Mouse stratum comeum

Figure 2. DSC thermograms for hairless mouse stratum comeum, extracted lipids and protein residue from -10 to 237°C.

The in situ precipitation technique and transmission electron microscopy have been used to investigate the effect of DMSO on percutaneous absorption in the mouse barrier [27] and human SC [46]. Sharata and Burnette examined ultrastructural changes in mouse stratum comeum by determining the distribution of sulfide precipitates of topically applied, water-soluble tracers (Hg and Ni ) after application of enhancer [27]. For skin pretreated with DMSO, mercury and nickel precipitates were found within swollen basal stratum comeum cells as well as intercellularly and associated with the cell envelopes, but not below the stratum comeum-stratum granulosum interface. It was concluded that treatment with DMSO, as well as with other dipolar aprotic solvents such as DMF and DMA, alters the passive intercellular diffusion pathway by expanding the size of the basal stratum comeum cells, resulting in an increased free volume for tracer diffusion. 

Bouwstra et al. (1991) carried out more detailed calculations using the five orders of diffraction data obtained from SC with lipids recrystallized from 120 C. They used an iterative procedure that involved varying the bilayer electron density profile until the intensities calculated from the three-parameter model agreed with the observed intensities. In the case of mouse stratum comeum, the peaks are clearly resolved in untreated stratum comeum (Bouwstra et al., 1994 White et al., 1988), but in human SC the calculations can be carried out only after recrystallization of the lipids, because the peaks are unresolved in untreated skin. The results of their calculations are shown in Fig. 12. The electron density strip model shows three high and three low... 

Bouwstra, J. A., Gooris, G. S., Van der Spek, J. A., Lavrijsen, S. and Bras, W. (1994). The lipid and protein stmcture of mouse stratum comeum A wide- and small-angle diffraction study. Biochim. Biophys. Acta /2/2 183. 

Table 1 A Comparison Between the Lipid Organization in Pig, Human, and Mouse Stratum Comeum...

J. A. Bouwstra, G. S. Gooris, J. A. van der Spek, S. LavriJ.seii. and W, Bra.s. The lipid and protein structure of mouse stratum comeum a wide and small ungic diffraction study. Biochim Biophys. Acta 1212 (1994) I S3-192,... 

Figure 4 Electron micrograph of the lipid lamellae of hairless mouse stratum comeum. To visualize the lipid lamellae, the tissue was jfirst fixed in ruthenium tetroxide and then counterstained with uranyl acetate. Note the series of electron-lucent and electron-dense lamellae that span the entire length of the intercellular space. (Courtesy of Dr. Peter Elias.)...

Chloroform can also permeate the stratum comeum of rabbit skin (Torkelson et al. 1976) and mouse skin (Tsuruta 1975). Percutaneous absorption of chloroform across mouse skin was calculated to be approximately 38 pg/min/cm, indicating that the dermal absorption of chloroform occurs fairly rapidly in mice. No reliable studies report the percutaneous absorption of chloroform in humans however, a few clinical reports indicate that chloroform is used as a vehicle for drug delivery (King 1993). Islam et al. (1995) investigated the fate of topically applied chloroform in male hairless rats. For exposures under 4 minutes, chloroform-laden water was applied to shaved back skin for exposures of 4-30 minutes, rats were submerged in baths containing chloroform-laden water. Selected skin areas were tape-stripped a various number of times after various delay periods. It appeared that there was an incremental build-up of ehloroform in the skin over the first four minutes. When compared to uptake measured by bath concentration differences, approximately 88% of lost chloroform was not accounted for in the stratum comeum and was assumed to be systemically absorbed. 

Particles from cationic lipids may also be useful for antisense therapy of skin disease — a nontoxic increase in the oligonucleotide uptake by cultivated keratinocytes and a sebocyte cell line has been reported [66]. Moreover, cationic dendri-mers also efficiently transfer reporter gene DNA to human keratinocytes cultivated in vitro. In the skin of hairless mice, in vivo transfection was possible with complexes, yet reporter gene expression was localized to perifollicular areas. Transfection, however, failed with the naked plasmid. For prolonged contact, biodegradable membranes coated with dendrimer/DNA complexes were used [67]. This hints at a follicular uptake of these complexes and indicates that gene transfection also may be possible with human skin, which has a thicker stratum comeum compared with mouse skin (eight to ten vs. two to three layers [58]). 

In 1994, Menon and co-workers [74] similarly used TEM to visualize tracers in the stratum comeum after sonophoresis treatment. They applied colloidal lanthanum and fluorescein-conjugated dextran (MW 40,000) to hairless mouse skin and treated the site with 15 MHz (0.1 W/cm ) for 5 minutes. As before, the tracers were observed in intercellular lacunae at different levels of the stratum comeum (see Fig. 9). Electron microscopy of horizontal sections further revealed that the tracers were found within interconnected lacunae. It was suggested that sonophoresis may cause lipid-phase separation, thereby forming continuous chaimels that divide the lipid bilayers and amplify an intercellular transport pathway. 

Figure 5 Murine stratum comeum normal full thickness. Powder diffraction patterns obtained from mouse SC at 25°C. The upper figure shows the small-angle lamellar pattern produced by the intercellular lipid domains, with a repeat period of 131 2 A. The lower figure shows the wide-angle pattern produced by the lipid alkyl chains and the comeocyte envelope. See text. (Data from White et al., 1988.)...

Bentley, M.V., Vianna, R.F., Wilson, S., and Collett, J.H. (1997). Characterization of the influence of some cyclodextrins on the stratum comeum from the hairless mouse, J. Pharm. Pharmacol., 49 397-402. 

Elias, PJM., Brown, B .,Fritsch, P, Goerke, J., Gray, GM., and White, RJ. (1973) Localization and Composition of Lipids in Neonatal Mouse Stratum Granulosum and Stratum Comeum, J. Investig. Dermatol. 73,339—348. 

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