In silico analysis of arginine catabolism as a source of nitric oxide or polyamines in endothelial cells

A perfectly imperfect engine: Utilizing the digital twin paradigm in pulmonary hypertension

Pulmonary hypertension (PH) is a severe medical condition with a number of treatment options, the majority of which are introduced without consideration of the underlying mechanisms driving it within an individual and thus a lack of tailored approach to treatment. The one exception is a patient presenting with apparent pulmonary arterial hypertension and shown to have vaso-responsive disease, whose clinical course and prognosis is significantly improved by high dose calcium channel blockers. PH is however characterized by a relative abundance of available data from patient cohorts, ranging from molecular data characterizing gene and protein expression in different tissues to physiological data at the organ level and clinical information. Integrating available data with mechanistic information at the different scales into computational models suggests an approach to a more personalized treatment of the disease using model-based optimization of interventions for individual patients. That is, constructing digital twins of the disease, customized to a patient, promises to be a key technology for personalized medicine, with the aim of optimizing use of existing treatments and developing novel interventions, such as new drugs. This article presents a perspective on this approach in the context of a review of existing computational models for different aspects of the disease, and it lays out a roadmap for a path to realizing it.

Beyond protein synthesis: the emerging role of arginine in poultry nutrition and host-microbe interactions

Arginine is a functional amino acid essential for various physiological processes in poultry. The dietary essentiality of arginine in poultry stems from the absence of the enzyme carbamoyl phosphate synthase-I. The specific requirement for arginine in poultry varies based on several factors, such as age, dietary factors, and physiological status. Additionally, arginine absorption and utilization are also influenced by the presence of antagonists. However, dietary interventions can mitigate the effect of these factors affecting arginine utilization. In poultry, arginine is utilized by four enzymes, namely, inducible nitric oxide synthase arginase, arginine decarboxylase and arginine: glycine amidinotransferase (AGAT). The intermediates and products of arginine metabolism by these enzymes mediate the different physiological functions of arginine in poultry. The most studied function of arginine in humans, as well as poultry, is its role in immune response. Arginine exerts immunomodulatory functions primarily through the metabolites nitric oxide (NO), ornithine, citrulline, and polyamines, which take part in inflammation or the resolution of inflammation. These properties of arginine and arginine metabolites potentiate its use as a nutraceutical to prevent the incidence of enteric diseases in poultry. Furthermore, arginine is utilized by the poultry gut microbiota, the metabolites of which might have important implications for gut microbial composition, immune regulation, metabolism, and overall host health. This comprehensive review provides insights into the multifaceted roles of arginine and arginine metabolites in poultry nutrition and wellbeing, with particular emphasis on the potential of arginine in immune regulation and microbial homeostasis in poultry.

Peculiarities in the Amino Acid Composition of Sow Colostrum and Milk, and Their Potential Relevance to Piglet Development

The composition of mother's milk is considered the ideal diet for neonates. This study investigated how conserved or variable the amino acid profile of sow colostrum and milk is throughout lactation, compared with other studies in sows and other species. Twenty-five sows (parity one to seven) from one farm with gestation lengths of 114 to 116 d were sampled on d 0, 3, and 10 after parturition. The total amino acid profile of the samples was analyzed through ion-exchange chromatography, and the results were displayed as the percentage of total amino acid and compared with literature data. Most of the amino acid concentrations in sow milk decreased significantly (p < 0.05) throughout the lactation period, while the amino acid profile generally showed a conserved pattern, especially from d 3 to d 10, and was rather similar across different studies. Glutamine + glutamate was the most abundant amino acid in milk at all sampling moments, accounting for 14-17% of total amino acids. The proportions of proline, valine, and glycine in sow milk nearly accounted for 11%, 7%, and 6% respectively, and were higher compared to human, cow, and goat milk, while the methionine proportion was less than the other three. Compared to the large variations often reported in macronutrient concentrations, the amino acid profile of sow milk in the present study, as well as in others, seems well conserved across the lactation period. Similarities with characteristic differences were also observed between sow milk and piglet body composition, which might reflect the nutrition requirements of preweaning piglets. This study warrants further research exploring the link between the whole amino acid profile and the particular amino acids for suckling piglets and could facilitate insight for optimizing creep feed.

Flavonoid extract of saffron by-product alleviates hyperuricemia via inhibiting xanthine oxidase and modulating gut microbiota

Hyperuricemia was associated with the overproduction or inadequate excretion of uric acid, while its association with gut microbiota has emerged although few studies were focused on it. Previously, we have reported a flavonoid extract from saffron floral bio-residues lowered uric acid in potassium oxonate-induced hyperuricemic mice. In this study, the impacts of the flavonoid extract on potassium oxonate-induced hyperuricemic rats were evaluated through its effects on serum, renal, intestinal uric acid, and xanthine oxidase activity. At the same time, the microbial and metabolic features of the flavonoid extract against hyperuricemia were explored using 16S rRNA sequencing techniques and serum metabolomics, respectively. According to the results, the flavonoid extract lowered serum and intestinal uric acid levels in hyperuricemic rats without kidney damage. On the one hand, it inhibited serum and liver xanthine oxidase activities and down-regulated the expression of hepatic xanthine oxidase. On the other hand, it ameliorated the hyperuricemia-associated gut microbiota dysbiosis and alleviated the disturbance of serum metabolome, especially of lipid and amino acid metabolites. The results suggested that the flavonoid extract of saffron floral bio-residues exerts a potent antihyperuricemia effect by inhibiting xanthine oxidase to decrease uric acid production and modulating gut microbiota related to host metabolism.

