Oxygen-dependent reperfusion injury in the isolated rat lung

Pulmonary reperfusion injury in post-palliative intervention of oligaemic cyanotic CHD: a new catastrophic consequence or just revisiting the same old story?

Pulmonary reperfusion injury is a well-recognised clinical entity in the setting pulmonary artery angioplasty for pulmonary artery stenosis or chronic thromboembolic disease, but not much is known about this complication in post-palliative intervention of oligaemic cyanotic CHD. The pathophysiology of pulmonary reperfusion injury in this population consists of both ischaemic and reperfusion injury, mainly resulting in oxidative stress from reactive oxygen species generation, followed by endothelial dysfunction, and cytokine storm that may induce multiple organ dysfunction. Other mechanisms of pulmonary reperfusion injury are "no-reflow" phenomenon, overcirculation from high pressure in pulmonary artery, and increased left ventricular end-diastolic pressure. Chronic hypoxia in cyanotic CHD eventually depletes endogenous antioxidant and increased the risk of pulmonary reperfusion injury, thus becoming a concern for palliative interventions in the oligaemic subgroup. The incidence of pulmonary reperfusion injury varies depending on multifactors. Despite its inconsistence occurrence, pulmonary reperfusion injury does occur and may lead to morbidity and mortality in this population. The current management of pulmonary reperfusion injury is supportive therapy to prevent deterioration of lung injury. Therefore, a general consensus on pulmonary reperfusion injury is necessary for the diagnosis and management of this complication as well as further studies to establish the use of novel and potential therapies for pulmonary reperfusion injury.

Pilot Trial of Extended Hypothermic Lung Preservation to Analyze Ischemia-reperfusion Injury in Pigs

BACKGROUND

In lung transplantation (LT), the length of ischemia time is controversial as it was arbitrarily stablished. We ought to explore the impact of extended cold-ischemia time (CIT) on ischemia-reperfusion injury in an experimental model.

METHODS

Experimental, randomized pilot trial of parallel groups and final blind analysis using a swine model of LT. Donor animals (n=8) were submitted to organ procurement. Lungs were subjected to 6h (n=4) or 12h (n=4) aerobic hypothermic preservation. The left lung was transplanted and re-perfused for 4h. Lung biopsies were obtained at (i) the beginning of CIT, (ii) the end of CIT, (iii) 30min after reperfusion, and (iv) 4h after reperfusion. Lung-grafts were histologically assessed by microscopic lung injury score and wet-to-dry ratio. Inflammatory response was measured by determination of inflammatory cytokines. Caspase-3 activity was determined as apoptosis marker.

RESULTS

We observed no differences on lung injury score or wet-to-dry ratio any given time between lungs subjected to 6h-CIT or 12h-CIT. IL-1β and IL6 showed an upward trend during reperfusion in both groups. TNF-α was peaked within 30min of reperfusion. IFN-γ was hardly detected. Caspase-3 immunoexpression was graded semiquantitatively by the percentage of stained cells. Twenty percent of apoptotic cells were observed 30min after reperfusion.

CONCLUSIONS

We observed that 6 and 12h of CIT were equivalent in terms of microscopic lung injury, inflammatory profile and apoptosis in a LT swine model. The extent of lung injury measured by microscopic lung injury score, proinflammatory cytokines and caspase-3 determination was mild.

Pilot Trial of Extended Hypothermic Lung Preservation to Analyze Ischemia-reperfusion Injury in Pigs

BACKGROUND

In lung transplantation (LT), the length of ischemia time is controversial as it was arbitrarily stablished. We ought to explore the impact of extended cold-ischemia time (CIT) on ischemia-reperfusion injury in an experimental model.

METHODS

Experimental, randomized pilot trial of parallel groups and final blind analysis using a swine model of LT. Donor animals (n=8) were submitted to organ procurement. Lungs were subjected to 6h (n=4) or 12h (n=4) aerobic hypothermic preservation. The left lung was transplanted and re-perfused for 4h. Lung biopsies were obtained at (i) the beginning of CIT, (ii) the end of CIT, (iii) 30min after reperfusion, and (iv) 4h after reperfusion. Lung-grafts were histologically assessed by microscopic lung injury score and wet-to-dry ratio. Inflammatory response was measured by determination of inflammatory cytokines. Caspase-3 activity was determined as apoptosis marker.

RESULTS

We observed no differences on lung injury score or wet-to-dry ratio any given time between lungs subjected to 6h-CIT or 12h-CIT. IL-1β and IL6 showed an upward trend during reperfusion in both groups. TNF-α was peaked within 30min of reperfusion. IFN-γ was hardly detected. Caspase-3 immunoexpression was graded semiquantitatively by the percentage of stained cells. Twenty percent of apoptotic cells were observed 30min after reperfusion.

CONCLUSIONS

We observed that 6 and 12h of CIT were equivalent in terms of microscopic lung injury, inflammatory profile and apoptosis in a LT swine model. The extent of lung injury measured by microscopic lung injury score, proinflammatory cytokines and caspase-3 determination was mild.

Review 1: Lung transplant-from donor selection to graft preparation

For various end-stage lung diseases, lung transplantation remains one of the only viable treatment options. While the demand for lung transplantation has steadily risen over the last few decades, the availability of donor grafts is limited, which have resulted in progressively longer waiting lists. In the early years of lung transplantation, only the 'ideal' donor grafts are considered for transplantation. Due to the donor shortages, there is ongoing discussion about the safe use of 'suboptimal' grafts to expand the donor pool. In this review, we will discuss the considerations around donor selection, donor-recipient matching, graft preparation and graft optimisation.

Induction of homeostatic biological parameters in reward deficiency as a function of an iron-free multi-nutrient complex: Promoting hemoglobinization, aerobic metabolism, viral immuno-competence, and neuroinflammatory regulation

BACKGROUND

A common neurological condition worldwide is Reward Deficiency Syndrome (RDS) leading to both substance and non-substance addictive behaviors, that must be combatted by integrating both central nervous system and peripheral nervous system biological approaches. Integrity of hemoglobin is a crucial determining factor for the overall health functions. Nutrient repletion therapy should be a fundamental strategy to restore the healthy properties of blood. A unique patent-pending iron-free VMP35 formulation was engineered by our laboratory to restore iron-dependent hemoglobin in anemic cells using a proprietary Prodosome® absorption technology. This formulation, containing an array of nano-emulsified botanical ingredients rich in bioflavonoids, strengthens the structural integrity of connective tissues, and potentiates immune competence, cellular aerobic metabolism, and enhances efficient regulation of inflammatory events. We discuss the intricate aspects of strong vs. fragile immunity and consequential inflammatory responses to convey a deeper understanding of the varied and overly complex sequela of immunological behaviors and events. The effect of the VMP35 is mediated through highly absorbable nutritional/nutrigenomic repletion enabling improvements in the systemic set of functional behaviors. In fact, the iron-free VMP35 facilitates a "Systems Biology Approach" which restores hemoglobin status, reverses anaerobic hypoxia, improves competent immune responsivity, and regulates appropriate and controlled activation of general and neuro-inflammatory sequela. Under these pathogenic circumstances, iron-deficiency anemia has been misconceptualized, and a new nosological term, Chronic Anemia Syndrome, is proposed. The comparative therapeutic rationale of Reductionist vs. Systems Biology approaches is also explained in detail.

