Theoretical and experimental study of the antifreeze protein AFP752, trehalose and dimethyl sulfoxide cryoprotection mechanism: correlation with cryopreserved cell viability

Structural investigation, computational analysis, and theoretical cryoprotectant approach of antifreeze protein type IV mutants

Antifreeze proteins (AFPs) have unique features to sustain life in sub-zero environments due to ice recrystallization inhibition (IRI) and thermal hysteresis (TH). AFPs are in demand as agents in cryopreservation, but some antifreeze proteins have low levels of activity. This research aims to improve the cryopreservation activity of an AFPIV. In this in silico study, the helical peptide afp1m from an Antarctic yeast AFP was modeled into a sculpin AFPIV, to replace each of its four α-helices in turn, using various computational tools. Additionally, a new linker between the first two helices of AFPIV was designed, based on a flounder AFPI, to boost the ice interaction activity of the mutants. Bioinformatics tools such as ExPASy Prot-Param, Pep-Wheel, SOPMA, GOR IV, Swiss-Model, Phyre2, MODFOLD, MolPropity, and ProQ were used to validate and analyze the structural and functional properties of the model proteins. Furthermore, to evaluate the AFP/ice interaction, molecular dynamics (MD) simulations were executed for 20, 100, and 500 ns at various temperatures using GROMACS software. The primary, secondary, and 3D modeling analysis showed the best model for a redesigned antifreeze protein (AFP1mb, with afp1m in place of the fourth AFPIV helix) with a QMEAN (Swiss-Model) Z score value of 0.36, a confidence of 99.5%, a coverage score of 22%, and a p value of 0.01. The results of the MD simulations illustrated that AFP1mb had more rigidity and better ice interactions as a potential cryoprotectant than the other models; it also displayed enhanced activity in limiting ice growth at different temperatures.

Analysis of the Nonequilibrium Phase Change Behaviors of the Cryoprotectant Solutions for Cryopreservation of Human Red Blood Cells with Low-Concentration Glycerol

Recently, we proposed a low-glycerol cryoprotectant formulation (consisting of 0.4 M trehalose and 5% glycerol) for cryopreservation of human red blood cells (RBCs), which greatly reduced the concentration of glycerol, minimized intracellular ice damage, and achieved high recovery. Although this study was successful in cellular experiments, the nonequilibrium phase transition behaviors of the cryoprotective agent solution have not been systematically analyzed. Therefore, it is essential to provide reliable thermodynamic data to substantiate the viability of this cryopreservation technique. In this study, the phase change behaviors and thermal properties of typical trehalose and/or glycerol solutions quenched in liquid nitrogen were investigated using differential scanning calorimetry and cryomicroscopy. It was found that the glass transition temperatures of both the trehalose aqueous solution (<1.0 M) and glycerol aqueous solution (<40% w/v) did not vary apparently with the concentration at low concentrations, while they increased significantly with increasing concentration at high concentrations. Moreover, it was revealed that the inhibitory effect of trehalose on ice growth was affected by glycerol. We further found that the addition of low concentrations of glycerol facilitates the partial glass transition of trehalose solutions at low concentrations. The results of this work provide reliable thermodynamic data to support the cryopreservation of human RBCs with unusually low concentrations of glycerol.

Plunge-Freezing Cryopreservation of Tendons

Allograft transplantation is an important method for tendon reconstruction after injury, and its clinical success highly relies on the storage and transportation of the grafts. Cryopreservation is a promising strategy for tendon storage. In this study, we report a novel cryopreservation agent (CPA) formulation with a high biocompatibility for tendon cryopreservation. Mainly composed of natural zwitterionic betaine and the biocompatible polymer poly(vinylpyrrolidone) (PVP), it exhibited ideal abilities to depress the freezing point and inhibit ice growth and recrystallization. Notably, after cryopreservation via plunge-freezing for 1 month, Young's modulus (144 MPa, 98% of fresh tendons) and ultimate stress (46.7 MPa, 99% of fresh tendons) remained stable, and the cross-linking of collagen microfibers, protein structures, and glycosaminoglycan (GAG) contents changed slightly. These results indicate that the formulation (5 wt % betaine and 5 wt % PVP in phosphate-buffered saline, PBS solution) effectively maintains the biomechanical properties and tissue structure. This work offers a novel cryopreservation method for tendons and may also provide insights into the long-term preservation of various other tissues.

Furcellaran: Impact of Concentration, Rheological Properties, and Structure on Ice Recrystallization Inhibition Activity

Recrystallization is considered the main damaging mechanism during the frozen storage of biologic materials. In this study, furcellaran, a polysaccharide related to κ-carrageenan, was studied for its concentration-dependent effect on ice crystal growth and recrystallization. The structure and sulfate content of the utilized furcellaran was analyzed by 1H nuclear magnetic resonance spectroscopy, ion chromatography, and high-performance size-exclusion chromatography. Additionally, the rheological properties of furcellaran solutions were investigated. Our findings demonstrate that furcellaran inhibits ice growth as effectively as κ-carrageenan. Furthermore, the rheological properties change with increasing furcellaran concentration, resulting in a gel-like consistency at 5 g/L, which coincides with decreased recrystallization inhibition activity and larger crystals. This suggests that gel formation or a gel-like consistency has to be avoided for optimal recrystallization inhibition activity.

Improving vitrification efficiency of human in vitro matured oocytes by the addition of LEA proteins

STUDY QUESTION

Can the addition of late embryogenesis-abundant (LEA) proteins as a cryoprotective agent during the vitrification cryopreservation of in vitro matured oocytes enhance their developmental potential after fertilization?

SUMMARY ANSWER

LEA proteins improve the developmental potential of human in vitro matured oocytes following cryopreservation, mostly by downregulating FOS genes, reducing oxidative stress, and inhibiting the formation of ice crystals.

WHAT IS KNOWN ALREADY

Various factors in the vitrification process, including cryoprotectant toxicity, osmotic stress, and ice crystal formation during rewarming, can cause fatal damage to oocytes, thereby affecting the oocytes developmental potential and subsequent clinical outcomes. Recent studies have shown that LEA proteins possess high hydrophilicity and inherent stress tolerance, and can reduce low-temperature damage, although the molecular mechanism it exerts protective effects is still unclear.

STUDY DESIGN, SIZE, DURATION

Two LEA proteins extracted and purified by us were added to solutions for vitrification-warming of oocytes at concentrations of 10, 100, and 200 µg/mL, to determine the optimal protective concentration for each protein. Individual oocyte samples were collected for transcriptomic analysis, with each group consisting of three sample replicates.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Immature oocytes were collected from patients who were undergoing combined in vitro fertilization (IVF) treatment and who had met the designated inclusion and exclusion criteria. These oocytes underwent in vitro maturation (IVM) culture for experimental research. A fluorescence microscope was used to detect the levels of mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and calcium in the mitochondria of vitrified-warmed human oocytes treated with different concentrations of LEA proteins, and the protective effect of the protein on mitochondrial function was assessed. The levels of intracellular ice recrystallization inhibition (IRI) in human oocytes after vitrification-warming were characterized by the cryomicroscope, to determine the LEA proteins inhibitory effect on recrystallization. By analyzing transcriptome sequencing data to investigate the potential mechanism through which LEA proteins exert their cryoprotective effects.

