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At the 8th conference of Occupational and Environmental Exposure of the Skin to Chemicals (OEESC) (16-18 September 2019) in Dublin, Ireland, several researchers performing skin permeation assays convened to discuss in vitro skin permeability experiments. We, along with other colleagues, all of us hands-on skin permeation researchers, present here the results from our discussions on the available OECD guidelines. The discussions were especially focused on three OECD skin absorption documents, including a recent revision of one: i) OECD Guidance Document 28 (GD28) for the conduct of skin absorption studies (OECD, 2004), ii) Test Guideline 428 (TGD428) for measuring skin absorption of chemical in vitro (OECD, 2004), and iii) OECD Guidance Notes 156 (GN156) on dermal absorption issued in 2011 (OECD, 2011). GN156 (OECD, 2019) is currently under review but not finalized. A mutual concern was that these guidance documents do not comprehensively address methodological issues or the performance of the test, which might be partially due to the years needed to finalize and update OECD documents with new skin research evidence. Here, we summarize the numerous factors that can influence skin permeation and its measurement, and where guidance on several of these are omitted and often not discussed in published articles. We propose several improvements of these guidelines, which would contribute in harmonizing future in vitro skin permeation experiments.
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Congressos como Assunto/normas , Exposição Ambiental/normas , Fidelidade a Diretrizes/normas , Exposição Ocupacional/normas , Organização para a Cooperação e Desenvolvimento Econômico/normas , Absorção Cutânea/efeitos dos fármacos , Exposição Ambiental/prevenção & controle , Substâncias Perigosas/metabolismo , Substâncias Perigosas/toxicidade , Humanos , Irlanda , Exposição Ocupacional/prevenção & controle , Absorção Cutânea/fisiologiaRESUMO
BACKGROUND: Experimental work on skin hydration is technologically challenging, and mostly limited to observations where environmental conditions are constant. In some cases, like diapered baby skin, such work is practically unfeasible, yet it is important to understand potential effects of diapering on skin condition. To overcome this challenge, in part, we developed a computer simulation model of reversible transient skin hydration effects. METHODS: Skin hydration model by Li et al. (Chem Eng Sci, 138, 2015, 164) was further developed to simulate transient exposure conditions where relative humidity (RH), wind velocity, air, and skin temperature can be any function of time. Computer simulations of evaporative water loss (EWL) decay after different occlusion times were compared with experimental data to calibrate the model. Next, we used the model to investigate EWL and SC thickness in different diapering scenarios. RESULTS: Key results from the experimental work were: (1) For occlusions by RH=100% and free water longer than 30 minutes the absorbed amount of water is almost the same; (2) Longer occlusion times result in higher water absorption by the SC. The EWL decay and skin water content predictions were in agreement with experimental data. Simulations also revealed that skin under occlusion hydrates mainly because the outflux is blocked, not because it absorbs water from the environment. Further, simulations demonstrated that hydration level is sensitive to time, RH and/or free water on skin. In simulated diapering scenarios, skin maintained hydration content very close to the baseline conditions without a diaper for the entire duration of a 24 hours period. CONCLUSION: Different diapers/diaper technologies are known to have different profiles in terms of their ability to provide wetness protection, which can result in consumer-noticeable differences in wetness. Simulation results based on published literature using data from a number of different diapers suggest that diapered skin hydrates within ranges considered reversible.
