Jurij J. Hostýnek

Colorimetric method for quantifying human Stratum corneum removed by adhesive-tape stripping.

Tape-stripping of the skin is a useful method for removing the stratum corneum and obtaining more information about the function of this skill layer as the main barrier for skin penetration. The amount of stratum corneum removed is of relevance in establishing the concentration profile of chemicals within the stratum corneum after topical application. Weighing is the preferred method for measuring the amount stripped, but because it is often subject to artifacts, alternative methods are sought. We present a simple, colorimetric method for determining the amount stratum corneum removed by sequential adhesive-tape-stripping of human skin in vivo. The method is based on quantification of the sodium hydroxide soluble protein fraction using a commercially available protein assay similar to the Lowry assay. The method is shown to be an accurate and reproducible alternative to weighing, also demonstrating uniform removal of stratum corneum layers following the very initial strips.

Metals and the Skin

Certain metals, and many metal-based compounds, are inherently toxic, and their presence in occupational and environmental settings raises appropriate questions concerning human exposure. Contact of these materials with the skin represents an important route of exposure, which is not well characterized. The purpose of this review, therefore, is to assemble the available, useful information pertinent to risk assessment following dermal contact. Specifically, we summarize here: (1) data relevant to the qualitative and (where possible) quantitative evaluation of metal compound permeation through the skin; (2) the role of each metal in metabolism, particularly with respect to the skin, and the potentially toxic effects that may result from dermal contact; and (3) the immunological characteristics (including allergenicity) of the metals and their derivatives. In total, information on 31 metals has been reviewed. It is clear that many diverse factors determine the ability of metal-based species to permeate biological membranes, not all of which have been fully defined. Therefore, considerably more experimentation, targeted at the development of high-quality transport data, will be required before the specification of practically useful structure-activity relationships are possible.

In vitro permeation of nickel salts through human stratum corneum.

Allergic contact dermatitis due to nickel salts is common. It is therefore important to measure the permeation of these salts through the stratum corneum (SC), the primary rate-limiting domain in skin. An advanced diffusion system and analytical techniques now enable better measurement of the flux than was possible in earlier experiments. Human SC was prepared by trypsinization of dermatomed cadaver leg skin. The diffusion system included diffusion cells with a spiral line. Aqueous solutions of nickel salts (Ni(NO3)2, NiSO4, NiCl2 and Ni(-OOCCH3)2 at 1% Ni2+ concentration) were used as the donor solution (400 microL/cell). The receptor fluid, pure water, was collected up to 96 h after application of the donor solutions. Nickel concentrations in the donor and receptor fluid, as well as in the SC, were analysed using inductively coupled plasma mass spectrometry (ICP-MS) with a confidence limit of 0.5 ppb. Based on the total recovery of nickel from the experiments, about 98% of the dose remained in the donor solution, whereas 1% or less was retained in SC and less than 1% was found in the receptor fluid. Following an early surge, nickel permeates slowly across SC. The steady-state permeability coefficients of nickel were calculated from the flux data (approximately 5.2-8.5 x 10(-7) cm/h) with no significant difference among the salts. The results concur in principle with earlier studies conducted using the full-thickness human skin in vitro, and suggest that in vivo nickel ions may permeate simultaneously by routes of diffusion such as the shunt pathway, apart from slow transcellular/intercellular diffusion alone.

Allergic contact dermatitis elicitation thresholds of potent allergens in humans

Literature scoured for human allergenicity to individual chemicals yields a limited number of potent sensitizers, which can be classified in four categories: metals, botanicals, biocides and miscellany. Potency is defined as strong for substances eliciting eczematous reactions to patch concentrations of 500 ppm (parts per million) or less in sensitized individuals. Most data encountered stem from studies conducted on dermatology patients tested routinely for hypersensitivity; only few data have been generated by systematic serial dilution testing.

Fragrance allergens: Classification and ranking by QSAR.

Quantitative structure-activity relationship (QSAR) models which predict both skin penetration and cell mediated immunity for small molecular weight non-electrolytes developed earlier were validated on 74 known allergens and non-allergens chosen among fragrance chemicals in common use to test discriminating and grading power. While the test set used for classification was based on experience in humans exclusively, the rank model was tested for sensitization potency including guinea pig data also. In the classification test, 12 of 74 compounds fell in the indeterminate range and were non-classifiable by the present QSAR model. On the remaining 62 compounds the model performs with 90% sensitivity and 100% specificity at 92% concordance. The rank model correctly grades 65 of 74 compounds (88% concordance), with 60% specificity based on exact prediction of non-allergens (NON), and 95% sensitivity on allergens (ACD) allowing for a variance of +/- one level among weak, moderate and severe ratings. In combination, the two models perform with 93% overall concordance on the test set of 74 compounds.

