Application of Impedance-Based Techniques in Hepatology Research

Organ chips with integrated multifunctional sensors enable continuous metabolic monitoring at controlled oxygen levels

Despite remarkable advances in Organ-on-a-chip (Organ Chip) microfluidic culture technology, recreating tissue-relevant physiological conditions, such as the region-specific oxygen concentrations, remains a formidable technical challenge, and analysis of tissue functions is commonly carried out using one analytical technique at a time. Here, we describe two-channel Organ Chip microfluidic devices fabricated from polydimethylsiloxane and gas impermeable polycarbonate materials that are integrated with multiple sensors, mounted on a printed circuit board and operated using a commercially available Organ Chip culture instrument. The novelty of this system is that it enables the recreation of physiologically relevant tissue-tissue interfaces and oxygen tension as well as non-invasive continuous measurement of transepithelial electrical resistance, oxygen concentration and pH, combined with simultaneous analysis of cellular metabolic activity (ATP/ADP ratio), cell morphology, and tissue phenotype. We demonstrate the reliable and reproducible functionality of this system in living human Gut and Liver Chip cultures. Changes in tissue barrier function and oxygen tension along with their functional and metabolic responses to chemical stimuli (e.g., calcium chelation, oligomycin) were continuously and noninvasively monitored on-chip for up to 23 days. A physiologically relevant microaerobic microenvironment that supports co-culture of human intestinal cells with living Lactococcus lactis bacteria also was demonstrated in the Gut Chip. The integration of multi-functional sensors into Organ Chips provides a robust and scalable platform for the simultaneous, continuous, and non-invasive monitoring of multiple physiological functions that can significantly enhance the comprehensive and reliable evaluation of engineered tissues in Organ Chip models in basic research, preclinical modeling, and drug development.

Metabolism of Acetaminophen by Enteric Epithelial Cells Mitigates Hepatocellular Toxicity In Vitro

The gut-liver axis is defined by dietary and environmental communication between the gut, microbiome and the liver with its redox and immune systems, the overactivation of which can lead to hepatic injury. We used media preconditioning to mimic some aspects of the enterohepatic circulation by treating the human Caco-2 intestinal epithelial cell line with 5, 10 and 20 mM paracetamol (N-acetyl-para-aminophenol; APAP) for 24 h, after which cell culture supernatants were transferred to differentiated human hepatic HepaRG cells for a further 24 h. Cell viability was assessed by mitochondrial function and ATP production, while membrane integrity was monitored by cellular-based impedance. Metabolism by Caco-2 cells was determined by liquid chromatography with tandem mass spectrometry. Caco-2 cell viability was not affected by APAP, while cell membrane integrity and tight junctions were maintained and became tighter with increasing APAP concentrations, suggesting a reduction in the permeability of the intestinal epithelium. During 24 h incubation, Caco-2 cells metabolised 64-68% of APAP, leaving 32-36% of intact starting compound to be transferred to HepaRG cells. When cultured with Caco-2-preconditioned medium, HepaRG cells also showed no loss of cell viability or membrane integrity, completely in contrast to direct treatment with APAP, which resulted in a rapid loss of cell viability and membrane integrity and, ultimately, cell death. Thus, the pre-metabolism of APAP could mitigate previously observed hepatotoxicity to hepatic tight junctions caused by direct exposure to APAP. These observations could have important implications for the direct exposure of hepatic parenchyma to APAP, administered via the intravenous route.

New Microfluidic System for Electrochemical Impedance Spectroscopy Assessment of Cell Culture Performance: Design and Development of New Electrode Material

Electrochemical impedance spectroscopy (EIS) is widely accepted as an effective and non-destructive method to assess cell health during cell-culture. However, there is a lack of compact devices compatible with microfluidic integration and microscopy that could provide the real-time and non-invasive monitoring of cell-cultures using EIS. In this paper, we reported the design and characterization of a modular EIS testing system based on a patented technology. This device was fabricated using easily processable methodologies including screen-printing of the impedance electrodes and molding or micromachining of the cell culture chamber with an easy assembly procedure. Accordingly, to obtain processable, biocompatible and sterilizable electrode materials that lower the impact of interfacial impedance on TEER (Transepithelial electrical resistance) measurements, and to enable concomitant microscopy observations, we optimized the formulation of the electrode inks and the design of the EIS electrodes, respectively. First, electrode materials were based on carbon biocompatible inks enriched with IrOx particles to obtain low interfacial impedance electrodes approaching the performances of classical non-biocompatible Ag/AgCl second-species electrodes. Secondly, we proposed three original electrode designs, which were compared to classical disk electrodes that were optically compatible with microscopy. We assessed the impact of the electrode design on the response of the impedance sensor using COMSOL Multiphysics. Finally, the performance of the impedance spectroscopy devices was assessed in vitro using human airway epithelial cell cultures.

