Pre-ischaemic exogenous surfactant reduces pulmonary injury in rat ischaemia/reperfusion

Mechanistic Understanding of Lung Inflammation: Recent Advances and Emerging Techniques

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury characterized by an acute inflammatory response in the lung parenchyma. Hence, it is considered as the most appropriate clinical syndrome to study pathogenic mechanisms of lung inflammation. ARDS is associated with increased morbidity and mortality in the intensive care unit (ICU), while no effective pharmacological treatment exists. It is very important therefore to fully characterize the underlying pathobiology and the related mechanisms, in order to develop novel therapeutic approaches. In vivo and in vitro models are important pre-clinical tools in biological and medical research in the mechanistic and pathological understanding of the majority of diseases. In this review, we will present data from selected experimental models of lung injury/acute lung inflammation, which have been based on clinical disorders that can lead to the development of ARDS and related inflammatory lung processes in humans, including ventilation-induced lung injury (VILI), sepsis, ischemia/reperfusion, smoke, acid aspiration, radiation, transfusion-related acute lung injury (TRALI), influenza, Streptococcus (S.) pneumoniae and coronaviruses infection. Data from the corresponding clinical conditions will also be presented. The mechanisms related to lung inflammation that will be covered are oxidative stress, neutrophil extracellular traps, mitogen-activated protein kinase (MAPK) pathways, surfactant, and water and ion channels. Finally, we will present a brief overview of emerging techniques in the field of omics research that have been applied to ARDS research, encompassing genomics, transcriptomics, proteomics, and metabolomics, which may recognize factors to help stratify ICU patients at risk, predict their prognosis, and possibly, serve as more specific therapeutic targets.

Surfactant therapy in lung transplantation: A systematic review and meta-analysis

BACKGROUND

Despite numerous reports demonstrating the efficacy of exogenous surfactant therapy during lung transplantation, this strategy remains absent in routine clinical use. Here, we systematically review and meta-analyze the effect of exogenous surfactant on respiratory pathophysiological variables during lung transplantation.

METHODS

To identify relevant clinical and pre-clinical studies, we performed an electronic search of MEDLINE, EMBASE, and Cochrane CENTRAL from inception to June 11, 2021. In addition, research-in-progress databases were searched. Randomized and non-randomized adult and pediatric clinical studies and animal experiments that compared the use of surfactant for lung transplantation with a control group were included. The primary outcome was the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO₂/FiO₂ ratio).

RESULTS

From 1,041 citations, we identified 35 studies, of which 6 were clinical studies and 29 were pre-clinical. Thirty-two studies were included in the quantitative analysis. The administration of surfactant therapy during clinical lung transplantation significantly improved PaO₂/FiO₂ ratio in recipients (mean difference [MD] 93 mmHg, 95% confidence interval [CI] 25-160 mmHg, p < 0.01). Similar results were seen in pre-clinical settings (MD 201 mmHg, 95% CI 145-256 mmHg, p < 0.01). Moreover, surfactant benefited a range of important physiologic and biologic outcomes after preclinical lung transplantation. The overall certainty of evidence was very low.

CONCLUSIONS

Exogenous surfactant therapy improves post-transplant lung function; however, its effects on clinical outcomes remain uncertain. High-quality randomized controlled trials are needed to determine whether the physiologic benefits of surfactant therapy affect patient-important outcomes in lung transplant recipients.

Mechanical ventilation-induced alterations of intracellular surfactant pool and blood-gas barrier in healthy and pre-injured lungs

Mechanical ventilation triggers the manifestation of lung injury and pre-injured lungs are more susceptible. Ventilation-induced abnormalities of alveolar surfactant are involved in injury progression. The effects of mechanical ventilation on the surfactant system might be different in healthy compared to pre-injured lungs. In the present study, we investigated the effects of different positive end-expiratory pressure (PEEP) ventilations on the structure of the blood–gas barrier, the ultrastructure of alveolar epithelial type II (AE2) cells and the intracellular surfactant pool (= lamellar bodies, LB). Rats were randomized into bleomycin-pre-injured or healthy control groups. One day later, rats were either not ventilated, or ventilated with PEEP = 1 or 5 cmH₂O and a tidal volume of 10 ml/kg bodyweight for 3 h. Left lungs were subjected to design-based stereology, right lungs to measurements of surfactant proteins (SP−) B and C expression. In pre-injured lungs without ventilation, the expression of SP-C was reduced by bleomycin; while, there were fewer and larger LB compared to healthy lungs. PEEP = 1 cmH₂O ventilation of bleomycin-injured lungs was linked with the thickest blood–gas barrier due to increased septal interstitial volumes. In healthy lungs, increasing PEEP levels reduced mean AE2 cell size and volume of LB per AE2 cell; while in pre-injured lungs, volumes of AE2 cells and LB per cell remained stable across PEEPs. Instead, in pre-injured lungs, increasing PEEP levels increased the number and decreased the mean size of LB. In conclusion, mechanical ventilation-induced alterations in LB ultrastructure differ between healthy and pre-injured lungs. PEEP = 1 cmH₂O but not PEEP = 5 cmH₂O ventilation aggravated septal interstitial abnormalities after bleomycin challenge.

