Accumulation of oxidative DNA damage, 8-oxo-2'-deoxyguanosine, and change of repair systems during in vitro cellular aging of cultured human skin fibroblasts

The Relationship between Reactive Oxygen Species and the cGAS/STING Signaling Pathway in the Inflammaging Process

During Inflammaging, a dysregulation of the immune cell functions is generated, and these cells acquire a senescent phenotype with an increase in pro-inflammatory cytokines and ROS. This increase in pro-inflammatory molecules contributes to the chronic inflammation and oxidative damage of biomolecules, classically observed in the Inflammaging process. One of the most critical oxidative damages is generated to the host DNA. Damaged DNA is located out of the natural compartments, such as the nucleus and mitochondria, and is present in the cell's cytoplasm. This DNA localization activates some DNA sensors, such as the cGAS/STING signaling pathway, that induce transcriptional factors involved in increasing inflammatory molecules. Some of the targets of this signaling pathway are the SASPs. SASPs are secreted pro-inflammatory molecules characteristic of the senescent cells and inducers of ROS production. It has been suggested that oxidative damage to nuclear and mitochondrial DNA generates activation of the cGAS/STING pathway, increasing ROS levels induced by SASPs. These additional ROS increase oxidative DNA damage, causing a loop during the Inflammaging. However, the relationship between the cGAS/STING pathway and the increase in ROS during Inflammaging has not been clarified. This review attempt to describe the potential connection between the cGAS/STING pathway and ROS during the Inflammaging process, based on the current literature, as a contribution to the knowledge of the molecular mechanisms that occur and contribute to the development of the considered adaptative Inflammaging process during aging.

Activation of ALDH1A1 by omeprazole reduces cell oxidative stress damage

Under physiological conditions, cells produce low basal levels of reactive oxygen species (ROS); however, in pathologic conditions ROS production increases dramatically, generating high concentrations of toxic unsaturated aldehydes. Aldehyde dehydrogenases (ALDHs) are responsible for detoxification of these aldehydes protecting the cell. Due to the physiological relevance of these enzymes, it is important to design strategies to modulate their activity. It was previously reported that omeprazole activation of ALDH1A1 protected Escherichia coli cells overexpressing this enzyme, from oxidative stress generated by H2 O2 . In this work, omeprazole cell protection potential was evaluated in eukaryotic cells. AS-30D cell or hepatocyte suspensions were subjected to a treatment with omeprazole and exposure to light (that is required to activate omeprazole in the active site of ALDH) and then exposed to H2 O2 . Cells showed viability similar to control cells, total activity of ALDH was preserved, while cell levels of lipid aldehydes and oxidative stress markers were maintained low. Cell protection by omeprazole was avoided by inhibition of ALDHs with disulfiram, revealing the key role of these enzymes in the protection. Additionally, omeprazole also preserved ALDH2 (mitochondrial isoform) activity, diminishing lipid aldehyde levels and oxidative stress in this organelle, protecting mitochondrial respiration and transmembrane potential formation capacity, from the stress generated by H2 O2 . These results highlight the important role of ALDHs as part of the antioxidant system of the cell, since if the activity of these enzymes decreases under stress conditions, the viability of the cell is compromised.

Netrin-4 expression by human endothelial cells inhibits endothelial inflammation and senescence

Netrin-4, recognized in neural and vascular development, is highly expressed by mature endothelial cells. The function of this netrin-4 in vascular biology after development has remained unclear. We found that the expression of netrin-4 is highly regulated in endothelial cells and is important for quiescent healthy endothelium. Netrin-4 expression is upregulated in endothelial cells cultured under laminar flow conditions, while endothelial cells stimulated with tumor necrosis factor alpha resulted in decreased netrin-4 expression. Targeted reduction of netrin-4 in endothelial cells resulted in increased expression of vascular cell adhesion molecule 1 and intercellular adhesion molecule 1. Besides, these endothelial cells were more prone to monocyte adhesion and showed impaired barrier function, measured with electric cell-substrate impedance sensing, as well as in an 'organ-on-a-chip' microfluidic system. Importantly, endothelial cells with reduced levels of netrin-4 showed increased expression of the senescence-associated markers cyclin-dependent kinase inhibitor-1 and -2A, an increased cell size and decreased ability to proliferate. Consistent with the gene expression profile, netrin-4 reduction was accompanied with more senescent associated β-galactosidase activity, which could be rescued by adding netrin-4 protein. Finally, using human decellularized kidney extracellular matrix scaffolds, we found that pre-treatment of the scaffolds with netrin-4 increased numbers of endothelial cells adhering to the matrix, showing a pro-survival effect of netrin-4. Taken together, netrin-4 acts as an anti-senescence and anti-inflammation factor in endothelial cell function and our results provide insights as to maintain endothelial homeostasis and supporting vascular health.

Development of a solid-phase microextraction LC-MS/MS method for determination of oxidative stress biomarkers in biofluids

Recently the connection between oxidative stress and various diseases, including cancer and Alzheimer's, attracts notice as a pathway suitable for diagnostic purposes. 8-Oxo-deoxyguanosine and 8-oxo-deoxyadenosine produced from the interaction of reactive oxygen species with DNA become prominent as biomarkers. Several methods have been developed for their determination in biofluids, including solid-phase extraction and enzyme-linked immunosorbent assays. However, still, there is a need for reliable and fast analytical methods. In this context, solid-phase microextraction offers many advantages such as flexibility in geometry and applicable sample volume, as well as high adaptability to high-throughput sampling. In this study, a solid-phase microextraction method was developed for the determination of 8-oxo-deoxyguanosine and 8-oxo-deoxyadenosine in biofluids. The extractive phase of solid-phase microextraction consisted of hydrophilic-lipophilic balanced polymeric particles. In order to develop a solid-phase microextraction method suitable for the determination of the analytes in saliva and urine, several parameters, including desorption solvent, desorption time, sample pH, and ionic strength, were scrutinized. Analytical figures of merit indicated that the developed method provides reasonable interday and intraday precisions (<15% in both biofluids) with acceptable accuracy. The method provides a limit of quantification for both biomarkers at 5.0 and 10.0 ng/mL levels in saliva and urine matrices, respectively.

