Tobacco smoke-induced lung emphysema in guinea pigs is associated with increased interstitial collagenase

Animal models and mechanisms of tobacco smoke-induced chronic obstructive pulmonary disease (COPD)

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide, and its global health burden is increasing. COPD is characterized by emphysema, mucus hypersecretion, and persistent lung inflammation, and clinically by chronic airflow obstruction and symptoms of dyspnea, cough, and fatigue in patients. A cluster of pathologies including chronic bronchitis, emphysema, asthma, and cardiovascular disease in the form of hypertension and atherosclerosis variably coexist in COPD patients. Underlying causes for COPD include primarily tobacco use but may also be driven by exposure to air pollutants, biomass burning, and workplace related fumes and chemicals. While no single animal model might mimic all features of human COPD, a wide variety of published models have collectively helped to improve our understanding of disease processes involved in the genesis and persistence of COPD. In this review, the pathogenesis and associated risk factors of COPD are examined in different mammalian models of the disease. Each animal model included in this review is exclusively created by tobacco smoke (TS) exposure. As animal models continue to aid in defining the pathobiological mechanisms of and possible novel therapeutic interventions for COPD, the advantages and disadvantages of each animal model are discussed.

The Role of Mitochondria and Oxidative/Antioxidative Imbalance in Pathobiology of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common preventable and treatable disease, characterized by persistent airflow limitation that is usually progressive and associated with an enhanced chronic inflammatory response in the airways and the lung to noxious particles or gases. The major risk factor of COPD, which has been proven in many studies, is the exposure to cigarette smoke. However, it is 15-20% of all smokers who develop COPD. This is why we should recognize the pathobiology of COPD as involving a complex interaction between several factors, including genetic vulnerability. Oxidant-antioxidant imbalance is recognized as one of the significant factors in COPD pathogenesis. Numerous exogenous and endogenous sources of ROS are present in pathobiology of COPD. One of endogenous sources of ROS is mitochondria. Although leakage of electrons from electron transport chain and forming of ROS are the effect of physiological functioning of mitochondria, there are various intra- and extracellular factors which may increase this amount and significantly contribute to oxidative-antioxidative imbalance. With the coexistence with impaired antioxidant defence, all these issues lead to oxidative and carbonyl stress. Both of these states play a significant role in pathobiology of COPD and may account for development of major comorbidities of this disease.

Mmp1a and Mmp1b are not functional orthologs to human MMP1 in cigarette smoke induced lung disease

Matrix Metalloproteinase 1 (MMP1, collagenase-1) expression is implicated in a number of diseased states including emphysema and malignant tumors. The cigarette-smoke induced expression of this interstitial collegenase has been studied extensively and its inhibition proposed as a novel therapeutic treatment for tobacco related diseases such as chronic obstructive pulmonary disease (COPD) and lung cancer. However, a limitation in MMP1 research is the inability to take advantage of natural in vivo studies as most research has been performed in vitro or via animal models expressing human forms of the gene due to the lack of a rodent ortholog of MMP1. The present study examines the function of two possible mouse orthologs of human MMP1 known as Mmp1a and Mmp1b. Using genomic sequence analysis and expression analysis of these enzymes, the data demonstrate that neither MMP1a nor MMP1b behave in the same manner as human MMP1 in the presence of cigarette smoke. These findings establish that the two commonly proposed orthologs of MMP1, Mmp1a and Mmp1b, provide substantial limitations for use in examining MMP1 induced lung disease in mouse models of cigarette smoke emphysema.

Tobacco smoke induced COPD/emphysema in the animal model-are we all on the same page?

