Successful nonfreezing, subzero preservation of rat liver with 2,3-butanediol and type I antifreeze protein

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.

Current opinion: advances in machine perfusion and preservation of vascularized composite allografts - will time still matter?

PURPOSE OF REVIEW

A major hurdle hindering more widespread application of reconstructive transplantation is the very limited cold ischemia time (CIT) of vascularized composite allografts (VCAs). In this review, we discuss cutting edge machine perfusion protocols and preservation strategies to overcome this limitation.

RECENT FINDINGS

Several preclinical machine perfusion studies have demonstrated the multifactorial utility of this technology to extend preservation windows, assess graft viability prior to transplantation and salvage damaged tissue, yet there are currently no clinically approved machine perfusion protocols for reconstructive transplantation. Thus, machine perfusion remains an open challenge in VCA due to the complexity of the various tissue types. In addition, multiple other promising avenues to prolong preservation of composite allografts have emerged. These include cryopreservation, high subzero preservation, vitrification and nanowarming. Despite several studies demonstrating extended preservation windows, there are several limitations that must be overcome prior to clinical translation. As both machine perfusion and subzero preservation protocols have rapidly advanced in the past few years, special consideration should be given to their potential complementary utilization.

SUMMARY

Current and emerging machine perfusion and preservation technologies in VCA have great promise to transform the field of reconstructive transplantation, as every extra hour of CIT helps ease the complexities of the peri-transplant workflow. Amongst the many advantages, longer preservation windows may allow for elective procedures, improved matching, establishment of novel immunomodulatory protocols and global transport of grafts, ultimately enabling us the ability to offer this life changing procedure to more patients.

Chilling injury in human kidney tubule cells after subzero storage is not mitigated by antifreeze protein addition

By preventing freezing, antifreeze proteins (AFPs) can permit cells and organs to be stored at subzero temperatures. As metabolic rates decrease with decreasing temperature, subzero static cold storage (SZ-SCS) could provide more time for tissue matching and potentially lead to fewer discarded organs. Human kidneys are generally stored for under 24 h and the tubule epithelium is known to be particularly sensitive to static cold storage (SCS). Here, telomerase-immortalized proximal-tubule epithelial cells from humans, which closely resemble their progenitors, were used as a proxy to assess the potential benefit of SZ-SCS for kidneys. The effects of hyperactive AFPs from a beetle and Cryostasis Storage Solution were compared to University of Wisconsin Solution at standard SCS temperatures (4 °C) and at -6 °C for up to six days. Although the AFPs helped guard against freezing, lower storage temperatures under these conditions were not beneficial. Compared to cells at 4 °C, those stored at -6 °C showed decreased viability as well as increased lactate dehydrogenase release and apoptosis. This suggests that this kidney cell type might be prone to chilling injury and that the addition of AFPs to enable SZ-SCS may not be effective for increasing storage times.

Development of an industrial yeast strain for efficient production of 2,3-butanediol

As part of the transition from a fossil resources-based economy to a bio-based economy, the production of platform chemicals by microbial cell factories has gained strong interest. 2,3-butanediol (2,3-BDO) has various industrial applications, but its production by microbial fermentation poses multiple challenges. We have engineered the bacterial 2,3-BDO synthesis pathway, composed of AlsS, AlsD and BdhA, in a pdc-negative version of an industrial Saccharomyces cerevisiae yeast strain. The high concentration of glycerol caused by the excess NADH produced in the pathway from glucose to 2,3-BDO was eliminated by overexpression of NoxE and also in a novel way by combined overexpression of NDE1, encoding mitochondrial external NADH dehydrogenase, and AOX1, encoding a heterologous alternative oxidase expressed inside the mitochondria. This was combined with strong downregulation of GPD1 and deletion of GPD2, to minimize glycerol production while maintaining osmotolerance. The HGS50 strain produced a 2,3-BDO titer of 121.04 g/L from 250 g/L glucose, the highest ever reported in batch fermentation, with a productivity of 1.57 g/L.h (0.08 g/L.h per gCDW) and a yield of 0.48 g/g glucose or with 96% the closest to the maximum theoretical yield ever reported. Expression of Lactococcus lactis NoxE, encoding a water-forming NADH oxidase, combined with similar genetic modifications, as well as expression of Candida albicans STL1, also minimized glycerol production while maintaining high osmotolerance. The HGS37 strain produced 130.64 g/L 2,3-BDO from 280 g/L glucose, with productivity of 1.58 g/L.h (0.11 g/L.h per gCDW). Both strains reach combined performance criteria adequate for industrial implementation.

