The Action of Polyene Antibiotics on Phospholipid-Cholesterol Structures

Abstract

Artificial spherules of phospholipid were prepared with and without cholesterol present, so as to sequester anions (H2PO4- or CrO4=) or glucose. The effect of several polyene antibiotics upon release of anions or glucose was determined, and it was found that, whereas filipin and etruscomycin released similar amounts of these markers whether or not cholesterol was preincorporated into the spherules, amphotericin B and nystatin were far more effective when cholesterol was preincorporated. Ergosterol could be substituted for cholesterol. Release of anions or glucose from spherules by other membrane-active agents, such as etiocholanolone, deoxycorticosterone, diethylstilbestrol, streptolysin S, or Triton X-100, was unaffected by the presence or the absence of cholesterol. It was found that an ovolecithin to cholesterol ratio of 15:1 was optimal for release of markers both by filipin and by amphotericin B. By electron microscopy, the lamellar substructure of polyene-disrupted spherules was seen to be altered. Whereas filipin or deoxycorticosterone induced such morphological changes in spherules prepared with and without cholesterol, amphotericin B produced morphological changes only in spherules formed in the presence of cholesterol. These studies support the hypotheses that polyene antibiotics interact with purified lipids present in biological membranes and that amphotericin B and nystatin preferentially disrupt membranous structures which contain cholesterol. They also show that filipin and etruscomycin disrupt spherules of pure phospholipid prepared in the absence of cholesterol, and thereby suggest qualitative differences in the mode of action of the several polyene antibiotics.