Pharmacokinetic analysis of hepatic uptake of galactosylated bovine serum albumin in a perfused rat liver

Riboflavin-Terminated, Multivalent Quantum Dot as Fluorescent Cell Imaging Probe

Bioconjugated nanoparticles are commonly used for targeting cellular/subcellular components, and labeling performance is known to depend on multivalency, i.e., the number of attached biomolecule per particle. However, these multivalency effects are largely unexplored. Here, we show that multivalency of nanoparticle-bound riboflavin controls the cellular interaction, cellular entry/exit mechanism, and subcellular trafficking property. We have synthesized riboflavin-functionalized quantum dot (QD) of 15-25 nm hydrodynamic size with average riboflavin multivalencies of 15, 30, and 70 [designated as QD(RF)₁₅, QD(RF)₃₀, and QD(RF)₇₀, respectively] and investigated their uptake mechanism in riboflavin receptor overexpressed KB cells. We found that increased multivalency from 15 to 70 increases the cellular interaction with QD, shifts the cell uptake mechanism from caveolae-clathrin to exclusive clathrin-mediated endocytosis, and enhances lysosomal trafficking. This work demonstrates the importance of multivalency of bioconjugated molecule at the nanoparticle surface toward biolabeling performance and should be optimized for best performance of designed nanobioconjugate.

Direct aqueous synthesis of cyanomethyl thioglycosides from reducing sugars; ready access to reagents for protein glycosylation

Unprotected carbohydrates can be directly converted into cyanooethyl thioglycosides, which in turn may be used for protein glycosylation, in a completely stereoselective manner by reaction with 2-chloro-1,3-dimethylimidazolinium chloride (DMC) and mercaptoacetonitrile in aqueous solution.

Evaluation of pullulan-functionalized doxorubicin nanoparticles for asialoglycoprotein receptor-mediated uptake in Hep G2 cell line

The present study discusses evaluation of pullulan-functionalized doxorubicin nanoparticles for asialoglycoprotein receptor-mediated uptake in the Hep G2 cell line. Doxorubicin hydrochloride (DOX) nanoparticles using polymers of different hydrophobic character, polyethylene sebacate (hydrophobic) and poly (lactic-co-glycolic acid) (intermediate hydrophobicity) with high entrapment efficiency and particle size were prepared by modified nanoprecipitation, using Gantrez AN 119 as complexing agent. Nanoparticles of Gantrez AN 119 were also prepared to represent a hydrophilic polymer. Cell uptake of DOX nanoparticles was found to be comparable to DOX solution irrespective of DOX concentration, nanoparticles size, and pullulan concentration. Furthermore, uptake of nanoparticles functionalized with or without pullulan prepared with polymers of different hydrophobic character revealed comparable uptake. Comparable uptake of DOX solution and DOX nanoparticles functionalized with or without pullulan suggest extracellular release of DOX as the mechanism of uptake from the nanoparticles. In vivo evaluation in hepatic cancer model is therefore essential to confirm the role of pullulan as asialoglycoprotein receptors ligand.

Enhanced liver targeting of 5-fluorouracil using galactosylated human serum albumin as a carrier molecule

The objective of this study was to develop a liver-specific antihepatocarcinoma agent. The galactosylated human serum albumin 5-fluorouracil conjugate (GHSA-5-FU) was prepared and tested for its chemical characteristic, biodistribution and primary cytotoxicity. The matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was applied to determined the molar ratio (moles of 5-FU/mole of G-HSA and moles of galactose/mole of HSA) of the conjugate. The liver targeting ability of GHSA-5-FU labeled by (131)I was evaluated by measuring the total radioactivity in organs after i.v. administration in mice and rabbits, and the cytotoxicity of the conjugate was assayed by MTT method. The results showed that the molar ratio of galactose to HSA was 50, and the 5-FU to GHSA was 15. Liver uptake in rabbits and mice peaked within 5-20 min after injection. The radioactivity (counts/g tissue) of the conjugate in the liver was several times higher than those in the other organs. The conjugate showed strong cytotoxicity, but no significant cytotoxicity difference was found between GHSA-5-FU and free 5-FU.

