Metabolic Disposition and Elimination of Cyadox in Pigs, Chickens, Carp, and Rats

Determination of marker residues of quinoxaline-1,4-di-N-oxides and its prototype identification by liquid chromatography tandem mass spectrometry

Quinoxaline-1,4-di-N-oxides (QdNOs), such as carbadox, olaquindox, mequindox, quinocetone, etc. are a class of antibacterial drugs. Prototype drugs residues can not be detected due to their rapid metabolism in animals. Quinoxaline-2-carboxylic acid (QCA) and 3-methyl-QCA (MQCA) are their common marker residues, so it has been always a challenge to trace the specific QdNOs drug used in food animal production. Herein, a liquid chromatography tandem mass spectrometry method was developed to determine QCA and MQCA, and meanwhile, the prototype drugs were identified by analyzing bis-desoxy QdNOs metabolites in single ion-pair monitoring mode. The method indicated that the average recoveries for QCA and MQCA were from 90 % to 105 % with relative standard deviations below 10 %, and the limits of quantification were 1.0 μg/kg. The limits of detection of five bis-desoxy QdNOs (qualitative markers) reached 0.5 μg/kg. This new analytical strategy can effectively solve the identification problem of QdNOs drugs in animal-derived food.

Advances in Metabolism and Metabolic Toxicology of Quinoxaline 1,4-Di-N-oxides

Quinoxaline 1,4-di-N-Oxides (QdNOs) have been used as synthetic antimicrobial agents in animal husbandry and aquaculture. The metabolism and potential toxicity have been also concerns in recently years. The metabolism investigations showed that there were 8 metabolites of Carbadox (CBX), 34 metabolites of Cyadox (CYA), 33 metabolites of Mequindox (MEQ), 35 metabolites of Olaquindox (OLA), and 56 metabolites of Quinocetone (QCT) in different animals. Among them, Cb3 and Cb8, M6, and O9 are metabolic residual markers of CBX, MEQ and OLA, which are associated with N → O reduction. Toxicity studies revealed that QdNOs exhibited severe tumorigenicity, cytotoxicity, and adrenal toxicity. Metabolic toxicology showed that toxicity of QdNOs metabolites might be related to the N → O group reduction, and some metabolites exhibited higher toxic effects than the precursor, which could provide guidance for further research on the metabolic toxicology of QdNOs and provide a wealth of information for food safety evaluation.

Metabolism and Tissue Elimination of Diaveridine in Swine, Chickens, and Rats Using Radioactive Tracing Coupled with LC-ESI-IT-TOF/MS

Diaveridine (DVD) has widespread use in food animals due to its antibacterial synergistic effects. This study revealed the metabolism, excretion, and tissue elimination of DVD in swine, chickens, and rats following oral gavage of 10 mg/kg b.w. tritium-labeled DVD using radioactive tracing coupled with liquid chromatography-electron spray ionization-ion trap-time-of-flight-mass spectrometry (LC-ESI-IT-TOF/MS). The metabolic pathways involved demethylation, α-hydroxylation, glucuronidation, and sulfonylation and produced four metabolites in swine (M0, DVD; M1, 3'/4'-demethyl-DVD; M2, 3'/4'-demethyl-DVD-O-glucuronide; M4, 2/4-glucuronidated-DVD) and five in chickens (M0∼M2; M3, α-hydroxy-DVD; M4) and rats (M0∼M3; M5, 3'/4'-demethyl-DVD-O-sulfation). M0 was dominant in the excreta of chicken and female and male rats, while M2 was mainly excreted in swine. Among the three species studied, M0 was the most persistent in the kidneys (t_1/2 3.15-3.89 d); therefore, M0 kidney levels are residue monitoring targets. This study enabled a thorough comprehension of the metabolism and pharmacokinetic characteristics of DVD in animals.

