Endothelial cell preservation at 10 degrees C minimizes catalytic iron, oxidative stress, and cold-induced injury

Studying the Pulmonary Endothelium in Health and Disease: An Official American Thoracic Society Workshop Report

Lung endothelium resides at the interface between the circulation and the underlying tissue, where it senses biochemical and mechanical properties of both the blood as it flows through the vascular circuit and the vessel wall. The endothelium performs the bidirectional signaling between the blood and tissue compartments that is necessary to maintain homeostasis while physically separating both, facilitating a tightly regulated exchange of water, solutes, cells, and signals. Disruption in endothelial function contributes to vascular disease, which can manifest in discrete vascular locations along the artery-to-capillary-to-vein axis. Although our understanding of mechanisms that contribute to endothelial cell injury and repair in acute and chronic vascular disease have advanced, pathophysiological mechanisms that underlie site-specific vascular disease remain incompletely understood. In an effort to improve the translatability of mechanistic studies of the endothelium, the American Thoracic Society convened a workshop to optimize rigor, reproducibility, and translation of discovery to advance our understanding of endothelial cell function in health and disease.

Metabolomic studies reveal an organ-protective hibernation state in donor lungs preserved at 10 °C

OBJECTIVE

Previous reports showed enhanced graft function in both healthy and injured porcine lungs after preservation at 10 °C. The objective of the study is to elucidate the mechanism of lung protection by 10 °C and identify potential therapeutic targets to improve organ preservation.

METHODS

Metabolomics data were analyzed from healthy and injured porcine lungs that underwent extended hypothermic preservation on ice and at 10 °C. Tissue sampled before and after preservation were subjected to untargeted metabolic profiling. Principal component analysis was performed to test for the separability of the paired samples. Significantly changed metabolites between the 2 time points were identified and analyzed to determine the underlying metabolic pathways. The levels of respiratory activity of lung tissue at hypothermic temperatures were confirmed using high resolution respirometry.

RESULTS

In both healthy and injured lungs (n = 5 per intervention), principal component analysis suggested minimal change in metabolites after ice preservation but significant change of metabolites after 10 °C preservation, which was associated with significantly improved lung function as assessed by ex vivo lung perfusion and lung transplantation. For healthy lungs, lipid energy pathway was found primarily active at 10 °C. For injured lungs, additional carbohydrate energy pathway and anti-ferroptosis pathways aiding organ repair were identified. These metabolic features are also key features involved in mammal hibernation.

CONCLUSIONS

Untargeted metabolomics revealed a dynamic metabolic gradient for lungs stored at 10 °C. Elucidating the underlying mechanisms behind this pathway regulation may lead to strategies that will allow organs "hibernate" for days, potentially making organ banking a reality.

Urinary biomarkers to predict severe fluid overload after cardiac surgery: a pilot study

Aim: To assess the predictive ability of urinary and plasma biomarkers and clinical routine parameters for subsequent severe fluid overload. Patients & methods: In a pilot study, we studied 100 adult patients after cardiac surgery. On intensive care unit admission, we measured biomarkers in urine (midkine, IL-6, neutrophil gelatinase-associated lipocalin [NGAL], hepcidin-25) and plasma (creatinine, urea, B-type natriuretic peptide, lactate, C-reactive protein, leukocytes, IL-6, NGAL, hepcidin-25) to predict postoperative severe fluid overload. Results: Urinary midkine, IL-6, NGAL and hepcidin-25 (all AUCs ≥0.79) predicted postoperative severe fluid overload (n = 5 patients). Urinary NGAL/hepcidin-25 ratio (AUC 0.867) predicted postoperative severe fluid overload after adjustment to EuroScore and need for norepinephrine on surgery day (odds ratio: 2.4). Conclusion: Urinary biomarkers on intensive care unit admission might be helpful to predict subsequent severe fluid overload after cardiac surgery.

