In vitro modulation of antioxidant enzyme levels in normal hamster kidney and estrogen-induced hamster kidney tumor

Manganese superoxide dismutase is a promising target for enhancing chemosensitivity of basal-like breast carcinoma

AIMS

Although earlier reports highlighted a tumor suppressor role for manganese superoxide dismutase (MnSOD), recent evidence indicates increased expression in a variety of human cancers including aggressive breast carcinoma. In the present article, we hypothesized that MnSOD expression is significantly amplified in the aggressive breast carcinoma basal subtype, and targeting MnSOD could be an attractive strategy for enhancing chemosensitivity of this highly aggressive breast cancer subtype.

RESULTS

Using MDA-MB-231 and BT549 as a model of basal breast cancer cell lines, we show that knockdown of MnSOD decreased the colony-forming ability and sensitized the cells to drug-induced cell death, while drug resistance was associated with increased MnSOD expression. In an attempt to develop a clinically relevant approach to down-regulate MnSOD expression in patients with basal breast carcinoma, we employed activation of the peroxisome proliferator-activated receptor gamma (PPARγ) to repress MnSOD expression; PPARγ activation significantly reduced MnSOD expression, increased chemosensitivity, and inhibited tumor growth. Moreover, as a proof of concept for the clinical use of PPARγ agonists to decrease MnSOD expression, biopsies derived from breast cancer patients who had received synthetic PPARγ ligands as anti-diabetic therapy had significantly reduced MnSOD expression. Finally, we provide evidence to implicate peroxynitrite as the mechanism involved in the increased sensitivity to chemotherapy induced by MnSOD repression.

INNOVATION AND CONCLUSION

These data provide evidence to link increased MnSOD expression with the aggressive basal breast cancer, and underscore the judicious use of PPARγ ligands for specifically down-regulating MnSOD to increase the chemosensitivity of this subtype of breast carcinoma.

Mitochondrial mechanisms of estrogen neuroprotection

Mitochondria have become a primary focus in our search not only for the mechanism(s) of neuronal death but also for neuroprotective drugs and therapies that can delay or prevent Alzheimer's disease and other chronic neurodegenerative conditions. This is because mitochrondria play a central role in regulating viability and death of neurons, and mitochondrial dysfunction has been shown to contribute to neuronal death seen in neurodegenerative diseases. In this article, we review the evidence for the role of mitochondria in cell death and neurodegeneration and provide evidence that estrogens have multiple effects on mitochondria that enhance or preserve mitochondrial function during pathologic circumstances such as excitotoxicity, oxidative stress, and others. As such, estrogens and novel non-hormonal analogs have come to figure prominently in our efforts to protect neurons against both acute brain injury and chronic neurodegeneration.

Reversible modulation of cell cycle kinetics in NIH/3T3 mouse fibroblasts by inducible overexpression of mitochondrial manganese superoxide dismutase

To study the mechanism(s) by which manganese-containing superoxide dismutase (MnSOD) mediates cellular growth inhibition, an inducible retroviral vector system regulated by the lac repressor was used to overexpress MnSOD protein in NIH/3T3 cells. Increased MnSOD activity led to decreased cell growth due to prolonged cell cycle transition times in G(1) and S phases without significant changes in G(2)/M phase. Changes in cell cycle transition time were reversible and tightly correlated with MnSOD levels. A transient increase of reactive oxygen species and concomitant decrease in mitochondrial membrane potential were documented following MnSOD induction. N-Acetyl-L-cysteine prevented growth inhibition by MnSOD. Our data suggest that MnSOD may serve a physiological function of regulating cell cycle progression through its prooxidant activity of generating hydrogen peroxide, resulting in coordination of mitochondrial redox state and cellular proliferation.

Myocardial antioxidant and oxidative stress changes due to sex hormones

The purpose of the present study was to examine myocardial antioxidant and oxidative stress changes in male and female rats in the presence of physiological sex hormone concentrations and after castration. Twenty-four 9-week-old Wistar rats were divided into four groups of 6 animals each: 1) sham-operated females, 2) castrated females, 3) sham-operated males, and 4) castrated males. When testosterone and estrogen levels were measured by radioimmunoassay, significant differences were observed between the castrated and control groups (both males and females), demonstrating the success of castration. Progesterone and catalase levels did not change in any group. Control male rats had higher levels of glutathione peroxidase (50%) and lower levels of superoxide dismutase (SOD, 14%) than females. Control females presented increased levels of SOD as compared to the other groups. After castration, SOD activity decreased by 29% in the female group and by 14% in the male group as compared to their respective controls. Lipid peroxidation (LPO) was assessed to evaluate oxidative damage to cardiac membranes by two different methods, i.e., TBARS and chemiluminescence. LPO was higher in male controls compared to female controls when evaluated by both methods, TBARS (360%) and chemiluminescence (46%). Castration induced a 200% increase in myocardial damage in females as determined by TBARS and a 20% increase as determined by chemiluminescence. In males, castration did not change LPO levels. These data suggest that estrogen may have an antioxidant role in heart muscle, while testosterone does not.

