Biomedical subjects

Daniel Tomé

Publications and source records attributed to Daniel Tomé.

54 records · Page 3Linked to original sources

PubMed2003

Contribution of plasma proteins to splanchnic and total anabolic utilization of dietary nitrogen in humans.

Splanchnic tissues are largely involved in the postprandial utilization of dietary amino acids, but little is yet known, particularly in humans, about the relative contributions of different splanchnic protein pools to splanchnic and total postprandial anabolism. Our aim was to develop a compartmental model that could distinguish dietary nitrogen (N) incorporation among splanchnic constitutive, plasma (splanchnic exported), and peripheral proteins after a mixed-protein meal in humans. Eight healthy subjects were fed a single mixed meal containing 15N-labeled soy protein, and dietary N postprandial kinetics were measured in plasma free amino acids, proteins, and urea and urinary urea and ammonia. These experimental data and others previously obtained for dietary N kinetics in ileal effluents under similar experimental conditions were used to develop the compartmental model. Six hours after the mixed-meal ingestion, 31.5, 7.5, and 21% of ingested N were predicted to be incorporated into splanchnic constitutive, splanchnic exported, and peripheral proteins, respectively. The contribution of splanchnic exported proteins to total splanchnic anabolism from dietary N was predicted to be approximately 19% and to remain steady throughout the simulation period. Model behavior and its predictions were strongly in line with current knowledge of the system and the scarce, specific data available in the literature. This model provides the first data concerning the anabolism of splanchnic constitutive proteins in the nonsteady postprandial state in humans. By use of only slightly invasive techniques, this model could help to assess how the splanchnic anabolism is modulated under different nutritional or pathophysiological conditions in humans.

Abdomen↗

PubMed2003

A high-protein diet enhances satiety without conditioned taste aversion in the rat.

In order to determine the respective roles of conditioned food aversion, satiety and palatability, we studied behavioral responses to a 50% total milk protein diet, compared with those to a normal protein diet containing 14% total milk protein. Different paradigms were employed, including meal pattern analysis, two-choice testing, flavor testing, a behavioral satiety sequence (BSS) and taste reactivity. Our experiments showed that only behavioral and food intake parameters were disturbed during the first day when an animal ate the high-protein (P50) diet, and that most parameters returned to baseline values as soon as the second day of P50. Rats adapted to P50 did not acquire a conditioned taste aversion (CTA) but exhibited satiety, and a normal BSS. The initial reduction in high-protein diet intake appeared to result from the lower palatability of the food combined with the satiety effect of the high-protein diet and the delay required for metabolic adaptation to the higher protein level.

Animals↗

PubMed2003

Pharmacokinetics and feeding responses to muramyl dipeptide in rats.

N-acetyl-muramyl-L-alanine-D-isoglutamine or muramyl dipeptide (MDP) is the minimally active subunit of bacterial peptidoglycan. During a systemic infection, the involvement of MDP has been demonstrated in food intake depression by the macrophage hydrolysis of Gram-positive bacteria. Under normal conditions, mammals are constantly exposed to the release of endogenous MDP from degraded gut flora and that of exogenous MDP from the diet. However, MDP digestion and absorption in the gastrointestinal tract are not fully understood, and their physiological significance needs to be clarified. After gavage (1.5 mg/kg), very low levels of MDP were found in the systemic circulation of rats and feeding patterns were not altered. In contrast, after the intraperitoneal injection of a similar dose, a depression in food intake was observed. The rats reduced their meal frequency and constant feeding rate, showing signs of satiety. The behavioral satiety sequence (BSS) was modified by behavioral changes, similar to those which appear during sickness, such as an increase in resting and a reduction in grooming. Our data suggest that the hypophagic effect of MDP may result from satiety and sickness behavior.

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMed2003

Postprandial kinetics of dietary amino acids are the main determinant of their metabolism after soy or milk protein ingestion in humans.

