Sex difference in human fingertip recognition of micron-level randomness as unpleasant.

We investigated sex difference in evaluation, using the human fingertip, of the tactile impressions of three different micron-scale patterns laser-engraved on plastic plates. There were two ordered (periodical) patterns consisting of ripples on a scale of a few micrometres and one pseudo-random (non-periodical) pattern; these patterns were considered to mimic the surface geometry of healthy and damaged human hair, respectively. In the first experiment, 10 women and 10 men ran a fingertip over each surface and determined which of the three plates felt most unpleasant. All 10 female participants reported the random pattern, but not the ordered patterns, as unpleasant, whereas the majority of the male participants did not. In the second experiment, 9 of 10 female participants continued to report the pseudo-random pattern as unpleasant even after their fingertip had been coated with a collodion membrane. In the third experiment, participants were asked to evaluate the magnitude of the tactile impression for each pattern. The results again indicated that female participants tend to report a greater magnitude of unpleasantness than male participants. Our findings indicate that the female participants could readily detect microgeometric surface characteristics and that they evaluated the random pattern as more unpleasant. Possible physical and perceptual mechanisms involved are discussed.

Acceleration of permeability barrier recovery by exposure of skin to 10-30 kHz sound.

BACKGROUND: Previous reports show that ultrasound can influence human brain electrical activity and systemic hormone levels in various parts of the body, other than the ear, so there may be an unknown ultrasound-responsive system in humans. OBJECTIVES: In the present study, we examined the effects of sound on skin permeability barrier homeostasis. METHODS: We broke the skin barrier of hairless mice by tape stripping, and then exposed the skin to sound for 1 h to evaluate the effect on barrier recovery rate. RESULTS: Exposure of skin to sound at frequencies of 10, 20 and 30 kHz for 1 h accelerated barrier recovery, and 20 kHz sound induced the fastest recovery. Application of 5 kHz sound had no effect on barrier recovery rate. Significant acceleration was observed even when the sound source was located 3 cm away from the skin surface. The recovery rate depended on the sound pressure. An electron-microscopic study indicated that lamellar body secretion between stratum corneum and stratum granulosum was increased by exposure to sound at 20 kHz. CONCLUSIONS: These results suggest that epidermal keratinocytes might be influenced by ultrasound in a manner that results in modulation of epidermal permeability barrier homeostasis.

Effect of endothelial nitric oxide synthase on epidermal permeability barrier recovery after disruption.

BACKGROUND: We previously demonstrated that neuronal nitric oxide synthase (nNOS) in epidermal keratinocytes is associated with epidermal permeability barrier homeostasis. OBJECTIVES: In the present study, we examined the contributions of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) to epidermal permeability barrier homeostasis. METHODS: We measured the barrier recovery rate after tape stripping of the epidermis of iNOS and eNOS knockout mice, and carried out electron-microscopic observation of the epidermis after acetone treatment. RESULTS: The barrier recovery rate of eNOS knockout mice was significantly faster than that of the wild-type control, while no significant difference was observed between iNOS knockout mice and wild-type mice. Electron-microscopic observation at 1 h after acetone treatment indicated that barrier recovery of both nNOS and eNOS mice was faster than that of wild-type mice, and lamellar body secretion was accelerated in both types of knockout mice. CONCLUSIONS: These results suggested that both nNOS and eNOS play roles in epidermal barrier homeostasis and lamellar body secretion.

Function of oleic acid on epidermal barrier and calcium influx into keratinocytes is associated with N-methyl D-aspartate-type glutamate receptors.

