The fate of plasmid DNA after intravenous injection in mice: involvement of scavenger receptors in its hepatic uptake

PURPOSE

We examined the stability and disposition characteristics of a naked plasmid DNA pCAT as a model gene after intravenous injection in mice to construct the strategy of in vivo gene delivery systems.

METHODS

After the injection of pCAT to the mice, stability, tissue distribution, hepatic cellular localization, and effect of some polyanions on the hepatic uptake were studied.

RESULTS

The in vitro study demonstrated that the pCAT was rapidly degraded in mouse whole blood with a half-life of approximately 10 min at a concentration of 100 micrograms/ml. After intravenous injection, pCAT was degraded at a significantly faster rate than that observed in the whole blood, suggesting that pCAT in vivo was also degraded in other compartments. Following intravenous injection of [32P] pCAT, radioactivity was rapidly eliminated from the plasma due to extensive uptake by the liver. Hepatic accumulation occurred preferentially in the non-parenchymal cells. The hepatic uptake of radioactivity derived from [32P] pCAT was inhibited by preceding administration of polyanions such as polyinosinic acid, dextran sulfate, maleylated and succinylated bovine serum albumin but not by polycytidylic acid. These findings indicate that pCAT is taken up by the liver via scavenger receptors on the non-parenchymal cells. Pharmacokinetic analysis revealed that the apparent hepatic uptake clearance was fairly close to the liver plasma flow.

CONCLUSIONS

These findings provide useful information for the development of delivery systems for in vivo gene therapy.

Galactosylated proteins are recognized by the liver according to the surface density of galactose moieties

The recognition of 111In-labeled galactosylated superoxide dismutase (Gal-SOD) and galactosylated bovine serum albumin (Gal-BSA) by the liver was investigated in mice after intravenous injection. 111In-labeled galactosylated proteins were recovered in the liver by amounts that were highly dependent on the degree of galactose modification and the administered dose. The distribution patterns were analyzed based on a physiological pharmacokinetic model including an uptake process with Michaelis-Menten kinetics in the liver and hepatic plasma flow. The Michaelis constant of hepatic uptake of 111In-Gal-SOD was observed to inversely correlate with the number of galactose residues, without a significant change in maximum rate of uptake or extrahepatic clearance. This relation could be applied to 111In-Gal-BSA and other galactosylated proteins by using the surface density of galactose residues as a degree of modification, suggesting galactose density controls ligand recognition by the asialoglycoprotein receptor. The analysis also indicated that increasing galactose density higher than 1.0 x 10(-3) molecules/A2 did not affect the distribution of galactosylated proteins due to limitation by the hepatic plasma flow rate. In conclusion, efficient delivery of proteins modified with galactose to the liver will be achieved by controlling both the galactose density on the protein surface and the administered dose.

Effect of n-butyric acid on epithelial cell proliferation of pig colonic mucosa in short-term culture

Short-chain fatty acids (SCFA) such as acetic, propionic and n-butyric acids produced by hindgut bacteria stimulate gut epithelial cell proliferation through afferent neural and efferent non-neural systemic transmissions beside a probable local mechanism. In the present study, we developed an experimental system using pig hindgut mucosa in short term culture to clarify the mechanism of the local trophic effect of SCFA. Pig mucosal tissue pieces of the distal colon were cultured in RPMI 1640 medium containing glutamine, 20% (v/v) newborn calf serum and n-butyric acid (0, 0.5, 1.0 or 5.0 mmol/L). Crypt cell production rate from 0.5 to 3.5 and from 21 to 24 hours of culture was measured. Butyric acid increased crypt cell production rate of pit distal colon only at 5 mmol/L. The effect of butyric acid did not differ between samples of different length of n-butyric acid exposure. The effect of n-butyric acid in this study resembled to that found in human biopsied specimens of the colon. The present results also indicated that epithelial cells of pig colonic mucosa in short-term culture presented here retained the proliferative activity and the responsiveness to n-butyric acid.

