Blockade of indoleamine 2,3-dioxygenase reduces mortality from peritonitis and sepsis in mice by regulating functions of CD11b+ peritoneal cells

Neuroimmune modulation by tryptophan derivatives in neurological and inflammatory disorders

The nervous and immune systems are highly developed, and each performs specialized physiological functions. However, they work together, and their dysfunction is associated with various diseases. Specialized molecules, such as neurotransmitters, cytokines, and more general metabolites, are essential for the appropriate regulation of both systems. Tryptophan, an essential amino acid, is converted into functional molecules such as serotonin and kynurenine, both of which play important roles in the nervous and immune systems. The role of kynurenine metabolites in neurodegenerative and psychiatric diseases has recently received particular attention. Recently, we found that hyperactivity of the kynurenine pathway is a critical risk factor for septic shock. In this review, we first outline neuroimmune interactions and tryptophan derivatives and then summarized the changes in tryptophan metabolism in neurological disorders. Finally, we discuss the potential of tryptophan derivatives as therapeutic targets for neuroimmune disorders.

Integrative analysis of metabolomics and transcriptomics to uncover biomarkers in sepsis

To utilize metabolomics in conjunction with RNA sequencing to identify biomarkers in the blood of sepsis patients and discover novel targets for diagnosing and treating sepsis. In January 2019 and December 2020, blood samples were collected from a cohort of 16 patients diagnosed with sepsis and 11 patients diagnosed with systemic inflammatory response syndrome (SIRS). Non-targeted metabolomics analysis was conducted using liquid chromatography coupled with mass spectrometry (LC-MS/MS technology), while gene sequencing was performed using RNA sequencing. Afterward, the metabolite data and sequencing data underwent quality control and difference analysis, with a fold change (FC) greater than or equal to 2 and a false discovery rate (FDR) less than 0.05.Co-analysis was then performed to identify differential factors with consistent expression trends based on the metabolic pathway context; KEGG enrichment analysis was performed on the crossover factors, and Meta-analysis of the targets was performed at the transcriptome level using the public dataset. In the end, a total of five samples of single nucleated cells from peripheral blood (two normal controls, one with systemic inflammatory response syndrome, and two with sepsis) were collected and examined to determine the cellular location of the essential genes using 10× single cell RNA sequencing (scRNA-seq). A total of 485 genes and 1083 metabolites were found to be differentially expressed in the sepsis group compared to the SIRS group. Among these, 40 genes were found to be differentially expressed in both the metabolome and transcriptome. Functional enrichment analysis revealed that these genes were primarily involved in biological processes related to inflammatory response, immune regulation, and amino acid metabolism. Furthermore, a meta-analysis identified four genes, namely ITGAM, CD44, C3AR1, and IL2RG, which were highly expressed in the sepsis group compared to the normal group (P < 0.05). Additionally, scRNA-seq analysis revealed that the core genes ITGAM and C3AR1 were predominantly localized within the macrophage lineage. The primary genes ITGAM and C3AR1 exhibit predominant expression in macrophages, which play a significant role in inflammatory and immune responses. Moreover, these genes show elevated expression levels in the plasma of individuals with sepsis, indicating their potential as valuable subjects for further research in sepsis.

IDO/Kynurenine; novel insight for treatment of inflammatory diseases

Inflammation and oxidative stress play pivotal roles in pathogenesis of many diseases including cancer, type 2 diabetes, cardiovascular disease, atherosclerosis, neurological diseases, and inflammatory diseases such as inflammatory bowel disease (IBD). Inflammatory mediators such as interleukins (ILs), interferons (INF-s), and tumor necrosis factor (TNF)-α are related to an extended chance of inflammatory diseases initiation or progression due to the over expression of the nuclear factor Kappa B (NF-κB), signal transducer of activators of transcription (STAT), nod-like receptor family protein 3 (NLRP), toll-like receptors (TLR), mitogen-activated protein kinase (MAPK), and mammalian target of rapamycin (mTOR) pathways. These pathways are completely interconnected. Theindoleamine 2,3 dioxygenase (IDO) subset of the kynurenine (KYN) (IDO/KYN), is a metabolic inflammatory pathway involved in production of nicotinamide adenine dinucleotide (NAD + ). It has been shown that IDO/KYN actively participates in inflammatory processes and can increase the secretion of cytokines that provoke inflammatory diseases. Data were extracted from clinical and animal studies published in English between 1990-April 2022, which were collected from PubMed, Google Scholar, Scopus, and Cochrane library. IDO/KYN is completely associated with inflammatory-related pathways, thus leading to the production of cytokines such as TNF-α, IL-1β, and IL-6, and ultimately development and progression of various inflammatory disorders. Inhibition of the IDO/KYN pathway might be a novel therapeutic option for inflammatory diseases. Herein, we gathered data on probable interactions of the IDO/KYN pathway with induction of some inflammatory diseases.

