Nitric oxide homeostasis as a target for drug additives to cardioplegia

Cardiac endothelial ischemia/reperfusion injury-derived protein damage-associated molecular patterns disrupt the integrity of the endothelial barrier

Human cardiac microvascular endothelial cells (HCMECs) are sensitive to ischemia and vulnerable to damage during reperfusion. The release of damage-associated molecular patterns (DAMPs) during reperfusion induces additional tissue damage. The current study aimed to identify early protein DAMPs in human cardiac microvascular endothelial cells subjected to ischemia-reperfusion injury (IRI) using a proteomic approach and their effect on endothelial cell injury. HCMECs were subjected to 60 min of simulated ischemia and 6 h of reperfusion, which can cause lethal damage. DAMPs in the culture media were subjected to liquid chromatography-tandem mass spectrometry proteomic analysis. The cells were treated with endothelial IRI-derived DAMP medium for 24 h. Endothelial injury was assessed by measuring lactate dehydrogenase activity, morphological features, and the expression of endothelial cadherin, nitric oxide synthase (eNOS), and caveolin-1. The top two upregulated proteins, DNAJ homolog subfamily B member 11 and pyrroline-5-carboxylate reductase 2, are promising and sensitive predictors of cardiac microvascular endothelial damage. HCMECs expose to endothelial IRI-derived DAMP, the lactate dehydrogenase activity was significantly increased compared with the control group (10.15 ± 1.03 vs 17.67 ± 1.19, respectively). Following treatment with endothelial IRI-derived DAMPs, actin-filament dysregulation, and downregulation of vascular endothelial cadherin, caveolin-1, and eNOS expressions were observed, along with cell death. In conclusion, the early protein DAMPs released during cardiac microvascular endothelial IRI could serve as novel candidate biomarkers for acute myocardial IRI. Distinct features of impaired plasma membrane integrity can help identify therapeutic targets to mitigate the detrimental consequences mediated of endothelial IRI-derived DAMPs.

HTK-N as a new preservation solution for human kidney preservation: Results of a pilot randomized controlled clinical phase II trial in living donor transplantation

BACKGROUND

HTK-N was developed based on the traditional HTK preservation solution, resulting in stronger protection against reactive oxygen species as well as better tolerance to hypothermia and ischemia. Aim of the present study was to compare HTK-N to HTK in clinical kidney transplantation demonstrating safety and non-inferiority.

METHODS

We performed a randomized controlled single blinded clinical phase II trial in patients undergoing living donor kidney transplantation. After retroperitoneoscopic nephrectomy kidneys were either perfused and stored with classical HTK solution or the new HTK-N solution. Primary endpoint was the glomerular filtration rate (eGFR according to CKD EPI) 3 months after transplantation. Secondary endpoints included graft and patient survival beside others.

RESULTS

The study included 42 patients, of which 22 were randomized in the HTK-N group and 20 in the HTK group. The primary end point showed a mean eGFR of 55.4 ± 14.0 ml/min/1.73 m² in the HTK group compared to a GFR of 57.2 ± 16.7 ml/min/m² in the HTK-N group (P = .72). Regarding secondary endpoints, there were no apparent differences. Posttransplant graft and patient survival was 100%.

CONCLUSION

This study is the first clinical application of HTK-N for kidney preservation and demonstrates non-inferiority compared to HTK in the setting of living donor kidney transplantation.

HTK-N: Modified Histidine-Tryptophan-Ketoglutarate Solution-A Promising New Tool in Solid Organ Preservation

