Membrane Disintegration Caused by the Steroid Saponin Digitonin Is Related to the Presence of Cholesterol.

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.

Mechanistic investigation of interactions between steroidal saponin digitonin and cell membrane models.

Digitonin is an amphiphilic steroidal saponin, a class of natural products that can bind to cholesterol and lyse cells. Despite the known cell membrane lysis activity, it remains unclear how it interacts with cell membranes. In the present work, the interaction mechanism between digitonin and cell membrane models has quantitatively been investigated using a combination of physical techniques. It has been demonstrated that digitonin molecules bind specifically to cholesterol in the membrane, resulting in the formation of cholesterol-digitonin complexes on the membrane surface by removing cholesterol from the membrane core. Changes in the mass density and the film mechanics caused by the digitonin were determined by using quartz crystal microbalance with dissipation (QCM-D), and the combination of X-ray reflectivity (XRR) and dual polarization interferometry (DPI) yielded the hydration level of the cholesterol-digitonin complexes. From differential scanning calorimetry (DSC) analysis, supporting evidence was obtained that cholesterol was removed from the membrane core.

UV-triggered dopamine polymerization: control of polymerization, surface coating, and photopatterning.

UV irradiation is demonstrated to initiate dopamine polymerization and deposition on different surfaces under both acidic and basic pH. The observed acceleration of the dopamine polymerization is explained by the UV-induced formation of reactive oxygen species that trigger dopamine polymerization. The UV-induced dopamine polymerization leads to a better control over polydopamine deposition and formation of functional polydopamine micropatterns.