Pulmonary ischemia/reperfusion injury: a quantitative study of structure and function in isolated heart-lungs of the rat

Evaluation of Donor Lungs for Transplantation: The Efficacy of Screening Bronchoscopy for Detecting Donor Aspiration and Its Relationship to the Resulting Allograft Function in Corresponding Recipients

BACKGROUND

Potential organ donors often have suffered anoxic and/or traumatic brain injury during which they may have experienced aspiration of gastric material (AGM). Evaluation of such donors typically includes a screening bronchoscopic examination during which determinations of aspiration are made. The efficacy of this visual screening and its relationship to post-transplant allograft function are unknown.

METHODS

Before procurement, bronchoscopy was performed on donors in which both bronchoalveolar lavage fluid (BALF) was collected and a visual inspection made. As a marker of AGM, BALF specimens were analyzed for the presence of bile salts. Data collected on the corresponding recipients included primary graft dysfunction (PGD) score, post-transplant spirometry, acute rejection scores (ARS), and overall survival.

RESULTS

Of 31 donors evaluated, bronchoscopies revealed only 2 with visual evidence of AGM, whereas BALF analysis for bile salts indicated AGM in 14. As such, screening bronchoscopy had a sensitivity of only 7.1%. Visual detection of AGM via bronchoscopy was not associated with any resulting grade of PGD (χ2 = 2.96, P = .23); however, AGM defined by detection of bile salts was associated (χ2 = 7.56, P = .02). Over the first post-transplant year, the corresponding recipients experienced a similar improvement in allograft function (χ2 = 1.63, P = .69), ARS (P = .69), and survival (P = .24).

CONCLUSION

Visual inspection during a single bronchoscopic examination of lung donors underestimates the prevalence of AGM. The detection of bile salts in donor BALF is associated with early allograft dysfunction in the corresponding recipients but not with later allograft proficiency, acute rejection responses, or 1-year post-transplant survival.

Hidden Microatelectases Increase Vulnerability to Ventilation-Induced Lung Injury

Mechanical ventilation of lungs suffering from microatelectases may trigger the development of acute lung injury (ALI). Direct lung injury by bleomycin results in surfactant dysfunction and microatelectases at day 1 while tissue elastance and oxygenation remain normal. Computational simulations of alveolar micromechanics 1-day post-bleomycin predict persisting microatelectases throughout the respiratory cycle and increased alveolar strain during low positive end-expiratory pressure (PEEP) ventilation. As such, we hypothesize that mechanical ventilation in presence of microatelectases, which occur at low but not at higher PEEP, aggravates and unmasks ALI in the bleomycin injury model. Rats were randomized and challenged with bleomycin (B) or not (H = healthy). One day after bleomycin instillation the animals were ventilated for 3 h with PEEP 1 (PEEP1) or 5 cmH₂O (PEEP5) and a tidal volume of 10 ml/kg bodyweight. Tissue elastance was repetitively measured after a recruitment maneuver to investigate the degree of distal airspace instability. The right lung was subjected to bronchoalveolar lavage (BAL), the left lung was fixed for design-based stereology at light- and electron microscopic level. Prior to mechanical ventilation, lung tissue elastance did not differ. During mechanical ventilation tissue elastance increased in bleomycin-injured lungs ventilated with PEEP = 1 cmH₂O but remained stable in all other groups. Measurements at the conclusion of ventilation showed the largest time-dependent increase in tissue elastance after recruitment in B/PEEP1, indicating increased instability of distal airspaces. These lung mechanical findings correlated with BAL measurements including elevated BAL neutrophilic granulocytes as well as BAL protein and albumin in B/PEEP1. Moreover, the increased septal wall thickness and volume of peri-bronchiolar-vascular connective tissue in B/PEEP1 suggested aggravation of interstitial edema by ventilation in presence of microatelectases. At the electron microscopic level, the largest surface area of injured alveolar epithelial was observed in bleomycin-challenged lungs after PEEP = 1 cmH₂O ventilation. After bleomycin treatment cellular markers of endoplasmic reticulum stress (p-Perk and p-EIF-2α) were positive within the septal wall and ventilation with PEEP = 1 cmH₂O ventilation increased the surface area stained positively for p-EIF-2α. In conclusion, hidden microatelectases are linked with an increased pulmonary vulnerability for mechanical ventilation characterized by an aggravation of epithelial injury.

The effect of sphingosine-1-phosphate on the endothelial glycocalyx during ischemia-reperfusion injury in the isolated rat heart

OBJECTIVE

Sphingosine-1-phosphate is a natural metabolite that is cardioprotective, but its effects on endothelial glycocalyx damage during ischemia-reperfusion are unknown. Therefore, we investigated the effect of sphingosine-1-phosphate on the endothelial glycocalyx during ischemia-reperfusion.

METHODS

Isolated hearts from Wistar rats were perfused on a Langendorff system with Krebs-Henseleit buffer and pretreated with sphingosine-1-phosphate (10 nmol/L) before ischemia-reperfusion. Infarct size was measured by triphenyl tetrazolium chloride staining (n ≥ 6 per group). Cardiac edema was assessed by calculating total water content (n = 7 per group) and histologically quantifying the interstitial compartment (n ≥ 3 per group). The post-ischemic coronary release of syndecan-1 was quantified using ELISA. Syndecan-1 immunostaining intensity was assessed in perfusion-fixed hearts (n ≥ 3 per group).