METHODS

The efficacy of the novel therapeutic iron-free VMP35 liquid nutraceutical is detailed in restoring iron-dependent hemoglobin to RBCs and boosting cellular morphology, viability, and immune competence, thereby reducing the need for prolonging inflammatory sequela.

RESULTS

This was demonstrated in a previous IRB approved multi-subject human study. In addition, two recent case studies report dramatic restorative benefits of nutrient repletion therapy of the VMP35 on subjects having experienced near-fatal events, which confirmed the findings explained in this manuscript.

CONCLUSIONS

This novel iron-free VMP35 modulates an array of homeostatic biological parameters such as enhanced hemoglobinization, aerobic metabolism, viral immuno-competence, and inflammatory regulation. Further research, examining mechanistic and beneficial effects in athletic performance, is in progress. Importantly, during these troubled immune challenging times, modulating an array of homeostatic immunological and inflammatory dysfunctions are tantamount to improved population outcomes.

TRIAL REGISTRATION

The Clinical investigation in a total of 38 subjects was conducted under an Institutional Review Board (IRB) from the Path Foundation in New York, NY (#13-009 April 25, 2013). The two case studies were done at Lancaster General Hospital, Lancaster, PA, and Jefferson University Hospital, Philadelphia, PA, USA. Both studies were retrospectively registered.

Proteome Investigation of Rat Lungs subjected to Ex Vivo Perfusion (EVLP)

Ex vivo lung perfusion (EVLP) is an emerging procedure that allows organ preservation, assessment and reconditioning, increasing the number of marginal donor lungs for transplantation. However, physiological and airflow measurements are unable to unveil the molecular mechanisms responsible of EVLP beneficial effects on lung graft and monitor the proper course of the treatment. Thus, it is urgent to find specific biomarkers that possess these requirements but also accurate and reliable techniques that identify them. The purpose of this study is to give an overview on the potentiality of shotgun proteomic platforms in characterizing the status and the evolution of metabolic pathways during EVLP in order to find new potential EVLP-related biomarkers. A nanoLC-MS/MS system was applied to the proteome analysis of lung tissues from an optimized rat model in three experimental groups: native, pre- and post-EVLP. Technical and biological repeatability were evaluated and, together with clustering analysis, underlined the good quality of data produced. In-house software and bioinformatics tools allowed the label-free extraction of differentially expressed proteins among the three examined conditions and the network visualization of the pathways mainly involved. These promising findings encourage further proteomic investigations of the molecular mechanisms behind EVLP procedure.

Investigation of the preventive effect of proanthocyanidin in ischemia-reperfusion injury in lung transplantation: An experimental study

Background

This study aims to investigate the preventive effect of proanthocyanidin against ischemia-reperfusion injury after lung transplantation.

Methods

The study included 12 swines (weighing 35±5 kg) and separated into four groups. Groups 1 and 3 were identified as control groups and left upper lobectomy was performed. Groups 2 and 4 were identified as transplantation groups and left lower lobectomy and heterotransplantation were performed. Proanthocyanidin was only given to groups 3 and 4. Tissue samples were analyzed under light microscope and histopathological findings were recorded.

Results

There was no statistically significant difference between control groups in terms of the numerical values of histopathological findings that include congestion (p=0.565), alveolar edema (p=0.197) and peribronchial inflammation (p=0.444). However, numerical values of acute cellular rejection were statistically significantly different between transplantation groups (p=0.048). Mean oxidative stress enzyme levels were higher in group 2 compared to group 4; however, the difference was not statistically significant (p>0.05).

Conclusion

According to the findings of our experimental study, proanthocyanidin can be safely used in lung transplantation based on its preventive effect in ischemia-reperfusion injury that may lead to morbidity and mortality.

A Mechanistic Study on the Amiodarone-Induced Pulmonary Toxicity

Amiodarone- (AM-) induced pulmonary toxicity (AIPT) is still a matter of research and is poorly understood. In attempting to resolve this issue, we treated Sprague-Dawley rats with AM doses of 80 mg/kg/day/i.p. for one, two, three, and four weeks. The rats were weighed at days 7, 14, 21, and 28 and bronchoalveolar lavages (BAL) were obtained to determine total leukocyte count (TLC). For each group, lung weighing, histopathology, and homogenization were performed. Fresh homogenates were used for determination of ATP content, lipid peroxides, GSH, catalase, SOD, GPx, GR activities, NO, and hydroxyproline levels. The results showed a significant decrease in body weight and GSH depletion together with an increase in both lung weight and lung/body weight coefficient in the first week. Considerable increases in lung hydroxyproline level with some histopathological alterations were apparent. Treatment for two weeks produced a significant increase in BAL fluid, TLC, GR activity, and NO level in lung homogenate. The loss of cellular ATP and inhibition of most antioxidative protective enzymatic system appeared along with alteration in SOD activity following daily treatment for three weeks, while, in rats treated with AM for four weeks, more severe toxicity was apparent. Histopathological diagnosis was mostly granulomatous inflammation and interstitial pneumonitis in rats treated for three and four weeks, respectively. As shown, it is obvious that slow oedema formation is the only initiating factor of AIPT; all other mechanisms may occur as a consequence.

Oxidative Stress and Lung Ischemia-Reperfusion Injury

Ischemia-reperfusion (IR) injury is directly related to the formation of reactive oxygen species (ROS), endothelial cell injury, increased vascular permeability, and the activation of neutrophils and platelets, cytokines, and the complement system. Several studies have confirmed the destructiveness of the toxic oxygen metabolites produced and their role in the pathophysiology of different processes, such as oxygen poisoning, inflammation, and ischemic injury. Due to the different degrees of tissue damage resulting from the process of ischemia and subsequent reperfusion, several studies in animal models have focused on the prevention of IR injury and methods of lung protection. Lung IR injury has clinical relevance in the setting of lung transplantation and cardiopulmonary bypass, for which the consequences of IR injury may be devastating in critically ill patients.

Shear stress-related mechanosignaling with lung ischemia: lessons from basic research can inform lung transplantation

Cessation of blood flow represents a physical event that is sensed by the pulmonary endothelium leading to a signaling cascade that has been termed "mechanotransduction." This paradigm has clinical relevance for conditions such as pulmonary embolism, lung bypass surgery, and organ procurement and storage during lung transplantation. On the basis of our findings with stop of flow, we postulate that normal blood flow is "sensed" by the endothelium by virtue of its location at the interface of the blood and vessel wall and that this signal is necessary to maintain the endothelial cell membrane potential. Stop of flow is sensed by a "mechanosome" consisting of PECAM-VEGF receptor-VE cadherin that is located in the endothelial cell caveolae. Activation of the mechanosome results in endothelial cell membrane depolarization that in turn leads to activation of NADPH oxidase (NOX2) to generate reactive oxygen species (ROS). Endothelial depolarization additionally results in opening of T-type voltage-gated Ca(2+) channels, increased intracellular Ca(2+), and activation of nitric oxide (NO) synthase with resultant generation of NO. Increased NO causes vasodilatation whereas ROS provide a signal for neovascularization; however, with lung transplantation overproduction of ROS and NO can cause oxidative injury and/or activation of proteins that drive inflammation and cell death. Understanding the key events in the mechanosignaling cascade has important lessons for the design of strategies or interventions that may reduce injury during storage of donor lungs with the goal to increase the availability of lungs suitable for donation and thus improving access to lung transplantation.

