Spectroscopic studies of amphotericin B solubilized in nanoscale bilayer membranes.
Nanodisks (ND) are discrete nanometer scale phospholipid bilayers whose perimeter is circumscribed by amphipathic apolipoproteins. The membranous environment of ND serves as a matrix for solubilizing the polyene antibiotic amphotericin B (AMB). The spectral properties of AMB in ND are dependent upon AMB concentration. Whereas AMB-ND prepared at a concentration of 2.5 mg AMB per 10 mg phospholipid are consistent with AMB self association in the ND membrane environment, AMB-ND prepared at 0.25 or 0.025 mg AMB per 10 mg phospholipid give rise to spectra reminiscent of AMB in organic solvent. Incubation of ND prepared at a phospholipid/AMB ratio of 400:1 (w/w) at 37 degrees C for 1 h induced a shift in absorbance and near UV circular dichroism spectra consistent with antibiotic self-association. The kinetics of this spectral transition were investigated as a function of incubation temperature. While no change in A388 nm occurred in incubations at 20 degrees C, a time-dependent decrease in A388 nm was observed at 25, 30 and 37 degrees C. Inclusion of ergosterol in the ND membrane attenuated temperature-induced AMB spectral changes. In Saccharomyces cerevisiae growth inhibition assays, ND containing self associated AMB were somewhat less effective than ND possessing a greater proportion of monomeric AMB. On the other hand, inclusion of ergosterol or cholesterol in the ND particle did not alter the growth inhibition properties of AMB-ND. The miniature membrane environment of ND provides a novel milieu for solubilization and characterization of lipophilic biomolecules.
Lipid Biology in Health and Disease Research Group, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, USA.
Peter L
PL
Hargreaves
Thanh-Son
TS
Nguyen
Robert O
RO
Ryan
D000666:Amphotericin B / Q000737:chemistry* / Q000494:pharmacology; D000935:Antifungal Agents / Q000737:chemistry / Q000494:pharmacology; D002784:Cholesterol / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004337:Drug Carriers / Q000737:chemistry; D004875:Ergosterol / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry*; D012441:Saccharomyces cerevisiae / Q000187:drug effects; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D013696:Temperature
D000935:Antifungal Agents; D004337:Drug Carriers; D008051:Lipid Bilayers; D000666:Amphotericin B; D002784:Cholesterol; D004875:Ergosterol