Mammalian Cell Desiccation: Facing The Challenges

Comb-like Pseudopeptides Enable Very Rapid and Efficient Intracellular Trehalose Delivery for Enhanced Cryopreservation of Erythrocytes

Cell cryopreservation plays a key role in the development of reproducible and cost-effective cell-based therapies. Trehalose accumulated in freezing- and desiccation-tolerant organisms in nature has been sought as an attractive nontoxic cryoprotectant. Herein, we report a coincubation method for very rapid and efficient delivery of membrane-impermeable trehalose into ovine erythrocytes through reversible membrane permeabilization using pH-responsive, comb-like pseudopeptides. The pseudopeptidic polymers containing relatively long alkyl side chains were synthesized to mimic membrane-anchoring fusogenic proteins. The intracellular trehalose delivery efficiency was optimized by manipulating the side chain length, degree of substitution, and concentration of the pseudopeptides with different hydrophobic alkyl side chains, the pH, temperature, and time of incubation, as well as the polymer-to-cell ratio and the concentration of extracellular trehalose. Treatment of erythrocytes with the comb-like pseudopeptides for only 15 min yielded an intracellular trehalose concentration of 177.9 ± 8.6 mM, which resulted in 90.3 ± 0.7% survival after freeze-thaw. The very rapid and efficient delivery was found to be attributed to the reversible, pronounced membrane curvature change as a result of strong membrane insertion of the comb-like pseudopeptides. The pseudopeptides can enable efficient intracellular delivery of not only trehalose for improved cell cryopreservation but also other membrane-impermeable cargos.

Dry Preservation of Spermatozoa: Considerations for Different Species

The current gold standard for sperm preservation is storage at cryogenic temperatures. Dry preservation is an attractive alternative, eliminating the need for ultralow temperatures, reducing storage maintenance costs, and providing logistical flexibility for shipping. Many seeds and anhydrobiotic organisms are able to survive extended periods in a dry state through the accumulation of intracellular sugars and other osmolytes and are capable of returning to normal physiology postrehydration. Using techniques inspired by nature's adaptations, attempts have been made to dehydrate and dry preserve spermatozoa from a variety of species. Most of the anhydrous preservation research performed to date has focused on mouse spermatozoa, with only a small number of studies in nonrodent mammalian species. There is a significant difference between sperm function in rodent and nonrodent mammalian species with respect to centrosomal inheritance. Studies focused on reproductive technologies have demonstrated that in nonrodent species, the centrosome must be preserved to maintain sperm function as the spermatozoon centrosome contributes the dominant nucleating seed, consisting of the proximal centriole surrounded by pericentriolar components, onto which the oocyte's centrosomal material is assembled. Preservation techniques used for mouse sperm may therefore not necessarily be applicable to nonrodent spermatozoa. The range of technologies used to dehydrate sperm and the effect of processing and storage conditions on fertilization and embryogenesis using dried sperm are reviewed in the context of reproductive physiology and cellular morphology in different species.

Stabilization of Transfected Cells Expressing Low-Incidence Blood Group Antigens: Novel Methods Facilitating Their Use as Reagent-Cells

Background

The identification of erythrocyte antibodies in the serum of patients rely on panels of human red blood cells (RBCs), which coexpress many antigens and are not easily available for low-incidence blood group phenotypes. These problems have been addressed by generating cell lines expressing unique blood group antigens, which may be used as an alternative to human RBCs. However, the use of cell lines implies several drawbacks, like the requirement of cell culture facilities and the high cost of cryopreservation. The application of cell stabilization methods could facilitate their use as reagent cells in clinical laboratories.

Methods

We generated stably-transfected cells expressing low-incidence blood group antigens (Di^a and Lu^a). High-expresser clones were used to assess the effect of TransFix^® treatment and lyophilization as cell preservation methods. Cells were kept at 4°C and cell morphology, membrane permeability and antigenic properties were evaluated at several time-points after treatment.

Results

TransFix^® addition to cell suspensions allows cell stabilization and proper antigen detection for at least 120 days, despite an increase in membrane permeability and a reduction in antigen expression levels. Lyophilized cells showed minor morphological changes and antigen expression levels were rather conserved at days 1, 15 and 120, indicating a high stability of the freeze-dried product. These stabilized cells have been proved to react specifically with human sera containing alloantibodies.

