In vivo measurement of nitric oxide production in porcine gut, liver and muscle during hyperdynamic endotoxaemia

Ion Channels Remodeling in the Regulation of Vascular Hyporesponsiveness During Shock

Shock is characterized with vascular hyporesponsiveness to vasoconstrictors, thereby to cause refractory hypotension, insufficient tissue perfusion, and multiple organ dysfunction. The vascular hyporeactivity persisted even though norepinephrine and fluid resuscitation were administrated, it is of critical importance to find new potential target. Ion channels are crucial in the regulation of cell membrane potential and affect vasoconstriction and vasodilation. It has been demonstrated that many types of ion channels including K+ channels, Ca2+ permeable channels, and Na+ channels exist in vascular smooth muscle cells and endothelial cells, contributing to the regulation of vascular homeostasis and vasomotor function. An increasing number of studies suggested that the structural and functional alterations of ion channels located in arteries contribute to vascular hyporesponsiveness during shock, but the underlying mechanisms remained to be fully clarified. Therefore, the expression and functional changes in ion channels in arteries associated with shock are reviewed, to pave the way for further exploring the potential of ion channel-targeted compounds in treating refractory hypotension in shock.

Identifying potential biomarkers and therapeutic targets for dogs with sepsis using metabolomics and lipidomics analyses

Sepsis is a diagnostic and therapeutic challenge and is associated with morbidity and a high risk of death. Metabolomic and lipidomic profiling in sepsis can identify alterations in metabolism and might provide useful insights into the dysregulated host response to infection, but investigations in dogs are limited. We aimed to use untargeted metabolomics and lipidomics to characterize metabolic pathways in dogs with sepsis to identify therapeutic targets and potential diagnostic and prognostic biomarkers. In this prospective observational cohort study, we examined the plasma metabolomes and lipidomes of 20 healthy control dogs and compared them with those of 21 client-owned dogs with sepsis. Patient data including signalment, physical exam findings, clinicopathologic data and clinical outcome were recorded. Metabolites were identified using an untargeted mass spectrometry approach and pathway analysis identified multiple enriched metabolic pathways including pyruvaldehyde degradation; ketone body metabolism; the glucose-alanine cycle; vitamin-K metabolism; arginine and betaine metabolism; the biosynthesis of various amino acid classes including the aromatic amino acids; branched chain amino acids; and metabolism of glutamine/glutamate and the glycerophospholipid phosphatidylethanolamine. Metabolites were identified with high discriminant abilities between groups which could serve as potential biomarkers of sepsis including 13,14-Dihydro-15-keto Prostaglandin A₂; 12(13)-DiHOME (12,13-dihydroxy-9Z-octadecenoic acid); and 9-HpODE (9-Hydroxyoctadecadienoic acid). Metabolites with higher abundance in samples from nonsurvivors than survivors included 3-(2-hydroxyethyl) indole, indoxyl sulfate and xanthurenic acid. Untargeted lipidomic profiling revealed multiple sphingomyelin species (SM(d34:0)+H; SM(d36:0)+H; SM(d34:0)+HCOO; and SM(d34:1D3)+HCOO); lysophosphatidylcholine molecules (LPC(18:2)+H) and lipophosphoserine molecules (LPS(20:4)+H) that were discriminating for dogs with sepsis. These biomarkers could aid in the diagnosis of dogs with sepsis, provide prognostic information, or act as potential therapeutic targets.

Clinical Study on the Efficacy and Safety of Arginine Administered Orally in Association with Other Active Ingredients for the Prevention and Treatment of Sarcopenia in Patients with COVID-19-Related Pneumonia, Hospitalized in a Sub-Intensive Care Unit

In order to evaluate the efficacy of oral supplementation with 3 g of arginine per day associated with creatine, L-carnitine, aspartic acid, magnesium, selenium and vitamins C and E (Argivit© Aesculapius Farmaceutici) in the prevention and treatment of sarcopenia in patients with COVID-19-related pneumonia, we conducted a parallel randomized study comparing it with standard therapy alone. Forty patients on standard therapy plus supplementation were compared with a control group of 40 patients, all hospitalized at the sub-intensive care unit of the Del Mare Hospital in Naples, with a clinical diagnosis of SARS-CoV-2 infection and COVID-19 pneumonia. Muscle strength was assessed with the handgrip test and muscle ultrasound. Arginine-supplemented patients had an average grip strength of 23.5 at the end of hospitalization compared with 22.5 in the untreated group with less reduction, showing statistical significance (p < 0.001). In the same way, the thickness of the vastus lateralis quadriceps femoris muscle measured at the end of hospitalization showed less reduction on ultrasound, with a higher average value in the group receiving treatment than in the group of patients without supplementation (p < 0.001). Upon discharge there was a 58.40% reduction in ventilation days in patients with arginine supplementation compared with the control group.

Microcirculatory Function during Endotoxemia-A Functional Citrulline-Arginine-NO Pathway and NOS3 Complex Is Essential to Maintain the Microcirculation

Competition for the amino acid arginine by endothelial nitric-oxide synthase (NOS3) and (pro-)inflammatory NO-synthase (NOS2) during endotoxemia appears essential in the derangement of the microcirculatory flow. This study investigated the role of NOS2 and NOS3 combined with/without citrulline supplementation on the NO-production and microcirculation during endotoxemia. Wildtype (C57BL6/N background; control; n = 36), Nos2-deficient, (n = 40), Nos3-deficient (n = 39) and Nos2/Nos3-deficient mice (n = 42) received a continuous intravenous LPS infusion alone (200 μg total, 18 h) or combined with L-citrulline (37.5 mg, last 6 h). The intestinal microcirculatory flow was measured by side-stream dark field (SDF)-imaging. The jejunal intracellular NO production was quantified by in vivo NO-spin trapping combined with electron spin-resonance (ESR) spectrometry. Amino-acid concentrations were measured by high-performance liquid chromatography (HPLC). LPS infusion decreased plasma arginine concentration in control and Nos3^−/− compared to Nos2^−/− mice. Jejunal NO production and the microcirculation were significantly decreased in control and Nos2^−/− mice after LPS infusion. No beneficial effects of L-citrulline supplementation on microcirculatory flow were found in Nos3^−/− or Nos2^−/−/Nos3^−/− mice. This study confirms that L-citrulline supplementation enhances de novo arginine synthesis and NO production in mice during endotoxemia with a functional NOS3-enzyme (control and Nos2^−/− mice), as this beneficial effect was absent in Nos3^−/− or Nos2^−/−/Nos3^−/− mice.

