Study On The Mechanism Of Lactobacillus Delbrueckii In Reducing Blood Lipids Of Growing-Finishing Pigs

Pork is the most popular meat in China.Reduction of abdominal and subcutaneous fat deposition and lowering intake of excessive fat and cholesterol have been a hot topic in swine nutrition.Numerous studies showed that the addition of lactic acid bacteria preparations to the diet or meal can reduce triglycerides and cholesterol contents in humans or animals,but its mechanism is still unclear.We speculated that Lactobacillus delbrueckii might reduce serum cholesterol levels by interfering with the enterohepatic circulation of bile acids in the ileal segment and lowering the serum triglyceride(TG)contents via regulating TG metabolism in parenteral tissues via short-chain fatty acids(SCFA)in the hindgut segment based on our previous studies in pigs,however we did not uncover its mechanism by further trails.Therefore,the study was mainly to investigate the mechanism of Lactobacillus delbrueckii in reducing blood lipid levels in growing-finishing pigs based on cholesterol and triglyceride metabolism.The main results were as follows:1、Study on the biological characteristics of Lactobacillus delbrueckii.Exp.1,The results showed that the colonies of Lactobacillus delbrueckii had typical characteristics of lactic acid bacteria.Its growth curve showed an “S” type,and the logarithmic growth phase appeared after culture in MRS liquid medium for about 4 h,and then is followed by the stable phase after about 8 h.The bacteria had a good cholesterol clearance with a 34.82% of clearance rate in vitro,and resistance to acid and alkali with a high survival rate under p H=2~8.High abundance of lactic acid bacteria detected by RT-PCR technique were found in the ileal and colonic mucosa of SD rats in Lactobacillus delbrueckii treatment,indicating that Lactobacillus delbrueckii had a good colonization ability.The BSH2 gene sequence on genome of Lactobacillus delbrueckii was identified by PCR amplification technique,and the BSH activity was also verified via in vitro culture.2、Mechanism of Lactobacillus delbrueckii in reducing the serum cholesterol levels in growing-finishing pigs.Exp.2,twelve “Landrace × large” crossbred barrows with average initial body weight of(38.70±5.33)kg were selected and randomly divided into two groups.Pigs were fed with corn-soybean diets with either 0(CON)or 0.1% Lactobacillus delbrueckii(CON+LD)for 28 days,respectively.Compared with the Con,the CON+LD decreased(P<0.05)the serum total cholesterol(TC)and total bile acid(TBA)contents and promoted(P<0.05)fecal total cholesterol(TC)and total bile acid(TBA)excretion in pigs.Dietary Lactobacillus delbrueckii increased(P<0.05)the abundance of Lactobacillus in ileal digesta,promoted(P<0.05)the dissociation of ieal conjugated BAs,and altered BA composition in serum and liver.Dietary Lactobacillus delbrueckii down-regulated(P<0.05)the m RNA expression of ileal bile acid transporter(ASBT)and ileal bile acid-binding protein(IBABP),hepatic farnesoid X receptor(FXR),fibroblast growth factor(FGF19)and small heterodimer partner receptor(SHP),but upregulated(P<0.05)the m RNA expression of hepatic high-density lipoprotein receptor(HDLR),low-density lipoprotein receptor(LDLR),sterol regulatory element-binding protein-2(SREBP-2)and cholesterol-7α hydroxylase(CYP7A1).Our results indicated that Lactobacillus delbrueckii interfered with ileal bile acid reabsorption,promoted fecal bile acid excretion and enhanced the conversion of hepatic cholesterol to bile acid to reduce serum cholesterol levels.3、Mechanism of Lactobacillus delbrueckii in reducing the serum triglyceride levels in growing-finishing pigs.Samples from Exp.2 were collected and analyzed,and the results showed that dietary Lactobacillus delbrueckii significantly decreased the content of triglyceride(TG)in the serum of pigs(P<0.05),increased the serum levels of free fatty acid(FFA)and LEP(P<0.05),and tended to elevate serum butyric acid concentrations.The butyric acid contents in colonic digesta were enhanced(P<0.05),and the acetic acid and propionic acid contents was tended