Protection against Metabolic Associated Fatty Liver Disease by Protocatechuic Acid.

Gut microbiota-diet interaction has been identified as a key factor of metabolic associated fatty liver disease (MAFLD). Recent studies suggested that dietary polyphenols may protect against MAFLD by regulating gut microbiota; however, the underlying mechanisms remain elusive. We first investigated the effects of cyanidin 3-glucoside and its phenolic metabolites on high-fat diet induced MAFLD in C57BL/6J mice, and protocatechuic acid (PCA) showed a significant positive effect. Next, regulation of PCA on lipid metabolism and gut microbiota were explored by MAFLD mouse model and fecal microbiota transplantation (FMT) experiment. Dietary PCA reduced intraperitoneal and hepatic fat deposition with lower levels of transaminases (AST & ALT) and inflammatory cytokines (IL-1β, IL-2, IL-6, TNF-α & MCP-1), but higher HDL-c/LDL-c ratio. Characterization of gut microbiota indicated that PCA decreased the Firmicutes/Bacteroidetes ratio mainly by reducing the relative abundance of genus , which was positively correlated with the levels of LDL-c, AST, ALT and most of the up-regulated hepatic lipids by lipidomics analysis. FMT experiments showed that caused hepatic inflammation, fat deposition and insulin resistance with decreased expression of carnitine palmitoyltransferase-1 alpha (), which can be reversed by PCA through inhibiting . Transcriptomics analysis suggested that caused a significant decrease in the expression of fibroblast growth factor 1 (), and PCA recovered the expression of with insulin-like growth factor binding protein 2 (), insulin receptor substrate 1 () and insulin receptor substrate 2 (). These results demonstrated that high proportion of gut accelerates MAFLD with decreased expression of and , which can be prevented by dietary supplementation of PCA.