Sonography of the skin at 100 MHz enables in vivo visualization of stratum corneum and viable epidermis in palmar skin and psoriatic plaques

A main drawback of 20-25 MHz ultrasound units for skin imaging is their limited resolution. We used a transducer with a center frequency of 95 MHz and a resolution of 8.5 microm axially and 27 microm laterally - an almost 10-fold increase compared with 20 MHz. By means of a new scanning technology we reached a depth of field of 3.2 mm. We examined normal palmar skin, normal glabrous skin on the abdomen, the upper back, the calf and the dorsal forearm, and 35 lesions of psoriasis vulgaris. From 11 psoriatic plaques biopsies were taken for correlation with the sonograms. In normal palmar skin, the horny layer is represented as an echopoor band below the skin entry echo, traversed by echorich coils, which correspond to eccrine sweat gland ducts. The thickness of this band significantly increases after occlusive application of petrolatum. Its lower border is defined by an echorich line, representing the stratum corneum/stratum Malpighii-interface. Underneath, a second echopoor band is visible, which corresponds to the viable epidermis plus the papillary dermis, bordered by the scattered echo reflexes of the reticular dermis. This band is also visible in glabrous skin; however, the stratum corneum cannot be detected. In psoriatic lesions, the thickened horny layer appears echorich; after application of petrolatum, its echodensity decreases. Below, the acanthotic epidermis plus the dermis with the inflammatory infiltrate are represented as an echopoor band. There is an excellent correlation between the sonometric thickness of this band and the histometric thickness of the acanthosis plus the infiltrated dermis. Our results show that 100 MHz sonography is a valuable tool for in vivo examination of the upper skin layers.     

Composition of free long-chain (sphingoid) bases in stratum corneum of normal and pathologic human skin conditions.

The composition of molecular species of free long-chain bases (FLCB) isolated from stratum corneum of various human skin conditions was analyzed by the high-performance liquid chromatographic and fast atom bombardment mass spectrometric methods. FLCB with carbon length ranging from 16 to 20 comprised about 0.3% of total lipids in stratum corneum of normal and pathologic skin conditions. Major FLCB included sphinganines and sphingenines with 18 to 20 carbons and some phytosphingosines such as t17:1, t18:1, t18:0, t20:1, and t20:0. Compared with stratum corneum of normal lower legs, molar percentages of FLCB having 18 carbons and those with 20 carbons were slightly higher and lower, respectively, in normal plantar epidermis, showing site-related differences in normal skin. Psoriatic scales and hyperkeratotic stratum corneum from clavus and plantar keratoderma contained increased levels of FLCB with 18 carbons and decreased levels of FLCB with 20 carbons. These findings may reflect abnormal keratinization in hyperkeratotic skin conditions.     

The effect of ultraviolet radiation on the water-reservoir functions of the stratum corneum.

The stratum corneum plays an important role in keeping the skin surface supple and flexible. After exposure to sunlight, the skin may become dry and scaly. In the present study, the water content, hygroscopicity and water-holding capacity of the stratum corneum were examined after ultraviolet B (UVB) exposure to the guinea pig skin. Manually depilated back skin was exposed once to 1, 2 and 3 times the minimal erythema dose of UVB, and a time course study was performed. Our study demonstrated the following: The water content, water-holding capacity and hygroscopicity decreased after UVB irradiation. They decreased roughly dependent on UVB dose. The decreased water content and water-holding capacity were noted on day 1 and persisted until day 10 to 14. In contrast, the decrease in hygroscopicity became apparent 3 days after exposure and returned to the preirradiated state on day 7. The impaired functional parameters were partially prevented by topical application of a sunscreen. These results indicate that a single exposure to UVB can damage the function of the stratum corneum.     

