Hydrogen sulfide protects against cognitive impairment induced by hepatic ischemia and reperfusion via attenuating neuroinflammation

Circulating Exosomes Mediate Neurodegeneration Following Hepatic Ischemia-reperfusion Through Inducing Microglial Pyroptosis in the Developing Hippocampus

BACKGROUND

Poor neurodevelopmental outcomes after pediatric liver transplantation seriously affect the long-term quality of life of recipients, in whom hepatic ischemia reperfusion (HIR) is considered to play a pivotal role. However, the link between HIR and brain injury remains unclear. Because circulating exosomes are considered as the key mediators of information transmission over long distances, we aimed to assess the role of circulating exosomes in HIR-induced hippocampal injury in young rats.

METHODS

We administered exosomes extracted from the sera of HIR model rats to normal young rats via the tail vein. Western blotting, enzyme-linked immunosorbent assay, histological examination, and real-time quantitative polymerase chain reaction were used to evaluate the role of exosomes in neuronal injury and activation of microglial pyroptosis in the developing hippocampus. Primary microglial cells were cocultured with exosomes to further assess the effect of exosomes on microglia. To further explore the potential mechanism, GW4869 or MCC950 was used to block exosome biogenesis or nod-like receptor family protein 3, respectively.

RESULTS

Serum-derived exosomes played a crucial role in linking HIR with neuronal degeneration in the developing hippocampus. Microglia were found to be the target cells of ischemia-reperfusion derived exosomes (I/R-exosomes). I/R-exosomes were taken up by microglia and promoted the occurrence of microglial pyroptosis in vivo and in vitro. Moreover, the exosome-induced neuronal injury was alleviated by suppressing the occurrence of pyroptosis in the developing hippocampus.

CONCLUSIONS

Microglial pyroptosis induced by circulating exosomes plays a vital role in developing hippocampal neuron injury during HIR in young rats.

Targeting AGEs-RAGE pathway inhibits inflammation and presents neuroprotective effect against hepatic ischemia-reperfusion induced hippocampus damage

BACKGROUND

The present study aimed to investigate the role of AGEs-RAGE signaling and its potential as a treatment target in hepatic ischemia-reperfusion (HIR)-induced hippocampus damage.

METHODS

HIR operation was conducted in mice, followed by collection of hippocampus tissue at 1 day, 3 days and 7 days. Additionally, low dose, moderate dose and high dose FPS-ZM1 (RAGE inhibitor) was intraperitoneally injected into HIR mice. Besides, sham operation was conduced in mice which served as control.

RESULTS

HIR increased the hippocampal damage and enhanced its neuron apoptosis within 3 days, which recovered to some extent from day 3 to day 7 post operation. Meanwhile, the expressions of AGEs, RAGE, the downstream proteins in AGEs-RAGE signaling pathway (including PI3K, pAKT, pNKκB p65 and pERK1/2), and the inflammatory cytokines (including IL-1β, IL-6, TNF-α) were increased within 3 days, but were reduced from day 3 to day 7 post operation by HIR. Notably, moderate and high dose of FPS-ZM1 attenuated hippocampal damage, inhibited its neuron apoptosis, inactivated AGEs-RAGE signaling, and suppressed the expressions of inflammatory cytokines (including IL-1β, IL-6, TNF-α); but lose dose of FPS-ZM1 failed to achieve these effects.

CONCLUSIONS

Targeting AGEs-RAGE pathway inhibits inflammation and presents neuroprotective effect against HIR-induced hippocampus damage.

