© 2000 American Heart Association, Inc.
Atherosclerosis and Lipoproteins |
Hyperbaric Oxygen Reduces the Progression and Accelerates the Regression of Atherosclerosis in Rabbits
From the Departments of Molecular Biology & Immunology (B.J.K., A.L., L.D.) and Integrative Physiology (J.W.), University of North Texas Health Science Center, Fort Worth, Tex.
Correspondence to Ladislav Dory, PhD, Department of Molecular Biology & Immunology, University of North Texas Health Science Center, 3500 Camp Bowie Blvd, Fort Worth, TX 76107. E-mail ldory{at}hsc.unt.edu
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Abstract—We studied the effect of hyperbaric oxygen (HBO) treatment on the extent of diet-induced accumulation of lipid oxidation products in rabbit plasma and tissues, on plasma paraoxonase activity, and on the extent of progression and regression of atherosclerotic lesions in the rabbit aorta. HBO treatment of cholesterol-fed rabbits dramatically reduces the development of arterial lesions despite having little or no effect on plasma or individual lipoprotein cholesterol concentrations. Compared with no treatment in cholesterol-fed animals, HBO treatment also substantially reduces the accumulation of lipid oxidation products (conjugated dienes, trienes, and thiobarbituric acid–reactive substances) in plasma, in the low density lipoprotein and high density lipoprotein fractions of plasma, in the liver, and in the aortic tissues. In addition, HBO treatment prevents the decrease in plasma paraoxonase activity observed in rabbits fed cholesterol-rich diets. Similarly, in regression studies, HBO treatment has no effect on the rate of plasma (or lipoprotein) cholesterol decline but significantly accelerates aortic lesion regression compared with no treatment. Direct measures of aortic cholesterol content support these morphological observations. On the basis of these results, we conclude that repeated, but relatively short, exposure to HBO induces an antioxidant defense mechanism(s) that is responsible for retarding the development or accelerating the regression of atherosclerotic lesions.
Key Words: hyperbolic oxygen • atherosclerosis • paraoxonase • hypercholesterolemia • lipid oxidation
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Atherosclerosis is the leading cause of death in Western society. Several lines of evidence suggest that oxidized lipoproteins play an important role in the etiology of this disease. Oxidized LDL is a powerful atherogenic agent that is able to bypass the normal feedback–regulated cellular cholesterol uptake by peripheral cells and lead to foam cell production.1 2 3 It has been isolated from atherosclerotic lesions.4 5 Oxidized LDLs potentiate monocyte–endothelial cell interaction,6 regulate cytokine expression,7 8 and stimulate chemotactic factor expression.9 10 They have also been shown to induce apoptosis in vascular cells.11 12 13 In contrast, the addition of antioxidants to the diet has been shown to decrease the progression of atherosclerosis in animal models.14 15 16 Oxidized HDLs appear to lose their ability to protect against atherosclerosis,17 including their ability to promote reverse cholesterol transport,18 one of the major putative mechanisms of protection against peripheral cholesterol accumulation.19 Myeloperoxidase, a heme protein secreted by phagocytes, appears to be a major catalyst for the in vivo formation of oxidized lipoproteins.20 21 Active enzyme has been found in atherosclerotic lesions.22
Hyperbaric oxygen (HBO) treatment is primarily used in the treatment of carbon monoxide poisoning and healing of problematic wounds in diabetic patients.23 24 25 Because diabetic patients are already at significantly increased risk of atherosclerosis,26 27 we wondered whether the additional periodic exposure to 100% oxygen at higher pressures would further increase this risk.
Repeated exposure to HBO or hyperoxia may be expected to lead to increased formation of hydrogen peroxide, a major reactant in the myeloperoxidase-catalyzed formation of hypochlorous acid,28 29 which, in turn, may modify plasma LDL and promote its rapid uptake by macrophages. Similar modification of HDL may reduce its ability to promote cholesterol efflux from peripheral cells.19
On the other hand, repeated exposure to HBO may induce the production of antioxidant enzymes/reagents by tissues,30 31 including the arterial wall, which, in turn, may reduce the extent of formation of oxidized lipoproteins and atherosclerosis.
In the present study, we tested the hypothesis that HBO accelerates the progression of atherosclerosis in rabbits fed an atherogenic diet. Surprisingly, we found that repeated exposure to HBO for short periods of time significantly reduces the progression of fatty streak formation compared with no exposure to HBO. Equally significant is our finding that HBO accelerates the regression of preestablished lesions. These observations extend our understanding of the etiology of atherosclerosis and have important implications in the treatment of this disease.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Animals and Diets
Male New Zealand White rabbits (initial weight 1.5 to 2 kg) were used for these studies. All animals were individually caged in stainless-steel wire-bottomed cages in a temperature- and humidity-controlled room on a 12-hour light/dark cycle. Our animal care facility is accredited by the American Association for the Accreditation of Laboratory Animal Care, and all procedures were reviewed and approved by the Institutional Animal Care and Use Committee.
