Hypothermic storage of coronary endothelial cells reduces nitric oxide synthase activity and expression

Time Window Is Important for Adenosine Preventing Cold-induced Injury to the Endothelium

Cold cardioplegia is used to induce heart arrest during cardiac surgery. However, endothelial function may be compromised after this procedure. Accordingly, interventions such as adenosine, that mimic the effects of preconditioning, may minimize endothelial injury. Herein, we investigated whether adenosine prevents cold-induced injury to the endothelium. Cultured human cardiac microvascular endothelial cells were treated with adenosine for different durations. Phosphorylation and expression of endothelial nitric oxide synthase (eNOS), p38MAPK, ERK1/2, and p70S6K6 were measured along with nitric oxide (NO) production using diaminofluorescein-2 diacetate (DAF-2DA) probe. Cold-induced injury by hypothermia to 4°C for 45 minutes to mimic conditions of cold cardioplegia during open heart surgery was induced in human cardiac microvascular endothelial cells. Under basal conditions, adenosine stimulated NO production, eNOS phosphorylation at serine 1177 from 5 minutes to 4 hours and inhibited eNOS phosphorylation at threonine 495 from 5 minutes to 6 hours, but increased phosphorylation of ERK1/2, p38MAPK, and p70S6K only after exposure for 5 minutes. Cold-induced injury inhibited NO production and the phosphorylation of the different enzymes. Importantly, adenosine prevented these effects of hypothermic injury. Our data demonstrated that adenosine prevents hypothermic injury to the endothelium by activating ERK1/2, eNOS, p70S6K, and p38MAPK signaling pathways at early time points. These findings also indicated that 5 minutes after administration of adenosine or release of adenosine is an important time window for cardioprotection during cardiac surgery.

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.

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.

Nitric oxide homeostasis as a target for drug additives to cardioplegia

The vascular endothelium of the coronary arteries has been identified as the important organ that locally regulates coronary perfusion and cardiac function by paracrine secretion of nitric oxide (NO) and vasoactive peptides. NO is constitutively produced in endothelial cells by endothelial nitric oxide synthase (eNOS). NO derived from this enzyme exerts important biological functions including vasodilatation, scavenging of superoxide and inhibition of platelet aggregation. Routine cardiac surgery or cardiologic interventions lead to a serious temporary or persistent disturbance in NO homeostasis. The clinical consequences are "endothelial dysfunction", leading to "myocardial dysfunction": no- or low-reflow phenomenon and temporary reduction of myocardial pump function. Uncoupling of eNOS (one electron transfer to molecular oxygen, the second substrate of eNOS) during ischemia-reperfusion due to diminished availability of L-arginine and/or tetrahydrobiopterin is even discussed as one major source of superoxide formation. Therefore maintenance of normal NO homeostasis seems to be an important factor protecting from ischemia/reperfusion (I/R) injury. Both, the clinical situations of cardioplegic arrest as well as hypothermic cardioplegic storage are followed by reperfusion. However, the presently used cardioplegic solutions to arrest and/or store the heart, thereby reducing myocardial oxygen consumption and metabolism, are designed to preserve myocytes mainly and not endothelial cells. This review will focus on possible drug additives to cardioplegia, which may help to maintain normal NO homeostasis after I/R.

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

There is growing evidence that oxidative stress plays an important role in mediating the injury induced by hypothermia during the preservation of cells and tissues for clinical or research use. In cardiovascular allografts, endothelial cell loss or injury may lead to impaired control of vascular permeability and tone, thrombosis, and inflammation. We hypothesized that hypothermia-induced damage to the endothelium is linked to increases in intracellular catalytic iron pools and oxidative stress. In this study, bovine aortic endothelial cells and cell culture methods were used to model the response of the endothelium of cardiovascular tissues to hypothermia. Confluent cells were stored at 0 degrees C to 25 degrees C and cell damage was measured by lipid peroxidation (LPO) and lactate dehydrogenase release. Varying the bleomycin-detectible iron (BDI) in cells modulated cold-induced LPO and cell injury. In untreated cells, injury was highest at 0 degrees C and a minimum at 10 degrees C. A similar temperature-dependent trend was found in BDI levels and cell plating efficiencies. Arrhenius plots of cell killing and iron accumulation rates showed biphasic temperature dependence, with minima at 10 degrees C and matching activation energies above and below 10 degrees C. These findings imply that the mechanisms underlying the hypothermic increase in catalytic iron, oxidative stress, and cell killing are the same and that preservation of the endothelium may be optimized at temperatures above those routinely used.

