Long-term dose-dependent response of Mequindox on aldosterone, corticosterone and five steroidogenic enzyme mRNAs in the adrenal of male rats

NH2-MIL-53(Al) Polymer Monolithic Column for In-Tube Solid-Phase Microextraction Combined with UHPLC-MS/MS for Detection of Trace Sulfonamides in Food Samples

In this study, a novel monolithic capillary column based on a NH2-MIL-53(Al) metal-organic framework (MOF) incorporated in poly (3-acrylamidophenylboronic acid/methacrylic acid-co-ethylene glycol dimethacrylate) (poly (AAPBA/MAA-co-EGDMA)) was prepared using an in situ polymerization method. The characteristics of the MOF-polymer monolithic column were investigated by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, Brunauer-Emmett-Teller analysis, and thermogravimetric analysis. The prepared MOF-polymer monolithic column showed good permeability, high extraction efficiency, chemical stability, and good reproducibility. The MOF-polymer monolithic column was used for in-tube solid-phase microextraction (SPME) to efficiently adsorb trace sulfonamides from food samples. A novel method combining MOF-polymer-monolithic-column-based SPME with ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was successfully developed. The linear range was from 0.015 to 25.0 µg/L, with low limits of detection of 1.3-4.7 ng/L and relative standard deviations (RSDs) of < 6.1%. Eight trace sulfonamides in fish and chicken samples were determined, with recoveries of the eight analytes ranging from 85.7% to 113% and acceptable RSDs of < 7.3%. These results demonstrate that the novel MOF-polymer-monolithic-column-based SPME coupled with UHPLC-MS/MS is a highly sensitive, practical, and convenient method for monitoring trace sulfonamides in food samples previously extracted with an adequate solvent.

Mequindox induces apoptosis, DNA damage, and carcinogenicity in Wistar rats

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 110 mg/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 κB (NF-κB) signaling pathway. In addition, MEQ increased the incidence of tumors in rats. Phosphorylated histone H2AX (γ-H2AX) is identified as a biomarker of cellular response to DNA double-strand breaks (DSB). Our data demonstrated that γ-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.

Gestational chronodisruption leads to persistent changes in the rat fetal and adult adrenal clock and function

KEY POINTS

Light at night is essential to a 24/7 society, but it has negative consequences on health. Basically, light at night induces an alteration of our biological clocks, known as chronodisruption, with effects even when this occurs during pregnancy. Here we explored the developmental impact of gestational chronodisruption (chronic photoperiod shift, CPS) on adult and fetal adrenal biorhythms and function. We found that gestational chronodisruption altered fetal and adult adrenal function, at the molecular, morphological and physiological levels. The differences between control and CPS offspring suggest desynchronization of the adrenal circadian clock and steroidogenic pathway, leading to abnormal stress responses and metabolic adaptation, potentially increasing the risk of developing chronic diseases.

ABSTRACT

Light at night is essential to a 24/7 society, but it has negative consequences on health. Basically, light at night induces an alteration of our biological clocks, known as chronodisruption, with effects even when this occurs during pregnancy. Indeed, an abnormal photoperiod during gestation alters fetal development, inducing long-term effects on the offspring. Accordingly, we carried out a longitudinal study in rats, exploring the impact of gestational chronodisruption on the adrenal biorhythms and function of the offspring. Adult rats (90 days old) gestated under chronic photoperiod shift (CPS) decrease the time spent in the open arm zone of an elevated plus maze to 62% and increase the rearing time to 170%. CPS adults maintained individual daily changes in corticosterone, but their acrophases were distributed from 12.00 h to 06.00 h. CPS offspring maintained clock gene expression and oscillation, nevertheless no daily rhythm was observed in genes involved in the regulation and synthesis of steroids. Consistent with adult adrenal gland being programmed during fetal life, blunted daily rhythms of corticosterone, core clock gene machinery, and steroidogenic genes were observed in CPS fetal adrenal glands. Comparisons of the global transcriptome of CPS versus control fetal adrenal gland revealed that 1078 genes were differentially expressed (641 down-regulated and 437 up-regulated). In silico analysis revealed significant changes in Lipid Metabolism, Small Molecule Biochemistry, Cellular Development and the Inflammatory Response pathway (z score: 48-20). Altogether, the present results demonstrate that gestational chronodisruption changed fetal and adult adrenal function. This could translate to long-term abnormal stress responses and metabolic adaptation, increasing the risk of developing chronic diseases.

