KL-6, a human MUC1 mucin, promotes proliferation and survival of lung fibroblasts

Proteomic Analysis of Transbronchial Biopsies to Discover Novel Biomarkers for Early Identification of Chronic Lung Allograft Dysfunction

Background

Chronic lung allograft dysfunction (CLAD) is a major contributor to poor long-term survival after lung transplantation (LTx). There is a paucity of validated tissue biomarkers which limits the early detection of CLAD. The aim of this study was to discover novel tissue proteins in CLAD.

Methods

A longitudinal cohort study analyzed 15 tissue specimens from 2 groups of bilateral LTx recipients; those with CLAD (n = 3) and those without CLAD (n = 3). In both groups, transbronchial biopsies (TBBx) were retrieved from 2 timepoints; stable surveillance at 90 d after transplant, and during episodes of acute lung allograft dysfunction. In the CLAD cohort, additional tissue from explant CLAD lungs collected at retransplantation was analyzed. Proteomics analysis and immunohistochemistry were used to identify and validate differentially expressed proteins.

Results

Tissue upregulation of a number of proteins including SerpinB1, SerpinH1, Cofilin 1, MUC1, COL15A1, COL4A4, and Coronin1B was found in recipients with CLAD. This finding was present when comparing CLAD onset and explant pathology to stable surveillance among recipients with CLAD and evident when compared with recipients without CLAD. Most of the upregulated tissue proteins in patients with CLAD had collectively critical roles in leukocytes migration and activation, inflammation, free radicals production and oxidative stress, epithelial-mesenchymal transition, myofibroblasts activation, and excessive deposition of extracellular matrix, which in turn enhance the risk of lung fibrosis and graft rejection. We also found exclusive expression of HLA-DQB1, JCHAIN, SAP18, FUCA1, MZB1, G3BP2, and BTF3 in CLAD cases, indicating they could be specific biomarkers of CLAD.

Conclusions

This study identifies distinct proteomes that are linked to CLAD development and consequently may be a useful indicator for identifying LTx patients at higher risk of CLAD.

Krebs von den Lungen-6 (KL-6) as a diagnostic and prognostic biomarker for non-neoplastic lung diseases

Important advancements have been made in understanding the pathogenetic mechanisms underlying acute and chronic lung disorders. But although a wide variety of innovative biomarkers have and are being investigated, they are not largely employed to evaluate non-neoplastic lung diseases. The current work aims to examine the use of Krebs von den Lungen-6 (KL-6), a mucin-like glycoprotein predominantly expressed on the surface of type II alveolar epithelial cells (AEC2s), to evaluate the stage, response to treatment, and prognosis in patients with non-neoplastic lung disorders. Data analysis suggests that KL-6 can be utilized as an effective diagnostic and prognostic biomarker in individuals with interstitial lung disease and as a predictor of clinical outcomes in subjects with SARS-CoV-2-related pneumonia. Moreover, KL-6 can be reliably used in routine clinical settings to diagnose and predict the outcome of patients with chronic obstructive pulmonary disease (COPD) exacerbation. The optimal cut-off points within the European population should be defined to improve KL-6's diagnostic efficacy.

Research progress of KL-6 in respiratory system diseases

This article comprehensively elucidates the discovery of Krebs von den Lungen-6 (KL-6), its structural features, functional mechanisms, and the current research status in various respiratory system diseases. Discovered in 1985, KL-6 was initially considered a tumor marker, but its elevated levels in interstitial lung disease (ILD) led to its recognition as a relevant serum marker for ILD. KL-6 is primarily produced by type 2 alveolar epithelial cell regeneration. Over the past 30 years since the discovery of KL-6, the number of related research papers has steadily increased annually. Following the coronavirus disease 2019 (COVID-19) pandemic, there has been a sudden surge in relevant literature. Despite KL-6's potential as a biomarker, its value in the diagnosis, treatment, and prognosis varies across different respiratory diseases, including ILD, idiopathic pulmonary fibrosis (IPF), COVID-19, and lung cancer. Therefore, as an important serum biomarker in respiratory system diseases, the value of KL-6 still requires further investigation.

Cohort study of serological biomarkers for interstitial lung disease in patients with rheumatoid arthritis

OBJECTIVE

Interstitial lung disease (ILD) is an important cause of mortality in patients with rheumatoid arthritis (RA). Early RA-ILD detection is essential to improve prognosis. Here, we investigated eight serological biomarkers that may contribute to RA-ILD detection.

METHOD

Fifty-five patients from the Early Rheumatoid Arthritis Program were evaluated for ILD with high-resolution computed tomography (HRCT) and pulmonary function tests (PFTs) using the SCAPIS protocol. Blood samples were obtained for biomarker analysis, and patients' clinical records were reviewed. We defined ILD using five different models based on the measurements used to confirm ILD: Model A = HRCT; B = PFTs; C = A plus B; D = C plus symptoms; and E = D plus inhalations.

RESULTS

Among 55 patients, two had an ILD diagnosis before the study, but over one-third fulfilled the ILD criteria. Cancer antigen 15-3 (CA15-3) and matrix metalloproteinase-7 (MMP-7) differentiated between RA with and without ILD (all p < 0.05). Surfactant protein D (SP-D) showed similar trends, as did macrophage inflammatory protein-1β (MIP-1β) and chitinase 3-like protein-1 (YKL-40). Based on Pearson's correlation coefficients, MIP-1β and YKL-40 were significantly correlated with DAS28 (MIP-1β: 0.3; YKL-40: 0.4), ESR (MIP-1β: 0.3; YKL-40: 0.4), and CRP (only MIP-1β: 0.4) (all p < 0.05). CA15-3 was correlated with rheumatoid factor and anti-citrullinated peptide antibodies (Pearson's correlation 0.3; both p = 0.03).

CONCLUSIONS

CA15-3 was the most significant biomarker for ILD detection in RA patients with stable low disease activity, closely followed by MMP-7. SP-D, MIP-1β, and YKL-40 may also contribute to RA-ILD diagnosis.

Fecal microbiome extract downregulates the expression of key proteins at the interface between airway remodelling and lung cancer pathogenesis in vitro

Lung cancer (LC) is the leading cause of cancer-related mortality, and it is caused by many factors including cigarette smoking. Despite numerous treatment strategies for LC, its five-year survival is still poor (<20 %), attributable to treatment resistance and lack of early diagnosis and intervention. Importantly, LC incidence is higher in patients affected by chronic respiratory diseases (CRDs) such as asthma and chronic obstructive pulmonary disorder (COPD), and LC shares with other CRDs common pathophysiological features including chronic inflammation, oxidative stress, cellular senescence, and airway remodelling. Remodelling is a complex process resulting from the aberrant activation of tissue repair secondary to chronic inflammation, oxidative stress, and tissue damage observed in the airways of CRD patients, and it is characterized by irreversible airway structural and functional alterations, concomitantly with tissue fibrosis, epithelial-to-mesenchymal transition (EMT), excessive collagen deposition, and thickening of the basement membrane. Many processes involved in remodelling, particularly EMT, are also fundamental for LC pathogenesis, highlighting a potential connection between CRDs and LC. This provides rationale for the development of novel treatment strategies aimed at targeting components of the remodelling pathways. In this study, we tested the in vitro therapeutic activity of rat fecal microbiome extract (FME) on A549 human lung adenocarcinoma cells. We show that treatment with FME significantly downregulates the expression of six proteins whose function is at the forefront between airway remodelling and LC development: Snail, SPARC, MUC-1, Osteopontin, MMP-2, and HIF-1α. The results of this study, if confirmed by further investigations, provide proof-of-concept for a novel approach in the treatment of LC, focused on tackling the airway remodelling mechanisms underlying the increased susceptibility to develop LC observed in CRD patients.

Baseline Blood Levels of Mucin-1 Are Associated with Crucial On-Treatment Adverse Outcomes in Patients with Idiopathic Pulmonary Fibrosis Receiving Antifibrotic Pirfenidone

Mucin-1 is a multi-functional glycoprotein expressed by type II alveolocytes and may be detectable in the circulation following pulmonary fibrosis. The prognostic utility of baseline pre-treatment blood levels of mucin-1 in patients with idiopathic pulmonary fibrosis (IPF) receiving antifibrotics has not yet been fully established. We retrospectively studied a cohort of patients (from two hospitals) with IPF who were receiving pirfenidone for >12 weeks. Baseline blood mucin-1 levels were measured via sandwich enzyme-linked immunosorbent assays. We investigated the performance of mucin-1 levels in longitudinally predicting the risks of acute exacerbation of IPF (AE-IPF) and severe adverse outcomes (SAO), including lung transplantation and death. Seventy patients were included; 20 developed AE-IPF; and 31 had SAO during the follow-up period. Patients with baseline mucin-1 levels ≥2.5 ng/mL had enhanced risks of AE-IPF (adjusted hazard ratio [aHR], 14.07; 95% confidence interval [CI], 4.26-46.49) and SAO within 2 years (aHR, 7.87; 95% CI, 2.86-21.70) and anytime during the follow-up (aHR, 4.68; 95% CI, 2.11-10.39). The risks increased across subgroups with increasing mucin-1 levels. Patients in the "mucin-1 ≥ 2.5" group also exhibited an accelerated decline in DLCO. This study supports baseline blood mucin-1 levels as a biomarker for IPF that predicts adverse outcomes during pirfenidone treatment.

