Antifibrotic Effects of Thymus syriacus Essential Oil in Bleomycin-Induced Pulmonary Fibrosis via Suppression of the TGF-β1/Smad2 Axis

Background: Pulmonary fibrosis (PF) is an irreversible interstitial lung disease in which the TGF-β/SMAD signaling pathway plays a critical role in its pathogenesis. Due to the anti-inflammatory and antioxidant properties of Thymus species, it is hypothesized that they may suppress pulmonary fibrosis by modulating the TGF-β/SMAD pathway. This study aimed to investigate the potential antifibrotic effects of Thymus syriacus essential oil (TS) on the TGF-β/SMAD pathway in bleomycin-induced PF. Methods: PF was induced with bleomycin, and TS was administered at concentrations of 50 and 100 mg/mL for 28 days. mRNA and protein levels of TGF-β1, SMAD2, COL1, and α-SMA in lung tissues isolated were analyzed using real-time PCR and ELISA. TNF-α levels in BALF were measured by ELISA. ROS and MDA levels in lung issues were determined using 2,7-DHCFDA and TBARS tests, respectively. Histopathological evaluation was performed using Hematoxylin–Eosin and Masson’s trichrome staining. Blood samples were analyzed for kidney, liver, and cardiac toxicity markers. The chemical composition of TS was determined by GC–MS. Results: TS significantly reduced levels of TGF-β1, SMAD2, COL1, α-SMA, TNF-α, ROS and MDA compared to the BLM group. PF alterations were markedly attenuated by TS treatment. Thymol, p-cymene and carvacrol were identified as major constituents of TS. Conclusion: Overall, TS alleviates pulmonary fibrosis by suppressing the TGF-β/SMAD2 signaling pathway.