Autophagy Plays a Protective Role in Sodium Hydrosulfide-Induced Acute Lung Injury by Attenuating Oxidative Stress and Inflammation in Rats

Sodium hydrosulfide (NaHS), as an exogenous hydrogen sulfide (H₂S) donor, has been used in various pathological models. NaHS is usually considered to be primarily protective, however, the toxic effect of NaHS has not been well elucidated. The aim of this study was to investigate whether NaHS (1 mg/kg) can induce acute lung injury (ALI is a disease process characterized by diffuse inflammation of the lung parenchyma) and define the mechanism by which NaHS-induced ALI involves autophagy, oxidative stress, and inflammatory response. Wistar rats were randomly divided into three groups (control group, NaHS group, and 3-MA + NaHS group), and samples from each group were collected from 2, 6, 12, and 24 h. We found that intraperitoneal injection of NaHS (1 mg/kg) increased the pulmonary levels of H₂S and oxidative stress-related indicators (reactive oxygen species, myeloperoxidase, and malondialdehyde) in a time-dependent manner. Intraperitoneal injection of NaHS (1 mg/kg) induced histopathological changes of ALI and inhibition of autophagy exacerbated the lung injury. This study demonstrates that administration of NaHS (1 mg/kg) induces ALI in rats and autophagy in response to ROS is protective in NaHS-induced ALI by attenuating oxidative stress and inflammation.

Hydrogen sulfide: An endogenous regulator of the immune system

Hydrogen sulfide (H₂S) is now recognized as an endogenous signaling gasotransmitter in mammals. It is produced by mammalian cells and tissues by various enzymes - predominantly cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) - but part of the H₂S is produced by the intestinal microbiota (colonic H₂S-producing bacteria). Here we summarize the available information on the production and functional role of H₂S in the various cell types typically associated with innate immunity (neutrophils, macrophages, dendritic cells, natural killer cells, mast cells, basophils, eosinophils) and adaptive immunity (T and B lymphocytes) under normal conditions and as it relates to the development of various inflammatory and immune diseases. Special attention is paid to the physiological and the pathophysiological aspects of the oral cavity and the colon, where the immune cells and the parenchymal cells are exposed to a special "H₂S environment" due to bacterial H₂S production. H₂S has many cellular and molecular targets. Immune cells are "surrounded" by a "cloud" of H₂S, as a result of endogenous H₂S production and exogenous production from the surrounding parenchymal cells, which, in turn, importantly regulates their viability and function. Downregulation of endogenous H₂S producing enzymes in various diseases, or genetic defects in H₂S biosynthetic enzyme systems either lead to the development of spontaneous autoimmune disease or accelerate the onset and worsen the severity of various immune-mediated diseases (e.g. autoimmune rheumatoid arthritis or asthma). Low, regulated amounts of H₂S, when therapeutically delivered by small molecule donors, improve the function of various immune cells, and protect them against dysfunction induced by various noxious stimuli (e.g. reactive oxygen species or oxidized LDL). These effects of H₂S contribute to the maintenance of immune functions, can stimulate antimicrobial defenses and can exert anti-inflammatory therapeutic effects in various diseases.

Toxic effects of hydrogen sulfide donor NaHS induced liver apoptosis is regulated by complex IV subunits and reactive oxygen species generation in rats

In recent years, the protective effect of hydrogensulfide donor sodium hydrosulfide(NaHS) on multiple organs has been widely reported. The study aimed to explorethe effect of commonly used concentration of NaHS on theliver and its potential damage mechanism. Rats divided into 4 groups: control, NaHS I (1 mg/kg), II (3 mg/kg) and III(5 mg/kg) groups, and each group is divided into four-timepoints (2, 6, 12, and 24 hours). Results showed that H2S concentration increased, mitochondrial complex IV activity inhibited, the COX I and IV subunits and mitochondrial apoptosis pathway-related proteins expression increased in atime- and dose-dependent manner. We confirmed that 1 mg/kg NaHS had no injuryeffect on the liver, 3 and 5 mg/kg NaHS inhibitsthe activity of mitochondrial complex IV by promoting COX I and IV subunits expression, leading to the increase in ROS and ultimately inducing apoptosis and liver injury.

