Pitfalls in antiprotease therapy of emphysema

Z α1-antitrypsin confers a proinflammatory phenotype that contributes to chronic obstructive pulmonary disease

RATIONALE

Severe α1-antitrypsin deficiency caused by the Z variant (Glu342Lys; ZZ-AT) is a well-known genetic cause for emphysema. Although severe lack of antiproteinase protection is the critical etiologic factor for ZZ-AT-associated chronic obstructive pulmonary disease (COPD), some reports have suggested enhanced lung inflammation as a factor in ZZ-AT homozygotes.

OBJECTIVES

To provide molecular characterization of inflammation in ZZ-AT.

METHODS

Inflammatory cell and cytokine profile (nuclear factor-κB, IL-6, tumor necrosis factor-α), intracellular polymerization of Z-AT, and endoplasmic reticulum (ER) stress markers (protein kinase RNA-like ER kinase, activator transcription factor 4) were assessed in transgenic mice and transfected cells in response to cigarette smoke, and in explanted lungs from ZZ and MM individuals with severe COPD.

MEASUREMENTS AND MAIN RESULTS

Compared with M-AT, transgenic Z-AT mice lungs exposed to cigarette smoke had higher levels of pulmonary cytokines, neutrophils, and macrophages and an exaggerated ER stress. Similarly, the ER overload response was greater in lungs from ZZ-AT homozygotes with COPD, and was particularly found in pulmonary epithelial cells. Cigarette smoke increased intracellular Z-AT polymers, ER overload response, and proinflammatory cytokine release in Z-AT-expressing pulmonary epithelial cells, which could be prevented with an inhibitor of polymerization, an antioxidant, and an inhibitor of protein kinase RNA-like ER kinase.

CONCLUSIONS

We show here that aggregation of intracellular mutant Z-AT invokes a specific deleterious cellular inflammatory phenotype in COPD. Oxidant-induced intracellular polymerization of Z-AT in epithelial cells causes ER stress, and promotes excess cytokine and cellular inflammation. This pathway is likely to contribute to the development of COPD in ZZ-AT homozygotes, and therefore merits further investigation.

IL-18 induces emphysema and airway and vascular remodeling via IFN-γ, IL-17A, and IL-13

RATIONALE

Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation, alveolar destruction, and airway and vascular remodeling. However, the mechanisms that lead to these diverse alterations have not been defined.

OBJECTIVES

We hypothesized that IL-18 plays a central role in the pathogenesis of these lesions.

METHODS

We generated and characterized lung-specific, inducible IL-18 transgenic mice.

MEASUREMENTS AND MAIN RESULTS

Here we demonstrate that the expression of IL-18 in the mature murine lung induces inflammation that is associated with the accumulation of CD4(+), CD8(+), CD19(+), and NK1.1(+) cells; emphysema; mucus metaplasia; airway fibrosis; vascular remodeling; and right ventricle cardiac hypertrophy. We also demonstrate that IL-18 induces type 1, type 2, and type 17 cytokines with IFN-γ-inhibiting macrophage, lymphocyte, and eosinophil accumulation while stimulating alveolar destruction and genes associated with cell cytotoxicity and IL-13 and IL-17A inducing mucus metaplasia, airway fibrosis, and vascular remodeling. We also highlight interactions between these responses with IL-18 inducing IL-13 via an IL-17A-dependent mechanism and the type 1 and type17/type 2 responses counterregulating each another.

CONCLUSIONS

These studies define the spectrum of inflammatory, parenchymal, airway, and vascular alterations that are induced by pulmonary IL-18; highlight the similarities between these responses and the lesions in COPD; and define the selective roles that type 1, type 2, and type 17 responses play in the generation of IL-18-induced pathologies.

Proteases and emphysema

PURPOSE OF REVIEW

The protease-antiprotease theory of emphysema is widely accepted, but exactly which cells/proteases play a role continues to be a controversial subject.

RECENT FINDINGS

Reports in humans show increased metalloproteinase activity in emphysema, but the exact role of metalloproteinases remains unclear. In laboratory animals, neutrophils turn out to be crucial, and neutrophil influx correlates well with measurements of matrix destruction. Neutrophil influx is linked to metalloproteinase activity, and in mice MMP12-induced release of tumor necrosis factor-alpha drives neutrophil infiltration. Serine elastase inhibitors, knockout of neutrophil elastase, and interference with tumor necrosis factor-alpha signaling all provide significant protection against smoke-induced emphysema, but metalloproteinase inhibitors may yield greater protection. In genetically modified mice, emphysema can be produced by overexpression of mediators such as tumor necrosis factor-alpha, interferon-gamma, or interleukin-13, and these models show evidence of metalloproteinase, cysteine protease, and serine protease attack with complicated relationships among these mediators. Collagen breakdown also appears to be important in the genesis of emphysema. Pro-apoptotic agents produce emphysema as well, possibly via an elastolytic pathway.

