Effects of skin metabolism on percutaneous penetration of lipophilic drugs

Effects of skin metabolism on percutaneous penetration of drugs with high lipophilicity were studied in vitro using rat skin pretreated with and without an esterase inhibitor, diisopropyl phosphorofluoridate [also known as diisopropyl fluorophosphate (DFP)]. Without DFP, about 96% of the total penetrated amount appeared as metabolized p-hydroxybenzoic acid in the receptor fluid after application of butylparaben, whereas about 30% penetrated as intact form after application of propylparaben. On the other hand, metabolized p-hydroxybenzoic acid was not defected in the receptor fluid under pretreatment with DFP. DFP significantly decreased (p < 0.05) the total amount that penetrated after application of butylparaben, but it did not significantly affect that of propylparaben. The results indicate that skin metabolism directly affects total amount that penetrated in the case of highly lipophilic drugs, and it was found that the higher metabolic rate to hydrophilic drugs is, the greater the amount that penetrated the skin would be. Thus, when optimal prodrugs are designed for the purpose of enhancing percutaneous penetration, we propose that the bioconversion rate to parent drugs as well as the lipophilicity of prodrugs becomes an important consideration.

Augmented inhibitory effect of superoxide dismutase on superoxide anion release from macrophages by direct cationization

Superoxide dismutase (SOD) was modified into cationized form (Cat-SOD) in order to enhance its pharmacological efficacy based on an electrostatic interaction. The inhibitory effect of Cat-SOD on superoxide anion release from inflammatory macrophages and its cellular interaction were studied in vitro. Cat-SOD exhibited an excellent inhibitory effect on superoxide anion release from the macrophages, and this effect surpassed those of native SOD and SOD modified with mannose (Man-SOD) which is taken up via mannose receptor-mediated endocytosis by macrophages. In the presence of colchicine, a microtubule-disruptive agent, the inhibitory effect of Cat-SOD was slightly impaired, whereas the effect of Man-SOD completely disappeared. The intracellular localization of fluorescein isothiocyanate-labeled SOD, Cat-SOD and Man-SOD observed by confocal laser microscopy supported the difference in their abilities to eliminate superoxide anions. The different sensitivities of Cat-SOD and Man-SOD to colchicine were also confirmed by the confocal laser microscopic images, suggesting their distinct intracellular trafficking pathways in the macrophages. In conclusion, Cat-SOD is desirable for its pharmacological activity, which is probably the result of its ability to be delivered to the vicinity of NADPH-oxidase which locates in the cell membrane and generates superoxide anions.

Non-polarized secretion of mouse interferon-beta from gene-transferred human intestinal Caco-2 cells

PURPOSE

The intestinal epithelium is considered to be a feasible target for somatic gene therapy. To this end, Caco-2 cells derived from human colon carcinoma were transfected with a mouse interferon-beta (IFN-beta) expression vector and several stable sublines were established; this hetero-specific cytokine allows unexpected cellular effects to be avoided. Using the highest mouse IFN-beta-producing sublines, the mode of IFN secretion was examined.

METHODS

The secretion polarity of mouse IFN-beta in its gene-transduced Caco-2 sublines was studied in a bicameral culture system in which the chambers were separated by microporous filters.

RESULTS

Mouse IFN-beta was secreted to the same extent from both apical and basolateral surfaces of the transduced cells regardless of cell aging.

CONCLUSIONS

These results suggest that in the intestinal epithelium exogenous gene products such as IFNs can be delivered to both the luminal and blood sides in vivo. Thus, the intestinal epithelium may be suitable for systemic and local delivery of therapeutic proteins by gene transfer.

Physicochemical and disposition characteristics of antisense oligonucleotides complexed with glycosylated poly(L-lysine)

