| Natural derived polyphenols are known for their potent antioxidation and antiglycation activities,which contribute to the health protection activities of mulberry,a kind of phenol-abundant fruit.Recent studies showed that polyphenols protect cells from oxidative stress and insulin resistance.Methylglyoxal(MG)is an important dicarbonyl compound generated in several metabolic procedures.MG damages the functional integrity of biomolecules by nonezymatic glycation,which is closely related to oxidative insults and damage of glucose tolerance.At present,there is still lack of studies aiming at the deleterious effects of MG on cellular redox status and glucose uptake.Moreover,detoxification activity of MG by phenolic compounds and the relationship between polyphenol profile of mulberry and its bioactivity still need to be further investigated.In this study,polyphenols were extracted from mulberry fruits and separated into six fractions(F1-F6).Anthocyanin was also seperated from the sorosis due to its relatively high activity.Simulated in vitro models were used and different fractions from mulberry phenolic extract were studied for their antioxidant and antiglycation activities.Also,human hepatoma cell line HepG2 was used for the determination of ameliorative effects of mulberry anthocyanin extract(MAE)on oxidative stress and impaired glucose uptake induced by MG.This study intends to evaluate protective activities of the phenolic compounds from mulberry fruits and provide novel and safety way for the prevention and treatment of dicarbonyl relative conditions.The main results of this study are as follows:(1)All fractions separated from mulberry polyphenol extract showed DPPH,ABTS radical scavenging activities,ferric reducing activities and antiglycation activivties in different degrees.There were five phenolic acids(protocatechuic acid,p-hydroxybenzoic acid,caffeic acid,p-coumaric acid and o-coumaric acid),two anthocyanins(cyanidin-3-glucoside,cyaniding-3-rutinoside),two flavonoids(quercetin,rutin)detected in the fractions;F3 was highest on total anthocyanin and antiglycation activities(P<0.05)among fractions,while F5 was most phenol abundant and showed strongest antioxidant activity(P<0.05);antioxidant and antiglycation activities of the fractions were significantly correlated to the total anthocyanin contents and total phenol contents(P<0.05),respectively.(2)3mmol/L MG treatment caused significant decrease of the HepG2 cell viability(P<0.05)and increase of intracellular reactive oxygen species(P<0.05).The MG stimulated cells showed lower levels of antioxidant enzymes like superoxide dismutase(SOD),catalase(CAT)and glutathione peroxidase(GPx)activities(P<0.05),diminished glutathione and reduced/oxidized glutathione ratio.The lipid peroxidation and protein oxidation levels rose after MG treatment.MG induced severe toxic effect and oxidative stress state on HepG2 cells.On the other hand,MAE protected cells from MG toxicity and oxidative damages.MAE increased cell viability,conserved SOD,CAT and GPx activities,improved GSH content and GSH/GSSG ratios,inhibited the ROS overproduction and oxidative damages.(Cho et al.)Treated with 0.8mmol/L of MG,the insulin stimulated glucose uptake and glycogen synthesis of HepG2 cells were significantly inhibited(P<0.05).However,MAE improved ability of glucose uptake and reversed the glycogen decreasing that was induced by MG.MG treatment also deactivated the Akt2 by inhibiting the phosphorylation of Ser474 and increased the level of GLUT2,while MAE treantment significantly raised Akt2 activity and decreased GLUT2 level.MG induced significant increase of AKT2 and GLUT2 mRNA levels(P<0.05)and decline of IRS1 mRNA level.However,MAE reversed the effects of MG on transcriptional states of these proteins. |
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