Noninvasive detection of endotoxin-induced mucus hypersecretion in rat lung by MRI

Pathophysiological Consequences of a Break in S1P1-Dependent Homeostasis of Vascular Permeability Revealed by S1P1 Competitive Antagonism

RATIONAL

Homeostasis of vascular barriers depends upon sphingosine 1-phosphate (S1P) signaling via the S1P1 receptor. Accordingly, S1P1 competitive antagonism is known to reduce vascular barrier integrity with still unclear pathophysiological consequences. This was explored in the present study using NIBR-0213, a potent and selective S1P1 competitive antagonist.

RESULTS

NIBR-0213 was tolerated at the efficacious oral dose of 30 mg/kg BID in the rat adjuvant-induced arthritis (AiA) model, with no sign of labored breathing. However, it induced dose-dependent acute vascular pulmonary leakage and pleural effusion that fully resolved within 3-4 days, as evidenced by MRI monitoring. At the supra-maximal oral dose of 300 mg/kg QD, NIBR-0213 impaired lung function (with increased breathing rate and reduced tidal volume) within the first 24 hrs. Two weeks of NIBR-0213 oral dosing at 30, 100 and 300 mg/kg QD induced moderate pulmonary changes, characterized by alveolar wall thickening, macrophage accumulation, fibrosis, micro-hemorrhage, edema and necrosis. In addition to this picture of chronic inflammation, perivascular edema and myofiber degeneration observed in the heart were also indicative of vascular leakage and its consequences.

CONCLUSIONS

Overall, these observations suggest that, in the rat, the lung is the main target organ for the S1P1 competitive antagonism-induced acute vascular leakage, which appears first as transient and asymptomatic but could lead, upon chronic dosing, to lung remodeling with functional impairments. Hence, this not only raises the question of organ specificity in the homeostasis of vascular barriers, but also provides insight into the pre-clinical evaluation of a potential safety window for S1P1 competitive antagonists as drug candidates.

Fractional ventilation mapping using inert fluorinated gas MRI in rat models of inflammation and fibrosis

The purpose of this study was to extend established methods for fractional ventilation mapping using (19) F MRI of inert fluorinated gases to rat models of pulmonary inflammation and fibrosis. In this study, five rats were instilled with lipopolysaccharide (LPS) in the lungs two days prior to imaging, six rats were instilled with bleomycin in the lungs two weeks prior to imaging and an additional four rats were used as controls. (19) F MR lung imaging was performed at 3 T with rats continuously breathing a mixture of sulfur hexafluoride and O2 . Fractional ventilation maps were obtained using a wash-out approach, by switching the breathing mixture to pure O2 , and acquiring images following each successive wash-out breath. The mean fractional ventilation (r) was 0.29 ± 0.05 for control rats, 0.23 ± 0.10 for LPS-instilled rats and 0.19 ± 0.03 for bleomycin-instilled rats. Bleomycin-instilled rats had a significantly decreased mean r value compared with controls (P = 0.010). Although LPS-instilled rats had a slightly reduced mean r value, this trend was not statistically significant (P = 0.556). Fractional ventilation gradients were calculated in the anterior/posterior (A/P) direction, and the mean A/P gradient was -0.005 ± 0.008 cm(-1) for control rats, 0.013 ± 0.005 cm(-1) for LPS-instilled rats and 0.009 ± 0.018 cm(-1) for bleomycin-instilled rats. Fractional ventilation gradients were significantly different for control rats compared with LPS-instilled rats only (P = 0.016). The ventilation gradients calculated from control rats showed the expected gravitational relationship, while ventilation gradients calculated from LPS- and bleomycin-instilled rats showed the opposite trend. Histology confirmed that LPS-instilled rats had a significantly elevated alveolar wall thickness, while bleomycin-instilled rats showed signs of substantial fibrosis. Overall, (19)F MRI may be able to detect the effects of pulmonary inflammation and fibrosis using a simple and inexpensive imaging approach that can potentially be translated to humans.

Non-Invasive Detection of Lung Inflammation by Near-Infrared Fluorescence Imaging Using Bimodal Liposomes

Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome results in respiratory obstruction and severe lung inflammation. Critical characteristics of ALI are alveolar edema, infiltration of leukocytes (neutrophils and monocytes), release of pro-inflammatory cytokines and chemokines into broncho-alveolar lavage fluid, and activation of integrin receptors. The purpose of the study was to demonstrate non-invasive detection of lung inflammation using integrin receptor targeted fluorescence liposomes. An inflammation similar to that observed in ALI was elicited in rodents by intra-tracheal instillation of interleukin-1beta (IL-1beta). Cyclic arginine glycine-(D)-aspartic acid-peptide (cRGD-peptide) grafted fluorescence liposomes were administered to ALI induced male Sprague-Dawley rats for targeting lung integrin receptors. Near-infrared fluorescence imaging (NIRFI) was applied for visualization and quantitation of lung inflammation. NIRFI signals were correlated with inflammatory cellular and biochemical markers of lungs. A positive correlation was observed between NIRF signals and lung inflammation markers. Compared to control group, an intense NIRF signal was observed in ALI induced rats in the window 6-24 h post-IL-1beta instillation. Interaction of integrin receptors with targeted liposomes was assumed to contribute to intense NIRF signal. RT-PCR studies showed an elevated lung expression of alphavbeta5 integrin receptors, 12 h post-IL-1beta instillation. In vitro studies demonstrated integrin receptor specificity of targeted liposomes. These targeted liposomes showed binding to alphavbeta5 integrin receptors expressed on alveolar cells. Non-invasive detection of lung inflammation was demonstrated using a combination of integrin receptor targeting and NIRFI.

