Arginine deficiency affects early B cell maturation and lymphoid organ development in transgenic mice

Shuttle between arginine and lysine: influence on cancer immunonutrition

Amino acids which are essential nutrients for all cell types' survival are also recognised to serve as opportunistic/alternative fuels in cancers auxotrophic for specific amino acids. Accordingly, restriction of amino acids has been utilised as a therapeutic strategy in these cancers. Contrastingly, amino acid deficiencies in cancer are found to greatly impair immune functions, increasing mortality and morbidity rates. Dietary and supplemental amino acids in such conditions have revealed their importance as 'immunonutrients' by modulating cellular homeostasis processes and halting malignant progression. L-arginine specifically has attracted interest as an immunonutrient by acting as a nodal regulator of immune responses linked to carcinogenesis processes through its versatile signalling molecule, nitric oxide (NO). The quantum of NO generated directly influences the cytotoxic and cytostatic processes of cell cycle arrest, apoptosis, and senescence. However, L-lysine, a CAT transporter competitor for arginine effectively limits arginine input at high L-lysine concentrations by limiting arginine-mediated effects. The phenomenon of arginine-lysine antagonism can, therefore, be hypothesised to influence the immunonutritional effects exerted by arginine. The review highlights aspects of lysine's interference with arginine-mediated NO generation and its consequences on immunonutritional and anti-cancer effects, and discusses possible alternatives to manage the condition. However, further research that considers monitoring lysine levels in arginine immunonutritional therapy is essential to conclude the hypothesis.

Wet-food diet promotes the recovery from surgery of castration and control of body weight in adult young cats

Inappropriate dietary management may lead to delayed recovery from castration surgery and significant weight gain in cats after castration. Wet canned food often exhibits more advantageous characteristics than dry food (e.g., higher palatability and digestibility, and lower energy density). This study compared the effects of canned and dry food on surgical recovery and weight management in cats after castration. Eighteen healthy cats (weighed 4.33 ± 1.04 kg and aged 18-months old) were allocated to one of the two dietary treatments (N = 9/group), dry (CON) and canned food (CAN) balanced for sex and initial BW. Cats were fed ad libitum for 7 weeks, including one week before surgery (week 0) and 6 weeks after surgery (week 1-6). Daily dry matter intake (DMI), and weekly body weight (BW) and body condition score (BCS) was obtained. Feces were collected for measuring nutrient digestibility and concentrations of short-chain fatty acids (SCFA) and branched-chain fatty acids (BCFA). Physical pain and wound surface assessment were performed at week 1. Blood was also collected intermittently for measuring biochemical indices and untargeted metabolomics analysis. Results indicated that BW, BCS and daily DMI in CON group increased (P < 0.05) over time after castration, but were maintained relatively stable in CAN group. Cats in CAN group exhibited less pain-related behavior as reflected by lower score of comfort (P < 0.05) and vocalization (P < 0.10), improved wound surface assessment (P < 0.10), lower level of lipase (P < 0.10) and ratio of blood urea nitrogen/serum creatinine (BUN/SC; P < 0.05), and higher level of superoxide dismutase (SOD; P < 0.05) in week 1 than CON cats. Meanwhile, the CAN group had significantly higher concentration of immunoglobulin G (IgG) on days 5 and 7, and higher level of high-density lipoprotein cholesterol (HDL-C; P < 0.10) but lower triglyceride (TG; P < 0.05) than CON group on day 20 and 48. Fecal total and most individual SCFA increased significantly from week 1 to week 6 regardless of diet, but the increase of butyric acid over time only occurred in CON group (P < 0.05). Also, serum metabolomic analysis revealed differential metabolic pathways between the two groups. Overall, compared with the dry food, the canned food tested in our study promoted cat wound recovery by reducing pain and increasing immune and antioxidative capacity after sterilizing surgery, and helped to maintain healthy body condition in cats after castration.

