Allosteric modulation of the adenosine A2A receptor by cholesterol

Cholesterol is a major component of the cell membrane and commonly regulates membrane protein function. Here, we investigate how cholesterol modulates the conformational equilibria and signaling of the adenosine A2A receptor (A2AR) in reconstituted phospholipid bilayers. GTP hydrolysis assays show that cholesterol is a weak positive allosteric modulator of A2AR, as seen through enhanced basal signaling and a small decrease in agonist EC50. Fluorine nuclear magnetic resonance (19F NMR) spectroscopy suggests that this enhancement arises from an increase in the receptor’s active state populations and stronger G protein coupling. 19F NMR of fluorinated cholesterol analogs reveals transient and non-specific interactions with A2AR, indicating a lack of high-affinity binding sites or direct allosteric modulation. This is confirmed by computational analysis which suggests that cholesterol contacts confer a weak and possibly negative allosteric effect. The combined results suggest that the observed cholesterol allostery in A2AR is likely a result of indirect membrane effects through cholesterol-mediated changes in membrane properties, as shown by membrane fluidity measurements and high-pressure NMR.

Quantitative 3D imaging of partially saturated granular materials under uniaxial compression

Gauging the mechanical effect of partial saturation in granular materials is experimentally challenging due to the very low suctions resulting from large pores. To this end, a uniaxial (zero radial stress) compression test may be preferable to a triaxial one where confining pressure and membrane effects may erase the contribution of this small suction; however, volume changes are challenging to measure. This work resolves this limitation by using X-ray imaging during in situ uniaxial compression tests on Hamburg Sand and glass beads at three different initial water contents, allowing a suction-dependent dilation to be brought to the light. The acquired tomography volumes also allow the development of air–water and solid–water interfacial areas, water clusters and local strain fields to be measured at the grain scale. These measurements are used to characterise pertinent micro-scale quantities during shearing and to relate them to the measured macroscopic response. The new and well-controlled data acquired during this experimental campaign are hopefully a useful contribution to the modelling efforts—to this end they are shared with the community.

Effect of L- to D-Amino Acid Substitution on Stability and Activity of Antitumor Peptide RDP215 against Human Melanoma and Glioblastoma

The study investigates the antitumor effect of two cationic peptides, R-DIM-P-LF11-215 (RDP215) and the D-amino acid variant 9D-R-DIM-P-LF11-215 (9D-RDP215), targeting the negatively charged lipid phosphatidylserine (PS) exposed by cancer cells, such as of melanoma and glioblastoma. Model studies mimicking cancer and non-cancer membranes revealed the specificity for the cancer-mimic PS by both peptides with a slightly stronger impact by the D-peptide. Accordingly, membrane effects studied by DSC, leakage and quenching experiments were solely induced by the peptides when the cancer mimic PS was present. Circular dichroism revealed a sole increase in β-sheet conformation in the presence of the cancer mimic for both peptides; only 9D-RDP215 showed increased structure already in the buffer. Ex vitro stability studies by SDS-PAGE as well as in vitro with melanoma A375 revealed a stabilizing effect of D-amino acids in the presence of serum, which was also confirmed in 2D and 3D in vitro experiments on glioblastoma LN-229. 9D-RDP215 was additionally able to pass a BBB model, whereupon it induced significant levels of cell death in LN-229 spheroids. Summarized, the study encourages the introduction of D-amino acids in the design of antitumor peptides for the improvement of their stable antitumor activity.

TREATMENT AND PREVENTION OF POST-CHEMOTHERAPY THROAT DRYING IN ONCOLOGY PATIENTS WITH NATURAL DRUG – ISLA MINT

Isla Mint is a natural drug, which has been used to treat the inflammation and dryness of oral mucosa, is extracted from the plant Iceland moss (Scientific name: Cetraria islandica). It contains substances that are characterized by its protective mucous membrane effects and its anti-irritant effect. The dose and therapeutic effectiveness have been analyzed in this clinical study.

Plasma Membrane Effects of Sphingolipid-Synthesis Inhibition by Myriocin in CHO Cells: A Biophysical and Lipidomic Study

Two main strategies for establishing the cellular effects of a given enzyme activity suppression are (a) the use of a stably mutated cell line that lacks a functional gene, or (b) treating the wild type with an inhibitory compound that affects the same gene-product protein. In this work, myriocin was used to block the serine palmitoyltransferase (SPT) enzyme of CHO cells and the subsequent biophysical changes in membranes were measured and compared with results obtained with a genetically modified CHO cell line containing a defective SPT (the LY-B cell line). Similar effects were observed with both approaches: sphingomyelin values were markedly decreased in myriocin-treated CHO cells and, in consequence, their membrane molecular order (measured as laurdan general polarization) and mechanical resistance (AFM-measured breakthrough force values) happened to be lower than in the native, non-treated cells. Cells treated with myriocin reacted homeostatically to maintain membrane order, synthesizing more fully saturated and less polyunsaturated glycerophospholipids than the non-treated ones, although they achieved it only partially, their plasma membranes remaining more fluid and less penetrable than those from the control cells.