Antifreeze Proteins: Novel Applications and Navigation towards Their Clinical Application in Cryobanking

Antifreeze proteins (AFPs) or thermal hysteresis (TH) proteins are biomolecular gifts of nature to sustain life in extremely cold environments. This family of peptides, glycopeptides and proteins produced by diverse organisms including bacteria, yeast, insects and fish act by non-colligatively depressing the freezing temperature of the water below its melting point in a process termed thermal hysteresis which is then responsible for ice crystal equilibrium and inhibition of ice recrystallisation; the major cause of cell dehydration, membrane rupture and subsequent cryodamage. Scientists on the other hand have been exploring various substances as cryoprotectants. Some of the cryoprotectants in use include trehalose, dimethyl sulfoxide (DMSO), ethylene glycol (EG), sucrose, propylene glycol (PG) and glycerol but their extensive application is limited mostly by toxicity, thus fueling the quest for better cryoprotectants. Hence, extracting or synthesizing antifreeze protein and testing their cryoprotective activity has become a popular topic among researchers. Research concerning AFPs encompasses lots of effort ranging from understanding their sources and mechanism of action, extraction and purification/synthesis to structural elucidation with the aim of achieving better outcomes in cryopreservation. This review explores the potential clinical application of AFPs in the cryopreservation of different cells, tissues and organs. Here, we discuss novel approaches, identify research gaps and propose future research directions in the application of AFPs based on recent studies with the aim of achieving successful clinical and commercial use of AFPs in the future.

Structural diversity of marine anti-freezing proteins, properties and potential applications: a review

Cold-adapted organisms, such as fishes, insects, plants and bacteria produce a group of proteins known as antifreeze proteins (AFPs). The specific functions of AFPs, including thermal hysteresis (TH), ice recrystallization inhibition (IRI), dynamic ice shaping (DIS) and interaction with membranes, attracted significant interest for their incorporation into commercial products. AFPs represent their effects by lowering the water freezing point as well as preventing the growth of ice crystals and recrystallization during frozen storage. The potential of AFPs to modify ice growth results in ice crystal stabilizing over a defined temperature range and inhibiting ice recrystallization, which could minimize drip loss during thawing, improve the quality and increase the shelf-life of frozen products. Most cryopreservation studies using marine-derived AFPs have shown that the addition of AFPs can increase post-thaw viability. Nevertheless, the reduced availability of bulk proteins and the need of biotechnological techniques for industrial production, limit the possible usage in foods. Despite all these drawbacks, relatively small concentrations are enough to show activity, which suggests AFPs as potential food additives in the future. The present work aims to review the results of numerous investigations on marine-derived AFPs and discuss their structure, function, physicochemical properties, purification and potential applications.

Anti freeze proteins (Afp): Properties, sources and applications - A review

Extreme cold marine and freshwater temperatures (below 4 °C) induce massive deterioration to the cell membranes of organisms resulting in the formation of ice crystals, consequently causing organelle damage or cell death. One of the adaptive mechanisms organisms have evolved to thrive in cold environments is the production of antifreeze proteins with the functional capabilities to withstand frigid temperatures. Antifreeze proteins are extensively identified in different cold-tolerant species and they facilitate the persistence of cold-adapted organisms by decreasing the freezing point of their body fluids. Various structurally diverse types of antifreeze proteins detected possess the ability to modify ice crystal growth by thermal hysteresis and ice recrystallization inhibition. The unique properties of antifreeze proteins have made them a promising resource in industry, biomedicine, food storage and cryobiology. This review collates the findings of the various studies carried out in the past and the recent developments observed in the properties, functional mechanisms, classification, distinct sources and the ever-increasing applications of antifreeze proteins. This review also summarizes the possibilities of the way forward to identify new avenues of research on anti-freeze proteins.

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.

2,3-Butanediol production using soy-based nitrogen source and fermentation process evaluation by a novel isolate of Bacillus licheniformis BL1

2,3-Butanediol (2,3-BDO) has varied applications in chemical, pharmaceutical, & food industry. Microorganisms belonging to Klebsiella, Enterobacter & Serratia genera are well-known producers of 2,3-BDO. However, they have limited usage in industrial-scale owing to their pathogenic nature. A nonpathogenic soil isolate identified as Bacillus licheniformis (BL1) was thus investigated for 2,3-BDO production. Soy flakes, soy flour, defatted soy, and soybean meal-based hydrolysates replaced yeast extract and peptone as nitrogen sources. Defatted soy flakes and soybean meal hydrolysate led to an equivalent 2,3-BDO yield and productivity as compared to that of Yeast Extract and peptone. The pH and oxygen variation influenced the proportion of various products of the mixed acid-butanediol pathway. Further, the batch mode fermentation with soy hydrolysate and optimized process parameter resulted in 2,3-BDO titer, yield and productivity of 11.06 g/L, 0.43 g/g and 0.48 g/L h respectively. Glucose concentration above 5% was inhibitory and led to reduction in the specific growth rate of BL1 in batch cultivation. Intermittent glucose feeding in fed-batch mode overcame this substrate limitation resulting in increased titers (49.8 g/L) and productivity (0.62 g/L h). Modified medium containing soy hydrolysate as nitrogen source with fermentation process optimization resulted in 67% decrease in medium cost for 2,3-BDO production.

