Plasma Enterolactone Research Articles

Dietary lignans, plasma enterolactone levels, and metabolic risk in men: exploring the role of the gut microbiome

BackgroundThe conversion of plant lignans to bioactive enterolignans in the gastrointestinal tract is mediated through microbial processing. The goal of this study was to examine the relationships between lignan intake, plasma enterolactone concentrations, gut microbiome composition, and metabolic risk in free-living male adults.ResultsIn 303 men participating in the Men’s Lifestyle Validation Study (MLVS), lignan intake was assessed using two sets of 7-day diet records, and gut microbiome was profiled through shotgun sequencing of up to 2 pairs of fecal samples (n = 911). A score was calculated to summarize the abundance of bacteria species that were significantly associated with plasma enterolactone levels. Of the 138 filtered species, plasma enterolactone levels were significantly associated with the relative abundances of 18 species at FDR < 0.05 level. Per SD increment of lignan intake was associated with 20.7 nM (SEM: 2.3 nM) higher enterolactone concentrations among participants with a higher species score, whereas the corresponding estimate was 4.0 nM (SEM: 1.7 nM) among participants with a lower species score (P for interaction < 0.001). A total of 12 plasma metabolites were also significantly associated with these enterolactone-predicting species. Of the association between lignan intake and metabolic risk, 19.8% (95%CI: 7.3%-43.6%) was explained by the species score alone, 54.5% (95%CI: 21.8%-83.7%) by both species score and enterolactone levels, and 79.8% (95%CI: 17.7%-98.6%) by further considering the 12 plasma metabolites.ConclusionWe identified multiple gut bacteria species that were enriched or depleted at higher plasma levels of enterolactone in men. These species jointly modified the associations of lignan intake with plasma enterolactone levels and explained the majority of association between lignan intake and metabolic risk along with enterolactone levels and certain plasma metabolites.

Gut microbiota–derived metabolites and risk of coronary artery disease: a prospective study among US men and women

Accumulating evidence has suggested that human gut microbiota metabolize certain dietary compounds and subsequently produce bioactive metabolites that may exert beneficial or harmful effects on coronary artery disease (CAD) risk. This study examined the joint association of 2 gut microbiota metabolites, enterolactone and trimethylamine N-oxide (TMAO), that originate from intake of plant-based foods and animal products, respectively, in relation to CAD risk. A prospective nested case-control study of CAD was conducted among participants who were free of diabetes, cardiovascular disease, and cancer in the Nurses' Health Study II and the Health Professionals Follow-up Study. Plasma concentrations of enterolactone and TMAO, as well as choline and L-carnitine, were assayed among 608 CAD case-control pairs. A high enterolactone and low TMAO profile was associated with better diet quality, especially higher intake of whole grains and fiber and lower intake of red meats, as well as lower concentrations of plasma triglycerides and C-reactive protein. Participants with a high enterolactone/low TMAO profile had a significantly lower risk of CAD: the multivariate-adjusted OR was 0.58 (95% CI: 0.38, 0.90), compared with participants with a low enterolactone/high TMAO profile. No significant interaction between enterolactone and TMAO on CAD risk was observed. Neither TMAO nor enterolactone alone were associated with CAD risk in pooled analyses. In women, a higher enterolactone concentration was significantly associated with a 54% lower CAD risk (P trend=0.03), although the interaction by sex was not significant. Our results show that a profile characterized by high enterolactone and low TMAO concentrations in plasma is linked to a healthful dietary pattern and significantly associated with a lower risk of CAD. Overall, these data suggest that, compared with individual markers, multiple microbiota-derived metabolites may facilitate better differentiation of CAD risk and characterization of the relations between diet, microbiota, and CAD risk.

