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

Modulation of Oxidative Status by Normoxia and Hypoxia on Cultures of Human Dermal Fibroblasts: How Does It Affect Cell Aging?

Reactive oxygen species (ROS) production in the skin is among the highest compared to other organs, and a clear correlation exists between ROS production and skin aging. Many attempts are underway to reduce oxidative stress in the skin by topical treatment or supplementation with antioxidants/cosmeceuticals, and cultures of human dermal fibroblasts (HDF) are widely used for these studies. Here, we examined the influence of oxygen tension on cell aging in HDF and how this impacted ROS production, the enzymatic and nonenzymatic antioxidant response system, and the efficacy of this defense system in limiting DNA damage and in modulating gene expression of proteins involved in the extracellular matrix, linked to skin aging. We investigated a selection of parameters that represent and reflect the behavior of cellular responses to aging and oxygen tension. Serial passaging of HDF under normoxia (21%) and hypoxia (5%) leads to cell aging as confirmed by β-galactosidase activity, p16 expression, and proliferation rate. However, in HDF under 21% O₂, markers of aging were significantly increased compared to those under 5% O₂ at matched cell passages despite having lower levels of intracellular ROS and higher levels of CoQ₁₀, total GSH, SOD1, SOD3, and mitochondrial superoxide anion. miRNA-181a, which is known to be upregulated in HDF senescence, was also analyzed, and indeed, its expression was significantly increased in old cells at 21% O₂ compared to those at 5% O₂. Upregulation of MMP1 and downregulation of COL1A1 along with increased DNA damage were also observed under 21% O₂ vs 5% O₂. The data highlight that chronic exposure to atmospheric 21% O₂ is able to trigger hormetic adaptive responses in HDF that however fail, in the long term, to prevent cellular aging. This information could be useful in further investigating molecular mechanisms involved in adaptation of skin fibroblasts to oxidative stress and may provide useful hints in addressing antiaging strategies.

Age associated oxidative damage in lymphocytes

Lymphocytes are an important immunological cell and have been played a significant role in acquired immune system; hence, may play in pivotal role in immunosenescence. Oxidative stress has been reported to increase in elderly subjects, possibly arising from an uncontrolled production of free radicals with aging and decreased antioxidant defenses. This study was aimed to evaluate the level of lipid-protein damage and antioxidant status in lymphocytes of healthy individuals to correlate between oxidative damage with the aging process. Twenty healthy individuals of each age group (11-20; 21-30; 31-40; 41-50; and 51-60 years) were selected randomly. Blood samples were drawn by medical practitioner and lymphocytes were isolated from blood samples. Malondialdehyde (MDA), protein carbonyls (PC) level were evaluated to determine the lipid and protein damage in lymphocytes. Superoxide dismutase (SOD), catalase (CAT), glutathione and glutathione dependent enzymes were estimated to evaluate the antioxidant status in the lymphocytes. Increased MDA and PC levels strongly support the increased oxidative damage in elderly subject than young subjects. The results indicated that, balance of oxidant and antioxidant systems in lymphocytes shifts in favor of accelerated oxidative damage during aging. Thus oxidative stress in lymphocytes may particular interest in aging and may play important role in immunosenescence.

Active ingredients against human epidermal aging

The decisive role of the epidermis in maintaining body homeostasis prompted studies to evaluate the changes in epidermal structure and functionality over the lifetime. This development, along with the identification of molecular mechanisms of epidermal signaling, maintenance, and differentiation, points to a need for new therapeutic alternatives to treat and prevent skin aging. In addition to recovering age- and sun-compromised functions, proper treatment of the epidermis has important esthetic implications. This study reviews active ingredients capable of counteracting symptoms of epidermal aging, organized according to the regulation of specific age-affected epidermal functions: (1) several compounds, other than retinoids and derivatives, act on the proliferation and differentiation of keratinocytes, supporting the protective barrier against mechanical and chemical insults; (2) natural lipidic compounds, as well as glycerol and urea, are described as agents for maintaining water-ion balance; (3) regulation of immunological pathogen defense can be reinforced by natural extracts and compounds, such as resveratrol; and (4) antioxidant exogenous sources enriched with flavonoids and vitamin C, for example, improve solar radiation protection and epidermal antioxidant activity. The main objective is to provide a functional classification of active ingredients as regulatory elements of epidermal homeostasis, with potential cosmetic and/or dermatological applications.

