Spectroscopic studies of amphotericin B solubilized in nanoscale bilayer membranes

Biochim Biophys Acta. 2006 Jan;1758(1):38-44. doi: 10.1016/j.bbamem.2006.01.001. Epub 2006 Jan 26.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amphotericin B / chemistry*
  • Amphotericin B / pharmacology
  • Antifungal Agents / chemistry
  • Antifungal Agents / pharmacology
  • Cholesterol / metabolism
  • Cholesterol / pharmacology
  • Dose-Response Relationship, Drug
  • Drug Carriers / chemistry
  • Ergosterol / metabolism
  • Ergosterol / pharmacology
  • Kinetics
  • Lipid Bilayers / chemistry*
  • Nanostructures / chemistry*
  • Saccharomyces cerevisiae / drug effects
  • Spectrophotometry, Ultraviolet / methods*
  • Temperature

Substances

  • Antifungal Agents
  • Drug Carriers
  • Lipid Bilayers
  • Amphotericin B
  • Cholesterol
  • Ergosterol