372 research outputs found
Conceptual, methodological and computational issues concerning the compartmental modeling of a complex biological system: postprandial inter-organ metabolism of dietary nitrogen in humans.
No full textA multi-compartmental model has been developed to describe dietary nitrogen (N) postprandial distribution and metabolism in humans. This paper details the entire process of model development, including the successive steps of its construction, parameter estimation and validation. The model was built using experimental data on dietary N kinetics in certain accessible pools of the intestine, blood and urine in healthy adults fed a [15N]-labeled protein meal. A 13-compartment, 21-parameter model was selected from candidate models of increasing order as being the minimum structure able to properly fit experimental data for all sampled compartments. Problems of theoretical identifiability and numerical identification of the model both constituted mathematical challenges that were difficult to solve because of the large number of unknown parameters and the few experimental data available. For this reason, new robust and reliable methods were applied, which enabled (i) a check that all model parameters could theoretically uniquely be determined and (ii) an estimation of their numerical values with satisfactory precision from the experimental data. Finally, model validation was completed by first verifying its a posteriori identifiability and then carrying out external validation
Multicompartmental modeling of a complex physiological system: special emphasis on the steps of a priori identifiability and parameter estimation.
No full textBioavailability of dietary proteins and amino acids in humans
No full textInternational audienceIn humans, dietary proteins are the only bioavailable source of nitrogen. The amino acids they contain are necessary to sustain protein synthesis and turnover. Among the 20 amino acids that make up proteins, 9 of them are indispensable because they can’t be de novo synthetized. Together with amino acid composition, protein bioavailability is an important criteria of protein quality. Efficiency of protein digestion is a critical step that impacts protein bioavailability. In healthy people, the protein source is a determinant factor of protein bioavailability. Milk proteins are the highest digestible (95 %) followed by meat (94 %) while most purified plant proteins are digestible at a level of 90-91 % (Oberli et al, 2015). Other nutrients that are present in the food matrices, such as fibers or polyphenols, can decrease protein digestion efficiency. After intestinal absorption, metabolic losses through urea production also influences protein bioavailability. This depends not only on the amino acid composition but also on the speed of digestion. For instance, whey proteins are less retained postprandially (67 %) than caseins (73 %) due to their rapid digestion kinetic, while their amino acid composition is excellent (Lacroix et al, 2006). Wheat proteins exhibit a lower postprandial retention (65 %) than other plant sources such as soy or pea (73 %), as a result of their poor lysine content (Bos et al, 2005). In vivo measurement of protein bioavailability faces with important methodological barriers. Because peptide and amino acid absorption occurs in the small intestine and that proteins and peptides entering to the colon are fermented by microbiota, digestibility should be measured at the ileal level. However, this implies invasive procedures, such as cannula in pigs or intestinal tubes in humans, to collect ileal effluents. As a consequence, measurements are often performed at the fecal level, especially in rats, to calculate a value of PD-CAAS (Protein Digestibility Corrected Amino Acid Score) that has been recommended as a criteria of protein quality by the FAO. Fecal measurements overestimate protein digestibility because nitrogen that is transferred to ammonia by microbiota is partly absorbed in the colon, but the error is considered as acceptable. More recently (FAO, 2011), FAO has recommended to assess the digestion of each indispensable amino acid, instead of the total protein, to calculate a DIAAS (Digestible Indispensable Amino Acid Score). For milk and soy proteins, ileal digestibility has revealed differences of 4-5 % among amino acids in humans (Gaudichon et al, 2002). In people for which protein intake is limited and/or of poor quality, these variations can result in non-adequate intake of some amino acids compared to requirements. To provide DIAAS values, fecal measurements are not reliable anymore because the impact of microbial metabolism on individual amino acid content is high. Another important methodological issue related to protein bioavailability is the discrimination between endogenous and exogenous proteins in the digestive and metabolic losses. Endogenous losses can be assessed using protein free diets but the use of stable isotopes is the most accurate to follow the digestive and metabolic fate of dietary proteins and amino acids. Among labelling methods, 15N has been widely used to intrinsically label all amino acids of the protein, especially in plants and ruminants. 