Effects And Mechanism Of L-theanine Prevents The Impairment Of Immune Function In Mice By Heat Stress

Heat stress refers to a series of immune responses when the external temperature exceeds the body’s ability to regulate itself.When the degree of heat stress exceeds the maximum bearing range of the body,it can affect growth and development,cause tissue damage,immune function damage and a series of other hazards.Enhancing immune function and maintaining the health of the body through food nutrition intervention is an important development direction of food nutrition science.Plant bioactive ingredients have the advantage of being multi-pathway and multi-targets benefits in mitigating heat stress,and with great potential.As a non-protein amino acid naturally found in tea,L-Theanine has various physiological functions such asregulating immunity,antioxidation,and anti-heat stress,etc.However,few studies have been conducted on the use of L-Theanine for the prevention of immune function damage by heat stress.For this reason,in this study,SPF-grade BALB/c male mice were used as experimental subjects,and three groups of three different doses L-Theanine in low(100mg/kg·d^-1),medium(200mg/kg·d^-1)and high(400mg/kg·d^-1)were fed with normal mice for 28 days,fed water and heat stress treatment on 29-35d after 28d of gavage（pre-prevention intervention）,and normal mice for 35 days and heat stress treatment for 29-35 days（long-term preventive intervention）,by means of physiological and biochemical index detection,pathological observation of tissue section,Western blotting and other technical methods,from the aspects of mouse growth performance,tissue morphology,serum biochemical index,liver tissue antioxidant index,protein expression in the pathway related to heat stress and immunity,etc.,to study and analyze the preventive effect of L-Theanine on the immune function of mice induced by heat stress and its mechanism were studied and analyzed,to provide a scientific basis for maintaining body health under heat stress,promoting the diversified development of food nutrition intervention and the deep utilization of L-theanine.The main results and conclusions are as follows:（1）Compared to the blank control group,the heat stress group showed damage to liver and jejunum tissue,decreased body mass（P<0.01）,up-regulated serum inflammato ry factors TNF-α,IL-6,IL-1βcontents,AST,ALT enzyme activities（P<0.01）and liver M DA contents（P<0.01）,down-regulated liver antioxidant enzymes SOD,CAT,GSH-PX acti vities（P<0.01）.Compared with heat stress group,all dose of L-Theanine pre-pre vention and long-term prevention reduced liver and jejunum tissue injury,pro moting increased body mass in mice under heat stress（P<0.01）;down-regulate d the contents of serum inflammatory factors TNF-α,IL-6 and IL-1β（P<0.01）;down-regulated the contents of MDA in liver tissue（P<0.01）;up-regulated the activity of antioxidant enzymes SOD,CAT and GSH-Px in liver tissue（P<0.01）,among them,the activities of serum AST and ALT were down-regulat ed in the middle-dose L-Theanine pre-prevention group and each dose L-Th eanine long-term prevention group（P<0.01）.The L-Theanine long-term prevent ion middle-dose group has the better effect.（2）Based on the above results,the blank control group,heat stress group and each medium-dose L-Theanine intervention group were selected for Wes tern blotting analysis.Compared to the blank control group,heat stress significantly up-regulated ASK1,MK2,HSP27 proteins expression and p-P65/P65（P<0.05）levels,and s ignificantly down-regulated MEK3,MEK6,MSK1 proteins expression and p-P38/P38（P<0.05）levels.Compared with the heat stress groups,the L-Theanine pre-preventio n and L-Theanine long-term prevention groups significantly down-regulated MK2 and HSP27 protein expression（P<0.05）,and up-regulated MEK3 and MS K1 proteins expression and p-P38/P38 levels（P<0.05）.Among them,the L-The anine long-term prevention group also significantly down-regulated ASK1 pr otein expression,p-P65/P65 levels（P<0.05）and up-regulated MEK6 protein ex pression（P<0.05）.The L-theanine long-term prevention middle-dose group has the better effect.In summary,all dose of L-Theanine pre-prevention and long-term prevention groups can promote the growth performance of mice under heat stress treatment;reduce the damage of liver and jejunum caused by heat stress;inhibiting the up-regulation of TNF-α,IL-6,IL-βcontents,AST,ALT enzyme activities and MDA contents by heat stress,inhibiting the inactivation of antioxidant enzymes SOD,CAT and GSH-Px caused by heat stress.Its mechanism of action is as follows:By mediating the P38 signaling pathway,inhibiting the overexpression of MK2 and down-regulating the increase of p-P65/P65 caused by the overexpression of HSP27 protein downstream of MK2,the inflammatory response caused by heat stress is prevented to reduce the damage to the immune function of the body.