Langmuir monolayer studies of the interaction of monoamphiphilic pentacyclic triterpenes with anionic mitochondrial and bacterial membrane phospholipids - searching for the most active terpene.

The interactions of three representative monoamphiphilic pentacyclic triterpenes (PTs) with cardiolipins (CL) and phosphatidylglycerols (PG) extracted from mitochondrial and bacterial membranes were comparatively characterized in binary Langmuir monolayers. The studied terpenes: lupeol, α- and β-amyrin are isomeric compounds known from their broad biological activity. Anticancer and antimicrobial activity of PTs is often correlated with their propensity of being incorporated into mitochondrial and bacterial membranes and their specific interactions with cardiolipins. In our studies on 18 model systems surface pressure (π)-mean molecular area (A) isotherms were registered at five different component proportions in each system. Thermodynamic analysis complemented by in situ Brewster angle microscopy visualization of the investigated mixed films enabled the thorough characterization of the studied systems. It turned out that the investigated terpenes interact more favorably with PG molecules as compared to CLs. For most of the system containing CLs the values of ΔG(exc) were positive which was interpreted as the ability of the terpenes to disintegrate the membranes rich in CLs. Our results confirmed also that in the light of thermodynamic criterion α-amyrin exhibited the highest potential to disintegrate the CL containing domains in mitochondrial and bacterial membranes. The probable origin of the observed specific interactions between α-amyrin and investigated phospholipids could be explained based on the phenomenon of chiral discrimination. The obtained results were also widely discussed in reference to the biological activity of the studied compounds.
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