Vascular Biology |
From the Department of Medicine and Aging (F.C., M.M., M.F., B.P., A.I., F. Chiarelli, F. Cuccurullo, A.M.) and the Department of Biomedical Science (M.R., P.C.), University of Chieti "G DAnnunzio" School of Medicine, Chieti, Italy, and the Division of Cardiology (L.P., G.M., E.D.), "Spirito Santo" Hospital, Pescara, Italy.
Correspondence to Andrea Mezzetti, MD, Centro per la Prevenzione dellAterosclerosi, la Diagnosi e Terapia delllpertensione Arteriosa e delle Dislipidemie, Nuovo Policlinico SS. Annunziata, Via dei Vestini 66, 66013 Chieti, Italy. E-mail mezzetti{at}unich.it
| Abstract |
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Key Words: angioplasty restenosis monocyte chemoattractant protein-1 superoxide anion monocytes
| Introduction |
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Monocyte chemoattractant protein-1 (MCP-1) is the prototype of the C-C chemokine ß subfamily and exhibits its most potent chemotactic activity toward monocytes6 and T lymphocytes.7 In addition to promoting the transmigration of circulating monocytes into tissues, MCP-1 exerts various effects on monocytes, including superoxide anion induction,8 cytokine production, and adhesion molecule expression.9 MCP-1 expression is induced by inflammatory cytokines, peptide growth factors, or minimally modified LDL in monocytes, endothelial cells, and vascular smooth muscle cells.10 11 Elevated levels of MCP-1 have been found in patients with myocardial infarction12 and heart failure,8 as well as after myocardial reperfusion.13 Moreover, increased MCP-1 has been detected in the aorta after balloon injury11 and in atherosclerotic lesions but not in normal arteries,14 and its expression is correlated with vascular macrophage accumulation.15 Thus, the weight of the available evidence indicates that MCP-1 is a key factor initiating the inflammatory process of atherogenesis and sustaining the proliferative response to vessel injury.16
Although increased MCP-1 has been observed in animal models after balloon injury11 and critically implicated in postprocedural intimal hyperplasia,17 18 to the best of our knowledge, no studies have demonstrated whether MCP-1 is enhanced after PTCA in humans and contributes to luminal renarrowing.
Thus, in the present study, we set out to investigate the possible role of MCP-1 in restenosis after PTCA. In addition, we tested the hypothesis that MCP-1 exerts its effect, at least in part, by inducing O2- generation in circulating monocytes.
| Methods |
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Patients were excluded from the study for the following reasons: if the stenosed coronary artery segment could not be dilated; if initially successful angioplasty was followed by persistent abrupt closure; if a Q-wave infarction occurred in the territory of the dilated artery; if angioplasty was unsuccessful, necessitating emergency revascularization; if the results of angioplasty were suboptimal and a stent was implanted; or if follow-up angiography was lost. None of the participating subjects were taking vitamins, dietary supplements, or drugs with known antioxidant activity. All patients received aspirin (100 mg daily) for the entire study period. Informed consent was obtained from each subject. The study protocol was approved by the Institutional Ethical Committee.
Angioplasty Procedure and Follow-Up
Evaluation
Balloon angioplasty was performed according to
standard techniques. Patients were discharged with aspirin and any
other necessary medication. They were specifically asked not to take
additional vitamins and mineral supplements, and the American Heart
Association Step 1 Diet19 was
taught to all patients. After successful angioplasty, patients returned
for a clinical control after 15 days and 1, 3, and 6 months. Patients
were readmitted for follow-up coronary angiography 6 months
after angioplasty.
Quantitative Coronary
Angiography
The 4 coronary arteriograms (obtained before
the procedure, immediately after the procedure, 15 minutes after the
procedure, and at the 6-month follow-up visit) were analyzed by
an experienced cardiologist using the Philips H 4000 Quantitative
Coronary Analysis. Measurements were made in a single
projection, showing the most severe stenosis. Whenever
possible, the same projection was used in all 4 arteriograms to
allow more accurate comparison. The variation among repeated
measurements of the percentage of stenosis was 7% when frames
recorded 1 to 6 months apart were
analyzed.
Definitions
Restenosis in a previously successfully
dilated lesion was defined as recurrent lumen diameter stenosis
>50% at follow-up angiography, as determined by quantitative
coronary angiography. The continuous variable luminal loss
was defined as the change in minimal lumen diameter (MLD) during
follow-up normalized for vessel size, according to the following
equation: relative loss (RLOSS)= [(postintervention MLD-follow-up
MLD)/vessel size]x100%; the equation reflects the degree of luminal
renarrowing.5 The vessel size
is the value of the reference diameter function at the minimal position
of the obstruction.
