Glycyrrhetinic acid alleviates acute lung injury by PI3K/AKT suppressing macrophagic Nlrp3 inflammasome activation

Glycyrrhetinic acid (GA), a triterpene saponins, has been widely proven to have multiple medicinal properties. Our study aimed to figure out the protective effect of GA on acute lung injury (ALI) and the underlying mechanism. The LPS-induced ALI model mice were intratracheally administrated with 10 mg/kg LPS. Pretreatment with GA (10, 20, 40 mg/kg, i.g.) ameliorated acute lung injury pathological damage, macrophage infiltration and lung edema. In the lung tissue, immunofluorescence (IF) and Immunohistochemistry (IHC) were performed to detect macrophage Nod-like receptor 3 (Nlrp3) inflammasome activation and interleukin-1β (IL-1β) protein expression. In macrophages, the co-localization of Nlrp3 with caspase-1 and Nlrp3 with ASC were assessed by IF. The translational and transcriptional level of Nlrp3, cle-caspase-1 and apoptosis-associated speck-like protein containing CARD (ASC), were examined by Western blot and Real time PCR (RT-PCR). The protein expression of Cle-caspase-1 was remarkably suppressed via sh-Nlrp3 transfection compared with LPS groups. GA notably attenuated ALI by inhibiting Nlrp3 formation and activation. Furthermore, GA downregulated the production of reactive oxygen species (ROS) and the phosphorylation level of PI3K and AKT in macrophages. These findings indicate that GA ameliorated ALI in mice by suppressing the activation of Nlrp3 inflammasome which may be mediated by ROS-PI3K/AKT pathway. GA may serve as a promising agent for the attenuation of ALI-related inflammation and pathology.