MAIN RESULTS AND THE ROLE OF CHANCE

The secondary structures of AfrLEA2 and AfrLEA3m proteins were shown to consist of a large number of α-helices and the proteins were shown to be highly hydrophilic, in agreement with previous reports. Confocal microscopy results showed that the immunofluorescence of AfrLEA2-FITC and AfrLEA3m-FITC-labeled proteins appeared to be extracellular and did not penetrate the cell membrane compared with the fluorescein isothiocyanate (FITC) control group, indicating that both AfrLEA2 and AfrLEA3m proteins were extracellular. The group treated with 100 µg/mL AfrLEA2 or AfrLEA3m protein had more uniform cytoplasmic particles and fewer vacuoles compared to the 10 and 200 µg/mL groups and were closest to the fresh group. In the 100 µg/mL groups, MMPs were significantly higher while ROS and calcium levels were significantly lower than those in the control group and were closer to the levels observed in fresh oocytes. Meanwhile, 100 µg/mL of AfrLEA2 or AfrLEA3m protein caused smaller ice crystal formation in the IRI assay compared to the control group treated with dimethylsulphoxide (DMSO) and ethylene glycol (EG); thus, the recrystallization inhibition was superior to that with the conventional cryoprotectants DMSO and EG. Further results revealed that the proteins improved the developmental potential of human oocytes following cryopreservation, likely by downregulating FOS genes and reducing oxidative stress.

LIMITATIONS, REASONS FOR CAUTION

The in vitro-matured metaphase II (IVM-MII) oocytes used in the study, due to ethical constraints, may not accurately reflect the condition of MII oocytes in general. The AfrLEA2 and AfrLEA3m proteins are recombinant proteins and their synthetic stability needs to be further explored.

WIDER IMPLICATIONS OF THE FINDINGS

LEA proteins, as a non-toxic and effective cryoprotectant, can reduce the cryoinjury of oocytes during cryopreservation. It provides a new promising method for cryopreservation of various cell types.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Key Research and Development Program of China (2022YFC2703000) and the National Natural Science Foundation of China (52206064). The authors declare no competing interest.

TRIAL REGISTRATION NUMBER

N/A.

Microplate-Based Cryopreservation of Adherent-Cultured Human Cell Lines Using Amino Acids and Proteins

With the progression of regenerative medicine and cell therapy, the importance of cryopreservation techniques for cultured cells continues to rise. Traditional cryoprotectants, such as dimethyl sulfoxide and glycerol, are effective in cryopreserving suspended cells, but they do not demonstrate sufficient efficacy for two-dimensional (2D)-cultured cells. In the past decade, small molecules and polymers have been studied as cryoprotectants. Some L-amino acids have been reported to be natural and biocompatible cryoprotectants. However, the cryoprotective effects of D-amino acids have not been investigated for such organized cells. In the present study, the cryoprotective effects of D- and L-amino acids and previously reported cryoprotectants were assessed using HepG2 cells cultured on a microplate without suspending the cells. d-Proline had the highest cryoprotective effect on 2D-cultured cells. The composition of the cell-freezing solution and freezing conditions were then optimized. The d-proline-containing cell-freezing solution also effectively worked for other cell lines. To minimize the amount of animal-derived components, fetal bovine serum in the cell freezing solution was substituted with bovine serum albumin and StemFit (a commercial supplement for stem cell induction). Further investigations on the mechanism of cryopreservation suggested that d-proline protected enzymes essential for cell survival from freeze-induced damage. In conclusion, an effective and xeno-free cell-freezing solution was produced using d-proline combined with dimethyl sulfoxide and StemFit for 2D-cultured cells.

Elevated fucose content enhances the cryoprotective performance of anionic polysaccharides

Biological cryopreservation often involves using a cryoprotective agent (CPA) to mitigate lethal physical stressors cells endure during freezing and thawing, but effective CPA concentrations are cytotoxic. Hence, natural polysaccharides have been studied as biocompatible alternatives. Here, a subset of 26 natural polysaccharides of various chemical composition was probed for their potential in enhancing the metabolic post-thaw viability (PTV) of cryopreserved Vero cells. The best performing cryoprotective polysaccharides contained significant fucose amounts, resulting in average PTV 2.8-fold (up to 3.1-fold) compared to 0.8-fold and 2.2-fold for all non-cryoprotective and cryoprotective polysaccharides, respectively, outperforming the optimized commercial CryoStor™ CS5 formulation (2.6-fold). Stoichiometrically, a balance between fucose (18-35.7 mol%), uronic acids (UA) (13.5-26 mol%) and high molecular weight (MW > 1 MDa) generated optimal PTV. Principal component analysis (PCA) revealed that fucose enhances cell survival by a charge-independent, MW-scaling mechanism (PC1), drastically different from the charge-dominated ice growth disruption of UA (PC2). Its neutral nature and unique properties distinguishable from other neutral monomers suggest fucose may play a passive role in conformational adaptability of polysaccharide to ice growth inhibition, or an active role in cell membrane stabilization through binding. Ultimately, fucose-rich anionic polysaccharides may indulge in polymer-ice and polymer-cell interactions that actively disrupt ice and minimize lethal volumetric fluctuations due to a balanced hydrophobic-hydrophilic character. Our research showed the critical role neutral fucose plays in enhancing cellular cryopreservation outcomes, disputing previous assumptions of polyanionicity being the sole governing predictor of cryoprotection.

Human Natural Killer Cells Cryopreserved without DMSO Sustain Robust Effector Responses

Natural killer (NK) cell-based immunotherapy has benefitted from the multiple strengths that NK cells offer in adoptive transfer settings, not the least of which is their safety and potential for allogeneic use. Such use, however, necessitates the cryopreservation of NK cell-based therapy products to support logistical efforts in deploying these cells in different locations, decentralized from the point of collection or manufacturing. DMSO, the most commonly used cryoprotective agent (CPA), has been effective in protecting immune cells during freezing and thawing, but its ability to induce molecular and genetic changes to immune cells as well as its toxicity has stimulated interest in alternative CPAs. However, replacing DMSO's ability to act intracellularly has been difficult, and the sensitivity of human peripheral blood-derived NK cells to freezing and thawing-induced damage has meant that investigations into the potential of replacing DMSO are lacking. As a first step toward establishing the feasibility of cryopreserving human NK cells with CPAs' alternative to DMSO, we investigate the potential of using noncell-penetrating and cell-penetrating CPAs to recover NK cells post-thaw without DMSO. Here, we find that cryoprotection using cell-penetrating CPAs can retain the viability of human peripheral blood-derived NK cells to a comparable degree to DMSO. In addition, non-DMSO-cryopreserved human NK cells were as cytotoxic as those cryopreserved with DMSO and displayed a comparable level of surface markers of activation. In summary, we present the first example of the potential of developing non-DMSO CPA formulations that could be deployed in future cell therapy regimens.

