Preliminary Study On The Effect Of Antimicrobial Peptide KR-32 On Liver Function Of Diarrhea Piglets

In breeding,due to psychological and environmental factors during the weaning period,piglets will produce strong stress,which is particularly serious within one week after weaning,often resulting in "post-weaning stress syndrome" such as diarrhea.The liver is one of the organs most vulnerable to stress damage.Studies have found that weaning stress can cause severe oxidative stress damage and apoptosis in the liver of piglets.The liver is an important place for nutrient absorption and metabolism.At present,most of the research on piglet weaning stress focuses on intestinal damage,and there are few studies on liver function damage.Studies have found that antimicrobial peptides can alleviate liver inflammation and improve antioxidant capacity through host immune regulation and protect human or mouse liver health.The new antibacterial peptides designed and improved by man-made make up the shortcomings of natural antibacterial peptides.The previous research of this research group found that the artificially designed new α-helical antibacterial peptide KR-32 has good bactericidal and antiviral effects in vitro,and it can effectively alleviate the absorption of fatty acids in the intestine of weaned piglets in vivo and improve the growth performance of piglets.The effect of liver function has not been reported yet.Therefore,this study focused on the effect of antimicrobial peptide KR-32 on diarrhea and liver function in weaned piglets,and through the establishment of LPS-induced liver injury model in mice,the antimicrobial peptide KR-32 regulates the liver mechanism of action of lipid metabolism has been initially explored.The specific content and results of the study are as follows:1.Effect of antibacterial peptide KR-32 on diarrhea,inflammation,lipid metabolism and liver function indexes in weaned piglets.Twelve Duroc × Yorkshire × Landrace diarrhea piglets with similar body weight after 7 days of weaning were selected and randomly divided into a control group and an antimicrobial peptide KR-32 group with 6 pigs in each group.Each piglet of the antibacterial peptide KR-32 group was intraperitoneally injected with 5 mg of the antibacterial peptide KR-32 once a day,and the control group was injected with the same volume of physiological saline.The treatment time was 3 consecutive days.The results of the study found that the antibacterial peptide KR-32 was effective in alleviating diarrhea in piglets.The diarrhea rate and diarrhea index of the control group diarrhea piglets increased during the test period,while the diarrhea piglets in the antibacterial peptide KR-32 group were treated with antibacterial peptide KR-32.During the course of treatment,the diarrhea rate and diarrhea index showed a gradual decline.After 3 days of treatment,the diarrhea rate dropped below 20%and the diarrhea index decreased below 0.5.The results show that intraperitoneal injection of the antimicrobial peptide KR-32 can effectively alleviate diarrhea in weaned piglets.Antibacterial peptide KR-32 has a significantly reduced proinflammatory cytokine content in the serum of diarrhea piglets treated with antibacterial peptide KR-32 compared with the control group in reducing inflammation in piglets(P<0.05).The results suggest that antibacterial peptide KR-32 may alleviate the inflammatory response of diarrhea piglets by reducing the levels of serum proinflammatory factors IL-6,TNF-α,and IL-8;in terms of the effect of antimicrobial peptide KR-32 on lipid metabolism and liver function related indicators of diarrhea piglets,antibacterial peptides Compared with the control group diarrhea piglets in the KR-32 group,the serum triglyceride,total bile acid,and albumin levels were significantly increased(P<0.05),and the serum total cholesterol,total protein,and globulin levels were significantly higher.(P<0.05),serum total bilirubin content was not significantly different,serum liver function indicators Alanine aminotransferase(ALT),aspartate aminotransferase(AST),γ-glutamyl transpeptidase glutamyl transpeptidase(GGT)content was significantly reduced(P<0.05),suggesting that weaning stress and diarrhea in piglets may cause disorders of lipid metabolism and liver functional damage.Antimicrobial peptide KR-32 can effectively relieve liver damage.The test results in this part show that the antimicrobial peptide KR-32 can alleviate the stress and diarrhea and inflammation of piglets during weaning,while maintaining the stability of liver function and body lipid metabolism.2.The effect of antibacterial peptide KR-32 on LPS-induced liver tissue pathological damage and lipid metabolism