Age-stratified serum levels of isoflavones and proportion of equol producers in Japanese and Korean healthy men

Associations of soy product intake with all-cause, cardiovascular disease and cancer mortality: Guangzhou Biobank Cohort Study and updated meta-analyses

PURPOSE

We examined the associations of soy product intake with all-cause, cardiovascular disease (CVD), and cancer mortality and mediations through CVD risk factors based on the Guangzhou Biobank Cohort Study (GBCS), and conducted updated meta-analyses.

METHODS

A total of 29,825 participants aged 50 + years were included. Causes of death were identified through record linkage. Soy product intake was assessed by food frequency questionnaire. Cox proportional hazards regression was used to analyze the associations between soy product intake and mortality, yielding hazard ratios (HRs) and 95% confidence intervals (CIs). Mediation analyses with CVD risk factors as mediators, and updated meta-analyses were conducted.

RESULTS

During 454,689 person-years of follow-up, 6899 deaths occurred, including 2694 CVD and 2236 cancer. Participants who consumed soy product of 1-6 portions/week, versus no consumption, had significantly lower risks of all-cause and CVD mortality (adjusted HR (95% CI) 0.91 (0.86, 0.97) and 0.87 (0.79, 0.96), respectively). In participants who consumed soy product of ≥ 7 portions/week, the association of higher intake with lower CVD mortality was modestly mediated by total cholesterol (4.2%, 95% CI 1.0-16.6%). Updated meta-analyses showed that the highest level of soy product intake, versus the lowest, was associated with lower risks of all-cause and CVD mortality (pooled HR (95% CI) 0.92 (0.88, 0.96) and 0.92 (0.87, 0.98), respectively).

CONCLUSION

Moderate and high soy product intake were associated with lower risks of all-cause and CVD mortality. Our findings provide support for current dietary guidelines recommending moderate soy product intake, and contribute additional evidence regarding the potential protective effects of high soy product intake.

Impacts of endocrine-disrupting chemicals on prostate function and cancer

Because of their historical mode of action, endocrine-disrupting chemicals (EDCs) are associated with sex-steroid receptors, namely the two estrogen receptors (ERα and ERβ) and the androgen receptor (AR). Broadly, EDCs can modulate sex-steroid receptor functions. They can also indirectly impact the androgen and estrogen pathways by influencing steroidogenesis, expression of AR or ERs, and their respective activity as transcription factors. Additionally, many of these chemicals have multiple cellular targets other than sex-steroid receptors, which results in a myriad of potential effects in humans. The current article reviews the association between prostate cancer and the endocrine-disrupting functions of four prominent EDC families: bisphenols, phthalates, phytoestrogens, and mycoestrogens. Results from both in vitro and in vivo models are included and discussed to better assess the molecular mechanisms by which EDCs can modify prostate biology. To overcome the heterogeneity of results published, we established common guidelines to properly study EDCs in the context of endocrine diseases. Firstly, the expression of sex-steroid receptors in the models used must be determined before testing. Then, in parallel to EDCs, pharmacological compounds acting as positive (agonists) and negative controls (antagonists) have to be employed. Finally, EDCs need to be used in a precise range of concentrations to modulate sex-steroid receptors and avoid off-target effects. By adequately integrating molecular endocrinology aspects in EDC studies and identifying their underlying molecular mechanisms, we will truly understand their impact on prostate cancer and distinguish those that favor the progression of the disease from those that slow down tumor development.

