Relationships between the cellular glutathione level and in vitro life span of human diploid fibroblasts

Intracellular Glutathione in Human Peritoneal Mesothelial Cells Exposed in vitro to Dialysis Fluid

Effect of peritoneal dialysis fluids on glutathione (GSH/GSSG) level in human peritoneal mesothelial cells was tested in in vitro experiments. To mimic in vivo conditions, cells were initially exposed to dialysis fluids (Dianeal 1.36%, Dianeal 2.27%, Dianeal 3.86%) that subsequently were diluted with dialysate effluent at time intervals. GSH/GSSG concentration in cells initially decreased but returned to normal values thereafter. This decrease in the intracellular concentration of glutathione was less when pH of the tested dialysis fluid was adjusted to 7.3. In further experiments with mesothelial cells exposed to Earle's salts solution supplemented with glucose and/or lactate, we have shown that in the presence of low pH, lactate is the main factor causing depletion of intracellular glutathione. When added to the dialysis solution at a concentration of 0.1 mM, L-2-oxothiazolidine-4-carboxylate, a precursor of glutathione, not only prevents the initial decrease in glutathione concentration but also augments the final intracellular level of this thiol.

Action of bis(betachloroethyl)sulphide (BCES) on human epidermis reconstituted in culture: Morphological alterations and biochemical depletion of glutathione

Human keratinocyte cultures were treated with bis(betachloroethyl)sulphide (BCES), an alkylating and vesicant agent. At concentrations of 5 x 10(-4) to 5 x 10(-3)m, spontaneous detachment of the epithelium from the culture plate was observed, reproducing in vitro the cutaneous vesication observed in vivo. Progressive cellular alterations were shown with increasing concentrations of BCES (5 x 10(-5) to 5 x 10(-3)m). At low concentrations (5 x 10(-5)m), lesions of the nucleus, a significant target for BCES, were observed, along with lesions in the cytoplasmic organelles. An acute, dose-dependent depletion of cellular glutathione was observed, which occurred within 1 hr of treatment. Mechlorethamine, an analogue of BCES, induced at equivalent doses the same glutathione depletion and similar spontaneous detachment in vitro. We suggest that BCES, in addition to its genetic effects, acts by direct metabolic toxicity and induces glutathione depletion by direct conjugation. The lesions obtained in vitro reproduced those observed in vivo. Human keratinocyte cultures can be proposed as a good model for the study of the mechanisms of action of BCES.

Effects of methanolic extracts from broad beans on cellular growth and antioxidant enzyme activity

OBJECTIVE

There are several reports of cellular-aging-dependent alterations in the antioxidant capacity of human fibroblasts. Fibroblasts show slower the growth rate at late passages (referred to hereafter as old cells) than at early passages (referred to hereafter as young cells). Antioxidants may control cellular growth by modulating reactive oxygen species (ROS). Methanolic extracts from broad beans (MEBB) contain phenolic compounds and have ROS-scavenging activities. In this study, we investigated the effects of MEBB on cellular growth and antioxidant levels in normal human lung fibroblasts.

METHODS

To determine cytosolic superoxide dismutase (SOD) activities, cytosolic glutathione peroxidase (GSH-Px) activities, catalase activities, reduced glutathione (GSH) concentrations, and growth rate, MEBB treatments were performed on young and old cells.

RESULTS

In young and old cells treated with 120 μg/ml MEBB, the growth rates increased by 28.1 and 15.2%, respectively, compared with controls. The MEBB treatment of young cells caused a 62.5% increase in SOD activity, but the treatment of old cells caused a 39.5% decrease. The catalase activities of the young and old cells treated with MEBB were equal to those of control cells. Young and old cells treated with MEBB were equal to the control cells in terms of GSH-Px activity. The GSH concentrations in the young and old cells treated with 120 μg/ml MEBB increased by 22.1 and 45.9%, respectively.

CONCLUSION

These studies elucidated a new cellular growth mechanism whereby human lung fibroblasts modulate intracellular GSH levels via the action of MEBB.