A local lymph-node assay validation study of a structure-activity relationship model for contact allergens

A structure-activity relationship model for prediction of contact allergenic potential of chemicals had previously been developed. The model had been shown to be able to classify known allergens and nonallergens using data on physicochemical and reactivity parameters of functional groups by discriminant two-value multiple regression analysis. To investigate the model, six selected chemicals which had not been previously investigated for allergenicity were studied with both the model and a murine local lymph-node assay. The same compounds were predicted to be allergens (3-bromo-2-coumaranone, 1-nitrocyclohexene and alpha-acryloyloxy-beta, beta-dimethyl-beta-butyrolactone) and nonallergens (1-carbethoxy-4-piperidone, 6,7-dimethoxy-2-tetralone and 9-acetylanthracene) by both the model and the local lymph-node assay.

Is There Evidence that Geraniol Causes Allergic Contact Dermatitis

The fragrance material geraniol has been cited as a frequent cause of allergic contact dermatitis. A review of the literature shows that when the underlying clinical and experimental data are analyzed, a clear cause-effect relationship has infrequently or rarely been established. On the basis of the generally weak sensitizing potential of this substance coupled with its generally low exposure conditions, the prevalence of clinical cases would not be expected to be particularly high. This is not to say that geraniol is a frequent inducer of type IV allergy in members of the public. It remains to be seen, however, how often such allergy, once established, is responsible for any of the cases of allergic contact dermatitis commonly ascribed in the literature. Indeed, in some cases, patch-test conditions may not be optimal for differentiating between clinically relevant and irrelevant allergy to geraniol. Because of the numerous publications on geraniol-positive patch-test publications, a future effort to ascertain how many of these represent clinical intolerance is indicated. This will also permit determination of the NOEL (no observed effect level) in patch and use testing.

Is There Evidence that Anisyl Alcohol Causes Allergic Contact Dermatitis

The fragrance material anisyl alcohol has been cited as a moderately frequent cause of allergic contact dermatitis. A review of the literature shows that when the underlying clinical and experimental data are analyzed, a clear cause-effect relationship has infrequently or rarely been established. On the basis of the generally weak sensitizing potential of this substance coupled with its generally low exposure conditions, the prevalence of clinical cases would not be expected to be particularly high. This is not to say that anisyl alcohol is a frequent inducer of type IV allergy in members of the public. However, it remains to be seen how often such an allergy, once established, is responsible for any of the cases of allergic contact dermatitis commonly ascribed in the literature. Indeed, in some cases, patch test conditions may not be optimal for differentiating between clinically relevant and irrelevant allergy to anisyl alcohol.

Menthol: A Review of Its Sensitization Potential

Menthol, a cyclic terpene alcohol found in high concentrations in oils of peppermint and cornmint, has been widely used in over-the-counter medications, cosmetics and confectionery for over a century. However, its clinical pharmacology remains incompletely understood and its sensitization potential and irritant properties have not been thoroughly studied. Analysis of the menthol structure in a quantitative structure-activity relationship model does not identify any protein-reactive functions. Considering the extensive use of menthol there have been only few reports of adverse dermatological effects. After performing an extensive review of the reported cases of sensitization to menthol, we concluded that the literature does not adequately document the clinical relevance of the patch test reactions nor the impact of irritant reactions. We propose a comprehensive approach when testing with a nonstandard substance such as menthol.

Is There Evidence That Alpha-Iso-Methylionone Causes Allergic Contact Dermatitis?

The fragrance material alpha-iso-methylionone, or ‘gamma-methylionone’, has been cited as a moderately frequent cause of allergic contact dermatitis. A review of the literature shows that when the underlying clinical and experimental data are analyzed, a clear cause-effect relationship has infrequently or rarely been established. On the basis of the generally weak sensitizing potential of this substance, coupled with its generally low exposure conditions, the prevalence of clinical cases would not be expected to be particularly high. This is not to say that alpha-iso-methylionone is a frequent inducer of low-intensity but sub-clinical, type IV allergy in members of the public. It remains to be seen however, how often such allergy, once established, is responsible for any of the cases of allergic contact dermatitis commonly ascribed in the literature. Indeed, in some cases, patch test conditions may not be optimal for differentiating between clinically relevant and irrelevant allergy to alpha-iso-methylionone. Prospective screening patch test studies combined with appropriate follow-up to ascertain clinical relevance should clarify these issues.