Quantitative aspects of the metabolism of lignans in pigs fed fibre-enriched rye and wheat bread

Comparative Study on the Absorption and Metabolism of Pinoresinol and Pinoresinol-4-O-β-D-Glucopyranoside in Mice

SCOPE

Lignans are a group of phenolic compounds commonly found in plants, often in the form of glycosides. This study investigates the differences in the digestion, absorption, and metabolism of lignans and their glucosides using pinoresinol (PIN) and pinoresinol-4-O-β-D-glucopyranoside (PMG).

METHODS AND RESULTS

After oral administration mice PIN and PMG with a dose of 0.1 µmol kg-1 . The results showed that the stomach and small intestine rapidly absorbe PIN and PMG in their prototype form. After oral administration of 0.25 h, serum levels of PIN and PMG reach peak values of 61.14 and 52.97 ng mL-1 , respectively. This indicates a faster PIN absorption rate than PMG, likely due to the glycosides attach to the parent compound, with concentrations of 1574.14 and 876.75 ng g-1 , respectively. Pharmacokinetic analysis reveals that PIN has a greater area under the curve and a longer half-life than PMG in serum and liver. Moreover, mice in the PIN group exhibit higher metabolite levels in the serum and liver compared to those in the PMG group.

CONCLUSION

The deglycosylation process that occurs during the pickling of white radish facilitates the absorption and metabolism of the lignans fraction in the body.

The role of rye bran and antibiotics on the digestion, fermentation process and short-chain fatty acid production and absorption in an intact pig model

The effects of arabinoxylan (AX)-rich rye bran based diet (RB) and antibiotics on digestion, fermentation and short-chain fatty acids (SCFA) absorption were studied compared with an iso-dietary fibre (DF) cellulose based diet (CEL). Thirty female pigs (body weight 72.5 ± 3.9 kg) were fed a standard swine diet in week 1, CEL as wash-out for bran-associated bioactive components in week 2 and then divided into 3 groups fed either the CEL (n = 10) or RB (n = 20) for 2 weeks, where 10 pigs from RB had daily intramuscular antibiotic injections (RB+) and the other 10 pigs were untreated (RB-) in week 4. In RB, the degradation of AX mainly occurred in caecum and proximal colon (P < 0.01) and to a higher extent than cellulose, which on the other hand, irrespective of antibiotic treatment, was less degraded in the RB groups than in the CEL (P < 0.01). The apparent digestibility of fat and protein in the distal small intestine was lower for RB than CEL (P < 0.05), the protein digestibility remained lower in most of the colon, and the digestibility was not affected by treatment with antibiotics. The colonic concentrations of SCFA, acetate and propionate as well as the butyrate concentration in the distal colon were lower with the RB treatments compared with CEL (P < 0.01). Caecal butyrate concentrations were on the other hand higher, and a significant reduction was seen with antibiotic treatment (P < 0.001). The daily net absorption of SCFA and acetate was lower with RB than with CEL (P < 0.01). In conclusion, RB resulted in different DF degradation processes and SCFA production compared with CEL, whereas antibiotic treatment had marginal effects on the intestinal DF degradation but hampered butyrate production.

LC-MS/MS Quantification Reveals Ample Gut Uptake and Metabolization of Dietary Phytochemicals in Honey Bees (Apis mellifera)

The honey bee pollen/nectar diet is rich in bioactive phytochemicals and recent studies have demonstrated the potential of phytochemicals to influence honey bee disease resistance. To unravel the role of dietary phytochemicals in honey bee health it is essential to understand phytochemical uptake, bioavailability, and metabolism but presently limited knowledge exists. With this study we aim to build a knowledge foundation. For 5 days, we continuously fed honey bees on eight individual phytochemicals and measured the concentrations in whole and dissected bees by HPLC-MS/MS. Ample phytochemical metabolization was observed, and only 6-30% of the consumed quantities were recovered. Clear differences in metabolization rates were evident, with atropine, aucubin, and triptolide displaying significantly slower metabolism. Phytochemical gut uptake was also demonstrated, and oral bioavailability was 4-31%, with the highest percentages observed for amygdalin, triptolide, and aucubin. We conclude that differences in the chemical properties and structure impact phytochemical uptake and metabolism.

