Targeting c-Src/PKC<b>α</b>/MAPK/NF-<b>κ</b>B: Salvianolic Acid A as a Protective Agent against Silica Nanoparticle-Induced Lung Inflammation

Background: Silica nanoparticles (SiNPs), commonly utilized in industrial and biomedical fields, are known to provoke pulmonary inflammation by elevating cyclooxygenase-2 (COX-2) levels in human pulmonary alveolar epithelial cells (HPAEpiCs). Salvianolic acid A (SAA), a water-soluble polyphenol extracted from Salvia miltiorrhiza (Danshen), possesses well-documented antioxidant and anti-inflammatory activities. Nevertheless, its potential to counteract SiNP-induced inflammatory responses in the lung has not been thoroughly explored. Objective: This study aimed to evaluate the protective role and mechanistic actions of SAA against SiNP-triggered inflammation in both cellular and animal models. Methods: HPAEpiCs were pre-incubated with SAA prior to SiNP exposure to investigate changes in COX-2 expression and prostaglandin E2 (PGE2) secretion. A murine model of SiNP-induced lung inflammation was used for in vivo validation. Key inflammatory signaling proteins, including c-Src, PKCα, p42/p44 MAPK, and NF-κB p65, were analyzed for phosphorylation status. NF-κB promoter activity was also assessed. Pharmacological inhibitors and siRNA-mediated silencing were employed to verify the signaling cascade responsible for COX-2 regulation. Results: SAA treatment markedly suppressed SiNP-induced upregulation of COX-2 and PGE2 in both HPAEpiCs and mouse lung tissues. SAA also reduced the activation (phosphorylation) of c-Src, PKCα, p42/p44 MAPK, and NF-κB p65, alongside diminishing NF-κB transcriptional activity. Functional studies using inhibitors and gene silencing further supported the involvement of these pathways in mediating the observed anti-inflammatory effect. Conclusion: By concurrently targeting several upstream pro-inflammatory signaling pathways, SAA demonstrates robust potential in alleviating SiNP-induced lung inflammation. These results highlight SAA as a promising candidate for therapeutic intervention in environmentally triggered respiratory conditions.