Prediction of human percutaneous absorption from in vitro and in vivo animal experiments.

Although anatomical and structural similarities between the skin of minipigs and humans are often reported, few percutaneous pharmacokinetic studies have been conducted in minipigs. The objective of this study was to clarify the usefulness of minipigs for estimating the percutaneous absorption of various drugs in humans. The absorption of several marketed drugs was observed in mice, rats and minipigs both in vivo and in vitro, and results were compared with those in humans. For all six model drugs, after percutaneous administration in vivo, fraction of dose absorbed (F) from the skin was the lowest in minipigs among the four species studied, including humans. In vitro drug permeation results were similar, with the lowest permeability observed in minipigs. However, combined use of both in vitro permeation and in vivo absorption data from minipigs using triple pack approach resulted in better prediction of human F values than data obtained from mice. These results suggest some qualitative, but not quantitative, similarities between the drug absorption process across the skin of minipigs and humans. In conclusion, minipigs appear to be a promising model animal for predicting percutaneous drug absorption in humans, however, more in vivo and in vitro studies are needed to improve predictability.

Usefulness of minipigs for predicting human pharmacokinetics: Prediction of distribution volume and plasma clearance.

In this study, advantages of minipigs to use in preclinical study for new drug development were evaluated in terms of prediction of human pharmacokinetic (PK) parameters of various drugs. Fourteen model drugs having diverse physicochemical properties were selected and intravenously administered to mice, rats and minipigs to obtain their PK parameters. The human volume of distribution (Vd) and clearance (CL) of model drugs were predicted from PK parameters in each animal species. When Vd of 14 drugs in each species were directly compared with those in humans, minipigs showed the highest correlation. Correction of Vd with an unbound fraction of drugs in tissues further improved the correlation. Allometric scaling that included minipig data resulted in high accuracy in the prediction of human Vd, clearly indicating an importance of minipig data. Minipigs also showed the high predictability of human CL. The prediction of human CL by allometric scaling showed a high accuracy when the data of minipigs were included. In conclusion, potential advantages of minipigs for predicting human Vd and CL were clearly demonstrated. Reliable prediction of human PK from data of minipigs appears to be possible in preclinical PK study, without relying on PK analysis in other species.

Physicochemical properties and structures of room-temperature ionic liquids. 3. Variation of cationic structures.

A series of room-temperature ionic liquids (RTILs) were prepared with different cationic structures, 1-butyl-3-methylimidazolium ([bmim]), 1-butylpyridinium ([bpy]), N-butyl-N-methylpyrrolidinium, ([bmpro]), and N-butyl-N,N,N-trimethylammonium ([(n-C(4)H(9))(CH(3))(3)N]) combined with an anion, bis(trifluoromethane sulfonyl)imide ([(CF(3)SO(2))(2)N]), and the thermal property, density, self-diffusion coefficients of the cation and anion, viscosity, and ionic conductivity were measured over a wide temperature range. The self-diffusion coefficient, viscosity, ionic conductivity, and molar conductivity follow the Vogel-Fulcher-Tamman equation for temperature dependencies, and the best-fit parameters have been estimated, together with the linear fitting parameters for the density. The relative cationic and anionic self-diffusion coefficients for the RTILs, independently determined by the pulsed-field-gradient spin-echo NMR method, appear to be influenced by the shape of the cationic structure. A definite order of the summation of the cationic and anionic diffusion coefficients for the RTILs: [bmim][(CF(3)SO(2))(2)N] > [bpy][(CF(3)SO(2))(2)N] > [bmpro][(CF(3)SO(2))(2)N] > [(n-C(4)H(9))(CH(3))(3)N][(CF(3)SO(2))(2)N], has been observed, which coincides with the reverse order to the viscosity data. The ratio of molar conductivity obtained from the impedance measurements to that calculated by the ionic diffusivity using the Nernst-Einstein equation quantifies the active ions contributing to ionic conduction in the diffusion components and follows the order: [bmpro][(CF(3)SO(2))(2)N] > [(n-C(4)H(9))(CH(3))(3)N][(CF(3)SO(2))(2)N] > [bpy][(CF(3)SO(2))(2)N] > [bmim][(CF(3)SO(2))(2)N] at 30 degrees C.

Electron transfer reactions of glucose oxidase at Au111 electrodes modified with phenothiazine derivatives.

