Adjustment of Dysregulated Ceramide Metabolism in a Murine Model of Sepsis-Induced Cardiac Dysfunction

Ceramides in peripheral arterial plaque lead to endothelial cell dysfunction

Background

Peripheral arterial atheroprogression is increasingly prevalent, and is a risk factor for major limb amputations in individuals with risk factors such as diabetes. We previously demonstrated that bioactive lipids are significantly altered in arterial tissue of individuals with diabetes and advanced peripheral arterial disease.

Methods

Here we evaluated whether sphingolipid ceramide 18:1/16:0 (C16) is a cellular regulator in endothelial cells and peripheral tibial arterial tissue in individuals with diabetes.

Results

We observed that C16 is the single most elevated ceramide in peripheral arterial tissue from below the knee in individuals with diabetes (11% increase, P < .05). C16 content in tibial arterial tissue positively correlates with sphingomyelin (SPM) content in patients with and without diabetes (r2 = 0.5, P < .005; r2 = 0.17, P < .05; respectively). Tibial arteries of individuals with diabetes demonstrated no difference in CERS6 expression (encoding ceramide synthase 6; the predominate ceramide synthesis enzyme), but higher SMPD expression (encoding sphingomyelin phosphodiesterase that catalyzes ceramide synthesis from sphingomyelins; P < .05). SMPD4, but not SMPD2, was particularly elevated in maximally diseased (Max) tibial arterial segments (P < .05). In vitro, exogenous C16 caused endothelial cells (HUVECs) to have decreased proliferation (P < .03), increased apoptosis (P < .003), and decreased autophagy (P < .008). Selective knockdown of SMPD2 and SMPD4 decreased native production of C16 (P < .01 and P < .001, respectively), but only knockdown of SMPD4 rescued cellular proliferation (P < .005) following exogenous supplementation with C16.

Conclusions

Our findings suggest that C16 is a tissue biomarker for peripheral arterial disease severity in the setting of diabetes, and can impact endothelial cell viability and function.

Clinical relevance

Peripheral arterial disease and its end-stage manifestation known as chronic limb-threatening ischemia (CLTI) represent ongoing prevalent and intricate medical challenges. Individuals with diabetes have a heightened risk of developing CLTI and experiencing its complications, including wounds, ulcers, and major amputations. In the present study, we conducted a comprehensive examination of the molecular lipid composition within arterial segments from individuals with CLTI, and with and without diabetes. Our investigations unveiled a striking revelation: the sphingolipid ceramide 18:1/16:0 emerged as the predominant ceramide species that was significantly elevated in the peripheral arterial intima below the knee in patients with diabetes. Moreover, this heightened ceramide presence is associated with a marked impairment of endothelial cell function and viability. Additionally, our study revealed a concurrent elevation in the expression of sphingomyelin phosphodiesterases, enzymes responsible for catalyzing ceramide synthesis from sphingomyelins, within maximally diseased arterial segments. These findings underscore the pivotal role of ceramides and their biosynthesis enzymes in the context of CLTI, offering new insights into potential therapeutic avenues for managing this challenging disease process.

Acid sphingomyelinase promotes diabetic cardiomyopathy via NADPH oxidase 4 mediated apoptosis

BACKGROUND

Increased acid sphingomyelinase (ASMase) activity is associated with insulin resistance and cardiac dysfunction. However, the effects of ASMase on diabetic cardiomyopathy (DCM) and the molecular mechanism(s) underlying remain to be elucidated. We here investigated whether ASMase caused DCM through NADPH oxidase 4-mediated apoptosis.

