Hydrogen Sulfide Protects Against Ammonia-Induced Neurotoxicity Through Activation of Nrf2/ARE Signaling in Astrocytic Model of Hepatic Encephalopathy

Objective: Hepatic encephalopathy (HE) characterized by neuropsychiatric abnormalities is a major complication of cirrhosis with high mortality. However, the pathogenesis of HE has not been fully elucidated. This study aimed to determine endogenous hydrogen sulfide (H(2)S) in the blood of HE patients and investigate the role of H(2)S in an astrocytic model of HE. Methods: Patients with and without HE were recruited to determine plasma H(2)S levels and blood microbial 16S rRNA gene. Rat astrocytes were employed as a model of HE by treatment of NH(4)Cl. Exogenous H(2)S was preadded. Cell viability was measured by Cell Counting Kit-8 (CCK-8) assay, and cell death was evaluated by lactate dehydrogenase (LDH) release. Apoptosis was determined by Hoechst 33342/Propidium Iodide (PI) Double Staining and Western blot analysis of apoptosis-related protein expression. Intracellular reactive oxygen species (ROS) levels were assessed by flow cytometer. Expressions of Nrf2 and its downstream regulated genes were examined by immunofluorescence staining and Western blot, respectively. Nrf2 gene knockdown was performed by antisense shRNA of Nrf2 gene. Results: There was a significant decrease in H(2)S levels in cirrhotic patients with HE compared with without HE. Blood microbiota analyses revealed that certain strains associated with H(2)S production were negatively correlated with HE. In vitro, H(2)S markedly attenuated NH(4)Cl-induced cytotoxicity, oxidative stress, and apoptosis. This effect was mediated by Nrf2/ARE signaling, and knockdown of Nrf2 expression abolished the antagonistic effect of H(2)S on NH(4)Cl-induced neurotoxicity in astrocytes. Conclusion: Levels of H(2)S and bacteria associated with H(2)S production are decreased in HE, and H(2)S functions as the neuroprotector against NH(4)Cl-induced HE by activating Nrf2/ARE signaling of astrocytes.