¹¹¹Indium is an unreliable in vivo label for vascular endothelial cells

Abstract

We studied the retention of ¹¹¹Indium-labeled canine endothelial cells on 32 grafts (16 dogs). Canine endothelial cells were harvested from the external jugular veins, grown in culture, and labeled with¹¹¹Indium oxine; 10⁶ factor VIII positive cells were inoculated on fibronectin-coated, 4 mmlD Hytrel grafts and cultured 18 hours to reach confluence. An autologous seeded graft was interposed in each of the common carotid arteries and exposed to flow for six hours.¹¹¹Indium label was measured pre- and postperfusion and corrected for decay. Twenty-five grafts from 13 dogs were available for study. Scanning electron microscopic planimetry was used to determine percent surface coverage by six mutually exclusive surface characteristics: endothelial cells, bare graft, white blood cells on graft, white blood cellson endothelium, white blood cells under endothelium, and thrombus. ¹¹¹Indium retention was compared with percent coverage by scanning electron microscopy using regression analysis.¹¹¹Indium labeling projected an erroneous retention of 41% at zero percent coverage (r=0.67; p<0.01). Multiple regression analysis revealed an equivalent distribution of¹¹¹Indium label over nonendothelial portions of the flow surface and indicated a leak rate into the circulation of 25.6% of the initial¹¹¹Indium label over six hours. We conclude that: 1)¹¹¹Indium labeling data usually overestimates endothelial cell retention; 2) an average of 4.67%/hour is lost into the general circulation; 3)¹¹¹Indium label can be found equally on surfaces of thrombus, white blood cells, and hydrophilic Hytrel graft; and 4)¹¹¹Indium labeling is not a reliable method forin vivo studies of endothelial cell retention.