METHODS AND RESULTS

We used pharmacological and genetic approaches coupled with study of murine and cell line samples to reveal the mechanisms initiated by ASMase in diabetic hearts. The protein expression and activity of ASMase were upregulated, meanwhile ceramide accumulation was increased in the myocardium of HFD mice. Inhibition of ASMase with imipramine (20 mg Kg^-1 d^-1) or siRNA reduced cardiomyocyte apoptosis, fibrosis, and mitigated cardiac hypertrophy and cardiac dysfunction in HFD mice. The similar effects were observed in cardiomyocytes treated with high glucose (HG, 30 mmol L^-1) + palmitic acid (PA, 100 μmol L^-1) or C16 ceramide (CER, 20 μmol L^-1). Interestingly, the cardioprotective effect of ASMase inhibition was not accompanied by reduced ceramide accumulation, indicating a ceramide-independent manner. The mechanism may involve activated NADPH oxidase 4 (NOX4), increased ROS generation and triggered apoptosis. Suppression of NOX4 with apocynin prevented HG + PA and CER incubation induced Nppb and Myh7 pro-hypertrophic gene expression, ROS production and apoptosis in H9c2 cells. Furthermore, cardiomyocyte-specific ASMase knockout (ASMase^Myh6KO) restored HFD-induced cardiac dysfunction, remodeling, and apoptosis, whereas NOX4 protein expression was downregulated.

CONCLUSIONS

These results demonstrated that HFD-mediated activation of cardiomyocyte ASMase could increase NOX4 expression, which may stimulate oxidative stress, apoptosis, and then cause metabolic cardiomyopathy.

CARDIOMYOCYTE REPROGRAMMING IN ANIMAL MODELS OF SEPTIC SHOCK

ABSTRACT

Cardiomyocyte reprogramming plays a pivotal role in sepsis-induced cardiomyopathy through the induction or overexpression of several factors and enzymes, ultimately leading to the characteristic decrease in cardiac contractility. The initial trigger is the binding of LPS to TLR-2, -3, -4, and -9 and of proinflammatory cytokines, such as TNF, IL-1, and IL-6, to their respective receptors. This induces the nuclear translocation of nuclear factors, such as NF-κB, via activation of MyD88, TRIF, IRAK, and MAPKs. Among the latter, ROS- and estrogen-dependent p38 and ERK 1/2 are proinflammatory, whereas JNK may play antagonistic, anti-inflammatory roles. Nuclear factors induce the synthesis of cytokines, which can amplify the inflammatory signal in a paracrine fashion, and of several effector enzymes, such as NOS-2, NOX-1, and others, which are ultimately responsible for the degradation of cardiomyocyte contractility. In parallel, the downregulation of enzymes involved in oxidative phosphorylation causes metabolic reprogramming, followed by a decrease in ATP production and the release of fragmented mitochondrial DNA, which may augment the process in a positive feedback loop. Other mediators, such as NO, ROS, the enzymes PI3K and Akt, and adrenergic stimulation may play regulatory roles, but not all signaling pathways that mediate cardiac dysfunction of sepsis do that by regulating reprogramming. Transcription may be globally modulated by miRs, which exert protective or amplifying effects. For all these mechanisms, differentiating between modulation of cardiomyocyte reprogramming versus systemic inflammation has been an ongoing but worthwhile experimental challenge.

Potential Drug Targets for Ceramide Metabolism in Cardiovascular Disease

Cardiovascular disease poses a significant threat to the quality of human life. Metabolic abnormalities caused by excessive caloric intake have been shown to lead to the development of cardiovascular diseases. Ceramides are structural molecules found in biological membranes; they are crucial for cell survival and lipid metabolism, as they maintain barrier function and membrane fluidity. Increasing evidence has demonstrated that ceramide has a strong correlation with cardiovascular disease progression. Nevertheless, it remains a challenge to develop sphingolipids as therapeutic targets to improve the prognosis of cardiovascular diseases. In this review, we summarize the three synthesis pathways of ceramide and other intermediates that are important in ceramide metabolism. Furthermore, mechanistic studies and therapeutic strategies, including clinical drugs and bioactive molecules based on these intermediates, are discussed.

microRNA-193-3p attenuates myocardial injury of mice with sepsis via STAT3/HMGB1 axis

Objective

Little is known regarding the functional role of microRNA-193-3p (miR-193-3p) in sepsis. Hence, the aim of the present study was to investigate the effect of miR-193-3p on myocardial injury in mice with sepsis and its mechanism through the regulation of signal transducers and activators of transcription 3 (STAT3).