The catalytic reaction of glucose oxidase (GOx) mediated by 3-(10-phenothiazyl)propionic acid (PT-PA) and phenothiazine-labeled poly(ethylene oxide) (PT-PEO1000) that are covalently bonded to Au(111) electrodes has been investigated. The PT-PA and PT-PEO1000 are reacted with 2-aminoethanethiol (AET), followed by the formation of a self-assembled monolayer (SAM) onto the Au surface. The PT group immobilized on the SAM of AET acts as an effective mediator for the electron transfer (ET) between the electrode and the FAD center of freely diffusing GOx in solution. The ET rate constant estimated from the catalytic current using a newly derived equation is larger by 1 order of magnitude for the PT-PA-modified system (1.1 x 10(5) dm(3) mol(-1) s(-1)) than for the PT-PEO1000 system (1.4 x 10(4) dm(3) mol(-1) s(-1)). The order of the magnitude of the ET rate constant clearly contrasts with the GOx hybrid systems that we previously investigated (Anal. Chem. 2003, 75, 910-917), in which the presence of the PEO spacer enhances the ET reaction rate. The reduction in the apparent PT concentration at the electrode interface due to the high mobility of the PEO chain, leading to low efficiency in the formation of an enzyme-mediator complex, is a possible reason for the lower mediation ability of PT-PEO1000 than that of PT-PA for the ET between the FAD group and PT(+) immobilized on the electrode. Inhibition of the penetration of GOx molecules into the monolayer and of the accessibility of some part of PT groups to GOx molecules could also be reasons for the lower mediation ability of PT-PEO1000 thickly modified on the electrode.

Physicochemical properties and structures of room temperature ionic liquids. 2. Variation of alkyl chain length in imidazolium cation.

The alkyl chain length of 1-alkyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([Rmim][(CF(3)SO(2))(2)N], R = methyl (m), ethyl (e), butyl (b), hexyl (C(6)), and octyl (C(8))) was varied to prepare a series of room-temperature ionic liquids (RTILs), and the thermal behavior, density, viscosity, self-diffusion coefficients of the cation and anion, and ionic conductivity were measured over a wide temperature range. The self-diffusion coefficient, viscosity, ionic conductivity, and molar conductivity change with temperature following the Vogel-Fulcher-Tamman equation, and the density shows a linear decrease. The pulsed-field-gradient spin-echo NMR method reveals a higher self-diffusion coefficient for the cation compared to that for the anion over a wide temperature range, even if the cationic radius is larger than that of the anion. The summation of the cationic and anionic diffusion coefficients for the RTILs follows the order [emim][(CF(3)SO(2))(2)N] > [mmim][(CF(3)SO(2))(2)N] > [bmim][(CF(3)SO(2))(2)N] > [C(6)mim][(CF(3)SO(2))(2)N] > [C(8)mim][(CF(3)SO(2))(2)N], which greatly contrasts to the viscosity data. The ratio of molar conductivity obtained from impedance measurements to that calculated by the ionic diffusivity using the Nernst-Einstein equation quantifies the active ions contributing to ionic conduction in the diffusion components, in other words, ionicity of the ionic liquids. The ratio decreases with increasing number of carbon atoms in the alkyl chain. Finally, a balance between the electrostatic and induction forces has been discussed in terms of the main contribution factor in determining the physicochemical properties.

Effect of a modification site on the electron-transfer reaction of glucose oxidase hybrids modified with phenothiazine via a poly(ethylene oxide) spacer.

Glucose oxidase [GOx-(PT-PEONH2)] hybrids are synthesized by attaching phenothiazine (PT) groups to aspartic and glutamic acid residues on the enzyme surface via poly(ethylene oxide) (PEO) spacers of different molecular weights. A fast oxidation of FADH2/FADH by PT+ with the aid of the local motion of a hydrophilic, long, flexible PEO spacer is achieved for the GOx-(PT-PEONH2) hybrids and yields greater electron-transfer (ET) rates than that for GOx-(PTNH2) hybrids, in which the PT groups are directly bonded to the GOx surface. The ET rate of GOx-(PT-PEONH2) hybrids depends on the molecular weight of PT-PEONH2, and the maximum is obtained at a molecular weight of 3000. The ET rates of GOx hybrids are compared in terms of the location of the PT modification and the length and structure of the spacer chain connection of the PT mediator to a surface amino acid residue. Greater ET rates are obtained for the modification at aspartic and glutamic acid residues than for the lysine modification when the PT groups are bonded directly or via a short PEO spacer chain. In contrast, no advantage of aspartic and glutamic acid residues over lysine residues in generating a fast oxidation of FADH2/FADH by PT+ is observed for GOx hybrids in which the PT groups are attached via longer PEO spacers. The long PEO spacer is able to compensate the disadvantage of lysine residues locating far from the FAD center in GOx hybrids whose mediation reactions are based on the so-called wipe mechanism.