In vivo evidence for antioxidant potential of estrogen in microvessels of female spontaneously hypertensive rats

In studies conducted in vitro, it has been demonstrated that estrogen has an antioxidant potential that may contribute to its protective effects on the cardiovascular system. However, the antioxidant effect of estrogen in vivo has not been demonstrated. To address this issue, in this study the effects of estrogen on oxidative stress were evaluated in microvessels studied in vivo. Oxidative stress was evaluated by using intravital microscopy in mesenteric arterioles from female spontaneously hypertensive rats (SHR) in physiological estrous (OE), ovariectomized (OVX), OVX treated with estradiol (E(2)), or estradiol + progesterone (E/P). The mesenteries were superfused with hydroethidine, a reduced and nonfluorescent precursor of ethidium bromide (EB). In the presence of reactive oxygen species, hydroethidine is transformed intracellularly in EB, which binds to DNA and can be detected by its red fluorescence. The percentage of EB-positive nuclei along the arteriolar wall in OVX (28.4 +/- 4.3) was significantly increased compared with OE (14.2 +/- 3.9; P<0.05). The OVX overproduction of oxyradicals was attenuated by E(2) (15.7 +/- 2.2) and E/P (14.8 +/- 0.8). Treatment with the superoxide dismutase mimetic MnTMPyP attenuated by 75% the oxidation of hydroethidine in both OE and OVX. Conversely, mannitol, that decomposes hydroxyl radical, and L-NAME, a nitric oxide synthase inhibitor, had no significant effects on hydroethidine oxidation. No differences on hydrogen peroxide plasma concentration were observed among the groups, suggesting that superoxide anion is the most likely oxyradical involved in the increased oxidative stress observed in OVX. The treatment of mesenteries with diphenyleneiodonium (DPI), an nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase inhibitor, but not with oxypurinol, a xanthine-oxidase inhibitor, produced a significant reduction of oxyradical generation in OVX microvessels and a slight decrease in those from OE. Chronic treatment of female SHR with losartan caused similar decreases in oxyradicals in both OE and OVX, whereas diclofenac and verapamil had no effects. Together these data suggest that estrogen reduces superoxide anion bioavailability in vivo. The antioxidant effect of estrogen, which can contribute to a less pronounced endothelial dysfunction in female SHR, may be dependent on a direct modulatory action of estrogen on NADPH activity.

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.

Oxygen insensitivity of the histochemical assay of glucose-6-phosphate dehydrogenase activity for the discrimination between nonmalignant and malignant cells

We review here the oxygen insensitivity of the histochemical assay of glucose-6-phosphate dehydrogenase (G6PDH) activity to detect cancer cells. This inexpensive and rapid assay can be performed within half an hour. Discrimination between cancerous and noncancerous cells is based on a combination of elevated G6PDH activity, decreased superoxide dismutase (SOD) activity, and decreased lipid peroxidation in cancer cells. The test discriminates between adenomas and carcinomas of the colon with a certainty of >80% and has a high prognostic value for survival of colon cancer patients. Pancreatitis and pancreatic cancer are discriminated with a certainty of 100%. Therefore, the test can be applied by pathologists to provide additional information in difficult cases of diagnosis of cancer and for prognosis.

17 beta-estradiol reduces glycoxidative damage in the artery wall

Glycoxidative damage in the vasculature has been linked to atherosclerotic cardiovascular disease. Estrogens protect against the development and progression of atherosclerosis. Because estrogens are potent antioxidants that also effect glucose metabolism, part of their protection against atherosclerosis could be through attenuation of glycoxidative damage in the vascular wall. In this study, we tested the hypothesis that chronic estradiol administration is associated with decreased levels of glycoxidative damage in arterial walls. We harvested and examined iliac arteries from ovariectomized, 8-month-old rats that had been implanted for 6 months with 1 of the following subcutaneous hormone pellets: low estradiol (2.5 mg estradiol), high estradiol (25 mg estradiol), P4 (200 mg progesterone), low estradiol and P4, placebo (no hormone), or control (no implant). Using pentosidine as a biomarker of glycoxidative damage, we found that all vessels from rats receiving estradiol (low estradiol, high estradiol, and low estradiol+P4) exhibited a 50% reduction in glycoxidative damage compared with P4, placebo, and control vessels (P<0.05). Consistent with this finding, we observed that estradiol-treated rats had a 30% decrease in tissue levels of hydroperoxides, a marker of oxidative stress. Finally, estradiol-treated rats had a small, but significant, decrease in plasma glucose levels (P<0.01). In summary, we report the novel finding that chronic estrogen administration is associated with significant decreases in glycoxidative damage and oxidative stress in the arterial wall. It seems likely that these actions may constitute a mechanism by which estrogen attenuates the progression of atherosclerosis.

