Regulation of arginase expression by T-helper II cytokines and isoproterenol

Pilot Study on Acute Effects of Pharmacological Intraperitoneal L-Homoarginine on Homeostasis of Lysine and Other Amino Acids in a Rat Model of Isoprenaline-Induced Takotsubo Cardiomyopathy

L-Arginine:glycine amidinotransferase (AGAT) catalyzes the formation of L-homoarginine (hArg) and L-ornithine (Orn) from L-arginine (Arg) and L-lysine (Lys): Arg + Lys ↔ hArg + Orn; equilibrium constant K_hArg. AGAT also catalyzes the formation of guanidinoacetate (GAA) and Orn from Arg and glycine (Gly): Arg + Gly ↔ GAA + Orn; equilibrium constant K_GAA. In humans, pharmacological hArg is metabolized to Lys. Low circulating and low excretory concentrations of hArg are associated with worse outcomes and mortality in the renal and cardiovascular systems. The metabolism and pharmacology of hArg have been little investigated. In the present study, we investigated the effects of pharmacological hArg (i.p., 0, 20, 220, 440 mg/kg at time point 0 min) on amino acids homeostasis in a rat model of isoprenaline-induced takotsubo cardiomyopathy (i.p., 50 mg/kg at time point 15 min). We measured by gas chromatography-mass spectrometry free and proteinic amino acids, as well as the polyamines putrescine and spermidine in the heart, lung, kidney, and liver of ten rats sacrificed at various time points (range, 0 to 126 min). hArg administration resulted in multiple changes in the tissue contents of several free and proteinic amino acids, as well as in the putrescine-spermidine molar ratio, an indicator of polyamines catabolism. Our results suggest that Lys and Arg are major metabolites of pharmacological hArg. Kidneys and heart seem to play a major metabolic role for hArg. Circulating Lys does not change over time, yet there is a considerable interchange of free Lys between organs, notably kidney and heart, during the presence of isoprenaline in the rats (time range, 15 to 90 min). Antidromic changes were observed for K_hArg and K_GAA, notably in the heart in this time window. Our study shows for the first time that free hArg and sarcosine (N-methylglycine) are positively associated with each other. The acute effects of high-dosed hArg administration and isoprenaline on various amino acids and on AGAT-catalyzed reaction in the heart, lung, kidney, and liver are detailed and discussed.

Cytokines and metabolic regulation: A framework of bidirectional influences affecting Leishmania infection

Leishmania, a protozoan parasite inflicting the complex of diseases called Leishmaniases, resides and replicates as amastigotes within mammalian macrophages. As macrophages are metabolically highly active and can generate free radicals that can destroy this parasite, Leishmania also devise strategies to modulate the host cell metabolism. However, the metabolic changes can also be influenced by the anti-leishmanial immune response mediated by cytokines. This bidirectional, dynamic and complex metabolic coupling established between Leishmania and its host is the result of a long co-evolutionary process. Due to the continuous alterations imposed by the host microenvironment, such metabolic coupling continues to be dynamically regulated. The constant pursuit and competition for nutrients in the host-Leishmania duet alter the host metabolic pathways with major consequences for its nutritional reserves, eventually affecting the phenotype and functionality of the host cell. Altered phenotype and functions of macrophages are particularly relevant to immune cells, as perturbed metabolic fluxes can crucially affect the activation, differentiation, and functions of host immune cells. All these changes can deterministically direct the outcome of an infection. Cytokines and metabolic fluxes can bidirectionally influence each other through molecular sensors and regulators to dictate the final infection outcome. Our studies along with those from others have now identified the metabolic nodes that can be targeted for therapy.

Amino Acids and Their Metabolism in Atherosclerosis

As a leading cause of death worldwide, cardiovascular disease is a global health concern. The development and progression of atherosclerosis, which ultimately gives rise to cardiovascular disease, has been causally linked to hypercholesterolemia. Mechanistically, the interplay between lipids and the immune system during plaque progression significantly contributes to the chronic inflammation seen in the arterial wall during atherosclerosis. Localized inflammation and increased cell-to-cell interactions may influence polarization and proliferation of immune cells via changes in amino acid metabolism. Specifically, the amino acids l -arginine (Arg), l -homoarginine (hArg) and l -tryptophan (Trp) have been widely studied in the context of cardiovascular disease, and their metabolism has been established as key regulators of vascular homeostasis, as well as immune cell function. Cyclic effects between endothelial cells, innate, and adaptive immune cells exist during Arg and hArg, as well as Trp metabolism, that may have distinct effects on the development of atherosclerosis. In this review, we describe the current knowledge surrounding the metabolism, biological function, and clinical perspective of Arg, hArg, and Trp in the context of atherosclerosis.

Macrophage-Derived IL1β and TNFα Regulate Arginine Metabolism in Neuroblastoma

Neuroblastoma is the most common childhood solid tumor, yet the prognosis for high-risk disease remains poor. We demonstrate here that arginase 2 (ARG2) drives neuroblastoma cell proliferation via regulation of arginine metabolism. Targeting arginine metabolism, either by blocking cationic amino acid transporter 1 (CAT-1)-dependent arginine uptake in vitro or therapeutic depletion of arginine by pegylated recombinant arginase BCT-100, significantly delayed tumor development and prolonged murine survival. Tumor cells polarized infiltrating monocytes to an M1-macrophage phenotype, which released IL1β and TNFα in a RAC-alpha serine/threonine-protein kinase (AKT)-dependent manner. IL1β and TNFα established a feedback loop to upregulate ARG2 expression via p38 and extracellular regulated kinases 1/2 (ERK1/2) signaling in neuroblastoma and neural crest-derived cells. Proteomic analysis revealed that enrichment of IL1β and TNFα in stage IV human tumor microenvironments was associated with a worse prognosis. These data thus describe an immune-metabolic regulatory loop between tumor cells and infiltrating myeloid cells regulating ARG2, which can be clinically exploited. SIGNIFICANCE: These findings illustrate that cross-talk between myeloid cells and tumor cells creates a metabolic regulatory loop that promotes neuroblastoma progression.

