Protection against Metabolic Associated Fatty Liver Disease by Protocatechuic Acid

ABSTRACT

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 Enterococcus, 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 Enterococcus faecalis caused hepatic inflammation, fat deposition and insulin resistance with decreased expression of carnitine palmitoyltransferase-1 alpha (CPT1α), which can be reversed by PCA through inhibiting Enterococcus faecalis. Transcriptomics analysis suggested that Enterococcus faecalis caused a significant decrease in the expression of fibroblast growth factor 1 (Fgf1), and PCA recovered the expression of Fgf1 with insulin-like growth factor binding protein 2 (Igfbp2), insulin receptor substrate 1 (Irs1) and insulin receptor substrate 2 (Irs2). These results demonstrated that high proportion of gut Enterococcus faecalis accelerates MAFLD with decreased expression of CPT1α and Fgf1, which can be prevented by dietary supplementation of PCA.

KEYWORDS:

• Enterococcus faecalis
• nonalcoholic fatty liver disease
• insulin
• protocatechuic acid
• gut microbiota

Acknowledgments

We thank Prof. Jian Sun of South China Agricultural University for providing the E. faecalis (ATCC 29212).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors’ contributions

Experimental execution, J.T., R.H., J.G., C.F., Y.L., M.L., and Z.H.; Writing – original draft preparation, J.T. and S.W.; Writing – review and editing, S.W., D.-X.H., J.H. and H.Z.; supervision, S.W. and J.H.

Data availability statement

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below:

Sequencing of microbiota (Accession number: PRJNA764448): https://dataview.ncbi.nlm.nih.gov/object/PRJNA764067?reviewer=tqhu8ektn4cof3nv6u0t1g8a2f.

Nucleotide sequences of E. faecalis in bacteriostasis and FMT experiments: https://submit.ncbi.nlm.nih.gov/subs/?search=SUB10571133.

Ethics approval and consent to participate

The experimental procedures were approved by the Hunan Agricultural University Institutional Animal Care and Use Committee (No. 2020034).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/19490976.2023.2238959

Additional information

Funding

This work was partially supported by the funds from the National Natural Science Foundation of China (32102578, U22A20515), Key R&D Program of Hunan Province (2021NK2010), Fellowship of China Postdoctoral Science Foundation (2021T140715, 2021M703545), and Grant-in-Aid for scientific research of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan (20K05928).