The food contaminant semicarbazide acts as an endocrine disrupter: Evidence from an integrated in vivo/in vitro approach

Investigation of the conversion mechanism of endogenous semicarbazide in shrimp on the amino acid level

Semicarbazide (SEM), the metabolite of antibiotic nitrofurazone, is often used as the biomarker to determine the use of nitrofurazone. Frequent false-positive events of SEM have brought great trouble to the aquatic industry in international trade. In this paper, the situation of endogenous SEM in aquatic products was investigated, and the possible mechanism of amino acid conversion into SEM was studied by establishing a simulated oxidation system and a urea system. The results revealed the presence of endogenous SEM in the muscle tissue of shrimps, and the content of SEM ranged from 0.56 to 5.28 ng/g, which presented as Macrobrachium nipponense>Macrobrachium rosenbergii>Procambarus clarkii. The increase in SEM production of control lysine under natural oxidation conditions suggests that oxidation has an effect on the conversion of SEM. Under the action of the simulated oxidation system, the SEM of Arginine, Lysine, Citrulline and Glutamine among the 21 amino acids were increased, and the polymer azine was formed. In combination with the structure of four amino acids, it was presumed that the group of amide is a key intermediate structure for the formation of endogenous SEM. In addition, under the urea system, the content of SEM produced by amino acids increased after the addition of urea, and the concentration of urea had a significant correlation with the content of SEM. Taken together, the production of endogenous SEM in shrimps is related to amino acids and urea, and the urea cycle and other substances containing amide structures should also be considered in future explorations.

Chromaticity Evolutionary Detection of Food Contaminant Semicarbazide through an Upconversion Luminescence-Based Nanosensor

Semicarbazide (SEM) is a widespread carcinogenic and neurotoxic food contaminant, originating from the metabolite of antibiotic nitrofurazone, which is used in aquaculture, or thermal decomposition byproduct of a flour blowing agent azodicarbonamide. Although optical detection technologies are powerful tools considering the advantages of fast response and visualization detection, there are few optical nanosensors for highly sensitive and visual assays of SEM due to no luminescence response and UV absorbance of SEM. Herein, an upconversion luminescence (UCL)-based nanosensor was designed for visual detection of SEM with high sensitivity and good selectivity. The nanosensor was constructed by combining upconversion nanoparticles (UCNPs) and phosphomolybdic acid (PMA), which was used as the specific recognition element of SEM. The developed nanosensor exhibited selective absorbance enhancement and UCL quenching behavior with the addition of SEM based on the inner filter effect (IFE). Since the change in absorbance translated into an exponential change in the luminescence, the sensitivity of the nanosensor was greatly improved. The nanosensor realized a highly sensitive and visual response to SEM in the linear range of 0.5-16 μM with a low limit of detection of 58 nM. Moreover, satisfactory recovery values ranging from 90 to 112% in spiked real samples indicated the practical applicability of the nanosensor. The nanosensor designed here provides a sensitive and convenient sensing strategy for visual detection of hazardous substances and is expected to develop the upconversion sensing application in food safety.

Determination of semicarbazide residue in human urine samples using liquid chromatography-tandem mass spectrometry

An ultra-performance liquid chromatography coupled with electrospray ionisation tandem mass spectrometry (UPLC-ESI-MS/MS) with pre-column derivatisation was developed and validated for the determination of semicarbazide in human urine. Urine samples were derivatised with 2-nitrobenzaldehyde and subsequently extracted with acetonitrile. Extracts were concentrated and then analysed by UPLC-MS/MS. The time per run was 7 min. Good results were observed for the linearity of matrix-matched calibration curves (R² > 0.99) in the concentration range of 1-100 µg/L. The absolute recovery ranged from 98.7% to 108.6%, with the relative standard deviations (RSDs) of 2.2%-3.6%. The limit of detection and quantification for the semicarbazide was 0.5 µg/L and 1 µg/L, respectively. The method showed good extraction efficiency, high sensitivity, and good reproducibility. It was suitable for the detection of semicarbazide in human urine. Residues of semicarbazide were between 1.0 and 41.5 μg/L in children's 24-h urine. This work is the first report on the quantitative analysis of SEM in 24-h human urine samples.