Process optimization for mass production of 2,3-butanediol by Bacillus subtilis CS13

BACKGROUND

Bacillus subtilis CS13 was previously isolated for 2,3-butanediol (2,3-BD) and poly-γ-glutamic acid (γ-PGA) co-production. When culturing this strain without L-glutamic acid in the medium, 2,3-BD is the main metabolic product. 2,3-BD is an important substance and fuel with applications in the chemical, food, and pharmaceutical industries. However, the yield and productivity for the B. subtilis strain should be improved for more efficient production of 2,3-BD.

RESULTS

The medium composition, which contained 281.1 g/L sucrose, 21.9 g/L ammonium citrate, and 3.6 g/L MgSO₄·7H₂O, was optimized by response surface methodology for 2,3-BD production using B. subtilis CS13. The maximum amount of 2,3-BD (125.5 ± 3.1 g/L) was obtained from the optimized medium after 96 h. The highest concentration and productivity of 2,3-BD were achieved simultaneously at an agitation speed of 500 rpm and aeration rate of 2 L/min in the batch cultures. A total of 132.4 ± 4.4 g/L 2,3-BD was obtained with a productivity of 2.45 ± 0.08 g/L/h and yield of 0.45 g_2,3-BD/g_sucrose by fed-batch fermentation. The meso-2,3-BD/2,3-BD ratio of the 2,3-BD produced by B. subtilis CS13 was 92.1%. Furthermore, 89.6 ± 2.8 g/L 2,3-BD with a productivity of 2.13 ± 0.07 g/L/h and yield of 0.42 g_2,3-BD/g_sugar was achieved using molasses as a carbon source.

CONCLUSIONS

The production of 2,3-BD by B. subtilis CS13 showed a higher concentration, productivity, and yield compared to the reported generally recognized as safe 2,3-BD producers. These results suggest that B. subtilis CS13 is a promising strain for industrial-scale production of 2,3-BD.

Evaluation of 2,3-Butanediol Production from Red Seaweed Gelidium amansii Hydrolysates Using Engineered Saccharomyces cerevisiae

Hyper-thermal (HT) acid hydrolysis of red seaweed Gelidium amansii was performed using 12% (w/v) slurry and an acid mix concentration of 180 mM at 150°C for 10 min. Enzymatic saccharification when using a combination of Celluclast 1.5 L and CTec2 at a dose of 16 U/ml led to the production of 12.0 g/l of reducing sugar with an efficiency of enzymatic saccharification of 13.2%. After the enzymatic saccharification, 2,3-butanediol (2,3-BD) fermentation was carried out using an engineered S. cerevisiae strain. The use of HT acid-hydrolyzed medium with 1.9 g/l of 5-hydroxymethylfurfural showed a reduction in the lag time from 48 to 24 h. The 2,3-BD concentration and yield coefficient at 72 h were 14.8 g/l and 0.30, respectively. Therefore, HT acid hydrolysis and the use of the engineered S. cerevisiae strain can enhance the overall 2,3-BD yields from G. amansii seaweed.

Hypothermic preservation of rat hearts using antifreeze glycoprotein

Antifreeze proteins are an effective additive for low-temperature preservation of solid organs. Here, we compared static hypothermic preservation with and without antifreeze glycoprotein (AFGP), followed by nonfreezing cryopreservation of rat hearts. The heart was surgically extracted and immersed in one of the cardioplegia solutions after cardiac arrest. Control rat hearts (n=6) were immersed in University of Wisconsin (UW) solution whereas AFGP-treated hearts (AFGP group) (n=6) were immersed in UW solution containing 500 ?g/ml AFGP. After static hypothermic preservation, a Langendorff apparatus was used to reperfuse the coronary arteries with oxygenated Krebs-Henseleit solution. After 30, 60, 90, and 120 min, the heart rate (HR), coronary flow (CF), cardiac contractile force (max dP/dt), and cardiac diastolic force (min dP/dt) were measured. Tissue water content (TWC) and tissue adenosine triphosphate (ATP) levels in the reperfused preserved hearts were also assessed. All the parameters were compared between the control and AFGP groups. Compared with the control group, the AFGP group had significantly (p<0.05) higher values of the following parameters: HR at 60, 90, and 120 min; CF at all four time points; max dP/dt at 90 min; min dP/dt at 90 and 120 min; and tissue ATP levels at 120 min. TWC did not differ significantly between the groups. The higher HR, CF, max dP/dt, min dP/dt, and tissue ATP levels in the AFGP compared with those in control hearts suggested that AFGP conferred superior hemodynamic and metabolic functions. Thus, AFGP might be a useful additive for the static/nonfreezing hypothermic preservation of hearts.

