Food matrix structure (from Biscuit to Custard) has an impact on folate bioavailability in healthy volunteers.

PURPOSE: We examined the impact of matrix food structure on post-prandial folate bioavailability (and other macronutrients) in human volunteers using a randomized, controlled, crossover experimental design. METHODS: Twelve healthy male volunteers (22.6 ± 0.4 years old) were offered four food models (differing in matrix structure: Custard, Pudding, Sponge cake and Biscuit) to which 1 mg of folic acid was added, according to a randomized, controlled, crossover experimental design. Plasma folates, glucose, insulin, alpha amino nitrogen and triglycerides were measured over the post-prandial period (from T0 to T480 min). RESULTS: Food matrix structure was capable of altering folate plasma availability. The highest folate availability was observed for pudding and to a lesser extent Sponge cake whereas the lowest was for the two matrices presenting extreme rheological properties: Custard (liquid) (P < 0.05 total AUC) and to a lesser extent Biscuit (hard solid) (P < 0.05, AUC 180 min). The analysis of plasma kinetics of appearance of other nutrients/metabolites helps to understand/explain the lower bioavailability of folates in Custard and Biscuit. CONCLUSION: A least overall efficient bio-accessibility of all macronutrients and folic acid is observed in the gut lumen for Biscuit (delayed/incomplete destructuration of biscuit along the digestive tract). On the contrary, the lower folic acid absorption observed with custard does not fit with the rapid plasma appearance of other nutrients and should require further investigation.

Slight chronic elevation of C-reactive protein is associated with lower aerobic fitness but does not impair meal-induced stimulation of muscle protein metabolism in healthy old men.

Ageing impairs the muscle anabolic effect of food intake, which may explain muscle loss and an increased risk of sarcopenia. Ageing is also associated with low grade inflammation (LGI), which has been negatively correlated with muscle mass and strength. In rodents, the muscle anabolic resistance observed during ageing and sarcopenia has been ascribed to the development of the LGI. We aimed to investigate this relationship in humans. We studied protein metabolism and physical fitness in healthy elderly volunteers with slight chronic C-reactive protein. Two groups of healthy elderly volunteers were selected on the presence (or not) of a chronic, slight, elevation of CRP (Control: <1; CRP+: >2 mg l(-1) and <10 mg l(-1) , for 2 months). Body composition, short performance battery test, aerobic fitness and muscle strength were assessed. Whole body and muscle protein metabolism and the splanchnic extraction of amino acids were assessed using [(13) C]leucine and [(2) H]leucine infusion. The anabolic effect of food intake was measured by studying the volunteers both at the post-absorptive and post-prandial states. Slight chronic CRP elevation resulted in neither an alteration of whole body, nor skeletal muscle protein metabolism at both the post-absorptive and the post-prandial states. However, CRP+ presented a reduction of physical fitness, increased abdominal fat mass and post-prandial insulin resistance. Plasma cytokines (interleukin-1, interleukin-6, tumour necrosis factor α) and markers of endothelial inflammation (intercellular adhesion molecule, vascular cell adhesion molecule, selectins) were similar between groups. An isolated elevated CRP in healthy older population does not indicate an impaired skeletal muscle anabolism after food intake, nor an increased risk of skeletal muscle wasting. We propose that a broader picture of LGI (notably with elevated pro-inflammatory cytokines) is required to impact muscle metabolism and mass. However, an isolated chronic CRP elevation could predict a decrease in aerobic fitness and insulin resistance installation in elderly individuals.

Development of a protein food based on texturized wheat proteins, with high protein digestibility and improved lysine content.