Cellular and acellular ex vivo lung perfusion preserve functional lung ultrastructure in a large animal model: a stereological study

Background

Ex vivo lung perfusion (EVLP) is used by an increasing number of transplant centres. It is still controversial whether an acellular or cellular (erythrocyte enriched) perfusate is preferable. The aim of this paper was to evaluate whether acellular (aEVLP) or cellular EVLP (cEVLP) preserves functional lung ultrastructure better and to generate a hypothesis regarding possible underlying mechanisms.

Methods

Lungs of 20 pigs were assigned to 4 groups: control, ischaemia (24 h), aEVLP and cEVLP (both EVLP groups: 24 h ischaemia + 12 h EVLP). After experimental procedures, whole lungs were perfusion fixed, samples for light and electron microscopic stereology were taken, and ventilation, diffusion and perfusion related parameters were estimated.

Results

Lung structure was well preserved in all groups. Lungs had less atelectasis and higher air content after EVLP. No significant group differences were found in alveolar septum composition or blood-air barrier thickness. Small amounts of intraalveolar oedema were detected in both EVLP groups but significantly more in aEVLP than in cEVLP.

Conclusions

Both EVLP protocols supported lungs well for up to 12 h and could largely prevent ischaemia ex vivo reperfusion associated lung injury. In both EVLP groups, oedema volume remained below the level of functional relevance. The group difference in oedema formation was possibly due to inferior septal perfusion in aEVLP.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0942-5) contains supplementary material, which is available to authorized users.

Unbiased Quantitation of Alveolar Type II to Alveolar Type I Cell Transdifferentiation during Repair after Lung Injury in Mice

The alveolar epithelium consists of squamous alveolar type (AT) I and cuboidal ATII cells. ATI cells cover 95-98% of the alveolar surface, thereby playing a critical role in barrier integrity, and are extremely thin, thus permitting efficient gas exchange. During lung injury, ATI cells die, resulting in increased epithelial permeability. ATII cells re-epithelialize the alveolar surface via proliferation and transdifferentiation into ATI cells. Transdifferentiation is characterized by down-regulation of ATII cell markers, up-regulation of ATI cell markers, and cell spreading, resulting in a change in morphology from cuboidal to squamous, thus restoring normal alveolar architecture and function. The mechanisms underlying ATII to ATI cell transdifferentiation have not been well studied in vivo. A prerequisite for mechanistic investigation is a rigorous, unbiased method to quantitate this process. Here, we used SPCCreERT2;mTmG mice, in which ATII cells and their progeny express green fluorescent protein (GFP), and applied stereologic techniques to measure transdifferentiation during repair after injury induced by LPS. Transdifferentiation was quantitated as the percent of alveolar surface area covered by ATII-derived (GFP⁺) cells expressing ATI, but not ATII, cell markers. Using this methodology, the time course and magnitude of transdifferentiation during repair was determined. We found that ATI cell loss and epithelial permeability occurred by Day 4, and ATII to ATI cell transdifferentiation began by Day 7 and continued until Day 16. Notably, transdifferentiation and barrier restoration are temporally correlated. This methodology can be applied to investigate the molecular mechanisms underlying transdifferentiation, ultimately revealing novel therapeutic targets to accelerate repair after lung injury.

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.

