The pentaene macrolide antibiotic filipin prefers more rigid DPPC bilayers: a fluorescence pressure dependence study

Filipin is a pentaene macrolide antibiotic which was previously shown to in corporate more extensively into DPPC bilayers below the main phase transiti on temperature than above this temperature. This result was extremely unusu al because drugs tend to be expelled from ordered gel phases. However, such results could not be safely attributed to the phase change of the bilayer itself because the temperature was changing concomitantly. In this work we changed the bilayer phase isothermally (53 degrees C by hydrostatic pressur e variation and discovered that filipin has a slightly more extensive incor poration in the pure DPPC gel phase (P > ca, 54.4 MPa): K-p,K-lc approximat e to 3 x 10(3) vs. K-p,K-gel approximate to 6 x 10(3). The presence of ster ols (45% molar ergosterol or cholesterol) caused an increase in the partiti on coefficients, regardless of pressure, ergosterol having a more pronounce d effect (K-p approximate to 2 x 10(4)-6 x 10(4)). K-p was pressure depende nt in both cases, but mainly with cholesterol (K-p approximate to 2 x 10(3) -2 x 10(4)), At variance with cholesterol, when ergosterol was used, no pha se transition was detected. This difference cannot be due to a more extende d uptake of filipin by cholesterol-containing membranes, and so must be due to specific interactions with cholesterol. In agreement with this finding, we discovered that filipin is more tightly packed (lower partial molar vol ume) in the cholesterol-rich phase than in the ergosterol-rich phase. Our r esults also point to a 2:1 DPPC:cholesterol stoichiometry in the cholestero l-rich phase (17% molar cholesterol). All partition coefficients were calcu lated from steady-state fluorescence anisotropy measurements. (C) 1999 Else vier Science B.V. All rights reserved.