The Reproductive Toxicity of Mequindox in a Two-Generation Study in Wistar Rats

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.

Mequindox-Induced Kidney Toxicity Is Associated With Oxidative Stress and Apoptosis in the Mouse

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

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.

UPLC-MS/MS Method for Simultaneous Determination of Three Major Metabolites of Mequindox in Holothurian

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 μg/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 μg/kg, while the limit of quantification (LOQ) ranged from 0.79 to 1.59 μg/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.

Prevalence and molecular characterization of oqxAB in clinical Escherichia coli isolates from companion animals and humans in Henan Province, China

Background

The plasmid-encoded multidrug efflux pump oqxAB confers bacterial resistance primarily to olaquindox, quinolones, and chloramphenicol. The aims of this study were to investigate the prevalence of oqxAB among Escherichia coli isolates from dogs, cats, and humans in Henan, China and the susceptibilities of E. coli isolates to common antibiotics.

Methods

From 2012 to 2014, a total of 600 samples which included 400 rectal samples and 200 clinical human specimens were tested for the presence of E. coli. All isolates were screened for oqxAB genes by PCR and sequencing. The MICs of 11 antimicrobial agents were determined by the broth microdilution method. A total of 30 representative oqxAB-positive isolates were subjected to ERIC-PCR and MLST. Additionally, conjugation experiments and southern hybridizations were performed.

Results

Of 270 isolates, 58.5% (62/106) of the isolates from dogs, 56.25% (36/64) of the isolates from cats, and 42.0% (42/100) of the isolates from humans were positive for the oqxAB. Olaquindox resistance was found for 85.7%-100% of oqxAB-positive isolates. Of oqxAB-positive isolates from dogs, cats, and humans, ciprofloxacin resistance was inspected for 85.8%, 59.1%, and 93.8%, respectively. Several oqxAB-positive isolates were demonstrated by ERIC-PCR and MLST, and have high similarity. Phylogenetic analysis showed that oqxAB-positive isolates could be divided into 7 major clusters. OqxAB-positive conjugants were obtained, southern hybridization verified that the oqxAB gene complex was primarily located on plasmids.

Conclusion

In conclusion, oqxAB-positive isolates were widespread in animals and humans in Henan, China. Carriage of oqxAB on plasmids of E. coli isolates may facilitate the emergence of multidrug resistant and its transmission via horizontal transfer, and might pose a potential threat to public health.

Mechanisms of the Testis Toxicity Induced by Chronic Exposure to Mequindox

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.

Toxic metabolites, Sertoli cells and Y chromosome related genes are potentially linked to the reproductive toxicity induced by mequindox

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.

Preparation of T-2-glucoronide with Rat Hepatic Microsomes and Its Use along with T-2 for Activation of the JAK/STAT Signaling Pathway in RAW264.7 Cells

T-2 toxin (T-2), one of the most toxic trichothecene A-type mycotoxins, is biotransformed in animal tissues to modified T-2s (mT-2s) including T-2-glucuronide (T-2-GlcA). In this study, the optimal conditions for T-2-GlcA synthesis were established, and the JAK/STAT pathway in RAW264.7 cells was used to study the toxicity of T-2-GlcA. Because many mT-2 standards are not readily available, optimal conditions for T-2-GlcA synthesis in vitro were established by incubating T-2 with rat liver microsomes, UDPGA, and 0.2% Triton X-100 for 90 min. qRT-PCR and Western blot results showed 21- and 760-fold increases in IL-6 mRNA expression induced by T-2-GlcA and T-2, respectively. Similar differences were observed in JAK3, SOCS2/3, and CIS mRNA expression. T-2-GlcA induced a dose-responsive decrease in STAT1 mRNA expression, whereas the result with T-2 was the opposite. Moreover, the phosphorylation of STAT3 induced by T-2-GlcA was higher than that by T-2, whereas the phosphorylation of STAT1 was to the contrary. Overall, the results show that T-2-GlcA was somewhat toxic, but activation of the JAK/STAT pathway in RAW264.7 was higher by T-2.

Toxic metabolites, MAPK and Nrf2/Keap1 signaling pathways involved in oxidative toxicity in mice liver after chronic exposure to Mequindox

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-кB signaling pathways, as well as the altered metabolism of MEQ, were involved in oxidative toxicity mediated by MEQ in vivo.

