Flow cytometric measurement of glutathione content of human cancer biopsies

Spectral flow cytometry: Fundamentals and future impact

Spectral flow cytometry has emerged as a significant player in the cytometry marketplace, with the potential for rapid growth. Despite a slow start, the technology has made significant strides in advancing various areas of single-cell analysis utilized by the scientific community. The integration of spectral cytometry into clinical laboratories and diagnostic processes is currently underway and is expected to garner a significant level of widespread acceptance in the near future. However, incorporating a new methodological approach into existing research programs can lead to misunderstandings or even misuse. This chapter offers an introductory yet comprehensive explanation of the scientific principles that form the foundation of spectral cytometry. Specifically, it delves into the unmixing processes that are utilized for data analysis. This overview is designed for those who are new to the field and seeking an informative guide to this exciting emerging technology.

Novel use of the fluorescent dye 5-(and-6)-chloromethyl SNARF-1 acetate for the measurement of intracellular glutathione in leukemic cells and primary lymphocytes

Glutathione (GSH) plays an important role in protecting cells against injury, particularly during oxidative stress. Alterations in GSH metabolism are becoming the focus of attention in many diseases such as cancer, neurodegeneration, and AIDS. As such, a rapid assessment of GSH levels in a clinical setting is of increasing importance. We tested the efficacy of the thiol-labeling fluorescent dye CM-SNARF in its ability to measure variations in GSH concentration using a visible-light flow cytometer. GSH levels in I83, Jurkat, and primary lymphocytes were depleted with buthionine sulfoximine (BSO) or diamide, or increased with N-acetylcysteine (NAC). Following each treatment, cells were divided and either labeled with CM-SNARF followed by flow cytometry analysis, or assayed for GSH using a biochemical method. BSO treatment caused a maximal 87-90% decrease in GSH and 68-76% decrease in fluorescence units. Diamide depleted GSH 91-95%, corresponding to a fluorescence decrease of 85-88%. NAC treatment increased GSH levels 27% and fluorescence 12-19%. The overall correlation (R2) between mean GSH concentration and mean fluorescence was 0.80-0.88. CM-SNARF can be used to semi-quantitatively and rapidly determine intracellular variations in GSH concentration in the range of 10-150 nmoles GSH/mg protein.

Use of flow cytometry and monochlorobimane to quantitate intracellular glutathione concentrations in feline leukocytes

Oxidative stress and abnormal glutathione metabolism is thought to play an important role in various diseases of cats. However, current assays for the reduced form of glutathione (GSH) are time-consuming and semi-quantitative and do not allow assessment of GSH concentrations in individual cell populations. Therefore, we developed a flow cytometric assay for rapid determination of intracellular GSH concentrations in feline blood leukocytes. The assay was based on the ability of the non-fluorescent substrate monochlorobimane (mBCl) to form fluorescent adducts with GSH in a reaction catalyzed by the enzyme glutathione-S-transferase. Using flow cytometry, we found that mBCl was sensitive and specific for intracellular detection of the reduced form of GSH in feline leukocytes. Intracellular GSH concentrations were also stable for at least 24h in EDTA preserved whole blood samples stored at 4 degrees C. Neutrophils and monocytes from normal cats had significantly higher intracellular concentrations of GSH than T cells and B cells. The effects of FIV infection on intracellular GSH concentrations in cats were assessed using flow cytometry. We found that neutrophils from FIV-infected cats had significantly increased GSH concentrations, whereas intracellular GSH concentrations were significantly decreased in CD4(+) and CD8(+) lymphocytes from FIV-infected cats, compared to age-matched control animals. We conclude that a flow cytometric assay based on mBCl may be used to accurately and rapidly assess the effects of various disease states and treatments on GSH concentration in cat leukocytes and to help assess intracellular oxidative stress.

Multifunctional redox catalysts as selective enhancers of oxidative stress

Certain cancer cells proliferate under conditions of oxidative stress (OS) and might therefore be selectively targeted by redox catalysts. Among these catalysts, compounds containing a chalcogen and a quinone redox centre are particularly well suited to respond to the presence of OS. These catalysts combine the specific electrochemical features of quinones and chalcogens. They exhibit high selectivity and efficiency against oxidatively stressed rat PC12, human Jurkat and human Daudi cells in cell culture, where their mode of action most likely involves the catalytic activation of existent and the generation of new reactive oxygen species. The high efficiency and selectivity shown by these catalysts makes them interesting for the development of anti-cancer drugs.

