RESUMEN
OBJECTIVES: Retinoic acid (RA) and benzoyl peroxide (BP) were studied, comparing their keratolytic efficacy and water barrier disruption to that of salicylic acid (SA), a well-established keratolytic, under similar conditions. PATIENTS/METHODS: Six volunteers were included in this blinded study. Eleven randomized test sites were marked on the volar forearms, containing sites for untreated skin at time zero, unoccluded, occlusion, and vehicle controls for 3 and 6 h, and each of BP, RA, and SA solutions for 3 and 6 h. At each time point, occlusion at 5 of the test sites was removed, and chromameter measurements were performed over 30 min. Each site then underwent 25 stratum corneum (SC) tape strippings. At 1, 5, and 30 min after the last stripping at each site, TEWL measurements were performed. Quantitative protein analysis of the SC from the tapes was then performed. RESULTS AND CONCLUSION: after 3 h, bp was significantly more effective in disrupting sc cohesion than sa and ra, indicating bp is a moderate keratolytic agent in addition to its antimicrobial properties. After 6 h, all three agents were similarly effective in keratolysis. Barrier disruption, as measured by TEWL, paralleled depth of SC removal. SA tended to exhibit the greatest keratolytic efficacy superficially, hence its clinical effectiveness in superficial conditions such as comedonal acne, whereas BP was more effective at deeper levels, complimenting its antimicrobial effects and enabling it to treat deeper, more inflammatory lesions. None of the agents significantly affected skin erythema. These techniques provide a robust and rapid assay for in vivo keratolytic demonstration.
Asunto(s)
Peróxido de Benzoílo/farmacología , Queratolíticos/farmacología , Ácido Salicílico/farmacología , Tretinoina/farmacología , Adulto , Agua Corporal/metabolismo , Humanos , Persona de Mediana Edad , Piel/efectos de los fármacos , Piel/metabolismoRESUMEN
Investigating the processes that led to the end of the last interglacial period is relevant for understanding how our ongoing interglacial will end, which has been a matter of much debate (see, for example, refs 1, 2). A recent ice core from Greenland demonstrates climate cooling from 122,000 years ago driven by orbitally controlled insolation, with glacial inception at 118,000 years ago. Here we present an annually resolved, layer-counted record of varve thickness, quartz grain size and pollen assemblages from a maar lake in the Eifel (Germany), which documents a late Eemian aridity pulse lasting 468 years with dust storms, aridity, bushfire and a decline of thermophilous trees at the time of glacial inception. We interpret the decrease in both precipitation and temperature as an indication of a close link of this extreme climate event to a sudden southward shift of the position of the North Atlantic drift, the ocean current that brings warm surface waters to the northern European region. The late Eemian aridity pulse occurred at a 65 degrees N July insolation of 416 W m(-2), close to today's value of 428 W m(-2) (ref. 9), and may therefore be relevant for the interpretation of present-day climate variability.
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Clima Desértico , Cubierta de Hielo , Océano Atlántico , Europa (Continente) , Agua Dulce/química , Sedimentos Geológicos/química , Alemania , Groenlandia , Historia Antigua , Polen/fisiología , Cuarzo/química , Lluvia , Temperatura , Factores de Tiempo , Árboles/fisiología , Movimientos del AguaRESUMEN
BACKGROUND/AIMS: Examination of stratum corneum (SC) content with tape stripping and a colorimetric method is increasingly used. We examined the possible use of microplates in tandem with a colorimetric method to examine SC removed with tape stripping. As a corollary to this examination, the homogeneity of tape strips was examined. METHOD: The commonly used Lowry assay was adapted for 96-well plates. Tapes were divided into four regions and sample disks of 5 mm diameter were taken from each and analyzed for SC mass using the adapted Lowry assay. RESULTS: Homogeneity of SC removal over different areas across a tape strip is limited. CONCLUSION: Quantification of SC by means of a 96-well microplate-based colorimetric method is feasible and shortens the time of analysis. However, when using D-Squame tape disks, SC removal on a limited area of the tape is not predictive for SC removal on the entire tape as removal is inhomogenous. Therefore, SC protein extraction should be performed on a large enough area, eventually on the entire tape when quantifying SC mass removed by tape stripping.
