Comparisons of catalytic selectivity of cytochrome P450 subfamily enzymes from different species

Cytochrome P450 26A1 Contributes to the Maintenance of Neuropathic Pain

The cytochrome P450 proteins (CYP450s) have been implicated in catalyzing numerous important biological reactions and contribute to a variety of diseases. CYP26A1, a member of the CYP450 family, carries out the oxidative metabolism of retinoic acid (RA), the active metabolite of vitamin A. Here we report that CYP26A1 was dramatically upregulated in the spinal cord after spinal nerve ligation (SNL). CYP26A1 was mainly expressed in spinal neurons and astrocytes. HPLC analysis displayed that the content of all-trans-RA (at-RA), the substrate of CYP26A1, was reduced in the spinal cord on day 7 after SNL. Inhibition of CYP26A1 by siRNA or inhibition of CYP26A1-mediated at-RA catabolism by talarozole relieved the SNL-induced mechanical allodynia during the maintenance phase of neuropathic pain. Talarozole also reduced SNL-induced glial activation and proinflammatory cytokine production but increased anti-inflammatory cytokine (IL-10) production. The RA receptors RARα, RXRβ, and RXRγ were expressed in spinal neurons and glial cells. The promoter of Il-10 has several binding sites for RA receptors, and at-RA directly increased Il-10 mRNA expression in vitro. Finally, intrathecal IL-10 attenuated SNL-induced neuropathic pain and reduced the activation of astrocytes and microglia. Collectively, the inhibition of CYP26A1-mediated at-RA catabolism alleviates SNL-induced neuropathic pain by promoting the expression of IL-10 and suppressing glial activation. CYP26A1 may be a potential therapeutic target for the treatment of neuropathic pain.

In-vitro metabolism of LXY18, an orally available, potent blocker of AURKB relocation in mitosis

This study investigated the metabolism of LXY18, a quinolone-based compound that suppresses tumorigenesis by blocking AURKB localization. Metabolite profiling of LXY18 in liver microsomes from six species and human S9 fractions revealed that LXY18 undergoes various conserved metabolic reactions, such as N-hydroxylation, N-oxygenation, O-dealkylation, and hydrolysis, resulting in ten metabolites. These metabolites were produced through a combination of CYP450 enzymes, and non-CYP450 enzymes including CES1, and AO. Two metabolites, M1 and M2 were authenticated by chemically synthesized standards. M1 was the hydrolyzed product catalyzed by CES1 whereas M2 was a mono-N-oxidative derivative catalyzed by a CYP450 enzyme. AO was identified as the enzyme responsible for the formation of M3 with the help of AO-specific inhibitors and LXY18 analogs, 5b and 5c. M1 was the intermediate of LXY18 to produce M7, M8, M9, and M10. LXY18 potently inhibited 2C19 with an IC₅₀ of 290 nM but had a negligible impact on the other CYP450s, indicating a low risk of drug-drug interaction. Altogether, the study provides valuable insights into the metabolic process of LXY18 and its suitability as a drug candidate. The data generated serves as a significant reference point for conducting further safety assessments and optimizing drug development.

Phase I Metabolism of Pterostilbene, a Dietary Resveratrol Derivative: Metabolite Identification, Species Differences, Isozyme Contribution, and Further Bioactivation

Pterostilbene (PTE), a dietary derivative of resveratrol, displayed pleiotropic health-promoting activities. This study aimed to explore the metabolic profiles and species differences of the phase I metabolism of PTE and to investigate subsequent detoxification after PTE bioactivation. PTE was found to be biotransformed to two pharmacologically active metabolites, pinostilbene and 3'-hydroxypterostilbene, in vivo and in vitro with substantial species differences. Human CYP1A2 was proved to be mainly responsible for the demethylation and 3'-hydroxylation of PTE, with its contribution to a demethylation of 94.5% and to a 3'-hydroxylation of 97.9%. An in vitro glutathione trapping experiment revealed the presence of an ortho-quinone intermediate formed by further oxidation of 3'-hydroxypterostilbene. Human glutathione S-transferase isoforms A2, T1, and A1 inactivated the ortho-quinone intermediate by catalyzing glutathione conjugation, implicating a potential protective pathway against PTE bioactivation-derived toxicity. Overall, this study provided a comprehensive view of PTE phase I metabolism and facilitated its further development as a promising nutraceutical.

A Transversal Approach Combining In Silico, In Vitro and In Vivo Models to Describe the Metabolism of the Receptor Interacting Protein 1 Kinase Inhibitor Sibiriline

Sibiriline is a novel drug inhibiting receptor-interacting protein 1 kinase (RIPK1) and necroptosis, a regulated form of cell death involved in several disease models. In this study, we aimed to investigate the metabolic fate of sibiriline in a cross-sectional manner using an in silico prediction, coupled with in vitro and in vivo experiments. In silico predictions were performed using GLORYx and Biotransformer 3.0 freeware; in vitro incubation was performed on differentiated human HepaRG cells, and in vivo experiments including a pharmacokinetic study were performed on mice treated with sibiriline. HepaRG culture supernatants and mice plasma samples were analyzed with ultra-high-performance liquid chromatography, coupled with tandem mass spectrometry (LC-HRMS/MS). The molecular networking bioinformatics tool applied to LC-HRMS/MS data allowed us to visualize the sibiriline metabolism kinetics. Overall, 14 metabolites, mostly produced by Phase II transformations (glucuronidation and sulfation) were identified. These data provide initial reassurance regarding the toxicology of this new RIPK1 inhibitor, although further studies are required.

