Circulating enterolactone and prostate cancer risk: a Nordic nested case-control study

Association between polyphenol subclasses and prostate cancer: a systematic review and meta-analysis of observational studies

Background

The effect of polyphenol subclasses on prostate cancer (PCA) is controversial. Therefore, the purpose of this study was to investigate the relationship between polyphenol subclasses and PCA incidence.

Methods

From the establishment of the database to December 2023, a systematic search was conducted on PubMed, Web of Science, Embase, and Cochrane Library to identify relevant observational studies. The adjusted odds ratio (OR) and corresponding 95% confidence interval (95% CI) were used to assess the association.

Results

A total of 38 studies (11 were cohort studies and 27 were case-control studies), composing 824,933 participants, were included in this meta-analysis after excluding irrelevant records. The findings of the study revealed that men who consumed dietary polyphenols had a significantly higher risk of PCA compared to those who never or rarely consumed dietary polyphenols (OR = 1.01, p = 0.023), especially dietary flavonol (OR = 1.05, p = 0.042), flavanol (OR = 1.03, p = 0.026) and anthocyanin (OR = 1.06, p = 0.001). Neither total nor subclasses of dietary polyphenols have an effect on non-localized or high-grade PCA (OR = 1.01, p = 0.518). Dietary isoflavones tended to reduce the incidence of local or low-grade PCA, although there was no statistically significant difference (OR = 1.00, p = 0.081). Regarding serum/plasma polyphenol, total polyphenol (OR = 0.95, p = 0.002), genistein (OR = 0.92, p = 0.029) and enterolactone (OR = 0.92, p = 0.022) can reduce the incidence of PCA. No association was observed between total/subclasses of urinary polyphenols and PCA risk.

Conclusion

Polyphenols seem to generally increase the risk of PCA in the male population. The effect of polyphenols on PCA is affected by factors such as polyphenol subclasses, their forms (serum/plasma, urinary, dietary), and PCA-related factors (like PCA stage).

Systematic review registration

identifier: CRD42022322699.

Intake of the Total, Classes, and Subclasses of (Poly)Phenols and Risk of Prostate Cancer: A Prospective Analysis of the EPIC Study

Existing epidemiological evidence regarding the potential role of (poly)phenol intake in prostate cancer (PCa) risk is scarce and, in the case of flavonoids, it has been suggested that their intake may increase PCa risk. We investigated the associations between the intake of the total and individual classes and subclasses of (poly)phenols and the risk of PCa, including clinically relevant subtypes. The European Prospective Investigation into Cancer and Nutrition (EPIC) cohort included 131,425 adult men from seven European countries. (Poly)phenol intake at baseline was assessed by combining validated center/country-specific dietary questionnaires and the Phenol-Explorer database. Multivariable-adjusted Cox proportional hazards models were used to estimate the hazard ratios (HR) and 95% confidence intervals (CI). In total, 6939 incident PCa cases (including 3501 low-grade and 710 high-grade, 2446 localized and 1268 advanced, and 914 fatal Pca cases) were identified during a mean follow-up of 14 years. No associations were observed between the total intake of (poly)phenols and the risk of PCa, either overall (HRlog2 = 0.99, 95% CI 0.94-1.04) or according to PCa subtype. Null associations were also found between all classes (phenolic acids, flavonoids, lignans, and stilbenes) and subclasses of (poly)phenol intake and the risk of PCa, overall and according to PCa subtype. The results of the current large prospective cohort study do not support any association between (poly)phenol intake and PCa incidence.

Immunomodulatory actions of a Polynesian herb Noni (Morinda citrifolia) and its clinical applications

Morinda citrifolia (Noni) is a popular traditional medicinal plant consumed in various forms in several countries around the world as a complementary and alternative treatment due to its established health benefits. Noni is rich in bioactive substances and has significantly exhibited pro-oxidant and immunomodulatory effects. In this review, we highlight the pharmacological basis related to the phytochemicals and polysaccharides present in Noni and its potential therapeutic effects. We screened electronic databases such as PubMed, Google Scholar, Scopus for scientific literature. Our results indicate that Noni is beneficial for various diseases with its crude extracts showing therapeutic benefit for a wide range of pathological diseases. We believe that further pharmacological and toxicological studies in addition to well-designed controlled clinical trials can validate Noni to be an effective and novel natural product for prophylactic and therapeutic use of several diseases.

Bacterial metabolism as responsible of beneficial effects of phytoestrogens on human health

Phytoestrogens (PE) are compounds found in plants such as soy (isoflavones), flax seeds and cereals (lignans) and pomegranates (ellagitannins). PE have shown estrogenic/antiestrogenic, antioxidant, anti-inflammatory, antineoplastic and apoptotic activities. The human studies are showing promising although inconsistent results about the beneficial effects of PE on ameliorating the menopausal symptoms or reducing the risk of certain cancers, cardiovascular disease or diabetes. The effects of PE on the organism are mediated by the intestinal microbiota, which transforms them into bioactive PE such as genistein, equol, enterolignans and certain urolithins. In this work, we review the most recent findings about the bacteria able to metabolize PE, together with the latest studies on the effects of PE on health. In addition, we describe the possible factors hindering the demonstration of the beneficial effect of PE on health, evincing the importance of measuring the actual circulating PE in order to encompass the variability of PE metabolism due to the intestinal microbiota. With this in mind, we also explore an approach to ensure the access to bioactive PE.

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.

Anticancer and antimetastatic potential of enterolactone: Clinical, preclinical and mechanistic perspectives

Currently cancer is the second leading cause of death globally and worldwide incidence and mortality rates of all cancers of males and females are rising tremendously. In spite of advances in chemotherapy and radiation, metastasis and recurrence are considered as the major causes of cancer related deaths. Hence there is a mounting need to develop new therapeutic modalities to treat metastasis and recurrence in cancers. A significant amount of substantiation from epidemiological, clinical and laboratory research highlights the importance of diet and nutrition in cancer chemoprevention. Enterolactone (EL) is a bioactive phenolic metabolite known as a mammalian lignan derived from dietary lignans. Here in we review the reported anti-cancer properties of EL at preclinical as well as clinical level. Several in-vivo and in-vitro studies have provided strong evidence that EL exhibits potent anti-cancer and/or protective properties against different cancers including breast, prostate, colo-rectal, lung, ovarian, endometrial, cervical cancers and hepatocellular carcinoma. Reported laboratory studies indicate a clear role for EL in preventing cancer progression at various stages including cancer cell proliferation, survival, angiogenesis, inflammation and metastasis. In clinical settings, EL has been reported to reduce risk, decrease mortality rate and improve overall survival particularly in breast, prostate, colon, gastric and lung cancer. Further, the in-vitro human cell culture studies provide strong evidence of the anticancer and antimetastatic mechanisms of EL in several cancers. This comprehensive review supports an idea of projecting EL as a promising candidate for developing anticancer drug or adjunct dietary supplements and nutraceuticals.

