Flexible bronchoscopy in molecular biology

Flexible fiberoptic bronchoscopy has allowed researchers to use the bench to bedside approach in the study and therapy of lung diseases. Through bronchoscopy, the lung is a relatively convenient source of samples for the direct evaluation of human gene expression and function. Sampling of respiratory epithelium is performed by brushing with a cytology brush, whereas the epithelial lining fluid and the inflammatory cells in the bronchoalveolar space are obtained by bronchoalveolar lavage. Furthermore, bronchoscopy has been a cornerstone essential to gene therapy trials for lung disease.

Nitric oxide synthase 2 through an autocrine loop via respiratory epithelial cell-derived mediator

Respiratory epithelium expresses nitric oxide synthase 2 (NOS2) continuously in vivo; however, mechanisms responsible for its expression are only partially understood. We definitively identify an autocrine mechanism of induction and maintenance of NOS2 in human airway epithelial cells through the synthesis and secretion of a soluble mediator. Short exposure of human airway cells to interferon (IFN)-γ leads to prolonged NOS2 expression. Transfer of the overlying culture medium (conditioned medium) induces NOS2 expression in other airway epithelial cells, suggesting the presence of an intermediary substance regulating NOS2 expression in an autocrine loop. Characterization of the soluble mediator reveals that it is stable and transferable in conditioned medium for up to 7 days. However, soluble mediator does not induce NOS2 mRNA in human alveolar macrophages, indicating that the response to soluble mediator is unique to human respiratory epithelium. Soluble mediator is heat labile but is not inactivated by acid treatment, unlike IFN-γ itself. Importantly, IFN regulatory factor-1, which is critical for murine NOS2 expression, is expressed and activated by soluble mediator through the signal transducer and activator of transcription-1-dependent pathway. Based on these findings, we propose novel regulatory mechanisms for NOS2 expression in human airway epithelium.

Double-stranded rna dependence of nitric oxide synthase 2 expression in human bronchial epithelial cell lines BET-1A and BEAS-2B

The human airway epithelium expresses abundant nitric oxide synthase 2 (NOS2) in vivo. Although NOS2 is easily induced by cytokines in primary cultured human airway epithelial cells and lung adenocarcinoma cell line A549, the human bronchial epithelial cell lines BEAS-2B and BET-1A do not express NOS2 in response to cytokines. Mechanisms regulating NOS2 expression in human respiratory epithelial cells are complex, but we have recently shown that NOS2 expression in primary human airway epithelial cells occurs in response to double-stranded RNA (dsRNA) through activation of signaling proteins including nuclear factor (NF)-kappaB and interferon (IFN) regulatory factor (IRF)-1. In this context, we hypothesized that BEAS-2B and BET-1A cells may express NOS2 in response to dsRNA. Here, we show that although cytokines (IFN-gamma, tumor necrosis factor-alpha and interleukin-1beta) do not induce NOS2 expression in BEAS-2B or BET-1A cells, addition of dsRNA to this cytokine mix enables BEAS-2B cells to express NOS2. IFN-gamma and dsRNA induction of NOS2 in BET-1A cells occurs in a serum concentration-dependent manner, with a minimum of 3 d of serum treatment necessary for BET-1A cells to acquire the potential to induce NOS2. Importantly, dsRNA strongly activates NF-kappaB and IRF-1 in BEAS-2B cells, transcription factors essential for NOS2 gene expression in other cell lines. On the basis of these results, dsRNA-activated signaling pathways are clearly important for NOS2 expression in human respiratory epithelial cells. With conditions for NOS2 expression characterized, these cell lines are a convenient in vitro system to investigate the mechanisms regulating NOS2 expression in human respiratory epithelial cells.

Eosinophils are a major source of nitric oxide-derived oxidants in severe asthma: characterization of pathways available to eosinophils for generating reactive nitrogen species

Eosinophil recruitment and enhanced production of NO are characteristic features of asthma. However, neither the ability of eosinophils to generate NO-derived oxidants nor their role in nitration of targets during asthma is established. Using gas chromatography-mass spectrometry we demonstrate a 10-fold increase in 3-nitrotyrosine (NO(2)Y) content, a global marker of protein modification by reactive nitrogen species, in proteins recovered from bronchoalveolar lavage of severe asthmatic patients (480 +/- 198 micromol/mol tyrosine; n = 11) compared with nonasthmatic subjects (52.5 +/- 40.7 micromol/mol tyrosine; n = 12). Parallel gas chromatography-mass spectrometry analyses of bronchoalveolar lavage proteins for 3-bromotyrosine (BrY) and 3-chlorotyrosine (ClY), selective markers of eosinophil peroxidase (EPO)- and myeloperoxidase-catalyzed oxidation, respectively, demonstrated a dramatic preferential formation of BrY in asthmatic (1093 +/- 457 micromol BrY/mol tyrosine; 161 +/- 88 micromol ClY/mol tyrosine; n = 11 each) compared with nonasthmatic subjects (13 +/- 14.5 micromol BrY/mol tyrosine; 65 +/- 69 micromol ClY/mol tyrosine; n = 12 each). Bronchial tissue from individuals who died of asthma demonstrated the most intense anti-NO(2)Y immunostaining in epitopes that colocalized with eosinophils. Although eosinophils from normal subjects failed to generate detectable levels of NO, NO(2-), NO(3-), or NO(2)Y, tyrosine nitration was promoted by eosinophils activated either in the presence of physiological levels of NO(2-) or an exogenous NO source. At low, but not high (e.g., >2 microM/min), rates of NO flux, EPO inhibitors and catalase markedly attenuated aromatic nitration. These results identify eosinophils as a major source of oxidants during asthma. They also demonstrate that eosinophils use distinct mechanisms for generating NO-derived oxidants and identify EPO as an enzymatic source of nitrating intermediates in eosinophils.

High levels of exhaled nitric oxide (NO) and NO synthase III expression in lesional smooth muscle in lymphangioleiomyomatosis

Smooth-muscle proliferation is the hallmark of lymphangioleiomyomatosis (LAM). Although little is known about the pathogenesis of LAM, nitric oxide (NO) is a key regulator of smooth-muscle proliferation. NO is linked to the pathogenesis of other lung diseases such as asthma, in part by the finding of higher-than-normal levels of exhaled NO. If NO were involved in the abnormal smooth-muscle proliferation in LAM, we reasoned that exhaled NO from individuals with LAM would also differ from that of healthy control subjects. To evaluate this hypothesis, we studied exhaled NO in individuals with LAM in comparison with healthy and asthmatic women using a chemiluminescent NO analyzer. Women with LAM had higher exhaled NO than did healthy women but lower than asthmatic women (NO [parts per billion] median (25 to 75%): LAM 8 [7 to 15] [n = 28], control 6 [5 to 8] [n = 21], asthma 14 [8 to 25] [n = 22]; Kruskal-Wallis P < 0.001). Immunohistochemical studies on formalin-fixed, paraffin-embedded sections of surgical and autopsy material from lungs of individuals with LAM showed diffuse NO synthase III (NOSIII) expression in the lesional smooth muscle of LAM similar to that in the vascular endothelium. NOSIII expression was limited to the vascular endothelium and bronchial smooth muscle in healthy control lungs. The increased NO and the presence of NOSIII expression in lesional smooth muscle warrants further study into the potential role for NO in the pathogenesis of LAM.

