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(Circulation. 1999;99:2003-2010.)
© 1999 American Heart Association, Inc.
Clinical Investigation and Reports |
Intracranial Arteries of Human Fetuses Are More Resistant to Hypercholesterolemia-Induced Fatty Streak Formation Than Extracranial Arteries
From the Department of Clinical and Experimental Medicine (C.N.), the Department of Human Pathology (F.d.N., F.P.D.), and the Department of Molecular and Cellular Biology (G.P.), Federico II University of Naples (Italy), and the Department of Medicine (C.N., J.L.W., W.P.), University of California, San Diego, La Jolla.
Correspondence to Wulf Palinski, MD, or Claudio Napoli, MD, Department of Medicine, 0682, University of California, San Diego, 9500 Gilman Dr, MTF 110, La Jolla, CA 92093. E-mail palinski{at}ucsd.edu/cnapoli@ucsd.edu
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Abstract |
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Background—Atherosclerotic lesions in intracranial arteries occur later and are less extensive than in extracranial arteries. To investigate potential mechanisms responsible for this difference, in particular the atherogenic response to hypercholesterolemia and LDL oxidation, we compared the extent of fatty streak formation and the composition of these very early lesions in intracranial arteries of human fetuses from normocholesterolemic and hypercholesterolemic mothers with those in extracranial arteries.
Methods and Results—Lesions were quantified by computer-assisted image analysis of 30 oil red O–stained sections, each from the middle cerebral, basilar, and common carotid arteries and the abdominal aorta of human fetuses (spontaneous abortions and premature newborns who died within 12 hours of birth; both of fetal age 6.2±1.3 months) from 43 hypercholesterolemic mothers and 34 normocholesterolemic mothers. Macrophages, apolipoprotein B, and 2 epitopes of oxidized LDL in lesions were determined immunocytochemically. Activities of superoxide dismutase, catalase, and glutathione peroxidase in the arterial wall were also determined. Lesion numbers and sizes were dramatically greater in the abdominal aorta (area of the largest lesion per section: 66.5±10.9 x103 µm2) and the carotid (11.6±5.3 x103 µm2) than in the basilar and middle cerebral artery (0.4±0.1 and 0.8±0.2 x103 µm2, respectively; P<0.0001). Hypercholesterolemia resulted in a significant increase of lesion size in extracranial arteries but only a marginal increase in intracranial arteries. In analogy, hypercholesterolemia induced a much greater increase in the intimal presence of macrophages, apolipoprotein B, and oxidized LDL (oxidation-specific epitopes) in extracranial than in intracranial arteries. Immunocytochemistry did not indicate that lesions of intracranial arteries contain relatively less oxidized LDL than similar-size lesions of extracranial arteries. Activities of Mn–superoxide dismutase but not of Zn–superoxide dismutase, catalase, or glutathione peroxidase were significantly higher in both intracranial arteries.
Conclusions—Exposure to hypercholesterolemia during fetal development results in extensive formation of fatty streaks in extracranial but not intracranial arteries. The fact that such a difference in lesion formation occurs in the absence of many other atherogenic risk factors found later in life suggests that differences in the atherogenic response to hypercholesterolemia are an important contributor to the slower onset of the disease in intracranial vessels in adults. Fetal arteries may allow elucidation of the mechanisms responsible, for example, better protection of intracranial arteries against free radical–mediated atherogenic processes.
