Morphology and thickness of the human stratum corneum

Dietary supplementation with a wheat polar lipid complex improves skin conditions in women with dry skin and mild-to-moderate skin aging

BACKGROUND

Aging, menopause, and seasonal changes alter the lipid composition of the outermost skin layer, the stratum corneum, resulting in dry and itchy skin.

AIMS

This clinical trial aimed at evaluating the effects of a wheat polar lipid complex (WPLC) on skin characteristics in women showing dry and wrinkled skin, investigating its effects in a subgroup of postmenopausal women, and assessing if benefits were maintained after supplementation.

METHODS

Seventy-two women with dry and wrinkled skin were recruited in this double-blind, randomized, parallel-group study, and allocated to three groups of 24 subjects, each including at least 10 postmenopausal women. For 56 days, subjects consumed the WPLC supplement (oil or powder), or the placebo. Skin hydration, transepidermal water loss (TEWL), elasticity, and profilometry were evaluated at baseline, after 14, 28, and 56 days of supplementation, and 56 days after the end of supplementation. Additionally, a lipidomic analysis was performed to examine changes in superficial skin layers over 56 days.

RESULTS

Dietary supplementation with WPLC rapidly improved all parameters. It increased skin hydration, smoothness, and elasticity while decreasing TEWL, roughness, and wrinkle depth after only 14 days of supplementation. These effects were also observed in the subpopulation of postmenopausal women and led to an improved self-perception of skin. For all the parameters, outcomes were not maintained after the supplementation was stopped. The lipidomic analysis revealed 10 compounds evolving over the 56 days of WPLC supplementation.

CONCLUSION

WPLC supplementation improved skin hydration, smoothness, elasticity, and wrinkledness within 14 days and, as expected, did not last after supplementation was stopped.

Migration of polycyclic aromatic hydrocarbons from a polymer surrogate through the stratum corneum layer of the skin

In this study, we determined partition (K_sc/m) and diffusion (D_sc) coefficients of five different polycyclic aromatic hydrocarbons (PAH) migrating from squalane into and through the stratum corneum (s.c.) layer of the skin. Carcinogenic PAH have previously been detected in numerous polymer-based consumer products, especially those dyed with carbon black. Upon dermal contact with these products, PAH may penetrate into and through the viable layers of the skin by passing the s.c. and thus may become bioavailable. Squalane, a frequent ingredient in cosmetics, has also been used as a polymer surrogate matrix in previous studies. K_sc/m and D_sc are relevant parameters for risk assessment because they allow estimating the potential of a substance to become bioavailable upon dermal exposure. We developed an analytical method involving incubation of pigskin with naphthalene, anthracene, pyrene, benzo[a]pyrene and dibenzo[a,h]pyrene in Franz diffusion cell assays under quasi-infinite dose conditions. PAH were subsequently quantified within individual s.c. layers by gas chromatography coupled to tandem mass spectrometry. The resulting PAH depth profiles in the s.c. were fitted to a solution of Fick's second law of diffusion, yielding K_sc/m and D_sc. The decadic logarithm logK_sc/m ranged from -0.43 to +0.69 and showed a trend to higher values for PAH with higher molecular masses. D_sc, on the other hand, was similar for the four higher molecular mass PAH but about 4.6-fold lower than for naphthalene. Moreover, our data suggests that the s.c./viable epidermis boundary layer represents the most relevant barrier for the skin penetration of higher molecular mass PAH. Finally, we empirically derived a mathematical description of the concentration depth profiles that better fits our data. We correlated the resulting parameters to substance specific constants such as the logarithmic octanol-water partition coefficient logP, K_sc/m and the removal rate at the s.c./viable epidermis boundary layer.

Continuous Removal of Single Cell Layers by Tape Stripping the Stratum Corneum - a Histological Study

