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79 Publications visible to you, out of a total of 79
A Predictive 3D Multi-Scale Model of Biliary Fluid Dynamics in the Liver Lobule

Abstract (Expand)

Bile, the central metabolic product of the liver, is transported by the bile canaliculi network. The impairment of bile flow in cholestatic liver diseases has urged a demand for insights into its … regulation. Here, we developed a predictive 3D multi-scale model that simulates fluid dynamic properties successively from the subcellular to the tissue level. The model integrates the structure of the bile canalicular network in the mouse liver lobule, as determined by high-resolution confocal and serial block-face scanning electron microscopy, with measurements of bile transport by intravital microscopy. The combined experiment-theory approach revealed spatial heterogeneities of biliary geometry and hepatocyte transport activity. Based on this, our model predicts gradients of bile velocity and pressure in the liver lobule. Validation of the model predictions by pharmacological inhibition of Rho kinase demonstrated a requirement of canaliculi contractility for bile flow in vivo. Our model can be applied to functionally characterize liver diseases and quantitatively estimate biliary transport upon drug-induced liver injury.

Authors: Kirstin Meyer, Oleksandr Ostrenko, Georgios Bourantas, Hernan Morales-Navarrete, Natalie Porat-Shliom, Fabian Segovia-Miranda, Hidenori Nonaka, Ali Ghaemi, Jean-Marc Verbavatz, Lutz Brusch, Ivo Sbalzarini, Yannis Kalaidzidis, Roberto Weigert, Marino Zerial

Date Published: 1st Mar 2017

Publication Type: Not specified

The importance of drug transporter characterization to precision medicine.

Abstract

Not specified

Authors: P. Fisel, A. T. Nies, E. Schaeffeler, M. Schwab

Date Published: 1st Feb 2017

Publication Type: Not specified

A multilevel framework to reconstruct anatomical 3D models of the hepatic vasculature in rat livers

Abstract (Expand)

The intricate (micro)vascular architecture of the liver has not yet been fully unravelled. Although current models are often idealized simplifications of the complex anatomical reality, correct … morphological information is instrumental for scientific and clinical purposes. Previously, both vascular corrosion casting (VCC) and immunohistochemistry (IHC) have been separately used to study the hepatic vasculature. Nevertheless, these techniques still face a number of challenges such as dual casting in VCC and limited imaging depths for IHC. We have optimized both techniques and combined their complementary strengths to develop a framework for multilevel reconstruction of the hepatic circulation in the rat. The VCC and micro-CT scanning protocol was improved by enabling dual casting, optimizing the contrast agent concentration, and adjusting the viscosity of the resin (PU4ii). IHC was improved with an optimized clearing technique (CUBIC) that extended the imaging depth for confocal microscopy more than five-fold. Using in-house developed software (DeLiver), the vascular network - in both VCC and IHC datasets - was automatically segmented and/or morphologically analysed. Our methodological framework allows 3D reconstruction and quantification of the hepatic circulation, ranging from the major blood vessels down to the intertwined and interconnected sinusoids. We believe that the presented framework will have value beyond studies of the liver, and will facilitate a better understanding of various parenchymal organs in general, in physiological and pathological circumstances.

Authors: Geert Peeters, Charlotte Debbaut, Wim Laleman, Adrian Friebel, Diethard Monbaliu, Ingrid Vander Elst, Jan R Detrez, Tim Vandecasteele, Tim Johann, Thomas De Schryver, Luc Van Hoorebeke, Kasper Favere, Jonas Verbeke, Dirk Drasdo, Stefan Hoehme, Patrick Segers, Pieter Cornillie, Winnok H De Vos

Date Published: 28th Dec 2016

Publication Type: Not specified

Computational Lipidomics and Lipid Bioinformatics: Filling In the Blanks.