Soy proteins have been shown to result in lower postprandial nitrogen retention than milk proteins, but the mechanisms underlying these differences have not been elucidated. To investigate this question, we measured the postprandial kinetics of the appearance of individual (15)N-amino acids in the serum of healthy adults after the ingestion of either (15)N-soy (n = 8) or (15)N-milk proteins (n = 8) in a mixed single meal (46 kJ/kg). The kinetics of total and dietary amino acids (AA) in the peripheral circulation were characterized by an earlier and higher peak after soy protein ingestion. Dietary AA levels peaked at 2.5 h in the soy group vs. 3.9 h in the milk group (P < 0.02). This time interval difference between groups was associated with a faster transfer of dietary N into urea in the soy group (peak at 3 vs. 4.75 h in the milk group, P < 0.005) and a higher level of incorporation into the serum protein pool from 3 to 8 h after the soy meal. The dietary AA pattern in the peripheral blood closely reflected the dietary protein AA pattern. Postprandial glucose, insulin, and glucagon levels and profiles did not differ between groups. Soy AA were digested more rapidly and were directed toward both deamination pathways and liver protein synthesis more than milk AA. We conclude that differences in the metabolic postprandial fates of soy and milk proteins are due mainly to differences in digestion kinetics; however, the AA composition of dietary proteins may also play a role.

Adult↗

PubMed2003

Threonine deprivation rapidly activates the system A amino acid transporter in primary cultures of rat neurons from the essential amino acid sensor in the anterior piriform cortex.

Omnivores show recognition of essential (indispensable) amino acid deficiency by changing their feeding behavior within 20 min, yet the cellular mechanisms of amino acid sensation in eukaryotes are poorly understood. The anterior piriform cortex (APC) of the brain in rats or its analog in birds likely houses the in vivo amino acid chemosensor. Because amino acid transporters adapt rapidly to essential amino acid deficiency in several cell models, we hypothesized that activation of electrogenic amino acid transport in APC neurons might contribute to the function of the amino acid sensor. We evaluated transport systems in primary cultures of neurons from the APC, hippocampus and cerebellum, or glia, incubated in complete or threonine-devoid (deficient) medium. After 10 min in deficient medium, uptake of threonine or a system A-selective substrate, methyl amino-isobutyric acid, was increased 60% in APC neurons only (P < 0.05). These results demonstrated upregulation of system A, an electrogenic amino acid-sodium symporter. This depletion-induced activation required sodium, intact intracellular trafficking, and phosphorylation of signal transduction-related kinases. Efflux studies showed that other transporter types were functional in the APC; they appeared to be altered dynamically in threonine-deficient cells in response to rapid increases in system A activity. The present data provided support for the chemical sensitivity of the APC and its role as the brain area housing the indispensable amino acid chemosensor. They also showed a region-specific, phosphorylation-dependent activation of the system A transporter in the brain in response to threonine deficiency.

Amino Acid Transport System A↗

PubMed2003

Total subdiaphragmatic vagotomy does not suppress high protein diet-induced food intake depression in rats.

This study was undertaken to determine whether the subdiaphragmatic vagus nerve is involved in the depression of food intake induced by the ingestion of a high protein diet (P50) in rats. After total subdiaphragmatic vagotomy (Vago group) or sham surgery (Sham group), rats consumed the control diet for a 2-wk recovery period and then both groups consumed the high protein diet for 16 d. Daily food intake, meal pattern analysis and behavioral satiety sequence were measured. Total subdiaphragmatic vagotomy did not modify the daily intake of the control diet or suppress the dramatic depression in food intake produced by acute transition to a high protein diet. However, the daily intake of a high protein diet was slightly reduced under acute conditions or even after adaptation (P < 0.005). Analysis of meal parameters and the behavioral satiety sequence after adaptation indicated no major metabolic distress. In conclusion, these results suggest that the subdiaphragmatic vagus nerve does not constitute an obligatory pathway for the transfer of information to the brain, resulting in a depression of high protein diet intake. In contrast, a defect in this visceral regulating system could reinforce the metabolic-associated food intake depression signal.

Animals↗

PubMed2003

Increasing habitual protein intake accentuates differences in postprandial dietary nitrogen utilization between protein sources in humans.

