ESR study of membrane perturbation and the lysis of liposomes induced by chlorpromazine.

The mechanism of interaction between chlorpromazine (CPZ) and artificial lipid membranes, negatively or positively charged liposomes was studied by an electron spin resonance (ESR) technique. Analysis by a 5-doxyl stearic acid (DS) spin probe indicated that regardless of the electric charge of liposomes, CPZ disordered the hydrophobic region near the surface of lipid membranes at CPZ/lipid > 1. In the same CPZ/lipid range, the lysis of liposomes was observed, and it was considered that the formation of the CPZ/lipid mixed micelles as a consequence of this collapse of liposomes would probably lead to the disordering of the 5-DS reporting region. As to the middle portion of the fatty acyl chains reported by the 12-DS spin probe, the membrane disordering action of CPZ was only detected with the negatively charged liposomes at a ratio of CPZ/lipid < 1, but no membrane alteration was observed with the positively charged liposomes, regardless of the concentration range of CPZ used. In comparing these two opposite results, it is conceivable that the disordering at the 12-DS reporting region was probably induced by the cationized CPZ which would enter into the hydrocarbon-polar interface, leading to an expansion of the space between the hydrocarbon chains at this area. Also, a strong influence of CPZ on the innermost portion of the lipid bilayers was observed with both the negatively and positively charged liposomes, as reported by the 16-DS probe. This perturbing action presumably occurred when undissociated CPZ molecules penetrated into the center of the bilayers (lipid core), which could have resulted in a reduction of hydrophobic interactions of the lipid molecules.