Survival and graft function in a large animal lung transplant model after 30 h preservation and substitution of the nitric oxide pathway

Inhaled Pulmonary Vasodilators and Thoracic Organ Transplantation: Does Evidence Support Its Use and Cost Benefit?

In heart transplantation, pulmonary hypertension and increased pulmonary vascular resistance followed by donor right ventricular dysfunction remain a major cause of perioperative morbidity and mortality. In lung transplantation, primary graft dysfunction remains a major obstacle because it can cause bronchiolitis obliterans and mortality. Pulmonary vasodilators have been used as an adjunct therapy for heart or lung transplantation, mainly to treat pulmonary hypertension, right ventricular failure, and associated refractory hypoxemia. Among pulmonary vasodilators, inhaled nitric oxide is unique in that it is selective in pulmonary circulation and causes fewer systemic complications such as hypotension, flushing, or coagulopathy. Nitric oxide is expected to prevent or attenuate primary graft dysfunction by decreasing ischemia-reperfusion injury in lung transplantation. However, when considering the long-term benefit of these medications, little evidence supports their use in heart or lung transplantation. Current guidelines endorse inhaled vasodilators for managing immediate postoperative right ventricular failure in lung or heart transplantation, but no guidance is offered regarding agent selection, dosing, or administration. This review presents the current evidence of inhaled nitric oxide in lung or heart transplantation as well as comparisons with other pulmonary vasodilators including cost differences in consideration of economic pressures to contain rising pharmacy costs.

Donor pretreatment with tetrahydrobiopterin saves pancreatic isografts from ischemia reperfusion injury in a mouse model

Depletion of the nitric oxide synthase cofactor tetrahydrobiopterin (H4B) during ischemia and reperfusion is associated with severe graft pancreatitis. Since clinically feasible approaches to prevent ischemia reperfusion injury (IRI) by H4B-substitution are missing we investigated its therapeutic potential in a murine pancreas transplantation model using different treatment regimens. Grafts were subjected to 16 h cold ischemia time (CIT) and different treatment regimens: no treatment, 160 μM H4B to perfusion solution, H4B 50 mg/kg prior to reperfusion and H4B 50 mg/kg before recovery of organs. Nontransplanted animals served as controls. Recipient survival and endocrine graft function were assessed. Graft microcirculation was analyzed 2 h after reperfusion by intravital fluorescence microscopy. Parenchymal damage was assessed by histology and nitrotyrosine immunohistochemistry, H4B tissue levels by high pressure liquid chromatography (HPLC). Compared to nontransplanted controls prolonged CIT resulted in significant microcirculatory deterioration. Different efficacy according to route and timing of administration could be observed. Only donor pretreatment with H4B resulted in almost completely abrogated IRI-related damage showing graft microcirculation comparable to nontransplanted controls and restored intragraft H4B levels, resulting in significant reduction of parenchymal damage (p < 0.002) and improved survival and endocrine function (p = 0.0002 each). H4B donor pretreatment abrogates ischemia-induced parenchymal damage and represents a promising strategy to prevent IRI following pancreas transplantation.

cGMP increases antioxidant function and attenuates oxidant cell death in mouse lung microvascular endothelial cells by a protein kinase G-dependent mechanism