It is appropriate to characterize the nutritional value of dietary proteins in humans through the specific study of dietary nitrogen metabolism during the postprandial period. However, the influence of the habitual protein intake on this variable has not been studied. We aimed to describe the influence of prior protein intake on the specific metabolic utilization of dietary nitrogen in humans. Healthy men and women were adapted for 7 d to two diets with a normal [NP, 1 g/(kg x d)] and high protein content [HP, 2 g/(kg x d)]. After each period, they were studied for an 8-h postmeal period after ingesting a single (15)N-labeled mixed meal (0.41 g/kg protein) containing either milk (n = 12) or soy protein (n = 8). The HP diet reduced the peak of dietary N incorporation into free serum amino acids in the soy group but had no effect in the milk group. The incorporation of dietary N into plasma protein was higher after soy than after milk protein, but habitual protein level had no effect. The postprandial retention of milk protein was reduced by the HP diet compared with the NP diet by only 5% and that of soy protein was diminished by 13% (protein source: P < 0.0001, protein level: P < 0.0001, interaction: P < 0.001). In conclusion, the efficiency of the meal N postprandial retention was lower after HP adaptation, but this decrease was much more pronounced for soy than for milk protein, indicating that increasing the habitual protein intake accentuates differences in metabolic utilization among dietary proteins.

Adult↗

PubMed2002

Wistar rats allowed to self-select macronutrients from weaning to maturity choose a high-protein, high-lipid diet.

The aim of this work was to study the evolution of rat food choice in relation to their age and metabolic parameters. Eighty Wistar rats were studied from birth to 13 weeks of age. At weaning, six litters were fed on a macronutrient self-selecting diet and four on a standard diet. In self-selecting males, protein intake was maximal at Week 7 of age and then plateaued (Week 13), whereas in females, protein consumption peaked at Week 7 and then steadily decreased. Females showed a strong and early preference for fat, which increased continuously with age. Males and females ingested their total energy intake during the dark period (respectively, 79% and 70%). Simple meals (composed of one item) were mainly ingested during the light phase, while mixed meals (at least two items) were ingested during the night. In males, most mixed meals began with carbohydrate bouts and finished with proteins, while in females no particular choice was observed at the beginning of meals, but most of them ended with protein bouts. Body weights of either male and female self-selecting or control fed rats were not significantly different at the end of the experiment. Differences between dietary groups in body fat mass were not observed with the exception of higher subcutaneous fat found in self-selecting rats. Moreover, insulinemia was lower in both male and female self-selecting rats. The high-protein, high-fat diet chosen by the self-selecting rats could be linked to a prevention of the age-related insulin resistance.

Adipose Tissue↗

PubMed2002

Protein is more potent than carbohydrate for reducing appetite in rats.

The purpose of this study was to characterize further the effects of loads of protein versus carbohydrate on subsequent food intake in rats. We used an intraoral cannula to deliver isoenergetic isovolumic loads, in a tightly controlled time frame allowing for both metabolic responses and orosensory components of the load. Our results showed that the gluten load (GLT-100%) induced a greater depression in food intake than an isocaloric wheat starch load (GLT-0%). The types of protein used in the load (total milk protein vs. GLT) did not seem to influence their appetite-suppressive effect. There was a dose-dependent effect of the satiating effects of the protein loads, the GLT-100% load being more effective than either the GLT-35% or GLT-50% loads. Pattern analysis of the meal following the load suggested that animals were more satiated by protein, at least when loads contained 35% or 50% of protein, than by carbohydrate. At least 1 day was necessary before we saw a significant decrease in the energy intake following the protein loads. Thus, the animals had to learn the postingestive effects of the loads before the response stabilized. Taken together, the present results confirm that protein has a greater satiating effect than carbohydrate and extend these results by revealing that the larger the proportion of protein in the food, the larger the satiating effect, and that the quality of protein does not seem to play a significant role.

Animals↗

PubMed2002

Ileal losses of nitrogen and amino acids in humans and their importance to the assessment of amino acid requirements.