Herbicides glyphosate and glufosinate ammonium negatively affect human sperm mitochondria respiration efficiency

The widespread cultivation of genetically modified organisms (GMOs) led to a widespread use of selective herbicides to which GMOs are resistant, thus increasing the concern about human exposure to them. Glyphosate (GLY) and glufosinate ammonium (GA), the active principles of the main formulations, have been investigated for their effects on human health, mainly cancer and reproductive toxicity. However, little is known about their effects on the molecular mechanisms related to sperm quality. To investigate the effects of GLY and GA on mitochondrial respiration efficiency, we took advantage of our already established ex vivo human sperm mitochondria assay. Since spermatozoa are highly regulated by sex steroids, we tested at first testosterone (T), di-hydroxytestosterone (DHT), 17β-estradiol (E2) and progesterone (P4). Then, we tested the effects of GLY and GA and of the hormone-like flavonoid quercetin (QRC) in a dose-dependent manner. The 0.1-1000 nM concentration range has been considered because it covers both the sexual hormones physiologically relevant concentrations (10 nM), triggering endogenously hormone-dependent signaling pathways, and the estimated (nM range) QRC dietary intake. Subsequently, co-incubation experiments were carried out with the two herbicides in the presence of 10 nM of each sex steroid and QRC. We found that: i) DHT and QRC are able to significantly reduce mitochondrial functionality at concentrations ≥ 10 nM; ii) GLY and GA negatively affect mitochondrial respiration efficiency; iii) in the presence of 10 nM DHT, the negative effect of GLY was increased; iiii) DHT, QRC and GA target mitochondria by using a mechanism different from GLY.

Food-added azodicarbonamide alters haematogical parameters, antioxidant status and biochemical/histomorphological indices of liver and kidney injury in rats

OBJECTIVES

Azodicarbonamide (ADA) is a dough enhancer currently used as a replacement for potassium bromate in the process of bread-making in countries such as Nigeria. However, comprehensive information on the toxicological profile of ADA is not readily available. The present study investigated the toxicological effects of ADA in rats.

METHODS

Twenty-four adult rats were randomly assigned into four groups of six rats each. Animals in group A served as the control (administered standard diet), whereas animals in groups B, C and D were fed ADA in food at 1, 2 and 4%, respectively. Standard or ADA diet was fed to the animals daily for a period of 28 days. Body weight was measured weekly, whereas food and water consumption was measured daily. On day 28, animals were fasted overnight after which they were euthanised. Blood samples taken were used for assessment of fasting blood glucose, haematological parameters, serum lipids, antioxidant status, lipid peroxidation status, electrolytes and urea, plasma proteins and biochemical parameters of liver and kidney injury. The liver and kidneys were then excised and processed for general histological study.

RESULTS

The results showed that repeated administration of ADA was associated with dose-related decrease in weight gain, decrease in overall food consumption, decreased superoxide dismutase activity/glutathione level and increased lipid peroxidation. There was also biochemical and morphological evidence of liver and kidney injury.

CONCLUSIONS

These findings suggest that food-added ADA could be injurious to the body cells and organs in rats.