Abstract MP68: Dietary Lignan and Cardio-metabolic Risk: Exploring the Role of the Gut Microbiome

Background and Study Purpose: The conversion of plant lignans to enterolignans for absorption is mediated through the gut microbiota. We explored the interconnections between the intake of dietary lignans, circulating concentrations of plasma enterolignans, the gut microbiome, and cardio-metabolic risk factors (LDL-cholesterol, HDL-cholesterol, &amp; triglycerides). Design and method: The study was a repeated cross-sectional survey of up to 4 stool samples. Dietary lignan intake was assessed by two 7 day weighed records administered to coincide with fecal sample collection. DNA was extracted from 916 samples provided by 301 participants, and RNA was extracted from 369 samples from a subgroup of 96 participants. P&lt;0.25 after false discovery rate correction was considered statistically significant. Results: A high ratio of plasma enterolactone to dietary lignan was significantly associated with the relative abundance of 35 species (24 enriched and 11 depleted species), including 8 Bacteroidetes and 13 Firmicutes species. Greater dietary lignan was only significantly associated with a lower plasma ratio of triglyceride to HDL when plasma enterolactone was high. The association between dietary lignans and ratio of TG to HDL was mainly mediated by plasma enterolactone level (mediation effect: 74.3%, P=0.002), which was partially captured by the weighted species score (mediation effect: 28.6%, P=0.02). We observed several significant interactions between dietary lignans and presence of species on ratio of TG to HDL, suggesting that the protective effect of dietary lignans on CVD risk factor depends on the presence/abundance of certain microbiota. The relative abundance of microbial pathways involved in I-isoleucine biosynthesis and glutaryl-coa degradation pathways were significantly greater in in participants with a higher level of plasma enterolactone. Conclusion: The health benefits of dietary lignans on lipid levels may be modified by the greater enrichment of biologically relevant microbiota species. FIGURE

Pre-diagnostic plasma enterolactone concentrations are associated with lower mortality among individuals with type 2 diabetes: a case-cohort study in the Danish Diet, Cancer and Health cohort

Aims/hypothesisThe phytoestrogen enterolactone is a gut microbiota-derived metabolite of plant lignans with suggested beneficial properties for health. In the current study, we investigated the association between pre-diagnostic plasma enterolactone concentrations and mortality among individuals diagnosed with type 2 diabetes.MethodsIn a population of people diagnosed with diabetes, nested within the Danish Diet, Cancer and Health cohort, we conducted a case-cohort study including a random sample of n = 450 cases (deceased) and a randomly selected subcohort of n = 850 (in total n = 617 deaths). Information on diagnosis, vital status and cause of death was obtained from Danish registers. Cox proportional hazard models with special weighting were applied to assess all-cause and cause-specific mortality.ResultsThe median enterolactone concentration of the current population was low, 10.9 nmol/l (5th percentile to 95th percentile: 1.3–59.6), compared with previously reported concentrations from the Diet, Cancer and Health cohort. Pre-diagnostic enterolactone concentrations were associated with lower all-cause mortality when assessed linearly per doubling in concentration (log2) (HR 0.91 [95% CI 0.85, 0.96]) and according to quartiles (HR 0.63 [95% CI 0.48, 0.84]) for the highest quartile of enterolactone compared with the lowest quartile. For cause-specific mortality, only death from diabetes (registered as underlying cause of death) reached statistical significance.Conclusions/interpretationBased on this large cohort of people with diabetes with detailed and complete baseline and follow-up information, pre-diagnostic enterolactone concentrations were inversely associated with mortality. To our knowledge, this is the first study on enterolactone and type 2 diabetes mortality. Our findings call for further exploration of enterolactone in type 2 diabetes management.

Factors Explaining Interpersonal Variation in Plasma Enterolactone Concentrations in Humans.

Lignans are diphenolic plant compounds with potential health modulating properties that are absorbed to the circulation and metabolized to the enterolignans enterodiol (END) and enterolactone (ENL) by gut microbiota. Epidemiological studies have inconsistently shown that a high lignan intake and circulating ENL are associated with reduced risk of breast‐, prostate‐, and colorectal cancer as well as cardiovascular disease and total and cause‐specific mortality. Inconsistencies can be due to interpersonal variation of ENL formation or responses. The aim of this review is to identify and evaluate the impact of factors influencing variability in plasma concentrations of the main enterolignan, ENL. The main determinants of plasma ENL concentrations are intake of lignan and lignan‐rich foods, composition and activity of intestinal microflora, antimicrobial use, nutrient intake, BMI, smoking, sex, and age. Composition and activity of the intestinal microbiota appear to be the most critical factor governing interpersonal variability in plasma ENL concentration followed by the use of antibiotics. Future studies with combined data from gut microbiota and metabolomics with food intake and life style data can be used to estimate the relative contribution of the different factors to ENL concentration in quantitative terms.

