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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:1032-1038.)
© 1997 American Heart Association, Inc.

Articles

Organ Loci of Catabolism of Short Truncations of ApoB

Xian-Feng Zhu; Davide Noto; Rick Seip; Aviv Shaish; ; Gustav Schonfeld

From the Division of Atherosclerosis, Nutrition, and Lipid Research, Washington University School of Medicine, St Louis, Mo (X.F.Z., A.S., G.S.); Cattedra Di Patologia Speciale Medica, E Matodiolgia Clinica, Istituto di Patologia Medica II, Universita di Palermo, Italy (D.N.); and the Human Performance Lab, University of Nebraska, Kearney (R.S.).

Correspondence to Xien-Feng Zhu, Division of Atherosclerosis, Nutrition, and Lipid Research, Washington University School of Medicine, 660 S. Euclid Ave, St. Louis, MO 63110.

Abstract Truncations of apolipoprotein (apo) B shorter than 3200 amino acids (3200/4536=apoB-70) do not possess the LDL receptor–recognition domain and are not recognized by altered cells with normally functioning LDL receptors. To ascertain which organs remove such truncated apoB–containing particles, we isolated apoB-31–, apoB-38.9–, and apoB-43.7–containing particles from plasmas of familial hypobetalipoproteinemia heterozygous humans by a combination of sequential ultracentrifugation and preparative electrophoresis. Particles with labeled ¹²⁵I- or ¹³¹I-dilactitol tyramine (I-DLT), were injected into New Zealand White rabbits, along with I-DLT–apoB-100–containing LDLs, and the decay of ¹²⁵I- and ¹³¹I-TCA–precipitated counts was followed over 24 hours. At the end of 24 hours, rabbits were anesthetized and their bodies perfused. Organs were removed and homogenized, and TCA-precipitable counts determined. Fractional catabolic rates of apoB truncation particles were two to five times greater than those of apoB-100 LDLs. ApoB truncations accumulated in adrenals at one fifth the rates of apoB-100 LDL, compatible with the functional absences of LDL receptor–recognition domains in truncated apoBs. The major organ of uptake for apoB-100-LDLs was the liver, whereas truncation particles were readily removed by the kidney (kidney: liver uptake ratios were 0.10 to 0.30 for apoB-100 LDLs and 1.03 to 3.77 for truncations). Spleens accumulated little of either apoB-100 or truncation particles, suggesting particles were not "damaged" or aggregated. Thus, the absence of >56% of the carboxyl end of apoB-100 increases the plasma clearance and redirects the organ uptake of the apoB truncation–containing lipoproteins from liver to kidney.

Key Words: lipoproteins • apoB • apoB truncations • dilactitol tyramine

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