Redox regulation, gene expression and longevity

Lifespan can be lengthened by genetic and environmental modifications. Study of these might provide valuable insights into the mechanism of aging. Low doses of radiation and short-term exposure to heat and high concentrations of oxygen prolong the lifespan of the nematode Caenorhabditis elegans. These might be caused by adaptive responses to harmful environmental conditions. Single-gene mutations have been found to extend lifespan in C. elegans, Drosophila and mice. So far, the best-characterized system is the C. elegans mutant in the daf-2, insulin/IGF-I receptor gene that is the component of the insulin/IGF-I signaling pathway. The mutant animals live twice as long as the wild type. The insulin/IGF-I signaling pathway regulates the activity of DAF-16, a FOXO transcription factor. However, the unified explanation for the function of DAF-16 transcription targets in the lifespan extension is not yet fully established. As both of the Mn superoxide dismutase (MnSOD) isoforms (sod-2 and sod-3) are found to be targets of DAF-16, we attempted to assess their functions in regulating lifespan and oxidative stress responsivity. We show that the double deletions of sod-2 and sod-3 genes induced oxidative-stress sensitivity but do not shorten lifespan in the daf-2 mutant background, indicating that oxidative stress is not necessarily a limiting factor for longevity. Furthermore, the deletion in the sod-3 gene lengthens lifespan in the daf-2 mutant. We conclude that the MnSOD systems in C. elegans fine-tune the insulin/IGF-I-signaling based regulation of longevity by acting not as anti-oxidants but as physiological-redox-signaling modulators.

Early onset senescence occurs when fibroblasts lack the glutamate-cysteine ligase modifier subunit

Cellular senescence is the irreversible entry of cells into growth arrest. Senescence of primary cells in culture has long been used as an in vitro model for aging. Glutamate-cysteine ligase (GCL) controls the synthetic rate of the important cellular antioxidant glutathione (GSH). The catalytic subunit of GCL, GCLC, is catalytically active and essential for life. By contrast the modifier subunit of GCL, GCLM, is dispensable in mice. Although it is recognized that GCLM increases the rate of GSH synthesis, its physiological role is unclear. Herein, we show that loss of Gclm leads to premature senescence of primary murine fibroblasts as characterized by: (a) diminished growth rate, (b) cell morphology consistent with senescence, (c) increases in senescence-associated beta-galactosidase activity, and (d) cell cycle arrest at the G(1)/S and G(2)/M boundaries. These changes are accompanied by increased intracellular ROS, accumulation of DNA damage, and induction of p53 and p21 proteins. We also found that N-acetylcysteine increases intracellular GSH and prevents premature senescence in Gclm(-/-) cells. These results suggest that the control of GCLM, which in turn controls aspects of the cellular redox environment via GSH, is important in determining the replicative capacity of the cell.

Replicative senescence: a critical review

Human cells in culture have a limited proliferative capacity. After a period of vigorous proliferation, the rate of cell division declines and a number of changes occur in the cells including increases in size, in secondary lysosomes and residual bodies, nuclear changes and a number of changes in gene expression which provide biomarkers for senescence. Although human cells in culture have been used for over 40 years as models for understanding the cellular basis of aging, the relationship of replicative senescence to aging of the organism is still not clear. In this review, we discuss replicative senescence in the light of current information on signal transduction and mitogenesis, cell stress, apoptosis, telomere changes and finally we discuss replicative senescence as a model of aging in vivo.