Targeting Progression in Pulmonary Fibrosis: An Overview of Underlying Mechanisms, Molecular Biomarkers, and Therapeutic Intervention

Interstitial lung diseases comprise a heterogenous range of diffuse lung disorders, potentially resulting in pulmonary fibrosis. While idiopathic pulmonary fibrosis has been recognized as the paradigm of a progressive fibrosing interstitial lung disease, other conditions with a progressive fibrosing phenotype characterized by a significant deterioration of the lung function may lead to a burden of significant symptoms, a reduced quality of life, and increased mortality, despite treatment. There is now evidence indicating that some common underlying biological mechanisms can be shared among different chronic fibrosing disorders; therefore, different biomarkers for disease-activity monitoring and prognostic assessment are under evaluation. Thus, understanding the common pathways that induce the progression of pulmonary fibrosis, comprehending the diversity of these diseases, and identifying new molecular markers and potential therapeutic targets remain highly crucial assignments. The purpose of this review is to examine the main pathological mechanisms regulating the progression of fibrosis in interstitial lung diseases and to provide an overview of potential biomarker and therapeutic options for patients with progressive pulmonary fibrosis.

Role of BAL and Serum Krebs von den Lungen-6 (KL-6) in Patients with Pulmonary Fibrosis

Background: Interstitial lung diseases (ILDs) encompass a diverse group of disorders affecting the lung interstitium, leading to inflammation, fibrosis, and impaired respiratory function. Currently, the identification of new diagnostic and prognostic biomarkers for ILDs turns out to be necessary. Several studies show the role of KL-6 in various types of interstitial lung disease and suggest that serum KL-6 levels can be used as a prognostic marker of disease. The aim of this study was to analyze KL-6 expression either in serum or bronchoalveolar lavage samples in order to: (i) make a serum vs. BAL comparison; (ii) better understand the local behavior of fibrosis vs. the systemic one; and (iii) evaluate any differences in patients with progressive fibrosis (PPF) versus patients with non-progressive fibrosis (nPPF). Methods: We used qRT-PCR to detect KL-6 expression both in serum and BAL samples. Mann-Whitney's U test was used to compare the differential expression between groups. Results: In serum, KL-6 is more highly expressed in PPF than in non-progressive fibrosis (p = 0.0295). This difference is even more significant in BAL (p < 0.001). Therefore, it is clear that KL-6 values are related to disease progression. Significant differences were found by making a comparison between BAL and serum. KL-6 was markedly higher in serum than BAL (p = 0.0146). Conclusions: This study identifies KL-6 as a promising biomarker for the severity of the fibrosing process and disease progression in ILDs, with significantly higher levels observed in PPF compared to nPPF. Moreover, the marked difference in KL-6 levels between serum and BAL emphasizes its potential diagnostic and prognostic relevance, providing enlightening insights into both the local and systemic aspects of ILDs.

Clinical characteristics and prognostic impact of acute exacerbations in patients with interstitial lung disease and lung cancer: A single-center, retrospective cohort study

BACKGROUND

Although acute exacerbation (AE) after treatment for lung cancer (LC) is a poor prognostic factor in patients with interstitial lung disease associated with lung cancer (ILD-LC), the risk of AE according to cancer treatment type remains unclear. Therefore, in the present study, we aimed to investigate the association between AE and treatment received for LC in patients with ILD-LC.

METHODS

We conducted a retrospective study of patients with ILD-LC who had undergone treatment for LC between January 2018 and December 2022. The primary study outcome was the incidence of AE within 12 months of treatment for LC according to treatment type. The association between AE and all-cause mortality was evaluated as a secondary outcome.

RESULTS

Among a total of 137 patients, 23 (16.8%) developed AE within 12 months of treatment for LC. The incidence of AE according to treatment type was 4.3% for surgery, 16.2% for radiotherapy, 15.6% for chemotherapy, and 54.5% for concurrent chemoradiation therapy (CCRT). Patients who received CCRT were more likely to develop AE, even after adjustment for covariables (hazard ratio [HR], 15.39; 95% confidence interval [CI]: 4.00-59.19; p < 0.001). In addition, AE within 12 months of treatment for LC was associated with an increased risk of all-cause mortality (HR, 2.82; 95% CI: 1.13-7.04; p = 0.026).

CONCLUSION

Among treatment options for patients with ILD-LC, CCRT was associated with an increased risk for AE. In addition, patients with AE had a higher mortality rate than patients without AE.

Prognostic value of serum Krebs von den Lungen-6 (KL-6) levels in COVID-19 pneumonia

BACKGROUND AND OBJECTIVES

Krebs von den Lungen-6 (KL-6), expressed by damaged type II pneumocytes, is useful in the diagnosis and severity assessment of many diffuse interstitial lung diseases. The objective of our study was to determine the prognostic value of the initial KL-6 plasma level in COVID-19 pneumonia.

METHODS

All patients hospitalized for a suspected COVID-19 pneumonia between March and May 2020 in our Chest department of a French university hospital were included. KL-6 serum concentrations were measured within 72 h of diagnostic suspicion by chemiluminescence enzyme immunoassay Survival analysis was performed using a Cox regression and modeled by a Kaplan-Meier curve.

RESULTS

Sixty-six COVID-19 patients (average age = 64 ± 14 years, 71.2 % males) with KL-6 serum measurement were included. Median KL-6 serum concentration was 409 ± 312 U/mL. KL-6 was significantly higher in men (p = 0.003), elders (p = 0.0001) and in patients with greater Charlson's score (p = 0.002). Higher KL-6 concentration was significantly associated with in-hospital mortality (HR: 8.66; 95 % CI:1.1-69.2, p = 0.014), radiological extension of lesions on chest CT scan (p = 0.004) and higher WHO severity score (p = 0.042), but not with admission in intensive care unit. In 9 (14 %) non-surviving COVID-19 patients, KL-6 serum concentration increased whereas it remained stable or decreased in survivors. At 3 months follow-up (n = 48), DLCO was negatively correlated with the initial KL-6 value (r = 0.47, p = 0.001), while FVC, FEV1 and MRC score were not.

CONCLUSION

Initial KL-6 serum concentration is significantly associated with in-hospital mortality, unfavorable outcome, and persistent impairment of DLCO at 3 months. Initial KL-6 plasma determination appears as a prognostic biomarker in COVID-19 pneumonia.

Krebs von den Lungen-6 as a Potential Predictive Biomarker in Fibrosing Interstitial Lung Diseases

BACKGROUND

As fibrosing interstitial lung diseases (fILDs) are associated with high mortality, monitoring of disease activity under treatment is highly relevant. Krebs von den Lungen-6 (KL-6) is associated with the presence and severity of different fILDs, mainly in Asian patient populations.

OBJECTIVES

Our aim was to evaluate KL-6 as a predictive biomarker in fILDs in Caucasian patients.

METHODS

Consecutive patients with fILDs were recruited prospectively and serum concentrations of KL-6 were measured at baseline (BL), after 6 and 12 months (6 Months, 12 Months). Clinical characteristics including pulmonary function tests were assessed at 6-monthly visits and correlated with KL-6 BL levels as well as with KL-6 level changes.

RESULTS

A total of 47 fILD patients were included (mean age: 65 years, 68% male). KL-6 levels at BL were significantly higher in fILD patients than in healthy controls (n = 44, mean age: 45, 23% male) (ILD: 1,757 ± 1960 U/mL vs. control: 265 ± 107 U/mL, p < 0.0001). However, no differences were noted between ILD subgroups. KL-6 decreased significantly under therapy (6M∆BL-KL6: -486 ± 1,505 mean U/mL, p = 0.032; 12M∆BL-KL6: -547 ± 1,782 mean U/mL, p = 0.041) and KL-6 level changes were negatively correlated with changes in pulmonary function parameters (forced vital capacity [FVC]: r = -0.562, p < 0.0001; DLCOSB: r = -0.405, p = 0.013). While neither absolute KL-6 levels at BL nor KL-6 level changes were associated with ILD progression (FVC decline ≥10%, DLCOSB decline ≥15% or death), patients with a stable FVC showed significantly decreasing KL-6 levels (p = 0.022).

CONCLUSIONS

A decline of KL-6 under therapy correlated with a clinically relevant stabilization of lung function. Thus, KL-6 might serve as a predictive biomarker, which however must be determined by larger prospective cohorts.

Correlation of the High-Resolution Computed Tomography Patterns of Intrathoracic Sarcoidosis with Serum Levels of SAA, CA 15.3, SP-D, and Other Biomarkers of Interstitial Lung Disease

Studies on the serum biomarkers of granulomatous inflammation and pulmonary interstitial disease in intrathoracic sarcoidosis have shown conflicting results. We postulated that differences in the concentrations of serum biomarkers can be explained by the heterogenous patterns of sarcoidosis seen on thoracic HRCT. Serum biomarker levels in 79 consecutive patients, newly diagnosed with intrathoracic sarcoidosis, were compared to our control group of 56 healthy blood donors. An analysis was performed with respect to HRCT characteristics (the presence of lymph node enlargement, perilymphatic or peribronchovascular infiltrates, ground-glass lesions, or fibrosis), CXR, and disease extent. Serum levels of CXCL9, CXCL10, CTO, and CCL18 were statistically significantly increased in all patients compared to controls. Serum levels of CA15.3 were statistically significantly increased in all patients with parenchymal involvement. SAA was increased in patients with ground-glass lesions while SP-D levels were statistically significantly increased in patients with lung fibrosis. Only SP-D and CA15.3 showed a significant correlation to interstitial disease extent. In conclusion, we found that sarcoidosis patients with different HRCT patterns of intrathoracic sarcoidosis have underlying biochemical differences in their serum biomarkers transcending Scadding stages. The stratification of patients based on both radiologic and biochemical characteristics could enable more homogenous patient selection for further prognostic studies.

