Changes in enzyme activities in skin fibroblasts derived from persons of various ages

N6-benzyladenine and kinetin influence antioxidative stress parameters in human skin fibroblasts

N6-benzyladenine and kinetin are adenine-type cytokinins that play various roles in many aspects of plant development and stimulate anabolic processes in plant cells. The aim of this study was to examine the effect of N6-benzyladenine and kinetin on basic oxidative stress parameters, such as antioxidative enzyme activity, reduced glutathione and thiol group content, and lipid peroxidation. The results show a stimulatory effect of kinetin and N6-benzyladenine on antioxidative enzyme activity, as well as reduced glutathione and thiol group content. Cytokinins caused a decrease in membrane phospholipid peroxidation and exhibited protective properties against malondialdehyde production. The present findings reveal that both N6-benzyladenine and kinetin exhibit multiple and complex actions in fibroblast cells in vitro. Both show antioxidant properties and are potentially powerful agents with applications in the prevention and treatment of many diseases connected with oxidative stress in skin, for example, psoriasis.

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.

'The effect of micronutrients on superoxide dismutase in senescent fibroblasts'

The specific activities of zinc/copper (Zn/Cu)-superoxide dismutase (SOD-1) and manganese (Mn)-superoxide dismutase (SOD-2) were assayed in young passage 5 fibroblasts and in serially subcultured cells that were characterized as senescent at passages 15-35. SOD-1 and SOD-2 activities did not significantly change in senescent and young cells cultured in either routine medium [minimum essential medium 1 (MEM1)], or in Zn, Cu and Mn supplemented medium (MEM2) containing normal human plasma levels of the cations. SOD-1 and SOD-2 activities, however, underwent parallel progressive significant activity increases in senescent passage 20 and 25 cells, which peaked in value in passage 30 and 35 cells subcultured in supplemented medium (MEM3) containing triple human plasma levels of the cations. Concurrently, superoxide radical generation rates underwent progressive significant increases in senescent passage 15-25 cells, which peaked in value in passage 30 and 35 cells subcultured in MEM1 or MEM2. These rates, however, were significantly lowered in senescent cells subcultured in MEM3. We infer that it was only possible to significantly stimulate SOD-1 and SOD-2 activities in senescent MEM3 cultured cells enabling them to combat oxidative stress.

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.

Resistance of Cultured Human Skin Fibroblasts from Old and Young Donors to Oxidative Stress and Their Glutathione Peroxidase Activity

BACKGROUND

It has been suggested that oxidative stress is involved in the aging process and that the resistance of animals to oxidative stress may decrease with advancing aging. However, there are only a limited number of reports of studies on the relationship between aging and resistance to oxidative stress.

OBJECTIVE

The aim of this work is to examine the relationship between the resistance of human skin fibroblasts to oxidative stress and donor age, and the relevance of antioxidant enzyme activities to this resistance.

METHODS

Percent cell survival was determined by the trypan blue exclusion test and the neutral red method. Superoxide dismutase activity was assayed by the method of Oyanagi, catalase activity by the method of Aebi, and glutathione peroxidase activity by the method of Flohé and Günzler. Reduced glutathione concentration was measured by the method of Griffith. Antioxidant enzyme mRNA levels were estimated by reverse transcription polymerase chain reactions (RT-PCR).

RESULTS

The percent survivals of cultured human skin fibroblasts, derived from young and old donors (referred to as young and old cells, respectively), under oxidative stress from hydrogen peroxide, linoleic acid hydroperoxide, or ultraviolet light B were examined. Old cells were more resistant to such oxidative stress than young cells. The activity of glutathione peroxidase was higher by 46.1% in old cells than in young cells, although there was no difference between their relative glutathione peroxidase mRNA levels. Further, there was no difference between their activities of copper/zinc superoxide dismutase, manganese superoxide dismutase, or catalase. However, the relative mRNA levels of copper/zinc superoxide dismutase and manganese superoxide dismutase were lower by 13.9 and 20.9% in old cells than in young cells, respectively, while there was no difference between the levels of catalase.

CONCLUSIONS

These results suggest that old cells are more resistant to oxidative stress than young cells, presumably because of an increase in cellular glutathione peroxidase activity.

