Wildfire Variable Toxicity: Identifying Biomass Smoke Exposure Groupings through Transcriptomic Similarity Scoring

Abstract

The prevalence of wildfires continues to grow globally with exposures resulting in increased disease risk. Characterizing these health risks remains difficult due to the wide landscape of exposures that can result from different burn conditions and fuel types. This study tested the hypothesis that biomass smoke exposures from variable fuels and combustion conditions group together based on similar transcriptional response profiles, informing which wildfire-relevant exposures may be considered as a group for health risk evaluations. Mice (female CD-1) were exposed via oropharyngeal aspiration to equal mass biomass smoke condensates produced from flaming or smoldering burns of eucalyptus, peat, pine, pine needles, or red oak species. Lung transcriptomic signatures were used to calculate transcriptomic similarity scores across exposures, which informed exposure groupings. Exposures from flaming peat, flaming eucalyptus, and smoldering eucalyptus induced the greatest responses, with flaming peat grouping with the pro-inflammatory agent lipopolysaccharide. Smoldering red oak and smoldering peat induced the least transcriptomic response. Groupings paralleled pulmonary toxicity markers, though they were better substantiated by higher data dimensionality and resolution provided through -omic-based evaluation. Interestingly, groupings based on smoke chemistry signatures differed from transcriptomic/toxicity-based groupings. Wildfire-relevant exposure groupings yield insights into risk assessment strategies to ultimately protect public health.

Wildfire plume ageing in the Photochemical Large Aerosol Chamber (PHOTO-LAC)

“…14,15 Wildfire-related PM2.5 has been found to be more relevant for respiratory health than other sources, 16 but fuel composition and combustion conditions triggered different mutagenicity and lung toxicity observed in in vivo models. 17–19…”

“…14,15 Wildre-related PM2.5 has been found to be more relevant for respiratory health than other sources, 16 but fuel composition and combustion conditions triggered different mutagenicity and lung toxicity observed in in vivo models. [17][18][19] It is well known that biomass burning aerosols are rapidly transformed in the atmosphere ("atmospheric ageing") and increase in organic matter by oxidative gas-to-particle conversion, which is called secondary organic aerosol (SOA) formation. 20 However, in dense biomass burning plumes, the ambient level of hydroxyl radicals, the main atmospheric oxidant during daytime, decreases so other oxidants may increase in relative importance.…”

The Effects of Wildfire Smoke on Asthma and Allergy

“…As reviewed by Tuazon et al [ 53 ], potential mechanisms for which there is supporting evidence include alteration of Th1/Th2 immune balance, epigenetic modifications, oxidative stress, alterations in responses to infectious agents, disrupted epithelial barrier function in the respiratory tract, and coincident increases in wildfires and allergen exposure due to global warming. Additional recent literature in these areas is summarized below and in Table 2 [references [ 54 - 75 ]. While WFS-specific data are only starting to emerge, some recent experimental data from PM 2.5 exposure are also relevant to mechanistic hypotheses.…”

“…2022 Dec 6;56(23):17,131–17,142. [ 75 ] Mice exposed to variety of Wood smoke sources Other Flaming peat, flaming eucalyptus, smoldering eucalyptus result in lung transcriptomic changes similar to endotoxin WS wood smoke, PM 2.5 particulate matter ≤ 2.5 μm in diameter; PAH polycyclic aromatic hydrocarbons, TRAP traffic-related air pollution …”

“…Experimental studies have been published recently using animal or cell culture models. Koval and colleagues [ 75 ] assessed lung transcriptomic signatures in female mice exposed to biomass smoke condensates produced from a variety of biogenic sources relevant to wildfires. While exposure to emission condensates from smoldering red oak and smoldering peat caused moderate transcriptomic changes, exposures from flaming peat, flaming eucalyptus, and smoldering eucalyptus induced the greatest transcriptomic responses, with similarity to the pro-inflammatory agent lipopolysaccharide.…”