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Predictive Model for Dermal Exposure Assessment
Published in Rhoda G.M. Wang, Water Contamination and Health, 2020
Annette L. Bunge, Gordon L. Flynn, Richard H. Guy
The difference between the curves labeled in and out corresponds to the mass of chemical within the stratum corneum at any time. As illustrated in Figure 1, because some chemical resides in the stratum corneum itself, the cumulative mass entering the stratum corneum is always greater than that exiting from that skin. We argue that chemical absorbed into the stratum corneum invariably continues to transport into the viable tissue even after the chemical exposure ends. This is so because desquamation of the stratum corneum is too slow to compete with diffusion of chemical into the body.
Exposure Assessment
Published in Ted W. Simon, Environmental Risk Assessment, 2019
Substances applied to the skin may evaporate before penetration or may diffuse through the stratum corneum. Substances that penetrate the stratum corneum may be metabolized in the germinative layer of the epidermis or may continue to the capillaries in the dermis. In addition, some substances may bind irreversibly to lipids or proteins in skin and be sequestered. Sequestered chemicals in the skin may eventually be absorbed or may be lost by desquamation.205 Hence, studies that measure the amount of material lost from the skin surface may tend to overestimate dermal permeation. Measurements of actual permeation to the blood must also be conducted with care.
The Role of Biological Lipids in Skin Conditioning
Published in Randy Schueller, Perry Romanowski, Conditioning Agents for Hair and Skin, 2020
The lipid composition of human stratum corneum lipids displays striking regional variations that could reflect differences in stratum corneum thickness, turnover, desquamation, and/or permeability. However, the barrier properties of these sites are not explicable by either site-related differences in thickness or the number of cell layers in the stratum corneum. Instead, an inverse relationship exists between the lipid weight percentage and the permeability properties of a particular skin site (57,58). In addition to total lipid content, significant regional differences occur in the compositional profile of stratum corneum lipids over different skin sites. For example, the proportion of sphingolipids and cholesterol is much higher in palmoplantar stratum corneum than on the extensor surfaces of the extremities, abdominal, or facial stratum corneum (59). However, the significance of these differences in lipid distribution is not known, because the absolute quantities of each of these fractions is dependent on the lipid weight percentage of the stratum corneum at each anatomical site. Thus, despite the high proportions of sphingolipids and cholesterol in palmar stratum corneum, when adjusted for the 2% lipid weight of this site, the absolute amounts of sphingolipids and cholesterol in the intercellular spaces are still much lower than in other, more lipid-enriched sites. Moreover, functional interpretations require consideration not only of lipid distribution and weight percentages, but also information about site-related variations in the fatty acid profiles of esterified species, and at present these data are not available.
Efficacy of soap and water based skin decontamination using in vivo animal models: a systematic review
Published in Journal of Toxicology and Environmental Health, Part B, 2021
Anuk Burli, Nadia Kashetsky, Aileen Feschuk, Rebecca M. Law, Howard I. Maibach
Many studies demonstrated that the efficacy of decontamination depends upon the chemical contaminant skin residence time. The longer a chemical or toxin remains on the skin, the more likely percutaneous penetration begins, allowing the substance to be absorbed into the skin and reach systemic circulation (Moody and Maibach 2006). At this point, decontamination removal plateaus (Maibach and Wester 1989; Wester, Melendres, and Maibach 1992). Only some in vivo studies regarding decontamination efficacy compared immediate versus delayed decontamination (Braue et al. 2011). By determining decontamination efficacy after an extended time period, soap and water may be at a limited decontaminating capacity, and no longer able to effectively remove toxins. Further, decreased availability of the contaminating agent at the surface leads to further diminished decontaminating agent effectiveness. In addition, only some experiments included both a “rubbing” component and a “solvent” component, helping facilitate desquamation of stratum corneum especially with cells undergoing exfoliation, washing away the toxin with it (Wester et al. 1990). In addition, increasing the soap concentration and length of cleansing time, might affect decontamination (Maibach and Wester 1989).
A Physiological-Based Pharmacokinetic Model For The Broad Spectrum Antimicrobial Zinc Pyrithione: II. Dermal Absorption And Dosimetry In The Rat
Published in Journal of Toxicology and Environmental Health, Part A, 2021
Gary L. Diamond, Nicholas P. Skoulis, A. Robert Jeffcoat, J Frank Nash
The estimate of 1.9 · 10−6 cm/hr (±2.9 · 10−6 SD) for the permeability coefficient based upon in vitro skin penetration data provided a starting place for statistically optimizing the KPS parameter in the model (10−5 to 10−7 cm/hr). The fugitive loss constant (KFUG) was optimized over a range of 10−5-10−1, based upon a reported desquamation rate for human skin of approximately 10−9 cm/sec and a stratum corneum desquamation thickness of 1 µm (Sugino et al. 2014). The corresponding rate constant would be approximately 3 · 10−3/hr. In addition to desquamation, other non-absorptive mechanisms may participate in loss of ZnPT from the absorption site, including radial diffusion, which might lower the driving source for diffusive absorption (Rush et al. 2015). The dissolution rate coefficient was optimized over a range of 10−4-2 · 10−1, with the upper end of the range based upon observations made of ZnPT on guinea pigs skin showing that ZnPT particles required approximately 6 hr to dissolve, depending upon the particle size (Black, Howes, and Rutherford 1975). The value for CSKMAX was optimized over a range of 1 − 100 mg/L, based upon estimates of 5 mg/L for water solubility of ZnPT (Rush et al. 2015).
Genetic variants affecting chemical mediated skin immunotoxicity
Published in Journal of Toxicology and Environmental Health, Part B, 2022
Isisdoris Rodrigues de Souza, Patrícia Savio de Araujo-Souza, Daniela Morais Leme
Through a step-wise process of differentiation, keratinocytes form a physical barrier. The structure and function of this barrier are largely dependent on the SC, which is the outermost layer of the epidermis (Fujii 2020). The SC consists of terminally differentiated keratinocytes (called corneocytes) and intercellular lipids, which provide a physical and hydrophobic barrier. Tight junction (TJ) proteins seal adjacent keratinocytes in the stratum granulosum (SG), acting as a second barrier beneath the SC (Fujii 2020). The formation of the SC barrier occurs in terms of the following 5 categories: 1) FLG metabolism; 2) cornified envelope; 3) intercellular lipids; 4) corneodesmosome, and 5) corneocyte desquamation (Egawa and Kabashima 2018).