Mechanisms of Fish Macrophage Antimicrobial Immunity

Overcrowding conditions and temperatures shifts regularly manifest in large-scale infections of farmed fish, resulting in economic losses for the global aquaculture industries. Increased understanding of the functional mechanisms of fish antimicrobial host defenses is an important step forward in prevention of pathogen-induced morbidity and mortality in aquaculture setting. Like other vertebrates, macrophage-lineage cells are integral to fish immune responses and for this reason, much of the recent fish immunology research has focused on fish macrophage biology. These studies have revealed notable similarities as well as striking differences in the molecular strategies by which fish and higher vertebrates control their respective macrophage polarization and functionality. In this review, we address the current understanding of the biological mechanisms of teleost macrophage functional heterogeneity and immunity, focusing on the key cytokine regulators that control fish macrophage development and their antimicrobial armamentarium.

Assessment of leukocyte activity in mice devoid of the glucocorticoid receptor in the noradrenergic system (GRDBHCre)

Disturbances in brain monoamines, overactivity of the hypothalamo-pituitary adrenal (HPA) axis and pro-inflammatory tendency in the immune system are the key features of depressive disorders. Recently, several murine lines with mutations in glucocorticoid receptors (GRs) have been generated and these animals may be utilized for study depressive-like disorders. In the present study, we have investigated whether selective ablation of GRs in noradrenergic neurons affects functional properties of leukocytes and redirects them towards pro-inflammatory activity. Transgenic mice selectively devoid of GRs on noradrenergic cells were constructed using the Cre/loxP approach. Peritoneal leukocytes were collected from mutant and wild type (WT) animals of both sexes and were cultured in vitro for 24h both in basal conditions and after application of selected pro- or anti-inflammatory stimuli. Metabolic activity and adherence were measured in basal conditions. Nitric oxide (NO) synthesis and arginase (ARG) activity were assessed as the markers of functional status of the cells. Because adult mutant mice lack adrenal medulla and thereby peripheral adrenaline, we modulated pro- and anti-inflammatory culture conditions by addition of noradrenaline (10-6M). Finally, effects of in vivo pro-inflammatory challenge (with intraperitoneal administration of lipopolysaccharide) on properties of leukocytes were assessed 24h (in both sexes) and 48h later (in males only). The experiments indicated that selective ablation of GR in noradrenergic neurons did not affect fundamental properties of peritoneal leukocytes and exerted effects only under conditions of selected pro- or anti-inflammatory stimuli in vitro. Stronger response to pro-inflammatory stimulation in terms of NO synthesis and ARG activity may suggest pro-inflammatory tendency in mutant mice. In vivo inflammatory challenge failed to show any effect of GR ablation on selected parameters of leukocyte activity. Both in vitro studies and in vivo challenge revealed mainly sex-related differences in leukocyte activity.

Recombinant IL-4/13A and IL-4/13B induce arginase activity and down-regulate nitric oxide response of primary goldfish (Carassius auratus L.) macrophages

We report on the expression analysis and functional characterization of IL-4/13A and IL-4/13B in goldfish. Quantitative analysis indicated the highest expression in the heart, spleen, brain, and kidney, with comparable expression patterns for both IL-4/13A and IL-4/13B. The mRNA levels of IL-4/13A and IL-4/13B in the immune cells examined were highest in macrophage and monocytes. Assessment of spleen mRNA following infection with Trypanosoma carassii, a prominent protozoan pathogen of fish, revealed decrease in IL-4/13B and arginase expression 14 days post infection, followed by an increase in IL-4/13B and arginase-2 at 28 days post infection. Recombinant forms of IL-4/13A and IL-4/13B induced an increase in arginase activity in macrophages in a dose-dependent manner. Recombinant IL-4/13A and IL-4/13B also induced significant increase in mRNA levels of arginase -2 in macrophages at 6, 12, 18 and 24 h after treatment. Furthermore, treatment with both IL-4/13 recombinants interfered with the IFNγ-induced nitric oxide response of macrophages. Our results suggest a conserved role of IL-4/IL-13 in induction of alternative activation phenotype in teleost macrophages.

IL-13 Neutralization Modulates Function of Type II Polarized Macrophages in vivo in a Murine T-Cell Lymphoma

IL-13 is a Th2 cytokine that suppresses the effector function and alters the phenotype and function of macrophages switching to alternatively activated or type II polarized macrophages. The type II polarized macrophages or M2 phenotype differ from normal macrophages greatly in terms of receptor expression, cytokine and NO production, that show tumor promoting function rather than tumoricidal function of classically activated macrophages. The chemokines CCL-22 and CCL-17 produced by either tumor cells or alternatively activated macrophages attract Th2 cells preferentially, which increase the local concentration of Th2 cytokines including IL-13 that further skewed the normal phenotype of macrophages at the site of the tumor micro-environment. Therefore, it is possible to restore the phenotype and function of alternatively activated macrophages by eliminating or blocking the activities of these cytokines. In the present investigation, we show that by blocking the activity/signaling of one of its major constituents IL-13, the iNOS expression and correspondingly NO production increases. The observation signifies its efficacy towards a novel approach for cancer therapy by modulating the function of tumor-associated macrophages (TAM) in vivo for the first time.

