Long-term,large scale cryopreservation of insect cells at −80 °C

Standard tissue culture methods advise freezing cells in small aliquots (≤1 × 10⁷ cells in 1 mL), and storing in liquid nitrogen. This is inconvenient for laboratories culturing large quantities of insect cells for recombinant baculovirus expression, owing to the length of time taken to produce large scale cultures from small aliquots of cells. Liquid nitrogen storage requires use of specialized cryovials, personal protective equipment and oxygen monitoring systems. This paper describes the long-term, large scale cryopreservation of 8 × 10⁸ insect cells at −80 °C, using standard 50 mL conical tubes to contain a 40 mL cell suspension. Sf9, Sf21 and High 5 cells were recovered with a viability > 90 % after storage for one year under these conditions, which compared favorably with the viability of cells stored in liquid nitrogen for the same length of time. Addition of green fluorescent protein encoding baculovirus demonstrated that cells were “expression ready” immediately post thaw. Our method enables large scale cultures to be recovered rapidly from stocks cryopreserved at −80 °C, thus avoiding the inconvenience, hazards and expense associated with liquid nitrogen.

Electronic supplementary material

The online version of this article (doi:10.1007/s10616-014-9781-5) contains supplementary material, which is available to authorized users.     

The influence on enzyme activity of storage of tissue blocks at −70° C

Summary Blocks of tissue from various organs of the rat have been chilled by precipitate immersion in n-hexane cooled to –70° C, and then stored at –70° C. At various intervals (up to 14 days) after chilling, cryostat sections were prepared from these blocks and assayed for the activity of a variety of enzymes. Enzyme activity was measured by scanning and integrating microdensitometry. With the exception of acid phosphatase and cytochrome oxidase, all enzymes assayed were stable for at least 7 days after storage at –70° C and most were stable for 14 days. Storage of fresh-frozen sections at –30° C in the cabinet of the cryostat, for up to 24 h, had little effect on enzyme activity.     

Cryopreservation at −80°C of Agaricus blazei on rice grains

The preservation of Agaricus blazei is generally done by mycelial subculturing, but this technique may cause genetic degenerations. Despite this, there is not an efficient protocol established to preserve this fungus and cryopreservation could be an alternative. This study aimed to evaluate two freezing protocols for cryopreservation at −80°C of A. blazei strains. Five fungus strains grown on rice grains with husk and were transferred to glycerol (10%) in cryovials. Next, the cryovials were submitted to two freezing temperature protocols: (1) cryopreservation starting at 25°C, then at 8°C for 30 min and kept at −80°C; (2) cryopreservation starting at 25°C, then 8°C for 30 min, −196°C for 15 min and kept at −80°C. After 1 year of cryopreservation, the cryovials were thawed in a water bath at 30°C for 15 min and transferred to malt extract agar medium. It was concluded that the one-year cryopreservation process of A. blazei, grown on rice grains and cryopreserved at −80°C in glycerol 10%, is viable. The slow freezing, from 8 to −80°C, is effective whereas the fast freezing, from 8 to −196°C and then to −80°C, is ineffective. The different genetic characteristics among the strains of this fungus do not interfere in the cryopreservation process.     

Cryopreservation of functionally active blood nuclear cell membranes at −80°C

Structural and functional changes in cytoplasmic membranes and cell organelles play a crucial role in cell damage at low temperatures. These changes are reversible if adequate measures are taken to protect biological membranes against cold-induced injuries. In this study, the possibility of cryopreservation of membrane integrity by long-term storage of samples at low temperatures (?80°C) is demonstrated using differentiated nuclear blood cells as an example. In addition to classical methods, freezing of human leukocyte suspensions was carried out in a novel nontoxic cryoprotecting solution under a newly developed exponential freezing program based on the use of cryoprotectors and repair additives. This program ensures the same cryopreservation effect as the linear program, but is economically more efficient and less labor-consuming. After exponential freezing in a cryoprotecting solution and storage at ?80°C, blood leukocytes retain their eosin resistance (91 ± 5% of thawed leukocytes) and phagocytic activity (76.7 ± 14.7% of thawed neutrophils) for 180 days. The novel technology of cell cryopreservation employing a nontoxic cryoprotecting solution, exponential freezing program, and fast thawing is economically efficient, easy to perform and applicable to storage of any animal cells.     