Deciphering the species differences in CES1A-mediated hydrolytic metabolism by using a bioluminescence substrate

Carboxylesterases 1A (CES1A) is a key enzyme responsible for the hydrolytic metabolism of a great deal of endogenous and exogenous substrates bearing ester- or amide-bond(s). This study aimed to decipher the species difference in CES1A-mediated hydrolytic metabolism by using a newly developed bioluminescence CES1A sensor (termed NLMe) as the probe substrate, while the liver microsomes from six different mammalian species (human, cynomolgus monkey, dog, minipig, rat and mouse) were used as the enzyme sources. Metabolite profiling demonstrated that all tested liver microsomes from various species could catalyze NLMe hydrolysis, but significant difference in hydrolytic rate was observed. Kinetic plots of NLMe hydrolysis in liver microsomes from different species showed that the inherent clearance rates (C_lint) of NLMe in human liver microsomes (HLM), cynomolgus monkey liver microsomes (CyLM), and pig liver microsome (PLM) were comparable, while the C_lint values of NLMe in dog liver microsomes (DLM), mouse liver microsomes (MLM), and rat liver microsomes (RLM) were relatively small. Moreover, chemical inhibition assays showed that NLMe hydrolysis in all tested liver microsomes could be competently inhibited by BNPP (a potent broad-spectrum inhibitor of CES), but CUA (a selective inhibitor of human CES1A) only inhibited NLMe hydrolysis in human liver microsomes and dog liver microsomes. In summary, the species differences in CES1A-catalyzed NLMe hydrolysis were carefully investigated from the views of the similarities in metabolite profile, hydrolytic kinetics and inhibitor response. All these findings provide new insights into the species differences in CES1A-mediated hydrolytic metabolism and suggest that it is necessary for the pharmacologists to choose appropriate animal models to replace humans for evaluating the in vivo effects of CES1A inhibitors.

Evaluation of Zuo-Gui Yin Decoction Effects on Six CYP450 Enzymes in Rats Using a Cocktail Method by UPLC-MS/MS

Background. Zuo-Gui Yin Decoction (ZGYD), a traditional Chinese prescription, is mainly used in various kinds of andrology and gynecology diseases. However, the study on the interaction of ZGYD and drugs has not been reported. Therefore, evaluating the interaction between ZGYD and metabolic enzymes is helpful to guide rational drug use. Objective. This study was conducted to explore the effects of ZGYD on the activity and mRNA expressions of six Cytochrome P450 (CYP450) enzymes in rats and to provide a basis for its rational clinical use. Methods. Sprague-Dawley rats were randomly divided into control, ZGYD high, medium, and low-dose group ( $n=6$ ). The concentrations of six probe substrates in plasma of rats in each group were determined by UPLC-MS/MS. In addition, RT-PCR and Western blot were used to determine the effects of ZGYD on the expression of CYP450 isoforms in the liver. Results. Compared with the control group, the main pharmacokinetic parameters AUC(0-t), AUC (0~∞), of omeprazole, dextromethorphan, and midazolam in the high-dose group were significantly decreased, while the CL of these were significantly increased. The gene expressions of CYP2C11 and CYP3A1 were upregulated in the ZGYD medium, high-dose group. The protein expression of CYP2C11 was upregulated in the high-dose group, and the protein expression of CYP3A1 was upregulated in the medium, high-dose group. Conclusion. The results showed that ZGYD exhibited the induction effects on CYP2C11 and CYP3A1 (CYP2C19 and CYP3A4 in humans) in rats. However, no significant change in CYP1A2, CYP2B1, CYP2C7, and CYP2D2 activities was observed. It would be useful for the safe and effective usage of ZGYD in clinic.

DMSO-free highly differentiated HepaRG spheroids for chronic toxicity, liver functions and genotoxicity studies

The liver is essential in the elimination of environmental and food contaminants. Given the interspecies differences between rodents and humans, the development of relevant in vitro human models is crucial to investigate liver functions and toxicity in cells that better reflect pathophysiological processes. Classically, the differentiation of the hepatic HepaRG cell line requires high concentration of dimethyl sulfoxide (DMSO), which restricts its usefulness for drug-metabolism studies. Herein, we describe undifferentiated HepaRG cells embedded in a collagen matrix in DMSO-free conditions that rapidly organize into polarized hollow spheroids of differentiated hepatocyte-like cells (Hepoid-HepaRG). Our conditions allow concomitant proliferation with high levels of liver-specific functions and xenobiotic metabolism enzymes expression and activities after a few days of culture and for at least 4 weeks. By studying the toxicity of well-known injury-inducing drugs by treating cells with 1- to 100-fold of their plasmatic concentrations, we showed appropriate responses and demonstrate the sensitivity to drugs known to induce various degrees of liver injury. Our results also demonstrated that the model is well suited to estimate cholestasis and steatosis effects of drugs following chronic treatment. Additionally, DNA alterations caused by four genotoxic compounds (Aflatoxin B₁ (AFB₁), Benzo[a]Pyrene (B[a]P), Cyclophosphamide (CPA) and Methyl methanesulfonate (MMS)) were quantified in a dose-dependent manner by the comet and micronucleus assays. Their genotoxic effects were significantly increased after either an acute 24 h treatment (AFB₁: 1.5-6 μM, CPA: 2.5-10 μM, B[a]P: 12.5-50 μM, MMS: 90-450 μM) or after a 14-day treatment at much lower concentrations (AFB₁: 0.05-0.2 μM, CPA: 0.125-0.5 μM, B[a]P: 0.125-0.5 μM) representative to human exposure. Altogether, the DMSO-free 3D culture of Hepoid-HepaRG provides highly differentiated and proliferating cells relevant for various toxicological in vitro assays, especially for drug-preclinical studies and environmental chemicals risk assessment.

The steroid metabolome of pregnancy, insights into the maintenance of pregnancy and evolution of reproductive traits

Modes of mammalian reproduction are diverse and not always conserved among related species. Progesterone is universally required to supports pregnancy but sites of synthesis and metabolic pathways vary widely. The steroid metabolome of mid-to late gestation was characterized, focusing on 5α-reduced pregnanes in species representing the Perissodactyla, Cetartiodactyla and Carnivora using mass spectrometry. Metabolomes and steroidogenic enzyme ortholog sequences were used in heirarchial analyses. Steroid metabolite profiles were similar within orders, whales within cetartiodactyls for instance, but with notable exceptions such as rhinoceros clustering with goats, and tapirs with pigs. Steroidogenic enzyme sequence clustering reflected expected evolutionary relationships but once again with exceptions. Human sequences (expected outgroups) clustered with perissodactyl CYP11A1, CYP17A1 and SRD5A1 gene orthologues, forming outgroups only for HSD17B1 and SRD5A2. Spotted hyena CYP19A1 clustered within the Perissodactyla, between rhinoceros and equid orthologues, whereas CYP17A1 clustered within the Carnivora. This variability highlights the random adoption of divergent physiological strategies as pregnancy evolved among genetically similar species.

