Pentamethylquercetin Improves Glucolipid Metabolism Disorder And Endoplasmic Reticulum Stress In Diabetic GK Rats And In HepG2Cells Induced By Palmitic Acid

Pentamethylquercetin (PMQ) is one of natural polymethoxylated favones andpresent in some plants, such as seabuckthorn. Our laboratory prepared PMQ bysemisynthesis through fully methylating quercetin. Our previous results have shownthe anti-diabetic effects of pentamethylquercetin in neonatally streptozotocin-induceddiabetic rats. PMQ ameliorate metabolic syndrome induced by neonatal monosodiumglutamine treatment in mice, cardiac hypetrophy induced by pressure overload. In thisstudy, we used GK rats to further evaluate the anti-diabetic effects of PMQ andchoosed the liver as the target organ to investigate the effects of PMQ on ER stress. Atthe same time, in vitro experiment through treating HepG2cell with palmitic acidsodium and observe the influence of PMQ to glucolipid metabolism as well as ERstress.Part I PMQ improves glucolipid metabolism and ER stress inDiabtetic GK ratsObjective: To investigate the effects of PMQ on type2diabetes and endoplasmicreticulum stress in GK reats. Methods: Male GK and wistar rats were used at12weeks of age. GK rats were randomly divided to6groups including model group,PMQ groups (2.5,5,10,20mg/kg) and metformin group (300mg/kg) based on theblood fasting glucose levels. Rats were fed with medicated feed (adding PMQ ormetformin) for16weeks continuously. Body weight gain and the water and foodintake were recorded regularly. Oral glucose tolerance test (OGTT) was tested at the16th week. Fed and fasting blood glucose, serum triglyceride (TG), total cholesterol(TC) and insulin levels were measured respectively. RT-PCR method was performedto test glucose transporter2(Glut2), C/EBP homology protein (CHOP),Immunoglobulin heavy chain binding protein (Bip) mRNA expression levels in livers.Results:1) Compared to normal group (wistar rats), the model group (GK rats) showpolyphagia, polydipsia, polyuria and less body weight gain; hyperglycemia,hypercholesterolemia, hyperinsulinemia and impaired glucose tolerance; decreasedGlut2mRNA expression level and significantly increased CHOP and Bip mRNAexpression level in livers.2）Compared to model group rats, PMQ and metformintreatment have obviously ameliorated postprandial blood glucose, TC and TG level and glucose tolerance; decreased fasting insulin levels and increased postprandialinsulin levels. At the same time, Glut2mRNA expression was enhenced and CHOPand Bip mRNA expression was reduced in livers. Conclutions: PMQ and metforminhas significant protective effects on GK rats and the reducing the endoplasmicreticulum stress level may be one of important mechanisms. PartⅡ PMQ improves glucolipid metabolism abnormalityand endoplasmic reticulum stress induced bypalmitic acid in HepG2cellsObjective: To observe the effect of PMQ on glucolipid metabolism abnormality andendoplasmic reticulum stress induced by palmitate in HepG2cells. Methods: AfterHepG2cells were cultured in DMEM containing10%fetal bovine serum for24h, thecells were cultured in medium containing1%fetal bovine serum for12h in order tobe synchronized, and then were incubated for another24h with medium containingdifferent concentration palmitic acid sodium (300,500,800,1000μM). The mediumcontaining concentration of palmitate that doesn’t affect cell vitality and could reducecell glucose consumption was selected as induction medium to induce HepG2cellsglucolipid metabolism abnormality and endoplasmic reticulum stress. Cells wereco-cultured in induction medium containing PMQ (0.1,0.3,1.0,3.0,10.0μM) ormetformin (100μM) for24h. Results:1）The medium containing palmitate (500μM)was selected as induction medium. Compared with control group, palmitate (500μM)played no obvious influence on cell vitality, but decreased cell glucose consumptionand enhanced cell TG levels. In adiition, palmitate reduced Glut2mRNA expressionlevel and increased CHOP and Bip mRNA expression levels.2) Compared withpalmitate group, PMQ group cells showed increased cell glucose consumption and reduced cell TG level. PMQ could restor the Glut2/CHOP/Bip mRNA expressionlevels. Conclutions: PMQ can improve glucolipid metabolism abnormality andendoplasmic reticulum stress induced by palmitic acid in HepG2. The results suggestthe reduced endoplasmic reticulum stress may be one of mechanisms of PMQanti-diabetic efficacy.