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.

Effects of a mitogen-activated protein kinase inhibitor on allergic airways inflammation in the rat studied by magnetic resonance imaging.

We recently described a new model to study non-invasively with magnetic resonance imaging (MRI) the effects of compounds to prevent and/or resolve airway inflammation induced by ovalbumin in the lungs of actively sensitised rats. We report here the effects of 4-(4-fluorophenyl)-2-(1-methylpiperidin-4-yl)-5-(2-(1-(S)-phenylethyl)amino-4-pyridinyl)thiazole fumarate (Compound 1), which exhibits inhibitory activity against p38alpha and p38beta2 and residual activity on c-Jun amino-terminal kinase (JNK)2 mitogen-activated protein (MAP) kinases, on the oedematous signals detected by MRI and generated by antigen challenge in the lungs of sensitized rats. Compound 1 (10 mg kg(-1)) given orally 1 h prior to allergen challenge significantly reduced the oedematous signal measured at 24 h. Similar effects were seen with a synthetic corticosteroid, mometasone furoate (0.3 mg kg(-1)), given intratracheally 3 h prior to challenge. For both compounds, inhibition of the oedematous signal was accompanied by reductions in the inflammatory parameters in the bronchoalveolar lavage fluid measured 24 h after challenge with ovalbumin. Compound 1 (10 mg kg(-1)) administered 24 h after challenge with ovalbumin did not change the rate of resolution of the signal detected by MRI in the lungs. In contrast, mometasone furoate (0.3 mg kg(-1)) significantly increased resolution of these signals, which was evident 3 h after drug administration and maintained to 48 h post challenge. Collectively, our data suggest that the p38 MAP kinase inhibitor Compound 1 shows a different profile than glucocorticosteroids since its ability to resolve existing inflammation is limited.

Resolution of the oedema associated with allergic pulmonary inflammation in rats assessed noninvasively by magnetic resonance imaging.

1. Magnetic resonance imaging (MRI) was used to study noninvasively the effects of compounds to resolve inflammation induced by ovalbumin (OVA) challenge in the lungs of actively sensitised rats. 2. Marked oedematous signals were detected between 24 and 96 h following OVA in vehicle-treated animals. When administered 24 h after OVA, budesonide, a glucocorticosteroid, or 4-(8-benzo[1,2,5]oxadiazol-5-yl-[1,7]naphthyridin-6-yl)-benzoic acid (NVP-ABE171), a selective phosphodiesterase 4 inhibitor, increased the rate of resolution of established oedematous signals detected by MRI. The effect was evident 3 h after drug administration and the signals were nearly fully resolved at 96 h postchallenge. 3. The drug-induced rapid resolution of MRI signals was not accompanied by changes in parameters of inflammation in the bronchoalveolar lavage fluid, but was associated with perivascular oedema detected histologically. 4. In conclusion, the effects of anti-inflammatory drugs on a component of allergic inflammation can be monitored by following with MRI the rate of resolution of the associated oedematous signals.

Effects of immunomodulators on airways hyperresponsiveness to adenosine induced in actively sensitised Brown Norway rats by exposure to allergen.

We have recently demonstrated a marked and selective augmentation of the bronchoconstrictor response to adenosine in actively sensitised Brown Norway (BN) rats challenged with ovalbumin (OA). The augmented response is mediated by 5-hydroxytryptamine (5-HT) released as a consequence of mast cell activation. We describe here the effects of budesonide, a clinically used glucocorticosteroid, IMM125, a hydroxyethyl derivative of D-serine-cyclosporine, MLD987, a close analogue of ascomycin and SAR943, a rapamycin derivative, on the hyperresponsiveness to adenosine induced in actively sensitised BN rats by exposure to allergen. Bronchoconstrictor responses to adenosine elicited 3 h following intratracheal (i.t.) instillation of OA, 0.3 mg kg(-1) were reduced dose-dependently by budesonide, IMM125, and MLD987, given i.t. 25 and 1 h prior to allergen challenge. In contrast, SAR943 had no effect on responses to adenosine. Responses to methacholine and 5-HT were minimally affected by these agents. Bronchoconstrictor responses to bradykinin were dose-dependently reduced by budesonide, but unaffected following IMM125, MLD987 or SAR943 pre-treatment. Challenge with OA at a dose of 0.3 mg kg(-1), induced increases in bronchoalveolar lavage (BAL) fluid, leukocyte numbers, eosinophil peroxidase (EPO) and myeloperoxidase (MPO) activities and protein concentration measured 24 h post challenge. Budesonide (1 mg kg(-1) given i.t. 25 and 1 h prior to OA challenge) induced reductions in the BAL fluid parameters of inflammation; IMM125 and MLD987, at a dose of 1 mg kg(-1) had no significant effect whereas SAR943 reduced lymphocyte numbers. Thus, budesonide, IMM125 and MLD987 block the hyperresponsiveness to adenosine induced by allergen challenge in sensitised rats. In the case of budesonide the effect is associated with a powerful, generalised anti-inflammatory effect although an effect directly on the mast cells is also likely. With IMM125 and MLD987, the effect is seen at doses that are not anti-inflammatory and may reflect direct suppression of mast cell activation by these agents.

Pulmonary inflammation monitored noninvasively by MRI in freely breathing rats.

A detailed analysis has been carried out of the correlation between the signals detected by MRI in the rat lung after allergen or endotoxin challenge and parameters of inflammation determined in the broncho-alveolar lavage (BAL) fluid. MRI signals after allergen correlated highly significantly with the BAL fluid eosinophil number, eosinophil peroxidase activity and protein concentration. Similar highly significant correlations were seen when the anti-inflammatory glucocorticosteroid, budesonide, manifested against allergen. In contrast, following endotoxin challenge, mucus was the sole BAL fluid parameter that correlated significantly with the long lasting signal detected by MRI. Since edema is an integral component of pulmonary inflammation, MRI provides a noninvasive means of monitoring the course of the inflammatory response and should prove invaluable in profiling anti-inflammatory drugs in vivo. Further, the prospect of noninvasively detecting a sustained mucus hypersecretory phenotype in the lung brings an important new perspective to models of chronic obstructive pulmonary diseases.