Attenuation of lung graft reperfusion injury by a nitric oxide donor

Therapeutic benefits of nitric oxide in lung transplantation

Lung transplantation is an evolutionary procedure from its experimental origin in the twentieth century and is now recognized as an established and routine life-saving intervention for a variety of end-stage pulmonary diseases refractory to medical management. Despite the success and continuous refinement in lung transplantation techniques, the widespread application of this important life-saving intervention is severely hampered by poor allograft quality offered from donors-after-brain-death. This has necessitated the use of lung allografts from donors-after-cardiac-death (DCD) as an additional source to expand the pool of donor lungs. Remarkably, the lung exhibits unique properties that may make it ideally suitable for DCD lung transplantation. However, primary graft dysfunction (PGD), allograft rejection and other post-transplant complications arising from unavoidable ischemia-reperfusion injury (IRI) of transplanted lungs, increase morbidity and mortality of lung transplant recipients annually. In the light of this, nitric oxide (NO), a selective pulmonary vasodilator, has been identified as a suitable agent that attenuates lung IRI and prevents PGD when administered directly to lung donors prior to donor lung procurement, or to recipients during and after transplantation, or administered indirectly by supplementing lung preservation solutions. This review presents a historical account of clinical lung transplantation and discusses the lung as an ideal organ for DCD. Next, the author highlights IRI and its clinical effects in lung transplantation. Finally, the author discusses preservation solutions suitable for lung transplantation, and the protective effects and mechanisms of NO in experimental and clinical lung transplantation.

Creatine Supply Attenuates Ischemia-Reperfusion Injury in Lung Transplantation in Rats

Ischemia-reperfusion injury (IRI) is one of the factors limiting the success of lung transplantation (LTx). IRI increases death risk after transplantation through innate immune system activation and inflammation induction. Some studies have shown that creatine (Cr) protects tissues from ischemic damage by its antioxidant action. We evaluated the effects of Cr supplementation on IRI after unilateral LTx in rats. Sixty-four rats were divided into four groups: water + 90 min of ischemia; Cr + 90 min of ischemia; water + 180 min of ischemia; and Cr + 180 min of ischemia. Donor animals received oral Cr supplementation (0.5 g/kg/day) or vehicle (water) for five days prior to LTx. The left lung was exposed to cold ischemia for 90 or 180 min, followed by reperfusion for 2 h. We evaluated the ventilatory mechanics and inflammatory responses of the graft. Cr-treated animals showed a significant decrease in exhaled nitric oxide levels and inflammatory cells in blood, bronchoalveolar lavage fluid and lung tissue. Moreover, edema, cell proliferation and apoptosis in lung parenchyma were reduced in Cr groups. Finally, TLR-4, IL-6 and CINC-1 levels were lower in Cr-treated animals. We concluded that Cr caused a significant decrease in the majority of inflammation parameters evaluated and had a protective effect on the IRI after LTx in rats.

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.

Lung ischemia-reperfusion injury: a molecular and clinical view on a complex pathophysiological process

Lung ischemia-reperfusion injury remains one of the major complications after cardiac bypass surgery and lung transplantation. Due to its dual blood supply system and the availability of oxygen from alveolar ventilation, the pathogenetic mechanisms of ischemia-reperfusion injury in the lungs are more complicated than in other organs, where loss of blood flow automatically leads to hypoxia. In this review, an extensive overview is given of the molecular and cellular mechanisms that are involved in the pathogenesis of lung ischemia-reperfusion injury and the possible therapeutic strategies to reduce or prevent it. In addition, the roles of neutrophils, alveolar macrophages, cytokines, and chemokines, as well as the alterations in the cell-death related pathways, are described in detail.

Recipient treatment with L-arginine attenuates donor lung injury associated with hemorrhagic shock

BACKGROUND

Organ donors are frequently trauma victims, but the impact of donor hemorrhagic shock and resuscitation (HSR) on pulmonary graft function has not been assessed. L-arginine treatment during reperfusion increases the production of endothelial nitric oxide and thus ameliorates ischemia-reperfusion injury. Objective of the present porcine study was to investigate the effect of donor hemorrhage on pulmonary graft function and potential beneficial effects of L-arginine administration.

