Project

Discipline

stroke; optical imaging; magnetic resonance imaging; blood-brain barrier; thrombosis; neutrophils

Lead
Lay summary
Stroke poses a massive disease burden, but only few effective therapies exist yet. Intensive research effort has focused on the role of inflammation after cerebral ischemia because inflammation occurs for hours and even days after onset of ischemia, providing an extended window for therapy. However, therapeutic targeting of inflammation is hampered by the fact that processes are dynamic and interact in a complex and often multifaceted way. Techniques that would allow visualizing of such processes non-invasively would facilitate the development of therapies. To date, such techniques for use in experimental models and patients are not yet available. Neutrophils can exert many different effects in the immune response following tissue injury and repair. Activated neutrophils can secrete substances, which can contribute to the breakdown of tissue barriers like the blood-brain barrier. Furthermore, neutrophils can extrude extracellular traps, which can serve as scaffold for fibrin and hence contribute to the formation of a thrombus. By exerting these actions, neutrophils could contribute to ischemic brain injury. Still, large gaps remain in the understanding on how these actions engage in the evolution of the ischemic injury and how they are involved in blood-brain barrier (BBB) impairment, hemorrhagic transformation (HT) and thrombosis. The object of the project is to address these questions using non-invasive imaging techniques such as near-infrared fluorescence (NIRF) imaging and magnetic resonance imaging with dedicated imaging probes, experimental models of cerebral ischemia, genetic mouse models and pharmacology to bridge the gap in knowledge on how neutrophils mediate blood-brain barrier impairment, hemorrhagic transformation and thrombosis after focal cerebral ischemia. For this purpose, imaging assays for visualizing neutrophil proteolysis, adhesion and thrombus formation will be developed and validated. The combined use of imaging modalities and multiple imaging probes will enable to investigate several processes relevant for BBB impairment, HT and thrombosis and their interaction in-vivo in a mouse model of cerebral ischemia. Imaging will be employed to test new therapies for application together with thrombolytic therapy with recombinant tissue plasminogen activator and to guide the application of this therapy. The aim is to make thrombolysis safer and more applicable.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Communication	Title	Media	Place	Year

Title	Year

Number	Title	Start	Funding scheme

Stroke poses a massive disease burden, but only few effective therapies exist yet. Intensive research effort has focused on the role of inflammation after cerebral ischemia because inflammation occurs for hours and even days after onset of ischemia, providing an extended window for therapy. However, therapeutic targeting of inflammation is hampered by the fact that processes are dynamic and interact in a complex and often multifaceted way. Techniques that would allow visualizing of such processes non-invasively would facilitate the development of therapies. To date, such techniques for use in experimental models and patients are not yet available.Neutrophils can exert many different effects in the immune response following tissue injury and repair. Activated neutrophils can secrete substances, which can contribute to the breakdown of tissue barriers like the blood-brain barrier. Furthermore, neutrophils can extrude extracellular traps, which can serve as scaffold for fibrin and hence contribute to the formation of a thrombus. By exerting these actions, neutrophils could contribute to ischemic brain injury. Still, large gaps remain in the understanding on how these actions engage in the evolution of the ischemic injury and how they are involved in blood-brain barrier impairment, hemorrhagic transformation and thrombosis.My proposal focuses on using non-invasive imaging techniques such as near-infrared fluorescence (NIRF) imaging and magnetic resonance imaging (MRI) with dedicated imaging probes, experimental models of cerebral ischemia, genetic mouse models and pharmacology to bridge the gap in knowledge on how neutrophils mediate blood-brain barrier (BBB) impairment, hemorrhagic transformation (HT) and thrombosis after focal cerebral ischemia. For this purpose, imaging assays for visualizing neutrophil proteolysis, adhesion and thrombus formation will be developed and validated. The combined use of imaging modalities and multiple imaging probes will enable to investigate several processes relevant for BBB impairment, HT and thrombosis and their interaction in-vivo in a mouse model of cerebral ischemia. Imaging will be employed to test new therapies for application together with thrombolytic therapy with recombinant tissue plasminogen activator (rtPA) and to guide the application of this therapy. The aim is to make thrombolysis safer and more applicable. Aim 1: Specific molecular imaging of neutrophil elastase and avß3 integrin expression after cerebral ischemia. The hypotheses will be tested if neutrophil elastase and neutrophil adhesion are involved in BBB impairment after cerebral ischemia. The study aims at developing and validating NIRF imaging assays for visualizing non-invasively avß3 integrin expression and neutrophil elastase activity in a mouse model of cerebral ischemia with NIRF imaging. The time course of these processes will be monitored in groups of animals and differences in BBB impairment and ischemic lesion volume after genetic and pharmacological inhibition of neutrophil elastase activity and avß3 integrin expression will be assessed.Aim 2: Imaging of neutrophil-mediated BBB impairment for treatment stratification before thrombolysis with rtPA. The study aims to evaluate neutrophil elastase activity, avß3 expression and matrix metalloproteinase imaging for their capability to predict BBB impairment and HT in a mouse model of cerebral ischemia. More specifically, two hypotheses will be tested: that imaging of neutrophil-mediated BBB impairment can be used to predict the risk of developing HT after thrombolytic therapy and that imaging can be used for treatment stratification prior to thrombolysis. MRI techniques will be used to assess BBB function and outcome before and after thrombolytic therapy. In addition, the question if pharmacological inhibition of neutrophil-mediated BBB impairment can reduce HT and prolong the time window for rtPA treatment will be studied. For this purpose, neutrophil-mediated BBB impairment will be inhibited prior to thrombolysis and the effects on BBB impairment, number of cerebral microbleeds and hemorrhages and lesion volume will be assessed with MRI and histology. Aim 3: Imaging of neutrophil-mediated thrombosis after cerebral ischemia. The hypotheses will be tested that neutrophils are involved in the formation of microthrombi after cerebral ischemia and that this process contributes to the evolution of postischemic blood flow obstruction and promotes the progression of ischemic lesion. The aim of the study is to use NIRF probes and a fibrin-targeted MRI contrast agent to image neutrophil elastase activity, avß3 expression and thrombus formation with NIRF imaging and MRI in-vivo. The effect on cerebral blood flow and lesion volume will be monitored with MRI. Furthermore, the question whether mice which have a high degree of microthrombi will benefit from anti-coagulant therapy will be studied by abolishing local thrombosis and improving blood flow.