Two separate experimental protocols were used to assess the effects of HBO treatment on the progression and regression of atherosclerosis. In the progression studies, atherosclerosis was induced by feeding the animals laboratory rabbit chow supplemented with 1% cholesterol and 10% hydrogenated coconut oil. A slightly less atherogenic diet was used for the regression studies (rabbit chow supplemented with 0.5% cholesterol). Dyets, Inc, supplied both diets. The change in the diet composition was to reduce, in the regression study, the extent of hepatic hyperlipidemia and liver damage noted in 2 animals during the progression study.
Experimental Protocol
Progression Studies
Two separate progression studies were carried out. After 2 weeks
of acclimatization, the animals were randomly divided into 3 groups.
The animals in the control group (n=3, study 1; n=4, study 2) were fed
standard rabbit chow diet; the remaining animals were fed the
atherogenic diet. Half of the rabbits fed the atherogenic diet also
received daily HBO treatment (n=5 in both studies). The other half of
the cholesterol-fed animals (n=5 and 6 in studies 1 and 2,
respectively) received mock HBO treatment (no oxygen) to provide a
similar amount of overall handling. This portion of the studies lasted
10 weeks. HBO treatment was initiated 1 week before the start of the
diet. The data from studies 1 and 2 were pooled for analyses,
but selected parameters were measured in only 1 of the
studies.
Regression Study
All 18 animals used in the regression study were fed the
atherogenic diet, as described above. After 10 weeks on the diet, 6
animals, selected at random, were euthanized, and the aortic fatty
streak formation and cholesterol deposition were studied,
as described below. This group provided baseline values for the
atherosclerotic lesions developed before the start of regression with
and without HBO treatment. The remaining 12 animals were randomly
divided into 2 equal groups and switched to the regular chow diet to
induce the regression of established fatty streaks in the presence or
absence of daily HBO treatment. The regression period lasted 10
weeks.
HBO Treatment
The HBO treatment was administered in a specialized HBO chamber
for animals. HBO treatment (5 days per week) consisted of a 15-minute
compression period to 2.5 atm (absolute) or a pressure equivalent to
49.5 feet of sea water, followed by 90 minutes of 100% oxygen at 2.5
atm (absolute), followed by a 15-minute decompression period. The total
treatment time was 120 minutes. A similar protocol is used for treating
humans.32
Atherosclerotic Lesion Evaluation
At the end of the experiment, the rabbits were
anesthetized with ketamine and xylazine (35 and 10
mg/kg body wt, respectively), and blood was obtained by cardiac
puncture. The abdomen and chest were opened, and the organs were
perfused with ice-cold saline. The liver was removed, blotted dry,
weighed, frozen in liquid nitrogen, and stored at -70°C until
analysis. The aorta from the ascending arch to the ileal
bifurcation was removed, washed with ice-cold PBS, and dissected free
of adventitia and adipose tissue.
In the progression study, a small segment of arch was transferred to the fixative (4% formaldehyde and 1% glutaraldehyde in PBS, pH 7.4). The fixed segment of aortic arch was embedded in paraffin, cut into thin sections, and stained with hematoxylin and eosin. Six slides from each segment were evaluated by light microscopy by an observer blinded to the study protocol. The remaining aorta was cut into 3 segments (arch, thoracic, and abdominal), weighed, and stored at -70°C until analysis.
In the regression study, the aortas were opened longitudinally, pinned flat on a wax bed immersed in ice-cold PBS, and photographed. The total aortic area and the intimal area covered with atherosclerotic lesion were quantified from enlarged scanned photographs by use of Diversity version 1.0 software (PDI) and a Scanmaster-SM3 scanner (Howtek, Inc).
After photography, the aortas were cut into 3 segments as described above, blotted dry, weighed, and stored at -70°C until analysis.
Biochemical Analyses of Plasma, Liver, and Aorta
Plasma and Plasma Lipoproteins
In both studies, blood was collected by cardiac puncture at the
time of euthanasia and transferred into heparinized tubes and tubes
containing EDTA (1.5 mg/mL). In addition, in the regression study,
small samples of blood (3 mL) were collected in heparinized tubes from
the ear artery before the start of the atherogenic diet and at
intervals thereafter until the end of the study. Blood was collected
after a 12- to 16-hour fast. Plasma was obtained by low-speed
centrifugation at 4°C. Lipoproteins were isolated
within 24 hours of obtaining the plasma. Aliquots of plasma were
adjusted to a density of 1.3 g/mL with the use of KBr and 1 mmol/L
CaCl2. Plasma was then sequentially layered under
NaCl-KBr salt solutions, and the lipoprotein fractions were separated
by density gradient ultracentrifugation, essentially as
previously described.33 Cholesterol content of
plasma and of the lipoprotein fractions was determined by an enzymatic
procedure adapted to the microtiter plate assay.34
Aliquots of plasma containing butylated hydroxytoluene (100 µg/mL)
were kept at -20°C for thiobarbituric acid–reactive substance(s)
(TBARS) assays (see below).