Inhibition of 20-hydroxyeicosatetraenoic acid biosynthesis by vitamin E analogs in human and bovine cytochrome P450 microsomes

Dairy cattle are predisposed to disease around the time of calving due to dysfunctional inflammatory responses. Oxylipids are lipid-derived mediators that regulate all aspects of the inflammatory response, and shifts in oxylipid profiles are correlated with disease risk. For example, 20-hydroxyeicosatetraenoic acid (HETE) is an oxylipid derived from cytochrome P450 enzymes (CYP450) found at significantly greater concentrations around calving and during clinical disease. Biosynthesis of 20-HETE occurs almost exclusively from two specific CYP450 of which CYP450 family four sub-family F member two (CYP4F2) is the major contributor to 20-HETE production in humans. To further study the activities of 20-HETE and potentially reduce its production in vivo, mitigation methods must be explored. Additional substrates of CYP4F2, such as vitamin E, are known to both increase and decrease the metabolism of other CYP4F2 substrates. This study aimed to determine whether vitamin E analogs may reduce the production of 20-HETE through competition for CYP4F2 activity in human CYP4F2, bovine-kidney and bovine-mammary microsomes. Gamma-tocopherol reduced 20-HETE production from human and bovine-kidney microsomes (35.3% and 27.5%, respectively) whereas γ-tocotrienol only reduced 20-HETE production from human microsomes (40.1%). Finally, bovine-mammary microsomes did not produce a quantifiable amount of 20-HETE, suggesting basal mammary CYP4F2 activity may not be a significant contributor to 20-HETE found in milk. Together, these data show that analogs of vitamin E can reduce the production of 20-HETE, potentially through competition with arachidonic acid for metabolism by CYP4F2, posing a potential means for limiting 20-HETE production during clinical diseases of dairy cattle.

Cytochrome P450 2E1 and its roles in disease

Cytochrome P450 (P450) 2E1 is the major P450 enzyme involved in ethanol metabolism. That role is shared with two other enzymes that oxidize ethanol, alcohol dehydrogenase and catalase. P450 2E1 is also involved in the bioactivation of a number of low molecular weight cancer suspects, as validated in vivo in mouse models where cancers could be attenuated by deletion of Cyp2e1. P450 2E1 does not have a role in global production of reactive oxygen species but localized roles are possible, e.g. in mitochondria. The structures, conformations, and catalytic mechanisms of P450 2E1 have some unusual features among P450s. The concentration of hepatic P450 varies ≥10-fold among humans, possibly in part due to single nucleotide variants. The level of P450 2E1 may have relevance in the rates of oxidation of drugs, particularly acetaminophen and anesthetics.

Medications in Space: In Search of a Pharmacologist's Guide to the Galaxy

Medications have been used during space missions for more than half a century, yet our understanding of the effects of spaceflight on drug pharmacokinetics and pharmacodynamics is poor. The space environment induces time-dependent alterations in human physiology that include fluid shifts, cardiovascular deconditioning, bone and muscle density loss, and impaired immunity. This review presents the current knowledge on the physiological effects of spaceflight that can translate into altered drug disposition and activity and eventually to inadequate treatment. It describes findings from studies in astronauts along with mechanistic studies in animal models and in vitro systems. Future missions into deeper space and the emergence of commercial spaceflight will require a more detailed understanding of space pharmacology to optimize treatment in astronauts and space travelers.

A comprehensive review of cytochrome P450 2E1 for xenobiotic metabolism

Cytochrome P450 2E1 (CYP2E1) plays a vital role in drug-induced hepatotoxicity and cancers (e.g. lung and bladder cancer), since it is responsible for metabolizing a number of medications and environmental toxins to reactive intermediate metabolites. CYP2E1 was recently found to be the highest expressed CYP enzyme in human livers using a proteomics approach, and CYP2E1-related toxicity is strongly associated with its protein level that shows significant inter-individual variability related to ethnicity, age, and sex. Furthermore, the expression of CYP2E1 demonstrates regulation by extensive genetic polymorphism, endogenous hormones, cytokines, xenobiotics, and varying pathological states. Over the past decade, the knowledge of pharmacology, toxicology, and biology about CYP2E1 has grown remarkably, but the research progress has yet to be summarized. This study presents a timely systematic review on CYP2E1's xenobiotic metabolism, genetic polymorphism, and inhibitors, with the focus on their clinical relevance for the efficacy and toxicity of various CYP2E1 substrates. Moreover, several knowledge gaps have been identified towards fully understanding the potential interactions among different CYP2E1 substrates in clinical settings. Through in-depth analyses of these knowns and unknowns, we expect this review will aid in future drug development and improve management of CYP2E1 related clinical toxicity.

Genetic diversity of cytochrome P450 2A with different metabolic activities in domestic cats

Knowledge of genetic polymorphisms of cytochrome P450 (CYP), the most important xenobiotic metabolizing enzyme, is very limited in cats. Preliminarily, we investigated genetic polymorphisms in CYP2A13, one of the major CYP isoforms in the liver and lung. Four synonymous and three non-synonymous polymorphic variants were identified in feline CYP2A13 in domestic cats in Japan, without an obvious major type. Metabolic parameters, Km and Vmax, of coumarin hydroxylation of CYP2A13 were shown to range within two times for the identified non-synonymous polymorphic variants by using heterologous coexpression system in Escherichia coli. The results confirmed the polymorphic nature of CYP2A13 as a basis for effective application of medicines and prevention of adverse reactions in treatment of domestic cats.

Effects of formaldehyde on detoxification and immune responses in silver pomfret (Pampus argenteus)

Formaldehyde can effectively control ectoparasites in silver pomfret (Pampus argenteus). However, there is limited information on the effects of formaldehyde treatment at a molecular level in fishes. In the present study, transcriptome profiling was conducted to investigate the effects of formaldehyde treatment (80 mg/L, bath for 1 h every day for three consecutive days) on the liver and kidney tissues of silver pomfret. A total of 617959982 clean reads were obtained and assembled into 265760 unigenes with an N50 length of 1507 bp, and the assembled unigenes were all annotated by alignment with public databases. A total of 2204 differentially expressed genes (DEGs) were detected in the liver and kidney tissues, and they included 7 detoxification- related genes and 9 immune-related genes, such as CYP450, GST, MHC I & II, and CCR. In addition, 1440 DEGs were mapped to terms in the GO database, and 1064 DEGs were mapped to the KEGG database. The expression of 4 detoxification-related genes and 6 immune-related genes in three days formaldehyde treatment were analyzed using RT-qPCR, and the antioxidant enzyme levels were also determined. The results indicate differential expression of detoxification- and immune-related genes during the three days formaldehyde treatment. Our data could provide a reference for the treatment of parasites to avoid high mortality and help in understanding the molecular activity in fishes after formaldehyde exposure.

