Search Results (137)

Kratom alkaloids are classified as aromatic pentacyclic indole and substituted carbonyl oxindole alkaloids. This study investigates the metabolism and interactions of indole alkaloids using in silico tools, including ADMET Predictor 13.0™, to assess pharmacokinetic and metabolic profiles. The analysis examined absorption, distribution, metabolism, and excretion (ADME), focusing on cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzyme interactions, drug transporters, and clearance. Most indole alkaloids showed strong substrate interaction and inhibition of CYP3A4 (79–99% confidence) and induction of CYP1A2 (up to 94% confidence). Among UGT enzymes, UGT1A1 demonstrated the highest substrate affinity (97%), while none interacted with UGT2B15. All alkaloids showed strong P-glycoprotein (Pgp) interaction but minimal inhibition of BCRP. Mitralactonine exhibited the highest skin permeability, and Mitralactonal showed maximal jejunal permeability. Most indole alkaloids demonstrated significant blood–brain barrier penetration (up to 99% confidence) and compliance with Lipinski’s rule of five. Predictive modeling indicated notable effects on hepatic microsomal clearance parameters. This investigation offers the first comprehensive in silico ADMET profiling of kratom indole alkaloids, uncovering their CYP3A4 inhibition potential and metabolic liabilities to prioritize candidates for safer therapeutic development, though limited by model biases, applicability domain restrictions, and inability to fully capture biological complexity, stereochemistry, or interindividual variability necessitating experimental in vitro and in vivo validation. Full article

This study evaluated the protective effects of naringin (NG) against intestinal injury in 7-day-old piglets infected with porcine epidemic diarrhea virus (PEDV). Eighteen piglets (Duroc × Landrace × Large, body weight = 2.58 ± 0.05 kg) were divided into three treatment groups based on similar body weights and equal numbers of males and females: the blank control group (CON group), the PEDV infection group (PEDV group), and the NG intervention + PEDV infection group (NG + PEDV group) (n = 6 per group). The experiment lasted for 11 days, comprising a pre-feeding period from days 0 to 3 and a formal experimental period from days 4 to 10. On days 4–10 of the experiment, piglets in the NG + PEDV group were orally administered NG (10 mg/kg). On Day 8 of the experiment, piglets in the PEDV and NG + PEDV groups were inoculated with PEDV (3 mL, 10⁶ 50% tissue culture infective dose (TCID₅₀) per milliliter). On day 11 of the experiment, piglets were euthanized for sample collection. PEDV infection caused significant intestinal damage, including a decreased (p < 0.05) villus height in the duodenum and ileum and an increased (p < 0.05) crypt depth in all intestinal segments. This intestinal damage was accompanied by an impaired absorptive function, as indicated by reduced (p < 0.05) serum D-xylose. Further results showed that PEDV compromised the intestinal antioxidant capacity by decreasing (p < 0.05) glutathione peroxidase and catalase activities, and it stimulated the intestinal inflammatory response by upregulating (p < 0.05) the expression of key inflammatory genes, including regenerating family member 3 gamma (REG3G; duodenum, jejunum, colon), S100 calcium binding protein A9 (S100A9; ileum, colon), interleukin 1 beta (IL-1β; ileum, colon), and S100 calcium binding protein A8 (S100A8; colon). PEDV also suppressed the intestinal lipid metabolism pathway by downregulating (p < 0.05) the ileal expression of Solute Carrier Family 27 Member 4 (SLC27A4), Microsomal Triglyceride Transfer Protein (MTTP), Apolipoprotein A4 (APOA4), Apolipoprotein C3 (APOC3), Diacylglycerol O-Acyltransferase 1 (DGAT1), and Cytochrome P450 Family 2 Subfamily J Member 34 (CYP2J34). Moreover, PEDV suppressed the intestinal antiviral ability by downregulating (p < 0.05) interferon (IFN) signaling pathway genes, including MX dynamin like GTPase 1 (MX1) and ISG15 ubiquitin like modifier (ISG15) in the duodenum; weakened intestinal water and ion transport by downregulating (p < 0.05) aquaporin 10 (AQP10) and potassium inwardly rectifying channel subfamily J member 13 (KCNJ13) in the duodenum, aquaporin 7 (AQP7) and transient receptor potential cation channel subfamily V member 6 (TRPV6) in the ileum, and TRPV6 and transient receptor potential cation channel subfamily M member 6 (TRPM6) in the colon; and inhibited intestinal digestive and absorptive function by downregulating (p < 0.05) phosphoenolpyruvate carboxykinase 1 (PCK1) in the duodenum and sucrase-isomaltase (SI) in the ileum. Notably, NG effectively counteracted these detrimental effects. Moreover, NG activated the IFN signaling pathway in the jejunum and suppressed PEDV replication in the colon. In conclusion, NG alleviates PEDV-induced intestinal injury by enhancing the antioxidant capacity, suppressing inflammation, normalizing the expression of metabolic and transport genes, and improving the antiviral ability. Full article