Neural tone and cardio-renal outcomes in patients with type 2 diabetes mellitus: a review of the literature with a focus on SGLT2 inhibitors

Recent clinical trials involving the systemic effects of sodium-glucose cotransporter 2 inhibitors (SGLT2i) have revealed beneficial outcomes pertaining to the microvascular sequelae of type 2 diabetes mellitus (T2DM) such as nephropathy, as well as macrovascular effects such as major adverse cardiovascular effects (MACE). Such findings have spurred the elevation of these agents to level A-tiers of recommendation within clinical guidelines addressing the management of complicated T2DM. While the mechanisms of SGLTi (-flozin drugs) are still being elucidated, a paucity of data exists within the literature appraising the role of neuromodulation and associated mechanisms in the aforementioned outcome studies. Given the role of the nervous system in orchestrating the pathologic processes that hamper cardio-renal status, insight into this topic offers an expanded perspective on T2DM. In this review we investigate the mechanisms by which SGLTi improve cardio-renal function in T2DM patients with emphases on neural tone and nervous system physiology.

Effects of Dietary L-arginine Supplementation from Conception to Post- Weaning in Piglets

Weaned piglets experience sudden changes in their dietary patterns such as withdrawal from the easily digestible watery milk to a coarse cereal diet with both systemic and intestinal disruptions coupling with the expression of pro-inflammatory proteins which affects the immune system and the concentrations of haptoglobin including both positive and negative acute-phase proteins in the plasma. L-arginine is an important protein amino acid for piglets, but its inadequate synthesis is a nutritional problem for both sows and piglets. Recent studies indicated that dietary supplementation of L-arginine increased feed intake, uterine growth, placental growth and nutrient transport, maternal growth and health, embryonic survival, piglets birth weight, piglet's growth, and productivity, and decreased stillbirths. L-arginine is essential in several important pathways involved in the growth and development of piglets such as nitric oxide synthesis, energy metabolism, polyamine synthesis, cellular protein production and muscle accretion, and the synthesis of other functional amino acids. However, the underlying molecular mechanism in these key pathways remains largely unresolved. This review was conducted on the general hypothesis that L-arginine increased the growth and survival of post-weaning piglets. We discussed the effects of dietary L-arginine supplementation during gestation, parturition, lactation, weaning, and post-weaning in pigs as each of these stages influences the health and survival of sows and their progenies. Therefore, the aim of this review was to discuss through a logical approach the effects of L-arginine supplementation on piglet's growth and survival from conception to postweaning.

Arginine metabolism and its protective effects on intestinal health and functions in weaned piglets under oxidative stress induced by diquat

The intestine plays key roles in maintaining body arginine (Arg) homoeostasis. Meanwhile, the intestine is very susceptible to reactive oxygen species. In light of this, the study aimed to explore the effects of Arg supplementation on intestinal morphology, Arg transporters and metabolism, and the potential protective mechanism of Arg supplementation in piglets under oxidative stress. A total of thirty-six weaned piglets were randomly allocated to six groups with six replicates and fed a base diet (0·95 % Arg,) or base diet supplemented with 0·8 % and 1·6 % l-Arg for 1 week, respectively. Subsequently, a challenge test was conducted by intraperitoneal injection of diquat, an initiator of radical production, or sterile saline. The whole trial lasted 11 d. The diquat challenge significantly decreased plasma Arg concentration at 6 h after injection (P<0·05), lowered villus height in the jejunum and ileum (P<0·05) as well as villus width and crypt depth in the duodenum, jejunum and ileum (P<0·05). Oxidative stress significantly increased cationic amino acid transporter (CAT)-1, CAT-2 and CAT-3, mRNA levels (P<0·05), decreased arginase II (ARGII) and inducible nitric oxide synthase mRNA levels, and increased TNF- α mRNA level in the jejunum (P<0·05). Supplementation with Arg significantly decreased crypt depth (P<0·05), suppressed CAT-1 mRNA expression induced by diquat (P<0·05), increased ARGII and endothelial nitric oxide synthase mRNA levels (P<0·05), and effectively relieved the TNF- α mRNA expression induced by diquat in the jejunum (P<0·05). It is concluded that oxidative stress decreased Arg bioavailability and increased expression of inflammatory cytokines in the jejunum, and that Arg supplementation has beneficial effects in the jejunum through regulation of the metabolism of Arg and suppression of inflammatory cytokine expression in piglets.