Methylxanthines Inhibit Primary Amine Oxidase and Monoamine Oxidase Activities of Human Adipose Tissue

Background: Methylxanthines including caffeine and theobromine are widely consumed compounds and were recently shown to interact with bovine copper-containing amine oxidase. To the best of our knowledge, no direct demonstration of any interplay between these phytochemicals and human primary amine oxidase (PrAO) has been reported to date. We took advantage of the coexistence of PrAO and monoamine oxidase (MAO) activities in human subcutaneous adipose tissue (hScAT) to test the interaction between several methylxanthines and these enzymes, which are involved in many key pathophysiological processes. Methods: Benzylamine, methylamine, and tyramine were used as substrates for PrAO and MAO in homogenates of subcutaneous adipose depots obtained from overweight women undergoing plastic surgery. Methylxanthines were tested as substrates or inhibitors by fluorimetric determination of hydrogen peroxide, an end-product of amine oxidation. Results: Semicarbazide-sensitive PrAO activity was inhibited by theobromine, caffeine, and isobutylmethylxanthine (IBMX) while theophylline, paraxanthine, and 7-methylxanthine had little effect. Theobromine inhibited PrAO activity by 54% at 2.5 mM. Overall, the relationship between methylxanthine structure and the degree of inhibition was similar to that seen with bovine PrAO, although higher concentrations (mM) were required for inhibition. Theobromine also inhibited oxidation of tyramine by MAO, at the limits of its solubility in a DMSO vehicle. At doses higher than 12 % v/v, DMSO impaired MAO activity. MAO was also inhibited by millimolar doses of IBMX, caffeine and by other methylxanthines to a lesser extent. Conclusions: This preclinical study extrapolates previous findings with bovine PrAO to human tissues. Given that PrAO is a potential target for anti-inflammatory drugs, it indicates that alongside phosphodiesterase inhibition and adenosine receptor antagonism, PrAO and MAO inhibition could contribute to the health benefits of methylxanthines, especially their anti-inflammatory effects.

Determination of 5-nitro-2-furaldehyde as marker residue for nitrofurazone treatment in farmed shrimps and with addressing the use of a novel internal standard

We developed a significantly improved ultra-high performance liquid chromatography-tandem mass spectrometry method for determination of 5-nitro-2-furaldehyde (NF) as a surrogate using a novel internal standard for the detection of nitrofurazone. We used 2,4-dinitrophenylhydrazine derivatization and furfural as the internal standard. Derivatization was easily performed in HCl using ultrasonic manipulation for 5 min followed by liquid extraction using ethyl acetate. The samples were concentrated and purified using reverse phase and alumina cartridges in tandem. The derivatives were separated using a linear gradient elution on a C₁₈ column with methanol and water as the mobile phase in negative ionization mode and multiple reaction monitoring. Under the optimized conditions, the calibration curves were linear from 0.2 to 20 μg/L with correlation coefficients >0.999. Mean recoveries were 80.8 to 104.4% with the intra- and inter-day relative standard deviations <15% at spiking levels of 0.1 to 10 μg/kg. The limits of detection and quantification were 0.05 and 0.1 μg/kg, respectively. This method is a robust tool for the identification and quantitative determination of NF in shrimp samples.

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.

The anti-estrogenicity of chronic exposure to semicarbazide in female Japanese flounders (Paralichthys olivaceus), and its potential mechanisms

This study investigated the anti-estrogenic effects of chronic exposure to a new marine pollutant, semicarbazide (SMC; 1, 10, and 100μg/L), in female Paralichthys olivaceus, as well as the associated mechanism. After 130days of exposure, plasma 17β-estradiol and testosterone concentrations, and hepatic estrogen receptors, vitellogenin, and choriogenin mRNA levels decreased significantly in SMC-exposed groups. Moreover, down-regulation of genes in the hypothalamic-pituitary-gonadal axis, including gonadotropin-releasing hormone, gonadotropic hormones and their receptors, the steroidogenic acute regulatory protein, 17α-hydroxylase, 17β-hydroxysteroid dehydrogenase, and cytochrome P450 19A, was observed after SMC exposure. Furthermore, the kisspeptin/g protein-coupled receptor 54 (kiss/gpr54) system and gamma-aminobutyric acid-ergic (GABAergic) system were also affected by SMC: SMC significantly down-regulated mRNA expression of kiss2, gpr54, and the GABA synthesis enzyme gad67. Our results demonstrated for the first time that environmentally relevant concentrations of SMC exerted anti-estrogenicity in female flounders, providing theoretical support for ecological risk assessments of SMC in marine environments.

