Endotoxemia affects organ protein metabolism differently during prolonged feeding in pigs

Effects of acute intravenous lipopolysaccharide administration on the plasma lipidome and metabolome in lactating Holstein cows experiencing hyperlipidemia

INTRODUCTION

The effects of lipopolysaccharides (i.e., endotoxin; LPS) on metabolism are poorly defined in lactating dairy cattle experiencing hyperlipidemia.

OBJECTIVES

Our objective was to explore the effects of acute intravenous LPS administration on metabolism in late-lactation Holstein cows experiencing hyperlipidemia induced by intravenous triglyceride infusion and feed restriction.

METHODS

Ten non-pregnant lactating Holstein cows (273 ± 35 d in milk) were administered a single bolus of saline (3 mL of saline; n [Formula: see text] 5) or LPS (0.375 [Formula: see text]g of LPS/kg of body weight; n [Formula: see text] 5). Simultaneously, cows were intravenously infused a triglyceride emulsion and feed restricted for 16 h to induce hyperlipidemia in an attempt to model the periparturient period. Blood was sampled at routine intervals. Changes in circulating total fatty acid concentrations and inflammatory parameters were measured. Plasma samples were analyzed using untargeted lipidomics and metabolomics.

RESULTS

Endotoxin increased circulating serum amyloid A, LPS-binding protein, and cortisol concentrations. Endotoxin administration decreased plasma lysophosphatidylcholine (LPC) concentrations and increased select plasma ceramide concentrations. These outcomes suggest modulation of the immune response and insulin action. Lipopolysaccharide decreased the ratio of phosphatidylcholine to phosphatidylethanomanine, which potentially indicate a decrease in the hepatic activation of phosphatidylethanolamine N-methyltransferase and triglyceride export. Endotoxin administration also increased plasma concentrations of pyruvic and lactic acids, and decreased plasma citric acid concentrations, which implicate the upregulation of glycolysis and downregulation of the citric acid cycle (i.e., the Warburg effect), potentially in leukocytes.

CONCLUSION

Acute intravenous LPS administration decreased circulating LPC concentrations, modified ceramide and glycerophospholipid concentrations, and influenced intermediary metabolism in dairy cows experiencing hyperlipidemia.

The Amino Acids Sensing and Utilization in Response to Dietary Aromatic Amino Acid Supplementation in LPS-Induced Inflammation Piglet Model

Dietary supplementation with aromatic amino acids (AAAs) has been demonstrated to alleviate intestinal inflammation induced by lipopolysaccharide (LPS) in the piglets. But the mechanism of AAA sensing and utilization under inflammatory conditions is not well-understood. The study was conducted with 32 weanling piglets using a 2 × 2 factorial arrangement (diet and LPS challenge) in a randomized complete block design. Piglets were fed as basal diet or the basal diet supplemented with 0.16% tryptophan (Trp), 0.41% phenylalanine (Phe), and 0.22% tyrosine (Tyr) for 21 days. The results showed that LPS treatment significantly reduced the concentrations of cholecystokinin (CCK) and total protein but increased leptin concentration, the activities of alanine transaminase, and aspartate aminotransferase in serum. Dietary supplementation with AAAs significantly increased the serum concentrations of CCK, peptide YY (PYY), and total protein but decreased the blood urea nitrogen. LPS challenge reduced the ileal threonine (Thr) digestibility, as well as serum isoleucine (Ile) and Trp concentrations, but increased the serum concentrations of Phe, Thr, histidine (His), alanine (Ala), cysteine (Cys), and serine (Ser) (P < 0.05). The serum-free amino acid concentrations of His, lysine (Lys), arginine (Arg), Trp, Tyr, Cys, and the digestibilities of His, Lys, Arg, and Cys were significantly increased by feeding AAA diets (P < 0.05). Dietary AAA supplementation significantly increased the serum concentrations of Trp in LPS-challenged piglets (P < 0.05). In the jejunal mucosa, LPS increased the contents of Ala and Cys, and the mRNA expressions of solute carrier (SLC) transporters (i.e., SLC7A11, SLC16A10, SLC38A2, and SLC3A2), but decreased Lys and glutamine (Gln) contents, and SLC1A1 mRNA expression (P < 0.05). In the ileal mucosa, LPS challenge induced increasing in SLC7A11 and SLC38A2 and decreasing in SLC38A9 and SLC36A1 mRNA expressions, AAAs supplementation significantly decreased mucosal amino acid (AA) concentrations of methionine (Met), Arg, Ala, and Tyr, etc. (P < 0.05). And the interaction between AAAs supplementation and LPS challenge significantly altered the expressions of SLC36A1 and SLC38A9 mRNA (P < 0.05). Together, these findings indicated that AAAs supplementation promoted the AAs absorption and utilization in the small intestine of piglets and increased the mRNA expressions of SLC transports to meet the high demands for specific AAs in response to inflammation and immune response.

Immune and metabolic effects of rumen-protected methionine during a heat stress challenge in lactating Holstein cows

Multiparous, lactating Holstein cows (n = 32) were randomly assigned to one of two dietary treatments [TMR with rumen-protected Met (RPM) or TMR without RPM (CON)], and within each dietary treatment group cows were randomly assigned to one of two environmental treatment groups in a split-plot crossover design. In phase 1 (9 d), all cows were fed ad libitum and in thermoneutral conditions (TN). In phase 2 (9 d), group 1 (n = 16) was exposed to a heat stress (HS) challenge (HSC). Group 2 cows (n = 16) were pair-fed (PFTN) to HSC counterparts and remained in TN. After a 21-d washout period, the study was repeated (period 2) and the environmental treatments were inverted relative to treatments from phase 2 of period 1, while dietary treatments remained the same for each cow. During phase 1, cows in RPM had greater plasma Met concentration compared with cows in CON (59 and 30 µM, respectively; P < 0.001). Cows in PFTN had a greater decrease (P < 0.05) in plasma insulin than cows in HSC at 4 h (-2.7 µIU/mL vs. -0.7 µIU/mL) and 8 h (-7.7 µIU/mL vs. -0.4 µIU/mL) during phase 2. Compared with cows in PFTN, cows in HSC had an increase (P < 0.05) in plasma serum amyloid A (-59 µg/mL vs. +58 µg/mL), serum haptoglobin (-3 µg/mL vs. +33 µg/mL), plasma lipopolysaccharide binding protein (-0.27 and +0.11 µg/mL), and plasma interleukin-1β (-1.9 and +3.9 pg/mL) during phase 2. In conclusion, HSC elicited immunometabolic alterations; however, there were limited effects of RPM on cows in HSC.

