Role of connective tissues in large pulmonary airways

Chronic Obstructive Pulmonary Disease. A Biomarker and a Potential Therapy

This article assesses developments in cardiorespiratory medicine since the Nobel Prize in Physiology or Medicine was awarded in 1956 for advancements in the study of cardiorespiratory disease. In chronic obstructive pulmonary disease, advances were accelerated by the discovery of a genetically determined cause for pulmonary emphysema in the genetic abnormality alpha-1 antitrypsin deficiency. This causes a deficiency of the inhibitor of neutrophil elastase, which results in increased degradation of lung elastin and the development of pulmonary emphysema. This discovery gave focus to two amino acids that reside only in body elastin, desmosine and isodesmosine, which can be measured as biomarkers of elastin degradation in body fluids with increased accuracy and sensitivity. Studies of this biomarker have shown that augmentation therapy in alpha-1 antitrypsin deficiency does decrease lung and body elastic tissue degradation and in the RAPID (Randomized, Placebo-controlled Trial of Augmentation Therapy in Alpha-1 Proteinase Inhibitor Deficiency) Study, over 4 years, showed a preservation of lung density by computer tomography correlating with decreases in plasma levels of desmosine and isodesmosine. This insight indicates the potential of agents that prevent lung elastin degradation. Such an agent is hyaluronan aerosol, which is deficient in post mortem lungs with chronic obstructive pulmonary disease and has been shown to block elastin degradation, possibly by a barrier function. Thus it would appear that hyaluronan could have therapeutic potential in chronic obstructive pulmonary disease.

Linking optics and mechanics in an in vivo model of airway fibrosis and epithelial injury

Chronic mucosal and submucosal injury can lead to persistent inflammation and tissue remodeling. We hypothesized that microstructural and mechanical properties of the airway wall could be derived from multiphoton images. New Zealand White rabbits were intubated, and the tracheal epithelium gently denuded every other day for five days (three injuries). Three days following the last injury, the tracheas were excised for multiphoton imaging, mechanical compression testing, and histological analysis. Multiphoton imaging and histology confirm epithelial denudation, mucosal ulceration, subepithelial thickening, collagen deposition, immune cell infiltration, and a disrupted elastin network. Elastase removes the elastin network and relaxes the collagen network. Purified collagenase removes epithelium with subtle subepithelial changes. Young's modulus [(E) measured in kiloPascal] was significantly elevated for the scrape injured (9.0+/-3.2) trachea, and both collagenase (2.6+/-0.4) and elastase (0.8+/-0.3) treatment significantly reduced E relative to control (4.1+/-0.7). E correlates strongly with second harmonic generation (SHG) signal depth decay for enzyme-treated and control tracheas (R(2)=0.77), but not with scrape-injured tracheas. We conclude that E of subepithelial connective tissue increases on repeated epithelial wounding, due in part to changes in elastin and collagen microstructure and concentration. SHG depth decay is sensitive to changes in extracellular matrix content and correlates with bulk Young's modulus.

Leukocyte elastase inhibition therapy in cystic fibrosis: role of glycosylation on the distribution of alpha-1-proteinase inhibitor in blood versus lung

Cystic fibrosis patients demonstrate an increased susceptibility to bacterial lung infections. Airway infiltration by neutrophils will then lead to an increase in human leukocyte elastase (HLE) within the extracellular compartment, thereby producing deleterious effects. Here, we investigated the properties and tissue distribution of an unglycosylated, recombinant form of the HLE inhibitor alpha-1-proteinase inhibitor (alpha(1)-antitrypsin rhalpha1PI) when it is administered to the airway surface. We produced rhalpha1PI using a bacterial expression system and found the purified protein to be indistinguishable from blood-purified, glycosylated alpha1PI at inhibiting elastase in vitro. In contrast to intravenous administration, direct delivery of either alpha1PI or rhalpha1PI to the airway surface of CD-1 mice by nasal instillation produced similar highly detectable levels of protein in bronchoalveolar lavage at all time points, suggesting that glycosylation of alpha1PI does not play the same critical role in determining protein stability at the respiratory surface as it does in the vascular compartment. Interestingly, this unglycosylated rhalpha1PI was also highly protective against elastase-mediated injury 24 h after rhalpha1PI instillation and was consistently found to be significantly more protective than glycosylated blood-derived alpha1PI. Thus, these results provide evidence that aerosol delivery of rhalpha1PI could be an effective strategy for controlling HLE-dependent pathophysiology associated with cystic fibrosis lung disease.

