Identification of key metabolic changes during liver fibrosis progression in rats using a urine and serum metabolomics approach

Reversibility of hepatic fibrosis is an intrinsic response to chronic injury, and with on-going damage, fibrosis can progress to its end-stage consequence, cirrhosis. Non-invasive and reliable biomarkers for early detection of liver fibrosis are needed. Based on the CCl4-induced liver fibrosis rat model, urinary and serum metabolic profiling performed by LC-QTOF-MS associated with histological progression were utilized to identify liver fibrosis-specific potential biomarkers for early prediction and to reveal significant fibrotic pathways and their dynamic changes in different stages of liver fibrosis. Finally, nine differential metabolites in urine and ten in serum were selected and identified involving the most relevant metabolic pathways. Perturbations of tryptophan, valine, leucine, isoleucine, and citrate (TCA) cycle metabolites, along with sphingolipid and glycerophospholipid metabolites, occurred from the onset of liver fibrosis. Furthermore, dysregulation of valine and bile acid biosynthesis metabolites occurred in the intermediate and advanced stages. More importantly, among these metabolites, urinary kynurenic acid, 5-hydroxyindoleacetyl glycine, 4-(2-amino-3-hydroxyphenyl)-2,4-dioxobutanoic acid and serum sphinganine, sphingomyelin, L-leucine, L-tryptophan, and LysoPC(17: 0) changed at all time points and may serve as potential early biomarkers for the diagnosis of hepatic fibrosis and as therapeutic targets. Overall, this work evaluates the potential of these metabolites for the early detection of liver fibrosis.