Indium-111-labeled low-density lipoprotein binds with higher affinity to the human liver as compared to iodine-123-low-density-labeled lipoprotein.
The interaction of 111In-low-density lipoprotein (LDL) and 123I-LDL with human liver-plasma membranes was investigated and compared. LDLs were isolated by sequential ultracentrifugation and radiolabeled either with 123I (using lodogen or iodine-monochloride) each followed by purification with gel-chromatography or dialysis) or 111In (using cyclic DTPA-anhydride). LDL concentrations of 0.1 to 32 micrograms protein/ml were used for direct binding assays investigating the specific binding of labeled LDL (in the presence of a 50-fold excess of unlabeled LDL) to human liver apoB-receptors. In separate experiments, displacement of bound 111In-(123I)-LDL by unlabeled LDL was studied. Human liver plasma membranes bound 239 +/- 26 ng protein of 111In-LDL/mg protein and 148 +/- 18 ng protein of 123I-LDL/mg protein specifically (p less than 0.001). The corresponding dissociation constants were 0.6 +/- 0.2 and 1.2 +/- 0.7 micrograms protein/ml, respectively (p less than 0.001). The capacity of unlabeled LDL to displace bound 111In-LDL was four times higher than that for 123I-LDL (IC50: 1.7 +/- 0.7 versus 7.7 +/- 1.0 micrograms protein/ml). No significant differences among the different methods of iodination of LDL were found. The findings show that 111In-labeled lipoproteins might be a better ligand for lipoprotein-receptor binding studies as compared to radioiodinated lipoprotein products.
Wilhelm Auerswald Atherosclerosis Research Group (ASF), Vienna, Austria.
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I
Virgolini
P
P
Angelberger
S R
SR
Li
F
F
Koller
E
E
Koller
J
J
Pidlich
G
G
Lupattelli
H
H
Sinzinger
D000328:Adult; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008077:Lipoproteins, LDL; D008099:Liver / Q000737:chemistry* / Q000000981:diagnostic imaging; D008297:Male; D011869:Radioligand Assay; D011877:Radionuclide Imaging; D011973:Receptors, LDL / Q000378:metabolism
D007457:Iodine Radioisotopes; D008077:Lipoproteins, LDL; D011973:Receptors, LDL