13C is often used to label a single amino acid that is considered to be representative of all the other amino acids in the protein. Multitracer methods were recently proposed (FAO, 1994) as an alternative method to remove the methodological barriers related to DIAAS calculation, by throwing off the invasive procedures to collect effluents. Nevertheless, these methods are complex and they need to be developed and validated.In conclusion, bioavailability of protein and amino acids is an important criteria of protein quality. It is an important issue in the view of finding alternative protein sources to preserve environment and to feed humans over the world in the near future. However, it must be kept in mind that its assessment in humans faces with methodological complexity.*Bos C et al. Postprandial metabolic utilization of wheat protein in humans. Am J Clin Nutr. 2005;81(1):87-94. *FAO. Dietary protein quality evaluation in human nutrition. Rome: 2011.*FAO. Research approaches and methods for evaluating the protein quality of human foods. Rome: 2014.*Gaudichon C et al. Ileal losses of nitrogen and amino acids in humans and their importance to the assessment of amino acid requirements. Gastroenterology. 2002;123(1):50-9. *Lacroix M et al. Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement.*Oberli M et al. High True Ileal Digestibility but Not Postprandial Utilization of Nitrogen from Bovine Meat Protein in Humans Is Moderately Decreased by High-Temperature, Long-Duration Cooking. J Nutr. 2015 Oct;145(10):2221-8
Bioavailability of dietary proteins and amino acids in humans
No full textInternational audienceIn humans, dietary proteins are the only bioavailable source of nitrogen. The amino acids they contain are necessary to sustain protein synthesis and turnover. Among the 20 amino acids that make up proteins, 9 of them are indispensable because they can’t be de novo synthetized. Together with amino acid composition, protein bioavailability is an important criteria of protein quality. Efficiency of protein digestion is a critical step that impacts protein bioavailability. In healthy people, the protein source is a determinant factor of protein bioavailability. Milk proteins are the highest digestible (95 %) followed by meat (94 %) while most purified plant proteins are digestible at a level of 90-91 % (Oberli et al, 2015). Other nutrients that are present in the food matrices, such as fibers or polyphenols, can decrease protein digestion efficiency. After intestinal absorption, metabolic losses through urea production also influences protein bioavailability. This depends not only on the amino acid composition but also on the speed of digestion. For instance, whey proteins are less retained postprandially (67 %) than caseins (73 %) due to their rapid digestion kinetic, while their amino acid composition is excellent (Lacroix et al, 2006). Wheat proteins exhibit a lower postprandial retention (65 %) than other plant sources such as soy or pea (73 %), as a result of their poor lysine content (Bos et al, 2005). In vivo measurement of protein bioavailability faces with important methodological barriers. Because peptide and amino acid absorption occurs in the small intestine and that proteins and peptides entering to the colon are fermented by microbiota, digestibility should be measured at the ileal level. However, this implies invasive procedures, such as cannula in pigs or intestinal tubes in humans, to collect ileal effluents. As a consequence, measurements are often performed at the fecal level, especially in rats, to calculate a value of PD-CAAS (Protein Digestibility Corrected Amino Acid Score) that has been recommended as a criteria of protein quality by the FAO. Fecal measurements overestimate protein digestibility because nitrogen that is transferred to ammonia by microbiota is partly absorbed in the colon, but the error is considered as acceptable. More recently (FAO, 2011), FAO has recommended to assess the digestion of each indispensable amino acid, instead of the total protein, to calculate a DIAAS (Digestible Indispensable Amino Acid Score). For milk and soy proteins, ileal digestibility has revealed differences of 4-5 % among amino acids in humans (Gaudichon et al, 2002). In people for which protein intake is limited and/or of poor quality, these variations can result in non-adequate intake of some amino acids compared to requirements. To provide DIAAS values, fecal measurements are not reliable anymore because the impact of microbial metabolism on individual amino acid content is high. Another important methodological issue related to protein bioavailability is the discrimination between endogenous and exogenous proteins in the digestive and metabolic losses. Endogenous losses can be assessed using protein free diets but the use of stable isotopes is the most accurate to follow the digestive and metabolic fate of dietary proteins and amino acids. Among labelling methods, 15N has been widely used to intrinsically label all amino acids of the protein, especially in plants and ruminants. 