Optimization of Storage Temperature for Retention of Undifferentiated Cell Character of Cultured Human Epidermal Cell Sheets

Cultured epidermal cell sheets (CES) containing undifferentiated cells are useful for treating skin burns and have potential for regenerative treatment of other types of epithelial injuries. The undifferentiated phenotype is therefore important for success in both applications. This study aimed to optimize a method for one-week storage of CES for their widespread distribution and use in regenerative medicine. The effect of storage temperatures 4 °C, 8 °C, 12 °C, 16 °C, and 24 °C on CES was evaluated. Analyses included assessment of viability, mitochondrial reactive oxygen species (ROS), membrane damage, mitochondrial DNA (mtDNA) integrity, morphology, phenotype and cytokine secretion into storage buffer. Lowest cell viability was seen at 4 °C. Compared to non-stored cells, ABCG2 expression increased between temperatures 8–16 °C. At 24 °C, reduced ABCG2 expression coincided with increased mitochondrial ROS, as well as increased differentiation, cell death and mtDNA damage. P63, C/EBPδ, CK10 and involucrin fluorescence combined with morphology observations supported retention of undifferentiated cell phenotype at 12 °C, transition to differentiation at 16 °C, and increased differentiation at 24 °C. Several cytokines relevant to healing were upregulated during storage. Importantly, cells stored at 12 °C showed similar viability and undifferentiated phenotype as the non-stored control suggesting that this temperature may be ideal for storage of CES.

The analysis of viability for mammalian cells treated at different temperatures and its application in cell shipment

Mammalian cells are very important experimental materials and widely used in biological and medical research fields. It is often required that mammalian cells are transported from one laboratory to another to meet with various researches. Conventional methods for cell shipment are laborious and costive despite of maintaining high viability. In this study we aimed to develop a simple and low-cost method for cell shipment by investigating the viabilities of different cell lines treated at different temperatures. We show that the viability of mammalian cells incubated at 1°C or 5°C significantly reduced when compared with that at 16°C or 22°C. Colony formation assays revealed that preservation of mammalian cells at 1°C or 5°C led to a poorer recovery than that at 16°C or 22°C. The data from proliferation and apoptotic assays confirmed that M2 cells could continue to proliferate at 16°C or 22°C, but massive death was caused by apoptosis at 1°C or 5°C. The morphology of mammalian cells treated under hypothermia showed little difference from that of the untreated cells. Quantitative RT-PCR and alkaline phosphatase staining confirmed that hypothermic treatment did not change the identity of mouse embryonic stem cells. A case study showed that mammalian cells directly suspended in culture medium were able to be shipped for long distance and maintained a high level of viability and recovery. Our findings not only broaden the understanding to the effect of hypothermia on the viability of mammalian cells, but also provide an alternative approach for cell shipment.

Effect of Storage Temperature on the Phenotype of Cultured Epidermal Cells Stored in Xenobiotic-Free Medium

PURPOSE

Cultured epidermal cell sheets (CECS) are used in the treatment of large area burns to the body and have potential to treat limbal stem cell deficiency (LSCD) as shown in animal studies. Despite widespread use, storage options for CECS are limited. Short-term storage allows flexibility in scheduling surgery, quality control and improved transportation to clinics worldwide. Recent evidence points to the phenotype of cultured epithelial cells as a critical predictor of post-operative success following transplantation of CECS in burns and in transplantation of cultured epithelial cells in patients with LSCD. This study, therefore assessed the effect of a range of temperatures, spanning 4-37 °C, on the phenotype of CECS stored over a 2-week period in a xenobiotic-free system.

MATERIALS AND METHODS

Progenitor cell (p63, ΔNp63α and ABCG2) and differentiation (C/EBPδ and CK10) associated marker expression was assessed using immunocytochemistry. Immunohistochemistry staining of normal skin for the markers p63, ABCG2 and C/EBPδ was also carried out. Assessment of progenitor cell side population (SP) was performed using JC1 dye by flow cytometry.

