The Effect of Magnesium Sulfate on Lipopolysaccharide Tolerance in Human Monocytes

Abstract

Binding of lipopolysaccharide (LPS) to toll-like receptor 4 induces release of pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α) and leads to inflammatory pathologies. An immunosuppression status develops together with LPS-induced inflammation named LPS tolerance, which refers to downregulation of LPS signaling after pre-exposure of LPS, providing protection against hyperactive inflammation. During LPS tolerance, production of cytokines is mitigated, and phenotype of immune cells is altered. Magnesium is a crucial micronutrient, and used as an anti-inflammatory agent in clinical. Though the anti-inflammatory effect of magnesium through inhibiting LPS signaling has been demonstrated, the effect of magnesium on LPS tolerance remains unknown. In this study, we investigated modulation of magnesium sulfate (MgSO4) on LPS tolerance. To induce LPS tolerance, THP-1 cells (a human leukemia monocyte cell line) were stimulated with LPS (200 ng/ml, 2 hours) after pre-exposure of LPS (200 ng/ml, 24 hours) with or without pretreatment of MgSO4 (20 mM, 24 hours). Proliferation, morphological changes, adherence or TNF-α release, as well as the capacity of migration or phagocytosis were studied. From our results, MgSO4 mitigated TNF-α release by LPS-tolerant cells. MgSO4 also strengthened the inhibitory effect of LPS tolerance on proliferation or morphological changes. Besides, MgSO4 enhanced LPS tolerance-triggered upregulation of migration, but not phagocytosis. In summary, MgSO4 enhances LPS tolerance and alters activities of LPS-tolerant monocytes. Our findings addressed the role of MgSO4 in immune system, and also provided evidence for a novel mechanism underlying the anti-inflammatory effect of MgSO4.