(Stroke. 2001;32:225.)
© 2001 American Heart Association, Inc.
Original Contributions |
From the Departments of Neurological Surgery (M.S., I.D., M.N., K.T., K.I., T.T., T.O.), Molecular Biology and Biochemistry (Y.N.), and Faculty of Health Sciences (S.A.), Okayama University Medical School (Japan).
Correspondence to Isao Date, MD, Department of Neurological Surgery, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama 700-8558, Japan. E-mail idate333{at}med.okayama-u.ac.jp
| Abstract |
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MethodsTwenty-four New Zealand White rabbits were divided into 4 groups: (1) no treatment (control group, n=6); (2) blood injection without pretreatment (SAH-only group, n=6); (3) blood injection with pretreatment by vehicle (SAH+vehicle group, n=6); and (4) blood injection with pretreatment by 3-AB (SAH+3-AB group, n=6). We used the single-hemorrhage model of SAH, injecting autologous arterial blood into the cisterna magna. Angiography was performed before (baseline) and after (day 2) SAH, and the diameter of the basilar artery (BA) was measured. Animals were euthanatized after the second angiogram. After perfusion and fixation, the brains were cut into sections for hematoxylin and eosin and immunohistochemical staining for poly(ADP-ribosyl)ation.
ResultsIn the control group, there were no differences in the BA lumen caliber between baseline and day 2 (96.8±10.4%). Cerebral vasospasm in the SAH+3-AB group (88.2±6.2%) was remarkably attenuated in comparison with that in the SAH-only group (64.9±8.0%) and the SAH+vehicle group (65.6±10.8%). The BA in the SAH+3-AB group showed less corrugation of the tunica elastica interna than that in the SAH-only and SAH+vehicle groups. Staining for poly(ADP-ribosyl)ation was markedly inhibited in smooth muscle and adventitial cells of the BA in the SAH+3-AB group compared with other groups.
ConclusionsInhibiting ADP-ribosylation attenuates cerebral vasospasm after SAH in rabbits, and PARP activation may play an important role in the development of cerebral vasospasm.
Key Words: nitric oxide synthase subarachnoid hemorrhage vasospasm rabbits
| Introduction |
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B (NF-
B), and inducible
nitric oxide synthase (iNOS), all of which are responsible for
inflammation. Recent experimental data show that PARP activation is
associated with the pathogenesis of a variety of inflammatory diseases,
such as
arthritis12 13
and
meningitis.14
Cerebral vasospasm is an important cause of morbidity and
mortality after subarachnoid hemorrhage (SAH). Although
the pathogenesis of vasospasm is not fully understood, an inflammatory
response has been suggested to be
involved.15 16 17
Oxyhemoglobin in hemolysate within a subarachnoid clot is
considered one of the candidates responsible for delayed vasospasm
because it releases free radicals, such as superoxide anions and
hydroxyl radicals, during auto-oxidation to
methemoglobin.18 In
addition, the induction of iNOS has been observed in the cerebral
vessel wall and the mononuclear and polymorphonuclear cells
infiltrating the subarachnoid space after SAH in
rats.19 20 21
Thus, the nitric oxide metabolite peroxynitrite may be associated with
vasospasm. These free radicals may cause inflammation by injuring the
vessel wall. These findings may also indicate the possible activation
of PARP during cerebral vasospasm. Polin et
al17 showed that adhesion
molecules were elevated in the cerebrospinal fluid of patients after
SAH. We previously demonstrated that inhibiting the NF-
B
transcription factor, which is known to be essential in iNOS induction
and closely related to inflammation, attenuated cerebral
vasospasm.22 On the basis of
these findings, we assumed that an inflammatory response after SAH
plays a significant role in the pathogenesis of cerebral vasospasm. In
this study we investigated the role of PARP in cerebral vasospasm using
3-aminobenzamide (3-AB), a specific inhibitor of
PARP,4 5 6 8 9 10 11
in a rabbit SAH model.
| Materials and Methods |
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Induction of Experimental SAH
The rabbit single-hemorrhage model of SAH was
used. All animals subjected to SAH were anesthetized by the
administration of ketamine (50 mg/kg IM) and pentobarbital (20
mg/kg IV). The atlanto-occipital membrane was exposed through an
occipitocervical midline incision, and a 24-gauge butterfly needle was
inserted. After the withdrawal of 1 mL of cerebrospinal fluid, the
vehicle (PBS) or drug (3-AB+PBS) was given. One minute later,
autologous arterial blood (1 mg/kg) from the auricular
artery was carefully injected into the cisterna magna. Thereafter, the
animals were placed head down for 30 minutes so that the basilar artery
(BA) was suffused with the autologous blood.
Cerebral Angiography
In all animals, left vertebrobasilar angiography was
performed 5 days before (baseline) and 2 days after (day 2) the
induction of SAH to measure the diameter of the BA. The animals were
anesthetized as described above under spontaneous respiration.