Metabolic Disposition and Elimination of Tritum-Labeled Sulfamethoxazole in Pigs, Chickens and Rats

Sulfamethoxazole (SMZ), as a sulfa antibiotic, is often used in the treatment of various infectious diseases in animal husbandry. At present, SMZ still has many unresolved problems in the material balance, metabolic pathways, and residual target tissues in food animals. Therefore, in order to solve these problems, the metabolism, distribution, and elimination of SMZ is investigated in pigs, chickens, and rats by radioactive tracing methods, and the residue marker and target tissue of SMZ in food animals were determined, providing a reliable basis for food safety. After a single administration of [³H]-SMZ (rats and pigs by intramuscular injection and chickens by oral gavage), the total radioactivity was rapidly excreted, with more than 93% of the dose excreted within 14 days in the three species. Pigs and rats had more than 75% of the administered volume recovered by urine. After 7 days of continuous administration, within the first 6 h, radioactivity was found in almost all tissues. The highest radioactivity and longest persistence in pigs was in the liver, while in chickens it was in the liver and kidneys, most of which was removed within 14 days. A total of six, three and three metabolites were found in chickens, rats and pigs, respectively. N₄-acetyl-sulfamethoxazole (S1) was the main metabolite of SMZ in rats, pigs and chickens. The radioactive substance with the longest elimination half-life is sulfamethoxazole (S0), so S0 was suggested to be the marker residue in pigs and chickens.

Development of radioactive tracing coupled with LC/MS-IT-TOF methodology for the discovery and identification of diaveridine metabolites in pigs

We developed a sensitive and reliable method by coupling radiotracing with LC/MS-IT-TOF to identify diaveridine metabolites. Tritium-labeled diaveridine was orally administered to pigs and their organs, blood, bile, and excreta were collected. Under optimized conditions, radioactive recovery was >90% and the highest numbers of metabolites were detected. MCX-based solid-phase extraction was conducted for urine, plasma, and bile purification. Methanol-chloroform 1:1 (v/v), methanol-chloroform 6:1 (v/v), methanol, methanol-chloroform 1:1 (v/v), and methanol were used as solvents to extract feces, liver, kidney, fat and muscle, respectively. The method validation confirmed satisfactory ³H-H exchange efficiency (<5%), chromatographic column efficiency (≥97.5%), LOQ (10.73 μg/kg), and analytical accuracy (97.6-107.8%) and precision (RSD < 5%). Moreover, novel in vivo metabolites were detected in the pigs, including D2 (3'-desmethyl-diaveridine monoglucuronide), D3 (diaveridine monoglucuronide). Hence, the analytical method developed herein lays an empirical foundation for further systematic studies of the diaveridine metabolism.

Oxidative Stress Modulation and Radiosensitizing Effect of Quinoxaline-1,4-Dioxides Derivatives

Background:

Quinoxaline-1,4-dioxide (QNX) derivatives are synthetic heterocyclic compounds with multiple biological and pharmacological effects.

Objective:

In this study, we investigated the oxidative status of quinoxaline-1,4-dioxides derivatives in modulating melanoma and glioma cell lines, based on previous results from the research group and their capability to promote cell damage by the production of Reactive Oxygen Species (ROS).

Methods:

Using in vitro cell cultures, the influence of 2-amino-3-cyanoquinoxaline-1,4-dioxide (2A3CQNX), 3- methyl-2-quinoxalinecarboxamide-1,4-dioxide (3M2QNXC) and 2-hydroxyphenazine-1,4-dioxide (2HF) was evaluated in metabolic activity, catalase activity, glutathione and 3-nitrotyrosine (3-NT) quantitation by HPLC in malignant melanocytes (B16-F10, MeWo) and brain tumor cells (GL-261 and BC3H1) submitted to radiotherapy treatments (total dose of 6 Gy).

Results:

2HF increased the levels of 3-NT in non-irradiated MeWo and glioma cell lines and decreased cell viability in these cell lines with and without irradiation.

Conclusions:

Quinoxaline-1,4-dioxides derivatives modulate the oxidative status in malignant melanocytes and brain tumor cell lines and exhibited a potential radiosensitizer in vitro action on the tested radioresistant cell lines.

