(Hypertension. 2001;37:270.)
© 2001 American Heart Association, Inc.
Scientific Contributions |
From the Department of Geriatric Medicine (Keiko Matsumoto, R.M., A.M., N.T., M.A., J.H., T.O.), Osaka University Medical School, Osaka; Kankyo Bailis Research Institute (H.S.), Shiga; and Division of Biochemistry (Kunio Matsumoto, T.N.), Biochemical Research Center, Osaka University Medical School, Osaka, Japan.
Correspondence to Ryuichi Morishita, MD, PhD, Associate Professor, Department of Geriatric Medicine, Osaka University Medical School, 2-2 Yamada-oka, Suita 565, Japan. E-mail morishit{at}geriat.med.osaka-u.ac.jp
| Abstract |
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Key Words: endothelium muscle, smooth, vascular angiotensin angiotensin-converting enzyme inhibitors remodeling
| Introduction |
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| Methods |
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Histological Studies
For histological analyses, a
segment of each artery was perfusion-fixed with 4%
paraformaldehyde. Medial and luminal areas were
measured on a digitizing tablet (model 2200, South Micro Instruments)
after the segment was stained with
hematoxylin.13 The medial
area was readily demarcated as the vessel area between the internal and
external elastic laminae. At least 3 individual sections from the
middle of each arterial segment were analyzed.
Animals were coded so that analysis was performed without
knowledge of which treatment each animal
received.
Evaluation of Vasodilator Properties in
Response to Bradykinin
Freshly harvested vessels were cleaned of fat and
connective tissue, cut into helical strips, and mounted in 30-mL organ
baths that contained Krebs-Henseleit buffer (KNB; in mmol/L: NaCl
120, KCl 4.7, CaCl2 2.5,
MgSO4 1.2,
KH2PO4 1.2,
NaHCO3 25, glucose 5.5; pH 7.4) maintained at
37°C and oxygenated with 95%
O2/5% CO2. Vessels were
equilibrated for 60 minutes and bathing fluid was changed every 15
minutes. Isometric tension studies were performed with a Grass model 7D
polygraph. Optimal resting tension was determined in baseline studies,
and response to vasoactive drugs was
determined.14 Cumulative
dose-response curves to KCl (1 to 100 mmol/L) were established.
Vessels were then submaximally precontracted with KCl (typically
50 mmol/L), and endothelial function was evaluated
by determination of vascular relaxation to bradykinin
(10-8 to 10-4
mol/L) in the presence of indomethacin
(3x10-6 mol/L). In the present study,
we evaluated the vasodilator response to bradykinin but not
acetylcholine, because response of porcine coronary artery to
acetylcholine was vasospastic rather than vasodilatory in the presence
of normal
endothelium.15
Contractile responses were measured from the polygraph chart and
expressed as a percentage of the maximal relaxation induced by
papaverine (10-4 mol/L). Nitric-oxide
mediation of bradykinin responses was confirmed by blocking
bradykinin-induced relaxation with
N-methyl-L-arginine
(1 mmol/L), a specific competitive inhibitor of nitric
oxide synthase.
Nw-nitro-L-arginine
methyl ester (L-NAME) was administered 20 minutes before, vessels were
contracted with KCl (50 mmol/L), and endothelial
function was evaluated by determining vascular relaxation to
bradykinin.
Northern Blot Analysis
RNA was extracted by use of RNAzol (Tel-Test Inc),
from balloon-injured coronary arteries 1 month after balloon
injury. For Northern blot analysis, 20 µg of total RNA was
subjected to electrophoresis on 1.5% agarose-formaldehyde denaturing
gel and transferred to a nitrocellulose membrane (Amersham
International plc). The filter was baked, prehybridized, and
hybridized. Full-length complementary DNA (cDNA) for HGF labeled with
random-primer kit (Amersham) was used as a probe for Northern blotting.
The filter then was washed and exposed to X-ray
film.
Statistical Analysis
All values are expressed as mean±SEM. ANOVA with a
subsequent Bonferroni or Dunnett test was used to determine
significance of differences in multiple comparisons. Values of
P<0.05 were considered
statistically significant.
| Results |
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Our previous studies demonstrated negative regulation of local HGF expression by Ang II in various cells, including VSMC.8 9 17 Thus, we further examined the effect of Ang II on local vascular HGF production in a balloon-injury porcine coronary artery model, because the significant contribution of Ang II is well known in the pathogenesis of neointimal formation in this model.18 19 Porcine coronary artery was treated with perindopril (an ACE inhibitor) and vehicle from 7 days before to 28 days after balloon injury. Administration of perindopril resulted in a significant reduction of neointimal to medial area after balloon injury (Figure 2a and b; P<0.01). In contrast, no significant changes in medial area were observed in each group (vehicle, 1.07±0.27; perindopril, 0.86±0.06 mm2; not significant). Lumen area of vessels treated with perindopril was significantly increased compared with vehicle (vehicle, 0.66±0.16 mm2; perindopril, 1.10±0.11 mm2; P<0.05), whereas medial area was slightly reduced but not to a level of significance (vehicle, 1.07±0.27 mm2; perindopril, 0.86±0.06 mm2; not significant). These data suggest that treatment with perindopril may affect negative remodeling, although further studies with intravascular ultrasound are necessary. Vascular HGF mRNA was significantly increased in balloon-injured coronary artery treated with perindopril versus vehicle (Figure 1; P<0.01).