The angiography catheter was inserted into the right femoral artery and
positioned at the origin of the left vertebral artery. We injected 1 mL
of contrast medium through the catheter and performed the angiography
using a digital subtraction angiography system (Advantex/AFM, GE
Company) at the same magnification for each animal. During these
procedures, arterial blood pressure was recorded on a
monitor (Omniace RT3100, NEC Corp) connected to the catheter, and blood
gases and body temperature were measured and strictly maintained at
standard levels. For the second angiogram, the left femoral artery was
used.
Perfusion and Fixation
All animals were euthanatized after the second
angiogram. To do this, we performed a thoracotomy, closed the
descending aorta, inserted a catheter into the left ventricle, and
perforated the right atrium. After perfusion and fixation with 4%
paraformaldehyde, each animals brain was removed and
stored overnight in paraformaldehyde at
4°C.
Histological
Examination
For histological examination, the
brains were embedded in paraffin and cut into 4-µm sections. They
were then stained with hematoxylin and eosin and observed under a light
microscope.
Immunohistochemistry
To clarify poly(ADP-ribosyl)ation through PARP
activation, we performed immunohistochemical staining with the
Vectastain Elite ABC kit (Vector Laboratories). The paraffin-embedded
sections were deparaffinized, and the production of
endogenous peroxidase was halted by placing the specimens
in 0.6% H2O2 in methanol
for 10 minutes. The sections were blocked with normal horse serum for
20 minutes and then were incubated with a primary monoclonal antibody
at 1:200 dilution for 1 hour at 37°C. The primary monoclonal antibody
used for this study was the mouse anti-poly(ADP-ribose) monoclonal
antibody (4335-MC-100, Trevigen), which recognizes
poly(ADP-ribosyl)ated proteins. The slides were washed in PBS. They
were then incubated with biotinylated anti-mouse IgG secondary antibody
at 1:200 dilution for 30 minutes and with ABC reagent solution for 30
minutes. The sections were stained with diaminobenzidine
tetrahydrochloride and counterstained with hematoxylin. Negative
controls were performed without the primary
antibody.
Statistical Analysis
We measured the diameter of the BA at 3 points:
0.2 mm above the union of the bilateral vertebral arteries, just
below the anterior inferior cerebellar arteries, and
0.2 mm below the top of the BA. Three blinded investigators
measured the arterial diameter, and the mean of the 3
points was calculated as the diameter of the BA. We calculated a
percentage of the BA diameter on day 2 relative to the baseline for
each rabbit, and the results were expressed as the mean±SD.
Angiographic measurement was statistically evaluated by ANOVA with the
Bonferroni/Dunn post hoc test; these statistical differences were
considered significant when
P<0.05. There was no
mortality. All of the operated animals were
analyzed.
| Results |
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Histological
Analysis
The BAs exhibited subendothelial
thickening and severe corrugation of the tunica elastica interna in the
SAH-only
(Figure 3A
and 3B
) and SAH+vehicle groups
(Figure 3C
). In contrast, the tunica elastica interna of the
SAH+3-AB vessels had a smooth appearance, and morphological changes in
the vascular structure did not occur
(Figure 3D
).
|
Immunohistochemistry of
Poly(ADP-Ribose)
Poly(ADP-ribose)positive cells could be identified
clearly in the endothelial cells, smooth muscle cells,
and adventitial cells of the SAH-only group (data not shown) and the
SAH+vehicle group
(Figure 4A
and 4B
). Immunoreactivity was shown mainly in the
nuclei. Poly(ADP-ribosyl)ation after SAH was inhibited by 3-AB,
especially in smooth muscle cells and adventitial cells. In the
SAH+3-AB group, approximately one third of the smooth muscle cells and
adventitial cells were positive for poly(ADP-ribose), although almost
all of them were positive in the SAH-only and SAH+vehicle groups. In
addition, the staining intensity of positive cells was decreased in the
SAH+3-AB group
(Figure 4C
and 4D
). The negative controls did not show
poly(ADP-ribose) immunoreactivity.
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| Discussion |
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The insult of SAH elevates cytokines in
cerebrospinal
fluid.31 32 33
Either these cytokines or oxidative stress, both of which are
related to an inflammatory response, mediates iNOS expression and
NF-
B activation in smooth muscle
cells34 35 36
and
macrophages.37 38
Although the relationship between iNOS and vasospasm remains
controversial,39 some
authors report the expression of iNOS in the cerebral vessel wall and
the mononuclear cells and polymorphonuclear cells infiltrating into
the subarachnoid space during
vasospasm.19 20 21
Widenka et al21 demonstrated
iNOS induction in endothelial cells, smooth muscle
cells, and, above all, in adventitial cells of the rat BA after SAH.
The overproduction of nitric oxide by iNOS may produce
peroxynitrite, a free radical, which leads to tissue damage and lipid
peroxidation.40 Moreover, we
previously demonstrated that preventing the development of NF-
B, a
transcription factor whose activation is necessary for iNOS
expression,35 36 41
inhibited cerebral
vasospasm.22 Peroxynitrite
may also further activate PARP.
