Binding of vascular anticoagulant alpha (annexin V) to the aortic intima of the hypercholesterolemic rabbit. An autoradiographic study.

Qualitative ultrastructural autoradiography was used to study the binding of the vascular anticoagulant alpha (annexin V) to normal and atherosclerotic (AS) rabbit aortic intima. Recombinant annexin V was labelled with 125I by the Iodogen method. Rabbits were fed a hypercholesterolemic (HC) diet up to 10 months. After laparotomy and exsanguination, the aortae were perfused with dilutions of 125I-annexin V (I-AV) for 10-15 min, either on ice or at 22 degrees C and then perfusion-fixed with aldehydes. Fragments of the labelled aortae were used for en face contact autoradiography, followed by Sudan Black staining of intimal lipid. Specimens were also included in Epon and sectioned for light- and electron-microscopic autoradiography. The binding of I-AV was increased on the AS aortae as compared with the normal ones, with an apparent preference for the lesioned areas. Microscopically, I-AV was found at the luminal front of aortic intima, on endothelial cells (EC), on macrophage foam cells, and on their disrupted remnants. The presence of the AV binding sites (reportedly known to interact with high affinity with phosphatidylserine) in the rabbit AS aortic intima, together with other known procoagulant conditions, may contribute to the initiation of coagulation events into the lesioned vascular wall, and may offer a rationale for the use of annexin V as an anticoagulant drug.