Metabolism of cyadox by the intestinal mucosa microsomes and gut flora of swine, and identification of metabolites by high-performance liquid chromatography combined with ion trap/time-of-flight mass spectrometry

The Spectrum of Antimicrobial Activity of Cyadox against Pathogens Collected from Pigs, Chicken, and Fish in China

Cyadox has potential use as an antimicrobial agent in animals. However, its pharmacodynamic properties have not been systematically studied yet. In this study, the in vitro antibacterial activities of cyadox were assayed, and the antibacterial efficacy of cyadox against facultative anaerobes was also determined under anaerobic conditions. It was shown that Clostridium perfringens and Pasteurella multocida (MIC = 0.25 and 1 μg/mL) from pigs, Campylobacter jejuni and Pasteurella multocida from poultry, E. coli, Streptococcus spp., and Flavobacterium columnare from fish were highly susceptible to cyadox (MIC= 1 and 8 μg/mL). However, F. columnare has no killing effect for drug tolerance. Under in vitro anaerobic conditions, the antibacterial activity of cyadox against most facultative anaerobes was considerably enhanced Under anaerobic conditions for the facultative anaerobes, susceptible bacteria were P. multocida, Aeromonas spp. (including A. hydrophila, A. veronii, A. jandaei, A. caviae, and A. sobria, excluding A. punctata), E. coli, Salmonella spp. (including S. choleraesui, S. typhimurium, and S. pullorum), Proteus mirabilis, Vibrio fluvialis, Yersinia ruckeri, Erysipelothrix, Acinetobacter baumannii, and Streptococcus agalactiae (MICs were 0.25~8 μg/mL, MBCs were 1–64 μg/mL). Intermediate bacteria were Enterococcus spp. (including E. faecalis and E. faecium), Yersinia enterocolitica, and Streptococcus spp. (MICs mainly were 8~32 μg/mL, MBCs were 16~128 μg/mL). This study firstly showed that cyadox had strong antibacterial activity and had the potential to be used as a single drug in the treatment of bacterial infectious diseases.

Drug response in association with pharmacogenomics and pharmacomicrobiomics: towards a better personalized medicine

Researchers have long been presented with the challenge imposed by the role of genetic heterogeneity in drug response. For many years, Pharmacogenomics and pharmacomicrobiomics has been investigating the influence of an individual's genetic background to drug response and disposition. More recently, the human gut microbiome has proven to play a crucial role in the way patients respond to different therapeutic drugs and it has been shown that by understanding the composition of the human microbiome, we can improve the drug efficacy and effectively identify drug targets. However, our knowledge on the effect of host genetics on specific gut microbes related to variation in drug metabolizing enzymes, the drug remains limited and therefore limits the application of joint host-microbiome genome-wide association studies. In this paper, we provide a historical overview of the complex interactions between the host, human microbiome and drugs. While discussing applications, challenges and opportunities of these studies, we draw attention to the critical need for inclusion of diverse populations and the development of an innovative and combined pharmacogenomics and pharmacomicrobiomics approach, that may provide an important basis in personalized medicine.

Sanguinarine metabolism and pharmacokinetics study in vitro and in vivo

Sanguinarine (SA) is a benzo[c] phenanthridine alkaloid which has a variety of pharmacological properties. However, very little was known about the pharmacokinetics of SA and its metabolite dihydrosanguinarine (DHSA) in pigs. The purpose of this work was to study the intestinal metabolism of SA in vitro and in vivo. Reductive metabolite DHSA was detected during incubation of SA with intestinal mucosa microsomes, cytosol, and gut flora. After oral (p.o.) administration of SA, the result showed SA might be reduced to DHSA in pig intestine. After i.m. administration, SA and DHSA rapidly increased to reach their peak concentrations (C_max , 30.16 ± 5.85, 5.61 ± 0.73 ng/ml, respectively) at 0.25 hr. Both compounds were completely eliminated from the plasma after 24 hr. After single oral administration, SA and DHSA rapidly increased to reach their C_max (3.41 ± 0.36, 2.41 ± 0.24 ng/ml, respectively) at 2.75 ± 0.27 hr. The half-life (T_1/2 ) values were 2.33 ± 0.11 hr and 2.20 ± 0.12 hr for SA and DHSA, respectively. After multiple oral administration, the average steady-state concentrations (C_ss ) of SA and DHSA were 3.03 ± 0.39 and 1.42 ± 0.20 ng/ml. The accumulation indexes for SA and DHSA were 1.21 and 1.11. The work reported here provides important information on the metabolism sites and pharmacokinetic character of SA. It explains the reasons for low toxicity of SA, which is useful for the evaluation of its performance.

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.

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.

