Imaging of apoptosis (programmed cell death) with 99mTc annexin

Apoptosis (programmed cell death) ¡sa critical element in normal physiology and in many disease processes. Phosphatidylserine (PS), one component of cell membrane phospholipids, is nor mally confined to the inner leaflet of the plasma membrane. Early in the course of apoptosis, this phospholipid is rapidly exposed on the cell's outer surface. Annexin V, an endogenous human protein, has a high affinity for membrane-bound PS. This protein has been labeled with fluorescein and has been used to detect apoptosis in vitro. We describe the use of radiolabeled annexin V to detect apoptosis in vivo. The results are compared to histologie and flow cytometric methods to identify cells and tissues undergo ing apoptosis. Methods: Annexin V was coupled to hydrazinoni-cotinamide (HYNIC) and radiolabeled with 99mTc.Bioreactivity of 99mTc-HYNICannexin V was compared with fluorescein isothio-cyanate (FITC)-labeled annexin V in cultures of Jurkat T-cel