Circulating isoflavone and lignan concentrations and prostate cancer risk: a meta-analysis of individual participant data from seven prospective studies including 2,828 cases and 5,593 controls

Phytoestrogens may influence prostate cancer development. This study aimed to examine the association between prediagnostic circulating concentrations of isoflavones (genistein, daidzein, equol) and lignans (enterolactone and enterodiol) and the risk of prostate cancer. Individual participant data were available from seven prospective studies (two studies from Japan with 241 cases and 503 controls and five studies from Europe with 2,828 cases and 5,593 controls). Because of the large difference in circulating isoflavone concentrations between Japan and Europe, analyses of the associations of isoflavone concentrations and prostate cancer risk were evaluated separately. Prostate cancer risk by study-specific fourths of circulating concentrations of each phytoestrogen was estimated using multivariable-adjusted conditional logistic regression. In men from Japan, those with high compared to low circulating equol concentrations had a lower risk of prostate cancer (multivariable-adjusted OR for upper quartile [Q4] vs. Q1 = 0.61, 95% confidence interval [CI] = 0.39-0.97), although there was no significant trend (OR per 75 percentile increase = 0.69, 95 CI = 0.46-1.05, ptrend = 0.085); Genistein and daidzein concentrations were not significantly associated with risk (ORs for Q4 vs. Q1 = 0.70, 0.45-1.10 and 0.71, 0.45-1.12, respectively). In men from Europe, circulating concentrations of genistein, daidzein and equol were not associated with risk. Circulating lignan concentrations were not associated with the risk of prostate cancer, overall or by disease aggressiveness or time to diagnosis. There was no strong evidence that prediagnostic circulating concentrations of isoflavones or lignans are associated with prostate cancer risk, although further research is warranted in populations where isoflavone intakes are high.

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.

Longitudinal biobanks-based study on the joint effects of infections, nutrition and hormones on risk of prostate cancer

Background To evaluate the individual and combined effects of enterolactone, vitamin D, free testosterone, Chlamydia trachomatis and HPV-18 on the risk of prostate cancer in a large population-based biochemical material that combined three Nordic serum sample banks. Material and methods A joint cohort of 209 000 healthy men was followed using cancer registry linkages. From this cohort altogether 699 incident cases of prostate cancer were identified. Four controls were selected by incidence density sampling and matching for country, age and date of the blood sampling. Complete data for all investigated exposures was available for 483 eligible cases and 1055 eligible controls. Multivariate regression analyses were performed to investigate the solitary and combined effects. Results The solitary effects were small. Significantly increased risk [rate ratio 1.6 (95% CI 1.0-2.5)] was found in those seronegative for C. trachomatis infection. The joint effect in risk levels of enterolactone and vitamin D was antagonistic [observed rate ratio (RR) 1.4 (1.0-2.1), expected RR 2.0 (1.0-4.1)] as well as that of HPV-18 and C. trachomatis [observed RR 1.9 (0.8-4.5), expected RR 9.9 (1.1-87.0)]. Conclusion A large follow-up study combining data from several previously investigated exposures to investigate joint effects found no evidence that exposure to two risk factors would increase the risk of prostate cancer from that expected on basis of exposure to one risk factor. If anything, the results were consistent with antagonistic interactions.

Phytoestrogens and risk of prostate cancer: a meta-analysis of observational studies

Background

Epidemiologic studies have reported various results relating phytoestrogens to prostate cancer (PCa). The aim of this study was to provide a comprehensive meta-analysis on the extent of the possible association between phytoestrogens (including consumption and serum concentration) and the risk of PCa.

Methods

Eligible studies were retrieved via both computer searches and review of references. The summary relative risk ratio (RR) or odds ratio (OR) and 95 % confidence interval (CI) were calculated with random effects models.

Results

A total of 11 studies (2 cohort and 9 case–control studies) on phytoestrogen intake and 8 studies on serum concentration were included in the meta-analysis. The pooled odds ratio (OR) showed a significant influence of the highest phytoestrogens consumption (OR 0.80, 95 % CI 0.70–0.91) and serum concentration (OR 0.83, 95 % CI 0.70–0.99) on the risk of PCa. In stratified analysis, high genistein and daidzein intake and increased serum concentration of enterolactone were associated with a significant reduced risk of PCa. However, no significant associations were observed for isoflavone intake, lignans intake, or serum concentrations of genistein, daidzein, or equol.

Conclusions

The overall current literature suggests that phytoestrogen intake is associated with a decreased risk of PCa, especially genistein and daidzein intake. Increased serum concentration of enterolactone was also associated with a significant reduced risk of PCa. Further efforts should be made to clarify the underlying biological mechanisms.

Metabolism of secoisolariciresinol-diglycoside the dietary precursor to the intestinally derived lignan enterolactone in humans

Secoisolariciresinol-diglycoside (SDG), a natural dietary lignan of flaxseeds now available in dietary supplements, is converted by intestinal bacteria to the mammalian lignans enterodiol and enterolactone. High levels of these lignans in blood and urine are associated with reduced risk of many chronic diseases. Our objective was to determine the bioavailability and pharmacokinetics of SDG in purified flaxseed extracts under dose-ranging and steady-state conditions, and to examine whether differences in secoisolariciresinol-diglycoside purity influence bioavailability. Pharmacokinetic studies were performed on healthy postmenopausal women after oral intake of 25, 50, 75, 86 and 172 mg of secoisolariciresinol-diglycoside. Extracts differing in secoisolariciresinol-diglycoside purity were compared, and steady-state lignan concentrations measured after daily intake for one week. Blood and urine samples were collected at timed intervals and secoisolariciresinol, enterodiol and enterolactone concentrations measured by mass spectrometry. Secoisolariciresinol-diglycoside was efficiently hydrolyzed and converted to secoisolariciresinol. Serum concentrations increased rapidly after oral intake, peaking after 5-7 h and disappearing with a plasma elimination half-life of 4.8 h. Maximum serum concentrations of the biologically active metabolites, enterodiol and enterolactone were attained after 12-24 h and 24-36 h, respectively, and the half-lives were 9.4 h and 13.2 h. Linear dose-responses were observed and secoisolariciresinol bioavailability correlated (r(2) = 0.835) with cumulative lignan excretion. There were no significant differences in the pharmacokinetics of extracts differing in purity, and steady-state serum lignan concentrations were obtained after one-week of daily dosing. In conclusion, this study defines the pharmacokinetics of secoisolariciresinol-diglycoside and shows it is first hydrolyzed and then metabolized in a time-dependent sequence to secoisolariciresinol, enterodiol and ultimately enterolactone, and these metabolites are efficiently absorbed.

Measuring exposure to the polyphenol metabolome in observational epidemiologic studies: current tools and applications and their limits

Much experimental evidence supports a protective role of dietary polyphenols against chronic diseases such as cardiovascular diseases, diabetes, and cancer. However, results from observational epidemiologic studies are still limited and are often inconsistent. This is largely explained by the difficulties encountered in the estimation of exposure to the polyphenol metabolome, which is composed of ~500 polyphenols distributed across a wide variety of foods and characterized by diverse biological properties. Exposure to the polyphenol metabolome in epidemiologic studies can be assessed by the use of detailed dietary questionnaires or the measurement of biomarkers of polyphenol intake. The questionnaire approach has been greatly facilitated by the use of new databases on polyphenol composition but is limited by bias as a result of self-reporting. The use of polyphenol biomarkers holds much promise for objective estimation of polyphenol exposure in future metabolome-wide association studies. These approaches are reviewed and their advantages and limitations discussed by using examples of epidemiologic studies on polyphenols and cancer. The current improvement in these techniques, along with greater emphasis on the intake of individual polyphenols rather than polyphenols considered collectively, will help unravel the role of these major food bioactive constituents in disease prevention.

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 high circulating 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 ≤4 nmol/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 (<47 pg/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 (≥47 pg/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.