Lignans and Gut Microbiota: An Interplay Revealing Potential Health Implications

Plant polyphenols are a broad group of bioactive compounds characterized by different chemical and structural properties, low bioavailability, and several in vitro biological activities. Among these compounds, lignans (a non-flavonoid polyphenolic class found in plant foods for human nutrition) have been recently studied as potential modulators of the gut-brain axis. In particular, gut bacterial metabolism is able to convert dietary lignans into therapeutically relevant polyphenols (i.e., enterolignans), such as enterolactone and enterodiol. Enterolignans are characterized by various biologic activities, including tissue-specific estrogen receptor activation, together with anti-inflammatory and apoptotic effects. However, variation in enterolignans production by the gut microbiota is strictly related to both bioaccessibility and bioavailability of lignans through the entire gastrointestinal tract. Therefore, in this review, we summarized the most important dietary source of lignans, exploring the interesting interplay between gut metabolites, gut microbiota, and the so-called gut-brain axis.

Dietary Phenolics against Breast Cancer. A Critical Evidence-Based Review and Future Perspectives

Breast cancer (BC) is the most common malignancy and the leading cause of cancer-related death in adult women worldwide. Over 85% of BC cases are non-hereditary, caused by modifiable extrinsic factors related to lifestyle, including dietary habits, which play a crucial role in cancer prevention. Although many epidemiological and observational studies have inversely correlated the fruit and vegetable consumption with the BC incidence, the involvement of their phenolic content in this correlation remains contradictory. During decades, wrong approaches that did not consider the bioavailability, metabolism, and breast tissue distribution of dietary phenolics persist behind the large currently existing gap between preclinical and clinical research. In the present review, we provide comprehensive preclinical and clinical evidence according to physiologically relevant in vitro and in vivo studies. Some dietary phenolics such as resveratrol (RSV), quercetin, isoflavones, epigallocatechin gallate (EGCG), lignans, and curcumin are gaining attention for their chemopreventive properties in preclinical research. However, the clinical evidence of dietary phenolics as BC chemopreventive compounds is still inconclusive. Therefore, the only way to validate promising preclinical results is to conduct clinical trials in BC patients. In this regard, future perspectives on dietary phenolics and BC research are also critically discussed.

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.

Naturally Lignan-Rich Foods: A Dietary Tool for Health Promotion?

Dietary guidelines universally advise adherence to plant-based diets. Plant-based foods confer considerable health benefits, partly attributable to their abundant micronutrient (e.g., polyphenol) content. Interest in polyphenols is largely focused on the contribution of their antioxidant activity to the prevention of various disorders, including cardiovascular disease and cancer. Polyphenols are classified into groups, such as stilbenes, flavonoids, phenolic acids, lignans and others. Lignans, which possess a steroid-like chemical structure and are defined as phytoestrogens, are of particular interest to researchers. Traditionally, health benefits attributed to lignans have included a lowered risk of heart disease, menopausal symptoms, osteoporosis and breast cancer. However, the intake of naturally lignan-rich foods varies with the type of diet. Consequently, based on the latest humans' findings and gathered information on lignan-rich foods collected from Phenol Explorer database this review focuses on the potential health benefits attributable to the consumption of different diets containing naturally lignan-rich foods. Current evidence highlight the bioactive properties of lignans as human health-promoting molecules. Thus, dietary intake of lignan-rich foods could be a useful way to bolster the prevention of chronic illness, such as certain types of cancers and cardiovascular disease.