Increased arginine, lysine, and methionine levels can improve the performance, gut integrity and immune status of turkeys but the effect is interactive and depends on challenge conditions

Arginine (Arg), lysine (Lys), and methionine (Met) can be used to support the health status of turkeys. The present study investigated selected performance, gut integrity, and immunological parameters in turkeys reared in optimal or challenge conditions. The experiment lasted for 28 days, and it had a completely randomized 2 × 3 factorial design with two levels of dietary Arg, Lys and Met (high or low) and challenge with Clostridium perfringens (C. perfringens), Escherichia coli lipopolysaccharide (LPS) or no challenge (placebo). Increased dietary levels of Arg, Lys and Met had a beneficial effect on turkey performance and immunological parameters, and it improved selected indicators responsible for maintaining gut integrity in different challenge conditions. Under optimal conditions (with no challenge), high ArgLysMet diets did not compromise bird performance and they improved selected performance parameters in challenged birds. The immune system of turkeys was not excessively stimulated by high ArgLysMet diets, which did not disrupt the redox balance and had no negative effect on gut integrity. High ArgLysMet diets increased the expression levels of selected genes encoding nutrient transporters and tight junction proteins. However, the influence exerted by different dietary inclusion levels of Arg, Lys and Met on gut integrity was largely determined by the stressor (C. perfringens vs. LPS). Further studies are required to investigate the role of Arg, Lys and Met levels in the diet on the immune response, gut function and performance of turkeys in different challenge conditions.

Epithelial argininosuccinate synthetase is dispensable for intestinal regeneration and tumorigenesis

The epithelial signaling pathways involved in damage and regeneration, and neoplastic transformation are known to be similar. We noted upregulation of argininosuccinate synthetase (ASS1) in hyperproliferative intestinal epithelium. Since ASS1 leads to de novo synthesis of arginine, an important amino acid for the growth of intestinal epithelial cells, its upregulation can contribute to epithelial proliferation necessary to be sustained during oncogenic transformation and regeneration. Here we investigated the function of ASS1 in the gut epithelium during tissue regeneration and tumorigenesis, using intestinal epithelial conditional Ass1 knockout mice and organoids, and tissue specimens from colorectal cancer patients. We demonstrate that ASS1 is strongly expressed in the regenerating and Apc-mutated intestinal epithelium. Furthermore, we observe an arrest in amino acid flux of the urea cycle, which leads to an accumulation of intracellular arginine. However, loss of epithelial Ass1 does not lead to a reduction in proliferation or increase in apoptosis in vivo, also in mice fed an arginine-free diet. Epithelial loss of Ass1 seems to be compensated by altered arginine metabolism in other cell types and the liver.

The immune status, oxidative and epigenetic changes in tissues of turkeys fed diets with different ratios of arginine and lysine

In the present experiment, it was assumed that the appropriate dietary ratio of arginine (Arg) to lysine (Lys) can improve the immune status and growth performance of turkeys. The aim of this study was to evaluate the effects of two inclusion rates of Arg relative to Lys in turkey diets with Lys content consistent with National Research Council (NRC) recommendations or 10% higher on the immune status of birds and indicators of protein and DNA damage due to oxidation, nitration or epigenetic changes. Another goal was to determine which dietary Arg:Lys ratio stimulates the immune response of turkeys vaccinated against Ornithobacterium rhinotracheale. The experiment was performed on 576 turkeys randomly assigned to four groups with two levels of Lys (low = NRC recommendation or high = NRC + 10%) and two levels of Arg (95% or 105% Arg relative to the content of dietary Lys). It was found that the Lys content of turkey diets should be 10% higher than that recommended by the NRC and combined with the higher Arg level (105% of Lys). Although the above Arg:Lys ratio did not improve the growth performance of birds, it stimulated their immune system and reduced protein nitration as well as protein and DNA oxidation.

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.

Metabolic Regulation of Immune Responses to Mycobacterium tuberculosis: A Spotlight on L-Arginine and L-Tryptophan Metabolism

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a leading cause of death worldwide. Despite decades of research, there is still much to be uncovered regarding the immune response to Mtb infection. Here, we summarize the current knowledge on anti-Mtb immunity, with a spotlight on immune cell amino acid metabolism. Specifically, we discuss L-arginine and L-tryptophan, focusing on their requirements, regulatory roles, and potential use as adjunctive therapy in TB patients. By continuing to uncover the immune cell contribution during Mtb infection and how amino acid utilization regulates their functions, it is anticipated that novel host-directed therapies may be developed and/or refined, helping to eradicate TB.