Asunto(s)
Algoritmos , Vendajes , Epidermis/fisiología , Proteínas/metabolismo , Estaciones del Año , Manejo de Especímenes/métodos , Adhesividad , Adolescente , Adulto , Anciano , Femenino , Humanos , Masculino , Proteínas/análisis , Estadística como AsuntoRESUMEN
Keratolytic efficacy of topical preparations containing salicylic acid was studied in humans utilizing adhesive tape stripping and quantifying SC removal by protein analysis. In combination with tape stripping, squamometry was used to evaluate the influence of salicylic acid on skin surface scaliness and desquamation. Furthermore, skin barrier perturbation and skin irritancy was recorded and related to the dermatopharmacological effect of the preparations. In contrast to squamometry, tape stripping combined with protein analysis was sensitive in detecting keratolytic effect of salicylic acid within hours of application. Importantly, whereas the pH of the preparations only minimally influenced efficacy, local dermatotoxicity was significantly increased at acidic pH. This indicates that the quest to increase the amount of free, non-dissociated SA is, in fact, counterproductive as the more acidic preparations resulted in skin irritation and barrier disruption.
Asunto(s)
Administración Cutánea , Evaluación de Medicamentos/métodos , Queratolíticos/uso terapéutico , Ácido Salicílico/efectos adversos , Adulto , Dermatología/métodos , Dermatología/tendencias , Eritema/inducido químicamente , Femenino , Humanos , Concentración de Iones de Hidrógeno , Queratolíticos/administración & dosificación , Queratolíticos/química , Masculino , Mentol/administración & dosificación , Mentol/efectos adversos , Ácido Salicílico/administración & dosificación , Pruebas de Irritación de la Piel/métodos , Fenómenos Fisiológicos de la Piel/efectos de los fármacos , Soluciones/administración & dosificación , Soluciones/efectos adversos , Soluciones/química , Factores de Tiempo , Pérdida Insensible de Agua/efectos de los fármacos , Pérdida Insensible de Agua/fisiologíaRESUMEN
BACKGROUND: Tape stripping is a common method for investigating stratum corneum (SC) physiology as well as bioavailability and bioequivalence of topical drugs. OBJECTIVES: To investigate the influence of procedures (anatomical site, pressure, pressure duration, tape removal rate) inherent in each stripping protocol on changes in skin physiology. METHODS: Tape stripping was performed using tapes on the forearm, forehead and back. On the forearm different pressures (165 and 330 g cm(-2)), durations of pressure (2 and 10 s), and removal rate (slow and rapid removal) were used. Changes in skin physiology were evaluated by measurement of transepidermal water loss (TEWL) and hydration. RESULTS: A significant influence of all parameters on the TEWL increase as a function of tape strip number was observed. The fastest increase was demonstrated on the forehead, followed by the back and, lastly, the forearm. Rapid removal produced a protracted increase in comparison with slow removal. Pressure for 10 s induced a faster increase in TEWL than 2 s pressure. Likewise, pressure at 330 g cm(-2) induced an earlier increase than pressure at 165 g cm(-2). Skin hydration was not influenced by the variables tested. CONCLUSIONS: Tape stripping results are influenced dramatically by all investigated parameters. A dynamic SC stress test to investigate SC cohesion more closely is proposed based on the present observations.