Rapid cryopreservation of five mammalian and one mosquito cell line at −80°C while attached to flasks in a serum free cryopreservative

Cell culturing, and the requisite storage of cell lines at ultra-low temperatures, is used in most laboratories studying or using eukaryotic proteomics, genomics, microarray, and RNA technologies. In this study we have observed that A72(dog), CRFK(cat), NB324K(human), MCF7(human), WI38(human), and C636(mosquito) cells were effectively cryopreserved at −80°C while attached to the substratum of 25cm² tissue culture flasks. This was accomplished using a serum free crypreservative recently developed by Corsini and co-workers. The technique allows for significant savings of time and money in laboratories that rapidly process numerous cell lines.     

Biosynthetic capacity of hepatocytes after storage at 4°C

Capacity to synthesize glucose, urea, and ketone bodies is well maintained in hepatocytes after storage for at least 24 h at 4 degrees C. Substrates and albumin are the only requirements.     

A method to maintain mammalian cells for days alive at 4 °C

This paper describes a method for the temporary storage of cultured cells. Cells from recently completed cell monolayers were trypsinized and then centrifuged. After centrifugation, the supernatant and pellet were kept at 4 °C for one week. After storage, the supernatant was discarded, the cells were resuspended and used for seeding new flasks and for titration of virus. The cells not only remained viable, but also rapidly formed new monolayers and allowed immediate infection and growth of viruses. We conclude that this method can be a helpful asset to cell culture experiments.     

Water and electrolyte contents and extracellular space of rabbit kidneys after perfusion and storage for 24 hr at 4 °C

Rabbit kidneys were perfused with 50 ml of various solutions at 4 °C and then stored in the same solution at 4 °C for 24 hr. The solutions studied were as follows: WF1 was a balanced electrolyte solution resembling extracellular fluid; in WF2, sufficient glucose was added to raise the osmolality to 400 mosmol/kg; in WF3, one half (70 mmol) of the NaCl was omitted, but in this and in all subsequent solutions the total osmolality was maintained at 400 mosmol/kg by the inclusion of an appropriate amount of glucose; in WF4, 70 meq of Na⁺ was replaced by K⁺, in WF5, 70 meq of Na⁺ was replaced by Mg²⁺.After storage, cortical slices were cut from each kidney, and the extracellular space was measured with ⁵¹Cr-EDTA, water content by drying to constant weight, and total Na⁺ and K⁺ by flame photometry. Intracellular Na⁺ and K⁺ concentrations were calculated.It was found that the water content of all the perfused kidneys was increased but was lowest when the osmolality had been raised to 400 mosmol/kg with glucose, and the ionic strength was normal; the kidneys perfused with WF5 had the lowest water content. Gained water was generally distributed equally between the intracellular and the extracellular space, but cell swelling was prevented by the WF5 solution. All kidneys gained Na⁺ and all except those perfused with WF4 (the high-K⁺ solution) lost K⁺, but the loss was least with WF5.Overall, the changes during storage were least in the kidneys perfused with the highosmolality, high-Mg²⁺ solution, WF5. It is suggested that this solution may be useful as a washout fluid for short-term renal preservation.     

Effect of in vitro storage at 4 °C on survival and proliferation of poplar shoots

Shoot explants of in vitro proliferating cultures of Populus tremula (L.) x Populus tremuloides (L.) were stored for three months at 4°C, in dark or light, in basal culture medium with or without 2-isopentenyladenine (2iP), and in rooting medium with naphthalene acetic acid. They were transferred to cold at different times after subculturing. One hundred percent of shoots survived all tested conditions, in spite of leaf browing and necrosis. After transfer to 24°C for 2 weeks and a normal multiplication cycle, the shoots proliferated at a rate similar to controls or at a higher rate in the case of shoots introduced into the cold 7 or 14 days after subculture and stored in dark on medium containing 2iP.Abbreviations 2iP 2-isopentenyladenine - NAA naphthaleneacetic acid - MS Murashige & Skoog (1962) medium     

Recovery of viable cells from rabbit skin biopsies after storage at ?20°C for up to 10?days