Association Between Telomere Length, Chronic Kidney Disease, and Renal Traits: A Systematic Review

Telomere length (TL) is an important biological variable that can influence a variety of disease-related complex traits as well as host-environment interactions such as drug and nutritional responses. Chronic kidney disease (CKD) is a common global health challenge especially with the currently aging world population. We conducted a PubMed database search according to the preferred reporting items for systematic reviews and meta-analysis (PRISMA) guidelines for systematic reviews. Studies in adults (18 years and above) in which TL was determined and correlated with CKD, renal traits, and function were included, while animal model studies were excluded. Nine studies comprising 7829 participants, published between 2005 and 2016, met the inclusion criteria. These included eight observational studies (six being prospective), and one clinical trial. Participants in two studies were diabetic patients with varying stages of CKD, and nondialysis chronic glomerulonephritis CKD patients in two other studies. TL measurements used polymerase chain reaction in five studies, terminal restriction fragmentation in three studies, and quantitative fluorescence in situ hybridization in one study. Short TL was independently associated with increased risk of prevalent microalbuminuria in diabetic men with CKD (p = 0.007). Among CKD patients with heterogeneous etiologies, however, there was an unadjusted lower risk (p < 0.001). Short TL was significantly associated with CKD progression among smokers (p = 0.001) and diabetic patients (p = 0.03). On the other hand, long TL was paradoxically associated with longer diagnosed duration of moderate CKD. We postulate that shortening TL might be associated with CKD prevalence/occurrence or declining kidney function, but this association is likely offset by the cellular telomere reparative process in those surviving longer with CKD. This systematic review underscores the need for future omics and human genetics research to delineate the contribution of TL to CKD, renal dysfunction, and related health outcomes. Telomeres and telomerase activity hold great promise for CKD risk stratification and personalized medicine.

Intrauterine growth restriction-induced deleterious adaptations in endothelial progenitor cells: possible mechanism to impair endothelial function

Intrauterine growth restriction (IUGR) can induce deleterious changes in the modulatory ability of the vascular endothelium, contributing to an increased risk of developing cardiovascular diseases in the long term. However, the mechanisms involved are not fully understood. Emerging evidence has suggested the potential role of endothelial progenitor cells (EPCs) in vascular health and repair. Therefore, we aimed to evaluate the effects of IUGR on vascular reactivity and EPCs derived from the peripheral blood (PB) and bone marrow (BM) in vitro. Pregnant Wistar rats were fed an ad libitum diet (control group) or 50% of the ad libitum diet (restricted group) throughout gestation. We determined vascular reactivity, nitric oxide (NO) concentration, and endothelial nitric oxide synthase (eNOS) protein expression by evaluating the thoracic aorta of adult male offspring from both groups (aged: 19-20 weeks). Moreover, the amount, functional capacity, and senescence of EPCs were assessed in vitro. Our results indicated that IUGR reduced vasodilation via acetylcholine in aorta rings, decreased NO levels, and increased eNOS phosphorylation at Thr495. The amount of EPCs was similar between both groups; however, IUGR decreased the functional capacity of EPCs from the PB and BM. Furthermore, the senescence process was accelerated in BM-derived EPCs from IUGR rats. In summary, our findings demonstrated the deleterious changes in EPCs from IUGR rats, such as reduced EPC function and accelerated senescence in vitro. These findings may contribute towards elucidating the possible mechanisms involved in endothelial dysfunction induced by fetal programming.

PEX5, the shuttling import receptor for peroxisomal matrix proteins, is a redox-sensitive protein

Peroxisome maintenance depends on the import of nuclear-encoded proteins from the cytosol. The vast majority of these proteins is destined for the peroxisomal lumen and contains a C-terminal peroxisomal targeting signal, called PTS1. This targeting signal is recognized in the cytosol by the receptor PEX5. After docking at the peroxisomal membrane and release of the cargo into the organelle matrix, PEX5 is recycled to the cytosol through a process requiring monoubiquitination of an N-terminal, cytosolically exposed cysteine residue (Cys11 in the human protein). At present, the reason why a cysteine, and not a lysine residue, is the target of ubiquitination remains unclear. Here, we provide evidence that PTS1 protein import into human fibroblasts is a redox-sensitive process. We also demonstrate that Cys11 in human PEX5 functions as a redox switch that regulates PEX5 activity in response to intracellular oxidative stress. Finally, we show that exposure of human PEX5 to oxidized glutathione results in a ubiquitination-deficient PEX5 molecule, and that substitution of Cys11 by a lysine can counteract this effect. In summary, these findings reveal that the activity of PEX5, and hence PTS1 import, is controlled by the redox state of the cytosol. The potential physiological implications of these findings are discussed.

Oxidized extracellular DNA as a stress signal that may modify response to anticancer therapy

An increase in the levels of oxidation is a universal feature of genomic DNA of irradiated or aged or even malignant cells. In case of apoptotic death of stressed cells, oxidized DNA can be released in circulation (cfDNA). According to the results of the studies performed in vitro by our group and other researchers, the oxidized cfDNA serves as a biomarker for a stress and a stress signal that is transmitted from the "stressed" area i.e. irradiated cells or cells with deficient anti-oxidant defenses to distant (bystander) cells. In recipient cells, oxidized DNA stimulates biosynthesis of ROS that is followed up by an increase in the number of single strand and double strand breaks (SSBs and DSBs), and activation of DNA Damage Response (DDR) pathway. Effects of oxidized DNA are considered similar to that of irradiation. It seems that downstream effects of irradiation, in part, depend on the release of oxidized DNA fragments that mediate the effects in distant cells. The responses of normal and tumor cell to oxidized DNA may differ. It seems that tumor cells are more sensitive to oxidized DNA-dependent DNA damage, while developing pronounced adaptive response. This may suggest that in chemotherapy or irradiation-treated human body, the release of oxidized DNA from dying cancer cells may give a boost to remaining malignant cells by augmenting their survival and stress resistance. Further studies of the effects of oxidized DNA in both in vitro and in vivo systems are warranted.