N-O Reduction and ROS-Mediated AKT/FOXO1 and AKT/P53 Pathways Are Involved in Growth Promotion and Cytotoxicity of Cyadox

Cyadox is a novel derivative of quinoxaline-1,4-dioxides (QdNOs) with the potential to be developed as a feed additive. However, the pharmacological and toxicological bioactive molecules of cyadox and the molecular mechanism of its pharmacological and toxic actions remain unclear. In the present study, cyadox and its main metabolites of cy1, cy4, cy6, and cy12 were selected; the growth promotion characteristic was indicated by the mRNA level of EGF; and the cytotoxicity of cyadox was determined by methylthiazol tetrazolium bromide (MTT) assay, lactate dehydrogenase (LDH) release, and Annexin V-FITC/PI apoptosis detection kit with flow cytometry. The intracellular ROS, cyclin D1, and Akt/P53/FOXO1 signaling pathway were also investigated. Our data suggested that cyadox showed relatively higher activity than its metabolites, and the ROS was generated from N-O reduction of cyadox. Moreover, cyadox (2 μM) activated the Akt and increased the EGF, cyclin D1, and FOXO1 expression levels. Cyadox (100 μM) induced cytotoxicity in L02 cells in a concentration- and time-dependent manner. Additionally, the activated P53 pathway, hyperactivated Akt, and apoptosis were found in L02 cells after incubation with 100 μM cyadox. Our data demonstrated that Akt promoted cell survival when it was mildly activated by cyadox at 2 μM, and Akt leads to apoptosis when it was severely activated by cyadox at 100 μM. Thus, the present study revealed that N-O reduction of cyadox and ROS-mediated AKT/FOXO1 and AKT/P53 pathways were involved in growth promotion and cytotoxicity of cyadox.

A novel approach for the prediction of species-specific biotransformation of xenobiotic/drug molecules by the human gut microbiota

The human gut microbiota is constituted of a diverse group of microbial species harbouring an enormous metabolic potential, which can alter the metabolism of orally administered drugs leading to individual/population-specific differences in drug responses. Considering the large heterogeneous pool of human gut bacteria and their metabolic enzymes, investigation of species-specific contribution to xenobiotic/drug metabolism by experimental studies is a challenging task. Therefore, we have developed a novel computational approach to predict the metabolic enzymes and gut bacterial species, which can potentially carry out the biotransformation of a xenobiotic/drug molecule. A substrate database was constructed for metabolic enzymes from 491 available human gut bacteria. The structural properties (fingerprints) from these substrates were extracted and used for the development of random forest models, which displayed average accuracies of up to 98.61% and 93.25% on cross-validation and blind set, respectively. After the prediction of EC subclass, the specific metabolic enzyme (EC) is identified using a molecular similarity search. The performance was further evaluated on an independent set of FDA-approved drugs and other clinically important molecules. To our knowledge, this is the only available approach implemented as 'DrugBug' tool for the prediction of xenobiotic/drug metabolism by metabolic enzymes of human gut microbiota.

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.

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.

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

The metabolism, distribution, and elimination of cyadox (CYA) is investigated in pigs, chickens, carp, and rats to identify the marker residue and target tissue of CYA in food animals for food safety concerns. Following a single oral gavage of [(3)H]-CYA, the total radioactivity was rapidly excreted, with more than 95% of the dose excreted within 14 days in the four species. Fecal excretion of the total radioactivity was 66.2% and 51.6%, and urinary excretion of the total radioactivity was 28.35% and 44.3% in rats and pigs, respectively. Radioactivity was observed in nearly all of the tissues in the first 6 h after 7 days of consecutive oral dosing. The highest radioactivity and longest persistence were in the livers and kidneys, where the majority of the radioactivity was cleared within 7 days. A total of 15 metabolites were identified in rats, pigs, chickens, and carp, and eight new metabolites were identified for the first time in vivo. No parent drug could be detected in the tissues of rats and pigs. The major metabolites of CYA were Cy1, Cy3, and Cy6 in pigs, Cy1, Cy5, and Cy6 in chickens, Cy1, Cy2, and Cy4 in carp, and Cy1, Cy2, Cy4, and Cy5 in rats. Cy1 was suggested to be the marker residue, and the kidneys were identified as the target tissue of CYA in pigs and chickens. These results provide comprehensive information for the food safety evaluation of CYA in food animals and will improve the understanding of the pharmacology and toxicology of CYA in animals.

High performance liquid chromatography-tandem mass spectrometry method for ex vivo metabolic studies of a rhenium-labeled radiopharmaceutical for liver cancer

The radio-isotope rhenium-labeled N-[2-(triphenylmethyl)thioethyl]-3-aza-19-ethyloxycarbonyl-3-[2-(triphenylmethyl)thioethyl] octadecanoate) ligand (188Re-MN-16ET) is a novel therapeutic agent under preclinical evaluation for hepatoma. A reversed-phase high performance liquid chromatography coupled with a tandem mass spectrometric analysis method and diode array detector (DAD) involving a T type splitter was developed to characterize this pharmaceutical in rat liver tissue solution and determine its biotransformation rate. The separation was accomplished on a C18 column (chromolith silica, 4.6 mm x 100 mm) using an acetonitrile-ammonium acetate buffer gradient as the mobile phase. The detection was achieved by DAD set at 250nm and tandem mass spectrometry using electrospray ionization in the positive ion mode. Re-MN-16ET displayed a retention time of 23.2 min and a transition ion pair corresponding to m/z677 --> 631 for multiple reaction monitoring. Its biotransformation reaction in rat liver homogenate proceeded for 90 min in a 37°C water bath. The characterization was conducted using aliquots that were extracted and concentrated from the reaction mixture for various incubation times. Re-MN-16ET exhibited a biotransformation half-life (t1/2) of 8-9 min in liver tissue solution and was almost completely exhausted after 90 min. Two of its metabolites, consisting of the Re-labeled carboxylic acid derivative, predominately, and its corresponding demetallized disulfide ligand were found in the liver homogenate, providing a metabolism pathway for the radio-pharmaceutical.