To ameliorate ischemia-induced graft injury, optimal organ preservation remains a critical hallmark event in solid organ transplantation. Although numerous preservation solutions are in use, they still have functional limitations. Here, we present a concise review of a modified Histidine-Tryptophan-Ketoglutarate (HTK) solution, named HTK-N. Its composition differs from standard HTK solution, carrying larger antioxidative capacity and providing inherent toxicity as well as improved tolerance to cold aiming to attenuate cold storage injury in organ transplantation. The amino acids glycine, alanine and arginine were supplemented, N-acetyl-histidine partially replaced histidine, and aspartate and lactobionate substituted chloride. Several in vitro studies confirmed the superiority of HTK-N in comparison to HTK, being tested in vivo in animal models for liver, kidney, pancreas, small bowel, heart and lung transplantation to adjust ingredients for required conditions, as well as to determine its innocuousness, applicability and potential advantages. HTK-N solution has proven to be advantageous especially in the preservation of liver and heart grafts in vivo and in vitro. Thus, ongoing clinical trials and further studies in large animal models and consequently in humans are inevitable to show its ability minimizing ischemia-induced graft injury in the sequel of organ transplantation.

Modulating the Bioactivity of Nitric Oxide as a Therapeutic Strategy in Cardiac Surgery

Cardiac surgery, including cardioplegic arrest and extracorporeal circulation, causes endothelial dysfunction, which can lead to no-reflow phenomenon and reduction of myocardial pump function. Nitric oxide (NO) deficiency is involved in this pathologic process, thereby providing a fundamental basis for the use of NO replacement therapy. Presently used drugs and additives to cardioplegic and heart preservation solutions are not able to reliably protect endothelial cells and cardiomyocytes from ischemia-reperfusion injury. This review discusses promising NO-releasing compounds of various chemical classes for cardioplegia and reperfusion, which effectively maintain NO homeostasis under experimental conditions, and presents the mechanisms of their action on the cardiovascular system. Incomplete preclinical studies and a lack of toxicity assessment, however, hinder translation of these drug candidates into the clinic. Perspectives for modulation of endothelial function using NO-mediated mechanisms are discussed. They are based on the cardioprotective potential of targeting vascular gap junctions and endothelial ion channels, intracoronary administration of progenitor cells, and endothelial-specific microRNAs. Some of these strategies may provide important therapeutic benefits for human cardiovascular interventions.

Relation of Hypoalbuminemia to Response to Aspirin in Patients With Stable Coronary Artery Disease

Serum albumin (SA) level is a powerful cardiovascular prognostic marker, suggested to be involved in regulation of platelet function. High on-aspirin platelet reactivity (HAPR) is associated with increased risk for deleterious cardiovascular events. The aim of the present study was to evaluate the association between HAPR and albumin levels in patients with stable coronary artery disease (CAD) treated with aspirin. Patients with known stable CAD, who were taking aspirin (75 to 100 mg qd) regularly for at least 1 month, were screened for the present study. Exclusion criteria: cancer, sepsis or acute infection, active inflammatory/rheumatic disease, recent major surgery, chronic liver failure, the administration of other antiplatelet drugs, nonadherence with aspirin and thrombocytopenia. Blood was drawn from the participants and sent for SA level and platelet function test (VerifyNow). HAPR was defined as aspirin reaction units (ARU) >550. Overall 116 patients were analyzed; age 69 ± 10, 28% women. Twenty (17%) were hypoalbuminemic (≤3.5 g/dl). Hypoalbuminemic patients had similar characteristics to the normal albumin group except mildly higher creatinine in the former. SA levels were significantly lower in the hypoalbuminemic group (3.2 ± 0.2 g/dl vs 4.2 ± 0.4 g/dl, respectively, p <0.001) whereas mean ARU was significantly higher compared with the normal albumin group (548 ± 45 vs 444 ± 66 ARU, respectively, p <0.001). A significant inverse association was observed between SA and ARU with (R² = 0.67, p <0.001). Multivariate analysis adjusted for potential confounders found that albumin ≤3.5 is the strongest predictor of HAPR in patients with stable CAD (hazards ratio 4.9, 95% confidence interval 2.2 to 32, p = 0.002). In conclusion, hypoalbuminemia is strongly associated with HAPR in patients with stable CAD.