Monochlorobimane fluorometric method to measure tissue glutathione

Glutathione (GSH) is the principal intracellular low-molecular-weight thiol and plays a critical role in the cellular defense against agents that impose oxidative stress. A common technique to measure GSH uses reversed-phase high-performance liquid chromatography (HPLC) following derivatization with 5, 5'-dithiobis(2-nitrobenzoic acid), a technique, although reliable and sensitive, that is time consuming and laborious. A common technique to measure GSH in cultured cells is to add monochlorobimane to the culture medium where it readily enters cells to form a fluorescent GSH-monochlorobimane adduct that can be measured fluorometrically. This reaction is catalyzed by glutathione S-transferase. We reasoned that adding glutathione S-transferase and monochlorobimane to tissue homogenates would allow a rapid reliable method to measure GSH. The accuracy of the new test was assessed in homogenates of rat livers. One-half of each homogenate was assayed for GSH using a HPLC approach while the other half was assayed using the monochlorobimane approach. The two methods were found to give identical results. We conclude that the monochlorobimane fluorescent method is sufficiently specific to reliably measure tissue GSH.

The effect of in vitro phorone exposure on glutathione content and T cell antigen receptor (CD3)-stimulated calcium mobilization in murine splenic T lymphocytes

An increase in cytosolic free calcium ([Ca(2+)](i)) is one of the earliest events to occur in T lymphocytes following stimulation of the transmembrane T cell receptor/CD3 complex (TCR/CD3). This [Ca(2+)](i) mobilization has been found to be sensitive to intracellular thiol redox status, which in turn is modulated by cellular glutathione (GSH) content. We have previously reported that GSH depletion, by treatment with either the alpha, beta-carbonyl diethyl maleate or the aromatic halo-compound 1-chloro-2,4-dinitrobenzene, correlates with decreased [Ca(2+)](i) mobilization in anti-CD3 monoclonal antibody (mAb)-stimulated human peripheral blood lymphocytes (HPBL). This prompted us to determine whether this correlation between GSH content and TCR/CD3 signal transduction capability was also present in murine lymphocytes, since the mouse model is often used as a surrogate for the human immune system. The results presented here demonstrate that in vitro treatment with the alpha, beta-carbonyl phorone dose-dependently depletes intracellular GSH in murine splenic T lymphocytes. Both CD4(+) and CD8(+) T lymphocytes depleted of GSH by greater than 40% were found to have a decreased [Ca(2+)](i) mobilization following anti-CD3 mAb stimulation. Similar to what has been described for HPBL, these results indicate that the cellular GSH status influences the initial response of murine T lymphocytes to TCR/CD3 stimulation.

Determination of glutathione and related aminothiols by gas chromatography with flame photometric detection

A selective and sensitive method for the determination of glutathione (GSH) and related aminothiols such as cysteine (Cys), cysteinylglycine (CysGly) and gamma-glutamylcysteine (gamma-GluCys) by gas chromatography (GC) has been developed. GSH and related aminothiols were converted into their N,S-isopropoxycarbonyl methyl ester derivatives and measured by GC with flame photometric detection using a short capillary column (5 m x 0.53 mm i.d.) of cross-linked DB-1. The calibration curves were linear in the range 1-25 nmol for GSH and in the range 0.2-5 nmol for other aminothiols, and the detection limits of GSH, Cys, CysGly and gamma-GluCys were approximately 5, 0.2, 0.3 and 0.5 pmol per injection respectively. This method was successfully applied to blood samples without prior clean-up, and GSH and related aminothiols in these samples could be analysed without any influence from coexisting substances. Overall recoveries of GSH and other aminothiols added to blood samples were 88-107%. The analytical results of free and total blood GSH and related aminothiols in normal subjects are presented.

Kinetic analysis of glutathione in anchored cells with monochlorobimane

A method for the measurement of intracellular glutathione content and glutathione S-transferase activity with monochlorobimane in adherent cells is described. The method involves the kinetic analysis of monochlorobimane conjugation to glutathione over a relatively short period of time. This permits extrapolation over time for determination of equilibrium fluorescence intensity (relative glutathione level) from scan intensity data that follows first-order kinetics, minimizing problems commonly associated with the use of monochlorobimane. By using measured fluorescence intensity values from glutathione standards, a suspension calibration curve was generated and, subsequently, was used to determine the photomultiplier tube saturation rate. A theoretical intracellular calibration curve was then generated to quantify glutathione content in cells. This method was also applied to study the changes in glutathione in a variety of rodent and human cell lines and in selected cocultures of cells exhibiting similar or different glutathione levels. Comparison of the glutathione levels obtained with monochlorobimane and a standard colorimetric method (GSH-400) indicated good correlation between the two methods. These studies support the use of laser cytometry for measuring intracellular glutathione with monochlorobimane as well as changes in glutathione occurring in cells that establish physical contacts with other cells. Laser cytometric analysis of glutathione in anchored cells also provides opportunities to monitor individual cellular responses to a variety of experimental manipulations, such as responses to various toxic insults or the protective effects of gap junction-mediated intercellular communication.