Inhibition of Pasteurella multocida Adhesion to Rabbit Respiratory Epithelium Using Lectins

This study aimed to evaluate the ability of a panel of lectins to inhibit the ability of Pasteurella multocida to adhere to and affect the rabbit respiratory epithelium. Nasal septa from rabbit fetuses were cultured with various lectins before the addition of P. multocida. The percentage of bacteria adhering to the epithelium was evaluated semiquantitatively by indirect immunoperoxidase (IIP) staining. The goblet cells (GCs) were counted in semithin sections stained with toluidine blue and served as the main morphological criterion to evaluate the inhibitory effect of the lectins. The lectins PNA, WGA, RCA₁₂₀, and DBA significantly inhibited the adhesion of P. multocida to the ciliated epithelium (P < 0.05) and prevented the pathogen-induced increase in the number of GCs (P < 0.05) compared with those of positive control tissues. In addition, VVA, SJA, UEA I, DSL, SBA, and ECL significantly inhibited the increase in GCs compared with that of the control tissues. The results suggest that less aggressive therapeutic strategies, such as treatment with lectins, may represent alternative approaches to control bacterial respiratory infections.

MR imaging and targeting of a specific alveolar macrophage subpopulation in LPS-induced COPD animal model using antibody-conjugated magnetic nanoparticles

Purpose

Targeting and noninvasive imaging of a specific alveolar macrophage subpopulation in the lung has revealed the importance for early and better diagnosis and therapy of chronic obstructive pulmonary disease (COPD). In this study, the in vivo effect of pulmonary administration of iron oxide nanoparticles on the polarization profile of macrophages was assessed, and a noninvasive free-breathing magnetic resonance imaging (MRI) protocol coupled with the use of biocompatible antibody-conjugated superparamagnetic iron oxide (SPIO) nanoparticles was developed to enable specific targeting and imaging of a particular macrophage subpopulation in lipopolysaccharide-induced COPD mice model.

Materials and methods

Enzyme-linked immunosorbent assay, Real-time polymerase chain reaction, and flow cytometry analysis were performed to assess the biocompatibility of PEGylated dextran-coated SPIO nanoparticles. Specific biomarkers for M1 and M2 macrophages subsets were selected for conjugation with magnetic nanoparticles. MRI protocol using ultra-short echo time sequence was optimized to enable simultaneous detection of inflammation progress in the lung and detection of macrophages subsets. Flow cytometry and immunohistochemistry analysis were finally performed to confirm MRI readouts and to characterize the polarization profile of targeted macrophages.

Results

The tested SPIO nanoparticles, under the current experimental conditions, were found to be biocompatible for lung administration in preclinical settings. Cluster of differentiation (CD)86- and CD206-conjugated magnetic nanoparticles enabled successful noninvasive detection of M1 and M2 macrophage subpopulations, respectively, and were found to co-localize with inflammatory regions induced by lipopolysaccharide challenge. No variation in the polarization profile of targeted macrophages was observed, even though a continuum switch in their polarization might occur. However, further confirmatory studies are required to conclusively establish this observation.

Conclusion

Coupling of magnetic iron oxide nanoparticles with a specific antibody targeted to a particular macrophage subpopulation could offer a promising strategy for an early and better diagnosis of pulmonary inflammatory diseases using noninvasive MRI.

Ultrashort-TE MRI longitudinal study and characterization of a chronic model of asthma in mice: inflammation and bronchial remodeling assessment

Asthma is a chronic disease characterized by bronchial hyperresponsiveness (BHR), bronchial inflammation and remodeling. The great improvements in (1)H MRI ultrashort-TE (UTE) sequences in the last decade have allowed lung images with high-resolution and good signal-to-noise ratio to be obtained in parenchymal tissues. In this article, we present a UTE (1)H MRI high-resolution study of a chronic model of asthma in mice with the aim to longitudinally assess the main features of asthma using a fully noninvasive approach. Balb/c mice (n = 6) were sensitized with ovalbumin over a period of 75 days. The control group (n = 3) received normal saline on the same days. MRI acquisitions were performed on days 0, 38 and 78 to study the inflammatory volumes and bronchial remodeling (peribronchial signal intensity index, PBSI). Plethysmographic studies were performed on days 0, 39 and 79 to assess BHR to methacholine using the enhanced pause (Penh) ratio. The average inflammatory volume measured by MRI in the ovalbumin group (15.6 ± 2.4 μL) was increased significantly relative to control mice (-0.3 ± 0.7 μL) on day 38. The inflammatory volume was larger (34.2 ± 3.1 μL) on day 78 in the ovalbumin group. PBSI was significantly higher in the ovalbumin group on day 78 (1.53 ± 0.08) relative to the control group (1.16 ± 0.10), but not on day 38. After sensitization, asthmatic mice presented BHR to methacholine on days 39 and 79. Penh ratios correlated significantly with the inflammatory volume on day 39 and with the PBSI on day 79. This study shows, for the first time, that high-resolution UTE (1)H MRI of the lungs may allow the noninvasive quantification of peribronchial eosinophilic inflammation with airways occlusion by mucus and of bronchial remodeling in a murine asthma model that correlates with functional parameters.