Studies on the penetration of toxicologically or pharmaceutically relevant substances through the skin and, more specifically, through the stratum corneum (s.c.) often rely on the well-established method of tape stripping. Tape stripping involves the removal of skin layers by means of adhesive tape, which is usually followed by quantification of dermally applied substances in these layers. However, the amount of s.c. removed by each individual tape strip is still a matter of scientific debate. While some studies imply that the amount of s.c. adhering to each tape strip decreases with increasing depth into the s.c., others observed a constant removal rate. All these studies rely on the quantification of the amount of s.c. captured on individual or pooled tape strips. Here, we present an approach whereby we measured the amount of s.c. remaining on excised porcine skin in the process of tape stripping. Staining and bloating of the s.c. allowed to measure its thickness and to count individual s.c. layers, respectively. Histologically, we show that the s.c. remaining on the skin decreased linearly as a function of strips taken. We found that each tape strip removes about 0.4µm of s.c., which corresponds to approximately one cellular layer. With a high coefficient of determination (r²>0.95), we were able to linearly correlate the thickness of the remaining s.c., the number of remaining cell layers and the number of tape strips applied. Furthermore, we elaborate on possible reasons for the discrepancies reported in the scientific literature regarding the amount of s.c. removed by each tape strip.

Impact of airborne particulate matter on skin: a systematic review from epidemiology to in vitro studies

BACKGROUND

Air pollution is killing close to 5 million people a year, and harming billions more. Air pollution levels remain extremely high in many parts of the world, and air pollution-associated premature deaths have been reported for urbanized areas, particularly linked to the presence of airborne nano-sized and ultrafine particles.

MAIN TEXT

To date, most of the research studies did focus on the adverse effects of air pollution on the human cardiovascular and respiratory systems. Although the skin is in direct contact with air pollutants, their damaging effects on the skin are still under investigation. Epidemiological data suggested a correlation between exposure to air pollutants and aggravation of symptoms of chronic immunological skin diseases. In this study, a systematic literature review was conducted to understand the current knowledge on the effects of airborne particulate matter on human skin. It aims at providing a deeper understanding of the interactions between air pollutants and skin to further assess their potential risks for human health.

CONCLUSION

Particulate matter was shown to induce a skin barrier dysfunction and provoke the formation of reactive oxygen species through direct and indirect mechanisms, leading to oxidative stress and induced activation of the inflammatory cascade in human skin. Moreover, a positive correlation was reported between extrinsic aging and atopic eczema relative risk with increasing particulate matter exposure.

RF-INDUCED TEMPERATURE INCREASE IN A STRATIFIED MODEL OF THE SKIN FOR PLANE-WAVE EXPOSURE AT 6-100 GHZ

This study assesses the maximum temperature increase induced by exposure to electromagnetic fields between 6 and 100 GHz using a stratified model of the skin with four or five layers under plane wave incidence. The skin model distinguishes the stratum corneum (SC) and the viable epidermis as the outermost layers of the skin. The analysis identifies the tissue layer structures that minimize reflection and maximize the temperature increase induced by the electromagnetic field. The maximum observed temperature increase is 0.4°C for exposure at the present power density limit for the general population of 10 W m -2 . This result is more than twice as high as the findings reported in a previous study. The reasons for this difference are identified as impedance matching effects in the SC and less conservative thermal parameters. Modeling the skin as homogeneous dermis tissue can underestimate the induced temperature increase by more than a factor of three.

Unravelling effects of relative humidity on lipid barrier formation in human skin equivalents

Relative humidity (RH) levels vary continuously in vivo, although during in vitro generation of three-dimensional human skin equivalents (HSEs) these remain high (90-95%) to prevent evaporation of the cell-culture medium. However, skin functionality is directly influenced by environmental RH. As the barrier formation in HSEs is different, there is a need to better understand the role of cell-culture conditions during the generation of HSEs. In this study, we aim to investigate the effects of RH on epidermal morphogenesis and lipid barrier formation in HSEs. Therefore, two types of HSEs were developed at 90% or at 60% RH. Assessments were performed to determine epidermal morphogenesis by immunohistochemical analyses, ceramide composition by lipidomic analysis, and lipid organization by Fourier transform infrared spectroscopy and small-angle X-ray diffraction. We show that reduction of RH mainly affected the uppermost viable epidermal layers in the HSEs, including an enlargement of the granular cells and induction of epidermal cell activation. Neither the composition nor the organization of the lipids in the intercorneocyte space were substantially altered at reduced RH. In addition, lipid processing from glucosylceramides to ceramides was not affected by reduced RH in HSEs as shown by enzyme expression, enzyme activity, and substrate-to-product ratio. Our results demonstrate that RH directly influences epidermal morphogenesis, albeit the in vitro lipid barrier formation is comparable at 90% and 60% RH.

