Mequindox

Mequindox induces apoptosis, DNA damage, and carcinogenicity in Wistar rats.[Pubmed:30922968]

Food Chem Toxicol. 2019 Mar 25;127:270-279.

Mequindox (MEQ) is a synthetic antibacterial agent. Recent studies showed that MEQ and its primary metabolites exhibit strong genotoxicity to mammalian cells, and MEQ induced carcinogenicity in mice. These findings suggest that chronic exposure to MEQ could lead to an increased risk of cancer later in life. In the present study, four groups of Wistar rats (55 rats/sex/group) were fed with diets containing MEQ (0, 25, 55, and 110mg/kg) for 2 years. The results showed that the hematological system, liver, kidneys, and adrenal glands, as well as the developmental and reproductive systems, were the main targets for MEQ. Liver toxicity mediated by MEQ was associated with apoptosis and the nuclear factor kappaB (NF-kappaB) signaling pathway. In addition, MEQ increased the incidence of tumors in rats. Phosphorylated histone H2AX (gamma-H2AX) is identified as a biomarker of cellular response to DNA double-strand breaks (DSB). Our data demonstrated that gamma-H2AX expression was significantly increased in tumors. Thus, high levels of DSB might be responsible for carcinogenesis in rats, and further investigation is absolutely required to clarify the exact molecular mechanisms for carcinogenicity caused by MEQ in vivo.

Corrigendum: The Reproductive Toxicity of Mequindox in a Two-Generation Study in Wistar Rats.[Pubmed:30627103]

Front Pharmacol. 2018 Dec 21;9:1489.

[This corrects the article DOI: 10.3389/fphar.2018.00870.].

Corrigendum: Mequindox Induced Genotoxicity and Carcinogenicity in Mice.[Pubmed:30546310]

Front Pharmacol. 2018 Nov 29;9:1387.

[This corrects the article DOI: 10.3389/fphar.2018.00361.].

The Reproductive Toxicity of Mequindox in a Two-Generation Study in Wistar Rats.[Pubmed:30186160]

Front Pharmacol. 2018 Aug 17;9:870.

Mequindox (MEQ), belonging to quinoxaline-di-N-oxides (QdNOs), has been extensively used as a synthetic antibacterial agent. To evaluate the reproductive toxicity of MEQ, different concentrations of MEQ were administered to Wistar rats by feeding diets containing 0, 25, 55, 110, and 275 mg/kg, respectively. Each group consisting of 25 males and 25 females (F0) was treated with different concentrations of MEQ for 12-week period time, prior to mating and during mating, gestation, parturition and lactation. At weaning, 25 males and 25 females of F1 generation weanlings per group were randomly selected as parents for the F2 generation. Selected F1 weanlings were exposed to the same diet and treatment as their parents. The number of live litter and indexes of mating and fertility were significantly decreased in the F1 and F2 generation at 110 and 275 mg/kg groups. Significant decrease in pup vitality during lactation was observed in F1 litter at 275 mg/kg group, in F2 litter at 55, 110, and 275 mg/kg groups. A downward trend in the body weights was observed in F1 pups at 55, 110, and 275 mg/kg MEQ groups, and in F2 pups at 110 and 275 mg/kg MEQ groups. The changed levels of ALT, AST, CREA, BUN, UA, Na, and K were noted in the serum of rats. The histopathologic examination showed that MEQ induced toxicity in the liver, kidney, adrenal, uterus and testis. The no-observed-adverse-effect level (NOAEL) for reproduction toxicity of MEQ was 25 mg/kg diet. The malformations and severe maternal toxicity of MEQ caused adverse effects on the conceptus and embryo, which result in fetal malformations and fetal deaths. In summary, the present study showed that MEQ induced maternal, embryo and reproductive toxicities as well as teratogenicity in rats.

UPLC-MS/MS Method for Simultaneous Determination of Three Major Metabolites of Mequindox in Holothurian.[Pubmed:29805832]

J Anal Methods Chem. 2018 Apr 1;2018:2768047.

This study developed an ultraperformance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method for the detection of three major metabolites of Mequindox, including 3-methyl-quinoxaline-2-carboxylic acid, 1-desoxyMequindox, and 1,4-bisdesoxyMequindox (MQCA, 1-DMEQ, and BDMEQ), in holothurian. Target analytes were simplified with ultrasound-assisted acidolysis extracted without complicated enzymolysis steps. After that, each sample was centrifuged and purified by an Oasis MAX cartridge. Then, the processed samples were separated and monitored by UPLC-MS/MS. This developed method has been validated according to FDA criteria. At fortified levels of 2, 10, and 20 mug/kg, recoveries ranged from 82.5% to 93.5% with the intraday RSD less than 7.27% and interday RSD less than 11.8%. The limit of detection (LOD) of all the three metabolites ranged from 0.21 to 0.48 mug/kg, while the limit of quantification (LOQ) ranged from 0.79 to 1.59 mug/kg. On application to commercial samples, 14 of 20 samples were detected positive for the three target analytes, with positive rate at 70 percentage. The result indicated that this method was specific, sensitive, and suitable for the quantification and conformation of the three major metabolites of MEQ in holothurian.