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Fraldas para Adultos , Fraldas Infantis , Estado de Hidratação do Organismo/fisiologia , Fenômenos Fisiológicos da Pele , Perda Insensível de Água/fisiologia , Simulação por Computador , Desidratação/fisiopatologia , Humanos , Concentração Osmolar , Absorção Cutânea/fisiologia , Água/análiseRESUMO
OBJECTIVE: Skin transport properties of glycerine and water from binary mixtures contacting human skin were determined to better understand the mechanism of skin moisturization by aqueous glycerine formulations. METHODS: Steady-state permeation for 3 H2 O and 14 C-glycerine across split-thickness human skin in vitro and desorption dynamics of the same permeants in isolated human stratum corneum (HSC) were experimentally determined under near equilibrium conditions. These data were compared to a priori values developed in the context of a thermodynamic model for binary mixtures of glycerine and water and a previously determined water sorption isotherm for HSC. This allowed the estimation of diffusion and partition coefficients for each permeant in the HSC, as well as HSC thickness, as a function of composition of the contacting solution. These data may be used to estimate water retention and associated HSC swelling related to the absorption and slow release of glycerine from the skin. RESULTS: It took 6+ days for glycerine to completely desorb from HSC immersed in glycerine/water binary solutions. Desorption of both 3 H2 O and 14 C-glycerine from HSC was slower in pure water than from binary mixtures, a result that is largely explained by the greater swelling of HSC in water. Parametric relationships were developed for water and glycerine intradiffusivities in HSC as functions of HSC water content, and a mutual diffusion coefficient was estimated by analogy with glycerine/water binary solutions. The intradiffusivity of 14 C-glycerine in HSC as inferred from sorption/desorption experiments was shown to be approximately 10-fold less than that inferred from permeation experiments, whereas the corresponding values for 3 H2 O were comparable. CONCLUSION: These studies confirm that glycerine enters HSC in substantial quantities and has a long residence time therein. The coupling between bulk water and glycerine transport projected from binary solution data suggests the net effect of glycerine is to slow water loss from the skin. The data support the concept of glycerine as a humectant with an excellent balance of skin penetration and retention characteristics; however, they do not rule out the possibility of an additional biological effect on skin barrier homoeostasis.
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Emolientes , Glicerol/metabolismo , Pele/metabolismo , Água/metabolismo , Transporte Biológico , Humanos , PermeabilidadeRESUMO
Gene Cooper was a bright theoretician, a skilled product developer, and a motivational leader who applied his talents to the skin science area early in his career. His work led to the development of finite dose skin absorption models, chemical penetration enhancer technologies and quantitative structure-penetration relationships for chemicals contacting human skin. His ideas regarding the impact of molecular weight and lipid solubility on skin transport catalyzed the later development by Potts and Guy of the first successful skin permeability model. But Gene's most important contribution to the field was as a scientific role model and an inspirational leader who launched the careers of several young scientists, including the author of this article.
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Preparações Farmacêuticas/administração & dosagem , Absorção Cutânea , Administração Cutânea , Desenho de Fármacos , História do Século XX , História do Século XXI , Humanos , Modelos Biológicos , Peso Molecular , Preparações Farmacêuticas/química , Preparações Farmacêuticas/metabolismo , Relação Quantitativa Estrutura-Atividade , Pele/metabolismo , SolubilidadeRESUMO
BACKGROUND: Hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC) is a synthetic fragrance ingredient. Case reports of allergy to HICC appeared in the 1980s, and HICC has recently been included in the European baseline series. Human elicitation dose-response studies performed with different allergens have shown a significant relationship between the patch-test threshold and the repeated open application test (ROAT) threshold, which mimics some real-life exposure situations. Fragrance ingredients are special as significant amounts of allergen may evaporate from the skin. OBJECTIVES: The study aimed to investigate the relationship between elicitation threshold doses at the patch test and the ROAT, using HICC as the allergen. The expected evaporation rate was calculated. MATERIALS AND METHODS: Seventeen HICC-allergic persons were tested with a dilution series of HICC in a patch test and a ROAT (duration up to 21 days). Seventeen persons with no HICC allergy were included as control group for the ROAT. Results The response frequency to the ROAT (in microg HICC cm(-2) per application) was significantly higher than the response frequency to the patch test at one of the tested doses. Furthermore the response rate to the accumulated ROAT dose was significantly lower at half of the doses compared with the patch test. The evaporation rate of HICC was calculated to be 72% over a 24-h period. CONCLUSIONS: The ROAT threshold in dose per area per application is lower than the patch test threshold; furthermore the accumulated ROAT threshold is higher than the patch test threshold, which can probably be explained by the evaporation of HICC from the skin in the open test.
