Effect of application volume and area on the absorption of phenol red, as a model drug, from the liver surface in rats

Influence of oxygen uptake through the liver surface on the metabolism of ex vivo perfused liver during hypoxia

The low quality of transplants having undergone hypoxic injury can lead to postoperative complications. The aim of the present research is to estimate, by means of mathematical modeling, how the process of oxygen uptake through the liver surface influences the metabolism of ex vivo perfused liver under hypoxia. The value of oxygen uptake through the surface was established to depend on the degree of oxygenation of the perfusion medium. A decrease in the oxygenation of the perfusion medium resulted in a decreased oxygen uptake through the liver surface. Stoichiometric modeling of the liver metabolism shows that upon the decreased oxygenation of the perfusion medium more energy is required for the process of oxygen uptake through the surface even at a lower level as compared to the normal oxygen supply. The application of the Pareto optimality allows estimating the optimum distribution of the energy resources in liver under ex vivo conditions. Both upon the normal and decreased oxygenation of the perfusion medium, the phenomenon of "free competition" for the resource was observed, with the energy being optimally distributed among all the metabolic fluxes. Moreover, this energy is also spent on the accompanying processes, e.g. for the transport of interstitial fluid.

Effect of Metabolic Inhibitors on the Hepatic Disposition of 5-Fluorouracil after Application to the Rat Liver Surface

We evaluated the effects of 5-fluorouracil (5-FU) metabolic inhibitors, gimeracil or uridine, on the hepatic disposition of 5-FU after application to the liver surface in rats, aiming to enhance the availability of 5-FU in the liver. 5-FU solution with or without metabolic inhibitors was applied to the rat liver surface using a cylindrical diffusion cell. The liver, blood and the remaining solution in the diffusion cell were collected at specified times, and assayed for 5-FU content. 5-FU absorption properties were not altered by addition of gimeracil and uridine. The 5-FU concentration in the diffusion cell attachment site of the rat liver (site 1) at 0.1-0.4 M ratios of gimeracil to 5-FU was significantly higher than that of the control. On the contrary, the addition of uridine did not increase the 5-FU concentration at site 1. At a 0.1 M ratio of gimeracil to 5-FU, the maximum 5-FU plasma concentration was the lowest, and the area under the 5-FU concentration-time curve at site 1 was 3.4 times greater than that of the control. We demonstrated that applying 5-FU with gimeracil to the rat liver surface could increase the availability of 5-FU in the liver.

Effect of viscous additives on the absorption and hepatic disposition of 5-fluorouracil (5-FU) after application to liver surface in rats

Objectives  The aim was to study the effect of viscous additives on the absorption and hepatic disposition of 5-fluorouracil (5-FU) after application to the liver surface in rats. Methods  5-FU solution with or without viscous additives was applied to the rat liver surface with a cylindrical diffusion cell. Then, blood and the remaining solution in the diffusion cell were collected at selected times, followed by excision of the liver. The excised liver was divided into three sites and assayed for 5-FU content. Key findings  The absorption rate of 5-FU from the liver surface was decreased in the presence of carboxymethylcellulose sodium (CMC-Na) and polyvinyl alcohol (PVA) as compared with the control. The k(a) values of PVA 15% and CMC-Na 1% were reduced to about 80 and 67% of the control. The maximum plasma concentration of 5-FU was decreased by incorporation of viscous additives. The 5-FU concentration at the diffusion cell attachment site of the liver (site 1) plateaued at 180 min in the absence of viscous additives. On the other hand, the concentration of 5-FU at site 1 increased in a time-dependent manner until 360 min in the presence of viscous additives. Conclusion  Viscous additives might be useful for retaining drugs at their application site and controlling the rate of absorption from the liver surface.

[Development of drug delivery system by utilizing absorption from liver surface and its application]

Because it is difficult to achieve local drug activity following administration by the conventional intravenous and oral routes, I sought to develop a new route of administration utilizing drug absorption from the liver surface in order to target that organ. Although direct application to the liver surface should yield local drug distribution, drug absorption from the liver surface has not been reported in the literature. Therefore, we analyzed, as a model, the efficiency of absorption of several organic anions and dextrans of various molecular weights following application to the rat liver surface in vivo using a cylindrical diffusion cell. Each compound appeared gradually in the plasma, followed by excretion into the bile and/or urine, indicating the possibility of drug absorption from the liver surface. The absorption process from the liver surface may not involve a specific transport system because dose and transport inhibitors had no detectable effect. In addition, molecular weight was found to be a determinant of absorption through the liver surface. The efficiency of targeting desired region in the liver was enhanced considerably by application to the liver surface, compared to intravenous administration. Moreover, I have obtained several promising results from the application of this new drug delivery system to anticancer drugs and gene therapy. On the other hand, I have also clarified the characteristics of drug absorption from the surfaces of the kidney, stomach, cecum and small intestine, and plan to apply the physiological findings to other fields.