Re-evaluation of carrageenan (E 407) and processed Eucheuma seaweed (E 407a) as food additives

The present opinion deals with the re-evaluation of the safety of food-grade carrageenan (E 407) and processes Eucheuma seaweed (E 407a) used as food additives. Because of the structural similarities, the Panel concluded that processed Eucheuma seaweed can be included in the evaluation of food-grade carrageenan. Poligeenan (average molecular weight 10-20 kDa) has not been authorised as a food additive and is not used in any food applications. In its evaluation of carrageenan (E 407) and processed Eucheuma seaweed (E 407a), the Panel noted that the ADME database was sufficient to conclude that carrageenan was not absorbed intact; in a subchronic toxicity study performed with carrageenan almost complying with the EU specification for E 407 in rats, the no-observed-adverse-effect level (NOAEL) was 3,400-3,900 mg/kg body weight (bw) per day, the highest dose tested; no adverse effects have been detected in chronic toxicity studies with carrageenan in rats up to 7,500 mg/kg bw per day, the highest dose tested; there was no concern with respect to the carcinogenicity of carrageenan; carrageenan and processed Eucheuma seaweed did not raise a concern with respect to genotoxicity; the NOAEL of sodium and calcium carrageenan for prenatal developmental dietary toxicity studies were the highest dose tested; the safety of processed Eucheuma seaweed was sufficiently covered by the toxicological evaluation of carrageenan; data were adequate for a refined exposure assessment for 41 out of 79 food categories. However, the Panel noted uncertainties as regards the chemistry, the exposure assessment and biological and toxicological data. Overall, taking into account the lack of adequate data to address these uncertainties, the Panel concluded that the existing group acceptable daily intake (ADI) for carrageenan (E 407) and processed Eucheuma seaweed (E 407a) of 75 mg/kg bw per day should be considered temporary, while the database should be improved within 5 years after publication of this opinion.

Endocrine Disrupters and the Safety of Food Chains

Endocrine disrupters (ED) are a heterogeneous group of chemicals including persistent contaminants, pesticides, as well as compounds present in consumer products and natural substances. For most ED, the food chain is a current major exposure route for the general population. ED can enter the food chain through the living environment (e.g., feeds, fertilizers) of food-producing organisms, be directly employed in food production (e.g., pesticides) or be released from food contact materials (such as bisphenol A or phthalates); in addition, the endocrine disruption potential of some natural compounds in edible plants, including the so-called phytoestrogens, should not be overlooked. An exposure assessment has to consider the specific liability of food commodities to contamination with specific ED (e.g., polychlorinated and polybrominated chemicals in lipid-rich foods). The paper discusses the main toxicological research issues in order to support the risk assessment of ED in food chains, including: the potential for additive, 'cocktail' effects (as from multiple pesticide residues); the long-term effects on target body systems (e.g., reproductive, nervous) elicited by exposure during prenatal as well as postnatal life stage windows, and toxicant/nutrient interactions (e.g., thyroid-targeting ED and iodine status). Food safety systems should exploit the available knowledge to improve prevention of long-term risks along the whole food chain.

Semicarbazide disturbs the reproductive system of male zebrafish (Danio rerio) through the GABAergic system

Semicarbazide (SMC), an emerging water contaminant, exerts anti-estrogenic effects in female zebrafish. However, the exact influence of SMC on male reproduction remains unclear. In this study, adult male zebrafish were exposed to 1-1000μg/L SMC in a semi-static system for 28 d prior to examining the testicular somatic index (TSI), testis histology, plasma sex hormone levels, and the transcription of genes involved in reproduction. The results showed that testicular morphology was altered and TSI was down-regulated by high concentrations of SMC (≥100μg/L and 1000μg/L, respectively). Plasma testosterone and 17β-estradiol concentrations were significantly decreased by all of the SMC treatments, along with down-regulation of the corresponding steroidogenic gene transcripts. These changes were associated with the inhibition of gamma-aminobutyric acid synthesis and function, in addition to the decreased expression of reproductive regulators. Our results contribute to elucidating the mechanisms underlying the adverse reproductive effects of SMC in male zebrafish.

