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The high requirement of the gut for threonine has often been ascribed to the synthesis of mucins, secreted threonine-rich glycoproteins protecting the intestinal epithelium from injury. This requirement could be even greater during intestinal inflammation, when mucin synthesis is enhanced. In this study, we used an animal model to investigate the effects of an acute ileitis on threonine splanchnic fluxes. Eight adult multi-catheterized minipigs were fed with an enteral solution. Four of them were subjected to experimental ileitis involving direct administration of trinitrobenzene sulfonic acid (TNBS) into the ileum (TNBS-treated group) and the other 4 were not treated (control group). Threonine fluxes across the portal-drained viscera (PDV) were quantified with the use of simultaneous i.g. L-[[sup.15]N]threonine and i.v. L-[U-[sup.13]C]threonine infusions. Ileal mucosa was sampled for mucin fractional synthesis rate measurement, which was greater in the TNBS-treated group (114 [+ or -] 15%/d) than in the control group (61 [+ or -] 8%/d) (P = 0.021). The first-pass extraction of dietary threonine by the PDV and liver did not differ between groups and accounted for ~27 and 10% of the intragastric delivery, respectively. PDV uptake of arterial threonine increased from 25 [+ or -] 14 [micro]mol x [kg.sup.-1] x [h.sup.-1] in the control group to 171 [+ or -] 35 [micro]mol x [kg.sup.-1] x [h.sup.-1] in the TNBS-treated group (P < 0.001). In conclusion, ileitis increased intestinal mucin synthesis and PDV utilization of threonine from arterial but not luminal supply. This leads to the mobilization of endogenous proteins to meet the increased threonine demand associated with acute intestinal inflammation.

We hypothesized that the dietary threonine demand for the anabolic response may be increased more than that of other essential amino acids during sepsis. Using a flooding dose of either L-[1-[sup.13]C]valine or L-[U- [sup.13]C]threonine, we measured valine and threonine utilization for syntheses of plasma proteins (minus albumin), and wall, mucosal, and mucin proteins of the small intestine in infected (INF; d 2 and d 6 of postinfection) and control pair-fed (PF) rats. At d 2, the protein absolute synthesis rate (ASR) of INF rats was 21% (mucins) to 41% (intestinal wall) greater than that of PF when measured using valine as tracer, and 45% (mucosa) to 113% (mucins) greater than that of PF when measured with threonine as tracer. Plasma protein ASR was higher in INF than in PF rats, reaching 5- to 6-fold the value of PF. The utilization of both amino acid tracers for the protein synthesis was significantly increased by the infection in all compartments studied. The daily increased absolute threonine utilization for protein synthesis in gut wall plus plasma proteins was 446 [micro]mol/d compared with 365 [micro]mol/d for valine, and it represented 2.6 times the dietary threonine intake of rats at d 2. Most changes in protein ASR and threonine utilization observed at d 6 of postinfection were limited. In conclusion, sepsis increased the utilization of threonine for the anabolic splanchnic response. Because this threonine requirement is likely covered by muscle protein mobilization, increasing the threonine dietary supply would be an effective early nutritional management for patients with sepsis.

During the anabolic response associated with inflammation, mucin synthesis and colonic protection may be compromised by the limited availability of specific amino acids. We therefore determined the effect of dietary amino acid supplementation on the microbiota, mucin status, and mucosal damage in dextran sulfate sodium (DSS)-treated rats. From 8 d before to 28 d after colitis induction, male Sprague-Dawley rats (10 mo old, n = 8/group) were fed a control diet supplemented or not with 2 different doses of an amino acid cocktail containing L-threonine, L-serine, L-proline, and L-cysteine. All diets were isonitrogenous (adjusted with L-alanine). The higher dose of amino acids increased the number of Muc2-containing goblet cells in the surface epithelium of the ulcerated area, stimulated mucin production in the colon, and restored the mucin amino acid composition and mucosal content to healthy, control values. The colonic mucin synthesis rate was specifically stimulated by 95%, whereas the protein turnover was unchanged. All bacterial populations, markedly altered by the DSS treatment, were promoted. In conclusion, in inflammatory situations, an increase in threonine, serine, proline, and cysteine dietary supply can promote mucin synthesis, reequilibrate the gut microbiota, and thus favor colonic protection and mucosal healing. KEY WORDS: * mucin * amino acids * protein synthesis * intestine * rats