The development of plant-based protein foods may facilitate the decrease in animal product consumption in western countries. Wheat proteins, as a starch coproduct, are available in large amounts and are good candidates for this development. We investigated the effect of a new texturing process on wheat protein digestibility and implemented strategies aimed at enhancing the lysine content of the product developed. Protein true ileal digestibility (TID) was determined in minipigs. In a preliminary experiment, the TID of wheat protein (WP), texturized wheat protein (TWP), TWP enriched with free lysine (TWP-L), or with chickpea flour (TWP-CP) was measured and compared to beef meat proteins. In the main experiment, minipigs (n = 6) were fed a dish (blanquette type) containing 40 g of protein in the form of TWP-CP, TWP-CP enriched with free lysine TWP-CP+L, chicken filet, or texturized soy, together with quinoa (18.5 g of protein) in order to improve meal supply of lysine. Wheat protein texturing did not affect total amino acid TID (96.8 % for TWP vs 95.3 % for WP), which was not different from that of beef meat (95.8 %). Chickpea addition did not affect protein TID (96.5 % for TWP-CP vs 96.8 % for TWP). The Digestible Indispensable Amino Acid Score for adults of the dish combining TWP-CP+L with quinoa was 91, whereas it was 110 and 111 for the dishes containing chicken filet or texturized soy. The above results show that, by optimizing lysine content through the formulation of the product, wheat protein texturization can enable the development of protein-rich products of nutritional quality compatible with quality protein intake in the context of a complete meal.

Peripheral Amino Acid Appearance Is Lower Following Plant Protein Fibre Products, Compared to Whey Protein and Fibre Ingestion, in Healthy Older Adults despite Optimised Amino Acid Profile.

Plant-based proteins are generally characterised by lower Indispensable Amino Acid (IAA) content, digestibility, and anabolic properties, compared to animal-based proteins. However, they are environmentally friendlier, and wider consumption is advocated. Older adults have higher dietary protein needs to prevent sarcopenia, a disease marked by an accelerated loss of muscle mass and function. Given the lower environmental footprint of plant-based proteins and the importance of optimising dietary protein quality among older adults, this paper aims to assess the net peripheral Amino Acid (AA) appearance after ingestion of three different plant protein and fibre (PPF) products, compared to whey protein with added fibre (WPF), in healthy older adults. In a randomised, single-blind, crossover design, nine healthy men and women aged ≥65 years consumed four test meals balanced in AA according to the FAO reference protein for humans, matched for leucine, to optimally stimulate muscle protein synthesis in older adults. A fasted blood sample was drawn at each visit before consuming the test meal, followed by postprandial arterialise blood sampling every 30 min for 3 h. The test meal was composed of a soup containing either WPF or PPF 1-3. The PPF blends comprised pea proteins with varying additional rice, pumpkin, soy, oat, and/or almond protein. PPF product ingestion resulted in a lower maximal increase of postprandial leucine concentration and the sum of branched-chain AA (BCAA) and IAA concentrations, compared to WPF, with no effect on their incremental area under the curve. Plasma methionine and cysteine, and to a lesser extent threonine, appearance were limited after consuming the PPF products, but not WPF. Despite equal leucine doses, the WPF induced greater postprandial insulin concentrations than the PPF products. In conclusion, the postprandial appearance of AA is highly dependent on the protein source in older adults, despite providing equivalent IAA levels and dietary fibre. Coupled with lower insulin concentrations, this could imply less anabolic potential. Further investigation is required to understand the applicability of plant-based proteins in healthy older adults.

Cysteine fluxes across the portal-drained viscera of enterally fed minipigs: effect of an acute intestinal inflammation.

Cysteine is considered as a conditionally indispensable amino acid. Its dietary supply should thus be increased when endogenous synthesis cannot meet metabolic need, such as during inflammatory diseases. However, studies in animal models suggest a high first-pass extraction of dietary cysteine by the intestine, limiting the interest for an oral supplementation. We investigated here unidirectional fluxes of cysteine across the portal-drained viscera (PDV) of multi-catheterized minipigs, using simultaneous intragastric L-[(15)N] cysteine and intravenous L-[3,3D2] cysteine continuous infusions. We showed that in minipigs fed with an elemental enteral solution, cysteine first-pass extraction by the intestine is about 60% of the dietary supply, and that the PDV does not capture arterial cysteine. Beside dietary cysteine, the PDV release non-dietary cysteine (20% of the total cysteine release), which originates either from tissue metabolism or from reabsorption of endogenous secretion, such as glutathione (GSH) biliary excretion. Experimental ileitis induced by local administration of trinitrobenzene sulfonic acid, increased liver and ileal GSH fractional synthesis rate during the acute phase of inflammation, and increased whole body flux of cysteine. However, cysteine uptake and release by the PDV were not affected by ileitis, suggesting an adaptation of the intestinal sulfur amino acid metabolism in order to cover the additional requirement of cysteine linked to the increased GSH synthesis. We conclude that the small intestine sequesters large amounts of dietary cysteine during absorption, limiting its release into the bloodstream, and that the other tissues of the PDV (colon, stomach, pancreas, spleen) preferentially use circulating methionine or cysteine-containing peptides to cover their cysteine requirement.