Reflectance spectroscopy can quantify cutaneous haemoglobin oxygenation by oxygen uptake from the atmosphere after epidermal barrier disruption

Background: The supply of oxygen to the viable skin tissue within the upper layers is not only secured by the cutaneous blood vascular system, but to a significant part also by oxygen diffusion from the atmosphere through the horny layer. The aim of this study was to examine whether changes in haemoglobin oxygenation can be observed within the isolated perfused bovine udder skin used as a skin model by removing the upper horny layer by adhesive tape stripping.
Methods: Diffuse reflectance spectroscopy in the visible spectral range was used for non-invasive characterisation of haemoglobin oxygenation in skin under in vitro conditions. Mid-infrared attenuated total reflectance spectroscopy was employed for analysing the surface layer of the stratum corneum with respect to keratin, water and lipid components. Skin barrier disruption was achieved by repeated stripping of superficial corneocyte layers by adhesive tape.
Results and conclusion: Significant changes in skin haemoglobin oxygenation were observed for skin areas with reduced lipid concentration and a reduced stratum corneum layer, as determined from the quantitative evaluation of the diffuse reflectance skin spectra. The result can be interpreted as an increase of oxygen diffusion after the removal of the upper horny layer.     

Comparison of lipids from epidermal and palatal stratum corneum.

Stratum corneum has been isolated by tryptic digestion of porcine epidermis and palatal epithelium, and the lipid concentrations and compositions have been compared by thin-layer chromatography in conjunction with photodensitometry. Palatal stratum corneum contained 47 +/- 6 micrograms lipid/mg tissue or 115 +/- 16 micrograms lipid per cm2 of stratum corneum surface, whereas epidermal stratum corneum contained 105 +/- 17 micrograms lipid/mg tissue or 135 +/- 16 micrograms/cm2. The difference in total lipid content does not account for the tenfold higher permeability constant for the permeation of water through the former tissue compared to the latter; therefore, the difference in permeability must be based on differences in lipid composition. In this regard, palatal stratum corneum includes 12.1% phospholipids, although phospholipids were undetected in epidermal stratum corneum. Differences in the content and location of non-polar liquid-phase lipids may also be of significance for permeability. Other factors that may contribute to the greater permeability of the palatal horny layer relative to epidermal stratum corneum include generally lower proportions of cholesterol, fatty acids, and ceramides, a dramatically lower proportion of the linoleate-containing acylceramide, and a tenfold lower content of covalently bound lipids associated with the corneocyte envelope.     

Percutaneous absorption and the surface area of occluded skin

Scanning electron microscopy of samples of human skin occluded for 72 h, revealed that the hydrated stratum corneum not only swells, but develops multiple folds. Surface area estimations of such stratum corneum, utilizing stereo pairs of the photomicrographs, indicated a 37% increase over the normal, non-occluded horny layer values. It is speculated that the increase in absorptive area contributes to the increased skin permeability following occlusion.     

SOME LIGHT MICROSCOPICAL OBSERVATIONS ON THE STRATUM CORNEUM OF THE GUINEA-PIG, MAN AND COMMON SEAL

The stratum corneum of the guinea-pig back and of human upper arm epidermis, in formalin fixed tissue, is divisible under the light microscope into conjunctum and disjunctum sub-layers. The former is without discernible intracellular or intercellular spaces. It is stained uniformly with eosin and is rich in both bound phospholipids and bound sulphydryl groups. The disjunctum sub-layer shows dorso-ventral intercellular spaces and large intra-cellular spaces due to removal of unfixed soluble constituents of the keratinocytes by water, ethanol and xylene during histological processing. Osmium tetroxide precipitates many soluble chemical constituents so that the horny cells stain uniformly black. Large intracellular spaces in the disjunctum cells were shown by osmium staining in the guinea-pig horny layer, which has been previously leached experimentally in petroleum ether, ethanol and water. The stratum corneum of the common seal resembles the abnormal human parakeratotic layer in not showing intracellular spaces in eosin-stained sections. It is suggested that the thick phospholipid-rich horny layer in the seal may improve the waterproofing ability of the epidermis.     

The Azerbaijani scrub: a simple method to harvest large amounts of stratum corneum

BACKGROUND: The study of skin barrier constituents may require collection of much stratum corneum. Existing methods are inadequate and/or difficult. METHODS: A simple and safe method to harvest stratum corneum from glabrous human skin derives from the bathing practices of people in Azerbaijan. The method requires water immersion of the subject for 30 min immediately followed by vigorous scrubbing of skin with a moist rough crepe mitten. RESULTS: This scrubbing method causes the separation of large amounts of stratum corneum which is easily harvested. CONCLUSION: The method facilitates study of stratum corneum components, including intercellular lipids.     