The role of heat stress on the age related protein carbonylation

Since the proteins are involved in many physiological processes in the organisms, modifications of proteins have important outcomes. Protein modifications are classified in several ways and oxidative stress related ones take a wide place. Aging is characterized by the accumulation of oxidized proteins and decreased degradation of these proteins. On the other hand protein turnover is an important regulatory mechanism for the control of protein homeostasis. Heat shock proteins are a highly conserved family of proteins in the various cells and organisms whose expressions are highly inducible during stress conditions. These proteins participate in protein assembly, trafficking, degradation and therefore play important role in protein turnover. Although the entire functions of each heat shock protein are still not completely investigated, these proteins have been implicated in the processes of protection and repair of stress-induced protein damage. This study has focused on the heat stress related carbonylated proteins, as a marker of oxidative protein modification, in young and senescent fibroblasts. The results are discussed with reference to potential involvement of induced heat shock proteins. This article is part of a Special Issue entitled: Protein Modifications.

BIOLOGICAL SIGNIFICANCE

Age-related protein modifications, especially protein carbonylation take a wide place in the literature. In this direction, to highlight the role of heat shock proteins in the oxidative modifications may bring a new aspect to the literature. On the other hand, identified carbonylated proteins in this study confirm the importance of folding process in the mitochondria which will be further analyzed in detail.

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.

Effects of radical scavenger protein from broad beans on glutathione status in human lung fibroblasts

OBJECTIVE

Human diploid cells are more susceptible to oxidative stress at late passage than at early passage, presumably because of the decrease in cellular-reduced glutathione (GSH) concentration. Water-soluble protein (WSP) from broad beans scavenges free radicals. The effects of WSP on the glutathione system were examined in PDL 20 (early passage) and PDL 50 (late passage) human lung fibroblasts (TIG-1).

METHODS

To determine cytosolic glutathione peroxidase (GSH-Px) activities, glutathione reductase (GR) activities, oxidized glutathione (GSSG) concentrations, and GSSG/reduced glutathione (GSH) ratios, WSP and hydrocortisone (HC) treatments of TIG-1 cells (PDL 20→50 and PDL 50→75) were performed for 40 days. We also investigated the GSSG concentrations and GR activities in PDL 20 cells that were continuously treated with WSP until PDL 39 and 55.

RESULTS

GSSG concentrations decreased in WSP- and HC-treated PDL 50→75 cells. The GSSG/GSH ratios in PDL 50→75 cells became low after the treatments. Increases in GR activities were observed in treated PDL 50→75 cells. The decline in the GSSG concentration of PDL 50→75 cells correlated with the increase in GR activity. The GSSG levels in control cells were higher following cellular age, whereas the levels in treated cells were lower than those in the control. The studies on cellular age-related changes indicated that greater increases in GR activity were found in treated cells than in the control.

CONCLUSION

These results indicated that WSP influences the GSSG concentration that is associated with cellular aging, but the mechanism of GSSG reduction by WSP remains unknown. The enhancement of glutathione status following WSP treatment may be related to the delay in the cellular aging.

Effect of selenium supplementation on glutathione peroxidase and catalase activities in senescent cultured human fibroblasts

AIMS

To investigate the effect of senescence and selenium supplementation on glutathione peroxidase (cGPx) and catalase (CAT) activities, and concurrent hydrogen peroxide (H(2)O(2)) generation in subcultured human fibroblasts.

METHODS

cGPx and CAT activities and H(2)O(2) levels were assayed in presenescent passage 5 and 10 cells, and in senescent passage 20, 25, 30 and 35 cells cultured in routine medium (MEM1) and supplemented media MEM2 and MEM3 containing normal and triple human plasma levels of Se, respectively. Senescent cells were identified by studying their growth and replication states, and by monitoring their activity of key glucose and glycogen degradative enzymes.