Physiologically based pharmacokinetic modelling to guide drug delivery in older people

Older patients are generally not included in Phase 1 clinical trials despite being the population group who use the largest number of prescription medicines. Physiologically based pharmacokinetic (PBPK) modelling provides an understanding of the absorption and disposition of drugs in older patients. In this review, PBPK models used for the prediction of absorption and exposure of drugs after parenteral, oral and transdermal administration are discussed. Comparisons between predicted drug pharmacokinetics (PK) and observed PK are presented to illustrate the accuracy of the predictions by the PBPK models and their potential use in informing clinical trial design and dosage adjustments in older patients. In addition, a case of PBPK modelling of a bioequivalence study on two controlled release products is described, where PBPK predictions reproduced the study showing bioequivalence in healthy volunteers but not in older subjects with achlorhydria, indicating further utility in prospectively identifying challenges in bioequivalence studies.

Review of Stratum Corneum Impedance Measurement in Non-Invasive Penetration Application

Due to advances in telemedicine, mobile medical care, wearable health monitoring, and electronic skin, great efforts have been directed to non-invasive monitoring and treatment of disease. These processes generally involve disease detection from interstitial fluid (ISF) instead of blood, and transdermal drug delivery. However, the quantitative extraction of ISF and the level of drug absorption are greatly affected by the individual's skin permeability, which is closely related to the properties of the stratum corneum (SC). Therefore, measurement of SC impedance has been proposed as an appropriate way for assessing individual skin differences. In order to figure out the current status and research direction of human SC impedance detection, investigations regarding skin impedance measurement have been reviewed in this paper. Future directions are concluded after a review of impedance models, electrodes, measurement methods and systems, and their applications in treatment. It is believed that a well-matched skin impedance model and measurement method will be established for clinical and point-of care applications in the near future.

Confocal Raman microspectroscopy as an alternative method to investigate the extraction of lipids from stratum corneum by emulsifiers and formulations

The purpose of this study was to investigate the impact of emulsifiers and formulations on intercellular lipids of porcine stratum corneum (SC) and evaluate confocal Raman microscopy (CRM) as an alternative method in this research context. To this end, four different formulations were used: three conventional creams that contained ionic and/or non-ionic emulsifiers and one surfactants-free emulsion stabilized by a polymeric emulsifier. Additionally, all emulsifiers were tested in aqueous solution/dispersion in the respective concentrations as present in the formulations. CRM and HPTLC were used to analyse changes in SC lipid content after treatment. Furthermore, lipid extraction was visualized by fluorescence staining and SC thickness was measured by CRM and light microscopy. Various emulsifiers and emulsifier mixtures showed different impact on SC lipid content and SC thickness, while none of the tested formulations had any effect on SC lipids. Emulsifiers and their mixtures that reduced the lipids content also reduced SC thickness, indicating lipid extraction is the reason for SC thinning. Results from CRM and conventional methods showed a strong positive correlation for both lipid content and SC thickness measurements. With easy sample preparation and fast analytical readout, CRM has the potential to be a standardized analytical method for skin lipids investigation.

ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the age-dependent sensitivity to radiation carcinogenesis, including the effects of in-utero exposure.

Epidermal thickness measured by light microscopy: a methodological study

BACKGROUND/AIMS

Epidermal thickness is frequently measured by light microscopy. The preservation and staining methods may alter the proportions of the specimens and thereby influence the measurements. The aim of the present study was to describe: 1) a standardized light microscopic method to quantify the thicknesses of the stratum corneum and the cellular epidermal layers, 2) the variations according to preparation and staining techniques, and 3) the observer variability.

METHODS

One hundred and sixty skin biopsies from 67 human volunteers were included. The cellular epidermis and the stratum corneum were estimated in sections preserved by freezing and subsequent preparation with cryostat or formalin-paraffin techniques. The slides were stained with haematoxylin-eosin or er-ythrocin, and thicknesses of the stratum corneum and the cellular epidermis were measured by a calibrated ruler and an ocular grid, respectively.

RESULTS

The formalin fixation gave slightly higher values for the cellular epidermis than the cryostat technique. In comparison to erythrocin staining, haematoxylin-eosin gave a significantly thinner stratum corneum. No significant inter- or intra-observer variation was found for the thickness of the stratum corneum assessed twice by two experienced observers. However, the two observers differed slightly from each other on the thickness of the cellular epidermis.