Cytotoxicity of T-2 and modified T-2 toxins: induction of JAK/STAT pathway in RAW264.7 cells by hepatopancreas and muscle extracts of shrimp fed with T-2 toxin

T-2 can be biotransformed in animal tissues to modified T-2s (mT-2s). Food contaminated with T-2 and/or mT-2s is a hazard to both animals and humans, including the immune system. In this study, Litopenaeus vannamei were fed T-2 orally for 20 d, and hepatopancreas and muscle extracts, T-2, and T-2-glucuronide (T-2-GluA) were added to RAW264.7 in vitro and their effects on the JAK/STAT pathway were examined. STAT2 mRNA gene expression induced by hepatopancreas and muscle extracts was markedly higher compared with that of T-2 or T-2-GluA group. SCOSs, IL-6 and IL-1β mRNA gene expressions induced by hepatopancreas extract were greater than those induced by muscle extract. Muscle extract significantly activated STAT3 phosphorylation but inhibited STAT1 phosphorylation. Activation of the JAK/STAT pathway by hepatopancreas mT-2s was significantly higher than that by muscle extracts. Muscle and hepatopancreas extracts and T-2 also significantly induced IL-6 mRNA gene expression. With reference to phosphorylation levels, significant activation of JAK1 and STAT2 occurred with T-2 and JAK3 by muscle extract, JAK2 by hepatopancreas extract and STAT1 by T-2-GluA. This study showed that both T-2 and mT-2s are cytotoxic but the activation of the JAK/STAT pathway in RAW264.7 cells by T-2 was greater than that by mT-2s in hepatopancreas and muscle extracts from T-2-fed Litopenaeus vannamei.

The water extract of Veratrilla baillonii could attenuate the subacute toxicity induced by Aconitum brachypodum

BACKGROUND

Aconitum brachypodum Diels (Family Ranunculaceae) is a Chinese ethnodrug and is well known for both its therapeutic application and high toxicity. However, no detoxication strategy is available for the complete elimination of the toxicity of Aconitum plants. Veratrilla baillonii Franch is believed to possess antitoxic effects on the toxicity induced by Aconitum plants and has been clinically used for hundreds of time by Naxi and Lisu nationalities in Yunnan Province of China. To further address the mechanism of the detoxication of Veratrilla baillonii, the effect of water decoction of Veratrilla baillonii (WVBF) on subacute toxicology of SD rats induced by Aconitum brachypodum (CFA), a genus Aconitum, was determined and studied in the present work.

METHODS

The clinical behavior and number of survivors for different dosage of WVBF (25, 50, 100mg/kg) on CFA (4mg/kg) induced rats were observed until day 28. Histological changes and haematological parameters were evaluated. Moreover, Na⁺-K⁺-ATPase pathway in heart as well as key enzymes in liver were determined to further discuss the mechanism.

RESULTS

The results showed that the exposure of CFA led to some subacute toxicity to rats, especially male ones, accompanied with abnormality of serum biochemical index in rats' serum. The toxicological target organs of CFA may be the heart, liver, kidney and brain. It is demonstrated that WVBF could attenuate the toxicity induced by Aconitum brachypodum via promoting the metabolic enzymes CYP3A1 and CYP3A2 in liver, downregulating the expression of Sodium/Calcium exchanger 1 (NCX1) and SCN5A sodium channal mRNA, and inducing Na⁺/K⁺-ATPase activity in heart. This study provides insights into detoxifying measures of Aconitum plants.

CONCLUSIONS

Aconitum brachypodum may lead to subacute toxicity of rats after long term of administration, and the toxicity could be attenuated by Veratrilla baillonii via promoting the metabolic enzymes in liver, downregulating the expression of NCX1 and SCN5A mRNA, and inducing Na⁺/K⁺-ATPase activity in heart.

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.

Genomic and proteomic analysis of the inhibition of synthesis and secretion of aldosterone hormone induced by quinocetone in NCI-H295R cells

