Citrulline protects against LPS‑induced acute lung injury by inhibiting ROS/NLRP3‑dependent pyroptosis and apoptosis via the Nrf2 signaling pathway

Acute lung injury (ALI) is a common complication in patients with sepsis and is accompanied by high mortality. The present study aimed to investigate if the organic compound citrulline has a protective against lipopolysaccharide (LPS)-stimulated ALI and its potential mechanisms. ALI was induced in mice by intraperitoneal (i.p.) injection of LPS (10 mg/kg). Citrulline (1 g/kg/day) was administrated i.p. 7 days prior to LPS injection. Mouse lung vascular endothelial cells (MLVECs) were divided into five groups: Control, LPS, LPS + Cit, LPS + N-acetyl-L-cysteine (NAC) and LPS + Cit + ML385. Lung injury was determined by morphology changes. Apoptosis and pyroptosis were detected using western blot analysis and immunofluorescence. The present results indicated that citrulline can significantly attenuate ALI. Citrulline pretreatment decreased the expression of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome and decreased pyroptosis and apoptosis. Intervention with the total reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine attenuated NLRP3 inflammasome-associated pyroptosis and apoptosis in LPS-treated MLVECs. Citrulline pretreatment inhibited pyroptotic cell death and apoptosis induced by LPS. Citrulline decreased accumulation of intracellular ROS and activated the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. Furthermore, the Nrf2 inhibitor ML385 reversed ROS generation, NLRP3 inflammasome-mediated pyroptosis and apoptosis suppressed by citrulline. In summary, the present data demonstrated that citrulline may confer protection against ALI via inhibition of ROS/NLRP3 inflammasome-dependent pyroptosis and apoptosis via the Nrf2 signaling pathway.