Neonatal Piglets Can Synthesize Adequate Creatine, but Only with Sufficient Dietary Arginine and Methionine, or with Guanidinoacetate and Excess Methionine

BACKGROUND

Suckling piglets synthesize most of their creatine requirement, which consumes substantial amounts of arginine in order to synthesize guanidinoacetic acid (GAA) and methionine in order to transmethylate GAA to creatine.

OBJECTIVES

To determine whether supplemental GAA or creatine spare arginine and/or methionine for protein synthesis and, if GAA is supplemented, whether excess methionine is needed for conversion to creatine.

METHODS

Yucatan miniature piglets (9-11 days old; both sexes) were fed 1 of 5 elemental diets for 5 days: 1) low arginine (0.3 g·kg-1·d-1) and low methionine (0.20 g·kg-1·d-1; Base); 2) Base plus GAA (0.093 g·kg-1·d-1; +GAA); 3) Base plus GAA plus excess methionine (0.5 g·kg-1·d-1; +GAA/Met); 4) Base plus creatine (0.12 g·kg-1·d-1; +Cre); or 5) excess arginine (1.8 g·kg-1·d-1) and excess methionine (+Arg/Met). Isotope tracers were infused to determine whole-body GAA, creatine, and protein synthesis; tissues were analyzed for creatine synthesis enzymes and metabolite concentrations. Data were analyzed by 1-way ANOVA.

RESULTS

: GAA and creatine syntheses were 115% and 32% higher, respectively, with the +Arg/Met diet (P < 0.0001), in spite of 33% lower renal L-arginine: glycine amidinotransferase activity (P < 0.0001) compared to Base, suggesting substrate availability dictates synthesis rather than enzyme capacity. GAA or creatine supplementation reduced arginine conversion to creatine by 46% and 43%, respectively (P < 0.01), but did not spare amino acids for whole-body protein synthesis, suggesting that limited amino acids were diverted to protein at the expense of creatine synthesis. The +GAA/Met diet led to higher creatine concentrations in the kidney (2.6-fold) and liver (7.6-fold) than the +GAA diet (P < 0.01), suggesting excess methionine is needed for GAA conversion to creatine.

CONCLUSIONS

Piglets are capable of synthesizing sufficient creatine from the precursor amino acids arginine and methionine, or from GAA plus methionine.

Continuous elevation of procalcitonin in cirrhosis combined with hepatic carcinoma: a case report

BACKGROUND

Serum levels of procalcitonin (PCT) are considered a useful biomarker for the diagnosis of bacterial infection or inflammation. There are few reports of high PCT levels in end-stage liver disease regardless of bacterial infection. Here, we present a case of extremely high PCT levels (> 100 ng/mL) in a patient with severe cirrhosis combined with hepatic carcinoma.

CASE PRESENTATION

A 65-year-old man developed end-stage cirrhosis with hepatic carcinoma. Radiographic imaging showed a massive hepatocellular carcinoma with multiple loci lack of indications of resection. Hence, transcatheter hepatic arterial chemoembolization was performed three times over a period of 4 months. Before and after interventional therapies, the biochemistry laboratory results were only slightly abnormal except for persistently high PCT concentrations (> 100 ng/mL), irrespective of the evidence for bacterial infection or sepsis.

CONCLUSIONS

This case suggests that continuously high levels of PCT (> 100 ng/mL) may be present in advanced liver disease, particularly in complex situations such as decompensated cirrhosis and liver cancer, in the absence of severe infection or sepsis. This knowledge could expand the significance of PCT in liver disease.

Identification of Metabolic Changes in Ileum, Jejunum, Skeletal Muscle, Liver, and Lung in a Continuous I.V. Pseudomonas aeruginosa Model of Sepsis Using Nontargeted Metabolomics Analysis

Sepsis is a multiorgan disease affecting the ileum and jejunum (small intestine), liver, skeletal muscle, and lung clinically. The specific metabolic changes in the ileum, jejunum, liver, skeletal muscle, and lung have not previously been investigated. Live Pseudomonas aeruginosa, isolated from a patient, was given via i.v. catheter to pigs to induce severe sepsis. Eighteen hours later, ileum, jejunum, medial gastrocnemius skeletal muscle, liver, and lung were analyzed by nontargeted metabolomics analysis using gas chromatography/mass spectrometry. The ileum and the liver demonstrated significant changes in metabolites involved in linoleic acid metabolism: the ileum and lung had significant changes in the metabolism of valine/leucine/isoleucine; the jejunum, skeletal muscle, and liver had significant changes in arginine/proline metabolism; and the skeletal muscle and lung had significant changes in aminoacyl-tRNA biosynthesis, as analyzed by pathway analysis. Pathway analysis also identified changes in metabolic pathways unique for different tissues, including changes in the citric acid cycle (jejunum), β-alanine metabolism (skeletal muscle), and purine metabolism (liver). These findings demonstrate both overlapping metabolic pathways affected in different tissues and those that are unique to others and provide insight into the metabolic changes in sepsis leading to organ dysfunction. This may allow therapeutic interventions that focus on multiple tissues or single tissues once the relationship of the altered metabolites/metabolism to the underlying pathogenesis of sepsis is determined.

L-Arginine and L-Citrulline Supplementation Have Different Programming Effect on Regulatory T-Cells Function of Infantile Rats

Arginine is a semiessential amino acid in healthy adult human, but is essential for preterm, newborn or critically ill patients. Arginine can be supplied from our diet or de novo synthesis from citrulline. In conditions of sepsis or endotoxemia, arginine may be deficient and be accompanied with altered immune response. L-arginine supplementation can ameliorate dysregulated immune condition and improve prognosis. Many studies had tried L-arginine or L-citrulline supplementation to examine the effect on immune response in the adult population. Few had studied on the young children. In this study, we determined the effect of L-arginine and L-citrulline supplementation on the immune response of infantile rats. Male infantile rats received normal saline, L-arginine (200 mg/kg/day) or L-citrulline (200 mg/kg/day) intraperitoneally over postnatal day 8 to day 14. The infantile rats were then sacrificed. The blood was analyzed while the spleen was indicated for immune analysis after stimulation with concanavalin A (Con A) or lipopolysaccharide (LPS). We found L-arginine supplementation enhanced Th1 immune response by increasing IFN-γ production. Both the L-arginine and L-citrulline therapy can modulate regulatory T-cell (Treg) immune effects by increasing the IL-10 level. Only the L-citrulline group showed a TGF-β1 increase. Both L-arginine and L-citrulline therapy were also noted to decrease SMAD7 expression and enhance SIRT-1 abundance. However, FOXP3 expression was only modulated by L-citrulline treatment. We then concluded that L-arginine and L-citrulline supplementation can modulate the regulatory T-cells function differently for infantile rats.