Arginine supplementation modulates pig plasma lipids, but not hepatic fatty acids, depending on dietary protein level with or without leucine

Background

In the present study, the effect of arginine and leucine supplementation, and dietary protein level, were investigated in commercial crossbred pigs to clarify their individual or combined impact on plasma metabolites, hepatic fatty acid composition and mRNA levels of lipid sensitive factors. The experiment was conducted on fifty-four entire male pigs (Duroc × Pietrain × Large White × Landrace crossbred) from 59 to 92 kg of live weight. Each pig was randomly assigned to one of six experimental treatments (n = 9). The treatments followed a 2 × 3 factorial arrangement, providing two levels of arginine supplementation (0 vs. 1%) and three levels of basal diet (normal protein diet, NPD; reduced protein diet, RPD; reduced protein diet with 2% of leucine, RPDL).

Results

Significant interactions between arginine supplementation and protein level were observed across plasma lipids. While dietary arginine increased total lipids, total cholesterol, HDL-cholesterol, LDL-cholesterol, VLDL-cholesterol and triacylglycerols in NPD, the inverse effect was observed in RPD. Overall, dietary treatments had a minor impact on hepatic fatty acid composition. RPD increased 18:1c9 fatty acid while the combination of leucine and RPD reduced 18:0 fatty acid. Arginine supplementation increased the gene expression of FABP1, which contributes for triacylglycerols synthesis without affecting hepatic fatty acids content. RPD, with or without leucine addition, upregulated the lipogenic gene CEBPA but downregulated the fat oxidation gene LPIN1.

Conclusions

Arginine supplementation was responsible for a modulated effect on plasma lipids, which is dependent on dietary protein level. It consistently increased lipaemia in NPD, while reducing the correspondent metabolites in RPD. In contrast, arginine had no major impact, neither on hepatic fatty acids content nor on fatty acid composition. Likewise, leucine supplementation of RPD, regardless the presence of arginine, promoted no changes on total fatty acids in the liver. Ultimately, arginine, leucine and dietary protein reduction seem to be unrelated with fatty liver development.

Insight on the impacts of free amino acids and their metabolites on the immune system from a perspective of inborn errors of amino acid metabolism

INTRODUCTION

Amino acids (AAs) support a broad range of functions in living organisms, including several that affect the immune system. The functions of the immune system are affected when free AAs are depleted or in excess because of external factors, such as starvation, or because of genetic factors, such as inborn errors of metabolism. Areas covered: In this review, we discuss the current insights into how free AAs affect immune responses. When possible, we make comparisons to known disease states resulting from inborn errors of metabolism, in which changed levels of AAs or AA metabolites provide insight into the impact of AAs on the human immune system in vivo. We also explore the literature describing how changes in AA levels might provide pharmaceutical targets for safe immunomodulatory treatment. Expert opinion: The impact of free AAs on the immune system is a neglected topic in most immunology textbooks. That neglect is undeserved, because free AAs have both direct and indirect effects on the immune system. Consistent choices of pre-clinical models and better strategies for creating formulations are required to gain clinical impact.

Arginase-endothelial nitric oxide synthase imbalance contributes to endothelial dysfunction during chronic intermittent hypoxia

OBJECTIVE

Chronic intermittent hypoxia (CIH), the main feature of obstructive sleep apnoea, is associated with impaired vascular function despite unaltered response to nitric oxide donors. This study addressed whether arginase contributes to the endothelial dysfunction in CIH rats.

METHODS

Adult male Sprague-Dawley rats were exposed for 21 days to CIH (5% oxygen, 12 times/h, 8 h/day). The internal carotid arteries were isolated to study endothelial nitric oxide synthase (eNOS) and arginase-1 levels by western blot and immunohistochemistry, and their vasoactive responses using wire myography. Relaxation to sodium nitroprusside (SNP; nitric oxide donor) in the presence or absence of soluble guanylyl cyclase inhibitor, and acetylcholine with and without a NOS inhibitor [N(G)-nitro-L-arginine (L-NA)] and the arginase inhibitor BEC were determined.

RESULTS

Arteries from the CIH rats presented higher active contraction induced by KCl (3.5 ± 0.4 vs. 2.3 ± 0.2 N/m2), augmented media-to-lumen ratio (∼40%), decreased relaxation to acetylcholine (12.8 ± 1.5 vs. 30.5 ± 4.6%) and increased sensitivity to SNP (pD2 7.3 ± 0.1 vs. 6.7 ± 0.1). Arginase inhibition reversed the impaired acetylcholine-induced relaxation in CIH arteries (49.5 ± 7.4%), an effect completely blocked by L-NA. In the carotid arteries, arginase-1 protein level was increased, whereas eNOS levels decreased in the CIH arteries.

CONCLUSION

The current results suggest that endothelial dysfunction in CIH-induced hypertension may result from imbalanced arginase-1 to eNOS expression, vascular remodelling and increased contractile capacity, rather than decreased vascular response to nitric oxide.