Progress towards a more physiologic approach to donor heart preservation: the advantages of hyperpolarized arrest

BACKGROUND

The University of Wisconsin (UW) solution is the gold standard for heart preservation but has limitations in terms of both duration and adequacy of protection. Our laboratory has been interested in a more physiologic approach to heart preservation by maintaining the heart at its resting membrane potential (hyperpolarized arrest) with the K(ATP) channel agonist pinacidil. This study compared our extracellular solution (WashU) with the UW intracellular depolarizing solution and quantified the protective effect of pinacidil in both solutions.

METHODS

Thirty-two rabbit hearts received 1 of 4 solutions in a crystalloid-perfused Langendorff apparatus: (1) UW, (2) WashU containing 0.5 mmol/liter pinacidil, (3) UW with 0.5 mmol/liter pinacidil, or (4) WashU without pinacidil. Thirty minutes of perfusion was followed by data acquisition consisting of left ventricular pressure-volume curves generated by inflating an intraventricular balloon. All hearts were placed in cold storage for 8 hours, followed by 1 hour of reperfusion before data acquisition.

RESULTS

Post-ischemic developed pressure (DP) was better preserved by WashU (76.8% +/- 3.8%) than by UW (48.3% +/- 2.5%). Diastolic compliance was better preserved by WashU (239.9% +/- 77.2%) compared with UW (711.1% +/- 193.1%). Removing pinacidil from our solution resulted in decreased DP (46.6% +/- 3.2%) and diastolic compliance (688.8% +/- 158.2%) Adding pinacidil to UW had a limited effect on DP and compliance.

CONCLUSIONS

Our results support the superiority of the WashU hyperpolarizing solution for heart preservation over UW. Pinacidil was beneficial in maintaining cardiac function and compliance. This benefit was not observed when pinacidil was placed into the UW depolarizing solution.

S-nitroso human serum albumin attenuates ischemia/reperfusion injury after cardioplegic arrest in isolated rabbit hearts

BACKGROUND

Depletion of nitric oxide (NO) is associated with ischemia/reperfusion injury. The novel NO donor, S-nitroso human serum albumin (S-NO-HSA), could bridge NO depletion during reperfusion in cardiac transplantation and minimize ischemia/reperfusion injury.

METHODS

In an isolated erythrocyte-perfused working heart model, rabbit hearts were randomly assigned after assessment of hemodynamic baseline values to receive S-NO-HSA (0.2 micromol/100 ml, n = 8), L-arginine (10 mmol/100 ml, n = 8) or albumin (control) (0.2 micromol/100 ml, n = 8). After 20 minutes of infusion, the hearts were arrested and stored in Celsior (4 degrees C) enriched with respective drugs for 6 hours, followed by 75 minutes of reperfusion. Hemodynamic values were assessed and biopsy specimens were taken to determine calcium-ionophore stimulated release of NO and superoxide.

RESULTS

During early reperfusion, recovery of cardiac output (75% +/- 6% vs 49% +/- 5%, p < 0.05) and coronary flow (99% +/- 8% vs 70% +/- 5%, p < 0.05) were higher, and myocardial oxygen consumption was reduced in the S-NO-HSA Group compared with Control (4.08 +/- 0.46 ml/min/0.1 kg vs 6.78 +/- 0.38 ml/min/0.1 kg, p < 0.01). At the end of the experiment cardiac output (53% +/- 5% vs 27% +/- 5%, p < 0.01) was higher and left atrial pressure (115% +/- 9% vs 150% +/- 8%, p < 0.05) was lower in the S-NO-HSA Group compared with Control. NO release was increased (1,040 +/- 50 nmol/liter and 1,070 +/- 60 nmol/liter vs 860 +/- 10 nmol/liter, p < 0.01) and superoxide release diminished (31 +/- 5 nmol/liter and 38 +/- 5 nmol/liter vs 64 +/- 5 nmol/liter, p < .01) in the S-NO-HSA and L-arginine Groups compared with Control.

CONCLUSION

S-NO-HSA improved hemodynamic functions after prolonged hypothermic cardiac arrest by supplementing NO and thereby decreasing ischemia/reperfusion injury.

