Intrapulmonary gas mixing in panacinar- and centriacinar-induced emphysema in rats

Ventilation heterogeneity in smokers: role of unequal lung expansion and peripheral lung structure

Smoking-induced ventilation heterogeneity measured at the mouth via established washout indices [lung clearance index (LCI) and alveolar mixing efficiency (AME)] potentially results from unequal expansion, which can be quantified by computer tomography (CT), and structural changes down to the lung periphery, characterized by CT parametric response mapping indices [percentage of lung affected by functional small airway disease (PRM^fSAD) and emphysema (PRM^Emph)]. By combining CT imaging and nitrogen (N₂) washout tests in smokers, we specifically examined the roles of unequal lung expansion and peripheral structure. We first extracted three-dimensional maps of local lung expansion from registered inspiratory/expiratory CT images in 50 smokers (GOLD 0-IV) to compute for each smoker the theoretical N₂ washout concentration curve solely attributable to unequal local expansion. By a head-on comparison with washout N₂ concentrations measured at the mouth in the same smokers supine, we observed that 1) LCI increased from 4.8 ± 0.2 (SD) to 6.6 ± 0.8 (SD) due to unequal lung expansion alone and further increased to 9.0 ± 1.5 (SD) independent of local expansion and 2) AME decreased (from 100% by definition) to 95 ± 2 (SD)% due to unequal expansion alone and further decreased to 75 ± 7(SD)% independent of local expansion. In a multiple regression between the washout indices and CT-derived PRM^fSAD and PRM^Emph, LCI was related to PRM^fSAD (r = +0.58; P < 0.001), whereas AME was related to both PRM^fSAD (r_partial = -0.44; P = 0.002) and PRM^Emph (r_partial = -0.31; P = 0.033), in line with AME being dominated by alterations in peripheral structure. We conclude that smokers showing an increased LCI without corresponding AME decrease are predominantly affected by unequal lung expansion, whereas an AME decrease with a commensurate LCI increase indicates a smoking-induced alteration of peripheral structure.NEW & NOTEWORTHY A head-on comparison between imaging and multiple breath washout in supine smokers shows that computer tomography-measured unequal local lung expansion accounts for 50% or less of smoking-induced increase in ventilation heterogeneity. The contributions from unequal lung expansion and peripheral structure to the two main washout indices also explain their respective association with parametric response mapping indices.

Aerosol transport throughout inspiration and expiration in the pulmonary airways

Little is known about transport throughout the respiration cycle in the conducting airways. It is challenging to appropriately describe the time-dependent number of particles entering back into the model during exhalation. Modeling the entire lung is not feasible; therefore, multidomain methods must be used. Here, we present a new framework that is designed to simulate particles throughout the respiration cycle, incorporating realistic airway geometry and respiration. This framework is applied for a healthy rat lung exposed to  ∼ 1μm diameter particles, chosen to facilitate parameterization and validation. The flow field is calculated in the conducting airways (3D domain) by solving the incompressible Navier-Stokes equations with experimentally derived boundary conditions. Particles are tracked throughout inspiration by solving a modified Maxey-Riley equation. Next, we pass the time-dependent particle concentrations exiting the 3D model to the 1D volume conservation and advection-diffusion models (1D domain). Once the 1D models are solved, we prescribe the time-dependent number of particles entering back into the 3D airways to again solve for 3D transport. The coupled simulations highlight that about twice as many particles deposit during inhalation compared to exhalation for the entire lung. In contrast to inhalation, where most particles deposit at the bifurcation zones, particles deposit relatively uniformly on the gravitationally dependent side of the 3D airways during exhalation. Strong agreement to previously collected regional experimental data is shown, as the 1D models account for lobe-dependent morphology. This framework may be applied to investigate dosimetry in other species and pathological lungs.

Assessment of pulmonary microstructural changes by hyperpolarized 129Xe diffusion-weighted imaging in an elastase-instilled rat model of emphysema

BACKGROUND

The purpose of this study was to explore the feasibility of hyperpolarized ¹²⁹Xe diffusion-weighted imaging (DWI) for the evaluation of pulmonary microstructural changes in the presence of pancreatic porcine elastase (PPE)-induced pulmonary emphysema rat model.

