Platycodon grandiflorus root extract activates hepatic PI3K/PIP3/Akt insulin signaling by enriching gut Akkermansia muciniphila in high fat diet fed mice

Background: Increasing hepatic insulin signaling is found to be an important mechanism of Platycodon grandiflorus root to alleviate metabolic syndrome (MetS) symptoms such as insulin resistance, obesity, hyperlipidemia and hepatic steatosis, but the details are not yet clear. Since the main constituents of Platycodon grandiflorus root were hard to be absorbed by gastrointestinal tract, getting opportunity to interact with gut microbiota, we speculate the gut microorganisms may mediate its effect. Purpose: Our work aimed to confirm the critical role of gut microbes in the intervention of Platycodon grandiflorus root extract (PRE) on MetS, and investigate the mechanism. Methods: Biochemical analyses, glucose tolerance test and hepatic lipidomics analysis were used to evaluate the anti-MetS effect of PRE on high fat diet (HFD) fed mice. Perform 16S rDNA analysis, qPCR analysis and in vitro co-incubation experiment to study its effect on gut microbes, followed by fecal microbiota transplantation (FMT) experiment and antibiotics intervention experiment. Also, the effect of Akkermansia muciniphila treatment on HFD mice was investigated. Results: PRE alleviated lipid accumulation and insulin resistance in HFD mice and remodeled the fecal micro-biome. It also increased the gene expression of colonic tight junction proteins, alleviated metabolic endotoxemia and inflammation, so that reduced TNF-alpha induced hepatic JNK-dependent IRS-1 serine phosphorylation and the impairment of PI3K/PIP3/Akt insulin signaling pathway. A. muciniphila was one of the most significantly enriched microbes by PRE treatment, and its administration to HFD mice showed similar effects to PRE, repairing the gut barrier and activating hepatic PI3K/PIP3/Akt pathway. Finally, anti-MetS effect of PRE could be delivered to FMT recipients, and PRE could not further attenuate MetS in gut microbiota depleted mice. Conclusion: We demonstrated for the first time that PRE alleviated MetS in a gut microbiota dependent manner, and found activation of hepatic insulin signaling mediated by gut A. muciniphila was a potential mechanism of it.

Automated summary

This study confirmed the critical role of gut microbes in the intervention of Platycodon grandiflorus root extract (PRE) on metabolic syndrome (MetS), and investigated the mechanism. It was found that PRE exerted its effects by improving the gut microbiome. Additionally, PRE increased the gene expression of colonic tight junction proteins, alleviated metabolic endotoxemia and inflammation, and improved hepatic insulin signaling pathway. The study also demonstrated that the anti-MetS effect of PRE depended on the gut microbiota.