Nitrofurazone accumulates in avian eyes—a replacement for semicarbazide as a marker of abuse

The anti-androgenic effect of chronic exposure to semicarbazide on male Japanese flounder (Paralichthys olivaceus) and its potential mechanisms

Semicarbazide (SMC), a new marine pollutant, has anti-estrogenic effects on female Japanese flounder (Paralichthys olivaceus). However, whether SMC also affects the reproductive endocrine system of male marine organisms is currently unclear. In this study, Japanese flounder embryos were exposed to 1, 10, and 100 μg/L SMC for 130 days. Plasma testosterone (T) and 17β-estradiol (E₂) concentrations were significantly decreased in male flounders after SMC exposure. The expression of genes involved in T and E₂ synthesis, including steroidogenic acute regulatory protein, cytochrome P450 11A1, 17α-hydroxylase, 17β-hydroxysteroid dehydrogenase and cytochrome P450 19A, was down-regulated in the gonads, which may explain the decrease in plasma sex hormones levels. Moreover, SMC-mediated changes in the transcription of these steroidogenic genes were associated with reduced levels of follicle-stimulating hormone beta subunit (fshβ), luteinizing hormone beta subunit (lhβ), follicle-stimulating hormone receptor (fshr) and luteinizing hormone receptor (lhr) mRNA. In addition, down-regulated transcription of fshβ and lhβ in the SMC exposure groups was affected by reduced mRNA levels of seabream gonadotropin-releasing hormone (sbgnrh), g-protein-coupled receptor 54 (gpr54) in the kisspeptin/gpr54 system, as well as the gamma-aminobutyric acid (GABA) synthesis enzyme glutamic acid decarboxylase (gad). Overall, our results showed that environmentally relevant concentrations of SMC exerted anti-androgenic effects in male flounders via impacting HPG axis, kiss/gpr54 system and GABA synthesis, providing theoretical support for investigating reproductive toxicity of environmental pollutants that interfere with the neuroendocrine system.

Fe-Catalyzed tandem cyclization for the synthesis of 3-nitrofurans from homopropargylic alcohols and Al(NO3)3·9H2O

Al(NO3)3·9H2O as a nitro source for the synthesis of 3-nitrofurans from homopropargylic alcohols through Fe-catalyzed tandem cyclization is described. In this transformation, the substituted nitrofurans are obtained through nitration and cyclization. The substrate homopropargylic alcohols with different groups participate smoothly in this process and the desired substituted nitrofurans were obtained in moderate yields.

Semicarbazide-induced thyroid disruption in Japanese flounder (Paralichthys olivaceus) and its potential mechanisms

Semicarbazide (SMC) is a carcinogenic and genotoxic substance that has been found in aquatic systems. SMC may also cause thyroid follicular epithelial cell injury in rats, but the thyroid-disrupting properties of SMC and its potential mechanisms remain unclear. In this study, we exposed fertilized eggs of Japanese flounder (Paralichthys olivaceus) to 1, 10, 100, and 1000μg/L SMC for 55 d to assess the impact of SMC exposure on the thyroid system. The number of larvae in each metamorphic stage was counted, the concentrations of whole-body thyroid hormones (THs) 3,5,3'-triiodothyronine (T3) and thyroxine (T4) were measured, and the transcription levels of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis and gamma-aminobutyric acid (GABA) synthesis were quantified. The results showed that 10μg/L SMC significantly increased whole-body T3 levels, and 100 and 1000μg/L SMC markedly enhanced whole-body T4 and T3 levels. Furthermore, 100μg/L SMC exposure shortened the time it took for flounder larvae to complete metamorphosis by 2 d as compared to the control group. Thus, this study demonstrated that SMC exerted thyroid-disrupting effects on Japanese flounder. SMC-mediated stimulation of TH levels was primarily related to transcriptional alterations of pituitary-derived thyroid stimulating hormone β-subunit (tshβ) and hepatic deiodinase (id). In the 10 and 100μg/L SMC exposure groups, the increased TH levels may have resulted from inhibition of TH metabolism caused by down-regulation of id3 mRNA expression, while at 1000μg/L SMC-exposed group, up-regulation of tshβ and id1 transcripts was expected to enhance the synthesis of T4 and the conversion of T4 to T3 and, consequently, result in higher T4 and T3 levels. In addition, 1000μg/L SMC-induced down-regulation in glutamic acid decarboxylase gad65 and gad67 transcription may have also contributed to the increased TH levels. The thyroid-disrupting effects of 10 and 100μg/L SMC indicated that environmentally relevant concentrations of SMC posed potential environmental risks to aquatic organisms. Overall, our results demonstrated for the first time that SMC exhibited thyroid-disrupting properties by affecting the HPT axis and GABA synthesis, providing theoretical support for environmental risk assessment.