Mequindox-Induced Kidney Toxicity Is Associated With Oxidative Stress and Apoptosis in the Mouse.[Pubmed:29765325]

Front Pharmacol. 2018 May 1;9:436.

Mequindox (MEQ), belonging to quinoxaline-di-N-oxides (QdNOs), is a synthetic antimicrobial agent widely used in China. Previous studies found that the kidney was one of the main toxic target organs of the QdNOs. However, the mechanisms underlying the kidney toxicity caused by QdNOs in vivo still remains unclear. The present study aimed to explore the molecular mechanism of kidney toxicity in mice after chronic exposure to MEQ. MEQ led to the oxidative stress, apoptosis, and mitochondrial damage in the kidney of mice. Meanwhile, MEQ upregulated Bax/Bcl-2 ratio, disrupted mitochondrial permeability transition pores, caused cytochrome c release, and a cascade activation of caspase, eventually induced apoptosis. The oxidative stress mediated by MEQ might led to mitochondria damage and apoptosis in a mitochondrial-dependent apoptotic pathway. Furthermore, upregulation of the Nrf2-Keap1 signaling pathway was also observed. Our findings revealed that the oxidative stress, mitochondrial dysfunction, and the Nrf2-Keap1 signaling pathway were associated with the kidney apoptosis induced by MEQ in vivo.

Mequindox Induced Genotoxicity and Carcinogenicity in Mice.[Pubmed:29692735]

Front Pharmacol. 2018 Apr 10;9:361.

Mequindox (MEQ), acting as an inhibitor of deoxyribonucleic acid (DNA) synthesis, is a synthetic heterocyclic N-oxides. To investigate the potential carcinogenicity of MEQ, four groups of Kun-Ming (KM) mice (50 mice/sex/group) were fed with diets containing MEQ (0, 25, 55, and 110 mg/kg) for one and a half years. The result showed adverse effects on body weights, feed consumption, hematology, serum chemistry, organ weights, relative organ weights, and incidence of tumors during most of the study period. Treatment-related changes in hematology, serum chemistry, relative weights and histopathological examinations revealed that the hematological system, liver, kidneys, and adrenal glands, as well as the developmental and reproductive system, were the main targets after MEQ administration. Additionally, MEQ significantly increased the frequency of micronucleated normochromatic erythrocytes in bone marrow cells of mice. Furthermore, MEQ increased the incidence of tumors, including mammary fibroadenoma, breast cancer, corticosuprarenaloma, haemangiomas, hepatocarcinoma, and pulmonary adenoma. Interestingly, the higher incidence of tumors was noted in M25 mg/kg group, the lowest dietary concentration tested, which was equivalent to approximately 2.25 and 1.72 mg/kg b.w./day in females and males, respectively. It was assumed that the lower toxicity might be a reason for its higher tumor incidence in M25 mg/kg group. This finding suggests a potential relationships among the dose, general toxicity and carcinogenicity in vivo, and further study is required to reveal this relationship. In conclusion, the present study demonstrates that MEQ is a genotoxic carcinogen in KM mice.

Toxic metabolites, Sertoli cells and Y chromosome related genes are potentially linked to the reproductive toxicity induced by mequindox.[Pubmed:29152098]

Oncotarget. 2017 Sep 15;8(50):87512-87528.

Mequindox (MEQ) is a relatively new synthetic antibacterial agent widely applied in China since the 1980s. However, its reproductive toxicity has not been adequately performed. In the present study, four groups of male Kunming mice (10 mice/group) were fed diets containing MEQ (0, 25, 55 and 110 mg/kg in the diet) for up to 18 months. The results show that M4 could pass through the blood-testis barrier (BTB), and demonstrate that Sertoli cells (SCs) are the main toxic target for MEQ to induce spermatogenesis deficiency. Furthermore, adrenal toxicity, adverse effects on the hypothalamic-pituitary-testicular axis (HPTA) and Leydig cells, as well as the expression of genes related to steroid biosynthesis and cholesterol transport, were responsible for the alterations in sex hormones in the serum of male mice after exposure to MEQ. Additionally, the changed levels of Y chromosome microdeletion related genes, such as DDX3Y, HSF2, Sly and Ssty2 in the testis might be a mechanism for the inhibition of spermatogenesis induced by MEQ. The present study illustrates for the first time the toxic metabolites of MEQ in testis of mice, and suggests that SCs, sex hormones and Y chromosome microdeletion genes are involved in reproductive toxicity mediated by MEQ in vivo.

