Studies on the uptake of low molecular weight monomeric tris-galactosyl conjugates by the rat liver

The honeybee (Apis mellifera) developmental state shapes the genetic composition of the deformed wing virus-A quasispecies during serial transmission

The main biological threat to the western honeybee (Apis mellifera) is the parasitic mite Varroa destructor, largely because it vectors lethal epidemics of honeybee viruses that, in the absence of this mite, are relatively innocuous. The severe pathology is a direct consequence of excessive virus titres caused by this novel transmission route. However, little is known about how the virus adapts genetically during transmission and whether this influences the pathology. Here, we show that upon injection into honeybee pupae, the deformed wing virus type-A (DWV-A) quasispecies undergoes a rapid, extensive expansion of its sequence space, followed by strong negative selection towards a uniform, common shape by the time the pupae have completed their development, with no difference between symptomatic and asymptomatic adults in either DWV titre or genetic composition. This suggests that the physiological and molecular environment during pupal development has a strong, conservative influence on shaping the DWV-A quasispecies in emerging adults. There was furthermore no evidence of any progressive adaptation of the DWV-A quasispecies to serial intra-abdominal injection, simulating mite transmission, despite the generation of ample variation immediately following each transmission, suggesting that the virus either had already adapted to transmission by injection, or was unaffected by it.

Tissue distribution and metabolism of the [32P]-labeled oligodeoxynucleoside methylphosphonate-neoglycopeptide conjugate, [YEE(ah-GalNAc)3]-SMCC-AET-pUmpT7, in the mouse

Development of oligodeoxynucleotides (oligo-dNs) and their analogs as therapeutic agents is complicated by their low rate of transport across cellular membranes, which is required for interaction with the intracellular complementary nucleic acid sequences, and the lack of tissue-specific delivery. To overcome these obstacles, bioconjugates between cell surface receptor ligands and oligodeoxynucleoside methylphosphonates (oligo-MPs) have been constructed containing homogeneous, chemically defined covalent linkages. We have previously established that a model conjugate, [32P]-labeled [YEE(ah-GalNAc)3]-SMCC-AET-pUmpT7 (1), is delivered to Hep G2 cells in a ligand-specific manner, reaching a peak value of 26 pmol per 10(6) cells after 24 hours incubation at 37 degrees C (Hangeland et al., 1995). In this work, the in vivo behavior of this conjugate is explored. Administration of this conjugate to mice via tail vein injection demonstrates rapid uptake in liver to the extent of 69.9 +/- 9.9% of the injected dose after 15 minutes. Thereafter, the conjugate and its metabolites are rapidly cleared via the kidney and urine. Polyacrylamide gel electrophoresis analysis of extracts of Hep G2 cells and mouse liver reveal the conjugate 1 to be extensively metabolized. In contrast, the conjugate found in mouse urine is largely intact. These data show that this novel, biodegradable delivery vehicle represents a viable approach for the delivery of antisense oligo-MPs and other oligo-dN analogs to the liver for therapeutic and diagnostic applications.

Cholesterol derivative of a new triantennary cluster galactoside directs low- and high-density lipoproteins to the parenchymal liver cell

We have developed a new triantennary galactoside, in which the terminal galactose moieties are connected to the branching point of the cluster galactoside via a 20 A (2 nm) spacer [TG(20A)]. In vitro binding studies have demonstrated that introduction of a 20 A spacer resulted in avid and specific binding of the triantennary galactoside to the asialoglycoprotein receptor on the parenchymal liver cell. Derivatization of this galactoside with a cholesterol moiety afforded a compound [TG(20A)C] that lowered the serum cholesterol concentration when injected into rats. In the present study we have evaluated the direct effect of TG(20A)C on the in vivo fate of high-density lipoprotein (HDL) and low-density lipoprotein (LDL). A direct association of TG(20A)C with HDL and LDL was observed on mixing these components. Incorporation of TG(20A)C into 125I-HDL and 125I-LDL significantly accelerated the serum decay and concomitantly stimulated the hepatic uptake of these lipoproteins in rats. The liver uptake of TG(20A)C-loaded 125I-HDL or 125I-LDL could be inhibited by 81% and 82% respectively by preinjection of 150 mg of N-acetylgalactosamine, indicating that the enhanced liver uptake proceeded via galactose-specific receptors. More than 96% of the hepatic uptake of TG(20A)C-loaded 125I-HDL could be attributed to the parenchymal cell. Surprisingly, the parenchymal cell also accounted for 93% of the liver association of TG(20A)C-loaded 125I-LDL, suggesting that TG(20A)C stimulates the uptake and processing of both lipoproteins by the asialoglycoprotein receptor on the parenchymal liver cell. This contrasts with earlier data indicating that a triantennary cluster galactoside provided with a 4 A spacer between the terminal galactose moieties and the branching point of the dendrite stimulated hepatic uptake of LDL via the Kupffer cells. The parenchymal cell is the only liver cell type that is capable of irreversibly removing cholesterol from the body in the form of bile acids. The above results imply that administration of TG(20A)C not only facilitates the hepatic uptake of lipoprotein-derived cholesterol (esters) but also their elimination from the body. In addition, it might be possible to utilize TG(20A)C as a targeting device to selectively deliver large drug carriers and possibly genes to the parenchymal liver cell.