Hydrogen gas alleviates blood-brain barrier impairment and cognitive dysfunction of septic mice in an Nrf2-dependent pathway

Sepsis-associated encephalopathy (SAE) is a cognitive impairment caused by sepsis and is related to increased morbidity and mortality. Damage to the blood–brain barrier (BBB) has been proved to be one of the important causes of SAE. Molecular hydrogen (H2) is a promising method for the treatment of SAE, yet the underlying mechanism is not clear. This study was designed to demonstrate whether H2 can alleviate SAE by protecting the BBB, and whether it is protected by Nuclear factor erythroid-2-related factor 2 (Nrf2) and its downstream signaling pathways. Either a sham or a cecal ligation and puncture (CLP) procedure was applied to female wild-type (WT) and Nrf2-knock-out (Nrf2-/-) C57BL/6J mice. H2 (2%) was given for 60 min starting at 1 h and 6 h after the sham or CLP procedure. In addition, bEnd.3 cells cultured with medium which contained LPS, Saline, DMSO or ML385 (a Nrf2 inhibitor) were also used in the research. The 7-day survival rates were recorded. The Morris water maze was used to determine cognitive function. Pro-inflammatory and anti-inflammatory cytokines [tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), HMGB1, and IL-10), antioxidant enzymes, and oxidation products [superoxide dismutase (SOD), chloramphenicol acetyltransferase (CAT), malondialdehyde (MDA), and (8-iso-PGF2α)] were determined by enzyme-linked immunosorbent assay (ELISA). Brain water content, Dextran tracer, and Evans blue extravasation were used to detect the damage of the BBB. Western blot analysis was used to detect β-catenin, phosphorylated β-catenin, adhesion-linked protein VE-cadherin, and associated tight junction protein ZO-1. We found that H2 can improve survival in septic mice, decrease escape latency and platform crossing times, decrease pro-inflammatory cytokines and oxidative product levels in the mouse cortex, and increase the expression of anti-inflammatory factors in WT, but not Nrf2-/-, mice. Moreover, H2 can also decrease brain water content, extravascular dextran, extravascular Evans blue dye, and β-catenin level, and increase ZO-1 and VE-cadherin expressions in WT mice, but not in Nrf2-/- mice. Our result shows that H2 can protect the BBB by decreasing its permeability, thereby reducing SAE and improving cognitive function, which is mediated through Nrf2 and its downstream signaling pathways.