Glutathione metabolism in primary astrocyte cultures: flow cytometric evidence of heterogeneous distribution of GSH content

The time-course of intracellular glutathione (GSH) values after incubation with L-buthionine-(S,R)-sulfoximine (BSO), a selective inhibitor of gamma-glutamylcysteine synthetase, showed that glutathione turns over with a half-life of 5 h. Intracellular GSH was assayed by flow cytometry using three different methods. Astrocytes showed a narrow range of cellular size but a wide range of intracellular GSH. This heterogeneity was resolved into three distinct subpopulations which represent 20%, 35% and 45% of the total astrocyte number. The less abundant subpopulation had the lower GSH content, while the most abundant was the subpopulation with the higher content. Over 95% of astrocytes were in the G0/G1 phase of the cell cycle, the distribution of cytosolic pH was homogeneous and the number of viable cells at the time of the assay was 90%. These results show that several pools exist when astrocyte GSH is considered and these findings may be relevant to the understanding of brain GSH metabolism.

Intracellular glutathione heterogeneity in L1210 murine leukemia sublines made resistant to DNA-interacting anti-neoplastic agents

Intracellular glutathione (GSH) content was measured by flow cytometry using monochlorobimane (mBCl) and by the enzymatic assay in a set of 6 sublines of murine L1210 leukemia cells made resistant to DNA-interacting agents having distinct mechanisms of action: L-phenylalanine mustard (L-PAM), 1,3-bis(2-chloroethyl)-I-nitrosourea (BCNU), cisplatin (DDP), N-deformyl-N-(4-N,N-bis(2-chloroethylamino) benzoyl) distamycin A (FCE 24517), doxorubicin (DX) and 3'-deamino-3' (2-methoxy-4-morpholinyl)-doxorubicin (FCE 23762). A significant correlation was demonstrated between the mean intracellular mBCl fluorescence values measured by flow cytometry and levels of GSH measured by the classical enzymatic assay, despite the possible influence of glutathione-S-transferases and of other thiols on the mBCl fluorescence. Although less specific, the flow cytometric method is more informative than the enzymatic assay, allowing detection of fluorescence distributions, which we proved to be characteristic of each subline. In order to assess a procedure enabling a quantitative analysis to be made of intercellular GSH heterogeneity, we propose the use of appropriate thresholds and parameters of the mBCl flow cytometric distribution. By use of this analysis procedure, distinct types of alterations, with respect to the heterogeneity distribution of the parental L1210 cell line, have been evidenced in resistant cells. A uniform increase in mBCl fluorescence was observed among cells of the sublines resistant to L-PAM and FCE-24517. The mean mBCl fluorescence increase in sublines resistant to DX and DDP was due to a higher number of cells with fairly high mBCl fluorescence, but still within the range spanned by the parental cell line. A less heterogeneous mBCl fluorescence distribution was found in the L1210 subline resistant to FCE 23762, which was, however, similar to a cloned sensitive line. Though GSH was linked to the principal cause of drug resistance only in the L-PAM-resistant cell line, alterations in heterogeneity, as detected by mBCl fluorescence distributions, were found in 5 out of 6 resistant lines.

Identification of multi-drug resistant cells in sensitive Friend leukemia cells by quantitative videomicrofluorimetry

The cellular resistance to cytotoxic drugs, particularly to anthracyclines, remains a major problem in cancer chemotherapy. A number of biochemical mechanisms have been described, one of them being a lower accumulation of drugs in resistant cells. The accumulation of Ho33342 in sensitive and resistant Friend leukemia cells was studied by quantitative fluorescence image analysis, a method which allows investigations to be made on living tissues and cells. The intensity of fluorescence is related to the amount of Ho33342 accumulated into the cells and has been found to be more intense in sensitive cells than in resistant ones. Moreover, the retention of this vital dye was inversely related to the degree of resistance in the three resistant cell lines. The addition of verapamil, which is known to reverse resistance to anthracyclines, resulted in an increase of the amount of Ho33342 accumulated in the resistant cells. Ho33342 presents a higher quantum yield than any other anthracyclines, such as adriamycin and can be used as a microfluorimetric probe to identify the resistant cells in a heterogeneous cell population.