Aorta and Liver
The entire segment of aorta was finely minced with scissors, and
an aliquot was taken to measure lipid oxidation products. The
remaining tissue was homogenized in a phosphate buffer, and
the lipid was extracted from the homogenates as described
by Folch et al.35 The lipid-containing fraction was dried
under nitrogen and then redissolved in ethanol, and after appropriate
dilutions, total and free cholesterol levels were
determined by an enzymatic assay described above. Esterified
cholesterol was calculated as the difference between total
and free cholesterol. The same procedures were used for
pieces of liver obtained from different lobes.
Assessment of Lipid Oxidation
Lipid oxidation in plasma, plasma lipoproteins, liver, and
aortic tissue segments was measured by determining TBARS. TBARS were
determined essentially as described by Buege and Aust,36
by use of the standard curve of malondialdehyde equivalents generated
by acidic hydrolysis of 1,1,3,3-tetraethoxypropane. The extent of lipid
oxidation in the plasma and lipoprotein fractions was also assessed by
the determination of conjugated diene and triene concentrations after
absorption of the isopropanol extract at 233 nm (for conjugated dienes)
and 277 nm (conjugated trienes). Calculations were made with the use of
molar extinction coefficients: 2.8x104 mol
· L-1 · cm-1 and
2.3x104 mol ·
L-1 · cm-1 for
conjugated dienes and trienes, respectively.37
Determination of PON Activity
Paraoxonase (PON) activity in the plasma and lipoprotein
fractions was determined by an adaptation of the spectrophotometric
method of Furlong et al38 to the microtiter plate assay
method. Aliquots (10 µL) of diluted plasma (1:10) or the lipoprotein
fraction (0- to 5-fold) were placed in microtiter plate wells in
triplicate, and the reaction was initiated by adding 190 µL of the
substrate (1.2 mmol/L paraoxon in 0.26 mmol/L Tris-HCl, pH
8.5, and 25 mmol/L CaCl2). After a mixing,
the plate was read immediately at 405 nm to establish 0 time values.
Readings were repeated at 2-minute intervals for 10 minutes.
Nonenzymatic hydrolysis of paraoxon was subtracted from the total rate
of hydrolysis. The enzyme activity was calculated from the linear
portion of the plot (A405/time) by use of the
molar extinction coefficient for p-nitrophenol: 17 100
mol · L-1 ·
cm-1. One unit of PON activity equals 1
µmol of p-nitrophenol released per liter per minute.
Statistical Methods
Values reported in the text and in the Table
represent mean±SEM. One-way ANOVA followed by Bonferroni/Dunn
tests was performed to see whether any significant differences occurred
among groups. A value of P
0.05 was accepted as
statistically significant. All analyses were performed with the
use of StatView 4.5 statistical software (Abacus Concepts).
|
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Progression Studies
Atherosclerosis was induced in a group of rabbits by a 10-week regimen of cholesterol-supplemented rabbit chow (1% cholesterol). Half of these animals were exposed daily (5 times per week) to HBO; a third group of animals on a normal rabbit chow served as a control. At the end of the progression study, the body weights of cholesterol-fed HBO-treated rabbits (3.3±0.07 kg) were similar to the body weights of rabbits fed regular chow (3.2±0.11 kg) and significantly (P<0.05) higher than the body weights of cholesterol-fed untreated rabbits (2.8±0.07 kg). The liver weights were markedly increased in cholesterol-fed rabbits; HBO treatment had no additional effect.
As expected, the cholesterol-rich diet induced severe
hypercholesterolemia during the 10-week study;
plasma cholesterol levels increased >20-fold in the
cholesterol-fed rabbits (Figure 1A). The majority of the increase
(>67%) was accounted for by the VLDL+IDL fraction, whereas >30% of
the increase was in the LDL fraction. The levels of HDL
cholesterol decreased in both cholesterol-fed
groups, but the decrease was not statistically significant in the
HBO-treated group (data not shown). Overall, HBO treatment had little
or no effect on plasma cholesterol concentrations (Figure 1A) or distribution (not shown), with the exception of HDL
cholesterol noted above. The total liver
cholesterol content was >10-fold higher in
cholesterol-fed animals, and HBO treatment resulted in an
additional, although not significant, increase in hepatic
cholesterol content (Figure 1B). In contrast,
compared with cholesterol-fed animals not treated with HBO,
HBO-treated animals exhibited a profound and significant
(P<0.05) reduction in the accumulation of
cholesterol in the 3 aortic segments examined (Figure 1C through 1E). The aortic arch cholesterol content
increased >9-fold as a result of cholesterol feeding but
only 3-fold when accompanied by daily HBO treatment. Overall, HBO
treatment reduced the diet-induced accumulation of
cholesterol in the examined segments of aorta by
>50%.