Flaxseed Lignan Complex Consumption Causes Increased Plasma Enterolactone and Decreased HbA1C and Plasma C-Reactive Protein in Older Patients with Type 2 Diabetes

Background: Increased inflammation (as measured by elevated plasma C-reactive protein (CRP) concentrations and elevated HbA1C are linked in type 2 diabetes (T2D) progression. The objective was to test the novel hypothesis that in older T2D patients, flaxseed lignan complex (FLC; containing secoisolariciresinol diglucoside [SDG]) consumption would decrease HbA1C and plasma CRP, resulting in plasma CRP and HbA1C being significantly negatively correlated with elevated plasma enterolactone (ENL; an intestinal bacterial metabolite of SDG). ENL, but not SDG, undergoes intestinal absorption.

Pre-diagnostic plasma enterolactone concentrations and breast cancer prognosis among postmenopausal women – The Danish Diet, Cancer and Health cohort

High intakes of the phytoestrogen lignans and high blood concentrations of its main biomarker, enterolactone, has been associated with a better breast cancer prognosis. We investigated the association between pre-diagnostic plasma concentrations of enterolactone and breast cancer prognosis (i.e. recurrence, breast cancer-specific mortality and all-cause mortality). Plasma and data was available from the Danish Diet, Cancer and Health cohort. Information on treatment and clinical characteristics from registries and clinical databases and both pre-diagnostic and diagnostic plasma measurement of enterolactone on a sub-set. Enterolactone was quantified in plasma using a high-throughput LC-MS/MS method. We followed 1457 breast cancer cases from date of diagnosis and until censoring or end-of-follow-up (median 9 years), during this time 404 died (250 of breast cancer) and 267 experienced recurrence. Cox proportional hazards models were used to estimate hazard ratios (HR) with 95% confidence intervals (CI). Plasma enterolactone were borderline significantly associated with lower breast cancer-specific mortality (HRdoubling=0.93, 95% CI:0.86, 1.00, P=0.0501), but not associated with all-cause mortality (HRdoubling=0.95, 95% CI:0.89, 1.01) and recurrence (HRdoubling=0.96, 95% CI: 0.89, 1.04) in the models adjusted for smoking, schooling, BMI, physical activity and use of menopausal hormones. Adjusting further for clinical characteristics and treatment did not change the results considerably. In the sensitivity analyses, an inverse association was found with all-cause and breast cancer-specific mortality for those where blood was collected ≤5 years before diagnosis. Overall, no clear association was found between pre-diagnostic plasma concentrations of enterolactone and breast cancer prognosis.

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

PurposeEnterolactone (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.MethodsThe 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.ResultsThere 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|).ConclusionENL concentration was not consistently associated with lower prostate cancer risk, although it was weakly associated with a healthy lifestyle.

Short communication: The mammalian lignan enterolactone is absorbed by newborn dairy calves fed enterolactone-enriched milk

Flaxseed is the richest source of the plant lignan secoisolariciresinol diglucoside, which is converted to the mammalian lignans enterolactone (EL) and enterodiol by the gut microbiota of ruminants and humans. Enterolactone has been associated with improved animal and human health due to its antioxidant and anticarcinogenic properties. The objective of this study was to determine the pharmacokinetics of EL in newborn dairy calves fed milk replacer or EL-enriched milk. We hypothesized that newborn Holstein calves fed EL-enriched milk would have greater area under the curve and plasma concentration of EL compared with those fed milk replacer. On d 5 of life, calves were administered 2 L of milk replacer (n = 10; low-EL treatment: 123 nmol/L of EL) or 2 L of EL-enriched milk (n = 10; high-EL treatment: 481 nmol/L of EL) during the morning feeding (0700 h). Blood samples were taken from the jugular vein before (0 h) and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 12, 24, and 48 h after oral administration of treatments. The area under the curve for the plasma concentration of EL was analyzed according to the trapezoidal rule between 0 and 12 h after treatment administration, and it was greater in high- (26 nmol/L × h) than low-EL calves (4.30 nmol/L × h). Similarly, the maximum concentration of EL in plasma was greater in high- (5.06 nmol/L) versus low-EL calves (1.95 nmol/L). Furthermore, the time after treatment intake to reach maximum plasma concentration of EL was faster in high- (4.31 h) compared with low-EL (4.44 h) treatment. Calves were able to absorb EL, indicating that EL-enriched milk can potentially be used as source of EL to pre-weaned ruminants.