RESULTS

cGPx activity showed moderate increases in senescent cells at passages 20-35 subcultured in MEM1 or MEM2. This activity underwent highly significant progressive increases in the same senescent cells subcultured in MEM3. In contrast, CAT activity showed progressive, highly significant increases in senescent cells at passages 20-35 regardless of the culture medium type. Concurrent H(2)O(2) generation was significantly increased in passage 15-25 cells and peaked to higher levels in passage 30 and 35 cells cultured in MEM1 or MEM2. These rates, however, were significantly reduced in senescent passage 20-35 cells cultured in MEM3.

CONCLUSIONS

The highest cGPx activity and coupled lower H(2)O(2) generation were achieved in senescent cells cultured in MEM3.

Effects of oxygen, growth state, and senescence on the antioxidant responses of WI-38 fibroblasts

Mitotically active, growth-arrested cells and proliferatively senescent cultures of human fetal lung fibroblasts (WI-38) were exposed to six different oxygen tensions for various lengths of time and then analyzed to determine the responses of their antioxidant defense system. Glutathione (GSH) concentration increased as a function of ambient oxygen tension in early passage cultures; the effect was larger in exponentially growing cultures than in those in a state of contact-inhibited growth arrest, but was absent in senescent cells. Conversely, the activity of glutathione disulfide reductase was greater in growth-arrested cultures than in mitotically active cells irrespective of oxygen tension. Glucose-6-phosphate dehydrogenase was lowest in log-phase cells exposed to different oxygen tensions for 24 h and in senescent cells. Both hypoxia and hyperoxia depressed selenium-dependent glutathione peroxidase activity in early passage cultures, while the activity of the enzyme progressively declined with increasing oxygen in senescent cells. The GSH S-transferase activity was unresponsive to changes in ambient oxygen tension in either young or senescent cultures. Manganese-containing superoxide dismutase (MnSOD) activity was unaffected by oxygen tension, but was elevated in young confluent cultures as compared with cultures in log-phase growth. MnSOD activity was significantly higher in senescent cultures than in early passage cultures and was also responsive to increased oxygen tension in senescent cultures. Copper-zinc-containing superoxide dismutases activity was not affected by oxygen tension or the passage of time, but it declined in senescent cultures.

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.

Effects of epigallocatechin-3-gallate on mitochondrial integrity and antioxidative enzyme activity in the aging process of human fibroblast

Mitochondrial integrity and antioxidative enzyme activity are two of the determinants of intracellular reactive oxygen species (ROS) accumulation probably underlying the aging mechanism. In this study, epigallocatechin-3-gallate (EGCG) was examined for its antiaging effect on human diploid fibroblasts (HDF). EGCG was evaluated for its cytotoxicity, and LC50 values were 78.0 and 84.4 microM for young and old HDF, respectively. HDF treated with EGCG at 25 and 50 microM for 24 h considerably increased catalase, superoxide dismutase (SOD)1, SOD2, and glutathione peroxidase gene expressions and their enzyme activities, thus protecting HDF against H2O2-induced oxidative damage, accompanied with decreased intracellular ROS accumulation and well-maintained mitochondrial potential. Moreover, HDF treated with EGCG at 12.5 microM for long term showed less intracellular ROS with higher mitochondrial potential, more intact mitochondrial DNA, much elevated antioxidative enzyme efficiency, and more juvenile cell status compared to those of the untreated group. Taken together, in this study we investigated the effects of EGCG in the regulation of mitochondrial integrity and antioxidative enzyme activity of HDF, suggesting that EGCG can be considered one of the possible antiaging reagents in the future.

