Kun-Dan Decoction Ameliorates Insulin Resistance by Activating AMPK/mTOR-Mediated Autophagy in High-Fat Diet-Fed Rats

Abstract

Background: Metabolic syndrome is characterized by central obesity, hyperglycemia and hyperlipidemia. Insulin resistance is the leading risk factor for metabolic syndrome. Kun-Dan decoction (KD), a traditional Chinese medicine, has been applied to treat patients with metabolic syndrome for over ten years. It is increasingly recognized that autophagy deficiency is the key cause of metabolic syndrome. Therefore, we aimed to explore whether KD can activate autophagy to improve metabolic syndrome.Methods: Network pharmacology was used to explore the underlying mechanism of KD in the treatment of metabolic syndrome. The high-fat diet-fed rats and oleic acid-induced LO2 cells were employed in our study. Oral glucose tolerance test and insulin tolerance test, obesity and histological examination, serum cholesterol, triglyceride, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), homeostasis model assessment of insulin resistance (HOMA-IR) and insulin sensitivity in high-fat diet-fed rats were analyzed. Furthermore, the protein expressions of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), phospho-AMPK, mammalian target of rapamycin (mTOR), phospho-mTOR, p62, autophagy related protein (Atg) 5, Atg7, Atg12, Atg13, Atg16L1 and microtubule-associated protein 1A/1B-light chain 3 (LC3)-Ⅱ/Ⅰ were examined in rats and LO2 cells. Moreover, autophagy activator rapamycin and inhibitor 3-methyladenine, and small interfering RNA against Atg7 were utilized to verify the role of autophagy in the treatment of metabolic syndrome by KD in oleic acid-induced LO2 cells.Results: Results from network pharmacology indicated that targeted insulin resistance might be the critical mechanism of KD in the treatment of metabolic syndrome. We found that KD significantly suppressed obesity, serum cholesterol, triglyceride and LDL-C levels and increased serum HDL-C level in high-fat diet-fed rats. Furthermore, KD enhanced insulin sensitivity and attenuated HOMA-IR in high-fat diet-fed rats. Western blot showed that KD could enhance autophagy to increase the insulin sensitivity of high-fat diet-fed rats and oleic acid-induced LO2 cells. Furthermore, 3-methyladenine and small interfering RNA against Atg7 could reverse the protective effect of KD on LO2 cells. However, rapamycin could cooperate with KD to enhance autophagic activation to increase insulin sensitivity in LO2 cells.Conclusion: The induction of autophagy may be the major mechanism for KD to improve insulin resistance and metabolic syndrome.

Mitophagy: A potential therapeutic target for insulin resistance

“…Therefore, AMPK-mediated phosphorylation of ULK1 is critical for inducing mitophagy ( Trefts and Shaw, 2021 ) ( Figure 3A ). Seabright et al ( Seabright et al, 2020 ) recently found that AMPK activation promotes mitophagy by increasing mitochondrial fission and autophagy without the PINK1/Parkin pathway, and AMPK/mTOR activation improves IR, which has been demonstrated in many studies ( Wang et al, 2020 ; Zhu Y. et al, 2021 ; Su et al, 2021 ).…”

Network Pharmacology and Experimental Verification Strategies to Illustrate the Mechanism of Jian-Pi-Yi-Shen Formula in Suppressing Epithelial–Mesenchymal Transition

“…All chemical ingredients from the eight herbal medicines of JPYSF were collected from an online database, including a traditional Chinese medicine system pharmacology database and an analysis platform (TCMSP, https://tcmspw.com/tcmsp.php ), Integrative Pharmacology-based Research Platform of Traditional Chinese Medicine (TCMIP) v2.0 ( Xu et al, 2019 ; Su et al, 2021 ), and previous pieces of literature ( Wang F et al, 2020 ). All chemical ingredients were employed to evaluate the degree of drug absorption based on the criteria of oral bioavailability (OB ≥ 30%) and drug-like (DL ≥ 0.18) (mean value for all molecules within the DrugBank database).…”

Cellular Uptake, Metabolism and Sensing of Long-Chain Fatty Acids

“…BSAconjugated palmitic acid increases Akt/mTORC1 pathway via GPR40, and the mechanism by which palmitic acid regulate mTORC1 activity is probably its translocation onto lysosomal membranes [136,137]. Moreover, oleic acid activates Akt/mTORC1 and ERK/mTORC1 pathways via GPR40 or GPR120 [138], and inhibits AMPK signaling which is a negative regulator of mTORC1 [139][140][141][142]. There are few reports on stearic acid and mTORC1 activity, it can upregulate mTOR expression [143].…”

“…The downstream signaling pathways mediated by GPR40 or GPR120, the second messenger cAMP can activate downstream effector PKA and regulate ERK sequentially [138,146,147], and another downstream pathway PLC/DAG/IP3 in which DAG can excite PKC and ERK/mTORC1 [147,148], and IP3 leads to calcium release activating AMPK which is an upstream negative regulator of mTORC1 [139,140,142,149], and the third downstream pathway, PI3K/Akt pathway, can activate mTORC1 signaling [136,138,140,147]. Different G proteins mediate LCFAs to regulate mTORC1 signaling.…”