Definition of metabolism-dependent xenobiotic toxicity with co-cultures of human hepatocytes and mouse 3T3 fibroblasts in the novel integrated discrete multiple organ co-culture (IdMOC) experimental system: results with model toxicants aflatoxin B1, cyclophosphamide and tamoxifen

Development of a human liver microphysiological coculture system for higher throughput chemical safety assessment

Chemicals in the systemic circulation can undergo hepatic xenobiotic metabolism, generate metabolites, and exhibit altered toxicity compared with their parent compounds. This article describes a 2-chamber liver-organ coculture model in a higher-throughput 96-well format for the determination of toxicity on target tissues in the presence of physiologically relevant human liver metabolism. This 2-chamber system is a hydrogel formed within each well consisting of a central well (target tissue) and an outer ring-shaped trough (human liver tissue). The target tissue chamber can be configured to accommodate a three-dimensional (3D) spheroid-shaped microtissue, or a 2-dimensional (2D) cell monolayer. Culture medium and compounds freely diffuse between the 2 chambers. Human-differentiated HepaRG liver cells are used to form the 3D human liver microtissues, which displayed robust protein expression of liver biomarkers (albumin, asialoglycoprotein receptor, Phase I cytochrome P450 [CYP3A4] enzyme, multidrug resistance-associated protein 2 transporter, and glycogen), and exhibited Phase I/II enzyme activities over the course of 17 days. Histological and ultrastructural analyses confirmed that the HepaRG microtissues presented a differentiated hepatocyte phenotype, including abundant mitochondria, endoplasmic reticulum, and bile canaliculi. Liver microtissue zonation characteristics could be easily modulated by maturation in different media supplements. Furthermore, our proof-of-concept study demonstrated the efficacy of this coculture model in evaluating testosterone-mediated androgen receptor responses in the presence of human liver metabolism. This liver-organ coculture system provides a practical, higher-throughput testing platform for metabolism-dependent bioactivity assessment of drugs/chemicals to better recapitulate the biological effects and potential toxicity of human exposures.

Marketable 1,3-dimethylamylamine and caffeine-based thermogenic supplements: Regulatory genotoxicity assessment through in vitro and in silico approaches

The consumption of dietary supplements to enhance physical performance has increased significantly in the last century, especially thermogenic pre-workout supplements. Nevertheless, this industry has faced criticism for inadequate safety measures surveillance in regulatory issues regarding their products. The aims of our study were to investigate two pre-workout supplements with respect to (1) mutagenicity utilizing Salmonella/microsome assay; (2) genotoxicity employing cytokinesis-block micronucleus (CBMN) assay protocols; and (3) hepatocytoxicity using WST cell proliferation, activities of lactate dehydrogenase (LDH) and alkaline phosphatase using human liver carcinoma (HepG2) and mouse fibroblast (F C3H) cells. Oxidative stress was determined through glutathione (GSH) measurement and in silico for predictions of pharmacokinetics and toxicity for the most abundant isolated substances present in these supplements. Both supplements induced mutagenicity in all examined bacterial strains, especially in the presence of exogenous metabolism. Further, tested supplements significantly elevated the formation of micronuclei (MN) as well as other cellular phenomena. Concentration- and time-dependent curves were observed for hepatotoxicity in both studied cell lines. In addition, both supplements decreased levels of intracellular and extracellular GSH. In silico predictions showed that the isolated individual compounds failed to induce the observed outcomes. Our findings provide contributions to the molecular mechanisms underlying two pre-workout supplement-induced toxicity and the need for surveillance.

Metabolism and toxicity of usnic acid and barbatic acid based on microsomes, S9 fraction, and 3T3 fibroblasts in vitro combined with a UPLC-Q-TOF-MS method

