Bile acid binding in plasma: the importance of lipoproteins

Bile acid (BA) hydrophobicity, evaluated by the octanol-water partition coefficient, decreases along the series deoxycholic acid - chenodeoxycholic acid - hyodeoxycholic acid - ursodeoxycholic acid - cholic acid (CA) - ursocholic acid (UCA). In vitro experiments carried out using dialysis techniques (to determine the maximum BA binding) and ultrafiltration of plasma pre-incubated with 0.1 mM BA (to assess the distribution of BA between the different lipoprotein fractions) showed that the maximum binding of BA to plasma and lipoproteins follows the same order of hydrophobicity. The fraction not bound to proteins, greater with the hydrophilic BA (UCA and CA), is distributed in the lipoprotein fractions and in particular in high density lipoproteins.