Platelets have been labeled with a new neutral, lipid-soluble metal complex of indium 111 (111In) and tropolone. Unlike oxine, which is soluble in ethyl alcohol, tropolone is soluble in isotonic saline. Platelet labeling with 111In tropolone can be performed in both acid-citrate-dextrose (ACD) plasma and ACD saline within two hours. Labeling efficiency has been 80% to 90%. 111In tropolone in ACD saline and ACD plasma at tropolone concentrations of 5 and 10 micrograms/ml, respectively, and incubation of the platelets with the tracer at room temperature for 20 minutes were optimal conditions for labeling. The authors have developed an ACD-saline kit for convenient preparation of 111In-labeled platelets. No adverse effect of 111In tropolone on platelets has been observed in studies of biodistribution, recovery, and survival of platelets in rabbits and dogs.

Platelets have been labeled with a new, neutral, lipidsoluble metal-complex of Indium-111-tropolone (In-TPL). Unlike oxine, tropolone is soluble in isotonic saline. Oil/saline partition of In-111-oxine and In-TPL are 0.5 and 23.7 respectively. Platelet labeling with In-TPL was performed in both ACD-plasma and ACD-saline media within two hours' time. Increasing concentration of tropolone, citrate ion, and plasma proteins decreases plateletlabeling efficiency. Effects of pH, temperature, platelet concentration, and calcium ion concentration on platelet labeling were studied. In optimum platelet-labeling conditions, canine, rabbit, porcine, and human platelets have been labeled with a consistent labeling efficiency of 80-90%. The optimum labeling conditions are In-TPL in ACD- saline and ACD-plasma at tropolone concentration of 5 and 10 μg/ml respectively and 30 minutes’ incubation of platelets with the tracer at room temperature. A kit formulation for convenient routine preparation of In-111-labeled platelets has been developed. The function of the In-TPL- labeled platelets has been studied by their aggregability with adenosine diphosphate. The capacity of In-111-labeled platelets to aggregate in vitro does not correlate well with their ability to circulate in vivo. No adverse effect of In-TPL on platelets has been observed by studies of biodistribution, recovery, and platelet survival in dogs. Comparable mean platelet survival times of four repeated studies in five dogs were obtained in both ACD-saline and ACD-plasma. These results indicate that Indium-111 platelets labeled by tropolone carrier may be preferable to oxine carrier for studies of platelet survival, imaging sites of endothelial damage, and thrombus formation.

No abstract