3,3′-Diindolylmethane attenuates inflammation and fibrosis in radiation-induced lung injury by regulating NF-κB/TGF-β/Smad signaling pathways

Abstract

Objective: This study aims to investigate the protective effect of 3,3′-diindolylmethane (DIM) on the radiation-induced lung injury (RILI) model and to explore its possible mechanism. Methods: A mouse model of RILI was established by thoracic irradiation, and dexamethasone was used as a positive drug to investigate the effect of DIM on RILI mice. Lung histopathology was analyzed by HE staining and Masson staining. Then the levels of inflammatory cytokines (TGF-β, TNF-α, IL-1β, and IL-6), inflammatory cell counts, and activity of MPO were detected. The expression of TGFβ1/Smad signaling pathway-related proteins was determined by immunohistochemistry. qPCR was used to analyze the mRNA expression levels of inflammatory factors, α‑SMA and COL1A1. The expression of COX-2, NF-κB, IκBα, PI3K, and Akt proteins was assessed by Western blot. Results: Histopathological staining of lung tissues showed that DIM administration alleviated the pulmonary inflammation and fibrosis caused by RILI. Moreover, the content of inflammatory factors such as IL-1β and IL-6, the expression of NF-κB pathway-related proteins, and the counts of inflammatory cells were inhibited in lung tissue, indicating that DIM can inhibit the NF-κB pathway to reduce inflammation. In addition, DIM could down-regulate the mRNA levels of α-SMA, COL1A1, and downregulate TGFβ1, Smad3, and p-Smad2/3 in lung tissues. Conclusion: Our study confirms that DIM has the potential to treat RILI in vivo by inhibiting fibrotic and inflammatory responses in lung tissue through the TGFβ/Smad and NF-κB dual pathways, respectively.

Graphic Abstract

Keywords:

• 3,3′-Diindolylmethane
• inflammatory
• NF-κB
• pulmonary fibrosis
• radiation-induced lung injury
• TGFβ/Smad pathway

Data availability statement

The data set used and analyzed in this study can be obtained from the corresponding author upon reasonable request.

Additional information

Funding

This research was funded by Zhejiang Provincial Medicinal Health Program (No. 2020KY469 and 2021KY097) and Science and Technology Program of Traditional Chinese medicine in Zhejiang Province (No. 2020ZA021 and 2021ZA022).