BACKGROUND: Unsaturated fatty acids from sebum affect calcium dynamics in epidermal keratinocytes, disrupt the barrier function and induce abnormal keratinization. However, the mechanisms of these effects have not been clarified. OBJECTIVES: To investigate the function of unsaturated fatty acids in epidermis. METHODS: Antagonists of calcium channel receptors were applied to mouse skin together with oleic acid. Measurements were made of transepidermal water loss (TEWL), and hyperproliferation was assessed. The effects of the antagonists on calcium influx into cultured normal human keratinocytes and on cytokine production were also evaluated. RESULTS: N-methyl-d-aspartate (NMDA) receptor antagonists such as MK801 and D-AP5 specifically inhibited the increase in TEWL caused by oleic acid, and suppressed keratinocyte hyperproliferation. These compounds also inhibited the increase in the intracellular concentration of calcium ions induced by oleic acid. MK801 suppressed the production of interleukin-1alpha by keratinocytes induced by oleic acid. CONCLUSIONS: Unsaturated fatty acids such as oleic acid might function via NMDA receptors.

Methodology to improve epidermal barrier homeostasis: how to accelerate the barrier recovery?

Good water-impermeable barrier function is vital for healthy skin. Abnormality of the barrier function is observed in a variety of skin diseases, such as atopic dermatitis, psoriasis and contact dermatitis. Moreover, repeated barrier disruption induces epidermal hyperplasia and inflammation. On the other hand, acceleration of the barrier recovery prevents epidermal hyperplasia induced by barrier disruption in a dry environment. Thus, methods to improve the barrier function are very important for clinical dermatology. Recently, we have been searching for new reagents and/or new materials to improve barrier homeostasis. In this review, I will describe our recent findings and show how they provide the basis for a new perspective for clinical dermatology.

Tranexamic acid blocks the thrombin-mediated delay of epidermal permeability barrier recovery induced by the cedar pollen allergen, Cry j1.

We previously demonstrated that Cry j1, the major pollen allergen of Cryptomeria japonica (Japanese cedar), transiently increases protease activity and intracellular Ca2+ concentration in cultured human keratinocytes, and delays recovery after stratum corneum barrier disruption in human skin ex vivo. Topical application of tranexamic acid or trypsin-type serine protease inhibitors accelerates barrier recovery. We hypothesized that tranexamic acid might prevent the transient protease activity increase and the barrier recovery delay induced by Cry j1. Here, we tested this hypothesis and examined the mechanism involved. In cultured human keratinocytes, knock-down of protease-activated receptor 1 (PAR-1) reduced the transient increase of calcium induced by Cry j1, whereas knock-down of PAR-2 did not. Knock-down of thrombin significantly reduced the transient increases of calcium concentration and protease activity. Tranexamic acid, soybean trypsin inhibitor, or bivalirudin (a thrombin inhibitor) also reduced the calcium elevation induced by Cry j1 and/or thrombin. Co-application of tranexamic acid or bivalirudin with Cry j1 to human skin ex vivo blocked the delay of barrier recovery. These results suggest that thrombin and PAR-1 or PAR-1-like receptor might mediate the adverse effects of Cry j1 on human epidermal keratinocytes, and could open up a new strategy for treating inflammatory skin diseases.

Phosphorus restriction prevents parathyroid gland growth. High phosphorus directly stimulates PTH secretion in vitro.