NO chemical events in the human airway during the immediate and late antigen-induced asthmatic response

A wealth of evidence supports increased NO (NO.) in asthma, but its roles are unknown. To investigate how NO participates in inflammatory airway events in asthma, we measured NO. and NO. chemical reaction products [nitrite, nitrate, S-nitrosothiols (SNO), and nitrotyrosine] before, immediately and 48 h after bronchoscopic antigen (Ag) challenge of the peripheral airways in atopic asthmatic individuals and nonatopic healthy controls. Strikingly, NO(3)(-) was the only NO. derivative to increase during the immediate Ag-induced asthmatic response and continued to increase over 2-fold at 48 h after Ag challenge in contrast to controls [P < 0.05]. NO(2)(-) was not affected by Ag challenge at 10 min or 48 h after Ag challenge. Although SNO was not detectable in asthmatic airways at baseline or immediately after Ag, SNO increased during the late response to levels found in healthy controls. A model of NO. dynamics derived from the current findings predicts that NO. may have harmful effects through formation of peroxynitrite, but also subserves an antioxidant role by consuming reactive oxygen species during the immediate asthmatic response, whereas nitrosylation during the late asthmatic response generates SNO, safe reservoirs for removal of toxic NO. derivatives.

Extracellular glutathione peroxidase induction in asthmatic lungs: evidence for redox regulation of expression in human airway epithelial cells

A critical first-line antioxidant defense on the airway epithelial surface against reactive oxygen and nitrogen species (ROS and RNS) is extracellular glutathione peroxidase (eGPx). Little is known about the regulation of eGPx or its role in ROS-mediated lung diseases such as asthma. Here we show that eGPx is increased in the asthmatic airway in comparison to healthy controls. Higher levels of eGPx mRNA in asthmatic airway epithelium verified bronchial epithelial cells as the source for the increased eGPx. The eGPx mRNA in bronchial epithelial cells in vitro increased eightfold after exposure to ROS and glutathione, an essential cofactor for eGPx activity. Alterations in intracellular and extracellular oxidized and reduced glutathione were temporally associated with eGPx induction, further supporting redox mechanisms in gene expression. Overexpression of superoxide dismutase, but not catalase, inhibited induction and identified superoxide as a key intermediary. The eGPx mRNA half-life was not affected by ROS, suggesting a transcriptional mechanism for eGPx regulation. Fusion genes of deletion fragments of the eGPx gene 5' flanking region driving a reporter gene conclusively identified the ROS-responsive region, which contained the consensus DNA binding site for the redox-regulated transcription factor, activator protein 1.

Differential induction of extracellular glutathione peroxidase and nitric oxide synthase 2 in airways of healthy individuals exposed to 100% O(2) or cigarette smoke

Reactive oxygen species (ROS) is increased in the airway during the inhalation of 100% O(2) or cigarette smoke and participates in the development of tracheobronchitis. We hypothesized that inhaled ROS upregulates local extracellular ROS scavenging systems or reactive molecules, e.g., nitric oxide (NO). Extracellular glutathione peroxidase (eGPx) is synthesized by airway epithelium and alveolar macrophages, secreted into the surface epithelial lining fluid, and functions as a first-line defense against inhaled ROS. NO, produced by NO synthase 2 (NOS2), combines rapidly with ROS to form reactive nitrogen species (RNS). In this study, human airway epithelial cells and alveolar macrophages from healthy individuals before and after exposure to 100% O(2) for 12 h, or from cigarette-smoking individuals, were evaluated for eGPx and NOS2 messenger RNA (mRNA) expression. Hyperoxia increased NOS2 mRNA in airway epithelial cells by 2.5-fold but did not increase eGPx mRNA. In contrast, cigarette smoke upregulated eGPx mRNA over 2-fold in airway epithelial cells and alveolar macrophages but did not affect NOS2 expression. In vitro exposure of respiratory epithelial cells to ROS or RNS also increased eGPx expression. These findings define distinct molecular responses in the airway to different inhaled ROS, which likely influences the susceptibility of the airway to oxidative injury.

Interleukin-9 receptor expression in asthmatic airways In vivo

Inflammation of the airway wall is a defining feature in asthma and is likely the cause of the hyperreactivity and variable airflow limitation found in asthma. Immune response biased toward production of Th2 cytokines has been proposed as a mechanism in the pathogenesis of airway inflammation in asthma. The Th2 cytokine interleukin-9 (IL-9) is one candidate gene for asthma on the basis of position cloning and animal models of airway inflammation. To determine whether IL-9 is involved in the chronic inflammation of the asthmatic airway, we investigated the expression of IL-9 and the IL-9 specific receptor chain in asthmatic airways compared with healthy airways. IL-9 and IL-9 receptor expression in airway epithelial cells and bronchoalveolar lavage cells obtained at bronchoscopy of healthy (n = 9) and mild intermittent asthmatic individuals (n = 7) were studied by Northern analyses and reverse-transcription polymerase chain reaction technique. Primary and transformed human airway epithelial cells were also evaluated for IL-9 specific receptor chain expression in vitro. IL-9 was not detected in airways of healthy or mild asthmatic individuals. In contrast, IL-9 specific receptor chain expression was found in asthmatic airway samples but not in healthy controls. In vitro, airway epithelial cells did not express IL-9 specific receptor chain until stimulation with interferon gamma. Our results support that IL-9 may play a role in the mechanism leading to chronic airway inflammation and asthma.

Central role of double-stranded RNA-activated protein kinase in microbial induction of nitric oxide synthase

NO synthase 2 (NOS2) is induced in airway epithelium by influenza virus infection. NOS2 induction late in the course of viral infection may occur in response to IFN-gamma, but early in infection gene expression may be induced by the viral replicative intermediate dsRNA through the dsRNA-activated protein kinase (PKR). Since PKR activates signaling pathways important in NOS2 gene induction, we determined whether PKR is a component in the signal transduction pathway leading to NOS2 gene expression after viral infection of airway epithelium. We show that NOS2 gene expression in human airway epithelial cells occurs in response to influenza A virus or synthetic dsRNA. Furthermore, dsRNA leads to rapid activation of PKR, followed by activation of signaling components including NF-kappaB and IFN regulatory factor 1. NOS2 expression is markedly diminished and IFN regulatory factor 1 and NF-kappaB activation are substantially impaired in PKR null cells. Strikingly, NOS2 induction in response to LPS is abolished in PKR null cells, confirming a central role for PKR in the general signaling pathway to NOS2.

Molecular mechanisms of increased nitric oxide (NO) in asthma: evidence for transcriptional and post-translational regulation of NO synthesis

Evidence supporting increased nitric oxide (NO) in asthma is substantial, although the cellular and molecular mechanisms leading to increased NO are not known. Here, we provide a clear picture of the events regulating NO synthesis in the human asthmatic airway in vivo. We show that human airway epithelium has abundant expression of NO synthase II (NOSII) due to continuous transcriptional activation of the gene in vivo. Individuals with asthma have higher than normal NO concentrations and increased NOSII mRNA and protein due to transcriptional regulation through activation of Stat1. NOSII mRNA expression decreases in asthmatics receiving inhaled corticosteroid, treatment effective in reducing inflammation in asthmatic airways. In addition to transcriptional mechanisms, post-translational events contribute to increased NO synthesis. Specifically, high output production of NO is fueled by a previously unsuspected increase in the NOS substrate, l -arginine, in airway epithelial cells of asthmatic individuals. Finally, nitration of proteins in airway epithelium provide evidence of functional consequences of increased NO. In conclusion, these studies define multiple mechanisms that function coordinately to support high level NO synthesis in the asthmatic airway. These findings represent a crucial cornerstone for future therapeutic strategies aimed at regulating NO synthesis in asthma.