Prostate diseases and microbiome in the prostate, gut, and urine

The microbiome in various organs involves a vast network that plays a key role in the health and wellness of the human body. With recent advances in biological technologies such as high-throughput sequencing, transcriptomics, and metabolomics, it appears that the microbial signature varies dynamically among individuals, creating various roles in metabolism, local and systemic inflammation, and host immunity. Urinary and genital organs, including the prostate, seminal vesicles, and urinary bladder, are reservoirs of several bacterial, viral, and fungal communities. Accumulating evidence has suggested profound roles for the gut, urinary, and intraprostate microbiomes in genitourinary benign and malignant diseases. This review article addresses microbiome-related evidence for three major diseases involved in prostate cancer: chronic prostatitis (CP), benign prostatic hyperplasia (BPH), and prostate cancer (PCa). Symptomatic CP is known as CP/chronic pelvic pain syndrome. CP is one of the most common prostate diseases in young men, accounting for 8% of all men visiting a urologic clinic. Although oral medication is the gold standard therapy for patients with BPH, approximately 13% of men present with clinical progression within 4 years after the initiation of treatment, with 5% requiring surgical intervention. The identification of proinflammatory cytokines and pathogens responsible for the clinical progression of BPH is still underway. Several topics regarding the association between PCa and the microbiome are discussed in this review as follows: i) intraprostatic microbiome and the risk of PCa, ii) gut microbiome and PCa, iii) gut microbiome and the risk of radiation-induced side effects, iv) isoflavone intake and equol-producing intestinal flora on PCa, and v) the inhibitory effect of daidzein and equol on tumor growth and progression of PCa. Further studies are required for a comprehensive understanding between the urogenital microbiome and prostate pathogenesis to facilitate the development of preventive and therapeutic approaches for prostate diseases.

Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data

Soybeans are a rich source of isoflavones, which are classified as phytoestrogens. Despite numerous proposed benefits, isoflavones are often classified as endocrine disruptors, based primarily on animal studies. However, there are ample human data regarding the health effects of isoflavones. We conducted a technical review, systematically searching Medline, EMBASE, and the Cochrane Library (from inception through January 2021). We included clinical studies, observational studies, and systematic reviews and meta-analyses (SRMA) that examined the relationship between soy and/or isoflavone intake and endocrine-related endpoints. 417 reports (229 observational studies, 157 clinical studies and 32 SRMAs) met our eligibility criteria. The available evidence indicates that isoflavone intake does not adversely affect thyroid function. Adverse effects are also not seen on breast or endometrial tissue or estrogen levels in women, or testosterone or estrogen levels, or sperm or semen parameters in men. Although menstrual cycle length may be slightly increased, ovulation is not prevented. Limited insight could be gained about possible impacts of in utero isoflavone exposure, but the existing data are reassuring. Adverse effects of isoflavone intake were not identified in children, but limited research has been conducted. After extensive review, the evidence does not support classifying isoflavones as endocrine disruptors.

Daidzein Intake Is Associated with Equol Producing Status through an Increase in the Intestinal Bacteria Responsible for Equol Production

Equol is a metabolite of isoflavone daidzein and has an affinity to estrogen receptors. Although equol is produced by intestinal bacteria, the association between the status of equol production and the gut microbiota has not been fully investigated. The aim of this study was to compare the intestinal bacteria responsible for equol production in gut microbiota between equol producer and non-producer subjects regarding the intake of daidzein. A total of 1044 adult subjects who participated in a health survey in Hirosaki city were examined. The concentration of equol in urine was measured by high-performance liquid chromatography. The relative abundances of 8 bacterial species responsible for equol production in the gut microbiota was assessed using 16S rRNA amplification. There were 458 subjects identified as equol producers. The proportion of equol production status and the intake of daidzein increased with age. Daily intake of daidzein was larger in equol-producer. The intestinal bacteria, which convert daidzein to equol were present in both equol producers and non-producers. However, the relative abundance and the prevalence of Asaccharobacter celatus and Slackia isoflavoniconvertens were significantly higher in equol producers than those in equol non-producers. The intestinal bacteria that convert daidzein to equol are present in not only the equol producers but also in the non-producers. The daidzein intake is associated with the equol production status through an increase of A. celatus and S. isoflavoniconvertens in the gut microbiota.