Antibacterial activity of cyadox against Clostridium perfringens in broilers and a dosage regimen design based on pharmacokinetic-pharmacodynamic modeling

Necrotic enteritis is an intestinal disease caused by Clostridium perfringens (C. perfringens) that results in high economic losses to the poultry industry. The purpose of this study was to investigate the antibacterial activity of cyadox against C. perfringens and to formulate its dosage regimen based on pharmacokinetics/pharmacodynamics (PK/PD) modeling in broilers. The PK parameters of cyadox in ileum of healthy and infected broilers following oral administration at 30 mg/kg body weight (BW) were investigated and PD study the MIC, MBC, MPC, and PAE were determined. The time-killing curves were established in vitro and ex vivo to evaluate the antibacterial activity of cyadox against C. perfringens. The results revealed that the MIC of cyadox against C. perfringens was 1-16 μg/mL. After oral administration of cyadox, the peak concentration (C_max), maximum concentration time (T_max), and area under the concentration-time curve (AUC) in ileum content of broilers were 143.55-161.48 μg/mL, 1.08-1.25 h, and 359.51-405.69 μg h/mL respectively. After Integrating the in vivo PK and ex vivo PD data the AUC_24h/MIC values needed for bacteriostatic, bactericidal and bacterial eradication were 27.71 h, 78.93 h, and 165.14 h, respectively. By model validation, the cure rate was 85.71%. In conclusion, a dosage regimen of 14.02 mg/kg repeated after every 12 h for 3-5days was expected to be therapeutically effective in broilers against C. perfringens with MIC ≤2 μg/mL.

Disposition of cyadox in domesticated cats following oral, intramuscular, and intravenous administration

Cyadox (CYX) is a synthetic antibacterial agent of quinoxaline with much lower toxic effects. A safety criterion of CYX for clinical use was established by studying the pharmacokinetics and metabolism of CYX after oral (PO), intramuscular (IM), and intravenous (IV) administration. CYX was administered in six domesticated cats (three males and three females) by PO (40 mg/kg.b.w.), IM (10 mg/kg.b.w.), and IV (10 mg/kg.b.w.) routes in a crossover pattern. Highly sensitive liquid chromatography with ultraviolet detection (HPLC-UV) method was developed for detection of CYX and its metabolites present in plasma, urine, and feces. The bioavailability of CYX after PO and IM routes was 4.37% and 84.4%. The area under curves (AUC), mean resident time (MRT), and clearance (CL) of CYX and its metabolites revealed that CYX quickly metabolized into its metabolites. The total recovery of CYX and its main metabolites was >60% after each route. PO delivery suggesting first pass effect in cats that might make this route suitable for intestinal infection and IM injection could be better choice for systemic infections. Less ability of glucuronidation did not show any impact on CYX metabolism. The findings of present study provide detailed information for evaluation of CYX.

Synthesis of tritium-labeled cyadox, a promising antimicrobial growth-promoting agent with high specific activity

Cyadox is a new antimicrobial growth-promoting agent for food-producing animals. Studies on radiolabeled compounds enable the use of sensitive radiometric analytical methods and help in the elucidation of metabolic and elimination pathways. In the present study, 6-[³H]-cyadox with a high specific activity of 2.08 Ci/mmol was prepared by the catalytic bromine-tritium exchange of 4-bromo-2-nitroaniline followed by a three-step microscale synthesis, giving a high yield between 36.16% and 94.75%.

Pharmacokinetics and Metabolism of Cyadox and Its Main Metabolites in Beagle Dogs Following Oral, Intramuscular, and Intravenous Administration