A dissection of SARS‑CoV2 with clinical implications (Review)

We are being confronted with the most consequential pandemic since the Spanish flu of 1918‑1920 to the extent that never before have 4 billion people quarantined simultaneously; to address this global challenge we bring to the forefront the options for medical treatment and summarize SARS‑CoV2 structure and functions, immune responses and known treatments. Based on literature and our own experience we propose new interventions, including the use of amiodarone, simvastatin, pioglitazone and curcumin. In mild infections (sore throat, cough) we advocate prompt local treatment for the naso‑pharynx (inhalations; aerosols; nebulizers); for moderate to severe infections we propose a tried‑and‑true treatment: the combination of arginine and ascorbate, administered orally or intravenously. The material is organized in three sections: i) Clinical aspects of COVID‑19; acute respiratory distress syndrome (ARDS); known treatments; ii) Structure and functions of SARS‑CoV2 and proposed antiviral drugs; iii) The combination of arginine‑ascorbate.

Myeloid Cell-Derived Arginase in Cancer Immune Response

Amino acid metabolism is a critical regulator of the immune response, and its modulating becomes a promising approach in various forms of immunotherapy. Insufficient concentrations of essential amino acids restrict T-cells activation and proliferation. However, only arginases, that degrade L-arginine, as well as enzymes that hydrolyze L-tryptophan are substantially increased in cancer. Two arginase isoforms, ARG1 and ARG2, have been found to be present in tumors and their increased activity usually correlates with more advanced disease and worse clinical prognosis. Nearly all types of myeloid cells were reported to produce arginases and the increased numbers of various populations of myeloid-derived suppressor cells and macrophages correlate with inferior clinical outcomes of cancer patients. Here, we describe the role of arginases produced by myeloid cells in regulating various populations of immune cells, discuss molecular mechanisms of immunoregulatory processes involving L-arginine metabolism and outline therapeutic approaches to mitigate the negative effects of arginases on antitumor immune response. Development of potent arginase inhibitors, with improved pharmacokinetic properties, may lead to the elaboration of novel therapeutic strategies based on targeting immunoregulatory pathways controlled by L-arginine degradation.

Intestinal Permeability, Inflammation and the Role of Nutrients

The interaction between host and external environment mainly occurs in the gastrointestinal tract, where the mucosal barrier has a critical role in many physiologic functions ranging from digestion, absorption, and metabolism. This barrier allows the passage and absorption of nutrients, but at the same time, it must regulate the contact between luminal antigens and the immune system, confining undesirable products to the lumen. Diet is an important regulator of the mucosal barrier, and the cross-talk among dietary factors, the immune system, and microbiota is crucial for the modulation of intestinal permeability and for the maintenance of gastrointestinal tract (GI) homeostasis. In the present review, we will discuss the role of a number of dietary nutrients that have been proposed as regulators of inflammation and epithelial barrier function. We will also consider the metabolic function of the microbiota, which is capable of elaborating the diverse nutrients and synthesizing products of great interest. Better knowledge of the influence of dietary nutrients on inflammation and barrier function can be important for the future development of new therapeutic approaches for patients with mucosal barrier dysfunction, a critical factor in the pathogenesis of many GI and non-GI diseases.

Immunosuppression in Experimental Chagas Disease Is Mediated by an Alteration of Bone Marrow Stromal Cell Function During the Acute Phase of Infection

After infection with Trypanosoma cruzi, the etiologic agent of Chagas disease, immunosuppression, and apoptosis of mature lymphocytes contribute to the establishment of the parasite in the host and thereby to persistence and pathology in the chronic stage of infection. In a systemic mouse model of experimental Chagas disease, we have demonstrated a strong depletion of mature B cells in the spleen during the first 2 weeks of infection. Remarkably, the decrease in this cell population commenced already in the bone marrow from infected mice and was a concomitant of an increased apoptosis in pro- and pre-B cell populations. Pro- and pre-B cells in the bone marrow showed a significant reduction accompanied by a functional disturbance of bone marrow-derived stromal cells resulting in diminished levels of IL-7, an essential factor for the development of B cell precursors. Ex vivo, stromal cells isolated from the bone marrow of infected mice had a strikingly impaired capacity to maintain the development of pro- and pre-B cells obtained from uninfected animals. Together, the reduction of an active humoral immune response during acute Chagas disease suggests to be an initial immune evasion mechanism of the parasite to establish persistent infection. Therefore, prevention of B cell depletion by rescuing the stromal cells during this early phase, could give rise to new therapeutic approaches.