Biology of Bony Fish Macrophages

Macrophages are found across all vertebrate species, reside in virtually all animal tissues, and play critical roles in host protection and homeostasis. Various mechanisms determine and regulate the highly plastic functional phenotypes of macrophages, including antimicrobial host defenses (pro-inflammatory, M1-type), and resolution and repair functions (anti-inflammatory/regulatory, M2-type). The study of inflammatory macrophages in immune defense of teleosts has garnered much attention, and antimicrobial mechanisms of these cells have been extensively studied in various fish models. Intriguingly, both similarities and differences have been documented for the regulation of lower vertebrate macrophage antimicrobial defenses, as compared to what has been described in mammals. Advances in our understanding of the teleost macrophage M2 phenotypes likewise suggest functional conservation through similar and distinct regulatory strategies, compared to their mammalian counterparts. In this review, we discuss the current understanding of the molecular mechanisms governing teleost macrophage functional heterogeneity, including monopoetic development, classical macrophage inflammatory and antimicrobial responses as well as alternative macrophage polarization towards tissues repair and resolution of inflammation.

Effect of the association of 1-methyl-DL-tryptophan with paclitaxel on the expression of indoleamine 2,3-dioxygenase in cultured cancer cells from patients with breast cancer

Breast cancer is the most common type of cancer among women and the survival of patients affected by it is increasing, mainly due to several new approaches in early diagnosis and more effective treatments. The enzyme indoleamine 2,3-dioxygenase (IDO) is expressed in many cells, including tumor cells. IDO acts by inhibiting the proliferation of T lymphocytes, thus compromising their cytotoxic activity. 1-Methyl-DL-tryptophan (1MT) is a competitive inhibitor of IDO, which blocks its immunosuppressive effect. Paclitaxel is an antineoplastic drug largely used in breast cancer therapy. Thus, this study aimed to determine the in vitro effect of the association of 1MT and paclitaxel chemotherapy, as an approach to reduce tumor growth. It is believed that this would allow the restoration of T lymphocyte proliferation capability and its cytotoxic response. The supplemented cultures showed that the most significant differences in the expression of IDO were observed in the group treated with paclitaxel associated with 1-MT continuous supplementation, reducing enzyme expression from 12.06 to 3.56 %. This association was more effective in reducing IDO expression and could collaborate in developing a new therapeutic strategy for breast cancer treatment.

Parallel Expression of Enzyme Inhibitors of CD8T Cell Activity in Tumor Microenvironments and Secretory Endometrium

The divergent requirement for tolerance to support conception and protective response against sexually transmitted infections defines the unique immunological dynamics in the female reproductive tract (FRT). In part, these requirements are achieved by the cyclic modulation of cytolytic CD8T cell function in the FRT that underlie the respective immunosuppressive and immunocompetent milieus during the secretory and proliferative phases of the menstrual cycle. The CD8T cell function can be dampened by exposure to indoleamine 2,3-dioxygenase and/or arginase enzymes. Indeed, these 2 enzymes are known as primary inducers of immune suppression in tumor microenvironments. This review discusses the intriguing parallel expression of these 2 enzymes in tumor microenvironments and in the secretory endometrium. We surmise that investigating the underlying natural mechanisms that suppress and restore the immunocompetence of CD8T cells in the FRT each month may provide valuable insights into ways to artificially recapitulate these mechanisms and inhibit immune suppression in tumor microenvironments.

Macrophages expressing arginase 1 and nitric oxide synthase 2 accumulate in the small intestine during Giardia lamblia infection

Nitric oxide (NO) has been shown to inhibit Giardia lamblia in vitro and in vivo. This study sought to determine if Giardia infection induces arginase 1 (ARG1) expression in host macrophages to reduce NO production. Stimulations of RAW 264.7 macrophage-like cells with Giardia extract induced arginase activity. Real-time PCR and immunohistochemistry showed increased ARG1 and nitric oxide synthase 2 (NOS2) expression in mouse intestine following infection. Flow cytometry demonstrated increased numbers of macrophages positive for both ARG1 and NOS2 in lamina propria following infection, but there was no evidence of increased expression of ARG1 in these cells.

Cytokines Modulate the "Immune-Metabolism" Interactions during Behçet Disease: Effect on Arginine Metabolism

Aim and Methods. In this study, we evaluated NOS and arginase activities and their regulation during Behçet disease, a systemic chronic inflammatory disorder with uncertain etiology. The peripheral blood mononuclear cells of 36 patients and 15 control samples (PBMC) were cultured in either RPMI 1640, MEM, or DMEM complemented with 10% of FBS and antibiotics. Cultures were performed with or without the control or patients plasma. Subsequent treatment contained anticytokines (IL-6, TGF-β), a mitogenic effector (PHA), or NOS modulators (L-NMMA, BH4). Culture supernatants were harvested after 24 h of incubation. NO and urea measurements were, respectively, performed by modified Griess and Berthelot methods. Results. Higher urea levels were found in patients' plasma compared to the control's (P < 0.05). NOS modulators induced inverted production profiles for NO and urea (P < 0.05). Their results differed depending on the clinical findings (P < 0.05). It was also found that cytokine neutralization induced different response profiles in patients as opposed to control cultures (P < 0.05). Conclusion. Our results suggest that arginases can compete with NOS2 for L-arginine during Behçet disease. Both enzymes are regulated by environmental cytokines and substrate availability. Furthermore, it seems that NOS/arginase balance is dependent on clinical expression.

L-Arginine modulates neonatal lymphocyte proliferation through an interleukin-2 independent pathway

In cases of arginine depletion, lymphocyte proliferation, cytokine production and CD3ζ chain expression are all diminished. In addition to myeloid suppressor cells, polymorphonuclear cells (PMN) also exert T-cell immune suppressive effects through arginase-induced l-arginine depletion, especially during pregnancy. In this study, we investigated how arginase/l-arginine modulates neonatal lymphocyte proliferation. Results showed that the neonatal plasma l-arginine level was lower than in adults (48·1 ± 11·3 versus 86·5 ± 14·6 μm; P = 0·003). Neonatal PMN had a greater abundance of arginase I protein than adult PMN. Both transcriptional regulation and post-transcriptional regulation were responsible for the higher arginase I expression of neonatal PMN. Exogenous l-arginine enhanced neonate lymphocyte proliferation but not that of adult cells. The RNA-binding protein HuR was important but was not the only modulation factor in l-arginine-regulated neonatal T-cell proliferation. l-Arginine-mediated neonatal lymphocyte proliferation could not be blocked by interleukin-2 receptor blocking antibodies. These results suggest that the altered arginase/l-arginine cascade may be one of the mechanisms that contribute to altered neonatal immune responses. Exogenous l-arginine could enhance neonate lymphocyte proliferation through an interleukin-2-independent pathway.

