Comparison of in vitro and in situ ultrastructural cryoinjury and cryoprotection of mitochondria

Insect mitochondria as targets of freezing-induced injury

Many insects survive internal freezing, but the great complexity of freezing stress hinders progress in understanding the ultimate nature of freezing-induced injury. Here, we use larvae of the drosophilid fly, Chymomyza costata to assess the role of mitochondrial responses to freezing stress. Respiration analysis revealed that fat body mitochondria of the freeze-sensitive (non-diapause) phenotype significantly decrease oxygen consumption upon lethal freezing stress, while mitochondria of the freeze-tolerant (diapausing, cold-acclimated) phenotype do not lose respiratory capacity upon the same stress. Using transmission electron microscopy, we show that fat body and hindgut mitochondria swell, and occasionally burst, upon exposure of the freeze-sensitive phenotype to lethal freezing stress. By contrast, mitochondrial swelling is not observed in the freeze-tolerant phenotype exposed to the same stress. We hypothesize that mitochondrial swelling results from permeability transition of the inner mitochondrial membrane and loss of its barrier function, which causes osmotic influx of cytosolic water into the matrix. We therefore suggest that the phenotypic transition to diapause and cold acclimation could be associated with adaptive changes that include the protection of the inner mitochondrial membrane against permeability transition and subsequent mitochondrial swelling. Accumulation of high concentrations of proline and other cryoprotective substances might be a part of such adaptive changes as we have shown that freezing-induced mitochondrial swelling was abolished by feeding the freeze-sensitive phenotype larvae on a proline-augmented diet.

Subcellular fractionation of frozen skeletal muscle samples

Cell fractionation can be used to determine the localization and trafficking of proteins between cellular compartments such as the cytosol, mitochondria, and nuclei. Subcellular fractionation is usually performed immediately after tissue dissection because freezing may fragment cell membranes and induce organellar cross-contamination. Mitochondria are especially sensitive to freezing/thawing and mechanical homogenization. We proposed a protocol to improve the retention of soluble proteins in the mitochondrial fraction obtained from small amounts of frozen skeletal muscle. Fifty milligrams of the red portion of gastrocnemius muscle from Wistar rats were immediately processed or frozen in liquid nitrogen and stored at -80 °C for further processing. We compared the enrichment of subcellular fractions from frozen/fresh samples obtained with the modified protocol with those obtained by standard fractionation. Western blot analyses of marker proteins for cytosolic (alpha-tubulin), mitochondrial (VDAC1), and nuclear (histone-H3) fractions indicated that all of the procedures resulted in enriched subcellular fractions with minimal organellar cross-contamination. Notably, the activity of the soluble protein citrate synthase was higher in the mitochondrial fractions obtained with the modified protocol from frozen/fresh samples compared with the standard protocol. Therefore, our protocol improved the retention of soluble proteins in the mitochondrial fraction and may be suitable for subcellular fractionation of small amounts of frozen skeletal muscle samples.

Investigating membrane and mitochondrial cryobiological responses of HUVEC using interrupted cooling protocols

The success of cryopreservation protocols is largely based on membrane integrity assessments after thawing, since membrane integrity can be considered to give an upper limit in assessment of cell viability and the plasma membrane is considered to be a primary site of cryoinjury. However, the exposure of cells to conditions associated with low temperatures can induce injury to cellular structure and function that may not be readily identified by membrane integrity alone. Interrupted cooling protocols (including interrupted slow cooling without a hold time (graded freezing), and interrupted rapid cooling with a hold time (two-step freezing)), can yield important information about cryoinjury by separating the damage that occurs upon cooling to (and possibly holding at) a critical intermediate temperature range from the damage that occurs upon plunging to the storage temperature (liquid nitrogen). In this study, we used interrupted cooling protocols in the absence of cryoprotectant to investigate the progression of damage to human umbilical vein endothelial cells (HUVEC), comparing an assessment of membrane integrity with a mitochondrial polarization assay. Additionally, the membrane integrity response of HUVEC to interrupted cooling was investigated as a function of cooling rate (for interrupted slow cooling) and hold time (for interrupted rapid cooling). A key finding of this work was that under slow cooling conditions which resulted in a large number of membrane intact cells immediately post thaw, mitochondria are predominantly in a non-functional depolarized state. This study, the first to look directly at mitochondrial polarization throughout interrupted cooling profiles and a detailed study of HUVEC response, highlights the complexity of the progression of cell damage, as the pattern and extent of cell injury throughout the preservation process differs by injury site.