Dimensionality Reduction and Prediction of Impedance Data of Biointerface

Electrochemical impedance spectroscopy (EIS) is the golden tool for many emerging biomedical applications that describes the behavior, stability, and long-term durability of physical interfaces in a specific range of frequency. Impedance measurements of any biointerface during in vivo and clinical applications could be used for assessing long-term biopotential measurements and diagnostic purposes. In this paper, a novel approach to predicting impedance behavior is presented and consists of a dimensional reduction procedure by converting EIS data over many days of an experiment into a one-dimensional sequence of values using a novel formula called day factor (DF) and then using a long short-term memory (LSTM) network to predict the future behavior of the DF. Three neural interfaces of different material compositions with long-term in vitro aging tests were used to validate the proposed approach. The results showed good accuracy in predicting the quantitative change in the impedance behavior (i.e., higher than 75%), in addition to good prediction of the similarity between the actual and the predicted DF signals, which expresses the impedance fluctuations among soaking days. The DF approach showed a lower computational time and algorithmic complexity compared with principal component analysis (PCA) and provided the ability to involve or emphasize several important frequencies or impedance range in a more flexible way.

Electrical Impedance-Based Characterization of Hepatic Tissue with Early-Stage Fibrosis

Liver fibrosis is a key pathological precondition for hepatocellular carcinoma in which the severity is confidently correlated with liver cancer. Liver fibrosis, characterized by gradual cell loss and excessive extracellular matrix deposition, can be reverted if detected at the early stage. The gold standard for staging and diagnosis of liver fibrosis is undoubtedly biopsy. However, this technique needs careful sample preparation and expert analysis. In the present work, an ex vivo, minimally destructive, label-free characterization of liver biopsies is presented. Through a custom-made experimental setup, liver biopsies of bile-duct-ligated and sham-operated mice were measured at 8, 15, and 21 days after the procedure. Changes in impedance were observed with the progression of fibrosis, and through data fitting, tissue biopsies were approximated to an equivalent RC circuit model. The model was validated by means of 3D hepatic cell culture measurement, in which the capacitive part of impedance was proportionally associated with cell number and the resistive one was proportionally associated with the extracellular matrix. While the sham-operated samples presented a decrease in resistance with time, the bile-duct-ligated ones exhibited an increase in this parameter with the evolution of fibrosis. Moreover, since the largest difference in resistance between healthy and fibrotic tissue, of around 2 kΩ, was found at 8 days, this method presents great potential for the study of fibrotic tissue at early stages. Our data point out the great potential of exploiting the proposed needle setup in clinical applications.

In Vitro Methods for Measuring the Permeability of Cell Monolayers

Cell monolayers, including endothelial and epithelial cells, play crucial roles in regulating the transport of biomolecules to underlying tissues and structures via intercellular junctions. Moreover, the monolayers form a semipermeable barrier across which leukocyte transmigration is tightly regulated. The inflammatory cytokines can disrupt the epithelial and endothelial permeability, thus the reduced barrier integrity is a hallmark of epithelial and endothelial dysfunction related with numerous pathological conditions, including cancer-related inflammation. Therefore, the assessment of barrier function is critical in in vitro models of barrier-forming tissues. This review summarizes the commercially available in vitro systems used to measure the permeability of cellular monolayers. The presented techniques are separated in two large groups: macromolecular tracer flux assays, and electrical impedance measurement-based permeability assays. The presented techniques are briefly described and compared.

A Microfluidic Dielectric Spectroscopy System for Characterization of Biological Cells in Physiological Media

Dielectric spectroscopy (DS) is a promising cell screening method that can be used for diagnostic and drug discovery purposes. The primary challenge of using DS in physiological buffers is the electrode polarization (EP) that overwhelms the impedance signal within a large frequency range. These effects further amplify with the miniaturization of the measurement electrodes. In this study, we present a microfluidic system and the associated equivalent circuit models for real-time measurements of cell membrane capacitance and cytoplasm resistance in physiological buffers with 10 s increments. The current device captures several hundreds of biological cells in individual microwells through gravitational settling and measures the system's impedance using microelectrodes covered with dendritic gold nanostructures. Using PC-3 cells (a highly metastatic prostate cancer cell line) suspended in cell growth media (CGM), we demonstrate stable measurements of cell membrane capacitance and cytoplasm resistance in the device for over 15 min. We also describe a consistent application of the equivalent circuit model, starting from the reference measurements used to determine the system parameters. The circuit model is tested using devices with varying dimensions, and the obtained cell parameters between different devices are nearly identical. Further analyses of the impedance data have shown that accurate cell membrane capacitance and cytoplasm resistance can be extracted using a limited number of measurements in the 5 MHz to 10 MHz range. This will potentially reduce the timescale required for real-time DS measurements below 1 s. Overall, the new microfluidic device can be used for the dielectric characterization of biological cells in physiological buffers for various cell screening applications.

