The metabolism of olaquindox in rats, chickens and pigs

Four birds with one stone: Aggregation-induced emission-type zeolitic imidazolate framework-8 based bionic nanoreactor for portable detection of olaquindox in environmental water and swine urine by smartphone

The abuse of olaquindox (OLA) as both an antimicrobial agent and a growth promoter poses significant threats to the environment and human health. While nanoreactors have proven effective in hazard detection, their widespread adoption has been hindered by tedious chemical processes and limited functionality. In this study, we introduce a novel green self-assembly strategy utilizing invertase, horseradish peroxidase, antibodies, and gold nanoclusters to form an aggregation-induced emission-type zeolitic imidazolate framework-8 nanoreactor. The results demonstrate that the lateral flow immunoassay not only allows for qualitative naked eye detection but also enables optical analysis through the fluorescence generated by aggregated gold nanoclusters and enzyme-catalyzed enhancement of visible colorimetric signals. To accommodate more detection scenarios, the photothermal effects and redox reactions of the nanoreactor can fulfill the requirements of thermal sensing and electrochemical analysis for smartphone applications. Remarkably, the proposed approach achieves a detection limit 17 times lower than conventional methods. Besides, the maximum linear range spans from 0.25 to 5 μg/L with high specificity, and the recovery is 85.2-112.9% in environmental water and swine urine. The application of this high-performance nanoreactor opens up avenues for the construction of multifunctional biosensors with great potential in monitoring hazardous materials.

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.

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.

Rapidly photocatalytic mineralization of typical veterinary drugs with the SnO2/SnIn4S8 composite

Considering the high environmental risk, the remediation of veterinary drug pollutants aroused numerous concerning. In this paper, a novel photocatlyst, SnO₂/SnIn₄S₈, was fabricated by in situ precipitation and hydrothermal method and then employed to simulate photocatalytic degradation of olaquindox under visible light. The SEM, TEM, XRD, XPS and electrochemical results clearly showed that the n-type heterojunction between SnO₂ and SnIn₄S₈ was successfully constructed, which greatly reduce the recombination of the photogenic electron and holes, leading to the improvement of photocalytic performance and stability (recycled over 10 times). Besides, the SnO₂/SnIn₄S₈ composite also exhibited good ability to mineralize the olaquindox. Under the optimal condition (pH of 3, 1 g L^-1 of 30 wt% SnO₂/SnIn₄S₈ and 10 mg L^-1 of initial olaquindox concentration), the olaquindox could be fully and rapidly degraded in 25 min, and completely mineralized in 2 h (99.3 ± 1.7%). LC-QTOF-MS analysis evidently displayed 10 intermediates during the olaquindox degradation. In addition, with the attack of the reactive oxygen species (h⁺, •OH and •O₂^-), olaquindox could be effectively decomposed via deoxygenation, hydroxylation and carboxylation reactions. Importantly, compared to photodegradation, the photocatalytic process was an ideal way to eliminate the olaquindox form water because it could avoid the accumulation of toxic byproducts.

Tissue Depletion of Olaquindox and Its Six Metabolites in Pigs and Broilers: Identification of a Suitable Marker Residue

The depletion profiles of olaquindox and its six major metabolites, including O1 (N 1-deoxyolaquindox), O2 (deoxyolaquindox), O3 (2-carboxamide-3-methylquinoxaline-N 4-oxide), O4 (2-carboxymethylaminocarbonyl-3-methylquinoxaline-N 4-oxide), O5 (2-carboxymethylaminocarbonyl-3-methylquinoxaline), and O6 [3-methyl-quinoxaline-2-carboxylic acid (MQCA)] were studied with a sensitive and accurate HPLC-UV method in pigs and broilers after oral administration of olaquindox at the rate of 50 mg kg-1 feed for 14 consecutive days. Five medicated pigs and six medicated broilers and one control animal for each time point were anesthetized and killed at different time points (6 h and 1, 3, 7, and 14 days for pigs and 6 h and 1, 3, 5, and 7 days for broilers) after ingestion of the medicated feed ceased and samples of muscle, liver, kidney, and fat were collected. The samples were assayed using a liquid chromatographic method. Mean concentrations of O2 (deoxyolaquindox) metabolite residues in all tissues of pigs were higher than other metabolite residues at each time point. MQCA was detected at lower concentrations and eliminated more rapidly than deoxyolaquindox (calculated t 1/2 1.78-2.28 days vs. t 1/2 2.04-2.46 days). The elimination half-lives of deoxyolaquindox residue in broilers' liver and kidney tissues (t 1/2 >4 days) were much longer than those in pigs. Thus, the use of olaquindox in poultry is clearly inappropriate, as significant drug residues will occur without a withdrawal time. The results that deoxyolaquindox occurs at higher concentrations in kidney tissue and is more persistent than other residues in edible tissues of pigs which indicate that deoxyolaquindox is the most relevant marker residue and should be monitored in the routine surveillance of olaquindox-related residues in foods of animal origin.

