Drug-induced liver injury (DILI) is a severe adverse effect. The majority of DILI cases are idiosyncratic and several mechanisms have been postulated to explain why some subjects develop DILI with drugs that are safe for the majority of individuals. Major mechanisms proposed for DILI are based on the production of reactive metabolites, immune-mediated hepatotoxicity, a "danger signal" hypothesis and/or alterations in mitochondrial function. These mechanisms are compatible with the hypothesis for genetic variability in drug metabolism or bioactivation and are a major determinant for DILI. In this review we summarize present knowledge on underlying mechanisms, and clinical expression as well as genetic and non-genetic factors that modulate the risk of developing DILI. With regard to DILI pharmacogenomics, we summarize current evidence on the role of polymorphisms in genes coding for the drug-metabolizing enzymes CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, CYP3A5, NAT2, GSTM1, GSTT1, UGT1A1, UGT1A3, UGT1A9 and UGT2B7. Conclusive evidence for association with DILI risk has been obtained for non-mutated CYP2E1, slow NAT2 and slow GSTM1 genotypes. For the rest of the genes additional pharmacogenomics and toxicogenomics studies are required. We identify potential sources of heterogeneity in studies carried out so far as well as new genetic targets which require further investigation.

The diagnosis of drug-induced liver injury (DILI) is challenging and based on complex diagnostic criteria. DILI falls into two main categories i) intrinsic "dose-dependent" Type A reactions ii) "idiosyncratic" or Type B reactions (which are usually not predictable). Idiosyncratic reactions can be immunoallergic (hypersensitivity), or metabolic, although overlap between categories can occur. The aim of this review is to summarise the general view of underlying mechanisms in DILI and to highlight individual risk factors for developing hepatotoxicity. Polymorphisms of bioactivation/toxification pathways through CYP450 enzymes (Phase I), detoxification reactions (Phase II) and excretion/transport (Phase III) are explored together with immunological factors that might determine DILI. The importance of establishing a multidisciplinary and multi-centric network to promote the understanding and research in hepatotoxicity is underlined. Challenges such as genetic analyses for association studies and whole genome studies, pharmacogenetic testing and future approaches to study DILI are considered. Knowledge regarding these operational mechanisms could provide further insight for the prospective identification of susceptible patients at risk of developing drug-induced hepatotoxicity.

Currently, pharmaceutical preparations are serious contributors to liver disease, with hepatotoxicity ranking as the most frequent cause for acute liver failure and post-marketing regulatory decisions. The diagnostic approach of drug-induced liver injury (DILI) is still rudimentary and inaccurate because of the lack of reliable markers for use in general clinical practice. To incriminate any given drug in an episode of liver dysfunction is a step-by-step process that requires a high degree of suspicion, compatible chronology, awareness of the drug's hepatotoxic potential, the exclusion of alternative causes of liver damage, and the ability to detect the presence of subtle data that favour a toxic aetiology. Clinical and laboratory data may also be assessed with algorithms or clinical scales, which may add consistency to the clinical judgment by translating the suspicion into a quantitative score. The CIOMS/RUCAM instrument is considered at present the best method for assessing causality in DILI, although it could be improved through the use of large database of bona fide DILI cases for validation criteria.

The possible neuroprotective role of a novel and highly selective cyclooxygenase-2 inhibitor GW637185X was studied in a model of acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced injury of nigrostriatal dopaminergic (DA) neurons in the mouse. Stereological and microdensitometrical analysis of nigral tyrosine hydroxylase-immunoreactive cell bodies and striatal tyrosine hydroxylase-immunoreactive terminals, respectively, showed that GW637185X exerted a full protection against MPTP-induced degeneration of the nigro-striatal pathway. In contrast to earlier studies, these findings demonstrate that acute inhibition of cyclooxygenase-2 can result in a full neuroprotective effect not only on nigral DA cell bodies, but also on striatal DA terminals in the mouse MPTP model.