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

The emerging role of adaptor proteins in regulating innate immunity of sepsis

Sepsis is a life-threatening syndrome caused by a dysregulated immune response. A large number of adaptor proteins have been found to play a pivotal role in sepsis via protein-protein interactions, thus participating in inflammatory cascades, leading to the generation of numerous inflammatory cytokines, as well as oxidative stress and regulated cell death. Although available strategies for the diagnosis and management of sepsis have improved, effective and specific treatments are lacking. This review focuses on the emerging role of adaptor proteins in regulating the innate immunity of sepsis and evaluates the potential value of adaptor protein-associated therapeutic strategy for sepsis.

Post-translational modifications of Keap1: the state of the art

The Keap1-Nrf2 signaling pathway plays a crucial role in cellular defense against oxidative stress-induced damage. Its activation entails the expression and transcriptional regulation of several proteins involved in detoxification and antioxidation processes within the organism. Keap1, serving as a pivotal transcriptional regulator within this pathway, exerts control over the activity of Nrf2. Various post-translational modifications (PTMs) of Keap1, such as alkylation, glycosylation, glutathiylation, S-sulfhydration, and other modifications, impact the binding affinity between Keap1 and Nrf2. Consequently, this leads to the accumulation of Nrf2 and its translocation to the nucleus, and subsequent activation of downstream antioxidant genes. Given the association between the Keap1-Nrf2 signaling pathway and various diseases such as cancer, neurodegenerative disorders, and diabetes, comprehending the post-translational modification of Keap1 not only deepens our understanding of Nrf2 signaling regulation but also contributes to the identification of novel drug targets and biomarkers. Consequently, this knowledge holds immense importance in the prevention and treatment of diseases induced by oxidative stress.

Hydrogen sulfide ameliorates lipopolysaccharide-induced anxiety-like behavior by inhibiting checkpoint kinase 1 activation in the hippocampus of mice

Hydrogen sulfide (H2S), an endogenous gasotransmitter, exhibits the anxiolytic roles through its anti-inflammatory effects, although its underlying mechanisms remain largely elusive. Emerging evidence has documented that cell cycle checkpoint kinase 1 (Chk1)-regulated DNA damage plays an important role in the neurodegenerative diseases; however, there are few relevant reports on the research of Chk1 in neuropsychiatric diseases. Here, we aimed to investigate the regulatory role of H2S on Chk1 in lipopolysaccharide (LPS)-induced anxiety-like behavior focusing on inflammasome activation in the hippocampus. Cystathionine γ-lyase (CSE, a H2S-producing enzyme) knockout (CSE-/-) mice displayed anxiety-like behavior and activation of inflammasome-mediated inflammatory responses, manifesting by the increase levels of interleukin-1β (IL-1β), IL-6, and ionized calcium-binding adaptor molecule-1 (Iba-1, microglia marker) expression in the hippocampus. Importantly, expression of p-Chk1 and γ-H2AX (DNA damage marker) levels were also increased in the hippocampus of CSE-/- mice. LPS treatment decreased the expression of CSE and CBS while increased p-Chk1 and γ-H2AX levels and inflammasome-activated neuroinflammation in the hippocampus of mice. Moreover, p-Chk1 and γ-H2AX protein levels and cellular immunoactivity were significantly increased while CSE and CBS were markedly decreased in cultured BV2 cells followed by LPS treatment. Treatment of mice with GYY4137, a donor of H2S, inhibited LPS-induced increased in p-Chk1 and γ-H2AX levels, mitigated inflammasome activation and inflammatory responses as well as amelioration of anxiety-like behavior. Notably, SB-218078, a selective Chk1 inhibitor treatment attenuated the effect of LPS on inflammasome activation and inflammatory responses and the induction of anxiety-like behavior. Finally, STAT3 knockdown with AAV-STAT3 shRNA alleviated LPS-induced anxiety-like behavior and inhibited inflammasome activation in the hippocampus, and blockade of NLRP3 with MCC950 attenuated neuroinflammation induction and ameliorated LPS-induced anxiety-like behavior. Overall, this study indicates that downregulation of Chk1 activity by H2S activation may be considered as a valid strategy for preventing the progression of LPS-induced anxiety-like behavior.