Key Words: atherosclerosis • hypercholesterolemia • lipoproteins • brain • stroke • free radicals
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Introduction |
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The pathogenetic importance of hypercholesterolemia in atherogenesis and coronary heart disease has been well established by epidemiological studies and by the drastic reduction in cardiovascular morbidity and mortality achieved by cholesterol-lowering drugs.1 2 3 4 5 6 7 However, the role of hypercholesterolemia in atherosclerotic cerebrovascular disease is still debated.8 Although intracranial arteries eventually develop advanced atherosclerotic lesions, the onset of atherogenesis in intracranial arteries occurs much later in life and the severity of lesions is generally less pronounced than that in extracranial arteries, both in humans8 9 10 and nonhuman primates.11 Furthermore, recent clinical trials using intensive hypolipidemic therapy have been far less effective in reducing mortality from stroke than from coronary heart disease.2 3 6 12 13 14 In some of these trials, cholesterol lowering significantly decreased the incidence of nonfatal stroke,2 5 12 13 but it is not clear whether the reduction of nonfatal cerebrovascular events resulted primarily from a direct effect of lower LDL levels on lesion formation in intracranial arteries. The reduction of nonfatal strokes and transitory ischemic attacks could also be an indirect consequence of the reduction of atherosclerosis in the carotid arteries or could be due to direct effects of HMG-CoA reductase inhibitors (statins) on the arterial wall. To date, we do not know whether intracranial arteries respond differently to hypercholesterolemia than extracranial arteries, possibly as a result of anatomic peculiarities of brain arteries, or whether atherogenesis in intracranial arteries is governed by different atherogenic mechanisms altogether.
Investigations of the mechanism(s) responsible for the delayed onset and slower progression of cerebral atherosclerosis in humans are rendered more difficult by the complex interactions of proatherogenic factors in advanced lesions and by the impact of exogenous risk factors such as smoking, diabetes, diet, and hypertension in the adult population. A recent systematic assessment of fatty streak formation in human fetuses suggested that arteries of premature fetuses may provide a model to study mechanisms involved in lesion initiation, in particular the role of hypercholesterolemia, in the absence of many confounding factors occurring in adults.15 In that study, we showed that lesion formation in the aorta occurs much earlier than previously assumed and that lesion formation was greatly enhanced in fetuses from hypercholesterolemic mothers. Fatty streaks were most extensive in the abdominal aorta, where more advanced lesions are typically seen in youths and adults16 and contained characteristic elements of early lesions, such as intimal accumulations of LDL and monocyte/macrophages. Finally, immunocytochemical evidence indicated that oxidation of LDL was an important pathogenic factor in lesion formation in the fetal aorta (for review of the role of LDL oxidation in atherogenesis, see References 1717 to 19).
In the present study, we used human fetal arteries to investigate potential mechanisms responsible for the delayed atherogenesis in intracranial arteries. More specifically, we compared the extent of fatty streak formation and the composition of lesions in 2 fetal intracranial arteries to those in 2 extracranial arteries and determined the effect of hypercholesterolemia in these arteries. We also determined the total tissue activity of antioxidant enzymes in these arteries to establish whether differences in the capability to trap free radicals and/or the susceptibility to oxygen radical–mediated processes could contribute to differences in lesion formation.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Human Subjects
Arteries were obtained from spontaneously aborted fetuses (n=48) and premature newborns who died within 12 hours of birth (n=29) and were routinely subjected to autopsy at the Department of Human Pathology of the Federico II University of Naples. Because there was no difference in age between the spontaneously aborted fetuses and the premature newborns, all of these will be termed "fetuses." Mothers had presented with acute signs of imminent birth/abortion or with birth in progress. Causes of spontaneous abortion and premature death included trauma, eclampsia, and fetal genetic defects.
Fetuses were classified depending on maternal rather than fetal cholesterol levels. This was based on the results of our previous study, which demonstrated that fetal aortas from hypercholesterolemic mothers contained significantly more and larger fatty streaks than those from normocholesterolemic mothers.15 During early fetal development (up to the 6th month) fetal cholesterol levels (measured in venous blood before death) correlated very well with maternal ones. However, fetal cholesterol levels also showed a highly significant inverse correlation with fetal age, and no correlation between fetal and maternal cholesterol levels were found in older fetuses. Therefore the fetal cholesterol level of older fetuses may not accurately reflect their previous exposure to atherogenic levels of cholesterol and lesion formation. Furthermore, it is not clear what constitutes hypercholesterolemia in the fetus because the developing fetus undoubtedly has higher cholesterol requirements. For these reasons, an assessment of the atherogenic effect of hypercholesterolemia based on the fetal cholesterol level measured at a single time point (age) would not be meaningful.