Aging exacerbates acute lung injury-induced changes of the air-blood barrier, lung function, and inflammation in the mouse

Acute lung injury (ALI) is characterized by hypoxemia, enhanced permeability of the air-blood barrier, and pulmonary edema. Particularly in the elderly, ALI is associated with increased morbidity and mortality. The reasons for this, however, are poorly understood. We hypothesized that age-related changes in pulmonary structure, function, and inflammation lead to a worse prognosis in ALI. ALI was induced in young (10 wk old) and old (18 mo old) male C57BL/6 mice by intranasal application of 2.5 mg lipopolysaccharide (LPS)/kg body wt or saline (control mice). After 24 h, lung function was assessed, and lungs were either processed for stereological or inflammatory analysis, such as bronchoalveolar lavage fluid (BALF) cytometry and qPCR. Both young and old mice developed severe signs of ALI, including alveolar and septal edema and enhanced inflammatory BALF cells. However, the pathology of ALI was more pronounced in old compared with young mice with nearly sixfold higher BALF protein concentration, twice the number of neutrophils, and significantly higher expression of neutrophil chemokine Cxcl1, adhesion molecule Icam-1, and metalloprotease-9, whereas the expression of tight junction protein occludin significantly decreased. The old LPS mice had thicker alveolar septa attributable to higher volumes of interstitial cells and extracellular matrix. Tissue resistance and elastance reflected observed changes at the ultrastructural level in the lung parenchyma in ALI of young and old mice. In summary, the pathology of ALI with advanced age in mice is characterized by a greater neutrophilic inflammation, leakier air-blood barrier, and altered lung function, which is in line with findings in elderly patients.

Using electron microscopes to look into the lung

In the nineteenth century, there was a dispute about the existence of a lung alveolar epithelium which remained unsolved until the invention of electron microscopy (EM) and its application to the lung. From the early 1960s, Ewald Weibel became the master of lung EM. He showed that the alveolar epithelium is covered with a lining layer containing surfactant. Weibel also explained the phenomenon of "non-nucleated plates" observed already in 1881 by Albert Kölliker. Weibel's most significant contribution was to the development of stereological methods. Therefore, quantitative characterization of lung structure revealing structure-function relationships became possible. Today, the spectrum of EM methods to study the fine structure of the lung has been extended significantly. Cryo-preparation techniques are available which are necessary for immunogold labeling of molecules. Energy-filtering techniques can be used for the detection of elements. There have also been major improvements in stereology, thus providing a very versatile toolbox for quantitative lung phenotype analyses. A new dimension was added by 3D EM techniques. Depending on the desired sample size and resolution, the spectrum ranges from array tomography via serial block face scanning EM and focused ion beam scanning EM to electron tomography. These 3D datasets provide new insights into lung ultrastructure. Biomedical EM is an ever-developing field. Its high resolution remains unparalleled. Moreover, EM has the unique advantage of providing an "open view" into cells and tissues within their full architectural context. Therefore, EM will remain an indispensable tool for a better understanding of the lung's functional design.

A review of recent developments and applications of morphometry/stereology in lung research

Design-based stereology is the gold standard of morphometry in lung research. Here, we analyze the current use of morphometric and stereological methods in lung research and provide an overview on recent methodological developments and biological observations made by the use of stereology. Based on this analysis we hope to provide useful recommendations for a good stereological practice to further the use of advanced and unbiased stereological methods.

Evaluating acellular versus cellular perfusate composition during prolonged ex vivo lung perfusion after initial cold ischaemia for 24 hours

Normothermic ex vivo lung perfusion (EVLP) has developed as a powerful technique to evaluate particularly marginal donor lungs prior to transplantation. In this study, acellular and cellular perfusate compositions were compared in an identical experimental setting as no consensus has been reached on a preferred technique yet. Porcine lungs underwent EVLP for 12 h on the basis of an acellular or a cellular perfusate composition after 24 h of cold ischaemia as defined organ stress. During perfusion, haemodynamic and respiratory parameters were monitored. After EVLP, the lung condition was assessed by light and transmission electron microscopy. Aerodynamic parameters did not show significant differences between groups and remained within the in vivo range during EVLP. Mean oxygenation indices were 491 ± 39 in the acellular group and 513 ± 53 in the cellular group. Groups only differed significantly in terms of higher pulmonary artery pressure and vascular resistance in the cellular group. Lung histology and ultrastructure were largely well preserved after prolonged EVLP and showed only minor structural alterations which were similarly present in both groups. Prolonged acellular and cellular EVLP for 12 h are both feasible with lungs prechallenged by ischaemic organ stress. Physiological and ultrastructural analysis showed no superiority of either acellular or cellular perfusate composition.

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.

Controlled lung reperfusion to reduce pulmonary ischaemia/reperfusion injury after cardiopulmonary bypass in a porcine model

OBJECTIVES

Ischaemia/reperfusion (I/R) injury of the lungs contributes to pulmonary dysfunction after cardiac surgery with cardiopulmonary bypass (CPB), leading to increased morbidity and mortality of patients. This study investigated the value of controlled lung reperfusion strategies on lung ischaemia-reperfusion injury in a porcine CPB model.