Role of DNA methyltransferase 1 on the altered eNOS expression in human umbilical endothelium from intrauterine growth restricted fetuses

Reduced fetal growth associates with endothelial dysfunction and cardiovascular risk in both young and adult offspring and the nitric oxide (NO) system has been implicated in these effects. Epigenetic processes are likely to underlie such effects, but there is to date no evidence that endothelial dysfunction in early life results from epigenetic processes on key genes in the NO system, such as NOS3 (eNOS) and ARG2 (arginase-2). We determined basal DNA methylation status in NOS3 and ARG2 promoters, and DNA methyltransferase 1 (DNMT1) effect on eNOS and arginase-2 expression using human endothelial cells isolated from umbilical arteries (HUAEC) and veins (HUVEC) from control and intrauterine growth restricted (IUGR) fetuses. Compared with cells from control pregnancies, eNOS protein and mRNA levels were increased in HUAEC, but decreased in HUVEC, from IUGR, while arginase-2 levels were increased in IUGR-HUVEC. The NOS3 promoter showed a decrease in DNA methylation at CpG -352 in IUGR-HUAEC, and an increase in IUGR-HUVEC, when compared with control cells. Methylation in the hypoxia response element of the NOS3 promoter was increased in IUGR-HUAEC and decreased in HUVEC. Methylation in the AGR2 promoter in IUGR-HUVEC was decreased in a putative HRE, and without changes in IUGR-HUAEC. Silencing of DNMT1 expression normalized eNOS expression in IUGR endothelial cells, and restored the normal response to hypoxia in HUVEC, without effects on arginase-2. This data suggest that eNOS expression in IUGR-derived endothelial cells is programmed by altered DNA methylation, and can be reversed by transient silencing of the DNA methylation machinery.

An evolutionary firefly algorithm for the estimation of nonlinear biological model parameters

The development of accurate computational models of biological processes is fundamental to computational systems biology. These models are usually represented by mathematical expressions that rely heavily on the system parameters. The measurement of these parameters is often difficult. Therefore, they are commonly estimated by fitting the predicted model to the experimental data using optimization methods. The complexity and nonlinearity of the biological processes pose a significant challenge, however, to the development of accurate and fast optimization methods. We introduce a new hybrid optimization method incorporating the Firefly Algorithm and the evolutionary operation of the Differential Evolution method. The proposed method improves solutions by neighbourhood search using evolutionary procedures. Testing our method on models for the arginine catabolism and the negative feedback loop of the p53 signalling pathway, we found that it estimated the parameters with high accuracy and within a reasonable computation time compared to well-known approaches, including Particle Swarm Optimization, Nelder-Mead, and Firefly Algorithm. We have also verified the reliability of the parameters estimated by the method using an a posteriori practical identifiability test.

Modeling cellular compartmentation in one-carbon metabolism

Folate-mediated one-carbon metabolism (FOCM) is associated with risk for numerous pathological states including birth defects, cancers, and chronic diseases. Although the enzymes that constitute the biological pathways have been well described and their interdependency through the shared use of folate cofactors appreciated, the biological mechanisms underlying disease etiologies remain elusive. The FOCM network is highly sensitive to nutritional status of several B-vitamins and numerous penetrant gene variants that alter network outputs, but current computational approaches do not fully capture the dynamics and stochastic noise of the system. Combining the stochastic approach with a rule-based representation will help model the intrinsic noise displayed by FOCM, address the limited flexibility of standard simulation methods for coarse-graining the FOCM-associated biochemical processes, and manage the combinatorial complexity emerging from reactions within FOCM that would otherwise be intractable.

Protective effects of dietary arginine supplementation against oxidative stress in weaned piglets

Oxidative stress is detrimental to animals. Previous studies have indicated that arginine (Arg) may function as a potential substance against oxidative stress. The present study was conducted to explore the potential mechanisms behind the Arg-induced protective effects against oxidative stress in piglets. A total of thirty-six piglets were randomly allocated to six groups with six replicates per group. Piglets were subjected to three dietary treatments (namely two groups per treatment) in week 1 and fed with a basal diet (ArgL) or the basal diet supplemented with 0.8% (ArgM) or 1.6% (ArgH) L-Arg, respectively. On day 8, piglets were injected intraperitoneally either with diquat (10 mg/kg body weight) or sterile saline. The whole trial lasted 11 d. Results showed that dietary Arg supplementation did not affect growth performance in week 1. Oxidative stress significantly decreased the growth performance of piglets (P < 0.05). However, ArgH attenuated the negative effects of oxidative stress on feed intake and significantly increased the total antioxidant capacity in the liver under oxidative stress (P < 0.05). Both ArgM and ArgH enhanced the activities of plasma glutathione peroxidases and superoxide dismutases and decreased the IL-6 and TNF-a mRNA level in the liver under oxidative stress (P < 0.05). The present study not only shows that Arg can function as a potential nutrient to alleviate oxidative stress responses through the enhancement of antioxidant capacity, and inhibition of the expression of inflammatory cytokines, but the results also suggest that alleviation of oxidative stress responses using dietary nutrient components deserves further attention in the future.

