Raloxifene prevents intracellular invasion of pathogenic bacteria through modulation of cell metabolic pathways

Background: Pathogenic bacteria can invade and survive inside phagocytic and non-phagocytic cells and use them as a sanctuary against antibiotics. Induction of various host protective mechanisms, including autophagy, can be a novel and effective method to combat intracellular bacteria. Recent studies report that raloxifene, a selective oestrogen receptor modulator, can induce cellular autophagy. Objectives: To demonstrate the effect of raloxifene on intracellular invasion and proliferation of pathogenic bacteria and investigate raloxifene-induced metabolic changes in host cells. Methods: Autophagic induction was determined by the extent of nuclear fragmentation and expression levels of the LC3B protein. Intracellular invasion of MRSA strains into A549 lung epithelial cells and invasion of Mycobacterium abscessus into RAW264.7 macrophages were assessed by invasion and proliferation assays. Changes in host cell metabolism were examined by transcriptomic profiling using RNA sequencing. Results: Our data demonstrate increased autophagy in cells upon raloxifene treatment, which contributed to prevention of bacterial invasion and proliferation. Transcriptomic profiling of host cells revealed changes in cholesterol-related pathways and consequent increases in oxidative stress-related genes and in autophagic induction through the TRIM and GABA pathways. Conclusions: Our results demonstrate raloxifene's potential as a broad-spectrum antibacterial agent through autophagic induction in host cells and prevention of intracellular invasion and proliferation of pathogenic bacteria.