Tumor necrosis factor-alpha-induced inhibition of phosphatidylcholine synthesis by human type II pneumocytes is partially mediated by prostaglandins

Roles of Nrf2/HO-1 and ICAM-1 in the Protective Effect of Nano-Curcumin against Copper-Induced Lung Injury

Copper (Cu) is an essential trace element for maintaining normal homeostasis in living organisms. Yet, an elevated level of Cu beyond homeostatic capacity may lead to oxidative damage of cellular components in several organs, including the lungs. This work investigated the effects of curcumin (Curc) and nano-curcumin (nCurc) against Cu-induced lung injury, accenting the roles of oxidative stress, inflammation, and the nuclear factor erythroid 2-related factor/heme oxygenase-1 Nrf2/HO-1 pathway. Rats were challenged with 100 mg/kg of copper sulfate (CuSO4) while being treated with Curc or nCurc for 7 days. Cu-triggered lung oxidative stress detected as dysregulation of oxidative/antioxidant markers, a downregulation of Nrf-2/HO-1 signaling, and an increase in the inflammatory markers interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and intracellular adhesion molecule-1 (ICAM-1). Additionally, it decreased the expression of lung-specific proteins, surfactant protein-C (SP-C), and mucin-1 (MUC-1), induced apoptosis, and caused changes in lung histology. Curc and nCurc alleviated CuSO4-induced lung injury by suppressing oxidative damage and inflammation and activating Nrf-2/HO-1. They also prevented apoptosis and restored the normal expression of SP-C and MUC-1. We concluded that nCurc exhibited superior efficacy compared with Curc in mitigating CuSO4-induced lung injury. This was associated with reduced oxidative stress, inflammation, and apoptotic responses and increased Nrf2/HO-1 signaling and expression of SP-C and MUC-1.

Perioperative Pulmonary Atelectasis: Part I. Biology and Mechanisms

Pulmonary atelectasis is common in the perioperative period. Physiologically, it is produced when collapsing forces derived from positive pleural pressure and surface tension overcome expanding forces from alveolar pressure and parenchymal tethering. Atelectasis impairs blood oxygenation and reduces lung compliance. It is increasingly recognized that it can also induce local tissue biologic responses, such as inflammation, local immune dysfunction, and damage of the alveolar-capillary barrier, with potential loss of lung fluid clearance, increased lung protein permeability, and susceptibility to infection, factors that can initiate or exaggerate lung injury. Mechanical ventilation of a heterogeneously aerated lung (e.g., in the presence of atelectatic lung tissue) involves biomechanical processes that may precipitate further lung damage: concentration of mechanical forces, propagation of gas-liquid interfaces, and remote overdistension. Knowledge of such pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should guide optimal clinical management.

Free cholesterol-induced cytotoxicity a possible contributing factor to macrophage foam cell necrosis in advanced atherosclerotic lesions

A major characteristic of advanced atherosclerotic lesions is the necrotic, or lipid, core, which likely plays an important role in the clinical progression of these lesions. Recent data suggest that the necrotic core forms primarily as a consequence of macrophage foam cell necrosis. Lesional macrophages initially accumulate mostly cholesteryl esters, but macrophages in advanced lesions contain large amounts of unesterified, or free, cholesterol (FC). Although there are many theories as to why macrophage foam cells die in advanced lesions, the fact that a high FC:phospholipid (PL) ratio in cellular membranes can be toxic to cells suggests that FC-induced cytotoxicity may contribute to foam cell necrosis. The mechanism of FC cytotoxicity can be explained by disturbances in membrane protein function as a result of "stiffening" of the bilayer and by formation of intracellular FC crystals that can cause physical damage to cellular organelles. Macrophages appear to respond to FC loading by a fascinating adaptive response, namely the induction of PL biosynthesis, which initially keeps the cellular FC:PL ratio below toxic levels. Studies with cultured macrophages have demonstrated that a failure of this adaptive response leads to FC-induced foam cell cytotoxicity and necrosis, and thus a similar series of events in advanced atherosclerotic lesions could provide an explanation for the development of the necrotic core. (Trends Cardiovasc Med 1997;7: 256-263). © 1997, Elsevier Science Inc.

Cycloxygenase inhibition enhances the effects of surfactant therapy in endotoxin-induced rat model of ARDS

The present study examines the relationships between inflammation and surfactant protein (SP) expression in a rodent model of acute respiratory distress syndrome (ARDS). Rats were intratracheally instilled with lipopolysaccharide (LPS) for 72 hours to induce ARDS and further treated with exogenous surfactant. Prostaglandin E(2) (PGE(2)) levels, cycloxygenase (COX) activity and alterations in SP-A apoprotein were measured. COX and SP-A expressions in lung tissue and SP-A-positive cells were determined by Western blot and immunofluorescence, respectively. PGE(2) levels and COX activity and its expression were increased with LPS exposure, whereas SP-A protein and percentage of SP-A-positive cells were decreased, which were subsequently reverted back by exogenous surfactant instillation. Because inhibition of COX-2 action is proposed to be useful in various inflammatory lung injuries, these results suggest that COX-2 expression and the possible beneficial effects of its inhibition on lung inflammation and dysfunction with LPS-ARDS corresponds closely with reduced SP-A expression.

Ontogeny of pulmonary cyclooxygenase-1 (COX-1) and -2 (COX-2)

Prostaglandins synthesized by enzymatic reactions such as cyclooxygenases have been implicated in lung pathophysiology. The goal of this study was to delineate the pulmonary ontogeny of cyclooxygenase enzymes (COX-1 and COX-2) immunohistochemical expression and cellular localization in various microanatomic locations of lungs from pre-term, term, and post-natal lambs. Lung tissues were obtained at 115 and 130 days of gestation from pre-term lambs, 145 days (term; complete gestation), and 15 days post-natally. No significant differences were seen in lung COX-1 expression at various microanatomic locations during pre-term, term, or postnatally. Moderate to strong COX-1 expression was present in macrophages, alveolar septa, bronchial smooth muscle cells, bronchiolar smooth muscle cells, vascular endothelial cells, and vascular smooth muscle cells. Minimal COX-1 expression was present in bronchial and bronchiolar epithelial cells. Most microanatomic locations lacked COX-2 expression with the exception of weak expression that was present in bronchial and bronchiolar epithelial cells at 145 days of full gestation and 15 days post-natally. This work suggests that: (a) COX-1 is constitutively expressed in lungs from pre-term, term, and post-natal lambs in various microanatomic pulmonary locations, (b) there is differential expression of COX-1 and COX-2 in the developing lung, and (c) COX-2 does not appear to play a role in lung fetal development, at least in neonatal lambs.

