Comparison of glutathione levels measured using optimized monochlorobimane assay with those from ortho-phthalaldehyde assay in intact cells

Fluorometric glutathione assays have been generally preferred for their high specificity and sensitivity. An additional advantage offered by fluorescent bimane dyes is their ability to penetrate inside the cell. Their ability to react with glutathione within intact cells is frequently useful in flow cytometry and microscopy. Hence, the aims of our study were to use monochlorobimane for optimizing a spectrofluorometric glutathione assay in cells and then to compare that assay with the frequently used ortho-phthalaldehyde assay. We used glutathione-depleting agents (e.g., cisplatin and diethylmalonate) to induce cell impairment. For glutathione assessment, monochlorobimane (40μM) was added to cells and fluorescence was detected at 394/490nm. In addition to the regularly used calculation of glutathione levels from fluorescence change after 60min, we used an optimized calculation from the linear part of the fluorescence curve after 10min of measurement. We found that 10min treatment of cells with monochlorobimane is sufficient for evaluating cellular glutathione concentration and provides results entirely comparable with those from the standard ortho-phthalaldehyde assay. In contrast, the results obtained by the standardly used evaluation after 60min of monochlorobimane treatment provided higher glutathione values. We conclude that measuring glutathione using monochlorobimane with the here-described optimized evaluation of fluorescence signal could be a simple and useful method for routine and rapid assessment of glutathione within intact cells in large numbers of samples.

The determination of hepatic glutathione at tissue and subcellular level

INTRODUCTION

Glutathione (GSH) through its important function in the antioxidant protection of cells and in the conjugation of drugs and xenobiotics has crucial importance in pharmacology and toxicology. Since GSH is most often measured in liver tissue and different cell organelles it is important to choose the method that best suits for the determination of GSH.

METHODS

The GSH content of cell organelles isolated from control and BSO-treated liver tissues was determined by the GSH-NEM-HPLC-UV, monochlorobimane-GSH-HPLC-fluorescence method and DTNB-GSH recycling assay to find the most suitable method for GSH determination from cell organelles.

RESULTS

The GSH level of organelles could easily be measured by the monochlorobimane-HPLC-fluorescent method. The addition of monochlorobimane to the homogenisation buffer prevented the oxidation of GSH during isolation. The formation of monochlorobimane-GSH adduct was accelerated by the intrinsic GST activity of samples, however the omission of GST from the GSH standards could cause the overestimation of GSH content of biological samples. NEM is an excellent thiol protective agent and the GSH-NEM conjugate can be directly analysed by HPLC-UV, but the relatively high limit of detection made the method unsuitable for the determination of GSH from cell organelles. Although the DTNB-GSH recycling assay is quite simple and rapid the stabilization of GSH and the efficiency of detection lag behind the monochlorobimane-HPLC-fluorescent method.

DISCUSSION

The monochlorobimane-HPLC-fluorescent method can be advised for the determination of GSH from pharmacologically and toxicological relevant cell organelles and liver tissue whilst addition of monochlorobimane to the homogenisation buffer prevented the autoxidation of GSH.