Rye Bran Modified with Cell Wall-Degrading Enzymes Influences the Kinetics of Plant Lignans but Not of Enterolignans in Multicatheterized Pigs

Background: Whole-grain intake is associated with a lower risk of chronic Western-style diseases, possibly brought about by the high concentration of phytochemicals, among them plant lignans (PLs), in the grains.Objective: We studied whether treatment of rye bran with cell wall-degrading enzymes changed the solubility and kinetics of PLs in multicatheterized pigs.Methods: Ten female Duroc × Danish Landrace × Yorkshire pigs (60.3 ± 2.3 kg at surgery) fitted with permanent catheters were included in an incomplete crossover study. The pigs were fed 2 experimental diets for 1-7 d. The diets were rich in PLs and based on nontreated lignan-rich [LR; lignan concentration: 20.2 mg dry matter (DM)/kg] or enzymatically treated lignan-rich (ENZLR; lignan concentration: 27.8 mg DM/kg) rye bran. Plasma concentrations of PLs and enterolignans were quantified with the use of targeted LC-tandem mass spectrometry. Data were log transformed and analyzed with mixed-effects, 1-compartment, and asymptotic regression models.Results: The availability of PLs was 38% greater in ENZLR than in LR, and the soluble fraction of PLs was 49% in ENZLR compared with 35% in LR diets. PLs appeared in the circulation 30 min after intake of both the ENZLR and LR diets. Postprandially, consumption of ENZLR resulted in a 4-times-greater (P < 0.0001) plasma PL concentration compared with LR. The area under the curve (AUC) measured 0-360 min after ENZLR intake was ∼2 times higher than after LR intake. A 1-compartment model could describe the postprandial increase in plasma concentration after ENZLR intake, whereas an asymptotic regression model described the plasma concentrations after LR intake. Despite increased available and soluble PLs, ENZLR did not increase plasma enterolignans.Conclusion: The modification of rye bran with cell wall-degrading enzymes resulted in significantly greater plasma concentrations of PLs and the 4-h AUC, particularly syringaresinol, in multicatheterized pigs.

Effect of Antibiotics and Diet on Enterolactone Concentration and Metabolome Studied by Targeted and Nontargeted LC-MS Metabolomics

High plant lignan intake is associated with a number of health benefits, possibly induced by the lignan metabolite enterolactone (ENL). The gut microbiota plays a crucial role in converting dietary lignans into ENL, and epidemiological studies have shown that use of antibiotics is associated with lower levels of ENL. Here we investigate the link between antibiotic use and lignan metabolism in pigs using LC-MS/MS. The effect of lignan intake and antibiotic use on the gut microbial community and the pig metabolome is studied by 16S rRNA sequencing and nontargeted LC-MS. Treatment with antibiotics resulted in substantially lower concentrations of ENL compared with concentrations detected in untreated animals, whereas the plasma concentrations of plant lignans were unchanged. Both diet and antibiotic treatment affected the clustering of urinary metabolites and significantly altered the proportions of taxa in the gut microbiota. Diet, but not antibiotic treatment, affected the plasma lipid profile, and a lower concentration of LDL cholesterol was observed in the pigs fed a high lignan diet. This study provides solid support for the associations between ENL concentrations and use of antibiotics found in humans and indicates that the lower ENL concentration may be a consequence of the ecological changes in the microbiota.

Microbial and endogenous metabolic conversions of rye phytochemicals

Rye is one of the main cereals produced and consumed in the hemiboreal climate region. Due to its use primarily as wholegrain products, rye provides a rich source of dietary fibre as well as several classes of phytochemicals, bioactive compounds with potentially positive health implications. Here, we review the current knowledge of the metabolic pathways of phytochemical classes abundant in rye, starting from the microbial transformations occurring during the sourdough process and colonic fermentation and continuing with the endogenous metabolism. Additionally, we discuss the detection of specific metabolites by MS in different phases of their journey from the cereal to the target organs and excretion.

Validated LC-MS/MS Method for the Quantification of Free and Bound Lignans in Cereal-Based Diets and Feces

Despite the extensive literature describing the biological effects of phenolic compounds from cereals, little is known about their bioaccessibility in the food matrix. This paper describes a validated LC-MS/MS method for the quantification of free and total content (free + bound) of eight plant lignans (matairesinol, hydroxymatairesinol, secoisolariciresinol, lariciresinol, isolariciresinol, syringaresinol, medioresinol, and pinoresinol) and two enterolignans (enterodiol and enterolactone) in cereal-based diets/bread and feces. The method consisted of alkaline methanolic extraction combined with enzymatic hydrolyses, for the measurement of the total concentration of lignans, and methanolic extraction combined with enzymatic hydrolysis, for the measurement of free lignans, followed by solid phase extraction (SPE). The strength of this LC-MS/MS method is that it can be combined with different types of samples, because the SPE and LC-MS/MS platforms are similar to our previously published method for plasma and urine.

