Lung surfactant and pulmonary toxicology

Avian surfactant protein (SP)-A2 first arose in an early tetrapod before the divergence of amphibians and gradually lost the collagen domain

The air-liquid interface of the mammalian lung is lined with pulmonary surfactants, a mixture of specific proteins and lipids that serve a dual purpose-enabling air-breathing and protection against pathogens. In mammals, surfactant proteins A (SP-A) and D (SP -D) are involved in innate defence of the lung. Birds seem to lack the SP-D gene, but possess SP-A2, an additional SP-A-like gene. Here we investigated the evolution of the SP-A and SP-D genes using computational gene prediction, homology, simulation modelling and phylogeny with published avian and other vertebrate genomes. PCR was used to confirm the identity and expression of SP-A analogues in various tissue homogenates of zebra finch and turkey. In silico analysis confirmed the absence of SP-D-like genes in all 47 published avian genomes. Zebra finch and turkey SP-A1 and SP-A2 sequences, confirmed by PCR of lung homogenates, were compared with sequenced and in silico predicted vertebrate homologs to construct a phylogenetic tree. The collagen domain of avian SP-A1, especially that of zebra finch, was dramatically shorter than that of mammalian SP-A. Amphibian and reptilian genomes also contain avian-like SP-A2 protein sequences with a collagen domain. NCBI Gnomon-predicted avian and alligator SP-A2 proteins all lacked the collagen domain completely. Both avian SP-A1 and SP-A2 sequences form separate clades, which are most closely related to their closest relatives, the alligators. The C-terminal carbohydrate recognition domain (CRD) of zebra finch SP-A1 was structurally almost identical to that of rat SP-A. In fact, the CRD of SP-A is highly conserved among all the vertebrates. Birds retained a truncated version of mammalian type SP-A1 as well as a non-collagenous C-type lectin, designated SP-A2, while losing the large collagenous SP-D lectin, reflecting their evolutionary trajectory towards a unidirectional respiratory system. In the context of zoonotic infections, how these evolutionary changes affect avian pulmonary surface protection is not clear.

Ozone protects the rat lung from ischemia-reperfusion injury by attenuating NLRP3-mediated inflammation, enhancing Nrf2 antioxidant activity and inhibiting apoptosis

Ischemia-reperfusion injury (IRI) is a major cause of lung dysfunction during cardiovascular surgery, heart transplantation and cardiopulmonary bypass procedures, and the inflammatory response, oxidative stress, and apoptosis play key and allegedly maladaptive roles in its pathogenesis. The aim of this study was to initially elucidate whether ozone induces oxidative preconditioning by activating nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and secondly to determine whether ozone oxidative preconditioning (OzoneOP) protects the lung from IRI by attenuating nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3)-mediated inflammation, enhancing the antioxidant activity of Nrf2 and inhibiting apoptosis. Rats treated with or without OzoneOP (2 ml containing 100 µg/kg/day) were subjected to 1 h of lung ischemia followed by 2 h of reperfusion for 10 days. Lung damage, antioxidant capacity, inflammation and apoptosis were evaluated and compared among different groups after reperfusion. OzoneOP significantly ameliorated changes in lung morphology and protected the lung from IRI by attenuating oxidative stress, inflammation-induced injury and lung apoptosis. Moreover, OzoneOP increased the expression of Nrf2 and decreased the levels of NLRP3, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), un-cleavable cysteine-requiring aspartate protease-1 (procaspase-1), cysteine-requiring aspartate protease-1 (caspase-1) and interleukin-1β (IL-1β) in the rat lungs. In summary, these results provide new insights into the molecular events modulated by ozone and suggest that ozone therapy may be an integrative support for patients with lung IRI.

Physicochemical studies of direct interactions between lung surfactant and components of electronic cigarettes liquid mixtures

Direct physicochemical interactions between the major components of electronic cigarette liquids (e-liquids): glycerol (VG) and propylene glycol (PG), and lung surfactant (LS) were studied by determining the dynamic surface tension under a simulated breathing cycle using drop shape method. The studies were performed for a wide range of concentrations based on estimated doses of e-liquid aerosols (up to 2500 × the expected nominal concentrations) and for various VG/PG ratios. The results are discussed as relationships among mean surface tension, surface tension amplitude, and surface rheological properties (dilatational elasticity and viscosity) versus concentration and composition of e-liquid. The results showed that high local concentrations (>200 × higher than the estimated average dose after a single puffing session) may induce measurable changes in biophysical activity of LS; however, only ultra-high e-liquid concentrations inactivated the surfactant. Physiochemical characterization of e-liquids provide additional insights for the safety assessment of electronic nicotine delivery systems (ENDS).