Effect of S-equol and Soy Isoflavones on Heart and Brain

BACKGROUND

Observational studies in Asia show that dietary intake of soy isoflavones had a significant inverse association with coronary heart disease (CHD). A recent randomized controlled trial (RCT) of soy isoflavones on atherosclerosis in the US, however, failed to show their benefit. The discrepancy may be due to the much lower prevalence of S-equol producers in Westerners: Only 20-30% of Westerners produce S-equol in contrast to 50-70% in Asians. S-equol is a metabolite of dietary soy isoflavone daidzein by gut microbiome and possesses the most antiatherogenic properties among all isoflavones. Several short-duration RCTs documented that soy isoflavones improves arterial stiffness. Accumulating evidence shows that both atherosclerosis and arterial stiffness are positively associated with cognitive decline/dementia. Therefore, potentially, soy isoflavones, especially S-equol, are protective against cognitive decline/dementia.

METHODS/RESULTS

This narrative review of clinical and epidemiological studies provides an overview of the health benefits of soy isoflavones and introduces S-equol. Second, we review recent evidence on the association of soy isoflavones and S-equol with CHD, atherosclerosis, and arterial stiffness as well as the association of atherosclerosis and arterial stiffness with cognitive decline/ dementia. Third, we highlight recent studies that report the association of soy isoflavones and S-equol with cognitive decline/dementia. Lastly, we discuss the future directions of clinical and epidemiological research on the relationship of S-equol and CHD and dementia.

CONCLUSIONS

Evidence from observational studies and short-term RCTs suggests that S-equol is anti-atherogenic and improves arterial stiffness and may prevent CHD and cognitive impairment/ dementia. Well-designed long-term (≥ 2years) RCTs should be pursued.

Premenstrual symptoms interference and equol production status in Japanese collegiate athletes: A cross-sectional study

Aim

Consumption of soy isoflavones reduces the risk of estrogen‐related diseases, such as menopausal symptoms, osteoporosis, and cardiovascular disease. Equol is metabolized from the isoflavone daidzein by intestinal bacteria and has higher bioavailability than other isoflavones. Equol producers are believed to benefit from soybean consumption to a greater extent than non‐producers. Recently, we showed that equol non‐producers were at significant risk of premenstrual syndrome (PMS). Previously, we reported that PMS is a common menstrual problem in female athletes, and almost half of the studied athletes felt a negative effect of premenstrual symptoms on their athletic performance. This study was conducted to evaluate the relation between PMS and equol production status in Japanese collegiate athletes.

Methods

This was a cross‐sectional, observational study that included 88 Japanese female collegiate athletes. Equol production status was determined using urine samples collected after a soy challenge test. The subjects also completed a questionnaire about their premenstrual symptoms and their competitive career.

Results

The prevalence of equol producers was 29.5% in Japanese collegiate athletes. The athletic performance of 54.5% of athletes was found to suffer in competition or in practice due to premenstrual symptoms. In multivariate analysis, equol non‐producers (odds ratio, 3.34; 95% confidence interval, 1.03–12.20) and restriction of bodyweight (odds ratio, 4.94; 95% confidence interval, 1.47–20.00) were shown to be significant risk factors for poor athletic performance.

Conclusion

This study showed a relation between athletic performance and equol production status in Japanese collegiate athletes.

Effect of Soy and Soy Isoflavones on Obesity-Related Anthropometric Measures: A Systematic Review and Meta-analysis of Randomized Controlled Clinical Trials

