P4618Lack of CD31 results in microvascular plugging and increased infarction size in an experimental model of myocardial ischemia-reperfusion injury

Background

The success of coronary recanalization therapy for the treatment of myocardial infarction can be hampered by microvascular plugging which prevents effective reperfusion of the ischemic tissue. Due to its constitutive expression in platelets, leukocytes, and endothelial cells and its peculiar tyrosine phosphatase cell detaching signaling properties, the trans-homophilic CD31 receptor may be important to modulate platelet and leukocyte aggregation in the microvasculature.

Objective

To investigate the impact of CD31 genetic deficiency on the infarct size, peri-infarction microvascular plugging and macrophage phenotype in a mouse model of heart ischemia/reperfusion.

Methods

Cardiac ischemia was induced in WT and CD31 KO mice (n=30, 15 females and 15 males in each group) by surgical ligation of the left anterior descending coronary artery (LAD) for 45 minutes followed by reperfusion for 72 hours. The area at risk (AAR) and necrotic zone (NZ) were assessed using ImageJ software on three consecutive 1 mm thick slices of the left ventricle (LV) by a combination of a blue dye and 2,3,5-triphenyltetrazolium chloride staining. Parallel sets of experiments served to evaluate by both fluorescence microscopy and cytometry the presence of microvascular plugs and leukocyte phenotype in the infarction area as compared to the peri-necrotic myocardium.

Results

The AAR was similar in WT and CD31 KO mice (41,7±3,5 vs 37±2,9% of LV, NS) whereas the size of myocardial infarction was significantly greater in CD31 KO as compared to WT mice (23,4±2 vs 17,8±1,7% of LV, p<0,05). Immunofluorescent microscopy showed a dramatic increase in microvascular platelets-rich plugs around the infarction in CD31 KO mice (Figure), confirmed by cytometry analysis (9749±573 vs 5976±376 platelet-leukocyte aggregates/mg of tissue, p<0.001). Furthermore, we found that the ratio between M1 and M2 type macrophages in the peri-infarction myocardium was significantly increased in CD31 KO mice (0,7±0.07) as compared to WT mice (0,4±0.06, p<0,01).

Conclusions

Our data suggest that CD31 is important for reducing the size of necrosis following coronary recanalization procedures by preventing the no-reflow phenomenon due to microvascular plugging and by promoting a reparative phenotype of peri-infarction macrophages.

Acknowledgement/Funding

Institut Servier - ANRT (CIFRE doctoral grant)

Downstream Microvascular Thrombosis in Cortical Venules Is an Early Response to Proximal Cerebral Arterial Occlusion

Background

Previous experimental studies have shown that downstream microvascular thromboinflammation is involved in brain damage from acute ischemic stroke. Using intravital microscopy, we investigated and characterized the sequence of downstream microvascular thromboinflammation in an ischemia/reperfusion acute ischemic stroke model.

Methods and Results

Rats underwent transient monofilament middle cerebral artery (MCA) occlusion. Cerebral microcirculation in the MCA territory was exposed through a craniotomy and analyzed using real‐time intravital imaging coupled with laser Doppler interferometry. Leukocytes, platelets, fibrinogen, and blood–brain barrier permeability were analyzed by intravenous injection of fluorescent antibodies and bovine serum albumin. MCA occlusion induced a sudden and profound drop in downstream microvascular blood flow associated with leukocyte margination in the venous compartment. Leukocyte margination fostered fibrinogen deposition and thrombosis in postcapillary venules. Either in venules or arterioles, blood flow was not fully restored after MCA recanalization. Furthermore, venular thrombi persisted despite MCA recanalization, and leukocyte extravasation continued to develop in venules in association with blood–brain barrier disruption. Finally, microhemorrhages were occasionally observed, colocalizing with thrombosed venules characterized by marked leukocyte margination.

Conclusions

We showed that microvascular thrombosis in transient monofilament MCA occlusion and blood–brain barrier disruption are initiated immediately after occlusion and are propagated through the venous compartment in close association with marginating leukocytes. MCA occlusion–induced downstream microvascular thromboinflammation response was responsible for incomplete reperfusion after MCA recanalization and delayed microhemorrhages.