The water content of the stratum corneum in patients with atopic dermatitis. Measurement with the Corneometer CM 420

The dry looking skin seen in many patients with atopic dermatitis reflects a defect in the epidermal barrier, the stratum corneum, as demonstrated by an increased transepidermal water loss (TEWL) and a decreased ability of the stratum corneum to bind water. The absolute amount of water within the stratum corneum is of importance both for barrier properties and for the clinical appearance of the skin. This water content was measured with a new instrument, the Corneometer CM 420, which takes advantage of the high dielectric constant of water. Forty patients with atopic dermatitis were studied--20 with dry skin and 20 with clinically normal skin on non-eczematous areas. The stratum corneum in dry skin was found to have a lower content of water than that in the clinically normal skin (p less than 0.01). Clinically normal skin in patients with atopic dermatitis did not differ significantly from normal control skin. An experiment was performed in vitro in an attempt to correlate the values obtained with the Corneometer to the absolute amount of water within the corneum.     

Water modulation of stratum corneum chymotryptic enzyme activity and desquamation

Abstract Exposure to a dry environment leads to depletion of water from the peripheral stratum corneum layers in a process dependent on the relative humidity (RH) and the intrinsic properties of the tissue. We hypothesized that by modulating the water content of the stratum corneum in the surface layers, RH effects the rate of desquamation by modulating the activity of the desquamatory enzymes, and specifically stratum corneum chymotryptic enzyme (SCCE). Using a novel air interface in vitro desquamatory model, we demonstrated RH-dependent corneocyte release with desquamatory rates decreasing below 80% RH. Application of 10% glycerol or a glycerol-containing moisturizing lotion further increased desquamation, even in humid conditions, demonstrating that water was the rate-limiting factor in the final stages of desquamation. Furthermore, even in humid conditions desquamation was sub-maximal. In situ stratum corneum SCCE activity showed a dependence on RH: activity was significantly higher at 100% than at 44% RH. Further increases in SCCE activity were induced by applying a 10% glycerol solution. Since SCCE, a water-requiring enzyme, must function in the water-depleted outer stratum corneum, we sought to determine whether this enzyme has a tolerance to lowered water activity. Using concentrated sucrose solutions to lower water activity, we analysed the activity of recombinant SCCE and compared it to that of trypsin and chymotrypsin. SCCE activity demonstrated a tolerance to water restriction, and this may be an adaptation to maintain enzyme activity even within the water-depleted stratum corneum intercellular space. Overall these findings support the concept that in the upper stratum corneum, RH modulates desquamation by its effect upon SCCE activity, and possibly other desquamatory hydrolases. In addition, SCCE may be adapted to function in the water-restricted stratum corneum intercellular space. Received: 15 February 2001 / Revised: 27 April 2001 / Accepted: 25 July 2001     

Dry skin conditions, eczema and emollients in their management

Dry skin, which refers to roughened, flaky, or scaly skin that is less flexible than normal and dry to feel, is relatively common problem in all age groups, but is more common in elderly individuals. The water content of the stratum corneum is of paramount importance in maintaining the normal appearance and texture of human skin. The relative hydration of the stratum corneum is a composite of 3 factors viz. the rate of water transport from dermis to stratum corneum, the rate of surface loss of water and the rate of water binding ability of stratum corneum. Loss of integrity of the barrier function is a central factor in the development of dry skin conditions and eczema. The various factors involved in producing dry skin, various causes of dry skin and the role of emollients in the management of these conditions are discussed.     

Punctate porokeratotic keratoderma: some pathogenetic analyses of hyperproliferation and parakeratosis.

An 82-year-old Japanese woman had numerous palmoplantar keratotic plugs and pits, resembling 'music box spines'. Histological examination revealed compact columns of parakeratosis in the horny layer. Ultrastructually, the affected stratum corneum contained numberous variable-sized pyknotic nuclei, and cells in the stratum granulosum contained fewer keratohyalin granules. Autoradiographic analysis by [3H]thymidine [3H]TdR incorporation into epidermal cells of affected skin slices in organ culture revealed that only basal cells below the keratotic plug were stimulated to proliferate. Two-dimensional gel electrophoresis revealed that palmar keratotic plugs contained the keratin filaments that are specifically present in the plantar viable epidermal layer, or other hyperproliferative epithelial cells.     

