IN-VIVO DETECTION AND IMAGING OF PHOSPHATIDYLSERINE EXPRESSION DURINGPROGRAMMED CELL-DEATH

One of the earliest events in programmed cell death is the externaliza tion of phosphatidylserine, a membrane phospholipid normally restricte d to the inner leaflet of the lipid bilayer. Annexin V, an endogenous human protein with a high affinity for membrane bound phosphatidylseri ne, can be used in vitro to detect apoptosis before other well describ ed morphologic or nuclear changes associated with programmed cell deat h. We tested the ability of exogenously administered radiolabeled anne xin V to concentrate at sites of apoptotic cell death in vivo. After d erivatization with hydrazinonicotinamide, annexin V was radiolabeled w ith technetium 99m. In vivo localization of technetium 99m hydrazinoni cotinamide-annexin V was tested in three models: fuminant hepatic apop tosis induced by anti-Fas antibody injection in BALB/c mice; acute rej ection in ACI rats with transplanted heterotopic PVG cardiac allograft s; and cyclophosphamide treatment of transplanted 38C13 murine B cell lymphomas. External radionuclide imaging showed a two-to sixfold incre ase in the uptake of radiolabeled annexin V at sites of apoptosis in a ll three models. Immunohistochemical staining of cardiac allografts fo r exogenously administered annexin V revealed intense staining of nume rous myocytes at the periphery of mononuclear infiltrates of which onl y a few demonstrated positive apoptotic nuclei by the terminal deoxynu cleotidyltransferase-mediated UTP end labeling method. These results s uggest that radiolabeled annexin V can be used in vivo as a noninvasiv e means to detect and serially image tissues and organs undergoing pro grammed cell death.