METHODS

Pigs were subjected to routine CPB for 120 min with 60 min of blood cardioplegic cardiac arrest (CCA). Following CCA, the uncontrolled reperfusion (UR, n = 6) group was conventionally weaned from CPB. Two groups underwent controlled lung reperfusion strategies (CR group: controlled reperfusion conditions, n = 6; MR group: controlled reperfusion conditions and modified reperfusate, n = 6) via the pulmonary artery before CPB weaning. Sham-operated pigs (n = 7) served as controls. Animals were followed up until 4 h after CPB. Pulmonary function, haemodynamics, markers of inflammation, endothelial injury and oxidative stress as well as morphological lung alterations were analysed.

RESULTS

CPB (UR group) induced deterioration of pulmonary function (lung mechanics, oxygenation index and lung oedema). Also, controlled lung reperfusion groups (CR and MR) presented with pulmonary dysfunction after CPB. However, compared with UR, controlled lung reperfusion strategies (CR and MR) improved lung mechanics and reduced markers of oxidative stress, but without alteration of haemodynamics, oxygenation, inflammation, endothelial injury and lung morphology. Both controlled reperfusion groups were similar without relevant differences.

CONCLUSION

Controlled lung reperfusion strategies attenuated a decrease in lung mechanics and an increase in oxidative stress, indicating an influence on CPB-related pulmonary injury. However, they failed to avoid completely CPB-related lung injury, implying the need for additional strategies given the multifactorial pathophysiology of postoperative pulmonary dysfunction.

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.

Alterations of mouse lung tissue dimensions during processing for morphometry: a comparison of methods

Preservation of original tissue dimensions is an essential prerequisite for morphometric studies. Shrinkage occurring during tissue processing for histology may severely influence the appearance of structures seen under the microscope and stereological calculations. Therefore, shrinkage has to be avoided so that estimates obtained by application of unbiased stereology are indeed unbiased. The present study investigates the alterations of tissue dimensions of mouse lung samples during processing for histology. Different fixatives as well as embedding protocols are considered. Mouse lungs were fixed by instillation of either 4% formalin or a mixture of 1.5% glutaraldehyde/1.5% formaldehyde. Tissue blocks were sampled according to principles of stereology for embedding in paraffin, glycol methacrylate without treatment with osmium tetroxide and uranyl acetate, and glycol methacrylate including treatment with osmium tetroxide and uranyl acetate before dehydration. Shrinkage was investigated by stereological measurements of dimensional changes of tissue cut faces. Results show a shrinkage of the cut face areas of roughly 40% per lung during paraffin embedding, 30% during "simple" glycol methacrylate embedding, and <3% during osmium tetroxide/uranyl acetate/glycol methacrylate embedding. Furthermore, the superiority of the glutaraldehyde-containing fixative regarding shrinkage is demonstrated. In conclusion, the use of a glutaraldehyde-containing fixative and embedding in glycol methacrylate with previous treatment of the samples with osmium tetroxide and uranyl acetate before dehydration is recommended for stereological studies of the mouse lung.

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.

Therapeutic effect of surfactant inhalation during warm ischemia in an isolated rat lung perfusion model

Warm ischemia-reperfusion injury related to donation after cardiac death donors is a crucial and inevitable issue. As surfactant function is known to deteriorate during warm ischemia, we hypothesized that surfactant inhalation during warm ischemia would mitigate warm ischemia-reperfusion injury. We used an isolated rat lung perfusion model. The rats were divided into three groups: sham, control, and surfactant. In the control and surfactant groups, cardiac arrest was induced by ventricular fibrillation. Ventilation was restarted 110 min later; subsequently, the lungs were flushed, and heart and lung block was recovered. In the surfactant group, a natural bovine surfactant Surfacten(®) was inhaled for 3 min at the end of warm ischemia. Then, the lungs were reperfused for 80 min. Surfactant inhalation significantly improved graft functions, effectively increased lung tissue ATP levels, and significantly decreased mRNA levels of IL-6 and IL-6/IL-10 ratio at the end of reperfusion. Histologically, lungs in the surfactant group showed fewer signs of interstitial edema and hemorrhage, and significantly less neutrophilic infiltration than those in the control group. Our results indicated that surfactant inhalation in the last phase of warm ischemia maintained lung tissue energy levels and prevented cytokine production, resulting in the alleviation of warm ischemia-reperfusion injury.

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.