Introduction: Usnic acid (UA) and barbatic acid (BA), two typical dibenzofurans and depsides in lichen, have a wide range of pharmacological activities and hepatotoxicity concerns. This study aimed to clarify the metabolic pathway of UA and BA and illuminate the relationship between metabolism and toxicity. Methods: An UPLC-Q-TOF-MS method was developed for metabolite identification of UA and BA in human liver microsomes (HLMs), rat liver microsomes (RLMs), and S9 fraction (RS9). The key metabolic enzymes responsible for UA and BA were identified by enzyme inhibitors combined with recombinant human cytochrome P450 (CYP450) enzymes. The cytotoxicity and metabolic toxicity mechanism of UA and BA were determined by the combination model of human primary hepatocytes and mouse 3T3 fibroblasts. Results: The hydroxylation, methylation, and glucuronidation reactions were involved in the metabolic profiles of UA and BA in RLMs, HLMs, and RS9. CYP2C9, CYP3A4, CYP2C8, and UGT1A1 are key metabolic enzymes responsible for metabolites of UA and CYP2C8, CYP2C9, CYP2C19, CYP1A1, UGT1A1, UGT1A3, UGT1A7, UGT1A8, UGT1A9, and UGT1A10 for metabolites of BA. UA and BA did not display evident cytotoxicity in human primary hepatocytes at concentrations of 0.01-25 and 0.01-100 µM, respectively, but showed potential cytotoxicity to mouse 3T3 fibroblasts with 50% inhibitory concentration values of 7.40 and 60.2 µM. Discussion: In conclusion, the attenuated cytotoxicity of BA is associated with metabolism, and UGTs may be the key metabolic detoxification enzymes. The cytotoxicity of UA may be associated with chronic toxicity. The present results provide important insights into the understanding of the biotransformation behavior and metabolic detoxification of UA and BA.

Microfluidic Chip as a Tool for Effective In Vitro Evaluation of Cyclophosphamide Prodrug Toxicity

Most drugs are metabolized in the liver, which can lead to their activation or inactivation with a change in the parent compound pharmacology, as well as liver damage by active metabolites. Preclinical animal studies of drug safety do not always predict its effect on humans due to species specificity. Thus, for the rapid drug screening, and especially prodrugs, an in vitro system is required that allows predicting xenobiotic cytotoxicity with consideration of their metabolism in liver cells. The use of a microfluidic chip (BioClinicum) made it possible to cultivate a 2D culture of human HaCaT keratinocytes with spheroids of human hepatoma HepaRG cells. After incubation in a specially selected universal serum-free medium containing 3.8 mM cyclophosphamide, pronounced death of HaCaT cells was observed in comparison with culturing in the absence of liver cells.

Evaluation of the utility of the Beta Human Liver Emulation System (BHLES) for CFSAN's regulatory toxicology program

Microphysiological systems (MPS), such as organ-on-a-chip platforms, are an emerging alternative model that may be useful for predicting human physiology and/or toxicity. Due to the interest in these platforms, the Center for Food Safety and Applied Nutrition partnered with Emulate to evaluate the utility of the Beta Human Liver Emulation System (BHLES) for its regulatory science program. Using known hepatotoxic compounds (usnic acid, benzbromarone, tamoxifen, and acetaminophen) and compounds that have no reported human cases of liver toxicity (dimethyl sulfoxide, theophylline, and aminohippurate) the platforms' performance was evaluated. Chemical toxicity was assessed by albumin secretion, urea and LDH release, nuclei number, mitochondrial membrane potential, and apoptosis. System/platform performance was evaluated in terms of sensitivity and specificity, power, and variability and repeatability. Chemical interactions with the Chip material were also assessed. Preliminary findings suggested that for the model test compounds selected, the BHLES was able to accurately predict toxicity, demonstrated high sensitivity and specificity, high power, and low variability. However, some compounds interacted with the Chip material indicating variable exposure levels that should be accounted for when planning experimentation. The details of the evaluation are presented herein.

Physiologically relevant oxygen tensions differentially regulate hepatotoxic responses in HepG2 cells

This study evaluates the impact of physiologically relevant oxygen tensions on the response of HepG2 cells to known inducers and hepatotoxic drugs. We compared transcriptional regulation and CYP1A activity after a 48 h exposure at atmospheric culture conditions (20% O2) with representative periportal (8% O2) and perivenous (3% O2) oxygen tensions. We evaluated cellular responses in 2D and 3D cultures at each oxygen tension in parallel, using monolayers and a paper-based culture platform that supports cells suspended in a collagen-rich environment. Our findings highlight that the toxicity, potency, and mechanism of action of drugs are dependent on both culture format and oxygen tension. HepG2 cells in 3D environments at physiologic oxygen tensions better matched primary human hepatocyte data than HepG2 cells cultured under standard conditions. Despite altered transcriptional regulation with decreasing oxygen tensions, we did not observe the zonation patterns of drug-metabolizing enzymes found in vivo. Our approach demonstrates that oxygen is an important regulator of liver function but it is not the sole regulator. It also highlights the utility of the 3D paper-based culture platform for continued mechanistic studies of microenvironmental influences on cellular responses.