Blood Collection
For serum sampling, blood was collected from each
patient before and 24 hours after PTCA and drawn into pyrogen-free
blood collection tubes without additives. Tubes were immediately
immersed in melting ice and allowed to clot for 1 hour before
centrifugation at
1000g for 10 minutes. For
plasma sampling, blood was collected from each patient before PTCA and
1, 5, 15, and 180 days afterward. Blood was drawn into pyrogen-free
test tubes containing EDTA as anticoagulant. Tubes were immediately
immersed in melting ice and centrifuged
(1000g at 4°C for 15 minutes)
within 15 minutes after sampling. Multiple aliquots of serum and plasma
were stored at -80°C until analysis. Samples were frozen
and thawed only once.
Isolation of Blood Monocytes
The isolation of peripheral monocytes
from 5 healthy blood donors was assessed by an established
method.5 Briefly, monocytes
were isolated from the buffy-coat fraction, which was reconstituted
with PBS to 20 mL, layered on top of a Lymphoprep gradient (Nycomed),
and centrifuged at 800g
for 10 minutes at room temperature. The fraction containing the
mononuclear leukocytes was washed with PBS. Next, the erythrocytes were
lysed in ammonium chloride solution, and the remaining mononuclear
leukocytes were washed once with ammonium chloride solution and once
with PBS and resuspended in RPMI 1640 (GIBCO) with 2% FCS. The
percentage of monocytes in this fraction was determined from cytospin
preparations and, in general, amounted to 22%.
Superoxide Anion
(O2-) Assay
The purified mononuclear cells
(3x105/mL, 200 µL per well) were cultured
in 96-well trays (Costar) in RPMI 1640 with
L-glutamine (GIBCO) for 20
hours with 20% of serum from patients or healthy control subjects. For
processing of serum, 40 µL of serum from each patient or control
subject was added to monocyte culture immediately after thawing, at the
start of the culture period. In some experiments, neutralizing
monoclonal antibodies against MCP-1 (goat anti-human MCP-1, final
concentration 50 µg/mL, R&D System) or control mouse
IgG1 (final concentration 50 µg/mL, R&D
System) were also added to cell culture. After 20 hours in culture, the
generation of O2-
from adherent monocytes was measured by the superoxide
dismutaseinhibitable reduction of cytochrome
c.8
Because cells from different individuals could exhibit differing level
of reactive oxygen, each serum sample was tested separately on
monocytes from all 5 normal subjects, and the mean value was
considered.
Briefly, monocytes were washed twice in prewarmed Hanks balanced salt solution (HBSS) without phenol red (Biowhittaker). Thereafter, 100 µL of cytochrome c from horse heart (final concentration 2 mg/mL, Sigma Chemical Co) in phenol red-free HBSS, with or without stimulants (phorbol myristate acetate [PMA], final concentration 100 ng/mL, Sigma), was added to each well. At various time points, the optical density was read at 550 nm in a SpectraCount photometer (Packard). Reduction of cytochrome c in the presence of superoxide dismutase (SOD, final concentration 300 U/mL, Sigma) was subtracted from the values without SOD. The differences in optical density between comparable wells with or without SOD were converted to the equivalent O2- release by using the molecular extinction coefficient for cytochrome c.8 The O2- production is expressed as nanomoles per 60 minutes per 106 monocytes.
Enzyme Immunoassays
Concentrations of MCP-1, RANTES, and interleukin-8
(IL-8) in plasma were determined in duplicate by specific enzyme
immunoassays (BioSource) according to the manufacturers descriptions.
At our laboratory, the intra-assay and interassay coefficients of
variation were <8%.
Statistical Analysis
For clinical data, variables were compared by use
of the
2 test. An ANOVA for repeated
measures followed by a multiple comparison test (Scheffé test) was
performed to test the changes in biochemical variables measured
over time. Differences in biochemical variables between the
restenotic and nonrestenotic groups at each collection
time were analyzed by the Student unpaired
t test. The correlation between
MCP-1 and O2- and
the strength of the association of late lumen loss with MCP-1 and
monocyte O2-
generation was assessed by linear regression analysis. Each
variable that proved to be statistically significant in the
univariate regression analysis was assessed by
multiple regression to establish whether it was an independent risk
factor for late lumen loss. Multiple regression analysis was
adjusted for potential confounders (class of angina, cigarette smoking,
hypercholesterolemia, diabetes mellitus,
hypertension, age, concomitant therapy, and variables of procedural
methods). The data are expressed as proportions or as mean±SD.
