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Bile diversion lowers apolipoprotein A-I and A-IV mRNA levels in rat ileum
K Sonoyama1, H Nishikawa, S Kiriyama
1Laboratory of Food Biochemistry, Faculty of Agriculture, Hokkaido-University, Sapporo, Japan.
Abstract:
We recently reported that cholestyramine (a bile acid sequestrant) 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 apolipoprotein A-I expression.
Insights
Bile diversion significantly reduces ileal apolipoprotein A-I mRNA levels in rats, suggesting bile
Area of Science:
- Molecular Biology
- Gastroenterology
- Lipid Metabolism
Background:
- Cholestyramine, a bile acid sequestrant, was previously shown to lower ileal apolipoprotein A-I mRNA in rats.
- The precise mechanism and role of bile in regulating apolipoprotein A-I gene expression remain unclear.
Purpose of the Study:
- To investigate the effect of bile diversion on apolipoprotein A-I mRNA levels in the rat ileum.
- To determine if bile acids are the primary mediators of this effect.
Main Methods:
- Rats underwent bile diversion or sham surgery.
- Animals were fed diets with or without sodium taurocholate for seven days.
- Northern blot analysis was used to quantify jejunal and ileal apolipoprotein A-I and A-IV mRNA levels.
Main Results:
- Ileal apolipoprotein A-I and A-IV mRNA concentrations were significantly lower in bile-diverted rats compared to sham-operated rats.
- Jejunal mRNA levels and plasma lipid/apolipoprotein A-I concentrations did not differ between groups.
- The effect was observed regardless of sodium taurocholate supplementation in the diet.
Conclusions:
- Bile plays a crucial role in regulating ileal apolipoprotein gene expression at the pretranslational level.
- It remains undetermined whether bile acids themselves are the direct effectors.
- Plasma apolipoprotein A-I levels may be maintained by hepatic synthesis or secretion independent of intestinal synthesis.