Absorption of plant lignans from cereals in an experimental pig model

Plant lignans are diphenolic compounds ingested with whole grains and seeds and converted to enterolignans by the colonic microbiota. In the present study, we investigated absorption and metabolism of plant lignans and enterolignans in vivo after consumption of cereal-based diets. Six pigs fitted with catheters in the mesenteric artery and portal vein and with a flow probe attached to the portal vein along with twenty pigs for quantitative collection of urine were used for this study. The animals were fed bread based on wheat flour low in plant lignans and three lignan-rich breads based on whole-wheat grain, wheat aleurone flour or rye aleurone flour. Plant lignans and enterolignans in plasma were monitored daily at fast after 0-3 d of lignan-rich intake, and on the 4th day of lignan-rich intake a 10-h profile was completed. Urine samples were collected after 11 d of lignan-rich diet consumption. The concentrations of plant lignans were low at fast, and was 1·2-2·6 nmol/l after switching from the low-lignan diet to the lignan-rich diets. However, on the profile day, the concentration and quantitative absorption of plant lignans increased significantly from 33 nmol/h at fast to 310 nmol/h 0-2·5 h after ingestion with a gradual increase in the following periods. Quantitatively, the absorption of plant lignans across diets amounted to 7 % of ingested plant lignans, whereas the urinary excretion of plant lignans was 3 % across diets. In conclusion, there is a substantial postprandial uptake of plant lignans from cereals, suggesting that plant lignans are absorbed from the small intestine.

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

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

Whole grains beyond fibre: what can metabolomics tell us about mechanisms?

Dietary fibre alone does not fully explain the frequent association between greater intake of whole grains and reduced risk of disease in observational studies, and other phytochemicals or food structure may also play an important role. For all the observational evidence for the benefits of a whole-grain-rich diet, we have only limited knowledge of the mechanisms behind this reduction in disease risk, aside from the action of specific cereal fibres on reduction of blood cholesterol and the post-prandial glucose peak. Nutritional metabolomics, the global measurement and interpretation of metabolic profiles, assesses the interaction of food with the endogenous gene–protein cascade and the gut microbiome. This approach allows the generation of new hypotheses which account for systemic effects, rather than just focusing on one or two mechanisms or metabolic pathways. To date, animal and human trials using metabolomics to investigate mechanistic changes to metabolism on eating whole grains and cereal fractions have led to new hypotheses around mechanistic effects of whole grains. These include the role of cereals as a major source of dietary glycine betaine, a possible effect on phospholipid synthesis or metabolism, the role of branched-chain amino acids and improvements in insulin sensitivity, and the possibility that whole grains may have an effect on protein metabolism. These hypotheses help explain some of the observed effects of whole grains, although mechanistic studies using stable isotopes and fully quantitative measures are required to confirm these potential mechanisms.

Multicompartmental nontargeted LC-MS metabolomics: explorative study on the metabolic responses of rye fiber versus refined wheat fiber intake in plasma and urine of hypercholesterolemic pigs

