Tetrahydrocurcumin suppresses tumor growth in colorectal cancer through modulating linolenic acid metabolism

While tetrahydrocurcumin (THC) is a stable bioactive metabolite of curcumin, its role in modulating the gut microbiota-metabolism axis in colorectal cancer (CRC) remains unclear. This study aims to investigate the therapeutic effects of THC in CRC, with a focus on modulation of the gut microbiota and the associated metabolic changes. The efficacy of THC was evaluated in the human CRC cell line HCT116 and organoids in vitro using cell counting kit-8 (CCK-8), colony formation, apoptosis, and organoid viability assays. An azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced CRC mouse model was utilized to evaluate the therapeutic effects of THC in vivo , including histopathological analysis, organ indexes, and serum cytokine levels (TNF- α , IL-6, IL-1 β ) quantified via ELISA. Flow cytometry was used to analyze peripheral blood lymphocyte subpopulations. Gut microbiota composition was characterized by 16S rRNA sequencing, while metabolic profiling was conducted using untargeted metabolomics. The biological significance of alpha-linolenic acid (ALA), a key metabolite modulated by THC, was further investigated in vitro . THC suppressed CRC cells and organoid proliferation and induced apoptosis in vitro . In vivo , THC inhibited tumor progression, improved intestinal histopathology, and enhanced body weight and organ indices, particularly the thymus. ELISA analyses indicated a reduction in systemic inflammation, as evidenced by decreased serum levels of TNF- α , IL-6, and IL-1 β , alongside a diminished proportion of CD3 + CD279 + lymphocytes in peripheral blood. 16S rRNA sequencing revealed substantial alterations in gut microbiota composition, notably an increased abundance of Monoglobus and Acinetobacter . Additionally, metabolomic analysis identified 23 differentially regulated metabolites, including ALA, leucine, glutamic acid, and L -asparagine, which are implicated in tumor-associated metabolic pathways. Among these, ALA emerged as a prominent metabolite regulated by THC, demonstrating intrinsic antiproliferative effects against CRC cells and organoids in vitro , which were further potentiated in the presence of THC. In summary, THC exerts significant antitumor activity against AOM/DSS-induced CRC by attenuating inflammation, modulating immune responses, and reshaping gut microbiota composition and tumor-associated metabolic pathways. Notably, ALA, a key metabolite regulated by THC, exerts direct inhibitory effects on CRC cells growth in vitro , which are further enhanced in conjunction with THC treatment. These findings highlight THC as a promising therapeutic candidate for CRC, with potential implications for microbiota- and metabolism-targeted cancer interventions.