An improved simple method of mouse lung intubation

Optimizing anesthesia and delivery approaches for dosing into lungs of mice

Microbes, toxins, therapeutics, and cells are often instilled into lungs of mice to model diseases and test experimental interventions. Consistent pulmonary delivery is critical for experimental power and reproducibility, but we observed variation in outcomes between handlers using different anesthetic approaches for intranasal dosing in mice. We therefore used a radiotracer to quantify lung delivery after intranasal dosing under inhalational (isoflurane) versus injectable (ketamine/xylazine) anesthesia in C57BL/6 mice. We found that ketamine/xylazine anesthesia resulted in delivery of a greater proportion (52 ± 9%) of an intranasal dose to lungs relative to isoflurane anesthesia (30 ± 15%). This difference in pulmonary dose delivery altered key outcomes in models of viral and bacterial pneumonia, with mice anesthetized with ketamine/xylazine for intranasal infection with influenza A virus or Pseudomonas aeruginosa developing more robust lung inflammation responses relative to control animals randomized to isoflurane anesthesia. Pulmonary dosing efficiency through oropharyngeal aspiration was not affected by anesthetic method and resulted in delivery of 63 ± 8% of dose to lungs, and a nonsurgical intratracheal dosing approach further increased lung delivery to 92 ± 6% of dose. The use of either of these more precise dosing methods yielded greater experimental power in the bacterial pneumonia model relative to intranasal infection. Both anesthetic approach and dosing route can impact pulmonary dosing efficiency. These factors affect experimental power and so should be considered when planning and reporting studies involving delivery of fluids to lungs of mice.NEW & NOTEWORTHY Many lung research studies involve dosing fluids into lungs of mice. In this study, the authors measure lung deposition using intranasal (i.n.), oropharyngeal aspiration (o.a.), and intratracheal (i.t.) dosing methods in mice. Anesthetic approach and administration route were found to affect pulmonary dosing efficiency. The authors demonstrate that refinements to dosing techniques can enable reductions in the number of animals needed for bacterial and viral pneumonia studies.

To bead or not to bead: A review of Pseudomonas aeruginosa lung infection models for cystic fibrosis

Cystic fibrosis (CF) lung disease is characterised by recurring bacterial infections resulting in inflammation, lung damage and ultimately respiratory failure. Pseudomonas aeruginosa is considered one of the most important lung pathogens in those with cystic fibrosis. While multiple cystic fibrosis animal models have been developed, many fail to mirror the cystic fibrosis lung disease of humans, including the colonisation by opportunistic environmental pathogens. Delivering bacteria to the lungs of animals in different forms is a way to model cystic fibrosis bacterial lung infections and disease. This review presents an overview of previous models, and factors to consider when generating a new P. aeruginosa lung infection model. The future development and application of lung infection models that more accurately reflect human cystic fibrosis lung disease has the potential to assist in understanding the pathophysiology of cystic fibrosis lung disease and for developing treatments.

Optimizing anesthesia and delivery approaches for dosing into lungs of mice

Microbes, toxins, therapeutics and cells are often instilled into lungs of mice to model diseases and test experimental interventions. Consistent pulmonary delivery is critical for experimental power and reproducibility, but we observed variation in outcomes between handlers using different anesthetic approaches for intranasal dosing into mice. We therefore used a radiotracer to quantify lung delivery after intranasal dosing under inhalational (isoflurane) versus injectable (ketamine/xylazine) anesthesia in C57BL/6 mice. We found that ketamine/xylazine anesthesia resulted in delivery of a greater proportion (52±9%) of an intranasal dose to lungs relative to isoflurane anesthesia (30±15%). This difference in pulmonary dose delivery altered key outcomes in a model of viral pneumonia, with mice anesthetized with ketamine/xylazine for intranasal infection with influenza A virus developing worse lung pathology and more consistently losing body weight relative to control animals randomized to isoflurane anesthesia. Pulmonary dosing efficiency through oropharyngeal aspiration was not affected by anesthetic method and resulted in delivery of 63±8% of dose to lungs, and a non-surgical intratracheal dosing approach further increased lung delivery to 92±6% of dose. We conclude that anesthetic approach and dosing route can impact pulmonary dosing efficiency. These factors should be considered when planning and reporting studies involving delivery of fluids to lungs of mice.

Comparison of physical perturbation devices for enhancing lentiviral vector-mediated gene transfer to the airway epithelium

Natural airway defences currently impede the efficacy of viral vector-mediated airway gene therapy. Conditioning airways prior to vector delivery can disrupt these barriers, improving viral vector access to target receptors and airway stem cells. This study aimed to assess and quantify the in vivo histological and gene transfer effects of physical perturbation devices to identify effective conditioning approaches. A range of flexible wire baskets with varying configurations, a Brush, biopsy forceps, and a balloon catheter were examined. We first evaluated the histological effects of physical perturbation devices in rat tracheas that were excised 10 minutes after conditioning. Based on the histological findings, a selection of devices were used to condition rat tracheas in vivo before delivering a lentiviral vector containing the LacZ reporter gene. After 7 days, excised tracheas were X-gal processed and examined en face to quantify the area of LacZ staining. Histological observations 10 minutes after conditioning found that physical perturbation dislodged cells from the basement membrane to varying degrees, with some producing significant levels of epithelial cell removal. When a subset of devices were assessed for their ability to enhance gene transfer, only the NGage® wire basket (Cook Medical) produced a significant increase in the proportion of X-gal-stained area when compared to unconditioned tracheas (8-fold, p = 0.00025). These results suggest that a range of factors contribute to perturbation-enhanced gene transfer. Overall, this study supports existing evidence that physical perturbation can assist airway gene transfer, and will help to identify the characteristics of an effective device for airway gene therapy.

Full Assessment of Lung Mechanics Using Computer-Controlled, Forced Oscillation Technique

The forced oscillation technique (FOT) is a powerful and accurate method to quantify the mechanical properties of the airways and tissues of the respiratory system. Here we provide a detailed protocol for the measurement of mouse respiratory mechanical parameters. We present a procedure for mouse endotracheal intubation using a handcrafted intubation platform and confirmation module. The FlexiVentFX™ system (Scireq Inc.) is utilized for the thorough assessment of lung function with the FlexiWare™ software serving as a unit for the planning, experimentation, and analysis. The protocol has been standardized and adapted for use by our center for lung-function phenotyping of mouse models generated for the International Mouse Phenotyping Consortium (IMPC). The simplified steps, technical considerations, and integrated hardware-software demonstration make this protocol adaptable and implementable for researchers interested in using FOT for lung-function evaluation. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Support Protocol 1: Assembly of the FlexiVentFX™ system for measurements Support Protocol 2: FlexiWare database management Support Protocol 3: A guide for the construction of intubation platform and confirmation module Basic Protocol 1: Mouse endotracheal intubation Basic Protocol 2: Assessment of mouse basal lung function.

