Antioxidant enzyme levels as a function of growth state in cell culture

Overexpression of human catalase inhibits proliferation and promotes apoptosis in vascular smooth muscle cells

The role of reactive oxygen species, such as superoxide anions (O(2). (-)) and hydrogen peroxide (H(2)O(2)), in modulating vascular smooth muscle cell proliferation and viability is controversial. To investigate the role of endogenously produced H(2)O(2), rat aortic smooth muscle cells were infected with adenoviral vectors containing cDNA for human catalase (AdCat) or a control gene, beta-galactosidase (AdLacZ). Infection with AdCat resulted in dose-dependent increases in intracellular catalase protein, which was predominantly localized to peroxisomes. After infection with 100 multiplicity of infection (MOI) of AdCat, cellular catalase activity was increased by 50- to 100-fold, and intracellular H(2)O(2) concentration was reduced, as compared with control. Infection with AdCat reduced [(3)H]thymidine uptake, an index of DNA synthesis, in cells maintained in medium supplemented with 2% serum (0.37+/-0.09 disintegrations per minute per cell [AdLacZ] versus 0.22+/-0.08 disintegrations per minute per cell [AdCat], P<0.05). Five days after infection with 100 MOI of AdCat, cell numbers were reduced as compared with noninfected or AdLacZ-infected cells (157 780+/-8413 [AdCat], P<0.05 versus 233 700+/-3032 [noninfected] or 222 410+/-5332 [AdLacZ]). Furthermore, the number of apoptotic cells was increased 5-fold after infection with 100 MOI of AdCat as compared with control. Infection with AdCat resulted in induction of cyclooxygenase (COX)-2, and treatment with a COX-2 inhibitor overcame the AdCat-induced reduction in cell numbers. These findings indicate that overexpression of catalase inhibited smooth muscle proliferation while increasing the rate of apoptosis, possibly through a COX-2-dependent mechanism. Our results suggest that endogenously produced H(2)O(2) importantly modulates survival and proliferation of vascular smooth muscle cells.

Two distinct mechanisms for inhibition of cell growth in human prostate carcinoma cells with antioxidant enzyme imbalance

The purpose of the present study was to determine whether manganese superoxide dismutase (MnSOD) overexpression in DU145 human prostate carcinoma cells affected cell reduction-oxidation state (cell redox) and to correlate changes in cell redox status with cell cycle progression and plating efficiency. One MnSOD-overexpressing cell line had no change in other antioxidant enzymes (AEs) (nonadapted clone), whereas a second MnSOD-overexpressing cell line studied had an increase in catalase (CAT) activity (adapted clone). Correlation of biochemical studies with cell cycle studies suggested that heteroploidy observed in the nonadapted MnSOD-overexpressing cell line may be due to increased intracellular peroxides with resultant disruption of the microtubule network, while a decreased mitotic rate was associated with decreased ATP levels in mitosis. In contrast, the decrease in cell growth in the adapted cell line was demonstrated to be due to a decrease in plating efficiency. Our results demonstrate complex effects of AE imbalance on cell growth of DU145 prostate cancer cells.

Reactive oxygen intermediates regulate cellular response to apoptotic stimuli: an hypothesis

Production of reactive oxygen intermediates (ROI) has been thought for a long time to adversely affect the physiology and survival of a cell. There is now a growing body of evidence to suggest that ROI such as superoxide anion (O2*-) and hydrogen peroxide (H2O2) can influence the growth, as well as death, of animal cells in vitro. The observation that cells release O2*- or its dismutation product H2O2, either constitutively in the case of tumor cells or following cytokine stimulation, has led to the speculation that they might possibly serve as intercellular messengers to stimulate proliferation via mechanisms common to natural growth factors. However, as the balance between cell populations in an organism is tightly controlled by the rate of proliferation and death of constituent cells, an increase in cell numbers could reciprocally be viewed as deregulation of cell death. Hence, it is equally important to decipher how ROI influence the response of cells to signals that activate cell death pathway(s). We propose that ROI not only regulate proliferation but also affect cell sensitivity to triggers which activate the cellular suicide program (apoptosis) versus those that cause accidental (necrotic) cell death.