Antimicrobial responses of teleost phagocytes and innate immune evasion strategies of intracellular bacteria

During infection, macrophage lineage cells eliminate infiltrating pathogens through a battery of antimicrobial responses, where the efficacy of these innate immune responses is pivotal to immunological outcomes. Not surprisingly, many intracellular pathogens have evolved mechanisms to overcome macrophage defenses, using these immune cells as residences and dissemination strategies. With pathogenic infections causing increasing detriments to both aquacultural and wild fish populations, it is imperative to garner greater understanding of fish phagocyte antimicrobial responses and the mechanisms by which aquatic pathogens are able to overcome these teleost macrophage barriers. Insights into the regulation of macrophage immunity of bony fish species will lend to the development of more effective aquacultural prophylaxis as well as broadening our understanding of the evolution of these immune processes. Accordingly, this review focuses on recent advances in the understanding of teleost macrophage antimicrobial responses and the strategies by which intracellular fish pathogens are able to avoid being killed by phagocytes, with a focus on Mycobacterium marinum.

l-Citrulline Protects from Kidney Damage in Type 1 Diabetic Mice

RATIONALE

Diabetic nephropathy (DN) is a major cause of end-stage renal disease, associated with endothelial dysfunction. Chronic supplementation of l-arginine (l-arg), the substrate for endothelial nitric oxide synthase (eNOS), failed to improve vascular function. l-Citrulline (l-cit) supplementation not only increases l-arg synthesis, but also inhibits cytosolic arginase I, a competitor of eNOS for the use of l-arg, in the vasculature.

AIMS

To investigate whether l-cit treatment reduces DN in streptozotocin (STZ)-induced type 1 diabetes (T1D) in mice and rats and to study its effects on arginase II (ArgII) function, the main renal isoform.

METHODS

STZ-C57BL6 mice received l-cit or vehicle supplemented in the drinking water. For comparative analysis, diabetic ArgII knock out mice and l-cit-treated STZ-rats were evaluated.

RESULTS

l-Citrulline exerted protective effects in kidneys of STZ-rats, and markedly reduced urinary albumin excretion, tubulo-interstitial fibrosis, and kidney hypertrophy, observed in untreated diabetic mice. Intriguingly, l-cit treatment was accompanied by a sustained elevation of tubular ArgII at 16 weeks and significantly enhanced plasma levels of the anti-inflammatory cytokine IL-10. Diabetic ArgII knock out mice showed greater blood urea nitrogen levels, hypertrophy, and dilated tubules than diabetic wild type (WT) mice. Despite a marked reduction in collagen deposition in ArgII knock out mice, their albuminuria was not significantly different from diabetic WT animals. l-Cit also restored nitric oxide/reactive oxygen species balance and barrier function in high glucose-treated monolayers of human glomerular endothelial cells. Moreover, l-cit also has the ability to establish an anti-inflammatory profile, characterized by increased IL-10 and reduced IL-1β and IL-12(p70) generation in the human proximal tubular cells.

CONCLUSION

l-Citrulline supplementation established an anti-inflammatory profile and significantly preserved the nephron function during T1D.

Shaping the murine macrophage phenotype: IL-4 and cyclic AMP synergistically activate the arginase I promoter

Arginase I is a marker of murine M2 macrophages and is highly expressed in many inflammatory diseases. The basis for high arginase I expression in macrophages in vivo is incompletely understood but likely reflects integrated responses to combinations of stimuli. Our objective was to elucidate mechanisms involved in modulating arginase I induction by IL-4, the prototypical activator of M2 macrophages. IL-4 and 8-bromo-cAMP individually induce arginase I, but together they rapidly and synergistically induce arginase I mRNA, protein, and promoter activity in murine macrophage cells. Arginase I induction by IL-4 requires binding of the transcription factors STAT6 and C/EBPβ to the IL-4 response element of the arginase I gene. Chromatin immunoprecipitation showed that the synergistic response involves binding of both transcription factors to the IL-4 response element at levels significantly greater than in response to IL-4 alone. The results suggest that C/EBPβ is a limiting factor for the level of STAT6 bound to the IL-4 response element. The enhanced binding in the synergistic response was not due to increased expression of either STAT6 or C/EBPβ but was correlated primarily with increased nuclear abundance of C/EBPβ. Our findings also suggest that induction of arginase I expression is stochastic; that is, differences in induction reflect differences in probability of transcriptional activation and not simply differences in rate of transcription. Results of the present study also may be useful for understanding mechanisms underlying regulated expression of other genes in macrophages and other myeloid-derived cells in health and disease.

A performance evaluation of three drug-induced liver injury biomarkers in the rat: alpha-glutathione S-transferase, arginase 1, and 4-hydroxyphenyl-pyruvate dioxygenase

Alanine aminotransferase (ALT) activity is the most frequently relied upon reference standard for monitoring liver injury in humans and nonclinical species. However, limitations of ALT include a lack of specificity for diagnosing liver injury (e.g., present in muscle and the gastrointestinal tract), its inability to monitor certain types of hepatic injury (e.g., biliary injury), and ambiguity with respect to interpretation of modest or transient elevations (< 3× upper limit of normal). As an initial step to both understand and qualify additional biomarkers of hepatotoxicity that may add value to ALT, three novel candidates have been evaluated in 34 acute toxicity rat studies: (1) alpha-glutathione S-transferase (GSTA), (2) arginase 1 (ARG1), and (3) 4-hydroxyphenylpyruvate dioxygenase (HPD). The performance of each biomarker was assessed for its diagnostic ability to accurately detect hepatocellular injury (i.e., microscopic histopathology), singularly or in combination with ALT. All three biomarkers, either alone or in combination with ALT, improved specificity when compared with ALT alone. Hepatocellular necrosis and/or degeneration were detected by all three biomarkers in the majority of animals. ARG1 and HPD were also sensitive in detecting single-cell necrosis in the absence of more extensive hepatocellular necrosis/degeneration. ARG1 showed the best sensitivity for detecting biliary injury with or without ALT. All the biomarkers were able to detect biliary injury with single-cell necrosis. Taken together, these novel liver toxicity biomarkers, GSTA, ARG1, and HPD, add value (both enhanced specificity and sensitivity) to the measurement of ALT alone for monitoring drug-induced liver injury in rat.

