Anti-inflammatory effect of chlorogenic acid in Klebsiella pneumoniae-induced pneumonia by inactivating the p38MAPK pathway

Pneumonia is an inflammation-related respiratory infection and chlorogenic acid (CGA) possesses a wide variety of bioactive properties, such as anti-inflammation and anti-bacteria. This study explored the anti-inflammatory mechanism of CGA in Klebsiella pneumoniae (Kp)-induced rats with severe pneumonia. The pneumonia rat models were established by infection with Kp and treated with CGA. Survival rates, bacterial load, lung water content, and cell numbers in the bronchoalveolar lavage fluid were recorded, lung pathological changes were scored, and levels of inflammatory cytokines were determined by enzyme-linked immunosorbent assay. RLE6TN cells were infected with Kp and treated with CGA. The expression levels of microRNA (miR)-124–3p, p38, and mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MK2) in lung tissues and RLE6TN cells were quantified by real-time quantitative polymerase chain reaction or Western blotting. The binding of miR-124–3p to p38 was validated by the dual-luciferase and RNA pull-down assays. In vitro, the functional rescue experiments were performed using miR-124–3p inhibitor or p38 agonist. Kp-induced pneumonia rats presented high mortality, increased lung inflammatory infiltration and the release of inflammatory cytokines, and enhanced bacterial load, while CGA treatment improved rat survival rates and the above situations. CGA increased miR-124–3p expression, and miR-124–3p inhibited p38 expression and inactivated the p38MAPK pathway. Inhibition of miR-124–3p or activation of the p38MAPK pathway reversed the alleviative effect of CGA on pneumonia in vitro. CGA upregulated miR-124–3p expression and inactivated the p38MAPK pathway to downregulate inflammatory levels, facilitating the recovery of Kp-induced pneumonia rats.