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© 1997 American Heart Association, Inc.
Articles |
Fatty Streak Formation in Fat-Fed Mice Expressing Human Copper-Zinc Superoxide Dismutase
From the Department of Molecular and Nuclear Medicine, Life Sciences Division, Ernest Orlando Lawrence Berkeley National Laboratory, University of California, Berkeley, Calif. (D.L.T., E.L.G., J.G.V.), the Department of Medicine, Washington University, St. Louis, Mo. (C.L., J.W.H.), and the Department of Pediatrics, University of California, San Francisco, Calif. (E.L.C., C.J.E.).
Correspondence to Dr. Diane L. Tribble, Donner Laboratory, Room 465, University of California, Berkeley, CA 94720.
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Abstract |
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Abstract Studies in vitro have shown that copper-zinc superoxide dismutase (CuZn-SOD) inhibits a number of events putatively involved in atherogenesis, including cell-mediated oxidation of LDL. To investigate whether increased activity of CuZn-SOD reduces atherogenesis in vivo, we examined diet-induced fatty streak formation in CuZn-SOD transgenic mice (n=24) as compared with their nontransgenic littermates (n=28). Transgenic animals were originally created by introduction of an EcoRI-BamHI human genomic DNA fragment containing the CuZn-SOD gene and its regulatory elements into B6SJL zygotes. For the current studies, the transgene was bred for 12 generations into the atherosclerosis-susceptible C57BL/6 background. Animals were fed atherogenic diets (15% fat, 1.25% cholesterol, 0.5% Na cholate) starting at 10 weeks of age and extending for 18 weeks. At the end of the diet period, aortic SOD activity was two-fold higher in transgenics than nontransgenics (mean±SE: 46.7±5.8 versus 20.1±2.4 units/mg of protein, P<.001). Levels of protein-bound amino acid oxidation products (meta-, ortho-, and dityrosine) were either similar or lower in aorta and heart from transgenics as compared with nontransgenics, suggesting that amplification of CuZn-SOD activity above the normal complement had modest inhibitory effects on basal oxidative stress in these tissues. CuZn-SOD overexpression did not reduce the extent of lesion development as analyzed by quantitative lipid staining of serial sections of the proximal aorta; mean lesion areas (±SE) were 997±478 and 943±221 µ2 in transgenics and nontransgenics, respectively. Notably, the range of values for lesion area was 2.2-fold greater in transgenics (0-8403 versus 0-3868 µ2 in nontransgenics). Moreover, within this group, lesion area showed a significant positive correlation with SOD activity (r=.611, P<.03). These results do not support an antiatherogenic effect of CuZn-SOD over expression, and the possibility that high tissue SOD activity may potentiate atherogenesis in fat-fed atherosclerosis-susceptible mice.
Key Words: atherogenesis • diet • oxidation • transgenic mice
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Oxidative alterations affecting the properties of lipoproteins and arterial cells occur under a variety of oxidant stress conditions and may play a causal role in the development of atherosclerosis.1 2 Among the reactive oxygen species generated in vivo, the superoxide anion (O2-) has been implicated as a possible mediator of atherogenic oxidative alterations. The atherogenic potential of O2- has been inferred, in part, from observations of attenuating effects of superoxide dismutase (SOD), which catalyzes the dismutation of two molecules of O2- (+2H+) to molecular oxygen (O2) and hydrogen peroxide (H2O2) (Fig 1
). The latter is then further
metabolized to H2O by catalase or glutathione peroxidase.
Addition of SOD, either alone or in combination with these other
detoxication enzymes, has been shown to inhibit cell-mediated
lipoprotein oxidation3 4 5 and leukocyte adhesion to the
vascular endothelium6 7 and to facilitate
endothelium-derived relaxing factor-induced
vascular relaxation.8 9 10 11 Among the possible mechanisms for
these potentially antiatherogenic effects of SOD are inhibition of
oxidative alterations caused by O2- and its
reactive byproducts and prevention of
O2--mediated removal of nitric oxide
(endothelial-derived relaxing factor) (Fig 1). In
addition to these effects, Vaille and Jadot12 recently
reported that encapsulated SOD exhibits lipid-lowering effects in
fat-fed rats. Thus, it has been hypothesized that by a number of
mechanisms, enhanced SOD activity may be antiatherogenic.