True ileal amino acid digestibility and digestible indispensable amino acid scores (DIAASs) of plant-based protein foods.

Plant-based protein foods are increasingly common, but data on their nutritional protein quality are scarce. This study evaluated it for seitan (wheat-based food), tofu (soya-based food), soya milk, and a pea emulsion. The true ileal digestibility (TID) of their amino acids was determined in minipigs, to calculate the digestible indispensable amino acid score (DIAAS). The TID of the proteins was high and not significantly different between the foods tested: 97% for seitan, 95% for tofu, 92% for soya milk and 94% for pea emulsion. There were only minor differences in individual amino acid TIDs. DIAAS ranking was thus essentially driven by the amino acid composition of the food: soya-based food > pea emulsion > seitan. Nevertheless, the lower TID of sulphur-containing amino acids in tofu than in soya milk induced a significant decrease in DIAAS (from 117% to 97%), highlighting the importance of the matrix effect on nutritional protein quality.

Temporal changes in postprandial intragastric pH: Comparing measurement methods, food structure effects, and kinetic modelling.

Intragastric pH greatly affects food disintegration and the release of nutrients in the gut. Here, the behaviour of two liquid meals (soymilk, pea emulsion) and two solid meals (tofu, seitan) was tested in miniature pigs fitted with gastric cannula. For 5 h, intragastric pH was recorded using one of three methods: ex vivo measurements of chyme samples, in situ measurements using pH catheters, or in situ measurements using wireless pH capsules, both inserted through a pig's cannula. The pH values obtained with the two in situ methods were highly correlated. The liquid and solid foods yielded distinct pH kinetics. For the solids, pH simply decreased exponentially. For the liquids, pH increased rapidly and then plateaued for 2 h before dropping Food macrostructure and, to a lesser extent, food buffering capacity clearly had an impact on intragastric pH. We modelled changes in intragastric pH over time with food-dependent nonlinear equations.

Food Structure Modulates the Bioavailability of Triglycerides and Vitamin D, and Partly That of Lutein: A Randomized Trial with a Crossover Design in Adults.

SCOPE: The specific effect of the food matrix structure on fat-soluble micronutrient bioavailability is only partly understood. Evaluating fat-soluble micronutrient bioavailability after consumption of foods displaying similar composition but different structure is aimed at. METHODS AND RESULTS: Twelve healthy subjects are enrolled in a randomized, open label, crossover postprandial trial. Four different model foods are tested: custard, pudding, sponge cake, and biscuit. Vitamin D3 , lutein, and triglyceride chylomicron responses, evaluated as postprandial areas under the curve, are then assayed. Custard triglyceride response is higher than pudding and biscuit responses (up to +122.7%, p < 0.0001). Sponge cake vitamin D3 response is higher than biscuit response (+26.6%, p = 0.047). No difference between the model foods are observed regarding lutein responses. Triglyceride responses peak at 3 h for all conditions, while vitamin D3 and lutein peaks are delayed by 1 h with the biscuit matrix compared to other model foods. CONCLUSION: Food structure can significantly impact on triglyceride and vitamin D3 bioavailability in terms of absorbed amounts and/or maximum absorption time. The data highlight positive correlations between triglyceride, vitamin D, and lutein nutrient responses. These results are of particular interest to develop functional foods for population subgroups such as the elderly.

Effects of the apple matrix on the postprandial bioavailability of flavan-3-ols and nutrigenomic response of apple polyphenols in minipigs challenged with a high fat meal.