Age-dependent generation of reactive oxygen species in the skin of live hairless rats exposed to UVA light

Aging proceeds by highly complicated biochemical processes, in which the involvement of the reactive oxygen species (ROS) and free radicals has been implicated. Although the relationship between UV-induced photoaging and ROS generation has been proposed, it has been difficult to establish direct proof of the generation of ROS in the skin under UV exposure. Recently, we reported finding endogenously generated ROS in the skin of live mice after UVA light exposure by a method of in vivo chemiluminescent detection, in which superoxide anion radical (*O2-) and singlet oxygen species (1O2) are contributed. In light of the results, we tried to understand the age-dependent changes in ROS generation in the skin of hairless rats under UVA exposure. Chemiluminescent levels due to ROS in the untreated and UVA-exposed skin decreased age dependently, and the signal intensities in old rats were significantly lower than those in young rats. However, the ratios of chemiluminescent intensities in the UVA-exposed skin to those in the untreated skin were significantly enhanced in an age-dependent manner. These results suggest that the antioxidative ability against ROS generation in the skin, possessed by antioxidant enzymes and low molecular weight antioxidants, is lowered age dependently.

Aging- and photoaging-dependent changes of enzymic and nonenzymic antioxidants in the epidermis and dermis of human skin in vivo

This is a comprehensive study of the changes in major antioxidant enzymes and antioxidant molecules during intrinsic aging and photoaging processes in the epidermis and dermis of human skin in vivo. We show that the activities of superoxide dismutase and glutathione peroxidase are not changed during these processes in human skin in vivo. Interestingly, the activity of catalase was significantly increased in the epidermis of photoaged (163%) and naturally aged (118%) skin (n = 9), but it was significantly lower in the dermis of photoaged (67% of the young skin level) and naturally aged (55%) skin compared with young (n = 7) skin. The activity of glutathione reductase was significantly higher (121%) in naturally aged epidermis. The concentration of alpha-tocopherol was significantly lower in the epidermis of photoaged (56% of young skin level) and aged (61%) skin, but this was not found to be the case in the dermis. Ascorbic acid levels were lower in both epidermis (69% and 61%) and dermis (63% and 70%) of photoaged and naturally aged skin, respectively. Gluta thione concentrations were also lower. Uric acid did not show any significant changes. Our results suggest that the components of the antioxidant defense system in human skin are probably regulated in a complex manner during the intrinsic aging and photoaging processes.

Altered levels of primary antioxidant enzymes in progeria skin fibroblasts

Free radicals are involved in the aging process. In this study, the profile of primary antioxidant enzymes that scavenge reactive oxygen species (ROS) was examined for the first time in human skin fibroblasts from progeria, a premature aging disease. Altered levels of antioxidant enzymes were found in progeria cells. Basal levels of MnSOD were decreased in progeria cells as well as a blunted induction in response to chronic stress. This change may contribute to the accelerated aging process in progeria cells. In contrast, the levels of CuZnSOD showed no progeria-related change. Two H2O2 removing enzymes demonstrated a significant reduction in progeria cells: only 50% of normal CAT activity and 30% of normal GPX activity can be detected in progeria cells. This diminished H2O2 removing capacity in progeria cells may lead to an imbalance of intracellular ROS and therefore may play an important role in the development of progeria.

Stimulation of hepatocyte growth factor production by ascorbic acid and its stable 2-glucoside

Hepatocyte growth factor (HGF), a cytokine which is generally produced by mesenchymal cells, has mitogenic, motogenic and morphogenic activities in epithelial cells and it also has tumor-suppressing activities. Induction of HGF production may be involved in organ regeneration, wound healing and embryogenesis. We examined the effects of ascorbic acid (AsA), which stimulates the proliferation of fibroblasts, and its stable derivative, 2-O-alpha-D-glucopyranosyl-L-ascorbic acid (AA-2G), on HGF production by human skin fibroblasts. Basal HGF secretion was significantly stimulated by more than 0.1 mM AsA or AA-2G. Both vitamins synergistically enhanced HGF secretion stimulated by growth factors such as epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), cholera toxin and other inducers. Induction by EGF or bFGF was most markedly potentiated by the vitamins. HGF production by the KG-1 human leukemia cell line was also augmented by AsA or AA-2G. Another stable AsA derivative, ascorbic acid 2-phosphate (AA-2P) effectively promoted basal and EGF-induced HGF secretion by the fibroblasts, but ascorbic acid 2-sulfate (AA-2S) was much less effective. Intracellular AsA levels increased after the addition of AA-2G and AA-2P as well as AsA, but not after AA-2S. The effect of AA-2G was completely abrogated by the simultaneous addition of castanospermine, an alpha-glucosidase inhibitor, suggesting that the active form of AA-2G is AsA. Constitutive and EGF-induced HGF gene expression was also up-regulated after adding AsA or AA-2G to the cells. These results indicated that AsA acts alone or in synergy with several inducers to stimulate the production and gene expression of HGF in human skin fibroblasts and that the stable AsA derivative AA-2G is as effective as AsA in promoting HGF production.