Immunonutrition: does it have a role in improving recovery in patients receiving a stem cell transplant?

Numerous clinical trials have demonstrated that immunomodulating diets (IMDs) reduce treatment complications such as the risk of acquired infections, length of hospital stay, and wound complications in patients receiving planned surgery. These complications are possibly exacerbated by malnutrition at the time of surgery, resulting in decreased cell-mediated and humoral immune responses, which can be improved with the utilization of IMDs both prior to and following surgery. Although numerous randomized studies have investigated IMDs in the surgical setting, IMDs have not been well studied to evaluate whether their use improves outcomes for other patient groups with high incidence of malnutrition and acquired infections. Patients receiving stem cell transplantation following preparative myeloablative chemotherapy for treatment of a hematologic malignancy would be a prime example of another patient group who would share these characteristics. Given the proposed mechanism of action by which IMDs have aided recovery after surgery, it is reasonable to expect that IMDs may aid recovery after stem cell transplantation, and current preclinical and clinical data support the need for further clinical studies.

Pollutant particles induce arginase II in human bronchial epithelial cells

Exposure to particulate matter (PM) is associated with adverse pulmonary effects, including induction and exacerbation of asthma. Recently arginase was shown to play an important role in the pathogenesis of asthma. In this study, it was postulated that PM exposure might induce arginase. Human bronchial epithelial cells (HBEC) obtained from normal individuals by endobronchial brushings cultured on an air-liquid interface were incubated with fine Chapel Hill particles (PM₂.₅, 100 μg/ml) for up to 72 h. Arginase activity, protein expression, and mRNA of arginase I and arginase II were measured. PM₂.₅ increased arginase activity in a time-dependent manner. The rise was primarily due to upregulation of arginase II. PD153035 (10 μM), an epidermal growth factor (EGF) receptor antagonist, attenuated the PM₂.₅-induced elevation in arginase activity and arginase II expression. Treatment of HBEC with human EGF increased arginase activity and arginase II expression. Pretreatment with catalase (200 U/ml), superoxide dismutase (100 U/ml), or apocynin (5 μg/ml), an NAD(P)H oxidase inhibitor, did not markedly affect arginase II expression. Treatment of HBEC with arginase II siRNA inhibited the expression of arginase II by 60% and increased IL-8 release induced by PM₂.₅. These results indicate that PM exposure upregulates arginase II activity and expression in human bronchial epithelial cells, in part via EGF-dependent mechanisms independent of oxidative stress. The elevated arginase II activity and expression may be a mechanism underlying adverse effects induced by PM exposure in asthma patients.

Apoptotic cell-derived factors induce arginase II expression in murine macrophages by activating ERK5/CREB

Apoptotic cell (AC)-derived factors alter the physiology of macrophages (MΦs) towards a regulatory phenotype, characterized by reduced nitric oxide (NO) production. Impaired NO formation in response to AC-conditioned medium (CM) was facilitated by arginase II (ARG II) expression, which competes with inducible NO synthase for L-arginine. Here we explored signaling pathways allowing CM to upregulate ARG II in RAW264.7 MΦs. Sphingosine-1-phosphate (S1P) was required and acted synergistically with a so far unidentified factor to elicit high ARG II expression. S1P activated S1P(2), since S1P(2) knockdown prevented ARG II upregulation. Furthermore, ERK5 knockdown attenuated CM-mediated ARG II protein induction. CREB was implicated as shown by EMSA analysis and decoy-oligonucleotides scavenging CREB in RAW264.7 MΦs, which blocked ARG II expression. We conclude that AC-derived S1P binds to S1P(2) and acts synergistically with other factors to activate ERK5 and concomitantly CREB. This signaling cascade shapes an anti-inflammatory MΦ phenotype by ARG II induction.

Immunosupression and infection after major surgery: a nutritional deficiency

T cell dysfunction significantly increases susceptibility to infections and organ failure after trauma or surgery (physical injury). This coincides with a persistent drop in arginine availability, a necessary amino acid for normal T cell function. Recent data led to the identification of a novel mechanism of T cell suppression caused by the depletion of arginine through the induction of arginase 1 (ARG1) in a specialized group of immature myeloid cells, now named myeloid-derived suppressor cells (MDSC). In addition to T cell dysfunction, arginine depletion leads to the decrease in nitric oxide (NO) production. Dietary therapy containing arginine at supraphysiologic concentrations along with other components such as omega-3 fat acids, antioxidants, nucleotides, and vitamin A is associated with improvement in T cell function, NO production, and a significant decrease in infection rates. The authors propose that a pathologic decrease in arginine availability is an identifiable nutrition deficiency syndrome that worsens outcomes if left untreated.