Design for cell-specific targeting of proteins utilizing sugar-recognition mechanism: effect of molecular weight of proteins on targeting efficiency

Hepatic targeting of proteins utilizing the sugar-recognition mechanism was investigated in mice after intravenous injection. Five proteins with different molecular weights, i.e., bovine gamma-globulins (IgG), bovine serum albumin (BSA), recombinant human superoxide dismutase (SOD), soybean trypsin inhibitor (STI), and chicken egg white lysozyme (LZM), were modified with 2-imino-2-methoxyethyl 1-thiogalactoside to obtain galactosylated proteins (Gal-IgG, Gal-BSA, Gal-SOD, Gal-STI, and Gal-LZM). The numbers of galactose residues were 38, 20, 11, 6, and 5 for Gal-IgG, Gal-BSA, Gal-SOD, Gal-STI, and Gal-LZM, respectively. All galactosylated proteins were dose-dependently taken up by the liver and the relative amount accumulated in the liver was decreased with an increase of the administered dose. At low doses (0.05 and 0.1 mg/kg), Gal-IgG, Gal-BSA, and Gal-SOD could be taken up by the liver up to more than 70-80% of dose within 10 min after intravenous injection, but the maximum amounts accumulated in the liver were approximately 40 and 30% of the dose for Gal-STI and Gal-LZM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal disposition characteristics of oligonucleotides modified at terminal linkages in the perfused rat kidney

To clarify the renal disposition characteristics of oligonucleotides at the organ level, the renal handling of model end-capped oligonucleotides, 3'-methoxyethylamine 5'-biotin-decathymidylic acid containing phosphoramidate modifications at 3'- and 5'-terminal internucleoside linkages (T10) and its phosphorothioate (Ts10), were studied in the perfused rat kidney. In a single-pass indicator dilution experiment, venous outflow and urinary excretion patterns and tissue accumulation of radiolabeled oligonucleotides were evaluated under filtering or nonfiltering conditions. No significant binding to bovine serum albumin (BSA) in the perfusate was observed for T10, whereas more than 90% of Ts10 bound to BSA. The steady-state distribution volume of T10 calculated from the venous outflow pattern was larger than that of inulin, which corresponds to the extracellular volume of the kidney, whereas the distribution volume of Ts10 was larger than that of BSA (the intravascular volume). These results suggested their interaction with the vascular wall. Rapid urinary excretion was observed for T10, similar to inulin used as a marker of golmerular filtration rate. On the other hand, urinary excretion of Ts10 was greatly restricted due to its high binding ability (> 90%) to BSA in the perfusate. A significant amount of T10 and Ts10 was accumulated in the kidney (T10, 1.8% of injected dose; Ts10, 1.3%) compared with inulin (0.2%) and BSA (< 0.1%). The accumulation of these oligonucleotides was ascribed to both tubular reabsorption and uptake from the capillary side. In addition, the uptake of T10 from the capillary side was significantly inhibited by simultaneous injection of dextran sulfate, suggesting that the oligonucleotide was taken up as an anionic molecule. These findings will be useful information for the development of delivery systems for antisense oligonucleotides.

In vivo disposition characteristics of plasmid DNA complexed with cationic liposomes

To control disposition and hence gene expression, we investigated the disposition characteristics of plasmid DNA complexed with the cationic liposomes Lipofectin and LipofectACE after intravenous injection in mice via the tail vein. The optimum ratios of DNA and liposome complexes were selected through in vitro cytotoxicity and transfection studies. The highest transfection was found at the DNA:liposome ratio of 1:5 w/w. Hence, this ratio was used for in vivo disposition studies, and the distribution patterns were compared with that of naked pCAT. Following intravenous injection of [32P] pCAT, radioactivity was rapidly eliminated from plasma and approximately 60% of the dose was taken up by the liver within 1.5 min. In the case of LipofectACE samples, radioactivity elimination from plasma was equally rapid, but its accumulation was observed in both the liver (35%) and the lung (45%). For Lipofectin samples, radioactivity was initially accumulated in both the liver (55%) and the lung (25%), but lung accumulation was not sustained beyond 5 min after administration. Both liposomal samples showed in vivo gene expression in the lung, heart, kidney and spleen, but not in the liver. Thus, the present study demonstrated that disposition and gene expression of pCAT can be controlled by complex formation with liposomes.