Health risk assessment of heavy metals via consumption of dietary vegetables using wastewater for irrigation in Swabi, Khyber Pakhtunkhwa, Pakistan

Health assumptions to the population due to the utilization of contaminated vegetables have been a great concern all over the world. In this study, an investigation has been conducted to ascertain metal concentrations in the wastewater, soil and commonly consumed vegetables from the vicinity of Gadoon Industrial Estate Swabi, Khyber Pakhtunkhwa Pakistan. Physicochemical parameters such as pH, electrical conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS) and total solids (TS) and heavy metals such as Pb, Cr, Cd, Ni, Zn, Cu, Fe, Mn were determined using Atomic Absorption Spectrophotometer (AAS). Moreover, possible health risks due to the consumption of vegetables have also been estimated. pH and TSS in wastewater were found to be higher than the permissible limit set by WHO (1996). These results revealed that Cr concentration in the wastewater was above the permissible limits of United States Environmental Protection Agency (USEPA) which may lead to a detrimental effect on soil quality deterioration, ultimately leading to food contamination. ANOVA analysis demonstrated a significant difference in soil samples for Pb, Cr, Cd, Ni, Zn and Cu at p ≤ 0.001, for Mn at p ≤ 0.05 while no significant difference was observed for Fe respectively. ANOVA analysis also exhibited the highest mean value for Pb, Cr, Cd and Zn in vegetables. A substantial positive correlation was found among the soil and vegetable contamination. The transfer factor for Cr, Pb, Zn, Mn, Ni, Cd and Cu was greater than 0.5 due to contamination caused by domestic discharges and industrial effluents. Health assessment via consumption of dietary vegetables revealed a higher level than the permissible limit (HRI > 1) for Pb and Cd in children and adults. Enrichment factor (EF) due to consumption of vegetables was found higher for Pb and Cr respectively. Based on the findings of this study, there would be a significant risk to the consumers associated with consumptions of vegetables being cultivated in Gadoon Industrial Estate area of district Swabi. Therefore, strict regulatory control measures are highly recommended for the safety of vegetables originated from the study area.

Metabolic flux analysis of branched-chain amino and keto acids (BCAA, BCKA) and β-hydroxy β-methylbutyric acid across multiple organs in the pig

Branched-chain amino acids (BCAA) and their metabolites the branched-chain keto acids (BCKA) and β-hydroxy β-methylbutyric acid (HMB) are involved in the regulation of key signaling pathways in the anabolic response to a meal. However, their (inter)organ kinetics remain unclear. Therefore, branched-chain amino acids (BCAA) [leucine (Leu), valine (Val), isoleucine (Ile)], BCKA [α-ketoisocaproic acid (KIC), 3-methyl-2-oxovaleric acid (KMV), 2-oxoisovalerate (KIV)], and HMB across organ net fluxes were measured. In multi-catheterized pigs (n = 12, ±25 kg), net fluxes across liver, portal drained viscera (PDV), kidney, and hindquarter (HQ, muscle compartment) were measured before and 4 h after bolus feeding of a complete meal (30% daily intake) in conscious state. Arterial and venous plasma were collected and concentrations were measured by LC- or GC-MS/MS. Data are expressed as mean [95% CI] and significance (P < 0.05) from zero by the Wilcoxon Signed Rank Test. In the postabsorptive state (in nmol/kg body wt/min), the kidney takes up HMB (3.2[1.3,5.0]) . BCKA is taken up by PDV (144[13,216]) but no release by other organs. In the postprandial state, the total net fluxes over 4 h (in µmol/kg body wt/4 h) showed a release of all BCKA by HQ (46.2[34.2,58.2]), KIC by the PDV (12.3[7.0,17.6]), and KIV by the kidney (10.0[2.3,178]). HMB was released by the liver (0.76[0.49,1.0]). All BCKA were taken up by the liver (200[133,268]). Substantial differences are present in (inter)organ metabolism and transport among the BCAA and its metabolites BCKA and HMB. The presented data in a translation animal model are relevant for the future development of optimized clinical nutrition.NEW & NOTEWORTHY Branched-chain amino acids (BCAA) and their metabolites the branched-chain keto acids (BCKA) and β-hydroxy β-methylbutyric acid (HMB) are involved in the regulation of key signaling pathways in the anabolic response to a meal. Substantial differences are present in (inter)organ metabolism and transport among the BCAA and its metabolites BCKA and HMB. The presented data in a translation animal model are relevant for the future development of optimized clinical nutrition.

Amino Acids in Beef Cattle Nutrition and Production

Proteins have been recognized for a long time as an important dietary nutritional component for all animals. Most amino acids were isolated and characterized in the late nineteenth and early twentieth century. Initially dietary proteins were ranked high to low quality by growth and N balance studies. By the 1950s interest had shifted to studying the roles of individual amino acids in amino acid requirements by feeding studies with non-ruminants as rodents, poultry and pigs. The direct protein feeding approaches followed by measurements of nutritional outcomes were not possible however in ruminants (cattle and sheep). The development of measuring free amino acids by ion exchange chromatography enabled plasma amino acid analysis. It was thought that plasma amino acid profiles were useful in nutritional studies on proteins and amino acids. With non-ruminants, nutritional interpretations of plasma amino acid studies were possible. Unfortunately with beef cattle, protein/amino acid nutritional adequacy or requirements could not be routinely determined with plasma amino acid studies. In dairy cows, however, much valuable understanding was gained from amino acid studies. Concurrently, others studied amino acid transport in ruminant small intestines, the role of peptides in ruminant N metabolism, amino acid catabolism (in the animal) with emphasis on branched-chain amino acid catabolism. In addition, workable methodologies for studying protein turnover in ruminants were developed. By the 1990s, nutritionists could still not determine amino acid requirements with empirical experimental studies in beef cattle. Instead, computer software (expert systems) based on the accumulated knowledge in animal and ruminal amino acids, energy metabolism and protein production were realized and revised frequently. With these tools, the amino acid requirements, daily energy needs, ruminal and total gastrointestinal tract digestion and performance of growing beef cattle could be predicted.

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.

Immune System Stimulation Reduces the Efficiency of Whole-Body Protein Deposition and Alters Muscle Fiber Characteristics in Growing Pigs

Simple Summary

Disease reduces growth and protein retention in pigs. Protein retention is the balance between two energy-consuming processes in the body of pigs: protein synthesis and breakdown. Previous reports on the effects of disease on these components of protein metabolism and their consecutive effects on protein retention are inconsistent. In addition, limited information is available about the effects of disease on the composition of muscle fibers in pigs. Thus, we evaluated these parameters, since they help us to understand protein metabolism during disease in pigs. We used twelve gilts; five were used as a control and seven were made ill. Experimental diets were designed to supply nutrients that closely met the daily requirements of each group. Protein synthesis, protein breakdown, and protein retention were measured over 72 h. Pigs were then euthanized and various muscles were sampled. Our findings suggested that disease not only reduces protein retention by decreasing protein synthesis and protein breakdown, but also by reducing the efficiency of protein deposition. In other words, ill pigs synthesize more protein per unit of protein retention, compared to healthy pigs. In addition, disease reduces muscle mass and changes the composition of the muscle fibers. The latter might negatively affect pork quality.