RESULTS

P63 expression remained relatively constant throughout the temperature range but was significantly lower compared to control between 20 and 28 °C (p < 0.05). High C/EBPδ together with low p63 suggested more differentiation beginning at 20 °C and above. Lower CK10 and C/EBPδ expression most similar to control was seen at 12 °C. The percentage of ABCG2 positive cells was most similar to control between 8 and 24 °C. Between 4 and 24 °C, the SP fluctuated, but was not significantly different compared to control. Results were supported by staining patterns indicating differentiation status associated with markers in normal skin sections.

CONCLUSIONS

Lower storage temperatures, and in particular 12 °C, merit further investigation as optimal storage temperature for maintenance of undifferentiated phenotype in CECS.

Effect of storage temperature on cultured epidermal cell sheets stored in xenobiotic-free medium

Cultured epidermal cell sheets (CECS) are used in regenerative medicine in patients with burns, and have potential to treat limbal stem cell deficiency (LSCD), as demonstrated in animal models. Despite widespread use, short-term storage options for CECS are limited. Advantages of storage include: flexibility in scheduling surgery, reserve sheets for repeat operations, more opportunity for quality control, and improved transportation to allow wider distribution. Studies on storage of CECS have thus far focused on cryopreservation, whereas refrigeration is a convenient method commonly used for whole skin graft storage in burns clinics. It has been shown that preservation of viable cells using these methods is variable. This study evaluated the effect of different temperatures spanning 4°C to 37°C, on the cell viability, morphology, proliferation and metabolic status of CECS stored over a two week period in a xenobiotic–free system. Compared to non-stored control, best cell viability was obtained at 24°C (95.2±9.9%); reduced cell viability, at approximately 60%, was demonstrated at several of the temperatures (12°C, 28°C, 32°C and 37°C). Metabolic activity was significantly higher between 24°C and 37°C, where glucose, lactate, lactate/glucose ratios, and oxygen tension indicated increased activation of the glycolytic pathway under aerobic conditions. Preservation of morphology as shown by phase contrast and scanning electron micrographs was best at 12°C and 16°C. PCNA immunocytochemistry indicated that only 12°C and 20°C allowed maintenance of proliferative function at a similar level to non-stored control. In conclusion, results indicate that 12°C and 24°C merit further investigation as the prospective optimum temperature for short-term storage of cultured epidermal cell sheets.

Enzyme-triggered CO-releasing molecules (ET-CORMs): evaluation of biological activity in relation to their structure

Acyloxydiene-Fe(CO)3 complexes act as enzyme-triggered CO-releasing molecules (ET-CORMs) and can deliver CO intracellularly via esterase-mediated hydrolysis. The protective properties of structurally different ET-CORMs on hypothermic preservation damage and their ability to inhibit VCAM-1 expression were tested on cultured human umbilical vein endothelial cells (HUVEC) and renal proximal tubular epithelial cells (PTEC) using a structure-activity approach. Cytotoxicity of ET-CORMs, protection against hypothermic preservation damage, and inhibition of VCAM-1 expression were assessed. Cytotoxicity of 2-cyclohexenone and 1,3-cyclohexanedione-derived ET-CORMs was more pronounced in HUVEC compared to PTEC and was dependent on the position and type of the ester (acyloxy) substituent(s) (acetate>pivalate>palmitate). Protection against hypothermic preservation injury was only observed for 2-cyclohexenone-derived ET-CORMs and was not mediated by the ET-CORM decomposition product 2-cyclohexenone itself. Structural requirements for protection by these ET-CORMs were different for HUVEC and PTEC. Protection was affected by the nature of the ester functionality in both cell lines. VCAM-1 expression was inhibited by both 2-cyclohexenone- and 1,3-cyclohexanedione-derived ET-CORMs. 2-Cyclohexenone, but not 1,3-cyclohexanedione, also inhibited VCAM-1 expression. We demonstrate that structural alterations of ET-CORMs significantly affect their biological activity. Our data also indicate that different ET-CORMs behave differently in various cell types (epithelial vs endothelial). These findings warrant further studies not only to elucidate the structure-activity relation of ET-CORMs in mechanistic terms but also to assess if structural optimization will yield ET-CORMs with restricted cell specificity.