Stability and pharmacokinetic characteristics of oligonucleotides modified at terminal linkages in mice

To construct the strategy for delivery systems that can control in vivo disposition of antisense oligonucleotides, we studied the stability and basic pharmacokinetic characteristics of oligonucleotides. Decathymidylic acid (T10), a model oligodeoxynucleotide, and its derivatives, 5'-biotin-T10) and 3'-methoxyethylamine 5'-biotin-T10 (3'M5'B-T10), containing phosphoroamidate modification at 3'- and/or 5'-terminal internucleoside linkages, were synthesized. In phosphate-buffered saline (PBS, pH 7.4) containing 10% mouse serum, unmodified T10 was degraded with a half-life of 45 minutes; the degradation half-lives of 5'B-T10 and 3'M5'B-T10 were 11 and 30 h, respectively. In mouse whole blood, 3'M5'B-T10 was relatively stable, and 45% remained intact after 1 h incubation. After intravenous injection of [3H]3'M5'B-T10 into mice at a dose of 1 mg/kg, the radioactivity was rapidly cleared from plasma with a half-life of 2 minutes and accumulated in the kidney, liver, and gallbladder. About 30% of the dose was excreted in the urine within 60 minutes. A much more rapid degradation of [3H]3'M5'B-T10 was observed in vivo than expected from in vitro experiments: more than 90% of the radioactivity in plasma was degradation product at 2 minutes after injection. These results suggested that enzymatic degradation occurred in some compartments in addition to the blood pool. The apparent urinary excretion clearance of [3H]3'M5'B-T10 was close to that of inulin, whereas the apparent hepatic uptake clearance was much greater than that of inulin and comparable to that of dextran sulfate, which is taken up by the liver by scavenger receptors for polyanions.(ABSTRACT TRUNCATED AT 250 WORDS)

Skin penetration enhancement of acyclovir by prodrug-enhancer combination

The effectiveness of prodrug-enhancer combination in skin penetration enhancement was studied using acyclovir and its lipophilic prodrug, acyclovir butyrate, with octanol/water partition coefficient of 0.0123 and 0.402, respectively. In the in vitro diffusion experiment with rat skin, the total amount of acyclovir appearing in the receptor phase after administration of the aqueous suspension of acyclovir butyrate was smaller than that obtained after administration of acyclovir, but their permeability coefficients were almost equal. An enhancer, 1-geranylazacycloheptan-2-one (GACH) did not show a large penetration enhancement of acyclovir (3.37-fold) but demonstrated extensive enhancement effect on the prodrug (12.3-fold). Most of the prodrug appeared in the form of acyclovir in the receptor phase without GACH, but the appearance ratio of acyclovir to total flux decreased with an increase in pretreatment doses of GACH.

Improvement of the pulmonary absorption of (Asu1,7)-eel calcitonin by various protease inhibitors in rats

The effects of protease inhibitors, Na-glycocholate, bacitracin, bestatin, nafamostat mesilate and soybean trypsin inhibitor (STI) on the pulmonary absorption of (Asu1,7)-eel calcitonin (ECT, molecular weight 3363) were investigated in rats. The pulmonary absorption of ECT was estimated by measuring its hypocalcemic effect. When ECT alone was administered into the lung, the pharmacological availability of ECT was 2.7%. Co-administration with STI or bestatin did not change the pharmacological effect of ECT. However, Na-glycocholate, bacitracin and nafamostat mesilate caused a significant hypocalcemic effect following the pulmonary absorption of ECT and a maximal effect was noted in the presence of 20 mM bacitracin, approaching the effect after intravenous administration of ECT. Bacitracin and Na-glycocholate reduced the degradation of 111In-ECT in rat lung homogenate. Therefore, protease inhibitors effectively improved the pulmonary absorption of ECT.