Abstract

The effects of immune system stimulation (ISS), induced by repeated injection of Escherichia coli lipopolysaccharide, on the whole-body protein synthesis versus degradation rates, the efficiency of protein deposition (PD), and muscle fiber characteristics in pigs were evaluated. Twelve growing gilts were assigned to two levels of amino acid intake that was predicted based on the potential of each group’s health status for PD and feed intake. Isotope tracer, nitrogen balance, and immunohistochemical staining techniques were used to determine protein turnover, PD, and muscle fiber characteristics, respectively. Protein synthesis, degradation, and PD were lower in immune-challenged pigs than in control pigs (p < 0.05). Strong tendencies for a higher protein synthesis-to-PD ratio (p = 0.055) and a lower protein synthesis-to-degradation ratio (p = 0.065) were observed in immune-challenged pigs. A decrease in muscle cross-sectional area of fibers and a shift from myosin heavy chain (MHC)-II towards MHC-I fibers (p < 0.05) were observed in immune-challenged pigs. These results indicated that ISS reduces PD not only by suppressing the whole-body protein synthesis and degradation rates, but also by decreasing the efficiency of PD in growing pigs. In addition, ISS induces atrophy in skeletal muscles and favors a slow-twitch oxidative fiber type composition.

Inhibition of jejunal protein synthesis and breakdown in Pseudomonas aeruginosa-induced sepsis pig model

Maintenance of gut integrity has long been recognized as crucial for survival in sepsis, but alterations in protein metabolism have not previously been documented. Therefore, in the present study, we measured in a Pseudomonas aeruginosa-induced porcine sepsis model fractional protein synthesis (FSR) and breakdown rates (FBR) in jejunal mucosa in a fasted, conscious state. FSR was measured by the incorporation rate of stable tracer amino acid (l-[ring-¹³C₆]phenylalanine) into tissue protein. FBR was determined using the relation between blood arterial enrichment and intracellular enrichment of phenylalanine in consecutive mucosal biopsies after a pulse of l-[¹⁵N]phenylalanine. Additionally, we determined the FSR in jejunum, ileum, liver, muscle, and lung tissue. We found in this sham-controlled acute sepsis pig model (control: n = 9; sepsis: n = 13) that jejunal mucosal protein turnover is reduced with both decreased FSR (control: 3.29 ± 0.22; sepsis: 2.32 ± 0.12%/h, P = 0.0008) and FBR (control: 0.72 ± 0.12; sepsis: 0.34 ± 0.04%/h, P = 0.006). We also found that FSR was unchanged in ileum and muscle, whereas it was higher in the liver (control: 0.87 ± 0.05; sepsis: 1.05 ± 0.06%/h, P = 0.041). Our data, obtained with a translational acute sepsis model, suggest that jejunal mucosal protein metabolism is diminished in acute sepsis. Comparison with other tissues indicates that the most serious acute metabolic changes in sepsis occur in the jejunum rather than the muscle. NEW & NOTEWORTHY In a highly translational acute sepsis model, presented data suggest that jejunal mucosal protein metabolism is diminished in acute sepsis, even if the origin of the sepsis is not located in the gut. Comparison with other tissues indicates that the most serious acute changes in the protein synthesis rates in sepsis occur in the gut rather than the muscle. Therefore, we hypothesize that preventing a compromised gut is critical to maintain gut function during sepsis.

The Systemic Alterations of Lipids, Alanine-Glucose Cycle and Inter-Organ Amino Acid Metabolism in Swine Model Confirms the Role of Liver in Early Phase of Septic Shock

Septic shock is a medical emergency and is one of the main causes of mortality in critically ill patients. Given the pathophysiological complexity of sepsis spectrum and progression in clinical settings, animal models become essential tools to improve patient care, and to understand key mechanisms that may remain masked from the heterogeneity of clinical practice. Our aim was to verify whether the metabolic constellations we previously reported for septic shock patients appear also in our septic shock swine model as systemic markers of early disturbances in energy metabolism and hepatic homeostasis. Septic shock was induced in anesthetized, instrumented, and ventilated adult swines by polymicrobial peritonitis. Hemodynamic and serial measurements of arterial and mixed venous blood gasses were made. Laboratory measurements and mass spectrometry-based targeted quantitative plasma metabolomics were performed in blood samples collected at baseline, at shock and at fully resuscitation after fluids and vasopressors administration. Data elaboration was performed by multilevel and multivariate analysis. Changes in hemodynamic, blood chemistry, and inflammatory markers were in line with a septic shock phenotype. Time course alteration of systemic metabolites were characterized by marked decreased in phosphatidylcholines and lysophosphatidylcholines species, altered alanine-glucose cycle and inter-organ amino acid metabolism, pointing toward an early hepatic impairment similarly to what we previously reported for septic shock. This is the first study in which an experimental swine model of septic shock recapitulates the main metabolic derangements reported in a clinical setting of shock. These events occur within hours from infections and may act as early metabolic features to assist in evaluating subclinical hepatic alterations and pave the way to improve the management of septic shock.

Characteristics of a Pseudomonas aeruginosa induced porcine sepsis model for multi-organ metabolic flux measurements

Survival of sepsis is related to loss of muscle mass. Therefore, it is imperative to further define and understand the basic alterations in nutrient metabolism in order to improve targeted sepsis nutritional therapies. We developed and evaluated a controlled hyperdynamic severe sepsis pig model that can be used for in vivo multi-organ metabolic studies in a conscious state. In this catheterized pig model, bacteremia was induced intravenously with 109 CFU/h Pseudomonas aeruginosa (PA) in 13 pigs for 18 h. Both the PA and control (nine) animals received fluid resuscitation and were continuously monitored. We examined in detail their hemodynamics, blood gases, clinical chemistry, inflammation, histopathology and organ plasma flows. The systemic inflammatory response (SIRS) diagnostic scoring system was used to determine the clinical septic state. Within 6 h from the start of PA infusion, a septic state developed, as was reflected by hyperthermia and cardiovascular changes. After 12 h of PA infusion, severe sepsis was diagnosed. Disturbed cardiovascular function, decreased portal drained viscera plasma flow (control: 37.6 ± 4.6 mL/kg body weight (bw)/min; PA 20.3 ± 2.6 mL/kg bw/min, P < 0.001), as well as moderate villous injury in the small intestines were observed. No lung, kidney or liver failure was observed. Acute phase C-reactive protein (CRP) and interleukin-6 (IL-6) levels did not change in the PA group. However, significant metabolic changes such as enhanced protein breakdown, hypocalcemia and hypocholesterolemia were found. In conclusion, PA-induced bacteremia in a catheterized pig is a clinically relevant model for acute severe sepsis and enables the study of complex multi-organ metabolisms.

