Single-cell investigation by laser scanning confocal microscopy of cytochemical alterations resulting from extracellular oxidant challenge

In Situ Evaluation of Oxidative Stress in Rat Fatty Liver Induced by a Methionine- and Choline-Deficient Diet

Nonalcoholic fatty liver disease (NAFLD) is a serious health problem in developed countries. We documented the effects of feeding with a NAFLD-inducing, methionine- and choline-deficient (MCD) diet, for 1-4 weeks on rat liver oxidative stress, with respect to a control diet. Glycogen, neutral lipids, ROS, peroxidated proteins, and SOD2 were investigated using histochemical procedures; ATP, GSH, and TBARS concentrations were investigated by biochemical dosages, and SOD2 expression was investigated by Western Blotting. In the 4-week-diet period, glycogen stores decreased whereas lipid droplets, ROS, and peroxidated proteins expression (especially around lipid droplets of hepatocytes) increased. SOD2 immunostaining decreased in poorly steatotic hepatocytes but increased in the thin cytoplasm of macrosteatotic cells; a trend towards a quantitative decrease of SOD expression in homogenates occurred after 3 weeks. ATP and GSH values were significantly lower for rats fed with the MCD diet with respect to the controls. An increase of TBARS in the last period of the diet is in keeping with the high ROS production and low antioxidant defense; these TBARS may promote protein peroxidation around lipid droplets. Since these proteins play key roles in lipid mobilization, storage, and metabolism, this last information appears significant, as it points towards a previously misconsidered target of NAFLD-associated oxidative stress that might be responsible for lipid dysfunction.

Oxidative stress in aging human skin

Oxidative stress in skin plays a major role in the aging process. This is true for intrinsic aging and even more for extrinsic aging. Although the results are quite different in dermis and epidermis, extrinsic aging is driven to a large extent by oxidative stress caused by UV irradiation. In this review the overall effects of oxidative stress are discussed as well as the sources of ROS including the mitochondrial ETC, peroxisomal and ER localized proteins, the Fenton reaction, and such enzymes as cyclooxygenases, lipoxygenases, xanthine oxidases, and NADPH oxidases. Furthermore, the defense mechanisms against oxidative stress ranging from enzymes like superoxide dismutases, catalases, peroxiredoxins, and GSH peroxidases to organic compounds such as L-ascorbate, α-tocopherol, beta-carotene, uric acid, CoQ10, and glutathione are described in more detail. In addition the oxidative stress induced modifications caused to proteins, lipids and DNA are discussed. Finally age-related changes of the skin are also a topic of this review. They include a disruption of the epidermal calcium gradient in old skin with an accompanying change in the composition of the cornified envelope. This modified cornified envelope also leads to an altered anti-oxidative capacity and a reduced barrier function of the epidermis.

Carbonylated proteins are eliminated during reproduction in C. elegans

Oxidatively damaged proteins accumulate with age in many species (Stadtman (1992) Science257, 1220-1224). This means that damage must be reset at the time of reproduction. To visualize this resetting in the roundworm Caenorhabditis elegans, a novel immunofluorescence technique that allows the detection of carbonylated proteins in situ was developed. The application of this technique revealed that carbonylated proteins are eliminated during C. elegans reproduction. This purging occurs abruptly within the germline at the time of oocyte maturation. Surprisingly, the germline was markedly more oxidized than the surrounding somatic tissues. Because distinct mechanisms have been proposed to explain damage elimination in yeast and mice (Aguilaniu et al. (2003) Science299, 1751-1753; Hernebring et al. (2006) Proc Natl Acad Sci USA103, 7700-7705), possible common mechanisms between worms and one of these systems were tested. The results show that, unlike in yeast (Aguilaniu et al. (2003) Science299, 1751-1753; Erjavec et al. (2008) Proc Natl Acad Sci USA105, 18764-18769), the elimination of carbonylated proteins in worms does not require the presence of the longevity-ensuring gene, SIR-2.1. However, similar to findings in mice (Hernebring et al. (2006) Proc Natl Acad Sci USA103, 7700-7705), proteasome activity in the germline is required for the resetting of carbonylated proteins during reproduction in C. elegans. Thus, oxidatively damaged proteins are eliminated during reproduction in worms through the proteasome. This finding suggests that the resetting of damaged proteins during reproduction is conserved, therefore validating the use of C. elegans as a model to study the molecular basis of damage elimination.