Hepatitis B surface protein docked vesicular carrier for site specific delivery to liver

The intrinsic liver tropism of liposomes can be augmented by the addition of targeting features such as the incorporation of hepatotropic elements of the hepatitis viruses. Hepatitis B virus is known to infect hepatocytes after viremia by asialoglycoprotein receptor mediated uptake. However, the specificity of hepatitis B virus surface protein (HBsAg) towards hepatocytes has confronting reports. In the present study, we evaluated the functional ability of HBsAg to be employed as a ligand for targeting hepatocytes. We prepared (14)C labeled small unilamellar vesicles (SUVs) composed of egg PC/Cholesterol/N-glutarylphosphatidylethanolamine (NGPE) in a 60:30:10 molar ratio. HBsAg was covalently linked to SUVs using a water-soluble carbodiimide (EDC) mediated conjugation with NGPE. In vitro cell binding and uptake studies revealed that bioprotein docked carrier system was efficiently taken up by HepG2 cells by the receptor mediated endocytosis. The biodistribution behaviour of plain and HBsAg coated liposomes was also examined followed by intravenous injection. The study revealed that almost 75% of the radioactivity was recovered in the liver after 4 h of injection that was nearly three-fold greater in magnitude than the plain liposomes. Further, fractionation of liver into liver parenchymal cells (PC) and non-parenchymal cells confirmed the preferential localization of the HBsAg coated liposomal carrier in the parenchymal cells.

Uptake characteristics of galactosylated emulsion by HepG2 hepatoma cells

Galactosylated (Gal) emulsions containing various molar ratios of cholesten-5-yloxy-N-(4-((1-imino-2-D-thiogalactosylethyl)amino)butyl)formamide (Gal-C4-Chol) as a ligand for asialoglycoprotein receptors were prepared to study the effect of the galactose content of Gal-emulsions labeled with [3H]cholesteryl hexadecyl ether on their targeted delivery to hepatocytes. The uptake characteristics of Gal-emulsions having Gal-C4-Chol of 1, 3, 4, 6, and 9 mol% were evaluated in HepG2 cells which possess asialoglycoprotein receptors and NIH3T3 cells which are lack of asialoglycoprotein receptors. The uptake and internalization by HepG2 cells was enhanced by the addition of Gal-C4-Chol to the Gal-emulsions whereas the uptake of Gal-emulsions by NIH3T3 cells was not much and was comparable with that of bare-emulsions. In the presence of excess Gal-BSA, the uptake of Gal-emulsions having Gal-C4-Chol of 4, 6, and 9% was inhibited suggesting asialoglycoprotein receptor mediated uptake. Moreover, Gal-emulsions having Gal-C4-Chol of 4, 6, and 9% showed a slight increase in surface binding and exhibited extensive uptake and internalization into HepG2 cells. The present study strongly suggested that the Gal-emulsions are taken up by the asialoglycoprotein receptor-mediated endocytosis and galactose density of Gal-emulsions is important for effective recognition and cell internalization.

Effect of Galactose Density on Asialoglycoprotein Receptor-Mediated Uptake of Galactosylated Liposomes

Galactosylated (Gal) liposomes containing various molar ratios of cholesten-5-yloxy-N-(4-((1-imino-2-D-thiogalactosylethyl)formamide (Gal-C4-Chol) as a ligand for asialoglycoprotein receptors were prepared to study the effect of the galactose content of Gal-liposomes labeled with [3H]cholesteryl hexadecyl ether on their targeted delivery to hepatocytes. The uptake characteristics of Gal-liposomes having Gal-C4-Chol of 1.0%, 2.5%, 3.5%, 5.0%, and 7.5% were evaluated. The uptake and internalization by HepG2 cells was enhanced by the addition of Gal-C4-Chol to the Gal-liposomes. In the presence of excess galactose, the uptake of Gal-liposomes having Gal-C4-Chol of 3.5%, 5.0%, and 7.5% was inhibited suggesting asialoglycoprotein receptor mediated uptake. After intravenous injection, Gal-liposomes having Gal-C4-Chol of 3.5%, 5.0%, and 7.5%, rapidly disappeared from the blood and exhibited rapid liver accumulation with up to about 80% of the dose within 10 min whereas Gal-liposomes having low Gal-C4-Chol (1.0% and 2.5%) showed a slight improvement in liver accumulation compared with bare-liposomes. Gal-liposomes with high Gal-C4-Chol are preferentially taken up by hepatocytes and the highest uptake ratio by parenchymal cells (PC) and nonparenchymal cells (NPC) (PC/NPC ratio) was observed with Gal-liposomes having of 5.0% Gal-C4-Chol. We report here that the galactose density of Gal-liposomes prepared by Gal-C4-Chol is important for both effective recognition by asialoglycoprotein receptors and cell internalization.

Are novel scavenger-like receptors involved in the hepatic uptake of heparin?