Myeloid-Derived Suppressor Cells Impair B Cell Responses in Lung Cancer through IL-7 and STAT5

Myeloid-derived suppressor cells (MDSCs) are known suppressors of antitumor immunity, affecting amino acid metabolism and T cell function in the tumor microenvironment. However, it is unknown whether MDSCs regulate B cell responses during tumor progression. Using a syngeneic mouse model of lung cancer, we show reduction in percentages and absolute numbers of B cell subsets including pro-, pre-, and mature B cells in the bone marrow (BM) of tumor-bearing mice. The kinetics of this impaired B cell response correlated with the progressive infiltration of MDSCs. We identified that IL-7 and downstream STAT5 signaling that play a critical role in B cell development and differentiation were also impaired during tumor progression. Global impairment of B cell function was indicated by reduced serum IgG levels. Importantly, we show that anti-Gr-1 Ab-mediated depletion of MDSCs not only rescued serum IgG and IL-7 levels but also reduced TGF-β1, a known regulator of stromal IL-7, suggesting MDSC-mediated regulation of B cell responses. Furthermore, blockade of IL-7 resulted in reduced phosphorylation of downstream STAT5 and B cell differentiation in tumor-bearing mice and administration of TGF-β-blocking Ab rescued these IL-7-dependent B cell responses. Adoptive transfer of BM-derived MDSCs from tumor-bearing mice into congenic recipients resulted in significant reductions of B cell subsets in the BM and in circulation. MDSCs also suppressed B cell proliferation in vitro in an arginase-dependent manner that required cell-to-cell contact. Our results indicate that tumor-infiltrating MDSCs may suppress humoral immune responses and promote tumor escape from immune surveillance.

Regulation of Intestinal Epithelial Cells Properties and Functions by Amino Acids

Intestinal epithelial cells (IECs) line the surface of intestinal epithelium, where they play important roles in the digestion of food, absorption of nutrients, and protection of the human body from microbial infections, and others. Dysfunction of IECs can cause diseases. The development, maintenance, and functions of IECs are strongly influenced by external nutrition, such as amino acids. Amino acids play important roles in regulating the properties and functions of IECs. In this article, we briefly reviewed the current understanding of the roles of amino acids in the regulation of IECs' properties and functions in physiological state, including in IECs homeostasis (differentiation, proliferation, and renewal), in intestinal epithelial barrier structure and functions, and in immune responses. We also summarized some important findings on the effects of amino acids supplementation (e.g., glutamine and arginine) in restoring IECs' and intestine functions in some diseased states. These findings will further our understanding of the important roles of amino acids in the homeostasis of IECs and could potentially help identify novel targets and reagents for the therapeutic interventions of diseases associated with dysfunctional IECs.

Cross-modulation of pathogen-specific pathways enhances malnutrition during enteric co-infection with Giardia lamblia and enteroaggregative Escherichia coli

Diverse enteropathogen exposures associate with childhood malnutrition. To elucidate mechanistic pathways whereby enteric microbes interact during malnutrition, we used protein deficiency in mice to develop a new model of co-enteropathogen enteropathy. Focusing on common enteropathogens in malnourished children, Giardia lamblia and enteroaggregative Escherichia coli (EAEC), we provide new insights into intersecting pathogen-specific mechanisms that enhance malnutrition. We show for the first time that during protein malnutrition, the intestinal microbiota permits persistent Giardia colonization and simultaneously contributes to growth impairment. Despite signals of intestinal injury, such as IL1α, Giardia-infected mice lack pro-inflammatory intestinal responses, similar to endemic pediatric Giardia infections. Rather, Giardia perturbs microbial host co-metabolites of proteolysis during growth impairment, whereas host nicotinamide utilization adaptations that correspond with growth recovery increase. EAEC promotes intestinal inflammation and markers of myeloid cell activation. During co-infection, intestinal inflammatory signaling and cellular recruitment responses to EAEC are preserved together with a Giardia-mediated diminishment in myeloid cell activation. Conversely, EAEC extinguishes markers of host energy expenditure regulatory responses to Giardia, as host metabolic adaptations appear exhausted. Integrating immunologic and metabolic profiles during co-pathogen infection and malnutrition, we develop a working mechanistic model of how cumulative diet-induced and pathogen-triggered microbial perturbations result in an increasingly wasted host.

