Protein cytoplasmic delivery using polyampholyte nanoparticles and freeze concentration

Development of Macromolecular Cryoprotectants for Cryopreservation of Cells

Cryopreservation is a common way for long-term storage of therapeutical proteins, erythrocytes, and mammalian cells. For cryoprotection of these biosamples to keep their structural integrity and biological activities, it is essential to incorporate highly efficient cryoprotectants. Currently, permeable small molecular cryoprotectants such as glycerol and dimethyl sulfoxide dominate in cryostorage applications, but they are harmful to cells and human health. As acting in the extracellular space, membrane-impermeable macromolecular cryoprotectants, which exert remarkable membrane stabilization against cryo-injury and are easily removed post-thaw, are promising candidates with biocompatibility and feasibility. Water-soluble hydroxyl-containing polymers such as poly(vinyl alcohol) and polyol-based polymers are potent ice recrystallization inhibitors, while polyampholytes, polyzwitterions, and bio-inspired (glyco)polypeptides can significantly increase post-thaw recovery with reduced membrane damages. In this review, the synthetic macromolecular cryoprotectants are systematically summarized based on their synthesis routes, practical utilities, and cryoprotective mechanisms. It provides a valuable insight in development of highly efficient macromolecular cryoprotectants with valid ice recrystallization inhibition activity for highly efficient and safe cryopreservation of cells.

Bridging polymer chemistry and cryobiology

Polymers, especially charged polymers, are the key to a sustainable future, as they have the capability to act as alternatives to plastics, reduce the impact of global warming, and offer solutions to global environmental pollution problems. Biomaterial polymers have proven to be incredibly effective in a multitude of applications, including clinical applications. In the fields of cryobiology and cryopreservation, polymers have emerged as credible alternatives to small molecules and other compounds, yielding excellent results. This review outlines the results of research in the areas of polymer chemistry and cryobiology, which have not been discussed together previously. Herein, we explain how recent polymer research has enabled the development of polymeric cryoprotectants with novel mechanisms and the development of novel methods for the intracellular delivery of substances, such as drugs, using a cryobiological technique called the freeze-concentration effect. Our findings indicate that interdisciplinary collaboration between cryobiologists and polymer chemists has led to exciting developments that will further cell biology and medical research.

Design of an Ice Recrystallization-Inhibiting Polyampholyte-Containing Graft Polymer for Inhibition of Protein Aggregation

Freezing-induced damage to proteins, through osmotic stress and ice recrystallization, during protein processing and long-term storage is a serious concern and may lead to loss of protein activity owing to denaturation. In this study, graft copolymers composed of a cryoprotective polymer (capable of preventing osmotic stress) and poly(vinyl alcohol) (PVA; known for its high ice recrystallization inhibition (IRI) property) were developed. The polymers had high IRI activity, albeit slightly lower than that of PVA alone, but substantially higher than that of succinylated ε-poly-l-lysine (PLLSA) alone. The graft polymers showed an efficiency higher than that of PVA or PLLSA alone in protecting proteins from multiple freeze-thaw cycles, as well as during prolonged freezing, indicating a synergy between PVA and PLLSA. The PLLSA-based graft polymer is a promising material for use in protein biopharmaceutics for the long-term storage of proteins under freezing conditions.

A comprehensive review of the structures and properties of ionic polymeric materials

This review focuses on the mechanistic approach, the structure–property relationship and applications of ionic polymeric materials.

Cytosolic delivery of quantum dots mediated by freezing and hydrophobic polyampholytes in RAW 264.7 cells

Quantum dots (QDs) can be delivered efficiently inside macrophages using a freeze-concentration approach. In this study, we introduced a new, facile, high concentration-based freezing technology of low toxicity. We also developed QD-conjugated new hydrophobic polyampholytes using poly-l-lysine (PLL), a naturally derived polymer, which showed sustained biocompatibility, stability over one week, and enhanced intracellular delivery. When freeze-concentration was applied, the QD-encapsulated hydrophobic polyampholytes showed a higher tendency to adsorb onto the cell membrane than the non-frozen molecules. Interestingly, we observed that the efficacy of adsorption of QDs on RAW 264.7 macrophages was higher than that on fibroblasts. Furthermore, the intracellular delivery of QDs using hydrophobic polyampholytes was higher than those of PLL and QDs. In vitro studies revealed the efficient endosomal escape of QDs in the presence of hydrophobic polyampholytes and freeze-concentration. Collectively, these observations indicated that the promising combination of freeze-concentration and hydrophobic polyampholytes may act as an effective and versatile strategy for the intracellular delivery of QDs, which can be used for biological diagnosis and therapeutic applications.

