Glutathione Regulates Interleukin-2 Activity on Cytotoxic T-cells

Effect of ageing on human plasma glutathione concentrations as determined by high-performance liquid chromatography with fluorimetric detection

A convenient method for the determination of reduced glutathione (GSH) and oxidized glutathione (GSSG) in human plasma by high-performance liquid chromatography with fluorescence detection is reported. This assay involves direct addition of human plasma to methanolic monobromobimane, for simultaneous protein precipitation and thiol derivatization. The assay was validated by addition of authentic GSH and GSSG to plasma samples. Plasma glutathione levels in Chinese male and female volunteers were found to decrease with increasing age (age groups 20-30, 30-40, 40-50, 50-60, and > 60; mean +/- S.E.M. 0.95 +/- 0.03, 0.77 +/- 0.02, 0.67 +/- 0.03, 0.51 +/- 0.02, 0.48 +/- 0.02 microM for male volunteers and 1.11 +/- 0.06, 0.76 +/- 0.03, 0.61 +/- 0.03, 0.53 +/- 0.04 and 0.43 +/- 0.04 microM for female volunteers). GSSG levels, in both males and females, did not show a correlation with age. There were no significant differences in GSH or GSSG levels among male and female volunteers of the same age group. These results suggest that elderly persons might be more susceptible to oxidative injury due to decreased plasma glutathione levels.

The modulation of IL-2 dependent proliferation of CTLL-2 cells by 2-methyl-thiazolidine-2,4-dicarboxylic acid

It is known that cysteine and other thiol compounds are able to modulate the immune response. The extracellular concentration of cysteine was shown to determine the intracellular level of glutathione (GSH). Thus cysteine, by enhancing GSH production, is able to affect some T-cell functions like IL-2 dependent cell proliferation and the generation of cytotoxic T cells. However, physiologically blood plasma cysteine is maintained at a very low concentration. The use of cysteine as a therapeutic compound in vivo is strongly limited due to its cytotoxicity. Recent studies demonstrate that N-acetyl-cysteine (NAC) as well as a variety of thiazolidine derivatives (TDs), which are the products of the reaction of L-cysteine with carbonyl compounds, could serve as a 'delivery' system for cysteine into the cell. In the present study, we have shown that 2-methyl-thiazolidine-2,4,-dicarboxylic acid (CP), the product of condensation of L-cysteine and pyruvate, strongly increases the proliferation of one particular cell line, IL-2 dependent CTLL-2 cells. We have also shown that this compound significantly increases the intracellular level of non-protein sulfhydryls (NPSH), but we did not find any correlation between NPSH levels and cell viability and proliferation. In contrast to CP, free cysteine showed its toxic properties by affecting cell viability of different cell lines and also by cancelling the influence of CP on the proliferation of CTLL cells.

Redox signalling and the control of cell growth and death

Cells maintain a reduced intracellular state in the face of a highly oxidizing extracellular environment. Redox signalling pathways provide a link between external stimuli, through the flavoenzyme-mediated NADPH-dependent reduction of intracellular peptide thiols, such as glutathione, thioredoxin, glutaredoxin, and redox factor-1, to the posttranslational redox modification of certain intracellular proteins. This can affect the proteins' correct folding, assembly into multimeric complexes, enzymatic activity, and their binding as transcription factors to specific DNA sequences. Such changes have been linked to altered cell growth and death.

Harry M. Vars Research Award. Glutamine enhances immunoregulation of tumor growth

BACKGROUND

It is known that tumor progression is associated with a depletion in host glutamine (Gln) stores and a depression of natural killer (NK) cell activity. After demonstrating an in vitro dependence of NK cell activity on Gln and glutathione concentration, this study evaluated the effects of oral Gln on Gln and glutathione metabolism, NK cell activity, and tumor growth in the tumor-bearing rat.

METHODS

Two days before tumor implantation, rats (n = 32) were randomized to receive Gln (1 g/kg/d) or an isonitrogenous amount of glycine by gavage and pair-fed food. On day 21 after tumor implantation, rats were killed, and tumors were measured and processed for glutaminase activity, glutathione content, and tumor morphometrics. Splenic lymphocytes were assayed for NK cell activity via a chromium (51Cr) release assay using YAC (NK-cell-sensitive mouse tumor cell line) target cells. Blood Gln and glutathione were measured. A second set of rats (n = 16) were treated similarly except that ketamine was given twice weekly to suppress NK cell activity.

RESULTS

During the 3-week study period, tumor growth was decreased by 40% in the Gln group. This decrease in growth was associated with a 30% increase in NK cell activity. Administration of ketamine to rats completely reversed the higher NK cell activity and decreased the tumor growth seen in the Gln-treated group.

CONCLUSIONS

These data indicate that oral Gln supplementation, through support of host Gln stores and glutathione production, may decrease tumor growth by enhancing NK cell activity.

