Hormone effects of zearalenone in nonhuman primates

Provocative tests with Kisspeptin-10 and GnRH set the scene for determining social status and environmental impacts on reproductive capacity in male African lions (Panthera leo)

Understanding the hypothalamic factors regulating reproduction facilitates maximising the reproductive success of breeding programmes and in the management and conservation of threatened species, including African lions. To provide insight into the physiology and pathophysiology of the hypothalamic-pituitary-gonadal reproductive axis in lions, we studied the luteinising hormone (LH) and steroid hormone responses to gonadotropin-releasing hormone (GnRH) and its upstream regulator, kisspeptin. Six young (13.3 ± 1.7 months, 56.2 ± 4.3 kg) and four adult (40.2 ± 1.4 months, 174 ± 6 kg) male lions (Ukutula Conservation Centre, South Africa) were used in this study. Lions were immobilised with a combination of medetomidine and ketamine and an intravenous catheter was placed in a jugular, cephalic or medial saphenous vein for blood sampling at 10-min intervals for 220 min. The ten-amino acid kisspeptin which has full intrinsic activity (KP-10, 1 µg/kg) and GnRH (1 µg/kg) were administered intravenously to study their effects on LH and steroid hormone plasma concentrations, measured subsequently by ELISA and liquid chromatography tandem mass spectrometry (LC-MS/MS), respectively. Basal LH levels were similarly low between the age groups, but testosterone and its precursor levels were higher in the adult animals. Adult lions showed a significant LH response to KP-10 (10-fold) and GnRH (11-fold) administration (p < 0.05 and P < 0.001, respectively) whereas in young lions LH increased significantly only in response to GnRH. In adults alone, testosterone and its precursors steadily increased in response to KP-10, with no significant further increase in response to GnRH. Plasma levels of glucocorticoids in response to KP-10 remained unchanged. We suggest that provocative testing of LH and steroid stimulation with kisspeptin provides a new and sensitive tool for determining reproductive status and possibly an index of exposure to stress, environmental insults such as disease, endocrine disruptors and nutritional status. 272 words.

Effects of zearalenone and its derivatives on the synthesis and secretion of mammalian sex steroid hormones: A review

Zearalenone (ZEA), a non-steroidal estrogen mycotoxin produced by several species of Fusarium fungi, can be metabolized into many other derivatives by microorganisms, plants, animals and humans. It can affect mammalian reproductive capability by impacting the synthesis and secretion of sex hormones, including testosterone, estradiol and progesterone. This review summarizes the mechanisms in which ZEA and its derivatives disturb the synthesis and secretion of sex steroid hormones. Because of its structural analogy to estrogen, ZEA and its derivatives can exert a variety of estrogen-like effects and engage in estrogen negative feedback regulation, which can result in mediating the production of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the pituitary gland. ZEA and its derivatives can ultimately reduce the number of Leydig cells and granulosa cells by inducing oxidative stress, endoplasmic reticulum (ER) stress, cell cycle arrest, cell apoptosis, and cell regeneration delay. Additionally, they can disrupt the mitochondrial structure and influence mitochondrial functions through overproduction of reactive oxygen species (ROS) and aberrant autophagy signaling ways. Finally, ZEA and its derivatives can disturb the expressions and activities of the related steroidogenic enzymes through cross talking between membrane and nuclear estrogen receptors.

MiR-7 Mediates the Zearalenone Signaling Pathway Regulating FSH Synthesis and Secretion by Targeting FOS in Female Pigs

Zearalenone (ZEA) acts as an environmental endocrine disruptor (EED) to cause health detriments. miRNAs were reported to influence the synthesis and secretion of pituitary hormones. However, the interactions between ZEA and miRNAs and related mechanisms remain unclear. The aims of this study were to determine whether and how miR-7 affects animal reproduction by its interactions with ZEA in the pig pituitary, which is sensitive to ZEA and has been used as an important animal model in medical research. Expressions of miRNA were detected by real-time PCR, in situ hybridization, and immunohistochemistry. The effects of ZEA, miR-7, and their interactions in the pituitary gland were identified by using an ovariectomized pig model, transfecting miR-7 mimics and inhibitor, radioimmunoassay, luciferase reporter assay, and Western blotting. The ZEA dosage was 7.5 mg/kg body weight in vivo and 1 μM in vitro. Our results demonstrate miR-7 acts to regulate gonadotropin synthesis and secretion. Furthermore, we found that ZEA leads to reproductive defects by enhancing miR-7 expression, which subsequently inhibits FSH synthesis and secretion. In vitro and in vivo experiments revealed that the effects of ZEA rely on G protein-coupled estrogen receptor 1, and miR-7 functions by mediating ZEA signaling pathway and targeting the Finkel-Biskis-Jinkins murine osteosarcoma viral oncogene homolog (FOS) gene. These findings show that miRNAs are key intrinsic factors regulating pituitary gonadotropins by mediating EED signaling in pituitary glands, and the actions of miRNAs and EEDs should be seriously considered in related studies about medical practice and animal production.

