Enterolactone and breast cancer: methodological issues may contribute to conflicting results in observational studies

Tailoring Potential Natural Compounds for the Treatment of Luminal Breast Cancer

Breast cancer (BC) is the most diagnosed cancer worldwide, mainly affecting the epithelial cells from the mammary glands. When it expresses the estrogen receptor (ER), the tumor is called luminal BC, which is eligible for endocrine therapy with hormone signaling blockade. Hormone therapy is essential for the survival of patients, but therapeutic resistance has been shown to be worrying, significantly compromising the prognosis. In this context, the need to explore new compounds emerges, especially compounds of plant origin, since they are biologically active and particularly promising. Natural products are being continuously screened for treating cancer due to their chemical diversity, reduced toxicity, lower side effects, and low price. This review summarizes natural compounds for the treatment of luminal BC, emphasizing the activities of these compounds in ER-positive cells. Moreover, their potential as an alternative to endocrine resistance is explored, opening new opportunities for the design of optimized therapies.

Distribution, biosynthesis and therapeutic potential of lignans

Lignans have long been known for their abundant therapeutic properties due to their polyphenolic structure. Linseed is the richest plant source of lignans and has been studied widely for their properties. The most prevalent lignan, secoisolariciresinol diglucoside (SDG), is consumed with linseed and converted into mammalian lignans, enterodiol (END) and enterolactone (ENL), by the gut microbiota. SDG can easily be assessed using HPLC and its deglycosylated form viz secoisolariciresinol can be asses using GC-MS techniques. Variety of extraction and analysis methods has been reported for plant lignans. SDG is known to have therapeutic properties including anti-oxidant, anti-cancerous, anti-inflammatory, modulation of gene expression, anti-diabetic, estrogenic and anti-estrogenic. Despite a large number of bioactivities, strong evidences for the underlying mechanisms for most of the properties are still unknown. SDG is most studied for its anti-cancerous properties. But the use of lignans as anti-carcinogenic agent is limited and commercially not reported due to challenges of purification at commercial level, rapid metabolism, untargeted delivery and toxic compounds associated with lignans. Exploration of more prominent and active derivatives of SDG and their targeted drug delivery should be an important research toward the use of bioactive lignans of linseed.

Dietary Factors and Breast Cancer Prognosis among Breast Cancer Survivors: A Systematic Review and Meta-Analysis of Cohort Studies

Simple Summary

While most systematic reviews have focused on the association between dietary factors and breast cancer incidence, this current study focuses on the association between comprehensive dietary factors and breast cancer prognosis among breast cancer survivors by systematic review and meta-analysis. We reviewed a total of 63 cohort studies to assess the association between dietary factors and breast cancer prognosis by subgroup analysis with prediagnostic or postdiagnostic dietary intake, menopausal status, and dietary or supplementary micronutrient intake. We found that unhealthy dietary patterns, including the intake of beer and saturated fat, exacerbated the risk of breast cancer prognosis; however, the supplementation of most vitamins was desirable for breast cancer prognosis. Therefore, this study’s systematic review and meta-analysis provide useful dietary information for the development of dietary guidelines/recommendations to improve prognosis among breast cancer survivors.

Abstract

Few studies have summarized the association between dietary factors and breast cancer (BC) prognosis among breast cancer survivors (BCS). Therefore, we carried out a systematic review and meta-analysis to determine the associations between dietary factors and BC prognosis among BCS. We performed a literature search in PubMed and Embase to investigate the association between dietary factors and BC prognosis. We applied a random-effects model to compute the hazard ratio/relative risk and their 95% confidence intervals and heterogeneity (Higgins I²) and to generate forest plots using STATA. Among the 2279 papers identified, 63 cohort studies were included in the systematic review and meta-analysis. Our main finding was that higher consumption of beer and saturated fat negatively affected BC prognosis. However, the intake of lignans, fiber, multivitamins, and antioxidants was negatively associated with the risk of mortality. Furthermore, we performed subgroup analyses by menopausal status and dietary or supplementary micronutrient intake. Most trends were similar to the main findings; in particular, the vitamin C, vitamin D, and vitamin E supplements decreased the risk of mortality. This study’s current systematic review and meta-analysis provide comprehensive dietary information for the development of dietary guidelines/recommendations to improve prognosis among BCS.

