Spermine causes loss of innate immune response to Helicobacter pylori by inhibition of inducible nitric-oxide synthase translation

L-Arginine and immune modulation: A pharmacological perspective on inflammation and autoimmune disorders

L- Arginine (2-Amino-5-guanidinovaleric acid, L-Arg) is a semi-essential amino acid that is mainly produced within the urea cycle. It acts as a key precursor in the synthesis of proteins, urea, creatine, prolamines (including putrescine, spermine, and spermidine), proline, and nitric oxide (NO). WhenL-Arg is metabolized, it produces NO, glutamate, and prolamines, which all play important regulatory roles in various physiological functions. In addition to its metabolic roles,L-Arg significantly influences immune responses, especially in the context of inflammation and autoimmune diseases. It affects the activity of immune cells by modulating T-cell function, the polarization of macrophages, and the release of cytokines. Importantly,L-Arg plays a dual role in immune regulation, functioning as both an immunostimulatory and immunosuppressive agent depending on the specific cellular and biochemical environments. This review examines the immunopharmacological mechanisms of L-Arg, emphasizing its involvement in inflammatory responses and its potential therapeutic uses in autoimmune conditions like rheumatoid arthritis, multiple sclerosis, and inflammatory bowel disease. By influencing the pathways of nitric oxide synthase (NOS) and arginase (ARG), L-Arg helps maintain immune balance and contributes to the pathophysiology of diseases. Gaining a better understanding of the pharmacological effects of L-Arg on immune regulation could yield new perspectives on targeted treatments for immune-related diseases. Exploring its impact on immune signaling and metabolic pathways may result in novel therapeutic approaches for chronic inflammatory and autoimmune disorders.

Macrophage biology in the pathogenesis of Helicobacter pylori infection

Infection with H. pylori induces chronic gastric inflammation, progressing to peptic ulcer and stomach adenocarcinoma. Macrophages function as innate immune cells and play a vital role in host immune defense against bacterial infection. However, the distinctive mechanism by which H. pylori evades phagocytosis allows it to colonize the stomach and further aggravate gastric preneoplastic pathology. H. pylori exacerbates gastric inflammation by promoting oxidative stress, resisting macrophage phagocytosis, and inducing M1 macrophage polarization. M2 macrophages facilitate the proliferation, invasion, and migration of gastric cancer cells. Various molecular mechanisms governing macrophage function in the pathogenesis of H. pylori infection have been identified. In this review, we summarize recent findings of macrophage interactions with H. pylori infection, with an emphasis on the regulatory mechanisms that determine the clinical outcome of bacterial infection.

Arginine metabolism in myeloid cells in health and disease

Metabolic flexibility is key for the function of myeloid cells. Arginine metabolism is integral to the regulation of myeloid cell responses. Nitric oxide (NO) production from arginine is vital for the antimicrobial and pro-inflammatory responses. Conversely, the arginase 1 (ARG1)-dependent switch between the branch of NO production and polyamine synthesis downregulates inflammation and promotes recovery of tissue homeostasis. Creatine metabolism is key for energy supply and proline metabolism is required for collagen synthesis. Myeloid ARG1 also regulates extracellular arginine availability and T cell responses in parasitic diseases and cancer. Cancer, surgery, sepsis and persistent inflammation in chronic inflammatory diseases, such as neuroinflammatory diseases or arthritis, are associated with dysregulation of arginine metabolism in myeloid cells. Here, we review current knowledge on arginine metabolism in different myeloid cell types, such as macrophages, neutrophils, microglia, osteoclasts, tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs) and myeloid-derived suppressor cells (MDSCs). A deeper understanding of the function of arginine metabolism in myeloid cells will improve our knowledge on the pathology of several diseases and may set the platform for novel therapeutic applications.

Serum Metabolites Relate to Mucosal and Transmural Inflammation in Paediatric Crohn Disease

BACKGROUND AND AIMS

We aimed to identify serum metabolites associated with mucosal and transmural inflammation in paediatric Crohn disease [pCD].

METHODS

In all, 56 pCD patients were included through a pre-planned sub-study of the multicentre, prospective, ImageKids cohort, designed to develop the Paediatric Inflammatory Crohn magnetic resonance enterography [MRE] Index [PICMI]. Children were included throughout their disease course when undergoing ileocolonoscopy and MRE and were followed for 18 months, when MRE was repeated. Serum metabolites were identified using liquid chromatography/mass spectroscopy. Outcomes included: PICMI, the simple endoscopic score [SES], faecal calprotectin [FCP], and C-reactive protein [CRP], to assess transmural, mucosal, and systemic inflammation, respectively. Random forest models were built by outcome. Maximum relevance minimum redundancy [mRMR] feature selection with a j-fold cross-validation scheme identified the best subset of features and hyperparameter settings.

RESULTS

Tryptophan and glutarylcarnitine were the top common mRMR metabolites linked to pCD inflammation. Random forest models established that amino acids and amines were among the most influential metabolites for predicting transmural and mucosal inflammation. Predictive models performed well, each with an area under the curve [AUC] > 70%. In addition, serum metabolites linked with pCD inflammation mainly related to perturbations in the citrate cycle [TCA cycle], aminoacyl-tRNA biosynthesis, tryptophan metabolism, butanoate metabolism, and tyrosine metabolism.

CONCLUSIONS

We extend on recent studies, observing differences in serum metabolites between healthy controls and Crohn disease patients, and suggest various associations of serum metabolites with transmural and mucosal inflammation. These metabolites could improve the understanding of pCD pathogenesis and assessment of disease severity.

Preliminary study on the potential impact of probiotic combination therapy on Helicobacter pylori infection in children using 16S gene sequencing and untargeted metabolomics approach

Objective

The purpose of this study was to explore the potential mechanism of Helicobacter pylori (Hp) eradication by probiotic therapy through 16S rRNA gene sequencing technology and untargeted metabolomics.

Methods

Twenty four Hp-infected children were recruited from the Shanxi Bethune Hospital, and 24 healthy children were recruited as a blank control group. Group A: fecal samples from 24 healthy children. Group B: fecal samples of 24 children with Hp infection. Group B1 (n = 15): fecal samples of group B treated with probiotic therapy for 2 weeks. Group B2 (n = 19): fecal samples of group B treated with probiotic therapy for 4 weeks. The above fecal samples were analyzed by 16S rRNA gene sequencing technology and untargeted metabolomics.

Results

There was no significant difference in alpha diversity and beta diversity among the four groups, but many bacteria with statistical difference were found in each group at the bacterial genus level and phylum level. LEfSe results showed that in group B, Porphyromonadaceae, Shigella and other microorganisms related to intestinal microecological dysbiosis were enriched. And in group B2, abundant characteristic microorganisms were found, namely Bacillales and Prevotella. KEGG metabolic pathway enrichment analysis showed that groups B1 and B2 were involved in 10 metabolic pathways potentially related to probiotic treatment: purine metabolism, nitrogen metabolism, arginine biosynthesis, alanine, aspartic acid and glutamate metabolism, glyoxylic acid and dicarboxylic acid metabolism, unsaturated fatty acid biosynthesis, fatty acid extension, fatty acid degradation, pyrimidine metabolism, fatty acid biosynthesis.

Conclusion

Probiotic therapy can inhibit Hp to some extent and can relieve gastrointestinal symptoms, making it a preferred therapy for children with Hp infection and functional abdominal pain. Hp infection can reduce the diversity of intestinal microbes, resulting in the disturbance of intestinal microbiota and changes in the relative abundance of microbiota in children, while probiotic therapy can restore the diversity of intestinal microbes and intestinal microecological balance.

