PLASMA FACTORS AFFECTING THE IN-VITRO CONVERSION OF HIGH-DENSITY-LIPOPROTEINS LABELED WITH A NONTRANSFERABLE MARKER

We studied the in vitro conversion of HDL(3) labeled with a radioiodinated diacyl lipid associating peptide (diLAP). DiLAP was previously shown to be nontransferable, which permitted its' use as a reliable marker of HDL particles. DiLAP-labeled HDL, was incubated for 23 h at 37 degrees C in human or rat plasma or in reconstituted media containing delipidated plasma and/or lipoproteins and/or partially purified CETP. At the end of the incubations, the samples were adjusted to a density of 1.125 g/ml and ultracentrifuged. The two resulting fractions containing HDL(2) and HDL(3), respectively, were analyzed by gradient gel electrophoresis. Depending upon experimental conditions, diLAP-labeled HDL(3) was converted into HDL(2b)- and/or small HDL(3c)-like particles. LCAT inhibition and to a lesser extent CETP promoted the formation of small HDL(3c). Reactivation of LCAT led to the disappearance of small HDL(3c). No HDL(3c) formed from HDL(2) even in the absence of LCAT activity. When the incubations were performed in the presence of 100 mM thimerosal, which inhibited PLTP but not CETP activity, the conversion of diLAP-labeled HDL(3) into HDL(2) was almost completely blocked. Collective consideration of these data indicates that the formation of small HDL is moderately facilitated by CETP; that small HDL are converted to larger HDL species by LCAT and that the transformation of HDL(3) into HDL(2) is a process which largely depends upon PLTP activity.