Molecular mechanism of olaquindox-induced hepatotoxicity and the hepatic protective role of curcumin

Olaquindox (OLA) is a chemosynthetic growth promoter, which could promote the treatment of bacterial infections and improve feed energy efficiency. Hepatotoxicity is still a poor feature associated with the adverse effects of OLA. The present study aimed to investigate the molecular mechanism of OLA-induced hepatotoxicity and the protective role of curcumin in mice and HepG2 cells. The result showed that representative biomarkers involved in mitochondrial pathway, p53 pathway, mitogen-activated protein kinase (MAPK) pathway, autophagy and antioxidant pathway were activated. Furthermore, curcumin attenuated OLA-induced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and liver damage in mice. In addition, cell viability of HepG2 was enhanced by curcumin pretreatment at 5, 10 and 20 μM. Meanwhile, curcumin markedly ameliorated OLA-induced oxidative stress, apoptosis and mitochondrial dysfunction. Moreover, curcumin pretreatment significantly up-regulated the expressions of nuclear factor erythroid-2-related factor 2 (Nrf2) and heme oxygenase-1(HO-1) and down-regulated the expressions of nuclear factor-kappaB (NF-kB) and p53 through reduced the nuclear translocation of NF-kB induced by OLA. In summary, our findings indicated that OLA-induced hepatotoxicity involved in mitochondrial apoptosis, autophagy, p53 pathway, Nrf2/HO-1 pathways, and curcumin regulated OLA-induced liver damage, oxidative stress and apoptosis via activation of Nrf2/HO-1 pathway and suppression of p53 and NF-kB pathway.

Analysis of Nosiheptide in Food Animal Tissues via Its Unique Degradation Product by Liquid Chromatography-Tandem Mass Spectrometry after Alkaline Hydrolysis

Very weak signals of fragment ions of nosiheptide could be observed using liquid chromatography-tandem mass spectrometry. The preparation of 4-hydroxymethyl-3-methyl-1H-indole-2-carboxylic acid (HMIA), a specific fragment of nosiheptide, by alkaline hydrolysis is described. HMIA showed a good mass spectrometric signal in negative electrospray ionization mode. In the new method, the nosiheptide residue in muscle tissue was hydrolyzed with sodium hydroxide aqueous solution; this was followed by cleanup using mixed mode cartridges. Identification and quantification of nosiheptide were carried out by analyzing HMIA in hydrolysate of muscles. Nosiheptide showed a good linear relationship (r > 0.996) in the calibration range of 2-500 μg/kg, and a low limit of quantification of 2 μg/kg was obtained in swine, chicken, and fish muscles. Recoveries of nosiheptide from spiked muscle samples were 85-108% with relative standard deviations less than 10%. The proposed method was successfully applied for the detection of the nosiheptide residue in medicated animal tissues samples.

