Tomomi Hatanaka

Prediction of Skin Permeability of Drugs: Comparison of Human and Hairless Rat Skin

Abstract— Relationships between skin permeability and physicochemical properties of drugs were examined to establish a predictive method for the steady‐state permeation rate of drugs through human skin. Human skin permeation properties fell into two categories: one in which the permeability coefficient is correlated to the partition coefficient, revealed with lipophilic drugs; and the other in which the permeability coefficients are almost constant, shown with hydrophilic drugs. The stratum corneum, the main barrier in skin, could be considered as a membrane with two parallel permeation pathways: lipid and pore pathways, and an equation for predicting the steady‐state permeation rate of drugs was derived. The skin permeabilities of drugs for man were compared with those for hairless rat. The species difference in skin permeability found was suggested to be due to the difference in skin permeation pathways, since lipid content and water uptake of the stratum corneum varied between human and hairless rat skin.

Effect of vehicle on the skin permeability of drugs: polyethylene glycol 400-water and ethanol-water binary solvents

Abstract A predictive method for skin permeability of drugs from polyethylene glycol 400 (PEG)-water and ethanol (EtOH)-water binary solvents is proposed. The method is based on a permeation model, in which the stratum corneum is assumed to be a membrane having two parallel permeation pathways: lipid and pore pathways. Skin permeability of several drugs with a variety of physicochemical properties from various PEG-water and EtOH-water solvents was tested. In PEG-water solvents, almost the same skin permeation rate of lipophilic drugs was obtained independent of the solvent, whereas the permeability coefficient of hydrophilic drugs decreased with increasing PEG fraction. The solvent viscosity was increased and the skin permeability of solvents was decreased by addition of PEG, suggesting the decreased diffusion of the drugs in the pore pathway. EtOH, in contrast, markedly enhanced the skin permeation rate of lipophilic drugs, though no such effect was found on hydrophilic drugs. The enhancing ratio in permeation of lipophilic drugs was dependent not on the lipophilicity of the drug but on the EtOH fraction in the solvent. EtOH-water solvents increased the fluidity of skin lipids, although the extraction of lipids by EtOH-water solvents was relatively low. These results suggest that EtOH enhances diffusion in the lipid pathway. Equations for predicting the skin permeability of a drug from various PEG-water and EtOH-water binary solvents were then derived. The skin permeation behavior of a drug can be predicted by its solubility in octanol and vehicle based on the parallel skin permeation pathway model.

An Application of the Hydrodynamic Pore Theory to Percutaneous Absorption of Drugs

Skin permeability of drugs was evaluated based on the hydrodynamic pore theory. Four polar solutes were used, with differing molecular sizes—ethylene glycol, 1,3-butylene glycol, antipyrine and sucrose—and isosorbide dinitrate was also selected as a lipophilic drug. The skin permeations of solvent (D2O) and one of these drugs were measured simultaneously under various osmotic pressures to calculate the reflection coefficient. The clearance of isosorbide dinitrate was independent of the solvent flux, whereas a linear relationship was obtained between the solvent flux and the clearance of each hydrophilic drug except for sucrose. The reflection coefficient of the hydrophilic drugs increased with increasing molecular radius. These results suggest that the convective flow contributes significantly to the total skin permeability of hydrophilic drugs and that the extent of contribution decreases with increasing molecular size of the drugs. The pore radius of the skin barrier could be estimated from the reflection coefficient of the hydrophilic drugs and the resulting value was compared with that for the other absorption sites, jejunum, rectum, and nose. The apparent water influx was also compared to assess the volume occupied by the pores. The pore radius and apparent influx of skin were lower than those for the other absorption sites, which is apparently one reason for low skin permeability of drugs, especially hydrophilic drugs.