Exacerbation of Thromboinflammation by Hyperglycemia Precipitates Cerebral Infarct Growth and Hemorrhagic Transformation

BACKGROUND AND PURPOSE

Admission hyperglycemia is associated with a poor outcome in acute ischemic stroke. How hyperglycemia impacts the pathophysiology of acute ischemic stroke remains largely unknown. We investigated how preexisting hyperglycemia increases ischemia/reperfusion cerebral injury.

METHODS

Normoglycemic and streptozotocin-treated hyperglycemic rats were subjected to transient middle cerebral artery occlusion. Infarct growth and brain perfusion were assessed by magnetic resonance imaging. Markers of platelet, coagulation, and neutrophil activation were measured in brain homogenates and plasma. Downstream microvascular thromboinflammation (DMT) was investigated by intravital microscopy.

RESULTS

Hyperglycemic rats had an increased infarct volume with an increased blood-brain barrier disruption and hemorrhagic transformation rate compared with normoglycemic rats. Magnetic resonance imaging scans revealed that hyperglycemia enhanced and accelerated lesion growth and was associated with hemorrhagic transformation originating from territories that were still not completely reperfused at 1 hour after middle cerebral artery recanalization. Intravital microscopy and analysis of brain homogenates showed that DMT began immediately after middle cerebral artery occlusion and was exacerbated by hyperglycemia. Measurement of plasma serotonin and matrix metalloproteinase-9 indicated that platelets and neutrophils were preactivated in hyperglycemic rats. Neutrophils from hyperglycemic diabetic patients showed increased adhesion to endothelial cells as compared with neutrophils from normoglycemic donors in flow chamber experiments.

CONCLUSIONS

We show that hyperglycemia primes the thromboinflammatory cascade, thus, amplifying middle cerebral artery occlusion-induced DMT. DMT exacerbation in hyperglycemic rats impaired reperfusion and precipitated neurovascular damage, blood-brain barrier disruption, and hemorrhagic transformation. Our results designate DMT as a possible target for reduction of the deleterious impact of hyperglycemia in acute ischemic stroke.

Alteplase Reduces Downstream Microvascular Thrombosis and Improves the Benefit of Large Artery Recanalization in Stroke

BACKGROUND AND PURPOSE

Downstream microvascular thrombosis (DMT) is known to be a contributing factor to incomplete reperfusion in acute ischemic stroke. The aim of this study was to determine the timing of DMT with intravital imaging and to test the hypothesis that intravenous alteplase infusion could reduce DMT in a transient middle cerebral artery occlusion (MCAO) rat stroke model.

METHODS

Rats were subjected to 60-minute transient MCAO. Alteplase (10 mg/kg) was administered 30 minutes after the beginning of MCAO. Real-time intravital fluorescence microscopy through a dura-sparing craniotomy was used to visualize circulating blood cells and fibrinogen. Cerebral microvessel patency was quantitatively evaluated by fluorescein isothiocyanate-dextran perfusion.

RESULTS

Immediately after MCAO, platelet and leukocyte accumulation were observed mostly in the venous compartment. Within 30 minutes after MCAO, microthrombi and parietal fibrin deposits were detected in postcapillary microvessels. Alteplase treatment significantly (P=0.006) reduced infarct volume and increased the percentage of perfused vessels during MCAO (P=0.02) compared with saline. Plasma levels of fibrinogen from alteplase-treated rats showed a rapid and profound hypofibrinogenemia. In vitro platelet aggregation demonstrated that alteplase reduced platelet aggregation (P=0.0001) and facilitated platelet disaggregation (P=0.001). These effects were reversible in the presence of exogenous fibrinogen.

CONCLUSIONS

Our data demonstrate that DMT is an early phenomenon initiated before recanalization. We further show that alteplase-dependent maintenance of downstream perfusion during MCAO improves acute ischemic stroke outcome through a fibrinogen-dependent platelet aggregation reduction. Our results indicate that early targeting of DMT represents a therapeutic strategy to improve the benefit of large artery recanalization in acute ischemic stroke.