Polyamine metabolism in Leishmania: from arginine to trypanothione

Polyamines (PAs) are essential metabolites in eukaryotes, participating in a variety of proliferative processes, and in trypanosomatid protozoa play an additional role in the synthesis of the critical thiol trypanothione. The PAs are synthesized by a metabolic process which involves arginase (ARG), which catalyzes the enzymatic hydrolysis of L-arginine (L-Arg) to L-ornithine and urea, and ornithine decarboxylase (ODC), which catalyzes the enzymatic decarboxylation of L-ornithine in putrescine. The S-adenosylmethionine decarboxylase (AdoMetDC) catalyzes the irreversible decarboxylation of S-adenosylmethionine (AdoMet), generating the decarboxylated S-adenosylmethionine (dAdoMet), which is a substrate, together with putrescine, for spermidine synthase (SpdS). Leishmania parasites and all the other members of the trypanosomatid family depend on spermidine for growth and survival. They can synthesize PAs and polyamine precursors, and also scavenge them from the microenvironment, using specific transporters. In addition, Trypanosomatids have a unique thiol-based metabolism, in which trypanothione (N1-N8-bis(glutathionyl)spermidine, T(SH)(2)) and trypanothione reductase (TR) replace many of the antioxidant and metabolic functions of the glutathione/glutathione reductase (GR) and thioredoxin/thioredoxin reductase (TrxR) systems present in the host. Trypanothione synthetase (TryS) and TR are necessary for the protozoa survival. Consequently, enzymes involved in spermidine synthesis and its utilization, i.e. ARG, ODC, AdoMetDC, SpdS and, in particular, TryS and TR, are promising targets for drug development.

Alternatively activated macrophages engage in homotypic and heterotypic interactions through IL-4 and polyamine-induced E-cadherin/catenin complexes

Alternatively activated macrophages (AAMs), triggered by interleukin-4 (IL-4) and IL-13, play a modulating role during Th2 cytokine-driven pathologies, but their molecular armament remains poorly characterized. Here, we established E-cadherin (Cdh1) as a selective marker for IL-4/IL-13-exposed mouse and human macrophages, which is STAT6-dependently induced during polarized Th2 responses associated with Taenia crassiceps helminth infections or allergic airway inflammation. The IL-4-dependent, arginase-1/ornithine decarboxylase-mediated production of polyamines is important for maximal Cdh1 induction, unveiling a novel mechanism for IL-4-dependent gene transcription. At the macrophage surface, E-cadherin forms a functional complex with the catenins that accumulates at sites of cell contact. Macrophage-specific deletion of the Cdh1 gene illustrates the implication of E-cadherin in IL-4-driven macrophage fusion and heterotypic interactions with CD103(+) and KLRG1(+) T cells. This study identifies the E-cadherin/catenin complex as a discriminative, partly polyamine-regulated feature of IL-4/IL-13-exposed alternatively activated macrophages that contributes to homotypic and heterotypic cellular interactions.

The liaison between apoptotic cells and macrophages--the end programs the beginning

The efficient execution of apoptotic cell death with the clearance of apoptotic debris by phagocytes is a key regulatory mechanism ensuring tissue homeostasis. Failure in this execution program contributes to the pathogenesis of many human diseases. In this review, we describe the current knowledge regarding the interaction of apoptotic cells with their professional 'captors', the macrophages, with special emphasis on the immunological outcome. Removal of apoptotic cells must be considered as a process that actively delivers signals to polarize macrophages, which are fundamental for the resolution of inflammation. However, the sculpting of macrophage responses by apoptotic cells can be misused under certain inflammatory disease conditions, including tumor development.

Effect of citrulline and glutamine on nitric oxide production in RAW 264.7 cells in an arginine-depleted environment

BACKGROUND

Nitric oxide (NO) is a highly reactive free radical essential for antimicrobial and tumor immunity as well as endothelial function. Arginine is a limiting factor in NO synthesis. Citrulline can be converted to arginine and might restore NO production when arginine availability is limited, while glutamine may competitively inhibit citrulline availability. We aimed to assess how these amino acids interact to generate NO using an in vitro model.

METHODS

RAW 264.7 cells were exposed to various amino acid concentrations before and after lipopolysaccharide (LPS) stimulation, and NO production was assessed.

RESULTS

NO production directly correlated up to 200 microM with arginine available after LPS stimulation (R(2) = 0.99). Provided the same arginine concentrations following LPS stimulation, low arginine precultured cells produced significantly less NO than high arginine precultured cells (P < .01). Citrulline added to low arginine preculture significantly increased NO production compared to cells in low arginine alone (P < .01). When glutamine was withdrawn before and after LPS stimulation, cells precultured in low arginine and citrulline produced NO equivalent to that of high arginine precultured cells. Additional citrulline provided after LPS stimulation additionally improved NO production beyond that observed in cells precultured in high arginine (P < .01), and NO production became less dependent on arginine availability (R(2) = 0.78).

CONCLUSION

Arginine availability is a limiting factor for NO production. Citrulline is a potential substitute to restore NO production when arginine availability is limited. Glutamine appears to be an important modulator that interferes with citrulline-mediated NO production.

L-arginine metabolism and its impact on host immunity against Leishmania infection

Leishmaniasis is a vector-borne disease found in many countries worldwide. The causative agent of the disease, Leishmania spp., lives as an obligate intracellular parasite within mammalian hosts. Since tissue macrophages are major target cells for parasite replication, the outcome of infection depends largely on the activation status of these cells. L-arginine is a crucial amino acid required for both nitric oxide (NO)-mediated parasite killing and polyamine-mediated parasite replication. This review highlights the significance of L-arginine as a factor determining the outcomes of Leishmania infection in vitro and its influences on host immune responses in vivo. Various therapeutic approaches targeting L-arginine metabolic pathways during infections with Leishmania are also discussed.