RESULTS

Pretreatment with sphingosine-1-phosphate decreased infarct size in isolated hearts subjected to ischemia-reperfusion (P = .01 vs ischemia-reperfusion). However, sphingosine-1-phosphate had no effect on syndecan-1 levels in the coronary effluent or on the intensity of the syndecan-1 immunostaining signal in cardiac tissue. Heart total water content was not significantly different between control and ischemic groups but was significantly decreased in hearts treated with sphingosine-1-phosphate alone.

CONCLUSION

These results suggest that sphingosine-1-phosphate-induced cardioprotection against ischemia-reperfusion injury is not mediated by the maintenance of syndecan-1 in the endothelial glycocalyx.

Surfactant Protein B Deficiency Induced High Surface Tension: Relationship between Alveolar Micromechanics, Alveolar Fluid Properties and Alveolar Epithelial Cell Injury

High surface tension at the alveolar air-liquid interface is a typical feature of acute and chronic lung injury. However, the manner in which high surface tension contributes to lung injury is not well understood. This study investigated the relationship between abnormal alveolar micromechanics, alveolar epithelial injury, intra-alveolar fluid properties and remodeling in the conditional surfactant protein B (SP-B) knockout mouse model. Measurements of pulmonary mechanics, broncho-alveolar lavage fluid (BAL), and design-based stereology were performed as a function of time of SP-B deficiency. After one day of SP-B deficiency the volume of alveolar fluid V(alvfluid,par) as well as BAL protein and albumin levels were normal while the surface area of injured alveolar epithelium S(AEinjure,sep) was significantly increased. Alveoli and alveolar surface area could be recruited by increasing the air inflation pressure. Quasi-static pressure-volume loops were characterized by an increased hysteresis while the inspiratory capacity was reduced. After 3 days, an increase in V(alvfluid,par) as well as BAL protein and albumin levels were linked with a failure of both alveolar recruitment and airway pressure-dependent redistribution of alveolar fluid. Over time, V(alvfluid,par) increased exponentially with S(AEinjure,sep). In conclusion, high surface tension induces alveolar epithelial injury prior to edema formation. After passing a threshold, epithelial injury results in vascular leakage and exponential accumulation of alveolar fluid critically hampering alveolar recruitability.

Stereological assessment of the blood-air barrier and the surfactant system after mesenchymal stem cell pretreatment in a porcine non-heart-beating donor model for lung transplantation

More frequent utilization of non-heart-beating donor (NHBD) organs for lung transplantation has the potential to relieve the shortage of donor organs. In particular with respect to uncontrolled NHBD, concerns exist regarding the risk of ischaemia/reperfusion (IR) injury-related graft damage or dysfunction. Due to their immunomodulating and tissue-remodelling properties, bone-marrow-derived mesenchymal stem cells (MSCs) have been suspected of playing a beneficial role regarding short- and long-term survival and function of the allograft. Thus, MSC administration might represent a promising pretreatment strategy for NHBD organs. To study the initial effects of warm ischaemia and MSC application, a large animal lung transplantation model was generated, and the structural organ composition of the transplanted lungs was analysed stereologically with particular respect to the blood-gas barrier and the surfactant system. In this study, porcine lungs (n = 5/group) were analysed. Group 1 was the sham-operated control group. In pigs of groups 2-4, cardiac arrest was induced, followed by a period of 3 h of ventilated ischaemia at room temperature. In groups 3 and 4, 50 × 10⁶ MSCs were administered intravascularly via the pulmonary artery and endobronchially, respectively, during the last 10 min of ischaemia. The left lungs were transplanted, followed by a reperfusion period of 4 h. Then, lungs were perfusion-fixed and processed for light and electron microscopy. Samples were analysed stereologically for IR injury-related structural parameters, including volume densities and absolute volumes of parenchyma components, alveolar septum components, intra-alveolar oedema, and the intracellular and intra-alveolar surfactant pool. Additionally, the volume-weighted mean volume of lamellar bodies (lbs) and their profile size distribution were determined. Three hours of ventilated warm ischaemia was tolerated without eliciting histological or ultrastructural signs of IR injury, as revealed by qualitative and quantitative assessment. However, warm ischaemia influenced the surfactant system. The volume-weighted mean volume of lbs was reduced significantly (P = 0.024) in groups subjected to ischaemia (group medians of groups 2-4: 0.180-0.373 μm³) compared with the sham control group (median 0.814 μm³). This was due to a lower number of large lb profiles (size classes 5-15). In contrast, the intra-alveolar surfactant system was not altered significantly. No significant differences were encountered comparing ischaemia alone (group 2) or ischaemia plus application of MSCs (groups 3 and 4) in this short-term model.