BACKGROUND & AIMS: Irreversible amino acid losses at the human ileum are not taken into account when tracer-derived amino acid requirements are calculated because the data available are scarce. We have investigated amino acid losses at the ileal level in humans after ingestion of a protein meal. METHODS: Thirteen volunteers ingested a single meal of 15N milk or soy proteins. The appearance of 15N and 15N amino acids in the ileal effluents collected using an ileal tube was monitored for 8 hours. RESULTS: In the soy group, higher losses of endogenous nitrogen, especially originating from amino acids, were observed, as well as a higher flow rate of dietary non-amino acid nitrogen. With soy protein, the digestibilities of valine, threonine, histidine, tyrosine, alanine, and proline were significantly lower than with milk. Ileal losses of leucine, valine, and isoleucine amounted to 12, 10, and 7 mg x kg(-1) x day(-1), respectively. Threonine ileal loss (9-12 mg x kg(-1) x day(-1)) was particularly high compared with the current amino acid requirement. CONCLUSIONS: Amino acid losses at the human terminal ileum are substantial and depend on the type of dietary protein ingested. Although it remains unclear whether intact amino acids are absorbed in the colon, we suggest that ileal losses should be considered an important component of amino acid requirements.

Adult↗

PubMed2002

The bioavailability and postprandial utilisation of sweet lupin (Lupinus albus)-flour protein is similar to that of purified soyabean protein in human subjects: a study using intrinsically 15N-labelled proteins.

Sweet lupin (Lupinus albus), a protein-rich legume devoid of anti-nutritional factors, is considered to have a high potential for protein nutrition in man. Results concerning the nutritional value of lupin protein are, however, conflicting in animals and very scarce in human subjects. Furthermore, where fibre-rich protein sources are concerned, the long-term nutritional results are often obscured, particularly since fibre-promoted colonic fermentation may bias the energy supply and redistribute N flux. We therefore studied, during the postprandial phase, the bioavailability and utilisation of lupin-flour protein in nine healthy men who had ingested a mixed meal containing intrinsically 15N-labelled lupin flour as the protein source (Expt 1). The real ileal digestibility (RID) and ileal endogenous N losses (IENL) were assessed using a perfusion technique at the terminal ileum, and the N content and 15N enrichment of ileal samples. Lupin flour exhibited a high RID of 91 (SD 3)% and low IENL (5-4 (SD 1.3) mmol N/h). Postprandial dietary deamination was also assessed from body dietary urea and urinary dietary N excretion, and compared with results in nine healthy men following an iso-energetic meal containing a 15N-soyabean-protein isolate with a similar RID, as a control (Expt 2). Postprandial dietary deamination was similar after lupin and soyabean meals (17 (SD 2) and 18 (SD 4)% ingested N respectively). We therefore conclude that lupin protein is highly bioavailable, even if included in fibre-rich flour, and that it can be used with the same efficiency as soyabean protein to achieve postprandial protein gain in healthy human subjects.

Adult↗

PubMed2002

Body weight, body composition, and energy metabolism in lean and obese Zucker rats fed soybean oil or butter.

BACKGROUND: Dietary fat composition is thought to affect body weight regulation independent of the amount of fat ingested. OBJECTIVE: We analyzed the feeding behavior, body weight gain, body composition, and energy metabolism in lean and obese rats fed a diet in which fat was in the form of either butter or soybean oil. DESIGN: Ten lean (Fa/?) and 10 obese (fa/fa) adult Zucker rats were divided into 4 groups according to a 2 x 2 experimental design. They were fed a normally balanced diet over 11 wk in which 30% of energy was either soybean oil or butter. Food intake, body weight gain, and body composition were measured. Indirect calorimetry was used to study energy metabolism at rest and in relation to feeding and activity. RESULTS: Food intake increased similarly in lean and obese rats after butter feeding. Body weight gain increased in obese rats and decreased in lean rats after butter feeding. Body weight gain in obese rats was due mainly to an increase in the weight of lean tissues besides muscle, whereas adiposity and distribution of fat between the various pads did not change. Resting metabolic rates and postprandial lipid oxidation increased in butter-fed obese rats. Lipid oxidation during exercise was not significantly different between obese and lean rats. Fat oxidation increased in butter-fed lean rats during treadmill running at moderate intensity. CONCLUSIONS: In obese rats, basal metabolism and postprandial lipid oxidation increased during butter feeding, which appeared to prevent fat accumulation in the long term. In lean rats, butter feeding favored lipid utilization by working muscles, an observation that deserves further investigation in terms of endurance and performance.

