Subcellular localization and modification with ageing of glutathione, glutathione peroxidase and glutathione reductase activities in human fibroblasts

The critical role of mitochondrial lipid peroxidation in ferroptosis: insights from recent studies

Ferroptosis is a regulated form of necrotic cell death reliant on iron-catalyzed lipid peroxidation. Although the precise involvement of mitochondria in ferroptosis remains incompletely elucidated, recent research indicates that mitochondrial oxidative events wield a pivotal influence in this mechanism. This article centers on the most recent discoveries, spotlighting the significance of mitochondrial lipid peroxidation in the occurrence of ferroptosis. Modern investigative tools, such as mitochondria-specific dyes responsive to lipid peroxidation and antioxidants targeting mitochondria, have been employed to delve into this phenomenon. The authors' recent empirical evidence demonstrates that mitochondrial lipid peroxidation, quantified using the innovative fluorescent ratiometric probe MitoCLox, takes place prior to the onset of ferroptotic cell death. The mitochondria-targeted antioxidant SkQ1 hinders mitochondrial lipid peroxidation and thwarts ferroptosis, all while leaving unaffected the buildup of reactive oxygen species within the cytoplasm, an antecedent to mitochondrial lipid peroxidation. Similarly, the redox agent methylene blue, impeding the genesis of reactive oxygen species in complex I of the electron transport chain, also imparts a comparable protective effect. These findings collectively imply that reactive oxygen species originating from complex I might hold particular significance in fomenting mitochondrial lipid peroxidation, a pivotal trigger of ferroptosis.

Functional Analysis of GSTK1 in Peroxisomal Redox Homeostasis in HEK-293 Cells

Peroxisomes serve as important centers for cellular redox metabolism and communication. However, fundamental gaps remain in our understanding of how the peroxisomal redox equilibrium is maintained. In particular, very little is known about the function of the nonenzymatic antioxidant glutathione in the peroxisome interior and how the glutathione antioxidant system balances with peroxisomal protein thiols. So far, only one human peroxisomal glutathione-consuming enzyme has been identified: glutathione S-transferase 1 kappa (GSTK1). To study the role of this enzyme in peroxisomal glutathione regulation and function, a GSTK1-deficient HEK-293 cell line was generated and fluorescent redox sensors were used to monitor the intraperoxisomal GSSG/GSH and NAD⁺/NADH redox couples and NADPH levels. We provide evidence that ablation of GSTK1 does not change the basal intraperoxisomal redox state but significantly extends the recovery period of the peroxisomal glutathione redox sensor po-roGFP2 upon treatment of the cells with thiol-specific oxidants. Given that this delay (i) can be rescued by reintroduction of GSTK1, but not its S16A active site mutant, and (ii) is not observed with a glutaredoxin-tagged version of po-roGFP2, our findings demonstrate that GSTK1 contains GSH-dependent disulfide bond oxidoreductase activity.

LAURDAN fluorescence and phasor plots reveal the effects of a H2O2 bolus in NIH-3T3 fibroblast membranes dynamics and hydration

Fluorescence spectroscopy, coupled with microscopy, opens new frontiers for the study of dynamic processes with high spatio-temporal resolution. The application of phasor plots to FLIM and hyperspectral imaging demonstrate unprecedented capabilities to study complex photophysics at the subcellular level. Using these approaches we studied the effects of an H2O2 bolus on NIH-3T3 membranes dynamics monitored by LAURDAN fluorescence. Exposure of NIH-3T3 cells to a bolus of H2O2 modifies the cell membranes and, in particular, the plasma membrane in a complex manner. The LAURDAN results reveal that the peroxide treatment decreases membrane fluidity but surprisingly increases dipolar relaxation around the excited probe. Using the Multidimensional-phasor approach we elucidated the complex photophysics of LAURDAN incorporated into cell membrane after H2O2 exposure. The results indicate the occurrence of LAURDAN fast-diffusion from gel↔ld phases in membranes exposed to a H2O2 bolus. An ad hoc hypothesis is presented to interpret the results in the context of H2O2 oxidative distress/eustress.

Iron as a catalyst of human low-density lipoprotein oxidation: Critical factors involved in its oxidant properties

Iron-induced human LDL oxidation, which is relevant to atherosclerosis, has not yet been properly investigated. We addressed such issue using iron(II) and (III) basically in the presence of phosphates, which are present in vivo and influence iron oxidative properties, at pH 4.5 and 7.4, representative, respectively, of the lysosomal and plasma environment. In 10mM phosphate buffered saline (PBS), iron(II) induces substantial LDL oxidation at pH 4.5 at low micromolar concentrations, while at pH 7.4 has low oxidative effects; iron(III) promotes small LDL oxidation only at pH 4.5. In 10mM sodium acetate/NaCl buffer, pH 4.5, iron-induced LDL oxidation is far higher than in PBS, highlighting the relevance of phosphates in the inhibitory modulation of iron-induced LDL oxidation. LDL oxidation is related to iron binding to the protein and lipid moiety of LDL, and requires the presence of iron(II) bound to LDL together with iron(III). Chemical modification of LDL carboxyl groups, which could bind iron especially at pH 4.5, decreases significantly iron binding to LDL and iron-induced LDL oxidation. Hydroxyl radical scavengers are ineffective on iron-induced LDL oxidation, which is inhibited by metal chelation, scavengers of alkoxyl/peroxyl radicals, or removal of LDL lipid hydroperoxides (LOOH). Overall, substantial human LDL oxidation is induced LOOH-dependently by iron(II) at pH 4.5 even in the presence of phosphates, suggesting the occurrence of iron(II)-induced LDL oxidation in vivo within lysosomes, where pH is about 4.5, iron(II) and phosphates coexist, plasma with its antioxidants is absent, and glutathione peroxidase is poorly expressed resulting in LOOH accumulation.