13C is often used to label a single amino acid that is considered to be representative of all the other amino acids in the protein. Multitracer methods were recently proposed (FAO, 1994) as an alternative method to remove the methodological barriers related to DIAAS calculation, by throwing off the invasive procedures to collect effluents. Nevertheless, these methods are complex and they need to be developed and validated.In conclusion, bioavailability of protein and amino acids is an important criteria of protein quality. It is an important issue in the view of finding alternative protein sources to preserve environment and to feed humans over the world in the near future. However, it must be kept in mind that its assessment in humans faces with methodological complexity.*Bos C et al. Postprandial metabolic utilization of wheat protein in humans. Am J Clin Nutr. 2005;81(1):87-94. *FAO. Dietary protein quality evaluation in human nutrition. Rome: 2011.*FAO. Research approaches and methods for evaluating the protein quality of human foods. Rome: 2014.*Gaudichon C et al. Ileal losses of nitrogen and amino acids in humans and their importance to the assessment of amino acid requirements. Gastroenterology. 2002;123(1):50-9. *Lacroix M et al. Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement.*Oberli M et al. High True Ileal Digestibility but Not Postprandial Utilization of Nitrogen from Bovine Meat Protein in Humans Is Moderately Decreased by High-Temperature, Long-Duration Cooking. J Nutr. 2015 Oct;145(10):2221-8
Dietary protein regulates hepatic constitutive protein anabolism in rats in a dose-dependent manner and independently of energy nutrient composition
No full textInternational audienceChevalier L, Bos C, Azzout-Marniche D, Dardevet D, Tome D, Gaudichon C. Dietary protein regulates hepatic constitutive protein anabolism in rats in a dose-dependent manner and independently of energy nutrient composition. Am J Physiol Regul Integr Comp Physiol 299: R1720-R1730, 2010. First published October 6, 2010; doi:10.1152/ajpregu.00497.2010.-We had previously observed that drastic increases in protein consumption greatly modified hepatic protein anabolism in rats, but the confounding effects of other macronutrient changes or a moderate protein increase to generate the same modifications have not yet been established. This study examined the metabolic and hormonal responses of rats subjected to 14-day isoenergetic diets containing normal, intermediate, or high-protein levels (NP: 14% of energy, IP: 33%, HP: 50%) and different carbohydrate (CHO) to fat ratios within each protein level. Fasted or fed rats (n = 104) were killed after the injection of a flooding dose of C-13-valine. The hepatic protein content increased in line with the dietary protein level (P < 0.05). The hepatic fractional synthesis rates (FSR) of protein were significantly influenced by both the protein level and the nutritional state (fasted vs. fed) (P < 0.0001) but not by the CHO level, reaching on average 110%/day, 92%/day, and 83%/day in rats fed the NP, IP, and HP diets, respectively. The FSR of plasma albumin and muscle did not differ between diets, while feeding tended to increase muscle FSR. Proteolysis, especially the proteasome-dependent system, was down-regulated in the fed state in the liver when protein content increased. Insulin decreased with the CHO level in the diet. Our results reveal that excess dietary protein lowers hepatic constitutive, but not exported, protein synthesis rates, independently of the other macronutrients, and related changes in insulin levels. This response was observed at the moderate levels of protein intake (33%) that are plausible in a context of human consumption
Adaptation to a high-protein diet progressively increases the postprandial accumulation of carbon skeletons from dietary amino acids in rats
No full textWe aimed to determine whether oxidative pathways adapt to the overproduction of carbon skeletons resulting from the progressive activation of amino acid (AA) deamination and ureagenesis under a high-protein (HP) diet. Ninety-four male Wistar rats, of which 54 were implanted with a permanent jugular catheter, were fed a normal protein diet for 1 wk and were then switched to an HP diet for 1, 3, 6, or 14 days. On the experimental day, they were given their meal containing a mixture of 20 U-[N-15]-[C-13] AA, whose metabolic fate was followed for 4 h. Gastric emptying tended to be slower during the first 3 days of adaptation. N-15 excretion in urine increased progressively during the first 6 days, reaching 29% of ingested protein. (CO2)-C-13 excretion was maximal, as early as the first day, and represented only 16% of the ingested proteins. Consequently, the amount of carbon skeletons remaining in the metabolic pools 4 h after the meal ingestion progressively increased to 42% of the deaminated dietary AA after 6 days of HP diet. In contrast, C-13 enrichment of plasma glucose tended to increase from 1 to 14 days of the HP diet. We conclude that there is no oxidative adaptation in the early postprandial period to an excess of carbon skeletons resulting from AA deamination in HP diets. This leads to an increase in the postprandial accumulation of carbon skeletons throughout the adaptation to an HP diet, which can contribute to the sustainable satiating effect of this diet
Les critères de qualité des protéines ont-il évolué?