Lignans extracted from Vitex negundo possess cytotoxic activity by G2/M phase cell cycle arrest and apoptosis induction

Evn-50 is a lignan compounds mixture extracted from Vitex negundo, a widely used herb in traditional Chinese medicine. This study is aimed to define the spectrum of cytotoxic activity of EVn-50, and also to investigate mechanisms underlying the anticancer actions via assessing the influence on cell cycle using EVn-50, and the lignan compound VB1 purified from EVn-50. The cytotoxic effect of EVn-50 and VB1 was determined with SRB assay using a panel of cancer cell lines. Breast cancer cell line MDA-MB-435 and liver cancer cell line SMMC-7721 were selected for further evaluating the effect of EVn-50 or VB1 on cell cycle by flow cytometric analysis. Apoptosis exerted by EVn-50 or VB1 was measured by TUNEL assay and DAPI staining, and Western blot analysis was utilized to assess the influence on expression and phosphorylation of proteins which are closely related to cell cycle and apoptosis. EVn-50 possessed a broad spectrum of in vitro anticancer activity for those tested cancer cells, especially sensitive to MDA-MB-435, SKOV-3, BXPC-3, SMMC-7721, MCF-7, HO-8910, SGC-7901, BEL-7402, HCT-116, and 786-O, with the respective IC50 below 10 μg/ml. Treatment with EVn-50 or VB1 resulted in arresting the MDA-MB-435 and SMMC-7721 cells at G2/M phase, which was further supported by observations of increased phosphorylation of Histone 3 at Ser10, phosphorylation of Cdk1 at Tyr15, expression of cyclin B1, and decreased expression of Cdc25c. Moreover, we found that exposure of MDA-MB-435 cells to EVn-50 or VB1 caused obvious apoptosis of MDA-MB-435 cells. Our data show that EVn-50, lignan compounds extracted from Vitex negundo, possesses a broad spectrum cytotoxic effect via arresting cancer cells at G2/M phase cell cycle and subsequently inducing apoptosis.

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.

Rye bread consumption in early life and reduced risk of advanced prostate cancer

OBJECTIVE

To determine whether consumption of whole-grain rye bread, oatmeal, and whole-wheat bread, during different periods of life, is associated with risk of prostate cancer (PCa).

METHODS

From 2002 to 2006, 2,268 men, aged 67-96 years, reported their dietary habits in the AGES-Reykjavik cohort study. Dietary habits were assessed for early life, midlife, and current life using a validated food frequency questionnaire. Through linkage to cancer and mortality registers, we retrieved information on PCa diagnosis and mortality through 2009. We used regression models to estimate odds ratios (ORs) and hazard ratios (HRs) for PCa according to whole-grain consumption, adjusted for possible confounding factors including fish, fish liver oil, meat, and milk intake.

RESULTS

Of the 2,268 men, 347 had or were diagnosed with PCa during follow-up, 63 with advanced disease (stage 3+ or died of PCa). Daily rye bread consumption in adolescence (vs. less than daily) was associated with a decreased risk of PCa diagnosis (OR = 0.76, 95 % confidence interval (CI): 0.59-0.98) and of advanced PCa (OR = 0.47, 95 % CI: 0.27-0.84). High intake of oatmeal in adolescence (≥5 vs. ≤4 times/week) was not significantly associated with risk of PCa diagnosis (OR = 0.99, 95 % CI: 0.77-1.27) nor advanced PCa (OR = 0.67, 95 % CI: 0.37-1.20). Midlife and late life consumption of rye bread, oatmeal, or whole-wheat bread was not associated with PCa risk.

CONCLUSION

Our results suggest that rye bread consumption in adolescence may be associated with reduced risk of PCa, particularly advanced disease.

Estrogens and prostate cancer: etiology, mediators, prevention, and management

The mainstay targets for hormonal prostate cancer (PCa) therapies are based on negating androgen action. Recent epidemiologic and experimental data have pinpointed the key roles of estrogens in PCa development and progression. Racial and geographic differences, as well as age-associated changes, in estrogen synthesis and metabolism contribute significantly to the etiology. This article summarizes how different estrogens/antiestrogens/estrogen mimics contribute to prostate carcinogenesis, the roles of the different mediators of estrogen in the process, and the potentials of new estrogenic/antiestrogenic compounds for prevention and treatment of PCa.

Nordic biological specimen bank cohorts as basis for studies of cancer causes and control: quality control tools for study cohorts with more than two million sample donors and 130,000 prospective cancers

The Nordic countries have a long tradition of large-scale biobanking and comprehensive, population-based health data registries linkable on unique personal identifiers, enabling follow-up studies spanning many decades. Joint Nordic biobank-based studies provide unique opportunities for longitudinal molecular epidemiological research. The Nordic Biological Specimen Banks working group on Cancer Causes and Control (NBSBCCC) has worked out very precise quality assurance principles for handling of the samples, based on the tradition in biobank culture. The aim of this paper is to demonstrate how high standards of quality assurance can also be developed for the data related to the subjects and samples in the biobanks. Some of the practices adopted from the strong Nordic cohort study experience evidently improve quality of nested case-control studies nested in biobank cohorts. The data quality requirements for the standardised incidence ratio calculation offer a good way to check and improve accuracy of person identifiers and completeness of follow-up for vital status, which are crucial in case-control studies for picking up right controls for the cases. The nested case-control design applying incidence-density sampling is recommended as an optimal design for most biobank-based studies. It is demonstrated how some types of biobanks have a period immediately after sampling, when the cancer risk is not comparable with the cancer risk in the base population, and how many of the biobanks never represent the normal average population of the region. The estimates on the population-representativeness of the biobanks assist in interpretation of generalisability of results of the studies based on these samples, and the systematic tabulations of numbers of cancer cases will serve in study power estimations. The well over 130,000 prospective cancer cases registered among subjects in the NBSBCCC biobank cohorts have already offered unique possibilities for tens of strong studies, but for rare exposure-outcome combinations predictions on future numbers of cases improve the chance to select the right moment when the study will have accurate statistical power.

Flaxseed ingestion alters ratio of enterolactone enantiomers in human serum

Enterolactone (EL) is an enterolignan found in human subjects. In this pilot study, the enantiomeric ratios of serum EL were determined in serum from healthy adults during consumption of habitual diet, and after an 8-day supplementation with flaxseed (25 g/day). (−)EL dominated in all serum samples collected during habitual diet consumption. However, the ratio of (−)EL and (+)EL enantiomers differed markedly between individuals. Flaxseed ingestion increased significantly the proportion of (+)EL in all subjects. Moreover, a small but significant increase in serum (−)EL concentration was measured. After flaxseed ingestion, (−)EL concentrations correlated with those of (+)EL suggesting that the stereochemistry of the parent plant lignan in flaxseed is not a major determinant of EL formation in human subjects. Comparison of EL concentrations obtained with the validated chromatographic methods (HPLC-MS/MS, HPLC-CEAD, and GC-MS) and the time-resolved fluoroimmunoassay (TR-FIA) revealed that the immunoassay method underestimates human serum EL concentrations after the flaxseed ingestion.