Piper nigrum ethanolic extract rich in piperamides causes ROS overproduction, oxidative damage in DNA leading to cell cycle arrest and apoptosis in cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

Ayurvedic and Chinese traditional medicine and tribal people use herbal preparations containing Piper nigrum fruits for the treatment of many health disorders like inflammation, fever, asthma and cancer. In Brazil, traditional maroon culture associates the spice Piper nigrum to health recovery and inflammation attenuation.

AIMS OF THE STUDY

The aim of the current work was to evaluate the relationship between reactive oxygen species (ROS) overproduction, DNA fragmentation, cell cycle arrest and apoptosis induced by Piper nigrum ethanolic extract and its antitumor activity.

METHODS

The plant was macerated in ethanol. Extract constitution was assessed by TLC, UV-vis and ESI-IT-MS/MS spectrometry. The cytotoxicity, proliferation and intracellular ROS generation was evaluated in MCF-7 cells. DNA damage effects were evaluated through intercalation into CT-DNA, plasmid DNA cleavage and oxidative damage in CT-DNA. Tumor growth inhibition, survival time increase, apoptosis, cell cycle arrest and oxidative stress were assessed in Ehrlich ascites carcinoma-bearing mice.

RESULTS

Extraction yielded 64mg/g (36% piperine and 4.2% piperyline). Treatments caused DNA damage and reduced cell viability (EC50=27.1±2.0 and 80.5±6.6µg/ml in MCF-7 and HT-29 cells, respectively), inhibiting cell proliferation by 57% and increased ROS generation in MCF-7 cells (65%). Ehrlich carcinoma was inhibited by the extract, which caused reduction of tumor growth (60%), elevated survival time (76%), cell cycle arrest and induced apoptosis. The treatment with extract increased Bax and p53 and inhibited Bcl-xL and cyclin A expression. It also induced an oxidative stress in vivo verified as enhanced lipid peroxidation and carbonyl proteins content and increased activities of glutathione reductase, superoxide dismutase and catalase. GSH concentration was decreased in tumor tissue from mice.

CONCLUSION

The ethanolic extract has cytotoxic and antiproliferative effect on MCF-7 cells and antitumor effect in vivo probably due to ROS overproduction that induced oxidative stress affecting key proteins involved in cell cycle arrest at G1/S and triggering apoptosis. Finally, the overall data from this study are well in line with the traditional claims for the antitumor effect of Piper nigrum fruits.

Sex-dependent mitochondrial respiratory impairment and oxidative stress in a rat model of neonatal hypoxic-ischemic encephalopathy

Increased male susceptibility to long-term cognitive deficits is well described in clinical and experimental studies of neonatal hypoxic-ischemic encephalopathy. While cell death signaling pathways are known to be sexually dimorphic, a sex-dependent pathophysiological mechanism preceding the majority of secondary cell death has yet to be described. Mitochondrial dysfunction contributes to cell death following cerebral hypoxic-ischemia (HI). Several lines of evidence suggest that there are sex differences in the mitochondrial metabolism of adult mammals. Therefore, this study tested the hypothesis that brain mitochondrial respiratory impairment and associated oxidative stress is more severe in males than females following HI. Maximal brain mitochondrial respiration during oxidative phosphorylation was two-fold more impaired in males following HI. The endogenous antioxidant glutathione was 30% higher in the brain of sham females compared to males. Females also exhibited increased glutathione peroxidase (GPx) activity following HI injury. Conversely, males displayed a reduction in mitochondrial GPx4 protein levels and mitochondrial GPx activity. Moreover, a 3-4-fold increase in oxidative protein carbonylation was observed in the cortex, perirhinal cortex, and hippocampus of injured males, but not females. These data provide the first evidence for sex-dependent mitochondrial respiratory dysfunction and oxidative damage, which may contribute to the relative male susceptibility to adverse long-term outcomes following HI. Lower basal GSH levels, lower post-hypoxic mitochondrial glutathione peroxidase (mtGPx) activity, and mitochondrial glutathione peroxidase 4 (mtGPx4) protein levels may contribute to the susceptibility of the male brain to oxidative damage and mitochondrial dysfunction following neonatal hypoxic-ischemia (HI). Treatment of male pups with acetyl-L-carnitine (ALCAR) protects against the loss of mtGPx activity, mtGPx4 protein, and increases in protein carbonylation after HI. These findings provide novel insight into the pathophysiology of sexually dimorphic outcomes following HI.

Reductive stress linked to small HSPs, G6PD, and Nrf2 pathways in heart disease

SIGNIFICANCE

Aerobic organisms must exist between the dueling biological metabolic processes for energy and respiration and the obligatory generation of reactive oxygen species (ROS) whose deleterious consequences can reduce survival. Wide fluctuations in harmful ROS generation are circumvented by endogenous countermeasures (i.e., enzymatic and nonenzymatic antioxidants systems) whose capacity decline with aging and are enhanced by disease states.

RECENT ADVANCES

Substantial efforts on the cellular and molecular underpinnings of oxidative stress has been complemented recently by the discovery that reductive stress similarly predisposes to inheritable cardiomyopathy, firmly establishing that the biological extremes of the redox spectrum play essential roles in disease pathogenesis.

CRITICAL ISSUES

Because antioxidants by nutritional or pharmacological supplement to prevent or mitigate disease states have been largely disappointing, we hypothesize that lack of efficacy of antioxidants might be related to adverse outcomes in responders at the reductive end of the redox spectrum. As emerging concepts, such as reductive, as opposed, oxidative stress are further explored, there is an urgent and critical gap for biochemical phenotyping to guide the targeted clinical applications of therapeutic interventions.

FUTURE DIRECTIONS

New approaches are vitally needed for characterizing redox states with the long-term goal to noninvasively assess distinct clinical states (e.g., presymptomatic, end-stage) with the diagnostic accuracy to guide personalized medicine.

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.