|
We also examined the levels of TBARS, a measure of overall lipid
oxidation, in plasma and various tissues. HBO treatment resulted in a
marked reduction in TBARS formation in all compartments examined
compared with no treatment. As shown in Figure 1F
, plasma TBARS
were elevated 11-fold in the untreated cholesterol-fed
rabbits but only 3-fold in cholesterol-fed HBO-treated
rabbits. Significantly, HBO treatment prevented the increase in liver
TBARS seen in rabbits receiving the cholesterol-rich diet
(Figure 1G). HBO treatment was also very effective in preventing
the diet-related increases in aortic tissue TBARS (Figure 1H
through 1J). Pooled data from the 2 progression studies on the plasma
concentration of conjugated dienes, trienes, and PON activities are
presented in the Table.
Cholesterol feeding induced a 3-fold increase in
plasma-conjugated diene and triene concentrations, and HBO treatment
inhibited these increases by >60%. Similarly, plasma TBARS
concentrations increased 11-fold in the cholesterol-fed
rabbits, but HBO treatment inhibited this increase by >70%.
Concomitant with increases in plasma TBARS and conjugated diene and
triene concentrations, plasma PON activity in
cholesterol-fed rabbits decreased by >40%. In contrast,
PON activity in HBO-treated rabbits remained unchanged.
The concentrations of dienes, trienes, TBARS, and PON activities in
specific lipoprotein fractions were assessed in study 2, and the
results are shown in the Table. Although in the majority of
cases a convincing trend is observed, the smaller number of animals in
the second study precluded many of the reported differences to reach
statistical significance at P<0.05. Treatment with HBO
inhibited the diet-induced increases in LDL- and HDL-conjugated dienes
and trienes. It was also very effective in decreasing the extent of
TBARS accumulation in these lipoprotein fractions. HBO treatment had
little or no effect on the levels of lipid oxidation products in
the VLDL+IDL fraction of plasma lipoproteins.
The cholesterol-rich diet reduced total plasma PON activities by >40%. Because the great majority of plasma PON is associated with the HDL fraction, it is not surprising that this reduction came at the expense of HDLs. The large decrease in the HDL-associated PON was accompanied by small increases in PON activities in the LDL and VLDL+IDL fractions. Overall, HBO treatment completely prevented the diet-induced reduction of HDL-associated PON activity.
In agreement with the significantly lower arterial tissue
cholesterol, histomorphological examination of fixed aortic
arches from HBO-treated rabbits revealed little if any fatty streak
formation, the initial stage of atherogenesis. Figure 2 shows typical
representative sections of aortic arches from the 3
groups of rabbits. In the absence of HBO treatment,
cholesterol feeding led to a massive accumulation of
macrophage-foam cells in the subendothelial
layer (Figure 2c), typical of extensive fatty streaks and
suggestive of progressive atherogenesis. Only occasional and small
groups of macrophage-foam cells were observed in the aortic
arches of HBO-treated rabbits (Figure 2b).
|
Regression Studies
To examine the effect of HBO treatment on existing lesions, 18
rabbits were fed a cholesterol-rich diet for 10 weeks.
Plasma cholesterol concentrations rose rapidly during the
10-week induction period, nearly to the levels seen in the
cholesterol-fed rabbits in the progression study, despite a
lower content of cholesterol (0.5% versus 1%
cholesterol). At this point, 6 control animals were
euthanized to provide reference values for the various variables
examined. The remaining animals were switched to normal rabbit chow for
an additional 10-week period; half of these animals were exposed daily
to HBO. Plasma cholesterol concentrations fell rapidly and
in a nearly identical manner in both groups of rabbits during this
period (Figure 1K). Liver cholesterol content
(Figure 1L) also fell rapidly in both groups of rabbits, but HBO
treatment resulted in a significantly greater decrease than that
produced by rabbit chow alone. Rabbit chow alone was ineffective in
significantly lowering thoracic or abdominal aortic
cholesterol content but was effective in significantly
lowering aortic arch cholesterol content. In contrast, the
combination of rabbit chow and HBO treatment effectively and
significantly lowered the cholesterol content in all 3
sections of the aorta (Figure 1M through 1O).