Cyadox (Cyx) is an antibacterial drug of the quinoxaline group that exerts markedly lower toxicity in animals, compared to its congeners. Here, the pharmacokinetics and metabolism of Cyx after oral (PO), intramuscular (IM), and intravenous (IV) routes of administration were studied to establish safety criteria for the clinical use of Cyx in animals. Six beagle dogs (3 males, 3 females) were administered Cyx through PO (40 mg kg⁻¹ b.w.), IM (10 mg kg⁻¹ b.w.), and IV (10 mg kg⁻¹ b.w.) routes with a washout period of 2 weeks in a crossover design. Highly sensitive high-performance liquid chromatography with ultraviolet detection (HPLC-UV) was employed for determination of Cyx and its main metabolites, 1, 4-bisdesoxycyadox (Cy1), cyadox-1-monoxide (Cy2), N-(quinoxaline-2-methyl)-cyanide acetyl hydrazine (Cy4), and quinoxaline-2-carboxylic acid (Cy6) in plasma, urine and feces of dogs. The oral bioavailability of Cyx was 4.75%, suggesting first-pass effect in dogs. The concentration vs. time profile in plasma after PO administration indicates that Cyx is rapidly dissociated into its metabolites and eliminated from plasma earlier, compared to its metabolites. The areas under the curve (AUC) of Cyx after PO, IM and IV administration were 1.22 h × μg mL⁻¹, 6.3 h × μg mL⁻¹, and 6.66 h × μg mL⁻¹, while mean resident times (MRT) were 7.32, 3.58 and 0.556 h, respectively. Total recovery of Cyx and its metabolites was >60% with each administration route. In feces, 48.83% drug was recovered after PO administration, while 18.15% and 17.11% after IM and IV injections, respectively, suggesting renal clearance as the major route of excretion with IM and IV administration and feces as the major route with PO delivery. Our comprehensive evaluation of Cyx has uncovered detailed information that should facilitate its judicious use in animals by improving understanding of its pharmacology.

The critical role of oxidative stress in the toxicity and metabolism of quinoxaline 1,4-di-N-oxides in vitro and in vivo

Quinoxaline 1,4-dioxide derivatives (QdNOs) have been widely used as growth promoters and antibacterial agents. Carbadox (CBX), olaquindox (OLA), quinocetone (QCT), cyadox (CYA) and mequindox (MEQ) are the classical members of QdNOs. Some members of QdNOs are known to cause a variety of toxic effects. To date, however, almost no review has addressed the toxicity and metabolism of QdNOs in relation to oxidative stress. This review focused on the research progress associated with oxidative stress as a plausible mechanism for QdNO-induced toxicity and metabolism. The present review documented that the studies were performed over the past 10 years to interpret the generation of reactive oxygen species (ROS) and oxidative stress as the results of QdNO treatment and have correlated them with various types of QdNO toxicity, suggesting that oxidative stress plays critical roles in their toxicities. The major metabolic pathways of QdNOs are N→O group reduction and hydroxylation. Xanthine oxidoreductase (XOR), aldehyde oxidase (SsAOX1), carbonyl reductase (CBR1) and cytochrome P450 (CYP) enzymes were involved in the QdNOs metabolism. Further understanding the role of oxidative stress in QdNOs-induced toxicity will throw new light onto the use of antioxidants and scavengers of ROS as well as onto the blind spots of metabolism and the metabolizing enzymes of QdNOs. The present review might contribute to revealing the QdNOs toxicity, protecting against oxidative damage and helping to improve the rational use of concurrent drugs, while developing novel QdNO compounds with more efficient potentials and less toxic effects.

High risk of adrenal toxicity of N1-desoxy quinoxaline 1,4-dioxide derivatives and the protection of oligomeric proanthocyanidins (OPC) in the inhibition of the expression of aldosterone synthetase in H295R cells

Quinoxaline 1,4-dioxide derivatives (QdNOs) with a wide range of biological activities are used in animal husbandry worldwide. It was found that QdNOs significantly inhibited the gene expression of CYP11B1 and CYP11B2, the key aldosterone synthases, and thus reduced aldosterone levels. However, whether the metabolites of QdNOs have potential adrenal toxicity and the role of oxidative stress in the adrenal toxicity of QdNOs remains unclear. The relatively new QdNOs, cyadox (CYA), mequindox (MEQ), quinocetone (QCT) and their metabolites, were selected for elucidation of their toxic mechanisms in H295R cells. Interestingly, the results showed that the main toxic metabolites of QCT, MEQ, and CYA were their N1-desoxy metabolites, which were more harmful than other metabolites and evoked dose and time-dependent cell damage on adrenal cells and inhibited aldosterone production. Gene and protein expression of CYP11B1 and CYP11B2 and mRNA expression of transcription factors, such as NURR1, NGFIB, CREB, SF-1, and ATF-1, were down regulated by N1-desoxy QdNOs. The natural inhibitors of oxidant stress, oligomeric proanthocyanidins (OPC), could upregulate the expression of diverse transcription factors, including CYP11B1 and CYP11B2, and elevated aldosterone levels to reduce adrenal toxicity. This study demonstrated for the first time that N1-desoxy QdNOs have the potential to be the major toxic metabolites in adrenal toxicity, which may shed new light on the adrenal toxicity of these fascinating compounds and help to provide a basic foundation for the formulation of safety controls for animal products and the design of new QdNOs with less harmful effects.

