A new way for punicalagin to alleviate insulin resistance: regulating gut microbiota and autophagy

Background: Insulin resistance, defined as a diminished ability to respond to the stimulation of insulin, is the main line for a variety of metabolic-related diseases. Punicalagin (PU), a hydrolyzable tannin of pomegranate juice, exhibits multiple biological properties, including anti-oxidant, anti-cancer and anti-inflammatory activities. Objective: This research study aimed at determining the protective effect of PU on insulin resistance and to uncover the underlying mechanism based on the gut microbiota, IKKβ/NF-κB pathway, and autophagy. Design: An insulin resistance animal model was established using C57BL/6 mice fed with a high-fat diet (HFD) for 8 weeks. The model included two groups continuing a HFD for 12 weeks with or without administering via gavage with PU 20 mg/kg/day. Changes in fasting plasma glucose levels, fasting serum insulin levels, glucose and insulin tolerance, glycolipid metabolism, gut microbiota composition (16S rRNA gene sequencing), inflammatory responses, and autophagy in the liver were evaluated. Body weight gain, glycolipid metabolic disorder, liver injury, as well as systemic and hepatic insulin sensitivity, were significantly attenuated after supplementing with PU. Results: This research study revealed that PU alleviated HFD-induced glucose and lipid disorders, liver injury and insulin resistance; decreased the Firmicutes/Bacteroides ratio, decreased the abundance of Coprococcus and Anaerotruncus, and increased Rikenellaceae; and decreased serum and liver tumor necrosis factor-alpha and interleukin-1β levels, inhibited liver IKKβ and NF-κB phosphorylation; and increased liver autophagy-related proteins LC3-II, P62, and Beclin1, and increased the number of liver autophagosomes. Conclusion: PU can improve HFD-induced insulin resistance, improved liver glucose and lipid metabolism disorder and liver injury, and the potential mechanism is that PU inhibited the IKKβ/NF-κB inflammatory pathway by regulating gut microbiota homeostasis and up-regulating liver autophagy activity