Soy may be a suitable food for anti-obesity efforts because of its high protein and isoflavone content. We conducted this meta-analysis to evaluate potential effects of soy and soy isoflavones on weight, waist circumference, and fat mass. PubMed, MEDLINE, Scopus, EMBASE, and Cochrane databases were searched. Twenty-four trials with soy and 17 trials with isoflavones passed the eligibility stage. According to the results, soy showed no overall statistically significant effect on weight, waist circumference, or fat mass, but a significant increasing effect on weight was observed in some circumstances: for instance, in obese subjects [mean difference (MD): 0.80 kg; 95% CI: 0.15, 1.45 kg; P = 0.02], with ingestions of ≥40 g soy protein/d (MD: 0.94 kg; 95% CI: 0.11, 1.77 kg; P = 0.03), with short-term applications (1-3 mo) (MD: 0.45 kg; 95% CI: 0.05, 0.86 kg; P = 0.03), and when soy was compared with meat (MD: 0.36 kg; 95% CI: 0.09, 0.64 kg; P = 0.03) and whey protein (MD: 1.53 kg; 95% CI: 0.10, 2.96 kg; P = 0.04). In contrast to the effects of soy on weight, soy significantly decreased waist circumference in older ages (MD: -0.36 cm; 95% CI: -0.71, -0.01 cm; P = 0.04), in women (MD: -0.32 cm; 95% CI: -0.57, -0.08 cm; P = 0.01), and at doses of <40 g soy protein/d (MD: -0.31 cm; 95% CI: -0.57, -0.05 cm; P = 0.02). Isoflavone studies, conducted only in women, showed that isoflavones may reduce body mass index (BMI; in kg/m2) (MD: -0.26; 95% CI: -0.55, 0.04; P = 0.085), especially in dosages <100 mg/d (MD: -0.48; 95% CI: -0.90, -0.06; P = 0.02) and in intervention periods of 2-6 mo (MD: -0.28; 95% CI: -0.56, 0.00; P = 0.053), but no effect was observed in higher doses or longer intervention periods. Also, a trend for reduced BMI after consumption of isoflavones was observed in Caucasians (MD: -0.35; 95% CI: -0.74, 0.04; P = 0.08). Overall, results showed that, although soy is the major source of isoflavones, soy and isoflavones may have different impacts on weight status.

Probiotics: a proactive approach to health. A symposium report

This report summarises talks given at the 8th International Yakult Symposium, held on 23-24 April 2015 in Berlin. Two presentations explored different aspects of probiotic intervention: the small intestine as a probiotic target and inclusion of probiotics into integrative approaches to gastroenterology. Probiotic recommendations in gastroenterology guidelines and current data on probiotic efficacy in paediatric patients were reviewed. Updates were given on probiotic and gut microbiota research in obesity and obesity-related diseases, the gut-brain axis and development of psychobiotics, and the protective effects of equol-producing strains for prostate cancer. Recent studies were presented on probiotic benefit for antibiotic-associated diarrhoea and people with HIV, as well as protection against the adverse effects of a short-term high-fat diet. Aspects of probiotic mechanisms of activity were discussed, including immunomodulatory mechanisms and metabolite effects, the anti-inflammatory properties of Faecalibacterium prausnitzii, the relationship between periodontitis, microbial production of butyrate in the oral cavity and ageing, and the pathogenic mechanisms of Campylobacter. Finally, an insight was given on a recent expert meeting, which re-examined the probiotic definition, advised on the appropriate use and scope of the term and outlined different probiotic categories and the prevalence of different mechanisms of activity.

HIV-1 Tat and cocaine mediated synaptopathy in cortical and midbrain neurons is prevented by the isoflavone Equol

Illicit drugs, such as cocaine, are known to increase the likelihood and severity of HIV-1 associated neurocognitive disorders (HAND). In the current studies synaptic integrity was assessed following exposure to low concentrations of the HIV-1 viral protein Tat 1-86B, with or without cocaine, by quantifying filamentous actin (F-actin) rich structures (i.e., puncta and dendritic spines) on neuronal dendrites in vitro. In addition, the synapse-protective effects of either R-Equol (RE) or S-Equol (SE; derivatives of the soy isoflavone, daidzein) were determined. Individually, neither low concentrations of HIV-1 Tat (10 nM) nor low concentrations of cocaine (1.6 μM) had any significant effect on F-actin puncta number; however, the same low concentrations of HIV-1 Tat + cocaine in combination significantly reduced dendritic synapses. This synaptic reduction was prevented by pre-treatment with either RE or SE, in an estrogen receptor beta dependent manner. In sum, targeted therapeutic intervention with SE may prevent HIV-1 + drug abuse synaptopathy, and thereby potentially influence the development of HAND.

Plasma genistein and risk of prostate cancer in Chinese population

Objectives

Genistein is one of the main soy isoflavones in our daily diet. There were studies proving that high-dietary intake of genistein may relate to the low morbidity and mortality of prostate cancer (PCa) in the Asian population. Since there were few studies of plasma genistein level in the Chinese population, we performed this study to preliminarily evaluate the associations among plasma genistein, epidemiologic factors and PCa in a Chinese population.