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.

Increased susceptibility of late passage human diploid fibroblasts to oxidative stress

Three strains of human diploid fibroblasts, TIG-3, TIG-7, and MRC-5, were serially cultivated. The susceptibility of early-passage and late-passage cells at 20-30 and 60-70 population doubling levels, respectively, to hydrogen peroxide, the superoxide radical (exposure to the hypoxanthine-xanthine oxidase system), or linoleic acid hydroperoxide was examined for lactate dehydrogenase release. The susceptibility of late-passage cells to such oxidative stress was considerably enhanced compared with early-passage cells. The concentration of reduced glutathione in late-passage cells was lower by 24-44% on a per-cell-number basis and by 86.0-94.5% on a per-protein-quantity basis than in early-passage cells. In addition, the activity of catalase in late-passage cells was lower by 19-46% compared with early-passage cells. There was, however, no difference between the mRNA levels of catalase in early-passage and late-passage cells. The activities and mRNA levels of copper/zinc superoxide dismutase, manganese superoxide dismutase, and glutathione peroxidase in late-passage cells were all higher than in early-passage cells. These results suggest that late-passage cells are more susceptible to oxidative stress than early-passage cells presumably because of decreases in cellular reduced glutathione concentration and catalase activity, and that their primary defense against oxidative stress is reduced glutathione.

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.

Expression and regulation of superoxide dismutase activity in human skin fibroblasts from donors of different ages

We have determined the activities, protein, and mRNA abundances as well as the level of transcriptional activation of two intracellular forms of the free radical metabolizing enzyme superoxide dismutase in 29 human skin fibroblast lines established from donors of different ages. SOD-1 (a copper and zinc containing form of SOD) and SOD-2 (a manganese containing form of the enzyme) activities were both observed to be significantly lower in cell lines derived from fetal skin than in lines established from postnatal skin (ages 17-94 years). The percent of total activity contributed by SOD-1 decreased in an age-associated manner from approximately 50% in the fetal lines to less than 20% in lines established from old tissue donors. All of the cell lines were screened to exclude the possibility that they contained a polymorphism known to influence SOD-2 activity. Northern blot analysis revealed three SOD-1 mRNA transcripts that were 0.5, 0.7, and 1.9 kb in length. Although SOD-1 protein abundance was lower in fetal lines than in lines derived from postnatal donors, SOD-1 mRNA abundance did not differ between fetal cells and cell lines derived from young donors. SOD-2 protein abundance and mRNA abundance were both significantly lower in fetal lines than in postnatal lines. No postnatal age-dependent differences were observed in any of the SOD-2 parameters examined. Nuclear run-on analysis revealed that fetal cell lines exhibited a lower level of transcriptional initiation for SOD-1 than postnatal lines. The transcription of SOD-2 was readily detected in postnatal lines, but undetectable in fetal lines. These results are consistent with multiple levels of control for SOD-1 expression and with a strong transcriptional influence on SOD-2 expression.

Antioxidant defence mechanism of the skin against UV irradiation: study of the role of catalase using acatalasaemia fibroblasts

To clarify the role of catalase, an antioxidant enzyme, in response to UV irradiation, we compared the effects of irradiation on cytotoxicity, activities of antioxidant enzymes, total glutathione concentrations, lipid peroxidation and the rate of collagen synthesis in skin fibroblasts from a patient with acatalasaemia and in those from a normal individual. The cells were irradiated with UVA (6 and 12 J/cm2 or UVB (0.5 and 1 J/cm2). Cell survival curves after UV irradiation were similar in cells from both subjects. Although superoxide dismutase activity in acatalasaemia cells was higher than in the control cells before irradiation, after irradiation the activity decreased in acatalasaemia cells (76% with 12 J/cm2 UVA, 47% with 1 J/cm2 UVB), but remained unchanged in control cells. Total glutathione concentrations also decreased in acatalasaemia cells (60% with 12 J/cm2) in response to UVA irradiation, but remained unchanged in control cells. Lipid peroxidation did not increase significantly in either cell type. The rate of collagen synthesis decreased to a similar extent in response to UV exposure in the two cell types (60-80% with 8.2 J/cm2 UVA, 40-50% with 10 mJ/cm2 UVB). We conclude from the results of cytotoxicity and lipid peroxidation that although acatalasaemia cells were killed by hydrogen peroxide at low concentrations with a single UV exposure, catalase functions only to a small degree as an antioxidant enzyme. There remains the possibility, however, that a deficiency of catalase may chronically damage the skin resulting in a reduced defence function of superoxide dismutase and glutathione with repeated exposures to UV, which is becoming more common in our daily life.