The disposition characteristics of a 20 mer antisense phosphodiester oligonucleotide (PO) and its fully phosphorothioated derivative (PS) alone or complexed with glycosylated poly(L-lysine) (galactosylated polylysine, Gal-PLL; mannosylated polylysine, Man-PLL) were studied in mice in relation to their physicochemical characteristics. Good complex formation was obtained at a ratio of 1:0.6, w/w [oligonucleotides (ODNs)/carrier]. The 1:0.6 weight ratio of ODNs/Gal-PLL and ODNs/Man-PLL complexes had zeta potentials of -27 to -31 mV and mean particle size of 100 to 160 nm. After intravenous injection, 35S-labeled ODNs were eliminated rapidly from the circulation; however, their organ disposition characteristics depended on their type. Complex formation with glycosylated PLL increased the hepatic uptake and decreased the urinary clearance of these ODNs to a great extent. These complexes were taken up by both liver parenchymal cells (PC) and nonparenchymal cells (NPC). However, ODNs/Gal-PLL complexes showed a fairly high PC concentration, whereas ODNs/Man-PLL complexes distributed equally to both PC and NPC. The hepatic uptakes of PS/Gal-PLL and PS/Man-PLL complexes were partially inhibited by prior administration of Gal-BSA and Man-BSA, respectively, suggesting their hepatic uptake via the respective receptor-mediated endocytosis. However, uptake by galactose receptors of Kupffer cells, zeta potential, particle size, and Kupffer cell phagocytosis also seem to influence their uptake process. In conclusion, this study illustrates that ODNs can be delivered to hepatocytes and macrophages via galactose and mannose receptors, respectively.

A physiological role of interferon (IFN)-beta derived from tumor: tumor growth of a mouse bladder carcinoma line MBT-2 is partially suppressed by autocrine IFN-beta

Although some tumor cells endogenously produce a wide variety of cytokines, their physiological roles remain to be fully understood. In this study, we found that mouse subcutaneous tumor induced by inoculation of bladder tumor MBT-2 cells into syngeneic mice secreted a significant amount of interferon (IFN), whereas the cells exhibited no IFN production in in vitro cell culture. Typing experiment using IFN-specific neutralizing antibodies showed that the tumor-derived IFN was exclusively beta type. Since the MBT-2 tumor tissues were homogenous and not infiltrated by immune cells, MBT-2 cells themselves were considered to be IFN-beta producers. By intraperitoneal injection of neutralizing anti-IFN-beta antibodies into MBT-2 cell-inoculated mice, the tumor growth was substantially precipitated and survival days of the tumor-bearing mice were shortened. As the in vitro cell growth of MBT-2 cells was dose-dependently inhibited by IFN-beta, it was suggested that apparent immunogenicity of MBT-2 tumor is partially mediated by tumor suppression by autocrine IFN-beta.

[Cancer gene therapy by direct intratumoral injection: gene expression and intratumoral pharmacokinetics of plasmid DNA]

Pharmacokinetic properties and gene expression of naked plasmid DNA and its cationic liposome complexes after intratumoral injection were studied. Using Walker 256 tissue-isolated tumor perfusion system, we quantified the recovery of naked plasmid DNA and cationic liposome complexes in the tumor, leakage from the tumor surface and the venous outflow after intratumoral injection. Approximately 50% of naked plasmid DNA was eliminated from the tumor at 2 hr after injection, while more than 90% of plasmid DNA was retained in the tumor when complexed with cationic liposome. However, distribution of these complexes in the tumor was restricted only in the vicinity of the injection site. Furthermore, we have examined the expression of chloramphenicol acetyltransferase (CAT) DNA constructs (naked pCMV-CAT) and its cationic liposome (DC-chol) complexes after intratumoral injection into subcutaneous rat Walker 256 carcinosarcoma. Significant gene expression was observed in both cases, but localization of gene expressing cells in the tumor tissue was limited to the vicinity of the injection site. Thus the pharmacokinetic and gene expression studies have demonstrated that in vivo gene expression in the tumor can be achieved by direct injection of naked plasmid DNA. In addition, there is a possibility that restricted localization of naked DNA and its cationic liposome complexes in tumor inhibits gene expression.

In vivo evaluation of acyclovir prodrug penetration and metabolism through rat skin using a diffusion/bioconversion model

PURPOSE

In order to evaluate the in vivo penetration of prodrugs which undergo metabolism in skin, we analyzed the in vivo penetration profiles of acyclovir prodrugs based on a two-layer skin diffusion model in consideration of metabolic process.

METHODS

Acyclovir prodrugs (e.g., valerate, isovalerate and pivarate) were used as model prodrugs and the amounts excreted in urine were measured after percutaneous application. In vivo penetration profiles were then estimated by employing a deconvolution method and the penetration of acyclovir prodrugs was analyzed using a diffusion model. Subsequently, diffusion, partitioning and metabolic parameters were compared under in vitro and in vivo conditions.