Maternal lipoprotein and triglyceride levels were
determined at admission to the hospital. Total, VLDL, and HDL
cholesterol levels were measured with the use of an
automated enzymatic procedure and kits from Boehringer Mannheim
Italia. VLDL fractions were separated by
ultracentrifugation.20 HDL was determined
in the supernatant after sodium/phosphotungstate/magnesium chloride
precipitation. LDL cholesterol levels were calculated from
Friedewald's modified formula (LDL cholesterol=total
cholesterol minus VLDL and HDL
cholesterol).21 Mothers with total
cholesterol levels >180 to 200 mg/dL (depending on age)
were classified as hypercholesterolemic. Fetal
cholesterol levels in venous blood were routinely measured
before death. In addition, in a subset of cases,
cholesterol levels were also determined in a blood sample
obtained from cerebral arteries at autopsy. Data on maternal and fetal
age, plasma lipid levels, and other clinical parameters are
summarized in Tables 1
and 2.
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The protocol of these studies was approved by the Human Ethics Committee of Federico II University, Naples.
Preparation of Aortic Sections
Fetal arteries were obtained within 3.5 hours after death. Under
a stereo microscope, 8- to 12-mm-long segments of the proximal
abdominal aorta and the common carotid, basilar, and middle cerebral
arteries were dissected, washed thoroughly with cold sterile PBS
containing 2 mmol/L EDTA, and placed in ice-cold PBS containing
50 µmol/L butylated hydroxytoluene, 0.001% aprotinin, 50
µmol/L EDTA, and 0.008% chloramphenicol, equilibrated with nitrogen.
Each arterial segment was then divided into 2 parts. One of
these was immersed in OTC medium, flash-frozen in liquid nitrogen, and
7-µm-thick sections were prepared with a cryotome for morphometric
determination of lipid-rich lesions. The second part of each
arterial segment was fixed in buffered 10% formalin,
paraffin embedded, and 12 to 15 serial sections (5 to 7 µm
thick) were prepared for immunocytochemistry.
Morphometric Assessment of Lesions
Thirty cryosections from each artery were stained with oil
red O and counterstained with hematoxylin. The following
parameters were determined by computer-assisted image
analysis15 : (1) the intimal/medial ratio and the
outer circumference of the artery (for a subgroup of sections only);
(2) the presence of oil red O–positive intimal lipid accumulations and
number of lipid accumulations per section; (3) the cumulative area of
all lipid accumulations per section: The measurement of the areas of
lipid accumulation was given preference over that of the entire
intimal area because it avoids the error associated with determining
the boundary between intima and media in early lesions. To permit a
direct comparison of lesion formation between arteries of different
size, data were then corrected by dividing the cumulative lesion area
by the average cross-sectional surface area
(area=
xr2, with r=outer
radius) of each artery; (4) the surface area of the single largest
lesion encountered in each section: This was to provide a measure of
early atherogenesis with a more traditional definition of lesions (ie,
areas with increased intimal/medial ratio containing both lipid
accumulations and macrophage/foam cells).