Targeted delivery of superoxide dismutase to macrophages via mannose receptor-mediated mechanism

Human recombinant superoxide dismutase (SOD) was modified into a mannosylated form (Man-SOD), and its cellular uptake and inhibitory effect on superoxide anion release were studied in vitro, using cultured mouse peritoneal macrophages. [111In]Man-SOD was taken up by the macrophages to a great extent, whereas no significant uptake was observed for native and galactosylated SOD. The uptake of Man-SOD was inhibited significantly at a low temperature and by the presence of mannan, mannose and colchicine, demonstrating the targeted delivery of Man-SOD via mannose receptor-mediated endocytosis. Man-SOD exhibited a superior inhibitory effect on superoxide anion release from inflammatory macrophages stimulated by phorbol-myristate acetate. The present study suggested the potential of Man-SOD as a therapeutic agent for the inflammatory disease mediated by superoxide anions generated by macrophages.

Comparative analysis of percutaneous absorption enhancement by d-limonene and oleic acid based on a skin diffusion model

Percutaneous absorption-enhancing effects of d-limonene and oleic acid were investigated using three model drugs with different lipophilicities in in vitro diffusion experiments with guinea pig skin. Pretreatment of the skin with d-limonene resulted in a large penetration enhancement for the lipophilic butylparaben (BP) and amphiphilic 6-mercaptopurine (6-MP) but had little effect on the hydrophilic mannitol (MT). Oleic acid caused a large effect only on 6-MP penetration. The penetration profiles were analyzed with a two-layer skin diffusion model consisting of stratum corneum with polar and nonpolar routes and viable epidermis plus dermis. Through curve-fitting, six parameters corresponding to drug diffusivity and partitioning in these three regions of the skin were obtained, and the mechanisms of enhancers were assessed in comparison with those of 1-geranylazacycloheptan-2-one (GACH) reported previously. Increased penetration was caused mainly by modification of the barrier property of the nonpolar route in the stratum corneum in all cases. In the nonpolar route, d-limonene increased mainly drug diffusivity, while GACH enhanced predominantly drug partitioning. On the other hand, oleic acid moderately increased both parameters.

[Control of in vivo characteristics of gene and antisense DNA disposition]

In order to construct a strategy for control of in vivo disposition characteristics of gene and antisense DNA, in vivo stability and basic pharmacokinetic properties of DNA were investigated. A model gene, plasmid DNA (pCAT), and model oligonucleotide (thymidine 10-mer; T10) derivatives with phosphoroamidate substitution at the 3' and/or 5'-terminal internucleotide linkage, were rapidly degraded in vivo after intravenous injection into mice. The degradation rates were much faster than those observed in in vitro experiments using plasma and whole blood, suggesting that they underwent enzymatic degradation in other compartments than the blood pool. More than 70% of injected pCAT was taken up by the liver within 5 minutes, and the uptake clearance was almost identical to the plasma flow rate in the liver. On the other hand, T10 derivatives were rapidly excreted in the urine and taken up by the kidney and liver. The urinary excretion clearance was close to the glomerular filtration rate. In an attempt to control T10 disposition characteristics, the oligonucleotide was conjugated to a macromolecular carrier, carboxymethyl dextran (CMD). The T10-CMD conjugate exhibited increased in vivo stability and prolonged plasma circulation time. Thus, the present study has shown that macromolecular conjugation is a useful approach to improve in vivo disposition of antisense oligonucleotides.