The role of nitric oxide synthase/ nitric oxide in infection-related cancers: Beyond antimicrobial activity

As a free radical and endogenous effector molecule, mammalian endogenous nitric oxide (NO) is mainly derived from nitric oxide synthase (NOS) via L-arginine. NO participates in normal physiological reactions and provides immune responses to prevent the invasion of foreign bacteria. However, NO also has complex and contradictory biological effects. Abnormal NO signaling is involved in the progression of many diseases, such as cancer. In the past decades, cancer research has been closely linked with NOS/ NO, and many tumors with poor prognosis are associated with high expression of NOS. In this review, we give a overview of the biological effects of NOS/ NO. Then we focus on the oncogenic role of iNOS/ NO in HPV, HBV, EBV and H. pylori related tumors. In fact, there is growing evidence that iNOS could be used as a potential therapeutic target in cancer therapy. We emphasize that the pro-tumor effect of NOS/ NO is greater than the anti-tumor effect.

Citrulline and ADI-PEG20 reduce inflammation in a juvenile porcine model of acute endotoxemia

Background

Arginine is a conditionally essential amino acid that is depleted in critically ill or surgical patients. In pediatric and adult patients, sepsis results in an arginine-deficient state, and the depletion of plasma arginine is associated with greater mortality. However, direct supplementation of arginine can result in the excessive production of nitric oxide (NO), which can contribute to the hypotension and macrovascular hypo-reactivity observed in septic shock. Pegylated arginine deiminase (ADI-PEG20, pegargiminase) reduces plasma arginine and generates citrulline that can be transported intracellularly to generate local arginine and NO, without resulting in hypotension, while maintaining microvascular patency. The objective of this study was to assess the efficacy of ADI-PEG20 with and without supplemental intravenous citrulline in mitigating hypovolemic shock, maintaining tissue levels of arginine, and reducing systemic inflammation in an endotoxemic pediatric pig model.

Methods

Twenty 3-week-old crossbred piglets were implanted with jugular and carotid catheters as well as telemetry devices in the femoral artery to measure blood pressure, body temperature, heart rate, and respiration rate. The piglets were assigned to one of three treatments before undergoing a 5 h lipopolysaccharide (LPS) infusion protocol. Twenty-four hours before LPS infusion, control pigs (LPS; n=6) received saline, ADI-PEG20 pigs (n=7) received an injection of ADI-PEG20, and seven pigs (ADI-PEG20 + CIT pigs [n=7]) received ADI-PEG20 and 250 mg/kg citrulline intravenously. Pigs were monitored throughout LPS infusion and tissue was harvested at the end of the protocol.

Results

Plasma arginine levels decreased and remained low in ADI-PEG20 + CIT and ADI-PEG20 pigs compared with LPS pigs but tissue arginine levels in the liver and kidney were similar across all treatments. Mean arterial pressure in all groups decreased from 90 mmHg to 60 mmHg within 1 h of LPS infusion but there were no significant differences between treatment groups. ADI-PEG20 and ADI-PEG20 + CIT pigs had less CD45+ infiltrate in the liver and lung and lower levels of pro-inflammatory cytokines in the plasma.

Conclusion

ADI-PEG20 and citrulline supplementation failed to ameliorate the hypotension associated with acute endotoxic sepsis in pigs but reduced systemic and local inflammation in the lung and liver.

Polyamines: the pivotal amines in influencing the tumor microenvironment

Cellular proliferation, function and survival is reliant upon maintaining appropriate intracellular polyamine levels. Due to increased metabolic needs, cancer cells elevate their polyamine pools through coordinated metabolism and uptake. High levels of polyamines have been linked to more immunosuppressive tumor microenvironments (TME) as polyamines support the growth and function of many immunosuppressive cell types such as MDSCs, macrophages and regulatory T-cells. As cancer cells and other pro-tumorigenic cell types are highly dependent on polyamines for survival, pharmacological modulation of polyamine metabolism is a promising cancer therapeutic strategy. This review covers the roles of polyamines in various cell types of the TME including both immune and stromal cells, as well as how competition for nutrients, namely polyamine precursors, influences the cellular landscape of the TME. It also details the use of polyamines as biomarkers and the ways in which polyamine depletion can increase the immunogenicity of the TME and reprogram tumors to become more responsive to immunotherapy.

Dysregulated cellular metabolism in atherosclerosis: mediators and therapeutic opportunities

Accumulating evidence over the past decades has revealed an intricate relationship between dysregulation of cellular metabolism and the progression of atherosclerotic cardiovascular disease. However, an integrated understanding of dysregulated cellular metabolism in atherosclerotic cardiovascular disease and its potential value as a therapeutic target is missing. In this Review, we (1) summarize recent advances concerning the role of metabolic dysregulation during atherosclerosis progression in lesional cells, including endothelial cells, vascular smooth muscle cells, macrophages and T cells; (2) explore the complexity of metabolic cross-talk between these lesional cells; (3) highlight emerging technologies that promise to illuminate unknown aspects of metabolism in atherosclerosis; and (4) suggest strategies for targeting these underexplored metabolic alterations to mitigate atherosclerosis progression and stabilize rupture-prone atheromas with a potential new generation of cardiovascular therapeutics.

Illuminating the structure-function landscape of an evolutionary nonconserved motif in the arginases of Helicobacter gastric pathogens

The bimetallic enzyme arginase catalyses the conversion of L-arginine to L-ornithine and urea. In Helicobacter pylori (a known human gastric pathogen), this enzyme is an important virulence factor. In spite of the conservation of the catalytic and the metal-binding residues, the H. pylori homolog possesses a 13-residue motif (-153 ESEEKAWQKLCSL165 -) present in the middle of the protein sequence, whose role was recently elucidated. Despite several reviews available on arginases, no report has thoroughly illustrated the underlying basis for the importance of the above motif of the H. pylori enzyme in structure and function. In this review, we systematically describe a mechanistic basis for its importance in structure and function based on the known data. This motif of the H. pylori enzyme is present exclusively in the arginases of other Helicobacter gastric pathogens, where the critical residues are conserved, implying that the nonconserved stretch has been selected during the evolution of the enzyme in these gastric pathogens in a specific manner to perform its role in the structure and function. The combined information can be useful for understanding the function of arginases in other Helicobacter gastric pathogens. Additionally, this knowledge can be utilised to screen and design new small molecule inhibitors, specific to the arginases of these pathogens.

Involvement of Nitric Oxide in Protecting against Radical Species and Autoregulation of M1-Polarized Macrophages through Metabolic Remodeling

When the expression of NOS2 in M1-polarized macrophages is induced, huge amounts of nitric oxide (•NO) are produced from arginine and molecular oxygen as the substrates. While anti-microbial action is the primary function of M1 macrophages, excessive activation may result in inflammation being aggravated. The reaction of •NO with superoxide produces peroxynitrite, which is highly toxic to cells. Alternatively, however, this reaction eliminates radial electrons and may occasionally alleviate subsequent radical-mediated damage. Reactions of •NO with lipid radicals terminates the radical chain reaction in lipid peroxidation, which leads to the suppression of ferroptosis. •NO is involved in the metabolic remodeling of M1 macrophages. Enzymes in the tricarboxylic acid (TCA) cycle, notably aconitase 2, as well as respiratory chain enzymes, are preferential targets of •NO derivatives. Ornithine, an alternate compound produced from arginine instead of citrulline and •NO, is recruited to synthesize polyamines. Itaconate, which is produced from the remodeled TCA cycle, and polyamines function as defense systems against overresponses of M1 macrophages in a feedback manner. Herein, we overview the protective aspects of •NO against radical species and the autoregulatory systems that are enabled by metabolic remodeling in M9-polarized macrophages.

