Abstract
BACKGROUND: We have previously shown that a whole flaxseed supplemented diet decreased the onset and severity of ovarian cancer in the laying hen, the only known animal model of spontaneous ovarian cancer. Flaxseed is rich in omega-3 fatty acids (OM3FA), mostly α-Linoleic acid (ALA), which gets converted to Docosahexaenoic acid (DHA) by the action of delta-6 desaturase enzyme. Ingestion of flaxseed also causes an increase in production of 2-methoxyestradiol (2MeOE2) via the induction of the CYP1A1 pathway of estrogen metabolism. We have previously reported that the flaxseed diet induces apoptosis via p38-MAPK pathway in chicken tumors. The objective of this study was to investigate the effect of the flaxseed diet on ovarian cancer in chickens, focusing on two hallmarks of cancer, apoptosis and angiogenesis. RESULTS: The anti-cancer effects of two active biologically derived compounds of flax diet, 2MeOE2 and DHA, were individually tested on human ovarian cancer cells and in vivo by the Chick Chorioallantoic Membrane (CAM) assay. Our results indicate that a flaxseed-supplemented diet promotes apoptosis and inhibits angiogenesis in chicken tumors but not in normal ovaries. 2MeOE2 promotes apoptosis in human ovarian cancer cells, inhibits angiogenesis on CAM and its actions are dependent on the p38-MAPK pathway. DHA does not have any pro-apoptotic effect on human ovarian cancer cells but has strong anti-angiogenic effects as seen on CAM, but not dependent on the p38-MAPK pathway. CONCLUSIONS: Dietary flaxseed supplementation promotes a pro-apoptotic and anti-angiogenic effect in ovarian tumors, not in normal ovaries. The biologically derived active compounds from flaxseed diet act through different pathways to elicit their respective anti-cancer effects. A flaxseed-supplemented diet is a promising approach for prevention of ovarian cancer as well as having a significant potential as an adjuvant treatment to supplement chemotherapeutic agents for treatment of advanced stages of ovarian cancer.
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Key Points
Ovarian cancer is one of the deadliest gynecological cancers, ranking fifth in all cancer-related deaths in women. The laying hen provides the only animal model that develops the disease naturally. Histologically, the disease closely resembles the human form of the disease. Previousresearch using the chicken model has shown that a flaxseed diet can reduce both the severity and incidence of ovarian cancer.
Estradiol is metabolized in the liver through its hydroxylation by three different cytochrome P450 (CYP) enzymes. CYP1A1 produces the 2-hydroxy metabolites, while CYP1B1 and CYP3A4 yield 4-hydroxy and 16-hydroxy metabolites, respectively. 2-hydroxy estrogens can be readily converted into 2-methoxy estrogens by catechol-O-methyltransferase enzyme (COMT). 2-methoxyestradiol (2MeOE2) is easily excreted and known to be the least potent estrogenic metabolite while the 4-hydroxyestradiol is readily oxidized to a genotoxic compound, 3,4 quinone. Therefore, the whole flax diet favors the CYP1A1 pathway for generation of 2MeOE2, resulting in a higher 2-hydroxy:16-hydroxy estradiol ratio, which has been shown to be protective against postmenopausal breast cancer. A flax diet promotes the CYP1A1 pathway of estrogen metabolism while decreasing both CYP1B1 and CYP3A4 in the pre-neoplastic chicken ovaries. The upregulation in CYP1A1 enzyme also parallels the increase in 2-hydroxy: 16-hydroxy estradiol ratio and the 2MeOE2 level in the serum of chickens. 2MeOE2 is an established anti-proliferative and anti-apoptotic agent. A whole flax diet promotes apoptosis in the chicken ovaries and also activation of the p38-MAPK pathway. The objective of this study was to explore mechanisms of the anti-cancer effects of the flaxseed diet in ovarian carcinogenesis and explore how the biologically active components of flaxseed diets, 2MeOE2 and DHA, accomplish their actions, focusing on apoptosis and angiogenesis.
The present study demonstrated that 2MeOE2 promotes apoptosis and inhibits angiogenesis in vitro and both the actions are dependent on the p38-MAPK pathway. DHA has an anti-angiogenic effect but does not induce apoptosis in ovarian cancer cells, and its effects are not p38-MAPK dependent. The effects of 2MeOE2 and DHA were independent of ER-α expression in human ovarian cancer cells. The flax oil diet did not cause a significant increase in apoptosis in normal or cancerous chicken ovaries. However, whole flax diet had a much greater pro-apoptotic effect than the DFM diet on chicken ovarian tumors, suggesting an anti-cancer entourage effect provided by the whole flaxseed-supplemented diet where the pro-apoptotic effect of the whole seed exceeds the sum of the effects of the individual components.
A flaxseed-supplemented diet, which increases the systemic production of 2MeOE2 and DHA, induces apoptosis and decreases angiogenesis in ovarian tumors but not in normal ovarian tissues. 2MeOE2 and DHA both have anti-angiogenic effects. 2MeOE2 has pro-apoptotic effects but not DHA. Anti-cancer actions of 2MeOE2 are dependent on p38-MAPK pathway, however the actions of DHA do not involve p38-MAPK. Dietary supplementation with flaxseed may help prevent ovarian cancer in women or help them live with ovarian cancer instead of die from it.