Interferences of zearalenone, zearalanol or estradiol-17 beta with the steroid-metabolizing enzymes of the human prostate gland

Towards A New Approach for the Description of Cyclo⁻2,4-Dihydroxybenzoate, A Substance Which Effectively Mimics Zearalenone in Imprinted Polymers Designed for Analyzing Selected Mycotoxins in Urine

A method of purifying cyclododecyl 2,4-dihydroxybenzoate as a potential replacement template molecule for preparation of molecularly-imprinted polymers for isolation of zearalenone in urine was developed. Full physicochemical characteristics of cyclododecyl 2,4-dihydroxybenzoate for the first time included crystallographic analysis and molecular modelling, which made possible the determination of the similarity between the cyclododecyl 2,4-dihydroxybenzoate and zearalenone molecules. The obtained molecularly-imprinted polymers show very high in vitro selectivity towards zearalenone due to specific interactions (e.g., hydrogen bonding, molecular recognition interaction). The achieved extraction recovery exceeds 94% at the tested concentration levels (20–500 ng·mL⁻¹) with a relative standard deviation below 2%. Immunosorbents were found to have lower recoveries (below 92.5%) and RSD value between 2 and 4% for higher concentrations of the studied substance (400 ng·mL⁻¹).

Invited review: Diagnosis of zearalenone (ZEN) exposure of farm animals and transfer of its residues into edible tissues (carry over)

The aim of the review was to evaluate the opportunities for diagnosing the zearalenone (ZEN) exposure and intoxication of farm animals by analyzing biological specimens for ZEN residue levels. Metabolism is discussed to be important when evaluating species-specific consequences for the overall toxicity of ZEN. Besides these toxicological facts, analytics of ZEN residues in various animal-derived matrices requires sensitive, matrix-adapted multi-methods with low limits of quantification, which is more challenging than the ZEN analysis in feed. Based on dose-response experiments with farm animals, the principle usability of various specimens as bio-indicators for ZEN exposure is discussed with regard to individual variation and practicability for the veterinary practitioner. ZEN residue analysis in biological samples does not only enable evaluation of ZEN exposure but also allows the risk for the consumer arising from contaminated foodstuffs of animal origin to be assessed. It was compiled from literature that the tolerable daily intake of 0.25 μg ZEN/kg body weight and day is exploited to approximately 8%, when a daily basket of animal foodstuffs and associated carry over factors are assumed at reported ZEN contamination levels of complete feed.

Signal transduction through the Ras/Erk pathway is essential for the mycoestrogen zearalenone-induced cell-cycle progression in MCF-7 cells

Zearalenone is a naturally occurring estrogenic contaminant of moldy feeds and is present in high concentrations in dairy products and cereals. Zearalenone was postulated to contribute to the overall estrogen load of women, but the mechanisms of its action are not known. We demonstrated that zearalenone could stimulate the growth of estrogen receptor-positive human breast carcinoma cell line MCF-7. In addition, zearalenone functioned as an antiapoptotic agent by increasing the survival of MCF-7 cell cultures undergoing apoptosis caused by serum withdrawal. Treatment of these cells with 100 nM zearalenone induced cell-cycle transit after increases in the expression of c-myc mRNA and cyclins D1, A, and B1 and downregulation of p27(Kip-1). G(1)/G(2)-phase kinase activity and phosphorylation of the retinoblastoma gene product was also evident. Flow cytometric analysis demonstrated entry of cells into the S and G(2)/M phases of the cell cycle, and phosphorylation of histone H3 occurred 36 h after zearalenone treatment. Ectopic expression of a dominant-negative p21(ras) completely abolished the zearalenone-induced DNA synthesis in these cells, and the specific inhibitor PD98059 for mitogen/extracellular-regulated protein kinase kinase arrested S-phase entry induced by zearalenone. These data suggest that the mitogen-activated protein kinase signaling cascade is required for zearalenone's effects on cell-cycle progression in MCF-7 cells. Given the presence of this mycotoxin in cereals, milk, and meat, the possibility that zearalenone is a potential promoter of breast cancer tumorigenesis should be investigated further. Mol. Carcinog. 30:88-98, 2001.