The interaction of Helicobacter pylori with cancer immunomodulatory stromal cells: New insight into gastric cancer pathogenesis

Gastric cancer is the fourth most common cause of cancer-linked deaths in the world. Gastric tumor cells have biological characteristics such as rapid proliferation, high invasiveness, and drug resistance, which result in recurrence and poor survival. Helicobacter pylori (H. pylori) has been proposed as a first-class carcinogen for gastric cancer according to the 1994 world health organization (WHO) classification. One of the important mechanisms by which H. pylori affects the gastric environment and promotes carcinogenesis is triggering inflammation. H. pylori induces an inflammatory response and a plethora of different signal transduction processes, leading to gastric mucosal disturbance, chronic gastritis, and a multi-step complex pathway that initiates carcinogenesis. It seems undeniable that the interaction between various cell types, including immune cells, gastric epithelium, glands, and stem cells, is vital for the progression and development of carcinogenesis concerning H. pylori. The interactions of H. pylori with surrounding cells play a key role in cancer progression. In this review, we discuss the interplay between H. pylori and tumor-supportive cells, including mesenchymal stem cells (MSCs), cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), and myeloid derived-suppressor cells (MDSCs) in gastric cancer. It is hoped that clarifying the specific mechanisms for 'cross-talk' between H. pylori and these cells will provide promising strategies for developing new treatments.

The role of polyamine metabolism in remodeling immune responses and blocking therapy within the tumor immune microenvironment

The study of metabolism provides important information for understanding the biological basis of cancer cells and the defects of cancer treatment. Disorders of polyamine metabolism is a common metabolic change in cancer. With the deepening of understanding of polyamine metabolism, including molecular functions and changes in cancer, polyamine metabolism as a new anti-cancer strategy has become the focus of attention. There are many kinds of polyamine biosynthesis inhibitors and transport inhibitors, but not many drugs have been put into clinical application. Recent evidence shows that polyamine metabolism plays essential roles in remodeling the tumor immune microenvironment (TIME), particularly treatment of DFMO, an inhibitor of ODC, alters the immune cell population in the tumor microenvironment. Tumor immunosuppression is a major problem in cancer treatment. More and more studies have shown that the immunosuppressive effect of polyamines can help cancer cells to evade immune surveillance and promote tumor development and progression. Therefore, targeting polyamine metabolic pathways is expected to become a new avenue for immunotherapy for cancer.

Polyamines in cancer: integrating organismal metabolism and antitumour immunity

The natural mammalian polyamines putrescine, spermidine and spermine are essential for both normal and neoplastic cell function and replication. Dysregulation of metabolism of polyamines and their requirements is common in many cancers. Both clinical and experimental depletion of polyamines have demonstrated their metabolism to be a rational target for therapy; however, the mechanisms through which polyamines can establish a tumour-permissive microenvironment are only now emerging. Recent data indicate that polyamines can play a major role in regulating the antitumour immune response, thus likely contributing to the existence of immunologically 'cold' tumours that do not respond to immune checkpoint blockade. Additionally, the interplay between the microbiota and associated tissues creates a tumour microenvironment in which polyamine metabolism, content and function can all be dramatically altered on the basis of microbiota composition, dietary polyamine availability and tissue response to its surrounding microenvironment. The goal of this Perspective is to introduce the reader to the many ways in which polyamines, polyamine metabolism, the microbiota and the diet interconnect to establish a tumour microenvironment that facilitates the initiation and progression of cancer. It also details ways in which polyamine metabolism and function can be successfully targeted for therapeutic benefit, including specifically enhancing the antitumour immune response.

Tumor microbiome metabolism: A game changer in cancer development and therapy

Accumulating recent evidence indicates that the human microbiome plays essential roles in pathophysiological states, including cancer. The tumor microbiome, an emerging concept that has not yet been clearly defined, has been proven to influence both cancer development and therapy through complex mechanisms. Small molecule metabolites produced by the tumor microbiome through unique biosynthetic pathways can easily diffuse into tissues and penetrate cell membranes through transporters or free diffusion, thus remodeling the signaling pathways of cancer and immune cells by interacting with biomacromolecules. Targeting tumor microbiome metabolism could offer a novel perspective for not only understanding cancer progression but also developing new strategies for the treatment of multiple cancer types. Here, we summarize recent advances regarding the role the tumor microbiome plays as a game changer in cancer biology. Specifically, the metabolites produced by the tumor microbiome and their potential effects on the cancer development therapy are discussed to understand the importance of the microbial metabolism in the tumor microenvironment. Finally, new anticancer therapeutic strategies that target tumor microbiome metabolism are reviewed and proposed to provide new insights in clinical applications.

Helicobacter pylori-Mediated Oxidative Stress and Gastric Diseases: A Review

Gastric cancer is considered to be a type of gastrointestinal tumor and is mostly accompanied by Helicobacter pylori (HP) infection at the early stage. Hence, the long-term colonization of the gastric mucosa by HP as a causative factor for gastrointestinal diseases cannot be ignored. The virulence factors secreted by the bacterium activate the signaling pathway of oxidative stress and mediate chronic inflammatory response in the host cells. The virulence factors also thwart the antibacterial effect of neutrophils. Subsequently, DNA methylation is induced, which causes continuous cell proliferation and evolution toward low-grade-differentiated gastric cells. This process provides the pathological basis for the occurrence of progressive gastric cancer. Therefore, this review aims to summarize the oxidative stress response triggered by HP in the gastric mucosa and the subsequent signaling pathways. The findings are expected to help in the formulation of new targeted drugs for preventing the occurrence of early gastric cancer and its progression to middle and advanced cancer.

Mycobacterium Lrp/AsnC family transcriptional factor modulates the arginase pathway as both a sensor and a transcriptional repressor

L-Arginine is the precursor of nitric oxide (NO), a host immune effector against intracellular pathogens including Mycobacterium tuberculosis (M. tb). Pathogens including M. tb have evolved various strategies targeting arginine to block the production of NO for better survival and proliferation. However, L-arginine metabolism and regulation in Mycobacterium are poorly understood. Here, we report the identification of M. smegmatis MSMEG_1415 (homolog of M. tb Rv2324) as an arginine-responsive transcriptional factor regulating the arginase pathway. In the absence of L-arginine, MSMEG_1415 acts as a repressor to inhibit the transcription of the roc (for arginine, ornithine catabolism) gene cluster, thereby switching off the arginase pathway. Treatment with L-arginine relieves the transcriptional inhibition of MSMEG_1415 on the roc gene cluster to activate the arginase pathway. Moreover, the L-arginine-MSMEG_1415 complex activates the transcription of the roc gene cluster by recognizing and binding a 15-bp palindrome motif, thereby preventing the excess accumulation of L-arginine in M. smegmatis. Physiologically, MSMEG_1415 confers mycobacteria resistance to starvation and fluoroquinolones exposure, suggestive of its important role in M. smegmatis persistence. The results uncover a unique regulatory mechanism of arginine metabolism in mycobacteria and identify M. tb Rv2324 as an attractive candidate target for the design of drugs against tuberculosis.

