Jennifer Poelmans

Magnetic resonance imaging for noninvasive assessment of lung fibrosis onset and progression: cross-validation and comparison of different magnetic resonance imaging protocols with micro-computed tomography and histology in the bleomycin-induced mouse model.

ObjectivesBleomycin instillation is frequently used to model lung fibrosis, although the onset and severity of pathology varies highly between mice. This makes non–invasive fibrosis detection and quantification essential to obtain a comprehensive analysis of the disease course and to validate novel therapies. Magnetic resonance imaging (MRI) of lung disease progression and therapy may provide such a sensitive in vivo readout of lung fibrosis, bypassing radiotoxicity concerns (when using micro-CT [&mgr;CT]) and elaborate invasive end point measurements (histology). We aimed to optimize and evaluate 3 different lung MRI contrast and acquisition methods to visualize disease onset and progression in the bleomycin-induced mouse model of lung fibrosis using a small-animal MRI scanner. For validation, we compared the MRI results with established &mgr;CT and histological measures of lung fibrosis. Materials and MethodsFree-breathing bleomycin-instilled and control mice were scanned in vivo with respiration-triggered conventional, ultrashort echo time and self-gated MRI pulse sequences (9.4 T) and &mgr;CT at baseline and weekly at days 7, 14, 21, and 28 after bleomycin instillation. After the last imaging time point, the mice were killed and the lungs were isolated for criterion standard histological analysis of lung fibrosis and quantification of lung collagen content for validation of the imaging results. The agreement between quantitative MRI and &mgr;CT data and standard measurements was analyzed by linear regression. ResultsAll 3 MRI protocols were able to visualize and quantify lung pathology onset and progression in individual bleomycin-instilled mice. In vivo MRI results were in excellent agreement with in vivo &mgr;CT and criterion standard histological measures of lung fibrosis. Ultrashort echo time MRI appeared particularly useful for detecting early disease; self-gated MRI, for improved breathing motion handling. DiscussionMagnetic resonance imaging sensitively visualizes and quantifies lung fibrosis in vivo, which makes it a noninvasive, translatable, safe, and potentially more versatile alternative to invasive methods or &mgr;CT, thereby stimulating pathogenesis and preclinical research.

Longitudinal micro-CT provides biomarkers of lung disease that can be used to assess the effect of therapy in preclinical mouse models, and reveal compensatory changes in lung volume

ABSTRACT In vivo lung micro-computed tomography (micro-CT) is being increasingly embraced in pulmonary research because it provides longitudinal information on dynamic disease processes in a field in which ex vivo assessment of experimental disease models is still the gold standard. To optimize the quantitative monitoring of progression and therapy of lung diseases, we evaluated longitudinal changes in four different micro-CT-derived biomarkers [aerated lung volume, lung tissue (including lesions) volume, total lung volume and mean lung density], describing normal development, lung infections, inflammation, fibrosis and therapy. Free-breathing mice underwent micro-CT before and repeatedly after induction of lung disease (bleomycin-induced fibrosis, invasive pulmonary aspergillosis, pulmonary cryptococcosis) and therapy (imatinib). The four lung biomarkers were quantified. After the last time point, we performed pulmonary function tests and isolated the lungs for histology. None of the biomarkers remained stable during longitudinal follow-up of adult healthy mouse lungs, implying that biomarkers should be compared with age-matched controls upon intervention. Early inflammation and progressive fibrosis led to a substantial increase in total lung volume, which affects the interpretation of aerated lung volume, tissue volume and mean lung density measures. Upon treatment of fibrotic lung disease, the improvement in aerated lung volume and function was not accompanied by a normalization of the increased total lung volume. Significantly enlarged lungs were also present in models of rapidly and slowly progressing lung infections. The data suggest that total lung volume changes could partly reflect a compensatory mechanism that occurs during disease progression in mice. Our findings underscore the importance of quantifying total lung volume in addition to aerated lung or lesion volumes to accurately document growth and potential compensatory mechanisms in mouse models of lung disease, in order to fully describe and understand dynamic processes during lung disease onset, progression and therapy. This is highly relevant for the translation of therapy evaluation results from preclinical studies to human patients. Summary: Quantifying not only aerated lung volume or lesion volumes but also the total lung volume from micro-CT is essential to document growth as well as potential compensatory mechanisms in the evaluation of mouse models of lung diseases and their therapy.

