The effects of long duration chronic exposure to hexavalent chromium on single live cells interrogated by scanning electrochemical microscopy

Investigating the Role of Extracellular Matrix Stiffness in Modulating the Ferroptosis Process in Hepatocellular Carcinoma Cells via Scanning Electrochemical Microscopy

Extracellular matrix (ECM) stiffness modulates a variety of cellular processes, including ferroptosis, a process with significant potential implications for hepatocellular carcinoma (HCC) fibrosis and cirrhosis. However, the exact relationship between ECM stiffness and HCC ferroptosis is yet unclarified, partially due to the lack of in situ information on key parameters of the ferroptosis process of living HCC cells. This study pioneers the use of in vitro mechanical microenvironment models of HCC and the scanning electrochemical microscopy (SECM) technique for understanding this interplay. We first cultured HuH7 cells on 4.0, 18.0, and 44.0 kPa polyacrylamide (PA) gels to simulate early, intermediate, and advanced HCC ECM stiffness, respectively. Then, we used SECM to in situ monitor changes in cell membrane permeability, respiratory activity, and reactive oxygen species (ROS) levels of erastin-induced HuH7 cells on PA gels, finding that increasing ECM stiffness potentiates ferroptosis, including increased membrane permeabilization and H2O2 release as well as reduced respiratory activity. Through further transcriptome sequencing and molecular biology measurements, we identified a critical role for focal adhesion kinase (FAK)-mediated yes-associated protein (YAP) in regulating the ferroptosis process dependent on ECM stiffness, which provides novel insights into the mechanical regulation of ferroptosis in HCC cells and may pave the way for innovative therapeutic strategies.

Temperature Effect on the Electrochemical Current Response during Scanning Electrochemical Microscopy of Living Cells

Scanning electrochemical microscopy (SECM) is being used increasingly to monitor electrochemical processes at the interface of living cells and electrodes. This allows the detection and quantification of biomarkers that further the understanding of various diseases. Rapid SECM experiments are often carried out without monitoring the analyte solution temperature or are performed at room temperature. The reported research demonstrates that temperature control is crucial during SECM imaging of living cells to obtain reliable data. In this study, a SECM-integrated thermostatic ring on the sample stage enabled imaging of living biological cells in a constant height mode at various temperatures. Two-dimensional line scans were conducted while scanning single Adenocarcinoma Cervical cancer (HeLa) cells. Numerical modeling was carried out to evaluate the effect of the temperature on the electrochemical current response of living cells to compare the apparent heterogeneous rate constant (k0), representing cellular reaction kinetics. This study reveals that even slight temperature variations of approximately 2 °C affect the reaction kinetics of single living cells, altering the measured current during SECM.

In Situ and Quantitatively Monitoring the Dynamic Process of Ferroptosis in Single Cancer Cells by Scanning Electrochemical Microscopy

Ferroptosis, as a promising therapeutic strategy for cancers, has aroused great interest. Quantifying the quick dynamic changes in key parameters during the early course of ferroptosis can provide insights for understanding the underlying mechanisms of ferroptosis and help the development of therapies targeting ferroptosis. However, in situ and quantitatively monitoring the quick responses of living cancer cells to ferroptosis at the single-cell level remains technically challenging. In this work, we selected HuH7 cells (hepatocellular carcinoma (HCC) cells) as a cell model and Erastin as a typical ferroptosis inducer. We utilized scanning electrochemical microscopy (SECM) to quantitatively and in situ monitor the early course of ferroptosis in HuH7 cells by characterizing the three key parameters of cell ferroptosis (i.e., cell membrane permeability, respiratory activity, and the redox state). The SECM results show that the membrane permeability of ferroptotic HuH7 cells continuously increased from 0 to 8.1 × 10-5 m s-1, the cellular oxygen consumption was continuously reduced by half, and H2O2 released from the cells exhibited periodic bursts during the early course of ferroptosis, indicating the gradually destroyed cell membrane structure and intensified oxidative stress. Our work realizes, for the first time, the in situ and quantitative monitoring of the cell membrane permeability, respiratory activity, and H2O2 level of the early ferroptosis process of a single living cancer cell with SECM, which can contribute to the understanding of the physiological process and underlying mechanisms of ferroptosis.

Allergic Contact Dermatitis in Refractory Brick Production Worker: A Case Report

In this study, we investigated a 42-year-old man working in a refractory brick (RB) production line who had allergic contact dermatitis (ACD) due to skin exposure to chromium (Cr). He had visited a dermatologist several times over a five-month period and although he had been medically treated, the symptoms reappeared after he returned to work and resumed exposure. Finally, with the announcement of the definite diagnosis of ACD through a patch test, it was decided to exclude him from exposure, and after 20 days, the symptoms went through the recovery process. No new recurring episodes were reported during the six-month follow-up period.