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.

Effect of supplemental dietary leucine and immune system stimulation on whole-body nitrogen utilization in starter pigs

The increase in circulating pro-inflammatory cytokines following an immune challenge (e.g., with bacterial lipopolysaccharide [LPS]) causes a disruption in normal AA metabolism and increases visceral protein synthesis at the expense of muscle protein synthesis. The objective of this study was to determine the effect of supplemental dietary Leu on the dynamics of whole body nitrogen (N) retention in starter pigs before and after immune system stimulation (ISS) induced by LPS. A total of 28 starter pigs (14.46 ± 0.73 kg BW) were assigned to isoenergetic and isonitrogenous diets formulated to supply essential AA 10% above estimated requirements for maximum whole-body protein deposition (PD) and to contain increasing amounts of Leu: CON (1.36% SID Leu); LEU-M (2.04% SID Leu); and LEU-H (2.72% SID Leu). Pigs were housed in metabolic crates, scale-fed every 4 h based on BW, and adjusted to dietary treatments for 5 d. The 108-h N-balance experiment was divided into two periods: prechallenge (before LPS challenge; six 12-h collections) and challenge (after LPS challenge; three 12-h collections) periods. In both periods, blood was collected to determine plasma AA and urea N concentrations. At the start of the challenge period, one-half of the pigs fed CON and all pigs fed LEU-M and LEU-H were challenged with LPS (ISS+; 30 µg/kg injected intramuscularly); the remaining pigs fed CON were injected with saline (ISS-). Whole-body N retention was determined during subsequent 12-h collections. Plasma free Leu concentration increased linearly with increasing Leu content in the diet before LPS was administered (CON, 124 µmol/L; LEU-M, 185 µmol/L; LEU-H, 227 µmol/L; < 0.01). During the prechallenge period, N retention was lower in pigs fed LEU-M ( < 0.01) and there was no difference between pigs fed CON and LEU-H (7.91, 7.18, and 7.71 g/12 h for CON, LEU-M, and LEU-H, respectively). During the challenge period, N retention in pigs fed CON was higher in ISS- than ISS+ (5.37 vs. 3.83 g/12 h; < 0.01) but was not affected by diet in ISS+ pigs (3.83, 3.21, and 3.45 g/12 h for CON, LEU-M, and LEU-H, respectively; > 0.10). In healthy pigs, feeding a high excess of dietary Leu induced an anabolic response to compensate for reduced N retention that occurred in pigs fed an intermediate excess of dietary Leu. There was no effect of supplemental Leu on N retention in pigs after an LPS challenge.

Dietary Leucine Supplementation Decreases Whole-Body Protein Turnover before, but Not during, Immune System Stimulation in Pigs

BACKGROUND

Immune system stimulation (ISS) adversely affects protein metabolism and reduces pig productivity. Leu has a regulatory role in skeletal muscle and whole-body protein turnover, which may be affected by ISS.

OBJECTIVE

We sought to determine the effect of supplemental Leu intake on whole-body protein turnover in pigs before and during ISS.

METHODS

Pigs [mean ± SD initial body weight (BW): 10.6 ± 1.1 kg] were surgically fitted with jugular vein catheters and assigned to 1 of 3 treatments: 1.36% standardized ileal-digestible (SID) Leu (CON; n = 13); 2.04% SID Leu (LEU-M; n = 8); and 2.72% SID Leu (LEU-H; n = 7). Pigs were infused continuously with 0.66 ± 0.05 mmol ¹⁵N ⋅ kg BW^-1 ⋅ d^-1 to determine whole-body protein kinetics. The study consisted of a 72-h prechallenge period followed by a 36-h challenge period. At the start of the challenge period, ISS was induced in all LEU-M and LEU-H pigs and half of the CON pigs with LPS (ISS+); the remaining CON pigs were administered saline (ISS-).

RESULTS

Whole-body protein synthesis (309, 273, and 260 ± 14 mmol N ⋅ kg BW^-1 ⋅ d^-1 for CON, LEU-M, and LEU-H pigs, respectively) and protein degradation (233, 203, and 185 ± 14 mmol N ⋅ kg BW^-1 ⋅ d^-1 for CON, LEU-M, and LEU-H pigs, respectively) were reduced with increasing Leu intake during the prechallenge period (P < 0.05). ISS reduced whole-body protein synthesis (203 compared with 169 ± 12 mmol N ⋅ kg BW^-1 ⋅ d^-1 for ISS- and ISS+ pigs fed CON, respectively; P < 0.05) and protein deposition (PD) (64.9 compared with 45.0 ± 2.9 mmol N ⋅ kg BW^-1 ⋅ d^-1 for ISS- and ISS+ pigs fed CON, respectively; P < 0.01), whereas ISS did not affect whole-body protein degradation. Leu intake did not affect whole-body protein synthesis or degradation in ISS+ pigs.

CONCLUSIONS

Our results indicate that supplemental Leu intake improves the efficiency of PD rather than PD directly in healthy pigs but did not affect whole-body protein turnover during ISS.

Whole-body and splanchnic amino acid metabolism in sheep during an acute endotoxin challenge

Supplemented protein or specific amino acids (AA) are proposed to help animals combat infection and inflammation. The current study investigates whole-body and splanchnic tissue metabolism in response to a lipopolysaccharide (LPS) challenge with or without a supplement of six AA (cysteine, glutamine, methionine, proline, serine and threonine). Eight sheep were surgically prepared with vascular catheters across the gut and liver. On two occasions, four sheep were infused through the jugular vein for 20 h with either saline or LPS from Escherichia coli (2 ng/kg body weight per min) in a random order, plus saline infused into the mesenteric vein; the other four sheep were treated with saline or LPS plus saline or six AA infused via the jugular vein into the mesenteric vein. Whole-body AA irreversible loss rate (ILR) and tissue protein metabolism were monitored by infusion of [ring-2H2]phenylalanine. LPS increased (P<0·001) ILR (+17 %), total plasma protein synthesis (+14 %) and lymphocyte protein synthesis (+386 %) but decreased albumin synthesis (-53 %, P=0·001), with no effect of AA infusion. Absorption of dietary AA was not reduced by LPS, except for glutamine. LPS increased the hepatic removal of leucine, lysine, glutamine and proline. Absolute hepatic extraction of supplemented AA increased, but, except for glutamine, this was less than the amount infused. This increased net appearance across the splanchnic bed restored arterial concentrations of five AA to, or above, values for the saline-infused period. Infusion of key AA does not appear to alter the acute period of endotoxaemic response, but it may have benefits for the chronic or recovery phases.

