Relationships of MMP-9 and TIMP-1 proteins with chronic obstructive pulmonary disease risk: A systematic review and meta-analysis.

BACKGROUND: We performed this meta-analysis in order to collect all the relevant studies to clarify the correlations of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) with chronic obstructive pulmonary disease (COPD).
MATERIALS AND METHODS: After a literature search in electronic databases, pertinent case-control studies investigating the correlations of MMP-9 and TIMP-1 protein expressions within a COPD setting were enrolled based on our strict inclusion and exclusion criteria. We used key words such as "chronic obstructive pulmonary disease," "COPD" or "COAD" or "chronic obstructive airway disease" and "matrix metalloproteinases" or "MMPs" to make a searching strategy in this study. STATA software (version 12.0, Stata Corporation, College Station, TX, USA) was utilized for statistical analysis.
RESULTS: A total of 20 studies were enrolled into this meta-analysis including 923 COPD patients and 641 healthy controls. The findings of this meta-analysis revealed that serum expression levels of MMP-9 and TIMP-1 protein in COPD patients were higher than those of healthy controls (MMP-9: SMD = 1.44, 95%CI = 0.85 ~ 2.04, P < 0.001; TIMP-1: SMD = 3.53, 95% CI = 2.31 ~ 4.75, P < 0.001). Subgroup analysis based on ethnicity revealed that both Caucasians and Asian COPD patients exhibited higher MMP-9 and TIMP-1 serum protein levels than healthy controls (MMP-9: SMD = 0.81, 95%CI = 0.15~1.48, P = 0.016; TIMP-1: SMD = 4.43, 95%CI = 1.98 ~ 6.87, P = 0.016) and in Caucasians (MMP-9: SMD = 2.30, 95%CI = 1.21 ~ 3.38, P < 0.001; TIMP-1: SMD = 2.86, 95%CI = 1.47 ~ 4.24, P < 0.001).
CONCLUSION: The result of this meta-analysis indicates that elevated levels of MMP-9 and TIMP-1 proteins may be correlated with the pathogenesis of COPD, and the two proteins may represent important biological markers for the early diagnosis of COPD.

INTRODUCTION

Chronic obstructive pulmonary disease (COPD), a type of obstructive lung disease, is characterized by chronic inflammation throughout the parenchyma, airways and pulmonary vasculature.[12] COPD is ranked as the fourth leading cause of death and effects more than 200 million people worldwide.[3] According to the statistics, the number of deaths from COPD between 1990 and 2010 has decreased slightly from 3.1 million to 2.9 million.[4] In the United States, there has been a pronounced increase in the mortality rate in women compared with a modest increase in men.[5] Host factors and environmental exposures are the major risk factors for COPD, and this disease frequently results from an interaction between these factors.[67] Host factors, such as a rare hereditary deficiency of alpha1-antitrypsin, and environmental factors such as tobacco smoke, indoor/outdoor air pollution and heavy exposure to occupational dusts and chemicals contribute to COPD pathogenesis.[89] It has been recognized that patients with COPD usually suffer from concurrent comorbidities, such as diabetes, lung cancer, cardiovascular and cerebrovascular diseases.[10] Numerous studies have indicated that COPD can be prevented by cessation of smoking and improving indoor and outdoor air quality.[111213] COPD patients also have treatment options based on the state of the disease, including vaccinations, rehabilitation, and inhaled bronchodilators and steroids, long-term oxygen therapy as well as lung transplantation.[141516] Recently, study has shown that matrix metalloproteinase (MMPs) and their inhibitors play a central role in lung remodeling in COPD.[17]

MMPs refer to a family of over twenty conserved and zinc-dependent endopeptidases, which modulates the cell proliferation, differentiation due to their enzymatic activities in turnover and degradation of extracellular matrix (ECM).[18] MMP-9 is one of the most important members of MMPs family, and is variously known as 92 kDa type IV collagenase, 92 kDa gelatinase or gelatinase B (GELB).[1920] It is well established that MMP-9, as an elastolytic endopeptidase produced in large quantities by activated macrophages and inflammatory cells, which may play a role in the development of human pulmonary emphysema.[21] MMP-9 is overexpressed in many solid tumors and it enhances the ability of tumor cell invasion and metastasis.[22] Tissue inhibitor of metalloproteinases consists of a family of 4 secreted proteins (TIMP 1-4), which bind MMPs in a ratio of 1: 1 manner to inhibit their proteolytic activity.[2324] TIMP-1 is as a natural inhibitor of MMPs and is a glycoprotein expressed in multiple tissues in many organisms.[25] In addition to its inhibitory role, TIMP-1 is able to promote cell proliferation and inhibit apoptosis as well as regulate cell growth in a wide range of cell types.[26] Accumulated evidence suggested that MMP-9 is inhibited by TIMP-1 and an imbalance in the MMP-9/TIMP-1 ratio could be involved in COPD pathogenesis.[27] However, this theory is contradicted by other studies.[2829] We conducted a meta-analysis based study to investigate the correlations between MMP-9 and TIMP-1 protein expressions with COPD.