A prospective, randomized, single-blind, multicentre, phase III study on organ preservation with Custodiol-N solution compared with Custodiol® solution in organ transplantation (kidney, liver and pancreas)

BACKGROUND

Organ preservation before transplantation is still a challenge. Both the University of Wisconsin and Bretschneider's histidine-tryptophan-ketoglutarate (HTK; Custodiol®) solution are standard for liver, kidney and pancreas preservation. Organ preservation with both solutions is comparable; recently, however, Custodiol® solution has been modified to Custodiol-N according to the needs of today. Thus, our study was defined to study its effect in clinical transplantation.

METHODS

Patients undergoing kidney transplantation (n = 412) (including approximately 30 combined kidney-pancreas) or liver transplantation (n = 202) receive grafts that have been cold stored in either Custodiol® or Custodiol-N to demonstrate noninferiority of Custodiol-N regarding both graft function and graft injury after transplantation.

DISCUSSION

Preclinical data have clearly shown that Custodiol-N is superior to Custodiol® in cold static organ preservation via mechanisms including inhibition of hypoxic cell injury, cold-induced cell injury and avoidance of adverse effects during warm exposure to the solution. Further clinical safety data on Custodiol-N for cardioplegia are available. Thus, this study was designed to compare Custodiol® with Custodiol-N for the first time in a prospective, randomized, single-blinded, multicentre, phase III clinical transplantation trial.

TRIAL REGISTRATION

Eudra-CT, 2017-002198-20. Registered on 28 November 2018.

Argon preconditioning enhances postischaemic cardiac functional recovery following cardioplegic arrest and global cold ischaemia

OBJECTIVES

Previous studies demonstrated that preconditioning with argon gas provided a marked reduction in inflammation and apoptosis and increased myocardial contractility in the setting of acute myocardial ischaemia-reperfusion (IR). There is substantial evidence that myocardial IR injury following cardioplegic arrest is associated with the enhancement of apoptosis and inflammation, which is considered to play a role in cardiac functional impairment. Therefore, the present study was designed to clarify whether preconditioning with argon gas enhances recovery of cardiac function following cardioplegic arrest.

METHODS

Sprague-Dawley rats were anaesthetized and ventilated and allocated to (i) the control group (control IR, n = 10) and (ii) the in vivo group (argon IR), which received 3 cycles of argon (50% argon, 21% oxygen and 29% nitrogen, n = 10) administered for 5 min interspersed with 5 min of a gas mixture (79% nitrogen and 21% oxygen). The hearts were excised and then evaluated in an erythrocyte-perfused isolated working heart system. Cold ischaemia (4°C) for 60 min was induced by histidine-tryptophan-ketoglutarate cardioplegia, followed by 40 min of reperfusion. Cardiac functional parameters were assessed. In left ventricular tissue samples, the expressions of extracellular-regulated kinase (ERK1/2), AKT serine/threonine kinase (Akt), jun N-terminal kinase (JNK), endothelial nitric oxide synthase (eNOS) and HMGB1: high-mobility group box 1 (HMGB1) protein were assessed by western blot, and high-energy phosphates were evaluated by high-performance liquid chromatography.

RESULTS

At the end of reperfusion, the rats preconditioned with argon showed significantly enhanced recovery of cardiac output (101 ± 6% vs 87 ± 11%; P < 0.01), stroke volume (94 ± 4% vs 80 ± 11%; P = 0.001), external heart work (100 ± 6% vs 81 ± 13%; P < 0.001) and coronary flow (90 ± 13% vs 125 ± 21%; P < 0.01) compared with the control IR group. These results were accompanied by a significant increase in the levels of myocardial phosphocreatine (23.71 ± 2.07 µmol/g protein vs the control IR group, 13.50 ± 4.75; P = 0.001) and maintained adenosine triphosphate levels (13.62 ±1.89 µmol/g protein vs control IR group adenosine triphosphate: 10.08 ± 1.94 µmol/g; P = 0.017). Additionally, preconditioning with argon markedly reduced the activation of JNK (0.11 ± 0.01 vs 0.25 ± 0.03; P = 0.005) and the expression of HMGB1 protein (0.52 ± 0.04 vs 1.5 ± 0.10; P < 0.001) following reperfusion.