Predicting the potential toxicity of 26 components in Cassiae semen using in silico and in vitro approaches

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A combination of in silico and in vitro methods was applied.

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The potential toxicity of 26 components isolated from Cassiae semen is predicted.

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Six compounds were predicted toxic to liver & ten compounds toxic to kidney.

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Special anthraquinones and anthraquinone-glucosides are potential toxicants.

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Specific group of anthraquinones influences hepatic or renal cytotoxicity.

Cassiae semen are dried and ripe seeds of Cassia obtusifolia L. or Cassia tora L. (Fabaceae) and have been made into roasted tea or used as a traditional medicine in Asian countries. However, it was reported to result in liver and renal toxicity. The components of Cassiae semen that induce hepatotoxicity or nephrotoxicity remain unknown. In the present study, we evaluate the potential toxicity of 26 newly isolated compounds from Cassiae semen using quantitative structure–activity relationship (QSAR) methods and co-culture of hepatic and renal cell approaches, and we aim to illustrate the relationship between the structural characteristics and cytotoxicity by general linear models (GLMs). Both the QSAR models and co-culture of hepatic and renal cell systems predicted that 6 compounds were potentially hepatotoxic, 10 compounds were potentially nephrotoxic, and specific anthraquinones and anthraquinone-glucosides were potential toxicants in Cassiae semen. Specific groups such as –OH and –OCH₃ at the R1, R2, R3, and R7 positions influenced the cytotoxicity.

Predicting Metabolism-Related Drug-Drug Interactions Using a Microphysiological Multitissue System

Drug-drug interactions (DDIs) occur when the pharmacological activity of one drug is altered by a second drug. As multimorbidity and polypharmacotherapy are becoming more common due to the increasing age of the population, the risk of DDIs is massively increasing. Therefore, in vitro testing methods are needed to capture such multiorgan events. Here, a scalable, gravity-driven microfluidic system featuring 3D microtissues (MTs) that represent different organs for the prediction of drug-drug interactions is used. Human liver microtissues (hLiMTs) are combined with tumor microtissues (TuMTs) and treated with drug combinations that are known to cause DDIs in vivo. The testing system is able to capture and quantify DDIs upon co-administration of the anticancer prodrugs cyclophosphamide or ifosfamide with the antiretroviral drug ritonavir. Dosage of ritonavir inhibits hepatic metabolization of the two prodrugs to different extents and decreases their efficacy in acting on TuMTs. The flexible MT compartment design of the system, the use of polystyrene as chip material, and the assembly of several chips in stackable plates offer the potential to significantly advance preclinical substance testing. The possibility of testing a broad variety of drug combinations to identify possible DDIs will improve the drug development process and increase patient safety.

Organs-on-a-Chip

Organs-on-chips, also known as "tissue chips" or microphysiological systems (MPS), are bioengineered microsystems capable of recreating aspects of human organ physiology and function and are in vitro tools with multiple applications in drug discovery and development. The ability to recapitulate human and animal tissues in physiologically relevant three-dimensional, multi-cellular environments allows applications in the drug development field, including; (1) use in assessing the safety and toxicity testing of potential therapeutics during early-stage preclinical drug development; (2) confirmation of drug/therapeutic efficacy in vitro; and (3) disease modeling of human tissues to recapitulate pathophysiology within specific subpopulations and even individuals, thereby advancing precision medicine efforts. This chapter will discuss the development and evolution of three-dimensional organ models over the past decade, and some of the opportunities offered by MPS technology that are not available through current standard two-dimensional cell cultures, or three-dimensional organoid systems. This chapter will outline future avenues of research in the MPS field, how cutting-edge biotechnology advances are expanding the applications for these systems, and discuss the current and future potential and challenges remaining for the field to address.

