High density lipoprotein interconversions in rat and man as assessed with a novel nontransferable apolipopeptide

A nontransferable peptide analog of a plasma apolipoprotein diacyl lipid-associating peptide (diLAP) incorporates into model reassembled high density lipoproteins (R-HDL). In whole plasma in vitro, diLAP irreversibly transfers to native rat HDL2 and human HDL3, but not to rat HDL1 or human HDL2. The rate of transfer is dependent on the physical state of the lipid in the R-HDL. Exogenous cholesterol promotes the formation of larger HDL. When diLAP-labeled R-HDL were injected into rats, the diLAP that initially associated with HDL2 transferred to HDL1 over a period of 48 h. The rate of clearance of diLAP-labeled HDL was slower than that of apoA-I. The liver was the preferred site for diLAP-labeled HDL1 uptake. In contrast, diLAP-labeled HDL2 were associated with liver, ovaries, and adrenal glands, with the adrenal grands exhibiting the highest specific association. DiLAP was not found in the kidneys. These data show that 1) rat HDL is cleared more slowly than rat apoA-I; 2) HDL is removed from the plasma compartment as a particle; 3) there are tissue-specific differences in the removal of rat HDL1 and HDL2; 4) HDL2 is a precursor to HDL1; and 5) cholesterol and the activity of lecithin:cholesterol acyltransferase are essential to HDL remodeling.