Evaluation of the metabolism and hepatotoxicity of xenobiotics utilizing precision-cut 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.

Metabolites in the regulatory risk assessment of pesticides in the EU

A large majority of chemicals is converted into metabolites through xenobiotic-metabolising enzymes. Metabolites may present a spectrum of characteristics varying from similar to vastly different compared with the parent compound in terms of both toxicokinetics and toxicodynamics. In the pesticide arena, the role of metabolism and metabolites is increasingly recognised as a significant factor particularly for the design and interpretation of mammalian toxicological studies and in the toxicity assessment of pesticide/metabolite-associated issues for hazard characterization and risk assessment purposes, including the role of metabolites as parts in various residues in ecotoxicological adversities. This is of particular relevance to pesticide metabolites that are unique to humans in comparison with metabolites found in in vitro or in vivo animal studies, but also to disproportionate metabolites (quantitative differences) between humans and mammalian species. Presence of unique or disproportionate metabolites may underlie potential toxicological concerns. This review aims to present the current state-of-the-art of comparative metabolism and metabolites in pesticide research for hazard and risk assessment, including One Health perspectives, and future research needs based on the experiences gained at the European Food Safety Authority.

Experimental Models for Studying Structural and Functional State of the Pathological Liver (Review)

Liver pathologies remain one of the leading causes of mortality worldwide. Despite a high prevalence of liver diseases, the possibilities of diagnosing, prognosing, and treating non-alcoholic and alcoholic liver diseases still have a number of limitations and require the development of new methods and approaches. In laboratory studies, various models are used to reconstitute the pathological conditions of the liver, including cell cultures, spheroids, organoids, microfluidic systems, tissue slices. We reviewed the most commonly used in vivo, in vitro, and ex vivo models for studying non-alcoholic fatty liver disease and alcoholic liver disease, toxic liver injury, and fibrosis, described their advantages, limitations, and prospects for use. Great emphasis was placed on the mechanisms of development of pathological conditions in each model, as well as the assessment of the possibility of reconstructing various key aspects of pathogenesis for all these pathologies. There is currently no consensus on the choice of the most adequate model for studying liver pathology. The choice of a certain effective research model is determined by the specific purpose and objectives of the experiment.

Gut Microbiota and the Quality of Oral Anticoagulation in Vitamin K Antagonists Users: A Review of Potential Implications

The efficacy and safety of vitamin K antagonists (VKAs) as oral anticoagulants (OACs) depend on the quality of anticoagulation control, as reflected by the mean time in therapeutic range (TTR). Several factors may be involved in poor TTR such as comorbidities, high inter-individual variability, interacting drugs, and non-adherence. Recent studies suggest that gut microbiota (GM) plays an important role in the pathogenesis of cardiovascular diseases, but the effect of the GM on anticoagulation control with VKAs is unknown. In the present review article, we propose different mechanisms by which the GM could have an impact on the quality of anticoagulation control in patients taking VKA therapy. We suggest that the potential effects of GM may be mediated first, by an indirect effect of metabolites produced by GM in the availability of VKAs drugs; second, by an effect of vitamin K-producing bacteria; and finally, by the structural modification of the molecules of VKAs. Future research will help confirm these hypotheses and may suggest profiles of bacterial signatures or microbial metabolites, to be used as biomarkers to predict the quality of anticoagulation. This could lead to the design of intervention strategies modulating gut microbiota, for example, by using probiotics.

Chemical warfare agent research in precision-cut tissue slices-a useful alternative approach

The use of chemical warfare agents (CWAs) in military conflicts and against civilians is a recurrent problem. Despite ongoing CWA research using in vitro or in vivo models, progress to elucidate mechanisms of toxicity and to develop effective therapies, decontamination procedures, and general countermeasures is still limited. Novel scientific approaches to address these questions are needed to expand perspectives on existing knowledge and gain new insights. To achieve this, the use of ex vivo techniques like precision-cut tissue slices (PCTSs) can be a valuable approach. Existing studies employing this economical and relatively easy to implement method show model suitability and comparability with the use of in vitro and in vivo models. In this article, we review research on CWAs in PCTSs to illustrate the advantages of the approach and to promote future applications.