The application of omics-based human liver platforms for investigating the mechanism of drug-induced hepatotoxicity in vitro

Drug-induced liver injury (DILI) complicates safety assessment for new drugs and poses major threats to both patient health and drug development in the pharmaceutical industry. A number of human liver cell-based in vitro models combined with toxicogenomics methods have been developed as an alternative to animal testing for studying human DILI mechanisms. In this review, we discuss the in vitro human liver systems and their applications in omics-based drug-induced hepatotoxicity studies. We furthermore present bioinformatic approaches that are useful for analyzing toxicogenomic data generated from these models and discuss their current and potential contributions to the understanding of mechanisms of DILI. Human pluripotent stem cells, carrying donor-specific genetic information, hold great potential for advancing the study of individual-specific toxicological responses. When co-cultured with other liver-derived non-parenchymal cells in a microfluidic device, the resulting dynamic platform enables us to study immune-mediated drug hypersensitivity and accelerates personalized drug toxicology studies. A flexible microfluidic platform would also support the assembly of a more advanced organs-on-a-chip device, further bridging gap between in vitro and in vivo conditions. The standard transcriptomic analysis of these cell systems can be complemented with causality-inferring approaches to improve the understanding of DILI mechanisms. These approaches involve statistical techniques capable of elucidating regulatory interactions in parts of these mechanisms. The use of more elaborated human liver models, in harmony with causality-inferring bioinformatic approaches will pave the way for establishing a powerful methodology to systematically assess DILI mechanisms across a wide range of conditions.

Models used to screen for the treatment of multidrug resistant cancer facilitated by transporter-based efflux

PURPOSE

Efflux transporters of the adenosine triphosphate-binding cassette (ABC)-superfamily play an important role in the development of multidrug resistance (multidrug resistant; MDR) in cancer. The overexpression of these transporters can directly contribute to the failure of chemotherapeutic drugs. Several in vitro and in vivo models exist to screen for the efficacy of chemotherapeutic drugs against MDR cancer, specifically facilitated by efflux transporters.

RESULTS

This article reviews a range of efflux transporter-based MDR models used to test the efficacy of compounds to overcome MDR in cancer. These models are classified as either in vitro or in vivo and are further categorised as the most basic, conventional models or more complex and advanced systems. Each model's origin, advantages and limitations, as well as specific efflux transporter-based MDR applications are discussed. Accordingly, future modifications to existing models or new research approaches are suggested to develop prototypes that closely resemble the true nature of multidrug resistant cancer in the human body.

CONCLUSIONS

It is evident from this review that a combination of both in vitro and in vivo preclinical models can provide a better understanding of cancer itself, than using a single model only. However, there is still a clear lack of progression of these models from basic research to high-throughput clinical practice.

Integrated Microphysiological Systems: Transferable Organ Models and Recirculating Flow

Studying and understanding of tissue and disease mechanisms largely depend on the availability of suitable and representative biological model systems. These model systems should be carefully engineered and faithfully reproduce the biological system of interest to understand physiological effects, pharmacokinetics, and toxicity to better identify new drug compounds. By relying on microfluidics, microphysiological systems (MPSs) enable the precise control of culturing conditions and connections of advanced in vitro 3D organ models that better reproduce in vivo environments. This review focuses on transferable in vitro organ models and integrated MPSs that host these transferable biological units and enable interactions between different tissue types. Interchangeable and transferrable in vitro organ models allow for independent quality control of the biological model before system assembly and building MPS assays on demand. Due to the complexity and different maturation times of individual in vitro tissues, off-chip production and quality control entail improved stability and reproducibility of the systems and results, which is important for large-scale adoption of the technology. Lastly, the technical and biological challenges and open issues for realizing and implementing integrated MPSs with transferable in vitro organ models are discussed.

Investigation of the effect of hepatic metabolism on off-target cardiotoxicity in a multi-organ human-on-a-chip system

Regulation of cosmetic testing and poor predictivity of preclinical drug studies has spurred efforts to develop new methods for systemic toxicity. Current in vitro assays do not fully represent physiology, often lacking xenobiotic metabolism. Functional human multi-organ systems containing iPSC derived cardiomyocytes and primary hepatocytes were maintained under flow using a low-volume pumpless system in a serum-free medium. The functional readouts for contractile force and electrical conductivity enabled the non-invasive study of cardiac function. The presence of the hepatocytes in the system induced cardiotoxic effects from cyclophosphamide and reduced them for terfenadine due to drug metabolism, as expected from each compound's pharmacology. A computational fluid dynamics simulation enabled the prediction of terfenadine-fexofenadine pharmacokinetics, which was validated by HPLC-MS. This in vitro platform recapitulates primary aspects of the in vivo crosstalk between heart and liver and enables pharmacological studies, involving both organs in a single in vitro platform. The system enables non-invasive readouts of cardiotoxicity of drugs and their metabolites. Hepatotoxicity can also be evaluated by biomarker analysis and change in metabolic function. Integration of metabolic function in toxicology models can improve adverse effects prediction in preclinical studies and this system could also be used for chronic studies as well.