Enhanced Lacto-Tri-Peptide Bio-Availability by Co-Ingestion of Macronutrients

Some food-derived peptides possess bioactive properties, and may affect health positively. For example, the C-terminal lacto-tri-peptides Ile-Pro-Pro (IPP), Leu-Pro-Pro (LPP) and Val-Pro-Pro (VPP) (together named here XPP) are described to lower blood pressure. The bioactivity depends on their availability at the site of action. Quantitative trans-organ availability/kinetic measurements will provide more insight in C-terminal tri-peptides behavior in the body. We hypothesize that the composition of the meal will modify their systemic availability. We studied trans-organ XPP fluxes in catheterized pigs (25 kg; n=10) to determine systemic and portal availability, as well as renal and hepatic uptake of a water-based single dose of synthetic XPP and a XPP containing protein matrix (casein hydrolyte, CasH). In a second experiment (n=10), we compared the CasH-containing protein matrix with a CasH-containing meal matrix and the modifying effects of macronutrients in a meal on the availability (high carbohydrates, low quality protein, high fat, and fiber). Portal availability of synthetic XPP was 0.08 ± 0.01% of intake and increased when a protein matrix was present (respectively 3.1, 1.8 and 83 times for IPP, LPP and VPP). Difference between individual XPP was probably due to release from longer peptides. CasH prolonged portal bioavailability with 18 min (absorption half-life, synthetic XPP: 15 ± 2 min, CasH: 33 ± 3 min, p<0.0001) and increased systemic elimination with 20 min (synthetic XPP: 12 ± 2 min; CasH: 32 ± 3 min, p<0.0001). Subsequent renal and hepatic uptake is about 75% of the portal release. A meal containing CasH, increased portal 1.8 and systemic bioavailability 1.2 times. Low protein quality and fiber increased XPP systemic bioavailability further (respectively 1.5 and 1.4 times). We conclude that the amount and quality of the protein, and the presence of fiber in a meal, are the main factors that increase the systemic bioavailability of food-derived XPP.

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.

Consequences of age-related splanchnic sequestration of leucine on interorgan glutamine metabolism in old rats

Dietary leucine (Leu) serves as a nitrogen donor for de novo glutamine (Gln) synthesis in muscle. However, aging is characterized by an increase in the splanchnic extraction of Leu (SPELeu), i.e., splanchnic sequestration (SSLeu), which may affect muscle Gln metabolism and its subsequent homeostasis at the whole-body level. The aim of the work was to assess the effect of age-related SSLeu on Gln metabolism in the muscle, gut, liver, kidney, and Gln exchanges among these organs during fed conditions. Young-adult (3-mo-old) or aged (24-mo-old), male Sprague-Dawley rats were studied during fed condition [infusion of amino acids (AA) into the duodenum from time 0 min (T0) to T60] under anesthesia. L-[5-15N]Gln and L[1-13C]Leu were infused into the jugular vein and L-[5,5,5-2H3]Leu into the duodenum. At T60, blood samples were taken from carotid artery, portal vein, hepatic vein, renal vein, and inferior vena cava for tracer-tracee ratio and AA level measurements. SSLeu was observed in old rats and was negatively correlated with muscle Gln production ( r = −0.501, P < 0.01). In addition, reduced Gln muscle release in old rats was accompanied by reduced Gln uptake by the gut and kidney. However, net Gln balance across organs was not different between young adult and old rats. During fed conditions in old rats, muscle Gln production and release are reduced in relation to the observed, increased SPELeu and reduced renal and intestinal Gln uptake to maintain whole-body Gln homeostasis. Our results demonstrate the existence of an age-related change of interorgan Gln metabolism, which may be, in part, driven by SSLeu.

Interactions of deoxynivalenol and lipopolysaccharides on tissue protein synthesis in pigs

Possible interactions between the Fusarium toxin deoxynivalenol and lipopolysaccharides on in vivo protein synthesis were investigated in selected porcine tissues. A total of 36 male castrated pigs (initial weight of 26 kg) were used. 24 pigs were fed a control diet and 12 a Fusarium-contaminated diet (chronic oral deoxynivalenol, 3.1 mg/kg diet) for 37 days. Tissue protein synthesis was measured in pigs fed control diet after intravenous infusion of deoxynivalenol (100 µg/kg live weight/h), lipopolysaccharides (7.5 µg/kg live weight/h) or a combination of both compounds on the day of the measurements, while six pigs from the chronic oral deoxynivalenol group were intravenously treated with lipopolysaccharides (7.5 µg/kg live weight/h). Deoxynivalenol challenge alone failed to alter protein synthesis parameters. Fractional protein synthesis rates were exclusively reduced in liver, spleen and small intestine of lipopolysaccharides-treated pigs. Intravenous deoxynivalenol co-exposure enhanced the impacts of lipopolysaccharides on protein synthesis parameters in the spleen and the small intestine to some extent, while a chronic oral pre-exposure with deoxynivalenol relieved its effects in the spleen. Whether these interactions occur in other tissues and under other study conditions, especially toxin doses and route of entry into the body, needs to be examined further.

Preparation of immunomodulatory hydrolysates from Alaska pollock frame

BACKGROUND

Immunomodulatory peptides can enhance body immunity. There have been few systematic investigations on preparing immunomodulatory peptides from Alaska pollock frame. The aim of this study was to obtain such peptides from Alaska pollock frame and determine their properties.

RESULTS

Trypsin protein hydrolysate (TPH) significantly enhanced the proliferation of spleen lymphocytes, T cells and peritoneal macrophages (P < 0.05). Compared with TPH with molecular weight (MW) > 2 kDa, TPH with MW < 2 kDa showed higher lymphocyte proliferation activity at 10, 50 and 500 µg ml(-1). The optimised hydrolysis conditions were a temperature of 50 °C, an enzyme dose of 24 U mg(-1) and a time of 290 min. The proliferation rate and degree of hydrolysis were 28.45 ± 1.79% and 16.87 ± 0.15% respectively. The main amino acids in TPH were proline, aspartate, glutamic acid and leucine. TPH had high solubility and low viscosity. TPH showed high stability under both acid and alkaline conditions or when digested by trypsin and/or pepsin.