Effect of ozone oxidative preconditioning in preventing early radiation-induced lung injury in rats

Ionizing radiation causes its biological effects mainly through oxidative damage induced by reactive oxygen species. Previous studies showed that ozone oxidative preconditioning attenuated pathophysiological events mediated by reactive oxygen species. As inhalation of ozone induces lung injury, the aim of this study was to examine whether ozone oxidative preconditioning potentiates or attenuates the effects of irradiation on the lung. Rats were subjected to total body irradiation, with or without treatment with ozone oxidative preconditioning (0.72 mg/kg). Serum proinflammatory cytokine levels, oxidative damage markers, and histopathological analysis were compared at 6 and 72 h after total body irradiation. Irradiation significantly increased lung malondialdehyde levels as an end-product of lipoperoxidation. Irradiation also significantly decreased lung superoxide dismutase activity, which is an indicator of the generation of oxidative stress and an early protective response to oxidative damage. Ozone oxidative preconditioning plus irradiation significantly decreased malondialdehyde levels and increased the activity of superoxide dismutase, which might indicate protection of the lung from radiation-induced lung injury. Serum tumor necrosis factor alpha and interleukin-1 beta levels, which increased significantly following total body irradiation, were decreased with ozone oxidative preconditioning. Moreover, ozone oxidative preconditioning was able to ameliorate radiation-induced lung injury assessed by histopathological evaluation. In conclusion, ozone oxidative preconditioning, repeated low-dose intraperitoneal administration of ozone, did not exacerbate radiation-induced lung injury, and, on the contrary, it provided protection against radiation-induced lung damage.

Harmful health effects of cigarette smoking

This is a comprehensive review on the harmful health effects of cigarette smoking. Tobacco smoking is a reprehensible habit that has spread all over the world as an epidemic. It reduces the life expectancy among smokers. It increases overall medical costs and contributes to the loss of productivity during the life span. Smoking has been shown to be linked with various neurological, cardiovascular, and pulmonary diseases. Cigarette smoke not only affects the smokers but also contributes to the health problems of the non-smokers. Exposure to environmental tobacco smoke contributes to health problems in children and is a significant risk factor for asthma. Cigarette smoke contains several carcinogens that alter biochemical defense systems leading to lung cancer.

Effect of twelve-months therapy with oral ambroxol in preventing exacerbations in patients with COPD. Double-blind, randomized, multicenter, placebo-controlled study (the AMETHIST Trial)

The objective of this prospective, randomized, double-blind, placebo-controlled, multicenter parallel-group study was to evaluate the effect of long-term ambroxol treatment in preventing exacerbations of chronic obstructive pulmonary disease (COPD). Two hundred and forty-two outpatients with COPD defined by ATS criteria with value of FEV1 between > or =60 and 80% of predicted and history of one or more exacerbations in the previous year were recruited by 26 Respiratory Medicine Centers in Italy and treated for 1 year with one ambroxol retard capsule of 75 mg twice daily or placebo. The percentage of patients free from exacerbation at 6 months was 63% with ambroxol and 60% with placebo (p=0.366) and at 12 months 56% with ambroxol and 53% with placebo (p=0.363). In a subset of 45 patients with more severe baseline symptoms, ambroxol therapy was associated with a significant higher percentage of patients free from exacerbation compared to placebo: 63 vs. 38% (p=0.038). In conclusion, we did not find a significant difference between long-term ambroxol therapy and placebo, in preventing exacerbations in patients with COPD. In patients with more severe respiratory symptoms at baseline, however, we observed a significant difference in the cumulative exacerbation-free persistence between ambroxol and placebo, suggesting that long-term muco-regulatory therapy with ambroxol could be useful in highly symptomatic patients with COPD.

Vitamin E deficiency sensitizes alveolar type II cells for apoptosis

Pre-term neonates and neonates in general exhibit physiological vitamin E deficiency and are at increased risk for the development of acute lung diseases. Apoptosis is a major cause of acute lung damage in alveolar type II cells. In this paper, we evaluated the hypothesis that vitamin E deficiency predisposes alveolar type II cells to apoptosis. Therefore, we measured markers of apoptosis in alveolar type II cells isolated from control rats, vitamin E deficient rats and deficient rats that were re-fed a vitamin E-enriched diet. Bax and cytosolic cytochrome c increased, and the mitochondrial transmembrane potential and Hsp25 expression was reduced in vitamin E deficiency. Furthermore, increased DNA-fragmentation and numbers of early and late apoptotic cells were seen, but caspases 3 and 8 activities and expression of Fas, Bcl-2, Bcl-x and p53 remained unchanged. Vitamin E depletion did not change the GSH/GSSG ratio and the activities of antioxidant enzymes. Thus, vitamin E deficiency may induce a reversible pro-apoptotic response in lung cells and sensitise them for additional insult. In agreement with this hypothesis, we demonstrate that in vivo hyperoxia alone does not induce apoptosis in type II cells of control rats but reversibly increases DNA-fragmentation and numbers of early apoptotic type II cells in vitamin E-depleted cells.