Pulmonary cyclooxygenase-1 (COX-1) and COX-2 cellular expression and distribution after respiratory syncytial virus and parainfluenza virus infection

Prostaglandins (PGs) play an important role in pulmonary physiology and various pathophysiological processes following infection. The initial step in the biosynthesis of PGs is regulated by two distinct cyclooxygenase enzymes, cyclooxygenase-1 (COX-1) and COX-2. The goal of this study was to investigate the pulmonary cellular localization and distribution of COX-1 and COX-2 in a neonatal lamb model following respiratory syncytial virus (RSV) and parainfluenza virus 3 (PI3) infection, organisms that also cause significant respiratory disease in children. No significant differences were seen in pulmonary COX-1 expression at various microanatomical locations following RSV or PI3 infection compared to controls. In contrast, COX-2 was upregulated following RSV and PI3 infection. Strong expression was restricted to bronchial and bronchiolar epithelial cells and macrophages, while minimal expression was present in the same microanatomical locations in the uninfected lungs. Other microanatomical locations in both the controls and the infected lungs lacked expression. This work suggests that during RSV or PI3 infection: (1) COX-1 cellular expression is not altered, (2) COX-2 cellular expression is upregulated in airway bronchiolar and bronchial epithelial cells and macrophages, (3) respiratory epithelium along with macrophages are important microanatomical compartments regulating the host inflammatory response during viral infection, and (4) COX-2 may be a potential target for RSV and PI3 therapy.

INTERLEUKIN-6 HAS NO EFFECT ON SURFACTANT OR LUNG FUNCTION IN DIFFERENT LUNG INSULTS

The current study determined if interleukin-6 (IL-6) had a causative role in the lung dysfunction and/or surfactant alterations associated with three different lung insults. IL-6 (or saline) was instilled into rats followed by mechanical ventilation in vivo for 4 hours. Also, IL-6 (-/-) and wild-type mice were subjected to 3 insults: ex vivo injurious mechanical ventilation; cecal ligation and perforation; and hyperoxia exposure. In all experiments, the presence or absence of IL-6 did not significantly influence gas exchange, lung compliance, or various surfactant measurements. These results suggest that IL-6 may have a limited role in the surfactant alterations observed in acute lung injury.

Long-term exposure to LPS enhances the rate of stimulated exocytosis and surfactant secretion in alveolar type II cells and upregulates P2Y2 receptor expression

Bacterial LPS is a potent proinflammatory molecule. In the lungs, LPS induces alterations in surfactant pool sizes and phospholipid (PL) contents, although direct actions of LPS on the alveolar type II cells (AT II) are not yet clear. For this reason, we studied short- and long-term effects of LPS on basal and agonist-stimulated secretory responses of rat AT II by using Ca(2+) microfluorimetry, a microtiter plate-based exocytosis assay, by quantitating PL and (3)H-labeled choline released into cell supernatants and by using quantitative PCR and Western blot analysis. Long term, but not short term, exposures to LPS led to prolonged ATP-induced Ca(2+) signals and an increased rate in vesicle fusions with an augmented release of surfactant PL. Most notably, the stimulatory effect of LPS was ATP-dependent and may be mediated by the upregulation of the purinergic receptor subtype P2Y(2). Western blot analysis confirmed higher levels of P2Y(2), and suramin, a P2Y receptor antagonist, was more effective in LPS-treated cells. From these observations, we conclude that LPS, probably via Toll-like receptor-4, induces a time-dependent increase in P2Y(2) receptors, which, by yet unknown mechanisms, leads to prolonged agonist-induced Ca(2+) responses that trigger a higher activity in vesicle fusion and secretion. We further conclude that chronic exposure to endotoxin sensitizes AT II to increase the extracellular surfactant pool, which aids in the pulmonary host defense mechanisms.

Surfactant in Newborn Compared with Adolescent Pigs

Surfactant composition and function differ between vertebrates, depending on pulmonary anatomy and respiratory physiology. Because pulmonary development in pigs is similar to that in humans, we investigated surface tension function, composition of phospholipid molecular species, and concentrations of surfactant protein (SP)-A to -D in term newborn pigs (NP) compared with adolescent pigs (AP), using the pulsating bubble surfactometer, mass spectrometry, high-performance liquid chromatography, and immunoblot techniques (IT). NP was more potent than AP surfactant in reaching minimal surface tension values near zero mN/m. Whereas SP-A and SP-D were comparable, SP-B and SP-C were increased 3- to 4-fold in NP surfactant. Moreover, fluidizing phospholipids such as palmitoylmyristoyl-PC (PC16:0/14:0) and palmitoylpalmitoleoyl-PC (PC16:0/16:1) were increased at the expense of PC16:0/16:0 (32.4 +/- 0.6 versus 44.5 +/- 3.2%, respectively). Whereas concentrations of total anionic phospholipids were similar in NP and AP surfactant (9.9 +/- 0.3 and 12.0 +/- 0.3%, respectively), phosphatidylinositol was the predominant anionic phospholipid in NP surfactant. We conclude that, compared with AP, NP surfactant displays better surface tension function under dynamic conditions, which is associated with increased concentrations of SP-B and SP-C, as well as fluidizing phospholipids at the expense of PC16:0/16:0.

Phospholipid metabolism in lung surfactant

Pulmonary surfactant is a mixture of lipids, mostly phospholipids, and proteins that allows for breathing with minimal effort. The current chapter discusses the metabolism of the phospholipids of this material. Surfactant phospholipids are synthesized in the type II epithelial cells of the lung. The lipids and surfactant proteins are assembled in intracellular storage organelles, called lamellar bodies, and are subsequently secreted into the alveolar space. Within this extracellular space surfactant undergoes several transformations. First the lamellar bodies unravel to form a highly organized lattice-like lipid:protein structure tubular myelin. Second, the organized structures, in particular tubular myelin, adsorb to form a lipid at the air-liquid interface of the alveoli. It is, in fact, this surface tension reducing film that is responsible for the physiological role of surfactant, to prevent lung collapse and allow ease of inflation. Third, the surface film is converted to a small vesicular form. Finally, these small vesicles are taken-up by the type II cells for recycling and degradation and by alveolar macrophages for degradation.