To examine the extent of regression of the fatty streak lesions in all
3 sections of the aorta, whole fresh aortas were opened and pinned flat
on a wax bed and photographed. The photographs were scanned, and the
raised areas (lesions) were evaluated by computer-aided planimetry. The
results are shown in Figure 3. Rabbit
chow alone resulted in a 30% reduction in raised opaque areas. The
combination of rabbit chow and HBO treatment resulted in 60% reduction
in fatty streak lesions. These observations correlate well with the
direct measures of aortic cholesterol content.
|
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
It is now well established that a major force in the peripheral accumulation of cholesterol is the oxidation of cholesterol-rich lipoproteins, such as LDL. Thus, modified LDL is subject to nonregulated uptake by macrophages within the vessel wall, leading to the formation of macrophage-foam cells,1 2 3 which are building blocks in fatty streak formation and the initiation of atherogenesis.
The present studies examine the effect of HBO on the development of aortic fatty streaks in cholesterol-fed rabbits as well as on the regression of preestablished lesions. We found that HBO treatment protects against the development of fatty streaks in cholesterol-fed rabbits. Accumulation of cholesterol, especially cholesteryl esters, in macrophage-foam cells is the hallmark of the atherosclerotic lesion. A cholesterol-rich diet markedly increased free and cholesteryl ester levels in all 3 segments of the aorta examined. This accumulation was dramatically reduced in the rabbits treated with HBO. The lipid data are supported by histomorphological examination of the sections taken from similar areas of the aortic arch segments. Of the 5 HBO-treated rabbits examined, 3 rabbits showed a complete absence of lesions, whereas the other 2 rabbits had far less pronounced lesion thickness and frequency compared with the cholesterol-fed untreated rabbits, all of whom showed marked lesion formation. The scarcity and mildness of lesions in the treated group suggest that HBO treatment arrests the development of fatty streaks in cholesterol-fed rabbits.
The differences in lesion formation seen in HBO-treated animals, compared with untreated animals, were not due to differences in plasma total or individual lipoprotein (VLDL, IDL, LDL, and HDL) cholesterol levels. These values were not significantly different in the 2 cholesterol-fed groups of animals. A major difference between the 2 cholesterol-fed groups of rabbits was the content of oxidized products in the LDL and HDL fractions. Compared with LDL and HDL from HBO-treated cholesterol-fed rabbits, LDL and HDL isolated from untreated cholesterol-fed rabbits were both enriched severalfold in conjugated dienes, trienes, and TBARS. The abundance of mildly oxidized LDL in untreated but not HBO-treated animals may explain the accelerated fatty streak formation in these animals. The increased content of oxidized products in the HDL fraction of the untreated rabbits may further decrease the protection normally afforded by HDL and the potentially antioxidant enzymes it may carry. These modifications are consistent with increased potential for the development of fatty streaks and atherosclerosis.
The reduction in the concentration of oxidation products in the tissue and plasma of HBO-treated rabbits is not surprising and is in agreement with previous reports.39 40 41 Furthermore, beneficial effects of hyperoxia (increased oxygen concentrations at normal pressure) on the progression42 and regression43 44 of atherosclerosis have been noted in the past. The previously reported changes have been modest relative to the results observed in control animals and compared with the results reported in the present study with the use of HBO.
The reduced oxidation of tissue and plasma lipids may well be a result of induced antioxidant activity. PON may play a role in this protection. Recent studies suggest that serum PON is an antioxidant enzyme involved in the detoxification of lipid peroxides.45 46 The profound decrease in HDL-associated (and total) PON activity in the untreated cholesterol-fed rabbits correlates well with the increased formation of oxidation products. Similar findings have been reported in atherosclerosis-susceptible (C57BL/6J) mice but not in atherosclerosis-resistant (C3H/HeJ) mice.47 It remains to be seen whether the observed decrease in plasma PON activities of the untreated cholesterol-fed rabbits is the result of decreased enzyme mass (reduced expression) or inhibition by the high concentration of lipid peroxides.45 48 The maintenance of normal plasma PON activity in HBO-treated rabbits may be a result of a counteracting mechanism inducing the expression of additional PON or be secondary to the reduced levels of lipid peroxides. Our data do not exclude the possibility that other enzymes, induced by the intermittent exposure to HBO, may also play an important role in "detoxifying" tissue or circulating lipoprotein-associated lipids.
Indeed, brief exposure to HBO/hyperoxia has been shown to increase the levels of glutathione in blood and to induce the expression of a number of antioxidant enzymes in tissues.31 49 These include heme oxygenase,49 50 which recently has been shown to offer protection from the development of atherosclerosis and to reduce oxidation products in HDL.51 52 Alternatively, the protective effect of HBO treatment may be mediated by the suppression of specific enzymes responsible for lipid oxidation. Our future studies will specifically address the regulation of expression, by exposure to HBO, of a number of candidate enzymes.
Although the finding that HBO inhibits the formation of fatty streaks has important implications for the prevention of atherosclerosis, the use of this treatment to accelerate regression could have profound implications for therapy of established disease. Our results demonstrate that HBO treatment markedly accelerates the regression process by a mechanism independent of plasma cholesterol concentrations.