Immunocytochemistry
Immunocytochemistry was performed as previously
described.15 In brief, duplicate serial sections of the
fixed and paraffin-embedded arterial segments were stained
with the following antibodies: (1) MDA2 and NA59, 2 murine
monoclonal antibodies against malondialdehyde (MDA)-lysine and
4-hydroxynonenal (4-HNE)-lysine epitopes, respectively22 :
These oxidation-specific epitopes occur on oxidized LDL and other
adducts between lipid peroxidation products and
proteins22 ; (2) NP1533975, a mouse monoclonal antibody
(IgG1) to human apolipoprotein B
(Boehringer Mannheim Italia); and (3) HAM-56, a monoclonal
antibody against human monocyte/macrophages23
(Axcel Accurate, Westbury, NY). All antibodies were used at a dilution
of 1:500. Epitopes recognized by the primary antibody were detected by
an avidin-biotin-peroxidase method.15
Determination of Enzymes in Arterial Wall
An additional set of arteries was homogenized in
potassium phosphate buffer, pH 7.4, containing 10 µmol/L
deferoxamine, 0.03% BHT, and 2% ethanol, equilibrated
with nitrogen (to reduce autoxidation), and centrifuged at
1000g for 15 minutes at 4°C to remove nuclei and tissue
debris. The supernatant was centrifuged again at
30000g for 35 minutes at 4°C. The pellet was separated
from the supernatant and both fractions stored at -70°C until the
assay was performed. Glutathione peroxidase activity was assayed by the
method of Lawrence and Burk24 from the rate of
oxidation of NADPH at 22°C in the presence of 1 mmol/L EDTA,
1 mmol/L NaN3, 0.2 nmol/L NADPH, 1 mmol/L GSH in 50
mmol/L potassium phosphate buffer, pH 7.0. The reaction mixture
contained 0.8 U glutathione reductase, and the reaction was started by
adding 2.5 nmol of H2O2.
Enzyme content of the arterial samples was then calculated
from the extinction coefficient of NADPH. Catalase activity was
determined by the method of Aebi25 that measures the
reduction of hydrogen peroxide by catalase. The rate of decrease of
absorbance at 240 nm on addition of a known amount of
arterial homogenate was followed in a
temperature-controlled spectrophotometer at 25°C. Extinction
coefficient for hydrogen peroxide was 
=43.6
mol-1 · cm-1.
Absolute enzyme activities were calculated from a standard curve
generated with purified catalase. Superoxide dismutase (SOD) activity
was evaluated by the spectrophotometric method of
Marklund26 on the basis of the spontaneous autoxidation of
pyrogallol at 25°C, with formation of end products with an
absorbance peak at 420 nm. This reaction is linearly dependent on the
presence of superoxide anions and is specifically inhibited by SOD.
Absolute enzyme activities were calculated from a standard curve
generated with purified human SOD obtained by recombinant DNA
technology (Biotechnology General, NY). To distinguish between the
copper/zinc-containing and the manganese-containing forms of the
enzyme, parallel measurements were performed in the presence of 1
µmol/L KCN, a selective inhibitor of the copper/zinc
form. All enzyme activities were normalized for the protein content of
each arterial sample, determined by the method of
Lowry,27 with BSA as standard.
Statistical Analysis
Results were analyzed by 1-way ANOVA followed by
Bonferroni's corrected t test, and a value of
P<0.05 was considered significant. Correlations between
fetal age and lesion sizes were tested by linear regression
analysis with SPSS software. Results are reported as
mean±SD.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Morphometric analysis of oil red O–stained sections of extracranial and intracranial arteries from both the normocholesterolemic and hypercholesterolemic groups revealed widespread occurrence of intimal lipid accumulations (Figure 1
). Even in the
normocholesterolemic group, more than half of all
sections through the middle cerebral and basilar arteries contained
signs of lesion formation (intimal lipid deposits) compared with 66%
in the common carotid and abdominal aorta (P<0.05). The
numbers of lesions per section (inserts in the bars of Figure 1)
were at least 3 times higher in extracranial than in intracranial
arteries. Both the percentage of sections containing lesions and the
number of lipid accumulations per section were significantly greater in
the carotid artery and abdominal aorta of the
hypercholesterolemic group compared with the respective
arteries in the normocholesterolemic group. In
contrast, the percentage of lesion-containing sections in intracranial
arteries was not significantly increased by
hypercholesterolemia. In the above assessment,
no differentiation was made between sites with minimal intimal changes
and established fatty streaks. Minimal lesions, found predominantly in
the middle cerebral and basilar arteries, had an intimal/medial ratio
of 0.128±0.095 (n=48), whereas the intimal/medial ratio of the largest
fatty streaks, found mostly in the carotid and aorta, was 0.688±0.155
(n=35).