The serpentine path to a novel mechanism-based inhibitor of acute inflammatory lung injury

The Comroe lecture on which this review is based described my research path during the past 45 years, beginning with studies of oxidant stress (hyperoxia) and eventuating in the discovery of a synthetic inhibitor of phospholipase A2 activity (called MJ33) that prevents acute lung injury in mice exposed to lipopolysaccharide. In between were studies of lung ischemia, lung surfactant metabolism, the protein peroxiredoxin 6 and its phospholipase A2 activity, and mechanisms for NADPH oxidase activation. These seemingly unrelated research activities provided the nexus for identification of a novel target and a potentially novel therapeutic agent for prevention or treatment of acute lung injury.

A novel nontoxic inhibitor of the activation of NADPH oxidase reduces reactive oxygen species production in mouse lung

1-Hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol (MJ33) is a fluorinated phospholipid analog that inhibits the phospholipase A2 (PLA2) activity of peroxiredoxin 6 (Prdx6). Prdx6 PLA2 activity is required for activation of NADPH oxidase 2 and subsequent generation of reactive oxygen species (ROS). In vitro, MJ33 inhibited agonist-stimulated production of ROS by the isolated perfused mouse lung, lung microvascular endothelial cells, and polymorphonuclear leukocytes. MJ33 (0.02-0.5 µmol MJ33/kg body weight) in mixed unilamellar liposomes was administered to C57BL/6 mice by either intratracheal (i.t.) or i.v. routes. Lung MJ33 content, measured by liquid chromatography/mass spectroscopy, showed uptake of 67-87% of the injected dose for i.t. and 23-42% for i.v. administration at 4 hours postinjection. PLA2 activity of lung homogenates was markedly inhibited (>85%) at 4 hours postadministration. Both MJ33 content and PLA2 activity gradually returned to near control levels over the subsequent 24-72 hours. Mice treated with MJ33 at 12.5-25 µmol/kg did not show changes (compared with control) in clinical symptomatology, body weight, hematocrit, and histology of lung, liver, and kidney during a 30- to 50-day observation period. Thus, the toxic dose of MJ33 was >25 µmol/kg, whereas the PLA2 inhibitory dose was approximately 0.02 µmol/kg, indicating a high margin of safety. MJ33 administered to mice prior to lung isolation markedly reduced ROS production and tissue lipid and protein oxidation during ischemia followed by reperfusion. Thus, MJ33 could be useful as a therapeutic agent to prevent ROS-mediated tissue injury associated with lung inflammation or in harvested lungs prior to transplantation.

Tissue damage and oxidant/antioxidant balance

The oxidant/antioxidant balance in healthy tissues is maintained with a predominance of antioxidants. Various factors that can lead to tissue damage disrupt the oxidant/antioxidant balance in favor of oxidants. In this study, disruptions of the oxidant/antioxidant balance in favor of oxidants were found to be a consequence of the over-consumption of antioxidants. For this reason, antioxidants are considered to be of importance in the prevention and treatment of various types of tissue damage that are aggravated by stress.

Amelioration of Ischemia–Reperfusion Injury in an Isolated Rabbit Lung Model Using OXANOH

Objective: Acute respiratory distress syndrome (ARDS) remains a major cause of morbidity and mortality. Oxygen-free radicals (OFRs) produced during ischemia and reperfusion (IR) have been implicated as the final common pathway in the pathogenesis of this syndrome. Spin traps have been shown to decrease IR injury in several animal lung models. The hydroxylamine, OXANOH (2-ethyl-2,5,5-trimethyl-3-oxazolidine) has been proposed as an ideal spin trap that would trap extra- and intracellular OFRs producing the stable radical, OXANO• (2-ethyl-2,5,5-trimethyl-3-oxazolidinoxyl). Electron microscopy was used to investigate whether OXANOH would protect against IR injury in the rabbit lung. Methods: OXANOH was obtained by hydrogenation of its stable radical, OXANO• using a safe laboratory technique. Several doses of OXANOH were tested to identify a nontoxic dose. Two quantitative methods were used based on the average surface area of the alveoli and average number of alveoli per unit surface area using scanning electron microscopy (SEM). A total of 20 animals were subjected to 2 hours of ischemia followed by 4 hours of reperfusion. On reperfusion, the 4 groups (N = 5) received no treatment, OXANOH, superoxide dismutase (SOD)/catalase, or oxypurinol. Results: A therapeutic dose of 250 μmol/L of OXANO• was suggested in this in vitro model. All the 3 treatments showed significantly less injury compared to the control group and that SOD/catalase was significantly different from OXANOH and oxypurinol ( P < .008). Conclusion: OXANOH ameliorated IR injury in the isolated rabbit lung, almost as effectively as SOD/catalase and oxypurinol.

Hypoxemic resuscitation from hemorrhagic shock prevents lung injury and attenuates oxidative response and IL-8 overexpression

We investigated whether hypoxemic resuscitation from hemorrhagic shock prevents lung injury and explored the mechanisms involved. We subjected rabbits to hemorrhagic shock for 60 min by exsanguination to a mean arterial pressure of 40 mm Hg. By modifying the fraction of the inspired oxygen, we performed resuscitation under normoxemia (group NormoxRes, P(a)O(2)=95-105 mm Hg) or hypoxemia (group HypoxRes, P(a)O(2)=35-40 mm Hg). Animals not subjected to shock constituted the sham group (P(a)O(2)=95-105 mm Hg). We performed bronchoalveolar lavage (BAL) fluid, lung wet-to-dry weight ratio, and morphological studies. U937 monocyte-like cells were incubated with BAL fluid from each group. Cell peroxides, malondialdehyde, proteins, and cytokines in the BAL fluid were lower in sham than in shocked animals and in HypoxRes than in NormoxRes animals. The inverse was true for ascorbic acid and reduced glutathione. Lung edema, lung neutrophil infiltration, myeloperoxidase, and interleukin (IL)-8 gene expression were reduced in lungs of HypoxRes compared with NormoxRes animals. A colocalized higher expression of IL-8 and nitrotyrosine was found in lungs of NormoxRes animals compared to HypoxRes animals. The BAL fluid of NormoxRes animals compared with HypoxRes animals exerted a greater stimulation of U937 monocyte-like cells for proinflammatory cytokine release, particularly for IL-8. In the presence of p38-MAPK and Syk inhibitors and monosodium urate crystals, IL-8 release was reduced. We conclude that hypoxemic resuscitation from hemorrhagic shock ameliorates lung injury and reduces oxygen radical generation and lung IL-8 expression.

Ischemic preconditioning by selective occlusion of the pulmonary artery in rats

OBJECTIVE

To evaluate the effect of lung ischemic preconditioning (IPC) on normothermic ischemia/reperfusion (I/R) injury in a rat model, quantifying the production of reactive oxygen species.