METHODS

Sixteen male Sprague-Dawley (SD) rats were randomly divided into two groups, the emphysema model group and control group. Experimental emphysematous models were made by instilling elastase into rat lungs of model group, the control group were instilled with isodose saline. Hyperpolarized ¹²⁹Xe magnetic resonance imaging (MRI) and histology were performed in all 16 rats after 30 days. DWIs were performed on a Bruker 7.0 T micro MRI, and the apparent diffusion coefficients (ADCs) were measured in all rats. Mean linear intercepts (MLIs) of pulmonary alveoli were measured on histology. The statistical analyses were performed about the correlation between the mean ADC of hyperpolarized ¹²⁹Xe in the whole lung and MLI of pulmonary histology metric.

RESULTS

The pulmonary emphysematous model was successfully confirmed by the histology and all scans were also successful. The ADC value of ¹²⁹Xe in the model group (0.0313±0.0005 cm²/s) was significantly increased compared with that of the control group (0.0288±0.0007 cm²/s, P<0.0001). Morphological differences such as MLI of pulmonary alveoli were observed between the two groups, the MLI of pulmonary alveoli in model group significantly increased (91±5 µm) than that of control group (50±3 µm, P<0.0001). Furthermore, the ADCs was moderately correlated with MLIs (r=0.724, P<0.01).

CONCLUSIONS

These results indicate that ¹²⁹Xe ADC value can quantitatively reflect the alveolar space enlargement and it is a promising biomarker for the detection of pulmonary emphysema.

Neutrophilic Inflammation in the Immune Responses of Chronic Obstructive Pulmonary Disease: Lessons from Animal Models

Chronic obstructive pulmonary disease (COPD) is a major cause of mortality worldwide, which is characterized by chronic bronchitis, destruction of small airways, and enlargement/disorganization of alveoli. It is generally accepted that the neutrophilic airway inflammation observed in the lungs of COPD patients is intrinsically linked to the tissue destruction and alveolar airspace enlargement, leading to disease progression. Animal models play an important role in studying the underlying mechanisms of COPD as they address questions involving integrated whole body responses. This review aims to summarize the current animal models of COPD, focusing on their advantages and disadvantages on immune responses and neutrophilic inflammation. Also, we propose a potential new animal model of COPD, which may mimic the most characteristics of human COPD pathogenesis, including persistent moderate-to-high levels of neutrophilic inflammation.

Aerosols in healthy and emphysematous in silico pulmonary acinar rat models

There has been relatively little attention given on predicting particle deposition in the respiratory zone of the diseased lungs despite the high prevalence of chronic obstructive pulmonary disease (COPD). Increased alveolar volume and deterioration of alveolar septum, characteristic of emphysema, may alter the amount and location of particle deposition compared to healthy lungs, which is particularly important for toxic or therapeutic aerosols. In an attempt to shed new light on aerosol transport and deposition in emphysematous lungs, we performed numerical simulations in models of healthy and emphysematous acini motivated by recent experimental lobar-level data in rats (Oakes et al., 2014a). Compared to healthy acinar structures, models of emphysematous subacini were created by removing inter-septal alveolar walls and enhancing the alveolar volume in either a homogeneous or heterogeneous fashion. Flow waveforms and particle properties were implemented to match the experimental data. The occurrence of flow separation and recirculation within alveolar cavities was found in proximal generations of the healthy zones, in contrast to the radial-like airflows observed in the diseased regions. In agreement with experimental data, simulations point to particle deposition concentrations that are more heterogeneously distributed in the diseased models compared with the healthy one. Yet, simulations predicted less deposition in the emphysematous models in contrast to some experimental studies, a likely consequence due to the shallower penetration depths and modified flow topologies in disease compared to health. These spatial-temporal particle transport simulations provide new insight on deposition in the emphysematous acini and shed light on experimental observations.