Quantitative biodistribution and pharmacokinetics of multimodal gadolinium-based nanoparticles for lungs using ultrashort TE MRI

OBJECTIVE

To study the biodistribution and lung pharmacokinetics of tracheally administered gadolinium-based contrast agents [gadoteric acid and multimodal ultra-small rigid platforms (USRPs)], to validate their pharmacokinetics against optical imaging of fluorescent USRPs, and to test their short-term toxicity.

MATERIALS AND METHODS

Ultrashort echo-time (UTE) lung proton magnetic resonance imaging (MRI) was performed at 4.7-Tesla (T) after the intratracheal instillation of different concentrations of contrast agent solutions in mice. Pharmacokinetic models were implemented on the absolute concentration calculated from the MRI signal enhancement measurements. Fluorescent USRPs were used to obtain optical images with the same protocol. Bronchoalveolar lavage inflammatory cell count and serum creatinine measurement were performed on four groups of instilled mice (sham, saline, USRPs, lipopolysaccharide).

RESULTS

MR and optical imaging showed similar kinetics of the USRPs, passing from the airways to the lung tissue and to the kidneys, with negligible hepatic clearance. No significant increase of lung and renal inflammation markers were observed in USRP-instilled animals.

CONCLUSION

A T 1-weighted radial UTE sequence was found to be valuable in quantitatively monitoring the biodistribution and pharmacokinetics of nanoparticles in the lungs of mice. The observed favorable pharmacokinetics, which was validated by fluorescence imaging, ensures the negligible toxicity of the nanoprobes, making the USRPs and the developed protocol good candidates for applications on selected lung diseases.

Interaction of Bordetella bronchiseptica and Its Lipopolysaccharide with In Vitro Culture of Respiratory Nasal Epithelium

The nasal septa of fetal rabbits at 26 days of gestation were harvested by cesarean section of the does while under anesthesia and then exposed to Bordetella bronchiseptica or its lipopolysaccharide (LPS) for periods of 2 and 4 hours. A total of 240 explants were used. The tissues were examined using the Hematoxylin & Eosin technique. Then, semithin sections (0.5 μm) were stained with toluidine blue and examined with indirect immunoperoxidase (IPI) and lectin histochemistry. The most frequent and statistically significant findings were as follows: (1) cell death and increased goblet cell activity when exposed to bacteria and (2) cell death, cytoplasmic vacuolation and infiltration of polymorphonuclear leukocytes when exposed to LPS. The lesions induced by the bacterium were more severe than with LPS alone, except for the cytoplasmic vacuolation in epithelial cells. IPI stained the ciliated border of the epithelium with the bacterium more intensely, while LPS lectin histochemistry preferentially labeled the cytoplasm of goblet cell. These data indicate that B. bronchiseptica and its LPS may have an affinity for specific glycoproteins that would act as adhesion receptors in both locations.

Macrophages are related to goblet cell hyperplasia and induce MUC5B but not MUC5AC in human bronchus epithelial cells

Airway goblet cell hyperplasia (GCH)--detectable by mucin staining--and abnormal macrophage infiltrate are pathological features present in many chronic respiratory disorders. However, it is unknown if both factors are associated. Using in-vivo and in-vitro models, we investigated whether macrophages are related with GCH and changes in mucin immunophenotypes. Lung sections from Sprague-Dawley rats treated for 48 h with one intra-tracheal dose of PBS or LPS (n=4-6 per group) were immunophenotyped for rat-goblet cells, immune, and proliferation markers. Human monocyte-derived macrophages (MDM) were pre-treated with or without LPS, immunophenotyped, and their supernatant, as well as cytokines at levels equivalent to supernatant were used to challenge primary culture of normal human bronchus epithelial cells (HBEC) in air-liquid interface, followed by MUC5B and MUC5AC mucin immunostaining. An association between increased bronchiolar goblet cells and terminal-bronchiolar proliferative epithelial cells confirmed the presence of GCH in our LPS rat model, which was related with augmented bronchiolar CD68 macrophage infiltration. The in-vitro experiments have shown that MUC5AC phenotype was inhibited when HBEC were challenged with supernatant from MDM pre-treated with or without LPS. In contrast, TNF-α and interleukin-1β at levels equivalent to supernatant from LPS-treated MDM increased MUC5AC. MUC5B was induced by LPS, supernatant from LPS-treated MDM, a mix of cytokines including TNF-α and TNF-α alone at levels present in supernatant from LPS-treated MDM. We demonstrated that macrophages are related with bronchiolar GCH, and that they induced MUC5B and inhibited MUC5AC in HBEC, suggesting a role for them in the pathogenesis of airway MUC5B-related GCH.

