Determination of glutathione in cells by capillary electrophoresis-laser induced fluorescence

Glutathione (GSH) is vital for oxidative stress resistance and heavy metals detoxification. It is significant to develop a sensitive and accurate quantitative GSH approach for the toxicity mechanism for studying heavy metals in cells. A high-sensitive capillary electrophoresis-laser induced fluorescence (CE-LIF) detection approach was proposed in this study to detect GSH content in cells. The approach employed HepG2 cells as an object and 2,3-naphthalenedicarboxaldehyde (NDA) with the active group of aromatic o-dialdehyde as a labeling reagent. The effects of buffer solution types, pH, additives on the GSH reaction rate with NDA, and the sensitivity of NDA-GSH were systematically investigated. The sensitivity of NDA-GSH and the reaction rate of GSH with NDA were compared in tris(hydroxymethyl)aminomethane (Tris) buffer solution at pH 7.4 or 9.2 and borate-Tris buffer solution at pH 9.2. The results revealed that the NDA-GSH sensitivity was the highest and the reaction rate of GSH and NDA was the fastest in borate buffer solution at pH 9.2. The effects of the four additives on the sensitivity of NDA-GSH were further compared. The best additive was revealed to be β-cyclodextrin (β-CD). GSH reacted with NDA to reach equilibrium within 5 min under the optimal experimental conditions, and the electrophoretic signal of NDA-GSH could be seen in 3 min. Quantitative analysis of GSH in HepG2 cells was performed using an external standard approach by determining a series of GSH standard solutions. The results revealed that the approach had a good linear relationship with the peak area vs. concentration (0.01-20.00 mmol/L) of GSH. The limit of detection (LOD) and limit of quantification (LOQ) of GSH were determined using signal-to-noise ratios of 3 (S/N=3) and 10 (S/N=10), which were 0.006 μmol/L and 0.020 μmol/L, respectively. The approach's spiked recoveries were 95.7%-112.6%, with relative standard deviations of the approach being 3.8%-5.0% (n=3). This approach offers high sensitivity, good stability, accuracy, and reliability. To study the relationship between the toxicity of arsenic and chromium on HepG2 cells and the content of GSH in HepG2 cells, the effects of arsenic and chromium with different valences on cell viability were analyzed. The results illustrated that the cytotoxicity of potassium dichromate (Cr(Ⅵ)) was the strongest. The variations of GSH content in HepG2 cells stimulated with arsenite (As(Ⅲ)), arsenate (As(Ⅴ)), chromium chloride (Cr(Ⅲ)), and Cr(Ⅵ) were analyzed by the proposed approach and analysis of intracellular GSH imaging. The results revealed that the stimulation group i. e. analyzed doses (low-dose 2 mg/L, high-dose 5 mg/L) of As(Ⅲ), As(Ⅴ), and Cr(Ⅲ) had no obvious effect on GSH content in HepG2 cells compared with the control group, whereas high-dose Cr(Ⅵ) can significantly reduce GSH content in HepG2 cells. Considering the analysis of cytotoxicity of As(Ⅲ), As(Ⅴ), Cr(Ⅲ), and Cr(Ⅵ), it shows that the content of GSH in HepG2 cells is related to cytotoxicity, and the content of GSH will decrease with the increase in cytotoxicity.