Longitudinal in vivo microcomputed tomography of mouse lungs: No evidence for radiotoxicity

Before microcomputed tomography (micro-CT) can be exploited to its full potential for longitudinal monitoring of transgenic and experimental mouse models of lung diseases, radiotoxic side effects such as inflammation or fibrosis must be considered. We evaluated dose and potential radiotoxicity to the lungs for long-term respiratory-gated high-resolution micro-CT protocols. Free-breathing C57Bl/6 mice underwent four different retrospectively respiratory gated micro-CT imaging schedules of repeated scans during 5 or 12 wk, followed by ex vivo micro-CT and detailed histological and biochemical assessment of lung damage. Radiation exposure, dose, and absorbed dose were determined by ionization chamber, thermoluminescent dosimeter measurements and Monte Carlo calculations. Despite the relatively large radiation dose delivered per micro-CT acquisition, mice did not show any signs of radiation-induced lung damage or fibrosis when scanned weekly during 5 and up to 12 wk. Doubling the scanning frequency and once tripling the radiation dose as to mimic the instant repetition of a failed scan also stayed without detectable toxicity after 5 wk of scanning. Histological analyses confirmed the absence of radiotoxic damage to the lungs, thereby demonstrating that long-term monitoring of mouse lungs using high-resolution micro-CT is safe. This opens perspectives for longitudinal monitoring of (transgenic) mouse models of lung diseases and therapeutic response on an individual basis with high spatial and temporal resolution, without concerns for radiation toxicity that could potentially influence the readout of micro-CT-derived lung biomarkers. This work further supports the introduction of micro-CT for routine use in the preclinical pulmonary research field where postmortem histological approaches are still the gold standard.

Longitudinal, in vivo assessment of invasive pulmonary aspergillosis in mice by computed tomography and magnetic resonance imaging

Invasive aspergillosis is an emerging threat to public health due to the increasing use of immune suppressive drugs and the emergence of resistance against antifungal drugs. To deal with this threat, research on experimental disease models provides insight into the pathogenesis of infections caused by susceptible and resistant Aspergillus strains and by assessing their response to antifungal drugs. However, standard techniques used to evaluate infection in a preclinical setting are severely limited by their invasive character, thereby precluding evaluation of disease extent and therapy effects in the same animal. To enable non-invasive, longitudinal monitoring of invasive pulmonary aspergillosis in mice, we optimized computed tomography (CT) and magnetic resonance imaging (MRI) techniques for daily follow-up of neutropenic BALB/c mice intranasally infected with A. fumigatus spores. Based on the images, lung parameters (signal intensity, lung tissue volume and total lung volume) were quantified to obtain objective information on disease onset, progression and extent for each animal individually. Fungal lung lesions present in infected animals were successfully visualized and quantified by both CT and MRI. By using an advanced MR pulse sequence with ultrashort echo times, pathological changes within the infected lung became visually and quantitatively detectable at earlier disease stages, thereby providing valuable information on disease onset and progression with high sensitivity. In conclusion, these non-invasive imaging techniques prove to be valuable tools for the longitudinal evaluation of dynamic disease-related changes and differences in disease severity in individual animals that might be readily applied for rapid and cost-efficient drug screening in preclinical models in vivo.

Nanoparticle-induced inflammation can increase tumor malignancy

Nanomaterials, such as aluminum oxide, have been regarded with high biomedical promise as potential immune adjuvants in favor of their bulk counterparts. For pathophysiological conditions where elevated immune activity already occurs, the contribution of nanoparticle-activated immune reactions remains unclear. Here, we investigated the effect of spherical and wire-shaped aluminum oxide nanoparticles on primary splenocytes and observed a clear pro-inflammatory effect of both nanoparticles, mainly for the high aspect ratio nanowires. The nanoparticles resulted in a clear activation of NLRP3 inflammasome, and also secreted transforming growth factor β. When cancer cells were exposed to these cytokines, this resulted in an increased level of epithelial-to-mesenchymal-transition, a hallmark for cancer metastasis, which did not occur when the cancer cells were directly exposed to the nanoparticles themselves. Using a syngeneic tumor model, the level of inflammation and degree of lung metastasis were significantly increased when the animals were exposed to the nanoparticles, particularly for the nanowires. This effect could be abrogated by treating the animals with inflammatory inhibitors. Collectively, these data indicate that the interaction of nanoparticles with immune cells can have secondary effects that may aggravate pathophysiological conditions, such as cancer malignancy, and conditions must be carefully selected to finely tune the induced aspecific inflammation into cancer-specific antitumor immunity. STATEMENT OF SIGNIFICANCE Many different types of nanoparticles have been shown to possess immunomodulatory properties, depending on their physicochemical parameters. This can potentially be harnessed as a possible antitumor therapy. However, in the current work we show that inflammation elicited by nanomaterials can have grave effects in pathophysiological conditions, where non-specific inflammation was found to increase cancer cell mobility and tumor malignancy. These data show that immunomodulatory properties of nanomaterials must be carefully controlled to avoid any undesired side-effects.

Bronchoscopic fibered confocal fluorescence microscopy for longitudinal in vivo assessment of pulmonary fungal infections in free-breathing mice

Respiratory diseases, such as pulmonary infections, are an important cause of morbidity and mortality worldwide. Preclinical studies often require invasive techniques to evaluate the extent of infection. Fibered confocal fluorescence microscopy (FCFM) is an emerging optical imaging technique that allows for real-time detection of fluorescently labeled cells within live animals, thereby bridging the gap between in vivo whole-body imaging methods and traditional histological examinations. Previously, the use of FCFM in preclinical lung research was limited to endpoint observations due to the invasive procedures required to access lungs. Here, we introduce a bronchoscopic FCFM approach that enabled in vivo visualization and morphological characterisation of fungal cells within lungs of mice suffering from pulmonary Aspergillus or Cryptococcus infections. The minimally invasive character of this approach allowed longitudinal monitoring of infection in free-breathing animals, thereby providing both visual and quantitative information on infection progression. Both the sensitivity and specificity of this technique were high during advanced stages of infection, allowing clear distinction between infected and non-infected animals. In conclusion, our study demonstrates the potential of this novel bronchoscopic FCFM approach to study pulmonary diseases, which can lead to novel insights in disease pathogenesis by allowing longitudinal in vivo microscopic examinations of the lungs.