Reduced host cell reactivation of oxidatively damaged DNA in ageing human fibroblasts

Many reports have linked oxidative damage to DNA and the associated avoidance and/or repair processes to carcinogenesis, ageing and neurodegeneration. Cancer incidence increases with age and there is evidence that oxidative stress plays a role in human ageing and neurodegeneration. Several reports have suggested that the accumulation of unrepaired DNA lesions plays a causal role in mammalian ageing. Since base excision repair (BER) is the main pathway for the repair of oxidative DNA lesions, the relationship of BER to human ageing and carcinogenesis is of considerable interest. The aim of the present study was to examine the relationship between donor age and increasing time of cells in tissue culture and the repair of oxidative DNA damage in primary human skin fibroblasts. Methylene blue (MB) acts as a photosensitizer and after excitation by visible light (VL) produces reactive oxygen species that result in oxidative damage to DNA. MB+VL produce predominantly 8-hydroxyguanine as well as other single base modifications in DNA that are repaired by BER. We used host cell reactivation (HCR) of a non-replicating recombinant human adenovirus, Ad5CMVlacZ, which expresses the β-galactosidase (β-gal) reporter gene, to measure BER of MB+VL-damaged DNA. HCR of β-gal activity for the MB+VL-treated reporter gene was examined in 10 fibroblast strains from normal donors of ages 2 to 82. The effect of cell passage number on HCR was also examined in human skin fibroblasts from 2 normal donors. We found a significant reduction in HCR with increasing cell passage number, indicating that BER decreases with increasing time of cells grown in tissue culture. We also found a significant correlation of donor age with HCR of the MB+VL-treated reporter gene for high passage number, but not for low passage number fibroblasts. The present study provides evidence that a decrease in BER of oxidatively damaged DNA may play a role in carcinogenesis, ageing and neurodegeneration.

Assessment of base-excision repair activity in fish cell lines: toward a new biomarker of exposure to environmental contaminants?

Amongst DNA-repair processes, base-excision repair (BER) is the major mechanism for removal of DNA-base lesions caused by environmental genotoxicants. BER has been proven to exist in fish but has not been investigated in fish cell-lines, although these constitute increasingly important tools in eco-toxicological assessment. The present study aims at highlighting BER capacity of RTL-W1 and RTG-W1, two trout cell lines used in eco-genotoxicity studies. This is realized by following the kinetics of strand-break repair after a short exposure to model genotoxicants-leading predominantly to BER-specific lesions-by means of the standard alkaline and Fpg-modified comet assays. Results show that both cell lines efficiently repair single-strand breaks and base-alkylation damages within 4h and 24h, respectively. Then, the study shows that after minor modifications of the protocol, the cell extract-based BERc assay can be used to evaluate the base-incision capacity of the cell lines and its variation after exposure of the cells to a model inhibitor of BER (3-aminobenzamide) and to environmental contaminants such as cadmium and tributyltin. This work provides a basis for the further development of DNA-repair activity in fish cell-lines as a new biomarker of genotoxicity.

Oxidized extracellular DNA as a stress signal in human cells

The term "cell-free DNA" (cfDNA) was recently coined for DNA fragments from plasma/serum, while DNA present in in vitro cell culture media is known as extracellular DNA (ecDNA). Under oxidative stress conditions, the levels of oxidative modification of cellular DNA and the rate of cell death increase. Dying cells release their damaged DNA, thus, contributing oxidized DNA fragments to the pool of cfDNA/ecDNA. Oxidized cell-free DNA could serve as a stress signal that promotes irradiation-induced bystander effect. Evidence points to TLR9 as a possible candidate for oxidized DNA sensor. An exposure to oxidized ecDNA stimulates a synthesis of reactive oxygen species (ROS) that evokes an adaptive response that includes transposition of the homologous loci within the nucleus, polymerization and the formation of the stress fibers of the actin, as well as activation of the ribosomal gene expression, and nuclear translocation of NF-E2 related factor-2 (NRF2) that, in turn, mediates induction of phase II detoxifying and antioxidant enzymes. In conclusion, the oxidized DNA is a stress signal released in response to oxidative stress in the cultured cells and, possibly, in the human body; in particular, it might contribute to systemic abscopal effects of localized irradiation treatments.

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.

Aging and photo-aging DNA repair phenotype of skin cells-evidence toward an effect of chronic sun-exposure

Several studies have demonstrated the deleterious effect of aging on the capacity of cells to repair their DNA. However, current existing assays aimed at measuring DNA repair address only a specific repair step dedicated to the correction of a specific DNA lesion type. Consequently they provide no information regarding the repair pathways that handle other types of lesions. In addition to aging, consequences of photo-exposure on these repair processes remain elusive. In this study we evaluated the consequence of aging and of chronic and/or acute photo-exposure on DNA repair in human skin fibroblasts using a multiplexed approach, which provided detailed information on several repair pathways at the same time. The resulting data were analyzed with adapted statistics/bioinformatics tools. We showed that, irrespective of the repair pathway considered, excision/synthesis was less efficient in non-exposed cells from elderly compared to cells from young adults and that photo-exposure disrupted this very clear pattern. Moreover, it was evidenced that chronic sun-exposure induced changes in DNA repair properties. Finally, the identification of a specific signature at the level of the NER pathway in cells repeatedly exposed to sun revealed a cumulative effect of UVB exposure and chronic sun irradiation. The uses of bioinformatics tools in this study was essential to fully take advantage of the large sum of data obtained with our multiplexed DNA repair assay and unravel the effects of environmental exposure on DNA repair pathways.