Heparin is an anionic macromolecular drug. It has been widely used as an anticoagulant, and numerous efforts to clarify the mechanism of its disposition in the body have been made to help expand its clinical applications, using its newly found biological activities, as well as to further improve its use in anticoagulant therapy. It has now been shown that heparin is taken up extensively not only by Kupffer cells but also by parenchymal cells in the liver, the major distribution organ, and a receptor-mediated endocytotic mechanism, which is shared by heparin analogs and various anionic macromolecules, is responsible for heparin uptake in both types of cells. Although the characteristics of the receptors for heparin in both cells have lots of similarities to those of scavenger receptors, the receptors in parenchymal cells do not accept acetylated low density lipoprotein (Ac-LDL) as a ligand, which is the only striking difference between them and major scavenger receptors. Although the receptors in Kupffer cells, which accept Ac-LDL as a ligand, may belong to class A scavenger receptors, this remains to be established. We therefore conclude at present that it is likely that novel scavenger-like receptors for heparin (heparin receptors) or unidentified scavenger receptors are responsible for heparin uptake in the liver.

Development of cell-specific targeting systems for drugs and genes

Cell-specific targeting systems for drugs and genes have been developed by using glycosylated macromolecule as a vehicle that can be selectively recognized by carbohydrate receptors. Pharmacokinetic analyses of the tissue distribution of glycosylated proteins came to the conclusion that the surface density of the sugar moiety on the protein derivative largely determines the binding affinity for the receptors and plasma lectin. Many glycosylated delivery systems have been developed and their usefulness investigated in various settings. Galactosylated polymers, when properly designed, were found to be effective in delivering prostaglandin E1 and other low-molecular-weight drugs selectively to hepatocytes. In addition, glycosylated superoxide dismutase and catalase were successfully developed with minimal loss of enzymatic activity. A simultaneous targeting of these two enzymes to liver nonparenchymal cells significantly prevented hepatic ischemia/reperfusion injury. On the other hand, galactosylated catalase, a derivative selectively delivered to hepatocytes, effectively inhibited hepatic metastasis of colon carcinoma cells in mice. Finally, hepatocyte-targeted in vivo gene transfer was achieved by synthesizing a multi-functional carrier molecule, which condenses plasmid DNA, delivering DNA to hepatocytes through recognition by asialoglycoprotein receptors, and releasing DNA from endosomes/lysosomes into cytoplasm.

Monitoring biodistribution of glycoproteins with modified sugar chains

Natural human interferon (hIFN)-gamma has mainly biantennary complex-type sugar chains. Previously, we successfully remodeled its sugar chain structure into: (a) highly branched types; or (b) highly sialylated types, by overexpression of: (a) N-acetylglucosaminyltransferase (GnT)-IV and/or GnT-V; or (b) sialyltransferases, in Chinese hamster ovary (CHO) cells. In addition, we prepared asialo hIFN-gammas by treatment with sialidase in vitro. In the present study, we assessed the bioactivity of remodeled hIFN-gamma in terms of antiviral activity, anticellular activity, and biodistribution. Structural changes to the sugar chains did not have a significant influence on the antiviral and anticellular activities of hIFN-gamma, although the attachment of the sugar chain itself affected both activities. However, the biodistribution differed significantly; the number of exposed galactose residues was the major determinant of the specific distribution to the liver and blood clearance rate of hIFN-gamma. This phenomenon was considered to be mediated by the hepatic asialoglycoprotein receptor (ASGP-R), and we showed a linear, not exponential, enhancement of the distribution to the liver with an increase in the number of exposed galactose residues. We also confirmed this tendency using fibroblast growth factor (FGF). Our observation is not the same as the "glycoside cluster effect." We thus provide important information on the character of modified recombinant glycoproteins.

Targeting efficiency of galactosylated liposomes to hepatocytes in vivo: effect of lipid composition

PURPOSE

To investigate the effects of the lipid composition of galactosylated liposomes on their targeted delivery to hepatocytes.

METHODS

Several types of liposomes with a particle size of about 90 nm were prepared using distearoyl-L-phosphatidylcholine (DSPC), cholesterol (Chol) and cholesten-5-yloxy-N-(4-((1-imino-2-D- thiogalactosylethyl)amino)butyl)formamide (Gal-C4-Chol), and labeled with [3H]cholesterol hexadecyl ether. Their tissue disposition was investigated in mice following intravenous injection. The binding and internalization characteristics were also studied in HepG2 cells.