Metabolism of cyclic phenones in rainbow trout in vitro assays

1. Cyclic phenones are chemicals of interest to the USEPA due to their potential for endocrine disruption to aquatic and terrestrial species.2. Prior to this report, there was very limited information addressing metabolism of cyclic phenones by fish species and the potential for estrogen receptor (ER) binding and vitellogenin (Vtg) gene activation by their metabolites.3. The main objectives of the current research were to characterize rainbow trout (rt) liver slice-mediated in vitro metabolism of model parent cyclic phenones exhibiting disparity between ER binding and ER-mediated Vtg gene induction, and to assess the metabolic competency of fish liver in vitro tests to help determine the chemical form (parent and/or metabolite) associated with the observed biological response.4. GC-MS, HPLC and LC-MS/MS technologies were applied to investigate the in vitro biotransformation of cyclobutyl phenyl ketone (CBP), benzophenone (DPK), cyclohexyl phenyl ketone (CPK) mostly in the absence of standards for metabolite characterization.5. It was concluded that estrogenic effects of the studied cyclic phenones are mediated by the parent chemical structure for DPK, but by active metabolites for CPK. A definitive interpretation was not possible for CBP and CBPOH (alcohol), although a contribution of both structures to gene induction is suspected.

Development of a Novel Ex-vivo 3D Model to Screen Amoebicidal Activity on Infected Tissue

Amoebiasis is a parasitic disease that causes thousands of deaths every year, its adverse effects and resistance to conventional treatments have led to the search of new treatment options, as well as the development of novel screening methods. In this work, we implemented a 3D model of intestine and liver slices from hamsters that were infected ex vivo with virulent E. histolytica trophozoites. Results show preserved histology in both uninfected tissues as well as ulcerations, destruction of the epithelial cells, and inflammatory reaction in intestine slices and formation of micro abscesses, and the presence of amoebae in the sinusoidal spaces and in the interior of central veins in liver slices. The three chemically synthetized compounds T-001, T-011, and T-016, which act as amoebicides in vitro, were active in both infected tissues, as they decreased the number of trophozoites, and provoked death by disintegration of the amoeba, similar to metronidazole. However, compound T-011 induced signs of cytotoxicity to liver slices. Our results suggest that ex vivo cultures of precision-cut intestinal and liver slices represent a reliable 3D approach to evaluate novel amoebicidal compounds, and to simultaneously detect their toxicity, while reducing the number of experimental animals commonly required by other model systems.

Maintenance of high quality rat precision cut liver slices during culture to study hepatotoxic responses: Acetaminophen as a model compound

Precision cut liver slices (PCLiS) represent a promising tool in reflecting hepatotoxic responses. However, the culture of PCLiS varies considerably between laboratories, which can affect the performance of the liver slices and thus the experimental outcome. In this study, we describe an easily accessible culture method, which ensures optimal slice viability and functionality, in order to set the basis for reproducible and comparable PCLiS studies. The quality of the incubated rat PCLiS was assessed during a 24h culture period using ten readouts, which covered viability (lactate dehydrogenase-, aspartate transaminase- and glutamate dehydrogenase-leakage, ATP content) and functionality parameters (urea, albumin production) as well as histomorphology and other descriptive characteristics (protein content, wet weight, slice thickness). The present culture method resulted in high quality liver slices for 24h. Finally, PCLiS were exposed to increasing concentrations of acetaminophen to assess the suitability of the model for the detection of hepatotoxic responses. Six out of ten readouts revealed a toxic effect and showed an excellent mutual correlation. ATP, albumin and histomorphology measurements were identified as the most sensitive readouts. In conclusion, our results indicate that rat PCLiS are a valuable liver model for hepatotoxicity studies, particularly if they are cultured under optimal standardized conditions.

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.

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.

Human-based systems in drug and chemical safety testing--toward replacement, the 'single R'

The Three Rs was a concept originally conceived as a means of reducing the suffering of laboratory animals that are used largely in identifying any potential safety issues with chemicals to which humans may be exposed. However, with growing evidence of the shortcomings of laboratory animal testing to reliably predict human responsiveness to such chemicals, questions are now being asked as to whether it is appropriate to use animals as human surrogates at all. This raises the question of whether, of the original Three Rs, two--Reduction and Refinement--are potentially redundant, and whether, instead, we should concentrate on the third R: Replacement. And if this is the best way forward, it is inevitable that this R should be based firmly on human biology. The present review outlines the current state-of-the-art regarding our access to human biology through in vitro, in silico and in vivo technologies, identifying strengths, weaknesses and opportunities, and goes on to address the prospect of achieving a single R, with some suggestions as to how to progress toward this goal.

