Low-molecular-weight components of the metabolome control the proliferative activity in cellular and bacterial cultures

Non-targeted Serum Metabolomics Identifies Candidate Biomarkers Panels Associated with Nonalcoholic Fatty Liver Disease: A Pilot Study in Russian Male Patients

Aims:

The aim of the present study was to explore changes in the serum metabolome of patients with NAFLD relative to healthy controls to identify biomarkers associated with steatosis or Non-Alcoholic Steatohepatitis (NASH).

Background:

The serum metabolome reflects changes at the organismal level. This is especially important in Non-Alcoholic Liver Disease (NAFLD), where changes in hormones, cytokines, enzymes and other metabolic alterations can affect the liver, as well as adipose tissue, skeletal muscle and other systems.

Objective:

The objectives were to conduct non-targeted serum metabolomics, data processing, and identification of candidate biomarkers, as well as panels and assessment of their prognostic value.

Materials and Methods:

Non-targeted metabolomic analysis of blood serum samples from 21 male patients with NAFLD (simple steatosis or NASH) and seven male Control group was performed using gas chromatography-mass spectrometry.

Results:

A total of 319 serum metabolites were detected in NAFLD and Control groups, several of which differed significantly between groups. The most discriminating biomarkers were 3-hydroxybutyric acid, 2-hydroxybutyric acid, 2,3-dihydroxybutyric acid, arabitol and 3-methyl-2-oxovaleric acid. Using a panel of three, four or more markers could distinguish patients with NAFLD from controls, and patients with NASH from those with simple steatosis.

Conclusion:

We identified candidate biomarkers for simple steatosis and NASH. Since NAFLD is a multifactorial disease, it is preferable to use a marker panel rather than individual metabolites. Markers may not only result from dysregulation of metabolic pathways in patients with NAFLD, they may also reflect adaptive responses to disease, including functional changes in the intestinal microbiota.

The role of bacterial metabolites derived from aromatic amino acids in non-alcoholic fatty liver disease

The review deals with the role of aromatic amino acids and their microbial metabolites in the development and progression of non-alcoholic fatty liver disease (NAFLD). Pathological changes typical for NAFLD, as well as abnormal composition and/or functional activity of gut microbiota, results in abnormal aromatic amino acid metabolism. The authors discuss the potential of these amino acids and their bacterial metabolites to produce both negative and positive impact on the main steps of NAFLD pathophysiology, such as lipogenesis and inflammation, as well as on the liver functions through regulation of the intestinal barrier and microbiota-gut-liver axis signaling. The review gives detailed description of the mechanism of biological activity of tryptophan and its derivatives (indole, tryptamine, indole-lactic, indole-propyonic, indole-acetic acids, and indole-3-aldehyde) through the activation of aryl hydrocarbon receptor (AhR), preventing the development of liver steatosis. Bacteria-produced phenyl-alanine metabolites could promote liver steatosis (phenyl acetic and phenyl lactic acids) or, on the contrary, could reduce liver inflammation and increase insulin sensitivity (phenyl propionic acid). Tyramine, para-cumarate, 4-hydroxyphenylacetic acids, being by-products of bacterial catabolism of tyrosine, can prevent NAFLD, whereas para-cresol and phenol accelerate the progression of NAFLD by damaging the barrier properties of intestinal epithelium. Abnormalities in bacterial catabolism of tyrosine, leading to its excess, stimulate fatty acid synthesis and promote lipid infiltration of the liver. The authors emphasize a close interplay between bacterial metabolism of aromatic amino acids by gut microbiota and the functioning of the human body. They hypothesize that microbial metabolites of aromatic amino acids may represent not only therapeutic targets or non-invasive biomarkers, but also serve as bioactive agents for NAFLD treatment and prevention.