Regulation of neuroinflammation by matrix metalloproteinase-8 inhibitor derivatives in activated microglia and astrocytes

Matrix metalloproteinases (MMPs) play a pivotal role in neuroinflammation that is associated with neurodegenerative diseases. Our group recently reported that MMP-8 mediates inflammatory reactions by modulating the processing of TNF-α. To improve the efficacy of the currently available MMP-8 inhibitor (M8I), we have synthesized structurally modified M8I derivatives (comp 2, 3, 4, 5) and compared their efficacy with original compound (comp 1). Among M8I derivatives, comp 2, 3, and 5 inhibited the production of NO, ROS, and IL-6 more efficiently than the original compound in lipopolysaccharide (LPS)-stimulated microglia. When we compared the anti-inflammatory mechanisms of the most effective derivative, comp 3, with comp 1, comp 3 suppressed the mRNA expression of iNOS and cytokines more efficiently than comp 1. Although comp 1 inhibits only TNF-α processing, comp 3 additionally inhibits the expression of TNF-α. Both compounds inhibited LPS-induced activity of MAP kinases, NF-κB, and AP-1, while they increased heme oxygenase-1 expression by upregulating AMPK-Nrf2 signaling. Overall, the effect of comp 3 on anti-inflammatory signaling was much stronger than comp 1. We verified the anti-inflammatory effects of comp 1 and 3 in the LPS-injected mouse brain and primary cultured astrocytes. Comp 1 and 3 suppressed microglial activation, astrogliosis, and proinflammatory gene expression in the brain. Moreover, the compounds inhibited proinflammatory gene expression in the cultured astrocytes. Collectively, our data suggest that the MMP- 8 inhibitor may be a promising therapeutic agent for neuroinflammatory disorders.