title: Amphotericin B-phospholipid interactions responsible for reduced mammalian cell toxicity.
abstract: When interacting with phospholipid in an aqueous environment, amphotericin B forms unusual structures of markedly reduced toxicity (Janoff et al. (1988) Proc. Natl. Acad. Sci. USA 85, 6122-6126). These structures, which appear ribbon-like by freeze-fracture electron microscopy (EM), are found exclusively at amphotericin B to lipid mole ratios of 1:3 to 1:1. At lower mole ratios they occur in combination with liposomes. Circular dichroism (CD) spectra revealed two distinct modes of lipid-amphotericin B interaction, one for liposomes and one for the ribbon-like structures. In isolated liposomes, amphotericin B which comprised 3-4 mole percent of the bulk lipid was monomeric and exhibited a hemolytic activity comparable to amphotericin B suspended in deoxycholate. Above 3-4 mole percent amphotericin B, ribbon-like structures emerged and CD spectra indicated drug-lipid complexation. Minimal inhibitory concentrations for Candida albicans of liposomal and complexed amphotericin B were comparable and could be attributed to amphotericin a release as a result of lipid breakdown within the ribbon-like material by a heat labile extracellular yeast product (lipase). Negative stain EM of the ribbon-like structures indicated that the ribbon-like appearance seen by freeze-fracture EM arises as a consequence of the cross-fracturing of what are aggregated, collapsed single lamellar, presumably interdigitated, membranes. Studies examining complexation of amphotericin B with either DMPC or DMPG demonstrated that headgroup interactions played little role in the formation of the ribbon-like structures. With these results we propose that ribbon-like structures result from phase separation of amphotericin B-phospholipid complexes within the phospholipid matrix such that amphotericin B release, and thus acute toxicity, is curtailed. Formation of amphotericin B-lipid structures such as those described here indicates a possible new role for lipid as a stabilizing matrix for drug delivery of lipophilic substances, specifically where a highly ordered packing arrangement between lipid and compound can be achieved.
authors.affiliation: Liposome Company, Inc., Princeton, NJ.
authors.forename: W R
authors.initials: WR
authors.lastname: Perkins
authors.forename: S R
authors.initials: SR
authors.lastname: Minchey
authors.forename: L T
authors.initials: LT
authors.lastname: Boni
authors.forename: C E
authors.initials: CE
authors.lastname: Swenson
authors.forename: M C
authors.initials: MC
authors.lastname: Popescu
authors.forename: R F
authors.initials: RF
authors.lastname: Pasternack
authors.forename: A S
authors.initials: AS
authors.lastname: Janoff
mesh_terms: D000666:Amphotericin B / Q000494:pharmacology* / Q000633:toxicity; D002176:Candida albicans / Q000187:drug effects; D002250:Carbon Radioisotopes; D004347:Drug Interactions; D004912:Erythrocytes / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects; D066298:In Vitro Techniques; D008826:Microbial Sensitivity Tests; D008854:Microscopy, Electron; D010743:Phospholipids / Q000494:pharmacology*; D013057:Spectrum Analysis
chemical_list: D002250:Carbon Radioisotopes; D010743:Phospholipids; D000666:Amphotericin B