Statistical significance was considered to be indicated by a value of
P<0.05. All calculations were
performed by using the computer program SPSS
8.0.
| Results |
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Circulating Levels of MCP-1 in Patients With or
Without Restenosis After PTCA
The time course of MCP-1 biosynthesis during the
study is depicted in
Figure 1
. In both groups of patients, MCP-1 was
significantly increased when measured after PTCA throughout the study
(P<0.0001, ANOVA). There was
no notable difference between patients with or without
restenosis before PTCA (480±42 versus 470±69 [mean±SD]
pg/mL, respectively). Nevertheless, after PTCA in restenotic
patients, enhanced MCP-1 persisted as statistically significant
(P<0.0001) throughout the
study, whereas in the nonrestenotic patients, MCP-1 levels
normalized 15 days after the procedure
(Figures 1
and 2
). Thus, MCP-1 was significantly higher
(P<0.0001) in the patients
with restenosis at 1 (816±176 versus 618±102 pg/mL), 5
(755±158 versus 594±111 pg/mL), 15 (715±80 versus 450±54 pg/mL,
Figure 2
), and 180 (712±94 versus 453±76 pg/mL) days after
PTCA.
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Baseline levels of plasma MCP-1 averaged 498±54 (mean±SD)
pg/mL in the patients with unstable angina (n=35). This rate of
biosynthesis was significantly higher
(P<0.0001) than that in the
patients with stable angina (412±32 [mean±SD] pg/mL, n=15).
However, differences in MCP-1 biosynthesis between patients with or
without restenosis could not be accounted for by class of
angina (unstable versus stable), cigarette smoking,
hypercholesterolemia, diabetes mellitus,
hypertension, age, diet, concomitant therapy, or procedural
methods, because these potential confounders were equally
represented in the 2 groups
(Table 1
).
Moreover, to explore the specificity of the observed
response in the broader group of chemokines and to determine whether
chemokines targeting other cell types could be also involved in the
pathophysiology of restenosis, we analyzed the time
course of RANTES and IL-8 after PTCA. In both groups of patients,
RANTES and IL-8 were significantly increased when measured 1 and 5 days
after PTCA, but they achieved normalization 15 days after the
procedure, with no notable differences between patients with or without
restenosis
(Figure 3
).
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Relationship Between MCP-1 and Generation of
ROS From Monocytes
MCP-1 has been reported to induce enhanced ROS
generation in monocytes.8 To
further examine the relation between MCP-1 and monocyte activity in
patients who had undergone PTCA, the effect of serum collected from
patients before and 24 hours after PTCA on the generation of
O2- in monocytes
was studied. In this experiment, 50 nonhospitalized healthy volunteers
(28 males and 22 females, aged 60±8 years) without any clinically
detectable pathological condition were also studied as a control group.
Monocytes from 5 healthy blood donors were evaluated for spontaneous
and PMA-stimulated
O2- generation
after they were cultured for 20 hours in medium supplemented with
either 20% serum from 50 patients subjected to PTCA with
broad-spectrum MCP-1 levels (range 270 to 1190 pg/mL) or 20% serum
from 50 healthy blood donors (<300 pg/mL). Monocytes spontaneously
generated considerable levels of
O2- when they were
cultured with serum collected from patients before and 24 hours after
PTCA; the levels were significantly higher in the subset of patients
with restenosis (8±2 versus 5.9±2 nmol/60 minutes per
106 monocytes
[P=0.002] and 10.2±2 versus
8±2 nmol/60 minutes per 106 monocytes
[P=0.001], respectively;
Figure 4
). In contrast, no detectable spontaneous
O2- generation was
measured in monocytes cultured with serum from healthy donors
(Figure 4
). The stronger stimulatory effect of serum from
restenotic patients on the spontaneous generation of
O2- in monocytes
was blocked by an inhibitory monoclonal antibody for MCP-1
(8±2 versus 6±1.2 nmol/60 minutes per 106
monocytes [P<0.05] and
10.2±2 versus 8.1±1 nmol/60 minutes per
106 monocytes
[P<0.03], respectively, for
samples collected before and 24 hours after PTCA), thus confirming the
critical role of MCP-1 in enhanced monocyte
O2- generation
(Figure 4
). PMA-stimulated
O2- generation was
also enhanced when monocytes were cultured with serum from patients;
again, the most marked effect of serum was at the highest MCP-1 level,
which was statistically significant
(P=0.003) in the samples
collected 24 hours after PTCA (57±5 versus 45±6 nmol/60 minutes per
106 monocytes,
Figure 4
). Accordingly, a strongly positive correlation
(P<0.0001) between plasma
MCP-1 and either spontaneous or stimulated monocyte
O2- generation was
found before PTCA
(R2=0.691
and
R2=0.404,
respectively) and after PTCA
(R2=0.284
and
R2=0.420,
respectively;
Figure 5
).