SDS-PAGE analysis of whole and fractionated psoriatic epidermis

The SDS-PAGE patterns of keratinous proteins extracted from whole epidermis and fractionated epidermal cells were studied. Those from the whole and fractionated epidermal cells of psoriatic involved skin showed an extra 58,000 dalton polypeptide in addition to the four major polypeptides (M.W.: 67,000, 63,000, 59,000 and 55,000) which were demonstrated to be common to normal epidermis and psoriatic-uninvolved epidermis. The stratum corneum of psoriatic involved skin did not contain a 67,000 dalton polypeptide which was present in the stratum corneum of normal and psoriatic uninvolved skin. The presence of the additional 58,000 dalton polypeptide may be due to abnormal synthesis of keratin proteins in the psoriatic epidermis, since this additional polypeptide was present in the lower living layers of the psoriatic epidermis as well. On the other hand, the absence of the 67,000 dalton polypeptide in the psoriatic stratum corneum may be due to enzymatic modifications during the transition from the living cell layers to the horny layer.     

【开放获取】皮肤干燥是通透屏障功能受损的表现吗？

【摘要】 有学者认为,皮肤干燥是表皮通透屏障功能受损的表现,但目前尚没有足够的证据证明这一观点。实际上,皮肤干燥是角质层含水量降低的表现。角质层含水量主要由角质层天然保湿因子的量决定,而表皮通透屏障功能则主要由角质层脂质的质和量以及结构蛋白决定。如果皮肤干燥是由表皮通透屏障功能降低所致,那么,角质层含水量应当与透皮失水率呈负相关性。但是研究表明,无论是正常人皮肤、鱼鳞病皮损或皮脂腺缺乏的小鼠皮肤,角质层含水量与透皮失水率均无负相关性。相反,有研究显示,人角质层含水量与透皮失水率呈正相关性。因此,皮肤干燥似乎不是表皮通透屏障功能受损的表现。     

Functional and morphological analysis of the horny layer of pityriasis alba

The affected skin of pityriasis alba showed functional defects in both hygroscopicity and water-holding capacity detectable by water sorption-desorption test. Furthermore using skin surface biopsy technique in 5 patients, we noted that the mean area of corneocyte obtained from the affected skin of pityriasis alba was smaller and that the surface of that area showed a more prominent villous pattern than the adjacent normal skin in scanning electron microscopical observation. In this study we demonstrated the abnormalities of the horny layer in pityriasis alba, which suggest that the condition is similar to a dermatitic change and that its hypopigmentation may be due to postinflammatory mechanisms.     

‘Hints’ in the horn: diagnostic clues in the stratum corneum

The stratum corneum or horny layer is the uppermost layer of the epidermis, and is mainly responsible for the skin's barrier function. In spite of its complexity at the ultrastructural and molecular level, the features accessible to visualization on conventional histology are relatively limited. Nevertheless, knowledge of subtle clues that one may observe in the stratum corneum can prove useful in a wide range of situations in dermatopathology. We herein review a selection of common and rare entities in which the horny layer may reveal significantly important hints for the diagnosis. These clues include parakeratosis and its different patterns (focal, confluent, alternating, associated with spongiosis, epidermal hyperplasia or lichenoid changes), subcorneal acantholysis, infectious organisms in the stratum corneum (including fungal, bacterial and parasitic), thickening or thinning of the stratum corneum and the presence of different kinds of pigment. Even when normal, the horny layer may prove to be useful when seen in association with severe epidermal damage, a combination of features testifying to the acute nature of the underlying pathological process.     