Reduction of rigidity in human activated natural killer cells by thioglycollate treatment

Successful delivery of effector cells to tumor vasculature and the expression of cellular activities, such as extravasation and tumor infiltration are important aspects of the immune intervention of neoplastic disease. The structural rigidity of the effector cell, an indication of its cytoskeletal characteristics, plays an important role in influencing cellular functions and hemodynamic behavior as well as systemic distribution. The present study was designed to identify an agent which can modify the viscoelastic properties of human natural killer cells. A reducing compound, thioglycollate (TGA), was found to be an effective agent. Changes in cellular rigidity with respect to dose and duration of treatment with TGA were quantified. Micropipet aspiration was used to measure the resistance of NK cells to an imposed external deformation. Cultures of adherent human NK cells were expanded in interleukin 2 (IL-2) for 14 days, removed from culture and resuspended in medium with IL-2 and selected concentrations of TGA ranging from 0.032 mg/ml to 0.250 mg/ml. At 24 h intervals, the cell samples were removed and tested for their viscoelastic properties. Following 24 h of incubation, only TGA at 0.032 mg/ml produced a significant increase in cellular deformability. At 48 h of incubation, NK cell deformability was twice that obtained at 24 h. Higher concentrations of TGA also produced increased deformability after 48 h of incubation. Following 72 h of incubation, all concentrations of TGA tested produced increased deformability; however, the 0.032 mg/ml concentration produced the highest level of deformability combined with high viability (> 95%) as well as activated cell morphology. This treatment did not significantly alter the cytotoxic activity of these cells against a sensitive tumor target cell. These findings indicate that short term culture with TGA may be used to significantly reduce NK cell rigidity without decreasing cell viability or function. Thus, TGA may be a useful compound for altering the rheological properties of activated lymphocytes prior to adoptive transfer.

Glutathione increases interleukin-2 production in human lymphocytes

It is known that glutathione (GSH) has an immunological effect on several features of the immune system. The present study investigated the effects of GSH on interleukin-2 (IL-2) production from normal human peripheral blood lymphocytes (PBL). The results showed that both exogenous GSH and 2-mercaptoethanol (2-ME) significantly increased intracellular GSH levels after PBL were incubated with both agents. IL-2 production from PBL was markedly increased at the presence of exogenous GSH (0.5-8 mmol/l) or 2-ME (12.5-50 mumol/l) which corresponded to 1.57-2.82 nmol/10(6) cells and 1.41 - 1.80 nmol/10(6) cells of intracellular concentrations of GSH, respectively. However, IL-2 production seemed to reach a steady level when exogenous GSH concentrations in cell culture were between 2 and 8 mmol/l. The findings also showed that there was a positive correlation between the IL-2 concentrations and intracellular GSH levels. This study indicated that both exogenous GSH and 2-ME were able to elevate intracellular GSH levels and the increased intracellular GSH could increase IL-2 production in vitro. It is suggested that GSH may exert its effects on the immune system via the regulation of IL-2 synthesis.

Imbalance between oxidants and antioxidants in the lungs of HIV-seropositive individuals

Following the initial infection with HIV, there is evidence of immune dysfunction despite an apparent normal clinical state. In the context that the lung is a major site affected by opportunistic infection, and that some components of the immune system are activated during early HIV infection, we hypothesized that there may be activation of alveolar macrophages (AM), a key component of the pulmonary host defense system. Compared to cells from normal individuals, AM of asymptomatic HIV-seropositive (HIV+) individuals (CDC-stage II) spontaneously released significantly more superoxide anion (O2-.) (P < 0.002). The O2-. release by AM of HIV-infected individuals was comparable to the spontaneous O2-.-release by AM of cigarette smokers (P > 0.6), a condition often associated with chronic damage of respiratory tissues. The destructive effects of oxidants are normally suppressed by antioxidant defense systems. Evaluation of the concentrations of glutathione, a major component of the pulmonary antioxidant protective screen, demonstrated that the HIV+ state is also characterized by a significant glutathione deficiency in lung epithelial lining fluid (P < 0.001) and in venous plasma (P < 0.001). This suggests that the alveolar structures of HIV+ individuals are continuously exposed to increased amounts of toxic oxygen radicals without adequate protection, i.e. the reactive oxygen metabolites may cause sufficient tissue damage culminating in interstitial lung disease. Further, since many immune functions are susceptible to injury by extracellular oxidants, the consequences of an unsuppressed oxidant burden in the lung may amplify the extent of local immunocompromise. In addition, since glutathione plays an important role in modulating lymphocyte activation and effector functions independent of its antioxidant activity, the systemic glutathione deficiency may contribute to the progressive global immune dysfunction that characterizes HIV infection.

Exogenous glutathione attenuates the antiproliferative effect of buthionine sulfoximine

Buthionine sulfoximine (BSO) inhibits proliferation of human lung carcinoma A549 cells in a manner that does not correlate with intracellular glutathione (GSH) depletion, nor does it reflect overt toxic effects of BSO. However, BSO inhibits uptake by A549 cells of cystine, which is an essential amino acid for cell growth in culture. Thus, it is hypothesized that inhibition of cellular cystine uptake is, or is partially, responsible for the antiproliferative effect of BSO. It has been shown that the gamma-glutamyl amino acid transport system plays a role in cystine transport across cell membranes. This transport system requires extracellular GSH for its operation. BSO, by inhibiting intracellular GSH synthesis, would reduce GSH export and decrease extracellular GSH levels. Therefore, the present study was undertaken to examine the effect of exogenously added GSH on BSO inhibition of cellular cystine uptake and its relationship to the antagonistic effect of GSH on BSO antiproliferation. A549 cells were treated with 10 mM BSO and exogenous GSH was added to these BSO-treated cultures. Effects of exogenous GSH on BSO antiproliferation and cellular GSH depletion were determined simultaneously as a function of time. The effect of GSH on BSO inhibition of cystine accumulation was measured using [35S]cystine. The results obtained demonstrate that exogenously added GSH partially overcame BSO antiproliferation. The GSH antagonistic effect did not correlate with repletion of intracellular GSH, but it did correlate with recovery of BSO-inhibited cystine accumulation. Exogenous GSH also enhanced proliferation of non-BSO treated cells at concentrations below 1.0 mM. The results of this study suggest that BSO inhibition of cystine uptake may represent one mechanism by which BSO exerts its antiproliferative effect. The antagonistic effect of exogenous GSH on BSO antiproliferation may result from recovery of BSO-inhibited cystine uptake, although other mechanisms responsible for the GSH antagonistic effect may also exist.

