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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:1630-1636.)
© 1997 American Heart Association, Inc.

Articles

Role of Free Apolipoprotein A-I in Cholesterol Efflux

Formation of Pre–-Migrating High-Density Lipoprotein Particles

Bela Asztalos; Wenwu Zhang; Paul S. Roheim; ; Laurence Wong

From the Division of Lipoprotein Metabolism and Pathophysiology, Department of Physiology, Louisiana State University Medical Center, New Orleans, La.

Correspondence to Laurence Wong, Division of Lipoprotein Metabolism and Pathophysiology, Department of Physiology, Louisiana State University Medical Center, New Orleans, LA 70112.

Abstract This article characterizes products formed by the interaction of purified apolipoprotein (apo) A-I and human fibroblasts. Fibroblasts were incubated with different concentrations of purified apoA-I (1 to 30 µg/mL) in tissue culture medium for different periods of time (0 to 24 hours). The medium was then characterized by one- (agarose) and two-dimensional (agarose : polyacrylamide nondenaturing gradient gel) electrophoresis. At any given concentration of apoA-I, the rate of cellular cholesterol efflux appeared linear over 24 hours. Incubating purified apoA-I with fibroblasts for 4 hours, we detected five pre- lipoproteins with particle sizes between 114 and 684 kDa. Formation of pre- lipoproteins was concentration-dependent. At low concentrations (below 5 µg/mL apoA-I), all purified apoA-I (with pre-ß mobility) was converted to pre- lipoproteins. At higher concentrations (greater than 5 µg/mL apoA-I), more apoA-I remained with pre-ß mobility. The pre- lipoproteins were characterized by colocalization of apoA-I particles with ¹⁴C-cholesterol and ³²P-phospholipids. Results showed that the pre- particle of lowest molecular weight contained phospholipid and apoA-I but no cholesterol. The remaining pre- particles contained all three substances. When pre- particles were subjected to ultracentrifugation, all particles floated at d<1.21 g/mL with some of the smallest phospholipid apoA-I only particles being present in the d>1.21 g/mL fraction. Based on these results, we postulated that in the first stages of reverse cholesterol transport, pre- lipoproteins are formed by the interaction of lipid free apoA-I and peripheral cells.

Key Words: high-density lipoproteins • pre- lipoproteins • pre-ß lipoproteins • cholesterol efflux • fibroblasts • cholesterol • two-dimensional electrophoresis • apolipoprotein A-I • phospholipids

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