Frozen animal tissues are thought to be appropriate for use as a donor for somatic cell nuclear transfer. This makes the freezing for long term storage a valuable tool for breeders needing to protect an animal population that is endangered by sanitary problems or for cryobanking of genetic resources. We report the successful cryopreservation of explants of skin derived from small biopsies from rabbit ear biopsies by using a protocol that can be easily performed by usual breeders, which are not equipped with cooling devices. By optimizing the procedure, we show that small biopsies can be kept at -20°C in a physiological solution containing 10% DMSO for up to 20 days before being deeply frozen in liquid nitrogen for long-term storage. After 10 days of storage at -20°C, the rate of viability of biopsies was similar to the control one (86 and 82% respectively). After 20 days of storage at -20°C, the rate of viability was dramatically lowered (39%), but it still allows to recover a significant population of viable cells from the preserved sample. Being appropriate to places lacking specific device, such a very simple technique may contribute to facilitate genome banking policies dedicated to the management of genetic resources in wild and domestic animals.     

Survival of mouse oocytes after being cooled in a vitrification solution to -196°C at 95° to 70,000°C/min and warmed at 610° to 118,000°C/min: A new paradigm for cryopreservation by vitrification

There is great interest in achieving reproducibly high survivals of mammalian oocytes (especially human) after cryopreservation, but the results to date have not matched the interest. A prime cause of cell death is the formation of more than trace amounts of intracellular ice, and one strategy to avoid it is vitrification. In vitrification procedures, cells are loaded with high concentrations of glass-inducing solutes and cooled to −196 °C at rates high enough to presumably induce the glassy state. In the last decade, several devices have been developed to achieve very high cooling rates. Nearly all in the field have assumed that the cooling rate is the critical factor. The purpose of our study was to test that assumption by examining the consequences of cooling mouse oocytes in a vitrification solution at four rates ranging from 95 to 69,250 °C/min to −196 °C and for each cooling rate, subjecting them to five warming rates back above 0 °C at rates ranging from 610 to 118,000 °C/min. In samples warmed at the highest rate (118,000 °C/min), survivals were 70% to 85% regardless of the prior cooling rate. In samples warmed at the lowest rate (610 °C/min), survivals were low regardless of the prior cooling rate, but decreased from 25% to 0% as the cooling rate was increased from 95 to 69,000 °C/min. Intermediate cooling and warming rates gave intermediate survivals. The especially high sensitivity of survival to warming rate suggests that either the crystallization of intracellular glass during warming or the growth by recrystallization of small intracellular ice crystals formed during cooling are responsible for the lethality of slow warming.     

Changes in sperm membrane and ROS following cryopreservation of liquid boar semen stored at 15 °C

Boar semen is occasionally transferred to different locations in liquid form at 15 °C for cryopreservation. However, the use of frozen boar semen is limited due to the high susceptibility of boar sperm to cold shock. The aim of this study was to help improve the quality of frozen boar semen by determining the changes in sperm membrane and ROS during the cryopreservation processes of 15 °C-stored boar semen. Semen was collected from ten Duroc boars and transferred to our laboratory in liquid form stored at 15 °C. After cooling to 5 °C and freezing-thawing, conventional sperm parameters (total motility, progressive motility, and normal morphology), plasma membrane integrity, acrosomal membrane status, and intracellular ROS were evaluated. Sperm function, as assessed by conventional parameters, was unaffected by cooling but was decreased by freezing-thawing (P<0.05). However, the cooling and freezing-thawing processes led to damages in the sperm plasma membrane, and the cooling process caused increase in mean PNA (peanut agglutinin)-fluorescence intensity in viable acrosome-intact sperm (P<0.05). In ROS evaluation, the cooling process decreased intracellular (·)O(2) and H(2)O(2) in viable sperm (P<0.05), while the freezing-thawing process increased intracellular H(2)O(2) (P<0.05) without change in intracellular (·)O(2) in viable sperm. Our results suggest that, in liquid boar semen stored at 15 °C, cooling may be primarily responsible for the destabilization of sperm membranes in viable sperm, while freezing-thawing may induce reductions in sperm function with increase in membrane damage and H(2)O(2).     