The role of polyamines in gastric cancer

Advancements in our understanding of polyamine molecular and cellular functions have led to increased interest in targeting polyamine metabolism for anticancer therapeutic benefits. The polyamines putrescine, spermidine, and spermine are polycationic alkylamines commonly found in all living cells and are essential for cellular growth and survival. This review summarizes the existing research on polyamine metabolism and function, specifically the role of polyamines in gastric immune cell and epithelial cell function. Polyamines have been implicated in a multitude of cancers, but in this review, we focus on the role of polyamine dysregulation in the context of Helicobacter pylori-induced gastritis and subsequent progression to gastric cancer. Due to the emerging implication of polyamines in cancer development, there is an increasing number of promising clinical trials using agents to target the polyamine metabolic pathway for potential chemoprevention and anticancer therapy.

Arginine-dependent immune responses

A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.

An evolutionary non-conserved motif in Helicobacter pylori arginase mediates positioning of the loop containing the catalytic residue for catalysis

The binuclear metalloenzyme Helicobacter pylori arginase is important for pathogenesis of the bacterium in the human stomach. Despite conservation of the catalytic residues, this single Trp enzyme has an insertion sequence (-153ESEEKAWQKLCSL165-) that is extremely crucial to function. This sequence contains the critical residues, which are conserved in the homolog of other Helicobacter gastric pathogens. However, the underlying basis for the role of this motif in catalytic function is not completely understood. Here, we used biochemical, biophysical and molecular dynamics simulations studies to determine that Glu155 of this stretch interacts with both Lys57 and Ser152. These interactions are essential for positioning of the motif through Trp159, which is located near Glu155 (His122-Trp159-Tyr125 contact is essential to tertiary structural integrity). The individual or double mutation of Lys57 and Ser152 to Ala considerably reduces catalytic activity with Lys57 to Ala being more significant, indicating they are crucial to function. Our data suggest that the Lys57-Glu155-Ser152 interaction influences the positioning of the loop containing the catalytic His133 so that this His can participate in catalysis, thereby providing a mechanistic understanding into the role of this motif in catalytic function. Lys57 was also found only in the arginases of other Helicobacter gastric pathogens. Based on the non-conserved motif, we found a new molecule, which specifically inhibits this enzyme. Thus, the present study not only provides a molecular basis into the role of this motif in function, but also offers an opportunity for the design of inhibitors with greater efficacy.

Bacterial infection reinforces host metabolic flux from arginine to spermine for NLRP3 inflammasome evasion

Hosts recognize cytosolic microbial infection via the nucleotide-binding domain-like receptor (NLR) protein family, triggering inflammasome complex assembly to provoke pyroptosis or cytokine-related caspase-1-dependent antimicrobial responses. Pathogens have evolved diverse strategies to antagonize inflammasome activation. Here, Edwardsiella piscicida gene-defined transposon library screening for lactate dehydrogenase (LDH) release in nlrc4^-/- bone marrow-derived macrophages (BMDMs) demonstrates that genes clustered in the bacterial arginine metabolism pathway participate in NLRP3 inflammasome inhibition. Blocking arginine uptake or putrescine export significantly relieves NLRP3 inflammasome inhibition, indicating that this bacterium rewires its arginine metabolism network during infection. Moreover, intracellular E. piscicida recruits the host arginine importer (mCAT-1) and putrescine exporter (Oct-2) to bacterium-containing vacuoles, accompanied by reduced arginine and accumulated cytosolic spermine. Neutralizing E. piscicida-induced cytosolic spermine enhancement by spermine synthetase or extracellular spermine significantly alters NLRP3 inflammasome activation. Importantly, accumulated cytosolic spermine inhibits K⁺ efflux-dependent NLRP3 inflammasome activation. These data highlight the mechanism of bacterial gene-mediated arginine metabolism control for NLRP3 inflammasome evasion.

Hypusination Orchestrates the Antimicrobial Response of Macrophages

Innate responses of myeloid cells defend against pathogenic bacteria via inducible effectors. Deoxyhypusine synthase (DHPS) catalyzes the transfer of the N-moiety of spermidine to the lysine-50 residue of eukaryotic translation initiation factor 5A (EIF5A) to form the amino acid hypusine. Hypusinated EIF5A (EIF5AHyp) transports specific mRNAs to ribosomes for translation. We show that DHPS is induced in macrophages by two gastrointestinal pathogens, Helicobacter pylori and Citrobacter rodentium, resulting in enhanced hypusination of EIF5A. EIF5AHyp was also increased in gastric macrophages from patients with H. pylori gastritis. Furthermore, we identify the bacteria-induced immune effectors regulated by hypusination. This set of proteins includes essential constituents of antimicrobial response and autophagy. Mice with myeloid cell-specific deletion of Dhps exhibit reduced EIF5AHyp in macrophages and increased bacterial burden and inflammation. Thus, regulation of translation through hypusination is a critical hallmark of the defense of eukaryotic hosts against pathogenic bacteria.

Antunes I, Dömling A, H. Elsinga P. Arginase as a Potential Biomarker of Disease Progression: A Molecular Imaging Perspective

Arginase is a widely known enzyme of the urea cycle that catalyzes the hydrolysis of L-arginine to L-ornithine and urea. The action of arginase goes beyond the boundaries of hepatic ureogenic function, being widespread through most tissues. Two arginase isoforms coexist, the type I (Arg1) predominantly expressed in the liver and the type II (Arg2) expressed throughout extrahepatic tissues. By producing L-ornithine while competing with nitric oxide synthase (NOS) for the same substrate (L-arginine), arginase can influence the endogenous levels of polyamines, proline, and NO•. Several pathophysiological processes may deregulate arginase/NOS balance, disturbing the homeostasis and functionality of the organism. Upregulated arginase expression is associated with several pathological processes that can range from cardiovascular, immune-mediated, and tumorigenic conditions to neurodegenerative disorders. Thus, arginase is a potential biomarker of disease progression and severity and has recently been the subject of research studies regarding the therapeutic efficacy of arginase inhibitors. This review gives a comprehensive overview of the pathophysiological role of arginase and the current state of development of arginase inhibitors, discussing the potential of arginase as a molecular imaging biomarker and stimulating the development of novel specific and high-affinity arginase imaging probes.

The role of polyamines in the regulation of macrophage polarization and function

Naturally occurring polyamines are ubiquitously distributed and play important roles in cell development, amino acid and protein synthesis, oxidative DNA damage, proliferation, and cellular differentiation. Macrophages are essential in the innate immune response, and contribute to tissue remodeling. Naïve macrophages have two major potential fates: polarization to (1) the classical pro-inflammatory M1 defense response to bacterial pathogens and tumor cells, and (2) the alternatively activated M2 response, induced in the presence of parasites and wounding, and also implicated in the development of tumor-associated macrophages. ODC, the rate-limiting enzyme in polyamine synthesis, leads to an increase in putrescine levels, which impairs M1 gene transcription. Additionally, spermidine and spermine can regulate translation of pro-inflammatory mediators in activated macrophages. In this review, we focus on polyamines in macrophage activation patterns in the context of gastrointestinal inflammation and carcinogenesis. We seek to clarify mechanisms of innate immune regulation by polyamine metabolism and potential novel therapeutic targets.

Energy metabolism manipulates the fate and function of tumour myeloid-derived suppressor cells

In recent years, a large number of studies have been carried out in the field of immune metabolism, highlighting the role of metabolic energy reprogramming in altering the function of immune cells. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells generated during a large array of pathological conditions, such as cancer, inflammation, and infection, and show remarkable ability to suppress T-cell responses. These cells can also change their metabolic pathways in response to various pathogen-derived or inflammatory signals. In this review, we focus on the roles of glucose, fatty acid (FA), and amino acid (AA) metabolism in the differentiation and function of MDSCs in the tumour microenvironment, highlighting their potential as targets to inhibit tumour growth and enhance tumour immune surveillance by the host. We further highlight the remaining gaps in knowledge concerning the mechanisms determining the plasticity of MDSCs in different environments and their specific responses in the tumour environment. Therefore, this review should motivate further research in the field of metabolomics to identify the metabolic pathways driving the enhancement of MDSCs in order to effectively target their ability to promote tumour development and progression.