A Concise History of Mycotoxin Research

Toxigenic fungi and mycotoxins entered human food supplies about the time when mankind first began to cultivate crops and to store them from one season to the next, perhaps 10,000 years ago. The storage of cereals probably initiated the transition by mankind from hunter-gatherer to cultivator, at the same time providing a vast new ecological niche for fungi pathogenic on grain crops or saprophytic on harvested grain, many of which produced mycotoxins. Grains have always been the major source of mycotoxins in the diet of man and his domestic animals. In the historical context, ergotism from Claviceps purpurea in rye has been known probably for more than 2000 years and caused the deaths of many thousands of people in Europe in the last millennium. Known in Japan since the 17th century, acute cardiac beriberi associated with the consumption of moldy rice was found to be due to citreoviridin produced by Penicillium citreonigrum. This toxin was believed to be only of historic importance until its reemergence in Brazil a few years ago. Other Penicillium toxins, including ochratoxin A, once considered to be a possible cause of Balkan endemic nephropathy, are treated in a historical context. The role of Fusarium toxins in human and animal health, especially T-2 toxin in alimentary toxic aleukia in Russia in the 1940s and fumonisins in equine leucoencephalomalasia, is set out in some detail. Finally, this paper documents the story of the research that led to our current understanding of the formation of aflatoxins in grains and nuts, due to the growth of Aspergillus flavus and its role, in synergy with the hepatitis B virus, in human liver cancer. During a period of climate change and greatly reduced crop diversity on a global basis, researchers tasked with monitoring the food system need to be aware of fungal toxins that might have been rare in their working careers that can reappear.

In vitro mycotoxin binding to bovine uterine steroid hormone receptors

The mycotoxins, aflatoxin B(1), aflatoxin M(1), aflatoxicol and zearalenone were tested for binding to bovine endometrial estrogen and progestin receptors. Radioinert estradiol-17beta, estrone, testosterone, and cholesterol were evaluated for binding to the estrogen receptor. Zearalenone and aflatoxicol but not aflatoxins B(1) and M(1) competed with estradiol-17beta for the estrogen receptor. The order of binding affinities for the estrogen receptor were zearalenone > estradiol-17beta > estrone > aflatoxicol. The affinity of zearalenone for the estrogen receptor was 2-3 times that of estradiol-17beta. Progesterone, cortisol, radioinert R 5020, and cholesterol were evaluated for binding to the progestin receptor. None of the tested compounds except R 5020 and progesterone competed for the progestin receptor. The significance of aflatoxicol binding to the estrogen receptor is unclear. It is proposed that aflatoxicol binding to the receptor may alter gene expression in target tissues or act at the level of the hypothalamus to inhibit gonadotropin secretion and ovulation. These effects could explain reports of reduced fertility in domestic animals following ingestion of aflatoxin contaminated feedstuffs. It is also suggested that the mechanism of adverse effects on fertility of chronic aflatoxin ingestion in cattle and other livestock should be more thoroughly investigated.

Mycotoxins in root extracts of American and Asian ginseng bind estrogen receptors alpha and beta

The estrogenic activity of ginseng has been the subject of conflicting reports. Cell proliferation, induction of estrogen-responsive genes, and isolated cases of adverse reactions such as postmenopausal vaginal bleeding and gynecomastia have been reported after ginseng treatment. Other studies report antiproliferative effects with no induction of estrogen-responsive genes. We developed estrogen receptor (ER) alpha and ER alpha competitive binding assays using recombinant receptors and [(3)H]-17 alpha-estradiol to detect phytoestrogens in extracts of Asian ginseng root (Panax ginseng C. A. Meyer) and American ginseng root (Panax quinquefolius L.). Root extracts contained substances that bound both receptor isoforms. These substances had a two to three times greater affinity for ER alpha. Significantly higher binding was found in methanol extracts than in hot water extracts. Subsequent analysis of the extracts revealed significant ER binding attributable to zearalenone, the estrogenic mycotoxin produced by several Fusarium species. The ER showed no binding affinity for Rb1 and Rg1, the major ginsenosides found in P. quinquefolius and P. ginseng, respectively. Thus, ginseng extraction methods, plant species tested, and mycotoxin contaminants may help to explain the disparate literature reports. The prevalence and health significance of fungal contamination in herbal products used for medicinal purposes should be further investigated.