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The primary aim of the present study was to test whether amplification of tissue SOD activity reduces atherosclerosis development in susceptible mice. This was accomplished by measuring diet-induced atherogenesis in C57BL/6 mice expressing human copper/zinc (CuZn)-SOD. This SOD isoenzyme is present in the cytosol and nucleus of all cells and accounts for the bulk of tissue SOD activity.13 14 Many previous studies have shown that increased expression of CuZn-SOD confers protection against acute or short-term oxidative injury in tissues from transgenic animals and in transfected cells,15 16 17 18 19 20 although evidence to the contrary also exists.21 22 23 Still relatively unexplored are the effects of increased expression of CuZn-SOD on chronic or degenerative conditions, including atherosclerosis, that are believed to arise in part from the accumulated effects of oxidative injury.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Transgenic Mice
Transgenic mice were initially developed by introduction of an EcoRI-BamHI human genomic DNA fragment containing SOD1 and its regulatory elements into B6SJL zygotes.24 For the present studies, transgenic mice of strain TgHS/SF-218/10 were used. These animals contain a 14-kilobase segment encompassing the entire gene (in eight tandem copies) and all necessary regulatory sequences. The SOD1 transgene was bred for 12 generations into the atherosclerosis-susceptible C57BL/6 background. These mice are now designated C57BL/6-TgN(SOD1)10cje. Strain C57BL/6J mice used for breeding were obtained from Jackson Laboratories (Bar Harbor, Me).
Transgenic mice were readily identified using polyacrylamide gel electrophoresis separation of red blood cell extracts, with staining for SOD activity as previously described.24 Mouse and human SOD are each composed of two identical subunits, and the transgene is expressed in a manner similar to humans, with two transcripts in a 1-4 ratio. The human enzyme is synthesized in an active form capable of forming human-mouse heterodimers. Transgenic animals display two prominent bands corresponding to the mouse-human heterodimer and the human homodimer, whereas nontransgenic mice display only one band corresponding to the mouse homodimer.
Female offspring from the final mating, comprising 24 transgenic and 28 nontransgenic mice, were placed on an atherogenic diet (15% fat, 1.25% cholesterol, 0.5% Na cholate) starting at 10 weeks of age and extending for 18 weeks. Afterward, the animals were sacrified for measurement of aortic SOD activity, plasma lipids and lipoproteins, and aortic lesion area. In parallel experiments, lipoprotein oxidizability and tissue levels of oxidized amino acids were evaluated. Animals were fasted overnight before tissue blood and collection.
Isolation of Tissues and Blood
The heart and upper section of the aorta were removed from the
chest cavity and placed in a 0.9% saline solution at room temperature;
the blood was flushed out with continued contraction of the heart
muscle. After 1 hour, hearts were trimmed of excess tissue and placed
in 10% phosphate-buffered formalin for 24 hours to 48 hours before
gelatin embedding and cryosectioning.25 The spinal column
was removed and placed in 0.9% saline for 1 hour to 2 hours. The
abdominal aorta, used for measurement of SOD activity was excised from
the bone and tissue, washed in 0.9% saline to remove red blood cells,
and stored at -80°C in 0.9% saline containing 0.005% gentamycin
for up to 2 weeks.
For studies measuring heart and aortic levels of oxidized amino acids, animals were anesthetized with intraperitoneal Avertin and perfused with cold (4°C) antioxidant buffer (1 mmol/L of butylated hydroxytoluene, 100 µmol/L diethylanetriaminepentaacetic acid, 100 µM 1% ethanol, 50 mmol/L of phosphate buffer, pH 7.4) by injection into the left ventricle; flow exited through the vena cava, which had been severed below the renal artery. The heart and abdominal aorta were isolated as described above, washed and minced in cold antioxidant buffer, and immediately frozen in liquid N2.
For measurements of lipids and lipoproteins, blood was removed from the chest cavity immediately after excision of the heart using a pasteur pipette flushed with ethylene diamine tetraacetic acid solution and was placed in a 1.5-ml Eppendorf tube containing ethylene diamine tetraacetic acid. Plasma was isolated by centrifugation at 2000xg under refrigeration (4°C).
SOD Activity
Tissue was thawed and then minced and homogenized in
three volumes of phosphate-buffered saline, pH 7.4. An aliquot was
removed for determination of total tissue protein using a modification
of the method of Lowry.26 Hemoglobin (which interferes
with the SOD activity assay) was removed by ethanol-chloroform
precipitation as previously described for the purification of CuZn-SOD
from red blood cells.27 The supernatant was collected
after centrifugation (15,000xg, 10
minutes), and SOD activity was determined by monitoring the extent of
inhibition of O2--mediated nicotinamide
adenine dinucleotide phosphate oxidation at 345
nm.28 Reactions were carried out at 37°C in a
thermostatically controlled Shimadzu UV2101-PC scanning
spectrophotometer.