Significance of glutathione in lung disease and implications for therapy

Glutathione is a tripeptide that contains an important thiol (sulfhydryl) group within the central cysteine amino acid. Glutathione is involved in numerous vital processes where the reducing potential of the thiol is used. Several lung disorders are believed to be characterized by an increase in alveolar oxidant burden, potentially depleting alveolar and lung glutathione. Low glutathione has been linked to abnormalities in the lung surfactant system and the interaction between glutathione and antiproteases in the epithelial lining fluid of patients. Normal levels of intracellular glutathione may exert a critical negative control on the elaboration of proinflammatory cytokines. The increase of intracellular reactive oxygen species is believed to correlate with the activation of NF-kappa B, a transcription activator linked to the elaboration of several cytokines. There is now sufficient data to strongly implicate free radical injury in the genesis and maintenance of several lung disorders in humans. This information is substantial and will help the development of clinical studies examining a variety of inflammatory lung disorders.

Interferon decreases serum lipid peroxidation products of hepatitis C patients

Thiobarbituric acid reactive substances (TBARS) concentration in serum has been determined in healthy subjects and in patients suffering acute hepatitis and chronic cases of hepatitis C. Treatment with interferon of the chronic active hepatitis C patients, 5 x 10(6) U three times a week during 2 months, led in those patients whose SGPT activity normalized in serum, to a concomitant decrease in serum TBARS content. The possible theoretical involvement of peroxidation and antioxidants in this beneficial effect of interferon in hepatitis C patients is discussed. The results presented confirm the value of TBARS as laboratory test in the management of liver diseases and as a useful tool for the study of pathogenic and/or therapeutic mechanisms of this viral infection.

Correction of glutathione deficiency in the lower respiratory tract of HIV seropositive individuals by glutathione aerosol treatment

BACKGROUND

Concentrations of glutathione, a ubiquitous tripeptide with immune enhancing and antioxidant properties, are decreased in the blood and lung epithelial lining fluid of human immunodeficiency virus (HIV) seropositive individuals. Since the lung is the most common site of infection in those who progress to AIDS it is rational to consider whether it is possible to safely augment glutathione levels in the epithelial lining fluid of HIV seropositive individuals, thus potentially improving local host defence.

METHODS

Purified reduced glutathione was delivered by aerosol to HIV seropositive individuals (n = 14) and the glutathione levels in lung epithelial lining fluid were compared before and at one, two, and three hours after aerosol administration.

RESULTS

Before treatment total glutathione concentrations in the epithelial lining fluid were approximately 60% of controls. After three days of twice daily doses each of 600 mg reduced glutathione, total glutathione levels in the epithelial lining fluid increased and remained in the normal range for at least three hours after treatment. Strikingly, even though > 95% of the glutathione in the aerosol was in its reduced form, the percentage of oxidised glutathione in epithelial lining fluid increased from 5% before treatment to about 40% three hours after treatment, probably reflecting the use of glutathione as an antioxidant in vivo. No adverse effects were observed.

CONCLUSIONS

It is feasible and safe to use aerosolised reduced glutathione to augment the deficient glutathione levels of the lower respiratory tract of HIV seropositive individuals. It is rational to evaluate further the efficacy of this tripeptide in improving host defence in HIV seropositive individuals.

Reduced glutathione recovers the impairment of the proliferative response of splenic lymphocytes from vitamin E-deficient rats

The effect of reduced glutathione (GSH) on the Con A induce proliferative response of splenic lymphocytes from rats fed a normal or vitamin E-deficient diet has been investigated. The animals were killed when they were 12 months old and after 11 months of dietary treatment. As was expected, a decreased response, measured in terms of blast transformation or [(3)H]thymidine incorporation, was observed in vitamin E-deficient animals when compared with the control group. This pattern can be accounted for by the large number of dead cells found in deficient animals. GSH addition into the culture medium resulted in a strong increase of the response in both groups and it eliminated the difference caused by the different dietary regimens. Taking into account that, during proliferation, an increase of respiration occurs which increases the risk of free radical production, present data suggest that GSH may substitute vitamin E in protecting the cells.