Conclusions

Both stabilization methods allow long-term preservation of the transfected cells antigenic properties and may facilitate their distribution and use as reagent-cells expressing low-incidence antigens, overcoming the limited availability of such rare RBCs.

Nanoparticle-mediated intracellular delivery enables cryopreservation of human adipose-derived stem cells using trehalose as the sole cryoprotectant

In this study, pH responsive genipin-cross-linked Pluronic F127-chitosan nanoparticles (GNPs) was synthesized to encapsulate trehalose for intracellular delivery to cryopreserve primary human adipose-derived stem cells (hADSCs). Trehalose is a disaccharide of glucose used by lower organisms to survive extreme cold in nature and has been used to cryopreserve various biomacromolecules. However, it does not enter mammalian cells because of its highly hydrophilic nature, and has only been used in combination with other cell-penetrating cryoprotectants (such as dimethyl sulfoxide, DMSO) to cryopreserve mammalian cells. Our data show that trehalose can be efficiently encapsulated in our GNPs for intracellular delivery, which enables cryopreservation of primary hADSCs using the nontoxic sugar as the sole cryoprotectant. This capability is important because the conventional approach of cryopreserving mammalian cells using highly toxic (at body temperature) cell-penetrating cryoprotectants requires multistep washing of the cryopreserved cells to remove the toxic cryoprotectant for further use, which is time-consuming and associated with significant cell loss (∼10% during each washing step). By contrast, the trehalose-cryopreserved cells can be used without washing, which should greatly facilitate the wide application of the burgeoning cell-based medicine.

Dry state preservation of nucleated cells: progress and challenges

Effective stabilization of nucleated cells for dry storage would be a transformative development in the field of cell-based biosensors and biotechnologic devices, as well as regenerative medicine and other areas in which stem cells have clinical utility. Ultimately, the tremendous promise of cell-based products will only be fully realized when stable long-term storage becomes available without the use of liquid nitrogen and bulky, energetically expensive freezers. Significant progress has been made over the last 10 years toward this goal, but obstacles still remain. Loading cells with the protective disaccharide trehalose has been achieved by several different techniques and has been shown to increase cell survival at low water contents. Likewise, the protective effect of heat shock proteins and other compounds have also been explored alone and in combination with trehalose. In some cases, the benefit of these molecules is seen not initially upon rehydration, but over time during cellular recovery. Other considerations, such as inhibiting apoptosis and utilizing isotonic buffer conditions have also provided stepwise increases in cell viability and function following drying and rehydration. In all these cases, however, a low level of residual water is required to achieve viability after rehydration. The most significant remaining challenge is to protect nucleated cells such that this residual water can be safely removed, thus allowing vitrification of intra- and extracellular trehalose and stable dry state storage at room temperature.

Non-ideal solution thermodynamics of cytoplasm

Quantitative description of the non-ideal solution thermodynamics of the cytoplasm of a living mammalian cell is critically necessary in mathematical modeling of cryobiology and desiccation and other fields where the passive osmotic response of a cell plays a role. In the solution thermodynamics osmotic virial equation, the quadratic correction to the linear ideal, dilute solution theory is described by the second osmotic virial coefficient. Herein we report, for the first time, intracellular solution second osmotic virial coefficients for four cell types [TF-1 hematopoietic stem cells, human umbilical vein endothelial cells (HUVEC), porcine hepatocytes, and porcine chondrocytes] and further report second osmotic virial coefficients indistinguishable from zero (for the concentration range studied) for human hepatocytes and mouse oocytes.

Direct action of radiation on mummified cells: modeling of computed tomography by Monte Carlo algorithms

X-ray imaging is a nondestructive and preferred method in paleopathology to reconstruct the history of ancient diseases. Sophisticated imaging technologies such as computed tomography (CT) have become common for the investigation of skeletal disorders in human remains. Researchers have investigated the impact of ionizing radiation on living cells, but never on ancient cells in dry tissue. The effects of CT exposure on ancient cells have not been examined in the past and may be important for subsequent genetic analysis. To remedy this shortcoming, we developed different Monte Carlo models to simulate X-ray irradiation on ancient cells. Effects of mummification were considered by using two sizes of cells and three different phantom tissues, which enclosed the investigated cell cluster. This cluster was positioned at the isocenter of a CT scanner model, where the cell hit probabilities P(0,1,…, n) were calculated according to the Poisson distribution. To study the impact of the dominant physics process, CT scans for X-ray spectra of 80 and 120 kVp were simulated. Comparison between normal and dry tissue phantoms revealed that the probability of unaffected cells increased by 21 % following cell shrinkage for 80 kVp, while for 120 kVp, a further increase of unaffected cells of 23 % was observed. Consequently, cell shrinkage caused by dehydration decreased the impact of X-ray radiation on mummified cells significantly. Moreover, backscattered electrons in cortical bone protected deeper-lying ancient cells from radiation damage at 80 kVp X-rays.