Metabolism, Distribution, and Elimination of Mequindox in Pigs, Chickens, and Rats

Mequindox (MEQ), a quinoxaline-N,N-dioxide antibacterial agent used to control bacterial enteritis in various food-producing animals, is a potential violative residue in food animal-derived products. The disposition and elimination of MEQ in rats, pigs, and chickens was comprehensively investigated to identify the marker residue and target tissue of MEQ in food animals for residue monitoring. Following a single oral administration, 62-71% of MEQ was rapidly excreted via urine and feces in all species within 24 h. Urinary excretion of radioactivity was 84 and 83.5% of the administered dose in rats and pigs, respectively. More than 92% of the administered dose was excreted in all species within 15 days. Radioactivity was found in nearly all tissues at the first 6 h after dosing, with the majority of radioactivity cleared within 4-6 days. The highest radioactivity and longest persisting time were found to be in the liver and kidney. Totals of 11, 12, and 7 metabolites were identified in rats, chickens, and pigs, respectively. No parent drug could be detected in any of the tissues of pigs and chickens. 3-Methyl-2-acetyl quinoxaline (M1), 3-methyl-2-(1-hydroxyethyl) quinoxaline-N4-monoxide (M4), and 3-methyl-2-(1-hydroxyethyl) quinoxaline-1,4-dioxide (M6) were the common and major metabolites of MEQ in all three species. Additionally, 3-methyl-2-(1-hydroxyethyl) quinoxaline (M5), 3-hydroxymethyl-2-ethanol quinoxaline-1,4-dioxide (M7), and 3-methyl-2-(1-hydroxyethyl) quinoxaline-N1-monoxide (M8) were the major metabolites of MEQ in rats, pigs, and chickens, respectively. M1 was designated to be the marker residue of MEQ in pigs and chickens. These results provide scientific data for the determination of marker residues and withdrawal time of MEQ in food animals and improve the understanding of the toxicity and disposition of MEQ in animals.

Estimation of residue depletion of cyadox and its marker residue in edible tissues of pigs using physiologically based pharmacokinetic modelling

Physiologically based pharmacokinetic (PBPK) models are powerful tools to predict tissue distribution and depletion of veterinary drugs in food animals. However, most models only simulate the pharmacokinetics of the parent drug without considering their metabolites. In this study, a PBPK model was developed to simultaneously describe the depletion in pigs of the food animal antimicrobial agent cyadox (CYA), and its marker residue 1,4-bisdesoxycyadox (BDCYA). The CYA and BDCYA sub-models included blood, liver, kidney, gastrointestinal tract, muscle, fat and other organ compartments. Extent of plasma-protein binding, renal clearance and tissue-plasma partition coefficients of BDCYA were measured experimentally. The model was calibrated with the reported pharmacokinetic and residue depletion data from pigs dosed by oral gavage with CYA for five consecutive days, and then extrapolated to exposure in feed for two months. The model was validated with 14 consecutive day feed administration data. This PBPK model accurately simulated CYA and BDCYA in four edible tissues at 24-120 h after both oral exposure and 2-month feed administration. There was only slight overestimation of CYA in muscle and BDCYA in kidney at earlier time points (6-12 h) when dosed in feed. Monte Carlo analysis revealed excellent agreement between the estimated concentration distributions and observed data. The present model could be used for tissue residue monitoring of CYA and BDCYA in food animals, and provides a foundation for developing PBPK models to predict residue depletion of both parent drugs and their metabolites in food animals.