Eosinophils generate brominating oxidants in allergen-induced asthma

Eosinophils promote tissue injury and contribute to the pathogenesis of allergen-triggered diseases like asthma, but the chemical basis of damage to eosinophil targets is unknown. We now demonstrate that eosinophil activation in vivo results in oxidative damage of proteins through bromination of tyrosine residues, a heretofore unrecognized pathway for covalent modification of biologic targets in human tissues. Mass spectrometric studies demonstrated that 3-bromotyrosine serves as a specific "molecular fingerprint" for proteins modified through the eosinophil peroxidase-H(2)O(2) system in the presence of plasma levels of halides. We applied a localized allergen challenge to model the effects of eosinophils and brominating oxidants in human lung injury. Endobronchial biopsy specimens from allergen-challenged lung segments of asthmatic, but not healthy control, subjects demonstrated significant enrichments in eosinophils and eosinophil peroxidase. Baseline levels of 3-bromotyrosine in bronchoalveolar lavage (BAL) proteins from mildly allergic asthmatic individuals were modestly but not statistically significantly elevated over those in control subjects. After exposure to segmental allergen challenge, lung segments of asthmatics, but not healthy control subjects, exhibited a >10-fold increase in BAL 3-bromotyrosine content, but only two- to threefold increases in 3-chlorotyrosine, a specific oxidation product formed by neutrophil- and monocyte-derived myeloperoxidase. These results identify reactive brominating species produced by eosinophils as a distinct class of oxidants formed in vivo. They also reveal eosinophil peroxidase as a potential therapeutic target for allergen-triggered inflammatory tissue injury in humans.

Primary pulmonary hypertension: update on pathogenesis and novel therapies

Primary pulmonary hypertension is a progressive and fatal disease that chiefly affects young adults. Although its etiology is a mystery, recent research has uncovered several biochemical derangements in this disorder, and new therapies are prolonging survival.

Rapid loss of superoxide dismutase activity during antigen-induced asthmatic response

Loss of superoxide dismutase activity occurs within minutes of an acute asthmatic response to segmental antigen instillation into the lung of individuals with atopic asthma. Decreased activity undoubtedly contributes to airway inflammation and injury through increased formation of reactive oxygen and nitrogen species, and suggests that enrichment of lung antioxidants is therapeutic for asthma.

Nitric oxide regulation of asthmatic airway inflammation with segmental allergen challenge

BACKGROUND

Despite evidence of increased nitric oxide (NO) in asthmatic compared with healthy individuals, the role of NO in airway inflammation is unclear.

OBJECTIVE

The purpose of the study was to determine the in vivo effects of localized allergen challenge on airway NO levels and transcription factor activation.

METHODS

In this study localized allergen challenge was used as a model of asthmatic exacerbation to determine the relationship of NO to airway inflammation.

RESULTS

With allergen challenge, asthmatic patients had a rise in airway NO levels, whereas NO levels in healthy controls did not change. The increased NO in asthma with allergen challenge compared with healthy control subjects was associated with an increase in inflammatory cytokines (GM-CSF and macrophage inflammatory protein-1) in epithelial lining fluid and eosinophilic infiltrate in bronchoalveolar lavage fluid (BAL) and biopsy specimens. To investigate the mechanisms of cytokine gene expression, activation of the transcription factors activator protein-1 and nuclear factor-kappaB (NF-kappaB) in cells from BAL were evaluated. Activator protein-1 was not activated before or after local allergen challenge. In contrast, NF-kappaB activation was less in BAL cells from asthmatic patients with increased NO in comparison with controls.

CONCLUSION

Our studies are the first to suggest an inverse correlation between NF-kappaB and airway NO in a localized segmental allergen challenge model in allergic asthmatic patients. The current study demonstrates that activation of the inflammatory response (eg, cytokines, cellular infiltrate) in allergic asthmatic patients is temporally associated with increased airway NO. We propose that NO that is up-regulated by cytokines is part of an autoregulatory feedback loop (ie, allergen challenge stimulates inflammatory cytokine production, which in turn stimulates NO production, and NO down-regulates cytokine production).

Nitric oxide blocks nuclear factor-kappaB activation in alveolar macrophages

Nitric oxide (NO) is an important endogenous regulatory molecule implicated in both proinflammatory and antiinflammatory processes in the lung. Previously, we demonstrated that in human alveolar macrophages (AM), NO decreased inflammatory cytokine production, including that of interleukin-1beta, tumor necrosis factor-alpha and macrophage inflammatory protein-1alpha. One mechanism by which NO could regulate such diverse cytokine production is through effects on the transcription factor nuclear factor-kappaB (NF-kappaB), which controls the expression of the genes for these inflammatory cytokines and growth factors. We therefore investigated whether NO affects NF-kappaB activation in AM in vitro and in vivo. In vitro studies with AM showed that NF-kappaB activation by lipopolysaccharide (LPS) is decreased by NO in a dose-dependent manner. NO prevented an LPS-mediated decrease in the NF-kappaB inhibitory protein IkappaB-alpha. In asthma, airway NO levels are increased, whereas in primary pulmonary hypertension (PPH), airway NO levels are lower than in healthy lungs. In vivo investigations were conducted with freshly isolated AM from healthy controls, asthmatic individuals, and PPH patients. Healthy individuals had airway NO levels of 8 +/- 2 ppb (mean +/- SEM), which is associated with low NF-kappaB activation. Asthma patients with airway NO levels > 17 ppb showed minimal NF-kappaB activation, whereas asthmatic individuals with NO levels </= 17 ppb showed greater NF-kappaB activation. PPH patients with low NO (1 +/- 1 ppb) had prominent NF-kappaB activation. These in vivo studies in asthma and PPH support the in vitro observation of an inverse relationship between NO and NF-kappaB activation. One mechanism by which NO blocks cytokine production involves IkappaB.

Variant forms of DNA polymerase beta in primary lung carcinomas

DNA polymerase beta (pol beta) provides most of the gap-filling synthesis at apurinic/apyrimidine sites of damaged DNA in the base excision repair pathway. A truncated form of the pol beta protein is expressed in colon and breast cancers. However, the role of the pol beta gene in lung cancer is not known. Thus, we investigated a possible occurrence of pol beta variants in primary lung tumors. The entire cDNA of pol beta obtained by RT-PCR amplification was analyzed for nucleotide sequencing in lung tumor and matched normal lung tissue of the same patient. Three types of variants were detected in squamous, non-small, or large cell carcinomas. The most common variant was a deletion of 87 bp from pol beta cDNA at a site corresponding to exon 11. In addition, a variant exhibiting deletions of 87 and 140 bp together with an insertion of 105 bp was identified in three lung tumors. This is the first report of the occurrence of pol beta variants, possibly splicing variants, in lung cancer. A truncated pol beta protein resulting from variant forms of the gene may impact the function of the enzyme and increase susceptibility to carcinogenesis.

Increased glutathione and glutathione peroxidase in lungs of individuals with chronic beryllium disease

Reactive oxygen species (ROS) are mediators of chronic tissue damage and fibrosis. Endogenous antioxidants may increase in response to oxidants and reduce tissue injury. We investigated the antioxidant response of the lungs to the chronic release of ROS, as occurs in the immune-specific granulomatous inflammation of chronic beryllium disease (CBD), and compared it with that in healthy controls and individuals exposed to cigarette smoke. The antioxidants superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and glutathione (GSH) were quantitated in lung epithelial lining fluid (ELF) and serum from control subjects (n = 10), cigarette smokers (n = 8), and individuals with CBD (n = 9). GPx activity and extracellular GPx (eGPx) protein were increased in the ELF of subjects with CBD in comparison with that of control subjects and smokers (eGPx in ELF: controls, 1.3 +/- 0.2 microgram/ml, smokers, 1.9 +/- 0.3 microgram/ml, CBD, 3.8 +/- 0.8 microgram/ml; p = 0.002; GPx U/ml ELF, controls 1.4 +/- 0.3, smokers 1.8 +/- 0.4, CBD, 4.5 +/- 1, p = 0.02). Smokers' ELF had higher levels of GSH than that of controls, but CBD patients' ELF contained much more GSH than that of either controls or smokers (p < 0.001). Increases in GSH were correlated with eGPx, indicating similar inducing mechanisms for these antioxidants. Thus, coordinate augmentation of the glutathione antioxidant system occurs in granulomatous lung inflammation.