Phenylalanine isotope pulse method to measure effect of sepsis on protein breakdown and membrane transport in the pig

The primed-continuous (PC) phenylalanine (Phe) stable isotope infusion methodology is often used as a proxy for measuring whole body protein breakdown (WbPB) in sepsis. It is unclear if WbPB data obtained by an easy-to-use single IV Phe isotope pulse administration (PULSE) are comparable to those by PC. Compartmental modeling with PULSE could provide us more insight in WbPB in sepsis. Therefore, in the present study, we compared PULSE with PC as proxy for WbPB in an instrumented pig model with Pseudomonas aeruginosa-induced severe sepsis (Healthy: n = 9; Sepsis: n = 13). Seventeen hours after sepsis induction, we compared the Wb rate of appearance (WbR_a) of Phe obtained by PC (L-[ring-¹³C₆]Phe) and PULSE (L-[¹⁵N]Phe) in arterial plasma using LC-MS/MS and (non)compartmental modeling. PULSE-WbR_a was highly correlated with PC-WbR_a (r = 0.732, P < 0.0001) and WbPB (r = 0.897, P < 0.0001) independent of the septic state. PULSE-WbR_a was 1.6 times higher than PC-WbR_a (P < 0.001). Compartmental and noncompartmental PULSE modeling provide comparable WbR_a values, although compartmental modeling was more sensitive. WbPB was elevated in sepsis (Healthy: 3,378 ± 103; Sepsis: 4,333 ± 160 nmol·kg BW^-1·min^-1, P = 0.0002). With PULSE, sepsis was characterized by an increase of the metabolic shunting (Healthy: 3,021 ± 347; Sepsis: 4,233 ± 344 nmol·kg BW^-1·min^-1, P = 0.026). Membrane transport capacity was the same. Both PC and PULSE methods are able to assess changes in WbR_a of plasma Phe reflecting WbPB changes with high sensitivity, independent of the (patho)physiological state. The easy-to-use (non)compartmental PULSE reflects better the real WbPB than PC. With PULSE compartmental analysis, we conclude that the membrane transport capacity for amino acids is not compromised in severe sepsis.

Arginine and citrulline and the immune response in sepsis

Arginine, a semi-essential amino acid is an important initiator of the immune response. Arginine serves as a precursor in several metabolic pathways in different organs. In the immune response, arginine metabolism and availability is determined by the nitric oxide synthases and the arginase enzymes, which convert arginine into nitric oxide (NO) and ornithine, respectively. Limitations in arginine availability during inflammatory conditions regulate macrophages and T-lymfocyte activation. Furthermore, over the past years more evidence has been gathered which showed that arginine and citrulline deficiencies may underlie the detrimental outcome of inflammatory conditions, such as sepsis and endotoxemia. Not only does the immune response contribute to the arginine deficiency, also the impaired arginine de novo synthesis in the kidney has a key role in the eventual observed arginine deficiency. The complex interplay between the immune response and the arginine-NO metabolism is further underscored by recent data of our group. In this review we give an overview of physiological arginine and citrulline metabolism and we address the experimental and clinical studies in which the arginine-citrulline NO pathway plays an essential role in the immune response, as initiator and therapeutic target.

Multitracer stable isotope quantification of arginase and nitric oxide synthase activity in a mouse model of pseudomonas lung infection

Cystic fibrosis airways are deficient for L-arginine, a substrate for nitric oxide synthases (NOSs) and arginases. The rationale for this study was to quantify NOS and arginase activity in the mouse lung. Anesthetized unventilated mice received a primed constant stable isotope intravenous infusion containing labeled L-arginine, ornithine, and citrulline. The isotopic enrichment of each of the infused isotopomers and its product amino acids were measured in plasma and organ homogenates using liquid chromatography-tandem mass spectrometry. The effect of infection was studied three days after direct tracheal instillation of Pseudomonas-coated agar beads. In the infusion model, lung infection resulted in a significant (28-fold) increase in NOS activity in lung but not in trachea, kidney, liver, or plasma. Absolute rates of arginase activity in solid tissues could not be calculated in this model. In an isolated lung perfusion model used for comparison increased NOS activity in infected lungs was confirmed (28.5-fold) and lung arginase activity was increased 9.7-fold. The activity of L-arginine metabolizing enzymes can be measured using stable isotope conversion in the mouse. Accumulation of L-ornithine in the whole mouse model hindered the exact quantification of arginase activity in the lung, a problem that was overcome utilizing an isolated lung perfusion model.

Isotopic study of L-Arginine kinetics in the lung during pseudomonas sepsis in an ovine model

The objective of the study is to investigate how L-Arginine pulmonary metabolism is altered in response Pseudomonas aeruginosa (P. aeruginosa) induced septic conditions using an ovine model.

METHODS

Seven female sheep were infused with a primed-constant infusion of L-[(15)N2-guanidino, 5, 5, (2)H2] L-Arginine for 28 hs. After the initial 4 hs of the L-Arginine infusion, a continuous infusion of live Pseudomonas aeruginosa bacteria started for 24 hs. A NO synthase (NOS) inhibitor, N(G)-Methyl-L-arginine (L-NMA), infusion was added during the last 4 hs of the bacterial infusion. Blood samples were taken at specific time points for isotopic enrichment during control, septic and NOS blocking phases of the study.

RESULTS

We observed that the level of total delivery of L-Arginine to the lungs was significantly decreased in septic phase after 24 hours of pseudomonas infusion. In contrast, the fractional uptake and metabolism of L-Arginine by the lungs was doubled during septic phase relative to the control phase (MARG-basal = 100% vs. MARG-septic = 220 ± 56%, P < 0.05). NO production in the lungs was also significantly increased. Infusion of L-NMA markedly blunted this elevated NO production and attenuated the total arginine metabolized in the septic lungs (MARG-septic = 220 ± 56% vs. MARG-NO blocking = -25 ± 20%; P < 0.05). We demonstrated sepsis induced by P. aeruginosa infusion caused an increase in the fractional uptake and metabolic rate of arginine in the lungs. Furthermore, our data suggests that arginine was mainly consumed via arginine - NO pathway, which might be responsible for this enhanced arginine metabolic activity in the septic lungs.

Isotopic study of L-Arginine kinetics in the lung during pseudomonas sepsis in an ovine model

The objective of the study is to investigate how L-Arginine pulmonary metabolism is altered in response Pseudomonas aeruginosa (P. aeruginosa) induced septic conditions using an ovine model.