CONCLUSION

It is found that thickness measurements of the stratum corneum and the cellular epidermis are reliably performed on cryostatic cut sections stained with haematoxylin-eosin.

Regional variations in transepidermal water loss, eccrine sweat gland density, sweat secretion rates and electrolyte composition in resting and exercising humans

Literature from the past 168 years has been filtered to provide a unified summary of the regional distribution of cutaneous water and electrolyte losses. The former occurs via transepidermal water vapour diffusion and secretion from the eccrine sweat glands. Daily insensible water losses for a standardised individual (surface area 1.8 m2) will be 0.6-2.3 L, with the hands (80-160 g.h-1) and feet (50-150 g.h-1) losing the most, the head and neck losing intermediate amounts (40-75 g.h-1) and all remaining sites losing 15-60 g.h-1. Whilst sweat gland densities vary widely across the skin surface, this same individual would possess some 2.03 million functional glands, with the highest density on the volar surfaces of the fingers (530 glands.cm-2) and the lowest on the upper lip (16 glands.cm-2). During passive heating that results in a resting whole-body sweat rate of approximately 0.4 L.min-1, the forehead (0.99 mg.cm-2.min-1), dorsal fingers (0.62 mg.cm-2.min-1) and upper back (0.59 mg.cm-2.min-1) would display the highest sweat flows, whilst the medial thighs and anterior legs will secrete the least (both 0.12 mg.cm-2.min-1). Since sweat glands selectively reabsorb electrolytes, the sodium and chloride composition of discharged sweat varies with secretion rate. Across whole-body sweat rates from 0.72 to 3.65 mg.cm-2.min-1, sodium losses of 26.5-49.7 mmol.L-1 could be expected, with the corresponding chloride loss being 26.8-36.7 mmol.L-1. Nevertheless, there can be threefold differences in electrolyte losses across skin regions. When exercising in the heat, local sweat rates increase dramatically, with regional glandular flows becoming more homogeneous. However, intra-regional evaporative potential remains proportional to each local surface area. Thus, there is little evidence that regional sudomotor variations reflect an hierarchical distribution of sweating either at rest or during exercise.

The viscoelastic, hyperelastic and scale dependent behaviour of freshly excised individual skin layers

Micro-devices using mechanical means to target skin for improved drug and vaccine delivery have great promise for improved clinical healthcare. Fully realizing this promise requires a greater understanding of key micro-biomechanical properties for each of the different skin layers - that are both the mechanical barriers and biological targets of these devices. Here, we performed atomic force microscopy indentation on a micro-nano scale to quantify separately, in fresh mouse skin, the viscous and elastic behaviour of the stratum corneum, viable epidermis and dermis. By accessing each layer directly, we examined the response to nanoindentation at sub-cellular and bulk-cellular scale. We found that the dermis showed greatest mechanical stiffness (elastic moduli of 7.33-13.48 MPa for 6.62 μm and 1.90 μm diameter spherical probes respectively). In comparison, the stratum corneum and viable epidermis were weaker at 0.75-1.62 MPa and 0.49-1.51 MPa respectively (again with the lower values resulting from indentations with the large probe 6.62 μm). The living cell layer of the epidermis (viable epidermis) showed greatest viscoelasticity - almost fully relaxing from shallow indentation - whilst the other layers reached a plateau after relaxing by around 40%. With small scale (sub-micron) AFM indentation, we directly determined the effects of different layer constituents - in particular, the dermis showed that some indents contacted collagen fibrils and others contacted ground substance/cellular areas. This work has far reaching implications for the design of micro-devices using mechanical means to deliver drugs or vaccines into the skin; providing key characterized mechanical property values for each constituent of the target delivery material.

Cultured human keratinocytes for optical transmission measurement

The challenges of measuring optical properties of human tissues include the thickness of the sample, homogenization, or crystallization from freezing of the tissue. This investigation demonstrates a method to avoid these problems by growing optically thin samples of human keratinocytes as a substitute for ex vivo epidermis samples. Several methods of growth were investigated. Resulting samples were measured on a spectrophotometer for transmission between 300 nm and 2600 nm. The efficacy of the cell growth was confirmed with histological examination of several cultured keratinocyte samples. Limitations were the requirement to measure samples immediately after removal from the incubation environment, and the absence of the irregular structures of normal skin such as hair and glands.