Response of the cell membrane-cytoskeleton complex to osmotic and freeze/thaw stresses. Part 2: The link between the state of the membrane-cytoskeleton complex and the cellular damage

In an earlier paper [35], we examined the mutual interaction between the actin cytoskeleton and the cell membrane and explored the role this interaction plays during freeze/thaw. In this follow-up paper, we investigate the physical and chemical stresses induced by freeze/thaw and explore the different mechanisms of damage caused by these stresses. Our results showed that changes in cell volume during freeze/thaw and the unfrozen water content in the solution alter the cytoskeleton stiffness, and the available membrane material. Combined with unfavorable ice-membrane interactions and increasing membrane stiffness, increased de-structuring of the membrane (such as bleb and microvilli formation) synergistically act on the membrane-cytoskeleton system generating irreversible damage.

Sugars comparable to glutathione as hemoglobin oxidation protectants during vacuum drying

One of the most significant challenges to stabilization of blood in the dry state is mitigation of hemoglobin oxidation. Here, oxidation of free hemoglobin vacuum desiccated in phosphate-buffered saline alone reached 65%±5%. Arabinose, glucose, sucrose, trehalose, and raffinose at 100 mM were shown to reduce oxidation to 24%±2%, 23%±2%, 3%±1%, 8%±3%, and 7%±2%, respectively. For comparison, 100 mM glutathione allowed 5%±2% hemoglobin oxidation. Oxidation protection provided by glucose, sucrose, and trehalose was shown to increase with concentration between 5 and 100 mM, plateauing thereafter. Oxidation of hemoglobin dried in the presence of 100 mM trehalose was shown to increase with decreasing initial pH.

The induction of anhydrobiosis in the sleeping chironomid: current status of our knowledge

An African chironomid, Polypedilum vanderplanki, is the only insect known to be capable of extreme desiccation tolerance, or anhydrobiosis. In the 1950s and 1960s, Hinton strenuously studied anhydrobiosis in this insect from a physiological standpoint; however, nobody has afterward investigated the phenomenon. In 2000, research on mechanisms underlying anhydrobiosis was resumed due to successful establishment of a rearing system for P. vanderplanki. This review is focused on the latest findings on the physiological and molecular mechanisms underlying the induction of anhydrobiosis in P. vanderplanki. Early experiments demonstrated that the induction of anhydrobiosis was possible in isolated tissues and independent from the control of central nervous system. However, to achieve successful anhydrobiosis, larvae need a slow regime of desiccation, allowing them to synthesize molecules, which will protect cells and tissues against the deleterious effects of dehydration. Trehalose, a nonreducing disaccharide, which accumulates in P. vanderplanki larvae up to 20% of the dry body mass, is thought to replace the water in its tissues. Similarly, highly hydrophilic proteins called the late embryogenesis abundant (LEA) proteins are expressed in huge quantities and act as a molecular shield to protect biological molecules against aggregation and denaturation. This function is shared by heat shock proteins, which are also upregulated during the desiccation process. At the same time, desiccating larvae express various antioxidant molecules and enzymes, to cope with the massive oxidative stress, which is responsible for general damage to membranes, proteins, and DNA in dehydrating cells. Finally, specific water channels, called aquaporins, accelerate dehydration, and trehalose together with LEA proteins forms a glassy matrix, which protects the biological molecules and the structural integrity of larvae in the anhydrobiotic state.

