Calprotectin inhibition attenuates silica-induced lung fibrosis.

Respirable silica exposure adversely affects lung tissue immunopathology, triggering oxidative bursts in macrophages and neutrophils, releasing Damage-associated molecular patterns (DAMPs), including calprotectin proteins, S100A8, and S100A9. Calprotectin constitutes up to 45% of these innate immune cells, and serum levels of these alarmins correlate with inflammation, fibrosis, remodelling, and drug response in chronic diseases, including inflammatory bowel disease, asthma, and cystic fibrosis. The consequence of releasing calprotectin protein could trigger the pro-fibrotic effect of silicosis. This study aimed to investigate the role of calprotectin (S100A8/S100A9) as a pro-inflammatory and pro-fibrotic mediator in silica-induced lung fibrosis and evaluated the therapeutic potential of the calprotectin inhibitor, paquinimod. Using a mouse model of silicosis, silica exposure significantly elevated calprotectin expression, lung inflammation, and fibrosis, as evidenced by increased levels of epithelial-to-mesenchymal transition (EMT) markers, collagen deposition, and matrix metalloproteinases (MMPs). In vitro, stimulation of human bronchial fibroblasts with S100A8/S100A9 upregulated fibrotic markers (COL1A1 and α-SMA), which were reduced by inhibitors of TLR4 and RAGE receptors, as well as by paquinimod. Treatment with paquinimod effectively reduced these pathological changes, normalized calprotectin levels, decreased fibrosis scores, and attenuated NF-κB activation. These findings highlighted calprotectin's pivotal role in silica-induced lung fibrosis and inflammation, suggesting that its inhibition could be a promising therapeutic approach for silicosis and other fibro-inflammatory lung diseases. Further research is warranted to explore the precise mechanisms linking calprotectin to lung fibrosis and its potential as a biomarker and therapeutic target.