Evaluation of Enhanced Peritoneum Permeability in Methylglyoxal-treated Rats as a Diagnostic Method for Peritoneal Damage

PURPOSE

As peritoneal damage in long-term peritoneal dialysis therapy is a major problem correlated to patient prognosis, diagnosis of peritoneal damage is important. To develop a diagnostic method for peritoneal damage, we focused on hyperpermeability across the peritoneum in a pathogenic peritoneal damage condition. In this study, disposition characteristics of an intraperitoneally injected marker substance in peritoneal damaged rats were analyzed.

MATERIALS AND METHODS

Peritoneal damaged rats were prepared by intraperitoneal injection of a glucose degradation product, methylglyoxal (MGO), for five or ten consecutive days. Phenolsulfonphthalein (PSP), as a marker substance, was intraperitoneally or intravenously injected into MGO-treated rats. Subsequently, the PSP disposition characteristics were pharmacokinetically analyzed.

RESULTS

In both cases of 5 and 10 days treatment of MGO, absorption of PSP after intraperitoneal injection was significantly enhanced. Plasma concentration and urinary excretion of PSP in MGO-treated rats were also higher than those in saline-treated rats in the early phase. On the contrary, there was no significant difference in terms of the pharmacokinetic parameters of intravenously injected PSP in saline- or MGO-treated rats. These results indicated that intraperitoneally injected MGO primarily acts on the peritoneal membrane; therefore, the peritoneal permeability of the marker substance was enhanced.

CONCLUSION

We demonstrated that pharmacokinetic analysis of peritoneum permeability might be a potent diagnostic method for peritoneal damage in experimental animals and patients receiving peritoneal dialysis.

Spleen-Selective Gene Transfer Following the Administration of Naked Plasmid DNA onto the Spleen Surface in Mice

The purpose of present study was to examine spleen-selective gene transfer following the administration of naked plasmid DNA (pDNA) onto the spleen surface in mice. Gene expression in the spleen and other tissues was evaluated based on firefly luciferase activity. Six hours after spleen surface instillation of naked pDNA, high gene expression in the spleen was observed. On the contrary, intravenous and intraperitoneal administration of naked pDNA resulted in no detectable gene expression. After instilling naked pDNA onto the spleen surface, gene expression in the spleen was significantly higher than those in other tissues. Six hours after instillation of naked pDNA onto the spleen surface, gene expression in the spleen reached the peak value, and thereafter decreased gradually. By utilizing a glass-made diffusion cell that is able to limit the contact dimension between the spleen surface and naked pDNA solution administered, site-specific gene expression in the spleen was found. This novel gene transfer method is expected to be a safe and effective strategy for DNA vaccine against serious infectious diseases and cancers.

Unilateral Lung-Selective Gene Transfer Following the Administration of Naked Plasmid DNA onto the Pulmonary Pleural Surface in Mice

The purpose of the present study was to examine unilateral lung-selective gene transfer following the administration of naked plasmid DNA (pDNA) onto the pulmonary pleural surface in mice. Naked pDNA was administered intravenously, intraperitoneally, and instilled onto the right pulmonary pleural surface. Four hours later, right pulmonary pleural surface instillation of naked pDNA resulted in high gene expression in the right lung. On the contrary, intravenous and intraperitoneal administration of naked pDNA resulted in no detectable gene expression. After instilling naked pDNA onto the right or left pulmonary pleural surface, gene expressions in the applied lung were significantly higher than those in the other lung and tissues. In addition, gene expressions were detected only in the intrathoracic tissues, not in the intraperitoneal tissues. Four hours after instillation of naked pDNA onto the right pulmonary pleural surface, gene expression in the right lung was the highest, and thereafter gene expression in the right lung decreased gradually. This novel gene transfer method is expected to be a safe and effective treatment against serious lung diseases.