Hydrogen sulfide inhibits gene expression associated with aortic valve degeneration by inducing NRF2-related pro-autophagy effect in human aortic valve interstitial cells

Aortic valve stenosis (AS) is the most common valvular heart disease but there are currently no effective medical treatments that can delay disease progression due to a lack of knowledge of the precise pathophysiology. The expression of sulfide: quinone oxidoreductase (SQOR) and nuclear factor erythroid 2-related factor 2 (NRF2) was decreased in the aortic valve of AS patients. However, the role of SQOR and NRF2 in the pathophysiology of AS has not been found. We investigated the effects of hydrogen sulfide (H2S)-releasing compounds on diseased aortic valve interstitial cells (AVICs) to explain the cellular mechanism of SQOR and elucidate the medical value of H2S for AS treatment. Sodium hydrosulfide (NaHS) treatment increased the expression of SQOR and NRF2 gene and consequently induced the NRF2 target genes, such as NAD(P)H quinone dehydrogenase 1 and cystathionine γ-lyase. In addition, NaHS dose-dependently decreased the expression level of fibrosis and inflammation-related genes (MMP9, TNF-α, IL6) and calcification-related genes (ALP, osteocalcin, RUNX2, COL1A1) in human AVICs. Furthermore, NaHS activated the AMPK-mTOR pathway and inhibited the PI3K-AKT pathway, resulting in a pro-autophagy effect in human AVICs. An NRF2 inhibitor, brusatol, attenuated NaHS-induced AMPK activation and decreased the autophagy markers Beclin-1 and LC3AB, suggesting that the mechanism of action of H2S is related to NRF2. In conclusion, H2S decreased gene expression levels related to aortic valve degeneration and activated AMPK-mTOR-mediated pro-autophagy function associated with NRF2 in human AVICs. Therefore, H2S could be a potential therapeutic target for the development of AS treatment.

Echinocystic acid alleviated hypoxic-ischemic brain damage in neonatal mice by activating the PI3K/Akt/Nrf2 signaling pathway

Neonatal hypoxic-ischemic encephalopathy (HIE) is considered a major cause of death and long-term neurological injury in newborns. Studies have demonstrated that oxidative stress and apoptosis play a major role in the progression of neonatal HIE. Echinocystic acid (EA), a natural plant extract, shows great antioxidant and antiapoptotic activities in various diseases. However, it has not yet been reported whether EA exerts a neuroprotective effect against neonatal HIE. Therefore, this study was undertaken to explore the neuroprotective effects and potential mechanisms of EA in neonatal HIE using in vivo and in vitro experiments. In the in vivo study, a hypoxic-ischemic brain damage (HIBD) model was established in neonatal mice, and EA was administered immediately after HIBD. Cerebral infarction, brain atrophy and long-term neurobehavioral deficits were measured. Hematoxylin and eosin (H&E), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and dihydroethidium (DHE) staining were performed, and the contents of malondialdehyde (MDA) and glutathione (GSH) were detected. In the in vitro study, an oxygen-glucose deprivation/reperfusion (OGD/R) model was employed in primary cortical neurons, and EA was introduced during OGD/R. Cell death and cellular ROS levels were determined. To illustrate the mechanism, the PI3K inhibitor LY294002 and Nrf2 inhibitor ML385 were used. The protein expression levels of p-PI3K, PI3K, p-Akt, Akt, Nrf2, NQO1, and HO-1 were measured by western blotting. The results showed that EA treatment significantly reduced cerebral infarction, attenuated neuronal injury, and improved brain atrophy and long-term neurobehavioral deficits in neonatal mice subjected to HIBD. Meanwhile, EA effectively increased the survival rate in neurons exposed to OGD/R and inhibited oxidative stress and apoptosis in both in vivo and in vitro studies. Moreover, EA activated the PI3K/Akt/Nrf2 pathway in neonatal mice following HIBD and in neurons after OGD/R. In conclusion, these results suggested that EA alleviated HIBD by ameliorating oxidative stress and apoptosis via activation of the PI3K/Akt/Nrf2 signaling pathway.

Electroacupuncture Alleviates Neuroinflammation by Inhibiting the HMGB1 Signaling Pathway in Rats with Sepsis-Associated Encephalopathy

Sepsis-Associated Encephalopathy (SAE) is common in sepsis patients, with high mortality rates. It is believed that neuroinflammation is an important mechanism involved in SAE. High mobility group box 1 protein (HMGB1), as a late pro-inflammatory factor, is significantly increased during sepsis in different brain regions, including the hippocampus. HMGB1 causes neuroinflammation and cognitive impairment through direct binding to advanced glycation end products (RAGE) and Toll-like receptor 4 (TLR4). Electroacupuncture (EA) at Baihui (GV20) and Zusanli (ST36) is beneficial for neurological diseases and experimental sepsis. Our study used EA to treat SAE induced by lipopolysaccharide (LPS) in male Sprague-Dawley rats. The Y maze test was performed to assess working memory. Immunofluorescence (IF) and Western blotting (WB) were used to determine neuroinflammation and the HMGB1 signaling pathway. Results showed that EA could improve working memory impairment in rats with SAE. EA alleviated neuroinflammation by downregulating the hippocampus's HMGB1/TLR4 and HMGB1/RAGE signaling, reducing the levels of pro-inflammatory factors, and relieving microglial and astrocyte activation. However, EA did not affect the tight junctions' expression of the blood-brain barrier (BBB) in the hippocampus.

