Würzburg,
Germany-
Ischemic stroke is the third leading cause of death and
permanent disability in industrialized countries. Currently, the
anticoagulant therapies available to treat ischemic stroke offer
moderate benefit on stroke progression and recurrence, but this
is outweighed by a significant increase in the rate of ICH.
During ischemia, platelets can adhere to hypoxic endothelial
cells by binding of their glycoprotein (GP) Ib receptor to von
Willebrand factor (vWF) on the endothelial surface.
Additionally, subendothelial matrix proteins are exposed,
allowing firm attachment of platelets to the vessel by binding
of collagens to their GPVI receptor. These processes lead to
activation of platelet GPIIb/IIIa and platelet aggregation.
Christoph Kleinschnitz, MD et al from the University of Würzburg
in Würzburg, Germany tested the hypothesis that blocking
platelet aggregation and activation at various steps in these
pathways may reduce infarct size following ischemic stroke.
Their results, published in the
May 1, 2007 issue of Circulation, showed that targeting
platelet GPIb or GPVI receptors protects mice from ischemic
brain injury in an experimental stroke model without increasing
bleeding complications. In contrast, blockade of the final
common pathway of platelet aggregation with anti-GPIIb/IIIa
antibodies had no positive effect on stroke outcome and
dose-dependently raised the incidence of ICH and mortality.
Complete
blockade of GPIbα receptors was achieved by
intravenous injection of 100 µg Fab fragments of the
monoclonal antibody p0p/B to mice undergoing 1 hour of transient
middle cerebral artery (MCA) occlusion. This was
administered in one group 1 hour before the induced ischemia,
and in another group, it was given 1 hour after the induction of
the ischemia. GPIIb/IIIa receptors were blockaded by injection
of 100 µg, 20 µg, or 10µg. JON/A F(ab)2 IV 1 hour
before the start of the experiment. GPVI function was inhibited
by 100 µg JAQ1 IP 5 days before infarct induction. The tMCAO
model was used to induce focal cerebral ischemia. This involved
inserting a silicon rubber-coated 6.0 nylon monofilament into
the right common carotid artery and advancing it to occlude the
MCA. After one hour, the occluding filament was removed. After
recovery from anesthesia and again after 24 hours, neurological
function was assessed. At 24 hours after transient
MCA occlusion, cerebral infarct volumes were assessed
by 2,3,5-triphenyltetrazolium chloride staining. Magnetic
resonance imaging (MRI) was performed repeatedly at 24 hours and
at 7 days after stroke on a 1.5-T MR unit in order to assess the
frequency of ICH over time.
In
mice treated with anti-GPIb Fabα 1 hour before MCA occlusion,
ischemic lesions were reduced to ≈40% compared with
controls (28.5±12.7 versus 73.9±17.4 mm3,
respectively; P<0.001). Application of anti-GPIbα Fab 1
hour after MCA occlusion also reduced brain
infarct volumes (24.5±7.7 mm3; P<0.001)
and improved the neurological status. Similarly,
depletion of GPVI significantly diminished the
infarct volume but to a lesser extent (49.4±19.1 mm3;
P<0.05). Additionally, the disruption of early steps
of platelet activation was not accompanied by an increase
in bleeding complications as revealed by serial
magnetic resonance imaging. In contrast, blockade of
the final common pathway of platelet aggregation with
anti-GPIIb/IIIa F(ab)2 fragments did not reduce
stroke size and functional outcome but increased the
incidence of ICH and mortality after transient MCA
occlusion in a dose-dependent manner.
These results
show that inhibition of early steps of platelet adhesion to the
ischemic endothelium and the subendothelial matrix diminishes
infarct development without causing ICH. Thus, selective
blocking of platelet receptor GPIb may offer a novel and safe
treatment strategy for acute stroke in humans in the future.
Co-authors:
Miroslava Pozgajova, PhD; Mirko Pham, MD; Martin Bendszus, MD;
Bernhard Nieswandt, PhD; Guido Stoll, MD