Asunto(s)
Epidermis/fisiología , Fenómenos Fisiológicos de la Piel , Manejo de Especímenes/métodos , Adhesivos , Adulto , Biometría/métodos , Agua Corporal/metabolismo , Femenino , Humanos , Masculino , Persona de Mediana Edad , Presión , Absorción Cutánea/fisiología , Factores de Tiempo , Pérdida Insensible de Agua/fisiologíaRESUMEN
Exposure to ultraviolet radiation or ozone leads to skin damage including oxidation of skin biomolecules, as well as to depletion of constitutive antioxidants. The highly organized stratum corneum forming the main barrier against most xenobiotics is particularly susceptible to such damage and possible barrier perturbation may be the consequence. Whereas ample evidence exists for an increased permeability for different solutes including water after exposure to ultraviolet radiation, such an effect has not yet been reported for ozone. This study reports on the effect of such oxidative stressors using the hairless mouse as the skin model and measuring temperature-controlled transepidermal water loss (TEWL) as an indicator for skin barrier integrity. First, a strong dependency of the TEWL on skin temperature was observed, an effect that was clearly more pronounced than that found in man. Given this temperature dependency in untreated animals, we proceeded to determine the effects of both ultraviolet radiation and ozone on TEWL over a relevant physiological skin temperature range. Solar-simulated ultraviolet radiation (0.75-3 minimal erythemal dose) resulted in a delayed and dose-dependent skin barrier disruption over the entire temperature range investigated. Conversely, daily ozone exposure at 2 ppm for 1 week, however, did not significantly alter TEWL up to 72 h after the last exposure. The results demonstrate a differential response of the epidermis to two environmental stressors associated with oxidative damage; they suggest that chronic ozone exposure at relevant environmental levels does not lead to a detectable skin barrier defect, while solar UV exposure was demonstrated to increase epidermal water loss. Furthermore, experimental evidence clearly suggests that future studies applying TEWL measurements in animal models should be performed under carefully controlled skin temperature conditions.
Asunto(s)
Oxidantes Fotoquímicos/efectos adversos , Ozono/efectos adversos , Fenómenos Fisiológicos de la Piel , Temperatura Cutánea , Rayos Ultravioleta/efectos adversos , Pérdida Insensible de Agua , Animales , Exposición a Riesgos Ambientales/efectos adversos , Femenino , Ratones , Ratones Pelados , Estrés Oxidativo/efectos de los fármacos , Estrés Oxidativo/fisiología , Estrés Oxidativo/efectos de la radiación , Fenómenos Fisiológicos de la Piel/efectos de los fármacos , Fenómenos Fisiológicos de la Piel/efectos de la radiación , Temperatura Cutánea/efectos de los fármacos , Temperatura Cutánea/efectos de la radiación , Pérdida Insensible de Agua/efectos de los fármacos , Pérdida Insensible de Agua/fisiología , Pérdida Insensible de Agua/efectos de la radiaciónRESUMEN
Human skin models, such as EpiDerm and Episkin, are not easily mounted into static or dynamic diffusion cells that are commonly used to perform bioavailability studies with human skin ex vivo. For various reasons, such as fragility, small sample size, and other morphological constraints, skin absorption studies with human skin models are often carried out on the delimited skin surface obtained by gluing a ring onto the reconstituted epidermis and manually exchanging the receptor solution. However, such an experimental setup is prone to artifacts. Discontinuous removal of the receptor fluid leads to alternating sink conditions, and an area of application smaller than the area in contact with the receptor fluid, as well as imperfect seal of the glued ring, may result in inaccurate penetration rates. Human skin models were shown to be relatively easily mounted into In-Line cells (PermeGear Inc.), vertical diffusion cells which appear to be appropriately designed for such a purpose. In-Line cells allowed accurate determination of solute penetration as well as automated sampling of receptor fluid. Excised human skin can be mounted into these cells as well, making it possible to compare penetration rates through different types of skin samples under identical conditions. Using mannitol as a reference compound, penetration profiles and epidermal distribution similar to those obtained with human skin ex vivo were obtained both with EpiDerm and Episkin. Under the present conditions, human skin models were more permeable to mannitol than excised human skin, which was only slightly permeable to mannitol. Due to these experimental innovations and to the good agreement with the absorption characteristics through human skin ex vivo, EpiDerm and Episkin seem to be promising human skin models for testing the cutaneous bioavailability of topical products in vitro.
