Hyaluronan and procollagen type III aminoterminal peptide in serum and bronchoalveolar lavage fluid from patients with pulmonary fibrosis

The correlation between serum levels of laminin, type IV collagen, type III procollagen N-terminal peptide and hyaluronic acid with the progression of post-COVID-19 pulmonary fibrosis

COVID-19 patients often suffer from post-COVID-19 acute sequelae (PASC). Pulmonary fibrosis has the most significant long-term impact on the respiratory health of patients, known as post-COVID-19 pulmonary fibrosis (PC19-PF). PC19-PF can be caused by acute respiratory distress syndrome (ARDS) or COVID-19-induced pneumonia. Individuals who experience COVID-19 pneumonia symptoms (including cough, shortness of breath, dyspnea on exertion, and desaturation) for at least 12 weeks after diagnosis, almost all develop PC19-PF. Extracellular matrix molecules: laminin (LN), type IV collagen (IV Col), procollagen III N-terminal peptide (PIIINP), and hyaluronic acid (HA) are involved in the development and progression of PC19-PF. This study aimed to investigate the relationship between the progression of PC19-PF and serum levels of laminin, IV COL, PIIINP, and hyaluronic acid. This retrospective study included 162 PC19-PF patients treated and 160 healthy controls who received treatment at Shenzhen Longgang District Third People's Hospital, Hebei PetroChina Central Hospital and Changzhi People's Hospital from January 2021 to December 2023. Serum levels of LN, IV COL, PIIINP, and HA were detected by chemiluminescence immunoassay using commercial kits. Predicted forced vital capacity percentage (FVC% pred), predicted carbon monoxide lung diffusion capacity percentage (DLCO% pred), high-resolution computed tomography (HRCT) scores were assessed, and patient mortality was compared with healthy controls. Serum levels of LN, IV Col, PIIINP, and HA were significantly higher in PC19-PF or CTD-ILD patients than in healthy controls (all p < 0.05), and they were further elevated in acute exacerbation cases (all p < 0.01). In patients, HA was positively associated with HRCT scores and negatively associated with FVC% pred and DLCO% pred (all p < 0.05). Serum levels of LN, IV COL, PIIINP, and HA were significantly lower in surviving patients than in those who deceased (all p > 0.05). Serum levels of LN, IV C, PIIINP, and HA may affect the progression of PC19-PF and may serve as indicators of PC19-PF severity.

Association of serum levels of laminin, type IV collagen, procollagen III N-terminal peptide, and hyaluronic acid with the progression of interstitial lung disease

Noninvasive and convenient tests to assess pulmonary fibrosis and disease progression in interstitial lung diseases (ILDs) are currently unavailable. The extracellular matrix molecules, laminin (LN), type IV collagen (IVC), procollagen III N-terminal peptide (PIIINP), and hyaluronic acid (HA) are involved in ILD development and progression. This study aims to investigate the association of disease progression and serum levels of LN, IVC, PIIINP, and HA in patients with ILD. This retrospective study included 323 patients (162 cases of idiopathic pulmonary fibrosis [IPF] and 161 cases of connective tissue diseases ILD [CTD-ILD]) treated in Shanghai Pulmonary Hospital between January 2013 and January 2015 and 160 healthy controls. Serum LN, IVC, PIIINP, and HA were analyzed by radioimmunoassay. Data of the percentage of forced vital capacity in the prediction value (FVC%pred), the percentage of diffusing capacity of the lung for carbon monoxide in the prediction value (DLCO%pred), high resolution computed tomography (HRCT) score, and patient mortality were collected. Serum LN, IVC, PIIINP, and HA were significantly increased in the patients with IPF or CTD-ILD compared with the healthy controls (all P < .05) and were further elevated in the acute exacerbation cases (all P < .05). Serum LN, IVC, PIIINP, and HA positively correlated with HRCT score and negatively correlated with FVC%pred and DLCO%pred significantly in the patients (all P < .05). The survived patients had significantly lower serum LN, IVC, PIIINP, and HA than the dead patients (all P < .05). Serum levels of LN, IVC, PIIINP, and HA may reflect ILD progression and may be indicators for the severity of ILDs.