Malnourished children are exposed to multiple sequential, and oftentimes, persistent enteropathogens. Intestinal microbial disruption and inflammation are known to contribute to the pathogenesis of malnutrition, but how co-pathogens interact with each other, with the resident microbiota, or with the host to alter these pathways is unknown. Using a new model of enteric co-infection with Giardia lamblia and enteroaggregative Escherichia coli in mice fed a protein deficient diet, we identify host growth and intestinal immune responses that are differentially mediated by pathogen-microbe interactions, including parasite-mediated changes in intestinal microbial host co-metabolism, and altered immune responses during co-infection. Our data model how early life cumulative enteropathogen exposures progressively disrupt intestinal immunity and host metabolism during crucial developmental periods. Furthermore, studies in this co-infection model reveal new insights into environmental and microbial determinants of pathogenicity for presently common, but poorly understood enteropathogens like Giardia lamblia, that may not conform to existing paradigms of microbial pathogenesis based on single pathogen-designed models.

Inhibition of B Lymphopoiesis by Adipocytes and IL-1-Producing Myeloid-Derived Suppressor Cells

B lymphopoiesis declines with age, and this decline correlates with increased adipose tissue in the bone marrow (BM). Also, adipocyte-derived factors are known to inhibit B lymphopoiesis. Using cocultures of mouse BM cells with OP9 stromal cells, we found that adipocyte-conditioned medium induces the generation of CD11b(+)Gr1(+) myeloid cells, which inhibit B cell development in vitro. Adipocyte-conditioned medium-induced CD11b(+)Gr1(+) cells express Arg1 (arginase) and Nos2 (inducible NO synthase) and suppress CD4(+) T cell proliferation, indicating that these cells are myeloid-derived suppressor cells (MDSCs). Blocking arginase and inducible NO synthase did not restore B lymphopoiesis, indicating that inhibition is not mediated by these molecules. Transwell and conditioned-medium experiments showed that MDSCs inhibit B lymphopoiesis via soluble factors, and by cytokine array we identified IL-1 as an important factor. Addition of anti-IL-1 Abs restored B lymphopoiesis in BM cultures containing MDSCs, showing that MDSC inhibition of B lymphopoiesis is mediated by IL-1. By treating hematopoietic precursors with IL-1, we found that multipotent progenitors are targets of IL-1. This study uncovers a novel function for MDSCs to inhibit B lymphopoiesis through IL-1. We suggest that inflammaging contributes to a decline of B lymphopoiesis in aged individuals, and furthermore, that MDSCs and IL-1 provide therapeutic targets for restoration of B lymphopoiesis in aged and obese individuals.

Dietary essentiality of "nutritionally non-essential amino acids" for animals and humans

Based on growth or nitrogen balance, amino acids (AA) had traditionally been classified as nutritionally essential (indispensable) or non-essential (dispensable) for animals and humans. Nutritionally essential AA (EAA) are defined as either those AA whose carbon skeletons cannot be synthesized de novo in animal cells or those that normally are insufficiently synthesized de novo by the animal organism relative to its needs for maintenance, growth, development, and health and which must be provided in the diet to meet requirements. In contrast, nutritionally non-essential AA (NEAA) are those AA which can be synthesized de novo in adequate amounts by the animal organism to meet requirements for maintenance, growth, development, and health and, therefore, need not be provided in the diet. Although EAA and NEAA had been described for over a century, there are no compelling data to substantiate the assumption that NEAA are synthesized sufficiently in animals and humans to meet the needs for maximal growth and optimal health. NEAA play important roles in regulating gene expression, cell signaling pathways, digestion and absorption of dietary nutrients, DNA and protein synthesis, proteolysis, metabolism of glucose and lipids, endocrine status, men and women fertility, acid-base balance, antioxidative responses, detoxification of xenobiotics and endogenous metabolites, neurotransmission, and immunity. Emerging evidence indicates dietary essentiality of "nutritionally non-essential amino acids" for animals and humans to achieve their full genetic potential for growth, development, reproduction, lactation, and resistance to metabolic and infectious diseases. This concept represents a new paradigm shift in protein nutrition to guide the feeding of mammals (including livestock), poultry, and fish.