Background/Objectives: Cytochrome P450 (CYP) enzymes are crucial for drug metabolism, yet inter-individual variability in their activity remains a significant clinical challenge. Current phenotyping methods are often impractical or even impossible, particularly in forensic toxicology and vulnerable populations. This proof-of-concept study investigated the feasibility of using in vitro assays with human liver microsomes (HLM) and recombinant CYP enzymes (isoenzymes), combined with untargeted metabolomics, to identify potential endogenous biomarker candidates indicative of CYP phenotype. Methods: This study uses in vitro incubations of HLM and isoenzymes in tandem with targeted and untargeted LC-(HR)MS and metabolomics techniques as well as statistical processing. Results: We demonstrate that HLM and isoenzymes maintain activity in the presence of complex biological matrices (blood/plasma), enabling metabolomic profiling. Untargeted analysis of assays in plasma revealed numerous potential biomarkers, with several showing significant correlations to enzyme activity. Conclusions: While identification remains the major challenge, this approach offers a promising avenue for developing accessible and efficient methods for indirect CYP phenotyping, potentially facilitating investigations in scenarios where traditional approaches are limited. This work provides a foundation for future studies focused on further developing in vitro assays and validating the proposed biomarkers, as well as establishing their utility in clinical and forensic settings. Full article

Background/Objectives: Metabolic enzymes are crucial for the detoxification of exogenously administered drugs, especially enzymes expressed in the intestine and the liver. Recent advancements in analytical methodologies enable sensitive and specific quantitative measurements of proteins, facilitating a more accurate evaluation of their expression and relative contribution to drug metabolism. Methods: The aim of the study was to characterize the protein expression levels of 16 Cytochrome P450s (CYP450s) and 2 carboxylesterases (CESs) in human liver and intestinal tissues using absolute quantification by HPLC-MS/MS. Human hepatocytes (HHEP) and human liver microsomes (HLM) were utilized, along with a novel intestinal preparation from cryopreserved human intestinal mucosa (CHIM), to perform proteomic analyses. Results: A comprehensive evaluation of 16 CYP450s and 2 CES enzyme expression in human liver and intestinal tissues is provided to reflect their relative abundance. Among the various in vitro systems evaluated, 14 of 16, 15/16, and 7/16 CYP450 of the isoforms analyzed were detected in HHEP, HLM, and CHIM, respectively. In hepatic systems, CYP2C9 exhibited the highest expression among CYP450 isoforms, a trend consistently observed in both HHEP and HLM. CYP3A4 was the most abundantly expressed isoform in CHIM preparations. Across all systems tested, CES1 and CES2 showed the highest overall protein expression levels, surpassing those of the CYP450s. Conclusions: Our findings demonstrate that the absolute quantification method employed is reliable, producing consistent results across two different in vitro hepatic systems (HHEP and HLM). This study supports the utility of absolute quantification approaches for accurately profiling drug-metabolizing enzymes and provides new, valuable insights to improve in vitro/in vivo extrapolation and more informed predictive pharmacokinetic modeling strategies. Full article

