Hydrogen attenuates sepsis-associated encephalopathy by NRF2 mediated NLRP3 pathway inactivation.

OBJECTIVE: Sepsis-associated encephalopathy (SAE) is a major cause of mortality worldwide. Oxidative stress, inflammatory response and apoptosis participate in the pathogenesis of SAE. Nuclear factor erythroid 2-related factor 2 (Nrf2) and nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) pathway is involved in oxidative stress and inflammatory response. We reported that hydrogen gas protected against sepsis in wild-type (WT) but not Nrf2 knockout (KO) mice. Therefore, it is vital to identify the underlying cause of hydrogen gas treatment of sepsis-associated encephalopathy.

METHODS: SAE was induced in WT and Nrf2 KO mice by cecal ligation and puncture (CLP). As a NLRP3 inflammasome inhibitor, MCC950 (50 mg/kg) was administered by intraperitoneal (i.p.) injection before operation. Hydrogen gas (H2)-rich saline solution (5 mL/kg) was administered by i.p. injection at 1 h and 6 h after sham and CLP operations. Brain tissue was collected to assess the NLRP3 and Nrf2 pathways by western blotting, reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence.

RESULTS: SAE increased NLRP3 and Nrf2 expression in microglia. MCC950 inhibited SAE-induced NLRP3 expression, interleukin (IL)-1β and IL-18 cytokine release, neuronal apoptosis and mitochondrial dysfunction. SAE increased NLRP3 and caspase-1 expression in WT mice compared to Nrf2 KO mice. Hydrogen increased Nrf2 expression and inhibited the SAE-induced expression of NLRP3, caspase-1, cytokines IL-1β and IL-18, neuronal apoptosis, and mitochondrial dysfunction in WT mice but not Nrf2 KO mice.

CONCLUSION: SAE increased NLRP3 and Nrf2 expression in microglia. Hydrogen alleviated inflammation, neuronal apoptosis and mitochondrial dysfunction via inhibiting Nrf2-mediated NLRP3 pathway.