Methods

Between 2012 and 2013, 100 men over the age of 40 underwent prostate biopsy for PCa at Huashan Hospital, Shanghai, China. Clinical information, epidemiologic information and blood samples were collected prior to biopsy for each patient. All patients underwent 10-core ultrasound-guided transperineal prostate biopsy, and the pathology results were collected after biopsy. We measured the plasma genistein concentration of the blood samples and analyzed the results along with the clinical and epidemiologic information.

Results

Among the 100 patients, 46 (46.0 %) were diagnosed with PCa. The median plasma genistein concentration of non-PCa patients (728.6 ng/ml) was significantly higher than that of PCa patients (513.0 ng/ml) (P < 0.05). In the univariate analysis, we found that age and smoking history were related to PCa (P < 0.05). In the multivariate analysis, we found that age, smoking history and plasma genistein were related to PCa (P < 0.05). The age-adjusted odds ratio of PCa risk comparing plasma genistein level above median to that below median was 0.31 (95 % CI 0.13–0.71).

Conclusion

Our study suggested that high concentration of plasma genistein level may contribute to the low incidence of prostate cancer in Chinese population.

Plasma isoflavone concentration is associated with decreased risk of type 2 diabetes in Korean women but not men: results from the Korean Genome and Epidemiology Study

AIMS/HYPOTHESIS

To examine the association between soybean products and risk of type 2 diabetes, we measured four isoflavone biological markers--genistein, daidzein, glycitein and equol--in a nested case-control study.

METHODS

The study population was composed of 693 cases (316 women and 377 men) and 698 matched controls (317 women and 381 men) within the Korean Genome and Epidemiology Study. The concentrations of isoflavone biomarkers were measured using HPLC-MS/MS on plasma samples that were collected at baseline. A stratified analysis was undertaken to examine the association between plasma isoflavone concentrations and risk of type 2 diabetes according to sex and equol production. Logistic regression models were used to compute ORs and 95% CIs adjusted for confounders.

RESULTS

In women, compared with the lowest quartile of plasma concentration of genistein, the highest quartile exhibited a significantly decreased risk of diabetes (OR 0.58, 95% CI 0.35, 0.95). When stratified by equol-producing status in women, the OR for diabetes in the highest vs the lowest quartile of genistein concentration was 0.31 (95% CI 0.16, 0.60) in equol producers, but genistein concentration was not associated with risk of diabetes in equol non-producers (p for interaction = 0.013). In men, isoflavone concentrations were not associated with risk of diabetes, regardless of equol-producing status.

CONCLUSIONS/INTERPRETATION

High plasma concentrations of genistein were associated with a decreased risk of type 2 diabetes in women. This inverse association was prominent in equol-producing participants. These results suggest a beneficial effect of a high intake of soybean products on risk of type 2 diabetes in women.

Counts of Slackia sp. strain NATTS in intestinal flora are correlated to serum concentrations of equol both in prostate cancer cases and controls in Japanese men

BACKGROUND

Isoflavones, which are included in soybeans, have been suggested to protect against prostate cancer. Equol, one of isoflavones, is an intestinally derived bacterial metabolite of daidzein. A newly identified equol-producing bacterium, Slackia sp. strain NATTS, with a high equol-producing activity was isolated from human feces in Japanese adults. Counts of Slackia sp. strain NATTS in intestinal flora have not been assessed with regard to prostate cancer risk. In this study, we investigated the association of serum isoflavones and counts of Slackia sp. strain NATTS with prostate cancer risk in a case-control study.

MATERIALS AND METHODS

Concentrations of isoflavones and counts of Slackia sp. strain NATTS in feces were measured from 44 patients with prostate cancer and 28 hospital controls. The risk of prostate cancer was evaluated in terms of odds ratios (ORs) and 95% confidence intervals (CIs) by the logistic regression analysis.