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Variables Predictive for Late Lumen
Loss
To investigate whether MCP-1 and MCP-1dependent
oxidant stress could contribute to luminal renarrowing after PTCA, we
assessed the association between MCP-1 and monocyte
O2- generation with
the degree of luminal renarrowing (RLOSS) at 6 months after PTCA. RLOSS
showed a positive correlation
(P<0.0001) with plasma MCP-1
levels measured 1
(R2=0.335),
5
(R2=0.357),
15
(R2=0.722),
and 180
(R2=0.601)
days after PTCA. Moreover, a positive correlation with either
spontaneous and stimulated monocyte
O2- generation was
found 24 hours after PTCA
(R2=0.171
[P=0.003] and
R2=0.239
[P<0.0001], respectively).
Finally, multivariate regression analysis
showed that only the plasma level of MCP-1 measured 15 days after PTCA
was a statistically significant independent predictor for luminal
renarrowing after PTCA (ß=0.688,
P<0.0001;
Figure 6
).
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| Discussion |
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In the present study, patients who underwent PTCA
experienced a critical increase in circulating MCP-1 after the
procedure, which was significantly more evident and prolonged in those
with restenosis
(Figure 1
). In fact, whereas in the patients without
restenosis, MCP-1 plasma levels returned to baseline after 15
days
(Figures 1
and 2
), in the patients with restenosis,
the changes persisted throughout the study. Thus, the differences
between the 2 groups became evident 24 hours after PTCA and persisted
as statistically significant during the whole period of examination
(Figure 1
).
The striking effect of angioplasty in increasing MCP-1 raises the question of the origin of this chemokine. MCP-1 is produced by monocytes, endothelial cells, and fibroblasts.10 Macrophages and smooth muscle cells, the major types of cells left in the atherosclerotic lesion after PTCA, can also elaborate MCP-1.10 11 Several studies have shown that PTCA results in persistent platelet activation.20 Activated platelets have been found to stimulate MCP-1 production in monocytes through enhanced RANTES secretion and direct platelet-monocyte contact mediated by P-selectin expression on the platelet surface.21 Such a mechanism for enhanced MCP-1 expression in leukocytes has recently been found to be operative in patients with acute myocardial infarction,22 and it is conceivable that such a platelet-monocyte interaction may also contribute to the enhanced MCP-1 levels in patients who undergo coronary angioplasty. Moreover, the observation of Aukrust et al,8 who showed that monocytes isolated from patients with heart disease released higher amounts of MCP-1 than did cells from healthy control subjects and may therefore contribute to the elevated MCP-1 levels in the setting of pathological conditions, is of particular interest.
Whatever the cellular source(s), the enhanced levels of
MCP-1 may indirectly and directly have important
pathophysiological consequences in patients who
undergo PTCA, as shown by the statistically significant relationship
between MCP-1 and late lumen loss at the 6-month follow-up
(Figure 6
). MCP-1 has chemotactic activity for monocytes and
lymphocytes6 7 and
has been postulated to be a major signal for the accumulation of
mononuclear leukocytes after vessel
injury.6 11 There
are several reports suggesting that infiltration of lymphocytes and
monocytes into the vessel wall after PTCA by various mechanisms may
lead to progressive luminal
renarrowing.2 4 By
playing a pivotal role in the recruitment of these cells into sites of
inflammation,6 11
MCP-1 may thus indirectly play an important role in the pathogenesis of
restenosis after PTCA. The possible importance of MCP-1 for the
induction of intimal hyperplasia was recently illustrated by Stark et
al,17 who showed that
upregulation of MCP-1 gene expression in vein grafts resulted in the
recruitment of monocytes and tissue macrophages to the vein
wall, which led to obliterative stenosis and graft failure.