gamma-Tocotrienol prevents oxidative stress-induced telomere shortening in human fibroblasts derived from different aged individuals

The effects of palm gamma-tocotrienol (GGT) on oxidative stress-induced cellular ageing was investigated in normal human skin fibroblast cell lines derived from different age groups; young (21-year-old, YF), middle (40-year-old, MF) and old (68-year-old, OF). Fibroblast cells were treated with gamma-tocotrienol for 24 hours before or after incubation with IC50 dose of H2O2 for 2 hours. Changes in cell viability, telomere length and telomerase activity were assessed using the MTS assay (Promega, USA), Southern blot analysis and telomere repeat amplification protocol respectively. Results showed that treatment with different concentrations of gamma-tocotrienol increased fibroblasts viability with optimum dose of 80 microM for YF and 40 microM for both MF and OF. At higher concentrations, gamma-tocotrienol treatment caused marked decrease in cell viability with IC50 value of 200 microM (YF), 300 microM (MF) and 100 microM (OF). Exposure to H2O2 decreased cell viability in dose dependent manner, shortened telomere length and reduced telomerase activity in all age groups. The IC50 of H2O2 was found to be; YF (700 microM), MF (400 microM) and OF (100 microM). Results showed that viability increased significantly (p < 0.05) when cells were treated with 80 microM and 40 microM gamma-tocotrienol prior or after H2O2-induced oxidative stress in all age groups. In YF and OF, pretreatment with gamma-tocotrienol prevented shortening of telomere length and reduction in telomerase activity. In MF, telomerase activity increased while no changes in telomere length was observed. However, post-treatment of gamma-tocotrienol did not exert any significant effects on telomere length and telomerase activity. Thus, these data suggest that gamma-tocotrienol protects against oxidative stress-induced cellular ageing by modulating the telomere length possibly via telomerase.

Induction effect of coadministration of soybean isoflavones and sodium nitrite on DNA damage in mouse stomach

We have already found that nitrite-treated isoflavones exhibit genotoxic activities toward Salmonella typhimurium TA 100 and 98 strains (submitted: nitrite-treated genistein). However, we have not demonstrated genotoxic activity induced by simultaneous treatment with isoflavones and NaNO(2)in vivo. In the present study, we examined whether coadministration of isoflavones (such as daidzein and genistein) and NaNO(2) induces DNA damage in the stomach of ICR male mice. Mice were coadministered with isoflavones (1mg/kg body weight) and NaNO(2) (10mg/kg body weight), and dissected to collect tissues at 1, 3, and 6h after administration. We used comet assay combined with repair enzyme formamidopyrimidine-N-glycosylase (FPG) to detect FPG-sensitive sites. An HPLC-ECD system was employed to determine 8-oxo-2'-deoxyguanosine (8-oxodG) in the stomach. In addition, we observed leukocyte infiltration by histopathological investigation, and measured total superoxide dismutase (SOD) in the stomach. We confirmed that oxidative DNA damage in the stomach was significantly increased by coadministration. Total SOD activities were also significantly stimulated by coadministration. However, the induction of inflammation in the stomach was not found. These data suggest that coadministration of isoflavones and NaNO(2) can cause DNA damage in the stomach because of the formation of radicals.

DNA polymerases involved in the incorporation of oxidized nucleotides into DNA: their efficiency and template base preference

Genetic information must be duplicated with precision and accurately passed on to daughter cells and later generations. In order to achieve this goal, DNA polymerases (Pols) have to faithfully execute DNA synthesis during chromosome replication and repair. However, the conditions under which Pols synthesize DNA are not always optimal; the template DNA can be damaged by various endogenous and exogenous genotoxic agents including reactive oxygen species (ROS), and ROS oxidize dNTPs in the nucleotide pool from which Pols elongate DNA strands. Both damaged DNA and oxidized dNTPs interfere with faithful DNA synthesis by Pols, inducing various cellular abnormalities, such as mutations, cancer, neurological diseases, and cellular senescence. In this review, we focus on the process by which Pols incorporate oxidized dNTPs into DNA and compare the properties of Pols: efficiency, i.e., k(cat)/K(m), k(pol)/K(d) or V(max)/K(m), and template base preference for the incorporation of 8-oxo-dGTP, an oxidized form of dGTP. In general, Pols involved in chromosome replication, the A- and B-family Pols, are resistant to the incorporation of 8-oxo-dGTP, whereas Pols involved in repair and/or translesion synthesis, the X- and Y-family Pols, incorporate nucleotides in a relatively efficient manner and tend to incorporate it opposite template dA rather than template dC, though there are several exceptions. We discuss the molecular mechanisms by which Pols exhibit different template base preferences for the incorporation of 8-oxo-dGTP and how Pols are involved in the induction of mutations via the incorporation of oxidized nucleotides under oxidative stress.

Suppression of oxidative stress by resveratrol after isometric contractions in gastrocnemius muscles of aged mice

This study tested the hypothesis that resveratrol supplementation would lower oxidative stress in exercised muscles of aged mice. Young (3 months) and aged (27 months) C57BL/6 mice received a control or a 0.05% trans-resveratrol-supplemented diet for 10 days. After 7 days of dietary intervention, 20 maximal electrically evoked isometric contractions were obtained from the plantar flexors of one limb in anesthetized mice. Exercise was conducted for three consecutive days. Resveratrol supplementation blunted the exercise-induced increase in xanthine oxidase activity in muscles from young (25%) and aged (53%) mice. Resveratrol lowered H(2)O(2) levels in control (13%) and exercised (38%) muscles from aged animals, reduced Nox4 protein in both control and exercised muscles of young (30%) and aged mice (40%), and increased the ratio of reduced glutathione to oxidized glutathione in exercised muscles from young (38%) and aged (135%) mice. Resveratrol prevented the increase in lipid oxidation, increased catalase activity, and increased MnSOD activity in exercised muscles from aged mice. These data show that dietary resveratrol suppresses muscle indicators of oxidative stress in response to isometric contractions in aged mice.

