The Mechanisms Of Soybean 7S Protein On Gastrointestinal Function Regulation

In recent years,with the prevalence of obesity and related metabolic diseases,the health benefits of dietary plant proteins have been widely concerned.A large number of epidemiological investigations and animal experiments showed that dietary soybean protein has a variety of metabolic regulatory effects,such as improving lipid metabolism,regulating blood pressure and reducing the risk of cardiovascular diseases.Soybean 7S protein is an important functional component of soybean protein,which is involved in the regulation of lipid metabolism and liver lipid metabolism.However,the regulatory mechanisms are still unclear.The gastrointestinal tract is an important site for food digestion and plays a key role in nutrient absorption,energy homeostasis,immune regulation and lipid metabolism.The study of regulation of soybean 7S protein on gastrointestinal functions is helpful to reveal the mechanisms of metabolic regulation of soybean 7S protein.In this study,the gastrointestinal regulatory mechanism of soybean 7S protein were systematically studied via a combination of in vitro and in vivo experiments from three main aspects,including gastrointestinal mucus barrier,gut microbiota and cholic acid metabolism.Hope to provide theoretical basis for understanding the health regulation function of soybean protein.The main results are as follows:（1）The effects of soybean 7S protein on gastric mucus barrier were studied.Soybean 7S protein has pepsin resistant properties.In this study,two structural components of soybean 7S protein were isolated by pepsin hydrolysis combined with ultrafiltration.MS/MS analysis revealed the obtained structural components were derived from core region（CR）and extension region（ER）of soybean 7S protein subunits,respectively.And the two components were designated as CR fragments and ER peptides,respectively.Firstly,biophysical methods were used to systematically study the interaction between CR fragments and mucin,which including quartz crystal microbalance（QCM-D）,Langmuir monolayer,isothermal titration calorimetry（ITC）and particle tracking experiments.It was found that CR fragments could enhance the barrier function of mucus layer via interaction with mucin.Meanwhile,we also demonstrated the gastric protective effects of CR fragments against aspirin-induced acute gastric injury in rats.These results demonstrated that the gastric protective effects of soybean 7S protein mainly from pepsin resistant CR fragments.The CR fragments enhanced the barrier function of gastric mucus layer through the interaction with mucin,thus playing a protective role on gastric mucosa.This study provides a new understanding of the gastric protective effect of soybean protein.（2）The effects of soybean 7S protein and its structural components on gut microbiota composition and metabolism were studied using in vitro fermentation model.Gut microbiota composition and short chain fatty acids（SCFAs）analysis of fermentation samples showed that different structural components of soybean 7S protein have different impacts on gut microbiota composition and metabolism.Particularly,ER peptides selectively inhibited the gut Gram-negative bacteria and significantly increased the production of SCFAs.Lipopolysaccharide（LPS）is a major structural component of the outer membrane of Gram-negative bacteria and an important risk factor for metabolic diseases.The interactions between ER peptides and bacterial lipopolysaccharide（LPS）were analyzed by ITC and Langmuir monolayer.The results showed that in the presence of Ca²⁺,ER peptides exhibited high affinity to LPS,can formβ-sheet-rich aggregation structures on the LPS monolayer,and inhibit the growth of Gram-negative bacteria by weakening the stability of LPS outer membrane.In addition,inhibition of gut Gram-negative bacteria reduces LPS load,which is closely associated with improved body metabolism.This study revealed the mechanisms of soybean 7S protein regulating gut microbiota from the perspective of peptides and LPS interaction.This provides a new understanding for the improvement of metabolic diseases of soybean protein.（3）The effects of soybean 7S protein and its structural components on lipid metabolism and gut microbiota composition were investigated in rats fed a high-fat diet.The analysis of body weight changes and serum biochemical indexes showed that soybean 7S protein and ER peptides inhibited body weight gain and significantly reduced serum triglyceride levels in high-fat diet rats.The gut microbial analysis of rat fecal samples showed that ER peptides affected the composition and gene function of gut microbiota,particularly soybean 7S protein group and ER peptides group showed the similar gene function distribution of gut microbiota.This study showed that the regulating effects of soybean 7S protein on blood lipid metabolism and gut microbiota mainly from the extension region of soybean 7S protein subunits.Meanwhile,the regulation of lipid metabolism of soybean 7S protein is closely related to gut microbiota.（4）The metabolic regulation mechanism of soybean 7S protein and its structural components was further explored in this section.Untargeted metabolome analysis of rat serum samples showed that high-fat diet significantly affected the serum metabolism profile of rats,especially the metabolism of lipid-related substances.ER peptides significantly altered the profile of serum cholic acid metabolism in high-fat diet rats.Furthermore,targeted metabolomics analysis was used to study the cholic acid metabolism of rat fecal samples,and it was found that ER peptides significantly increased the content of primary and secondary cholic acid in rat fecal samples.These results further confirmed that the regulation of lipid metabolism of soybean 7S protein mainly from ER peptides.ER peptides regulated lipid metabolism by increasing intestinal cholic acid excretion.Meanwhile,the increased cholic acid content in the intestinal tract affected the composition of gut microbiota.In turn,gut microbiota metabolized primary cholic acid into secondary cholic acid and further participated in the regulation process of lipid metabolism in rats.This study revealed that the structural component of soybean 7S protein extension region regulates lipid metabolism by influencing gut microbiota and cholic acid metabolism.This provides a theoretical basis for understanding the health effects of soybean protein.