Open-source hardware- and software-based cryomicroscopy system for investigation of phase transitions in cryobiological research

The development of inexpensive equipment adapted for the study of a specific biological object is very important for cryobiology. In the presented work, we have proposed a simple system for microscopy utilising open-source platform Arduino. Testing this system showed that it had sufficient sensitivity to determine the physical processes occurring in a cryopreserved sample such as intra- and extracellular water crystallisation and salt eutectic. Utilising this system, we investigated the mechanisms of cryoprotection and cryodamage of testis interstitial cells (ICs) in cryoprotective media, which included cryoprotective agents such as dimethyl sulphoxide (Me2 SO), as well as foetal bovine serum or polymers (dextran, hydroxyethyl starch and polyethylene glycol). It was shown that a serum-/xeno-free medium that included 0.7 M Me2 SO and 100 mg/mL dextran was able to reduce intracellular water crystallisation in cells, change the structure of extracellular ice, and reduce salt eutectic and recrystallisation. All these effects correlated with better IC survival after cryopreservation in the medium. This medium is potentially less toxic as it has lower concentrations of Me2 SO compared to serum-containing media developed for cryopreservation of testicular cells. This would pave a way for the creation of nontoxic serum-free compositions that does not require removal before use of cryopreserved living cells for laboratory practice or in clinics.

Physicochemical Mechanisms of Protection Offered by Agarose Encapsulation during Cryopreservation of Mammalian Cells in the Absence of Membrane-Penetrating Cryoprotectants

During freeze/thaw, cells are exposed to mechanical, thermal, chemical, and osmotic stresses, which cause loss of viability and function. Cryopreservation agents such as dimethyl sulfoxide (DMSO) are deployed to minimize freeze/thaw damage. However, there is a pressing need to eliminate DMSO from cryopreservation solutions due to its adverse effects. This is of the highest priority especially for cryopreservation of infusible/transplantable cell therapy products. In order to address this issue, we introduce reversible encapsulation in agarose hydrogels in the presence of the membrane-impermeable cryoprotectant, trehalose, as a viable, safe, and effective cryopreservation method. Our findings, which are supported by IR spectroscopy and differential scanning calorimetry analyses, demonstrate that encapsulation in 0.75% agarose hydrogels containing 10-20% trehalose inhibits mechanical damage induced by eutectic phase change, devitrification, and recrystallization, resulting in post-thaw viability comparable to the gold standard 10% DMSO.

A biocompatible cell cryoprotectant based on sulfoxide-containing amino acids: mechanism and application

The preservation of cells at cryogenic temperatures requires the presence of cryoprotectants (CPAs). Dimethyl sulfoxide (DMSO), as a state-of-the-art CPA, is widely used for the storage of many types of cells. However, its intrinsic toxicity is still an obstacle for its applications in clinical practice. Herein, we report a DMSO analogue, L-methionine sulfoxide (Met(O)-OH), as a CPA for cell cryopreservation. The molecular-level cryopreservation roles of Met(O)-OH were investigated by experiments and molecular dynamics simulations. The results also found that Met(O)-OH showed high ice recrystallization inhibition (IRI) activity and the ice crystals in Met(O)-OH solution tend to be relatively round and smooth; moreover, the ice size was significantly reduced to 30.26 μm compared with pure water (135.87 μm) or DMSO solution (45.08 μm). At the molecular level, Met(O)-OH could stably bind the surface of the ice crystals and form more stable hydrogen bonds with ice compared with L-methionine. Moreover, Met(O)-OH could significantly reduce the damage to cells caused by osmotic shock and did not change the cell viability even at high concentration (4%). Based on these results, nucleated L929 cells and anuclear sheep red blood cells (SRBCs) were used as cell models to investigate the cryopreservation activity of Met(O)-OH. The results suggested that, under the optimum protocol, Met(O)-OH showed an effective post-thaw survival efficiency with ultrarapid freezing, and the post-thaw survival efficiency of L929 cells reached 84.0%. This work opens up the possibility for an alternative to traditional toxic CPA DMSO, and provides insights for the development of DMSO analogues with non-toxic/low toxicity for cell cryoprotection applications.

Trehalose in Biomedical Cryopreservation-Properties, Mechanisms, Delivery Methods, Applications, Benefits, and Problems

Cells and tissues are the foundation of translational medicine. At present, one of the main technological obstacles is their preservation for long-term usage while maintaining adequate viability and function. Optimized storage techniques must be developed to make them safer to use in the clinic. Cryopreservation is the most common long-term preservation method to maintain the vitality and function of cells and tissues. But, the formation of ice crystals in cells and tissues is considered to be the main mechanism that could harm cells and tissues during freezing and thawing. To reduce the formation of ice crystals, cryoprotective agents (CPAs) must be added to the cells and tissues to achieve the cryoprotective effect. However, conventional cryopreservation of cells and tissues often needs to use toxic organic solvents as CPAs. As a result, cryopreserved cells and tissues may need to go through a time-consuming washing process to remove CPAs for further applications in translational medicine, and multiple valuable cells are potentially lost or killed. Currently, trehalose has been researched as a nontoxic CPA due to its cryoprotective ability and stability during cryopreservation. Nevertheless, trehalose is a nonpermeable CPA, and the lack of an effective intracellular trehalose delivery method has become the main obstacle to its use in cryopreservation. This article illustrated the properties, mechanisms, delivery methods, and applications of trehalose, summarized the benefits and limits of trehalose, and summed up the findings and research direction of trehalose in biomedical cryopreservation.

A highly active mineral-based ice nucleating agent supports in situ cell cryopreservation in a high throughput format

Cryopreservation of biological matter in microlitre scale volumes of liquid would be useful for a range of applications. At present, it is challenging because small volumes of water tend to supercool, and deep supercooling is known to lead to poor post-thaw cell viability. Here, we show that a mineral ice nucleator can almost eliminate supercooling in 100 µl liquid volumes during cryopreservation. This strategy of eliminating supercooling greatly enhances cell viability relative to cryopreservation protocols with uncontrolled ice nucleation. Using infrared thermography, we demonstrate a direct relationship between the extent of supercooling and post-thaw cell viability. Using a mineral nucleator delivery system, we open the door to the routine cryopreservation of mammalian cells in multiwell plates for applications such as high throughput toxicology testing of pharmaceutical products and regenerative medicine.