Chronic Obstructive Pulmonary Disease (COPD) is one of the foremost causes of death worldwide. It is primarily caused by tobacco smoke, making it an easily preventable disease, but facilitated by genetic α-1 antitrypsin deficiency. In addition to active smokers, health problems also occur in people involuntarily exposed to second hand smoke (SHS). Currently, the relationship between SHS and COPD is not well established. Knowledge of pathogenic mechanisms is limited, thereby halting the advancement of new treatments for this socially and economically detrimental disease. Here, we attempt to summarize tobacco smoke studies undertaken in animal models, applying both mainstream (direct, nose only) and side stream (indirect, whole body) smoke exposures. This overview of 155 studies compares cellular and molecular mechanisms as well as proteolytic, inflammatory, and vasoreactive responses underlying COPD development. This is a difficult task, as listing of exposure parameters is limited for most experiments. We show that both mainstream and SHS studies largely present similar inflammatory cell populations dominated by macrophages as well as elevated chemokine/cytokine levels, such as TNF-α. Additionally, SHS, like mainstream smoke, has been shown to cause vascular remodeling and neutrophil elastase-mediated proteolytic matrix breakdown with failure to repair. Disease mechanisms and therapeutic interventions appear to coincide in both exposure scenarios. One of the more widely applied interventions, the anti-oxidant therapy, is successful for both mainstream and SHS. The comparison of direct with indirect smoke exposure studies in this review emphasizes that, even though there are many overlapping pathways, it is not conclusive that SHS is using exactly the same mechanisms as direct smoke in COPD pathogenesis, but should be considered a preventable health risk. Some characteristics and therapeutic alternatives uniquely exist in SHS-related COPD.

Attacking the multi-tiered proteolytic pathology of COPD: new insights from basic and translational studies

Protease activity in inflammation is complex. Proteases released by cells in response to infection, cytokines, or environmental triggers like cigarette smoking cause breakdown of the extracellular matrix (ECM). In chronic inflammatory diseases like chronic obstructive pulmonary disease (COPD), current findings indicate that pathology and morbidity are driven by dysregulation of protease activity, either through hyperactivity of proteases or deficiency or dysfunction their antiprotease regulators. Animal studies demonstrate the accuracy of this hypothesis through genetic and pharmacologic tools. New work shows that ECM destruction generates peptide fragments active on leukocytes via neutrophil or macrophage chemotaxis towards collagen and elastin derived peptides respectively. Such fragments now have been isolated and characterized in vivo in each case. Collectively, this describes a biochemical circuit in which protease activity leads to activation of local immunocytes, which in turn release cytokines and more proteases, leading to further leukocyte infiltration and cyclical disease progression that is chronic. This circuit concept is well known, and is intrinsic to the protease-antiprotease hypothesis; recently analytic techniques have become sensitive enough to establish fundamental mechanisms of this hypothesis, and basic and clinical data now implicate protease activity and peptide signaling as pathologically significant pharmacologic targets. This review discusses targeting protease activity for chronic inflammatory disease with special attention to COPD, covering important basic and clinical findings in the field; novel therapeutic strategies in animal or human studies; and a perspective on the successes and failures of agents with a focus on clinical potential in human disease.

Emerging role of MAP kinase pathways as therapeutic targets in COPD

Studies examining the cellular mechanisms of inflammation and protease production in the lung tissue and airways of COPD patients have shed light on the important role of kinase-based signaling cascades. These pathways can be activated by environmental stimuli such as tobacco smoke, and by endogenous signals such as cytokines, growth factors, and inflammation-derived oxidants. The three most widely characterized cascades are those directed by the classical mitogen activated protein (MAP) kinase (ERK1/2), stress activated protein kinase/c-Jun N-terminal protein kinase, and p38 enzymes. These phosphorylation cascades transmit and amplify extracellular, receptor-mediated signals through the cytoplasm of the cell to activate nuclear transcription factors which bind and induce expression of target genes. The result is tight control of diverse cellular events, and rapid responses to external stimuli. However, recent research suggests that constitutive or aberrant activation of MAP kinases contributes to several COPD-associated phenotypes, including mucus overproduction and secretion, inflammation, cytokine expression, apoptosis, T cell activation, matrix metalloproteinase production, and fibrosis. This review explores the biological functions of the MAP kinase pathways in the pathogenesis of COPD, their activation by cigarette smoke, and discusses the potential role of MAP kinase inhibitors in COPD therapy.