RESULTS

Although total penetration amounts at the end of the experiment were similar for the three prodrugs, the ratio of intact prodrug to total penetration amount differed significantly. Moreover, the excretion and absorption profiles were also very different for each prodrug. Enzymatic hydrolysis rate constants calculated under in vivo conditions were considerably larger than those obtained in the skin homogenate and in vitro penetration experiments.

CONCLUSIONS

The present skin diffusion/bioconversion model combined with computer analysis enables us to comprehensively account for diffusion, partitioning and metabolism during in vivo percutaneous absorption. Nevertheless, different enzymatic hydrolysis rate constants obtained under both in vivo and in vitro conditions demonstrate the difficulty of obtaining accurate values for in vivo enzymatic activity from related in vitro experiments.

Development of targeted delivery systems for nucleic acid drugs

Our increased understanding of disease pathogenesis is the basis for developing novel nucleic acid drugs. The main challenge encountered in this development is how to maintain therapeutically meaningful concentrations of the drugs in the vicinity of their targets for the desired periods. The intrinsic difficulty arises from the fact that nucleic acid drugs are not readily transported across membranes. Hence, their delivery and transport characteristics at the whole body, organ and cellular levels need to be thoroughly examined. Liposomes and receptor-mediated polycation systems are promising carriers for their delivery in vivo. There are many barriers to be overcome for successful antisense and gene therapies. Along with other factors, disposition, stability against nucleases, binding to cell surface receptor and internalization, and intracellular trafficking affect the in vivo delivery and efficacy of nucleic acid drugs. This review article discusses the delivery and transport of these compounds.

Renal disposition of recombinant human interleukin-11 in the isolated perfused rat kidney

PURPOSE

To clarify the mechanism of the renal clearance of recombinant human interleukin- 11 (rhIL- 1), we investigated the renal disposition characteristics of rhIL-11 in the perfused rat kidney.

METHODS

The disposition characteristics of (111)In-labeled rhIL-11 were analyzed using a single-pass indicator dilution technique and statistical moment analysis in the perfused rat kidney under filtering and nonfiltering conditions.

RESULTS

Steady-state distribution volume (Vd) calculated from the venous outflow patterns of rhIL-11 at the doses of 0.3 to 10 microg/kidney was between 0.35 and 0.40 ml/g kidney. However, Vd at the highest dose decreased to a value almost identical to that of bovine serum albumin, suggesting that there is a reversible and saturable interaction between the capillary wall and rhIL-11 molecule. In filtering kidney, a remarkable accumulation of rhIL-11 was observed while its urinary excretion was highly restricted at all doses. In nonfiltering kidney, rhIL-11 showed a decreased but still significant renal uptake. Taken together, the marked renal uptake of rhIL-11 may be explained by both efficient tubular reabsorption and significant uptake from the capillary side. These processes were not saturable within the tested dose range. These characteristics of rhIL-11 are likely based on non-specific electrostatic interaction with the tissues due to its cationic charge in the cytokine.

CONCLUSIONS

The renal disposition processes of rhIL-11 were clarified at organ level in a quantitative manner. These findings agree well with previous observations in an in vivo disposition study in mice.

Nonviral vectors for in vivo gene delivery: physicochemical and pharmacokinetic considerations

The use of nonviral vectors is an attractive in vivo gene delivery strategy that is simpler than, and lacks some risks inherent in, viral systems. Liposomes and receptor-mediated polycation systems are promising carriers for delivery and expression of plasmid DNA encoding genes into the target cells. Many barriers need to be overcome for successful in vivo DNA delivery using these carrier systems. Such factors as extent of DNA condensation, particle size of the DNA complex, route of administration, stability against nucleases, target sites, in vivo disposition, binding to cell surface receptor and internalization, and intracellular trafficking affect in vivo gene delivery and expression. This review will provide a critical discussion of the merits and limitations of liposomal and polycationic carrier systems for gene transfer from the viewpoints of their physicochemical and pharmacokinetic properties.