Adenoviral reporter gene transfer to the human trabecular meshwork does not alter aqueous humor outflow. Relevance for potential gene therapy of glaucoma

Obstruction of the aqueous humor outflow from the anterior chamber of the eye leads to an elevation of intraocular pressure in glaucoma, the second major cause of blindness worldwide. Our goal is to be able to modulate aqueous humor outflow resistance by gene transfer to the cells of the trabecular meshwork (TM). We have previously shown that adenoviral vectors are able to transfer a reporter gene to the TM of postmortem human donors. However, assessing gene therapy for glaucoma requires models that can monitor changes in aqueous humor outflow facility (C = flow/pressure). In this study we used four replication-deficient adenoviruses in two such perfusion models. In the first model, whole porcine eyes were infected, perfused at constant pressure and flow changes recorded for 5 h. In the second one, anterior segments from human eyes were infected, perfused at constant flow and pressure changes recorded for 3 days. A single dose of 10(8) adenovirus plaque forming units (pfu) causes a reduction in C while single doses of 10(7), 10(6) and 10(5) p.f.u. do not affect outflow facility and retain positive gene transfer. These findings indicate that adenovirus, at effective doses, could become useful vectors for gene therapy of glaucoma.

Human vascular endothelial cells express oxytocin receptors

Pharmacological studies in humans and animals suggest the existence of vascular endothelial vasopressin (AVP)/oxytocin (OT) receptors that mediate a vasodilatory effect. However, the nature of the receptor subtype(s) involved in this vasodilatory response remains controversial, and its coupled intracellular pathways are unknown. Thus, we set out to determine the type and signaling pathways of the AVP/OT receptor(s) expressed in human vascular endothelial cells (ECs). Saturation binding experiments with purified membranes of primary cultures of ECs from human umbilical vein (HUVEC), aorta (HAEC), and pulmonary artery (HPAEC) and [3H]AVP or [3H]OT revealed the existence of specific binding sites with a greater affinity for OT than AVP (Kd = 1.75 vs. 16.58 nM). Competition binding experiments in intact HUVECs (ECV304 cell line) with the AVP antagonist [125I]4-hydroxyphenacetyl-D-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-NH2 or the OT antagonist [125I]D(CH2)5[O-Me-Tyr-Thr-Orn-Tyr-NH2]vasotocin, and various AVP/OT analogs confirmed the existence of a single class of surface receptors of the classical OT subtype. RT-PCR experiments with total RNA extracted from HUVEC, HAEC, and HPAEC and specific primers for the human V1 vascular, V2 renal, V3 pituitary, and OT receptors amplified the OT receptor sequence only. No new receptor subtype could be amplified when using degenerate primers. DNA sequencing of the coding region of the human EC OT receptor revealed a nucleotide sequence 100% homologous to that of the uterine OT receptor reported previously. Stimulation of ECs by OT produced mobilization of intracellular calcium and the release of nitric oxide that was prevented by chelation of extra- and intracellular calcium. No stimulation of cAMP or PG production was noted. Finally, OT stimulation of ECs led to a calcium- and protein kinase C-dependent cellular proliferation response. Thus, human vascular ECs express OT receptors that are structurally identical to the uterine and mammary OT receptors. These endothelial OT receptors produce a calcium-dependent vasodilatory response via stimulation of the nitric oxide pathway and have a trophic action.

Characterization of inducible nitric oxide synthase expression in human airway epithelium

Nitric oxide is an important mediator of inflammatory responses in the lung and a key regulator of pulmonary vascular and bronchomotor tone. We have shown that the inducible nitric oxide synthase (iNOS) isoform is continuously expressed in human airway epithelium at mRNA and protein/activity levels in vivo. However, removal of epithelial cells from the in vivo airway environment resulted in rapid loss of iNOS expression, which suggested that expression is dependent upon conditions and/or factors present in the airway. To investigate the mechanisms responsible for maintenance of expression in vivo, we evaluated regulation of iNOS expression in primary human airway epithelial cells. Interferon-gamma (IFN-gamma) was sufficient for induction of iNOS in primary human airway epithelial cells (HAEC) in vitro, and interleukin-4 (IL-4) potentiated the expression through stabilization of iNOS mRNA. The IFN-gamma/IL-4-induced iNOS expression in HAEC was delayed in onset and prolonged with expression up to 1 week. Furthermore, transfer of overlying culture media [conditioned media (CM)] to other HAEC led to iNOS induction. Interestingly, IFN-gamma/IL-4 induction of iNOS was dependent on new protein synthesis, whereas CM induction of iNOS was not. IFN-gamma and IL-4 activated signal transducers and activators of transcription (STAT1 and STAT6) in HAEC, but CM transfer to HAEC produced even higher levels of STAT1 activation than achieved by direct addition of cytokines. Thus, IFN-gamma/IL-4, which occurs in human lung lining fluid, led to iNOS expression in human airway epithelium through production of soluble mediators and stabilization of mRNA.

Biochemical reaction products of nitric oxide as quantitative markers of primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a rare and fatal disease of unknown etiology. Inflammatory oxidant mechanisms and deficiency in nitric oxide (NO) have been implicated in the pathogenesis of pulmonary hypertension. In order to investigate abnormalities in oxidants and antioxidants in PPH, we studied intrapulmonary NO levels, biochemical reaction products of NO, and antioxidants (glutathione [GSH], glutathione peroxidase [GPx], and superoxide dismutase [SOD]) in patients with PPH (n = 8) and healthy controls (n = 8). Intrapulmonary gases and fluids were sampled at bronchoscopy. Pulmonary hypertension was determined by right-heart catheterization. NO and biochemical reaction products of NO in the lung were decreased in PPH patients in comparison with healthy controls (NO [ppb] in airway gases: control, 8 +/- 1; PPH, 2.8 +/- 0. 9; p = 0.016; and NO products [microM] in bronchoalveolar lavage fluid [BALF]: control, 3.3 +/- 1.05; PPH, 0.69 +/- 0.21; p = 0.03). However, GSH in the lungs of PPH patients was higher than in those of controls (GSH [microM] in BALF: 0.55 +/- 0.04; PPH, 0.9 +/- 0.1; p = 0.015). SOD and GPx activities were similar in the two groups (p >/= 0.50). Biochemical reaction products of NO were inversely correlated with pulmonary artery pressures (R = -0.713; p = 0.047) and with years since diagnosis of PPH (R = -0.776; p = 0.023). NO reaction products are formed through interactions between oxidants and NO, with the end products of reaction dependent upon the relative levels of the two types of molecules. The findings of the study therefore show that NO and oxidant reactions in the lung are related to the increased pulmonary artery pressures in PPH.

iNOS expression in human intestinal microvascular endothelial cells inhibits leukocyte adhesion

Increased nitric oxide (NO) production by inducible nitric oxide synthase (iNOS) has been associated with intestinal inflammation, including human inflammatory bowel disease. However, NO can downregulate endothelial activation and leukocyte adhesion, critical steps in the inflammatory response. Using primary cultures of human intestinal microvascular endothelial cells (HIMEC), we determined the role of NO in the regulation of HIMEC activation and interaction with leukocytes. Both nonselective (NG-monomethyl-L-arginine) and specific (N-iminoethyl-L-lysine) competitive inhibitors of iNOS significantly increased binding of leukocytes by HIMEC activated with cytokines and lipopolysaccharide. Increased adhesion was reversible with the NOS substrate L-arginine and was not observed in human umbilical vein endothelial cells (HUVEC). Activation of HIMEC significantly upregulated HIMEC iNOS expression and NO production. NOS inhibitors did not augment cell adhesion molecule levels in activated HIMEC but did result in sustained increases in intracellular reactive oxygen species. In addition, antioxidant compounds reversed the effect of NOS inhibitors on HIMEC-leukocyte interaction. Taken together, these data suggest that after HIMEC activation, iNOS-derived NO is an endogenous antioxidant, downregulating leukocyte binding and potentially downregulating intestinal inflammation.