A simplified method for bronchoalveolar lavage in mice by orotracheal intubation avoiding tracheotomy

Bronchoalveolar lavage (BAL) represents an important method to sample immune cells and soluble substances from the lungs of humans and animals suffering from respiratory disease. The mouse is the most commonly used model organism to study lung disease. Performing BAL in mice is difficult due to their small size and the currently used method requires tracheotomy, a complex and time-consuming procedure. Here, we describe a simple alternative procedure that avoids this step. To perform the BAL, a rigid, olive tip cannula is inserted from the mouth into the trachea under visual inspection. This novel method requires minimal training, is simple, fast, inexpensive and should be useful for researchers studying mouse models of human lung disease.

The Effects of Conditioning and Lentiviral Vector Pseudotype on Short- and Long-Term Airway Reporter Gene Expression in Mice

A gene addition therapy into the conducting airway epithelium is a potential cure for cystic fibrosis lung disease. Achieving sustained lung gene expression has proven difficult due to the natural barriers of the lung. The development of lentiviral (LV) vectors pseudotyped with viral envelopes that have a natural tropism to the airway has enabled persistent gene expression to be achieved in vivo. The aims of this study were to compare the yields of hemagglutinin (HA) and vesicular stomatitis virus-glycoprotein (VSV-G) pseudotyped HIV-1 vectors produced under the same conditions by our standard LV vector production method. We then sought to measure gene expression in mouse airways and to determine whether lysophosphatidylcholine (LPC) conditioning enhances short- and long-term gene expression. C57Bl/6 mouse airways were conditioned with 10 μL of 0.1% LPC or saline control, followed 1 h later by a 30 μL dose of an HA or VSV-G pseudotyped vector carrying either the LacZ or luciferase reporter genes. LacZ expression was assessed by X-gal staining after 7 days, while lung luminescence was quantified regularly for up to 18 months by bioluminescent imaging. The HA pseudotyped vectors had functional titers 25 to 60 times lower than the VSV-G pseudotyped vectors. Conditioning the lung with LPC significantly increased the total number of LacZ-transduced cells for both pseudotypes compared to saline control. Regardless of LPC conditioning, the VSV-G pseudotype produced higher initial levels of gene expression compared to HA. LPC conditioning did not increase the number of transduced basal cells for either pseudotype compared to saline, and was not required for long-term gene expression. Both pseudotyped vectors effectively transduced the upper conducting airways of wild-type mice. The use of LPC conditioning before vector delivery was not required in mouse lungs to produce long-term gene expression, but did improve short-term gene expression.

Validating in vivo hyperpolarized 129 Xe diffusion MRI and diffusion morphometry in the mouse lung

PURPOSE

Diffusion and lung morphometry imaging using hyperpolarized gases are promising tools to quantify pulmonary microstructure noninvasively in humans and in animal models. These techniques assume the motion encoded is exclusively diffusive gas displacement, but the impact of cardiac motion on measurements has never been explored. Furthermore, although diffusion morphometry has been validated against histology in humans and mice using 3 He, it has never been validated in mice for 129 Xe. Here, we examine the effect of cardiac motion on diffusion imaging and validate 129 Xe diffusion morphometry in mice.

THEORY AND METHODS

Mice were imaged using gradient-echo-based diffusion imaging, and apparent diffusion-coefficient (ADC) maps were generated with and without cardiac gating. Diffusion-weighted images were fit to a previously developed theoretical model using Bayesian probability theory, producing morphometric parameters that were compared with conventional histology.

RESULTS

Cardiac gating had no significant impact on ADC measurements (dual-gating: ADC = 0.020 cm2 /s, single-gating: ADC = 0.020 cm2 /s; P = .38). Diffusion-morphometry-generated maps of ADC (mean, 0.0165 ± 0.0001 cm2 /s) and acinar dimensions (alveolar sleeve depth [h] = 44 µm, acinar duct radii [R] = 99 µm, mean linear intercept [Lm ] = 74 µm) that agreed well with conventional histology (h = 45 µm, R = 108 µm, Lm = 63 µm).

CONCLUSION

Cardiac motion has negligible impact on 129 Xe ADC measurements in mice, arguing its impact will be similarly minimal in humans, where relative cardiac motion is reduced. Hyperpolarized 129 Xe diffusion morphometry accurately and noninvasively maps the dimensions of lung microstructure, suggesting it can quantify the pulmonary microstructure in mouse models of lung disease.

Improved preclinical hyperpolarized 129 Xe ventilation imaging with constant flip angle 3D radial golden means acquisition and keyhole reconstruction

Hyperpolarized (HP) 129 Xe MRI is increasingly used to noninvasively probe regional lung structure and function in the preclinical setting. As in human imaging, the primary barrier to quantitative imaging with HP gases is nonequilibrium magnetization, which is depleted by T1 relaxation and radio frequency excitation. Preclinical HP gas imaging commonly involves mechanically ventilating small animals and encoding k-space over tens or hundreds of breaths, with small subsets of k-space data collected within each breath. Breath-to-breath magnetization renewal enables the use of large flip angles, but the resulting magnetization decay generates large view-to-view differences in within-breath signal intensity, leading to artifacts and degraded image quality. This deleterious signal decay has motivated the use of variable flip angle (VFA) sampling schemes, in which the flip angle is progressively increased to maintain constant view-to-view signal intensity. However, VFA imaging complicates data acquisition and provides only a global correction that fails to compensate for regional differences in signal dynamics. When constant flip angle (CFA) imaging is used alongside 3D radial golden means acquisition, the center of k-space is sampled with every excitation, thereby encoding signal dynamics alongside imaging data. Here, keyhole reconstruction is used to generate multiple images to capture in-breath HP 129 Xe signal dynamics in mice and thus provide flip angle maps to quantitatively correct images without extra data collection. These CFA images display SNR that is not significantly different from VFA images, and further, high frequency k-space scaling can be used to mitigate decay-induced image artifacts. Results are supported by point spread function calculations and simulations of radial imaging with preclinical signal dynamics. Together, these results show that CFA 3D radial golden means ventilation imaging provides comparable image quality with VFA in small animals and allows for keyhole reconstruction, which can be used to generate flip angle maps and correct images for signal depletion.

Preclinical hyperpolarized 129 Xe MRI: ventilation and T2 * mapping in mouse lungs at 7 T using multi-echo flyback UTE

Fast apparent transverse relaxation (short T2 *) is a common obstacle when attempting to perform quantitative 1 H MRI of the lungs. While T2 * times are longer for pulmonary hyperpolarized (HP) gas functional imaging (in particular for gaseous 129 Xe), T2 * can still lead to quantitative inaccuracies for sequences requiring longer echo times (such as diffusion weighted images) or longer readout duration (such as spiral sequences). This is especially true in preclinical studies, where high magnetic fields lead to shorter relaxation times than are typically seen in human studies. However, the T2 * of HP 129 Xe in the most common animal model of human disease (mice) has not been reported. Herein, we present a multi-echo radial flyback imaging sequence and use it to measure HP 129 Xe T2 * at 7 T under a variety of respiratory conditions. This sequence mitigates the impact of T1 relaxation outside the animal by using multiple gradient-refocused echoes to acquire images at a number of effective echo times for each RF excitation. After validating the sequence using a phantom containing water doped with superparamagnetic iron oxide nanoparticles, we measured the 129 Xe T2 * in vivo for 10 healthy C57Bl/6 J mice and found T2 * ~ 5 ms in the lung airspaces. Interestingly, T2 * was relatively constant over all experimental conditions, and varied significantly with sex, but not age, mass, or the O2 content of the inhaled gas mixture. These results are discussed in the context of T2 * relaxation within porous media.