Possible role of ascorbic acid in the oxidative damage induced by inhaled crystalline silica particles

The selective interaction of ascorbic acid with crystalline silica (quartz) has been studied by measuring the ascorbic acid consumption (by means of UV/vis and IR spectroscopy) and the release of silicon when quartz particles or amorphous silica (Aerosil 50) is incubated in ascorbic acid solution. At a physiological ascorbic acid concentration, quartz, and not amorphous silica, reacts, suggesting the formation of a 1:1 silicon-ascorbate complex, while at higher concentrations, the reacting amount of ascorbic acid exceeds the amount of silicon that is released. Silicon tetrahedra bearing free silanols at the quartz surface are selectively attached by ascorbic acid. The particle-derived hydroxyl radical yield in the presence of hydrogen peroxide is increased on ascorbic acid-treated quartz in comparison with the original sample. The results presented herein are relevant because the depletion of ascorbic acid from the lung lining layer and the increased potential in particle-derived free radical generation may both contribute to the oxidative damage following inhalation of crystalline silica.

Effect of budesonide and salbutamol on surfactant properties

The objective of this study was to evaluate the in vitro effect of budesonide and salbutamol on the surfactant biophysical properties. The surface-tension properties of two bovine lipid extracts [bovine lipid extract surfactant (BLES) and Survanta] and a rat lung lavage natural surfactant were evaluated in vitro by the captive bubble surfactometer. Measurements were obtained before and after the addition of a low and high concentration of budesonide and salbutamol. Whereas salbutamol had no significant effect, budesonide markedly reduced the surface-tension-lowering properties of all surfactant preparations. Surfactant adsorption (decrease in surface tension vs. time) was significantly reduced (P < 0.01) at a high budesonide concentration with BLES, both concentrations with Survanta, and a low concentration with natural surfactant. At both concentrations, budesonide reduced (P < 0.01) Survanta film stability (minimal surface vs. time at minimum bubble volume), whereas no changes were seen with BLES. The minimal surface tension obtained for all surfactant preparations was significantly higher (P < 0.01), and the percentage of film area compression required to reach minimum surface tension was significantly lower after the addition of budesonide. In conclusion, budesonide, at concentrations used therapeutically, adversely affects the surface-tension-lowering properties of surfactant. We speculate that it may have the same adverse effect on the human surfactant.

Animal models of pulmonary infection in the compromised host: potential usefulness for studying health effects of inhaled particles

Pulmonary infection leading to pneumonia is a significant cause of morbidity and mortality worldwide. Airborne particles have been associated with pneumonia through epidemiological research, but the mechanisms by which particles affect the incidence of pneumonia are not well established. The purpose of this review is to examine the potential of animal models to improve our understanding of the mechanisms by which inhaled particles might affect the incidence and resolution of pulmonary infection. The pathogenesis of pneumonia in most animal models differs from that in humans because humans frequently have underlying diseases that predispose them to infection with relatively low doses of pathogens. Normal, healthy animals lack the underlying pathology often found in humans and clear bacteria and viruses rapidly from their lungs. To overcome this, animals are administered large inocula of pathogens, are treated with agents that cause mucosal lesions, or are treated with immunosuppressive drugs. Alternatively, pathogenic bacteria are protected from phagocytosis by encasing them in agar. No one animal model will replicate a human disease in its entirety, and the choice of model depends upon how well the animal infection mimics the particular human response being examined. The advantages and disadvantages of animal models in current use for bacterial and viral infections important in the etiology of human pneumonia are reviewed in detail. Considerable data indicate that prior exposure to particles compromises the ability of experimental animals to resolve a subsequent infection. In addition, information is available on the effects of particle exposure on various portions of respiratory defense including phagocytic function, ciliary movement, inflammation, and antibody response in the absence of infection. In contrast, little research to date has examined the consequences of particle exposure on the host defense mechanisms of animals already infected or on their ability to resolve their infection.

Regional clearance of solute from peripheral airway epithelia: recovery after sublobar exposure to ozone

The influence of local exposure to ozone (O3) on respiratory epithelial permeability of sublobar lung segments was studied by using aerosolized 99mTc-diethylenetriamine pentaacetic acid (DTPA; mol wt, 492). Two bronchoscopes were inserted through an endotracheal tube in anesthetized, mechanically ventilated, mixed breed dogs and were wedged into sublobar bronchi located in the right and left lower lobes, respectively. Segments were ventilated via the bronchoscope with 5% CO2 in air delivered at 200 ml/min, and an aerosol of 99mTc-DTPA was generated and delivered through the scope and into the sublobar segment over a 30-s period. Clearance of 99mTc-DTPA was measured simultaneously from right and left lower lung segments at baseline and 1, 7, and 14 days after a 6-h sublobar exposure to filtered air or 400 parts per billion O3. O3 treatment significantly decreased the clearance halftime (t50) of 99mTc-DTPA by 50% from the baseline mean of 32.3 to 16.0 min at 1 day postexposure. After 7 days of recovery, t50 was still reduced by 28. 8%; however, by 14 days postexposure, clearance of 99mTc-DTPA had recovered, and the t50 had a mean value of 30.0 min. 99mTc-DTPA clearance was not altered by exposure to filtered air, and t50 values were comparable to baseline at 1, 7, and 14 days postexposure. These results reveal that a single local exposure to O3 increases transepithelial clearance, but only for epithelia directly exposed to O3, and that 7-14 days of recovery are required before permeability to small-molecular-weight solutes returns to normal.