METHODS

Seven female sheep were infused with a primed-constant infusion of L-[(15)N2-guanidino, 5, 5, (2)H2] L-Arginine for 28 hs. After the initial 4 hs of the L-Arginine infusion, a continuous infusion of live Pseudomonas aeruginosa bacteria started for 24 hs. A NO synthase (NOS) inhibitor, N(G)-Methyl-L-arginine (L-NMA), infusion was added during the last 4 hs of the bacterial infusion. Blood samples were taken at specific time points for isotopic enrichment during control, septic and NOS blocking phases of the study.

RESULTS

We observed that the level of total delivery of L-Arginine to the lungs was significantly decreased in septic phase after 24 hours of pseudomonas infusion. In contrast, the fractional uptake and metabolism of L-Arginine by the lungs was doubled during septic phase relative to the control phase (MARG-basal = 100% vs. MARG-septic = 220 ± 56%, P < 0.05). NO production in the lungs was also significantly increased. Infusion of L-NMA markedly blunted this elevated NO production and attenuated the total arginine metabolized in the septic lungs (Mnitrate-septic = 43.6 ± 5.7 vs. Mnitrate-septic + L-NMA = 13.4 ± 5.1 umol/kg/min; p < 0.05). We demonstrated sepsis induced by P. aeruginosa infusion caused an increase in the fractional uptake and metabolic rate of arginine in the lungs. Furthermore, our data suggests that arginine was mainly consumed via arginine - NO pathway, which might be responsible for this enhanced arginine metabolic activity in the septic lungs.

Stimulated nitric oxide production and arginine deficiency in children with cystic fibrosis with nutritional failure

OBJECTIVE

To determine whether upregulated whole body de novo arginine synthesis and protein breakdown are present as a compensatory mechanism to meet the increased demand for arginine and nitric oxide (NO) production in pediatric patients with cystic fibrosis (CF) and nutritional failure.

STUDY DESIGN

In 16 children with CF, studied at the end of antibiotic treatment for a pulmonary exacerbation, and 17 healthy controls, whole body arginine, citrulline (Cit), and protein turnover were assessed by stable isotope methodology and de novo arginine synthesis, arginine clearance, NO synthesis, protein synthesis and breakdown, and net protein balance were calculated. The plasma isotopic enrichments and amino acid concentrations were measured by liquid chromatography-tandem mass spectrometry.

RESULTS

Increased arginine clearance was found in patients with CF (P < .001), whereas whole body NO production rate and plasma arginine levels were not different. Whole body arginine production (P < .001), de novo arginine synthesis, and protein breakdown and synthesis (P < .05) were increased in patients with CF, but net protein balance was comparable. Patients with CF with nutritional failure (n = 7) had significantly higher NO production (P < .05), de novo arginine synthesis, Cit production (P < .001), and plasma Cit concentration (P < .05) and lower plasma arginine concentration (P < .05) than those without nutritional failure (n = 9).

CONCLUSIONS

Nutritional failure in CF is associated with increased NO production. However, up-regulation of de novo arginine synthesis and Cit production was not sufficient to meet the increased arginine needs leading to arginine deficiency.

Metabolomics as a novel approach for early diagnosis of pediatric septic shock and its mortality

RATIONALE

Septic shock is a significant cause of morbidity and mortality in the pediatric population. Early recognition of septic shock and appropriate treatment increase survival rate; thus, developing new diagnostic tools may improve patients' outcomes.

OBJECTIVES

To determine whether a metabolomics approach could be useful in the diagnosis and prognosis of septic shock in pediatric intensive care unit (PICUs).

METHODS

Serum samples were collected from 60 patients with septic shock, 40 PICU patients with systemic inflammatory response syndrome (not suspected of having an infection), and 40 healthy children. Proton nuclear magnetic resonance spectroscopy spectra were analyzed and quantified using targeted profiling methodology.

MEASUREMENTS AND MAIN RESULTS

Multivariate statistical analysis was applied to detect specific patterns in metabolic profiles and to highlight differences between patient samples. Supervised analysis afforded good predictive models and managed to separate patient populations. Some of the metabolite concentrations identified in serum samples changed markedly, indicating their influence on the separation between patient groups. These metabolites represent a composite biopattern of the pediatric metabolic response to septic shock and might be considered as the basis for a biomarker panel for the diagnosis of septic shock and its mortality in PICU.

CONCLUSIONS

Our results indicate that nuclear magnetic resonance metabolite profiling might serve as a promising approach for the diagnosis and prediction of mortality in septic shock in a pediatric population and that quantitative metabolomics methods can be applied in the clinical evaluations of pediatric septic shock.

Bench-to-bedside review: sepsis - from the redox point of view

The pathogenesis of sepsis and its progression to multiple organ dysfunction syndrome and septic shock have been the subject of investigations for nearly half a century. Controversies still exist with regard to understanding the molecular pathophysiology of sepsis in relation to the complex roles played by reactive oxygen species, nitric oxide, complements and cytokines. In the present review we categorise the key turning points in sepsis development and outline the most probable sequence of events leading to cellular dysfunction and organ failure under septic conditions. We have applied an integrative approach in order to fuse current state-of-the-art knowledge about redox processes involving hydrogen peroxide, nitric oxide, superoxide, peroxynitrite and hydroxyl radical, which lead to mitochondrial respiratory dysfunction. Finally, from this point of view, the potential of redox therapy targeting sepsis is discussed.

Effects of L-arginine pretreatment on nitric oxide metabolism and hepatosplanchnic perfusion during porcine endotoxemia

BACKGROUND

Sepsis is accompanied by an increased need for and a decreased supply of arginine, reflecting a condition of arginine deficiency.

OBJECTIVE

The objective was to evaluate the effects of l-arginine pretreatment on arginine-nitric oxide (NO) production and hepatosplanchnic perfusion during subsequent endotoxemia.

DESIGN

In a randomized controlled trial, pigs (20-25 kg) received 3 μg . kg(-1) . min(-1) lipopolysaccharide (LPS; 5 endotoxin units/ng) intravenously and saline resuscitation. l-Arginine (n = 8; 5.3 μmol . kg(-1) . min(-1)) or saline (n = 8) was infused starting 12 h before LPS infusion and continued for 24 h after the endotoxin infusion ended. Whole-body appearance rates, portal-drained viscera (PDV), and liver fluxes of arginine, citrulline, NO, and arginine de novo synthesis were measured by using stable-isotope infusion of [(15)N(2)]arginine and [(13)C-(2)H(2)]citrulline. Hepatosplanchnic perfusion was assessed by using a primed continuous infusion of para-aminohippuric acid and jejunal intramucosal partial pressure of carbon dioxide and was related to systemic hemodynamics.

