(Circulation. 2000;102:1330.)
© 2000 American Heart Association, Inc.
Basic Science Reports |
From the Montreal Heart Institute and Department of Pharmacology, University of Montreal, Montreal, Québec, Canada.
Correspondence to Martin G. Sirois, PhD, Montreal Heart Institute, 5000 Belanger St, Montreal, Québec, Canada H1T 1C8. E-mail mgsirois{at}icm.umontreal.ca
| Abstract |
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Methods and ResultsA bolus of antisense PDGFR-ß delivered into injured rat carotid arteries reduced PDGFR-ß protein overexpression by >90% from day 3 to 28 after injury. At day 28 after injury, compared with injured untreated carotids, treatment with antisense PDGFR-ß reduced intimal hyperplasia by 58% and medial VSMC migration by 49% and improved vascular reendothelialization by 100% and vascular reactivity (EC50) to acetylcholine by 5-fold.
ConclusionsA single-bolus luminal delivery of antisense PDGFR-ß to injured rat carotids reduced intimal hyperplasia, improved the reendothelialization process, and led to the recovery of endothelium-dependent regulation of vascular tone.
Key Words: gene therapy angioplasty growth substances restenosis
| Introduction |
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Reports support the role of platelet-derived growth factor (PDGF)
in mediating arterial intimal hyperplasia after an
angioplasty and in the formation of atherosclerotic
lesions.7 8 9 10 PDGF is secreted as 3 different isoforms:
PDGF-AA, -AB, and -BB, and binds to 2 distinct subtype receptors,
PDGFR-
and -ß, which can form homodimers and
heterodimers.11 12 PDGF dimers and both PDGF receptor
subtypes are overexpressed in VSMCs from human atherosclerotic plaques
and at sites of postangioplasty repair in animal and human
arteries.10 13 14 15
In rats, administration of polyclonal antibodies to all forms of PDGF before and after balloon injury (BI) of carotid arteries inhibited intimal hyperplasia but not the first wave of proliferation in the media.16 17 18 Interestingly, antibodies directed against the PDGF-B chain blocked intimal thickening, whereas antibodies to the PDGF-A chain prevented intimal hyperplasia.19 Infusion of PDGF-BB into a carotid BI in rats increased intimal thickening but had little effect on intimal VSMC proliferation, suggesting that the decrease in intimal hyperplasia was due to the inhibition of medial VSMC migration.20
We recently reported that a sustained perivascular delivery for 14 days of an antisense (AS) oligomer complementary to specific PDGFR-ß mRNA sequences after a BI in rat carotids prevented PDGFR-ß protein overexpression and intimal hyperplasia.15 The aim of the present study was to investigate whether a single endovascular delivery of AS PDGFR-ß would be sufficient to reduce intimal hyperplasia by limiting either VSMC migration or proliferation. We also investigated the possibility that inhibition of PDGFR-ß overexpression would favor endothelial regrowth and the return of vasomotor activity.
| Methods |
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AS Oligonucleotide Therapy
We used an AS oligonucleotide phosphorothioate
backbone sequence to the murine PDGFR-ß mRNA subunit (AS-PDGFR-ß:
TATCACTCCTGGAAGCCC). A scrambled (SCR) sequence (SCR-PDGFR-ß:
GTGATAGTATGCCGAGCA) was used as control. In the present study, we
used only 1 AS sequence, because we showed the efficiency of this AS in
a previous report.15 After BI of the left common carotid
artery, we introduced a 22-gauge infusion cannula into the external
carotid arteriotomy and administered 0.2 mL of 0.9% NaCl solution to
flush the residual blood-borne elements. The AS or SCR
oligonucleotide solution (200 µg/25 µL of PBS 0.01
mol/L) was infused into the temporarily isolated segment of the left
common carotid artery for a 30-minute period. Then the arteriotomy was
ligated, the left common carotid artery was released, the wounds were
closed, and the animals were returned to their cages. The protocol was
performed in accordance with the Canadian Council on Animal Care
guidelines.
Evaluation of Vascular Reactivity
Carotid arteries were harvested at death and placed in
Krebs-Ringer solution. Rings of 4 to 5 mm from the medial portion
of the left (treated) and right (untreated) carotids were mounted with
2 triangle 5-0 stainless steel wires. The adjacent segments
(distal and proximal) were fixed in formalin for analysis.
