Quantitative characterization of capsaicin-induced TRPV1 ion channel activation in HEK293 cells by impedance spectroscopy

TRPV1 blockers as potential new treatments for psychiatric disorders

The transient receptor potential vanilloid-1 channel (TRPV1) is responsible for decoding physical and chemical stimuli. TRPV1 is activated by capsaicin (a compound from chili peppers), heat (above 43°C) and acid environment, playing a major role in pain, inflammation and body temperature. Molecular and histological studies have suggested TRPV1 expression in specific brain regions, where it can be activated primarily by the endocannabinoid anandamide, fostering studies on its potential role in psychiatric disorders. TRPV1 blockers are effective in various animal models predictive of anxiolytic and antipanic activities, in addition to reducing conditioned fear. In models of antidepressant activity, these compounds reduce behavioral despair and promote active stress-coping behavior. TRPV1 blockers also reduce the effects of certain drugs of abuse and revert behavioral changes in animal models of neurodevelopmental disorders. The main limiting factor in developing TRPV1 blockers as therapeutic agents concerns their effects on body temperature, particularly hyperthermia. New compounds, which block specific states of the channel, could represent an alternative. Moreover, compounds blocking both TRPV1 and the anandamide-hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), termed dual TRPV1/FAAH blockers, have been investigated with promising results. Overall, preclinical studies yield favorable results with TRPV1 blockers in animal models of psychiatric disorders.

Reactive Sputtered Silicon Nitride as an Alternative Passivation Layer for Microelectrode Arrays in Sensitive Bioimpedimetric Cell Monitoring

Microelectrode arrays (MEAs) are widely used to study the behavior of cells noninvasively and in real time. While the design of MEAs focuses mainly on the electrode material or its application-dependent modification, the passivation layer, which is crucial to define the electrode area and to insulate the conducting paths, remains largely unnoticed. Because often most cells are in direct contact with the passivation layer rather than the electrode material, biocompatible photoresists such as SU-8 are almost exclusively used. However, SU-8 is not without limitations in terms of optical transmission, optimal cell support, or compatibility within polymer-based microfluidic lab on chip systems. Here, we established a silicon nitride (SiN) passivation by physical vapor deposition (PVD), which was optimized and evaluated for impedance spectroscopy-based monitoring of cells. Surface characteristics, biocompatibility, and electrical insulation capability were investigated and compared to SU8 in detail. To investigate the influence of the SiN passivation on the impedimetric analysis of cells, HEK-293 A and MCF-7 were chosen as adherent cell models and measured on microelectrodes of 50-200 μm in diameter. The results clearly revealed an overall suitability of SiN as alternative passivation. While for the smallest electrode size a cell line dependent comparable or slightly decreased cell signal could be observed in comparison with SU-8, a significant higher cell signal was observed for microelectrodes larger than 50 μm in diameter. Furthermore, a high suitability for the bonding of PEGDA and PDMS microfluidic structures on the SiN passivation layer without any leakage could be demonstrated.

Correlation between electrical characteristics and biomarkers in breast cancer cells

Both electrical properties and biomarkers of biological tissues can be used to distinguish between normal and diseased tissues, and the correlations between them are critical for clinical applications of conductivity (σ) and permittivity (ε); however, these correlations remain unknown. This study aimed to investigate potential correlations between electrical characteristics and biomarkers of breast cancer cells (BCC). Changes in σ and ε of different components in suspensions of normal cells and BCC were analyzed in the range of 200 kHz-5 MHz. Pearson's correlation coefficient heatmap was used to investigate the correlation between σ and ε of the cell suspensions at different stages and biomarkers of cell growth and microenvironment. σ and ε of the cell suspensions closely resembled those of tissues. Further, the correlations between Na⁺/H⁺ exchanger 1 and ε and σ of cell suspensions were extremely significant among all biomarkers (p_ε < 0.001; p_σ < 0.001). There were significant positive correlations between cell proliferation biomarkers and ε and σ of cell suspensions (p_ε/σ < 0.05). The microenvironment may be crucial in the testing of cellular electrical properties. ε and σ are potential parameters to characterize the development of breast cancer.

