Gene Regulations Of Bile Acids Classic Synthesis Pathway

PartⅠThe effect of high cholesterol intake on gene regulation of bile acids classic synthesis pathwayObjective To detect the different effect of short term(2 days) and relative long term(2 weeks) high cholesterol intake on serum cholesterol,bile acid,CYP7A1 and the activative status of FXR and LXR on New Zealand white rabbit.Methods Thirty-six New Zealand white rabbits were divided into four groups randomizely:2 days control group,2 days cholesterol group,2 weeks control group,2 weeks cholesterol group.Each group contain 9 rabbits.The control groups were fed regular forage for 2 days or 2 weeks.The cholesterol groups were fed 2%cholesterol forage.Serum cholesterol,LDL,bile acid and hepatic CYP7A1 activity,CYP7A1 mRNA,FXR target gene SHP mRNA and BSEP mRNA,LXR target gene ABCA1 mRNA and CETP mRNA were measured.Results There's no statistically difference between two control groups (P＞0.05).Total cholesterol and LDL were higher in cholesterol groups compared with those in controls,and 2 weeks were higher than those in 2 days(P＜0.05 ).There's no statistically difference in bile acid between 2 days cholesterol group and control (P＞0.05).Bile acid in 2 weeks group was higher than that in control(P＜0.05). Hepatic CYP7A1 activity and mRNA in 2 day group elevated compared with control group(P＜0.05);2 weeks group were decreased compared with those in control group(P＜0.05).There's no statistically difference in SHPmRNA,BSEP mRNA between 2 days cholesterol group and control(P＞0.05 ).SHPmRNA,BSEP mRNA were elevated compared with those in control(P＜0.05).ABCA1mRNA,CETP mRNA were elevated in cholesterol groups compared with those in controls(P＜0.05 ) and were higher in 2 weeks cholesterol group than those in 2 days cholesterol group (P＜0.05).Conclusions High cholesterol intake elevated serum total cholesterol and LDL level. Short term cholesterol intake activated hepatic LXR and CYP7A1,then bile acid synthesis increased.As bile acid level was not yet elevated,the activity of FXR remained unchanged.After relative long term cholesterol intake,bile acid level elevated and FXR was activated.Though LXR was further activated,the inhibition effect of FXR on CYP7A1 override the activation effect of LXR,CYP7A1 activity decreased and bile acid systhesis decreased.PartⅡThe gene regulation of cholestyramine on bile acid classic synthesis pathway and its mechanisms of lowering serum cholesterolObjective To investigate gene regulation mechanisms of cholestyramine on bile acid classic synthesis pathway and its mechanisms of lowering serum cholesterol.Methods Twenty New Zealand white rabbits were randomizely divided into cholestyramine group and control group,10 rabbits each group.The cholestyramine group was administrated 20ml cholestyramine suspension by gavage for 2 weeks.The control group was administrated 20ml distilled water by gavage for 2 weeks.Serum total cholesterol,LDL,bile acid and hepatic CYP7A1 activity,CYP7A1 mRNA,SHP mRNA and LDL mRNA were measured.Results Total cholesterol and LDL were decreased in cholestyramine group compared with those in control group(P＜0.05).There's no statistically difference in bile acid between two groups(P＞0.05).CYP7A1 activity and mRNA were elevated in cholestyramine group compared with those in control group(P＜0.05).SHP mRNA and BSEP mRNA were declined in cholestyramine group compared with those in control group(P＜0.05 ).LDL mRNA was elevated in cholestyramine group compared with that in control group(P＜0.05).Conclusions Cholestyramine disturbed the reflux of bile acid from intestinal to liver, which inactivated FXR and the inhibition effect of FXR on CYP7A1 was weakened. The activity of CYP7A1 elevated and the bile acid classic synthesis increased,which compensated for the loss of bile acid from intestine and consumpted hepatic LDL.As a result,the liver uptook more LDL from circulation so that serum LDL was declined.PartⅢThe effect of cholestyramine on bile acid and cholesterol metabolism in cholesterol fed New Zealand white rabbit Objective To investigate the effect of cholestyramine on bile acid classic synthesis pathway and metabolism of cholesterol in cholesterol fed New Zealand white rabbits.Methods Thirty New Zealand white rabbits were randomizely divided into 3 groups: control group,model group and cholestyramine group,10 rabbits each group.The control group was fed regular forage and administrated 20ml distilled water by garage for 4 weeks.The model group was fed 1%cholesterol forage and administrated 20ml distilled water by gavage for 4 weeks.The cholesyramine group was fed 1% cholesterol forage and administrated 20ml cholestyramine suspension by gavage for 4 weeks.Serum total cholesterol,LDL,bile acid and hepatic HMGCoA reductase activity,CYP7A1 activity,CYP7A1 mRNA,SHP mRNA,BSEP mRNA and LDL mRNA were measured.Results Total cholesterol and LDL level elevated in model group and cholestyramine group compared with those in control group(P＜0.01).Total cholesterol and LDL decreased in cholestyramine group compared with those in model group(P＜0.01). Bile acid level elevated in model group and cholestyramine group compared with that in control group(P＜0.01).There's no statistically difference in bile acid between cholestyramine group and model group(P＞0.05).CYP7A1 activity and mRNA decreased in model group compared with those in control group(P＜0.01).CYP7A1 activity and mRNA elevated in cholestyramine group compared with those in model group(P＜0.01 ).HMGCoA reductase activity decreased in model group compared with that in control group(P＜0.01) HMGCoA reductase activity elevated in cholestyramine group compared with that in model group(P＜0.01),but there's no statistically difference in HMGCoA reductase activity between cholestyramine group and model group(P＞0.05).SHP mRNA and BSEP mRNA were elevated in model group and cholestyramine group compared with those in control(P＜0.01 ).SHP mRNA and BSEP mRNA decreased in cholestyramine group compared with those in model group(P＜0.01).LDL mRNA was decreased in model group compared with that in control group(P＜0.01 ).LDL mRNA was elevated in cholestyramine group compared with that in control group and model group(P＜0.01 ).Conclusions Long term cholesterol intake activated hepatic FXR,so that CYP7A1 activity and mRNA decreased;HMGCoA reductase activity and LDL mRNA decreased;serum cholesterol,LDL and bile acid level elevated.Cholestyramine intervention lowered FXR activity,CYP7A1 activity and mRNA elevated,HMGCoA reductase activity and LDL mRNA increased,then serum cholesterol,LDL level decreased while bile acid level remained unchanged.