Mercuric chloride down-regulates T cell interferon-gamma production in brown Norway but not in Lewis rats; role of glutathione

Injection of a low dose of mercuric chloride into Brown Norway (BN) rats caused a marked decrease in the concanavalin A (ConA)-induced generation of interferon-gamma-producing cells (IFN-gamma pc) in spleen cell cultures prepared 1 h after mercury administration. A second injection 48 h later caused a further diminution of IFN-gamma pc down to 30% of the number generated in splenocyte cultures of phosphate-buffered saline (PBS)-injected controls. Injection of Lewis rats with either one or two doses of HgCl2 revealed no inhibitory effect on splenic IFN-gamma production. The presence of the reduced form of glutathione (GSH) in the culture medium was found to be essential in these experiments. In the absence of GSH there was an overall 20-fold reduction of the number of IFN-gamma pc in splenocyte cultures of normal or PBS-injected rats, which was further reduced to a 60- to 70-fold-lower level in cultures of rats exposed to HgCl2. This mercury-mediated extra reduction could be fully reversed with an excess (2 mM) of GSH in Lewis but not in BN splenocyte cultures. Since the bivalent Hg2+ ion is known to bind to and inactivate sulfhydryl groups of proteins and low molecular weight thiols, most notably GSH, we investigated a possible role for thiols in IFN-gamma production. It was found that the generation of IFN-gamma pc in normal BN and Lewis splenocyte cultures was strongly dependent on GSH or its precursor cysteine in the culture medium. Other thiol compounds were also effective but disulfides were completely inactive. Depletion of intracellular GSH in ConA-stimulated splenocytes by buthionine sulfoximide (BSO), an inhibitor of de novo GSH biosynthesis, strongly inhibited the generation of IFN-gamma pc. The inhibitory effect of BSO was not abolished by the addition of interleukin-2 (IL-2), but was mimicked with antibodies directed to the IL-2 receptor. The data stress the importance of GSH in the enhancement of IL-2-mediated IFN-gamma production and are most consistent with a model in which mercury interferes with T cell IFN-gamma production by affecting the intracellular availability of GSH. The strain-specific susceptibility to mercury-mediated inhibition of IFN-gamma production is discussed.

Loss of suppression of GSH synthesis at low cell density in primary cultures of rat hepatocytes

Primary cultures of adult rat hepatocytes shift into the growth phase when plated at low density (LD). We used this model to examine changes in glutathione (GSH) metabolism, since cells undergoing active growth may be more susceptible to environmental toxins. When primary cultures of adult rat hepatocytes were plated on collagen or Matrigel-precoated dishes, cell number and GSH varied inversely. This density effect on cell GSH occurred as early as 2 h after plating, when the media contained 1 mM methionine, but was delayed until 20 h if the media contained only 0.5 mM cystine. The density effect on GSH synthesis occurred in the absence of serum, hormones, changes in cell volume, GSH efflux, ATP levels, and uptake of methionine or cystine and was blocked by cycloheximide or actinomycin D. When methionine was available, the cellular cysteine level was 65% higher at LD than at high density (HD). gamma-Glutamylcysteine synthetase (GCS) activity was 64% higher at LD than at HD. GSH synthetase activity was unaffected by density. Both the increase in cellular cysteine levels and GCS activity were blocked by cycloheximide and actinomycin D. When cells were cocultured using cluster plates and Transwell inserts for 4 h, cell GSH of HD cells was unaffected by the density of cocultured cells; however, LD cells exhibited significantly lower GSH and GCS activity when cocultured with HD cells than when cocultured with LD cells. Cysteine levels were elevated in the LD cells regardless of the density of cocultured cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione influences the proliferation as well as the extent of mitochondrial activation in rat splenocytes

The time-dependent changes of mitochondrial membrane potential and mass have been investigated on rat splenic lymphocytes stimulated with Con A in the presence and absence of reduced glutathione (GSH). Rhodamine-123 (Rh-123) and nonyl acridine orange (NAO) were used as specific dyes to monitor the membrane potential and mass of mitochondria, respectively. The percentage of cells showing blast transformation and the level of Rh-123 or NAO uptake were analyzed by flow cytometry. Present results demonstrate that a large number of cells showed activated mitochondria already at 24 hr after Con A stimulation and the activation of these organelles was not related to blast transformation. The addition of GSH into the culture medium increased the number of cells responding to mitogenic stimulation. In parallel it augmented the percentage of lymphocytes with activated mitochondria and also prevented their depolarization.

Effects of 2-mercaptoethanol and buthionine sulfoximine on cystine metabolism by and proliferation of mitogen-stimulated human and mouse lymphocytes

Cysteine is an essential amino acid for lymphocytes and its anabolic products are intimately involved in lymphocyte activation. The purpose of this study was to assess the uptake and subsequent utilization of cyst(e)ine by mitogen-stimulated human peripheral blood mononuclear cells (PBMC), to evaluate the effect of an exogenous thiol, 2-mercaptoethanol (2ME), on these processes, and to compare human and mouse lymphocyte reactivities. Unlike mouse lymphocytes, the proliferation of human T-cells was inhibited by addition of 2ME although 2ME enhanced cystine uptake. Optimal responses to T-cell mitogens (Con A and PHA) were obtained with a cystine concentration of greater than or equal to 25 and 200 microM for human and mouse cells, respectively, and 2ME enhanced DNA synthesis of Con A-stimulated mouse cells regardless of the cystine dose; however, 2ME enhanced the response of human cells only in the presence of suboptimal doses of cystine. To assess whether 2ME's inability to enhance human PBMC responses was related to their glutathione (GSH) content, the human PBMC were pretreated with buthionine sulfoximine (BSO, an inhibitor of GSH synthesis). Even when the initial intracellular GSH concentration was lowered to below that of mouse lymphocytes, 2ME still inhibited proliferation. In contrast, addition of 2ME to human PBMC maintained in the presence of BSO enhanced the proliferative response suggesting that a critical level of thiols is needed for proliferation. The ability of 2ME to enhance proliferative responses in cystine deficient medium supports this contention. Consistent with thiol involvement in activation, Con A increased [35S]cystine uptake 2-fold within 4 h of incubation and enhanced subsequent conversion of cystine into cysteine and GSH. Interestingly, BSO treatment only slightly inhibited Con A-induced protein synthesis (5%), but it significantly suppressed conversion of cystine into cysteine or GSH (80-95%) and blocked DNA synthesis (90%). Overall, the results indicate that various differential thiol characteristics must exist between human and mouse lymphocytes and that a reducing equivalent is necessary for DNA synthesis but not lymphocyte activation.