β-glucuronidase activity and enterolactone concentration in ruminal fluid, plasma, urine, and milk of Holstein cows fed increased levels of flax (Linum usitatissimum) meal

The main mammalian lignan present in milk of dairy cows fed flax products is enterolactone (EL), but the relationship between EL concentration in milk and body fluids when cows are fed increased proportions of flax meal (FM) is unknown. The objectives were to investigate the effects of increased levels of FM on EL concentration in milk, plasma, urine, and ruminal fluid and the activity of β-glucuronidase in ruminal fluid and feces. Eight rumen-cannulated cows were assigned to a double 4×4 Latin square design with four 21 d periods and four diets: control diet with no FM (CON) or a diet with 50, 100 and 150g/kg of FM. Concentrations of EL in urine, ruminal fluid, milk, and plasma increased linearly with FM supplementation. Spearman’s correlation coefficients were significant for all comparisons except that only a trend was observed between concentration of EL in urine and that in ruminal fluid before feeding. The strongest correlation was observed between EL concentration in ruminal fluid post-feeding and that in milk. Feeding increased proportions of FM in the diet had no effect on β-glucuronidase activity. Unlike to what is observed in non-ruminant animals, present results suggest that the activity of β-glucuronidase in the rumen is of little importance for the absorption of EL and its transfer in milk and other physiological fluids. Further studies are required to better understand and improve EL production and absorption, which could contribute to enhance animal health and the transfer of antioxidant components in milk.

Use of antibiotics is associated with lower enterolactone plasma concentration.

High enterolactone levels may have health benefits in relation to risk of noncommunicable diseases. Enterolactone is produced by the colonic microbiota after intake of lignans and treatment with antimicrobials may result in altered enterolactone production. This study investigates the association between antibiotic use and enterolactone concentration. Using LC-MS/MS, enterolactone concentrations were quantified in plasma samples from 2237 participants from the Diet, Cancer and Health cohort. The participants were healthy at enrollment, but were later diagnosed with cancer. At enrollment, participants had blood drawn and completed a food frequency questionnaire and lifestyle questionnaire. Antibiotic use was assessed as reimbursed antibiotic prescriptions up to 12 months before enrollment. Antibiotic use ≤3 months before enrollment was associated with a 41% (Δcrude : -41; 95% CI: -52, -28) lower enterolactone concentration in women and 12% in men (Δcrude : -12; 95% CI: -31, 11), while antibiotic use >3-12 months before enrollment was associated with 26% lower enterolactone in women (Δcrude : -26; 95% CI: -37, -14) and 14% in men (Δcrude : -14; 95% CI: -28, 1). Use of antibiotics up to 12 months before enrollment was associated with lower plasma enterolactone levels, especially among women.

Effects of duodenal infusion of sunflower oil on β-glucuronidase activity and enterolactone concentration in dairy cows fed flax meal

Microbial β-glucuronidase activity is important for the absorption of enterolignans. This study was performed to evaluate the effects of dietary flax meal and abomasal infusion of sunflower oil (SO) on activity of β-glucuronidase in ruminal fluid and feces, and concentration of enterolactone (EL) in ruminal fluid, plasma, urine and milk. Eight rumen fistulated lactating Holstein cows were assigned to a double 4×4 Latin square design with a 2×2 factorial arrangement of treatments: (1) control diet with no FM (CO); (2) diet containing 137g/kg flax meal (FM); (3) CO and infusion of 250g SO/d in the abomasum; and (4) FM and infusion of 250g SO/d in the abomasum. Activity of β-glucuronidase in ruminal fluid was similar among diets. Cows fed the FM diets had lower fecal β-glucuronidase activity than those fed the CO diets. Infusion of SO lowered fecal β-glucuronidase activity. Supplementation with FM increased EL concentration in plasma, urine and prefeeding ruminal fluid, and SO reduced EL concentration in ruminal fluid before feeding. Dietary FM and SO infusion had no effect on milk EL concentration. Overall, the metabolism of flax lignans and the absorption of enterolignans were not affected by the presence of SO, a rich source of n-6 fatty acids, in the intestine as indicated by similar concentrations of EL in ruminal fluid (pool of 2, 4 and 6h postfeeding), plasma and urine. These results suggest that the effect of fat on the metabolism of lignans may differ between results observed in the present experiment with ruminant animals and those obtained in previous studies with non-ruminant animals.