Low-dose adrenomedullin-2/intermedin(8-47) reduces pulmonary ischemia/reperfusion injury

Adrenomedullin-2/intermedin stabilizes the pulmonary microvascular barrier challenged by application of thrombin ex vivo and by experimental ventilation in vivo. Here, we test the hypothesis that adrenomedullin-2/intermedin(8-47) protects mouse lungs from ischemia/reperfusion injury in vivo. C57BL/6 mice were anesthetized, intubated, ventilated, and heparinized. Blood vessels and the main bronchus of the left lung were clamped for 90min. Thereafter, lungs were reperfused for 120min. Five min before clamping and before reperfusion, mice obtained intravenous injections of adrenomedullin-2/intermedin(8-47). After reperfusion, mice were sacrificed and bronchoalveolar lavage of the left and the right lung was performed separately. The integrity of the blood-air barrier was investigated by electron microscopy using stereological methods. In response to ischemia/reperfusion injury, intraalveolar leukocytes accumulated in the ischemic lung. Two applications of 10ng/kg body weight adrenomedullin-2/intermedin(8-47) dramatically reduced leukocyte infiltration to about 15% (p≤0.001). Also the proportion of the subpopulation of neutrophil granulocytes decreased (12% vs 5%, p=0.013). Electron microscopy revealed a protection of the blood-air barrier by adrenomedullin-2/intermedin(8-47). Adrenomedullin-2/intermedin(8-47) ameliorates early ischemia/reperfusion injury in mouse lungs by protecting the integrity of the blood-air barrier and by potently reducing leukocyte influx into the alveolar space. Adrenomedullin-2/intermedin(8-47) might be of therapeutic interest in lung transplantation and cardiopulmonary bypass.

Mesenchymal stem cell pretreatment of non-heart-beating-donors in experimental lung transplantation

Background

Lung transplantation (LTx) is still limited by organ shortage. To expand the donor pool, lung retrieval from non-heart-beating donors (NHBD) was introduced into clinical practice recently. However, primary graft dysfunction with inactivation of endogenous surfactant due to ischemia/reperfusion-injury is a major cause of early mortality. Furthermore, donor-derived human mesenchymal stem cell (hMSC) expansion and fibrotic differentiation in the allograft results in bronchiolitis obliterans syndrome (BOS), a leading cause of post-LTx long-term mortality. Therefore, pretreatment of NHBD with recipient-specific bone-marrow-(BM)-derived hMSC might have the potential to both improve the postischemic allograft function and influence the long-term development of BOS by the numerous paracrine, immunomodulating and tissue-remodeling properties especially on type-II-pneumocytes of hMSC.

Methods

Asystolic pigs (n = 5/group) were ventilated for 3 h of warm ischemia (groups 2–4). 50x106 mesenchymal-stem-cells (MSC) were administered in the pulmonary artery (group 3) or nebulized endobronchially (group 4) before lung preservation. Following left-lung-transplantation, grafts were reperfused, pulmonary-vascular-resistance (PVR), oxygenation and dynamic-lung-compliance (DLC) were monitored and compared to control-lungs (group 2) and sham-controls (group 1). To prove and localize hMSC in the lung, cryosections were counter-stained. Intra-alveolar edema was determined stereologically. Statistics comprised ANOVA with repeated measurements.

Results

Oxygenation (p = 0.001) and PVR (p = 0.009) following endovascular application of hMSC were significantly inferior compared to Sham controls, whereas DLC was significantly higher in endobronchially pretreated lungs (p = 0.045) with overall sham-comparable outcome regarding oxygenation and PVR. Stereology revealed low intrapulmonary edema in all groups (p > 0.05). In cryosections of both unreperfused and reperfused grafts, hMSC were localized in vessels of alveolar septa (endovascular application) and alveolar lumen (endobronchial application), respectively.

Conclusions

Preischemic deposition of hMSC in donor lungs is feasible and effective, and endobronchial application is associated with significantly better DLC as compared to sham controls. In contrast, transvascular hMSC delivery results in inferior oxygenation and PVR. In the long term perspective, due to immunomodulatory, paracrine and tissue-remodeling effects on epithelial and endothelial restitution, an endobronchial NHBD allograft-pretreatment with autologous mesenchymal-stem-cells to attenuate limiting bronchiolitis-obliterans-syndrome in the long-term perspective might be promising in clinical lung transplantation. Subsequent work with chronic experiments is initiated to further elucidate this important field.

Electronic supplementary material

The online version of this article (doi:10.1186/s13019-014-0151-3) contains supplementary material, which is available to authorized users.

Effects of exogenous surfactant on the non-heart-beating donor lung graft in experimental lung transplantation - a stereological study

The use of non-heart-beating donor (NHBD) lungs may help to overcome the shortage of lung grafts in clinical lung transplantation, but warm ischaemia and ischaemia/reperfusion injury (I/R injury) resulting in primary graft dysfunction represent a considerable threat. Thus, better strategies for optimized preservation of lung grafts are urgently needed. Surfactant dysfunction has been shown to contribute to I/R injury, and surfactant replacement therapy is effective in enhancing lung function and structural integrity in related rat models. In the present study we hypothesize that surfactant replacement therapy reduces oedema formation in a pig model of NHBD lung transplantation. Oedema formation was quantified with (SF) and without (non-SF) surfactant replacement therapy in interstitial and alveolar compartments by means of design-based stereology in NHBD lungs 7 h after cardiac arrest, reperfusion and transplantation. A sham-operated group served as control. In both NHBD groups, nearly all animals died within the first hours after transplantation due to right heart failure. Both SF and non-SF developed an interstitial oedema of similar degree, as shown by an increase in septal wall volume and arithmetic mean thickness as well as an increase in the volume of peribron-chovascular connective tissue. Regarding intra-alveolar oedema, no statistically significant difference could be found between SF and non-SF. In conclusion, surfactant replacement therapy cannot prevent poor outcome after prolonged warm ischaemia of 7 h in this model. While the beneficial effects of surfactant replacement therapy have been observed in several experimental and clinical studies related to heart-beating donor lungs and cold ischaemia, it is unlikely that surfactant replacement therapy will overcome the shortage of organs in the context of prolonged warm ischaemia, for example, 7 h. Moreover, our data demonstrate that right heart function and dysfunctions of the pulmonary vascular bed are limiting factors that need to be addressed in NHBD.

