The cyanogen bromide fragment I of asialoorosomucoid is transported more efficiently than asialoorosomucoid in rat hepatocytes

Cell Specificity of Macromolecular Assembly of Cholesteryl and Galactoside Groups-Conjugated Pullulan

Galactose or lactose groups were conjugated to cholesterol-bearing pullulan (CHP). The CHP derivatives obtained formed monodisperse nanoparticles upon self-aggregation in water. Nanoparticles of galactoside-conjugated CHP self-aggregates were specifically internalized by rat hepatocytes and HepG2 cells. Galactoside-bearing CHP-coated liposome or oil droplet of O/W-emulsion was also taken up by HepG2 cells. Tissue distribution of the nanoparticle CHP self-aggregates changed dramatically with chemical conjugation of the galactose moiety. Galactoside-bearing nanoparticles were specifically accumulated in the liver.

Effect of rate of intracellular transport and diacytosis on cytotoxicity of hybrid toxins. Study with hybrids using hepatic asialoglycoprotein receptor-mediated endocytosis

The effects of diacytosis and intracellular transport rate on cytotoxicity of hybrid toxins were studied with conjugates of diphtheria toxin fragment A (DTA) to asialoorosomucoid (ASOR) and its reduced and carboxymethylated cyanogen bromide fragment I (RC-ASCNBr-I) in cultured rat hepatocytes. In the hepatocytes the kinetics of uptake of the conjugate of asialoorosomucoid (DTA-ASOR) and that of the conjugate of the cyanogen bromide fragment (DTA-RC-ASCNBr-I) were quite similar, but the rate of accumulation of DTA moiety into the lysosomes, as determined by Percoll density gradient centrifugation, was found to be greater for the latter than the former. However, after internalization, DTA-RC-ASCNBr-I was diacytosed to a lesser extent than that of DTA-ASOR, particularly when colchicine was present during internalization. Analysis of the subunits of DTA-ASOR internalized by the hepatocytes indicated that they were accumulated disproportionately in a time-dependent manner so that the glycoprotein moiety was accumulated progressively more than the toxin moiety. Cytotoxicity of DTA-ASOR toward the hepatocytes was 2-times as much as that of DTA-RC-ASCNBr-I. Colchicine enhanced the toxicity of DTA-RC-ASCNBr-I (33-fold) to a greater extent than that of DTA-ASOR (12-fold). The difference in enhancement by colchicine was also observed in the rate of cell intoxication by the conjugates. Both conjugates were more toxic to the hepatocytes after incubation with the cells at 18 degrees C than at 37 degrees C. In the presence of vanadate (0.2 mM), which enhanced diacytosis, toxicity of DTA-ASOR decreased by 5-fold. After incubation with the hepatocytes, a partial dissociation of DTA-ASOR was found to occur independently of the receptor-mediated endocytosis. Taken together, these results indicate that diacytosis, subunit dissociation and rapid transport of conjugate toward lysosomes affect kinetically the rate of accumulation of the conjugate into a yet unidentified compartment of toxin translocation.

Diacytosis of asialoglycoprotein in isolated hepatocytes is dependent on the structure of ligand and cellular distribution of the receptors

Diacytosis, degradation and retention of 125I-labeled asialoorosomucoid (ASOR), its reduced and carboxymethylated N-terminal cyanogen bromide-cleaved fragment (RC-ASCNBr-I) and asialofetuin preloaded into isolated rat or rabbit hepatocytes for various periods of time were compared. In rat hepatocytes preloaded with a saturating concentration (3.10(-8) M) of the ligands, the proportion of the preloaded ligands distributed to degradation and diacytosis was fairly constant during 4 h of preincubation. In addition, a small portion of the preloaded ligands was neither diacytosed nor degraded, but was retained intracellularly. Diacytosis of 125I-ASOR (29%) was greater than that of either 125I-RC-ASCNBr-I (23%) or 125I-asialofetuin (15%). Diacytosis of 125I-ASOR, when preloaded in the presence of 5 microM colchicine, was significantly enhanced by 79% (increasing from 29% to 52%), whereas those of 125I-RC-ASCNBr-I and 125I-asialofetuin were not significantly altered (with average increases of 14% and 19%, respectively). The fraction of the preloaded 125I-asialofetuin (69%) and 125I-RC-ASCNBr-I (68.6%) that was degraded was slightly higher than that of 125I-ASOR (64%) and all was decreased by colchicine. The fraction of all three ligands retained by the cells was increased 2- to 4-fold by colchicine. The extents of retention of 125I-asialofetuin and 125I-ASCNBr-I were greater than that of 125I-ASOR, particularly after preloaded for more than 2 h. Preloading of the cells with ligands at a non-saturating concentration (6.5.10(-10) M) did not change these patterns of ligand distribution. Conjugation of diphtheria toxin fragment A (DTA) to ASOR or RC-ASCNBr-I also did not significantly alter the pattern of ligand distribution. In rabbit hepatocytes containing more asialoglycoprotein receptors than rat cells, 125I-ASOR was diacytosed to a greater extent (50%, -colchicine; 61%, + cholchicine) but degraded to a lesser extent (33%, -colchicine; 13%, + colchicine) than was observed in rat cells. The extent of retention of 125I-ASOR in rabbit cells was also greater than that in rat cells. A similar pattern of differences between rabbit and rat hepatocytes was observed for 125I-DTA-ASOR. These results indicate that intracellular sorting of internalized asialglycoproteins between diacytosis and degradation is dependent on both the structure of the ligand and the distribution of the cellular receptors.