Randomized Phase IIB Trial of the Lignan Secoisolariciresinol Diglucoside in Premenopausal Women at Increased Risk for Development of Breast Cancer

We conducted a multiinstitutional, placebo-controlled phase IIB trial of the lignan secoisolariciresinol diglucoside (SDG) found in flaxseed. Benign breast tissue was acquired by random periareolar fine needle aspiration (RPFNA) from premenopausal women at increased risk for breast cancer. Those with hyperplasia and ≥2% Ki-67 positive cells were eligible for randomization 2:1 to 50 mg SDG/day (Brevail) versus placebo for 12 months with repeat bio-specimen acquisition. The primary endpoint was difference in change in Ki-67 between randomization groups. A total of 180 women were randomized, with 152 ultimately evaluable for the primary endpoint. Median baseline Ki-67 was 4.1% with no difference between arms. Median Ki-67 change was -1.8% in the SDG arm (P = 0.001) and -1.2% for placebo (P = 0.034); with no significant difference between arms. As menstrual cycle phase affects proliferation, secondary analysis was performed for 117 women who by progesterone levels were in the same phase of the menstrual cycle at baseline and off-study tissue sampling. The significant Ki-67 decrease persisted for SDG (median = -2.2%; P = 0.002) but not placebo (median = -1.0%). qRT-PCR was performed on 77 pairs of tissue specimens. Twenty-two had significant ERα gene expression changes (<0.5 or >2.0) with 7 of 10 increases in placebo and 10 of 12 decreases for SDG (P = 0.028), and a difference between arms (P = 0.017). Adverse event incidence was similar in both groups, with no evidence that 50 mg/day SDG is harmful. Although the proliferation biomarker analysis showed no difference between the treatment group and the placebo, the trial demonstrated use of SDG is tolerable and safe.

The association between soy isoflavone intake and menopausal symptoms after breast cancer diagnosis: a prospective longitudinal cohort study on Chinese breast cancer patients

PURPOSE

This study investigated the association between soy isoflavone intake and menopausal symptoms (MPS) among Chinese women with early stage breast cancer in a prospective cohort study.

METHODS

In an on-going prospective cohort study that involved 1462 Chinese women with early stage breast cancer, MPS were assessed at 18, 36 and 60 months after cancer diagnosis using the validated menopausal rating scale (MRS) questionnaire. Daily soy food intake for the previous 12 months was assessed at the same time using a validated food frequency questionnaire. The associations between MPS and soy isoflavone intake were evaluated in multivariable logistic regression analyses.

RESULTS

The prevalence of MPS was almost the same during the first 60 months after cancer diagnosis, which were 64.5%, 65.2%, and 63.9% at 18, 36, and 60 months, respectively. Patients with MPS tended to be younger than those without MPS. The intake of soy isoflavones was not associated with the total score of MRS at 18-month follow-up [highest vs lowest tertile, odds ratio (OR) = 1.00, 95% CI 0.75-1.34]. Similarly, no significant association was noted at 36-month (OR = 1.25, 95% CI 0.92-1.69) and 60-month (OR = 1.21, 95% CI 0.84-1.74) follow-up. With regards to specific domain within MRS, the risk of symptoms presenting in somatic domain was higher among breast cancer patients who were in the highest tertile of soy isoflavone intake at 36 months post-diagnosis (OR = 1.44, 95% CI 1.07-1.94, P-trend = 0.02), compared with the lowest tertile, where a stronger significant association was noted among patients who were younger than 60 years (OR = 1.52, 95% CI 1.05-2.20, P-trend = 0.03) and pre-menopausal (OR = 3.81, 95% CI 1.85-8.11, P-trend < 0.01).

