Correspondence

Fatal liver complications with flutamide

The liver performs a variety of essential functions; hence drug-induced liver injury (DILI) is a serious concern that can ultimately lead to the withdrawal of a drug from the market or discontinuation of drug development. However, the mechanisms of drug-induced liver injury are not always clear. We hypothesized that drugs may inhibit the liver recovery process, especially bile canalicular (BC) network reformation, leading to persistent liver injury and deterioration, and tested this hypothesis in the present work. The BC structure disappeared in mice following treatment with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or thioacetamide (TAA) for 4 weeks, then reappeared after 4 weeks of receiving a normal diet. By contrast, reconstruction of the BC structure was suppressed in mice fed a diet containing 0.3% benzbromarone (BBR; which can induce fatal liver injury in clinical settings) after liver injury. Plasma ALT levels were increased significantly in mice treated with BBR after DDC or TAA treatment, compared with BBR alone. To confirm whether BBR has a direct inhibitory effect on hepatocytes, we also examined BC reformation in primary cultured mouse hepatocytes with a sandwich configuration. Under these culture conditions, the BC network rapidly reformed from days 2 and 3 after seeding. During the reformation period, BBR inhibited BC reformation significantly. These results suggest that BBR inhibits BC reconstruction and delays recovery from pre-existing liver injury.

Cytochrome P450 1A2 (CYP1A2) is one of the most abundant and important drug metabolizing enzymes in human liver. However, little is known about the post-transcriptional regulation of CYP1A2, especially the mechanisms involving microRNAs (miRNAs). This study applied a systematic approach to investigate the post-transcriptional regulation of CYP1A2 by miRNAs. Candidate miRNAs targeting the 3′-untranslated region (3′-UTR) of CYP1A2 were screened in silico, resulting in the selection of sixty-two potential miRNAs for further analysis. The levels of two miRNAs, hsa-miR-132-5p and hsa-miR-221-5p, were inversely correlated with the expression of CYP1A2 mRNA transcripts in normal human liver tissue samples represented in The Cancer Genome Atlas (TCGA) dataset. The interactions between these miRNAs and cognate CYP1A2 mRNA sequences were evaluated using luciferase reporter gene studies and electrophoretic mobility shift assays, by which a direct interaction was confirmed involving hsa-miR-132-5p and a cognate binding site present in the CYP1A2 3′-UTR. Experiments by which hsa-miR-132-5p or random miRNA controls were introduced into HepG2, Huh-7 and HepaRG hepatic cell lines showed that only hsa-miR-132-5p suppressed the endogenous and lansoprazole-induced expression of CYP1A2, at biological activity, protein production, and mRNA transcript levels. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and lactate dehydrogenase (LDH) assays showed that hsa-miR-132-5p attenuates CYP1A2-mediated, lansoprazole-enhanced, flutamide-induced hepatic cell toxicity. Results from multilayer experiments demonstrate that hsa-miR-132-5p suppresses the expression of CYP1A2 and that this suppression is able to decrease the extent of an adverse drug-drug interaction involving lansoprazole and flutamide.

Flutamide (FLU), an oral, nonsteroidal antiandrogen drug used in the treatment of prostate cancer, is associated with idiosyncratic hepatotoxicity that sometimes causes severe liver damage, including cholestasis, jaundice, and liver necrosis. To understand the mechanism of toxicity, a combination of aryl hydrocarbon receptor (Ahr)-deficient (Ahr^−/−) mice, primary hepatocytes, luciferase reporter gene assays, in silico ligand docking and ultra-performance chromatography-quadrupole time-of-flight mass spectrometry-based metabolomics was used. A significant increase of liver weights, and liver and serum bile acid levels was observed after FLU treatment, indicating hepatomegaly and disrupted bile acid homeostasis. Expression of the AhR gene battery was markedly increased in livers of wild-type mice Ahr^+/+ treated with FLU, while no change was noted in Ahr^−/− mice. Messenger RNAs encoded by AhR target genes were induced in primary mouse hepatocytes cultured with FLU, which confirmed the in vivo results. Ligand-docking analysis further predicted that FLU is an AhR agonist ligand which was confirmed by luciferase reporter gene assays. Multivariate data analysis showed that bile acids were responsible for the separation of vehicle- and FLU-treated Ahr^+/+ mice, while there was no separation in Ahr^−/− mice. Expression of mRNA encoding the bile acid transporter ABCC4 was increased and farnesoid X receptor signaling was inhibited in the livers of Ahr^+/+ mice, but not in Ahr^−/− mice treated with FLU, in agreement with the observed downstream metabolic alterations. These findings provide new insights into the mechanism of liver injury caused by FLU treatment involving activation of AhR and the alterations of bile acid homeostasis, which could guide clinical application.

The early identification of hepatotoxicity is a fundamental goal of preclinical safety studies in drug discovery and early development. Sensitive biomarkers warrant the determination of potential underlying mechanisms that help characterizing a disruption of physiological conditions prior to cell death. This study shows the potential of different lipid peroxidation products, namely isoprostanes and hydroxynonenal (HNE) derivatives, to serve as early safety biomarkers of hepatotoxicity caused by oxidative stress as underlying mechanism. The hepatotoxic drug flutamide was used as model compound in primary hepatocytes. Incubation conditions were optimized by the addition of hydrogen peroxide generating substrates enhancing the cellular response upon oxidative stress. A time and dose dependent response of different isoprostanes and prostaglandins (15R-prostaglandin D₂, prostaglandin E₂, 13,14-dihydro-15-keto prostaglandin E₂ and 5‑iso prostaglandin F_2α-VI) became manifest after 6 and 24 h of treatment in 3.8- to 17.4-fold increased concentrations where no overt hepatocellular damage was observed. For HNE-mercapturic acid and its metabolite dihydroxynonene-mercapturic acid a similar response was evident with a 20- and 10-fold increase from control after 24 h of treatment, respectively. These data indicate that lipid peroxidation products as markers of reactive oxygen species are more sensitive than conventional cytotoxicity markers for an early detection of drug-induced liver injury.

Idiosyncratic (host-dependent) and therefore unpredictable drug-induced liver injury (DILI) is rare but nevertheless has become a major clinical problem. This is mainly due to the large number of drugs causing DILI and the large consumer populations worldwide, but also is a consequence of an increased awareness of the inherent hepatotoxic potential of many drugs. Idiosyncratic DILI is also the single major cause for withdrawal of successfully launched drugs or for discontinuation of drugs in development. This chapter summarizes the currently known mechanisms of DILI and the determinants of susceptibility and risk modulators in patients. Certain drugs (or their metabolites) cause immunoallergic reactions whose mechanisms are poorly understood. In many other cases of nonimmune-mediated DILI, reactive intermediates causing electrophilic or oxidative stress are involved. Importantly, direct mitochondrial injury through a number of distinct mechanisms is an increasingly recognized hazard. However, it is much less well understood why the majority of patients do not develop liver injury and what underlying mechanisms put a small subset of patients at an increased risk. Genetic polymorphisms of drug-metabolizing enzymes, HLA (human leukocyte antigen) haplotypes, or detoxifying enzymes are involved but cannot fully explain the low incidence. More recent paradigms are based on a multifactorial pathogenesis and include underlying inflammatory conditions or genetic or acquired abnormalities in mitochondrial function that may increase both the penetrance and expressivity of the intrinsic toxicity of a drug.