Successful sub-zero non-freezing preservation of rat lungs at -2 degrees C utilizing a new supercooling technology

Supercooled preservation of cultured primary rat hepatocyte monolayers

Supercooled preservation (SCP) is a technology that involves cooling a substance below its freezing point without initiating ice crystal formation. It is a promising alternative to prolong the preservation time of cells, tissues, engineered tissue products, and organs compared to the current practices of hypothermic storage. Two-dimensional (2D) engineered tissues are extensively used in in vitro research for drug screening and development and investigation of disease progression. Despite their widespread application, there is a lack of research on the SCP of 2D-engineered tissues. In this study, we presented the effects of SCP at -2 and -6°C on primary rat hepatocyte (PRH) monolayers for the first time and compared cell viability and functionality with cold storage (CS, + 4°C). We preserved PRH monolayers in two different commercially available solutions: Hypothermosol-FRS (HTS-FRS) and the University of Wisconsin (UW) with and without supplements (i.e., polyethylene glycol (PEG) and 3-O-Methyl-Α-D-Glucopyranose (3-OMG)). Our findings revealed that UW with and without supplements were inadequate for the short-term preservation of PRH monolayers for both SCP and CS with high viability, functionality, and monolayer integrity. The combination of supplements (PEG and 3-OMG) in the HTS-FRS solution outperformed the other groups and yielded the highest viability and functional capacity. Notably, PRH monolayers exhibited superior viability and functionality when stored at -2°C through SCP for up to 3 days compared to CS. Overall, our results demonstrated that SCP is a feasible approach to improving the short-term preservation of PRH monolayers and enables readily available 2D-engineered tissues to advance in vitro research. Furthermore, our findings provide insights into preservation outcomes across various biological levels, from cells to tissues and organs, contributing to the advancement of bioengineering and biotechnology.

Sub-Zero Non-Freezing of Vascularized Composite Allografts Preservation in Rodents

Ischemia is a major limiting factor in Vascularized Composite Allotransplantation (VCA) as irreversible muscular injury can occur after as early as 4-6 hours of static cold storage (SCS). Organ preservation technologies have led to the development of storage protocols extending rat liver ex vivo preservation up to 4 days. Development of such a protocol for VCAs has the added challenge of inherent ice nucleating factors of the graft, therefore this study focused on developing a robust protocol for VCA supercooling. Rodent partial hindlimbs underwent subnormothermic machine perfusion (SNMP) with several loading solutions, followed by cryoprotective agent (CPA) cocktail developed for VCAs. Storage occurred in suspended animation for 24h and VCAs were recovered using SNMP with modified Steen. This study shows a robust VCA supercooling preservation protocol in a rodent model. Further optimization is expected to allow for its application in a transplantation model, which would be a breakthrough in the field of VCA preservation.

Supercooling: A Promising Technique for Prolonged Organ Preservation in Solid Organ Transplantation, and Early Perspectives in Vascularized Composite Allografts

Ex-vivo preservation of transplanted organs is undergoing spectacular advances. Machine perfusion is now used in common practice for abdominal and thoracic organ transportation and preservation, and early results are in favor of substantially improved outcomes. It is based on decreasing ischemia-reperfusion phenomena by providing physiological or sub-physiological conditions until transplantation. Alternatively, supercooling techniques involving static preservation at negative temperatures while avoiding ice formation have shown encouraging results in solid organs. Here, the rationale is to decrease the organ's metabolism and need for oxygen and nutrients, allowing for extended preservation durations. The aim of this work is to review all advances of supercooling in transplantation, browsing the literature for each organ. A specific objective was also to study the initial evidence, the prospects, and potential applications of supercooling preservation in Vascularized Composite Allotransplantation (VCA). This complex entity needs a substantial effort to improve long-term outcomes, marked by chronic rejection. Improving preservation techniques is critical to ensure the favorable evolution of VCAs, and supercooling techniques could greatly participate in these advances.