Ageing effects on the expression of cell defence genes after UVA irradiation in human male cutaneous fibroblasts using cDNA arrays

Ageing is a multifactorial process in which reactive oxygen species (ROS) are thought to be implicated. ROS cause oxidative alterations on cell constituents, and damage accumulation can lead to mutations in DNA. Modulation of gene expression during ageing is now quite documented but results are often controversial and/or incomplete. As ultraviolet A is one of the exogenous factors involved in skin ageing, by the production of ROS, we further document the modifications in gene expression during ageing process and response to an oxidative stress. For this purpose, we used a cDNA macroarray containing 82 genes related to cell defence, essentially represented by antioxidant and DNA repair proteins. Ageing-associated gene expression was assessed in normal skin human fibroblasts from three age groups: children (n=4), adults (n=4) and olders (n=3), at the basal state and after a 5J/cm2 UVA irradiation. Analysis revealed that 22 genes were never detected, whereas certain were always expressed such as those related to antioxidant defence, extracellular matrix (ECM) regulator and XPC. Transcripts related to ECM, MMP1 and MMP3 were increased with age and after UVA irradiation, independently of age. It appeared that transcripts involved in the redox status control (TXN and APEX) decreased as a function of age, at the basal state and after irradiation, respectively. Most of transcripts involved in DNA repair were not detected but repression of POLD1 in the adult group and induction of XRCC5 and LIG4 were observed after UVA irradiation, as a function of age. In the basal state, the transcript of GAS1, regulator of cell cycle arrest in G1 phase was found to be decreased with age. HMOX1 increased after UVA irradiation. In conclusion, the decrease in expression of some antioxidant system, cell cycle control gene and extracellular matrix enzymes, particularly after UV exposure can explain the occurrence of photoaging.

Age-dependent DNA repair and cell cycle distribution of human skin fibroblasts in response to UVA irradiation

Ageing process in cells is associated with oxidative stress. Ultraviolet A produces reactive oxygen species responsible for accumulation of DNA and cellular damage. After the evaluation of antioxidant enzyme activities and oxidative stress markers at the basal state, we have studied the responses to UVA stress of coetaneous fibroblasts, isolated from different male donors (2-88 years, n=23) in terms of cytotoxicity, genotoxicity and DNA repair capacities. For this purpose, we have determined level of DNA damage using the comet assay (single strand breaks and alkali-labile sites) and the cell cycle distribution after a 5 J/cm2 irradiation. No differences with age were observed for antioxidant enzyme activities and oxidative stress markers. DNA strand breaks after UVA irradiation (5-20 J/cm2), was found to be age-dependent. DNA repair was slow and also significantly affected by ageing. The cell cycle distribution analysis showed that high repair correlated with high proliferative capacities at basal level. Twenty-four hours after the stress, fraction of young fibroblasts blocked in G1 phase was significantly increased whereas significant modifications concerned the G2-M phase for adult and older fibroblasts. These results indicate an age-dependent decline in the DNA repair capacities correlated with modifications of the cell cycle parameters.

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.

Antioxidant enzyme activity in human stratum corneum shows seasonal variation with an age-dependent recovery

The stratum corneum, as the body's principal barrier to the environment, is continuously exposed to environmental sources of reactive oxygen species like ultraviolet light, ozone, and pollution. Reactive oxygen species are believed to be involved in cancer, aging, and inflammatory skin disorders. We have developed a method to measure catalase and superoxide dismutase activity on tape strippings from the human stratum corneum and demonstrated a gradient of antioxidant enzyme activity across the stratum corneum with decreasing levels towards the skin surface. Sun exposure resulted in a seasonal variation of the catalase activity in stratum corneum, with low activities in summer and higher activities in winter for the same person, whereas superoxide dismutase activity in stratum corneum did not seem to vary in those conditions. Exposure of human skin to broadband ultraviolet-A resulted in a dose-dependent deactivation of the catalase activity in stratum corneum within 24 h, whereas exposure to ultraviolet-B had no effect. Superoxide dismutase activity in stratum corneum was not affected by ultraviolet-A or ultraviolet-B irradiation within 24 h. After exposure to a dose of 15 J per cm2 broadband ultraviolet-A, full recovery of the catalase activity occurred in 3-4 wk at an age-dependent rate. We conclude that sun exposure results in a disturbed catalase to superoxide dismutase ratio in the stratum corneum. This may lead to an increased vulnerability to oxidative damage in stratum corneum barrier components. These results therefore stress the importance of providing efficient protection for this internal defense mechanism in sun-exposed areas of the skin.