Endothelial eNOS/arginase imbalance contributes to vascular dysfunction in IUGR umbilical and placental vessels

Placental vascular tone is critically influenced by nitric oxide (NO) derived from endothelial NO synthase (eNOS) activity. Placental vessels from pregnancies complicated with intrauterine growth restriction present altered NOS-dependent vasodilation. Arginase-2 competes with eNOS for l-arginine and counteracts the NOS-dependent relaxation in umbilical vessels from normal pregnancies. However there is no data regarding the contribution of arginase activity on the impaired endothelial function in IUGR placenta. We studied whether arginase-2 participates in IUGR-related placental vascular dysfunction counteracting eNOS-dependent relaxation, and the regulation of arginase-2 and eNOS expression in endothelial cells from IUGR umbilical arteries (HUAEC) and veins (HUVEC). In IUGR-derived umbilical arteries (UA) and veins (UV), and chorionic arteries (CA), NOS-dependent vasoactive response in the presence and absence of BEC (arginase inhibitor) was studied. Protein levels of eNOS (total and Ser(1177)-P-eNOS), arginase-2 and arginase activity were determined in IUGR HUAEC and HUVEC. In IUGR vessels eNOS-dependent relaxation was reduced, being improved by BEC. This effect was higher in arteries than veins, and in chorionic compared with umbilical vessels. In cultured IUGR endothelial cells, arginase-2 protein expression and activity were increased in HUVEC, without changes in HUAEC. In IUGR-derived endothelium there was a generalized reduction in the in vitro eNOS activation (Ser(1177)-P-eNOS/eNOS), and therefore a decreased eNOS/arginase activity ratio. Here we provide ex vivo and in vitro evidence for a vascular role of arginase throughout placental vasculature, negatively controlling NOS activity. This effect seems to be crucial in the pathophysiology of endothelial dysfunction present in IUGR feto-placental vessels.

Modeling gas phase nitric oxide release in lung epithelial cells

Nitric oxide (NO) is present in exhaled breath and is generally considered to be a noninvasive marker of airway inflammation, and is thus of particular relevance to monitoring asthma. NO is produced when L-arginine is converted to L-citrulline by NO synthase (NOS); however, L-arginine is also the substrate for arginase and both enzymes are upregulated in asthma. Recent reports have speculated that enhanced expression of one or both enzymes could lead to a limitation in substrate availability, and hence impact downstream targets or markers such as exhaled NO. The non-linear nature and vastly different kinetics of the enzymes make predictions difficult, particularly over the wide range of enzyme activity between baseline and inflammation. In this study, we developed a steady state model of L-arginine transmembrane transport, NO production, diffusion, and gas phase NO release from lung epithelial cells. We validated our model with experimental results of gas phase NO release and intracellular l-arginine concentration in A549 cells, and then performed a sensitivity analysis to determine relative impact of each enzyme on NO production. Our model predicts intracellular L-arginine and gas phase NO release over a wide range of initial extracellular L-arginine concentrations following stimulation with cytomix (10ng/ml TNF-α, IL-1β, and INF-γ). Relative sensitivity analysis demonstrates that enhanced arginase activity has little impact on l-arginine bioavailability for NOS. In addition, NOS activity is the dominant parameter which impacts gas phase NO release.

Regulatory cross-talk of mouse liver polyamine and methionine metabolic pathways: a systemic approach to its physiopathological consequences

Both polyamines and methionine derivatives are nitrogen compounds directly related to the regulation of gene expression. In silico predictions and experimental evidence suggest a cross-talk between polyamine and methionine metabolism in mammalian tissues. Since liver is the major organ that controls nitrogen metabolism of the whole organism, it is the best tissue to further test this hypothesis in vivo. In this work, we studied the effects of the chronic administration of a methionine-supplemented diet (0.5% Met in drinking water for 5 months) on the liver of mice (designated as MET-mice). Metabolic and proteomic approaches were performed and the data obtained were subjected to biocomputational analysis. Results showed that a supplemental methionine intake can indeed regulate biogenic amine metabolism in an in vivo model by multiple mechanisms including metabolic regulation and specific gene demethylation. Furthermore, putative systemic effects were investigated by molecular and cellular biology methods. Among other results, altered expression levels of multiple inflammation and cell proliferation/death balance markers were found and macrophage activation was observed. Overall, the results presented here will be of interest across a variety of biomedical disciplines, including nutrition, orphan diseases, immunology and oncology.

A combined model of hepatic polyamine and sulfur amino acid metabolism to analyze S-adenosyl methionine availability

Many molecular details remain to be uncovered concerning the regulation of polyamine metabolism. A previous model of mammalian polyamine metabolism showed that S-adenosyl methionine availability could play a key role in polyamine homeostasis. To get a deeper insight in this prediction, we have built a combined model by integration of the previously published polyamine model and one-carbon and glutathione metabolism model, published by different research groups. The combined model is robust and it is able to achieve physiological steady-state values, as well as to reproduce the predictions of the individual models. Furthermore, a transition between two versions of our model with new regulatory factors added properly simulates the switch in methionine adenosyl transferase isozymes occurring when the liver enters in proliferative conditions. The combined model is useful to support the previous prediction on the role of S-adenosyl methionine availability in polyamine homeostasis. Furthermore, it could be easily adapted to get deeper insights on the connections of polyamines with energy metabolism.