Methods

The mice model of sepsis was established by cecal ligation and puncture (CLP), septic mice were injected with miR-193-3p agomir, miR-193-3p antagomir or siRNA-STAT3. The expression of miR-193-3p, STAT3 and HMGB1 in the myocardial tissue of septic mice were detected. Cardiac ultrasound, hemodynamics, myocardial injury markers, inflammatory factors and cardiomyocyte apoptosis in septic mice were measured.

Results

MiR-193-3p expression was reduced while STAT3 expression was increased in septic mice. Down-regulated STAT3 or up-regulated miR-193-3p improved cardiac function, attenuated myocardial injury, inflammation and cardiomyocyte apoptosis in septic mice. Knockdown STAT3 reversed the role of inhibited miR-193-3p for mice with sepsis. miR-193-3p targeted STAT3, thereby inhibiting HMGB1 expression.

Conclusion

This study provides evidence that miR-193-3p targets STAT3 expression to reduce HMGB1 expression, thereby reducing septic myocardial damage. MiR-193-3p might be a potential candidate marker and therapeutic target for sepsis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03022-x.

The lipid biology of sepsis

Sepsis, defined as the dysregulated immune response to an infection leading to organ dysfunction, is one of the leading causes of mortality around the globe. Despite the significant progress in delineating the underlying mechanisms of sepsis pathogenesis, there are currently no effective treatments or specific diagnostic biomarkers in the clinical setting. The perturbation of cell signaling mechanisms, inadequate inflammation resolution, and energy imbalance, all of which are altered during sepsis, are also known to lead to defective lipid metabolism. The use of lipids as biomarkers with high specificity and sensitivity may aid in early diagnosis and guide clinical decision making. In addition, identifying the link between specific lipid signatures and their role in sepsis pathology may lead to novel therapeutics. In this review, we discuss the recent evidence on dysregulated lipid metabolism both in experimental and human sepsis focused on bioactive lipids, fatty acids, and cholesterol as well as the enzymes regulating their levels during sepsis. We highlight not only their potential roles in sepsis pathogenesis but also the possibility of using these respective lipid compounds as diagnostic and prognostic biomarkers of sepsis.

Chrysin Ameliorates Sepsis-Induced Cardiac Dysfunction Through Upregulating Nfr2/Heme Oxygenase 1 Pathway

ABSTRACT

The incidence of myocardial dysfunction caused by sepsis is high, and the mortality of patients with sepsis can be significantly increased. During sepsis, oxidative stress and inflammation can lead to severe organ dysfunction. Flavone chrysin is one of the indispensable biological active ingredients for different fruits and vegetables and has antioxidant and anti-inflammatory properties. However, it is not clear whether chrysin is an effective treatment for heart dysfunction caused by sepsis. We found that it had protective effects against the harmful effects caused by LPS, manifested in improved survival, normalized cardiac function, improved partial pathological scores of myocardial tissue, and remission of apoptosis, as well as reduced oxidative stress and inflammation. Mechanism studies have found that chrysin is an important antioxidant protein, a key regulator of heme oxygenase 1 (HO-1). We found that HO-1 levels were increased after LPS intervention, and chrysin further increased HO-1 levels, along with the addition of Nrf2, a regulator of antioxidant proteins. Pretreatment with PD98059, an extracellular signal-regulated kinase-specific inhibitor, blocked chrysin-mediated phosphorylation of Nrf2 and the nuclear translocation of Nrf2. The protective effect of chrysin on sepsis-induced cardiac dysfunction was blocked by ZnPP, which is a HO-1 blocker. Chrysin increased antioxidant activity and reduced markers of oxidative stress (SOD and MDA) and inflammation (MPO and IL-1β), all of which were blocked by ZnPP. This indicates that HO-1 is the upstream molecule regulating the protective effect of chrysin. Thus, by upregulation of HO-1, chrysin protects against LPS-induced cardiac dysfunction and inflammation by inhibiting oxidative stress.

