Effect of elastase pretreatment on rat lung strip induced constriction

Effects of elastase digestion on the murine vaginal wall biaxial mechanical response

Although the underlying mechanisms of pelvic organ prolapse (POP) remain unknown, disruption of elastic fiber metabolism within the vaginal wall extracellular matrix has been highly implicated. It has been hypothesized that elastic fiber fragmentation correlates to decreased structural integrity and increased risk of prolapse; however, the mechanisms by which elastic fiber damage may contribute to prolapse are poorly understood. Further, the role of elastic fibers in normal vaginal wall mechanics has not been fully ascertained. Therefore, the objective of this study is to investigate the contribution of elastic fibers to murine vaginal wall mechanics. Vaginal tissue from C57BL/6 female mice were mechanically tested using biaxial extension-inflation protocols before and after intraluminal exposure to elastase. Elastase digestion induced marked changes in the vaginal geometry, and biaxial mechanical properties, suggesting that elastic fibers may play an important role in vaginal wall mechanical function. Additionally, a constitutive model that considered two diagonal families of collagen fibers with a slight preference towards the circumferential direction described the data reasonably well before and after digestion. The present findings may be important to determine the underlying structural and mechanical mechanisms of POP, and aid in the development of growth and remodeling models for improved assessment and prediction of changes in structure-function relationships with prolapse development. Keywords: vaginal wall, women's health, mechanical testing, pelvic floor disorders, elastic fibers Disclosures: none.

Effects of Rho-kinase inhibition in lung tissue with chronic inflammation

We evaluated whether Rho-kinase inhibition (Y-27632) modulated distal lung responsiveness, inflammation, extracellular matrix remodeling and oxidative stress activation in guinea pigs (GPs) with chronic allergic inflammation. GPs were submitted to inhalation of ovalbumin (OVA-2×/week/4 weeks). From the 5th inhalation on, the Rho-kinase inhibitor group animals were submitted to Y-27632 inhalation 10min before each inhalation of OVA. Seventy-two hours after the seventh inhalation, the oscillatory mechanics of the distal lung strips were assessed under the baseline condition and after the ovalbumin challenge. Subsequently, the lung slices were submitted to morphometry. Rho-kinase inhibition in the ovalbumin-exposed animals attenuated distal lung elastance and resistance, eosinophils, IL-2, IL-4, IL-5, IL-13, TIMP-1, MMP-9, TGF-β, IFN-γ, NF-κB and iNOS-positive cells and the volume fraction of 8-iso-PGF2α, elastic, collagen and actin in alveolar walls compared with the OVA group (P<0.05). Rho-kinase inhibition contributed to the control of distal lung responsiveness, eosinophilic and Th1/Th2 responses and extracellular matrix remodeling in an animal model of chronic allergic inflammation.

Dynamic nonlinearity of lung tissue: effects of strain amplitude and stress level

Lung tissue presents substantial nonlinear phenomena not accounted for by linear models; however, nonlinear approaches are less available. Our aim was to characterize the behavior of total harmonic distortion, an index of nonlinearity, in lung tissue strips under sinusoidal deformation at a single frequency as a function of strain amplitude and operational stress. To that end, lung parenchymal strips from healthy rats ( n = 6) were subjected to sinusoidal deformation (1 Hz) at different strain amplitudes (Δε = 4, 8, 12, 16, and 20%) and operating stresses (σop = 6, 8, 10, 12, 14, and 16 hPa). Additional rats ( n = 9) were intratracheally instilled with saline or bleomycin (2.5 U/kg, 3 times 1 wk apart), killed 28 days after the last instillation, and their lung tissue strips were studied at 5 and 10 hPa σop and 5% Δε. In both cases, harmonic distortion (HD%) of input (strain) and output (stress) signals were determined. In healthy strips, HD% increased linearly with Δε, stress amplitude, and minimum stress by cycle variations, but showed no significant change with σop levels. A prediction model could be determined as a function of operational stress and stress amplitude. Harmonic distortion was significantly increased in bleomycin-treated strips compared with controls and showed positive correlation with E behavior in both normal and diseased strips. We concluded that HD% can be useful as a single and simple parameter of lung tissue nonlinearity.

