Study On The Preventive Activity And Mechanism Of Diabetes Mellitus Of Extracts From A. Chinensis

The inhibitory effects onα-glucosidase,Dipeptidyl Peptidase-4（DPP-IV）and the formation of Advanced Glycation End（AGE）products of the ethanol extract,the free phenolic fraction,the insoluble-bound phenolic and the esterified phenolic from Rhus chinensis Mill.Fruits were evaluated in the present study.Two extraction methods with the best inhibitory effects were selected for further in vitro simulated gastrointestinal digestion,and their digestive characteristics and in vitro anti-diabetic activity were evaluated.Finally,the effect of the ethanol extract of R.chinensis fruits on high sugar and high fat diet combined with STZ-induced type 2 diabetes was measured.The purpose of this study is to provide a scientific basis for further development and utilization of fruit as a functional food for the prevention or improvement of diabetes.And the major results were as follows:（1）The free phenolic fraction possessed the highest content of phenolic（434.14±21.31mg gallic acid equivalents/g of extracts）,the ethanol extract ranked secondly（361.33±19.90 mg gallic acid equivalents/g of extracts）.And the free phenolic fraction exhibited the strongest inhibitory effect againstα-glucosidase and DPP-IV,with the IC₅₀ values of 0.56±0.04 and 66.08±1.36μg/m L.The ethanol extract took the second place,with the IC₅₀ values of 1.36±0.04 and 125.83±3.34μg/m L.Insoluble-bound phenolic fraction had the strongest inhibition on the formation of AGEs,with the IC₅₀ value of 0.43±0.03 mg/m L.The results of correction analysis suggested that myricetin O-gallate and myricetin-3-O-（6″-galloyl）glycoside were the two compounds who contributed most remarkably towardα-glucosidase inhibition,di-O-galloyl-glucoside and its isomer were contributed most significantly on DPP-IV.While myricetin-3-O-rhamnoside and protocatechuic acid displayed a strongest positive correction with AGEs-gengration.Myricetin-3-O-rhamnoside and quercetin-3-O-rhamnoside were the two major compounds in the extracts,and they exhibited additive or synergistic effects onα-glucosidase inhibition whereas antagonistic effect on the inhibition of DPP-Ⅳ.（2）After the simulated gastrointestinal digestion,the ethanol extract and the free phenolic fraction possessed the strong ABTS and DPPH free radical scavenging activities and biological activities to improve insulin resistance.Simulated gastrointestinal digestion affect the phenolics differently in ethanol extract and the free phenolic fraction.The total phenol content of ethanol extract increased after simulated gastric digestion,but decreased after simulated intestinal digestion.However,the change trend of the free phenolic fraction was just the opposite.The scavenging ability of ROS free radical and the inhibition ofα-glucosidase,DPP-IV and AGEs-formation were almost consistent with the content of the total polyphenols.At this time,quercetin-3-O-arabinoside and quercetin-3-O-rhamnoside were the most influential compounds onα-glucosidase and DPP-IV,while triglyceride glucose and its isomers had the strongest correlation with AGEs.After simulated digestion,quercetin-3-O-rhamnoside,the most important compound in these samples,can interact with the key amino acid residues inα-glucosidase,DPP-IV and BSA protein through hydrogen bond and hydrophobic interaction,thus inhibiting their activity.（3）The ethanol extract of R.chinensis fruits could improve the dyslipidemia,repair oxidative stress injury;protect islet cells,improve insulin secretion,improve insulin resistance to reduce the blood glucose level and glycosylated hemoglobin content in diabetic mice caused by high sugar and high fat diet combined with STZ.