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We then determined the area of the intimal lipid accumulations. To
compare lesion formation in extracranial and intracranial arteries,
potential differences in the size of these vessels have to be taken
into consideration. We first measured the area of the single largest
lesion in each section, a parameter that should be
independent of the vascular caliber (at least in arteries of roughly
the same size). On the basis of the outer circumferences of the
(non–perfusion-fixed) arteries, we calculated the following outer
diameters: abdominal aorta, 2.4±0.7 mm (n=22); common carotid
artery, 2.6±0.5 mm (n=33); basilar artery, 2.1±0.3 mm
(n=34); middle cerebral artery, 1.1±0.2 mm (n=30). As shown in
Figure 2, the size of the largest lesion
per section was significantly greater in the abdominal aorta and the
carotid than in the basilar and middle cerebral artery
(P<0.0001). Similar results were obtained when the
cumulative size of all lesions per section was measured (not shown).
Even when the cumulative lesion areas were corrected for the vascular
size (by dividing by the cross-sectional surface area of each artery)
(Figure 2, inset), the lesion size was significantly greater in
the abdominal aorta and the carotid than in the basilar and middle
cerebral artery (P<0.0001).
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In addition to highlighting the striking difference in absolute lesion
size between intracranial and extracranial arteries, these data also
indicated that brain arteries were less susceptible to
hypercholesterolemia than extracranial vessels,
as previously noted in Figure 1
. Although
hypercholesterolemia generally resulted in a
significant increase in lesion size, the relative increase was much
greater in extracranial arteries. For example, the area of the single
largest lesion in each section increased by 97% in the common carotid
and 397% in the abdominal aorta, compared with only 32% and 49% in
the middle cerebral and basilar artery, respectively (Figure 2).
The increase in the abdominal aorta was even more striking (+764%)
when lesion sizes were expressed as the corrected cumulative lesion
area (Figure 2, inset). Furthermore, the absolute increases in
lesion areas caused by hypercholesterolemia
were much greater in extracranial than in intracranial arteries. For
example, the area of the greatest lesion in
hypercholesterolemic extracranial arteries increased by
7.1 to 60.6x103 µm2
compared with the respective normocholesterolemic
arteries but only by 119 to 225 µm2 in
intracranial arteries.
No significant correlations were found between fetal age and lesion
sizes, expressed either as the corrected cumulative lesion area (Figure 3) or the area of the greatest lesion per
section (not shown). When data from the
normocholesterolemic and
hypercholesterolemic groups were pooled, the
correlation coefficient ranged from R=0.091 to
R=0.219. Multiple regression analysis of data by
group (normocholesterolemic and
hypercholesterolemic) also did not indicate a
significant correlation between lesion size and age. In contrast, a
highly significant correlation existed between lesion sizes and total
plasma cholesterol levels of the mothers, as one would
expect, because maternal plasma cholesterol levels had been
used to define the groups (data not shown).
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) and
normocholesterolemic (
) groups. Lesion sizes are
reported as average lesion area per section corrected for
cross-sectional area of each artery.
In addition to the morphometric determinations on 30 oil red O–stained
sections of each arterial segment, paraffin-embedded serial
sections of all arterial segments of the 77 fetuses were
immunostained and assessed for the intimal presence of
apolipoprotein B, oxidation-specific epitopes (oxidized LDL), and
macrophages. Results are shown in Figure 4. The carotid artery and abdominal aorta
but not the middle cerebral and basilar artery of the
hypercholesterolemic group contained significantly more
intimal macrophages, LDL, and oxidized LDL than those of the
normocholesterolemic group (P<0.05). As
expected from the smaller numbers and sizes of lesions in these
arteries (Figures 1 and 2), the percentage of sections showing
immunostaining for each of these epitopes was
significantly lower in intracranial than in extracranial arteries, but
no significant differences in relative lesion composition were
seen.
