Expression and Clinical Significance of MMP-1 and MMP-7 in Pneumonia, Pulmonary Fibrosis, and Lung Cancer

Summary

This study aims to evaluate the expression levels and clinical significance of matrix metalloproteinase-1 (MMP-1) and matrix metalloproteinase-7 (MMP-7) in patients diagnosed with pneumonia, pulmonary fibrosis, and lung cancer. The objective is to explore their potential diagnostic value and assess their relevance as non-invasive biomarkers for differentiating between these pulmonary conditions.

Abstract

This study aimed to investigate the expression levels and clinical significance of matrix metalloproteinase-1 (MMP-1) and matrix metalloproteinase-7 (MMP-7) in patients with pneumonia, pulmonary fibrosis (PF), and lung cancer (LC). A total of 136 pneumonia cases, 15 PF cases, 64 LC cases, and 47 healthy controls were retrospectively included from Shaanxi Provincial Nuclear Industry 215 Hospital between October 2023 and April 2024. Serum concentrations of MMP-1 and MMP-7 were quantified using chemiluminescence immunoassay. Positivity rates were compared across groups, and Spearman's correlation was used to examine the association between age and MMP expression. Receiver operating characteristic (ROC) analysis was performed to determine optimal cut-off values and assess diagnostic performance. Median serum MMP-1 levels were higher in the LC group (22.9 ng/mL; IQR: 11.65-30.0) and PF group (26.5 ng/mL; IQR: 14.4-30.0) compared with the pneumonia group (15.4 ng/mL; IQR: 9.34-28.75) (p < 0.05). Similarly, MMP-7 levels were elevated in the LC (4.52 ng/mL; IQR: 3.55-6.20) and PF (5.05 ng/mL; IQR: 4.00-7.44) groups compared with the pneumonia (2.35 ng/mL; IQR: 1.87-3.36) and healthy control (2.27 ng/mL; IQR: 1.88-2.81) groups (p < 0.05). Significant intergroup differences in positivity rates were observed (p < 0.05). Age was positively correlated with both MMP-1 (rs = 0.215, p < 0.001) and MMP-7 (rs = 0.531, p < 0.001), with the correlation stronger for MMP-7. No statistically significant differences were found between sexes for MMP-1 (z = -1.033, p = 0.301) or MMP-7 (z = -1.326, p = 0.185). MMP-7 demonstrated high diagnostic accuracy for LC (cutoff = 3.325 ng/mL; sensitivity = 84.4%; specificity = 97.9%) and PF (cutoff = 3.66 ng/mL; sensitivity = 80.0%; specificity = 97.9%). In contrast, the diagnostic performance of MMP-1 and MMP-7 for pneumonia was relatively limited. These findings suggest that MMP-7 may serve as a useful non-invasive biomarker for differentiating between PF and LC, while the clinical utility of MMP-1 remains limited due to low specificity.

Introduction

Mycoplasma pneumoniae is a leading pathogen of community-acquired pneumonia, with recent epidemiological trends indicating an increase in both sporadic infections and cyclical global outbreaks occurring every 2 to 6 years^1,2. While most cases are self-limiting, severe pneumonia is recognized as a potential trigger for pulmonary fibrosis (PF), a progressive interstitial lung disease characterized by alveolar epithelial injury, aberrant tissue repair, fibroblast proliferation, and extracellular matrix deposition that culminate in irreversible scarring³. A retrospective cohort study in 2019 reported that post-inflammatory PF, marked by focal fibrotic changes, was present in approximately 20.2% of cases⁴.

Pulmonary fibrosis is the most prevalent subtype of interstitial pneumonia and is associated with poor prognosis and substantial socioeconomic burden. Furthermore, its progression significantly elevates the risk of lung cancer (LC), with prior studies indicating an incidence rate between 2.7% and 48% among PF patients, markedly higher than in healthy populations^5,6. LC remains the most common malignant neoplasm and the primary cause of cancer-related mortality. Alarmingly, only 25% of cases are detected at an early stage, which severely hampers clinical management and survival outcomes^7,8. Clinically, the co-occurrence of PF and LC presents a complex diagnostic and therapeutic challenge, while the transition from pneumonia to PF is often subtle and under-recognized. Despite their severity, these pulmonary conditions currently lack effective, non-invasive biomarkers for early detection and prognosis evaluation.

