Effect Of Sandalwood Seed Oil On Insulin Resistance In Obese Rats Induced By High Fat High Surcose Diet

ObjectiveThe aim of the present study was to investigate the effect of sandalwood seed oil(SSO)on high-fat/high-sucrose(HFHS)diet induced insulin resistance(IR)compared with fish oil(FO),sunflower oil(SO)and linseed oil(LO).The protein expression levels of phosphatidylinositol 3 kinase(PI3K)/protein kinase B(AKT)insulin signaling pathway,c-Jun N-terminal kinase(JNK)/nuclear factor kappa-B(NF-?B)inflammatory signaling pathway in liver tissues and gut microbiota were detected to explore the molecular mechanism of the preventive effect.Methods1.Study design: Fifty male Sprague-Dawley rats were given free access to water and standard diet.After one week of adaption period,the rats were randomly divided into the following five groups(n=10): normal control group(N),SSO group,FO group,SO group and LO group.The experimental diet was modified based on AIN-93 G.The N group was fed a standard diet(contains 64% carbohydrate,20% protein and 7% fat).The other four groups were fed a HFHS-diet(contains 27% sucrose and 15% lard)that contains 7% of SSO,FO,SO or LO respectively.Moreover,fasting blood samples were collected from ophthalmic venous plexus at baseline as well as 4 weeks,8 weeks and 12 weeks after intervention.After 12 weeks feeding,all the rats were sacrificed followed 12 hours fasting.Blood was harvested and centrifuged at 3000 r/min for 10 min at 4°C to prepare serum.Fresh tissues were collected,quickly frozen in liquid nitrogen,and stored at-80°C for further analyses.2.Laboratory analysis: Serum fasting blood glucose(FBG),total cholesterol(TC),triglycerides(TG),high density lipoprotein-cholesterol(HDL-C)and low density lipoprotein-cholesterol(LDL-C)were measured with an automatic analyser.The serum levels of fasting serum insulin(FINS),tumor necrosis factor-?(TNF-?),interleukin 1?(IL-1?),interleukin 6(IL-6)and free fatty acids(FFA)were determined using ELISA kits.TC and TG in liver were determined using chemical kits.The homeostasis model assessment-insulin resistance(HOMA-IR)was calculated using the formula below:HOMA-IR= FBG×FINS/22.5.The fatty acid composition in serum was determined by Gas Chromatography(GC).The protein levels of gene related to PI3K/AKT insulin signaling pathway in liver and skeletal muscle,including insulin receptor(INSR),insulin-like growth factor receptor(IGFR),insulin receptor substrate-1(IRS-1),phosphorylation of IRS(p-IRS,ser1101),PI3 K,AKT,phosphorylation of AKT(p-AKT,tyr308),forkhead box transcription factor O1(FOXO1)and glucose transporter 4(GLUT4)were detected by western-blot analysis.Meanwhile,the protein levels of gene related to JNK and NF-?B inflammatory signaling pathway in liver,including JNK,phosphorylation of JNK(p-JNK,thr183/185),NF-?B,TNF-?,IL-1? and IL-6 were detected by western-blot analysis.Miseq sequencing of 16 Sr RNA gene was used to analyze the gut microbiota composition in the feces of rats.Results1.SSO,FO and LO groups reduced FBG,FINS,HOMA-IR levels and improved glucose tolerance and insulin sensitivity in HFHS-fed rats compared with SO group.And,SSO supplementation increased the level of docosahexaenoic acid(DHA)in serum and reduced the heterotopic fatty deposition in liver.2.Compared with the SO group,SSO,FO and LO supplementation improved the protein levels of INSR,PI3 K,AKT,p-AKT,GLUT4 and decreased the expression of p-IRS and FOXO1 in the liver and skeletal muscle,indicating that SSO,FO and LO improved the transduction of the PI3K/AKT insulin signaling pathway.3.Compared with the SO group,SSO,FO and LO groups inhibited the protein levels of JNK,p-JNK,NF-?B,IL-1?,IL-6 and TNF-? in the liver,indicating that SSO inhibited the transduction of the JNK/NF-?B inflammatory signaling pathway.SSO,FO and LO groups also reduced the serum levels of pro-inflammatory cytokines.4.SSO,FO and LO groups significantly improved the structure and composition of gut microbiota in HFHS-fed rats compared whith the SO group.SSO,FO and LO supplementation increased the relative abduance of beneficial bacteria,like Verrucomicrobia,Oscillospira,Ruminococcus and suppressed the relative abduance of harmful bacteria,including Actinobacteria,Blautia.And,the ratio of Firmicutes to Bacteroidete was significantly reduced.SSO supplementation increased the relative abduance of beneficial bacteria,like Allobaculum and Akkermansia,compared with FO and LO groups.Correlation analysis showed that the changes of gut microbiota were significantly correlated with the IR related metabolic parameters in HFHS-fed rats.ConclusionOur finding demonstrated that dietary SSO ameliorated IR,and the mechanism was related to activated the PI3K/AKT insulin signaling pathway,inhibited the JNK/NF-?B inflammatory signaling pathway and modulated the structure of gut microbiota.These findings provide novel insights into the development of SSO as potential functional foods for prevention of IR-related metabolic disorders.