A multicompartmental nontargeted LC-MS metabolomics approach was used to study the metabolic responses on plasma and urine of hypercholesterolemic pigs after consumption of diets with contrasting dietary fiber composition (whole grain rye with added rye bran versus refined wheat). To study the metabolic responses, we performed a supervised multivariate data analyses used for pattern recognition, which revealed marked effects of the diets on both plasma and urine metabolic profiles. Diverse pools of metabolites were responsible for the discrimination between the diets. Elevated levels of phenolic compounds and dicarboxylic acids were detected in urine of pigs after rye consumption compared to refined wheat. Furthermore, consumption of rye was characterized by lower levels of linoleic acid derived oxylipins and cholesterol in the plasma metabolic profiles. These results indicate that higher consumption of nonrefined dietary fiber is reflected in higher excretion of phenolic compounds and dicarboxylic acids in urine and lower levels of linoleic acid derived oxylipins and cholesterol in plasma, which can be linked to beneficial health effects of rye components. On the other hand, pro-inflammatory lipid mediators were detected in higher concentration after rye consumption compared to refined wheat, which is opposite to what would be expected. These may indicate that even though a positive lowering effect with respect to cholesterol and fatty acids was achieved, this effect of rye dietary fiber was not sufficient to prevent inflammation in pigs. Moreover, we performed an alignment of the metabolic profiles between the breads consumed by pigs, plasma, and urine with the purpose to follow the metabolic fate of the compounds and to identify their pathways. One metabolite was identified in all three compartments, 16 metabolites were similar between bread and plasma, 3 were similar between plasma and urine, and 2 were similar between bread and urine. The use of multicompartmental metabolomics offered higher order information, including intercompartment relationships, and provided novel targets for future research.

Plasma and urine concentrations of bioactive dietary benzoxazinoids and their glucuronidated conjugates in rats fed a rye bread-based diet

Thorough knowledge of the absorption and metabolism of dietary benzoxazinoids is needed to understand their health-promoting effects. In this study, the fates of these bioactive compounds were examined by LC-MS/MS in plasma, urine, and feces after ingesting a daily dose of 4780 ± 68 nmol benzoxazinoids from rye bread using Wistar rats as a model. HBOA-glc (2-β-D-glucopyranosyloxy-1,4-benzoxazin-3-one) was the predominant benzoxazinoid in the plasma (74 ± 27 nmol/L), followed by DIBOA-glc (2-β-D-glucopyranosyloxy-4-hydroxy-1,4-benzoxazin-3-one) and HBOA. The total level of benzoxazinoids in the urine was 1176 ± 66 nmol/d, which corresponds to approximately 25% of the total dietary intake. The urinary benzoxazinoid profile differed from that of plasma with HBOA-glc and DIBOA-glc (647 ± 31 and 466 ± 33 nmol/d, respectively) as the major urinary components. The glucuronide conjugates of HBOA and DIBOA were detected in both the plasma and urine. N-dehydroxylation was found to be a critical step in the absorption of hydroxamic acids. This unprecedented study will trigger future interest in the biological effects of benzoxazinoids in whole grain rye and wheat diets in humans and other animals.

Bioactive benzoxazinoids in rye bread are absorbed and metabolized in pigs

Recently, bioactive benzoxazinoids were discovered in cereal grains and bakery products. In this study, we studied the uptake, distribution, and metabolism of these secondary metabolites using a pig model. Twelve benzoxazinoid compounds and their 4 transformation products were quantified in the pigs' diets and biofluids using high-performance liquid chromatography coupled to electrospray ionization triple quadrupole mass spectrometry. The 2-β-D-glucopyranosyloxy-4-hydroxy-1,4-benzoxazin-3-one (DIBOA-glc) was the most dominant benzoxazinoid (232 nmol/g DM) seconded by the double-hexose derivative of DIBOA (provisionally characterized here as DIBOA-glc-hex) in the rye-based diet. DIBOA-glc (derived from the diet and intestinal deglycosylation of DIBOA-glc-hex) was apparently reduced to 2-β-D-glucopyranosyloxy-1,4-benzoxazin-3-one (HBOA-glc), the most dominant benzoxazinoid in the blood (829 nmol/L). The benzoxazinoid compounds were excreted in the urine, with HBOA-glc (18 μmol/L) as a major metabolite. In this study, we determined for the first time the bioavailability of dietary benzoxazinoids that have high digestibility, distribution, and metabolism in mammals. These findings could be a milestone for the exploitation of healthful and pharmacological properties of benzoxazinoids.