Effects of ambient oxygen concentration on the growth and antioxidant defenses of of human cell cultures established from fetal and postnatal skin

Oxygen toxicity is believed to arise from changes in the rates at which cells generate reactive oxygen species (ROS). Sensitivity to hyperoxia has been postulated to depend on levels of antioxidant defense. Human cells obtained from fetal tissues have lower antioxidant defenses than those obtained from adult tissue. The present study was performed to determine whether the differences in fetal and adult antioxidant defense levels modulated their responses to changes in the ambient oxygen concentration. Our results demonstrate that oxygen modulates the proliferation of human fetal and adult skin fibroblasts in a similar fashion. In general, skin fibroblasts grew better at approximately 31 mm Hg, regardless of donor age. Manganese superoxide dismutase, catalase, and glutathione peroxidase activities were lower in fetal cells than in adult fibroblasts. Copper/zinc superoxide dismutase and glucose-6-phosphate dehydrogenase were similar in fetal and postnatal tissues and were unaltered appreciably by hyperoxic exposure. Glutathione concentration increased at higher oxygen tensions; however, the increase was much greater in fetal cells than in cultures derived from adult skin. These observations demonstrate that the capacity of fetal and adult cells to cope with oxidative stress, while similar, result from distinct mechanisms.

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.

Effect of a diet supplemented with thioproline on murine macrophage function in a model of premature ageing

A previous study has shown that diet supplementation with thioproline (thiazolidine-4-carboxylic acid, TCA), an intracellular sulfhydril antioxidant and free radical scavenger, stimulates lymphocyte functions in old mice. In the present work, the effect of thioproline ingestion on the phagocytic functions of peritoneal macrophages, namely adherence, chemotaxis, phagocytosis and superoxide anion production was studied in adult female OF1-Swiss mice, that were fed thioproline (0.1% w/w) for five weeks, starting this ingestion at the age of 22 +/- 2 weeks. Mice were divided into a fast and a slow group based on their exploratory activity, which was assessed by their performance in a T-shaped maze. Slow mice showed a worse phagocytic activity with respect to fast animals. After thioproline treatment, a stimulation of all the functions studied as well as a neutralization of the superoxide radical were observed. The effect of this antioxidant was stronger in the slow than in the fast group. Thus, a diet supplemented with thioproline may enhance the immune functions, especially when they are depressed.

Premature induction of aging in sublethally H2O2-treated young MRC5 fibroblasts correlates with increased glutathione peroxidase levels and resistance to DNA breakage

Human MRC5 fibroblasts, at different passages in cultures, were used as an in vitro model to assess variations and/or induction of aging parameters under basal conditions or following sublethal oxidative stress by H2O2. DNA sensitivities to oxidatively-induced breakage, rather than basal levels of damaged DNA, were significantly different between cultures at low and high population doubling level (PDL): old cells maintained most of their DNA integrity even at high concentrations of H2O2, while young cells showed more extensive DNA damage which developed in a dose-dependent fashion. However, young cells pretreated with low doses of H2O2 exhibited increased resistance against further oxidative damage to DNA thus reproducing a senescent-like profile of sensitivity. In turn, DNA from old cultures incubated in a NAD precursor-free medium was more prone to H2O2-induced strand breaks mimicking DNA sensitivity of young cells. The extent of oxidatively-induced DNA damage in MRC5 populations correlated inversely with the levels of glutathione peroxidase (GPx) activity that almost doubled when cells passed from the young to the senescent stage. In addition, H2O2-pretreatment of young cells induced an increase in GPx expression approaching old cell values and promoted also the premature appearance of neutral beta-galactosidase activity and decreased c-fos expression upon serum stimulation, both of which were assumed to be characteristic traits of the senescent phenotype.

Hyaluronan production in vitro by fetal lung fibroblasts and epithelial cells exposed to surfactants of N-acetylcysteine

Fetal human lung fibroblasts and feline lung epithelial cells were exposed to either a surfactant or N-acetylcysteine in various concentrations for 24-48 hours, after which the hyaluronan concentration in the culture medium was determined. Most of the experiments showed no stimulatory effect of either artificial or natural surfactant on hyaluronan synthesis. N-acetylcysteine 5-100 mg/mL induced progressive stimulation of hyaluronan synthesis by human fetal lung fibroblasts, resulting in a maximum hyaluronan concentration six times that released by unexposed cells. A slight increase in hyaluronan synthesis was also observed after exposure of feline fetal lung epithelial cells to N-acetylcysteine 50-100 micrograms/mL.

