Omega-3 Polyunsaturated Fatty Acids Time-Dependently Reduce Cell Viability and Oncogenic MicroRNA-21 Expression in Estrogen Receptor-Positive Breast Cancer Cells (MCF-7).

Key Findings

To date, no in vitro studies have looked at the miRNA-mediated response of breast cancer cells to ALA alone or ALA:EPA:DHA combination. MiRNA-21 (miR-21) is an oncomiR found to be overexpressed in the serum and breast tissue of breast cancer patients compared to healthy controls. This study aimed to determine the effect of ALA alone and combined with EPA and DHA at the blood molar ratios seen in either humans (1.0:1.0:2.5, ALA:EPA:DHA) or animals (mice) (1.0:0.4:3.1, ALA:EPA:DHA) post FSO consumption (containing ALA) on MCF-7 cell viability, miR-21 and one of its targets, PTEN expression. Overall, the results suggest that ALA alone and combined with EPA and DHA at ratios seen in mice and humans post-ALA consumption are able to reduce cell viability and modulate miR-21 expression but they are not directly associated with PTEN gene and protein expressions. The susceptibility of miR-21 to n-3 PUFAs appears to be temporal in nature, and also specific to the type of n-3 PUFA and dosage. Higher DHA concentrations seen in the AnR treatment appear to be most effective at reducing miR-21 expression over the greatest temporal range. Results suggest that time course experiments are crucial when elucidating miRNA-dependent pathways in breast cancer, particularly for clinical applications.

ABSTRACT

The omega-3 polyunsaturated fatty acid (n-3 PUFA), α-linolenic acid (ALA), and its metabolites, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), independently reduce the growth of breast cancer cells in vitro, but the mechanisms, which may involve microRNA (miRNA), are still unclear. The expression of the oncomiR, miR-21, is reduced by DHA treatment, but the effects of ALA on miR-21, alone or combined with EPA and DHA under physiologically relevant concentrations, have not been investigated. The effects of ALA alone and +/-EPA and DHA at the blood molar ratios seen in either humans (1.0:1.0:2.5, ALA:EPA:DHA) or mice (1.0:0.4:3.1, ALA:EPA:DHA) post flaxseed oil consumption (containing ALA) were assessed in vitro in MCF-7 breast cancer cells. Cell viability and the expression of miR-21 and its molecular target, phosphatase and tension homolog (PTEN, gene and protein), at different time points, were examined. At 1, 3, 48 and 96 h ALA alone and 24 h animal ratio treatments significantly reduced MCF-7 cell viability, while 1 and 3 h ALA alone and human and animal ratio treatments all significantly reduced miR-21 expression, and 24 h animal ratio treatment reduced miR-21 expression; these effects were not associated with changes in PTEN gene or protein expressions. We showed for the first time that ALA alone or combined with EPA and DHA at levels seen in human and animal blood post-ALA consumption can significantly reduce cell viability and modulate miR-21 expression in a time- and concentration-dependent manner, with the animal ratio containing higher DHA having a greater effect. The time dependency of miR-21 effects suggests the significance of considering time as a variable in miRNA studies, particularly of miR-21.