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Given the restoration of vascular HGF mRNA by perindopril, we hypothesized that increase in vascular HGF might enhance reendothelialization in balloon-injured vessels. Indeed, overexpression of human HGF vector in rat balloon-injured vessels resulted in a significant increase in reendothelialized area as assessed by Evans blue dye staining.20 If so, enhanced reendothelialization by increased vascular HGF would result in restoration of anatomical integrity and recovery of physiological function. Therefore, we examined vasomotor response to an endothelium-dependent agonist. As shown in Figure 3, vehicle-treated arteries demonstrated a lack of vasodilator response to bradykinin administration, whereas normal arteries demonstrated nice vasodilative response to bradykinin. Of importance, administration of bradykinin into precontracted vessels treated with perindopril resulted in significant dilatation compared with injured vessels treated with vehicle (Figure 4 and 5; P<0.01). Endothelium-dependent dilatation in arteries treated with perindopril is also supported by the observation that the increase in dilatation was completely abolished by administration of L-NAME.
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| Discussion |
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This phenomenon provides the interesting hypothesis that disruption of the autocrine-paracrine local HGF system, which maintains endothelial cell growth, by Ang II may result in abnormal growth of VSMC and endothelial dysfunction, given that endothelial cells secrete antiproliferative substances.1 2 Therefore, we further examined the pathophysiological roles of the vascular HGF system in cardiovascular disease. As was expected, administration of perindopril significantly increased local HGF expression associated with the inhibition of neointimal formation. Because HGF is an endothelium-specific growth factor and thus stimulated growth of endothelial cells,3 4 increased local HGF production would probably stimulate regeneration of endothelial cells after balloon injury. Of particular interest, vasodilator response of balloon-injured coronary arteries was restored by treatment with perindopril versus vehicle. This restoration of vasodilatation was completely abolished by administration of L-NAME, which suggests that rapid regeneration or stabilization of endothelial cells might be related to recovery of vasodilator response to bradykinin. Administration of an ACE inhibitor restored endothelial dysfunction after percutaneous transluminal coronary angioplasty in human subjects.10 Increased local HGF production may participate in the improvement of endothelial dysfunction observed in those cases treated with ACE inhibitors. Additionally, our preliminary results showed that in vivo gene transfer of HGF into balloon-injured artery resulted in significant inhibition of neointimal formation and restoration of endothelial dysfunction by reendothelialization.20 Increased local HGF production by ACE inhibition may have therapeutic value against abnormal VSMC growth through stimulation of reendothelialization in addition to blockade of Ang IImediated VSMC growth. The present studies in porcine coronary arteries may provide information more applicable to humans, although studies in rat carotid artery models have been reported.8 Our hypothesis is supported by the previous observation that an ACE inhibitor, perindopril, stimulated endothelial regrowth after arterial injury in a rabbit model.26 The contribution of increase in local HGF expression by ACE inhibition to endothelial function may also be more general, given that treatment with ACE inhibitors is well known to improve endothelial dysfunction in human hypertensive patients.27 28 However, the present study has limitations. Recent studies demonstrated the lack of chymase, an alternative Ang IIgenerating enzyme, in a porcine model.29 In human restenosis, presence of chymase may diminish the utility of ACE inhibitors, although further studies are necessary to determine this matter.
In the present study, we demonstrated that treatment with perindopril significantly inhibited neointimal formation and improved endothelial dysfunction in porcine balloon-injured coronary artery, accompanied by an increase in local vascular HGF production. Given the strong mitogenic activity of HGF on endothelial cells, increased local vascular HGF production by ACE inhibition may have therapeutic value against abnormal VSMC growth and endothelial dysfunction by enhancing reendothelialization after balloon injury. Negative regulation of local HGF production, probably by Ang II, may play a physiological role in vascular disease, given the activation of the vascular renin angiotensin system in atherosclerosis, restenosis, and hypertension in humans and in experimental models.18 19 23 24
| Acknowledgments |
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Received April 11, 2000; first decision May 3, 2000; accepted August 29, 2000.
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