Response of the cell membrane-cytoskeleton complex to osmotic and freeze/thaw stresses

In order to develop successful cryopreservation protocols a better understanding of the freeze- and dehydration-induced changes occurring in the cell membrane and its underlying support, the actin cytoskeleton, is required. In this study, we compared the biophysical response of model mammalian cells (human foreskin fibroblasts) to hyperosmotic stress and freeze/thaw. Transmitted light, infrared spectroscopy, fluorescence- and cryo-microscopy were used to investigate the changes in the cell membrane and the actin cytoskeleton. We observed that a purely hyperosmotic challenge at room temperature resulted in bleb formation. A decrease in temperature abrogated the blebbing behavior, but was accompanied by a decrease in viability. These results suggested that cell survival depended on the availability of the membrane material to accommodate the volumetric expansion back to the original cell volume at isotonic conditions. Our data also showed that freeze/thaw stresses altered the cell membrane morphology resulting in a loss of membrane material. There was also a significantly lower incidence of blebbing after freeze/thaw as compared to isothermal osmotic stress experiments at room temperature. Significant depolymerization of the actin cytoskeleton was seen in cells whose membranes had been compromised by freeze/thaw stresses. Actin depolymerization using cytochalasin D affected the stability of the membrane against mechanical stress at isothermal conditions. This study shows that both the membrane and cytoskeleton, as a system, are involved in the osmotic and freeze/thaw-induced responses of the mammalian cells.

Collapse temperature of solutions important for lyopreservation of living cells at ambient temperature

In this study, the collapse temperature was determined using the freeze-drying microscopy (FDM) method for a variety of cell culture medium-based solutions (with 0.05-0.8 M trehalose) that are important for long-term stabilization of living cells in the dry state at ambient temperature (lyopreservation) by freeze-drying. Being consistent with what has been reported in the literature, the collapse temperature of binary water-trehalose solutions was found to be similar to the glass transition temperature (T'(g) approximately -30 degrees C) of the maximally freeze-concentrated trehalose solution (approximately 80 wt% trehalose) during the freezing step of freeze-drying, regardless of the initial concentration of trehalose. However, the effect of the initial trehalose concentration on the collapse temperature of the cell culture medium-based trehalose solutions was identified to be much more significant, particularly when the trehalose concentration is less than 0.2 M (the collapse temperature can be as low as -65 degrees C). We also determined that cell density from 1 to 10 million cells/mL and ice seeding at high subzero temperatures (-4 and -7 degrees C) have negligible impact on the solution collapse temperature. However, ice seeding does significantly affect the ice crystal morphology formed during the freezing step and therefore the drying rate. Finally, bulking agents (mannitol) could significantly affect the collapse temperature only when trehalose concentration is low (<0.2 M). However, improving the collapse temperature by using a high concentration of trehalose might be preferred to the addition of bulking agents in the solutions for freeze-drying of living cells. We further confirmed the applicability of the collapse temperature measured with small-scale (2 microL) samples using the FDM system to freeze-drying of large-scale (1 mL) samples using scanning electron microscopy (SEM) data. Taken together, the results reported in this study should provide useful guidance to the development of optimal freeze-drying protocols for lyopreservation of living cells at ambient temperature for easy maintenance and convenient wide distribution to end users, which is important to the eventual success of modern cell-based medicine.

Ectoines in cell stress protection: uses and biotechnological production

Microorganisms produce and accumulate compatible solutes aiming at protecting themselves from environmental stresses. Among them, the wide spread in nature ectoines are receiving increasing attention by the scientific community because of their multiple applications. In fact, increasing commercial demand has led to a multiplication of efforts in order to improve processes for their production. In this review, the importance of current and potential applications of ectoines as protecting agents for macromolecules, cells and tissues, together with their potential as therapeutic agents for certain diseases are analyzed and current theories for the understanding of the molecular basis of their biological activity are discussed. The genetic, biochemical and environmental determinants of ectoines biosynthesis by natural and engineered producers are described. The major limitations of current bioprocesses used for ectoines production are discussed, with emphasis on the different microorganisms, environments, molecular engineering and fermentation strategies used to optimize the production and recovery of ectoines. The combined application of both bioprocess and metabolic engineering strategies, allowing a deeper understanding of the main factors controlling the production process is also stated. Finally, this review aims to summarize and update the state of the art in ectoines uses and applications and industrial scale production using bacteria, emphasizing the importance of reactor design and operation strategies, together with the metabolic engineering aspects and the need for feedback between wet and in silico work to optimize bioproduction.

