Abstract
Herbs for diabetic therapy are wieldy used and generally good efficacy as expected. However the effective components from natural sources have not been fully evaluated. Insulin receptor kinase (IRK) belongs to the class of tyrosine kinase that mediate their activity by phosphorylation tyrosine residues. The structure of IRK (PDB number: 1GAG) was choose as the template to do molecular docking by Discovery studio software based on docking energy and hydrogen bound numbers. Thirty-one compounds extracted from diabetic therapy herbs were applied to do virtual screening for synergistic insulin function via targeting of IRK and further investigated its underlying mechanism by glucose transporter 4 (GLUT4) translocation and insulin signaling pathway. After molecular dock screening, antroquinonol (Antrodia cinnamomea), curcumin (Curcuma longa), docosanol (Saccharum sinensis peel), tetracosanol (Saccharum sinensis peel), and rutin (Toona sinensis leaves) were found to have high target–ligand affinity score with IRK. At intracellular molecular signaling level, only docosanol, tetracosanol and rutin were increased the phosphorylation of insulin receptor (InsR, Tyr1158/Tyr1162/Tyr1163) and Akt (Thr308); curcumin and antroquinonol might serve as a potential agent for glycaemic control via AMPK signaling pathways. Moreover, the mouse myotubes were treated with five potential compounds alone and combination with or without insulin and InsR antagonist (S961) to test the GLUT4 translocation and glucose uptake assay in vitro. Five potential compounds restored S961-induced down-regulated translocation of GLUT4 and/or glucose uptake. Finally, natural compound for the ability of improving hyperglycemia was confirmed by Oral Glucose Tolerance Test (OGTT). The data showed that all of them could restore S961-induced hyperglycemia. According to the results, the potency of tetracosanol was better than docosanol and the hydroxyl group of tetracosanol was critical function group for IRK activity. Based on the above experiments, natural products selected in this study could be divided into two different anti-hyperglycemic strategy, insulin signal (docosanol, tetracosanol, and rutin) and AMPK-dependent (antroquinonol and curcumin) activation. Antroquinonol and tetracosanol may be the pharmaceutical potential candidates that are in combination with of the insulin or an insulin analogue in sensitizing insulin function by targeting on GLUT4 translocation for treating diabetes mellitus.