High-Throughput Methods in the Discovery and Study of Biomaterials and Materiobiology

The complex interaction of cells with biomaterials (i.e., materiobiology) plays an increasingly pivotal role in the development of novel implants, biomedical devices, and tissue engineering scaffolds to treat diseases, aid in the restoration of bodily functions, construct healthy tissues, or regenerate diseased ones. However, the conventional approaches are incapable of screening the huge amount of potential material parameter combinations to identify the optimal cell responses and involve a combination of serendipity and many series of trial-and-error experiments. For advanced tissue engineering and regenerative medicine, highly efficient and complex bioanalysis platforms are expected to explore the complex interaction of cells with biomaterials using combinatorial approaches that offer desired complex microenvironments during healing, development, and homeostasis. In this review, we first introduce materiobiology and its high-throughput screening (HTS). Then we present an in-depth of the recent progress of 2D/3D HTS platforms (i.e., gradient and microarray) in the principle, preparation, screening for materiobiology, and combination with other advanced technologies. The Compendium for Biomaterial Transcriptomics and high content imaging, computational simulations, and their translation toward commercial and clinical uses are highlighted. In the final section, current challenges and future perspectives are discussed. High-throughput experimentation within the field of materiobiology enables the elucidation of the relationships between biomaterial properties and biological behavior and thereby serves as a potential tool for accelerating the development of high-performance biomaterials.

Single-cell impedance analysis of osteogenic differentiation by droplet-based microfluidics

Single-cell analysis is critical to understanding its heterogeneity and biological processes, such as stem cell differentiation, and elucidating the underlying mechanisms of cellular metabolism. New tools to promote intercellular variability studies help elucidate cellular regulation mechanisms. Here an impedance measurement and analysis system was built to monitor the osteogenic differentiation of single bone marrow mesenchymal stem cells (BM-MSCs) in droplets. The biochip including a microelectrode array was designed based on droplet microfluidics and fabricated. A novel theoretical electrical model was proposed to simulate the electrical properties of cells in the droplets. Impedance measurements showed that single cells are substantially heterogeneous during osteoblast differentiation at different stages (days 0, 7, 14 and 21) and different cell passages (passages 6, 7 and 11). This result was consistent with the appearance of two biomarkers (alkaline phosphatase and calcium nodules), which are the gold standard biomarkers of osteoblastogenesis and differentiation. The device enabled highly efficient single-cell trapping, accurate positioning, and sensitive, label-free and noninvasive impedance measurements of individual cells with multiple channels. This system provides a strategy for exploring the processes of osteoblastogenesis and differentiation at the single-cell level and has substantial potential for applications in the biomedical field.

High-Density Electrical Recording and Impedance Imaging With a Multi-Modal CMOS Multi-Electrode Array Chip

Multi-electrode arrays, both active or passive, emerged as ideal technologies to unveil intricated electrophysiological dynamics of cells and tissues. Active MEAs, designed using complementary metal oxide semiconductor technology (CMOS), stand over passive devices thanks to the possibility of achieving single-cell resolution, the reduced electrode size, the reduced crosstalk and the higher functionality and portability. Nevertheless, most of the reported CMOS MEA systems mainly rely on a single operational modality, which strongly hampers the applicability range of a single device. This can be a limiting factor considering that most biological and electrophysiological dynamics are often based on the synergy of multiple and complex mechanisms acting from different angles on the same phenomena. Here, we designed a CMOS MEA chip with 16,384 titanium nitride electrodes, 6 independent operational modalities and 1,024 parallel recording channels for neuro-electrophysiological studies. Sixteen independent active areas are patterned on the chip surface forming a 4 × 4 matrix, each one including 1,024 electrodes. Electrodes of four different sizes are present on the chip surface, ranging from 2.5 × 3.5 μm² up to 11 × 11.0 μm², with 15 μm pitch. In this paper, we exploited the impedance monitoring and voltage recording modalities not only to monitor the growth and development of primary rat hippocampal neurons, but also to assess their electrophysiological activity over time showing a mean spike amplitude of 144.8 ± 84.6 μV. Fixed frequency (1 kHz) and high sampling rate (30 kHz) impedance measurements were used to evaluate the cellular adhesion and growth on the chip surface. Thanks to the high-density configuration of the electrodes, as well as their dimension and pitch, the chip can appreciate the evolutions of the cell culture morphology starting from the moment of the seeding up to mature culture conditions. The measurements were confirmed by fluorescent staining. The effect of the different electrode sizes on the spike amplitudes and noise were also discussed. The multi-modality of the presented CMOS MEA allows for the simultaneous assessment of different physiological properties of the cultured neurons. Therefore, it can pave the way both to answer complex fundamental neuroscience questions as well as to aid the current drug-development paradigm.