Protein-bound Oxidized Amino Acids
Frozen tissue samples (
50 mg, wet weight) were pulverized in
liquid N2 using a stainless steel mortar and pestle and
were then delipidated by incubation with methanol and water-washed
diethyl ether for 10 minutes on ice. The protein was precipitated by
centrifugation (500xg, 10 minutes),
extracted with water-washed diethyl ether, dried under N2,
and immediately suspended in 0.5 ml of 6 N Sequenal-grade HCl (Pierce
Chemical, Rockford Il). Isotopically labeled internal standards were
added and samples were hydrolyzed at 110°C for 24 hours under
N2. Amino acids were converted to their N-propyl ester,
N2O-per pentafluoropropyl derivatives, and were quantified
as previously described29 using stable isotope dilution
negative-ion chemical-ionization gas chromatography
mass spectrometry on a Hewlett Packard 5890 gas chromatograph
equipped with a 12-m DB-1 capillary column (0.20 mm id, 0.33-µm
thickness; J & W Scientific, Folsom, Calif) interfaced with a Hewlett
Packard 5988A mass spectrometer with extended mass range.
Quantification was based on an external calibration curve using each
amino acid as a standard and the corresponding isotopically labeled
amino acids as internal standards, which were present at a final
ratio of 1 to 10 mole per mole of naturally occurring amino acids.
Plasma Total and HDL Cholesterol
Cholesterol concentrations were assayed using an
enzymatic cholesterol kit (Boehringer Mannheim,
Indianapolis, Ind). HDL cholesterol was measured after
precipitating very low, intermediate, and low density lipoproteins
(VLDLs, IDLs, and LDLs) with polyethylene glycol.30
Oxidative Susceptibility of d1.006-1.063-g/ml Lipoproteins
Lipoproteins of d1.006-1.063 g/ml were isolated from
plasma by two sequential ultracentrifugation steps at
the indicated densities and were dialyzed against phosphate-buffered
saline, pH 7.4, to remove ethylene diamine tetraacetic acid before
oxidation. Oxidation was initiated by addition of 5µM
CuCl2, and conjugated diene formation was evaluated by
monitoring the increase in absorbance at 234 nm.31
Reactions were carried out at 37°C in a Shimadzu UV2101-PC scanning
spectrophotometer equipped with a thermostated 6-position automatic
sample changer. Initial absorbance was set at zero, and absorbance was
recorded every 2 minutes for 10 hours.
Aortic Lesion Area
Aortic lesion areas were determined by quantitative lipid
staining of serial sections of the proximal aortas as previously
described in detail by Paigen et al.25 Briefly, hearts
were embedded in 25% gelatin and frozen in OCT compound (Miles, Inc.,
Elkhart, Ind), and sequential 10-µm sections were cut along the
ascending aorta, beginning where the aorta is rounded and the valve
leaflets are clearly distinct to the region where the valves are no
longer apparent (encompassing 350 µm). Alternate sections
were saved on slides, stained with Oil Red O and hematoxylin, and
counterstained with light green. Oil Red O-stained areas were measured
using five sections taken at 80-µm intervals. Measurements were
performed using a 20x20-µm grid on a microscope eyepiece. The length
of a lesion along the aortic perimeter and the average thickness were
multiplied to obtain the cross-sectional area (in
µm2).
Statistical Analyses
Differences in tissue SOD activity, protein-bound oxidized amino
acids, plasma total and HDL cholesterol, and rates of
conjugated diene formation between transgenics and nontransgenics were
evaluated using two-group t tests. Differences in aortic
lesion areas were evaluated using both the two-group t test
and the Mann-Whitney U test. Relationships between SOD activity and
aortic lesion area were evaluated using Spearman's rank correlation
coefficients. All significance levels were based on two-tailed
tests.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Aortic SOD Activity
To determine the extent to which SOD activity was enhanced in the aortic tissue of transgenic mice, we measured SOD activity in abdominal aortas obtained from a subset of 16 transgenics and 19 nontransgenic littermates. Mean values (±SE) were 46.7±5.8 and 20.1±2.4 (units per mg of protein, P<.001), respectively, with only a modest overlap in the distributions of activities between the two groups (Fig 2
). The ratio of SOD activities in the
aortas of transgenics versus nontransgenics (2.2) was similar to those
previously reported for other tissues, including brain (2.9) and
pancreas (2.2).32 Differences of a similar magnitude also
were observed in peritoneal macrophages (3.3) and liver (2.8)
from a subset of three mice per group (data not shown).