Mechanisms of cigarette smoke-induced COPD: insights from animal models

Cigarette smoke-induced animal models of chronic obstructive pulmonary disease support the protease-antiprotease hypothesis of emphysema, although which cells and proteases are the crucial actors remains controversial. Inhibition of either serine or metalloproteases produces significant protection against emphysema, but inhibition is invariably accompanied by decreases in the inflammatory response to cigarette smoke, suggesting that these inhibitors do more than just prevent matrix degradation. Direct anti-inflammatory interventions are also effective against the development of emphysema, as are antioxidant strategies; the latter again decrease smoke-induced inflammation. There is increasing evidence for autoimmunity, perhaps directed against matrix components, as a driving force in emphysema. There is intriguing but controversial animal model evidence that failure to repair/failure of lung maintenance also plays a role in the pathogenesis of emphysema. Cigarette smoke produces small airway remodeling in laboratory animals, possibly by direct induction of fibrogenic growth factors in the airway wall, and also produces pulmonary hypertension, at least in part through direct upregulation of vasoactive mediators in the intrapulmonary arteries. Smoke exposure causes goblet cell metaplasia and excess mucus production in the small airways and proximal trachea, but these changes are not good models of either chronic bronchitis or acute exacerbations. Emphysema, small airway remodeling, pulmonary hypertension, and mucus production appear to be at least partially independent processes that may require different therapeutic approaches.

Matrix metalloproteinases in destructive pulmonary pathology

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that have a number of important physiological roles including remodelling of the extracellular matrix, facilitating cell migration, cleaving cytokines, and activating defensins. However, excess MMP activity may lead to tissue destruction. The biology of MMP and the role of these proteases in normal pulmonary immunity are reviewed, and evidence that implicates excess MMP activity in causing matrix breakdown in chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), sarcoidosis, and tuberculosis is discussed. Evidence from both clinical studies and animal models showing that stromal and inflammatory cell MMP expression leads to immunopathology is examined, and the mechanisms by which excess MMP activity may be targeted to improve clinical outcomes are discussed.

Mycobacterium tuberculosis, but not vaccine BCG, specifically upregulates matrix metalloproteinase-1

RATIONALE

Pulmonary cavitation is fundamental to the global success of Mycobacterium tuberculosis. However, the mechanisms of this lung destruction are poorly understood. The biochemistry of lung matrix predicts matrix metalloproteinase (MMP) involvement in immunopathology.

METHODS

We investigated gene expression of all MMPs, proteins with a disintegrin and metalloproteinase domain, and tissue inhibitors of metalloproteinases in M. tuberculosis-infected human macrophages by real-time polymerase chain reaction. MMP secretion was measured by zymography and Western analysis, and expression in patients with pulmonary tuberculosis was localized by immunohistochemistry.

RESULTS

MMP-1 and MMP-7 gene expression and secretion are potently upregulated by M. tuberculosis, and no increase in tissue inhibitor of metalloproteinase expression occurs to oppose their activity. Dexamethasone completely suppresses MMP-1 but not MMP-7 gene expression and secretion. In patients with active tuberculosis, macrophages express MMP-1 and MMP-7 adjacent to areas of tissue destruction. MMP-1 but not MMP-7 expression and secretion are relatively M. tuberculosis specific, are not upregulated by tuberculosis-associated cytokines, and are prostaglandin dependent. In contrast, the vaccine M. bovis bacillus Calmette-Guérin (BCG) does not stimulate MMP-1 secretion from human macrophages, although M. tuberculosis and BCG do upregulate MMP-7 equally. BCG-infected macrophages secrete reduced prostaglandin E2 concentrations compared with M. tuberculosis-infected macrophages, and prostaglandin pathway supplementation augments MMP-1 secretion from BCG-infected cells.

