Anti-inflammatory treatment of meconium aspiration syndrome: Benefits and risks

Meconium aspiration syndrome (MAS) is a major cause of respiratory insufficiency in the term and post-term newborns. There are several pathomechanisms participating in this disorder, particularly the airway obstruction, surfactant dysfunction, inflammation, lung edema, pulmonary vasoconstriction and bronchoconstriction. Inflammatory changes resulting from meconium aspiration cause severe impairment of lung parenchyma and surfactant, and influence the reactivity of both vascular and airway smooth muscle. Therefore, anti-inflammatory drugs may be of benefit in the management of MAS. This article reviews the pharmacological actions and side effects of various anti-inflammatory drugs used up to now in the experimental models of MAS and in the treatment of newborns with meconium aspiration.     

How to overcome surfactant dysfunction in meconium aspiration syndrome?

Surfactant dysfunction in meconium aspiration syndrome (MAS) is caused by meconium components, by plasma proteins leaking through the injured alveolocapillary membrane and by substances originated in meconium-induced inflammation. Surfactant inactivation in MAS may be diminished by several ways. Firstly, aspirated meconium should be removed from the lungs to decrease concentrations of meconium inhibitors coming into the contact with surfactant in the alveolar compartment. Once the endogenous surfactant becomes inactivated, components of surfactant should be substituted by exogenous surfactant at a sufficient dose, and surfactant administration should be repeated, if oxygenation remains compromised. To delay the inactivation by inhibitors, exogenous surfactants may be enriched with surfactant proteins, phospholipids, or other substances such as polymers. Finally, to diminish an adverse action of products of meconium-induced inflammation on both endogenous and exogenously delivered surfactant, anti-inflammatory drugs may be administered. A combined therapeutic approach may result in better outcome in patients with MAS and in lower costs of treatment.     

Meconium aspiration syndrome treatment - new approaches using old drugs

Presently, modern medicine does not offer any disease-modifying treatment for meconium aspiration syndrome (MAS). Several medications with already established safety profiles when employed for similar or other conditions could be useful for MAS treatment. N-Acetylcysteine and DNAse have the capability to reduce viscosity and thickness of meconium by breaking disulfide bonds and slicing DNA, respectively. N-Acetylcysteine, antiprotease drugs, or low pH buffer solutions may have the capability to neutralize meconium's digestive enzymes responsible for lung damage in patients with MAS. All these compounds have great potential to reduce meconium's pathogenic properties which in turn could alleviate MAS severity.     

In vitro inhibition of biophysical surface properties and change in ultrastructures of exogenous pulmonary surfactant by albumin or fibrinogen.

In order to observe the effects of serum albumin and fibrinogen on biophysical surface properties and the morphology of pulmonary surfactant in vitro, we measured the surface adsorption rate, dynamic minimum and maximum surface tension (min-, max-ST) by Pulsating Bubble Surfactometer, and demonstrated ultrastructures on a series of mixtures with varying concentrations of albumin or fibrinogen and Surfactant-TA. The albumin and fibrinogen significantly inhibited the adsorption rate and ST-lowering properties of surfactant through increasing STs of adsorption rate, min-ST, and max-ST. The characteristic morphology of the Surfactant-TA changed from lamellar rod-like structure with open ends into spherical structures with loss of their open ends by mixing with albumin or fibrinogen. These inhibitory effects of albumin and fibrinogen on surface properties of surfactant were dependent upon the increasing concentration of albumin or fibrinogen. We concluded that albumin and fibrinogen significantly altered surfactant function and its ultrastructural morphology in vitro. These findings support the concept that albumin and fibrinogen-induced surfactant dysfunction may play an important role in the pathophysiology of adult respiratory distress syndrome, and this adverse effect of albumin and fibrinogen on surfactant might be overcome by administration of large doses of exogenous surfactant.     

Regulation of platelet-activating factor synthesis in human monocytes by dipalmitoyl phosphatidylcholine

