Abstract
In the present investigation we studied the molecular mechanisms of the monodesmosidic saponin digitonin on natural and artificial membranes. We measured the hemolytic activity of digitonin on red blood cells (RBCs). Also different lipid membrane models (large unilamellar vesicles, LUVs, and giant unilamellar vesicles, GUVs) in the presence and absence of cholesterol were employed. The stability and permeability of the different vesicle systems were studied by using calcein release assay, GUVs membrane permeability assay using confocal microscopy (CM) and fluorescence correlation spectroscopy (FCS) and vesicle size measurement by dynamic light scattering (DLS). The results support the essential role of cholesterol in explaining how digitonin can disintegrate biological and artificial membranes. Digitonin induces membrane permeability or causes membrane rupturing only in the presence of cholesterol in an all-or-none mechanism. This effect depends on the concentrations of both digitonin and cholesterol. At low concentrations, digitonin induces membrane permeability while keeping the membrane intact. When digitonin is combined with other drugs, a synergistic potentiation can be observed because it facilitates their uptake.
Highlights
Saponins are natural glycosides, which are widely distributed in the plant kingdom and in some marine animals like sea cucumbers (Holothuriidae) and sea stars (Asteroidea) [1,2]
The aim of this work was to study the molecular interactions of digitonin with natural and artificial membranes present in red blood cells (RBCs) and in different lipid membrane models
Defebrinated sheep red blood cells were mixed with differing concentrations of digitonin and the effect on membrane permeability was determined photometrically by measuring hemoglobin leakage
Summary
Saponins are natural glycosides, which are widely distributed in the plant kingdom and in some marine animals like sea cucumbers (Holothuriidae) and sea stars (Asteroidea) [1,2]. Saponins are mainly divided into monodesmosides with a single sugar chain and bidesmosides with two sugar chains. Monodesmosides exhibit strong membrane activities which are due to their amphiphilic molecular structure with a lipophilic aglycone and a hydrophilic sugar side chain. A main characteristic of saponins is their foaming, soap-like behavior in aqueous solution, leading to their name (Latin sapo = soap) [3]. The aglycone moiety of saponins is generally referred to as the sapogenin, to which one or more sugar molecules are attached. Steroidal saponins consist of a steroidal aglycone, a C27 spirostane skeleton, generally comprised of a six-ring structure. Triterpenoid saponins consist of a triterpenoid aglycone, with a C30 skeleton and a pentacyclic structure
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