Imaging Cyclophosphamide-Induced Intramedullary Apoptosis in Rats Using

Intramedullary apoptosis of hematopoietic tissue is believed to play a major role in the pathophysiology of myelodysplastic syndrome. Annexin V, a specific marker of the early to interme-diate phases of apoptosis, has been applied to the in vitro study of bone marrow aspirates. A noninvasive measure of intramed-ullary apoptosis in vivo that could serially monitor the clinical progression of myelodysplastic syndrome may be helpful. Methods: We used 99mTc-radiolabeled annexin V and radionu-clide gamma camera imaging to serially study the sites, extent, and severity of intramedullary apoptosis induced by cyclophos-phamide treatment. Results: Intravenously administered radio-labeled annexin V localized preferentially in the femur, pelvis, vertebrae, and spleen; increased uptake in these organs was easily visualized as early as 8 h after injection of 100 mg/kg cyclophosphamide in 8- to 10-wk-old animals. Higher doses o