Potential biomarkers for diagnosis and disease evaluation of idiopathic pulmonary fibrosis

ABSTRACT

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease characterized by progressive lung fibrogenesis and histological features of usual interstitial pneumonia. IPF has a poor prognosis and presents a spectrum of disease courses ranging from slow evolving disease to rapid deterioration; thus, a differential diagnosis remains challenging. Several biomarkers have been identified to achieve a differential diagnosis; however, comprehensive reviews are lacking. This review summarizes over 100 biomarkers which can be divided into six categories according to their functions: differentially expressed biomarkers in the IPF compared to healthy controls; biomarkers distinguishing IPF from other types of interstitial lung disease; biomarkers differentiating acute exacerbation of IPF from stable disease; biomarkers predicting disease progression; biomarkers related to disease severity; and biomarkers related to treatment. Specimen used for the diagnosis of IPF included serum, bronchoalveolar lavage fluid, lung tissue, and sputum. IPF-specific biomarkers are of great clinical value for the differential diagnosis of IPF. Currently, the physiological measurements used to evaluate the occurrence of acute exacerbation, disease progression, and disease severity have limitations. Combining physiological measurements with biomarkers may increase the accuracy and sensitivity of diagnosis and disease evaluation of IPF. Most biomarkers described in this review are not routinely used in clinical practice. Future large-scale multicenter studies are required to design and validate suitable biomarker panels that have diagnostic utility for IPF.

Serum Osteopontin, KL-6, and Syndecan-4 as Potential Biomarkers in the Diagnosis of Coal Workers' Pneumoconiosis: A Case-Control Study

Background

Coal worker's pneumoconiosis (CWP) is a chronic occupational disease mainly caused by coal dust inhalation in miners. This study aimed to investigate the clinical value of Osteopontin (OPN), KL-6, Syndecan-4 and Gremlin-1 as serum biomarkers in CWP.

Patients and Methods

We integrated reported lung tissues transcriptome data in pneumoconiosis patients with silica-exposed alveolar macrophage microarray data to identify four CWP-associated serum biomarkers. The serum concentrations of Osteopontin, Krebs von den Lungen-6 (KL-6), Syndecan-4 and Gremlin-1 were measured in 100 healthy controls (HCs), 100 dust-exposed workers (DEWs) and 200 patients of CWP. Receiver operating characteristic (ROC) curve analysis was used to determine the sensitivity, specificity, cut-off value and area under the curve (AUC) value of biomarkers.

Results

The pulmonary function parameters decreased sequentially, and the serum OPN, KL-6, Syndecan-4 and Gremlin-1 concentrations were increased sequentially among the HC, DEW and CWP groups. Among all participants, multivariable analysis revealed that these four biomarkers were negatively correlated with the pulmonary function parameters (all p<0.05). Compared with HCs, patients with higher OPN, KL-6, Syndecan-4 and Gremlin-1 had higher risk for CWP. The combination of OPN, KL-6, and Syndecan-4 can improve the diagnostic sensitivity and specificity of CWP patients differentiated from HCs or DEWs.

Conclusion

OPN, KL-6 and Syndecan-4 are novel biomarkers that can be used for CWP auxiliary diagnosis. The combination of three biomarkers can improve the diagnostic values of CWP.

Biomarker Profiles Associated with COVID-19 Severity and Mortality

Introduction: The aim of this study was to analyze biomarkers that might predict the severity and progression of the SARS-CoV-2 infection, both in the acute phase and after recovery. Methods: Unvaccinated patients infected with the original strain of COVID-19 requiring ward (Group 1, n = 48) or ICU (Group 2, n = 41) admission were included. At the time of admission (visit 1), a clinical history was acquired, and blood samples were obtained. One and six months after discharge from the hospital (visits 2 and 3, respectively), a clinical history, lung function tests, and blood samples were carried out. At visit 2, patients also underwent a chest CT scan. Different cytokines (IL-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12p70, IL-13, IL-17A, G-CSF, GM-CSF, IFN-ɣ, MCP-1, MIP-1β, and TNF-α) and lung fibrosis biomarkers (YKL-40 and KL-6) were measured in blood samples obtained at visits 1, 2, and 3. Results: At visit 1, IL-4, IL-5, and IL-6 levels were higher in Group 2 (p = 0.039, 0.011, and 0.045, respectively), and IL-17 and IL-8 levels were higher in Group 1 (p = 0.026 and 0.001, respectively). The number of patients in Groups 1 and 2 who died during hospitalization was 8 and 11, respectively. YKL-40 and KL-6 levels were higher in patients who died. Serum YKL-40 and KL-6 levels determined at visit 2 correlated negatively with FVC (p = 0.022 and p = 0.024, respectively) and FEV1 (p = 0.012 and p = 0.032, respectively) measured at visit 3. KL-6 levels also correlated negatively with the diffusing capacity of the lungs for carbon monoxide (DLCO, p = 0.001). Conclusions: Patients who required ICU admission had higher levels of Th2 cytokines, while patients admitted to the ward showed an innate immune response activation, with IL-8 release and Th1/Th17 lymphocyte contribution. Increased levels of YKL-40 and KL-6 were associated with mortality in COVID-19 patients.

Biomonitoring Exposure and Early Diagnosis in Silicosis: A Comprehensive Review of the Current Literature

Silicosis is a particular form of lung fibrosis attributable to occupational exposure to crystalline silica. The occupational exposure to crystalline silica also increases the risk of chronic obstructive pulmonary disease (COPD), cancer and lung infections, especially pulmonary tuberculosis. Silicosis is currently diagnosed in previously exposed workers by standard chest X-ray, when lesions are visible and irreversible. Therefore, it would be necessary to find specific and non-invasive markers that could detect silicosis in earlier stages, before the occurrence of X-ray opacities. In this narrative review, we present several diagnostic, monitoring and predictive biomarkers with high potential in the management of silicosis, such as: pro- and anti-inflammatory cytokines (TNF (Tumour necrosis factor-α), IL-1 (Interleukin-1), IL-6, IL-10), CC16 (Clara cell 16, an indirect marker of epithelial cell destruction), KL-6 (Krebs von den Lungen 6, an indirect marker of alveolar epithelial damage), neopterin (indicator of cellular immunity) and MUC5B gene (Mucin 5B, a gel-forming mucin in mucus). Studies have shown that all the aforementioned markers have a high potential for early diagnosis or evaluation of progression in silicosis and represent promising alternatives to radiology. We consider that a multicentric study is needed to evaluate these biomarkers in correlation with occupational history, histopathological examination, imaging signs and pulmonary functions tests on large groups of subjects to better evaluate the accuracy of the presented biomarkers.

Increased KL-6 levels in moderate to severe COVID-19 infection

BACKGROUND

The global coronavirus disease 2019 (COVID-19) has presented significant challenges and created concerns worldwide. Besides, patients who have experienced a SARS-CoV-2 infection could present post-viral complications that can ultimately lead to pulmonary fibrosis. Serum levels of Krebs von den Lungen 6 (KL-6), high molecular weight human MUC1 mucin, are increased in the most patients with various interstitial lung damage. Since its production is raised during epithelial damages, KL-6 could be a helpful non-invasive marker to monitor COVID-19 infection and predict post-infection sequelae.

METHODS

We retrospectively evaluated KL-6 levels of 222 COVID-19 infected patients and 70 healthy control. Serum KL-6, fibrinogen, lactate dehydrogenase (LDH), platelet-lymphocytes ratio (PLR) levels and other biological parameters were analyzed. This retrospective study also characterized the relationships between serum KL-6 levels and pulmonary function variables.

RESULTS

Our results showed that serum KL-6 levels in COVID-19 patients were increased compared to healthy subjects (470 U/ml vs 254 U/ml, P <0.00001). ROC curve analysis enabled us to identify that KL-6 > 453.5 U/ml was associated with COVID-19 (AUC = 0.8415, P < 0.0001). KL-6 level was positively correlated with other indicators of disease severity such as fibrinogen level (r = 0.1475, P = 0.0287), LDH level (r = 0,31, P = 0,004) and PLR level (r = 0.23, P = 0.0005). However, KL-6 levels were not correlated with pulmonary function tests (r = 0.04, P = 0.69).

CONCLUSIONS

KL-6 expression was correlated with several disease severity indicators. However, the association between mortality and long-term follow-up outcomes needs further investigation. More extensive trials are required to prove that KL-6 could be a marker of disease severity in COVID-19 infection.

