Stimulation of liver-directed cholesterol flux in mice by novel N-acetylgalactosamine-terminated glycolipids with high affinity for the asialoglycoprotein receptor

Abstract

Objective - Interventions that promote liver-directed cholesterol flux can suppress atherosclerosis, as demonstrated for scavenger receptor-BI overexpression in hypercholesterolemic mice. In analogy, we speculate that increasing lipoprotein flux to the liver via the asialoglycoprotein receptor (ASGPr) may be of therapeutic value in hypercholesterolemia. Methods and Results - A bifunctional glycolipid (LCO-Tyr-GalNAc3) with a high-nanomolar affinity for the ASGPr (inhibition constant 2.1±0.2 nmol/L) was synthesized that showed rapid association with lipoproteins on incubation with serum. Prior incubation of LCO-Tyr-GalNAc3 with radiolabeled low-density lipoprotein or high-density lipoprotein (0.5 μg/μg of protein) resulted in a dramatic induction of the liver uptake of these lipoproteins when injected intravenously into mice (70±3% and 78±1%, respectively, of the injected dose at 10 minutes of low-density lipoprotein and high-density lipoprotein), as mediated by the ASGPr on hepatocytes. Intravenously injected LCO-Tyr-GalNAc3 quantitatively incorporated into serum lipoproteins and evoked a strong and persistent (≥48 hour) cholesterol-lowering effect in normolipidemic mice (37±2% at 6 hours) and hyperlipidemic apoE -/- mice (32±2% at 6 hours). The glycolipid was also effective on subcutaneous administration. Conclusions - LCO-Tyr-GalNAc3 is very effective in promoting cholesterol uptake by hepatocytes and, thus, may be a promising alternative for the treatment of those hyperlipidemic patients who do not respond sufficiently to conventional cholesterol-lowering therapies. © 2005 American Heart Association, Inc.