Cryoprotective Mechanism of DMSO Induced by the Inhibitory Effect on Eutectic NaCl Crystallization

Cryopreservation is a critical procedure in autologous hematopoietic stem cell transplantation. Dimethyl sulfoxide (DMSO) is the cryoprotectant of choice. Optimization of the cryopreservation protocol in the past revealed a dramatic loss of cell viability associated with a reduction of the DMSO concentration below 2 vol % in the freezing medium. The cryoprotective mechanism of DMSO is usually ascribed to the ability to suppress ice formation and reduce the adverse effects of the freeze-concentrated solution. This work proposes an alternative hypothesis considering the detrimental impact of NaCl eutectic crystallization on cell viability. Thermoanalytical and microstructural analysis of the DMSO effect on eutectic phase transformation of cryoprotective mixtures revealed a correlation between the loss of cell viability and eutectic NaCl crystallization. DMSO inhibits the eutectic crystallization of NaCl and preserves cell viability. Thermodynamic description of the inhibitory action and possible mechanism of cryoinjury are provided.

Submilligram Level of Beetle Antifreeze Proteins Minimize Cold-Induced Cell Swelling and Promote Cell Survival

Hypothermic (cold) preservation is a limiting factor for successful cell and tissue transplantation where cell swelling (edema) usually develops, impairing cell function. University of Wisconsin (UW) solution, a standard cold preservation solution, contains effective components to suppress hypothermia-induced cell swelling. Antifreeze proteins (AFPs) found in many cold-adapted organisms can prevent cold injury of the organisms. Here, the effects of a beetle AFP from Dendroides canadensis (DAFP-1) on pancreatic β-cells preservation were first investigated. As low as 500 µg/mL, DAFP-1 significantly minimized INS-1 cell swelling and subsequent cell death during 4 °C preservation in UW solution for up to three days. However, such significant cytoprotection was not observed by an AFP from Tenebrio molitor (TmAFP), a structural homologue to DAFP-1 but lacking arginine, at the same levels. The cytoprotective effect of DAFP-1 was further validated with the primary β-cells in the isolated rat pancreatic islets in UW solution. The submilligram level supplement of DAFP-1 to UW solution significantly increased the islet mass recovery after three days of cold preservation followed by rewarming. The protective effects of DAFP-1 in UW solution were discussed at a molecular level. The results indicate the potential of DAFP-1 to enhance cell survival during extended cold preservation.

Evaluation of Nrf2/ARE Signaling Pathway in the Presence of Pentoxifylline as a Cryoprotectant in Mouse Spermatogonial Stem Cells

The process of spermatogonial stem cell cryopreservation (SSCs) in young male cancer survivors is associated with increased reactive oxygen species (ROS), DNA fragmentation, apoptosis, decreased cell activity, and finally reduced fertility of SSCs. Therefore, it is necessary to add cryoprotectants to the freezing medium to minimize the injuries associated with cryopreservation. In addition, the Nrf2/ARE pathway is a main cellular pathway that regulates the antioxidant defense system. The purpose of this study was to evaluate the cryoprotective effect of pentoxifylline (PTX) on SSCs after freezing-thawing through the Nrf2/ARE pathway. SSCs extracted from neonatal mice testes were isolated and their purity was measured by flow cytometry with GDNF family receptor alpha-1 (GFRα1) and inhibitor of differentiation 4 (ID4). After culturing, the cells were frozen in different groups for 1 month. After freezing-thawing, cell viability, colonization rate, and intracellular ROS, malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) were evaluated. Quantitative real-time polymerase chain reaction and western blotting were done to assess the expression levels of Nrf2, Keap-1, PI3K, and AKT genes and proteins. The survival and colonization rates of SSCs, SOD, and CAT levels, and Nrf2, PI3K, and AKT expression levels were significantly higher in the PTX group compared with the other cryopreservation groups. The Keap-1 expression level and the ROS and MDA production levels also decreased significantly in the PTX group (p-value <0.05). According to our findings, PTX can activate the antioxidant defense through the Nrf2/ARE signaling pathway; therefore, it could be a suitable cryoprotectant candidate for freezing and long-term storage of SSCs in the clinical setting.

Toxicity Profiles and Protective Effects of Antifreeze Proteins From Insect in Mammalian Models

Antifreeze proteins (AFPs), found in many cold-adapted organisms, can protect them from cold and freezing damages and have thus been considered as additional protectants in current cold tissue preservation solutions that generally include electrolytes, osmotic agents, colloids and antioxidants, to reduce the loss of tissue viability associated with cold-preservation. Due to the lack of toxicity profile studies on AFPs, their inclusion in cold preservation solutions has been a trial-and-error process limiting the development of AFPs' application in cold preservation. To assess the feasibility of translating the technology of AFPs for mammalian cell cold or cryopreservation, we determined the toxicity profile of two highly active beetle AFPs, DAFP1 and TmAFP, from Dendroides canadensis and Tenebrio molitor in this study. Toxicity was examined on a panel of representative mammalian cell lines including testicular spermatogonial stem cells and Leydig cells, macrophages, and hepatocytes. Treatments with DAFP1 and TmAFP at up to 500μg/mL for 48 and 72hours were safe in three of the cell lines, except for a 20% decrease in spermatogonia treated with TmAFP. However, both AFPs at 500μg/mL or below reduced hepatocyte viability by 20 to 40% at 48 and 72h. At 1000μg/mL, DAFP1 and TmAFP reduced viability in most cell lines. While spermatogonia and Leydig cell functions were not affected by 1000μg/mL DAFP1, this treatment induced inflammatory responses in macrophages. Adding 1000μg/ml DAFP1 to rat kidneys stored at 4°C for 48hours protected the tissues from cold-related damage, based on tissue morphology and gene and protein expression of two markers of kidney function. However, DAFP1 and TmAFP did not prevent the adverse effects of cold on kidneys over 72hours. Overall, DAFP1 is less toxic at high dose than TmAFP, and has potential for use in tissue preservation at doses up to 500μg/mL. However, careful consideration must be taken due to the proinflammatory potential of DAFP1 on macrophages at higher doses and the heighten susceptibility of hepatocytes to both AFPs.

Intracellular and Extracellular Antifreeze Protein Significantly Improves Mammalian Cell Cryopreservation

Cell cryopreservation is an essential part of the biotechnology, food, and health care industries. There is a need to develop more effective, less toxic cryoprotective agents (CPAs) and methods, especially for mammalian cells. We investigated the impact of an insect antifreeze protein from Anatolica polita (ApAFP752) on mammalian cell cryopreservation using the human embryonic kidney cell line HEK 293T. An enhanced green fluorescent protein (EGFP)-tagged antifreeze protein, EGFP-ApAFP752, was transfected into the cells and the GFP was used to determine the efficiency of transfection. AFP was assessed for its cryoprotective effects intra- and extracellularly and both simultaneously at different concentrations with and without dimethyl sulfoxide (DMSO) at different concentrations. Comparisons were made to DMSO or medium alone. Cells were cryopreserved at -196 °C for ≥4 weeks. Upon thawing, cellular viability was determined using trypan blue, cellular damage was assessed by lactate dehydrogenase (LDH) assay, and cellular metabolism was measured using a metabolic activity assay (MTS). The use of this AFP significantly improved cryopreserved cell survival when used with DMSO intracellularly. Extracellular AFP also significantly improved cell survival when included in the DMSO freezing medium. Intra- and extracellular AFP used together demonstrated the most significantly increased cryoprotection compared to DMSO alone. These findings present a potential method to improve the viability of cryopreserved mammalian cells.