Platelet-activating factor (PAF) has a major role in inflammatory responses within the lung. This study investigates the effect of pulmonary surfactant on the synthesis of PAF in human monocytic cells. The pulmonary surfactant preparation Curosurf significantly inhibited lipopolysaccharide (LPS)-stimulated PAF biosynthesis (P<0.01) in a human monocytic cell line, Mono mac-6 (MM6), as determined by (3)H PAF scintillation-proximity assay. The inhibitory properties of surfactant were determined to be associated, at least in part, with the 1,2-dipalmitoyl phosphatidylcholine (DPPC) component of surfactant. DPPC alone also inhibited LPS-stimulated PAF biosynthesis in human peripheral blood monocytes. DPPC treatment did not affect LPS-stimulated phospholipase A(2) activity in MM6 cell lysates. However, DPPC significantly inhibited LPS-stimulated coenzyme A (CoA)-independent transacylase and acetyl CoA:lyso-PAF acetyltransferase activity. DPPC treatment of MM6 cells decreased plasma membrane fluidity as demonstrated by electron paramagnetic resonance spectroscopy coupled with spin labeling. Taken together, these findings indicate that pulmonary surfactant, particularly the DPPC component, can inhibit LPS-stimulated PAF production via perturbation of the cell membrane, which inhibits the activity of specific membrane-associated enzymes involved in PAF biosynthesis.     

Light and electron microscopic studies of the pulmonary alveolar surfactant.

22 methods of light and electron microscopy have been tested for the identification of the pulmonary alveolar surfactant. Among the non electron microscopic methods Romhányi's anisotropic staining with toluidine blue was the most serviceable. In addition to simple performance it allows the identification of the smallest alteration -- not to be identified by other methods -- of the alveolar surfactant. Among the electron microscopic technics Ruthenium Red staining and Dermer's tricomplex method yielded the best results. Given that different chemical components of the alveolar surfactant will be identified by these 2 methods they supplement each other favourably. In the study of human cadaver material Baker's phospholipid reaction and Romhányi's anisotropic toluidine blue reaction is being used.     

Two hypolipidemic peroxisome proliferators increase the number of lamellar bodies in alveolar cells type II of the rat lung

Male rats treated with either clofibrate or nafenopin, two peroxisome proliferating compounds with potent hypolipidemic properties, show identical structural changes in their lungs. In both cases, two types of lung cells were affected by these agents: (i) the alveolar epithelial cells type II and (ii) the intraalveolar macrophages. These lung cells are known to be involved in the metabolism of the pulmonary surfactant which serves to reduce the surface tension within alveoli. The size of the alveolar cells type II was conspicuously increased in the treated lungs. Compared to controls, intraalveolar macrophages apparently were slightly more numerous. Their enlarged cytoplasm was strongly vacuolated. The osmiophilic lamellar bodies within alveolar cells type II represent the intracellular presecretory pulmonary surfactant. Their number per individual alveolar cell type II was estimated by means of light microscopic morphometry on Epon-embedded semithin sections. Compared to control lungs, the number was increased by about 30% in rats treated with clofibrate (11.4 +/- 0.5 lamellar inclusions in the control cells; P less than 0.001). The increase in the number of lamellar bodies per type II cell was close to 60% in animals fed the nafenopin diet. In contrast the frequency of alveolar cells type II, estimated per area of lung tissue, remained unchanged. These results demonstrate that clofibrate and nafenopin, two drugs with hypolipidemic properties, cause identical structural changes in the rodent lung. It is concluded from these data that (i) the morphological changes observed in the surfactant metabolizing cells represent a specific action of hypolipidemic agents at the lungs and (ii) hypolipidemic peroxisome proliferators influence the metabolism of the pulmonary surfactant.     

Meconium aspiration syndrome induces complement-associated systemic inflammatory response in newborn piglets

The pathophysiology of meconium aspiration syndrome (MAS) is complex. We recently showed that meconium is a potent activator of complement. In the present study, we investigated whether the complement activation occurring in experimental MAS is associated with a systemic inflammatory response as judged by granulocyte activation and cytokine and chemokine release. MAS was induced by the instillation of meconium into the lungs of newborn piglets (n = 8). Control animals (n = 5) received saline under otherwise identical conditions. Haemodynamic and lung dynamic data were recorded. Complement activation, revealed by the terminal sC5b-9 complex (TCC), and cytokines [interleukin (IL)-6 and IL-8] were measured in plasma samples by enzyme immunoassays. The expression of CD18, CD11b and oxidative burst in granulocytes was measured in whole blood by flow cytometry. Plasma TCC increased rapidly in the MAS animals in contrast with controls (P < 0.0005). The TCC concentration correlated closely with oxygenation index (r = 0.48, P < 0.0005) and ventilation index (r = 0.57, P < 0.0005) and inversely with lung compliance (r = -0.63, P < 0.0005). IL-6 and IL-8 increased in MAS animals compared with the controls (P = 0.002 and P < 0.001, respectively). Granulocyte oxidative burst declined significantly in the MAS animals compared with the controls (P < 0.02). TCC correlated significantly with IL-6 (r = 0.64, P < 0.0005) and IL-8 (r = 0.32; P = 0.03) and inversely with oxidative burst (r = -0.37; P = 0.02). A systemic inflammatory response associated with complement activation is seen in experimental MAS. This reaction may contribute to the pathogenesis of MAS.     