METHODS

In the control-group (n=6), lungs were harvested from donors without hypotensive periods. In the HSR-group (n=6) and HSR-Arg-group (n=6), donors were subjected to hemorrhagic shock (40% blood shed) and resuscitation before harvest. Left lungs were transplanted after hypothermic preservation of 18 hr, and graft function was observed for 6 hr after reperfusion. Recipients in the HSR-Arg-group received a bolus of L-arginine (50 mg/kg BW) intravenously 5 min before reperfusion followed by a continuous intravenous administration of L-arginine 200 mg/kg BW for 2 hr. Tissue specimens and bronchoalveolar lavage fluid were obtained at the end of the observation period.

RESULTS

Donor lung function did not differ between study groups. Compared with the control group, pulmonary graft gas exchange was significantly impaired in the HSR-group. Graft function in the HSR-Arg-group did not differ from control organs. Neutrophil fraction, protein content, and malondialdehyde levels in the bronchoalveolar lavage fluid in the HSR-group were higher compared with control and HSR-Arg-Group.

CONCLUSION

Although fulfilling ideal donor criteria, pulmonary graft function of lungs harvested from donors subjected to HSR is impaired, but improves significantly when l-arginine is administered during reperfusion.

Determination of interleukin-6 in lung transplantation: association with primary graft dysfunction

INTRODUCTION AND OBJECTIVE

Primary graft dysfunction (PGD) secondary to damage caused by ischemia/reperfusion is responsible for significant morbidity. It constitutes the main cause of early death following implantation. Our objective was to verify the association between PGD and activation of the inflammatory cascade by measuring interleukin-6 (IL-6) in the blood and the bronchoalveolar lavage (BAL) of the recipient.

MATERIALS AND METHODS

The 31 patients, including 22 bipulmonary and 9 unipulmonary cases, had severe PGD (ISHLT grade II) defined by: (1) radiographic infiltrates during the first 72 hours after transplantation, (2) PO2/FiO2 ratio <200 in the first 72 hours after the operation, and (3) no other cause of dysfunction. BAL and peripheral arterial blood samples were extracted prior to implantation (baseline level) and at 12, 24, and 48 hours after reperfusion. Samples were frozen to -80 degrees C until determination of IL-6 using an immunoassay technique (ELISA).

RESULTS

In the 31 transplants (100%), there were elevated IL-6 contents in the BAL and blood compared with the baseline level (P < .0001). Among 11 patients with severe PGD (38.70%) In the BAL samples the concentration of IL-6 was significantly elevated (P < .05) compared with patients without PGD (P < .031). These finding were also observed in blood (P < .016) obtained at 12 hours. The analyses at 24 and 48 hours showed higher levels of IL-6 in the PGD group, although they were not significant.

CONCLUSIONS

There was a significant elevation of IL-6 in blood and BAL during the first few hours after reperfusion of the graft, which was directly related to the development of PGD.

The endothelin axis and gelatinase activity in alveolar macrophages after brain-stem death injury: a pilot study

BACKGROUND

Endothelin-1 (ET-1) is a potent vasoconstricting mitogen that has been implicated in the development of primary graft dysfunction. Increased activity of matrix metalloproteinases (MMPs), specifically MMP-2 and -9, has been associated with tissue damage in acute lung injury and after lung transplantation. Using a validated model of brain-stem death (BSD), we aimed to determine whether alveolar macrophage up-regulation in the pulmonary system is an early feature of BSD injury and if expression levels of ET-1, endothelin A receptors (ET(A)R) and endothelin B receptors (ET(B)R), as well as MMP-2 and -9, are increased in comparison to sham controls.

METHODS

Six control and 8 experimental Wistar-Kyoto rats had a balloon catheter inserted into their subdural space. In the experimental group the balloon was inflated for 4 hours. Lung specimens were immunohistochemically labeled with CD68, ET-1, ET(A)R, ET(B)R, MMP-2 and MMP-9, and 10 fields per slide were assessed.

