Journal of Lipid Research, Vol. 12, 545-552, September 1971
Copyright © 1971 by Lipid Research, Inc.

Utilization of free fatty acids complexed to human plasma lipoproteins by mammalian cell suspensions

Arthur A. Spector and Janice M. Soboroff

Departments of Internal Medicine and Biochemistry, and The Clinical Research Center, University of Iowa, Iowa City, Iowa 52240

The purpose of this study was to determine whether lipoprotein-bound free fatty acid could be utilized by isolated mammalian cells. Ehrlich ascites tumor cells were incubated in vitro with radioactive free fatty acids that were bound to human plasma lipoproteins. Under these conditions, lipoprotein-bound free fatty acids were readily taken up by the cells. After 2 min of incubation with free fatty acids bound to low density lipoproteins, most of the radioactivity that was associated with the cells was in the form of free fatty acids. As the incubation continued, increasing amounts of radioactivity were incorporated into CO₂ and cell lipids, particularly phospholipids. Most of the free fatty acid uptake was the result of fatty acid transfer from low density lipoproteins to the cell, not from irreversible incorporation of the intact free fatty acid-low density lipoprotein complex. Fatty acid uptake increased as the ratio of free fatty acid to low density lipoprotein was raised. When albumin was added to the medium, free fatty acid uptake decreased. A large percentage of the newly incorporated cellular radioactivity was released into the medium if the cells were exposed subsequently to a solution containing albumin. Most of the released radioactivity was in the form of free fatty acid. The results with this experimental model suggest that lipoprotein-bound free fatty acid, like albumin-bound free fatty acid, is readily available for uptake by isolated cells. The mechanism of free fatty acid utilization by the Ehrlich cell is similar when either low density lipoprotein or serum albumin serves as the fatty acid carrier.

Supplementary key words Ehrlich ascites cells • transport • uptake • serum albumin • oxidation • esterification • release

Submitted on March 4, 1971
Accepted on May 20, 1971

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