CONCLUSIONS

M. tuberculosis specifically upregulates MMP-1 in a cellular model of human infection and in patients with tuberculosis. In contrast, vaccine BCG, which does not cause lung cavitation, does not upregulate prostaglandin E2-dependent MMP-1 secretion.

Mechanics, nonlinearity, and failure strength of lung tissue in a mouse model of emphysema: possible role of collagen remodeling

Enlargement of the respiratory air spaces is associated with the breakdown and reorganization of the connective tissue fiber network during the development of pulmonary emphysema. In this study, a mouse (C57BL/6) model of emphysema was developed by direct instillation of 1.2 IU of porcine pancreatic elastase (PPE) and compared with control mice treated with saline. The PPE treatment caused 95% alveolar enlargement ( P = 0.001) associated with a 29% lower elastance along the quasi-static pressure-volume curves ( P < 0.001). Respiratory mechanics were measured at several positive end-expiratory pressures in the closed-chest condition. The dynamic tissue elastance was 19% lower ( P < 0.001), hysteresivity was 9% higher ( P < 0.05), and harmonic distortion, a measure of collagen-related dynamic nonlinearity, was 33% higher in the PPE-treated group ( P < 0.001). Whole lung hydroxyproline content, which represents the total collagen content, was 48% higher ( P < 0.01), and α-elastin content was 13% lower ( P = 0.16) in the PPE-treated group. There was no significant difference in airway resistance ( P = 0.7). The failure stress at which isolated parenchymal tissues break during stretching was 40% lower in the PPE-treated mice ( P = 0.002). These findings suggest that, after elastolytic injury, abnormal collagen remodeling may play a significant role in all aspects of lung functional changes and mechanical forces, leading to progressive emphysema.

Tumor Necrosis Factor-α Drives 70% of Cigarette Smoke–induced Emphysema in the Mouse

Mice lacking tumor necrosis factor-alpha (TNF-alpha) receptors (TNFRKO mice) do not develop an inflammatory infiltrate or matrix breakdown after a single acute cigarette smoke exposure. To determine the role of TNF-alpha in the long-term development of emphysema, mice were exposed to smoke for 6 months. TNFRKO mice demonstrated an 11% increase in mean linear intercept; wild-type mice had a 38% increase. TNFRKO mice had 65% fewer neutrophils and no increase in macrophages in lavage fluid. Whole lung matrix metalloprotease (MMP)-2, MMP-9, MMP-12, MMP-13, and matrix type-1 (MT1)-MMP proteins were increased in wild-type mice, but smaller increases in MMP-12, MMP-13, and MT1-MMP were also seen in TNFRKO mice. Lavage matrix breakdown products were elevated in wild-type mice and only partially reduced by anti-neutrophil antibody, implying both neutrophil- and non-neutrophil-mediated matrix breakdown. We conclude that TNF-alpha-mediated processes, probably driving neutrophil influx, are responsible for approximately 70% of airspace enlargement and the majority of inflammatory cell influx/matrix breakdown in the mouse model. TNF-alpha causes increased MMP production, but some increased MMP activity is present even in TNFRKO mice. These findings imply a second TNF-alpha-independent process, possibly related to direct MMP attack on matrix, that produces the remaining 30% of airspace enlargement.

Cigarette smoke exposure potentiates bleomycin-induced lung fibrosis in guinea pigs

