Chicoric Acid Presented NLRP3-Mediated Pyroptosis through Mitochondrial Damage by PDPK1 Ubiquitination in an Acute Lung Injury Model

Chicoric acid (CA), a functional food ingredient, is a caffeic acid derivative that is mainly found in lettuce, pulsatilla, and other natural plants. However, the anti-inflammatory effects of CA in acute lung injury (ALI) remain poorly understood. This study was conducted to investigate potential drug usage of CA for ALI and the underlying molecular mechanisms of inflammation. C57BL/6 mice were given injections of liposaccharide (LPS) to establish the in vivo model. Meanwhile, BMDM cells were stimulated with LPS+ATP to build the in vitro model. CA significantly alleviated inflammation and oxidative stress in both the in vivo and in vitro models of ALI through the inhibition of NLR family pyrin domain-containing 3 (NLRP3)-mediated pyroptosis. In addition, CA attenuated mitochondrial damage to suppress NLRP3-mediated pyroptosis in the in vivo and in vitro models of ALI by suppressing the production of reactive oxygen species (ROS) via inhibiting the Akt/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. CA inhibited the interaction between Akt at T308 and phosphoinositide-dependent kinase-1 (PDPK1) at S549, thus promoting the phosphorylation of the Akt protein. Furthermore, CA directly targeted the PDPK1 protein and accelerated PDPK1 ubiquitination, indicating that 91-GLY, 111-LYS, 126-TYR, 162-ALA, 205-ASP, and 223-ASP might be responsible for the interaction between PDPK1 and CA. In conclusion, CA from Lettuce alleviated NLRP3-mediated pyroptosis in the ALI model through ROS-induced mitochondrial damage by activating Akt/Nrf2 pathway via PDPK1 ubiquitination. The present study suggests that CA might be a potential therapeutic drug to treat or prevent ALI in pneumonia or COVID-19.