Gene therapy for oxidant injury-related diseases: adenovirus-mediated transfer of superoxide dismutase and catalase cDNAs protects against hyperoxia but not against ischemia-reperfusion lung injury

Hyperoxia and ischemia-reperfusion cause profound lung cellular damage mediated, in part, by generation of oxygen radicals. We hypothesized that gene therapy can be used to overcome oxidant injury by augmenting intracellular antioxidant enzymes. Adult rats were injected intratracheally with an adenovirus (Ad) vector encoding human superoxide dismutase (CuZn-SOD) or catalase cDNA, a mixture of both Ad vectors, or a control Ad vector containing no exogenous gene. Expression of human catalase and CuZn-SOD was demonstrated 3 days later in distal lung epithelial cells and alveolar macrophages, using ELISA and immunochemistry. After exposure to 100% O2 for 62 hr, survival was greater in rats injected with the catalase and/or SOD Ad vectors than in control rats. Ischemia-reperfusion injury was evaluated in the isolated perfused lung model. Overexpression of SOD worsened ischemia-reperfusion injury. Interestingly, concomitant overexpression of catalase prevented this adverse effect, but did not protect against ischemia-reperfusion injury. We conclude that Ad-mediated transfer to lungs of both catalase and SOD cDNAs protects from pulmonary O2 toxicity. Absence of protection against ischemia-reperfusion using intratracheal Ad injections may be related to the lack of endothelial protection, despite epithelial expression of catalase and SOD.

Nitric oxide synthesis in the lung. Regulation by oxygen through a kinetic mechanism

In this study, we show that oxygen regulates nitric oxide (NO) levels through effects on NO synthase (NOS) enzyme kinetics. Initially, NO synthesis in the static lung was measured in bronchiolar gases during an expiratory breath-hold in normal individuals. NO accumulated exponentially to a plateau, indicating balance between NO production and consumption in the lung. Detection of NO2-, NO3-, and S-nitrosothiols in lung epithelial lining fluids confirmed NO consumption by chemical reactions in the lung. Interestingly, alveolar gas NO (estimated from bronchiolar gases at end-expiration) was near zero, suggesting NO in exhaled gases is not derived from circulatory/systemic sources. Dynamic NO levels during tidal breathing in different airway regions (mouth, trachea, bronchus, and bronchiole) were similar. However, in individuals breathing varying levels of inspired oxygen, dynamic NO levels were notably dependent on O2 concentration in the hypoxic range (KmO2 190 microM). Purified NOS type II enzyme activity in vitro was similarly dependent on molecular oxygen levels (KmO2 135 microM), revealing a means by which oxygen concentration affects NO levels in vivo. Based upon these results, we propose that NOS II is a mediator of the vascular response to oxygen in the lung, because its KmO2 allows generation of NO in proportion to the inspired oxygen concentration throughout the physiologic range.

Role of nitric oxide in poly(I-C)-induced endothelial cell expression of leukocyte adhesion molecules

Polyinosinic-polycytidylic acid [poly(I-C)] is a synthetic double-stranded RNA (dsRNA) that simulates a viral-infected state in cells. It has been shown that viral infection, as well as poly(I-C), stimulates leukocyte adhesion to endothelial cell (EC) monolayers and that this is mediated through the surface expression of the adhesion molecules E-selectin, vascular cell adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule 1. We have tested the involvement of nitric oxide (NO) in poly(I-C)-induced monocytic cell adhesion to human vascular EC. Using primary cultured EC for these studies, we confirmed the results from previous reports that these cells have higher basal levels of NO production than passaged cells. Poly(I-C)-induced monocytic cell adhesion to primary EC was concentration-dependently inhibited by 40-74% by the nitric oxide synthase (NOS) inhibitor NG-methyl-L-arginine (L-NMA), as well as three other NOS inhibitors, without significantly affecting interleukin-1 beta-induced adhesion. L-NMA inhibited poly(I-C)-induced surface expression of E-selectin and VCAM-1 by 25 and 45%, respectively, and mRNA levels of E-selectin and VCAM-1 by 62 and 74%, respectively. Primary EC transiently transfected with a plasmid containing an E-selectin promoter-driven luciferase reporter gene showed that L-NMA treatment reduced poly(I-C)-induced E-selectin promoter activity to basal levels. Electrophoretic mobility shift analysis indicated that poly(I-C)-induced nuclear factor-kappa B (NF-kappa B) binding to a radiolabeled oligonucleotide corresponding to the consensus NF-kappa B binding domain of the E-selectin promoter was decreased by L-NMA pretreatment. Hence, NO appears to augment E-selectin gene expression in response to poly(I-C) at the transcriptional level in vascular EC. Collectively, these data support the hypothesis that NO augments poly(I-C)-induced EC activation. These data suggest a novel role for NO as a response mediator in dsRNA-induced leukocyte adhesion to EC.

Inhaled corticosteroids and beta-agonists inhibit oxidant production by bronchoalveolar lavage cells from normal volunteers in vivo

To study the anti-inflammatory mechanisms of inhaled corticosteroids and beta-agonist therapies, we evaluated basal and stimulus-induced superoxide production by human airway inflammatory cells obtained by bronchoalveolar lavage from normal volunteers before and after 3 weeks of an inhaled corticosteroid (flunisolide) and beta-agonist (metaproterenol). Assay of superoxide production by the bronchoalveolar lavage cells was performed in the presence of media alone or media containing phorbol ester by optical density determination of reduced ferricytochrome c at 550 nm. Interleukin-1 beta released from unstimulated cells and cells stimulated with lipopolysaccharide was quantitated by enzyme immunoassay. Interestingly, phorbol ester-stimulated superoxide production was strikingly inhibited (P < 0.05) by inhaled therapies, while stimulus induced Interleukin-1 beta production was not significantly affected (P = 0.12). Suppression of oxidant production by airway inflammatory cells may be a major mechanism for the beneficial anti-inflammatory effects of inhaled corticosteroids and beta-agonists.

Nitric oxide inhibits inflammatory cytokine production by human alveolar macrophages

High levels of nitric oxide (NO) have been reported in exhaled air of asthmatic individuals. Because alveolar macrophages (AM) are major producers of cytokines, and bronchoalveolar lavage fluid (BALF) from asthmatic individuals contains increased levels of inflammatory cytokines, this study was undertaken to determine whether NO modified the production of inflammatory cytokines by human AM. AM were obtained from normal volunteers by fiberoptic bronchoscopy. Tumor necrosis factor-alpha (TNF-alpha) production stimulated by lipopolysaccharide (LPS; 0.5 microg/ml) was measured with an enzyme-linked immunosorbent assay (ELISA). NO generated from 2,2-(hydroxynitrosohydrazono)-bis-ethanamine (DETA NONOate) (0.1 to 1.0 mM) inhibited TNF-alpha secretion in a dose-dependent manner. At 1 mM DETA NONOate, mean inhibition (+/- SEM) of TNF-alpha secretion was 56 +/- 4% (P = 0.002). To determine whether this effect was cytokine specific, interleukin-1beta (IL-1beta) and macrophage inflammatory protein-1alpha (MIP-1alpha) were evaluated, and DETA NONOate was also found to inhibit both of these cytokines. Basal cytokine levels from unstimulated AM were unaffected by NO. These findings indicate that NO is a potent inhibitor of cytokine production by stimulated human AM.