The Rise and Fall of Hyaluronan in Respiratory Diseases

In normal airways, hyaluronan (HA) matrices are primarily located within the airway submucosa, pulmonary vasculature walls, and, to a lesser extent, the alveoli. Following pulmonary injury, elevated levels of HA matrices accumulate in these regions, and in respiratory secretions, correlating with the extent of injury. Animal models have provided important insight into the role of HA in the onset of pulmonary injury and repair, generally indicating that the induction of HA synthesis is an early event typically preceding fibrosis. The HA that accumulates in inflamed airways is of a high molecular weight (>1600 kDa) but can be broken down into smaller fragments (<150 kDa) by inflammatory and disease-related mechanisms that have profound effects on HA pathobiology. During inflammation in the airways, HA is often covalently modified with heavy chains from inter-alpha-inhibitor via the enzyme tumor-necrosis-factor-stimulated-gene-6 (TSG-6) and this modification promotes the interaction of leukocytes with HA matrices at sites of inflammation. The clearance of HA and its return to normal levels is essential for the proper resolution of inflammation. These data portray HA matrices as an important component of normal airway physiology and illustrate its integral roles during tissue injury and repair among a variety of respiratory diseases.

The role of TLRs in neutrophil activation

Neutrophils are key innate immune effector cells that are rapidly recruited to sites of infection and inflammation to provide early defence against invading microorganisms. This function is facilitated by the expression of Toll-like receptor (TLR) family members by neutrophils, allowing the recognition of an extensive repertoire of pathogen-associated molecular patterns (PAMPs) and thus triggering the response to invading pathogens. TLR activation leads to important cellular processes including reactive oxygen species (ROS) generation, cytokine production and increased survival, all of which can contribute to the pathogenesis of chronic inflammation when signalling becomes dysregulated. In turn, inflammation and tissue injury results in the release of endogenous TLR ligands, known as damage-associated molecular patterns (DAMPs), which are a rapidly growing class of potent inflammatory stimuli. DAMPs act in an autocrine manner, alerting the host of damage, but can also amplify inflammation leading to further tissue damage. This review highlights recent literature on neutrophil TLR function and regulation during disease, and provides an overview of the recently emerging area of neutrophil responses to DAMPs.

DAMPening inflammation by modulating TLR signalling

Damage-associated molecular patterns (DAMPs) include endogenous intracellular molecules released by activated or necrotic cells and extracellular matrix (ECM) molecules that are upregulated upon injury or degraded following tissue damage. DAMPs are vital danger signals that alert our immune system to tissue damage upon both infectious and sterile insult. DAMP activation of Toll-like receptors (TLRs) induces inflammatory gene expression to mediate tissue repair. However, DAMPs have also been implicated in diseases where excessive inflammation plays a key role in pathogenesis, including rheumatoid arthritis (RA), cancer, and atherosclerosis. TLR activation by DAMPs may initiate positive feedback loops where increasing tissue damage perpetuates pro-inflammatory responses leading to chronic inflammation. Here we explore the current knowledge about distinct signalling cascades resulting from self TLR activation. We also discuss the involvement of endogenous TLR activators in disease and highlight how specifically targeting DAMPs may yield therapies that do not globally suppress the immune system.

Enhanced levels of hyaluronan in lungs of patients with COPD: relationship with lung function and local inflammation

BACKGROUND

Chronic inflammation and airway remodelling are characteristics of chronic obstructive pulmonary disease (COPD). Hyaluronan (HA) is an extracellular matrix compound with proinflammatory activity. HA levels in induced sputum from patients with COPD were measured and related to local inflammation. The expression of hyaluronan synthase 2 (HAS2) and hyaluronidase 2 (HYAL2) was analysed in lung tissue.

METHODS

Sputum was obtained from 18 patients with COPD (forced expiratory volume in 1 second (FEV(1)) 62% predicted (range 20-76)) and 14 healthy smokers. HA and inflammatory markers were measured using ELISA assays. Lung sections were obtained from five patients with severe COPD (FEV(1) <30%) and from five smokers, and mRNA levels of HAS2 and HYAL2 were analysed by polymerase chain reaction.