Quantitative microscopy of the lung: a problem-based approach. Part 2: stereological parameters and study designs in various diseases of the respiratory tract

Design-based stereology provides efficient methods to obtain valuable quantitative information of the respiratory tract in various diseases. However, the choice of the most relevant parameters in a specific disease setting has to be deduced from the present pathobiological knowledge. Often it is difficult to express the pathological alterations by interpretable parameters in terms of volume, surface area, length, or number. In the second part of this companion review article, we analyze the present pathophysiological knowledge about acute lung injury, diffuse parenchymal lung diseases, emphysema, pulmonary hypertension, and asthma to come up with recommendations for the disease-specific application of stereological principles for obtaining relevant parameters. Worked examples with illustrative images are used to demonstrate the work flow, estimation procedure, and calculation and to facilitate the practical performance of equivalent analyses.

Small interfering RNA efficiently suppresses adhesion molecule expression on pulmonary microvascular endothelium

Background. Adhesion molecules are known to influence postoperative organ function, they are hardly involved in the inflammatory response following the ischemia-reperfusion injury. We sought to investigate the potency of small interfering RNAs to suppress adhesion molecule expression in human pulmonary microvascular endothelial cells. Methods. Human lung microvascular endothelial cells were transfected with specific siRNA followed by a stimulation of the cells with an inflammatory cytokine. Adhesion molecule expression was determined by FACS-analysis, and reduction of intracellular mRNA was determined by qRT-PCR. Furthermore, the attachment of isolated neutrophils on the endothelial layer was determined after siRNA transfection. Results. In summary, siRNA transfection significantly decreased the percentage positive cells in a single cocktail transfection of each adhesion molecule investigated. Adhering neutrophils were diminished as well. Conclusion. siRNA might be a promising tool for the effective suppression of adhesion molecule expression on pulmonary microvascular cells, potentially minimizing leukocyte-endothelial depending interactions of a pulmonary allograft.

Microscopy-based quantitative analysis of lung structure: application in diagnosis

INTRODUCTION

Stereology provides a set of methods that are appropriate for a microscopy-based quantitative assessment of lung structure. In general, the aim of stereology is to obtain information on three-dimensional structures from two-dimensional sections of these structures. The inherent impartiality of stereological principles is critical in order to meet the requirements of 'good laboratory practice'.

AREAS COVERED

This article is a systematic review of the applications of stereology to characterize pathological alterations of emphysema, fibrosis, acute lung injury and tumor grading. The reader is provided with a general overview of unbiased or design-based stereology and is provided with some examples of how these methods could be integrated into a diagnostic work-up of lung diseases in humans and animal models. The article also reviews the implications of a published statement, which defines standards for quantitative assessment of lung structure based on stereology, by the American Thoracic Society and the European Respiratory Society.

EXPERT OPINION

In view of the recently published standards for quantitative assessment of lung structure, unbiased stereological methods are strongly recommended, particularly as they provide valuable information in diagnosing lung diseases and allow a statistically valid quantitative comparison between different groups. Future developments will make the application of stereology in lung biology and pathology even more efficient. Moreover, there is also the potential for combing the principles of stereology with other imaging modalities (e.g., radiological), which will allow for non-invasive lung stereology.

Ultrastructural changes of the intracellular surfactant pool in a rat model of lung transplantation-related events

BACKGROUND

Ischemia/reperfusion (I/R) injury, involved in primary graft dysfunction following lung transplantation, leads to inactivation of intra-alveolar surfactant which facilitates injury of the blood-air barrier. The alveolar epithelial type II cells (AE2 cells) synthesize, store and secrete surfactant; thus, an intracellular surfactant pool stored in lamellar bodies (Lb) can be distinguished from the intra-alveolar surfactant pool. The aim of this study was to investigate ultrastructural alterations of the intracellular surfactant pool in a model, mimicking transplantation-related procedures including flush perfusion, cold ischemia and reperfusion combined with mechanical ventilation.

METHODS

Using design-based stereology at the light and electron microscopic level, number, surface area and mean volume of AE2 cells as well as number, size and total volume of Lb were determined in a group subjected to transplantation-related procedures including both I/R injury and mechanical ventilation (I/R group) and a control group.

RESULTS

After I/R injury, the mean number of Lb per AE2 cell was significantly reduced compared to the control group, accompanied by a significant increase in the luminal surface area per AE2 cell in the I/R group. This increase in the luminal surface area correlated with the decrease in surface area of Lb per AE2. The number-weighted mean volume of Lb in the I/R group showed a tendency to increase.

CONCLUSION

We suggest that in this animal model the reduction of the number of Lb per AE2 cell is most likely due to stimulated exocytosis of Lb into the alveolar space. The loss of Lb is partly compensated by an increased size of Lb thus maintaining total volume of Lb per AE2 cell and lung. This mechanism counteracts at least in part the inactivation of the intra-alveolar surfactant.