RESULTS

Arginine supplementation before LPS increased whole-body NO production in the PDV but not in the liver. Furthermore, it increased blood flow in the portal vein but not in the aorta and hepatic artery. During endotoxin infusion, arginine pretreatment was associated with an increased whole-body arginine appearance and NO production in the gut. Additional effects included a preserved mean arterial pressure, the prevention of an increase in pulmonary arterial pressure, an attenuated metabolic acidosis, and an attenuated increase in the intramucosal partial pressure of carbon dioxide.

CONCLUSION

Arginine treatment starting before endotoxemia appears to be beneficial because it improves hepatosplanchnic perfusion and oxygenation during prolonged endotoxemia, probably through an enhancement in NO synthesis, without causing deleterious systemic side effects.

Reduced caloric intake during endotoxemia reduces arginine availability and metabolism

BACKGROUND

Inadequate caloric intake increases the risk of sepsis-induced complications. Metabolic changes during sepsis indicate that the availability of the amino acid l-arginine decreases. Availability of arginine may further decrease during reduced caloric intake, which thereby limits the adaptive response of arginine-nitric oxide metabolism during sepsis.

OBJECTIVE

We tested the hypothesis that reduced caloric intake during endotoxemia, as an experimental model for sepsis, further reduces arginine availability.

DESIGN

In a randomized trial, a 7-d reduced caloric intake feed regimen (RE; n = 9) was compared with a normal control feed regimen (CE; n = 9), before 24 h of endotoxemia, as a model for sepsis. Whole-body arginine-nitric oxide metabolism and protein metabolism were measured by using a stable-isotope infusion of [(15)N(2)]arginine, [(13)C-(2)H(2)]citrulline, [(2)H(5)]phenylalanine, and [(2)H(2)]tyrosine. Plasma pyruvate and lactate concentrations were determined by fully automated HPLC.

RESULTS

Pre-endotoxin arginine appearance was significantly lower in the RE group than in the CE group (P = 0.002). During endotoxemia, arginine appearance increased in the CE animals but not in the RE animals (P = 0.04). In addition, nitric oxide production was significantly lower in the RE animals (P < 0.0001). Protein synthesis was significantly lower at the start of endotoxin infusion (P < 0.05) and remained lower during endotoxemia in the RE group than in the CE group (P < 0.001). The lactate:pyruvate ratio was not higher in the RE group than in the CE group before endotoxemia but increased significantly during endotoxemia in the RE group (P = 0.04).

CONCLUSION

A well-nourished condition before prolonged endotoxemia results in a better ability to adapt to endotoxin-induced metabolic deterioration of arginine-nitric oxide metabolism than does reduced caloric intake before endotoxemia.

Pros and cons of L-arginine supplementation in disease

The amino acid arginine and one of its metabolites NO have gathered broad attention in the last decade. Although arginine is regarded as a conditionally essential amino acid in disease, L-arginine supplementation in severe illness has not found its way into clinical practice. This might be due to the invalid interpretation of results from studies with immune-enhancing diets containing L-arginine amongst other pharmaconutrients. However, not much attention is given to research using L-arginine as a monotherapy and the possibility of the alternative hypothesis: that L-arginine supplementation is beneficial in disease. The present review will discuss data from studies in healthy and diseased animals and patients with monotherapy of L-arginine to come to an objective overview of positive and negative aspects of L-arginine supplementation in disease with special emphasis on sepsis, cancer, liver failure and wound healing.

Exogenous arginine in sepsis

Sepsis is a severe condition in critically ill patients and is considered an arginine deficiency state. The rationale for arginine deficiency in sepsis is mainly based on the reduced arginine levels in sepsis that are associated with the specific changes in arginine metabolism related to endothelial dysfunction, severe catabolism, and worse outcome. Exogenous arginine supplementation in sepsis shows controversial results with only limited data in humans and variable results in animal models of sepsis. Since in these studies the severity of sepsis varies but also the route, timing, and dose of arginine, it is difficult to draw a definitive conclusion for sepsis in general without considering the influence of these factors. Enhanced nitric oxide production in sepsis is related to suggested detrimental effects on hemodynamic instability and enhanced oxidative stress. Potential mechanisms for beneficial effects of exogenous arginine in sepsis include enhanced (protein) metabolism, improved microcirculation and organ function, effects on immune function and antibacterial effects, improved gut function, and an antioxidant role of arginine. We recently performed a study indicating that arginine can be given to septic patients without major effects on hemodynamics, suggesting that more studies can be conducted on the effects of arginine supplementation in septic patients.

A multitracer stable isotope quantification of the effects of arginine intake on whole body arginine metabolism in neonatal piglets

We have previously shown that deficient arginine intake increased the rate of endogenous arginine synthesis from proline. In this paper, we report in vivo quantification of the effects of arginine intake on total endogenous arginine synthesis, on the rates of conversion between arginine, citrulline, ornithine, and proline, and on nitric oxide synthesis. Male piglets, with gastric catheters for diet and isotope infusion and femoral vein catheters for blood sampling, received a complete diet for 2 days and then either a generous (+Arg; 1.80 g x kg(-1) x day(-1); n = 5) or deficient (-Arg; 0.20 g.kg(-1).day(-1); n = 5) arginine diet for 5 days. On day 7, piglets received a primed, constant infusion of [guanido-(15)N(2)]arginine, [ureido-(13)C;5,5-(2)H(2)]citrulline, [U-(13)C(5)]ornithine, and [(15)N;U-(13)C(5)]proline in an integrated study of the metabolism of arginine and its precursors. Arginine synthesis (micromol x kg(-1) x h(-1)) from both proline (+Arg: 42, -Arg: 74, pooled SE: 5) and citrulline (+Arg: 67, -Arg: 120; pooled SE: 15) were higher in piglets receiving the -Arg diet (P < 0.05); and for both diets proline accounted for approximately 60% of total endogenous arginine synthesis. The conversion of proline to citrulline (+Arg: 39, -Arg: 67, pooled SE: 6) was similar to the proline-to-arginine conversion, confirming that citrulline formation limits arginine synthesis from proline in piglets. Nitric oxide synthesis (micromol x kg(-1) x h(-1)), measured by the rate conversion of [guanido-(15)N(2)]arginine to [ureido-(15)N]citrulline, was greater in piglets receiving the +Arg diet (105) than in those receiving the -Arg diet (46, pooled SE: 10; P < 0.05). This multi-isotope method successfully allowed many aspects of arginine metabolism to be quantified simultaneously in vivo.