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Aldeídos/efeitos adversos , Alérgenos/efeitos adversos , Cicloexanos/efeitos adversos , Cicloexenos/efeitos adversos , Dermatite Alérgica de Contato/diagnóstico , Testes do Emplastro/métodos , Perfumes/efeitos adversos , Adulto , Alérgenos/administração & dosagem , Dermatite Alérgica de Contato/etiologia , Relação Dose-Resposta a Droga , Feminino , Humanos , Modelos Logísticos , Masculino , Pessoa de Meia-Idade , Perfumes/química , Adulto JovemRESUMO
In vitro measurements of skin absorption are an increasingly important aspect of regulatory studies, product support claims, and formulation screening. However, such measurements are significantly affected by skin variability. The purpose of this study was to determine inter- and intralaboratory variation in diffusion cell measurements caused by factors other than skin. This was attained through the use of an artificial (silicone rubber) rate-limiting membrane and the provision of materials including a standard penetrant, methyl paraben (MP), and a minimally prescriptive protocol to each of the 18 participating laboratories. "Standardized" calculations of MP flux were determined from the data submitted by each laboratory by applying a predefined mathematical model. This was deemed necessary to eliminate any interlaboratory variation caused by different methods of flux calculations. Average fluxes of MP calculated and reported by each laboratory (60 +/- 27 microg cm(-2) h(-1), n = 25, range 27-101) were in agreement with the standardized calculations of MP flux (60 +/- 21 microg cm(-2) h(-1), range 19-120). The coefficient of variation between laboratories was approximately 35% and was manifest as a fourfold difference between the lowest and highest average flux values and a sixfold difference between the lowest and highest individual flux values. Intralaboratory variation was lower, averaging 10% for five individuals using the same equipment within a single laboratory. Further studies should be performed to clarify the exact components responsible for nonskin-related variability in diffusion cell measurements. It is clear that further developments of in vitro methodologies for measuring skin absorption are required.
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Técnicas de Laboratório Clínico/normas , Variações Dependentes do Observador , Técnicas de Laboratório Clínico/estatística & dados numéricos , Difusão , Cultura em Câmaras de Difusão/métodos , Cultura em Câmaras de Difusão/normas , Cultura em Câmaras de Difusão/estatística & dados numéricos , Internacionalidade , Controle de Qualidade , Padrões de Referência , Valores de Referência , Absorção Cutânea/fisiologiaRESUMO
Non-invasive and accurate access of biomarkers remains a holy grail of the biomedical community. Human eccrine sweat is a surprisingly biomarker-rich fluid which is gaining increasing attention. This is especially true in applications of continuous bio-monitoring where other biofluids prove more challenging, if not impossible. However, much confusion on the topic exists as the microfluidics of the eccrine sweat gland has never been comprehensively presented and models of biomarker partitioning into sweat are either underdeveloped and/or highly scattered across literature. Reported here are microfluidic models for eccrine sweat generation and flow which are coupled with review of blood-to-sweat biomarker partition pathways, therefore providing insights such as how biomarker concentration changes with sweat flow rate. Additionally, it is shown that both flow rate and biomarker diffusion determine the effective sampling rate of biomarkers at the skin surface (chronological resolution). The discussion covers a broad class of biomarkers including ions (Na(+), Cl(-), K(+), NH4 (+)), small molecules (ethanol, cortisol, urea, and lactate), and even peptides or small proteins (neuropeptides and cytokines). The models are not meant to be exhaustive for all biomarkers, yet collectively serve as a foundational guide for further development of sweat-based diagnostics and for those beginning exploration of new biomarker opportunities in sweat.