CONCLUSIONS

Preconditioning with argon enhanced cardiac functional recovery in rat hearts arrested with histidine-tryptophan-ketoglutarate cardioplegia, thereby representing a potential novel cardioprotective approach in cardiac surgery.

Protective efficacy of dinitrosyl iron complexes with reduced glutathione in cardioplegia and reperfusion

Disturbed homeostasis of nitric oxide (NO) is one of the causes of myocardial ischemia/reperfusion (I/R) injury during open-heart surgery. This study was designed to explore mechanisms of action of dinitrosyl iron complexes with reduced glutathione ({(GS^-)₂Fe⁺(NO⁺)₂}⁺, DNIC-GS) added to crystalloid cardioplegia or reperfusion solution in isolated working rat hearts. Hearts of male Wistar rats were subjected to cardioplegic arrest by St. Thomas' Hospital cardioplegic solution (STH) and normothermic global ischemia followed by reperfusion. DNIC-GS were used with STH or during early reperfusion. Lactate dehydrogenase (LDH) activity in the coronary effluent and myocardial contents of adenine nucleotides, phosphocreatine, and lactate were determined spectrophotometrically. Reactive oxygen species (ROS) formation in the coronary effluent and myocardial DNIC content was assessed by EPR technique. Cardioplegia or reperfusion with DNIC-GS significantly improved recovery of coronary flow and cardiac function compared with control. Carboxy-[2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidozoline-1-oxy-3-oxide] (C-PTIO), a selective NO scavenger, reduced/abolished protective action of DNIC-GS. Enhanced recovery of cardiac function with DNIC-GS reduced LDH release in the coronary effluent, augmented recovery of myocardial energy state, and decreased formation of ROS-generating systems at reperfusion. Beneficial effects of DNIC-GS were related to the transfer of [Fe(NO)₂] cores to thiol groups of myocardial proteins to form intracellular DNIC pools. The study concluded that DNIC-GS is a promising adjunct agent for metabolic and antioxidant protection of the heart during cardioplegic arrest and reperfusion.

Protective effects of a modified apelin-12 and dinitrosyl iron complexes in experimental cardioplegic ischemia and reperfusion

The maintenance of nitric oxide (NO) bioavailability has been recognized as an important component of myocardial protection during cardiac surgery. This study was designed to evaluate the efficacy of using two NO-donating compounds in cardioplegia and reperfusion: (i) a modified peptide apelin-12 (MA12) that activates endothelial NO synthase (eNOS) and (ii) dinitrosyl iron complexes with reduced glutathione (DNIC-GS), a natural NO vehicle. Isolated perfused working rat hearts were subjected to normothermic global ischemia and reperfusion. St. Thomas' Hospital cardioplegic solution (STH) containing 140 μM MA12 or 100 μM DNIC-GS was used. In separate series, 140 μM MA12 or 100 μM DNIC-GS was administered at early reperfusion. Metabolic state of the hearts was evaluated by myocardial content of high-energy phosphates and lactate. Lactate dehydrogenase (LDH) activity in myocardial effluent was used as an index of cell membrane damage. Cardioplegia with MA12 or DNIC-GS improved recovery of coronary flow and cardiac function, and reduced LDH leakage in perfusate compared with STH without additives. Cardioplegic arrest with MA12 significantly enhanced preservation of high-energy phosphates and decreased accumulation of lactate in reperfused hearts. The overall protective effect of cardioplegia with MA12 was significantly greater than with DNIC-GS. The administration of MA12 or DNIC-GS at early reperfusion also increased metabolic and functional recovery of reperfused hearts. In this case, recovery of cardiac contractile and pump function indices was significantly higher if reperfusion was performed with DNIC-GS. The results show that MA12 and DNIC-GS are promising adjunct agents for protection of the heart during cardioplegic arrest and reperfusion.