Drugs, Metabolites, and Lung Accumulating Small Lysosomotropic Molecules: Multiple Targeting Impedes SARS-CoV-2 Infection and Progress to COVID-19

Lysosomotropism is a biological characteristic of small molecules, independently present of their intrinsic pharmacological effects. Lysosomotropic compounds, in general, affect various targets, such as lipid second messengers originating from lysosomal enzymes promoting endothelial stress response in systemic inflammation; inflammatory messengers, such as IL-6; and cathepsin L-dependent viral entry into host cells. This heterogeneous group of drugs and active metabolites comprise various promising candidates with more favorable drug profiles than initially considered (hydroxy) chloroquine in prophylaxis and treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections/Coronavirus disease 2019 (COVID-19) and cytokine release syndrome (CRS) triggered by bacterial or viral infections. In this hypothesis, we discuss the possible relationships among lysosomotropism, enrichment in lysosomes of pulmonary tissue, SARS-CoV-2 infection, and transition to COVID-19. Moreover, we deduce further suitable approved drugs and active metabolites based with a more favorable drug profile on rational eligibility criteria, including readily available over-the-counter (OTC) drugs. Benefits to patients already receiving lysosomotropic drugs for other pre-existing conditions underline their vital clinical relevance in the current SARS-CoV2/COVID-19 pandemic.

Keep Your Friends Close, but Your Enemies Closer: Role of Acid Sphingomyelinase During Infection and Host Response

Breakdown of the inert and constitutive membrane building block sphingomyelin to the highly active lipid mediator ceramide by extracellularly active acid sphingomyelinase is tightly regulated during stress response and opens the gate for invading pathogens, triggering the immune response, development of remote organ failure, and tissue repair following severe infection. How do one enzyme and one mediator manage all of these affairs? Under physiological conditions, the enzyme is located in the lysosomes and takes part in the noiseless metabolism of sphingolipids, but following stress the protein is secreted into circulation. When secreted, acid sphingomyelinase (ASM) is able to hydrolyze sphingomyelin present at the outer leaflet of membranes to ceramide. Its generation troubles the biophysical context of cellular membranes resulting in functional assembly and reorganization of proteins and receptors, also embedded in highly conserved response mechanisms. As a consequence of cellular signaling, not only induction of cell death but also proliferation, differentiation, and fibrogenesis are affected. Here, we discuss the current state of the art on both the impact and function of the enzyme during host response and damage control. Also, the potential role of lysosomotropic agents as functional inhibitors of this upstream alarming cascade is highlighted.

New Approaches to Identify Sepsis Biomarkers: The Importance of Model and Sample Source for Mass Spectrometry

Septic shock is a systemic inflammatory response syndrome associated with circulatory failure leading to organ failure with a 40% mortality rate. Early diagnosis and prognosis of septic shock are necessary for specific and timely treatment. However, no predictive biomarker is available. In recent years, improvements in proteomics-based mass spectrometry have improved the detection of such biomarkers. This approach can be performed on different samples such as tissue or biological fluids. Working directly from human samples is complicated owing to interindividual variability. Indeed, patients are admitted at different stages of disease development and with signs of varying severity from one patient to another. All of these elements interfere with the identification of early, sensitive, and specific septic shock biomarkers. For these reasons, animal models of sepsis, although imperfect, are used to control the kinetics of the development of the pathology and to standardise experimentation, facilitating the identification of potential biomarkers. These elements underline the importance of the choice of animal model used and the sample to be studied during preclinical studies. The aim of this review is to discuss the relevance of different approaches to enable the identification of biomarkers that could indirectly be relevant to the clinical setting.

