Negative Pressure Pneumomediastinum: A Novel Concept of Spontaneous Pneumomediastinum Without Mediastinal Widening Following Weight Loss

Purpose

Spontaneous pneumomediastinum, supposedly attributed to air leakage from the respiratory tract, is a common complication of interstitial lung disease often resulting in mediastinal widening. However, several cases of pneumomediastinum without mediastinal widening have been observed. This study aimed to investigate the cause of pneumomediastinum in patients without mediastinal widening.

Patients and Methods

This study included 41 patients diagnosed with pneumomediastinum using computed tomography (CT) between July 2011 and September 2021 at Yokohama Minamikyosai Hospital; patients had undergone previous CT showing no gas density. Based on a comparison with previous CT images, the patients were classified into two groups: without mediastinal widening and with mediastinal widening.

Results

Of the 41 patients, 13 and 28 had pneumomediastinum without and with mediastinal widening, respectively. There were no significant differences in the sex, age, body mass index, or pneumomediastinum distribution between the groups. However, the rate of weight loss per month was significantly greater in the group without mediastinal widening than in that with mediastinal widening. No significant differences were observed in the respiratory function test results between the two groups; that said, 10 of the 13 patients without mediastinal widening had restrictive disorders. Pulmonary disease in this group included idiopathic pulmonary fibrosis (n = 6), interstitial lung disease with collagen disease (n = 4), and other disease (n = 1). Pneumomediastinum occurred during periods of weight loss in all patients without widening, excluding two patients without data.

Conclusion

Pneumomediastinum without mediastinal widening occurs during rapid weight loss and is often associated with restrictive lung disorders. The negative pressure attributed to the decreased plasticity of the lungs, which complements the space where the mediastinal fat has disappeared, is presumably the cause of pneumomediastinum. This pathophysiology is different from that of conventional pneumomediastinum attributed to increased intrapleural space pressure; thus, we propose to name the abovementioned pathophysiology "negative pressure pneumomediastinum".

GSK-3 Inhibition Modulates Metalloproteases in a Model of Lung Inflammation and Fibrosis

Idiopathic pulmonary fibrosis (IPF) is mainly characterized by aberrant extracellular matrix deposition, consequent to epithelial lung injury and myofibroblast activation, and inflammatory response. Glycogen synthase kinase 3 (GSK-3) is a serine-threonine kinase involved in several pathways, and its inhibition has been already suggested as a therapeutic strategy for IPF patients. There is evidence that GSK-3 is able to induce matrix metalloproteinase (MMP) expression and that its inhibition modulates MMP expression in the tissues. The aim of our study was to investigate the role of GSK-3 and its inhibition in the modulation of MMP-9 and -2 in an in vivo mouse model of lung fibrosis and in vitro using different cell lines exposed to pro-inflammatory or pro-fibrotic stimuli. We found that GSK-3 inhibition down-modulates gene expression and protein levels of MMP-9, MMP-2, and their inhibitors TIMP-1 and TIMP-2 in inflammatory cells harvested from bronchoalveolar lavage fluid (BALF) of mice treated with bleomycin as well as in interstitial alveolar macrophages and cuboidalized epithelial alveolar cells. To the same extent, GSK-3 inhibition blunted the increased MMP-9 and MMP-2 activity induced by pro-fibrotic stimuli in a human lung fibroblast cell line. Moreover, the αSMA protein level, a marker of fibroblast-to-myofibroblast transition involved in fibrosis, was decreased in primary fibroblasts treated with TGFβ following GSK-3 inhibition. Our results confirm the implication of GSK-3 in lung inflammation and fibrosis, suggesting that it might play its role by modulating MMP expression and activity but also pushing fibroblasts toward a myofibroblast phenotype and therefore enhancing extracellular matrix deposition. Thus, its inhibition could represent a possible therapeutic strategy.

The Transcription Factor SCX is a Potential Serum Biomarker of Fibrotic Diseases

Fibrosing diseases are causes of morbidity and mortality around the world, and they are characterized by excessive extracellular matrix (ECM) accumulation. The bHLH transcription factor scleraxis (SCX) regulates the synthesis of ECM proteins in heart fibrosis. SCX expression was evaluated in lung fibroblasts and tissue derived from fibrotic disease patients and healthy controls. We also measured SCX in sera from 57 healthy controls, and 56 Idiopathic Pulmonary Fibrosis (IPF), 40 Hypersensitivity Pneumonitis (HP), and 100 Systemic Sclerosis (SSc) patients. We report high SCX expression in fibroblasts and tissue from IPF patients versus controls. High SCX-serum levels were observed in IPF (0.663 ± 0.559 ng/mL, p < 0.01) and SSc (0.611 ± 0.296 ng/mL, p < 0.001), versus controls (0.351 ± 0.207 ng/mL) and HP (0.323 ± 0.323 ng/mL). Serum levels of the SCX heterodimerization partner, TCF3, did not associate with fibrotic illness. IPF patients with severely affected respiratory capacities and late-stage SSc patients presenting anti-topoisomerase I antibodies and interstitial lung disease showed the highest SCX-serum levels. SCX gain-of-function induced the expression of alpha-smooth muscle actin (α-SMA/ACTA2) in fibroblasts when co-overexpressed with TCF3. As late and severe stages of the fibrotic processes correlated with high circulating SCX, we postulate it as a candidate biomarker of fibrosis and a potential therapeutic target.