From pure compounds to complex exposure: Effects of dietary cadmium and lignans on estrogen, epidermal growth factor receptor, and mitogen activated protein kinase signaling in vivo.

Exposure to environmental endocrine active compounds correlates with altered susceptibility to disease in human populations. Chemical risk assessment is single compound based, although exposure often takes place as heterogeneous mixtures of man-made and natural substances within complex matrices like diet. Here we studied whether the effects of cadmium and enterolactone on endocrine endpoints in dietary exposure can be predicted based on pure compound effects. Ovariectomized estrogen reporter ERE-luciferase (ERE-luc) mice were maintained on diets that intrinsically contain increasing concentrations of cadmium and enterolactone precursors for three and 21 days. The activation of the ERE-luc, epidermal growth factor receptor (EGFR), mitogen activated protein kinase (MAPK)-ERK1/2, and classical estrogen responses were measured. Interactions between the diets and endogenous hormone were evaluated by challenging the animals with 17ß-estradiol. Compared to animals on basal purified diet, mice consuming experimental diets were exposed to significantly higher levels of cadmium and enterolactone, yet the exposure remained comparable to typical human dietary intake. Surprisingly, we could not detect effects on endpoints regulated by pure enterolactone, such as ERE-luc activation. However, cadmium accumulation in the liver was accompanied with activation of EGFR and MAPK-ERK1/2 in line with our earlier CdCl2 studies. Further, attenuation of 17ß-estradiol-induced ERE-luc response in liver by experimental diets was observed. Our findings indicate that the exposure context can have substantial effects on the activity of endocrine active compounds in vivo. Thus, whenever possible, a context that mimics human exposure should be tested along with pure compounds.

Dietary sources of lignans and isoflavones modulate responses to estradiol in estrogen reporter mice.

Dietary phytoestrogens, such as the lignan metabolite enterolactone (ENL) and the isoflavone genistein (GEN), are suggested to modulate the risk of estrogen-dependent disease (e.g., breast cancer) through regulation of estrogen signaling. However, the effects of complex food items containing lignans or isoflavones on estrogen receptor (ER) transactivation have not been assessed so far. In this study, the modulation of ER-mediated signaling by dietary sources of lignans (cereals and flaxseed) and isoflavones (soy) was studied in vivo. Adult ovariectomized 3 x ERE-luciferase (luc) reporter mice received isocaloric diets supplemented with flaxseed, rye, wheat, or soy for 40 h or two weeks, and an additional group of mice was challenged with 17beta-estradiol (E(2)) following the two-week dietary intervention. In non-E(2)-treated mice, soy diet induced luc expression in liver, mammary gland, and pituitary gland while the other diets had no effects. Interestingly, all diets modulated the E(2)-induced luc expression. In particular rye diet efficiently reduced E(2)-induced luc expression as well as uterine growth, the hallmark of estrogen action in vivo. It is concluded that dietary sources of lignans and isoflavones can modulate estrogen signaling in vivo. The results suggest intriguing possibilities for the modulation of the risk of estrogen-dependent diseases by dietary means.

Determination of plant and enterolignans in human serum by high-performance liquid chromatography with tandem mass spectrometric detection.

An HPLC-MS/MS method was validated for the determination of the plant lignans 7-hydroxymatairesinol (HMR), matairesinol (Mat), secoisolariciresinol (Seco), lariciresinol (Lar), and cyclolariciresinol (CLar) and for the enterolignans 7-hydroxyenterolactone (HEL), enterodiol (ED), and enterolactone (EL) in human serum. The method included sample enzymatic hydrolysis, solid-phase extraction, and lignan analysis using a triple quadrupole mass spectrometer with electrospray ionisation in the multiple-reaction monitoring mode. The serum lignans were quantified using deuterated Mat or EL as internal standards. The method met the validation criteria for selectivity, intra- and inter-assay precision, and accuracy. The method was applied to ten serum samples collected from healthy individuals (five men and five women) consuming their habitual Finnish diet. All lignans except HMR and Seco were found in quantifiable amounts in the samples. All serums contained EL; the average concentration was 34 nM. In three individuals, the serum concentration of plant lignans was higher than that of enterolignans. Using the method, common dietary plant lignans and their major metabolites can be reliably quantified in human serum at low-nanomolar concentrations in a simple and rapid way.

Urinary excretion of lignans after administration of isolated plant lignans to rats: the effect of single dose and ten-day exposures.

The difference in urinary excretion of mammalian and plant lignans in rats was determined after oral administration of equivalent doses (25 mg/kg of body weight) of 7-hydroxymatairesinol (HMR), lariciresinol (LAR), matairesinol (MR), and secoisolariciresinol (SECO). Twenty-four hours-urine samples were collected after a single dose and after administration of one dose/day for 10 days. Eight lignans were analysed in urine extracts using a high-performance liquid chromatography-tandem mass spectrometry method showing good sensitivity and repeatability. After a single dose of HMR, LAR, MR, and SECO, the main metabolites were 7-hydroxyenterolactone (HENL), cyclolariciresinol (CLAR), enterolactone (ENL), and enterodiol (END), respectively, but after 10-day exposure ENL was the main metabolite of all the tested lignans, showing a considerably higher excretion than after a single dose. Metabolic transformations of plant lignans into each other could also be observed.