Endothelial cell preservation at hypothermic to normothermic conditions using clinical and experimental organ preservation solutions

INTRODUCTION

Endothelial barrier function is pivotal for the outcome of organ transplantation. Since hypothermic preservation (gold standard) is associated with cold-induced endothelial damage, endothelial barrier function may benefit from organ preservation at warmer temperatures. We therefore assessed endothelial barrier integrity and viability as function of preservation temperature and perfusion solution, and hypothesized that endothelial cell preservation at subnormothermic conditions using metabolism-supporting solutions constitute optimal preservation conditions.

METHODS

Human umbilical vein endothelial cells (HUVEC) were preserved at 4-37°C for up to 20 h using Ringer's lactate, histidine-tryptophan-ketoglutarate solution, University of Wisconsin (UW) solution, Polysol, or endothelial cell growth medium (ECGM). Following preservation, the monolayer integrity, metabolic capacity, and ATP content were determined as positive parameters of endothelial cell viability. As negative parameters, apoptosis, necrosis, and cell activation were assayed. A viability index was devised on the basis of these parameters.

RESULTS

HUVEC viability and barrier integrity was compromised at 4°C regardless of the preservation solution. At temperatures above 20°C, the cells' metabolic demands outweighed the preservation solutions' supporting capacity. Only UW maintained HUVEC viability up to 20°C. Despite high intracellular ATP content, none of the solutions were capable of sufficiently preserving HUVEC above 20°C except for ECGM.

CONCLUSION

Optimal HUVEC preservation is achieved with UW up to 20°C. Only ECGM maintains HUVEC viability at temperatures above 20°C.

Freezing mammalian cells for production of biopharmaceuticals

Cryopreservation techniques utilize very low temperatures to preserve the structure and function of living cells. Various strategies have been developed for freezing mammalian cells of biological and medical significance. This paper highlights the importance and application of cryopreservation for recombinant mammalian cells used in the biopharmaceutical industry to produce high-value protein therapeutics. It is a primer that aims to give insight into the basic principles of cell freezing for the benefit of biopharmaceutical researchers with limited or no prior experience in cryobiology. For the more familiar researchers, key cell banking parameters such as the cell density and hold conditions have been reviewed to possibly help optimize their specific cell freezing protocols. It is important to understand the mechanisms underlying the freezing of complex and sensitive cellular entities as we implement best practices around the techniques and strategies used for cryopreservation.

Proteomic analysis of endothelial cold-adaptation

BACKGROUND

Understanding how human cells in tissue culture adapt to hypothermia may aid in developing new clinical procedures for improved ischemic and hypothermic protection. Human coronary artery endothelial cells grown to confluence at 37°C and then transferred to 25°C become resistant over time to oxidative stress and injury induced by 0°C storage and rewarming. This protection correlates with an increase in intracellular glutathione at 25°C. To help understand the molecular basis of endothelial cold-adaptation, isolated proteins from cold-adapted (25°C/72 h) and pre-adapted cells were analyzed by quantitative proteomic methods and differentially expressed proteins were categorized using the DAVID Bioinformatics Resource.