A brief review of applications of antifreeze proteins in cryopreservation and metabolic genetic engineering

Antifreeze proteins (AFPs) confer the ability to survive at subzero temperatures and are found in many different organisms, including fish, plants, and insects. They prevent the formation of ice crystals by non-colligative adsorption to the ice surface and are essential for the survival of organisms in cold environments. These proteins are also widely used for cryopreservation, food technology, and metabolic genetic engineering over a range of sources and recipient cell types. This review summarizes successful applications of AFPs in the cryopreservation of animals, insects, and plants, and discusses challenges encountered in cryopreservation. Applications in metabolic genetic engineering are also described, specifically with the overexpression of AFP genes derived from different organisms to provide freeze protection to sensitive crops seasonally exposed to subzero temperatures. This review will provide information about potential applications of AFPs in the cryopreservation of animals and plants as well as in plant metabolic genetic engineering in hopes of furthering the development of cold-tolerant organisms.

Protecting activity of desiccated enzymes

Protein-based biological drugs and many industrial enzymes are unstable, making them prohibitively expensive. Some can be stabilized by formulation with excipients, but most still require low temperature storage. In search of new, more robust excipients, we turned to the tardigrade, a microscopic animal that synthesizes cytosolic abundant heat soluble (CAHS) proteins to protect its cellular components during desiccation. We find that CAHS proteins protect the test enzymes lactate dehydrogenase and lipoprotein lipase against desiccation-, freezing-, and lyophilization-induced deactivation. Our data also show that a variety of globular and disordered protein controls, with no known link to desiccation tolerance, protect our test enzymes. Protection of lactate dehydrogenase correlates, albeit imperfectly, with the charge density of the protein additive, suggesting an approach to tune protection by modifying charge. Our results support the potential use of CAHS proteins as stabilizing excipients in formulations and suggest that other proteins may have similar potential.

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.

Diversity Analysis and Bioresource Characterization of Halophilic Bacteria Isolated from a South African Saltpan

Though intensive research has been channeled towards the biotechnological applications of halophiles and other extremophilic microbes, these studies have not been, by any means, exhaustive. Saline environments still offer a vast diversity of microbes with potential to produce an array of natural products which can only be unlocked by concerted research efforts. In this study, a combination of culture and molecular approaches were employed to characterize halophilic bacteria from saltpan water samples and profile their potential biotechnological applications. Physicochemical analysis of the water samples showed that pH was alkaline (pH 8.8), with a salinity of 12.8%. 16S rRNA gene targeted amplicon analysis produced 10 bacterial phyla constituting of Bacteroidetes (30.57%), Proteobacteria (15.27%), Actinobacteria (9.05%), Planctomycetes (5.52%) and Cyanobacteria (3.18%). Eighteen strains were identified using sequencing analysis of the culturable bacterial strains. From these, the strains SP7 and SP9 were positive for cellulase production while the strains SP4, SP8 and SP22 were positive for lipase production. Quantitative enzyme assays showed moderate extracellular cellulase activity (1.95 U/mL) and lipase activity (3.71 U/mL) by the isolate SP9 and SP4 respectively. Further, of the six isolates, the isolate SP9 exhibited exploitable potential in the bioremediation of hydrocarbon pollution as demonstrated by its fairly high activity against benzanthracene (70% DCPIP reduction). Elucidation of the isolates secondary metabolites showed the production of the molecules 2,3-butanediol, hexahydro-3-(2-methylpropyl)pyrrole[1,2a]pyrazine-1,4-dione, aziridine, dimethylamine and ethyl acetate (GC-MS) and oxypurinol and 5-hydroxydecanoic acid (LC-MS), particularly by the isolate Salinivibrio sp. SP9. Overall, the study showed that the isolated halophiles can produce secondary metabolites with potential industrial and pharmaceutical application.

Marine Antifreeze Proteins: Structure, Function, and Application to Cryopreservation as a Potential Cryoprotectant

Antifreeze proteins (AFPs) are biological antifreezes with unique properties, including thermal hysteresis(TH),ice recrystallization inhibition(IRI),and interaction with membranes and/or membrane proteins. These properties have been utilized in the preservation of biological samples at low temperatures. Here, we review the structure and function of marine-derived AFPs, including moderately active fish AFPs and hyperactive polar AFPs. We also survey previous and current reports of cryopreservation using AFPs. Cryopreserved biological samples are relatively diverse ranging from diatoms and reproductive cells to embryos and organs. Cryopreserved biological samples mainly originate from mammals. Most cryopreservation trials using marine-derived AFPs have demonstrated that addition of AFPs can improve post-thaw viability regardless of freezing method (slow-freezing or vitrification), storage temperature, and types of biological sample type.