Recent research has highlighted matrix metalloproteinases (MMPs) as potential biomarkers implicated in fibrotic lung diseases⁹. These zinc-dependent endopeptidases are involved in extracellular matrix degradation and the regulation of various signaling pathways. Under pathological conditions, MMPs contribute to tissue remodeling, inflammation, and tumor progression. In particular, their role in promoting invasion and metastasis in LC has been increasingly documented^10,11. Among them, MMP-1 and MMP-7 have emerged as candidates of interest in both fibrotic and malignant lung processes.

Compared to imaging modalities and traditional tumor markers such as carcinoembryonic antigen (CEA) or cytokeratin fragment (CYFRA21-1), MMP-1 and MMP-7 offer a more dynamic reflection of extracellular remodeling and epithelial injury. Notably, MMP-7 has demonstrated superior specificity in distinguishing pulmonary fibrosis from inflammation and malignancy in early-stage disease settings. Furthermore, serum-based detection of MMPs is minimally invasive, rapid, and compatible with automated chemiluminescence platforms, allowing for scalable clinical application. This methodological simplicity enhances feasibility in both acute and chronic care settings, particularly where radiological tools are limited or where biopsy is contraindicated.

This study investigates the serum expression levels of MMP-1 and MMP-7 in patients with pneumonia, pulmonary fibrosis, and lung cancer, with the aim of evaluating their potential diagnostic utility and clinical relevance.

Protocol

This study was approved by the Medical Ethics Committee of Shaanxi Provincial Nuclear Industry 215 Hospital (Approval No. 2023-LC-011) and was conducted in accordance with the principles of the Declaration of Helsinki. Informed consent was obtained from all participants or their legal guardians prior to enrollment.

1. Patient details

A total of 64 patients (45 males, 19 females) diagnosed with lung cancer (LC) were enrolled between October 2023 and April 2024. Diagnosis and treatment adhered to the Clinical Diagnosis and Treatment Guidelines for Lung Cancer (Chinese Medical Association, 2023 Edition). Inclusion criteria were as follows: progressive dyspnea lasting more than 3 months, dry cough, restrictive lung function impairment with decreased diffusing capacity for carbon monoxide (DLCO), exertional arterial hypoxemia, and presence of inspiratory crackles upon auscultation. Exclusion criteria included a prior history of radiotherapy or chemotherapy, concurrent systemic diseases (e.g., hematologic, endocrine, hepatic, or renal conditions), pregnancy or lactation, and incomplete clinical documentation.

Fifteen patients (11 males, 4 females) with idiopathic pulmonary fibrosis (PF) were included during the same period. Patients with identifiable causes of interstitial lung disease-such as drug-induced fibrosis, occupational/environmental exposure, or autoimmune/connective tissue disorders, were excluded. Although the sample size for this group was limited due to the lower prevalence of PF in clinical practice, all eligible cases within the study period were included to maximize representativeness.

A total of 136 patients (76 males, 60 females) with pneumonia were recruited. Among them, 98 were diagnosed with community-acquired bacterial pneumonia, 28 with Mycoplasma pneumoniae pneumonia, and 10 with viral pneumonia, confirmed by microbiological and radiographic findings. Most cases were mild to moderate; patients requiring intensive care were excluded. Individuals with concurrent respiratory disorders, systemic infections, cardiopulmonary dysfunction, or other serious systemic conditions were also excluded.

2. Data collection

Sample preparation and measurement of MMP-1 and MMP-7

Venous blood samples (5 mL) were collected into heparin lithium-coated tubes under sterile conditions. Within 30 min of collection, plasma was separated by centrifugation at 3000 × g for 10 min at 4 °C. The supernatant was transferred to clean polypropylene tubes and stored at -20 °C, with no more than two freeze-thaw cycles allowed per sample.

Prior to analysis, samples were thawed at room temperature and gently mixed using a low-speed vortex for 10 s. If visible layering was present, additional vortexing was performed until the plasma appeared homogeneous. To ensure clarity, samples were re-centrifuged at 3000 × g for 5 min, and the resulting supernatant was used for measurement.