Stomach-Selective Gene Transfer Following the Administration of Naked Plasmid DNA onto the Gastric Serosal Surface in Mice

The purpose of the present study was to achieve a stomach-selective gene transfer following the administration of naked plasmid DNA (pDNA) onto the gastric serosal surface in mice. Gene expression in the stomach and other tissues was evaluated by firefly luciferase activity. Six hours after gastric serosal surface instillation of naked pDNA, high gene expression in the stomach was observed. On the contrary, intravenous and intraperitoneal injection of naked pDNA exhibited no detectable gene expression. Following instillation of naked pDNA onto the gastric serosal surface, gene expression in the stomach was significantly higher than in other tissues. Gene expression in the stomach was highest 12 h after the instillation and thereafter decreased gradually. Utilizing a glass-made diffusion cell that is able to limit the contact dimension between the gastric serosal surface and the naked pDNA solution administered, site-specific gene expression in the stomach was achieved. This novel gene transfer method is expected to be a safe and effective treatment against serious stomach diseases.

Regional Delivery of Model Compounds and 5-Fluorouracil to the Liver by Their Application to the Liver Surface in Rats: Its Implication for Clinical Use

PURPOSE

The purpose of this study was to examine drug distribution in the liver after drug application to the rat liver surface.

METHODS

Phenolsulfonphthalein (PSP) and fluorescein isothiocyanate dextran (MW 4400, FD-4) as model compounds or 5-fluorouracil (5-FU) was applied to the rat liver surface by employing a cylindrical diffusion cell (i.d. 9 mm, 0.64 cm2). Then, blood and the remaining solution in the diffusion cell were collected at selected times, followed by excision of the liver. The excised liver was divided into three sites: the region under the diffusion cell attachment site (site 1), the applied lobe except for site 1 (site 2), and non-applied lobes (site 3).

RESULTS

In the case of i.v. administration, there were no differences in PSP concentrations among the three sites of the rat liver, and the concentrations rapidly decreased. On the other hand, the PSP concentration in site 1 after application to the rat liver surface was considerably higher than in site 2 and site 3. In addition, the area under the curve (AUC) value (AUCsite1), calculated from the PSP concentration profile in site 1, was about 10 times larger than that in site 3. A similar trend of regional delivery advantage by liver surface application was observed in the case of the macromolecule model FD-4, with a marked AUCsite1 of about 5 times larger than the other two sites. Moreover, we clarified that the anticancer drug 5-FU preferentially distributed in site 1 after application to the rat liver surface.

CONCLUSION

These results demonstrate the possibility of regional delivery of drugs to the liver by application to the liver surface.

Absorption of phenolsulfonphthalein as a model across the mesenteric surface in rats to determine the drug absorption route after intraperitoneal administration

The purpose of this study was to clarify the absorption characteristics of a drug across the mesenteric surface, which occupies a large area of absorption in the peritoneal cavity, in order to determine the drug absorption route after intraperitoneal administration. Absorption of phenolsulfonphthalein (PSP) as a model after application to the mesenteric surface was investigated in rats by employing a cylindrical diffusion cell attached to the mesentery with or without blood vessels. PSP was absorbed from the rat mesenteric surface, followed by its appearance in the plasma and bile, regardless of blood vessel existence. The absorption ratios of PSP in 6 h were calculated to be 92.1 and 83.6% from the mesenteric surface with and without blood vessels, respectively. We then employed an experimental system in which a polyethylene (PE) cap was stuck on the surface of the other side to exclude the influence of absorption of the drug from the other organ surfaces that penetrated across the mesentery. The PE cap decreased the appearance of PSP in the plasma from the mesenteric surface with blood vessels and eliminated the PSP absorption completely from the mesenteric surface without blood vessels. Accordingly, blood vessels on the mesenteric surface must actually play an important role in drug absorption, but the contribution of the mesenteric surface to drug absorption from the peritoneal cavity is unlikely to be significant because there is a small effective area of blood vessels.

Absorption characteristics of compounds with different molecular weights after application to the unilateral kidney surface in rats

