Hair follicles of young Wistar strain hairless rats: a histological study

Utility of hairless rats as a model for predicting transdermal pharmacokinetics in humans

This study investigated the use of HWY hairless rats to predict human plasma concentrations of drugs following dermal application.Utilizing a deconvolution method, pharmacokinetic parameters (e.g. in vivo absorption rates) were determined for six transdermal drugs in hairless rats. Obtained data were used to simulate the human plasma concentration-time profiles of transdermal drugs, which were then compared with clinical data in humans. Because hairless rats have lower hair follicle density than do humans, the impact of hair follicle density on skin permeability to hydrophilic compounds was also evaluated.Pharmacokinetic parameters showed low intra-individual variability in hairless rats. Simulated concentration profiles for compounds with logarithm of the octanol-water partition coefficient exceeding two were comparable to clinical data, but simulated concentration profiles for hydrophilic compounds (i.e. bisoprolol and nicotine) at maximum concentration differed from clinical data by more than two-fold. Finally, in vitro permeability to bisoprolol and nicotine was higher in human skin than in hairless rat skin, but hair follicle plugging reduced human skin permeability.In vivo skin absorption data from HWY hairless rats help to predict human concentration profiles for lipophilic compounds. However, the data underestimate human absorption of hydrophilic compounds.

Cone of skin exists in rat: A "hypertrophic scarring free" animal

Cone of skin is deemed to be related to hypertrophic scarring and absent in such traditionally "hypertrophic scarring and keloid free" animals as rat. The purpose of our study is to determine whether the cone of skin exists in rat. If it was, why it was ignored, and what was the meaning of it. The depilation of left dorsum of 32 male Sprague-Dawley rats was performed using a wax/rosin mixture. Skin samples were harvested on 0 d, 3 d, 9 d, 15 d, 21 d, 27 d, 33 d, and 39 d after depilation and stained by hematoxylin and eosin methods. Light microscopic observation of the dermis-fat interface was studied at 25× magnification. It was observed that, "dome" like fat tissue bulged up into the dermis from 3 d to 27 d and hair follicle bulged down into the "dome" like fat tissue from 15 d to 27 d and a "cone" like structure was seen. Cone of skin exists in rat in certain stages of hair follicle cycle, which is a valuable addition to the scientific literature and might be a challenge to the relation between cone of skin and hypertrophic scarring. Anat Rec, 299:1140-1144, 2016. © 2016 Wiley Periodicals, Inc.

Kyoto rhino rats derived by ENU mutagenesis undergo congenital hair loss and exhibit focal glomerulosclerosis

N-ethyl-N-nitrosourea (ENU) mutagenesis is an important tool for studying gene function and establishing human disease models. Here, we report the characterization of a novel hairless mutant rat strain that carries a recessive mutation called Kyoto rhino (krh), which was created by ENU-mutagenesis. We produced a F344-krh strain through inbreeding without backcrossing to F344 rats. The krh/krh rats lost their coat hair by eight weeks of age. They also developed wrinkled skin, cystic hair canals and long curved nails by four months of age. Markedly dilated hair follicles that contained keratin debris were observed during histological analysis of the skin. The krh locus was mapped near the hairless (Hr) gene on chromosome 15. Sequence analysis revealed a nonsense mutation (c. 1238 C>A, p. S413X) in the Hr gene. The truncated HR protein was deduced to lack a zinc-finger domain and repression domains. In aged Hr(krh)/Hr(krh) rats, focal glomerulosclerosis (FGS) was observed in which collapsed glomeruli contained protein exudates in Bowman's capsule. Mesangial matrices that had proliferated in segments and foot processes that were fused in podocytes were also observed. The Hr(krh)/Hr(krh) rats also suffered from significant proteinuria. Given its breeding history, the F344-Hr(krh) strain may harbor ENU-induced mutation(s) that underlie FGS in addition to having the Hr(krh) mutation. The F344-Hr(krh) rat is a useful model of skin disease and may provide a new model system for the examination of the pathogenesis of FGS.

Keratinization of outer root sheath cells is prevented by contact with inner root sheath of rat hair follicles

The purpose of the present study was to elucidate why keratinocytes of the outer root sheath (ORS) do not keratinize in situ. Two possibilities were considered--inhibition of keratinization is caused by contact of ORS with inner root sheath (IRS) or insufficient supply of keratinization promoting factors from the surrounding tissues to the ORS. In order to distinguish between these possibilities mid-segments of hair follicles were liberated from the dermis by dissection followed by collagenase digestion. ORS cells were then either allowed to migrate from the mid-segments or were kept on the agarose layer which prevented cell spreading and preserved three dimensional structure of hair root. Cultures were stimulated with calcium or EGF, and studied morphologically at the light and transmission electron microscope level. The level of mRNA for differentiation cell markers was also studied by RealTime PCR. ORS cells growing in a medium with low Ca2+ content formed monolayers, which after elevation of Ca2+ produced multilayers with cells containing keratohyalin-like granules. Ca2+ or EGF treatment upregulated expression of involucrin, filaggrin and keratinocyte differentiation associated protein (Kdap). Culture of mid-segments of hair follicles in low calcium culture medium kept on agarose increased expression of filaggrin and Kdap, but downregulated expression of involucrin. Stimulation by Ca2+ further increased expression of filaggrin and Kdap, but had no effect on the level of involucrin expression. EGF stimulated expression of filaggrin only. It is concluded that IRS exerted an inhibitory effect on the expression of involucrin, an essential component of the cornified envelope, thus preventing keratinization of ORS cells in situ. On the other hand, improved access of nutrients or promoting factors of keratinization to the mid-segment of hair follicles augmented expression of filaggrin and Kdap, proteins engaged in the differentiation of keratinocytes but not involved in its terminal phase.