Mechanisms of the Testis Toxicity Induced by Chronic Exposure to Mequindox.[Pubmed:29018347]

Front Pharmacol. 2017 Sep 26;8:679.

Mequindox (MEQ) is a synthetic antimicrobial agent widely used in China since the 1980s. Although the toxicity of MEQ is well recognized, its testis toxicity has not been adequately investigated. In the present study, we provide evidence that MEQ triggers oxidative stress, mitochondrion dysfunction and spermatogenesis deficiency in mice after exposure to MEQ (0, 25, 55, and 110 mg/kg in the diet) for up to 18 months. The genotoxicity and adrenal toxicity may contribute to sperm abnormalities caused by MEQ. Moreover, using LC/MS-IT-TOF analysis, two metabolites, 3-methyl-2-(1-hydroxyethyl) quinoxaline-N4-monoxide (M4) and 3-methyl-2-(1-hydroxyethyl) quinoxaline-N1-monoxide (M8), were detected in the serum of mice, which directly confirms the relationship between the N-->O group reduction metabolism of MEQ and oxidative stress. Interestingly, only M4 was detected in the testes, suggesting that the higher reproductive toxicity of M4 than M8 might be due to the increased stability of M4-radical (M4-R) compared to M8-radical (M8-R). Furthermore, the expression of the blood-testis barrier (BTB)-associated junctions such as tight junctions, gap junctions and basal ectoplasmic specializations were also examined. The present study demonstrated for the first time the role of the M4 in testis toxicity, and illustrated that the oxidative stress, mitochondrion dysfunction and interference in spermatogenesis, as well as the altered expression of BTB related junctions, were involved in the reproductive toxicity mediated by MEQ in vivo.

Pharmacokinetics of Mequindox and Its Marker Residue 1,4-Bisdesoxymequindox in Swine Following Multiple Oral Gavage and Intramuscular Administration: An Experimental Study Coupled with Population Physiologically Based Pharmacokinetic Modeling.[Pubmed:28640606]

J Agric Food Chem. 2017 Jul 19;65(28):5768-5777.

Mequindox (MEQ) is a quinoxaline-N,N-dioxide antibiotic used in food-producing animals. MEQ residue in animal-derived foods is a food safety concern. The tissue distribution of MEQ and its marker residue 1,4-bisdesoxyMequindox (M1) were determined in swine following oral gavage or intramuscular injection twice daily for 3 days. The experimental data were used to construct a flow-limited physiologically based pharmacokinetic (PBPK) model. The model predictions correlated with available data well. Monte Carlo analysis showed that the times needed for M1 concentrations to fall below limit of detection (5 mug/kg) in liver for the 99th percentile of the population were 27 and 34 days after oral gavage and intramuscular administration twice daily for 3 days, respectively. This population PBPK model can be used to predict depletion kinetic profiles and tissue residues of MEQ's marker residue M1 in swine and as a foundation for scaling to other quinoxaline-N,N-dioxide antibiotics and to other animal species.

Toxic metabolites, MAPK and Nrf2/Keap1 signaling pathways involved in oxidative toxicity in mice liver after chronic exposure to Mequindox.[Pubmed:28157180]

Sci Rep. 2017 Feb 3;7:41854.

Mequindox (MEQ) is a synthetic antimicrobial agent of quinoxaline-1,4-dioxide group (QdNOs). The liver is regarded as the toxicity target of QdNOs, and the role of N --> O group-associated various toxicities mediated by QdNOs is well recognized. However, the mechanism underlying the in vivo effects of MEQ on the liver, and whether the metabolic pathway of MEQ is altered in response to the pathophysiological conditions still remain unclear. We now provide evidence that MEQ triggers oxidative damage in the liver. Moreover, using LC/MS-ITTOF analysis, two metabolites of MEQ were detected in the liver, which directly confirms the potential connection between N --> O group reduction metabolism of MEQ and liver toxicity. The gender difference in MEQ-induced oxidative stress might be due to adrenal toxicity and the generation of M4 (2-isoethanol 1-desoxyMequindox). Furthermore, up-regulation of the MAPK and Nrf2-Keap1 family and phase II detoxifying enzymes (HO-1, GCLC and NQO1) were also observed. The present study demonstrated for the first time the protein peroxidation and a proposal metabolic pathway after chronic exposure of MEQ, and illustrated that the MAPK, Nrf2-Keap1 and NF-small ka, CyrillicB signaling pathways, as well as the altered metabolism of MEQ, were involved in oxidative toxicity mediated by MEQ in vivo.