CONCLUSION

The present study provided further evidence that soy isoflavone consumption was not associated with MPS among Chinese breast cancer patients. In fact, patients with higher intake of soy isoflavone have increased risk of experiencing somatic symptoms.

The Microbiome-Estrogen Connection and Breast Cancer Risk

The microbiome is undoubtedly the second genome of the human body and has diverse roles in health and disease. However, translational progress is limited due to the vastness of the microbiome, which accounts for over 3.3 million genes, whose functions are still unclear. Numerous studies in the past decade have demonstrated how microbiome impacts various organ-specific cancers by altering the energy balance of the body, increasing adiposity, synthesizing genotoxins and small signaling molecules, and priming and regulating immune response and metabolism of indigestible dietary components, xenobiotics, and pharmaceuticals. In relation to breast cancer, one of the most prominent roles of the human microbiome is the regulation of steroid hormone metabolism since endogenous estrogens are the most important risk factor in breast cancer development especially in postmenopausal women. Intestinal microbes encode enzymes capable of deconjugating conjugated estrogen metabolites marked for excretion, pushing them back into the enterohepatic circulation in a biologically active form. In addition, the intestinal microbes also break down otherwise indigestible dietary polyphenols to synthesize estrogen-like compounds or estrogen mimics that exhibit varied estrogenic potency. The present account discusses the potential role of gastrointestinal microbiome in breast cancer development by mediating metabolism of steroid hormones and synthesis of biologically active estrogen mimics.

Flaxseed Lignans as Important Dietary Polyphenols for Cancer Prevention and Treatment: Chemistry, Pharmacokinetics, and Molecular Targets

Cancer causes considerable morbidity and mortality across the world. Socioeconomic, environmental, and lifestyle factors contribute to the increasing cancer prevalence, bespeaking a need for effective prevention and treatment strategies. Phytochemicals like plant polyphenols are generally considered to have anticancer, anti-inflammatory, antiviral, antimicrobial, and immunomodulatory effects, which explain their promotion for human health. The past several decades have contributed to a growing evidence base in the literature that demonstrate ability of polyphenols to modulate multiple targets of carcinogenesis linking models of cancer characteristics (i.e., hallmarks and nutraceutical-based targeting of cancer) via direct or indirect interaction or modulation of cellular and molecular targets. This evidence is particularly relevant for the lignans, an ubiquitous, important class of dietary polyphenols present in high levels in food sources such as flaxseed. Literature evidence on lignans suggests potential benefit in cancer prevention and treatment. This review summarizes the relevant chemical and pharmacokinetic properties of dietary polyphenols and specifically focuses on the biological targets of flaxseed lignans. The consolidation of the considerable body of data on the diverse targets of the lignans will aid continued research into their potential for use in combination with other cancer chemotherapies, utilizing flaxseed lignan-enriched natural products.

Plasma enterolactone and risk of prostate cancer in middle-aged Swedish men

Purpose

Enterolactone (ENL) is formed in the human gut after consumption of lignans, has estrogenic properties, and has been associated with risk of prostate cancer. We examined the association between plasma ENL levels and prostate cancer in a nested case–control study within the population-based Malmö Diet and Cancer cohort. We also examined the association between plasma ENL and dietary and lifestyle factors.

Methods

The study population consisted of 1010 cases occurring during a mean follow-up of 14.6 years, and 1817 controls matched on age and study entry date. We used national registers (95%) and hospital records (5%) to ascertain cases. Diet was estimated by a modified diet history method. Plasma ENL concentrations were determined by a time-resolved fluoroimmunoassay. Odds ratios were calculated by unconditional logistic regression.