RESULTS

HA levels were significantly higher in the sputum from patients with COPD than controls. The COPD population appeared to consist of two subpopulations with either high or moderate HA levels. The subgroup of patients with high HA levels had lower FEV(1) than the moderate HA group. In addition, neutrophil influx and levels of interleukin-8, and the soluble tumour necrosis factor receptors R55 and R75 were significantly higher in patients with high HA levels than in those with moderate HA levels and controls. Semiquantitative analysis revealed enhanced expression of HYAL2 in lung tissue of patients with severe COPD compared with control subjects.

CONCLUSION

These data indicate a relationship between HA levels, local inflammation and severity of disease, and suggest enhanced breakdown of HA in the lungs of patients with COPD.

Connective tissue responses in acute community-acquired pneumonia

Circulating connective tissue components including the aminoterminal propeptides of type III collagen (PIIINP), type I collagen (PINP) and hyaluronan were determined in patients hospitalised for pneumonia of suspected bacterial origin. Ninety patients were included, 64 of these were followed prospectively for up to 21 days after initiation of therapy. Serum PIIINP was determined by RIA, s-PINP by ELISA, and s-hyaluronan by a radiometric assay. S-PIIINP rose significantly above the zero value within 24 h in both pneumococcal pneumonia (T0: 5.3 microg/l, 95% CI: 2.7-8.1 microg/l vs. T1: 6.7 microg/l, 95% CI: 3.8-9.1, P<0.01) and in pneumonia of unknown aetiology (T0: 4.0 microg/l, 95% CI: 3.6-4.8 vs. T1: 4.5 microg/l, 95% CI: 3.8-5.1, P<0.05) followed by a gradual decline. At T1, S-PIIINP was higher in pneumococcal pneumonia compared with pneumonia of unknown aetiology (P<0.05). By contrast, s-PINP tended to decline within 24 h in both pneumococcal pneumonia (T1: 30 microg/l, 95% CI: 23-40, ns) and in pneumonia of unknown aetiology (T1: 32 microg/l, 95% CI: 22-42, ns) followed by a steady increase. The PINP antigen size distribution remained constant throughout the follow-up period. S-hyaluronan in pneumococcal pneumonia paralleled s-PIIINP reaching a peak value on day 1 (121 microg/l, 95% CI: 65-191, P=0.38). There was a positive correlation between s-PIIINP and C-reactive protein (CRP). The study demonstrates, that community-acquired pneumonia elicits a differentiated mesenchymal response, which is turned down in response to successful antibiotic therapy.

Extensive surface phenotyping of alveolar macrophages in interstitial lung disease

There is increasing evidence implicating activated macrophages in the pathogenesis of interstitial and other lung diseases. We investigated whether there was a unique pattern of cell surface expression that constituted a disease-specific phenotype on alveolar macrophages from patients with interstitial lung disease (ILD). Macrophage cell surface receptor expression of 19 selected markers was assessed by indirect immunofluorescence and flow cytometry in bronchoalveolar lavage (BAL) fluids from patients with idiopathic pulmonary fibrosis (IPF, n = 4), scleroderma (SCL-ILD, n = 14), mild asthma (n = 7), allergy without asthma (n = 2), and normal subjects (n = 9). There was increased expression of adhesion receptors (CD11c, CD29, CD36, CD44, CD49e, CD54), receptors involved in signal transduction and/or inflammation (CD13, CD45, CD53), and other markers (CD9, CD52, CD71, CD98, HLA Class I) on macrophages from ILD patients compared to the non-ILD group. Most markers upregulated on macrophages in ILD were significantly inversely correlated with clinical parameters of disease activity such as FEV(1), FVC, and DL(CO) and positively correlated with numbers of BAL neutrophils and eosinophils. Increased expression of several cell surface markers suggests that activated alveolar macrophages may contribute to the pathophysiology of IPF and SCL-ILD.