Modulation of antioxidant enzymes, reactive oxygen species, and glutathione levels in manganese superoxide dismutase-overexpressing NIH/3T3 fibroblasts during the cell cycle

NIH/3T3 mouse embryo fibroblasts were transfected with the cDNA for manganese superoxide dismutase (MnSOD). Previous studies showed characteristic unique AE profiles in nonsynchronous populations of parental, control plasmid-transfected, and MnSOD-overexpressing NIH/3T3 cell lines. However, the present study showed that during S and M phases of the cell cycle, antioxidant enzyme (AE) levels were altered in MnSOD-overexpressing cell lines towards levels in S and M phases of parental and control plasmid-transfected cells. Because of the demonstration that MnSOD overexpression inhibits cell growth in both nonmalignant and malignant cells, the present study was designed to measure AEs, reactive oxygen species (ROS), and glutathione levels in various phases of the cell cycle in both parental NIH/3T3 cells and NIH/3T3 cells overexpressing MnSOD, to try to determine whether AEs, ROS, and glutathione levels could have a possible regulatory role in cell cycle progression. In all cell lines studied, ROS levels were lower in M than S phase of the cell cycle. Total glutathione and glutathione disulfide levels were greatly increased during the M phase of the cell cycle compared with quiescence and S phase in all cell lines studied. This suggests that oxidative stress exists in M phase of the cell cycle with total glutathione levels increased to decrease oxidative stress. Analysis of MnSOD-overexpressing cell clones showed a correlation of decreased cell growth with an increase in ROS in S phase of the cell cycle and a decrease in glutathione in mitosis. The data strongly suggest that specific levels of cell redox state are necessary for cells to successfully progress through the various phases of the cell cycle.

Inhibition of cell proliferation: a mechanism likely to mediate the prevention of neuronal cell death by melatonin

In a previous work we demonstrated that melatonin is able to prevent apoptosis induced by low doses of 6-hydroxydopamine (6-OHDA) in undifferentiated and neuronal PC12 cells. We also reported how this neurohormone was able to prevent the decrease in the mRNA for antioxidant enzymes caused by 6-OHDA. Although the antioxidant capability of melatonin seems to be clearly implicated in its antiapoptotic activity, literature suggests that its antiproliferative property could also be involved in its prevention of apoptosis. In the present work we demonstrated that melatonin is able to inhibit cell proliferation in undifferentiated PC12 cells, decreasing cell number and the total amount of DNA, and the mRNA for the histone H4, which are known to increase during DNA synthesis. Melatonin does not decrease the number of cells in nonproliferating PC12 cells, indicating that it does not cause cell death. Additionally, we demonstrate that other inhibitors of cell proliferation, as well as other antioxidants, are able to mimic the antiapoptotic effect of melatonin. This is interpreted to mean that melatonin acts by both mechanisms to inhibit apoptosis caused by 6-OHDA and the findings support the hypothesis of a relationship between oxidative stress and regulation of the cell cycle.

A Rac1 effector site controlling mitogenesis through superoxide production

The Rac GTP-binding protein controls signal transduction pathways that are critical for mitogenesis and oncogenesis (1,2). The biochemical nature of these signaling pathways is presently unknown. Here we report that a region in Rac1 (residues 124-135), previously defined as the insert region (3), is essential for its mitogenic activity. Deletion of this region does not interfere with the ability of Rac1 to induce cytoskeletal changes or to activate the Jun kinase mitogen-activated protein kinase cascade but abrogates Rac1-induced stimulation of DNA synthesis and Rac1-mediated superoxide production in quiescent fibroblasts. Treatment of cells with agents that abolish superoxide generation inhibits specifically the mitogenic effect of Rac1. Our results identify an effector site in Rac1 that is necessary for mitogenic signaling and implicate superoxide generation as a candidate effector pathway of Rac1-dependent cell growth.