In Situ and Quantitatively Imaging of Heat-Induced Oxidative State and Oxidative Damage of Living Neurons Using Scanning Electrochemical Microscopy

Central nervous system is sensitive and vulnerable to heat. Oxidative state and oxidative damage of neurons under heat stress are vital for understanding early consequences and mechanisms of heat-related neuronal injury, which remains elusive partly due to the technical challenge of in situ and quantitative monitoring methods. Herein, a temperature-controlled scanning electrochemical microscopy (SECM) platform with programmable pulse potential and depth scan modes is developed for in situ and quantitatively monitoring of oxygen consumption, extracellular hydrogen peroxide level, and cell membrane permeability of neurons under thermal microenvironment of 37-42 °C. The SECM results show that neuronal oxygen consumption reaches a maximum at 40 °C and then decreases, extracellular H₂ O₂ level increases from 39 °C, and membrane permeability increases from 2.0 ± 0.6 × 10^-5 to 7.2 ± 0.8 × 10^-5 m s^-1 from 39 to 42 °C. The therapeutic effect on oxidative damage of neurons under hyperthermia conditions (40-42 °C) is further evaluated by SECM and fluorescence methods, which can be partially alleviated by the potent antioxidant edaravone. This work realizes in situ and quantitatively observing the heat-induced oxidative state and oxidative damage of living neurons using SECM for the first time, which results can contribute to a better understanding of the heat-related cellular injury mechanism.

Evaluation of the effect of nitrate and chloride on Cd(II)-induced cell oxidative stress by scanning electrochemical microscopy

Cadmium (Cd) is one of the most prevalent toxic metal pollutants, which is widely distributed in various environmental media and organisms. Literature studies have documented that Cd could stimulate cellular oxidative stress, and the increased intracellular reactive oxygen species (ROS) might destroy certain proteins and DNA and subsequently lead to cell apoptosis. Although several studies have studied the co-exposure between cadmium and other metals, information on the potential effects of Cd and its counterions is still lacking. In the present study, we explored the effects of nitrate and chloride on oxidative stress induced by Cd(II) at environmental exposure levels in human breast cancer cells (MCF-7) using scanning electrochemical microscopy (SECM). After incubation in CdCl₂ or Cd(NO₃)₂, ROS production is concentration-dependent and time-dependent, and the variation trend is consistent. When MCF-7 cells were incubated at a constant Cd²⁺ concentration, it was found that the higher the concentration ratio of Cd(NO₃)₂/CdCl₂, the less ROS was generated. Combined with cell-viability, intracellular acidification as well as antioxidants system tests, we observed that nitrate could be reduced to nitrite and then inhibit Cd-induced oxidative stress. Benefitting from real-time in situ imaging of cells by SECM, H₂O₂ was detected and quantified in a noninvasive way, and the effect of Cd at environmental exposure levels on cellular oxidative stress was explored deeper and more comprehensively. Prospectively, cytotoxicological methods based on the SECM technique would be established to explore toxic pollutant co-exposure issues at environmental exposure levels.

Application of scanning electrochemical microscopy for topography imaging of supported lipid bilayers

Oxidative stress in cellular environments may cause lipid oxidation and membrane degradation. Therefore, studying the degree of lipid membrane morphological changes by reactive oxygen and nitrogen species will be informative in oxidative stress-based therapies. This study introduces the possibility of using scanning electrochemical microscopy as a powerful imaging technique to follow the topographical changes of a solid-supported lipid bilayer model induced by reactive species produced from gas plasma. The introduced strategy is not limited to investigating the effect of reactive species on the lipid bilayer but could be extended to understand the morphological changes of the lipid bilayer due to the action of membrane proteins or antimicrobial peptides.

In situ monitoring of the effect of Cu2+ on the membrane permeability of a single living cell with a dual-electrode tip of a scanning electrochemical microscope

Here, an Au-Cu dual-electrode tip was designed to monitor the effect of Cu²⁺ on the membrane permeability of a single living cell in situ using scanning electrochemical microscopy. The probe approach curves (PACs) were obtained using potassium ferricyanide as a redox mediator. Meanwhile, according to the simulation, theoretical PACs could be acquired. Thus, the cell membrane permeability coefficient (P_m) values were obtained by overlapping the experimental PACs with the theoretical values. Cu²⁺ was directly generated by electrolyzing the Cu electrode of the dual-electrode tip to investigate its effect on the cell membrane permeability in situ. This work has potential value to improve the understanding of the mechanism of acute heavy metal damage on the cell membrane and will also help clarify the role of heavy metal ions in physiological or pathological processes.