1-Aminobenzotriazole: A Mechanism-Based Cytochrome P450 Inhibitor and Probe of Cytochrome P450 Biology

1-Aminobenzotriazole (1-ABT) is a pan-specific, mechanism-based inactivator of the xenobiotic metabolizing forms of cytochrome P450 in animals, plants, insects, and microorganisms. It has been widely used to investigate the biological roles of cytochrome P450 enzymes, their participation in the metabolism of both endobiotics and xenobiotics, and their contributions to the metabolism-dependent toxicity of drugs and chemicals. This review is a comprehensive evaluation of the chemistry, discovery, and use of 1-aminobenzotriazole in these contexts from its introduction in 1981 to the present.

Organs-on-a-Chip: A Fast Track for Engineered Human Tissues in Drug Development

Organs-on-a-chip (OOCs) are miniature tissues and organs grown in vitro that enable modeling of human physiology and disease. The technology has emerged from converging advances in tissue engineering, semiconductor fabrication, and human cell sourcing. Encompassing innovations in human stem cell technology, OOCs offer a promising approach to emulate human patho/physiology in vitro, and address limitations of current cell and animal models. Here, we review the design considerations for single and multi-organ OOCs, discuss remaining challenges, and highlight the potential impact of OOCs as a fast-track opportunity for tissue engineering to advance drug development and precision medicine.

Multiorgan Microphysiological Systems for Drug Development: Strategies, Advances, and Challenges

Traditional cell culture and animal models utilized for preclinical drug screening have led to high attrition rates of drug candidates in clinical trials due to their low predictive power for human response. Alternative models using human cells to build in vitro biomimetics of the human body with physiologically relevant organ-organ interactions hold great potential to act as "human surrogates" and provide more accurate prediction of drug effects in humans. This review is a comprehensive investigation into the development of tissue-engineered human cell-based microscale multiorgan models, or multiorgan microphysiological systems for drug testing. The evolution from traditional models to macro- and microscale multiorgan systems is discussed in regards to the rationale for recent global efforts in multiorgan microphysiological systems. Current advances in integrating cell culture and on-chip analytical technologies, as well as proof-of-concept applications for these multiorgan microsystems are discussed. Major challenges for the field, such as reproducibility and physiological relevance, are discussed with comparisons of the strengths and weaknesses of various systems to solve these challenges. Conclusions focus on the current development stage of multiorgan microphysiological systems and new trends in the field.

Metabolism-dependent cytotoxicity of citrinin and ochratoxin A alone and in combination as assessed adopting integrated discrete multiple organ co-culture (IdMOC)

Citrinin (CTN) and ochratoxin A (OTA) can be present as co-contaminants in cereals, foods and feed commodities, and can affect human health. Metabolism-dependent toxicity of these two mycotoxins, separately as well as in combination, is not yet understood. To fill this gap we adopted integrated discrete multiple organ co-culture (IdMOC) technique, which obviates animal experiments from the perspectives of species difference as well as animal welfare concerns. IdMOC facilitates co-culture of a metabolically competent cell (HepG2) and a metabolically incompetent cell (3T3) that are physically separated but provides for extracellular product(s) from one cell to interact with the other. After ascertaining that HepG2 is metabolically competent and 3T3 is not, adopting luciferin-IPA metabolism assay, CTN and OTA were tested separately and in combination in the co-culture set-up, when both proved to be metabolism-dependent cytotoxic agents. Hepatocytes metabolize CTN into a diffusible product that is cytotoxic to 3T3 cells but the cytotoxicity of OTA appears to be limited to the hepatocytes, i.e., local acting. As a combination at a concentration of 20% of IC₅₀ of each, CTN forms a reactive metabolite that diffuses out of HepG2 to cause cytotoxicity to 3T3 cells synergistically with OTA parent molecule. The CYP isoenzymes involved in the metabolism OTA and CTN were identified adopting in silico methods which indicated that OTA and CTN can bind CYP proteins at specific sites.