Cytoplasmic glutathione redox status determines survival upon exposure to the thiol-oxidant 4,4'-dipyridyl disulfide

Dipyridyl disulfide (DPS) is a highly reactive thiol oxidant that functions as electron acceptor in thiol-disulfide exchange reactions. DPS is very toxic to yeasts, impairing growth at low micromolar concentrations. The genes TRX2 (thioredoxin), SOD1 (superoxide dismutase), GSH1 (gamma-glutamyl-cysteine synthetase) and, particularly, GLR1 (glutathione reductase) are required for survival on DPS. DPS is uniquely thiol-specific, and we found that the cellular mechanisms for DPS detoxification differ substantially from that of the commonly used thiol oxidant diamide. In contrast to this oxidant, the full antioxidant pools of glutathione (GSH) and thioredoxin are required for resistance to DPS. We found that DPS-sensitive mutants display increases in the disulfide form of GSH (GSSG) during DPS exposure that roughly correlate with their more oxidizing GSH redox potential in the cytosol and their degree of DPS sensitivity. DPS seems to induce a specific disulfide stress, where an increase in the cytoplasmic/nuclear GSSG/GSH ratio results in putative DPS target(s) becoming sensitive to DPS.

Glutathione reductase and a mitochondrial thioredoxin play overlapping roles in maintaining iron-sulfur enzymes in fission yeast

In the fission yeast Schizosaccharomyces pombe, the pgr1+ gene encoding glutathione (GSH) reductase (GR) is essentially required for cell survival. Depletion of GR caused proliferation arrest at the G1 phase of the cell cycle under aerobic conditions. Multicopy suppressors that restore growth were screened, and one effective suppressor was found to be the trx2+ gene, encoding a mitochondrial thioredoxin. This suggests that GR is critically required for some mitochondrial function(s). We found that GR resides in both cytosolic and organellar fractions of the cell. Depletion of GR lowered the respiration rate and the activity of oxidation-labile Fe-S enzymes such as mitochondrial aconitase and cytosolic sulfite reductase. Trx2 did not reverse the high ratio of oxidized glutathione to GSH or the low respiration rate observed in GR-depleted cells. However, it brought the activity of oxidation-labile Fe-S enzymes to a normal level, suggesting that the maintenance of Fe-S enzymes is a critical factor in the survival of S. pombe. The activity of succinate dehydrogenase, an oxidation-insensitive Fe-S enzyme, however, was not affected by GR depletion, suggesting that GR is not required for the biogenesis of the Fe-S cluster. The total iron content was greatly increased by GR depletion and was brought to a nearly normal level by Trx2. These results indicate that the essentiality of GR in the aerobic growth of S. pombe is derived from its role in maintaining oxidation-labile Fe-S enzymes and iron homeostasis.

Oxidant and antioxidant balance in the airways and airway diseases

Although oxygen is a prerequisite to life, at concentrations beyond the physiological limits it may be hazardous to the cells. Since the lungs are directly exposed to very high amounts of oxygen, it is imperative for the organ to possess defences against possible oxidative challenge. The lungs are therefore endowed with an armamentarium of a battery of endogenous agents called antioxidants. The antioxidant species help the lungs ward off the deleterious consequences of a wide variety of oxidants/reactive oxygen species such as superoxide anion, hydroxyl radical, hypohalite radical, hydrogen peroxide and reactive nitrogen species such as nitric oxide, peroxynitrite, nitrite produced endogenously and sometimes accessed through exposure to the environment. The major non-enzymatic antioxidants of the lungs are glutathione, vitamins C and E, beta-carotene, uric acid and the enzymatic antioxidants are superoxide dismutases, catalase and peroxidases. These antioxidants are the first lines of defence against the oxidants and usually act at a gross level. Recent insights into cellular redox chemistry have revealed the presence of certain specialized proteins such as peroxiredoxins, thioredoxins, glutaredoxins, heme oxygenases and reductases, which are involved in cellular adaptation and protection against an oxidative assault. These molecules usually exert their action at a more subtle level of cellular signaling processes. Aberrations in oxidant: antioxidant balance can lead to a variety of airway diseases, such as asthma, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis which is the topic of discussion in this review.

Alternative start sites in the Saccharomyces cerevisiae GLR1 gene are responsible for mitochondrial and cytosolic isoforms of glutathione reductase

To combat oxidative damage, eukaryotic cells have evolved with numerous anti-oxidant factors that are often distributed between cytosolic and mitochondrial pools. Glutathione reductase, which regenerates the reduced form of glutathione, represents one such anti-oxidant factor, yet nothing is known regarding the partitioning of this enzyme within the cell. Using the bakers' yeast Saccharomyces cerevisiae as a model, we provide evidence that a single gene, namely GLR1, encodes both the mitochondrial and cytosolic forms of glutathione reductase. A deletion in GLR1 drastically increases levels of oxidized glutathione in these two subcellular compartments. The GLR1 gene has two inframe start codons that are both used as translation initiation sites. Translation from the first codon generates the mitochondrial form that includes a mitochondrial targeting signal, whereas translation from the second codon produces the cytosolic form that lacks this sequence. Our results indicate that the sequence context of the two AUG codons influences the efficiency of translation initiation at each site, which in turn affects the relative levels of cytosolic and mitochondrial Glr1p. This method of subcellular distribution of glutathione reductase may be conserved in mammalian cells as well.

A novel NADH kinase is the mitochondrial source of NADPH in Saccharomyces cerevisiae

Mitochondria require NADPH for anti-oxidant protection and for specific biosynthetic pathways. However, the sources of mitochondrial NADPH and the mechanisms of maintaining mitochondrial redox balance are not well understood. We show here that in Saccharomyces cerevisiae, mitochondrial NADPH is largely provided by the product of the POS5 gene. We identified POS5 in a S.cerevisiae genetic screen for hyperoxia-sensitive mutants, or cells that cannot survive in 100% oxygen. POS5 encodes a protein that is homologous to NAD(+) and NADH kinases, and we show here that recombinant Pos5p has NADH kinase activity. Pos5p is localized to the mitochondrial matrix of yeast and appears to be important for several NADPH-requiring processes in the mitochondria, including resistance to a broad range of oxidative stress conditions, arginine biosynthesis and mitochondrial iron homeostasis. Pos5p represents the first member of the NAD(H) kinase family that has been identified as an important anti-oxidant factor and key source of the cellular reductant NADPH.