Lung parenchymal mechanics in health and disease

The mechanical properties of lung tissue are important determinants of lung physiological functions. The connective tissue is composed mainly of cells and extracellular matrix, where collagen and elastic fibers are the main determinants of lung tissue mechanical properties. These fibers have essentially different elastic properties, form a continuous network along the lungs, and are responsible for passive expiration. In the last decade, many studies analyzed the relationship between tissue composition, microstructure, and macrophysiology, showing that the lung physiological behavior reflects both the mechanical properties of tissue individual components and its complex structural organization. Different lung pathologies such as acute respiratory distress syndrome, fibrosis, inflammation, and emphysema can affect the extracellular matrix. This review focuses on the mechanical properties of lung tissue and how the stress-bearing elements of lung parenchyma can influence its behavior.

Single and repeated bleomycin intratracheal instillations lead to different biomechanical changes in lung tissue

Single dose of bleomycin induces acute alveolitis followed by a reparative process whilst a repeated dose results in progressive fibrosis, which may lead to distinct lung tissue biomechanical changes. To test this hypothesis, rats were intratracheally instilled with saline (N=11) or bleomycin (2.5U/kg) once (SD, N=8) or three times (RD, N=9) one week apart, and sacrificed 28 days after challenge. Forced oscillatory mechanics as well as the amount of collagen fibre and myeloperoxidase content (MPO(L)) were studied in lung tissue strips. Both elastic modulus (H), tissue damping (G), and MPO(L) increased only in RD-challenged rats. Although fibroblast focus was found in RD, collagen fibre content increased in both challenged groups. However, the amount of collagen fibre in SD group was not enough to induce lung tissue mechanical changes. In conclusion, repeated doses of bleomycin induce inflammatory and fibrogenic behaviour with biomechanical changes mimicking interstitial lung disease in humans.

Different strains of mice present distinct lung tissue mechanics and extracellular matrix composition in a model of chronic allergic asthma

The impact of genetic factors on asthma is well recognized but poorly understood. We tested the hypothesis that different mouse strains present different lung tissue strip mechanics in a model of chronic allergic asthma and that these mechanical differences may be potentially related to changes of extracellular matrix composition and/or contractile elements in lung parenchyma. Oscillatory mechanics were analysed before and after acetylcholine (ACh) in C57BL/10, BALB/c, and A/J mice, subjected or not to ovalbumin sensitization and challenge. In controls, tissue elastance (E) and resistance (R), collagen and elastic fibres' content, and alpha-actin were higher in A/J compared to BALB/c mice, which, in turn, were more elevated than in C57BL/10. A similar response pattern was observed in ovalbumin-challenged animals irrespective of mouse strain. E and R augmented more in ovalbumin-challenged A/J [E: 22%, R: 18%] than C57BL/10 mice [E: 9.4%, R: 11%] after ACh In conclusion, lung parenchyma remodelled differently yielding distinct in vitro mechanics according to mouse strain.

Effects of amiodarone on lung tissue mechanics and parenchyma remodeling

We studied the results of chronic oral administration of amiodarone on in vitro lung tissue mechanics, light and electron microscopy. Fifteen Wistar male rats were divided into three groups. In control (CTRL) group animals received saline (0.5 mL/day). In amiodarone (AMIO) groups, amiodarone was administered by gavage at a dose of 175 mg/kg 5 days per week for 6 (6AMIO) or 12 weeks (12AMIO). Lung tissue strips were analyzed 24h after the last drug administration. Tissue resistance and elastance were higher in 6AMIO and 12AMIO than in CTRL, while hysteresivity was similar in all groups. Total amount of collagen fibers in lung parenchyma increased progressively with the time course of the lesion. However, at 6 weeks there was an increase in the amount of type III collagen fibers, while in 12AMIO mainly type I collagen fibers were found. In our study amiodarone increased lung tissue impedance that was accompanied by matrix remodeling and lesion of type II pneumocytes.