Anticoagulant action of low, physiologic, and high albumin levels in whole blood

Albumin is the most abundant plasma protein. Critical illness is often associated with altered, predominately decreased, serum albumin levels. This hypoalbuminaemia is usually corrected by administration of exogenous albumin. This study aimed to track the concentration-dependent influence of albumin on blood coagulation in vitro. Whole blood (WB) samples from 25 volunteers were prepared to contain low (19.3 ± 7.7 g/L), physiological (45.2 ± 7.8 g/L), and high (67.5 ± 18.1 g/L) levels of albumin. Haemostatic profiling was performed using a platelet function analyzer (PFA) 200, impedance aggregometry, a Cone and Platelet analyzer (CPA), calibrated automated thrombogram, and thrombelastometry (TEM). Platelet aggregation-associated ATP release was assessed via HPLC analysis. In the low albumin group, when compared to the physiological albumin group, we found: i) shortened PFA 200-derived closure times indicating increased primary haemostasis; ii) increased impedance aggregometry-derived amplitudes, slopes, ATP release, as well as CPA-derived average size indicating improved platelet aggregation; iii) increased TEM-derived maximum clot firmness and alpha angles indicating enhanced clot formation. TEM measurements indicated impaired clot formation in the high albumin group compared with the physiological albumin group. Thus, albumin exerted significant anticoagulant action. Therefore, low albumin levels, often present in cancer or critically ill patients, might contribute to the frequently occurring venous thromboembolism.

The nitric oxide donor, S-nitroso human serum albumin, as an adjunct to HTK-N cardioplegia improves protection during cardioplegic arrest after myocardial infarction in rats

OBJECTIVES

Currently available cardioplegic solutions provide excellent protection in patients with normal surgical risk; in high-risk patients, however, such as in emergency coronary artery bypass surgery, there is still room for improvement. As most of the cardioplegic solutions primarily protect myocytes, the addition of substances for protection of the endothelium might improve their protective potential. The nitric oxide donor, S-nitroso human serum albumin (S-NO-HSA), which has been shown to prevent endothelial nitric oxide synthase uncoupling, was added to the newly developed histidine-tryptophan-ketoglutarat (HTK-N) cardioplegia in an isolated heart perfusion system after subjecting rats to acute myocardial infarction (MI) and reperfusion.

METHODS

In male Sprague-Dawley rats, acute MI was induced by ligation for 1 h of the anterior descending coronary artery. After 2 h of in vivo reperfusion hearts were evaluated on an isolated erythrocyte-perfused working heart model. Cold ischaemia (4°C) for 60 min was followed by 45 min of reperfusion. Cardiac arrest was induced either with HTK (n = 10), HTK-N (n = 10) or HTK-N + S-NO-HSA (n = 10). In one group (HTK-N + S-NO-HSA plus in vivo S-NO-HSA; n = 9) an additional in vivo infusion of S-NO-HSA was performed.

RESULTS

Post-ischaemic recovery of cardiac output (HTK: 77 ± 4%, HTK-N: 86 ± 7%, HTK-N + S-NO-HSA: 101 ± 5%, in vivo S-NO-HSA: 93 ± 8%), external heart work (HTK: 79 ± 5%, HTK-N: 83 ± 3%, HTK-N + S-NO-HSA: 101 ± 8%, in vivo S-NO-HSA: 109 ± 13%), coronary flow (HTK: 77 ± 4%, HTK-N: 94 ± 6%, HTK-N + S-NO-HSA: 118 ± 15%, in vivo S-NO-HSA: 113 ± 3.17%) [HTK-N + S-NO-HSA vs HTK P < 0.001; HTK-N + S-NO-HSA vs HTK-N P < 0.05] and left atrial diastolic pressure (HTK: 122 ± 31%, HTK-N: 159 ± 43%, HTK-N + S-NO-HSA: 88 ± 30, in vivo S-NO-HSA: 62 ± 10%) [HTK-N + S-NO-HSA vs HTK P < 0.05; in vivo S-NO-HSA vs HTK-N P < 0.05] were significantly improved in both S-NO-HSA-treated groups compared with HTK and HTK-N, respectively. This was accompanied by better preservation of high-energy phosphates (adenosine triphosphate; energy charge) and ultrastructural integrity on transmission electron microscopy. However, no additional benefit of in vivo S-NO-HSA infusion was observed.