RESULTS

Compared with [H]DSPC/Chol (60:40) liposomes, [3H]DSPC/Chol/Gal-C4-Chol (60:35:5) liposomes exhibit extensive hepatic uptake. Separation of the liver cells showed that galactosylated liposomes are preferentially taken up by hepatocytes, whereas those lacking Gal-C4-Chol distribute equally to hepatocytes and nonparenchymal cells (NPC). Increasing the molar ratio of DSPC to 90% resulted in enhanced NPC uptake of both liposomes, suggesting their uptake via a mechanism other than asialoglycoprotein receptors. DSPC Chol/Gal-C4-Chol (60:35:5) and DSPC/Chol/Gal-C4-Chol (90:5:5) liposomes exhibited similar binding to the surface of HepG2 cells, but the former were taken up faster by the cells.

CONCLUSIONS

The recognition of galactosylated liposomes by the asialoglycoprotein receptors is dependent on the lipid composition. Cholesterol-rich galactosylated liposomes, exhibiting less non-specific interaction and greater receptor-mediated uptake, are better for targeting drugs to hepatocytes in vivo.

Pharmacokinetics and preventive effects of targeted catalase derivatives on hydrogen peroxide-induced injury in perfused rat liver

PURPOSE

To investigate the pharmacokinetics and preventive effects of liver-targeted catalase (CAT) derivatives on hepatic injury caused by reactive oxygen species.

METHODS

The hepatic uptake of 111In-CAT, galactosylated (Gal-), mannosylated (Man-) and succinylated (Suc-) CAT was investigated in isolated perfused rat livers in a single-pass constant infusion mode. Then, pharmacokinetic parameters were obtained by fitting equations derived from a one-organ pharmacokinetic model to the outflow profile. Their effects in preventing hydrogen peroxide-induced injury were determined by lactate dehydrogenase (LDH) release from the perfused liver.

RESULTS

The extraction of CAT derivatives by the liver was dose-dependent, and increased by the chemical modifications described. After being bound to the cell surface, chemically modified CAT derivatives were internalized by the liver faster than CAT. Preperfusion of a CAT derivative significantly reduced LDH release by hydrogen peroxide at least for 30 min, and Man-CAT and Suc-CAT effectively inhibited this release.

CONCLUSIONS

Internalized CAT derivatives are also effective in degrading hydrogen peroxide and targeted delivery of CAT to liver nonparenchymal cells by mannosylation or succinylation is a useful method for the prevention of hepatic injury caused by reactive oxygen species.

Pharmacokinetic evaluation of high pulmonary disposition of clarithromycin after systemic administration

1. The distribution characteristics of clarithromycin to the lung were investigated in vivo and in isolated lung perfusion experiments. The in-vivo integration plot analysis showed that the pulmonary uptake and extracellular distribution in the lung were significantly higher for clarithromycin than for erythromycin. 2. In the rat lung single-pass perfusion study, the pulmonary extraction ratio (E(ss)) of clarithromycin at steady-state was significantly higher than that of erythromycin, and the E(ss) of clarithromycin tended to decrease as the inflow concentration increased, suggesting the involvement of carrier-mediated transport in the pulmonary disposition of clarithromycin. 3. The outflow patterns of clarithromycin or erythromycin at various inflow concentrations were simultaneously analysed based on a pharmacokinetic model, which consists of the non-specific binding site, the specific binding site and the subsequent uptake process. The parameters obtained suggested that clarithromycin would have the higher affinity and higher capacity for the specific binding site, and the higher equilibrium constant for the non-specific binding site than erythromycin. 4. The simulation study using those parameters demonstrated that clarithromycin could be bound to the specific binding site and subsequently taken up more extensively than erythromycin. 5. A multiple-indicator dilution study also indicated that clarithromycin was more readily associated and extracted with the lung than with erythromycin. In the inhibition study, it was suggested that the pulmonary uptake of clarithromycin could be ascribed not only to the non-specific binding depending on its lipophilic nature, but also in part to some specialized mechanisms such as organic cation transporters.

Pharmaceutical strategies utilizing recombinant human serum albumin

Gene manipulation techniques open up the possibility of making recombinant human serum albumin (rHSA) or mutants with desirable therapeutic properties and for protein fusion products. rHSA can serve as a carrier in synthetic heme protein, thus reversibly carrying oxygen. Myristoylation of insulin results in a prolonged half-life because of self aggregation and increased albumin binding. Preferential albumin uptake by tumor cells serves as the basis for albumin-anticancer drug conjugate formulation. Furthermore, drug targeting can be achieved by incorporating drugs into albumin microspheres whereas liver targeting can be achieved by conjugating drug with galactosylated or mannosylated albumin. Microspheres and nanoparticles of different sizes can, with or without drugs and/or radioisotopes, be used for drug delivery or diagnostic purposes. In vivo implantation of albumin fusion protein expressing cells encapsulated in HSA-alginate coated beads showed promising results compared to organoids in rats. Chimeric peptide strategy with cationized albumin as the transport can deliver drugs via receptor mediated transcytosis through the blood brain barrier. Gene bearing, albumin microbubbles containing ultrasound contrast agents can non-invasively deliver gene after destruction by ultrasound. Various site-directed mutants of HSA can be tailor made depending on the application required.