A texture analysis approach to quantify ventilation changes in hyperpolarised ³He MRI of the rat lung in an asthma model

In preclinical research, allergic asthma is investigated in rats sensitised with the antigen ovalbumin (OVA), followed by a challenge with aerosolised OVA to induce an inflammatory reaction of the lower airways. This causes diffuse, nonfocal ventilation defects that lead to heterogeneously distributed signal intensities in hyperpolarised (HP) (3)He MR images, which are difficult to assess directly by diagnostic grading or volumetry. Texture analysis can characterise these changes and does not require segmentation of the lung structures prior to the analysis. The aim of this work was to evaluate a texture analysis approach to quantify changes in lung ventilation in HP (3)He MRI of OVA-challenged rats. OVA-challenged animals were treated with two different compound doses to evaluate the sensitivity of the texture analysis. Four groups were investigated using HP (3)He MRI at 4.7 T: controls, vehicle-treated, and low- and high-dose budesonide-treated rats. In addition, broncho-alveolar lavage was performed and the eosinophil cell count was used as a biological reference marker. First-order texture, geometrical features and features based on second-order statistics using run-length and grey-level co-occurrence matrices were calculated. In addition, wavelet transforms were applied to compute first-order statistics on multiple scales. The texture analysis was able to show significant differences between the control and untreated vehicle groups as well as between the vehicle and treatment groups. This is in agreement with the findings of the eosinophil cell counts, which were used as a marker for the severity of inflammation. However, not all features used in the different texture analysis methods could differentiate between the treatment groups. In conclusion, texture analysis can be used to quantify changes in lung ventilation as measured with HP (3)He MRI after therapeutic intervention with budesonide.

MRI of the lung: non-invasive protocols and applications to small animal models of lung disease

Magnetic resonance imaging (MRI) can be used in pre-clinical studies as a non-invasive imaging tool for assessing the morphological and functional impact of lung diseases and for evaluating the efficacy of potential treatments for airways diseases. Hyperpolarized gases ((3)He or (129)Xe) MRI provides insight into the lung ventilation function. Lung proton MRI provides information on lung diseases associated with inflammatory activity or with changes in lung tissue density. These imaging techniques can be implemented with non-invasive protocols appropriate for longitudinal investigations in small animal models of lung diseases. This chapter will detail two (3)He and proton lung MR imaging protocols applied on two models of lung pathology in rodents.

ENaC-mediated effects assessed by MRI in a rat model of hypertonic saline-induced lung hydration

BACKGROUND AND PURPOSE

The epithelial sodium channel (ENaC) regulates airway mucosal hydration and mucus clearance. The lack of such regulation in cystic fibrosis patients leads to desiccation of the airway lumen, resulting in mucostasis that establishes the environment for infections. Osmotic agents and negative ENaC regulators can be used to restore mucosal hydration. We aimed to assess whether: (i) osmotically driven fluid flux into the rat lung could be quantified in vivo by magnetic resonance imaging (MRI); and (ii) the MRI signals could be modulated through the regulation of ENaC function.

EXPERIMENTAL APPROACH

Lung images from spontaneously breathing rats were acquired following intra-tracheal (i.t.) administration of physiological or hypertonic saline (HS). Compounds known to modulate the ENaC function were given i.t. prior to saline. Volumes of fluid signals were quantified on the images.

KEY RESULTS

A tonicity-dependent increase in lung fluid was demonstrated following HS administration. Pretreatment with the ENaC blockers, amiloride or 552-02, resulted in an enhancement of HS-induced lung fluid signals, which were detectable for up to 4 h, consistent with a role for ENaC in fluid clearance. Aprotinin, a serine protease inhibitor that attenuates ENaC function, likewise enhanced the HS-induced increase in lung fluid signal, while alpha(1)-anti-trypsin was without significant effect.

CONCLUSIONS AND IMPLICATIONS

Proton MRI provides a non-invasive technique for studying modulators of lung fluid hydration in rat lung in vivo. The pharmacological sensitivity of MRI-detected fluid signals is consistent with ENaC-mediated fluid reabsorption after HS. This target-related readout may be used to characterize new ENaC modulators.

Leukotriene A(4) hydrolase inhibition attenuates allergic airway inflammation and hyperresponsiveness

RATIONALE

Allergic asthma is characterized by reversible airway obstruction, lung inflammation, and airway hyperresponsiveness (AHR). Previous studies using leukotriene B(4) (LTB(4)) receptor 1-deficient mice and adoptive transfer experiments have suggested that LTB(4) plays a role in lung inflammation and AHR.

OBJECTIVES

In this study, we used a leukotriene A(4) hydrolase (LTA(4)H) inhibitor as a pharmacological tool to directly examine the role of LTB(4) in a mast cell-dependent murine model of allergic airway inflammation.

METHODS

We used the forced oscillation technique to test the effects of an LTA(4)H inhibitor dosed during the challenge phase on AHR. Lung tissue and lavage were collected for analysis.

MEASUREMENTS AND MAIN RESULTS

Treatment with an LTA(4)H inhibitor improved multiple parameters encompassing AHR and lung function. Significant decreases in inflammatory leukocytes, cytokines, and mucin were observed in the lung lumen. Serum levels of antigen-specific IgE and IgG1 were also decreased. Labeled antigen uptake by lung dendritic cells and subsequent trafficking to draining lymph nodes and the lung were decreased on LTA(4)H inhibitor treatment. Provocatively, inhibition of LTA(4)H increased lipoxin A(4) levels in lung lavage fluid.

CONCLUSIONS

These data suggest that LTB(4) plays a key role in driving lung inflammation and AHR. Mechanistically, we provide evidence that inhibition of LTA(4)H, affects recruitment of both CD4(+) and CD8(+) T cells, as well as trafficking of dendritic cells to draining lymph nodes, and may beneficially modulate other pro- and antiinflammatory eicosanoids in the lung. Inhibition of LTA(4)H is thus a potential therapeutic strategy that could modulate key aspects of asthma.