Pharmacokinetic analysis of drug disposition after intratumoral injection in a tissue-isolated tumor perfusion system

PURPOSE

The purpose of this study was to establish an experimental system for evaluation of the intratumoral behavior of drugs after intratumoral injection using perfused tissue-isolated tumor preparations of Walker 256 carcinoma (3.46-9.73g, n = 16).

METHODS

We quantified the recovery of Phenol Red (model drug) in the tumor, leakage from the tumor surface and the venous outflow after intratumoral injection using perfused tissue-isolated tumors, and analyzed venous appearance curves based on a pharmacokinetic model in which the tumor tissue was assumed to be divided into two compartments, i.e., well- and poorly-perfused regions.

RESULTS

In small tumors (Type 1, 5.42 +/- 0.39 g), the drug appeared immediately in the venous outflow, and the amount remaining in the tumor tissue at 2 hr after injection was small. In contrast the venous appearance rate reached a significantly lower peak a few minutes after injection, and a large amount of injected drug remained in some large tumors (Type 2.8.17 +/- 0.51 g). Pharmacokinetic analysis revealed that there was a correlation between tumor weight and the rate constants of transfer from the poorly-perfused region to the well-perfused region, and between the rate constants of transfer from the well-perfused region to the venous outflow and dosing ratios into the well-perfused region.

CONCLUSIONS

An experimental system and analytical method were established for the evaluation of the intratumoral behavior of drugs after intratumoral injection using a tissue-isolated tumor perfusion system. This experimental system will be useful in analyzing the antitumor drug disposition after intratumoral injection.

Disposition of oligonucleotides in isolated perfused rat kidney: involvement of scavenger receptors in their renal uptake

The objective of this study was to clarify the renal disposition characteristics of a 20-mer model phosphodiester oligonucleotide and its partially (PS3) and fully (PS) phosphorothioated derivatives, in isolated rat perfused kidney. Venous outflow and urinary excretion pattern, as well as tissue accumulation of radioactivity after bolus injection of 32P-labeled oligonucleotides, were evaluated under both filtering and nonfiltering conditions. The binding affinity of oligonucleotides to bovine serum albumin in the perfusate increased as the number of sulfur atoms present in the oligonucleotide molecules increased, resulting in 21, 60 and 86% binding to bovine serum albumin for phosphodiester oligonucleotide, PS3 and PS, respectively. The apparent steady-state distribution volumes of the oligonucleotides, as calculated from the venous outflow patterns, were larger than that of inulin, which corresponds to the extracellular volume of the kidney, suggesting their interaction with tissue from the vascular space. PS showed the largest distribution volume. Urinary excretion of oligonucleotides was greatly restricted, compared with that of inulin, which was used as a marker of glomerular filtration rate. The accumulation of these oligonucleotides was ascribed to both tubular reabsorption and uptake from the capillary side. The uptake of oligonucleotides from the capillary side increased as the number of sulfur atoms present in the molecules increased, suggesting sulfur atom-dependent interactions between oligonucleotides and renal tissue. In addition, the uptake of PS3 was a saturable process. Furthermore, coadministration of dextran sulfate and polyinosinic acid inhibited the renal uptake of PS3, whereas polycytidic acid and 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid did not, suggesting that oligonucleotides were taken up via the scavenger receptor-mediated process for polyanions. These findings provide valuable information for the development of delivery systems for antisense oligonucleotides.

Development and pharmacokinetics of galactosylated poly-L-glutamic acid as a biodegradable carrier for liver-specific drug delivery

PURPOSE

A biodegradable carrier for the liver-specific delivery of drugs was developed using poly-L-glutamic acid (PLGA) modified with galactose (galactosylated PLGA or Gal-PLGA), and its feasibility was investigated in mice.

METHODS

111In-PLGA and 111In-Gal-PLGAs were injected in mice and their distribution and biodegradation properties were studied.

RESULTS

After intravenous injection. 111In-PLGA was rapidly eliminated from the plasma and recovered mainly in the kidneys and urine. Approximately 15% of the dose was recovered in the liver, predominantly in the nonparenchymal cells. 111In-Gal-PLGAs were taken up by the liver parenchymal cells. Derivatives having 16 or more galactose residues were taken up by the liver to a higher extent (> 60% of the dose). The hepatic clearance of 111In-Gal-PLGAs correlated with their number of galactose residues. 111In-Gal18-PLGA was degraded into low-molecular weight products in the liver.