An insect antifreeze protein from Anatolica polita enhances the cryoprotection of Xenopus laevis eggs and embryos

Cryoprotection is of interest in many fields of research, necessitating a greater understanding of different cryoprotective agents. Antifreeze proteins have been identified that have the ability to confer cryoprotection in certain organisms. Antifreeze proteins are an evolutionary adaptation that contributes to the freeze resistance of certain fish, insects, bacteria and plants. These proteins adsorb to an ice crystal's surface and restrict its growth within a certain temperature range. We investigated the ability of an antifreeze protein from the desert beetle Anatolica polita, ApAFP752, to confer cryoprotection in the frog Xenopus laevis. Xenopus laevis eggs and embryos microinjected with ApAFP752 exhibited reduced damage and increased survival after a freeze-thaw cycle in a concentration-dependent manner. We also demonstrate that ApAFP752 localizes to the plasma membrane in eggs and embryonic blastomeres and is not toxic for early development. These studies show the potential of an insect antifreeze protein to confer cryoprotection in amphibian eggs and embryos.

Red Blood Cell Cryopreservation with Minimal Post-Thaw Lysis Enabled by a Synergistic Combination of a Cryoprotecting Polyampholyte with DMSO/Trehalose

From trauma wards to chemotherapy, red blood cells are essential in modern medicine. Current methods to bank red blood cells typically use glycerol (40 wt %) as a cryoprotective agent. Although highly effective, the deglycerolization process, post-thaw, is time-consuming and results in some loss of red blood cells during the washing procedures. Here, we demonstrate that a polyampholyte, a macromolecular cryoprotectant, synergistically enhances ovine red blood cell cryopreservation in a mixed cryoprotectant system. Screening of DMSO and trehalose mixtures identified optimized conditions, where cytotoxicity was minimized but cryoprotective benefit maximized. Supplementation with polyampholyte allowed 97% post-thaw recovery (3% hemolysis), even under extremely challenging slow-freezing and -thawing conditions. Post-thaw washing of the cryoprotectants was tolerated by the cells, which is crucial for any application, and the optimized mixture could be applied directly to cells, causing no hemolysis after 1 h of exposure. The procedure was also scaled to use blood bags, showing utility on a scale relevant for application. Flow cytometry and adenosine triphosphate assays confirmed the integrity of the blood cells post-thaw. Microscopy confirmed intact red blood cells were recovered but with some shrinkage, suggesting that optimization of post-thaw washing could further improve this method. These results show that macromolecular cryoprotectants can provide synergistic benefit, alongside small molecule cryoprotectants, for the storage of essential cell types, as well as potential practical benefits in terms of processing/handling.

A Combination of Synthetic Molecules Acts as Antifreeze for the Protection of Skin against Cold-Induced Injuries

Seasonal and occupational exposure of the human body to extreme cold temperatures can result in cell death in the exposed area due to the formation of ice crystals. This leads to superficial or deep burn injury and compromised functionality. Currently available therapeutics can be ineffective in extreme cases, and thus, it is necessary to develop prophylactic strategies. In this study, we have devised a combination of known synthetic cryopreservative agents (termed SynAFP) and evaluated their potential antifreeze applications on skin. The prophylactic activity of SynAFP in vitro is indicated by improved cellular revival and cell viability, retention of the cytoskeleton, and normal cell cycle progression even after cold stress. A comprehensive whole-cell proteomic approach revealed that in the presence of SynAFP, cold-induced downregulation of proteins involved in cell-cell adhesion and upregulation of those related to mitochondrial stress were ameliorated. Pre-application of SynAFP in mice facing a frostbite challenge prevents their skin from incurring significant injury as confirmed through macroscopic and histological examination. Moreover, multiple applications of SynAFP on mouse skin at room temperature did not compromise skin integrity. SynAFP was also formulated in anAloe vera-based cream (referred to as fSynAFP), which offered similar protection under cold stress conditions. Thus, SynAFP can be considered as a potential candidate for formulating a topical intervention for protection from cold-induced injuries to skin.

DeepFoci: Deep learning-based algorithm for fast automatic analysis of DNA double-strand break ionizing radiation-induced foci

DNA double-strand breaks (DSBs), marked by ionizing radiation-induced (repair) foci (IRIFs), are the most serious DNA lesions and are dangerous to human health. IRIF quantification based on confocal microscopy represents the most sensitive and gold-standard method in radiation biodosimetry and allows research on DSB induction and repair at the molecular and single-cell levels. In this study, we introduce DeepFoci - a deep learning-based fully automatic method for IRIF counting and morphometric analysis. DeepFoci is designed to work with 3D multichannel data (trained for 53BP1 and γH2AX) and uses U-Net for nucleus segmentation and IRIF detection, together with maximally stable extremal region-based IRIF segmentation. The proposed method was trained and tested on challenging datasets consisting of mixtures of nonirradiated and irradiated cells of different types and IRIF characteristics - permanent cell lines (NHDFs, U-87) and primary cell cultures prepared from tumors and adjacent normal tissues of head and neck cancer patients. The cells were dosed with 0.5-8 Gy γ-rays and fixed at multiple (0-24 h) postirradiation times. Under all circumstances, DeepFoci quantified the number of IRIFs with the highest accuracy among current advanced algorithms. Moreover, while the detection error of DeepFoci remained comparable to the variability between two experienced experts, the software maintained its sensitivity and fidelity across dramatically different IRIF counts per nucleus. In addition, information was extracted on IRIF 3D morphometric features and repair protein colocalization within IRIFs. This approach allowed multiparameter IRIF categorization of single- or multichannel data, thereby refining the analysis of DSB repair processes and classification of patient tumors, with the potential to identify specific cell subclones. The developed software improves IRIF quantification for various practical applications (radiotherapy monitoring, biodosimetry, etc.) and opens the door to advanced DSB focus analysis and, in turn, a better understanding of (radiation-induced) DNA damage and repair.