(1)H and hyperpolarized (3)He MR imaging of mouse with LPS-induced inflammation

PURPOSE

To evaluate the lipopolysaccharide (LPS) model of chronic obstructive pulmonary disease (COPD) in mouse with (1)H and hyperpolarized (HP) (3)He MR imaging.

MATERIALS AND METHODS

Axial slices of the lung volume were acquired with HP (3)He and (1)H MRI at 4, 24, and 48 h after LPS exposure. A quantitative ventilation index was calculated from two HP (3)He acquisitions. A bronchoalveolar lavage (BAL) for a cell count was performed following magnetic resonance imaging (MRI).

RESULTS

The LPS exposure resulted in a significant increase of cells in BAL, with maximum at 48 h. Lesions on (3)He images were characterized by ventilation defects, whereas lesions on (1)H images were hyperintense and were attributed to edema. The number of lesions was at maximum at 48 h. At this time point, and for both (3)He and (1)H MRI, the volume of the lesions was significantly higher for LPS-exposed mice compared to controls. At 4, 24, and 48 h the ventilation index from the (3)He data was significantly smaller for the LPS-exposed animals compared to controls.

CONCLUSION

The time point 48 h after LPS exposure was advantageous for MRI evaluation. Functional read-out with (3)He MRI seems to be more sensitive than conventional (1)H MRI.

Magnetic resonance methods and applications in pharmaceutical research

This review presents an overview of some recent magnetic resonance (MR) techniques for pharmaceutical research. MR is noninvasive, and does not expose subjects to ionizing radiation. Some methods that have been used in pharmaceutical research MR include magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) methods, among them, diffusion-weighted MRI, perfusion-weighted MRI, functional MRI, molecular imaging and contrast-enhance MRI. Some applications of MR in pharmaceutical research include MR in metabonomics, in vivo MRS, studies in cerebral ischemia and infarction, degenerative joint diseases, oncology, cardiovascular disorders, respiratory diseases and skin diseases. Some of these techniques, such as cardiac and joint imaging, or brain fMRI are standard, and are providing relevant data routinely. Skin MR and hyperpolarized gas lung MRI are still experimental. In conclusion, considering the importance of finding and characterizing biomarkers for improved drug evaluation, it can be expected that the use of MR techniques in pharmaceutical research is going to increase in the near future.

Bleomycin-induced lung injury assessed noninvasively and in spontaneously breathing rats by proton MRI

PURPOSE

To apply proton magnetic resonance imaging (MRI) techniques to assess noninvasively and in spontaneously breathing rats, structural changes following a single intratracheal administration of bleomycin (BLM).

MATERIALS AND METHODS

Rats were scanned by MRI prior to BLM or vehicle administration and at six hours, 24 hours, week 1, and at weeks 2, 3, 6, and 8 after treatment. Bronchoalveolar lavage (BAL) fluid and histological analyses were performed at 24 hours, and at weeks 1 and 8 (histology only).

RESULTS

Prominent MRI fluid signals were detected in the lungs of BLM-treated rats one week after challenge. These signals correlated with increased inflammatory parameters in BAL fluid and with marked perivascular and parenchymal infiltration with inflammatory cells in histological slices. At week 2 the MRI signals due to edema resolved, but nevertheless an increase in MRI signal intensity from the lung parenchyma was apparent. In some areas of the right lung the MRI signal intensity in the parenchyma decreased between weeks 2 and 8. These observations were in line with histology demonstrating collagen deposition and atelectasis (hallmarks of fibrosis) at week 1 and a partial recovery of the lung parenchyma at week 8.

CONCLUSION

The data demonstrate the ability of proton MRI to detect BLM-induced lung fibrosis as well as the acute inflammatory response caused by the agent.

Effects of theophylline on chronic inflammatory lung injury induced by LPS exposure in guinea pigs

BACKGROUND

Pathogenesis of COPD is, at least in part, attributable to the chronic accumulation of neutrophils in the airways, and morphological changes such as hyperplasia of goblet cells in the airways are often observed in this disease. These structural changes were induced in guinea pigs by repetitive inhalations of LPS, and the effects of theophylline and dexamethasone were examined.

METHODS

Male Hartley Guinea pigs weighing about 300 g were exposed to a nebulized solution of LPS (30 microg/mL) for 1 hour. Exposure to LPS was performed 15 times at 48-hour intervals. Histological analysis was performed, and infiltration of leukocytes in BALF, airway hyperreactivity and hydroxyproline content of the lung were measured 24 or 48 hours after the final exposure of LPS. Drugs were administered every day until 30 minutes before the final exposure.

RESULTS

Repetitive exposure to LPS induced an influx of inflammatory cells into the BALF. Histological changes such as accumulation of inflammatory cells in the lung parenchyma, enlargement of alveoli, swelling of the alveolar walls and goblet cell hyperplasia in the airways were observed. Airway hyperreactivity and increased lung hydroxyproline content were also found in this model of chronic inflammatory lung injury. Some of these changes induced by repetitive LPS exposure were improved by treatment with theophylline or dexamethasone.

CONCLUSIONS

Theophylline improved airway injury as well as airway hyperreactivity induced by repetitive exposure of the guinea pigs to LPS. These results suggest that theophylline treatment has ameliorative effects on airway disease with chronic inflammation.

