Effects And Mechanisms Of L-theanine On Metabolism Of Glucose,Lipid And Protein

Glucose,lipid and protein are three main nutrients of life activities,the metabolic process of which are interrelated,interacted and transformed.Any metabolic disorder will lead to abnormalities or diseases in the body.With the development of social economy,the high-sugar,high-fat and high-salt diet,which can easily cause metabolic disorders and metabolic syndrome,has become a dietary normality of the public.Maintaining normal metabolism and promoting body health is an important development direction of food nutrition intervention.Plant bioactive components are one of the main resources for scientific research and industrial application of food nutrition intervention.L-theanine,a new food ingredient,is a non-protein amino acid peculiar in traditional food tea.It has many kinds of biological activities,such as tranquilizing effect,antioxidant,regulating immunity and enhancing learning and cognitive ability.However,present studies mainly focus on the biological activity and molecular mechanism of L-theanine through cell and animal models,but rarely on the regulatory effects and mechanism of L-theanine on the metabolism of nutrients such as glucose,lipid and protein in normal organisms.Therefore,this study applies three different doses of L-theanine(low(100 mg·kg-1),medium(200 mg·kg-1)and high(400 mg·kg-1))to intervene in SPF-grade healthy SD male rats for 28 days,employing ELISA,qRT-PCR and Western blot,aimed to investigate the effect and the molecular mechanism of L-theanine on the metabolism of glucose,lipid and protein via studying the boby weight,liver morphology,blood biochemical parameters and the expression of key enzymes,genes,proteins and signaling pathway in glucose,lipid and protein synthesis,decomposition,transformation of rats.So as to provide scientific basis for maintaining normal metabolism of nutrients and body health,promoting diversified development of food nutritional intervention and further utilization of L-theanine.The main results and conclusions are as follows:(1)The effects and molecular mechanisms on glucose metabolism.Compared with the normal group,L-theanine intervention may promote the weight gain of rats(P>0.05),but had no effect on the liver morphology.L-theanine at medium and high dose increased the content of hepatic glycogen and muscle glycogen(P<0.05).Three dose of L-theanine up-regulated the expression of PFK mRNA in liver and skeletal muscle(P<0.05).L-theanine at low dose down-regulated the expression of PCK1 mRNA and G6 PC mRNA in liver,and the expression of GSK-3β mRNA in skeletal muscle(P<0.05);L-theanine intervention up-regulated the expression of PFKL protein in liver(P<0.01),and up-regulated the expression of GLUT2 and GYS2 protein in liver(P<0.05)and the low and medium doses reach significant effect(P<0.01).L-theanine at low and medium dose up-regulated the expression of PCK1 protein(P<0.01),and the low dose suppressed the phosphorylation of GSK-3β in liver(P<0.01);Meanwhile,L-theanine up-regulated the expression of PFKM and GYS1 protein in skeletal muscle(P<0.05),suppressed the phosphorylation level of GSK-3β protein(P<0.05),and the low and high dose reached significant level(P<0.01).(2)The effects and molecular mechanisms on lipid metabolism.Compared with the normal group,LDL-C content decreased in low dose group(P<0.05),the activity of ACC in liver decreased in middle and high dose group(P<0.05).The activity of CPT-1 in liver increased in middle dose group(P<0.05);The expression of PPARa,CPT-1 and LxRa mRNA in liver was up-regulated in low and high dose group(P<0.05),while the expression of FAS mRNA was down-regulated(P<0.05).The phosphorylation level of ACC1 protein was suppressed in low dose group(P<0.05).The expression of FASN and HMGCR protein was down-regulated in L-theanine groups(P<0.01).The expression of PPARa protein and LXRa protein in liver was up-regulated in low and middle dose group(P<0.01).The expression of SREBP-1c protein was down-regulated in L-theanine treated groups(P<0.05),and the low and middle dose reached significantly level(P<0.01).