Overexpression of human superoxide dismutase inhibits oxidation of low-density lipoprotein by endothelial cells

Oxidation of LDL in the subendothelial space has been proposed to play a key role in atherosclerosis. Endothelial cells produce superoxide anions (O2.-) and oxidize LDL in vitro; however, the role of O2.- in endothelial cell-induced LDL oxidation is unclear. Incubation of human LDL (200 microg/mL) with bovine aortic endothelial cells (BAECs) for 18 hours resulted in a 4-fold increase in LDL oxidation compared with cell-free incubation (22.5+/-1.1 versus 6.3+/-0.2 [mean+/-SEM] nmol malondialdehyde/mg LDL protein, respectively; P<0.05). Under similar conditions, incubation of LDL with porcine aortic endothelial cells resulted in a 5-fold increase in LDL oxidation. Inclusion of exogenous copper/zinc superoxide dismutase (Cu/ZnSOD, 100 microg/mL) in the medium reduced BAEC-induced LDL oxidation by 79%. To determine whether the intracellular SOD content can have a similar protective effect, BAECs were infected with adenoviral vectors containing cDNA for human Cu/ZnSOD (AdCu/ZnSOD) or manganese SOD (AdMnSOD). Adenoviral infection increased the content and activity of either Cu/ZnSOD or MnSOD in the cells and reduced cellular O2.- release by two thirds. When cells infected with AdCu/ZnSOD or AdMnSOD were incubated with LDL, formation of malondialdehyde was decreased by 77% and 32%, respectively. Two other indices of LDL oxidation, formation of conjugated dienes and increased LDL electrophoretic mobility, were similarly reduced by SOD transduction. These data suggest that production of O2.- contributes to endothelial cell-induced oxidation of LDL in vitro. Furthermore, adenovirus-mediated transfer of cDNA for human SOD, particularly Cu/ZnSOD, effectively reduces oxidation of LDL by endothelial cells.

Inhibition of cell growth in NIH/3T3 fibroblasts by overexpression of manganese superoxide dismutase: mechanistic studies

NIH/3T3 mouse fibroblasts were transfected with the cDNA for manganese superoxide dismutase (MnSOD), and two clones overexpressing MnSOD activity were subsequently characterized by comparison with parental and control plasmid-transfected cells. One clone with a 1.8-fold increase in MnSOD activity had a 1.5-fold increase in glutathione peroxidase (GPX) activity (increased GPX-adapted clone), while a second clone with a 3-fold increase in MnSOD activity had a 2-fold decrease in copper, zinc superoxide dismutase (CuZnSOD) activity (decreased CuZnSOD-adapted clone). Increased reactive oxygen species (ROS) levels compared with parental or control plasmid-transfected cells were observed in nonsynchronous cells in the increased GPX-adapted clone, but not in the decreased CuZnSOD-adapted clone. The two MnSOD-overexpressing clones showed different sensitivities to agents that generate oxidative stress. Flow cytometry analysis of the cell cycle showed altered cell cycle progression in both MnSOD-overexpressing clones. During logarithmic growth, both MnSOD-overexpressing clones showed increased mitochondrial membrane potential compared with parental and control plasmid-transfected cells. Both MnSOD-overexpressing clones showed a decrease in mitochondrial mass at the postconfluent phase of growth, suggesting that mitochondrial mass may be regulated by MnSOD and/or ROS levels. Our results indicate that adaptation of fibroblasts to overexpression of MnSOD can involve more than one mechanism, with the resultant cell phenotype dependent on the adaptation mechanism utilized by the cell.

Regulation of cyclo-oxygenase gene expression in rat smooth muscle cells by catalase