Background/Objectives: The ¹³C-Methacetin Breath Test (MBT) is a non-invasive tool to evaluate hepatic microsomal function via exhaled ¹³CO₂, reflecting cytochrome P450 1A2 (CYP1A2)-mediated metabolism. Despite decades of evidence demonstrating its utility in diagnosing cirrhosis, stratifying liver disease severity, and predicting outcomes, MBT adoption remains limited due to methodological inconsistencies and variable diagnostic thresholds. This review aimed to summarize MBT data in adults and assess its diagnostic and prognostic performance. Methods: A literature review was conducted using PubMed, Web of Science, and Scopus. Eligible studies included those applying oral or intravenous methacetin with defined reference values or diagnostic cutoffs. Outcomes of interest were percent dose recovery (PDR), cumulative PDR (cPDR), and LiMAx^® values. Due to heterogeneity in protocols, units, and endpoints, results were synthesized narratively. Results: Healthy individuals typically demonstrated rapid metabolism (e.g., cPDR30 10–15%), whereas cirrhotic patients showed significantly reduced values (e.g., cPDR30 ≈ 1%). Diagnostic cutoffs varied widely (<0.35% to <8%), reflecting methodological and population differences. MBT reliably identified advanced liver disease but showed inconsistent sensitivity for early-stage fibrosis and metabolic dysfunction-associated steatotic liver disease. Variability in dosing, timing, measurement duration, and analytic technique limited cross-study comparability. Conclusions: MBT is a validated, dynamic marker of liver function with both diagnostic and prognostic relevance. However, inconsistent protocols and thresholds hinder its clinical implementation. Standardization of MBT procedures, reference ranges, and reporting metrics is essential. A harmonized protocol (“MBT-60”), supported by multicenter validation, demographic stratification, and direct comparison with structural and serologic liver tests, is recommended to facilitate MBT integration into routine hepatology practice. Full article

Background/Objectives: Although several studies have been reported on the modulation of Cytochrome P450 by resveratrol, inconsistencies in the results obtained require further investigation. Here, we report the results of in vivo and in vitro experiments investigating the effect of resveratrol on CYP1A2, which participates in the biotransformation of several drugs used for the treatment of human malignancies. Methods: Male Wistar rats were exposed to resveratrol through diet (1%) for 30 days, and the hepatic CYP1A2 activity and protein concentration were assayed at the end of the treatment. Additionally, the capacity of the phytochemical to interfere with the induction of CYP1A2 by benzo[a]pyrene (50 mg/kg body weight) was also studied. The inhibition of CYP1A2 activity in rat liver microsomal and recombinant human enzymes by resveratrol, as well as its inhibitory kinetics and type of inhibition, were compared. Results: No significant increase in the protein concentration of hepatic CYP1A2 was found in resveratrol-treated rats, but it induces CYP1A2 activity and enhances the induction effect of benzo[a]pyrene. In silico and in vitro experiments demonstrated that resveratrol binds to the active site of human CYP1A2 through hydrophobic interactions with PHE125, PHE226, PHE260, and ALA317, and hydrogen bonds with SER122 and ASP313. It inhibits human recombinant CYP1A2 activity as well as that in rat liver microsomes, with IC₅₀ values of 46 µM and 485 µM, respectively. Resveratrol showed a mixed type of inhibition of recombinant human protein and a competitive inhibition of rat liver microsomal CYP1A. Conclusions: We can conclude that resveratrol is an in vitro inhibitor of CYP1A2, but it increases the benzo[a]pyrene CYP induction effect in vivo. Full article

Drug-induced autoimmune hepatitis (DIAIH) is a rare and complex disorder caused by drugs that are commonly metabolized by hepatic microsomal cytochrome P450 (CYP) pathways. Whereas DIAIH presents generally with a single clinical flare, in rare cases its clinical course shows two different, consecutively emerging flares. The aim of this report was to analyze details of this rare but interesting phenomenon and to help improve appropriate causality evaluation in patients with suspected iDILI or DIAIH to provide better insight into the pathomechanistic steps leading the diseases. A clinical course with two flares was found in a DIAIH patient treated with varenicline, a smoking cessation drug, and in another patient experiencing DIAIH following intravenous application of infliximab used to treat ankylosing spondylitis. In both patients, the first flare was determined as a typical liver injury with increased serum activities of alanine aminotransferase (ALT) and normal titers of serum autoimmune parameters, classified as an acute liver injury analogous to idiosyncratic DILI (iDILI), with verified causality using a modified version of RUCAM (Roussel Uclaf Causality Assessment Method). After an interval of around two months from the cessation of varenicline use, the second flare emerged, as evidenced by increased serum ALT values now associated with newly increased serum autoimmune titers of antinuclear antibodies (ANAs), classifying this flare as hepatic autoimmune injury with verified causality for varenicline using the simplified autoimmune hepatitis (AIH) score. A similar clinical DIAIH course of a continuous disease with two flares was described for the second patient, who received infliximab and experienced an interval of one month between the first and second flare. Interestingly to note, neither varenicline nor infliximab is degraded via a CYP pathway, and the metabolic disposition of both drugs is low. In sum, DIAIH can develop with two consecutive flares caused by two drugs not metabolized by CYPs and with slow drug disposition, raising the question of whether this phenomenon of two flares can occur in additional cases of DIAIH due to other drugs metabolized by CYPs or non-CYPs, a question to be resolved by DILI experts in future cases of iDILI and DIAIH. Full article

