Regulatory Effect And Mechanism Of L-Theanine On Immune Function In High Protein Diet

The protein level in diet is closely related to the body immunity,and the unreasonable dietary pattern is one of the main factors affecting the body health.Long-term intake of unreasonable high-protein diet will lead to oxidative stress,inflammatory response,metabolic disorders and other issues in the body,and thus affect the body’s immunity.With the economic development and the improvement of consumption level,high protein diet mode has gradually become a dietary trend,protein nutrition(especially fish,meat and other animal protein foods)in the daily dietary structure of the intake ratio is increasing.Therefore,it is of great significance to pay attention to the adverse effects and hazards caused by long-term intake of high protein diet.L-theanine,as a characteristic non-protein amino acid in tea,can regulate the body’s immunity and protein metabolism,but it is still unclear whether it can play a role in regulating the body’s immunity in the high protein diet mode.In the experiment,male SD rats of six weeks old were fed with different doses of L-theanine(100 mg/kg/d,200 mg/kg/d and 400 mg/kg/d)at different protein energy supply ratios(20%,30%,40% and 50%)for 40 days,and hematoxylin-eosin staining,ELISA,and biochemical kit were used.The regulation of L-theanine on that immune function of SD rat in a protein diet with different levels was analyze in this study.on this basis,the regulatory mechanism of L-theanine on the immune function of the body in a high protein diet was explored by applying protein omics,metabolomics and Western blot.The main research results and conclusions are as follows:(1)The regulatory effect of L-theanine on immune function of SD rats in high protein diet mode.Compared with normal diet rats,when the dietary protein energy supply ratio is40% or more,the level of pro-inflammatory factors in high-protein diet rats is up-regulated,and the oxidative balance of liver is destroyed,showing inflammatory reaction and liver injury,which has a negative impact on organism immunity.L-theanine intervention can effectively alleviate the increase of liver index caused by high-protein diet,inhibit the increase of serum AST and ALT activities and the levels of inflammatory markers CRP and IFN-γ,and increase the content of immunoglobulin Ig G,reduce the liver damage and systemic inflammation caused by high-protein diet in rats,and enhance the body immunity.At the same time,it can reduce the contents of MDA,TNF-α and IL-6 in liver tissue of rats fed with high protein diet,increase the activities of antioxidant enzymes CAT,T-SOD and IL-10,and reduce the oxidative damage and inflammatory reaction of liver tissue of rats fed with high protein diet,and the high-dose group of L-theanine has the best effect.In addition,L-theanine can increase the content of anti-inflammatory factor IL-10 in normal diet rats.(2)Regulation mechanism of L-theanine on immune function of SD rats in high protein diet mode.Compared with normal diet rats,high protein diet can promote STAT3 phosphorylation by up-regulating TRIM14,and then inhibit PPARα and downstream target genes,promote the expression of pro-inflammatory factor IL-6 and TNF-α,and inhibit the expression of anti-inflammatory factor IL-10 in normal diet rats.On the contrary,by downregulating the expression of FABP5,L-theanine inhibited the signal pathway of IL-6/STAT3 in high-protein diet,relieved the inhibition of PPARα,reduced the expression of proinflammatory factors TNF-α and IL-6,increased the expression of anti-inflammatory factor IL-10,maintained the homeostasis of the body and played an immunomodulatory role.In addition,in normal diet rats,L-theanine down-regulated the expression of EPHX2 protein,which could interfere with the dissociation of IκBα,thus inhibiting the activation of NF-κB and the expression of TREM1,and promoting the expression of anti-inflammatory factor IL-10 in liver tissue of normal diet rats.To sum up,through this study,it was found that the high-protein dietary pattern with 40%or more protein to energy ratio promoted the expression of inflammatory factors and the imbalance of oxidation balance,and the intervention of L-theanine could improve this phenomenon.On the mechanism,high protein diet mediates the inflammation in normal diet rats through IL-6/STAT3/PPARα pathway.L-theanine can alleviate the adverse effects induced by high-protein diet through FABP5/IL-6/STAT3/PPARα pathway,and play an immunomodulatory role.At the same time,L-theanine can also play an immune enhancement role in normal diet through EPHX2/IκBα/TREM1 pathway.