Occurrence and levels of nitrofuran metabolites in sea cucumber from Dalian, China

The occurrence and levels of nitrofuran metabolites (NFMs) in sea cucumber (SC) from Dalian, China, are reported. Four metabolites including 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), 3-amino-2-oxazolidinone (AOZ), semicarbazide (SEM) and 1-aminohydantoin (AHD) in different SC products (fresh, instant and dry salted SCs) were measured. The frequency of occurrence for NFMs in all SC samples was 42.7%. The total NFM concentrations ranged from non-detectable to 64.6 ng g^-1, with a mean of 3.59 ng g^-1. AOZ and SEM were the dominant congeners, accounting for 40.1% and 59.1% of the total NFMs, respectively. The concentrations and patterns varied among different regions. Higher levels of NFMs were found in the fresh SC products, and the order for the average concentration of ∑₄NFM was fresh > dry salted > instant.

Anti-estrogenic effect of semicarbazide in female zebrafish (Danio rerio) and its potential mechanisms

Semicarbazide (SMC), a member of the hydrazine family, has various toxic effects and has been detected in organisms, aquatic environments, and food. SMC exposure inhibited the transcription of hepatic vitellogenin and estrogen receptors in female zebrafish (Danio rerio), suggesting that it had anti-estrogenic properties. In order to elucidate the mechanisms underlying these, we exposed female zebrafish to SMC and used enzyme-linked immunosorbent assays to examine plasma 17β-estradiol (E2) and testosterone (T) levels. Gonad histology was analyzed and the mRNA expression of genes involved in the reproductive axis, the gamma-aminobutyric acid (GABA) shunt, and leptin was quantified by real-time PCR. Zebrafish were exposed to 1, 10, 100, or 1000μg/L SMC in a semi-static system for 96hours or 28 days. Plasma E2 levels were significantly decreased and ovarian maturation was inhibited by SMC, suggesting that its anti-estrogenic effect was exerted by reducing endogenous E2 levels. This was likely due to the SMC-mediated inhibition of cytochrome P450 (CYP) 19A mRNA levels, because this enzyme catalyzes the conversion of T to E2 in the gonads. In addition, down-regulation of the mRNA expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase, steroidogenic acute regulatory protein, CYP17, and 17beta-hydroxysteroid dehydrogenase was observed; this was predicted to reduce T concentrations and further contribute to the reduced E2 levels. SMC-induced changes in the expression of these steroidogenic genes correlated with decreased transcription of gonadotropic hormones (follicle-stimulating hormone and luteinizing hormone) and significantly elevated leptin expression. Furthermore, SMC also altered expression of the key enzyme in gamma-aminobutyric acid (GABA) synthesis, GABA receptors, and salmon gonadotropin-releasing hormone, thus affecting gonadotropin expression. Overall, SMC acted at multiple sites related to reproduction to reduce plasma E2 levels, consequently exerting an anti-estrogenic effect in female zebrafish. These effects were observed at environmentally relevant concentrations and highlight the importance of controlling SMC contamination.

