IMMUNOSPECIFIC SCINTILLATION PROXIMITY ASSAY OF CHOLESTERYL ESTER TRANSFER PROTEIN-ACTIVITY

We describe a novel, immunospecific scintillation proximity assay for determining cholesteryl ester transfer protein (CETP) activity in tota l human serum and in reconstituted experimental mixtures. The assay is based on the measurement of radiolabeled cholesteryl esters transferr ed from a tracer dose of biosynthetically labeled high-density lipopro tein subfraction 3 to unlabeled apolipoprotein (ape) B-containing lipo proteins. The radioactivity content of the apo B-containing lipoprotei n fraction can be evaluated without separating the donor from the acce ptor lipoprotein substrates, and is measured through the formation of ternary complexes involving the radiolabeled apo B-containing lipoprot eins, specific antiapo B antibodies from sheep, and anti-sheep antibod y-labeled fluoromicrospheres. Good correspondences were observed betwe en CETP activity values obtained either with the ultracentrifugation m ethod or the immunospecific scintillation proximity assay (n = 70; r = 0.94; P = 0.0001), and between values obtained for either fresh or fr ozen serum samples (n = 70; r = 0.93; P = 0.0001). Because of its pote ntial for automation, the immunospecific scintillation proximity assay may constitute a convenient tool to measure serum CETP activity in th e clinical laboratory.