CONCLUSIONS

The advantageous in vivo properties of Gal-PLGA as a liver-specific biodegradable carrier of drugs were demonstrated in mice.

Macromolecular carrier systems for targeted drug delivery: pharmacokinetic considerations on biodistribution

This review article describes the current status and future perspectives of site-specific drug delivery by means of macromolecular carrier systems. Basic aspects and recent advances of targeted delivery of 1) conventional drugs, 2) protein drugs, and 3) gene medicines including antisense oligonucleotides and plasmid DNA, are reviewed from a pharmacokinetic perspective. Successful in vivo application of macromolecular carrier systems requires pharmacokinetic considerations at whole body, organ, cellular and subcellular levels. The integration of simultaneous research progress in the multidisciplinary fields such as biochemistry, cell and molecular biology, pharmacology, and pharmacokinetics will accelerate the emergence of marketed drugs with macromolecular carrier systems.

Disposition characteristics of plasmid DNA in the single-pass rat liver perfusion system

PURPOSE

To define the hepatic uptake mechanism of a plasmid DNA, we quantitated the uptake of pCAT (plasmid DNA encoding chloramphenicol acetyltransferase reporter gene fused to simian virus 40 promoter), a model plasmid, after a single pass through the perfused rat liver using albumin- and erythrocyte-free Krebs-Ringer bicarbonate buffer (pH 7.4).

METHODS

[32P]pCAT was introduced momentarily into this system from the portal vein as a bolus input or constant infusion mode, and the outflow patterns and hepatic uptake were evaluated using statistical moment analysis.

RESULTS

The venous outflow samples had electrophoretic bands similar to that of the standard pCAT, suggesting that the plasmid is fairly stable in the perfusate during liver perfusion. In bolus experiments, pCAT was largely taken up by the liver and the uptake was decreased with increase in injected dose. Statistical moment analysis against outflow patterns demonstrated that the apparent volume of distribution of pCAT was greater than that of human serum albumin, indicating a significant reversible interaction with the tissues. The results of collagenase perfusion experiments suggest that the hepatic accumulation of pCAT occurred preferentially in the nonparenchymal cells (NPC). The amount of total recovery in the liver decreased substantially by preceding administration of polyinosinic acid, dextran sulfate, succinylated bovine serum albumin, but not by polycytidylic acid. This suggests that pCAT is taken up by the liver via scavenger receptors for polyanions on the NPC. In constant infusion experiments, the presence of 2,4-dinitrophenol and NH4Cl caused a significant increase in the outflow concentration of [32P]pCAT and decrease by half in the total hepatic recovery than that of plasmid DNA administered alone, suggesting that plasmid DNA may undergo internalization by the NPC.

CONCLUSIONS

The liver plays an important role in the elimination of plasmid DNA and a successful delivery system will be required to avoid its recognition by the scavenger receptors on the liver NPC.

Theoretical design of prodrug-enhancer combination based on a skin diffusion model: prediction of permeation of acyclovir prodrugs treated with 1-geranylazacycloheptan-2-one

PURPOSE

A theoretical design of percutaneous penetration enhancement in which prodrug derivation and enhancer application are combined is proposed based on the skin diffusion model and it is experimentally verified.

METHODS

Employing acyclovir as a model drug, the hypothesis was tested by synthesis of its prodrugs and evaluation of their in vitro permeation in the rat skin, with or without a penetration enhancer, 1-geranylazacycloheptan-2-one(GACH).

RESULTS

Among five acyclovir prodrugs, those with higher lipophilicities (propionate, butyrate, valerate, and hexanoate prodrugs) showed greater skin penetration than those of hydrophilic prodrugs (acetate), when administered in combination with GACH. Furthermore, the observed enhancement ratios were in good agreement with those predicted by theoretical consideration.

CONCLUSIONS

Thus, skin permeation of prodrugs applied with an enhancer can be predicted and optimized by model analysis.

