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Adverse outcome pathways (AOPs) describe causal relationships between molecular perturbation and adverse cellular effects and are being increasingly adopted for linking in vitromechanistic toxicology to in vivodata from regulatory toxicity studies. In this work, a case study was performed by developing a bioassay toolbox to assess key events in the recently proposed AOP for chemically induced liver steatosis. The toolbox is comprised of in vitroassays to measure nuclear receptor activation, gene and protein expression, lipid accumulation, mitochondrial respiration, and formation of fatty liver cells. Assay evaluation was performed in human HepaRG hepatocarcinoma cells exposed to the model compound cyproconazole, a fungicide inducing steatosis in rodents. Cyproconazole dose-dependently activated RARα and PXR, two molecular initiating events in the steatosis AOP. Moreover, cyproconazole provoked a disruption of mitochondrial functions and induced triglyceride accumulation and the formation of fatty liver cells as described in the AOP. Gene and protein expression analysis, however, showed expression changes different from those proposed in the AOP, thus suggesting that the current version of the AOP might not fully reflect the complex mechanisms linking nuclear receptor activation and liver steatosis. Our study shows that cyproconazole induces steatosis in human liver cells in vitroand demonstrates the utility of systems-based approaches in the mechanistic assessment of molecular and cellular key events in an AOP. AOP-driven in vitrotesting as demonstrated can further improve existing AOPs, provide insight regarding molecular mechanisms of toxicity, and inform predictive risk assessment.

In hepatocytes, the amount of the Spot 14 (S14) protein is closely related to the full expression of enzymes involved in the glycolytic and lipogenic pathways. In the present study we address the role played by this protein in the control of transcription of the L-type pyruvate kinase (L-PK) gene in primary hepatocytes. We show that human S14, which by itself does not bind to the L-PK promoter, physically interacts with the human chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1) and induces the switch of this factor from a repressor to an activator. However, the enhancing activity of S14 and COUP-TF1 depends on the presence of a proximal GC-rich box (the L0 element) that specifically binds nuclear proteins from the livers of rats fed a glucose-rich diet. Moreover, the L0 element, which strongly binds dephosphorylated specificity protein 1 (Sp1), loses all affinity when this factor is phosphorylated by cAMP-dependent protein kinase. Mutations that affect binding of Sp1 and nuclear proteins to the L0 box also decrease basal transcription and impair glucose responsiveness of the promoter. These results therefore shed light on the mechanism by which the S14 protein, whose concentration rapidly rises after glucose intake, contributes to the full activity of the L-PK promoter.

Successful liver transplantation depends on adequate preservation of cellular function. We therefore tested the effects of two currently used liver preservation fluids, Euro-Collins (EC) solution and University of Wisconsin (UW) solution, on the viability and some functional activities of hepatocytes isolated from human livers. Cells in primary culture were maintained under hypoxic (95% N2/5% CO2) and hypothermic (4°C) conditions for 24 h, either in EC or UW solution. This treatment did not result in significant hepatocyte damage, as judged by phase contrast microscopy, intracellular LDH release, and the MTT mitochondrial test. However, neutral red uptake indicated that lysosomal functions were slightly affected (35% decrease) when compared to control conditions. At the end of the hypoxia/hypothermia period, hepatocyte monolayers were incubated at 37°C under normoxic conditions for 24 h, in order to simulate the reperfusion of a transplanted liver. Three drugs-midazolam, diazepam, zidovudine-were used as diagnostic substrates to check the metabolic abilities of human hepatocytes replaced in normal conditions. Both phase I (hydroxylation, demethylation) and phase II (glucuronidation) metabolic reactions were affected by the hypoxia/hypothermia shock. Indeed, a 30%–50% decrease in these activities was observed as compared to values obtained in control hepatocytes. No difference could, however, be found at the cellular level regarding the solution used for cold storage. These results suggest that the superiority of UW over EC solution, already reported in clinical practice after transplantation of preserved human livers, was not due to a better preservation of the hepatocytes.

Vinca alkaloids, including vinblastine, vincristine, vindesine and vinorelbine, are widely used antineoplastic drugs, either as single agents or in combination with other drugs. The mechanism of action of these cell cycle-dependent agents is the inhibition of tubulin polymerisation into microtubules. Numerous studies have been conducted in animals and humans, using various in vivoand in vitromodels, to investigate the pharmacological behaviour of this class of antitumour drug. Studies in cellular pharmacology demonstrate that vinca alkaloids are transported by multiple mechanisms, including passive diffusion and energy- and temperature-dependent active transport systems. Moreover, active efflux of drug is involved in the P-glycoprotein-mediated multidrug resistance to vinca alkaloids. This phenomenon may be modulated, in vivoand in vitro, by calcium antagonists and calmodulin inhibitors. The clinical pharmacokinetics of vinca alkaloids after intravenous bolus injection, continuous infusion and oral administration are characterised by a large apparent total volume of distribution, high total plasma clearance and long terminal elimination half-life. Biliary excretion is the main elimination pathway, with low urinary excretion. Pharmacokinetic parameters of vinca alkaloids are time- and dose-dependent, and large inter- and intra-individual variabilities have been observed. Human hepatic P-450IIIA cytochromes are involved in the metabolism of vindesine, vinblastine and probably other vinca alkaloids. Therefore, the possibility of drug-drug interactions must be considered when coadministering drugs in combination cancer chemotherapy. Development of newer semisynthetic analogues of vinca alkaloids and conjugation of vinca alkaloids with monoclonal antibodies may result in derivatives with increased antitumour activity and less clinical toxicity.

The kinetics of distribution and elimination in rats of the antitumor drug navelbine and of two of its analogues, Na-formyl navelbine and deacetyl navelbine amide, have been studied by radioimmunoassay and compared with the kinetics obtained with vinblastine and vincristine. Fitting to two-exponential curves was used to derive pharmacokinetic parameters. Clearance was found to parallel toxicity for all drugs: it increases from 0.19 l h-1 kg-1 for vincristine to 0.41 for Na-formyl navelbine, 1.4 for vinblastine, 2.3 for navelbine, and 2.6 for deacetyl navelbine amide. Terminal half-lives were longer for the Naformyl-substituted alkaloids (around 13 h) than for the others (8–10 h). We have also studied navelbine kinetics in cancer patients entered in recent navelbine clinical trials and found that navelbine pharmacokinetics are characterized by fast and extensive distribution, high clearance (0.92±0.27 l h-1 kg-1), and a relatively long terminal half-life (31.2±4.4 h). Relationships between chemical structure, pharmacokinetic properties, and toxicity or therapeutic efficiency within the Vinca alkaloid series are discussed, together with the relevance of animal models such as the rat in the screening of new antitumor drugs.

A human liver plasma membrane model for the evaluation of the specific binding and transport processes of drugs presenting high hepatic clearance such as vinca alkaloids was developed. Uptake of the two structural antitumor analogs, navelbine (NVB) and vincristine (VCR), which exhibit wide variabilities in their respective pharmacokinetic parameters and antitumor spectra, was investigated. The high yield, the enzymatic profile and the retention of physiologic transport capacities, as demonstrated by taurocholate uptake, revealed that this membrane preparation was well suited for studies of hepatic drug transport systems. For both drugs two distinct processes were observed: mainly membrane binding and transport. NVB was found to bind to the membrane vesicles more intensively than VCR, but the transport processes were almost identical. However only NVB uptake seems to involve Na+-dependent processes. These significant differences may be related to the respective lipophilicity of the drugs. The more lipophilic molecule (NVB) presents the highest uptake, which is presumably at the origin of its greatest distribution volume in vivo.