Introduction of the exogenous NADH coenzyme regeneration system and its influence on intracellular metabolic flux of Paenibacillus polymyxa

The NAD(+)-dependent formate dehydrogenase (FDH) gene from Candida boidinii was introduced into Paenibacillus polymyxa ZJ-9. The effects of this exogenous gene on the growth of the recombinant strain P. polymyxa XG-1, FDH activity, intracellular NADH and NAD(+) level and the synthesis of R,R-2,3-butanediol (R,R-2,3-BD) were determined. Results from the fermentation in the 7.5L bioreactor showed that the exogenous FDH was highly expressed in the recombinant strain. The titers of NADH, lactic acid, ethanol, NADH/NAD(+), and CO2 excretion rate (CER) of the recombinant strain increased considerably, while acetoin and formic acid decreased significantly. The highest titers of R,R-2,3-BD by the recombinant strain in batch and fed-batch fermentation were 36.8g/L and 51.3g/L, increased 10.2% and 8.0% compared with the parent strain, respectively. This study confirmed that coenzyme regeneration system can manipulate substance metabolism in bacteria, and is an efficient way for promoting the synthesis of NADH-dependent products.

Frostbite protection in mice expressing an antifreeze glycoprotein

Ectotherms in northern latitudes are seasonally exposed to cold temperatures. To improve survival under cold stress, they use diverse mechanisms to increase temperature resistance and prevent tissue damage. The accumulation of anti-freeze proteins that improve cold hardiness occurs in diverse species including plants, arthropods, fish, and amphibians. We previously identified an Ixodes scapularis anti-freeze glycoprotein, named IAFGP, and demonstrated its cold protective function in the natural tick host and in a transgenic Drosophila model. Here we show, in a transgenic mouse model expressing an anti-freeze glycoprotein, that IAFGP protects mammalian cells and mice from cold shock and frostbite respectively. Transgenic skin samples showed reduced cell death upon cold storage ex vivo and transgenic mice demonstrated increased resistance to frostbite injury in vivo. IAFGP actively protects mammalian tissue from freezing, suggesting its application for the prevention of frostbite, and other diseases associated with cold exposure.

Recombinant Dendroides canadensis antifreeze proteins as potential ingredients in cryopreservation solutions

Expanding cryopreservation methods to include a wider range of cell types, such as those sensitive to freezing, is needed for maintaining the viability of cell-based regenerative medicine products. Conventional cryopreservation protocols, which include use of cryoprotectants such as dimethylsulfoxide (Me2SO), have not prevented ice-induced damage to cell and tissue matrices during freezing. A family of antifreeze proteins (AFPs) produced in the larvae of the beetle, Dendroides canadensis allow this insect to survive subzero temperatures as low as -26°C. This study is an assessment of the effect of the four hemolymph D. canadensis AFPs (DAFPs) on the supercooling (nucleating) temperature, ice structure patterns and viability of the A10 cell line derived from the thoracic aorta of embryonic rat. Cryoprotectant solution cocktails containing combinations of DAFPs in concentrations ranging from 0 to 3mg/mL in Unisol base mixed with 1M Me2SO were first evaluated by cryomicroscopy. Combining multiple DAFPs demonstrated significant supercooling point depressing activity (∼9°C) when compared to single DAFPs and/or conventional 1M Me2SO control solutions. Concentrations of DAFPs as low as 1 μg/mL were sufficient to trigger this effect. In addition, significantly improved A10 smooth muscle cell viability was observed in cryopreservation experiments with low DAFP-6 and DAFP-2 concentrations in combination with Me2SO. No significant improvement in viability was observed with either DAFP-1 or DAFP-4. Low and effective DAFP concentrations are advantageous because they minimize concerns regarding cell cytotoxicity and manufacturing cost. These findings support the potential of incorporating DAFPs in solutions used to cryopreserve cells and tissues.

Utilizing avidity to improve antifreeze protein activity: a type III antifreeze protein trimer exhibits increased thermal hysteresis activity

Antifreeze proteins (AFPs) are ice growth inhibitors that allow the survival of several species living at temperatures colder than the freezing point of their bodily fluids. AFP activity is commonly defined in terms of thermal hysteresis, which is the difference observed for the solution freezing and melting temperatures. Increasing the thermal hysteresis activity of these proteins, particularly at low concentrations, is of great interest because of their wide range of potential applications. In this study, we have designed and expressed one-, two-, and three-domain antifreeze proteins to improve thermal hysteresis activity through increased binding avidity. The three-domain type III AFP yielded significantly greater activity than the one- and two-domain proteins, reaching a thermal hysteresis of >1.6 °C at a concentration of <1 mM. To elucidate the basis of this increase, the data were fit to a multidomain protein adsorption model based on the classical Langmuir isotherm. Fits of the data to the modified isotherms yield values for the equilibrium binding constants for the adsorption of AFP to ice and indicate that protein surface coverage is proportional to thermal hysteresis activity.

