Effects Of L-theanine On Fat Browning Function And Gut Microbiota Changes In Obese Mice Induced By High-fat Diet

L-theanine(LTh)is one of the important non-protein amino acids in tea,which has a good effect on weight loss and lipid reduction.The purpose of this study was to investigate the effect of LTh on liver lipid degeneration,fat browning,and gut microbiota changes in obese mice induced by high-fat diet(HFD).Thirty 7-week-old C57BL/6 male mice with uniform body weight were randomly divided into 3 treatment groups after one week of adaptive feeding.They were fed with low-fat diet(LFD),high-fat diet,or high-fat diet supplemented with 30 mg/kg/d(BW)LTh solution(HFD + LTh)respectively.The trial period lasted for 12 weeks.Experiment 1: The appearance indices,serum indices,liver tissue morphology and m RNA expression of lipid metabolism-related genes were analyzed and determined.The results showed that: 1)Compared with the HFD mice,the weight gain of LFD and HFD +LTh mice was significantly reduced(P <0.01).2)Compared with the HFD mice,white adipose tissue index(P <0.05),liver weight(P <0.01),serum triglycerides(TG)(P <0.05),total cholesterol(T-CHO)(P <0.05),the concentration of alanine aminotransferase(ALT)(P <0.05)and insulin(P <0.05)were significantly reduced in the LFD or the HFD +LTh mice,and the HFD mice treated with LTh had better glucose tolerance.3)Compared with the HFD mice,liver lipid deposition and the m RNA expression of lipid synthesis-related genes(Fas,Srebp-1c,Acacaα)(P <0.05)were significantly reduced,and lipid breakdown-related genes(Pparα,Cpt-1α,Mcad)(P <0.05)m RNA expression was significantly increased in the LFD or HFD + LTh mice.Experiment 2: By using the brown fat and subcutaneous white adipose tissue samples collected in Experiment 1,the tissue morphology,thermogenesis-related genes,lipid metabolism-related genes,beige fat marker genes,UCP1 and Cyto C protein expression were analyzed and determined.The results showed that: 1)Compared with the HFD mice,the expression of thermogenesis-related genes(Ucp1,Prdm16,Cox7 al,Pgc-1α)and UCP1 and Cyto C protein was significantly increased in brown adipose tissue and subcutaneous white adipose tissue in the LFD or HFD + LTh mice(P <0.05).2)Compared with the HFD mice,the size of white adipocytes,and the m RNA expression of lipid synthesis-related genes(Fas,Srebp-1c,Scd1)(P <0.05)were significantly reduced,and the m RNA expression of lipid decomposition related genes(Pparα,Cpt-1α,Pdk4,Mcad)(P <0.05)and beige fat marker genes(CD137,Tbx1,Tmem26)(P <0.05)was significantly increased in subcutaneous white adipose tissue in the LFD or HFD + LTh mice.Experiment 3: Using the stool samples collected in Experiment 1 were used to perform 16 S r DNA high-throughput sequencing and short-chain fatty acid content analysis.The results showed that: 1)Compared with the HFD mice,the ratio of Firmicutes and Bacteroides was significantly lower in the LFD or HFD + LTh mice(P <0.05).2)Compared with the HFD mice,the content of short-chain fatty acids was significantly increased in the feces of the LFD or the HFD + LTh mice(P <0.05).In summary,LTh improves the metabolic characteristics of obesity by reducing liver lipid degeneration,enhancing fat browning and improving gut microbiota composition in HFD mice,which may be a mechanism of LTh-mediated beneficial metabolic health.