Fine particulate matter (PM2.5) is a major air pollutant linked to respiratory diseases. Its inhalation leads to lung injury, primarily through inflammatory responses and oxidative stress. Omega-3 polyunsaturated fatty acids (ω-3 PUFAs), particularly EPA and DHA, possess anti-inflammatory and antioxidant properties, making them potential therapeutic agents. The gut microbiota plays a crucial role in maintaining health and is influenced by both environmental exposures (like PM2.5) and diet (ω-3 PUFA intake). The gut-lung axis highlights the bidirectional communication between the gut and lung, suggesting that manipulating the gut microbiota may influence lung health. This study hypothesized that ω-3 PUFA supplementation protects against PM2.5-induced lung injury by modifying the gut microbiota and lung metabolic profile. The aim was to evaluate the efficacy of ω-3 PUFA supplementation on PM2.5-induced lung injury and explore the underlying mechanisms through untargeted LC-MS metabolomics and 16S rRNA gene sequencing.

Numerous studies link short-term and long-term PM2.5 exposure to increased respiratory diseases such as COPD, asthma, and lung cancer. While the mechanisms aren't fully understood, inflammation and oxidative stress are considered crucial. ω-3 PUFAs have shown benefits in various health contexts due to their anti-inflammatory and antioxidant actions. While some research suggests ω-3 PUFAs alleviate PM2.5-induced lung injury, the precise mechanisms require further investigation. The gut microbiota's role in health and disease, its influence on the gut-lung axis, and its modification by PM2.5 exposure and ω-3 PUFA intake are increasingly recognized, making this a relevant area of study.

Male C57BL/6 N mice were divided into four groups (n=15 per group): control, PM2.5-exposed, ω-3 PUFA-supplemented, and ω-3 PUFA-supplemented + PM2.5-exposed. The ω-3 PUFA-supplemented groups received an ω-3 PUFA-enriched diet (21 g/kg) for six weeks. PM2.5 exposure was achieved through intratracheal instillation during weeks 5 and 6. After two weeks of PM2.5 exposure, mice were sacrificed, and bronchoalveolar lavage fluid (BALF), serum, lung tissue, and colon content samples were collected. Histological analysis assessed lung injury. Enzyme-linked immunosorbent assays (ELISAs) measured inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-17) in BALF and serum. Oxidative stress markers (ROS, MDA, GSH, T-SOD) were also measured. Untargeted LC-MS/MS metabolomics analyzed lung tissue metabolites, and 16S rRNA gene sequencing determined gut microbiota composition. Statistical analyses included Student's t-tests, ANOVA, and correlation tests.

ω-3 PUFA supplementation significantly ameliorated PM2.5-induced lung histopathological injury, reducing inflammation and oxidative stress. Levels of inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-17) were significantly lower in the ω-3 PUFA-supplemented + PM2.5 group compared to the PM2.5-exposed group. Similarly, oxidative stress markers showed significant improvements with ω-3 PUFA supplementation. LC-MS/MS metabolomics revealed significant differences in lung metabolite profiles between groups, with ω-3 PUFA supplementation reversing many of the PM2.5-induced changes. Pathway enrichment analysis implicated VEGF signaling, asthma, arachidonic acid metabolism, and α-linolenic acid metabolism. 16S rRNA sequencing showed that PM2.5 exposure decreased gut microbiota diversity, an effect partially mitigated by ω-3 PUFA supplementation. Specific changes in the relative abundance of various bacterial phyla and genera were observed. Correlation analysis revealed associations between specific gut microbiota changes and altered lung metabolites.

The findings support the hypothesis that ω-3 PUFA supplementation protects against PM2.5-induced lung injury. The observed reductions in inflammation and oxidative stress are consistent with the known anti-inflammatory and antioxidant properties of ω-3 PUFAs. The alterations in lung metabolites and gut microbiota further suggest mechanisms by which ω-3 PUFAs exert their protective effects. The modulation of arachidonic acid metabolism and α-linolenic acid metabolism is particularly noteworthy, given their roles in inflammation. The interaction between gut microbiota and lung metabolism highlights the gut-lung axis's importance in PM2.5-induced lung injury.

ω-3 PUFA supplementation effectively mitigates PM2.5-induced lung injury in mice, demonstrating potential preventive and therapeutic value. This protective effect is linked to reduced inflammation and oxidative stress, altered lung metabolic profiles, and modulation of the gut microbiota. Future research could focus on identifying specific microbial species and metabolites involved in the gut-lung axis, and explore the clinical translation of ω-3 PUFA supplementation for PM2.5-related respiratory diseases.

The study used intratracheal instillation of PM2.5, which may not perfectly replicate human inhalation exposure. The study did not analyze specific components of ambient PM2.5 responsible for the observed effects, nor did it investigate the potential roles of soybean polyphenols. Shotgun metagenomics could provide more comprehensive information on the gut microbiota's function. The pathway analysis was exploratory and didn't account for effect direction. Further verification of the correlation between key microbiota and metabolites is needed.