Arginine and immunity

For many years, dietary arginine supplementation, often combined with other substances, has been used as a mechanism to boost the immune system. Considerable controversy, however, exists as to the benefits and indications of dietary arginine due in part to a poor understanding of the role played by this amino acid in maintaining immune function. Emerging knowledge promises to clear this controversy and allow for arginine's safe use. In myeloid cells, arginine is mainly metabolized either by inducible nitric oxide (NO) synthases (iNOS) or by arginase 1, enzymes that are stimulated by T helper 1 or 2 cytokines, respectively. Thus, activation of iNOS or arginase (or both) reflects the type of inflammatory response in a specific disease process. Myeloid suppressor cells (MSC) expressing arginase have been described in trauma (in both mice and humans), intra-abdominal sepsis, certain infections, and prominently, cancer. Myeloid cells expressing arginase have been shown to accumulate in patients with cancer. Arginase 1 expression is also detected in mononuclear cells after trauma or surgery. MSC efficiently deplete arginine and generate ornithine. Through arginine depletion, MSC may control NO production and regulate other arginine-dependent biological processes. Low circulating arginine has been documented in trauma and cancer, suggesting that MSC may exert a systemic effect and cause a state of arginine deficiency. Simultaneously, T lymphocytes depend on arginine for proliferation, zeta-chain peptide and T-cell receptor complex expression, and the development of memory. T-cells cocultured with MSC exhibit the molecular and functional effects associated with arginine deficiency. Not surprisingly, T-cell abnormalities, including decreased proliferation and loss of the zeta-chain, are observed in cancer and after trauma.

Apoptotic cells induce arginase II in macrophages, thereby attenuating NO production

In recent years it has become apparent that removal of apoptotic cells (AC) by professional phagocytes alters the macrophage phenotype. This change is characterized by attenuated proinflammatory cytokine expression and NO production, which mechanistically remained unexplained. With the intention to explore molecular mechanisms underlying reduced NO formation, we showed that NO production in IFNgamma-stimulated murine RAW264.7 macrophages exposed to AC but not to either necrotic or viable human Jurkat cells was significantly reduced although iNOS expression remained high compared with controls. Analyzing iNOS activity in the cell extracts by using the radioactive L-arginine/citrulline conversion assay revealed increased ornithine production over citrulline in cells exposed to AC. RT-PCR, Western blot, and luciferase reporter analysis supported the idea of an arginase II increase in response to AC. The involvement of arginase in modulating NO formation in response to AC was substantiated by the arginase inhibitor N(omega)-hydroxy-nor-L-arginine. Moreover, knockdown of arginase II by siRNA allowed recovery of NO production. Experiments with AC-conditioned medium demonstrated that a soluble lipid factor, rather than phagocytosis of AC, modulated NO production in macrophages. We conclude that AC release a lipid factor to modulate NO formation in macrophages via arginase II up-regulation, thereby contributing to innate immune regulation.

The role of cyclic-AMP on arginase activity by a murine macrophage cell line (RAW264.7) stimulated with lipopolysaccharide from Actinobacillus actinomycetemcomitans

AIMS

The aim of the present study was to determine the role of cyclic adenosine monophosphate (cAMP) on arginase activity in a murine macrophage cell line (RAW264.7 cells) stimulated with lipopolysaccharide (LPS) from Actinobacillus actinomycetemcomitans.

MATERIALS AND METHODS

The cells were treated with A. actinomycetemcomitans LPS for 24 h. The effects of SQ22536 (an adenylyl cyclase inhibitor), ODQ (a guanylyl cyclase inhibitor), dibutyryl cAMP (a cAMP analog), 8-bromo cyclic guanosine monophosphate (a cGMP analog), forskolin (an adenylyl cylase activator), and cycloheximide (a protein synthesis inhibitor) on arginase activity in A. actinomycetemcomitans LPS-stimulated RAW264.7 cells were also determined. Arginase activity was assessed in LPS-stimulated cells in the presence of 3-isobutyl-1-methylxanthine (IBMX), siguazodan and rolipram [phosphodiesterase (PDE) inhibitors] as well as KT5720 [a protein kinase A (PKA) inhibitor].

RESULTS

Arginase activity in A. actinomycetemcomitans LPS-stimulated RAW264.7 cells was suppressed by SQ22536 but not ODQ. Enhancement of arginase activity was observed in the presence of cAMP analog or forskolin but not cGMP analog. Cycloheximide blocked arginase activity in the cells in the presence of cAMP analog or forskolin with or without A. actinomycetemcomitans LPS. IBMX augmented arginase activity in A. actinomycetemcomitans LPS-stimulated cells. Rolipram (a PDE4 inhibitor) increased the levels of arginase activity higher than siguazodan (a PDE3 inhibitor) in the antigen-stimulated cells. The effect of cAMP analog or forskolin on arginase activity in the presence or absence of A. actinomycetemcomitans LPS was blocked by the PKA inhibitor (KT5720).

CONCLUSION

The results of the present study suggest that A. actinomycetemcomitans LPS may stimulate arginase activity in murine macrophages (RAW264.7 cells) in a cAMP-PKA-dependent pathway.

Oxidative-nitrosative stress and post-translational protein modifications: implications to lung structure-function relations. Arginase modulates NF-kappaB activity via a nitric oxide-dependent mechanism

NF-kappaB is a versatile transcription factor that regulates a wide array of processes, including inflammation and survival, and plays a critical role in the etiology of inflammatory lung diseases. Nitric oxide (NO) has been suggested to play an antiinflammatory role through S-nitrosation of components of NF-kappaB pathway. NO production can be modulated by changing the availability of its substrate, L-arginine. Arginases compete with NO synthases (NOSs) for their common substrate, L-arginine, and thereby have the potential to alter the signaling function of NO. The goal of the present study was to determine the impact of arginase manipulation on NO, and subsequent effects on NF-kappaB activation, in lung epithelial cells. Our results demonstrate that reduction of arginase activity enhanced cellular content of NO and S-nitrosated proteins, and resulted in decreases in TNF-alpha- or LPS-stimulated NF-kappaB DNA binding and transcriptional activity, in association with enhanced S-nitrosation of p50. The effects of arginase inhibition on NF-kappaB were reversed by the generic NOS inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME), suggesting a causal role for NO in the attenuation of NF-kappaB induced by arginase suppression. Conversely, overexpression of arginase I decreased cellular S-nitrosothiol content and enhanced IkappaB kinase activity and NF-kappaB DNA binding, and decreased S-nitrosation of p50. Collectively, our data point to a regulatory mechanism wherein NF-kappaB is controlled through arginase-dependent regulation of NO levels, which may impact on chronic inflammatory diseases that are accompanied by NF-kappaB activation and upregulation of arginases.