The role of tobacco smoking in the development and outcome of pulmonary fibrosis is uncertain. To approach the effects of cigarette smoke on bleomycin-induced lung fibrosis, we studied five groups of guinea pigs: 1) controls, 2) instilled with bleomycin (B), 3) exposed to tobacco smoke for 6 wk (TS), 4) bleomycin instillation plus tobacco smoke exposure for 6 wk (B+TS), and 5) tobacco smoke exposure for 6 wk and bleomycin after smoking (TS/B). Guinea pigs receiving bleomycin and tobacco smoke exposure exhibited higher fibrotic lesions including a significant increase in the number of positive alpha-smooth muscle actin cells compared with bleomycin alone (B+TS, 3.4 +/- 1.2%; TS/B, 3.7 +/- 1.5%; B, 2.3 +/- 1.5%; P < 0.01). However, only the TS/B group reached a significant increase in lung collagen compared with the bleomycin group (TS/B, 3.5 +/- 0.7; B +/- TS, 2.9 +/- 0.4; B, 2.4 +/- 0.2 mg hydroxyproline/lung; P < 0.01). Bronchoalveolar lavage (BAL) from TS/B showed an increased number of eosinophils and higher levels of IL-4 and tissue inhibitor of metalloproteinase-2 (P < 0.01 for all comparisons) and induced a significant increase in fibroblast proliferation (P < 0.05). Importantly, smoke exposure alone induced an increase in BAL neutrophils, matrix metalloproteinase-9, and fibroblast proliferation compared with controls, suggesting that tobacco smoke creates a profibrotic milieu that may contribute to the increased bleomycin-induced fibrosis.

Progressive adult-onset emphysema in transgenic mice expressing human MMP-1 in the lung

Mice with lung-specific expression of human matrix metalloproteinase-1 (MMP-1) develop emphysematous changes similar to those seen in smoking-induced emphysema in humans. Morphometric analyses of three transgenic lines [homozygous colony (Col) 34, Col 50, and Col 64] with varying temporal expression of MMP-1 were undertaken to determine the validity of this animal as a model of adult-onset emphysema. Line 50 mice, which have early expression of MMP-1 (14 days postconception), exhibited morphometric changes by 5 days of age. In contrast, homozygous line 34 and 64 with delayed expression (birth and 2 wk of age) were normal up until 4 wk of age when progressive changes in their mean linear intercept were first noted. In contrast, heterozygous mice from line 34 with lower transgene expression did not develop emphysema until 1 yr of age. The changes in mean linear intercept coincided with an increase in lung compliance. Emphysema in these mice was associated with decreased immunostaining for type III collagen within the alveolar septa. This study provides evidence that MMP-1 induces progressive adult-onset emphysema by the selective degradation of type III collagen within the alveolar wall.

Macrophage metalloelastase mediates acute cigarette smoke-induced inflammation via tumor necrosis factor-alpha release

The cells and proteases that mediate cigarette smoke-induced emphysema are controversial, with evidence favoring either neutrophils and neutrophil-derived serine proteases or macrophages and macrophage-derived metalloproteases as the important effectors. We recently reported that both macrophage metalloelastase (MMP-12) and neutrophils are required for acute cigarette smoke-induced connective tissue breakdown, the precursor of emphysema. Here we show how these disparate observations can be linked. Both wild-type (MMP-12 +/+) mice and mice lacking MMP-12 (MMP-12 -/-) demonstrated rapid increases in whole-lung nuclear factor-kappaB activation and gene expression of proinflammatory cytokines after cigarette smoke exposure, indicating that a lack of MMP-12 does not produce a global failure to upregulate inflammatory mediators. However, only MMP-12 +/+ mice demonstrated increased whole-lung tumor necrosis factor-alpha (TNF-alpha) protein or release of TNF-alpha from cultured alveolar macrophages exposed to smoke in vitro. Levels of whole-lung E-selectin, an endothelial activation marker, were increased in only MMP-12 +/+ mice. These findings suggest that, acutely, MMP-12 mediates smoke-induced inflammation by releasing TNF-alpha from macrophages, with subsequent endothelial activation, neutrophil influx, and proteolytic matrix breakdown caused by neutrophil-derived proteases. TNF-alpha release may be a general mechanism whereby metalloproteases drive cigarette smoke-induced inflammation.

