An interventional study of Indole-3-propionic acid (IPA) and Placebo in Healthy, sponsored by Glostrup University Hospital, Copenhagen. Recruiting at 1 site in Denmark. Open to participants aged 18 Years to 65 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2025-08-08.
Sponsored by Glostrup University Hospital, Copenhagen · Not applicable, Interventional, and Basic science
The goal of this trial is to investigate the biological effects of oral supplementation with indole-3-propionic acid (IPA) taken twice daily in healthy adults. The main scientific questions are:
Participants will:
Indole-3-propionic acid (IPA) is a gut bacterial metabolite with the amino acid tryptophan as substrate. In vitro and animal studies suggest that IPA could contribute to regulating inflammation and metabolic function, preventing oxidative damage and upregulating expression of brain-derived neurotrophic factor. With this study we aim to investigate the biochemical effects of IPA at supraphysiological levels in humans.
Glostrup University Hospital, Copenhagen is the lead sponsor of 106 studies on the registry; 5 are open to participants now.
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Placebo
Dietary Supplement: Placebo
IPA: total daily dose of 1000 mg
Dietary Supplement: Indole-3-propionic acid (IPA)
Two capsules are taken every morning and two capsules are taken every evening for 14 consecutive days. Active capsules are taken orally and contain 250 mg of IPA each.
Two capsules are taken every morning and two capsules are taken every evening for 14 consecutive days. Placebo capsules are taken orally and contain maltodextrin.
Regulatory T cells (first primary outcome)
FoxP3+CD25+CD127- regulatory T cells expressed as a percentage of single, live CD3+CD4+CD8- lymphocytes. Analysed in freshly isolated peripheral blood mononuclear cells using a Symphony A3 flowcytometer.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
Brain-derived neurotrophic factor (second primary outcome)
Brain-derived neurotrophic factor measured in platelet-free plasma samples using ELISA or mesoscale.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
Th1/Th2 ratio in PBMCs
Th1/Th2 ratio calculated from T cell profiling of freshly isolated peripheral blood mononuclear cells (PBMCs) using a Symphony A3 flowcytometer. Th1 cells are defined as the CXCR3+CCR4-CCR6-CCR10- non-Treg population and expressed as a percentage of single, live CD3+CD4+CD8-CD45RA- lymphocytes. Th2 cells are defined as the CXCR3-CCR4+CCR6-CCR10- non-Treg population and expressed as a percentage of single, live CD3+CD4+CD8-CD45RA- lymphocytes. Panel antigens: FVS780, CD3, CD4, CD8, CD45RA, CCR7, CXCR3, CCR6, CCR4, CCR10, CD25, CD127, FoxP3.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
Th17/mTreg ratio in PBMCs
Th17/mTreg ratio calculated from T cell profiling of freshly isolated peripheral blood mononuclear cells (PBMCs) using a Symphony A3 flowcytometer. Th17 cells are defined as the CXCR3-CCR4+CCR6+CCR10- non-Treg population and expressed as a percentage of single, live CD3+CD4+CD8-CD45RA- lymphocytes. mTreg (memory Tregs) are defined as the FoxP3+CD25+CD127-CD45RA- population and expressed as a percentage of single, live CD3+CD4+CD8-CD45RA- lymphocytes Panel antigens: FVS780, CD3, CD4, CD8, CD45RA, CCR7, CXCR3, CCR6, CCR4, CCR10, CD25, CD127, FoxP3.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
Th17.1 cells in PBMCs
Th17.1 cells in freshly isolated peripheral blood mononuclear cells (PBMCs) characterized using a Symphony A3 flowcytometer. Th17.1 cells are defined as the CXCR3+CCR4-CCR6+CCR10- non-Treg population and expressed as a percentage of single, live CD3+CD4+CD8-CD45RA- lymphocytes Panel antigens: FVS780, CD3, CD4, CD8, CD45RA, CCR7, CXCR3, CCR6, CCR4, CCR10, CD25, CD127, FoxP3.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
CRP
C-reactive protein (CRP) measured in plasma (mg/L) as a biomarker of infection and systemic inflammation. Lower-limit of quantification: 0,4 mg/L. Values below 0,4 mg/L are imputed as 0,2 mg/L.
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Triglycerides
Plasma triglycerides (mmol/l).
