An untargeted multi-technique metabolomics approach to studying intracellular metabolites of HepG2 cells exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

<p>Abstract</p> <p>Background</p> <p><it>In vitro </it>cell systems together with omics methods represent promising alternatives to conventional animal models for toxicity testing. Transcriptomic and proteomic approaches have been widely applied <it>in vitro </it>but relatively few studies have used metabolomics. Therefore, the goal of the present study was to develop an untargeted methodology for performing reproducible metabolomics on <it>in vitro </it>systems. The human liver cell line HepG2, and the well-known hepatotoxic and non-genotoxic carcinogen 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), were used as the <it>in vitro </it>model system and model toxicant, respectively.</p> <p>Results</p> <p>The study focused on the analysis of intracellular metabolites using NMR, LC-MS and GC-MS, with emphasis on the reproducibility and repeatability of the data. State of the art pre-processing and alignment tools and multivariate statistics were used to detect significantly altered levels of metabolites after exposing HepG2 cells to TCDD. Several metabolites identified using databases, literature and LC-nanomate-Orbitrap analysis were affected by the treatment. The observed changes in metabolite levels are discussed in relation to the reported effects of TCDD.</p> <p>Conclusions</p> <p>Untargeted profiling of the polar and apolar metabolites of <it>in vitro </it>cultured HepG2 cells is a valid approach to studying the effects of TCDD on the cell metabolome. The approach described in this research demonstrates that highly reproducible experiments and correct normalization of the datasets are essential for obtaining reliable results. The effects of TCDD on HepG2 cells reported herein are in agreement with previous studies and serve to validate the procedures used in the present work.</p

Steady states of the Parker instability

We study the linear properties, nonlinear saturation and a steady, strongly nonlinear state of the Parker instabilityin galaxies. We consider magnetic buoyancy and its consequences with and without cosmic rays. Cosmic rays aredescribed using the fluid approximation with anisotropic, non-Fickian diffusion. To avoid unphysical constraintson the instability (such as boundary conditions often used to specify an unstable background state), nonideal MHDequations are solved for deviations from a background state representing an unstable magnetohydrostatic equilibrium.We consider isothermal gas and neglect rotation. The linear evolution of the instability is in broad agreement withearlier analytical and numerical models; but we show that most of the simplifying assumptions of the earlier workdo not hold, such that they provide only a qualitative rather than quantitative picture. In its nonlinear stage theinstability has significantly altered the background state from its initial state. Vertical distributions of both magneticfield and cosmic rays are much wider, the gas layer is thinner, and the energy densities of both magnetic field andcosmic rays are much reduced. The spatial structure of the nonlinear state differs from that of any linear modes. Atransient gas outflow is driven by the weakly nonlinear instability as it approaches saturation