Acute cigarette smoke-induced connective tissue breakdown requires both neutrophils and macrophage metalloelastase in mice

The cells/proteases responsible for the development of smoke-induced emphysema is an area of intense investigation. Mice with knockout of macrophage metalloelastase genes (MME(-/-)) do not develop emphysema after smoke exposure, but we also observed that neutrophils (PMN) in lavage appeared to be a requirement for acute connective tissue breakdown. In this study we exposed mice to cigarette smoke and examined lavage PMN, macrophages (MAC), desmosine (DES, a measure of elastin breakdown) and hydroxyproline (HP, a measure of collagen breakdown) 24 h afterwards. MME(+/+) mice exposed to smoke showed elevations in PMN, DES, and HP, but no elevations were seen in MME-deficient mice. Both PMN influx and increased levels of DES/HP could be restored by administering MAC from MME(+/+) mice to MME-deficient mice and then exposing them to smoke. RS113456, a metalloprotease inhibitor, also prevented PMN influx and connective tissue breakdown. Western blots against mouse alpha(1)-antitrypsin (alpha(1)AT) showed that alpha(1)AT was not protected in MME-deficient mice, nor by administration of RS113456. We conclude that, in mice, acute smoke-induced connective tissue breakdown, the precursor to emphysema, requires both PMN and MME, that PMN influx appears to be secondary to MAC activation, and that this process initially does not involve protection of alpha(1)AT from metalloprotease attack.

Spontaneous air space enlargement in the lungs of mice lacking tissue inhibitor of metalloproteinases-3 (TIMP-3)

Tissue inhibitors of metalloproteinases regulate ECM degradation by matrix metalloproteinases (MMPs). We have developed a mouse line deficient for tissue inhibitor of metalloproteinases-3 (TIMP-3), the only TIMP known to reside within the ECM. Homozygous Timp-3-null animals develop spontaneous air space enlargement in the lung that is evident at 2 weeks after birth and progresses with age of the animal. As early as 13 months of age animals become moribund. Lung function, measured by carbon monoxide uptake, is impaired in aged null animals. Lungs from aged null animals have reduced abundance of collagen, enhanced degradation of collagen in the peribronchiolar space, and disorganization of collagen fibrils in the alveolar interstitium, but no increase in inflammatory cell infiltration or evidence of fibrosis in comparison with controls. Using in situ zymography, we show that lungs from aged null animals have heightened MMP activity over wild-type and heterozygotic animals. Finally, TIMP-3-null fibroblast cultures demonstrate enhanced destruction of ECM molecules in vitro. We propose that the deletion of TIMP-3 results in a shift of the TIMP/MMP balance in the lung to favor ECM degradation, culminating in incapacitating illness and a shorter life span.

The role of collagenase in emphysema

The extracellular matrix is essential for the integrity of the lung and when disrupted can lead to the architectural changes seen in emphysema. The etiology of emphysema is believed to be due to an imbalance in the proteases and antiproteases within the lung. Studies have focused on elastolytic enzymes as the primary agents in disease pathogenesis, however, recent data suggest that collagenases may also be involved in the destruction of lung tissue in emphysema. It is hoped that this expanded understanding of the pathophysiology of emphysema will lead to improved therapy in the treatment of the disease.

Cloning and expression of guinea pig TIMP-2. Expression in normal and hyperoxic lung injury

Tissue inhibitors of metalloproteinases (TIMPs) play a key regulatory role in extracellular matrix remodeling. By screening a lung library with a human TIMP-2 cDNA probe, we have isolated the cDNA corresponding to guinea pig TIMP-2. The 3.5-kb cDNA presents an open reading frame that predicts a protein of 220 amino acids showing 97.2, 96.8, 97.2, and 77.3% overall identity with human, mouse, rat, and chicken TIMP-2, respectively. Guinea pig TIMP-2 cDNA was expressed in CHO-K1 cells, showing a protein with the expected molecular weight and activity. Northern blot analysis revealed TIMP-2 expression in brain, kidney, intestine, spleen, heart, and lung. Transforming growth factor-beta downregulated TIMP-2 mRNA in guinea pig lung fibroblasts, whereas a variety of other stimuli showed no effect. In normal and hyperoxia-exposed lungs, TIMP-2 mRNA was mainly localized in alveolar macrophages and epithelial cells. No quantitative differences were found by Northern blot. These results confirm that TIMP-2 is highly conserved in mammals and largely expressed in lungs.

