Investigation into the possible natural occurence of semicarbazide in Macrobrachium rosenbergii prawns

Research progress on metabolites of nitrofurazone in aquatic products

The carcinogenic and teratogenic risks of nitrofurazone (NFZ) led to its restriction in aquatic products. Semicarbazide (SEM), one of its metabolites, is a primary focus of modern monitoring techniques. However, the SEM residue in aquatic products is believed to be formed through endogenous mechanisms, especially for aquatic crustaceans. In this article, we will discuss the source of SEM, including its usage as an antibiotic in aquatic products (nitrofurazone), its production during food processing (azodicarbonamide and hypochlorite treatment), its occurrence naturally in the body, and its intake from the environment. SEM detection techniques were divided into three groups: derivatization, extraction/purification, and analytical methods. Applications based on liquid chromatography and its tandem mass spectrometry, immunoassay, and electrochemical methods were outlined, as were the use of various derivatives and their assisted derivatization, as well as extraction and purification techniques based on liquid-liquid extraction and solid-phase extraction. The difficulties of implementing SEM for nitrofurazone monitoring in aquatic products from crustaceans are also discussed. Possible new markers and methods for detecting them are discussed. Finally, the present research on monitoring illicit nitrofurazone usage through its metabolites is summarised, and potential problems that need to be overcome by continuing research are proposed with an eye toward giving references for future studies.

Depletion kinetics of semicarbazide in giant river prawn (Macrobrachium rosenbergii) following nitrofurazone oral administration and its occurrence in an aquaculture farm

Semicarbazide (SEM), a marker residue used to monitor the use of prohibited drug nitrofurazone (NFZ), is commonly found in wild crustaceans, implying the natural origin. However, the difference between endogenous and exogenous SEM has rarely been investigated. So, tissue-bound SEM was determined in samples collected from giant river prawns cultured in an aquaculture farm and in samples from an experiment where giant river prawns were fed twice a day with NFZ at 30 mg/kg for 5 days. At day 10 of drug withdrawal, muscle SEM of the NFZ-fed prawn was 17.78 ng/g and depleted to 1.18 ng/g at day 90 (half-life 20.31 days) which was significantly higher than the control prawn (usually ≤ 0.1 ng/g). In contrast, the average SEM in the shell was independent of NFZ treatment. SEM was not found in the aquaculture farm samples, implying that the SEM in cultured prawn did not originate from SEM contamination.

The presence of semicarbazide in crustaceans collected from natural habitats in Thailand

Semicarbazide (SEM) has been used as a marker residue of the banned veterinary drug nitrofurazone (NFZ). Although evidence indicates that SEM can be found in some natural crustaceans that have never been exposed to NFZ, such information is limited to a few species. The present study aimed to investigate the natural occurrence of SEM in wild crustaceans in Thailand. A total of 14 species, all economically important food animals, were captured from different regions of Thailand. Tissue-bound SEM and its parent drug NFZ were determined by the UPLC-MS/MS and LC-MS methods, respectively. The results showed that while NFZ was not detected in any samples, the tissue-bound SEM could be found in every natural crustacean species investigated. However, the prevalence and concentration varied greatly. The occurrence of SEM in the freshwater palaemonid Macrobrachium prawns is generally much higher than in the marine penaeid shrimps/prawns. SEM was found in 33% and 80% of the giant river prawn (Macrobrachium rosenbergii) muscles (<0.10-0.46 ng/g) and shells (3.68-13.22 ng/g), respectively. In contrast, SEM was not detected in the muscles of penaeid shrimps/prawns (with few exceptions), but it was occasionally found in the shells at low levels (usually <1 ng/g). The shells of saltwater crabs also contained higher levels of SEM than the muscles. For instance, the highest SEM levels detected in the mud crab (Scylla sp.) muscles and shells were 0.40 and 22.75 ng/g, respectively. However, the situation was reversed for the rice-field crab (Sayamia sp. and Esanthelphusa sp.), in which SEM was not detected in all shells but detected in the muscles (up to 1.46 ng/g). The fact that SEM is often found in wild crustaceans implies a natural origin of this substance. Consequently, using SEM as a marker residue of NFZ is controversial and should be reconsidered.