The pulmonary matrix, glycosaminoglycans and pulmonary emphysema

This paper reviews recent evidence of the effect of intratracheal hyaluronan (HA) to limit the induction of experimental emphysema in hamsters. Experimental emphysema was induced by both neutrophil and pancreatic elastase instilled intratracheally. Emphysema was quantified anatomically by measurement of alveolar mean linear intercept. Hyaluronidase, instilled intratracheally, enhanced the induction of experimental emphysema. Air-space size measured one week after intratracheal instillation of elastase showed that administration of 1 mg HA immediately following elastase administration resulted in a marked reduction in air-space enlargement (82 microM vs 122 microM, p < 0.01). Similarly, animals given either 1 or 2 mg HA 2 h before elastase or 2mg HA 1 h after elastase showed a significant decrease in air-space enlargement compared to controls (96 microM, 88 microM vs 120 microM and 66 microM vs 104 microM, respectively; p < 0.05. Experimental emphysema induced by neutrophil elastase was also limited by the administration of 1 or 4 mg of HA, administered 2 h prior to elastase (57 and 59 microM, respectively vs 64 for controls, p < 0.05). Characterization of administered HA showed a mean molecular weight of 104,800 Da, less than 5% protein and a uronic acid/hexosamine ratio of 1, which is characteristic of HA. Studies using fluorescein-labeled hyaluronan (HA) showed fluorescence associated with interstitial, pleural and vascular elastic fibers. The mechanism of attachment of the administered HA to elastin remains unknown. Fluorescein labeling of elastin was visible for at least 4 h post-instillation. These studies indicate a protective effect of hyaluronan against elastase degradation of pulmonary elastin in vivo by both pancreatic and neutrophil elastases. The anatomical studies further suggest a mechanism of protective coating of hyaluronan which may limit access to pulmonary elastin from neutrophils and alveolar macrophages. Results also suggest that a reduction in pulmonary hyaluronan content increases the susceptibility of elastin to degradation by elastases. These studies provide evidence for an antielastase effect of hyaluronan which is not dependent upon enzyme inhibition but on anatomical protection of pulmonary elastin by other mechanisms.

Aerosolized prolastin suppresses bacterial proliferation in a model of chronic Pseudomonas aeruginosa lung infection

High levels of active neutrophil elastase (HNE) are present in the respiratory secretions of patients with cystic fibrosis (CF). We hypothesized that aerosolized Prolastin (alpha(1)-protease inhibitor or alpha(1)PI, purified from human blood) could suppress airway neutrophil inflammation and accelerate bacterial clearance from the lung in a model of chronic Pseudomonas aeruginosa lung infection. Because human alpha(1)PI effectively inhibits rat as well as human neutrophil elastase (NE) activity in vitro, we choose to test this hypothesis using a rat agar bead model of chronic P. aeruginosa lung infection. In this model, aerosolized Prolastin significantly decreased elastase activity (p < 0.01), lung neutrophil counts (p < 0.01), and bacterial colony counts (p < 0.01). Prolastin had no direct bactericidal effect on P. aeruginosa in vitro. Lung tissue histopathology revealed a marked decrease in lung inflammation in animals treated with Prolastin. These studies indicate that Prolastin can significantly decrease the elastase burden in the chronically infected lung. In addition, not only does Prolastin suppress lung inflammation, but it also markedly decreases P. aeruginosa density in a rat model of chronic P. aeruginosa lung infection. These data suggest that aerosolized alpha(1)PI may represent a useful nonantibiotic adjunct in the treatment and control of infection and inflammation associated with CF lung disease.

