ROLE OF THE STEROL SUPERLATTICE IN THE PARTITIONING OF THE ANTIFUNGALDRUG NYSTATIN INTO LIPID-MEMBRANES

Nystatin isolated from Streptomyces is a polyene antibiotic that is fr equently used in the treatment and prophylaxis of fungal infections. H ere, the fractional sterol concentration dependencies of the partition coefficient for partitioning of nystatin into ergosterol/dimyristoyl- L-alpha-phosphatidylcholine (DMPC), cholesterol/DMPC, l/1-palmitoyl-2- oleoyl-L-alpha-phosphatidylcholine (POPC), and almitoyl-2-oleoyl-L-alp ha-phosphatidylethanolamine (POPE) multilamellar vesicles have been de termined fluorometrically at 37 degrees C using similar to 0.3-1.0 mol % sterol concentration increments over a wide concentration range (e. g., 18-54 mol % sterol). This unconventional approach of varying membr ane sterol content, in contrast to previous studies using large sterol concentration increments (e.g., 10 mol %), leads to a striking observ ation. The partition coefficient of nystatin changes dramatically with membrane sterol content in a well-defined alternating manner, display ing a local minimum at or very close to the critical sterol mole fract ions (e.g., 20.0, 22.2, 25.0, 33.3, 40.0, and 50.0 mol % sterol) predi cted for sterols regularly distributed in either hexagonal or centered rectangular superlattices. In ergosterol/DMPC bilayers, for example, there is a >3-fold increase in nystatin partitioning with a minute cha nge (similar to 1 mol %) in sterol content on either side of the criti cal sterol mole fraction, 25.0 mol %. These results provide semifuncti onal evidence supporting the sterol regular distribution model [Chong, P. L.-G. (1994) Proc. Natl. Acad Sci. U.S.A. 91, 10069-10073]. More i mportantly, these results reveal a new membrane phenomenon, that is, t hat nystatin partitioning is affected by the extent of sterol regular distribution in the plane of the membrane. This phenomenon occurs not only in saturated (e.g., DMPC) but also in unsaturated (e.g., POPC) li pid membranes, and persists in the presence of polar headgroup heterog eneity (e.g., POPC/POPE). This membrane property points to a new metho d for studying the interactions of polyene antibiotics with sterol-con taining membranes, and the need to consider the membrane sterol conten t of the target cells when administering nystatin or other polyene ant ibiotics.