Assessment of information to substantiate a health claim on the prevention of prostate cancer by lignans

Lignans and their in vivo metabolites, especially enterolactone (ENL), have attracted substantial interest as potential chemopreventive agents for prostate cancer. Preclinical and clinical interventions performed with lignan-rich flaxseed that use surrogate biomarkers as endpoints suggest that lignans may attenuate prostate carcinogenesis in individuals with increased risk or with diagnosed cancer. No unequivocal prostate cancer risk reduction has been found for lignans in epidemiological studies, suggesting that lignan concentrations found in populations consuming a regular non-supplemented diet are not chemopreventive in prostate cancer. Presumably, the main obstacles in assessing the efficacy of food lignans is limited knowledge of the serum and tissue lignan concentrations required for the putative prevention. Further clinical studies performed with the purified compounds are required to substantiate a health claim.

Blood biochemistry and the risk of cancer

A longitudinal study based on a serum sample bank was carried out in Finland to find out the association between biochemical substances and the subsequent risk of cancer. The objective was to evaluate the consistency between means of individually estimated levels of these compounds and levels based on pooling. Levels of alpha-tocopherol, beta-carotene, retinol, retinol-binding protein, and ceruloplasmin were estimated by primary site and sex and partly by age and morphology. The concentrations in pooled samples were consistently lower than the averages of the individual samples. On the basis of individual samples, all the five biochemical compounds had a rather consistent protective effect on the risk of cancers at most primary sites. This protective effect disappeared in the pool analyses, and more than half of exposure contrasts showed an opposite sign. For ceruloplasmin, the effect of pooling was smaller but not negligible. The results of this study emphasize the demand to standardize the collecting, handling, and analysing of samples in serum banks. They are, furthermore, consistent with the hypothesis that pooling of biochemical samples affects the levels of the substances and may affect the conclusions of epidemiological studies on causes of diseases.

Urinary phytoestrogen excretion and prostate cancer risk: a nested case-control study in the Multiethnic Cohort

BACKGROUND

Phytoestrogens are of special interest in prostate cancer research because populations in Asia with a high consumption of phytoestrogens have a lower incidence of the disease than comparable populations in Western countries.

METHODS

This case-control study is nested within a large multiethnic cohort in Hawaii and California. Urine samples were analysed for daidzein, genistein, equol, and enterolactone among 249 incident prostate cancer cases and 404 controls matched on age, race/ethnicity, date/time of specimen collection, and fasting status.

RESULTS

The median excretion of daidzein was 0.173 nmol mg(-1) creatinine in cases and 0.291 in controls (P=0.01), and the median excretion of genistein was 0.048 in cases and 0.078 in controls (P=0.05). An inverse association was seen for daidzein overall (odds ratio for the highest vs lowest quintile=0.55, 95% confidence interval=0.31-0.98, P(trend)=0.03) and seemed to apply to localized (P(trend)=0.08) as well as advanced or high-grade cancer (P(trend)=0.09). This association was consistent across the four ethnic groups examined. Although the relationship was weaker for genistein, the odds ratios and trends were similarly inverse. Urinary excretion of equol and enterolactone was not significantly related to prostate cancer risk.

CONCLUSION

Our findings suggest that high intake of isoflavones, as reflected by urinary excretion of daidzein and genistein, may be protective against prostate cancer.

Dietary phenolics: chemistry, bioavailability and effects on health

There is much epidemiological evidence that diets rich in fruit and vegetables can reduce the incidence of non-communicable diseases such as cardiovascular diseases, diabetes, cancer and stroke. These protective effects are attributed, in part, to phenolic secondary metabolites. This review summarizes the chemistry, biosynthesis and occurrence of the compounds involved, namely the C6-C3-C6 flavonoids-anthocyanins, dihydrochalcones, flavan-3-ols, flavanones, flavones, flavonols and isoflavones. It also includes tannins, phenolic acids, hydroxycinnamates and stilbenes and the transformation of plant phenols associated with food processing (for example, production of black tea, roasted coffee and matured wines), these latter often being the major dietary sources. Events that occur following ingestion are discussed, in particular, the deglycosylation, glucuronidation, sulfation and methylation steps that occur at various points during passage through the wall of the small intestine into the circulatory system and subsequent transport to the liver in the portal vein.We also summarise the fate of compounds that are not absorbed in the small intestine, but which pass into the large intestine where they are degraded by the colonic microflora to phenolic acids, which can be absorbed into the circulatory system and subjected to phase II metabolism prior to excretion. Initially, the protective effect of dietary phenolics was thought to be due to their antioxidant properties which resulted in a lowering of the levels of free radicals within the body.However, there is now emerging evidence that themetabolites of dietary phenolics,which appear in the circulatory systemin nmol/L to low mmol/L concentrations, exertmodulatory effects in cells through selective actions on different components of the intracellular signalling cascades vital for cellular functions such as growth, proliferation and apoptosis. In addition, the intracellular concentrations required to affect cell signalling pathways are considerably lower than those required to impact on antioxidant capacity. The mechanisms underlying these processes are discussed.

Plasma phyto-oestrogens and prostate cancer in the European Prospective Investigation into Cancer and Nutrition

We examined plasma concentrations of phyto-oestrogens in relation to risk for subsequent prostate cancer in a case–control study nested in the European Prospective Investigation into Cancer and Nutrition. Concentrations of isoflavones genistein, daidzein and equol, and that of lignans enterolactone and enterodiol, were measured in plasma samples for 950 prostate cancer cases and 1042 matched control participants. Relative risks (RRs) for prostate cancer in relation to plasma concentrations of these phyto-oestrogens were estimated by conditional logistic regression. Higher plasma concentrations of genistein were associated with lower risk of prostate cancer: RR among men in the highest vs the lowest fifth, 0.71 (95% confidence interval (CI) 0.53–0.96, P trend=0.03). After adjustment for potential confounders this RR was 0.74 (95% CI 0.54–1.00, P trend=0.05). No statistically significant associations were observed for circulating concentrations of daidzein, equol, enterolactone or enterodiol in relation to overall risk for prostate cancer. There was no evidence of heterogeneity in these results by age at blood collection or country of recruitment, nor by cancer stage or grade. These results suggest that higher concentrations of circulating genistein may reduce the risk of prostate cancer but do not support an association with plasma lignans.

