Comparison of anti-HBV activity of beta-D- and beta-L-DDA-5'monophosphate prodrugs and effectiveness in combination with lamivudine.

We have investigated the effects of several beta-D-ddA 5'-monophospate (beta-D-ddAMP), and their corresponding beta-L-enantiomers prodrugs against HBV replication. All ddAMP prodrugs inhibited HBV replication in a dose-dependent manner.

Use of USPIO-induced magnetic susceptibility artifacts to identify sentinel lymph nodes and lymphatic drainage patterns. I. Dependence of artifact size with subcutaneous Combidex dose in rats.

Subcutaneously administered Combidex contrast agent produced characteristic magnetic susceptibility artifacts in gradient-echo (GE) images of rat brachial and axillary lymph nodes. These artifacts were useful in the rapid location and identification of normal sentinel lymph nodes. A linear dose response was observed with maximum artifact size in transverse images and was used noninvasively to study lymphatic drainage patterns.

Development of an immunoassay for larch arabinogalactan and its use in the detection of larch arabinogalactan in rat blood.

We describe a sensitive and convenient immunoassay for larch arabinogalactan and demonstrate its specificity for larch arabinogalactan. Anti-larch arabinogalactan antiserum is about 10(4) and 10(6) times more selective for detecting larch arabinogalactan than antiserum binds to branch terminal disaccharides consisting of the terminal beta-D-galactosyl residue and the penultimate branch (1-->6)-beta-D-galactosyl residue. It does not bind L-arabinose. The sensitivity of the assay for larch arabinogalactan is less than 0.1 microgram/mL. The application of the assay for measuring arabinogalactan pharmacokinetics in rat blood is illustrated.

Antiviral activity of a conjugate of adenine-9-beta-D-arabinofuranoside 5'-monophosphate and a 9 kDa fragment of arabinogalactan.

An arabinogalactan conjugate containing a 9 kDa fragment of arabinogalactan and adenine-9-beta-D-arabinofuranoside 5'-monophosphate (araAMP), denoted AG(9 kDa)-araAMP, has been synthesized and characterized. In 2.2.15 (human hepatoblastoma) cells, the attachment of araAMP to AG(9 kDa), a ligand of the asialoglycoprotein receptor, decreased the effective concentration for inhibiting extracellular hepatitis B virus (HBV) production by 90% (EC90) from 17 to 0.9 microM adenine arabinoside (araA) equivalents, and increased the cytotoxic concentration (CC50) from 188 to > 17 300 microM araA equivalents. Hence, the selectivity index (CC50/EC90) of araA was improved from 11 (188/17) to > 19200 (17 300/0.9) by conjugation with the 9 kDa fragment of arabinogalactan. AG(9 kDa)-araAMP did not affect the production of viral RNA or viral proteins. In the woodchuck hepatitis model, AG(9 kDa)-araAMP inhibited woodchuck hepatitis virus (WHV) DNA replication at a dose of 0.3 mg of araA equivalents per kg; in this case, AG(9 kDa)-araAMP was 20-30 times more potent than was unconjugated araA. AG(9 kDa)-araAMP was effective by intramuscular or subcutaneous administration. The reduction in HBV DNA levels obtained in 2.2.15 cells and of WHV DNA levels in woodchucks was sustained after treatment with AG(9 kDa)-araAMP ceased. In both cases, viral DNA gradually returned to pre-treatment levels.

Larch arabinogalactan for hepatic drug delivery: isolation and characterization of a 9 kDa arabinogalactan fragment.

Purified arabinogalactan [AG(37 kDa)] from Larix occidentalis is composed of repeating units of similar molecular weight and composition. A 9 kDa arabinogalactan [AG(9 kDa)] has been obtained in high yield from AG(37 kDa) either by autoclaving at 121 degrees C or by exposure to alkaline solution in the presence of sodium borohydride. The weight average molecular weight of AG(37 (kDa) was determined to be 37 and 38 kDa by intensity light scattering and sedimentation equilibrium, respectively. The weight average molecular weight of AG(9 kDa) was determined to be 9.1 and 9.5 kDa by intensity light scattering and sedimentation equilibrium, respectively. MALDI-TOF mass spectrometry yielded a molecular weight at the peak of the distribution of 8.3 kDa for AG(9 kDa). Both AG(37 kDa) and AG(9 kDa) exhibited narrow molecular-weight distributions (Mw/Mn approximately 1.2). AG(37 kDa) and AG(9 kDa) exhibit nearly identical 13C-NMR spectra, monosaccharide composition, and sugar linkages. It is proposed that AG(37 kDa) is composed of covalently bound subunits of AG(9 kDa). AG(37 kDa) and AG(9 kDa) bind isolated hepatocyte asialoglycoprotein receptor equally well. As a result AG(9 kDa) is a candidate for use in hepatocyte directed drug delivery and may be more desirable for such use than is AG(37 kDa).