Pharmacokinetics behaviors of l-menthol after inhalation and intravenous injection in rats and its inhibition effects on CYP450 enzymes in rat liver microsomes

1. l-Menthol, as a kind of monocyclic terpene, is widely used in inhalation formulations, food and tobacco. The purpose of this study was to investigate the pharmacokinetic behavior of l-menthol as well as its influence on the activities of cytochrome P450 enzymes. 2. The pharmacokinetic behaviors of l-menthol after inhalation (50 mg/kg) and intravenous injection (10 mg/kg) were investigated. A rat liver microsomal model was adopted to elucidate the inhibitory effect of l-menthol on CYP1A2, CYP2C11, CYP2D1/2, CYP2D4, CYP2E1 and CYP3A1 using phenacetin, tolbutamide, omeprazole, dextromethorphan, chlorzoxazone and testosterone as probe drugs, respectively. 3. The plasma concentration reached the C_max within 1.0 h (inhalation) and descended with the T_1/2 of 8.53 and 6.69 h for inhalation and i.v. administration, respectively. IC₅₀ for inhibition of l-menthol on CYP 450 enzymes were 4.35 μM for 2D4, 8.67 μM for 1A2, 13.02 μM for 3A1, 14.78 μM for 2D1/2, 234.9 μM for 2C11 and 525.4 μM for 2E1, respectively. 4. The results illustrate the pharmacokinetic process of l-menthol in rats and provide information for further rational applications. l-Menthol had moderate inhibitions on CYP2D4 and 1A2, which might affect the disposition of medicines primarily dependent on these pathways.

Phylogenetic analysis of the cytochrome P450 (CYP450) nucleotide sequences of the horse and predicted CYP450s of the white rhinoceros (Ceratotherium simum) and other mammalian species

Background

The plight of the white rhinoceros (Ceratotherium simum) and the increasing need of treatment options for injured poaching victims led to the necessity to expand the knowledge on applicable drugs in this endangered species. With very little information available on drug pharmacokinetics in rhino, veterinarians have to rely on information generated from other species. The horse being a closely related species, has served as the model for dose extrapolations. However, from recent research on enrofloxacin and carprofen, the white rhino showed considerable differences in the pharmacokinetic properties of these drugs in comparison to the horse. While the reason for the differences is unknown, a likely cause may be a difference in present cytochrome P450 (CYP450), which may result in the rhino being genetically deficient in certain enzyme families.

Methods

For this paper we assess the degree of similarity of the CYP genome sequences across the different species, using BLAT (BLAST-like alignment tool) for the alignment of the nucleotide sequences of the equine CYP450 with potential homologous nucleotide sequences of the published database from white rhinos and other mammalian species (cow, pig, dog, sheep, elephant, mouse and human).

Results

The white rhino nucleotide sequences were 90.74% identical to the equine sequences. This was higher than the degree of similarity between any of the other evaluated species sequences. While no specific CYP family were found to be deficient in the published rhino genome, the horse genome contained additional genetic sequence for a larger number of iso-enzymes that were not present in the rhino.

Discussion

In pharmacokinetic study, it is well known that absence of a metabolic enzyme will result in constraints in drug metabolism and drug elimination. While this was our speculation, comparison to the horse and other mammalian species indicate that all the described CYP genes required for metabolism are present within the rhino genome. These results leave functional differences in enzyme activity and a lack of isoenzymes as the likely reason for the constraint in drug metabolism. Despite a more than 90% similarity of the equine and rhino gene sequences, seemingly small differences can have major effects on drug metabolism. Thus, in spite of the close anatomical relationship, the rhino should not simply be treated like a big horse.

Circadian Regulation of Hepatic Cytochrome P450 2a5 by Peroxisome Proliferator-Activated Receptor γ

Human CYP2A6 (Cyp2a5 in mice) plays an important role in metabolism and detoxification of various drugs and chemicals. Here, we investigated a potential role of peroxisome proliferator-activated receptor γ (Ppar-γ) in circadian regulation of the Cyp2a5 enzyme. We first showed that Cyp2a5 mRNA and protein in mouse liver displayed robust circadian oscillations. Consistent with a circadian protein pattern, Cyp2a5-mediated 7-hydroxylation of coumarin was circadian time-dependent. Formation of 7-hydroxycoumarin was more extensive at a dosing time of Zeitgeber time 2 (ZT2) than that at ZT14. Interestingly, the nuclear receptor Ppar-γ was also a circadian gene. Circadian Ppar-γ protein level was strongly correlated with the Cyp2a5 mRNA level (r = 0.989). Furthermore, Ppar-γ activation (by a selective agonist, rosiglitazone) upregulated Cyp2a5 expression in Hepa-1c1c7 cells, whereas Ppar-γ knockdown downregulated Cyp2a5 expression. Also, Ppar-γ knockdown blunted the rhythmicity of Cyp2a5 mRNA in serum-shocked Hepa-1c1c7 cells. In addition, a combination of promoter truncation analysis, mobility shift, and chromatin immunoprecipitation assays revealed that Ppar-γ directly bound to a PPAR response element (i.e., the -1418- to -1396-bp region) within Cyp2a5 promoter and activated the gene transcription. Taken together, Ppar-γ was a transcriptional activator of Cyp2a5, and its rhythmic expression contributed to circadian expression of Cyp2a5.