Results

There were no significant associations between plasma ENL and incidence of all prostate cancer (odds ratio 0.99 [95% confidence interval 0.77–1.280] for the highest ENL quintile versus lowest, p for trend 0.66). However, in certain subgroups of men, including men with abdominal obesity (p for interaction = 0.012), we observed associations between high ENL levels and lower odds of high-risk prostate cancer. Plasma ENL was positively associated with consumption of high-fibre bread, fruit, tea, and coffee; with age, and with height, while it was negatively associated with smoking and waist circumference; however, although significant, all associations were rather weak (r ≤ |0.14|).

Conclusion

ENL concentration was not consistently associated with lower prostate cancer risk, although it was weakly associated with a healthy lifestyle.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-017-1530-z) contains supplementary material, which is available to authorized users.

Differential and directional estrogenic signaling pathways induced by enterolignans and their precursors

Mammalian lignans or enterolignans are metabolites of plant lignans, an important category of phytochemicals. Although they are known to be associated with estrogenic activity, cell signaling pathways leading to specific cell functions, and especially the differences among lignans, have not been explored. We examined the estrogenic activity of enterolignans and their precursor plant lignans and cell signaling pathways for some cell functions, cell cycle and chemokine secretion. We used DNA microarray-based gene expression profiling in human breast cancer MCF-7 cells to examine the similarities, as well as the differences, among enterolignans, enterolactone and enterodiol, and their precursors, matairesinol, pinoresinol and sesamin. The profiles showed moderate to high levels of correlation (R values: 0.44 to 0.81) with that of estrogen (17β-estradiol or E₂). Significant correlations were observed among lignans (R values: 0.77 to 0.97), and the correlations were higher for cell functions related to enzymes, signaling, proliferation and transport. All the enterolignans/precursors examined showed activation of the Erk1/2 and PI3K/Akt pathways, indicating the involvement of rapid signaling through the non-genomic estrogen signaling pathway. However, when their effects on specific cell functions, cell cycle progression and chemokine (MCP-1) secretion were examined, positive effects were observed only for enterolactone, suggesting that signals are given in certain directions at a position closer to cell functions. We hypothesized that, while estrogen signaling is initiated by the enterolignans/precursors examined, their signals are differentially and directionally modulated later in the pathways, resulting in the differences at the cell function level.

Gastrointestinal microbiome and breast cancer: correlations, mechanisms and potential clinical implications

Gastrointestinal microbiome plays as a symbiont which provides protection effect against invading pathogens, aids in the immune system development, nutrient reclamation and absorption as well as molecule breakdown. And it may avert carcinogenesis through these biological activities. By now, studies have been carried out to elaborate the association between gastrointestinal microbiome and breast cancer. It has been implicated that breast cancer was substantially associated with estrogen-dependent and estrogen-independent functions of gastrointestinal microbiome. Evidence from animal experiments also confirmed mammary tumor-related changes in microbial community. The possible mechanisms involve estrogen metabolism, immune regulation, obese status and so forth. Based on the current evidence, cues on future management strategies of breast cancer such as antibiotics and dietary interventions are proposed. In conclusion, large-scale clinical studies and bench-based researches are needed to validate the associations and elaborate the mechanisms, so as to reduce the risk of breast cancer and improve the outcomes of those already diagnosed.

Antagonism of human formyl peptide receptor 1 with natural compounds and their synthetic derivatives

Formyl peptide receptor 1 (FPR1) regulates a wide variety of neutrophil functional responses and plays an important role in inflammation and the pathogenesis of various diseases. To date, a variety of natural and synthetic molecules have been identified as FPR1 ligands. Here, we review current knowledge on natural products and natural product-inspired small molecules reported to antagonize and/or inhibit the FPR1-mediated responses. Based on this literature, additional screening of selected commercially available natural compounds for their ability to inhibit fMLF-induced Ca(2+) mobilization in human neutrophils and FPR1 transfected HL-60 cells, and pharmacophore modeling, natural products with potential as FPR1 antagonists are considered and discussed in this review. The identification and characterization of natural products that antagonize FPR1 activity may have potential for the development of novel therapeutics to limit or alter the outcome of inflammatory processes.