Effects of chronic L-NAME treatment lung tissue mechanics, eosinophilic and extracellular matrix responses induced by chronic pulmonary inflammation

The importance of lung tissue in asthma pathophysiology has been recently recognized. Although nitric oxide mediates smooth muscle tonus control in airways, its effects on lung tissue responsiveness have not been investigated previously. We hypothesized that chronic nitric oxide synthase (NOS) inhibition by N(omega)-nitro-L-arginine methyl ester (L-NAME) may modulate lung tissue mechanics and eosinophil and extracellular matrix remodeling in guinea pigs with chronic pulmonary inflammation. Animals were submitted to seven saline or ovalbumin exposures with increasing doses (1 approximately 5 mg/ml for 4 wk) and treated or not with L-NAME in drinking water. After the seventh inhalation (72 h), animals were anesthetized and exsanguinated, and oscillatory mechanics of lung tissue strips were performed in baseline condition and after ovalbumin challenge (0.1%). Using morphometry, we assessed the density of eosinophils, neuronal NOS (nNOS)- and inducible NOS (iNOS)-positive distal lung cells, smooth muscle cells, as well as collagen and elastic fibers in lung tissue. Ovalbumin-exposed animals had an increase in baseline and maximal tissue resistance and elastance, eosinophil density, nNOS- and iNOS-positive cells, the amount of collagen and elastic fibers, and isoprostane-8-PGF(2alpha) expression in the alveolar septa compared with controls (P<0.05). L-NAME treatment in ovalbumin-exposed animals attenuated lung tissue mechanical responses (P<0.01), nNOS- and iNOS-positive cells, elastic fiber content (P<0.001), and isoprostane-8-PGF(2alpha) in the alveolar septa (P<0.001). However, this treatment did not affect the total number of eosinophils and collagen deposition. These data suggest that NO contributes to distal lung parenchyma constriction and to elastic fiber deposition in this model. One possibility may be related to the effects of NO activating the oxidative stress pathway.

Impact of lung remodelling on respiratory mechanics in a model of severe allergic inflammation

We developed a model of severe allergic inflammation and investigated the impact of airway and lung parenchyma remodelling on in vivo and in vitro respiratory mechanics. BALB/c mice were sensitized and challenged with ovalbumin in severe allergic inflammation (SA) group. The control group (C) received saline using the same protocol. Light and electron microscopy showed eosinophil and neutrophil infiltration and fibrosis in airway and lung parenchyma, mucus gland hyperplasia, and airway smooth muscle hypertrophy and hyperplasia in SA group. These morphological changes led to in vivo (resistive and viscoelastic pressures, and static elastance) and in vitro (tissue elastance and resistance) lung mechanical alterations. Airway responsiveness to methacholine was markedly enhanced in SA as compared with C group. Additionally, IL-4, IL-5, and IL-13 levels in the bronchoalveolar lavage fluid were higher in SA group. In conclusion, this model of severe allergic lung inflammation enabled us to directly assess the role of airway and lung parenchyma inflammation and remodelling on respiratory mechanics.

