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

Abstract

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.

GYY4137 protected the integrity of the blood‐brain barrier via activation of the Nrf2/ARE pathway in mice with sepsis

“…[48][49][50] Regarding the mechanisms underlying the activation of the Nrf2/ARE pathway, earlier studies demonstrated that through the sulfhydrylation of Keap1, H 2 S induces the separation of the Nrf2-Keap1 complex, thus activating the Nrf2/ARE pathway. 51 In our study, we found that GYY4137 significantly induced the translocation of Nrf2 into the nucleus and the consequent expression of HO-1 and NQO1. Moreover, GYY4137 led to the considerable sulfhydrylation of Keap1.…”

“…Recent studies have indicated that the activation of the Nrf2/ARE pathway not only reduced oxidative stress but also inhibited inflammation and apoptosis 48‐50 . Regarding the mechanisms underlying the activation of the Nrf2/ARE pathway, earlier studies demonstrated that through the sulfhydrylation of Keap1, H 2 S induces the separation of the Nrf2‐Keap1 complex, thus activating the Nrf2/ARE pathway 51 . In our study, we found that GYY4137 significantly induced the translocation of Nrf2 into the nucleus and the consequent expression of HO‐1 and NQO1.…”

GPX4‐Regulated Ferroptosis Mediates S100‐Induced Experimental Autoimmune Hepatitis Associated with the Nrf2/HO‐1 Signaling Pathway

“…Nrf2, a master controller of the antioxidant response, is a transcription factor that is often aberrantly regulated in oxidative stress [41]. The stability of inactivated Kelch-like 13 Oxidative Medicine and Cellular Longevity ECH-associated protein 1 (Keap1)/Nrf2 heterodimers is maintained by thiol antioxidants in the cytosol under nonstress conditions [42].…”

Hydrogen sulphide attenuates neuronal apoptosis of substantia nigra by re‐establishing autophagic flux via promoting leptin signalling in a 6‐hydroxydopamine rat model of Parkinson's disease

“…76 Importantly, H 2 S protects against ammonia-induced neurotoxicity through activation of Nrf2/ARE signalling in astrocytic model of hepatic encephalopathy. 77 Therefore, the role of astrocytes in the protective effect of H 2 S in neuronal apoptosis of PD may be meaningful research interests. Finally, although our research on the protective mechanism of H 2 S is based on the acute protection of H 2 S against PD, we believe that the research on the underlying mechanism is not only to deepen the understanding of the acute protection of H 2 S against PD, also to provide a theoretical basis for the long-term protection of H 2 S against PD.…”