Up-regulation of cytochrome P450 and phase II enzymes by xenobiotics in precision-cut tissue slices

Exploring precision-cut liver slices for comparative xenobiotic metabolism profiling in swine and cattle

In vitro systems are useful tools for unravelling species differences in xenobiotic metabolism.The current work aimed to validate the technique of precision-cut liver slices (PCLS) for comparative studies on xenobiotic metabolism in swine and cattle.PCLS from swine (n = 3) and cattle (n = 3) were produced using a Brendel-VitronTM Tissue Slicer and cultured for 6 h. Tissue viability was preserved throughout the whole culture period.Metabolic viability was evaluated using the anthelmintics albendazole (ABZ) and fenbendazole (FBZ) as model drugs, as well as other substrates of hepatic monooxygenases: benzydamine (BZ) N-oxygenase (FMO-dependent), and the O-dealkylations of 7-ethoxyresorufin (EROD, CYP1A1-dependent) and 7-methoxyresorufin (MROD, CYP1A2-dependent).ABZ S-oxygenation resulted 6-fold (cattle) and 13.6-fold (swine) higher (p = 0.001) compared to FBZ S-oxygenation.Similar BZ N-oxygenation and EROD activities were observed in PCLS cultures from both species. MROD was 2.5-fold higher (p = 0.033) in swine than in cattle. Similarly, ABZ S-oxygenation was 1.7-fold higher (p = 0.0002) in swine than in cattle. Conversely, a 82% higher (p = 0.0003) rate of FBZ S-oxygenation was evidenced in PCLS cultures from cattle compared to those from swine.Overall, this work shows that PCLS cultures are useful to obtain relevant information on species differences in xenobiotic metabolism.

Analyzing the metabolic fate of oral administration drugs: A review and state-of-the-art roadmap

The key orally delivered drug metabolism processes are reviewed to aid the assessment of the current in vivo/vitro experimental systems applicability for evaluating drug metabolism and the interaction potential. Orally administration is the most commonly used state-of-the-art road for drug delivery due to its ease of administration, high patient compliance and cost-effectiveness. Roles of gut metabolic enzymes and microbiota in drug metabolism and absorption suggest that the gut is an important site for drug metabolism, while the liver has long been recognized as the principal organ responsible for drugs or other substances metabolism. In this contribution, we explore various experimental models from their development to the application for studying oral drugs metabolism of and summarized advantages and disadvantages. Undoubtedly, understanding the possible metabolic mechanism of drugs in vivo and evaluating the procedure with relevant models is of great significance for screening potential clinical drugs. With the increasing popularity and prevalence of orally delivered drugs, sophisticated experimental models with higher predictive capacity for the metabolism of oral drugs used in current preclinical studies will be needed. Collectively, the review seeks to provide a comprehensive roadmap for researchers in related fields.

In vitro airway models from mice, rhesus macaques, and humans maintain species differences in xenobiotic metabolism and cellular responses to naphthalene

The translational value of high-throughput toxicity testing will depend on pharmacokinetic validation. Yet, popular in vitro airway epithelia models were optimized for structure and mucociliary function without considering the bioactivation or detoxification capabilities of lung-specific enzymes. This study evaluated xenobiotic metabolism maintenance within differentiated air-liquid interface (ALI) airway epithelial cell cultures (human bronchial; human, rhesus, and mouse tracheal), isolated airway epithelial cells (human, rhesus, and mouse tracheal; rhesus bronchial), and ex vivo microdissected airways (rhesus and mouse) by measuring gene expression, glutathione content, and naphthalene metabolism. Glutathione levels and detoxification gene transcripts were measured after 1-h exposure to 80 µM naphthalene (a bioactivated toxicant) or reactive naphthoquinone metabolites. Glutathione and glutathione-related enzyme transcript levels were maintained in ALI cultures from all species relative to source tissues, while cytochrome P450 monooxygenase gene expression declined. Notable species differences among the models included a 40-fold lower total glutathione content for mouse ALI trachea cells relative to human and rhesus; a higher rate of naphthalene metabolism in mouse ALI cultures for naphthalene-glutathione formation (100-fold over rhesus) and naphthalene-dihydrodiol production (10-fold over human); and opposite effects of 1,2-naphthoquinone exposure in some models-glutathione was depleted in rhesus tissue but rose in mouse ALI samples. The responses of an immortalized bronchial cell line to naphthalene and naphthoquinones were inconsistent with those of human ALI cultures. These findings of preserved species differences and the altered balance of phase I and phase II xenobiotic metabolism among the characterized in vitro models should be considered for future pulmonary toxicity testing.