Characterization of an animal model of severe sepsis associated with respiratory dysfunction

PURPOSE

Pathophysiological studies in humans regarding sepsis are difficult to perform due to ethical and methodological concerns. In this context, animal models of sepsis can be useful to better understand this condition and to test therapeutic strategies. The purpose of this study was to characterize a feasible and clinically relevant model of sepsis in pigs that could be useful for testing different therapeutic interventions.

METHODS

5 White Large pigs were anesthetized, arterial and pulmonary catheters were introduced, and sepsis was induced by fecal peritonitis. Several biochemical indicators of organ dysfunction and infectious parameters were measured. The pigs were monitored until death, when fragments of organs were removed for pathology. Three animals without peritonitis served as controls and were sacrificed 24 hours after surgery without developing significant changes in organ function.

RESULTS

Septic pigs survived 17 hours on average (range, 16-18 h), and Escherichia coli was recovered from blood cultures. They developed a significant decrease in left ventricular work and a nonsignificant reduction in mixed venous oxygen saturation. Respiratory dysfunction was characterized by a decrease in the PaO2/FiO2 ratio and respiratory compliance. Pathology of the lungs revealed areas of pulmonary collapse, hemorrhage, pulmonary congestion, and discrete neutrophil infiltrate.

CONCLUSIONS

Fecal peritonitis in pigs is a clinically relevant model of sepsis associated with acute lung injury without direct pulmonary insult. This model may prove to be useful for studying pathogenic aspects of secondary lung injury as well as for validating ventilatory or pharmacologic interventions.

Plasma citrulline concentration: a reliable marker of small bowel absorptive capacity independent of intestinal inflammation

OBJECTIVES

Postabsorptive plasma citrulline concentration has been proposed as a reliable marker of small bowel absorptive capacity in short bowel patients. The aim of this study was to address the potentially confounding impact of intestinal inflammation.

METHODS

Fifty-five patients were selected according to diagnosis, small bowel length, and degree of bowel inflammation. (a) Crohn's disease (CD) with massive small bowel resection leaving </=50 cm (N = 6), (b) CD with 50-150 cm remaining (N = 9), (c) CD with no resection but active inflammation (high C-reactive protein [CRP] and Crohn's Disease Activity Index [CDAI] >220) (N = 7), (d) CD without resection or active inflammation (normal CRP and CDAI <150) (N = 9), (e) mesenteric infarction (MI) with resection leaving </=50 cm (N = 6), (f) MI leaving 50-150 cm (N = 6), (g) active celiac disease (N = 6), (h) healthy volunteers (N = 6). Postabsorptive fasting plasma citrulline was measured using reverse-phase, high performance liquid chromatography. Absorptive capacity and permeability were also measured after oral sugar-mix ingestion (5 g lactulose, 1 g L-rhamnose, 0.5 g D-xylose).

RESULTS

The plasma citrulline strongly correlated with small bowel length (P < 0.0001) and xylose absorption (P < 0.001). No correlation was found with CDAI, permeability, CRP, albumin, sedimentation rate, white cell count, or platelet count. Citrulline was significantly higher (P < 0.0004) in CD and MI patients with a remnant small bowel length of 50-150 cm (mean 21.0 micromol/L) than in those with length </=50 cm (mean 9.2 micromol/L).

CONCLUSIONS

Plasma citrulline concentration is a simple and reliable surrogate for small bowel absorptive capacity and is not influenced by intestinal inflammation.

Biomarkers of arginine and lysine excess

Arginine supplementation is used in several disease states. In arginine-deficient states, supplementation is a logical choice of therapy. However, the definition of an arginine-deficient state is complex. For example, plasma arginine levels could be within normal range but intracellular arginine levels could be reduced because of membrane transport problems. Lysine competes with arginine for transport into the cell. In these situations, arginine supplementation of higher than required levels is proposed. Arginine has several important functions in metabolism as it is a precursor of metabolically active components such as nitric oxide (NO), ornithine, creatine, and polyamines. Supplementing arginine in excess could potentially overstimulate metabolism via enhanced production of NO. NO is a reactive component that, via production of radicals, will inactivate proteins. NO is also a powerful vasodilator, which could lead to severe hemodynamic instability. A good marker for excess supplementation of arginine or lysine could be an increased or reduced production rate of NO. However, NO production is difficult to measure because NO is a very labile component and is rapidly oxidized in blood. Stable isotope-labeled arginine and citrulline are used to trace the arginine-NO route. During supplementation of arginine in septic pigs or patients in septic shock, NO production, measured with stable isotope technology, is enhanced.

Methods using stable isotopes to measure nitric oxide (NO) synthesis in the l-arginine/NO pathway in health and disease

Nitric oxide (NO) is an important gaseous radical involved in many physiological processes. It is produced from the amino acid L-arginine by the action of nitric oxide synthases (NOS) in what is called the L-arginine/NO pathway. Tracking its metabolic fate in biological fluids is of particular interest as it may indicate how the human body responds in health and disease. However, due to its short life span (a few seconds) it is very difficult to accurately monitor any up- or down-regulation in body fluids in vivo. As a consequence, methods have been developed based on the measurement of the NO-derived products nitrite and nitrate or on the substrate of NO, L-arginine and its simultaneously generated product, L-citrulline. Considering only a fraction of the endogenous L-arginine pool is used for the synthesis of NO, NO-production cannot be estimated by measuring changes in the concentrations of L-arginine and/or L-citrulline alone. Instead, to estimate NO-related changes in the L-arginine and/or L-citrulline pools a form of tagging these metabolites for the NOS-mediated reaction is required. The application of stable isotopes is an elegant way to track NOS-mediated changes. The present paper is focussed on the application of various combinations of chromatography and mass spectrometry to measure isotopic enrichments resulting from the conversion of L-arginine to NO and L-citrulline in a one-to-one stoichiometry. In addition, the various aspects and principles involved in the application of stable isotopes in metabolic studies in general and the study of the activity of NOS in particular are discussed.

A proteomic analysis of liver mitochondria during acute endotoxemia

OBJECTIVE

Accumulating evidence indicates that mitochondrial function is impaired in vital organs during sepsis. In addition to oxidative phosphorylation, mitochondria participate in diverse cellular functions ranging from protein and lipid metabolism to programmed cell death. We analyzed liver mitochondrial protein expression patterns (i.e., proteomics) during acute endotoxemia to discover novel insights into mitochondrial responses to acute systemic inflammation.

DESIGN

A normotensive endotoxemia model was employed in which altered mitochondrial morphology occurs under conditions minimizing the potentially confounding effects of tissue hypoxia and acidosis.

SETTING

University medical research laboratory.

SUBJECTS

Random-source, adult, male cats.