DMSO as new, counterintuitive excipient for freeze-drying human keratinocytes

DMSO is widely used as powerful cryoprotectant for the storage and transport of frozen cells. Beyond this established application of DMSO, we could now show that it has also promising lyoprotectant effects in the field of lyophilisation of therapeutic cells. Freeze-drying of HaCaT keratinocytes in 10% HES, 5% HE and in presence of DMSO led to an increase in cell membrane integrity from 25.3 ± 2.7 % without DMSO to 41.4 ± 4.3 % with 2% DMSO, as determined by trypan blue exclusion. Interruption of the lyophilisation cycle at different sampling points showed a rapid decrease of cell membrane integrity below a critical residual moisture content. DMSO was able to stabilise cell membranes below this moisture level up to a final residual moisture content of less than 1%. Furthermore, DMSO increased the total protein content of cells after freeze-drying and subsequent SDS PAGE analysis indicated that certain abundant proteins were better preserved with the use of DMSO. Owed to its low vapour pressure, a significant part of DMSO is not removed during freeze-drying and remains as plasticiser in the lyophilised cake. However, a T_g above 60°C for 2% DMSO indicates that samples can still be stored at temperatures of 2-8°C. Also, no macroscopic or microscopic collapse can be observed by SEM or BET measurements and DMSO addition leads even to more elegant cakes with reduced cake cracking. With a better preservation of cell membranes and cellular structures, DMSO can contribute to the still unsolved problem of freeze-drying cells of higher complexity.

Human serum albumin and chromatin condensation rescue ex vivo expanded γδ T cells from the effects of cryopreservation

Clinical applications of gamma delta (γδ) T cells have advanced from initial interest in expanding γδ T cells in vivo to the development of a manufacturing process for the ex vivo expansion. To develop an "off-the-shelf" allogeneic γδ T cell product, the cell manufacturing process must be optimized to include cryopreservation. It is known that cryopreservation can dramatically reduce viability of primary cells and other cell types after thawing, although the exact effects of cryopreservation on γδ T cell health and functionality have not yet been characterized. Our aim was to characterize the effects of a freeze/thaw cycle on γδ T cells and to develop an optimized protocol for cryopreservation. γδ T cells were expanded under serum-free conditions, using a good manufacturing practice (GMP) compliant protocol developed by our lab. We observed that cryopreservation reduced cell survival and increased the percentage of apoptotic cells, two measures that could not be improved through the use of 5 GMP compliant freezing media. The choice of thawing medium, specifically human albumin (HSA), improved γδ T cell viability and in addition, chromatin condensation prior to freezing increased cell viability after thawing, which could not be further improved with the use of a general caspase inhibitor. Finally, we found that cryopreserved cells had depolarized mitochondrial membranes and reduced cytotoxicity when tested against a range of leukemia cell lines. These studies provide a detailed analysis of the effects of cryopreservation on γδ T cells and provide methods for improving viability in the post-thaw period.

Important parameters affecting quality of vitrified donor oocytes

For group of 281 oocytes obtained from 43 stimulated donors and cryopreserved by vitrification protocol using Cryotop and Kitazato medium we determined important parameters of oocytes collection and vitrification processes which strongly affect the probability that warmed oocytes will produce high-quality embryos for transfer. The probability to obtain high-quality embryos for transfer from vitrified and warmed oocytes was highest when two conditions were fulfilled: 1. oocytes were incubated before vitrification for 7-10 h and 2. stimulated ovaries of donors in one cycle produced a smaller number of oocytes (<7 oocytes from one donor per stimulated cycle). The probable reasons for these observations were: 1. early vitrification (less than 7 h) before final oocyte metaphase II maturation negatively affected the crucial process of post-warm remodelling of spindles and chromosomes, which reduced the fertilization and utilization rates, 2. the evaluated vitrification protocol amplifies negative impact of membrane defects of oocytes of those cohorts containing more than 6 oocytes - freezing places great demands on the integrity and elasticity of the cell membranes. The fact that cryopreservation influences a complex state of oocytes was confirmed by confocal microscopy.

Lipid Remodeling Confers Osmotic Stress Tolerance to Embryogenic Cells during Cryopreservation

Plant species conservation through cryopreservation using plant vitrification solutions (PVS) is based in empiricism and the mechanisms that confer cell integrity are not well understood. Using ESI-MS/MS analysis and quantification, we generated 12 comparative lipidomics datasets for membranes of embryogenic cells (ECs) of Magnolia officinalis during cryogenic treatments. Each step of the complex PVS-based cryoprotocol had a profoundly different impact on membrane lipid composition. Loading treatment (osmoprotection) remodeled the cell membrane by lipid turnover, between increased phosphatidic acid (PA) and phosphatidylglycerol (PG) and decreased phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The PA increase likely serves as an intermediate for adjustments in lipid metabolism to desiccation stress. Following PVS treatment, lipid levels increased, including PC and PE, and this effectively counteracted the potential for massive loss of lipid species when cryopreservation was implemented in the absence of cryoprotection. The present detailed cryobiotechnology findings suggest that the remodeling of membrane lipids and attenuation of lipid degradation are critical for the successful use of PVS. As lipid metabolism and composition varies with species, these new insights provide a framework for technology development for the preservation of other species at increasing risk of extinction.

Multifunctional Poly(vinyl alcohol) Nanocomposite Organohydrogel for Flexible Strain and Temperature Sensor

Hydrogels are important for stretchable and wearable multifunctional sensors, but their application is limited by their low mechanical strength and poor long-term stability. Herein, a conductive organohydrogel with a 3D honeycomb structure was prepared by integrating carbon nanotubes (CNTs) and carbon black (CB) into a poly(vinyl alcohol)/glycerol (PVA/Gly) organohydrogel. Such a nanocomposite organohydrogel is built on a physical cross-linking network formed by the hydrogen bonds among PVA, glycerol, and water. CNTs and CB had an add-in synergistic impact on the mechanical and electrical performances of the PVA/Gly organohydrogel because of the distinct aspect ratios and geometric shapes. The prepared organohydrogel integrated with a tensile strength of 4.8 MPa, a toughness of 15.93 MJ m^-3, and flexibility with an elongation at break up to 640%. The organohydrogels also showed good antifreezing feature, long-term moisture retention, self-healing, and thermoplasticity. Sensors designed from these organohydrogels displayed high stretching sensitivity to tensile strain and temperature, with a gauge factor of 2.1 within a relatively broad strain range (up to ∼600% strain), a temperature coefficient of resistance of -0.935%·°C^-1, and long-term durability. The sensors could detect full-range human physiological signals and respond to the change in temperature, which are highly desired for multifunctional wearable electronic devices.