Scanning electron microscopic study of capillary change in bleomycin-induced pulmonary fibrosis.

The architectural changes which occur in the capillaries are difficult to illustrate without a three-dimensional tool, such as scanning electron microscopy. Therefore, a scanning electron microscopic study was occasionally undertaken to show the capillary changes of lung fibrosis. Fibrosis was induced in twenty rats by an intratracheal injection of bleomycin. After 30 days the rats were sacrificed, and light microscopy and scanning electron microscopy were performed. The vascular trees of both lungs were cast with methacrylate. Light microscopically, the pulmonary fibrosis was patchy and inflammatory cell infiltration was rather sparse. Scanning electron microscopically, the intercapillary spaces became wider; and some capillaries revealed large irregular dilatation. The pleural and alveolar capillaries were variably dilated. The pleural capillary diameter was increased (P = 0.06), and the capillary plexus diameter was decreased (P = 0.00). Distance between the capillary branches of the pleural surface was increased (P = 0.06). The appearance of irregularly shaped capillaries, an increase in diameter with variable dilatation of alveolar capillary rings and a decrease in branching between the capillaries, resulting in a loss of surface area are the main scanning electron microscopic findings of the remodeling which occurs pulmonary capillaries in bleomycin-induced pulmonary fibrosis.     

The effect of dextran to restore the activity of pulmonary surfactant inhibited by albumin

Pulmonary surfactant is crucial to maintain the proper functioning of the respiration system. Certain types of blood proteins (e.g. albumin) were found to inhibit the activity of pulmonary surfactant. Axisymmetric Drop Shape Analysis (ADSA) was used to study the effect of dextran to restore the activity of an albumin-inhibited pulmonary surfactant. It was found that dextran could effectively restore surface tension properties of the inhibited surfactant in vitro. Furthermore, dextran improved the performance of pulmonary surfactants when albumin was absent. It was found that when a surfactant film was under high compression (e.g. above 70% surface area reduction), the presence of dextran increased film stability, so that the film could sustain high surface pressures without being collapsing.     

Amiodarone lung toxicity in a cardiac transplant candidate initially diagnosed by fine-needle aspiration: cytologic, histologic, and electronmicroscopic findings

A cardiac transplant candidate with ischemic cardiomyopathy developed bilateral small parenchymal opacities in lower lobes of the lung. A fine-needle aspiration (FNA) was performed that revealed changes characteristic of amiodarone toxicity. Subsequently performed lung biopsies and electron microscopic studies confirmed the initial FNA diagnosis. The patient has been successfully transplanted with marked improvement in his clinical findings. This is the first case of amiodarone lung toxicity where the diagnosis was initially suggested based on the FNA findings. We also describe the clinical, cytological, histological, and electron microscopic (EM) findings of amiodarone-related pulmonary toxicity and provide a review of the literature.     

ECMO for meconium aspiration syndrome: support for relaxed entry criteria

We compared the morbidity of patients with meconium aspiration syndrome (MAS) with that in patients with all other respiratory conditions treated with extracorporeal membrane oxygenation (ECMO) (no MAS). If ECMO for MAS was associated with a lower complication rate, then relaxed ECMO entry criteria could be considered. A retrospective review was performed of all patients in the national extracorporeal life support (ELSO) registry from 1989 to 2004. Complications were divided into mechanical, hematologic, neurologic, renal, pulmonary, cardiovascular, infectious, and metabolic categories. MAS and no-MAS patients were divided into veno-venous (VV) or veno-arterial (VA) ECMO categories, based on mode of ECMO used, and number of complications per patient in each category was determined. Statistical significance was determined by Chi-square test. A total of 1587 patients (700 MAS, 887 no MAS) on VV ECMO and 2723 (572 MAS, 2151 no MAS) on VA ECMO were identified with a total of 2415 complications in MAS and 9550 in no-MAS patients. Overall, MAS patients had a significantly lower number of complications per patient in each category versus no-MAS patients. These results indicate that regardless of type of ECMO, there are fewer complications on ECMO in MAS versus no-MAS patients. These data support the consideration of relaxed ECMO entry criteria for MAS.     