An exploratory study on isochoric supercooling preservation of the pig liver

This study was motivated by the increasing interest in finding ways to preserve organs in a supercooled state for transplantation. Previous research with small volumes suggests that the isochoric (constant volume) thermodynamic state enhances the stability of supercooled solutions. The primary objective of this study was to investigate the feasibility of storing a large organ, such as the pig liver, in a metastable isochoric supercooled state for clinically relevant durations. To achieve this, we designed a new isochoric technology that employs a system consisting of two domains separated by an interior boundary that can transfer heat and pressure, but not mass. The liver is preserved in one of these domains in a solution with an intracellular composition, which is in osmotic equilibrium with the liver. Pressure is used to monitor the thermodynamic state of the isochoric chamber. In this feasibility study, two pig livers were preserved in the device in an isochoric supercooled state at -2°C. The experiments were terminated voluntarily, one after 24 h and the other after 48 h of supercooling preservation. Pressure measurements indicated that the livers did not freeze during the isochoric supercooling preservation. This is the first proof that organs as large as the pig liver can remain supercooled for extended periods of time in an isotonic solution in an isochoric system, despite an increased probability of ice nucleation with larger volumes. To serve as controls and to test the ability of pressure monitoring to detect freezing in the isochoric chamber, an experiment was designed in which two pig livers were frozen at -2°C for 24 h and the pressure monitored. Histological examination with H&E stains revealed that the supercooled liver maintained a normal appearance, even after 48 h of supercooling, while tissues in livers frozen to -2°C were severely disrupted by freezing after 24 h.

Macromolecular cryoprotectants for the preservation of mammalian cell culture: lessons from crowding, overview and perspectives

Cryopreservation is a process used for the storage of mammalian cells at a very low temperature, in a state of 'suspended animation.' Highly effective and safe macromolecular cryoprotectants (CPAs) have gained significant attention as they obviate the toxicity of conventional CPAs like dimethyl sulfoxide (DMSO) and reduce the risks involved in the storage of cultures at liquid nitrogen temperatures. These agents provide cryoprotection through multiple mechanisms, involving extracellular and intracellular macromolecular crowding, thereby impacting the biophysical and biochemical dynamics of the freezing medium and the cryopreserved cells. These CPAs vary in their structures and physicochemical properties, which influence their cryoprotective activities. Moreover, the introduction of polymeric crowders in the cryopreservation media enables serum-free storage at low-DMSO concentrations and high-temperature vitrification of frozen cultures (-80 °C). This review highlights the need for macromolecular CPAs and describes their mechanisms of cryopreservation, by elucidating the role of crowding effects. It also classifies the macromolecules based on their chemistry and their structure-activity relationships. Furthermore, this article provides perspectives on the factors that may influence the outcomes of the cell freezing process or may help in designing and evaluating prospective macromolecules. This manuscript also includes case studies about cellular investigations that have been conducted to demonstrate the cryoprotective potential of macromolecular CPAs. Ultimately, this review provides essential directives that will further improve the cell cryopreservation process and may encourage the use of macromolecular CPAs to fortify basic, applied, and translational research.

Towards increasing stallion sperm longevity by storage at subzero temperatures in the absence of ice

The aim of cell preservation technologies is to slow down damaging reactions by lowering the storage temperature. Upon dilution in a stabilizing extender, stallion sperm can be stored at refrigerator temperatures for several days. Cryopreservation allows storage for decades, but freezing and thawing cause damage and viability losses. It is assumed that by storing cells at subzero temperatures in a non-frozen supercooled state, the damaging effects of ice formation can be avoided. In this study, we have investigated if stallion sperm can be stored at -10°C in the absence of ice, and compared viability during supercooled storage with that during storage at 5°C. We found that addition of 2% Ficoll-400 to buffered saline and covering with mineral oil depressed the sample freezing point and inhibited surface-catalyzed nucleation. This allowed storage in a supercooled state at -10°C for up to 7 days. Supplementing specimens with sperm, however, increased the incidence of sample freezing. Nonetheless, with 50×10⁶ sperm mL^-1, about 40% of the samples turned out to be non-frozen. Adding 100 mM sucrose was found to preserve sperm membrane intactness during supercooled storage, although this resulted in lower percentages as found with refrigerated storage. Sperm motility appeared to be lost during supercooled storage but could be partly restored by substituting buffered saline with a milk-based extender as base medium. Percentages of membrane intact sperm, however, were found to be lower. Supercooled storage holds promise for semen preservation, but further optimization of the storage solution is required to preserve sperm motility.

High Sub-Zero Organ Preservation: A Paradigm of Nature-Inspired Strategies

The field of organ preservation is filled with advancements that have yet to see widespread clinical translation, with some of the more notable strategies deriving their inspiration from nature. While static cold storage (SCS) at 2 °C to 4 °C is the current state-of-the-art, it contributes to the current shortage of transplantable organs due to the limited preservation times it affords combined with the limited ability of marginal grafts (i.e. those at risk for post-transplant dysfunction or primary non-function) to tolerate SCS. The era of storage solution optimization to minimize SCS-induced hypothermic injury has plateaued in its improvements, resulting in a shift towards the use of machine perfusion systems to oxygenate organs at normothermic, sub-normothermic, or hypothermic temperatures, as well as the use of sub-zero storage temperatures to leverage the protection brought forth by a reduction in metabolic demand. Many of the rigors that organs are subjected to at low sub-zero temperatures (-80 °C to -196 °C) commonly used for mammalian cell preservation have yet to be surmounted. Therefore, this article focuses on an intermediate temperature range (0 °C to -20 °C), where much success has been seen in the past two decades. The mechanisms leveraged by organisms capable of withstanding prolonged periods at these temperatures through either avoiding or tolerating the formation of ice has provided a foundation for some of the more promising efforts. This article therefore aims to contextualize the translation of these strategies into the realm of mammalian organ preservation.