Quinoxaline 1,4-dioxides (QdNOs) are widely used as a kind of antibacterial growth promoter in animal husbandry. The adrenal cortex was found to be one of the main toxic targets of QdNOs, accompanied by a decreased aldosterone level. However, the way in which QdNOs decrease production of the hormone aldosterone is far from clear. To illustrate the mechanism by which QdNOs damage the adrenal cortex and decrease aldosterone hormone levels, the QdNOs were screened to choose the drug with most toxic effects on aldosterone production, and then to reveal the mechanism between the gene and protein profiles in human adrenocortical cells (NCI-H295R cells). The results found that quinocetone (QCT) showed the highest adrenal toxic effect among QdNOs. After exposing H295R cells to 10 and 20μM QCT for 24h, compared with blank cells, the gene and protein expression profiles obtained were analyzed by microarray and MALDI TOF/TOF mass spectrometry, respectively. The results of microarray analysis suggested that ABCG1 and SREBF1, which were involved in the cholesterol biosynthetic and metabolic processes, and CYP17A1, NR4A2 and G6PD, which were related to aldosterone biosynthesis, were important molecular targets. It has been speculated that PKC and ERK pathways might be involved in the reduction of aldosterone production caused by QCT, through enhanced mRNA expression of CYP17A1. Additionally, JNK and p38MAPK signal transduction pathways might participate in apoptosis induced by QCT. Twenty-nine and 32 protein spots were successfully identified when cells were treated with 10 and 20μM QCT, respectively. These identified proteins mainly included material synthesis and energy metabolism-related proteins, transcription/translation processing-related proteins, signal transduction proteins, cytoskeletal proteins, molecular chaperones, proteins related to response to stress, and transport proteins. Further investigations suggested that oxidative stress caused by QCT was exacerbated through disruption of the Keap1/Nrf2/ARE anti-oxidative stress pathway. Taken together, the data demonstrated for the first time that the Keap1/Nrf2/ARE pathway plays a crucial role in adrenal toxicity, and that CYP17A1 was the key switch to reduce the aldosterone production induced by QCT. Furthermore, large numbers of genes and proteins and entry points for research in the inhibition of aldosterone synthesis induced by QCT were offered, which will provide new insight into the adrenal toxicity of QdNOs and help to provide a theoretical foundation for the formulation of safety controls for products obtained from animals and to design new QdNOs with less harmful effects.

Quinoxaline 1,4-di-N-Oxides: Biological Activities and Mechanisms of Actions

Quinoxaline 1,4-di-N-oxides (QdNOs) have manifold biological properties, including antimicrobial, antitumoral, antitrypanosomal and antiinflammatory/antioxidant activities. These diverse activities endow them broad applications and prospects in human and veterinary medicines. As QdNOs arouse widespread interest, the evaluation of their medicinal chemistry is still in progress. In the meantime, adverse effects have been reported in some of the QdNO derivatives. For example, genotoxicity and bacterial resistance have been found in QdNO antibacterial growth promoters, conferring urgent need for discovery of new QdNO drugs. However, the modes of actions of QdNOs are not fully understood, hindering the development and innovation of these promising compounds. Here, QdNOs are categorized based on the activities and usages, among which the antimicrobial activities are consist of antibacterial, antimycobacterial and anticandida activities, and the antiprotozoal activities include antitrypanosomal, antimalarial, antitrichomonas, and antiamoebic activities. The structure-activity relationship and the mode of actions of each type of activity of QdNOs are summarized, and the toxicity and the underlying mechanisms are also discussed, providing insight for the future research and development of these fascinating compounds.

Antitoxic effect of Veratrilla baillonii on the acute toxicity in mice induced by Aconitum brachypodum, one of the genus Aconitum

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum brachypodum Diels (Family Ranunculaceae) is well known for both its good therapy and high toxicity in Yunnan and Sichuan provinces in China. Noticeably, Veratrilla baillonii Franch (Family Gentianaceae), an ethnodrug used by Naxi and Lisu nationalities in Yunnan Province, has been widely considered to possess antitoxic effects on Aconitum plants in herbal therapy and folklore medicines.

MATERIALS AND METHODS

The present study was conducted to determine the detoxic activities of the water decoction of Veratrilla baillonii Franch (WVBF) on the the chloroform fraction of Aconitum brachypodum Diels (CFA) induced acute toxicity in mice. The physiological (symptoms, body weight, etc.) as well as pathological and clinical biochemistry parameters were assessed and used as the markers for the toxicity. (1)H nuclear magnetic resonance (NMR) based metabolic approach was adopted to further discuss the mechanism.

RESULTS

The acute poisoning effects of CFA on mice were observed at doses of 20-62.5mgkg(-1), resulting in an oral median lethal dose (LD50) of 41.3mgkg(-1). Histologically, distinct degenerative changes of the heart, liver and kidney were observed. The biochemistry parameters in the serum as well as metabolites in heart and brain were also altered. However, WVBF (25-200mg/kg) attenuated all the acute toxicity and pathological changes, properly regulated the biochemistry parameters, and reversed the concentration alterations for some metabolites in the heart and brain of mice induced by 40mg/kg of CFA to a certain extent.

