Mechanisms of 15-Epi-LXA4-Mediated HO-1 in Cytoprotection Following Inflammatory Injury.

INTRODUCTION: Heme oxygenase-1 (HO-1) is a protective protein in oxidative stress response. LXA4 is an "inflammatory braking signal" that is widely studied at present. The purpose of this study was to elucidate that LXA4 can protect cells by inducing HO-1 in human pulmonary microvascular endothelial cells (HPMECs) as in vitro model to explain acute lung injury after severe acute pancreatitis. METHODS: This study was performed in two parts: (1) To investigate the mechanisms of lipoxin A4-induced HO-1 expression in vitro, the study subjects were divided into four groups: a control group, LXA4 group (50 ng/mL LXA4), inhibitor group (50 ng/mL LXA4 + 20 µM LY294002 or 50 ng/mL LXA4 + 2 nmol/mL Bis II), and agonist group (50 ng/mL insulin-like growth factor 1, PMA). Western blotting was used to detect the expression of p-Akt, Akt, protein kinase C (PKC), p-Nrf2, Nrf2, and Keap1, and the location of Nrf2 was detected using immunofluorescence. The activation of antioxidant responsive element induced by Nrf2 was detected using Electrophoretic Mobility Shift Assay and (2) to investigate the cytoprotection of HO-1 induced by LXA4 in vitro, the subjects were divided into four groups: a control group, tumor necrosis factor α (TNF-α) group (50 ng/mL), LXA4 group (50 ng/mL TNF-α + 50 ng/mL LXA4), and Zinc protoporphyrin IX group (pretreated with 0.5 µM Zinc protoporphyrin IXfor 12 h, followed by 50 ng/mL TNF-α + 50 ng/mL LXA4). BCECF/AM-labeled THP-1 cells were used to analyze the adhesion of HPMECs, and a mitochondrial membrane potential assay kit with JC-1 was used to analyze the apoptosis of HPMECs. RESULTS: In part one, (1) LXA4 upregulated the expression of HO-1 in a dose-dependent manner and (2) LXA4 activated the PI3K/Akt and PKC pathways and modulated the phosphorylation and subsequent depolymerization of Nrf2 from Keap1, promoting the translocation of Nrf2 to the nucleus. In part two, (1) LXA4 reversed the changes in mitochondrial membrane potential to alleviate apoptosis in HPMECs and (2) LXA4 attenuated the adhesion of HPMECs induced by TNF-α. CONCLUSIONS: LXA4 can activate the PI3K/Akt and PKC pathways and induce the phosphorylation of Nrf2, resulting in the upregulation of HO-1. In addition, LXA4 alleviates adhesion and protects mitochondrial function by upregulating the expression of HO-1, which exerts cytoprotection in severe acute pancreatitis-induced lung injury.