Cell membrane permeability coefficients determined by single-step osmotic shift are not applicable for optimization of multi-step addition of cryoprotective agents: As revealed by HepG2 cells

High throughput method for simultaneous screening of membrane permeability and toxicity for discovery of new cryoprotective agents

Vitrification is the most promising method for cryopreservation of complex structures such as organs and tissue constructs. However, this method requires multimolar concentrations of cell-permeant cryoprotective agents (CPAs), which can be toxic at such elevated levels. The selection of CPAs for organ vitrification has been limited to a few chemicals; however, there are numerous chemicals with properties similar to commonly used CPAs. In this study, we developed a high-throughput method that significantly increases the speed of cell membrane permeability measurement, enabling ~100 times faster permeability measurement than previous methods. The method also allows assessment of CPA toxicity using the same 96-well plate. We tested five commonly used CPAs and 22 less common ones at both 4 °C and room temperature, with 23 of them passing the screening process based on their favorable toxicity and permeability properties. Considering its advantages such as high throughput measurement of membrane permeability along with simultaneous toxicity assessment, the presented method holds promise as an effective initial screening tool to identify new CPAs for cryopreservation.

HepG2 cells undergo regulatory volume decrease by mechanically induced efflux of water and solutes

This study challenges the conventional belief that animal cell membranes lack a significant hydrostatic gradient, particularly under anisotonic conditions, as demonstrated in the human hepatoma cell line HepG2. The Boyle van't Hoff (BvH) relation describes volumetric equilibration to anisotonic conditions for many cells. However, the BvH relation is simple and does not include many cellular components such as the cytoskeleton and actin cortex, mechanosensitive channels, and ion pumps. Here we present alternative models that account for mechanical resistance to volumetric expansion, solute leakage, and active ion pumping. We found the BvH relation works well to describe hypertonic volume equilibration but not hypotonic volume equilibration. After anisotonic exposure and return isotonic conditions cell volumes were smaller than their initial isotonic volume, indicating solutes had leaked out of the cell during swelling. Finally, we observed HepG2 cells undergo regulatory volume decrease at both 20 °C and 4 °C, indicating regulatory volume decrease to be a relatively passive phenomenon and not driven by ion pumps. We determined the turgor-leak model, which accounts for mechanical resistance and solute leakage, best fits the observations found in the suite of experiments performed, while other models were rejected.

Silymarin mediated osmotic responses and damage in HepG2 cell suspensions and monolayers

Maintenance of cells within a volume range compatible with their functional integrity is a critical determinant of cell survival after cryopreservation, and quantifying this osmotically induced damage is a part of the rational design of improved cryopreservation protocols. The degree that cells tolerate osmotic stress significantly impacts applicable cryoprotocols, but there has been little research on the time dependence of this osmotic stress. Additionally, the flavonoid silymarin has been shown to be hepatoprotective. Therefore, here we test the hypotheses that osmotic damage is time-dependent and that flavonoid inclusion reduces osmotic damage. In our first experiment, cells were exposed to a series of anisosmotic solutions of graded hypo- and hypertonicity for 10-40 min, resulting in a conclusion that osmotically induced damage is time dependent. In the next experiment, adherent cells preincubated with silymarin at the concentration of 10-4 mol/L and 10-5 mol/L showed a significant increase in cell proliferation and metabolic activity after osmotic stress compared to untreated matched controls. For instance, when adherent cells preincubated with 10-5 mol/L silymarin were tested, resistance to osmotic damage and a significant increase (15%) in membrane integrity was observed in hypo-osmotic media and a 22% increase in hyperosmotic conditions. Similarly, significant protection from osmotic damage was observed in suspended HepG2 cells in the presence of silymarin. Our study concludes that osmotic damage is time dependent, and the addition of silymarin leads to elevated resistance to osmotic stress and a potential increase in the cryosurvival of HepG2 cells.

Effect of cryoprotectant concentration on bovine oocyte permeability and comparison of two membrane permeability modelling approaches

The plasma membrane permeability to water and cryoprotectant (CPA) significantly impacts vitrification efficiency of bovine oocytes. Our study was designed to determine the concentration-dependent permeability characteristics for immature (GV) and mature (MII) bovine oocytes in the presence of ethylene glycol (EG) and dimethyl sulphoxide (Me₂SO), and to compare two different modeling approaches: the two parameter (2P) model and a nondilute transport model. Membrane permeability parameters were determined by consecutively exposing oocytes to increasing concentrations of Me₂SO or EG. Higher water permeability was observed for MII oocytes than GV oocytes in the presence of both Me₂SO and EG, and in all cases the water permeability was observed to decrease as CPA concentration increased. At high CPA concentrations, the CPA permeability was similar for Me₂SO and EG, for both MII and GV oocytes, but at low concentrations the EG permeability of GV oocytes was substantially higher. Predictions of cell volume changes during CPA addition and removal indicate that accounting for the concentration dependence of permeability only has a modest effect, but there were substantial differences between the 2P model and the nondilute model during CPA removal, which may have implications for design of improved methods for bovine oocyte vitrification.

A Freezing Protocol for Hematopoietic Stem Cells

Especially in the field of autologous transplantation, it has been found necessary to develop methods that ensure long-term storage with maintenance of functionality of the cells to bridge the therapy-related temporal separation of collection and application.Based on the experiences of more than 40 years, some practical considerations, especially regarding the cell concentration, final volume, and possibly other exogenous substances, should be considered when establishing a protocol for the routine cryopreservation of peripheral blood stem cells. In the following chapter, we describe a freezing protocol for cryopreservation of peripheral blood stem cells which was used and optimized over the past 8 years and was applied to the cryopreservation of more than 2000 peripheral stem cell transplants.