Nitric oxide synthase distribution and expression with ischemic preconditioning of the rat liver

This study was undertaken to identify nitric oxide synthase (NOS) isoforms responsible for the generation of cytoprotective NO during liver ischemic preconditioning (IPC). Sprague-Dawley rats were subjected to 45 min lobar ischemia followed by 2 h reperfusion. L-arginine or Nomega-nitro-L-arginine methyl ester (L-NAME) was administered to stimulate or block NO synthesis. Study groups (n=6) had 1) sham laparotomy, 2) ischemia reperfusion (IR), 3) IPC with 5 min ischemia and 10 min reperfusion before IR, 4) L-arginine before IR, or 5) L-NAME + IPC before IR. Liver function tests, nitrite + nitrate (NOx) and plasma amino acids were analyzed. The endothelial cell and inducible isoforms of NOS (eNOS and iNOS) were identified using immunohistochemistry and Western blotting. Both IPC and L-arginine treatment increased NOx (P<0.05) and improved serum liver enzymes (P<0.05) when compared with IR. These effects were prevented by L-NAME. Hepatic vein NOx was significantly higher than circulating NOx. iNOS expression was absent within the groups. The preconditioned livers were associated with up-regulation of eNOS expression and also increased L-arginine levels. The effects of L-arginine administration were similar to those evident following IPC. Thus, cytoprotective NO generation during IPC of the liver was a result of increased eNOS expression and increased L-arginine substrate availability.

NOS substrate during cardioplegic arrest and cold storage decreases stunning after heart transplantation in a rat model

BACKGROUND

In this study, we evaluated how adding L-arginine to Centre de Résonance Magnétique Biologique et Médicale (CRMBM) solution affected myocardial performance during post-ischemic in vivo reperfusion.

METHODS

Experiments were conducted using a modified Lewis-Lewis heterotopic heart transplantation model, with a total ischemic time of 3 hours followed by 1 or 24 hours of blood reperfusion. Heart grafts were arrested using intra-aortic injection of CRMBM solution, either supplemented or not supplemented with 2 mmol/liter L-arginine (n = 12 in each group). We measured systolic indexes and simultaneously performed phosphorus magnetic resonance spectroscopy ((31)P MRS). We quantified total endothelial nitric oxide synthase (eNOS) protein using the Western blot test of freeze-clamped hearts.

RESULTS

Contractility during early reperfusion was significantly better in grafts arrested with CRMBM solution enriched with L-arginine: mean rate pressure product, 11249 +/- 1548 vs 5637 +/- 1118 mm Hg/min (p = 0.05), and maximal first derivative of the pressure signal (dP/dt(max)), 1721 +/- 177 vs 1214 +/- 321 mm Hg/sec (p = 0.013). Conversely, during late reperfusion, contractility did not relate to the nature of the preservation solution. The presence of L-arginine in the CRMBM solution did not alter time-related variations of high-energy phosphate ratios measured using in vivo (31)P MRS. The eNOS protein level decreased significantly during early compared with late reperfusion, with no effect caused by L-arginine.

CONCLUSIONS

During early reperfusion, the limited myocardial stunning observed with CRMBM solution containing L-arginine does not relate to energy metabolism but to better preservation of the NO pathway.

The use of ischaemic vessels as prostheses or tissue engineering scaffolds after cryopreservation

OBJECTIVE

to evaluate the condition of organ donor arteries subjected to prolonged cold-ischaemia followed by cryopreservation, for their possible use as vascular grafts.

MATERIALS AND METHODS

fresh specimens of human iliac artery from organ donors were used as controls. These arteries were divided into two portions, one of which was cryopreserved in an automated freezer. A further group of arteries was immersed in Wisconsin solution and kept for 4 days at 4 degrees C (cold-ischaemia). After this period, the arteries were also cut into two, and one of these portions was cryopreserved. All the cryopreserved arterial segments were stored for a month and then subjected to automated gradual thawing. The thawed specimens were evaluated by light microscopy, scanning and transmission electron microscopy, immunohistochemical analysis (MMPs, elastin, CD31, von Willebrand factor) and the in situ detection of fragmented DNA (TUNEL method).

RESULTS

the most marked changes induced by cryopreservation were partial vessel deendothelialisation and morphological changes in cells of the intima that were in the process of detachment. No significant changes were observed in the medial layer, other than discrete elastic fibre fragmentation. Following cold-ischaemia, the endothelium was the most affected layer, with large denuded areas and exposure of the fibroelastic layer. Increased MMP-2 expression was also noted after cold-ischaemia. When subjected to both cold-ischaemia and cryopreservation, a large proportion of endothelial cells showed positivity for the TUNEL technique, however, no significant difference was observed between the ischaemic and the ischaemic/cryopreserved specimens.

CONCLUSIONS

prolonged cold-ischaemia causes some additional damage to the arterial wall compared to cryopreservation alone. However, the structural component of the ischaemic vessel remains in a condition that is suitable for subsequent cryopreservation and use as a vessel substitute or a scaffold for tissue engineering.