Drug-induced modulation of IL-2 production in experimental murine trypanosomiasis

In this study we evaluated the effects of N-acetyl-cysteine and indomethacin in restoring IL-2 producing ability in vitro of splenocytes from mice infected with Trypanosoma equiperdum. Spleen cells from these mice were found to produce significantly lower levels of interleukin-2 (IL-2) in response to mitogen stimulation than spleen cells from uninfected control mice. This was accompanied by considerable suppression of IL-2-receptor expression, which was not attributable to the elimination of a particular T-cell subset. Impairment of IL-2 production was not due to a primary defect in L3T4+ T-cells, but rather to the presence of both adherent and non-adherent suppressor cells that apparently acted via prostaglandin-independent and dependent mechanisms. In fact, the IL-2-producing ability of lymphocytes from infected mice could be efficiently restored by in vitro exposure to N-acetyl-cysteine or indomethacin.

Effects of glutathione on the synthesis and turnover of interleukin-2 receptors

Internalization of IL-2 is important for its biological activities. The internalization of IL-2 was regulated by the duration of glutathione (GSH) treatment in CTLL-2 and CT-4R cells. Flow cytometric studies showed that the level of surface IL-2 receptors was not increased by GSH treatment. Northern blot analysis showed that the mRNA of IL-2Rp55 and IL-2Rp70, the two major components of the high-affinity IL-2 receptors, was increased 6 hr after GSH treatment. The appearance rate of membrane IL-2 receptors in GSH-treated cells was faster than that of the untreated cells. GSH also shortened the half-life (from 5 to less than or equal to 3 hr) and thus increased the turnover of the surface high-affinity IL-2 receptors. These results suggest that although GSH does not affect the level of surface IL-2 receptors, GSH may regulate the internalization of IL-2 by enhancing the synthesis and turnover of surface IL-2 receptors.

Vitamin E effects on in vitro immunoglobulin M and interleukin-1 beta production and transcription in dairy cattle

Experiments were conducted to determine the effect of dietary vitamin E on in vitro IgM and interleukin-1 production and its transcription by bovine peripheral blood mononuclear cells. Cells were isolated from Jersey cows and cultured with pokeweed mitogen, a T-cell-dependent, B-lymphocyte mitogen, to stimulate polyclonal IgM production. Addition of 55 and 110 ng/ml of alpha-tocopherol at time 0 to cell cultures containing pokeweed mitogen significantly enhanced IgM production compared with control cultures containing pokeweed mitogen alone. Cultures supplemented with 55 ng/ml of alpha-tocopherol at 0, 24, or 48 h after incubation with mitogen had enhanced IgM production compared with control cultures incubated for the same duration. However, addition of alpha-tocopherol to cultures at 72 and 96 h did not affect IgM production. Production of interleukin-1 in culture supernatants obtained 24 h after stimulation with pokeweed mitogen was similar between control cultures and cultures supplemented with alpha-tocopherol. At 48 h, secretion of interleukin-1 was maintained in the supplemented cultures but declined in control cultures. Mononuclear cells obtained from steers receiving vitamin E supplement or control steers were used to examine the effects of in vivo vitamin E status on interleukin-1 mRNA expression. Concanavalin A-stimulated cells from Jersey steers fed diets supplemented with vitamin E expressed 55% higher interleukin-1 mRNA than cells from control steers.

Dichotomy of glutathione regulation of the activation of resting and preactivated lymphocytes

The present study has examined the effect of GSH on two lines of IL-2-dependent activated killer cells, LAK cells and alpha CD3-activated killer (CD3-AK) cells. We found that GSH added during first 24 hr decreased the generation of LAK and CD3-AK cells from resting lymphocytes, whereas after 48 hr of activation, the addition of GSH increased the killer cell activity. In addition, BSO, an inhibitor of GSH biosynthesis, decreased the proliferation and cytotoxic activities of activated killer cells, and the inhibitory effect was reversed by GSH. These results indicate that GSH downregulates the generation of LAK or CD3-AK cells from resting lymphocytes, but it upregulates the further differentiation of preactivated killer cells. The effect of GSH thus varied with the state of activation of the killer cells. Culturing CD3-AK cells in GSH did not change the distribution of T cell subsets, did not affect the cells' ability to produce lymphokine (IL-2), and did not induce suppressor cells. One striking change as revealed by flow cytometry analysis was that the levels of IL-2 receptor and TCR (alpha/beta)-CD3 were reduced by 80 and 30%, respectively, after 48 hr culturing in GSH. Determination of the mRNA of IL-2 receptor suggests that a post-transcriptional block existed. It appears that the negative effect of GSH on the function of surface IL-2 receptors or T cell receptors on resting lymphocytes severely affected the signal transduction through these receptors and thus abrogated or reduced LAK or CD3-AK cell response. In contrast, for preactivated killer cells, upregulation by intracellular GSH of IL-2 utilization is a dominant effect, thus allowing further differentiation of these killer cells. Our results indicate that the balance between the activation signal (IL-2 or alpha CD3) and the immunoregulatory signal (induced by GSH) may determine the outcome of the immune response.

