Interaction of the Saponin Aescin with Ibuprofen in DMPC Model Membranes

Abstract

In the present work, we study the interaction of the saponin aescin with the nonsteroidal anti-inflammatory drug (NSAID) ibuprofen at concentrations of 1.2-2.5 mM. These amounts are higher than those usually used for medication (10-300 μM) to show possible structures and formulations for orally absorbed drug delivery systems. It is shown how the interaction of both substances, separately or together, alters the thermotropic phase behavior of the 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayer in the presence of different amounts of aescin, ranging from 20 μM to 1 mM. The methods of choice are differential scanning calorimetry (DSC), and additionally wide-angle (WAXS) and small-angle X-ray scattering (SAXS). We found that these two additives, aescin and ibuprofen, alter the temperature-dependent structural appearance of the DMPC membrane depending on the aescin and drug content. The presence of the saponin and the drug become visible on different length scales, i.e., ranging from a global structural change to inner-membrane interactions. DSC reveals that the drug and saponin alter the cooperativity of the DMPC phase transition in a concentration-dependent manner. Furthermore, there is a significant difference between the drug-containing compared to the drug-free systems. By WAXS, we could resolve that aescin reverses the strong impact of ibuprofen on the diffraction peak of DMPC. Both molecules interact strongly with the phospholipid headgroups. This becomes visible in a changing area per lipid and shifting phase transition to higher temperatures. SAXS experiments reveal that the addition of ibuprofen leads to major morphological changes in the phospholipid bilayer. SAXS experiments performed on representative samples do not only cover the drug-saponin interaction within the bilayer from the structural perspective but also confirm the visually observed macroscopic concentration and temperature-dependent phase behavior. Vesicular shape of extruded samples is conserved at low aescin contents. At intermediate aescin content, aggregation between vesicles occurs, whereby the strength of aggregation is reduced by ibuprofen. At high aescin contents, DMPC bilayers are solubilized. The kind of formed structures depends on temperature and drug content. At low temperature, separated bilayer sheets are formed. Their size increases with ibuprofen in a concentration-dependent manner. At high temperature, the drug-free system reorganizes into stacked sheets. Whereas sheets at 5 mol % ibuprofen close to vesicles, the ones with 10 mol % of the drug increase massively in size. Altogether, ibuprofen was found to rather enhance than inhibit structural and thermotropic membrane modifications induced by the aescin on the DMPC model membrane.

Self-Assembly of the Bio-Surfactant Aescin in Solution: A Small-Angle X-ray Scattering and Fluorescence Study

“…Whereas, the XSLDs of the solvent (H 2 O) were corrected for temperature (XSLD H 2 O (10 • C) = 9.47 × 10 −6 Å −2 and XSLD H 2 O (40 • C) = 9.40 × 10 −6 Å −2 ), for aescin, the same value was used at both temperatures (XSLD(aescin) = 13.4 × 10 −6 Å −2 ). The XSLD of aescin was derived from its molar volume determined from the chemical structure with Chemsketch [59] (see also [60]). The polydispersity of the cylinder radius σ(R) was also fitted but remained in the range from 0-10 %.…”

The Biosurfactant β-Aescin: A Review on the Physico-Chemical Properties and Its Interaction with Lipid Model Membranes and Langmuir Monolayers

“…Similar effects resulting from headgroup-drug interactions were observed for non-steroidal anti-inflammatory drugs (NSAIDs) known to interact with phospholipids headgroups from the inside of the bilayer [54]. The presence of the stiff saponin backbone in the bilayer distorts the temperature-driven cooperative phase transition of DMPC molecules and the bilayer becomes fluidized at lower temperatures [21]. At around 6 mol% of the saponin the signal broadens significantly and is only weakly visible indicating different structures in the samples.…”

“…The reverse effect to the one of cholesterol was found for the non-steroidal anti-inflammatory drug (NSAID) ibuprofen [21] at similar experimental conditions. In this work, which was conducted at pH 7.4 in a 50 mM phosphate buffer solution, both, the β-aescin and ibuprofen molecules are deprotonated.…”

“…β-Aescin was more efficient in diminishing GIC growth compared to present clinically used drugs. Moreover, as other saponins, it shows a hemolytic effect and seems to interact with non-steroidal anti-inflammatory drugs inside lipid membranes [21]. Vinarov et al have shown that β-aescin might also help to solubilize hydrophobic drugs [22].…”

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…A combination of USAXS, SAXS, and contrast variation SANS allowed the determination of the ultrastructure of Escherichia coli bacterial cell membrane [47] in vivo, thereby demonstrating the potential for monitoring the action of antimicrobial peptide on real cell membranes. SAXS was used to probe quantitatively the effect of additives aescin and ibuprofen on the structural parameters of a model phospholipid (DMPC) membrane and temperature-dependent phase transitions depending on the quantity of these additives [48]. The presence of these compounds are visible on the structure at different length scales ranging from the global morphology to inner membrane interactions.…”