In silico prediction and in vivo analysis of antiestrogenic potential of 2-isopropylthioxanthone (2-ITX) in juvenile goldfish (Carassius auratus)

Previous studies have shown both anti-estrogenic and anti-androgenic activities of 2-isopropylthioxanthone (2-ITX), a well known food contaminant, in in vitro assays. However, no data are available on the anti-estrogenic potentials and risks of 2-ITX in aquatic organisms. This work evaluated the potential endocrine disrupting effects of 2-ITX at the level of estrogen receptor (ER) signaling cascade using juvenile goldfish (Carassius auratus) as model. Firstly, we investigated the ligand binding efficiency of 2-ITX to the ligand binding domains (LBD) of goldfish ER subtypes using a molecular docking approach. Secondly, we assessed the effects of 2-ITX on E2-induced hepatic expression of ERα1, ERβ1, ERβ2, and vitellogenin (VTG) in vivo. Crosstalk between ER-VTG and aryl hydrocarbon receptor 2 (AhR2)-cytochrome P4501A (CYP1A) was also investigated. Fish were injected with increasing doses of 2-ITX ranging from 2 to 10µg/g BW, and results were compared to the effect of tamoxifen, a well-known ER modulator. We observed that compared to ERβ, the interaction potentials of 2-ITX to goldfish ERα1 LBD was more stable in the inactive receptor conformation. The in silico docking simulation analysis also revealed that 2-ITX acted as agonist for the goldfish AhR2 LBDs suggesting the ability of this compound to activate the cross-talk between the ERα- and AhR-signaling pathways. In vivo experiments confirm in silico simulation predictions demonstrating that 2-ITX reduced the estrogenicity of E2 at both transcriptional and post-transcriptional levels, indicating a clear anti-estrogenic effect. Co-exposure of E2 and 2-ITX also resulted in a significant decrease of CYP1A gene expression with respect to 2-ITX alone. Results from these studies collectively revealed that the antiestrogenic property of 2-ITX can be ascribed to a combination of effects on multiple signaling pathways suggesting the potential for this environmental contaminant to affect the hormonal control of reproductive processes in fish.

Automated In-Injector Derivatization Combined with High-Performance Liquid Chromatography-Fluorescence Detection for the Determination of Semicarbazide in Fish and Bread Samples

Semicarbazide (1) is a widespread genotoxic food contaminant originating as a metabolic byproduct of the antibiotic nitrofurazone used in fish farming or as a thermal degradation product of the common flour additive azodicarbonamide. The goal of this study is to develop a simple and sensitive high-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) method for the detection of compound 1 in food products. In comparison to existing methods for the determination of compound 1, the reported method combining online precolumn derivatization and HPLC-FLD is less labor-intensive, produces higher sample throughput, and does not require the use of expensive analytical instruments. After validation of accuracy and precision, this method was applied to determine the amount of compound 1 in fish and bread samples. Comparative studies using an established liquid chromatography coupled with tandem mass spectrometry method did not yield systematically different results, indicating that the developed HPLC-FLD method is accurate and suitable for the determination of compound 1 in fish and bread samples.

