In Vitro Evaluation of Potential Hepatotoxicity Induced ...

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Abstract:The liver is the most important target for toxicity caused by drugs. This vulnerability is a ... mechanistic changes involved in the drug-induced toxic injury.
Current Pharmaceutical Design, 2010, 16, 000-000

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In Vitro Evaluation of Potential Hepatotoxicity Induced by Drugs M.J. Gómez-Lechón1,2*, A. Lahoz1, L. Gombau3, J.V. Castell1,2,4 and M.T. Donato1,2,4 1

Unidad de Hepatología Experimental. Centro de Investigación, Hospital La Fe, Avda Campanar 21, 46009-Valencia, Spain, CIBERehd: Centro de Investigación Biomédica en Red en el Área Temática de Enfermedades Hepáticas y Digestivas, Fondo de Investigación Sanitaria, Barcelona, Spain, 3Unidad Mixta Hospital La Fe- Advancell. Centro de Investigación Hospital La Fe. Avda. Campanar 21, 46009-Valencia. Spain, 4Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Valencia, Spain 2

Abstract:The liver is the most important target for toxicity caused by drugs. This vulnerability is a consequence of the functional features of the liver and their role in the metabolic elimination of most drugs. Therefore, evaluation of potential hepatotoxicity represents a critical step in the development of new drugs. The liver is very active in metabolising foreign compounds and, although biotransformation reactions generally parallel detoxification processes, the formation of reactive metabolites is relatively frequent. Thus, drug-induced hepatotoxicity can be due to the administered compound itself or to metabolites formed by hepatic metabolism. The most important systems to study hepatotoxicity and metabolic activity in vitro are liver slices, isolated liver cells in suspensions or in primary cultures including co-culture methods and special 3D techniques, various subcellular fractions and hepatic cell lines. These models can be used for cytotoxicity and genotoxicity screening, and also to identify the mechanisms involved in drug-induced hepatotoxicity. Assessment of current cytotoxicity and hepatic-specific biochemical effects are limited by the inability to measure a wide spectrum of potential mechanistic changes involved in the drug-induced toxic injury. A convenient selection of end-points allows a multiparametric evaluation of drug toxicity. In this regard, omic (cytomic, metabonomic, proteomic and toxicogemic) approaches help defining patterns of hepatotoxicity for early identification of potential adverse effects of the drug to the liver. The development of robust in vitro-based multiparametric screening assays covering a wider spectrum of key effects will heighten the predictive capacity for human hepatotoxicity, and accelerate the drug development process.

Keywords: Hepatocytes, hepatotoxicity, hepatotoxins, metabonomics, toxicogenomics, proteomics, cytomics, cytochrome P450. INTRODUCTION Drug-induced liver injury is the most frequent cause of hepatic dysfunction, drug failures during clinical trials and post-market withdrawal of an approved drug [1]. The central role of the liver in the intermediary and energetic metabolism, and in drug biotransformation processes, accounts for the organ`s vulnerability making it a major target of the toxic effect of drugs. The lists of drugs with potential hepatotoxic action include those not marketed or withdrawn from the market due to hepatototoxicity, approved drugs that have acquired black box warnings because of hepatotoxicity, and others with clinical reports of potential associated liver injury (for updated lists see [2-5]). A major goal for the pharmaceutical industry is to market safer drugs with fewer side effects, predictable pharmacokinetic properties and quantifiable drug-drug interactions. Therefore, evaluation of potential hepatotoxicity represents a critical step in the development of new drugs. Compound prioritization and optimization constitute a critical task in drug development, and the establishment of in vitro screening systems reflecting human in vivo toxicity is demanded for earlier safety assessment. Human cellular models constitute valuable tools to understand the molecular and cellular processes of drug- induced liver injury and underlie susceptibility. Current cytotoxicity assessments have been limited by their inability to measure multiple mechanistic parameters that capture a wide spectrum of potential cytopathological changes. By examining the effects on a hepatocyte-specific metabolism, it is possible to discover whether relevant hepatic functions are altered by the presence of a xenobiotic [6]. However by to addressing this issue, the development of robust in vitro-based multiparametric screening assays covering a wider spectrum of key effects will heighten the predictive capacity for human hepatotoxicity, and accelerate the *Address correspondence to this author at the Unidad de Hepatología Experimental. Centro de Investigación, Hospital La Fe, Avda Campanar 21, 46009-Valencia, Spain; Tel: ???????????; Fax: ???????????; E-mail: [email protected] 1381-6128/10 $55.00+.00

drug development process. The technological advances in the fields of genomics, proteomics, metabonomics and cytomics play a very important role in uncovering novel biochemical pathways and biomarkers of hepatotoxicity. Although biochemical mechanisms of drug-induced toxicity are complex, a risk assessment profile/ decision-making guide can be obtained for each drug candidate by combining these screening methods into a panel of assays. In vitro assays are already being applied to a large set of marketed drugs that produce toxicity by numerous and different mechanisms to assess correlations with human toxicity [2, 3, 7-10]. These strategies will enable the toxicological profiles of drugs and the concordance between in vitro and in vivo results to be determined. It is desirable for the advance of the omics to lead to personalized medication in which the beneficial effects of a drug are maximized and the toxicity risk is minimized. HEPATOTOXINS AND CLINICAL PATTERNS Substances capable of producing liver damage and, more specifically, hepatocyte damage, are known as hepatotoxins. Intrinsic hepatotoxins are substances that exert their effects in all individuals in a dose-dependent, and hence, predictable manner. The injury can be due to either the drug itself or a metabolite. Thus, these toxins can interfere directly with the cell metabolism or become toxic once they have been bioactivated [1, 11, 12]. Drugs that fall into this category cause reproducible injuries in animals, and such injuries are dose-related. Acetaminophen is a classic example of a known intrinsic or predictable hepatotoxin at supertherapeutic doses [13]. Another classic example is carbon tetrachloride [14]. Many cases of drug-induced hepatotoxicity are related to idiosyncratic reactions. Idiosyncratic hepatotoxicity has a geno- or phenotypic basis that results in the over/under expression of drug metabolizing enzymes, a different drug metabolism pattern, and eventually in the abnormal production of a toxic metabolite (metabolic idiosyncrasy), which is dose-dependent in susceptible individuals [15-17]. Idiosyncratic hepatotoxicity can also be elicited by an immune-mediated hepatocyte injury (allergic hepatitis) [18, © 2010 Bentham Science Publishers Ltd.

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19]. Immune-mediated hepatitis appears in individuals who have had previous asymptomatic contacts with the drug, regardless of the dose administered, thus triggering a hypersensitivity reaction in the liver [18]. Idiosyncrasy is a very rare event (