Biliary excretion of polystyrene microspheres with covalently linked FITC fluorescence after oral and parenteral administration to male Wistar rats

To further our understanding of microspheres as a drug delivery system, the biliary excretion of covalently linked FITC fluorescence polystyrene microspheres of various diameters was investigated after oral and parenteral administration to male Wistar rats. About 36%, 16% 3% and 1% of the dose was excreted into the bile after parenteral injection of 50 nm, 500 nm, 1 micron and 3 microns diameter microspheres, respectively, over 24 h. In addition, about 30%, 11%, 1%, and 1% of the dose, respectively, was found in the blood at 24 h. After oral administration of 50 nm, 500 nm, and 1 micron microspheres, the recovery was about 18%, 8% and 1% of the dose in the bile and about 9%, 1%, and 0% in the blood, respectively. No 3 microns microspheres were detected in the bile or blood after oral administration. Particles were not detected in the urine of any group tested. Thus, the present study demonstrated that biliary excretion plays an important role in the disposition of microspheres administered by the oral or parenteral routes, and there is a size-related excretion of microspheres into the bile.

Uptake characteristics of oligonucleotides in the isolated rat liver perfusion system

The objective of this study was to examine the hepatic disposition characteristics of 20-mer model phosphodiester oligonucleotide (PO) and its partially phosphorothioated (PS3) and fully phosphorothioated (PS) derivatives in the single-pass isolated rat liver perfusion system. [32P]-labeled oligonucleotides were momentarily introduced into this system through the portal vein as a bolus input mode, and the venous outflow patterns were evaluated using statistical moment analysis. The apparent volumes of distribution of these oligonucleotides were greater than those of reference substances for vascular space (erythrocytes) and extracellular space (human serum albumin), indicating a significant interaction between oligonucleotides and the liver. Significant hepatic uptake of oligonucleotides was also observed. About 20%, 36%, and 52% of the injected dose (3 micrograms/rat) was taken up by the liver during a single passage after bolus injection of PO, PS3, and PS, respectively. In the case of PS injection, slow efflux from the liver was observed in the latter phase of perfusion. This suggests that the hepatic uptake process of these oligonucleotides greatly depended on their types. The results of collagenase perfusion experiments suggest that PS3 oligonucleotides were taken up by both liver parenchymal and nonparenchymal cells. The amount of total recovery in the liver decreased substantially by coadministration of polyinosinic acid, dextran sulfate, polycytidic acid and 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid. This suggests that PS3 was taken up by the liver as an anionic molecule in a nonspecific manner.

Mannosylated superoxide dismutase inhibits hepatic reperfusion injury in rats

Superoxide anion radical (O2-) is one factor related to ischemia/reperfusion injury to the liver. The sites of O2- production and injury have yet to be determined. Superoxide dismutase (SOD), a specific scavenger for O2-, has an inhibitory effect on injury caused by O2-. SOD is of low molecular weight; hence, it has a short half-life in the circulating blood. Mannosylated SOD is taken up in sinusoidal endothelial cells of the liver by receptor-mediated endocytosis. In rats with an occluded inflow against 70% of the liver for 30 min followed by reperfusion there were elevations of serum aspartate aminotransferase and alanine aminotransferase, and lipid peroxide concentrations in liver tissue were significantly inhibited by intravenous administration of mannosylated SOD compared to treatment with normal saline. Electron microscopic examination showed that mannosylated SOD protected against damage to the sinusoidal endothelial cells caused by ischemia/reperfusion and that conventional SOD had no such protective effect. Thus, O2- produced by ischemia/reperfusion apparently damages sinusoidal endothelial cells, and damage to hepatic parenchymal cells is secondary. Mannosylated SOD deserves further study for possible use in surgical resection of the liver and for liver transplantations.

Characterization of LLC-PK1 kidney epithelial cells as an in vitro model for studying renal tubular reabsorption of protein drugs

PURPOSE

The purpose of this study was to assess whether LLC-PK1 renal epithelial cells could serve as an in vitro model for studying the renal tubular reabsorption of protein drugs.

METHODS

The association of 111In-labeled model protein drugs, bovine serum albumin (BSA), superoxide dismutase (SOD), soybean trypsin inhibitor (STI), and [Asu1.7]-eel calcitonin (Asu-ECT), with the monolayers of LLC-PK1 renal epithelial cells was characterized under various conditions.