SUMMARY

The idea that a single protease or a single type of inflammatory cell is responsible for human emphysema is unlikely to be true; rather, there are complex interactions among proteases, and between proteases and other mediators. The problem at this time is attempting to sort out the numerous candidate effector agents and to determine which of the animal models are relevant to human disease, since there may be considerable discrepancies in the types of proteases and their roles between laboratory animals and humans. There is now good evidence from animal models that antiproteolytic therapy can be of benefit in ameliorating cigarette smoke-induced emphysema.

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.

Tetracycline-controlled transcriptional regulation systems: advances and application in transgenic animal modeling

Since the first tetracycline-controlled transcriptional activation system was designed nearly a decade ago, new variants, modifications, and improvements have been steadily added to this powerful set of tools for temporal control of transgene expression in mammalian systems. Tetracycline-based externally regulatable (Tet-based) systems have been successfully used to control the expression of numerous transgenes in cultured cells and in whole organisms, especially in mice. The application of these systems has provided invaluable insights into the function and regulation of a variety of genes under physiological and pathological conditions. Because of the favorable characteristics of the inducing agent doxycycline and the efficiency and effectiveness of the operating mechanism, the Tet-based systems have attracted substantial attention from the transgenic research community and are rapidly gaining popularity. The original tetracycline-controlled transcriptional activator (tTA) is a regulator with tight control of target gene expression and a broad range of inducibility. The reverse tetracycline-controlled transcriptional activator (rtTA) activates the responsive elements only in the presence of doxycycline, giving a convenient control over the target transgene. The recently developed tetracycline-controlled transcriptional silencer (tTS) has been successfully used in cultured cells and in transgenic mice. In combination with rtTA, tTS actively suppresses background expression or "leakiness" without impeding the inducibility of the target gene, providing a true "On/Off" transgenic switch. New variants of Tet-based regulators with improved features are still emerging and the utilities of these systems are constantly being tested.

Interferon gamma induction of pulmonary emphysema in the adult murine lung

Chronic inflammation containing CD8(+) lymphocytes, neutrophils, and macrophages, and pulmonary emphysema coexist in lungs from patients with chronic obstructive pulmonary disease. Although this inflammatory response is believed to cause the remodeling that is seen in these tissues, the mechanism(s) by which inflammation causes emphysema have not been defined. Here we demonstrate that interferon gamma (IFN-gamma), a prominent product of CD8(+) cells, causes emphysema with alveolar enlargement, enhanced lung volumes, enhanced pulmonary compliance, and macrophage- and neutrophil-rich inflammation when inducibly targeted, in a transgenic fashion, to the adult murine lung. Prominent protease and antiprotease alterations were also noted in these mice. They included the induction and activation of matrix metalloproteinase (MMP)-12 and cathepsins B, H, D, S, and L, the elaboration of MMP-9, and the selective inhibition of secretory leukocyte proteinase inhibitor. IFN-gamma causes emphysema and alterations in pulmonary protease/antiprotease balance when expressed in pulmonary tissues.

Inducible targeting of IL-13 to the adult lung causes matrix metalloproteinase- and cathepsin-dependent emphysema

Cigarette smoke exposure is the major cause of chronic obstructive pulmonary disease (COPD). However, only a minority of smokers develop significant COPD, and patients with asthma or asthma-like airway hyperresponsiveness or eosinophilia experience accelerated loss of lung function after cigarette smoke exposure. Pulmonary inflammation is a characteristic feature of lungs from patients with COPD. Surprisingly, the mediators of this inflammation and their contributions to the pathogenesis and varied natural history of COPD are not well defined. Here we show that IL-13, a critical cytokine in asthma, causes emphysema with enhanced lung volumes and compliance, mucus metaplasia, and inflammation, when inducibly overexpressed in the adult murine lung. MMP-2, -9, -12, -13, and -14 and cathepsins B, S, L, H, and K were induced by IL-13 in this setting. In addition, treatment with MMP or cysteine proteinase antagonists significantly decreased the emphysema and inflammation, but not the mucus in these animals. These studies demonstrate that IL-13 is a potent stimulator of MMP and cathepsin-based proteolytic pathways in the lung. They also demonstrate that IL-13 causes emphysema via a MMP- and cathepsin-dependent mechanism(s) and highlight common mechanisms that may underlie COPD and asthma.