Gut microbiota and neuroinflammation in pathogenesis of hypertension: A potential role for hydrogen sulfide

Inflammation and gut dysbiosis are hallmarks of hypertension (HTN). Hydrogen sulfide (H2S) is an important freely diffusing molecule that modulates the function of neural, cardiovascular and immune systems, and circulating levels of H2S are reduced in animals and humans with HTN. While most research to date has focused on H₂S produced endogenously by the host, H2S is also produced by the gut bacteria and may affect the host homeostasis. Here, we review an association between neuroinflammation and gut dysbiosis in HTN, with special emphasis on a potential role of H2S in this interplay.

Hydrogen Sulfide Protects against Paraquat-Induced Acute Liver Injury in Rats by Regulating Oxidative Stress, Mitochondrial Function, and Inflammation

In addition to the lung, the liver is considered another major target for paraquat (PQ) poisoning. Hydrogen sulfide (H₂S) has been demonstrated to be effective in the inhibition of oxidative stress and inflammation. The aim of this study was to investigate the protective effect of exogenous H₂S against PQ-induced acute liver injury. The acute liver injury model was established by a single intraperitoneal injection of PQ, evidenced by histological alteration and elevated serum aminotransferase levels. Different doses of NaHS were administered intraperitoneally one hour before exposure to PQ. Analysis of the data shows that exogenous H₂S attenuated the PQ-induced liver injury and oxidative stress in a dose-dependent manner. H₂S significantly suppressed reactive oxygen species (ROS) generation and the elevation of malondialdehyde content while it increased the ratio of GSH/GSSG and levels of antioxidant enzymes including SOD, GSH-Px, HO-1, and NQO-1. When hepatocytes were subjected to PQ-induced oxidative stress, H₂S markedly enhanced nuclear translocation of Nrf2 via S-sulfhydration of Keap1 and resulted in the increase in IDH2 activity by regulating S-sulfhydration of SIRT3. In addition, H₂S significantly suppressed NLRP3 inflammasome activation and subsequent IL-1β excretion in PQ-induced acute liver injury. Moreover, H₂S cannot reverse the decrease in SIRT3 and activation of the NLRP3 inflammasome caused by PQ in Nrf2-knockdown hepatocytes. In summary, H₂S attenuated the PQ-induced acute liver injury by enhancing antioxidative capability, regulating mitochondrial function, and suppressing ROS-induced NLRP3 inflammasome activation. The antioxidative effect of H₂S in PQ-induced liver injury can at least partly be attributed to the promotion of Nrf2-driven antioxidant enzymes via Keap1 S-sulfhydration and regulation of SIRT3/IDH2 signaling via Nrf2-dependent SIRT3 gene transcription as well as SIRT3 S-sulfhydration. Thus, H₂S supplementation can form the basis for a promising novel therapeutic strategy for PQ-induced acute liver injury.

Hydrogen Sulfide as a Novel Regulatory Factor in Liver Health and Disease

Hydrogen sulfide (H₂S), a colorless gas smelling of rotten egg, has long been recognized as a toxic gas and environment pollutant. However, increasing evidence suggests that H₂S acts as a novel gasotransmitter and plays important roles in a variety of physiological and pathological processes in mammals. H₂S is involved in many hepatic functions, including the regulation of oxidative stress, glucose and lipid metabolism, vasculature, mitochondrial function, differentiation, and circadian rhythm. In addition, H₂S contributes to the pathogenesis and treatment of a number of liver diseases, such as hepatic fibrosis, liver cirrhosis, liver cancer, hepatic ischemia/reperfusion injury, nonalcoholic fatty liver disease/nonalcoholic steatohepatitis, hepatotoxicity, and acute liver failure. In this review, the biosynthesis and metabolism of H₂S in the liver are summarized and the role and mechanism of H₂S in liver health and disease are further discussed.