Polyamine catabolism and oxidative damage

Polyamines (PAs) are indispensable polycations ubiquitous to all living cells. Among their many critical functions, PAs contribute to the oxidative balance of the cell. Beginning with studies by the Tabor laboratory in bacteria and yeast, the requirement for PAs as protectors against oxygen radical-mediated damage has been well established in many organisms, including mammals. However, PAs also serve as substrates for oxidation reactions that produce hydrogen peroxide (H2O2) both intra- and extracellularly. As intracellular concentrations of PAs can reach millimolar concentrations, the H2O2 amounts produced through their catabolism, coupled with a reduction in protective PAs, are sufficient to cause the oxidative damage associated with many pathologies, including cancer. Thus, the maintenance of intracellular polyamine homeostasis may ultimately contribute to the maintenance of oxidative homeostasis. Again, pioneering studies by Tabor and colleagues led the way in first identifying spermine oxidase in Saccharomyces cerevisiae. They also first purified the extracellular bovine serum amine oxidase and elucidated the products of its oxidation of primary amine groups of PAs when included in culture medium. These investigations formed the foundation for many polyamine-related studies and experimental procedures still performed today. This Minireview will summarize key innovative studies regarding PAs and oxidative damage, starting with those from the Tabor laboratory and including the most recent advances, with a focus on mammalian systems.

Distinct Immunomodulatory Effects of Spermine Oxidase in Colitis Induced by Epithelial Injury or Infection

Polyamines have been implicated in numerous biological processes, including inflammation and carcinogenesis. Homeostatic regulation leads to interconversion of the polyamines putrescine and the downstream metabolites spermidine and spermine. The enzyme spermine oxidase (SMOX), which back-converts spermine to spermidine, contributes to regulation of polyamine levels, but can also have other effects. We have implicated SMOX in gastric inflammation and carcinogenesis due to infection by the pathogen Helicobacter pylori. In addition, we reported that SMOX can be upregulated in humans with inflammatory bowel disease. Herein, we utilized Smox-deficient mice to examine the role of SMOX in two murine colitis models, Citrobacter rodentium infection and dextran sulfate sodium (DSS)-induced epithelial injury. In C. rodentium-infected wild-type (WT) mice, there were marked increases in colon weight/length and histologic injury, with mucosal hyperplasia and inflammatory cell infiltration; these changes were ameliorated in Smox-/- mice. In contrast, with DSS, Smox-/- mice exhibited substantial mortality, and increased body weight loss, colon weight/length, and histologic damage. In C. rodentium-infected WT mice, there were increased colonic levels of the chemokines CCL2, CCL3, CCL4, CXCL1, CXCL2, and CXCL10, and the cytokines IL-6, TNF-α, CSF3, IFN-γ, and IL-17; each were downregulated in Smox-/- mice. In DSS colitis, increased levels of IL-6, CSF3, and IL-17 were further increased in Smox-/- mice. In both models, putrescine and spermidine were increased in WT mice; in Smox-/- mice, the main effect was decreased spermidine and spermidine/spermine ratio. With C. rodentium, polyamine levels correlated with histologic injury, while with DSS, spermidine was inversely correlated with injury. Our studies indicate that SMOX has immunomodulatory effects in experimental colitis via polyamine flux. Thus, SMOX contributes to the immunopathogenesis of C. rodentium infection, but is protective in DSS colitis, indicating the divergent effects of spermidine.

Effects of probiotic bacteria on mucosal polyamines levels in dogs with IBD and colonic polyps: a preliminary study

Spermine (SPM) and its precursor putrescine (PUT), regulated by ornithine decarboxylase (ODC) and diamino-oxidase (DAO), are polyamines required for cell growth and proliferation. Only a few studies have investigated the anti-inflammatory and tumour inhibitory properties of probiotics on mucosal polyamine levels. We investigated the effects of a high concentration multistrain probiotic for human use on colonic polyamine biosynthesis in dogs. Histological sections (inflammatory bowel disease, n=10; polyposis, n=5) were assessed after receiving 112 to 225×109 lyophilised bacteria daily for 60 days at baseline (T0) and 30 days after treatment end (T90). Histology scores, expression of PUT, SPM, ODC and DAO, and a clinical activity index (CIBDAI) were compared at T0 and T90. In polyps, cellular proliferation (Ki-67 expression), and apoptosis (caspase-3 protein expression) were also evaluated. After treatment, in inflammatory bowel disease significant decreases were observed for CIBDAI (P=0.006) and histology scores (P<0.001); PUT, SPM and ODC expression increased (P<0.01). In polyps, a significant decrease in polyamine levels, ODC activity, and Ki-67, and a significant increase in caspase-3 positivity and DAO expression (P=0.005) was noted. Our results suggest potential anti-proliferative and anti-inflammatory effects of the probiotic mixture in polyps and inflammation, associated with reduced mucosal infiltration and up-regulation of PUT, SPM, and ODC levels.

l-Arginine Uptake by Cationic Amino Acid Transporter Promotes Intra-Macrophage Survival of Leishmania donovani by Enhancing Arginase-Mediated Polyamine Synthesis

The survival of intracellular protozoan parasite, Leishmania donovani, the causative agent of Indian visceral leishmaniasis (VL), depends on the activation status of macrophages. l-Arginine, a semi-essential amino acid plays a crucial regulatory role for activation of macrophages. However, the role of l-arginine transport in VL still remains elusive. In this study, we demonstrated that intra-macrophage survival of L. donovani depends on the availability of extracellular l-arginine. Infection of THP-1-derived macrophage/human monocyte-derived macrophage (hMDM) with Leishmania, resulted in upregulation of l-arginine transport. While investigating the involvement of the transporters, we observed that Leishmania survival was greatly impaired when the transporters were blocked either using inhibitor or siRNA-mediated downregulation. CAT-2 was found to be the main isoform associated with l-arginine transport in L. donovani-infected macrophages. l-arginine availability and its transport regulated the host arginase in Leishmania infection. Arginase and inducible nitric oxide synthase (iNOS) expression were reciprocally regulated when assayed using specific inhibitors and siRNA-mediated downregulation. Interestingly, induction of iNOS expression and nitric oxide production were observed in case of inhibition of arginase in infected macrophages. Furthermore, inhibition of l-arginine transport as well as arginase resulted in decreased polyamine production, limiting parasite survival inside macrophages. l-arginine availability and transport regulated Th1/Th2 cytokine levels in case of Leishmania infection. Upregulation of l-arginine transport, induction of host arginase, and enhanced polyamine production were correlated with increased level of IL-10 and decreased level of IL-12 and TNF-α in L. donovani-infected macrophages. Our findings provide clear evidence for targeting the metabolism of l-arginine and l-arginine-metabolizing enzymes as an important therapeutic and prophylactic strategy to treat VL.

Ancillary Activity: Beyond Core Metabolism in Immune Cells

Immune cell function and fate are intimately linked to engagement of metabolic pathways. The contribution of core metabolic pathways to immune cell bioenergetics has been vigorously investigated in recent years. However, precisely how other peripheral metabolic pathways support immune cells beyond energy generation is less well understood. Here we survey the literature and highlight recent advances in our understanding of several ancillary metabolic pathways and how they support processes beyond ATP production and ultimately contribute to protective immunity.