COVID-19/SARS-CoV-2 Infection: Lysosomes and Lysosomotropism Implicate New Treatment Strategies and Personal Risks

In line with SARS and MERS, the SARS-CoV-2/COVID-19 pandemic is one of the largest challenges in medicine and health care worldwide. SARS-CoV-2 infection/COVID-19 provides numerous therapeutic targets, each of them promising, but not leading to the success of therapy to date. Neither an antiviral nor an immunomodulatory therapy in patients with SARS-CoV-2 infection/COVID-19 or pre-exposure prophylaxis against SARS-CoV-2 has proved to be effective. In this review, we try to close the gap and point out the likely relationships among lysosomotropism, increasing lysosomal pH, SARS-CoV-2 infection, and disease process, and we deduce an approach for the treatment and prophylaxis of COVID-19, and cytokine release syndrome (CRS)/cytokine storm triggered by bacteria or viruses. Lysosomotropic compounds affect prominent inflammatory messengers (e.g., IL-1B, CCL4, CCL20, and IL-6), cathepsin-L-dependent viral entry of host cells, and products of lysosomal enzymes that promote endothelial stress response in systemic inflammation. As supported by recent clinical data, patients who have already taken lysosomotropic drugs for other pre-existing conditions likely benefit from this treatment in the COVID-19 pandemic. The early administration of a combination of antivirals such as remdesivir and lysosomotropic drugs, such as the antibiotics teicoplanin or dalbavancin, seems to be able to prevent SARS-CoV-2 infection and transition to COVID-19.

Metabolomics approach based on utra-performance liquid chromatography coupled to mass spectrometry with chemometrics methods for high-throughput analysis of metabolite biomarkers to explore the abnormal metabolic pathways associated with myocardial dysfunction

Ultra-performance liquid chromatography/mass spectrometry-based metabolomics can been used for discovery of metabolite biomarkers to explore the metabolic pathway of diseases. Identification of metabolic pathways is key to understanding the pathogenesis and mechanism of disease. Myocardial dysfunction induced by sepsis (SMD) is a severe complication of septic shock and represents major causes of death in intensive care units; however its pathological mechanism is still not clear. In this study, ultrahigh-pressure liquid chromatography with mass spectrometry-based metabolomics with chemometrics anaylsis and multivariate pattern recognition analysis were used to detect urinary metabolic profile changes in a lipopolysaccharide-induced SMD mouse model. Multivariate statistical analysis including principal component analysis and orthogonapartial least squares discriminant analysis for the discrimination of SMD was conducted to identify potential biomarkers. A total of 19 differential metabolites were discovered by high-resolution mass spectrometry-based urinary metabolomics strategy. The altered biochemical pathways based on these metabolites showed that tyrosine metabolism, phenylalanine metabolism, ubiquinone biosynthesis and vitamin B6 metabolism were closely connected to the pathological processes of SMD. Consequently, integrated chemometric analyses of these metabolic pathways are necessary to extract information for the discovery of novel insights into the pathogenesis of disease.

β3-Adrenergic receptor blockade reduces mortality in endotoxin-induced heart failure by suppressing induced nitric oxide synthase and saving cardiac metabolism

The β₃-adrenergic receptor (β₃AR) is related to myocardial fatty acid metabolism and its expression has been implicated in heart failure. In this study, we investigated the role of β₃AR in sepsis-related myocardial dysfunction using lipopolysaccharide (LPS)-induced endotoxemia as a model of cardiac dysfunction. We placed mice into three treatment groups and treated each with intraperitoneal injections of the β₃AR agonist CL316243 (CL group), the β₃AR antagonist SR59230A (SR group), or normal saline (NS group). Survival rates were significantly improved in the SR group compared with the other treatment groups. Echocardiography analyses revealed cardiac dysfunction within 6-12 h of LPS injections, but the outcome was significantly better for the SR group. Myocardial ATP was preserved in the SR group but was decreased in the CL-treated mice. Additionally, quantitative PCR analysis revealed that expression levels of genes associated with fatty acid oxidation and glucose metabolism were significantly higher in the SR group. Furthermore, the expression levels of mitochondrial membrane protein complexes were preserved in the SR group. Electron microscope studies showed significant accumulation of lipid droplets in the CL group. Moreover, inducible nitric oxide synthase (iNOS) protein expression and nitric oxide were significantly reduced in the SR group. The in vitro study demonstrated that β₃AR has an independent iNOS pathway that does not go through the nuclear factor-κB pathway. These results suggest that blockading β₃AR improves impaired energy metabolism in myocardial tissues by suppressing iNOS expression and recovers cardiac function in animals with endotoxin-induced heart failure.NEW & NOTEWORTHY Nitric oxide production through stimulation of β₃-adrenergic receptor (β₃AR) may improve cardiac function in cases of chronic heart failure. We demonstrated that the blockade of β₃AR improved mortality and cardiac function in endotoxin-induced heart failure. We also determined that LPS-induced inducible nitric oxide synthase has a pathway that is independent of nuclear factor-κB, which worsened cardiac metabolism and mortality in the acute phase of sepsis. Treatment with the β₃AR antagonist had a favorable effect. Thus, the blockade of β₃AR could offer a novel treatment for sepsis-related heart failure.