A two-dimensional morphological study of corneocytes from healthy dogs and cats and from dogs with atopic dermatitis

The aim of this study was to determine the dimensions of corneocytes collected from healthy dogs and cats, and from dogs suffering from atopic dermatitis. Samples were collected from the inner pinna, lateral thorax and the groin. D-Squame adhesive discs were used to collect corneocytes from the skin surface and image analysis software was used for measurements. Two differently shaped cells were identified in both animal species. The most common cell type was polygonal, often hexagonal or pentagonal and regular while the second type was smaller, elongated and variable in size and shape. The polygonal cells are corneocytes which probably originate from the interfollicular epidermis. The mean diameter and surface area for healthy canine polygonal corneocytes were 38-43.5 microm and 1092-1436 microm(2). The equivalent Figures for cats were 39.6-48.5 microm and 1183-1772 microm(2). Feline polygonal corneocytes were generally larger than those of the dog. Both feline and canine polygonal corneocytes collected from the ear were generally smaller than those from other body sites. Atopic canine polygonal corneocytes collected from the groin were significantly smaller than healthy groin corneocytes. In healthy dogs the mean length, breadth and surface area of elongated cells were 26.6-35.9 microm, 7.6-10.3 microm and 168.6-240.2 microm(2). The equivalent values for cats were 20.0-37.8 microm, 6.8-9.9 microm and 117.6-245.6 microm(2). The exact nature of the elongated cells is not known but they may be cell fragments or folded corneocytes. They were more common in densely haired skin suggesting the hair follicle as their origin.

Drying stress and damage processes in human stratum corneum

SYNOPSIS

The drying stresses that develop in stratum corneum (SC) are crucial for its mechanical and biophysical function, its cosmetic feel and appearance, and play a central role in processes of dry skin damage. However, quantitative methods to characterize these stresses are lacking and little understanding exists regarding the effects of drying environment, chemical exposures and moisturizing treatments. We describe the application of a substrate curvature technique adapted for biological tissue to accurately characterize SC drying stresses as a function of time following environmental pre-conditioning and chemical treatment in a range of drying environments. SC stresses were observed to increase to stress levels of up to approximately 3 MPa over periods of 8 h depending on pretreatment and drying environment. A unique relationship between the SC stress and water in the drying environment was established. The effect of glycerol on lowering SC stresses and damaging surfactants on elevating SC stresses were quantified. Extensions of the method to continuous monitoring of SC stresses in response to changes in environmental moisture content and temperature are reported. Finally, a biomechanics framework to account for the SC drying stress as a mechanical driving force for dry skin damage is presented.

The kinetics of transdermal ethanol exchange

The kinetics of ethanol transport from the blood to the skin surface are incompletely understood. We present a mathematical model to predict the transient exchange of ethanol across the skin while it is being absorbed from the gut and eliminated from the body. The model simulates the behavior of a commercial device that is used to estimate the blood alcohol concentration (BAC). During the elimination phase, the stratum corneum of the skin has a higher ethanol concentration than the blood. We studied the effect of varying the maximum BAC and the absorption rate from the gut on the relationship between BAC and equivalent concentration in the gas phase above the skin. The results showed that the ethanol concentration in the gas compartment always took longer to reach its maximum, had a lower maximum, and had a slower apparent elimination rate than the BAC. These effects increased as the maximum BAC increased. Our model's predictions are consistent with experimental data from the literature. We performed a sensitivity analysis (using Latin hypercube sampling) to identify and rank the importance of parameters. The analysis showed that outputs were sensitive to solubility and diffusivity within the stratum corneum, to stratum corneum thickness, and to the volume of gas in the sampling chamber above the skin. We conclude that ethanol transport through the skin is primarily governed by the washin and washout of ethanol through the stratum corneum. The dynamics can be highly variable from subject to subject because of variability in the physical properties of the stratum corneum.

Intradermal ballistic delivery of micro-particles into excised human skin for pharmaceutical applications

A unique form of needle-free drug and vaccine delivery is under investigation. The principle of the concept is to accelerate pharmaceuticals in particle form to a momentum sufficient to penetrate the outer layer of the human skin for a pharmacological effect. The relationship between the key particle impact parameters and particle penetration depth in excised human skin has been experimentally determined. Research devices have been used to deliver particles of a range of radii (0.89-53 microm), and density (1.08-18.2 g/cm3) at controlled and incremental impact velocities between 160 and 640 m/s. Analysis of the particle impact data reveals particle penetration depth as a function of particle density, radius and impact velocity. The experimental relationship provides a criterion for the optimal selection of particle parameters and velocity to target specific layers within the skin. Furthermore, some sources of variability in penetration depth have also been established. The experimental data have also been compared with a mechanistic Unified Penetration Model with good agreement.