No full textInternational audienceLa qualité des protéines dépend de leur capacité à fournir des acides aminés indispensables en quantité suffisante pour permettre, notamment, une synthèse optimale des protéines corporelles. Plusieurs critères sont utilisés pour rendre compte de cette capacité, en se basant sur des mesures in vivo chez l’Homme ou sur modèle animal, ou sur l’analyse de la composition en acides aminés des protéines. Les approches in vivo sont, soit des mesures de croissance chez le rat (coefficient d’efficacité protéique), soit des mesures de biodisponibilité digestive (digestibilité, absorption) et métabolique (rétention azotée, valeur biologique) des protéines. Les mesures de digestibilité des protéines, et surtout des acides aminés, présentent des contraintes méthodologiques fortes et des développements ont été proposés récemment pour s’affranchir du recours à des méthodes invasives. Le critère basé sur la composition des protéines le plus utilisé est le PD-CAAS (score chimique corrigé de la digestibilité de la protéine). L’Organisation des Nations Unies pour l’alimentation et l’agriculture (FAO) a proposé en 2011 de le remplacer par le DIAAS (score chimique corrigé de la digestibilité des acides aminés) ce qui le rend plus difficile à déterminer en raison des freins méthodologiques relatifs à la mesure des digestibilités individuelles des acides aminés. Ces indices basés sur les scores chimiques dépendent par principe fortement de la composition de la protéine, mais aussi du profil de besoin en acides aminés de l’Homme dont la dernière mise à jour date de 2007
Evolution and significance of amino acid scores for protein quality
No full textInternational audienceAmino acid scores have become very popular protein quality scores since their definition and recommendation by FAO expert groups. The chemical score is the central pillar of this method, and has been refined with digestibility correction factors, such as protein digestibility for the PD-CAAS and amino acid digestibility for the DIAAS. Several elements need to be taken into account to properly determine these scores, not only from a methodological point of view but also in order to reconcile regulation, pragmatism, accuracy and also biological significance. This review offers a reminder of the main points raised in the FAO reports on protein and AA requirements in 1995 and 2007, and on protein quality in 1991 and 2013. It also highlights the factors that most impact score metrics, and in particular the choice of reference pattern and protein determination in the food. Lastly, the scores are compared, and versus another quality score based on the physiological response, the protein efficiency ratio.</div
[C-13] GC-C-IRMS analysis of methylboronic acid derivatives of glucose from liver glycogen after the ingestion of [C-13] labeled tracers in rats
No full textWe developed a complete method to measure low [C-13] enrichments in glycogen. Fourteen rats were fed a control diet. Six of them also ingested either [U-C-13] glucose (n = 2) or a Mixture of 20 [U-C-13] amino acids (n = 4). Hepatic glycogen was extracted, digested to glucose and purified on anion-cation exchange resins. After the optimization of methylboronic acid derivatization using GC-MS, [C-13] enrichment of extracted glucose was measured by GC-C-IRMS. The accuracy was addressed by measuring the enrichment excess of a calibration curve, which observed values were in good agreement with the expected values (R = 0.9979). Corrected delta values were -15.6 +/- 1.6 delta C-13 (parts per thousand) for control rats (n = 8) and increased to -5 to delta C-13 (parts per thousand) parts per thousand and 12-14 delta C-13 (parts per thousand) parts per thousand after the ingestion of [U-C-13] amino acids or [U-C-13] glucose as oral tracers, respectively. The method enabled the determination of dietary substrate transfer into glycogen. The sequestration of dietary glucose in liver glycogen 4 h after the meal was 35% of the ingested dose whereas the transfer of carbon skeletons from amino acids was only 0.25 to 1%
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