RESULTS

The ratio of alveolar macrophages to polymorphonuclear neutrophils was significantly greater in the BSD group than in controls (9 +/- 4.1 vs 3 +/- 0.5, p = 0.004) and adventitial macrophages increased in BSD lung parenchyma (p < 0.0001). ET-1, ET(A)R and ET(B)R levels were elevated in the experimental group (27.6 +/- 5.7 vs 7 +/- 2.3, 36.1 +/- 4.6 vs 17.7 +/- 2.6 and 60 +/- 7.1 vs 19.8 +/- 3.7, p < 0.0001 inclusive). BSD expression of MMP-2 and MMP-9 was double that of controls (14.9 +/- 3.4 vs 30.7 +/- 3.4 and 14.2 +/- 2.2 vs 37 +/- 3.6, respectively, p < 0.0001 inclusive).

CONCLUSIONS

Alveolar macrophages are rapidly recruited after BSD and may affect peri-operative lung function via increased expression of ET-1, ET(A)R, ET(B)R, MMP-2 and MMP-9.

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.

Lung ischemia-reperfusion injury: implications of oxidative stress and platelet-arteriolar wall interactions

Pulmonary ischemia-reperfusion (IR) injury may result from trauma, atherosclerosis, pulmonary embolism, pulmonary thrombosis and surgical procedures such as cardiopulmonary bypass and lung transplantation. IR injury induces oxidative stress characterized by formation of reactive oxygen (ROS) and reactive nitrogen species (RNS). Nitric oxide (NO) overproduction via inducible nitric oxide synthase (iNOS) is an important component in the pathogenesis of IR. Reaction of NO with ROS forms RNS as secondary reactive products, which cause platelet activation and upregulation of adhesion molecules. This mechanism of injury is particularly important during pulmonary IR with increased iNOS activity in the presence of oxidative stress. Platelet-endothelial interactions may play an important role in causing pulmonary arteriolar vasoconstriction and post-ischemic alveolar hypoperfusion. This review discusses the relationship between ROS, RNS, P-selectin, and platelet-arteriolar wall interactions and proposes a hypothesis for their role in microvascular responses during pulmonary IR.

Inflammatory response to pulmonary ischemia-reperfusion injury

Lung ischemia-reperfusion (IR) injury is one of the most important complications following lung transplant and cardiopulmonary bypass. The pulmonary dysfunction following lung IR has been well documented. Recent studies have shown that ischemia and reperfusion of the lung may each play significant yet differing roles in inducing lung injury. The mechanisms of injury involving neutrophil activation, and the release of numerous inflammatory mediators and oxygen radicals also contributes to lung cellular injury, pneumocyte necrosis, and apoptosis. We herein review the current understanding of the underlying mechanism involved in lung IR injury. The biomolecular mechanisms and interactions which lead to the inflammatory response, pneumocyte necrosis, and apoptosis following lung IR therefore warrant further investigation.

Selective inducible nitric oxide synthase (iNOS) inhibition attenuates remote acute lung injury in a model of ruptured abdominal aortic aneurysm

OBJECTIVE

Abdominal aortic aneurysm rupture is associated with a systemic inflammatory response syndrome and acute lung injury. Using a selective inducible nitric oxide synthase (iNOS) inhibitor, N(6)-(iminoethyl)-lysine (L-NIL), we explored the role of iNOS in the early pro-inflammatory signaling and acute lung injury in experimental abdominal aortic aneurysm rupture.

MATERIALS AND METHODS

Anesthetized rats were randomized to sham control or shock and clamp (s + c) groups, which underwent one hour of hemorrhagic shock, followed by 45 minutes of supramesenteric aortic clamping, and then two hours resuscitated reperfusion. Animals in s + c were randomized to receive intravenous L-NIL at 50 microg/kg/h or saline at the start of reperfusion. Pulmonary permeability to (125)I-labeled albumin, myeloperoxidase (MPO) activity, cytokine levels, and semi-quantitative RT-PCR for mRNA were indicators of microvascular permeability, leuco-sequestration, and pro-inflammatory signaling, respectively.

RESULTS

Lung permeability index were significantly increased in s + c compared to sham (4.43 +/- 0.96 versus 1.30 +/- 0.17, P < 0.01), and attenuated by L-NIL treatment (2.14 +/- 0.70, P < 0.05). Lung tissue MPO activity was significantly increased in s + c compared to sham (2.80 +/- 0.32 versus 1.03 +/- 0.29, P < 0.002), and attenuated by L-NIL treatment (1.50 +/- 0.20, P < 0.007). Lung tissue iNOS activity was significantly increased in s + c compared to sham animals (P < 0.05), and attenuated by L-NIL treatment (P < 0.05). Lung tissue iNOS mRNA was upregulated 8-fold in s + c compared to sham (P < 0.05). Data represents mean +/- standard error mean, comparisons with ANOVA.