Recent Development of the Molecular and Cellular Mechanisms of Hydrogen Sulfide Gasotransmitter

Hydrogen sulfide has been recently identified as the third biological gasotransmitter, along with the more well studied nitric oxide (NO) and carbon monoxide (CO). Intensive studies on its potential as a therapeutic agent for cardiovascular, inflammatory, infectious and neuropathological diseases have been undertaken. Here we review the possible direct targets of H₂S in mammals. H₂S directly interacts with reactive oxygen/nitrogen species and is involved in redox signaling. H₂S also reacts with hemeproteins and modulates metal-containing complexes. Once being oxidized, H₂S can persulfidate proteins by adding -SSH to the amino acid cysteine. These direct modifications by H₂S have significant impact on cell structure and many cellular functions, such as tight junctions, autophagy, apoptosis, vesicle trafficking, cell signaling, epigenetics and inflammasomes. Therefore, we conclude that H₂S is involved in many important cellular and physiological processes. Compounds that donate H₂S to biological systems can be developed as therapeutics for different diseases.

Hydrogen Sulfide Donor GYY4137 Rescues NRF2 Activation in Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) can cause severe respiratory illness in infants, immunocompromised, and older adults. Despite its burden, no vaccine or specific treatment is available. RSV infection is associated with increased reactive oxygen species (ROS) production, degradation of the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2), and decreased antioxidant enzymes (AOEs), leading to oxidative damage and lung injury. Hydrogen sulfide (H2S) is an endogenous gaseous molecule that plays a physiological role in numerous cellular processes and a protective role in multiple pathological conditions, displaying vasoactive, cytoprotective, anti-inflammatory, and antioxidant activities. H2S can promote NRF2 activation through the sulfhydration of Kelch-like ECH-associated protein 1, the cytoplasmic repressor of NRF2. Here we investigated whether increasing cellular H2S levels could rescue NRF2 and NRF2-dependent gene expression in RSV-infected primary airway epithelial cells. We found that treatment with the H2S donor GYY4137 significantly increased NRF2 levels and AOEs gene expression by decreasing KEAP1 levels, and by modulating pathways involved in RSV-induced NRF2 degradation, such as NRF2 ubiquitination, and promyelocytic leukemia (PML) protein levels. These results suggest that the administration of exogenous H2S can positively impact the altered redox balance associated with RSV infection, which represents an important determinant of RSV-induced lung disease.

Protein S-sulfhydration: Unraveling the prospective of hydrogen sulfide in the brain, vasculature and neurological manifestations

Hydrogen sulfide (H₂S) and hydrogen polysulfides (H₂S_n) are essential regulatory signaling molecules generated by the entire body, including the central nervous system. Researchers have focused on the classical H₂S signaling from the past several decades, whereas the last decade has shown the emergence of H₂S-induced protein S-sulfhydration signaling as a potential therapeutic approach. Cysteine S-persulfidation is a critical paradigm of post-translational modification in the process of H₂S signaling. Additionally, studies have shown the cross-relationship between S-sulfhydration and other cysteine-induced post-translational modifications, namely nitrosylation and carbonylation. In the central nervous system, S-sulfhydration is involved in the cytoprotection through various signaling pathways, viz. inflammatory response, oxidative stress, endoplasmic reticulum stress, atherosclerosis, thrombosis, and angiogenesis. Further, studies have demonstrated H₂S-induced S-sulfhydration in regulating different biological processes, such as mitochondrial integrity, calcium homeostasis, blood-brain permeability, cerebral blood flow, and long-term potentiation. Thus, protein S-sulfhydration becomes a crucial regulatory molecule in cerebrovascular and neurodegenerative diseases. Herein, we first described the generation of intracellular H₂S followed by the application of H₂S in the regulation of cerebral blood flow and blood-brain permeability. Further, we described the involvement of S-sulfhydration in different biological and cellular functions, such as inflammatory response, mitochondrial integrity, calcium imbalance, and oxidative stress. Moreover, we highlighted the importance of S-sulfhydration in cerebrovascular and neurodegenerative diseases.

