The Combination of LPS and Melatonin Induces M2 Macrophage Apoptosis to Prevent Lung Cancer

Abstract

Background and objectives: Lasting LPS stimulation changes macrophages toward the M2 phenotype therefore resulting in immunodepression. Melatonin can improve sleep, adjust the time difference, regulate immunity, and anti-tumor. This study is to observe whether melatonin can induce M2 macrophage apoptosis to reverse lasting LPS-induced immunodepression for lung cancer prevention and explore the possible mechanism. Methods:The effects of LPS alone or in combination with melatonin on macrophage phenotypes were assessed by surface markers, morphological changes, cytokines, autophagy, and autophagic efflux. The anti-cancer effect was evaluated in the lung carcinogenic model and lung cancer allograft model. Melatonin-related targets and pathways were predicted by network pharmacology.Results: Single LPS stimulation polarized macrophages to M1 phenotype, whereas LPS stimulation lasting for 7d polarized macrophages to M2 phenotype. However, combination treatment of lasting LPS and 10 µM melatonin inhibited the polarization of macrophages towards an M2-like phenotype and exerted a continuous antitumor effect. In the urethane-induced lung carcinoma model, long-lasting LPS administration (>4 times) facilitated macrophage polarization toward the M2 phenotype and promoted lung carcinogenesis, which was abrogated by macrophage depletion, while melatonin alone or in combination with lasting LPS could decrease M2-like macrophages and prevented carcinogenesis. In the Lewis lung cancer allograft model, melatonin decreased M2 macrophages and promoted the tumor-suppressing effect of short-term LPS administration (<4 times). Network pharmacology indicated that melatonin regulates macrophages by targeting the multi-protein network.Conclusions: Melatonin as a key maintainer of macrophage phenotype can induce LPS-stimulated M2 macrophage apoptosis to reverse system immunodepression for lung cancer prevention.