METHODS

Forty-seven male Wistar rats were randomized into four groups: control, sham, I/R and IPC. Control group animals were anesthetized and killed by decapitation, after which pneumonectomy was performed and the left lungs were stored in liquid nitrogen. Sham, IPC and I/R group rats were anesthetized, tracheostomized, ventilated, anticoagulated and submitted to left thoracotomy with dissection of the left pulmonary artery for clamping. Sham group rats underwent dissection of the left pulmonary artery, I/R group rats underwent 30 min of total hilar clamping, and IPC group rats underwent 5-min clamping of the left pulmonary artery followed by 30 min of total hilar clamping. Lungs were reperfused for 90 min and ventilated with the same parameters, with additional positive end-expiratory pressure of 1 cmH2O. Hemodynamic and blood gas values were obtained prior to thoracotomy, prior to total hilar clamping, after 30 min of reperfusion and after 90 min of reperfusion. Lipid peroxidation was determined by measuring levels of thiobarbituric acid reactive substances.

RESULTS

There were no significant differences among the groups in terms of the levels of thiobarbituric acid reactive substances. Nor were there any significant differences among the sham, I/R and IPC groups in terms of arterial oxygen tension, arterial carbon dioxide tension or hemodynamic values.

CONCLUSIONS

In an in situ I/R rat model, 5-min IPC of the left pulmonary artery does not attenuate I/R injury.

Long-acting oral phosphodiesterase inhibition preconditions against reperfusion injury in an experimental lung transplantation model

OBJECTIVES

Ischemia-reperfusion injury remains a devastating complication of lung transplantation. Phosphodiesterase inhibitors have been shown to precondition tissues against ischemia-reperfusion injury. Little is known, however, about the utility of phosphodiesterase inhibition in reperfusion injury after lung transplantation. We evaluated the long-acting phosphodiesterase-5 inhibitor, tadalafil, in an ex vivo lung transplant model.

METHODS

New Zealand White rabbits (4 kg), were given oral tadalafil (n = 11) 24 hours before lung harvest and compared with rabbits given oral vehicle alone (n = 11). Lungs were recovered with Perfadex solution (Vitrolife, Kungsbacka, Sweden) and cold stored for 18 hours. After storage, lung blocks were reperfused with donor rabbit blood in an ex vivo apparatus. Pulmonary artery pressures were recorded with serial arterial and venous blood gas sampling and animals served as their own controls. Phosphodiesterase-5 and protein kinase G tissue activity assays confirmed drug effects. Luminol chemiluminescence assay was used to measure reactive oxygen species and levels of endothelial and inducible nitric oxide synthase were measured.

RESULTS

Extended cold storage, followed by reperfusion produced a consistent reproducible decrease in oxygenation and increase in pulmonary pressure. Tadalafil-treated animals exhibited greater Pao(2) throughout the course of reperfusion (P = .001) Mean pulmonary artery pressure was lower in tadalafil-treated animals (22 vs 40 mm Hg; P = .04). Phosphodiesterase-5 activity was decreased (143 +/- 8 vs 205 +/- 32 mP; P < .001) with protein kinase G activity increased (25 +/- 12 vs 12 +/- 2.4 fU/microg; P = .01) in the experimental group confirming that oral pretreatment resulted in active phosphodiesterase inhibition in the lung tissue. Reactive oxygen species (as measured by luminol activity) were decreased in tadalafil-treated animals (7.8 +/- 1.5 vs 10.2 +/- 1.2 relative light units; P = .003).

CONCLUSIONS

Our experimental model demonstrates that oral donor pretreatment with a long-acting phosphodiesterase inhibitor is an effective strategy for improving pulmonary performance after reperfusion. Importantly, phosphodiesterase enzymes and their downstream effectors may play a critical role in reperfusion injury after lung transplantation.

Ischemia-reperfusion injury in the lung: quantitation using electron microscopy

BACKGROUND

The primary objectives of this study were to determine the time course of ischemia-reperfusion injury in an isolated rabbit lung model and to quantify this damage using electron microscopic methodology coupled with statistical analyses.

MATERIALS AND METHODS

Eight groups of isolated rabbit lungs (n = 5 per group) were subjected to predetermined periods of ischemia-reperfusion. Two hours of ischemia and 4 hours of reperfusion were concluded to be necessary to induce optimal ischemia-reperfusion injury in this model. Four other groups were subjected to 2 hours of ischemia followed by selected periods of reperfusion. These groups were compared to 4 control groups that were perfused for comparable time periods but without the initial ischemia. New quantitative methods were developed based on the average surface area of the alveoli and average number of alveoli per unit surface area, using scanning electron microscopic examination.

RESULTS

Ischemia per se caused substantial damage. Restoration of volume and nutrients reversed this damage at 1 hour of reperfusion, but severe damage was evident at 4 hours of reperfusion, as reported by subjective and blinded examination. By using the new quantitative methods, there was a significant difference between the groups (P < .005) according to the time of post-ischemia-reperfusion, which correlated with the subjective evaluation of damage.

CONCLUSIONS

These 2 new quantitative techniques provide an objective assessment of damage in the isolated rabbit lung model, suggesting that they warrant further consideration in similar studies of ischemia reperfusion injury.

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.

Preconditioning effects of peroxynitrite in the rat lung

Ischaemic preconditioning of the lung leads to a protective effect against ischaemia-reperfusion injury, but the underlying mechanisms of this protection are not well documented in the lung. The aim of this study was to investigate the role of endogenous and exogenous peroxynitrite (ONOO(-)) in preconditioning of isolated rat lungs. Lungs, obtained from male rats, were mounted on a perfusion apparatus, perfused by Krebs-Henseleit solution at the rate of 0.03mlg(-1)min(-1) and inflated with room air. Pulmonary perfusion pressure was measured by a pressure transducer and recorded continuously on a computer by using data acquisition system. Lungs were preconditioned for 5min by either ischaemia or ONOO(-) administration at 10microM, which were followed by 5min reperfusion and 2h of ischaemia and 10min reperfusion. Two hours of ischaemia without preconditioning depressed potassium chloride (KCl)-and phenylephrine hydrochloride (PE)-induced responses. Pretreatment of the lungs with ONOO(-) scavenger, uric acid (1mM), or poly ADP-ribose synthase inhibitors, 3-aminobenzamid (3-AB, 1mM) or nicotinamide (1mM), reversed the effects ischaemia and ONOO(-)-induced preconditioning and decreased KCl- and PE-induced increases in perfusion pressures. Wet/dry weight ratio was markedly reduced in ischaemia and ONOO(-)-induced preconditioning groups indicating that preconditioning prevents lung oedema. Lung malondialdehyde (MDA) levels were significantly depressed in ischaemic and ONOO(-) preconditioning groups. These results suggest that ONOO(-) is able to precondition the isolated rat lung and plays a significant role in the protective effects of preconditioning.

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.

Low-dose carbon monoxide inhalation prevents ischemia/reperfusion injury of transplanted rat lung grafts

BACKGROUND

Carbon monoxide (CO), a byproduct of heme catalysis by heme oxygenases, has been shown to provide protection against ischemia/reperfusion (I/R) injury. We examined the cytoprotective effect of CO at a low concentration on cold I/R injury of transplanted lung grafts.

