Melatonin inhibits matrix metalloproteinase-9 (MMP-9) activation in the lipopolysaccharide (LPS)-stimulated RAW 264.7 and BV2 cells and a mouse model of meningitis.

We explored anti-inflammatory potential of melatonin against the lipopolysaccharide (LPS)-induced inflammation in vivo and in vitro. RAW 264.7 and BV2 cells were stimulated by LPS, followed by the treatment with melatonin or vehicle at various time intervals. In a mouse model of meningitis induced by LPS, melatonin (5mg/kg) or vehicle was intravenously injected at 30min postinsult. The activity of matrix metalloproteinase-2 (MMP-2) and metalloproteinase-9 (MMP-9) was determined by gelatin zymography. Nuclear factor-kappa B (NFκB) translocation and binding activity were determined by immunocytochemistry and electrophoretic mobility shift assay (EMSA). Our results showed that either pretreatment or cotreatment with melatonin at 50-500 µm effectively inhibited the LPS-induced proMMP-9 activation in the RAW 264.7 and BV2 cells, respectively (P<0.05). This melatonin-induced proMMP-9 inhibition remained effective when treatment was delayed up to 2 and 6hr postinsult for RAW 264.7 and BV2 cells, respectively (P<0.05 for both groups). Additionally, melatonin significantly attenuated the rises of circulatory and cerebral MMP-9 activity, respectively (P<0.05) and reduced the loss of body weight (P<0.05) in mice with meningitis. Moreover, melatonin (50µm) effectively inhibited nuclear factor-kappa B (NFκB) translocation and binding activity in the LPS-treated RAW 264.7 and BV2 cells, respectively (P<0.05). These results demonstrate direct inhibitory actions of melatonin against postinflammatory NFκB translocation and MMP-9 activation and highlight its ability to inhibit systemic and cerebral MMP-9 activation following brain inflammation.