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Franziska Boess

Publications and source records attributed to Franziska Boess.

9 recordsLinked to original sources
PubMed2006

Gene expression analysis of the hepatotoxicant methapyrilene in primary rat hepatocytes: an interlaboratory study.

Genomics technologies are used in several disciplines, including toxicology. However, these technologies are relatively new, and their applications require further investigations. When investigators apply these technologies to in vitro experiments, two major issues need to be clarified: a) can in vitro toxicity studies, in combination with genomics analyses, be used to predict the toxicity of a compound; and b) are the generated toxicogenomics data reproducible between laboratories? These questions were addressed by an interlaboratory study with laboratories of four pharmaceutical companies. We evaluated gene expression patterns from cultured rat primary hepatocytes after a 24-hr incubation with methapyrilene (MP). Extensive data analysis showed that comparison of genomics data from different sources is complex because both experimental and statistical variability are important confounding factors. However, appropriate statistical tools allowed us to use gene expression profiles to distinguish high-dose-treated cells from vehicle-treated cells. Moreover, we correctly identified MP in an independently generated in vitro database, underlining that in vitro toxicogenomics could be a predictive tool for toxicity. From a mechanistic point of view, despite the observed site-to-site variability, there was good concordance regarding the affected biologic processes. Several subsets of regulated genes were obtained by analyzing the data sets with one method or using different statistical analysis methods. The identified genes are involved in cellular processes that are associated to the exposure of primary hepatocytes to MP. Whether they are specific for MP and are cause or consequence of the toxicity requires further investigations.

Animals↗
PubMed2005

Assessment of hepatotoxic liabilities by transcript profiling.

Male Wistar rats were treated with various model compounds or the appropriate vehicle controls in order to create a reference database for toxicogenomics assessment of novel compounds. Hepatotoxic compounds in the database were either known hepatotoxicants or showed hepatotoxicity during preclinical testing. Histopathology and clinical chemistry data were used to anchor the transcript profiles to an established endpoint (steatosis, cholestasis, direct acting, peroxisomal proliferation or nontoxic/control). These reference data were analyzed using a supervised learning method (support vector machines, SVM) to generate classification rules. This predictive model was subsequently used to assess compounds with regard to a potential hepatotoxic liability. A steatotic and a non-hepatotoxic 5HT(6) receptor antagonist compound from the same series were successfully discriminated by this toxicogenomics model. Additionally, an example is shown where a hepatotoxic liability was correctly recognized in the absence of pathological findings. In vitro experiments and a dog study confirmed the correctness of the toxicogenomics alert. Another interesting observation was that transcript profiles indicate toxicologically relevant changes at an earlier timepoint than routinely used methods. Together, these results support the useful application of toxicogenomics in raising alerts for adverse effects and generating mechanistic hypotheses that can be followed up by confirmatory experiments.

Animals↗
PubMed2004

In vitro investigation on the impact of Solutol HS 15 on the uptake of colchicine into rat hepatocytes.

In the current investigation, the impact of the surface-active formulation ingredient Solutol HS 15 on the uptake of colchicine into freshly isolated rat hepatocytes was investigated using a centrifugal filtration technique through a silicone oil layer. Colchicine is taken up into the cells by an active transport mechanism. When conducting the experiment at 37 degrees C, it was found that at concentrations below its critical micellar concentration (CMC) of 0.021% (0.0003 and 0.003%, w/v), Solutol HS 15 did not impact the uptake of colchicine. By contrast, at a Solutol HS 15 concentration above its CMC (0.03%, w/v), the amount of colchicine taken up into the cells as well as its uptake velocity were significantly decreased. However, in control experiments performed at 4 degrees C, a temperature at which active transport processes should be significantly slowed down, Solutol HS 15 at 0.03% did not affect colchicine uptake and/or its association with the cells. The described findings might be rationalized by inhibition of colchicine transport either due to direct interaction at the transport site or due to alterations of membrane properties in the presence of Solutol HS 15 at concentrations above its CMC. Moreover, a strong molecular interaction between Solutol HS 15 and colchicine as well as an incorporation of colchicine into micelles formed by Solutol HS 15, this way resulting in a limited contact of colchicine with the cells, cannot be excluded as contributors to the observed effect.