PARP is involved in regulating the NF-
B signaling pathway
leading to the induction of iNOS, and the pharmacological and genetic
inhibition of PARP impairs the expression of iNOS by decreasing NF-
B
activation.42 43 44 45
These findings are consistent with ours, which show that
inhibiting PARP with 3-AB reduced the degree of vasospasm in smooth
muscle cells and adventitial cells.
Cytokines produced during SAH stimulate the
expression of adhesion molecules, including intercellular adhesion
molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), and
E-selectin on the endothelial
surface.46 These adhesion
molecules may contribute to vasospasm because they promote leukocytic
adhesion to and migration across the vascular
endothelium, thereby initiating tissue injury. They are
found to be elevated in cerebrospinal fluid of patients with SAH
because of endothelial damage and breaking of the
blood-brain barrier.17 In a
rat model of SAH, the expression of ICAM-1 was observed on the
endothelial surface and in the medial layer of the
vessel wall.16 Bavbek et
al47 demonstrated that
administering monoclonal antibodies against ICAM-1 or CD18 attenuated
vasospasm in the BA after SAH in rabbits. Thai et
al48 documented similar
findings in a rat femoral artery model of vasospasm with ibuprofen, an
inhibitor of both ICAM-1 and VCAM-1 expression. The
expression of ICAM-1 in myocardial ischemia and reperfusion
injury is inhibited by the genetic disruption of PARP, and in vitro
studies have demonstrated that the pharmacological inhibition of PARP
with 3-AB reduces ICAM-1
expression.49 ICAM-1
expression by inflammatory cytokines has been also shown to be
under the control of
NF-
B.50 51 52
Since PARP is required to activate NF-
B, it is reasonable to
assume that the activation of PARP participates in regulating ICAM-1
expression. On the basis of these findings, we assume that
downregulating adhesion molecules by inhibiting PARP attenuates
vasospasm. Our experiment did not inhibit PARP activation in the
endothelial layer but only in the medial and
adventitial layers. The route used to administer the drug, ie, the
adventitial side, may be the reason that PARP expression could not be
inhibited in the endothelial layer. Further study is
required to clarify this issue.
A high concentration of 3-AB acts as a scavenger of the hydroxyl radical,9 13 53 and free radical scavengers are of benefit in the treatment of vasospasm. In experimental and clinical studies, free radical scavengers and lipid peroxidation inhibitors have been shown to suppress the contraction of the cerebral artery after SAH.54 55 56 57
In this study the pharmacological inhibition of PARP with 3-AB attenuated vasospasm. These findings provide the first evidence of the role of PARP in the pathogenesis of cerebral vasospasm. We anticipate that inhibiting PARP can offer a new therapy for patients suffering vasospasm, but further studies are required to elucidate the mechanism of vasospasm that involves PARP activation.
| Acknowledgments |
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Received May 24, 2000; revision received August 28, 2000; accepted September 7, 2000.
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| Introduction |
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These results are interesting and seem to provide more support for the idea that an inflammatory process possibly mediated by free radicals contributes to vasospasm. Let us address the limitations of this experiment first before recommending another drug for treatment of vasospasm that might be destined to fail like so many others. No appropriate randomization schedule was used, and interpretation of the results was not blinded. There is no result presented that proves that the effects observed were due to inhibition of poly(ADP-ribose) polymerase. Reduction of poly(ADP-ribosyl)ated protein is associated with the reduction in vasospasm but only association is shown. Any treatment that reduces vasospasm in this model might reduce markers of arterial injury, such as poly(ADP-ribosyl)ated protein, if it is a marker of injury. Finally, at 2 days after SAH in rabbits, there is moderate vasospasm that is not resistant to vasodilators,R2 which might correspond to the early, mildest form of vasospasm in man; whether inhibiting processes that account for this will reduce severe, prolonged vasospasm is open to question.
The theory that free radicals and inflammation contribute to vasospasm is simplistic. Inflammation and generation of free radicals are complex processes that potentially have beneficial and detrimental effects. Nonspecific inhibition of either process may not be beneficial. Indeed, tirilazad, a potent inhibitor of iron-dependent lipid peroxidation and probably other free radical reactions, was not of unequivocal benefit to patients with subarachnoid hemorrhage and may have been detrimental to patients with ischemic stroke.R1 Similarly, the role of inflammation in vasospasm is unclear. Vasospasm was not recognized as a clinical problem in patients with infectious meningitis, and when they do develop infarcts, the topography is not that of the vasospasm which occurs after SAH. Finally, one would like to have some rational basis for the therapy. While 3-aminobenzamide may inhibit inflammation, why would it reduce vasospasm 48 hours after SAH, at a time when the arterial narrowing in this model is due mainly to active smooth muscle contraction and is reversible with papaverine? It is the authors responsibility now to present detailed data to confirm or refute the hypothesis that activation of poly(ADP-ribose) polymerase mediates vasospasm 48 hours after SAH in rabbits.
Received May 24, 2000; revision received August 28, 2000; accepted September 7, 2000.
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