Synthesis and spectroscopic characterization of 13 C4 -labeled 4-cyano-2-oxobutyraldehyde semicarbazone: A metabolite of nitrofurazone

Nitrofurazone usage in food-producing animals is prohibited in most countries, including the United States. Regulatory agencies regularly monitor its use in domestic, export/import animals' food products by measuring the semicarbazide (SEM) metabolite as a biomarker of nitrofurazone exposure. However, the use of SEM is controversial because it is also produced in food naturally and thus gives false positive results. A cyano-metabolite, 4-cyano-2-oxobutyraldehyde semicarbazone (COBS), is proposed as an alternate specific marker of nitrofurazone to distinguish nitrofurazone from treated or untreated animals. A synthetic method was developed to produce COBS via metallic hydrogenation of nitrofurazone. The product was isolated and characterized by one- and two-dimensional nuclear magnetic spectroscopy (NMR) experiments, Fourier-transform infrared spectroscopy (FT-IR), and mass spectrometry. The developed synthetic procedure was further extended to synthesize isotopically labeled 4-[13 C]-cyano-2-oxo- [2, 3, 4-13 C3 ]-butyraldehyde semicarbazone. Labeled COBS is useful as an internal standard for its quantification in food-producing animals. Thus, the developed method provides a possibility for its commercial synthesis to procure COBS. This is the first synthesis of the alternate specific marker metabolite of nitrofurazone for possible usage in regulatory analysis to solve a real-world problem.

Facile synthesis of 14 C-nitrofurazone from 14 C-urea

The veterinary drug nitrofurazone (5-nitro-2-furaldehyde semicarbazone) exhibits excellent antimicrobial properties but its application in food-producing animals is prohibited. The illegal use of nitrofurazone is regularly monitored by food regulatory agencies. Currently, semicarbazide (SEM) is used as a marker of nitrofurazone exposure. However, the use of SEM as a marker of nitrofurazone is under scrutiny after evidence of a high incidence of false positive tests. To overcome the current dilemma, it is necessary to identify a nitrofurazone-specific marker analyte which requires conducting nitrofurazone metabolism studies in food-producing animals. The use of carbon-14 labeled nitrofurazone would facilitate metabolism studies and structural elucidation of nitrofurazone metabolites of possible utility as a marker compound. In the present work, a synthetic method is described to procure radiolabeled nitrofurazone that incorporates 14 C- carbon at the semicarbazide moiety. The method incorporates 14 C-carbon via employing readily available and more economically affordable [14 C]-urea compared with [14 C]-semicarbazide. To the best of our knowledge, there is no report on the synthesis of 5-nitro-2-furaldehyde [14 C]-semicarbazone from 14 C-urea. The developed method involves monoamination of [14 C]-urea followed by a condensation reaction with 5-nitro-2-furaldehyde to produce 5-nitro-2-furaldehyde [14 C]-semicarbazone in 85% yield with greater than 98% radiochemical purity.

Survey of Meat Collected from Commercial Broiler Processing Plants Suggests Low Levels of Semicarbazide Can Be Created during Immersion Chilling

ABSTRACT

Semicarbazide (SEM) is routinely employed as an indicator for the use of nitrofurazone, a banned antimicrobial. The validity of SEM as a nitrofurazone marker has been scrutinized because of other possible sources of the compound. Nonetheless, a U.S. trade partner rejected skin-on chicken thighs because of SEM detection and suspected nitrofurazone use. Because nitrofurazone has been banned in U.S. broiler production since 2003, we hypothesized that incidental de novo SEM formation occurs during broiler processing. To assess this possibility, raw leg quarters were collected from 23 commercial broiler processing plants across the United States and shipped frozen to our laboratory, where liquid chromatography-mass spectrometry was used to quantitatively assess for SEM. Leg quarter samples were collected at four points along the processing line: hot rehang (transfer from the kill line to the evisceration line), prechill (before the chilling process), postchill (immediately following chilling), and at the point of pack. Thigh meat with skin attached was removed from 535 leg quarters and analyzed in triplicate for SEM concentrations. The concentrations ranged from 0 to 2.67 ppb, with 462 (86.4%) of 535 samples below the regulatory decision level of 0.5 ppb of SEM. The 73 samples over the 0.5-ppb limit came from 21 plants; 53 (72.6%) of positive samples were in meat collected after chilling (postchill or point of pack). The difference in both prevalence and concentration of SEM detected before and after chilling was highly significant (P < 0.0001). These data support our hypothesis that SEM detection in raw broiler meat is related to de novo creation of the chemical during processing.

