Study On The Hypolipidemic Effect Of Lotus Seed Resistant Starch And Its Mechanism

Type 2 diabetes is a rapidly growing chronic disease caused by metabolic disorders worldwide.Using a healthy diet to control blood glucose level has become a main means of preventing and controlling type 2 diabetes.Reported studies showed that the consumption of resistant starch could exhibit a promising effect on the controlling blood glucose level.Lotus seeds,the mature seeds of Nelumbo nucifera Gaertn,have been consumed as a traditional healthy food in China for a long history.Lotus seed starch is a kind of specific starch with high amylose content(42%),and could easily be retrograded to form resistant starch.Resistant starch,which is not digested and absorbed by the human small intestine,can enter the colon and be fermented and ultilized by intestinal flora,thus exerting its physiological effects such as hypoglycemic effect,hypolipidemic effect,and preventing cardiovascular diseases and colon cancer.Lotus seed resistant starch has a promising prospect in the development of low GI(glycemic index)foods and hypoglycemic functional foods.However,its effect of regulating blood glucose and its mechanism have not been well studied.The study was carried out to investigate the effects of different mothods on the molecular structural and physicochemical properties of lotus seed resistant starch.Using diabetic mice as model animals,analyzed the relationship of the dosage of lotus seed resistant starch and its hypoglycemic effect,and the influence on the intestinal environment after fermentation.Moreover,with the application of transcriptome study,16S rDNA sequencing and bioinformatics analysis,the effects of lotus seed resistant starch on composition of gut microbiota and genome-wide gene expression and pathway changes at the molecular level were studied,which could contribute to the understanding of the molecular mechanism of hypoglycemic effect of lotus seed resistant starch.1.Production and analysis of lotus seed resistant starchThe study was carried out to investigate the effects of heat-moisture treatment(HMT),repeated heat-moisture treatment(RHMT)and citric acid-repeated heat-moisture treatment(ARHMT)on the formation of lotus seed resistant starchs and their structural and physicochemical properties.Compared with HMT,the yield of lotus seed resistant starch prepared by RHMT was slightly improved without the significant difference(p>0.05),while ARHMT silightly decreased the yield,and the difference was not significant(p>0.05).Different applied methods could all destroy the shape of lotus seed starch granule to form a compact massive structure with rough surface,and exhibited a significant impact on the sizes of lotus seed starch particles.In the order of largest to smallest in size:ARHMT>RHMT>HMT.XRD results showed that all of the three methods were able to cause the recrystallization of lotus seed starch,and changed the starch type from the original C-type to B-type,which was consistent with the NMR results.Compared with lotus seed starch,the thermal stability of the resistant starch of lotus seed was improved,and among them resistant starch prepared by HMT has the highest thermal stability.The water holding capacity and oil holding capacity of the lotus seed resistant starchs were significantly improved.Swelling powers of resistant starchs were significantly lower than that of native starch,while solubility of resistant starch prepared by ARHMT was significantly improved.In conclusion,HMT is suitable for the preparation of lotus seed resistant starch in terms of preparation cost,yield and its physicochemical properties.2.Study on the hypoglycemic effect of lotus seed resistant starch in diabetic miceThe hypoglycemic effects of low,medium and high doses(5%,10%and 15%)of lotus seed resistant starch were investigated in the type 2 diabetic mice induced by high sugar and fat diet and STZ injection.Compared with the control group,the fasting blood glucose level of diabetic mice after intervention with low,medium and high doses of resistant starch decreased by 16.0%,32.0%and 33.6%,respectively(p<0.01).Lotus seed resistant starch could also effectively improve glucose tolerance in diabetic mice,improve peripheral tissue sensitivity to insulin and improve insulin resistance.The analyze results of blood lipid composition in diabetes mice showed that three doses of lotus seed resistant starch intervention could all effectively restore the lipid metabolism disorder.The contents of serum total cholesterol(TC)were decreased by 9.8%,19.8%and 9.8%respectively,and the contents of serum triglyceride(TG)were decreased by 24.7%,33.3%and 37.6%,respectively.Meanwhile,the contents of high density lipoprotein cholesterol(HDL-c)were increased by 24.3%-40.7%.The hypoglycemic effect of the lotus seed resistant starch was positively correlated with the dosage,but the effects between medium and high dose groups showed no significant difference.Taking into account,the medium dose(10%)of lotus seed resistant starch is an appropriate dosage that could effectively control blood sugar.3.Effects of lotus seed resistant starch on gene expression and metabolic pathways in diabetic miceThrough RNA-seq high-throughput sequencing technology,pancreas transcriptome profiles were complied and the differentially expressed genes were identified in diabetic mice fed with and without lotus seed resistant starch,which followed by bioinformatics analysis using the GO and KEGG enrichment analysis methods.Transcriptome analysis results showed that the supplementation of lotus seed resistant starch could induce 511 differential expressed genes in diabetic mice,which are involved in 155 metabolic pathways.Bioinformatics analysis results showed that,due to the intervention of lotus seed resistant starch,the pathways,directly or indirectly related to hypoglycemic effect,involved in the immune system,endocrine system,coenzyme factor and the metabolism of vitamin,amino acid metabolism,carbohydrate metabolism and lipid metabolism,were regulated through the differentially expressed genes related to signal transduction,signaling molecules and response pathways.Meanwhile,it also affected the pathways involved in the pancreatic tissue cell growth and apoptosis,intracellular transport and catabolism,and other pathways.The pathways significantly associated with the hypoglycemic effect of lotus seed resistant starch include type 2 diabetes,pancreatic secretion,FoxO signaling,MAPK signaling,AI3k-Akt and p53 signaling.4.Effects of lotus seed resistant starch on the intestinal environment and microflora composition in diabetic miceAfter 6 weeks of dietary intervention of 10%lotus seed resistant starch,the symptoms of intestinal environmental imbalance in diabetic mice were relieved,and the secretion of incretins was promoted.The ingestion of lotus seed resistant starch significantly(p<0.01)increased SCFAs concentration in diabetic mice,especially for propionic acid,butyric acid and isobutyric acid.Lotus seed resistant starch could regulate the gut microbiota in diabetic mice,mainly through increasing the abundance of bacteroides and significantly inhibiting the proliferation of proteobacteria,but has little effects on verrucomicrobia and actinomycetes.Under the combined action of high sugar and fat feed and diabetic symptoms,the relationship between the intervention of lotus seed resistant starch and the change of proteobacteria abundance might have an important correlation with its hypoglycemic effect.Lotus seed resistant starch could promote the abundance of intestinal bifidobacteria and lactobacillus in diabetic mice,and effectively inhibited the excessiveproliferation of enterobacter.