Stevioside attenuates bleomycin-induced pulmonary fibrosis by activating the Nrf2 pathway and inhibiting the NF-κB and TGF-β1/Smad2/3 pathways

Objective: This study aimed to investigate the effects of stevioside (STE) on pulmonary fibrosis (PF) and the potential mechanisms. Methods: In this study, a mouse model of PF was established by a single intratracheal injection of bleomycin (BLM, 3 mg/kg). The experiment consisted of four groups: control group, BLM group, and STE treatment groups (STE 50 and 100 mg/kg). ELISA and biochemical tests were conducted to determine the levels of TNF-α, IL-1β, IL-6, NO, hydroxyproline (HYP), SOD, GSH, and MDA. Histopathological changes and collagen deposition in lung tissues were observed by HE and Masson staining. Immunohistochemistry was performed to determine the levels of collagen I-, collagen III-, TGF-β1- and p-Smad2/3-positive cells. Western blot analysis was used to measure the expression of epithelial-mesenchymal transition (EMT) markers, including α-SMA, vimentin, E-cadherin, and ZO-1, as well as proteins related to the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, nuclear transcription factor-κB (NF-κB) pathway, and TGF-β1/Smad2/3 pathway in lung tissues. Results: STE significantly alleviated BLM-induced body weight loss and lung injury in mice, decreased HYP levels, and reduced the levels of collagen I- and collagen III-positive cells, thereby decreasing extracellular matrix (ECM) deposition. Moreover, STE markedly improved oxidative stress (MDA levels were decreased, while SOD and GSH activity were enhanced), the inflammatory response (the levels of TNF-α, IL-1β, IL-6, and NO were reduced), and EMT (the expression of α-SMA and vimentin was downregulated, and the expression of E-cadherin and ZO-1 was upregulated). Further mechanistic analysis revealed that STE could activate the Nrf2 pathway and inhibit the NF-κB and TGF-β1/Smad2/3 pathways. Conclusion: STE may alleviate oxidative stress by activating the Nrf2 pathway, suppress the inflammatory response by downregulating the NF-κB pathway, and inhibit EMT progression by blocking the TGF-β1/Smad2/3 pathway, thereby improving BLM-induced PF.

[Rutaecarpine protects against bleomycin-induced pulmonary fibrosis through inhibiting Notch1/eIF3a signaling pathway in rats]

To investigate whether the protection of rutaecarpine against bleomycin-induced pulmonary fibrosis is mediated by inhibiting Notch1/eukaryotic initiation factor 3a (eIF3a) signaling pathway, and whether these effects are related to the synthesis and release of calcitonin gene-related peptide (CGRP) and inhibition of epithelial-mesenchymal transition (EMT) of alveolar epithelial cells, male Sprague-Dawley rats were randomly divided into five groups (n=12), respectively, Control group, bleomycin group, rutaecarpine (100, 300 mg·kg⁻¹) group and capsaicin plus rutaecarpine (300 mg·kg⁻¹) group. Bleomycin (5 mg·kg⁻¹) was used to induce pulmonary fibrosis rat model. Rats were given capsaicin (50 mg·kg⁻¹) by subcutaneous injections 1 days before and 7, 14, 21 days after induce pulmonary fibrosis rat model to deplete endogenous CGRP. At the end of experiments, blood was collected from carotid artery to determinate the plasma levels of CGRP by ELISA. Pulmonary tissue change was observed by HE staining. Masson's trichrome stain was used to demonstration collagen deposition. The collagen I expression in pulmonary tissue was measured by immunohistochemisty. The expression of CGRP, Notch1, eIF3a, collagen I, vimentin, alpha-smooth muscle actin (α-SMA), E-cadherin and zonula occludens-1 (ZO-1) was detected by qPCR or Western blot. Compared with the control group, the pulmonary tissue of the bleomycin group showed significant fibrosis, including significant disturbed alveolar structure, marked thickening of the interalveolar septa and dense interstitial infiltration by inflammatory cells and fibroblasts, and concomitantly with the decrease in plasma CGRP and expression of CGRP. Importantly the expression of E-cadherin and ZO-1 was decreased and expression of Notch1, eIF3a, collagen I, vimentin and α-SMA was increased in bleomycin group (P<0.05 or P<0.01). Compared with the bleomycin group, rutaecarpine (100, 300 mg·kg⁻¹) group significantly reduced bleomycin-induced pulmonary injury concomitantly with the increase in plasma CGRP and expression of CGRP. Importantly the expression of E-cadherin and ZO-1 was increased and expression of Notch1, eIF3a, collagen I, vimentin and α-SMA was decreased by rutaecarpine treatment (P<0.05 or P<0.01). All these effects of rutaecarpine were abolished by capsaicin.These results suggest that rutaecarpine protects against bleomycin-induced pulmonary fibrosis by inhibiting Notch1/eIF3a signaling pathway, alleviating EMT process, which is related to the increased synthesis and release of CGRP.