Cholesterol-derivatized galactosides have been devised in order to induce liver uptake of lipoproteins via the galactose-recognizing asialoglycoprotein receptor in the liver. In this study we describe the derivatization of a newly developed triantennary cluster galactoside having high affinity for the asialoglycoprotein receptor, N-[[tris-O-(3,6,9-trioxaundecanyl-beta-D-galactopyranosyl)methoxymethyl]methyl]-N-alpha-[1-(6-methyladipyl)]glycinamide (TG(20 Angstrom)) with cholesterol. Hereto, TG(20 Angstrom) was coupled to glycine-(5-cholesten-3 beta-yl ester) in the presence of (benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate, affording, N-[[tris-O-(3,6,9-trioxaundecanyl-beta-D-galactopyranosyl)methoxymethyl]methyl]N-alpha-[1-(6-5-cholesten-3 beta-yloxy)glycyl)adipyl]glycinamide (TG(20 Angstrom)C) in 46% yield. This compound is an amphiphilic, water-soluble compound. In aqueous solution it readily formed small micelles (4.9 +/- 1.2 nm) consisting of approximately 20 molecules. Upon incubation with human serum, TG(20 Angstrom)C spontaneously incorporated into the most prominent serum lipoproteins, i.e., low-density lipoprotein (LDL) and high-density lipoprotein (HDL), thereby inducing an increase in buoyant density of these lipoproteins. The integrity of HDL and LDL, as judged from particle size analysis of both lipoproteins, was not altered by incubation with up to 0.33% of TG(20 Angstrom)C (w/v). Following intravenous bolus injection into rats, TG(20 Angstrom)C induced a dose-de],endent decrease in the serum cholesterol content of maximally 44%, at a dose of 1.9 mg kg(-1). This makes TG(20 Angstrom)C at least 30-fold more effective than the previously developed N-[[tris-O-(beta-D-galactopyranosyl)methyl]methyl]-N-alpha-[4-(5-cholesten-3 beta-yloxy)succinyl]glycinamide (TG(4 Angstrom)C, provided with a cluster galactoside that displayed a 2000-fold lower affinity for the asialoglycoprotein receptor than TG(20 Angstrom). In conclusion, the hypocholesterolemic activity of a cholesterylated galactoside can be strongly enhanced by using a cluster galactoside with higher affinity for the asialoglycoprotein receptor.
