Effects Of (2-carboxyethyl) Dimethylsulfonium Bromide Supplementation Under The All-plant Protein Diet On Growth Performance And Intestinal Health And The Possible Mechanisms For On-growing Grass Carp (Ctenopharyngodon Idellus)

This study aimed to investigate the effects of(2-Carboxyethyl)dimethylsulfonium Bromide(Br-DMPT)supplementation under the all-plant protein diet on the growth performance and intestinal health and the possible mechanisms of on-growing grass carp(Ctenopharyngodon idella)and estimated the appropriate levels of Br-DMPT supplementation based on different indices.A total of 540 healthy grass carp(216.49 ± 0.29 g)were randomly divided into six groups and fed one fish meal(FM)diet and five all-plant protein diets with graded levels of Br-DMPT(0.00,130.00,260.00,390.00 and 520.00 mg/kg diet)for 60 days,investigating the effects of dietary Br-DMPT supplementation on growth performance,digestive enzyme activities,intestinal bacteria flora of on-growing grass carp.Then a challenge trial was conducted by injecting 24 fish from each group with Aeromonas hydrophila for 14 days to explore the effects of dietary Br-DMPT on fish intestinal physical barrier function(antioxidant ability,anti-apoptosis ability and tight junctional protein)and immune function as well as the potential mechanisms in on-growing grass carp.Results demonstrated that compared to the FM diet group,the all-plant protein diet group significantly reduced feed intake(FI)and percentage weight gain(PWG),the intestinal development[intestinal weight(IW),intestinal length(IL)]and digestive enzyme activities,disrupted the balance of intestinal bacteria flora and significantly increased the enteritis in on-growing grass carp(P<0.05).However,these parameters could be improved to the levels similar or even superior to FM diet group with Br-DMPT supplementation level up to 260mg/kg under the all-plant protein diet.Further study found that dietary Br-DMPT supplementation increased feed intake and digestive enzyme activities in the intestine was partly related to improved Neuropeptide Y content and cholecystokinin content,respectively.Meanwhile,the enhanced disease resistance might be related to the increased immune function and physical barrier function in the intestine of on-growing grass carp.Results showed that appropriate Br-DMPT supplementation under the all-plant protein diet(1)decreased the ROS,MDA and PC contents,up-regulated the mRNA levels of MnSOD,CAT,GPx,GST and GR(rather than CuZnSOD),elevated antioxidant enzymes activities and GSH content(P<0.05),which were partially by activating[Keap1a(rather than Keap1b)/Nrf2]signaling;(2)down-regulated the mRNA levels of APaf-1,Bax,caspase-3,-7,-8 and-9 and up-regulated the mRNA levels of Bcl-2,Mcl-1,IAP(P<0.05),which were partially by inhibiting Fas ligand(FasL)(only in the DI),c-Rel,c-Jun-N-terminal kinase(JNK)signaling pathways;(3)down-regulated the mRNA levels of claudin-12,-15a and-15b,up-regulated the mRNA levels of zonula occludens 1(ZO-1),occluding(only in the DI),claudin-b,-c,-f,-7a,-7b and-11(not ZO-2,claudin-3c)(P<0.05),which were partially by inhibiting myosin light chain kinase(MLCK)signaling;(4)increased LZ and ACP activities and C3,C4 and IgM contents and up-regulated the mRNA levels of?-defensin-1,hepcidin,LEAP-2A and LEAP-2B and Mucin2(P<0.05),contributing to the enhanced antimicrobial ability in the intestine;(5)down-regulated the mRNA levels of pro-inflammatory cytokine TNF-?,IFN-?2,IL-1?,IL-6,IL-8,IL-15,IL-17D,IL-12p40(not IL-12p35),up-regulated the mRNA levels of anti-inflammatory cytokine IL-10,IL-11,TGF-?1,IL-4/13A(not TGF-?2 and IL-4/13B)(P<0.05),which were partially by inhibiting IKK?(not IKK?and IKK?)/I?B?/NF-?Bp65(rather than NF-?Bp52)signaling and activating TOR/(S6K1 and 4EBP)signaling,respectively.In summary,the appropriate Br-DMPT supplementation under the all-plant protein diet enhanced the production performance,intestinal development and intestinal digestive capacity,balanced intestinal bacteria flora and increased the ability against enteritis of ongrowing grass carp,which were comparable with those in the FM diet group.Br-DMPT increased the ability against enteritis of on-growing grass carp was closely related to the physical barrier function and immune function in the intestine,as are displayed in following aspects:(1)the appropriate Br-DMPT supplementation under the all-plant protein diet improved the antioxidant capacity partially by activating Nrf2 signaling,enhanced the barrier function of tight junction protein partially by inhibiting MLCK signaling and inhibited apoptosis partially by inhibiting the death receptor pathway and mitochondria pathway,which contributed to strengthening the physical barrier function in the intestine of ongrowing grass carp.(2)the appropriate Br-DMPT supplementation under the all-plant protein diet improved the antibacterial compounds production and attenuated inflammation partially by activating TOR signaling and inhibiting NF-?B signaling,which lead to enhancing the immune function in the intestine of on-growing grass carp.Finally,based on FI,PWG,the ability to combat enteritis,PC and MDA content,IgM content,and LZ activities in the PI,appropriate Br-DMPT supplementation level under all-plant protein diets for on-growing grass carp(216-759 g)were estimated as to be 282.78,278.30,295.43,326.52,299.25,301.73,320.36 mg/kg,respectively.