RESULTS

The detection proportions of Slackia sp. strain NATTS in cases and controls were 34.1% and 25.0%, respectively. Counts of Slackia sp. strain NATTS were significantly correlated with serum concentrations of equol both in cases and controls (Spearman correlation coefficients, rs=0.639 and rs=0.572, p<0.01, respectively). Serum concentrations of genistein, daidzein, glycitein, and equol were not significantly associated with risk of prostate cancer.

CONCLUSIONS

This study found that counts of Slackia sp. strain NATTS correlated with serum concentrations of equol both in prostate cancer cases and controls, but serum isoflavone concentrations were not associated with risk of prostate cancer in our patients.

Therapeutic perspectives of epigenetically active nutrients

Many nutrients are known for a wide range of activities in prevention and alleviation of various diseases. Recently, their potential role in regulating human health through effects on epigenetics has become evident, although specific mechanisms are still unclear. Thus, nutriepigenetics/nutriepigenomics has emerged as a new and promising field in current epigenetics research in the past few years. In particular, polyphenols, as part of the central dynamic interaction between the genome and the environment with specificity at physiological concentrations, are well known to affect mechanisms underlying human health. This review summarizes the effects of dietary compounds on epigenetic mechanisms in the regulation of gene expression including expression of enzymes and other molecules responsible for drug absorption, distribution, metabolism and excretion in cancer, metabolic syndrome, neurodegenerative disorders and hormonal dysfunction.

Effects of short-term fructooligosaccharide intake on equol production in Japanese postmenopausal women consuming soy isoflavone supplements: a pilot study

BACKGROUND

Recent studies suggest that some of the clinical effectiveness of soy or daidzein, which is a type of isoflavone, may be attributed to a person's ability to produce equol from daidzein. Equol, which is a metabolite of one of the major soybean isoflavones called daidzein, is produced in the gastrointestinal tract by certain intestinal microbiota where present. Habitual dietary patterns may alter the intestinal bacterial profile, and influence the metabolism of isoflavones and the production of equol. Fructooligosaccharides (FOS) have a prebiotic activity as well as being a dietary fibre. The purpose of the present study was to determine whether FOS supplementation increases equol production in equol producers and stimulates equol production in equol non-producers in Japanese postmenopausal women.

METHODS

A soy challenge was used to assess equol-producer status prior to the start of the study in healthy postmenopausal Japanese women. The study involved 4 separate groups in randomised crossover design. First, subjects were classified as equol producers (n = 25) or non-producers (n = 18), and then they were randomly assigned to the FOS or control group. All subjects received a daily dose of 37 mg isoflavone conjugates in the capsule (21 mg aglycone form) and either FOS (5 g/day) or sucrose as control, in a randomised crossover study design. Equol -production was assessed by testing the serum and urine before and after the 2-week supplementation period.

RESULTS

The analyses were conducted on 34 subjects completed the study, 21 (61.8%) were classified as equol producers, and 13 (38.2%) as non-producers. Significant differences were observed in the interaction effect of time × equol state after 1 week of intervention (p = 0.006). However there were no effects after 2 weeks of intervention (p = 0.516). Finally, in both equol producers and non-producers, FOS supplementation did not affect the serum equol concentration or the urinary equol to daidzein concentration ratios.

CONCLUSIONS

We have reported that FOS intervention (5 g/day for 2 weeks) does not significantly modulate the capacity of intestinal microbiota to produce equol in postmenopausal Japanese women, in either equol producers or non-producers in this pilot study. Further larger investigations that explore the roles of specific intestinal microbiota in equol production will enable the establishment of dietary conditions that are required to enhance equol production.

Levels of urinary isoflavones and lignan polyphenols in Japanese women

OBJECTIVES

High consumption of soybean products has been associated with a reduced risk of hormone-sensitive tumors. Soybean products contain phytoestrogens, such as daidzein, and sesame seeds contain secoisolariciresinol. These compounds are further metabolized to equol, enterodiol, and enterolactone by intestinal bacteria. However, individual differences in the metabolizing potential remain unclear. The aim of this study was to evaluate the urinary daidzein, equol, enterodiol, and enterolactone concentrations in women from several different regions of Japan according to age group.

