Intrahepatic levels of microbiome-derived hippurate associates with improved metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is characterised by lipid accumulation in the liver and is often associated with obesity and type 2 diabetes. The gut microbiome recently emerged as a significant player of liver metabolism and health through the production of bioactive compounds that are beneficial for its host - "postbiotics". Circulating hippurate, a host-microbial co-metabolite produced by conjugating microbial benzoate with glycine in the host-liver, is associated with human gut microbial gene richness and with metabolic health. Here, we first report significant associations among MASLD/MASH traits, plasma and hepatic hippurate in 318 individuals with obesity. Further analysis of the 318 patient's hepatic transcriptome showed that liver and plasma hippurate are inversely associated with MASLD, implicating lipid metabolism and regulation of inflammatory responses pathways. These observations strongly point towards a direct mechanistic role of hepatic hippurate in MASLD pathophysiology. To test a potential beneficial role for hippurate in hepatic insulin resistance, we profiled the metabolome of immortalised human hepatocytes (IHH) using ultra-high-performance liquid chromatography coupled to high-resolution tandem mass spectrometry (UHPLC-MS/MS), and characterised intracellular triglyceride accumulation and glucose internalisation after a 24 h insulin exposure. Hippurate treatment inhibited lipid accumulation and rescued insulin resistance induced by 24-hour chronic insulin in IHH. Hippurate also improved hepatocyte metabolic profiles by increasing the abundance of metabolites involved in energy homeostasis (that are depleted by chronic insulin treatment) while decreasing those involved in inflammation. Altogether, our results further highlight hippurate as a mechanistic marker of metabolic health, by its ability to improve metabolic homeostasis as a postbiotic candidate.