Increasing evidence suggests that endothelial cytotoxicity from reactive oxygen species (ROS) contributes to the pathogenesis of acute lung injury. Treatments designed to increase intracellular cGMP attenuate ROS-mediated apoptosis and necrosis in several cell types, but the mechanisms are not understood, and the effect of cGMP on pulmonary endothelial cell death remains controversial. In the current study, increasing intracellular cGMP by either 8pCPT-cGMP (50 microM) or atrial natriuretic peptide (10 nM) significantly attenuated cell death in H(2)O(2)-challenged mouse lung microvascular (MLMVEC) monolayers. 8pCPT-cGMP also decreased perfusate LDH release in isolated mouse lungs exposed to H(2)O(2) or ischemia-reperfusion. The protective effect of increasing cGMP in MLMVECs was accompanied by enhanced endothelial H(2)O(2) scavenging (measured by H(2)O(2) electrode) and decreased intracellular ROS concentration (measured by 2',7'-dichlorofluorescin fluorescence) as well as decreased phosphorylation of p38 MAPK and Akt. The cGMP-mediated cytoprotection and increased H(2)O(2) scavenging required >2 h of 8pCPT-cGMP incubation in wild-type MLMVEC and were absent in MLMVEC from protein kinase G (PKG(I))-/- mice suggesting a PKG(I)-mediated effect on gene regulation. Catalase and glutathione peroxidase 1 (Gpx-1) protein were increased by cGMP in wild-type but not PKG(I)-/- MLMVEC monolayers. Both the cGMP-mediated increases in antioxidant proteins and H(2)O(2) scavenging were prevented by inhibition of translation with cycloheximide. 8pCPT-cGMP had minimal effects on catalase and Gpx-1 mRNA. We conclude that cGMP, through PKG(I), attenuated H(2)O(2)-induced cytotoxicity in MLMVEC by increasing catalase and Gpx-1 expression through an unknown posttranscriptional effect.

Inhaled Nitric Oxide Does Not Prevent Pulmonary Edema After Lung Transplantation Measured By Lung Water Content

STUDY OBJECTIVE

In order to assess the effects of inhaled nitric oxide (iNO) in preventing early-onset lung edema from occurring after lung transplantation, we measured extravascular lung water (EVLW) in a group of lung transplant recipients who were at high risk for developing ischemia-reperfusion-induced lung injury.

DESIGN

Prospective, randomized study.

SETTINGS

Surgical ICU in a teaching hospital.

PATIENTS

Thirty double-lung transplant recipients.

INTERVENTIONS

Patients were randomized to receive or not receive 20 ppm iNO at the time of reperfusion (ie, before any occurrence of lung edema). In the NO group, iNO was then administered for a 12-h period. A double-dilution technique was used for the serial assessment of EVLW, intrathoracic blood volume, and cardiac index. Standard hemodynamic and pulmonary parameters were also recorded during the first 3 postoperative days.

MEASUREMENTS AND RESULTS

Patients who received iNO did not have a different lung water content compared to control subjects (p = 0.61 [by analysis of variance (ANOVA)]). Blood oxygenation (ie, Pao(2)/fraction of inspired oxygen [Fio(2)] ratio) did not differ between the two groups (p = 0.61 [by ANOVA]). In both groups, EVLW and Pao(2)/Fio(2) ratio dropped significantly over time, regardless of the use of iNO (p < 0.01 [by ANOVA]).

CONCLUSIONS

In the population studied, prophylactic iNO that was administered at 20 ppm had no effect on pulmonary edema formation and resolution following lung transplantation.

Cytoprotective function of tetrahydrobiopterin in rat liver ischemia/reperfusion injury

BACKGROUND

Tetrahydrobiopterin (BH(4)) is a key coenzyme of nitric oxide synthase (NOS), which is associated with a cytoprotective function in various ischemia-reperfusion (I/R) injury models. There have been a few reports on the efficacy of BH(4) in the treatment of I/R injury in other organs; therefore, the aim of this study was to investigate the effect of BH(4) related with NOS reaction in hepatic I/R injury.

METHODS

A model of 70% liver I/R injury with a 100-minute ischemic time was created in rats, and the non-ischemic lobes were then resected. The rats were given BH(4) (BH(4) group) or saline solution (saline group) before reperfusion. The specific inducible NOS blocker 1400W was used to evaluate the effect of endogenous inducible NOS in the I/R hepatic injury. Survival, nitric oxide products (nitrate and nitrite), NOS expression, and nitrotyrosine (ie, the peroxynitrite product) were measured after reperfusion.

