Free fatty acids activate a high-affinity saturable pathway for degradation of low-density lipoproteins in fibroblasts from a subject homozygous for familial hypercholesterolemia

Biochemistry. 1992 May 19;31(19):4628-36. doi: 10.1021/bi00134a013.


This paper describes a mechanism for degradation of low-density lipoprotein (LDL) in fibroblasts unable to synthesize the LDL receptor. In this cell line, long-chain free fatty acids (FFA) activated 125I-LDL uptake; unsaturated FFA were the most efficient. The first step of this pathway was the binding of LDL apoB to a single class of sites on the plasma membrane and was reversible in the presence of greater than or equal to 10 mM suramin. Binding equilibrium was achieved after a 60-90-min incubation at 37 degrees C with 1 mM oleate; under these conditions, the apparent Kd for 125I-LDL binding was 12.3 micrograms/mL. Both cholesterol-rich (LDL and beta-VLDL) and triglyceride-rich (VLDL) lipoproteins, but not apoE-free HDL, efficiently competed with 125I-LDL for this FFA-induced binding site. After LDL bound to the cell surface, they were internalized and delivered to lysosomes; chloroquine inhibited subsequent proteolysis of LDL and thereby increased the cellular content of the particles. A physiological oleate to albumin molar ratio, i.e., 1:1 (25 microM oleate and 2 mg/mL albumin), was sufficient to significantly (p less than 0.01) activate all three steps of this alternate pathway: for example, 644 +/- 217 (25 microM oleate) versus 33 +/- 57 (no oleate) ng of LDL/mg of cell protein was degraded after incubation (2 h, 37 degrees C) with 50 micrograms/mL 125I-LDL. We speculate that this pathway could contribute to the clearance of both chylomicron remnants and LDL.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Albumins / pharmacology
  • Animals
  • Apolipoproteins B / chemistry
  • Binding, Competitive
  • Cell Line
  • Cold Temperature
  • Fatty Acids, Nonesterified / pharmacology*
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism*
  • Homozygote*
  • Humans
  • Hyperlipoproteinemia Type II / genetics
  • Hyperlipoproteinemia Type II / metabolism*
  • Iodine Radioisotopes
  • Kinetics
  • Lipoproteins, LDL / chemistry
  • Lipoproteins, LDL / drug effects
  • Lipoproteins, LDL / metabolism*
  • Oleic Acid
  • Oleic Acids / pharmacology
  • Protein Binding
  • Rabbits
  • Receptors, LDL / drug effects
  • Suramin / metabolism


  • Albumins
  • Apolipoproteins B
  • Fatty Acids, Nonesterified
  • Iodine Radioisotopes
  • Lipoproteins, LDL
  • Oleic Acids
  • Receptors, LDL
  • Oleic Acid
  • Suramin