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Protein-bound Oxidized Amino Acids in Aortic and Heart
Tissue
In general, amplification of tissue SOD activity has been shown to
reduce tissue oxidative injury in a dose-dependent
manner,15 16 17 18 19 20 although in some experimental models, a
paradoxical increase in injury has been observed with high SOD
activity.21 22 23 33 34 35 36 To evaluate the effects of CuZn-SOD
overexpression on tissue oxidative injury, we measured levels of
meta-tyrosine, ortho-tyrosine, and dityrosine in
aortas and hearts from six transgenic and six nontransgenic mice. These
stable metabolites are markers of oxidative stress conditions involving
H2O2, OH·, and reactive
nitrogen,37 38 all of which may be altered by more
efficient metabolism of O2-.
Values in aortic tissue were determined using a single pooled sample as
necessitated by the small sample volume and a minimal sample
requirement of 50 mg (wet weight). As shown in Table 1 tissue levels of the metabolites were
similar for transgenics and nontransgenics. There was, however, a
significant difference in levels of dityrosine in the heart; the mean
value was 33% lower in transgenics. Thus, amplification of tissue SOD
activity above the normal complement appeared to have modest
inhibitory effects on basal oxidative injury within this
tissue. Notably, dityrosine levels were greater in heart than aortic
tissue, possibly reflecting the greater metabolic activity
and hence oxidative burden in the former. It is noteworthy that the
heart has been shown to be severely affected in mice lacking
Mn-SOD,39 suggesting that this organ may be particularly
vulnerable to O2--mediated injury. The basis
for the selective difference in dityrosine is presently unclear but
is consistent with observations in other tissues under other
oxidative stress conditions (Leeuwenburgh and Heinecke, unpublished
observations).
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Plasma Total and HDL Cholesterol Levels and Lipoprotein
Oxidative Susceptibility
Liposome-encapsulated SOD lowers plasma total
cholesterol and raises HDL cholesterol in
fat-fed animals.12 Since such effects could have an impact
on atherosclerosis susceptibility, we evaluated whether
amplification of tissue SOD activity altered plasma total and HDL
cholesterol levels in our fat-fed mice. In contrast to this
previous observation, we did not observe any effect of SOD on plasma
total or HDL cholesterol levels, as indicated by the lack
of differences in these parameters between transgenics and
nontransgenics on the high-fat diet (Table 2). There also were no differences in
lipoprotein oxidative susceptibility, as assessed from the course of
conjugated diene formation (data not shown). The lack of an effect of
CuZn-SOD overexpression on in vitro lipoprotein oxidizability was not
unexpected, however, given that intracellular SOD is unlikely to affect
the intrinsic oxidizability of circulating lipoproteins.
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Aortic Lesion Area
Aortic lesion areas for individual mice are depicted in Fig 3. Mean values (±SE) were 997±478
µ2 in transgenics versus 943±221 µ2 in
nontransgenics, and they were not significantly different when
evaluated using the two-group t test (P=.57).
Median values were 233 µ2 for transgenics and 367
µ2 for nontransgenics when all animals were included, and
534 µ2 and 734 µ2, respectively, when
animals that did not develop lesions were excluded. These values were
not significantly different by the Mann-Whitney U test (for nonnormal
distributions, P=.46). Thus, contrary to expectations based
on studies in vitro, amplification of tissue CuZn-SOD activity in vivo
did not appear to be antiatherogenic. The lack of a protective effect
was further suggested by observations that the range of lesion areas
was 2.2-fold greater in transgenics (0-8403 versus 0-3868
µ2 in nontransgenics) and that within transgenics, SOD
activity was a significant positive predictor of lesion area
(Spearman's rank correlation coefficient: .611, P<.03)
(Fig 4). A similar relationship was not
observed in nontransgenics (data not shown).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Superoxide dismutase, either alone or in combination with catalase and glutathione peroxidase, has been shown to inhibit a number of events putatively involved in atherogenesis,3 4 5 6 7 8 9 10 11 thus implicating O2- and/or its reactive byproducts in the pathogenesis of this disease and raising the possibility that increased SOD activity may be antiatherogenic. In the current studies, we evaluated the antiatherogenic potential of SOD by examining atherosclerosis development in fat-fed C57BL/6 mice expressing human CuZn-SOD. Our results showed that despite a greater than twofold increase in aortic SOD activity, the aortic lesion area is not reduced in transgenics relative to nontransgenics after 18 weeks on an atherogenic diet. Moreover, contrary to expectations, aortic SOD activity was positively rather than negatively correlated with lesion area in transgenic animals.
These results do not rule out the involvement of O2- in atherogenesis since there are a number of alternative explanations. First, localization of SOD within the extracellular compartment may be critical to its protective effects. Second, dose-dependent protective effects of SOD may be observed over a different range of activities. And third, the protective effects of SOD may be obscured by deleterious consequences of SOD overexpression. The existence of multiple and counteractive effects of SOD is not unexpected given the numerous consequences of increased O2- removal and the multifactorial nature of atherosclerosis.