dysfunction in mice.Further explore the effect of antimicrobial peptide KR-32 on liver lipid metabolism,including its regulation of liver pathological damage,inflammation,and lipid metabolism.Thirty-six 6-week-old C57BL/6 mice were evenly divided into three groups(Control group,LPS group,LPS+KR-32 group),LPS group and LPS+KR-32 group were injected intraperitoneally with LPS,and the rest were injected with PBS buffer.After 2 days of treatment,the LPS+KR-32 group was intraperitoneally injected with the antimicrobial peptide KR-32,and the remaining group was treated with PBS buffer for 3 days.At the end of the test,the mice were given gastric fat to compare the differences in liver lipid metabolism.The results showed that in terms of the effect of antimicrobial peptide KR-32 on liver pathological damage,antimicrobial peptides can significantly reduce the increase in relative liver weight induced by LPS(P<0.05),and H&E staining showed that LPS can cause liver tissue structural disease in mice Changes in the antibacterial peptide KR-32 significantly improved the morphology and structure of liver cells.At the same time,compared with the LPS group,the antibacterial peptide KR-32 significantly reduced the levels of ALT and AST in the serum(P<0.05).In terms of alleviating liver inflammation,compared with the control group,the expression levels of proinflammatory factors IL-6,IL-1 β,TNF-α,and MCP-1 in the liver tissue of mice in the LPS group were significantly higher than those in the control group and the antimicrobial peptide KR-32.In the treatment group(P<0.05),the levels of anti-inflammatory factors IL-10 and TGF-β in the LPS group were significantly lower than those in the antimicrobial peptide KR-32 group(P<0.05).The above results indicate that the antimicrobial peptide KR-32 may regulate the expression of liver inflammatory factors relieves liver inflammation and improves pathological damage.In terms of the effect of antibac-terial peptide KR-32 on liver lipid metabolism damage,oil red O staining results in liver tissue of mice showed that LPS treatment caused abnormal lipid droplets between liver cells.Aggregation and triglyceride content in liver tissue compared with the control group(P<0.05),lipid droplet aggregation in liver tissues of mice in the LPS+KR-32 group was significantly alleviated,and the triglyceride content was significantly lower than that in the LPS group(P<0.05).The results showed that compared with the control group,mice in the LPS group had liver protein synthesis-related factors,sterol regulatory element binding protein-1c(SREBP-lc),fatty acid synthase The expression levels of FAS,Acetyl Co A carboxylase(ACC)were significantly higher than those in the control group and the LPS+KR-32 group(P<0.05).In terms of lipid oxidation pathway,the LPS and LPS+KR-32 groups The expression levels of carnitine palmitoyl transferase(cpt1α),cytochrome P450 enzyme 4A10(cyp4α10),and cytochrome P450 enzyme 4A14(cyp4α14)were significantly lower than those in the control group(P<0.05).Compared with the LPS group,the expression of lipid oxidation-related transcript on factor peroxisome proliferator-activated receptor-a(PPAR-α)in the LPS+KR-32 group was significantly increased.In the lipid transport pathway,peroxidation Proteasome-activated receptor-gamma(PPAR-y)and fatty acid transport protein(CD36)protein expression levels showed no differences in the results,suggesting that the test does not activate PPAR-γ—CD36 pathway to increase the utilization of liver lipids.The above results indicate that LPS may upregulate the lipid synthesis pathw ay SREBP-1c-FAS/ACC,and at the same time down-regulate the PPAR-α-cpt1/cyp4α10/cyp4α14 lipid oxidation pathway,resulting in obstruction of lipid utilization,causing lipid droplet accumulation in the liver,antibacterial Peptide KR-32 reduces lipid synthesis by down-regulating the SREBP-1c-FAS/ACC pathway,while increasing PPAR-α expression to increase lipid oxidation and alleviate lipid droplet aggregation in the liver.In summary,antibacterial peptide KR-32 can effectively alleviate the symptoms of diarrhea,inflammation and liver damage caused by weaning stress in piglets,and promote the health of weaned piglets.It was further verified in mouse experiments that antibacterial peptides can alleviate LPS-induced liver pathological damage and lipid metabolism disorders in mice.It was initially found that they may play a role in regulating lipid metabolism pathways of SREBP-1c-FAS/ACC and PPAR-α The role of this study is to provide a basis for promoting the application of the antimicrobial peptide KR-32 in breeding and production to promote healthy liver function and relieve weaning stress in piglets.