Effects of relative humidity and ambient temperature on the ballistic delivery of micro-particles to excised porcine skin

The effectiveness of ballistic particle delivery to the skin is often dependent upon breaching the stratum corneum (SC) and targeting cells within defined layers of the viable epidermis. This paper experimentally determines the influence of relative humidity (RH) and temperature on the ballistic delivery of particles to the skin. Gold particles of radius 0.9+/-0.6 microm were accelerated by a hand-held supersonic device to impact freshly excised porcine skin at 410-665 m per s. Increasing the RH from 15% to 95% (temperature at 25 degrees C) led to a particle penetration increase by a factor of 1.8. Temperature increases from 20 degrees C to 40 degrees C (RH at 15%) enhanced particle penetration 2-fold. In both cases, these increases were sufficient to move the target layer from the SC to the viable epidermis. Relative trends in particle penetration compared well with predictions from a theoretical model well. Calculated absolute penetration depths are 6-fold greater than the measurements. The inversely calculated dynamic yield stress of the SC is up to a factor of 10 higher than reported quasi-static measurements, due to changes in tissue failure modes over a strain-rate range spanning 10 orders of magnitude. If targeted particle delivery is required, it is recommended that the environmental RH and temperature be monitored.

Estudo das alterações relacionadas com a idade na pele humana, utilizando métodos de histo-morfometria e autofluorescência

FUNDAMENTOS: O processo de envelhecimento tecidual é evidente nas modificações visíveis na pele, resultando em importantes implicações psicológicas para o indivíduo e crescente interesse científico. OBJETIVOS: O presente trabalho objetivou analisar as alterações da pele normal com o envelhecimento mediante estratégias de histomorfometria e autofluorescência. MÉTODOS: Foram coletadas amostras de pele do abdômen de 18 cadáveres, incluindo cinco indivíduos jovens (menos de 20 anos), sete indivíduos com idade intermediária (20-60 anos) e seis indivíduos idosos (mais de 60 anos). Foram feitos cortes histológicos em parafina seguidos de coloração pela Hematoxilina-Eosina (H&E) e pelo tricrômio de Van Gieson-elastina. Avaliaram-se a espessura da epiderme e derme, e a superfície de contato epidermo-dérmica. Investigaram-se ainda as modificações qualitativas do aparelho colágeno-elástico, considerando sua disposição espacial na derme. Espécimes corados em H&E também foram utilizados para autofluorescência. RESULTADOS: A espessura da epiderme e derme do grupo idoso foi significativamente diminuída (p<0,05) em relação aos demais grupos. Os grupos idoso e intermediário exibiram acentuada redução na superfície de contato epiderme-derme (p<0,05). Detectaram-se a perda da distribuição em rede das fibras elásticas com sua progressiva fragmentação, alterações da compactação do colágeno e espessamento da membrana basal com o envelhecimento. CONCLUSÃO: O envelhecimento leva à redução da espessura da derme e epiderme, bem como ao aplanamento da junção dermo-epidérmica. As mudanças da pele ao longo da vida nem sempre seguem um perfil linear, mostrando drásticas alterações nas últimas décadas de vida. O método de autofluorescência mostrou-se um instrumento valioso no estudo da complexa relação espacial das fibras elásticas e colágenas.

Visualization of the lipid barrier and measurement of lipid pathlength in human stratum corneum

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.