Arginase of Helicobacter Gastric Pathogens Uses a Unique Set of Non-catalytic Residues for Catalysis

Helicobacter pylori arginase, a bimetallic enzyme, is crucial for pathogenesis of the bacterium in human stomach. Despite conservation of the signature motifs in all arginases, the H. pylori homolog has a non-conserved motif (¹⁵³ESEEKAWQKLCSL¹⁶⁵), whose role was recently shown to be critical for its stability and function. The sequence analysis also reveals the presence of this motif with critical residues in the homolog of other Helicobacter gastric pathogens. However, the underlying mechanism for its significance in catalytic function is not clearly understood. Using H. pylori arginase, our studies reveal that the interactions of His122 and Tyr125 with Trp159 are indispensable for tertiary structural intactness through optimal positioning of the motif and thus for the catalytic function. The single and double mutants of His122 and Tyr125 not only enhanced the solvent accessibility and conformational flexibility of Trp159 in the holo protein, but also showed complete loss of catalytic activity. An intact bimetallic center and unaltered substrate binding indicate that proper positioning of the motif by aromatic-aromatic contact is vital for the generation of a catalytically active conformation. Additionally, the metal ions provide higher stability to the holo protein. We also identified the presence of these two residues exclusively in arginase of other Helicobacter gastric pathogens, which may have similar function. Therefore, to the best of our knowledge, these findings highlight for the first time that arginase of all Helicobacter gastric pathogens utilizes a unique non-catalytic triad for catalysis, which could be exploited for therapeutics.

Matrine promotes NT3 expression in CNS cells in experimental autoimmune encephalomyelitis

Neurotrophin 3 (NT3) is a potent neurotrophic factor for promoting remyelination and recovery of neuronal function; upregulation of its expression in the central nervous system (CNS) is thus of major therapeutic importance for neurological deficits. Matrine (MAT), a quinolizidine alkaloid derived from the herb Radix Sophorae Flavescent, has been recently reported to effectively ameliorate clinical signs in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), by secreting antiinflammatory cytokines. In the present study, our goal was to investigate whether MAT could affect NT3 expression of glial cells in the CNS, the major cell populations in the CNS foci of MS/EAE. We found that MAT markedly upregulated NT3 expression in the CNS not only by microglia/macrophages and astrocytes, but also by oligodendrocyte precursor cells, indicative of both paracrine and autocrine effects on myelinating cells. While MAT treatment reduced the numbers of iNOS⁺ M1, but increased Arg1⁺ M2 microglia/macrophage phenotypes, NT3 expression was upregulated in both phenotypes. These results indicate that MAT therapy for EAE acts, at least in part, by stimulating local production of NT3 by glial cells in the CNS, which protects neural cells from CNS inflammation-induced tissue damage.

Oxidative Stress Resulting From Helicobacter pylori Infection Contributes to Gastric Carcinogenesis

Helicobacter pylori is a gram-negative, microaerophilic bacterium that infects the stomach and can lead to, among other disorders, the development of gastric cancer. The inability of the host to clear the infection results in a chronic inflammatory state with continued oxidative stress within the tissue. Reactive oxygen species and reactive nitrogen species produced by the immune and epithelial cells damage the host cells and can result in DNA damage. H pylori has evolved to evoke this damaging response while blunting the host's efforts to kill the bacteria. This long-lasting state with inflammation and oxidative stress can result in gastric carcinogenesis. Continued efforts to better understand the bacterium and the host response will serve to prevent or provide improved early diagnosis and treatment of gastric cancer.

Arginine Metabolism in Myeloid Cells Shapes Innate and Adaptive Immunity

Arginine metabolism has been a key catabolic and anabolic process throughout the evolution of the immune response. Accruing evidence indicates that arginine-catabolizing enzymes, mainly nitric oxide synthases and arginases, are closely integrated with the control of immune response under physiological and pathological conditions. Myeloid cells are major players that exploit the regulators of arginine metabolism to mediate diverse, although often opposing, immunological and functional consequences. In this article, we focus on the importance of arginine catabolism by myeloid cells in regulating innate and adaptive immunity. Revisiting this matter could result in novel therapeutic approaches by which the immunoregulatory nodes instructed by arginine metabolism can be targeted.

Macrophages induce resistance to 5-fluorouracil chemotherapy in colorectal cancer through the release of putrescine

The development of chemoresistance to 5-fluorouracil (5-FU) is a major obstacle for sustained effective treatment of colorectal cancer (CRC), with the mechanisms being not fully understood. Here we demonstrated that tumor associated macrophages (TAMs) became activated during treatment with 5-FU and secreted factors that protected the CRC cells against chemotherapy with 5-FU. By performing metabolomics analysis, we identified putrescine, a member of polyamines, inducing resistance to 5-FU-triggered CRC apoptosis and tumor suppression via JNK-caspase-3 pathway. Noteworthily, either pharmacological or genetic blockage of ornithine decarboxylase (ODC) prevented TAMs-induced chemoresistance to 5-FU in vitro and in vivo. Our findings show that TAMs are potent mediators of resistance to 5-FU chemotherapy and uncover potential targets to enhance chemotherapy sensitivity in patients with CRC.

The first description of complete invertebrate arginine metabolism pathways implies dose-dependent pathogen regulation in Apostichopus japonicus

In this study, three typical members representative of different arginine metabolic pathways were firstly identified from Apostichopus japonicus, including nitric oxide synthase (NOS), arginase, and agmatinase. Spatial expression analysis revealed that the AjNOS transcript presented negative expression patterns relative to those of Ajarginase or Ajagmatinase in most detected tissues. Furthermore, Vibrio splendidus-challenged coelomocytes and intestine, and LPS-exposed primary coelomocytes could significantly induce AjNOS expression, followed by obviously inhibited Arginase and AjAgmatinase transcripts at the most detected time points. Silencing the three members with two specific siRNAs in vivo and in vitro collectively indicated that AjNOS not only compete with Ajarginase but also with Ajagmatinase in arginine metabolism. Interestingly, Ajarginase and Ajagmatinase displayed cooperative expression profiles in arginine utilization. More importantly, live pathogens of V. splendidus and Vibrio parahaemolyticus co-incubated with primary cells also induced NO production and suppressed arginase activity in a time-dependent at an appropriate multiplicity of infection (MOI) of 10, without non-pathogen Escherichia coli. When increasing the pathogen dose (MOI = 100), arginase activity was significantly elevated, and NO production was depressed, with a larger magnitude in V. splendidus co-incubation. The present study expands our understanding of the connection between arginine's metabolic and immune responses in non-model invertebrates.

Arginine Metabolism in Bacterial Pathogenesis and Cancer Therapy

Antibacterial resistance to infectious diseases is a significant global concern for health care organizations; along with aging populations and increasing cancer rates, it represents a great burden for government healthcare systems. Therefore, the development of therapies against bacterial infection and cancer is an important strategy for healthcare research. Pathogenic bacteria and cancer have developed a broad range of sophisticated strategies to survive or propagate inside a host and cause infection or spread disease. Bacteria can employ their own metabolism pathways to obtain nutrients from the host cells in order to survive. Similarly, cancer cells can dysregulate normal human cell metabolic pathways so that they can grow and spread. One common feature of the adaption and disruption of metabolic pathways observed in bacterial and cancer cell growth is amino acid pathways; these have recently been targeted as a novel approach to manage bacterial infections and cancer therapy. In particular, arginine metabolism has been illustrated to be important not only for bacterial pathogenesis but also for cancer therapy. Therefore, greater insights into arginine metabolism of pathogenic bacteria and cancer cells would provide possible targets for controlling of bacterial infection and cancer treatment. This review will summarize the recent progress on the relationship of arginine metabolism with bacterial pathogenesis and cancer therapy, with a particular focus on arginase and arginine deiminase pathways of arginine catabolism.