Manipulation of renal disposition of human recombinant superoxide dismutase by chemical modification

The renal disposition characteristics of superoxide dismutase (SOD) and its derivatives, including macromolecular conjugates with polyethylene glycol and carboxymethyl-dextran, a cationized derivative, and glycosylated derivatives with galactose and mannose, were studied in the isolated perfused rat kidney. Renal disposition processes, such as glomerular filtration, tubular reabsorption, and uptake from the capillary side, were quantitatively determined by single-pass indicator dilution experiments under filtering and nonfiltering kidney conditions. Native SOD had a high glomerular filtration rate (40% of that of inulin) and was effectively reabsorbed in the tubules, while no significant uptake was observed from capillary side. Macromolecular conjugates showed restricted glomerular filtration due to an increase in molecular size. Cationization of SOD greatly enhanced its association with the tissue, not only from the luminal side but also from the capillary side, based upon electrostatic interaction. Galactosylated and mannosylated SOD showed reduced tubular reabsorption and increased exposure of the luminal surface to the enzyme. In addition, a small but significant uptake of mannosylated SOD from the capillary side was observed. This uptake was dose-dependent and completely inhibited by mannan, suggesting that mannose receptor-mediated endocytosis existed in the capillary side of the kidney. Thus, we can manipulate the renal disposition profiles of SOD by changing its physicochemical or biological properties through chemical modification.

In vivo and in vitro analysis of skin penetration enhancement based on a two-layer diffusion model with polar and nonpolar routes in the stratum corneum

In vitro and in vivo skin penetration of three drugs with different lipophilicities and the enhancing effects of 1-geranylazacycloheptan-2-one (GACH) were studied in rats. In vivo drug absorption profiles obtained by deconvolution of urinary excretion profiles were compared to the corresponding in vitro data obtained with a diffusion experiment. In vivo skin penetration of lipophilic butylparaben was considerably greater than that observed in vitro, while hydrophilic mannitol and acyclovir showed low penetration in both systems without GACH pretreatment. On the other hand, GACH enhanced mannitol and acyclovir penetration, especially in the in vivo system. Analysis of absorption profiles, using a two-layer skin model with polar and nonpolar routes in the stratum corneum, suggested that the diffusion length of a viable layer (viable epidermis and dermis) was shorter in vivo than in vitro and the effective area of the polar route in the stratum corneum was larger in vitro without GACH pretreatment. GACH increased the partitioning of acyclovir into the nonpolar route to the same extent in both systems. In addition, GACH increased the effective area of the polar route in vivo, probably because of enhanced water permeability; however, this effect was smaller in vitro since the stratum corneum was already hydrated even without GACH pretreatment.

Improvement of therapeutic effect of human recombinant superoxide dismutase on ischemic acute renal failure in the rat via cationization and conjugation with polyethylene glycol

Therapeutic effect of superoxide dismutase (SOD) and three derivatives: a conjugate with polyethylene glycol (SOD-PEG2), a cationized derivative (cSOD), and a mannosylated derivative (Man-SOD), on acute renal failure induced by ischemia/reperfusion was studied in rats. SOD and derivatives were administered intravenously to the rat after nephrectomy of the right kidney and before and after 60 min occlusion of the left renal artery. At 48 hr after reperfusion, the renal function was evaluated by determining the urinary excretion rate of 14C-inulin injected intravenously. No therapeutic effect on the impaired renal function was shown in the case of low dose SOD (2600 unit/kg) treatment. In contrast, administration of cSOD which was shown to be taken up by the isolated perfused kidney from its capillary side and SOD-PEG2 which maintained high plasma concentration exhibited significant therapeutic effect, as did SOD at ten-fold higher dose (26,000 unit/kg). On the other hand, renal damage was promoted by Man-SOD. Thus, the present study demonstrated that chemical modification may improve the therapeutic effect of SOD on the ischemic acute renal failure and increased SOD concentration in the renal vascular space is an important factor for the improved effect.