Food matrix interactions with polyphenols can affect their bioavailability and as a consequence may modulate their biological effects. The aim of this study was to determine if the matrix and its processing would modulate the bioavailability and the postprandial nutrigenomic response to a dietary inflammatory stress of apple flavan-3-ol monomers. We carried out an acute randomized controlled study in minipigs challenged with a high fat meal (HFM) supplemented with raw fruit, puree, or apple phenolic extract with matched content of flavan-3-ol monomers. Fasting and postprandial blood samples were collected over 3 h to quantify flavan-3-ol monomers in sera by UPLC-Q-TOF/MS and to isolate peripheral blood mononuclear cells (PBMCs) for assessing the changes in the gene expression profile using a microarray analysis. When compared to the extract-supplemented meal, the peak of the total flavan-3-ol concentration was reduced by half with both raw apple and puree supplements. The apple matrices also affected the gene expression profile as revealed by the Principal Component Analysis of the microarray data from PBMCs which discriminated the supplementation of HFM with the polyphenol extract from those with raw apples or puree. A total of 309 genes were identified as differentially expressed by the apple-derived products compared to HFM, with 63% modulated only in the presence of the food matrix (apple and puree). The number of differentially modulated genes was higher with the puree (246) than with the unprocessed apple (182). Pathway enrichment analyses revealed that genes affected by the apple-derived products control inflammation and leukocyte transendothelial migration both involved in the onset of atherosclerotic processes. Overall, this study showed that the two apple matrices reduce the postprandial serum concentration of flavon-3-ols whereas they increase the nutrigenomic response of PBMCs. The biological processes identified as modulated by the apple products suggest an attenuation of the transient pro-inflammatory response induced by a HFM. The differences observed between the nutrigenomic responses support that the apple matrix and its processing affect the nutrigenomic response, probably by increasing the bioavailability of other apple phytochemicals. To conclude, this study raises awareness for considering the impact of the food matrix and its processing on the biological response of polyphenols in nutritional studies.

Intestinal inflammation increases gastrointestinal threonine uptake and mucin synthesis in enterally fed minipigs.

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-[(15)N]threonine and i.v. L-[U-(13)C]threonine infusions. Ileal mucosa was sampled for mucin fractional synthesis rate measurement, which was greater in the TNBS-treated group (114 +/- 15%/d) than in the control group (61 +/- 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 approximately 27 and 10% of the intragastric delivery, respectively. PDV uptake of arterial threonine increased from 25 +/- 14 micromol x kg(-1) x h(-1) in the control group to 171 +/- 35 micromol x kg(-1) x h(-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.

Differential response of protein metabolism in splanchnic organs and muscle to pectin feeding.

The aim of the present study was to determine whether the addition of soluble fibre in the diet affected protein metabolism in the intestinal tissues, some visceral organs and in skeletal muscle. A diet supplemented with pectin (80 g/kg) was fed to young growing rats and the effect on organ mass and protein metabolism in liver, spleen, small and large intestines and gastrocnemius muscle was monitored and compared with the control group. Protein synthesis rates were determined by measuring [13C]valine incorporation in tissue protein. In the pectin-fed rats compared with the controls, DM intake and body weight gain were reduced (9 and 20 %, respectively) as well as gastrocnemius muscle, liver and spleen weights (6, 14 and 11 %, respectively), but the intestinal tissues were increased (64 %). In the intestinal tissues all protein metabolism parameters (protein and RNA content, protein synthesis rate and translational efficiency) were increased in the pectin group. In liver the translational efficiency was also increased, whereas its protein and RNA contents were reduced in the pectin group. In gastrocnemius muscle, protein content, fractional and absolute protein synthesis rates and translational efficiency were lower in the pectin group. The stimulation of protein turnover in intestines and liver by soluble fibre such as pectins could be one of the factors that explain the decrease in muscle turnover and whole-body growth rate.

The matrix of fruit & vegetables modulates the gastrointestinal bioaccessibility of polyphenols and their impact on dietary protein digestibility.

Fruit and vegetables (F&V) polyphenols have numerous positive health effects, ascribed either to their antioxidant activity within the gastrointestinal tract (GIT) or to bioactivity of their absorbed metabolites. The effect of the F&V matrix on the gastrointestinal bioaccessibility of polyphenols was investigated along with its possible interaction with protein digestion. Minipigs were fed a complete meal with either cubed F&V (apple, plum, artichoke) added, or the corresponding phenolic extract (PE). Gastric and ileal chymes were kinetically collected over the postprandial period. The overall polyphenol bioaccessibility in the stomach was found to be 1.5% and 3.1% after F&V and PE consumption, respectively. The lower release rate from artichoke than from apple showed evidence of a plant effect. Flavanol monomers and glucoside conjugates were not recovered in the ileum in agreement with their absorption in the upper GIT. Interestingly, PE, but not F&V, significantly decreased the speed and efficiency of dietary protein digestion.