Abstract (Expand)

Lipids are highly diverse metabolites of pronounced importance in health and disease. While metabolomics is a broad field under the omics umbrella that may also relate to lipids, lipidomics is an … emerging field which specializes in the identification, quantification and functional interpretation of complex lipidomes. Today, it is possible to identify and distinguish lipids in a high-resolution, high-throughput manner and simultaneously with a lot of structural detail. However, doing so may produce thousands of mass spectra in a single experiment which has created a high demand for specialized computational support to analyze these spectral libraries. The computational biology and bioinformatics community has so far established methodology in genomics, transcriptomics and proteomics but there are many (combinatorial) challenges when it comes to structural diversity of lipids and their identification, quantification and interpretation. This review gives an overview and outlook on lipidomics research and illustrates ongoing computational and bioinformatics efforts. These efforts are important and necessary steps to advance the lipidomics field alongside analytic, biochemistry, biomedical and biology communities and to close the gap in available computational methodology between lipidomics and other omics sub-branches.

Authors: J. Pauling, E. Klipp

Date Published: 22nd Dec 2016

Publication Type: Not specified

Epigenome-wide association study of body mass index, and the adverse outcomes of adiposity.

Abstract (Expand)

Approximately 1.5 billion people worldwide are overweight or affected by obesity, and are at risk of developing type 2 diabetes, cardiovascular disease and related metabolic and inflammatory disturbances. … Although the mechanisms linking adiposity to associated clinical conditions are poorly understood, recent studies suggest that adiposity may influence DNA methylation, a key regulator of gene expression and molecular phenotype. Here we use epigenome-wide association to show that body mass index (BMI; a key measure of adiposity) is associated with widespread changes in DNA methylation (187 genetic loci with P < 1 x 10(-7), range P = 9.2 x 10(-8) to 6.0 x 10(-46); n = 10,261 samples). Genetic association analyses demonstrate that the alterations in DNA methylation are predominantly the consequence of adiposity, rather than the cause. We find that methylation loci are enriched for functional genomic features in multiple tissues (P < 0.05), and show that sentinel methylation markers identify gene expression signatures at 38 loci (P < 9.0 x 10(-6), range P = 5.5 x 10(-6) to 6.1 x 10(-35), n = 1,785 samples). The methylation loci identify genes involved in lipid and lipoprotein metabolism, substrate transport and inflammatory pathways. Finally, we show that the disturbances in DNA methylation predict future development of type 2 diabetes (relative risk per 1 standard deviation increase in methylation risk score: 2.3 (2.07-2.56); P = 1.1 x 10(-54)). Our results provide new insights into the biologic pathways influenced by adiposity, and may enable development of new strategies for prediction and prevention of type 2 diabetes and other adverse clinical consequences of obesity.

Authors: S. Wahl, A. Drong, B. Lehne, M. Loh, W. R. Scott, S. Kunze, P. C. Tsai, J. S. Ried, W. Zhang, Y. Yang, S. Tan, G. Fiorito, L. Franke, S. Guarrera, S. Kasela, J. Kriebel, R. C. Richmond, M. Adamo, U. Afzal, M. Ala-Korpela, B. Albetti, O. Ammerpohl, J. F. Apperley, M. Beekman, P. A. Bertazzi, S. L. Black, C. Blancher, M. J. Bonder, M. Brosch, M. Carstensen-Kirberg, A. J. de Craen, S. de Lusignan, A. Dehghan, M. Elkalaawy, K. Fischer, O. H. Franco, T. R. Gaunt, J. Hampe, M. Hashemi, A. Isaacs, A. Jenkinson, S. Jha, N. Kato, V. Krogh, M. Laffan, C. Meisinger, T. Meitinger, Z. Y. Mok, V. Motta, H. K. Ng, Z. Nikolakopoulou, G. Nteliopoulos, S. Panico, N. Pervjakova, H. Prokisch, W. Rathmann, M. Roden, F. Rota, M. A. Rozario, J. K. Sandling, C. Schafmayer, K. Schramm, R. Siebert, P. E. Slagboom, P. Soininen, L. Stolk, K. Strauch, E. S. Tai, L. Tarantini, B. Thorand, E. F. Tigchelaar, R. Tumino, A. G. Uitterlinden, C. van Duijn, J. B. van Meurs, P. Vineis, A. R. Wickremasinghe, C. Wijmenga, T. P. Yang, W. Yuan, A. Zhernakova, R. L. Batterham, G. D. Smith, P. Deloukas, B. T. Heijmans, C. Herder, A. Hofman, C. M. Lindgren, L. Milani, P. van der Harst, A. Peters, T. Illig, C. L. Relton, M. Waldenberger, M. R. Jarvelin, V. Bollati, R. Soong, T. D. Spector, J. Scott, M. I. McCarthy, P. Elliott, J. T. Bell, G. Matullo, C. Gieger, J. S. Kooner, H. Grallert, J. C. Chambers