Comprehensive gene expression profiling of rat lung reveals distinct acute and chronic responses to cigarette smoke inhalation

Chronic obstructive pulmonary disease (COPD) is a smoking-related disease that lacks effective therapies due partly to the poor understanding of disease pathogenesis. The aim of this study was to identify molecular pathways that could be responsible for the damaging consequences of smoking. To do this, we employed Gene Set Enrichment Analysis to analyze differences in global gene expression, which we then related to the pathological changes induced by cigarette smoke (CS). Sprague-Dawley rats were exposed to whole body CS for 1 day and for various periods up to 8 mo. Gene Set Enrichment Analysis of microarray data identified that metabolic processes were most significantly increased early in the response to CS. Gene sets involved in stress response and inflammation were also upregulated. CS exposure increased neutrophil chemokines, cytokines, and proteases (MMP-12) linked to the pathogenesis of COPD. After a transient acute response, the CS-exposed rats developed a distinct molecular signature after 2 wk, which was followed by the chronic phase of the response. During this phase, gene sets related to immunity and defense progressively increased and predominated at the later time points in smoke-exposed rats. Chronic CS inhalation recapitulated many of the phenotypic changes observed in COPD patients including oxidative damage to macrophages, a slowly resolving inflammation, epithelial damage, mucus hypersecretion, airway fibrosis, and emphysema. As such, it appears that metabolic pathways are central to dealing with the stress of CS exposure; however, over time, inflammation and stress response gene sets become the most significantly affected in the chronic response to CS.

Lung MRI for experimental drug research

Current techniques to evaluate the efficacy of potential treatments for airways diseases in preclinical models are generally invasive and terminal. In the past few years, the flexibility of magnetic resonance imaging (MRI) to obtain anatomical and functional information of the lung has been explored with the scope of developing a non-invasive approach for the routine testing of drugs in models of airways diseases in small rodents. With MRI, the disease progression can be followed in the same animal. Thus, a significant reduction in the number of animals used for experimentation is achieved, as well as minimal interference with their well-being and physiological status. In addition, under certain circumstances the duration of the observation period after disease onset can be shortened since the technique is able to detect changes before these are reflected in parameters of inflammation determined using invasive procedures. The objective of this article is to briefly address MRI techniques that are being used in experimental lung research, with special emphasis on applications. Following an introduction on proton techniques and MRI of hyperpolarized gases, the attention is shifted to the MRI analysis of several aspects of lung disease models, including inflammation, ventilation, emphysema, fibrosis and sensory nerve activation. The next subject concerns the use of MRI in pharmacological studies within the context of experimental lung research. A final discussion points towards advantages and limitations of MRI in this area.

Capsaicin-induced mucus secretion in rat airways assessed in vivo and non-invasively by magnetic resonance imaging

BACKGROUND AND PURPOSE

An up-regulation of the sensory neural pathways in the lung has been implicated in asthma and chronic obstructive pulmonary disease (COPD) and is thought to contribute to mucus hypersecretion, an essential feature of both diseases. The aim of this study was to assess non-invasively the acute effects (up to 60 min) of sensory nerve stimulation by capsaicin in the lung, using magnetic resonance imaging (MRI).

EXPERIMENTAL APPROACH

Male Brown Norway rats were imaged prior to and 10, 30 and 60 min after intra-tracheal challenge with capsaicin (30 microg kg(-1)) or vehicle (0.5% ethanol solution). In subsequent studies, pre-treatment with the transient receptor potential vanilloid (TRPV)-1 antagonist, capsazepine; the dual neurokinin (NK) 1 and NK2 receptor antagonist, DNK333 and the mast cell stabilizer, di-sodium cromoglycate (DSCG) was used to modulate the effects of capsaicin.

KEY RESULTS

Diffuse fluid signals were detected by MRI in the lung as early as 10 min after capsaicin, remaining constant 30 and 60 min after treatment. Broncho-alveolar lavage (BAL) fluid analysis performed 60 min after capsaicin revealed increased mucin concentration. Capsazepine (3.5 mg kg(-1)), DNK333 (10 mg kg(-1)) but not DSCG (10 mg kg(-1)) administered prophylactically were able to block the effect of capsaicin in the airways.

CONCLUSIONS AND IMPLICATIONS

These observations suggest that the fluid signals detected by MRI after capsaicin administration reflected predominantly the release of mucus following activation of sensory nerves. They point to the opportunity of non-invasively assessing with MRI the influence of neuronal mechanisms in animal models of asthma and COPD.

Proton MRI as a noninvasive tool to assess elastase-induced lung damage in spontaneously breathing rats

Elastase-induced changes in lung morphology and function were detected in spontaneously breathing rats using conventional proton MRI at 4.7 T. A single dose of porcine pancreatic elastase (75 U/100 g body weight) or vehicle (saline) was administered intratracheally (i.t.) to male Brown Norway (BN) rats. MRI fluid signals were detected in the lungs 24 hr after administration of elastase and resolved within 2 weeks. These results correlated with perivascular edema and cellular infiltration observed histologically. Reductions in MRI signal intensity of the lung parenchyma, and increases in lung volume were detected as early as 2 weeks following elastase administration and remained uniform throughout the study, which lasted 8 weeks. Observations were consistent with air trapping resulting from emphysema detected histologically. In a separate experiment, animals were treated daily intraperitoneally (i.p.) with all-trans-retinoic acid (ATRA; 500 microg/kg body weight) or its vehicle (triglyceride oil) starting on day 21 after elastase administration and continuing for 12 days. Under these conditions, ATRA did not elicit a reversal of elastase-induced lung damage as measured by MRI and histology. The present approach complements other validated applications of proton MRI in experimental lung research as a method for assessing drugs in rat models of respiratory diseases.