Exposure of HL-60 human leukaemic cells to 4-hydroxynonenal promotes the formation of adduct(s) with alpha-enolase devoid of plasminogen binding activity

HNE (4-hydroxynonenal), the major product of lipoperoxidation, easily reacts with proteins through adduct formation between its three main functional groups and lysyl, histidyl and cysteinyl residues of proteins. HNE is considered to be an ultimate mediator of toxic effects elicited by oxidative stress. It can be detected in several patho-physiological conditions, in which it affects cellular processes by addition to functional proteins. We demonstrated in the present study, by MS and confirmed by immunoblotting experiments, the formation of HNE-alpha-enolase adduct(s) in HL-60 human leukaemic cells. Alpha-enolase is a multifunctional protein that acts as a glycolytic enzyme, transcription factor [MBP-1 (c-myc binding protein-1)] and plasminogen receptor. HNE did not affect alpha-enolase enzymatic activity, expression or intracellular localization, and did not change the expression and localization of MBP-1 either. Confocal and electronic microscopy results confirmed the plasma membrane, cytosolic and nuclear localization of alpha-enolase in HL-60 cells and demonstrated that HNE was colocalized with alpha-enolase at the surface of cells early after its addition. HNE caused a dose- and time-dependent reduction of the binding of plasminogen to alpha-enolase. As a consequence, HNE reduced adhesion of HL-60 cells to HUVECs (human umbilical vein endothelial cells). These results could suggest a new role for HNE in the control of tumour growth and invasion.

Age-related differences in oxidative protein-damage in young and senescent fibroblasts

Aging is accompanied by an accumulation of oxidized proteins and cross-linked modified protein material. The intracellular formation and accumulation of highly oxidized and cross-linked proteins, the so-called lipofuscin, is a typical sign of senescence. However, little is known whether the lipofuscin accumulation during aging is related to environmental conditions, as oxidative stress, and whether the accumulation of oxidized proteins and lipofuscin is preferentially taking place in the cytosol or the nucleus and finally, what is the role of lysosomes in this process. Therefore, we investigated human skin fibroblasts in an early stage of proliferation ("young cells") and in a late stage ("senescent cells"). Such cells were compared for the amount of protein carbonyls and lipofuscin and their distribution within the cytosol and the nucleus. Furthermore, cells were exposed to single and repeated doses of hydrogen peroxide and paraquat, measuring the same set of parameters. In addition to that the role of the proteasome to degrade oxidized proteins in young and senescent cells was tested. Furthermore, detailed microscopic analysis was performed testing the intracellular distribution of lipofuscin. The results clearly demonstrated that repeated/chronic oxidative stress induces a senescence-like phenotype of the distribution of oxidized proteins as well as of lipofuscin. It could be demonstrated that most of the lipofuscin is located in lysosomes and that senescent cells contain less lysosomes not lipofuscin-laden in comparison to young cells.

Antioxidant capacity and protein oxidation in cerebrospinal fluid of amyotrophic lateral sclerosis

BACKGROUND

The causes of Amyotrophic Lateral Sclerosis (ALS) are unknown. A bulk of evidence supports the hypothesis that oxidative stress and mitochondrial dysfunction can be implicated in ALS pathogenesis. METHODS =: We assessed, in cerebrospinal fluid (CSF) and in plasma of 49 ALS patients and 8 controls, the amount of oxidized proteins (AOPP, advanced oxidation protein products), the total antioxidant capacity (FRA, the ferric reducing ability), and, in CSF, two oxidation products, the 4-hydroxynonenal and the sum of nitrites plus nitrates.

RESULTS

The FRA was decreased (p = 0.003) in CSF, and AOPP were increased in both CSF (p = 0.0039) and plasma (p = 0.001) of ALS patients. The content of AOPP was differently represented in CSF of ALS clinical subsets, resulting in increase in the common and pseudopolyneuropathic forms (p < 0.001) and nearly undetectable in the bulbar form, as in controls. The sum of nitrites plus nitrates and 4-hydroxynonenal were unchanged in ALS patients compared with controls.