YKL-40 and KL-6 Levels in Serum and Sputum of Patients Diagnosed With Hypersensitivity Pneumonitis

BACKGROUND

YKL-40 (chitinase 3-like-1) and Krebs von den Lungen-6 (KL-6) are 2 promising biomarkers that may have an important role in the management of interstitial lung diseases (ILD).

OBJECTIVE

The aim of this study was to investigate the values of KL-6 and YKL-40 as biomarkers in the diagnosis and prognosis of patients with hypersensitivity pneumonitis (HP).

METHODS

A cross-sectional study conducted in 49 patients diagnosed with HP due to exposure to birds (n = 32) or fungi (n = 17), 48 patients with other ILD, and 67 healthy volunteers. Patients with HP were divided into fibrotic and nonfibrotic. Serum and sputum YKL-40 and KL-6 levels were determined using commercial enzyme-linked immunosorbent assay kits. Receiver operating characteristic (ROC) curves were used to determine the sensitivity and specificity of both biomarkers for the diagnosis of HP. Pulmonary function tests were performed in patients during follow-up.

RESULTS

KL-6 and YKL-40 levels were significantly higher in serum of patients with HP exposed to birds with a fibrotic pattern than in controls (P < .0001 and .0055, respectively). Serum KL-6 levels were also significantly higher in patients with fibrotic HP exposed to fungi compared with the control group (P = .0001). In patients with HP exposed to fungi, sputum KL-6 and YKL-40 levels were higher in those with a fibrotic pattern (P = .0289 and .016, respectively). ROC analysis showed that the range between 55-121 ng/mL for serum YKL-40 levels and 346-1441 U/mL for serum KL-6 levels had the best sensitivity and specificity for discriminating between patients with HP, healthy controls, and patients with idiopathic pulmonary fibrosis (IPF). In patients with HP, serum KL-6 levels correlated negatively with total lung capacity (r = -0.485; P = .0103) and diffusing capacity of the lungs for carbon monoxide (r = -0.534; P = .0002) at 12 months.

CONCLUSIONS

Both KL-6 and YKL-40 proteins seem to be capable of distinguishing patients with HP from healthy individuals and from patients with IPF. Their sensitivity and specificity confirm their potential role as biomarkers. KL-6 may also be a predictor of disease progression.

Heme oxygenase-1 as an important predictor of the severity of COVID-19

Background and objective

A cytokine storm is caused by inflammatory cells, including pro-inflammatory macrophage phenotype (M1), and play a critical role in the pathogenesis of COVID-19, in which diffuse alveolar damage occurs in the lungs due to oxidative stress exposure. Heme oxygenase (HO)-1 is a stress-induced protein produced by the anti-inflammatory / anti-oxidative macrophage phenotype (M2), which also produces soluble CD163 (sCD163). In our study, we investigated and determined that serum HO-1 can be a predictive biomarker for assessing both the severity and the outcome of COVID-19 patients.

Method

The serum concentrations of HO-1 and sCD163 of COVID-19 patients were measured on admission. The relationship between these biomarkers and other clinical parameters and outcomes were evaluated.

Results

Sixty-four COVID-19 patients (11 mild, 38 moderate, and 15 severe cases) were assessed. The serum HO-1 tended to increase (11.0 ng/mL vs. 24.3 ng/mL vs. 59.6 ng/mL with severity). Serum HO-1 correlated with serum lactate dehydrogenase (R = 0.422), C-reactive protein (R = 0.463), and the ground glass opacity (GGO) and consolidation score (R = 0.625) of chest computed tomography. The serum HO-1 showed a better area under the curve (AUC) for predicting ICU admission than the serum sCD163 (HO-1; 0.816 and sCD163; 0.743). In addition, composite parameters including serum HO-1 and the GGO and consolidation score showed a higher AUC for predicting ICU admission than the AUC of a single parameter.

Conclusion

Clinically, serum HO-1, reflecting the activation of M2, could be a very useful marker for evaluating disease severity and predicting prognoses for COVID-19 patients. In addition, controlling activated M2 might be a preventative COVID-19 therapeutic target.

Peak value of serum KL-6 may be useful for predicting poor prognosis of severe COVID-19 patients

BACKGROUND

Serum Krebs von den Lungen 6 (KL-6), which reflects alveolar epithelial injury, was reported to be useful to predict the progression of pneumonitis induced by COVID-19 in the early phase. This study aimed to evaluate the peak value of serum KL-6 during hospitalization for COVID-19 to discover a more useful biomarker for predicting prognosis in COVID-19 patients.

METHODS

In this retrospective, single-center, observational study, we analyzed the data of 147 hospitalized patients who required supplemental oxygen, high-flow oxygen therapy, or invasive mechanical ventilation for respiratory failure due to COVID-19 from March 2020 to February 2021. We extracted data on patient sex, age, comorbidities, treatment, and biomarkers including the initial and peak values of KL-6. Inclusion criteria were examination of the studied biomarkers at least once within 3 days of admission, then at least once a week, and at a minimum, at least twice during the entire hospitalization. Area under the receiver operating curve (AUC) was analyzed to determine the accuracy of several biomarkers including KL-6 and LDH for predicting poor prognosis defined as survivors requiring invasive mechanical ventilation for over 28 days or non-survivors of COVID-19. Univariable and multivariate logistic regression analyses were performed to investigate the prognostic value of the baseline characteristics and biomarkers.

RESULTS

Among the 147 patients, 108 (73.5%) had a good prognosis and 39 (26.5%) had a poor prognosis. The AUC analysis indicated that peak KL-6 showed precise accuracy in the discrimination of patients with poor prognosis (AUC 0.89, p < 0.001). The best cut-off value for KL-6 concentration was 966 U/mL (sensitivity 81.6%, specificity84.3%). After adjustment, increasing peak values of KL-6 or LDH were associated with a high risk of poor prognosis, with an adjusted odds ratio of 1.35 for peak value of KL-6, per 100 U/mL increase (95% CI 1.17-1.57, p < 0.001) and 2.16 for peak value of LDH, per 100 U/L increase (95% CI 1.46-3.20, p < 0.001).

CONCLUSIONS

Peak values of KL-6 and LDH measured during hospitalization might help to identify COVID-19 patients with respiratory failure who are at higher risk for a poor prognosis.

Mammalian Neuraminidases in Immune-Mediated Diseases: Mucins and Beyond

Mammalian neuraminidases (NEUs), also known as sialidases, are enzymes that cleave off the terminal neuraminic, or sialic, acid resides from the carbohydrate moieties of glycolipids and glycoproteins. A rapidly growing body of literature indicates that in addition to their metabolic functions, NEUs also regulate the activity of their glycoprotein targets. The simple post-translational modification of NEU protein targets-removal of the highly electronegative sialic acid-affects protein folding, alters protein interactions with their ligands, and exposes or covers proteolytic sites. Through such effects, NEUs regulate the downstream processes in which their glycoprotein targets participate. A major target of desialylation by NEUs are mucins (MUCs), and such post-translational modification contributes to regulation of disease processes. In this review, we focus on the regulatory roles of NEU-modified MUCs as coordinators of disease pathogenesis in fibrotic, inflammatory, infectious, and autoimmune diseases. Special attention is placed on the most abundant and best studied NEU1, and its recently discovered important target, mucin-1 (MUC1). The role of the NEU1 - MUC1 axis in disease pathogenesis is discussed, along with regulatory contributions from other MUCs and other pathophysiologically important NEU targets.

KL-6 as a Biomarker of Interstitial Lung Disease Development in Patients with Sjögren Syndrome: A Retrospective Case–Control Study

Objective

Krebs von den Lungen-6 (KL-6) is expressed on regenerating type II pneumocytes and has been recognized as biomarkers in interstitial lung disease (ILD). We aim to identify the role of the serum KL-6 level in patients with newly diagnosed Sjögren syndrome (SS), as well as the correlation between the immunoassays.

Methods

Patients with newly diagnosed SS and receiving HRCT for clinical reason during follow-up were included. Baseline KL-6 level was measured via enzyme-linked immunosorbent assay (ELISA) and latex particle-enhanced turbidimetric immunoassay (LETIA).

Results

Of the 39 patients, 21 (53.85%) developed interstitial lung disease (ILD) by the conclusion of the follow-up period. The median time to diagnosis of ILD was 2.24 years (IQR 1.15–4.34) in the ILD group. The median serum KL-6 level, measured using ELISA, was 1232 U/mL (IQR 937–2242) and 764.5 U/mL (IQR 503.25–1035.75) in the ILD group and the non-ILD group, respectively (p = 0.001). The median LETIA for serum KL-6 was 329 U/mL (IQR 235–619) and 245 U/mL (IQR 215.25–291) in the ILD group and the non-ILD group, respectively (p = 0.074).

Conclusion

Serum KL-6 levels were higher in newly diagnosed SS patients with ILD diagnosis during follow-up. Thus, the serum KL-6 level can serve as a valuable biomarker to identify hidden ILD in patients with newly diagnosed SS patients. However, the immunoassay procedure may influence the efficacy of the prediction and its clinical association.

