| This study was conducted to determine the regulatory effect of L-tryptophan(Trp)on the intestinal inflammation,mucosal barrier function,immunemodulation and potential underlying mechanisms in animals.Experiment 1 The objective was to determine the effects of dietary supplementation with Trp on acetate-induced intestinal inflammation in weaned piglets.Fifty-four 21 day-weaned crossbred castrated male piglets(6.92±0.04 kg body weight(BW))were randomly allotted into one of six groups(3 Trp levels × 2 acetate levels):0%Trp,0%Trp+acetate,0.2%Trp,0.2%Trp+acetate,0.4%Trp,and 0.4%Trp+acetate;9 piglets per group.Piglets were fed a basal diet supplemented with 0%,0.2%or 0.4%of Trp throughout the 12 d-period of trail after a 3 d-period of adaptation.During d 0-7 of the trail,piglets in each group had free access to the diet as indicated.On d 8 of the trail,piglets were intrarectally administrated with 10 mL of 10%acetate or 0.9%saline served as control.During d 8-12 of the trail,piglets of other 5 groups were pair-fed the same amount of feed per kg BW as piglets in the acetate group.Compared with control piglets,dietary supplementation with 0.2%Trp increased daily weight gain and effeciency of feed utilization during d 0-7 of the trail(P<0.05);dietary supplementation with 0.2%and 0.4%Trp restored acetate-induced adverse changes,including reductions in daily weight gain and efficiency of feed utilization during d 8-12 of the trail(P<0.05).Acetate-induced colonic structural damage,down-regulation of tight junction protein ZO-1(P<0.05),up-regulation of inflammatory mediators(IL-lβ,IL-8 and TLR4)(P<0.05),activation of STAT3,NF-κB and Cleaved-Caspase-3(P<0.05),as well as down-regulation of gene expression of serotonin(5-HT)re-uptake transporter(SERT)were partially reversed by Trp(P<0.05).Therefore,dietary supplementation of Trp attenuated acetate-induced intestinal inflammation was associated with 5-HT signaling.Experiment 2 The objective was to determine the potential underlying mechanim of Trp in alleviating dextran sodium sulfate(DSS)-induced intestinal inflammation in mice.A Total of 40 eight-week old male C57BL/6J mice(19.9±0.22 g BW)were randomly divided into four groups(2 Trp levels x 2 DSS levels):control,DSS,Trp,and Trp+DSS;5 replicates,and 2 mice per replicate.Mice were supplemented with 0 or 0.1 mg Trp/g BW/d in water for 17 d.DSS(2%w/v)was orally administrated on d 8-15.Results indicated that Trp attenuated the severity of DSS colitis by increasing feed and water intake,abolished partially the body weight loss,mortality rate,colon shortening,disease actitvity index and colonic morphology(P<0.05).Trp alleviated DSS-induced intestinal barrier dysfunction and inflammation by regulating tight junction protein(ZO-1,Occludin and Claudin-1)and gene expression of mucin(MUC1 and MUC2)(P<0.05),inhibiting infiltration of inflammatory cells and sepressing pro-inflammaoty mediators(IL-6,TNF-a,IL-17a,G-CSF and MIP-1a)(P<0.05),and enhancing anti-inflammaoty cytokines(TGF-β2 and TGF-β3)(P<0.05).DSS-induced activation of inflammatory signaling(TLR2,TLR4 and NF-κB)was reversed by Trp(P<0.05).Trp also prevented DSS-induced intestinal damage and inflammation in jejunum.This function of Trp was related to the maintenance of 5-HT content(the inhibition of down-regulation of SERT and TPH1 in colon and jejunum,respectively)(P<0.05),and the regulation of 5-HT receptors(up-regulation of HTR1A and HTR4 both in colon and jejunum)(P<0.05).Therefore,Trp alleviates DSS-induced body weigh loss and mortality rate in mice,in which 5-HT signaling was involved.Experiment 3 The objective was to determine the effects of Trp on lipopolysaccharide(LPS)-induced glucose and amino acids transport in rats.Twenty-four 7-week Sprague Dawley rats were randomly divided into one of three groups(control,LPS or Trp + LPS).Mice were supplemented with 0 or 0.1 mg Trp/g BW/d in water for 7 d,and then were intraperitoneally injected with LPS(5 mg/kg BW)on d 8.After 24 h,rats were sacrificed to obain jejunal tissues for the analysis of transport of glucose and amino acids by the using of Ussing chamber.Results demonstrated that Trp alleviated LPS-induced elevation of intestinal permeability in the jejunum(P<0.05),and enhanced transport of glucose and amino acids(glutamate,arginine,glutamine,Trp,threonine and leucine)(P<0.05).LPS-induced down-regulation of glucose transporter(SGLT1)and animo acid transporters(SNAT2 and LAT2)as well as Na+/K+-ATPase(ATP1A2)were reversed by Trp(P<0.05).These findings demonstrated that dietary supplementation with Trp improved intestinal barrier function and attenuated gut inflammatory response by regulating tight junction proteins and inflammatory mediators,inhibiting inflammatory signaling pathways,and enhancing the transport of glucose and amino acids.5-HT signaling might be a critical molecule that conferred to the protective effect of Trp in intestinal inflammation.Trp may serve as effective nutritional stratege that can be used to prevent gut inflammation in animals and human beings. |
PDF Full Text Request