METHODS

Orthotopic left lung transplantation was performed in syngenic Lewis to Lewis rat combination. Grafts were preserved in University of Wisconsin solution at 4 degrees C for 6 hours. Donors and/or recipients were exposed to CO (250 ppm) in air for 1 hour before surgery and then continuously post-transplantation.

RESULTS

Blood oxygen partial pressure of graft pulmonary veins in the CO-treated group versus the air-treated group was significantly higher. The increase of messenger RNA of inflammatory mediators such as interleukin-6, tumor necrosis factor-alpha, inducible nitric oxide synthase, and cycloooxygenase-2 was markedly inhibited in the CO-treated group. The expression of phosphorylated-extracellular signal-regulated protein kinase 1/2 was significantly reduced in the CO-treated group. CO treatment reduced the number of infiltrating macrophages into the lung grafts. Vascular endothelial cells detected by CD31 stain were well preserved in CO-treated grafts, while those in air-treated grafts were faint and interrupted.

CONCLUSIONS

These results demonstrate that exogenous low-dose CO treatment of donors and recipients can prevent lung I/R injury and significantly improve function of lung grafts after extended cold preservation and transplantation.

Influence of Inflated Lung Pressure on Lung Mechanical Properties during Cold Storage in Rats

The degree of lung inflation pressure during cold storage has a deep connection with lung functions after reperfusion. However, the change of the lung mechanical properties during cold storage at the different lung inflation pressure is unknown. We investigated the change of the mechanical properties both at the organ and the tissue level under different inflated lung pressure soon after the cold storage. In group I, the lungs were not preserved. In group II, the lungs were preserved in deflated condition. In groups III and IV, the lungs were inflated with room air at pressures of 14 and 25 cm H2O. After 24-hour storage, the input impedance (Z) was measured by a computer-controlled small animal ventilator (n = 8 each group). All data were analyzed using a homogeneous linear model, which includes airway resistance (R(aw)), tissue elastance (H), and tissue damping (G). Hysteresivity (eta) was calculated as G/H. After Z measurement, the tissue elasticity (Eqs) obtained from the quasi-static stress-strain curve was compared. We also analyzed the biochemical changes of surfactant in bronchoalveolar lavage (BAL) fluid. R(aw )was significantly lower in groups III and IV than in group I (p < 0.01). Hysteresivity (eta) was significantly lower in group IV than in groups I and III (p < 0.05). Eqs was significantly higher in groups III and IV than in groups I and II (p < 0.01). The total protein level in the BAL fluid of the preserved groups was significantly higher compared with group I (p < 0.01). We conclude that hyperinflated storage would deteriorate lung tissue mechanical properties.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

Dose-related effects of theophylline added to modified euro-collins solution used for hypothermic preservation of lung

OBJECTIVE

To investigate the dose-related effects of theophylline in prevention of ischemia-reperfusion injury of the lung.

DESIGN

Experimental study.

SETTINGS

University hospital.

PARTICIPANTS

Thirty Wistar rats.

INTERVENTIONS

In experimental group 1 (G-I) (n = 5) 20 mg/L, in G-II (n = 5) 100 mg/L, in G-III (n = 5) 400 mg/L, and in G-IV (n = 5) 1000 mg/L of theophylline was added to modified Euro-Collins solution and perfused the lungs. Lungs were extracted without an ischemic period in control group 1 (C-I) and perfused with modified Euro-Collins solution in control group 2 (C-II). Lungs were kept in a hypothermic state for 6 hours and then ventilated for 30 minutes with 100% O(2).

MEASUREMENTS AND MAIN RESULTS

Tissue levels of dien congugate (DC) and malonylaldehyde (MDA) were measured. Comparison of 6 groups revealed statistically significant differences for DC and MDA (p < 0.0001 for both comparisons). Both DC and MDA levels of C-II were found to be higher than G-III and G-IV (p = 0.008). DC and MDA levels of G-III and G-IV were significantly lower than G-I and G-II (p = 0.008 for all comparisons).

CONCLUSION

The results of this study showed that 400 mg/L and 1000 mg/L of theophylline added to the modified Euro-Collins solution decreased the intermediate products of lipid peroxidation. Theophylline merits further investigation in ischemia-reperfusion studies as a potentially beneficial agent.

PECAM-directed delivery of catalase to endothelium protects against pulmonary vascular oxidative stress

Targeted delivery of drugs to vascular endothelium promises more effective and specific therapies in many disease conditions, including acute lung injury (ALI). This study evaluates the therapeutic effect of drug targeting to PECAM (platelet/endothelial cell adhesion molecule-1) in vivo in the context of pulmonary oxidative stress. Endothelial injury by reactive oxygen species (e.g., H2O2) is involved in many disease conditions, including ALI/acute respiratory distress syndrome and ischemia-reperfusion. To optimize delivery of antioxidant therapeutics, we conjugated catalase with PECAM antibodies and tested properties of anti-PECAM/catalase conjugates in cell culture and mice. Anti-PECAM/catalase, but not an IgG/catalase counterpart, bound specifically to PECAM-expressing cells, augmented their H2O2-degrading capacity, and protected them against H2O2 toxicity. Anti-PECAM/catalase, but not IgG/catalase, rapidly accumulated in the lungs after intravenous injection in mice, where it was confined to the pulmonary endothelium. To test its protective effect, we employed a murine model of oxidative lung injury induced by glucose oxidase coupled with thrombomodulin antibody (anti-TM/GOX). After intravenous injection in mice, anti-TM/GOX binds to pulmonary endothelium and produces H2O2, which causes lung injury and 100% lethality within 7 h. Coinjection of anti-PECAM/catalase protected against anti-TM/GOX-induced pulmonary oxidative stress, injury, and lethality, whereas polyethylene glycol catalase or IgG/catalase conjugates afforded only marginal protective effects. This result validates vascular immunotargeting as a prospective strategy for therapeutic interventions aimed at immediate protective effects, e.g., for augmentation of antioxidant defense in the pulmonary endothelium and treatment of ALI.

Immunotargeting of catalase to the pulmonary endothelium alleviates oxidative stress and reduces acute lung transplantation injury

Vascular immunotargeting may facilitate the rapid and specific delivery of therapeutic agents to endothelial cells. We investigated whether targeting of an antioxidant enzyme, catalase, to the pulmonary endothelium alleviates oxidative stress in an in vivo model of lung transplantation. Intravenously injected enzymes, conjugated with an antibody to platelet-endothelial cell adhesion molecule-1, accumulate in the pulmonary vasculature and retain their activity during prolonged cold storage and transplantation. Immunotargeting of catalase to donor rats augments the antioxidant capacity of the pulmonary endothelium, reduces oxidative stress, ameliorates ischemia-reperfusion injury, prolongs the acceptable cold ischemia period of lung grafts, and improves the function of transplanted lung grafts. These findings validate the therapeutic potential of vascular immunotargeting as a drug delivery strategy to reduce endothelial injury. Potential applications of this strategy include improving the outcome of clinical lung transplantation and treating a wide variety of endothelial disorders.

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.

Optimal alveolar oxygen concentration for cold storage of the lung

BACKGROUND

Ischemia of the lung is different from that of solid organs because the lung contains gas in the alveoli. However, the optimal gas composition in the alveoli during cold storage remains uncertain. We investigated the relationship between the alveolar oxygen concentration and reperfusion injury.