RNA Sequencing of Epithelial Cell/Fibroblastic Foci Sandwich in Idiopathic Pulmonary Fibrosis: New Insights on the Signaling Pathway

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease characterized by irreversible scarring of the distal lung. IPF is best described by its histopathological pattern of usual interstitial pneumonia (UIP), characterized by spatial heterogeneity with alternating interstitial fibrosis and areas of normal lung, and temporal heterogeneity of fibrosis characterized by scattered fibroblastic foci (FF), dense acellular collagen and honeycomb changes. FF, comprising aggregated fibroblasts/myofibroblasts surrounded by metaplastic epithelial cells (EC), are the cardinal pathological lesion and their presence strongly correlates with disease progression and mortality. We hypothesized that the EC/FF sandwich from patients with UIP/IPF has a distinct molecular signature which could offer new insights into the crosstalk of these two crucial actors in the disease. Laser capture microdissection with RNAseq was used to investigate the transcriptome of the EC/FF sandwich from IPF patients versus controls (primary spontaneous pneumothorax). Differentially expressed gene analysis identified 23 up-regulated genes mainly related to epithelial dysfunction. Gene ontology analysis highlighted the activation of different pathways, mainly related to EC, immune response and programmed cell death. This study provides novel insights into the IPF pathogenetic pathways and suggests that targeting some of these up-regulated pathways (particularly those related to secreto-protein/mucin dysfunction) may be beneficial in IPF. Further studies in a larger number of lung samples, ideally from patients with early and advanced disease, are needed to validate these findings.

Review: Serum Biomarkers of Lung Fibrosis in Interstitial Pneumonia with Autoimmune Features-What Do We Already Know?

Interstitial pneumonia with autoimmune features (IPAF) belongs to a group of diseases called interstitial lung diseases (ILDs), which are disorders of a varied prognosis and course. Finding sufficiently specific and sensitive biomarkers would enable the progression to be predicted, the natural history to be monitored and patients to be stratified according to their treatment. To assess the significance of pulmonary fibrosis biomarkers studied thus far, we searched the PubMed, Medline and Cochrane Library databases for papers published between January 2015 and June 2021. We focused on circulating biomarkers. A primary review of the databases identified 38 articles of potential interest. Overall, seven articles fulfilled the inclusion criteria. This review aims to assess the diagnostic and prognostic value of molecules such as KL-6, SP-A, SP-D, circulating fibrocytes, CCL2, CXCL13, CXCL9, CXCL10 and CXCL11. All of these biomarkers have previously been studied in idiopathic pulmonary fibrosis (IPF) and connective tissue disease-associated interstitial lung disease (CTD-ILD). IPAF is a disorder of a heterogeneous nature. It explains the lack of coherent observations in terms of correlations with functional parameters. There is still no meta-analysis of pulmonary fibrosis biomarkers in IPAF. This is mainly due to the heterogeneity of the methodology and groups analysed in the research. More research in this area is needed.

Comparison of Clinical Features between the High and Low Serum KL-6 Patients with Acute Exacerbation of Interstitial Lung Diseases

Background

Serum Krebs von den Lungen-6 (KL-6) measurement is widely used to assess disease activity or prognosis in patients with interstitial lung diseases (ILDs). However, the clinical differences between high and low serum KL-6 levels at the time of acute exacerbation (AE) of ILD are not well known.

Methods

Clinical parameters including age, sex, Charlson Comorbidity Index score (CCIS), blood biomarkers, high-resolution CT findings, and disease mortality were retrospectively compared between high and low KL-6 (cutoff value: 1000 U/mL) patients at the time of diagnosis of AE of ILDs.

Results

Thirty-eight high serum KL-6 and 57 low serum KL-6 patients were included. There was no significant difference in 6-month mortality between them (P = 0.685), whereas serum lactate dehydrogenase was a significant predictor of 6-month mortality in the high serum KL-6 patients (odds ratio (OR): 1.006; 95% confidence interval (CI): 1.003–1.009; P < 0.001), and CCIS (OR: 1.502; 95% CI: 1.242–1.838; P < 0.001) and sex (OR: 5.751; 95% CI: 1.121–105.163; P = 0.033) were significant predictors in low serum KL-6 patients. In addition, the incidences of congestive heart failure, symptomatic chronic pulmonary disease, cerebrovascular disease, and second metastatic solid tumours were significantly higher in nonsurvivors with low serum KL-6 than in other groups (P < 0.05).

Conclusions

The clinical features in patients with AEs of ILDs may differ depending on the serum KL-6 level, and clinicopathological examination according to this subtyping guided by the serum KL-6 level is essential.

The Potential of Lung Epithelium Specific Proteins as Biomarkers for COVID-19-Associated Lung Injury

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection was first reported in Wuhan, China, and was declared a pandemic by the World Health Organization (WHO) on 20 March 2020. The respiratory system is the major organ system affected by COVID-19. Numerous studies have found lung abnormalities in patients with COVID-19, including shortness of breath, respiratory failure, and acute respiratory distress syndrome. The identification of lung-specific biomarkers that are easily measurable in serum would be valuable for both clinicians and patients with such conditions. This review is focused on the pneumoproteins and their potential to serve as biomarkers for COVID-19-associated lung injury, including Krebs von den Lungen-6 (KL-6), surfactant proteins (SP-A, SP-B, SP-C, SP-D), and Clara cell secretory protein (CC16). The current findings indicate the aforementioned pneumoproteins may reflect the severity of pulmonary manifestations and could serve as potential biomarkers in COVID-19-related lung injury.

The role of lung ultrasound B-lines and serum KL-6 in the screening and follow-up of rheumatoid arthritis patients for an identification of interstitial lung disease: review of the literature, proposal for a preliminary algorithm, and clinical application to cases

Screening and follow-up of interstitial lung disease associated with rheumatoid arthritis (RA-ILD) is a challenge in clinical practice. In fact, the majority of RA-ILD patients are asymptomatic and optimal tools for early screening and regular follow-up are lacking. Furthermore, some patients may remain oligosymptomatic despite significant radiological abnormalities. In RA-ILD, usual interstitial pneumonia (UIP) is the most frequent radiological and pathological pattern, associated with a poor prognosis and a high risk to develop acute exacerbations and infections. If RA-ILD can be identified early, there may be an opportunity for an early treatment and close follow-up that might delay ILD progression and improve the long-term outcome.In connective tissue disease-associated interstitial lung disease (CTD-ILD), lung ultrasound (LUS) with the assessment of B-lines and serum Krebs von den Lungen-6 antigen (KL-6) has been recognized as sensitive biomarkers for the early detection of ILD. B-line number and serum KL-6 level were found to correlate with high-resolution computed tomography (HRCT), pulmonary function tests (PFTs), and other clinical parameters in systemic sclerosis-associated ILD (SSc-ILD). Recently, the significant correlation between B-lines and KL-6, two non-ionizing and non-invasive biomarkers, was demonstrated. Hence, the combined use of LUS and KL-6 to screen and follow up ILD in RA patients might be useful in clinical practice in addition to existing tools. Herein, we review relevant literature to support this concept, propose a preliminary screening algorithm, and present 2 cases where the algorithm was used.

The Epithelial-Immune Crosstalk in Pulmonary Fibrosis

Interactions between the lung epithelium and the immune system involve a tight regulation to prevent inappropriate reactions and have been connected to several pulmonary diseases. Although the distal lung epithelium and local immunity have been implicated in the pathogenesis and disease course of idiopathic pulmonary fibrosis (IPF), consequences of their abnormal interplay remain less well known. Recent data suggests a two-way process, as illustrated by the influence of epithelial-derived periplakin on the immune landscape or the effect of macrophage-derived IL-17B on epithelial cells. Additionally, damage associated molecular patterns (DAMPs), released by damaged or dying (epithelial) cells, are augmented in IPF. Next to “sterile inflammation”, pathogen-associated molecular patterns (PAMPs) are increased in IPF and have been linked with lung fibrosis, while outer membrane vesicles from bacteria are able to influence epithelial-macrophage crosstalk. Finally, the advent of high-throughput technologies such as microbiome-sequencing has allowed for the identification of a disease-specific microbial environment. In this review, we propose to discuss how the interplays between the altered distal airway and alveolar epithelium, the lung microbiome and immune cells may shape a pro-fibrotic environment. More specifically, it will highlight DAMPs-PAMPs pathways and the specificities of the IPF lung microbiome while discussing recent elements suggesting abnormal mucosal immunity in pulmonary fibrosis.

Heme Oxygenase-1 in Patients With Interstitial Lung Disease: A Review of the Clinical Evidence

The clinical course and rate of progression of interstitial lung disease (ILD) are extremely variable among patients. For the purpose of monitoring disease activity, ILD diagnosis, and predicting disease prognosis, there are various biomarkers, including symptoms, physiological, radiological, and pathological findings, and peripheral blood and bronchoalveolar lavage fluid results. Of these, blood biomarkers such as sialylated carbohydrate antigen, surfactant proteins-A and -D, CC-chemokine ligand 18, matrix metalloprotease-1 and -7, CA19-9, and CA125 have been previously proposed. In the future, heme oxygenase-1 (HO-1) may also become a candidate ILD biomarker; it is a 32-kDa heat shock protein converting heme to carbon monoxide, biliverdin/bilirubin, and free iron to play a role in the pulmonary cytoprotective reaction in response to various stimuli. Recent research suggests that HO-1 can increase in lung tissues of patients with ILD, reflecting anti-inflammatory M2 macrophage activation, and the measurement of HO-1 levels in peripheral blood can be useful for evaluating the severity of lung damage in ILD and for predicting subsequent fibrosis formation.