Animals↗

PubMed2002

Approaches to quantifying protein metabolism in response to nutrient ingestion.

The investigation of protein metabolism under various nutritional and physiological conditions has been made possible by the use of indirect, principally tracer-based methods. Most studies were conducted at the whole-body level, mainly using steady-state isotopic techniques and equations based on simple two-pool models, in which amino acids are either free or protein bound. Because whole-body methods disregard regional contributions to protein metabolism, some regional approaches have tried to distinguish the distribution of protein kinetics in the different tissues. The organ-balance tracer technique, involving the arteriovenous catheterization of regions or organs with concomitant isotopic tracer infusion, distinguishes between amino acid uptake and release in the net amino acid balance and measures protein synthesis and degradation under steady-state conditions. Last, the importance has become clear of the difference in dietary and endogenous amino acids recycled from proteolysis for anabolic and catabolic pathways. In humans, the dual tracer technique, which consists of the simultaneous oral/enteral administration and intravenous infusion of different tracers of the same amino acid, allows an estimate of the splanchnic uptake of amino acids administered. Furthermore, the whole-body retention of labeled dietary nitrogen after the ingestion of a single protein meal has enabled a clearer understanding of the metabolic fate of dietary amino acids. Based on such data, a newly developed compartmental model provides a simulation of the regional distribution and metabolism of ingested nitrogen in the fed state by determining its dynamic fate through free and protein-bound amino acids in both the splanchnic and peripheral areas in humans.

Amino Acids↗

PubMed2002

Peripheral and splanchnic metabolism of dietary nitrogen are differently affected by the protein source in humans as assessed by compartmental modeling.

We used a previously developed compartmental model to assess the postprandial distribution and metabolism of dietary nitrogen (N) in the splanchnic and peripheral areas after the ingestion of a single mixed meal containing either (15)N-labeled milk or soy purified protein. Although the lower whole-body retention of dietary N from soy protein was measured experimentally, the splanchnic retention of dietary N was predicted by the model not to be affected by the protein source, and its incorporation into splanchnic proteins was predicted to reach approximately 35% of ingested N at 8 h after both meals. However, dietary N intestinal absorption and its appearance in splanchnic free amino acids were predicted to be more rapid from soy protein and were associated with a higher deamination, concomitant with a higher efficiency of incorporation of dietary N into proteins in the splanchnic bed. In contrast, soy protein was predicted to cause a reduction in peripheral dietary N uptake, as a consequence of both similar splanchnic retention and increased oxidation compared with milk protein. In addition, protein synthesis efficiency was reduced in the peripheral area after soy protein intake, leading to dietary N incorporation in peripheral proteins that fell from 26 to 19% of ingested N 8 h after milk and soy protein ingestion, respectively. Such a model thus enables a description of the processes involved in the differential metabolic utilization of dietary proteins and constitutes a valuable tool for further definition of the notion of protein quality during the period of protein gain.

Amino Acids↗

PubMed2002

The regionalization of PepT1, NBAT and EAAC1 transporters in the small intestine of rats are unchanged from birth to adulthood.

The ontogenetic development of PepT1, NBAT and EAAC1 along the vertical and horizontal axes of the rat small intestine was evaluated using semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. The proximodistal profiles of mRNA levels showed that PepT1 was evenly distributed, whereas NBAT had greater expression in the proximal part, and EAAC1 in the distal part. These regionalizations were the same from postnatal days 4 to 50. PepT1 and NBAT proteins were detected in the microvilli of enterocytes along the length of the villi. NBAT was also found in the cytoplasm. Surprisingly, EAAC1 was located exclusively in the microvilli of enterocytes in the crypt and the bases of the villi. These protein expression patterns were similar in all parts of the small intestine (proximal, median and distal), at all ages. We conclude that the expression of PepT1, NBAT or EAAC1 are differently regulated according to both the horizontal and vertical axes.