Continuous elimination of oxidized nucleotides is necessary to prevent rapid onset of cellular senescence

Reactive oxygen species (ROS) appear to play a role in limiting both cellular and organismic lifespan. However, because of their pleiotropic effects, it has been difficult to ascribe a specific role to ROS in initiating the process of cellular senescence. We have studied the effects of oxidative DNA damage on cell proliferation, believing that such damage is of central importance to triggering senescence. To do so, we devised a strategy to decouple levels of 8-oxoguanine, a major oxidative DNA lesion, from ROS levels. Suppression of MTH1 expression, which hydrolyzes 8-oxo-dGTP, was accompanied by increased total cellular 8-oxoguanine levels and caused early-passage primary and telomerase-immortalized human skin fibroblasts to rapidly undergo senescence, doing so without altering cellular ROS levels. This senescent phenotype recapitulated several salient features of replicative senescence, notably the presence of senescence-associated beta-galactosidase (SA beta-gal) activity, apparently irreparable genomic DNA breaks, and elevation of p21(Cip1), p53, and p16(INK4A) tumor suppressor protein levels. Culturing cells under low oxygen tension (3%) largely prevented the shMTH1-dependent senescent phenotype. These results indicate that the nucleotide pool is a critical target of intracellular ROS and that oxidized nucleotides, unless continuously eliminated, can rapidly induce cell senescence through signaling pathways very similar to those activated during replicative senescence.

Aging-dependent regulation of antioxidant enzymes and redox status in chronically loaded rat dorsiflexor muscles

This study compares changes in the pro-oxidant production and buffering capacity in young and aged skeletal muscle after exposure to chronic repetitive loading (RL). The dorsiflexors from one limb of young and aged rats were loaded 3 times/week for 4.5 weeks using 80 maximal stretch-shortening contractions per session. RL increased H2O2 in tibialis anterior muscles of young and aged rats and decreased the ratio of reduced/oxidized glutathione and lipid peroxidation in aged but not young adult animals. Glutathione peroxidase (GPx) activity decreased whereas catalase activity increased with RL in muscles from young and aged rats. RL increased CuZn superoxide disumutase (SOD) and Mn SOD protein concentration and CuZn SOD activity in muscles from young but not aged animals. There were no changes in protein content for GPx-1 and catalase or messenger RNA for any of the enzymes studied. These data show that aging reduces the adaptive capacity of muscles to buffer increased pro-oxidants imposed by chronic RL.

Vulnerability to oxidative stress and different patterns of senescence in human peritoneal mesothelial cell strains

Both the ascites fluid-derived mesothelial cell line LP-9 and primary cultures of human omentum-derived mesothelial cells (HOMCs) are commonly used in experimental studies. However, they seem to have a different replicative potential in vitro. In the present study, we have attempted to determine the causes of this discrepancy. HOMCs were found to divide fewer times and enter senescence earlier than LP-9 cells. This effect was coupled with earlier increases in the expression of senescence-associated-beta-galactosidase and cell cycle inhibitors p16INK4a and p21WAF1. Moreover, almost 3 times as many early-passage HOMCs as LP-9 cells bore senescence-associated DNA damage foci. In sharp contrast to LP-9 cells, the foci present in HOMCs localized predominantly outside the telomeres, and the HOMC telomere length did not significantly shorten during senescence. Compared with LP-9 cells, HOMCs were found to enter senescence with significantly lower levels of lipofuscin and damaged DNA, and markedly decreased glutathione contents. In addition, early-passage HOMCs generated significantly more reactive oxygen species either spontaneously or in response to exogenous oxidants. These results indicate that compared with LP-9 cells, HOMCs undergo stress-induced telomere-independent premature senescence, which may result from increased vulnerability to oxidative DNA injury.

Antioxidant levels represent a major determinant in the regenerative capacity of muscle stem cells

Stem cells are classically defined by their multipotent, long-term proliferation, and self-renewal capabilities. Here, we show that increased antioxidant capacity represents an additional functional characteristic of muscle-derived stem cells (MDSCs). Seeking to understand the superior regenerative capacity of MDSCs compared with myoblasts in cardiac and skeletal muscle transplantation, our group hypothesized that survival of the oxidative and inflammatory stress inherent to transplantation may play an important role. Evidence of increased enzymatic and nonenzymatic antioxidant capacity of MDSCs were observed in terms of higher levels of superoxide dismutase and glutathione, which appears to confer a differentiation and survival advantage. Further when glutathione levels of the MDSCs are lowered to that of myoblasts, the transplantation advantage of MDSCs over myoblasts is lost when transplanted into both skeletal and cardiac muscles. These findings elucidate an important cause for the superior regenerative capacity of MDSCs, and provide functional evidence for the emerging role of antioxidant capacity as a critical property for MDSC survival post-transplantation.