Efficient methods to remediate PCA (p-chloroaniline)-polluted environments are urgent due to the widespread persistence and toxicity of PCA in the environment. Microbial degradation presents a promising approach for remediating PCA pollution. However, the PCA-degrading fungi still have yet to be explored. This study confirmed the highly PCA-degrading efficiency of an isolated fungus, Isaria fumosorosea SP535. This fungus can achieve a PCA degradation efficiency of 100% under optimal conditions characterized by an initial PCA concentration of 1.0 mM, pH of 7.0 and a temperature of 25 °C. SEM and TEM analyses revealed that the toxicity of PCA resulted in roughened surfaces of Isaria fumosorosea SP535 hyphae, voids in the cytoplasm, and thickened cell walls. PCA addition significantly elevated the activities of cytochrome P450 monooxygenase in both cell-free extracts and microsomal fractions in the media, suggesting the important role of the P450 system in PCA metabolization by Isaria fumosorosea SP535. The results provide a microbial resource and fundamental knowledge for addressing PCA pollution. Full article

Chronic alcohol consumption induces oxidative stress not only in the liver but also in the gastrointestinal tract, where prolonged intestinal ethanol absorption plays a pivotal and underrecognized role. This review reframes ethanol pharmacokinetics to emphasize sustained jejunal and ileal uptake, which maintains elevated blood alcohol levels and perpetuates redox imbalance across the gut–liver axis. We integrate recent findings on ethanol-induced barrier dysfunction, CYP2E1-mediated ROS production, microbial dysbiosis, and mitochondrial disruption, proposing that the intestine is an active site of injury and a driver of systemic inflammation. Key mechanistic insights reveal that gut-derived endotoxins, compromised epithelial integrity, and microbiome–mitochondria interactions converge to exacerbate hepatic and extrahepatic damage. We further explore emerging therapeutic strategies—ranging from NAD⁺ repletion and probiotics to fecal microbiota transplantation—that target this upstream pathology. Recognizing prolonged intestinal ethanol absorption as a clinically meaningful phase offers new directions for early intervention and redox-based treatment in alcohol-associated disease. Full article

The metabolism of drugs and foreign substances in humans typically involves multiple enzymatic steps, particularly in phase-1 biotransformation in the liver, where various cytochrome P450 monooxygenases (CYPs) play crucial roles. This complexity can lead to a wide range of metabolites. Understanding the contributions of individual CYPs and their interactions within these intricate enzyme cascades can be challenging. We recently developed an in vitro biotransformation platform employing various Chinese Hamster Ovarian (CHO) cell clones. These clones express human cytochrome P450 oxidoreductase (CPR), and each is defined by a specific human CYP enzyme expression, thus exhibiting no detectable endogenous CYP enzyme activity (mono-CYP CHO platform). In this study, we investigated whether the mono-CYP CHO platform is a suitable tool for modeling complex drug metabolization reactions in vitro. Tamoxifen (TAM) was selected as a model substance due to its role as a prodrug widely used in breast cancer therapy, where its main active metabolite, endoxifen, arises from a two-step metabolism primarily involving the CYP system. Specifically, the combined activity of CYP3A4 and CYP2D6 is believed to be essential for efficient endoxifen production. However, the physiological metabolization pathway of TAM is more complex and interconnected, and the reasons for TAM’s therapeutic success and variability among patients are not yet fully understood. Analogous to our recently introduced mono-CYP3A4 CHO cells, we generated a CHO cell line expressing human CPR and CYP2D6, including analysis of CYP2D6 expression and specific activity. Comparative studies on the metabolization of TAM were performed with both mono-CYP CHO models individually and in co-culture with intact cells as well as with isolated microsomes. Supernatants were analyzed by HPLC to calculate individual CYP activity for each metabolite. All the picked mono-CYP2D6 clones expressed similar CYP2D6 protein amounts but showed different enzyme activities. Mono-CYP2D6 clone 18 was selected as the most suitable for TAM metabolization based on microsomal activity assays. TAM conversion with mono-CYP2D6 and -3A4 clones, as well as the combination of both, resulted in the formation of the expected main metabolites. Mono-CYP2D6 cells and microsomes produced the highest detected amounts of 4-hydroxytamoxifen and endoxifen, along with N-desmethyltamoxifen and small amounts of N,N-didesmethyltamoxifen. N-desmethyltamoxifen was the only TAM metabolite detected in notable quantities in mono-CYP3A4, while 4-hydroxytamoxifen and endoxifen were present only in trace amounts. In CYP2D6/3A4 co-culture and equal mixtures of both CYP microsomes, all metabolites were detected at concentrations around 50% of those in individual clones, indicating no significant synergistic effects. In conclusion, our mono-CYP CHO model confirmed the essential role of CYP2D6 in synthesizing the active TAM metabolite endoxifen and indicated that CYP2D6 is also involved in producing the by-metabolite N,N-didesmethyltamoxifen. The differences in metabolite spectra between the two mono-CYP models highlight the CYP specificity and sensitivity of our in vitro system. Full article