Dual Thermo- and pH-Responsive Behavior of Double Zwitterionic Graft Copolymers for Suppression of Protein Aggregation and Protein Release

Graft copolymers consisting of two different zwitterionic blocks were synthesized via reversible addition fragmentation chain transfer polymerization. These polymers showed dual properties of thermo- and pH-responsiveness in an aqueous solution. Ultraviolet-visible spectroscopy and dynamic light scattering were employed to study the phase behavior under varying temperatures and pH values. Unlike the phase transition temperatures of other graft copolymers containing nonionic blocks, the phase transition temperature of these polymers was easily tuned by changing the polymer concentration. Owing to the biocompatible and stimuli-responsive nature of the polymers, this system was shown to effectively release proteins (lysozyme) while simultaneously protecting them against denaturation. The positively charged lysozyme was shown to bind with the negatively charged polymer at the physiological pH (pH 7.4). However, it was subsequently released at pH 3, at which the polymer exhibits a positive charge. Protein aggregation studies using a residual enzymatic activity assay, circular dichroism, and a Thioflavin T assay revealed that the secondary structure of the lysozyme was retained even after harsh thermal treatment. The addition of these polymers helped the lysozyme retain its enzymatic activity and suppressed its fibrillation. Both polymers showed excellent protein protection properties, with the negatively charged polymer exhibiting slightly superior protein protection properties to those of the neutral polymer. To the best of the authors' knowledge, this is the first study to develop a graft copolymer system consisting of two different zwitterionic blocks that shows dual thermo- and pH-responsive properties. The presence of the polyampholyte structure enables these polymers to act as protein release agents, while simultaneously protecting the proteins from severe stress.

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.

Trapped! A Critical Evaluation of Methods for Measuring Total Cellular Uptake versus Cytosolic Localization

Biomolecules have many properties that make them promising for intracellular therapeutic applications, but delivery remains a key challenge because large biomolecules cannot easily enter the cytosol. Furthermore, quantification of total intracellular versus cytosolic concentrations remains demanding, and the determination of delivery efficiency is thus not straightforward. In this review, we discuss strategies for delivering biomolecules into the cytosol and briefly summarize the mechanisms of uptake for these systems. We then describe commonly used methods to measure total cellular uptake and, more selectively, cytosolic localization, and discuss the major advantages and drawbacks of each method. We critically evaluate methods of measuring "cell penetration" that do not adequately distinguish total cellular uptake and cytosolic localization, which often lead to inaccurate interpretations of a molecule's cytosolic localization. Finally, we summarize the properties and components of each method, including the main caveats of each, to allow for informed decisions about method selection for specific applications. When applied correctly and interpreted carefully, methods for quantifying cytosolic localization offer valuable insight into the bioactivity of biomolecules and potentially the prospects for their eventual development into therapeutics.

An introduction to zwitterionic polymer behavior and applications in solution and at surfaces

Zwitterionic polymers, including polyampholytes and polybetaines, are polymers with both positive and negative charges incorporated into their structure. They are a unique class of smart materials with great potential in a broad range of applications in nanotechnology, biomaterials science, nanomedicine and healthcare, as additives for bulk construction materials and crude oil, and in water remediation. In this Tutorial Review, we aim to highlight their structural diversity and design criteria, and their preparation using modern techniques. Their behavior, both in solution and at surfaces, will be examined under a range of environmental conditions. Finally, we will exemplify how their unique behaviors give rise to specific properties tailored to a selection of their numerous applications.

Hydrophobic Polyampholytes and Nonfreezing Cold Temperature Stimulate Internalization of Au Nanoparticles to Zwitterionic Liposomes

Nanomedicine relies on the effective internalization of nanoparticles combined with polymeric nanocarriers into living cells. Thus, exploration of internalization is essential for improving the efficacy of nanoparticle-based strategies in clinical practice. Here, we investigated the physicochemical internalization of gold nanoparticles (AuNPs) conjugated with hydrophobic polyampholytes into cell-sized liposomes at a low but nonfrozen temperature. The hydrophobic polyampholytes localized in the disordered phase of the membrane, and internalization of AuNPs was enhanced in the presence of hydrophobic polyampholytes together with incubation at -3 °C as compared to 25 °C. These results contribute toward a mechanistic understanding for developing a model nanomaterials-driven delivery system based on hydrophobic polyampholytes and low temperature.

Comparative analysis of the cellular entry of polystyrene and gold nanoparticles using the freeze concentration method

Despite advances in nanoparticle delivery, established physical approaches, such as electroporation and sonication, result in cell damage, limiting their practical applications. In this study, we proposed a unique freeze concentration-based technique and evaluated the efficacy of the method using two types of nanoparticles: citrate-capped gold nanoparticles and carboxylated polystyrene nanoparticles. We further compared the internalisation behaviour of particles of various sizes with and without freezing. Confocal microscopic images showed that the uptake efficacy of 50 nm nanomaterials was greater than that of 100 nm particles. Polystyrene nanoparticles of 50 nm size had more favourable adsorption and internalisation behaviours compared to those of gold nanoparticles after freeze concentration. We also examined the possible endocytic pathways involved in the uptake of gold and polystyrene nanoparticles, and found that the route differed between non-frozen and frozen conditions. Overall, we determined the influence of the freeze concentration strategy on both nanomaterial internalisation and the endocytic uptake pathway. Our findings provide a mechanistic understanding of the internalisation of nanoparticles using a freezing approach and thereby contribute to further developments in nanotherapeutic applications.