Dietary phosphorus (P) restriction is known to ameliorate secondary hyperparathyroidism in renal failure patients. In early renal failure, this effect may be mediated by an increase in 1,25-(OH)2D3, whereas in advanced renal failure, P restriction can act independent of changes in 1,25-(OH)2D3 and serum ionized calcium (ICa). In this study, we examined the effects of dietary P on serum PTH, PTH mRNA, and parathyroid gland (PTG) hyperplasia in uremic rats. Normal and uremic rats were maintained on a low (0.2%) or high (0.8%) P diet for 2 mo. PTG weight and serum PTH were similar in both groups of normal rats and in uremic rats fed the 0.2% P diet. In contrast, there were significant increases in serum PTH (130 +/- 25 vs. 35 +/- 3.5 pg/ml, P < 0.01), PTG weight (1.80 +/- 0.13 vs. 0.88 +/- 0.06 microg/gram of body weight, P < 0.01), and PTG DNA (1.63 +/- 0.24 vs. 0.94 +/- 0.07 microg DNA/gland, P < 0.01) in the uremic rats fed the 0.8% P diet as compared with uremic rats fed the 0.2% P diet. Serum ICa and 1,25-(OH)2D3 were not altered over this range of dietary P, suggesting a direct effect of P on PTG function. We tested this possibility in organ cultures of rat PTGs. While PTH secretion was acutely (30 min) regulated by medium calcium, the effects of medium P were not evident until 3 h. During a 6-h incubation, PTH accumulation was significantly greater in the 2.8 mM P medium than in the 0.2 mM P medium (1,706 +/- 215 vs. 1,033 +/- 209 pg/microg DNA, P < 0.02); the medium ICa was 1.25 mM in both conditions. Medium P did not alter PTH mRNA in this system, but cycloheximide (10 microg/ml) abolished the effect of P on PTH secretion. Thus, the effect of P is posttranscriptional, affecting PTH at a translational or posttranslational step. Collectively, these in vivo and in vitro results demonstrate a direct action of P on PTG function that is independent of ICa and 1,25-(OH)2D3.

Histamine H1 and H2 receptor antagonists accelerate skin barrier repair and prevent epidermal hyperplasia induced by barrier disruption in a dry environment.

Keratinocytes have histamine H1 and H2 receptors, but their functions are poorly understood. To clarify the role of histamine receptors in the epidermis, we examined the effects of histamine receptor antagonists and agonists applied epicutaneously on the recovery of skin barrier function disrupted by tape stripping in hairless mice. Histamine H2 receptor antagonists famotidine and cimetidine accelerated the recovery of skin barrier function, but histamine and histamine H2 receptor agonist dimaprit delayed the barrier repair. Application of compound 48/80, a histamine releaser, also delayed the recovery. Imidazole, an analog of histamine, had no effect. The histamine H1 receptor antagonists diphenhydramine and tripelennamine accelerated the recovery. Histamine H3 receptor agonist Nalpha-methylhistamine and antagonist thioperamide had no effect. In addition, topical application of famotidine or diphenhydramine prevented epidermal hyperplasia in mice with skin barrier disrupted by acetone treatment in a dry environment (humidity < 10%) for 4 d. In conclusion, both the histamine H1 and H2 receptors in the epidermis are involved in skin barrier function and the cutaneous condition of epidermal hyperplasia.

trans-4-(Aminomethyl)cyclohexane carboxylic acid (T-AMCHA), an anti-fibrinolytic agent, accelerates barrier recovery and prevents the epidermal hyperplasia induced by epidermal injury in hairless mice and humans.

Because wounding the epidermis increases proteolytic activity and because disorders associated with barrier dysfunction have elevated protease activity, we studied the effect of protease inhibitors on the time course of barrier recovery and on the development of epidermal hyperplasia induced by repeated injury. After injuries to the epidermis produced by tape stripping, acetone treatment, or detergent (SDS) treatment that disrupt the barrier, a single application of 5% tranexamic acid [4-(aminomethyl)cyclohexane carboxylic acid, t-AMCHA], a well known anti-plasmin reagent, accelerated barrier recovery in both hairless mouse and human skin. In contrast, neither aminocaproic acid nor aminobutyric acid, inactive analogs of t-AMCHA, affected the time course of barrier recovery. Several trypsin-like serine protease inhibitors, e.g., leupeptin, TLCK, and PMSF, also accelerated barrier repair. In contrast other types of protease inhibitors, e.g., EDTA, pepstatin, N-ethylmaleimide, chymostatin, and TPCK, did not accelerate barrier recovery. We next evaluated the effects of daily topical application of t-AMCHA on epidermal hyperplasia, induced by repeated tape stripping or acetone treatment for 7 d. The degree of hyperplasia, quantified by the measurement of epidermal thickness, was reduced in both models by repeated applications of t-AMCHA. Finally, proteolytic activity in both human and mouse epidermis increased 1-2 h after epidermal injuries that disrupt the barrier. These results demonstrate that the inhibition of plasmin, a serine protease, accelerates barrier recovery and inhibits the epidermal hyperplasia induced by repeated barrier disruption, perhaps by decreasing the extent of attendant epidermal injury.

