Effects of bile salts on the structural integrity of liposomes.

The effects of the bile salts, sodium taurocholate and sodium glycocholate on the structural integrity of liposomes of different lipid compositions were studied. The bile salt concentrations were in the range encountered in the human intestine and the incubations were conducted at 37 degrees C. Two measures of liposome integrity were used: (a) changes in their light-scattering properties; and (b) release of entrapped potassium chromate. The results show that "fluid" liposomes, i.e., those prepared from phospholipids whose phase transition temperatures are below 37 degrees C, were totally disrupted in the presence of 10 mM bile salts at pH 7.4, and their entire contents were released. In the case of liposomes prepared from phospholipids with phase transition temperatures above 37 degrees C, the effect of the bile salts became less pronounced as the phase transition temperature increased. Nevertheless, a considerable proportion of the entrapped marker compound was released from liposomes with phase transition temperatures as high as 60 degrees C. The relevance of these results to the reported liposome-mediated gastrointestinal uptake of insulin is discussed.