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The retention of radioactivity in human, rat, and dog following a single injected dose of radiolabeled etidronate disodium (EHDP) is shown to follow power-law decay curves with similar slopes for times up to 4, 60, and 80 days, respectively. During this period retention declines with time according to a weak inverse power of the time since dosing, with an exponent ranging from -0.05 (dog) to -0.09 (human and rat). Direct analyses of dog bones either 90 days after a single dose or 365 days after cessation of chronic dosing indicate a more rapid bone clearance of EHDP than predicted by the initial power law. Direct skeletal analysis also shows a more rapid loss of radioactivity in the rat between 60 and 365 days, indicative of either a second power law or a terminal exponential phase in the retention function occurring after 60 days. These data are used to estimate the minimum and maximum amounts of drug that would remain in the body following long-term treatment in humans. For the intermittent cyclic EHDP treatment (ICT) regimen for osteoporosis (repeated cycles of 14 daily doses of 400 mg orally followed by 76 days drug free), the projected retention of EHDP after 3 years of treatment is 25-50 times the daily absorbed dose. Thus, for a 60 kg woman with a daily absorbed dose of 12 mg, the retained mass of EHDP would be about 300-600 mg.(ABSTRACT TRUNCATED AT 250 WORDS)
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Osso e Ossos/metabolismo , Ácido Etidrônico/farmacocinética , Adulto , Animais , Cães , Feminino , Humanos , Masculino , Osteoporose/metabolismo , Ratos , Ratos EndogâmicosRESUMO
As part of a program to establish structure-activity relationships for vanilloids, analogs of the pungent principle capsaicin, the alkyl chain portion of the parent structure (and related compounds derived from homovanillic acid) was varied. In antinociceptive and antiinflammatory assays (rat and mouse hot plate and croton oil-inflamed mouse ear), compounds with widely varying alkyl chain structures were active. Short-chain compounds were active by systemic administration in the assays mentioned above but they retained the high pungency and acute toxicity characteristic of capsaicin. In contrast, the long chain cis-unsaturates, NE-19550 (vanillyloleamide) and NE-28345 (oleylhomovanillamide), were orally active, less pungent, and less acutely toxic than capsaicin. The potential of these compounds as antiinflammatory/analgesic agents is discussed in light of recent data on the mechanism of action of vanilloids on sensory nerve fibers.
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Analgésicos , Anti-Inflamatórios não Esteroides , Capsaicina/análogos & derivados , Analgésicos/química , Analgésicos/farmacologia , Animais , Anti-Inflamatórios não Esteroides/química , Anti-Inflamatórios não Esteroides/farmacologia , Capsaicina/química , Capsaicina/toxicidade , Óleo de Cróton , Ácido Homovanílico/análogos & derivados , Ácido Homovanílico/química , Temperatura Alta , Inflamação/induzido quimicamente , Inflamação/tratamento farmacológico , Masculino , Camundongos , Camundongos Endogâmicos ICR , Estrutura Molecular , Medição da Dor , Ratos , Ratos Sprague-Dawley , Relação Estrutura-AtividadeRESUMO
The computed tomographic appearance of three cases of cerebral toxoplasmosis is described. Two of the patients were children with Hodgkin disease and the third was an adult with systemic lupus erythematosus. All patients were severely immunosuppressed. Computed tomography showed single or multiple hypodense rounded areas with peripheral annular contrast enhancement, suggesting pyogenic cerebral abscesses. Pathologic correlation is presented. The importance of diagnosis and early treatment is emphasized.
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Encefalopatias/diagnóstico por imagem , Tomografia Computadorizada por Raios X , Toxoplasmose/diagnóstico por imagem , Adulto , Edema Encefálico/diagnóstico por imagem , Criança , Pré-Escolar , Doença de Hodgkin/complicações , Humanos , Lúpus Eritematoso Sistêmico/complicações , MasculinoRESUMO
Despite the considerable success in predicting the steady-state dermal absorption rates of chemical compounds from large reservoirs applied to skin, correspondingly little progress has been made in predicting the absorption rate and extent for small doses of topically applied compounds. In the latter case, steady-state absorption rates are generally not obtained, and rapid evaporation or penetration of the dose solvent makes application of permeability coefficient models problematic. This report presents a new analysis of the finite dose problem in terms of a diffusion model with three parameters-a characteristic time for diffusion, h2/D; a skin solubility factor, S(m)h; and a capacity factor for absorption of the dose during the dry down period, M*. These parameters can be related to the molecular weight and oil and water solubilities of the permeant in a manner similar to models describing steady-state absorption from saturated solutions. Some variation of the parameter values based on the chemical nature and volume of the dose solvent is anticipated. The applicability of the model is demonstrated by analyzing the in vitro absorption rates of varying doses of vanillylnonamide (VN, synthetic capsaicin) applied to excised human skin from propylene glycol. The analysis shows that a three-parameter model that assigns all of the resistance to transport to diffusion through the stratum corneum is able to explain most of the significant features of VN absorption through skin.