Effect of hyperoxia on the composition of the alveolar surfactant and the turnover of surfactant phospholipids, cholesterol, plasmalogens and vitamin E

Experimental and clinical studies have provided evidence for the involvement of oxygen free radicals in development of acute and chronic lung diseases. Hyperoxia is very often an indispensable therapeutic intervention which seems to impose oxidative stress on lung tissue. We measured the effect of hyperoxia (80% O2 for 20 h) (1) on the lipid composition of pulmonary surfactant treated in vitro, (2) on surfactant lipid synthesis and secretion of type II pneumocytes in primary culture, (3) on the lipid composition and on the SP-A content of rat lung lavages and (4) on the turnover of phospholipids, cholesterol, plasmalogens and vitamin E in type II pneumocytes, lamellar bodies and lavages of adult rat lungs. (1) Hyperoxia of lung lavages in vitro reduces the vitamin E content significantly but does not change the relative proportion of PUFA or the content of plasmalogens. (2) Hyperoxia does not affect the biosynthesis or secretion of surfactant lipids and plasmalogens by type pneumocytes in primary culture. (3) Hyperoxic treatment of rats increases the SP-A content and reduces the vitamin E content significantly but does not change the concentration of other lipid components of lung lavage. (4) The vitamin E turnover, measured in type II pneumocytes, lamellar bodies and lung lavages, is increased 2-fold in these fractions. In contrast, the turnover of surfactant cholesterol and surfactant lipids does not change. (5) Hyperoxia caused an increase of the vitamin E uptake by type II pneumocytes resulting in a vitamin E enrichment of lamellar bodies. From these results we conclude that type II pneumocytes are able to regulate the turnover of lipophilic constituents of the alveolar surfactant independently of each other. Hyperoxia caused type II pneumocytes to increase the vitamin E content of lamellar bodies. The lipid and SP-A content of alveolar fluid can be regulated independently each other.

Toxic oxidant species and their impact on the pulmonary surfactant system

In this review the effects of oxidant inhalation on the pulmonary surfactant system of laboratory animals are discussed. Oxidant lung injury is a complex phenomenon with many aspects. Inhaled oxidants interact primarily with the epithelial lining fluid (ELF), a thin layer covering the epithelial cells of the lung which contains surfactant and antioxidants. In the upper airways this layer is thick and contains high levels of antioxidants. Therefore oxidant injury in this area is rare and is more common in the lower airways where the ELF is thin and contains fewer antioxidants. In the ELF oxidants can react with antioxidants or biomolecules, resulting in inactivation of the biomolecules or in the formation of even more reactive agents. Oxidation of extracellular surfactant constituents may impair its function and affect breathing. Oxidized ELF constituents may promote inflammation and edema, which will impair the surfactant system further. Animal species differences in respiratory tract anatomy, ventilatory rate, and antioxidant levels influence susceptibility to oxidants. The oxidant exposure dose dictates injury, subsequent repair processes, and tolerance induction.

Enhancement of the macrophage oxidative burst by immunoglobulin coating of respirable fibers: fiber-specific differences between asbestos and man-made fibers

The ability of long amosite asbestos fibers (LFA), vitreous fibers (MMVF 21 and CODE 100/475), and ceramic fibers (silicon carbide and RCF 1) to stimulate superoxide production in isolated rat alveolar macrophages is examined. The cells were exposed to both naked fibers (uncoated) and fibers coated with rat immunoglobulin (IgG), a normal component of lung lining fluid. The affinity for IgG of the various fibers was assessed by quantifying the binding of 125I-labeled IgG onto the fiber surface. Naked fibers stimulated a modest release of superoxide anion from alveolar macrophages, which was not obviously dose dependent. When IgG was adsorbed onto fibers of MMVF 21 and RCF 1, there was a dramatic increase in superoxide release, which correlated well with their high affinity for IgG.IgG-adsorbed code 100/475 and silicon carbide whiskers (SiCW) stimulated only modest superoxide release, and the fibers showed a correspondingly poor affinity for the opsonin. Conversely, the adsorbed fibers of LFA, generated a dramatic increase in superoxide release from the macrophages, despite a relatively poor adsorption of IgG. This study demonstrates the potential for components of the lung lining fluid to modify the response of alveolar macrophages to respirable natural and man-made fibers. It also draws attention to fiber-specific differences in adsorptive capacity and subsequent biological activity between these fiber types in vitro and, by implication, in vivo.