Dietary flax meal and abomasal infusion of flax oil on microbial β-glucuronidase activity and concentration of enterolactone in ruminal fluid, plasma, urine and milk of dairy cows

This study was performed to evaluate the effects of dietary flax meal (FM) and abomasal infusion of flax oil (FO) and their interaction on activity of β-glucuronidase in ruminal fluid and feces, and concentration of the mammalian lignan enterolactone (EL) in ruminal fluid, plasma, urine, and milk. Rumen fermentation characteristics and the pH in ruminal fluid and feces were also investigated to determine any potential interference with β-glucuronidase activity and EL concentration. Eight rumen fistulated lactating Holstein cows were assigned to a double 4×4 Latin square design with a 2×2 factorial arrangement of treatments: (1) control diet with no FM (CON); (2) diet containing 124g/kg FM (FMD) in the dry matter (DM); (3) CON and 250g FO/day infused in the abomasum; and (4) FMD and 250g FO/day infused in the abomasum. Abomasal infusion of FO had no effect on β-glucuronidase activity in the gastrointestinal tract and EL concentration of ruminal fluid, plasma, urine, and milk. Dietary FM and abomasal infusion of FO had no effect on fecal pH and microbial activity of β-glucuronidase in ruminal fluid and feces. Dietary FM increased concentrations of EL in ruminal fluid, plasma, urine, and milk. Molar proportion of propionate was increased and that of isovalerate was decreased with FM supplementation. Abomasal infusion of FO had no effect on ruminal concentration of ammonia N. Dietary FM had no effect on ruminal pH. As abomasal infusion of FO had no effect on β-glucuronidase activity in the gastro-intestinal tract and EL concentration, our results suggest that polyunsaturated fatty acids such as n-3 do not interfere with the absorption of mammalian lignans. Moreover, feeding 124g/kg DM FM with a source of FA rich in n-3 bypassing the rumen increases EL concentration in physiological fluids of dairy cows, especially milk, which can be used as a strategy to optimize the concentration of mammalian lignans in milk and their potential beneficial effects on human health.

Short communication: Concentrations of the mammalian lignan enterolactone in preovulatory follicles and the correlation with intrafollicular estradiol in dairy cows fed extruded flaxseed

Flaxseed is a rich source of lignans that can be metabolized to the mammalian lignan enterolactone (EL), which may elicit weak estrogenic or antiestrogenic effects. The objectives of this study were to examine the effects of feeding an extruded flaxseed supplement to dairy cows on concentrations of EL in plasma and preovulatory follicles and the association with intrafollicular estradiol (E2). Twenty-four multiparous 256-d-pregnant Israeli Holstein cows were fed either a standard diet both pre- and postpartum (control; n=12) or provided with an extruded flaxseed supplement (n=12), at 7.9 and 9.2% of dry matter, pre- and postpartum, respectively. Follicular fluid (FF) aspirations were conducted at 84±16 d in lactation as follows: 7 to 8 d following behavioral estrus, cows were injected with prostaglandin F2α and 48h later follicles >7mm were aspirated. Follicles were regarded as preovulatory when the E2-to-progesterone ratio was >1. Plasma EL concentrations were not different between treatment groups; however, concentrations of EL in FF of preovulatory follicles were 1.7 times higher in extruded flaxseed-supplemented cows than in control. Across-treatment analysis revealed a positive correlation between concentrations of EL in plasma and in FF. In addition, intrafollicular EL concentrations were positively correlated with E2 concentrations (r=0.50), and with the intrafollicular E2-to-progesterone ratio. In conclusion, supplementing dairy cows with extruded flaxseed increased EL concentrations in preovulatory follicles. Intrafollicular EL was correlated with E2 concentrations; therefore, the possible effects of EL from flaxseed on follicular steroidogenesis should be considered.

Targeted LC-MS/MS Method for the Quantitation of Plant Lignans and Enterolignans in Biofluids from Humans and Pigs.