Cancer immunosuppression and autoimmune disease: beyond immunosuppressive networks for tumour immunity

Cancer immunosuppression evolves by constitution of an immunosuppressive network extending from a primary tumour site to secondary lymphoid organs and peripheral vessels and is mediated by several tumour-derived soluble factors (TDSFs) such as interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta) and vascular endothelial growth factor (VEGF). TDSFs induce immature myeloid cells and regulatory T cells in accordance with tumour progression, resulting in the inhibition of dendritic cell maturation and T-cell activation in a tumour-specific immune response. Tumour cells grow by exploiting a pro-inflammatory situation in the tumour microenvironment, whereas immune cells are regulated by TDSFs during anti-inflammatory situations--mediated by impaired clearance of apoptotic cells--that cause the release of IL-10, TGF-beta, and prostaglandin E2 (PGE2) by macrophages. Accumulation of impaired apoptotic cells induces anti-DNA antibodies directed against self antigens, which resembles a pseudo-autoimmune status. Systemic lupus erythematosus is a prototype of autoimmune disease that is characterized by defective tolerance of self antigens, the presence of anti-DNA antibodies and a pro-inflammatory response. The anti-DNA antibodies can be produced by impaired clearance of apoptotic cells, which is the result of a hereditary deficiency of complements C1q, C3 and C4, which are involved in the recognition of phagocytosis by macrophages. Thus, it is likely that impaired clearance of apoptotic cells is able to provoke different types of immune dysfunction in cancer and autoimmune disease in which some are similar and others are critically different. This review discusses a comparison of immunological dysfunctions in cancer and autoimmune disease with the aim of exploring new insights beyond cancer immunosuppression in tumour immunity.

Production of nitric oxide during graft rejection is regulated by the Th1/Th2 balance, the arginase activity, and L-arginine metabolism

BACKGROUND

Production of nitric oxide (NO) by graft infiltrating macrophages has been proposed as an important effector mechanism of allograft rejection. Although high levels of NO are generated during allograft rejection, undetectable or only limited amounts of NO were found in rejected skin xenografts.

METHODS

BALB/c mice were grafted with skin transplants from syngeneic, allogeneic or xenogeneic (rat) donors. The production of NO, cytokines and arginase in the grafts was determined by spectrophotometry, enzyme-linked immunosorbent assay, or polymerase chain reaction. Effects of depletion of CD4+ cells, neutralization of interleukin (IL)-4 or application of arginase inhibitors N(omega)-hydroxy-L-arginine (L-NOHA) and L-valine on production of NO in rejected xenografts were evaluated.

RESULTS

Rejection of rat skin xenografts, on the contrary to rejection of allografts, was associated with a local high production of Th2 cytokines IL-4 and IL-10, overexpression of arginase genes, strongly enhanced arginase activity and attenuated NO generation in the graft. The supernatants obtained after cultivation of skin xenograft (but not allograft or syngeneic graft) explants contained a high arginase activity and strongly suppressed NO production by activated macrophages. This suppression was completely inhibited by L-NOHA or was overcome by an excess of exogenous L-arginine, a substrate for NO synthesis. Cocultivation of xenograft explants that did not produce NO with arginase inhibitors L-NOHA or L-valine restored NO generation in the graft.

CONCLUSION

The results suggest that upregulation of arginase activity by Th2 cytokines during xenograft rejection limits the bioavailability of L-arginine for the inducible NO synthase and thus attenuates generation of NO by the graft-infiltrating macrophages.

Arginase activity in a murine macrophage cell line (RAW264.7) stimulated with lipopolysaccharide from Actinobacillus actinomycetemcomitans

AIMS

The aim of the present study was to determine whether or not lipopolysaccharide from Actinobacillus actinomycetemcomitans could stimulate arginase activity in a murine macrophage cell line (RAW264.7 cells).

METHODS

RAW264.7 cells were treated with A. actinomycetemcomitans-lipopolysaccharide or lipopolysaccharide from Escherichia coli for 24 h. The effect of polymyxin B, l-norvaline, dl-norvaline, dexamethasone and cytokines (interferon-gamma and interleukin-4) on arginase activity in A. actinomycetemcomitans-lipopolysaccharide-stimulated cells was also determined. The cells were pretreated with anti-CD14, anti -toll-like receptor 2, or anti-toll-like receptor 4 antibody prior to stimulation with A. actinomycetemcomitans-lipopolysaccharide. Arginase activity was determined by a colorimetric assay.

RESULTS

A. actinomycetemcomitans-lipopolysaccharide stimulated arginase activity in RAW264.7 cells in a dose-dependent manner, but was less potent than E. coli-lipopolysaccharide. Polymyxin B and l-norvaline, but not dl-norvaline, blocked the arginase activity in A. actinomycetemcomitans-lipopolysaccharide-stimulated cells. Dexamethasone and interleukin-4 but not interferon-gamma augmented arginase activity in A. actinomycetemcomitans-lipopolysaccharide-stimulated cells. Treatment of the cells with anti-CD14 and anti-toll-like receptor 4 but not anti-toll-like receptor 2 antibody decreased arginase activity in A. actinomycetemcomitans-lipopolysaccharide-stimulated cells.

CONCLUSION

The results of the present study suggest that lipopolysaccharide from A. actinomycetemcomitans via CD14/toll-like receptor 4 complex molecules and the regulatory control of glucocorticoid and cytokines may stimulate arginase activity in RAW264.7 cells.