In this study, to better understand the mechanisms of the profound impact of alcohol consumption on drug pharmacokinetics, efficacy, and toxicity, we characterized the alcohol-induced changes in the ensemble of drug-metabolizing enzymes and transporters (DMETs) in the human liver by performing global proteomic analysis of human liver microsomes from 94 donors. DMET protein levels were analyzed concerning alcohol consumption, smoking history, and sex using non-parametric tests, which were further strengthened by correlational analysis. To this end, we used a provisional index of alcohol exposure formulated based on the relative abundances of four marker proteins best correlating with the level of alcohol consumption. Alcohol-induced changes in the cytochrome P450 pool include significant increases in CYP2E1, CYP2B6, CYP2J2, and NADPH-cytochrome P450 reductase levels and the lowering of CYP1A2, CYP2C8, CYP2C9, CYP4A11, and cytochrome b₅. Changes in UDP-glucuronosyltransferase (UGT) abundances comprise elevated UGT1A6, UGT1A9, and UGT2A1, and reduced UGT1A3, UGT1A4, UGT2B7, UGT2B10, and UGT2B15 levels. Tobacco smokers showed elevated CYP1A2, UGT1A6, and UGT2B4 and reduced FMO3, FMO4, and FMO5 levels, while in females, CYP1A2, UGT2B17, and UGT2B15 levels were lower, and UGT2A3 and STS were higher compared to males. The alcohol-induced changes in the DMET ensemble at the protein level reported herein provide deep insights into how alcohol impacts drug and xenobiotic metabolism. Full article

Background/Objectives: Perillyl alcohol (POH), a monoterpene natural product derived from the essential oils of plants such as perilla (Perilla frutescens), is currently in phase I and II clinical trials as a chemotherapeutic agent. In this study, we investigated the effect of POH on cytochrome P450 (CYP) activity for evaluating POH–drug interaction potential. Methods: The investigation was conducted using pooled human liver microsomes (HLMs), recombinant CYP3A4 (rCYP3A4) enzymes, and human pluripotent stem cell-derived hepatic organoids (hHOs) employing liquid chromatography-tandem mass spectrometry. Results: POH inhibited the activities of CYP2A6 and CYP2B6 with K_i of 6.35 and 3.78 μM, respectively, whereas it stimulated CYP3A4 activity in pooled HLMs incubated with midazolam (MDZ). In a direct CYP inhibition assay using HLMs, activities of CYP2C9, CYP2C19, and CYP2E1 were also inhibited by POH, with IC₅₀ values greater than 50 μM, but those of CYP1A2, CYP2C8, CYP2D6, and CYP3A4 (testosterone) were not significantly inhibited. In pooled HLMs, the V_max/K_m value of 1′-hydroxy MDZ, but not that of 4-hydroxy MDZ, was increased 2.7-fold by 100 μM POH compared with that in the absence of POH. Moreover, stimulation of MDZ 1′-hydroxylation by CYP3A4 was observed in hHOs and rCYP3A4 with cytochrome b₅ but not rCYP3A4 without cytochrome b₅. Furthermore, activation of CYP3A4-mediated metabolism by POH was observed in HLMs incubated with fimasartan but not atorvastatin, buspirone, donepezil, nifedipine, or tadalafil, suggesting a substrate-dependent activation of CYP3A4 by POH. Conclusions: POH inhibits CYP2A6 and CYP2B6, but it activates CYP3A4. These findings underscore the need for further evaluation of the interactions of clinical drugs with POH. Full article