CONCLUSIONS

These data suggest that in our model of ruptured abdominal aortic aneurysm iNOS plays a crucial role in reperfusion lung injury. Selective inhibition of iNOS during early reperfusion prevents neutrophil mediated acute lung injury.

CONTINUOUS INFUSION OF NITROGLYCERIN IMPROVES PULMONARY GRAFT FUNCTION OF NON???HEART-BEATING DONOR LUNGS

BACKGROUND

The warm ischemic period of lungs harvested from a non-heart-beating donor (NHBD) results in an increased ischemia-reperfusion injury after transplantation. The intravenous application of nitroglycerin (NTG), a nitric oxide (NO) donor, proved to be beneficial during reperfusion of lung grafts from heart-beating donors. The objective of the present study was to investigate the effect of nitroglycerin on ischemia-reperfusion injury after transplantation of long-term preserved NHBD-lungs.

METHODS

Sixteen pigs (body weight, 20-30 kg) underwent left lung transplantation. In the control group (n=5), lungs were flushed (Perfadex, 60 mL/kg) and harvested immediately after cardiac arrest. In the NHBD group (n=5) and the NHBD-NTG group (n=6), lungs were flushed 90 min (warm ischemia) after cardiac arrest. After a total ischemia time of 19 hr, lungs were reperfused and graft function was observed for 5 hr. Recipient animals in the NHBD-NTG group received 2 microg/kg/min of NTG administered intravenously during the observation period starting 5 min before reperfusion. Tissue specimens and bronchoalveolar lavage fluid (BALF) were obtained at the end of the observation period.

RESULTS

Compared with the control group, pulmonary gas exchange was significantly impaired in the NHBD group, whereas graft function in the NHBD-NTG group did not change. Leukocyte fraction and protein concentration in the BALF and histologic alteration of the NHBD-NTG group were not different from controls.

CONCLUSIONS

Continuous infusion of NTG in the early reperfusion period improves pulmonary graft function of NHBD lungs after long-term preservation. The administration of an NO donor during reperfusion may favor the use of NHBD lungs to alleviate the critical organ shortage in lung transplantation.

Increased expression of nitric oxide synthase in human lung transplants after nitric oxide inhalation

BACKGROUND

The effects of the ischemia-reperfusion process of organ transplantation on nitric oxide (NO) synthase (NOS) in humans are unknown. The effects of NO inhalation on endogenous NOS expression and activity are controversial. The authors hypothesized that NO inhalation may affect ischemia-reperfusion-induced alterations of the endogenous NOS system.

METHODS

The authors performed lung biopsy on patients in a randomized phase II clinical trial of NO inhalation during lung transplantation. After lung implantation, 20 ppm of NO or placebo gas was administered 10 min after the start of reperfusion. Lung tissues were collected from 20 patients (NO, n=9; placebo, n=11) after cold and warm ischemia, 1 hr and 2 hr after reperfusion. The protein levels of NOS isoforms were analyzed by Western blotting and the total NOS activity was measured.

RESULTS

The protein levels of inducible NOS did not change significantly in either of the groups. In contrast, during the 2-hr reperfusion period, constitutive NOS (neuronal NOS [nNOS] and endothelial NOS) tended to decrease in the placebo group, but gradually increased in the NO group. After 2 hr of reperfusion, the nNOS protein in the NO group was significantly higher than that in the placebo group (P <0.05). However, the total NOS activity remained at low levels in both groups.

CONCLUSIONS

NO inhalation-induced increase of constitutive NOS proteins indicates the interaction between inhaled NO molecules and lung tissues. However, the activity of these newly synthesized NOS proteins remains suppressed during the ischemia-reperfusion period of lung transplantation.

