Effects Of LPS Induction On Liver And Intestinal Injury,antioxidant Capacity And Fecal Metabolites Of Weaned Piglets

Many studies have shown that pigs are considered as good model animals for human physiology and pathology research.During the weaned period,piglets are vulnerable to pathogenic microorganism due to the feed transformation,environmental changes,and an immature autoimmune system.Especially bacterial infection,which lead to slow growth,tissue damage and even the death of piglets.Therefore,we explored the effects of continuous low-dose LPS induction on serum enzyme activity,antioxidant capacity,morphology of liver and intestine,mRNA expression related to liver and intestine injury and fecal metabolites in weaned piglets.Forty-eight 28-day-old weaned piglets(6.65±1.19kg)were randomly divided into the LPS group and the control group(CON group).The experimental period was thirteen days,and piglets were injected with the same volume of LPS solution(100μg/kg)and normal saline every day by intraperitoneal injection.On the 1st,5th,9th and 13 th day of the experiment,six piglets were selected from the two groups,and the blood was collected from the anterior vena cava.Biochemical indexes related to liver function and intestinal permeability were determined,so as to preliminarily assessment the liver and intestine injury;Serum antioxidant indexes were detected to evaluate the antioxidant capacity of the body as a whole.Subsequently,the piglets were dissected by abdominal cavity,and the liver,jejunum and ileum were collected,and the liver index was measured by weighing the liver.Some liver and intestine tissues were fixed in 4% paraformaldehyde,and the morphological structure and pathological changes were observed by H&E staining;The remaining part was frozen in the refrigerator at-80℃ for the detection of tissue antioxidant parameters and RTq PCR,so as to evaluate the effects of LPS induction on antioxidant capacity,and the expression levels of TLR4 signaling pathway,inflammatory factors and intestinal tight junction protein-related mRNA in liver and intestine.In addition,on the 7th day of the experiment,six piglets were randomly selected from the two groups to stimulate the anal defecation reaction,and fresh feces were collected for non-targeted metabonomics detection to explore the effect of LPS induction on the metabolites of piglets’ feces.The main results are as follows:1.LPS induced oxidative stress damage in piglets,and weakened the antioxidant capacity of the body.(1)T-AOC,GSH-Px and SOD in serum of piglets were significantly decreased on the 5th day after LPS induction;the changes of CAT activity and MDA content increased significantly on the 1st and 13 th day after LPS induction,respectively.(2)T-AOC and GSH-Px in the liver of piglets in LPS group decreased significantly,while SOD and CAT increased significantly,especially on the 1st and 5th day after LPS induction.(3)The activities of CAT and GSH-Px in jejunum of piglets were significantly decreased on the 9th day after LPS induction.(4)CAT activity in ileum of piglets in LPS group decreased significantly on the 9th day;On the 13 th day after LPS induction,T-AOC decreased and MDA content increased significantly.2.LPS induced liver dysfunction and injury in piglets at the early stage,and reduced the damage at the later stage.(1)The liver weight and liver index of piglets in LPS group increased significantly,especially on the 9th day after LPS induction.(2)On the 1st,5th and9 th day of continuous induction,the serum related indexes AST,ALT and ALP of liver function in LPS group increased significantly.(3)On the 1st and 5th day of LPS-induced piglet,liver tissue was damaged,and the phenomena of hepatocyte vacuolation,karyopycnosis and inflammatory cell infiltration appeared.(4)On the 1st and 5th day of LPS-induced piglets,the mRNA expressions of TLR4,MyD88,NF-κB,TNF-α,IL-6 and IL-10 in liver were significantly increased,but there was no significant difference compared with the control group in the later period of continuous induction.3.LPS induction would increase the intestinal permeability of piglets and cause barrier damage.(1)Serological indexes related to intestinal barrier function,D-LA and DAO,were significantly increased in LPS group,especially on the 5th and 9th day of LPS induction.(2)On the 9th and 13 th day of LPS-induced piglets,intestinal villi in jejunum and ileum were broken,crypts deepened and the ratio of the two increased significantly.(3)On the 5th day after LPS-induced piglets,the mRNA expression of TLR4,NF-κB,TNF-α and IL-6 in jejunum were significantly increased;and the mRNA expression of TLR4,MyD88,NF-κB and TNF-α in ileum increased significantly,while the mRNA expression of IL-10 decreased,the gene expression in ileum were the most obvious on the 9th day after LPS induction.(4)The mRNA expression of ZO-1,Claudin-1 and Occludin in jejunum and ileum of the LPS group showed a downward trend,especially on the 5th and 9th day after LPS induction.4.LPS induction led to the changes of fecal metabolites in piglets.Compared with the control group,a total of 109 different metabolites were screened in feces of LPS group,which caused the disorder of protein digestion and absorption pathway,resulting in the upregulation of butyrate and down-regulation of indole and methionine in this pathway.To sum up,it will lead to oxidative stress,liver and intestine damage and changes of fecal metabolites in the early stage of piglet stress induced by continuous low-dose LPS;At the later stage of LPS induction,the injury of liver and intestine was alleviated,which may be attributed to the immune defense system and tolerance to endotoxin.In this experiment,the pathological situation of liver and intestine and immune defense response of weaned piglets in response to bacterial infection were analyzed,which provided new evidence for exploring the pathogenesis of gram-negative bacterial infection in piglets.