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Systemic inflammation associated with sepsis can induce neuronal hyperexcitability, leading to enhanced seizure predisposition and occurrence. Brain microglia are rapidly activated in response to systemic inflammation and, in this activated state, release multiple cytokines and signaling factors that amplify the inflammatory response and increase neuronal excitability. NADPH oxidase (NOX) enzymes promote microglial activation through the generation of reactive oxygen species (ROS), such as superoxide anion. We hypothesized that NOX isoforms, particularly NOX2, are potential targets for prevention of sepsis-associated seizures.
To reduce NADPH oxidase 2-derived ROS production, mice with deficits of NOX regulatory subunit/NOX2 organizer p47phox (p47phox−/−) or NOX2 major subunit gp91phox (gp91phox−/−) were used or the NOX2-selective inhibitor diphenyleneiodonium (DPI) was used to treat wild-type (WT) mice. Systemic inflammation was induced by intraperitoneal injection of lipopolysaccharide (LPS). Seizure susceptibility was compared among mouse groups in response to intraperitoneal injection of pentylenetetrazole (PTZ). Brain tissues were assayed for proinflammatory gene and protein expression, and immunofluorescence staining was used to estimate the proportion of activated microglia.
Increased susceptibility to PTZ-induced seizures following sepsis was significantly attenuated in gp91phox−/− and p47phox−/− mice compared with WT mice. Both gp91phox−/− and p47phox−/− mice exhibited reduced microglia activation and lower brain induction of multiple proconvulsive cytokines, including TNFα, IL-1β, IL-6, and CCL2, compared with WT mice. Administration of DPI following LPS injection significantly attenuated the increased susceptibility to PTZ-induced seizures and reduced both microglia activation and brain proconvulsive cytokine concentrations compared with vehicle-treated controls. DPI also inhibited the upregulation of gp91phox transcripts following LPS injection.
Our results indicate that NADPH oxidases contribute to the development of increased seizure susceptibility in mice after sepsis. Pharmacologic inhibition of NOX may be a promising therapeutic approach to reducing sepsis-associated neuroinflammation, neuronal hyperexcitability, and seizures.