The safety evaluation of food flavouring substances: the role of metabolic studies

The safety assessment of a flavour substance examines several factors, including metabolic and physiological disposition data. The present article provides an overview of the metabolism and disposition of flavour substances by identifying general applicable principles of metabolism to illustrate how information on metabolic fate is taken into account in their safety evaluation. The metabolism of the majority of flavour substances involves a series both of enzymatic and non-enzymatic biotransformation that often results in products that are more hydrophilic and more readily excretable than their precursors. Flavours can undergo metabolic reactions, such as oxidation, reduction, or hydrolysis that alter a functional group relative to the parent compound. The altered functional group may serve as a reaction site for a subsequent metabolic transformation. Metabolic intermediates undergo conjugation with an endogenous agent such as glucuronic acid, sulphate, glutathione, amino acids, or acetate. Such conjugates are typically readily excreted through the kidneys and liver. This paper summarizes the types of metabolic reactions that have been documented for flavour substances that are added to the human food chain, the methodologies available for metabolic studies, and the factors that affect the metabolic fate of a flavour substance.

Formalin-Fixed Paraffin-Embedded Tissues-An Untapped Biospecimen for Biomonitoring DNA Adducts by Mass Spectrometry

The measurement of DNA adducts provides important information about human exposure to genotoxic chemicals and can be employed to elucidate mechanisms of DNA damage and repair. DNA adducts can serve as biomarkers for interspecies comparisons of the biologically effective dose of procarcinogens and permit extrapolation of genotoxicity data from animal studies for human risk assessment. One major challenge in DNA adduct biomarker research is the paucity of fresh frozen biopsy samples available for study. However, archived formalin-fixed paraffin-embedded (FFPE) tissues with clinical diagnosis of disease are often available. We have established robust methods to recover DNA free of crosslinks from FFPE tissues under mild conditions which permit quantitative measurements of DNA adducts by liquid chromatography-mass spectrometry. The technology is versatile and can be employed to screen for DNA adducts formed with a wide range of environmental and dietary carcinogens, some of which were retrieved from section-cuts of FFPE blocks stored at ambient temperature for up to nine years. The ability to retrospectively analyze FFPE tissues for DNA adducts for which there is clinical diagnosis of disease opens a previously untapped source of biospecimens for molecular epidemiology studies that seek to assess the causal role of environmental chemicals in cancer etiology.

In Vitro Antioxidant Potential and Effect of a Glutathione-Enhancer Dietary Supplement on Selected Rat Liver Cytochrome P450 Enzyme Activity

BACKGROUND

There is considerable evidence that many people take dietary supplements including those of herbal origin as an alternative therapy to improve their health. One such supplement, with an amalgam of constituents, is CellGevity®. However, the effect of this dietary supplement on drug-metabolizing enzymes is poorly understood, as it has not been studied extensively. Therefore, we investigated the effect of CellGevity dietary supplement on selected rat liver microsomal cytochrome P450 (CYP) enzymes, the most common drug-metabolizing enzymes. We also determined the total antioxidant potential of this dietary supplement in vitro.

METHODS

To determine the antioxidant potential of CellGevity dietary supplement, 2,2-diphenyl-2-picryl-hydrazyl (DPPH), total phenolic, and flavonoid assays were used after initial preparation of a solution form of the supplement (low dose, LD; 4 mg/kg and high dose, HD; 8 mg/kg). Rats received oral administration of these doses of the supplement for 7 days, after which the effect of the supplement on selected liver CYP enzymes was assessed using probe substrates and spectroscopic and high-performance liquid chromatographic methods. Rats which received daily administration of 80 mg/kg of phenobarbitone and distilled water served as positive and negative controls, respectively.

RESULTS

The IC₅₀ value of the supplement 0.34 ± 0.07 mg/ml compared to 0.076 ± 0.03 mg/ml of the BHT (positive control). The total phenolic content of the supplement at a concentration of 2.5 mg/ml was 34.97 g gallic acid equivalent (GAE)/100 g while its total flavonoid content at a concentration of 2.5 mg/ml was 6 g quercetin equivalent (QE)/100 g. The supplement significantly inhibited rat CYP2B1/2B2 (LDT 92.4%; HDT 100%), CYP3A4 (LDT 81.2%; HDT 71.7%), and CYP2C9 (LDT 21.7%; HDT 28.5%) while it had no significant inhibitory effect on CYPs 1A1/1A2, CYP1A2, and CYP2D6.

CONCLUSION

CellGevity dietary supplement possesses moderate antioxidant activity in vitro and has an inhibitory effect on selected rat liver CYP enzymes, suggesting its potential interaction with drugs metabolized by CYP enzymes.

Pharmacodynamic studies of voriconazole: informing the clinical management of invasive fungal infections

INTRODUCTION

Voriconazole is a broad-spectrum antifungal agent commonly used to treat invasive fungal infections (IFI), including aspergillosis, candidiasis, Scedosporium infection, and Fusarium infection. IFI often occur in immunocompromised patients, leading to increased morbidity and mortality.

AREAS COVERED

The objective of this review is to summarize the pharmacodynamic properties of voriconazole and to provide considerations for potential optimal dosing strategies. Studies have demonstrated superior clinical response when an AUC/MIC >25 or Cmin/MIC >1 is attained in adult patients, correlating to a trough concentration range as narrow as 2-4.5 mg/L; however, these targets are poorly established in the pediatric population. Topics in this discussion include voriconazole use in multiple age groups, predisposing patient factors for IFI, and considerations for clinicians managing IFI. Expert commentary: The relationship between voriconazole dosing and exposure is not well defined due to the large inter- and intra-subject variability. Development of comprehensive decision support tools for individualizing dosing, particularly in children who require higher dosing, will help to increase the probability of achieving therapeutic efficacy and decrease sub-therapeutic dosing and adverse events.

Evaluation of the Ecstasy influence on tramadol and its main metabolite plasma concentration in rats

BACKGROUND

Tramadol is prone to be abused alone, or in combination with 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy). It was reported that 95% of people with a history of substance abuse in the United States used tramadol in 2004. According to the WHO report in 2016, there was a growing number of tramadol abusers alone or in combination with psychoactive substances such as MDMA in particular in some Middle East countries. Higher concentrations of tramadol in plasma may lead to adverse drug reactions or lethal intoxication. In this study, the effect of MDMA on the pharmacokinetics of tramadol was examined in male rats.