Acute respiratory distress syndrome in the septic surgical patient

The acute respiratory distress syndrome (ARDS) is a process of acute inflammatory lung injury that affects a diverse array of surgical and medical patients. The syndrome is mediated by a complex and interacting system of chemical mediators produced by several types of pulmonary cells. Regardless of the predisposing causes, activation of the nuclear factor kappa B seems to be, at the molecular level, a signature event of ARDS, leading to the rapid activation of intracellular signaling pathways, which coordinate the induction of multiple genes encoding inflammatory mediators. There are at least two compelling reasons for promoting an understanding of these interactions and their molecular mediators and second messengers: new therapies intended to modulate these factors continue to be developed, and the levels of some of these molecules, most notably cytokines, may serve as early indicators of the onset of ARDS.

Surfactant strengthens the inhibitory effect of C-reactive protein on human lung macrophage cytokine release

In this study we investigated the effect of acute-phase levels of C-reactive protein (CRP) on cytokine production by pulmonary macrophages in the presence or absence of pulmonary surfactant. Both human alveolar and interstitial macrophages as well as human surfactant were obtained from multiple organ donor lungs. Precultured macrophages were stimulated with LPS alone or together with IFN-gamma in the presence or absence of CRP, surfactant, and combinations. Releases of TNF-alpha and of IL-1beta to the medium were determined. We found that CRP could modulate lung inflammation in humans by decreasing the production of proinflammatory cytokines by both alveolar and interstitial macrophages stimulated with LPS alone or together with IFN-gamma. The potential interaction between CRP and surfactant phospholipids did not overcome the effect of either CRP or surfactant on TNF-alpha and IL-1beta release by lung macrophages. On the contrary, CRP and pulmonary surfactant together had a greater inhibitory effect than either alone on the release of proinflammatory cytokines by lung macrophages.

Pulmonary-specific expression of tumor necrosis factor-alpha alters surfactant lipid metabolism

Tumor necrosis factor (TNF)-alpha is a major cytokine implicated in inducing acute and chronic lung injury, conditions associated with surfactant phosphatidylcholine (PtdCho) deficiency. Acutely, TNF-alpha decreases PtdCho synthesis but stimulates surfactant secretion. To investigate chronic effects of TNF-alpha, we investigated PtdCho metabolism in a murine transgenic model exhibiting lung-specific TNF-alpha overexpression. Compared with controls, TNF-alpha transgenic mice exhibited a discordant pattern of PtdCho metabolism, with a decrease in PtdCho and disaturated PtdCho (DSPtdCho) content in the lung, but increased levels in alveolar lavage. Transgenics had lower activities and increased immunoreactive levels of cytidylyltransferase (CCT), a key PtdCho biosynthetic enzyme. Ceramide, a CCT inhibitor, was elevated, and linoleic acid, a CCT activator, was decreased in transgenics. Radiolabeling studies revealed that alveolar reuptake of DSPtdCho was significantly decreased in transgenic mice. These observations suggest that chronic expression of TNF-alpha results in a complex pattern of PtdCho metabolism where elevated lavage PtdCho may originate from alveolar inflammatory cells, decreased surfactant reuptake, or altered surfactant secretion. Reduced parenchymal PtdCho synthesis appears to be attributed to CCT enzyme that is physiologically inactivated by ceramide or by diminished availability of activating lipids.

Activation of type II alveolar epithelial cells during acute endotoxemia

Lung injury induced by acute endotoxemia is associated with increased generation of inflammatory mediators such as nitric oxide and eicosanoids, which have been implicated in the pathophysiological process. Although production of these mediators by alveolar macrophages (AM) has been characterized, the response of type II cells is unknown and was assessed in the present studies. Acute endotoxemia caused a rapid (within 1 h) and prolonged (up to 48 h) induction of nitric oxide synthase-2 (NOS-2) in type II cells but a delayed response in AM (12-24 h). In both cell types, this was associated with increased nitric oxide production. Although type II cells, and to a lesser extent AM, constitutively expressed cyclooxygenase-2, acute endotoxemia did not alter this activity. Endotoxin administration had no effect on mitogen-activated protein kinase or protein kinase B-alpha (PKB-alpha) expression. However, increases in phosphoinositide 3-kinase and phospho-PKB-alpha were observed in type II cells. The finding that this was delayed for 12-24 h suggests that these proteins do not play a significant role in the regulation of NOS-2 in this model. After endotoxin administration to rats, a rapid (within 1-2 h) activation of nuclear factor-kappaB was observed. This response was transient in type II cells but was sustained in AM. Interferon regulatory factor-1 (IRF-1) was also activated rapidly in type II cells. In contrast, IRF-1 activation was delayed in AM. These data demonstrate that type II cells, like AM, are highly responsive during acute endotoxemia and may contribute to pulmonary inflammation.

Respiratory distress after intratracheal bleomycin: selective deficiency of surfactant proteins B and C

Intratracheal bleomycin in rats is associated with respiratory distress of uncertain etiology. We investigated the expression of surfactant components in this model of lung injury. Maximum respiratory distress, determined by respiratory rate, occurred at 7 days, and surfactant dysfunction was confirmed by increased surface tension of the large-aggregate fraction of bronchoalveolar lavage (BAL). In injured animals, phospholipid content and composition were similar to those of controls, mature surfactant protein (SP) B was decreased 90%, and SP-A and SP-D contents were increased. In lung tissue, SP-B and SP-C mRNAs were decreased by 2 days and maximally at 4--7 days and recovered between 14 and 21 days after injury. Immunostaining of SP-B and proSP-C was decreased in type II epithelial cells but strong in macrophages. By electron microscopy, injured lungs had type II cells lacking lamellar bodies and macrophages with phagocytosed lamellar bodies. Surface activity of BAL phospholipids of injured animals was restored by addition of exogenous SP-B. We conclude that respiratory distress after bleomycin in rats results from surfactant dysfunction in part secondary to selective downregulation of SP-B and SP-C.