Emerging In Vitro Liver Technologies for Drug Metabolism and Inter-Organ Interactions

In vitro liver models provide essential information for evaluating drug metabolism, metabolite formation, and hepatotoxicity. Interfacing liver models with other organ models could provide insights into the desirable as well as unintended systemic side effects of therapeutic agents and their metabolites. Such information is invaluable for drug screening processes particularly in the context of secondary organ toxicity. While interfacing of liver models with other organ models has been achieved, platforms that effectively provide human-relevant precise information are needed. In this concise review, we discuss the current state-of-the-art of liver-based multiorgan cell culture platforms primarily from a drug and metabolite perspective, and highlight the importance of media-to-cell ratio in interfacing liver models with other organ models. In addition, we briefly discuss issues related to development of optimal liver models that include recent advances in hepatic cell lines, stem cells, and challenges associated with primary hepatocyte-based liver models. Liver-based multiorgan models that achieve physiologically relevant coupling of different organ models can have a broad impact in evaluating drug efficacy and toxicity, as well as mechanistic investigation of human-relevant disease conditions.

Generalized Additive Mixed-Models for Pharmacology Using Integrated Discrete Multiple Organ Co-Culture

Integrated Discrete Multiple Organ Co-culture (IDMOC) is emerging as an in-vitro alternative to in-vivo animal models for pharmacology studies. IDMOC allows dose-response relationships to be investigated at the tissue and organoid levels, yet, these relationships often exhibit responses that are far more complex than the binary responses often measured in whole animals. To accommodate departure from binary endpoints, IDMOC requires an expansion of analytic techniques beyond simple linear probit and logistic models familiar in toxicology. IDMOC dose-responses may be measured at continuous scales, exhibit significant non-linearity such as local maxima or minima, and may include non-independent measures. Generalized additive mixed-modeling (GAMM) provides an alternative description of dose-response that relaxes assumptions of independence and linearity. We compared GAMMs to traditional linear models for describing dose-response in IDMOC pharmacology studies.

In vitro evaluation of hepatotoxic drugs in human hepatocytes from multiple donors: Identification of P450 activity as a potential risk factor for drug-induced liver injuries

A possible risk factor for drug-induced hepatotoxicity is drug metabolizing enzyme activity, which is known to vary among individuals due to genetic (genetic polymorphism) and environmental factors (environmental pollutants, foods, and medications that are inhibitors or inducers of drug metabolizing enzymes). We hypothesize that hepatic cytochrome P450-dependent monooxygenase (CYP) activity is one of the key risk factors for drug induced liver injuries (DILI) in the human population, especially for drugs that are metabolically activated to cytotoxic/reactive metabolites. Human hepatocytes from 19 donors were evaluated for the activities of 8 major P450 isoforms: CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4. Extensive individual variations were observed, consistent with what is known to be in the human population. As CYP3A4 is known to be one of the most important P450 isoforms for drug metabolism, studies were performed to evaluate the relationship between the in vitro cytotoxicity of hepatotoxic drugs and CYP3A4 activity. In a proof of concept study, hepatocytes from six donors (lots) representing the observed range of CYP3A4 activities were chosen for the evaluation of in vitro hepatotoxicity of four drugs known to be associated with acute liver failure: acetaminophen, cyclophosphamide, ketoconazole, and tamoxifen. The hepatocytes were cultured in collagen-coated plates and treated with the hepatotoxicants for approximately 24 h, followed by viability determination based on cellular adenosine triphosphate (ATP) contents. HH1023, the lot of hepatocytes with the highest CYP3A4 activity, was found to be the most sensitive to the cytotoxicity of all 4 hepatotoxic drugs, thereby suggesting that high CYP3A4 activity may be a risk factor. To further validate the relationship, a second study was performed with hepatocytes from 16 donors. In this study, the hepatocytes were quantified for CYP3A4 activity at the time of treatment. Results of the second study show confirm the correlation between with high CYP3A4 activity and sensitivity to hepatotoxic drugs. Our results with primary cultured hepatocytes from multiple donors support the hypothesis that elevated P450 activity may be a risk factor for drug-induced liver injuries.

Metabolism of kurarinone by human liver microsomes and its effect on cytotoxicity

CONTEXT

Kurarinone, the most abundant prenylated flavonoid in Sophora flavescens Aiton (Leguminosae), is a promising antitumor therapeutic. However, it shows significant hepatotoxicity. Furthermore, how kurarinone is metabolized in humans remains unclear.

OBJECTIVE

The objective of this study is to investigate kurarinone metabolism in human liver microsomes (HLMs) and the role of metabolism in kurarinone-induced cytotoxicity.