Gelatinases A and B are up-regulated in rat lungs by subacute hyperoxia: pathogenetic implications

Subacute hyperoxia may cause basement membrane disruption and subsequent fibrosis. To test the role of extracellular matrix degradation in hyperoxic damage, we analyzed the expression of gelatinases A and B and tissue inhibitors of metalloproteinases (TIMP)-1 and TIMP-2 in rats exposed to 85% O2. Oxygen-exposed rats were studied at 1, 3, 5, and 7 days, and compared with air-breathing rats. Lung mRNAs assayed by Northern and in situ hybridization showed an up-regulation of lung gelatinases A and B from the 3rd day on. Gelatinase A was localized in alveolar macrophages and in interstitial and alveolar epithelial cells. Gelatinase B mRNA and protein were localized in macrophages and bronchiolar and alveolar epithelial cells. Increased gelatinase A and B activities were demonstrated in bronchoalveolar lavage. TIMP-1 and TIMP-2 were constitutively expressed, and only TIMP-1 displayed a moderate increase with hyperoxia. To elucidate transcriptional mechanisms for increased gelatinase B expression after hyperoxia, nuclear transcription factor-kappabeta activation was explored. Oxidative stress significantly increased the lung expression of nuclear transcription factor-kappabeta (p65) protein, and nuclear transcription factor-kappabeta activation and increased levels of gelatinases A and B were found in isolated type II alveolar cells obtained from hyperoxic rats. Conceivably, subacute hyperoxia induces excessive gelatinase activity, which may contribute to lung damage.

Effect of exposure of guinea pigs to cigarette smoke on elastolytic activity of pulmonary macrophages

STUDY OBJECTIVE

To determine the effect of exposure to cigarette smoke on the elastolytic activity of guinea pigs' alveolar macrophages (AMs), and to compare elastolytic activity of AMs obtained by BAL with that of lung macrophages (LMs) obtained from minced lung tissue.

METHODS

AMs were obtained by BAL from seven adult guinea pigs exposed to cigarette smoke for 5 d/wk during 6 weeks, as well as from age-matched control guinea pigs. From each animal, one lung was used to obtain LMs by mincing and teasing the lung, followed by enzymatic digestion and isolation of mononuclear cells by Hypaque-Ficoll separation. The other lung was inflated and fixed to quantitate emphysema by the destructive index (DI). Elastolytic activity (microgram of elastin degraded by 10(6) macrophages) was determined at 24, 48, and 72 h, by culturing AMs and LMs (1 x 10(6) cells in 1 mL of medium) in 3H-elastin-coated wells.

RESULTS

In animals exposed to cigarette smoke, the total number of BAL cells (8.6+/-2.1 x 10(6)) and DI (21.8+/-8.1) were significantly higher than in nonexposed animals (6.4+/-1.8 x 10(6), p<0.05 for cells, and 12.1+/-4.1, p<0.01 for DI). Elastolytic activity of AMs from smoke-exposed guinea pigs was significantly higher at 24, 48, and 72 h than elastolytic activity of AMs from control animals (19.0+/-9.4 vs 10.0+/-5.3, p<0.05 at 72 h). Likewise, elastolytic activity of LMs was significantly higher in exposed than nonexposed guinea pigs (11.8+/-7.7 vs 7.4+/-5.0 at 72 h, p<0.05). Elastolytic activity of LMs was not significantly different from elastolytic activity of AMs, both in exposed guinea pigs (11.8+/-7.7 vs 19.0+/-9.4 at 72 h) and nonexposed animals (7.4+/-5.0 vs 10.0+/-5.3 at 72 h).

CONCLUSIONS

These results indicate that elastolytic activity of both AMs and LMs of guinea pigs increases significantly after exposure to cigarette smoke and that AMs and LMs have similar elastolytic activities.