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Piel Artificial/normas , Piel/metabolismo , Disponibilidad Biológica , Cámaras de Difusión de Cultivos/métodos , Cámaras de Difusión de Cultivos/normas , Evaluación Preclínica de Medicamentos/métodos , Evaluación Preclínica de Medicamentos/normas , Humanos , Manitol/farmacocinética , Absorción Cutánea/efectos de los fármacos , Absorción Cutánea/fisiologíaRESUMEN
BACKGROUND/AIMS: Tape stripping of human stratum corneum has been performed to measure stratum corneum mass, barrier function, drug reservoir and percutaneous penetration. However, the technique itself requires further development to facilitate interpretation. METHODS: In this study we quantified stratum comeum (SC) tape stripping and water kinetic parameters utilizing three types of adhesive tapes, in an in vivo randomized clinical trial. Stratum corneum was tape stripped, and the mass of SC removed by each tape was quantified utilizing a protein assay. Transepidermal water loss (TEWL) was measured and barrier disruption and SC water kinetics calculated. Three commonly utilized acrylate adhesive tapes were utilized and a comparison made between them. RESULTS: Each type of tape successfully stripped the stratum corneum, but the rayon tape did not induce SC barrier disruption. Neither the type of tape nor the site stripped significantly influenced the mass of SC removed. Water kinetic parameters did not differ significantly for the tapes that did induce barrier disruption. Individual variation in barrier disruption to water following tape stripping was demonstrated. CONCLUSION: The tapes utilized removed a similar amount of SC. The tapes have a different propensity to cause barrier disruption. Some individuals do not demonstrate increased TEWL despite an equivalent mass of SC being removed compared to those who do show a response.
Asunto(s)
Adhesivos , Absorción Cutánea/fisiología , Piel/patología , Manejo de Especímenes/métodos , Adulto , Celulosa , Femenino , Humanos , Masculino , Polietileno , Valores de Referencia , Pérdida Insensible de Agua/fisiologíaRESUMEN
Human studies have convincingly demonstrated pronounced photoprotective effects of 'natural' and synthetic antioxidants when applied topically before UVR exposure. Particularly with respect to UVB-induced skin damage such as erythema formation, the photoprotective effects of antioxidants are significant when applied in distinct mixtures in appropriate vehicles. Topical application of such combinations may result in a sustained antioxidant capacity of the skin, possibly due to antioxidant synergisms. And, since UVA-induced skin alterations are believed to be largely determined by oxidative processes [26], topical administration of antioxidants might be particularly promising [27, 28]. In fact, topical application of antioxidants or antioxidant mixtures resulted in a remarkable increase in the minimal dose to induce immediate pigment darkening after UVA exposure [18, 23] and diminished the severity of UVA-induced photodermatoses [22] in humans. In conclusion, regular application of skin care products containing antioxidants may be of the utmost benefit in efficiently preparing our skin against exogenous oxidative stressors occurring during daily life. Furthermore, sunscreening agents may also benefit from combination with antioxidants resulting in increased safety and efficacy of such photoprotective products [11, 29].