RESULTS

Cells adapted to 25°C expressed changes in the abundance of 219 unique proteins representing a broad range of categories such as translation, glycolysis, biosynthetic (anabolic) processes, NAD, cytoskeletal organization, RNA processing, oxidoreductase activity, response-to-stress and cell redox homeostasis. The number of proteins that decreased significantly with cold-adaptation exceeded the number that increased by 2:1. Almost half of the decreases were associated with protein metabolic processes and a third were related to anabolic processes including protein, DNA and fatty acid synthesis. Changes consistent with the suppression of cytoskeletal dynamics provided further evidence that cold-adapted cells are in an energy conserving state. Among the specific changes were increases in the abundance and activity of redox proteins glutathione S-transferase, thioredoxin and thioredoxin reductase, which correlated with a decrease in oxidative stress, an increase in protein glutathionylation, and a recovery of reduced protein thiols during rewarming from 0°C. Increases in S-adenosylhomocysteine hydrolase and nicotinamide phosphoribosyltransferase implicate a central role for the methionine-cysteine transulfuration pathway in increasing glutathione levels and the NAD salvage pathway in increasing the reducing capacity of cold-adapted cells.

CONCLUSIONS

Endothelial adaptation to mild-moderate hypothermia down-regulates anabolic processes and increases the reducing capacity of cells to enhance their resistance to oxidation and injury associated with 0°C storage and rewarming. Inducing these characteristics in a clinical setting could potentially limit the damaging effects of energy insufficiency due to ischemia and prevent the disruption of integrated metabolism at low temperatures.

Polyampholytes as Cryoprotective Agents for Mammalian Cell Cryopreservation

Cryoprotective agents (CPAs) such as dimethyl sulfoxide (DMSO), glycerol, ethylene glycol, and propylene glycol have been used for the cryopreservation of cells and tissues. DMSO is the most effective CPA but shows high cytotoxicity and can effect differentiation. ∈-Poly-l-lysine (PLL) derivatives show higher cryopreservation efficiency than the conventional CPAs. Culture medium solutions with 7.5 w/w% of PLL whose amino groups of more than 50 mol% were converted to carboxyl groups by succinic anhydride showed higher postthaw survival efficiency of L929 cells than those of current CPAs without the addition of any proteins. In addition, rat mesenchymal stem cells were cryopreserved more effectively than with DMSO and fully retained the potential for proliferation and differentiation. Furthermore, many kinds of cells could be cryopreserved with PLL having the appropriate ratio of COOH groups, regardless of the cell types, including adhesive and floating cells, human- and mouse-derived cells, primary cells, and established cell lines. The properties might be associated with the antifreeze protein properties. These results indicate that these polymeric extracellular CPAs may replace current CPAs and the high viability after thawing and nonnecessity of serum ensure that these CPAs may be used in various preservation fields.

Impaired autoregulation of cerebral blood flow during rewarming from hypothermic cardiopulmonary bypass and its potential association with stroke

BACKGROUND

Patient rewarming after hypothermic cardiopulmonary bypass (CPB) has been linked to brain injury after cardiac surgery. In this study, we evaluated whether cooling and then rewarming of body temperature during CPB in adult patients is associated with alterations in cerebral blood flow (CBF)-blood pressure autoregulation.

METHODS

One hundred twenty-seven adult patients undergoing CPB during cardiac surgery had transcranial Doppler monitoring of the right and left middle cerebral artery blood flow velocity. Eleven patients undergoing CPB who had arterial inflow maintained at >35 degrees C served as controls. The mean velocity index (Mx) was calculated as a moving, linear correlation coefficient between slow waves of middle cerebral artery blood flow velocity and mean arterial blood pressure. Intact CBF-blood pressure autoregulation is associated with an Mx that approaches 0. Impaired autoregulation results in an increasing Mx approaching 1.0. Comparisons of time-averaged Mx values were made between the following periods: before CPB (baseline), during the cooling and rewarming phases of CPB, and after CPB. The number of patients in each phase of CPB with an Mx >4.0, indicative of impaired CBF autoregulation, was determined.