Bioinspired l-Proline Oligomers for the Cryopreservation of Oocytes via Controlling Ice Growth

Various types of cells are routinely cryopreserved in modern regenerative and cell-based medicines. For instance, the oocyte is one of the most demanding cells to be cryopreserved in genetic engineering and human-assisted reproductive technology (ART). However, the usage of cryopreserved oocytes in ART clinics is still limited mainly because of the unstable survival rate. This is due to the fact that oocytes are more prone to be damaged by ice crystals in comparison to other cells, as oocytes are larger in size and surface area. Meanwhile, oocytes contain more water, and thus, ice crystals are easier to form inside the cells. Currently, to avoid injury by the formed ice crystals, cryopreservation (CP) of oocytes has to use large amounts of small molecules as cryoprotectants such as dimethyl sulfoxide (DMSO) and ethylene glycol (EG), which can permeate into the cell and prevent ice formation inside. However, these molecules are chemically and epigenetically toxic to cells. Therefore, great efforts have been focused on reducing the amount of DMSO and EG used for oocyte CP. In nature, the antifreeze (glyco)proteins (AFGPs) locate extracellularly with the ability to protect living organisms from freezing damage via controlling ice growth. Inspired by this, biocompatible and nontoxic L-proline oligomers (L-Pro_n), which have the same polyproline II helix structure as that of AFGPs, are first employed for the CP of oocytes. The experimental results reveal that L-Pro₈ has a profound activity in inhibiting ice growth as that of AFGP8. Also, by the addition of 50 mM L-Pro₈, the amount of DMSO and EG can be greatly reduced by ca. 1.8 M for oocyte CP; moreover, the survival rate of the cryopreserved oocytes is increased up to 99.11%, and the coefficient of variance of the survival rate is decreased from 7.47 to 2.15%. These results mean that almost all oocytes can survive after CP with our method; importantly, the mitochondrial function as a critical criterion for the quality of the frozen-thawed oocytes is also improved. It is proposed that with the addition of L-Pro₈, the extracellular ice growth is slowed down, which prevents the direct injuries of cells by large ice crystals and the accompanying osmotic pressure increase. As such, this work is not only significant for meeting the ever-increasing demand by the ART clinics but also gives guidance for designing materials in controlling ice growth during CP of other cells and tissues.

The protective effect of Leucosporidium-derived ice-binding protein (LeIBP) on bovine oocytes and embryos during vitrification

Ice-binding proteins (IBPs) facilitate organism survival under extreme conditions by inhibiting thermal hysteresis and ice recrystallization. IBPs have been widely used as cryoprotectants to cryopreserve mammalian gametes and embryos. In the present study, we evaluated the protective effects of an Arctic yeast, Leucosporidium sp. AY30 derived ice-binding protein (LeIBP), on the vitrification of bovine metaphase II (MII) oocytes and embryos. When oocytes and embryos were frozen using the two-step vitrification method, the survival rate was significantly increased in the presence of LeIBP. The LeIBP supplementation decreased the levels of intracellular reactive oxygen species (ROS) and enhanced mitochondrial functions in the vitrified-warmed oocytes. Furthermore, LeIBP improved the developmental potential and suppressed apoptosis of the embryos derived from vitrified-warmed oocytes. Collectively, these data indicate that LeIBP can be used as a promising cryoprotectant to prevent cryoinjury during vitrification in bovine oocytes.

Simple Syntheses of New Pegylated Trehalose Derivatives as a Chemical Tool for Potential Evaluation of Cryoprotectant Effects on Cell Membrane

In our work, we developed the synthesis of new polyfunctional pegylated trehalose derivatives and evaluated their cryoprotective effect using flow cytometry. We showed that new compounds (modified trehaloses) bound to appropriate extracellular polymeric cryoprotectants could be helpful as a chemical tool for the evaluation of their potential toxic cell membrane influences. Our aim was to form a chemical tool for the evaluation of cryoprotectant cell membrane influences, which are still not easily predicted during the freezing/thawing process. We combined two basic cryoprotectants: polyethyleneglycols (PEGs) and trehalose in the new chemical compounds—pegylated trehalose hybrids. If PEG and trehalose are chemically bound and trehalose is adsorbed on the cell surface PEGs molecules which are, due to the chemical bonding with trehalose, close to the cell surface, can remove the cell surface hydration layer which destabilizes the cell membrane. This was confirmed by the comparison of new material, PEG, trehalose, and their mixture cryoprotective capabilities.

Trehalose-Based Polyethers for Cryopreservation and Three-Dimensional Cell Scaffolds

The capability to slow ice growth and recrystallization is compulsory in the cryopreservation of cells and tissues to avoid injuries associated with the physical and chemical responses of freezing and thawing. Cryoprotective agents (CPAs) have been used to restrain cryoinjury and improve cell survival, but some of these compounds pose greater risks for the clinical application of cryopreserved cells due to their inherent toxicity. Trehalose is known for its unique physicochemical properties and its interaction with the phospholipids of the plasma membrane, which can reduce cell osmotic stress and stabilized the cryopreserved cells. Nonetheless, there has been a shortage of relevant studies on the synthesis of trehalose-based CPAs. We hereby report the synthesis and evaluation of a trehalose-based polymer and hydrogel and its use as a cryoprotectant and three-dimensional (3D) cell scaffold for cell encapsulation and organoid production. In vitro cytotoxicity studies with the trehalose-based polymers (poly(Tre-ECH)) demonstrated biocompatibility up to 100 mg/mL. High post-thaw cell membrane integrity and post-thaw cell plating efficiencies were achieved after 24 h of incubation with skin fibroblast, HeLa (cervical), and PC3 (prostate) cancer cell lines under both controlled-rate and ultrarapid freezing protocols. Differential scanning calorimetry and a splat cooling assay for the determination of ice recrystallization inhibition activity corroborated the unique properties of these trehalose-based polyethers as cryoprotectants. Furthermore, the ability to form hydrogels as 3D cell scaffolds encourages the use of these novel polymers in the development of cell organoids and cryopreservation platforms.

Methods of Cryoprotectant Preservation: Allogeneic Cellular Bone Grafts and Potential Effects

Debridement of the bone surface during a surgical fusion procedure initiates an injury response promoting a healing cascade of molecular mediators released over time. Autologous grafts offer natural scaffolding to fill the bone void and to provide local bone cells. Commercial bone grafting products such as allografts, synthetic bone mineral products, etc., are used to supplement or to replace autologous grafts by supporting osteoinductivity, osteoconductivity, and osteogenesis at the surgical site. To assure osteogenic potential, preservation of allogeneic cells with cryoprotectants has been developed to allow for long-term storage and thus delivery of viable bone cells to the surgical site. Dimethyl sulfoxide (DMSO) is an intracellular cryoprotectant commonly used because it provides good viability of the cells post-thaw. However, there is known cytotoxicity reported for DMSO when cells are stored above cryogenic temperatures. For most cellular bone graft products, the cryoprotectant is incorporated with the cells into the other mineralized bone and demineralized bone components. During thawing, the DMSO may not be sufficiently removed from allograft products compared to its use in a cell suspension where removal by washing and centrifugation is available. Therefore, both the allogeneic cell types in the bone grafting product and the local cell types at the bone grafting site could be affected as cytotoxicity varies by cell type and by DMSO content according to reported studies. Overcoming cytotoxicity may be an additional challenge in the formation of bone at a wound or surgical site. Other extracellular cryoprotectants have been explored as alternatives to DMSO which preserve without entering the cell membrane, thereby providing good cellular viability post-thaw and might abrogate the cytotoxicity concerns.

