Dynamic patterns of USPIO enhancement can be observed in macrophages after ischemic brain damage

Cells of the mononuclear phagocytotic system (MPS) are often found near to or within ischemic tissue and can potentially aggravate cellular damage. Hence, visualization of those cells would allow demarcation of putatively affected from intact tissue. Experimental MRI studies have shown that ultrasmall particles of dextran-coated iron oxide (USPIO) are internalized into cells of the MPS. To test if this cell tagging method may be also applied to cerebral infarction, USPIOs were administered to Fisher rats 5.5 h after permanent occlusion of the middle cerebral artery (pMCAO). During the first 2 days USPIO were preferentially found in patches within the lesion and in surrounding areas. On day 4, USPIOs expanded within the core of the lesion. On day 7 they were found predominantly within the boundary area. Histological analysis showed large populations of macrophages containing iron particles in the infarcted tissue. We conclude, therefore, that it is possible to monitor MPS activity after focal cerebral ischemia using USPIOs.