We have studied, in detail, the effect of catalase, one of the naturally occurring antioxidant enzymes, on the expression of cyclo-oxygenase (COX) mRNA and protein in rat aortic smooth muscle cells (RASMC). The activity of COX enzyme within the cells was also determined. Catalase either alone or in combination with interleukin-1beta (IL-1beta) enhanced mRNA and protein expression for cyclo-oxygenase 2 (COX-2) in a concentration-dependent manner. However, it did not affect the expression of mRNA or protein for cyclo-oxygenase 1 (COX-1). The expression of mRNA for COX-2 induced by catalase was blocked completely by actinomycin D (ACT) or cycloheximide (CHX). In comparison, expression of mRNA for COX-2 stimulated by IL-1beta was inhibited by actinomycin D, but not by cycloheximide. This suggests that induction of the synthesis of mRNA for COX-2 by catalase and IL-1beta involves different mechanisms. In particular, the induction of mRNA for COX-2 by catalase requires on-going protein and RNA synthesis, but the induction following exposure to IL-1beta does not. The increase in expression of mRNA for COX-2 induced by catalase may be related to the ability of catalase to stimulate cyclic AMP response element (CRE) and NF-IL6 transcription factors, but not nuclear factor kappa B (NF-kappaB), for electrophoretic mobility shift assays (EMSA) showed that catalase enhanced nuclear factor binding to cyclic AMP response element and NF-IL6 but not to NF-kappaB. Catalase exerted a biphasic effect on prostaglandin synthesis. At low concentrations it enhanced prostaglandin production, but at high concentrations it tended to inhibit it. These findings suggest that catalase has differential and multiple effects on COX expression and activity in rat aortic smooth muscle cells.

Oxidative stress and superoxide dismutase in development, aging and gene regulation

Free radicals and other reactive oxygen species are produced in the metabolic pathways of aerobic cells and affect a number of biological processes. Oxidation reactions have been postulated to play a role in aging, a number of degenerative diseases, differentiation and development as well as serving as subcellular messengers in gene regulatory and signal transduction pathways. The discovery of the activity of superoxide dismutase is a seminal work in free radical biology, because it established that free radicals were generated by cells and because it made removal of a specific free radical substance possible for the first time, which greatly accelerated research in this area. In this review, the role of reactive oxygen in aging, amyotrophic lateral sclerosis (a neurodegenerative disease), development, differentiation, and signal transduction are discussed. Emphasis is also given to the role of superoxide dismutases in these phenomena.

Hydroperoxides mediate lithium effects on regeneration in Hydra

Regeneration experiments in Hydra have shown that lithium long-term treatment apparently causes a transformation of prospective head into foot tissue. Although lithium ions are known to interfere with the PI-PKC signal-transduction system and evidence has been provided that this system plays a role in pattern formation in Hydra, its role in mediating the lithium effect on patterning is still obscure. The present study provides evidence that H2O2 and presumably also lipid hydroperoxides mediate the lithium effects. First, the perturbation of pattern formation is strikingly stronger in the strain Hydra vulgaris than in Hydra magnipapillata, and similar strain-specific differences are found in the long lasting accumulation of hydroperoxides following lithium treatment. Second, the antioxidant vitamins E and C, which suppress peroxide accumulation, and the H2O2-degrading enzyme catalase significantly protect H. vulgaris from lithium effects. Lithium treatment also negatively affects overall DNA synthesis in a similar strain-specific manner, which, however, cannot be rescued by antioxidant vitamins. The lithium-activated source of peroxide production differs from another source, which generates peroxide in untreated polyps of both strains. The results suggest that lithium treatment-induced peroxide accumulation in H. vulgaris provokes a cytotoxic response showing foot-like characteristics. Nevertheless, a role of peroxides as messengers in pattern forming processes can not be excluded.

Down-regulation of manganese-superoxide dismutase gene expression in idiopathic nephrotic syndrome