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 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.

Overexpression of manganese superoxide dismutase in DU145 human prostate carcinoma cells has multiple effects on cell phenotype

BACKGROUND

Recent studies suggest that the gene for manganese superoxide dismutase (MnSOD) is a candidate tumor-suppressor gene. The present study was designed to study the effect of overexpression of MnSOD on cultured human prostate carcinoma cells.

METHODS

DU145 human prostate carcinoma cells were transfected with the cDNA for manganese superoxide dismutase (MnSOD), and two clones overexpressing MnSOD activity were subsequently characterized by comparison with parental and plasmid control-transfected cells.

RESULTS

One clone overexpressing MnSOD had no change in other antioxidant enzymes (AEs) (nonadapted), while a second clone showed an increase in catalase activity (adapted). Sensitivity of parental, plasmid control-transfected, and MnSOD cDNA-transfected cells to agents that generate oxidative stress correlated with AE profiles. Both clones overexpressing MnSOD activity showed increased reactive oxygen species levels under basal cell culture conditions. Both clones overexpressing MnSOD activity showed inhibition of cell growth in vitro and in vivo compared with parental and plasmid control-transfected cells. Flow cytometry studies using mitochondrial-specific probes showed equal mitochondrial mass in all cell lines, but altered mitochondrial membrane potential in MnSOD-overexpressing clones compared with parental or plasmid control-transfected cells.

CONCLUSIONS

Our results suggest novel mechanisms by which MnSOD overexpression may modulate the malignant phenotype, with potential applications in developing new therapies for prostate cancer.

17 beta-Estradiol prevents dysfunction of canine coronary endothelium and myocardium and reperfusion arrhythmias after brief ischemia/reperfusion

BACKGROUND

Brief myocardial ischemia is associated with myocardial and coronary endothelial dysfunction caused by oxygen free radicals released during reperfusion. Estrogen, known to have antioxidant activity, may prevent these complications.

METHODS AND RESULTS

We assessed the effect of 2 weeks of treatment with 17 beta-estradiol (E, 100 micrograms.kg-1.d-1, n = 12) or placebo (P, n = 15) on myocardial and coronary endothelial function during the first 2 hours of reperfusion in dogs subjected to 15 minutes of ischemia induced by occlusion of the left anterior descending coronary artery (LAD). Our results show that the incidence of ventricular arrhythmias significantly decreased in E (3 of 12) compared with P (11 of 15). Systolic shortening, significantly depressed in P during early reperfusion, was maintained at preischemic levels in E. During reperfusion, the increase in LAD flow to acetylcholine, attenuated in P (60 +/- 6%), was preserved in E endothelium. (151 +/- 28%) and was associated with increased serum nitrite/nitrate concentration. n-Pentane in exhaled gas in vivo, an index of lipid peroxidation, increased significantly during early reperfusion in P (from 9.1 +/- 1.9 to 41.6 +/- 13.0 ppb, P < .05) but not in E (23.0 +/- 6.9 ppb). In vitro, arterial segments from E generated significantly less superoxide anion after hypoxia/reoxygenation than those from P. Ischemic/reperfused LAD segments from E also revealed a better preservation of endothelium-dependent relaxation in vitro (maximum relaxation, 42 +/- 4% versus 24 +/- 4% in P; P < .05).

CONCLUSIONS

Estrogen protects against endothelial and myocardial dysfunction resulting from brief ischemia/reperfusion. This protection may relate to an antioxidant effect of estrogen.

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

Manganese superoxide dismutase (MnSOD) levels were monitored as a function of time in culture to determine whether these levels were altered at logarithmic growth versus when the cells exhibited density limitation of growth. For comparison, activities of the antioxidant enzymes copper, zinc superoxide dismutase (CuZnSOD), catalase, and glutathione peroxidase were also evaluated. Four cell lines were studied, two of which exhibited density limitation of growth and two of which did not. Each cell line showed a unique antioxidant enzyme profile. The two cell lines that showed density limitation of growth also demonstrated induction of MnSOD at the time when the cells stopped proliferating in culture, whereas the other two cell lines did not show induction of MnSOD. There was no strict correlation between density limitation of growth and activities of the other antioxidant enzymes. To determine whether SOD varied with various phases of the cell cycle, NIH/3T3 cells were synchronized using serum starvation, and then SOD activities were measured during quiescence (G0) and the phase of DNA synthesis (S-phase). MnSOD was decreased during S-phase compared with G0, whereas CuZnSOD was increased during S-phase compared with G0, demonstrating alteration of SOD activities with varying phases of the cell cycle. This study suggests the possibility that increased MnSOD may correlate with decreased cell proliferation and suggests significant alterations in SOD activities during the cell cycle.