Prolonged Cold Ischemia Time in Mouse Heart Transplantation Using Supercooling Preservation

BACKGROUND

Supercooling preservation techniques store a donor organ below 0°C without freezing. This has great advantages in inhibiting metabolism and preserving the organ in comparison to conventional preservation at 4°C. We developed a novel supercooling technique using a liquid cooling apparatus and novel preservation and perfusion solutions. The purpose of this study was to evaluate the preservation effect of our supercooling preservation technique in a mouse heart transplantation model.

METHODS

Syngeneic heterotopic heart transplantation was performed in 3 groups of mice: (1) the nonpreservation group, in which the cardiac grafts were transplanted immediately after retrieval; (2) the conventional University of Wisconsin (UW) group, in which the cardiac grafts were stored in UW solution at 4°C for different periods of time; and (3) the supercooling group, in which the cardiac grafts were stored in a novel supercooling preservation solution at -8°C for different periods of time. The maximal preservation time was investigated. Twenty-four-hour sample data were collected and analyzed to compare supercooling preservation to conventional UW preservation.

RESULTS

Our technique yielded a stable -8°C supercooling state. Cardiac graft revival was successfully achieved after supercooling preservation for 144 hours, and long-term survival was observed after supercooling preservation for 96 hours. Posttransplant outcomes, including myocardial ischemia-reperfusion injury, oxidative stress-related damage, and myocardial cell apoptosis, were improved in comparison to conventional 4°C UW preservation.

CONCLUSIONS

Supercooling heart preservation at -8°C greatly prolonged the preservation time and improved the posttransplant outcomes in comparison to conventional 4°C UW preservation. Supercooling preservation is a promising technique for organ preservation.

The efficacy of ice recrystallization inhibitors in rat lung cryopreservation using a low cost technique for ex vivo subnormothermic lung perfusion

Although lung transplant remains the only option for patients with end-stage lung failure, short preservation times result in an inability to meet patient demand. Successful cryopreservation may ameliorate this problem; however, very little research has been performed on lung cryopreservation due to the inability to prevent ice nucleation or growth. Therefore, this research sought to characterize the efficacy of a small-molecule ice recrystallization inhibitor (IRI) for lung cryopreservation given its well-documented ability to control ice growth. Sprague-Dawley heart-lung blocks were perfused at room temperature using a syringe-pump. Cytotoxicity of the IRI was assessed through the subsequent perfusion with 0.4% (w/v) trypan blue followed by formalin-fixation. Ice control was assessed by freezing at a chamber rate of -5 °C/min to -20 °C and cryofixation using a low-temperature fixative. Post-thaw cell survival was determined by freezing at a chamber rate of -5 °C/min to -20 °C and thawing in a 37 °C water bath before formalin-fixation. In all cases, samples were paraffin-embedded, sliced, and stained with eosin. The IRI studied was found to be non-toxic, as cell membrane integrity following perfusion was not significantly different than controls (p = 0.9292). Alveolar ice grain size was significantly reduced by the addition of this IRI (p = 0.0096), and the addition of the IRI to DMSO significantly improved post-thaw cell membrane integrity when compared to controls treated with DMSO alone (p = 0.0034). The techniques described here provide a low-cost solution for rat ex vivo lung perfusion which demonstrated that the ice control and improved post-thaw cell survival afforded by IRI-use warrants further study.

Current techniques and the future of lung preservation

Although lung transplant remains the only option for patients suffering from end-stage lung failure, donor supply is insufficient to meet demand. Static cold preservation is the most common method to preserve lungs in transport to the recipient; however, this method does not improve lung quality and only allows for 8 h of storage. This results in lungs which become available for donation but cannot be used due to failure to meet physiologic criteria or an inability to store them for a sufficient time to find a suitable recipient. Therefore, lungs lost due to failure to meet physiological or compatibility criteria may be mitigated through preservation methods which improve lung function and storage durations. Ex situ lung perfusion (ESLP) is a recently developed method which allows for longer storage times and has been demonstrated to improve lung function such that rejected lungs can be accepted for donation. Although greater use of ESLP will help to improve donor lung utilization, the ability to cryopreserve lungs would allow for organ banking to better utilize donor lungs. However, lung cryopreservation research remains underrepresented in the literature despite its unique advantages for cryopreservation over other organs. Therefore, this review will discuss the current techniques for lung preservation, static cold preservation and ESLP, and provide a review of the cryopreservation challenges and advantages unique to lungs.