Tissue deposition and residue depletion of cyadox and its three major metabolites in pigs after oral administration

Tissue deposition and residue depletion profiles of cyadox (Cyx) and its three major metabolites, including 1,4-bisdesoxycyadox (Cy1), 4-desoxycyadox (Cy2), and quinoxaline-2-carboxylic acid (QCA), in pigs after multiple oral administrations were determined. Thirty-five healthy adult pigs were randomly divided into seven groups and orally treated with Cyx at a dosage of 20 mg/kg of body weight for five consecutive days. Each group of five pigs was randomly slaughtered 12, 24, 72, 120, 168, 216, and 264 h after the last dosing, and tissue samples, including muscle, liver, kidney, and fat, were collected and analyzed via the liquid chromatography-tandem mass spectrometry method. The concentration-time data of Cyx and its three metabolites (Cy1, Cy2, and QCA) were analyzed with WinNonlin. Results showed that metabolites of Cyx were quickly generated in swine tissues and the concentrations of QCA in kidney were higher than those of Cyx and other metabolites in all edible tissues. These results provide further insight into the metabolism of Cyx and confirmation of the residue marker and target tissue of Cyx in pigs.

Mechanism of porcine liver xanthine oxidoreductase mediated N-oxide reduction of cyadox as revealed by docking and mutagenesis studies

Xanthine oxidoreductase (XOR) is a cytoplasmic molybdenum-containing oxidoreductase, catalyzing both endogenous purines and exogenous compounds. It is suggested that XOR in porcine hepatocytes catalyzes the N-oxide reduction of quinoxaline 1,4-di-N-oxides (QdNOs). To elucidate the molecular mechanism underlying this metabolism, the cDNA of porcine XOR was cloned and heterologously expressed in Spodoptera frugiperda insect cells. The bovine XOR, showing sequence identity of 91% to porcine XOR, was employed as template for homology modeling. By docking cyadox, a representative compound of QdNOs, into porcine XOR model, eight amino acid residues, Gly47, Asn352, Ser360, Arg427, Asp430, Asp431, Ser1227 and Lys1230, were located at distances of less than 4Å to cyadox. Site-directed mutagenesis was performed to analyze their catalytic functions. Compared with wild type porcine XOR, G47A, S360P, D431A, S1227A, and K1230A displayed altered kinetic parameters in cyadox reduction, similarly to that in xanthine oxidation, indicating these mutations influenced electron-donating process of xanthine before subsequent electron transfer to cyadox to fulfill the N-oxide reduction. Differently, R427E and D430H, both located in the 424-434 loop, exhibited a much lower K(m) and a decreased V(max) respectively in cyadox reduction. Arg427 may be related to the substrate binding of porcine XOR to cyadox, and Asp430 is suggested to be involved in the transfer of electron to cyadox. This study initially reveals the possible catalytic mechanism of porcine XOR in cyadox metabolism, providing with novel insights into the structure-function relationship of XOR in the reduction of exogenous di-N-oxides.

Impact of cyadox on human colonic microflora in chemostat models

The aim of this study was to evaluate the microbiological safety of cyadox, a new member of quinoxaline-1,4-dioxides (QdNOs), on human intestinal flora. Four chemostats containing human fecal flora were exposed to 0, 16, 32, and 128 μg/mL of cyadox, respectively. Bacterial populations, resistance rates of two predominant bacteria and short-chain fatty acids (SCFA) were monitored daily prior to and during drug MOA Laboratory of Risk Assessment for Quality and Safety of Livestock and Poultry Products exposure. Colonization resistance (CR) of each community was determined by three successive daily challenges of Salmonella typhimurium. Efflux pump gene (oqxAB) in the Escherichia coli and Enterococcus strains were analyzed by PCR amplification and DNA sequencing. No change in SCFA was observed after exposure to different concentrations of cyadox. Lower concentration of cyadox (16 μg/mL) had no adverse effect on human microflora. However, higher concentrations of cyadox (32 and 128 μg/mL) could change bacterial population and increase the proportion of resistant E. coli and Enterococcus. More than 26% (12/46) of cyadox resistant E. coli strains contained oqxAB gene, while all the resistant Enterococcus were negative to oqxAB gene. Relationship between the occurrence of oqxAB gene and cyadox exposure is inconclusive. Our data indicated that 16 μg/mL might be the no observed effect concentration (NOEC) of cyadox. Derived microbiological acceptable daily intake (mADI) would be 1552.03 μg/kg d. The data obtained in present study indicated that cyadox was a safe member of QdNOs family of antimicrobial agents.

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.