Diterpenoid alkaloids isolated from Delphinium trichophorum alleviate pulmonary fibrosis via the TGF-β/Smad pathway in 3T6 and HFL-1 cells

Delphinium trichophorum Franch (DTF), a species endemic to China, has been widely used for centuries in Tibet as an indigenous medicine for treating cough, pneumonia, and pulmonary fibrosis. Hetisine-type C₂₀-diterpenoid alkaloids have been reported to be characteristic and active ingredients. Herein, five ones with relatively high contents in D. trichophorum, including 2α,11α,13β-triacetylhetisine (DTF1), trichodelphinine A (DTF2), trichodelphinine D (DTF3), 2α-acetyl-11α,13β-dihydroxyhetisine (DTF4), and trichodelphinine C (DTF5), were investigated for anti-fibrosis effects using fibroblasts induced by TGF-β1 or LPS for the first time. The results showed that all five tested compounds decreased hydroxyproline (HYP) levels and inhibited the abnormal proliferation of 3T6 and HFL-1 cells induced by either TGF-β1 or LPS. Moreover, DTF1 and DTF2 attenuated the production of collagen (Col-1 and Col-3) at relatively low doses, suggesting their higher efficiency among the five alkaloids. Based on large-scale ligand-based pharmacophore modeling, TGFBR1 was screened as a potential target for these tested alkaloids. The molecular docking results also exhibited high-affinity interactions between TGFBR1 and five alkaloids, especially DTF1 and DTF2. Further experiments revealed that DTF1 and DTF2 could inhibit the expression of TGF-β1 and α-SMA and the phosphorylation of Smad3 and Smad4 while restoring the expression of Smad7 protein. Overall, DTF1 and DTF2 may reduce collagen generation and delay the development of pulmonary fibrosis by inhibiting the activation of the TGF-β/Smad signaling pathway. Our results provide experimental and theoretical evidence for DTF1 and DTF2 as superior candidates for further development of anti-fibrotic drugs.