HIGHLIGHTS

Presence of nitrofurans and their metabolites in gelatine

Following the detection of semicarbazide (SEM) in gelatine by Italian Authorities, at levels exceeding by three times the reference point for action (RPA) of 1 μg/kg, set out by Commission Regulation (EU) 2019/1871 for nitrofurans and their metabolites, the European Commission mandated EFSA to investigate the available sources of nitrofurans and their metabolites in gelatine. European Commission also asked EFSA to provide approaches that would distinguish SEM occurring due to illegal treatment with nitrofurazone from SEM produced during food processing. The literature indicates that SEM, both free and bound to macromolecules, could occur also in food products such as gelatine, during food processing, arising from the use of disinfecting agents and/or from reactions of various food components and, therefore, SEM cannot be considered as an unequivocal marker of the abuse of nitrofurazone in animal production. It is recommended to investigate in more detail which processing conditions lead to the formation of SEM in gelatine during its production and what levels can be found. One potential approach to distinguishing between SEM from nitrofurazone and SEM from other sources in food products, such as gelatine, might be based on determining the ratio of bound:free SEM in a sample of gelatine. However, whether the ratio of bound:free SEM would unequivocally distinguish between SEM arising from nitrofurazone abuse or from other sources still needs to be demonstrated.

Semicarbazide Accumulation, Distribution and Chemical Forms in Scallop (Chlamys farreri) after Seawater Exposure

Simple Summary

Semicarbazide is considered the characteristic metabolite of nitrofurazone and it is often used as a marker to monitor the illegal use of nitrofurazone in foods. Recent studies have indicated that semicarbazide pollution can be introduced in many ways and this compound is a newly recognized pollutant type in the environment that accumulates in aquatic organisms throughout the food chain. Scallops are the third most consumed shellfish in China. We therefore studied the accumulation, chemical forms, and distribution of semicarbazide in scallop tissues. Semicarbazide added to tank seawater resulted in its accumulation in both free and tissue-bound forms and the levels varied according to tissue and were present in all tissues examined. The levels were highest in viscera and the lowest in muscle. The levels of semicarbazide in the environment and in cultured shellfish should be monitored to ensure food quality and safety and human health.

Abstract

Semicarbazide is a newly recognized marine pollutant and has the potential to threaten marine shellfish, the ecological equilibrium and human health. In this study, we examined the accumulation, distribution, and chemical forms of semicarbazide in scallop tissues after exposure to 10, 100, and 1000 μg/L for 30 d at 10 °C. We found a positive correlation between semicarbazide residues in the scallops and the exposure concentration (p < 0.01). Semicarbazide existed primarily in free form in all tissues while bound semicarbazide ranged from 12.1 to 32.7% and was tissue-dependent. The time for semicarbazide to reach steady-state enrichment was 25 days and the highest levels were found in the disgestive gland, followed by gills while levels in gonads and mantle were similar and were lowest in adductor muscle. The bioconcentration factor (BCF) of semicarbazide at low exposure concentrations was higher than that at high exposure concentrations. These results indicated that the scallop can uptake semicarbazide from seawater and this affects the quality and safety of these types of products when used as a food source.

Confirmation of five nitrofuran metabolites including nifursol metabolite in meat and aquaculture products by liquid chromatography-tandem mass spectrometry: Validation according to European Union Decision 2002/657/EC

LC-MS/MS method for confirmation of nitrofuran metabolites in meat and aquaculture products, including the nifursol metabolite (DNSH), was developed. The nitrofuran metabolites investigated were as follows: 3-amino-2-oxazolidinone (AOZ), 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), 1-aminohydantoine (AHD), semicarbazide (SEM) and 3,5-dinitrosalicylic acid hydrazide (DNSH). The sample preparation includes a washing step, allowing to analyze only the fraction of protein-bound residues. The final optimized recovery solvent for injection was found to be a mixture of ammonium acetate 2 mM/acetonitrile (60/40 ; v/v). Matrix effects and stability in biological matrix and standard solution for DNSH have been also carried out. Method performances were assessed using criteria of the Decision (EC) No 2002/657 and considering the proposed-for-adoption reference point for action (RPA) of 0.50 µg.kg^-1 under Reg 1871/2019. Trueness ranged 86.5%-103.7% and precision ranged 2.0%-6.5% on intra-laboratory reproducibility conditions. Decision limit (CCα) ranged 0.028-0.182 μg.kg^-1 and capability of detection limit (CCβ) ranged 0.032-0.233 µg.kg^-1.

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.