Experiments were performed in organ chambers filled with 25 mL of
Krebs-Ringer solution and indomethacin 0.01 mmol/L
and gassed with 95% O2/5%
CO2 at 37°C. Vessels were passively stretched
(
1.5 g) while the contraction generated by a depolarizing solution
containing physiological KCl (20 mmol/L) was
assessed. The organ chamber was rinsed with fresh Krebs-Ringer solution
and equilibrated for 45 minutes. Phenylephrine (PE;
10-6 mol/L) was used to
achieve a submaximal contraction. An
endothelium-dependent vasorelaxation was induced by the
addition of cumulative acetylcholine (ACh) concentrations
(10-9 to
3.17x10-5 mol/L). Calcium
ionophore A23187
(2.5x10-7 mol/L) was
added to obtain the maximal endothelium-dependent
vasorelaxation. Sodium nitroprusside
(10-5 mol/L) was added to
mediate a direct VSMC relaxation.
Immunohistochemistry of PDGFR-ß, PCNA, and ecNOS
Expression
The immunohistochemistry procedures on arterial
sections were performed as described previously.15 The
primary antibodies used were rabbit polyclonal anti-human PDGFR-ß IgG
(UBI), monoclonal anti-human proliferative cell nuclear antigen (PCNA)
IgG (Zymed Laboratories Inc), and monoclonal anti-human
endothelial cell constitutive nitric oxide synthase
(ecNOS) IgG (Transduction Laboratories)].
Statistical Analysis
Data are mean±SEM. Statistical comparisons were determined by
ANOVA followed by an unpaired Students t test with
Bonferronis correction for multiple comparisons. Data were considered
significantly different if a value of P<0.05 was observed.
Relaxation is expressed as a percentage of preconstricting tone.
EC50 (concentration of ACh producing a
half-maximal relaxation) has been calculated for each segment with the
Statview program.
| Results |
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Treatment with AS-PDGFR-ß prevented PDGFR-ß protein overexpression
in medial VSMCs at days 3 and 7 by 90% and 93%, respectively
(P<0.001). Similarly, PDGFR-ß protein level was reduced
by 60% (P<0.05) in intimal VSMCs at day 7 (Figures
1C and 2) and was at the basal level observed in native
medial VSMCs at day 14 (Figure 2
). Three days after injury,
treatment with an SCR oligomer reduced the PDGFR-ß protein expression
on medial VSMCs by 42% (P<0.05). This reduction, however,
was significantly less (P<0.05) than the reduction mediated
by the AS-PDGFR-ß (90%) (Figure 2
). At day 7, SCR treatment
did not reduce PDGFR-ß protein expression in medial or intimal VSMCs
(Figures 1D
and 2
), and by day 14 the PDGFR-ß protein
expression returned to basal levels (Figure 2
).
Neointimal Hyperplasia
The intimal and medial areas (mm2) and the
I:M area ratio were determined after a vascular injury. The medial
areas in BI rat carotid arteries at days 7, 14, and 28 after injury
were 0.101±0.007, 0.109±0.005, and 0.105±0.004
mm2, respectively (Figure 3A
) and fluctuated by <14% compared
with the medial area of native carotid arteries (data not shown).
Treatment of the BI carotid arteries with AS-PDGFR-ß increased the
medial area by 33%, 3%, and 13% at days 7, 14, and 28, respectively
(P<0.01 at day 7 and P=NS at days 14 and 28).
SCR treatment increased the medial area by 23%, 14%, and 16.5%
(P=NS at day 7 and P<0.05 at days 14 and 28)
(Figure 3A
).
|
Intimal hyperplasia developed during the first 7 days and was maximal
within 14 days. The intimal areas in BI groups at days 7, 14, and 28
were 0.025±0.005, 0.116±0.012, and 0.091±0.011
mm2 (Figure 3B
). An AS-PDGFR-ß treatment
reduced the intimal hyperplasia by 37%, 40%, and 56%
(P=0.07 [NS], P<0.05, and P<0.01)
at days 7, 14, and 28, respectively, whereas the SCR treatment did not
reduce the intimal hyperplasia (Figure 3B
). The I:M area ratios
in BI carotids were 0.256±0.047, 1.102±0.126, and 0.899±0.099,
respectively (Figure 3C
). An AS-PDGFR-ß treatment reduced
these ratios by 50%, 47%, and 58% (P=0.08 [NS],
P<0.01, P<0.001), respectively, whereas the SCR
treatment did not significantly alter the I:M area ratios compared with
BI groups (Figure 3C
).