Supercooling as a viable non-freezing cell preservation method of rat hepatocytes

Supercooling preservation holds the potential to drastically extend the preservation time of organs, tissues and engineered tissue products, and fragile cell types that do not lend themselves well to cryopreservation or vitrification. Here, we investigate the effects of supercooling preservation (SCP at -4(o)C) on primary rat hepatocytes stored in cryovials and compare its success (high viability and good functional characteristics) to that of static cold storage (CS at +4(o)C) and cryopreservation. We consider two prominent preservation solutions a) Hypothermosol (HTS-FRS) and b) University of Wisconsin solution (UW) and a range of preservation temperatures (-4 to -10 (o)C). We find that there exists an optimum temperature (-4(o)C) for SCP of rat hepatocytes which yields the highest viability; at this temperature HTS-FRS significantly outperforms UW solution in terms of viability and functional characteristics (secretions and enzymatic activity in suspension and plate culture). With the HTS-FRS solution we show that the cells can be stored for up to a week with high viability (~56%); moreover we also show that the preservation can be performed in large batches (50 million cells) with equal or better viability and no loss of functionality as compared to smaller batches (1.5 million cells) performed in cryovials.

Antifreeze peptides and glycopeptides, and their derivatives: potential uses in biotechnology

Antifreeze proteins (AFPs) and glycoproteins (AFGPs), collectively called AF(G)Ps, constitute a diverse class of proteins found in various Arctic and Antarctic fish, as well as in amphibians, plants, and insects. These compounds possess the ability to inhibit the formation of ice and are therefore essential to the survival of many marine teleost fishes that routinely encounter sub-zero temperatures. Owing to this property, AF(G)Ps have potential applications in many areas such as storage of cells or tissues at low temperature, ice slurries for refrigeration systems, and food storage. In contrast to AFGPs, which are composed of repeated tripeptide units (Ala-Ala-Thr)_n with minor sequence variations, AFPs possess very different primary, secondary, and tertiary structures. The isolation and purification of AFGPs is laborious, costly, and often results in mixtures, making characterization difficult. Recent structural investigations into the mechanism by which linear and cyclic AFGPs inhibit ice crystallization have led to significant progress toward the synthesis and assessment of several synthetic mimics of AFGPs. This review article will summarize synthetic AFGP mimics as well as current challenges in designing compounds capable of mimicking AFGPs. It will also cover our recent efforts in exploring whether peptoid mimics can serve as structural and functional mimics of native AFGPs.

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.

Enhanced activity of meso-secondary alcohol dehydrogenase from Klebsiella species by codon optimization

Meso-secondary alcohol dehydrogenases (meso-SADH) from Klebsiella oxytoca KCTC1686 and Klebsiella pneumoniae KCTC2242 were codon optimized and expressed in Escherichia coli W3110. The published gene data of K. pneumoniae NTUH-K2044 (NCBI accession number AP006725), K. pneumoniae 342 (NCBI accession number CP000964), and K. pneumoniae MGH 78578 (NCBI accession number CP000647), were compared with the meso-SADH sequences of each strain, respectively. Codon-optimized meso-SADH enzymes of K. oxytoca and K. pneumoniae showed approximately twofold to fivefold increased enzyme activities for acetoin reduction over native enzymes. The highest activities for each strain were obtained at 30-37 °C and pH 6-7 (yielding 203.1 U/mg of protein and 156.5 U/mg of protein, respectively). The increased enzyme activity of the codon-optimized enzymes indicated that these modified enzymes could convert acetoin into 2,3-butanediol with a high yield.

Conjugation of type I antifreeze protein to polyallylamine increases thermal hysteresis activity

Antifreeze proteins (AFPs) are ice binding proteins found in some plants, insects, and Antarctic fish allowing them to survive at subzero temperatures by inhibiting ice crystal growth. The interaction of AFPs with ice crystals results in a difference between the freezing and melting temperatures, termed thermal hysteresis, which is the most common measure of AFP activity. Creating antifreeze protein constructs that reduce the concentration of protein needed to observe thermal hysteresis activities would be beneficial for diverse applications including cold storage of cells or tissues, ice slurries used in refrigeration systems, and food storage. We demonstrate that conjugating multiple type I AFPs to a polyallylamine chain increases thermal hysteresis activity compared to the original protein. The reaction product is approximately twice as active when compared to the same concentration of free proteins, yielding 0.5 °C thermal hysteresis activity at 0.3 mM protein concentration. More impressively, the amount of protein required to achieve a thermal hysteresis of 0.3 °C is about 100 times lower when conjugated to the polymer (3 μM) compared to free protein (300 μM). Ice crystal morphologies observed in the presence of the reaction product are comparable to those of the protein used in the conjugation reaction.