INTERVENTIONS

Hemodynamic resuscitation and maintenance of acid-base balance and tissue oxygen availability were provided to preserve baseline homeostatic conditions. Treatment groups received isotonic saline vehicle (control; n = 5) or endotoxin (lipopolysaccharide, LPS, at 3.0 mg/kg intravenously; n = 5]. Liver samples were obtained 4 h posttreatment, and mitochondrial proteins were isolated and quantitatively compared using two-dimensional gel electrophoresis. Differentially expressed proteins (> 1.5-fold change relative to controls) were identified using mass spectrometry.

MEASUREMENTS AND RESULTS

Among over 500 protein spots that were separated 14 were differentially expressed in mitochondria of LPS-treated animals relative to matching controls. Spectrometric analyses demonstrated increased expression of urea cycle enzymes, heat shock protein (HSP) 60 and manganese superoxide dismutase, whereas expression of HSP70, F(1)-ATPase and key enzymes regulating lipid metabolism was reduced.

CONCLUSIONS

Considering the known functions of each of the proteins exhibiting altered expression, it is likely that the observed changes in liver mitochondrial protein expression are reflective of significant changes in mitochondrial function in response to endotoxemia.

Measuring splanchnic amino acid metabolism in vivo using stable isotopic tracers1,2

The splanchnic bed comprises the liver and the portal-drained viscera (PDV). The PDV, which include the stomach, intestines, pancreas, and spleen, represent 4 to 6% of BW, yet they account for 20 to 35% of whole-body protein turnover and energy expenditure. Because the PDV are the first to be exposed to the diet, their nutrient needs are met first. Consequently, the extraction of dietary nutrients, especially AA, by the intestine will have a critical influence on their availability to peripheral tissues and therefore, on whole body requirements. Moreover, the systemic availability of dietary AA is a key determinant of lean body growth rate. A complicating factor in the measurement of intestinal nutrient use is that the intestinal epithelial cells receive nutrients from 2 sources: the diet and the arterial circulation. However, combining measurements of the net portal balance with those of isotopic enrichments from enterally and intravenously administered stable isotope-labeled AA provides an in vivo model that can be used to determine the proportion of AA extracted by the intestine from either source. Using this technique in fed animals demonstrated that the PDV contribute significantly to the use of essential (>60% of threonine) and nonessential (>90% of glutamate) AA provided by the diet. The relative use by the PDV of individual AA from the diet and arterial inputs varies widely, and dietary AA are the preferred fuel over dietary glucose. Stable isotope-labeled AA also enable the determination of the metabolic fate of individual AA. Using this technique, studies have shown that an insufficient protein supply or the mode of feeding affects AA use by the PDV, and consequently, may affect whole-body growth.

Nitric oxide synthase inhibition in sepsis? Lessons learned from large-animal studies

Nitric Oxide (NO) plays a controversial role in the pathophysiology of sepsis and septic shock. Its vasodilatory effects are well known, but it also has pro- and antiinflammatory properties, assumes crucial importance in antimicrobial host defense, may act as an oxidant as well as an antioxidant, and is said to be a "vital poison" for the immune and inflammatory network. Large amounts of NO and peroxynitrite are responsible for hypotension, vasoplegia, cellular suffocation, apoptosis, lactic acidosis, and ultimately multiorgan failure. Therefore, NO synthase (NOS) inhibitors were developed to reverse the deleterious effects of NO. Studies using these compounds have not met with uniform success however, and a trial using the nonselective NOS inhibitor N(G)-methyl-l-arginine hydrochloride was terminated prematurely because of increased mortality in the treatment arm despite improved shock resolution. Thus, the issue of NOS inhibition in sepsis remains a matter of debate. Several publications have emphasized the differences concerning clinical applicability of data obtained from unresuscitated, hypodynamic rodent models using a pretreatment approach versus resuscitated, hyperdynamic models in high-order species using posttreatment approaches. Therefore, the present review focuses on clinically relevant large-animal studies of endotoxin or living bacteria-induced, hyperdynamic models of sepsis that integrate standard day-to-day care resuscitative measures.

The role of arginine in infection and sepsis

Sepsis is a systemic response to an infection, with high morbidity and mortality rates. Metabolic changes during infection and sepsis could be related to changes in metabolism of the amino acid L-arginine. In sepsis, protein breakdown is increased, which is a key process to maintain arginine delivery because both endogenous de novo arginine production from citrulline and food intake are reduced. Arginine catabolism, on the other hand, is markedly increased by enhanced use of arginine via the arginase and nitric oxide pathways. As a result, lowered plasma arginine levels are usually found. Arginine may therefore be considered as an essential amino acid in sepsis, and supplementation could be beneficial in sepsis by improving microcirculation and protein anabolism. L-Arginine supplementation in a hyperdynamic pig model of sepsis prohibits the increase in pulmonary arterial blood pressure, improves muscle and liver protein metabolism, and restores the intestinal motility pattern. Arguments raised against arginine supplementation are mainly pointed at stimulating nitric oxide (NO) production, with concerns about toxicity of increased NO and hemodynamic instability with refractory hypotension. NO synthase inhibition, however, increased mortality. Arginine supplementation in septic patients has transient effects on hemodynamics when supplied as a bolus but seems without hemodynamic side effects when supplied continuously. In conclusion, arginine could have an essential role in infection and sepsis.

Effects of long-term intravenous and intragastric L-arginine intervention on jejunal motility and visceral nitric oxide production in the hyperdynamic compensated endotoxaemic pig

Alterations in L-arginine availability and nitric oxide (NO) synthesis in the intestinal muscularis may contribute to disturbed small intestinal motility that is observed during endotoxaemia. The aim of this study was to evaluate the effect of L-arginine infusion on visceral NO production and jejunal motility in hyperdynamic compensated endotoxaemic pigs. Fasted and saline-resuscitated pigs were intravenously infused for 24 h with endotoxin (lipopolysaccharide, 50 ng kg(-1) min(-1)) or saline (n = 6). Endotoxaemic pigs received either intravenous L-arginine (n = 6, 5.3 micromol kg(-1) min(-1)) or L-alanine (isocaloric, n = 6). After 24 h, intravenous L-arginine or L-alanine infusion was continued intragastrically for 32-h in an enteral meal. During (0-24 h) and 1 day postendotoxaemia (48-56 h), jejunal motility was recorded by manometry and analysed for migrating motor complex (MMC) characteristics. Visceral NO production was measured at 24 and 48 h by 15N2-arginine-to-15N-citrulline conversion. Visceral NO production was increased during endotoxaemia and was higher in L-arginine than in L-alanine-treated pigs. One day postendotoxaemia, visceral NO synthesis was still increased in L-arginine but not in L-alanine-treated animals. Endotoxaemia shortened the MMC cycle duration and accelerated the MMC propagation velocity. Both were restored by L-arginine. Similar motility disturbances were observed one day postendotoxaemia and were also compensated by L-arginine infusion.

