Phenylalanine stable isotope tracer labeling of cow milk and meat and human experimental applications to study dietary protein-derived amino acid availability

Reitelseder, Søren; Tranberg, Britt; Agergaard, Jakob; Dideriksen, Kasper; Højfeldt, Grith; Merry, Marie Emily; Storm, A. C.; Poulsen, Kristian Raaby; Hansen, Erik T.; Hall, Gerrit van; Lund, Peter; Holm, Lars

doi:10.1016/j.clnu.2020.03.017

Cited by 15 publications

(16 citation statements)

References 61 publications

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“…The concentrations of nutrient solutions were selected to be within the range that is typically ingested. For instance, popular sweetened beverages contain around 300 mM glucose (Ventura et al, 2011), vinegar can contain up to 1.17 M acetic acid (Akiba et al, 2015), and the concentration of L-phe in beef is around 70 mmol/kg (Reitelseder et al, 2020). ATP (Tocris), GLP-1 (7-36)-amide (Phoenix Pharmaceuticals), CCK-8 (PolyPeptides Laboratories), hexamethonium bromide (Sigma), ondansetron (Sigma), and TNP-ATP Tocriswere prepared as stock solutions and diluted to the final concentration using standard Krebs solution.…”

Section: Nutrients and Drugsmentioning

confidence: 99%

Luminal nutrients activate distinct patterns in submucosal and myenteric neurons in the mouse small intestine

Fung

Hao

Obata

et al. 2021

Preprint

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Nutrient signals sensed by enteroendocrine cells are conveyed to the enteric nervous system (ENS) to initiate intestinal reflexes. We addressed whether there are specific enteric pathways dedicated to detecting different luminal nutrients. Calcium imaging was performed on intact jejunal preparations from Wnt1-cre;R26R-GCaMP3 and Villin-cre;R26R-GCaMP3 mice which express a fluorescent calcium indicator in their ENS or intestinal epithelium, respectively. Glucose, acetate, and L-phenylalanine were perfused onto the mucosa whilst imaging underlying enteric neurons. Nutrient transport or diffusion across the mucosa was mimicked by applying nutrients onto sensory nerve endings in a villus, or onto myenteric ganglia. The nutrients perfused onto the mucosa each elicited Ca2+ transients in submucosal neurons and in distinct patterns of myenteric neurons. Notably, the neurochemical subtypes of myenteric neurons that responded differed between the nutrients, while submucosal responders were predominantly cholinergic. Nutrients applied into villi or onto ganglia did not elicit specific neuronal responses but did stimulate Ca2+ signaling in the mucosal epithelium. These data suggest that nutrients are first detected at the level of the epithelium and that the ENS is capable of discriminating between different compositions of luminal content. Furthermore, our data show that responses to mucosal stimulation are primarily in the myenteric plexus and submucosal neurons respond secondarily.

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Section: Nutrients and Drugsmentioning

confidence: 99%

Luminal nutrients activate distinct patterns in submucosal and myenteric neurons in the mouse small intestine

Fung

Hao

Obata

et al. 2021

Preprint

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“…Five Danish Holstein Friesian cows were infused with stable isotopes, four with L-[ring-D 5 ]phenylalanine and 1 cow with L-[ 15 N]-phenylalanine, the protocol is described in detail elsewhere (21). In brief, milk was collected from 11 milkings, pasteurized and caseinate and…”

Section: Production Of Intrinsically Labeled Proteins (Given On Day 21)mentioning

confidence: 99%

Impact of habituated dietary protein intake on fasting and postprandial whole-body protein turnover and splanchnic amino acid metabolism in elderly men: a randomized, controlled, crossover trial