Energy balance, physical activity, and cancer risk

This chapter posits that cancer is a complex and multifactorial process as demonstrated by the expression and production of key endocrine and steroid hormones that intermesh with lifestyle factors (physical activity, body size, and diet) in combination to heighten cancer risk. Excess weight has been associated with increased mortality from all cancers combined and for cancers of several specific sites. The prevalence of obesity has reached epidemic levels in many parts of the world; more than 1 billion adults are overweight with a body mass index (BMI) exceeding 25. Overweight and obesity are clinically defined indicators of a disease process characterized by the accumulation of body fat due to an excess of energy intake (nutritional intake) relative to energy expenditure (physical activity). When energy intake exceeds energy expenditure over a prolonged period of time, the result is a positive energy balance (PEB), which leads to the development of obesity. This physical state is ideal for intervention and can be modulated by changes in energy intake, expenditure, or both. Nutritional intake is a modifiable factor in the energy balance-cancer linkage primarily tested by caloric restriction studies in animals and the effect of energy availability. Restriction of calories by 10 to 40% has been shown to decrease cell proliferation, increasing apoptosis through anti-angiogenic processes. The potent anticancer effect of caloric restriction is clear, but caloric restriction alone is not generally considered to be a feasible strategy for cancer prevention in humans. Identification and development of preventive strategies that "mimic" the anticancer effects of low energy intake are desirable. The independent effect of energy intake on cancer risk has been difficult to estimate because body size and physical activity are strong determinants of total energy expenditure. The mechanisms that account for the inhibitory effects of physical activity on the carcinogenic process are reduction in fat stores, activity related changes in sex-hormone levels, altered immune function, effects in insulin and insulin-like growth factors, reduced free radical generation, and direct effect on the tumor. Epidemiologic evidence posits that the cascade of actions linking overweight and obesity to carcinogenesis are triggered by the endocrine and metabolic system. Perturbations to these systems result in the alterations in the levels of bioavailable growth factors, steroid hormones, and inflammatory markers. Elevated serum concentrations of insulin lead to a state of hyperinsulinemia. This physiological state causes a reduction in insulin-like growth factor-binding proteins and promotes the synthesis and biological activity of insulin-like growth factor (IGF)-I, which regulates cellular growth in response to available energy and nutrients from diet and body reserves. In vitro studies have clearly established that both insulin and IGF-I act as growth factors that promote cell proliferation and inhibit apoptosis. Insulin also affects on the synthesis and biological availability of the male and female sex steroids, including androgens, progesterone, and estrogens. Experimental and clinical evidence also indicates a central role of estrogens and progesterone in regulating cellular differentiation, proliferation, and apoptosis induction. Hyperinsulinemia is also associated with alterations in molecular systems such as endogenous hormones and adipokines that regulate inflammatory responses. Obesity-related dysregulation of adipokines has the ability to contribute to tumorigenesis and tumor invasion via metastatic potential. Given the substantial level of weight gain in industrialized countries in the last two decades, there is great interest in understanding all of the mechanisms by which obesity contributes to the carcinogenic process. Continued focus must be directed to understanding the various relationships between specific nutrients and dietary components and cancer cause and prevention. A reductionist approach is not sufficient for the basic biological mechanisms underlying the effect of diet and physical activity on cancer. The joint association between energy balance and cancer risk are hypothesized to share the same underlying mechanisms, the amplification of chemical mediators that modulate cancer risk depending on the responsiveness to those hormones to the target tissue of interest. Disentangling the connection between obesity, the insulin-IGF axis, endogenous hormones, inflammatory markers, and their molecular interaction is vital.

Lack of prospective associations between plasma and urinary phytoestrogens and risk of prostate or colorectal cancer in the European Prospective into Cancer-Norfolk study

Dietary phytoestrogens are suggested to reduce the risk of prostate and colorectal cancer, but the results of epidemiologic studies have not yielded consistent support for this proposed effect, possibly due to inadequate databases of phytoestrogen levels in foods. Biomarkers of phytoestrogen intakes may provide a clearer insight into the relationship between phytoestrogen exposure and the risk of prostate or colorectal cancer risks. From the European Prospective into Cancer-Norfolk cohort (ages 45-75), serum and urine samples were analyzed for seven phytoestrogens [daidzein, enterodiol, enterolactone, genistein, glycitein, O-desmethylangolensin (O-DMA), and equol] among 193 cases of prostate cancer and 828 controls, and 221 cases of colorectal cancer with 889 controls. Summary variables of total lignans (enterodiol and enterolactone) and total isoflavones (daidzein, genistein, O-DMA, equol, and glycitein) were created and analyzed in conjunction with individual phytoestrogens. Logistic regression analyses revealed that there was no significant association between prostate cancer risk and total serum isoflavones [odds ratio (OR), 1.01; 95% confidence interval (CI), 0.93-1.10] or total serum lignans (OR, 0.94; 95% CI, 0.86-1.04) or between colorectal cancer risk and total serum isoflavones (OR, 1.01; 95% CI, 0.94-1.08) or total serum lignans (OR, 1.03; 95% CI, 0.94-1.12). Similarly, null associations were observed for individual serum phytoestrogens and for all urinary phytoestrogen biomarkers. In conclusion, we have found no evidence to support an inverse association between phytoestrogen exposure and prostate or colorectal cancer risk.

Enterolactone restricts the proliferation of the LNCaP human prostate cancer cell line in vitro

Ecological data suggest a long-term diet high in plant material rich in biologically active compounds, such as the lignans, can significantly influence the development of prostate cancer over the lifetime of an individual. The capacity of a pure mammalian lignan, enterolactone (ENL), to influence the proliferation of the LNCaP human prostate cancer cell line was investigated as a function of cell density, metabolic activity, expression and secretion of prostate specific antigen (PSA), cell cycle profile, and the expression of genes involved in development and progression of prostate cancer. Treatment with a subcytotoxic concentration of ENL (60 muM for 72 h) was found to reduce: cell density (57.5%, SD 7.23, p < 0.001), metabolic activity (55%, SD 0.03, p < 0.001), secretion of PSA (48.50% SD 4.74, p = 0.05) and induce apoptosis (8.33-fold SD 0.04, p = 0.001) compared to untreated cells. Cotreatment with 10 muM etoposide was found to increase apoptosis by 50.17% (SD 0.02, p < 0.001). Additionally, several key genes (e. g. MCMs, survivin and CDKs) were beneficially regulated by ENL treatment (p < 0.05). The data suggest that the antiproliferative activity of ENL is a consequence of altered expression of cell cycle associated genes and provides novel molecular evidence for the antiproliferative properties of a pure lignan in prostate cancer.

Dietary phytoestrogens are not associated with risk of overall breast cancer but diets rich in coumestrol are inversely associated with risk of estrogen receptor and progesterone receptor negative breast tumors in Swedish women

Results from epidemiological and experimental studies indicate that phytoestrogens may protect against breast cancer. Because one of the biological effects of phytoestrogens is probably estrogenic, it's possible that the preventive effect on breast cancer differs by estrogen receptor (ER) or progesterone receptor (PR) status of the tumor. We evaluated the associations between dietary phytoestrogen (isoflavonoids, lignans, and coumestrol) intake and risk of breast cancer and whether the ER/PR statuses of the tumor influence this relationship. In 1991-2 a prospective population-based cohort study among Swedish pre- and postmenopausal women was performed, making questionnaire data available for 45,448 women. A total of 1014 invasive breast cancers were diagnosed until December 2004. Cox proportional hazards models were performed to estimate multivariate risk ratios, 95% CI for associations with risk of breast cancer. Intakes of lignan, isoflavonoid, or coumestrol were not associated with breast cancer risk overall or before or after 50 y of age. The effects of lignans or isoflavonoids were independent of receptor status. However, intake of coumestrol was associated with decreased risk of receptor negative tumors (ER-PR-) but not positive tumors. The risk of ER-PR- tumors was significantly lower (50%) in women with intermediate coumestrol intake compared with those who did not consume any. In conclusion, we found no association between intake of isoflavonoids or lignans and breast cancer risk. Our results of a decreased risk of ER-PR- tumors in women with intermediate intake of coumestrol could be due to chance because of the low intake. The results should be confirmed in other studies.

Lignans and human health

This review focuses on the possible role in human health of the consumption of lignan-rich foods. Most of the plant lignans in human foods are converted by the intestinal microflora in the upper part of the large bowel to enterolactone and enterodiol, called mammalian or enterolignans. The protective role of these compounds, particularly in chronic Western diseases, is discussed. Evidence suggests that fiber- and lignan-rich whole-grain cereals, beans, berries, nuts, and various seeds are the main protective foods. Many factors, in addition to diet, such as intestinal microflora, smoking, antibiotics, and obesity affect circulating lignan levels in the body. Lignan-rich diets may be beneficial, particularly if consumed for life. Experimental evidence in animals has shown clear anticarcinogenic effects of flaxseed or pure lignans in many types of cancer. Many epidemiological results are controversial, partly because the determinants of plasma enterolactone are very different in different countries. The source of the lignans seems to play a role because other factors in the food obviously participate in the protective effects. The results are promising, but much work is still needed in this area of medicine.