Supercooling preservation technology in food and biological samples: a review focused on electric and magnetic field applications

Freezing has been widely recognized as the most common process for long-term preservation of perishable foods; however, unavoidable damages associated with ice crystal formation lead to unacceptable quality losses during storage. As an alternative, supercooling preservation has a great potential to extend the shelf-life and maintain quality attributes of fresh foods without freezing damage. Investigations for the application of external electric field (EF) and magnetic field (MF) have theorized that EF and MF appear to be able to control ice nucleation by interacting with water molecules in foods and biomaterials; however, many questions remain open in terms of their roles and influences on ice nucleation with little consensus in the literature and a lack of clear understanding of the underlying mechanisms. This review is focused on understanding of ice nucleation processes and introducing the applications of EF and MF for preservation of food and biological materials.

Subzero organ preservation: the dawn of a new ice age?

PURPOSE OF REVIEW

Herein, we review the field of subzero organ preservation with a focus on recent developments in hepatic supercooling.

RECENT FINDINGS

Organ preservation is making a rapid shift from the decade old standard of storage on ice toward techniques that improve organ availability as well as preservation time. Long-term organ preservation would have tremendous benefits to the organ transplantation field, including better organ allocation, donor-recipient matching, as well as reduced preservation injury, and subsequent improvement of donor organ use. The formation of ice has proven an important limiting factor and novel techniques attempt to control or prevent freezing using cryoprotective agents, and highly controlled cooling regimens. Various techniques have been employed over the previous decades, including true organ freezing, vitrification, and subzero nonfreezing or supercooling. For most techniques, successful transplantation following long-term subzero preservation has remained elusive. Supercooling, however, recently delivered the first promising results, yielding survival after up to 4 days of supercooled preservation at -6°C.

SUMMARY

As the field of organ preservation undergoes significant development, the field of subzero preservation also receives renewed interest. Although many obstacles remain to be overcome to make subzero preservation feasible, novel techniques are beginning to show their potential in achieving long-term preservation.

Subzero 12-hour Nonfreezing Cryopreservation of Porcine Heart in a Variable Magnetic Field

BACKGROUND

A novel subzero nonfreezing heart preservation method has been developed. It uses a refrigerating device that generates a variable magnetic field, allowing the whole organ to be cooled simultaneously to a supercooled state without the use of cryoprotectant. As a fundamental experiment for heart preservation, we verified whether this novel method is able to suppress anaerobic metabolism and reduce damage in the hearts of large animals.

METHODS

Twelve porcine hearts were collected and preserved for 12 hours using a simple immersion method. The hearts were divided into 2 groups: 6 underwent nonfreezing preservation at -3°C in a variable magnetic field (subzero group), and 6 underwent conventional preservation at 4°C (conventional group). The quantity of anaerobic metabolism and the degree of ultrastructural change in the 2 groups were evaluated and compared.

RESULTS

The concentration of adenosine triphosphate in the myocardial tissue was significantly greater in the subzero group than in the conventional group (21.06±5.87 μmol/g vs 5.96±3.41 μmol/g; P < 0.05). The accumulated lactate concentration was significantly lower in the subzero group than in the conventional group (6.58±2.28 μmol/g vs 11.15±3.74 μmol/g; P < 0.05). The Flameng score, an index of ultrastructural changes to the mitochondria, was significantly lower in the subzero group than in the conventional group (1.28±0.40 vs 2.73±0.30; P < 0.05).

CONCLUSIONS

Subzero nonfreezing preservation using a variable magnetic field resulted in a remarkable suppression of anaerobic metabolism and myocardial protection in porcine hearts.

Supercooling enables long-term transplantation survival following 4 days of liver preservation

The realization of long–term human organ preservation will have groundbreaking effects on the current practice of transplantation. Herein we present a novel technique based on sub–zero non–freezing tissue preservation and extracorporeal machine perfusion that allows transplantation of rat livers preserved for up to 4 days, thereby tripling the viable preservation duration.