Lung eosinophils increase vagus nerve-mediated airway reflex bronchoconstriction in mice

Eosinophils mediate airway hyperresponsiveness by increasing vagally mediated reflex bronchoconstriction. Here, we tested whether circulating or airway eosinophils change nerve function. Airway resistance in response to aerosolized 5-hydroxytryptamine (5-HT, 10-300 mM) was measured in wild-type mice or transgenic mice that overexpress IL5 in T cells (+IL5T), overexpress IL5 in airway epithelium (+IL5AE), or overexpress IL5 but are devoid of eosinophils (+IL5AE/-Eos). Inflammatory cells in bronchoalveolar lavage (BAL), blood, and bone marrow were quantified. Blood eosinophils were increased in +IL5T and +IL5AE mice compared with wild-type mice. +IL5T mice had increased eosinophils in bone marrow while +IL5AE mice had increased eosinophils in BAL. Eosinophils surrounding large airways were significantly increased only in +IL5AE mice. With intact vagal innervation, aerosolized 5-HT significantly increased airway resistance in +IL5AE mice. 5-HT-induced bronchoconstriction was blocked by vagotomy or atropine, demonstrating that it was mediated via a vagal reflex. Airway resistance was not increased in +IL5AE/-Eos mice, demonstrating that it required lung eosinophils, but was not affected by increased bone marrow or blood eosinophils or by increased IL5 in the absence of eosinophils. Eosinophils did not change M3 function on airway smooth muscle, since airway responses to methacholine in vagotomized mice were not different among strains. Eosinophils surrounding large airways were sufficient, even in the absence of increased IL5 or external insult, to increase vagally mediated reflex bronchoconstriction. Specifically blocking or reducing eosinophils surrounding large airways may effectively inhibit reflex hyperresponsiveness mediated by vagus nerves in eosinophilic asthma.

Attenuating Neurogenic Sympathetic Hyperreflexia Robustly Improves Antibacterial Immunity After Chronic Spinal Cord Injury

Spinal cord injury (SCI) disrupts critical physiological systems, including the cardiovascular and immune system. Plasticity of spinal circuits below the injury results in abnormal, heightened sympathetic responses, such as extreme, sudden hypertension that hallmarks life-threatening autonomic dysreflexia. Moreover, such sympathetic hyperreflexia detrimentally impacts other effector organs, including the spleen, resulting in spinal cord injury-induced immunodeficiency. Consequently, infection is a leading cause of mortality after SCI. Unfortunately, there are no current treatments that prophylactically limit sympathetic hyperreflexia to prevent subsequent effector organ dysfunction. The cytokine soluble tumor necrosis factor α (sTNFα) is upregulated in the CNS within minutes after SCI and remains elevated. Here, we report that commencing intrathecal administration of XPro1595, an inhibitor of sTNFα, at a clinically feasible, postinjury time point (i.e., 3 d after complete SCI) sufficiently diminishes maladaptive plasticity within the spinal sympathetic reflex circuit. This results in less severe autonomic dysreflexia, a real-time gauge of sympathetic hyperreflexia, for months postinjury. Remarkably, delayed delivery of the sTNFα inhibitor prevents sympathetic hyperreflexia-associated splenic atrophy and loss of leukocytes to dramatically improve the endogenous ability of chronic SCI rats to fight off pneumonia, a common cause of hospitalization after injury. The improved immune function with XPro1595 correlates with less noradrenergic fiber sprouting and normalized norepinephrine levels in the spleen, indicating that heightened, central sTNFα signaling drives peripheral, norepinephrine-mediated organ dysfunction, a novel mechanism of action. Thus, our preclinical study supports intrathecally targeting sTNFα as a viable strategy to broadly attenuate sympathetic dysregulation, thereby improving cardiovascular regulation and immunity long after SCI.SIGNIFICANCE STATEMENT Spinal cord injury (SCI) significantly disrupts immunity, thus increasing susceptibility to infection, a leading cause of morbidity in those living with SCI. Here, we report that commencing intrathecal administration of an inhibitor of the proinflammatory cytokine soluble tumor necrosis factor α days after an injury sufficiently diminishes autonomic dysreflexia, a real time gauge of sympathetic hyperreflexia, to prevent associated splenic atrophy. This dramatically improves the endogenous ability of chronically injured rats to fight off pneumonia, a common cause of hospitalization. This preclinical study could have a significant impact for broadly improving quality of life of SCI individuals.

Determination of reliable lung function parameters in intubated mice

Background

Animal models and, in particular, mice models, are important tools to investigate the pathogenesis of respiratory diseases and to test potential new therapeutic drugs. Lung function measurement is a key step in such investigation. In mice, it is usually performed using forced oscillation technique (FOT), negative pressure-driven forced expiratory (NPFE) and pressure-volume (PV) curve maneuvers. However, these techniques require a tracheostomy, which therefore only allows end-point measurements. Orotracheal intubation has been reported to be feasible and to give reproducible lung function measurements, but the agreement between intubation and tracheostomy generated-data remains to be tested.

Methods

Using the Flexivent system, we measured lung function parameters (in particular, forced vital capacity (FVC), forced expiratory volume in the first 0.1 s (FEV0.1), compliance (Crs) of the respiratory system, compliance (C) measured using PV loop and an estimate of inspiratory capacity (A)) in healthy intubated BALB/cJ mice and C57BL/6 J mice and compared the results with similar measurements performed in the same mice subsequently tracheostomized after intubation, by means of paired comparison method, correlation and Bland-Altman analysis. The feasibility of repetitive lung function measurements by intubation was also tested.

Results

We identified parameters that are accurately evaluated in intubated animals (i.e., FVC, FEV0.1, Crs, C and A in BALB/cJ and FVC, FEV0.1, and A in C57BL/6 J). Repetitive lung function measurements were obtained in C57BL/6 J mice.

Conclusion

This subset of lung function parameters in orotracheally intubated mice is reliable, thereby allowing relevant longitudinal studies.

Supplementary information

Supplementary information accompanies this paper at (10.1186/s12931-019-1177-9).