L-Arginine stimulates proliferation and prevents endotoxin-induced death of intestinal cells

This study tested the hypothesis that L-arginine (Arg) may stimulate cell proliferation and prevent lipopolysaccharide (LPS)-induced death of intestinal cells. Intestinal porcine epithelial cells (IPEC-1) were cultured for 4 days in Arg-free Dulbecco's modified Eagle's-F12 Ham medium (DMEM-F12) containing 10, 100 or 350 microM Arg and 0 or 20 ng/ml LPS. Cell numbers, protein concentrations, protein synthesis and degradation, as well as mammalian target of rapamycin (mTOR) and Toll-like receptor 4 (TLR4) signaling pathways were determined. Without LPS, IPEC-1 cells exhibited time- and Arg-dependent growth curves. LPS treatment increased cell death and reduced protein concentrations in IPEC-1 cells. Addition of 100 and 350 microM Arg to culture medium dose-dependently attenuated LPS-induced cell death and reduction of protein concentrations, in comparison with the basal medium containing 10 microM Arg. Furthermore, supplementation of 100 and 350 microM Arg increased protein synthesis and reduced protein degradation in both control and LPS-treated IPEC-1 cells. Consistent with the data on cell growth and protein turnover, addition of 100 or 350 microM Arg to culture medium increased relative protein levels for phosphorylated mTOR and phosphorylated ribosomal protein S6 kinase-1, while reducing the relative levels of TLR4 and phosphorylated levels of nuclear factor-kappaB in LPS-treated IPEC-1 cells. These results demonstrate a protective effect of Arg against LPS-induced enterocyte damage through mechanisms involving mTOR and TLR4 signaling pathways, as well as intracellular protein turnover.

Impacts of amino acid nutrition on pregnancy outcome in pigs: mechanisms and implications for swine production

Pigs suffer up to 50% embryonic and fetal loss during gestation and exhibit the most severe naturally occurring intrauterine growth retardation among livestock species. Placental insufficiency is a major factor contributing to suboptimal reproductive performance and reduced birth weights of pigs. Enhancement of placental growth and function through nutritional management offers an effective solution to improving embryonic and fetal survival and growth. We discovered an unusual abundance of the arginine family of AA in porcine allantoic fluid (a reservoir of nutrients) during early gestation, when placental growth is most rapid. Arginine is metabolized to ornithine, proline, and nitric oxide, and these compounds possess a plethora of physiological functions. Nitric oxide is a vasodilator and angiogenic factor, whereas both ornithine and proline are substrates for placental synthesis of polyamines, which are key regulators of protein synthesis and angiogenesis. Additionally, arginine, leucine, glutamine, and proline activate the mammalian target of rapamycin cell-signaling pathway to enhance protein synthesis and cell proliferation in placentae. To translate basic research on AA biochemistry and nutrition into application, dietary supplementation with 0.83% l-arginine to gilts on d 14 to 28 or d 30 to 114 of gestation increased the number and litter birth weight of live-born piglets. In addition, supplementing the gestation diet with 0.4% l-arginine plus 0.6% l-glutamine enhanced the efficiency of nutrient utilization, reduced variation in piglet birth weight, and increased litter birth weight. By regulating syntheses of nitric oxide, polyamines, and proteins, functional AA stimulate placental growth and the transfer of nutrients from mother to embryo or fetus to promote conceptus survival, growth, and development.

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.

First steps in computational systems biology: A practical session in metabolic modeling and simulation

A comprehensive understanding of biological functions requires new systemic perspectives, such as those provided by systems biology. Systems biology approaches are hypothesis-driven and involve iterative rounds of model building, prediction, experimentation, model refinement, and development. Developments in computer science are allowing for ever faster numerical simulations of mathematical models. Mathematical modeling plays an essential role in new systems biology approaches. As a complex, integrated system, metabolism is a suitable topic of study for systems biology approaches. However, up until recently, this topic has not been properly covered in biochemistry courses. This communication reports the development and implementation of a practical lesson plan on metabolic modeling and simulation.

Amino acids: metabolism, functions, and nutrition

Recent years have witnessed the discovery that amino acids (AA) are not only cell signaling molecules but are also regulators of gene expression and the protein phosphorylation cascade. Additionally, AA are key precursors for syntheses of hormones and low-molecular weight nitrogenous substances with each having enormous biological importance. Physiological concentrations of AA and their metabolites (e.g., nitric oxide, polyamines, glutathione, taurine, thyroid hormones, and serotonin) are required for the functions. However, elevated levels of AA and their products (e.g., ammonia, homocysteine, and asymmetric dimethylarginine) are pathogenic factors for neurological disorders, oxidative stress, and cardiovascular disease. Thus, an optimal balance among AA in the diet and circulation is crucial for whole body homeostasis. There is growing recognition that besides their role as building blocks of proteins and polypeptides, some AA regulate key metabolic pathways that are necessary for maintenance, growth, reproduction, and immunity. They are called functional AA, which include arginine, cysteine, glutamine, leucine, proline, and tryptophan. Dietary supplementation with one or a mixture of these AA may be beneficial for (1) ameliorating health problems at various stages of the life cycle (e.g., fetal growth restriction, neonatal morbidity and mortality, weaning-associated intestinal dysfunction and wasting syndrome, obesity, diabetes, cardiovascular disease, the metabolic syndrome, and infertility); (2) optimizing efficiency of metabolic transformations to enhance muscle growth, milk production, egg and meat quality and athletic performance, while preventing excess fat deposition and reducing adiposity. Thus, AA have important functions in both nutrition and health.