Hydrogen Sulfide: A Potential Novel Therapy for the Treatment of Ischemia

Hydrogen sulfide (H2S) is a novel signaling molecule most recently found to be of fundamental importance in cellular function as a regulator of apoptosis, inflammation, and perfusion. Mechanisms of endogenous H2S signaling are poorly understood; however, signal transmission is thought to occur via persulfidation at reactive cysteine residues on proteins. Although much has been discovered about how H2S is synthesized in the body, less is known about how it is metabolized. Recent studies have discovered a multitude of different targets for H2S therapy, including those related to protein modification, intracellular signaling, and ion channel depolarization. The most difficult part of studying hydrogen sulfide has been finding a way to accurately and reproducibly measure it. The purpose of this review is to: elaborate on the biosynthesis and catabolism of H2S in the human body, review current knowledge of the mechanisms of action of this gas in relation to ischemic injury, define strategies for physiological measurement of H2S in biological systems, and review potential novel therapies that use H2S for treatment.

Hydrogen sulfide attenuates chronic restrain stress-induced cognitive impairment by upreglulation of Sirt1 in hippocampus

Chronic restraint stress (CRS) has detrimental effects on cognitive function. Hydrogen sulfide (H₂S), as a neuromodulator, regulates learning and memory. Hippocampus is a key structure in learning and memory. Sirt1 (silence signal regulating factor 1) plays an important role in modulating cognitive function. Therefore, our present work was to investigate whether H₂S meliorates CRS-induced damage in hippocampus and impairment in cognition, and further to explore whether the underlying mechanism is via upreglulating Sirt1. In our present work, the behavior experiments [Y-maze test, Novel object recognition (NOR) test, Morris water maze (MWM) test] showed that sodium hydrosulfide (NaHS, a donor of H₂S) blocked CRS-induced cognitive impairments in rats. NaHS inhibited CRS-induced hippocampal oxidative stress as evidenced by decrease in MDA level as well as increases in GSH content and SOD activity. NaHS rescued CRS-generated ER stress as evidenced by downregulations of CPR78, CHOP, and cleaved caspase-12. NaHS reduced CRS-exerted apoptosis as evidenced by decreases in the number of TUNEL-positive cells and Bax expression as well as increase in Bcl-2 expression. NaHS upregulated the expression of Sirt1 in the hippocampus of CRS-exposed rats. Furthermore, inhibited Sirt1 by Sirtinol reversed the protective effects of NaHS against CRS-produced cognitive dysfunction and oxidative stress, ER stress as well as apoptosis in hippocampus. Together, these results suggest that H₂S meliorates CRS-induced hippocampal damage and cognitive impairment by upregulation of hippocampal Sirt1.

NaHS Protects against the Impairments Induced by Oxygen-Glucose Deprivation in Different Ages of Primary Hippocampal Neurons

Brain ischemia leads to poor oxygen supply, and is one of the leading causes of brain damage and/or death. Neuroprotective agents are thus in great need for treatment purpose. Using both young and aged primary cultured hippocampal neurons as in vitro models, we investigated the effect of sodium hydrosulfide (NaHS), an exogenous donor of hydrogen sulfide, on oxygen-glucose deprivation (OGD) damaged neurons that mimick focal cerebral ischemia/reperfusion (I/R) induced brain injury. NaHS treatment (250 μM) protected both young and aged hippocampal neurons, as indicated by restoring number of primary dendrites by 43.9 and 68.7%, number of dendritic end tips by 59.8 and 101.1%, neurite length by 36.8 and 66.7%, and spine density by 38.0 and 58.5% in the OGD-damaged young and aged neurons, respectively. NaHS treatment inhibited growth-associated protein 43 downregulation, oxidative stress in both young and aged hippocampal neurons following OGD damage. Further studies revealed that NaHS treatment could restore ERK1/2 activation, which was inhibited by OGD-induced protein phosphatase 2 (PP2A) upregulation. Our results demonstrated that NaHS has potent protective effects against neuron injury induced by OGD in both young and aged hippocampal neurons.