Docosahexaenoic acid inhibits the invasion and migration of colorectal cancer by reversing EMT through the TGF-β1/Smad signaling pathway

The primary cause of mortality in colorectal cancer (CRC) patients is tumor metastasis. The epithelial-mesenchymal transition (EMT) stands out as a crucial factor promoting the metastasis of CRC. Previous findings suggest a potential inhibitory effect of docosahexaenoic acid (DHA) on CRC metastasis, but the precise mechanism remains unknown, this study aims to explore this issue. We assessed metastasis and recurrence, all-cause mortality, and cancer-related mortality rates according to DHA intake in independent CRC cohorts (n = 367) by survival analysis. The ability of DHA to block CRC cell migration and invasion was tested using transwell and wound-healing assays. The regulation of EMT marker genes in CRC by DHA was detected by quantitative real-time PCR (qPCR) and immunoblotting, and the effect of DHA on the TGF-β1/Smad signaling pathway was further investigated. These cellular findings were validated using a subcutaneous CRC mouse model. Survival analyses showed that lower DHA intake was associated with a higher risk of CRC metastasis and a poorer prognosis. In vitro experiments showed that DHA inhibits the TGF-β1/Smad signaling pathway and regulates downstream transcription factors, thereby reversing the EMT and inhibiting invasion and migration. In the mouse model, dietary DHA supplementation effectively increased blood DHA concentrations and inhibited CRC metastasis. Our study demonstrated that DHA inhibits CRC invasion and metastasis by inhibiting the TGF-β1/Smad signaling pathway. Increased intake of DHA among CRC patients may provide additional benefits to the prognosis of colorectal cancer.