DNase I acutely increases cystic fibrosis sputum elastase activity and its potential to induce lung hemorrhage in mice

The potential of DNase I to increase cystic fibrosis sputum elastase activity and lung damage was evaluated. Sputum from CF patients induced little lung hemorrhage when instilled intranasally in C57BL/6 mice. However, sputum treated in vitro by the addition of 1 mg/ml bovine DNase I showed increased neutrophil elastase activity (7.97 +/- 1.56 versus 3.91 +/- 0.62 microM, p < 0.01) and induced marked lung hemorrhage in mice (bronchoalveolar lavage fluid hemoglobin = 192.8 +/- 40.7 versus 44.5 +/- 12.0 microg/ml, p < 0.01). These effects were not observed with DNase I alone in phosphate buffer and were suppressed by the human neutrophil elastase inhibitor methoxysuccinyl-alanyl-alanyl-prolyl-valine-chloromethylketone (MeOSAAPV-CMK). In vivo administration of 2.5 mg aerosolized recombinant human DNase I to patients with CF resulted in a 2.2-fold increase of sputum elastase activity within 1 h of treatment. Elastase levels returned to pre-rhDNase therapy levels 24 h after aerosol treatment. Sputum collected 1 h after rhDNase on 4 separate days from two of six patients in which elastase levels were highest, induced lung hemorrhage when instilled intranasally in mice. We conclude that DNase I therapy of patients with cystic fibrosis can acutely increase the elastase activity of sputum and also its potential to induce hemorrhage in the murine lung.

Rabbit trachealis tension responses to receptor-mediated agonists are diminished by elastase

The present study examined the effects of elastase, in concentrations present in respiratory secretions, on airway smooth muscle contractile responses in vitro and the magnitude of the airway epithelial inhibition of smooth muscle tension. Experiments were performed on 126 full-thickness tracheal strips from 25 rabbits. Isometric tension responses to acetylcholine (10(-8) to 10(-4) M) and potassium chloride (10 to 110 mM) were examined before and after a 5-min exposure to either porcine pancreatic elastase (PPE) or human neutrophil elastase (HNE). PPE (5 to 40 micrograms/100 microliters) reduced the tension response to acetylcholine but had no effect on the tension response to potassium chloride. PPE and HNE (20 micrograms/100 microliters) produced similar effects. Mechanical removal of the epithelium per se significantly (P less than 0.005) decreased the ED50 response to acetylcholine but did not affect maximal tension. However, the airway epithelial inhibitory effect on the acetylcholine tension response was similar in the presence and absence of PPE (20 micrograms/100 microliters). These data suggest that the diminution of tracheal smooth muscle tension responses to receptor-mediated agonists induced by elastase is a direct effect on the muscle and is not mediated by an effect of elastase on the respiratory epithelium.

The effect of shape, age and extension on the compliance of equine tracheal segments

The influence of the age and weight of the animal as well as that of the extension and the shape of the trachea on the mechanical properties of the cervical trachea was studied in 33 isolated tracheal segments obtained from freshly slaughtered horses. The relationship between intraluminal pressure and volume was determined in the cervical tracheal segments positioned firstly under normal longitudinal tension and secondly in hyperextension. At the same time, changes in the area of the cross-section of the lumen (X-SA) at the midpoint of the segment were measured using photographs obtained by slit-lamp transillumination and endoscopy. The sagittal (DS) and transverse (DT) diameters were determined for each segment and the DT/DS ratio was calculated to give an estimate of the shape of the X-SA. The results showed that (i) neither the age nor the weight of the horses had any influence on the mechanical properties of the trachea; (ii) extension decreases the compressibility of the tracheal segment in vitro; (iii) there is a wide variation in the extrathoracic tracheal X-SA shape in horses; and (iv) the shape of the X-SA has a major influence on the mechanical properties of the trachea. It was concluded that (i) hyperextension of the neck will partly facilitate respiration at high levels of ventilation by elongating the trachea and by decreasing its collapsibility; and (ii) the tracheal collapse which may occur during high levels of ventilation will be more or less important depending on the individual X-SA shape.

