Regulation And Mechanism Of L-Theanine On Intestinal Absorption And Transport Of Amino Acids

The intestine is the main site for the body to absorb and transport nutrients such as amino acids,and when the intestinal tract utilization rate of glutamine is increased,the consumption of other amino acids can be reduced.The new food ingredient L-theanine is a characteristic non-protein amino acid in tea,especially green tea.Similar to the structure of glutamine,its catabolic product glutamate is a precursor of glutamine.It plays a role in neuroprotection and anti-depression by regulating the concentration of glutamic acid and glutamine in the body.Studies have revealed that L-theanine can protect the intestine and regulate immunity,but whether L-theanine can regulate the absorption and transport of amino acids and other nutrients and its mechanism remians to be explored.This study use different dose of L-theanine[low(100 mg/kg),medium(300 mg/kg)and high(400 mg/kg)]to intervene in healthy KM male mice aged 4 weeks for 28 days.Employing HE staining,biochemical index analysis,qRT-PCR and Western blot to study the weight,intestinal morphology,content of free amino acids in intestine and serum,expression of mRNA and proteins of amino acid transporter and related signaling pathways,aimed to study and analyse the regulating effect and the mechanism of L-theanine on intestinal amino acid uptake and transport.Besides,this study explored the effects and mechanisms of L-theanine(300 mg/kg),instant green tea(300mg/kg),EGCG(300 mg/kg),L-theanine+EGCG[(60 mg L-theanine+240 mg EGCG)/kg]on intestinal amino acid uptake and transport.In order to provide a scientific basis for the diversified development of food nutrition intervention and the promotion of the deep utilization of L-theanine and other tea functional components.The main findings and conclusions are as follows:1)Regulation and mechanism of L-theanine on intestinal amino acid absorption.Compared with the normal group,there was no significant change in food intake,body weight gain,and organ index in the L-theanine groups.The high-dose group increased the content of AKP and TP,decreased the content of BUN in serum(P<0.05),and had no significant difference with the effect of glutamine intervention.The most free amino acid content of serum and ileum decreased in each dose group.With the increasing of L-theanine intervention dose,the villus length of each part increased.The villus height,V/C ratio and the content of amino acid related to intestinal growth of duodenum and jejunum were increased at medium and high doses of L-theanine groups.2)Regulating effect and mechanism of L-theanine on intestinal amino acid transport in mice.Compared with normal control group,L-theanine at low dose up-regulated the mRNA expression of 4F2hc,y~+LAT1,ASCT2 in duodenum,EAAT3,y~+LAT1,CAT1,ASCT2 and B~0AT1 in jejunal,and EAAT3,EAAT1,4F2hc,y~+LAT1,CAT1,ASCT2 and B~0AT1 in ileum(P<0.05),the protein levels of 4F2hc and y~+LAT1 in duodenum,EAAT3,y~+LAT1,CAT1,ASCT2 and B~0AT1 in jejunal and 4F2hc,y~+LAT1 and CAT1 in ileum(P<0.05).And the phosphorylation levels of mTOR and S6 in duodenum and ileum and S6 in jejunum were increased in L-theanine low dose group(P<0.05).L-theanine at middle and high dose up-regulted the the mRNA and protein levels of EAAT3,EAAT1,4F2hc,y~+LAT1,CAT1,ASCT2 and B~0AT1(P<0.05),and increased phosphorylation levels of mTOR,S6K1 and S6(P<0.05)in duodenum,jejunum and ileum.3)The synergistic regulation and the mechanism of L-theanine and EGCG on intestinal absorption and transport of amino acids.Compared with the normal group,L-Theanine+EGCG group reduced the contents of some essential amino acids in serum and most free amino acids in ileum,and increased the content of most free amino acids in duodenum and jejunum which was higher than that of L-theanine group and EGCG group.The EGCG group increased the contents of some non-essential amino acids in serum and free amino acids in duodenum,and decreased the contents of most free amino acids in jejunum and ileum(P<0.05).The instant green tea increased the contents of some non-essential amino acids in serum and most free amino acids in duodenum and jejunum,and decreased the contents of most free amino acids in ileum(P<0.05).The mechanism of which were as follows,L-Theanine+EGCG group up-regulated the mRNA levels of EAAT1,4F2hc,ASCT2,y~+LAT1 and B~0AT1 in duodenal,EAAT3,CAT1,ASCT2 and B~0AT1 in jejunum,EAAT3,EAAT1 and y~+LAT1 in ileum(P<0.05),and the protein levels of EAAT3,EAAT1,4F2hc,y~+LAT1,CAT1,ASCT2 and B0AT1 in duodenum,jejunum and ileum(P<0.05),and increased the phosphorylation levels of S6K1 and S6 in duodenum,jejunum and ileum(P<0.05).The EGCG group up-regulated the mRNA levels of y~+LAT1 in duodenal,EAAT3,CAT1,4F2hc,ASCT2 and B~0AT1 in jejunum,EAAT3,EAAT1,y~+LAT1,4F2hc,B~0AT1 and ASCT2 in ileum(P<0.05)and the protein levels of EAAT3,EAAT1,ASCT2,y~+LAT1 and CAT1 in jejunum,EAAT1 and CAT1 in jejunum,EAAT1,y~+LAT1 and CAT1 in ileum(P<0.05),and increased the phosphorylation level of S6K1 and S6 in duodenal,and S6 in ileum(P<0.05).The instant green tea group up-regulated the mRNA levels of EAAT1and B~0AT1 in duodenal,EAAT3,EAAT1,CAT1,ASCT2 and B~0AT1 in jejunum,EAAT3,EAAT1,y~+LAT1,CAT1,4F2hc and B~0AT1 in ileum(P<0.05),and the protein levels of EAAT3,EAAT1,4F2hc,y~+LAT1,CAT1,ASCT2 and B~0AT1 in duodenum,jejunum and ileum(P<0.05),and increased the phosphorylation levels of S6K1 and S6 in duodenum and ileum,and mTOR and S6 in jejunum(P<0.05).In conclusion,L-theanine can increase the duodenum,jejunum villus height,V/C ratio and the content of amino acid related to intestinal growth by improving intestinal morphology,increasing the expression of intestinal amino acid transporter mRNA and protein,increasing the phosphorylation level of downstream protein of mTOR signaling pathway,and promoting protein metabolism.Increasing the content of free amino acids in duodenum and jejunum,reducing the content of serum amino acids and improving the efficiency of amino acid benefit for the body.The synergistic intervention of L-theanine and EGCG is more conducive to improving the content of free amino acids in intestinal tissues,but the effect of L-theanine on the expression of intestinal amino acid transporter and phosphorylation of downstream protein of mTOR signaling pathway is less effective than that of L-theanine.