Effects Of Condensed Tannins On Growth Performance,Intestinal Structure And Immune Function As Well As The Mechanisms In On-growing Grass Carp(Ctenopharyngodon Idella)

This study used the on-growing grass carp(Ctenopharyngodon idella)as the research subject,for the first time to investigate the effects of condensed tannins,a common antinutritional factors in the animal feedstuffs sources,on the growth performance and intestinal health and its possible mechanisms in on-growing grass carp.The experiment first carried out a 70-day feeding trial designed a total of six different levels of condensed tannins treatment groups to observe the effects of condensed tannins on the growth performance,intestinal growth,intestinal microbes,intestinal tissue morphology and structural integrity of intestine and potential mechanisms in on-growing grass carp.And then carrying out digestion experiment with three groups for 10 days to investigate the impact of condensed tannins on the feedstuff utilization in on-growing grass carp.Finally,the fish from growth trial were intraperitoneal injection with Aeromonas hydrophila for 14 days to ascertain the influences of condensed tannins on the enteritis and immune function and underlying mechanisms in on-growing grass carp.The results showed that compared with the control group,condensed tannins(?30 g/kg)significantly decreased the growth performance(PWG and FI)(P<0.05),reduced the feed apparent digestibility coefficients,depressed the intestinal growth and microbes amounts,caused the intestinal histopathological lesions as well as increased enteritis morbidity,then damaged the intestinal health in on-growing grass carp.The detriment caused by condensed tannins on the intestine mitght be associated with the harm of the structural integrity and immune function of on-growing grass carp.The results related to intestinal structural integrity showed that condensed tannins,(1)increased the contents of ROS(P<0.05)and oxidative damage production(MDA and PC)(P<0.05),decreased the activities and gene expression of antioxidant enzymes SOD,CAT,GPx,GST and GR(except GSTP1)as well as down-regulated the Nrf2 signaling molecule mRNA levels in the three intestinal segments of fish(P<0.05);(2)increased the gene expression of caspase(-2,-3,-7,-8 and-9)(P<0.05),up-regulated the mRNA levels of apoptosis-related factor ligand(FasL),pro-apoptotic protein(Bax)and apoptosis protein activating factor(Apaf-1)(P<0.05),down-regulated the mRNA levels of anti-apoptotic protein(Bcl-2,Mcl-1and IAP)as well as up-regulated the mRNA levels of JNK and p38 MAPK signaling molecules in the three intestinal segments of fish(P<0.05)and then activated the death receptor and mitochondrial apoptosis pathways;(3)reduced the gene expression of ZO-1,ZO-2(not in the PI),occludin,claudin(-c,-f,-3c,-7a,-7b,-11,-15 a and-15b)(except claudin-b)as well as down-regulated the mRNA levels of MLCK signaling in the three intestinal segments of fish(P<0.05).These results related to intestinal immune function presented that condensed tannins,(1)decreased the activities of LZ and ACP and the contents of C3,C4 and IgM as well as down-regulated the Hepcidin,LEAP-2A,-2B,Mucin2 and ?-defensin-1 mRNA levels in the three intestinal segments of fish(P<0.05);(2)down-regulated the mRNA levels of anti-inflammatory cytokines,such as TGF-?1,TGF-?2(not in MI and DI),IL-4/13A(not IL-4/13B),IL-10 and IL-11 as well as regulated the signaling molecules,namely downregulated TOR and S6K1 and up-regulated 4E-BP2(not 4E-BP1)the mRNA levels and decreased the p-TOR protein levels in the three intestinal segments of fish(P<0.05);(3)upregulated the mRNA levels of pro-inflammatory cytokines,such as IFN-?2,IL-1?,IL-6,IL-8(not in PI),IL-12p35,IL-12p40,IL-15 and IL-17D(except TNF-?)as well as regulated the signaling molecules,namely down-regulated I?B? and up-regulated IKK?,?,?,NF-?Bp65(not NF-?Bp52)and c-Rel mRNA levels and increased the nuclear NF-?Bp65 protein levels in the three intestinal segments of fish(P<0.05).Conclusion and summary,condensed tannins reduced the the growth performance and damaged intestinal health,which closely relied on the structural integrity and immune function of intestine in on-growing grass carp.Further study of this experiment showed that condensed tannins,(1)might depress the Keap1 a,1b/Nrf2 signaling pathway to reduce the mRNA levels and activities of antioxidant enzymes resulting in decreasing antioxidant damage ability,activate JNK and p38 MAPK signaling pathway to aggravate intestinal apoptosis and inhibite MLCK signaling pathway to damage tight junction which together damaged intestinal structure integrity of fish;(2)might decrease the activities and content of innate and adaptive immune substances,depress TOR/S6K1,4E-BP2(not 4E-BP1)signaling pathway to decrease anti-inflammatory cytokines mRNA levels and activate IKK?,?,?/I?B?/NF-?Bp65(not NF-?Bp52),c-Rel signaling pathway to increase proinflammatory cytokines mRNA levels which together aggravated intestinal inflammatory response and decreased intestinal immune function of fish.Finally,based on the PWG,PC contnent in the PI and enteritis morbidity,the maximum tolerance levels of condensed tannins for on-growing grass carp were estimated to be 18.63,17.04 and 17.36 g/kg diet,respectively.