Serum markers of pulmonary epithelial damage in systemic sclerosis-associated interstitial lung disease and disease progression

BACKGROUND AND OBJECTIVE

The course of systemic sclerosis-associated interstitial lung disease (SSc-ILD) is highly variable, and accurate prognostic markers are needed. KL-6 is a mucin-like glycoprotein (MUC1) expressed by type II pneumocytes, while CYFRA 21-1 is expressed by alveolar and bronchiolar epithelial cells. Both are released into the blood from cell injury.

METHODS

Serum KL-6 and CYFRA 21-1 levels were measured in a retrospective (n = 189) and a prospective (n = 118) cohort of SSc patients. Genotyping of MUC1 rs4072037 was performed. Linear mixed-effect models were used to evaluate the relationship with change in lung function parameters over time, while association with survival was evaluated with Cox proportional hazard analysis.

RESULTS

In both cohorts, KL-6 and CYFRA 21-1 were highest in patients with lung involvement, and in patients with extensive rather than limited ILD. KL-6 was higher in patients carrying the MUC1 rs4072037 G allele in both cohorts. In patients with SSc-ILD, serum KL-6, but not CYFRA 21-1, was significantly associated with DL_CO decline in both cohorts (P = 0.001 and P = 0.004, respectively), and with FVC decline in the retrospective cohort (P = 0.005), but not the prospective cohort. When combining the cohorts and subgrouping by severity (median CPI = 45.97), KL-6 remained predictive of decline in DL_CO in both milder (P = 0.007) and more severe disease (P = 0.02) on multivariable analysis correcting for age, gender, ethnicity, smoking history and MUC1 allele carriage.

CONCLUSION

Our results suggest serum KL-6 predicts decline in lung function in SSc, suggesting its clinical utility in risk stratification for progressive SSc-ILD.

Krebs von den Lungen 6 decreased in the serum and muscle of GNE myopathy patients

UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase (GNE) is necessary for sialic acid biosynthesis. GNE myopathy is caused by a defect in GNE, and hyposialylation is a key factor in the pathomechanism of GNE myopathy. Although candidates for evaluating hyposialylation have been reported, it is difficult to measure them in routine clinical practice. Sialylation is necessary for synthesis of various glycoproteins, including Krebs von den Lungen‐6 (KL‐6)/mucin 1 (MUC1). Here we report that KL‐6/MUC1 is decreased in GNE myopathy. We observed that KL‐6 levels were decreased in the serum of patients with GNE myopathy, and that KL‐6 and MUC1‐C were also decreased in muscle biopsy specimens from these patients. An immunofluorescent study revealed that KL‐6 and MUC1‐C were not present in the sarcolemma but were, instead, localized in rimmed vacuoles in specimens from patients with GNE myopathy. KL‐6 is already used to detect lung diseases in clinical practice, and this glycoprotein may be a novel candidate for evaluating hyposialylation in GNE myopathy.

Comparative diagnostic efficacy of serum Krebs von den Lungen-6 and surfactant D for connective tissue disease-associated interstitial lung diseases: A meta-analysis

PURPOSE

The aim of the study was to estimate and compare the diagnostic accuracy of serum Krebs von den Lungen-6 (KL-6) and surfactant protein D (SP-D) for identifying interstitial lung disease (ILD) from non-ILD among connective tissue disease (CTD) patients.

MATERIALS AND METHODS

Original articles on the diagnostic accuracy of serum KL-6 and SP-D in differentiating CTD-ILD from CTD-nonILD were identified from three public databases. The overall quality of evidence and methodologic quality of each eligible study were assessed by the Grading of Recommendations, Assessment, Development and Evaluation approach and Quality Assessment of Diagnostic Accuracy Studies, respectively. We used the bivariate model to calculate random-effect sensitivity, specificity, likelihood ratios, and area under curve. Furthermore, trial sequential analysis (TSA) was used to determine whether sample sizes incorporated in the meta-analysis were powerful for evaluating the diagnostic utility. Bayesian network analysis was performed to compare the diagnostic accuracy of 2 serum biomarkers in differentiating ILD among CTD patients and various subgroups.

RESULTS

Twenty-nine studies were included in the quantitative synthesis. No threshold effects were observed (all P values >.05). For diagnosis of ILD among CTD patients, overall sensitivity and specificity of serum KL-6 were 0.76 (95% confidence interval [CI]: 0.68-0.82) and 0.89 (95% CI: 0.83-0.93), whereas those for serum SP-D were 0.65 (95% CI: 0.45-0.80) and 0.88 (95% CI: 0.80-0.93). Comprehensive comparison of 2 circulating biomarkers using back-calculated likelihood ratio (LR) demonstrated that serum KL-6 corresponded to a higher LR+ and a lower LR- in comparison to serum SP-D, as well as in SSc-ILD. TSA indicated that evidence for serum KL-6 and SP-D in identifying CTD-ILD is powerful; nonetheless, more trials were needed for validation of serum KL-6 and SP-D in differentiating CTD-ILD subtypes, including different CTD and ethnicities.

CONCLUSIONS

This meta-analysis suggested that serum KL-6 had superior diagnostic accuracy to SP-D for differentiating ILD from non-ILD among CTD patients, providing a convenient and non-invasive approach for screening and management of ILD among CTD patients.

Circulating lung biomarkers in idiopathic lung fibrosis and interstitial lung diseases associated with connective tissue diseases: Where do we stand?

Interstitial lung diseases (ILDs) are complex diseases with various courses where personalized medicine is highly expected. Biomarkers are indicators of physiological, pathological processes or of pharmacological response to therapeutic interventions. They can be used for diagnosis, risk-stratification, prediction and monitoring of treatment response. To better delineate the input and pitfalls of biomarkers in ILDs, we performed a systematic review and meta-analysis of literature in MEDLINE and Embase databases from January 1960 to February 2019. We focused on circulating biomarkers as having the highest generalizability. Overall, 70 studies were included in the review and 20 studies could be included in the meta-analysis. This review highlights that ILD associated with connective tissue diseases (CTD-ILD) and idiopathic pulmonary fibrosis (IPF) share common biomarkers, suggesting common pathophysiological pathways. KL-6 and SP-D, could diagnose lung fibrosis in both IPF and CTD-ILD, with KL-6 having the strongest value (OR: 520.95[110.07-2465.58], p<0.001 in IPF and OR:26.43[7.15-97.68], p<0.001 in CTD-ILD), followed by SPD (OR: 33.81[3.20-357.52], p = 0.003 in IPF and 13.24 [3.84-45.71] in SSc-ILD), MMP7 appeared as interesting for IPF diagnosis (p<0.001), whereas in SSc, CCL18 was associated with ILD diagnosis. Both CCL18 and KL-6 were predictive for the outcomes of ILDs, with higher predictive values for CCL18 in both IPF (OR:10.22[4.72-22.16], p<0.001 and in SSc [2.62[1.71-4.03], p<0.001). However, disease specific biomarkers are lacking and large longitudinal studies are needed before the translational use of the potential biomarkers in clinical practice. With the recent availability of new effective therapies in ILDs, further studies should assess response to treatment.

Use of serum KL-6 level for detecting patients with restrictive allograft syndrome after lung transplantation

KL-6 is an antigen produced mainly by damaged type II pneumocytes that is involved in interstitial lung disease. Chronic lung allograft dysfunction (CLAD) after lung transplantation (LT) is a major concern for LT clinicians, especially in patients with restrictive allograft syndrome (RAS). We investigated KL-6 levels in serum and bronchoalveolar lavage fluid (BALF) as a potential biomarker of the RAS phenotype. Levels of KL-6 in serum and BALF were measured in 73 bilateral LT recipients, and patients were categorized into 4 groups: stable (ST), infection (LTI), bronchiolitis obliterans syndrome (BOS), and RAS. We also studied a healthy cohort to determine reference values for serum KL-6. The highest levels of KL-6 were found in the serum of patients with RAS (918 [487.8–1638] U/mL). No differences were found for levels of KL-6 in BALF. Using a cut-off value of 465 U/mL serum KL-6 levels was able to differentiate RAS patients from BOS patients with a sensitivity of 100% and a specificity of 75%. Furthermore, higher serum KL-6 levels were associated with a decline in Forced Vital Capacity (FVC) at 6 months after sample collection. Therefore, KL-6 in serum may well be a potential biomarker for differentiating between the BOS and RAS phenotypes of CLAD in LT recipients.

MUC1 intracellular bioactivation mediates lung fibrosis

BACKGROUND

Serum KL6/mucin 1 (MUC1) has been identified as a potential biomarker in idiopathic pulmonary fibrosis (IPF), but the role of MUC1 intracellular bioactivation in IPF is unknown.

OBJECTIVE

To characterise MUC1 intracellular bioactivation in IPF.