Reductive metabolism of 5 alpha-dihydrotestosterone by rat ventral and dorsolateral prostate: kinetic parameters of the enzymes

In male sex accessory organs the active androgen 5 alpha-dihydrotestosterone (DHT) is metabolized to 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) and 5 alpha-androstane-3 beta, 17 beta-diol (3 beta-diol) by the reductase activities of 3 alpha-hydroxysteroid oxidoreductase (3 alpha-HSOR; EC 1.1.1.50) and 3 beta-hydroxysteroid oxidoreductase (3 beta-HSOR; EC 1.1.1.51). After separation of radiosubstrate and products by HPLC, these enzymes activities in subcellular preparations of rat ventral and dorsolateral prostate were determined from the conversion of [3H]DHT to the radiometabolites 3 alpha-diol and 3 beta-diol and 3 beta-triols (5 alpha-androstane-3 beta, 6 alpha, 17 beta-triol plus 5 alpha-androstane-3 beta, 7 alpha, 17 beta-triol). Whereas both enzymes were found in the dorsolateral prostate, 3 beta-HSOR reductase activity was near the limit of detection in ventral prostate. Unlike the equal distribution of 3 alpha-HSOR reductase between the microsomal and cytosol fractions of the ventral prostate, both 3 alpha- and 3 beta-HSOR reductase activities of the dorsolateral prostate are mainly confined to its cytosol fraction. Km and Vmax of the 3 alpha- and 3 beta-HSOR reductases in dorsolateral prostate cytosol were 1.8 microM, 24.6 pmol.mg-1 min-1 and 25.4 microM, 45.7 pmol.mg-1 min-1, respectively. We surmise from these and earlier studies that 3 beta-HSOR reductase is the rate-limiting prostatic enzyme in the catabolic disposition of intracellular DHT.

Metabolism of zearalenone by sow intestinal mucosa in vitro

Homogenized intestinal mucosa samples from sows were incubated with zearalenone in the presence of NADPH or UDPGA. In addition, UDPglucuronosyltransferase activity in the microsomal fraction of mucosa was determined using 1-naphthol as substrate. In the presence of NADPH, zearalenone was reduced to both alpha- and beta-zearalenol (0.37 +/- 0.18 and 0.29 +/- 0.11 nmol/mg protein/hr in the duodenum and jejunum, respectively). The beta-isomer was the predominant metabolite. Glucuronide conjugation of zearalenone was very high compared with the level of reduction occurring (11.3 +/- 6.1 and 9.4 +/- 5.8 nmol conjugated/mg protein/hr in the duodenum and jejunum, respectively). There was no correlation between the rates of glucuronide conjugation of zearalenone and 1-naphthol, indicating that they depend upon two different isoenzymes of UDPglucuronosyltransferase.

Esterogenic effect of zearalenone on the uterine acetyl cholinesterase in female rats

A single dose of zearalenone (10 micrograms/g LBW) was injected intraperitoneally to Wistar Albino rats at the age of 50-100 days. The uterine acetyl cholinesterase enzyme was significantly increased in the treated animals compared to that in the controls. Therefore, zearalenone would be considered as an esterogenic effector for increasing the uterine acetyl cholinesterase which enhances uterine relaxation and subsequently improves its function for pregnancy in prematured-animals. Unlike estradiol, it was interesting to find that the estrogenicity of zearalenone was increased by the moderating progesterone hormone. Moreover, it was revealed in this study that the injected dose of zearalenone had no deleterious effects on the pregnant rats at 10-12 days period of gestation. The harmful effects of zearalenone on pregnant animals cited in the literature were reviewed.

