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

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

Metabolite Identification and Pharmacokinetic Behavior of Diaveridine in the Plasma of Pigs and Chickens Based on Radioactive Tracing Coupled With LC/MS-IT-TOF Assay

Diaveridine (DVD) is widely used for the prevention and treatment of coccidiosis and leucocytozoonosis infections in food-producing animals. To gain a better understanding of DVD metabolism and pharmacokinetics in healthy Landrace/Doric Cross castrated male pigs and both female and male Cobb 500 broiler chickens, a method involving radioactive tracing coupled with LC/MS-IT-TOF was developed for the identification and quantitation of DVD and its metabolites in pig and chicken plasma, and then was applied to investigate DVD pharmacokinetics. A simple MCX solid phase extraction procedure was adopted for sample preparation. After a single oral administration of 3H-DVD (10 mg/kg BW), three radioactive compounds (D0: DVD; D1: 3'-desmethyl-DVD; and D2: monoglucuronide of 3'-desmethyl-DVD) were identified in pig plasma, while only two radioactive compounds (D0 and D2) were identified in chicken plasma. In both species, the C max values for all detected compounds were reached at 2 h after dosing. The C max order was D2 (1.38 μg/ml) > D0 (0.49 μg/ml) > D1 (0.24 μg/ml) in pigs and D0 (1.55 μg/ml) > D2 (0.27 μg/ml) in chickens. The longer t 1/2 (elimination half-life) of D0 contributed to the slow elimination of DVD-related compounds. The t 1/2β of D0 in pigs (66.41 h) was significantly longer than that in chickens (48.30 h), but the t 1/2 of total DVD-related metabolites in pigs (42.86 h) was lower than that in chickens (56.11 h). These findings suggested that the metabolism and pharmacokinetics of DVD in pigs and chickens were significantly different, and that this would affect its effectiveness, toxicology, and food safety in these animals.

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.

Generic Hapten Synthesis, Broad-Specificity Monoclonal Antibodies Preparation, and Ultrasensitive ELISA for Five Antibacterial Synergists in Chicken and Milk

An antibody with broad specificity and principally depending on hapten structure and size is a key reagent for developing a class-selective immunoassay. In the present study, three new generic haptens of antibacterial synergists (ASGs) were proposed using trimethoprim as the starting molecule. These haptens contained carboxyl groups on the meta position of trimethoxybenzene for conjugating to protein, while, the common moiety of ASGs, i.e., diaminopyrimidine, was intentionally and maximally exposed to the immune system in animals in order to induce antibodies with broad specificity against ASGs. Five monoclonal antibodies (mAbs) were finally obtained, and 5C4 from the hapten with a short spacer arm, named Hapten A, showed not only uniform broad specificity but also high affinity to all five ASGs. We further determined the possible recognition mechanism of mAbs in terms of conformational and electronic aspects. An indirect competitive ELISA (icELISA)-based 5C4 was established and exhibited IC₅₀ values of 0.067-0.139 μg L^-1 with cross-reactivity of 48.2%-418.7% for the five ASGs in buffer under optimal conditions. The calculated limits of detection of the icELISA for chicken and milk were 0.06-0.8 μg kg^-1 and 0.05-0.6 μg L^-1, respectively. The recoveries in spiked chicken and milk samples were 75.2%-101.4% with a coefficient of variation less than 14.3%. In summary, we have developed, for the first time, a rapid and reliable icELISA for ASGs with significantly improved sensitivity and class selectivity.

Comparative pharmacokinetics of diaveridine in pigs and chickens following single intravenous and oral administration

Comparative pharmacokinetic profiles of diaveridine following single intravenous and oral dose of 10 mg/kg body weight in healthy pigs and chickens were investigated, respectively. Concentrations of diaveridine in plasma samples were determined using a validated high-performance liquid chromatography-ultraviolet (HPLC-UV) method. The concentration-time data were subjected to noncompartmental kinetic analysis by WinNonlin program. The corresponding pharmacokinetic parameters in pigs or chickens after single intravenous administration were as follows, respectively: t_1/2β (elimination half-life) 0.74 ± 0.28 and 3.44 ± 1.07 h; V_d (apparent volume of distribution) 2.70 ± 0.99 and 3.86 ± 0.92 L/kg; Cl_B (body clearance) 2.59 ± 0.62 and 0.80 ± 0.14 L/h/kg; and AUC_0-∞ (area under the blood concentration vs. time curve) 4.11 ± 1.13 and 12.87 ± 2.60 μg∙h/mL. The corresponding pharmacokinetic parameters in pigs or chickens after oral administration were as follows, respectively: t_1/2β 1.78 ± 0.41 and 2.91 ± 0.57 h; C_max (maximum concentration) 0.43 ± 0.24 and 1.45 ± 0.57 μg/mL; T_max (time to reach C_max ) 1.04 ± 0.67 and 3.25 ± 0.71 h; and AUC_0-∞ 1.33 ± 0.55 and 9.28 ± 2.69 μg∙h/mL. The oral bioavailability (F) of diaveridine in pigs or chickens was determined to be 34.6% and 72.2%, respectively. There were significant differences between the pharmacokinetics profiles in these two species.

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.