Mechanism Of Anthocyanins From Purple Sweet Potato In Slowing Starch Digestion And Alleviating High-fructose/high-fat Induced Metabolic Syndrome

Diabetes has become a global public health concern due to its high incidence and severe complications.Insulin resistance is the center of type 2 diabetes.With the dietary changes,carbohydrate intake increases gradually,leading to the rapid rise in postprandial blood glucose and insulin in healthy individual.The persistently high level of blood insulin may bring about insulin resistance thereby causing hyperglycemia,which eventually develops into type 2 diabetes.In addition,Insulin resistance is strongly associated with hyperuricemia.The increasing intake of fructose results in the prevalence of metabolic syndrome represented by insulin resistance and hyperuricemia.The clinical drugs for controlling postprandial blood glucose(such as α-glucosidase inhibitors acarbose)and reducing uric acid(such as xanthine oxidase inhibitors allopurinol)have certain side effects,and the application is limited.Therefore,it has become the focus in recent years to find natural products with little toxicity that can effectively delay starch digestion,manage hyperglycemia,and improve fructose induced metabolic syndrome.This study was aimed to explore the effect of purple sweet potato anthocyanins on starch digestion and high fructose/ high fat induced metabolic syndrome,as well as the underlying molecular mechanism.The monoacylated and diacylated anthocyanin fractions were prepared according to previous method in our lab.In order to explore the structure-activity relationship between nonacylated/ monoacylated/ diacylated anthocyanins,α-Amylase and α-glucosidase inhibition experiments were performed in vitro using commercial anthocyanin extracts,blueberry anthocyanin fractions and purple sweet potato anthocyanin fractions,and then we investigated the regulatory effect of diacylated anthocyanins fraction on postprandial blood glucose in rats.The interaction mechanisms between diacylated anthocyanins fraction and α-amylase or α-glucosidase were explored by enzyme inhibition kinetics and various spectroscopic methods.Molecular docking,pharmacophore model and 3D-QSAR model were applied to study the interaction modes between purple sweet potato acylated anthocyanins and specific amino acid residues in the active sites of α-amylase and α-glucosidase,as well as reveal the structure-activity relationship and the role of acyl groups.Next,we evaluated the effects of diacylated anthocyanins on improving insulin resistance and hyperuricemia in high fructose/ high fat induced metabolic syndrome mice,and explored its possible molecular mechanism in regulating metabolic abnormalities and protecting renal function.It is expected to provide scientific evidences for natural flavonoids in preventing hyperglycemia and managing fructose induced metabolic syndrome.Also,it provides theoretical potential for the usage of diacylated anthocyanins from purple sweet potato as ingredients in high value-added functional foods.The main conclusions are as follows(1)The results showed that Diacylated AF-PSP had the best inhibitory activity against α-amylase and α-glucosidase among all anthocyanin samples.At the same time,we speculated that the acyl groups of anthocyanins may affect the inhibitory activities ofα-amylase and α-glucosidase.the inhibitory mechanism of Diacylated AF-PSP againstα-glucosidase and diacylated α-glucosidase may be the combination of Diacylated AF-PSP with α-amylase and α-glucosidase in a high affinity single binding site by hydrogen bonds thereby occupying the active center.Meanwhile Diacylated AF-PSP changed surface hydrophobicity and environmental polarity around the amino acid residues in the enzymes,affecting the conformation of the enzyme and the entrance of active site.Thus,it was prevented that the substrate entered into the catalytic site.Diacylated AF-PSP could inhibit the rise of postprandial blood glucose in mice after administration of starch,and the blood glucose peak and AUC decreased significantly.Acyl groups on anthocyanins could interact with amino acid residues around the active sites,thus enhancing the binding stability.The type of acyl groups and the structure of parent nucleus might affect the inhibitory activity of purple sweet potato anthocyanins.(2)The metabolic syndrome was successfully induced in mice fed by high fructose and high fat diet,which caused hyperlipidemia,hyperuricemia,insulin resistance and other symptoms.Diacylated AF-PSP administration could inhibit liver XO activity thereby reducing serum uric acid in mice.It can relieve lipid metabolism disorder,liver lipid accumulation and liver oxidative stress,enhance insulin utilization and sensitivity,lower blood glucose,improve insulin resistance,and alleviate pathological changes of kidney in mice,as well as regulate of fructose metabolism related enzyme m RNA expression,restore normal fructose metabolism,gluconeogenesis,and tricarboxylic acid cycle processes.Also,fructose,glucose,and uric acid related renal transporter expression were reduced,thus the reabsorption of fructose,glucose,and uric acid by kidney was decreased.Diacylated AF-PSP treatment alleviated the inflammatory reaction of kidney,and then restored the normal physiological structure and function of kidney in mice.