Visualization of intracellular ice crystals formed in very rapidly frozen cells at −27 °C

Tumor cells of an ascites sarcoma of rat were primarily frozen very rapidly with the original host ascitic fluid at ?27 °C by the spraying method. Frozen specimens were fractured and replicated at about ?100 °C under vacuum by a special spray-sandwich method for freeze-etching, and the morphological appearance of ice crystals formed in and around the frozen cells were observed by electron microscopy.The cells cooled very rapidly at ?27 °C actually froze intracellularly, and intracellular ice crystals ranged from 0.03 to 0.5 μm in grain size due to the initial freezing rate of the specimens. In the cells having granulous intracellular ice crystals less than 0.05 μm in grain size, cytoplasmic organelles seemed to maintain their original structures.We suggested in our previous report that these tumor cells, frozen very rapidly at temperatures above ?30 °C, survived intracellular freezing as long as they remained translucent, and optically no ice crystals appeared within them, as seen in intact unfrozen cells. It may therefore be concluded that the tumor cells frozen very rapidly at temperatures near ?30 °C actually freeze intracellularly and probably maintain their viability as long as the size of individual intracellular ice-crystals is kept smaller than 0.05 μm, although the exact critical size of innocuous intracellular ice crystals is uncertain.     

“A simple and rapid method for isolating lichen photobionts“

For decades, lichenologists have developed numerous and varied methods to isolate lichen photobionts. Most procedures are tedious, slow, and require several months after the initial isolation to obtain clones. Furthermore, the purity of the isolated photobionts obtained by more rapid methods is not sufficient to establish phycobiont axenic cultures. We have developed a new method for isolating lichen photobionts from fruticose, foliose and crustose lichens. Basically, it involves homogenization of lichen thalli (from 15 mg to 2 g), a one-step centrifugation through Percoll ®, followed by washing with Tween 20 and sonication. With this simple and rapid method (which takes less than 2 h), photobiont cells are obtained in sufficient quantity and purity to obtain dozens of axenic algal cultures.     

A simple method for calculating decomposition and accumulation of ‘young’ soil organic matter

Summary In previous simple models describing decomposition of organic matter, the rate of decomposition was usually assumed to be constant. Experimental evidence has shown this is not true. The objective of this study was therefore to find a relationship between decomposition rate and time. This resulted in an equation (Eqn 5), that can be used for many types of organic materials, provided their apparent initial age is known. This age is related to the humification coefficient and varies from 1 year for green matter to 14 years for some peats. Formulas to calculate accumulation and decomposition of young soil organic matter were also derived.It was demonstrated that apparent differences in soil organic matter quality, found after 25 years of different fertilizing practices, were related to the proportion of young soil organic matter.     

Distribution of follicles in canine ovary – A simple and rapid method for counting follicles-

The distribution of follicles within canine ovarian cortex was evaluated to estimate follicular homogeneity. The analysis of follicular homogeneity prior to ovarian tissue transplantation limits the impact if follicular heterogeneity on experimental results. In this report, ovarian fragments from 14 immature bitches were embedded in OCT compound. Sections (5-μm-thick) were cut on a cryostat and stained with methylene blue. The mean number follicles ranged from 3.7 to 15.6/mm² in the 14 ovaries examined. The variance and distortion ranged from 2.05 to 144.30 and −2.09 and 2.01, respectively. The distribution of follicles was considered even, when the variance value was lower than 10 or between 10 and 16; and absolute value of distortion was inferior to 1. The distribution of follicles within ovarian cortex in 9 of 14 bitches was judged uneven. These results indicated that follicles were not homogeneously distributed within the ovarian cortex of the majority of bitches.     

A simple method of using ø(ρz) curves for the x-ray microanalysis of frozen-hydrated bulk biological samples

As an alternative to the conventional ZAF correction for microprobe analysis, a combined absorption and atomic number correction can be obtained from ø(ρz) curves. This can be easily applied to the analysis of bulk frozen-hydrated biological samples using inorganic standards. It is shown that the method is accurate by analysis of a number of organic and inorganic compounds and gelatine models. Because the corrections vary little with changes in protein concentration over the normal cellular range, iterative ø(ρz) computations are not necessary and the correction procedure is therefore fast and simple.