Effect of glutathione augmentation on lipid peroxidation after spinal cord injury

Lipid peroxidation (LPO) is considered a major factor in damage spread after spinal cord injury (SCI). Therapies that limit LPO after SCI have demonstrated some utility in clinical trials, but more effective treatments are needed. In the present study the effects of augmenting SC levels of the endogenous antioxidant glutathione (GSH) on LPO after SCI were studied in a rat contusion injury model. A significant decrease in GSH occurred 1h after SCI which was paralleled by increases of 123% in malondialdehyde (MDA) and >500% in the 4-hydroxyalkenals (4-HA's), two LPO products. SC irrigation with gamma-glutamylcysteine (GC) preserved GSH and reduced 4-HA's below naive levels but had no effect on MDA. By 24 h after SCI, MDA returned to naive levels but 4-HA's were still elevated. Once again, GC treatment reduced 4-HA's. 4-HA's are much more reactive than MDA and are considered among the most toxic LPO products. These results suggest that (1) conditions after SCI may favor particular branches of the LPO pathway leading to differential LPO product levels, (2) MDA measurement is not by itself an adequate test for the presence or magnitude of LPO after SCI, (3) binding of GSH to 4-HA's may be an important mechanism by which the GSH system confers protection against LPO after SCI, and (4) SC GSH can be augmented after trauma by local irrigation with GC. These results also suggest that GSH augmentation may be an effective strategy for curtailment of LPO-mediated damage in acute phase SCI.

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

Effects of in vitro cellular aging on the content of 8-oxo-2'-deoxyguanosine, a typical oxidation product of DNA bases, were examined in cultured human skin fibroblasts. The 8-oxo-2'-deoxyguanosine content in the DNA of TIG-3S cells established from skin tissues of a fetal donor increased immediately before the cessation of proliferation. TIG-114 and TIG-104 cells established from skin tissues of adult and aged donors, respectively, showed similar changes in 8-oxo-2'-deoxyguanosine content during in vitro cellular aging. The accumulation of 8-oxo-2'-deoxyguanosine in late-passage cells was dependent on the number of cell divisions, and not on the cultivation time. Increases in the activities of superoxide dismutase and glutathione peroxidase were observed prior to the increase in 8-oxo-2'-deoxyguanosine content, while the catalase activity decreased gradually during in vitro cellular aging at late-passage. Furthermore, the activities of 8-oxo-2'-deoxyguanosine endonuclease and DNA polymerases decreased with the progression of proliferation. These results indicate that defense systems against oxidative stress in late-passage cells remain sufficiently active before the cessation of cell division, but that repair systems against oxidative damage decay at late-passage. Oxidative stress beyond the antioxidant capacity and/or repair activity seems to result in an accumulation of 8-oxo-2'-deoxyguanosine in late-passage cells.

Mitochondrial GPx1 decreases induced but not basal oxidative damage to mtDNA in T47D cells

The production of oxyradicals by mitochondria (mt) is a source of oxidative damage to mtDNA such as 8-oxo-dG lesions that may lead to mutations and mitochondrial dysfunction. The potential protection of mtDNA by glutathione peroxidase-1 (GPx1) was investigated in GPx1-proficient (GPx-2) and GPx1-deficient (Hygro-3) human breast T47D cell transfectants. GPx activity and GPx1-like antigen concentration in mitochondria were respectively at least 100-fold and 20- to 25-fold higher in GPx2 than Hygro-3 cells. In spite of this large difference in peroxide-scavenging capacity, the basal 8-oxo-dG frequency in mtDNA, assessed by carefully controlled postlabeling assay, was strikingly similar in both cell lines. In contrast, in response to menadione-mediated oxidative stress, induction of 8-oxo-dG and DNA strand breaks was much lower in the GPx1-proficient mitochondria (e.g., +14% 8-oxo-dG versus +54% in Hygro-3 after 1-h exposure to 25 microM menadione, P < 0.05). Our data indicate that the mitochondrial glutathione/GPx1 system protected mtDNA against damage induced by oxidative stress, but did not prevent basal oxidative damage to mtDNA, which, surprisingly, appeared independent of GPx1 status in the T47D model.

Redox capacity of cells affects inactivation of glutathione reductase by nitrosative stress

Glutathione reductase (GR) plays a pivotal role in maintaining glutathione (GSH) in its reduced form. We have isolated a cDNA for rat GR and constructed a baculovirus system to produce recombinant GR on a large scale. This protein was purified by simple, two-step chromatographic procedure using DE52 and 2',5'-ADP Sepharose. Tissue distributions of GR were examined by Northern and Western blotting with a rabbit antibody to purified GR. GR was expressed in the order of reactivity; kidney, colon, liver, stomach, etc. Western blot analysis showed that both the cytosolic and the mitochondrial fractions of liver homogenate gave immunoreactive bands of similar size. This indicates that the same gene products exist in these fractions. Since nitric oxide (NO) produced under inflammatory conditions causes nitrosative stress and affects the redox states of surrounding tissues, we investigated the effects of NO donors on the enzymatic activities of purified GR. S-nitrosoglutathione (GSNO), 3-morpholinosydnonimine N-ethylcarbamide (SIN-1), and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) at 1 mM gave 39, 15, and 12% inhibitions, respectively. In RAW 264.7 cells the GR activity was reported to be inhibited by GSNO. In A549 cells, however, no such change in the activity, protein levels and mRNA of GR was noted. Since these cells have a much higher redox capacity than RAW 264.7 cells as judged by GR activity and thioredoxin reductase activity it wound minimize cellular damage, including inactivation of GR caused by nitrosative stress.