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
non-HDL cholesterol
Non-HDL cholesterol calculated as total cholesterol minus HDL cholesterol (mmol/l)
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
C-peptide
Proinsulin C-peptide (pmol/l) measured in plasma.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
Fasting glucose
Plasma glucose (mmol/l). Participants abstain from eating and drinking after 22.00 the day before. Only water is allowed. Fasting blood samples are taken between 8.00-10.00 in the morning.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
F2-isoprostanes
F2-isoprostanes with a specific focus on 8-iso-prostaglandin F2α measured in blood or morningurine samples as a marker of lipid oxidation.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
8-oxo-dG
8-oxo-dG (8-Oxo-2'-deoxyguanosine) measured in blood or morningurine samples as a marker of DNA-related stress damage.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Serum metabolomics
Targetted and untargetted liquid-chromatography mass-spectrometry-based metabolomics of serum samples. Targetted analyses aim to quantify indole-3-propionic acid and its metabolites (biomarker of compliance as well as absorptive and metabolic capacity), other bacterial- and host metabolites of tryptophan as well as short-chain fatty acids.
Time frame: Four samples in total. Day 1 prior to and again 1.5 hour after intake of first capsule of IPA/ placeblo. Day 15 prior to and again 1.5 hour after intake of last capsule of IPA/ placebo.
Total cholesterol
Plasma cholesterol (mmol/l).
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
VLDL cholesterol
Plasma very low-density lipoproteins (mmol/l).
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
LDL cholesterol
Plasma low-density lipoprotein (LDL) (mmol/l).
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
HDL cholesterol
Plasma high-density lipoprotein (HDL) (mmol/l).
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
Malondialdehyde
Malondialdehyde measured in blood or morningurine samples as a marker of oxidative stress.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Protein carbonyls
Protein carbonyls measured in blood or morningurine samples as a marker of protein oxidation.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Glycated hemoglobin (HbA1c)
HbA1c (IFCC, mmol/mol) measured in whole blood. Estimated average glucose values (mmol/l) are also calculated automatically from HbA1c by our laboratory.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
T cell profiling
Targetted and untargetted T cell profiling of freshly isolated peripheral blood mononuclear cells (PBMCs) using a Symphony A3 flowcytometer. Panel antigens: FVS780, CD3, CD4, CD8, CD45RA, CCR7, CXCR3, CCR6, CCR4, CCR10, CD25, CD127, FoxP3. Target populations: Naïve: CD45RA+CCR7+, Central memory: CD45RA-CCR7+, Effector memory: CD45RA-CCR7-, TEMRA: CD45RA+CCR7-, Th1: CXCR3+CCR4-CCR6-CCR10-, Th2: CXCR3-CCR4+CCR6-CCR10-, Th17: CXCR3-CCR4+CCR6+CCR10-, Th17.1: CXCR3+CCR4-CCR6+CCR10-, Th22: CXCR3-CCR4+CCR6+CCR10+, as well as expression of chemokine receptors on cytotoxic T cells and regulatory T cells. An untargetted approach may be employed to allow for unbiased identification of changes in novel, yet uncharacterized populations.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
Changes in the gut microbiome
Characterization of the gut microbiome using molecular biology methods such as 16s rRNA sequencing.
Time frame: Fecal samples are collected at three time points: prior to supplementation (earliest 48 hours prior to first visit (day 1)), short after initiation of supplementation (day 3 or soonest thereafter) and again earliest 48 hours prior to last visit.
Characterization of the metabolic activity of the gut microbiota
Targetted and untargetted liquid-chromatography mass-spectrometry-based metabolomics. Targetted analyses aim to quantify indole-3-propionic acid, other bacterial- and host metabolites of tryptophan as well as short-chain fatty acids.
Time frame: Fecal samples are collected at three time points: prior to supplementation (earliest 48 hours prior to first visit (day 1)), short after initiation of supplementation (day 3 or soonest thereafter) and again earliest 48 hours prior to last visit.
Bacterial polysaccharides
Endotoxin, capsular polysaccharides or other bacterial polysaccharides measured in blood samples as biomarker of bacterial translocation across the intestinal epithelium.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Pre-haptoglobin 2
Measurement of pre-haptoglobin 2 in blood samples as a biomarker of intestinal permeability.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Intestinal fatty acid binding protein
Measurements of intestinal fatty acid binding protein in blood samples as a biomarker of enterocyte damage.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Citrulline
Measurement of citrulline in blood samples as a biomarker of intestinal function.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Calprotectin
Calprotectin measured in fecal samples as a biomarker of intestinal inflammation.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Neopterin
Neopterin measured in morningurine samples as a biomarker of systemic inflammation.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
suPAR
Soluble urokinase plasminogen activator receptor (suPAR) measured in blood samples.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Microvesicles
Flow cytometric analyses of microvesicles/ microparticles in platelet-free plasma as biomarker of systemic inflammation.
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Endothelial progenitor cells
Flow cytometric analyses of endothelial progenitor cells measured in platelet-free plasma as biomarker of systemic inflammation
Time frame: Results from samples taken on day 15 and adjusted for results from day 1.