The aim of the present study is to clarify the absorption mechanism of a drug from the kidney surface membrane in rats. We studied the absorption characteristics of phenolsulfonphthalein (PSP) and other compounds with different molecular weights after their application to the rat kidney surface in vivo, employing a cylindrical diffusion cell (i.d. 6 mm, area 0.28 cm(2)). The time course of free PSP amounts remaining in the diffusion cell obeyed first-order kinetics at a dose of 1 mg, and its rate constant k(a) was calculated to be 0.0137 min(-1). Absorption ratios of PSP in 4 h were calculated (from the amount recovered from the diffusion cell) to be 91.4, 96.4 and 97.7% at doses of 0.5, 1 and 1.5 mg, respectively. The area under the curve for the plasma concentration profile of free PSP was proportional to the application dose. It is thus suggested that the absorption process of PSP from the rat kidney surface does not approach saturation at a dose of 1.5 mg. Also, no significant difference was seen in the k(a) values within the dose range of 0.5-1.5 mg, which were estimated by curve-fitting the plasma concentration profiles of free PSP in a two-compartment model with first-order absorption. Furthermore, we examined the importance of molecular weight on the absorption from the kidney surface using fluorescein isothiocyanate-dextrans (FDs) with molecular weights of 4400 (FD-4), 11,000 (FD-10), 40,500 (FD-40) or 69,000 (FD-70), including the organic anions bromphenol blue and bromosulfonphthalein. The absorption ratios of FDs from the rat kidney surface in 6 h decreased with an increase in the molecular weight (76.1% for FD-4, 54.4% for FD-10, 11.5% for FD-40 and 3.9% for FD-70). A linear relationship was observed between k(a) and the reciprocal value of z the square root of the molecular weight of these compounds. The limit of absorption from the rat kidney surface was extrapolated to be at a molecular weight of approximately 130,000.

[Development of drug delivery system based on a new administration route for targeting to the specific region in the liver]

Development of drug delivery systems to achieve site-specific delivery or prolonged retention in the circulation has attracted attention, because new types of drugs are expected to be created with advances in life science and biotechnology such as the Human Genome Project. We have tried to develop a new administration route for drug targeting to the liver, since drug administration by the intravenous and oral routes makes it difficult to achieve a local site of action in the liver. Although direct application to the liver surface should result in local drug distribution, drug absorption from the liver surface has not been reported in the literature. Therefore we analyzed the absorption mechanism of several organic anions and dextrans with different molecular weights as model drugs, after application to the rat liver surface in vivo, employing a cylindrical diffusion cell. Every compound appeared gradually in the plasma, followed by excretion into the bile and/or urine, indicating the possibility of drug absorption from the liver surface. A specific transport system might not be involved in the absorption process from the liver surface, because the effect of dose and transport inhibitors on the absorption was not recognized. In addition, molecular weight was found to be a determining factor in absorption from the liver surface. The targeting efficacy was considerably enhanced by application to the liver surface, as compared with intravenous administration. Moreover, we have identified important physicochemical and pharmaceutical factors determining the absorption rate of a drug from the liver surface for clinical use. Consequently, drug application to the liver surface could improve availability in the desired site of a new drug such as bioactive compounds and genomic medicines, by combination with appropriate chemical and pharmaceutical formulation modifications.

Influence of liver disease on phenolsulfonphthalein absorption from liver surface to examine possibility of direct liver surface application for drug targeting

We have examined the influence of liver disease on drug absorption from the liver surface membrane, regarded as the first barrier for drug targeting to the liver. The main purpose of this study is to examine the possibility of direct liver surface application as a drug targeting method. We employed rats intoxicated with carbon tetrachloride (CCl(4)) or D-galactosamine (GAL) as the liver disease model, and examined drug absorption characteristics after application to the liver surface, by utilizing a cylindrical diffusion cell. In the liver-intoxicated rats, about 90% of a low molecular weight drug, phenolsulfonphthalein (PSP), as a model was absorbed from the liver surface in 6 h, similar to the normal rats (no treatment). Although the absorption rate was increased in the CCl(4) group, whereas slightly retarded absorption was observed in GAL group, there should be no serious problem for the clinical use of liver surface application. The PSP absorption from the liver surface in the CCl(4) group was indicated to obey first-order kinetics by elimination profile from the diffusion cell. The first-order absorption rate constant K(a) values of PSP from the liver surface, obtained by a compartment model and elimination profile, were increased 1.3-fold in the CCl(4) group compared to the control. Moreover, we performed drug application to the liver surface in the peritoneal cavity to assume clinical use. The K(a) of PSP in the CCl(4) group was about 4-fold larger than in the normal group, implying the importance of estimating changes in peritoneal drug absorption as a result of liver disease. Consequently, it is expected that there will be no marked decline in the absorption rate from the liver surface in a liver disease state, leading us to apply this administration method for liver targeting.