Date Published: 21st Dec 2016

Publication Type: Not specified

NAFLD is associated with methylation shifts with relevance for the expression of genes involved in lipoprotein particle composition.

Abstract (Expand)

Non-alcoholic fatty liver disease (NAFLD) is characterized by the accumulation of triglycerides, cholesterol and toxic free fatty acids and is related to low vitamin D levels. In an analysis of specific … gene sets we elucidate to what extent NAFLD associates to epigenetic and related transcriptional changes in gene networks regulating lipid, energy and vitamin D balance. Two gene clusters responsible for lipid homeostasis (74 genes) and vitamin D and energy balance (31 genes) were investigated with regard to average epigenetic shifts within the first 1500bp next to the transcriptional start site. Three cohorts from two published genome wide driven studies that used a microarray approach were investigated including altogether 103 NAFLD and 75 liver healthy subjects. In the first two steps associations between NAFLD abundance, strength of fibrosis and methylation were investigated in two cohorts by multiple linear regression analyses, correcting for important clinical and demographic parameters. Methylation associated strength of transcription in genes showing significant NAFLD related methylation changes were studied in a third step using a third cohort and applying Pearson's correlation and robust linear regression analyses. 41 genes in gene cluster 1 and 14 genes in cluster 2 were significantly differentially methylated in dependency of NAFLD and hepatic fibrosis. We detect new genes significantly changed in methylation, including APO family members (lipid transport), NPC1L1, STARD (cholesterol transport) and GRHL (energy homeostasis). Our results allow novel insights into the hepatic epigenetic regulation of genes important for lipid and vitamin D balance in NAFLD.

Authors: J. Mwinyi, A. E. Bostrom, C. Pisanu, S. K. Murphy, W. Erhart, C. Schafmayer, J. Hampe, C. Moylan, H. B. Schioth

Date Published: 18th Dec 2016

Publication Type: Not specified

Longitudinal micro-computed tomography monitoring of progressive liver regeneration in a mouse model of partial hepatectomy.

Abstract (Expand)

The partial hepatectomy (PH) model is widely used to study liver regeneration. Currently, the extent of regeneration is analyzed by measuring the weight of the liver post-mortem or by magnetic resonance … imaging. In this study we aimed to determine whether liver volume gain can be accurately measured using micro-computed tomography (microCT). Approximately 42% of the liver was removed by ligation in C57BL/6 N mice. Mice were divided into two study groups. In group 1 conventional characterization of liver hyperplasia was performed by weighing the liver post-mortem. In group 2, liver volume gain was determined by microCT volume estimation. MicroCT results showed equivalent regeneration rates compared with the conventional method without the need to mathematically determine initial liver weights before PH. This parameter is strongly influenced by the age, strain and sex of the mice. In addition non-invasive microCT determination of volume gain over multiple time-points using the same animal reduces the number of animals needing to be used (in line with the 3R principle of replacement, reduction and refinement).

Authors: O. M. Will, T. Damm, G. M. Campbell, W. von Schonfells, Y. Acil, M. Will, A. Chalaris-Rissmann, M. Ayna, C. Drucker, C. C. Gluer

Date Published: 8th Dec 2016

Publication Type: Not specified

Functional properties of hepatocytes in vitro are correlated with cell polarity maintenance.

