Melatonin modulates microsomal PGE synthase 1 and NF-E2-related factor-2-regulated antioxidant enzyme expression in LPS-induced murine peritoneal macrophages

Background and Purpose Increasing evidence demonstrates that melatonin regulates inflammatory and immune processes acting as both an activator and inhibitor of these responses. Nevertheless, the molecular mechanisms of its anti-inflammatory action remain unclear. Here we have characterized the cellular mechanisms underlying the redox modulation of LPS-stimulated inflammatory responses in murine peritoneal macrophages by melatonin to provide insight into its anti-inflammatory effects. Experimental Approach Murine peritoneal macrophages were isolated and treated with melatonin in the presence or absence of LPS (5gmL(-1)) for 18h. Cell viability was determined using sulforhodamine B assay and NO production was measured using the Griess reaction. Pro-inflammatory enzymes and transcription factors were detected by Western blotting. Key Results Without affecting cell viability, melatonin (12.5, 25, 50 and 100M) reduced the level of nitrites, inducible NOS (iNOS), COX-2 and microsomal PGE synthase-1 (mPGES1) protein, and p38 MAPK phosphorylation, and prevented NF-B translocation. Furthermore, melatonin treatment significantly increased NF-E2-related factor 2 (Nrf2) and haem oxygenase 1 (HO1) protein levels in murine macrophages exposed to LPS. Conclusions and Implications Melatonin reduced pro-inflammatory mediators and enhanced the expression of HO1 via NF-B, p38 MAPK and Nrf2 cascade signalling pathways in murine macrophages. Thus, melatonin might be a promising target for diseases associated with overactivation of macrophages.