An oxidant stress has been shown to prevail in experimental and clinical nephrotic syndrome. Such oxidant stress may be induced by a reduced activity of antioxidant systems. We examined the altered expression of manganese-superoxide dismutase (Mn-SOD), an antioxidant enzyme, in patients with idiopathic nephrotic syndrome, in whom an increased oxidant stress had been demonstrated. The Mn-SOD activities in peripheral blood mononuclear cells obtained from 12 patients with active nephrotic syndrome (6.0 +/- 1.1 years of age, mean +/- SE) and hypoproteinemia were 42% lower (p < 0.05) than in 12 control subjects (5.5 +/- 0.5 years of age) with normal serum total protein concentrations. Reverse-transcriptase polymerase chain reaction also demonstrated that Mn-SOD messenger RNA expression in the patients with nephrotic syndrome was, on average, 59% lower than in control subjects. Because expressions of some genes are sensitive to serum, the serum dependency of Mn-SOD gene transcription was studied in glomerular endothelial cells transfected with a luciferase reporter gene fused with a rat Mn-SOD DNA fragment of -806 to +22 bp of the transcription initiation site (-806:+22). When these cells were exposed to different concentrations of fetal bovine serum (0.5% to 15%), the transcriptional activities determined by luciferase activities were proportional to serum concentrations. This serum-dependent transcriptional activation was also demonstrated by the fragment (-220:+22) but not by the fragment (-220:-20). When glomerular endothelial cells transfected with the fragment (-220:+22) were treated with 5% serum from patients with active nephrotic syndrome, transcriptional activation was more than 80% less than that by 5% serum from control subjects without nephrosis. These results indicate that Mn-SOD gene transcription is regulated at least in part by serum, and that the serum-dependent transcription of the gene is diminished in patients with idiopathic nephrotic syndrome. The regulatory region of serum-dependent gene transcription resides within its early promoter region. Our findings suggest that down-regulation of antioxidant enzyme transcription may contribute increased oxidant stress in idiopathic nephrotic syndrome.

Antioxidant enzymes in malignant prostate cell lines and in primary cultured prostatic cells

The antioxidant enzymes catalase, glutathione reductase (GR), glutathione S-transferase (GST), glutathione peroxidase (GPx), and superoxide dismutase (SOD) were determined in the androgen-response LNCaP and androgen-nonresponsive PC-3 and DU 145 cells as well as in prostatic epithelial cell cultures of benign and malignant human prostatic tissue. There were no differences between the enzyme activities of the human primary cell cultures from cancerous tissue and their normal counterparts. The enzyme activities of the three permanent cell lines were either higher (SOD, catalase, GR) or lower (GST, GPx) than in the primary cell cultures. In LNCaP cells catalase and GR were significantly higher, GST, in contrast, was significantly lower than in PC-3 and DU 145 cells. GST in PC-3 and DU 145 cells, and SOD in all the three cell lines showed no significant differences. Catalase, GPx and GR values were significantly different in the three permanent cell lines. The different enzymatic equipment of the prostate cancer cell lines provides the basis for experimental testing of new concepts of cancer treatment with the help of systematic modulations of the antioxidant defence systems in prostate cancer.

The influence of cell growth, detoxifying enzymes and DNA repair on hydrogen peroxide-mediated DNA damage (measured using the comet assay) in human cells

Single-cell gel electrophoresis (the comet assay) is a sensitive method for detecting strand breaks at the level of individual cells. Cells embedded in agarose are lysed, electrophoresed, and fluorescently stained. Breaks in the DNA release its supercoiling and allow DNA to extend toward the anode, resembling a comet. We have used the comet assay to investigate the influence of growth state, xenobiotic detoxifying enzymes, and DNA repair processes on the response of cultured human cells to oxidative damage. HepG2 and Caco-2 cells are differentiated liver and colon cell lines, respectively. HeLa and GM1899A cells are relatively unspecialized epithelial and lymphoblastoid cells. Substrate-dependent cells showed a cyclical fluctuation of glutathione (GSH) with respect to growth. Enzyme activities (glutathione reductase, glutathione peroxidase, and catalase) varied considerably between cell types and changed with cell growth state. Hydrogen peroxide induced more DNA damage in actively dividing cells than in confluent cultures. Sensitivity to oxidative injury did not correlate with detoxifying enzyme activity. Rather, differences in susceptibility between cells could be correlated with differences in DNA repair capacity. This study highlights the need to standardize experimental conditions if the comet assay is to be employed in the study of genotoxicity.

