title: Neutron Scattering Studies of the Effects of Formulating Amphotericin B with Cholesteryl Sulfate on the Drug's Interactions with Phospholipid and Phospholipid-Sterol Membranes.
abstract: Langmuir surface pressure, small-angle neutron scattering (SANS), and neutron reflectivity (NR) studies have been performed to determine how formulation of the antifungal drug amphotericin B (AmB), with sodium cholesteryl sulfate (SCS)-as in Amphotec-affects its interactions with ergosterol-containing (model fungal cell) and cholesterol-containing (model mammalian cell) membranes. The effects of mixing AmB in 1:1 molar ratio with cholesteryl sulfate (yielding AmB-SCS micelles) are compared against those of free AmB, using monolayers and bilayers formed from palmitoyloleoylphosphatidylcholine (POPC) in the absence and presence of 30 mol % ergosterol or cholesterol, in all cases employing a 1:0.05 molar ratio of lipid:AmB. Analyses of the (bilayer) SANS and (monolayer) NR data indicate that the equilibrium changes in membrane structure induced in sterol-free and sterol-containing membranes are the same for free AmB and AmB-SCS. Stopped-flow SANS experiments, however, reveal that the structural changes to vesicle membranes occur far more rapidly following exposure to AmB-SCS vs free drug, with the kinetics of these changes varying with membrane composition. With POPC vesicles, the structural changes induced by AmB-SCS become apparent only after several minutes, and equilibrium is reached after ∼30 min. The corresponding onset of changes in POPC-ergosterol and POPC-cholesterol vesicles, however, occurs within ∼5 s, with equilibrium reached after 10 and 120 s, respectively. The rate of insertion of AmB into POPC-sterol membranes is thus increased through formulation as AmB-SCS. Moreover, the differences in monolayer surface pressure and SANS structure-change equilibration times suggest significant rearrangement of AmB within these membranes following insertion. The reduced times to equilibrium for the POPC-ergosterol vs POPC-cholesterol systems are consistent with the known differences in affinity of AmB for these two sterols, and the reduced time to equilibrium for AmB-SCS interaction with POPC-ergosterol membranes vs that for free AmB is consistent with the reduced host toxicity of Amphotec.
authors.affiliation: †Institute of Pharmaceutical Science, King's College London, Franklin Wilkins Building, 150 Stamford Street, London SE1 9NH, U.K.
authors.forename: F
authors.initials: F
authors.lastname: Foglia
authors.forename: S E
authors.initials: SE
authors.lastname: Rogers
authors.forename: J R P
authors.initials: JR
authors.lastname: Webster
authors.forename: F A
authors.initials: FA
authors.lastname: Akeroyd
authors.forename: K F
authors.initials: KF
authors.lastname: Gascoyne
authors.affiliation: †Institute of Pharmaceutical Science, King's College London, Franklin Wilkins Building, 150 Stamford Street, London SE1 9NH, U.K.
authors.forename: M J
authors.initials: MJ
authors.lastname: Lawrence
authors.affiliation: †Institute of Pharmaceutical Science, King's College London, Franklin Wilkins Building, 150 Stamford Street, London SE1 9NH, U.K.
authors.forename: D J
authors.initials: DJ
authors.lastname: Barlow
mesh_terms: D000666:Amphotericin B / Q000737:chemistry*; D002788:Cholesterol Esters / Q000737:chemistry*; D008567:Membranes, Artificial; D010713:Phosphatidylcholines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*
chemical_list: D002788:Cholesterol Esters; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D010743:Phospholipids; C068538:liposomal amphotericin B; D000666:Amphotericin B; C007045:cholesteryl sulfate; C028694:1-palmitoyl-2-oleoylphosphatidylcholine