SMC Count
The induction of a carotid BI did not affect the medial VSMC count
throughout the first 14 days compared with native vessels (467±38
cells) (Figure 4
). At day 28 after
injury, however, all groups demonstrated an increased number of medial
VSMCs compared with native media. The VSMC count increased by 11%
(P=NS) in the untreated BI group, by 32%
(P<0.05) in the AS-PDGFR-ßtreated group, and by 47%
(P<0.01) in the SCR-treated group. The difference between
the AS-PDGFR-ß and the BI groups was not significant (Figure
4). At days 7, 14, and 28, the number of intimal VSMCs in BI
arteries was 422±67, 1285±100, and 1004±126, respectively.
AS-PDGFR-ß reduced the number of intimal VSMCs at days 7, 14, and 28
by 47%, 33%, and 50% (P<0.05, P<0.05,
P<0.01), respectively, compared with the BI group. The SCR
oligomer did not reduce the intimal VSMC count at any time point
(Figure 4
).
|
SMC Density
The medial density of VSMCs in native carotid arteries was
4253±160 VSMCs/mm2. The fluctuation density of
medial VSMCs at days 3, 7, 14, and 28 after injury in BI or
AS-PDGFR-ß or SCR-treated groups was always <20% compared with
the VSMC density observed in native medial VSMCs. The variation of
medial VSMC density between the BI group and the groups treated either
with AS-PDGFR-ß or SCR oligomer was also <20% (data not shown). The
intimal VSMC densities in the BI group at days 7, 14, and 28 after
injury were 14 762±1143, 11 466±496, and 11 939±681
VSMCs/mm2. The AS-PDGFR-ß significantly reduced
the intimal VSMC density by 29% only at day 7 (data not shown).
SMC Proliferative Activity
In native carotid arteries, the percentage of proliferative medial
VSMCs was 1.2±0.4% (Figures 5A
and 6
). At days 3 and 7 in the BI group, PCNA
expression on medial VSMCs increased to 7.8±2.4% (P<0.01)
and 6.8±1.3% (P<0.001) compared with native medial VSMCs
and returned to the basal level of PCNA expression observed in
uninjured medial VSMCs by day 14 (Figures 5B
and 6
).
Intimal VSMC PCNA expression was quantified from days 7 to 28 after
injury. In the BI group, the percentage of PCNA expression at day 7 was
9.8±2.4%, and it returned to near basal expression by day 14 (Figures
5B and 6). A treatment with AS-PDGFR-ß or SCR oligomer
did not significantly reduce PCNA overexpression on medial and intimal
VSMCs compared with the BI group at any time point (Figures 5C
and 5D
and 6).
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Vascular Reendothelialization
To evaluate the extent of reendothelialization,
immunohistochemical staining was performed to detect the expression of
ecNOS. In native carotid arteries, ecNOS-positive cells covered
96.7±0.5% of the internal elastic lamina (Figures 7A
and 8
).
Immediately after the passage (3 times) of an inflated balloon, the
degree of endothelialization (day 0) was reduced to
2.7±0.3% (Figures 7B
and 8
). In the BI group,
reendothelialization occurred but remained incomplete
(Figures 7C
and 8
). Treatment with AS-PDGFR-ß increased
the extent of reendothelialization at each time point
compared with the BI group (Figures 7D
and 8
). The
application of SCR oligomer did not favor
reendothelialization (Figure 8
).
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Ex Vivo Carotid Vascular Reactivity
Segments of carotid arteries were precontracted to submaximal
level with PE (10-6
mol/L). PE-induced contraction in endothelium-intact
native arteries (E+; 0.68±0.04 g) was less than in freshly denuded
arteries (day 0; 1.38±0.12 g). At 14 and 28 days after injury,
PE-induced contraction varied between 0.97±0.11 and 1.28±0.10 g in BI
or AS-PDGFR-ß and SCR-treated arteries (data not shown).
On PE-precontracted arteries, ACh induced a complete relaxation of
endothelium-intact segments (E+; Figure 9
). The relaxant effect of ACh, which was
absent in freshly denuded arteries (BI day 0) and maximal on days 14
and 28, produced only 13.4±3.7% (day 14) and 36.1±6.8% (day 28) of
vasorelaxation (Figure 9
). AS-PDGFR-ß but not SCR
significantly improved (time-dependently) the efficacy of ACh-induced
relaxation compared with the BI group (Figure 9
). After the
addition of the highest concentration of ACh
(3.17x10-5 mol/L), the
calcium ionophore A23187
(10-7 mol/L) was added to
obtain the maximal endothelium-dependent
vasorelaxation. The addition of A23187 to injured carotid arteries
either untreated (BI) or treated with the AS-PDGFR-ß or SCR oligomers
never induced >10% relaxation at 14 and 28 days after injury (Figure
9). Sodium nitroprusside
(10-5 mol/L), which
induces a direct VSMC relaxation, produced 100% relaxation in all
treated groups (Figure 9
).