Acceleration mechanism of bioavailable Fe(Ⅲ) on Te(IV) bioreduction of Shewanella oneidensis MR-1: Promotion of electron generation, electron transfer and energy level

The release of highly toxic tellurite into the aquatic environment poses significant environmental risks. The acceleration mechanism and tellurium nanorods (TeNPs) characteristics with bioavailable ferric citrate (Fe(III)) were investigated in the tellurite (Te(IV)) bioreduction. Experiments showed that 5 mM Fe(III) increased the Te(IV) bioreduction rate from 0 to 12.40 mg/(L·h). Cyclic voltammetry, electrochemical impedance spectroscopy and Tafel were used to investigate electron transfer during Te(IV) bioreduction. NADH production (electron production) was significantly enhanced to 138% by Fe(III). Meanwhile Fe(III) stimulated the increase of cytochrome c, resulting in increased electron transport system activity. In addition, Fe(III) facilitated the secretion of extracellular polymeric substances (EPS) and reduced cell membrane permeability, thus reducing the toxicity of Te(IV) to cells. The increase of ATP provided energy for the metabolic process of Te(IV) bioreduction, playing an active role in cell activity. Based on the above analysis, the acceleration mechanism of Fe(III) on Te(IV) bioreduction was proposed from the aspects of electron generation, electron transfer and energy level. Zeta potential and FT-IR spectra indicated that the stability of TeNPs contributed to the covered EPS. This study provides further understanding the acceleration mechanism of Te(IV) bioreduction and promising strategy for improving the stability of TeNPs.

Effect of hexavalent chromium on the biodegradation of tetrabromobisphenol A (TBBPA) by Pycnoporus sanguineus

The influence of Cr(VI) on the degradation of tetrabromobisphenol A (TBBPA) by a typical species of white rot fungi, Pycnoporus sanguineus, was investigated in this study. The results showed that P. sanguineus together with its intracellular and extracellular enzyme could effectively degrade TBBPA. The degradation efficiency of TBBPA by both P. sanguineus and its enzymes decreased significantly when Cr(VI) concentration increased from 0 to 40 mg/L. The subsequent analysis about cellular distribution of TBBPA showed that the extracellular amount of TBBPA increased with the increment of Cr(VI) concentration, but the content of TBBPA inside fungal cells exhibited an opposite variation tendency. The inhibition of TBBPA degradation by P. sanguineus was partly attributed to the increase of cell membrane permeability and the decrease of cell membrane fluidity caused by Cr(VI). In addition, the decline of H⁺-ATPase and Mg²⁺-ATPase activities was also an important factor contributing to the suppression of TBBPA degradation in the system containing concomitant Cr(VI). Moreover, the activities of two typical extracellular lignin-degrading enzymes of P. sanguineus, MnP and Lac, were found to descend with ascended Cr(VI) level. Cr(VI) could also obviously suppress the gene expression of four intracellular enzymes implicated in TBBPA degradation, including two cytochrome P450s, glutathione S-transferases and pentachlorophenol 4-monooxygenase, which resulted in a decline of TBBPA degradation efficiency by fungal cells and intracellular enzyme in the presence of Cr(VI). Overall, this study provides new insights into the characteristics and mechanisms involved in TBBPA biodegradation by white rot fungi in an environment where heavy metals co-exist.

Effects of Cr(VI)-induced calcium-sensing receptor activation on DF-1 cell pyroptosis

This study aims to investigate the effects of Cr(VI)-induced calcium-sensing receptor (CaSR) activation on DF-1 cell pyroptosis. Previous studies show that Cr(VI) could accumulate in the body of chickens and change Ca levels. Hence, a Ca-related pathway may be an important mechanism participating in some pathological processes. Pyroptosis level, which is meditated by CaSR, increases under Cr(VI) accumulation. In the present study, pyroptosis was determined by flow cytometry to detect SYTOX blue and caspase-1 staining followed by morphological observation. Interleukin (IL)-1β and IL-18 levels were detected by ELISA, while CaSR protein and [Ca²⁺]_i contents were detected by Western blot and fluorescence microplate spectrophotometry, respectively. The results showed that Cr(VI) causes DF-1 cell pyroptosis in a time- and dose-dependent manner and that this effect is caspase-1 dependent. Further experiments indicated that pyroptosis could be induced by Cr(VI) and is accompanied by up-regulated [Ca²⁺]_i content. CaSR inhibition led to decreases in pyroptosis level. Some mechanisms may be involved in Cr(VI)-triggered CaSR activation and enhance DF-1 cell pyroptosis. Taken together, the results of this study support future investigations on Cr(VI)-induced pyroptosis in DF-1 cells.