Differences in enhancing effect of 1-menthol, ethanol and their combination between hairless rat and human skin

The differences in skin permeation enhancing effect by 1-menthol, ethanol and their combination between hairless rat and human skin were investigated by measuring the permeation of isosorbide dinitrate (ISDN) as a model drug and all components in the donor vehicle through excised skin. Deuterium oxide (D20) and ethanol-d6(EtOD) were used in place of water and ethanol, respectively. Vehicle compositions containing enhancers were 5% 1-menthol/D20 (MW), 40% EtOD/D20 (EW) and 5% I-menthol/40% EtOD/D20 (MEW). D20 (W) was also used as a control vehicle. The permeability of each component (including ISDN) through human skin was lower than that through hairless rat skin in all the vehicles. A strong enhancement effect was achieved only by the combination of I-menthol and ethanol (MEW) in human skin. The most marked difference in enhancing effect between hairless rat and human skin was observed with the application of MW. Comparison of the cumulative amount of each component between human and rat (human/rat) using MW showed 1-menthol to be sol12, ISDN sol18 and D20 sol130. With MEW, on the other hand, human/rat ratios were similar (I-menthol, 13 ISDN, 13; EtOD, 13; D20, 12) independent of the component species. In addition, there was a lag time of about 2 h for all components when MEW was applied to human skin, whereas no lag time was observed in hairless rat skin. Lipid leached from skin to the donor compartment was followed to evaluate the species difference. The results suggested that differences in lipid leaching between human and hairless rat skin might be one reason for the variation in enhancing effect or lag time.

Stereoselective skin permeation of organic nitrates: application of partitioning and porous transport theories

Abstract The effect of the stereochemistry of organic nitrates on rat skin permeability was investigated. Skin permeabilities significantly differed between dinitrates and mononitrates, and also among their diastereomers. The maximum flux and permeability coefficient of dinitrate diastereomers from water were dependent on the solubility in octanol and the octanol/water partition coefficient, respectively. On the other hand, the key parameters determining the maximum flux and permeability coefficient of mononitrate isomers were the aqueous solubility and diffusivity. These results suggest that dinitrate diastereomers permeate across skin via the lipid domain of the stratum corneum according to a partitioning mechanism, and that skin permeation of mononitrate isomers occurs via an aqueous domain by a porous mechanism. Factors raising stereoselectivity in skin permeation of organic nitrates were closely related with stereostructure, especially the functional groups at the exo position, of diastereomers. The interaction between the functional groups and surrounding molecules thus causes the differences in physicochemical properties and skin permeability of stereoisomers.

Effect of Several Adsorbents on the Gastrointestinal Absorption of Paraquat

The effect of several adsorbents on paraquat poisoning was investigated (1) by measuring the saturated amount of the poison adhered on the adsorbentsin vitro and (2) by assaying the blood level of paraquat in the rat inin situ intestinal absorption experiments. Activated charcoal powder, natural aluminum silicate, and cationic exchange resins (calcium polystyrene sulfonate and sodium polystyrene sulfonate) were used as adsorbents. The steady-state blood level of paraquat in its absorption experiment with the cationic exchange resins was markedly lower than those without the resins or with other adsorbents. A good relationship was achieved between the calculated AUC or absorption rate (in situ) and the saturated adsorption amount (in vitro). The rank order of the effect was sodium polystyrene sulfonate>calcium polystyrene sulfonate>natural aluminum silicate>activated charcoal powder. The effect of sodium polystyrene sulfonate after intestinal washing with physiological saline was also measured, and a synergistic effect (marked decrease in blood paraquat level) was found as compared with the intestinal washing alone. The simultaneous use of G.I. washing and powerful adsorbent was scientifically proven to be most beneficial.

Alopecia areata susceptibility variant identified by MHC risk haplotype sequencing reproduces symptomatic patched hair loss in mice

Background Alopecia areata (AA) is a highly heritable multifactorial and complex disease. However, no convincing susceptibility gene has yet been pinpointed in the major histocompatibility complex (MHC), a region in the human genome known to be associated with AA as compared to other regions. Results By sequencing MHC risk haplotypes, we identified a variant (rs142986308, p.Arg587Trp) in the coiled-coil alpha-helical rod protein 1 (CCHCR1) gene as the only non-synonymous variant in the AA risk haplotype. Using CRISPR/Cas9 for allele-specific genome editing, we then phenocopied AA symptomatic patched hair loss in mice engineered to carry the Cchcr1 risk allele. Skin biopsies of these alopecic mice showed strong up-regulation of hair-related genes, including hair keratin and keratin-associated proteins (KRTAPs). Using transcriptomics findings, we further identified CCHCR1 as a novel component of hair shafts and cuticles in areas where the engineered alopecic mice displayed fragile and impaired hair. Conclusions These results suggest an alternative mechanism for the aetiology of AA based on aberrant keratinization, in addition to generally well-known autoimmune events.