Bile Diversion Lowers Apolipoprotein A-I and A-IV mRNA Levels in Rat Ileum.

Abstract

SummaryWe recently reported that cholestyramine (a bile acid se questrant) lowered ileal apolipoprotein A-I mRNA level in rats. To obtain further information about this phenomenon, in this study, we investigated whether bile diversion lowers apolipoprotein A-I mRNA level in the ileum of rats. Bile-diverted rats were fed a diet with no added Na taurocholate (control diet) or with 0.4% Na taurocholate for 7 days. Sham-operated rats were also fed the control diet for the same period. Northern blot analysis revealed that the relative concentrations of jejunal apolipoprotein A-I and A-IV mRNA at the end of experimental period did not differ between groups while ileal apolipoprotein A-I and A-IV mRNA concentrations were significantly lower in bile-diverted rats fed the control and Na taurocholate-containing diets than in sham-operated rats. Plasma total and HDL cholesterol concentrations were the same in all groups. Relative concentration of apolipoprotein A-I in plasma also did not change. These results suggest that the bile plays an important role in ileal apolipoprotein gene expression at the pretranslational stage, but it is still unclear whether the effector is the bile acid or not. The unchanged concentration of plasma apolipoprotein A-I may have resulted from the constant secretion independent of synthesis in the intestine or the larger contribution from the liver which is another principal site for apolipo protein A-I expression.

Effect of White Wheat Bread Containing Sugar Beet Fiber on Serum Lipids and Hepatic mRNA in Rats Fed on a Cholesterol-Free Diet

“…Sonoyama et al have reported that the plasma cholesterol concentration was significantly lower in rats fed with sugar beet fiber than in those fed with a fiber-free or cholestyramine diet, this difference being due mainly to a lower HDL cholesterol concentration. 4) However, in this study, not only the HDL cholesterol, but also the non-HDL cholesterol concentration was reduced in the group fed with white wheat bread containing sugar beet fiber. The result for the serum non-HDL cholesterol concentration agreed with the report of Fukushima et al 5) It may be possible that the reduced serum HDL and non-HDL cholesterol concentrations were due to the white wheat bread, because the serum HDL and non-HDL cholesterol concentrations in the white wheat bread group were also lower than those in the control group.…”

“…4) Fukushima et al have also reported that sugar beet fiber lowered the serum total cholesterol level by enhancing hepatic LDL receptor mRNA. 5) Shortchain fatty acids (SCFAs), particularly propionate, a fermentable metabolite of soluble fiber, may be involved in lowering the serum cholesterol concentration.…”

Effect of bile duct obstruction on the expression of intestinal mRNA related to cholesterol and bile acid metabolism in the rat

“…Intestinal Apo AIV synthesis is stimulated by fat absorption. In the rat, the intestinal Apo AIV mRNA level was lowered by diversion of bile 22 . These findings suggest that intestinal Apo AIV expression is also primarily regulated by the factors in the lumen.…”

Lipid-Lowering Drugs Acting at the Level of the Gastrointestinal Tract

“…Although BAS decreased hepatic apo AII gene expression in rats, they did not influence serum apo AII concentrations in humans [28,84,86]. Furthermore, colestyramine did not change hepatic apo AIV gene expression in rats, although jejunal and ileal apo AIV gene expression was lowered; there is no evidence of such effects in humans [85][86][87]. Colestyramine did not influence hepatic apo E gene expression in rats [88].…”