METHODS

Five hundred urine samples collected from Japanese women living in Sapporo, Sendai, Kyoto, Kochi, and Naha were analyzed for daidzein, equol, enterodiol, and enterolactone concentration by gas chromatography-mass spectrometry.

RESULTS

The urinary isoflavone and lignan polyphenol levels did not differ significantly among the sampling sites, except for daidzein, which was highest in urine collected at Naha. The prevalence of equol producers was 39 % in the total study cohort. In equol producers, a positive correlation was observed between the urinary daidzein and equol levels (r = 0.399, p < 0.001). However, there was no significant difference between daidzein concentrations in equol producers and non-producers. Moreover, the levels of enterodiol and enterolactone were higher in equol producers than in equol non-producers. In the multivariate logistic analyses, two factors, Sendai dwelling and current smoking, were found to be significant [equol producers to non-producers: odds ratio 2.15 (95 % confidence interval: 1.17-4.02) and odds ratio 0.32 (0.15-0.63), respectively].

CONCLUSIONS

Our data suggest that geographic factors and smoking status should be considered during the evaluation of equol in urine samples and that the same pathway may be responsible for the metabolism of both isoflavones and lignan polyphenols.

Chemoprevention of prostate cancer: soy isoflavones and curcumin

The burden of increasing morbidity and mortality due to prostate cancer imposes a need for new, effective measures of prevention in daily life. The influence of lifestyle on carcinogenesis in Asian men who migrate to Western cultures supports a causal role for dietary, environmental, and genetic factors in the epidemiology of prostate cancer. Chemoprevention, a prophylactic approach that uses nontoxic natural or synthetic compounds to reverse, inhibit, or prevent cancer by targeting specific steps in the carcinogenic pathway, is gaining traction among health care practitioners. Soy isoflavones and curcumin, staples of the Asian diet, have shown promise as functional factors for the chemoprevention of prostate cancer because of their ability to modulate multiple intracellular signaling pathways, including cellular proliferation, apoptosis, inflammation, and androgen receptor signaling. Recent evidence has revealed the DNA damage response (DDR) to be one of the earliest events in the multistep progression of human epithelial carcinomas to invasive malignancy. Soy isoflavones and curcumin activate the DDR, providing an opportunity and rationale for the clinical application of these nutraceuticals in the chemoprevention of prostate cancer.

Prostate cancer chemoprevention by soy isoflavones: role of intestinal bacteria as the "second human genome"

It has been found that the composition of intestinal microbiota can indicate the risk of disease to each individual. The concepts of biodynamics as used by the Benziger Winery in California, which treats every part of an agricultural environment as a living, breathing entity, can be usefully used in the construction of a system for cancer prevention, which seeks to use the relationship of coexistence (symbiosis) shared between people and intestinal symbiosis, that is, microbiota. Changes in the incidence rate of cancer among Japanese emigrants to Hawaii demonstrate the effect of the changes in the living environment. This leads to the hypothesis that an intake of soy-derived food products and the metabolization of the isoflavones they contain by intestinal microbiota is one of the factors for the significant difference in the incidence rate of prostate cancer among Asian and European/North American populations. It is further hypothesized that isoflavones, particularly equol, are a key factor in the difference in incidence rate between Asia and the West. It is suggested that not having equol converting bacteria in the intestine (non-equol producers) can be a risk factor for prostate cancer and that one direction for future research will be to examine the possibility of improving the intestinal environment to enable equol production.

Does equol production determine soy endocrine effects?

Isoflavones, a group of phytoestrogens, are selective oestrogen receptor (ER) modulators. They may positively impact endocrine-related conditions but the current evidence is sparse. Equol, a non-steroidal oestrogen, is produced by the metabolism of the isoflavone daidzein by intestinal bacteria. In Western countries, 30-50% of individuals metabolize daidzein into equol and are known as equol producers. Equol production may be the source of benefit from isoflavones in endocrine disease.