Stratum corneum lipids in skin xerosis

Lipids of the stratum corneum are implicated in cohesion and desquamation of the stratum corneum as well as in the maintenance of normal barrier function. Evidence linking the intercellular lipids to such processes has mainly been derived from studies on acquired or inherited diseases of lipid metabolism manifesting abnormalities in the structure and the function of the stratum corneum. We have studied the composition of stratum corneum lipids in clinically normal individuals with typical xerosis or 'winter dry skin' in order to establish if the lipid composition differs from that of normal individuals, showing no signs of xerosis. The amount of total stratum corneum lipids was not related to xerosis (22.0 +/- 1.8 micrograms/cm2 for normal skin, and 26.3 +/- 2.9 micrograms/cm2 for severe xerosis), and no correlation was evident between polar lipids, cholesterol sulfate (2.8 +/- 0.5% for normal skin, and 1.6 +/- 0.2% for severe xerosis), or ceramides types I-VI, and dry skin. It therefore appears that dramatic changes in stratum corneum lipids are not detectable in normal 'winter dry' skin. However, a decreased proportion of neutral lipids (sterol esters, triglycerides), coupled to increased amounts of free fatty acids, were found associated to the severity of dry skin. Apart from a decline in the sebaceous function and in esterases activity, winter dry skin does not appear to be associated to dramatic changes in polar stratum corneum lipids.     

A method to evaluate skin moisturizers in vivo

Blank demonstrated that water is the only plasticizer of human stratum corneum. Moisturizers attempt to add and hold water within the horny layer, and have previously been evaluated subjectively or in vitro. By passing a stream of dry nitrogen over skin, then through an electrolytic moisture analyzer, moisture present at the skin surface will be detected. This technique has been utilized to measure transepidermal water loss and the inhibition of water loss from skin by various investigators. However, when this same procedure is done on normal human skin, higher values indicate the presence of more moisture. The more moisture detectable at the surface, the more moisture available for keratin to absorb. By applying the moisturizers to plastic film and the skin, it can be demonstrated that water is not detectable after a few minutes on the plastic, but is detectable on skin at higher than control (transepidermal water loss) values for several hours. The technique can demonstrate enhanced moisturization from plastic occlusion and wet dressings as well as the drying effect of benzoyl peroxide gels. It allows objective rank ordering of moisturizers by monitoring moisture enhancement rather than occlusivity of applied substances.     

Cell replacement in the human stratum corneum in old age

SUMMARY. Staining of the human stratum corneum in vivo with fluorescent tetrachlorsalicylanilide has been used to measure the transit time of horny cells in the normal forearm skin of aged people. Stratum corneum thickness was estimated by counting the horny cell layers in biopsy specimens of epidermis, visualized by hydration in alkali. From the two parameters thus obtained, stratum corneum replacement rates were: calculated.
In 6 aged men, transit times varied between 20 and 36 (mean 26) days, and replacement rates between 30 and 47 (mean 34) hr. per cell layer. These data suggest reduced epidermal mitotic activity compared with that of young men.
In 5 aged women, transit times varied between 17 and 26 (mean 20) days and replacement rates between 16 and 31 (mean 24) hr. per cell layer. This faster replacement in old women compared with old men is not much slower than that observed in young adults.     

Hyaluronan exists in the normal stratum corneum

Hyaluronan is well known to exist as a water-sorbed macromolecule in the extracellular matrix. We here examined whether hyaluronan exists in the normal stratum corneum. High performance liquid chromatography was used to quantify hyaluronan content in the stratum corneum, epidermis (including stratum corneum), and dermis of mice, with the resulting dry weights being 22.3 +/- 2.9, 15.1 +/- 1.5, and 738.6 +/- 31.6 microg per g, respectively. Normal mouse skin was then labeled with [3H]-glucosamine in an organ culture, and accumulation of [3H]-labeled hyaluronan and its molecular mass were determined separately for the stratum corneum, epidermis, and dermis. In the stratum corneum, [3H]-labeled hyaluronan was accumulated linearly over the 3-d culture period. After the 3-d culture period, the epidermis synthesized twice the amount (expressed as dpm per mg dry weight) of [3H]-labeled hyaluronan as the dermis, whereas the stratum corneum and dermis showed nearly the same content of [3H]-labeled hyaluronan. The molecular mass of [3H]-labeled hyaluronan was highest (>1.0 x 106) in the dermis and clearly lower (<6.0 x 104) in the stratum corneum. Based on these results, we here confirm that hyaluronan is supplied from keratinocytes beneath the stratum corneum layer, and is present in the normal stratum corneum. We speculate that hyaluronan may play a role in moisturizing the stratum corneum and/or regulating its mechanical properties.