Expression of hydrogen peroxide and glutathione metabolizing enzymes in human skin fibroblasts derived from donors of different ages

We have examined the activities and mRNA abundance of two hydrogen peroxide metabolizing enzymes (glutathione peroxidase and catalase), glutathione concentration, and the activities of several enzymes that influence glutathione concentration, including glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G-6-PD), and gamma-glutamylcysteine synthetase (gamma-GCS), in 29 skin fibroblast lines derived from donors ranging in age from 14 gestational weeks to 94 years of age. H2O2 metabolizing enzyme activities and mRNA abundances were greater in skin fibroblast cultures established from postnatal donors than in fetally derived cultures. There were no significant differences in either of these parameters in cell lines established from postnatal donors of different ages. Total glutathione concentration decreased with age, but GR activity appeared to be unaffected by age. In order to estimate the ability of the cultures to produce NADPH (an important component of cellular redox status and a cofactor for GR), we determined glucose-6-phosphate dehydrogenase activity and mRNA abundance. We were unable to directly measure gamma-GCS activity or mRNA abundance in any of the skin lines or in fetal lung fibroblast; however, we were able to indirectly demonstrate the presence of this enzyme by stimulating fetal lung fibroblasts with H2O2 following treatment with L-buthionine-S,R-sulfoximine (BSO), an inhibitor of gamma-GCS activity. These results show that some, but not all, age-associated differences in antioxidant defense levels are maintained in a culture environment and are consistent with the hypothesis that developmental stages of life are associated with lower antioxidant defense levels than are present in postnatal phases of life.

Relevance of oxidative stress to the limited replicative capacity of cultured human diploid cells: the limit of cumulative population doublings increases under low concentrations of oxygen and decreases in response to aminotriazole

Human diploid cells, TIG-7, were serially cultivated under 1%, 5% or 21% (air) oxygen. The limit of their cumulative population doublings was extended by 16% or 10% under 1% or 5% oxygen, respectively, as compared with that under 21% oxygen. When TIG-7 cells were serially cultivated in the presence of 10 mM or 20 mM 3-amino-1H-1,2,4-triazole, an inhibitor of catalase scavenging hydrogen peroxide, the limit of their cumulative population doublings was shortened by 4.4% or 14.4%, respectively, as compared with untreated cells. In addition, long-term, rather than short-term, exposure of TIG-7 cells to aminotriazole retarded cell growth. Treatment with aminotriazole caused decreases not only in catalase activity but also in superoxide dismutase activity and reduced glutathione concentration, and an increase in glutathione peroxidase activity. These results suggest that the limit of the cumulative population doublings of human diploid cells is extended or shortened under decreasing or increasing oxidative stress, respectively. Oxidative stress may be relevant to replicative capacity, and a causative factor for oxidative stress may be hydrogen peroxide.

Stimulation by the antioxidant thioproline of the lymphocyte functions of old mice

Diet supplementation with thioproline (thiazolidine-4-carboxylic acid), an intracellular sulfhydryl antioxidant and free radical scavenger, may slow the aging process of metazoans and prolongs their life span. In the present experiment Swiss mice fed thioproline (0.07%, w/w) from 13 to 22 months of age were used. Six- and 22-month-old mice fed standard diet were used as controls. Two important functions of lymphocytes, the proliferative response to the mitogen Concanavalin A (Con A) and the mobility, both spontaneous and directed to a chemoattractant gradient (chemotaxis), were analyzed in lymphocytes from axillary nodes, spleen and thymus. Mobility and chemotaxis were studied by Boyden's technique, using filters of 3 microns pore diameter, 3 h of incubation and fmet-leu-phe at 10(-8) M as chemoattractant. The proliferative response was estimated as 3H-thymidine incorporation in lymphocytes incubated for 72 h in the presence of Con A (1 and 5 micrograms/ml). The results show a decrease in mobility, chemotaxis and lymphoproliferative response in old mice in comparison to adults. However, a significant increase in these functions was observed in old mice fed thioproline. The advantage of using this antioxidant for immunostimulation during aging, a stage of life characterized by a decreased immune response, is discussed.