Abstract (Expand)

Exploring the cell biology of hepatocytes in vitro could be a powerful strategy to dissect the molecular mechanisms underlying the structure and function of the liver in vivo. However, this approach … relies on appropriate in vitro cell culture systems that can recapitulate the cell biological and metabolic features of the hepatocytes in the liver whilst being accessible to experimental manipulations. Here, we adapted protocols for high-resolution fluorescence microscopy and quantitative image analysis to compare two primary hepatocyte culture systems, monolayer and collagen sandwich, with respect to the distribution of two distinct populations of early endosomes (APPL1 and EEA1-positive), endocytic capacity, metabolic and signaling activities. In addition to the re-acquisition of hepatocellular polarity, primary hepatocytes grown in collagen sandwich but not in monolayer culture recapitulated the apico-basal distribution of EEA1 endosomes observed in liver tissue. We found that such distribution correlated with the organization of the actin cytoskeleton in vitro and, surprisingly, was dependent on the nutritional state in vivo. Hepatocytes in collagen sandwich also exhibited faster kinetics of low-density lipoprotein (LDL) and epidermal growth factor (EGF) internalization, showed improved insulin sensitivity and preserved their ability for glucose production, compared to hepatocytes in monolayer cultures. Although no in vitro culture system can reproduce the exquisite structural features of liver tissue, our data nevertheless highlight the ability of the collagen sandwich system to recapitulate key structural and functional properties of the hepatocytes in the liver and, therefore, support the usage of this system to study aspects of hepatocellular biology in vitro.

Authors: A. Zeigerer, A. Wuttke, G. Marsico, S. Seifert, Y. Kalaidzidis, M. Zerial

Date Published: 1st Dec 2016

Publication Type: Not specified

Impact of Membrane Drug Transporters on Resistance to Small-Molecule Tyrosine Kinase Inhibitors.

Abstract (Expand)

Small-molecule inhibitors of tyrosine kinases (TKIs) are the mainstay of treatment for many malignancies and represent novel treatment options for other diseases such as idiopathic pulmonary fibrosis. … Twenty-five TKIs are currently FDA-approved and >130 are being evaluated in clinical trials. Increasing evidence suggests that drug exposure of TKIs may significantly contribute to drug resistance, independently from somatic variation of TKI target genes. Membrane transport proteins may limit the amount of TKI reaching the target cells. This review highlights current knowledge on the basic and clinical pharmacology of membrane transporters involved in TKI disposition and their contribution to drug efficacy and adverse drug effects. In addition to non-genetic and epigenetic factors, genetic variants, particularly rare ones, in transporter genes are promising novel factors to explain interindividual variability in the response to TKI therapy.

Authors: C. Neul, E. Schaeffeler, A. Sparreboom, S. Laufer, M. Schwab, A. T. Nies

Date Published: 25th Oct 2016

Publication Type: Not specified

Polymorphic variation in TPMT is the principal determinant of TPMT phenotype: A meta-analysis of three genome-wide association studies.

Abstract (Expand)

Thiopurine-related hematotoxicity in pediatric acute lymphoblastic leukemia (ALL) and inflammatory bowel diseases has been linked to genetically defined variability in thiopurine S-methyltransferase … (TPMT) activity. While gene testing of TPMT is being clinically implemented, it is unclear if additional genetic variation influences TPMT activity with consequences for thiopurine-related toxicity. To examine this possibility, we performed a genome-wide association study (GWAS) of red blood cell TPMT activity in 844 Estonian individuals and 245 pediatric ALL cases. Additionally, we correlated genome-wide genotypes to human hepatic TPMT activity in 123 samples. Only genetic variants mapping to chromosome 6, including the TPMT gene region, were significantly associated with TPMT activity (P < 5.0 x 10-8 ) in each of the three GWAS and a joint meta-analysis of 1,212 cases (top hit P = 1.2 x 10-72 ). This finding is consistent with TPMT genotype being the primary determinant of TPMT activity, reinforcing the rationale for genetic testing of TPMT alleles in routine clinical practice to individualize mercaptopurine dosage.

Authors: R. Tamm, R. Magi, R. Tremmel, S. Winter, E. Mihailov, A. Smid, A. Moricke, K. Klein, M. Schrappe, M. Stanulla, R. Houlston, R. Weinshilboum, I. Mlinaric Rascan, A. Metspalu, L. Milani, M. Schwab, E. Schaeffeler

Date Published: 23rd Oct 2016

Publication Type: Not specified

Computational Modeling of Lipid Metabolism in Yeast.