Hepatic adaptation compensates inactivation of intestinal arginine biosynthesis in suckling mice

Suckling mammals, including mice, differ from adults in the abundant expression of enzymes that synthesize arginine from citrulline in their enterocytes. To investigate the importance of the small-intestinal arginine synthesis for whole-body arginine production in suckling mice, we floxed exon 13 of the argininosuccinate synthetase (Ass) gene, which codes for a key enzyme in arginine biosynthesis, and specifically and completely ablated Ass in enterocytes by crossing Ass (fl) and Villin-Cre mice. Unexpectedly, Ass (fl/fl) /VilCre (tg/-) mice showed no developmental impairments. Amino-acid fluxes across the intestine, liver, and kidneys were calculated after determining the blood flow in the portal vein, and hepatic and renal arteries (86%, 14%, and 33%, respectively, of the transhepatic blood flow in 14-day-old mice). Relative to control mice, citrulline production in the splanchnic region of Ass (fl/fl) /VilCre (tg/-) mice doubled, while arginine production was abolished. Furthermore, the net production of arginine and most other amino acids in the liver of suckling control mice declined to naught or even changed to consumption in Ass (fl/fl) /VilCre (tg/-) mice, and had, thus, become remarkably similar to that of post-weaning wild-type mice, which no longer express arginine-biosynthesizing enzymes in their small intestine. The adaptive changes in liver function were accompanied by an increased expression of genes involved in arginine metabolism (Asl, Got1, Gpt2, Glud1, Arg1, and Arg2) and transport (Slc25a13, Slc25a15, and Slc3a2), whereas no such changes were found in the intestine. Our findings suggest that the genetic premature deletion of arginine synthesis in enterocytes causes a premature induction of the post-weaning pattern of amino-acid metabolism in the liver.

Effect of dietary arginine supplementation on reproductive performance of mice with porcine circovirus type 2 infection

The objective of this study was to investigate whether supplemental dietary arginine increases reproductive performance in mice infected with porcine circovirus type2 (PCV2). A total of 50KM female mice were allotted randomly to the arginine group (0.6% arginine+gestation diet) and control group (1.22% alanine+gestation diet). All the mice began to mate after 14 days of treatment with our prepared feed and challenged with PCV2 at the dose of 100 TCID50 (50% tissue culture infection dose, TCID50) after 7 days of pregnancy. Abortion rate, litter number, litter birth weight, the daily weight gain in the first 7 days and survival rate in the first 2 weeks of the neonates were calculated. The serum progesterone, estrogen, nitric oxide and superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC) on the 14th day of pregnancy were measured. Arginine supplementation decreased the abortion rate of pregnant mice and mortality of neonates caused by PCV2 infection. Further, litter number, litter birth weight and the daily weight gain of neonates increased in the arginine group compared to the control group. Arginine supplementation increased significantly the serum progesterone (P<0.01) and nitric oxide levels (P<0.05), but had little effect on the serum estrogen level. SOD activity and T-AOC in the arginine group were significantly higher (P<0.01) than the control group. In conclusion, arginine supplementation partially reversed the reproductive failure in mice caused by PCV2 infection.

Arginine decreases Cryptosporidium parvum infection in undernourished suckling mice involving nitric oxide synthase and arginase

OBJECTIVE

This study investigated the role of L-arginine supplementation to undernourished and Cryptosporidium parvum-infected suckling mice.

METHODS

The following regimens were initiated on the fourth day of life and injected subcutaneously daily. The C. parvum-infected controls received L-arginine (200 mmol/L) or phosphate buffered saline. The L-arginine-treated mice were grouped to receive NG-nitro-arginine methyl ester (L-NAME) (20 mmol/L) or phosphate buffered saline. The infected mice received orally 10(6) excysted C. parvum oocysts on day 6 and were euthanized on day 14 at the infection peak.

RESULTS

L-arginine improved weight gain compared with the untreated infected controls. L-NAME profoundly impaired body weight gain compared with all other groups. Cryptosporidiosis was associated with ileal crypt hyperplasia, villus blunting, and inflammation. L-arginine improved mucosal histology after the infection. L-NAME abrogated these arginine-induced improvements. The infected control mice showed an intense arginase expression, which was even greater with L-NAME. L-arginine decreased the parasite burden, an effect that was reversed by L-NAME. Cryptosporidium parvum infection increased urine NO(3)(-)/NO(2)(-) concentrations compared with the uninfected controls, which was increased by L-arginine supplementation, an effect that was also reversed by L-NAME.

CONCLUSION

These findings show a protective role of L-arginine during C. parvum infection in undernourished mice, with involvement of arginase I and nitric oxide synthase enzymatic actions.