Lignans have gained nutritional interest due to their promising role in the prevention of lifestyle diseases. However, epidemiological studies are in need of more evidence to link the intake of lignans to this promising role. In this context, it is necessary to study large population groups to obtain sufficient statistical power. Therefore, there is a demand for fast, sensitive, and accurate methods for quantitation with high throughput of samples. This paper presents a validated LC-MS/MS method for the quantitation of eight plant lignans (matairesinol, hydroxymatairesinol, secoisolariciresinol, lariciresinol, isolariciresinol, syringaresinol, medioresinol, and pinoresinol) and two enterolignans (enterodiol and enterolactone) in both human and pig plasma and urine. The method showed high selectivity and sensitivity allowing quantitation of lignans in the range of 0.024-100 ng/mL and with a run time of only 4.8 min per sample. The method was successfully applied to quantitate lignans in biofluids from ongoing studies with humans and pigs.

Pharmacokinetics and Bioavailability of Plant Lignan 7-Hydroxymatairesinol and Effects on Serum Enterolactone and Clinical Symptoms in Postmenopausal Women: A Single-Blinded, Parallel, Dose-Comparison Study

Objective: 7-Hydroxymaitairesinol (7-HMR) is a naturally occurring plant lignan found in whole grains and the Norway spruce (Piciea abies). The purpose of this study was to evaluate the bioavailability of a proprietary 7-HMR product (HMRlignan, Linnea SA, Locarno, Switzerland) through measurement of lignan metabolites and metabolic precursors. Methods: A single-blind, parallel, pharmacokinetic and dose-comparison study was conducted on 22 postmenopausal females not receiving hormone replacement therapy. Subjects were enrolled in either a 36 mg/d (low-dose) or 72 mg/d dose (high-dose) regimen for 8 weeks. Primary measured outcomes included plasma levels of 7-HMR and enterolactone (ENL), and single-dose pharmacokinetic analysis was performed on a subset of subjects in the low-dose group. Safety data and adverse event reports were collected as well as data on hot flash frequency and severity. Results: Pharmacokinetic studies demonstrated 7-HMR C max = 757.08 ng/ml at 1 hour and ENL C max = 4.8 ng/ml at 24 hours. From baseline to week 8, plasma 7-HMR levels increased by 191% in the low-dose group (p < 0.01) and by 1238% in the high-dose group (p < 0.05). Plasma ENL levels consistently increased as much as 157% from baseline in the low-dose group and 137% in the high-dose group. Additionally, the mean number of weekly hot flashes decreased by 50%, from 28.0/week to 14.3/week (p < 0.05) in the high-dose group. No significant safety issues were identified in this study. Conclusion: The results demonstrate that HMRlignan is quickly absorbed into the plasma and is metabolized to ENL in healthy postmenopausal women. Clinically, the data demonstrate a statistically significant improvement in hot flash frequency. Doses up to 72 mg/d HMRlignan for 8 weeks were safe and well tolerated in this population.

Plasma enterolactone and breast cancer risk in the Nurses’ Health Study II

Lignans are plant-based phytoestrogens with both estrogenic and anti-estrogenic properties that may be important for breast carcinogenesis. Retrospective studies have observed decreased breast cancer risk associated with highcirculating enterolactone concentrations, a biomarker of lignan intake, but results from prospective studies are conflicting. To prospectively examine this association, we measured plasma enterolactone levels in 802 breast cancer cases and 802 matched controls nested among predominantly premenopausal women in the Nurses' Health Study II cohort. We used conditional logistic regression and polytomous logistic regression models, adjusting for known breast cancer risk factors, to calculate relative risks (RR) and 95% confidence intervals (CI). Compared to women with enterolactone concentrations ≤4nmol/L, the multivariate-adjusted RRs for breast cancer were 1.18 (95% CI 0.86-1.62), 0.91 (95% CI 0.66-1.25), and 0.96 (95% CI 0.70-1.33) for women with enterolactone levels in the second to the fourth quartiles, respectively; P trend=0.60. Results were similar across tumors defined by estrogen and progesterone receptor status. Among premenopausal women with follicular estradiol levels below the median (<47pg/mL), women in the highest category of enterolactone levels had a 51% lower breast cancer risk compared to those in the lowest category (95% CI 0.27-0.91); P trend=0.02. No association was observed among women with high-follicular estradiol levels (≥47pg/mL), (comparable RR=1.39, 95% CI 0.73-2.65; P interaction=0.02). We did not observe an overall association between plasma enterolactone and breast cancer risk in a large nested case-control study of US women. However, a significant inverse association was observed among premenopausal women with low-follicular estradiol levels, suggesting that enterolactone may be important in a low-estrogen environment. This should be confirmed in future studies.