Endothelial progenitor cells dysfunction and senescence: contribution to oxidative stress

The identification of endothelial progenitor cells (EPCs) has led to a significant paradigm in the field of vascular biology and opened a door to the development of new therapeutic approaches. Based on the current evidence, it appears that EPCs may make both direct contribution to neovascularization and indirectly promote the angiogenic function of local endothelial cells via secretion of angiogenic factors. This concept of arterial wall repair mediated by bone marrow (BM)-derived EPCs provided an alternative to the local "response to injury hypothesis" for development of atherosclerotic inflammation. Increased oxidant stress has been proposed as a molecular mechanism for endothelial dysfunction, in part by reducing nitric oxide (NO) bioavailability. EPCs function may also be highly dependent on a well-controlled oxidant stress because EPCs NO bioavailability (which is highly sensitive to oxidant stress) is critical for their in vivo function. The critical question is whether oxidant damage directly leads to an impairment in EPCs function. It was revealed that activation of angiotensin II (Ang II) type 1 receptor stimulates nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase in the vascular endothelium and leads to production of reactive oxygen species. We observed that Ang II accelerates both BM- and peripheral blood (PB)-derived EPCs senescence by a gp91phox-mediated increase of oxidative stress, resulting in EPCs dysfunction. Consistently, both Ang II receptor 1 blockers (ARBs) and angiotensin converting enzyme (ACE) inhibitors have been reported to increase the number of EPCs in patients with cardiovascular disease. In this review, we describe current understanding of the contributions of oxidative stress in cardiovascular disease, focusing on the potential mechanisms of EPCs senescence.

Nitric oxide and endothelial cellular senescence

Cellular senescence is characterized by permanent exit from the cell cycle and the appearance of distinct morphological and functional changes associated with an impairment of cellular homeostasis. Many studies support the occurrence of vascular endothelial cell senescence in vivo, and the senescent phenotype of endothelial cells can be transformed from anti-atherosclerotic to pro-atherosclerotic. Thus, endothelial cell senescence promotes endothelial dysfunction and may contribute to the pathogenesis of age-associated vascular disorders. Emerging evidence suggests that increasing nitric oxide (NO) bioavailability or endothelial NO synthase (eNOS) activity activates telomerase and delays endothelial cell senescence. In this review, we discuss the potential mechanisms underlying the ability of NO to prevent endothelial cell senescence and describe the possible changes in the NO-mediated anti-senescence effect under pathophysiological conditions, including oxidative stress and hyperglycemia. Further understanding of the mechanisms underlying the anti-senescence effect of NO in endothelial cells will provide insights into the potential of eNOS-based anti-senescence therapy for age-associated vascular disorders.

Altered 8-oxoguanine glycosylase in mild cognitive impairment and late-stage Alzheimer's disease brain

Eight-hydroxy-2'-deoxyguanosine (8-OHdG) is increased in the brain in late-stage Alzheimer's disease (LAD) and mild cognitive impairment (MCI). To determine if decreased base-excision repair contributes to these elevations, we measured oxoguanine glycosylase 1 (OGG1) protein and incision activities in nuclear and mitochondrial fractions from frontal (FL), temporal (TL), and parietal (PL) lobes from 8 MCI and 7 LAD patients, and 6 age-matched normal control (NC) subjects. OGG1 activity was significantly (P<0.05) decreased in nuclear specimens of FL, TL, and PL in MCI and LAD and in mitochondria from LAD FL and TL and MCI TL. Nuclear OGG1 protein was significantly decreased in LAD FL and MCI and LAD PL. No differences in mitochondrial OGG1 protein levels were found. Overall, our results suggest that decreased OGG1 activity occurs early in the progression of AD, possibly mediated by 4-hydroxynonenal inactivation and may contribute to elevated 8-OHdG in the brain in MCI and LAD.

Cellular senescence, cardiovascular risk, and CKD: a review of established and hypothetical interconnections

Cellular senescence is associated with shortened or damaged telomeres and is characterized by permanent exit from the cell cycle, morphological changes, and altered function. It develops after repeated cell divisions and also can be induced prematurely by stress conditions. The senescent phenotype, depending on cell type and atherosclerosis phase, seems to be a proatherosclerotic one: it promotes endothelial dysfunction and appears to be implicated in plaque destabilization, as well as in endothelial progenitor cell alteration. Many traditional and nontraditional cardiovascular disease risk factors induce senescence in a variety of vascular cells. Several of these factors, such as diabetes, hypertension, oxidative stress, and inflammation, are clustered in patients with chronic kidney disease. In a limited number of recent studies, stress-induced premature cellular senescence in this biologically aged population also was described. The hypothesis that premature cellular senescence might be considered an additional atherosclerosis-inducing factor in patients with chronic kidney disease is proposed.

Processing of DNA damage clusters in human cells: current status of knowledge

Eukaryotic cells exposed to DNA damaging agents activate important defensive pathways by inducing multiple proteins involved in DNA repair, cell cycle checkpoint control and potentially apoptosis. After the acceptance of the hypothesis that oxidatively generated clustered DNA lesions (OCDL: closely spaced DNA lesions) can be induced even by low doses of ionizing radiation or even endogenously, and significant advances have been made in the understanding of the biochemistry underlying the repair of closely spaced DNA lesions, many questions still remain unanswered. The major questions that have to be answered in the near future are: 1) how human cells process these types of DNA damage if they repair them at all, 2) under what conditions a double strand break (DSB) may be created during the processing of two closely spaced DNA lesions and 3) what type of repair protein interactions govern the processing of complex DNA damage? The data existing so far on human cells and tissues are very limited and in some cases contradicting. All of them though agree however on the major importance of gaining mechanistic insights on the pathways used by the cell to confront and process complex DNA damage located in a small DNA volume and the need of more in depth analytical studies. We selectively review recently-obtained data on the processing of non-DSB DNA damage clusters in human cells and tissues and discuss the current status of knowledge in the field.