Exponential analysis of the lung pressure-volume curve in newborn mammals

The compliance of the lung (per unit of lung weight) is less in newborn mammals than in adults. This could result from a smaller volume of airspaces per unit weight and/or a lower lung distensibility. The isolated role of lung distensibility was evaluated by using a mathematical description of the pressure-volume (P-V) curve during lung deflation. Deflation limbs of static P-V curves in newborns of six species (four experimentally obtained and two taken from the literature) ranging from total lung capacity to the resting volume (Vr) were fitted by a monoexponential function of the type V = B - Ae-KP, where B equals Vmax at infinite P, A equals the difference between Vmax and V at P = O, and K is a constant representing lung distensibility. Unlike in adults, in newborns the monoexponential fitting provided an adequate description of the P-V curve for only a relatively small range of transpulmonary pressure (from P at Vr to 10-15 cm H2O). The K value of this portion of the curve was similar among species but higher than in adult mammals, averaging 0.240 cm H2O-1. This suggests a similar lung structure in the different species. Since lung distensibility in newborns is larger than in adults, the fact that a unit mass of lung in the newborn is less compliant should be due to the smaller volume of its airspaces.

Bronchial collapse in obstructive lung disease

A 57-year-old man who died suddenly with severe bilateral mainstem bronchial collapse is described, and an alteration of the elastic tissue in the membranous portion of the bronchi is identified. The morphologic abnormalities, physiologic dynamics, and potential clinical consequences of such an alteration are discussed.

Effects of a molecular change in collagen on lung structure and mechanical function

Semicarbazide, a lathyrogen, was given to growing rats to elucidate the consequences of altering the molecular structure of fibrous proteins within the lung. Static pressure-volume (P-V) measurements during deflation of saline-filled lungs showed normal recoil pressure and compliance values within the physiological range of lung volume. Quasi-static P-V measurements were also normal during slow reinflation, even beyond physiological limits to a recoil pressure of 20 cm H20. However, the lungs of experimental rats ruptured at much lower recoil pressures than controls. Histology was normal in lungs fixed at 20 cm H20. In contrast, lungs showed dilation of terminal air spaces, rupture of alveolar walls, and an increase in mean linear intercept in experimental compared with control specimens, when fixed at 30 cm H20. Biochemical analyses revealed reduced cross-linking of lung collagen without change in its total content. There were no detectable changes in the quantity or quality of lung elastin. It is concluded that semicarbazide may selectively impair the maturation of lung collagen and that immaturity of lung collagen is associated with a reduction in the tensile strength of lung tissue, without changes in elasticity within physiological volume limits.

Effects of elastase, collagenase, and papain on structure and function of rat lungs in vitro

Present concepts of the roles of collagen and elastin in lung elastic behavior and maintenance of lung structure have been largely inferred from anatomical observations or from studies of isolated fibers in vitro. Based on the intimate association of elastin and collagen it has been postulated that elastin contributes little to elastic behavior and that collagen is the major determinant of lung structure. Using clostridial collagenase, pancreatic elastase, and papain we have selectively degraded these fibers and studied the resulting changes in elastic behavior and structure of rat lungs in vitro.Pressure-volume curves were recorded during continuous slow air inflation and deflation (10.5 ml/min) before and after the intratracheal instillation of 0.5 ml of control or enzyme solution. Surface tension-lowering activity of lavaged material was studied. All lungs were fixed inflated at 25 cm H(2)O pressure and whole lung sections were stained for elastin, collagen, and reticulin. Collagenase produced a marked susceptibility to pleural rupture but did not alter elastic behavior or lung structure. Elastase and papain produced segments of lung with increased compliance; this change was not due to alteration in surface forces but was associated with decreased tissue elastic recoil. Histologically, altered tissue recoil correlated well with evidence of damaged elastin fibers. In contrast to previous concepts these results suggest that elastin is the major connective tissue determinant of lung structure and elastic behavior.

Serum elastase inhibitor deficiency and alpha 1-antitrypsin deficiency in patients with obstructive emphysema

A decreased inhibition of pancreatic elastase has been detected in the serums of six patients with alpha(1)-antitrypsin deficiency. Five have severe clinical and physiological pulmonary emphysema. This observation extends the defect of inhibition by serum to a second, biologically active proteolytic enzyme in this form of familial emphysema.