High fat feeding and dietary L-arginine supplementation differentially regulate gene expression in rat white adipose tissue

Dietary L-arginine (Arg) supplementation reduces white-fat gain in diet-induced obese rats but the underlying mechanisms are unknown. This study tested the hypothesis that Arg treatment affects expression of genes related to lipid metabolism in adipose tissue. Four-week-old male Sprague-Dawley rats were fed a low-fat (LF) or high-fat (HF) diet for 15 weeks. Thereafter, lean or obese rats continued to be fed their same respective diets and received drinking water containing 1.51% Arg-HCl or 2.55% L: -alanine (isonitrogenous control). After 12 weeks of Arg supplementation, rats were euthanized to obtain retroperitoneal adipose tissue for analyzing global changes in gene expression by microarray. The results were confirmed by RT-PCR analysis. HF feeding decreased mRNA levels for lipogenic enzymes, AMP-activated protein kinase, glucose transporters, heme oxygenase 3, glutathione synthetase, superoxide dismutase 3, peroxiredoxin 5, glutathione peroxidase 3, and stress-induced protein, while increasing expression of carboxypeptidase-A, peroxisome proliferator activated receptor (PPAR)-alpha, caspase 2, caveolin 3, and diacylglycerol kinase. In contrast, Arg supplementation reduced mRNA levels for fatty acid binding protein 1, glycogenin, protein phosphates 1B, caspases 1 and 2, and hepatic lipase, but increased expression of PPARgamma, heme oxygenase 3, glutathione synthetase, insulin-like growth factor II, sphingosine-1-phosphate receptor, and stress-induced protein. Biochemical analysis revealed oxidative stress in white adipose tissue of HF-fed rats, which was prevented by Arg supplementation. Collectively, these results indicate that HF diet and Arg supplementation differentially regulate gene expression to affect energy-substrate oxidation, redox state, fat accretion, and adipocyte differentiation in adipose tissue. Our findings provide a molecular mechanism to explain a beneficial effect of Arg on ameliorating diet-induced obesity in mammals.

The polyamine and histamine metabolic interplay in cancer and chronic inflammation

PURPOSE OF REVIEW

To provide an update on the major research contributing to deciphering the metabolic interplay of polyamines/histamine and its impact in cancer and chronic inflammation.

RECENT FINDINGS

The most recent and relevant findings that might reflect a link between the polyamines/histamine metabolic interplay and the development of cancer and chronic inflammation-related diseases include: the observation that histamine catabolism is downregulated in the colonic mucosa of patients with colonic adenoma; the finding that some polyamine and histamine-related metabolites are different between a breast cancer cell line and a reference mammary epithelial cell line; and the demonstration of the critical role that mast cells (a cell type in which the polyamine/histamine metabolic interplay has been confirmed) play in the development of pancreatic tumors. There is still, however, a lack of specific studies elucidating the exact contribution of the polyamine/histamine metabolic interplay in these clinical settings.

SUMMARY

In mammalian cells, a polyamine/histamine metabolic interplay has been extensively proven; however, its ultimate effect on human health largely depends on the cell type and environment. Information on this topic is currently fragmented in the literature. In order to develop efficient intervention strategies, it will be necessary to establish an integrated and holistic view of the role of the polyamine/histamine metabolic interplay in each pathological state.

Nitric oxide and vascular insulin resistance

Obesity and type-II diabetes are growing major health issues worldwide. They are the leading risk factors for vascular insulin resistance, which plays an important role in the pathogenesis of cardiovascular disease, the leading cause of death in developed nations. Recent studies have shown that reduced synthesis of nitric oxide (NO; a major vasodilator) from L-arginine in endothelial cells is a major factor contributing to the impaired action of insulin in the vasculature of obese and diabetic subjects. The decreased NO generation results from a deficiency of (6R)-5,6,7,8-tetrahydrobiopterin [BH4; an essential cofactor for NO synthase (NOS)], as well as increased generation of glucosamine (an inhibitor of the pentose cycle for the production of NADPH, another cofactor for NOS) from glucose and L-glutamine. Accordingly, endothelial dysfunction can be prevented by (1) enhancement of BH4 synthesis through supplementation of its precursor (sepiapterin) via the salvage pathway; (2) transfer of the gene for GTP cyclohydrolase-I (the first and key regulatory enzyme for de novo synthesis of BH4); or (3) dietary supplementation of L-arginine (which stimulates GTP cyclohydrolase-I expression and inhibits hexosamine production). Modulation of the arginine-NO pathway by BH4 and arginine is beneficial for ameliorating vascular insulin resistance in obesity and diabetes.

