Nicotinamide N-oxide Inhibits Microglial Pyroptosis by Upregulating Mitophagy and Alleviates Neural Damage in Rats after TBI

Traumatic brain injury (TBI) is a severe injury characterized by neuroinflammation and oxidative stress. NAMO (Nicotinamide n-oxide) has anti-inflammatory and inhibits microglial overactivation in neurological disorders. However, the role and mechanism of NAMO in microglial pyroptosis after TBI are unknown. The aim of this study was to investigate the effects of NAMO on TBI and its potential mechanisms through in vivo and in vitro models. In this study, western blot assays were performed by extracting brain tissue mitochondria, and the results showed that NAMO promoted the expression of mitophagy-associated proteins (p62, LC3B, and TOMM20), reduced ROS levels, and inhibited pyroptosis-associated proteins (NLRP3, GSDMD, GSDMD-N, and Caspase-1) and inflammatory cytokines (IL-1β and IL-18). We followed up with immunofluorescence co-localization of GSDMD and IBA 1, which showed that NAMO inhibited microglial pyroptosis. In addition, NAMO promoted neurological recovery after TBI. In vitro experiments showed that NAMO upregulated mitophagy, improved mitochondrial dysfunction, and reduced ROS levels in microglia following lipopolysaccharide (LPS) + adenosine triphosphate (ATP) stimulation in HMC3 cells. We also found that NAMO inhibited pyroptosis-related proteins. To further illustrate whether NAMO affects pyroptosis through mitophagy, we applied the mitophagy inhibitor Mdivi-1 in both in vivo and in vitro models. The results showed that Mdivi-1 reversed NAMO's inhibitory effect on microglial pyroptosis. Taken together, our findings demonstrate that NAMO improves neurological recovery by inhibiting microglial pyroptosis through upregulation of mitophagy, suggesting that NAMO could be a potential therapeutic agent for TBI.