CONCLUSION

Our results, while confirming the occurrence of oxidative stress in ALS, indicate how its effects can be stratified and therefore implicated differently in the pathogenesis of different clinical forms of ALS.

Oxidized proteins: intracellular distribution and recognition by the proteasome

The formation of oxidized proteins is one of the highlights of oxidative stress. In order not to accumulate such proteins have to be degraded. The major proteolytic system responsible for the removal of oxidized proteins is the proteasome. The proteasome is distributed throughout the cytosolic and nuclear compartment of mammalian cells, with high concentrations in the nucleus. On the other hand a major part of protein oxidation is taking place in the cytosol. The present review highlights the current knowledge on the intracellular distribution of oxidized proteins and put it into contrast with the concentration and distribution of the proteasome.

Prooxidant reactions promoted by soluble and cell-bound gamma-glutamyltransferase activity

Recent studies have provided evidence for the prooxidant roles played by molecular species originating during the catabolism of glutathione (GSH) effected by gamma-glutamyltransferase (GGT), an enzyme normally present in serum and on the outer surface of numerous cell types. The reduction of metal ions by GSH catabolites is capable of inducing the redox cycling processes, leading to the production of reactive oxygen species and other free radicals. Through the action of these reactive compounds, cell membrane GGT activity can ultimately produce oxidative modifications on a variety of molecular targets, involving oxidation and/or S-thiolation of protein thiol groups in the first place. This chapter is a survey of the procedures most suitable to reveal GGT-dependent prooxidant reactions and their effects at the cellular and extracellular level, including methods in histochemistry, cytochemistry, and biochemistry, with special reference to methods for the evaluation of protein thiol redox status.

Up-regulation of the 31 kDa dehydroascorbate reductase in the modified skeletal muscle cell (nurse cell) during Trichinella spp. infection

Ascorbic acid (AA) is an important factor of defence against oxidative stress. AA is maintained in the reduced functional form by glutathione (GSH)-dependent dehydroascorbate (DHA) reducing enzymes, including the cytosolic glutaredoxin, the microsomal protein disulphide isomerase, and a DHA reductase of 31 kDa, hereafter referred to as DHAR, purified from rat liver cytosol and human red cells. As these mechanisms have rarely been studied in parasites, we looked for the possible presence of this 31 kDa protein in Trichinella spiralis L(1) larvae. Biochemical data, immunoblot analysis and immunohistochemical studies suggested the absence of this protein within parasites at this stage. However, they possess a low DHA reducing ability, which is probably due to the presence of glutaredoxin. On the other hand, immunohistochemical studies performed in histological sections of muscle tissue from Trichinella-infected animals showed an increase in DHAR in the nurse cell (NC) of T. spiralis- and Trichinella britovi-infected animals, compared with the surrounding muscle fibres. This result was confirmed by immunoblot analysis, whereas no such increase was observed in Trichinella pseudospiralis-infected animals. In the modified skeletal muscle cell also haeme oxygenase 1 increased, as well as lipoperoxidised proteins. Both findings suggest an oxidative stress of the NC, which might be related to the intense inflammatory reaction which surrounds the NC-parasite complex. Another possibility to explain the increase in DHAR could be that the NC needs to recycle a substantial amount of AA to synthesise the collagen capsule.

Antioxidants in dermocosmetology: from the laboratory to clinical application

Oxygen situated in cutaneous cells can be activated by light. This makes the integumentary apparatus particularly vulnerable to oxidative damage and is responsible for the immediate cutaneous damage that is the basis of late phenomena, such as photo-induced ageing and tumours. Thus, the cosmetic industry has undertaken research and development into antioxidant-based products able to protect the skin from the effect of pro-oxidizing noxae. This review re-examines both antioxidants suitable for dermatological application and skin care products with antioxidant capacity, as well as the laboratory methods used to evaluate the effects and in vivo efficacy of antioxidants.