|
| Discussion |
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After a BI, PDGFR-ß protein expression increased in the media and the neointima. This was maximal at day 7 and returned to its baseline level at day 14. These results are in agreement with previous reports that have shown transient PDGFR-ß protein overexpression in rat and human injured arteries.10 14 Bilder et al21 reported that a selective PDGFR-ß tyrosine kinase inhibitor given orally twice a day for 28 days decreased by 30% the I:M area ratio in injured porcine coronary arteries. Banai et al22 showed that a local intravascular delivery of a PDGF-receptor tyrosine kinase blocker reduced by 40% the I:M area ratio of BI porcine femoral arteries. Finally, Hart et al23 showed that repeated intravenous administration of mouse/human chimeric antiPDGFR-ß antibodies combined with a sustained heparin delivery decreased the I:M area ratio by 40% in BI baboon saphenous arteries. In our study, the single-bolus endovascular application of AS-PDGFR-ß was sufficient to prevent the overexpression of PDGFR-ß protein throughout the entire 28 days of our experiment, and this might explain why our treatment was more efficient (58%) in reducing the development of intimal hyperplasia than the above-mentioned studies. In our previous report,15 the sustained perivascular application of AS-PDGFR-ß reduced the I:M area ratio by 60% to 80%. Our present results suggest that a sustained release of the AS-PDGFR-ß is not necessary to achieve its optimal biological effect and reinforce the concept that the blockade of initial events after acute vascular injury might be sufficient to have prolonged benefits.23 24
We calculated the number of medial and intimal VSMCs and their density
per square millimeter (VSMCs/mm2), as well as the
VSMC proliferative activity in the different groups studied. Although
medial VSMC count was increased 28 days after injury in all 3 groups,
medial VSMC density at each time point in BI and AS-PDGFR-ß or SCR
oligomertreated groups never fluctuated by >20% compared with VSMC
density observed in the media of native carotid arteries. AS-PDGFR-ß
treatment reduced the number of intimal VSMCs at days 7, 14, and 28 by
up to 50% compared with the BI group without altering intimal VSMC
density at days 14 and 28. In addition, a treatment with either the
AS-PDGFR-ß or the SCR oligomer did not significantly reduce PCNA
overexpression at any time point in medial and intimal VSMCs as
observed in the BI group (Figures 5
and 6
). These results
demonstrate that the treatment of an injured rat carotid artery with
AS-PDGFR-ß did not alter the proliferative activity of the medial or
intimal VSMCs. Thus, the reduction in intimal VSMC number and the I:M
area ratio is attributed to the inhibition of medial VSMC migration
into intima.
We observed that the passage of an inflated balloon in rat carotid arteries led to an almost complete denudation of the endothelium. In the untreated BI arteries, a progressive reendothelialization was achieved, but <25% of the luminal area was covered by day 28. The application of AS-PDGFR-ß increased the extent of reendothelialization by 2-fold at each time point, such that nearly 50% of the neointima was covered by neoendothelial cells at 28 days. This result, combined with a 58% reduction of the I:M ratio observed in the same carotid arteries treated with AS-PDGFR-ß, supports the hypothesis that the inhibition of VSMC migration from the injured media has the double beneficial effects of reducing intimal hyperplasia and improving the vascular healing process.
Finally, our results demonstrate that the contractile (PE) and relaxant (sodium nitroprusside) properties of VSMCs were unaltered by the different treatments. Most importantly, at 14 days and more convincingly at 28 days after injury, AS-PDGFR-ß treatment significantly improved endothelium-dependent relaxation. The maximal relaxation produced by ACh more than doubled, and the estimated concentration of ACh needed to induce 50% of its maximal relaxation was reduced by 2- and 5-fold at 14 and 28 days, respectively, compared with injured untreated carotid arteries. Our results suggest that a 50% reendothelialization of injured rat carotid arteries might be sufficient to induce an almost complete endothelium-dependent vasorelaxation as observed in native arteries.
In conclusion, we have shown that the local endovascular delivery of a single bolus of AS-PDGFR-ß at the injury site is sufficient to block the initial and delayed PDGFR-ß protein overexpression, reduce the formation of intimal hyperplasia, and improve the degree of reendothelialization sufficiently to restore endothelium-dependent relaxant function to the injured carotid arteries. These data demonstrate the clinical potential of AS-PDGFR-ß to prevent accelerated arteriopathies and promote vascular healing of injured areas.
| Acknowledgments |
|---|
Received February 18, 2000; revision received April 6, 2000; accepted April 7, 2000.
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