METHODS AND RESULTS

The expression and phosphorylation of Thr⁴¹ and Tyr⁴⁶ on the intracellular MUC1-cytoplasmic tail (CT) was increased in patients with IPF (n=22) compared with healthy subjects (n=21) and localised to fibroblasts and hyperplastic alveolar type II cells. Transforming growth factor (TGF)-β1 phosphorylated SMAD3 and thereby increased the phosphorylation of MUC1-CT Thr⁴¹ and Tyr⁴⁶ in lung fibroblasts and alveolar type II cells, activating β-catenin to form a phospho-Smad3/MUC1-CT and MUC1-CT/β-catenin nuclear complex. This nuclear complex promoted alveolar epithelial type II and fibroblast to myofibroblast transitions, as well as cell senescence and fibroblast proliferation. The inhibition of MUC1-CT nuclear translocation using the inhibitor, GO-201 or silencing MUC1 by siRNA, reduced myofibroblast transition, senescence and proliferation in vitro. Bleomycin-induced lung fibrosis was reduced in mice treated with GO-201 and in MUC1-knockout mice. The profibrotic lectin, galectin-3, directly activated MUC1-CT and served as a bridge between the TGF-β receptor and the MUC1-C domain, indicating TGF-β1-dependent and TGF-β1-independent intracellular bioactivation of MUC1.

CONCLUSIONS

MUC1 intracellular bioactivation is enhanced in IPF and promotes fibrotic processes that could represent potential druggable targets for IPF.

Clinical Research on Prognostic Evaluation of Subjects With IPF by Peripheral Blood Biomarkers, Quantitative Imaging Characteristics and Pulmonary Function Parameters

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is an irreversible and progressive fatal interstitial lung disease with a poor prognosis. The aim of this study is to investigate the predictive value of combined blood biomarkers, pulmonary function and quantitative monitoring by computer-aided diagnosis (CAD) system in IPF patients.

METHODS

Pulmonary baseline function and pathological features of 126 patients with IPF were analyzed using spirometry and chest X-ray. Patients were divided into survival group and non-survival group after 5 years follow-up. The relationships the levels of peripheral blood biomarkers, quantitative imaging characteristics and pulmonary function were analyzed between the two groups.

RESULTS

The baseline level of serum Krebs von den Lungen-6 (KL-6) and C-X-C motif chemokine 13 (CXCL13) were moderately or highly correlated with annual changes in forced vital capacity (FVC), carbon monoxide diffusing capacity (DLCO), total lung capacity (TLC), total interstitial lung disease (ILD) lesions, and the volume changes of reticular. The baseline level of serum KL-6 was higher than the cut-off value of 800.0U/ml and baseline level of serum CXCL13 was higher than the cut-off value of 62.0pg/ml. IPF patients with baseline levels of serum KL-6 and CXCL13 lower than the cut-off value had longer median survival time.

CONCLUSIONS

Serum KL-6 and CXCL13 may be predictive biomarkers for the outcomes of patients with IPF patients and their baseline levels were related to the progression of pulmonary function and quantitative monitoring by CAD system.

Mucins as a New Frontier in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common idiopathic interstitial pulmonary disease with a median survival of 3–5 years after diagnosis. Recent evidence identifies mucins as key effectors in cell growth and tissue remodeling processes compatible with the processes observed in IPF. Mucins are classified in two groups depending on whether they are secreted (secreted mucins) or tethered to cell membranes (transmembrane mucins). Secreted mucins (MUC2, MUC5AC, MUC5B, MUC6-8 and MUC19) are released to the extracellular medium and recent evidence has shown that a promoter polymorphism in the secreted mucin MUC5B is associated with IPF risk. Otherwise, transmembrane mucins (MUC1, MUC3, MUC4, MUC12-17 and MUC20) have a receptor-like structure, sensing the external environment and activating intracellular signal transduction pathways essential for mucosal maintenance and damage repair. In this context, the extracellular domain can be released to the external environment by metalloproteinase action, increased in IPF, thus activating fibrotic processes. For example, several studies have reported increased serum extracellular secreted KL6/MUC1 during IPF acute exacerbation. Moreover, MUC1 and MUC4 overexpression in the main IPF cells has been observed. In this review we summarize the current knowledge of mucins as promising druggable targets for IPF.

Serum KL-6 level is a prognostic marker in patients with anti-MDA5 antibody-positive dermatomyositis associated with interstitial lung disease

Objective

This study aimed to investigate the clinical significance of Krebs von den Lungen‐6 (KL‐6) serum levels in patients with anti‐MDA5 antibody‐positive dermatomyositis (anti‐MDA5⁺ DM) having interstitial lung disease (ILD), especially in the amyopathic DM phenotype.

Methods

The serum KL‐6 level was measured using a chemiluminescence enzyme immunoassay (CLEIA) in patients with anti‐MDA5⁺ DM, including clinically amyopathic dermatomyositis (CADM)‐ILD and classic DM‐ILD, and healthy donors. The baseline and post‐treatment serum KL‐6 levels were determined in 39 patients with CADM‐ILD who experienced remission or acute exacerbation. The association between laboratory findings, high‐resolution computed tomography (HRCT) scores, pulmonary function tests (PFTs), and the predictive value of baseline KL‐6 level for death was analyzed.

Results

The serum KL‐6 levels were significantly higher in patients with CADM‐ILD (1339 ± 1329 U/mL) compared with DM‐ILD (642.3 ± 498.4 U/mL) and healthy donors (162.4 ± 54.01 U/mL). The KL‐6 levels correlated positively with chest HRCT scores, serum lactate dehydrogenase, serum ferritin levels, and PFTs, but not with erythrocyte sedimentation rate. During follow‐up, the post‐treatment serum KL‐6 levels significantly reduced in the remission/stable group, but increased in the acute exacerbation group. Higher levels of ferritin and KL‐6 and HRCT scores were independently associated with poor prognosis. The 1‐year survival rate was significantly lower in patients with high KL‐6 level than in those with low KL‐6 level.

Conclusion

The serum KL‐6 levels may be a useful marker for predicting and monitoring ILD in Chinese patients with anti‐MDA5⁺ DM, especially amyopathic DM phenotype.

Evaluation of the Diagnostic Efficacies of Serological Markers KL-6, SP-A, SP-D, CCL2, and CXCL13 in Idiopathic Interstitial Pneumonia

<b><i>Background:</i></b> The objective of this study was to evaluate the diagnostic value of serological markers Krebs von den Lungen-6 (KL-6), surfactant protein-A (SP-A), SP-D, chemokine ligand 2 (CCL2), and chemokine 13 (CXCL13) in idiopathic interstitial pneumonia (IIP). <b><i>Methods:</i></b> Patients with IIP aged 18–80 years from the First Affiliated Hospital of Guangzhou Medical University were enrolled in this retrospective case-control study. Data on the general patient characteristics, laboratory test results, chest high-resolution CT, and pulmonary function test results were collected. The diagnosis of idiopathic pulmonary fibrosis (IPF) was based on the international practice guidelines for the diagnosis and treatment of IPF, a collaborative effort published by the American Thoracic Society (ATS)/European Respiratory Association (ERS), Japanese Respiratory Society, and Latin American Thoracic Society. The diagnostic criteria of non-IPF (N-IPF) followed the consensus classification of the IIPs, which was jointly issued by the ATS and ERS in 2002. The diagnosis of interstitial pneumonia with autoimmune features (IPAF) was based on the official research statement on IPAF, which was jointly issued by the ATS and ERS in 2015. Serum levels of KL-6, SP-A, SP-D, CCL2, and CXCL13 were measured. The differences in the expression of these biomarkers and their correlation with the severity of the disease were analyzed. The sensitivity, specificity, cutoff value, and area under the curve (AUC) value for each of the indices were determined using the receiver operating characteristic (ROC) curve analysis. <b><i>Findings:</i></b> Between September 2015 and October 2017, 69 patients with IIP. Of these patients, 19 had IPF, 23 had N-IPF, and 27 had IPAF. We also enrolled 20 age- and gender-matched patients with pneumonia and 15 uninfected individuals as normal control. The serum levels of KL-6, SP-A, ­SP-D, CCL2, and CXCL13 were significantly higher in patients with IIP than in patients with pneumonia and the normal controls. The detection of these markers was found to have better diagnostic efficacy in patients with IIP than in those with pneumonia. Of these markers above, KL-6 had the highest diagnostic value (AUC 0.96, 95% CI 0.93–0.99). Based on a logistics regression analysis, the combination of KL-6, CCL2, and CXCL13 had an improved diagnostic efficacy for IIP. In patients with IIP, the serum levels of KL-6, SP-A, CCL2, and CXCL13 all showed a significant negative correlation with the diffusing capacity of the lungs for carbon monoxide (DLCO; <i>r</i> = –0.36, –0.37, –0.36, –0.30, respectively; all <i>p</i> &#x3c; 0.05). Although their expression levels along with that of SP-D were elevated in patients with IPF, N-IPF, and IPAF, it was difficult to distinguish between these 3 conditions by detecting the 5 serum biomarkers together. Our findings indicate that the serum levels of KL-6, SP-A, SP-D, CCL2, and CXCL13 are notably elevated in patients with IIP and show significant correlation with the severity of interstitial lung lesions. Additionally, we further explore the diagnostic efficacy of 5 biomarkers in different types of IIP. It is the first time that the level of serum marker CXCL13 of N-IPF and IPAF patients was higher than IPF patients, which further enriched the study on serum markers for IIPs. Between September 2015 and October 2017, 69 patients with IIP. Of these patients, 19 had IPF, 23 had N-IPF, and 27 had IPAF. We also enrolled 20 age- and gender-matched patients with pneumonia and 15 uninfected individuals as normal control. The serum levels of KL-6, SP-A, SP-D, CCL2, and CXCL13 were significantly higher in patients with IIP than in patients with pneumonia and the normal controls. Of these markers above, KL-6 had the highest diagnostic value (AUC 0.96, 95% CI 0.93–0.99). Based on a logistics regression analysis, the combination of KL-6, CCL2, and CXCL13 had an improved diagnostic efficacy for IIP. In patients with IIP, the serum levels of KL-6, SP-A, CCL2, and CXCL13 all showed a significant negative correlation with the DLCO (<i>r</i> = –0.36, –0.37, –0.36, –0.30, respectively; all <i>p</i> &#x3c; 0.05). Our findings indicate that the serum levels of KL-6, ­SP-A, SP-D, CCL2, and CXCL13 are notably elevated in patients with IIP and show significant correlation with the severity of interstitial lung lesions. Additionally, we further explore the diagnostic efficacy of 5 biomarkers in different types of IIP. It is the first time that the level of serum marker CXCL13 of N-IPF and IPAF patients was higher than IPF patients, which further enrich the study on serum markers in IIPs. <b><i>Interpretation:</i></b> Although the combined detection of KL-6, CCL3, and CXCL13 significantly improves the diagnosis of IIP, detection of all the 5 markers together is unable to distinguish between IPF, N-IPF, and IPAF.