Ischaemia-reperfusion injury in orthotopic mouse lung transplants - a scanning electron microscopy study

Lung ischaemia-reperfusion (I/R) injury remains a major cause of graft failure in lung transplantation (Tx). With the implementation of orthotopic lung Tx in mice, a physiological model on the base of a perfused and ventilated graft became available for the investigation of I/R injury. Using the scanning electron microscopy (SEM) technique, we here present an analysis of early and late morphological changes of pulmonary I/R injury. Syngeneic lungs were orthotopically transplanted between C57BL/6 mice. Grafts were exposed to 2 h of cold ischaemia. Transplants and right lungs were examined by SEM with corresponding haematoxylin-eosin histology 30 min and 4 h after reperfusion. Thirty minutes after reperfusion, the alveolar surface of transplants showed a discontinued lining of surfactant, while the lining of the non-transplanted lung was normal. Within the graft, leucocytes displayed an irregular surface with development of pseudopodia, and microvilli were detected on the membrane of pneumocytes. At 4 h after reperfusion, leucocytes significantly increased in numbers within the alveolar space. Also, the number of microvilli on pneumocytes increased significantly. Similar to these, the endothelium of vessels increasingly developed microvilli from 30 min towards 4 h after reperfusion. The airways of transplanted grafts showed mild changes with thickening of the bronchial epithelium and a destruction of kinocilia. Taken together, SEM detects pathological events of I/R that are previously not described in normal histology. These findings may influence the interpretation of studies investigating the I/R injury in the mouse model of lung Tx.

Quantitative analysis of delayed neuronal death in the hippocampal subfields of SHRSP and SHR

Transient forebrain ischemia and reperfusion induces delayed neuronal death (DND) in the hippocampal Cornu Ammonis 1 (CA1) subfield of stroke-prone spontaneously hypertensive rat (SHRSP). The vulnerability to DND is potentially related to the genetic susceptibility to stroke in this strain. To elucidate the mechanism of DND in SHRSP, however, it is essential to establish a method for quantitative evaluation of DND, which is not available yet. Male SHRSPs and spontaneously hypertensive rats (SHRs) at 12 weeks of age were used in the experiment. The bilateral common carotid arteries were surgically occluded with aneurysmal clips for 10 min. The brain was taken out 7 days after the experiment of the transient ischemia, and was sliced into serial coronal sections. Quantitative estimation of the number of viable pyramidal cells in the CA1 and CA2/3 subfields was performed based on the stereology with a random and systematic sampling. The transient ischemia and reperfusion (TIR) significantly reduced the number of viable pyramidal cells in CA1 of SHRSP (61000 +/- 20100 in TIR vs. 128500 +/- 21900 in the sham-operation, P < 0.000001 by Student's t-test), while no significant difference was observed in SHR (140300 +/- 30800 in TIR vs. 128200 +/- 16700 in the sham-operation, P = 0.35). Further analysis revealed a dorsal-ventral gradient in the distribution of DND in CA1 of SHRSP with the most severe change in the dorsal area. The quantitative measurement using a stereological method is useful in the precise evaluation of DND in SHRSP. This method can be applied in the studies of effects of medical treatments on the 'ischemia/reperfusion' insult.

Pathogenesis, management, and consequences of primary graft dysfunction

Primary graft dysfunction continues to be a major contributing factor to morbidity and mortality after lung transplantation. This condition is presumed to be the result of ischemia-reperfusion injury, which is associated with the release of endogenous substances that can activate the innate immune system. Primary graft dysfunction has been shown to be an independent risk factor for the development of bronchiolitis obliterans syndrome indicating that it can shape alloimmune responses. In this review, we focus on the classification, pathogenesis, possible prevention strategies, management and consequences of primary graft dysfunction.

Exogenous surfactant application in a rat lung ischemia reperfusion injury model: effects on edema formation and alveolar type II cells

Background

Prophylactic exogenous surfactant therapy is a promising way to attenuate the ischemia and reperfusion (I/R) injury associated with lung transplantation and thereby to decrease the clinical occurrence of acute lung injury and acute respiratory distress syndrome. However, there is little information on the mode by which exogenous surfactant attenuates I/R injury of the lung. We hypothesized that exogenous surfactant may act by limiting pulmonary edema formation and by enhancing alveolar type II cell and lamellar body preservation. Therefore, we investigated the effect of exogenous surfactant therapy on the formation of pulmonary edema in different lung compartments and on the ultrastructure of the surfactant producing alveolar epithelial type II cells.

Methods

Rats were randomly assigned to a control, Celsior (CE) or Celsior + surfactant (CE+S) group (n = 5 each). In both Celsior groups, the lungs were flush-perfused with Celsior and subsequently exposed to 4 h of extracorporeal ischemia at 4°C and 50 min of reperfusion at 37°C. The CE+S group received an intratracheal bolus of a modified natural bovine surfactant at a dosage of 50 mg/kg body weight before flush perfusion. After reperfusion (Celsior groups) or immediately after sacrifice (Control), the lungs were fixed by vascular perfusion and processed for light and electron microscopy. Stereology was used to quantify edematous changes as well as alterations of the alveolar epithelial type II cells.