Arginine deficiency causes runting in the suckling period by selectively activating the stress kinase GCN2

Suckling "F/A2" mice, which overexpress arginase-I in their enterocytes, develop a syndrome (hypoargininemia, reduced hair and muscle growth, impaired B-cell maturation) that resembles IGF1 deficiency. The syndrome may result from an impaired function of the GH-IGF1 axis, activation of the stress-kinase GCN2, and/or blocking of the mTORC1-signaling pathway. Arginine deficiency inhibited GH secretion and decreased liver Igf1 mRNA and plasma IGF1 concentration, but did not change muscle IGF1 concentration. GH supplementation induced Igf1 mRNA synthesis, but did not restore growth, ruling out direct involvement of the GH-IGF1 axis. In C2C12 muscle cells, arginine withdrawal activated GCN2 signaling, without impacting mTORC1 signaling. In F/A2 mice, the reduction of plasma and tissue arginine concentrations to ∼25% of wild-type values activated GCN2 signaling, but mTORC1-mediated signaling remained unaffected. Gcn2-deficient F/A2 mice suffered from hypoglycemia and died shortly after birth. Because common targets of all stress kinases (eIF2α phosphorylation, Chop mRNA expression) were not increased in these mice, the effects of arginine deficiency were solely mediated by GCN2.

Bone marrow cell derived arginase I is the major source of allergen-induced lung arginase but is not required for airway hyperresponsiveness, remodeling and lung inflammatory responses in mice

Background

Arginase is significantly upregulated in the lungs in murine models of asthma, as well as in human asthma, but its role in allergic airway inflammation has not been fully elucidated in mice.

Results

In order to test the hypothesis that arginase has a role in allergic airway inflammation we generated arginase I-deficient bone marrow (BM) chimeric mice. Following transfer of arginase I-deficient BM into irradiated recipient mice, arginase I expression was not required for hematopoietic reconstitution and baseline immunity. Arginase I deficiency in bone marrow-derived cells decreased allergen-induced lung arginase by 85.8 ± 5.6%. In contrast, arginase II-deficient mice had increased lung arginase activity following allergen challenge to a similar level to wild type mice. BM-derived arginase I was not required for allergen-elicited sensitization, recruitment of inflammatory cells in the lung, and proliferation of cells. Furthermore, allergen-induced airway hyperresponsiveness and collagen deposition were similar in arginase-deficient and wild type mice. Additionally, arginase II-deficient mice respond similarly to their control wild type mice with allergen-induced inflammation, airway hyperresponsiveness, proliferation and collagen deposition.

Conclusion

Bone marrow cell derived arginase I is the predominant source of allergen-induced lung arginase but is not required for allergen-induced inflammation, airway hyperresponsiveness or collagen deposition.

Arginine metabolism and nutrition in growth, health and disease

L-Arginine (Arg) is synthesised from glutamine, glutamate, and proline via the intestinal-renal axis in humans and most other mammals (including pigs, sheep and rats). Arg degradation occurs via multiple pathways that are initiated by arginase, nitric-oxide synthase, Arg:glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine, and agmatine with each having enormous biological importance. Arg is also required for the detoxification of ammonia, which is an extremely toxic substance for the central nervous system. There is compelling evidence that Arg regulates interorgan metabolism of energy substrates and the function of multiple organs. The results of both experimental and clinical studies indicate that Arg is a nutritionally essential amino acid (AA) for spermatogenesis, embryonic survival, fetal and neonatal growth, as well as maintenance of vascular tone and hemodynamics. Moreover, a growing body of evidence clearly indicates that dietary supplementation or intravenous administration of Arg is beneficial in improving reproductive, cardiovascular, pulmonary, renal, gastrointestinal, liver and immune functions, as well as facilitating wound healing, enhancing insulin sensitivity, and maintaining tissue integrity. Additionally, Arg or L-citrulline may provide novel and effective therapies for obesity, diabetes, and the metabolic syndrome. The effect of Arg in treating many developmental and health problems is unique among AAs, and offers great promise for improved health and wellbeing of humans and animals.

Tumor growth decreases NK and B cells as well as common lymphoid progenitor

BACKGROUND

It is well established that chronic tumor growth results in functional inactivation of T cells and NK cells. It is less clear, however, whether lymphopoeisis is affected by tumor growth.

PRINCIPAL FINDINGS

In our efforts of analyzing the impact of tumor growth on NK cell development, we observed a major reduction of NK cell numbers in mice bearing multiple lineages of tumor cells. The decrease in NK cell numbers was not due to increased apoptosis or decreased proliferation in the NK compartment. In addition, transgenic expression of IL-15 also failed to rescue the defective production of NK cells. Our systematic characterization of lymphopoeisis in tumor-bearing mice indicated that the number of the common lymphoid progenitor was significantly reduced in tumor-bearing mice. The number of B cells also decreased substantially in tumor bearing mice.

