Ternary complex formation of lanthanides and radiolanthanides with phosphate and serum proteins

Radioyttrium was recently reported to form ternary complexes with phosphate and serum proteins in blood. In the present work it was investigated wheth er the trivalent radiolanthanides react in a chemically similar way. In sys tematic binding studies using gel filtration a ternary complex formation be tween different lanthanides, phosphate and serum proteins could be identifi ed. The tendency to build a ternary compound of the type Ln((III)) - phosph ate - serum protein, however, is dependent on the ionic radii of the lantha nides. Whereas the light and transition lanthanides have a strong inclinati on to build a ternary complex, this tendency is weaker for the heavier ones . Taking into account the high content of phosphate in human blood, the corre sponding ternary complexes of radiolanthanides represent an important trans port form of these elements in blood. This finding may contribute to an und erstanding of the nuclear medical observation on the biodistribution of rad iolanthanides. The heavy radiolanthanides can be classified as bone seeking metals, whereas the light and transition lanthanide elements accumulate ma inly in the liver and the spleen. For the lighter radiolanthanides the corr esponding ternary complexes thus represent an important transport form in b lood. This physicochemical form of lanthanides mainly results in reticulo e ndothelial accumulation; on the other hand, the lower tendency of heavier l anthanides leads to preferential skeletal deposition.