The Role of Plasma Membrane Viscosity in the Response and Resistance of Cancer Cells to Oxaliplatin

Maintenance of the biophysical properties of membranes is essential for cell survival upon external perturbations. However, the links between a fluid membrane state and the drug resistance of cancer cells remain elusive. Here, we investigated the role of membrane viscosity and lipid composition in the responses of cancer cells to oxaliplatin and the development of chemoresistance. Plasma membrane viscosity was monitored in live colorectal cancer cells and tumor xenografts using two-photon excited fluorescence lifetime imaging microscopy (FLIM) using the fluorescent molecular rotor BODIPY 2. The lipid profile was analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS). It was found that the plasma membrane viscosity increased upon oxaliplatin treatment, both in vitro and in vivo, and that this correlated with lower phosphatidylcholine and higher cholesterol content. The emergence of resistance to oxaliplatin was accompanied by homeostatic adaptation of the membrane lipidome, and the recovery of lower viscosity. These results suggest that maintaining a constant plasma membrane viscosity via remodeling of the lipid profile is crucial for drug resistance in cancer.

Dabigatran Etexilate Induces Cytotoxicity in Rat Gastric Epithelial Cell Line via Mitochondrial Reactive Oxygen Species Production

Dabigatran is a novel oral anticoagulant that directly inhibits free and fibrin-bound thrombins and exerts rapid and predictable anticoagulant effects. While the use of this reagent has been associated with an increased risk of gastrointestinal bleeding, the reason why dabigatran use increases gastrointestinal bleeding risk remains unknown. We investigated the cytotoxicity of dabigatran etexilate and tartaric acid, the two primary components of dabigatran. The cytotoxicity of dabigatran etexilate and tartaric acid was measured in a cell viability assay. Intracellular mitochondrial reactive oxygen species (mitROS) production and lipid peroxidation were measured using fluorescence dyes. Cell membrane viscosity was measured using atomic force microscopy. The potential of ascorbic acid as an inhibitor of dabigatran cytotoxicity was also evaluated. The cytotoxicity of dabigatran etexilate was higher than that of tartaric acid. Dabigatran etexilate induced mitROS production and lipid peroxidation and altered the cell membrane viscosity. Ascorbic acid inhibited the cytotoxicity and mitROS production induced by dabigatran etexilate. Therefore, we attributed the cytotoxicity of dabigatran to dabigatran etexilate, and proposed that the cytotoxic effects of dabigatran etexilate are mediated via mitROS production. Additionally, we demonstrated that dabigatran cytotoxicity can be prevented via antioxidant treatment.

Lattice Boltzmann simulations on the tumbling to tank-treading transition: effects of membrane viscosity

The tumbling to tank-treading (TB-TT) transition for red blood cells (RBCs) has been widely investigated, with a main focus on the effects of the viscosity ratio λ (i.e., the ratio between the viscosities of the fluids inside and outside the membrane) and the shear rate γ ˙ applied to the RBC. However, the membrane viscosity μ m plays a major role in a realistic description of RBC dynamics, and only a few works have systematically focused on its effects on the TB-TT transition. In this work, we provide a parametric investigation on the effect of membrane viscosity μ m on the TB-TT transition for a single RBC. It is found that, at fixed viscosity ratios λ , larger values of μ m lead to an increased range of values of capillary number at which the TB-TT transition occurs; moreover, we found that increasing λ or increasing μ m results in a qualitatively but not quantitatively similar behaviour. All results are obtained by means of mesoscale numerical simulations based on the lattice Boltzmann models. This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’.

Assessing the use of ellipsoidal microparticles for determining lipid membrane viscosity

The viscosity of lipid membranes sets the timescales of membrane-associated flows and therefore influences the dynamics of a wide range of cellular processes. Techniques to measure membrane viscosity remain sparse, however, and reported measurements to date, even of similar systems, give viscosity values that span orders of magnitude. To address this, we improve a method based on measuring both the rotational and translational diffusion of membrane-anchored microparticles and apply this approach and one based on tracking the motion of phase-separated lipid domains to the same system of phase-separated giant vesicles. We find good agreement between the two methods, with inferred viscosities within a factor of two of each other. Our technique uses ellipsoidal microparticles, and we show that the extraction of physically meaningful viscosity values from their motion requires consideration of their anisotropic shape. The validation of our method on phase-separated membranes makes possible its application to other systems, which we demonstrate by measuring the viscosity of bilayers composed of lipids with different chain lengths ranging from 14 to 20 carbon atoms, revealing a very weak dependence of two-dimensional viscosity on lipid size. The experimental and analysis methods described here should be generally applicable to a variety of membrane systems, both reconstituted and cellular.

Viscosity of fluid membranes measured from vesicle deformation

Viscosity is a key mechanical property of cell membranes that controls time-dependent processes such as membrane deformation and diffusion of embedded inclusions. Despite its importance, membrane viscosity remains poorly characterized because existing methods rely on complex experimental designs and/or analyses. Here, we describe a facile method to determine the viscosity of bilayer membranes from the transient deformation of giant unilamellar vesicles induced by a uniform electric field. The method is non-invasive, easy to implement, probe-independent, high-throughput, and sensitive enough to discern membrane viscosity of different lipid types, lipid phases, and polymers in a wide range, from 10−8 to 10−4 Pa.s.m. It enables fast and consistent collection of data that will advance understanding of biomembrane dynamics.