MATERIALS AND METHODS

The UDP-glucuronosyltransferase isoforms (UGTs) involved in kurarinone glucuronidation were identified using chemical inhibitors (100-1000 µM phenylbutazone; 10-100 µM β-estradiol; 10-100 µM 1-naphthol; 10-500 µM propofol; and 100-1000 µM fluconazole) and recombinant human UGTs. Kurarinone (2-500 µM) was incubated with HLMs and UGTs (0.5 mg/mL) for 15 min to determine enzyme kinetic parameters. The IC50 value of kurarinone (10-200 µM) was evaluated in a HLMs/3T3 cell co-culture system.

RESULTS

Kurarinone is extensively converted to two glucuronides (M3 and M4) in HLMs. M3 formation was catalyzed by multiple UGT1As, with UGT1A3 showing the highest intrinsic clearance (120.60 mL/min/mg). M4 formation was catalyzed by UGT1A1, UGT2B4, and UGT2B7. UGT1A1 showed the highest intrinsic clearance (60.61 mL/min/mg). The kinetic profiles of the five main UGTs and HLMs fit substrate inhibition kinetics, with Km values ranging from 5.20 to 46.52 µM, Vmax values ranging from 0.20 to 3.06 µmol/min/mg, and Ksi values ranging from 25.58 to 230.30 µM. The kurarinone IC50 value was 93 μM in the control group, 102 μM in HLMs with NADPH, and 160 μM in HLMs with UDPGA.

DISCUSSION AND CONCLUSION

Kurarinone glucuronidation is a detoxification pathway. This information may help to elucidate the risk factors regulating kurarinone toxicity.

Evaluation of Adverse Drug Properties with Cryopreserved Human Hepatocytes and the Integrated Discrete Multiple Organ Co-culture (IdMOC(TM)) System

Human hepatocytes, with complete hepatic metabolizing enzymes, transporters and cofactors, represent the gold standard for in vitro evaluation of drug metabolism, drug-drug interactions, and hepatotoxicity. Successful cryopreservation of human hepatocytes enables this experimental system to be used routinely. The use of human hepatocytes to evaluate two major adverse drug properties: drug-drug interactions and hepatotoxicity, are summarized in this review. The application of human hepatocytes in metabolism-based drug-drug interaction includes metabolite profiling, pathway identification, P450 inhibition, P450 induction, and uptake and efflux transporter inhibition. The application of human hepatocytes in toxicity evaluation includes in vitro hepatotoxicity and metabolism-based drug toxicity determination. A novel system, the Integrated Discrete Multiple Organ Co-culture (IdMOC) which allows the evaluation of nonhepatic toxicity in the presence of hepatic metabolism, is described.

Scientific concepts and applications of integrated discrete multiple organ co-culture technology

Over several decades, animals have been used as models to investigate the human-specific drug toxicity, but the outcomes are not always reliably extrapolated to the humans in vivo. Appropriate in vitro human-based experimental system that includes in vivo parameters is required for the evaluation of multiple organ interaction, multiple organ/organ-specific toxicity, and metabolism of xenobiotic compounds to avoid the use of animals for toxicity testing. One such versatile in vitro technology in which human primary cells could be used is integrated discrete multiple organ co-culture (IdMOC). IdMOC system adopts wells-within-well concept that facilitates co-culture of cells from different organs in a discrete manner, separately in the respective media in the smaller inner wells which are then interconnected by an overlay of a universal medium in the large containing well. This novel in vitro approach mimics the in vivo situation to a great extent, and employs cells from multiple organs that are physically separated but interconnected by a medium that mimics the systemic circulation and provides for multiple organ interaction. Applications of IdMOC include assessment of multiple organ toxicity, drug distribution, organ-specific toxicity, screening of anticancer drugs, metabolic cytotoxicity, etc.