Effect of Rooibos tea (Aspalathus linearis) on chick skeletal muscle cell growth in culture

Rooibos tea (RT) extract contains natural antioxidants and scavenging agents. We investigated the effects of different concentrations of RT extract in medium on growth and changes of growth parameters of cultured chick embryonic skeletal muscle cells. Presence of 2, 10 and 100% of RT extract in the culture of primary cells significantly inhibited cell proliferation. The inhibition of cell growth reflected on decreased DNA, RNA and protein contents in primary cell culture and fibroblasts and myoblasts. The ability of the primary cells, fibroblasts and myoblasts to synthesize DNA and protein in the presence of RT extract, measured as an amount of [3H]thymidine and [3H]leucine incorporated into DNA and de novo synthesized protein, corresponded with decreasing DNA and protein contents in all three cell types. The inhibition effect of RT rose with increasing concentration of the tea extract in the culture medium. Ornithine decarboxylase activity was significantly affected only by 100% RT extract in every examined cell types. These results suggest that the inhibitory effect of RT extract on the growth of primary cells, fibroblasts and myoblasts is due to the potent scavenging activity of the RT extract.

Antioxidant-induced changes of the AP-1 transcription complex are paralleled by a selective suppression of human papillomavirus transcription

Considering the involvement of a redox-regulatory pathway in the expression of human papillomaviruses (HPVs), HPV type 16 (HPV-16)-immortalized human keratinocytes were treated with the antioxidant pyrrolidine-dithiocarbamate (PDTC). PDTC induces elevated binding of the transcription factor AP-1 to its cognate recognition site within the viral regulatory region. Despite of increased AP-1 binding, normally indispensable for efficient HPV-16 transcription, viral gene expression was selectively suppressed at the level of initiation of transcription. Electrophoretic mobility supershift assays showed that the composition of the AP-1 complex, predominantly consisting of Jun homodimers in untreated cells, was altered. Irrespective of enhanced c-fos expression, c-jun was phosphorylated and became primarily heterodimerized with fra-1, which was also induced after PDTC incubation. Additionally, there was also an increased complex formation between c-jun and junB. Because both fra-1 and junB overexpression negatively interferes with c-jun/c-fos trans-activation of AP-1-responsive genes, our results suggest that the observed block in viral transcription is mainly the consequence of an antioxidant-induced reconstitution of the AP-1 transcription complex. Since expression of the c-jun/c-fos gene family is tightly regulated during cellular differentiation, defined reorganization of a central viral transcription factor may represent a novel mechanism controlling the transcription of pathogenic HPVs during keratinocyte differentiation and in the progression to cervical cancer.

Antioxidant defense system in differentially hydrogen peroxide sensitive L5178Y sublines

Two sublines of L5178Y (LY) murine lymphoma, differing in sensitivity to hydrogen peroxide, served as a cellular model for examination of the antioxidant defense system. The contribution of catalase, glutathione peroxidase (G-Px) and glutathione were evaluated. Sensitivity to 3-amino-1,2,4-triazole (AMT), inhibitor of catalase, was higher in LY-R (hydrogen peroxide sensitive) than in LY-S (hydrogen peroxide resistant) cells. Accordingly, activity of catalase was twofold lower in LY-R than in LY-S cells. G-Px activity was about two times higher in LY-R than in LY-S cells. After induction with selenium it increased 15.6 times in LY-R cells and 50.3 times in LY-S cells. Reduced glutathione (GSH) content (and possibly other monobromobimane-reactive thiols) were determined fluorimetrically with monobromobimane and fluorescence found 54% higher in LY-S than in LY-R cells. Inhibition of catalase caused GSH decrease in LY-S cells; this decrease was abrogated by inducing G-Px by selenium treatment. On the contrary, in LY-R cells inhibition of catalase decreased GSH content only slightly and selenium treatment did not further change the GSH level. DNA damage (estimated by "comet" assay) was the same in hydrogen peroxide-treated cells in the presence or absence of AMT; however, after induction of G-Px by selenium, DNA damage was considerably lowered. This sparing effect of selenium was accompanied by decreased growth inhibition in selenium pretreated, hydrogen peroxide-treated cell cultures.

