The Incorporation of Dietary Protein-Derived Amino Acids in Duodenal Epithelium (GutFeeding)

The Incorporation of Dietary Protein-Derived Amino Acids in Duodenal Mucosal Protein in Young and Older Males

Rationale: Aging is accompanied by a blunted muscle protein synthetic response to protein ingestion.This anabolic resistance may be related to decreased postprandial amino acid release in the circulation, due to greater amino acid extraction by splanchnic tissues in older individuals. It has been suggested that extracted amino acids are utilized by intestinal epithelial cells for cell proliferation, generating new cells to maintain healthy mucosa. So far, there is no evidence that dietary protein-derived amino acids are taken up and incorporated in intestinal mucosal protein in vivo in humans. Furthermore, there is no evidence that this process is impacted by age.

Objective: To assess the postprandial incorporation of dietary protein-derived amino acids in intestinal mucosal protein in healthy young and older males.

Study design: Cross-sectional, non-therapeutic intervention study design

Study population: 5 healthy, non-obese (BMI 18.5-30kg/m2) young adult males (age: 18-35y inclusive) and 5 community dwelling older males (age: 67+y).

Intervention: Continuous intravenous stable isotope amino acid tracer infusion will be applied, in combination with oral ingestion of 20g intrinsically labelled milk protein, with plasma, muscle and duodenal mucosa biopsy samples collected at different time points throughout the experimental test day.

Main study parameters/endpoints: The primary study outcome is the postprandial (0-5h) incorporation of dietary protein-derived amino acids in duodenal mucosal protein following the ingestion of 20g intrinsically labelled milk protein. Secondary study parameters include postprandial plasma availability of dietary protein-derived amino acids and fractional duodenal mucosal protein synthetic rate.

Study Overview

• Status: Completed
• Conditions: Protein Malabsorption
• Intervention / Treatment: Dietary supplement: Intrinsically labelled milk protein

Detailed Description

Skeletal muscle tissue is in a constant state of remodelling, regulated by the balance between tissue protein synthesis and breakdown rates, with a turnover rate of 1-2% per day. It has been well established that protein ingestion is a major anabolic stimulus for muscle protein synthesis. Dietary protein ingestion provides amino acids that stimulate protein synthesis by both functioning as substrate and as signalling molecules that upregulate anabolic pathways.

The anabolic properties of dietary protein largely depend on the protein digestion and amino acid absorption kinetics and subsequent increase in plasma amino acid availability. Following protein ingestion, protein is cleaved into small peptides and amino acids by digestive enzymes. Subsequently, these amino acids are absorbed across the intestinal mucosa by various membrane-bound transporters. The majority of dietary protein derived amino acids is released into the systemic circulation and transported and taken up by various peripheral tissues in the postprandial phase. However, a substantial part of the ingested protein does not become available in the circulation. This part is either not (yet) digested and absorbed, or the absorbed amino acids are taken up by splanchnic tissues, such as the gut and liver, providing precursors for de novo tissue protein synthesis, termed first-pass splanchnic extraction. Previous work in our laboratory has estimated that up to 40% of the protein derived amino acids are taken up and incorporated in the intestinal tract and liver tissues. The intestine is the most highly regenerative organ in the human body, regenerating its epithelium every 3 to 5 days. It has been suggested that the absorbed amino acids are utilized by epithelial cells for rapid cell proliferation, generating new cells to maintain healthy mucosa. Human studies on the incorporation of dietary protein-derived amino acids in intestinal mucosal protein have not been performed. Therefore, the aim of the present explorative in vivo study is to assess, for the first time, the incorporation of dietary protein-derived amino acids in duodenal mucosal protein in humans, and the systemic availability of dietary protein-derived amino acids.

Aging is accompanied by a blunted muscle protein synthetic response to protein ingestion. This proposed anabolic resistance may be related to a decreased postprandial amino acid release in the circulation, due to impairments in protein digestion and amino acid absorption, and greater first-pass splanchnic amino acid extraction in older individuals. Whether dietary protein-derived amino acid incorporation in intestinal mucosal protein is increased with aging remains to be established. Therefore, the current study will use the data on incorporation of dietary protein-derived amino acids in duodenal mucosal protein and postprandial amino acid plasma availability obtained in young and older individuals to evaluate potential age-related differences.

Two primary hypotheses will be tested:

1. It is hypothesized that part of the absorbed amino acids will be directly incorporated in duodenal epithelium within 5 hours after protein ingestion.
2. It is hypothesized that the extent of postprandial incorporation of dietary protein derived amino acids in duodenal epithelium will be greater in older compared to young males.