Metallothionein expression and stress responses in aging human diploid fibroblasts

Metallothioneins (MTs) are low molecular weight proteins with a high cysteine content that are inducible by heavy metals and by other conditions of environmental stress. This laboratory was investigated in human diploid fibroblasts the induction of MTs by cadmium and by dexamethasone, and the induction of heat shock proteins, as models for age-related changes in gene expression that reflect the ability of old cells to respond to environmental stress. Old cells were more sensitive to the toxic effects of CdCl2 in the concentration range 100-175 microM. Analysis of 35S-cysteine-labelled cell extracts by polyacrylamide gel electrophoresis and fluorography showed that in the absence of any inducer, old cells have a 3.7-fold increase over young cells in the basal level of MT. The rate and extent of induction of MT by CdCl2 was reduced in old cells: Exposure of old cells to 100 microM CdCl2 for 18 h resulted in MT levels about 33% of the amount in young cells. Northern blot analysis showed that the changes in MT protein levels occurred in parallel with changes in mRNA levels, which implicates transcriptional control as the origin of these aging changes. These young/old differences in MT synthesis were maintained in density-arrested cultures, indicating that the aging changes were not due to differences in the cell cycle status of these cell populations. The rate and extent of induction of a 68-kDa heat shock protein were also reduced in old cells, which showed an increase in basal, uninduced level of this protein similar to MT. In contrast, old cells retained the ability to synthesize MTs in response to dexamethasone at a rate similar to that in young cells.

Effect of aging on metabolic zonation in rat liver: acinar distribution of GSH metabolism

The effect of age on the glutathione antioxidant system and its acinar distribution in rat liver was studied. GSH/GSSG ratio in blood and liver was lower in old than in young rats. Hepatic glutathione peroxidase and glutathione S-transferase activities were higher in old than in young rats, whereas hepatic gamma-glutamyl transpeptidase activity was lower in old than in young rats. Glutathione reductase and glucose-6-phosphate dehydrogenase activities did not change with age in rat liver. Total glutathione levels and glutathione peroxidase activity were higher in periportal than in perivenous areas of young rats, but this heterogeneous distribution did not occur in old rats. No change with age was found in hepatic zonation of glutathione reductase and glucose-6-phosphate dehydrogenase.

N-acetylcysteine in experimental and clinical acute lung injury

Clinically, lung injury is characterized by one or more of the following: altered gas exchange, dyspnea, decreased static compliance, and nonhydrostatic pulmonary edema. Although many antioxidants have been investigated in in vitro systems and in animal models, only some are at the developmental stage, or safe for clinical trials. Considerable evidence has recently accumulated supporting the hypothesis that leukocyte activation involves release of large quantities of highly reactive oxygen radicals, and hydrogen peroxide is partially responsible for diffuse microvascular and tissue injury in septic patients. Granulocyte depletion in animal models reduces the degree of fall in dynamic lung compliance and the increase in airflow resistance, lymph flow, and hypoxemia secondary to endotoxin administration. We hypothesized that the partial benefit derived from granulocyte depletion was due to the effective removal of a major source of oxygen radicals. Among the list of free radical scavengers, N-acetylcysteine stands out, because of its established usefulness in at least one human disease thought to be secondary to free radical organ damage (acetaminophen or paracetamol overdose). It is an extremely safe agent with a wide toxic-therapeutic window. An increasing number of animal studies indicate efficacy for this agent in the prevention and therapy of lung injury involving toxic oxygen species. We developed a randomized, double-blind protocol for the study of intravenous N-acetylcysteine in patients with established adult respiratory distress syndrome (ADRS). Results of this trial are preliminary. Nevertheless, they indicate that plasma and red cell glutathione levels are decreased in ADRS patients, and that N-acetylcysteine increases plasma cysteine as well as plasma and red cell glutathione. There are also indications that cardiopulmonary physiology is favorably affected by such therapy including improvements in chest radiograph edema scores, pulmonary vascular resistance, static compliance, oxygen delivery, and oxygen consumption.