In vitro and ex vivo models in inhalation biopharmaceutical research - advances, challenges and future perspectives

Oral inhalation results in pulmonary drug targeting and thereby reduces systemic side effects, making it the preferred means of drug delivery for the treatment of respiratory disorders such as asthma, chronic obstructive pulmonary disease or cystic fibrosis. In addition, the high alveolar surface area, relatively low enzymatic activity and rich blood supply of the distal airspaces offer a promising pathway to the systemic circulation. This is particularly advantageous when a rapid onset of pharmacological action is desired or when the drug is suffering from stability issues or poor biopharmaceutical performance following oral administration. Several cell and tissue-based in vitro and ex vivo models have been developed over the years, with the intention to realistically mimic pulmonary biological barriers. It is the aim of this review to critically discuss the available models regarding their advantages and limitations and to elaborate further which biopharmaceutical questions can and cannot be answered using the existing models.

Xenobiotica-metabolizing enzymes in the lung of experimental animals, man and in human lung models

The xenobiotic metabolism in the lung, an organ of first entry of xenobiotics into the organism, is crucial for inhaled compounds entering this organ intentionally (e.g. drugs) and unintentionally (e.g. work place and environmental compounds). Additionally, local metabolism by enzymes preferentially or exclusively occurring in the lung is important for favorable or toxic effects of xenobiotics entering the organism also by routes other than by inhalation. The data collected in this review show that generally activities of cytochromes P450 are low in the lung of all investigated species and in vitro models. Other oxidoreductases may turn out to be more important, but are largely not investigated. Phase II enzymes are generally much higher with the exception of UGT glucuronosyltransferases which are generally very low. Insofar as data are available the xenobiotic metabolism in the lung of monkeys comes closed to that in the human lung; however, very few data are available for this comparison. Second best rate the mouse and rat lung, followed by the rabbit. Of the human in vitro model primary cells in culture, such as alveolar macrophages and alveolar type II cells as well as the A549 cell line appear quite acceptable. However, (1) this generalization represents a temporary oversimplification born from the lack of more comparable data; (2) the relative suitability of individual species/models is different for different enzymes; (3) when more data become available, the conclusions derived from these comparisons quite possibly may change.

Transcriptomic characterization of bovine primary cultured hepatocytes; a cross-comparison with a bovine liver and the Madin-Darby bovine kidney cells

Bovine primary cultured hepatocytes (CHs) are widely used in vitro models for liver toxicity testing. However, little is known about their whole-transcriptome profile and its resemblance to the normal liver tissue. In the present study, we profiled - by microarray - the whole-transcriptome of bovine CHs (n=4) and compared it with the transcriptomic landscape of control liver samples (n=8), as well the Madin-Darby bovine kidney (MDBK) cells (n=4). Compared with liver tissue, the bovine CHs relatively expressed (fold change >2, P<0.05) about 2155 and 2073 transcripts at a lower and higher abundance, respectively. Of those expressed at a lower abundance, many were drug biotransformation enzyme-coding genes, such as the cytochrome P450 family (CYPs), sulfotransferases, methyltransferases, and glutathione S-transferases. Also, several drug transporters and solute carriers were expressed at a lower abundance in bovine CHs. 'Drug metabolism', 'PPAR signaling', and 'metabolism of xenobiotics by CYPs' were among the most negatively-enriched pathways in bovine CHs compared with liver. A qPCR cross-validation using 8 selected genes evidenced a high correlation (r=0.95, P=0.001) with the corresponding microarray results. Although from a kidney origin, and albeit to a lower extent compared to bovine CHs, the MDBK cells showed a basal expression of many CYP-coding genes. Our study provides a whole-transcriptome-based evidence for the bovine CHs and hepatic tissue resemblance. Overall, the bovine CHs' transcriptomic profile might render it unreliable as an in vitro model to study drug metabolism.