Microbial 2,3-butanediol production: a state-of-the-art review

2,3-butanediol is a promising bulk chemical due to its extensive industry applications. The state-of-the-art nature of microbial 2,3-butanediol production is reviewed in this paper. Various strategies for efficient and economical microbial 2,3-butanediol production, including strain improvement, substrate alternation, and process development, are reviewed and compared with regard to their pros and cons. This review also summarizes value added derivatives of biologically produced 2,3-butanediol and different strategies for downstream processing. The future prospects of microbial 2,3-butanediol production are discussed in light of the current progress, challenges, and trends in this field. Guidelines for future studies are also proposed.

Subzero nonfreezing storage of C3A hepatocytes for use in bioartificial liver support systems

AIM: To investigate whether subzero nonfreezing storage (-0.8 °C) is superior to conventional cold storage in preservation of C3A hepatocytes for use in bioartificial liver support systems.

METHODS: C3A hepatocytes suspended in University of Wisconsin (UW) solution were divided into three groups: subzero nonfreezing group (-0.8 °C), zero nonfreezing group (0 °C) and control group (4 °C). After 24, 48 and 72 hours of hypothermic storage, cell viability and apoptosis were detected by flow cytometry; intracellular adenosine triphosphate (ATP) content, lactate dehydrogenase (LDH) release, lactic acid production, urea synthesis and albumin secretion were determined; and cell morphological changes were observed.

RESULTS: Compared to the zero nonfreezing group and the control group, after 72 hours of hypothermic storage, the percentage of viable C3A hepatocytes was significantly higher (86.49% ± 2.80% vs 81.50% ± 2.83% and 77.83% ± 3.40%, respectively; both P < 0.05), and cell apoptosis rate was significantly lower (1.26% ± 0.84% vs 5.34% ± 1.20% and 9.16% ± 1.99%, respectively; both P < 0.05) in the subzero nonfreezing group. Lactic acid and LDH production was more significantly suppressed (lactic acid: 10.38 μg/10⁶ cells ± 1.40 μg/10⁶ cells vs 12.02 μg/10⁶ cells ± 1.64 μg/106 cells and 17.41 μg/10⁶ cells ± 2.40 μg/10⁶ cells; LDH: 80.10 U/L ± 11.10 U/L vs 120.04 U/L ± 14.32 U/L and 148.98 U/L ± 15.37 U/L, respectively; all P < 0.05), and the ability of hepatocytes to synthesize urea and secrete albumin was better maintained in the subzero nonfreezing group (both P < 0.05). Moreover, cells in the subzero nonfreezing storage group had lower death rate and better cellular morphology. A burr-like structure around the cell membrane and an intracellular vacuole-like structure were found in cells in the zero nonfreezing group and the control group, but not in the subzero nonfreezing group.

CONCLUSION: Subzero nonfreezing storage (-0.8 °C) of hepatocytes to construct a "ready-to-use" hepatocyte bank like the "blood bank" will efficiently promote the development of bioartificial liver support systems.

Biotechnological production of 2,3-butanediol--current state and prospects

Biotechnological production of 2,3-butanediol (hereafter referred to as 2,3-BD) from wastes and excessive biomass is a promising and attractive alternative for traditional chemical synthesis. In the face of scarcity of fossil fuel supplies the bio-based process is receiving a significant interest, since 2,3-BD may have multiple practical applications (e.g. production of synthetic rubber, plasticizers, fumigants, as an antifreeze agent, fuel additive, octane booster, and many others). Although the 2,3-BD pathway is well known, microorganisms able to ferment biomass to 2,3-BD have been isolated and described, and attempts of pilot scale production of this compound were made, still much has to be done in order to achieve desired profitability. This review summarizes hitherto gained knowledge and experience in biotechnological production of 2,3-BD, sources of biomass used, employed microorganisms both wild type and genetically improved strains, as well as operating conditions applied.

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

BACKGROUND

A lower temperature, namely below 0 degrees C, has been thought to be desirable for organ preservation because of the lower rate of metabolism; however, its benefits are still poorly understood. Supercooling is a non-freezing state of liquid below the freezing point, and the new development of a refrigerator for supercooling has now made it possible to preserve organs at sub-zero temperatures in a non-frozen state without cryoprotectants.