Mechanical ventilation of isolated septic rat lungs: effects on surfactant and inflammatory cytokines

The effects of mechanical ventilation (MV) on the surfactant system and cytokine secretion were studied in isolated septic rat lungs. At 23 h after sham surgery or induction of sepsis by cecal ligation and perforation (CLP), lungs were excised and randomized to one of three groups: 1) a nonventilated group, 2) a group subjected to 1 h of noninjurious MV (tidal volume = 10 ml/kg, positive end-expiratory pressure = 3 cmH(2)O), or 3) a group subjected to 1 h of injurious MV (tidal volume = 20 ml/kg, positive end-expiratory pressure = 0 cmH(2)O). Nonventilated sham and CLP lungs had similar compliance, normal lung morphology, surfactant, and cytokine concentrations. Injurious ventilation decreased compliance, altered surfactant, increased cytokines, and induced morphological changes compared with nonventilation in sham and CLP lungs. In these lungs, the surfactant system was similar in sham and CLP lungs; however, tumor necrosis factor-alpha and interleukin-6 levels were significantly higher in CLP lungs. We conclude that injurious ventilation altered surfactant independent of sepsis and that the CLP lungs were predisposed to the secretion of larger amounts of cytokines because of ventilation.

Sphingomyelin metabolites inhibit sphingomyelin synthase and CTP:phosphocholine cytidylyltransferase

Tissue injury in inflammation involves the release of several cytokines that activate sphingomyelinases and generate ceramide. In the lung, the impaired metabolism of surfactant phosphatidylcholine (PC) accompanies this acute and chronic injury. These effects are long-lived and extend beyond the time frame over which tumor necrosis factor (TNF)-alpha and interleukin-1beta are elevated. In this paper, we demonstrate that in H441 lung cells these two processes, cytokine-induced metabolism of sphingomyelin and the inhibition of PC metabolism, are directly interrelated. First, metabolites of sphingomyelin hydrolysis themselves inhibit key enzymes necessary for restoring homeostasis between sphingomyelin and its metabolites. Ceramide stimulates sphingomyelinases as effectively as TNF-alpha, thereby amplifying the sphingomyelinase activation, and TNF-alpha, ceramide, and sphingosine all inhibit PC:ceramide phosphocholine transferase (sphingomyelin synthase), the enzyme that restores homeostasis between sphingomyelin and ceramide pools. Second, ceramide inhibits PC synthesis, probably because of its effects on CTP:phosphocholine cytidylyltransferase, the rate-limiting enzymatic step in de novo PC synthesis. The data presented here suggest that TNF-alpha may be an inhibitor of phospholipid metabolism in inflammatory tissue injury. These actions may be amplified because of the ability of metabolites of sphingomyelin to inhibit the pathways that should restore the normal ceramide-sphingomyelin homeostasis.

CTP:phosphocholine cytidylyltransferase inhibition by ceramide via PKC-alpha, p38 MAPK, cPLA2, and 5-lipoxygenase

In a companion paper (Vivekananda J, Smith D, and King RJ. Am J Physiol Lung Cell Mol Physiol 281: L98-L107, 2001), we demonstrated that tumor necrosis factor (TNF)-alpha inhibited the activity of CTP:phosphocholine cytidylyltransferase (CT), the rate-limiting enzyme in the de novo synthesis of phosphatidylcholine (PC), and that its actions were likely exerted through a metabolite of sphingomyelin. In this paper, we explore the signaling pathway employed by TNF-alpha using C2 ceramide as a cell-penetrating sphingolipid representative of the metabolites induced by TNF-alpha. We found that in H441 cells, as reported in other cell types, cytosolic phospholipase A2 (cPLA2) is activated by TNF-alpha. We also observed that the inhibiting action of C2 ceramide on CT requires protein kinase C-alpha, p38 mitogen-activated protein kinase, and cPLA2. The actions of C2 ceramide on CT activity can be duplicated by adding 2 microM lysoPC to these cells. Furthermore, we found that the effects of C2 ceramide are dependent on 5-lipoxygenase but that cyclooxygenase II is unimportant. We hypothesize that CT activity is inhibited by the lysoPC generated as a consequence of the activation of cPLA2 by protein kinase C-alpha and p38 mitogen-activated protein kinase. The other product of the activation of cPLA2, arachidonic acid, is a substrate for the synthesis of leukotrienes, which raise intracellular Ca2+ levels and complete the activation of cPLA2.

Glucagon-like peptide-1(7-36) amide stimulates surfactant secretion in human type II pneumocytes

To determine the influence of glucagon-like peptides on the secretion of human pulmonary surfactant, we used human type II pneumocytes. In these cells, GLP-1(7-36) amide and exendin-4 stimulated phosphatidylcholine secretion (PC) and cAMP formation in a concentration-dependent manner; these effects were reversed by exendin(9-39). No changes were observed with other related peptides. The mechanism by which GLP-1(7-36) amide exerts its stimulatory effect was investigated with various agents that are well known to be stimulators or inhibitors of PC secretion. Thus, 8-bromo-cAMP increased and both Rp-cAMPS and H-89, the latter an inhibitor of protein kinase A (PKA), reduced pulmonary surfactant secretion in type II pneumocytes. Also, GLP-1(7-36) amide and TPA exerted additive effects in stimulating PC secretion, and Calph C, a potent inhibitor of protein kinase C (PKC), blocked most of the effect of GLP-1(7-36) amide. By contrast, both the calcium ionophore A23187 and GLP-1(7-36) amide had additive effects in increasing PC secretion, and the specific inhibitor of Ca(2+)-calmodulin-dependent protein kinase (Ca-CM-PK), KN-62, inhibited the effect of A23187 but did not alter the stimulatory action of GLP-1(7-36) amide. Our findings suggest that both PKA and PKC are involved in the stimulatory effects of GLP-1(7-36) amide on PC secretion, whereas this peptide has no effect on PC secretion through a Ca-CM-PK mechanism.