[Organoids for the advancement of intraoperative diagnostic procedures]

In the context of cancer surgery, there is always a trade-off between oncological safety and preservation of function. This is especially true in pelvic surgery due to the close relationship to the pelvic floor muscles, blood supply and nerves. Currently, risk models, preoperative imaging, the surgeon's assessment, and the intraoperative frozen section serve as the basis for decision-making. New imaging techniques and standardization in frozen section have significantly improved this in recent years. However, limitations remain due to time delays as well as more difficult correct anatomical assignment in the follow-up. Alternative intraoperative techniques may overcome this limitation in the future. Patient-derived organoids have emerged as an important new research vehicle in recent years. They are based on tumor stem cells that, under special culture conditions, form three-dimensional replicas of the original tissue. This makes them ideally suited for testing individual system therapies but also as a validation technique for new intraoperative diagnostic procedures. The Research Training Group 2543/I, which is funded by the German Research Foundation, is researching the potential of new diagnostic methods in an interdisciplinary team regarding validation in addition to intraoperative frozen sections.

Comparison of Leading Biosensor Technologies to Detect Changes in Human Endothelial Barrier Properties in Response to Pro-Inflammatory TNFα and IL1β in Real-Time

Electric Cell-Substrate Impedance Sensing (ECIS), xCELLigence and cellZscope are commercially available instruments that measure the impedance of cellular monolayers. Despite widespread use of these systems individually, direct comparisons between these platforms have not been published. To compare these instruments, the responses of human brain endothelial monolayers to TNFα and IL1β were measured on all three platforms simultaneously. All instruments detected transient changes in impedance in response to the cytokines, although the response magnitude varied, with ECIS being the most sensitive. ECIS and cellZscope were also able to attribute responses to particular endothelial barrier components by modelling the multifrequency impedance data acquired by these instruments; in contrast the limited frequency xCELLigence data cannot be modelled. Consistent with its superior impedance sensing, ECIS exhibited a greater capacity than cellZscope to distinguish between subtle changes in modelled endothelial monolayer properties. The reduced resolving ability of the cellZscope platform may be due to its electrode configuration, which is necessary to allow access to the basolateral compartment, an important advantage of this instrument. Collectively, this work demonstrates that instruments must be carefully selected to ensure they are appropriate for the experimental questions being asked when assessing endothelial barrier properties.

The effects of MgS nanoparticles-Cisplatin-bio-conjugate on SH-SY5Y neuroblastoma cell line

Magnesium sulfide nanoparticles (MgS NPs) is a nanomaterial that has an important place in diagnosis, treatment, diagnosis, and drug delivery systems. Neuroblastoma, a type of brain cancer, is an extremely difficult cancer to treat with today's treatment options. This study was carried out to determine the cytotoxic, oxidant, and antioxidant effects on the neuroblastoma cancer line (SH-SY5Y cell line) along with the green synthesis and characterization of MgS NPs structures. MgS NPs were synthesized by green synthesis using Na₂S and Punica granatum, a cleaner method for toxic effects, and characterized using Scanning Electron Microscopy, Fourier Transform Infrared spectroscopy, X-Ray diffraction methods. In cell culture, SH-SY5Y cells were grown in a suitable nutrient medium under favorable conditions. Five different doses of MgS NPs (10, 25, 50, 75, and 100 µg/mL) were applied to the cell line for 24 h. The analysis of the MgS NPs applications was performed with MTT cytotoxicity test and total oxidant and total antioxidant tests. According to the data obtained, 75 μg/mL MgS NPs application decreased cancer cell viability up to 48.54%. MgS NPs exhibited a dose-dependent effect on the SH-SY5Y cell line. Also, it was determined that MgS NPs increased oxidant activity in neuroblastoma cells, which was compatible with the cytotoxicity test. As a result, MgS NPs exhibited an effective activity on the neuroblastoma cell line. It was clearly seen that NPs obtained by green synthesis prevented the related cancer line from proliferating.

Impedance-based drug-resistance characterization of colon cancer cells through real-time cell culture monitoring

Interest in impedance-based cellular assays is rising due to their remarkable advantages, including label-free, low cost, non-invasive, non-destructive, quantitative and real-time monitoring. In order to test their potential in cancer treatment decision and early detection of chemoresistance, we devised a new custom-made impedance measuring system based on electric cell-substrate impedance sensing (ECIS), optimized for long term impedance measurements. This device was employed in a proof of concept cell culture impedance analysis for the characterization of chemo-resistant colon cancer cells. Doxorubicin-resistant HT-29 cells were used for this purpose and monitored for 140 h. Analysis of impedance-based curves reveal different trends from chemo-sensitive and chemo-resistant cells. An impedance-based cytoxicity assay with different concentrations of doxorubicin was also performed using ECIS. The obtained results confirm the feasibility of ECIS in the study of drug resistance and show promises for studies of time-dependent factors related to physiological and behavioral changes in cells during resistance acquisition. The methodology presented herein, allows the continuous monitoring of cells under normal culture conditions as well as upon drug exposure. The ECIS device used, sets the basis for high-throughput early detection of resistance to drugs, administered in the clinical practice to cancer patients, and for the screening of new drugs in vitro, on patient-derived cells.