Monitoring the Health Status of Mice with Bleomycin-induced Lung Injury by Using Body Condition Scoring

Well-defined, humane endpoints aid in monitoring animal health status during disease development. Body condition scoring (BCS) is a method for assessing health status in mouse studies where wasting and death are potential endpoints. Whether BCS is useful in monitoring animals with bleomycin-induced lung injury has not been reported. Body weight (BW) is a common humane endpoint for this model, but because the lungs increase in weight as BW decreases, the animal's true physical condition could be masked when using BW as the sole endpoint criterion. Therefore, our goal here was to assess the usefulness of BCS in monitoring health status in a mouse model of lung injury. Lung injury was caused by acute instil- lation of the fibrogenic antibiotic bleomycin into the lungs through the trachea. Male C57BL/6 mice received bleomycin (0.075 U) dissolved in saline or saline alone. Bleomycin instillation led to a doubling of lung weight and decreases in both BW and BCS, compared with saline instillation. The changes in BW and BCS were significantly correlated with lung weight. When the adjusted BW was used (corrected for the increase in lung weight), the correlation was unchanged, suggesting that the increase in lung weight did not significantly mask the decrease in BW. Bleomycin instillation caused decreases in both soleus and visceral epididymal fat masses. The change in BCS was significantly correlated with both soleus and VEF mass, suggesting that BCS is reflective of the systemic loss of muscle and fat mass. Our findings suggest that BW and BCS are significantly correlated to lung injury in the bleomycin model of lung fibrosis and that BCS is an appropriate alternative humane endpoint in this mouse model.

A simple and safe method for tracheal intubation using a supraglottic intubation-aid device in mice

Although mice are a commonly used animal species in experimental medicine, airway management of this species is not easy due to their small size. In order to develop a new method of tracheal intubation in mice, we produced a supraglottic intubation-aid conduit (SIAC) for mice, and tested the efficacy of this device in spontaneously breathing mice anesthetized with sevoflurane inhalation. The success rate of tracheal intubation with the crude prototype of the SIAC was 50% and adverse effects on respiration and some trauma in the upper airway were occasionally observed. After refining the size and shape of the SIAC, the success rate of tracheal intubation with the refined prototype of the SIAC was 100% without any serious adverse effects. This study showed that it is possible to produce a supraglottic airway device to aid tracheal intubation in mice and that the shape and size of the SIAC play a crucial role in successful tracheal intubation in mice.

Lobe-Specific Gene Vector Delivery to Rat Lungs Using a Miniature Bronchoscope

For respiratory research utilizing gene vector delivery to the lung, the size of rodent models has typically necessitated relatively "blind" dosing via the nose, via an endotracheal tube, or through a surgical incision into the trachea. This commonly results in a limited ability to dose specific small regions of the lung reliably, and contributes to high levels of transduction variability between animals. The resultant poor reliability, reproducibility, and high variability compromises statistical capability, and so demands greater animal sample sizes than should be feasible. The first reliable targeted gene vector dosing of small regions in rat lungs has been designed and successfully implemented using a miniature rigid bronchoscope containing a working channel. Using this setup, this technique can currently access airway branches down to at least the fourth generation in the lungs of rats >200 g in body weight, allowing dosing and re-dosing of specific lobes via airway branch points in the lung tree. Here, the protocol for performing this minimally invasive technique is reported, along with the effect of delivering vesicular stomatitis virus G pseudotyped lentivirus to selected lung lobes. Examples of other applications, such as delivery of agar beads, are also shown. It is expected that the availability of this technique will substantially enhance gene vector studies in rat models for a range of lung diseases.

Optimal tube length of orotracheal intubation for mice

Endotracheal tube (ETT) management is an essential technique in handling mice with mechanical ventilators. Malposition into bronchi causes not only lethal complications for them but also less efficient mechanical ventilation. However, in general, it is difficult to know whether the ETT is placed with appropriate depth into the trachea of mice. We measured the distance from incisors to the bifurcation of trachea of multiple mice, and created a new estimation formula to obtain the suitable ETT length for mice with a body weight range from 17 g to 25 g: length (mm) = 0.5 × bodyweight (g) + 7. However, millimeter step adjustments are impracticable. Thus, slightly shorter than 2 cm (18-20 mm) may be the universal ETT length for mice with bodyweight > 17 g. Furthermore, their foot size may be a good alternative to predict the individual optimal ETT length for mice.

Delivery of Therapeutics to the Lung

Pulmonary delivery in animal models can be performed using either direct administration methods or by passive inhalation. Direct pulmonary delivery requires the animal to be endotracheally intubated, whereas passive delivery uses a nose-only or a whole-body chamber. Endotracheal delivery of therapeutics and vaccines allows investigators to deliver the payload directly into the lung without the limitations associated with passive pulmonary administration methods. Additionally, endotracheal delivery can achieve deep lung delivery without the involvement of other exposure routes and is more reproducible and quantitative than passive pulmonary delivery in terms of accurate dosing. Here we describe the endotracheal delivery of both liquids and dry powders for preclinical models of treatment and exposure.

Gene therapy for Cystic Fibrosis: Improved delivery techniques and conditioning with lysophosphatidylcholine enhance lentiviral gene transfer in mouse lung airways

Purpose/Aim: Cystic fibrosis (CF) is the most common, fatal recessive genetic disease among the Caucasian population. Gene therapy has the potential to treat CF long term, however physiological barriers can prevent VSV-G pseudotyped lentiviral (LV) vectors from efficiently accessing the relevant receptors on the basolateral membrane of airway epithelial cells. The aims of this experiment were to use our new dose delivery techniques to determine whether conditioning the mouse lung conducting airways with lysophosphatidylcholine (LPC) improves the level of airway gene expression.

MATERIALS AND METHODS

Anaesthetised normal C57Bl/6 mice were intubated with an endotracheal cannula to non-invasively facilitate airway access. The airways were conditioned with 0.1% LPC, 0.3% LPC, or PBS (control) instilled via the ET tube. One hour later a VSV-G pseudotyped LV vector carrying the LacZ transgene was delivered. LacZ expression was measured by X-gal staining of the excised lungs 3 months after gene delivery.

RESULTS

Endotracheal intubation enabled precise dose delivery to the trachea and conducting airways. The cartilaginous airways of the groups conditioned with 0.1% and 0.3% LPC contained significantly larger numbers of LacZ positive cells compared to the PBS control group. In the LPC conditioned groups the majority of cell transduction was in ciliated epithelial cells.

CONCLUSION

LPC conditioning prior to LV vector delivery, substantially enhanced the level of conducting airway gene expression after a single gene vector delivery. These results extend the previously established effectiveness of this protocol for producing gene expression in the nasal airways to the lung airways, the primary site of deleterious pathophysiology in CF individuals.