Effect of sepsis on the action potential and cardiac serotonin response in rats

The current study aimed to investigate the effect of sepsis on rat serotonin (5-HT) responses and cardiac action potentials. A total of 20 rats were randomly divided into a sepsis and control group (each, n=10). Rat hearts were harvested and perfused using the Langendorff method 18-h after the induction of sepsis, which was assessed using cecal puncture. Cardiac action potential was subsequently measured using a multichannel electrophysiology instrument. Immunohistochemistry and quantitative analysis were performed to identify the effect of sepsis on myocardial 5-HT expression. The results revealed that mitochondrial changes were present in septic rat hearts. Heart rate (361.10±12.29 bpm vs. 348.60±12.38 bpm; P<0.05) was significantly higher, atrial action potential duration (106.40±2.95 ms vs. 86.60±4.12 ms; P<0.01) was significantly longer and the area (0.62±0.06 µm² vs. 0.39±0.05 µm²; P<0.05) and number (0.92±0.02/field vs. 0.46±0.01/field; P<0.01) of myocardial cells were significantly higher in the septic compared with the control group. These results demonstrated that 5-HT prolongs the atrial action potential, increases heart rate and aggravates myocardial injury, indicating that it may therefore be one of the factors that leads to cardiac dysfunction in sepsis.

High-throughput metabolic profiling, combined with chemometrics and bioinformatic analysis reveals functional alterations in myocardial dysfunction

High-throughput metabolic profiling technology has been used for biomarker discovery and to reveal underlying metabolic mechanisms.

Acid Sphingomyelinase Inhibition Stabilizes Hepatic Ceramide Content and Improves Hepatic Biotransformation Capacity in a Murine Model of Polymicrobial Sepsis

Liver dysfunction during sepsis is an independent risk factor leading to increased mortality rates. Specifically, dysregulation of hepatic biotransformation capacity, especially of the cytochrome P450 (CYP) system, represents an important distress factor during host response. The activity of the conserved stress enzyme sphingomyelin phosphodiesterase 1 (SMPD1) has been shown to be elevated in sepsis patients, allowing for risk stratification. Therefore, the aim of the present study was to investigate whether SMPD1 activity has an impact on expression and activity of different hepatic CYP enzymes using an animal model of polymicrobial sepsis. Polymicrobial sepsis was induced in SMPD1 wild-type and heterozygous mice and hepatic ceramide content as well as CYP mRNA, protein expression and enzyme activities were assessed at two different time points, at 24 h, representing the acute phase, and at 28 days, representing the post-acute phase of host response. In the acute phase of sepsis, SMPD1^+/+ mice showed an increased hepatic C16- as well as C18-ceramide content. In addition, a downregulation of CYP expression and activities was detected. In SMPD1^+/- mice, however, no noticeable changes of ceramide content and CYP expression and activities during sepsis could be observed. After 28 days, CYP expression and activities were normalized again in all study groups, whereas mRNA expression remained downregulated in SMPD^+/+ animals. In conclusion, partial genetic inhibition of SMPD1 stabilizes hepatic ceramide content and improves hepatic monooxygenase function in the acute phase of polymicrobial sepsis. Since we were also able to show that the functional inhibitor of SMPD1, desipramine, ameliorates downregulation of CYP mRNA expression and activities in the acute phase of sepsis in wild-type mice, SMPD1 might be an interesting pharmacological target, which should be further investigated.