Reproductive actions of phytoestrogens

This chapter reviews the reproductive actions of phytoestrogens, comparing mechanisms of action, dose-response relationships, and human exposures. Although a wide range of biochemical actions have been reported for phytoestrogens, in vitro tests suggest that phytoestrogens may be more likely to act through receptor-mediated mechanisms than through enzyme inhibition. Epithelial cell proliferation in the reproductive tract and anestrus are well-documented actions of isoflavonoids in experimental studies of animals. However, thus far, soy-based diets have generally failed to produce epithelial proliferation in ovariectomized rats and monkeys or menopausal women, and clinical studies have produced mixed evidence for effects of soy isoflavones on the human menstrual cycle or post-menopausal gonadotropin secretion. There has been considerable interest in the use of phytoestrogens as oestrogen replacement therapy in menopausal women. Reported results of initial clinical trials have been mixed, and it is unclear whether isoflavones in presently advised doses can substantially reduce menopausal symptoms. Some recent trials with oral isoflavone supplements report reductions in hot flushes, vaginal dryness, and breast pain. There is also limited clinical evidence for protective actions of isoflavones in mammary cancer. Like other oestrogenic substances, the isoflavonoids are effective differentiating agents in rodent models of development. The consequences of these actions for humans is of interest due to the high concentrations of isoflavonoids in some infant formulae. Thus, it is likely that some humans may experience greater exposure to phytoestrogens in infancy than in any other lifestage. At the time of writing, no ill effects of such exposure have been reported.

Reproductive alterations in female C57BL/Crgl mice exposed neonatally to zearalenone, an estrogenic mycotoxin

Newborn female mice were injected daily for 5 days with 1 microgram zearalenone (Z, a weakly estrogenic mycotoxin present in cereal grains), resulting in ovary-dependent reproductive tract alterations at 8 months of age. Corpora lutea were absent from 25 of 34 (74%) Z-treated mice, indicating ovarian dysfunction. Fifty-six percent of Z-treated mice had dense collagen deposition in the uterine stroma and lacked uterine glands. Squamous metaplasia of the uterine luminal epithelium was found in 59% of Z-treated mice, and altered vaginal epithelium was found in 32% (2 mice had dysplastic lesions). Ovariectomized Z-treated mice were indistinguishable from ovariectomized controls.

Effect of zearalenone and estradiol benzoate on serum concentrations of LH, FSH and prolactin in ovariectomized gilts

Six ovariectomized gilts were given zearalenone (Z), estradiol benzoate (EB) or vehicle in a replicated 3 x 3 Latin square design. Zearalenone was added to 2.3 kg of a corn-soybean ration at a dose of 1 mg Z/kg body weight; EB was given intramuscularly at 0.1 mg EB/kg body weight. Control gilts received vehicle solvent for both Z and EB. Blood samples were collected from indwelling jugular cannulas at 6-h intervals for 48 h before Z, EB or vehicle was given. After treatment, blood samples were drawn at 6-h intervals for an additional 84 h. Serum concentrations of luteinizing hormone (LH) decreased (P<0.001) from 4.67 ng/ml to 0.29 ng/ml within 6 h of EB. From 54 to 84 h after EB, serum concentrations of LH rose to 15.60 ng/ml (P<0.001). Serum concentrations of LH were reduced (P<0.001) in a similar pattern after Z (3.70 ng/ml to 0.49 ng/ml), but a rise in serum LH was not observed 54 to 84 h after Z (1.30 ng/ml). Serum concentrations of LH remained unchanged (P=0.55) in gilts given vehicle. Serum concentrations of follicle stimulating hormone (FSH) were suppressed (P<0.03) at 6 h in EB (19.10 vs 11.35 ng/ml) and Z gilts (16.16 vs 11.41 ng/ml) but remained unchanged in vehicle gilts. Serum concentrations of FSH did not change in EB or Z gilts during the next 36 h. These data indicate that the suppressive action of Z on serum concentrations of LH and FSH was similar to that of EB, while the biphasic stimulatory effect of EB for LH was not manifested by Z.

