Short-interval exposure to ambient fine particulate matter (PM2.5) exacerbates the susceptibility of pulmonary damage in setting of lung ischemia-reperfusion injury in rodent: Pharmacomodulation of melatonin

This study tested the hypothesis that exposure to ambient fine particulate matter (PM _2.5 ) pollution increased susceptibility of rat lung to damage from acute ischemia-reperfusion (IR) injury that was reversed by melatonin (Mel) treatment. Male-adult SD rats (n = 30) were categorized into group 1 (normal control), group 2 (PM _2.5 only), group 3 (IR only at day 8 after PM _2.5 exposure), group 4 (PM _2.5 + IR) and group 5 (PM _2.5 + IR + Mel), and all animals were sacrificed by day 10 after PM _2.5 exposure. Oxygen saturation (%) was significantly higher in group 1 than in other groups and significantly lower in group 4 than in groups 2, 3 and 5 but it did not differ among the latter three groups (p < 0.01). Pulmonary protein expressions of inflammation (MMP-9/TNF-α/NF-kB), oxidative stress (NOX-1/NOX-2/oxidized protein), apoptosis (mitochondrial-Bax/caspase-3/PARP) and fibrosis were lowest in group 1, highest in group 4, significantly higher in group 5 than in groups 2 and 3 (all p < 0.0001), but they did not differ between groups 2 and 3. Inflammatory cell infiltration in lung parenchyma, specific inflammatory cell surface markers (CD14+, F4/88+), allergic inflammatory cells (IgE+, eosinophil+), number of goblet cells, thickness of tracheal epithelial layer and fibrotic area exhibited an identical pattern of protein expressions to inflammation among the five groups (all p < 0.0001). In conclusion, lung parenchymal damage and a rigorous inflammatory response were identified in rodent even with short-term PM _2.5 exposure.