Lung inflammation and vascular remodeling after repeated allergen challenge detected noninvasively by MRI

Magnetic resonance imaging (MRI) has been used previously to follow noninvasively inflammatory processes in rat acute models of lung inflammation. Here the technique was applied to a model involving repeated intratracheal administration of ovalbumin (OA). Anatomical MRI was performed at different time points with respect to a single or multiple OA challenges in Brown Norway rats actively sensitized to the allergen. Vascular permeability was assessed using dynamic contrast-enhanced MRI (DCE-MRI). Bronchoalveolar lavage (BAL) fluid analysis and histology were performed to validate the MRI data. The time course of MRI signals after a single OA challenge reached a maximum at 48 h and decreased significantly at 96 h. After the second and subsequent challenges, the maximum signal occurred at 6 h with a time-dependent decline over the remainder of the time course. A reduction of the inflammatory response following repeated administration of OA was also detected by BAL fluid analysis. The decrease in vascular permeability assessed by DCE-MRI in repeatedly OA-challenged rats was consistent with the thickening of the vascular wall for vessels of diameter up to 300 microm revealed by histology. Angiogenesis of vessels smaller than 30 microm was also detected histologically. These results suggest that MRI can be used to detect the inflammatory response and vascular remodeling associated with chronic airway inflammation in rat models involving repeated administration of allergen. As the contrast agent used in the DCE-MRI experiments is approved for clinical use, there is potential to translate the approach to patients.

Identification with MRI of the pleura as a major site of the acute inflammatory effects induced by ovalbumin and endotoxin challenge in the airways of the rat

Inflammatory effects in the rat lung have been investigated, non-invasively by MRI, at early time points (3 and 6 h) after ovalbumin (OA) or endotoxin (LPS) challenges. Six hours after challenge with OA, a strong, even inflammatory signal was present around the periphery of the lung in a region corresponding to the pleura. Histological analysis confirmed the presence of marked edema associated with the pleural cavity of OA-treated animals. Lower levels of pleural edema were observed in MRI and histological evaluation of LPS-treated animals and no abnormality was observed in actively sensitized and naïve, saline-treated groups. Diffuse edematous signals were detected in the lung 3 and 6 h after challenge with OA or LPS; the signal volumes were larger at both time points following OA instillation. Bronchoalveolar lavage (BAL) fluid analysis performed 6 h after challenge revealed increased levels of protein and greater cellular activation in OA- than in LPS-treated animals. Furthermore, increased levels of peribronchial edema were found by histology 6 h after OA. BAL fluid and histological assessments demonstrated that the inflammatory signals were due to edema and not mucus as no significant changes in BAL mucin concentrations or differences in goblet cells were identified between OA or LPS challenge and their respective vehicle groups. Our data show that MRI is able to detect, non-invasively, inflammatory signals in both the lung and the pleura in spontaneously breathing animals, highlighting its potential to study the consequences of pulmonary insults on both sites.

Effect of adenosine A2A receptor activation in murine models of respiratory disorders

Activation of the adenosine A(2A) receptor has been postulated as a possible treatment for lung inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD). In this report, we have studied the anti-inflammatory properties of the reference A(2A) agonist CGS-21680, given intranasally at doses of 10 and 100 microg/kg, in a variety of murine models of asthma and COPD. After an acute ovalbumin challenge of sensitized mice, prophylactic administration of CGS-21680 inhibited the bronchoalveolar lavage fluid inflammatory cell influx but not the airway hyperreactivity to aerosolized methacholine. After repeated ovalbumin challenges, CGS-21680 given therapeutically inhibited the bronchoalveolar lavage fluid inflammatory cell influx but had no effect on the allergen-induced bronchoconstriction, the airway hyperreactivity, or the bronchoalveolar lavage fluid mucin levels. As a comparator, budesonide given intranasally at doses of 0.1-1 mg/kg fully inhibited all the parameters measured in the latter model. In a lipopolysaccharide-driven model, CGS-21680 had no effect on the bronchoalveolar lavage fluid inflammatory cell influx or TNF-alpha, keratinocyte chemoattractant, and macrophage inflammatory protein-2 levels, but potently inhibited neutrophil activation, as measured by bronchoalveolar lavage fluid elastase levels. With the use of a cigarette smoke model of lung inflammation, CGS-21680 did not significantly inhibit bronchoalveolar lavage fluid neutrophil infiltration but reversed the cigarette smoke-induced decrease in macrophage number. Together, these results suggest that activation of the A(2A) receptor would have a beneficial effect by inhibiting inflammatory cell influx and downregulating inflammatory cell activation in asthma and COPD, respectively.