Structural organization of the human glutathione reductase gene: determination of correct cDNA sequence and identification of a mitochondrial leader sequence

The primary structure of human glutathione reductase gene (GSR) was determined by genomic cloning. The gene structure of human GSR spans 50 kb, consists of 13 exons, and was found to be highly similar to the mouse GSR gene. The coding sequence of human GSR resides on all 13 exons. An N-terminal arginine-rich mitochondrial leader sequence was present, with high homology to the murine leader sequence, between two in-frame start codons in the first exon. The 5' and 3' intron/exon splice junctions, with one exception, followed the general consensus sequences for intron spliced donor and acceptance sites.

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.

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.

Effects of G6PD overexpression in NIH3T3 cells treated with tert-butyl hydroperoxide or paraquat

The major physiological role of glucose-6-phosphate dehydrogenase (G6PD) is to provide NADPH, which is required for reductive biosynthesis and for detoxification of free radicals and peroxides in mature red blood cells. To study the function of G6PD in non-erythroid cells, we examined the sensitivity of NIH3T3 cells transfected with a plasmid containing human G6PD cDNA to tert-butyl hydroperoxide (TBH) and paraquat. Two transfected clones which had a sixteen-fold (H7 clone) and six-fold (H6 clone) increase in their intracellular G6PD activity were compared with control cells transfected with a vector alone. Cells with high-level expression of human G6PD were 2.3 (H6) to 3.7 (H7) times more resistant to TBH than control cells. The antioxidant (anti-TBH) abilities in H6 and H7 cells were revealed by (1) a significant increase in the intracellular level of NADPH and glutathione, (2) a reduction of fluorescent intensity of the oxidant-sensitive dye, 2',7'-dichlorofluorescin diacetate, and (3) a significant reduction in the production of oxidized adducts generated by lipid peroxidation. In contrast, cells overexpressing G6PD were very sensitive to paraquat, a superoxide-producing herbicide. The concentrations of paraquat required to produce a 50% decrease in cell viability of H7, H6 and control cells were 0.80 mM, 1.14 mM, and 2.19 mM, respectively. The cytotoxicity of paraquat correlated with the expression level of NADPH in the cells. In this study, overexpression of human G6PD in NIH3T3 cells had different effects on the toxicity of TBH vs. paraquat. Reduction of NADP+ to NADPH by G6PD protects cells from oxidative damage by TBH, but appears to enhance the toxicity of paraquat.

Effects of antioxidant enzyme modulations on interleukin-1-induced nuclear factor kappa B activation

Nuclear factor kappa B (NF-kappa B) is a potent and pleiotropic transcription factor that can be activated by a wide variety of inducers, including interleukin-1 (IL-1). Although the detailed activation mechanism of NF-kappa B is still under investigation, it requires both phosphorylation and degradation of its inhibitory subunit I kappa B and the presence of an oxidative environment. In this study, we systematically evaluated the influence of glutathione peroxidase, glutathione reductase and catalase on IL-1-induced NF-kappa B activation by analysing the effect of specific inhibitors of these enzymes. For the three antioxidant enzymes mentioned, their inhibition correlated with an overactivation of NF-kappa B, particularly for glutathione peroxidase. Inversely, we tested the response of glutathione peroxidase-transfected cells on NF-kappa B activation, which was lower as compared with the parental cells. Furthermore, interleukin-6 production also correlated perfectly with the reduced level of NF-kappa B activation is these experiments. The results clearly show that NF-kappa B activation is, strongly dependent on the antioxidant potential of the cells, especially on the activity of reduced glutathione-dependent enzymes such as glutathione peroxidase. The results support the hypothesis that the level of the oxidised glutathione:reduced glutathione ratio and the activity of intracellular antioxidant enzymes play a major role in NF-kappa B tine tuning.

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.

Cultured AIDS-related Kaposi's sarcoma cells retain a proliferative bioenergetic profile but demonstrate reduced cytoprotective capabilities

Features of AIDS-related Kaposi's sarcoma (AIDS-KS), such as the multifocal presentation at mucosal and epidermal sites subjected to trauma, suggest that AIDS-KS is initially a reactive hyperplasia that subsequently progresses to a neoplasia. It is recognized that there is an association between sustained inflammatory states and the subsequent development of neoplasia (e.g., ulcerative colitis/colonic adenocarcinoma). Furthermore, patients who develop AIDS-KS experience both a constant immune stimulation due to sustained high levels of virus-induced cytokines and, because of a sparing effect on their phagocytic cells, retention of the phagocytic inflammatory response. A component of phagocytic activation is the initiation of the oxidative burst, resulting in the generation of reactive oxygen species (ROS), which can be mutagenic to host cells if released beyond the phagolysosome and not inactivated. Our results demonstrate that cultured AIDS-KS cells possess decreased cytoprotective capabilities. Relative to either dermal fibroblasts, or human microvascular endothelial cells (HMECs), AIDS-KS cells contained significantly lower levels of glutathione, a tripeptide integral in both cytoprotection and maintenance of cellular thiol status. While HMECs increased catalase activity during culture in the cytokine-rich KS milieu (control medium supplemented with conditioned medium from MOT, an HTLV II-infected cell line), AIDS-KS cells demonstrated reduced catalase function under these conditions. Furthermore, HMEC cultures showed an inherent biochemical responsiveness, by increasing catalase activity following exposure to exogenous H2O2. In contrast, the catalase activity of AIDS-KS cells decreased following H2O2 challenge. Our results show that an inherent deficiency in cellular cytoprotection is present in AIDS-KS cells and suggest that oxidant stress may function in the development and progression of AIDS-KS.

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.