A novel method for preparation of animal models of liver damage: liver targeting of carbon tetrachloride in rats

Animal models prepared by treatment with toxic compounds such as a carbon tetrachloride have been used to examine drug disposition in hepatic diseases. However, it is possible that these compounds accumulate and cause damage to other organs as they are administered systemically. In this study, we used the liver surface application technique to deliver a toxic compound to the liver to prepare an appropriate animal model in which only the liver is significantly damaged. To restrict the absorption area in the liver, a cylindrical diffusion cell was attached to the liver surface of male Wistar rats. Twenty-four hours after direct addition of carbon tetrachloride to the diffusion cell, plasma levels of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT), and hepatic malondialdehyde (MDA) concentration were increased, while there were no changes in plasma creatinine or renal MDA level. On the other hand, not only GOT, GPT and hepatic MDA, but also creatinine and renal MDA levels were markedly increased by p.o. and i.p. administration of carbon tetrachloride, suggesting renal damage. These results indicated that the animal models of liver damage prepared by utilizing drug delivery techniques to accumulate toxic compounds in the liver would enable us to investigate the precise effects of hepatic disorder on drug disposition.

Absorption characteristics of model compounds with different molecular weights from the serosal caecal surface in rats

The purpose of this study was to clarify the absorption characteristics of drugs across the serosal caecal surface membrane, occupying a large absorption area in the peritoneal cavity in rats. Absorption of phenolsulfonphthalein (PSP) and fluorescein isothiocyanate dextrans (FDs) as model drugs after application to the rat serosal caecal surface was investigated using a cylindrical diffusion cell. PSP was absorbed from the rat serosal caecal surface, followed by appearance in the plasma and bile. The time course of the remaining PSP amount in the diffusion cell obeyed first-order kinetics, and the rate constant, Ka, was calculated to be 8.01 x 10(-3) min(-1). No significant difference was seen in the absorption ratio of PSP, which was approximately 90% in 6 h for three doses (0.3, 0.5 and 1 mg), suggesting linear absorption. Moreover, the absorption ratios of FDs from the rat serosal caecal surface at 3 h decreased with an increase in the molecular weight (24.7% for FD4, 12.8% for FD-10 and 3.4% for FD-40).

Effect of instillation method on the absorption of phenolsulphonphthalein as a model drug from the liver and small intestinal serosal surface in rats

We have examined the effect of the instillation method on the absorption of a drug from the liver and the small intestinal serosal surface in rats. We performed continuous microinstillation via an infusion pump and bolus instillation via a syringe, using phenolsulphonphthalein (phenol red) as the model drug. After continuous microinstillation of phenolsulphonphthalein 2.35 mg in 235 microL for 5 min on the liver and small intestinal serosal surface in rats, the AUC (area under the curve) of the plasma concentration profile up to 60 min was significantly higher compared with bolus instillation. A similar trend was observed after continuous microinstillation of phenolsulphonphthalein 2.35 mg in 117.5 microL for 2.5 min. The calculated absorption rate constants (Ka) after continuous microinstillation of phenolsulphonphthalein based on a two-compartment model with first-order absorption were higher than those after bolus instillation on the liver and small intestinal serosal surface at either instillation concentration. Moreover, Ka was increased after continuous microinstillation of 2.35 mg in 117.5 microL at either instillation site. Instillation of phenolsulphonphthalein on the liver surface resulted in a 1.2- to 2.3-fold higher Ka compared with the small intestinal serosal surface. This tendency was marked after continuous microinstillation of 2.35 mg in 117.5 microL. In conclusion, absorption could be enhanced by instilling a small amount of drug solution on the liver surface gradually and continuously, suggesting a promising approach for instillation site-selective drug delivery in the peritoneal cavity.

Effect of viscous additives on drug absorption from the liver surface in rats using phenol red as a model

The purpose of this study is to obtain information that can be used to improve controlled release and residence time of drugs on the liver surface. Using carboxymethylcellulose sodium salt (CMC-Na) and polyvinyl alcohol (PVA), we examined the effect of viscous formulations on the absorption of phenol red as a model. In the presence of 3% CMC-Na or 15% PVA, the maximum plasma concentration of phenol red decreased after application to the rat liver surface using a cylindrical glass cell. The absorption ratios in 6 h calculated from the remaining amount of phenol red in the glass cell were 68.6, 60.5 and 48.7% (control: 73.1%) in the presence of 1 or 3% CMC-Na and 15% PVA, respectively. As a result of the reduction in the absorption ratio, the amount of phenol red excreted into the bile and urine in 6 h was decreased by the addition of the viscous additives. The decrease in absorption rate was characterized by a pharmacokinetic analysis of the plasma concentration profile. The change in absorption rate differed between the viscous additives, reflecting the result of the in vitro release experiment. Accordingly, the possibility that the drug absorption rate from the liver surface can be altered by viscous additives was suggested to have a promising prospect for therapeutic use.