γ-glutamylcysteine exhibits anti-inflammatory effects by increasing cellular glutathione level

Sepsis is a life-threatening organ dysfunction caused by dysregulated host response to infection and characterized by redox imbalance and severe oxidative stress. Glutathione (GSH) serves several vital functions, including scavenging free radicals and maintaining intracellular redox balance. Extracellular GSH is unable to be taken into the majority of human cells, and the GSH prodrug N-acetyl-l-cysteine (NAC) does not exhibit promising clinical effects. γ-glutamylcysteine (γ-GC), an intermediate dipeptide of the GSH-synthesis pathway and harboring anti-inflammatory properties, represents a relatively unexplored option for sepsis treatment. The anti-inflammatory efficiency of γ-GC and the associated molecular mechanism need to be explored. In vivo investigation showed that γ-GC reduced sepsis lethality and attenuated systemic inflammatory responses in mice, as well as inhibited lipopolysaccharide (LPS)-stimulated production of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), high-mobility group box 1 (HMGB1), and nitric oxide (NO) and the expression of inducible NO synthase and cyclooxygenase 2 in RAW264.7 cells. Moreover, both in vivo and in vitro experiments demonstrated that γ-GC exhibited better therapeutic effects against inflammation compared with N-acetyl-L-cysteine (NAC) and GSH. Mechanistically, γ-GC suppressed LPS-induced reactive oxygen species accumulation and GSH depletion. Inflammatory stimuli, such as LPS treatment, upregulated the expression of glutathione synthetase via activating nuclear factor-erythroid 2-related factor (Nrf2) and nuclear factor kappa B (NF-κB) pathways, thereby promoting synthesis of GSH from γ-GC. These findings suggested that γ-GC might represent a potential therapeutic agent for sepsis treatment.

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γ-GC reduces sepsis lethality and attenuates inflammatory responses in BALB/c mice.

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γ-GC suppresses LPS-induced inflammation, ROS accumulation, and GSH depletion.

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Nrf2 and NF-κB pathways are essential for upregulating GSS level to promote GSH synthesis from γ-GC.

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γ-GC is more effective in attenuation inflammation than NAC and GSH.

Acid Sphingomyelinase Inhibition Prevents Development of Sepsis Sequelae in the Murine Liver

The molecular mechanisms of maladaptive response in liver tissue with respect to the acute and post-acute phase of sepsis are not yet fully understood. Long-term sepsis survivors might develop hepatocellular/hepatobiliary injury and fibrosis. Here, we demonstrate that acid sphingomyelinase, an important regulator of hepatocyte apoptosis and hepatic stellate cell (HSC) activation, is linked to the promotion of liver dysfunction in the acute phase of sepsis as well as to fibrogenesis in the long-term. In both phases, we observed a beneficial effect of partial genetic sphingomyelinase deficiency in heterozygous animals (smpd1^+/−) on oxidative stress levels, hepatobiliary function, macrophage infiltration and on HSC activation. Strikingly, similar to heterozygote expression of SMPD1, either preventative (p-smpd1^+/+) or therapeutic (t-smpd1^+/+) pharmacological treatment strategies with desipramine – a functional inhibitor of acid sphingomyelinase (FIASMA) – significantly improved liver function and survival. The inhibition of sphingomyelinase exhibited a protective effect on liver function in the acute-phase, and the reduction of HSC activation diminished development of sepsis-associated liver fibrosis in the post-acute phase of sepsis. In summary, targeting sphingomyelinase with FDA-approved drugs is a novel promising strategy to overcome sepsis-induced liver dysfunction.