Modulation of human microvascular endothelial cell bioenergetic status and glutathione levels during proliferative and differentiated growth

During angiogenesis, formerly differentiated human microvascular endothelial cells (HMECs) return to a proliferative growth state. Many fundamental questions regarding HMEC function, such as how HMECs adapt to changes in bioenergetic requirements upon return to proliferative growth, remained unanswered. In this study, we evaluated whether modifications in HMEC bioenergetic profiles and glutathione (GSH) levels accompanied the cellular transition between differentiated and proliferative growth. To provide insight into the continuum of cellular adaptations that occur during this transition, we used a method recently developed in our laboratory that induces a state of morphological and functional predifferentiation in HMECs. Cellular morphology, in conjunction with flow cytometric DNA analyses and HMEC functional assays (the directed migration and intercellular association involved in microtubule formation) were employed to validate the HMEC culture state of growth. Analysis of the HPLC nucleotide profiles disclosed several findings common to all culture growth states. These uniform findings, e.g., cellular energy charges > 0.90, and highly reduced redox states, revealed that cultured HMECs maintain high rates of oxidative metabolism. However, there were also significant, culture growth state related differences in the nucleotide profiles. Proliferative HMECs were shown to possess significantly higher (relative to both large vessel endothelial cells, and differentiated HMECs) levels of GSH and specific nucleotides which were related with a return to the active cell cycle-ATP, GTP, UTP, and CTP, and NADPH. Further, the nucleotide profiles and GSH levels of the predifferentiated HMECs were determined to be intermediate between levels obtained for the proliferative and differentiated HMECs. The results of this study demonstrate that the capacity to modulate their cellular bioenergetic status during growth state transitions is one of the adaptations that enable HMECs to retain a growth state reciprocity. In addition, our findings also show that HMECs, especially during the proliferative growth state, are biochemically distinct from endothelial cells harvested from large vessels, and therefore suggest that HMECs are the cells of choice to employ when studying diseases that affect the human microvasculature.

Molecular characterization of the trypanothione reductase gene from Crithidia fasciculata and Trypanosoma brucei: comparison with other flavoprotein disulphide oxidoreductases with respect to substrate specificity and catalytic mechanism

Trypanothione reductase belongs to the family of flavoprotein disulphide oxidoreductases that include glutathione reductases, dihydrolipoamide dehydrogenases and mercuric reductases. Trypanothione reductase and its substrate, trypanothione disulphide, are unique to parasitic trypanosomatids responsible for several tropical diseases. The crystal structure of the enzyme from Crithidia fasciculata is currently under investigation as an aid in the design of selective inhibitors with a view to producing new drugs. We report here the cloning and sequencing of the genes for trypanothione reductase from C. fasciculata and Trypanosoma brucei. Alignment of the deduced amino acid sequences with 21 other members of this family provides insight into the role of certain amino acid residues with respect to substrate specificity and catalytic mechanism as well as conservation of certain elements of secondary structure.

Age related changes in anti-oxidative enzymes in cardiomyopathic hamster hearts

Membrane abnormalities and a shortened life span are closely associated with the progressive cardiomyopathy of dystrophic hamsters. In the present work we investigate whether this membrane damage is associated with changes in the primary membrane defences (the anti-oxidative enzymes). We measured the levels of superoxide dismutase (SOD), glutathione peroxidase (GSH.Px), and catalase (CAT) in hearts of normal and cardiomyopathic (CHF 147) hamsters, aged 17 days to 12 months. In normal hearts all the enzyme activities follow a U-shaped curve: unweaned animals have 20-40% higher enzyme activities and 11-month-old hamsters 50-160% higher activities than adolescent or adult hamster hearts. Changes in this age-related pattern of enzyme activities are seen in dystrophic hearts in all but the 17-20-day-old animals. At 30 days of age and older, GSH.Px activities are decreased and SOD and CAT activities increased in cardiomyopathic hamsters compared to normal animals. SOD, while elevated, seems less affected than GSH.Px and CAT as the disease progresses. The changes in both absolute activities and ratio of activities of the anti-oxidative enzymes parallel the changes in the cardiomyopathic pathology. This work supports the view that the progressive cardiomyopathy of CHF 147 hamsters may be associated with changes in primary membrane defenses.

Alteration of enzymes in ageing human fibroblasts in culture. V. Mechanisms of glutathione peroxidase modification

Ageing of WI-38 fibroblasts in culture was used as a model in order to investigate the evolution and the alteration of the key antioxidant enzyme glutathione peroxidase. The activity of glutathione peroxidase is influenced by the presence of selenium in the culture medium and we have also shown that the specific activity of this enzyme does not decrease during ageing, but rather slightly increases. No alteration could be detected by immunotitration. Also the kinetic parameter Km for tert-butyl hydroperoxide has not changed. However, the heat resistance of the enzyme dramatically decreases with ageing. Dilutions of the enzyme preparations had the same influence on the thermosensitivity of the enzyme. This dilution effect is most probably linked to the dissociation of the enzyme subunits into dimers and monomers. Moreover, the kinetic of thermoinactivation curves are best explained by consecutive reactions of inactivation with an intermediary enzyme form. These observations strongly support the hypothesis that ageing is associated with an increased dissociation constant of the tetrameric glutathione peroxidase leading to an easier dissociation of the enzyme in old cells.

Oxidants and antioxidants in proliferative senescence

In terms of the amount of experimental research it has generated the free radical theory of ageing is one of the most popular hypotheses to explain this ubiquitous phenomenon. From the theory two postulates were derived: either cellular defence mechanisms against free radical-dependent oxidants deteriorate during ageing of cells, or essential, unrepairable damages are imparted to the cell by oxidants regardless of the activity of antioxidant defence systems. The many reports dealing with a putative breakdown in antioxidant defence systems failed to positively support this postulate. However, a minor depletion in cellular glutathione by exposure to a model lipophilic peroxide led to a significant decrement in DNA and protein synthesis. In other words, the glutathione redox cycle is intrinsically fallible with respect to defending the cellular DNA replication system against this model lipophilic peroxide. Interestingly, after ageing in culture cells a partial uncoupling of the NADPH-producing and -consuming systems tends to take place. Experiments involving the addition of antioxidants to the culture medium have failed to significantly extend the lifespan of cultured diploid somatic cells. The level of antioxidants appears to be a modulator rather than a primary determinant of cellular ageing in culture. Several lines of evidence suggest that DNA damages accumulate during ageing of the organism, but no oxidant-related DNA damage has been pinpointed in the cultured cell system. Human mutants with defects in antioxidant enzymes have not shown conclusive signs of accelerated ageing. Cells from patients with Werner's syndrome (progeria of the adult), on the other hand, do not suffer from a defect in their antioxidant defence system, nor do they accumulate more than normal amounts of autofluorescent products resulting from lipid peroxidation. The recent finding that Werner's syndrome constitutes a mutator phenotype may prompt the comparison of oxidant- and ageing-related mutation spectra in order to investigate a mutational theory of ageing as a new derivative from the free radical hypothesis.