Pulmonary inflammation disrupts surfactant function during Pneumocystis carinii pneumonia

During Pneumocystis carinii pneumonia (PCP) in mice, the degree of pulmonary inflammation correlates directly with the severity of lung function deficits. Therefore, studies were undertaken to determine whether the host inflammatory response contributes to PCP-related respiratory impairment, at least in part, by disrupting the pulmonary surfactant system. Protein and phospholipid content and surfactant activity were measured in the lavage fluid of infected mice in either the absence or presence of an inflammatory response. At 9 weeks postinfection with P. carinii, nonreconstituted SCID mice exhibited no signs of pulmonary inflammation, respiratory impairment, or surfactant dysfunction. Lavage fluid obtained from these mice had protein/phospholipid (Pr/PL) ratios (64% +/- 4.7%) and minimum surface tension values (4.0 +/- 0.9 mN/m) similar to those of P. carinii-free control mice. However, when infected SCID mice were immunologically reconstituted, an intense inflammatory response ensued. Pr/PL ratios (218% +/- 42%) and minimum surface tension values (27.2 +/- 2.7 mN/m) of the lavage fluid were significantly elevated compared to those of the lavage fluid from infected, nonreconstituted mice (P < 0.05). To examine the specific role of CD8(+) T-cell-mediated inflammation in surfactant dysfunction during PCP, mice with defined T-cell populations were studied. P. carinii-infected, CD4(+)-depleted mice had elevated lavage fluid Pr/PL ratios (126% +/- 20%) and elevated minimum surface tension values (16.3 +/- 1.0 mN/m) compared to normal mice (P < 0.05). However, when infected mice were additionally depleted of CD8(+) cells, Pr/PL ratios were normal and surfactant activity was improved. These findings demonstrate that the surfactant pathology associated with PCP is related to the inflammatory process rather than being a direct effect of P. carinii. Moreover, CD8(+) lymphocytes are involved in the mechanism leading to surfactant dysfunction.

Cyclooxygenase-2 in human perinatal lung

Cyclooxygenases-1 and -2 are the key enzymes in the conversion of arachidonic acid to prostanoids. Cyclooxygenase-2 (COX-2) takes part both in inflammation and in control of cell growth. COX-2 immunohistochemistry was performed on lung tissues from autopsies, with four groups included: fetuses (n = 4, GA = 16.0 to 32.0 wk), preterm infants (n = 10, GA = 23.0 to 29.9 wk), term infants (n = 6, GA = 38.7 to 42.0 wk), and infants with bronchopulmonary dysplasia (BPD) (n = 4, GA = 28.9 to 30.7 wk). COX-2 staining occurred exclusively in the epithelial cells resembling type II pneumocytes in the alveolae, and in ciliated epithelial cells in the bronchi. In fetuses, moderate intensity alveolar staining was seen in 90-100% cells lining the alveolar epithelium. In preterm infants, high intensity alveolar staining was seen in a scattered pattern. In term infants, the alveolar staining was also scattered, but with a lower proportion of positive cells. In BPD no staining appeared in alveolar epithelial cells. The most intense bronchial staining was found in fetuses and the least intense in term infants; staining was also seen in BPD. COX-2 is present in human perinatal lung from the gestational age of 16 wk, in a changing pattern. We suggest that COX-2 may, in addition to participating in inflammation, also play a developmental role in the perinatal lung.

Tumor necrosis factor-alpha inhibits expression of CTP:phosphocholine cytidylyltransferase

We investigated the effects of tumor necrosis factor alpha (TNFalpha), a key cytokine involved in inflammatory lung disease, on phosphatidylcholine (PtdCho) biosynthesis in a murine alveolar type II epithelial cell line (MLE-12). TNFalpha significantly inhibited [(3)H]choline incorporation into PtdCho after 24 h of exposure. TNFalpha reduced the activity of CTP:phosphocholine cytidylyltransferase (CCT), the rate-regulatory enzyme within the CDP-choline pathway, by 40% compared with control, but it did not alter activities of choline kinase or cholinephosphotransferase. Immunoblotting revealed that TNFalpha inhibition of CCT activity was associated with a uniform decrease in the mass of CCTalpha in total cell lysates, cytosolic, microsomal, and nuclear subfractions of MLE cells. Northern blotting revealed no effects of the cytokine on steady-state levels of CCTalpha mRNA, and CCTbeta mRNA was not detected. Incorporation of [(35)S]methionine into immunoprecipitable CCTalpha protein in pulse and pulse-chase studies revealed that TNFalpha did not alter de novo synthesis of enzyme, but it substantially accelerated turnover of CCTalpha. Addition of N-acetyl-Leu-Leu-Nle-CHO (ALLN), the calpain I inhibitor, or lactacystin, the 20 S proteasome inhibitor, blocked the inhibition of PtdCho biosynthesis mediated by TNFalpha. TNFalpha-induced degradation of CCTalpha protein was partially blocked by ALLN or lactacystin. CCT was ubiquitinated, and ubiquitination increased after TNFalpha exposure. m-Calpain degraded both purified CCT and CCT in cellular extracts. Thus, TNFalpha inhibits PtdCho synthesis by modulating CCT protein stability via the ubiquitin-proteasome and calpain-mediated proteolytic pathways.

Effects of intratracheal instillation of TNF-alpha on surfactant metabolism

Tumor necrosis factor-alpha (TNF-alpha) has been shown to play an integral role in the pathogenesis of the acute respiratory distress syndrome. This disorder is characterized by a deficiency of alveolar surfactant, a surface-active material that is composed of key hydrophobic proteins and the major lipid disaturated phosphatidylcholine (DSPC). We investigated how TNF-alpha might alter DSPC content in rat lungs by instilling the cytokine (2.5 microg) intratracheally for 10 min and then assaying parameters of DSPC synthesis and degradation in alveolar type II epithelial cells, which produce surfactant. Cells isolated from rats given TNF-alpha had 26% lower levels of phosphatidylcholine compared with control. TNF-alpha treatment also decreased the ability of these cells to incorporate [(3)H]choline into DSPC by 45% compared with control isolates. There were no significant differences in the levels of choline substrate or choline transport between the groups. However, TNF-alpha produced a 64% decrease in the activity of cytidylyltransferase, the rate-regulatory enzyme required for DSPC synthesis. TNF-alpha administration in vivo also tended to stimulate phospholipase A(2) activity, but it did not alter other parameters for DSPC degradation such as activities for phosphatidylcholine-specific phospholipase C or phospholipase D. These observations indicate that TNF-alpha decreases the levels of surfactant lipid by decreasing the activity of a key enzyme involved in surfactant lipid synthesis. The results do not exclude stimulatory effects of the cytokine on phosphatidylcholine breakdown.