Results

Surfactant treatment decreased the intraalveolar edema formation (mean (coefficient of variation): CE: 160 mm³ (0.61) vs. CE+S: 4 mm³ (0.75); p < 0.05) and the development of atelectases (CE: 342 mm³ (0.90) vs. CE+S: 0 mm³; p < 0.05) but led to a higher degree of peribronchovascular edema (CE: 89 mm³ (0.39) vs. CE+S: 268 mm³ (0.43); p < 0.05). Alveolar type II cells were similarly swollen in CE (423 μm³(0.10)) and CE+S (481 μm³(0.10)) compared with controls (323 μm³(0.07); p < 0.05 vs. CE and CE+S). The number of lamellar bodies was increased and the mean lamellar body volume was decreased in both CE groups compared with the control group (p < 0.05).

Conclusion

Intratracheal surfactant application before I/R significantly reduces the intraalveolar edema formation and development of atelectases but leads to an increased development of peribronchovascular edema. Morphological changes of alveolar type II cells due to I/R are not affected by surfactant treatment. The beneficial effects of exogenous surfactant therapy are related to the intraalveolar activity of the exogenous surfactant.

Impact of preservation solution on the extent of blood-air barrier damage and edema formation in experimental lung transplantation

A major aim in lung transplantation is to prevent the loss of structural integrity due to ischemia and reperfusion (I/R) injury. Preservation solutions protect the lung against I/R injury to a variable extent. We compared the influence of two extracellular-type preservation solutions (Perfadex, or PX, and Celsior, or CE) on the morphological alterations induced by I/R. Pigs were randomly assigned to sham (n = 4), PX (n = 5), or CE (n = 2) group. After flush perfusion with PX or CE, donor lungs were excised and stored for 27 hr at 4 degrees C. The left donor lung was implanted into the recipient, reperfused for 6 hr, and, afterward, prepared for light and electron microscopy. Intra-alveolar, septal, and peribronchovascular edema as well as the integrity of the blood-air barrier were determined stereologically. Intra-alveolar edema was more pronounced in CE (219.80 +/- 207.55 ml) than in PX (31.46 +/- 15.75 ml). Peribronchovascular (sham: 13.20 +/- 4.99 ml; PX: 15.57 +/- 5.53 ml; CE: 31.56 +/- 5.78 ml) and septal edema (thickness of alveolar septal interstitium, sham: 98 +/- 33 nm; PX: 84 +/- 8 nm; CE: 249 +/- 85 nm) were only found in CE. The blood-air barrier was similarly well preserved in sham and PX but showed larger areas of swollen and fragmented epithelium or endothelium in CE. The present study shows that Perfadex effectively prevents intra-alveolar, septal, and peribronchovascular edema formation as well as injury of the blood-air barrier during I/R. Celsior was not effective in preserving the lung from morphological I/R injury.

Nitrogen dioxide induces apoptosis and proliferation but not emphysema in rat lungs

BACKGROUND

Apoptosis of alveolar septal cells has been linked to emphysema formation. Nitrogen dioxide, a component of cigarette smoke, has been shown to induce alveolar epithelial cell apoptosis in vitro. It is hypothesised that exposure of rats to nitrogen dioxide may result in increased alveolar septal cell apoptosis in vivo with ensuing emphysema-that is, airspace enlargement and loss of alveolar walls.

METHODS

Fischer 344 rats were exposed to 10 ppm nitrogen dioxide for 3, 7, 21 days or 21 days followed by 28 days at room air. Age-matched control rats were exposed to room air for 3, 21 or 49 days. Lungs fixed at 20 cm fluid column, embedded in paraffin wax, glycol methacrylate and araldite, were analysed by design-based stereology. Alveolar septal cell apoptosis (transferase dUTP nick end labelling assay, active caspase 3) and proliferation (Ki-67), airspace enlargement, total alveolar surface area, and absolute alveolar septal volume as well as the ultrastructural composition of the alveolar wall were quantified.

RESULTS

Nitrogen dioxide resulted in an eightfold increase in alveolar septal cell apoptosis at day 3 and a 14-fold increase in proliferation compared with age-matched controls. Airspace enlargement, indicated by a 20% increase in mean airspace chord length, was evident by day 7 but was not associated with loss of alveolar walls. By contrast, nitrogen dioxide resulted in an increase in the total surface area and absolute volume of alveolar walls comprising all compartments. The ratio of collagen to elastin, however, was reduced at day 21. Lungs exposed to nitrogen dioxide for 21 days exhibited quantitative structural characteristics as seen in control lungs on day 49.

CONCLUSIONS

Nitrogen dioxide exposure of rats results in increased alveolar septal cell turnover leading to accelerated lung growth, which is associated with an imbalance in the relative composition of the extracellular matrix, but fails to induce emphysema.