Gastrointestinal comfort
Self-reported (questionnaire) gastrointestinal symptoms of bloating, pain, rumbling, flatulence, constipation, hard stools and diarrhea evaluated using a visual analogue scale as well as a question on the frequency of defecation.
Time frame: Gastrointestinal symptoms are assessed on day 1 and day 15.
Gastrointestinal transit time
Measurement of transit time through the digestive system using a so-called maize test. Participants consume 100 grams of sweet maize in the morning between 5.30-10.00 while still in a fasting state. The exact date and time of consumption is registered and so is the exact date and time when maize is observed for the first time in feces. Transit time is expressed as the difference between the ingestion and fecal excretion timepoints in hours.
Time frame: The maize test is performed at baseline (maize is ingested five days before visit 1) and repeated on day 10 (five days before visit 2).
Stool consistency
Classification of stool consistency using the Bristol Stool Chart. Numerical scale ranging from 1 (separate hard lumps) to 7 (liquid consistency with no solid pieces) with one-unit increments.
Time frame: Bristol stool chart is used in association with each maize test and collection of fecal samples (earliest 48 hours prior to first visit and day 3 or soonest thereafter and again earliest 48 hours prior to last visit (day 15)).
Fecal pH
pH of collected fecal samples
Time frame: Fecal samples are collected at three time points: prior to supplementation (earliest 48 hours prior to first visit (day 1)), short after initiation of supplementation (day 3 or soonest thereafter) and again earliest 48 hours prior to last visit (day 15).
Antibody-coating of bacteria
Characterization of IgA, IgG and IgM-coating of bacteria from fecal samples using bacterial flow cytometry.
Time frame: Fecal samples are collected at three time points: prior to supplementation (earliest 48 hours prior to first visit (day 1)), short after initiation of supplementation (day 3 or soonest thereafter) and again earliest 48 hours prior to last visit (day 15).
Immunoglobulin G
Plasma immunoglobulin G (g/l)
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (just before first supplement/placebo dose).
Immunoglobulin A
Plasma immunoglobulin A (g/l)
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Leucocyte counts
Total leucocytes as well as basophils, eosinophils, lymphocytes, monocytes, neutrophils as well as the joint group of metamyelo-, myelo- and promyelocytes. All counted in whole blood samples (10\^9/l).
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (just before first supplement/placebo dose).
Hemoglobin
Hemoglobin measured in whole blood (mmol/l).
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Alanine transaminase
Plasma alanine transaminase (ALT, U/l) as a biomarker of liver function.
Time frame: Results from fasting blood samples taken on day 15 and adjusted for results from day 1 (fasting just before first supplement/placebo dose).
Alkaline phosphatase
Alkaline phosphatase (U/l) as a biomarker of liver function.
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Aspartate aminotransferase
Aspartate aminotransferase also known as aspartate transaminase measured in plasma (U/l) as a biomarker of liver damage.
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Bilirubin
Bilirubins measured in plasma (µmol/L) as a biomarker of liver function.
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Coagulation factors II + VII + X
Coagulation factors II + VII + X (INR: International Normalized Ratio) measured in plasma as a biomarker of liver function.
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Lactate dehydrogenase (LDH)
Lactate dehydrogenase measured in plasma (U/l).
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Creatinine
Plasma creatinine (µmol/L) as a biomarker of kidney function.
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose)
eGFR
Estimated glomerular filtration rate (eGFR/ 1,73m² (ml/min)) as a biomarker of kidney function.
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Albumin
Albumin measured in plasma (g/l).
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
25-OH-vitamin D
Plasma 25-OH-vitamin D (D3+D2) (nmol/L)
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
TSH
Thyroid-stimulating hormone (TSH) measured in plasma (mU/L)
Time frame: Results from blood samples taken on day 15 (just before last supplement/placebo dose) and adjusted for results from day 1 (just before first supplement/placebo dose).
Blood pressure
Blood pressure (mm Hg) defined as the lowest value obtained across three measurements.
Time frame: Measured on day 1 and then again on day 15
PDFs hosted by the registry, ClinicalTrials.gov.
Plan to share: Yes — Individual participant data that underlie the results reported in published articles, after deidentification (text, tables, figures, and appendices).
Supporting information: Study protocol, Statistical analysis plan, Analytic code
Time frame: Beginning 3 months and ending 5 years following publication of the article they are presented in.
Access criteria: Researchers who provide a methodologically sound proposal can access the IPD to achieve the aims of the approved proposal. Proposals should be directed to jette.lautrup.battistini@regionh.dk. To gain access, data requestors will need to sign a data access agreement. Data and explanatory files will be made available at a third party website.
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Studies of the drug tested here: 3-(indol-3-yl)propionic acid
Glostrup University Hospital, Copenhagen →