RESULTS

During cooling, Mx (left, 0.29 +/- 0.18; right, 0.28 +/- 0.18 [mean +/- SD]) was greater than that at baseline (left, 0.17 +/- 0.21; right, 0.17 +/- 0.20; P <or= 0.0001). Mx increased during the rewarming phase of CPB (left, 0.40 +/- 0.19; right, 0.39 +/- 0.19) compared with baseline (P <or= 0.001) and the cooling phase (P <or= 0.0001), indicating impaired CBF autoregulation. After CPB, Mx (left, 0.27 +/- 0.20; right, 0.28 +/- 0.21) was higher than at baseline (left, P = 0.0004; right, P = 0.0003), no different than during the cooling phase, but lower than during rewarming (left, P <or= 0.0001; right, P <or= 0.0005). Forty-three patients (34%) had an Mx >or=0.4 during the cooling phase of CPB and 68 (53%) had an average Mx >or=0.4 during rewarming. Nine of the 11 warm controls had an average Mx >or=0.4 during the entire CPB period. There were 7 strokes and 1 TIA after surgery. All strokes were in patients with Mx >or= 0.4 during rewarming (P = 0.015). The unadjusted odds ratio for any neurologic event (stroke or transient ischemic attack) for patients with Mx >or= 0.4 during rewarming was 6.57 (95% confidence interval, 0.79 to 55.0, P < 0.08).

CONCLUSIONS

Hypothermic CPB is associated with abnormal CBF-blood pressure autoregulation that is worsened with rewarming. We found a high rate of strokes in patients with evidence of impaired CBF autoregulation. Whether a pressure-passive CBF state during rewarming is associated with risk for ischemic brain injury requires further investigation.

Hypothermic preconditioning of endothelial cells attenuates cold-induced injury by a ferritin-dependent process

Hypothermia for myocardial protection or storage of vascular grafts may damage the endothelium and impair vascular function upon reperfusion/rewarming. Catalytic iron pools and oxidative stress are important mediators of cold-induced endothelial injury. Because endothelial cells are highly adaptive, we hypothesized that hypothermic preconditioning (HPC) protects cells at 0 degrees C by a heme oxygenase-1 (HO-1) and ferritin-dependent mechanism. Storage of human coronary artery endothelial cells at 0 degrees C caused the release of lactate dehydrogenase, increases in bleomycin-detectible iron (BDI), and increases in the ratio of oxidized/reduced glutathione, signifying oxidative stress. Hypoxia increased injury at 0 degrees C but did not increase BDI or oxidative stress further. HPC at 25 degrees C for 15-72 h attenuated these changes by an amount achievable by pretreating cells with 10-20 microM deferoxamine, an iron chelator, and protected cell viability. Treating cells with hemin chloride at 37 degrees C transiently increased intracellular heme, HO-1, BDI, and ferritin. Elevated heme/iron sensitized cells to 0 degrees C but ferritin was protective. HPC increased iron maximally after 2 h at 25 degrees C and ferritin levels peaked after 15 h. HO-1 was not induced. When HPC-mediated increases in ferritin were blocked by deferoxamine, protection at 0 degrees C was diminished. We conclude that HPC-mediated endothelial protection from hypothermic injury is an iron- and ferritin-dependent process.

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.

Green tea polyphenols affect skin preservation in rats and improve the rate of skin grafts

Green tea polyphenols have been recently reported to promote the preservation of tissues, such as blood vessels, corneas, nerves, islet cells, articular cartilage, and myocardium, at room temperature. These findings indicate the possibility of a new method of tissue banking without freezing. A main active ingredient of green tea, epigallocatechin-3-gallate (EGCG), is a polyphenol that possesses antioxidant, antimicrobial, antiproliferative, and free radical scavenging effects. This study examined the effects of EGCG regarding skin preservation. Skin sample biopsy specimens measuring 1 x 1 cm from GFP rats were held in sterile containers with 50 ml preserving solution at 4 degrees C and 37 degrees C for up to about 8 weeks. Periodically, some of the preserved skin specimens were directly examined histologically and others were transplanted into nude mice. Histological examinations of skin preserved at 4 degrees C revealed a degeneration of the epidermal and dermal layers from 5 weeks in all groups. In the groups preserved at 37 degrees C, degeneration and flakiness of the epidermal layer were demonstrated starting at 2 weeks preservation regardless of addition of EGCG. After 2-7 weeks of preservation the rat skin grafted to nude mice in the EGCG groups stored at 4 degrees C showed successful engraftment. However, grafts preserved at 4 degrees C without EGCG and at 37 degrees C did not demonstrate GFP-positive keratinocyte or fibroblasts. In conclusion, the present findings suggest the future clinical usefulness of EGCG for skin preservation without freezing; however, the mechanism by which EGCG promotes skin preservation still remains unclear.