With regard to localization, atherogenic oxidative events attributed to O2- are suggested to occur, in part, within the intracellular compartment. For example, it has been argued that since NO· is generated intracellularly, the diffusion-limited reaction between NO· and O2- is likely to occur largely within this compartment.11 Likewise, intracellular O2- has been implicated in mediating the increased expression of cell-surface adhesion factors.6 7 40 The lack of an antiatherogenic effect of overexpressing CuZn-SOD does not support a major role for these or other intracellular O2-mediated events in the development of atherosclerosis in fat-fed mice. In contrast, oxidative damage to lipoproteins and the vascular endothelium are attributed primarily to oxygen-derived species that are either generated extracellularly or released into the extracellular space as cellular oxidative waste or in association with the oxidative burst.1 2 3 4 5 Epstein et al41 previously showed that the elevation in intracellular SOD activity does not diminish phorbol ester-stimulated O2- release in peritoneal macrophages from CuZn-SOD transgenics. Thus, oxidative injury resulting from O2- released during the oxidative burst may not be affected. These processes are more likely to be under the control of extracellular SOD, which is located primarily within the interstitial matrix or anchored to cell-surface heparan sulfate proteoglycans.43
In addition to localization, the direction and extent of change in SOD activity may determine whether it is effective in altering atherogenesis. The normal complement of SOD is already quite efficient in O2- removal. Thus, a two- to-threefold enhancement in tissue SOD activity may not promote a similar reduction in O2- mediated events, except perhaps under conditions of extreme oxidative stress. We observed that basal levels of dityrosine, used as a stable marker of oxidative injury, were 30% lower in tissue from transgenics, suggesting that CuZn-SOD overexpression modestly reduced oxidative injury in these animals. It is possible that this change may be insufficient to have an effect on atherosclerosis susceptibility, and/or that the antiatherogenic effects of SOD may be more apparent when activity is reduced rather than increased relative to the normal complement, with a corresponding increase in oxidative injury and atherogenesis.
The high tissue SOD activity achieved with SOD overexpression also could promote a paradoxical increase in oxidative injury. Several investigators have observed that in terms of oxidation endpoints, the dose-dependent effects of SOD are characterized by a bell-shaped curve.35 36 There is a range over which increasing SOD activity improves protection against oxidative injury. Yet as the activity is increased further, there is a diminution in protection and, in some cases, an exacerbation of oxidative injury.21 22 23 Similar effects could underlie our observation of a positive association between aortic SOD activity and lesion area in CuZn-SOD transgenics.
High SOD activity could enhance oxidative injury by increasing rates of
formation of distal oxidants. Increased formation of
H2O2 (a product of SOD, see Fig 1
), in the
absence of elevations in enzymes responsible for its elimination
(catalase and glutathione peroxidase), could lead to increased
formation of OH·. Several investigators have reported elevated
activities of other antioxidant enzymes in tissues from transgenics,
but results have been equivocal.22 44 In separate
experiments involving heart and liver tissue from four animals per
group, we did not detect differences in either catalase or glutathione
peroxidase activity (data not shown), although notably, these results
were obtained on the chow diet. SOD also could increase oxidant
formation by interacting directly with peroxynitrate in a reaction that
has been shown to yield the highly reactive nitronium ion
(NO2+).45 The lack of elevated
tissue levels of oxidized protein-bound tyrosine in transgenics argues
against a substantial increase in oxidant formation, although we cannot
comment on reactions involving reactive nitrogen because nitrotyrosine
would be the major oxidation product. It is important to note that
our experiments were performed under basal oxidative stress conditions
and that overall tissue levels of oxidation products may not adequately
characterize events within critical microenvironments.
Some evidence also suggests that excess scavenging of
O2- may be detrimental by reducing the ability
of cells to mount a response to oxidative stress. A number of examples
exist,46 47 48 although most involve prokaryotes in which it
has been shown that O2--generating agents
activate a stress response involving the induction of 40
polypeptides. Among these are several proteins with distinct
antioxidant properties including manganese SOD, endonuclease IV, and
glucose 6-phosphate dehydrogenase.48 Disruption of this
response has been shown to cause hypersensitivity to subsequent
oxidative insult. Oxidant-responsive regulatory elements also are
present in eukaryotic cells,49 although
less is known about their role in promoting an adaptive response or the
involvement of O2- as a regulatory signal.