Oxygen modulates the growth of skin fibroblasts

Elevated oxygen tensions are inhibitory to the growth of skin fibroblasts. Skin fibroblasts grow better at oxygen tensions below 137 mm Hg regardless of seeding density. A wide range of oxygen tensions, including those in the physiological range, strongly modulate the growth of human skin fibroblasts. There were no significant differences between the responses of fetal and postnatal cell lines to changes in ambient oxygen tension. In all cases, higher oxygen tensions significantly impeded cell growth. Seeding cells at 10(4) cells/cm(2) afforded some protection from the deleterious effects of hyperoxia. Oxygen tensions exceeding the amount present in ambient room air also impeded cell growth at this higher seeding density, but the effect did not become significant until the oxygen partial pressure reached 241 mm Hg. At lower oxygen tensions, cells seeded at 10(3) cells/cm(2) grew more rapidly than did cells seeded at 10(4) cells/cm(2). These findings may have implications for the treatment of poorly healing wounds with hyperbaric oxygen.

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.

Induction of glutathione synthesis in human keratinocytes by Ginkgo biloba extract (EGb761)

The objective of the present study was to characterize the action of Ginkgo biloba extract (EGb761) and its sub-fractions on glutathione homeostasis in a human keratinocyte cell culture model. Cells were incubated with EGb761, its purified flavonoid (quercetin, kaempferol, rutin) or terpenoids (gingkolides A, B, C, J, bilobalide) constituents or the vehicle for up to 72 hours. Incubation of keratinocytes with the purified flavonoids or terpenoids did not affect cellular GSH levels. However, EGb761 treatment (up to 200 microg/ml) resulted in a dose-dependent increase of cellular GSH. Western blot analysis of extracts from cells treated with EGb761 revealed increased levels of the catalytic subunit of gamma-glutamylcysteinyl synthetase (gamma-GCS), the rate-limiting enzyme in GSH synthesis. The abundance of mRNA for the catalytic subunit (assayed by RT-PCR) was also increased by the treatment with EGb761. Increased levels of cellular GSH by EGb761 were also observed in other cell lines including those from human bladder and liver as well as in murine macrophages indicating that the induction of gamma-GCS mRNA, protein and GSH may be an ubiquitous effect of EGb761 in mammalian cells.

Antioxidants may contribute in the fight against ageing: an in vitro model

Elderly humans have altered cellular redox levels and dysregulated immune responses, both of which are key events underlying the progression of chronic degenerative diseases of ageing, such as atherosclerosis and Alzeimer's disease. Poorly maintained cellular redox levels lead to elevated activation of nuclear transcription factors such as NFkB and AP-1. These factors are co-ordinately responsible for a huge range of extracellular signalling molecules responsible for inflammation, tissue remodelling, oncogenesis and apoptosis, progessess that orchestrate many of the degenerative processess associated with ageing. It is now clear that levels of endogenous anti-oxidants such as GSH decrease with age. This study aimed to investigate the potential of exogenous anti-oxidants to influence inflammatory responses and the ageing process itself. We investigated the potential of the dietary antioxidant, quercetin, to reverse the age related influences of GSH depletion and oxidative stress using in vitro human umbilical vein endothelial cells (HUVEC) and human skin fibroblast (HSF) cell models. Oxidative stress-induced inflammatory responses were investigated in a GSH depletion and a Phorbol 12-myristate 13-acetate (PMA)-induced stress model. As measured with a sensitive HPLC fluorescence method, GSH in HUVEC was depleted by the addition of L-buthionine-[S,R]-sulfoxiniine (BSO), a gamma-glutamylcysteine synthetase inhibitor, to the culture medium at a concentration of 0.25 mM. Time course studies revealed that the GSH half-life was 4.6 h in HUVEC. GSH depletion by BSO for 24 h led to a slight increase in intracellular adhesion molecule - 1 (ICAM1) expression and prostaglandin E2 (PGE2) secretion in both types of cells. However, GSH depletion markedly enhanced PMA-induced ICAM and PGE2 production in HUVEC. Responses were progressively elevated following prolonged BSO treatment. Inhibition studies showed that 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine (H7), a protein kinase C (PKC) inhibitor, not only abolished most of PMA-induced ICAM-1 expression and PGE2, production, but also eliminated GSH depletion-enhanced PMA stimulation. This enhancement was also inhibited by supplementation with quercetin. The results clearly demonstrate that GSH depletion increased the susceptibility of vascular endothelial cells and fibroblasts to oxidative stress associated inflammatory stimuli. This increased in vitro susceptibility may be extrapolated to the in vivo situation of ageing, providing a useful model to study the influence of micronutrients on the ageing process. In conclusion, these data suggest that dietary antioxidants could play a significant role in the reduction of inflammatory responses.