Arabinogalactan for hepatic drug delivery.

Arabinogalactan, a polysaccharide from the tree Larix occidentalis, has been purified and its biological and physical properties described. Intravenous injection of radiolabeled arabinogalactan (4 mg/kg) in rats resulted in 52.5% of the dose being present in the liver, while prior injection of asialofetuin (100 mg/kg) reduced hepatic radioactivity to 3.54%. Gel chromatography indicates arabinogalactan is a single species of 19 kDa, while light scattering gave a molecular weight of 40 kDa. Glycosyl linkage analysis of arabinogalactan is consistent with a highly branched structure comprising a backbone of 1,3-linked galactopyranose connected by 1,3-glycosidic linkages, comprised of 3,4,6-,3,6-, and 3,4- as well as 3-linked residues. In the carbon-13 NMR spectra, the major resonances of arabinogalactan are assigned to beta-galactopyranose, beta-arabinofuranose, and beta-arabinopyranose. Arabinogalactan produced no adverse reactions in single intravenous dose (mouse, 5000 mg/kg) and repeat dose toxicity studies (rats, 500 mg/kg/day, 90 days). When tritiated arabinogalactan was injected, radioactivity cleared from the liver with a half-life of 3.42 days. Arabinogalactan has properties that make it suitable as a carrier for delivering diagnostic or therapeutic agents to hepatocytes via the asialoglycoprotein receptor.

Magnetic resonance microscopy of mouse embryos.

The increased use of the mouse as a model for various aspects of mammalian biology has caused a renewed interest in developing strategies for examining and comparing normal and abnormal mouse embryonic development and anatomy. In this study, we have explored the use of magnetic resonance microscopy as a tool for these purposes. Techniques for the fixation, embedding, perfusion, and image acquisition of mouse embryos are described. The perfusion of bovine serum albumin-diethylenetriamine pentaacetic anhydride-gadolinium as a contrast agent enhances images of the developing embryonic vasculature during critical stages of organogenesis and allows for comparisons when embryos have been treated with teratogens such as retinoic acid. The acquired three-dimensional data sets are available for archiving, distributing, and postacquisition manipulations such as computer segmentation of anatomical structures.

A functionalized superparamagnetic iron oxide colloid as a receptor directed MR contrast agent.

We have synthesized a surface functionalized superparamagnetic iron oxide colloid whose clearance from the vascular compartment was inhibited by asialofetuin but not fetuin. Unlike other particulate or colloidal magnetic resonance (MR) contrast agents, the agent of the current communication is not withdrawn from the vascular compartment by cells of the macrophage-monocyte phagocytic system, as indicated by its selective increase in hepatic relaxation rates. Because of this we refer to this colloid as a hepatic selective (HS) MR contrast agent. At 20 mumol Fe/kg the HS MR agent darkened MR images of liver. The HS MR agent exhibited no acute toxicity when injected into rats at 1800 mumol Fe/kg. Based on these observations, surface functionalized superparamagnetic iron oxide colloids may be the basis of MR contrast agents internalized by receptor mediated endocytosis generally, and by the asialoglycoprotein receptor in particular.

Ferrite particles: a new magnetic resonance imaging contrast agent. Lack of acute or chronic hepatotoxicity after intravenous administration.

Intravenous administration of ferrite particles may be useful as contrast agents for magnetic resonance (MR) imaging of the liver. We studied several sensitive biochemical parameters of hepatocellular function and toxicity in rats after intravenous ferrite injections to determine whether there was any evidence of iron-induced hepatotoxicity. Light microscopy and iron determinations were performed on the liver, spleen, lung, and kidney. Forty-eight hours after a massive (250 mg iron per kilogram) ferrite injection, liver, spleen, and lung nonheme iron concentrations were markedly increased. Microscopy showed this iron to be entirely in reticuloendothelial cells. Despite the large increase in hepatic iron concentration, we found no evidence of hepatic mitochondrial or microsomal lipid peroxidation or organelle dysfunction, sensitive biochemical indicators of iron-induced hepatocellular injury. At 10 to 11 weeks after administration of ferrite in smaller doses (30 mg iron per kilogram), results of all biochemical and morphologic studies were normal. Furthermore, quantitative iron determinations and microscopic studies suggest that ferrite particles may be partially degraded and that iron is cleared from the liver during a 3-month period. Because ferrite particles are taken up by reticuloendothelial cells, hepatocellular function is not impaired and iron-induced hepatocellular injury does not occur.