High content analysis of an in vitro model for metabolic toxicity: results with the model toxicants 4-aminophenol and cyclophosphamide

In vitro models that accurately and rapidly assess hepatotoxicity and the effects of hepatic metabolism on nonliver cell types are needed by the U.S. Department of Defense and the pharmaceutical industry to screen compound libraries. Here, we report the first use of high content analysis on the Integrated Discrete Multiple Organ Co-Culture (IdMOC) system, a high-throughput method for such studies. We cultured 3T3-L1 cells in the presence and absence of primary human hepatocytes, and exposed the cultures to 4-aminophenol and cyclophosphamide, model toxicants that are respectively detoxified and activated by the liver. Following staining with calcein-AM, ethidium homodimer-1, and Hoechst 33342, high content analysis of the cultures revealed four cytotoxic endpoints: fluorescence intensities of calcein-AM and ethidium homodimer-1, nuclear area, and cell density. Using these endpoints, we observed that the cytotoxicity of 4-aminophenol in 3T3-L1 cells in co-culture was less than that observed for 3T3-L1 monocultures, consistent with the known detoxification of 4-aminophenol by hepatocytes. Conversely, cyclophosphamide cytotoxicity for 3T3-L1 cells was enhanced by co-culturing with hepatocytes, consistent with the known metabolic activation of this toxicant. The use of IdMOC plates combined with high content analysis is therefore a multi-endpoint, high-throughput capability for measuring the effects of metabolism on toxicity.

Biomarkers and human hepatocytes

The accuracy of preclinical safety evaluation to predict human toxicity is hindered by species difference in drug metabolism and toxic mechanism between human and nonhuman animals. In vitro human-based experimental systems allowing the assessment of human-specific drug properties represent a logical and practical approach to provide human-specific information. An advantage of in vitro approaches is that they require only limited amounts of time and resources, and, most importantly, do not invoke harm to human patients. Human hepatocytes, with complete hepatic metabolizing enzymes, transporters and cofactors, represent a practical and useful experimental system to assess drug metabolism. The use of human hepatocytes to evaluate two major adverse drug properties, drug–drug interactions and hepatotoxicity, are reviewed. The application of human hepatocytes in metabolism-based drug–drug interactions includes metabolite profiling, pathway identification, CYP450 inhibition, CYP450 induction, and uptake and efflux transporter inhibition. The application of human hepatocytes in toxicity evaluation includes in vitro hepatotoxicity and metabolism-based drug toxicity determination. Correlation of drug toxicity with proteomics and genomics data may allow the discovery of clinical biomarkers for early detection of liver toxicity.

Predictivity of dog co-culture model, primary human hepatocytes and HepG2 cells for the detection of hepatotoxic drugs in humans

Drug induced liver injury (DILI) is a major cause of attrition during early and late stage drug development. Consequently, there is a need to develop better in vitro primary hepatocyte models from different species for predicting hepatotoxicity in both animals and humans early in drug development. Dog is often chosen as the non-rodent species for toxicology studies. Unfortunately, dog in vitro models allowing long term cultures are not available. The objective of the present manuscript is to describe the development of a co-culture dog model for predicting hepatotoxic drugs in humans and to compare the predictivity of the canine model along with primary human hepatocytes and HepG2 cells. After rigorous optimization, the dog co-culture model displayed metabolic capacities that were maintained up to 2 weeks which indicates that such model could be also used for long term metabolism studies. Most of the human hepatotoxic drugs were detected with a sensitivity of approximately 80% (n=40) for the three cellular models. Nevertheless, the specificity was low approximately 40% for the HepG2 cells and hepatocytes compared to 72.7% for the canine model (n=11). Furthermore, the dog co-culture model showed a higher superiority for the classification of 5 pairs of close structural analogs with different DILI concerns in comparison to both human cellular models. Finally, the reproducibility of the canine system was also satisfactory with a coefficient of correlation of 75.2% (n=14). Overall, the present manuscript indicates that the dog co-culture model may represent a relevant tool to perform chronic hepatotoxicity and metabolism studies.

Microfabricated mammalian organ systems and their integration into models of whole animals and humans

While in vitro cell based systems have been an invaluable tool in biology, they often suffer from a lack of physiological relevance. The discrepancy between the in vitro and in vivo systems has been a bottleneck in drug development process and biological sciences. The recent progress in microtechnology has enabled manipulation of cellular environment at a physiologically relevant length scale, which has led to the development of novel in vitro organ systems, often termed 'organ-on-a-chip' systems. By mimicking the cellular environment of in vivo tissues, various organ-on-a-chip systems have been reported to reproduce target organ functions better than conventional in vitro model systems. Ultimately, these organ-on-a-chip systems will converge into multi-organ 'body-on-a-chip' systems composed of functional tissues that reproduce the dynamics of the whole-body response. Such microscale in vitro systems will open up new possibilities in medical science and in the pharmaceutical industry.