Lignan content of selected foods from Japan

Lignans constitute a group of phytochemicals widely distributed in the human diet. Once ingested, most dietary lignans are metabolized by the gut microflora to enterolactone and enterodiol, also known as enterolignans. Together with isoflavones and coumestrol, enterolignans have been traditionally classified as phytoestrogens, plant-derived compounds that exhibit estrogen-like activity. In addition to a higher intake of vegetables, many studies have suggested that the presence of phytoestrogens in the Japanese diet is one of the factors that might explain the reduced incidence of certain chronic diseases in Japanese populations compared with Western countries. Being a vegetable-based diet, exposure to dietary lignans should be high, but to assess this exposure, a lignan food database is required. Stable isotope-dilution gas chromatography coupled with mass spectrometry was used to quantify six plant lignans in 86 food items commonly consumed in Japan. These data will complement the previous databases and most importantly expand the knowledge of occurrence of lignans in food to Eastern diets.

Nordic biological specimen banks as basis for studies of cancer causes and control--more than 2 million sample donors, 25 million person years and 100,000 prospective cancers

The Nordic countries have a long tradition of large-scale biobanking and comprehensive, population-based health data registries linkable on unique personal identifiers, enabling follow-up studies spanning many decades. Joint Nordic biobank-based studies provide unique opportunities for longitudinal molecular epidemiological research. The purpose of the present paper is to describe the possibilities for such joint studies, by describing some of the major Nordic biobank cohorts with a standardised calculation of the cancer incidence in these cohorts. Altogether two million donors have since 1966 donated more than four million biological samples, stored at -20 degrees C to -135 degrees C, to 17 biobank cohorts in Finland, Iceland, Norway and Sweden. As a result of joint database handling principles, the accuracy of personal identifiers and completeness of follow-up for vital status in all participating biobanks was improved. Thereafter, the cancer incidence was determined using follow-up through the national cancer registries. Biobanks based on random samples of population typically showed slightly lower cancer incidence rates than the general population, presumably due to better participation rates among health-conscious subjects. On the other hand, biobanks including samples for viral screening or clinical testing showed 1.5 to 2.1 fold increased incidence of cancer. This excess was very high immediately after sampling, but for some cancer sites remained elevated for years after clinical sampling. So far, more than 100 000 malignant neoplasms have occurred after sample donation, and the annual increase of the cancer cases in these cohorts is about 10 000. The estimates on the population-representativity of the biobanks will assist in interpretation of generalizability of results of future studies based on these samples, and the systematic tabulations of numbers of cancer cases will serve in study power estimations. The present paper summarizes optimal study designs of biobank-based studies of cancer.

Phyto-oestrogens and risk of prostate cancer in Scottish men

A population-based case–control study of diet, inherited susceptibility and prostate cancer was undertaken in the lowlands and central belt of Scotland to investigate the effect of phyto-oestrogen intake and serum concentrations on prostate cancer risk. A total of 433 cases and 483 controls aged 50–74 years were asked to complete a validated FFQ and provide a non-fasting blood sample. Multivariate logistic regression analysis found significant inverse associations with increased serum concentrations of enterolactone (adjusted OR 0·40, 95 % CI 0·22, 0·71] and with the consumption of soy foods (adjusted OR 0·52, 95 % CI 0·30, 0·91). However, no significant associations were observed for isoflavone intake or serum genistein, daidzein and equol. This study supports the hypotheses that soy foods and enterolactone metabolised from dietary lignans protect against prostate cancer in older Scottish men.

Phytoestrogen Exposure, Polymorphisms in COMT, CYP19, ESR1, and SHBG Genes, and Their Associations With Prostate Cancer Risk

Prospective phytoestrogen exposure was assessed using both biomarkers and estimates of intake in 89 British men recruited into the Norfolk arm of the European Prospective Investigation into Cancer and Nutrition study, men who subsequently developed prostate cancer. Results were compared with those from 178 healthy men matched by age and date of recruitment. Levels of seven phytoestrogens (daidzein, genistein, glycitein, O-desmethylangolensin, equol, enterodiol, and enterolactone) were measured in spot urine and serum samples. Five single-nucleotide polymorphisms in COMT, CYP19, ESR1, and SHBG genes were genotyped. Urinary levels of all phytoestrogens correlated strongly with serum levels. Correlation coefficients ranged from 0.63 (glycitein) to 0.88 (daidzein) (P < 0.001). Urinary and serum levels correlated significantly with isoflavone intake assessed from food diaries (R = 0.15-0.20; P < 0.05) but not with that from a food-frequency questionnaire. Odds ratios for phytoestrogen exposure, as assessed using the four methods, were not significantly associated with prostate cancer risk (P = 0.15-0.94). Men with the CC genotype for the ESRI PvuII polymorphism had significantly higher risk for prostate cancer compared with men with the TT genotype [adjusted odds ratio = 4.65 (1.60-13.49); P = 0.005]. Our results utilizing a combined prospective exposure provide no evidence that phytoestrogens alter prostate cancer risk in British men, whereas the C allele for the PvuII polymorphism may be associated with increased risk.

Rye bran diet increases epithelial cell apoptosis and decreases epithelial cell volume in TRAMP (transgenic adenocarcinoma of the mouse prostate) tumors

A rye bran diet has been suggested to retard prostate cancer growth and increase tumor cell apoptosis in animal models and in men with prostate cancer. Transgenic mice designed to develop prostate cancer (transgenic adenocarcinoma of the mouse prostate, TRAMP) were therefore treated with a rye bran diet. TRAMP mice were fed a rye bran (n = 13) or a control diet (n = 15) from 4 to 24 wk of age. Tumor histology, cell proliferation, and apoptosis were accessed using stereological and immunohistochemical techniques. In the dorsolateral prostate lobe in TRAMP mice, epithelial cell apoptosis was increased by 31%, and the volume fraction of epithelial cells was reduced by 20% (P < 0.05) in the rye bran-treated group compared with the control diet group. There were, however, no significant changes detected in lobe weights or tumor grade. In conclusion, a rye bran diet increases epithelial apoptosis and reduces the epithelial cell fraction in TRAMP tumors.

Plasma Enterolignans Are Associated with Lower Colorectal Adenoma Risk

Lignans are biphenolic compounds that occur in foods of plant origin such as whole grains, seeds, fruits and vegetables, and beverages, such as coffee and tea. Plant lignans are converted by intestinal bacteria into the enterolignans, enterodiol and enterolactone. Enterolignans possess several biological activities, whereby they may influence carcinogenesis. We studied the associations between plasma enterolignans and the risk of colorectal adenomas in a Dutch case-control study. Colorectal adenomas are considered to be precursors of colorectal cancer. Cases (n = 532) with at least one histologically confirmed colorectal adenoma and controls (n = 503) with no history of any type of adenoma were included. Plasma enterodiol and enterolactone concentrations were measured by liquid chromatography with tandem mass spectrometry. Associations were stronger for incident than for prevalent cases. When only incident cases (n = 262) were included, high compared to low plasma concentrations of enterodiol were associated with a reduction in colorectal adenoma risk after adjustment for confounding variables. Enterodiol odds ratios (95% confidence intervals) were 1.00, 0.69 (0.42-1.13), 0.60 (0.37-0.99), and 0.53 (0.32-0.88) with a significant trend (P = 0.01) through the quartiles. Although enterolactone plasma concentrations were 10-fold higher, enterolactone's reduction in risk was not statistically significant (P for trend = 0.09). Use of oral antibiotic therapy could decrease the plasma concentrations of enterolactone. Exclusion of antibiotic users resulted in similar odds ratios for both enterolignans, but the association for enterolactone became somewhat stronger (P = 0.05 versus P = 0.09). We observed a substantial reduction in colorectal adenoma risk among subjects with high plasma concentrations of enterolignans, in particular, enterodiol. These findings could be important in the prevention of colorectal adenomas.

