Pyrogallol, an absorbable microbial gallotannins-metabolite and mango polyphenols (Mangifera Indica L.) suppress breast cancer ductal carcinoma in situ proliferation in vitro
Mango is rich in bioactive absorbable polyphenols, but also contains considerable amounts of unabsorbable gallotannins at varying degrees of polymerization. Gallotannins are not absorbable upon consumption and have rarely been considered in the discussion of health benefits of polyphenols. Therefore, the objective of this study was to investigate the anti-proliferative activities of the major microbial metabolite of gallotannins, pyrogallol (PG) and a low molecular weight fraction of mango (Mangifera Indica L.) polyphenols (ML) and involved pathways including the AKT/mTOR signaling axis in an in situ breast cancer cell line, MCF10DCIS.COM. Fluorouracil (5-FU), a widely used genotoxic cancer therapeutic, was used a positive control and in combination with ML and PG to assess potential interactions. Concentrations that were non-cytotoxic in non-cancer cells were identified in non-cancer mammary fibroblasts (MCF-12F) and only non-cytotoxic dietarily relevant concentrations were selected for the investigation in MCF10DCIS.COM cancer cells. In addition to proliferation and viability, mRNA and expression of total and phosphorylated protein were investigated. Results show that both, ML and PG significantly reduced proliferation in MCF10DCIS.COM, but did not significantly reduce viability following a 48 h exposure. ML significantly reduced mRNA expression of mTOR and HIF-1α, while PG significantly reduced mRNA of IGF-1R, AKT, mTOR and HIF-1α. ML and PG reduced total protein expression of IGF-1R, IR, AKT, mTOR, and P70S6K. In addition, PG reduced IRS protein. Both treatments also had an effect on phosphorylated protein levels, with PG significantly reducing IGF-1R, AKT, and P70S6K levels. ML had a similar effect and significantly decreased IR, AKT, and P70S6K phosphorylation levels. Within the low concentration-range, ML and PG did not interact with the cytotoxic activities of 5-FU. Overall, the AKT/mTOR signaling axis appears to be implicated as causal in decreased proliferation induced by diet-relevant concentrations of ML and PG.