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Abstract

The binding of bile salts by cholestyramine may be influenced by other anions, as the Langmuir adsorption coefficients for three bile salts tested were similar to the model anion, citrate. However, the selectivity coefficient indicated preferential binding of cholate anion in comparison to citrate anion. Binding experiments confirmed cholestyramine's preference for bile salts as the presence of other anions reduced but did not prevent the binding of cholate anion. Binding of cholate anion was reduced in direct relationship to the citrate anion concentration. Prior exposure of cholestyramine to citrate anion caused the binding of cholate anion to decrease slightly. Sequential exposure of cholestyramine to simulated gastric fluid and simulated intestinal fluid containing cholate anion resulted in a decrease in cholate binding which was attributed to competition with anions present in the gastrointestinal fluids. Components of tomato juice and orange juice, fluids, commonly used to enhance ingestion of cholestyramine, also reduced the binding of cholate anion.

Bile Acid Measurements Using a Cholestyramine-Coated TSM Acoustic Wave Sensor

“…The sensitivity of the frequency response increases in the order cholate ≈ glycocholate < taurocholate ≪ taurodeoxycholate. The approximately equal affinity of cholestyramine for the trihydroxy bile acids has been observed in previous studies, although a slight increase in affinity for taurocholate has also been noted. ,,,− The high sensitivity observed for the dihydroxy bile acid taurodeoxycholate is attributed to the much greater hydrophobicity of this molecule compared to the trihydroxy bile acids and is direct evidence of the importance of hydrophobic interactions in addition to the ionic interaction. The increased affinity of cholestyramine for dihydroxy bile acids has also been confirmed in other studies. ,,,,,, In both injection media the pH and equilibrium bile salt concentrations are above the p K a and below the cmc values for all four bile acids .…”

“…As in the regeneration studies, we again invoke Coulomb's law and attribute this effect to the greater strength of ionic interaction of the resin with trivalent (citrate) vs monovalent (cholate) anions. Kos et al have also observed, in indirect competitive binding studies, the ability of citrate to reduce the amount of binding to cholate but noted that there was still preferential binding of cholate over citrate. On the basis of the frequency changes in Figure , we estimate that at equimolar concentrations citrate reduces the amount of bound cholate by ∼40%, indicating a slight preference of cholestyramine for cholate over citrate.…”

“…Cholestryamine is a styrene−divinylbenzene copolymer bearing quaternary ammonium groups (Figure ). Its bile acid sequestering ability has been proposed to operate mainly through the ionic interaction of the positively charged ammonium group and the negative charge on the ionized form of the bile acid, i.e., ion exchange. , However, several reports have also indicated that hydrophobic interactions may also be important. ,−

1 Structure of cholestyramine.

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