CONCLUSION

TPH showed high immunomodulatory activity, with molecular weight and amino acid composition being the important factors affecting this activity. TPH had high solubility, low viscosity and high stability. As a good immunomodulator, TPH may therefore have wide application.

Have we enough glutamine and how does it work? A clinician's view

There is a gap between the scientific basis of the claim that in several disease states glutamine is lacking and the widespread belief that supplementation of glutamine to the nutritional regimen is beneficial in severely ill patients. Glutamine shortage exists when consuming tissues, playing a crucial role in the response to trauma and disease, receive insufficient amounts of glutamine. In these tissues (immune system, wound), glutamine is only partly oxidized but has more specific roles as nontoxic nitrogen carrier, precursor of several crucial metabolites required for cell proliferation and for maintenance of the redox potential, and as osmolyte. In inflammatory states, glutamine concentrations in plasma and tissues are decreased due to many disease-related factors, precluding its use as a reliable indicator of shortage. Isotope studies have yielded equivocal results, precluding their use as a reliable indicator of glutamine shortage or adequacy. The increase in the net release of glutamine from peripheral tissues to central tissues (immune system, liver, spleen, wound) in inflammatory states provides a better basis for the necessity to supplement the organism with extra glutamine in these conditions. Glutamine supplementation was beneficial in a few studies in burn or trauma patients. The clinical benefit of parenteral glutamine supplementation in patients with severe inflammation has been demonstrated more convincingly. The amounts of glutamine supplemented approximate the amounts released by peripheral tissues and utilized by central organs operative in host defense and are therefore in the physiological range.

Features, causes and consequences of splanchnic sequestration of amino acid in old rats

Rationale

In elderly subjects, splanchnic extraction of amino acids (AA) increases during meals in a process known as splanchnic sequestration of amino acids (SSAA). This process potentially contributes to the age-related progressive decline in muscle mass via reduced peripheral availability of dietary AA. SSAA mechanisms are unknown but may involve an increased net utilization of ingested AA in the splanchnic area.

Objectives

Using stable isotope methodology in fed adult and old rats to provide insight into age-related SSAA using three hypotheses: 1) an increase in protein synthesis in the gut and/or the liver, 2) an increase in AA oxidation related to an increased ureagenesis, and 3) Kupffer cell (KC) activation consequently to age-related low-grade inflammation.

Findings

Splanchnic extraction of Leu (SPELeu) was doubled in old rats compared to adult rats and was not changed after KC inactivation. No age-related effects on gut and liver protein synthesis were observed, but urea synthesis was lower in old rats and negatively correlated to liver Arg utilization. Net whole-body protein synthesis and arterial AA levels were lower in old rats and correlated negatively with SPELeu.

Conclusion

SSAA is not the consequence of age-related alterations in ureagenesis, gut or liver protein synthesis or of KC activity. However, SSAA may be related to reduced net whole-body protein synthesis and consequently to the reduced lean body mass that occurs during aging.

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.

Dangers, and benefits of the cytokine mediated response to injury and infection

The inflammatory response is essential for survival in an environment where continuous exposure to noxious events threaten the integrity of the organism. However, the beneficial effects of the response are influenced by factors, which disadvantage individuals within a population. These factors include malnutrition, infection, genotype, gender, pre-existing inflammation, and chronic intoxication. Although the inflammatory response is generally successful in dealing with noxious events, life-long exposure to these events takes its toll on the integrity of the body and becomes apparent as chronic disease, atherosclerosis, organ failure, and frailty. Progress in ameliorating the consequences of lifetime exposure to inflammatory events can only occur if a fuller understanding can be obtained of the factors, which influence the persistence and outcome of the inflammatory response at an individual level. A multitude of studies has shown that specific nutrients, diets, and dietary restriction are able to modulate the inflammatory response in the population as a whole. To advance in this area, precise knowledge is needed of how the disadvantageous factors, mentioned above, affect the individual's response to anti-inflammatory nutrients.

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.

Amino acids augment muscle protein synthesis in neonatal pigs during acute endotoxemia by stimulating mTOR-dependent translation initiation

In skeletal muscle of adults, sepsis reduces protein synthesis by depressing translation initiation and induces resistance to branched-chain amino acid stimulation. Normal neonates maintain a high basal muscle protein synthesis rate that is sensitive to amino acid stimulation. In the present study, we determined the effect of amino acids on protein synthesis in skeletal muscle and other tissues in septic neonates. Overnight-fasted neonatal pigs were infused with endotoxin (LPS, 0 and 10 microg.kg(-1).h(-1)), whereas glucose and insulin were maintained at fasting levels; amino acids were clamped at fasting or fed levels. In the presence of fasting insulin and amino acids, LPS reduced protein synthesis in longissimus dorsi (LD) and gastrocnemius muscles and increased protein synthesis in the diaphragm, but had no effect in masseter and heart muscles. Increasing amino acids to fed levels accelerated muscle protein synthesis in LD, gastrocnemius, masseter, and diaphragm. LPS stimulated protein synthesis in liver, lung, spleen, pancreas, and kidney in fasted animals. Raising amino acids to fed levels increased protein synthesis in liver of controls, but not LPS-treated animals. The increase in muscle protein synthesis in response to amino acids was associated with increased mTOR, 4E-BP1, and S6K1 phosphorylation and eIF4G-eIF4E association in control and LPS-infused animals. These findings suggest that amino acids stimulate skeletal muscle protein synthesis during acute endotoxemia via mTOR-dependent ribosomal assembly despite reduced basal protein synthesis rates in neonatal pigs. However, provision of amino acids does not further enhance the LPS-induced increase in liver protein synthesis.

Protein breakdown on whole-body and organ level in non-cachectic tumour-bearing mice undergoing surgery

BACKGROUND & AIMS

Since both cancer and surgery are known to alter protein turnover, we investigated how the presence of tumour affects post-operative protein breakdown.

METHODS

Controls and tumour-bearing non-cachectic mice were studied, both with and without laparotomy (n=8 per group). One day after laparotomy, stable isotopes of phenylalanine and 3-methylhistidine were used in a steady-state protocol to assess total protein breakdown on whole-body level and in muscle, intestines, liver and kidney, in addition to whole-body myofibrillar protein breakdown and body composition. Proteasomal chymotrypsin-like activity was measured to determine activity of the ATP-dependent ubiquitin pathway.

RESULTS

On whole-body level, the presence of tumour increased total protein breakdown from 47+/-6 to 58+/-4 nmol/10 g/min (p<0.05) and myofibrillar protein breakdown from 0.70+/-0.04 to 1.22+/-0.14 nmol/10 g/min (p<0.05) without affecting protein breakdown in organs, body composition or proteasomal activity. Laparotomy increased myofibrillar protein breakdown in controls (from 0.70+/-0.04 to 0.98+/-0.12 nmol/10 g/min, p<0.05) and tumour-bearing mice (from 1.22+/-0.14 to 1.54+/-0.22 nmol/10 g/min, p=0.15) to a similar extent.