The Immune Battle against Helicobacter pylori Infection: NO Offense

Helicobacter pylori is a successful pathogen of the human stomach. Despite a vigorous immune response by the gastric mucosa, the bacterium survives in its ecological niche, thus favoring diseases ranging from chronic gastritis to adenocarcinoma. The current literature demonstrates that high-output of nitric oxide (NO) production by the inducible enzyme NO synthase-2 (NOS2) plays major functions in host defense against bacterial infections. However, pathogens have elaborated several strategies to counteract the deleterious effects of NO; this includes inhibition of host NO synthesis and transcriptional regulation in response to reactive nitrogen species, allowing the bacteria to face the nitrosative stress. Moreover, NO is also a critical mediator of inflammation and carcinogenesis. In this context, we review the recent findings on the expression of NOS2 in H. pylori-infected gastric tissues and epithelial cells, the role of NO in H. pylori-related diseases and H. pylori gene expression, and the mechanisms whereby H. pylori regulates NO synthesis by host cells.

Dual role of arginine metabolism in establishing pathogenesis

Arginine is an integral part of host defense when invading pathogens are encountered. The arginine metabolite nitric oxide (NO) confers antimicrobial properties, whereas the metabolite ornithine is utilized for polyamine synthesis. Polyamines are crucial to tissue repair and anti-inflammatory responses. iNOS/arginase balance can determine Th1/Th2 response. Furthermore, the host arginine pool and its metabolites are utilized as energy sources by various pathogens. Apart from its role as an immune modulator, recent studies have also highlighted the therapeutic effects of arginine. This article sheds light upon the roles of arginine metabolism during pathological conditions and its therapeutic potential.

Metabolism links bacterial biofilms and colon carcinogenesis

Bacterial biofilms in the colon alter the host tissue microenvironment. A role for biofilms in colon cancer metabolism has been suggested but to date has not been evaluated. Using metabolomics, we investigated the metabolic influence that microbial biofilms have on colon tissues and the related occurrence of cancer. Patient-matched colon cancers and histologically normal tissues, with or without biofilms, were examined. We show the upregulation of polyamine metabolites in tissues from cancer hosts with significant enhancement of N(1), N(12)-diacetylspermine in both biofilm-positive cancer and normal tissues. Antibiotic treatment, which cleared biofilms, decreased N(1), N(12)-diacetylspermine levels to those seen in biofilm-negative tissues, indicating that host cancer and bacterial biofilm structures contribute to the polyamine metabolite pool. These results show that colonic mucosal biofilms alter the cancer metabolome to produce a regulator of cellular proliferation and colon cancer growth potentially affecting cancer development and progression.

Changes in the proteomic profile during the differential polarization status of the human monocyte-derived macrophage THP-1 cell line

Macrophages are heterogeneous and plastic populations that are an essential component of inflammation and host defense. To understand how macrophages respond to cytokine signals, we used 2DE to identify protein profiles in macrophages stimulated with interleukin 4 (M2) and those stimulated with lipopolysaccharide and interferon γ (M1). In total, 32 differentially expressed proteins in THP-1 cells were identified by MALDI-TOF MS/MS analysis. The different proteins were mainly involved in cellular structure, protein metabolism, stress response, oxidative response, and nitric oxide production during macrophage polarization. In particular, proteins playing important roles in production of nitric oxide (NO) were downregulated in M2 macrophages. Many antioxidant and heat shock proteins, which are related to oxidative response, were upregulated in M2 macrophages. More importantly, a remarkable decrease in intracellular ROS and NO production were detected in M2 macrophages. Our results provide a proteomic profile of differentially polarized macrophages and validate the function of the identified proteins, which may indicate possible mechanism of macrophage polarization process.

Spermine reverses lipopolysaccharide-induced memory deficit in mice

Background

Lipopolysaccharide (LPS) induces neuroinflammation and memory deficit. Since polyamines improve memory in various cognitive tasks, we hypothesized that spermine administration reverses LPS-induced memory deficits in an object recognition task in mice. The involvement of the polyamine binding site at the N-methyl-D-aspartate (NMDA) receptor and cytokine production in the promnesic effect of spermine were investigated.

Methods

Adult male mice were injected with LPS (250 μg/kg, intraperitoneally) and spermine (0.3 to 1 mg/kg, intraperitoneally) or ifenprodil (0.3 to 10 mg/kg, intraperitoneally), or both, and their memory function was evaluated using a novel object recognition task. In addition, cortical and hippocampal cytokines levels were measured by ELISA four hours after LPS injection.

Results

Spermine increased but ifenprodil decreased the recognition index in the novel object recognition task. Spermine, at doses that did not alter memory (0.3 mg/kg, intraperitoneally), reversed the cognitive impairment induced by LPS. Ifenprodil (0.3 mg/kg, intraperitoneally) reversed the protective effect of spermine against LPS-induced memory deficits. However, spermine failed to reverse the LPS-induced increase of cortical and hippocampal cytokine levels.

Conclusions

Spermine protects against LPS-induced memory deficits in mice by a mechanism that involves GluN2B receptors.

Induced nitric oxide synthetase and peroxiredoxin expression in intramucosal poorly differentiated gastric cancer of young patients

To investigate the relationship between oxidative stress and gastric carcinogenesis of poorly differentiated adenocarcinoma in young patients, we analyzed the surgically resected specimens of 22 young patients (21-30 years) and 29 older patients (41-72 years) with intramucosal gastric cancer of the poorly differentiated type. We used immunohistochemical staining to evaluate the expression of 8-hydroxydeoxyguanosine (8OHdG), induced nitric oxide synthetase (iNOS), and antioxidant enzymes (thioredoxin [TRX] and peroxiredoxin [PRDX1, 2 and 3]). We assessed these proteins in the cancer, noncancerous gastric foveolar epithelium and noncancerous mucosal neck. In both the young and older patient groups, the 8OHdG and TRX expressions were gradually increased in cancer cells compared with the noncancerous foveolar epithelial cells and the noncancerous mucosal neck cells (P < 0.001). Although the iNOS and PRDXs expressions were increased in the noncancerous mucosal neck cells compared with the noncancerous foveolar epithelial cells, regardless of age (P < 0.001), the iNOS and PRDX2 expression in the cancer cells were significantly reduced in the young patients compared with the older patients (P < 0.001, P < 0.05). In conclusion, the reduced expression of iNOS or PRDX2 may play an important role in the carcinogenesis of gastric cancer associated with Helicobacter pylori-induced chronic active gastritis in young patients.

Micro-scale strategy to detect spermine and spermidine by MALDI-TOF MS in foods and identification of apoptosis-related proteins by nano-flow UPLC-MS/MS after treatment with spermine and spermidine

Spermine and spermidine are multiple-nitrogen compounds found in many foods. Both compounds are essential for cell growth and human health. This study established a simple and fast method of detecting spermine and spermidine in food samples by matrix-assisted laser desorption/ionization combined with time-of-flight mass spectrometry (MALDI-TOF MS). After a simple sample preparation procedure, spermine and spermidine were directly detected by MALDI-TOF MS with no additional purification procedure. The calibration curves for spermine and spermidine ranged from 0.1 to 10 μg/mL. In intra- and inter-batch assays of three different concentrations of spermine and spermidine, all relative standard deviations and relative errors were below 18.9%. These experimental results confirmed the practicability and effectiveness of the proposed MALDI-TOF MS method for fast determination of spermine and spermidine in food samples. Furthermore, since spermine and spermidine have important roles in apoptosis, up-regulation and down-regulation of spermine and spermidine during apoptosis were analyzed. After treating NRK-52E cells with spermine and spermidine, the cells were lysed, and cell proteins were collected, and digested. Apoptosis-related proteins were then identified by tandem MS.