Atmospheric oxygen accelerates the induction of a post-mitotic phenotype in human dermal fibroblasts: the key protective role of glutathione

It has been proposed that ageing of human dermal fibroblasts occurs as a multi-stage process during which cells progress from a mitotic to a post-mitotic state. We describe the development of a simple and novel cell-cloning model for identifying and quantifying the different fibroblast morphotypes associated with the induction of post mitotic behaviour. We have found that under atmospheric (20%) oxygen tension a significant proportion of human dermal fibroblasts are rapidly induced to switch from a mitotic to a post-mitotic phenotype. In contrast, under more physiological (4%) oxygen conditions, the induction of a post-mitotic phenotype is largely prevented. Increasing oxidative stress by addition of hydrogen peroxide or depletion of glutathione also induced a switch from a mitotic to a post-mitotic phenotype in these cells, whereas addition of the anti-oxidant N-acetylcysteine under atmospheric (20%) oxygen tension potently inhibited this process. In addition, a statistically significant correlation was observed between the magnitude of intracellular glutathione depletion and the reduction in the population of mitotic cells in this model. We propose that the switch from a mitotic to a post-mitotic phenotype represents a process of cellular ageing and that standard atmospheric oxygen tension imposes a substantial oxidative stress on dermal fibroblasts which accelerates this process in culture. The data also suggest that intracellular glutathione levels strongly influence the induction of a post-mitotic phenotype and that, by implication, depletion of glutathione may play a significant role in the progression of cellular ageing in human skin.

Is beta-galactosidase staining a marker of senescence in vitro and in vivo?

Cytochemically detectable beta-galactosidase (beta-gal) at pH 6.0 has been reported to increase during the replicative senescence of fibroblast cultures and has been used widely as a marker of cellular senescence in vivo and in vitro. In this study, we have characterized changes in senescence-associated (SA) beta-gal staining in early and late passage cultures, cultures established from donors of different ages, virally immortalized cells, and tissue slices obtained from donors of different ages. The effects of different culture conditions were also examined. While we confirm the previous report that SA beta-gal staining increased in low-density cultures of proliferatively senescent cells, we were unable to demonstrate that it is a specific marker for aging in vitro. Cultures established from donors of different ages stained for SA beta-gal activity as a function of in vitro replicative age, not donor age. We also failed to observe any differences in SA beta-gal staining in skin cells in situ as a marker of aging in vivo. The level of cytochemically detectable SA beta-gal was elevated in confluent nontransformed fibroblast cultures, in immortal fibroblast cultures that had reached a high cell density, and in low-density, young, normal cultures oxidatively challenged by treatment with H2O2. Although we clearly demonstrate that SA beta-gal staining in cells is increased under a variety of different conditions, the interpretation of increased staining remains unclear, as does the question of whether the same mechanisms are responsible for the increased SA beta-gal staining observed in senescent cells and changes observed in cells under other conditions.

