| With increases in living standards,high-fat and high-protein diets,which can cause metabolic disorders or metabolic syndrome,have become more popular among people.The dietary fiber pattern plays an important factor in human health~3 by in preventing cardiovascular and cerebrovascular diseases such as hyperlipidemia,hyperglycemia,and atherosclerosis.Dietary fiber can be fermented by gut microbiota such as Bacteroides,Trichinella,Bromorum,and other microbiota in the colon to produce short-chain fatty acids(SCFAs)because of the difficulty of digesting and absorbing fiber in the small intestine.As a new food ingredient,L-theanine(LTA),a characteristic non-protein amino acid,in has shown favorable effects on improving intestinal mucosal immunity.LTA can protect the intestinal structure of enterotoxin-producing E.coli-induced immune stress in mice,inhibit over-expression of RIP2 and nuclear factor-?B mRNA,inhibit expression of p65 and p38proteins,and improve non-specific immunity in the intestinal mucosa.It can also regulate intestinal non-specific immunity by inhibiting the expression levels of inflammatory cytokines NOD1,NOD2 and NF-?B,reducing the degree of lipid peroxidation and improving the antioxidant capacity.Additionally,LTA is essential for maintaining intestinal integrity and function.However,how LTA regulates SCFA metabolism and intestinal mucosal immune function via SCFA metabolism has not been examined.Here,we performed a 28-day feeding experiment in Sprague-Dawley rats to investigate the effects of different doses of LTA on intestinal mucosal immunity and the regulation of SCFAs metabolism.50 SD rats of four weeks old were randomly divided into normal feed group(Control A),dietary fiber feed group(Control B),LTA high-weight group(LTA500),LTA middle-weight group(LTA300),and LTA low-weight group(LTA100).Fedding for 28 days,research and analysis of L-Theanin in the dietary fiber diet pattern improves the function of intestinal mucosal immunity by regulating SCFA metabolism,providing scientific basis for improving the intestinal mucosal immune function,promoting the diversified development of food nutrition intervention,and the in-depth use of L-theanine.The main findings and conclusions are as follows:(1)Effect of L-theanine on intestinal immunity.L-theanine can increase the content of ileal immunoglobulin.IgA,IgE,and IgG contents were higher in the Control B than in the Control A group(P<0.05).The IgE content was higher in the LTA100 than in the Control B group(P<0.05).The IgA and IgG contents were significantly higher in the LTA100 than in the Control B group(P<0.01).IgA,IgE,and IgG contents were significantly higher in the LTA300 group than in the Control B group(P<0.01).IgA and IgG contents were significantly higher in the LTA500 than in the Control B group(P<0.01).The villi height and villi height/crypt depth(V/C)in the jejunum as well as the crypt depth in the duodenum and ileum were higher in the Control B than in the Control A group(P<0.05).Crypt depth in the jejunum and height of villi in ileum were significantly higher in Control B than in Control A(P<0.01).The height of villi and crypt depth,crypt depth,and V/C in the ileum and V/C in the jejunum were higher in LTA100 than in Control B(P<0.05).The height of villi,crypt depth,and V/C in the ileum and height of villi in the jejunum were higher in LTA300 than in Control B(P<0.05).The height of villi and V/C in the jejunum and V/C in the ileum were higher in LTA500 than in Control B(P<0.05).(2)Intestinal pH and gut microbiota.Compared to the pH of Control A,the pH of Control B decreased but did not reach a significant level.Compared with the pH of Control B,the pH of each dose of L-theanine group decreased,and the pH of LTA500 decreased to a significant level(P<0.01).Compared with Control A,the abundance and uniformity of bacteria in Control B are higher.In each theanine-treated group,the abundance and uniformity of bacterial flora in LTA500 were higher than those in LTA300 and LTA100.The proportions of Bacteroides and Bromococcus were higher in the Control B than in the Control A group(P<0.05).The proportion of Trichospira was significantly higher in the Control B than in the Control A group(P<0.01).The proportions of Bromococcus was higher in the LTA 100(P<0.05).The proportion of with Bacteroides,Trichospira and Bromococcusthe were significantly higher in the LTA300 and LTA500 groups(P<0.01).