RESULTS

The cellular association of these proteins was temperature-dependent and varied according to the protein. Saturation kinetics were observed for STI association, with the apparent Km and Vmax values determined to be 66.3 micrograms/ml and 250 ng/mg protein/min, respectively. The association of STI decreased with increases in medium pH from 5.4 to 8.4 and was inhibited significantly by 2,4-dinitrophenol, sodium azide, cytochalasin B, and colchicine, suggesting that the cellular association involved endocytosis. Mutual inhibition was observed in competitive binding experiments with the four protein drugs, suggesting that they shared a common binding site on the luminal membrane of LLC-PK1 cells. Taken together, these findings show that a variety of protein drugs bind to LLC-PK1 cells in a non-specific manner and possibly undergo endocytosis, a phenomenon that is similar to in vivo proximal tubular reabsorption.

CONCLUSIONS

LLC-PK1 renal epithelial cells would be a suitable model system for the study of the renal proximal tubular reabsorption of protein drugs.

A deconvolution method for estimating the first-pass metabolism of orally administered drugs

A deconvolution method for estimating the first-pass metabolism of orally administered drugs is proposed. This analysis can be carried out without assuming any pharmacokinetic models. The applicability of the deconvolution method was evaluated by application to the plasma concentration-time courses of aspirin and its metabolite, salicylic acid, reconstructed from pharmacokinetic parameters for orally administered drugs. The estimated absorption profiles for aspirin and salicylic acid were in fairly good agreement with the theoretical ones, although a series of numerical calculations is involved in the procedures. The potential of the present method was also confirmed by applying it to pharmacokinetic data with random errors.

Disposition characteristics of recombinant human interleukin-11 after a bolus intravenous administration in mice

The pharmacokinetics and disposition characteristics of recombinant human interleukin-11 (rhIL-11) after systemic administration of 10 to 1000 micrograms/kg was investigated in mice. After a bolus i.v. injection of 100 micrograms/kg of 111In-labeled rhIL-11, radioactivity disappeared rapidly from the circulation after a biexponential function. Plasma clearance profiles based on immunoreactivity and biological activity were identical to the disappearance pattern of radioactivity in the early phase after injection. In the range of 10 to 100 micrograms/kg, pharmacokinetic parameter estimates such as the T1/2 alpha and total body clearance were almost constant, suggesting that pharmacokinetics of rhIL-11 were linear within this dose range. 111In-labeled rhIL-11 distributed mainly to the kidney and liver; within 10 min, 40 and 20% of the dose, respectively, accumulated. On the other hand, the urinary excretion ratio was very small (ca., 1% of the dose), suggesting that rhIL-11 was cleared rapidly by glomeruler filtration followed by efficient tubular reabsorption. Pharmacokinetic analysis of the tissue distribution data demonstrated large kidney and hepatic uptake clearances. At the highest dose (1000 micrograms/kg), total body clearance significantly decreased, due primarily to saturation of hepatic uptake. These findings will provide useful information for the development of rhIL-11.

Physicochemical and pharmacokinetic characteristics of plasmid DNA/cationic liposome complexes

The objectives of this study were (i) to characterize the plasmid DNA encoding the chloramphenicol acetyltransferase reporter gene (pCAT) complexed with cationic liposomes (Lipofectin and LipofectACE) in terms of particle size and zeta potential, (ii) to compare pharmacokinetic characteristics, and (iii) to study the hepatic uptake mechanisms. DNA/LipofectACE complexes showed a negative zeta potential of -36 mV at 1:5 w/w ratio, but a positive zeta potential of (19 mV at 1:10 w/w ratio. Lipofectin samples showed a positive zeta potential) of 21-28 mV at these ratios. These preparations showed a wide particle size distribution ranging from 600 to 1200 nm. Following intravenous injection of 1:10 w/w ratio [32P]pCAT/liposome complexes at a dose of 0.1 mg DNA/kg into the tail vein of mice, radioactivity was rapidly eliminated from the plasma and almost 50-60% of the dose was taken up by the liver within 5 min after administration. Plasmid DNA/liposome complexes were predominantly taken up by the liver nonparenchymal cells. The hepatic uptake was inhibited by preceding administration of dextran sulfate (DS), but not by polycytidic acid (poly[C]) and polyinosinic acid (poly[I]), suggesting the involvement of a phagocytic process. We suggest that these complexes are preferentially taken up by the liver nonparenchymal cells mainly via Kupffer cell phagocytosis.