Age-associated decline in gamma-glutamylcysteine synthetase gene expression in rats

Although glutathione (GSH) concentration has been reported to diminish with age, the mechanism underlying such age-associated decline in the GSH content is not well understood. In this study, we compared the gene expression of both subunits of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in de novo GSH synthesis, in young, adult, and old Fisher 344 rats. It was found that GCS activity was significantly decreased with increased age in liver, kidney, lung, and red blood cells (RBC). Parallel with the decreased enzyme activity, the protein and mRNA contents of both GCS subunits also changed inversely with age in liver, kidney, and lung, implying a decreased GCS gene expression during aging. Such a reduced GCS gene expression was accompanied by a decline in total GSH content without any change in cysteine concentration. Furthermore, the decreased GCS gene expression in old rats was not associated with a decline in the plasma insulin or cortisol level. This study showed, for the first time, that the expression of both GCS subunit genes was decreased in some organs of old rats, which would result in a reduced rate of GSH biosynthesis. Such decline in GSH synthetic capacity may underlie the observed decrease in GSH content during aging.

Gamma-glutamylcysteine synthetase activity in human lung epithelial (A549) cells: factors influencing its measurement

Despite the central role of gamma-glutamylcysteine synthetase (gammaGCS) in lung antioxidant defenses, the limited studies of the activity of this enzyme in respiratory cells have produced variable results. This study has examined the factors, which may influence the measurement of gammaGCS activity in cultured human lung epithelial cells (A549). Although a source of potential error, gammaGCS activity in A549 cell extracts did not vary significantly when appropriately assayed by three different methods or after removal of the endogenous inhibitor, glutathione (GSH). However, gammaGCS activity did increase significantly during the early stages of cell proliferation (3.50 +/- 0.31 vs. 2.35 +/- 0.16 nmol/min/10(6) cells for baseline, p < .001) and thereafter returned to baseline levels during the later stages of cell growth. Variations in initial plating density also significantly altered gammaGCS activity (3.11 +/- 0.14 vs. 4.04 +/- 0.50 nmol/min/10(6) cells, at 0.25 x 10(5) and 0.58 x 10(5) cells/cm2, respectively, p < .001) and GSH content (45.43 +/- 4.43 vs. 63.64 +/- 3.28 nmol/10(6) cells at 0.25 x 10(5) and 0.58 x 10(5) cells/cm2, respectively, p < .001) during the early stages of cell proliferation. In addition, gammaGCS activity and GSH content were highest in A549 cells grown in medium containing cystine as the predominant sulfur-containing amino acid. These results suggest that gammaGCS activity of A549 cells is strongly dependent on initial plating density, stage of cell growth and sulfur amino acid content of the medium and may account for some of the variation in values reported by different investigators. Whether gammaGCS has an important role in the early phase of cell proliferation needs further investigation.

Serum selenium levels and blood glutathione peroxidase activities in vitiligo

It has recently been shown that patients with vitiligo can accumulate epidermal hydrogen peroxide (H2O2) in association with low catalase levels. This study examined serum selenium levels and blood glutathione peroxidase activities in 61 patients and controls. The results showed high serum selenium levels in 56% of the patients. As at least one isoform of glutathione peroxidase requires selenium for its activity, enzyme activities were also evaluated. The overall results were not significantly different compared with controls, but further age-related analysis of the data indicated significantly lower activities in patients up to 46 years. As glutathione peroxidase can also efficiently degrade H2O2, the results of this study could indicate an additional impaired H2O2 metabolism in vitiligo.

Differences in electron transport potential, antioxidant defenses, and oxidant generation in young and senescent fetal lung fibroblasts (WI-38)

The activities and mRNA abundances of enzymes that regulate the rate of electron flow through the electron transport chain (ETC), including NADH dehydrogenase, succinate dehydrogenase, and cytochrome c oxidase, were examined in young and senescent fetal lung fibroblasts (WI-38). We also determined the activities and mRNA abundances of antioxidant defenses including superoxide dismutase, catalase, and glutathione peroxidase. We confirmed our previous report of a senescence-related increase in the abundance of ND4, a mitochondrially encoded subunit of NADH dehydrogenase. The activities of cytochrome c oxidase and NADH dehydrogenase were also elevated in senescent cultures. No differences were observed in the mRNA abundances of COX-1, a mitochondrially encoded subunit of cytochrome c oxidase or of nuclearly encoded subunits of various electron transport components (SD, COX-4, and ND 51). Lucigenin-detected chemiluminescence and H2O2 generation were both elevated in senescent cells. Catalase activity was also elevated in senescent fibroblasts. However, no differences in catalase mRNA abundance were observed. A small decrease in GSH peroxidase (GPx) mRNA abundance was observed in senescent cells. No other changes in the activities or mRNA abundances of any of the antioxidant defenses were observed in early and late passage cultures. The relationships between oxidant generation, mitochondrial enzyme activities, and antioxidant defense observed during proliferative senescence are dissimilar to those detected between fetal and postnatal fibroblasts as well as those found between fibroblast lines obtained from young and old individuals. The relevance of the differences between these models is discussed.

