Mechanisms And Regulating Strategies Of Dietary AGEs-Interfered Energy Homeostasis

In recent decades,with the progressive of food industrialization,the supply and consumption of processed and ultra-processed foods have increased dramatically,contributing to the global pandemic of obesity and diabetes mellitus,which has become a worldwide public health problem threatening human health and social development.Among them,advanced glycation end-products（AGEs）produced during food processing are considered to be one of the critical factors contributing to the risk of obesity and diabetes mellitus.However,most studies on dietary AGEs have focused on their pro-inflammatory effects at home and abroad,and there is a lack of systematic studies on their intervention in the development of obesity and diabetes.Based on the Lepr^db/dbgenotype diabetic mouse model,Caco-2 enterocyte model and LO2 hepatocyte model,combining with modern histological techniques and bioinformatics methods,such as metabolomics,transcriptomics,metabolic flow technology,high-throughput sequencing,the effects of dietary AGEs on the development of obesity and diabetes through the regulation of hepatic transcriptional,glucose and lipid metabolism,inhibition of mitochondrial electron transport chain,and promotion of lipid synthesis were investigated in-depth and systematically.A stepwise categorization approach was used to gradually limit the range of dietary AGEs that are harmful to the organism in batches through three independent cellular experiments,and finally the key components of dietary AGEs that exert biohazardous effects were obtained.The potential of oatβ-glucan as a targeted dietary supplement to alleviate the biohazardous effects of dietary AGEs was explored,and the molecular mechanism of oatβ-glucan regulation of dietary AGEs-mediated disorders of glucose and lipid metabolism was mastered.The study is cutting-edge and scientifically important,and systematically complements the hazard mechanisms of dietary AGEs and the types of AGEs that produce hazards,which is of guiding significance for the targeted mitigation of dietary AGEs-mediated biohazards.The main contents and results of this thesis are as follows:Using Lepr^db/dbgenotype diabetic mice as a model and casein-AGEs as a study system,we investigated the effect of dietary AGEs on the inflammatory response mediated through the receptor system（RAGE,the receptor of AGEs）.However,the assay results showed that the biohazardousness caused by long-term intake of dietary AGEs may not be related to RAGE,which is different from the results of most similar studies.The present study obtained a high AGEs diet by glycating casein and then preparing feed by the glycated casein,which effectively avoided the destruction of heat-sensitive nutrients and avoided the production of many other food hazards,including lipid peroxides;and thus,obtained more reliable conclusions.In terms of the mechanisms by which dietary AGEs promote abnormal weight gain and exacerbate the diabetic phenotype in mice,we investigated the"direct"and"indirect"pathways which interfering the body’s metabolism based on plasma metabolomics,high-throughput sequencing of gut microbiota,and multi-omics association analysis,thus affecting the development and progression of diabetes.This part of the study breaks through the past stereotypical understanding of dietary AGEs mediating inflammation in the body and proposes a novel mechanism based on metabolic regulation of dietary AGEs affecting the development of diabetes and obesity.In order to elucidate the mechanism of biohazard of dietary AGEs,we first investigated the absorption and transport mechanism of foodborne AGEs.We examined the in vitro transmembrane transport capacity of different structural AGEs in the gastrointestinal digestion products ofβ-casein-AGEs based on the Caco-2 monolayer cell model,and analyzed the conformational relationships between modification type/amino acid neighbor effect and transmembrane capacity,and identified the following mechanisms:GO-H,CML,CEL,Ala–GO-H–Glu,Thr–Glu–MG-H,CML–Ala–Val and Ile–Asn–CML.free and tripeptide-bound AGEs were the types of AGEs readily transported across the membrane.Second,using Caco-2cells as a model,we demonstrated that free AGEs were the main AGEs components interfering with cellular energy homeostasis by comparing changes such as mitochondrial energy production levels before and after inhibition of transport of peptide-bound AGEs using Irbesartan.In terms of their intervention mechanisms on energy homeostasis,free AGEs were found to directly interfere with mitochondrial energy production,reduce mitochondrial membrane potential,alter mitochondrial ultrastructure,impede AMPK activation and NAD⁺-dependent SIRT6 expression thereby inhibiting the cellular energy sensing-feedback pathway,and interact with TP to inhibit mt DNA repair.Finally,using Nε-（1-carboxymethyl）lysine（CML）,a representative free AGEs with easy transport,as a study system and LO2 cells as a model,we verified that free AGEs with easy transmembrane transport act as a key component to induce disorders of glucolipid metabolism and energy homeostasis in the organism/cell,and explored the molecular mechanism of CML to inhibit glucose metabolism The molecular mechanism of CML inhibition of glucose metabolism and promotion of lipid accumulation was investigated.During glucose metabolism,CML inhibited glycolysis by promoting glucose-6-phosphatase expression,inhibited the tricarboxylic acid cycle by inhibiting the conversion of cis-aconitate to isocitrate,and inhibited oxidative phosphorylation by inhibiting mitochondrial respiratory chain enzyme complex III（Bcs1l）expression.In terms of lipid metabolism,dietary AGEs inhibited the initiation of PPARγand cellular transport of glucose and gluconeogenesis by activating the AKT-Fox O1 signaling pathway,and activated the downstream action of acetyl coenzyme A carboxylase（ACC）by promoting the expression of carbohydrate-responsive element binding protein（Ch REBP）,and consequently promoted cellular lipid accumulation.It is evident that dietary AGEs in their free form interfere with the energy homeostasis,glucose metabolism and lipid synthesis of the organism,thus causing harm to the organism.Based on the above findings on the hazard mechanisms of foodborne AGEs,an active polysaccharide,oatβ-glucan,with significant efficacy in regulating glucose and lipid metabolism was selected,and a targeted intervention strategy for the inhibition/elimination of casein-AGEs-mediated disorders of glucose and lipid metabolism by oatβ-glucan supplementation was constructed.And the mechanism of the effect of oatβ-glucan was distinguished by setting two types of intake:"simultaneous intake with high-AGEs diet"and"intake with high-AGEs diet every second day."The dietary supplementation of oatβ-glucan was found to be effective in reducing body weight gain,lowering blood glucose,glycated hemoglobin,and plasma insulin levels,improving insulin resistance,and alleviating lipid accumulation in organs and fatty degeneration in adipose tissues in Lepr^db/dbmice,which regardless of the intake method.However,as for hepatic lipid accumulation,simultaneous intake with high-AGEs diet was more effective in reducing hepatic lipid accumulation than intake with high-AGEs diet every second day.The transcriptional regulatory ability of oatβ-glucan on the set of genes related to hepatic glucose and lipid metabolism was analyzed by transcriptomic techniques,showing that the promoting effect of oatβ-glucan on hepatic glucose metabolic capacity was mainly attributed to the inhibition of digestion and absorption of dietary AGEs,while the promoting effect of oatβ-glucan on hepatic lipid metabolism was mainly attributed to the probiotic effect of oatβ-glucan itself.Our thesis promotes the study of the harmful mechanisms of dietary AGEs from the perspectives of bioavailability,glucose and lipid metabolism,and energy homeostasis.The constructed mitigation strategy based on oatβ-glucan dietary supplementation has great effect on anti-AGEs-mediated obesity and diabetes phenotypes,and the obtained results and proposed mechanism have critical academic value and practical significance.