Metabolic dysfunction-associated steatotic liver disease (MASLD) encompasses a spectrum of liver disorders ranging from simple steatosis-a relatively benign and non-progressive condition-to metabolic dysfunction-associated steatohepatitis (MASH), characterized by hepatocellular inflammation. MASLD is now the leading cause of chronic liver disease worldwide, affecting approximately one in three adults, particularly those with obesity or type 2 diabetes.
Recent studies have highlighted a strong interconnection between the gut microbiota, the liver, metabolism, and the immune system, collectively referred to as the gut-liver axis. Alterations in the gut microbiota are observed at all stages of MASLD, and several microbial metabolites-such as trimethylamine, bile acids, short-chain fatty acids, and ethanol-have been implicated in disease progression.
Emerging evidence points to a role for gut-derived metabolites of tryptophan (Trp) and phenylalanine (Phe), including phenylacetic acid (PAA), 3-(4-hydroxyphenyl)-lactate (HPL), and phenyllactate (PL). These compounds have been associated with the severity of MASLD, particularly with hepatic steatosis and fibrosis. Elevated plasma levels of aromatic amino acids (AAAs), such as L-phenylalanine and L-tyrosine, are also correlated with increased hepatic fat content.
A newly identified Phe-derived metabolite, N-acetyl-phenylalanine (NAPA), together with PAA, HPL, and PL, has been shown to correlate with hepatic steatosis. These metabolites can induce steatosis both in vitro and in vivo, acting through the disruption of endoplasmic reticulum-mitochondria interactions. They therefore represent potential new therapeutic targets.
These four metabolites of interest (NAPA, PAA, HPL, PL) can be produced both by gut bacteria and through endogenous human metabolism. Positive correlations between plasma NAPA concentrations and specific bacterial species have been observed, although the responsible taxa remain to be identified.
HYPOTHESIS
We hypothesize that the gut microbiota of MASLD patients produces aromatic amino acid-derived metabolites, contributing to the elevated plasma concentrations observed in these patients
Two complementary strategies will be used : Human Microbiota Culture and Fecal Microbiota Transplantation
Age between 18 and 80 years.
Non-diabetic participant (fasting blood glucose < 1.26 g/L, or absence of insulin therapy or oral antidiabetic medication).
Body mass index (BMI) between 18 and 30 kg/m².
For women of childbearing potential, use of at least one recognized effective contraceptive method.
Participant with active inflammatory, infectious, cardiovascular, or neoplastic disease.
Participant with a history of colectomy, small bowel resection, or cholecystectomy.
Participant who received antibiotics, prebiotics, or probiotics within the past 3 months.
Participant using laxatives (more than 2 doses per day over the past 3 months).
Single group
stool sampling, dietary assessment, and collection of blood and urine samples
Procedure/SurgeryMASLD group includes individuals receiving routine clinical care for liver-related conditions. During their scheduled medical visits, participants undergo standard clinical assessments and routine blood tests. Additional research-specific procedures-such as stool sampling, dietary assessment, and collection of blood and urine samples-are carried out without altering routine patient management. A fraction of blood sample is used for NAPA measurement. Stool samples are collected at home and returned directly to the Endocrinology, Diabetes and Nutrition Department within 24 hours after collection. Healthy volunteers undergo the same research-specific procedures as patients but exclusively for research purposes, with no routine-care-related assessments.
Concentration of NAPA in Stool Culture Medium
Quantification of the metabolite N-acetyl-phenylalanine (NAPA) in the culture medium of stool samples cultivated using the MiPro in vitro human gut microbiota culture system.
Concentration of Selected AAA-Derived Metabolites in Stool Culture Medium
Quantification of selected aromatic amino acid (AAA)-derived metabolites in the culture medium of stool samples cultivated using the MiPro in vitro human gut microbiota culture system.
Gut Microbiota Composition in Stool Samples
Characterization of gut microbiota composition in stool samples who produce NAPA or other metabolites of interest, to identify bacterial species potentially involved in metabolite production. Microbiota profiling will be performed on a stool sample using bacterial DNA sequencing methods (16S rRNA gene sequencing or shotgun metagenomics).
Concentration of NAPA in plasma
The quantification of NAPA level will be performed on plasma samples
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