Residue depletion of nifuroxazide in broiler chicken

BACKGROUND

Several nitrofuran drugs have been prohibited for use in food producing animals due to their carcinogenic and mutagenic effects. However, one of the nitrofurans, nifuroxazide, is still used as a veterinary drug in some countries. This study was conducted to investigate the residue depletion of nifuroxazide in broiler chicken. Chickens were fed with dietary feeds containing 50 mg kg⁻¹ of nifuroxazide for seven consecutive days. Liver, kidney, muscle and plasma samples were collected at different withdrawal periods, and the residues of parent nifuroxazide and its acid-hydrolysable side chain, 4-hydroxybenzhydrazide (HBH), in these samples were determined.

RESULTS

Nifuroxazide was metabolised in vivo and its metabolite HBH was formed. Parent nifuroxazide was not detectable in these samples after 14 days of cessation. HBH was detectable in these samples even after 28 days of cessation and the total HBH residues were higher than 1.0 ng g⁻¹. Furthermore, the residue level of tissue bound HBH was much higher than that of free HBH.

CONCLUSION

The tissue-bound HBH could be used as a marker to monitor the residue of nifuroxazide in chicken and the best target tissue should be liver. This is the first paper reporting the residue depletion of nifuroxazide in chicken.

Multiresidue analysis of antibiotics in food of animal origin using liquid chromatography-mass spectrometry

Antibiotics are the most important drugs administered in veterinary medicine. Their use in food-producing animals may result in antibiotic residues in edible tissues, which are monitored to protect human and animal health, support the enforcement of regulations, provide toxicological assessment data, and resolve international trade issues. This chapter provides basic characterization of the most important classes of antibiotics used in food-producing animals (aminoglycosides, amphenicols, β-lactams, macrolides and lincosamides, nitrofurans, quinolones, sulfonamides, and tetracyclines), along with examples of practical liquid chromatographic-(tandem) mass spectrometric methods for analysis of their residues in food matrices of animal origin. The focus is on multiresidue methods that are favored by regulatory and other food testing laboratories for their ability to analyze residues of multiple compounds in a time- and cost-effective way.

Semicarbazide is non-specific as a marker metabolite to reveal nitrofurazone abuse as it can form under Hofmann conditions

Detecting illegal nitrofurazone treatment of food-producing animals has been undermined by the reliance on semicarbazide as a marker metabolite for analysis because, during processing, semicarbazide forms in a variety of foods not exposed to nitrofurazone by previously unexplained pathways. In this study, formation of semicarbazide was examined under dairy product processing conditions. Hypochlorite dosed into milk on an industrial scale, at concentrations extreme for unintentional residues, produced monochloramine, but, without pH adjustment, hypochlorite alone did not generate semicarbazide. Dosed hypochlorite and peroxyacetic acid each generated low ng g(-1) levels of semicarbazide in milk (and whey) only when used in conjunction with localised high pH conditions, which can occur during both anion exchange and neutralisation. Dosed hydroxyurea generated semicarbazide at any pH, with greatest levels formed at high pH. Detecting nitrofurazone abuse can be better accomplished by analysis either for nitrofurazone itself or for the marker metabolite 5-nitro-2-furaldehyde, rather than semicarbazide.

The identification of potential alternative biomarkers of nitrofurazone abuse in animal derived food products

Semicarbazide (SEM) was considered to be a characteristic protein-bound side-chain metabolite of the banned veterinary drug nitrofurazone and used as a marker of nitrofurazone abuse. It was recently discovered that SEM can arise in food from sources other than nitrofurazone. This uncertainty over the source of SEM may be overcome if alternative markers specific to tissue-bound nitrofurazone residues can be determined. The structure of nitrofurazone metabolites in vivo and particular proteins to which they are bound are not known. These proteins with altered structure due to the presence of the drug metabolites can be considered as potential alternative biomarkers of nitrofurazone abuse. The proteins implicated in the in vivo binding of nitrofurazone were separated and identified. A crude mixture of proteins extracted from the liver of a rat treated with the drug was separated using a series of different techniques such as preparative isoelectric focusing and size exclusion HPLC. Multiple fractions were assayed by LC-MS/MS to detect the presence of SEM. The proteins containing SEM residues were identified by peptide mass mapping using trypsin digestion and MALDI-TOF. The first protein identified as containing high concentration of SEM was albumin. It was also shown that low molecular weight species within a protein mixture whose main constituent was glutathione S-transferase contained a high concentration of SEM. The chemical composition of these components is under investigation. Preliminary data suggest the SEM forms part of a nitrofurazone metabolite conjugated to glutathione.