Effect of a magnetic field on Drosophila under supercooled conditions

Under subzero degree conditions, free water contained in biological cells tends to freeze and then most living things die due to low temperatures. We examined the effect of a variable magnetic field on Drosophila under supercooled conditions (a state in which freezing is not caused even below the freezing point). Under such supercooled conditions with the magnetic field at 0°C for 72 hours, -4°C for 24 hours and -8°C for 1 hour, the Drosophila all survived, while all conversely died under the supercooled conditions without the magnetic field. This result indicates a possibility that the magnetic field can reduce cell damage caused due to low temperatures in living things.

Subzero 24-hr nonfreezing rat heart preservation: a novel preservation method in a variable magnetic field

BACKGROUND

A new supercooling system using a variable magnetic field has been recently developed. Subzero nonfreezing preservation has been believed to be a beneficial method because of the lower metabolic rate. The purpose of this study was to evaluate the hemodynamic and metabolic effects of rat heart preservation in a variable magnetic field without cryoprotectants.

METHODS

Rat hearts were perfused ex vivo for 120 min after 24-hr preservation in two groups (n=6 each): (1) conventional storage group, in which the hearts were stored at 4°C, and (2) the subzero group, in which the hearts were preserved at -3°C in a variable magnetic field.

RESULTS

Reperfusion cardiac performance after preservation was significantly preserved in the subzero group compared with the conventional group with respect to heart rate, coronary flow, the peak positive dP/dt, and the peak negative dP/dt (P<0.05). Edema after reperfusion was significantly decreased (P<0.05), and the adenosine triphosphate level was higher in the subzero group (P<0.05).

CONCLUSIONS

The rat hearts preserved in a variable magnetic field at -3°C showed better hemodynamic and metabolic performance than those preserved using conventional storage at 4°C.

Therapeutic effect of surfactant inhalation during warm ischemia in an isolated rat lung perfusion model

Warm ischemia-reperfusion injury related to donation after cardiac death donors is a crucial and inevitable issue. As surfactant function is known to deteriorate during warm ischemia, we hypothesized that surfactant inhalation during warm ischemia would mitigate warm ischemia-reperfusion injury. We used an isolated rat lung perfusion model. The rats were divided into three groups: sham, control, and surfactant. In the control and surfactant groups, cardiac arrest was induced by ventricular fibrillation. Ventilation was restarted 110 min later; subsequently, the lungs were flushed, and heart and lung block was recovered. In the surfactant group, a natural bovine surfactant Surfacten(®) was inhaled for 3 min at the end of warm ischemia. Then, the lungs were reperfused for 80 min. Surfactant inhalation significantly improved graft functions, effectively increased lung tissue ATP levels, and significantly decreased mRNA levels of IL-6 and IL-6/IL-10 ratio at the end of reperfusion. Histologically, lungs in the surfactant group showed fewer signs of interstitial edema and hemorrhage, and significantly less neutrophilic infiltration than those in the control group. Our results indicated that surfactant inhalation in the last phase of warm ischemia maintained lung tissue energy levels and prevented cytokine production, resulting in the alleviation of warm ischemia-reperfusion injury.

Hypothermic machine perfusion ameliorates ischemia-reperfusion injury in rat lungs from non-heart-beating donors

BACKGROUND

The use of non-heart-beating donors (NHBD) has come into practice to resolve the shortage of donor lungs. This study investigated whether hypothermic machine perfusion (HMP) can improve the quality of NHBD lungs.

METHODS

An uncontrolled NHBD model was achieved in male Lewis rats. Ninety minutes after cardiac arrest, HMP was performed for 60 min at 6°C to 10°C. The first study investigated the physiological lung functions during HMP and the lung tissue energy levels before and after HMP. The second study divided the rats into three groups (n=6 each): no ischemia group; 90-min warm ischemia+60-min HMP+120-min static cold storage (SCS) (HMP group); and 90-min warm ischemia+180-min SCS group. All lungs were reperfused for 60 min at 37°C. Lung functions were evaluated at given timings throughout the experiments. Oxidative damage during reperfusion was evaluated immunohistochemically with a monoclonal antibody against 8-hydroxy-2'-deoxyguanosine.

RESULTS

The first study revealed that lung functions were stable during HMP. Lung tissue energy levels decreased during warm ischemia but were significantly increased by HMP (P<0.05). The second study confirmed that HMP significantly decreased pulmonary vascular resistance, increased pulmonary compliance, and improved pulmonary oxygenation. The ratio of 8-hydroxy-2'-deoxyguanosine positive cells to total cells significantly increased in the SCS group (P<0.01).

CONCLUSIONS

Short-term HMP improved lung tissue energy levels that decreased during warm ischemia and ameliorated ischemia-reperfusion injury with decreased production of reactive oxygen species.