The mechanisms leading to hypoalbuminemia in sepsis were explored by measuring plasma volume, albumin distribution, plasma albumin transcapillary escape rate (TER), and efflux (TER x albumin intravascular pool). These parameters were quantified in infected rats, injected intravenously with live Escherichia coli, and pair-fed and well-fed rats using an injection of [sup.35]S-albumin and measuring plasma and whole body albumin concentrations. Animals were studied on days 1, 6, and 10 after infection. In pair-fed rats, neither albumin distribution nor exchange rate between the intra- and extravascular compartments was modified. The increase of plasma volume after infection partly explained hypoalbuminemia. Infection resulted in a reduction of the total albumin pool of the body all along the experimental period, indicating a net loss of the protein. Albumin TER (%/day) was significantly increased 1 and 6 days after infection, but the absolute efflux was increased only on day 1. Normal values were observed on day 10. Therefore, an accelerated plasma efflux contributes to hypoalbuminemia only during the early period of sepsis. During this phase, the protein was retained in the extravascular space where it was probably catabolized. Later on, other factors are probably involved. plasma albumin escape; albumin distribution; infection

Aging induces a dysregulation of immune and inflammation functions that may affect protein synthesis rates in lymphoid tissue and plasma proteins. We quantified in vivo synthesis rates of thymus, spleen and plasma proteins, including albumin and acute phase proteins, in adult (8 mo old) and old (22 mo old) rats using the flooding dose method [L-(1-[sup.13]C) phenylalanine]. Immunosenescence was reflected by thymus atrophy and spleen hypertrophy in old rats but not in adult rats. A low albumin plasma level associated with high concentrations of fibrinogen, [[alpha].sub.2]-macroglobulin, [[alpha].sub.1]-acid glycoprotein and proteins other than albumin revealed a low grade inflammation in old rats. Protein fractional synthesis rates (FSR) and protein synthesis efficiencies of thymus were 29 and 26% lower in old than in adult rats, respectively; these variables did not differ in spleen. Protein absolute synthesis rates (ASR) of the thymus and spleen were 76% lower and 67% greater in old than adult rats, respectively. The FSR and ASR of albumin and other plasma proteins were greater in old than in adult rats. Protein synthesis measurement is a valuable nonimmunological tool to assess, in vivo, immune and inflammatory variables. Alterations in secondary lymphoid organs and plasma protein synthesis may contribute to the significant repartitioning of amino acids in old compared with adult rats and may be involved in sarcopenia. KEY WORDS: * aging * inflammation * lymphoid tissues * protein synthesis * rats

Bacterial infection alters whole-body protein homeostasis. Although immune cells are of prime importance for host defense, the effect of sepsis on their protein synthesis rates is poorly documented. We analyzed protein synthesis rates in rat primary lymphoid tissues and circulating lymphocytes after infection. Male Sprague-Dawley rats were studied 1, 2, 6 or 10 d after an intravenous injection of live Escherichia coli. Control healthy rats consumed food ad libitum (d 0) or were pair-fed to infected rats. Protein synthesis was quantified using a flooding dose of L-(4,4,4-[sup.2][H.sub.3])valine. Sepsis induced a delayed increase in total blood leukocytes and a rapid and persistent inversion of the counts. Basal fractional rates of protein synthesis (ks) were 117, 73 and 29%/d in bone marrow, thymus and circulating lymphocytes, respectively. Pair-feeding strongly depressed the absolute protein synthesis rates (ASR) of bone marrow (d 2 and 10) and thymus (d 2-10). The infection per se increased bone marrow, thymus and circulating lymphocyte ks but at various postinfection times. It decreased bone marrow (d 1) and thymus (d 1 and 2) ASR but increased lymphocyte (d 2 and 10) and bone marrow (d 10) ASR. Our results reflect the deleterious effect of anorexia on primary lymphoid tissues. The host defense against bacterial infection exhibited time- and tissue-dependent modifications of protein synthesis, indicating that blood lymphocyte protein data are not representative of the immune system as a whole. Optimization of nutritional supports would be facilitated by including protein synthesis measurements of the immune system. J. Nutr. 132: 2028-2032, 2002. KEY WORDS: * rats * sepsis * protein synthesis * lymphoid tissues * circulating lymphocytes