MATERIALS AND METHODS

Literature search

Literatures were comprehensively screened for studies that explored the correlations of MMP-9 and TIMP-1 protein expression with COPD by utilizing the following electronic databases: PubMed, EBSCO, Ovid, Medline, Springerlink, Wiley Online Library, Web of Science, Chinese Biomedical Database, the Chinese Journal Full-Text Database, China National Knowledge Infrastructure (CNKI), the WANFANG Database and the Weipu Journal Database (since inception to October 1st, 2014). Additional pertinent literatures were obtained by manual search. Likewise, the combination of key words and free words was applied in the process of collecting literature with a highly efficient and sensitive searching strategy: (“pulmonary disease, chronic obstructive” or “chronic respiratory diseottom” or “COPD” or “chronic obstructive pulmonary disease” or “COAD” or “chronic obstructive airway disease” or “chronic obstructive lung disease” or “airflow obstruction, chronic” or “pulmonary emphysema”) and (“matrix metalloproteinases” or “metalloproteinases, matrix” or “MMPs” or “MMP”).

Inclusion and exclusion criteria

The following inclusion criteria were applied to published articles for the present studies:

Study types should be case-control study concerning the correlation of MMP-9 and TIMP-1 protein expression with COPD;

Subjects should include COPD patients and healthy controls;

Detection method should be enzyme-linked immunosorbent assay (ELISA);

End outcomes should include the expressions of MMP-9 and TIMP-1 protein in serum.

Only the studies with the largest sample sizes or latest study were considered when the extracted studies were published by the same authors, using the same case materials. The corresponding exclusion criteria were:

Reviews, letters, non-human research and literature duplications;

Studies unrelated to the research theme;

Lack of document data integrity;

Non-English and non-Chinese studies.

Data extraction and quality assessment

Two investigators independently carried out data extraction on the basis of a predefined form. The main data information including first author, publication time, country, language, ethnicity, disease type, detection method, the number of cases and controls, age, gender, sample source, sample size, expressions of MMP-9 and TIMP-1 protein were displayed in the current meta-analysis. Any disputes appeared in the process of data extraction was resolved through discussion with the multiple researchers. The quality of enrolled studies was assessed by critical appraisal skill program (CASP) criteria by two independent investigators (http://www.casp-uk.net/). The CASP criteria are scored as follows: The study address a clearly focused issue (CASP01); the research problem is appropriate and the research design answers the research problem (CASP02); the cases recruited in an accep way (CASP03); the controls selected in an accep way (CASP04); the measurement for exposure factors is accurate to minimize bias (CASP05); the study controls other important confounding factors (CASP06); the research result is complete (CASP07); the research result is precise (CASP08); the research result is reliable (CASP09); the research result is applicable to the local population (CASP10); the research result fit with other available evidence (CASP11).

Statistical analysis

The STATA statistical software (Version 12.0, Stata Corporation, College Station, TX, USA) was used in the current meta-analysis. The correlations of MMP-9 and TIMP-1 protein expressions with COPD were estimated after the calculation of the summary standard mean difference (SMD) with 95% confidence interval (95%CI). Z test was employed to detect the significance of overall effect size.[30] Heterogeneity among studies was evaluated by the Cochran's Q-statistic (P < 0.05 was considered significant) and I2 test (0%, no heterogeneity; 100%, maximal heterogeneity).[3132] Random effects model was used if there was considerable heterogeneity (P < 0.05 or I2 > 50%), otherwise fixed effects model was employed.[33] Univariate and multivariate meta-regression analysis were utilized to identify potential sources of heterogeneity, and further confirmed by means of Monte Carlo method.[3134] One-way sensitivity analysis was performed to evaluate whether removal of one single study could influence the overall outcomes. The Contuor-enhanced funnel plot and Egger's linear regression test was adopted to assess publication bias to ensure the reliability of the results. All tests were two-sided, and P < 0.05 indicating a significant difference.[35]