Effect of nitrogen dioxide inhalation on surfactant phosphatidylcholine synthesis in rat alveolar type II cells

After exposure of rats to NO2 (10 ppm, 72 h) type II pneumocytes were isolated and compared to cells from control animals in order to determine whether nitrogen dioxide inhalation affects surfactant phospholipid synthesis. (1) Exposed cells contained more DNA, protein and phospholipid than type II cells from controls. (2) Choline kinase, CTP: cholinephosphate cytidylyltransferase, and cholinephosphotransferase showed higher specific activities in the exposed cells. (3) In correspondence with this finding, the incorporation rates of choline into intermediate metabolic products were also higher in the NO2-exposed cells. (4) The pool sizes of the intermediate metabolic products of the CDP-choline-pathway for the synthesis of phosphatidylcholine were also higher in the cells isolated from exposed animals. This suggests that acute nitrogen dioxide exposure leads to an enhanced phospholipid synthesis that may be responsible for the higher amount of phospholipid detectable in lung lavage.

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

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.

Inhalation exposure of rats to metal aerosol. I. Effects on pulmonary surfactant and ascorbic acid

Female albino Wistar rats were exposed to less than 5 microns particles separated from nickel refinery waste. The generated aerosol of 50 mg m-3 mainly consisted of metal oxides, the most toxic being NiO and Cr2O3. The exposure of 5 h per day, 5 days per week, lasted for 4 weeks or 4 months. At the end of the exposure period the amounts of pulmonary surfactant and ascorbic acid were estimated in both exposed and control rats. The amount of pulmonary surfactant was elevated after both exposure times, while ascorbic acid increased significantly (P less than 0.02) only after 4 weeks of exposure.

Ventilation and secretion of pulmonary surfactant

Various factors are involved in the regulation of surfactant secretion: chemical agonist; local environmental factors such as mediators, locally produced hormones, and possibly pH; and finally, mechanical stress occurring during lung inflation. Here we suggest a model of regulation which is grouped into three levels: a basal autoregulatory mechanism with local factors being superimposed and a systemic level acting through hormones reaching the lung via the bloodstream. Depending on the situation, the different levels may vary in their importance. For the normal situation, in the absence of stress factors, we suggest the autoregulation of stretch-induced secretion and SP-A inhibition as indicated by in vitro experiments to be the prominent regulatory mechanism for surfactant secretion. From this model, mechanisms can be derived which indicate involvement of the surfactant system in, for example, obstructive lung disease. Support from the literature for this hypothesis is reviewed. Because quantitative measurement of the amount of surfactant-associated phospholipids cannot be done adequately at this time, we suggest testing the relatively risk-free application of exogenous surfactant in a pilot phase based on indications for its involvement and usefulness derived from animal and in vitro experiments.

Mechanisms of H2O2-mediated injury to type II cell surfactant metabolism and protection with PEG-catalase

Alterations in type II pneumocyte function, including surfactant biosynthesis, may play a significant role in the development and pathophysiology of oxidant-induced lung injury. The results of this study showed that type II cells exposed to 50-300 microM H2O2 demonstrated a dose-dependent decrease in phosphatidylcholine (PC) synthesis with only minimal changes in cell viability. The activities of the choline-phosphate cytidyltransferase and cholinephosphotransferase, specific enzymes of PC synthesis, were not significantly decreased by the exposure. However, the activity of glycerol-3-phosphate acyltransferase, a sulfhydryl-dependent enzyme involved in an early stage of phospholipid synthesis, was decreased by the exposures in a manner that was similar to that seen for PC synthesis. Further studies showed that incubation of type II cells with polyethylene glycol-conjugated catalase for 1 h resulted in an increase in the cell-associated catalase activity (53 +/- 5 vs. 6.7 +/- 1.5 units/mg protein for controls). Confocal microscopy analysis showed that a significant portion of this activity was located intracellularly. More importantly, these cells were protected from changes in PC synthesis rates when subsequently incubated with 300 microM H2O2. These results indicate that the deleterious effects of H2O2 on type II cell surfactant synthesis may be pharmacologically modified in vitro, a concept that may have utility with regard to the modulation of in vivo lung injuries.

Lung surfactant in respiratory distress syndrome

Severe respiratory failure is always associated with a defect in the surfactant system. Surfactant substitution in newborn infants with respiratory distress syndrome (RDS) has gained worldwide acceptance. In the present study, we have evaluated whether surfactant diagnostics are of use in choosing recipients of exogenous surfactant. In addition, we studied whether factors apparently unrelated to surfactant influence the degree of respiratory failure and surfactant responsiveness. In small preterm infants, the surfactant indices in amniotic fluid (L/S ratio and phosphatidylglycerol), within 3 days of birth, predicted the risk of RDS with a sensitivity of 90-100%, and a specificity of 50-85%. The surfactant indices, measured in BAL, predicted the risk of ARDS (which became evident 1 to 7 days later) with a sensitivity of 50-60% and a specificity of 59-65%. In small preterm infants with RDS, the amount of fluids given during the first day correlated positively with the degree of respiratory failure and negatively with the degree of surfactant responsiveness. According to an experimental study, in hydrostatic lung edema, exogenous surfactant is diluted by edema fluid and becomes sensitive to inhibitors of surfactant function. Beside dosage, quality, and time of administration, the management of patients largely dictates the responsiveness to exogenous surfactant.