Histochemical visualization of oxidant stress

Free radicals induce oxidative modification in distinct components of the living matter (lipid, proteins, and DNA). For qualitative and quantitative determination of free radical-induced modifications, different, more or less sensitive biochemical methods are available. Because of the high reactivity and short life of free radicals, ongoing oxidative damage is generally analyzed by measurement of secondary products-such as H(2)O(2), oxidized proteins, peroxidized lipids, and their breakdown products, oxidized DNA-or by fluorographic analysis in combination with fluorescent dyes such as dichlorofluorescin (DCFH). In addition, the determination of free radical-related oxidation products is usually carried out in plasma, urine, or, less frequently, in bioptic material. Consequently, biochemical data seldom reflect the effects of free radical insults in situ. The histochemical visualization of selected molecular markers of oxidative damage can often provide more valuable information concerning the in vivo distribution of oxidative processes. This review summarizes the methods currently available for histochemical detection and indirect visualization of free radical-induced alterations in tissues and isolated cells.

Membrane gamma-glutamyl transpeptidase activity of melanoma cells: effects on cellular H(2)O(2) production, cell surface protein thiol oxidation and NF-kappa B activation status

The metabolism of glutathione by membrane-bound γ-glutamyl transpeptidase (GGT) has been recently recognized as a basal source of hydrogen peroxide in the extracellular space. Significant levels of GGT activity are expressed by malignant tumours, and in melanoma cell lines they were found to correlate with the malignant behaviour. As hydrogen peroxide and other oxidants can affect signal transduction pathways at several levels, the present study was aimed to verify: (i) the occurrence of GGT-dependent production of hydrogen peroxide in melanoma cells; (ii) the effects of GGT-dependent prooxidant reactions on known redox-sensitive cellular targets, i.e. protein thiols, the nuclear transcription factor NF-kappa B and p53. Two melanoma Me665/2 cell clones, exhibiting traces of (clone 2/21) or high (clone 2/60) GGT activity, were studied. The occurrence of GGT-dependent production of hydrogen peroxide was apparent in 2/60 cells, in which it was accompanied by lower levels of cell surface protein thiols. In 2/60 cells, GGT expression was also associated with higher levels of NF-kappa B activation, as compared to GGT-poor 2/21 cell clone. Indeed, stimulation or inhibition of GGT activity in 2/60 cells resulted in progressive activation or inactivation of NF-kappa B, respectively. An analysis of the p53 gene product indicated lack of protein expression in 2/60 cells, whereas a mutant protein was highly expressed in 2/21 cells. Taken together, these results indicate that the expression of GGT activity can provide melanoma cells with an additional source of hydrogen peroxide, and that such prooxidant reactions are capable to modify protein thiols at the cell surface level. In addition, GGT expression results in an up-regulation of the transcription factor NF-kappa B, which could explain the higher metastatic behaviour reported for GGT-rich melanoma cells as compared to their GGT-poor counterparts.

Iron release and oxidant damage in human myoblasts by divicine

Divicine is an aglycone derived from vicine, a glucosidic compound contained in fava beans (Vicia faba major or broad beans). In this study, we investigated the effect of divicine on cultured human myoblasts from normal subjects, in order to see if the drug may induce signs of oxidant stress in these cells. Myoblasts incubated 24 hours in the presence of 1 mM divicine, showed an increase of carbonyl groups and 4-hydroxynonenal (4-HNE) bound to cell proteins, as well as a significant release of iron and lactate dehydrogenase in the culture medium. Desferrioxamine (DFO), an iron chelator, significantly prevented protein oxidation and formation 4-HNE adducts. Our results can be interpreted as indicating that divicine autooxidizes both at extracellular level and into myoblasts thus inducing the release of free iron, which initiates oxidation of cellular proteins and lipids. DFO protects the cells by subtracting the free iron both at intracellular and extracellular level.