Synergistic and antagonistic interactions of binary mixtures of polycyclic aromatic hydrocarbons in the upregulation of CYP1 activity and mRNA levels in precision-cut rat liver slices

The current studies investigate whether synergistic or antagonistic interactions in the upregulation of CYP1 activity occur in binary mixtures of polycyclic aromatic hydrocarbons (PAHs) involving benzo[a]pyrene and five other structurally diverse PAHs of varying carcinogenic activity. Precision-cut rat liver slices were incubated with benzo[a]pyrene alone or in combination with a range of concentrations of a second PAH, and ethoxyresorufin O-deethylase, CYP1A1 and CYP1B1 mRNA levels determined. Concurrent incubation of benzo[a]pyrene with either dibenzo[a,h]anthracene or fluoranthene in liver slices led to a synergistic interaction, at least at low concentrations, in that ethoxyresorufin O-deethylase activity was statistically higher than the added effects when the slices were incubated with the individual compounds. In contrast, benzo[b]fluoranthene and, at high doses only, dibenzo[a,l]pyrene gave rise to antagonism, whereas 1-methylphenanthrene had no effect at all concentrations studied. When CYP1A1 mRNA levels were monitored, benzo[b]fluoranthene gave rise to an antagonistic response when incubated with benzo[a]pyrene, whereas all other compounds displayed synergism, with 1-methylphenathrene being the least effective. A similar picture emerged when CYP1B1 mRNA levels were determined, though the effects were less pronounced. In conclusion, it has been demonstrated that the benzo[a]pyrene-mediated upregulation of CYP1, at the mRNA and activity levels, is synergistically and antagonistically modulated by other PAHs. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 764-775, 2017.

Identification of cytochrome P450s involved in the metabolism of 6-benzyl-1-benzyloxymethyl-5-iodouracil (W-1) using human recombinant enzymes and rat liver microsomes in vitro

1. The aim of this study was to identify the hepatic metabolic enzymes, which involved in the biotransformation of 6-benzyl-1-benzyloxymethyl-5-iodouracil (W-1), a novel non-nucleoside reverse transcriptase inhibitor (NNRTI) in rat and human in vitro. 2. The parent drug of W-1 was incubated with rat liver microsomes (RLMs) or recombinant CYPs (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, and CYP3A5, respectively) in the presence or absence of nicotinamide adeninedinucleotide phosphate (NADPH)-regenerating system. The metabolites of W-1 were analyzed with liquid chromatography-ion trap-time of flight-mass spectrometry (LC-IT-TOF-MS). 3. The parent drug of W-1 was metabolized in a NADPH-dependent manner in RLMs. The kinetic parameters of prototype W-1 including K_m, V_max, and CL_int were 2.3 μM, 3.3 nmol/min/mg protein, and 1.4 mL/min/mg protein, respectively. Two metabolites M1 and M2 were observed in shorter retention times (2.988 and 3.188 min) with a higher molecular ion at m/z 463.0160 (both M1 and M2) than that of the W-1 parent drug (6.158 min with m/z 447.0218). The CYP selective inhibition and recombinant enzymes also showed that two hydroxyl metabolites M1 and M2 are mainly mediated by CYP2C19 and CYP3A4. 4. The identification of CYPs involved in W-1 biotransformation is important to understand and minimize, if possible, the potential of drug-drug interactions.

Murine precision-cut lung slices exhibit acute responses following exposure to gasoline direct injection engine emissions