A single dose of enterolactone activates estrogen signaling and regulates expression of circadian clock genes in mice

Enterolactone (EL) is an enterolignan produced by gut microbiota from dietary plant lignans. Epidemiological and experimental studies suggest that EL and plant lignans may reduce the risk of breast and prostate cancer as well as cardiovascular disease. These effects are thought to at least in part involve modulation of estrogen receptor activity. Surprisingly little is known about the in vivo estrogenicity of EL. In the present study, we investigated the target tissues of EL, the genes affected by EL treatment, and the response kinetics. Following a single dose of EL, luciferase was significantly induced in reproductive and nonreproductive tissues of male and female 3xERE-luciferase mice, indicating estrogen-like activity. Microarray analysis revealed that EL regulated the expression of only 1% of 17β-estradiol target genes in the uterus. The majority of these genes were traditional estrogen target genes, but also members of the circadian signaling pathway were affected. Kinetic analyses showed that EL undergoes rapid phase II metabolism and is efficiently excreted. In vivo imaging demonstrated that the estrogen response followed similar, fast kinetics. We conclude that EL activates estrogen signaling in both male and female mice and that the transient responses may be due to the fast metabolism of the compound. Lastly, EL may represent a link among diet, gut microbiota, and circadian signaling.

Can rye intake decrease risk of human breast cancer?

BACKGROUND

Rye contains more fibre and bioactive compounds than other cereals used for bread production. The fibre and compounds of the fibre complex could provide protection against breast cancer (BC).

OBJECTIVE

To review the evidence and theoretical background for a role of rye and some of its components in the prevention of BC.

DESIGN

A short review based to a great extent on the work by scientists in the Nordic countries.

RESULTS

Some of the possible mechanisms by which the fibre complex could reduce BC risk are presented. The fibre through its effect on fermentation increases esterification of bile acids reducing toxicity of the free bile acids and is involved in the production of butyrate with potential anticancer effects including BC. The fibre reduces the enterohepatic circulation of the oestrogens leading to lower plasma oestrogen concentrations. The fibre complex contains bioactive compounds such as lignans and alkylresorcinols that are antioxidative and potentially anticarcinogenic. In addition, vitamins, minerals, and phytic acid in rye may provide protection against BC.

CONCLUSION

Rye products made from wholegrain rye flour are likely to contribute to reduced BC risk.

Prolonged administration of secoisolariciresinol diglycoside increases lignan excretion and alters lignan tissue distribution in adult male and female rats

Limited information is available on lignan metabolism and tissue distribution between sexes and the effects of prolonged lignan exposure on tissue concentrations. In the present study, excretion and tissue distribution of lignans were compared after 1 d and 7 d administration of flaxseed lignan secoisolariciresinol diglycoside (SDG) in male and female rats. Sprague-Dawley rats were daily gavaged per os with 3H-SDG (3.7 kBq/g body weight (bwt)) and unlabelled SDG (5.3 microg/g bwt). Urine, faeces, serum and tissues (liver, kidneys, bladder, spleen, lungs, brain, thymus, heart, muscle, adipose, mammary gland, ovaries, vagina, uterus, testis, seminal vesicles, coagulating glands and ventral prostate) were collected at 0, 12 and 24 h after a single lignan dose or after the last dose of 7 d exposure. The sample total lignan content was measured as radioactivity by liquid scintillation counting. In both sexes, majority of radioactivity was excreted in faeces (40-83%) and urine (1.2-5.2%). 3H-SDG administration increased radioactivity in all tissues at all time points, and the levels were further increased after prolonged SDG exposure. Liver contained majority of the tissue lignans (48-56%) in both sexes after both exposure regimens. After prolonged SDG exposure, the serum lignan concentrations had reached a plateau which was approximately 4-fold of that of acute exposure, whereas in both sexes, concentrations in skin and kidneys still increased, indicating tissue accumulation. After prolonged exposure, females had higher lignan concentrations in heart and thymus at all time points, demonstrating sex-related differences in lignan tissue distribution and the possibility for sex-specific treatment responses. These findings facilitate identification of target tissues for local lignan actions in vivo.

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.