Metabolism of high concentrations of dietary zearalenone by young male turkey poults

Six male turkey poults (3 weeks of age) were fed a starter ration artificially contaminated with 800 mg zearalenone/kg for a 2-week period to examine zearalenone metabolism and residues in various tissues, excreta, and blood plasma. Zearalenone had no effect on either feed consumption or body weight gain. All the birds fed zearalenone frequently showed strutting behavior, displayed an increased size and coloration of caruncles and dewlaps, and had swollen vent tissue. None of these signs were seen among six control birds fed uncontaminated starter feed. Hormone analysis, however, revealed that the testosterone concentrations in blood plasma were the same in both controls and treated birds. Analysis after 14 days of feeding showed that most of the dietary zearalenone had been metabolized into alpha-zearalenol. Levels of zearalenone and alpha-zearalenol were: blood plasma 66 +/- 27 and 194 +/- 80 ng/ml, excreta 182 +/- 33 and 644 +/- 86 micrograms/g, lung 56 +/- 45 and 202 +/- 161 ng/g, heart 57 +/- 40 and 238 +/- 121 ng/g, kidney 122 +/- 25 and 477 +/- 53 ng/g, and liver 276 +/- 54 and 2715 +/- 590 ng/g, respectively. Only traces of beta-zearalenol could be detected in plasma, excreta, and the various tissues. The percentage alpha-zearalenol of total zearalenone plus alpha-zearalenol rose significantly in both blood plasma and excreta during the experimental period. Almost all zearalenone and alpha-zearalenol was found conjugated in blood plasma, and the conjugates consisted of both glucuronides and sulfate conjugates. Approximately 65% of all zearalenone and alpha-zearalenol in excreta was found to be conjugated.

Plasma and urinary levels of zearalenone and alpha-zearalenol in a prepubertal gilt fed zearalenone

One prepubertal gilt, fed 192 micrograms zearalenone/kg body weight/day for 4 days, showed plasma concentrations of alpha-zearalenol 3-4 times higher than of the parent compound during the treatment. Zearalenone and alpha-zearalenol could be traced in plasma until the 5th day and in urine until the 4th day of the posttreatment period. A maximum circulating amount of zearalenone plus alpha-zearalenol, 10.4 ng/ml plasma, was found on the 4th day of treatment followed by an urinary excretion of 305 ng/ml urine. All zearalenone and alpha-zearalenol in plasma and urine were bound to glucuronic acid. On the second day of treatment the animal showed oedema and reddening of the vulva which became more pronounced during the treatment. Hormone analysis, however, showed that the animal had no oestrus cycle during the 3 week experimental period.

Testosterone metabolism by homogenates of human prostates with benign hyperplasia: effects of zinc, cadmium and other bivalent cations

The effects of various quantities of Ba, Be, Ca, Cd, Co, Cu, Mg, Mn, Sr, Zn and EDTA on the formation of 5 alpha-reduced metabolites of testosterone (T) substrate and of 3 alpha-/3 beta-reduced metabolites of 5 alpha-dihydrotestosterone substrates by homogenates of 6 human hyperplastic prostate glands were studied in incubations at pH 7.4 with NADPH-generating system. Effects of these cations and EDTA on the VM and KM of the 5 alpha-reductase and 3 alpha-/3 beta-hydroxysteroid dehydrogenases (-HSD) were also measured. Quantities of 5 alpha-reduced T metabolites were significantly increased by Cd, Cu and Zn supplementations. These increments were shown to result from significant augmentations of the VM but no change in KM of the NADPH-dependent 5 alpha-reductase. Quantities of 3 alpha-reduced DHT metabolites were significantly decreased by Cd and Cu supplementations and resulted from an increase of the KM of the NADPH-dependent 3 alpha-HSD by Cd and both an increase of KM and a decrease of VM by Cu. Quantities of 3 beta-reduced DHT metabolites were significantly decreased by Cd and Cu supplementations. Increase of the KM of the NADPH-dependent 3 beta-HSD by Cd was found significant while Cu both increased the KM and decreased the VM of the enzyme. EDTA-related changes in 5 alpha-reductase activity were shown to result from the EDTA-induced decrease of the pH of the medium. No effect of EDTA was observed on the activities of both 3 alpha/3 beta-HSD.