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Anticarcinógenos/efectos adversos , Antioxidantes/administración & dosificación , Neoplasias Cutáneas/prevención & control , Administración Cutánea , Administración Tópica , Contaminantes Atmosféricos/efectos adversos , Animales , Anticarcinógenos/uso terapéutico , Antioxidantes/uso terapéutico , Ácido Ascórbico/administración & dosificación , Ácido Ascórbico/uso terapéutico , Esquema de Medicación , Flavonoides/administración & dosificación , Flavonoides/uso terapéutico , Humanos , Neoplasias Inducidas por Radiación/etiología , Neoplasias Inducidas por Radiación/prevención & control , Ozono/efectos adversos , Protectores contra Radiación/administración & dosificación , Protectores contra Radiación/uso terapéutico , Especies Reactivas de Oxígeno , Envejecimiento de la Piel/efectos de los fármacos , Neoplasias Cutáneas/etiología , Protectores Solares , Porcinos , Rayos Ultravioleta/efectos adversos , Vitamina E/administración & dosificación , Vitamina E/uso terapéuticoRESUMEN
Sequential adhesive tape stripping was implemented to characterize the penetration of nickel salts in human stratum corneum. Exposure areas of the salts in methanol applied open on arm and back skin in low volume were stripped 20 times to the level of the glistening layer at intervals of 30 min to 24 h post-dosing, and the strips analyzed for metal content by inductively coupled plasma-atomic emission spectroscopy. In the case of nickel chloride, sulfate, nitrate and acetate, material left on the skin surface, the depth-penetration profiles in the stratum corneum, and the dosage unaccounted for suggest the following conclusions: (a) Up to 24 h, most of the nickel dose applied remains on the skin surface or is adsorbed in the uppermost layers of the stratum corneum. (b) At higher concentrations, incomplete material recovery becomes discernible; within 24 h, nickel salts thus appear to penetrate beyond the stratum corneum to a minor degree, possibly via the skin shunts. (c) While the concentration gradients of nickel adsorbed vary with counter ion, anatomical site, dose and exposure time, for all variables tested the depth profiles converge to non-detectable levels (< 20 ppb) towards the level of the glistening layer. A notable exception is nickel as nitrate, for which levels continue at low but constant levels (1% of dose) beyond the third stratum corneum strip, indicative of intercellular diffusion. (d) Differences in material recovered suggest that the stratum corneum on the arm is more penetrable to nickel than stratum corneum on the back. (e) The counter ion in nickel salts plays a major part in their diffusion into the stratum corneum, suggestive of ion pairing. Overall, the data point to all three avenues of skin penetration by nickel: intracellular, intercellular, and transappendageal.
Asunto(s)
Dermatitis Alérgica por Contacto/etiología , Níquel/metabolismo , Absorción Cutánea , Adulto , Área Bajo la Curva , Femenino , Humanos , Masculino , Persona de Mediana Edad , Níquel/efectos adversos , Tiras Reactivas , Sales (Química)/efectos adversosRESUMEN
Sequential tape stripping was implemented on three healthy volunteers to examine the surface distribution of nickel through human stratum corneum in vivo following occlusive application of the metal as powder on the volar forearm. Exposure sites were stripped 20 times at intervals from 5 min to 96 h post-dosing and the strips analyzed for metal content by Inductively Coupled Plasma-Mass Spectroscopy with a detection limit for nickel of 0.5 ppb. The gradients of nickel distribution profiles increased proportionally with occlusion time, but after the 10th strip to the 20th strip continued at constant levels. Total nickel removed with 20 stratum corneum strips to the level of the glistening layer after maximum occlusion of 96 h was 41.6 micrograms/cm2 (+/- 12.2; average n = 3). In order to normalize the nickel depth distribution profiles, stratum corneum removed by stripping of untreated skin after occlusion was determined by weighing. Following application of nickel dust over 24 h, analysis of the 20th strip still indicated nickel present at 1.42 micrograms/cm2 (+/- 0.68; average n = 3). These data indicate that, in contact with skin, nickel metal is oxidized to form soluble, stratum corneum-diffusible compounds which may penetrate the intact stratum corneum, presumably by the intercellular route, and have the potential to elicit allergic reactions.
Asunto(s)
Dermatitis Alérgica por Contacto/etiología , Níquel/metabolismo , Absorción Cutánea , Adulto , Femenino , Humanos , Masculino , Persona de Mediana Edad , Níquel/efectos adversos , Polvos , Tiras Reactivas , Análisis de RegresiónRESUMEN
BACKGROUND: Photoprotective effects of topically applied antioxidants when applied before ultraviolet radiation (UVR) exposure are well known. Their protective effect when applied after UVR exposure is, however, less established. OBJECTIVE: In a randomized, double-blinded, placebo-controlled human study the short-term photoprotective effects of different antioxidants and of their combinations were evaluated when applied after UVR exposure. METHODS: Melatonin (N-acetyl-5-methoxytryptamine), vitamin E (alpha-tocopherol) and vitamin C (ascorbic acid) were topically administered alone or in combination following UVR exposure as single applications (immediately or 30 min after irradiation, respectively) or as multiple applications (three times: 30 min, 1 h and 2 h after irradiation). The erythemal reaction was evaluated visually and noninvasively with bioengineering methods (skin color and skin blood flow). RESULTS: No significant protective effect of melatonin or the vitamins when applied alone or in combination were obtained when antioxidants were applied after UVR exposure. No improved photoprotective effect was obtained when multiple applications were done. CONCLUSION: UVR-induced skin damage is a rapid event, and antioxidants possibly prevent such damage only when present in relevant concentration at the site of action beginning and during oxidative stress.