Plasma enterolactone and incidence of endometrial cancer in a case–cohort study of Danish women

The phyto-oestrogen enterolactone has been hypothesised to protect against hormone-dependent cancers, probably through its antioestrogenic potential. We investigated whether a higher level of plasma enterolactone was associated with a lower incidence of endometrial cancer in a case-cohort study in the ‘Diet, Cancer and Health’ cohort. The cohort study included 29 875 women aged 50–64 years enrolled between 1993 and 1997. Information on diet and lifestyle was provided by self-administrated questionnaires and blood was drawn from each participant. Time-resolved fluoroimmunoassay was used for biochemical determination of plasma enterolactone. A total of 173 cases and 149 randomly selected cohort members were included. We estimated incidence rate ratio (IRR) and 95% CI by a Cox proportional hazards model. A 20 nmol/l higher plasma concentration of enterolactone was associated with a non-significant lower risk of endometrial cancer (IRR 0.93, 95% CI 0.84, 1.04). When excluding women with low enterolactone concentrations (quartile 1) due to potential recent antibiotic use, the association became slightly stronger, but remained non-significant (IRR 0.90, 95% CI 0.79, 1.02). Menopausal status, hormone replacement therapy or BMI did not modify the association. In conclusion, we found some support for a possible inverse association between plasma enterolactone concentration and endometrial cancer incidence.

Effects of abomasal infusion of flaxseed (Linum usitatissimum) oil on microbial β-glucuronidase activity and concentration of the mammalian lignan enterolactone in ruminal fluid, plasma, urine and milk of dairy cows

Ruminal microbiota plays an important role in the conversion of plant lignans into mammalian lignans. The main mammalian lignan present in the milk of dairy cows fed flax products is enterolactone (EL). The objectives of the present study were to investigate the effects of abomasal infusion of flax oil on the metabolism of flax lignans and concentrations of EL in biological fluids of dairy cows. A total of six rumen-cannulated dairy cows were assigned within a 2 × 3 factorial arrangement of six treatments utilising flax hulls (0 and 15·9 % of DM) and abomasal infusion of flax oil (0, 250 and 500 g/d). There were six periods of 21 d each. Samples were collected during the last 7 d of each period and subjected to chemical analysis. Flax hull supplementation increased concentrations of EL in ruminal fluid, plasma, urine and milk, while flax oil infusion had no effect. Post-feeding, β-glucuronidase activity in the ruminal fluid of cows infused with 250 g flax oil was significantly lower for cows fed hulls than for those fed the control diet. The present study demonstrated that the presence of a rich source of n-3 fatty acids such as flax oil in the small intestine does not interfere with the absorption of the mammalian lignan EL and that lower ruminal β-glucuronidase activity had no effect on the conversion of flax lignans into EL in the rumen of dairy cows.

Mammary gene expression and activity of antioxidant enzymes and concentration of the mammalian lignan enterolactone in milk and plasma of dairy cows fed flax lignans and infused with flax oil in the abomasum

The objectives of the study were to investigate the effects of dietary supplementation of flax hulls and/or flax oil on the activity of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX)) in plasma and the mammary gland and the relative mRNA abundance of antioxidant genes in the mammary gland of dairy cows. A total of eight dairy cows were used in a replicated 4 × 4 Latin square design. There were four treatments: control with no flax hulls (CONT), 9·88% flax hulls in the DM (HULL), control with 500 g flax oil/d infused in the abomasum (COFO), 9·88% flax hulls in the DM and 500 g flax oil/d infused in the abomasum (HUFO). Plasma GPX activity tended to decrease with flax oil supplementation. Cows fed HULL had higher levels of CAT, GPX1 and SOD1 mRNA in the mammary gland and lower mRNA abundance of GPX3, SOD2 and SOD3 compared with those fed CONT. Abundance of CAT, GPX1, GPX3, SOD2 and SOD3 mRNA was down-regulated in the mammary gland of cows fed HUFO compared to those fed CONT. The mRNA abundance of CAT, GPX1, GPX3 and SOD3 was lower in the mammary gland of cows fed COFO than in the mammary gland of cows fed CONT. The present study demonstrates that flax hulls contribute to increasing the abundance of some antioxidant genes, which can contribute to protecting against oxidative stress damage occurring in the mammary gland and other tissues of dairy cows.