Blockade of Indoleamine 2,3-Dioxygenase attenuates lipopolysaccharide-induced kidney injury by inhibiting TLR4/NF-κB signaling

Blockade of indoleamine 2,3-dioxygenase (IDO) has been shown to alleviate lipopolysaccharide (LPS)-induced endotoxic shock and reduce sepsis mortality, but its effect on LPS-induced kidney damage has not been reported. Herein, we established a mouse kidney injury model by intraperitoneal injection of 10 mg/kg LPS and established an in vitro renal tubular epithelial cell injury model by stimulating TCMK-1 cells with 10 mg/L LPS. We found that pretreatment with 1-methyl tryptophan (1-MT), an IDO inhibitor, significantly improved LPS-induced mouse survival, and IDO knockout (KO) mice also had higher survival rates after LPS exposure than wild-type mice. At the same time, IDO KO or pretreatment with 1-MT not only reduced serum creatinine, blood urea nitrogen, renal tubular injury pathological score, but also inflammatory factors and oxidative stress status in serum or kidney of LPS-exposed mice. In vitro, blockade of IDO with 1-MT significantly inhibited LPS-induced apoptosis, inflammation and oxidative stress in TCMK-1 cells. In addition, blockade of IDO significantly inhibited LPS-activated TLR4/NF-κB signaling pathway in kidney of mice or in TCMK-1 cells. In conclusion, our results suggested that blockade of IDO attenuated kidney inflammation, apoptosis and oxidative stress to protect against LPS-induced septic kidney injury via inhibiting the TLR4/NF-κB signaling pathway.

Altered Tryptophan-Kynurenine Pathway in Delirium: A Review of the Current Literature

Delirium, a common form of acute brain dysfunction, is associated with increased morbidity and mortality, especially in older patients. The underlying pathophysiology of delirium is not clearly understood, but acute systemic inflammation is known to drive delirium in cases of acute illnesses, such as sepsis, trauma, and surgery. Based on psychomotor presentations, delirium has three main subtypes, such as hypoactive, hyperactive, and mixed subtype. There are similarities in the initial presentation of delirium with depression and dementia, especially in the hypoactive subtype. Hence, patients with hypoactive delirium are frequently misdiagnosed. The altered kynurenine pathway (KP) is a promising molecular pathway implicated in the pathogenesis of delirium. The KP is highly regulated in the immune system and influences neurological functions. The activation of indoleamine 2,3-dioxygenase, and specific KP neuroactive metabolites, such as quinolinic acid and kynurenic acid, could play a role in the event of delirium. Here, we collectively describe the roles of the KP and speculate on its relevance in delirium.

Effects of Ozone on Sickness and Depressive-like Behavioral and Biochemical Phenotypes and Their Regulation by Serum Amyloid A in Mice

Ozone (O₃) is an air pollutant that primarily damages the lungs, but growing evidence supports the idea that O₃ also harms the brain; acute exposure to O₃ has been linked to central nervous system (CNS) symptoms such as depressed mood and sickness behaviors. However, the mechanisms by which O₃ inhalation causes neurobehavioral changes are limited. One hypothesis is that factors in the circulation bridge communication between the lungs and brain following O₃ exposure. In this study, our goals were to characterize neurobehavioral endpoints of O₃ exposure as they relate to markers of systemic and pulmonary inflammation, with a particular focus on serum amyloid A (SAA) and kynurenine as candidate mediators of O₃ behavioral effects. We evaluated O₃-induced dose-, time- and sex-dependent changes in pulmonary inflammation, circulating SAA and kynurenine and its metabolic enzymes, and sickness and depressive-like behaviors in Balb/c and CD-1 mice. We found that 3 parts per million (ppm) O₃, but not 2 or 1 ppm O₃, increased circulating SAA and lung inflammation, which were resolved by 48 h and was worse in females. We also found that indoleamine 2,3-dioxygenase (Ido1) mRNA expression was increased in the brain and spleen 24 h after 3 ppm O₃ and that kynurenine was increased in blood. Sickness and depressive-like behaviors were observed at all O₃ doses (1-3 ppm), suggesting that behavioral responses to O₃ can occur independently of increased SAA or neutrophils in the lungs. Using SAA knockout mice, we found that SAA did not contribute to O₃-induced pulmonary damage or inflammation, systemic increases in kynurenine post-O₃, or depressive-like behavior but did contribute to weight loss. Together, these findings indicate that acute O₃ exposure induces transient symptoms of sickness and depressive-like behaviors that may occur in the presence or absence of overt pulmonary neutrophilia and systemic increases of SAA. SAA does not appear to contribute to pulmonary inflammation induced by O₃, although it may contribute to other aspects of sickness behavior, as reflected by a modest effect on weight loss.

Skeletal Muscle Myokine Expression in Critical Illness, Association With Outcome and Impact of Therapeutic Interventions

Context

Muscle expresses and secretes several myokines that bring about benefits in distant organs.

Objective

We investigated the impact of critical illness on muscular expression of irisin, kynurenine aminotransferases, and amylase; association with clinical outcome; and impact of interventions that attenuate muscle wasting/weakness.

Methods

We studied critically ill patients who participated in 2 randomized controlled trials (EPaNIC/NESCI) and documented time profiles in critically ill mice. Included in the study were 174 intensive care unit (ICU) patients (day 8 ± 1) vs 19 matched controls, and 60 mice subjected to surgery/sepsis vs 60 pair-fed healthy mice. Interventions studied included 7-day neuromuscular electrical stimulation (NMES), and withholding parenteral nutrition (PN) in the first ICU week (late PN) vs early PN. The main outcome measures were FNDC5 (irisin- precursor), KYAT1, KYAT3, and amylase mRNA expression in skeletal muscle.

Results

Critically ill patients showed 34% to 80% lower mRNA expression of FNDC5, KYAT1, and amylases than controls (P < .0001). Critically ill mice showed time-dependent reductions in all mRNAs compared with healthy mice (P ≤ .04). The lower FNDC5 expression in patients was independently associated with a higher ICU mortality (P = .015) and ICU-acquired weakness (P = .012), whereas the lower amylase expression in ICU survivors was independently associated with a longer ICU stay (P = .0060). Lower amylase expression was independently associated with a lower risk of death (P = .048), and lower KYAT1 expression with a lower risk of weakness (P = .022). NMES increased FNDC5 expression compared with unstimulated muscle (P = .016), and late PN patients had a higher KYAT1 expression than early PN patients (P = .022).