Opposite Effects of the Spinach Food Matrix on Lutein Bioaccessibility and Intestinal Uptake Lead to Unchanged Bioavailability Compared to Pure Lutein.

SCOPE: Food matrix is generally believed to alter carotenoid bioavailability, but its effect on xanthophylls is usually limited. This study thus aims to decipher the digestion-absorption process of lutein in the presence or not of a food matrix. METHODS: Lutein transfer to gastric-like lipid droplets or artificial mixed micelles was assessed when lutein was added to test meals either as a pure molecule ((all-E)-lutein) or in canned spinach ((Z) + (all-E)-lutein). The obtained mixed micelles were delivered to Caco-2 cells to evaluate lutein uptake. Finally postprandial plasma lutein responses were compared in minipigs after the two test meals. RESULTS: Lutein transfer to gastric-like lipid droplets and to mixed micelles was higher when lutein was added in spinach than when it was added as pure lutein (+614% and +147%, respectively, p < 0.05). Conversely, lutein uptake was less effective when micellar lutein was from a meal containing spinach than from a meal containing its pure form (-55%, p < 0.05). In minipigs, postprandial lutein response was delayed with spinach but not significantly different after the two test meals. CONCLUSION: Opposite effects at the micellarization and intestinal cell uptake steps explain the lack of effect of spinach matrix on lutein bioavailability.

Postprandial whole-body protein metabolism after a meat meal is influenced by chewing efficiency in elderly subjects.

BACKGROUND: The rate of protein digestion affects protein utilization in elderly subjects. Although meat is a widely consumed protein source, little is known of its digestion rate and how it can be affected by the chewing capacity of elderly subjects. OBJECTIVES: We used a [1-(13)C]leucine balance with a single-meal protocol to assess the absorption rate of meat protein and to estimate the utilization of meat protein in elderly subjects with different chewing efficiency. DESIGN: Twenty elderly volunteers aged 60-75 y were involved in the study. Ten of them had healthy natural dentition, and the other 10 were edentulous and wore complete dentures. Whole-body fluxes of leucine, before and after the meal (120 g beef meat), were measured with the use of a [1-(13)C]leucine intravenous infusion. RESULTS: A rapid increase in plasma aminoacidemia and plasma leucine entry rate was observed after meat intake in dentate subjects. In complete denture wearers the increase in leucine entry rate was delayed (P<0.05), and the amount of leucine appearing in peripheral blood during the whole postprandial period was lower than in dentate subjects (P<0.01). Postprandial whole-body protein synthesis was lower in denture wearers than in dentate subjects (30% compared with 48% of leucine intake, respectively; P<0.05). CONCLUSION: Meat proteins could be classified as fast digested proteins. However, this property depends on the chewing capacity of elderly subjects. This study showed that meat protein utilization for protein synthesis can be impaired by a decrease in the chewing efficiency of elderly subjects.

Effect of an enteral diet supplemented with a specific blend of amino acid on plasma and muscle protein synthesis in ICU patients.