Emerging evidence of the health benefits of S-equol, an estrogen receptor β agonist

Many clinical studies have been carried out to determine the health benefits of soy protein and the isoflavones contained in soy. S-equol is not present in soybeans but is produced naturally in the gut of certain individuals, particularly Asians, by the bacterial biotransformation of daidzein, a soy isoflavone. In those intervention studies in which plasma S-equol levels were determined, a concentration of >5-10 ng/mL has been associated with a positive outcome for vasomotor symptoms, osteoporosis (as measured by an increase in bone mineral density), prostate cancer, and the cardiovascular risk biomarkers low-density lipoprotein cholesterol and C-reactive protein. These studies suggest that S-equol may provide therapeutic benefits for a number of medical needs.

Cautions and research needs identified at the equol, soy, and menopause research leadership conference

This summary addresses the progress and limitations of existing research on the physiologic properties of the isoflavone daidzein metabolite equol. Previous research demonstrating that physiological equol is its S-enantiomer has led to the preparation of S-(-)equol-enriched products formed by the bacterial fermentation of soy germ. Although this product has interesting properties as described in this workshop, the following important issues must be addressed: 1) the product should be evaluated against a preparation containing an equal amount of pure S-(-)equol to determine whether other components resulting from the fermentation are contributing to the physiological effects; 2) evaluation of the cellular mechanisms of S-(-)equol using cell culture methods should be conducted at concentrations consistent with those encountered physiologically (in the nmol/L range) and in several cell lines representing a target tissue; and 3) in follow-up studies in animal models and in human clinical trials, standardized preparations of S-(-)equol should be made available. Research opportunities now exist to determine whether equol's apparent effects on menopausal symptoms (hot flashes, sleep disturbances, bone health) in equol producers can be extended to equol nonproducers. It will be important to ensure that such research is not complicated by cultural differences, differences in lifetime exposure to soy products, experimental techniques, and other variables. Further areas of research that would benefit from the availability of S-(-)equol preparations include its use in skin care (either as an antioxidant or as an estrogen receptor agonist) and in the treatment of brain injury as well as postmenopausal cognitive decline.

Isolation and characterization of the equol-producing bacterium Slackia sp. strain NATTS

Several kinds of carbohydrates such as sorbose, adonitol, and melezitose were found to enhance equol production from daidzein in an in vitro human fecal culture. Sorbose, one of the most effective carbohydrates, was used as a carbohydrate source for isolating the NATTS strain, which was a Gram-positive, non-spore-forming rod bacterium with high ability to convert daidzein to equol isolated from the 7th maintenance culture. The strain was found to belong to the genus Slackia family Coriobacteriaceae by 16S rRNA sequence-based analysis, and the prevalence of the Slackia sp. in Japanese adults was examined by reverse transcription-quantitative PCR (RT-qPCR), which was found to be 40% at a mean population level of 10(6) cells per gram of feces.

Isoflavone supplements stimulated the production of serum equol and decreased the serum dihydrotestosterone levels in healthy male volunteers

The aim of this study was to evaluate the effect of supplementing healthy men with soy isoflavones on the serum levels of sex hormones implicated in prostate cancer development. A total of 28 Japanese healthy volunteers (18 equol producers and 10 equol non-producers) between 30 and 59 years of age were given soy isoflavones (60 mg daily) supplements for 3 months, and the changes in their sex hormone levels were investigated at the baseline and after administration. The serum and urine concentrations of daidzein, genistein, and the levels of equol in the fasting blood samples and 24-h stored urine samples were also measured. All 28 volunteers completed the 3-month supplementation with isoflavone. No changes in the serum levels of estradiol and total testosterone were detected after 3-month supplementation. The serum levels of sex hormone-binding globulin significantly increased, and the serum levels of free testosterone and dihydrotestosterone (DHT) decreased significantly after 3-month supplementation. Among the 10 equol non-producers, equol became detectable in the serum of two healthy volunteers after 3-month supplementation. This study revealed that short-term administration of soy isoflavones stimulated the production of serum equol and decreased the serum DHT level in Japanese healthy volunteers. These results suggest the possibility of converting equol non-producers to producers by prolonged and consistent soy isoflavones consumption.