CONCLUSIONS

Addition of the NO donor, S-NO-HSA refines the concept of HTK-N cardioplegia in improving post-ischaemic myocardial perfusion. HTK-N with S-NO-HSA is a possible therapeutic option for patients who have to be operated on for acute MI.

Balance of nitric oxide and reactive oxygen species in myocardial reperfusion injury and protection

Depending on their concentrations, both nitric oxide (NO) and reactive oxygen species (ROS) take part either in myocardial ischemia reperfusion injury or in protection by ischemic and pharmacological preconditioning (Ipre) and postconditioning (Ipost). At the beginning of reperfusion, a transient release of NO is promptly scavenged by ROS to form the highly toxic peroxynitrite, which is responsible for a further increase of ROS through endothelial nitric oxide synthase uncoupling. The protective role of NO has suggested the use of NO donors to mimic Ipre and Ipost. However, NO donors have not always given the expected protection, possibly because they are responsible for the production of different amounts of ROS that depend on the amount of released NO. This review is focused on the role of the balance of NO and ROS in myocardial injury and its prevention by Ipre and Ipost and after the use of NO donors given with or without antioxidant compounds to mimic Ipre and Ipost.

Enhanced preservation of pig cardiac allografts by combining erythropoietin with glyceryl trinitrate and zoniporide

Erythropoietin has a tissue-protective effect independent of its erythropoietic effect that may be enhanced by combining it with the nitric oxide donor glyceryl trinitrate (GTN) and the sodium-hydrogen exchange inhibitor zoniporide in rat hearts stored with an extracellular-based preservation solution (EBPS). We thus sought to test this combination of agents in a porcine model of orthotopic heart transplantation incorporating donor brain death and total ischaemic time of approximately 260 min. Pig hearts were stored in one of four storage solutions: unmodified EBPS (CON), EBPS supplemented with GTN and zoniporide (GZ), EBPS supplemented with erythropoietin and zoniporide (EZ), or EBPS supplemented with all three agents (EGZ). A total of 4/5 EGZ hearts were successfully weaned from cardiopulmonary bypass compared with only 2/5 GZ hearts, 0/5 CON hearts and 0/5 EG hearts (p = 0.017). Following weaning from bypass EGZ hearts demonstrated superior contractility and haemodynamics than GZ hearts. All weaned hearts displayed impaired diastolic function. Release of troponin I from EGZ hearts was lower than all other groups. In conclusion, supplementation of EBPS with erythropoietin, glyceryl trinitrate and zoniporide provided superior donor heart preservation than all other strategies tested.

β2-Glycoprotein I inhibits endothelial cell migration through the nuclear factor κB signalling pathway and endothelial nitric oxide synthase activation

β2-GPI (β2-glycoprotein I) is a plasma glycoprotein ascribed with an anti-angiogenic function; however, the biological role and molecular basis of its action in cell migration remain unknown. The aim of the present study was to assess the contribution of β2-GPI to HAEC (human aortic endothelial cell) migration and the details of its underlying mechanism. Using wound healing and Boyden chamber assays, we found that β2-GPI inhibited endothelial cell migration, which was restored by its neutralizing antibody. NF-κB (nuclear factor κB) inhibitors and lentiviral siRNA (small interfering RNA) silencing of NF-κB significantly attenuated the inhibitory effect of β2-GPI on cell migration. Moreover, β2-GPI was found to induce IκBα (inhibitor of NF-κB) phosphorylation and translocation of p65 and p50. We further demonstrated that mRNA and protein levels of eNOS [endothelial NO (nitric oxide) synthase] and NO production were all increased by β2-GPI and these effects were remarkably inhibited by NF-κB inhibitors and siRNAs of p65 and p50. Furthermore, β2-GPI-mediated inhibition of cell migration was reversed by eNOS inhibitors and eNOS siRNAs. The findings of the present study provide novel insight into the ability of β2-GPI to inhibit endothelial cell migration predominantly through the NF-κB/eNOS/NO signalling pathway, which indicates a potential direction for clinical therapy in vascular diseases.