CONCLUSIONS

Whole-body total protein breakdown, total protein breakdown across organs, body composition or proteasomal activity were not affected by laparotomy. Tumour-bearing mice had increased total and myofibrillar protein breakdown on whole-body level even before weight loss was obvious. However, this did not affect the post-operative response in protein breakdown or body composition.

Modulation of muscle protein synthesis by insulin is maintained during neonatal endotoxemia

Sepsis promotes insulin resistance and reduces protein synthesis in skeletal muscle of adults. The effect of sepsis on insulin-stimulated muscle protein synthesis has not been determined in neonates, a highly anabolic population that is uniquely sensitive to insulin. Overnight fasted neonatal pigs were infused for 8 h with endotoxin [lipopolysaccharide (LPS), 0 and 10 mug.kg(-1).h(-1)]. Glucose and amino acids were maintained at fasting levels, insulin was clamped at either fasting or fed (2 or 10 muU/ml) levels, and fractional protein synthesis rates were determined at the end of the infusion. LPS infusion induced a septic-like state, as indicated by a sustained elevation in body temperature, heart rate, and cortisol. At fasting insulin levels, LPS reduced fractional protein synthesis rates in gastrocnemius muscle (-26%) but had no effect on the masseter and heart. By contrast, LPS stimulated liver protein synthesis (+28%). Increasing insulin to fed levels accelerated protein synthesis rates in gastrocnemius (controls by +38%, LPS by +60%), masseter (controls by +50%, LPS by +43%), heart (controls by +34%, LPS by +40%), and diaphragm (controls by +54%, LPS by +29%), and the response to insulin was similar in LPS and controls. Insulin did not alter protein synthesis in liver, kidney, or jejunum in either group. These findings suggest that acute endotoxemia lowers basal fasting muscle protein synthesis in neonates but does not alter the response of protein synthesis to insulin.

Altered interorgan response to feeding in patients with chronic obstructive pulmonary disease

BACKGROUND

Previously, we reported increased values for whole-body protein turnover in patients with chronic obstructive pulmonary disease (COPD) in the postabsorptive state.

OBJECTIVE

The objective was to investigate whether intake of a carbohydrate-protein meal influences whole-body protein turnover differently in COPD patients and control subjects.

DESIGN

Eight normal-weight patients with moderate COPD and 8 healthy control subjects were examined in the postabsorptive state and after 2 h of repeatedly ingesting a maltodextrin casein-based protein meal (0.02 g x kg body wt(-1) x 20 min(-1)). Combined simultaneous, continuous, intravenous infusion of L-[ring-2H5]-phenylalanine and L-[ring-2H2]-tyrosine tracer and oral repeated ingestion of 1-13C-phenylalanine were performed to measure whole-body protein synthesis (WbPS) and first-pass splanchnic extraction of phenylalanine. Endogenous rate of appearance of phenylalanine as the measure of whole-body protein breakdown (WbPB) and netWbPS was calculated as WbPS--WbPB. Arterialized venous blood was sampled for amino acid enrichment and concentration analyses.

RESULTS

Feeding induced an increase in WbPS and a reduction in WbPB. The reduction in WbPB was larger in the COPD group than in the control group (P < 0.05) and was related to the lower splanchnic extraction of phenylalanine in the patients. Consequently, netWbPS increased more after feeding in the COPD group than in the control group (P < 0.05).

CONCLUSION

Feeding induces more protein anabolism in normal-weight patients with moderate COPD than in healthy control subjects. This is probably because these COPD patients are characterized by an adaptive interorgan response to feeding to prevent or delay weight loss at this disease stage.

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.

NOS3 is involved in the increased protein and arginine metabolic response in muscle during early endotoxemia in mice

Sepsis is a severe catabolic condition. The loss of skeletal muscle protein mass is characterized by enhanced release of the amino acids glutamine and arginine, which (in)directly affects interorgan arginine and the related nitric oxide (NO) synthesis. To establish whether changes in muscle amino acid and protein kinetics are regulated by NO synthesized by nitric oxide synthase-2 or -3 (NOS2 or NOS3), we studied C57BL6/J wild-type (WT), NOS2-deficient (NOS2-/-), and NOS3-deficient (NOS3-/-) mice under control (unstimulated) and lipopolysaccharide (LPS)-treated conditions. Muscle amino acid metabolism was studied across the hindquarter by infusing the stable isotopes L-[ring-2H5]phenylalanine, L-[ring-2H2]tyrosine, L-[guanidino-15N2]arginine, and L-[ureido-13C,2H2]citrulline. Muscle blood flow was measured using radioactive p-aminohippuric acid dilution. Under baseline conditions, muscle blood flow was halved in NOS2-/- mice (P < 0.1), with simultaneous reductions in muscle glutamine, glycine, alanine, arginine release and glutamic acid, citrulline, valine, and leucine uptake (P < 0.1). After LPS treatment, (net) muscle protein synthesis increased in WT and NOS2-/- mice [LPS vs. control: 13 +/- 3 vs. 8 +/- 1 (SE) nmol.10 g(-1).min(-1) (WT), 18 +/- 5 vs. 7 +/- 2 nmol.10 g(-1).min(-1) (NOS2-/-); P < 0.05 for LPS vs. control]. This response was absent in NOS3-/- mice (LPS vs. control: 11 +/- 4 vs. 10 +/- 2 nmol.10 g(-1).min(-1)). In agreement, the increase in muscle arginine turnover after LPS was also absent in NOS3-/- mice. In conclusion, disruption of the NOS2 gene compromises muscle glutamine release and muscle blood flow in control mice, but had only minor effects after LPS. NOS3 activity is crucial for the increase in muscle arginine and protein turnover during early endotoxemia.

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.

Amino Acid Adequacy in Pathophysiological States

Amino acid utilization and, therefore, demand differ between the healthy state and various disease states. In the healthy state most circulating amino acids are derived from dietary proteins that are stored and broken down in the gut and released gradually into the portal circulation, and from continuous turnover of body protein. In disease states, the amino acid composition of amino acids derived from periferal protein breakdown and released in the circulation, is different, for example because a substantial part of the branched-chain amino acids is broken down to yield glutamine and alanine, which are released in the circulation. It appears to be advantageous to mimic this continuous autoinfusion in patients, dependent of parenteral of enteral tube feeding. In disease, different endpoints should be used to assess the adequacy of the administered amino acid mix. Maintenance of a positive nitrogen balance and growth is less important than support of wound healing and immune function. Several amino acids such as glutamine, cysteine, and taurine are shown or suggested to be conditionally essential in disease, and to form substrate in the stressed patient for anabolic processes in liver, immune system, and injured sites. Amino acid toxicity is rare, and protein restriction for patients with renal or liver failure is obsolete because this only aggravated malnutrition. A true example of protein toxicity consists of gastrointestinal hemorrhage that precipitates hepatic encephalopathy in liver insufficiency, most likely because hemoglobin is an unbalanced protein because it lacks the essential amino acid isoleucine.