Species differences in zearalenone-reductase activity

Thin-layer and high-pressure liquid chromatography (HPLC) were used to investigate in several animal species the hepatic metabolites of zearalenone (ZEN), a non-steroidal oestrogenic fungal toxin produced by species of Fusarium. ZEN was reduced to zearalenol (ZEL) by the S-9 fraction of rat-liver homogenates in the presence of NADH or NADPH. In this species ZEN reductase showed two peaks of activity at pH 4.5 and 7.4. Of the species tested, cows showed the highest activity of NADH-dependent ZEN reductase in the hepatic S-9 fraction, followed in decreasing order by mice, pigs, rats, rabbits and guinea-pigs. The S-9 fraction of hamster liver showed optimal activity at pH 5.5 and 8.0 with NADH and at pH 6.0 and 8.5 with NADPH; NADPH was more efficient than NADH only in this species. HPLC showed that alpha-ZEL was a major hepatic metabolite in the rat, mouse, pig, cow and rabbit in incubations at pH 4.5 with either NADH or NADPH and at pH 7.4 with NADH, although at pH 7.4 with NADPH, beta-ZEL was the predominant metabolite. In guinea-pigs, both alpha- and beta-ZELs were produced in roughly similar amounts irrespective of the pH and cofactor, while in hamsters beta-ZEL was the major metabolite. These findings indicate that there are two types of ZEN reductase differing in optimum pH and that the stereospecific reduction of ZEN depends on the source of S-9 and cofactors. Since the oestrogenic activity of alpha-ZEL is about ten times greater than that of ZEN, the possible presence of ZEN metabolites in edible tissues of livestock fed on ZEN-contaminated feeds is an important mycotoxicological problem.

Should we worry about animal growth promoters?

Estrogens and compounds with estrogenic activity have been used for many years as animal growth promoters and to synchronize estrus in cows. The resorcylic acid lactones (RALS), which include zearalenone, are being used increasingly for these purposes. These estrogenic mycotoxins, now produced commercially, have teratogenic, mutagenic, and carcinogenic properties. There is some evidence that their residues could remain in certain organs at the time the animal products come to market, and this may be of medical significance.

Radioimmunoassay for zearalenone and zearalanol in human serum: production, properties, and use of porcine antibodies

To produce antigens susceptible to raise antibodies for resorcylic acid lactones, the 6'-carboxymethyloxime derivatives of zearalenone and zearalanone were bound to bovine serum albumin. Pigs could be immunized by using these antigens, the best titer in antibodies being obtained with the zearalenone antigen. The porcine antibodies were specific for the resorcylic acid lactones of structural resemblance with zearalenone. This specificity made the antibodies usable for a radioimmunoassay of zearalenone and zearalanol, which may be found in human and animal sera. The range of the assay was between 0.25 and 10 ng. The limit of detection was 5 ppb (5 ng/ml) in human serum.

Testosterone metabolism by homogenates of human prostates with benign hyperplasia: effect of tissular concentrations of zinc, magnesium and copper

Zinc, magnesium and copper concentrations were measured in homogenates of 20 human prostates with benign hyperplasia and a significant direct relationship between zinc and magnesium contents was found. Activities of the testosterone-5 alpha-reductase in the same homogenates were not significantly changed according to the concentrations of the three metals but activities of the 3 alpha- and 3 beta-hydroxysteroid dehydrogenases were inversely related with the zinc concentrations of the tissue preparations. This inverse relationship may explain the known increased 5 alpha-dihydrotestosterone content in prostatic tissues with high zinc concentrations.

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.