Effect of a single dose of cadmium on pregnant Wistar rats and their offspring

Cadmium (Cd) is a well-known toxicant targeting many organs, among them placenta. This heavy metal also has embryonary and foetal toxicity. This study was undertaken to analyse the effect of a single Cd dose administered at 4, 7, 10 or 15 days of gestation on the offspring of pregnant rats sacrificed at 20 days of gestation. Cadmium chloride was administered subcutaneously at 10 mg/kg body weight to Wistar pregnant dams; control animals received a proportionate volume of sterile normal saline by the same route. Maternal uteri, livers, kidneys and lungs, and foetuses were examined at necropsy. Samples of maternal organs and whole foetuses were collected for histopathologic examination, determination of Cd levels and staining by the Alizarin red S technique. Results revealed a clear embryotoxic and a teratogenic effect of this heavy metal, the former as a significant increase in the number of resorptions, and the latter as significant decrease of the gestational sac weight, and the size and weight of foetuses of Cd-treated dams as well as induced malformations in skull bones, vertebrae and thoracic, and pelvian limbs. The deleterious effects found were similar to those previously reported for other animal models suggesting a high conservation of the pathogenic mechanisms of Cd. Additionally, many of the addressed aspects showed a slight dependence on the time of administration of the toxic that might be due to the accumulation of the metal in different organs, as we were able to demonstrate by the analysis of its concentration.

Occupational chronic obstructive pulmonary disease: an update

Chronic obstructive pulmonary disease represents a major cause of morbidity and mortality in industrialized and nonindustrialized countries. Although tobacco use remains the main factor associated with development of the disease, occupational risk factors represent an important and preventable cause. The most common occupationally related factors include exposure to organic dusts, metallic fumes, and a variety of other mineral gases and/or vapors. This article summarizes the literature on the subject and provides an update of the most recent advances in the field.

Copper deficiency induced emphysema is associated with focal adhesion kinase inactivation

BACKGROUND

Copper is an important regulator of hypoxia inducible factor 1 alpha (HIF-1α) dependent vascular endothelial growth factor (VEGF) expression, and is also required for the activity of lysyl oxidase (LOX) to effect matrix protein cross-linking. Cell detachment from the extracellular matrix can induce apoptosis (anoikis) via inactivation of focal adhesion kinase (FAK).

METHODOLOGY

To examine the molecular mechanisms whereby copper depletion causes the destruction of the normal alveolar architecture via anoikis, Male Sprague-Dawley rats were fed a copper deficient diet for 6 weeks while being treated with the copper chelator, tetrathiomolybdate. Other groups of rats were treated with the inhibitor of auto-phosphorylation of FAK, 1,2,4,5-benzenetetraamine tetrahydrochloride (1,2,4,5-BT) or FAK small interfering RNA (siRNA).

PRINCIPAL FINDINGS

Copper depletion caused emphysematous changes, decreased HIF-1α activity, and downregulated VEGF expression in the rat lungs. Cleaved caspase-3, caspase-8 and Bcl-2 interacting mediator of cell death (Bim) expression was increased, and the phosphorylation of FAK was decreased in copper depleted rat lungs. Administration of 1,2,4,5-BT and FAK siRNA caused emphysematous lung destruction associated with increased expression of cleaved capase-3, caspase-8 and Bim.

CONCLUSIONS

These data indicate that copper-dependent mechanisms contribute to the pathogenesis of emphysema, which may be associated with decreased HIF-1α and FAK activity in the lung.

[Liver growth factor improves pulmonary fibrosis secondary to cadmium administration in rats]

INTRODUCTION

Liver growth factor (LGF) is a liver mitogen with regenerating and anti-fibrotic activity even at extrahepatic sites. We used LGF in a lung fibrosis model induced by cadmium chloride (CdCl(2)), to study its antifibrotic capacity.

METHODS

Forty-two male Wistar rats were administered a single dose of 0.5ml/rat of CdCl2 0.025% (n=21) or the same volume of saline (control group, n=21). After 35 days, once a lesion was established, we started a 3 week treatment with LGF, after which we determined lung function--inspiratory capacity (IC), lung compliance (LC), forced vital capacity (FVC) and expiratory flow at 75% (FEF75%)-, lung morphometry--alveolar internal area (AIA), mean linear intersection (LM)-, and collagen (both by Sirius red and hydroxyproline residues) and elastin contents.