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Absorção Cutânea , Ácido Vanílico/análogos & derivados , Ácido Vanílico/farmacocinética , Animais , Difusão , HumanosRESUMO
The percutaneous absorption of three highly lipophilic analogs of capsaicin--vanillylnonanamide (VN), olvanil, and NE-21610--was measured in vivo in the CD:VAF rat, and in vitro through excised CD: VAF and SkH:Fz rat skin and human cadaver skin. Absorption and skin metabolism were monitored by radiolabel techniques. The rank order of penetration in all species was VN > olvanil > NE-21610, in accordance with that expected from their physical properties. Rat skin was more permeable than human skin by factors ranging from 4 to 8 for VN, 10 to 20 for olvanil, and approximately 10 to 100 for NE-21610. All three compounds were extensively metabolized during passage through fresh SkH:Fz rat skin, with the primary route of degradation for at least two of the compounds involving hydrolysis of the amide bond (the metabolites of NE-21610 were not identified). For the in vitro studies a range of receptor solutions was employed to determine a set of conditions that best mimicked in vivo absorption. The results with phosphate-buffered saline containing a preservative and 1-6% polyoxyethylene-20 oleyl ether (Oleth-20) were in good agreement with in vivo results for all three compounds for periods up to 24 h post-dose; after this time, in vivo absorption rates declined but in vitro rates remained relatively constant. Buffered saline or saline containing 0.5% bovine serum albumin led to marked underestimates of in vivo penetration for olvanil and NE-21610, whereas a 1:1 ethanol: water solution led to gross overestimates of the in vivo absorption rates for all three compounds.
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Capsaicina/análogos & derivados , Absorção Cutânea , Ácido Vanílico/análogos & derivados , Animais , Capsaicina/farmacocinética , Humanos , Técnicas In Vitro , Masculino , Ratos , Ácido Vanílico/farmacocinéticaRESUMO
Vanilloids are a class of compounds structurally related to capsaicin, the pungent principle of hot peppers, which are under development as a novel class of analgesics. Vanilloids undergo extensive first-pass metabolism when dosed orally to rats and mice. These compounds, as well as capsaicin, would be anticipated to be susceptible to three major routes of metabolism: (omega, beta)-oxidation of the alkyl side chain, hydrolysis of the amide bond and conjugation of the phenolic group. Olvanil [N-(3-methoxy-4-hydroxybenzyl)oleamide], radiolabelled with either 14C at the benzylic carbon or 3H in the oleyl side chain, was studied in various in vitro, in situ and in vivo metabolism models to determine the major route(s) of intestinal and hepatic metabolism in rats for this new class of compounds. Models used in metabolism studies included isolated hydrolytic enzymes, cell-free intestinal and liver supernatants, hepatocytes, enterocytes, perfused intestine and whole animal studies. Reversed-phase liquid chromatography (LC) with on-line radiochemical detection was used to examine the metabolic profiles from the different models. The major metabolic route for olvanil in both the intestine and the liver was found to be hydrolysis of the amide bond. The benefits of selective 14C and 3H labels in conjunction with LC with on-line radiochemical detection are discussed.
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Analgésicos/metabolismo , Anti-Inflamatórios não Esteroides/metabolismo , Capsaicina/análogos & derivados , Animais , Capsaicina/metabolismo , Cromatografia Líquida de Alta Pressão , Mucosa Intestinal/metabolismo , Fígado/metabolismo , Masculino , Perfusão , Radioquímica , Ratos , Ratos EndogâmicosRESUMO
Detailed models of solute transport through the stratum corneum (SC) require an interpretation of apparent bulk diffusion coefficients in terms of microscopic transport properties. Modern microscopy techniques provide a tool for evaluating one key property-lipid pathway tortuosity-in more detail than previously possible. Microscopic lipid pathway measurements on alkali expanded human SC stained with the lipid-soluble dyes methylene blue, Nile red, and oil red O are described. Brightfield, differential interference contrast, fluorescence, and laser scanning confocal optics were employed to obtain 2-dimensional (2-D) and 3-dimensional (3-D) images. The 2-D techniques clearly outlined the corneocytes. Confocal microscopy using Nile red yielded a well-delineated 3-D structure of expanded SC. Quantitative assessment of the 2-D images from a small number of expanded SC samples led to an average value of 3.7 for the ratio of the shortest lipid-continuous pathway to the width of the membrane. This was corrected for the effect of alkaline expansion to arrive at an average value of 12.7 for the same ratio prior to swelling.