• Study Type: Interventional
• Enrollment (Actual): 10
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Netherlands
  • Maastricht, Netherlands, 6229ER
    • Maastricht University Medical Center+

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Male sex
• Aged 18-35 years or 67+ years
• Body mass index (BMI) between 18.5 and 30 kg/m2

Exclusion Criteria:

• History of cardiovascular, respiratory, gastrointestinal, urogenital, neurological, psychiatric, dermatologic, musculoskeletal, metabolic, endocrine, haematological, immunologic disorders, allergy, major surgery and/or laboratory assessments which might limit participation in or completion of the study protocol, interfere with the execution of the experiment, or potential influence the study outcomes (to be decided by the principal investigator and responsible physician)
• Major abdominal surgery interfering with gastrointestinal function (upon judgement of the principal investigator and responsible physician)
• Use of medication which limit participation in or completion of the study protocol, interferes with the execution of the experiment, or potential influences the study outcomes (to be decided by the principal investigator and responsible physician)
• Use of supplementation (i.e. vitamin, pre- and probiotic supplementation) within 14 days prior to testing
• Administration of investigational drugs or participation in any scientific intervention study in the 14 days prior to the study, which may interfere with this study (upon judgement of the principal investigator and responsible physician)
• Specific diet (e.g. vegetarian, vegan, gluten free, no diary) within the study period
• Planning to lose weight during the study period
• Lactose intolerance
• Excessive alcohol consumption (defined as > 14 alcoholic consumptions per week)
• Smoking
• Drug use
• Donated blood two months prior to the test day
• Recent (<1 year) participation in amino acid tracer (L-[ring-2H5]-phenylalanine, L-[ring-2H3]-leucine, L-[ring-2H4]-lysine, L-[ring-2H2]-tyrosine) or intrinsically labelled protein ([1-13C]-phenylalanine, [1-13C]-leucine, [1-13C]-lysine) studies
• No given permission to register participation in electronic patient file at MUMC+ and to add records of gastroduodenoscopy

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Intrinsically labelled milk protein; 20 grams of protein dissolved in 500 mL of water	Dietary supplement: Intrinsically labelled milk protein; 20 grams of protein dissolved in 500 mL of water

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Postprandial incorporation of dietary protein-derived amino acids in duodenal mucosal protein	Assessed by duodenal mucosal protein-bound [1-13C]-phenylalanine enrichment (expressed as MPE)	0-5 hours
Impact of age on postprandial incorporation of dietary protein-derived amino acids in duodenal mucosal protein	Assessed by duodenal mucosal protein-bound [1-13C]-phenylalanine enrichment (expressed as MPE) in young and older adults	0-5 hours

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Plasma glucose concentrations	Plasma glucose concentrations	0-5 hours
Plasma insulin concentrations	Plasma insulin concentrations	0-5 hours
Postprandial plasma amino acid concentrations	Appearance of milk protein-derived amino acids in plasma over the full assessment period (5 h), as determined using stable isotope tracer methodology	0-5 hours
Fractional duodenal mucosal protein synthetic rate	Mucosal protein synthesis rates are calculated using L-ring-2H5-phenylalanine tracer and provided as 1 integrated value over the specified timeframe using plasma as precursor	0-5 hours
Fractional muscle protein synthetic rate	Muscle protein synthesis rates are calculated using L-ring-2H5-phenylalanine tracer and provided as 1 integrated value over the specified timeframe using plasma as precursor	0-5 hours
Fecal [1-13C]-phenylalanine enrichments (expressed as MPE)	Fecal protein excretion, assessed by fecal [1-13C]-phenylalanine enrichments (expressed as MPE)	Fecal sample of first feces after endoscopy
Fecal nitrogen content	Fecal protein excretion, assessed by fecal nitrogen content	Fecal sample of first feces after endoscopy
Fecal microbial metabolites	Microbial metabolites, including short-chain fatty acids, assessed by analyzing fecal samples	Fecal sample of first feces after endoscopy

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Age in years	Reported by participants	Baseline
Height in m	Stadiometer	Baseline
Dietary macronutrient intake	Assessed by written dietary intake records	2 days prior to experimental trial day
Body weight in kg	Scale	Baseline
BMI in kg/m2	Calculated from height and body weight	Baseline
Skeletal muscle mass	Bioelectrical impedance analysis	Baseline
Fat mass	Bioelectrical impedance analysis	Baseline
Systolic blood pressure in mmHg	Electrical sphygmomanometer	Baseline
Diastolic blood pressure in mmHg	Electrical sphygmomanometer	Baseline

Collaborators and Investigators

• Sponsor: Maastricht University Medical Center
• Collaborators: FrieslandCampina
• Investigators: Principal Investigator: Luc van Loon, Prof, Maastricht University Medical Center; Principal Investigator: Daisy Jonkers, Prof, Maastricht University Medical Center

Study record dates

Study Major Dates

• Study Start (Actual): July 24, 2023
• Primary Completion (Actual): April 5, 2024
• Study Completion (Actual): April 5, 2024

Study Registration Dates

• First Submitted: June 27, 2023
• First Submitted That Met QC Criteria: October 18, 2023
• First Posted (Actual): October 19, 2023

Study Record Updates

• Last Update Posted (Actual): April 30, 2024
• Last Update Submitted That Met QC Criteria: April 29, 2024
• Last Verified: October 1, 2023

More Information

Terms related to this study

• Keywords: Aging; Protein; Absorption; Gastrointestinal tract; Muscle protein synthesis; Intestinal mucosa; Digestion
• Additional Relevant MeSH Terms: Digestive System Diseases; Metabolic Diseases; Gastrointestinal Diseases; Intestinal Diseases; Malabsorption Syndromes; Molecular Mechanisms of Pharmacological Action; Chelating Agents; Sequestering Agents; Caseins
• Other Study ID Numbers: METC23-011

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No