Maternal high-fat diet in mice leads to innate airway hyperresponsiveness in the adult offspring

Maternal obesity prior to and during pregnancy has been associated with an increased incidence of childhood asthma. As diets rich in saturated fat are linked to obesity and inflammation, we created a murine model to investigate the effect of maternal high-fat diet (HFD) on adult offspring airway hyperreactivity (AHR), a cardinal feature of asthma. Balb/cByJ dams were fed a HFD (60% fat Calories) or normal-fat diet (NFD) (10% fat Calories) from 8 weeks prior to first breeding through their pregnancies. Pups were weaned to either a HFD or NFD (at 4 weeks of age). AHR was measured in the 10-week-old offspring following inhaled methacholine challenge by end-inflation technique. Bronchial alveolar lavage fluid (BALF) was analyzed for cell count, total protein, and IL-6. Offspring of HFD dams weaned to NFD had increased AHR compared to offspring of NFD dams weaned to NFD Offspring of HFD dams that remained on HFDs had increased AHR compared to offspring of NFD dams weaned to HFDs. Offspring of HFD dams had higher BALF cell counts, higher neutrophil percentage, greater total protein, and IL-6 in the BALF These results demonstrate that a maternal diet high in saturated fat through pregnancy and lactation plays a key role in programming adult offspring AHR.

An Improved Method for Rapid Intubation of the Trachea in Mice

Despite some anatomical and physiological differences, mouse models continue to be an essential tool for studying human lung disease. Bleomycin toxicity is a commonly used model to study both acute lung injury and fibrosis, and multiple methods have been developed for administering bleomycin (and other toxic agents) into the lungs. However, many of these approaches, such as transtracheal instillation, have inherent drawbacks, including the need for strong anesthetics and survival surgery. This paper reports a quick, reproducible method of intratracheal intubation that involves mild inhaled anesthesia, visualization of the trachea, and the use of a surrogate spirometer to confirm exposure. As a proof of concept, 8-12 week old C57BL/6 mice were administered either 2.0 U/kg of bleomycin or an equivalent volume of PBS, and both damage and fibrotic endpoints were measured post-exposure. This procedure allows researchers to treat a large cohort of mice in a relatively short period with little expense and minimal post-procedure care.

Efficacious and safe orotracheal intubation for laboratory mice using slim torqueable guidewire-based technique: comparisons between a modified and a conventional method

BACKGROUND

Tracheal intubation of laboratory mice remains essential yet challenging for most researchers. The aim of this study was to investigate whether this procedure can be more efficiently and safely accomplished by a novel method using slim and torqueable guidewires to guide access to the trachea.

METHODS

This study was carried out in an animal laboratory affiliated to a tertiary medical center. Mice weighing 22 to 28 g were subjected to various open-chest experiments after being anesthetized with intraperitoneal ketamine (100 mg/kg) and lidocaine hydrochloride (10 mg/kg). The oropharyngeal cavity was opened with angled tissue forceps, and the trachea was transilluminated using an external light. The vocal cords were then crossed using either the Conventional method with a 38-mm-long, end-blunted stiff needle as a guide for insertion of a 22-gauge, 25-mm-long intravenous catheter into the trachea, or the Modified method utilizing using a 0.014-inch-thin torqueable wire as the guide to introduce an identical tube over it into the trachea. The epithelial integrity of the trachea was later examined histologically when the animals were sacrificed either immediately after the surgery or at 28 days post-surgery, depending on the corresponding research protocols.

RESULTS

Orotracheal intubation was successfully completed in all mice using either the Conventional (N = 42) or the Modified method (N = 50). With the Modified method, intubation took less time (1.73 vs. 2.17 min, Modified vs. Conventional, p < 0.001) and fewer attempts (1.0 vs. 1.33, p < 0.001), and there were fewer procedural difficulties (0% vs. 16.7%, p = 0.009) and complications (0% vs. 11.9%, p = 0.041) compared with the Conventional method. Histological analysis revealed a significantly lower incidence of immediate (0% vs. 39%, p < 0.001) and late (0% vs. 58%, p < 0.001) injuries to the tracheal epithelial lining with the Modified method compared to the Conventional method.

CONCLUSIONS

Tracheal intubation for laboratory mice can be completed efficiently, safely and atraumatically using the proposed Modified method employing readily available inexpensive instruments.

Spinal cord injury-induced immune deficiency syndrome enhances infection susceptibility dependent on lesion level

Pneumonia is the leading cause of death after acute spinal cord injury and is associated with poor neurological outcome. In contrast to the current understanding, attributing enhanced infection susceptibility solely to the patient's environment and motor dysfunction, we investigate whether a secondary functional neurogenic immune deficiency (spinal cord injury-induced immune deficiency syndrome, SCI-IDS) may account for the enhanced infection susceptibility. We applied a clinically relevant model of experimental induced pneumonia to investigate whether the systemic SCI-IDS is functional sufficient to cause pneumonia dependent on spinal cord injury lesion level and investigated whether findings are mirrored in a large prospective cohort study after human spinal cord injury. In a mouse model of inducible pneumonia, high thoracic lesions that interrupt sympathetic innervation to major immune organs, but not low thoracic lesions, significantly increased bacterial load in lungs. The ability to clear the bacterial load from the lung remained preserved in sham animals. Propagated immune susceptibility depended on injury of central pre-ganglionic but not peripheral postganglionic sympathetic innervation to the spleen. Thoracic spinal cord injury level was confirmed as an independent increased risk factor of pneumonia in patients after motor complete spinal cord injury (odds ratio = 1.35, P < 0.001) independently from mechanical ventilation and preserved sensory function by multiple regression analysis. We present evidence that spinal cord injury directly causes increased risk for bacterial infection in mice as well as in patients. Besides obvious motor and sensory paralysis, spinal cord injury also induces a functional SCI-IDS ('immune paralysis'), sufficient to propagate clinically relevant infection in an injury level dependent manner.

Instillation and Fixation Methods Useful in Mouse Lung Cancer Research

The ability to instill live agents, cells, or chemicals directly into the lung without injuring or killing the mice is an important tool in lung cancer research. Although there are a number of methods that have been published showing how to intubate mice for pulmonary function measurements, none are without potential problems for rapid tracheal instillation in large cohorts of mice. In the present paper, a simple and quick method is described that enables an investigator to carry out such instillations in an efficient manner. The method does not require any special tools or lighting and can be learned with very little practice. It involves anesthetizing a mouse, making a small incision in the neck to visualize the trachea, and then inserting an intravenous catheter directly. The small incision is quickly closed with tissue adhesive, and the mice are allowed to recover. A skilled student or technician can do instillations at an average rate of 2 min/mouse. Once the cancer is established, there is frequently a need for quantitative histologic analysis of the lungs. Traditionally pathologists usually do not bother to standardize lung inflation during fixation, and analyses are often based on a scoring system that can be quite subjective. While this may sometime be sufficiently adequate for gross estimates of the size of a lung tumor, any proper stereological quantification of lung structure or cells requires a reproducible fixation procedure and subsequent lung volume measurement. Here we describe simple reliable procedures for both fixing the lungs under pressure and then accurately measuring the fixed lung volume. The only requirement is a laboratory balance that is accurate over a range of 1 mg-300 g. The procedures presented here thus could greatly improve the ability to create, treat, and analyze lung cancers in mice.