Energy status of pig donor organs after ischemia is independent of donor type

BACKGROUND

Literature is controversial whether organs from living donors have a better graft function than brain dead (BD) and non-heart-beating donor organs. Success of transplantation has been correlated with high-energy phosphate (HEP) contents of the graft.

METHODS

HEP contents in heart, liver, kidney, and pancreas from living, BD, and donation after cardiac death in a pig model (n=6 per donor type) were evaluated systematically. BD was induced under general anesthesia by inflating a balloon in the epidural space. Ten hours after confirmation, organs were retrieved. Cardiac arrest was induced by 9V direct current. After 10min of ventricular fibrillation without cardiac output, mechanical and medical reanimation was performed for 30min before organ retrieval. In living donors, organs were explanted immediately. Freeze-clamped biopsies were taken before perfusion with Celsior solution (heart) or University of Wisconsin solution (abdominal organs) in BD and living donors or with Histidine-Tryptophan-Ketoglutaric solution (all organs) in non-heart-beating donors, after perfusion, and after cold ischemia (4h for heart, 6h for liver and pancreas, and 12h for kidney). HEPs (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, and phosphocreatine), xanthine, and hypoxanthine were measured by high-performance liquid chromatography. Energy charge and adenosine triphosphate-to-adenosine diphosphate ratio were calculated.

RESULTS

After ischemia, organs from different donor types showed no difference in energy status. In all organs, a decrease of HEP and an increase in hypoxanthine contents were observed during perfusion and ischemia, irrespective of the donor type.

CONCLUSION

Organs from BD or non-heart-beating donors do not differ from living donor organs in their energy status after average tolerable ischemia.

Pathogenetic role of eNOS uncoupling in cardiopulmonary disorders

The homodimeric flavohemeprotein endothelial nitric oxide synthase (eNOS) oxidizes l-arginine to l-citrulline and nitric oxide (NO), which acutely vasodilates blood vessels and inhibits platelet aggregation. Chronically, eNOS has a major role in the regulation of blood pressure and prevention of atherosclerosis by decreasing leukocyte adhesion and smooth muscle proliferation. However, a disturbed vascular redox balance results in eNOS damage and uncoupling of oxygen activation from l-arginine conversion. Uncoupled eNOS monomerizes and generates reactive oxygen species (ROS) rather than NO. Indeed, eNOS uncoupling has been suggested as one of the main pathomechanisms in a broad range of cardiovascular and pulmonary disorders such as atherosclerosis, ventricular remodeling, and pulmonary hypertension. Therefore, modulating uncoupled eNOS, in particular eNOS-dependent ROS generation, is an attractive therapeutic approach to preventing and/or treating cardiopulmonary disorders, including protective effects during cardiothoracic surgery. This review provides a comprehensive overview of the pathogenetic role of uncoupled eNOS in both cardiovascular and pulmonary disorders. In addition, the related therapeutic possibilities such as supplementation with the eNOS substrate l-arginine, volatile NO, and direct NO donors as well as eNOS modulators such as the eNOS cofactor tetrahydrobiopterin and folic acid are discussed in detail.

Myocardial protection with the use of L-arginine and N-alpha-acetyl-histidine

OBJECTIVE

Effective myocardial preservation is an important condition for cardiac surgery, especially in heart transplantation with long ischemia times. During ischemia and reperfusion, myocardial function is altered by cold-induced ischemic injury. Cold-induced ischemic injury is triggered by cold storage and the amino acid histidine, a main component of the storage solution histidine-tryptophan-ketoglutarate (HTK). Cold-induced ischemic injury generates free oxygen radicals in an iron-dependent way. We investigated the efficacy of new modifications with the addition of L-arginine and N-alpha-acetyl-histidine to the well-established HTK solution (Custodiol) using a rat heart transplant model.