CycloAnt is an opioid peptide that produces potent and efficacious antinociception with significantly reduced side effects upon systemic administration in mice. To verify its CNS-mediated antinociception, we determined its binding affinity at the opioid receptors, its proteolytic stability in mouse serum, metabolic stability in mouse liver microsomes, and pharmacokinetics in mice. CycloAnt exhibited stability toward proteolytic degradation in serum and resistance against metabolism mediated by cytochrome P450 enzymes (CYP450s) and UDP-glucuronosyl transferases (UGTs) in mouse liver microsomes. A pharmacokinetic study of CycloAnt in mice confirmed that CycloAnt crossed the blood–brain barrier (BBB) with a brain-to-plasma ratio of 11.5%, a high extent of BBB transport for a peptide. To elucidate the structural basis underlying its BBB penetration, we investigated its conformation in water and DMSO using ¹H NMR spectroscopy. The results show that CycloAnt displays an extended conformation in water with most amide NHs being exposed, while in less polar DMSO, it adopts a compact conformation with all amide NHs locked in intramolecular hydrogen bonds. The chameleonic property helps CycloAnt permeate the BBB. Full article

Idiosyncratic drug-induced liver injury (iDILI) by flucloxacillin presents as both cholestatic and hepatocellular injury. Its mechanistic steps are explored in the present analysis as limited data exist on the cascade of events leading to iDILI in patients with an established diagnosis assessed for causality by the Roussel Uclaf Causality Assessment Method (RUCAM). Studies with human liver microsomes showed that flucloxacillin is a substrate of cytochrome P450 (CYP) with ist preferred isoforms CYP 3A4/3A7 that toxified flucloxacillin toward 5′-hydroxymethylflucloxacillin, which was cytotoxic to human biliary epithelial cell cultures, simulating human cholestatic injury. This provided evidence for a restricted role of the metabolic CYP-dependent hypothesis. In contrast, 5′-hydroxymethylflucloxacillin generated metabolically via CYP 3A4/3A7 was not cytotoxic to human hepatocytes due to missing genetic host features and a lack of non-parenchymal cells, including immune cells, which commonly surround the hepatocytes in the intact liver in abundance. This indicated a mechanistic gap regarding the clinical hepatocellular iDILI, now closed by additional studies and clinical evidence based on HLA B*57:01-positive patients with iDILI by flucloxacillin and a verified diagnosis by the RUCAM. Naïve T-cells from volunteers expressing HLA B*57:01 activated by flucloxacillin when the drug antigen was presented by dendritic cells provided the immunological basis for hepatocellular iDILI caused by flucloxacillin. HLA B*57:01-restricted activation of drug-specific T-cells caused covalent binding of flucloxacillin to albumin acting as a hapten. Following drug stimulation, T-cell clones expressing CCR4 and CCR9 migrated toward CCL17 and CCL25 and secreted interferon-γ and cytokines. In conclusion, cholestatic injury can be explained metabolically, while hepatocellular injury requires both metabolic and immune activation. Full article

Neonicotinoids, a neuro-effective class of insecticides, are heavily applied in agricultural activities worldwide. Poultry can be exposed to neonicotinoids by several routes, but the knowledge of neonicotinoid’s metabolism in poultry and its associated interspecies differences is highly limited. Hence, this study aims to investigate the species differences in metabolite formations, as well as cytochrome P450 (CYP)-dependent metabolism of four major neonicotinoid compounds, acetamiprid, imidacloprid, clothianidin, and thiamethoxam, in poultry. In vitro biotransformation assays using hepatic microsomes of chicken, ducks, geese, quails, and rats were conducted. Metabolites of neonicotinoids were then screened by LC/Q-TOF and quantified by LC/MS/MS. The results revealed an existence of interspecies differences in the formations of N-[(6-chloro-3-pyridyl) methyl] -N-methyl acetamidine (IM-1-5) of acetamiprid and dm-clothianidin of clothianidin between chicken and other species. In addition, the greatest CYP activities in the metabolism of most neonicotinoid substrates, such as acetamiprid to dm-acetamiprid, imidacloprid to hydroxylated-imidacloprid and imidacloprid-olefin, clothianidin to dm-clothianidin, and thiamethoxam to clothianidin, were found in chicken. These results suggested that the CYPs in chicken may have a greater capacity for metabolism of neonicotinoids compared to other poultry. This study further revealed that the maximum intrinsic clearance of dn-imidacloprid and dn-clothianidin in ducks may be superintended by CYP-mediated nitro-reductions of imidacloprid and clothianidin. Further studies employing CYP recombinant enzymes may be required to elucidate the specific CYP isoforms that may be involved in neonicotinoid metabolism in avian species. Full article