RESULTS

Pulmonary fibrosis in CdCl(2) rats was characterized by a marked decrease in pulmonary function with respect to healthy controls -reductions of 28% in IC, 38% in CL, 31% in FVC, and 54% in FEF75%- which was partially recovered after LGF injection -18% IC, 27% CL, 19% FVC and 35% FEF75%-; increase in collagen and elastin contents -165% and 76%, respectively, in CdCl2 rats, versus 110% and 34% after LGF injection-; and increases in AIA and LM, partially reverted by LGF.

CONCLUSIONS

Together, these data seem to demonstrate that LGF is able to improve lung function and partially reverts the increase in lung matrix proteins produced by CdCl(2) instillation.

Lung function in developing lambs: is it affected by preterm birth?

Children born before term often have reduced lung function, but the effects of preterm birth alone are difficult to determine owing to iatrogenic factors such as mechanical ventilation. Our objective was to determine the effects of preterm birth alone on airway resistance, airway reactivity, and ventilatory heterogeneity as an index of intrapulmonary gas mixing. Preterm birth was induced in sheep 12 days before term; controls were born at term (∼147 days). Lung function was assessed at 8 wk postterm. To assess medium-large airway function we measured airway resistance and reactivity to carbachol. Multiple breath N2 washout (MBW) was used to assess ventilatory heterogeneity in conducting (Scond) and acinar (Sacin) airways. Baseline airway resistance and responsiveness to carbachol were similar in preterm and term lambs. Airway responsiveness to carbachol was greater in females than males ( P < 0.05), and baseline airway resistance tended to be higher in females than males ( P = 0.06). There were no significant differences in ventilatory heterogeneity between preterm and term lambs; for all animals combined, mean Sacin was 0.29 ± 0.05 liter−1 and Scond was 0.26 ± 0.03 liter−1. Males had significantly higher Scond than females, indicating poorer gas mixing in small conducting airways; there was no sex difference in Sacin. We conclude that preterm birth per se in lambs does not affect baseline airway resistance, airway responsiveness, or ventilatory heterogeneity as measured by MBW. The observed sex-related differences in airway responsiveness and ventilatory heterogeneity in the conducting airways could help explain sex differences in lung function observed in humans.

Improving the cadmium-induced centriacinar emphysema model in rats by concomitant anti-oxidant treatment

1. The aim of the present study was to perform an evolutionary analysis of the morphometrical, biochemical and functional parameters of centriacinar emphysema induced by cadmium chloride (CdCl2) in rats and to determine the effects of concomitant N-acetylcysteine (NAC) administration. 2. Male Wistar rats were instilled orotracheally with either CdCl2 (n = 24) or saline (n = 24). One group of rats, consisting of both CdCl2- and saline-treated rats, was fed a normal diet (n = 24), whereas the other group received NAC (n = 24). 3. Changes in inspiratory capacity (IC), lung compliance (CL), expiratory flow at 75% (F75), forced vital capacity (FVC) and hydroxyproline content were assessed 2, 8, 21 and 45 days after instillation. Polymorphonuclear cells were evaluated 2 and 8 days after instillation and the mean linear intercept (Lm) was determined at 21 and 45 days. 4. Over time, CdCl2 instillation causes several changes that are bound up with centriacinar emphysema. The concomitant administration of NAC to CdCl2-treated rats partially reversed Lm at 21 days compared with CdCl2 alone (115 +/- 2 vs 127 +/- 2, respectively; P < 0.05). However, 45 days after instillation, NAC improved lung function in CdCl2-treated rats compared with that in the saline-treated control group (IC 14.64 vs 15.25, respectively (P = 0.054); FVC 16.94 vs 16.28, respectively (P = 0.052), F75 31.41 vs 32.48, respectively (P = 0.062)). In addition, 45 days after instillation, NAC reduced lung collagen content in both the saline-treated control (100 vs 81% alone and in the presence of NAC, respectively) and CdCL2-treated groups (213 vs 161% alone and in the presence of NAC, respectively). In addition, although the results were not significant, NAC tended to reduce Lm and enhance CL in NAC + CdCl2-treated rats. 5. In conclusion, NAC partially improved emphysematous changes and reduced collagen deposition, which diminished the CdCl2-induced fibrotic component of centriacinar emphysema.