Gasoline direct injection (GDI) engines are increasingly prevalent in the global vehicle fleet. Particulate matter emissions from GDI engines are elevated compared to conventional gasoline engines. The pulmonary effects of these higher particulate emissions are unclear. This study investigated the pulmonary responses induced by GDI engine exhaust using an ex vivo model. The physiochemical properties of GDI engine exhaust were assessed. Precision cut lung slices were prepared using Balb/c mice to evaluate the pulmonary response induced by one-hour exposure to engine-out exhaust from a laboratory GDI engine operated at conditions equivalent to vehicle highway cruise conditions. Lung slices were exposed at an air-liquid interface using an electrostatic aerosol in vitro exposure system. Particulate and gaseous exhaust was fractionated to contrast mRNA production related to polycyclic aromatic hydrocarbon (PAH) metabolism and oxidative stress. Exposure to GDI engine exhaust upregulated genes involved in PAH metabolism, including Cyp1a1 (2.71, SE=0.22), and Cyp1b1 (3.24, SE=0.12) compared to HEPA filtered air (p<0.05). GDI engine exhaust further increased Cyp1b1 expression compared to filtered GDI engine exhaust (i.e., gas fraction only), suggesting this response was associated with the particulate fraction. Exhaust particulate was dominated by high molecular weight PAHs. Hmox1, an oxidative stress marker, exhibited increased expression after exposure to GDI (1.63, SE=0.03) and filtered GDI (1.55, SE=0.04) engine exhaust compared to HEPA filtered air (p<0.05), likely attributable to a combination of the gas and particulate fractions. Exposure to GDI engine exhaust contributes to upregulation of genes related to the metabolism of PAHs and oxidative stress.

Maintenance of drug metabolism and transport functions in human precision-cut liver slices during prolonged incubation for 5 days

Human precision-cut liver slices (hPCLS) are a valuable ex vivo model that can be used in acute toxicity studies. However, a rapid decline in metabolic enzyme activity limits their use in studies that require a prolonged xenobiotic exposure. The aim of the study was to extend the viability and function of hPCLS to 5 days of incubation. hPCLS were incubated in two media developed for long-term culture of hepatocytes, RegeneMed^®, and Cellartis^®, and in the standard medium WME. Maintenance of phase I and II metabolism was studied both on gene expression as well as functional level using a mixture of CYP isoform-specific substrates. Albumin synthesis, morphological integrity, and glycogen storage was assessed, and gene expression was studied by transcriptomic analysis using microarrays with a focus on genes involved in drug metabolism, transport and toxicity. The data show that hPCLS retain their viability and functionality during 5 days of incubation in Cellartis^® medium. Albumin synthesis as well as the activity and gene expression of phase I and II metabolic enzymes did not decline during 120-h incubation in Cellartis^® medium, with CYP2C9 activity as the only exception. Glycogen storage and morphological integrity were maintained. Moreover, gene expression changes in hPCLS during incubation were limited and mostly related to cytoskeleton remodeling, fibrosis, and moderate oxidative stress. The expression of genes involved in drug transport, which is an important factor in determining the intracellular xenobiotic exposure, was also unchanged. Therefore, we conclude that hPCLS cultured in Cellartis^® medium are a valuable human ex vivo model for toxicological and pharmacological studies that require prolonged xenobiotic exposure.

Protective role of garlic oil against oxidative damage induced by furan exposure from weaning through adulthood in adult rat testis

Furan is produced in a wide variety of heat-treated foods via thermal degradation. Furan contamination is found to be relatively high in processed baby foods, cereal products, fruits juices, and canned vegetables. Several studies have demonstrated that furan is a potent hepatotoxin and hepatocarcinogen in rodents. However, few studies have investigated the toxic effects of furan in the testis. In addition, the exact mechanism(s) by which furan exerts toxicity in the testis has not been fully elucidated. In this study, we investigated the potential of furan exposure from weaning through adulthood to induce oxidative stress in adult rat testis, as well as the potential of garlic oil (GO) to ameliorate the induced toxicity. Our results reveal that furan administration significantly reduced serum testosterone levels and increased the levels of malondialdehyde (MDA); furthermore, furan administration decreased significantly the enzymatic activity of testicular antioxidants, including glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) and induced histopathological alterations in the testis. GO co-administration ameliorated the reduction in testosterone levels and dramatically attenuated the furan-induced oxidative and histopathological changes. In addition, Go significantly down-regulated the increased caspase-3 and cytochrome P450 2E1 (CYP2E1) expression in the furan-treated testis. To the best of our knowledge, this study is the first to demonstrate the furan-induced oxidative changes in the adult rat testis and the protective role of GO to ameliorate these changes through its antioxidant effects and its ability to inhibit CYP2E1 production.