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Células Epidérmicas , Bicamadas Lipídicas/análise , Compostos Azo , Soluções Tampão , Corantes , Epiderme/química , Corantes Fluorescentes , Humanos , Lipídeos de Membrana/análise , Azul de Metileno , Microscopia Confocal/métodos , Microscopia de Fluorescência , Oxazinas , Hidróxido de SódioRESUMO
Because of their potential for inducing allergic contact dermatitis (ACD) if used improperly, perfumes are carefully assessed for dermal safety prior to incorporation into cosmetic products. Exposure assessment for these materials often involves the conservative assumption of 100% absorption of each component. This report describes an improved method to estimate the absorption and evaporation of perfume ingredients from skin, based on their physico-chemical properties. The effect of environmental variables such as temperature and wind velocity can be accounted for in a logical way. This was accomplished using a first-order kinetic approach expected to be applicable for small doses applied to skin. Skin penetration rate was calculated as a fraction of the maximum flux estimated from the compound's lipid solubility, S(lip) (represented by the product of octanol/water partition coefficient, K(octt), and water solubility, S(w)), and molecular weight, MW. Evaporation rates were estimated from a modified Henry's Law approach with a stagnant boundary layer whose thickness is a function of surface airflow, v. At a given value of v, evaporation rate was assumed proportional to the ratio P(vp)/S(lip), where P(vp) is the vapour pressure of the ingredient at skin temperature, T. The model predicts a relationship for total evaporation from skin of the form %evap = 100x/(k+x) where x = P(vp)MW(2.7)/(K(oct)S(w)) and k is a parameter which depends only on v and T. Comparison with published data on perfume evaporation from human skin in vivo showed good agreement between theory and experiment for two closely related perfume mixtures (r(2) = 0.52-0.74, s = 12-14%, n = 10). Thus, the method would seem to have a good prospect of providing skin absorption estimates suitable for use in exposure assessment and improved understanding of dose-related contact allergy.
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Human in vivo fragrance evaporation data from a previously published study are reanalysed in terms of compartmental pharmacokinetic models in which the microscopic rate constants are functions of the physicochemical properties of the fragrance components. According to the proposed analysis, which is restricted to low doses, absorption and evaporation of each component are first-order processes occurring from either the skin (one-compartment model) or the skin and a more rapidly depleted vehicle layer (two-compartment models). Evaporation rates of ingredients from a 12-component mixture containing a musk fixative followed single exponential decays that were well described by the one-compartment model. An otherwise identical mixture without fixative yielded evaporation rates that could be characterized as biexponential decays associated with loss from two compartments. This result shows that ingredient interactions qualitatively and quantitatively change evaporation rate profiles of fragrance components; however, an attempt to account for these interactions explicitly by means of activity coefficients inserted as multipliers for the microscopic rate constants was unsuccessful. Re-examination of this approach in the context of a diffusion/evaporation model is suggested. The developed models have potential utility for dermal risk assessment and for prediction of aroma evolution following topical application of complex fragrances.
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Hypoxic-ischaemic injury of the central nervous system (CNS) in newborns is a very prevalent entity affecting 1 to 6 children per 1000 births. This injury may induce severe neurological sequelae. We present the analysis of 1028 consecutive cases of hypoxic-ischaemic CNS injuries of haemorrhagic pattern detected in autopsies performed at the Division of Anatomic Pathology, Hospital de Clínicas, University of Paraná, Brazil, from 1960 to 1995. The prevalence of these lesions was high (49.73%) amongst all autopsied newborns. The main types of haemorrhage were microscopical intra-parenchymal haemorrhages, intraventricular and periventricular haemorrhages and subarachnoid foci of bleeding. Our results emphasize that premature children constitute a high risk group for CNS haemorrhage needing special preventive therapeutic procedures to avoid neurological complications.