Human skin surface lipid film: an ultrastructural study and interaction with corneocytes and intercellular lipid lamellae of the stratum corneum

Sebum is a complex mixture of lipids, which is secreted by mammalian sebaceous glands, and forms a fluid film over the skin surface. After sebum is secreted, it becomes mixed with lipid from the keratinizing epithelium and forms the skin surface lipid film (SSLF). Until now, direct fine structural observation of the SSLF has been lacking. In the present work, we viewed the detailed structures of the human SSLF by ruthenium tetroxide staining. The results showed that the SSLF formed an amorphous sheet of variable thickness on the skin surface instead of forming lipid droplets, as had been the usual assumption. In general, its thickness was < 0.5 microm or even negligible in sebum-poor extremities. However, in the sebum-rich face, its thickness was > 4 microm in focal areas. Consistent with the thickness of SSLF, the sebum quantity showed great regional variation. It varied from 1 microg/cm2 (leg) to 189 +/- 42.7 microg/cm2 (mean +/- SD: face). The SSLF was composed of numerous fine granules of about 4-5 nm in a random orientation. Within the SSLF, variable amounts of deranged lipid lamellae derived from corneocytes were mixed with sebum. As well as on the skin surface, a similar amount of sebum was also found between the desquamating corneocytes in the uppermost several layers of the stratum corneum (SC). We also observed the presence of intercellular lipid lamellae in the outer layers of the SC: their lipid envelope remained intact even in desquamated corneocytes. Our results provide some new insights concerning the structure of the SSLF and its relationship with the SC.

The influence of skin structure on permeability: an intersite and interspecies comparison with hydrophilic penetrants

For reasons that are unclear, skin from various body sites has different permeability properties. We have used hydrophilic penetrants (water, ethanol, mannitol, and paraquat) to study the in vitro permeability of skin from marmoset (eight body sites), man, and rat. Skin structure (stratum corneum thickness and number of cell layers; epidermal and dermal thickness; number and area of hair follicle openings per mm2) was compared with permeability. There was no apparent relationship between skin structure and permeability to the most rapid penetrants, water and ethanol. Follicle area opening was the structural feature that varied most between species and between body sites. Different marmoset body sites showed a threefold range in follicle area but this did not appear to influence the absorption rates of the test penetrants. However, among the species there was an 80-times range in follicle area, which correlated with the observed differences in rate of mannitol and paraquat absorption. Thus, permeability could be related to inter-species differences in skin structure, but only with the relatively slowly absorbed test penetrants, mannitol and paraquat.

Interspecies and interregional analysis of the comparative histologic thickness and laser Doppler blood flow measurements at five cutaneous sites in nine species

Studies in dermatology, cutaneous pharmacology, and toxicology utilize skin from different animal species and body sites. However, regional differences exist in topical chemical percutaneous absorption studies in man and in animal. The objective of this study was to compare epidermal thickness and number of cell layers across species and body sites using both formalin-fixed paraffin and frozen sections. Cutaneous blood flow determined by laser Doppler velocimetry (LDV) was compared to histologic data. Six animals of each of the following species were used: monkeys, pigs, dogs, cats, cows, horses, rabbits, rats, and mice. Cutaneous blood flow was determined and 6-mm skin biopsies were taken directly from the following sites: buttocks, ear, humeroscapular joint, thoracolumbar junction, and abdominal area. When the two histologic methods were compared across all species and body sites, the thickness of the epidermis was significantly greater, and the thickness of the stratum corneum significantly less, in paraffin sections versus frozen sections (p less than 0.05). There were no differences in the number of viable cell layers determined by both methods. The values for LDV-determined blood flow did not significantly correlate (p greater than 0.05) to epidermal or stratum corneum thickness. However, regional and species differences were noted in all these parameters. In conclusion, these data indicate that thickness and LDV blood flow are independent and must be evaluated separately when comparisons are made between species and body sites. This work provides a data base for future comparative studies in which a knowledge of skin thickness or blood flow might be important variables.

The effect of washing on the thickness of the stratum corneum in normal and atopic individuals

The thickness of, and number of cell layers in, the stratum corneum and the living epidermis were determined on frozen sections of washed and unwashed skin from normal and atopic individuals of both sexes. The stratum corneum of atopic patients was thinner and had fewer layers of dead cells and intercellular lipid than normal, although the living epidermis was thicker. Regular washing with soap and water had no appreciable effect on the dimensions of the living epidermis of either group but caused a reduction in the number of cell layers and the amount of sudanophilic material in the stratum corneum of both. In atopic patients little surface lipid remained, suggesting that washing with soap and water may be detrimental to the barrier function of the stratum corneum in such patients.