(3)The effects and molecular mechanisms on protein metabolism.Compared with the normal group,L-theanine increased the content of Alb,and the low dose increased the content of TP(P<0.05).The expression of Rheb,eIF4 E and 4E-BP mRNA in liver was down-regulated in each dose group(P<0.05),while the expression of TSC1 m RNA was up-regulated(P<0.05)in high dose group;L-theanine treatment down-regulated the expression of Rheb and S6 mRNA in skeletal muscle(P<0.05),And the expression of mTOR mRNA was up-regulated in middle dose group(P<0.05).The expression of eIF4 E and 4E-BP mRNA was downregulated in low and high dose group(P<0.05);The phosphorylation level of mTOR in liver was up-regulated in low-dose group(P<0.05);The phosphorylation of p70S6 K protein in liver was up-regulated in low-dose and middle-dose group(P<0.01);The phosphorylation of S6 protein in liver was significantly increased in low-dose group(P<0.01);Meanwhile,the phosphorylation of mTOR and p70S6 K protein in skeletal muscle was up-regulated in lowdose group(P<0.01).And the phosphorylation level of S6 protein in skeletal muscle was upregulated in low and high dose groups(P<0.05).(4)The effects and molecular mechanisms on metabolic transformation of glucose,lipid and protein.Compared with the normal group,L-theanine at low dose up-regulated the expression of CS and LKB1 mRNA,down-regulated the expression of IGF1 R m RNA in liver(P<0.05),while high dose intervention up-regulated the expression of INSR,IRS2 and LKB1 mRNA in liver(P<0.05).Three doses of L-theanine down-regulated the expression of IGF1 mRNA(P<0.05).L-theanine at medium dose up-regulated the expression of PI3 K and AKT mRNA in skeletal muscle(P<0.05).L-theanine at low and high dose down-regulate the expression of skeletal muscle IGF1 and IGF1 R m RNA(P<0.05).L-theanine at low(P<0.01)and medium(P<0.05)dose up-regulated the expression of INSR,IRS2 and LKB1 protein in liver.And the expression of PI3 K and CS proteins and phosphorylation level of AKT and AMPK protein in liver were significantly increased(P<0.01).L-theanine intervention upregulated the expression of IGF1 R protein in liver(P<0.05),and the low and medium dose reached significant level(P<0.01).L-theanine at low dose up-regulated the expression of IGF1 R protein in skeletal muscle(P<0.01).L-theanine intervention promoted the phosphorylation of AMPK(P<0.05)and up-regulated the expression of PI3 K and CS proteins(P<0.01)in skeletal muscle.L-theanine at low and high dose up-regulated the phosphorylation level of AKT in skeletal muscle(P<0.05),and up-regulated the expression of INSR and IRS2 proteins(P<0.01).In conclusion,L-theanine can up-regulate the expression of key genes and proteins related to glycogen synthase by activating INSR/IRS/PI3K/AKT/GSK-3β/GYS pathway,and promote the synthesis of hepatic glycogen and muscle glycogen and increase glycogen accumulation;It can down-regulate the expression of key enzymes genes and proteins in gluconeogenesis by activating INSR/IRS/PI3K/AKT/PCK1 pathway,and inhibit the hepatic gluconeogenesis;It may also up-regulate the expression of key enzyme genes and proteins in EMP through LKB1/AMPK/PFK pathway,promote glucolysis and maintain blood sugar level;L-theanine can promote the oxidative decomposition of fatty acids by increasing the activity of CPT-1,and inhibit the de nove fatty acid synthesis via reducing FAS activity.Meanwhile,L-theanine can inhibit liver fat synthesis and reduce fat deposition by activating LKB1/AMPK/SREBP-1c/FAS or LKB1/AMPK/SREBP-1c/ACC1 pathway;L-theanine can promote cholesterol metabolism via PPARα/CPT-1 and PPARα/Lx Rα pathway.;L-theanine can promote protein synthesis by regulating INSR/IRS/PI3K/mTOR/p70S6K/S6 pathway,increase the content of TP and Alb,improve the nutritional status of the body,the efficiency of protein utilization and the growth performance of young rats;Besides,it can regulate the metabolic transformation of glucose,lipid and protein by activating INSR/IRS/PI3K/AKT and LKB1/AMPK pathway.