Characterization of cigarette smoke-induced inflammatory and mucus hypersecretory changes in rat lung and the role of CXCR2 ligands in mediating this effect

Repetitive, acute inflammatory insults elicited by cigarette smoke (CS) contribute to the development of chronic obstructive pulmonary disease (COPD), a disorder associated with lung inflammation and mucus hypersecretion. Presently, there is a poor understanding of the acute inflammatory mechanisms involved in this process. The aims of this study were to develop an acute model to investigate temporal inflammatory changes occurring after CS exposure. Rats were exposed to whole body CS (once daily) generated from filtered research cigarettes. Initial studies indicated the generation of a neutrophilic/mucus hypersecreting lung phenotype in <4 days. Subsequent studies demonstrated that just two exposures to CS (15 h apart) elicited a robust inflammatory/mucus hypersecretory phenotype that was used to investigate mechanisms driving this response. Cytokine-induced neutrophil chemoattractants (CINCs) 1-3, the rat growth-related oncogene-alpha family homologs, and IL-1beta demonstrated time-dependent increases in lung tissue or lavage fluid over the 24-h period following CS exposure. The temporal changes in the neutrophil chemokines, CINCs 1-3, mirrored increases in neutrophil infiltration, indicative of a role in neutrophil migration. In addition, a specific CXCR2 antagonist, SB-332235, effectively inhibited CS-induced neutrophilia in a dose-dependent manner, supporting this conclusion. This modeling of the response of the rat airways to acute CS exposure indicates 1) as few as two exposures to CS will induce a phenotype with similarities to COPD and 2) a novel role for CINCs in the generation of this response. These observations represent a paradigm for the study of acute, repetitive lung insults that contribute to the development of chronic disease.

1H MRI of pneumococcal pneumonia in a murine model

PURPOSE

To detect and quantify pulmonary lesions due to pneumococcal pneumonia in a murine model by (1)H MRI.

MATERIALS AND METHODS

Pneumonia was induced in mice (N = 5) by intranasal administration of about 1 x 10(6) colony-forming units (CFU) of Streptococcus pneumonie. A group of noninfected animals (N = 5) was used as a control group. MRI was performed, 48 hours after infection induction, at 4.7 T. ECG-gated gradient-echo (GRE) sequences with TE = 5 msec were used. After MRI examination, the animals were sacrificed for histological examination.

RESULTS

Lungs appeared at MRI as regions with signal intensity (SI) at the level of the noise. Lesions appeared as hyperintense regions over the background and were localized mainly in the apical part of the lungs, in the medial and peribronchial regions. The anatomical localization of the lesions was confirmed by histology. The total lesion volume quantified by MRI data correlated with the total lesion volume quantified by histology.

CONCLUSION

This work shows that standard (1)H MRI allows detection and quantification of lesions due to pneumococcal pneumonia in mice.

Characterization of diffusing capacity and perfusion of the rat lung in a lipopolysaccaride disease model using hyperpolarized 129Xe

The ability to quantify pulmonary diffusing capacity and perfusion using dynamic hyperpolarized (129)Xe NMR spectroscopy is demonstrated. A model of alveolar gas exchange was developed, which, in conjunction with (129)Xe NMR, enables quantification of average alveolar wall thickness, pulmonary perfusion, capillary diffusion length, and mean transit time. The technique was employed to compare a group of naïve rats (n = 10) with a group of rats with acute inflammatory lung injury (n = 10), caused by instillation of lipopolysaccaride (LPS). The measured structural and perfusion-related parameters were in agreement with reported values from studies using non-NMR methods. Significant differences between the groups were found in total diffusion length (control 8.5 +/- 0.5 microm, LPS 9.9 +/- 0.6 microm, P < 0.001), in capillary diffusion length (control 2.9 +/- 0.4 microm, LPS 3.9 +/- 1.0 microm, P < 0.05), and in pulmonary hematocrit (control 0.55 +/- 0.06, LPS 0.43 +/- 0.08, P < 0.01), whereas no differences were observed in alveolar wall thickness, pulmonary perfusion, and mean transit time. These results demonstrate the ability of the method to distinguish two main aspects of lung function, namely, diffusing capacity and pulmonary perfusion.

Magnetic resonance imaging in drug discovery: lessons from disease areas

Imaging technologies are presently receiving considerable attention in the pharmaceutical area owing to their potential to accelerate the drug discovery and development process. One of the principal imaging modalities is magnetic resonance imaging (MRI). The multiparametric nature of MRI enables anatomical, functional and even molecular information to be obtained non-invasively from intact organisms at high spatial resolution, thereby enabling a comprehensive characterization of a disease state and the corresponding drug intervention. The non-invasiveness of MRI strengthens the link between pre-clinical and clinical drug studies, making the technique attractive for pharmaceutical research.

Proton MRI of lung parenchyma reflects allergen-induced airway remodeling and endotoxin-aroused hyporesponsiveness: A step toward ventilation studies in spontaneously breathing rats

Proton signals from lung parenchyma were detected with the use of a gradient-echo sequence to noninvasively obtain information on pulmonary function in models of airway diseases in rats. Initial measurements carried out in artificially ventilated control rats revealed a highly significant negative correlation between the parenchymal signal and the partial pressure of oxygen (pO2) in the blood, for different amounts of oxygen administered. The magnitude of the signal intensity variations caused by changes in the oxygen concentration was larger than expected solely from the paramagnetic properties of molecular oxygen. Inhomogeneous line-broadening induced by lung inflation may explain the observed signal amplification. Experiments carried out in spontaneously breathing animals challenged with allergen or endotoxin revealed parenchymal signal changes that reflected the oxygenation status of the lungs and were consistent with airway remodeling or hyporesponsiveness. The results suggest that proton MRI of parenchymal tissue is a sensitive tool for probing the functional status of the lung in rat models of respiratory diseases. The method is complementary to the recently described noninvasive assessment by MRI of pulmonary inflammation in small rodents. Overall, these techniques provide invaluable information for profiling anti-inflammatory drugs in models of airway diseases.