Gonadotropin responsiveness to estrogens and low-level progesterone in the ovariectomized rhesus monkey

When estrogen is administered to gonadectomized rhesus monkeys in sufficient quantity, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels are initially suppressed and gonadotropin secretion is subsequently augmented. This study was designed to examine the ability of various orally administered estrogens to elicit biphasic pituitary responses in adult castrate rhesus monkeys and to investigate the role of low-level progesterone in altering these responses. In an incomplete block design, 13 treatments were constructed: (E2): 0.5, 5.0, 50 micrograms/kg; (DES): 0.05, 0.5, 5.0 micrograms/kg; zearalenone (Z): 10, 100, 1000 micrograms/kg; or oil vehicle, each combined with progesterone. The remaining treatments (5.0, 0.5, and 100 micrograms/kg of E2, DES, and Z, respectively) did not include progesterone. During six intervals, E2, DES, or Z was administered orally on Days 1, 2, and 3 and blood was sampled on Days 0, 3, and 8 of each period. A main effect of estrogen treatment was observed for LH and FSH secretion on Day 3 but not Day 8. There was no main effect of progesterone alone on release of either LH or FSH on days 3 or 8, nor were significant carry-over effects of progesterone, E2, DES, or Z on LH or FSH concentration apparent by Day 8 of any treatment. However, progesterone synergized with E2 to suppress Day 3 LH levels. Conversely, DES and Z interacted with progesterone to facilitate LH secretion at this time.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk assessment of the mycotoxin zearalenone

Trans-zearalenone, a resorcylic acid lactone, also known as F-2 toxin, is a nonsteroidal estrogenic mycotoxin produced by numerous species of Fusarium. As a result zearalenone is found in a number of cereal crops and their derived food products. A closely related substance "zeranol" (zearalanol) is at present being used in the United States and Canada as an anabolic agent in beef cattle. Zearalenone has been implicated in numerous incidences of mycotoxicosis in farm animals, especially pigs. In this report the health risks to Canadians due to the presence of zearalenone in food products have been evaluated. The first part of the report deals with the physicochemical aspects, mycology, laboratory production, and natural occurrence in plant products and animal products of zearalenone. The stability of zearalenone in foods and feeds, the effects of food processing, and the removal from foods and feeds by physicochemical means are also discussed. From these data the daily exposure of Canadians to zearalenone from food consumption has been estimated to be in the range of 0.05-0.10 microgram/kg b.w./day (mean and 90th percentile of eaters, respectfully) for young children, the highest consumption group on a body weight basis. The second part of the report deals with the metabolic disposition of zearalenone as well as the available toxicity data base of zearalenone in laboratory animals, farm animals, and humans. Studies in various species (rodents, rabbits, pigs, monkeys) including man have shown that zearalenone has estrogenic and anabolic activity. Its major effects are on reproduction, including reproductive organs and their function, leading to hyperestrogenism. Zearalenone has been implicated in numerous incidences of hyperestrogenism in farm animals, especially pigs. For reproductive effects a no adverse effect level (NOAEL) of 0.06 mg/kg b.w./day was estimated for the pubertal pig, the most sensitive species tested. Important differences in the biotransformation of zearalenone were noted, with greater amounts of alpha-zearalenol, the more estrogenic metabolite, formed in man and the pig compared to rodents. In addition, the biological half-life of these substances was longer in man than in other species tested. The binding of zearalenone to estrogen receptors was approximately 20-fold lower than that seen with 17 beta-estradiol in several assays.(ABSTRACT TRUNCATED AT 400 WORDS)

Conversion of zearalenone to zearalenone glycoside by Rhizopus sp

The microbial conversion of zearalenone by various species of fungi was studied. Among them, Rhizopus sp. was the sole fungus which produced a new metabolite from zearalenone in addition to alpha- and beta-zearalenol. The structure of the new metabolite was determined to be zearalenone 4-beta-D-glucopyranoside on the basis of mass, infrared, and nuclear magnetic resonance spectroscopies. The results suggest that the mycelium of Rhizopus sp. catalyzes the glycosidation at the C-4 position of zearalenone.

Zeranol--a 'nature-identical' oestrogen?