BACKGROUND & AIM: Polytrauma patients are characterized by a negative nitrogen balance and muscle wasting. Standard nutrition is relatively inefficient to improve muscle protein turnover. The aim of this study was to investigate the effect of enteral nutrition (EN) supplemented with specific amino acids on protein metabolism in polytrauma patients. METHODS: In a double blind study, 12 polytrauma patients were randomized to receive EN supplemented with either a mixture of cysteine, threonine, serine and aspartate (AA patients) or alanine at isonitrogenous levels (Ala patients). An intravenous infusion of l-[1-(13)C]-leucine was performed in the fed state between day 9 and 12 post-injury (Df) in patients and in a group of healthy volunteers (n=8) (EN+Ala) to measure whole body leucine kinetics, plasma and muscle protein synthesis rates. Nitrogen balance, 3-methyl histidine excretion were measured from day 3 to Df. RESULTS: The contribution of total plasma proteins to whole body protein synthesis was greatly increased, from 11% in healthy volunteers to about 25% in polytrauma patients. AA supplementation had no effect on nitrogen balance, leucine kinetics or plasma protein synthesis in patients. In contrast, the urinary excretion of 3-methyl histidine tended to decrease along the study in the AA supplemented group compared to an increase in the Ala group. Muscle protein synthesis tended to be higher in the AA group than in the Ala group (46%, P=0.065). CONCLUSION: During injury, an increased supply of cysteine, threonine, serine and aspartate could be able to better cover the specific amino requirements, thus resulting in improved muscle protein synthesis without impairment of acute phase protein synthesis.

In the elderly, meat protein assimilation from rare meat is lower than that from meat that is well done.

Background: Meat cooking conditions in in vitro and in vivo models have been shown to influence the rate of protein digestion, which is known to affect postprandial protein metabolism in the elderly.Objective: The present study was conducted to demonstrate the effect of cooking conditions on meat protein assimilation in the elderly. We used a single-meal protocol to assess the meat protein absorption rate and estimate postprandial meat protein utilization in elderly subjects.Design: The study recruited 10 elderly volunteers aged 70-82 y. Each received, on 2 separate occasions, a test meal exclusively composed of intrinsically 15N-labeled bovine meat (30 g protein), cooked at 55°C for 5 min [rare meat (RM)] or at 90°C for 30 min [fully cooked meat (FCM)], and minced. Whole-body fluxes of leucine, before and after the meal, were determined with the use of a [1-13C]leucine intravenous infusion. Meat protein absorption was recorded with the use of 15N enrichment of amino acids.Results: Postprandial time course observations showed a lower concentration in the plasma of indispensable amino acids (P < 0.01), a lower entry rate of meat leucine in the plasma (P < 0.01), and a lower contribution of meat nitrogen to plasma amino acid nitrogen (P < 0.001), evidencing lower peripheral bioavailability of meat amino acids with RM than with FCM. This was associated with decreased postprandial whole-body protein synthesis with RM than with FCM (40% compared with 56% of leucine intake, respectively; P < 0.01).Conclusions: Whereas meat cooking conditions have little effect on postprandial protein utilization in young adults, the present work showed that the bioavailability and assimilation of meat amino acids in the elderly is lower when meat is poorly cooked. In view to preventing sarcopenia, elderly subjects should be advised to favor the consumption of well-cooked meat. This trial was registered at clinicaltrials.gov as NCT02157805.

Methionine kinetics are altered in the elderly both in the basal state and after vaccination.

BACKGROUND: Inflammation is known to affect sulfur amino acid metabolism. Aging is associated with an increased prevalence of inflammatory conditions, but the metabolism of methionine has been poorly explored in the elderly. OBJECTIVES: The aims of this study were to compare methionine kinetics between elderly and young subjects and to explore the effect of aging on the response to a mild inflammatory challenge induced by a vaccination. DESIGN: Seven elderly volunteers aged 66-76 y and 8 young volunteers aged 22-26 y were studied before and 2 d after a vaccination (diphtheria, tetanus, poliomyelitis, and typhoid vaccines). Methionine kinetics were measured by using an infusion of L-[1-13C, methyl-2H3]methionine in the postabsorptive and fed states. RESULTS: Before vaccination, the contribution of homocysteine remethylation to methionine-methyl flux (Qm) and the ratio of remethylation to homocysteine transsulfuration were significantly lower in the elderly subjects than in the young subjects (P < 0.05). In contrast, the contribution of transsulfuration to methionine transmethylation was higher in the elderly (P < 0.05). Vaccination significantly increased the ratio of transsulfuration to transmethylation and decreased the ratio of remethylation to Qm (P < 0.05). CONCLUSIONS: The preferential methionine metabolism toward cysteine synthesis observed after vaccination suggests an increased requirement of sulfur amino acids even in mild inflammatory situations. The main finding of this study is a higher proportion of methionine entering the transsulfuration pathway in elderly subjects before vaccination. This finding suggests an increased cysteine demand during aging.