Enhanced Adsorption of a Protein-Nanocarrier Complex onto Cell Membranes through a High Freeze Concentration by a Polyampholyte Cryoprotectant

The transportation of biomolecules into cells is of great importance in tissue engineering and as stimulation for antitumor immune cells. Previous freezing strategies at ultracold temperatures (-80 °C) used for intracellular transportation exhibit certain limitations such as extended time requirements and harsh delivery system conditions. Thus, the need remains to develop simplified methods for safe nanomaterial delivery. Here, we demonstrated a unique strategy based on the ice-crystallization-induced freeze concentration for protein intracellular delivery in combination with a polyampholyte cryoprotectant. We found that upon sustained lowering of the temperature from -6 to -20 °C over a short duration, the adsorption of proteins onto the peripheral cell membrane was markedly increased through the facile ice-crystallization-induced freeze concentration. Furthermore, we proposed a freeze concentration factor (α) that depends on the freezing-point depression and is estimated from an analysis of the fraction of frozen water. Notably, the α values of the polyampholyte cryoprotectant were 8-fold higher than those of the currently used cryoprotectant dimethyl sulfoxide (DMSO) at particular temperatures of interest. Our results illustrate that the presence of a polyampholyte cryoprotectant significantly enhanced the adsorption of the protein/nanocarrier complex onto membranes compared to that obtained with DMSO because of the high freeze concentration. The present study demonstrated the direct relationship between freezing and the penetration of proteins across the periphery of the cell membrane by means of increased concentration during freezing. These results may be useful in providing a guideline for the intracellular delivery of biomacromolecules using ice-crystallization-induced continuous freezing combined with polyampholyte cryoprotectants.

Polyampholyte Hydrogels in Biomedical Applications

Polyampholytes are a class of polymers made up of positively and negatively charged monomer subunits. Polyampholytes offer a unique tunable set of properties driven by the interactions between the charged monomer subunits. Some tunable properties of polyampholytes include mechanical properties, nonfouling characteristics, swelling due to changes in pH or salt concentration, and drug delivery capability. These characteristics lend themselves to multiple biomedical applications, and this review paper will summarize applications of polyampholyte polymers demonstrated over the last five years in tissue engineering, cryopreservation and drug delivery.

A Freeze-Concentration and Polyampholyte-Modified Liposome-Based Antigen-Delivery System for Effective Immunotherapy

Immunotherapy is an exciting new approach to cancer treatment. The development of a novel freeze-concentration method is described that could be applicable in immunotherapy. The method involves freezing cells in the presence of pH-sensitive, polyampholyte-modified liposomes with encapsulated ovalbumin (OVA) as the antigen. In RAW 264.7 cells, compared to unfrozen, freeze-concentration of polyampholyte-modified liposomes encapsulating OVA resulted in efficient OVA uptake and also allowed its delivery to the cytosol. Efficient delivery of OVA to the cytosol was shown to be partly due to the pH-dependence of the polyampholyte-modified liposomes. Cytosolic OVA delivery also resulted in significant up-regulation of the major histocompatibility complex class I pathway through cross-stimulation, as well as an increase in the release of IL-1β, IL-6, and TNF-α. The results demonstrate that the combination of a simple freeze-concentration method and polyampholyte-modified liposomes might be useful in future immunotherapy applications.

Enhanced protein internalization and efficient endosomal escape using polyampholyte-modified liposomes and freeze concentration

Here we show a new strategy for efficient freeze concentration-mediated cytoplasmic delivery of proteins, obtained via the endosomal escape property of polyampholyte-modified liposomes. The freeze concentration method successfully induces the efficient internalization of proteins simply by freezing cells with protein and nanocarrier complexes. However, the mechanism of protein internalization remains unclear. Here, we designed a novel protein delivery carrier by modifying liposomes through incorporating hydrophobic polyampholytes therein. These complexes were characterized for particle size, encapsulation efficiency, and cytotoxicity. Flow cytometry and microscopic analysis showed that the adsorption and internalization of protein-loaded polyampholyte-modified liposomes after freezing were enhanced compared with that observed in unfrozen complexes. Inhibition studies demonstrated that the internalization mechanism differs between unmodified and polyampholyte-modified liposomes. Furthermore, polyampholyte-modified liposomes exhibited high efficacy in facilitating endosomal escape to enhance protein delivery to the cytoplasm with low toxicity. These results strongly suggest that the freeze concentration-based strategy could be widely utilised for efficient cargo delivery into the cytoplasm in vitro not only in cancer treatment but also for gene therapy as well.