Blocking stroke-induced immunodeficiency increases CNS antigen-specific autoreactivity but does not worsen functional outcome after experimental stroke

Stroke-induced immunodepression (SIDS) is an essential cause of poststroke infections. Pharmacological inhibition of SIDS appears promising in preventing life-threatening infections in stroke patients. However, SIDS might represent an adaptive mechanism preventing autoreactive immune responses after stroke. To address this, we used myelin oligodendrocyte glycoprotein (MOG) T-cell receptor transgenic (2D2) mice where >80% of peripheral CD4(+) T cells express a functional receptor for MOG. We investigated in a murine model of middle cerebral artery occlusion the effect of blocking SIDS by inhibiting body's main stress axes, the sympathetic nervous system (SNS) with propranolol and the hypothalamic-pituitary-adrenal axis (HPA) with mifepristone. Blockade of both stress axes robustly reduced infarct volumes, decreased infection rate, and increased long-term survival of 2D2 and C57BL/6J wild-type mice. Despite these protective effects, blockade of SIDS increased CNS antigen-specific Type1 T helper cell (Th1) responses in the brains of 2D2 mice 14 d after middle cerebral artery occlusion. One month after experimental stroke, 2D2 mice developed signs of polyradiculitis, which were diminished by SIDS blockade. Adoptive transfer of CD4(+) T cells, isolated from 2D2 mice, into lymphocyte-deficient Rag-1KO mice did not reveal differences between SIDS blockade and vehicle treatment in functional long-term outcome after stroke. In conclusion, inhibiting SIDS by pharmacological blockade of body's stress axes increases autoreactive CNS antigen-specific T-cell responses in the brain but does not worsen functional long-term outcome after experimental stroke, even in a mouse model where CNS antigen-specific autoreactive T-cell responses are boosted.

Miniaturized bronchoscopy enables unilateral investigation, application, and sampling in mice

Lung diseases, including pneumonia and asthma, are among the most prevalent human disorders, and murine models have been established to investigate their pathobiology and develop novel treatment approaches. Whereas bronchoscopy is valuable for diagnostic and therapeutic procedures in patients, no equivalent for small rodents has been established. Here, we introduce a miniaturized video-bronchoscopy system offering new opportunities in experimental lung research. With an outer diameter of 0.75 mm, it is possible to advance the optics into the main bronchi of mice. An irrigation channel allows bronchoalveolar lavage and unilateral application of substances to one lung. Even a unilateral infection is possible, enabling researchers to use the contralateral lung as internal control.

Mouse pneumonectomy model of compensatory lung growth

In humans, disrupted repair and remodeling of injured lung contributes to a host of acute and chronic lung disorders which may ultimately lead to disability or death. Injury-based animal models of lung repair and regeneration are limited by injury-specific responses making it difficult to differentiate changes related to the injury response and injury resolution from changes related to lung repair and lung regeneration. However, use of animal models to identify these repair and regeneration signaling pathways is critical to the development of new therapies aimed at improving pulmonary function following lung injury. The mouse pneumonectomy model utilizes compensatory lung growth to isolate those repair and regeneration signals in order to more clearly define mechanisms of alveolar re-septation. Here, we describe our technique for performing mouse pneumonectomy and sham pneumonectomy. This technique may be utilized in conjunction with lineage tracing or other transgenic mouse models to define molecular and cellular mechanism of lung repair and regeneration.

Visible, safe and certain endotracheal intubation using endoscope system and inhalation anesthesia for rats

Anesthesia strongly influences laboratory animals, and it can also greatly affect the experimental data. Rats rank only second to mice in the number used in research fields, such as organ transplantation, regenerative medicine and imaging. Therefore, appropriate and effective anesthesia, including the protocol of the endotracheal intubation and inhalation anesthesia, is crucial. Hence, we evaluated these methods in this study. Twelve Wistar rats were intraperitoneally injected with M/M/B: 0.3/4/5, comprising of medetomidine, midazolam and butorphanol at a dose of 0.3 mg/kg + 4.0 mg/kg + 5.0 mg/kg body weight/rat, respectively. An endotracheal tube was then intubated into the trachea. After intubation, the rats were connected to the inhalation anesthesia circuit using isoflurane, and vital signs were measured until 30 min after connection. All intubations were successfully finished within 1 min, and the values of the vital signs were normal and stable. In addition, histopathological observation of the trachea and lungs showed no trauma. These results suggest that this visible endotracheal intubation method is simple, reliable, safe and favorable with regard to the rats’ welfare.

Endotracheal intubation in mice via direct laryngoscopy using an otoscope

Mice, both wildtype and transgenic, are the principal mammalian model in biomedical research currently. Intubation and mechanical ventilation are necessary for whole animal experiments that require surgery under deep anesthesia or measurements of lung function. Tracheostomy has been the standard for intubating the airway in these mice to allow mechanical ventilation. Orotracheal intubation has been reported but has not been successfully used in many studies because of the substantial technical difficulty or a requirement for highly specialized and expensive equipment. Here we report a technique of direct laryngoscopy using an otoscope fitted with a 2.0 mm speculum and using a 20 G intravenous catheter as an endotracheal tube. We have used this technique extensively and reliably to intubate and conduct accurate assessments of lung function in mice. This technique has proven safe, with essentially no animal loss in experienced hands. Moreover, this technique can be used for repeated studies of mice in chronic models.

New visible endotracheal intubation method using the endoscope system for mice inhalational anesthesia

Appropriate and effective anesthesia is critical, because it has a strong influence on laboratory animals, and its affect greatly impacts the experimental data. Inhalational anesthesia by endotracheal intubation is currently prevailing in general anesthesia and is prefered over injection anesthesia, especially for large laboratory animals, because it is a safe and easy control agent. However, it is not common for small laboratory animals, because of the high degree of technical skills required. We assessed the capability of use for mice of the endotracheal intubation by using the endoscope system “TESALA AE-C1” and inhalational anesthesia using a ventilator. Endotracheal intubation was successfully performed on all 10 C57BL/6 mice injected with M/M/B: 0.3/4/5 comprised of medetomidine, midazoram and butorphanol, at a dose of 0.3 mg/kg + 4.0 mg/kg + 5.0 mg/kg body weight/mouse, respectively. After the intubated mice were connected with the inhalational anesthesia circuit and the ventilator, vital signs were measured until 15 min after the connection. The data with M/M/B: 0.3/4/5 showed stable and normal values, which indicated that this new endotracheal intubation method was simple, reliable and safe, which mean that this anesthesia is favorable in regard to the animal’s welfare.

A simple method of mouse lung intubation

A simple procedure to intubate mice for pulmonary function measurements would have several advantages in longitudinal studies with limited numbers or expensive animal. One of the reasons that this is not done more routinely is that it is relatively difficult, despite there being several published studies that describe ways to achieve it. In this paper we demonstrate a procedure that eliminates one of the major hurdles associated with this intubation, that of visualizing the trachea during the entire time of intubation. The approach uses a 0.5 mm fiberoptic light source that serves as an introducer to direct the intubation cannula into the mouse trachea. We show that it is possible to use this procedure to measure lung mechanics in individual mice over a time course of at least several weeks. The technique can be set up with relatively little expense and expertise, and it can be routinely accomplished with relatively little training. This should make it possible for any laboratory to routinely carry out this intubation, thereby allowing longitudinal studies in individual mice, thereby minimizing the number of mice needed and increasing the statistical power by using each mouse as its own control.