METHODS

The lungs inflated with 0% O2, 5% O2, room air, 50% O2, or 100% O2 were reperfused after 8 hR storage at 4 degrees C and pulmonary functions were measured for 120 min using an ex vivo rat lung model. The levels of high-energy phosphate and lipid peroxidation of the lung were analyzed after a PA flush, preservation, and reperfusion. Additionally, respiration of the mitochondria in the lungs was measured after preservation.

RESULTS

The pulmonary functions were significantly superior in the 5% O2 group than those in the 0% O2, 50% O2, and 100% O2 groups. Pulmonary edema developed in the 0% O2, 50% O2, and 100% O2 groups, but not in the 5% O2 group. After preservation, the energy level in the lungs decreased only in the 0% O2 group. Although lipid peroxidation of the lungs did not increase in any group after preservation, significant increases were observed in the room air, 50% O2 and 100% O2 groups after reperfusion. State 3 and 4 ratios of the mitochondrial respiration significantly decreased in the lungs of the room air, 50% O2 and 100% O2 groups.

CONCLUSIONS

Although the cold-preserved lungs require oxygen, hyperoxygenation induced mitochondrial dysfunction and increased lipid peroxidation and led to deleterious lung function after reperfusion. Therefore, hypoxic conditions that can maintain the energy level of the lung during cold storage would be optimal.

Involvement of c-Src in diperoxovanadate-induced endothelial cell barrier dysfunction

Reactive oxygen species (ROS) generated by activated leukocytes play an important role in the disruption of endothelial cell (EC) integrity, leading to barrier dysfunction and pulmonary edema. Although ROS modulate cell signaling, information remains limited regarding the mechanism(s) of ROS-induced EC barrier dysfunction. We utilized diperoxovanadate (DPV) as a model agent to explore the role of tyrosine phosphorylation in the regulation of EC barrier function. DPV disrupted EC barrier function in a dose-dependent manner. Tyrosine kinase inhibitors, genistein, and PP-2, a specific inhibitor of Src, reduced the DPV-mediated barrier dysfunction. Consistent with these results, DPV-induced Src activation was attenuated by PP-2. Furthermore, DPV increased the association of Src with cortactin and myosin light chain kinase, indicating their potential role as cytoskeletal targets for Src. Transient overexpression of either wild-type Src or a constitutively active Src mutant potentiated the DPV-mediated decline in barrier dysfunction, whereas a dominant negative Src mutant attenuated the response. These studies provide the first direct evidence for Src involvement in DPV-induced EC barrier dysfunction.

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.

Role of ischemic preconditioning on ischemia-reperfusion injury of the lung

STUDY OBJECTIVES

Ischemia-reperfusion injury of the lung frequently occurs after cardiopulmonary bypass, after pulmonary thromboembolectomy, and especially during lung transplantation. The protective effects of preconditioning on the heart, liver, bones, and various other organs have been previously evaluated. In this comparative study, we used isolated guinea pig lungs to show the effects of preconditioning on lung ischemia.

METHODS

The lungs (n = 10 in each group) were mounted on a modified Langendorff perfusion apparatus and perfused by Krebs-Henseleit solution for 30 min. We applied an ischemic preconditioning (5 min ischemia + 5 min perfusion, two times) in the experimental group. After 3 h of normothermic ischemia, the lungs were reperfused for 30 min. Pulmonary artery pressures and malondialdehyde (MDA) and glutathione (GSH) levels of the tissue and the perfusate were measured before and after the ischemic period and also at the end of reperfusion. Electron microscopic evaluation was done on randomly selected lungs of three animals in each group at the end of the experiment.

RESULTS

Both MDA and GSH levels of tissue and perfusate decreased in the experimental group after reperfusion, although the reduction in GSH levels did not reach statistical significance. The increase in pulmonary artery pressure was lower in the preconditioning group after reperfusion.

CONCLUSIONS

Our data showed that ischemic preconditioning of the lung may have a protective effect in ischemic-reperfusion injury.

Effect of ventilation on vascular permeability and cyclic nucleotide concentrations in ischemic sheep lungs

Ventilation during ischemia attenuates ischemia-reperfusion lung injury, but the mechanism is unknown. Increasing tissue cyclic nucleotide levels has been shown to attenuate lung ischemia-reperfusion injury. We hypothesized that ventilation prevented increased pulmonary vascular permeability during ischemia by increasing lung cyclic nucleotide concentrations. To test this hypothesis, we measured vascular permeability and cGMP and cAMP concentrations in ischemic (75 min) sheep lungs that were ventilated (12 ml/kg tidal volume) or statically inflated with the same positive end-expiratory pressure (5 Torr). The reflection coefficient for albumin (sigmaalb) was 0.54 +/- 0.07 and 0.74 +/- 0. 02 (SE) in nonventilated and ventilated lungs, respectively (n = 5, P < 0.05). Filtration coefficients and capillary blood gas tensions were not different. The effect of ventilation was not mediated by cyclic compression of alveolar capillaries, because negative-pressure ventilation (n = 4) also was protective (sigmaalb = 0.78 +/- 0.09). The final cGMP concentration was less in nonventilated than in ventilated lungs (0.02 +/- 0.02 and 0.49 +/- 0. 18 nmol/g blood-free dry wt, respectively, n = 5, P < 0.05). cAMP concentrations were not different between groups or over time. Sodium nitroprusside increased cGMP (1.97 +/- 0.35 nmol/g blood-free dry wt) and sigmaalb (0.81 +/- 0.09) in nonventilated lungs (n = 5, P < 0.05). Isoproterenol increased cAMP in nonventilated lungs (n = 4, P < 0.05) but had no effect on sigmaalb. The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester had no effect on lung cGMP (n = 9) or sigmaalb (n = 16) in ventilated lungs but did increase pulmonary vascular resistance threefold (P < 0.05) in perfused sheep lungs (n = 3). These results suggest that ventilation during ischemia prevented an increase in pulmonary vascular protein permeability, possibly through maintenance of lung cGMP by a nitric oxide-independent mechanism.

Ischemia-reperfusion lung injury in rabbits: mechanisms of injury and protection

To study the mechanisms responsible for ischemia-reperfusion lung injury, we developed an anesthetized rabbit model in which the effects of lung deflation, lung inflation, alveolar gas composition, hypothermia, and neutrophils on reperfusion pulmonary edema could be studied. Rabbits were anesthetized and ventilated, and the left pulmonary hilum was clamped for either 2 or 4 h. Next, the left lung was reperfused and ventilated with 100% oxygen. As indexes of lung injury, we measured arterial oxygenation, extravascular lung water, and the influx of a vascular protein (131I-labeled albumin) into the extravascular space of the lungs. The principal results were that 1) all rabbits with the deflation of the lung during ischemia for 4 h died of fulminant pulmonary edema within 1 h of reperfusion; 2) inflation of the ischemic lung with either 100% oxygen, air, or 100% nitrogen prevented the reperfusion lung injury; 3) hypothermia at 6-8 degreesC also prevented the reperfusion lung injury; 4) although circulating neutrophils declined during reperfusion lung injury, there was no increase in interleukin-8 levels in the plasma or the pulmonary edema fluid, and, furthermore, neutrophil depletion did not prevent the reperfusion injury; and 5) ultrastructural studies demonstrated injury to both the lung endothelium and the alveolar epithelium after reperfusion in deflated lungs, whereas the inflated lungs had no detectable injury. In summary, ischemia-reperfusion injury to the rabbit lung can be prevented by either hypothermia or lung inflation with either air, oxygen, or nitrogen.