In conclusion, susceptibility to diet-induced atherogenesis is not inhibited by overexpressing CuZn-SOD in C57BL/6 mice. Our observation of a positive relationship between aortic SOD activity and lesion area in transgenic mice raises the possibility that some of the effects of CuZn-SOD overexpression may be deleterious. Increased activity of CuZn-SOD may perturb the intracellular steady-state equilibrium of active oxygen species, which in turn may increase some types of oxidative injury and/or may lead to alterations in the adaptive response of cells to oxidative stress. These possibilities remain to be confirmed in studies directly addressing these issues.
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Acknowledgments |
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This research was supported by an institutional grant from Ernest Orlando Lawrence Berkeley National Laboratory (LBNL) to D.L.T., by National Institutes of Health grant AG08938 to C.J.E., and by a grant from the Markey Charitable Trust to the University of California San Francisco Program in Biological Sciences. This work was conducted at LBNL through the US Department of Energy under contract no. DE-AC03-76SF00098. We gratefully acknowledge Dr. Eddy Rubin for his role in initiating these studies. We also thank Dr. Ronald M. Krauss, for critical discussions during the preparation of this manuscript, and Patrick M. Thiel, for technical assistance.
Received July 26, 1996; accepted February 26, 1997.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Steinberg D, Parthasarathy S, Carew TE, Khoo JC, Witztum JL. Beyond cholesterol: modifications of low-density lipoprotein cholesterol that increase its atherogenicity. N Engl J Med.. 1988;320:915-924.[Medline] [Order article via Infotrieve]
2. Berliner JA, Haberland ME. The role of oxidized low-density lipoprotein in atherogenesis. Curr Opin Lipidol.. 1993;4:373-381.
3. Heinecke JW, Baker L, Rosen H, Chait A. Superoxide-mediated modification of low density lipoprotein by arterial smooth muscle cell. J Clin Invest.. 1986;77:757-761.
4. Cathcart MK, McNally AK, Morel DW, Chisolm GM III. Superoxide anion participation in human monocyte-mediated oxidation of low-density lipoprotein and conversion of low-density lipoprotein to a cytotoxin. J Immunol.. 1989;142:1963-1969.[Abstract]
5. Abdalla DS, Campa A, Monteiro HP. Low density lipoprotein oxidation by stimulated neutrophils and ferritin. Atherosclerosis.. 1992;97:149-159.[Medline] [Order article via Infotrieve]
6. Lehr HA, Becker M, Marklund SL, Hubner C, Arfors KE, Kohlschutter A, Messmer K. Superoxide-dependent stimulation of leukocyte adhesion by oxidatively modified LDL in vivo. Arterioscler Thromb. 1992;824-829.
7. Lehr HA, Kress E, Menger MD, Friedl HP, Hubner C, Arfors KE, Messner K. Cigarette smoke elicits leukocyte adhesion to endothelium in hamsters: inhibition by CuZn-SOD. Free Rad Biol Med.. 1993;14:573-581.[Medline] [Order article via Infotrieve]
8. Rubanyi GM, Vanhoutte PM. Superoxide anions and hyperoxia inactivate endothelium-derived relaxing factor. Am J Physiol. 1986;H822–H827.
9. Gryglewski RJ, Palmer RM, Moncada S. Superoxide anion is involved in the breakdown of endothelium-derived relaxing factor. Nature (Lond). 1986;320:454-456.[Medline] [Order article via Infotrieve]
10.
Ignarro LJ, Byrns RE, Buga GM, Wood KS, Chaudhuri G.
Pharmacological evidence that
endothelium-derived relaxing factor is nitric oxide:
use of pyrogallol and superoxide dismutase to study
endothelium-dependent and nitric oxide-elicited
vascular smooth muscle relaxation. J Pharmacol Exp
Ther.. 1988;244:181-189.
11.
White CR, Brock TA, Chang LY, Crapo J, Briscoe P, Ku D,
Bradley WA, Gianturco SH, Gore J, Freeman BA, Tarpey MM.
Superoxide and peroxynitrite in
atherosclerosis. Proc Natl Aca Sci
U S A.. 1994;91:1044-1048.
12. Vaille A, Jadot G. Normolipidaemic activity of liposomal-encapsulated superoxide dismutase in rats. Free Rad Res Commun.. 1990;11:241-250.[Medline] [Order article via Infotrieve]
13. White CW, Nguyen D-DH, Suzuki K, Taniguchi N, Rusakow LS, Avraham KB, Groner Y. Expression of manganese superoxide dismutase is not altered in transgenic mice with elevated level of copper-zinc superoxide dismutase. Free Rad Biol Med.. 1993;15:629-636.[Medline] [Order article via Infotrieve]
14.
Stålin P, Karlsson K, Johansson BO, Marklund SL.
The interstitium of the human arterial wall contains
very large amounts of extracellular superoxide dismutase.
Arterioscler Thromb Vasc Biol.. 1995;15:2032-2036.