Animals↗
PubMed2004

In vitro investigation on the impact of the surface-active excipients Cremophor EL, Tween 80 and Solutol HS 15 on the metabolism of midazolam.

The impact of the surface-active formulation ingredients Cremophor EL, Tween 80 and Solutol HS 15 on the intrinsic clearance (Clint) of midazolam (MDZ) was investigated in rat hepatocytes and microsomes. In rat hepatocytes with 0.003%, 0.03% and 0.3% (w/v) Solutol HS 15 already present in the incubation medium, the Clint was significantly reduced in a dose-dependent manner by about 25%, 30% and 50%, respectively. In the presence of Cremophor EL and Tween 80 a significant reduction in Clint by about 30% and 25%, respectively, was observed at 0.03% surfactant concentration. At 0.3% of Cremophor EL and Tween 80, Clint was reduced by about 50% and 20%, respectively. A reduction in Clint was also observed in experiments with rat liver microsomes. At surfactant concentrations up to 0.03%, cytotoxicity assays (lactate dehydrogenase release, adenosine triphosphate content) as well as light microscope investigations did not reveal any cytotoxic impact of the surfactants on the hepatocyte monolayer. A potential interaction of the surfactants with biological membranes was determined using phosphatidylcholine-cholesterol liposomes loaded with self-quenching concentrations of carboxyfluorescein. No marked release of carboxyfluorescein from the liposomes (that would be an indication for a surfactant-dependent disruption of membrane integrity) was observed up to concentrations of 0.03% of the different surfactants. It is concluded that cytochrome P450 3A mediated metabolism of MDZ seems to be prevented by all surfactants at concentrations above 0.03%. In our experiments the surfactants did not show toxic effects at concentrations that resulted in a decreased Clint of MDZ. Thus, a direct inhibition of the metabolizing enzymes, a molecular interaction with the microsomes as well as an alteration of membrane properties that did not yet result in a release of LDH have to be taken into consideration as reasons for the observed changes in the metabolism of MDZ.

Animals↗
PubMed2004

Discriminating different classes of toxicants by transcript profiling.

Male rats were treated with various model compounds or the appropriate vehicle controls. Most substances were either well-known hepatotoxicants or showed hepatotoxicity during preclinical testing. The aim of the present study was to determine if biological samples from rats treated with various compounds can be classified based on gene expression profiles. In addition to gene expression analysis using microarrays, a complete serum chemistry profile and liver and kidney histopathology were performed. We analyzed hepatic gene expression profiles using a supervised learning method (support vector machines; SVMs) to generate classification rules and combined this with recursive feature elimination to improve classification performance and to identify a compact subset of probe sets with potential use as biomarkers. Two different SVM algorithms were tested, and the models obtained were validated with a compound-based external cross-validation approach. Our predictive models were able to discriminate between hepatotoxic and nonhepatotoxic compounds. Furthermore, they predicted the correct class of hepatotoxicant in most cases. We provide an example showing that a predictive model built on transcript profiles from one rat strain can successfully classify profiles from another rat strain. In addition, we demonstrate that the predictive models identify nonresponders and are able to discriminate between gene changes related to pharmacology and toxicity. This work confirms the hypothesis that compound classification based on gene expression data is feasible.

Algorithms↗
PubMed2003

Gene expression in two hepatic cell lines, cultured primary hepatocytes, and liver slices compared to the in vivo liver gene expression in rats: possible implications for toxicogenomics use of in vitro systems.