These data suggest that HBO suppresses the recruitment and proliferation of macrophages and the formation of foam cells in atherosclerotic lesions, thereby inhibiting the initial development of atherosclerosis. This is brought about by increased protection against the formation of lipid-derived oxidation products. These observations further support the importance of oxidative processes in promoting atherogenesis. Elucidation of the details of this mechanism will provide new insights into the pathophysiology of atherosclerosis.
|
Acknowledgments |
|---|
This work was supported in part by a grant from Bank One and by National Institutes of Health grant R01 HL-45513 to L.D.
Received November 10, 1999; accepted February 28, 2000.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Steinberg D. Oxidative modification of LDL and atherogenesis. Circulation. 1997;95:1062–1071.
2.
Fogelman AM, Shechter I, Seager J, Hokom M, Child JS,
Edwards PA. Malondialdehyde alteration of low density lipoproteins
leads to cholesteryl ester accumulation in human
monocyte-macrophages. Proc Natl Acad Sci U S A. 1980;77:2214–2218.
3. Berliner JA, Heinecke JW. The role of oxidized lipoproteins in atherogenesis. Free Radic Biol Med. 1996;20:707–727.[Medline] [Order article via Infotrieve]
4. Yla-Herttuala S, Palinski W, Rosenfeld ME, Parthasarathy S, Carew TE, Butler S, Witztum JL, Steinberg D. Evidence for the presence of oxidatively modified low density lipoprotein in atherosclerotic lesion of rabbit and man. J Clin Invest. 1989;84:1086–1095.
5. Hazell LJ, Arnold L, Flowers D, Waeg G, Malle E, Stocker R. Presence of hypochlorite-modified proteins in human atherosclerotic lesions. J Clin Invest. 1996;97:1535–1544.[Medline] [Order article via Infotrieve]
6. Berliner JA, Territo MC, Sevanian A, Ramin S, Kim JA, Bamshad B, Esterson M, Fogelman AM. Formally modified low density lipoprotein stimulates monocyte endothelial interactions. J Clin Invest. 1990;85:1260–1266.
7.
Jovinge SP, Mikko S, Kallin B, Nilsson J. Human
monocyte/macrophages release TNF-
in response to
oxLDL. Arterioscler Thromb Vasc Biol. 1996;16:1573–1579.
8. Rosenfeld ME, Yla-Herttuala S, Lipton BA, Ord VA, Witztum JL, Steinberg D. Macrophage colony-stimulating factor mRNA and protein in atherosclerotic lesions of rabbits and humans. Am J Pathol. 1992;140:304–316.
9. Navab M, Imes SS, Hama SY, Hough GP, Ross LA, Bork RA, Valente AJ, Berliner JA, Drinkwater DC, Laks H, et al. Monocyte transmigration induced by modification of low density lipoproteins in co-cultures of human aortic wall cells is due to induction of monocyte chemotactic protein 1 synthesis, and is abolished by high density lipoprotein. J Clin Invest. 1991;88:2039–2046.
10.
Quinn MT, Parthasarathy S, Fong LG, Steinberg D.
Oxidatively modified low density lipoproteins: a potential role in
recruitment and retention of monocyte/macrophages during
atherogenesis. Proc Natl Acad Sci U S A. 1987;84:2995–2998.
11. Bjorkerud S, Bjorkerud B. Apoptosis is abundant in human atherosclerotic lesions, especially in inflammatory cells (macrophages and T cells), and may contribute to the accumulation of gruel and plaque instability. Am J Pathol. 1996;149:367–380.[Abstract]
12. Nishio E, Arimura S, Watanabe Y. Oxidized LDL induces apoptosis in cultured smooth muscle cells: a possible role for 7-ketocholesterol. Biochem Biophys Res Commun. 1996;223:413–418.[Medline] [Order article via Infotrieve]
13.
Kinscherf R, Claus R, Wagner M, Gehrke C, Kamencic H,
Hou D, Nauen O, Schmiedt W, Kovacs G, Pill J, et al. Apoptosis
caused by oxidized LDL is manganese superoxide dismutase and p53
dependent. FASEB J. 1998;12:461–467.
14.
Bjorkhem I, Henrikson-Freyschuss A, Breuer O,
Diczfalusy U, Berglund L, Henriksson P. The antioxidant butylated
hydroxytoluene protects against atherosclerosis.
Arterioscler Thromb. 1991;11:15–22.
15. Shaish A, Daugherty A, O’Sullivan F, Schonfeld G, Heinecke JW. Beta-carotene inhibits atherosclerosis in hypercholesterolemic rabbits. J Clin Invest. 1995;96:2075–2082.