Local effect of lung contusion on lung surfactant composition in multiple trauma patients

OBJECTIVE

The aim of this study was to investigate the direct influence of lung contusion on pulmonary surfactant in multiple trauma patients.

DESIGN

Prospective, nonrandomized study.

SETTING

University hospital, trauma intensive care unit.

PATIENTS

Eighteen multiple trauma patients with unilateral lung contusions and Injury Severity Scores >19 were studied prospectively.

INTERVENTIONS

Bronchoalveolar lavage was performed daily until either day 7 or extubation. Samples from the side of lung contusion (n = 62) and the contralateral, uninjured side (n = 62) were obtained at the same time in 14 patients. Total phospholipids, total phospholipid classes, and surfactant apoprotein A were quantified. Additionally, surfactant function was measured with a pulsating bubble surfactometer in four patients. All data are presented as mean +/- SEM. Statistical analyses were performed using programs of SPSS for Windows 6.1.3 (SPSS Inc., Chicago, IL) (Student's t-test; p < .05).

MEASUREMENTS AND MAIN RESULTS

Total phospholipids were significantly increased on the side of lung contusion (contusion side, 40+/-7 microg/mL; contralateral side, 21+/-3 microg/mL; p = .004). The percentage contents of phosphatidylcholine (contusion side, 87.1%+/-1.0%; contralateral side, 84.3%+/-1.0%; p = .04) and sphingomyelin (contusion side, 2.9%+/-0.3%; contralateral side, 1.9%+/-0.2%; p = .004) were significantly higher. In contrast, the percentage content of phosphatidylglycerol was significantly decreased (contusion side, 4.1%+/-0.1%; contralateral side, 6.9%+/-0.6%; p = .001). No alterations were found for the relative contents of phosphatidylethanolamine (contusion side, 2.4%+/-0.2%; contralateral side, 2.2%+/-0.2%; p = .47), phosphatidylinositol (contusion side, 3.5%+/-0.4%; contralateral side, 4.6%+/-0.5%; p = .06), and surfactant apoprotein A (contusion side, 7177+/-1404 ng/mL; contralateral side, 4513+/-787 ng/mL, p = .10). There was no statistical difference for minimal surface tension measured with the pulsating bubble surfactometer after 5 mins of oscillation (contusion side, 29.5+/-2.3 mN/m; contralateral side, 23.7+/-2.1 mN/m; p = .08).

CONCLUSIONS

Direct damage of lung parenchyma by lung contusion alters the composition of surfactant. No additional changes in surfactant function were observed that would argue in favor of functional compensation.

Effects of tumor necrosis factor alpha (TNF alpha) on the phospholipid metabolism of Tetrahymena pyriformis

The effect of (0.05 ng ml-1 and 0.1 ng ml(-1)) TNF alpha on the phospholipid metabolism of Tetrahymena pyriformis was studied. The amount of phosphatidyl choline (PC), phosphatidyl inositol (PI), phosphatidic acid (PA), phosphatidyl ethanolamine (PE), diacylglycerol (DAG), arachidonic acid (AA) and ceramide was higher, but the phosphatidyl inositol 4 phosphate (PIP) and phosphatidyl inositol bis-phosphate (PIP2) as well, as sphingomyelin (SM) content was lower in TNF alpha-treated cells than in the controls. In the culture medium (secreted forms) this situation was reversed. There were differences in the results gained by incorporation of [3H]-palmitic acid or 32P into the phospholipids. To control the functional effects of TNF alpha in Tetrahymena, the rate of cell division, the condensation of chromatin, the viability of cells and morphometrical values have been studied. The cytokine reduced cell growth, altered morphometric indices and increased chromatin condensation, however cell viability was not influenced. The results demonstrate the effects of TNF alpha at a low level of evolution, what is realized by changes in the phospholipid metabolism participating in signalling pathways.

Cyclooxygenase isoenzyme localization and mRNA expression in rat lungs

Prostanoid generation may proceed via both isoforms of cyclooxygenase, Cox-1 and Cox-2. Cox-1 is thought to be ubiquitously expressed, whereas Cox-2 is mostly assumed to be dynamically regulated, responding to inflammatory stimuli. The cellular localization of Cox-1 and Cox-2 in the lung, an organ with high cyclooxygenase activity, is not known. In normal rat lungs the expression and localization of Cox-1 and Cox-2 were examined with immunogold-silver staining and the RT-PCR technique. Quantitative image analysis of the staining intensity was performed by measuring mean gray values of digitized epipolarization images. Expression of both Cox-1 and Cox-2 was readily detectable in rat lungs. Cox-1 immunoreactivity localized predominantly to bronchial epithelial cells, smooth muscle cells of large hilum veins, and (with lower expression) to alveolar macrophages and pulmonary artery endothelial cells. The most intense Cox-2 staining was noted in macrophage- and mast cell-like cells, detected in close vicinity to the bronchial epithelium and in the connective tissue surrounding the vessels. In addition, strong Cox-2 expression was found in smooth muscle cells of partially muscular vessels and large veins of the hilum. Bronchial epithelial cells displayed Cox-2 immunoreactivity with limited intensity. Alveolar macrophages and alveolar septal cells were only occasionally stained with anti-Cox-2 antibodies. Both Cox-1 and Cox-2 are constitutively expressed in several cell types of normal rat lung, but display clearly different patterns of cellular localization. Cox-2 may not be related only to lung inflammation, but is suggested to be implicated in regulatory processes under physiological conditions as well.

The effect of clenbuterol and recombinant erythropoietin on tumor growth and the anemia caused by the Walker 256 carcinosarcoma

In patients with advanced cancer, anemia is a common complication indicative of a poor prognosis. Attempts to alleviate this have met with mixed success and interventions including erythropoietin often fail to elicit an appropriate response. We have used rats implanted with the Walker 256 carcinosarcoma as a model of non-responsive anemia. This study demonstrates that the provision of recombinant erythropoietin in the presence of clenbuterol, a beta2 agonist, attenuates both the cancer induced anemia and the growth of the tumor in this model. We hypothesize that this treatment relieves the tumor induced inhibition of hematopoiesis, which allows for not only an increase in hematocrit but an increased immunosurveillance resulting in tumor suppression.