Changes in Cryopreserved Cell Nuclei Serve as Indicators of Processes during Freezing and Thawing

The mechanisms underlying cell protection from cryoinjury are not yet fully understood. Recent biological studies have addressed cryopreserved cell survival but have not correlated the cryoprotection effectiveness with the impact of cryoprotectants on the most important cell structure, the nucleus, and the freeze/thaw process. We identified changes of cell nuclei states caused by different types of cryoprotectants and associate them with alterations of the freeze/thaw process in cells. Namely, we investigated both higher-order chromatin structure and nuclear envelope integrity as possible markers of freezing and thawing processes. Moreover, we analyzed in detail the relationship between nuclear envelope integrity, chromatin condensation, freeze/thaw processes in cells, and cryopreservation efficiency for dimethyl sulfoxide, glycerol, trehalose, and antifreeze protein. Our interdisciplinary study reveals how changes in cell nuclei induced by cryoprotectants affect the ability of cells to withstand freezing and thawing and how nuclei changes correlate with processes during freezing and thawing. Our results contribute to the deeper fundamental understanding of the freezing processes, notably in the cell nucleus, which will expand the applications and lead to the rational design of cryoprotective materials and protocols.

Challenges and Contradictions of Metal Nano-Particle Applications for Radio-Sensitivity Enhancement in Cancer Therapy

From the very beginnings of radiotherapy, a crucial question persists with how to target the radiation effectiveness into the tumor while preserving surrounding tissues as undamaged as possible. One promising approach is to selectively pre-sensitize tumor cells by metallic nanoparticles. However, though the "physics" behind nanoparticle-mediated radio-interaction has been well elaborated, practical applications in medicine remain challenging and often disappointing because of limited knowledge on biological mechanisms leading to cell damage enhancement and eventually cell death. In the present study, we analyzed the influence of different nanoparticle materials (platinum (Pt), and gold (Au)), cancer cell types (HeLa, U87, and SKBr3), and doses (up to 4 Gy) of low-Linear Energy Transfer (LET) ionizing radiation (γ- and X-rays) on the extent, complexity and reparability of radiation-induced γH2AX + 53BP1 foci, the markers of double stand breaks (DSBs). Firstly, we sensitively compared the focus presence in nuclei during a long period of time post-irradiation (24 h) in spatially (three-dimensionally, 3D) fixed cells incubated and non-incubated with Pt nanoparticles by means of high-resolution immunofluorescence confocal microscopy. The data were compared with our preliminary results obtained for Au nanoparticles and recently published results for gadolinium (Gd) nanoparticles of approximately the same size (2⁻3 nm). Next, we introduced a novel super-resolution approach-single molecule localization microscopy (SMLM)-to study the internal structure of the repair foci. In these experiments, 10 nm Au nanoparticles were used that could be also visualized by SMLM. Altogether, the data show that different nanoparticles may or may not enhance radiation damage to DNA, so multi-parameter effects have to be considered to better interpret the radiosensitization. Based on these findings, we discussed on conclusions and contradictions related to the effectiveness and presumptive mechanisms of the cell radiosensitization by nanoparticles. We also demonstrate that SMLM offers new perspectives to study internal structures of repair foci with the goal to better evaluate potential differences in DNA damage patterns.

Trehalose-functional glycopeptide enhances glycerol-free cryopreservation of red blood cells

Arginine- and trehalose-modified ε-polylysine (ε-PL) demonstrated a high synergistic function with trehalose for RBC cryopreservation.

Cryopreserved Cells Regeneration Monitored by Atomic Force Microscopy and Correlated With State of Cytoskeleton and Nuclear Membrane

Atomic force microscopy (AFM) helps to describe and explain the mechanobiological properties of living cells on the nanoscale level under physiological conditions. The stiffness of cells is an important parameter reflecting cell physiology. Here, we have provided the first study of the stiffness of cryopreserved cells during post-thawing regeneration using AFM combined with confocal fluorescence microscopy. We demonstrated that the nonfrozen cell stiffness decreased proportionally to the cryoprotectant concentration in the medium. AFM allowed us to map cell surface reconstitution in real time after a freeze/thaw cycle and to monitor the regeneration processes at different depths of the cell and even different parts of the cell surface (nucleus and edge). Fluorescence microscopy showed that the cytoskeleton in fibroblasts, though damaged by the freeze/thaw cycle, is reconstructed after long-term plating. Confocal microscopy confirmed that structural changes affect the nuclear envelopes in cryopreserved cells. AFM nanoindentation analysis could be used as a noninvasive method to identify cells that have regenerated their surface mechanical properties with the proper dynamics and to a sufficient degree. This identification can be important particularly in the field of in vitro fertilization and in future cell-based regeneration strategies.

Chromatin architecture changes and DNA replication fork collapse are critical features in cryopreserved cells that are differentially controlled by cryoprotectants

In this work, we shed new light on the highly debated issue of chromatin fragmentation in cryopreserved cells. Moreover, for the first time, we describe replicating cell-specific DNA damage and higher-order chromatin alterations after freezing and thawing. We identified DNA structural changes associated with the freeze-thaw process and correlated them with the viability of frozen and thawed cells. We simultaneously evaluated DNA defects and the higher-order chromatin structure of frozen and thawed cells with and without cryoprotectant treatment. We found that in replicating (S phase) cells, DNA was preferentially damaged by replication fork collapse, potentially leading to DNA double strand breaks (DSBs), which represent an important source of both genome instability and defects in epigenome maintenance. This induction of DNA defects by the freeze-thaw process was not prevented by any cryoprotectant studied. Both in replicating and non-replicating cells, freezing and thawing altered the chromatin structure in a cryoprotectant-dependent manner. Interestingly, cells with condensed chromatin, which was strongly stimulated by dimethyl sulfoxide (DMSO) prior to freezing had the highest rate of survival after thawing. Our results will facilitate the design of compounds and procedures to decrease injury to cryopreserved cells.

AFM Monitoring the Influence of Selected Cryoprotectants on Regeneration of Cryopreserved Cells Mechanical Properties

Cryopreservation of cells (mouse embryonic fibroblasts) is a fundamental task for wide range of applications. In practice, cells are protected against damage during freezing by applications of specific cryoprotectants and freezing/melting protocols. In this study by using AFM and fluorescence microscopy we showed how selected cryoprotectants (dimethyl sulfoxide and polyethylene glycol) affected the cryopreserved cells mechanical properties (stiffness) and how these parameters are correlated with cytoskeleton damage and reconstruction. We showed how cryopreserved (frozen and thawed) cells' stiffness change according to type of applied cryoprotectant and its functionality in extracellular or intracellular space. We showed that AFM can be used as technique for investigation of cryopreserved cells surfaces state and development ex vivo. Our results offer a new perspective on the monitoring and characterization of frozen cells recovery by measuring changes in elastic properties by nanoindentation technique. This may lead to a new and detailed way of investigating the post-thaw development of cryopreserved cells which allows to distinguish between different cell parts.