16. Pratico D, Tangirala RK, Rader DJ, Rokach J, Fitzgerald GA. Vitamin E suppresses isoprostane generation in vivo and reduces atherosclerosis in apoE-deficient mice. Nat Med. 1998;4:1189–1192.[Medline] [Order article via Infotrieve]
17. Watson AD, Berliner JA, Hama SY, LaDu BN, Faull KF, Fogelman AM, Navab M. Protective effect of high-density lipoprotein associated PON: inhibition of biological activity of minimally oxidized low density lipoprotein. J Clin Invest. 1995;96:2882–2891.
18.
Panzenboeck U, Raitmayer S, Reicher H, Lindner H,
Glatter O, Malle E, Sattler W. Effects of reagent and enzymatically
generated hypochlorite on physicochemical and metabolic
properties of high density lipoproteins. J Biol Chem. 1997;272:29711–29720.
19. Tall A. Plasma high density lipoproteins: metabolism and relationship to atherogenesis. J Clin Invest. 1990;86:379–384.
20. Heinecke JW, Li W, Francis GA, Goldstein JA. Tyrosyl radical generated by myeloperoxidase catalyzes the oxidative crosslinking of proteins. J Clin Invest. 1993;91:2866–2872.
21.
Savenkova MI, Mueller DM, Heinecke JW. Tyrosyl radical
generated by myeloperoxidase is a physiological
catalyst for initiation of lipid peroxidation in low density
lipoprotein. J Biol Chem. 1994;269:20394–20400.
22. Daugherty A, Rateri DL, Dunn JL, Heinecke JW. Myeloperoxidase, a catalyst for lipoprotein oxidation, is expressed in human atherosclerotic lesions. J Clin Invest. 1994;94:437–444.
23. Thom SR. Antagonism of carbon monoxide-mediated brain lipid peroxidation by hyperbaric oxygen. Toxicol Appl Pharmacol. 1990;105:340–344.[Medline] [Order article via Infotrieve]
24. Hammarlund C, Sunderberg T. Hyperbaric oxygen reduced size of chronic leg ulcers: a randomized double-blind study. Plast Reconstr Surg. 1994;93:829–833.[Medline] [Order article via Infotrieve]
25. Uhl E, Sirsjo A, Haapaniemi T, Nilsson G, Nylander G. Hyperbaric oxygen improves wound healing in normal and ischemic skin tissue. Plast Reconstr Surg. 1994;93:835–841.[Medline] [Order article via Infotrieve]
26. Garcia MJ, McNamara PM, Gordon T, Kannel WB. Morbidity and mortality in diabetics in the Framingham population: sixteen year follow-up study. Diabetes. 1974;23:105–111.[Medline] [Order article via Infotrieve]
27.
Santen RJ, Willis PW, Fajans SS.
Atherosclerosis in diabetes mellitus: correlations with
serum lipid levels, adiposity and serum insulin levels. Arch
Intern Med. 1972;130:833–843.
28.
Harrison JE, Schultz J. Studies on the chlorinating
activity of myeloperoxidase. J Biol Chem. 1976;251:1371–1374.
29. Heinecke JW. Mechanisms of oxidative damage of low density lipoprotein in human atherosclerosis. Curr Opin Lipidol. 1997;8:268–274.[Medline] [Order article via Infotrieve]
30.
Haugaard N. Cellular mechanisms of oxygen toxicity.
Physiol Rev. 1968;48:311–373.
31.
Harabin AL, Braisted JC, Flynn ET. Response of
antioxidant enzymes to intermittent and continuous hyperbaric oxygen.
J Appl Physiol. 1990;69:328–335.
32. Jain KK. Textbook of Hyperbaric Medicine. Toronto, Canada: Hogrese and Huber Publishers; 1990.
33. Terpstra AHM, Woodward CJ, Sanchez-Muniz F. Improved techniques for the separation of serum lipoproteins by density gradient ultracentrifugation: visualization by prestaining and rapid separation of serum lipoproteins from small volumes of serum. Anal Biochem. 1981;111:149–157.[Medline] [Order article via Infotrieve]
34. Shireman RB, Durieux J. Microplate methods for determination of serum cholesterol, high density lipoprotein cholesterol, triglycerides and apoproteins. Lipids. 1993;28:151–155.[Medline] [Order article via Infotrieve]
35.
Folch J, Lees M, Sloane Stanley GH. A simple method for
the isolation and purification of total lipids from animal tissues.
J Biol Chem. 1956;226:497–509.
