3-O-Acyl-epicatechins Increase Glucose Uptake Activity and GLUT4 Translocation through Activation of PI3K Signaling in Skeletal Muscle Cells

Tea catechins promote glucose uptake in skeletal muscle cells. In this study, we investigated whether the addition of an acyl group to the C-3 position of catechins to generate 3-O-acyl-catechins promoted glucose uptake in L6 myotubes. 3-O-Myristoyl-(-)-epicatechin (EC-C14) and 3-O-palmitoyl-(-)-epicatechin (EC-C16) promoted glucose uptake and translocation of glucose transporter (GLUT) 4 in the cells. The effect of 3-O-acyl-(-)-epicatechins was stronger than that of (-)-epicatechin (EC), whereas neither 3-O-myristoyl-(+)-catechin (C-C14) nor 3-O-palmitoyl-(+)catechin (C-C16) promoted glucose uptake or GLUT4 translocation as well as (+)-catechin (C). We further investigated an affinity of catechins and 3-O-acyl-catechins to the lipid bilayer membrane by using surface plasma resonance analysis. Maximum binding amounts of EC-C16 and C-C16 to the lipid bilayer clearly increased compared with that of (-)-EC and (+)-C, respectively. We also examined the mechanism of GLUT4 translocation and found EC-C14 and EC-C16 induced the phosphorylation of PI3K, but did not affect phosphorylation of Akt or IR. In conclusion, the addition of an acyl group to the C-3 position of (-)-EC increases its affinity for the lipid bilayer membrane and promotes GLUT4 translocation through PI3K-dependent pathways in L6 myotubes

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 cm2). 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 ka 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 ka 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 ka 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

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

We examined the importance of application volume and area in the absorption of phenol red as a model drug from the rat liver surface, for pharmaceutical formulation concerning administration form. When 1 mg of phenol red was applied to the rat liver surface in-vivo using a cylindrical glass cell (i.d. 9 mm) in three volumes (0.1, 0.2 or 0.334 mL), the shape of the plasma concentration pattern differed greatly, particularly the maximum concentration. These patterns were well fitted by a two-compartment model with first-order absorption, and the obtained absorption rate constant Ka decreased inversely according to the application volume. The absorption ratio and biliary recovery of phenol red at 6 h was increased with glass cell area (i.d. 6, 9 or 14 mm; area 0.28, 0.64 or 1.54 cm2). Furthermore, the permeability coefficient Papp derived from Ka did not depend on application area, indicating no difference in absorption characteristics of liver surface. This also implies transport of a drug by a passive diffusion from the liver surface. After intraperitoneal administration to the rat liver surface for clinical application, increase in application volume resulted in the delayed disappearance of phenol red from plasma. However, the difference was not as marked as that using a glass cell. The assumption that the effective area relating to the absorption changed with the application volume enabled us to estimate Papp. Consequently, we speculate absorbability can be estimated precisely by considering application volume and area

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 is to clarify 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 by sticking a polyethylene cap (PE cap) 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-sticking 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 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 due to there being a small effective area of blood vessels

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

The aim of this study is to examine the effect of the instillation method on absorption of a drug from the liver and small intestinal serosal surface in rats. We performed continuous microinstillation via an infusion pump and bolus instillation via a syringe. Phenol red as a model was absorbed after continuous microinstillation of 2.35 mg in 235 ?L for 5 min on the liver and small intestinal serosal surface in rats with a significantly higher AUC of the plasma concentration profile until 60 min, compared with that after bolus instillation. A similar trend was observed after continuous microinstillation of 2.35 mg in 117.5 ?L for 2.5 min. The calculated absorption rate constants Ka after continuous microinstillation of phenol red 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 ?L on either instillation site. In the comparison between instillation sites, instillation of phenol red on the liver surface resulted in 1.2 to 2.3-fold higher Ka, compared to small intestinal serosal surface. This tendency was marked after continuous microinstillation of 2.35 mg in 117.5 ?L. 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

In Vivo Ocular Pharmacokinetic Model for Designing Dosage Schedules and Formulations of Ophthalmic Drugs in Human

The purpose of this study was to develop an in vivo pharmacokinetic model and parameters for predicting the concentrations of ophthalmic drugs in the anterior chamber after instillation into human eyes. We have already reported the usefulness of mathematical model including a diffusion process in rabbits 1). Timolol was used as a model ophthalmic drug. The concentrations of timolol and fluorescein in the tear fluid were determined after instillation into the eyes of human volunteers. The in vivo pharmacokinetic parameters in the tear fluid were estimated by the elimination profile according to a one-compartment model. The concentrations of timolol in the aqueous humor were obtained from the data previously reported 2),3). Other parameters of timolol were estimated from the concentration profiles of timolol in the aqueous humor according to a pharmacokinetic model including a corneal diffusion process. The parameters for human were almost equal to those for rabbits reported previously 1). This mathematical model and in vivo parameters will be effective to estimate the adequate regimen for ophthalmic chemotherapy and develop the ocular drug delivery systems

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