Conclusion

Expression of the studied myokines was affected by critical illness and associated with clinical outcomes, with limited effects of interventions that attenuate muscle wasting or weakness.

Kynurenine Pathway-An Underestimated Factor Modulating Innate Immunity in Sepsis-Induced Acute Kidney Injury?

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection, and it accounts for about half of the cases of acute kidney injury (AKI). Although sepsis is the most frequent cause of AKI in critically ill patients, its pathophysiological mechanisms are not well understood. Sepsis has the ability to modulate the function of cells belonging to the innate immune system. Increased activity of indoleamine 2,3-dioxygenase 1 (IDO1) and production of kynurenines are the major metabolic pathways utilized by innate immunity cells to maintain immunological tolerance. The activation of the kynurenine pathway (KP) plays a dual role in sepsis—in the early stage, the induction of IDO1 elicits strong proinflammatory effects that may lead to tissue damage and septic shock. Afterwards, depletion of tryptophan and production of kynurenines contribute to the development of immunosuppression that may cause the inability to overpower opportunistic infections. The presented review provides available data on the various interdependencies between elements of innate immunity and sepsis-induced AKI (SAKI) with particular emphasis on the immunomodulatory significance of KP in the above processes. We believe that KP activation may be one of the crucial, though underestimated, components of a deregulated host response to infection during SAKI.

Therapeutic Effects of Retinoic Acid in Lipopolysaccharide-Induced Cardiac Dysfunction: Network Pharmacology and Experimental Validation

Purpose

Sepsis, which is deemed as a systemic inflammation reaction syndrome in the face of infectious stimuli, is the primary cause of death in ICUs. Sepsis-induced cardiomyopathy (SIC) may derive from systemic inflammation reaction and oxidative stress. Retinoic acid (RA) is recognized by its beneficial roles in terms of the immunoresponse to infections and antioxygen actions. However, the treatment efficacy and potential causal links of RA in SIC are still elusive.

Methods

By virtue of the STITCH database, we identified the targets of RA. Differentially expressed genes in SIC were acquired from the GEO database. The PPI network of intersected targets was established. GO and KEGG pathway enrichment analysis was completed. Hub genes were analyzed by cytoHubba plug-in. In the process of experimental validation, a mouse sepsis model was established by lipopolysaccharide (LPS), and the treated mice were intraperitoneally injected with RA or Dexamethasone (DEX) 60 min prior to LPS injections. Survival conditions, cardiac functions and antioxidant levels of the mice were assessed. Cardiac inflammation and injury were detected by HE and TUNEL. The levels of key genes and signal pathway expression were analyzed by RT-PCR and Western blot.

Results

PPARA, ITGAM, VCAM-1, IGF-1 and IL-6 were identified as key therapeutic targets of RA by network pharmacology. PI3K-Akt signaling pathway is the main regulatory pathway of RA. In vivo researches unraveled that RA can improve the survival rate and cardiac function of LPS-treated mice, inhibit inflammatory factors and myocardial injury, and regulate the expression of key therapeutic targets and key pathways, which is PI3K-Akt signaling pathway.

Conclusion

Network pharmacological method offers a predicative strategy to explore the treatment efficacy and causal links of RA in endotoxemic myocarditis. Through experimental verification, we discover that RA can reduce lipopolysaccharide-induced cardiac dysfunction by regulating the PI3K-Akt signaling pathway and key genes.

Nociceptor-derived Reg3γ prevents endotoxic death by targeting kynurenine pathway in microglia

Nociceptors can fine-tune local or systemic immunity, but the mechanisms of nociceptive modulation in endotoxic death remain largely unknown. Here, we identified C-type lectin Reg3γ as a nociceptor-enriched hormone that protects the host from endotoxic death. During endotoxemia, nociceptor-derived Reg3γ penetrates the brain and suppresses the expression of microglial indoleamine dioxygenase 1, a critical enzyme of the kynurenine pathway, via the Extl3-Bcl10 axis. Endotoxin-administered nociceptor-null mice and nociceptor-specific Reg3γ-deficient mice exhibit a high mortality rate accompanied by decreased brain HK1 phosphorylation and ATP production despite normal peripheral inflammation. Such metabolic arrest is only observed in the brain, and aberrant production of brain quinolinic acid, a neurotoxic metabolite of the kynurenine pathway, causes HK1 suppression. Strikingly, the central administration of Reg3γ protects mice from endotoxic death by enhancing brain ATP production. By identifying nociceptor-derived Reg3γ as a microglia-targeted hormone, this study provides insights into the understanding of tolerance to endotoxic death.

Indoleamine-2,3-Dioxygenase as a Perioperative Marker of the Immune System

Indoleamine-2,3-dioxygenase (IDO) is the “rate-limiting” enzyme in the kynurenine (Kyn) pathway of the tryptophan (Trp) catabolism. By its immune-modulatory effect, IDO initiates changes to the physiologically balanced immune state and plays a key role in the pathogenesis of various diseases, as well as in the perioperative setting during surgery. In autoimmune processes, highly malignant cancers such as glioblastoma or organ transplantation, IDO’s involvement has been studied extensively. However, in severe systemic infections, as present in sepsis, it is not yet completely understood. Hereafter, in this narrative review, we present the current knowledge of IDO’s implication on such complex immune-related processes. Moreover, we address the role of IDO as a predictive biomarker as well as a therapeutic target for immune-mediated diseases. Finally, we discuss IDO in the setting of surgical trauma-induced stress and highlight its promising use as a biomarker in the pre-operative setting for all disciplines involved in the decision-making process and treatment of patients undergoing surgery.