A principal mechanism for the cancer chemopreventive activity of phenethyl isothiocyanate is modulation of carcinogen metabolism

Isothiocyanates are small molecules characterized by high chemical reactivity that allows them to interact readily with cellular constituents eliciting a plethora of biological activities. They are present exclusively in cruciferous vegetables, as glucosinolates, the intake of which has been associated with cancer chemoprevention. When the physical structure of these vegetables is disturbed, e.g. during mastication, the enzyme myrosinase is released and converts the glucosinolates to isothiocyanates (R-N=C=S), where R can be aliphatic or aromatic. Although sulforaphane, an aliphatic isothiocyanate, has received most attention worldwide, the most extensively studied aromatic isothiocyanate is phenethyl isothiocyanate (PEITC), and there are substantial differences in biological activity between the two sub-classes. In animal cancer models, PEITC effectively antagonized the carcinogenicity of chemicals, especially nitrosocompounds. A principal mechanism of their action is to protect the integrity of DNA by decreasing the levels of the genotoxic metabolites of chemical carcinogens. Extensive studies established that PEITC modulates the metabolism of the tobacco-specific carcinogenic nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by inhibiting its cytochrome P450-mediated bioactivation. Moreover, PEITC is a potent inducer of detoxification enzymes such as quinone reductase, glutathione S-transferase and glucuronosyl transferase. PEITC is rapidly absorbed and is characterized by a large bioavailability; Cmax concentrations achieved in plasma after dietary intake are sufficient to modulate carcinogen metabolism. PEITC is primarily metabolized by glutathione conjugation and is excreted in the urine and bile as the mercapturate. The ability of PEITC to perturb carcinogen metabolism through modulation of cytochrome P450 and phase II detoxification enzymes is comprehensively and critically reviewed.

Toxins induce 'malaise' behaviour in the honeybee (Apis mellifera)

To avoid poisoning and death when toxins are ingested, the body responds with a suite of physiological detoxification mechanisms accompanied by behaviours that in mammals often include vomiting, nausea, and lethargy. Few studies have characterised whether insects exhibit characteristic 'malaise-like' behaviours in response to intoxication. Here, we used the honeybee to investigate how intoxication produced by injection or ingestion with three toxins with different pharmacological modes of action quinine, amygdalin, and lithium chloride affected behaviour. We found that toxin-induced changes in behaviour were best characterised by more time spent grooming. Bees also had difficulty performing the righting reflex and exhibited specific toxin-induced behaviours such as abdomen dragging and curling up. The expression of these behaviours also depended on whether a toxin had been injected or ingested. When toxins were ingested, they were least 10 times less concentrated in the haemolymph than in the ingested food, suggesting that their absorption through the gut is strongly regulated. Our data show that bees exhibit changes in behaviour that are characteristic of 'malaise' and suggest that physiological signalling of toxicosis is accomplished by multiple post-ingestive pathways in animals.

Metabolism of 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) atropisomers in tissue slices from phenobarbital or dexamethasone-induced rats is sex-dependent

1. Chiral polychlorinated biphenyls (PCBs) such as PCB 136 enantioselectively sensitize the ryanodine receptor (RyR). In light of recent evidence that PCBs cause developmental neurotoxicity via RyR-dependent mechanisms, this suggests that enantioselective PCB metabolism may influence the developmental neurotoxicity of chiral PCBs. However, enantioselective disposition of PCBs has not been fully characterized. 2. The effect of sex and cytochrome P450 (P450) enzyme induction on the enantioselective metabolism of PCB 136 was studied using liver tissue slices prepared from naïve control (CTL), phenobarbital (PB; CYP2B inducer) or dexamethasone (DEX; CYP3A inducer) pretreated adult Sprague-Dawley rats. PCB 136 metabolism was also examined in hippocampal slices derived from untreated rat pups. 3. In liver tissue slices, hydroxylated PCB (OH-PCB) profiles depended on sex and inducer pretreatment, and OH-PCB levels followed the rank orders male > female and PB > DEX > CTL. In contrast, the enantiomeric enrichment of PCB 136 and its metabolites was independent of sex and inducer pretreatment. Only small amounts of PCB 136 partitioned into hippocampal tissue slices and no OH-PCB metabolites were detected. 4. Our results suggest that enantioselective metabolism, sex and induction status of P450 enzymes in the liver may modulate the neurotoxic outcomes of developmental exposure to chiral PCBs.