Mechanisms of hepatic disposition of polystyrene microspheres in rats: effects of serum depend on the sizes of microspheres

To study the mechanisms of the hepatic disposition of polystyrene microspheres (MS), effects of serum on their hepatic disposition characteristics were investigated for MSs with particle sizes of 50 nm (MS-50) and 500 nm (MS-500) by isolated liver perfusion experiments. It was revealed that serum in the perfusate inhibited and promoted the hepatic disposition of MS-50 and MS-500 at 37 degrees C, respectively. However, pre-heating at 56 degrees C or pre-treatment with anti-C3 antibody of serum reduced the promotive effect of serum on the hepatic uptake of MS-500, suggesting that the complement system should be involved as opsonins for the hepatic uptake of MS-500. Hepatic disposition of both MSs at 4 degrees C was reduced by the addition of serum into the perfusate, which could be ascribed to the reduction of the surface hydrophobicity of MSs due to the adsorption of serum proteins onto the surface of MSs and to resultant decrease in non-specific disposition to the liver. From these results, serum was found to function both as the opsonin to enhance the hepatic uptake of MSs and as the inhibitor by reducing non-specific interaction between MSs and the plasma membrane. Whether serum promotes or inhibits the hepatic disposition of MSs would be dependent on the particle sizes of MSs.

Pharmacokinetic evaluation of mannosylated bovine serum albumin as a liver cell-specific carrier: quantitative comparison with other hepatotropic ligands

To assess the feasibility of mannosylated macromolecules as a liver-specific carrier system, hepatic uptake characteristics of mannosylated bovine serum albumin (Man-BSA) were pharmacokinetically investigated. After intravenous injection, 111In-Man18-BSA accumulated in the liver up to 70% of dose at 2h; the endothelial cells and Kupffer cells contributed about 66% and 21% of the uptake, respectively. In single-pass perfusion experiments using rat liver at varying inflow concentrations (0.1-2.0 microg/ml), 111In-Man18-BSA and 111In-Man33-BSA were continuously extracted by the liver and their extraction ratios decreased with the increasing inflow concentrations. The outflow curves of each 111In-Man-BSA at three concentrations were simultaneously fitted to a pharmacokinetic model including a binding to the cell surface and an internalization, by using a nonlinear regression program MULTI(RUNGE). The binding constant augmented with the increase in the number of mannose per BSA, whereas the internalization rate constant was quite comparable for both derivatives. The pharmacokinetic analysis has demonstrated that the uptake process of 111In-Man-BSA is characterized to possess fewer binding sites and a greater internalization rate in comparison with other liver-specific carriers such as galactosylated, succinylated and cationized BSAs. These results will provide useful information in designing drug targeting systems to the liver nonparenchymal cells via mannose receptors.

Disposition characteristics of glycosylated poly(amino acids) as liver cell-specific drug carrier

Potentials of glycosylated poly(amino acids) as carriers of drugs and/or polynucleotides to the liver were studied in mice in detail. Poly-L-glutamic acid (PLGA) and poly-L-lysine (PLL) were selected as carrier backbones and modified with 2-imino-2-methoxyethyl 1-thiogalactoside or mannoside to obtain galactosylated and mannosylated derivatives. After intravenous injection in mice at a dose of 1 mg/kg, Gal-PLGA and Man-PLGA were selectively taken up by the liver parenchymal cells (PC) and liver nonparenchymal cells (NPC), respectively. Moreover, the uptake of Gal-PLGA and Man-PLGA by the liver were significantly inhibited by the presence of Gal-BSA and Man-BSA, respectively. On the other hand, PLL was targeted to the liver without glycosylation. However, Gal-PLL and Man-PLL showed higher accumulation in the liver than unmodified PLL. Although Gal-PLL and Man-PLL showed different distribution between PC and NPC from that of PLL, the effect of the modifications was less pronounced than the cases of PLGA derivatives. In addition, these glycosylated poly(amino acids) investigated, regardless of the type of amino acid or the sugar grafted, were rapidly degraded to be eluted in the low molecular weight fractions in a gel filtration chromatography. These results suggest that glycosylated PLGAs can be useful carriers of low molecular drugs to the liver cells through conjugation, while glycosylated PLLs could be targetable carriers to the cells after the reduction of their cationic charge by complex formation with polynucleotides.