Højfeldt

Agergaard

Asmar

et al. 2020

The American Journal of Clinical Nutrition

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Background Efficacy of protein absorption and subsequent amino acid utilization may be reduced in the elderly. Higher protein intakes have been suggested to counteract this. Objectives We aimed to elucidate how habituated amounts of protein intake affect the fasted state of, and the stimulatory effect of a protein-rich meal on, protein absorption, whole-body protein turnover, and splanchnic amino acid metabolism. Methods Twelve men (65–70 y) were included in a double-blinded crossover intervention study, consisting of a 20-d habituation period to a protein intake at the RDA or a high amount [1.1 g · kg lean body mass (LBM)−1 · d−1 or >2.1 g · kg LBM−1 · d−1, respectively], each followed by an experimental trial with a primed, constant infusion of D8-phenylalanine and D2-tyrosine. Arterial and hepatic venous blood samples were obtained after an overnight fast and repeatedly 4 h after a standardized meal including intrinsically labeled whey protein concentrate and calcium-caseinate proteins. Blood was analyzed for amino acid concentrations and phenylalanine and tyrosine tracer enrichments from which whole-body and splanchnic amino acid and protein kinetics were calculated. Results High (compared with the recommended amount of) protein intake resulted in a higher fasting whole-body protein turnover with a resultant mean ± SEM 0.03 ± 0.01 μmol · kg LBM−1 · min−1 lower net balance (P < 0.05), which was not rescued by the intake of a protein-dense meal. The mean ± SEM plasma protein fractional synthesis rate was 0.13 ± 0.06%/h lower (P < 0.05) after habituation to high protein. Furthermore, higher fasting and postprandial amino acid removal were observed after habituation to high protein, yielding higher urea excretion and increased phenylalanine oxidation rates (P < 0.01). Conclusions Three weeks of habituation to high protein intake (>2.1 g protein · kg LBM−1 · d−1) led to a significantly higher net protein loss in the fasted state. This was not compensated for in the 4-h postprandial period after intake of a meal high in protein. This trial was registered at clinicaltrials.gov as NCT02587156.

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“…However, some challenges exist when daily protein recommendations are extrapolated from MPS, which have been determined in acute experimental studies in response to various doses of protein ingestion. Among these, the interaction between protein and energy intake [27] as the intake of other macronutrients and/or total energy is known to markedly affect postprandial aminoacidemia [28][29][30] and whole-body net protein balance [31]. In addition, the type of studies investigating the stimulatory effect of a bolus ingestion of protein rarely account for the habituated level of dietary intake (i.e., the protein intake the participant is accustomed to).…”

Section: Introductionmentioning

confidence: 99%

Daily Protein and Energy Intake Are Not Associated with Muscle Mass and Physical Function in Healthy Older Individuals—A Cross-Sectional Study

et al. 2020

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Dietary protein has a pivotal role in muscle mass maintenance with advancing age. However, an optimal dose and distribution of protein intake across the day as well as the interaction with energy intake for the maintenance of muscle mass and physical function in healthy older adults remain to be fully elucidated. The purpose of this study was to examine the association between muscle mass, strength, and physical function, and the total amount and distribution of protein and energy intake across the day in healthy older individuals. The research question was addressed in a cross-sectional study including 184 Danish men and woman (age: 70.2 ± 3.9 years, body mass: 74.9 ± 12.1 kg, Body Mass Index (BMI): 25.4 ± 3.7 kg/m2) where a 3-day dietary registration, muscle mass, strength, and functional measurements were collected. We found that neither daily total protein intake nor distribution throughout the day were associated with muscle mass, strength, or physical function. Consequently, we do not provide an incentive for healthy older Danish individuals who already adhere to the current internationally accepted recommended dietary protein intake (0.83 g/kg/day) to change dietary protein intake or its distribution pattern throughout the day.

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Phenylalanine stable isotope tracer labeling of cow milk and meat and human experimental applications to study dietary protein-derived amino acid availability

Abstract: Phenylalanine stable isotope tracer labeling of cow milk and meat and human experimental applications to study dietary protein-derived amino acid availability', Clinical Nutrition.

Cited by 15 publications

References 61 publications

Luminal nutrients activate distinct patterns in submucosal and myenteric neurons in the mouse small intestine

Luminal nutrients activate distinct patterns in submucosal and myenteric neurons in the mouse small intestine

Impact of habituated dietary protein intake on fasting and postprandial whole-body protein turnover and splanchnic amino acid metabolism in elderly men: a randomized, controlled, crossover trial

Daily Protein and Energy Intake Are Not Associated with Muscle Mass and Physical Function in Healthy Older Individuals—A Cross-Sectional Study

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