The effect of changes in thiol subcompartments on T-cell colony formation and cell cycle progression: relevance to AIDS

Recently, it has been shown that intra- and extracellular thiol levels are significantly lower than normal even in the relatively early stages of human immunodeficiency virus (HIV) infection. It is plausible that this deficiency could contribute both to the loss of T-cell function and the ability to replenish T cells associated with HIV infection. We had previously reported that the T-cell colony-forming cell (T-CFC) is impaired in HIV infection and that it can be enhanced with the thiol compounds 2-mercaptoethanol (2-ME) and N-acetylcysteine (NAC). In this study, the effect of the thiol-depleting reagents buthionine sulfoximine, cyclohexene-1-one, and copper phenanthroline on T-CFC formation and cell cycle progression was determined in HIV+ subject and/or controls. All three reagents inhibited T-CFC formation and cell cycle progression with a suggestion that colony formation by cells from HIV+ subjects was more sensitive to the effects of thiol depletion. 2-ME and NAC enhanced effect of NAC did not appear to involve increased protein kinase C translocation. Our results suggest that oxidation of membrane thiols, as well as depletion of intracellular glutathione, inhibits T-CFC formation as well as cell cycle progression for mitogen-stimulated cells in bulk culture.

Differential effects of glutathione depletion on T cell subsets

Glutathione (GSH) is known to play an important role in various lymphocyte functions. We now report that different T cell subsets express different requirements for intracellular GSH. Depletion of intracellular GSH by buthionine sulfoximine (BSO), a specific inhibitor of GSH biosynthesis, decreases the proportion of CD8+ cells (i.e., increases the CD4+/CD8+ ratio), and inhibits particularly the generation of large blast-like CD8+ cells and cytotoxic T lymphocyte (CTL) activity. CTL activity is restored by administration of exogenous GSH. Differential effects of GSH depletion were also seen at the level of individual T cell clones. The CD4+ helper T cell clone D10.G4.1.HD was found to express a high rate of interleukin 2 (IL-2) dependent DNA synthesis even after severe depletion of intracellular GSH, whereas other T cell clones including the clone 29 were severely inhibited by BSO. The results of these studies suggest that the decreased intracellular GSH levels of HIV-1 seropositive persons are probably not (directly) responsible for the selective depletion of the CD4+ T cell subset but may be responsible for a cellular dysfunction of the CD8+ subset and for the ultimate failure of the CTL to control the viral infection in these patients.

Low membrane transport activity for cystine in resting and mitogenically stimulated human lymphocyte preparations and human T cell clones

In order to determine whether the cysteine requirement of human T lineage cells is met primarily by extracellular cysteine or by cystine, amino-acid-transport activities were measured in resting and mitogenically stimulated human peripheral blood lymphocytes (PBL) and several human T cell clones and T cell tumors. The transport activity of the small neutral amino acids cysteine and alanine (ASC system) and the transport of the cationic amino acid arginine (y+ system) were found to be markedly increased after stimulation of PBL by the T cell mitogen phytohemagglutinin from Phaseolus vulgaris. The anionic transport activity for cystine and glutamate (Xc- system), in contrast, was extremely weak in both resting and activated human PBL and also in all human T cell lines under test. The weak system Xc- activity of human T lineage cells was further confirmed by an independent line of experiments showing that an increase of the extracellular concentration of glutamate, i.e. a competitive inhibitor of cystine transport, causes a decrease in the intracellular cystine levels in cells of the promonocytic line U937, but not in T lineage cells (Molt-4). A third set of experiments showed that the rate of DNA synthesis in mitogenically stimulated human PBL is strongly influenced by variations of the extracellular cysteine level, even in cultures with relatively high and approximately physiological concentrations of cystine. Cysteine cannot be replaced in this case by the addition of corresponding amounts of cystine or methionine. This demonstrates an important functional consequence of the weak cystine transport activity of human lymphocytes. The results may be relevant for the pathogenetic mechanism of the acquired immunodeficiency syndrome, since the mean plasma cysteine concentration of human-immunodeficiency-virus-1-seropositive persons was found to be strongly decreased in comparison with that of healthy blood donors, and since the cysteine level even of healthy persons is extremely low in comparison with all other protein-forming amino acids.

