Journal of Lipid Research, Vol. 20, 614-623, July 1979
Copyright © 1979 by Lipid Research, Inc.

Very low density lipoprotein. Fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis in vitro

Shlomo Eisenberg and Thomas Olivecrona

Lipid Research Laboratory, Department of Medicine B, Hadassah University Hospital, Jerusalem, Israel, and Department of Medical Chemistry, University of Umea, Sweden

In this study we have determined the fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis of rat plasma very low density lipoprotein (rat VLDL). The experiment was carried out in vitro with lipoprotein lipase purified from bovine milk, VLDL labeled with [¹⁴C]palmitate, [³H]cholesterol, [³²P]phospholipids, and ¹²⁵I-labeled apolipoprotein C and in plasma-devoid systems. Triglyceride hydrolysis ranged between 0 and 98.6%. [³²P]Phospholipids, unesterified [³H]cholesterol, and ¹²⁵I-labeled apolipoprotein C were removed from the VLDL (d < 1.019 g/ml) during lipolysis. About one-third of the [³²P]phosphatidylcholine was hydrolyzed to lysolecithin, and was transferred to the fraction d > 1.21 g/ml. The other two-thirds of the phospholipids were removed unhydrolyzed, mainly to the fraction d 1.04-1.21 g/ml. With the progression of the lipolysis, unesterified [³H]cholesterol was removed from VLDL at increasing rates, predominantly to the fraction d 1.04-1.21 g/ml. ¹²⁵I-Labeled apolipoprotein C removed from the VLDL partitioned between the fraction of d 1.04-1.21 g/ml and d > 1.21 g/ml. Negative-staining electron microscopy of the fraction d 1.04-1.21 g/ml (containing phospholipids, unesterified cholesterol, and apolipoprotein C) revealed many discoidal lipoproteins. [³H]Cholesteryl esters remained associated with the VLDL even when 70-80% of the triglycerides were hydrolyzed. These observations suggest that during in vitro lipolysis of VLDL, surface constituents leave the lipoprotein concomitantly with the hydrolysis of core triglycerides. The process of removal of surface constituents is independent of the presence of an acceptor lipoprotein and may occur in the form of a surface-fragment particle. —Eisenberg, S., and T. Olivecrona. Very low density lipoprotein. Fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis in vitro.

Supplementary key words lipoprotein lipase • triglyceride hydrolysis • [³²P]phospholipids • [³H]cholesterol • ¹²⁵I-labeled apolipoprotein C • low density lipoprotein • high density lipoprotein

Submitted on August 22, 1978
Revised on December 4, 1978
Accepted on March 15, 1979

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