Effect of age on antioxidants and molecular markers of oxidative damage in murine epidermis and dermis

This is the first study of antioxidants and oxidative-damage-related parameters in epidermis and dermis of the skin as a function of age. The four major antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase, and glutathione peroxidase), hydrophilic and lipophilic antioxidants, and lipid hydroperoxides were assayed in both epidermis and dermis of young and old hairless mice. Catalase, superoxide dismutase, and glutathione reductase had similar activity levels in young and old animals. Only glutathione peroxidase from epidermis showed an activity decrease due to age. This decrease became apparent when enzyme activity was expressed per mg of total cellular protein. Hydrophilic and lipophilic antioxidants did not change as a function of age, nor did lipid hydroperoxide levels. Both the absolute level of oxidized glutathione and the ratio of oxidized to reduced glutathione were higher in dermis from old mice. These results suggest that skin aging is not accelerated in old age due to a general decrease in the antioxidant capacity of the tissue. The data are compatible, however, with the idea that continuous damage to skin tissue by free radicals occurs throughout an organism's lifetime because scavenging cannot be 100% efficient.

Comparison of ascorbic acid and ascorbic acid 2-O-alpha-glucoside on the cytotoxicity and bioavailability to low density cultures of fibroblasts

Ascorbic acid 2-O-alpha-glucoside (AA-2G) is a stable ascorbate derivative which has vitamin C activity in vivo and in vitro. We studied whether AA-2G exerts a prooxidant action in cultured fibroblasts from chick embryo and human skin, as does ascorbic acid. At concentrations of 0.1-1.0 mM, ascorbic acid markedly reduced the viable cell number of low density cultures within 24 hr, whereas AA-2G had no such effect. The ascorbate cytotoxicity was dependent on the cell density at the time of its addition and it was characteristic of low density cultures. This cytotoxicity was completely prevented by catalase and partially by an Fe3+ ion chelator, desferrioxamine. In the early culture stage at which a morphological change in the fibroblasts began to occur, intracellular ascorbate concentrations in low density cultures after addition of ascorbic acid were much higher than in high density cultures. However, at the same concentrations, AA-2G did not cause an elevation even in low density cultures and it was also effective on collagen synthesis at high and medium densities. These results suggest that the abnormally accumulated ascorbic acid in the cells cultured at low density possibly amplifies the generation of oxygen radicals through the reduction of Fe3+ ions and subsequent oxidative reactions, leading to cell death. Therefore, it is concluded that AA-2G which supplies an adequate amount of ascorbic acid during culture period is a bioavailable ascorbate source without cytotoxicity.

Phorbol ester-induced secretion of human hepatocyte growth factor by human skin fibroblasts and its inhibition by dexamethasone

Human skin fibroblasts secreted a certain amount of human hepatocyte growth factor (hHGF), as determined by an enzyme-linked immunosorbent assay for hHGF. This hHGF secretion was remarkably stimulated by protein kinase C (PKC)-activating phorbol esters, which was inhibited by the simultaneous addition of dexamethasone. Pretreatment with phorbol 12-myristate 13-acetate (PMA) caused a down-regulation in hHGF secretion. hHGF secreted by the PMA-treated cells showed a potent hepatocyte growth-promoting activity which was neutralized by an anti-hHGF antiserum. These results indicate both that PMA-treated human skin fibroblasts produce biologically active hHGF and the possible involvement of PKC activation in this process.

Homoeostatic imbalance during cellular ageing: altered responsiveness

The inability of normal cells to maintain themselves for ever is a reflection of homoeostatic imbalance and a progressive failure of maintenance. Ageing cells respond less to growth stimulants whereas they show increased sensitivity to toxic agents including antibiotics, phorbol esters, radiation and other physical stresses. No major quantitative and qualitative defects in the receptor systems have been detected that could explain the reasons for altered responsiveness during ageing. Random metabolic defects in the processes involved in maintaining homoeostasis may be critical for causing homoeostatic imbalance, cellular ageing and death.