Oxidative DNA damage in mild cognitive impairment and late-stage Alzheimer's disease

Increasing evidence supports a role for oxidative DNA damage in aging and several neurodegenerative diseases including Alzheimer's disease (AD). Attack of DNA by reactive oxygen species (ROS), particularly hydroxyl radicals, can lead to strand breaks, DNA–DNA and DNA–protein cross-linking, and formation of at least 20 modified bases adducts. In addition, α,β-unsaturated aldehydic by-products of lipid peroxidation including 4-hydroxynonenal and acrolein can interact with DNA bases leading to the formation of bulky exocyclic adducts. Modification of DNA bases by direct interaction with ROS or aldehydes can lead to mutations and altered protein synthesis. Several studies of DNA base adducts in late-stage AD (LAD) brain show elevations of 8-hydroxyguanine (8-OHG), 8-hydroxyadenine (8-OHA), 5-hydroxycytosine (5-OHC), and 5-hydroxyuracil, a chemical degradation product of cytosine, in both nuclear and mitochondrial DNA (mtDNA) isolated from vulnerable regions of LAD brain compared to age-matched normal control subjects. Previous studies also show elevations of acrolein/guanine adducts in the hippocampus of LAD subjects compared to age-matched controls. In addition, studies of base excision repair show a decline in repair of 8-OHG in vulnerable regions of LAD brain. Our recent studies show elevated 8-OHG, 8-OHA, and 5,6-diamino-5-formamidopyrimidine in both nuclear and mtDNA isolated from vulnerable brain regions in amnestic mild cognitive impairment, the earliest clinical manifestation of AD, suggesting that oxidative DNA damage is an early event in AD and is not merely a secondary phenomenon.

DNA repair capacities of cutaneous fibroblasts: effect of sun exposure, age and smoking on response to an acute oxidative stress

BACKGROUND

Sun irradiation causes skin ageing and cancer through the accumulation of damage to cell components. Intrinsic ageing is also associated with accumulation of oxidized macromolecules.

OBJECTIVES

In this study we investigated the effects of sun exposure on response to an acute in vitro oxidative stress (H(2)O(2)) using normal human fibroblasts prepared from biopsies from 10 volunteers taken from sun-protected and sun-exposed sites.

METHODS

Time-course experiments measuring repair of DNA strand-breaks and formamidopyrimidine DNA N-glycosylase-sensitive sites were conducted using the single-cell gel electrophoresis (comet) assay.

RESULTS

Our results demonstrated that repair of strand-breaks was slower in sun-exposed compared with sun-protected cells. Interestingly, ageing was also associated with decreased DNA repair capacities for single-strand breaks in both sun-exposed and sun-protected cells whereas for formamidopyrimidine glycosylase (Fpg)-sensitive sites, this feature was in evidence only in sun-protected cells. Smoking, associated with age, was shown to have a markedly negative impact on DNA repair.

CONCLUSIONS

Taken together our data suggest that stresses like ageing, sun exposure and smoking might have an additive effect contributing to the overall heterogeneity and decrease of DNA repair capacities in human cells and so increase the danger of sun exposure for health. They also emphasize the importance of the quality of the biological samples when repair studies on skin cells are to be conducted.

Premature senescence of endothelial cells: Methusaleh's dilemma

Senescence has been considered a programmed cellular response, parallel to apoptosis, that is turned on when a cell reaches Hayflick's limit. Once cells enter the senescence program, they cease to proliferate and undergo a series of morphological and functional changes. Studies support a central role for Rb protein in controlling this process after it receives senescent signals from the p53 and p16 pathways. Cellular senescence is considered an essential contributor to the aging process and has been shown to be an important tumor suppression mechanism. In addition, emerging evidence suggests that senescence may also be involved in the pathogenesis of stem cell dysfunction and chronic human diseases. Under these circumstances cells undergo stress-induced premature senecence, which has several specific features. Focusing on endothelial cells, we discuss recent advances in our understanding of the stresses and their pathways that prompt the premature senescence response, evaluate their correlation with the apoptotic response, and examine their links to the development of chronic diseases and the impaired function of endothelial progenitor cells, with the emphasis on vasculopathy. Emerging novel therapeutic interventions based on recent experimental findings are also reviewed.

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.

Early loss of proliferative potential of human peritoneal mesothelial cells in culture: the role of p16INK4a-mediated premature senescence

Much has been learned about the mechanisms underlying cellular senescence. The pathways leading to senescence appear to vary, depending on the cell type and cell culture conditions. In this respect, little is known about senescence of human peritoneal mesothelial cells (HPMC). Previous studies have significantly differed in the reported proliferative lifespan of HPMC. Therefore, in the present study, we have examined how HPMC enter state of senescence under conditions typically used for HPMC culture. HPMC were isolated from omentum and grown into senescence. The cultures were assessed for the growth rate, the presence of senescence markers, activation of cell-cycle inhibitors, and the oxidative stress. HPMC were found to reach, on average, six population doublings before senescence. The terminal growth arrest was associated with decreased expression of Ki67 antigen, increased percentage of cells in the G1 phase, reduced early population doubling level cDNA-1 mRNA expression, and the presence of senescence-associated beta-galactosidase. Compared with early-passage cells, the late-passage HPMC exhibited increased expression of p16INK4a but not of p21Cip1. In addition, these cells generated more reactive oxygen species and displayed increased presence of oxidatively modified DNA (8-hydroxy-2'-deoxyguanosine). These results demonstrate that early onset of senescence in omentum-derived HPMC may be associated with oxidative stress-induced upregulation of p16INK4a.

Increased oxidative protein and DNA damage but decreased stress response in the aged brain following experimental stroke

Aged individuals experience the highest rate of stroke and have less functional recovery, but do not have larger infarcts. We hypothesized that aged individuals experience greater sublethal damage in peri-infarct cortex. Focal cortical stroke was produced in aged and young adult animals. After 30 min, 1, 3 and 5 days brain sections and Western blot were used to analyze markers of apoptotic cell death, oxidative DNA and protein damage, heat shock protein (HSP) 70 induction, total neuronal number and infarct size. Focal stroke produces significantly more oxidative DNA and protein damage and fewer cells with HSP70 induction in peri-infarct cortex of aged animals. There is no difference in infarct size or the number of cells undergoing apoptosis between aged and young adults. Stroke in the aged brain is associated with a greater degree of DNA and protein damage and a reduced stress response in intact, surviving tissue that surrounds the infarct.