Peroxynitrite-induced apoptosis in T84 and RAW 264.7 cells: attenuation by L-ascorbic acid

The free radicals nitric oxide and superoxide react to form peroxynitrite (ONOO-), a potent cytotoxic oxidant. This study was designed to evaluate whether addition of L-Ascorbic acid (AsC) into the culture medium decreases peroxynitrite-induced apoptosis in human intestinal epithelial (T84) and murine macrophage (RAW 264.7) cell lines. In Experiment 1, T84 and RAW 264.7 cells were divided in two protocols: (1) treated with 100-300 microM ONOO- and incubated for 4 h, and (2) treated with 10-100 microM ONOO- and incubated overnight (14 h). In Experiment 2, T84 and RAW 264.7 cells were treated with 300 microM ONOO- and 500 microM AsC and incubated for 4 h. In Experiment 3, T84 and RAW 264.7 cells were preincubated for 2 h with 500 microM AsC then exposed to 300 microM ONOO- for 4 h. Cell viability (necrosis) was assessed by trypan blue dye exclusion. Apoptosis was quantified with a cell death detection ELISA assay. In the 4 h protocol, ONOO- induced apoptosis in T84 and RAW 264.7 cells, at levels of 100-300 microM. Concentrations of ONOO- greater than 300 microM caused necrosis. In contrast, extension of the protocol to 14 h indicated that ONOO- induced apoptosis at lower concentrations (50;-75 microM), with concentrations > 75 microM resulting in necrosis. AsC administered to the media or with preincubation plus washout, decreased peroxynitrite-induced apoptosis in T84 and RAW 264.7 cells. These results indicate that ONOO- may contribute to the pathophysiology of gut inflammation by promoting cell death and ascorbic acid may protect against peroxynitrie-induced damage.

Nitration and inactivation of manganese superoxide dismutase in chronic rejection of human renal allografts

Inflammatory processes in chronic rejection remain a serious clinical problem in organ transplantation. Activated cellular infiltrate produces high levels of both superoxide and nitric oxide. These reactive oxygen species interact to form peroxynitrite, a potent oxidant that can modify proteins to form 3-nitrotyrosine. We identified enhanced immunostaining for nitrotyrosine localized to tubular epithelium of chronically rejected human renal allografts. Western blot analysis of rejected tissue demonstrated that tyrosine nitration was restricted to a few specific polypeptides. Immunoprecipitation and amino acid sequencing techniques identified manganese superoxide dismutase, the major antioxidant enzyme in mitochondria, as one of the targets of tyrosine nitration. Total manganese superoxide dismutase protein was increased in rejected kidney, particularly in the tubular epithelium; however, enzymatic activity was significantly decreased. Exposure of recombinant human manganese superoxide dismutase to peroxynitrite resulted in a dose-dependent (IC50 = 10 microM) decrease in enzymatic activity and concomitant increase in tyrosine nitration. Collectively, these observations suggest a role for peroxynitrite during development and progression of chronic rejection in human renal allografts. In addition, inactivation of manganese superoxide dismutase by peroxynitrite may represent a general mechanism that progressively increases the production of peroxynitrite, leading to irreversible oxidative injury to mitochondria.

Imbalance in the antioxidant pool in melanoma cells and normal melanocytes from patients with melanoma

In order to evaluate the free radical defense systems of melanocytes and their possible correlation with melanoma, we have studied in cultured normal human melanocytes (20), normal melanocytes from melanoma patients (15), and melanoma cells (40) the fatty acid pattern of membrane phospholipids as a target of peroxidative damage and the superoxide dismutase and catalase activities, vitamin E, and ubiquinone levels as intracellular antioxidants. Cells were cultured in the same medium and analyzed at III or IV passage. Compared to the values obtained in normal human melanocytes, melanoma cells showed on average: a) higher levels of polyunsaturated fatty acids, b) increased superoxide dismutase and decreased catalase activities, higher vitamin E, and lower ubiquinone levels. Among the normal melanocytes from melanoma patients studied, two groups were differentiated: a) cultures (7) with enzymatic and non-enzymatic antioxidants level similar to those of normal human melanocytes; b) cultures (8) with antioxidant patterns similar to those observed in melanoma cells. Polyunsaturated fatty acids were also increased in the latter group. The results indicate that in melanoma cells and in a percentage of normal melanocytes from melanoma patients, an imbalance in the antioxidant system can be detected that can lead to endogenous generation of reactive oxygen species and to cellular incapability of coping with exogenous peroxidative attacks. These alterations could be correlated with the malignant transformation of cells and with the progression of the disease.