Beneficial effect of amino acid supplementation, especially cysteine, on body nitrogen economy in septic rats.

BACKGROUND AND AIMS: Muscle wasting and increased synthesis of proteins and compounds involved in host defense characterize severe injury. The aims of the studies reported were to determine which amino acids exhibited an increased tissue content linked to anabolic processes in infected rats by comparison with healthy pair-fed controls, and to explore whether diets supplemented with these amino acids attenuate the catabolic response to infection. METHODS: Total amino acid content of the liver and the rest of the body were measured in control well-fed rats, in infected rats and their pair-fed controls 2 days after infection. In the nutritional protocols, infected rats were fed with a diet supplemented with alanine (basal diet), or threonine, serine, aspartate, asparagine and arginine (AA) or AA+cysteine (complete diet). RESULTS: Infection significantly increased liver total amino acid content by 38% for most amino acids. In contrast, the percentage increase was cysteine 79.3, threonine 45.3, aspartate-asparagine 46.3 and serine 46.5. Whole body without liver content of most amino acids decreased after infection due to the catabolic response, while the content of cysteine increased by 6% (P<0.05) and those of threonine and arginine did not decrease. After infection, animals fed the complete diet lost less weight than animals fed the basal diet (P<0.05). Furthermore, AA plus cysteine supplementation reduced significantly urinary nitrogen excretion and muscle wasting. CONCLUSIONS: The results provide evidence that diet supplementation with cysteine, threonine, serine, aspartate-asparagine and arginine supports the synthesis of vital proteins to spare body protein catabolism during infection.

Differential variation of mitochondrial H2O2 release during aging in oxidative and glycolytic muscles in rats.

Mitochondrial free radical (ROS) production could be involved in sarcopenia. Our aim was to measure this production in various muscles during aging. Male Wistar rats aged 4.5 and 24 months were used. H(2)O(2) release and protein carbonyls were evaluated in isolated mitochondria from an oxidative (soleus) and a glycolytic (tibialis anterior) muscle. Total and Mn-superoxide dismutase (SOD), catalase, glutathione peroxidase (GPX) and glutathione reductase (GR) activities were measured in tibialis anterior. In soleus, glutamate/malate supported mitochondrial H(2)O(2) release was lower than in tibialis anterior in young rats, but increased significantly with age. In tibialis anterior, glutamate/malate or succinate supported H(2)O(2) release was unchanged with age. ROS generators were complexes I and III. Mitochondrial carbonyl content remained stable during aging in both muscles but tended to be higher in tibialis anterior than in soleus. Tibialis anterior total SOD (+17%), catalase (+84%), and GPX (-17%) activities varied significantly with age but Mn-SOD was unchanged, suggesting an increase in cytosolic ROS production. In conclusion, the higher life-long H(2)O(2) release observed in tibialis anterior is consistent with the known sensitivity of glycolytic muscles to sarcopenia. The fact that the rate of H(2)O(2) release increases with age in soleus seems to have little impact.

Age-related changes in glutathione availability and skeletal muscle carbonyl content in healthy rats.

The free radical theory of aging proposes that oxidative stress plays a key role in the aging process. By altering muscle protein degradation rates, it could accelerate the age-related loss of muscle proteins. Glutathione (GSH), one of the main body antioxidants, could prevent this phenomenon, but its concentration decreases during aging. Our aims were to have a better understanding of the mechanisms of the age-related decrease in glutathione availability and of the links with sarcopenia. Male Wistar rats aged 6, 9, 12, 15, 19, 22, 25 and 28 months (n = 6 per age) were used to measure plasma and skeletal muscle protein carbonyl content, plasma total and free cyst(e)ine content, liver and muscle glutathione content as well as liver GSSG reductase, GSH peroxidase, GSH transferase and gamma glutamyl cysteine synthetase (GCS) activities. Although tissue glutathione content decreased with age, the other markers of oxidative stress were little changed during aging. In particular, muscle protein carbonyl content was unchanged. Variations in glutathione availability were not explained by cyst(e)ine availability but depended on gamma GCS activity. The stability of skeletal muscle carbonyl content during aging suggests a very efficient degradation of oxidized proteins in muscle.