Oxidative DNA damage and disease: induction, repair and significance

The generation of reactive oxygen species may be both beneficial to cells, performing a function in inter- and intracellular signalling, and detrimental, modifying cellular biomolecules, accumulation of which has been associated with numerous diseases. Of the molecules subject to oxidative modification, DNA has received the greatest attention, with biomarkers of exposure and effect closest to validation. Despite nearly a quarter of a century of study, and a large number of base- and sugar-derived DNA lesions having been identified, the majority of studies have focussed upon the guanine modification, 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-OH-dG). For the most part, the biological significance of other lesions has not, as yet, been investigated. In contrast, the description and characterisation of enzyme systems responsible for repairing oxidative DNA base damage is growing rapidly, being the subject of intense study. However, there remain notable gaps in our knowledge of which repair proteins remove which lesions, plus, as more lesions identified, new processes/substrates need to be determined. There are many reports describing elevated levels of oxidatively modified DNA lesions, in various biological matrices, in a plethora of diseases; however, for the majority of these the association could merely be coincidental, and more detailed studies are required. Nevertheless, even based simply upon reports of studies investigating the potential role of 8-OH-dG in disease, the weight of evidence strongly suggests a link between such damage and the pathogenesis of disease. However, exact roles remain to be elucidated.

Decline of nuclear and mitochondrial oxidative base excision repair activity in late passage human diploid fibroblasts

There are numerous studies documenting the increase of oxidative DNA damage in the nuclei and mitochondria of senescing cells as well as in tissues of aging animals. Here, we show that in IMR 90 human diploid fibroblasts, DNA repair activity is robust in both nuclear and mitochondrial extracts, however, the levels of activity differed against the three substrates tested. In extracts, cleavage of the 8-oxoguanine substrate, and to a lesser extent the dihydrouracil-containing substrate, occurred in a concerted reaction between the DNA glycosylases and the second enzyme in the reaction, hAPE. Cleavage of both the furan and the dihydrouracil-containing substrates was unchanged when nuclear extracts from early and late passage cells were compared. However, cleavage of the 8-oxoguanine substrate was substantially reduced in the nuclear extracts from late passage cells and significantly reduced transcription from the hOGG1 gene was observed. When mitochondrial extracts were examined, activity on all three substrates was significantly reduced, with the reduction in hAPE activity being the most marked. The reduction in cleavage of the furan substrate was not simply due to inactive mitochondrial AP endonuclease but a substantially reduced amount of hAPE protein; transcription from the hAPE gene was also reduced. Confocal microscopic analysis confirmed that hAPE was present in the mitochondria of early passage cells but greatly reduced in the mitochondria of late passage cells. Cytoplasmic extracts from late passage fibroblasts also showed reduced activity with all three substrates suggesting that the residual hAPE, and activities that recognized dihydrouracil, were preferentially targeted to the nuclei. Taken together the data support the concept that the increase in oxidative damage in the mitochondrial DNA of senescing cells and tissues from aging animals is due to reduced base excision repair activity.

Suppression of lipid hydroperoxide-induced oxidative damage to cellular DNA by esculetin

Linoleic acid hydroperoxide (LOOH) has been reported to cause an increase in the content of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a typical oxidation product of DNA bases, in cultured cells due to coexisting iron(III) ion. We examined whether coumarins are able to suppress the formation of 8-oxodG in the DNA of human diploid fibroblasts, TIG-7 cells, treated with LOOH and iron(III) ion. Cotreatment of TIG-7 cells with esculetin (6,7-dihydroxycoumarin) significantly suppressed the increase in 8-oxodG content induced by LOOH and iron(III) ion. Pretreatment of cells with esculetin for 24 h was also effective in protecting cellular DNA against oxidative damage induced by subsequent treatment with LOOH and iron(III) ion. Pretreatment with esculin, the 6-glucoside of esculetin, was effective, but to a lesser extent. Furthermore, the free radical-scavenging activities of coumarins and hydroxycinnamic acids were examined by measuring the inhibition of spin-adduct formation of hydroxyl radicals with 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Compounds bearing an ortho-catechol moiety, such as esculetin, fraxetin, and caffeic acid, significantly reduced the ESR signal intensities of the DMPO-OH spin adduct. These results indicate that esculetin is effective in protecting cells against DNA damage induced by oxidative stress and that the presence of an ortho-catechol moiety is important for antioxidant activities against reactive oxygen species.

Age-associated decrease of oxidative repair enzymes, human 8-oxoguanine DNA glycosylases (hOgg1), in human aging

8-Oxoguanine has been shown to be a dominant cause of oxidative DNA damage by oxygen free radicals in eukaryotic cells. The 8-oxoguanine repair-specific enzyme 8-oxoguanine-DNA glycosylase (hOgg1) was recently cloned and was observed to conduct mainly short-patch base-excision repair. It has also been suggested that reactive oxygen species play an important role in the cellular aging process. We explored the association between the hOgg1 enzyme activity in somatic cells of human subjects of various ages and the role of hOgg1(326) genetic polymorphism. An 8-oxoguanine-containing 28 mer oligonucleotide was end-labeled with gamma-32P ATP and incubated with protein extracts from peripheral blood lymphocytes (PBL) from 78 healthy individuals ranging in age from newborn to 91 years old. The hOgg1 repair activity toward the radiolabelled 8-oxoguanine-containing DNA was determined, and the results indicated a significant age-dependent decrease in the hOgg1 activity in their lymphocytes. Significantly reduced activity was also shown in those with Cysteine/Cysteine genotypes. The genders of the subjects were not shown to be associated. These results provide an important observation regarding the cellular hOgg1 activity in somatic cells during the normal human aging processes.