Percutaneous absorption of alkanoic acids I: A study of operational conditions

The rate of penetration of propionic and butyric acids through excised porcine skin was determined in vitro in specific apparatus allowing optimal control of operational conditions. In one technique, the rate was followed by continuous pH-stat titration of acid appearing in the perfusate, in another, by periodic monitoring of [14C]propionic acid in the perfusate. With the assumption that Fick's equation applies to the process of penetration, it was found that the permeability coefficient, Kp, increases with increasing mass of neat penetrant applied per unit area to the donor side, increases with increasing concentration of penetrant in n-heptane as vehicle, increases with increasing temperature, Ea = 11.4 kcal/mol, and decreases with decreasing perfusion rate of the acceptor side when this rate is smaller than 60 mL/h.

Percutaneous absorption of alkanoic acids II: Application of regular solution theory

The permeability coefficient, Kp, of pure unbranched alkanoic acids (C2-C7) applied to isolated porcine skin, reached a maximum in the solubility parameter (delta 2) range of 9.7-10 cal1 /2/cm3/2. When these and other penetrants were delivered from a solvent vehicle, the following linear relationships could be demonstrated: (a) between log Kp and the molar attraction constant of the penetrant [delta 2v2 or (-Ev)1/2] for six unbranched and six branched acids delivered from 1 M solution in n-heptane; (b) between Kp and the partial molal volume difference in n-heptane (-v2-v02) for the unbranched acids; and (c) between Kp and (-v2-v02) for propionic acid delivered from 1 M solutions in nine solvents having delta 1 values in the range 7.4-12.7 cal1 /2/cm3/2. Drug penetrability in a given series could be assessed from knowledge of the excess free energy of the penetrant in the delivery system used.

Cell population kinetics in hairless mouse epidermis following a single topical application of 12-O-tetradecanoylphorbol-13-acetate II

It is known that a single application of 17 nmol 12-O-tetradecanoylphorbol-13-acetate (TPA) to hairless mouse skin first induces (from 0-12 h) a short block in mitotic activity followed by a transient stimulation of proliferation (from 12-96 h) characterized by multiple waves of rapid proliferation in partly synchronized basal cells, leading to hyperplasia. The replication rate of basal cells, the number of basal and suprabasal (maturing) cells per unit of interfollicular epidermis and the number of squamous layers in the stratum corneum were recorded. Changes in the nuclear area of living cells were monitored by morphometry. The changes in the rate of basal cell proliferation are accompanied by concomitant waves of increased rates of cell maturation and cell loss, with a considerable reduction in epidermal cell transit time. When 14-15 squamous layers were observed, this resulted in an increased cell loss, which was visible as scaling from 24 h onwards. The total cell mass lost from 16 to 72 h after TPA application amounted to about 67% of the newborn cell mass. Thus the hyperplasia occurring after a single TPA treatment results from a considerably enhanced cell proliferation that exceeds concomitant increases in the rates of cell maturation and loss. There is no delayed maturation. The results are also consistent with the chalone theory of epidermal growth regulation, assuming that the G1 chalone is produced during cell maturation.

The action of a urea-lactic acid ointment in ichthyosis with particular reference to the thickness of the horny layer

The effect of urea-lactic acid ointment on the scales of ichthyotic skin was assessed using the 'cell swelling' technique of Christophers & Kligman. The thickness of the horny layer and of the scales was reduced both by the ointment and by the base. The formation of scales was shown to differ from that in psoriasis where the scale forms at the apex of th a rete peg and is symmetrical whereas in ichthyosis the separation of the scale may be at an entirely different depth at one margin. There is an increase in the number of 'T' cells in X-linked recessive ichthyosis.

Epidermal cell production rates

Labeling and mitotic index data and estimates for the length of the S and M phases of the cell cycle from the literature have been compared with new data obtained over a 24-hr period from various epidermal sites in mouse. It has been found that values obtained at a single time of the day may give misleading results. All data have been interpreted in terms of cell production rates per epidermal proliferative unit (EPU). The final conclusions after consideration of cell production rates, labeling and mitotic indices, epidermal transit times, and epidermal structure are that dorsal and ear skin have rather similar cell production rates while tail and foot rates are 4 to 7 times higher. A comparison has also been made between the mouse results and the available human data. Hairless mouse dorsum appears from structural and proliferative aspects to be the best model for some regions of human skin. A new model has been proposed for epidermal proliferation based on the EPU. The model suggests a role for the Langerhans cells and suggests that there is a program of sequential cellular maturity in the EPU originating at the level of a central basal stem cell through committed proliferative cells and ending with cell loss from the skin surface.