36. Buege JA, Aust SD. Microsomal lipid peroxidation. Methods Enzymol. 1978;52:302–310.[Medline] [Order article via Infotrieve]
37. Recknagel RO, Glende EA Jr. Spectrophotometric detection of lipid conjugated dienes. Methods Enzymol. 1984;105:331–337.[Medline] [Order article via Infotrieve]
38. Furlong CE, Richter RJ, Seidel SL, Costa LG, Motulsky AG. Spectrophotometric assay for the enzymatic hydrolysis of active metabolites of chlorpyrifos and parathion by plasma paraoxonase/arylesterase. Anal Biochem. 1989;180:242–247.[Medline] [Order article via Infotrieve]
39. Mengel CE, Kann HE Jr. Effects of in vivo hyperoxia on erythrocytes, III: in vivo peroxidation of erythrocyte lipid. J Clin Invest. 1966;45:1150–1156.
40. Raskin P, Lipman RL, Oloff CM. Effect of hyperbaric oxygen on lipid peroxidation in the lung. Aerosp Med. 1971;42:28–30.[Medline] [Order article via Infotrieve]
41.
Frank L, Bucher R, Roberts RJ. Oxygen toxicity in
neonatal and adult animals of various species. J Appl
Physiol. 1978;45:699–704.
42. Okamoto R, Hatani M, Tsukitani M, Suehiro A, Fujino M, Imai N, Takano S, Watanabe Y, Fukuzaki H. The effect of oxygen on the development of atherosclerosis in WHHL rabbits. Atherosclerosis. 1983;47:47–53.[Medline] [Order article via Infotrieve]
43. Kjeldsen K, Astrup P, Wanstrup J. Reversal of rabbit atheromatosis by hyperoxia. J Atheroscler Res. 1969;10:173–178.[Medline] [Order article via Infotrieve]
44. Vesselinovitch D, Wissler RW, Fisher-Dzoga K, Hughes R, Dubien L. Regression of atherosclerosis in rabbits, 1: treatment with low fat diet, hyperoxia and hypolipidemic agents. Atherosclerosis. 1974;19:259–275.[Medline] [Order article via Infotrieve]
45. Mackness MI, Mackness B, Durrington PN, Connelly PW, Hegele RA. Paraoxonase: biochemistry, genetics and relationship to plasma lipoproteins. Curr Opin Lipidol. 1996;7:69–76.[Medline] [Order article via Infotrieve]
46. Aviram M, Rosenblat M, Bisgaier CL, Newton RS, Primo-Parma SL, LaDu B. Paraoxonase inhibits high-density lipoprotein oxidation and preserves its function: a possible peroxidative role for paraoxonase. J Clin Invest.. 1998;101:1581–1590.[Medline] [Order article via Infotrieve]
47. Shih DM, Gu L, Hama S, Xia Y-R, Navab M, Fogelman AM, Lusis AJ. Genetic-dietary regulation of serum paraoxonase expression and its role in atherogenesis in a mouse model. J Clin Invest. 1996;97:1630–1639.[Medline] [Order article via Infotrieve]
48. Nishio E, Watanabe Y. Cigarette smoke extract inhibits plasma paraoxonase activity by modification of enzyme’s free thiols. Biochem Biophys Res Commun. 1997;236:289–293.[Medline] [Order article via Infotrieve]
49. Dennery PA, Spitz DR, Yang G, Tatarov A, Lees CS, Shegog ML, Poss KD. Oxygen toxicity and iron accumulation in the lungs of mice lacking heme oxygenase-2. J Clin Invest. 1998;101:1001–1011.[Medline] [Order article via Infotrieve]
50. Padgaonkar VA, Giblin FJ, Fowler K, Leverenz VR, Reddan JR, Dziedzic DC. Heme oxygenase synthesis is induced in cultured lens epithelium by hyperbaric oxygen or puromycin. Exp Eye Res. 1997;65:435–443.[Medline] [Order article via Infotrieve]
51. Ishikawa K, Navab M, Leitinger N, Fogelman AM, Lusis AJ. Induction of heme oxygenase-1 inhibits the monocyte transmigration induced by mildly oxidized LDL. J Clin Invest. 1997;100:1209–1216.[Medline] [Order article via Infotrieve]
52. Ishikawa K, Poss KD, Navab M, Fogelman AM, Tonegawa S, Lusis AJ. Vasculitis, atherosclerosis and altered high density lipoproteins in heme oxygenase-1 knockout mice. Circulation. 1999;98(suppl I):I-309. Abstract.
This article has been cited by other articles:
 |
|
 |
|
  S. Saito, K. Nishikawa, H. Obata, and F. Goto Autologous Bone Marrow Transplantation and Hyperbaric Oxygen Therapy for Patients With Thromboangiitis Obliterans Angiology, September 1, 2007; 58(4): 429 - 434. [Abstract] [PDF]
|
|
|
|
 |
|
 A. Pierce, J. Whitlark, and L. Dory Extracellular Superoxide Dismutase Polymorphism in Mice Arterioscler Thromb Vasc Biol, October 1, 2003; 23(10): 1820 - 1825. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||