Effect of human recombinant tumour necrosis factor-alpha and pentoxifylline on the ultrastructure of type II alveolar epithelial cells in pregnant and non-pregnant rabbits

An ultrastructural study was made of the morphological changes in type II alveolar epithelial cells (epII) of pregnant and non-pregnant rabbits, given human recombinant tumour necrosis factor-alpha (TNF-alpha) to induce experimental shock. TNF-alpha (biological activity 2-4 x 10(7) U/mg of protein) was injected once intraperitoneally, at a dose of 100 micrograms/kg body weight. The moderating effects of pentoxifylline (PTXF), given as four intraperitoneal doses (20 mg/kg) at 12-h intervals before injection of TNF-alpha, were also assessed. In animals treated with PTXF + TNF-alpha and with TNF-alpha only, damage to lung tissue, particularly to epII, was observed. Many epII had empty lamellar bodies. These changes were particularly distinct in the rabbits given TNF-alpha only. PTXF limited the degree of damage to epII, particularly that shown by the lamellar bodies. There were no significant differences in degree of damage to alveolar epithelial cells between pregnant and non-pregnant rabbits. Thus, the increased risk of severe complications due to shock observed in pregnancy may not be associated with changes in the surfactant system. However, further studies, particularly biochemical analysis of the surfactant, are necessary to confirm this.

Effects of early surfactant treatment persisting for one week after lung transplantation in rats

We investigated whether pulmonary surfactant in rat lung transplants recovered during the first week post-transplantation, along with symptoms of the reimplantation response, and whether this recovery was affected by early surfactant treatment. The severity of pulmonary injury was varied by transplanting left lungs with 6-h and 20-h ischemia (n = 12 and 19, respectively). Half of the transplants were treated by instillation of surfactant before reperfusion. Lungs from sham operated, and normal rats (n = 4 and 5, respectively) served as controls. The pulmonary injury severely impaired lung transplant function; 10 of the worst affected animals died. After 1 wk, symptoms of reimplantation response and properties of pulmonary surfactant were assessed. If untreated, the reimplantation response had almost resolved in the 6-h but not in the 20-h ischemia group; pulmonary surfactant, however, continued to be deficient in both ischemia groups (low amounts of surfactant phospholipids and surfactant protein A [SP-A]). Surfactant treatment improved the recovery from injury in the 20-h ischemia group resulting in normal lung function and amounts of surfactant phospholipids. Amounts of SP-A were not improved by surfactant treatment. In conclusion, early surfactant treatment enhances recovery from transplantation injury and is persistently beneficial for pulmonary surfactant in lung transplants.

Intraamniotic interleukin-1 accelerates surfactant protein synthesis in fetal rabbits and improves lung stability after premature birth

Intraamniotic infection is associated with increased IL-1 activity in amniotic fluid, increased incidence of preterm labor, and with decreased incidence of respiratory distress syndrome in infants born prematurely. We hypothesized that an elevated IL-1 in amniotic fluid promotes fetal lung maturation. On day 23 or 25 of gestation (term 31 d), either IL-1alpha (150 or 1,500 ng per fetus) or its antagonist IL-1 receptor antagonist (IL-1ra, 20 microg) was injected to the amniotic fluid sacs in one uterine horn, whereas the contralateral amniotic sacs were injected with vehicle. Within 40 h, IL-1alpha caused a dose-dependent increase in surfactant protein-A (SP-A) and SP-B mRNAs (maximally, fivefold), without affecting lung growth or increasing inflammatory cells in the lung. Both genders, and upper and lower lung lobes were similarly affected. IL-1ra did not modify SP-A, -B, or -C mRNA. IL-1 increased the intensity of staining of alveolar type II cells for SP-B, and the concentrations of SP-B, -A, and disaturated phosphatidylcholine in bronchoalveolar lavage. The dynamic lung compliance and the postventilatory expansion of lungs were increased two- to fourfold after IL-1alpha treatment. In fetal lung explants, IL-1alpha increased the expression of SP-A mRNA. IL-1 in amniotic fluid in preterm labor may promote lung maturation and thus be part of a host-defense mechanism that prepares the fetus for extrauterine life.

Effect of lung contusion on surfactant composition in multiple-trauma patients

OBJECTIVE

The aim of this study was to investigate alterations of the surfactant system in multiple-trauma patients (MTP) with lung contusion and the influence of single- or multiple-organ dysfunction syndrome (OF/MOF) on the surfactant system.

SETTING

University hospital, trauma-intensive care unit.

DESIGN

Prospective, nonrandomized study.

METHODS

MTP with an Injury Severity Score > 19 points have been recorded prospectively since 1992. Bronchoalveolar lavages were obtained daily either until day 14 or extubation. Three groups of MTP were compared: noL: MTP, no lung contusion (n = 14); LuCo-: MTP, lung contusion, no OF/MOF (n = 17); LuCo+: MTP, lung contusion, with OF/MOF (n = 10). Also, surfactant samples of 11 healthy volunteers (Con) were investigated and compared with MTP. All data were presented as mean +/- SEM. Statistical analysis were performed using programs of SPSS 6.0.1. (univariate ANOVA, Fisher's Exact Test, p < = 0.05).

RESULTS

There were no differences in sex and age. Injury Severity Score was significantly impaired in group LuCo+ (44 +/- 4), compared with groups noL (31 +/- 3) and LuCo- (34 +/- 3). Group noL showed no statistical differences for lung function, total protein, and total phospholipid content of the bronchoalveolar lavage compared with group LuCo-. Furthermore, the relative content of phosphatidylcholine and phosphatidylglycerol in total phospholipids and surfactant-associated protein A were not significantly altered compared with group LuCo-. Lung function in group LuCo+ was significantly impaired and led to hypoxemia on the day of trauma. Total protein content and total phospholipids were significantly elevated in group LuCo+ compared with groups noL and LuCo- on the first day. Also, the relative content of phosphatidylcholine was significantly increased in group LuCo+ up to day 4, compared with groups noL and LuCo-. In comparison with groups noL and LuCo-, a significant decrease of the relative content of phosphatidylglycerol was obtained in group LuCo+ up to day 7. The surfactant-associated protein A was increased in group LuCo+ during the whole observation time, compared with the other groups.