RESULTS

Baseline characteristics of included studies

A total of 667 articles, which studied the correlations between MMP-9 protein expression and COPD or between TIMP-1 protein expression and COPD, were initially reviewed. After excluded duplicates (n = 30), non-human studies (n = 203), letters, reviews, meta-analysis (n = 8) and unrelated topic (n = 355), 71 full-text articles remained. Twenty studies ultimately satisfied the inclusion criteria after we eliminated studies that were not case-control study (n = 11), studies not associated with MMP-9 or TIMP-1 (n = 23), studies unrelated to COPD (n = 16), and those that had insufficient information (n = 1).[2736373839404142434445464748495051525354] To compare the differences in MMP-9 and TIMP-1 protein expression between COPD patients and the healthy controls, 923 patients with COPD and 641 healthy controls were included as study subjects in this meta-analysis. All included studies were published between 2003 and 2014. Among the 20 case-control studies, 10 were performed in Asians, and another 10 were performed in Caucasians. Based on the country of the published studies, 9 studies were from China, 2 from Poland, 1 each from America, Japan, Germany, England, Mexico, Sweden, Turkey, Finland, and Czech Republic, respectively. All samples data were estimated from serum. Method for detecting MMP-9 and TIMP-1 proteins was enzyme linked immunosorbent assays (ELISA). Baseline characteristics and the quality scores of all included studies were displayed in Table 1 and Figure 1, respectively.

Table 1

Baseline characteristics of all included trails

Figure 1

Quality of all enrolled studies by critical appraisal skill program

Results of meta-analysis

Heterogeneity test revealed a significant heterogeneity among studies that compared serum MMP-9 and TIMP-1 protein expressions between COPD patients and the healthy controls (MMP-9: P < 0.001, I2 = 95.9%; TIMP-1: P < 0.001, I2 = 98.3%), and therefore a random-effects model was employed. The results of this meta-analysis suggested that the serum MMP-9 and TIMP-1 protein expressions were markedly higher in COPD patients compared with those in the healthy controls (MMP-9: SMD = 1.44, 95%CI = 0.85 ~ 2.04, P < 0.001; TIMP-1: SMD = 3.53, 95%CI = 2.31 ~ 4.75, P < 0.001) [Figure 2].

Figure 2

Forest plots of the correlation of MMP-9 with TIMP-1 and chronic obstructive pulmonary disease

Subgroup analysis based on ethnicity revealed that the serum MMP-9 and TIMP-1 protein levels in COPD patients were significantly higher than those in healthy controls in Asians (MMP-9: SMD = 0.81, 95%CI = 0.15 ~ 1.48, P = 0.016; TIMP-1: SMD = 4.43, 95%CI = 1.98 ~ 6.87, P = 0.016) and in Caucasians (MMP-9: SMD = 2.30, 95%CI = 1.21 ~ 3.38, P < 0.001; TIMP-1: SMD = 2.86, 95%CI = 1.47 ~ 4.24, P < 0.001). Additionally, as shown in Figure 3, subgroup analysis on the basis of sample size indicated that in both small sample size (n < 90) and large sample size (n > 90), the serum MMP-9 (n < 90: SMD = 1.41, 95%CI = 0.76 ~ 2.07, P < 0.001; n > 90: SMD = 1.48, 95%CI = 0.32 ~ 2.64, P = 0.012) and TIMP-1 (n < 90: SMD = 1.57, 95%CI = 0.56 ~ 2.57, P = 0.002; n > 90; SMD = 6.19, 95%CI = 3.41 ~ 8.97, P < 0.001) protein levels were markedly higher in COPD patients than those in healthy controls.

Figure 3

Forest plots for subgroup analysis investigating the correlation of MMP-9 with TIMP-1 and chronic obstructive pulmonary disease

Sensitivity analysis and publication bias

The sensitivity analysis demonstrated that any single study had no significant effect on the pooled SMDs. As shown in Figure 4, most included studies interspersed in the interval range of P less than 0.05. And P < 0.05 suggested there was publication bias among studies. The Contour-enhanced funnel plots of comparisons on MMP-9 and TIMP-1 protein expressions in serum between COPD patients and healthy controls indicated that there was publication bias (P < 0.05), which was further affirmed by Egger's test (P < 0.05) [Figure 4].

Figure 4

Sensitivity analyses and funnel plots of the correlation of MMP-9 with TIMP-1 and chronic obstructive pulmonary disease

Regression analysis

As shown in Figure 5, Tables 2 and 3, both univariate meta-regression and multivariate meta-regression analyses revealed that publication year, sample size, country, language, and ethnicity were not the source of heterogeneity among studies between serum MMP-9 protein levels and COPD.