Microarray technology allows the simultaneous analysis of mRNA expression levels of thousands of genes. In the field of toxicogenomics, this technology could help to identify potentially unsafe compounds based on the changes in mRNA expression patterns they induce. Rodent in vivo and in vitro systems are currently the experimental models of choice for predictive toxicology, especially in early phases of development. This study characterizes several hepatic in vitro systems based on mRNA expression profiles, comparing them to gene expression in liver tissue. The in vitro systems investigated comprise two rat liver cell lines (BRL3A and NRL clone 9), primary hepatocytes in conventional monolayer or in sandwich culture, and liver slices. The results demonstrate that liver slices exhibit the strongest similarity to liver tissue regarding mRNA expression, whereas the two cell lines are quite different from the whole liver. We were able to identify genes with strong changes in expression levels in all or at least one of the in vitro systems relative to whole liver. In particular, for some cytochrome P450s the differences observed on the mRNA expression level were paralleled by protein expression and enzymatic activity. In addition, the effect of time in culture was assessed. We were able to show a profound effect of the duration of culture. Expression patterns change most rapidly soon after cell isolation and culture initiation and stabilize with time in culture. The findings are discussed with respect to the usefulness of the various hepatic in vitro systems for microarray-based toxicological testing of compounds.

Animals↗
PubMed2002

Modulation of gene and protein expression by carbon tetrachloride in the rat liver.

The gene and protein expression changes after exposure to a toxic compound might help elucidate its mechanism of action. In this paper we investigated the effect of carbon tetrachloride (CCl(4)) on the gene and protein expression in rat livers. Adult Wistar rats were administered CCl(4) and livers were harvested 6 or 24 h thereafter. The analysis of mitochondrial proteins on 2D gels showed the upregulation of two proteins involved in stress (catalase and uricase). Among the downregulated proteins, enzymes related to the metabolism of lipids and aminoacids were affected. Additionally, alpha-2-macroglobulin and senescence marker protein, two proteins whose decrease in expression has been connected to hepatocyte damage, were decreased. Several of the upregulated genes are involved in stress response, DNA and protein damage, and repair. Genes coding for several enzymes involved in different metabolic pathways, including some P450, were downregulated in the treated animals. In conclusion, a single dose of CCl(4) caused gene and protein expression changes that can be related to its mechanism of toxicity. Results from both technologies support previous publications and provide possible new toxicity markers. However, the correlation between gene and protein expression at a given time point is less apparent, partly as a result of different regulatory mechanisms between gene and protein expression.

Animals↗
PubMed2002

Phytanic acid, a natural peroxisome proliferator-activated receptor (PPAR) agonist, regulates glucose metabolism in rat primary hepatocytes.

Phytanic acid, a metabolite of the chlorophyll molecule, is part of the human diet and is present in normal human serum at low micromolar concentrations. It was previously shown to be a ligand of the 9-cis-retinoic acid receptor and peroxisome proliferator-activated receptor (PPAR) a. PPAR agonists are widely used in the treatment of type 2 diabetes. Here, we report that phytanic acid is not only a transactivator of PPARa, but it also acts via PPARb and PPARg in CV-1 cells that have been cotransfected with the respective full-length receptor and an acyl-CoA oxidase-PPAR-responsive element-luciferase construct. We observed that, in contrast to other fatty acids, phytanic acid at physiological concentrations enhances uptake of 2-deoxy-D-glucose in rat primary hepatocytes. This result could be explained by the increase in mRNA expression of glucose transporters-1 and -2 and glucokinase, as determined by quantitative real-time reverse transcriptase-polymerase chain reaction. Compared with the PPARg-specific agonist ciglitazone, phytanic acid exerts only minor effects on the differentiation of C3H10T1/2 cells into mature adipocytes. These results clearly demonstrate that phytanic acid acts via different PPAR isoforms to modulate expression of genes involved in glucose metabolism, thus suggesting a potential role of phytanic acid in the management of insulin resistance.

Adipocytes↗