The Effect of Dextran Sulfate-as Model Glycosaminoglycan Analogue-on Membrane Lipids: DPPC, Cholesterol, and DPPC-Cholesterol Mixture. The Monolayer Study

The Structure of Oxysterols Determines Their Behavior at Phase Boundaries: Implications for Model Membranes and Structure-Activity Relationships

The presence of an additional polar group in the cholesterol backbone increases the hydrophilicity of resulting compounds (oxysterols), determines their arrangement at the phase boundary, and interactions with other lipids and proteins. As a result, physicochemical properties of biomembranes (i.e., elasticity, permeability, and ability to bind proteins) are modified, which in turn may affect their functioning. The observed effect depends on the type of oxysterol and its concentration and can be both positive (e.g., antiviral activity) or negative (disturbance of cholesterol homeostasis, signal transduction, and protein segregation). The membrane activity of oxysterols has been successfully studied using membrane models (vesicles, monolayers, and solid supported films). Membrane models, in contrast to the natural systems, provide the possibility to selectively examine the specific aspect of biomolecule-membrane interactions. Moreover, the gradual increase in the complexity of the used model allows to understand the molecular phenomena occurring at the membrane level. The interest in research on artificial membranes has increased significantly in recent years, mainly due to the development of modern and sophisticated physicochemical methods (static and dynamic) in both the micro- and nanoscale, which are applied with the assistance of powerful theoretical calculations. This review provides an overview of the most important findings on this topic in the current literature.

Dextran Sulfate Polymer Wafer Promotes Corneal Wound Healing

Eye injuries due to corneal abrasions, chemical spills, penetrating wounds, and microbial infections cause corneal scarring and opacification that result in impaired vision or blindness. However, presently available eye drop formulations of anti-inflammatory and antibiotic drugs are not effective due to their rapid clearance from the ocular surface or due to drug-related side effects such as cataract formation or increased intraocular pressure. In this article, we presented the development of a dextran sulfate-based polymer wafer (DS-wafer) for the effective modulation of inflammation and fibrosis and demonstrated its efficacy in two corneal injury models: corneal abrasion mouse model and alkali induced ocular burn mouse model. The DS-wafers were fabricated by the electrospinning method. We assessed the efficacy of the DS-wafer by light microscopy, qPCR, confocal fluorescence imaging, and histopathological analysis. These studies demonstrated that the DS-wafer treatment is significantly effective in modulating corneal inflammation and fibrosis and inhibited corneal scarring and opacification compared to the unsulfated dextran-wafer treated and untreated corneas. Furthermore, these studies have demonstrated the efficacy of dextran sulfate as an anti-inflammatory and antifibrotic polymer therapeutic.

25-hydroxycholesterol interacts differently with lipids of the inner and outer membrane leaflet - The Langmuir monolayer study complemented with theoretical calculations

25-hydroxycholesterol (25-OH), a molecule with unusual behavior at the air/water interface, being anchored to the water surface alternatively with a hydroxyl group at C(3) or C(25), has been investigated in mixtures with main membrane phospholipids (phosphatidylcholines - PCs, and phosphatidylethanolamines - PEs), characteristic of the outer and inner membrane leaflet, respectively. To achieve this goal, the classical Langmuir monolayer approach based on thermodynamic analysis of interactions was conducted in addition to microscopic imaging of films (in situ with BAM and after transfer onto mica with AFM), surface-sensitive spectroscopy (PM-IRRAS), as well as theoretical calculations. Our results show that the strength of interactions is primarily determined by the kind of polar group (strong, attractive interactions leading to surface complexes formation were found to occur with PCs while weak or repulsive ones with PEs). Subsequently, the saturation of phosphatidylcholines apolar chain(s) was found to be crucial for the structure of the formed complexes. Namely, saturated PC (DPPC) does not have preferences regarding the orientation of 25-OH molecule in surface complexes (which results in the two possible 25-OH arrangements), while unsaturated PC (DOPC) enforces one specific orientation of oxysterol (with C(3)-OH group). Our findings suggest that the transport of 25-OH between inner and outer membrane leaflet can proceed without orientation changes, which is thermodynamically advantageous. This explains results found in real systems showing significant differences in the rate of transmembrane transport of 25-OH and the other chain-oxidized oxysterols compared to their ring-oxidized analogues or cholesterol.