Effect of dietary protein on zearalenone metabolism and toxicity in the rat

Dispositions and tissue residue of zearalenone and its metabolites α-zearalenol and β-zearalenol in broilers

Zearalenone (ZEA) is a secondary fungal metabolite produced mainly by a Fusarium graminearum. To clarify the toxicokinetics, and residues of ZEA and its major metabolites α-zearalenol (α-ZOL) and β-zearalenol (β-ZOL) in chickens, ZEA was then administered intravenously (iv) or orally (po) to broiler chickens at a dosage of 1.2 mg/kg body weight. The concentrations of ZEA, α-ZOL and β-ZOL in the plasma and various tissues were quantified using LC-MS/MS. The plasma concentrations of ZEA were measurable up to 2 h after iv and po administration, and the concentrations of α-ZOL and β-ZOL were detected up to 4 h after both types of administration. A two-compartment model was developed to describe the toxicokinetic of ZEA in broilers. The values of t1/2β and Vd were 1.36 ± 0.29 h and 6.40 ± 0.89 l/kg, respectively. The absolute oral bioavailability was 29.66 ± 5.6%. ZEA, α-ZOL and β-ZOL were measurable in the vital organs after po administration. These results suggest that ZEA is absorbed from the gastrointestinal tract and it has ability to penetrate into the various tissues of broiler chickens.

Cytotoxicity effects induced by Zearalenone metabolites, alpha Zearalenol and beta Zearalenol, on cultured Vero cells

Zearalenone (Zen) is a non-steroidal estrogenic mycotoxin produced by several species of Fusarium. It has been implicated in several mycotoxicosis in farm animals and in humans. The major metabolites of this mycotoxin in various species are alpha and beta Zearalenol. In vivo, Zen is mainly reduced to these alcoholic metabolites which cause reproductive tract disorders and impaired fertility due to their estrogenic activities. In this study, we examined the cytotoxicity of alpha and beta Zearalenol in cultured cells. For this purpose, the MTT assay was carried out and the influence of alpha and beta Zearalenol on protein and DNA syntheses was assessed. To evaluate the cell stress caused by these two metabolites, oxidative stress measured by MDA induction and stress protein induction (Hsp 70, Hsp 27) were tested. Results showed that alpha and beta Zearalenol were metabolites that caused cytotoxicity by inhibiting cell viability, protein and DNA syntheses and inducing oxidative damage and over-expression of stress proteins. However, the Zen metabolites exhibited lower toxicity than Zen, with beta zearalenol being the more active of the two metabolites.

Effect of UDP-glucuronyltransferase induction on zearalenone metabolism

Experiments were conducted to determine the UDP-glucuronyltransferase (UDP-GT) isoenzyme which catalyzes zearalenone (Z) conjugation, and the effect of increased enzyme activity on Z metabolism. In competitive enzyme assays, the activity of rat liver UDP-GT towards Z was inhibited by 1-naphthol (NA), a GT1 substrate, and 4-hydroxybiphenyl (HB), a GT2 substrate. When enzyme activity was induced with either 3-methylcholanthrene (MC), a GT1 inducer, or phenobarbital (PB), a GT2 inducer, increased UDP-GT activity towards Z, NA and HB was observed. UDP-GT induction by PB increased urinary excretion of conjugated alpha-zearalenol. These results indicate that UDP-GT isoenzymes have overlapping substrate specificities, and that Z detoxification may be enhanced by UDP-GT enzyme induction, resulting in increased urinary excretion of conjugated alpha-zearalenol.

Measurement of the relative binding affinity of zearalenone, alpha-zearalenol and beta-zearalenol for uterine and oviduct estrogen receptors in swine, rats and chickens: an indicator of estrogenic potencies

1. The relative binding affinity of zearalenone, alpha-zearalenol, and beta-zearalenol for estrogen receptors was determined in the pig, rat and chicken. 2. Similar relative binding patterns were observed, with alpha-zearalenol exhibiting greater affinity than zearalenone and beta-zearalenol the least binding affinity in all species. 3. The relative binding affinity of alpha-zearalenol was greater in pig, than in rat and significantly greater than in chicken. 4. Interspecies differences in zearalenone sensitivity may be due to the binding affinity of alpha-zearalenol for estrogen receptors and differences in zearalenone metabolites formed.