Early changes of lung function and structure in an elastase model of emphysema--a hyperpolarized 3He MRI study

Early changes of lung function and structure were studied in the presence of an elastase-induced model of emphysema in 35 Sprague-Dawley rats at mild (5 U/100 g) and moderate (10 U/100 g) severities. Lung ventilation was measured on a regional basis (at a planar resolution of 3.2 mm) by hyperpolarized 3He MRI at 5 and 10 wk after model induction. Subsequent to imaging, average alveolar diameter was measured from histological slices taken from the centers of each lobe. Changes of mean fractional ventilation, mean linear intercept, and intrasubject heterogeneity of ventilation were studied during disease progression. Mean fractional ventilation was significantly different between healthy controls (0.23 +/- 0.04) and emphysematous animals at both time points in the 10-unit group (0.06 +/- 0.02 and 0.12 +/- 0.05, respectively). Changes in average alveolar diameter were not statistically observable until the 10th wk between healthy (37 +/- 10 microm) and emphysematous rats (73 +/- 25 and 95 +/- 31 microm, for 5 and 10 units, respectively). Assessment of function-structure correlation suggested that the majority of the decline in fractional ventilation occurred in the first 5 wk, while enlargement of alveolar diameters appeared primarily between the 5th and 10th wk. A thresholding metric, based on the 20th percentile of fractional ventilation over the entire lung, was utilized to detect the onset of the disease with confidence, independent of whether the regional ventilation measurements were normalized with respect to the delivered tidal volume and estimated functional residual capacity of each individual rat.

Evaluation of excised lung gas volume measurements in animals with genetic or induced emphysema

Emphysema, a leading cause of respiratory disability and mortality in humans, is characterized by destruction of alveolar walls and enlargement of airspaces. Animal studies are critical in understanding the pathogenesis of emphysema. However, current measurements of airspace enlargement and emphysema in small laboratory animals are labor intensive and may not be sensitive enough for measuring alterations in lung function and structure at the early stages of emphysema. In this study, we have investigated the excised lung gas volume (ELGV) measurement as a potential index for determining airspace enlargement in pallid mice with developing emphysema, in tight-skin mice with developed emphysema, or in Wistar rats with emphysema induced by an intratracheal instillation of pancreatic elastase. Our results showed that values of both ELGV per lung and per gram lung tissue were significantly increased in all three emphysema models, compared to control. The ELGV values were correlated well with morphometric evaluation of emphysema. Variations in transpulmonary pressures caused by different termination procedures were critical factors influencing the ELGV values. The present study demonstrates that ELGV measurement is a simple and sensitive method to monitor the development of emphysema.

Diffusion-weighted 19F-MRI of lung periphery: Influence of pressure and air-SF6 composition on apparent diffusion coefficients

Lung functional magnetic resonance imaging (MRI) has become a reality using different inert hyperpolarized gases, such as 3He and 129Xe, which have provided an extraordinary boost in lung imaging and has also attracted interest to other chemically inert gaseous contrast agents. In this context, we have recently demonstrated the first diffusion-weighted images using thermally polarized inhaled sulfur hexafluoride (SF6) in small animals. The aim of this study was to evaluate whether or not the diffusion coefficient of this fluorinated gas is sensitive to pulmonary structure, gas concentration and air pressure in the airways. Diffusion coefficients of SF6 (both pure and in air mixtures) measured in vitro at different pressures and 20 degrees C showed an excellent agreement with theoretical values. Measurements of diffusion coefficients were also performed in vivo and post-mortem on healthy rats, achieving satisfactory signal-to-noise ratios (SNRs), and SF6 gas was found to be in an almost completely restricted diffusion regime in the lung, i.e., the transport by molecular diffusion is delayed by collisions with barriers such as the alveolar septa. This observed low diffusivity means that this gas will be less sensitive to structural changes in the lungs than other magnetic resonance sensitive gas such as 3He, particularly at human scale. However, it is still possible that SF6 plays a role since it opens a new structural window. Thus, the interest of researchers in delimiting the important limiting technical factors that makes this process very challenging is obvious. Among them, T2 relaxation is very fast, so gradient systems with very fast switching rate and probably large radiofrequency (RF) power and high field systems will be needed for hexafluoride to be used in human studies.