Liposomes and pulmonary alveolar macrophages: functional and morphologic interactions

In vitro toxicity of liposomes and their functional and morphologic interactions with rat pulmonary alveolar macrophage (AMs) were investigated using viability (trypan blue exclusion), phagocytic and killing activity (uptake and digestion of live S. cerevisiae), surface adherence, respiratory burst (nitro-blue tetrazolium reduction), and morphometry (computerized image analysis) as indicators. Liposome stability in physiologic solutions and uptake of liposome-encapsulated carboxyfluorescein (CF) by AMs was assessed by fluorescence spectroscopy and microscopy. Liposomes made from saturated phospholipids and cholesterol were stable, whereas liposomes consisting of unsaturated phospholipids without cholesterol lost 30% to 40% of their content over 24 h. However, CF uptake was highest with unsaturated phospholipid preparations, whereas uptake of the three other formulations was comparable. Although liposome exposure did not affect macrophage viability, a reduction in the number of phagocytizing macrophages to 73% of control was noted after 24-h incubation with the highest lipid concentration tested (10 mumol/ml). Phagocytic killing was similar under all circumstances observed. The fraction of intracellularly killed yeast ranged from 32% to 42% for both control and experimental samples. An increase in cell surface area from 166.1 +/- 39.9 microns 2 on day O (n = 709) to 196.3 +/- 57.6 microns 2 on day 1 (n = 516) and 211.2 +/- 48.0 microns 2 on day 4 (n = 834) was observed after liposome treatment. The corresponding average cell areas of control samples did not change during the observation period. There was no net cell loss of adherence from monolayers as determined by protein assay. The respiratory burst, indicating generation of intracellular superoxide, was also similar--84% to 92% of experimental and control cells under all conditions showed a strong nitro-blue tetrazolium reduction. In summary, in vitro exposure of AMs to large concentrations of liposomes, although producing an increase in macrophage size, was not associated with aberrant macrophage morphologic features, function, or toxicity for the parameters examined.

Reactions of dinitrogen pentoxide and nitrogen dioxide with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine

The reactions of gaseous dinitrogen pentoxide (N2O5) and nitrogen dioxide (NO2) with 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine (POPC) coated on the inside surface of a glass reaction cell were studied at 298 K. Unsaturated phosphatidylcholines are significant components of pulmonary surfactant in the alveolar region of the lung and hence serve as a simple model to examine reactions of pulmonary surfactant with these oxidant air pollutants. Using high-performance liquid chromatography (HPLC), Fourier transform infrared and fast atom bombardment mass spectroscopy, the major products of reactions of POPC with N2O5 and NO2 were separated and identified. In the POPC-N2O5 reaction using either air or helium as a buffer gas, the nitronitrate, vinyl nitro and allylic nitro derivatives, as well as a small amount of the trans-isomer of the starting material, were obtained. The nature of the products obtained from the POPC-NO2 reaction depends on the concentration of NO2 as well as whether air is present. At low NO2 concentrations (PNO2/N2O4 less than or equal to 3.8 Torr) in air or in helium, the trans-isomer of POPC was formed almost exclusively. At higher NO2 concentrations (PNO2/N2O4 greater than or equal to 20 Torr) in helium, the dinitro, vinyl nitro and nitro alcohol derivatives were formed. In the presence of air (or 24% 18O2 in helium), a nitronitrate and a dinitronitrate were additional products. Mechanisms for the formation of the observed products and implications for the inhalation of oxides of nitrogen are discussed.

Effects of chronic exposure to ozone on pulmonary lipids in rats

Ozone is the most toxic component of photochemical oxidant air pollution. Exposure to high concentrations of ozone produces a variety of toxic effects in the lung, but it is not known to what extent prolonged exposure to low concentrations of ozone may contribute to the development of chronic lung disease. Phospholipids, important components of cellular membranes and surfactant, are necessary for the maintenance of normal lung structure and function. In order to test the effects of chronic exposure to environmentally relevant concentrations of ozone on phospholipid metabolism in the lung, rats were exposed to clean air or to 0.12, 0.25 or 0.50 ppm ozone for up to 18 months. The content and biosynthesis of phospholipids in both lung tissue and bronchopulmonary lavage fluid (surfactant) were measured. Incorporation of [14C]acetate into lung tissue phospholipids, an estimate of overall biosynthesis, decreased significantly at some time points in the study, while tissue phospholipid content tended to increase with both ozone concentration and with age. No changes were detected in phospholipid content of bronchopulmonary lavage fluid. These findings did not support the hypothesis that prolonged exposure of rats to environmentally relevant concentrations of ozone results in either qualitative or quantitative deficits in the pulmonary surfactant system.