Abstract (Expand)

Lipid metabolism is essential for all major cell functions and has recently gained increasing attention in research and health studies. However, mathematical modeling by means of classical approaches … such as stoichiometric networks and ordinary differential equation systems has not yet provided satisfactory insights, due to the complexity of lipid metabolism characterized by many different species with only slight differences and by promiscuous multifunctional enzymes. Here, we present an object-oriented stochastic model approach as a way to cope with the complex lipid metabolic network. While all lipid species are treated objects in the model, they can be modified by the respective converting reactions based on reaction rules, a hybrid method that integrates benefits of agent-based and classical stochastic simulation. This approach allows to follow the dynamics of all lipid species with different fatty acids, different degrees of saturation and different headgroups over time and to analyze the effect of parameter changes, potential mutations in the catalyzing enzymes or provision of different precursors. Applied to yeast metabolism during one cell cycle period, we could analyze the distribution of all lipids to the various membranes in time-dependent manner. The presented approach allows to efficiently treat the complexity of cellular lipid metabolism and to derive conclusions on the time- and location-dependent distributions of lipid species and their properties such as saturation. It is widely applicable, easily extendable and will provide further insights in healthy and diseased states of cell metabolism.

Authors: V. Schutzhold, J. Hahn, K. Tummler, E. Klipp

Date Published: 27th Sep 2016

Publication Type: Not specified

Computational Modeling of Lipid Metabolism in Yeast.

Abstract (Expand)

Lipid metabolism is essential for all major cell functions and has recently gained increasing attention in research and health studies. However, mathematical modeling by means of classical approaches … such as stoichiometric networks and ordinary differential equation systems has not yet provided satisfactory insights, due to the complexity of lipid metabolism characterized by many different species with only slight differences and by promiscuous multifunctional enzymes. Here, we present an object-oriented stochastic model approach as a way to cope with the complex lipid metabolic network. While all lipid species are treated objects in the model, they can be modified by the respective converting reactions based on reaction rules, a hybrid method that integrates benefits of agent-based and classical stochastic simulation. This approach allows to follow the dynamics of all lipid species with different fatty acids, different degrees of saturation and different headgroups over time and to analyze the effect of parameter changes, potential mutations in the catalyzing enzymes or provision of different precursors. Applied to yeast metabolism during one cell cycle period, we could analyze the distribution of all lipids to the various membranes in time-dependent manner. The presented approach allows to efficiently treat the complexity of cellular lipid metabolism and to derive conclusions on the time- and location-dependent distributions of lipid species and their properties such as saturation. It is widely applicable, easily extendable and will provide further insights in healthy and diseased states of cell metabolism.

Authors: V. Schutzhold, J. Hahn, K. Tummler, E. Klipp

Date Published: 27th Sep 2016

Publication Type: Not specified

The genetics of alcohol dependence and alcohol-related liver disease.

Abstract (Expand)

The susceptibility to developing alcohol dependence and significant alcohol-related liver injury is determined by a number of constitutional, environmental and genetic factors, although the nature and … level of interplay between them remains unclear. The familiality and heritability of alcohol dependence is well-documented but, to date, no strong candidate genes conferring increased risk have emerged, although variants in alcohol dehydrogenase and acetaldehyde dehydrogenase have been shown to confer protection, predominantly in individuals of East Asian ancestry. Population contamination with confounders such as drug co-dependence and psychiatric and physical co-morbidity may explain the essentially negative genome-wide association studies in this disorder. The familiality and hereditability of alcohol-related cirrhosis is not as well-documented but three strong candidate genes PNPLA3, TM6SF2 and MBOAT7, have been identified. The mechanisms by which variants in these genes confer risk and the nature of the functional interplay between them remains to be determined but, when elucidated, will undoubtedly increase our understanding of the pathophysiology of this disease. The way in which this genetic information could potentially inform patient management has yet to be determined and tested.

Authors: F. Stickel, C. Moreno, J. Hampe, M. Y. Morgan

Date Published: 27th Aug 2016

Publication Type: Not specified

Comparison of Gene Expression Patterns Between Mouse Models of Nonalcoholic Fatty Liver Disease and Liver Tissues From Patients.

