Intravenous heparinase inhibits remnant lipoprotein clearance from the plasma and uptake by the liver: in vivo role of heparan sulfate proteoglycans.

Abstract

Heparan sulfate proteoglycans (HSPG) are involved in the binding and uptake of apolipoprotein (apo) E-enriched remnant lipoproteins by cultured cells in vitro. To define the role of hepatic HSPG in remnant lipoprotein clearance in vivo, heparinase (30 units) was infused intravenously into mice to hydrolyze the liver HSPG and determine the effect of HSPG hydrolysis on remnant clearance by the liver. Liver HSPG were prelabeled by peritoneal injection of [35S]Na2SO4. Injection of heparinase decreased the amount of 35S-labeled liver HSPG by approximately 20-40% within 10-15 min. Heparinase infusion significantly inhibited the clearance of chylomicrons, chylomicron remnants, chylomicron remnants + apoE, rabbit beta-very low density lipoproteins (beta-VLDL), and beta-VLDL + apoE. Compared with saline injection in control mice, heparinase injection retarded the plasma clearance of the remnants by 1.5- to 2-fold and decreased liver uptake by 1.3- to 1.6-fold. Confocal fluorescence microscopy of thick slices of liver from mice injected with 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine-labeled beta-VLDL + apoE revealed markedly less intense fluorescence from hepatocytes in heparinase-treated animals compared with those in saline-treated control animals. Intravenous heparinase infusion did not inhibit the clearance of mouse low density lipoproteins (LDL), a ligand for the LDL receptor, and did not affect the clearance of alpha 2-macroglobulin, a ligand for the LDL receptor-related protein. The results suggest an important role of the liver HSPG in remnant clearance in vivo.