Effect of selenium and reducing agents on in vitro immunoglobulin M synthesis by bovine lymphocytes

A series of experiments was conducted to evaluate the effects of inorganic and organic forms of Se with or without reducing agents on in vitro IgM production by bovine lymphocytes. Peripheral mononuclear cells were isolated from nonlactating Jersey cows fed a diet with adequate Se. Cells were stimulated with pokeweed mitogen and, in addition, were cultured with various Se compounds at a concentration of 100 ng Se/ml. Mercaptoethanol (50 microM) and glutathione (1 mM) were included in cultures of cells stimulated by pokeweed mitogen with and without inorganic Se. Sodium selenite was less effective than selenomethionine and selenocystine in augmenting pokeweed mitogen-induced Ig synthesis. The addition of mercaptoethanol to pokeweed mitogen-stimulated control cultures enhanced in vitro IgM production, whereas the addition of glutathione had a negligible effect, but addition of either in combination with sodium selenite dramatically depressed IgM production. These results suggest that Se in inorganic or organic forms enhances B-cell function in vitro.

Regulation of intracellular glutathione levels and lymphocyte functions by lactate

The plasma concentration of lactate varies strongly under physiological and pathological conditions in the range of 1 to 30 mM. High but physiologically relevant lactate concentrations were previously shown to exert strong immunopotentiating effects and to augment the production of interleukin 2 (IL-2). However, the lactate derivative pyruvate can form covalent complexes with cysteine, suggesting the possibility that lactate may affect indirectly intracellular glutathione (GSH) levels and GSH-dependent lymphocyte functions. The experiments in this report now showed that 20-30 mM lactate had virtually no effect on the viability and intracellular protein content of mitogenically stimulated accessory cell-depleted splenic T cells or unfractionated spleen cells but indeed caused a marked decrease of the intracellular GSH level when compared with control cultures after 40-70 hr of incubation. The DNA synthesis of mitogenically stimulated splenic T cell cultures, i.e., a strongly GSH-dependent function, was also inhibited by lactate. This effect was overcome by high extracellular concentrations of GSH or cysteine. Lactate also inhibited the IL-2 consumption in mitogenically stimulated CD8+ T cell cultures and the activation of cytotoxic T lymphocytes in the late phase of mixed lymphocyte cultures. Additional experiments showed, finally, that lactate augments the incorporation of [14C]aspartate into 18 S and 28 S RNA, while incorporation of [14C]uridine is moderately inhibited, indicating that the de novo synthesis of pyrimidine nucleosides is markedly augmented in cells that are exposed to high extracellular lactate concentrations. Taken together, these studies show that high but physiologically relevant concentrations of lactate exert strong positive and negative effects on distinct aspects of T cell-mediated immune responses.

Glutathione and inflammatory disorders of the lung

Glutathione (GSH) is an essential tripeptide present in most eukaryotic cells. Because of its sulfhydryl group, GSH is a versatile molecule capable of protecting cells against oxidants and toxic xenobiotics. However, it also plays key roles in multiple metabolic pathways, such as the synthesis of certain leukotrienes, proteins, and DNA precursors as well as the activation of enzymes, the regulation of immune responses and others. Not only is GSH synthesized by cells for local use but it also participates in an elaborate intercellular exchange process regulated by the gamma-glutamyl cycle. Extracellular GSH in plasma and in alveolar epithelial lining fluid is thus subject to variations according to the degree of expression of gamma-glutamyl cycle enzymes and the rate of consumption of GSH by electrophilic molecules. Bronchoalveolar lavage has allowed us to observe many of these variations of GSH within the extracellular environment of the normal and diseased human lung. Studies of lung GSH have lead to a better understanding of pathogenic processes and have stimulated investigations of novel therapeutic approaches in lung inflammatory disorders.

Correlations and apparent contradictions in assessment of oxidant stress status in vivo

Oxidative modifications of biological molecules are essential, but uncontrolled or excessive oxidative activities appear to contribute to many disease states. The mechanisms through which excess oxidant activities cause injury have been studied most extensively for acute responses, particularly for drug-induced tissue damage and cell death, but substantial evidence suggests that chronically elevated oxidative activity may contribute to the development of diseases such as cancer. It is important that the correlation between oxidant stress status and cancer risk be examined directly in humans. A number of methods have been developed for assessing oxidant activities by measuring oxidized products in biological systems, but cross-comparison studies of these different methods are needed. In studies of mechanisms of acute hepatotoxicity, assessments of oxidant stress responses by different analytical methods often have provided data that appear at first glance to be contradictory. Marked oxidant stress responses may be indicated by one or more methods of analysis despite the lack of detectable change in other parameters, whereas in a second experimental model the responses may be reversed. These observations emphasize the need to integrate different analytical approaches into the assessment of oxidant activity in vivo and illustrate the importance for developing a better understanding of the chemical and physiological mechanisms through which the analytical methodologies are related.

Proliferative capacity of human peripheral blood lymphocytes sorted on the basis of glutathione content

Glutathione (GSH) is important in defense against oxygen free radical damage, in detoxification of xenobiotics, and in mitogenesis. The reducing conditions provided by low molecular weight thiols such as 2-mercaptoethanol (ME) have been shown to promote the growth of lymphocytes in culture. We wished to determine the effects of 2-ME on GSH content, and to determine to what extent GSH status affected lymphocyte proliferation. GSH content was quantitated in human peripheral blood lymphocytes (PBL) using a flow cytometric assay with monochlorobimane. This analysis was performed on PBL as well as on the CD4+ T-cell subset, as identified with fluorescent anti-CD4 monoclonal antibodies (mAb). Cells were viably sorted on the basis of their GSH content, and incubated for 3 days with mitogenic concentrations of PHA (for PBL) or anti-CD3 mAb (for CD4+ cells) in the presence of bromodeoxyuridine (BrdU). BrdU/Hoechst cell cycle analysis was then performed on these cells. High GSH sorted cells had a higher percentage of cells capable of entering the cell cycle than low GSH sorted cells. This data indicates that some of the heterogeneity in proliferative capacity within PBL in culture is directly or indirectly related to GSH content. Incubation of cells in 2-ME prevented the loss of GSH that occurs when cells are cultured. 2-ME improved the proliferative capacity of unsorted cells, and of cells sorted for high and low GSH. Acridine orange staining of anti-CD3 mAb stimulated cells sorted for high and low GSH indicated that an early event in cell activation was affected by GSH content.