The Deep Correlation between Energy Metabolism and Reproduction: A View on the Effects of Nutrition for Women Fertility

In female mammals, mechanisms have been developed, throughout evolution, to integrate environmental, nutritional and hormonal cues in order to guarantee reproduction in favorable energetic conditions and to inhibit it in case of food scarcity. This metabolic strategy could be an advantage in nutritionally poor environments, but nowadays is affecting women's health. The unlimited availability of nutrients, in association with reduced energy expenditure, leads to alterations in many metabolic pathways and to impairments in the finely tuned inter-relation between energy metabolism and reproduction, thereby affecting female fertility. Many energetic states could influence female reproductive health being under- and over-weight, obesity and strenuous physical activity are all conditions that alter the profiles of specific hormones, such as insulin and adipokines, thus impairing women fertility. Furthermore, specific classes of nutrients might affect female fertility by acting on particular signaling pathways. Dietary fatty acids, carbohydrates, proteins and food-associated components (such as endocrine disruptors) have per se physiological activities and their unbalanced intake, both in quantitative and qualitative terms, might impair metabolic homeostasis and fertility in premenopausal women. Even though we are far from identifying a "fertility diet", lifestyle and dietary interventions might represent a promising and invaluable strategy to manage infertility in premenopausal women.

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.

Identification and occurrence of endogenous semicarbazide in prawns and crabs from Zhejiang Province, China

Semicarbazide (SEM) is a side-chain metabolite of the antibiotic drug nitrofurazone (NFZ) and is employed as a conclusive marker for the use of banned NFZ. Recent studies have shown that SEM in aquatic crustaceans can be derived natively or from other sources. The presence and distribution of endogenous SEM within aquatic crustaceans is examined in this paper, which finds that the SEM content varies amongst the muscle, shell, and viscera of various prawn and crab species within the range of 0.35-26.62 ng g(-1). The effects of heating and hypochlorite treatment on SEM levels were examined. The results indicate that thermal processing introduced a more significant impact, resulting in a maximum SEM value of 15.48 ng g(-1) in a sample of shell of Portunus trituberculatus crab, while SEM levels in muscle samples were not affected by the duration of heating. Though 6% active chlorine treatment led to SEM production ranging between 39.9 and 196.4 ng g(-1) in muscle samples from various crustaceans, SEM is unlikely to originate from hypochlorite or chlorine in practice where there are limits to actual chlorine in sanitation water and facilities. 5-Nitro-2-furaldehyde (NF) was proposed as a selective marker to differentiate between endogenous SEM and NFZ-derived SEM in seafood.

Estrogenic endocrine disruptors: Molecular mechanisms of action

A comprehensive summary of more than 450 estrogenic chemicals including estrogenic endocrine disruptors is provided here to understand the complex and profound impact of estrogen action. First, estrogenic chemicals are categorized by structure as well as their applications, usage and effects. Second, estrogenic signaling is examined by the molecular mechanism based on the receptors, signaling pathways, crosstalk/bypassing and autocrine/paracrine/homeostatic networks involved in the signaling. Third, evaluation of estrogen action is discussed by focusing on the technologies and protocols of the assays for assessing estrogenicity. Understanding the molecular mechanisms of estrogen action is important to assess the action of endocrine disruptors and will be used for risk management based on pathway-based toxicity testing.

[Effect of semicarbazide on the peroxidation processes and Lewis carcinoma growth in mice]

Effects of various doses of semicarbazide on Lewis carcinoma metastasing and peroxidation processes in C57B1 mice have been investigated. In the animals with inoculated Lewis carcinoma, the semicarbazide in the dose of 1/120 LD50 had practical influence on the tumour growth and inhibited the metastasing into mice lungs (P < 0.05). Importantly, this dose significantly inhibited the formation of free radicals and active forms of oxygen against the background of decrease of the aldehydes level that was related to the acceptor properties of the drug.

An emerging water contaminant, semicarbazide, exerts an anti-estrogenic effect in zebrafish (Danio rerio)

To determine the endocrine disrupting effect of semicarbazide, an emerging water contaminant, the changes in transcript levels of hepatic estrogen-response genes including vitellogenin-1 (vtg-1), estrogen receptor α (ERα), and estrogen receptor β (ERβ) were measured in male and female zebrafish exposed to semicarbazide with or without exogenous 17β-estradiol (E2). Exposure of male zebrafish to semicarbazide for 96 h or 28 days resulted in no significant induction in hepatic vtg-1, ERα, or ERβ mRNA expression, indicating that semicarbazide has no estrogenic effect. However, a remarkable anti-estrogenic effect of semicarbazide was demonstrated: semicarbazide treatment of female zebrafish for 96 h and 28 days resulted in significant decreases in transcript levels of vtg-1, ERα, and ERβ, as well as decreases in the gonadosomatic index level after 28 days. Moreover, semicarbazide exposure significantly inhibited the induction of vtg-1, ERα and ERβ mRNA by E2 when male zebrafish were co-exposed for 28 days.

