Disordering Effects of Digitonin on Phospholipid Monolayers

Area of Science:

• Biophysics
• Lipidomics
• Pharmacology

Background:

• Digitonin, a steroidal saponin from Digitalis purpurea, exhibits diverse biological activities.
• Saponins are frequently utilized as models for investigating biological mechanisms.
• Understanding digitonin's interaction with lipids is crucial for elucidating its bioactivity.

Purpose of the Study:

• To investigate the effect of digitonin on the organization of zwitterionic and ionic phospholipid monolayers.
• To elucidate the selectivity of digitonin's interaction with different phospholipid headgroups and tail structures.
• To determine the impact of digitonin on the biophysical properties of lipid monolayers.

Main Methods:

• Langmuir monolayers of various phospholipids (DPPC, DMPE, POPC, POPE, DSPC, DSPE, DPPE, DPPS, DPPG) were used.
• Surface pressure relaxation, Infrared Reflection Absorption Spectroscopy (IRRAS), and fluorescence microscopy were employed.
• Analysis focused on changes in surface pressure and monolayer structure upon digitonin interaction.

Main Results:

• Digitonin adsorption at the air/water interface was observed, increasing surface pressure.
• Digitonin demonstrated selective interaction with phospholipids, influenced by headgroup and lipid tails.
• No disruptive effects on monolayers were observed; however, DPPE and DPPS monolayers showed disordering and an LC-LE transition.
• Digitonin could be easily removed from DPPE and DPPS monolayers via mechanical compression.

Conclusions:

• Digitonin interacts selectively with phospholipid monolayers, modulating lipid organization.
• The headgroup and lipid tails significantly influence digitonin's interaction.
• Digitonin can induce unique phase transitions in specific phospholipid monolayers without causing general disruption.
• The reversible nature of digitonin's interaction with certain monolayers offers potential for controlled applications.