Inflammatory related changes in lung tissue mechanics after bleomycin-induced lung injury

The impact of lung remodelling in respiratory mechanics has been widely studied in bleomycin-induced lung injury. However, little is known regarding the relationship between the amount of lung inflammation and pulmonary tissue mechanics. For this purpose, rats were intratracheally instilled with bleomycin (n=29) or saline (n=8) and sacrificed at 3, 7, or 15 days. Forced oscillatory mechanics as well as indices of remodelling (elastic fibre content and hydroxyproline) and inflammation (myeloperoxidase content, total cell count, alveolar wall thickness, and lung water content) were studied in lung tissue strips. Tissue resistance increased significantly at day 15, while hysteresivity was significantly higher in bleomycin group compared to control at all time points. Elastic fibres, hydroxyproline and myeloperoxidase contents augmented after bleomycin at days 7 and 15. Tissue resistance and hysteresivity were significantly correlated with myeloperoxidase, elastic fibre and lung water content. In conclusion, inflammatory structural changes and elastogenesis are the main determinants for hysteretic changes in this 2-week bleomycin-induced lung injury model.

Respiratory changes in a murine model of spontaneous systemic lupus erythematosus

The pathophysiology of systemic lupus erythematosus (SLE) has been very well described in many organs. However, the relation between extracellular matrix changes and lung dynamic mechanical behaviour deserves elucidation. To that end, pulmonary mechanics, lung morphometry and the amount of collagen and elastic fibres in the alveolar septa were analysed in mice with SLE [NZB/W (New Zealand Black/White) F1] and non-diseased NZW mice (control). Static (E(st)) and dynamic (E(dyn)) elastances, difference between dynamic and static elastances (DeltaE), airway resistance (R(aw)) and viscoelastic/inhomogeneous pressure (DeltaP(2)) were determined by the end-inflation occlusion method. Lungs were removed and prepared for histology. E(st), E(dyn), DeltaE and DeltaP(2) were higher in SLE than in control group, while R(aw) was similar in both groups. SLE group showed alveolar collapse and increased amount of elastic and collagen fibres. In conclusion, SLE mice showed an increase in elastic and viscoelastic/inhomogeneous pressures that was accompanied by deposition of collagen and elastic fibres in the alveolar septa.

Mouse strain dependence of lung tissue mechanics: Role of specific extracellular matrix composition

This study analyses the differences between C57BL/10 and BALB/c mice in lung tissue micromechanical behaviour and whether specific histological characteristics are related to the mechanical profile. C57BL/10 and BALB/c subpleural lung strips were submitted to multisinusoidal deformation with frequencies ranging between 0.2 and 3.1 Hz. Tissue resistance (R), elastance (E), and hysteresivity (eta) at each frequency were determined before and 30s, 1, 2, and 3 min after acetylcholine (ACh) treatment. BALB/c mice showed higher E and R, at baseline, as well as greater amount of collagen and elastic fibres, and alpha-actin than C57BL/10 mice. However, E, R, and eta augmented with the same magnitude after ACh treatment in both strains. Baseline R was correlated with collagen fibre content and with the volume proportion of alpha-actin, while E was correlated with elastic and collagen fibres, and alpha-actin contents. In conclusion, BALB/c and C57BL/10 mice present distinct tissue mechanical properties that are accompanied by specific extracellular matrix composition and contractile structures.

Lung parenchyma remodeling in a murine model of chronic allergic inflammation

This study tested the hypotheses that chronic allergic inflammation induces not only bronchial but also lung parenchyma remodeling, and that these histologic changes are associated with concurrent changes in respiratory mechanics. For this purpose, airway and lung parenchyma remodeling were evaluated by quantitative analysis of collagen and elastin, immunohistochemistry (smooth-muscle actin expression, eosinophil, and dendritic cell densities), and electron microscopy. In vivo (airway resistance, viscoelastic pressure, and static elastance) and in vitro (tissue elastance, resistance, and hysteresivity) respiratory mechanics were also analyzed. BALB/c mice were sensitized with ovalbumin and exposed to repeated ovalbumin challenges. A marked eosinophilic infiltration was seen in lung parenchyma and in large and distal airways. Neutrophils, lymphocytes, and dendritic cells also infiltrated the lungs. There was subepithelial fibrosis, myocyte hypertrophy and hyperplasia, elastic fiber fragmentation, and increased numbers of myofibroblasts in airways and lung parenchyma. Collagen fiber content was increased in the alveolar walls. The volume proportion of smooth muscle-specific actin was augmented in distal airways and alveolar duct walls. Airway resistance, viscoelastic pressure, static elastance, and tissue elastance and resistance were significantly increased. In conclusion, prolonged allergen exposure induced remodeling not only of the airway wall but also of the lung parenchyma, leading to in vivo and in vitro mechanical changes.