METHODS

Rat lungs were ventilated and perfused for 60 minutes in the 3 groups (n = 7 each): (1) the fresh group, in which the lungs were reperfused immediately after harvesting; (2) the 4 degrees C group, in which the lungs were stored after harvesting in ET-Kyoto solution at 4 degrees C for 17 hours before reperfusion; and (3) the supercooling group, in which lungs were preserved in ET-Kyoto solution at -2 degrees C for 17 hours.

RESULTS

Ischemia-reperfusion injury was significantly attenuated in the supercooling group, with a decrease in the pulmonary artery pressure (p < 0.02) and weight gain (p < 0.001), and an increase in the tidal volume (p = 0.001) and arterial oxygen tension (p < 0.001) compared with the 4 degrees C group. In the supercooling group, most of these indicators were equivalent to the fresh lung, with less damage to the endothelial cells of the pulmonary arteries and higher levels of adenosine triphosphate than in the 4 degrees C group.

CONCLUSIONS

Lungs stored using this new supercooling method of lung preservation showed better organ function than conventional storage at 4 degrees C.

Cloning and expression of Tenebrio molitor antifreeze protein in Escherichia coli

A novel antifreeze protein cDNA was cloned by RT-PCR from the larva of the yellow mealworm Tenebrio molitor. The coding fragment of 339 bp encodes a protein of 112 amino acid residues and was fused to the expression vectors pET32a and pTWIN1. The resulted expression plasmids were transformed into Escherischia coli strains BL21 (DE3), ER2566, and Origami B (DE3), respectively. Several strategies were used for expression of the highly disulfide-bonded beta-helix-contained protein with the activity of antifreeze in different expression systems. A protocol for production of refolded and active T. molitor antifreeze protein in bacteria was obtained.

In vitro studies of antifreeze glycoprotein (AFGP) and a C-linked AFGP analogue

Antifreeze glycoproteins (AFGPs) are a subclass of biological antifreezes found in deep sea Teleost fish. These compounds have the ability to depress the freezing point of the organism such that it can survive the subzero temperatures encountered in its environment. This physical property is very attractive for the cryopreservation of cells, tissues, and organs. Recently, our laboratory has designed and synthesized a functional carbon-linked (C-linked) AFGP analogue (1) that demonstrates tremendous promise as a novel cryoprotectant. Herein we describe the in vitro effects and interactions of C-linked AFGP analogue 1 and native AFGP 8. Our studies reveal that AFGP 8 is cytotoxic to human embryonic liver and human embryonic kidney cells at concentrations higher than 2 and 0.63 mg/mL, respectively, whereas lower concentrations are not toxic. The mechanism of this cytotoxicity is consistent with apoptosis because caspase-3/7 levels are significantly elevated in cell cultures treated with AFGP 8. In contrast, C-linked AFGP analogue 1 displayed no in vitro cytotoxicity even at high concentrations, and notably, caspase-3/7 activities were suppressed well below background levels in cell lines treated with 1. Although the results from these studies limit the human applications of native AFGP, they illustrate the benefits of developing functional C-linked AFGP analogues for various medical, commercial and industrial applications.

Conformational Study of Monomeric 2,3-Butanediols by Matrix-Isolation Infrared Spectroscopy and DFT Calculations

The FT-IR spectra of two diastereomers of 2,3-butanediol, (R,S) and (S,S), isolated in low-temperature argon and xenon matrixes were studied, allowing the identification of two different conformers for each compound. These conformers were characterized by a +/-gauche arrangement around the O-C-C-O dihedral angle, thus enabling the establishment of a very weak intramolecular hydrogen bond of the O...H-O type. No other forms of these compounds were identified in matrixes, despite the fact that these four conformers had calculated relative energies from 0 to 5.1 kJ mol(-1) and were expected to be thermally populated from 50 to 6% in the gaseous phase of each compound. The nonobservation of additional conformers was explained in terms of low barriers to intramolecular rotation, resulting in the conformational relaxation of the compounds during deposition of the matrixes. The barriers to internal rotation of the OH groups were computed to be less than 4 kJ mol(-1) and are easily overcome in matrixes within the family of conformers with the same heavy atom backbone. The barriers for intramolecular rearrangement of the O-C-C-O dihedral angle in both diastereomers were calculated to range from 20 to 30 kJ mol(-1). Interconversions between the latter conformers were not observed in matrixes, even after annealing up to 65 K. Energy calculations, barriers, and calculated infrared spectra were carried out at the DFT(B3LYP)/6-311++G theory. Additional MP2/6-311++G calculations of energies and vibrational frequencies were performed on the most relevant conformers. Finally, independent estimations of the hydrogen-bond enthalpy in the studied molecules were also obtained based on theoretical structural data and from vibrational frequencies (using well-established empirical correlations). The obtained values for -DeltaH for both diastereomers of 2,3-butanediol amount to ca. 6-8 kJ mol(-1).