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To further investigate the possibility that differences in lipid
oxidation may contribute to the greater resistance of intracranial
arteries to hypercholesterolemia, we determined
the activities of 4 antioxidant enzymes, ie, glutathione peroxidase,
catalase, as well as 2 forms of SOD, in a subset of all arteries. As
shown in Table 3, both the middle
cerebral and the basilar artery showed significantly greater
manganese-SOD activity than the aorta and carotid artery, whereas no
statistically significant differences in the activity of the other
antioxidant enzymes were detected between intracranial and extracranial
vessels.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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We have previously reported that very early lesions occur throughout the aorta of human fetuses and that aortic fatty streak formation is greatly enhanced by maternal—and presumably fetal—hypercholesterolemia.15 We have now shown that the first indications of an atherogenic process, for example, intimal thickening and lipid accumulation, were also present in brain arteries of fetuses, but that the number and size of these lesions was dramatically smaller in intracranial than in extracranial arteries. These results are consistent with clinical and pathological evidence suggesting that atherosclerosis in human brain arteries occurs much later than in coronaries and other extracranial arteries8 9 10 and with results obtained in some animal models.11 28 The second remarkable result of the present study was the observation that hypercholesterolemia led to a marked increase in lesion size in the aorta and carotid artery, whereas the relative increase in the basilar and middle cerebral arteries was much smaller. Furthermore, the size of lesions remained negligible in the brain arteries even in the presence of hypercholesterolemia compared with extracranial arteries. Although differences in the cholesterol exposure of the intracranial arteries were not likely to account for this, we nevertheless excluded this possibility by measuring plasma cholesterol levels in intracranial arteries in a subset of fetuses and showing that it did not differ significantly from that in peripheral veins (Table 1
). Therefore, the
difference in lesion formation points to a fundamental difference in
the response of intracranial arteries to exposure to the same level of
plasma cholesterol.
In the following, we will briefly address potential mechanisms that may
provide an explanation for the relative resistance of intracranial
arteries to hypercholesterolemia-induced
atherogenesis. However, it should be kept in mind that most of the
fetal lesions, in particular those in intracranial arteries, were early
fatty streaks visible only under the microscope and that no conclusions
can be drawn on the fate of the fetal lesions. It is generally assumed
that fatty streaks may progress to more advanced
lesions.16 29 30 31 On the other hand, we have previously
shown that at 
6 months of fetal age the correlation between fetal
and maternal cholesterol levels is lost and that fetal
cholesterol levels decrease with increasing fetal
age.15 It is therefore conceivable that many fetal lesions
regress when the fetal cholesterol levels decrease with
increasing age or during infancy, when cholesterol levels
tend to be low. Nevertheless, it is generally believed that the initial
events in atherogenesis are the same independent of whether the fatty
streak later regresses or progresses to a more advanced atherosclerotic
lesion. For this reason, we will use the term "atherogenesis" even
in context with the very early lesions seen in fetal arteries.
Our data suggest that atherogenesis in intracranial arteries of adults
may follow a somewhat different pathogenetic path than in extracranial
arteries. Because much of the brain's cholesterol needs
are met by de novo synthesis of cholesterol rather than by
uptake of plasma LDL32 33 and because it is known that the
vascular endothelium of intracranial capillaries forms
a tight barrier to large proteins (blood-brain
barrier),34 35 it is tempting to assume that a reduced
permeability to LDL accounts in part for the lesser atherogenic
response of the intracranial arteries to
hypercholesterolemia. However, our data suggest
that once LDL penetrates into the intima of intracranial arteries,
oxidation and the atherogenic events that follow17 18 19 are
not qualitatively different from events in extracranial arteries
(Figure 4).