A randomized trial of inhaled nitric oxide to prevent ischemia-reperfusion injury after lung transplantation

Inhalation of nitric oxide (NO) has been advocated as a method to prevent ischemia-reperfusion injury after lung transplantation. We enrolled 84 patients into a concealed, randomized, placebo-controlled trial to evaluate the effect of inhaled NO (20 ppm NO or nitrogen) initiated 10 minutes after reperfusion on outcomes after lung transplantation. The groups (n = 42) were balanced with respect to age, sex, lung disease, procedure, and total ischemic times. PaO2/FIO2 ratios were similar on admission to the intensive care unit (ICU) (NO 361 +/- 134; control patients 357 +/- 132), and over the duration of the study. There were no differences in hemodynamics between the two groups. Severe reperfusion injury (PaO2/FIO2 < 150) was present at the time of admission to the ICU in 14.6% NO patients versus 9.5% of control patients (p = 0.48). The groups had similar median times to first successful trial of unassisted breathing (25 vs. 27 hours; p = 0.76), successful extubation (32 vs. 34 hours; p = 0.65), ICU discharge (3.0 days for both groups), and hospital discharge (27 vs. 29 days; p = 0.563). Five NO versus six control patients died during their hospital stay. Adjusting for age, sex, lung disease etiology, presence of pulmonary hypertension, and total ischemic time did not alter these results. In conclusion, we did not detect a significant effect of inhaled NO administered 10 minutes after reperfusion on physiologic variables or outcomes in lung transplant patients.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.

Nitroglycerin alters alveolar type II cell ultrastructure after ischemia and reperfusion

BACKGROUND

Although administration of nitric oxide (NO) has been suggested to reduce pulmonary reimplantation response, concerns remain about cytotoxic side effects.

METHODS

Using light and electron microscopy, we examined the effects of the NO donor nitroglycerin (NTG) (0.1 mg/ml) as a supplement to the preservation solution Celsior on the structural integrity of rat lungs after extracorporeal ischemia (4 hours at 10 degrees C) and reperfusion (50 minutes) (IR). We performed evaluation in comparison with Celsior alone after IR using either standard antegrade perfusion through the pulmonary artery or retrograde perfusion through the left atrium as an alternative way to improve the preservation quality. Untreated, non-ischemic lungs served as controls (n = 5 per group). We recorded respiratory and hemodynamic parameters during reperfusion. Tissue collection using systematic uniform random sampling was representative for the whole organ and allowed stereologic quantification of structures.

RESULTS

After IR, histochemistry revealed no breaks in the alveolo-capillary barrier and we detected no alveolar flooding. Edema formed in the peribronchovascular cuffs, of which the volume fraction was increased (p =.008). Vasoconstriction of the smaller arteries accompanied antegrade flush, which occurred neither after administration of NTG nor after retrograde flush, as shown by immunostaining for alpha-smooth muscle actin. Treatment with NTG was associated with focal disintegration of Type II cells, which displayed edematous swelling of distinct cell compartments and lysis of mitochondria and cells. Nitroglycerin prevented alveolar collapse, which was increased in the other IR groups (p = 0.013). We observed alterations in intra-alveolar surfactant components.

CONCLUSION

These findings indicate pathologic effects of NTG treatment on alveolar epithelial integrity. Therefore, we suggest further critical evaluation of NTG/NO for therapeutic use in lung transplantation.

L-Arginine in lung graft preservation and reperfusion

BACKGROUND

Inhaled nitric oxide has been shown to ameliorate early lung graft dysfunction. It improves oxygenation by inducing pulmonary vasodilatation in well-ventilated lung areas, and it also modulates leukocyte-endothelium interactions. We used a porcine, single lung transplantation model to evaluate whether the benefits of exogenously administered gas could be achieved easier by adding L-arginine, the substrate of endogenous nitric oxide synthesis, as an additive to the flush solution and intravenously during reperfusion.

METHODS

Six pig lungs were flushed with modified Euro-Collins solutions containing L-arginine (2 g/liter). After cold (4 degrees C) storage, the left lung was transplanted. Ischemic time was 260 minutes. The recipients received intravenous boluses of L-arginine (30 mg/kg), followed by infusion (20 mg/kg/min) during the first 30 minutes of reperfusion. Six control animals received saline as placebo. We measured the blood flow and pulmonary vascular resistance (PVR) in the transplanted and in the native lung using a right heart bypass model. We measured blood gases, leukocyte counts, plasma free-radical trapping capacity, and diene conjugates in pulmonary venous blood and myeloperoxidase activity of the lung tissue.