CONCLUSIONS

WVBF significantly reduced the onset of the CFA toxicity. This study may contribute to further understanding of the toxicological and pharmacological profiles of Aconitum brachypodum and the detoxic property of Veratrilla baillonii.

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.

Cytotoxicity of mequindox and its metabolites in HepG2 cells in vitro and murine hepatocytes in vivo

Mequindox, a quinoxaline 1,4-dioxide, is widely used as a feed additive in the Chinese livestock industry because of its effective antibacterial properties. Many recent studies have found that mequindox is rapidly metabolized to numerous metabolites following administration to animals. There have, however, been few reports describing the cytotoxicity of mequindox metabolites. In this study, HepG2 cells were treated with mequindox (0, 2, 10, 50 or 100 μg/ml) or its major metabolites (0, 40, 100, 250 or 500 μg/ml) for 24h. Mice were administrated with mequindox (0, 50, 200 or 500 mg/kg.bw) for five days. DNA damage in the HepG2 cells and mouse hepatocytes was then assessed using an SCGE assay. The cell cycle of the HepG2 cells was also determined by flow cytometry. Mequindox was found to induce cell cycle arrest to the G2/M phase and cause dose-dependent DNA damage in HepG2 cells in vitro and in murine hepatocytes in vivo. Compared with mequindox, the major metabolites had much smaller effects on the cell cycle and caused much less DNA damage in HepG2 cells. And the results indicated that the process of metabolites formed by reduction of the MEQ acetyl group or reduction of the N → O groups could contribute to DNA damage in murine hepatocytes in vivo.

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.

Assessment of thirteen-week subchronic oral toxicity of cyadox in Beagle dogs

Cyadox (2-formylquinoxaline-N(1),N(4)-dioxide cyanocetylhydrazone) is a new antimicrobial agent and growth-promoter to be used in food-producing animals. Although its toxicity has been clearly documented in rodents, no study is available in non-rodent animals. Therefore, we studied the subchronic effects of cyadox in Beagle dogs to provide additional information with which to establish safety criteria for human exposure. For this purpose, 36 Beagle dogs, 18 males and 18 females, were divided into four groups and fed diets containing 0, 100, 450 and 2500 mg/kg of cyadox, respectively, for 13 weeks. It was found that there were no significant changes among the examined parameters, except for an increase in the level of serum potassium (K(+)) in 2500 mg/kg cyadox group in males at week 13 of the study. However, the K(+) level returned to normal during the recovery period. In conclusion, cyadox showed slight effects in Beagle dogs in the subchronic oral toxicity study. The no-observed-adverse-effect level of cyadox was considered to be 450 mg/kg diet, which equates to approximately 15.3-15.4 mg/kg b.w./day. The study provided subchronic effects of cyadox in Beagle dogs, suggesting that cyadox might present mild toxicity in non-rodents.

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.

Investigation of quinocetone-induced mitochondrial damage and apoptosis in HepG2 cells and compared with its metabolites

Quinocetone (QCT) has been widely used as an animal growth promoter in China. However, amounts of available data indicated that QCT probably had potential toxicity. The present study was aimed to investigate the genotoxicity, mitochondrial damage and apoptosis in HepG2 cells for QCT and its metabolites, DQCT and MQCA. QCT has seriously cytotoxic to HepG2 cells. The cell viability test and cytokinesis-block micronucleus test showed that the micronucleus frequency of cells treated with QCT has increased significantly, compared with DQCT and MQCA. With increasing of QCT concentrations, the genomic template stability and mitochondrial damage of HepG2 cells were aggravated. QCT-induced apoptosis in HepG2 cells were also observed. Data of caspase activities in measurement and real-time RT-PCR possibly suggested both of the mitochondria-dependent and mitochondria-independent pathways participated in the HepG2 cells apoptosis. However, all the results suggested that DQCT and MQCA showed only a little cytotoxic to HepG2 cells. In a word, QCT had toxic effects on HepG2 cells and resulted in the mitochondria-dependent and mitochondria-independent pathways of apoptosis, but the intermediate metabolites of QCT (DQCT and MQCA) were not.