Acute cigarette smoke-induced connective tissue breakdown is mediated by neutrophils and prevented by alpha1-antitrypsin

Recent studies have suggested that macrophage-derived metalloproteases are the critical mediators of cigarette smoke-induced emphysema, in contrast to earlier hypotheses that this process was mediated by neutrophil elastase. To determine whether smoke can acutely induce connective tissue breakdown in the lung and to examine the mediators of this process, we exposed C57-BL/6 mice to whole cigarette smoke and used high-performance liquid chromatography to examine lavage fluid levels of desmosine (DES), a marker of elastin breakdown, and hydroxyproline (HP), a marker of collagen breakdown. Smoke produced a dose-response increase in lavage neutrophils, DES, and HP, but not lavage macrophages (MACs). This effect was evident by 6 h after exposure to two cigarettes. Pretreatment with an antibody against polymorphonuclear leukocytes (PMNs) reduced lavage PMNs to undetectable levels after smoke exposure, did not affect MAC numbers, and prevented increases in lavage DES and HP. Intraperitoneal injection of a commercial human alpha1-antitrypsin (alpha1AT) 24 h before smoke exposure increased serum alpha1AT levels approximately 3-fold and completely abolished smoke-induced connective tissue breakdown as well as the increase in lavage PMNs, again without affecting MAC numbers. We conclude that in this model cigarette smoke can acutely induce connective tissue breakdown and that this effect is mediated by neutrophil-derived serine proteases, most likely neutrophil elastase. Exogenous alpha1AT is protective and appears to inhibit both matrix degradation and PMN influx, suggesting that alpha1AT has anti-inflammatory as well as antiproteolytic effects in this system.

Serine proteinase inhibitor therapy in alpha(1)-antitrypsin inhibitor deficiency and cystic fibrosis

Proteinase-antiproteinase imbalances are recognized in several diseases including the two most common lethal hereditary disorders of white populations, alpha(1)-antitrypsin (alpha(1)-AT) deficiency and cystic fibrosis (CF). In alpha(1)-AT deficiency, the type Z variant of alpha(1)-AT forms polymers in the endoplasmic reticulum of hepatocytes resulting in liver disease in childhood. The block in alpha(1)-AT processing in hepatocytes significantly reduces levels of circulating alpha(1)-AT. This may lead in young adults to panacinar emphysema due to insufficient protection of the lower respiratory tract from neutrophil elastase, permitting progressive destruction of the alveoli. In CF, chronic bacterial lung infections due to impaired mucociliary clearance lead to a vigorous influx of neutrophils in the airways. Released levels of neutrophil serine proteinases, particularly elastase, exceed the antiproteinase capacity of endogenous serine proteinase inhibitors in the airways. Progressive proteolytic impairment of multiple defense pathways in addition to endobronchial obstruction and airway wall destruction are thought to be responsible for the reduced life expectancy in CF patients. Strategies to augment the antiproteinase defenses in the airways of patients with severe alpha(1)-AT deficiency or CF include the intravenous or aerosol administration of serine proteinase inhibitors. Studies in both patient groups using plasma-derived or transgenic alpha(1)-AT, recombinant secretory leukoprotease inhibitor or synthetic elastase inhibitors show promising results concerning drug safety and efficacy.

Reduced capacity to inhibit elastase in abdominal aortic aneurysm

BACKGROUND

Loss of elastin in the aortic wall is an early event in abdominal aortic aneurysm (AAA). An imbalance in the protease-antiprotease system is proposed to be one of the factors that promote connective tissue destruction. We hypothesize that plasma from AAA patients will have a reduced inhibitory capacity in comparison to normal controls.

MATERIALS AND METHODS

Using an assay we developed, plasma (10 microliters), collected from AAA patients (n = 14) and normal controls (n = 13), was added to the elastase inhibition assay containing succinylated elastin substrate. The reaction was initiated with 13.9 units porcine pancreatic elastase (PPE). Elastase activity in the presence and absence of plasma was compared. Plasma elastase was also determined using the Merck PMN-elastase kit.

RESULTS

The relative activity of exogenous elastase (%) in the presence of AAA plasma (n = 14, mean age 73.4 years +/- 1.7 SEM) was 42.59% +/- 4.3 SEM, while that in the presence of control plasma (n = 13, mean age 73.9 years +/- 2.1 SEM) was 10.23% +/- 2.1 SEM (P < 0.0001). Analysis of plasma elastase (microgram/L) indicated that there was no significant difference between normal (n = 9, 207.33 microgram/L +/- 58.67 SEM) and AAA (n = 9, 145.34 microgram/L +/- 29.54 SEM) (P = 0.359).

CONCLUSION

There is a significant reduction in the plasma inhibitory capacity of elastase in AAA patients in comparison to normal controls, though plasma elastase level was not significantly different. The data presented here give experimental evidence to the protease-antiprotease imbalance in AAA patient plasma and may lead to the development of a measurable parameter to monitor AAA.