CONCLUSIONS

Multiple trauma leads to alterations in the surfactant system. The composition of surfactant was not further influenced by lung contusion alone. Only MTP with OF/MOF during the intensive care unit treatment showed significant alterations in surfactant composition and a decrease in lung function.

Evidence that the initial up-regulation of phosphatidylcholine biosynthesis in free cholesterol-loaded macrophages is an adaptive response that prevents cholesterol-induced cellular necrosis. Proposed role of an eventual failure of this response in foam cell necrosis in advanced atherosclerosis

Macrophages in atherosclerotic lesions accumulate free cholesterol (FC) as well as cholesteryl ester and appear to have high rates of phospholipid (PL) synthesis and increased PL mass. Previous short term (i.e. </=24 h) studies with cultured macrophages have shown that these cells respond to FC loading by up-regulating phosphatidylcholine biosynthesis. We propose that this response is adaptive by keeping the FC:PL ratio in the macrophages from reaching toxic levels. We further propose that one cause of macrophage necrosis, a prominent and important event in atherosclerosis, is an eventual decrease of this adaptive response. To explore these ideas, cultured macrophages were loaded with FC for up to 4 days and assayed for phosphatidylcholine biosynthesis, FC and PL mass, and cytotoxicity. For the first 24 h, cellular phosphatidylcholine biosynthesis and FC and PL mass increased 3-4-fold, and thus the FC:PL molar ratio was prevented from reaching very high levels; at this point, there were no overt signs of cytotoxicity. Over the next 24-48 h, however, phosphatidylcholine biosynthesis, and then phosphatidylcholine mass, began to decrease. Initially, the macrophages remained healthy and continued to accumulate FC, but eventually these macrophages, but not unloaded macrophages, became necrotic (swollen organelles and disrupted membranes). Lipoprotein dose studies indicated a close relationship between the onset of macrophage necrosis and the FC:PL ratio. To test further the causal nature of these relationships, cellular FC and PL mass were independently manipulated by using high density lipoprotein3 (HDL3) to decrease cellular FC and choline depletion to decrease cellular PC. As predicted by our hypotheses, HDL3 protected FC-loaded macrophages from necrosis, whereas choline depletion accelerated cytotoxic changes. These findings support the idea that the initial increase in phosphatidylcholine biosynthesis in FC-loaded macrophages is an adaptive response that prevents cholesterol-induced macrophage necrosis. We propose that an eventual failure of the PL response in foam cells may represent one cause of macrophage necrosis in advanced atherosclerotic lesions.

Cytokines and production of surfactant components

The production of pulmonary surfactant, a complex of lipids and proteins that reduces surface tension at the alveolar air-liquid interface, is developmentally regulated. Several hormones, most notably glucocorticoids, are known to accelerate maturation of the surfactant system. Cytokines are polypeptides that act mostly in a paracrine fashion and possess a wide spectrum of activities on multiple types of cells. Many cytokines are produced by different lung cells a various stages of fetal development or under pathological conditions affecting the fetus. In addition, cytokines present in amniotic fluid or in the blood stream may reach the fetal lungs. Some cytokines, including epidermal growth factor, transforming growth factor-alpha, and interferon-gamma have been shown to stimulate the production of surfactant components. On the other hand, tumor necrosis factor and transforming growth factor-beta downregulate the production of surfactant lipids and proteins. We have recently shown that the proinflammatory cytokine interleukin-1 (IL-I) enhances the expression of surfactant protein A (SP-A) in fetal rabbit lung explants. In addition, injection of IL-I into the amniotic fluid of fetal rabbits enhances the expression of surfactant proteins and improves the lung compliance of preterm animals. Preterm delivery is often associated with subclinical intraamniotic infection. In these cases, amniotic fluid concentrations of IL-I are often elevated. We propose that this cytokine accelerates maturation of the surfactant system in fetal lungs and thus prepares the fetus for extrauterine life.

Stimulation of CTP:phosphocholine cytidylyltransferase by free cholesterol loading of macrophages involves signaling through protein dephosphorylation

Free cholesterol-loaded macrophages in atheromata synthesize excess phosphatidylcholine (PC), which may be an important adaptive response to the excess free cholesterol (FC) load. We have recently shown that FC loading of macrophages leads to 2-4-fold increases in PC mass and biosynthesis and to the post-translational activation of the membrane-bound form of CTP:phosphocholine cytidylyltransferase (CT), a key enzyme in PC biosynthesis. Herein, we explore further the mechanism of CT activation in FC-loaded macrophages. First, enrichment of membranes from control macrophages with FC in vitro did not increase CT activity, and PC biosynthesis in vivo is up-regulated by FC loading even when CT and FC appear to be mostly in different intracellular sites. These data imply that FC activates membrane-bound CT by a signaling mechanism. That the proposed signaling mechanism involves structural changes in the CT protein was suggested by data showing that two different antibodies against synthetic CT peptides showed increased recognition of membrane-bound CT from FC-loaded cells despite no increase in CT protein. Since CT is phosphorylated, two-dimensional maps of peptides from 32P-labeled control and FC-loaded macrophages were compared: six peptide spots from membrane-bound CT, but none from soluble CT, were dephosphorylated in the FC-loaded cells. Furthermore, incubation of FC-loaded macrophages with the phosphatase inhibitor, calyculin A, blocked increases in both PC biosynthesis and antipeptide-antibody recognition of CT. Last, treatment of membranes from control macrophages with lambda phage protein phosphatase in vitro increased both CT activity (2-fold) and antipeptide-antibody recognition of CT; soluble CT activity and antibody recognition were not substantially affected by phosphatase treatment. In summary, FC loading of macrophages leads to the partial dephosphorylation of membrane-bound CT, and possibly other cellular proteins, which appears to be important in CT activation. This novel regulatory action of FC may allow macrophages to adapt to FC loading in atheromata.