Discovery of the Marker Residue of Olaquindox in Pigs, Broilers, and Carp

The excretion, metabolism, distribution, and residue depletion of olaquindox (OLA), an antibacterial and growth-promoting agent used in food-producing animals for decades without a clear understanding of metabolic fate, was completely studied in pigs, broilers, carp, and rats using a radio-tracing approach combined with liquid chromatography-ion trap/time-of-flight mass spectroscopy to define the scientific marker residue (MR). After a single gavage of [³H]OLA, over 92% of the dose was excreted via urine. OLA was transformed into eight metabolites (O1-O8) in pigs and broilers, four metabolites (O1, O2, O4, and O7) in carp, and nine metabolites (O1-O9) in rats. O2 was the major residue in edible tissues of four species and persisted for the longest time in the kidneys with the longest half-life of 3.52-4.6 d. Bisdesoxyolaquindox (O2) is designated to be the MR, and the kidneys are considered to be the target tissue for OLA in food producing animals. Monitoring for this metabolite would improve the food safety evaluation and residue control of this drug.

Subchronic toxicity and hepatocyte apoptosis of dietary olaquindox in common carp (Cyprinus carpio)

Olaquindox as one of the effective antimicrobial agents and growth-promoting feed additives, had been widely used in animal and fish production. However, few studies have been done to unveil its possible toxic effect and tissue injury on aquatic animal. In this study, the toxic effect and underlying mechanisms of olaquindox toxicity were investigated in common carp when feed with different doses of olaquindox for 90 days. The morbidity and mortality, pathological changes, hematology parameters, residue concentration in the tissues of common carp were assessed, hepatocyte apoptosis was detected through ultrastructural observation and flow cytometry methods. The results showed that the morbidity and mortality increased with the increasing dosages of dietary olaquindox, subchronic exposure to olaquindox caused remarkably pathological changes, including congestion and bleeding, intramuscular edema, vacuolar degeneration, degeneration and deformation in renal tubules architecture, respiratory epithelium fusion and intestinal epithelial microvilli disintegration. Besides, dietary olaquindox led to significant changes in blood biochemical parameters including red blood cell, hemoglobin, alanine aminotransferase and aspartate aminotransferase, an elevated residue concentration of olaquindox was detected in liver and kidney after exposure, hepatocyte apoptosis and necrosis were observed. Moreover, insulin-like growth factor I (IGF-I) mRNA level in liver was higher than normal level with the dose below 25 mg/kg olaquindox and was lower than normal level with the dose above 50 mg/kg. Our results demonstrated that dietary olaquindox may pose subchronic toxicity and residue in fish organs and provided scientific data for the safe application of olaquindox in fish.

Olaquindox disrupts tight junction integrity and cytoskeleton architecture in mouse Sertoli cells

Sertoli cells, by creating an immune-privileged and nutrition supporting environment, maintain mammalian spermatogenesis and thereby holds the heart of male fertility. Olaquindox, an effective feed additive in livestock industry, could potentially expose human into the risk of biological hazards due to its genotoxicity and cytotoxicity, highlighting the significance of determining its bio-safety regarding human reproduction. Herein, we deciphered the detrimental effects of olaquindox on male fertility by mechanistically unraveling how olaquindox intervenes blood-testis barrier in mouse. Olaquindox (400 μg/ml) exposure significantly compromised tight junction permeability function, decreased or dislocated the junction proteins (e.g., ZO-1, occludin and N-cadherin) and attenuated mTORC2 signaling pathway in primary Sertoli cells. Furthermore, olaquindox disrupted F-actin architecture through interfering with the expression of actin branching protein complex (CDC42-N-WASP-Arp3) and actin bunding protein palladin. Olaquindox also triggered severely DNA damage and apoptosis while inhibiting autophagic flux in Sertoli cell presumably due to the exacerbated generation of reactive oxygen species (ROS). Pre-treatment with antioxidant N-acetylcysteine effectively ameliorated olaquindox-induced exhaustion of ZO-1 and N-Cadherin proteins, DNA damage and apoptosis. More significantly, olaquindox disrupted the epigenetic status in Sertoli cells with hypermethylation and concomitantly hypoacetylation of H3K9 and H3K27. Overall, our study determines olaquindox targets Sertoli cells to affect BTB function through tight junction proteins and F-actin orgnization, which might disrupt the process of spermatogenesis.

