^99m Tc Annexin V Imaging of Neonatal Hypoxic Brain Injury

Abstract

Background and Purpose: -Delayed cell loss in neonates after cerebral hypoxic-ischemic injury (HII) is believed to be a major cause of cerebral palsy. In this study, we used radiolabeled annexin V, a marker of delayed cell loss (apoptosis), to image neonatal rabbits suffering from HII. Methods-Twenty-two neonatal New Zealand White rabbits had ligation of the right common carotid artery with reduction of inspired oxygen concentration to induce HII. Experimental animals (nϭ17) were exposed to hypoxia until an ipsilateral hemispheric decrease in the average diffusion coefficient occurred. After reversal of hypoxia and normalization of average diffusion coefficient values, experimental animals were injected with 99m Tc annexin V. Radionuclide images were recorded 2 hours later. Results-Experimental animals showed no MR evidence of blood-brain barrier breakdown or perfusion abnormalities after hypoxia. Annexin images demonstrated multifocal brain uptake in both hemispheres of experimental but not control animals. Histology of the brains from experimental animals demonstrated scattered pyknotic cortical and hippocampal neurons with cytoplasmic vacuolization of glial cells without evidence of apoptotic nuclei by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. Double staining with markers of cell type and exogenous annexin V revealed that annexin V was localized in the cytoplasm of scattered neurons and astrocytes in experimental and, less commonly, control brains in the presence of an intact blood-brain barrier. Conclusions-Apoptosis may develop after HII even in brains that appear normal on diffusion-weighted and perfusion MR. These data suggest a role of radiolabeled annexin V screening of neonates at risk for the development of cerebral palsy.

Monitoring the Protective Effects of Minocycline Treatment with Radiolabeled Annexin V in an Experimental Model of Focal Cerebral Ischemia

“…We previously showed that 99m Tc-labeled annexin V uptake correlated with neuronal apoptosis after a stroke (9,10). In this study we have extended our period of observation to 30 d after a stroke and have further defined the cell types that bind annexin V. Our data have shown that there is a shift in the proportion of annexin V2binding cells from predominately neurons at 24 h to microglial cells 7 d after a stroke.…”

Acutely and Retrospectively Diagnosed Perinatal Stroke

“…Studies on animal models of neonatal stroke have shown that after large unilateral neonatal hypoxic brain injury, apoptotic processes are present in both hemispheres. 26 No difference in side of brain damage was observed between children with early or delayed diagnosis of perinatal stroke.…”

In Vivo Detection of Apoptosis

“…Although annexin V is a relatively large protein (about half the molecular weight of albumin), it was shown early on that the protein can be internalized at sites of ischemic injury both in the heart and in the brain and cross the intact blood-brain barrier (39). The transport of exogenously administered annexin V, a protein normally found almost exclusively within cells, also must occur across a protein gradient, suggesting the existence of an energydependent pump mechanism.…”