Despite the prevalence of chronic inflammatory diseases in developed countries, few studies have considered the metabolic alterations observed in these disorders. To determine which perturbations in protein metabolism occur during chronic inflammation, and the consequences they have on nutritional requirements, a model of ulcerative colitis was adapted for use in adult rats. Adult Sprague-Dawley male rats (9 mo old) received dextran sulfate sodium (DSS) in their drinking water at 50 g/L for 9 d, then at 20 g/L for 18 d. A group of control rats, matched for age and weight, was pair-fed to the treated rats. DSS induced body weight loss and chronic inflammation characterized by an increase of spleen, liver, ileum and colon weights, of blood leukocytes and acute-phase protein levels. The main inflammatory site was the colon, which presented characteristic histological alterations and increased myeloperoxydase activity. Inflammation was accompanied by oxidative stress, characterized by increased plasma protein carbonyl content and increased liver glutathione concentration, but decreased glutathione concentration in muscle. This DSS-induced colitis led to a stimulation of protein synthesis in spleen (+223%), ileum (+40%) and colon (+63%). By contrast, protein synthesis in muscle slowed down (-23%). In conclusion, like acute inflammation, chronic inflammation induced a stimulation of protein metabolism in several splanchnic organs. In muscle, both protein synthesis and degradation were reduced. Taken together, these data are consistent with inadequate amino acid supply to meet the increased requirement resulting from chronic inflammation. KEY WORDS: * chronic inflammation * protein metabolism * oxidative stress * free amino acids

A study was conducted to examine the regulation of the acute phase response in vivo by analyzing the influence of pentoxifylline (PX) treatment in rats after an intravenous injection of Escherichia coli. Total RNA was determined from the liver single radial diffusion was carried out to determine albumin plasma levels. Results indicated that PX increased animal survival in lethal frameworks of infection and effective blocks LPS fever.

The role of insulin or insulin-like growth factor 1 (IGF-1) in the regulation of protein synthesis and degradation in the epitrochlearis was compared and contrasted after the administration of live Escherichia coli in the blood. The effects of the insulin and IGF-1 on skeletal muscle protein metabolism during the anorexic, hypermetabolic and recovery phases of the immunological response to bacteremia were analyzed. The findings suggest that defective protein synthesis and degradation were caused by an infectious attack independent of the nutritional state of the epitrochlearis.

In vivo cysteine metabolism during the inflammatory state has been studied minimally. We investigated cysteine metabolism (i.e. taurine, sulfate and glutathione formation) using a single dose of [35S] cysteine in septic rats that had been injected with live Escherichia coli into the tail vein and in control, pair-fed rats. Cysteine metabolites were separated by ion exchange chromatography, and radioactivity was counted in the different fractions. Radioactivity incorporated in tissue proteins was also measured after protein precipitation. [35S]Sulfate production was significantly lower in septic rats than in pair-fed rats. [35S]Taurine contents were significantly lower only in kidneys, spleen and gastrointestinal tract of septic rats. The higher production of [35S] taurine in the livers (the major site of taurine production) of septic rats could have a protective effect against oxidation. Glutathione concentrations were also significantly greater in liver, spleen, kidneys and gastrocnemius muscle of septic rats, presumably in order to combat oxidative stress induced by sepsis. [35S]Cysteine incorporation in glutathione was significantly higher in spleen and kidneys but not in liver of septic rats compared to pair-fed rats. This could be explained by the fact that, in liver, a greater amount of labeled glutathione had been utilized for host defense, or by a high level in glutathione turnover. Finally, [35S]cysteine incorporation into protein, in septic rats, was significantly greater than in pair-fed rats in spleen, lung and particulary in whole plasma proteins other than albumin, which mainly represent the acute-phase proteins. These data suggest an increased requirement for cysteine during sepsis in rats. KEY WORDS: cysteine, glutathione, rats, sulfate, taurine

Albumin, fibrinogen and muscle protein syntheses in the whole body, liver and muscle in patients with severe head injuries were investigated. Six head-injured subjects participated in an experiment where they were compared with a group of healthy individuals. Results showed that head-injured patients experienced an increase in plasma levels of C-reactive protein, haptoglobin, orosomucoid and fibrinogen, indicating a severe biological inflammatory response. On the other hand, plasma albumin concentrations and muscle fractional synthesis rate declined in the patients.

