Dietary intakes of omega-6 and omega-3 polyunsaturated fatty acids and the risk of breast cancer.

Experimental studies suggest detrimental effects of omega-6 polyunsaturated fatty acids (PUFA), and beneficial effects of omega-3 PUFAs on mammary carcinogenesis, possibly in interaction with antioxidants. However, PUFA food sources are diverse in human diets and few epidemiologic studies have examined whether associations between dietary PUFAs and breast cancer risk vary according to food sources or antioxidant intakes. The relationship between individual PUFA intakes estimated from diet history questionnaires and breast cancer risk was examined among 56,007 French women. During 8 years of follow-up, 1,650 women developed invasive breast cancer. Breast cancer risk was not related to any dietary PUFA overall; however, opposite associations were seen according to food sources, suggesting other potential effects than PUFA per se. Breast cancer risk was inversely associated with alpha-linolenic acid (ALA) intake from fruit and vegetables [highest vs. lowest quintile, hazard ratio (HR) 0.74; 95% confidence interval (CI) 0.63, 0.88; p trend < 0.0001], and from vegetable oils (HR 0.83; 95% CI 0.71, 0.97; p trend 0.017). Conversely, breast cancer risk was positively related to ALA intake from nut mixes (p trend 0.004) and processed foods (p trend 0.068), as was total ALA intake among women in the highest quintile of dietary vitamin E (p trend 0.036). A significant interaction was also found between omega-6 and long-chain omega-3 PUFAs, with breast cancer risk inversely related to long-chain omega-3 PUFAs in women belonging to the highest quintile of omega-6 PUFAs (p interaction 0.042). These results emphasize the need to consider food sources, as well as interactions between fatty acids and with antioxidants, when evaluating associations between PUFA intakes and breast cancer risk.

Acetyl-CoA carboxylase alpha is essential to breast cancer cell survival.

Activation of de novo fatty acid synthesis is a characteristic feature of cancer cells. We have recently described an interaction between acetyl-CoA carboxylase alpha (ACCalpha), a key enzyme in fatty acid synthesis, and BRCA1, which indicates a possible connection between lipid synthesis and genetic factors involved in susceptibility to breast and ovarian cancers. For this reason, we explored the role of ACCalpha in breast cancer cell survival using an RNA interference (RNAi) approach. We show that specific silencing of either the ACCalpha or the fatty acid synthase (FAS) genes in cancer cells results in a major decrease in palmitic acid synthesis. Depletion of the cellular pool of palmitic acid is associated with induction of apoptosis concomitant with the formation of reactive oxygen species (ROS) and mitochondrial impairment. Expression of a small interfering RNA (siRNA)-resistant form of ACCalpha mRNA prevented the effect of ACCalpha-RNAi but failed to prevent the effect of FAS gene silencing. Furthermore, supplementation of the culture medium with palmitate or with the antioxidant vitamin E resulted in the complete rescue of cells from both ACCalpha and FAS siRNA-induced apoptosis. Finally, human mammary epithelial cells are resistant to RNAi against either ACCalpha or FAS. These data confirm the importance of lipogenesis in cancer cell survival and indicate that this pathway represents a key target for antineoplastic therapy that, however, might require specific dietary recommendation for full efficacy.