Sepsis: an arginine deficiency state?

OBJECTIVE

Sepsis is a major health problem considering its significant morbidity and mortality rate. The amino acid L-arginine has recently received substantial attention in relation to human sepsis. However, knowledge of arginine metabolism during sepsis is limited. Therefore, we reviewed the current knowledge about arginine metabolism in sepsis.

DATA SOURCE

This review summarizes the literature on arginine metabolism both in general and in relation to sepsis. Moreover, arginine-related therapies are reviewed and discussed, which includes therapies of both nitric oxide (NO) and arginine administration and therapies directed toward inhibition of NO.

DATA

In sepsis, protein breakdown is increased, which is a key process to maintain arginine delivery, because both endogenous de novo production from citrulline and food intake are reduced. Arginine catabolism, on the other hand, is markedly increased by enhanced use of arginine in the arginase and NO pathways. As a result, lowered plasma arginine levels are usually found. Clinical symptoms of sepsis that are related to changes in arginine metabolism are mainly related to hemodynamic alterations and diminished microcirculation. NO administration and arginine supplementation as a monotherapy demonstrated beneficial effects, whereas nonselective NO synthase inhibition seemed not to be beneficial, and selective NO synthase 2 inhibition was not beneficial overall.

CONCLUSIONS

Because sepsis has all the characteristics of an arginine-deficiency state, we hypothesise that arginine supplementation is a logical option in the treatment of sepsis. This is supported by substantial experimental and clinical data on NO donors and NO inhibitors. However, further evidence is required to prove our hypothesis.

In vivo whole body and organ arginine metabolism during endotoxemia (sepsis) is dependent on mouse strain and gender

Arginine metabolism involves various organs such as the kidney, the intestines, and the liver, which act together in an interorgan axis. Major pathways for arginine production are protein breakdown and de novo arginine production from citrulline; disposal of arginine is mainly used for protein synthesis or used by the enzymes arginase and nitric oxide synthase (NOS). To assess in vivo organ arginine metabolism under normal conditions and during endotoxemia we used a mouse model, and analyzed for gender and strain differences. Male and female inbred FVB and C57BL6/J mice were anesthetized and catheterized to study whole body, gut, liver, renal and muscle metabolism, using a stable isotope infusion protocol. Animals were treated with saline or lipopolysaccharide. Plasma arginine levels tended to be higher in female mice, although levels were not significantly different from male mice (P = 0.09). Although not all significantly different, whole body arginine production and arginine clearance tended to be higher in C57BL6/J mice (P < 0.1), while citrulline (P = 0.05), NO (P = 0.08), and de novo arginine (P < 0.01) production were higher in FVB mice. During endotoxemia, NO production increased in general (P < 0.05), while whole body arginine clearance increased in FVB mice, but decreased in C57BL6/J mice (P < 0.01). At the organ level, portal-drained viscera (PDV) arginine metabolism was higher in FVB than in C57BL6/J mice (P < 0.05). During endotoxemia, liver arginine metabolism decreased in general (P < 0.05), while strain differences existed for PDV, muscle, and renal arginine metabolism. In conclusion, stable isotope techniques in multicatheterized mice allow measurements of arginine metabolism on whole body and organ level. Strain and gender differences are present in arginine metabolism under physiological conditions and during endotoxemia.

SELECTIVE INDUCIBLE NITRIC OXIDE SYNTHASE INHIBITION DURING LONG-TERM HYPERDYNAMIC PORCINE BACTEREMIA

We have recently demonstrated that selective inducible nitric oxide (NO) synthase (iNOS) inhibition with 1400W attenuated the hemodynamic and metabolic alterations affiliated with hyperdynamic porcine endotoxemia. In contrast to endotoxemia, limited evidence is available to document a relationship between NO and organ dysfunction in large animal bacteremic models. Therefore, using the same experimental setup, we investigated the role of selective iNOS blockade in porcine bacteremia induced and maintained for 24 h with a continuous infusion of live Pseudomonas aeruginosa. After 12 h of sepsis, animals received either vehicle (Control, n = 8) or continuous infusion of selective iNOS inhibitor, L-N6-(1-iminoethyl)-lysine (L-NIL; n = 8). Measurements were performed before, and 12, 18, and 24 h after P. aeruginosa infusion. L-NIL inhibited sepsis-induced increase in plasma nitrate/nitrite concentrations and prevented hypotension without affecting cardiac output. Despite comparable hepatosplanchnic macrocirculation, L-NIL blunted the progressive deterioration in ileal mucosal microcirculation and prevented mucosal acidosis. L-NIL largely attenuated mesenteric and hepatic venous acidosis, significantly improved P. aeruginosa-induced impairment of hepatosplanchnic redox state, and mitigated the decline in liver lactate clearance. Furthermore, the administration of L-NIL reduced the hepatocellular injury and prevented the development of renal dysfunction. Finally, treatment with L-NIL significantly attenuated the formation of 8-isoprostane concentrations, a direct marker of lipid peroxidation. Thus, selective iNOS inhibition with L-NIL prevented live bacteria from causing key features of metabolic derangements in porcine hyperdynamic sepsis. Underlying mechanisms probably include reduced oxidative stress with improved microcirculatory perfusion and restoration of cellular respiration.

Proteins and amino acids in enteral nutrition

PURPOSE OF REVIEW

This review reports recent findings on the effect of enterally fed protein and amino acids on metabolism, function, and clinical outcome, particularly during the neonatal period.

RECENT FINDINGS

Splanchnic tissues metabolize significant proportions of some enteral amino acids and this likely contributes to the higher requirement for these amino acids when they are provided enterally versus parenterally. Splanchnic tissues are particularly key in the provision of nutrition to preterm infants, who possess an exceedingly high protein anabolic drive, but limited tolerance to aggressive enteral feeding. The protein anabolic response to specific proteins is influenced by the rate of digestion and the pattern of feeding, as well as the amino acid composition of the proteins. The post-prandial rise in amino acids and insulin stimulates neonatal tissue protein synthesis by modulation of the nutrient and insulin signaling pathways that lead to translation initiation. A flurry of investigations into the metabolic response and clinical impact of individual amino acids suggests that leucine, glutamine, and arginine, in particular, have specific roles in regulating protein synthesis and immune function.

SUMMARY

Recent findings suggest that enteral nutrition support that provides an optimum combination of proteins and amino acids can have a beneficial impact on the clinical outcome of patients.