The influence of 2-hydroxypropyl-beta-cyclodextrin on the haemolysis induced by bile acids.

Cyclodextrins improve the water-solubility of drugs and can mask their haemolytic effect in parenteral use. Because the mechanism by which bile acids induce haemolysis is poorly understood, it has been investigated in the presence of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD). The haemolytic effect of 1.8 mM solutions of cholic acid, chenodeoxycholic acid (CDCA), deoxycholic acid and ursodeoxycholic acid (UDCA) in isotonic buffer at pH 7.4 was investigated at 37 degrees C in the presence of HP-beta-CyD at concentrations from 0.18 to 32 mM. No haemolytic effect was evident for cholic acid and UDCA. The haemolytic effect of the other bile acids was reduced by addition of HP-beta-CyD and was prevented at a molar ratio of 1:1 owing to complex formation. An HP-beta-CyD:bile acid molar ratio greater than 5:1 had a different effect on the erythrocyte membrane, irrespective of the identity of the bile acid; the effect was in accordance with the complexion affinities. In the absence of HP-beta-CyD, the haemolytic effect of CDCA and deoxycholic acid appeared related to their capacity to form a surface monolayer and to solubilize the components of the erythrocyte membrane. The haemolytic effect observed after complexation of the bile acids appeared to be solely the effect of HP-beta-CyD, which was able to form a reversible inclusion complex with lipophilic components of the erythrocyte membranes at concentrations higher than 12 mM.