Moreover, Furukawa et al18
showed that neutralization of MCP-1 before and immediately after
arterial injury may be effective in preventing intimal
hyperplasia.
MCP-1 may also more directly contribute to
restenosis. In the present study, we found that the raised
MCP-1 levels in serum from patients who developed restenosis
after PTCA had enhancing effects on spontaneous ROS generation in
monocytes
(Figure 4
). Thus, if this enhancement also occurs in vivo, it
may be directly involved in the response to vascular injury. In fact,
previous
studies4 23 24
suggest that after vascular injury, an oxidizing environment must exist
in the plasma and in the vessel wall that may influence vascular
remodeling. The generation of ROS has profound and wide-ranging effects
that can dramatically increase vascular toxicity and initiate a cascade
of molecular and cellular responses. Superoxide anions can react with
NO,25 reducing the vasoactive
levels of NO26 and
diminishing the response to endothelium-dependent
vasodilators via formation of peroxynitrite anion
(ONOO-), a highly reactive intermediate
with strong cytotoxic
potency.26 Furthermore, the
damaging free radicals in patients with enhanced oxidant stress may
cause either direct arterial wall injury or may initiate
and/or accelerate secondary processes, including inflammatory gene
induction,27 activation of
phagocyteplateletendothelial cell
interactions,28 29
protein peroxidation,30 and
depletion of antioxidants such as vitamins C and
E.24 In the present
study, we have also demonstrated the specific role of MCP-1 in enhanced
O2- generation in
patients who developed restenosis after PTCA by using
neutralizing antibody against human MCP-1
(Figure 4
). In fact, MCP-1 neutralization reduced the
generation of O2-
to the level observed in patients without restenosis. However,
O2- generation was
still higher with respect to healthy subjects, thus suggesting that
other stimuli are also involved in the complex scenario of acute
vascular response after PTCA.
Enhanced
O2- generation may
also amplify MCP-1 production. In fact, many vascular
biologists now accord a central role to augmented transcription of
several atherosclerosis-related genes by the
oxidant-sensitive regulatory pathway involving nuclear factor
B.31 Exposure to
extracellular O2-
removes the inhibitory effect of NO on MCP-1
expression,32 33
activates the nuclear factor-
B regulatory complex, and
triggers the transcription of genes that encode certain growth factors,
adhesion molecules, chemoattractant cytokines (such as MCP-1),
and enzymes that can influence extracellular matrix
metabolism.34
Thus, increased O2-
generation in monocytes may further enhance the synthesis of MCP-1 in
these cells through an autocrine
mechanism,35 possibly
representing a vicious circle implicated in
restenosis after balloon angioplasty. Moreover,
O2- generation
might evoke a secondary cytokine and growth factor response
from other types of cells in the lesion, including smooth muscle cells,
fibroblasts, and endothelial cells, and establish a
positive, self-stimulatory, paracrine feedback loop, amplifying and
sustaining the proliferative
response.2
We did not perform any measurements in patients who underwent stenting after PTCA; therefore, the generalizability of these results to the overall population of patients who are treated with percutaneous coronary intervention is uncertain and requires additional studies. However, when the present study was started, the efficacy of stenting was supported by a randomized trial only in highly selected patients with predominantly simple coronary stenosis, whereas there was not yet concrete evidence regarding the outcome among unselected patients.36 Another limitation is that the predictive value of MCP-1 measured 15 days after PTCA found in the present study needs to be considered cautiously because of the relatively small number of patients (and events). However, the prognostic value of this marker, if confirmed in larger clinical studies, could contribute to optimizing therapeutic resources in the complex scenario of interventional cardiology.
In conclusion, the present study supports the hypothesis that upregulation of MCP-1 gene expression after coronary angioplasty results in the recruitment of monocytes and tissue macrophages to the arterial wall, possibly contributing to a number of restenoses after PTCA. Moreover, these results suggest that the causative role of MCP-1 in restenosis is mediated, at least in part, by increased generation of O2-. Therefore, further understanding of the mechanism(s) by which MCP-1 is produced and acts after arterial injury may provide insight into therapies to limit the progression of atherosclerosis and restenosis after balloon angioplasty.
| Acknowledgments |
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Received July 17, 2000; accepted December 11, 2000.
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involvement of reduced nicotinamide adenine dinucleotide
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J Clin Invest. 1993;92:15641571.
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