Hydroxysteroid dehydrogenases of Pseudomonas testosteroni. Separation of a 17 beta-hydroxysteroid dehydrogenase from the 3(17) beta-hydroxysteroid dehydrogenase and comparison of the two enzymes.

When a crude extract of Pseudomonas testosteroni induced with testosterone was subjected to polyacrylamide gel electrophoresis, six bands that stained for 17 beta-hydroxysteroid dehydrogenase activity was observed. A protein fraction containing the enzyme corresponding to the fastest migrating band and devoid of the other hydroxysteroid dehydrogenase activities has been obtained. This preparation appears to be distinct from the previously isolated 3(17) beta-hydroxysteroid dehydrogenase (EC 1.1.1.51) in its chromatography properties on DEAE-cellulose, substrate and cofactor specificity, immunological properties and heat stability. The preparation appears devoid of 3alpha-, 3beta-, 11beta-, 17alpha-, 20alpha-, and 20beta-hydroxysteroid dehydrogenase activities. The enzyme transfers th 4-pro-S-hydrogen of NADH from estradiol-17beta (1,3,5(10)estratriene-3,17beta-diol) to estrone (3-hydroxy-1,3,5(10)-estratriene-17-one).

3(17)beta-Hydroxysteroid Dehydrogenase of Pseudomonas testosteroni. Ligand binding properties.

The binding of NAD and NADH to electrophoretically pure 3(17)beta-hydroxysteroid dehydrogenase of Pseudomonas testosteroni was determined by Fluorescence spectroscopy and gel filtration. Four moles of cofactor are bound/mol of tetrameric enzyme; the binding sites are equivalent and independent. The dissociation constants for NAD and NADH are 16 and 0.25 micronM, respectively. As measured by gel filtration in the absence of cofactor, 0.4 mol of estradiol-17 beta is bound/mol of tetrameric enzyme. Data obtained from isotope exchange at equilibrium indicate that the binding of the cofactor to the enzyme is favored over the binding of steroid, although each may bind in the absence of the other. The rates of cofactor dissociation from the ternary complexes are slower than the rates of steroid dissociation; cofactor dissociation is probably the rate-limiting step. Cofactor analogs modified in the pyridine moiety are cosubstrates, whereas modified adenine derivatives are not. The enzyme also utilized as substrate a number of potential steroid affinity labels; no enzyme inactivation by these compounds was observed.

Horse-liver alcohol dehydrogenase and Pseudomonas testosteroni 3(17)beta-hydroxysteroid dehydrogenase transfer epimeric hydrogens from NADH to 17beta-hydroxy-5alpha-androstan-3-one. An exception to one of the Alworth-Bentley rules.

In the reduction of 17beta-hydroxy-5alpha-androstan-3-one to the 3beta-alcohol, horse liver alcohol dehydrogenase utilizes the 4-pro-R hydrogen of NADH whereas the 3(17)beta-hydroxysteroid dehydrogenase of Pseudomonas testosteroni utulized the 4-pro-S hydrogen. These observations provide an exception to the rule proposed by Alworth and Bentley that with regard to the paired methylene hydrogens at C-4 of NADH and NADPH "the stereospecificity of a particular reaction is fixed and does not vary with the source of the enzyme preparation". It is also apparent that for these two enzymes, the selection of the side of NADH from which hydride is transferred to substrate cannot in both cases be dictated by the "best fit" of substrate and cofactor.

Catalytic competence, a new criterion for affinity labeling. Demonstration of the reversible enzymatic interconversion of estrone and estradiol-17 beta covalently bound to human placental estradiol-17 beta dehydrogenase.

Human placental estradiol-17beta dehydrogenase is rapidly inactivated upon treatment with 3-bromoacetoxyestrone. Pseudo-first order kinetic data are obtained and inactivation is accompanied by incorporation of 1 mol of 3-acetoxyestrone/mol of subunit (Mr =34,000). Treatment of the inactivated enzyme with (4S)-[4-2H]DPNH results in the formation of covalently bound [17alpha-2H]estradiol-17beta, which can be released by hydrolysis and identified by gas chromatography-mass sepctrometry. When (4R)-[4-2H]DPNH was used, deuterium was not transferred. Thus, the normal stereochemistry of hydridetransfer is preserved for both partners. After treatment with p-mercuribenzoate, affinity-labeled estradiol-17beta dehyrogenase is no longer able to caralyze reduction its covalently bound estrone; in the presence of DPNH and native enzyme, however, reduction occurs, demonstrating that affinity-labeled enzyme can itself serve as subtrate for native estradiol-17beta dehydrogenase. The reversible enzymatic interconversion of covalently bound estrone was demonstrated using a transhydrogenase assay. The ability of an enzyme to catalyze its normal reaction with a covalently bound substrate is termed catalytic competence, and is considered to be a new criterion for affinity labeling.