Pulmonary clearance of 99mTc-DTPA during halothane anaesthesia

We studied the integrity of the alveolo-capillary barrier during different forms of anaesthesia by measuring the pulmonary clearance of inhaled 99mTc-DTPA. We studied four groups of rabbits. Groups I and II were anaesthetized with nembuthal only and the fractional concentration of inspired oxygen (F1O2) was 0.30 and 1.00, respectively. Groups III and IV were anaesthetized with 1% halothane and F1O2 was 0.30 and 0.99, respectively. 99mTc-DTPA was administered as a fine aerosol and the clearance of the tracer from the lungs was subsequently measured with a gamma camera. The mean half-life of the tracer in the lungs in Groups I-IV was 60, 58, 59 and 26 min, respectively. The rapid pulmonary clearance of 99mTc-DTPA in Group IV indicates that halothane in combination with high oxygen concentration increases the permeability of the alveolo-capillary barrier. This may be due to effects on the pulmonary surfactant system and/or the alveolar epithelium.

Changes in surfactant in bronchoalveolar lavage fluid after hemithorax irradiation in patients with mesothelioma

Experimental studies have shown that the surfactant system of the lung is affected shortly after irradiation. It is unclear, however, whether surfactant plays a role in the pathogenesis of radiation pneumonitis. In the present study surfactant components (saturated phosphatidylcholine, surfactant protein A, phosphatidylglycerol, and phosphatidylinositol) and other phospholipids of bronchoalveolar lavage fluid (BAL) were studied in four patients with pleural mesothelioma before and during hemithorax irradiation (70 Gy) as well as zero, 1, 2, 3, and 4 months following irradiation. The concentrations of these same components and of soluble proteins were also estimated in the epithelial lining fluid (ELF) using urea as a marker of dilution. After radiotherapy, the concentrations of the surfactant components in ELF decreased to 12 to 55% of the control values before radiation, whereas the concentration of sphingomyelin in ELF increased ninefold. There were small changes in the other phospholipids. The concentration of soluble protein in ELF increased sevenfold. The minimum surface activity of crude BAL increased from 12 +/- 4 to 32 +/- 6 mN/m, and that of the sediment fraction of BAL increased from 7 +/- 4 to 22 +/- 6 mN/m, p less than 0.001. The protein-rich supernatant fraction of BAL from irradiated lung had a inhibitory effect on normal surfactant. There were significant correlations between the increasing severity of the radiologic changes on the one hand and, on the other, the saturated phosphatidylcholine/sphingomyelin ratio (p less than 0.001), the concentrations of soluble protein (p less than 0.001), and the concentrations of the surfactant components (p less than 0.02-0.001) in ELF.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the relative concentrations of surfactant phospholipids in young pigs with experimental pneumonia

Lung lavage fluids of 23 young pigs were investigated prior to and after experimental infection with Pasteurella multocida. Comparison of the phospholipid patterns showed an increase in the relative concentration of phosphatidylinositol and a decrease in that of phosphatidylglycerol in the diseased animals. The phosphatidylcholine-to-phosphatidylinositol and phosphatidylglycerol-to-phosphatidylethanolamine ratios were used as parameters to characterize the changing patterns. The reductions in these ratios following infection were found to be useful indicators of bacterial pneumonia. Immunization did not affect the characteristic variations. A rapid screening procedure involving solid-phase extraction, one-dimensional thin-layer chromatography and densitometric scanning of the plates was used.

Synthesis of phosphatidylcholines in ozone-exposed alveolar type II cells isolated from adult rat lung: is glycerolphosphate acyltransferase a rate-limiting enzyme?

Type II cells were exposed to ozone by gas diffusion through the thin Teflon bottom of culture dishes. The rate of phosphatidylcholine synthesis by type II cells, monitored by the incorporation of [Me-14C]choline, was impaired by ozone at concentrations that did not affect other cellular parameters. The enzymes choline kinase and cholinephosphate cytidylyltransferase were not susceptible to inactivation by ozone at concentrations at which the activity of glycerolphosphate acyltransferase was decreased. The enzyme activity of lactate dehydrogenase increased after ozone exposure. The specific activity of choline kinase in the cytosolic fraction of type II cells was fivefold that in whole lung. The metabolism of [Me-14C]choline was studied as a function of the choline concentration. Maximal rates of phosphatidylcholine synthesis were already attained at a concentration of 20 microM choline. Exposure of type II cells to ozone did not affect the recovery of label from [Me-14C]choline in choline phosphate and CDP choline. However, the maximal rate of phosphatidylcholine synthesis decreased after ozone exposure, which indicates that the decreased apparent activity of glycerolphosphate acyltransferase limits the supply of diacylglycerols and thereby the rate of phosphatidylcholine synthesis. If the flux through the diacylglycerol pathway was stimulated by the addition of palmitic acid, a higher maximal rate of phosphatidylcholine synthesis was observed. The uptake of [Me-14C]choline and the recovery of label in CDPcholine were not altered by the addition of different concentrations of palmitate. It is concluded that type II cells take up choline very efficiently, probably due to the high specific activity of choline kinase. At low choline concentrations the rate of phosphatidylcholine synthesis is determined by the supply of CDPcholine. At concentrations of choline in the upper physiological range, the rate of phosphatidylcholine synthesis is determined by the availability of diacylglycerols, which in turn is limited by the apparent activity of glycerolphosphate acyltransferase.