Interferon gamma and interleukin 4 stimulate prolonged expression of inducible nitric oxide synthase in human airway epithelium through synthesis of soluble mediators

Human respiratory epithelium expresses inducible nitric oxide synthase (iNOS) continuously in vivo, however mechanisms responsible for maintenance of expression are not known. We show that IFNgamma is sufficient for induction of iNOS in primary human airway epithelial cells (HAEC) in vitro, and IL-4 potentiates IFNgamma-induced iNOS expression in HAEC through stabilization of iNOS mRNA. IFNgamma/IL-4- induced iNOS expression in HAEC was delayed in onset and prolonged with expression up to 1 wk. Removal of overlying culture media resulted in loss of expression, while transfer of conditioned media induced iNOS mRNA in other HAEC. IFNgamma and IL-4 stimulation activated STAT1 and STAT6 in HAEC, but conditioned media transfer to HAEC produced even higher levels of STAT1 activation than achieved by direct addition of cytokines. Although cytokine induction of iNOS was dependent on new protein synthesis, conditioned media induction of iNOS in HAEC was not. Further, removal of overlying culture media from cells at different times after cytokine stimulation demonstrated that mediator synthesis and/or secretion important for induction and maintenance of iNOS occurs early after cytokine stimulation. In conclusion, a combination of IFNgamma/ IL-4, which occurs naturally in the lung epithelial lining fluid, leads to maintenance of iNOS expression in human airway epithelium through production of soluble mediators and stabilization of mRNA.

Decreased Cu,Zn-SOD activity in asthmatic airway epithelium: correction by inhaled corticosteroid in vivo

To investigate the antioxidant response of respiratory epithelium to the chronic airway inflammation in asthma, the major intracellular antioxidants [copper and zinc-containing superoxide dismutase (Cu,Zn-SOD) and manganese-containing SOD (Mn-SOD), catalase, and glutathione peroxidase] were quantitated in bronchial epithelial cells of healthy control and asthmatic individuals. Although catalase and glutathione peroxidase in bronchial epithelium of asthmatics were similar to control SOD activity in asthmatics not on inhaled corticosteroid (-CS) was lower than asthmatics on inhaled corticosteroid (+CS) and controls. Investigation of Mn-SOD and Cu,Zn-SOD activities revealed that the lower SOD activity in asthmatics -CS was because of decreased Cu,Zn-SOD activity. However, Mn-SOD and Cu,Zn-SOD mRNA and protein levels were similar among asthmatics -CS, asthmatics +CS, and controls. Importantly, Cu,Zn-SOD specific activity in asthmatics -CS was decreased in comparison with control and asthmatics +CS. Furthermore, in paired comparisons of asthmatics -CS and +CS, inhaled corticosteroids resulted in normalization of bronchial epithelial Cu,Zn-SOD specific activity. These findings suggest loss of Cu,Zn-SOD activity in asthma is related to inflammation, perhaps through oxidant inactivation of Cu,Zn-SOD protein.

Surfactant suppresses NF-kappa B activation in human monocytic cells

In addition to biophysical properties, pulmonary surfactant has immunomodulatory activity. We previously demonstrated that both synthetic (Exosurf) and modified natural surfactant (Survanta) downregulated endotoxin-stimulated inflammatory c ytokine mRNA levels and protein products (tumor necrosis factor-alpha [TNF], interleukin-1-beta [IL-1], interleukin-6 [IL-6]) in human alveolar macrophages. In this study, we report that both Exosurf and Survanta suppress TNF mRNA and secretion (85 +/- 4% mean percent inhibition +/- SEM by Exosurf; 71 +/- 6% by Survanta) by endotoxin-stimulated THP-1, a human monocytic cell line. Because surfactant downregulated inflammatory cytokine production similarly in both normal human alveolar macrophages and the THP-1 cell line, we used this cell line to investigate whether surfactant affected transcriptional mechanisms. Specifically, we examined nuclear factor-kappa B (NF-kappa B) activation because it is crucial in transcriptional regulation of many inflammatory cytokine genes including TNF, IL-1, and IL-6. Electrophoretic mobility shift assays showed that both surfactants decreased activation of NF-kappa B. The presence of both p65 and p50 NF-kappa B components in LPS-activated THP-1 cells was confirmed by specific antibody induction of supershifts in mobility assays. These results are the first to suggest that surfactant's suppressive effects on inflammatory cytokine production may involve transcriptional regulation through inhibition of NF-kappa B activation.

Quantitative assessment of the epithelial and inflammatory cell populations in large airways of normals and individuals with cystic fibrosis

Nasal and bronchial brushings and bronchial biopsies were evaluated from patients with cystic fibrosis (CF) and from normal subjects to quantify epithelial and inflammatory cell types. Epithelial in both groups were dominated by ciliated cells. The relative proportions of epithelial cells recovered by brushing and biopsy were similar, but with more basal cells from biopsies than from brushings. In nasal brushings, the numbers and percentages of epithelial subtypes were similar in both groups. In bronchial brushings, the number of recovered cells was 2.5-fold increased in the CF group compared with that in the normal group because of large numbers of neutrophils. The proportion of ciliated cells was lower in the CF group than in the normal group. Thus, even though the CF transmembrane conductance regulator mutations are expressed similarly in the nasal and bronchial epithelium in CF, the consequences are different, with little inflammation and no changes in the proportions of epithelial cells in the nasal epithelium, compared with marked neutrophil inflammation on the epithelial surface and significant changes in epithelial populations in the large airways. Airway brushing permits repetitive evaluation of the airway epithelium in CF, a useful methodology in the assessment of new therapies for this disorder.

Continuous nitric oxide synthesis by inducible nitric oxide synthase in normal human airway epithelium in vivo

Nitric oxide (NO) is an important mediator of inflammatory responses in the lung and a key regulator of bronchomotor tone. An airway NO synthase (NOS; EC 1.14.13.39) has been proposed as a source of endogenous NO in the lung but has not been clearly defined. Through molecular cloning, we conclusively demonstrate that NO synthesis in normal human airways is due to the continuous expression of the inducible NOS (iNOS) isoform in airway epithelial cells. Although iNOS mRNA expression is abundant in airway epithelial cells, expression is not detected in other pulmonary cell types, indicating that airway epithelial cells are unique in the continuous pattern of iNOS expression in the lung. In situ analysis reveals all airway epithelial cell types express iNOS. However, removal of epithelial cells from the in vivo airway environment leads to rapid loss of iNOS expression, which suggests expression is dependent upon conditions and/or factors present in the airway. Quantitation of NOS activity in epithelial cell lysates indicates nanomolar levels of NO synthesis occur in vivo. Remarkably, the high-level iNOS expression is constant in airway epithelium of normal individuals over time. However, expression is strikingly decreased by inhaled corticosteroids and beta-adrenergic agonists, medications commonly used in treatment of inflammatory airway diseases. Based upon these findings, we propose that respiratory epithelial cells are key inflammatory cells in the airway, functioning in host defense and potentially playing a role in airway inflammation.