RESULTS

Pulmonary vascular resistance was 4 to 5-fold higher in the transplanted lung than in the native lung, which received 80% of the total blood flow. L-arginine reduced PVR by 30% in the native lung (p < 0.001), but not in the transplanted lung. L-arginine had no effect on oxygenation or carbon dioxide exchange of the transplanted lung. Nor did L-arginine treatment have any effect on leukocyte sequestration or myeloperoxidase activity in the transplanted lung. The plasma antioxidant capacity in venous blood of the transplanted lung almost doubled shortly during early reperfusion without influence of L-arginine.

CONCLUSIONS

L-arginine reduced PVR in the native lung but did not improve pulmonary hemodynamics, gas exchange, or reduce leukocyte sequestration of the transplanted lung.

Up-regulation of inducible nitric oxide synthase in fibroblasts parallels the onset and progression of fibrosis in an experimental model of post-transplant obliterative airway disease

The main cause of mortality following lung transplantation is chronic rejection, manifesting morphologically as obliterative bronchiolitis (OB). It has been suggested that damage to the respiratory epithelium initiates proliferation of mesenchymal cells, leading to dense collagenous scarring in small airways. Inducible nitric oxide synthase (iNOS) is strongly expressed in the damaged epithelium in human OB, along with high levels of peroxynitrite, suggesting that endogenous NO mediates the epithelial destruction. To examine further the role of iNOS in this process, heterotopic airway implants were studied in rats, an acknowledged disease model. Specimens of iso- or allografted trachea, collected 3-60 days after implantation, were processed for histology and immunocytochemistry for iNOS and, as a marker of peroxynitrite formation, nitrotyrosine. In both iso- and allografts at the earliest stage (day 3), ischaemia was associated with severe epithelial damage or loss. These changes progressed until day 7 and were accompanied by strong expression of iNOS and nitrotyrosine in epithelial cells. In isografts, epithelial recovery was seen, with abundant iNOS immunoreactivity but little nitrotyrosine. In contrast, the epithelium in allografts did not regenerate and progressive inflammation and fibroproliferation occurred until complete obliteration of the tracheal lumen at day 60. The fibroproliferation was associated with changes in morphology of fibroblasts that were accompanied by alterations in their iNOS expression. iNOS immunoreactivity was dense in the plump fibroblasts of early lesions, in some cases as early as post-operative day 5, but very weak in elongated fibroblasts in totally occluded grafts. The intensity of immunoreactivity for nitrotyrosine corresponded to that of iNOS. These results indicate a dual role for NO in the airway obliteration that follows transplantation, through destruction of epithelium and stimulation of fibroblast activity.

Cytoprotective effects of nitroglycerin in ischemia-reperfusion-induced lung injury

Prevention of ischemia-reperfusion (IR) injury is crucial for successful lung transplantation. We investigated whether a nitric oxide donor, nitroglycerin (NTG), could suppress the oxidative stress of IR injury and improve pulmonary function after reperfusion in an ex vivo rat lung perfusion model. In Fresh group of animals, the lungs were flushed with perfusate, followed immediately by reperfusion, and no lung injury was observed. In NTG- and NTG+ groups of animals, the lungs were flushed with perfusate alone or perfusate containing NTG, respectively. Harvested lung and heart blocks from these latter two groups were immersed in the corresponding perfusate at 4 degrees C for 15 h, and were then reperfused for 60 min. Reperfusion induced pulmonary edema in the NTG- group, but not in the NTG+ group. Shunt fractions in NTG+ group were significantly lower than in the NTG- group throughout reperfusion. NTG had no effect on pulmonary arterial pressure or myeloperoxidase activity. In contrast, oxidative DNA damage assessed immunohistochemically with a monoclonal antibody against 8-hydroxy-2'-deoxyguanosine (8-OHdG) was significantly increased in the NTG- group, in the order alveolar epithelium > pulmonary endothelium > bronchial epithelium. NTG treatment significantly decreased staining with the anti-8-OHdG antibody in all three areas of tissue. Therefore, administration of NTG attenuates the oxidative stress of IR injury, and may improve pulmonary function after reperfusion.

Modulation of lung reperfusion injury by nitric oxide: impact of inspired oxygen fraction

BACKGROUND

Attempts to attenuate lung reperfusion injury by administration of inhaled nitric oxide have yielded conflicting results. We hypothesized that the inspired oxygen fraction may play an important role in determining the outcome of nitric oxide therapy.