Roles of reactive oxygen species: signaling and regulation of cellular functions

Reactive oxygen species (ROS) are the side products (H2O2, O2.-, and OH.) of general metabolism and are also produced specifically by the NADPH oxidase system in most cell types. Cells have a very efficient antioxidant defense to counteract the toxic effect of ROS. The physiological significance of ROS is that ROS at low concentrations are able to mediate cellular functions through the same steps of intracellular signaling, which are activated by natural stimuli. Moreover, a variety of natural stimuli act through the intracellular formation of ROS that change the intracellular redox state (oxidation-reduction). Thus, the redox state is a part of intracellular signaling. As such, ROS are now considered signal molecules at nontoxic concentrations. Progress has been achieved in studying the oxidative activation of gene transcription in animal cells and bacteria. Changes in the redox state of intracellular thiols are considered to be an important mechanism that regulates cell functions.

Effects of donor age on the expression of a marker of replicative senescence (EPC-1) in human dermal fibroblasts

EPC-1 (early population doubling level cDNA-1) is a quiescence-specific gene expressed at high levels by early passage WI-38 fibroblasts under conditions of either density-dependent growth arrest or serum deprivation. Late passage WI-38 cells lose the ability to express EPC-1 under all conditions tested. The decline in EPC-1 mRNA is gradual during the replicative life span and correlates inversely with the population doubling level (PDL) of the cells. The objective of this study was to determine whether the decline in EPC-7 mRNA abundance observed during proliferative senescence also occurs in cultures derived from donors of different ages. To address this question, we examined the abundance of EPC-1 mRNA in 28 skin fibroblast lines established from healthy donors of different ages ranging from 12 fetal weeks to 94 years. EPC-1 expression was measured, under conditions of growth arrest, prior to the end of the replicative life span of the cultures. Despite some variability in steady-state transcript levels among the cell lines, EPC-1 expression was significantly lower in cells derived from the fetal donor group (12-20 gestational weeks) than in cells derived from adult donors. An in vitro age-dependent decline in EPC-1 expression was observed in all the skin lines examined, independent of donor age; however, no significant difference was observed between the young adult donor group (17-33 years) and the old adult donor group (78-94 years). Thus, expression of EPC-1 is linked to the replicative age of the cells and whether the cells are derived from fetal skin or adult skin. In adults, EPC-1 expression is independent of donor age.

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.

Development and age-associated differences in electron transport potential and consequences for oxidant generation

We determined the activities of NADH dehydrogenase (ND), succinate dehydrogenase, and cytochrome c oxidase (COX) in 29 skin fibroblast lines established from donors ranging in age from 12 gestational weeks to 94 years. The results of this study demonstrate that all three of the enzyme activities examined are greater in adult-derived fibroblasts than in the fetal cell lines. The ratio of enzyme activities that control electron entry into and exit from the electron transport chain varied directly with lucigenin-detected chemiluminescence (an indicator of .O2- generation) and inversely with H2O2 generation. These results indicate a clear difference in the predominant oxidant species generated during fetal and adult stages of life. We also examined the mRNA abundances of different components of the electron transport chain complexes. We observed higher abundances of mitochondrial encoded mRNAs (COX 1 and ND 4) in cell lines established from adults than in fetal cells. No differences in the mRNA abundances of the nuclear encoded sequences (COX 4 and ND 51) were observed in fetal and postnatal-derived lines. Succinate dehydrogenase mRNA abundance was greater in cell lines established from postnatal donors than in fetal cell lines. No significant differences between cell lines established from young and old adults were detected in any of the parameters examined.