Tumor necrosis factor-alpha in ischemia and reperfusion injury in rat lungs

The effects of both recombinant rat tumor necrosis factor-alpha (TNF-alpha) and an anti-TNF-alpha antibody were studied in isolated buffer-perfused rat lungs subjected to either 45 min of nonventilated [ischemia-reperfusion (I/R)] or air-ventilated (V/R) ischemia followed by 90 min of reperfusion and ventilation. In the I/R group, the vascular permeability, as measured by the filtration coefficient (Kfc), increased three- and fivefold above baseline after 30 and 90 min of reperfusion, respectively (P < 0.001). Over the same time intervals, the Kfc for the V/R group increased five- and tenfold above baseline values, respectively (P < 0.001). TNF-alpha measured in the perfusates of both ischemic models significantly increased after 30 min of reperfusion. Recombinant rat TNF-alpha (50,000 U), placed into perfusate after baseline measurements, produced no measurable change in microvascular permeability in control lungs perfused over the same time period (135 min), but I/R injury was significantly enhanced in the presence of TNF-alpha. An anti-TNF-alpha antibody (10 mg/rat) injected intraperitoneally into rats 2 h before the lung was isolated prevented the microvascular damage in lungs exposed to both I/R and V/R (P < 0.001). These results indicate that TNF-alpha is an essential component at the cascade of events that cause lung endothelial injury in short-term I/R and V/R models of lung ischemia.

Controlled reperfusion prevents pulmonary injury after 24 hours of lung preservation

BACKGROUND

Posttransplantation lung reperfusion injury continues to be a major problem. We have shown that controlling the initial period of reperfusion limits this injury after 2 hours of warm lung ischemia. The effectiveness of this modality, however, is unknown after longer periods of cold ischemia, which more closely mimics the clinical situation.

METHODS

After baseline measurements, 10 pigs had the left lung flushed with a modified Euro-Collins solution, explanted, stored at 4 degrees C for 24 hours, and transplanted into 10 other pigs. Five (group 1) underwent uncontrolled reperfusion created by removal of the vascular clamps after implantation of the new left lung, mimicking the clinical situation. The other five (group 2) underwent controlled reperfusion, which we performed by taking blood from the femoral artery, mixing it with a crystalloid solution (using a mixer heater) to make the blood hyperosmolar, alkalotic, and substrate-enriched, and pumping it through a leukocyte-depleting filter into the transplanted lung for 10 minutes at a pressure of 20 to 30 mm Hg before removing the pulmonary artery clamp. The right pulmonary artery and bronchus were then ligated, and left lung function was assessed each hour for 4 hours and compared with baseline.

RESULTS

Controlled reperfusion (group 2) minimized the reperfusion injury, preserving posttransplant pulmonary compliance (92% +/- 1% versus 68% +/- 1%; p < 0.001), reducing the rise in pulmonary vascular resistance (27% +/- 2% versus 166% +/- 3%; p < 0.001), improving oxygenation (PO2, 425 +/- 14 versus 82 +/- 11 mm Hg; p < 0.001), and lowering myeloperoxidase activity (0.22 +/- 0.02 versus 0.45 +/- 0.02 deltaOD/mg protein per minute; p < 0.001) and tissue edema (83.0% +/- 0.3% versus 84.9% +/- 0.3%; p < 0.001) compared with uncontrolled reperfusion, which resulted in an injury so severe that 3 of 5 pigs died before the 4-hour measurements.

CONCLUSIONS

After 24 hours of cold ischemia uncontrolled reperfusion results in a severe pulmonary reperfusion injury. This injury is almost completely avoided by controlling the composition (modified solution and white blood cell filter) and conditions (pressure) of the reperfusion. Because this experiment mimics the clinical situation, it suggests surgeons should begin to use this modality to limit reperfusion injury after lung transplantation.

ATP-independent membrane depolarization with ischemia in the oxygen-ventilated isolated rat lung

We hypothesize that lung ischemic injury is related to cessation of flow leading to endothelial cell membrane depolarization and activation of oxidant-generating systems. Cell membrane potential was assessed in isolated, oxygen ventilated, Krebs-Ringer bicarbonate buffer-dextran-perfused rat lungs by lung surface fluorescence after infusion of bis-oxonol or 5,5',6,6'-tetrachloro-1, 1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1), voltage-sensitive dyes. Surface fluorometry showed increased bis-oxonol fluorescence (34.7 +/- 3.3% above baseline) and decreased JC-1 fluorescence (24.5 +/- 4.5% below baseline) with ischemia, compatible with membrane depolarization. Fluorescence change was initiated within 1-2 min of the onset of ischemia and was rapidly reversible with reperfusion. Fluorescence changes varied with perfusion flow rate; maximal increase occurred with the transition from 1.8 ml/min to zero flow. Elevation of static intravascular pressure resulted in only a minor increase of bis-oxonol fluorescence. In situ subpleural fluorescence microscopy showed that endothelial cells are the major site of the increased bis-oxonol fluorescence signal with ischemia. These results indicate that endothelial cell membrane depolarization represents an early event with lung ischemia. Since the adenosine triphosphate content of lung was unchanged with ischemia in the O2-ventilated lungs, we postulate that membrane depolarization results from elimination of shear stress, possibly via inactivation of flow-sensitive K+-channels.

Controlled reperfusion after lung ischemia: implications for improved function after lung transplantation

OBJECTIVES

Despite improvements in organ preservation, reperfusion injury remains a major source of morbidity and mortality after lung transplantation. This pilot study was designed to investigate the effects of controlled reperfusion after lung ischemia.

METHODS

Twenty adult pigs underwent 2 hours of warm lung ischemia by crossclamping the left bronchus and pulmonary artery. In five (group 1), the clamp was simply removed at the end of ischemia (uncontrolled reperfusion). The 15 other pigs underwent modified reperfusion using blood from the femoral artery to perfuse the lung through the pulmonary artery (pressure 40 to 50 mm Hg) for 10 minutes before removing the pulmonary artery clamp. In five (group 2), the blood was mixed with crystalloid, resulting in a substrate-enriched, hypocalcemic, hyperosmolar, alkaline solution. In five (group 3), the blood was circulated through a leukocyte-depleting filter, and the last five (group 4) underwent reperfusion with both a modified solution and white blood cell filter. Lung function was assessed 60 minutes after reperfusion, and biopsy specimens were taken.

RESULTS

Controlled reperfusion with both a white blood cell filter and modified solution (group 4) completely eliminated the reperfusion injury that occurred with uncontrolled reperfusion (group 1), resulting in complete preservation of compliance (98% +/- 1% vs 77% +/- 1%; p < 0.001, and arterial/alveolar ratio (97% +/- 2% vs 27% +/- 2%; p < 0.001); no increase in pulmonary vascular resistance (106% +/- 1% vs 198% +/- 1%; p < 0.001); lowered tissue edema (82.1% +/- 0.4% vs 84.3% +/- 0.2%; p < 0.001), and myeloperoxidase activity (0.18 +/- 0.02 vs 0.35 +/- 0.02 deltaOD/min/mg protein; p < 0.001). In contrast, using either a white blood cell filter or modified solution separately improved but did not avoid the reperfusion injury, resulting in pulmonary function and tissue edema levels that were intermediate between group 1 (uncontrolled reperfusion) and group 4 (white blood cell filter and modified solution).