Large-Ring Cyclodextrins as Chiral Selectors for Enantiomeric Pharmaceuticals

Large-ring cyclodextrins (CD) are cyclic glucans composed of 9 or more α-1,4-linked glucose units. They are minor side products of bacterial glucanotransferases (CGTases, EC 2.4.1.19) and have previously been available only in very small amounts for studies of their properties in supramolecular complex formation reactions. We engineered a CGTase to synthesize mainly large-ring CD facilitating their preparation in larger amounts. By reversed phase chromatography, we obtained single CD samples composed of 10 to 12 glucose units (CD10, CD11, and CD12) with a purity of >90 %. Their identity was confirmed by high resolution mass spectrometry and fragmentation analysis. We demonstrated the non-toxicity of CD10-CD12 for human cell lines by a cell proliferation assay and impedimetric monitoring. We then showed that CD10 and CD11 are efficient chiral selectors for the capillary electrophoretic separation of the enantiomeric pharmaceuticals fluvastatin, mefloquine, carvedilol, and primaquine.

Label-Free Whole Cell Biosensing for High-Throughput Discovery of Activators and Inhibitors Targeting G Protein-Activated Inwardly Rectifying Potassium Channels

Dynamic mass redistribution (DMR) and cellular dielectric spectroscopy (CDS) are label-free biosensor technologies that capture real-time integrated cellular responses upon exposure to extra- and intracellular stimuli. They register signaling routes that are accompanied by cell shape changes and/or molecular movement of cells proximal to the biosensor to which they are attached. Here, we report the unexpected observation that robust DMR and CDS signatures are also elicited upon direct stimulation of G protein-activated inwardly rectifying potassium (GIRK) channels, which are involved in the regulation of excitability in the heart and brain. Using ML297, a small-molecule GIRK activator, along with channel blockers and cytoskeletal network inhibitors, we found that GIRK activation exerts its effects on cell shape by a mechanism which depends on actin but not the microtubule network. Because label-free real-time biosensing (i) quantitatively determines concentration dependency of GIRK activators, (ii) accurately assesses the impact of GIRK channel blockers, (iii) is high throughput-compatible, and (iv) visualizes previously unknown cellular consequences downstream of direct GIRK activation, we do not only provide a novel experimental strategy for identification of GIRK ligands but also an entirely new angle to probe GIRK (ligand) biology. We envision that DMR and CDS may add to the repertoire of technologies for systematic exploitation of ion channel function and, in turn, to the identification of novel GIRK ligands in order to treat cardiovascular and neurological disorders.

A novel microfluidic microelectrode chip for a significantly enhanced monitoring of NPY-receptor activation in live mode

Lab-on-a-chip devices that combine, e.g. chemical synthesis with integrated on-chip analytics and multi-compartment organ-on-a-chip approaches, are a fast and attractive evolving research area. While integration of appropriate cell models in microfluidic setups for monitoring the biological activity of synthesis products or test compounds is already in focus, the integration of label-free bioelectronic analysis techniques is still poorly realized. In this context, we investigated the capabilities of impedance spectroscopy as a non-destructive real-time monitoring technique for adherent cell models in a microfluidic setup. While an initial adaptation of a microelectrode array (MEA) layout from a static setup revealed clear restrictions in the application of impedance spectroscopy in a microfluidic chip, we could demonstrate the advantage of a FEM simulation based rational MEA layout optimization for an optimum electrical field distribution within microfluidic structures. Furthermore, FEM simulation based analysis of shear stress and time-dependent test compound distribution led to identification of an optimal flow rate. Based on the simulation derived optimized microfluidic MEA, comparable impedance spectra characteristics were achieved for HEK293A cells cultured under microfluidic and static conditions. Furthermore, HEK293A cells expressing Y1 receptors were used to successfully demonstrate the capabilities of impedimetric monitoring of cellular alterations in the microfluidic setup. More strikingly, the maximum impedimetric signal for the receptor activation was significantly increased by a factor of 2.8. Detailed investigations of cell morphology and motility led to the conclusion that cultivation under microfluidic conditions could lead to an extended and stabilized cell-electrode interface.