Microengineered liver tissues for drug testing

Drug-induced liver injury (DILI) is a leading cause of drug attrition. Significant and well-documented differences between animals and humans in liver pathways now necessitate the use of human-relevant in vitro liver models for testing new chemical entities during preclinical drug development. Consequently, several human liver models with various levels of in vivo-like complexity have been developed for assessment of drug metabolism, toxicity, and efficacy on liver diseases. Recent trends leverage engineering tools, such as those adapted from the semiconductor industry, to enable precise control over the microenvironment of liver cells and to allow for miniaturization into formats amenable for higher throughput drug screening. Integration of liver models into organs-on-a-chip devices, permitting crosstalk between tissue types, is actively being pursued to obtain a systems-level understanding of drug effects. Here, we review the major trends, challenges, and opportunities associated with development and implementation of engineered liver models created from primary cells, cell lines, and stem cell-derived hepatocyte-like cells. We also present key applications where such models are currently making an impact and highlight areas for improvement. In the future, engineered liver models will prove useful for selecting drugs that are efficacious, safer, and, in some cases, personalized for specific patient populations.

Hepatic metabolism: a key component of herbal drugs research

Liver is the largest metabolic organ for a wide range of endogenous and exogenous compounds and plays a crucial part in the pharmacokinetics and pharmacodynamics through various metabolic reactions. This review provides a progressive description of hepatic metabolism of herbal drugs with respect to metabolic types and investigational methods. In addition, the problems encountered during the research process are discussed.

Evaluation of database-derived pathway development for enabling biomarker discovery for hepatotoxicity

Current testing models for predicting drug-induced liver injury are inadequate, as they basically under-report human health risks. We present here an approach towards developing pathways based on hepatotoxicity-associated gene groups derived from two types of publicly accessible hepatotoxicity databases, in order to develop drug-induced liver injury biomarker profiles. One human liver ‘omics-based and four text-mining-based databases were explored for hepatotoxicity-associated gene lists. Over-representation analysis of these gene lists with a hepatotoxicant-exposed primary human hepatocytes data set showed that human liver ‘omics gene lists performed better than text-mining gene lists and the results of the latter differed strongly between databases. However, both types of databases contained gene lists demonstrating biomarker potential. Visualizing those in pathway format may aid in interpreting the biomolecular background. We conclude that exploiting existing and openly accessible databases in a dedicated manner seems promising in providing venues for translational research in toxicology and biomarker development.

Oxidation of polychlorinated biphenyls by liver tissue slices from phenobarbital-pretreated mice is congener-specific and atropselective

Mouse models are powerful tools to study the developmental neurotoxicity of polychlorinated biphenyls (PCBs); however, studies of the oxidation of chiral PCB congeners to potentially neurotoxic hydroxylated metabolites (OH-PCBs) in mice have not been reported. Here, we investigate the atropselective oxidation of chiral PCB 91 (2,2',3,4',6-pentachlorobiphenyl), PCB 95 (2,2',3,5',6-pentachlorobiphenyl), PCB 132 (2,2',3,3',4,6'-hexachlorobiphenyl), PCB 136 (2,2',3,3',6,6'-hexachlorobiphenyl), and PCB 149 (2,2',3,4',5',6-hexachlorobiphenyl) to OH-PCBs in liver tissue slices prepared from female mice. The metabolite profile of PCB 136 typically followed the rank order 5-OH-PCB > 4-OH-PCB > 4,5-OH-PCB, and metabolite levels increased with PCB concentration and incubation time. A similar OH-PCB profile was observed with the other PCB congeners, with 5-OH-PCB/4-OH-PCB ratios ranging from 2 to 12. More 5-OH-PCB 136 was formed in liver tissue slices obtained from animals pretreated with phenobarbital (P450 2B inducer) or, to a lesser extent, dexamethasone (P450 2B and 3A enzyme inducer) compared to tissue slices prepared from vehicle-pretreated animals. The apparent rate of 5-OH-PCBs formation followed the approximate rank order PCB 149 > PCB 91 > PCB 132 ∼ PCB 136 > PCB 95. Atropselective gas chromatography revealed a congener-specific atropisomeric enrichment of major OH-PCB metabolites. Comparison of our results with published OH-PCB patterns and chiral signatures (i.e., the direction and extent of the atropisomeric enrichment) from rat liver microsomal revealed drastic differences between both species, especially following the induction of P450 2B enzymes. These species differences in the metabolism of chiral PCBs should be considered in developmental neurotoxicity studies of PCBs.

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.