TCS2 Increases Olaquindox-Induced Apoptosis by Upregulation of ROS Production and Downregulation of Autophagy in HEK293 Cells

Olaquindox, a feed additive, has drawn public attention due to its potential mutagenicity, genotoxicity, hepatoxicity and nephrotoxicity. The purpose of this study was to investigate the role of tuberous sclerosis complex (TSC2) pathways in olaquindox-induced autophagy in human embryonic kidney 293 (HEK293) cells. The results revealed that olaquindox treatment reduced the cell viability of HEK293 cells and downregulated the expression of TSC2 in a dose- and time-dependent manner. Meanwhile, olaquindox treatment markedly induced the production of reactive oxygen species (ROS), cascaded to autophagy, oxidative stress, and apoptotic cell death, which was effectively eliminated by the antioxidant N-acetylcysteine (NAC). Furthermore, overexpression of TSC2 attenuated olaquindox-induced autophagy in contrast to inducing the production of ROS, oxidative stress and apoptosis. Consistently, knockdown of TSC2 upregulated autophagy, and decreased olaquindox-induced cell apoptosis. In conclusion, our findings indicate that TSC2 partly participates in olaquindox-induced autophagy, oxidative stress and apoptosis, and demonstrate that TSC2 has a negative regulation role in olaquindox-induced autophagy in HEK293 cells.

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.

Further investigations into the genotoxicity of quinoxaline-di-N-oxides and their primary metabolites

Quinoxaline-di-N-oxides (QdNOs) are potential antibacterial agents with a wide range of biological properties. Quinocetone (QCT), carbadox (CBX), olaquindox (OLA), mequindox (MEQ) and cyadox (CYA) are classical QdNOs. Though the genotoxicity of parent drugs has been evaluated, the genotoxicity of their primary N → O reduced metabolites remains unclear. In the present study, a battery of four different short-term tests, mouse lymphoma assay (MLA), Ames test, chromosomal aberration assay in vitro and bone marrow erythrocyte micronucleus assay in vivo was carried out to investigate the genotoxicity of the six primary N → O reduced metabolites. Additionally, the genotoxicity of five parent drugs was evaluated by the MLA. Strong genotoxicity of N1-MEQ, B-MEQ and B-CBX was found in three of the assays but not in the Ames assay, and the rank order was N1-MEQ>B-MEQ>B-CBX that is consistent with prototype QdNOs. Negative results for the five QdNOs were noted in the MLA. We present for the first time a comparison of the genotoxicity of primary N → O reduced metabolites, and evaluate the ability of five QdNOs to cause mutations in the MLA. The present study demonstrates that metabolites are involved in genetic toxicity mediated by QdNOs, and improve the prudent use of QdNOs for public health.

Olaquindox induces DNA damage via the lysosomal and mitochondrial pathway involving ROS production and p53 activation in HEK293 cells

Olaquindox (OLA) is a potent antibacterial agent used as a feed additive and growth promoter. In this study, the genotoxic potential of OLA was investigated in the human embryonic kidney cell line 293 (HEK293). Results showed that OLA caused significant increases of DNA migration. Lysosomal membrane permeability and mitochondrial membrane potential were reduced after treatment with OLA. OLA was shown to induce ROS production and GSH depletion. The expression of p53 protein is increased in cells incubated with OLA. The activation of p53 and ATM gene was assessed by exposure to OLA. Furthermore, NAC reduced DNA migration, ROS formation, GSH depletion and the expression of the p53 protein and gene. And desipramine significantly decreased AO fluorescence intensity and the expression of the p53 protein and gene. These results support the assumption that OLA exerted genotoxic effects and induced DNA strand breaks in HEK293 cells, possibly through lysosomal-mitochondrial pathway involving ROS production and p53 activation.