METHODS

The effect of MDMA on Tmax, Cmax, area under the curve, elimination rate, and half-life of tramadol and its metabolites was examined. Two control and two treatment groups were designed. The treatment groups received MDMA 18 h before the administration of tramadol. Jugular vein blood samples were analyzed by high-performance liquid chromatography with fluorescent detector to determine the concentrations of tramadol and its metabolites. Independent-sample t-test was used to define the differences between pharmacokinetic parameters of control and treatment groups.

RESULTS

When tramadol administered intraperitoneally, the absorption rate of this drug was reduced, and a lower Cmax (40%) with longer Tmax (eight-fold) was achieved. MDMA exerted greater inhibitory effects on cytochrome P450 3A4 (CYP3A4) than on cytochrome P450 2D6 (CYP2D6). The M2 metabolite ratio was reduced by half, and because of the inhibition of M2 production, the M1 plasma concentration slightly increased.

CONCLUSIONS

According to the obtained data, MDMA treatment affected the absorption, distribution and metabolism phases of tramadol. This treatment increased the concentration of tramadol if administered intravenously and can latent the absorption of tramadol in oral route. However, MDMA was introduced as CYP2D6 inhibitor; in this study, MDMA inhibited CYP3A4 isoenzymes as well. This finding is important for the compounds that are metabolized through CYP3A4. It can be proposed that in abusers of MDMA who only receive tramadol for medical or nonmedical purposes in short intervals, the dangers of the intravenous administration of tramadol should be considered, and if tramadol is administered orally, the desired effect may not be achieved at the routine dose.

Xanthates As Useful Probes for Testing the Active Sites of Cytochromes P450 4A11 and 2E1

Xanthates (alkyl or aryl derivatives of dithiocarbonic acid) have been shown to be selective mechanism-based inactivators of cytochromes P450 2B1/2B6 and 2E1 due to covalent binding of a reactive intermediate to apoprotein after double hydrogen abstraction at α-carbon atom, suggesting interaction of the xanthate dithiocarbonic head with the enzyme heme. The structures of xanthates with a long alkyl chain are similar to the fatty acids. Saturated fatty acids (FA) such as lauric acid (LA), are metabolized by different cytochrome P450 isoforms to ω- and (ω-1)-hydroxy products, in humans done by CYP4A11 and CYP2E1, respectively. In the present study we aimed at elucidating the possible interactions of xanthates with two cytochrome P450 isoforms CYP4A11 and CYP2E1 involved in the metabolism of the FA. Our experiments showed that LA-ω-hydroxylation by CYP4A11 is inhibited in a competitive manner by xanthates with long alkyl chain (C12-xanthate being the most potent inhibitor). On the other hand LA-(ω-1)-hydroxylation reaction by purified CYP2E1 is inactivated by a mechanism-based type. The suggested differences in the interactions of C12-xanthate with the two cytochrome P450 isoforms were investigated by molecular modeling using docking approach. The results suggested that in CYP2E1 active site C12-xanthate coordinates to the heme with its most vulnerable dithiocarbonic head leading to a mechanism-based inactivation. In CYP4A11 xanthate alkyl chain is exposed to the heme, thus, a potenial ω-hydroxylated xanthate product could be formed, which could inhibit in a competitive manner the hydroxylation of LA. The observed differences of xanthates interactions with the active sites of the two similar cytochrome P450 isoforms (CYP4A11 and CYP2E1) involved in the metabolism of FA, which lead to different changes in the enzyme activity, suggest that xanthates can be used as probing tools for analyzing enzyme active sites when exploring useful and selective compounds influencing FA homeostasis.

Interspecies Variation of In Vitro Stability and Metabolic Diversity of YZG-331, a Promising Sedative-Hypnotic Compound

YZG-331, a synthetic adenosine derivative, express the sedative and hypnotic effects via binding to the adenosine receptor. The current study was taken to investigate the metabolic pathway of YZG-331 as well as species-specific differences in vitro. YZG-331 was reduced by 14, 11, 6, 46, and 11% within 120 min incubation in human, monkey, dog, rat, and mouse liver microsomes (LMs), respectively. However, YZG-331 was stable in human, monkey, dog, rat, and mouse liver cytoplasm. In addition, YZG-331 was unstable in rat or mouse gut microbiota with more than 50% of prototype drug degraded within 120 min incubation. Interestingly, the systemic exposure of M2 and M3 in rats and mice treated with antibiotics were significantly decreased in the pseudo germ-free group. YZG-331 could be metabolized in rat and human liver under the catalysis of CYP enzymes, and the metabolism showed species variation. In addition, 3 phase I metabolites were identified via hydroxyl (M1), hydrolysis (M2), or hydrolysis/ hydroxyl (M3) pathway. Flavin-containing monooxygenase 1 (FMO1) and FMO3 participated in the conversion of YZG-331 in rat LMs. Nevertheless, YZG-331 expressed stability with recombinant human FMOs, which further confirmed the species variation in the metabolism. Overall, these studies suggested that YZG-331 is not stable in LMs and gut microbiota. CYP450 enzymes and FMOs mediated the metabolism of YZG-331, and the metabolic pathway showed species difference. Special attention must be paid when extrapolating data from other species to humans.

Network analysis and cross species comparison of protein-protein interaction networks of human, mouse and rat cytochrome P450 proteins that degrade xenobiotics

Cytochrome P450 (CYP) enzymes that degrade xenobiotics play a critical role in the metabolism and biotransformation of drugs and xenobiotics in humans as well as experimental animal models such as mouse and rat. These proteins function as a network collectively as well as independently. Though there are several reports on the organization, regulation and functionality of various CYP enzymes at the molecular level, the understanding of organization and functionality of these proteins at the holistic level remain unclear. The objective of this study is to understand the organization and functionality of xenobiotic degrading CYP enzymes of human, mouse and rat using network theory approaches and to study species differences that exist among them at the holistic level. For our analysis, a protein-protein interaction (PPI) network for CYP enzymes of human, mouse and rat was constructed using the STRING database. Topology, centrality, modularity and robustness analyses were performed for our predicted CYP PPI networks that were then validated by comparison with randomly generated network models. Network centrality analyses of CYP PPI networks reveal the central/hub proteins in the network. Modular analysis of the CYP PPI networks of human, mouse and rat resulted in functional clusters. These clusters were subjected to ontology and pathway enrichment analysis. The analyses show that the cluster of the human CYP PPI network is enriched with pathways principally related to xenobiotic/drug metabolism. Endo-xenobiotic crosstalk dominated in mouse and rat CYP PPI networks, and they were highly enriched with endogenous metabolic and signaling pathways. Thus, cross-species comparisons and analyses of human, mouse and rat CYP PPI networks gave insights about species differences that existed at the holistic level. More investigations from both reductionist and holistic perspectives can help understand CYP metabolism and species extrapolation in a much better way.