to increase in the Con+LD.The abundance of Akkermansia,Lactobacillus,Parabacteroides and Butyrivibrio were increased,but the abundance of Romboutsia and Streptococcus were decreased(P<0.05)in colon digesta after Lactobacillus delbrueckii treatment.Dietary Lactobacillus delbrueckii upregulated m RNA expression of farnesol receptor(FXR),G-protein-coupled bile acid receptor(TGR5),glucagon-like peptide 1(GLP-1),monocarboxylate transporter 1(MTC)and sodium-dependent monocarboxylate transporter 1(SMCT1)(P<0.05)in colonic tissue.The m RNA expressions of carnitine palmitoyltransferase(CPT-1),angiopoietin-like protein 4(Angptl4),lipoprotein esterase(LPL)and triglyceride hydrolase(TGH)were up-regulated in liver tissues(P<0.05).Hepatic ipoprotein lipase(LPL)activity tended to increase,the m RNA expressions of hepatic CPT-1,Angptl4,LPL and TGH were up-regulated in liver tissues(P<0.05),but the m RNA expression of hepatic FAS,G protein-coupled receptors 41 and 43(GPR41 and GPR43)were down-regulated(P<0.05)in the Con+LD.Dietary Lactobacillus delbrueckii increased the m RNA expression of adenosine monophosphate-activated protein kinase(AMPK)in the longissimus dorsi(P<0.05).The m RNA expression of LPL,CPT-1,Angptl4 and CD36 was up-regulated,and adipocyte assay and differentiation dependent factor 1(ADD1)was tended to increased in subcutaneous adipose tissue(P<0.05)after Lactobacillus delbrueckii treatment.The m RNA expression of LPL,CPT-1,TGH,ADD1 and hormone-sensitive lipase(HSL)was up-regulated in leaf lard of pig fed Lactobacillus delbrueckii(P<0.05).The results suggested that Lactobacillus delbrueckii could participate in TG metabolism in liver,longissimus dorsi and adipose tissues via SCFA produced in hindgut,and promoted TG catabolism in tissues to lower serum TG levels.4、Study on the effects of Lactobacillus delbrueckii on the blood lipid metabolism of Ningxiang pigs.Exp.3,ninety-six Ningxiang pigs with average initial body weight of(33.28±1.15)kg were randomly divided into two groups and were fed with a basal diet(CON)and a basal diet supplemented with 0.1% Lactobacillus delbruecki(CON+LD)for 60 days,respectively.Compared with Con,the serum contents of TG,TC and LDL-C,and the HDL-C/LDL-C ratio,and the hepatic TG and TC contents of pigs in the Con+LD were decreased(P<0.05).Dietary Lactobacillus delbrueckii increased hepatic CYP7A1 activity(P<0.05),and tended to be increased hepatic HMGR activity.The m RNA expression of hepatic LPL and CPT-1were up-regulated(P<0.05),and FAS was tended to be increased in Con+LD.The m RNA expression of LPL in the subcutaneous adipose tissue was up-regulated(P<0.05),and the CPT-1 m RNA expression tended to be up-regulated after Lactobacillus delbrueckii treatment.Dietary Lactobacillus delbrueckii promoted fecal TBA extraction of Ningxiang Pigs(P<0.05).Our findings also implied that the effect of Lactobacillus delbrueckii on lowering blood lipid in lean meat commercial pigs is similar to that in Ningxiang Pigs(lardtype pig).In conclusion,(1)Lactobacillus delbrueckii own a good resistance to acid and alkaline,intestinal colonization ability,bile salt hydrolase activity and cholesterol clearance,which confer beneficial physiological functions to Lactobacillus delbrueckii.(2)Dietary Lactobacillus delbrueckii changed the ileal microbial composition,enhanced ileal bile acid deconjugation,reduced ileal bile acid reabsorption,promoted fecal bile acid excretion,interfered with enterohepatic circulation of bile acid,inhibited the FXR-FGF19 axis and enhanced hepatic bile acid synthesis of growing-finishing pigs.(3)Lactobacillus delbrueckii can reduce serum triglycerides in growing-finishing pigs via increasing Akkermansia,Megasphaera and Butyrivibrio abundance and acetic acid,propionic acid and butyric acid content in colonic digesta,and promoting lipolysis and energy expenditure in liver,muscle and adipose tissue.(4)Dietary Lactobacillus delbrueckii can improve the blood lipids of Ningxiang pigs via facilitating fecal TBA excretion,interfering with enterohepatic circulation of bile acid,and regulating hepatic enzyme activities related to lipid metabolism.