Burn Pit-Related Smoke Activates Respiratory Epithelial Oxidative Stress Response Pathways
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Background and Purpose:
Health effects of inhaled smoke from military burn pits include increased incidences of cardiopulmonary diseases, sinonasal disease, and cancers of the nervous system. Burn pit smoke is a complex mixture of particulate matter (PM), volatile organic compounds (VOCs), metals, PAHs, and other chemicals, but the role of specific smoke components on disease incidence or severity following exposure is not well understood. Our previous work has shown that the smoldering burn pit emissions reduced breathing frequency and minute volumes compared to clean air controls with filtered emissions mitigating the physiological response. The goal of this study was to characterize nasal epithelial transcriptomic changes that may predict adverse outcomes following short-term exposures to the particulate and gaseous phases of simulated burn pit smoke.
Methods:
Synthetic materials representative of wastes found in military burn pits (plastic (PL), plywood (PW), cardboard (CB), or a mixture (MX) of these 3 materials) were burned under smoldering conditions (510 °C, 0.84 modified combustion efficiency) to generate each atmosphere consisting of ~5-12 ppmV VOCs and ~40 mg PM/m3 (MMAD of all atmospheres < 2.5 mm). Female Balb/cJ mice (n = 8/group) were exposed nose-only to clean air only (CON), whole smoke from the 4 different combustion types, or filtered smoke without PM (PM ¿ 0.2 mg/m3) for 1 hr on 2 consecutive days, and samples of nasal septal epithelium were collected 4 hr after the final exposure. RNA was isolated from homogenized nasal tissue and whole transcriptome was analyzed by Illumina NovaSeq RNA sequencing, 30 million reads per sample. DESeq2 contrast function was used to compare differential gene expression of each waste group receiving whole smoke, with the CON group, filtered to require genes to have 5 or more samples with counts of 20 or more. Ingenuity Pathway Analysis (IPA) and Gene Set Enrichment Analysis (GSEA) were performed to determine the pathways impacted by exposure conditions and the relative expression levels of whole smoke compared to filtered smoke exposure.
Results:
Overall, the differential analysis unsupervised hierarchical clustering showed a uniform basal expression for the CON group, while the whole smoke groups provided different clustering. In comparison with the CON group, all whole smoke exposure groups showed modest gene expression changes in the septal nasal epithelium; MX (28 up, 51 down), PL (57 up, 39 down), CB (88 up, 12 down), and PW (141 up 29 down). By averaging the responses, the baseline control exposed animals differentiate themselves further from the exposure groups. Notably, the CB exposure shows a unique differential gene expression pattern compared with the other exposures, highlighted by the robust induction of NFE2L2/NRF2 oxidative stress response pathways. While MX and PL exposure groups also exhibit strong oxidative response, the PW exposed group does not. Comparing filtered vs whole smoke exposures, the CB and MX whole smoke exposure showed similarly clustered expression profiles with whole smoke upregulating more of the stress response pathways when compared to filtered smoke.
Conclusion:
We determine that gene expression, particularly in pathways associated with oxidative stress response, is significantly altered in the septal nasal epithelium following acute exposure to burn pit combustion emissions with greater induction of transcriptional changes in whole smoke compared to filtered only for certain material types.
(This abstract does not represent U.S. EPA policy; DoD award #W811XWH-18-1-0731 to I.J.)