Research was conducted to study ornithine alpha-ketoglutarate (OKG) characteristics in burn-injured rats. Tissue protein synthesis was examined in vivo using the large dose method while tissue free glutamine concentrations were determined in the acid-soluble fraction. Results indicated that enterally administered OKG modulates tissue protein metabolism and is characterized by anabolic and anticatabolic properties.

A two-pool model was developed to determine the metabolic fate of leucine in response to protein-deficient and protein-rich diets. Analysis of leucine kinetics in the splanchnic region of humans based on the two-pool model and experimental data indicated the role of protein intake in enhancing the uptake of leucine. Furthermore, the two-pool model provided a more accurate estimation of protein metabolism parameters at the whole body level by including data on splanchnic bed amino acid metabolism.

The isotopic labeling of very low-density lipoprotein (VLDL) apolipoprotien (apo)B100 at plateau proves a reliable method of estimating hepatic protein synthesis precursor pool. Measures of VLDL apoB100 after intravenous infusion of L-(1-13C)leucine indicate that leucine labeling incorporated into VLDL apoB100 is lower than plasma leucine or alpha-ketoisocaproate (KIC) enrichments. However, leucine-adoB enrichment is higher than plasma leucine and KIC labeling after the oral infusion of L-(5,5,5-2H3)leucine. Protein intake little affects these labeling measures.

The ability of insulin to prevent proteolysis is increased during experimentally induced hyperthyroidism indicating that insulin acts as an intermediary in the catabolic response to hyperthyroidism. Insulin also reduces protein synthesis during hyperthyroidism and plays an important role in saving the proteins in the body. Hyperthyroidism results in many metabolic changes such as increased gluconeogenesis, lipid metabolism and negative nitrogen balance.

A study of the variations in in vivo muscle protein synthesis with exercise, old age and nutritional states through an analysis of 12- and 24-month old male Wistar rats indicates a decrease in response of muscle protein synthesis to exercise and nutrition with age, accounting for postprandial anabolism. Basal muscle protein synthesis remains unaffected, while exercise or feeding does not induce the soleus and tibialis anterior muscles of old rats to synthesize proteins.

The effects of a daily porcine somatotropin injection on protein synthesis rate in muscle (longissimus), liver and intestine, as influenced by dietary protein, were investigated in 17 pigs. The measurements were made at wk 3 of treatment following 1 wk for adaptation to the diet and 1 wk for determination of nitrogen balance. The fractional rates of protein synthesis in the muscle, liver and intestine were measured using a flooding dose of L-(1-13C)valine. Positive responses of weight gain and nitrogen balance were observed, primarily at higher dietary protein intake, after porcine somatotropin treatment. As expected, porcine somatotropin-treated pigs had a higher proportion of muscle and less fat. Fractional protein synthesis rate was 16% higher in the liver of porcine somatotropin-treated pigs (P < 0.05). In the longissimus muscle fractional protein synthesis rate increased with porcine somatotropin dose from 3.2 to 3.7%/d and from 4.1 to 5.1%/d at low and high protein intake, respectively (P < 0.05). The effect of dietary protein on fractional protein synthesis rate in longissimus was significant, but there was no porcine somatotropin x protein interaction. Ribonucleic acid concentration followed the same pattern as fractional protein synthesis rate in liver and longissimus. In the duodenal tissue, porcine somatotropin treatment depressed fractional protein synthesis rate (P < 0.05) without an effect of dietary protein and RNA concentration did not change. In porcine somatotropin compared with placebo-treated pigs, plasma glucose, insulin and insulin-like growth factor-I concentrations were elevated whereas plasma thyroxine was depressed and plasma triiodothyronine remained constant. There was no clear effect of dietary protein on plasma hormones. We concluded that, in pigs fed an adequate level of protein, porcine somatotropin stimulates protein synthesis in the liver and the muscle, primarily through increased ribosomal capacity. J. Nutr. 123: 529-540, 1993.