RESULTS

On day 7, the survival rate was 62.5% in the BH(4) group, as opposed to 14.3% in the saline group (P = .0004); 1400W administration to the BH(4) group decreased the survival rate to 0% (P = .003). BH(4) prevented the significant increase in total bilirubin levels (P < .01) after 12-hour reperfusion. The increases in serum alanine transaminase levels (after 3 hours and 12 hours of reperfusion) were significantly (P < .01) attenuated in the BH(4) group. BH(4) increased the nitrate/nitrite concentrations in liver tissue (P < .05) and reduced nitrotyrosine production, and the protein assay showed that BH(4) increased inducible NOS and endothelial NOS expression. Histologic examination of the liver revealed that BH(4) mitigated the damage that was caused by liver I/R.

CONCLUSION

Exogenous BH(4) increased nitric oxide production, which attenuated the hepatic I/R injury.

Pyruvate-Modified Perfadex Improves Lung Function After Long-Term Hypothermic Storage

BACKGROUND

Lungs harvested for transplantation are stored while inflated with oxygen, which can serve to support oxidative metabolism. However, strategies aimed at increasing graft metabolism during storage have received little attention. In this study, we added pyruvate to the preservation solution Perfadex and measured the effects on oxidative metabolism and reperfusion lung function.

METHODS

Rat lungs were stored for 6 and 24 hours in low-potassium dextran solution at 10 degrees C containing either 5 mmol/liter uniformly carbon-13 (U-(13)C) labeled glucose (Perfadex), 32 mmol/liter 3-(13)C pyruvate (pyruvate), or both (combined). Oxidation of exogenous substrates was measured as the incorporation of (13)C into tricarboxylic acid cycle intermediates by magnetic resonance spectroscopy. Additional groups of lungs with each substrate modification were preserved for 6 or 24 hours and then reperfused.

RESULTS

Enrichment of tricarboxylic acid cycle intermediates was low in the Perfadex group (9% at 6 hours and 32% at 24 hours of storage, respectively). In contrast, enrichment was significantly increased in both the pyruvate group (50% and 59%, respectively) and combined group (39% and 54%, respectively) compared with the Perfadex group (p<0.01). Graft function was excellent after 6-hour storage in all groups. All lungs stored for 24 hours exhibited inferior lung function, but oxygenation, pulmonary artery pressures, and airway pressures in the combined group were significantly improved compared with the Perfadex group (p<0.05).

CONCLUSIONS

Preservation solution substrate composition influences graft metabolism during storage. The addition of pyruvate to Perfadex increases metabolism during storage and improves reperfusion lung function.

Tetrahydrobiopterin prevents cyclosporine-induced vasomotor dysfunction

BACKGROUND

Cyclosporine A (CsA) is associated with negative side effects such as endothelial injury, which may lead to transplant vasculopathy. CsA can impair nitric oxide (NO) homeostasis. Therefore, tetrahydrobiopterin (BH4), a NO synthase cofactor, may limit endothelial injury by improving NO production. Our study examines the effect of CsA and BH4 exposure on endothelial function.

METHODS

Lewis rats were injected with CsA, BH4, CsA+BH4, or saline intraperitoneally daily for 2 weeks. With use of a small vessel myograph, thoracic aortic segments were assessed for endothelial-dependent (Edep) and independent relaxation after exposure to acetylcholine and sodium nitroprusside. Sensitivity to vasospasm was evaluated after exposure to endothelin (ET)-1.

RESULTS

CsA exposure resulted in impaired Edep vasorelaxation compared with control (P=0.01). BH4 attenuated the deleterious effects of CsA. Compared with control, all treatment groups demonstrated significantly increased sensitivity to ET-1. Furthermore, endothelial nitric oxide synthase expression in the thoracic aorta was reduced after CsA treatment, and this reduction was attenuated by BH4 therapy (P<0.01). ETA receptor expression in the aorta was increased after CsA treatment, but BH4 treatment prevented CsA-induced ETA over-expression (P=0.004). However, ETB receptor expression was increased by BH4 treatment compared with CsA and control (P=0.02).