Aging↗

PubMed2002

A CLA mixture prevents body triglyceride accumulation without affecting energy expenditure in Syrian hamsters.

We examined the effects of feeding conjugated linoleic acids (CLA) to adult male hamsters on several components of energy metabolism and body composition. Hamsters (n = 54) were assigned for 6-8 wk to one of three diets: 1) a standard diet (in percentage energy: lipids, 33, carbohydrates, 49, and proteins, 18); 2) to the standard diet augmented with the 9c,11t-isomer of CLA to 1.6% of energy (R group); or 3) the standard diet augmented with the 9c,11t-isomer and the 10t,12c-CLA isomer to 3.2 (1.6 + 1.6) % of energy (CLA mix group). (15)N uniformly labeled milk-protein was included in the diet to measure the incorporation of dietary protein into liver and muscle. Basal metabolic rate, thermogenic response to feeding and energy expenditure during spontaneous activity or during an exercise at approximately 60% of VO(2max) were measured. Carnitine palmitoyltransferase-I (CPT-I), leptin, insulin and triiodothyronine concentrations, as well as the in vivo overall adiposity changes were also determined. After 6 wk, the whole-body triglyceride content determined in vivo by NMR was significantly higher in the R group than in the control and CLA mix groups. The CLA mix group differed from the others in the lack of body triglyceride accumulation between d 21 and d 45 of the study, and the appearance of a slight insulin-resistance (homeostatic model assessment index, P < 0.05). Paradoxically, the lack of effect on whole-body lipid oxidation was associated with a greater CPT-I-specific activity in tissues of both CLA-fed groups (P < 0.05). No other major effects of CLA feeding were detected. In conclusion, CLA supplementation in hamsters did not affect adipose weight or the components of energy expenditure despite a theoretically higher capacity of red muscle to oxidize lipids. Only a CLA mixture prevented whole-body triglyceride accumulation over time.

Animals↗

PubMed2002

Isotopic studies of protein and amino acid requirements.

The quantification of protein and amino acid requirements in health and disease is still an incompletely resolved issue, despite its importance to our knowledge of nutrition, to the clinical management of most health disorders and to food policy. However, the dynamic and adaptive features of protein metabolism render this determination difficult. The first nitrogen balance studies performed have demonstrated their limitations in providing accurate protein and amino acid requirements. Isotopic methods developed over the past 15 years have considerably enhanced the quantification of amino acid and protein requirements and our knowledge of the physiological phenomena underlying these needs. These methods are consistently being improved and producing new estimates for protein and amino acid requirements, together with a clearer understanding of this complex issue.

Amino Acids↗

PubMedDate not supplied

In vivo determination of amino acid bioavailability in humans and model animals.

Because the digestion of many dietary proteins is incomplete, and because there is a continuous (but variable) entry into the intestinal lumen of endogenous protein and amino acid nitrogen that is also subject to digestion, the fluxes of nitrogen, amino acids, and protein in the gut exhibit a rather complicated pattern. Methods to distinguish and quantitate the endogenous and dietary components of nitrogen and amino acids in ileal chyme or feces include the use of a protein-free diet, the enzyme-hydrolyzed protein method, different levels of protein intake, multiple regression methods, and stable-isotope labelling of endogenous or exogenous amino acids. Assessment of bioavailability can be made, with varying degrees of difficulty, in man directly but, for routine evaluation of foods, the use of model animals is attractive for several reasons, the main ones being cost and time. Various animals and birds have been proposed as models for man but, in determining their suitability as a model, their physiological, enzymological, and microbiological differences must be considered. Fecal or ileal digestibility measurements, as well as apparent and true nitrogen and amino acid digestibility measurements, have very different nutritional significance and can, thus, be used for different objectives. Measurements at the ileal level are critical for determining amino acid losses of both dietary and endogenous origin, whereas measurements at the fecal level are critical in assessing whole-body nitrogen losses. A complementary and still unresolved aspect is to take into account the recycling of intestinal nitrogen and bacterial amino acids to the body.

Amino Acids↗