CONCLUSIONS AND SIGNIFICANCE

Our data reveal a novel mechanism for tumor evasion of host immunity and suggest a new interpretation for the altered myeloid and lymphoid ratio in tumor bearing hosts.

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.

Adaptation to a long term (4 weeks) arginine- and precursor (glutamate, proline and aspartate)-free diet

BACKGROUND & AIMS

It is not known whether arginine homeostasis is negatively affected by a "long term" dietary restriction of arginine and its major precursors in healthy adults. To assess the effects of a 4-week arginine- and precursor-free dietary intake on the regulatory mechanisms of arginine homeostasis in healthy subjects.

METHODS

Ten healthy adults received a complete amino acid diet for 1 week (control diet) and following a break period, six subjects received a 4-week arginine, proline, glutamate and aspartate-free diet (APF diet). The other four subjects continued for 4 weeks with the complete diet. On days 4 and 7 of the first week and days 25 and 28 of the 4-week period, the subjects received 24-h infusions of arginine, citrulline, leucine and urea tracers.

RESULTS

During the 4-week APF, plasma arginine fluxes for the fed state, were significantly reduced. There were no significant differences for citrulline, leucine or urea fluxes. Arginine de novo synthesis was not affected by the APF intake. However, arginine oxidation was significantly decreased.

CONCLUSIONS

In healthy adults, homeostasis of arginine under a long term arginine- and precursor-free intake is achieved by decreasing catabolic rates, while de novo arginine synthesis is maintained.

Lack of effect of acute enteral arginine infusion on whole-body and intestinal protein metabolism in humans

Arginine is a conditionally essential amino acid and exerts anabolic effects. We studied the effects of enteral arginine on whole-body and duodenal protein metabolism. Eight healthy fasted volunteers received randomly a 5-hr enteral infusion of either arginine (Arg; 20 g) or an isonitrogenous amino acid mixture (AA) and an IV infusion of [13C]leucine. Duodenal biopsies were performed. Whole-body protein turnover and duodenal protein synthesis (FSR) were calculated from GC/MS-assessed enrichment. The mRNA levels for major components of proteolytic pathways, ubiquitin, cathepsin D, and m-calpain, were evaluated by RT-PCR. Results were compared using paired Wilcoxon test. Endogenous, oxidative, and nonoxidative leucine fluxes were not different after Arg and AA infusions, respectively. Duodenal mucosal protein FSR (71% +/- 26% vs 81% +/- 30%/day) and mRNA levels of ubiquitin, cathepsin D, and m-calpain were also similar after Arg and AA infusions. We conclude that in healthy subjects, arginine infusion exerts no effect on whole-body and duodenal protein metabolism. Whether arginine might specifically affect these parameters in catabolic or inflammatory situations remains to be determined.

L-Arginine stimulates intestinal intraepithelial lymphocyte functions and immune response in chickens orally immunized with live intermediate plus strain of infectious bursal disease vaccine

Infectious bursal disease (IBD) continues to pose potential threat to poultry industry all over the world. The disease can spell disaster not only through its infection but also by break of immunity in chickens vaccinated for other diseases. l-Arginine, a ubiquitous, semi-essential amino acid has emerged as an imunostimulant from variety of human and animal studies. In the present study, we demonstrate the stimulatory effects of l-arginine on intestinal intraepithelial lymphocyte (iIELs) functions as well as on systemic immune response in chickens orally vaccinated with live intermediate plus (IP) strain of IBD vaccine. Challenge studies with virulent IBDV revealed complete (100%) protection in IP + l-arginine group compared with 80% protection recorded in IP strain vaccinated chickens. Functional activities of iIELs evaluated by cytotoxicity assay demonstrated significantly high percentage cytotoxicity in IP + l-arginine groups compared with IP group (P < 0.05). Proliferative response of iIELs against IBDV antigen and Con-A was also significantly higher in IP + l-arginine group. Similar results were obtained with peripheral blood mononuclear cell blastogenic response to IBDV and Con-A analyzed as an indicator of systemic cell-mediated immune response. Orally administered IP strain vaccine elicited good antibody titres in both the groups, IP and IP + l-arginine, however, the antibody titres were significantly higher in IP + l-arginine group compared with IP vaccinated group (P < 0.05). These results clearly demonstrate that l-arginine stimulates intestinal and systemic immune response against IBDV.