(3)Metabolism and mechanism of short-chain fatty acids.Total SCFAs,propionic acid,and butyric acid contents were higher in the Control B group than in the Control A group(P<0.05).The values were also significantly higher in the LTA300 and LTA 500 groups than in the Control B group(P<0.01).Effects of L-Theanine on acetic acid metabolism in the liver.The expression of ACC1,SREBP-1c,SREBP-2,FASN,HMGCR,and LDLR mRNA was significantly lower in Control B than in Control A(P<0.01)(Table 7).The expression of SREBP-1c and HMGCR mRNA was higher in LTA100 than in Control B(P<0.05).The expression of LDLR mRNA was higher in LTA300 than in Control B(P<0.05).The expression of SREBP-1c,FASN,and HMGCR mRNA was significantly higher in LTA300than in Control B(P<0.01).The expression of HMGCR mRNA was higher in LTA500 than in Control B(P<0.05).The expression of ACC1,SREBP-1c,FASN,and LDLR mRNA was significantly higher in LTA500 than in Control B(P<0.01).The expression of ACC1,SREBP-1c,SREBP-2,FASN,HMGCR,and LDLR proteins was significantly lower in Control B than in Control A(P<0.05)(Fig.2).The expression of ACC1,LDLR,and SREBP-2 proteins was higher in LTA100 than in Control B(P<0.05).The expression of SREBP-1c and HMGCR proteins was significantly higher in LTA100 than in Control B.The expression of FASN,LDLR,SREBP-1c,and SREBP-2 proteins was higher in LTA300 than in Control B(P<0.05).The expression of ACC1 and HMGCR was significantly higher in LTA300 than in Control B(P<0.01).The expression of ACC1,SREBP-1c,SREBP-2,FASN,HMGCR,and LDLR proteins was significantly higher in LTA500 than in Control B(P<0.01).Effects of L-Theanine on propionate and butyrate metabolism in the colon.The expression of GLUT2,PCK1,G6PC,PFKM,GSK-3?,and SGLT1 mRNA was significantly higher in Control B than in Control A(P<0.01)(Table 8).The expression of GLUT2,PCK1,G6PC,PFKM,GSK-3?,and SGLT1 mRNA was significantly lower in LTA100 and LTA300 than in Control B(P<0.01).The expression of GLUT2,PCK1,G6PC,PFKM,and GSK-3?mRNA was lower in LTA500 than in Control B(P<0.05).The expression of SGLT1 mRNA was significantly lower in LTA500 than in Control B(P<0.01).The expression of GLUT2,PCK1,G6PC,PFKM,GSK-3?,and SGLT1 proteins was significantly higher in Control B than in Control A(P<0.01)(Fig.3).The expression of GLUT2,PCK1,G6PC,PFKM,GSK-3?,and SGLT1 proteins was lower in LTA100 than in Control B(P<0.05).The expression of GLUT2,PCK1,G6PC,PFKM,GSK-3?,and SGLT1 proteins was significantly lower in LTA300 than in Control B(P<0.01).The expression of PCK1,G6PC,PFKM,GSK-3?,and SGLT1 proteins was lower in LTA500than in Control B(P<0.05).Overall,our results showed that LTA can increase the proportion of SCFAs-producing gut microbiota,such as Bacteroides,Trichinella,and Rumenococcus,under dietary fiber feeding.LTA increased the contents of total SCFAs,acetic acid,propionic acid,and butyric acid under dietary fiber feeding.LTA improved the intestinal morphology and increased the contents of IgA,IgE,and IgG in the ileum under dietary fiber feeding.LTA affected acetic acid metabolism by upregulating the expression of FASN,ACC1,LDLR,HMGCR,and SREBP-1c mRNA and protein and improved cholesterol synthesis under dietary fiber feeding,thus maintaining the content of TC at normal levels.LTA can affect propionate and butyrate acid metabolism by downregulating the expression of G6PC and PCK1 at the mRNA and protein levels and inhibiting gluconeogenesis under dietary fiber feeding.This maintains the content of blood glucose at normal levels.Our results also show that LTA regulates SCFA metabolism and improves intestinal mucosal immune function by improving cholesterol synthesis in the liver and inhibiting gluconeogenesis in the colon. |
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