (former smokers with mild to moderate COPD (N = 9), healthy former smokers (N = 7), and control healthy never smokers (N = 8)) were exposed to DE (300 µg/m3 PM2.5) and filtered air (FA) for 2 h in a randomized order, separated by a 4-week washout. Endobronchial brushing samples were collected 24 h post-exposure and sequenced for the 16S microbiome, which was analyzed using QIIME2 and PICRUSt2 to examine diversity and metabolic functions, respectively. DE exposure altered airway microbiome metabolic functions in spite of statistically stable microbiome diversity. Affected functions included increases in: superpathway of purine deoxyribonucleosides degradation (pathway differential abundance 743.9, CI 95% 201.2 to 1286.6), thiazole biosynthesis I (668.5, CI 95% 139.9 to 1197.06), and L-lysine biosynthesis II (666.5, CI 95% 73.3 to 1257.7). There was an exposure-by-age effect, such that menaquinone biosynthesis superpathways were the most enriched function in the microbiome of participants aged >60, irrespective of smoking or health status. Moreover, exposure-by-phenotype analysis showed metabolic alterations in former smokers after DE exposure. These observations suggest that DE exposure induced substantial changes in the metabolic functions of the airway microbiome despite the absence of diversity changes.

Inhaled diesel exhaust alters the allergen-induced bronchial secretome in humans.

Diesel exhaust (DE) is a paradigm for traffic-related air pollution. Human adaptation to DE is poorly understood and currently based on oversimplified models. DE promotes allergic responses, but protein expression changes mediated by this interaction have not been systematically investigated. The aim of this study was to define the effect of inhaled DE on allergen-induced proteins in the lung.We performed a randomised and blinded controlled human crossover exposure study. Participants inhaled filtered air or DE; thereafter, contralateral lung segments were challenged with allergen or saline. Using label-free quantitative proteomics, we comprehensively defined DE-mediated alteration of allergen-driven secreted proteins (secretome) in bronchoalveolar lavage. We further examined expression of proteins selected from the secretome data in independent validation experiments using Western blots, ELISA and immunohistochemistry.We identified protein changes unique to co-exposure (DE+allergen), undetected with mono-exposures (DE or allergen alone). Validation studies confirmed that specific proteins (e.g. the antimicrobial peptide cystatin-SA) were significantly enhanced with DE+allergen compared to either mono-exposure.This study demonstrates that common environmental co-exposures can uniquely alter protein responses in the lungs, illuminating biology that mono-exposures cannot. This study highlights the value of complex human in vivo models in detailing airway responses to inhaled pollution.