Temperature effects on the aggregation state and activity of amphotericin B

Area of Science:

• Biochemistry
• Biophysics
• Membrane Biology

Background:

• Amphotericin B (AmB) is a vital antifungal agent.
• Its mechanism of action involves membrane interaction and pore formation.
• The role of Amphotericin B aggregation state in its activity is debated.

Purpose of the Study:

• To investigate the relationship between Amphotericin B aggregation and its membrane-disrupting activity.
• To determine the temperature-dependent behavior of Amphotericin B in cholesterol- vs. ergosterol-containing membranes.
• To elucidate the specific species (monomers vs. aggregates) responsible for Amphotericin B's channel-inducing properties.

Main Methods:

• Circular Dichroism (CD) spectroscopy was used to monitor Amphotericin B aggregation.
• Potassium (K+) leakage assays were performed using large unilamellar vesicles (LUVs) with varying lipid compositions.
• Temperature-dependent studies were conducted to assess the sensitivity of Amphotericin B activity.

Main Results:

• Increased temperature led to decreased Amphotericin B aggregation in aqueous solution.
• AmB's ability to induce K+ leakage from cholesterol-containing LUVs decreased significantly with rising temperature.
• Ergosterol-containing vesicles showed no clear temperature-dependent trend in AmB-induced K+ leakage.

Conclusions:

• These findings support a model where Amphotericin B aggregates, not monomers, are the primary species responsible for channel formation in cholesterol-containing membranes.
• The reduced aggregation at higher temperatures explains the decreased ionophore activity observed.
• The differential effect on cholesterol- vs. ergosterol-containing membranes highlights the importance of membrane sterol composition in Amphotericin B's mechanism of action.