High mobility group box 1 and adenosine are both released by endothelial cells during hypothermic preservation

Hypothermic preservation of solid allografts causes profound damage of vascular endothelial cells. This, in turn, might activate innate immunity. In the present study we employed an in vitro model to study to what extent supernatants of damaged endothelial cells are able to activate innate immunity and to study the nature of these signals. The expression of high mobility group box 1 (HMGB1) and adhesion molecules on human umbilical vein endothelial cell was studied by immunofluorescence, fluorescence activated cell sorter and Western blotting. Cytokine production was performed by enzyme-linked immunosorbent assay. HMGB1 expression was lost completely in endothelial cells after hypothermic preservation. This was associated with cell damage as it occurred only in untreated endothelial cell but not in cells rendered resistant to hypothermia-mediated damage by dopamine treatment. Only supernatants from hypothermia susceptible cells up-regulated the expression of interleukin (IL)-8 and adhesion molecules in cultured endothelial cells in an HMGB1-dependent manner. In whole blood assays, both supernatants of hypothermia susceptible and resistant cells inhibited tumour necrosis factor (TNF)-alpha production concomitantly with an increased IL-10 secretion. The activity of the supernatants was already found after 6 h of hypothermic preservation, and paralleled the decrease in intracellular adenosine triphosphate (ATP) levels. Modulation of TNF-alpha and IL-10 production by these supernatants was abrogated completely by prior treatment with adenosine deaminase and was similar to the response of an A2R agonist. Our study demonstrates that both HMGB1 and adenosine are released during hypothermic preservation. While release of HMGB1 is caused by cell damage, release of adenosine seems to be related to ATP hydrolysis, occurring in both susceptible and resistant cells.

Involvement of microtubules in the tolerance of cardiomyocytes to cold ischemia-reperfusion

Before transplantation, the heart graft is preserved by the use of cold storage in order to limit ischemia-reperfusion stress. However, sustained exposure to low temperature may induce myocardial ultrastructural damage, particularly microtubules (MT) disruption. Previous data suggested that tubulin-binding agents are able to attenuate cold-induced cytoskeleton alterations. Thus, the aim of the present work was to study the influence of docetaxel (DX, a tubulin-binding taxane) on the effects of deep hypothermia (4 degrees C) and of simulated cold ischemia-reperfusion on the MT network and oxidative stress of cardiomyocyte (CM) in monolayer cultures prepared from newborn rat ventricles. The MT network was explored by immunocytochemistry and Western-blotting, the cell stress by tetrazolium dye assay (MTT) and lactate dehydrogenase (LDH) release, and the superoxide production by the dihydroethidium probe (DHE). The MT assembly remained stable after 4 and 8 h of hypothermia. Tubulin acetylation was promoted in CM subjected to 4-h hypothermia. Low temperature reduced the mitochondrial function and increased the basal LDH release. The cold ischemia during 4 and 8 h preserved MT network. Docetaxel promoted MT polymerization and tubulin acetylation in basal and in cold conditions. This drug decreased the release of LDH induced by cold ischemia. Moreover, hypothermia (4 h) significantly raised the anion superoxide production. Docetaxel decreased this oxidative stress in the control CM and in CM submitted to 4 h of hypothermia. These data demonstrated that stabilizing MT with DX exerted a protective effect on CM subjected to hypothermia and to cold ischemia-reperfusion. Tubulin-ligands should be thus considered to improve the tolerance of the heart graft toward stressing conservative conditions.