Puberty dysregulation and increased risk of disease in adult life: possible modes of action

Puberty is the developmental window when the final maturation of body systems is orchestrated by hormones; lifelong sex-related differences and capacity to interact with the environment are defined during this life stage. Increased incidence in a number of chronic, multifactorial diseases could be related to environmental exposures during puberty: however, insight on the susceptibility of the peripubertal period is still limited. The estrogen/androgen balance is a crucial axis in harmonizing the whole pubertal development, pointing out the significance of exposures to endocrine disruptors. Besides the reproductive system, endocrine-related perturbations may affect the maturation of skeleton, adipose tissues, brain, immune system, as well as cancer predisposition. Thus, risk assessment of environmental stressors should duly consider specific aspects of the pubertal window. Besides endocrine-related mechanisms, suggested research priorities include signaling molecules (e.g., kisspeptins, dopamine) as xenobiotic targets and disturbances of specific pubertal methylation processes potentially involved in neurobehavioral disorders and cancer risk in adulthood.

Semicarbazide in Selected Bird's Nest Products

Currently, a number of food producers use hypochlorite to bleach food and inhibit the growth of bacteria, preserving the food. Because the presence of high amounts of nitrogen could result in the formation of semicarbazide (SEM), the bleaching process could be one of the predominant sources of SEM in food. To investigate this, we selected instant bottled bird's nest as an example of a food that is bleached in its production. SEM was detected in 27 of 28 instant bottled bird's nest samples. The levels of SEM detected mostly fell in the range of 5 to 50 μg/kg, which accounted for 75% of all samples measured. The SEM detected in the instant bottled bird's nest was found to have originated neither from the use of the antimicrobial agent nitrofurazone nor from azodicarbonamide, which is used as a blowing agent in gaskets used to seal the metal lid of the bottle. Instead, it could have originated from the bleaching process used in the preparation of the nests. Additionally, human exposure to SEM via consumption of instant bottled bird's nest for five subgroups of the population was estimated. Sensitivity analysis suggested that concentration of SEM in food is the most significant parameter governing human exposure via consumption of SEM-containing food.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

Oral Administration of Semicarbazide Limits Weight Gain together with Inhibition of Fat Deposition and of Primary Amine Oxidase Activity in Adipose Tissue

An enzyme hitherto named semicarbazide-sensitive amine oxidase (SSAO), involved in the oxidation of primary amines, is abundantly expressed in adipocytes. Although SSAO physiological functions remain unclear, several molecules inhibiting its activity have been described to limit fat accumulation in preadipocyte cultures or to reduce body weight gain in obese rodents. Here, we studied whether oral administration of semicarbazide, a prototypical SSAO inhibitor, limits fat deposition in mice. Prolonged treatment with semicarbazide at 0.125% in drinking water limited food and water consumption, hampered weight gain, and deeply impaired fat deposition. The adiposomatic index was reduced by 31%, while body mass was reduced by 15%. Such treatment completely inhibited SSAO, but did not alter MAO activity in white adipose tissue. Consequently, the insulin-like action of the SSAO substrate benzylamine on glucose transport was abolished in adipocytes from semicarbazide-drinking mice, while their insulin sensitivity was not altered. Although semicarbazide is currently considered as a food contaminant with deleterious effects, the SSAO inhibition it induces appears as a novel concept to modulate adipose tissue development, which is promising for antiobesity drug discovery.