Manifestations of cell damage after freezing and thawing

The nature of the primary lesions suffered by cells during freezing and thawing is unclear, although the plasma membrane is often considered the primary site for freezing injury. This study was designed to investigate the nature of damage immediately after thawing, by monitoring several functional tests of the cell and the plasma membrane. Hamster fibroblasts, human lymphocytes, and human granulocytes were subjected to a graded freeze-thaw stress in the absence of cryoprotective compound by cooling at -1 degree C/min to a temperature between -10 and -40 degrees C, and then were either warmed directly in water at 37 degrees C or cooled rapidly to -196 degrees C before rapid warming. Mitochondrial function in the cells was then assessed using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT), fluorescein diacetate (FDA), colony growth, and osmometric response in a hypertonic solution. Cells behaved as osmometers after cooling at -1 degree C/min to low temperatures at which there were no responses measured by other assays, indicating that the plasma membrane is not a primary site for injury sustained during slow cooling. These results also indicate that the FDA test does not measure membrane integrity, but reflects the permeability of the channels through which fluorescein leaves the cells. Fewer cells could respond osmotically after cooling under conditions where intracellular freezing was likely, implying that the plasma membrane is directly damaged by the conditions leading to intracellular freezing. A general model of freezing injury to nucleated mammalian cells is proposed in which disruption of the lysosomes constitutes the primary lesion in cells cooled under conditions where the cells are dehydrated at low temperatures.

The effect of rapid freezing on uveal melanomas

We studied the immediate effects of rapid freezing on 19 variously sized uveal melanomas that were subjected to cryoenucleation using liquid nitrogen and a cryoring by light and electron microscopy and tissue culture. The freezing time and the temperature of 11 lesions were recorded. The light microscopic finding of an intranuclear clear center with peripheral displacement of clumped chromatin against the nuclear membrane was suggestive of intranuclear ice crystal formation but did not indicate cellular death of the tumors. The major ultrastructural changes, including plasmalemmal breaks, dissolution of cytoplasmic matrix, and damage to various organelles, however, suggested acute necrosis in tumors not exceeding 7 mm in elevation. Failure of the melanoma cells to grow in tissue culture and positive staining with trypan blue support the contention of tumor death. The late effects of rapid freezing were also evaluated in another case of uveal melanoma. The eye was enucleated six months after cryopexy. Histopathologic findings showed that the tumor was necrotic. Failure of the neoplasm to regress (noted clinically) was related to edema and inflammatory infiltrates.

Freezing injury in the yeast respiratory system

The effect of freeze-thawing on the yeast respiratory system was studied at rapid rates of cooling. Freezing of whole cells with liquid nitrogen induced decrease of respiratory activity to under 20% of that of original cells. Mitochondria harvested from freeze-thawed cells have markedly decreased succinate oxidizing activity. Activity of succinate cytochrome c reductase was reduced significantly after freeze-thawing of whole cells while activities of succinate dehydrogenase and cytochrome c oxidase were reduced slightly. By spectrophotometric analysis it was found that about one-half the amount of cytochrome c + c1 was eluted from mitochondria to cytosol after freeze-thawing of cells. The activities of succinate oxidation in mitochondria from freeze-thawed cells were restored to normal levels by the addition of cytochrome c. Freeze-thawing of isolated mitochondria did not induce deactivation of succinate oxidizing activities and succinate cytochrome c reductase, and no elution of cytochrome c was observed. It was concluded that the decreased respiratory activities of yeast cells by freezing of cells with liquid nitrogen can be attributed primarily to the elution of cytochrome c from mitochondria.