Inhibition of Tryptophan Catabolism Is Associated With Neuroprotection During Zika Virus Infection

Zika virus (ZIKV) is an arbovirus belonging to Flaviviridae family that emerged as a global health threat due to its association with microcephaly and other severe neurological complications, including Guillain-Barré Syndrome (GBS) and Congenital Zika Syndrome (CZS). ZIKV disease has been linked to neuroinflammation and neuronal cell death. Neurodegenerative processes may be exacerbated by metabolites produced by the kynurenine pathway, an important pathway for the degradation of tryptophan, which induces neuronal dysfunction due to enhanced excitotoxicity. Here, we exploited the hypothesis that ZIKV-induced neurodegeneration can be rescued by blocking a target enzyme of the kynurenine pathway, the Indoleamine 2,3-dioxygenase (IDO-1). RT-PCR analysis showed increased levels of IDO-1 RNA expression in undifferentiated primary neurons isolated from wild type (WT) mice infected by ZIKV ex vivo, as well as in the brain of ZIKV-infected A129 mice. Pharmacological inhibition of IDO-1 enzyme with 1-methyl-D-tryptophan (1-MT), in both in vitro and in vivo systems, led to significant reduction of ZIKV-induced neuronal death without interfering with the ability of ZIKV to replicate in those cells. Furthermore, in vivo analyses using both genetically modified mice (IDO^-/- mice) and A129 mice treated with 1-MT resulted in reduced microgliosis, astrogliosis and Caspase-3 positive cells in the brain of ZIKV-infected A129 mice. Interestingly, increased levels of CCL5 and CXCL-1 chemokines were found in the brain of 1-MT treated-mice. Together, our data indicate that IDO-1 blockade provides a neuroprotective effect against ZIKV-induced neurodegeneration, and this is amenable to inhibition by pharmacological treatment.

Analysis of mRNA‑lncRNA and mRNA‑lncRNA-pathway co‑expression networks based on WGCNA in developing pediatric sepsis

Pediatric sepsis is a great threat to death worldwide. However, the pathogenesis has not been clearly understood until now in sepsis. This study identified differentially expressed mRNAs and lncRNAs based on Gene Expression Omnibus (GEO) database. And the weighted gene co-expression network analysis (WGCNA) was performed to explore co-expression modules associated with pediatric sepsis. Then, Gene Ontology (GO), KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway, mRNA‑lncRNA and mRNA‑lncRNA-pathway co-expression network analysis was conducted in selected significant module. A total of 1941 mRNAs and 225 lncRNAs were used to conduct WGCNA. And turquoise module was selected as a significant module that was associated with particular traits. The mRNAs functions associated with many vital processes were also shown by GO and KEGG pathway analysis in the turquoise module. Finally, 15 mRNAs (MAPK14, ITGAM, HK3, ALOX5, CR1, HCK, NCF4, PYGL, FLOT1, CARD6, NLRC4, SH3GLB1, PGS1, RAB31, LTB4R) and 4 lncRNAs (GSEC, NONHSAT160878.1, XR_926068.1 and RARA-AS1) were selected as hub genes in mRNA‑lncRNA-Pathway co-expression network. We identified 15 mRNAs and 4 lncRNAs as diagnostic markers, which have potential functions in pediatric sepsis. Our study provides more directions to study the molecular mechanism of pediatric sepsis.Abbreviations: mRNA: messenger RNA; lncRNA: long noncoding RNAs; GEO: Gene Expression Omnibus; WGCNA: weighted gene co-expression network analysis; GO: Gene Ontology; KEGG: Kyoto Encyclopedia of Genes and Genomes; SIRS: systemic inflammatory response syndrome; TOM: topological overlap measure; BP: biological process; MF: molecular function; CC: cellular component; ROC: receiver operating characteristic curve; AUC: area under curve; MAPK14: Mitogen-activated protein kinase 14; ALI: acute lung injury; ITGAM: Integrin subunit alpha M; HK3: Hexokinase 3; LPS: lipopolysaccharide; 5-LO: 5-lipoxygenase; LTs: leukotrienes; LTB4R: leukotriene B4 receptor.

Necroptosis is active and contributes to intestinal injury in a piglet model with lipopolysaccharide challenge

