Objective: To observe the therapeutic effect of Shenzhu Tiaopi granule (, STG) on insulin resistance (IR) in the liver of diabetic Goto-Kakizaki (GK) rat and investigate underlying mechanisms.
Methods: Ten 12-week-old male Wistar rats were assigned as normal control (NC) group, while 40 12-week-old male specific-pathogen-free GK rats were randomly divided into four experimental groups, 10 diabetic rats each. Animals were fed with a normal diet. Fasting blood glucose (FBG), water intake, and body weight were recorded during 6 weeks of daily single-dose treatment: STG low-dose group, 4.5 g/kg (STG-L); STG high-dose group,9 g/kg (STG-H); metformin group, 0.1 g/kg (MET); model control (MC) and NC groups, equal volume of 0.9% NaCl solution. The serum fasting insulin (FINS), C-Peptide and IR index (HOMA-IR) were detected every 2 weeks during treatment and glucose tolerance was measured in the 3rd day before the material was taken. After the 6-week STG treatment, Liver tissues were processed for hematoxylin-eosin staining to perform light microscopy analysis and for assessing expression and distribution of insulin receptor substrates (IRS-1) and glucose transporter (GLUT-4) by immunohistochemistry analysis. Expression levels of liver kinase B1 (LKB1) / adenosine 5'-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway proteins, including LKB1, phospho-AMPK (p-AMPK)/AMPK, phospho-mTOR (p-mTOR)/mTOR, and ribosomal protein S6 kinase polypeptide 1 (S6K1),were detected by Western blotting.
Results: STG significantly reduced the FBG level and liver fat deposition in diabetic GK rats. After STG treatment completion, FINS, HOMA-IR, C-Peptide and area under blood glucose curve (AUC) were lower in STG groups than in the MC group, indicating that IR was reduced and liver fat lesions were resolved. In liver tissues, STG groups displayed significantly higher IRS-1 and GLUT-4 expression than the MC group, along with increasedLKB1 and p-AMPK/AMPK expression and decreased p-mTOR/mTOR and phospho-S6K1expression, suggesting that STG stimulatedLKB1 activation of AMPK and suppressed them TOR/S6K1 downstream pathway.
Conclusion: Growing GK rats developed hepatic IR, but STG treatment significantly improved hyperglycemia and IR and resolved hepatic fatty lesions. Interestingly, STG treatment stimulated the expression of IRS-1 and GLUT-4 in the liver of diabetic GK rats, indicating a potential involvement in the regulation of theLKB1/AMPK/mTOR signaling pathway.
Keywords: Diabetes mellitu; Shenzhu Tiaopi granule; TOR serine-threonine kinase; insulin receptor substrate protein; insulin resistance.