CONCLUSION

Our findings suggest that CsA-induced vasomotor dysfunction is a result of alterations in both NO and ET-1 regulation and that BH4 may prevent the deleterious effects of CsA. However, the beneficial effects of BH4 are associated with increased sensitivity to ET-1. Therefore, a combination of BH4 and ET-1 blockade may prove to be an ideal combination for preservation of endothelial function.

Novel cardioprotective effects of tetrahydrobiopterin after anoxia and reoxygenation: Identifying cellular targets for pharmacologic manipulation

OBJECTIVES

Contemporary cardioprotective strategies to prevent perioperative ischemia-reperfusion injury have focused on the l-arginine nitric oxide pathway. Tetrahydrobiopterin is an absolute cofactor required for the enzyme nitric oxide synthase and is thus a critical determinant of nitric oxide production. We hypothesized that ischemia-reperfusion results in diminished levels of tetrahydrobiopterin, which might represent a key cellular defect underlying endothelial and myocyte dysfunction after ischemia-reperfusion. To this aim, we examined the effects of tetrahydrobiopterin supplementation in (1) an in vivo experimental model of global ischemia-reperfusion and (2) an in vitro human ventricular heart cell model of simulated ischemia-reperfusion. Measures of endothelial function, oxidant production, cell survival, and cardiac function were used to assess outcome.

METHODS

In study 1 Wistar rats were divided into one of 2 groups (n = 10 per group). One group received tetrahydrobiopterin (25 mg x kg(-1) x d(-1) for 7 days), and the other group served as the control group. Hearts were subjected to 30 minutes of ischemia followed by 30 minutes of reperfusion, and left ventricular developed pressure, left ventricular systolic pressure, and left ventricular end-diastolic pressure were determined by using the modified Langendorff technique. In study 2 we quantitated myocardial malondialdehyde, a marker of lipid peroxidation, in ventricular tissues from both groups of animals using butanol phase extraction and spectrophotometric analysis. In study 3 coronary vascular responses were determined in vascular segments of the left coronary artery in both groups of animals after ischemia-reperfusion. Endothelium-dependent and endothelium-independent vasodilatation to acetylcholine and sodium nitroprusside, respectively, were compared between groups. In study 4, using a human ventricular heart cell model of simulated ischemia-reperfusion, we studied the effects of tetrahydrobiopterin (20 micromol/L) on cellular injury (as assessed by means of trypan blue uptake).

RESULTS

After ischemia-reperfusion, myocardial dysfunction was evidenced by a decrease in left ventricular developed pressure and an increase in left ventricular end-diastolic pressure (P =.01 compared with baseline). Hearts from tetrahydrobiopterin-treated rats exhibited protection against ischemia-reperfusion injury (left ventricular developed pressure: 74 +/- 4 vs control 42 +/- 8 mm Hg, P =.01; left ventricular end-diastolic pressure: 12 +/- 3 vs 34 +/- 7 mm Hg, P =.01). Furthermore, tetrahydrobiopterin treatment attenuated the rise in malondialdehyde levels after ischemia-reperfusion (P =.01). After reperfusion, coronary endothelial function to acetylcholine was attenuated (P =.003 vs sham-treated mice), whereas responses to sodium nitroprusside remained unchanged. Tetrahydrobiopterin-treated rats exhibited an improvement in acetylcholine-mediated vasorelaxation (P =.01 vs ischemia-reperfusion group). Cellular injury, as assessed by means of trypan blue uptake, was higher in human ventricular heart cells subjected to simulated ischemia-reperfusion; this effect was prevented with tetrahydrobiopterin treatment (P =.001).

CONCLUSIONS

Supplemental tetrahydrobiopterin provides a novel cardioprotective effect on left ventricular function, endothelial-vascular reactivity, oxidative damage, and cardiomyocyte injury after ischemia-reperfusion injury and might represent an important cellular target for future operative myocardial protection strategies.