Necroptosis, a newly discovered form of programmed cell death that combines the features of apoptosis and necrosis, is important in various physiological and pathological disorders. However, the role of necroptosis on intestinal injury during sepsis has been rarely evaluated. This study aimed to investigate the presence of necroptosis in intestinal injury, and its contribution to intestinal injury in a piglet model challenged with Escherichia coli lipopolysaccharide (LPS). Firstly, a typical cell necrotic phenomenon was observed in jejunum of LPS-challenged pigs by transmission electron microscope. Protein expression of necroptosis signals including receptor-interacting protein kinase (RIP) 1, RIP3, and phosphorylated mixed-lineage kinase domain-like protein (MLKL), mitochondrial proteins including phosphoglycerate mutase family member 5 (PGAM5) and dynamin-related protein 1 (DRP1), and cytoplasmic high-mobility group box 1 (HMGB1) were time-independently increased in jejunum of LPS-challenged piglets, which was accompanied by the impairment of jejunal morphology, and digestive and barrier function indicated by lower activities of jejunal disaccharidases and protein expression of jejunal tight junction proteins claudin-1 and occludin. Pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6 were also dynamically induced in serum and jejunum of piglets after LPS challenge. Moreover, pretreatment with necrostatin-1 (Nec-1), an specific inhibitor of necroptosis, inhibited necroptosis indicated by decreased necrotic ultrastructural changes and decreased protein expression of RIP1, RIP3, and phosphorylated MLKL as well as PGAM5, DRP1, and cytoplasmic HMGB1. Nec-1 pretreatment reduced jejunal morphological injury, and improved digestive and barrier function. Nec-1 pretreatment also decreased the levels of serum and jejunal pro-inflammatory cytokines and the numbers of jejunal macrophages and monocytes. These findings indicate for the first time that necroptosis is present and contributes to LPS-induced intestinal injury. Nec-1 may have a preventive effect on intestinal injury during sepsis.

Kynurenine produced by indoleamine 2,3-dioxygenase 2 exacerbates acute liver injury by carbon tetrachloride in mice

Kynurenine (Kyn) plays an important role as an immune check-point molecule and regulates various immune responses through its aryl hydrocarbon receptor (Ahr). Kyn is synthesized by indoleamine 2,3-dioxygenase (Ido) and tryptophan 2,3-dioxygenase (Tdo). Ido contributes approximately 90% of tryptophan catabolism. Although Kyn is increased in various liver disorders, the roles of Kyn in liver injury are complicated because Ido1, Ido2, and Tdo are activated in different cell types. In this study, the roles of Ido2 in carbon tetrachloride (CCl₄; 1 ml/kg, i.p.)-induced acute liver injury were examined using Ido2 knockout mice and Ido2 inhibitor. After CCl₄ treatment, the ratio of Kyn to tryptophan and levels of Kyn in the liver were increased, accompanied by activation of Ahr-mediated signaling, as revealed by increased nuclear Ahr and Cyp1a1 mRNA. Knockout of Ido2 (Ido2^-/-) and treatment with Ido2 inhibitor 1-methyl-D-tryptophan (D-1MT; 100 mg/kg, i.p.) attenuated CCl₄-induced liver injury, with decreased induction of Ahr-mediated signaling. Administration of D-Kyn (100 mg/kg, i.p.) to Ido2^-/- mice canceled the effect of Ido2 deficiency and exacerbated acute liver damage by CCl₄ treatment. In addition, liver fibrosis induced by repeated CCl₄ administration was suppressed in Ido2^-/- mice. In conclusion, the action of Ido2 and Kyn in the liver may prevent severe hepatocellular damage and liver fibrosis.

Switch of NAD Salvage to de novo Biosynthesis Sustains SIRT1-RelB-Dependent Inflammatory Tolerance

A typical inflammatory response sequentially progresses from pro-inflammatory, immune suppressive to inflammatory repairing phases. Although the physiological inflammatory response resolves in time, severe acute inflammation usually sustains immune tolerance and leads to high mortality, yet the underlying mechanism is not completely understood. Here, using the leukemia-derived THP-1 human monocytes, healthy and septic human peripheral blood mononuclear cells (PBMC), we report that endotoxin dose-dependent switch of nicotinamide adenine dinucleotide (NAD) biosynthesis pathways sustain immune tolerant status. Low dose endotoxin triggered nicotinamide phosphoribosyltransferase (NAMPT)-dependent NAD salvage activity to adapt pro-inflammation. In contrast, high dose endotoxin drove a shift of NAD synthesis pathway from early NAMPT-dependent NAD salvage to late indoleamine 2,3-dioxygenase-1 (IDO1)-dependent NAD de novo biosynthesis, leading to persistent immune suppression. This is resulted from the IDO1-dependent expansion of nuclear NAD pool and nuclear NAD-dependent prolongation of sirtuin1 (SIRT1)-directed epigenetics of immune tolerance. Inhibition of IDO1 activity predominantly decreased nuclear NAD level, which promoted sequential dissociations of immunosuppressive SIRT1 and RelB from the promoter of pro-inflammatory TNF-α gene and broke endotoxin tolerance. Thus, NAMPT-NAD-SIRT1 axis adapts pro-inflammation, but IDO1-NAD-SIRT1-RelB axis sustains endotoxin tolerance during acute inflammatory response. Remarkably, in contrast to the prevention of sepsis death of animal model by IDO1 inhibition before sepsis initiation, we demonstrated that the combination therapy of IDO1 inhibition by 1-methyl-D-tryptophan (1-MT) and tryptophan supplementation rather than 1-MT administration alone after sepsis onset rescued sepsis animals, highlighting the translational significance of tryptophan restoration in IDO1 targeting therapy of severe inflammatory diseases like sepsis.