In vivo studies to highlight possible illegal treatments of rabbits with carbadox and olaquindox

For the treatment of rabbit dysentery and bacterial enteritis, veterinary practitioners often adopt veterinary medicinal products authorised for other food-producing species, but in some cases non-authorised drugs frequently used in the past, such as carbadox and olaquindox, might be illegally adopted. To verify the carbadox and olaquindox distribution and persistence in rabbit tissues, two independent in vivo studies were carried out. In the first study, 24 healthy rabbits received water medicated with carbadox at 100 mg l(-1) over a period 28 days, whereas in the second one, 24 healthy rabbits were administered water containing olaquindox at 100 mg l(-1). In each study rabbits were randomly assigned to four groups to be sacrificed respectively at 0, 5, 10 and 20 days from treatment withdrawal, for depletion studies. A control group of six animals was adopted for control and as a reservoir of blank tissues. Muscle and liver samples collected from each treated animal were stored at -20°C pending the analysis. Sensitive and robust liquid chromatography-tandem mass spectrometry analytical methods were set up for the parent compounds and their main metabolites quinoxaline-2-carboxylic acid, desoxycarbadox and 3-methylquinoxaline-2-carboxylic acid to verify their residual. Data collected demonstrate that the combination of liver as target matrix, quinoxaline-2-carboxylic acid and 3-methylquinoxaline-2-carboxylic acid as marker residue and enzymatic digestion is strategic to evidence carbadox and/or olaquindox illegal treatments in rabbits, even 20 days after treatment withdrawal at concentration levels higher than 0.5 µg kg(-1). This findings suggests that liver should be proposed as target matrix for official control in national monitoring plan.

Mechanism of adrenocortical toxicity induced by quinocetone and its bidesoxy-quinocetone metabolite in porcine adrenocortical cells in vitro

Quinocetone (QCT) is a new feeding antibacterial agent in the QdNOs family. The mechanism of its adrenal toxicity is far from clear. This study was conducted to estimate the adrenal cell damage induced by QCT and its bidesoxy-quinocetone (B-QCT) metabolite and to further investigate their mechanisms. Following doses of QCT increasing from 5 to 50 μM, cell apoptosis and necrosis, mitochondrial dysfunction and redox imbalance were observed in porcine adrenocortical cells. The mRNA levels of the six components of intermediary enzymes and the adrenal renin-angiotensin-aldosterone system (RAAS) displayed a dysregulation induced by QCT, indicating that QCT might influence aldosterone secretion not only through the upstream of the production but also through the downstream of the adrenal RAAS pathway. In contrast, B-QCT had few toxic effects on the cell apoptosis, mitochondrial dysfunction and redox imbalance. Moreover, LCMS-IT-TOF analysis showed that no desoxy metabolites of QCT were found in either cell lysate or supernatant samples. In conclusion, we reported on the cytotoxicity in porcine adrenocortical cells exposed to QCT via oxidative stress, which raised awareness that its toxic effects resulted from N→O groups, and its toxic mechanism might involve the interference of the steroid hormone biosynthesis pathway.

Genotoxicity of quinocetone, cyadox and olaquindox in vitro and in vivo

Quinocetone (QCT) and Cyadox (CYA) are important derivative of heterocyclic N-oxide quinoxaline (QdNO), used actively as antimicrobial feed additives in China. Here, we tested and compared the genotoxic potential of QCT and CYA with olaquindox (OLA) in Ames test, HGPRT gene mutation (HGM) test in V79 cells, unscheduled DNA synthesis (UDS) assay in human peripheral lymphocytes, chromosome aberration (CA) test, and micronucleus (MN) test in mice bone marrow. OLA was found genotoxic in all 5 assays. In Ames test, QCT produced His(+) mutants at 6.9 μg/plate in Salmonella typhimurium TA 97, at 18.2 μg/plate in TA 100, TA 1535, TA 1537, and at 50 μg/plate in TA 98. CYA produced His(+) mutants at 18.2 μg/plate in TA 97, TA 1535, and at 50 μg/plate in TA 98, TA 100 and TA 1537. QCT was found positive in HGM and UDS assay at concentrations ≥10 μg/ml while negative results were reported in CA test and MN test. Collectively, we found that OLA was more genotoxic than QCT and CYA. Genotoxicity of QCT was found at higher concentration levels in Ames test, HGM and UDS assays while CYA showed weak mutagenic potential to bacterial cells in Ames test.