Biopreservation of red blood cells--the struggle with hemoglobin oxidation

One of the least recognized causes of cellular damage during ex vivo preservation of red blood cells is oxidative injury to the hemoglobin. The latter has been associated with hemolysis through the release of toxic substances and oxidation of vital cell components. This review delineates some of the major pathways that link hemoglobin oxidation and cellular damage, and summarizes the incidence of red blood cell oxidative injury during hypothermic storage, cryopreservation and desiccation stress. Red blood cell hypothermic storage, despite its success, is not exempt from oxidative injury. Growing evidence portrays a time-dependant oxidative assault including formation of reactive oxygen species, attachment of denatured hemoglobin to membrane phospholipids and the release of hemoglobin-containing membrane microvesicles throughout storage. Similar symptoms have been observed in attempts to stabilize red blood cells in the dried state, in which methemoglobin levels of reconstituted red blood cells reached 50%. Factors affecting the rate of hemoglobin oxidation during red blood cell ex vivo storage include compromised antioxidant activity, high concentrations of glucose in the storage media and the presence of molecular oxygen. Hemoglobin oxidation largely dictates our ability to effectively preserve red blood cells. Understanding its origins along with investigating methods to minimize it can significantly improve the quality of our future blood products.

Drying and rehydration of DLPC/DSPC symmetric and asymmetric supported lipid bilayers: a combined AFM and fluorescence microscopy study

This work characterizes the impact of lipid symmetry/asymmetry on drying/rehydration reorganization in phase-separated dilauroylphosphatidylcholine (DLPC)/distearoylphosphatidylcholine (DSPC) supported lipid bilayers (SLBs) at the submicron and micron-scale. In addition the prevention of major drying/rehydration reorganization by the use of trehalose is demonstrated. Even though it was found using fluorescence microscopy that micrometer scale structure is preserved in the presence and absence of trehalose upon drying/rehydration, AFM and FRAP experiments successfully revealed major changes in the phase-separated structure such as defects, obstructions, lipid condensation, collapse structures, and complex incomplete DLPC-DSPC mixing/exchange in the absence of trehalose. In the presence of trehalose the membrane preserves its structure at the nanometer scale and mobility. We found that SLBs with asymmetric domain configurations underwent major rearrangements during drying and rehydration, whereas the symmetric domain configuration mainly rearranged during rehydration, that we hypothesize is related to lower transmembrane cohesiveness or lack of anchoring to the substrate in the case of the asymmetric domains.

Compatible solute influence on nucleic acids: many questions but few answers

Compatible solutes are small organic osmolytes including but not limited to sugars, polyols, amino acids, and their derivatives. They are compatible with cell metabolism even at molar concentrations. A variety of organisms synthesize or take up compatible solutes for adaptation to extreme environments. In addition to their protective action on whole cells, compatible solutes display significant effects on biomolecules in vitro. These include stabilization of native protein and nucleic acid structures. They are used as additives in polymerase chain reactions to increase product yield and specificity, but also in other nucleic acid and protein applications.

Interactions of compatible solutes with nucleic acids and protein-nucleic acid complexes are much less understood than the corresponding interactions of compatible solutes with proteins. Although we may begin to understand solute/nucleic acid interactions there are only few answers to the many questions we have. I summarize here the current state of knowledge and discuss possible molecular mechanisms and thermodynamics.

Hydrophilic protein associated with desiccation tolerance exhibits broad protein stabilization function

The ability of certain plants, invertebrates, and microorganisms to survive almost complete loss of water has long been recognized, but the molecular mechanisms of this phenomenon remain to be defined. One phylogenetically widespread adaptation is the presence of abundant, highly hydrophilic proteins in desiccation-tolerant organisms. The best characterized of these polypeptides are the late embryogenesis abundant (LEA) proteins, first described in plant seeds >20 years ago but recently identified in invertebrates and bacteria. The function of these largely unstructured proteins has been unclear, but we now show that a group 3 LEA protein from the desiccation-tolerant nematode Aphelenchus avenae is able to prevent aggregation of a wide range of other proteins both in vitro and in vivo. The presence of water is essential for maintenance of the structure of many proteins, and therefore desiccation stress induces unfolding and aggregation. The nematode LEA protein is able to abrogate desiccation-induced aggregation of the water-soluble proteomes from nematodes and mammalian cells and affords protection during both dehydration and rehydration. Furthermore, when coexpressed in a human cell line, the LEA protein reduces the propensity of polyglutamine and polyalanine expansion proteins associated with neurodegenerative diseases to form aggregates, demonstrating in vivo function of an LEA protein as an antiaggregant. Finally, human cells expressing LEA protein exhibit increased survival of dehydration imposed by osmotic upshift, consistent with a broad protein stabilization function of LEA proteins under conditions of water stress.