Metabolism of okadaic acid by NADPH-dependent enzymes present in human or rat liver S9 fractions results in different toxic effects

The lipophilic marine biotoxin okadaic acid (OA) represents a natural contaminant produced by algae accumulating in seafood. Acute intoxications result in diarrhetic shellfish poisoning causing symptoms like nausea, vomiting and abdominal cramps. OA was preincubated with liver enzymes present in S9 fractions from humans, rats and rats pretreated with enzyme inducers in the presence or absence of the cofactor NADPH to investigate hepatic metabolism. Cytotoxicity was examined in HepG2 cells and metabolites of OA were determined by LC-MS/MS. Strong cytotoxicity was observed in HepG2 cells treated with OA that was preincubated in S9 fractions without NADPH. However, neither metabolites nor a decrease of OA itself were found. The addition of NADPH to the S9 fractions of rats resulted in a decreased cytotoxicity of OA, but a stronger toxicity in HepG2 cells was observed from OA preincubated in human S9 fractions with NADPH. Metabolite profiles of each S9 mix revealed that higher amounts of detoxified metabolites were formed by NADPH-dependent enzymes of rats compared to the same enzymes of humans. These differences in OA detoxification by NADPH-dependent liver enzymes of rats and humans may be of significance in the extrapolation of toxicological data from animal models (rats to humans, for example).

Pyrethroid resistance in Aedes aegypti and Aedes albopictus: Important mosquito vectors of human diseases

Aedes aegypti and A. albopictus mosquitoes are vectors of important human disease viruses, including dengue, yellow fever, chikungunya and Zika. Pyrethroid insecticides are widely used to control adult Aedes mosquitoes, especially during disease outbreaks. Herein, we review the status of pyrethroid resistance in A. aegypti and A. albopictus, mechanisms of resistance, fitness costs associated with resistance alleles and provide suggestions for future research. The widespread use of pyrethroids has given rise to many populations with varying levels of resistance worldwide, albeit with substantial geographical variation. In adult A. aegypti and A. albopictus, resistance levels are generally lower in Asia, Africa and the USA, and higher in Latin America, although there are exceptions. Susceptible populations still exist in several areas of the world, particularly in Asia and South America. Resistance to pyrethroids in larvae is also geographically widespread. The two major mechanisms of pyrethroid resistance are increased detoxification due to P450-monooxygenases, and mutations in the voltage sensitive sodium channel (Vssc) gene. Several P450s have been putatively associated with insecticide resistance, but the specific P450s involved are not fully elucidated. Pyrethroid resistance can be due to single mutations or combinations of mutations in Vssc. The presence of multiple Vssc mutations can lead to extremely high levels of resistance. Suggestions for future research needs are presented.

Monkey-based research on human disease: the implications of genetic differences

Assertions that the use of monkeys to investigate human diseases is valid scientifically are frequently based on a reported 90-93% genetic similarity between the species. Critical analyses of the relevance of monkey studies to human biology, however, indicate that this genetic similarity does not result in sufficient physiological similarity for monkeys to constitute good models for research, and that monkey data do not translate well to progress in clinical practice for humans. Salient examples include the failure of new drugs in clinical trials, the highly different infectivity and pathology of SIV/HIV, and poor extrapolation of research on Alzheimer's disease, Parkinson's disease and stroke. The major molecular differences underlying these inter-species phenotypic disparities have been revealed by comparative genomics and molecular biology - there are key differences in all aspects of gene expression and protein function, from chromosome and chromatin structure to post-translational modification. The collective effects of these differences are striking, extensive and widespread, and they show that the superficial similarity between human and monkey genetic sequences is of little benefit for biomedical research. The extrapolation of biomedical data from monkeys to humans is therefore highly unreliable, and the use of monkeys must be considered of questionable value, particularly given the breadth and potential of alternative methods of enquiry that are currently available to scientists.

Difference in the Pharmacokinetics and Hepatic Metabolism of Antidiabetic Drugs in Zucker Diabetic Fatty and Sprague-Dawley Rats

The Zucker diabetic fatty (ZDF) rat, an inbred strain of obese Zucker fatty rat, develops early onset of insulin resistance and displays hyperglycemia and hyperlipidemia. The phenotypic changes resemble human type 2 diabetes associated with obesity and therefore the strain is used as a pharmacological model for type 2 diabetes. The aim of the current study was to compare the pharmacokinetics and hepatic metabolism in male ZDF and Sprague-Dawley (SD) rats of five antidiabetic drugs that are known to be cleared via various mechanisms. Among the drugs examined, metformin, cleared through renal excretion, and rosiglitazone, metabolized by hepatic cytochrome P450 2C, did not exhibit differences in the plasma clearance in ZDF and SD rats. In contrast, glibenclamide, metabolized by hepatic CYP3A, canagliflozin, metabolized mainly by UDP-glucuronosyltransferases (UGT), and troglitazone, metabolized by sulfotransferase and UGT, exhibited significantly lower plasma clearance in ZDF than in SD rats after a single intravenous administration. To elucidate the mechanisms for the difference in the drug clearance, studies were performed to characterize the activity of hepatic drug-metabolizing enzymes using liver S9 fractions from the two strains. The results revealed that the activity for CYP3A and UGT was decreased in ZDF rats using the probe substrates, and decreased unbound intrinsic clearance in vitro for glibenclamide, canagliflozin, and troglitazone was consistent with lower plasma clearance in vivo. The difference in pharmacokinetics of these two strains may complicate pharmacokinetic/pharmacodynamic correlations, given that ZDF is used as a pharmacological model, and SD rat as the pharmacokinetics and toxicology strain.