Identification of oxidative stress and responsive genes of HepG2 cells exposed to quinocetone, and compared with its metabolites

Quinocetone, a new quinoxaline 1,4-dioxide derivative used in food-producing animals in China, exerts genotoxic effects on HepG2 cells. It triggers significant cytotoxicity and genotoxicity in vitro, but the detailed mechanism by which quinocetone induces adverse biological effects is not yet known. We analyzed the mechanisms behind quinocetone intoxication by investigating oxidative stress based on non-enzymatic and enzymatic antioxidant activities, and by identifying differentially regulated genes of HepG2 cells exposed to quinocetone using polymerase chain reaction (PCR)-based suppression subtractive hybridization to illustrate the toxicity mechanism of quinocetone. Meanwhile, the characteristics of oxidative stress and differentially regulated genes induced by quinocetone metabolites, 1,4-bisdesoxyquinocetone and 3-methylquinoxaline-2-carboxylic acid, were investigated too. Results showed that quinocetone damaged the antioxidant defense abilities of HepG2 cells by reducing the activities of endogenous antioxidant enzymes, lowering glutathione concentration, and elevating malondialdehyde level. We identified 160 quinocetone-responsive genes that were associated with cell proliferation, glucose metabolism, oxidative stress, and apoptosis, such as NAD(P)H dehydrogenase, quinone 1; and prolyl 4-hydroxylase, beta polypeptide. The expressions of some differentially regulated genes were confirmed by real-time reverse transcription-polymerase chain reaction. However, quinocetone metabolites showed little effects on HepG2 cells. These results showed that reactive oxygen species were the key mediators of quinocetone cytotoxicity in HepG2 cells and that c-MYC-dependent activation of the mitochondrial apoptotic pathway may be associated with quinocetone-induced toxicity.

Systems responses of rats to mequindox revealed by metabolic and transcriptomic profiling

Mequindox is used as an antibiotic drug in livestock; however, its toxicity remains largely unclear. Previously, we investigated metabolic responses of mice to mequindox exposure. In order to evaluate dependences of animal species in response to mequindox insult, we present the metabolic consequences of mequindox exposure in a rat model, by employing the combination of metabonomics and transcriptomics. Metabolic profiling of urine revealed that metabolic recovery is achieved for rats exposed to a low or moderate dose of mequindox, whereas high levels of mequindox exposure trigger liver dysfunction, causing no such recovery. We found that mequindox exposure causes suppression of the tricarboxylic acid cycle and stimulation of glycolysis, which is in contrast to a mouse model previously investigated. In addition, mequindox dosage induces promotion of β-oxidation of fatty acids, which was confirmed by elevated expressions of acox1, hsd17b2, and cpt1a in liver. Furthermore, altered levels of N-methylnicotinate, 1-methylnicotinamide, and glutathione disulfide highlighted the promotion of vitamin B3 antioxidative cycle in rats exposed to mequindox. Moreover, mequindox exposure altered levels of gut microbiotal related co-metabolites, suggesting a perturbation of the gut microflora of the host. Our work provides a comprehensive view of the toxicological effects of mequindox, which is important in the usage of mequindox in animal and human food safety.

Mequindox induced cellular DNA damage via generation of reactive oxygen species

Mequindox, a quinoxaline-N-dioxide derivative that possesses antibacterial properties, has been widely used as a feed additive in the stockbreeding industry in China. While recent pharmacological studies have uncovered potential hazardous effects of mequindox, exactly how mequindox induces pathological changes and the cellular responses associated with its consumption remain largely unexplored. In this study, we investigated the cellular responses associated with mequindox treatment. We report here that mequindox inhibits cell proliferation by arresting cells at the G2/M phase of the cell cycle. Interestingly, this mequindox-associated deleterious effect on cell proliferation was observed in human, pig as well as chicken cells, suggesting that mequindox acts on evolutionarily conserved target(s). To further understand the mequindox-host interaction and the mechanism underlying mequindox-induced cell cycle arrest, we measured the cellular content of DNA damage, which is known to perturb cell proliferation and compromise cell survival. Accordingly, using γ-H2AX as a surrogate marker for DNA damage, we found that mequindox treatment induced cellular DNA damage, which paralleled the chemical-induced elevation of reactive oxygen species (ROS) levels. Importantly, expression of the antioxidant enzyme catalase partially alleviated these mequindox-associated effects. Taken together, our results suggest that mequindox cytotoxicity is attributable, in part, to its role as a potent inducer of DNA damage via ROS.