Metabolism via Arginase or Nitric Oxide Synthase: Two Competing Arginine Pathways in Macrophages

Macrophages play a major role in the immune system, both as antimicrobial effector cells and as immunoregulatory cells, which induce, suppress or modulate adaptive immune responses. These key aspects of macrophage biology are fundamentally driven by the phenotype of macrophage arginine metabolism that is prevalent in an evolving or ongoing immune response. M1 macrophages express the enzyme nitric oxide synthase, which metabolizes arginine to nitric oxide (NO) and citrulline. NO can be metabolized to further downstream reactive nitrogen species, while citrulline might be reused for efficient NO synthesis via the citrulline–NO cycle. M2 macrophages are characterized by expression of the enzyme arginase, which hydrolyzes arginine to ornithine and urea. The arginase pathway limits arginine availability for NO synthesis and ornithine itself can further feed into the important downstream pathways of polyamine and proline syntheses, which are important for cellular proliferation and tissue repair. M1 versus M2 polarization leads to opposing outcomes of inflammatory reactions, but depending on the context, M1 and M2 macrophages can be both pro- and anti-inflammatory. Notably, M1/M2 macrophage polarization can be driven by microbial infection or innate danger signals without any influence of adaptive immune cells, secondarily driving the T helper (Th)1/Th2 polarization of the evolving adaptive immune response. Since both arginine metabolic pathways cross-inhibit each other on the level of the respective arginine break-down products and Th1 and Th2 lymphocytes can drive or amplify macrophage M1/M2 dichotomy via cytokine activation, this forms the basis of a self-sustaining M1/M2 polarization of the whole immune response. Understanding the arginine metabolism of M1/M2 macrophage phenotypes is therefore central to find new possibilities to manipulate immune responses in infection, autoimmune diseases, chronic inflammatory conditions, and cancer.

Chlamydia trachomatis inhibits inducible NO synthase in human mesenchymal stem cells by stimulating polyamine synthesis

Chlamydia trachomatis is considered the most common agent of sexually transmitted disease worldwide. As an obligate intracellular bacterium, it relies on the host for survival. Production of NO is an effective antimicrobial defense mechanism of the innate immune system. However, whether NO is able to arrest chlamydial growth remains unclear. Similarly, little is known about the mechanisms underlying subversion of cellular innate immunity by C. trachomatis. By analyzing protein and mRNA expression in infected human mesenchymal stem cells, combined with RNA interference and biochemical assays, we observed that infection with C. trachomatis led to downregulated expression of inducible NO synthase (iNOS) in human mesenchymal stem cells in vitro. Furthermore, infection upregulated the expression of the rate-limiting enzyme in the polyamine biosynthetic pathway, ornithine decarboxylase, diverting the iNOS substrate l-arginine toward the synthesis of polyamines. Inhibition of ornithine decarboxylase activity using small interfering RNA or the competitive inhibitor difluoromethylornithine restored iNOS protein expression and activity in infected cells and inhibited chlamydial growth. This inhibition was mediated through tyrosine nitration of chlamydial protein by peroxynitrite, an NO metabolite. Thus, Chlamydia evades innate immunity by inhibiting NO production through induction of the alternative polyamine pathway.

Use of self-retaining barbed suture for rectal wall closure in transanal endoscopic microsurgery

BACKGROUND

The aim of this study was to investigate the safety and efficacy of self-retaining barbed sutures in comparison with monofilament clip-fixated sutures for rectal wall closure in transanal endoscopic microsurgery.

METHODS

Horizontal full-thickness wall defects (3.5 cm) of cattle rectal specimens were closed via transanal endoscopic microsurgery using a monofilament suture with clips at the end (Surgipro(®) 2/0; Covidien, Mansfield, MA, USA, n = 25) or a self-retaining barbed suture (V-Loc™ 180 3/0; Covidien, Mansfield, MA, USA, n = 25). The primary endpoint was the pneumatic leakage pressure of the suture line. As a secondary endpoint, suture time was evaluated.

RESULTS

The median pneumatic leakage pressure for barbed sutures was 45.5 mbar (range 17-106 mbar) and 33.5 mbar (range 19-106 mbar) for monofilament sutures (p = 0.58). A pneumatic leak at a critical pressure below 25 mbar occurred in 3 cases with barbed sutures and in 7 cases with monofilament sutures (p = 0.29). Median suturing time [19:25 min:s (range 12:00-33:30) vs. 20:41 (17:00-28:33), p = 0.23] did not differ between the two groups.

CONCLUSIONS

Barbed sutures display the same bursting pressure as monofilament sutures and their use for rectal wall closure seems feasible.

Effect of arginase inhibition on pulmonary L-arginine metabolism in murine Pseudomonas pneumonia

Rationale

Infection of the lung with Pseudomonas aeruginosa results in upregulation of nitric oxide synthases (NOS) and arginase expression, and both enzymes compete for L-arginine as substrate. Nitric oxide (NO) production may be regulated by arginase as it controls L-arginine availability for NOS. We here studied the effect of systemic arginase inhibition on pulmonary L-arginine metabolism in Pseudomonas pneumonia in the mouse.

Methods

Mice (C57BL/6, 8–10 weeks old, female) underwent direct tracheal instillation of Pseudomonas (PAO-1)-coated agar beads and were treated by repeated intra-peritoneal injections of the arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) or PBS until lungs were harvested on day 3 of the infection. L-arginine metabolites were quantified using liquid chromatography-tandem mass spectrometry, NO metabolites nitrate and nitrite by Griess reagent and cytokines by ELISA.

Results

NO metabolite concentrations (48.5±2.9 vs. 10.9±2.3 µM, p<0.0001), as well as L-ornithine (29.6±1.7 vs 2.3±0.4 µM, p<0.0001), the product of arginase activity, were increased in Pseudomonas infected lungs compared to naïve controls. Concentrations of the NOS inhibitor asymmetric dimethylarginine (ADMA) were also increased (0.44±0.02 vs. 0.16±0.01 µM, p<0.0001). Arginase inhibition in the infected animals resulted in a significant decrease in L-ornithine (14.6±1.6 µM, p<0.0001) but increase in L-arginine concentration (p<0.001), L-arginine/ADMA ratio (p<0.001), L-arginine availability for NOS (p<0.001), and NO metabolite concentrations (67.3±5.7 µM, p<0.05). Arginase inhibitor treatment also resulted in an increase in NO metabolite levels in animals following intratracheal injection of LPS (p = 0.015). Arginase inhibition was not associated with an increase in inflammatory markers (IFN-γ, IL-1β, IL-6, MIP-2, KC or TNF-α) in lung. Concentrations of the L-ornithine-dependent polyamines putrescine, spermidine and spermine were increased in Pseudomonas infected lungs (p<0.001, respectively) but were unaffected by ABH treatment.

Conclusions

Systemic arginase inhibition with ABH during Pseudomonas pneumonia in mice results in an increase in pulmonary NO formation but no pro-inflammatory effect.