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

We examined antioxidant enzyme activities (catalase, glutathione peroxidase, and superoxide dismutase) in cultured skin fibroblasts (passage number 2-3) derived from 30 persons of various ages. With increasing ages, catalase activity decreased, glutathione peroxidase activity increased slightly, and superoxide dismutase activity was unchanged. After UVA irradiation (4.8 joule/cm2) of the fibroblasts, only catalase activity decreased by 70%. This suggests that catalase may play an important role in the aging of human skin fibroblasts.

Comparative study of oxygen toxicity in human fibroblasts and endothelial cells

The resistance of human pulmonary fibroblasts (WI-38) and human umbilical vein endothelial cells to oxygen toxicity (1 atm O2) was compared. Endothelial cells were more sensitive than fibroblasts. They contained also less antioxidant enzymes except for SOD: respectively 132%, 96%, 70%, 59%, and 21% of the SOD, GSH peroxidase, GSH reductase, catalase, and G6PD content of fibroblasts. However, they contained 1.81-fold more GSH than fibroblasts. Their lower content of antioxidant enzymes can explain their higher sensitivity to oxygen. The efficiency of natural antioxidant molecules and enzymes in the protection of cells incubated 3 days under 1 atm O2 was studied. alpha-tocopherol added in the culture medium led to a significant protection, contrary to the result for ascorbic acid. Microinjection of catalase, SOD, and GSH peroxidase directly into the cells was also tested: the protection was concentration dependent for both types of cells but SOD did not protect the endothelial cells. Lower activities of the other enzymes were needed to achieve protection of the endothelial cells, compared to fibroblasts. Since endothelial cells were also shown to display lower antioxidant enzyme activities, it can be hypothesized that their content is optimized for survival in physiological conditions.

Importance of a threshold for error accumulation in cell degenerative processes. I. Modulation of the threshold in a model of free radical-induced cell degeneration

Antioxidant enzymes (catalase, superoxide dismutase and glutathione peroxidase) have been injected into human fibroblasts exposed to 2 atm O2 in order to test if the threshold of oxidative damage versus antioxidant defenses could be modulated and if the damage remains reversible beyond the threshold. Cell damage was estimated by thymidine incorporation and cell survival curves. The proportion of dividing cells, measured by thymidine incorporation, rapidly decreased after O2 incubation: no cells could divide after 15 h of hyperoxia. However, cells incubated for a short time and injected with a high concentration of any of the three enzymes divided like non-oxygen-incubated cells: the enzymes could protect the cells against their loss of division potential. However, when cells were incubated for a longer period and/or when the injected enzyme concentration was lower, cells were either less or not protected and could no longer divide. These results suggest the presence of a threshold for the oxidative damage which cannot be totally repaired and which impairs the cell division; this threshold can, however, be modulated by supplementation of antioxidant enzymes, glutathione peroxidase being the most efficient.

Antioxidant enzymatic activities and resistance to oxidative stress in primary and subcultured rat astroglial cells

The survival of neural tissues depends in part on the balance between the formation of free radicals due to oxidative metabolism and the transformation of the free radicals to non-toxic compounds. Serial subculture of rat glial cells as described here resulted in a decrease of the specific activities of several antioxidant enzymes and a glial specific marker for astrocytes. Thus, there was an increased susceptibility to oxidative stress in cultures by the third passage. These subcultured glial cell cultures may represent a useful model for the study of free radical induced neural damage that may be relevant to CNS trauma and aging.

Quantitative study of natural antioxidant systems for cellular nitrofurantoin toxicity

The toxicity of nitrofurantoin was studied on human WI-38 fibroblasts: this chemical was lethal when added at concentrations higher than 5.10(-5) M in the culture medium. The protection afforded by antioxidants was then tested: alpha-tocopherol gave at 10(-4) M a light protection in contrast to ascorbic acid which even became toxic at high concentrations. We also tested catalase, superoxide dismutase and glutathione peroxidase introduced intracellularly by the microinjection technique. On a molecular basis, glutathione peroxidase was 23-times more efficient than catalase and 3000-times more than superoxide dismutase. The results also showed that a similar range of enzyme concentrations was found for the protection against high oxygen pressure. This suggests that, in the case of both oxygen and nitrofurantoin toxicity, the peroxide derivatives are the most toxic intermediates of the free radical attacks.