Control of in vivo fate of albumin derivatives utilizing combined chemical modification

Three types of bovine serum albumin (BSA) derivatives such as lactosylated BSA (LBSA), mannosylated BSA (Man-BSA), and cationized BSA (cBSA) were synthesized and their hepatic disposition characteristics in mice were evaluated by pharmacokinetic analysis. At lower doses (< or = 1 mg/kg), LBSA and Man-BSA were very rapidly eliminated from the blood circulation due to uptake by parenchymal and nonparenchymal cells of the liver, respectively, via receptor-mediated endocytosis (Nishikawa et al., 1992; Nishida et al., 1991a, b). These uptake processes were nonlinear and the apparent hepatic uptake clearances (CLliver) were decreased at administered doses higher than 1 mg/kg, e.g. 10, 20, and 100 mg/kg. The liver accumulation of cBSA was also nonlinear, but its binding and/or uptake capacity in the liver was larger than those of LBSA and Man-BSA; i.e., CLliver decreased at doses higher than 20 mg/kg. In the next step, we modified these BSA derivatives by attaching polyethylene glycol (PEG), a modifier known to reduce the hepatic uptake and increase plasma retention, to achieve precise control of the in vivo disposition characteristics of BSA derivatives. By conjugation with PEG having a molecular weight of 10 kDa, the CLliver values of LBSA, Man-BSA, and cBSA were decreasing to one-seventh, one-fortyfifth, and one-onehundredthirtieth, respectively. However, liver accumulation of PEG modified LBSA and Man-BSA at 24 h after i.v. injection was not significantly different from unmodified BSA derivatives. These results suggest that it is possible to control the hepatic uptake of protein drugs by a combination of introduction of charge or sugar moieties and PEG conjugation.

Long circulating emulsion carrier systems for highly lipophilic drugs

With the aim of developing of emulsion carrier systems for lipophilic drugs with the potential for prolonged circulation in the blood or hepatic targeting, the in vivo disposition of four model compounds, i.e., [3H]prostaglandin E1, [3H]retinoic acid, [14C]cholesterol, and [14C]cholesteryl oleate with calculated log PC(oct) values of 2.15, 6.61, 9.46, and 18.3, respectively, injected with various emulsion formulations, were studied in mice. Small sized emulsions of about 100 nm in diameters, with compositions of egg phosphatidylcholine (PC): soybean oil = 1:1 (small PC emulsion) and PC: egg sphingomyelin (SM): soybean oil = 0.7:0.3:1 (small SM emulsion), and a conventional emulsion with a diameter of about 250 nm and a composition of PC: soybean oil = 1:1 (large PC emulsion) were compared. Highly lipophilic [14C]cholesteryl oleate, a marker of emulsion particles, indicated diverse in vivo behaviors; i.e., the small SM emulsion produced prolonged circulation in the blood, and the small PC emulsion followed this, while the large PC emulsion was rapidly uptake by the liver. Thus, a reduction in size and coating with SM on the surface of oil droplets resulted in avoidance of the reticuloendothelial system (RES). Disposition profiles of other test compounds differed, depending on their lipophilicities: [14C]cholesterol showed disposition patterns in all formulations similar to those of [14C]cholesteryl oleate, but moderately lipophilic [3H]prostaglandin E1 and [3H]retinoic acid showed common disposition profiles, regardless of emulsion types, suggesting their rapid release from the emulsion carriers. These results suggest that small SM emulsion and large PC emulsion can act respectively as long circulating and liver targeting carriers for highly lipophilic drugs with log PC(oct) larger than 9.

Specific uptake of succinylated proteins via a scavenger receptor-mediated mechanism in cultured brain microvessel endothelial cells

Cellular uptake of succinylated catalase (Suc-CAT; Mw 227 kDa), bovine serum albumin (Suc-BSA; Mw 70 kDa), superoxide dismutase (Suc-SOD; Mw 34 kDa) and soybean trypsin inhibitor (Suc-STI; Mw 21 kDa) was studied using primary cultures of bovine brain microvessel endothelial cells (BMECs) developed as an in vitro model of the blood-brain barrier. Large succinylated proteins (Suc-CAT, Suc-BSA) were taken up by BMECs whereas significant uptake was not observed for native proteins and small succinylated proteins (Suc-SOD, Suc-STI). Uptake of Suc-BSA was significantly inhibited at 4 degrees C and in the presence of endocytosis inhibitors. Large succinylated proteins, maleylated BSA and dextran sulfate also showed competitive inhibition against Suc-BSA uptake while small succinylated proteins and carboxymethyl dextran did not show any effect. These results indicate that microvessel endothelial cells obtained from the brain endocytose succinylated proteins via a scavenger receptor-mediated mechanism for polyanions, and in addition, the importance of molecular weight or total numbers of anionic charges per one molecule of proteins is suggested. Usefulness of direct succinylation of proteins for their delivery to the brain capillary endothelium is thus demonstrated.