Redox modulation of cell surface protein thiols in U937 lymphoma cells: the role of gamma-glutamyl transpeptidase-dependent H2O2 production and S-thiolation

The expression of gamma-glutamyl transpeptidase (GGT), a plasma membrane ectoenzyme involved in the metabolism of extracellular reduced glutathione (GSH), is a marker of neoplastic progression in several experimental models, and occurs in a number of human malignant neoplasms and their metastases. Because it favors the supply of precursors for the synthesis of GSH, GGT expression has been interpreted as a member in cellular antioxidant defense systems. However, thiol metabolites generated at the cell surface during GGT activity can induce prooxidant reactions, leading to production of free radical oxidant species. The present study was designed to characterize the prooxidant reactions occurring during GGT ectoactivity, and their possible effects on the thiol redox status of proteins of the cell surface. Results indicate that: (i) in U937 cells, expressing significant amounts of membrane-bound GGT, GGT-mediated metabolism of GSH is coupled with the extracellular production of hydrogen peroxide; (ii) GGT activity also results in decreased levels of protein thiols at the cell surface; (iii) GGT-dependent decrease in protein thiols is due to sulfhydryl oxidation and protein S-thiolation reactions; and (iv) GGT irreversible inhibition by acivicin is sufficient to produce an increase of protein thiols at the cell surface. Membrane receptors and transcription factors have been shown to possess critical thiols involved in the transduction of proliferative signals. Furthermore, it was suggested that S-thiolation of cellular proteins may represent a mechanism for protection of vulnerable thiols against irreversible damage by prooxidant agents. Thus, the findings reported here provide additional explanations for the envisaged role played by membrane-bound GGT activity in the proliferative attitude of malignant cells and their resistance to prooxidant drugs and radiation therapy.

Reactive oxygen species-induced molecular damage and its application in pathology

Recent studies have clarified that reactive oxygen species (ROS) are involved in a diversity of biological phenomena including radiation damage, carcinogenesis, ischemia-reperfusion injury, diabetes mellitus and neurodegenerative diseases. The breakthrough of these fruitful accomplishments was the discovery of an enzyme, superoxide dismutase, by McCord and Fridovich in 1968. In the 1970s and 80s, biochemists and radiation biologists were attracted by the role of ROS in its irreversible damage to biological molecules. In the 1990s, ROS were further found to be a reversible modulator of protein structure as well, and this led to a recent rapid data accumulation on the association of ROS and transcription factors. At the same time, methods to localize ROS-induced damage in paraffin-embedded tissues have been established. This owes to a successful production of antibodies against covalently modified structures specific for ROS-induced damage. The epitopes include 8-hydroxy-2'-deoxyguanosine and 4-hydroxy-2-nonenal-modified proteins. The present article reviews histochemical and immunohistochemical methods to localize ROS-induced damage in tissues and cells, further comments on the association of ROS with transcription factors, and shows a prospective view of ROS-induced carcinogenesis.

Modulation of human T lymphocyte proliferation by 4-hydroxynonenal, the bioactive product of neutrophil-dependent lipid peroxidation

The proliferative capacity of immune cells is known to be sensitive to conditions of oxidative stress and lipid peroxidation. We tested the hypothesis that activated neutrophils can induce peroxidation in extracellular lipid substrates, and evaluated the effects of 4-hydroxy-2,3-trans-nonenal (4-HNE)--the most reactive aldehydic product of lipid peroxidation--on mitogen-induced proliferation of human T lymphocytes. Neutrophils activated in the presence of extracellular lipid substrates (liposomes, cellular membranes) induced lipid peroxidation. By means of cytoimmunofluorescent labeling and confocal microscopy, the binding of 4-HNE to surface and cytoplasmic proteins of activated neutrophils was observed. Short (20 min) pre-treatment of cells with low concentrations of 4-HNE were able to dose-dependently decrease the proliferation of human peripheral blood lymphocytes challenged with PHA or anti-CD3 monoclonal antibody OKT3, as well as the proliferation of a tetanus specific human T-cell line challenged with tetanus toxoid. In these conditions, the binding of 4-HNE to surface and cytoplasmic proteins of lymphocytes was also observed. When the proliferative capacity of peripheral blood lymphocytes was monitored over several days after 4-HNE treatment and PHA challenge, a recovery and a rebound in cell proliferation was observed. Data reported indicate that the lipid peroxidation promoted by activated neutrophils can exert modulatory effects on the responsivity of human T cells, through the action of its most reactive product, 4-HNE.