Urinary enterolactone associated with liver enzyme levels in US adults: National Health and Nutrition Examination Survey (NHANES)

Phyto-oestrogens are a family of plant-derived xeno-oestrogens that appear to have beneficial effects on human health. To date, no data are available about phyto-oestrogen consumption affecting liver health in a population. The present study aimed to explore the relationship of urinary phyto-oestrogen metabolites with serum liver enzymes in US adults. A nationally representative sample of US adults in the National Health and Nutrition Examination Survey (NHANES) 2003–10 was analysed. The cross-sectional study sample consisted of 6438 adults with data on urinary phyto-oestrogen levels, serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and γ-glutamyl transaminase (GGT) concentrations and data on other potential confounders. Multivariate logistic regression and linear regression were applied to assess associations between urinary phyto-oestrogen levels and ALT, AST, ALP and GGT concentrations. We found a remarkable association between urinary enterolactone and GGT in both adult males (OR 0·37, 95 % CI 0·22, 0·61; P= 0·003) and females (OR 0·37, 95 % CI 0·26, 0·54; P= 0·009). Moreover, elevated enterolactone levels were inversely associated with ALT and AST levels in adult males. However, no association was present between levels of urinary daidzein, O-desmethylangolensin, equol, enterodiol or genistein with liver enzyme levels in this population. The present study results provide epidemiological evidence that urinary enterolactone levels are associated with liver GGT levels in humans. This suggests a potential protective effect of enterolactone on human liver function. However, the underlying mechanisms still need further investigation.

Global metabolomics reveals urinary biomarkers of breast cancer in a mcf-7 xenograft mouse model

Global metabolomics analysis has the potential to uncover novel metabolic pathways that are differentially regulated during carcinogenesis, aiding in biomarker discovery for early diagnosis and remission monitoring. Metabolomics studies with human samples can be problematic due to high inter-individual variation; however xenografts of human cancers in mice offer a well-controlled model system. Urine was collected from a xenograft mouse model of MCF-7 breast cancer and analyzed by mass spectrometry-based metabolomics to identify metabolites associated with cancer progression. Over 10 weeks, 24 h urine was collected weekly from control mice, mice dosed with estradiol cypionate (1 mg/mL), mice inoculated with MCF-7 cells (1 × 107) and estradiol cypionate (1 mg/mL), and mice dosed with MCF-7 cells (1 × 107) only (n = 10/group). Mice that received both estradiol cypionate and MCF-7 cells developed tumors from four weeks after inoculation. Five urinary metabolites were identified that were associated with breast cancer; enterolactone glucuronide, coumaric acid sulfate, capric acid glucuronide, an unknown metabolite, and a novel mammalian metabolite, "taurosebacic acid". These metabolites revealed a correlation between tumor growth, fatty acid synthesis, and potential anti-proliferative effects of gut microbiota-metabolized food derivatives. These biomarkers may be of value for early diagnosis of cancer, monitoring of cancer therapeutics, and may also lead to future mechanistic studies.

Validation of FFQ-based assessment of dietary lignans compared with serum enterolactone in Swedish women