[Lipoamide dehydrogenase, citrate synthase and beta-hydroxyacyl-CoA-dehydrogenase in skeletal muscle. IX. The influence of the rate of thawing on activity and subcellular distribution in fast and slow frozen bovine muscle]

Samples of bovine muscle (post rigor) were frozen at -30 degrees C at two different rates (1.27 min/degrees C and 13.10 min/degrees C) and thawed at different rates between 1.6 (22 degrees C) and 430 min/degrees C (0 degrees C). The activities of the mitochondrial enzymes lipoamide dehydrogenase, citrate synthase, and beta-hydroxyacyl-CoA-dehydrogenase were determined in the supernatant of the tissue homogenate in phosphate buffer (total activity) and in the press juice of the intact tissue (activity in the sarcoplasma). The rate of thawing did not show a significant influence on total enzyme activities. In most cases, however, slow thawing caused a greater release of the enzymes from the mitochondria into the sarcoplasmic fluid than fast thawing, this effect being apparently independent of the rate of freezing. The greater damage to mitochondrial membranes upon slow thawing cannot be due to a longer exposure of the muscle cell to increased ionic strength in the non-freezable part of the cell water at the "critical" temperature around -3 degrees C because freezing of muscle samples at -3 degrees C and incubating them at -3 degrees C for five days resulted neither in changes of the total enzyme activities nor in a release of the three mitochondrial enzymes. From these results it is concluded that the influence of thawing rate on the damage to muscle mitochondria is probably not due to ionic effects or to recrystallization phenomena in the ice phase.

[Influence of temperature and rate of freezing of bovine muscle on the subcellular distribution of some mitochondrial enzyme (author's transl)]

Samples of bovine muscle were frozen at -5 degrees, -10 degrees, -20 degrees, -40 degrees, -60 degreese, -80 degreese, and -196 degrees C at slow (about 1 degrees/10 min) and high freezing rate (maximum 1 degrres/0.05 min) and subsequently thawed at room temerature. The changes in the extractable activity ("total activity") of the enzymes aconitase (AC), fumarase (FU) succine dehydrogenase (SDH), glutamic oxaloacetic transaminase (GOT), the mitochondrial isozyme of the COT (GOTM) and glutamate pyruvate transaminase (GPT) by freezing and thawing were studied. Neither the temperature nor the rate of freezing influenced the total activity of these enzymes. The subcellular distribution of these enzymes was investigated by determination of the enzyme activities in the muscle press juice. Freezing at -5 degrees C hat only little influence, but between -10 degrees and -40 degrees or -60 degrees C the release of AC, FU, GOTM and GPT from the mitochondria into the sarcoplasma increased with falling temperature, apparently by increasing damage of the mitochondria. The extent of this effect was not significantly influenced by the rat of freezing. Between -60 degrees and -196 degrees C no further rise of this effect was observed. A release of SDH did not occur at all conditions of freezing. It is suggested that the damage of muscle mitochondria by freezing and thawing is mainly due to a dehydration process.

Characterization of autoantigenic sites on isolated dog heart mitochondria

1. Anti-heart mitochondria autoantibodies were developed in serum from dogs following experimental myocardial infarction. 2. Heart mitochondria frozen and thawed repeatedly in a sucrose/Tris-chloride buffer retained both their functional integrity as measured by the respiratory control ratio and their ability to serve as an antigen in a complement fixation test. Mitochondria frozen and thawed in a potassium chloride/Tris-chloride buffer lost both their functional integrity and their autoantigenic activity after one freeze-thaw cycle. 3. Extraction of the heart mitochondria with acetone/water mixtures to remove phospholipids from the membrane led to a complete loss of the ability of the mitochondria to react in the complement fixation test but did not affect the ability of the membranes to bind autoantibody in absorption experiments. 4. Treatment of the mitochondrial membranes with increasing concentrations of trypsin caused a loss of up to approximately 50% of the membrane protein with a gradual decrease in the autoantigenic activity of the membrane without impairment of the ability of the membrane to bind autoantibody. 5. Removal of up to 90% of the sialic acid of the mitochondrial membrane with neuraminidase resulted in a considerable increase in the complement-fixing autoantigenic activity of the membrane without changing the apparent ability of the membrane to bind autoantibody in absorption experiments. 6. Exposure of mitochondrial membranes to autoantibody and complement caused an inhibition of both an inner mitochondrial membrane enzyme, i.e. cytochrome oxidase (48%) and an outer mitochondrial membrane enzyme, i.e. NADH cytochrome c reductase (rotenone insensitive) (37%).