Systematic Analysis of Different Cell Spheroids with a Microfluidic Device Using Scanning Electrochemical Microscopy and Gene Expression Profiling

The 3D cell spheroid is an emerging tool that allows better recapitulating of in vivo scenarios with multiple factors such as tissue-like morphology and membrane protein expression that intimately coordinates with enzyme activity, thus providing a psychological environment for tumorigenesis study. For analyzing different spheroids, conventional optical imaging may be hampered by the need for fluorescent labeling, which could cause toxicity side effects. As an alternative approach, scanning electrochemical microscopy (SECM) enables label-free imaging. However, SECM for cell spheroid imaging is currently suffering from incapability of systematically analyzing the cell aggregates from spheroid generation, electrochemical signal gaining, and the gene expression on different individual cell spheroids. Herein, we developed a top-removable microfluidic device for cell aggregate yielding and SECM imaging methodology to analyze heterotypic 3D cell spheroids on a single device. This technique allows not only on-chip culturing of cell aggregates but also SECM imaging of the spheroids after opening the chip and subsequent qPCR assay of corresponding clusters. Through employment of the micropit arrays (85 × 4) with a top withdrawable microfluidic layer, uniformly sized breast tumor cell and fibroblast spheroids can be simultaneously produced on a single device. By leveraging voltage-switching mode SECM at different potentials of dual mediators, we evaluated alkaline phosphatase without disturbance of substrate morphology for distinguishing the tumor aggregates from stroma. Moreover, this method also enables gene expression profiling on individual tumor or stromal spheroids. Therefore, this new strategy can seamlessly bridge SECM measurements and molecular biological analysis.

Correlating Live Cell Viability with Membrane Permeability Disruption Induced by Trivalent Chromium

Cr(III) is often regarded as a trace essential micronutrient that can be found in many dietary supplements due to its participation in blood glucose regulation. However, increased levels of exposure have been linked to adverse health effects in living organisms. Herein, scanning electrochemical microscopy (SECM) was used to detect variation in membrane permeability of single cells (T24) resulting from exposure to a trivalent Cr-salt, CrCl₃. By employing electrochemical mediators, ferrocenemethanol (FcMeOH) and ferrocenecarboxylic acid (FcCOO^-), initially semipermeable and impermeable, respectively, complementary information was obtained. Three-dimensional COMSOL finite element analysis simulations were successfully used to quantify the permeability coefficients of each mediator by matching experimental and simulated results. Depending on the concentration of Cr(III) administered, three regions of membrane response were detected. Following exposure to low concentrations (up to 500 μM Cr(III)), their permeability coefficients were comparable to that of control cells, 80 μm/s for FcMeOH and 0 μm/s for FcCOO^-. This was confirmed for both mediators. As the incubation concentrations were increased, the ability of FcMeOH to permeate the membrane decreased to a minimum of 17 μm/s at 7500 μM Cr(III), while FcCOO^- remained impermeable. At the highest examined concentrations, both mediators were found to demonstrate increased membrane permeability. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability studies were also conducted on Cr(III)-treated T24 cells to correlate the SECM findings with the toxicity effects of the metal. The viability experiments revealed a similar concentration-dependent trend to the SECM cell membrane permeability study.

Analysing single live cells by scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) offers single live cell activities along its topography toward cellular physiology and pathology.

Biological imaging with scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) is a powerful and versatile technique for visualizing the local electrochemical activity of a surface as an ultramicroelectrode tip is moved towards or over a sample of interest using precise positioning systems. In comparison with other scanning probe techniques, SECM not only enables topographical surface mapping but also gathers chemical information with high spatial resolution. Considerable progress has been made in the analysis of biological samples, including living cells and immobilized biomacromolecules such as enzymes, antibodies and DNA fragments. Moreover, combinations of SECM with comple-mentary analytical tools broadened its applicability and facilitated multi-functional analysis with extended life science capabilities. The aim of this review is to present a brief topical overview on recent applications of biological SECM, with particular emphasis on important technical improvements of this surface imaging technique, recommended applications and future trends.