CONCLUSION

After 2 hours of warm pulmonary ischemia, (1) a severe lung injury occurs after uncontrolled reperfusion, (2) controlled reperfusion with either a modified reperfusion solution or white blood cell filter limits, but does not avoid, a lung reperfusion injury, (3) reperfusion using both a modified reperfusate and white blood cell filter results in complete preservation of pulmonary function. We therefore believe surgeons should control the reperfusate after lung transplantation to improve postoperative pulmonary function.

Characterization of local inflammatory response in an isolated lung perfusion model

BACKGROUND

Current phase I trials of isolated lung perfusion for treatment of pulmonary metastases have an arbitrarily determined length of perfusion. Our objective was to examine the temporal course of the local and distant inflammatory response as a function of the length of perfusion (ischemia) and subsequent reperfusion in an equivalent animal model.

METHODS

Sixty male Fischer 344 rats were randomized into four groups (n = 15). Each group underwent left isolated lung perfusion with buffered Hespan for 10, 30, 60, or 90 minutes. Subsequently, two subgroups of five animals within each group were allowed to reperfuse for 1 or 3 hours, respectively. Non-perfused right lung was used as control. At each time point, lung specimens were assayed for TNF-alpha by ELISA and histologic sections were examined.

RESULTS

There was no significant difference between the left and right lung tissue levels of TNF-alpha at the termination of the ischemic period. However, on reperfusion, the left lung TNF-alpha levels increased significantly above the ischemia baseline in all groups, with a greater magnitude of rise in the groups with 60 and 90 minutes of preceding ischemia (12,757 +/- 1985 vs. 3524 +/- 494 pg/g, and 16,914 +/- 1657 vs. 6530 +/- 1104 pg/g, respectively; p < 0.05). There was no significant elevation in tissue levels of TNF-alpha in the right lung. Histologic changes consistent with early pulmonary edema were first detected at 12 hours following onset of reperfusion.

CONCLUSIONS

Reperfusion following prolonged pulmonary ischemia during isolated lung perfusion results in a significant elevation of local tissue levels of TNF-alpha and may render the perfused lung vulnerable to the adverse effects of the inflammatory cascade.

Anoxia-reoxygenation versus ischemia in isolated rat lungs

Oxidant generation in anoxia-reoxygenation and ischemia-reperfusion was compared in isolated rat lungs. Anoxia-reoxygenation was produced by N2 ventilation followed by O2 ventilation. After anoxia, lung ATP content was decreased by 59%. Oxygenated ischemia was produced by discontinuing perfusion while ventilation with O2 was maintained. With anoxia-reoxygenation, oxidant generation, evaluated by oxidation of dichlorodihydrofluorescein (H2DCF) to fluorescent dichlorofluorescein, increased 3.6-fold, lung thiobarbituric acid reactive substances (TBARS) increased 342%, conjugated dienes increased 285%, and protein carbonyl content increased 46%. Pretreatment of lungs with 100 microM allopurinol inhibited the reoxygenation-mediated increase in lung fluorescence by 75% and TBARS by 69%. Oxygenated ischemia resulted in an approximately eightfold increase in lung H2DCF oxidation and a fourfold increase in TBARS, but allopurinol had no effect. On the other hand, 100 microM diphenyliodonium (DPI) inhibited the ischemia-mediated increase in lung fluorescence by 69% and lung TBARS by 70%, but it had no effect on the increase with anoxia-reoxygenation. Therefore, both ischemia-reperfusion and anoxia-reoxygenation result in oxidant generation by the lung, but a comparison of results with a xanthine oxidase inhibitor (allopurinol) and a flavoprotein inhibitor (DPI) indicate that the pathways for oxidant generation are distinctly different.

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.

Attenuation of lung graft reperfusion injury by a nitric oxide donor

OBJECTIVE

One of the primary features of ischemia-reperfusion injury is reduced production of protective autocoids, such as nitric oxide, by dysfunctional endothelium. Administration of a nitric oxide donor during reperfusion of lung grafts may therefore be beneficial through modulation of vascular tone and leukocyte and platelet function.

METHODS

Rat lung grafts were flushed with University of Wisconsin solution and reperfused for 1 hour in an ex vivo model incorporating a support animal. Group I grafts (n = 6) were reperfused immediately after explantation, group II (n = 6) and III (n = 5) grafts after 24 hours of storage at 4 degrees C. In group III, glyceryl trinitrate, a nitric oxide donor, was administered during the first 10 minutes of reperfusion at a rate of 200 micrograms/min. In an additional group (n = 5), 200 micrograms/min hydralazine was administered instead, to assess the effect of vasodilation alone.

RESULTS

Graft function in group II deteriorated compared with that in group I, with significant reduction of graft effluent oxygen tension and blood flow and elevation of pulmonary artery pressure, peak airway pressure, and wet/dry weight ratio. In contrast, in group III, glyceryl trinitrate treatment improved graft function to baseline levels in all these parameters. Administration of hydralazine, meanwhile, produced mixed results with only two out of five grafts functioning at control levels.

CONCLUSIONS

In this model, administration of glyceryl trinitrate to supplement the nitric oxide pathway in the early phase of reperfusion has a sustained beneficial effect on lung graft function after 24-hour hypothermic storage, probably through mechanisms beyond vasodilation alone.

Endothelial cell oxidant generation during K(+)-induced membrane depolarization

We tested the hypothesis that membrane depolarization may initiate oxidant generation in the endothelial cell. Depolarization was produced in bovine pulmonary arterial endothelial cells (BPAEC) in monolayer culture with varying external K+, or with glyburide (10 microM), tetraethylammonium (TEA, 10 mM), gramicidin (1 microM), or nigericin (2 microM). Evaluation of bisoxonol fluorescence of BPAEC indicated concentration-dependent depolarization by high K+ (2% change in fluorescence/mV change in membrane potential in the 5.9-48 mM range of K+) and essentially complete depolarization with glyburide. Generation of oxidants was assessed with o-phenylenediamine dihydrochloride (o-PD) oxidation in the presence of horseradish peroxidase (HRP). There was a time-dependent increase in o-PD oxidation with 24 mM K+, nigericin, and gramicidin over 2 hours compared with control. In 1 hour o-PD oxidation increased 2.8-fold for 24 mM and 3.7-fold for 48 mM K+ compared with control. Catalase reduced 24 mM K(+)-induced o-PD oxidation by 50%, while Cu/Zn-superoxide dismutase (SOD) abolished the increase. Oxidation of o-PD was reduced by 57% in the absence of HRP in the system. With K+ channel blockade, o-PD oxidation increased 3.8-fold with glyburide and 4.6-fold with TEA compared with control. These data indicate formation of H2O2 and possibly other oxidants with depolarization and suggest involvement of K(+)-channels in this process.