Phosphatidylcholine synthesis in isolated type II pneumocytes from ozone-exposed rats

Phosphatidylcholine (PC) synthesis by alveolar type II cells, as an indicator for the production of pulmonary surfactant, was studied after a 4-h exposure of rats to 4 mg ozone/m3 (2 ppm). Lung ravage fluid analysis after exposure revealed significant increases in proteins, which is indicative for pulmonary injury. When type II cells were isolated immediately and thereafter cultured for 20 h, the rate of PC synthesis in cells derived from ozone-exposed rats was not significantly different from that in cells from unexposed controls. Yet, a decreased rate of PC synthesis was observed when these cells were subsequently exposed to ozone in vitro. The activity of the enzyme glycerolphosphate acyltransferase (GPAT) was slightly enhanced in cultured type II cells isolated from ozone-exposed rats, while the lysophosphatidylcholine acyltransferase (LPCAT) activity was unchanged. However, ozone exposure of rats did result in a significant decrease of PC synthesis when measured in freshly prepared type II cell suspensions, although both GPAT and LPCAT activities were not affected. It is concluded that a decrease in pulmonary surfactant related PC synthesis after ozone exposure of rats can be demonstrated in freshly isolated type II pneumocytes. Cultured type II cells from exposed rats lack this effect and are therefore less useful to study changes in phospholipid biosynthesis after in vivo ozone exposure. The data on in vitro ozone exposure of cultured type II cells, however, support the view that ozone may impair pulmonary surfactant production.

Phospholipid synthesis in isolated alveolar type II cells exposed in vitro to paraquat and hyperoxia

Isolated alveolar epithelial type II cells were exposed to paraquat and to hyperoxia by gas diffusion through the thin Teflon bottom of culture dishes. After exposure, type II cells were further incubated in the presence of labelled substrates to assess their capacity to synthesize lipids. Hyperoxia alone (90% O2; 5 h) had minor effects on lipid metabolism in the type II cells. At low paraquat concentrations (5 and 10 microM), hyperoxia enhanced the paraquat-induced decrease of [Me-14C]choline incorporation into phosphatidylcholines. The incorporation rates of [Me-14C]choline, [1-14C]palmitate, [1-14C]glucose and [1,3-3H]glycerol into various phospholipid classes and neutral lipids were decreased by paraquat, depending on the concentration and duration of the exposure. The incorporation of [1-14C]acetate into phosphatidylcholines, phosphatidylglycerols and neutral lipids appeared to be very sensitive to inactivation by paraquat. At 5 microM-paraquat the rate of [1-14C]acetate incorporation was decreased to 50% of the control values. The rate of [1-14C]palmitate incorporation into lipids was much less sensitive; it even increased at low paraquat concentrations. At 10 microM-paraquat both NADPH and ATP were significantly decreased. It is concluded that lipid synthesis in isolated alveolar type II cells is extremely sensitive to paraquat. At low concentrations of this herbicide, lipid synthesis, and particularly fatty acid synthesis, is decreased. The effects on lipid metabolism may be partly related to altered NADPH and ATP concentrations.

A Fourier transform infrared spectrometry study of the reactions of phosphatidylcholines with gaseous N2O5 and NO2

The liquid lining of the alveolar region of the lung contains a surfactant which lowers the surface tension. The major active surface-tension-lowering compounds are phosphatidylcholines, some of which contain unsaturated fatty acid components. In order to determine whether these unsaturated moieties react with the gaseous air pollutant N2O5, which may be present in urban atmospheres at concentrations up to 15 ppb, phosphatidylcholines adsorbed on glass at 25 degrees C were exposed to mixtures of approximately 2 Toor (approximately 2600 ppm) N2O5 in 1 atm of air or argon in the gas phase. Nitronitrates were identified as products of the reactions of N2O5 with beta-oleoyl-gamma-palmitoyl L-alpha-phosphatidylcholine (OPPC) and dioleoyl L-alpha-phosphatidylcholine (DOPC) using Fourier transform infrared (FTIR) spectrometry and in the case of DOPC, fast atom bombardment mass spectrometry. FTIR studies also show that 2 Torr (approximately 2600 ppm) NO2 in 1 atm of air reacts with OPPC and DOPC to give new bands tentatively identified as nitronitrates. Finally, HNO3 was shown to react with OPPC, DOPC, and the saturated dipalmitoyl L-alpha-phosphatidylcholine to give products tentatively identified as nitrate salts and glycerol. These studies suggest that inhaled N2O5, if it reaches the alveolar region, is likely to react with unsaturated C = C groups in surfactant to form nitronitrates.