Protection of lung tissue against ischemia/reperfusion injury by preconditioning with inhaled nitric oxide in an in situ pig model of normothermic pulmonary ischemia

Topical administration of nitric oxide (NO) by inhalation is currently used as therapy in various pulmonary diseases, but preconditioning with NO to ameliorate lung ischemia/reperfusion (I/R) injury has not been fully evaluated. In this study, we investigated the effects of NO inhalation on functional pulmonary parameters using an in situ porcine model of normothermic pulmonary ischemia. After left lateral thoracotomy, left lung ischemia was maintained for 90 min, followed by a 5h reperfusion period (group I, n = 7). In group II (n = 6), I/R was preceded by inhalation of NO (10 min, 15 ppm). Animals in group III (n = 7) underwent sham surgery without NO inhalation or ischemia. In order to evaluate the effects of NO preconditioning, lung functional and hemodynamic parameters were measured, and the zymosan-stimulated release of reactive oxygen species in arterial blood was determined. Animals in group I developed significant pulmonary I/R injury, including pulmonary hypertension, a decreased pO(2) level in pulmonary venous blood of the ischemic lung, and a significant increase of the stimulated release of reactive oxygen species. All these effects were prevented, or the onset (release of reactive oxygen species) was delayed, by NO inhalation. These results indicate that preconditioning by NO inhalation before lung ischemia is protective against I/R injury in the porcine lung.

Reduced vascular endothelial growth factor correlates with alveolar epithelial damage after experimental ischemia and reperfusion

BACKGROUND

After clinical lung transplantation, the amount of vascular endothelial growth factor (VEGF) was found to be decreased in the bronchoalveolar lavage from lungs with acute lung injury. Since Type II pneumocytes are a major site of VEGF synthesis, VEGF depression may be an indicator of pulmonary epithelial damage after ischemia and reperfusion.

METHODS

Using an established rat lung model, we investigated the relationship between VEGF protein expression, oxygenation capacity and structural integrity after extracorporeal ischemia and reperfusion (ischemia 6 hours at 10 degrees C, reperfusion 50 minutes) and preservation with either low-potassium dextran solution (Perfadex 40 kD, n = 8) or Celsior (n = 6). Untreated, non-ischemic lungs served as controls (n = 5 per group). Perfusate oxygenation was recorded during reperfusion. An enzyme-linked immunoassay (ELISA) for VEGF protein and reverse transcription-polymerase chain reaction (RT-PCR) for mRNA splice variants were determined on tissue collected from the left lungs, whereas the right lungs were fixed by vascular perfusion for VEGF immunohistochemistry as well as structural analysis by light and electron microscopy. Tissue collection by systematic uniform random sampling was representative for the whole organ and allowed for quantification of structures by stereological means.

RESULTS

After ischemia and reperfusion, the 3 major VEGF isoforms, VEGF(120), VEGF(164) and VEGF(188), were present. VEGF protein expression was reduced, which correlated significantly with perfusate oxygenation (r = 0.736; p = 0.002) at the end of reperfusion. It was inversely related to Type II cell volume (r = 0.600; p = 0.047). VEGF protein was localized by immunohistochemistry in Type II pneumocytes, alveolar macrophages as well as bronchial epithelium, and staining intensity of Type II cells was reduced after ischemia and reperfusion. Alveolar edema did not occur but significant interstitial edema accumulated around vessels and in the blood-gas barrier, which showed a higher degree of epithelial damage after preservation with Celsior compared with the other groups.

CONCLUSIONS

Depression in VEGF protein expression can be considered an indicator for increased alveolar epithelial damage. Preservation with low-potassium dextran solution resulted in improved oxygenation and tissue integrity compared with Celsior.

Remote preconditioning lessens the deterioration of pulmonary function after repeated coronary artery occlusion and reperfusion in sheep

PURPOSE

We investigated whether remote organ preconditioning (RPC) can preserve pulmonary function following repeated myocardial ischemia/reperfusion in a model mimicking multi-vessel off-pump coronary artery bypass (OPCAB) revascularization.

METHODS

Nine sheep (Group-RPC) underwent RPC by three episodes of five-minute occlusion and five-minute reperfusion of the iliac artery. Five sheep (Group-C) were time-matched controls. Afterwards, ten-minute occlusion and reperfusion of the left anterior descending, the first diagonal and the left circumflex coronary arteries were performed consecutively. Hemodynamic and respiratory parameters and arterial blood gases were measured until 120 min after the final coronary reperfusion. Anesthesia was maintained with halothane in oxygen and nitrous oxide. Animals were ventilated with a tidal volume of 15-20 mL.kg(-1) in a non-rebreathing system, and a respiratory rate 14-16 min, with 5-cm H(2)O positive end expiratory pressure after thoracotomy.

RESULTS

Repeated coronary occlusion and reperfusion was associated in this experimental model with an increase in pulmonary vascular resistance (PVR) and pulmonary arterial pressure (PAP) and a decrease in PaO(2) and PaO(2)/FIO(2) in Group-C. After 120 min reperfusion, PaO(2) and PaO(2)/FIO(2) in Group-RPC were higher (192 +/- 69 mmHg and 241 +/- 78 vs 115 +/- 54 mmHg and 129 +/- 64, P < 0.05), while PVR and PAP were lower than in Group-C. At 120 min of reperfusion, PaO(2) and PaO(2)/FIO(2) were inversely correlated with PVR (P < 0.01).

CONCLUSIONS

RPC by transient occlusion of the iliac artery improves lung gas exchange after repeated coronary artery occlusion and reperfusion mimicking OPCAB surgery, and preserves low PVR in sheep.

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.

Raffinose improves 24-hour lung preservation in low potassium dextran glucose solution: a histologic and ultrastructural analysis

BACKGROUND

We have previously shown that the addition of raffinose to low potassium dextran (LPD) preservation solution improves transplanted rat lung function after 24 hours of storage. The mechanisms by which raffinose acts are unclear. The aim of this study was to examine the histologic and ultrastructural correlates of this enhanced pulmonary function after preservation with raffinose.