Abstract (Expand)

BACKGROUND & AIMS: Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder in industrialized countries. Mouse models of NAFLD have been used in studies of pathogenesis … and treatment, and have certain features of the human disease. We performed a systematic transcriptome-wide analysis of liver tissues from patients at different stages of NAFLD progression (ranging from healthy obese individuals to those with steatosis), as well as rodent models of NAFLD, to identify those that most closely resemble human disease progression in terms of gene expression patterns. METHODS: We performed a systematic evaluation of genome-wide messenger RNA expression using liver tissues collected from mice fed a standard chow diet (controls) and 9 mouse models of NAFLD: mice on a high-fat diet (with or without fructose), mice on a Western-type diet, mice on a methionine- and choline-deficient diet, mice on a high-fat diet given streptozotocin, and mice with disruption of Pten in hepatocytes. We compared gene expression patterns with those of liver tissues from 25 patients with nonalcoholic steatohepatitis (NASH), 27 patients with NAFLD, 15 healthy obese individuals, and 39 healthy nonobese individuals (controls). Liver samples were obtained from patients undergoing liver biopsy for suspected NAFLD or NASH, or during liver or bariatric surgeries. Data sets were analyzed using the limma R-package. Overlap of functional profiles was analyzed by gene set enrichment analysis profiles. RESULTS: We found differences between human and mouse transcriptomes to be significantly larger than differences between disease stages or models. Of the 65 genes with significantly altered expression in patients with NASH and 177 genes with significantly altered expression in patients with NAFLD, compared with controls, only 1-18 of these genes also differed significantly in expression between mouse models of NAFLD and control mice. However, expression of genes that regulate pathways associated with the development of NAFLD were altered in some mouse models (such as pathways associated with lipid metabolism). On a pathway level, gene expression patterns in livers of mice on the high-fat diet were associated more closely with human fatty liver disease than other models. CONCLUSIONS: In comparing gene expression profiles between liver tissues from different mouse models of NAFLD and patients with different stages of NAFLD, we found very little overlap. Our data set is available for studies of pathways that contribute to the development of NASH and NAFLD and selection of the most applicable mouse models (http://www.nash-profiler.com).

Authors: A. Teufel, T. Itzel, W. Erhart, M. Brosch, X. Y. Wang, Y. O. Kim, W. von Schonfels, A. Herrmann, S. Bruckner, F. Stickel, J. F. Dufour, T. Chavakis, C. Hellerbrand, R. Spang, T. Maass, T. Becker, S. Schreiber, C. Schafmayer, D. Schuppan, J. Hampe

Date Published: 19th Jun 2016

Publication Type: Not specified

Gender, Contraceptives and Individual Metabolic Predisposition Shape a Healthy Plasma Lipidome.

Abstract (Expand)

Lipidomics of human blood plasma is an emerging biomarker discovery approach that compares lipid profiles under pathological and physiologically normal conditions, but how a healthy lipidome varies … within the population is poorly understood. By quantifying 281 molecular species from 27 major lipid classes in the plasma of 71 healthy young Caucasians whose 35 clinical blood test and anthropometric indices matched the medical norm, we provided a comprehensive, expandable and clinically relevant resource of reference molar concentrations of individual lipids. We established that gender is a major lipidomic factor, whose impact is strongly enhanced by hormonal contraceptives and mediated by sex hormone-binding globulin. In lipidomics epidemiological studies should avoid mixed-gender cohorts and females taking hormonal contraceptives should be considered as a separate sub-cohort. Within a gender-restricted cohort lipidomics revealed a compositional signature that indicates the predisposition towards an early development of metabolic syndrome in ca. 25% of healthy male individuals suggesting a healthy plasma lipidome as resource for early biomarker discovery.

Authors: S. Sales, J. Graessler, S. Ciucci, R. Al-Atrib, T. Vihervaara, K. Schuhmann, D. Kauhanen, M. Sysi-Aho, S. R. Bornstein, M. Bickle, C. V. Cannistraci, K. Ekroos, A. Shevchenko

Date Published: 14th Jun 2016

Publication Type: Not specified

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