Animal models of amino acid metabolism: a focus on the intestine

One important advantage of animal models is that they permit invasive approaches and can be especially valuable when evaluating tissue and specific features of metabolism in situ. The focus of this presentation is current models, which are providing insights into the pivotal importance of the gastrointestinal tract in amino acid metabolism. Intestinal amino acid metabolism is conceptually and technically difficult to approach and multiple processes must be accounted for: protein synthesis and degradation; transit of amino acids in both directions across the basolateral surface of enterocytes, in addition to uptake on the apical side; arterio-portal differences as well as net portal appearance during uptake of defined amino acid mixtures appearing on the luminal side; first pass amino acid metabolism. These key features are largely impossible to study without access to invasive approaches in vivo and cannot be reproduced in vitro. Douglas Burrin, Ron Ball, and Vickie Baracos and their co-workers have used the domestic piglet to study intestinal protein metabolism in situ in three distinctly different and complementary approaches. Collectively, their approaches allow a means to describe the key elements of intestinal amino acid capture (and release) and the means to probe their physiological and pathological variation. It seems evident that the portal-drained viscera represent sites of quantitatively important amino acid catabolism, and that this capacity combined with hepatic metabolism would largely limit the possibility of toxic sequelae of amino acids taken orally.

NOS2 deficiency increases intestinal metabolism both in nonstimulated and endotoxemic mice

Animal studies have suggested that nitric oxide (NO) synthases (NOS) play a role in the regulation of protein metabolism in endotoxemia. We therefore investigated the role of inducible NOS (NOS2) on intestinal protein and neuronal NOS (NOS1) and endothelial NOS (NOS3) on amino acid metabolism. Three groups of mice were studied: 1) wild-type (WT), 2) NOS2 knockout (NOS2-KO), and 3) NOS2-KO + N(omega)-nitro-l-arginine methyl ester (NOS2-KO + l-NAME), both in nonstimulated and LPS-treated conditions. By infusion of the stable isotopes l-[phenyl-(2)H(5)]Phe, l-[phenyl-(2)H(2)]Tyr, l-[guanidino-(15)N(2)]Arg, and l-[ureido-(13)C; (2)H(2)]citrulline (Cit), intestinal protein, amino acid, and Arg/NO metabolism were studied on the whole body level and across intestine. In nonstimulated situations, NOS2 deficiency increased whole body protein turnover and intestinal Gln uptake and Cit production. In NOS2-KO + l-NAME, the above-mentioned changes were reversed. After LPS in WT, whole body NO and Cit production increased. In contrast to this, LPS decreased net intestinal Gln uptake, whole body NO, and Cit production in NOS2-KO mice. Treatment of NOS2-KO + l-NAME with LPS was lethal in eight of eleven mice (73%). The surviving mice in this group showed a major drop in intestinal protein breakdown and synthesis to almost zero. Thus both in baseline conditions and during endotoxemia, the absence of NOS2 upregulated NOS1 and/or NOS3, which increased intestinal metabolism. The drop in intestinal protein metabolism in the endotoxemic NOS2-KO + l-NAME group might play a role in mortality in that group.

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

1. During prolonged endotoxaemia, an increase in arginine catabolism may result in limiting substrate availability for nitric oxide (NO) production. These effects were quantitated in a chronically instrumented porcine endotoxaemia model. 2. Ten days prior to the beginning of the experiments, pigs were catheterized. On day 0, pigs received a continuous infusion of endotoxin (3 microg kg(-1) h(-1)) over 24 h and were saline resuscitated. Blood was drawn from the catheters at 0 and 24 h during primed-infusion of (15)N(2)-arginine and P-aminohippurate to assess (15)N(2)-arginine to (15)N-citrulline conversion and plasma flow rates, respectively, across the portal-drained viscera, liver and hindquarter. 3. During endotoxin infusion a hyperdynamic circulation with elevated heart rate, cardiac index and decreased mean arterial pressure was achieved, characteristic of the human septic condition. 4. Endotoxin induced NO production by the portal-drained viscera and the liver. The increased NO production was quantitatively matched by an increase in arginine disposal. Nitrite/nitrate levels remained unchanged during endotoxaemia. 5. Despite an increased arginine production from the hindquarter and an increased whole-body arginine appearance rate during endotoxin infusion, the plasma arginine concentration was lower in endotoxin-treated animals than in controls. 6 On a whole-body level, the muscle was found to serve as a major arginine supplier and, considering the lowered arginine plasma levels, seems critical in providing arginine as precursor for NO synthesis in the splanchnic region.

L-arginine supplementation in hyperdynamic endotoxemic pigs: effect on nitric oxide synthesis by the different organs

OBJECTIVES

Under septic conditions, the protective role of nitric oxide in the organs may become compromised at a time of increased demand as a result of decreased availability of L-arginine. It remains unknown whether supplementation with L-arginine, as a substrate, can modulate organ nitric oxide production.

DESIGN

Controlled study with laboratory animals.

SETTING

University research laboratory.

SUBJECTS

Female crossbred pigs.

INTERVENTION

Pigs were challenged with Escherichia coli endotoxin (intravenously) and received intravenous fluid resuscitation for 24 hrs to reproduce a model of long-lasting hyperdynamic endotoxemia. Pigs were infused with either L-arginine or L-alanine intravenously during endotoxin and via the intragastric route after cessation of endotoxin infusion. The effects of L-arginine supplementation on nitric oxide synthesis and the relationships with arginine metabolism were determined with a stable isotope infusion protocol. Also, organ nitrite plus nitrate fluxes were measured. Implantation of multiple catheters enabled in vivo measurements across the hindquarter muscle, the portal-drained viscera, the liver, and the kidneys.

MEASUREMENTS AND RESULTS

The isotope conversion method showed that L-arginine intervention significantly increased nitric oxide production by the portal-drained viscera, liver, and kidneys, resulting in elevated whole-body nitric oxide synthesis under endotoxemic and postendotoxemic conditions. Organ nitrite plus nitrate fluxes only tended to increase because of high variance among data.

CONCLUSIONS

In this endotoxemia model, supplemental use of L-arginine favored nitric oxide synthesis in various organs.