Synthesis and pharmacokinetics of a new liver-specific carrier, glycosylated carboxymethyl-dextran, and its application to drug targeting

To develop a new carrier system for hepatic targeting, carboxymethyl-dextran (CMD) was modified with galactose and mannose residues (Gal-CMD, Man-CMD), and their disposition characteristics were studied in mice using 14C-labeled dextran. At a dose of 1 mg/kg, i.v.-injected Gal-CMD and Man-CMD rapidly accumulated in the liver parenchymal and nonparenchymal cells, respectively, because of their preferential uptake via carbohydrate receptors in these cells. Pharmacokinetic analysis revealed that their uptake rates were sufficiently large for selective drug targeting. Targeting of cytosine beta-D-arabinoside (araC) was studied using Gal-CMD as a specific carrier to the hepatocytes. From the conjugate of araC with Gal-CMD, araC was released with a half-life of 36 hr in phosphate buffer (pH 7.4) and 23 hr in plasma. An in vivo biodistribution study demonstrated a disposition profile of the conjugated araC similar to that of the carrier, and selective delivery to hepatocytes of up to 80% of the dose was achieved. These findings suggest that glycosylated CMDs are carriers with a high affinity to liver parenchymal or nonparenchymal cells without any affinity to other tissues.

Analysis of skin penetration enhancement based on a two-layer skin diffusion model with polar and nonpolar routes in the stratum corneum: dose-dependent effect of 1-geranylazacycloheptan-2-one on drugs with different lipophilicities

The effects of 1-geranylazacycloheptan-2-one (GACH) on the in vitro skin penetration of seven drugs with various lipophilicities were studied. The penetration of drugs from aqueous vehicle through the guinea pig skin was increased depending on the pretreatment dose of GACH. The largest enhancement was observed for 5-fluorouracil (5-FU) and a bell-shaped relationship was obtained between enhancement ratio and the octanol/water partition coefficients of drugs. Further, Laplace transformed equations for percutaneous absorption of drug were derived from Fick's second law based on a two-layer skin diffusion model with polar and nonpolar routes in the stratum corneum. Through curve-fitting of their equations to penetration profiles using a nonlinear regression program MULTI(FILT) combined with a fast inverse Laplace transform (FILT) algorithm, the action mechanism of GACH was discussed in terms of its effect on the partitioning and diffusivity of drugs in each domain. With an increase in pretreatment dose of GACH, the estimated partition parameters of drugs into the nonpolar route increased but their diffusivities were little affected. The analysis based on a linear free-energy relationship suggested that the increase in partitioning of drugs into the nonpolar route was explained by its increasing polarity with GACH pretreatment.

Disposition characteristics of protein drugs in the perfused rat kidney

The renal disposition characteristics of 111In-labeled neocarzinostatin (NCS), soybean trypsin inhibitor (STI), and superoxide dismutase (SOD) were studied in the perfused rat kidney. In a single-pass indicator dilution experiment, venous and urinary recovery profiles and tissue accumulation of proteins were determined under filtering or nonfiltering conditions. In the nonfiltering kidney perfusion experiment, no significant tissue accumulation was observed, suggesting minimal uptake from the glomerular and peritubular capillary sides. Therefore, tissue recovery corresponded to that with tubular reabsorption after glomerular filtration. The total amount of NCS or STI being filtrated through glomeruli, the sum of tissue and urinary recoveries, was similar to that of inulin, but that of SOD was about half. Similarly, the steady-state distribution volumes (Vd) of NCS and STI obtained by moment analysis of their venous outflow curves were similar to that of inulin, while the Vd value of SOD was significantly lower. These results suggest the restricted passage of SOD through the glomerular and postglomerular capillary wall. The tubular reabsorption ratio of proteins against the total filtrated amount decreased with an increase in the administered dose, suggesting nonlinearity of reabsorption. SOD had the largest reabsorption ratio. Thus, this experimental system is useful for quantitative analysis of renal disposition of proteins.