METHODS

In a randomized, blinded study, rat lungs were flushed with LPD, or LPD containing 30 mmol/L of raffinose, and stored for 24 hours at 4 degrees C. Control lungs were flushed with LPD but not stored (n = 5 each group). Changes in postpreservation edema were determined. In addition, lungs were flushed with a trypan blue solution to quantify cell death, and examined using both light and electron microscopy.

RESULTS

The LPD lungs gained significantly more weight (25.5%+/-5.5%) compared with raffinose-LPD lungs (5.2%+/-5.3%; p < 0.0001). There were higher percentages of dead cells in the LPD lungs (29%+/-0.3% of total cells) compared with raffinose-LPD lungs (14%+/-1.4%; p < 0.001) and control lungs (0.2%+/-5%; p < 0.001). Control lungs maintained normal ultrastructure, whereas LPD lungs showed a decreased number of intact type II pneumocytes and significant cellular necrosis. Interstitial and alveolar edema with interstitial macrophage infiltration was also observed. Alveolar capillaries were collapsed. In contrast, raffinose-LPD lungs showed only mild alterations such as minimal interstitial edematous expansion, fewer damaged cells, and minimal capillary injury.

CONCLUSIONS

Raffinose exerts a cytoprotective effect on pulmonary grafts during preservation, which explains the previously documented improved function. This simple modification of LPD with raffinose may provide clinical benefit in extended pulmonary preservation.

Beneficial effect of lung preservation is related to ultrastructural integrity of tubular myelin after experimental ischemia and reperfusion

Ischemia/reperfusion (I/R) injury results in the impairment of surfactant activity. The hypothesis that the differences in lung preservation quality obtained by EuroCollins (EC) and Celsior (CE) solutions were related to surfactant alterations was tested. To avoid extensive structural damage and edema formation, which can secondarily affect the surfactant system, lungs were stored for a short ischemic period (2 h at 10 degrees C) and reperfused (50 min) in an isolated perfused rat lung model after preservation with either potassium-reduced (40 mmol) EC40 or with CE. Using a modified stereological approach ultrastructure, total amount and distribution of phospholipid membranes composing tubular myelin (tm) and small (s) and large (l) unilameliar vesicles (ul) were investigated in the organ in lungs fixed by vascular perfusion either in situ (controls) or after I/R (n = 5 per group). The total amount of intraalveolar surfactant was increased after I/R. However, a significant amount (p = 0.008) of tm was displaced into the alveolar lumen and showed wider meshes of the tm lattices than did the controls (p = 0.023) where almost all tm was epithelial. In lungs preserved with EC40, epithelial tm was significantly reduced (p = 0.018), resulting in a higher ratio (p = 0.034) of surface-inactive small ul (0.05 to 0.3 microm) to surface-active epithelial tm. In the CE group approximately 50% of the total tm pool was epithelial. This was accompanied by higher parenchymal air space and improved functional parameters. Epithelial and endothelial cell-specific immunostaining did not reveal any gross damage of the blood-gas barrier. In summary, improved lung function during reperfusion was associated with beneficial effects of lung preservation on tm integrity after I/R. These observations suggest that preservation solutions ameliorate events leading to surfactant disturbance even before extensive lung injury is manifested.

Ultrastructural alterations in intraalveolar surfactant subtypes after experimental ischemia and reperfusion

Ischemia and reperfusion (I/R) result in surfactant dysfunction. Whether the impairment of surfactant is a consequence or a cause of intraalveolar edema formation is still unknown. The cumulative effects of lung perfusion, ischemic storage, and subsequent reperfusion on surfactant ultrastructure and pulmonary function were studied in a rat isolated perfused lung model. The left lungs were fixed for electron microscopy by vascular perfusion either immediately after excision (control; n = 5) or after perfusion with modified Euro-Collins solution (EC), storage for 2 h at 4 degrees C in EC, and reperfusion for 40 min (n = 5). A stereological approach was chosen to discriminate between intraalveolar surfactant subtypes of edematous regions and regions free of edema. Intraalveolar edema seen after I/R in the EC group occupied 36 +/- 6% (mean +/- SEM) of the gas exchange region as compared with control lungs (1 +/- 1%; p = 0.008). Relative intraalveolar surfactant composition showed a decrease in surface active tubular myelin (3 +/- 1 versus 12 +/- 0%; p = 0.008) and an increase in inactive unilamellar forms (83 +/- 2 versus 64 +/- 5%; p = 0.008) in the EC group. These changes occurred both in edematous (tubular myelin, 3 +/- 1%; unilamellar forms, 88 +/- 6%) and in nonedematous regions (tubular myelin, 4 +/- 3%; unilamellar forms, 77 +/- 5%). The ultrastructural changes in surfactant were associated with an increase in peak inspiratory pressure during reperfusion. In conclusion, surfactant alterations seen after I/R are not directly related to the presence of edema fluid in the alveoli. Disturbances in intraalveolar surfactant after I/R are not merely the result of inactivation due to plasma protein leakage but may instead be responsible for an increased permeability of the blood-air barrier, resulting in a vicious cycle of intraalveolar edema formation and progressing surfactant impairment.