Variation in airway responsiveness of male C57BL/6 mice from 5 vendors

Mice are now the most commonly used animal model for the study of asthma. The mouse asthma model has many characteristics of the human pathology, including allergic sensitization and airway hyperresponsiveness. Inbred strains are commonly used to avoid variations due to genetic background, but variations due to rearing environment are not as well recognized. After a change in mouse vendors and a switch from C57BL/6J mice to C57BL/6N mice, we noted significant differences in airway responsiveness between the substrains. To further investigate the effect of vendor, we tested C57BL/6N mice from 3 other vendors and found significant differences between several of the substrains. To test whether this difference was due to genetic drift or rearing environment, we purchased new groups of mice from all 5 vendors, bred them in separate vendor-specific groups under uniform environmental conditions, and tested male first generation (F1) offspring at 8 to 10 wk of age. These F1 mice showed no significant differences in airway responsiveness, indicating that the rearing environment rather than genetic differences was responsible for the initial variation in pulmonary phenotype. The environmental factors that caused the phenotypic variation are unknown. However, differences between vendor in feed components, bedding type, or microbiome could have contributed. Whatever the basis, investigators using mouse models of asthma should be cautious in comparing data from mice obtained from different vendors.

Visualization of murine intranasal dosing efficiency using luminescent Francisella tularensis: effect of instillation volume and form of anesthesia

Intranasal instillation is a widely used procedure for pneumonic delivery of drugs, vaccine candidates, or infectious agents into the respiratory tract of research mice. However, there is a paucity of published literature describing the efficiency of this delivery technique. In this report we have used the murine model of tularemia, with Francisella tularensis live vaccine strain (FTLVS) infection, to evaluate the efficiency of pneumonic delivery via intranasal dosing performed either with differing instillation volumes or different types of anesthesia. FTLVS was rendered luminescent via transformation with a reporter plasmid that constitutively expressed the Photorhabdus luminescens lux operon from a Francisella promoter. We then used an IVIS Spectrum whole animal imaging system to visualize FT dissemination at various time points following intranasal instillation. We found that instillation of FT in a dose volume of 10 µl routinely resulted in infection of the upper airways but failed to initiate infection of the pulmonary compartment. Efficient delivery of FT into the lungs via intranasal instillation required a dose volume of 50 µl or more. These studies also demonstrated that intranasal instillation was significantly more efficient for pneumonic delivery of FTLVS in mice that had been anesthetized with inhaled (isoflurane) vs. parenteral (ketamine/xylazine) anesthesia. The collective results underscore the need for researchers to consider both the dose volume and the anesthesia type when either performing pneumonic delivery via intranasal instillation, or when comparing studies that employed this technique.

Micro-CT based experimental liver imaging using a nanoparticulate contrast agent: a longitudinal study in mice

Background

Micro-CT imaging of liver disease in mice relies on high soft tissue contrast to detect small lesions like liver metastases. Purpose of this study was to characterize the localization and time course of contrast enhancement of a nanoparticular alkaline earth metal-based contrast agent (VISCOVER ExiTron nano) developed for small animal liver CT imaging.

Methodology

ExiTron nano 6000 and ExiTron nano 12000, formulated for liver/spleen imaging and angiography, respectively, were intravenously injected in C57BL/6J-mice. The distribution and time course of contrast enhancement were analysed by repeated micro-CT up to 6 months. Finally, mice developing liver metastases after intrasplenic injection of colon carcinoma cells underwent longitudinal micro-CT imaging after a single injection of ExiTron nano.

Principal Findings

After a single injection of ExiTron nano the contrast of liver and spleen peaked after 4–8 hours, lasted up to several months and was tolerated well by all mice. In addition, strong contrast enhancement of abdominal and mediastinal lymph nodes and the adrenal glands was observed. Within the first two hours after injection, particularly ExiTron nano 12000 provided pronounced contrast for imaging of vascular structures. ExiTron nano facilitated detection of liver metastases and provided sufficient contrast for longitudinal observation of tumor development over weeks.

Conclusions

The nanoparticulate contrast agents ExiTron nano 6000 and 12000 provide strong contrast of the liver, spleen, lymph nodes and adrenal glands up to weeks, hereby allowing longitudinal monitoring of pathological processes of these organs in small animals, with ExiTron nano 12000 being particularly optimized for angiography due to its very high initial vessel contrast.

Double-contrast micro-CT colonoscopy in live mice

PURPOSE

Models of colon cancer in small rodents are of particular interest as they most closely simulate the development and growth of colonic cancer in humans. Micro-computed tomography has been used for detection of polyps in murine models of colon cancer. The study was performed to evaluate whether a novel high-speed continuous-rotation, single-breath-hold scanning protocol in combination with double-contrasting of the colon can be successfully applied for colonoscopy of live mice at acquisition times of 40 s.

METHODS

C57BL/6JApcMin/+ mice were intubated and ventilated. After double-contrasting the colon with barium and air, mice underwent continuous rotation micro-CT (mean resolution 41 × 41 × 53 μm) during a single-breath-hold period of 40 s. Sensitivity to detect colon polyps by four blinded radiologists was analysed. Number and location of polyps were verified in the excised colon. Radiation dose was measured using a thermoluminescence dosimeter placed within the distal colon.

RESULTS

In six of seven mice, a total of 12 polyps were detected in the explanted colon (one mouse without polyps). One tumor (8.3%) was located in the proximal third, seven tumors (58.1%) and four tumors (33.2%) were located in the middle and in the distal third of the colon, respectively. Mean tumor volume was 6.5 ± 3.6 mm(3). Sensitivity to detect colon polyps was 0.85 ± 0.1. Mean radiation dose was 0.241 ± 0.002 Gy.

CONCLUSION

Using a high-speed continuous rotation micro-CT protocol, double-contrast single-breath-hold colonoscopy in mice is feasible and yields sufficient contrast to visualize the proximal colonic folds and to detect colonic polyps in vivo.

Application of carbon monoxide diffusing capacity in the mouse lung

In the past decade the mouse has become the primary animal model of a variety of lung diseases. To assess various mechanisms underlying such pathologies, it is essential to make functional measurements that can reflect the developing pathology. In this regard, the diffusing capacity for carbon monoxide is a variable that directly reflects structural changes in the lung. Although measurement of single-breath diffusing capacity of the lung for carbon monoxide (DL(CO)) has also been previously reported in mice by a number of investigators, a number of technical issues have precluded routine and widespread use of this metric in mouse models. In the present report, we describe a means to quickly and simply measure a dimensionless variable closely related to the DL(CO) in mice, termed a diffusion factor for carbon monoxide (DF(CO)). The DF(CO) procedure involves a 9-s lung inflation with tracer gases in an anesthetized mouse, followed by a 1-min gas analysis time. We have tested the approach with two common models of lung pathology, elastase-induced emphysema and bleomycin-induced fibrosis. Results show a significant 15% reduction in DF(CO) in emphysema, and a 41% reduction in the fibrosis model. Repeat measurements within a mouse were found to be highly reproducible. This pulmonary function test can thus be used to detect structural changes with these pathological models. The method can also be used to measure changes in pulmonary blood volume, since the uptake of CO is highly dependent on this variable in addition to the gas exchange surface area.