Figure 5

Regression analyses of the correlation of MMP-9 with TIMP-1 and chronic obstructive pulmonary disease

Table 2

Meta-regression analyses of potential source of heterogeneity (MMP-9)

Table 3

Meta-regression analyses of potential source of heterogeneity (TIMP-1)

DISCUSSION

COPD is known as a progressive and incurable lung disease characterized by abnormal tissue repair, resulting in small airways fibrosis or emphysema.[55] Destruction of the ECM of the lung is a characteristic feature of COPD.[56] The MMP family members, a group of metzincin metalloproteases, function primarily extracellularly and are important in the maintenance and remodeling of tissues mainly through degradation of the ECM.[57] TIMPs, natural MMP inhibitors, control important cellular processes including proliferation, apoptosis and angiogenesis by mechanisms independent of their MMP inhibitory activity.[58] TIMP-1 and TIMP-2 are two main members that lead to pulmonary diseases with changes of alveolar structure in asthma or COPD. This balance plays an important role in optimal function while any over/under production of relevant proteinases can result in tissue damage and undesirable alterations in ECM.[59] MMPs and their inhibitors, play a central role in the lung remodeling in COPD, And their presence in the sputum and bronchoalveolar lavage are regarded as a sign of the local inflammation in COPD patients.[56] Inappropriate expression and excessive activity of several MMPs and TIMP, including MMP-9 and TIMP-1, has been implicated in the tissue destructive processes associated with chronic lung diseases including COPD.[4360]

To evaluate the roles MMP-9 and TIMP-1 in the pathogenesis of COPD, we performed a meta-analysis and uncovered that the serum MMP-9 and TIMP-1 protein levels in COPD patients were significantly higher than those in the healthy controls, suggesting that MMP-9 and TIMP-1 proteins indeed play a role in the pathogenesis of COPD through degradation of ECM. The ECM is a dynamic structure, and equilibrium between synthesis and degradation of ECM components is required for the maintenance of its homeostasis.[6162] MMP-9 is responsible for tissue remodeling and repairing by the degradation of basement membrane type IV collagen, it is released by macrophages that are derived from neutrophils and from circulating monocytes.[49] Increased MMP-9 activity can promote the degradation of alveolar wall basement membranes, and therefore plays a significant role in the development of emphysema and airway fibrosis.[63] TIMP-1 has been found as an MMP-9 activity inhibitor through binding to its precursors and active form.[64] Increased expressions of MMP-9 and TIMP-1 and alveolar macrophages trigger larger amounts of MMP-9 with greater enzymatic activity in COPD patients. The imbalances between the levels of MMP-9 and TIMP-1 might result in the aberrant ECM degradation or the accumulation of ECM proteins in pulmonary alveoli and small airway walls, which would lead to COPD.[6566]

Subgroup analyses on the basis of ethnicity and sample size indicated in Asians and Caucasians, and in small sample size and large sample size, the serum MMP-9 and TIMP-1 protein levels in COPD patients were consistently significantly higher than those in the healthy controls, further confirming the main result of this meta-analysis.

Several limitations of the present meta-analysis should be recognized. First, a potential important weakness about our included studies in meta-analysis is that the control participants are less than case group; second, some studies were excluded due to our failure to obtain original data from the communicating author third, this meta-analysis included data from Asians, Caucasians, Americans, but no studies from Africans and mixed population, consequently, our study is not representative of all ethnicities. In summary, our study revealed that the expression levels of MMP-9 and TIMP-1 protein markedly increased in serum of patients with COPD and an imbalance in the MMP-9/TIMP-1 ratio could be involved in COPD pathogenesis, suggesting MMP-9 and TIMP-1 protein could be an important biological indicator in prognosis of COPD. In the future, prospective studies with larger control participant size, more completely original data and no publication bias are needed to validate our results.

Financial support and sponsorship

This study was supported by National Natural Science Foundation of China (81470024).

Conflicts of interest

There are no conflicts of interest.

AUTHOR'S CONTRIBUTION

YL (Yangxue Li) contributed in the conception of the work, conducting the study, revising the draft, approval of the final version of the manuscript, and agreed for all aspects of the work. YL (Yang Lu), ZZ and JW contributed in conducting the study and agreed for all aspects of the work. JL and WW contributed in revising the draft, approval of the final version of the manuscript, and agreed for all aspects of the work. SL and LS contributed in the conception of the work, approval of the final version of the manuscript, and agreed for all aspects of the work.