Time course of respiratory mechanics and pulmonary structural remodelling in acute lung injury

The aim of this study was to evaluate the time course of in vivo and in vitro respiratory mechanics and examine whether these parameters could reflect the temporal changes in lung parenchyma remodelling in paraquat (PQ)-induced lung injury. Measurements were done 1, 3 and 8 weeks after the intraperitoneal (i.p.) injection of saline (control) or paraquat (7mgkg(-1)) in rats. Airway and tissue resistances increased from control in PQ1 and PQ3 and returned to control values in PQ8, in accordance with the magnitude of bronchoconstriction. Viscoelastic/inhomogeneous pressure, tissue elastance, the number of polymorphonuclear cells, and collagen fibre content in lung parenchyma increased in PQ1 and remained elevated in PQ3 and PQ8. Static elastance increased in PQ1, returned to control values after 3 weeks, and was correlated with the volume fraction of collapsed alveoli. In conclusion, there is a restoration of normal alveolar-capillary lung units with a gradual improvement in airway and tissue resistances and static elastance. However, the on-going fibrotic process kept elevated tissue elastance and viscoelastic/inhomogeneous pressure.

What increases type III procollagen mRNA levels in lung tissue: stress induced by changes in force or amplitude?

We hypothesized that stress determined by force could induce higher type III procollagen (PCIII) mRNA expression than the stress determined by amplitude. To that end, rat lung tissue strips were oscillated for 1h under different amplitudes [1, 5 and 10% of resting length (L(B)), at 0.5 x 10(-2) N] and forces (0.25 x 10(-2), 0.5 x 10(-2) and 10(-2)N, at 5% L(B)). Resistance (R), elastance (E) and hysteresivity (eta) were analysed during sinusoidal oscillations at 1Hz. After 1h of oscillation, PCIII mRNA expression was determined by Northern-blot and semiquantitative RT-PCR. Control value of PCIII mRNA was obtained from unstressed strips. E and R increased with augmenting force and decreased with increasing amplitude, while eta remained unaltered. PCIII mRNA expression increased significantly after 1h of oscillation at 10(-2)N and 5% L(B) and remained unchanged for 6h. In conclusion, the stress induced by force but not by amplitude led to the increment in PCIII mRNA expression.

On the preparation of lung strip for tissue mechanics measurement

It is widely believed that it is fundamental to degas and/or rinse the lung prior to the measurement of the tissue mechanics, so that the undesirable effects of surfactant and localized gas trapping are eliminated. However, one could hypothesize that these mechanisms are bound to disappear in the in vitro preparation since the small tissue sample remains suspended oscillating in an organ bath. To investigate the real necessity to follow these procedures, dynamic mechanical properties were studied in strips of lungs previously rinsed with saline, degassed by ventilation with 100% O(2), or without any of these prior procedures. Resistance, elastance, hysteresivity, and the amounts of airway, blood vessel, and alveolar wall were computed. There was no difference in either tissue mechanics or morphology among the groups. In conclusion, the time-consuming degassing and rinsing steps are not necessary to adequately prepare lung tissue for in vitro mechanical analysis, and eliminating these steps potentially helps preserving the intact microstructure of the tissue.