Orchestration of Tryptophan-Kynurenine Pathway, Acute Decompensation, and Acute-on-Chronic Liver Failure in Cirrhosis

Systemic inflammation (SI) is involved in the pathogenesis of acute decompensation (AD) and acute-on-chronic liver failure (ACLF) in cirrhosis. In other diseases, SI activates tryptophan (Trp) degradation through the kynurenine pathway (KP), giving rise to metabolites that contribute to multiorgan/system damage and immunosuppression. In the current study, we aimed to characterize the KP in patients with cirrhosis, in whom this pathway is poorly known. The serum levels of Trp, key KP metabolites (kynurenine and kynurenic and quinolinic acids), and cytokines (SI markers) were measured at enrollment in 40 healthy subjects, 39 patients with compensated cirrhosis, 342 with AD (no ACLF) and 180 with ACLF, and repeated in 258 patients during the 28-day follow-up. Urine KP metabolites were measured in 50 patients with ACLF. Serum KP activity was normal in compensated cirrhosis, increased in AD and further increased in ACLF, in parallel with SI; it was remarkably higher in ACLF with kidney failure than in ACLF without kidney failure in the absence of differences in urine KP activity and fractional excretion of KP metabolites. The short-term course of AD and ACLF (worsening, improvement, stable) correlated closely with follow-up changes in serum KP activity. Among patients with AD at enrollment, those with the highest baseline KP activity developed ACLF during follow-up. Among patients who had ACLF at enrollment, those with immune suppression and the highest KP activity, both at baseline, developed nosocomial infections during follow-up. Finally, higher baseline KP activity independently predicted mortality in patients with AD and ACLF. Conclusion: Features of KP activation appear in patients with AD, culminate in patients with ACLF, and may be involved in the pathogenesis of ACLF, clinical course, and mortality.

Postnatal changes in epigenetic modifications of neutrophils of foals are associated with increased ROS function and regulation of neutrophil function

Neonates of all species, including foals, are highly susceptible to infection, and neutrophils play a crucial role in innate immunity to infection. Evidence exists that neutrophils of neonatal foals are functionally deficient during the first weeks of life, including expression of cytokine genes such as IFNG. We hypothesized that postnatal epigenetic changes were likely to regulate the observed age-related changes in foal neutrophils. Using ChIP-Seq, we identified significant differences in trimethylated histone H3 lysine 4, an epigenetic modification associated with active promoters and enhancers, in neutrophils in foals at 30 days of age relative to 1 day of age. These chromatin changes were associated with genes implicated in immune responses and were consistent with age-related changes in neutrophil functional responses including ROS generation and IFN expression. Postnatal changes in epigenetic modifications suggest that environmentally-mediated cues help to promote maturation of neutrophil functional responses. Elucidating the environmental triggers and their signaling pathways could provide a means for improving innate immune responses of neonates to improve their ability to combat infectious diseases.

An integrated metabolomic strategy for the characterization of the effects of Chinese yam and its three active components on septic cardiomyopathy

This integrated metabolomic approach interpreted the effects of Chinese yam on septic cardiomyopathy and the roles of its major active components.

Rotavirus Degrades Multiple Interferon (IFN) Type Receptors To Inhibit IFN Signaling and Protects against Mortality from Endotoxin in Suckling Mice

STAT1 phosphorylation in response to exogenous interferon (IFN) administration can be inhibited by rotaviral replication both in vitro and in vivo In addition many rotavirus strains are resistant to the actions of different IFN types. The regulation by rotaviruses (RVs) of antiviral pathways mediated by multiple IFN types is not well understood. In this study, we find that during infection in vitro and in vivo, RVs significantly deplete IFN type I, II, and III receptors (IFNRs). Regulation of IFNRs occurred exclusively within RV-infected cells and could be abrogated by inhibiting the lysosomal-endosomal degradation pathway. In vitro, IFNR degradation was conserved across multiple RV strains that differ in their modes of regulating IFN induction. In suckling mice, exogenously administered type I, II, or III IFN induced phosphorylation of STAT1-Y701 within intestinal epithelial cells (IECs) of suckling mice. Murine EW strain RV infection transiently activated intestinal STAT1 at 1 day postinfection (dpi) but not subsequently at 2 to 3 dpi. In response to injection of purified IFN-α/β or -λ, IECs in EW-infected mice exhibited impaired STAT1-Y701 phosphorylation, correlating with depletion of different intestinal IFNRs and impaired IFN-mediated transcription. The ability of EW murine RV to inhibit multiple IFN types led us to test protection of suckling mice from endotoxin-mediated shock, an outcome that is dependent on the host IFN response. Compared to mortality in controls, mice infected with EW murine RV were substantially protected against mortality following parenteral endotoxin administration. These studies identify a novel mechanism of IFN subversion by RV and reveal an unexpected protective effect of RV infection on endotoxin-mediated shock in suckling mice.IMPORTANCE Antiviral functions of types I, II, and III IFNs are mediated by receptor-dependent activation of STAT1. Here, we find that RV degrades the types I, II, and III IFN receptors (IFNRs) in vitro In a suckling mouse model, RV effectively blocked STAT1 activation and transcription following injection of different purified IFNs. This correlated with significantly decreased protein expression of intestinal types I and II IFNRs. Recent studies demonstrate that in mice lipopolysaccharide (LPS)-induced lethality is prevented by genetic ablation of IFN signaling genes such as IFNAR1 and STAT1. When suckling mice were infected with RV, they were substantially protected from lethal exposure to endotoxin. These findings provide novel insights into the mechanisms underlying rotavirus regulation of different interferons and are likely to stimulate new research into both rotavirus pathogenesis and endotoxemia.

Activation of the tryptophan/serotonin pathway is associated with severity and predicts outcomes in pneumonia: results of a long-term cohort study

BACKGROUND

As part of the immune defense during infection, an increase in enzyme activity of indoleamine 2,3-dioxygenase (IDO) leads to a breakdown of tryptophan to kynurenine. In previous animal studies, therapeutic antagonism of IDO resulted in reduced sepsis mortality. We investigated the prognostic ability of tryptophan, serotonin, kynurenine and IDO (represented by the ratio of kynurenine/tryptophan) to predict adverse clinical outcomes in patients with community-acquired pneumonia (CAP).