This study assessed whole-body and tissue protein metabolism and the contribution of skin to whole-body protein synthesis during the post-weaning development of rats. Protein fractional synthesis rate was measured in muscle, skin and the whole body of 70-, 160-, 315- and 586-g rats by use of a continuous infusion of L-(U-14C)lysine. Rates of protein synthesis were then calculated, based on the tissue free and protein-bound lysine specific radioactivity at the end of the infusion. The fractional protein synthesis rate declined progressively in the skin (from 19.6 to 8.0 %/d), in muscle (from 18.9 to 4.8 %/d) and in whole body (from 25.0 to 8.5 %/d) throughout post-weaning development. Absolute synthesis rates (g/(d center dot 100 g body wt)) of whole-body and muscle proteins decreased by 54 and 50%, respectively. On the other hand, the amount of skin protein synthesized per 100 g body wt was 35% greater in 160-g and 315-g rats than in 70-g and 586-g rats. The absolute synthesis rate of muscle proteins as a percentage of whole-body protein synthesis remained fairly constant at a value close to 24%, whereas the skin contribution to whole-body protein synthesis increased from 12% in 70-g rats to 26% in 586-g rats. J. Nutr. 122: 2167-2173, 1992.

Malmezat, Thierry, Denis Breuille, Corinne Pouyet, Caroline Buffiere, Philippe Denis, Philippe Patureau Mirand, and Christiane Obled. Methionine transsulfuration is increased during sepsis in rats. Am J Physiol Endocrinol Metab 279: E1391-E1397, 2000.--Methionine transsulfuration in plasma and liver, and plasma methionine and cysteine kinetics were investigated in vivo during the acute phase of sepsis in rats. Rats were infected with an intravenous injection of live Escherichia coli, and control pair-fed rats were injected with saline. Two days after injection, the rats were infused for 6 h with [[sup.35]S]methionine and [[sup.15]N]cysteine. Transsulfuration was measured from the transfer rate of [sup.35]S from methionine to cysteine. Liver cystathionase activity was also measured. Infection significantly increased (P [is less than] 0.05) the contribution of transsulfuration to cysteine flux in both plasma and liver (by 80%) and the contribution of transsulfuration to plasma methionine flux (by 133%). Trans-sulfuration measured in plasma was significantly (P [is less than] 0.05) higher in infected rats than in pair-fed rats (0.68 and 0.25 [micro]mol [multiplied by] [h.sup.-1] [multiplied by] 100 [g.sup.-1], respective]y). However, liver cystathionase specific activity was decreased by 17% by infection (P [is less than] 0.05). Infection increased methionine flux (16%, P [is less than] 0.05) less than cysteine flux (38%, P [is less than] 0.05). Therefore, the plasma cysteine flux was higher than that predicted from estimate of protein turnover based on methionine data, probably because of enhanced glutathione turnover. Taken together, these results suggest an increased cysteine requirement in infection. methionine flux; cystathionase; components of cysteine flux

Ruot, Benoit, Denis Breuille, Fabienne Rambourdin, Gerard Bayle, Pierre Capitan, and Christiane Obled. Synthesis rate of plasma albumin is a good indicator of liver albumin synthesis in sepsis. Am J Physiol Endocrinol Metab 279: E244-E251, 2000.--Plasma albumin is well known to decrease in response to inflammation. The rate of albumin synthesis from both liver and plasma was measured in vivo by use of a large dose of L-[[sup.2][H.sub.3]-[sup.4]C]valine in rats injected intravenously with live Escherichia coli and in pair-fed control rats during the acute-phase period (2 days postinfection). The plasma albumin concentration was reduced by 50% in infected rats compared with pair-fed animals. Infection induced a fall in both liver albumin mRNA levels and albumin synthesis relative to total liver protein synthesis. However, absolute liver albumin synthesis rate (ASR) was not affected by infection. In plasma, albumin fractional synthesis rate was increased by 50% in infected animals compared with pair-fed animals. The albumin ASR estimated in the plasma was similar in the two groups. These results suggest that hypoalbuminemia is not due to reduced albumin synthesis during sepsis. Moreover, liver and plasma albumin ASR were similar. Therefore, albumin synthesis measured in the plasma is a good indicator of liver albumin synthesis. hypoalbuminemia; albumin expression; infection