Vulnerability of the human airway epithelium to hyperoxia. Constitutive expression of the catalase gene in human bronchial epithelial cells despite oxidant stress

Although catalase is a major intracellular antioxidant, the expression of the human catalase gene appears to be limited in the airway epithelium, making these cells vulnerable to oxidant stress. The basis for this limited gene expression was examined by evaluation of the expression of the endogenous gene in human bronchial epithelial cells in response to hyperoxia. Hyperoxia failed to upregulate endogenous catalase gene expression, in contrast to a marked increase in expression of the heat shock protein gene. Sequence analysis of 1.7 kb of the 5'-flanking region of the human catalase gene showed features of a "house-keeping" gene (no TATA box, high GC content, multiple CCAAT boxes, and transcription start sites). Transfection of human bronchial epithelial cells with fusion genes composed of various lengths of the catalase 5'-flanking region and luciferase as a reporter gene showed low level constitutive promoter activity that did not change after exposure to hyperoxia. Importantly, using a replication-deficient recombinant adenoviral vector containing the human catalase cDNA, levels of catalase were significantly increased in human airway epithelial cells and this was associated with increased survival of the cells when exposed to hyperoxia. These observations provide a basis for understanding the sensitivity of the human airway epithelium to oxidant stress and a strategy for protecting the epithelium from such injury.

In vivo antioxidant gene expression in human airway epithelium of normal individuals exposed to 100% O2

Human bronchial epithelium is exquisitely sensitive to high O2 levels, with tracheobronchitis usually developing after 12 h of exposure to 100% O2. To evaluate whether this vulnerability results from inability of the bronchial epithelium to provide adequate antioxidant protection, we quantified antioxidant gene expression in bronchial epithelium of normal volunteers at baseline and after exposure to 100% O2 in vivo. After 14.8 +/- 0.2 h of 100% O2, 24 of 33 individuals had evidence of tracheobronchitis. Baseline gene expression of CuZn superoxide dismutase (SOD), MnSOD, and catalase in bronchial epithelium was very low (CuZnSOD 4.1 +/- 0.8 transcripts/cell, MnSOD 5.1 +/- 0.9, catalase 1.3 +/- 0.2), with control gamma-actin expression relatively abundant (50 +/- 6 transcripts/cell). Importantly, despite 100% O2 exposure sufficient to cause tracheobronchitis in most individuals, antioxidant mRNA transcripts/cell in bronchial epithelium did not increase (P > 0.5). Catalase activity in bronchial epithelium did not change after exposure to hyperoxia (P > 0.05). Total SOD activity increased mildly (P < 0.01) but not sufficiently to protect the epithelium. Together, the very low levels of expression of intracellular antioxidant enzymes and the inability to upregulate expression at the mRNA level with oxidant stress likely have a role in human airway epithelium susceptibility to hyperoxia.

Protection of human endothelial cells from oxidant injury by adenovirus-mediated transfer of the human catalase cDNA

In a variety of disorders, endothelial cells are exposed to high levels of oxidants, generated within the cells and/or consequent to local inflammation. In the context of the sensitivity of endothelial cells to oxidant stress, particularly related to H2O2, we have designed a replication deficient recombinant adenovirus containing the human catalase cDNA (AdCL) to transfer the catalase cDNA to the endothelial cells, in order to augment intracellular anti-H2O2 protection. Human umbilical vein endothelial cells that were not infected or infected with control adenovirus maintained low levels of catalase mRNA. Endothelial cells infected with AdCL expressed AdCL-driven exogenous catalase mRNA, as early as 24 hr and at least for 7 days. Catalase protein levels were increased significantly over controls in cells infected with AdCL, as were catalase activity levels, with catalase activity correlated closely with levels of catalase protein. Importantly, when the endothelial cells were exposed to 500 microM H2O2, all the AdCL infected endothelial cells survived, compared to only 37% of the control cells. Thus, a recombinant adenovirus containing the human catalase cDNA is able to infect human endothelial cells in vitro and express high levels of functional intracellular catalase, protecting the cells against H2O2-mediated oxidant stress. These observations support the feasibility of the transfer of catalase cDNA to human endothelium to protect against oxidant injury.

Mechanisms of lipopolysaccharide-induced neutrophil retention. Relative contributions of adhesive and cellular mechanical properties

Intravascular LPS rapidly induces neutrophil sequestration in pulmonary capillaries by mechanisms that, although currently unknown, must take into account the size difference between the neutrophil and capillary diameter. To determine whether LPS alters neutrophil stiffness, and hence the ability of neutrophils to traverse capillaries, neutrophil passage through pulmonary capillaries was modeled by passage through filters with 6.5-microns pores. LPS increased retention in the pores in a concentration-dependent fashion that required the presence of heat-inactivated platelet-poor plasma, and was evident as early as 10 min after stimulation. The effect of LPS on the structural properties of the neutrophil was then studied. LPS induced f-actin reorganization in neutrophils in the presence of plasma. Disruption of actin organization and assembly with cytochalasin D completely inhibited early LPS-induced retention and attenuated retention at later timepoints, indicating that LPS-stimulated retention depends on filament organization. LPS-induced actin assembly and retention were abrogated by an antibody directed against CD14, a putative LPS receptor. CD18-dependent adherence of neutrophils contributed significantly to retention only at later timepoints with no significant contribution to retention at 20 min as determined by inhibition of adherence with the mAb 60.3. Morphometric assessment of neutrophil accumulation in the lungs of rabbits given 1 microgram LPS showed a marked increase in apparent neutrophil number, which was unaltered by antibodies to CD18, suggesting that mechanisms other than adhesion may account for accumulation in vivo. Direct measurements showed that neutrophil stiffness increased with exposure to LPS in a fashion similar to LPS-induced retention and actin organization. Pretreatment of neutrophils with cytochalasin D attenuated the increased stiffness. These data suggest that reorganization of filamentous-actin induced by LPS leads to cell stiffening and retention in capillary-sized pores. Although the organization of f-actin continues to be important in retention at later time points, adherence of cells also contributes significantly to cell retention. The changes in mechanical properties of the neutrophil may be important in the sequestration of neutrophils in pulmonary capillaries noted in endotoxemia.

Mechanisms of lipopolysaccharide-induced neutrophil retention. Relative contributions of adhesive and cellular mechanical properties

Intravascular LPS rapidly induces neutrophil sequestration in pulmonary capillaries by mechanisms that, although currently unknown, must take into account the size difference between the neutrophil and capillary diameter. To determine whether LPS alters neutrophil stiffness, and hence the ability of neutrophils to traverse capillaries, neutrophil passage through pulmonary capillaries was modeled by passage through filters with 6.5-microns pores. LPS increased retention in the pores in a concentration-dependent fashion that required the presence of heat-inactivated platelet-poor plasma, and was evident as early as 10 min after stimulation. The effect of LPS on the structural properties of the neutrophil was then studied. LPS induced f-actin reorganization in neutrophils in the presence of plasma. Disruption of actin organization and assembly with cytochalasin D completely inhibited early LPS-induced retention and attenuated retention at later timepoints, indicating that LPS-stimulated retention depends on filament organization. LPS-induced actin assembly and retention were abrogated by an antibody directed against CD14, a putative LPS receptor. CD18-dependent adherence of neutrophils contributed significantly to retention only at later timepoints with no significant contribution to retention at 20 min as determined by inhibition of adherence with the mAb 60.3. Morphometric assessment of neutrophil accumulation in the lungs of rabbits given 1 microgram LPS showed a marked increase in apparent neutrophil number, which was unaltered by antibodies to CD18, suggesting that mechanisms other than adhesion may account for accumulation in vivo. Direct measurements showed that neutrophil stiffness increased with exposure to LPS in a fashion similar to LPS-induced retention and actin organization. Pretreatment of neutrophils with cytochalasin D attenuated the increased stiffness. These data suggest that reorganization of filamentous-actin induced by LPS leads to cell stiffening and retention in capillary-sized pores. Although the organization of f-actin continues to be important in retention at later time points, adherence of cells also contributes significantly to cell retention. The changes in mechanical properties of the neutrophil may be important in the sequestration of neutrophils in pulmonary capillaries noted in endotoxemia.