Effects of various absorption promoters on pulmonary absorption of drugs with different molecular weights

The effects of various absorption promoters on the pulmonary absorption of drugs with different molecular weights were examined in rats. Phenol red and fluorescein isothiocyanate-labeled dextrans (FDs) with various molecular weights were used as model drugs and the absorption promoters used in this study were sodium glycocholate, sodium salicylate, ethylenediaminetetraacetic acid disodium salt (Na2-EDTA) and sodium caprate, all at a concentration of 1%. Of these absorption promoters, sodium glycocholate and sodium caprate appeared to be more effective for enhancing the pulmonary absorption of these drugs than sodium salicylate and Na2-EDTA. Furthermore, it was indicated that there is the optimal molecular weight to which each absorption promoter gives the largest enhancing effect on the pulmonary absorption of drugs.

Disposition characteristics of model macromolecules in the perfused rat kidney

The disposition characteristics of model macromolecules such as dextran (70 kDa), bovine serum albumin (BSA), and their charged derivatives were studied in the perfused rat kidney. In a single-pass indicator dilution experiment, venous and urinary recovery patterns and tissue accumulation of radiolabeled compounds were evaluated under filtering or nonfiltering conditions. In the filtering kidney, cationic macromolecules such as diethylaminoethyl-dextran (DEAE-dex) and cationized BSA (cBSA) accumulated in the kidney to a great extent whereas anionic and neutral macromolecules such as BSA, carboxymethyl-dextran (CM-dex), and dextran showed only small uptake. DEAE-dex and cBSA were distributed to both the medulla and cortex regions of the kidney and their recoveries in the kidney decreased as the injected dose increased. Similar tissue uptake was observed in the nonfiltering kidney perfusion system suggesting that they were mainly taken up by the kidney from the renal capillary side based on electrostatic interaction. In addition, the steady-state distribution volumes of cationic macromolecules calculated from venous outflow patterns were larger than those of the intravascular volume estimated from the distribution volumes of neutral and anionic macromolecules, suggesting their reversible interaction with the vascular wall. On the other hand, dextran derivatives with molecular weight distribution were excreted into urine based on glomerular permselectivity; i.e., cationic DEAE-dex and anionic CM-dex showed enhanced and restricted urinary excretion, respectively, compared with neutral dextran. In contrast, no significant excretion was observed for BSA and cBSA. The utility of the isolated rat kidney perfusion experiment for studying the renal disposition of macromolecular drugs was thus demonstrated.

Controlled biodistribution of highly lipophilic drugs with various parenteral formulations

Lipid carrier systems are considered effective for targeting highly lipophilic drugs, but little systematic information about the effect of the physicochemical and pharmaceutical characteristics of drugs and formulations on their performance has been obtained. 3H-Retinoic acid and 14C-cholesteryl oleate with different lipophilicities (log PCoct = 6.6 and 18, respectively) were selected as model drugs and the potential of formulations such as oil in water (o/w) emulsion, micellar solution, and liposomes for controlling their biodistribution was demonstrated. After intravenous injection in mice, 3H-retinoic acid showed similar disposition profiles irrespective of formulation type, suggesting its rapid dissociation from carriers. 14C-Cholesteryl oleate with extremely high lipophilicity revealed widely varied disposition profiles reflecting the distribution patterns of carriers: micellar solution and liposomes showed large AUC values and low hepatic clearances, while the use of emulsion as a carrier resulted in rapid clearance from blood circulation into the liver. The results suggested that these formulations can be used as targeting carriers for lipophilic drugs which, however, should have a sufficiently high lipophilicity of about log PCoct 9-16.