MATERIALS AND METHODS

Heterotopic transplantation was performed in Lewis rats (n = 20). After 1 hour of ischemic preservation and 1 hour of reperfusion, we assessed myocardial function and energy charge potential. The modifications of HTK solution included the addition of L-arginine, partial replacement of histidine with acetyl-histidine, and reduction of chloride concentration (HTK-1). In a second group, Custodiol served as the control.

RESULTS

After 1 hour of reperfusion, left ventricular systolic pressure (106 +/- 33 vs 69 +/- 9 mm Hg; P < .05) and minimum rate of pressure development (dP/dt) (-1388 +/- 627 vs -735 +/- 219 mm Hg/s; P < .05) were significantly higher among the HTK-1 group compared with the control group. Energy charge potential did not differ significantly between the groups.

CONCLUSION

This study showed that the novel modified HTK-1 solution improved myocardial contractility and relaxation after heart transplantation.

Deferoxamine, the newly developed iron chelator LK-614 and N-alpha-acetyl-histidine in myocardial protection

During cold storage of donor hearts, reactive oxygen species produced by intracellular redox-active chelatable iron potentially alter myocardial function. To reduce this cold-induced injury we investigated the efficacy of two new modifications of the well established histidine-tryptophan-ketogluterate (HTK) solution (Custodiol) with the addition of N-alpha-acetyl-l-histidine and iron-chelators in a heterotopic rat heart transplantation model. The donor hearts were cardioplegically arrested with 20 ml cardioplegia and stored for 1 h. Then the hearts were anastomosed to the abdominal aorta and vena cava of the recipient (n=30). After 1 h reperfusion, myocardial function and energy charge potential were measured in three groups: HTK-1: addition of l-arginine and N-alpha-acetyl-l-histidine; HTK-2: addition of iron-chelators deferoxamine and LK-614; traditional HTK - control. After 1 h reperfusion, left ventricular systolic pressure (106+/-33 vs. 60+/-39, vs. 67+/-8 mmHg, P<0.05) and dP/dt minimal (-1388+/-627 vs. -660+/-446, vs. 871+/-188 mmHg/s, P<0.05) were significantly higher in the HTK-1 group. Energy charge potentials were not significantly different. This study showed that the novel modified HTK-1 solution improves myocardial contractility and relaxation after heart transplantation. Nevertheless, addition of the iron-chelators deferoxamine and LK-614 diminished these beneficial effects.

Limitation of myocardial and endothelial injury of the rat heart graft after preservation with Centre de Résonance Magnétique Biologique et Médicale (CRMB) solution

Myocardial injury caused by prolonged storage compromises post-transplantation contractile performance and induces endothelial injury. The aim of this study was to compare a solution developed in our laboratory [Centre de Résonance Magnétique Biologique et Médicale (CRMBM) solution] with a widely used solution (Celsior, Genzyme, Saint Germain en Laye, France). Metabolic and contractile parameters as well as indexes of endothelial injury were measured in a heterotopic rat heart transplantation model with a 3-h ischaemia and a 1-h reperfusion. The two solutions were randomly used for cardioplegia and graft preservation in six experiments each. During reperfusion, developed pressure and rate pressure product were higher with CRMBM compared with Celsior (P = 0.0002 and P = 0.0135, respectively). Phosphocreatine and adenosine triphosphate (ATP) concentrations after reperfusion were significantly higher with CRMBM (P = 0.0069 and P = 0.0053, respectively). Endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) protein expression were decreased to the same extent after reperfusion compared with baseline with CRMBM (P = 0.0001 and P < 0.0001, respectively) and Celsior (P = 0.0007 and P < 0.0001, respectively). Total nitrate concentration (NOx) was significantly increased after reperfusion with CRMBM (P < 0.0001 versus baseline and P < 0.0001 versus Celsior). Na,K-ATPase activity was decreased in both groups versus baseline after reperfusion (P < 0.0001 for CRMBM and P < 0.0001 for Celsior). We showed limitation of both myocardial and endothelial damage with CRMBM compared with Celsior during heterotopic rat heart transplantation in vivo.