Dietary phytoestrogen, serum enterolactone and risk of prostate cancer: the cancer prostate Sweden study (Sweden)

OBJECTIVE

Based on evidence that phytoestrogens may protect against prostate cancer, we evaluated the associations between serum enterolactone concentration or dietary phytoestrogen intake and risk of prostate cancer.

METHODS

In our Swedish population-based case-control study, questionnaire-data were available for 1,499 prostate cancer cases and 1,130 controls, with serum enterolactone levels in a sub-group of 209 cases and 214 controls. Unconditional logistic regression was performed to estimate multivariate odds ratios (ORs) and 95% confidence intervals (CIs) for associations with risk of prostate cancer.

RESULTS

High intake of food items rich in phytoestrogens was associated with a decreased risk of prostate cancer. The OR comparing the highest to the lowest quartile of intake was 0.74 (95% CI: 0.57-0.95; p-value for trend: 0.01). In contrast, we found no association between dietary intake of total or individual lignans or isoflavonoids and risk of prostate cancer. Intermediate serum levels of enterolactone were associated with a decreased risk of prostate cancer. The ORs comparing increasing quartiles of serum enterolactone concentration to the lowest quartile were, respectively, 0.28 (95% CI: 0.15-0.55), 0.63 (95% CI: 0.35-1.14) and 0.74 (95% CI: 0.41-1.32).

CONCLUSIONS

Our results support the hypothesis that certain foods high in phytoestrogens are associated with a lower risk of prostate cancer.

Human Papillomavirus 16, 18, and 33 Infections and Risk of Prostate Cancer: A Nordic Nested Case-Control Study

Epidemiologic evidence of sexual history has emerged as a consistently found risk factor for prostate cancer. Some studies have reported an association between human papillomavirus (HPV) infections and prostate cancer. We did a nested case-control study within cohorts of more than 200,000 men enrolled in three Nordic biobanking projects. Follow-up using cancer registry linkages identified 804 prospectively occurring prostate cancer cases. Four control subjects per case were randomly selected from eligible sets of matched subjects that were alive and free of cancer at the time of diagnosis of the corresponding case and were matched to cases on biobank cohort, age (+/-2 years), county of residence, and date of blood sampling (+/-2 months in the Finnish and Swedish cohorts, +/-6 months in the Norwegian cohort). The serum samples were analyzed by standard ELISAs for the presence of immunoglobulin G antibodies against HPV types 16, 18, and 33. The joint HPV-16/HPV-18/HPV-33 seroprevalence in the joint cohort was 13.4% (107 of 799) among cases and 14.0% (363 of 2,596) among controls (odds ratio, 0.94; 95% confidence interval, 0.74-1.19). There were no noteworthy differences when the data were analyzed by different HPV type, country, or antibody levels. Our data do not support an association between serologic markers of HPV-16, HPV-18, and HPV-33 infections and risk of prostate cancer.

Dietary lignans: potential role in cancer prevention

Recent in vitro, animal, and epidemiological studies suggest that dietary lignans may be chemopreventive, potentially through anti-estrogenic, anti-angiogenic, pro- apoptotic, and anti-oxidant mechanisms. In this article, we review lignan food sources and metabolism, proposed anti-carcinogenic mechanisms, and the evidence for a role of lignans in breast, colon, and prostate cancer prevention from animal and epidemiologic literature. Although a number of in vitro and animal studies support a role for lignan-rich foods and purified lignans in the modulation of cancer events of the breast, prostate, and colon, epidemiological studies, sparse and often retrospective in nature, offer inconsistent findings. The most support for a role of lignans in cancer is observed for premenopausal breast cancer. Additional epidemiological studies that use a prospective design and well-developed food databases and questionnaires are needed to adequately evaluate the role of lignans in cancer prevention.

Dietary polyphenols and the prevention of diseases

Polyphenols are the most abundant antioxidants in the diet and are widespread constituents of fruits, vegetables, cereals, dry legumes, chocolate, and beverages, such as tea, coffee, or wine. Experimental studies on animals or cultured human cell lines support a role of polyphenols in the prevention of cardiovascular diseases, cancers, neurodegenerative diseases, diabetes, or osteoporosis. However, it is very difficult to predict from these results the effects of polyphenol intake on disease prevention in humans. One of the reasons is that these studies have often been conducted at doses or concentrations far beyond those documented in humans. The few clinical studies on biomarkers of oxidative stress, cardiovascular disease risk factors, and tumor or bone resorption biomarkers have often led to contradictory results. Epidemiological studies have repeatedly shown an inverse association between the risk of myocardial infarction and the consumption of tea and wine or the intake level of some particular flavonoids, but no clear associations have been found between cancer risk and polyphenol consumption. More human studies are needed to provide clear evidence of their health protective effects and to better evaluate the risks possibly resulting from too high a polyphenol consumption.

A validated method for the quantification of enterodiol and enterolactone in plasma using isotope dilution liquid chromatography with tandem mass spectrometry

Enterolactone and enterodiol are phytoestrogens with structural similarity to endogenous estrogens. Because of their biological activities, they may affect the development of several diseases. To quantify enterodiol and enterolactone in plasma, we developed and validated a liquid chromatography-tandem mass spectrometry method with electrospray ionization using 13C3 labeled isotopes. The method consists of a simple enzymatic hydrolysis and ether extraction followed by a rapid LC separation (run-time of 11 min). Detection limits as low as 0.15 nM for enterodiol and 0.55 nM for enterolactone were achieved. The within-run R.S.D. ranges from 3 to 6% and the between-run R.S.D. ranges from 10 to 14% for both enterolignans. This method allows simple, rapid, and sensitive quantification, and is suitable for measuring large numbers of samples.

Phytoestrogens and prostate cancer risk

BACKGROUND

Phytoestrogens are natural plant substances. The four main classes are isoflavones, flavonoids, coumestans, and lignans. Phytoestrogens have anti-carcinogenic potential. For evaluation of the effect of phytoestrogens on prostate cancer risk, we reviewed analytical epidemiological data.

METHODS

Up to now, there are few studies that have assessed the direct relation between the individual dietary intake of soy products and other nutrients with phytoestrogens and the risk of prostate cancer. We decided to review analytical epidemiological studies providing data on (a) dietary soy intake or flavonoids intake, (b) urinary excretion of isoflavones or lignans, or (c) blood measurements of isoflavones or lignans. Soy is used as a marker for isoflavone intake.