A multimodal imaging approach enables in vivo assessment of antifungal treatment in a mouse model of invasive pulmonary aspergillosis

ABSTRACT Aspergillus fumigatus causes life-threatening lung infections in immunocompromised patients. Mouse models are extensively used in research to assess the in vivo efficacies of antifungals. In recent years, there has been an increasing interest in the use of noninvasive imaging techniques to evaluate experimental infections. However, single imaging modalities have limitations concerning the type of information they can provide. In this study, magnetic resonance imaging and bioluminescence imaging were combined to obtain longitudinal information on the extent of developing lesions and fungal load in a leukopenic mouse model of invasive pulmonary aspergillosis (IPA). This multimodal imaging approach was used to assess changes occurring within lungs of infected mice receiving voriconazole treatment starting at different time points after infection. The results showed that IPA development depends on the inoculum size used to infect animals and that disease can be successfully prevented or treated by initiating intervention during early stages of infection. Furthermore, we demonstrated that a reduction in fungal load is not necessarily associated with the disappearance of lesions on anatomical lung images, especially when antifungal treatment coincides with immune recovery. In conclusion, multimodal imaging allows an investigation of different aspects of disease progression or recovery by providing complementary information on dynamic processes, which are highly useful for assessing the efficacy of (novel) therapeutic compounds in a time- and labor-efficient manner.

THU0064 Small Animal MRI for Non-Invasive Longitudinal Follow Up of Pulmonary Fibrosis in Mice

Background Pulmonary fibrosis, either idiopathic or secondary to diseases such as systemic sclerosis, is a devastating and life threatening disorder for which effective treatment is still lacking. The bleomycin-induced pulmonary fibrosis model is well-characterized and the most widely used mouse model. The resulting fibrosis is routinely quantified by labor-intensive end-stage histological assessments, requiring many animals and lack the ability to follow-up on disease progression and potential therapeutic effects in the individual animal. At present, imaging tools for the evaluation of lung disease with good temporal and spatial resolution in vivo are limited. Objectives To optimize and evaluate lung MRI protocols to visualize disease onset and progression in the bleomycin-induced model of lung fibrosis. We compared prospectively and retrospectively gated MRI sequences and validated our results with established CT imaging of lung fibrosis and histochemical techniques. Methods Animal Model: Male C57Bl/6 mice were intratracheally instilled with bleomycin (0.05U in 50 µl of PBS) or sham. The mice were scanned with MRI and CT at baseline and weekly until 3 weeks after instillation. After the last imaging time point, mice were sacrificed, ex vivo CT data were acquired and the lungs were isolated for histological analysis and quantification as described before 3. MRI images were acquired at 9.4T (Bruker Biospin, 20 cm) in combination with a 7.5cm quadrature coil, using the following sequences: (1) a respiratory triggered RARE sequence (TR 6000ms TEeff=15.9ms, 50slices of 0.5mm thick), (2) a respiratory triggered ultra short echo (UTE) sequence (FID mode, TR= 20ms, TE=0.4ms, 8 slices, 0.6mm slice thickness) and (3) a retrospectively gated FLASH sequence IntraGate ( TR/TE = 30/1.26 ms, 17 deg flip angle, 5 slices covering the lung, slice thickness 1 mm). For reconstruction, 70% of the respiration and ECG period was used (Paravision 5.1, Bruker)). MRI data were quantified using ImageJ. CT methods: retrospectively gated CT images were acquired on a small animal µCT scanner (SkyScan 1076, Bruker microCT) and quantified. Results The prospectively gated UTE and RARE protocols as well as retrospectively gated IntraGate-FLASH imaging were able to visualize an increase of hyperintense focal spots over time, corresponding to progression of lung fibrosis as corroborated by lung CT images. Quantification of the mean lung signal intensity shows an increase over time, which was confirmed by the decrease in aerated lung volume quantified from the CT data and by histology. UTE, RARE and IntraGate-FLASH images of control animals confirmed the absence of contrast without fibrosis induction. Conclusions The evaluated MRI protocols were all able to non-invasively visualize and quantify lung disease progression. Moreover, the IntraGate-FLASH protocol does not need setup of respiratory triggering for lung imaging, making it an easy to use and efficient alternative to more conventional sequences. Where CT provides poor soft tissue contrast, MRI has the potential to provide contrast differences between vasculature, fibrotic areas and inflammation, without concerns for radiotoxicity when scanning the same animal repeatedly. Disclosure of Interest None Declared