Comparison of rat and mouse pulmonary tissue mechanical properties and histology

The present study compares the dynamic mechanical properties and the contents of collagen and elastic fibers (oxytalan + elaunin + fully developed elastic fibers) of mice and rat lung strips. Resistance, elastance (E), and hysteresivity (eta) were obtained during sinusoidal oscillations. The relative amounts of blood vessel, bronchial, and alveolar walls, as well as the mean alveolar diameter were determined. In both species, resistance had a negative and E a positive dependence on frequency, whereas eta remained unchanged. Mice showed higher E and lower eta than rats. Although collagen and elastic fiber contents were similar in both groups, mice had more oxytalan and less elaunin and fully developed elastic fibers than rats. Rats showed less alveolar and more blood vessel walls and higher mean alveolar diameter than mice. In conclusion, mice and rats present distinct tissue mechanical properties, which are accompanied by specific extracellular fiber composition.

Lung tissue mechanics and extracellular matrix remodeling in acute lung injury

This study was undertaken to test whether there is structural remodeling of lung parenchyma that could lead to tissue mechanical changes at an early phase of varying degrees of acute lung injury (ALI). Tissue resistance (R), dynamic elastance (E), and hysteresivity (eta) were analyzed during sinusoidal oscillations of rat lung parenchymal strips 24 h after intraperitoneal injection of saline (C) or paraquat (P [10, 15, 25, and 30 mg/kg]). These strips were also stained in order to quantify the amount of collagen and of three types of elastic fibers (elaunin, oxytalan, and fully developed elastic fibers) in the alveolar septa. E augmented progressively from C to P25, but the data from the P25 and P30 groups were not different (p < 0.0001). R and eta increased from C to P10 and from P15 to P25 (p < 0.001). Collagen fiber content increased exponentially with the severity of the injury. Elaunin and fully developed elastic fibers remained unchanged in the five groups, while oxytalan fibers increased only in the P25 and P30 groups. In conclusion, the pronounced mechanical changes at the tissue level and fibroelastogenesis happened at an early phase of the disease and even in mildly abnormal lung parenchyma.

KEYWORDS

elastance; collagen fibers; elastin; paraquat

Frequency characteristics of lung tissue strip during passive stretch and induced pneumoconstriction

To investigate the frequency-dependent changes of lung tissue mechanics during pneumoconstriction, we studied guinea pig subpleural lung strips submitted to a multisinusoidal deformation composed of five equal-amplitude discrete frequencies ranging between 0.2 and 3.1 Hz. Strips were submitted to graded step stretch changes (SS) and to graded histamine stimulation (HS) in organ bath. Elastance, resistance, and hysteresivity were calculated at each frequency. The model accounting for the relationship between the complex Young's modulus and the angular frequency showed that the constant-phase hypothesis was satisfied in SS condition. However, HS modified all parameters in the model, and the constant-phase hypothesis could be rejected for HS of 10(-5) and 10(-3) M. The hysteresivity time course changed with angular frequency, but differently in the HS and SS conditions. Our results agree with a serial disposition of the connective matrix and contractile system in lung tissue. We conclude that pneumoconstriction induced significant structural changes at the level of the connective matrix.

Lung tissue mechanics and extracellular matrix composition in a murine model of silicosis

The dynamic mechanical properties of lung tissue and its contents of collagen and elastic fibers were studied in strips prepared from mice instilled intratracheally with saline (C) or silica [15 (S15) and 30 days (S30) after instillation]. Resistance, elastance, and hysteresivity were studied during oscillations at different frequencies on S15 and S30. Elastance increased from C to silica groups but was similar between S15 and S30. Resistance was augmented from C to S15 and S30 and was greater in S30 than in S15 at higher frequencies. Hysteresivity was higher in S30 than in C and S15. Silica groups presented a greater amount of collagen than did C. Elastic fiber content increased progressively along time. This increment was related to the higher amount of oxytalan fibers at 15 and 30 days, whereas elaunin and fully developed elastic fibers were augmented only at 30 days. Silicosis led not only to pulmonary fibrosis but also to fibroelastosis, thus assigning a major role to the elastic system in the silicotic lung.