Serum concentrations of Krebs von den Lungen-6, surfactant protein D, and matrix metalloproteinase-2 as diagnostic biomarkers in patients with asbestosis and silicosis: a case-control study

BACKGROUND

Asbestosis and silicosis are progressive pneumoconioses characterized by interstitial fibrosis following exposure to asbestos or silica dust. We evaluated the potential diagnostic biomarkers for these diseases.

METHODS

The serum concentrations of Krebs von den Lungen-6 (KL-6), surfactant protein D (SP-D), and matrix metalloproteinase-2 (MMP-2), MMP-7, and MMP-9 were measured in 43 patients with asbestosis, 45 patients with silicosis, 40 dust-exposed workers (DEWs) without pneumoconiosis, and 45 healthy controls (HCs). Chest high-resolution computed tomography (HRCT) images were reviewed by experts blinded to the clinical data. According to the receiver operating characteristic (ROC) curve, the ideal level of each biomarker and its diagnostic sensitivity were obtained.

RESULTS

The serum KL-6 and MMP-2 concentrations were highest in patients with asbestosis, particularly in comparison with those in DEWs and HCs (P<0.05). The serum SP-D concentration was significantly higher in patients with asbestosis than in patients with silicosis, DEWs, and HCs (P<0.01), whereas no significant difference was noted among patients with silicosis, DEWs, and HCs. No significant difference in the serum MMP-7 or -9 concentration was found among patients with asbestosis, patients with silicosis, DEWs, or HCs. Among patients with asbestosis, the serum KL-6 concentration was significantly correlated with the lung fibrosis scores on HRCT and negatively correlated with the forced vital capacity (FVC) % predicted and diffusing capacity of the lung for carbon monoxide (DL_CO) % predicted. The serum SP-D and MMP-2 concentrations were negatively correlated with the DL_CO % predicted (all P<0.05). The order of diagnostic accuracy according to the ROC curve was KL-6, SP-D, and MMP-2 in patients with asbestosis alone and in the combination of both patients with asbestosis and those with silicosis. The combination of all three biomarkers may increase the possibility of diagnosing asbestosis (sensitivity, 93%; specificity, 57%) and both asbestosis and silicosis (sensitivity, 83%; specificity, 62%).

CONCLUSIONS

KL-6, SP-D, and MMP-2 are available biomarkers for the adjuvant diagnosis of asbestosis and silicosis. The combination of all three biomarkers may improve the diagnostic sensitivity for asbestosis and silicosis.

Importance of serial changes in biomarkers in idiopathic pulmonary fibrosis

The clinical significance of serial changes in serum biomarkers in patients with idiopathic pulmonary fibrosis (IPF) remains to be established. This retrospective study was conducted to clarify the associations of serial changes in serum Krebs von den Lungen-6 (KL-6) and surfactant protein-D (SP-D) with changes in physiological indices and overall mortality in IPF. The study subjects were 75 patients with IPF. The 6 month change in serum KL-6 was significantly correlated with changes in the percentage of the predicted forced vital capacity (FVC % pred) and the percentage of the predicted diffusing capacity of the lung for carbon monoxide (% D_LCO), while the 6 month change in serum SP-D was correlated only with % D_LCO. During the mean follow-up period of 647 days, 22 (29.3%) patients died. An increase in serum KL-6 over a 6 month period was a significant predictor of mortality even after adjustment for %FVC, % D_LCO and serum KL-6 at the baseline (hazard ratio 1.10 per 100 U·mL^-1, 95% CI 1.01-1.18, p=0.03), whereas the 6 month increase in serum SP-D was not significant. Serial measurements of serum KL-6 may provide additional prognostic information compared to that provided by physiological parameters in patients with IPF.

MUC1 in lung adenocarcinoma: cross-sectional genetic and serological study

Background

Mucin 1 (MUC1) contributes to the growth and metastasis of various cancers, including lung cancer, and MUC1 gene length polymorphisms are associated with susceptibility to lung cancer and its prognosis. In contrast, the association between rs4072037, a single nucleotide polymorphism in MUC1, and lung cancer has not been well studied.

Methods

In the present study, we determined the rs4072037 genotype and measured serum KL-6 levels to evaluate the association between lung adenocarcinoma (ADC) and rs4072037 or serum KL-6 levels. DNA samples were available for 172 patients and these were included in the genomic analyses. In addition, 304 patients were included in the serum analyses. Furthermore, 276 healthy volunteers were included in both genomic and serum analyses.

Results

The rs4072037 genotype was not associated with susceptibility to lung ADC or its prognosis. Interestingly, serum KL-6 levels significantly differed according to rs4072037 genotype in those with T1 or T2 (P < 0.001), N0 or N1 (P = 0.002) and M0 (P < 0.001), but not in those with T3 or T4 (P = 0.882), N2 or N3 (P = 0.616) and M1a or M1b (P = 0.501). Serum KL-6 levels were significantly associated with the presence of lung ADC, as well as with its progression and prognosis, indicating the crucial involvement of KL-6/MUC1 in the development of lung cancer and its progression.

Conclusion

Based on these findings, we conclude that rs4072037 does not have a significant impact on the pathogenesis or prognosis of lung ADC, whereas serum KL-6 levels, which might reflecting the molecular length of MUC1, are significantly associated with lung ADC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3272-y) contains supplementary material, which is available to authorized users.

Blood Biomarkers in Idiopathic Pulmonary Fibrosis

PURPOSE

Idiopathic pulmonary fibrosis (IPF) is a progressive and lethal lung disease of unknown origin whose incidence has been increasing over the latest decade partly as a consequence of population ageing. New anti-fibrotic therapy including pirfenidone and nintedanib have now proven efficacy in slowing down the disease. Nevertheless, diagnosis and follow-up of IPF remain challenging.

METHODS

This review examines the recent literature on potentially useful blood molecular and cellular biomarkers in IPF. Most of the proposed biomarkers belong to chemokines (IL-8, CCL18), proteases (MMP-1 and MMP-7), and growth factors (IGBPs) families. Circulating T cells and fibrocytes have also gained recent interest in that respect. Up to now, though several interesting candidates are profiling there has not been a single biomarker, which proved to be specific of the disease and predictive of the evolution (decline of pulmonary function test values, risk of acute exacerbation or mortality).

CONCLUSION

Large scale multicentric studies are eagerly needed to confirm the utility of these biomarkers.

Soluble Receptor for Advanced Glycation End Products Quantifies Lung Injury in Polytraumatized Patients

BACKGROUND

Biomarkers caused by blunt chest trauma might leak into the vascular compartment and therefore reflect the severity of parenchymal lung injury (PLI). Five promising proteins were preselected after a literature scan. The objective of our study was to identify a biomarker that is released abundantly into the serum shortly after trauma and reliably quantifies the loss of functional lung tissue.

METHODS

Polytraumatized patients (aged ≥18 years, Injury Severity Score [ISS] ≥16) were included in our prospective observational study if they were admitted directly to our level I trauma center during the first hour after trauma occurred. Immediately after stabilizing the patient's condition, blood samples were taken and a whole-body computed tomographic (CT) scan was obtained. Biomarker levels were measured directly after admission and on day 2. PLI volume was calculated using volumetric analysis.

RESULTS

One hundred thirty patients met the inclusion criteria. Compared with a matched healthy control population, median levels of the soluble receptor for advanced glycation end products (sRAGE) was almost 3 times higher and decreased by 41% on day 2. Higher initial median sRAGE levels were detected in patients with PLI compared with patients without PLI and in individuals with severe PLI compared with those with mild PLI. Spearman correlation analysis and a univariate linear log regression model revealed a significant correlation/equation between initial sRAGE levels and relative PLI volume. Receiver operating characteristic (ROC) statistics identified the initial sRAGE level as an indicator of severe PLI.

CONCLUSIONS

sRAGE levels measured shortly after trauma seem to be a promising diagnostic tool to assess the severity of PLI in polytraumatized patients.