An introduction to hybrid ion trap/time-of-flight mass spectrometry coupled with liquid chromatography applied to drug metabolism studies

Metabolism studies play an important role at various stages of drug discovery and development. Liquid chromatography combined with mass spectrometry (LC/MS) has become a most powerful and widely used analytical tool for identifying drug metabolites. The suitability of different types of mass spectrometers for metabolite profiling differs widely, and therefore, the data quality and reliability of the results also depend on which instrumentation is used. As one of the latest LC/MS instrumentation designs, hybrid ion trap/time-of-flight MS coupled with LC (LC-IT-TOF-MS) has successfully integrated ease of operation, compatibility with LC flow rates and data-dependent MS(n) with high mass accuracy and mass resolving power. The MS(n) and accurate mass capabilities are routinely utilized to rapidly confirm the identification of expected metabolites or to elucidate the structures of uncommon or unexpected metabolites. These features make the LC-IT-TOF-MS a very powerful analytical tool for metabolite identification. This paper begins with a brief introduction to some basic principles and main properties of a hybrid IT-TOF instrument. Then, a general workflow for metabolite profiling using LC-IT-TOF-MS, starting from sample collection and preparation to final identification of the metabolite structures, is discussed in detail. The data extraction and mining techniques to find and confirm metabolites are discussed and illustrated with some examples. This paper is directed to readers with no prior experience with LC-IT-TOF-MS and will provide a broad understanding of the development and utility of this instrument for drug metabolism studies.

Genotoxicity evaluation of Mequindox in different short-term tests

Quinoxaline-1,4-dioxides (QdNOs) are the potent heterocyclic N-oxides with interesting biological properties such as antibacterial, anticandida, antitubercular, anticancer and antiprotozoal activities. Here, we tested and compared the mequindox (MEQ) for mutagenic abilities in a battery of different short term tests according to OECD guidelines. When compared with the controls, a strong mutagenicity of MEQ and carbadox (CBX) was observed with an approximate concentration-effect relationship in Salmonella reverse mutation test, chromosome aberration test, unscheduled DNA synthesis assay and HGPRT gene mutation test, in the absence and presence of S(9)-mix. In in vivo micronucleus test, CBX produced significant increase in the proportion of micronucleus formation than MEQ in mice bone marrow cells. From these results, we can conclude that MEQ had a strong genotoxic potential to mammalian cells in vitro as well as in vivo and its mutagenicity is slightly higher than CBX. Our results, for the 1st time, discuss the genotoxic potential of MEQ. These results not only confirm the earlier findings about CBX but also extend the knowledge and awareness about the genotoxic risk of QdNO derivatives.

Cytotoxicity and genotoxicity of 1,4-bisdesoxyquinocetone, 3-methylquinoxaline-2-carboxylic acid (MQCA) in human hepatocytes

Quinoxaline-1,4-dioxides, widely used as medicinal feed additives as antibacterial growth promoters, have been shown to exert diverse toxicities. Their toxicities are hypothesized to be closely related to the formation of N-oxide reductive metabolites. 1,4-Bisdesoxyquinocetone and MQCA are important N-oxide reductive metabolites of quinocetone or olaquindox. In this study, we evaluated the cytotoxicity and genotoxicity of the metabolites, 1,4-bisdesoxyquinocetone and MQCA, as well as their parental drugs (quinocetone and olaquindox) in two human hepatocyte cell lines, L-02 and Chang liver cells. All these compounds inhibited the growth of cells in a dose-dependent and time-dependent manner by the MTT assay. Hormesis effects were found in L-02 cells treated with quinocetone at low doses. In the comet assay, although the two metabolites induced dose-related DNA damage in both cell lines, the levels of damage were less than that demonstrated for the parent drugs. The flow cytometric analysis showed that only the two metabolites induced cell cycle arrest at the S phase, and a decrease in the G0/G1, G2/M phase of Chang liver cells, which was not found for the L-02 cells treated with any compounds. The results indicate that 1,4-bisdesoxyquinocetone and MQCA are toxic to L-02 and Chang liver cells, and provide important new information towards understanding the olaquindox and quinocetone toxic mechanisms.