METHODS

We measured tryptophan, serotonin and kynurenine on admission plasma samples from CAP patients included in a previous multicenter trial by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). We studied their association with inflammation (C-reactive protein), infection (procalcitonin) and clinical outcome.

RESULTS

Mortality in the 268 included patients was 45% within 6 years of follow-up. IDO and kynurenine showed a strong positive correlation with markers of infection (procalcitonin) and inflammation (C-reactive protein) as well as sepsis and CAP severity scores. Tryptophan showed similar, but negative correlations. In a multivariate regression analysis adjusted for age and comorbidities, higher IDO activity and lower tryptophan levels were strongly associated with short-term adverse outcome defined as death and/or ICU admission within 30 days with adjusted odds ratios of 9.1 [95% confidence interval (CI) 1.4-59.5, p=0.021] and 0.11 (95% CI 0.02-0.70, p=0.021). Multivariate analysis did not reveal significant associations for kynurenine and serotonin.

CONCLUSIONS

In hospitalized CAP patients, higher IDO activity and lower tryptophan levels independently predicted disease severity and short-term adverse outcome. Whether therapeutic modulation of IDO has positive effects on outcome needs further investigation.

Activation of the Serotonin Pathway is Associated with Poor Outcome in COPD Exacerbation: Results of a Long-Term Cohort Study

BACKGROUND/INTRODUCTION

Indoleamine 2,3-dioxygenase (IDO) metabolizes tryptophan to kynurenine. An increase of its activity is associated with severity in patients with pneumonia. In chronic obstructive pulmonary disease (COPD) patients, an elevation of serotonin has been reported. Experimental models showed that cigarette smoke inhibits monoamine oxidase (MAO) leading to higher levels of serotonin. We investigated the prognostic ability of tryptophan, serotonin, kynurenine, IDO, and tryptophan hydroxylase (TPH) to predict short- and long-term outcomes in patients with a COPD exacerbation.

METHODS

We measured tryptophan, serotonin, and kynurenine on admission plasma samples in patients with a COPD exacerbation from a previous trial by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). IDO and TPH were calculated as ratios of kynurenine over tryptophan, and serotonin over tryptophan, respectively. We studied their association with parameters measured in clinical routine at emergency department admission representing inflammation (C-reactive protein [CRP]), infection (procalcitonin [PCT]), oxygenation (SpO₂), as well as patients' clinical outcome, confirmed by structured phone interviews.

RESULTS

Mortality in the 149 included patients was 53.7% within six years of follow-up. While IDO activity showed strong positive correlations, tryptophan was negatively correlated with CRP and PCT. For 30-day adverse outcome defined as death and/or intensive care unit (ICU) admission, a multivariate regression analysis adjusted for age and comorbidities found strong associations for IDO activity (adjusted odds ratios of 31.4 (95%CI 1.1-857), p = 0.041) and TPH (adjusted odds ratios 27.0 (95%CI 2.2-327), p = 0.010). TPH also showed a significant association with mortality at 18 months, (hazard ratio 2.61 (95%CI 1.2-5.8), p = 0.020).

CONCLUSION

In hospitalized patients with a COPD exacerbation, higher IDO and TPH activities independently predicted adverse short-term outcomes and TPH levels were also predictive of 18-month mortality. Whether therapeutic modulation of the serotonin pathway has positive effects on outcome needs further investigation.

Intranasal vaccination with adjuvant-free S. aureus antigens effectively protects mice against experimental sepsis

Staphylococcus aureus (S. aureus) is a Gram-positive coccal bacterium comprising part of the human skin, nares and gastrointestinal tract normal microbiota. It is also an important cause of nosocomial/community-acquired infections in humans and animals, which can cause a diverse array of infections, including sepsis, which is a progressive systemic inflammation response syndrome that is frequently fatal. The emergence of drug-resistant strains and the high toxicity of the treatments used for these infections point out the need to develop an effective, inexpensive and safe vaccine that can be used prophylactically. In this work, we used an experimental sepsis model to evaluate the effectiveness of whole antigens from S. aureus (SaAg) given by the intranasal route to induce protective immunity against S. aureus infection in mice. BALB/c mice were vaccinated via intranasal or intramuscular route with two doses of SaAg, followed by biocompatibility and immunogenicity evaluations. Vaccinated animals did not show any adverse effects associated with the vaccine, as determined by transaminase and creatinine measurements. Intranasal, but not intramuscular vaccination with SaAg led to a significant reduction in IL-10 production and was associated with increased level of IFN-γ and NO. SaAg intranasal vaccination was able to prime cellular and humoral immune responses and inducing a higher proliferation index and increased production of specific IgG1/IgG2, which contributed to decrease the bacterial load in both liver and the spleen and improve survival during sepsis. These findings present the first evidence of the effectiveness of whole Ag intranasal-based vaccine administration, which expands the vaccination possibilities against S. aureus infection.