The use of implants of zeranol (alpha-zearalanol), a widely-used anabolic growth promoter, in food animals results in very low residues of this compound in the edible tissues. In comparison, residues of myco-oestrogens--specifically the beta-resorcylic acid lactones (RALs) such as zearalenone and its metabolites--commonly found as contaminants of cereals are much greater. Zeranol, the RALs and their metabolites are all closely related chemically, sterically and biologically. The biological effects of these compounds on reproduction, oestrogenicity, teratogenicity, genotoxicity and carcinogenicity are compared. No toxicological effects have been reported that cannot be attributed to the oestrogenic character of these molecules. In comparison with oestradiol, zeranol and the related myco-oestrogens are 100-1000 times less active hormonally. It is concluded that a likely no-observed-effect level (NOEL) for these compounds will be of the order of 0.05-0.1 mg/kg body weight/day. This would result in a safety margin greater than 500-fold between the expected dietary exposure to these compounds (considered together) and the likely NOEL. On the basis of exposure to zeranol alone, this margin of safety would increase to more than 35,000.

Naturally occurring oestrogens in foods--a review

This review is concerned with the presence of naturally occurring oestrogens in food plants and processed foods. Particular emphasis is placed on isoflavones and coumestans, both of which are true plant oestrogens, and the resorcylic acid lactones, more correctly classified as fungal oestrogens. The metabolism and mode of action of these compounds is discussed and their biological potencies, determined in both in vivo and in vitro studies, described. Current methods of analysis are indicated and the levels of these oestrogens in food plants, processed foods and foodstuffs are presented. Botanical, environmental or technological factors affecting the possible intake of plant and fungal oestrogens are mentioned and the hazard associated with such intake is compared with that originating from other dietary or medicinal hormonally active substances. Indications are given of the wide range of common food plants which have been reported to possess oestrogenic (uterotropic) activity, although it is emphasized that in general further work is necessary to substantiate these claims and to confirm the identities of the biologically active principles which have in some cases been proposed. In the concluding section suggestions are made for additional research considered important or necessary in this interesting area.

The toxicology of mycotoxins

Mycotoxin problems are one of great concern to health scientists. Toxic fungal metabolites such as aflatoxins, trichothecenes, zearalenone and others are contaminated in our environments and induce various diseases. In this manuscript, the author will summarize the recent advances on toxicology of mycotoxins in special references to toxicological characters, cytotoxicity, genotoxicity (mutagenicity and carcinogenicity), metabolism, and biochemical mode of action. Interaction of mycotoxins with cellular components will be reviewed in order to clarify the toxicological characteristics of mycotoxins such as aflatoxins, trichothecenes, zearalenone, toxic peptides, and anthraquinoid mycotoxins.

Transformations of zearalenone and alpha-zearalanol by homogenates of human prostate glands

The present study applied high-pressure liquid chromatography, gas chromatography/mass spectrometry and crystallizations to constant specific activity for identification of the radiometabolites of tritiated zearalenone and alpha-zearalanol in homogenates of human prostate glands. Radiolabelled zearalenone or alpha-zearalanol (6.3 microM) was incubated for 30 min at 37 degrees C with prostatic homogenate in 5 ml 0.067 M phosphate buffer (pH 7.4) containing 0.5 mM oxidized or reduced NAD or NADP. Reduction of zearalenone occurred only with NADPH while oxidation of alpha-zearalanol was favoured both by NADP+ and NAD+. Separation of the substrates from their metabolites by high-pressure liquid chromatography showed the radioactivity of the metabolite of zearalenone to be associated with the alpha-zearalenol carrier while that of the alpha-zearalanol metabolite was found with the zearalanone carrier. Crystallizations to constant specific activity after isotopic dilution and gas chromatography/mass spectrometry confirmed the identity and the radiochemical purity of the alpha-zearalanol substrate and of its zearalanone metabolite. In contrast, the poor radiochemical purity of the zearalenone substrate and of its alpha-zearalenol metabolite was explained by the presence of large quantities of cis-isomer contaminants which were identified by gas chromatography/mass spectrometry. Formation of the cis-isomer of zearalenone was shown to occur spontaneously in incubations with boiled homogenates. The other stereospecific reductions or oxidations of the substrates were due to the prostatic enzymes which could be those involved in the C19-steroid hormone metabolism.

Quantitation of zearalenone by gas-liquid chromatography on capillary glass columns

A procedure is described for the quantitation of zearalenone from corn by gas-liquid chromatography. An internal standard, zearalanone, is first mixed with the finely ground corn, followed by extraction with ethyl acetate, purification by thin-layer chromatography and formation of trimethyl silyl ether (TMS) and methyl oxime (MOX) derivatives. Positive identification of zearalenone is based upon the retention times of the TMS and MOX-TMS derivatives being identical with those of the standards, comparison of chromatograms from both derivatives and characteristic twin peaks of zearalenone MOX-TMS. The detection limit of 100 parts per 10(9) zearalenone in corn could only be improved by modification of the described procedure.