Disruption of the klotho gene causes pulmonary emphysema in mice. Defect in maintenance of pulmonary integrity during postnatal life

Homozygous mutant klotho (KL(-/-)) mice exhibit multiple phenotypes resembling human aging. In the present study, we focused on examining the pathology of the lungs of klotho mice and found that it closely resembled pulmonary emphysema in humans both histologically and functionally. Histology of the lung of KL(-/-) mice was indistinguishable from those of wild-type littermates up to 2 wk of age. The first histologic changes appeared at 4 wk of age, showing enlargement of the air spaces accompanied by destruction of the alveolar walls, and progressed gradually with age. In addition to these changes, we observed calcium deposits in type I collagen fibers in alveolar septa and degeneration of type II pneumocytes in 8- to 10-wk-old KL(-/-) mice. Pulmonary function tests revealed prolonged expiration time in KL(-/-) mice, which is comparable with the pathophysiology of pulmonary emphysema. The expression level of messenger RNA for type IV collagen, surfactant protein-A and mitochondrial beta-adenosine triphosphatase was significantly increased in KL(-/-) mice, which may represent a compensatory response to alveolar destruction. Additionally, the heterozygous mutant klotho mice also developed pulmonary emphysema late in life, around 120 wk of age. These findings indicate that klotho gene expression is essential to maintaining pulmonary integrity during postnatal life. The klotho mutant mouse is a useful laboratory animal model for examining the relationship between aging and pulmonary emphysema.     

Pulmonary responses to atmospheric pollutants. I: an ultrastructural study of fibrosing alveolitis evoked by petrol vapour.

Rats exposed to an atmosphere contaminated with petrol vapour at a concentration of 100 parts per million for up to 12 weeks exhibit a high incidence of electron microscopic changes in the lung parenchyma characterized by interstitial fibrosis with associated alveolar collapse. Initial changes appearing after 6 weeks include degeneration of endothelium and interstitial fibroblasts followed by hypertrophy of Type 2 pneumocytes. Subsequent degeneration of surfactant organelles of the hypertrophied Type 2 pneumocytes correlates with the appearance of focal alveolar collapse and associated interstitial fibrosis. Because of the rapidity with which lesions are induced in the rat lung, this experimental technique provides an economical and reproducible model for an integrated study of the sequential morphological and biochemical events preceding pulmonary fibrosis which might well lead to a better understanding of the enigmatic human syndrome of fibrosing alveolitis.     

Morpho-functional changes of surfactant system in pulmonary tuberculosis

A complex study of different cellular and extracellular surfactant elements in the dynamics of the spontaneous course of generalized tuberculosis was made in 240 guinea-pigs and 77 patients with different forms of active pulmonary tuberculosis by using electron microscopy, biochemistry, and physical chemistry. A diagnostic scheme was proposed for life-time assessment of surfactant in bronchoalveolar lavage specimens. Three degrees of changes in surfactant were identified; 1) adaptive rearrangement of its elements developing in local surfactant damages; 2) significantly impaired type 2 alveolocyte production of surfactant, which affects its biochemical composition and capacity of forming characteristic structures; 3) common morphological, biochemical, surface-active signs of surfactant decompensation, profound metabolic disturbances, alveolar epithelial destruction with cleared alveolocytes found in the lavage.     

The surfactant system of the adult lung: physiology and clinical perspectives

Summary Pulmonary surfactant is synthesized and secreted by alveolar type II cells and constitutes an important component of the alveolar lining fluid. It comprises a unique mixture of phospholipids and surfactant-specific proteins. More than 30 years after its first biochemical characterization, knowledge of the composition and functions of the surfactant complex has grown considerably. Its classically known role is to decrease surface tension in alveolar air spaces to a degree that facilitates adequate ventilation of the peripheral lung. More recently, other important surfactant functions have come into view. Probably most notable among these, surfactant has been demonstrated to enhance local pulmonary defense mechanisms and to modulate immune responses in the alveolar milieu. These findings have prompted interest in the role and the possible alterations of the surfactant system in a variety of lung diseases and in environmental impacts on the lung. However, only a limited number of studies investigating surfactant changes in human lung disease have hitherto been published. Preliminary results suggest that surfactant analyses, e.g., from bronchoalveolar lavage fluids, may reveal quantitative and qualitative abnormalities of the surfactant system in human lung disorders. It is hypothesized that in the future, surfactant studies may become one of our clinical tools to evaluate the activity and severity of peripheral lung diseases. In certain disorders they may also gain diagnostic significance. Further clinical studies will be necessary to investigate the potential therapeutic benefits of surfactant substitution and the usefulness of pharmacologic manipulation of the secretory activity of alveolar type II cells in pulmonary medicine.Abbreviations PC phospatidyleholine - DPPC dipalmitoylphosphatidylcholine - PG phosphatidylglycerol - PI phosphatidylinositol - SP-A, SP-B SP-C, SP-D surfactant-specific proteins A, B, C, and D - ARDS adult respiratory distress syndrome - IRDS infant respiratory distress syndrome - BAL bronchoalveolar lavage - IPF idiopathic pulmonary fibrosis - HP hypersensitivity pneumonitis - DIPD drug-induced pulmonary disease     

