Stratum corneum measuring

Walkley, K., Bound Water in Stratum Corneum Measured by Differential... 

Diffusion of Water Vapor in Newborn Rat Stratum Corneum. Measurement and interpretation of diffusion in heterogenous biological systems such as the stratum corneum are difficult compared with similar measurements for well-defined synthetic polymer systems, but studies of water diflFusion in stratum corneum are essential to a better understanding of those factors which contribute to the barrier function of the corneum. Water diffusion measurements under both equilibrium and non-equilibrium conditions are useful to probe the influence of temperature and other factors on stratum corneum macromolecular structure. 

Liron, Z., Wright, R.L., and McDougal, J.N. (1994b). Water diffusivity in porcine stratum corneum measured by a thermal gravimetric analysis technique, J. Pharm. Sci, 83 457-462. 

Figure 10 In vivo Raman spectra of different skin layers (a) stratum corneum, measured at skin surface (b) dermis, measured at 85 tm below the skin surface (c) spectrum of human collagen type I. Experimental conditions (a and b) microscope objective = Leica X63 numerical aperture = 0.70 excitation wavelength = 850 nm laser power =100 mW signal collection time =120 sec.

These diffusivities are estimates obtained by in vitro experiment (stratum corneum) or by comparison with small tissues in which diffusivities have been measured (all others). They do not account for regional variations across the body surface, so on both counts must be considered highly approximate. 

A standard Lowry-based protein assay has been adjusted to the special conditions encountered with skin [126], Basically, proteins reduce an alkaline solution of Cu(II)-tartrate to Cu(I) in a concentration-dependent manner. Then, the formation of a blue complex between Folin-Ciocalteau reagent (a solution of complex polymeric ions formed from phosphomolybdic and phosphotungstic heteropoly acids) and Cu(I) can be measured spectrophotometrically at 750 nm. A calibration curve can be obtained by dissolving known amounts of stratum corneum in 1 M sodium hydroxide. A piece of tape that has not been in contact with skin is subjected to an identical procedure and serves as negative control. The method was recently adapted to a 96-well plate format, notably reducing analysis times [129],... 

The human skin model assay involves measuring the effects of corrosives on viable cells in a reconstituted human skin equivalent. To be accepted as a valid human skin model, several criteria must be met. The artificial skin must comprise a functional stratum corneum with an underlying layer of viable cells. Furthermore, the barrier function of the stratum corneum, as well as the viability of the epidermis, must be verified with appropriate experimental setups. The chemicals to be tested are applied up to 4 h as a liquid or a wet powder onto the skin model. Afterwards, careful washing has to be performed, followed by investigation of the cell viability [e.g., with a (MTT)] reduction assay). 

Because of the possible effects of active and carrier-mediated processes and metabolic biotransformation, the issue of tissue viability is important for in vitro buccal mucosal experiments. The barrier nature of the buccal mucosa resides in the upper layers of the epithelium, where unlike in the stratum corneum, the cells contain a variety of functional organelles [119, 122, 125, 150], and so tissue viability may be an important component of the barrier function of the tissue. Various methods have been employed to assess the viability of excised buccal mucosa, including measurement of biochemical markers, microscopic methods, and linearity of transport data [42], While biochemical methods, including measurement of adenosine 5 -triphosphate (ATP) levels and utilization of glucose, provide information on the metabolic activity of the tissue, this does not necessarily relate to the barrier function of the tissue. In excised rabbit buccal mucosa, levels of ATP were measured and found to decline by 40% in 6 h, and this correlated well with transmission electron microscopic evaluation of the tissue (intact superficial cells) [32], In addition, the permeability of a model peptide was unaltered up to 6 h postmortem, but at 8 h, a significant change in permeability was observed [32], These investigators therefore claimed that excised rabbit buccal mucosa could be used for diffusion studies for 6 h. 

Substituting hx = 3.6 cm and K ip/w = K - into Eq. 28 Johnson et al. calculated solute lateral diffusion coefficients in stratum corneum bilayers from macroscopic permeability coefficients. Measurements with highly ionized or very hydrophilic compounds were not performed because of the possible transport along a nonlipoidal pathway. Comparison of the computed Aat values with experimentally determined data for fluorescent probes in extracted stratum corneum lipids [47] showed a highly similar curve shape. The diffusion coefficient for the lateral transport showed a bifunctional size dependence with a weaker size dependence for larger, lipophilic compounds (> 350 Da), than... 

The disposition of cocaine in nontraditional testing matrices has been described. For example, Lester et al.15 measured cocaine and benzoylecgonine (BE) concentrations in skin, interstitial fluid (IF), sebum, and stratum corneum in five volunteers after the intravenous 1-h infusion of 1 mg/kg cocaine d5. Peak cocaine concentrations in the skin were achieved at 1.5 h and were undetectable after 6 h. No BE was measured in the skin. Peak cocaine concentrations were achieved at 5 h after administration in the IF and were non detectable by 24 h. BE was found in the IF. In the sebum peak cocaine concentrations occurred between 3 to 24 h but in the stratum corneum cocaine was detected in only one subject. 

Potts, R. O., Guzek, D. B., Harris, R. R. and McKie, J. E. (1985) A noninvasive, in vivo technique to quantitatively, measure water concentration of the stratum corneum using attenuated total-reflectance infrared spectroscopy. Arch. Dermatol. Res. 277, 489-95. 

Fig. 12.2. Quantitative measurements of skin. Routine measurements of skin, in late anagen in this figure, include interfollicular epidermal thickness (circled area), hair follicle length (L), dermal thickness (D), hypodermal fat layer thickness (H, normally varies with the hair cycle), and full thickness (FT) from the surface of the stratum corneum to the top of the panniculus carnosus muscle.

Fig. 12.3. Epidermal measurements, mitotic figures, and apoptotic keratinocytes in a chronic proliferative dermatitis mutant (Sharplncpdm/Sharplncpdm) mouse. Routine hematoxylin- and eosin-stained paraffin histologic sections can be used to determine proliferation rates based on mitotic index (number of mitotic figures, circled in the figure, in the stratum basale per 1000 cells) or the presence and numbers of apoptotic epidermal keratinocytes (dotted arrows) when present. Epidermal thickness can be measured at high dry magnification (40x) to include the malpigian, living cell, layer (M), the stratum corneum thickness (SC), or the full thickness of the epidermis (M+SC).

Y. Takeuchi, H. Yasukawa, Y. Yamaoka, Y. Kato, Y. Morimoto, Y. Fukomori, and T. Fukada, Effect of fatty acids, fatty amines and propylene glycol on rat stratum corneum hpids and proteins in vitro measured by Fourier Transformed Infrared/Attenuated Total Reflectance spectroscopy. Chem. Pharm. Bull. 40 1887-1892 (1992). 

Absorption through the skin, percutaneous absorption, is an important mechanism by which xenobiotic substances can enter the body. The surface stratum corneum layer is the main barrier to such absorption, and when it is shed or compromised, skin is much more susceptible to penetration by xenobiotic substances. A test for the ability of a hydrophobic xenobiotic substance to penetrate skin is to measure the partitioning of such a substance between water and powdered stratum corneum cells. 

Norlen, L. etal., A new computer based system for rapid measurement of water diffusion through stratum corneum in vitro, J. Invest. Dermatol., 113, 533, 1999. 

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