The validity of using FFQ to assess dietary lignans is uncertain. We aimed to validate the use of FFQ for the assessment of dietary intake of lignans compared to the serum biomarker enterolactone, the main product of dietary lignans' metabolism in human subjects. A random sample of women, aged 55–75 years, from the Swedish Mammography Cohort was selected. Information from two FFQ, the FFQ-87 (sixty-seven food items) and the FFQ-97 (ninety-three food items), and blood samples were collected. Dietary intake of lignans (secoisolariciresinol, matairesinol, lariciresinol, pinoresinol, medioresinol and syringaresinol) was assessed by the FFQ. Serum concentrations of enterolactone were analysed by time-resolved fluoroimmunoassay. The correlation coefficient between energy-adjusted lignan intake and serum enterolactone was estimated in crude and multivariable-adjusted models, taking into account the factors potentially influencing the serum enterolactone. Among the 135 participants aged 55–75 years, with a mean BMI of 26·7 kg/m2, the average energy-adjusted intake of total lignans was 1616 (sd 424) and 1516 (sd 409) μg/d according to the FFQ-87 (forty-five food items containing lignans) and the FFQ-97 (sixty-five food items containing lignans), respectively. The mean concentration of serum enterolactone was 23·2 (sd 15·4) nmol/l. The adjusted Pearson's correlation between dietary intake of lignans assessed by the FFQ-97 and serum enterolactone was statistically significant (r 0·22, P= 0·01). No significant correlation was observed for the FFQ-87 (r 0·09, P= 0·30). The present study indicates that the FFQ-97 might be better than the FFQ-87 for assessing dietary intake of lignans, although the correlation was low.

Lignan transformation by gut bacteria lowers tumor burden in a gnotobiotic rat model of breast cancer

High dietary lignan exposure is implicated in a reduced breast cancer risk in women. The bacterial transformation of plant lignans to enterolignans is thought to be essential for this effect. To provide evidence for this assumption, gnotobiotic rats were colonized with the lignan-converting bacteria Clostridium saccharogumia, Eggerthella lenta, Blautia producta and Lactonifactor longoviformis (LCC rats). Germ-free rats were used as the control. All animals were fed a lignan-rich flaxseed diet and breast cancer was induced with 7,12-dimethylbenz(a)anthracene. The lignan secoisolariciresinol diglucoside was converted into the enterolignans enterodiol and enterolactone in the LCC but not in the germ-free rats. This transformation did not influence cancer incidence at the end of the 13 weeks experimental period but significantly decreased tumor numbers per tumor-bearing rat, tumor size, tumor cell proliferation and increased tumor cell apoptosis in LCC rats. No differences between LCC and control rats were observed in the expression of the genes encoding the estrogen receptors (ERs) α, ERβ and G-coupled protein 30. The same was true for IGF-1 and EGFR involved in tumor growth. The activity of selected enzymes involved in the degradation of oxidants in plasma and liver was significantly increased in the LCC rats. However, plasma and liver concentrations of reduced glutathione and malondialdehyde, considered as oxidative stress markers, did not differ between the groups. In conclusion, our results show that the bacterial conversion of plant lignans to enterolignans beneficially influences their anticancer effects.

Estimated enterolignans, lignan-rich foods, and fibre in relation to survival after postmenopausal breast cancer

Background:

Lignans – oestrogenic substances present in various foods – are associated with postmenopausal breast cancer risk, but not much is known regarding their effects on survival.

Methods:

In a follow-up study of 2653 postmenopausal breast cancer patients diagnosed between 2001 and 2005, vital status and causes of death were verified through end of 2009. Hazard ratios (HRs) and 95% confidence intervals (CIs) for estimated enterolignans, lignan-rich foods, and dietary fibre in relation to overall survival (OS) and breast cancer-specific survival (BCSS) were assessed using Cox proportional hazards models stratified by age at diagnosis and adjusted for prognostic/confounding factors.

Results:

Median follow-up time was 6.4 years, and 321 women died, 235 with breast cancer. High estimated enterolactone and enterodiol levels were associated with significantly lower overall mortality (highest quintile, HR=0.60, 95% CI=0.40–0.89, P_Trend=0.02 and HR=0.63, 95% CI=0.42–0.95, P_Trend=0.02, respectively). Fibre intake was also associated with a significantly lower overall mortality. Differentiated by median fibre intake, associations with estimated enterolignans were still evident at low but not high fibre intake. There was no effect modification by oestrogen receptor status and menopausal hormone therapy.

Conclusion:

Postmenopausal breast cancer patients with high estimated enterolignans may have a better survival.