Amphotericin B-sterol complex formation and competition with egg phosphatidylcholine: a monolayer study

Area of Science:

• Biochemistry
• Physical Chemistry
• Membrane Biophysics

Background:

• Amphotericin B is an antifungal polyene antibiotic.
• Sterols like cholesterol and ergosterol are key membrane components.
• Understanding drug-sterol interactions is crucial for antifungal drug development.

Purpose of the Study:

• To investigate the formation and stoichiometry of amphotericin B-sterol complexes in lipid monolayers.
• To compare the binding affinity of amphotericin B to cholesterol versus ergosterol.
• To elucidate the role of egg phosphatidylcholine in complex dissociation.

Main Methods:

• Utilized radiolabeled N-fructosyl-amphotericin B to study penetration into egg phosphatidylcholine/sterol monolayers.
• Measured surface pressure and radioactivity changes with varying amphotericin B concentration.
• Analyzed surface pressure-area isotherms to determine complex stoichiometry and interactions.

Main Results:

• Observed simultaneous increases in surface pressure and radioactivity upon amphotericin B penetration.
• Surface pressure reached saturation, but radioactivity did not, indicating complex formation.
• Evidence suggests a 2:1 stoichiometry for amphotericin B-sterol complexes.
• Demonstrated stronger interaction between amphotericin B and ergosterol compared to cholesterol.
• Showed that egg phosphatidylcholine dissociates the complex via competition for sterols.

Conclusions:

• Amphotericin B forms stable complexes with sterols in lipid monolayers.
• The binding affinity is sterol-dependent, favoring ergosterol over cholesterol.
• Egg phosphatidylcholine competes with amphotericin B for sterol binding sites, disrupting the complex.