Real-time effects of Cd(II) on the cellular membrane permeability

An isolated single-particle-based SECM tip interface for single-cell NO sensing

As a key factor in cellular metabolic processes, nitric oxide (NO) is a challenging target for in situ real-time monitoring due to its transient property and short diffusion distance. Scanning electrochemical microscopy (SECM) has unique advantages in single-cell analysis, which can obtain the electrochemical current by scanning the cell surface with a tip microelectrode. In particular, it can further improved the electrochemical response by enhancing the interface properties of its tip. Here, an interface design strategy based on platinum single nanoparticle (Pt NP) was developed, and fluorinated self-assembled monolayers (SAMs) were used to further improve its performance. This modified tip was used as an SECM probe for NO concentration monitoring and morphological imaging of single MCF-7 cells. It has the high sensitivity (164.7 μA/μM·cm²) and good selectivity for NO detection, which benefits from the efficient catalytic properties of Pt NPs and high mass transport and hydrophobic antifouling properties of the interface. Notably, it shows a superior performance in detecting the fluctuation of NO released by a single MCF-7-cell under the stimulation of cadmium (Cd), which demonstrates a promising method for using a single-particle-based tip in SECM applications.

Inhibitory effects of zinc chloride (ZnCl2), n-acetyl-L-cysteine (NAC), and calcium/calmodulin dependent protein kinase II inhibitor (KN93) on Cd2+-induced abnormal cell morphology and membrane permeability

Cadmium (Cd) could reduce abnormal cell morphology and membrane permeability, however, there are few studies on the detoxification of Cd-reduced cell membrane toxicity. In the present study, we firstly studied the effects of zinc chloride (ZnCl₂), n-acetyl-L-cysteine (NAC), and calcium/calmodulin dependent protein kinase II inhibitor (KN93) on cell membrane permeability, respectively; then, we studied the inhibitory effects of ZnCl₂, NAC, and KN93 on Cd²⁺-induced abnormal cell membrane permeability by scanning electrochemical microscopy (SECM) scanning imaging, transverse scanning curve and DPV technology. Our results showed that 10 μmol·L^-1 ZnCl₂, 0.5 mmol·L^-1 NAC and 5 μmol·L^-1 KN93 could significantly improve the activity of MCF-7 cells, while did not destroy the cell morphology and membrane permeability. 0.5 mmol·L^-1 NAC and 5 μmol·L^-1 KN93 could significantly inhibit the effects of Cd²⁺ on the morphology and membrane permeability of MCF-7 cells (p < 0.01). 10 μmol·L^-1 ZnCl₂ could significantly inhibit the effect of Cd on the membrane permeability of MCF-7 cells, however, it cannot completely eliminate the morphological changes of MCF-7 cells caused by Cd²⁺. The results of cell activity experiment showed that 10 μmol·L^-1 ZnCl₂, 0.5 mmol·L^-1 NAC and 5 μmol·L^-1 KN93 could inhibit the effect of Cd²⁺ on the activity of MCF-7 cells. By comparing the inhibitory effects of ZnCl₂, NAC and KN93 on Cd²⁺- induced cytotoxicity, 5 μmol·L^-1 KN93 had the robust effect on the maintenance of MCF-7 cell morphology and cell membrane integrity. Our research provided evidence on Zn supplement, NAC as antioxidant drugs, and KN93 as special inhibitor for the detoxification of Cd²⁺-reduced abnormal cell morphology and membrane permeability.

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.