Intestinal Fish Cell Barrier Model to Assess Transfer of Organic Chemicals in Vitro: An Experimental and Computational Study

We studied the role of the fish intestine as a barrier for organic chemicals using the epithelial barrier model built on the rainbow trout (Oncorhynchus mykiss) intestinal cell line, RTgutGC and the newly developed exposure chamber, TransFEr, specifically designed to work with hydrophobic and volatile chemicals. Testing 11 chemicals with a range of physicochemical properties (logK(ow): 2.2 to 6.3, logHLC: 6.1 to 2.3) and combining the data with a mechanistic kinetic model enabled the determination of dominant processes underlying the transfer experiments and the derivation of robust transfer rates. Against the current assumption in chemical uptake modeling, chemical transfer did not strictly depend on the logK(ow) but resulted from chemical-specific intracellular accumulation and biotransformation combined with paracellular and active transport. Modeling also identified that conducting elaborate measurements of the plastic parts, including the polystyrene insert and the PET filter, is unnecessary and that stirring in the TransFEr chamber reduced the stagnant water layers compared to theoretical predictions. Aside from providing insights into chemical uptake via the intestinal epithelium, this system can easily be transferred to other cell-based barrier systems, such as the fish gill or mammalian intestinal models and may improve in vitro-in vivo extrapolation and prediction of chemical bioaccumulation into organisms.

Extending the Concept of Predicting Fish Acute Toxicity In Vitro to the Intestinal Cell Line RTgutGC

Jenny Maner, Kristin Schirmer, Hannah Inka Schug

Testing chemicals for fish acute toxicity is a legal requirement in many countries as part of environmental risk assessment. To reduce the number of fish used, substantial efforts have been focused on alternative approaches. Prominently, the cell viability assay with the rainbow trout (Oncorhynchus mykiss) gill cell line, RTgill-W1, has proven to be highly predictive and robust. Like the gills, the intestine is considered a major site of chemical uptake and biotransformation, but, in contrast to the gills, it is expected to be exposed to more hydrophobic chemicals, which enter the fish via food. In the present study, we therefore aimed to extend the cell bioassay to the rainbow trout epithelial cell line from intestine, RTgutGC. Using 16 hydrophobic and volatile chemicals from the fragrance palette, we show that also the RTgutGC cell line can be used to predict fish acute toxicity of chemicals and yields intra-laboratory variability in line with other bioassays. By comparing the RTgutGC toxicity to a study employing the RTgill-W1 assay on the same group of chemicals, a fragrance-specific relationship was established that reflects an almost perfect 1:1 relationship between in vitro and in vivo toxicity results. Thus, both cell lines can be used to predict fish acute toxicity, either by extrapolating based on the in vivo-in vitro relationship or by taking the in vitro results at face value. We moreover demonstrate the derivation of non-toxic concentrations for downstream applications that rely on a healthy cell state, such as the assessment of biotransformation or chemical transfer.

SPEKTRUM AKADEMISCHER VERLAG-SPRINGER-VERLAG GMBH2020

TransFEr: a new device to measure the transfer of volatile and hydrophobic organic chemicals across an in vitro intestinal fish cell barrier

Kristin Schirmer, Hannah Inka Schug

Transfer of compounds across cellular barriers is a critical step of compound uptake into organisms. Using in vitro barrier systems to evaluate such transfer is attractive because of the higher throughput and reduced resource needs compared to animal studies. Thus far, however, studying the transfer of hydrophobic and volatile compounds was hampered by the unavailability of in vitro exposure systems that allow for stable and predictable chemical exposure concentrations. To overcome this limitation, we constructed a novel exposure chamber, TransFEr, and tested it with an in vitro epithelial barrier model using the rainbow trout (Oncorhynchus mykiss) intestinal cell line, RTgutGC. Key features of the chamber are its closed design and rotatable silicon segments, which can serve for chemical dosing and sampling. Using the fragrance damascone beta (log K-OW: 3.7, log HLC: -3.9) as a pilot chemical, we were able to demonstrate that our exposure chamber provides for stable chemical exposure concentrations and full mass balance. The RTgutGC epithelium served as barrier for damascone beta transfer, which we attribute to chemical retention and biotransformation in the intestinal cells. Nevertheless, substantial transfer of the chemical across the epithelium occurred. When a chemical sink, i.e. a silicon segment, was included in the basolateral chamber to mimic blood constituents binding in vivo, transfer was about three-fold enhanced. We suggest that the presented methodology can help to obtain insights into chemical uptake mechanisms via the intestinal or other epithelia of fish and other animals for hydrophobic and volatile chemicals.

ROYAL SOC CHEMISTRY2018

Computational studies for the description of electronic and optical properties for photocatalysis in Metal Organic Frameworks

Andres Adolfo Ortega Guerrero

Metal-organic frameworks(MOFs) are promising materials for photocatalytic applications. MOFs modular and porosity structure provides a platform to assemble photo-active and catalytic-sites building block units that can offer unique photo-physics. This feature is of great interest for H2 evolution photocatalytic applications. However, MOFs current photocatalysts do not meet the industrial need for their implementation as a technology due to performance limitations. Thus, elucidating and predicting the optical properties of MOFs will have wide implications in the development of MOF-based photocatalysts. Computational studies can be of great aid for the discovery of MOFs photocatalyst. Yet, this is a challenging task for computational chemistry given the complexity of the photophysical properties, the inorganic-organic nature, the number of atoms, and the unit cell size of MOFs. The principal goal of this thesis is the study MOFs photophysical properties for predicting their feasibility for photocatalytic applications. Density functional theory (DFT) and linear-response time-dependent DFT (LR-TDDFT) formalisms are used for the description of the light absorption, charge separation, and charge transfer properties of MOFs. We first address the dependence of the ligand in the UV/Vis optical absorption of porphyrin-based MOFs. The characterization of the excited states of the porphyrin ligands in MOFs requires an appropriate approximation for the description in periodic crystal MOFs. The selection of proper functionals and approximations within DFT/TDDFT calculations is necessary to overcome the erroneous description of properties like excitonic effects, optical transitions, and gap-renormalization. Later, we continue with the study of the charge separation in a porphyrin ruthenium-based MOF. We describe the importance of missing coordinated solvents anions in the metal node for the stability and charge transfer mechanism in the material. Within this study, we computed electron-hole interacting energy indicating a low electron-hole recombination rate. We next introduce a computational strategy to describing the long-lived electron-hole pairs and the long-rage charge transfer in MOFs. This description can be depicted by computing charge transfer numbers and the effective mass of carriers, respectively. This methodology can correctly predict the charge separation and the effective mass of 15 representative MOF structures promising for photocatalysis in agreement with the literature. Finally, we present an experimental and theoretical combined study investigation towards optimal photocatalytic hydrogen evolution reaction (HER) in MOFs. Isostructural pyrene-based MOFs with different transition metals allowed us a proper comparison. This study highlights the interplay between tunning electronic properties and crystal morphology on the photocatalytic HER performance of the MOFs. These results presented in this thesis can be exploited and transfer to the study of other MOFs for HER photocatalysis.

EPFL2021

Computational studies for the description of electronic and optical properties for photocatalysis in Metal Organic Frameworks

Andres Adolfo Ortega Guerrero

EPFL2021