Gases in Sepsis: Novel Mediators and Therapeutic Targets

Sepsis, a potentially lethal condition resulting from failure to control the initial infection, is associated with a dysregulated host defense response to pathogens and their toxins. Sepsis remains a leading cause of morbidity, mortality and disability worldwide. The pathophysiology of sepsis is very complicated and is not yet fully understood. Worse still, the development of effective therapeutic agents is still an unmet need and a great challenge. Gases, including nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S), are small-molecule biological mediators that are endogenously produced, mainly by enzyme-catalyzed reactions. Accumulating evidence suggests that these gaseous mediators are widely involved in the pathophysiology of sepsis. Many sepsis-associated alterations, such as the elimination of invasive pathogens, the resolution of disorganized inflammation and the preservation of the function of multiple organs and systems, are shaped by them. Increasing attention has been paid to developing therapeutic approaches targeting these molecules for sepsis/septic shock, taking advantage of the multiple actions played by NO, CO and H₂S. Several preliminary studies have identified promising therapeutic strategies for gaseous-mediator-based treatments for sepsis. In this review article, we summarize the state-of-the-art knowledge on the pathophysiology of sepsis; the metabolism and physiological function of NO, CO and H₂S; the crosstalk among these gaseous mediators; and their crucial effects on the development and progression of sepsis. In addition, we also briefly discuss the prospect of developing therapeutic interventions targeting these gaseous mediators for sepsis.

Emerging Trends and Hot Spots in Sepsis-Associated Encephalopathy Research From 2001 to 2021: A Bibliometric Analysis

Study Objectives

To evaluate sepsis-associated encephalopathy (SAE) research and to quantitatively and qualitatively predict research hot spots using bibliometric analysis.

Methods

We extracted relevant publications from the Web of Science Core Collection on July 28, 2021. We investigated the retrieved data by bibliometric analysis (e.g. co-cited and cluster analysis, keyword co-occurrence) using the software CiteSpace and VOSviewer, the Online Analysis Platform of Literature Metrology (http://bibliometric.com/) and Bibliometrix to analyse and predict the trends and hot spots in this field.

Main Results

We identified 1,582 published articles and reviews on SAE from 2001 to 2021. During this period, the number of manuscripts on SAE increased steadily and peaked in 2021. The USA and China were the leading countries that had a critical impact on SAE research. Among all institutions, Vanderbilt University and Pittsburgh University held leading positions and became central in the collaboration network. Among all the journals, Critical Care Medicine published the maximum number of manuscripts in the field of SAE within 20 years. Dal-Pizzol Felipe was the most productive author (61 papers) and received the largest number of citations (930 citations). Co-citation cluster analysis revealed that the most popular terms on SAE in the manner of cluster labels were critical illness, sepsis-associated encephalopathy, polymicrobial sepsis, posterior reversible encephalopathy syndrome, rat brain, intensive care unit, prior sepsis, molecular hydrogen, inflammation drive, metabolic encephalopathies, delirium pathophysiology, and clinical neuroscience. Keyword burst detection indicated that neuroinflammation, blood-brain barrier (BBB) and mitochondria dysfunction were the current research hot spots.

Conclusions

Our study revealed that neuroinflammation, blood-brain barrier, and mitochondria dysfunction had been the research foci of SAE over the past 20 years. These have emerged as the basis for transformation from basic research to clinical application in finding effective methods for the prevention and treatment of SAE.

Luteolin Confers Cerebroprotection after Subarachnoid Hemorrhage by Suppression of NLPR3 Inflammasome Activation through Nrf2-Dependent Pathway

Luteolin (LUT) possesses multiple biologic functions and has beneficial effects for cardiovascular and cerebral vascular diseases. Here, we investigated the protective effects of LUT against subarachnoid hemorrhage (SAH) and the involvement of underlying molecular mechanisms. In a rat model of SAH, LUT significantly inhibited SAH-induced neuroinflammation as evidenced by reduced microglia activation, decreased neutrophil infiltration, and suppressed proinflammatory cytokine release. In addition, LUT markedly ameliorated SAH-induced oxidative damage and restored the endogenous antioxidant systems. Concomitant with the suppressed oxidative stress and neuroinflammation, LUT significantly improved neurologic function and reduced neuronal cell death after SAH. Mechanistically, LUT treatment significantly enhanced the expression of nuclear factor-erythroid 2-related factor 2 (Nrf2), while it downregulated nod-like receptor pyrin domain-containing 3 (NLRP3) inflammasome activation. Inhibition of Nrf2 by ML385 dramatically abrogated LUT-induced Nrf2 activation and NLRP3 suppression and reversed the beneficial effects of LUT against SAH. In neurons and microglia coculture system, LUT also mitigated oxidative stress, inflammatory response, and neuronal degeneration. These beneficial effects were associated with activation of the Nrf2 and inhibitory effects on NLRP3 inflammasome and were reversed by ML385 treatment. Taken together, this present study reveals that LUT confers protection against SAH by inhibiting NLRP3 inflammasome signaling pathway, which may be modulated by Nrf2 activation.