Asunto(s)
Antioxidantes/farmacología , Eritema/prevención & control , Rayos Ultravioleta/efectos adversos , Administración Cutánea , Adulto , Ácido Ascórbico/farmacología , Método Doble Ciego , Eritema/etiología , Femenino , Humanos , Masculino , Melatonina/farmacología , Persona de Mediana Edad , Flujo Sanguíneo Regional , Piel/irrigación sanguínea , Piel/efectos de los fármacos , Piel/efectos de la radiación , Vitamina E/farmacologíaRESUMEN
In this randomized, double-blind human study, the short-term photoprotective effects of different antioxidants and their combinations were evaluated in vivo. Vitamin C (ascorbic acid), vitamin E (alpha-tocopherol) and melatonin (N-acetyl-5-methoxytryptamine) were topically applied, alone or in combination, 30 min before ultraviolet-irradiation of the skin. The erythemal reaction was evaluated visually and non-invasively using different bioengineering methods (skin colour and skin blood flow). The results showed a modest protective effect of the vitamins when applied alone and a dose-dependent photoprotective effect of melatonin. Topical application of combinations of both vitamins, or of melatonin with vitamins, enhanced the photoprotective response. Better protection was obtained by using the combination of melatonin with both vitamins. The role of reactive oxygen species and oxygen-derived free radicals, as well as potential sunscreening properties of the employed antioxidants, are discussed in view of possible mechanisms to explain this elevated photoprotective effect.
Asunto(s)
Antioxidantes/uso terapéutico , Eritema/prevención & control , Melatonina/uso terapéutico , Protectores contra Radiación/uso terapéutico , Rayos Ultravioleta/efectos adversos , Administración Cutánea , Adulto , Ácido Ascórbico/uso terapéutico , Método Doble Ciego , Quimioterapia Combinada , Eritema/etiología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Traumatismos por Radiación/prevención & control , Vitamina E/uso terapéuticoRESUMEN
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.
Asunto(s)
Epidermis/química , Epidermis/fisiología , Manejo de Especímenes/métodos , Adhesivos , Adulto , Vendajes , Calibración/normas , Colorimetría/métodos , Femenino , Humanos , Masculino , Persona de Mediana Edad , Reproducibilidad de los ResultadosRESUMEN
Soybean lecithin microemulsion gels offer promising features for the possible use as matrices in transdermal therapeutic systems. In order to assess the skin irritancy potential of the gel, acute and cumulative irriation tests were performed in human subjects in vivo using as comparison an unilamellar soybean lecithin liposome preparation and the solvent isopropyl palmitate (IPP). Acute irritation was tested in 151 volunteers in a 48-hour patch test, whereas cumulative irritation was assessed in a 21-day human repeated insult patch test in 20 volunteers. In the acute irritation test, discrete irritation (erythema only) developed with the gel in 2 subjects (1.3%), with the liposomes in 3 subjects (2.0%), and with IPP in 2 subjects (1.3%). For the assessment of cumulative irritation, the IT50 (irritation time of 50% of the test population) was calculated. IT50 was 13 days for the gel, 14 days for the liposomes and 17 days for IPP. This study shows a very low acute and a low cumulative irritancy potential for the soybean lecithin microemulsion gel making it a candidate matrix for transdermal therapeutic systems also under toxicological aspects.