Effect of chronic administration of phenobarbital on the hepatobiliary transport of phenol red: assessment by statistical moment analysis

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.

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.

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).

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.

Influence of pentobarbitone on in-vivo local disposition of diclofenac in rat liver

Because the liver is the main organ eliminating many drugs from the body and because pentobarbitone and other analogues can inhibit biliary secretion, the influence of pentobarbitone on hepatic local disposition of diclofenac has been investigated. Diclofenac was infused into the portal and femoral veins of non-anaesthetized rats (group A) and rats anaesthetized with pentobarbitone (group B) and the plasma concentration of diclofenac and the total amount of diclofenac excreted in the bile (in both cases intact diclofenac plus its glucuronide) were simultaneously monitored by HPLC at appropriate time intervals. The time-courses of plasma concentration and amount excreted in the bile were evaluated by moment analysis with trapezoidal integration. The hepatic recovery ratio (FH) was calculated by comparing the area under the curve (AUC) of plasma concentration after intravenous infusion with that after intraportal infusion. The mean biliary transit time (tb) was estimated by subtracting the mean residence time (MRT) of the plasma data from the mean biliary residence time (MRTb) of the biliary excretion data. The FH values of diclofenac were 0.664 in group A and 0.643 in group B. The biliary excretion ratio (Fb) of total diclofenac after intravenous administration was 27.0% in group A and 14.1% in group B. The tb values for total diclofenac were estimated to be 0.192 h (intravenous) and 0.159 h (intraportal) in group A, and 0.174 h and 0.238 in group B. Analysis of variance showed that differences among these four tb values were insignificant at the 5% level. The differences in the mean residence time (MRT), total clearance (CL) and distribution volume at steady state (Vss) were insignificant between groups A and B. Whereas total and the hepatic clearance of diclofenac were not affected by pentobarbitone, biliary clearance was extensively reduced. It took a relatively long time for diclofenac to move from the sinusoid into the bile and the time was not affected by pentobarbitone.

New hepatocellular diffusion model for analysis of hepatobiliary transport processes of drugs

A new hepatocellular diffusion model was developed to kinetically evaluate the hepatobiliary transport processes of drugs in the perfusion system, based on the physiological structure of the liver. Since the equations describing the hepatocellular diffusion phenomena were derived as image forms in the Laplace domain, the fast inverse Laplace transform (FILT) was adopted to manipulate the image equations. Cefixime and cefpiramide were selected as model drugs. The concentrations in the perfusate and the excreted amounts into the bile were simultaneously measured at appropriate intervals after the rapid administration of each drug into the portal vein. The hepatocellular diffusion model was fitted to the biliary excretion profiles from rat livers, by means of a nonlinear least squares program, MULTI(FILT). According to this model, the hepatobiliary transport process of drug is kinetically separated into three steps, that is, the diffusion into and through the hepatocytes, the transfer from the hepatocytes into the bile canaliculi, and the movement through the bile canaliculi to the outlet of bile duct. These steps are characterized by the diffusion rate constant through hepatocytes (kdif), the permeability rate constant into the bile canaliculi (kbmc) and the transit time through the bile canaliculi to the outlet of bile duct (tcan), respectively. It was demonstrated that kdif of cefixime (0.023 min-1) was significantly smaller than that of cefpiramide (0.044 min-1), while the differences in kbmc and tcan were not obvious between cefixime and cefpiramide. kbmc and tcan of both drugs were about 1.2 min-1 and about 1.0 min, respectively. These parameters were correlated to the excretion ratio into the bile (Fbile) and the mean transit time from the sinusoid through the hepatocytes to the outlet of bile duct (tbile).

Absorption of organic anions as model drugs following application to rat liver surface in-vivo

Absorption of organic anions (phenol red, bromphenol blue and bromosulphonphthalein) has been studied after their application to rat liver surface in-vivo, employing a cylindrical glass cell (i.d. 9 mm, area 0.64 cm2). Each drug appeared gradually in the blood with the peak level at about 1 h, after which its concentration declined slowly. Absorbed model drug was efficiently excreted into the bile. These observations appear to indicate the possibility of drug absorption from liver surface membrane. Absorption of model drugs was estimated to be more than 59% in 6 h. The biliary recovery and metabolism of phenol red did not change as compared with that after intravenous administration.

Therapeutic effects of superoxide dismutase derivatives modified with mono- or polysaccharides on hepatic injury induced by ischemia/reperfusion

Therapeutic effects of four types of recombinant superoxide dismutase (SOD) derivatives, conjugates with polysaccharides, carboxymethyl (SOD-CMD) and diethylaminoethyl (SOD-DEAED) dextrans and galactosylated (Gal-SOD) and mannosylated (Man-SOD) derivatives, on hepatic ischemia/reperfusion injury were studied in rats. Hepatic injury induced by transient occlusion and subsequent reflow of hepatic blood was evaluated by the analysis of biliary excretion of bromosulfophthalein (BSP) injected intravenously. At a dose of 10000 units/kg, native SOD and SOD-DEAE did not show any significant effect and SOD-CMD showed slight effect. On the other hand, Gal-SOD and Man-SOD, targeted to the liver parenchymal and nonparenchymal cells, respectively, by a receptor-mediated endocytosis, exhibited superior inhibitory effects. These results demonstrated that these glycosylated SOD derivatives were useful for the prevention of hepatic ischemia/reperfusion injury.