Biophysical properties and microfilament assembly in neutrophils: modulation by cyclic AMP

The microfilament lattice, composed primarily of filamentous (F)-actin, determines in large part the mechanical (deformability) properties of neutrophils, and thus may regulate the ability of neutrophils to transit a microvascular bed. Circulating factors may stimulate the neutrophil to become rigid and therefore be retained in the capillaries. We hypothesized that cell stiffening might be attenuated by an increase in intracellular cAMP. A combination of cell filtration and cell poking (mechanical indentation) was used to measure cell deformability. Neutrophils pretreated with dibutyryl cAMP (db-cAMP) or the combination of prostaglandin E2 (PGE2, a stimulator of adenylate cyclase) and isobutylmethylxanthine (IBMX, an inhibitor of phosphodiesterase) demonstrated significant inhibition of the n-formyl-methionyl-leucyl-phenylalanine (fMLP)-inducing stiffening. The inhibition of cell stiffening was associated with an increase in intracellular cAMP as measured by enzyme-linked immunoassay (EIA) and an increase in the activity of the cAMP-dependent kinase (A-kinase). Treatment with PGE2 and IBMX also resulted in a decrease in the F-actin content of stimulated neutrophils as assayed by NBD-phallacidin staining and flow cytometry or by changes in right angle light scattering. Direct addition of cAMP to electropermeabilized neutrophils resulted in attenuation of fMLP-induced actin assembly. Neutrophils stimulated with fMLP demonstrated a rapid redistribution of F-actin from a diffuse cortical location to a peripheral ring as assessed by conventional and scanning confocal fluorescence microscopy. Pretreatment of neutrophils with the combination of IBMX and PGE2 resulted in incomplete development and fragmentation of the cortical ring. We conclude that assembly and redistribution of F-actin may be responsible for cell stiffening after exposure to stimulants and that this response was attenuated by agents that increase intracellular cAMP, by altering the amount and spatial organization of the microfilament component of the cytoskeleton.

Mechanical properties of HL60 cells: role of stimulation and differentiation in retention in capillary-sized pores

Neutrophil sequestration in pulmonary capillaries occurs prior to the development of lung injury, but the mechanisms by which neutrophils are retained are unclear. We hypothesized that decreases in cell deformability, in the absence of an increase in cell surface adhesive properties, would be sufficient to cause cell retention in a filtration apparatus modeling the pulmonary microvasculature. The myelomonocytic cell line (HL60 cell line) was used to test the hypothesis since these cells were unable to increase adherence in response to n-formylmethionylleucylphenylalanine (FMLP) in either the undifferentiated state or when differentiated towards granulocytes. With differentiation, HL60 cell volume decreased, and f-actin organization changed from a thick cortical rim with focal areas of f-actin in undifferentiated cells to a thin rim in differentiated cells. Differentiated cells responded to FMLP by reorganizing f-actin and increasing stiffness. Undifferentiated cells did not exhibit changes in f-actin with stimulation, were stiffer than differentiated cells, and did not increase stiffness in response to FMLP. Cytochalasin D (CD), which disrupted the cytoarchitecture as assessed by confocal microscopy but did not affect cell volume or adherence, decreased the stiffness of undifferentiated and FMLP-stimulated differentiated cells, thus suggesting the importance of microfilament organization in the stiffness of these cells. Filtration of cells through 8-microns pores showed that undifferentiated cells were markedly retained and did not exhibit any further retention with FMLP. Differentiated cells exposed to FMLP exhibited a concentration-dependent increase in retention in 8-microns pores that was abolished by CD. In addition, CD reduced retention of undifferentiated cells, indicating that microfilament organization is an important factor in determining a cell's rheologic properties. In conclusion, FMLP-stimulated microfilament reorganization, which increased cell stiffness, was sufficient in the absence of adherence factors to cause cell retention in a filtration system. This lends support to the hypothesis that decreases in cell deformability contribute to neutrophil retention in the pulmonary microvasculature.

Effect of low-dose methotrexate on the disposition of glucocorticoids and theophylline

Low-dose methotrexate (MTX) therapy has been recently proposed as alternative therapy for patients with severe steroid-requiring asthma. Several questions have been raised regarding the mechanism of action, including alteration of pharmacokinetics of two medications used in these patients, specifically, glucocorticoids and theophylline. To address this question, pharmacokinetic studies were performed at baseline and after 6 weeks of treatment with either intramuscular MTX or placebo (folic acid). Plasma concentrations of theophylline were measured by fluorescence polarization immunoassay (TDx, Abbott Diagnostics, Abbott Park, Ill.). Prednisolone, methylprednisolone, and cortisol concentrations were measured by high-performance liquid chromatography. Fifteen adults were enrolled in the double-blind, placebo-controlled trial. No change in prednisolone pharmacokinetic parameters was found. Theophylline clearance decreased an average of 19% in patients randomized to receive MTX, from 48.0 +/- 2.0 ml/hr/kg to 38.9 +/- 3.6 ml/hr/kg (p less than 0.05). This change resembles change observed with theophylline and phenobarbital clearance in which a high degree of interpatient variability is observed. The most likely explanation for the change in theophylline clearance is inhibition of hepatic microsomal enzyme activity. Three patients complained of adverse effects, and dosage was reduced in one patient. The variable effect of MTX on theophylline clearance indicates that theophylline concentration monitoring should be performed in patients receiving both drugs.

Lack of benefit of methotrexate in severe, steroid-dependent asthma. A double-blind, placebo-controlled study

OBJECTIVE

To determine the effect of low-dose methotrexate in asthmatic patients on steroid use, asthma symptom scores, pulmonary function, airway reactivity, blood cellular components, and immunoglobulin E levels.

DESIGN

A randomized, double-blind, parallel, placebo-controlled, 13-week clinical trial with follow-up of patients in an open trial of methotrexate at the conclusion of the double-blind study.

SETTING

An asthma care outpatient clinic.

PATIENTS

From February 1988 to March 1990, 19 patients with severe, steroid-dependent asthma were enrolled in the study. Two of these patients were excluded from analysis.

INTERVENTIONS

Patients were administered methotrexate or placebo intramuscularly, to assure complete absorption, once weekly during the 13-week study.

RESULTS

Patients on methotrexate and placebo both significantly decreased their steroid dose by 39.6% (95% CI, 25.1% to 54.1%, P = 0.001) and 40.2% (CI, 17.9% to 67.4%, P = 0.003), respectively. Pulmonary function did not differ significantly between the methotrexate and placebo groups. In addition, airway reactivity and symptom scores were unchanged on methotrexate or placebo. No significant toxicities were seen during the course of the 13-week blinded study, but one patient on methotrexate and prednisone in the follow-up period developed Pneumocystis carinii pneumonia and died. Despite continuing methotrexate for up to 1 year, and increasing methotrexate to 30 mg weekly, no significant benefit of methotrexate on asthma control could be shown.

CONCLUSION

Our study does not support the use of methotrexate in the treatment of severe asthma.

Pleural effusion in Churg-Strauss syndrome

A 33-year-old man with a two-year history of asthma and sinusitis presented with wheezing, pleuritis, bilateral pleural effusions, and patchy basilar infiltrates on chest roentgenogram. Laboratory studies revealed peripheral blood eosinophilia, and pulmonary function studies showed an obstructive pattern which was bronchodilator responsive. Thoracocentesis yielded an acidotic exudative effusion with low glucose, low C3, eosinophilia, and a markedly increased rheumatoid factor. Open lung biopsy revealed extensive eosinophilic interstitial pneumonitis with necrotizing eosinophilic vasculitis. Although pleural effusions are present in 29 percent of Churg-Strauss patients, these effusions have not been well described. This report describes the pleural fluid findings in a case of Churg-Strauss syndrome.