The fact that oxidation of LDL occurred even in the early lesions of intracranial arteries of fetuses is consistent with the previously established presence of oxidation-specific epitopes in advanced lesions of human brain arteries.36 37 For lesions of the same size, no difference in staining for oxidation-specific epitopes was detectable between intracranial and extracranial arteries. However, given the semiquantitative nature of immunocytochemistry, we cannot rule out that subtle differences in intracellular and extracellular oxidative processes may exist in brain arteries, which in turn may affect gene expression of a number of adhesion molecules, cytokines, and other proatherogenic factors.18 Comparison of gene and protein expression between different intracranial and extracranial arteries of the same fetus and between normocholesterolemic and hypercholesterolemic fetuses, in the same artery, may offer a unique way to test this hypothesis.
It is also conceivable that the relative resistance of intracranial arteries to hypercholesterolemia is a consequence of functional differences of cerebral vascular cells independent of the intimal penetration of LDL. For example, endothelial dysfunction is thought to be one of the earliest manifestations of atherosclerosis,38 and some evidence indicates that intracranial arteries may be less susceptible to subtle damage. In vitro, exposure to mildly oxidized LDL resulted in impaired vasodilation of carotid but not basilar arteries,39 probably because the latter are better protected against interference of oxidized LDL with nitric oxide. The present observation that intracranial arteries contained significantly greater activity of the free radical scavenger Mn-SOD also suggests that intracranial arteries may be more resistant to oxidative processes. The finding of higher Mn-SOD activities in intracranial arteries, which develop fewer lesions, is also consistent with the recent observation by Topper et al40 that Mn-SOD (as well as nitric oxide synthase and cyclooxygenase 2) are differentially responsive to fluid mechanical stimuli and are selectively upregulated by steady laminar shear stress. Turbulent flow conditions are well known to be associated with increased lesion formation, whereas laminar shear stress is usually found in areas less prone to atherogenesis. It is therefore tempting to speculate that laminar flow conditions are more prevalent in intracranial arteries than in the aorta and carotid artery, where turbulence is more frequent, and that this results in the upregulation of Mn-SOD and other atheroprotective genes. A comparison of gene expression in intracranial and extracranial fetal arteries by differential display techniques would also test this assumption.
Finally, it is well recognized that atherogenesis is a multifactorial disease.41 42 It is therefore possible that the lower susceptibility of intracranial arteries to cholesterol-induced atherogenesis observed in adults results from the coincidence of lower blood pressure, decreased susceptibility to endothelial dysfunction, and other factors.
In conclusion, we have provided evidence that the atherogenic response of intracranial arteries to hypercholesterolemia is markedly reduced compared with extracranial arteries. A similar diminished pathogenic role of hypercholesterolemia in the formation of advanced atherosclerotic lesions in brain arteries could mean that lowering the mortality rate from stroke requires a much longer period of lipid-lowering intervention than is needed to reduce coronary heart disease death. Most importantly, the present results suggest that studies of human fetal arteries may enable us to elucidate some of the differences in the atherogenic mechanisms that exist between intracranial and extracranial arteries.
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Acknowledgments |
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This study was supported by grant 94.0055 from the Consiglio Nazionale delle Ricerche, grants 96/40% (Faculty of Medicine, Federico II University of Naples) and 96/60% (C.N. and F.P.D.) from the Ministero della Università e Ricerca Scientifica e Tecnologica (M.U.R.S.T.), grant ISS.33343/97 from the Italian National Institutes of Health (C.N.), grant HL-56989 (La Jolla Specialized Center of Research in Molecular Medicine and Atherosclerosis) from the National Heart, Lung, and Blood Institute (J.L.W. and W.P.), and grant M01-RR00827 (UCSD GCRC). Dr Napoli would like to dedicate this article to the memory of Dr Fulvio Pinto (1916 to 1981). The authors would like to thank Dr Giuseppe Santoro and Annalisa Scognamiglio for help in the determination of the activity of antioxidant enzymes and Dr P. Somma for assistance with histology and morphometry.
Received August 4, 1998; revision received January 16, 1999; accepted January 19, 1999.
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