Longitudinal assessment of lung cancer progression in the mouse using in vivo micro-CT imaging

PURPOSE

Small animal micro-CT imaging is being used increasingly in preclinical biomedical research to provide phenotypic descriptions of genomic models. Most of this imaging is coincident with animal death and is used to show the extent of disease as an end point. Longitudinal imaging overcomes the limitation of single time-point imaging because it enables tracking of the natural history of disease and provides qualitative and, where possible, quantitative assessments of the effects of an intervention. The pulmonary system is affected by many disease conditions, such as lung cancer, chronic obstructive pulmonary disease, asthma, and granulomatous disorders. Noninvasive imaging can accurately assess the lung phenotype within the living animal, evaluating not only global lung measures, but also regional pathology. However, imaging the lung in the living animal is complicated by rapid respiratory motion, which leads to image based artifacts. Furthermore, no standard mouse lung imaging protocols exist for longitudinal assessment, with each group needing to develop their own systematic approach.

METHODS

In this article, the authors present an outline for performing longitudinal breath-hold gated micro-CT imaging for the assessment of lung nodules in a mouse model of lung cancer. The authors describe modifications to the previously published intermittent isopressure breath-hold technique including a new animal preparation and anesthesia protocol, implementation of a ring artifact reduction, variable scanner geometry, and polynomial beam hardening correction. In addition, the authors describe a multitime-point data set registration and tumor labeling and tracking strategy.

RESULTS

In vivo micro-CT data sets were acquired at months 2, 3, and 4 posturethane administration in cancer mice (n = 5) and simultaneously in control mice (n = 3). 137 unique lung nodules were identified from the cancer mice while no nodules were detected in the control mice. A total of 411 nodules were segmented and labeled over the three time-points. Lung nodule metrics including RECIST, Ortho, WHO, and 3D volume were determined and extracted. A tumor incidence rate of 30.44 +/- 1.93 SEM for n = 5 was found with identification of nodules as small as 0.11 mm (RECIST) and as large as 1.66 mm (RECIST). In addition, the tumor growth and doubling rate between months 2-3 and 3-4 were calculated. Here, the growth rate was slightly higher in the second period based on the 3D volume data (0.12 +/- 0.13 to 0.13 +/- 0.17 microl) but significantly less based on the linear diameter metrics [RECIST (0.33 +/- 0.19 to 0.17 +/- 0.18 mm); Ortho (0.24 +/- 0.15 to 0.16 +/- 0.15 mm)], indicating the need to understand how each metric is obtained and how to correctly interpret change in tumor size.

CONCLUSIONS

In conclusion, micro-CT imaging provides a unique platform for in vivo longitudinal assessment of pulmonary lung cancer progression and potentially tracking of therapies at very high resolutions. The ability to evaluate the same subject over time provides for a sensitive assay that can be carried out on a smaller sample size. When integrated with image processing and analysis routines as detailed in this study, the data acquired from micro-CT imaging can now provide a very powerful assessment of pulmonary disease outcomes.

High-speed single-breath-hold micro-computed tomography of thoracic and abdominal structures in mice using a simplified method for intubation

OBJECTIVES

Respiratory gating with and without controlled ventilation has been applied for in vivo micro-computed tomography (micro-CT) of thoracic and abdominal structures in mice. We describe a simplified method for intubation and demonstrate its applicability for single-breath-hold micro-CT in mice.

METHODS

Mice (n = 10) were anesthetized, intubated, ventilated, and relaxed by intraperitoneal administration of rocuronium. Contrast-enhanced micro-CT of the complete thorax including the upper abdominal organs (80 kV; 37.5 μA; 190-degree rotation; 600 projections/20 seconds or 1200 projections/40 seconds; 39 × 39 × 50-μm voxel size) was performed with and without single-breath-hold technique.

RESULTS

The simplified method of intubation was fast (<1 minute) and required no special hardware in all mice. Relaxation of mice allowed prolonged single-breath-hold imaging of up to 40 seconds. Diameter of smallest identifiable lung vessels was 100 μm.

CONCLUSIONS

The presented simplified method for intubation in mice is fast, safe, and effective. Additional relaxation allowed high-resolution single-breath-hold micro-CT in mice.

Comparison of unrestrained plethysmography and forced oscillation for identifying genetic variability of airway responsiveness in inbred mice

Lung function detection in mice is currently most accurately measured by invasive techniques, which are costly, labor intensive, and terminal. This limits their use for large-scale or longitudinal studies. Noninvasive assays are often used instead, but their accuracy for measuring lung function parameters such as resistance and elastance has been questioned in studies involving small numbers of mouse strains. Here we compared parameters detected by two different methods using 29 inbred mouse strains: enhanced pause (Penh), detected by unrestrained plethysmography, and central airway resistance and lung elastance, detected by a forced oscillation technique. We further tested whether the phenotypic variations were determined by the same genomic location in genome-wide association studies using a linear mixed model algorithm. Penh, resistance, and elastance were measured in nonexposed mice or mice exposed to saline and increasing doses of aerosolized methacholine. Because Penh differed from airway resistance in several strains and because the peak genetic associations found for Penh, resistance, or elastance were located at different genomic regions, we conclude that using Penh as an indicator for lung function changes in high-throughput genetic studies (i.e., genome-wide association studies or quantitative trait locus studies) measures something fundamentally different than airway resistance and lung elastance.

Left-sided mouse intubation: description and evaluation

A method of left main bronchus intubation was developed based on a wire guide-based microscopic endotrachael mouse intubation technique. The authors used a 22 G x 1 inch catheter elongated by a 38-mm silicone tube, and a wire guide with a tag to assign the length of the wire completely covered by the silicon tube. The isoflurane-anesthetized mouse was hung perpendicularly with its incisors on a thread and transorally intubated under strict vision with the wire guide tip advanced 3 mm out of the catheter. Then the catheter was advanced about 6 to 8 mm into the trachea. Afterwards the wire guide was redrawn to the level of the catheter tip (blue tag on the wire guide appeared at the upper end of catheter) to prevent injury. Then the neck was pushed into a right lateral flexion with one finger against a foam block fixed on the vertical plate, causing a straight distance between mouth and left main bronchus. This positioning allows to gently advance the catheter into the left main bronchus by another about 20 mm, using the wire guide with its tip just within the tube, to achieve there a wedge position with gentle pressure.The technique had a success rate of more than 80% in 81 mice weighing 23 to 48 g. It may be of interest for unilateral lung intervention, e.g., with injurious substances or with drugs.