Dietary arginine supplementation enhances antioxidative capacity and improves meat quality of finishing pigs

The present study was conducted to test the hypothesis that dietary arginine supplementation may improve meat quality of finishing pigs. Beginning at approximately 60 kg body weight, pigs were fed a corn- and soybean meal-based diet supplemented with 0, 0.5 or 1% L-arginine until they reached a body weight of approximately 110 kg. On the last day of the experiment, pigs were food-deprived for 16 h before blood samples were obtained for analysis of amino acids, insulin, and other metabolites. Immediately thereafter, pigs were slaughtered for determination of carcass composition, muscle biochemical parameters, and meat quality. The result showed that arginine did not affect pig growth performance or carcass traits. However, 1% arginine decreased drip loss of pork muscle at 48 h postmortem, while increasing intramuscular fat content (P < 0.05). Supplementing 0.5 or 1% arginine to the diet increased arginine concentration and decreased cortisol level in serum, while enhancing antioxidative capacity and glutathione peroxidase activity in serum (P < 0.05). Additionally, 1% arginine increased antioxidative capacity in skeletal muscle (P < 0.05). Furthermore, 0.5 or 1% arginine decreased the cortisol receptor mRNA level in muscle (P < 0.05). Collectively, these results indicate that supplemental arginine improved meat quality and attenuated oxidative stress of finishing pigs.

Metabolomic analysis of the response of growing pigs to dietary L-arginine supplementation

Arginine plays an important role regulating nutrient metabolism, but the underlying mechanisms are largely unknown. This study was conducted to determine the effect of dietary arginine supplementation on the metabolome in serum of growing pigs using (1)H nuclear magnetic resonance spectroscopy. Sixteen 120-day-old pigs (48 +/- 1 kg) were randomly assigned to one of two groups, representing supplementation with 0 or 1.0% L: -arginine to corn- and soybean meal-based diets. Serum was collected after a 46-day period of treatment. Dietary arginine supplementation decreased fat deposition and increased protein accretion in the body. Principal component analysis showed that serum concentrations of low density lipoprotein, very low density lipoprotein, and urea were lower, but concentrations of creatinine, tricarboxylic acid cycle metabolites, ornithine, lysine and tyrosine were greater in arginine-supplemented than in control pigs. Additionally, the arginine treatment affected serum concentrations of nitrogenous and lipid signaling molecules (glycerophosphorylcholine and myo-inositol) and intestinal bacterial metabolites (formate, ethanol, methylamine, dimethylamine, acetate, and propionate). These novel findings suggest that dietary arginine supplementation alters the catabolism of fat and amino acids in the whole body, enhances protein synthesis in skeletal muscle, and modulates intestinal microbial metabolism in growing pigs.

Dietary supplementation with cholesterol and docosahexaenoic acid affects concentrations of amino acids in tissues of young pigs

Cholesterol and docosahexaenoic acid (DHA) are important nutrients for neural development of infants. However, little is known about the effect of cholesterol or DHA on concentrations of amino acids (AA) in neonatal tissues. This study was conducted with the piglet (an established model for studying human infant nutrition) to test the hypothesis that dietary supplementation with the lipids may modulate AA availability in tissues. Sixteen newborn pigs were nursed by sows for 24 h and then assigned to one of four treatment groups, representing supplementation with 0.0% (control), 0.2% cholesterol, 0.2% DHA, or cholesterol plus DHA to the basal milk-formula. All piglets were euthanized at 49 days of age. In brain, cholesterol supplementation reduced (P < 0.05) concentrations of glutamate, serine, glutamine, threonine, beta-alanine, alanine, methionine, isoleucine, leucine, and gamma-aminobutyrate but increased (P < 0.05) concentrations of glycine and lysine, whereas DHA supplementation similarly affected (P < 0.05) concentrations of the same AA (except for isoleucine and lysine) and taurine. In addition, concentrations of most AA in liver, muscle and plasma were substantially altered by dietary supplementation of cholesterol and DHA in a tissue-dependent manner. Further, DHA reduced concentrations of carnosine in skeletal muscle, as well as ammonia in both plasma and brain. The results reveal that cholesterol and DHA can regulate AA metabolism and availability in various tissues of piglets. These novel findings have important implications for designing the next generation of infant formula to optimize neonatal growth and development.

Development of an expression macroarray for amine metabolism-related genes

Cationic amino acids are the precursors of biogenic amines, histamine from histidine, and putrescine, spermidine and spermine from arginine/ornithine (and methionine), as well as nitric oxide. These amines play important biological roles in inter- and intracellular signaling mechanisms related to inflammation, cell proliferation and neurotransmission. Biochemical and epidemiological relationships between arginine-derived products and histamine have been reported to play important roles in physiopathological problems. In this communication, we describe the construction of an expression macroarray containing more than 30 human probes for most of the key proteins involved in biogenic amines metabolisms, as well as other inflammation- and proliferation-related probes. The array has been validated on human mast HMC-1 cells. On this model, we have got further support for an inverse correlation between polyamine and histamine synthesis previously observed on murine basophilic models. These tools should also be helpful to understand the amine roles in many other inflammatory and neoplastic pathologies.

Polyamines: metabolism to systems biology and beyond

Polyamines and the metabolic and physiopathological processes in which they are involved represent an active field of research that has been continuously growing since the seventies. In the last years, the trends in the focused areas of interest within this field since the 1970s have been confirmed. The impact of "-omics" in polyamine research remains too low in comparison with its deep impact on other biological research areas. These high-throughput approaches, along with systems biology and, in general, more systemic and holistic approaches should contribute to a renewal of this research area in the near future.