15. Chan PH, Yang GY, Chen SF, Carlson EJ, Epstein CJ. Post-traumatic brain injury and edema are reduced in transgenic mice overexpressing CuZn superoxide dismutase. Ann Neurol.. 1991;29:482-486.[Medline] [Order article via Infotrieve]
16.
Kinouchi H, Epstein CJ, Mizui T, Carlson EJ, Chen S,
Chan PH. Attenuation of focal cerebral ischemic injury
in transgenic mice overexpressing CuZn superoxide dismutase.
Proc Natl Aca Sci U S A.. 1991;88:11158-11162.
17. Przedborski S, Ksotic V, Jackson-Lewis V, Naini AB, Simonetti S, Fahn S, Carlson EJ, Epstein CJ, Cadet JL. Transgenic mice with increased Cu/Zn-superoxide dismutase activity are resistant to N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity. J Neurosci.. 1992;12:1658-1667.[Abstract]
18. Huang T-T, Carlson EJ, Leadon SA, Epstein CJ. Relationship of resistance to oxygen free radicals to CuZn-superoxide dismutase activity in transgenic, transfected and trisomic cells. FASEB J.. 1992;6:903-910.[Abstract]
19. Yang G, Chan PH, Chen JH, Carlson EJ, Chen SF, Weinstein P, Epstein CJ, Kamii H. Human copper-zinc superoxide dismutase transgenic mice are highly resistant to reperfusion injury after focal cerebral ischemia. Stroke. 1994;25:165-170.[Abstract]
20. Cadet JL, Sheng P, Ali S, Rothman R, Carlson E, Epstein CJ. Attenuation of metamphetamine-induced neurotoxicity in copper/zinc superoxide dismutase transgenic mice. J Neurochem.. 1994;62:380-383.[Medline] [Order article via Infotrieve]
21. Elroy-Stein O, Berstein Y, Groner Y. Overproduction of human CuZn-superoxide dismutase in transfected cells: extenuation of paraquat-mediated cytotoxicity and enhancement of lipid peroxidation. EMBO J.. 1986;5:615-622.[Medline] [Order article via Infotrieve]
22. Ceballos I, Delabar JM, Nicole A, Lynch RE, Hallewell RA, Kamoun P, Sinet PM. Expression of transfected human CuZn superoxide dismutase gene in mouse L cells and NS20Y neuroblastoma cells induces enhancement of glutathione peroxidase activity. Biochim Biophys Acta.. 1988;949:58-64.[Medline] [Order article via Infotrieve]
23.
Oury TD, HO Y-S, Piantadosi CA, Crapo JD.
Extracellular superoxide dismutase, nitric oxide, and central
nervous system O2 toxicity. Proc Natl Aca Sci
U S A.. 1992;89:9715-9719.
24.
Epstein CJ, Avraham KB, Lovett M, Smith S, Elroy-Stein
O, Rotman G, Bry C, Groner Y. Transgenic mice with increased
Cu/Zn-superoxide dismutase activity: animal model of dosage effects in
Down syndrome. Proc Natl Acad Sci U S A.. 1987;84:8044-8048.
25. Paigen B, Morrow A, Holmes PA, Mitchell D, Williams RA. Quantitative assessment of atherosclerotic lesions in mice. Atherosclerosis.. 1987;68:231-240.[Medline] [Order article via Infotrieve]
26. Markwell MAK, Haas SM, Bieber LL, Tolbert NE. A modification of the Lowry procedure to simplify protein determination in membrane and lipoprotein systems. Anal Biochem.. 1978;87:206-210.[Medline] [Order article via Infotrieve]
27.
McCord JM, Fridovich I. Superoxide dismutase. An
enzymic function for erythrocuprein (hemocuprein). J
Biol Chem.. 1969;244:6049-6055.
28. Paoletti F, Mocali A. Determination of superoxide dismutase activity by purely chemical system based on NAD(P)H oxidation. Methods Enzymol.. 1990;186:209-220.[Medline] [Order article via Infotrieve]
29. Leeuwenburgh C, Hansen P, Shaish A, Holloszy JO, Heinecke J. Muscle protein oxidation and antioxidant supplementation: mass spectrometric quantification of o,o'-dityrosine, o-tyrosine, and 3-nitrotyrosine in aging rats. Submitted for publication.
30.
Izzo C, Grillo F, Murador E. Improved method for
determination of high density lipoprotein cholesterol. I.
Isolation of high density lipoproteins by use of polyehtylene
glycol. Clin Chem.. 1981;27:371-374.
31. Esterbauer H, Gebicki J, Puhl H, Jurgens G. The role of lipid peroxidation and antioxidants in oxidative modification of LDL. Free Rad Biol Med.. 1992;13:341-390.[Medline] [Order article via Infotrieve]
32.