Role of neutrophils and alpha1-antitrypsin in coal- and silica-induced connective tissue breakdown

Mineral dusts produce emphysema, and administration of dust to rats results in the rapid appearance of desmosine and hydroxyproline in lavage fluid, confirming that dusts directly induce connective tissue breakdown. To examine the role of neutrophils and alpha1-antitrypsin (alpha1-AT) in this process, we instilled silica or coal into normal rats or rats that had been pretreated with antiserum against neutrophils. One day after dust exposure, lavage fluid neutrophils and desmosine and hydroxyproline levels were all elevated; treatment with antiserum against neutrophils reduced neutrophils by 75%, desmosine by 40-50%, and hydroxyproline by 25%. By 7 days, lavage fluid neutrophils and desmosine level had decreased, whereas macrophages and hydroxyproline level had increased. By ELISA analysis, lavage fluid alpha1-AT levels were increased four- to eightfold at both times. On Western blot, some of the alpha1-AT appeared as degraded fragments, and by HPLC analysis, 5-10% of the methionine residues were oxidized. At both times, lavage fluid exhibited considerably elevated serine elastase inhibitory capacity and also showed elevations in metalloelastase activity. We conclude that, in this model, connective tissue breakdown is initially driven largely by neutrophil-derived proteases and that markedly elevated levels of functional alpha1-AT do not prevent breakdown, thus providing in vivo support for the concept of quantum proteolysis proposed by Liou and Campbell (T. G. Liou and E. J. Campbell. Biochemistry 34: 16171-16177, 1995). Macrophage-derived proteases may be of increasing importance over time, especially in coal-treated animals.

Neutrophils and low-grade inflammation in the seemingly normal aging human lung

Lung function deteriorates with age and is associated with elastin loss, loss of elastic recoil and decline in diffusing capacity for carbon monoxide. To determine whether increased numbers of neutrophils can be found in the lower respiratory tract in healthy, clinically normal individuals who are more advanced in age, we performed bronchoalveolar lavage (BAL) on individuals in three discontinuous age groups (Group I, 19-36 years; Group II, 45-55 years; Group III, 64 83 years). We found that neutrophils were increased in many individuals in Group III compared to Group I. The neutrophil cell differential count was 1.44+/-0.18% (mean+/-S.E.M.) for Group I versus 3.88+/-0.81% for Group III (P < 0.01) and neutrophils x 10(3)/ml BAL fluid was 1.7+/-0.2 versus 7.2+/-1.7 for Group I versus Group III, respectively (P < 0.01). Similarly, interleukin-8 (IL-8) (8.5+/-1.7 vs 36.8+/-9.4 pg/ml, P < 0.01) and neutrophil elastase (NE) complexed to alpha1-antiprotease (1.2+/-0.1 vs 16.6+/-7.1 ng/ml, P < 0.02) were significantly elevated in the oldest versus youngest age group, although alpha1-antiprotease (582+/-86 vs 1178+/-148 ng/ml, P < 0.01) and elastase inhibitory capacity (EIC) (8.1+/-1.3 vs 17.7+/-1.9 micromol/ml, P < 0.01) were also significantly increased in the oldest age group. This cross-sectional investigation suggests that low-grade inflammation exists in the air spaces of many clinically normal, older individuals.

Patient-administered sequential spirometry in healthy volunteers and patients with alpha 1-antitrypsin deficiency

The launching of cheap, pocket-sized spirometers, with data storage capability, has made patient-administered sequential spirometry (PASS) an attractive method of monitoring ventilatory capacity. At present, little information is available on the quality of PASS, compared to laboratory spirometry. The aim of this study was to investigate whether patients could perform PASS without loss of reliability and reproducibility as compared with traditional laboratory spirometry. Ten healthy volunteers performed spirometry for 1 month and 10 emphysematous patients with alpha 1-antitrypsin deficiency (type PiZ) performed spirometry twice daily for up to 2 yr. To fulfil Good Clinical Practice criteria on full data documentation, a traditional direct recording spirometer, the Vitalograph R-model, was used. A decompression device was used for calibration and a 3.8% annual drift in volume registration was noted. This drift was largest for the first year. After training, all patients were able to perform unsupervised spirometry, producing technically correct forced expiratory curves. Reproducibility of FEV1 and FVC obtained by PASS was found to be as good as for laboratory spirometry. After adjustment for the diurnal variation, the residual variation of FEV1 was 2.5% (range 1.6-4.2%) for healthy volunteers and 5.6% (range 4.2-7.7%) for emphysematous patients. Forced vital capacity showed the same pattern. In conclusion, PASS is possible in highly motivated individuals without loss of reliability and reproducibility when compared to laboratory spirometry.