Interleukin-2 mRNA expression, lymphokine production and DNA synthesis in glutathione-depleted T cells

The stimulation of DNA synthesis in lymphocyte populations was previously shown to depend strongly on the intracellular glutathione (GSH) level. Since T cell growth is known to depend on interleukin 2 (IL-2), the experiments in this report were designed to determine whether intracellular GSH depletion may inhibit IL-2 production or the IL-2 dependent DNA synthesis. Our experiments revealed that IL-2 production and DNA synthesis of mitogenically stimulated splenic T cells have indeed different requirements for GSH. The addition of relatively high concentrations of GSH (5 mM) to cultures of concanavalin A (Con A)-stimulated splenic T cells was found to augment strongly the DNA synthesis but inhibited the production of IL-2. Moderate intracellular GSH levels, however, are apparently not inhibitory for IL-2 production, since intracellular GSH depletion by cysteine starvation or by graded concentrations of DL-buthionine sulfoximine (BSO) had virtually no effect on IL-2-specific mRNA expression and the production of T cell growth factor (TCGF). The DNA synthesis activity, in contrast, was strongly suppressed after GSH depletion with either method. As in cultures of splenic T cells, GSH depletion had no substantial effect on the induction of IL-2 mRNA and TCGF production in several mitogenically stimulated T cell clones. Taken together, our experiments suggest that complex immune response may operate best at intermediate GSH levels that are not too high to inhibit IL-2 production but sufficient to support DNA synthesis.

Macrophages regulate intracellular glutathione levels of lymphocytes. Evidence for an immunoregulatory role of cysteine

Macrophages consume cystine and generate approximately equivalent amounts of acid-soluble thiol. Stimulation of macrophages with bacterial lipopolysaccharide (LPS) or tumor necrosis factor (TNF) strongly augments the amount of thiol released into the culture supernatant. Cysteine constitutes most of the acid-soluble thiol. The intracellular glutathione level and the DNA synthesis activity in mitogenically stimulated lymphocytes are strongly increased by either exogenously added cysteine, or (syngeneic) macrophages. This cysteine dependency is observed even in the presence of relatively high extracellular cystine concentration as they occur in the blood plasma. The extracellular cysteine concentration also has a strong influence on the intracellular glutathione concentration, viability, and DNA synthesis of cycling T cell clones. Moreover, the cysteine concentration in the culture medium on Day 3 and Day 4 of a 5-day allogeneic mixed lymphocyte culture (i.e., in the late phase of incubation) has a strong influence on the generation of cytotoxic T cell activity, indicating that regulatory effects of cysteine are not restricted to the early phase of the blastogenic response. The inhibitory effect of cysteine starvation on the DNA synthesis of the T cell clones and on the activation of cytotoxic T lymphocytes can be explained essentially by the depletion of intracellular glutathione, since similar effects are observed after treatment with buthionine sulfoximine (BSO), a specific inhibitor of the glutathione biosynthesis. BSO has practically no influence, however, on the N alpha-benzyloxycarbonyl Ne-t-butyloxycarbonyl-L-lysine-thiobenzyl-ester (BLT)-esterase activity and hemolytic activity of the cell lysates from cytotoxic T cells against sheep red blood cells (perforin activity). Taken together, our experiments indicate that cysteine has a regulatory role in the immune system analogous to the hormone-like lymphokines and cytokines. It is released by macrophages at a variable and regulated rate and regulates immunologically relevant functions of lymphocytes in the vicinity.

Involvement of gamma-glutamyl peptides in osmoadaptation of Escherichia coli

Accumulation of K+ ions and glutamate plays a primary role in maintaining osmotic balance in Escherichia coli, as illustrated by the high concentrations of these ions present in cells growing in medium of high osmolality. We found that two gamma-glutamyl peptides and glutamine also accumulated during growth at high osmolarity. In a mutant unable to make trehalose growing in 1.3 osM medium, glutathione, gamma-glutamylglutamine, and glutamine accumulated to levels of 73, 33, and 140 mumol/g of protein, respectively. In such cells, K+ was present at 1,450 mumol/g of protein, indicating that glutathione and gamma-glutamylglutamine accounted for less than 10% of the low-molecular-weight anions accumulated with K+. However, glutathione is needed for wild-type osmotolerance in this species. A mutant deficient in glutathione because of an insertion in the gshA gene was unable to grow above 1.4 osM, grew more slowly at intermediate osmolarities, and took longer to adapt to growth following osmotic upshock. The involvement of glutathione in osmoregulation was independent of the effect of glutathione on K+ retention.