Oral N-acetylcysteine attenuates elastase-induced pulmonary emphysema in rats

STUDY OBJECTIVE

To study the effect of the antioxidant N-acetylcysteine (NAC) in the development of elastase-induced emphysema in rats.

MATERIALS AND METHODS

Wistar rats (n = 72) were orotracheally instilled with 75 IU elastase or saline solution. Eighteen rats from each group received the antioxidant NAC from 2 days before induction of the lesion until they were killed 2, 8, and 28 days after instillation. The effects of treatment were assessed by measuring collagen content for the left lung, a histopathology evaluation (ie, mean alveolar internal surface area (AIA) and mean linear intercept measurement), and lung function.

RESULTS

Twenty-eight days after elastase instillation, rats treated with NAC showed significant attenuation of the lesion in comparison with rats treated only with elastase, including the following: normalization of mean (+/- SEM) collagen content (1.23 +/- 0.09 vs 1.51 +/- 0.10 mg per left lung, respectively; p < 0.05); partial inhibition of mean AIA (14,860 +/- 1,135 vs 19,622 +/- 1,294 micro m(2), respectively; p < 0.05) and mean linear intercept (108.8 +/- 3.7 vs 123.0 +/- 4.2 micro m, respectively; p < 0.05); and increases and improvement in expiratory flows (27.8 +/- 1.2 vs 23.4 +/- 1.3 mL/s, respectively; p < 0.05). NAC was not able to avoid the compliance increase in the elastase-plus-NAC group.

CONCLUSION

Consistent with the results of anatomic, pathologic, and functional studies, NAC is able to attenuate the lesions induced by elastase in rats, which is in accordance with previous data supporting the idea that oxidant injury could contribute to the development of elastase-induced emphysema.

Noninvasive assessment of airway alterations in smokers: the small airways revisited

It has been shown that structural changes in small airways of smokers with average smoking histories greater than 35 pack-years could be reflected in the single-breath washout test. The more sophisticated multiple breath washout test (MBW) has the potential to anatomically locate the affected small airways in acinar and conductive lung zones through increased phase III slope indices S(acin) and S(cond), respectively. Pulmonary function, S(acin), and S(cond) were obtained in 63 normal never-smokers and in 169 smokers classified according to smoking history (< 10 pack-years; 10-20 pack-years; 20-30 pack-years; > 30 pack-years). Compared with never-smokers, significant changes in S(acin) (p = 0.02), S(cond) (p < 0.001), and diffusing capacity (DL(CO); p < 0.001) were detected from greater than 10 pack-years onwards. Spirometric abnormality was significant only from greater than 20 pack-years onwards. In smokers with greater than 30 pack-years and DL(CO) less than 60% predicted, the presence of emphysema resulted in disproportionally larger S(acin) than S(cond) increases. We conclude that S(cond) and S(acin) can noninvasively detect airway changes from as early as 10 pack-years onwards, locating the earliest manifestations of smoking-induced small airways alterations around the acinar entrance. In these early stages, the associated DL(CO) decrease may be a reflection of ventilation heterogeneity rather than true parenchymal destruction. In more advanced stages of smoking-induced lung disease, differential patterns of S(acin) and S(cond) are characteristic of the presence of parenchymal destruction in addition to peripheral airways alterations.