Correlation of Surface Toll-Like Receptor 9 Expression with IL-17 Production in Neutrophils during Septic Peritonitis in Mice Induced by E. coli

IL-17 is a proinflammatory cytokine produced by various immune cells. Polymorphonuclear neutrophils (PMNs) are the first line of defense in bacterial infection and express surface Toll-like receptor 9 (sTLR9). To study the relationship of sTLR9 and IL-17 in PMNs during bacterial infection, we infected mice with E. coli intraperitoneally to establish a septic peritonitis model for studying the PMNs response in peritoneal cavity. We found that PMNs and some of "giant cells" were massively accumulated in the peritoneal cavity of mice with fatal septic peritonitis induced by E. coli. Kinetically, the CD11b(+) PMNs were increased from 20-40% at 18 hours to >80% at 72 hours after infection. After E. coli infection, sTLR9 expression on CD11b(+) and CD11b(-) PMNs and macrophages in the PLCs were increased at early stage and deceased at late stage; IL-17 expression was also increased in CD11b(+) PMNs, CD11b(-) PMNs, macrophages, and CD3(+) T cells. Using experiments of in vitro blockage, qRT-PCR and cell sorting, we confirmed that PMNs in the PLCs did increase their IL-17 expression during E. coli infection. Interestingly, sTLR9(-)CD11b(+)Ly6G(+) PMNs, not sTLR9(+)CD11b(+)Ly6G(+) PMNs, were found to be able to increase their IL-17 expression. Together, the data may help understand novel roles of PMNs in septic peritonitis.

Therapeutic targeting of inflammation and tryptophan metabolism in colon and gastrointestinal cancer

Colorectal cancer (CRC) is the third most common cancer worldwide and the second leading cause of cancer death in the United States. Cytotoxic therapies cause significant adverse effects for most patients and do not offer cure in many advanced cases of CRC. Immunotherapy is a promising new approach to harness the body's own immune system and inflammatory response to attack and clear the cancer. Tryptophan metabolism along the kynurenine pathway (KP) is a particularly promising target for immunotherapy. Indoleamine 2,3-dioxygenase 1 (IDO1) is the most well studied of the enzymes that initiate this pathway and it is commonly overexpressed in CRC. Herein, we provide an in-depth review of how tryptophan metabolism and KP metabolites shape factors important to CRC pathogenesis including the host mucosal immune system, pivotal transcriptional pathways of neoplastic growth, and luminal microbiota. This pathway's role in other gastrointestinal (GI) malignancies such as gastric, pancreatic, esophageal, and GI stromal tumors is also discussed. Finally, we highlight how currently available small molecule inhibitors and emerging methods for therapeutic targeting of IDO1 might be applied to colon, rectal, and colitis-associated cancer.

Inhibition of indoleamine 2,3-dioxygenase 1 expression alters immune response in colon tumor microenvironment in mice

Indoleamine 2,3-dioxygenase (IDO), an enzyme that degrades the essential amino acid l-tryptophan along the kynurenine pathway, exerts immunomodulatory effects in a number of diseases. IDO expression is increased in tumor tissue and in draining lymph nodes; this increase is thought to play a role in tumor evasion by suppressing the immune response. A competitive inhibitor of IDO is currently being tested in clinical trials for the treatment of relapsed or refractory solid tumors, but the efficacy of IDO inhibition in colorectal tumors remains to be fully elucidated. In this study, we investigated the effect of IDO deficiency on colon tumorigenesis in mice by genetic deletion and pharmacological inhibition. Ido1-deficient^(−/−) mice were crossed with Apc^Min/+ mice or were administered azoxymethane with or without dextran sodium sulfate. Ido1 deficiency did not lead to significant differences in the size and number of colon tumors. Similarly, the pharmacological inhibition of IDO using 1-methyltryptophan (1-mT) also resulted in no significant differences in tumor size and number in Apc^Min/+ mice. However, Ido1 deficiency altered the immune response in the tumor microenvironment, showing a significant increase in mRNA expression of pro-inflammatory cytokines and a significant decrease in the number of Foxp3-positive regulatory T cells in the colon tumors of Ido1^(−/−) mice. Importantly, 1-mT treatment also significantly altered cytokine expression in the colon tumor tissues. These results suggest that IDO inhibition alone cannot sufficiently suppress colon cancer development in mice despite its immunomodulatory activity in the tumor microenvironment.

Role of indoleamine 2,3-dioxygenase in health and disease

IDO1 (indoleamine 2,3-dioxygenase 1) is a member of a unique class of mammalian haem dioxygenases that catalyse the oxidative catabolism of the least-abundant essential amino acid, L-Trp (L-tryptophan), along the kynurenine pathway. Significant increases in knowledge have been recently gained with respect to understanding the fundamental biochemistry of IDO1 including its catalytic reaction mechanism, the scope of enzyme reactions it catalyses, the biochemical mechanisms controlling IDO1 expression and enzyme activity, and the discovery of enzyme inhibitors. Major advances in understanding the roles of IDO1 in physiology and disease have also been realised. IDO1 is recognised as a prominent immune regulatory enzyme capable of modulating immune cell activation status and phenotype via several molecular mechanisms including enzyme-dependent deprivation of L-Trp and its conversion into the aryl hydrocarbon receptor ligand kynurenine and other bioactive kynurenine pathway metabolites, or non-enzymatic cell signalling actions involving tyrosine phosphorylation of IDO1. Through these different modes of biochemical signalling, IDO1 regulates certain physiological functions (e.g. pregnancy) and modulates the pathogenesis and severity of diverse conditions including chronic inflammation, infectious disease, allergic and autoimmune disorders, transplantation, neuropathology and cancer. In the present review, we detail the current understanding of IDO1’s catalytic actions and the biochemical mechanisms regulating IDO1 expression and activity. We also discuss the biological functions of IDO1 with a focus on the enzyme's immune-modulatory function, its medical implications in diverse pathological settings and its utility as a therapeutic target.