The utility of metabolic activation mixtures containing human hepatic post-mitochondrial supernatant (S9) for in vitro genetic toxicity assessment

In vitro genotoxicity assessment routinely employs an exogenous metabolic activation mixture to simulate mammalian metabolism. Activation mixtures commonly contain post-mitochondrial liver supernatant (i.e. S9) from chemically induced Sprague Dawley rats. Although Organization for Economic Cooperation and Development (OECD) test guidelines permit the use of other S9 preparations, assessments rarely employ human-derived S9. The objective of this study is to review and evaluate the use of human-derived S9 for in vitro genetic toxicity assessment. All available published genotoxicity assessments employing human S9 were compiled for analysis. To facilitate comparative analyses, additional matched Ames data using induced rat liver S9 were obtained for certain highly cited chemicals. Historical human and induced rat S9 quality control reports from Moltox were obtained and mined for enzyme activity and mutagenic potency data. Additional in vitro micronucleus data were experimentally generated using human and induced rat S9. The metabolic activity of induced rat S9 was found to be higher than human S9, and linked to high mutagenic potency results. This study revealed that human S9 often yields significantly lower Salmonella mutagenic potency values, especially for polycyclic aromatic hydrocarbons, aflatoxin B1 and heterocyclic amines (~3- to 350-fold). Conversely, assessment with human S9 activation yields higher potency for aromatic amines (~2- to 50-fold). Outliers with extremely high mutagenic potency results were observed in the human S9 data. Similar trends were observed in experimentally generated mammalian micronucleus cell assays, however human S9 elicited potent cytotoxicity L5178Y, CHO and TK6 cell lines. Due to the potential for reduced sensitivity and the absence of a link between enzyme activity levels and mutagenic potency, human liver S9 is not recommended for use alone in in vitro genotoxicity screening assays; however, human S9 may be extremely useful in follow-up tests, especially in the case of chemicals with species-specific metabolic differences, such as aromatic amines.

Identification and characterization of in vitro and in vivo metabolites of steroidal alkaloid veratramine

Veratramine, a steroidal alkaloid originating from Veratrum nigrum L., has demonstrated distinct anti-tumor and anti-hypertension effects, however, its metabolism has rarely been explored. The objective of the current study was to provide a comprehensive investigation of its metabolic pathways. The in vitro metabolic profiles of veratramine were evaluated by incubating it with liver microsomes and cytosols. The in vivo metabolic profiles in plasma, bile, urine and feces were monitored by UPLC-MS/MS after oral (20 mg/kg) and i.v. (50 µg/kg) administration in rats. Meanwhile, related P450s inhibitors and recombinant P450s and SULTs were used to identify the isozymes responsible for its metabolism. Eleven metabolites of veratramine, including seven hydroxylated, two sulfated and two glucuronidated metabolites, were characterized. Unlike most alkaloids, the major reactive sites of veratramine were on ring A and B instead of on the amine moiety. CYP2D6 was the major isozyme mediating hydroxylation, and substrate inhibition was observed with a Vmax , Ki and Clint of 2.05 ± 0.53 nmol/min/mg, 33.08 ± 10.13 µ m and 13.58 ± 1.27 µL/min/mg. SULT2A1, with Km , Vmax and Clint values of 19.37 ± 0.87 µ m, 1.51 ± 0.02 nmol/min/mg and 78.19 ± 8.57 µL/min/mg, was identified as the major isozyme contributing to its sulfation. In conclusion, CYP2D6 and SULT2A1 mediating hydroxylation and sulfation were identified as the major biotransformation for veratramine.

Identification and functional characterization of novel feline cytochrome P450 2A

1. Cytochrome P450s are the major metabolizing enzymes for xenobiotics in humans and other mammals. Although the domestic cat Felis catus, an obligate carnivore, is the most common companion animal, the properties of cytochrome P450 subfamilies are largely unknown. 2. We newly identified the feline CYP2A13, which consists of 494 deduced amino acids, showing the highest identity to CYP2As of dogs, followed by those of pigs, cattle and humans. 3. The feline CYP2A13 transcript and protein were expressed almost exclusively in the liver without particular sex-dependent differences. 4. The feline CYP2A13 protein heterogeneously expressed in Escherichia coli showed metabolic activity similar to those of human and canine CYP2As for coumarin, 7-ethoxycoumarin and nicotine. 5. The results indicate the importance of CYP2A13 in systemic metabolism of xenobiotics in cats.

Heterologous expression of equine CYP3A94 and investigation of a tunable system to regulate co-expressed NADPH P450 oxidoreductase levels

The activity of cytochrome P450 enzymes depends on the enzyme NADPH P450 oxidoreductase (POR). The aim of this study was to investigate the activity of the equine CYP3A94 using a system that allows to regulate the POR protein levels in mammalian cells. CYP3A94 and the equine POR were heterologously expressed in V79 cells. In the system used, the POR protein regulation is based on a destabilizing domain (DD) that transfers its instability to a fused protein. The resulting fusion protein is therefore degraded by the ubiquitin-proteasome system (UPS). Addition of “Shield-1” prevents the DD fusion protein from degradation. The change of POR levels at different Shield-1 concentrations was demonstrated by cytochrome c reduction, Western immunoblot analysis, and immunocytochemistry. The alteration of CYP3A94 activity was investigated using a substrate (BFC) known to detect CYP3A4 activity. Equine CYP3A94 was demonstrated to be metabolically active and its activity could be significantly elevated by co-expression of POR. Cytochrome c reduction was significantly increased in V79-CYP3A94/DD-POR cells compared to V79-CYP3A94 cells. Surprisingly, incubation with different Shield-1 concentrations resulted in a decrease in POR protein shown by Western immunoblot analysis. Cytochrome c reduction did not change significantly, but the CYP3A94 activity decreased more than 4-fold after incubation with 500 nM and 1 µM Shield-1 for 24 hours. No differences were obtained when V79-CYP3A94 POR cells with and without Shield-1 were compared. The basal activity levels of V79-CYP3A94/DD-POR cells were unexpectedly high, indicating that DD/POR is not degraded without Shield-1. Shield-1 decreased POR protein levels and CYP3A94 activity suggesting that Shield-1 might impair POR activity by an unknown mechanism. Although regulation of POR with the pPTuner system could not be obtained, the cell line V79-CYP3A94/DD-POR system can be used for further experiments to characterize the equine CYP3A94 since the CYP activity was significantly enhanced with co-expressed POR.