Kubisch HM, Wang J, Luche R, Carlson E, Bray TM,
Epstein CJ, Phillips JP. Copper/zinc superoxide dismutase
modulates susceptibility to type 1 diabetes. Proc Natl
Aca Sci U S A.. 1994;91:9956-9959.
33.
Liochev SI, Fridovich I. Effects of
overproduction of superoxide dismutase on the toxicity of
paraquat toward Escherichia coli. J Biol
Chem.. 1991;266:8747-8750.
34.
Scott MD, Meshnick SR, Eaton JW. Superoxide
dismutase-rich bacteria: paradoxical increase in oxidant
toxicity. J Biol Chem.. 1987;262:3640-3645.
35. Omar BA, Gad NM, Jordan MC, Striplin SP, Russell WJ, Downey JM, McCord JM. Cardioprotection by Cu,Zn-superoxide dismutase is lost at high doses in the reoxygenated heart. Free Rad Biol Med.. 1990;9:465-471.[Medline] [Order article via Infotrieve]
36. Nelson SK, Bose SK, McCord JM. The toxicity of high-dose superoxide dismutase suggests that superoxide can both initiate and terminate lipid peroxidation in the perfused heart. Free Rad Biol Med.. 1994;16:195-200.[Medline] [Order article via Infotrieve]
37.
Huggins TG, Wells-Knecht MC, Detorie NA, Baynes JW,
Thorpe SR. Formation of o-tyrosine and dityrosine in proteins
during radiolytic and metal-catalyzed oxidation. J
Biol Chem. 1993;268:12341-12347.
38. Beckman JS, Chen J, Ischiropoulos H, Crow JP. Oxidative chemistry of peroxynitrite. Methods Enzymol.. 1994;233:229-240.[Medline] [Order article via Infotrieve]
39. Li Y, Huang T-T, Carlson EJ, Melov S, Ursell PC, Olson JL, Noble LJ, Yoshimura MP, Berger C, Chan PH, Wallace DC, Epstein CJ. Dilated cardiomyopathy and neonatal lethality in mutant mice lacking manganese superoxide dismutase. Nat Genet.. 1995;11:376-381.[Medline] [Order article via Infotrieve]
40.
Vischer UM, Jornot L, Wollhein CB, Thelar J-M.
Reactive oxygen intermediates induce regulated secretion of von
Willebrand factor from cultured human vascular
endothelial cells. Blood.. 1995;85:3164-3172.
41. Epstein CJ, Berger CN, Carlson EJ, Chan PH, Haung TT. Models for Down syndrome: chromosome 21-specific genes in mice. In: Molecular Genetics of Chromosome 21 and Down Syndrome. New York, NY: Wiley-Liss, Inc., 1990:215-232.
42. Marklund SL. Expression of extracellular superoxide dismutase by human cell lines. Biochem J.. 1990;266:213-219.[Medline] [Order article via Infotrieve]
43. Marklund SL, Karlsson K. Binding of extracellular-superoxide dismutase C to cultured cell lines and to blood cells. Lab Invest.. 1989;60:659-666.[Medline] [Order article via Infotrieve]
44. Przedborski S, Jackson-Lewis V, Kostic V, Carlson E, Epstein CJ, Cadet JL. Superoxide dismutase, catalase, and glutathione per-oxidase activities in copper/zinc-superoxide dismutase transgenic mice. J Neurochem.. 1992;58:1760-1767.[Medline] [Order article via Infotrieve]
45. Ischiropoulos H, Zhu L, chen J, Tsai M, Martin JC, Smith CD, Beckman JS. Peroxynitrite-mediated tyrosine nitration catalyzed by superoxide dismutase. Arch Biochem Biophys.. 1992;298:431-437.[Medline] [Order article via Infotrieve]
46.
Walkup L, Kogoma T. J Bacteriol.. 1989;171:1476-1484.
47.
Greenberg JT, Demple B. J Bacteriol.. 1989;171:3933-3939.
48.
Greenberg JT, Monach P, Chou JH, Josephy PD, Demple B.
Positive control of a global antioxidant defense regulon
activated by superoxide-generating agents in Escherichia
coli. Proc Natl Acad Sci U S A.. 1990;87:6181-6185.
49. Marui N, Offermann MK, Swerlick R, Kunsch C, Rosen CA, Ahmad M, Alexander RW, Medford RM. Vascular adhesion molecule-1 (VCAM-1) gene transcription and expression are regulated through an antioxidant-sensitive mechanism in human vascular endothelial cells. J Clin Invest.. 1993;92:1866-1874.
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