Analysis of Endogenous Semicarbazide during the Whole Growth Cycle of Litopenaeus vannamei and Its Possible Biosynthetic Pathway

This research aims to analyze the biosynthetic pathway of endogenous semicarbazide (SEM) in shrimps using Litopenaeus vannamei as the model target. To achieve this objective, the content of SEM in L. vannamei throughout the whole growth cycle was monitored under the strict control of external environmental interference. Experimental results showed that SEM was found in the shrimp shell at all stages, with its content decreasing first and then increasing, and no SEM was detected in the shrimp muscle of each growth stage. This indicated that endogenous SEM in L. vannamei was derived from the shrimp shell. At the same time, the content of amino acids in the shrimp shell and the corresponding substances involved in the urea cycle in the entire growth cycle of shrimp were monitored. The correlation analysis between them and the changes in the SEM content in shrimp showed that arginine had the largest correlation coefficient (0.952) with the changes in the SEM content. The main substances of the urea cycle may be related to the production of SEM. In combination with the water environmental test of high ammonia nitrogen, it was presumed that the formation of endogenous SEM was related to the amidine group of arginine and amide structure of citrulline and urea. Arginine, citrulline, and urea in the urea cycle of L. vannamei eventually produced SEM via an oxaziridine intermediate under the action of hydrogen peroxide and ammonia, and a standardized reaction test was conducted to verify the hypothesis and, thus, provided a new idea for future endogenous SEM research.

Accurate Quantitation and Analysis of Nitrofuran Metabolites, Chloramphenicol, and Florfenicol in Seafood by Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry: Method Validation and Regulatory Samples

We developed and validated a method for the extraction, identification, and quantitation of four nitrofuran metabolites, 3-amino-2-oxazolidinone (AOZ), 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), semicarbazide (SC), and 1-aminohydantoin (AHD), as well as chloramphenicol and florfenicol in a variety of seafood commodities. Samples were extracted by liquid-liquid extraction techniques, analyzed by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), and quantitated using commercially sourced, derivatized nitrofuran metabolites, with their isotopically labeled internal standards in-solvent. We obtained recoveries of 90-100% at various fortification levels. The limit of detection (LOD) was set at 0.25 ng/g for AMOZ and AOZ, 1 ng/g for AHD and SC, and 0.1 ng/g for the phenicols. Various extraction methods, standard stability, derivatization efficiency, and improvements to conventional quantitation techniques were also investigated. We successfully applied this method to the identification and quantitation of nitrofuran metabolites and phenicols in 102 imported seafood products. Our results revealed that four of the samples contained residues from banned veterinary drugs.

Toward a List of Molecules as Potential Biosignature Gases for the Search for Life on Exoplanets and Applications to Terrestrial Biochemistry

Thousands of exoplanets are known to orbit nearby stars. Plans for the next generation of space-based and ground-based telescopes are fueling the anticipation that a precious few habitable planets can be identified in the coming decade. Even more highly anticipated is the chance to find signs of life on these habitable planets by way of biosignature gases. But which gases should we search for? Although a few biosignature gases are prominent in Earth's atmospheric spectrum (O2, CH4, N2O), others have been considered as being produced at or able to accumulate to higher levels on exo-Earths (e.g., dimethyl sulfide and CH3Cl). Life on Earth produces thousands of different gases (although most in very small quantities). Some might be produced and/or accumulate in an exo-Earth atmosphere to high levels, depending on the exo-Earth ecology and surface and atmospheric chemistry. To maximize our chances of recognizing biosignature gases, we promote the concept that all stable and potentially volatile molecules should initially be considered as viable biosignature gases. We present a new approach to the subject of biosignature gases by systematically constructing lists of volatile molecules in different categories. An exhaustive list up to six non-H atoms is presented, totaling about 14,000 molecules. About 2500 of these are CNOPSH compounds. An approach for extending the list to larger molecules is described. We further show that about one-fourth of CNOPSH molecules (again, up to N = 6 non-H atoms) are known to be produced by life on Earth. The list can be used to study classes of chemicals that might be potential biosignature gases, considering their accumulation and possible false positives on exoplanets with atmospheres and surface environments different from Earth's. The list can also be used for terrestrial biochemistry applications, some examples of which are provided. We provide an online community usage database to serve as a registry for volatile molecules including biogenic compounds.

KEY WORDS

Astrobiology-Atmospheric gases-Biosignatures-Exoplanets. Astrobiology 16, 465-485.

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.