RESULTS

Overall, the results of these studies do not show protective effects. Only four of these studies are prospective, and none of them found statistically significant prostate cancer reductions. Two prospective studies measured flavonoid intake and one reported a preventive effect on prostate cancer for the assumption of myricetin. One study assessed enterolactone concentrations in three different countries and showed no reduction in prostate cancer occurrence.

CONCLUSION

Few studies showed protective effect between phytoestrogen intake and prostate cancer risk.

Prospective study of plasma enterolactone and prostate cancer risk (Sweden)

OBJECTIVES

Enterolactone, a phytoestrogen produced by the intestinal microflora from precursors in plant foods, has been postulated to protect against hormone-dependent cancers. We studied the association between plasma enterolactone and risk of prostate cancer.

METHODS

In the Northern Sweden Health and Disease Cohort, enterolactone concentrations were measured by time-resolved fluoroimmunoassay in plasma taken from 265 men who were diagnosed with prostate cancer at a mean time of 5 years after blood collection, and in plasma from 525 control men, matched for age and date of blood collection.

RESULTS

There was no significant association between quartiles of plasma enterolactone and risk of prostate cancer. Odds ratios for prostate cancer, estimated by conditional logistic regression for increasing concentrations of enterolactone in quartiles were 1.00 (referent), 0.81 (95% confidence interval 0.52-1.27), 1.03 (0.67-1.58), and 1.22 (0.80-1.86). Adjustments for body mass index (BMI), smoking status and stratification for age, lag time, storage time and tumour characteristics did not materially alter risk estimates. Men with very low enterolactone levels, however, had significantly higher risk of prostate cancer, odds ratio for bottom decile versus all other deciles was 1.68 (1.03-2.74).

CONCLUSIONS

Our results do not support the hypothesis that enterolactone formed from dietary lignans protects against prostate cancer.

Anticancer effects of a plant lignan 7-hydroxymatairesinol on a prostate cancer model in vivo

Clinical intervention studies and experimental studies with lignan-rich diets suggest that lignans may have inhibitory effects on prostate cancer, but no clinical or experimental studies with purified lignans have been published. The purpose of this study was to investigate the effect of a plant lignan 7-hydroxymatairesinol (HMR) on LNCaP human prostate cancer xenografts in athymic mice. Athymic nude male mice were injected subcutaneously with LNCaP cells. Starting 3 days after tumor cell injections, a control diet or a control diet supplemented with 0.15% or 0.30% of HMR was administered to mice and the tumor take rate and growth was observed for 9 weeks. HMR diet inhibited the growth of LNCaP tumors. Mice treated with HMR had smaller tumor volume, lower tumor take rate, increased proportion of nongrowing tumors, and higher tumor cell apoptotic index compared with controls. Furthermore, the cell proliferation index was reduced in mice receiving the 0.30% HMR diet compared with mice receiving the control diet. Our results suggest that dietary HMR started at the early phase of the tumor development inhibits the growth of the LNCaP human prostate cancer xenografts in athymic male mice.

Pharmacokinetics of enterolignans in healthy men and women consuming a single dose of secoisolariciresinol diglucoside

High concentrations of enterolignans in plasma are associated with a lower risk of acute coronary events. However, little is known about the absorption and excretion of enterolignans. The pharmacokinetic parameters and urinary excretion of enterodiol and enterolactone were evaluated after consumption of their purified plant precursor, secoisolariciresinol diglucoside (SDG). Twelve healthy volunteers ingested a single dose of purified SDG (1.31 micromol/kg body wt). Enterolignans appeared in plasma 8-10 h after ingestion of the purified SDG. Enterodiol reached its maximum plasma concentration 14.8 +/- 5.1 h (mean +/- SD) after ingestion of SDG, whereas enterolactone reached its maximum 19.7 +/- 6.2 h after ingestion. The mean elimination half-life of enterodiol (4.4 +/- 1.3 h) was shorter than that of enterolactone (12.6 +/- 5.6 h). The mean area under the curve of enterolactone (1762 +/- 1117 nmol/L . h) was twice as large as that of enterodiol (966 +/- 639 nmol/L . h). The mean residence time for enterodiol was 20.6 +/- 5.9 h and that for enterolactone was 35.8 +/- 10.6 h. Within 3 d, up to 40% of the ingested SDG was excreted as enterolignans via urine, with the majority (58%) as enterolactone. In conclusion, a substantial part of enterolignans becomes available in the blood circulation and is subsequently excreted. The measured mean residence times and elimination half-lives indicate that enterolignans accumulate in plasma when consumed 2-3 times a day and reach steady state. Therefore, plasma enterolignan concentrations are expected to be good biomarkers of dietary lignan exposure and can be used to evaluate the effects of lignans.

Polyphenols and disease risk in epidemiologic studies

Plant polyphenols, a large group of natural antioxidants, are serious candidates in explanations of the protective effects of vegetables and fruits against cancer and cardiovascular diseases. Epidemiologic studies are useful for evaluation of the human health effects of long-term exposure to physiologic concentrations of polyphenols, but reliable data on polyphenol contents of foods are still scarce. The aim of this review is to summarize available epidemiologic data on the health effects of polyphenols, focusing on the flavonoid subclasses of flavonols, flavones, and catechins and on lignans. Data obtained to date suggest beneficial effects of both flavonoids and lignans on cardiovascular diseases but not on cancer, with the possible exception of lung cancer. There is a need for more research on stroke and lung diseases such as asthma and chronic obstructive pulmonary disease. Most studies to date have included only flavonols and flavones. With data becoming available for other polyphenols, these compounds should be included in future studies. Careful design of prospective studies is important to offset some of the major drawbacks of epidemiologic studies, including residual confounding (by smoking and other dietary factors) and exposure assessment.

The role of Vitamin D3 metabolism in prostate cancer

Vitamin D deficiency increases risk of prostate cancer. According to our recent results, the key Vitamin D hormone involved in the regulation of cell proliferation in prostate is 25(OH) Vitamin D3. It is mainly acting directly through the Vitamin D receptor (VDR), but partially also through its 1alpha-hydroxylation in the prostate. A deficiency of 25(OH) Vitamin D is common especially during the winter season in the Northern and Southern latitudes due to an insufficient sun exposure, but Vitamin D deficient diet may partially contribute to it. A lack of Vitamin D action may also be due to an altered metabolism or Vitamin D resistance. Vitamin D resistance might be brought up by several mechanisms: Firstly, an increased 24-hydroxylation may increase the inactivation of hormonal Vitamin D metabolites resulting in a Vitamin D resistance. This is obvious in the cancers in which an oncogenic amplification of 24-hydroxykase gene takes place, although an amplification of this gene in prostate cancer has not yet been described. During the aging, the activity of 24-hydroxylase increases, whereas 1alpha-hydroxylation decreases. Furthermore, it is possible that a high serum concentration of 25(OH)D3 could induce 24-hydroxylase expression in prostate. Secondly, Vitamin D receptor gene polymorphism or defects may result in a partial or complete Vitamin D resistance. Thirdly, an overexpression or hyperphosphorylation of retinoblastoma protein may result in an inefficient mitotic control by Vitamin D. Fourthly, endogenous steroids (reviewed by [D.M. Peehl, D. Feldman, Interaction of nuclear receptor ligands with the Vitamin D signaling pathway in prostate cancer, J. Steroid Biochem. Mol. Biol. (2004)]) and phytoestrogens may modulate the expression of Vitamin D metabolizing enzymes. In summary, the local metabolism of hormonal Vitamin D seems to play an important role in the development and progression of prostate cancer.