Nonreversible conductive airway ventilation heterogeneity in mild asthma

A multiple-breath washout technique was used to assess residual ventilation heterogeneity in the conductive and acinar lung zones of asthmatic patients after maximal beta(2)-agonist reversibility. Reversibility was assessed in 13 patients on two separate visits corresponding to a different baseline condition in terms of forced expiratory volume in 1 s [FEV(1); average FEV(1) over 2 visits: 92 +/- 21% of predicted (SE)]. On the visit corresponding to each patient's best baseline, 400 micro g salbutamol led to normal acinar ventilation heterogeneity, normal FEV(1), and normal peak expiratory flow; i.e., none was significantly different from that obtained in 13 matched controls. By contrast, conductive ventilation heterogeneity and forced expiratory flow after exhalation of 75% forced vital capacity remained significantly different from controls (P < or = 0.005 on both indexes). In addition, the degree of postdilation conductive ventilation heterogeneity was similar to what was previously obtained in asthmatic individuals with a 19% lower baseline FEV(1) and twofold larger acinar ventilation heterogeneity (Verbanck S, Schuermans D, Noppen M, Van Muylem A, Paiva M, and Vincken W. Am J Respir Crit Care Med 159: 1545-1550, 1999). We conclude that, even in the mildest forms of asthma, the most consistent pattern of non-beta(2)-agonist-reversible ventilatory heterogeneity is in the conductive lung zone, most probably in the small conductive airways.

Myosin heavy chain and physiological adaptation of the rat diaphragm in elastase-induced emphysema

BACKGROUND

Several physiological adaptations occur in the respiratory muscles in rodent models of elastase-induced emphysema. Although the contractile properties of the diaphragm are altered in a way that suggests expression of slower isoforms of myosin heavy chain (MHC), it has been difficult to demonstrate a shift in MHCs in an animal model that corresponds to the shift toward slower MHCs seen in human emphysema.

METHODS

We sought to identify MHC and corresponding physiological changes in the diaphragms of rats with elastase-induced emphysema. Nine rats with emphysema and 11 control rats were studied 10 months after instillation with elastase. MHC isoform composition was determined by both reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemistry by using specific probes able to identify all known adult isoforms. Physiological adaptation was studied on diaphragm strips stimulated in vitro.

RESULTS

In addition to confirming that emphysematous diaphragm has a decreased fatigability, we identified a significantly longer time-to-peak-tension (63.9 +/- 2.7 ms versus 53.9 +/- 2.4 ms). At both the RNA (RT-PCR) and protein (immunocytochemistry) levels, we found a significant decrease in the fastest, MHC isoform (IIb) in emphysema.

CONCLUSION

This is the first demonstration of MHC shifts and corresponding physiological changes in the diaphragm in an animal model of emphysema. It is established that rodent emphysema, like human emphysema, does result in a physiologically significant shift toward slower diaphragmatic MHC isoforms. In the rat, this occurs at the faster end of the MHC spectrum than in humans.

Gene therapy with galectin-3 inhibits bronchial obstruction and inflammation in antigen-challenged rats through interleukin-5 gene downregulation

The pathophysiology of asthma involves an intricate network of molecular and cellular interactions. Elevated Th2 cytokines (interleukin [IL]-5 and IL-4) associated with eosinophilic inflammation characterize allergic diseases and provide potential targets for immunomodulation. Recent evidence has demonstrated that galectin-3 induces selective downregulation of IL-5 gene expression in several cell types (eosinophils, T cell lines, and antigen specific T cells). Accordingly, we sought to elucidate whether in vivo intratracheal instillation of plasmid DNA encoding galectin-3 would inhibit an experimental asthmatic reaction in a rat model with increased eosinophils and T cells in bronchoalveolar fluid and impaired pulmonary function. We found that instillation of galectin-3 gene in these rats led to normalization of the eosinophil and T cell count in bronchoalveolar lavage fluid and that there was a strong concomitant inhibition of IL-5 mRNA in the lungs. As a consequence, galectin-3-treated rats showed recovery of pulmonary functional parameters, such as pulmonary pressure and expiratory flows. These data emphasize the potential utility of galectin-3 as a novel therapeutic approach for treatment of allergic asthma.

Sarcomeres are added in series to emphysematous rat diaphragm after lung volume reduction surgery

STUDY OBJECTIVES

The diaphragm adapts to its shortened state in experimental emphysema primarily by losing sarcomeres in series, thus reducing its optimal operating length. One would expect improved diaphragmatic function after lung volume reduction surgery (LVRS) only if the muscle can readapt to its elevated, lengthened postoperative position by either adding back sarcomeres or lengthening sarcomeres. We used a model of elastase-induced emphysema in rats to test the hypothesis that sarcomere addition occurs following LVRS.