METHODS

Rat lungs were reperfused in a circuit incorporating a support animal either immediately after flushing (group A) or after 24-hr hypothermic storage (groups B-D). During the first 10 min of reperfusion, grafts were ventilated with 95% oxygen in groups A and B, 95% oxygen and 20 ppm nitric oxide in group C, and 20% oxygen and 20 ppm nitric oxide in group D. Ventilation during the subsequent 50 min of reperfusion was with 100% oxygen only, in all groups.

RESULTS

Graft function in group B was poor compared to group A in terms of blood flow and pulmonary artery and peak airway pressures. In group C, although 5 out of 10 grafts functioned at control levels, the remainder performed poorly. Function in group D, on the other hand, was uniformly good.

CONCLUSIONS

Inhaled nitric oxide can prevent lung reperfusion injury, but this effect may be compromised by concurrent ventilation with high oxygen concentrations.

Beneficial effects of inhaled nitric oxide in hypoxaemic patients after coronary artery bypass surgery

OBJECTIVE

Arterial oxygenation may be impaired in the early period after open-heart surgery, with an associated increase in ventilation time, morbidity and hospital stay. We tested the hypothesis that inhaled nitric oxide could be a useful therapeutic adjunct in this setting. We sought to establish clinical benefits (if any), safety and the appropriate dose range of inhaled nitric oxide therapy in hypoxaemic patients after coronary artery bypass graft surgery.

METHODS

Forty patients who satisfied our definition of post-operative impaired oxygenation were prospectively randomised. The treatment group (n = 20) received nitric oxide in addition to ventilatory support. While the control group (n = 20) was managed only by conventional ventilatory support. Cardio-respiratory parameters and clinical outcome measures were compared.

RESULTS

We determined the optimum concentration of inhaled nitric oxide as 20 ppm in the majority (60%) of patients. Treatment improved arterial oxygenation (8.4 +/- 1.4 kPa before, 11.8 +/- 1.5 kPa after 4 h, P < 0.001) and this benefit was sustained with lower oxygen fractions required at 24 h (P < 0.001). A significantly shorter period of mechanical ventilation was required in the treatment group (mean ventilation hours 67.0 +/- 5.9 vs. 85.0 +/- 6.5, P < 0.05), although the study did not have the power to distinguish differences in ITU or overall hospital stay. Nitrous oxide and met-haemoglobin levels did not rise appreciably.

CONCLUSION

We have established the safety and efficacy of inhaled nitric oxide, at a dose of between 10 and 30 ppm, in this group of patients. We suggest that nitric oxide and a delivery system are useful adjuvants in a cardiac surgical intensive care unit.

Low-dose nitric oxide inhalation during initial reperfusion enhances rat lung graft function

BACKGROUND

In ischemia-reperfusion injury, the production of nitric oxide by dysfunctional endothelium falls rapidly within minutes of the onset of reperfusion. Replenishment during this critical early period using inhaled nitric oxide may benefit lung grafts through modulation of vascular tone, endothelial permeability, neutrophil and platelet function, and availability of reactive oxygen species.

METHODS

Rat lung grafts were flushed with 60 mL/kg cold University of Wisconsin solution and were reperfused either immediately (group I, n = 5) or after 24-hour 4 degrees C storage (groups II and III, n = 5 each), for 60 minutes in an ex vivo model incorporating a support animal. Graft ventilation was with room air. In group III, 20 parts per million inhaled nitric oxide was added during the initial 10 minutes of reperfusion, whereas in groups I and II, equivalent flows of nitrogen were added to standardize oxygen concentration.

RESULTS

Compared with group I, graft function in group II was poor, with reductions in oxygenation and blood flow and elevations of mean pulmonary artery pressure, peak airway pressure, and wet to dry weight ratio. In contrast, during nitric oxide inhalation in group III, graft function improved to control levels. This improvement was subsequently sustained throughout the reperfusion period.

CONCLUSIONS

Low-dose inhaled nitric oxide administration in the early phase of reperfusion of stored lung grafts can yield sustained improvement in function. There may be a role for inhaled nitric oxide in the prevention of reperfusion injury in transplanted lungs.