Quantification of MMP-1 and MMP-7 was performed using a fully automated chemiluminescence immunoassay analyzer (MAGLUMI X8, Snibe, Shenzhen, China). The instrument was operated in a two-step sandwich assay mode with a six-point calibration curve (logit-log fit). Each run included duplicate samples, automated 3-cycle washing, and reagent/sample volumes of 100 µL and 50 µL, respectively. Calibration was performed every 72 h, and results were considered valid only if internal quality controls (low, medium, high) fell within ±2 SD of the manufacturer's target ranges. All measurements were conducted in duplicate to ensure reproducibility.

Intra-assay and inter-assay coefficients of variation (CV) were 5.2% and 7.8% for MMP-1, and 4.6% and 6.5% for MMP-7, respectively, based on replicate QC measurements.

Although plasma is the preferred matrix in standard protocols, serum was used in this study due to practical constraints in sample handling. This substitution was consistently applied across all groups and accounted for in the interpretation. Any visibly hemolyzed or lipemic samples were excluded from analysis.

The positivity thresholds of 1.79 ng/mL for MMP-1 and 4.51 ng/mL for MMP-7 were not predefined by assay kits but were empirically derived in this study using ROC curve analysis and the maximum Youden index. These values should therefore be interpreted as cohort-specific and require validation in independent populations.

3. Statistical methods

Data normality was assessed using the Kolmogorov-Smirnov test, and homogeneity of variance was evaluated via Levene's test. For continuous variables, results were expressed as mean ± standard deviation or median (interquartile range), depending on data distribution. Two-group comparisons were performed using the Mann-Whitney U test, and multi-group comparisons using the Kruskal-Wallis H test.

4. Categorical data were analyzed using the chi-squared test

Correlation between age and MMP expression was assessed using Spearman's rank correlation coefficient. Age-adjusted comparisons between groups were additionally performed using analysis of covariance (ANCOVA) to control for confounding.

Diagnostic performance was evaluated by receiver operating characteristic (ROC) curve analysis, with optimal cut-off values determined using the maximum Youden index.

A two-tailed p-value of < 0.05 was considered statistically significant.

Results

Comparison of general information among LC, PF, pneumonia, and health examination groups

A statistically significant age difference was observed across the four groups: lung cancer (LC), pulmonary fibrosis (PF), pneumonia, and health examination controls (p < 0.05). Post-hoc analysis further confirmed that each pairwise comparison yielded a significant difference, indicating age heterogeneity among all partic...

Discussion

Respiratory diseases such as pneumonia, pulmonary fibrosis (PF), and lung cancer (LC) have shown a rising incidence in recent years, frequently presenting as overlapping or sequential clinical entities¹². Particularly concerning are cases of severe pneumonia progressing to PF or PF coexisting with LC, which pose significant diagnostic and therapeutic challenges. These conditions share inflammatory and fibrotic signaling pathways, and therapeutic interventions for one may inadvertently exacerbate t...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
–20 °C Freezer	Haier Biomedical, China	DW-20L262	Storage of serum samples
Automated chemiluminescence immunoassay analyzer (CLIA)	Snibe Diagnostics, Shenzhen, China	MAGLUMI-X8	Fully automated CLIA platform
Centrifuge (refrigerated, capable of 3000 ×g, 4 °C)	Eppendorf 5810R, Germany	022628167	For plasma/serum separation
MMP-1 Chemiluminescence Immunoassay Kit	Snibe Diagnostics, Shenzhen, China	130205001M	2-step sandwich CLIA
MMP-7 Chemiluminescence Immunoassay Kit	Snibe Diagnostics, Shenzhen, China	130205007M	2-step sandwich CLIA
Polypropylene storage tubes (1.5 mL / 2 mL)	Corning, USA	430659	Sample aliquots, –20 °C storage
Quality control sera (low, medium, high)	Snibe Diagnostics, Shenzhen, China	Provided with kit	For assay QC, ±2 SD acceptance
SPSS Statistics software v22.0	IBM Corp., Armonk, NY, USA	N/A	Statistical analysis
Sterile disposable syringe & needle (5 mL)	Jiangsu Jichun Medical Devices, China	Local hospital supply	For venipuncture blood collection
Venous blood collection tube (heparin lithium-coated, 5 mL)	BD Vacutainer / Becton Dickinson, USA	367884	Used for plasma/serum separation
Vortex mixer	Scientific Industries, USA	SI-0236	For homogenization before assay