DESIGN

A cohort of emphysematous rats was created by the intratracheal instillation of elastase. Five months after the instillation, one group of rats underwent measurement of in situ costal diaphragm length via laparotomy, the determination of optimal muscle fiber operating length (Lo) on stimulated diaphragm strips in vitro, and the measurement of sarcomere length by electron microscopy on strips fixed at Lo. Another group of rats underwent LVRS or sham sternotomy 5 months after the instillation, and 5 months following the operation these animals underwent the same series of diaphragmatic studies.

RESULTS

Lo was significantly greater in rats that underwent LVRS than those that underwent sternotomy (mean [+/- SE] Lo after LVRS, 2.50 +/- 0.08 cm; mean Lo after sternotomy, 2.27 +/- 0.06 cm; p = 0.013). There was no significant difference in sarcomere lengths between the two groups (2.95 +/- 0.04 vs 3.04 +/- 0.04 microm, respectively; p = 0.10). Using Lo as the length basis, the mean sarcomere number was calculated to be 8,712 +/- 192 in animals that had undergone LVRS and 7,144 +/- 249 in animals that had undergone sternotomy (p < 0.001).

CONCLUSION

Sarcomere length is not significantly altered but sarcomeres are added in series following LVRS in this experimental model of emphysema/LVRS. It is likely that this sarcomere addition is a prerequisite to the improvement in inspiratory muscle function that has been observed following LVRS in humans.

Inhaling gas with different CT densities allows detection of abnormalities in the lung periphery of patients with smoking-induced COPD

STUDY OBJECTIVES

To establish a novel method allowing detection of regional abnormalities in gas distribution at the acinar level by high-resolution CT (HRCT).

PARTICIPANTS

Nonsmoking control subjects (n = 28) and patients with smoking-induced COPD (n = 47).

MEASUREMENTS AND RESULTS

Changes in lung CT densities were examined by HRCT while the subjects inhaled a gas mixture consisting of 21% O(2) in SF(6) or 21% O(2) in He. HRCT images of the right upper and lower lung fields were obtained at the end of inspiration and expiration of the second and 60th breaths after the start of each gas. Introducing mean lung density (MLD) and relative area with low CT attenuation (%LAA), we analyzed the differences in acinar SF(6) and He distribution in the early phase (second breath) and in the equilibrium state (60th breath). We found that the differences in inspiratory MLD between the SF(6) and He images at the 60th breath were qualitatively consistent with the differences predicted from the physical properties of these gases. However, the differences in inspiratory MLD between the SF(6) and He images taken at the second breath were smaller than those at the 60th breath, especially in the smoking group with COPD. These differences in second-breath inspiratory MLD in the smoking group were smaller in the upper lung field than in the lower lung field. The differences in MLD between the two gases were not detected at end-expiration at the time of either the second or 60th breaths. The %LAA values did not differ between the SF(6) and He images in either the nonsmoking group or the smoking group.

CONCLUSIONS

SF(6)/He-associated HRCT images obtained at end-inspiration, but not at end-expiration, in the early breathing phase are useful for predicting acinar gas distribution abnormalities in patients with COPD.

Lung function and ventilation inhomogeneity in rat lungs after allergen challenge

We studied the early response to ovalbumin challenge in sensitized Brown-Norway rats through its effect on N(2), He, and SF(6) phase III slopes of the single-breath washout and on indexes of lung function. Sensitized rats showed varying degrees of response in terms of pulmonary pressure (PL), with increases ranging between 125 and 225% of baseline. The sensitized rats presented decreased quasistatic compliance, forced vital capacity, and end-expiratory flow, with all three lung function indexes showing a significant negative correlation with corresponding PL values. They also showed significant positive correlations of PL with the N(2), He, and SF(6) phase III slopes, reflecting diffusion-convection-dependent inhomogeneities generated by conformation changes throughout the entire rat lung. In addition, the rats showing the most marked PL increases (>150% baseline PL) also revealed a reversal of the SF(6)-He slope difference because of a more marked SF(6) than He slope increase. This latter finding suggests that the degree of structural heterogeneity during early response is even more marked in the most peripheral rat lung generations.