Enzyme immunoassay for semicarbazide—The nitrofuran metabolite and food contaminant

Semicarbazide (SEM), the marker residue for the banned nitrofuran veterinary antibiotic nitrofurazone (NFZ), has been detected regularly in foods (47% of recent nitrofuran EU Rapid Alerts involve SEM). However, the validity of SEM as a definitive marker for NFZ has been undermined by SEM arising from other sources including azodicarbonamide, a plastics blowing agent and flour treatment additive. An inexpensive screening test for SEM in food matrices is needed--all SEM testing currently uses expensive LC-MS/MS instrumentation. We now report the first production of antibodies against derivatised SEM. A novel carboxyphenyl SEM derivative was used to raise a polyclonal antibody that has been incorporated into a semi-quantitative microtitre plate ELISA, validated according to the criteria set out in Commission Decision 2002/657/EC, for use with chicken muscle. The antibody is highly specific for derivatised SEM, cross-reactivity being 1.7% with NFZ and negligible with a wide range of other nitrofurans and poultry drugs. Samples are derivatised with o-nitrobenzaldehyde and simultaneously protease digested before extraction by cation exchange SPE. The ELISA has a SEM detection capability (CCbeta) of 0.25 microg kg(-1) when a threshold of 0.21 microg kg(-1) is applied to the selection of samples for confirmation (lowest observed 0.25 microg kg(-1) fortified sample, n=20), thus satisfying the EU nitrofurans' minimum required performance limit of 1 microg kg(-1). NFZ-incurred muscles (12) containing SEM at 0.5-5.0 microg kg(-1) by LC-MS/MS, all screened positive by this ELISA protocol which is also applicable to egg and chicken liver.

Detection, accumulation and distribution of nitrofuran residues in egg yolk, albumen and shell

Nitrofuran antibiotics have been banned for use in food-producing animals in many countries, including the European Union, owing to the threat they pose to human health. Research continues into the accumulation of these drugs in animal tissues and into the appropriate methods for their detection. In this study, an LC-MS/MS method is presented for the detection of the parent compounds, furazolidone, nitrofurantoin, furaltadone and nitrofurazone, in eggs. The parent compounds are first extracted into ethyl acetate, fats are removed by partition between acetonitrile and hexane, and the concentrated sample is analysed by LC-MS/MS. Decision limits (CCalpha) for the parents were < or =1 microg kg-1 for all four compounds. Within-day and between-day CVs are well within the limits stated in Commission Decision 2002/657/EC. The method provides an alternative to the testing of side-chain metabolites in eggs, which is particularly important in the case of nitrofurazone, where semicarbazide contamination of food has been attributed to sources other than nitrofurazone use. This method was used together with a method for the detection of the side-chain metabolite compounds, 3-amino-2-oxazolidinone (AOZ), 3-amino-5-morpholinomethyl-1,3-oxazolidin-2-one (AMOZ), 1-amino-hydantoin (AHD) and semicarbazide (SEM), to study the accumulation and distribution of nitrofurans in eggs. Eggs were collected from four groups of hens that had been treated with one of the nitrofurans at a feed concentration of 300 mg kg-1 for 1 week. Parent compounds and metabolites were found in the yolk, albumen and shell. Albumen/yolk ratios for the parent compounds were 0.7, 0.82, 0.83 and 0.31 for furazolidone, furaltadone, nitrofurantoin and nitrofurazone, respectively. Ratios for the side-chain metabolites were 1.02, 1.06, 0.83 and 0.55 for AOZ, AMOZ, AHD and SEM, respectively. However, 50% of the total SEM residues were found in eggshell. This may be significant if eggshell products reach the consumer.