Changes in Morphology and Cellular Replacement of Surface Epithelia in Human Gastric Mucosa Affected by Different Pathological Changes: A Scanning Electron Microscopical Study of Human Gastric Biopsy Material

The surface epithelium of normal gastric mucosa shows a constant turnover, migrating from the proliferation zone at the neck of the gastric glands to the mucosal surface. The cytologic changes associated with the concomitant cellular differentiation were so far studied in sections by light and electron microscopy only. With these methods neither the changes of surface morphology associated with cellular maturation nor the shedding of surface epithelia can be recorded. With the scanning electron microscope it is possible to study especially these changes of the mucosal surface plus those of the single surface epithelia over a wide range of magnification and with a sufficient depth of focus.In this study therefore an attempt was made to correlate some scanning electron microscopic findings concerning these changes of mucosal and cellular surface with the results of parallel light microscopic examinations. For this purpose double biopsies of human gastric mucosa were taken during routine endoscopic examination. One of these biopsies was processed for light microscopic examination after formaldehyde fixation. The other was fixed in buffered glutaraldehyde solution and 1 % OS04 solution and thereafter the material was processed for scanning electron microscopic study by dehydration against an increasing acetone gradient, critical point drying and sputter coating of the dry specimens which were mounted on metal stubs with conductive silver.Some aspects of surface morphology of the mucosa and the single cells in correlation to different types of gastritis are demonstrated and the morphological expressions of cytological degeneration and shedding from the mucosal surface are commented on.     

Enterobacter agglomerans lipopolysaccharide-induced changes in pulmonary surfactant as a factor in the pathogenesis of byssinosis.

Lipopolysaccharide (LPS) from Enterobacter agglomerans and pulmonary surfactant mixtures were centrifuged in discontinuous sucrose gradients to determine whether LPS bound to surfactant and examined in a Langmuir trough with a Wilhelmy balance to determine whether LPS altered the surface activity of surfactant. The LPS was found to bind to the surfactant and altered its surface tension properties. The binding of LPS to surfactant in the lung may change the physiological properties of surfactant and be a possible mechanism for the pathogenesis of byssinosis.     

Influence of serum protein and albumin addition on the structure and activity of an exogenous pulmonary surfactant

The comparative analysis of the deleterious action of albumin and total serum proteins (SP) might help to understand the nature of the interaction surfactant--SP. This study evaluated the effects of serum proteins and albumin on bulk shear viscosity, surface tension, surface area reduction, and the ratio between the light and heavy subtypes of surfactant suspensions. Our results showed a correlation between the bulk viscosity and aggregation degree of surfactant suspensions. The addition of albumin or SP induced the transformation from the heavy to the light subtype, reducing the viscosity. SP caused disaggregation and inactivation, whereas albumin caused only disaggregation without loss of surface activity. When SP were removed, the heavy fraction obtained recovered its surface activity. We conclude that the disaggregation may not be the primary cause for the loss of surface activity. Surfactant inactivation by a serum component, different from albumin, would be probably due to a physical interaction, a phenomenon that is reversed when SP are removed.     

Identification of a cell membrane protein that binds alveolar surfactant.

Alveolar surfactants are complex mixtures of proteins and phospholipids produced by type II alveolar cells and responsible for lowering pulmonary surface tension. The process by which surfactant is produced and exported and by which its production by pulmonary cells is regulated are not well understood. This study was designed to identify a cellular receptor for surfactant constituents. To do so, monoclonal anti-idiotypic antibodies directed against antibodies to porcine and rabbit surfactant proteins were prepared. These monoclonal anti-idiotypic antibodies bind both alveolar lining and bronchial epithelial cells in rabbit, porcine, and human lungs. Macrophages and other nonepithelial cells do not react with these antibodies. Western blot analysis indicates that both A2R and A2C recognize the same proteins in both pig and rabbit lungs: a 30-kd protein and additional proteins at 52 and 60 kd. Preincubating lung wash cells with A2C or A2R prevents binding of porcine or rabbit surfactant preparations, respectively, by these cells. Preincubating frozen sections of lung tissue with surfactant inhibits binding of A2R and A2C to the lung. Antibody directed to a cell membrane protein that recognizes alveolar surfactant may be useful in elucidating the structure and function of this receptor and in understanding the cellular physiology and pathophysiology of the surfactant system.