Tyrosyl-tRNA synthetase from baker's yeast. Order of substrate addition, discrimination of 20 amino acids in aminoacylation of tRNATyr-C-C-A and tRNATyr-C-C-A(3'NH2)

The order of substrate addition to tyrosyl-tRNA synthetase from baker's yeast was investigated by bisubstrate kinetics, product inhibition and inhibition by dead-end inhibitors. The kinetic patterns are consistent with a random bi-uni uni-bi ping-pong mechanism. Substrate specificity with regard to ATP analogs shows that the hydroxyl groups of the ribose moiety and the amino group in position 6 of the base are essential for recognition of ATP as substrate. Specificity with regard to amino acids is characterized by discrimination factors D which are calculated from kcat and Km values obtained in aminoacylation of tRNATyr-C-C-A. The lowest values are observed for Cys, Phe, Trp (D = 28,000-40,000), showing that, at the same amino acid concentrations, tyrosine is 28,000-40,000 times more often attached to tRNATyr-C-C-A than the noncognate amino acids. With Gly, Ala and Ser no misacylation could be detected (D greater than 500,000); D values of the other amino acids are in the range of 100,000-500,000. Lower specificity is observed in aminoacylation of the modified substrate tRNATyr-C-C-A(3'NH2) (D1 = 500-55,000). From kinetic constants and AMP-formation stoichiometry observed in aminoacylation of this tRNA species, as well as in acylating tRNATyr-C-C-A hydrolytic proof-reading factors could be calculated for a pretransfer (II 1) and a post-transfer (II 2) proof-reading step. The observed values of II 1 = 12-280 show that pretransfer proof-reading is the main correction step whereas post-transfer proof-reading is marginal for most amino acids (II 2 = 1-2). Initial discrimination factors caused by differences in Gibbs free energies of binding between tyrosine and noncognate amino acids are calculated from discrimination and proof-reading factors. Assuming a two-step binding process, two factors (I1 and I2) are determined which can be related to hydrophobic interaction forces. The tyrosine side chain is bound by hydrophobic forces and hydrogen bonds formed by its hydroxyl group. A hypothetical model of the amino acid binding site is discussed and compared with results of X-ray analysis of the enzyme from Bacillus stearothermophilus.

Oxygen toxicity protecting enzymes in the human brain

Regional distribution of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase activities were studied in 22 anatomic sites of 5 human brains. No significant regional differences were observed in cytosolic activities of any enzyme studied, nor in particulate activities of superoxide dismutase, catalase and glutathione reductase, whereas particulate glutathione peroxidase activities were distributed unevenly, the highest activities observed in the basal nucleus and amygdala. There were significant interindividual differences in the activities of each enzyme. This was shown to result partly from the decrease of cytosolic superoxide dismutase and catalase activities with age, concurrently with age-related decrease of particulate glutathione peroxidase and glutathione reductase activities.

Influence of cumene hydroperoxide and 4-hydroxynonenal on the glutathione metabolism during in vitro ageing of human skin fibroblasts

Cumene hydroperoxide (Chp) and 4-hydroxynonenal (HNE) were used to investigate the effect of peroxidative challenge upon the glutathione (GSH) metabolism of human skin fibroblasts. Cellular GSH contents decreased during short-term incubations with Chp and oxidised glutathione (GSSG) was formed concomitantly. During longer incubations the GSH level was restored and the substrate flux through the pentose phosphate shunt increased. So in the presence of hydroperoxides the GSH level is maintained by reduction of GSSG. HNE caused a strong decrease in cellular GSH contents. Prolonged incubation with HNE lead to a rise in GSH contents above the basal level. The flux through the pentose phosphate shunt did not change during exposure to HNE. Hence, during incubation with HNE the cell maintains its GSH content by de novo synthesis of GSH. This conclusion is further substantiated by the findings with a cell strain deficient in GSH synthetase. These cells survived if incubated with Chp but not if exposed to HNE. GSH contents of normal cells from phase II (young) cultures and from phase III (aged) cultures responded similarly to Chp during short-term incubations and during a week of culture with the test compound. The flux through the pentose phosphate shunt rose much more in phase III than in phase II cells when incubated with the same concentration series of Chp. We conclude that during in vitro ageing the amount of NADPH needed to maintain cellular GSH levels in the presence of hydroperoxides increases, while the capacity to respond to such a challenge is not affected.

Comparative study of the enzymatic defense systems against oxygen-derived free radicals: the key role of glutathione peroxidase

Human WI-38 diploid fibroblasts have been cultivated under high toxic O2 pressure, and their survival curves are reported. Superoxide dismutase, catalase, or glutathione peroxidase provided some protection when injected in the cells exposed to O2. This protective effect, recorded after 3 or 4 days of incubation, was the most pronounced when cells were injected just before oxygen exposure. Quantitative injection assays have been performed for the three enzymes. Surprisingly, glutathione peroxidase was found to be much more effective than both catalase and superoxide dismutase, the latter being particularly inefficient.

De novo synthesis of glutathione in human fibroblasts during in vitro ageing and in some metabolic diseases as measured by a flow cytometric method

A flow cytometric method to determine cellular GSH contents has been developed. This method is fast and simple and enables the determination of GSH contents in intact cells. Results obtained with the new method correlate well with the results obtained by a specific biochemical assay for GSH (r = 0.9984; n = 7). The method has been used to determine GSH recovery rates in cultured fibroblasts from healthy subjects and from patients with Werner's syndrome, Spielmeyer-Vogt syndrome and Fanconi's anemia. No obvious differences in GSH recovery rates were observed. GSH recovery rates were also not affected after in vitro ageing. Experiments with cells deficient in GSH synthetase revealed that the observed GSH recovery is exclusively due to de novo synthesis.

Alteration of enzymes in ageing human fibroblasts in culture. IV. Effect of glutathione on the alteration of glucose-6-phosphate dehydrogenase

Alteration and inactivation of glucose-6-phosphate dehydrogenase (G6PD) can be induced in human fibroblasts by incubation of a cell supernatant at 4 degrees C and pH 7.4. When added in such conditions, glutathione (GSH) had a stabilizing effect on the enzyme. On the other hand, substances which are known to deplete the cells of their GSH content, dramatically increase the inactivation rate. When analysed by gel filtration after 24 h of incubation at 4 degrees C, the inactive G6PD appears as a dimeric protein when GSH is present, while as a monomer in the control experiment. Reactivation of the monomers was stimulated with GSH. The heat inactivation of the dimeric fraction first started with a sharp activity increase of 20%. This increase vanished when the enzyme was first reactivated before the thermolability experiment. We propose that what is called altered G6PD is the expression of a quick reactivation of an inactive, labile dimer. Finally, a schematic view of the G6PD alteration is proposed.