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 at molar blood ratios. 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. This study is the first to address the time- and n-3 PUFA concentration-dependent nature of cell viability and miR-21 expression in human breast cancer cells. The authors showed that miR-21 expression is significantly decreased following shorter treatment periods (1 and 3 h), regardless of n-3 PUFA treatment (ALA +/− EPA + DHA at AnR or HuR) but this was not associated with changes in its validated molecular target, PTEN, at either the gene or protein level. In the current study, treatment concentrations were modeled based on the relative blood levels of ALA, EPA and DHA observed after FSO interventions in mice and humans, where mice have been shown to have relatively more DHA and less EPA (ALA:EPA:DHA = 1.0:1.0:2.5 in human, versus 1.0:0.4:3.1 in mice). Additional work with n-3 PUFAs has also shown that the IC50 values for the fatty acids are as follows: ALA > EPA > DHA, demonstrating that DHA possesses the greatest bioactive capacity, which enables DHA to most significantly impact cell death.

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.