Cholesterol sulfate inhibits proteases that are involved in desquamation of stratum corneum.

We previously reported that desmosomes play a key role in the adhesion of corneocytes, and their digestion by two types of serine proteases leads to desquamation. Patients with recessive X-linked ichthyosis show hyperkeratosis attributable to desmosomes, associated with an increased content of cholesterol sulfate (CS) and an increased thickness of stratum corneum. In this study, therefore, we examined the possibility that CS provokes the abnormal desquamation, acting as a protease inhibitor. Scaling was induced on mice after topical application of chymostatin and leupeptin. Visible scale was also observed on mice after topical application of CS. We found that the stratum corneum thickness of CS-treated mice was increased in comparison with that of vehicle-treated mice. The thickness of the epidermis and the labeling index with proliferating cell nuclear antigen from CS-treated mice was almost the same as that from vehicle-treated mice. Moreover, in the stratum corneum of CS-treated mice, the content of desmosomes was higher than that in vehicle-treated mice. CS also inhibited the protease-induced cell dissociation of human stratum corneum sheets. In vitro, CS competitively inhibited both types of serine protease: the Ki for trypsin was 5.5 x 10(-6) M and that for chymotrypsin was 2.1 x 10(-6) M. These results indicate that CS retards desquamation by acting as a protease inhibitor. Thus, accumulation of stratum corneum in recessive X-linked ichthyosis may be a result of the inhibition by excessive CS of proteases involved in the dissolution of desmosomes, required for desquamation of the stratum corneum.

Low humidity stimulates epidermal DNA synthesis and amplifies the hyperproliferative response to barrier disruption: implication for seasonal exacerbations of inflammatory dermatoses.

Although seasonal changes in humidity are thought to exacerbate various skin diseases, whether these flares can be attributed to prolonged exposure to extremes in environmental humidities has not been studied systematically. We recently showed that prolonged exposure to high versus low humidities induced profound changes in epidermal structure and permeability barrier homeostasis. Therefore, we asked here whether comparable extremes in humidity could initiate not only homeostatic, but also potentially pathophysiologic alterations. We showed first that exposure to low humidity increases epidermal DNA synthesis in normal murine epidermis. Moreover, exposure to a low humidity for 48 h further amplifies the DNA synthetic response to barrier disruption, resulting in marked epidermal hyperplasia. Additionally, exposure to a dry environment for 48 h prior to barrier disruption results in dermal mast cell hypertrophy, degranulation, as well as histologic evidence of inflammation. To demonstrate the role of changes in external moisture on these phenomena, we applied either an occlusive, water-impermeable plastic membrane, Petrolatum, or a nonocclusive humectant, both to nonperturbated and to perturbed skin. All three forms of treatment prevented the epidermal hyperplasia and dermal mast cell hypertrophy and degranulation induced by exposure to low humidity. These studies indicate that (i) exposure to changes in environmental humidity alone induces increased keratinocyte proliferation and markers of inflammation, and (ii) that these changes are attributable to changes in stratum corneum moisture content. Finally, these studies provide evidence that changes in environmental humidity contribute to the seasonal exacerbations/amelioration of cutaneous disorders, such as atopic dermatitis and psoriasis, diseases which are characterized by a defective barrier, epidermal hyperplasia, and inflammation.

Recessive x-linked ichthyosis: role of cholesterol-sulfate accumulation in the barrier abnormality.

Cholesterol sulfate is a multifunctional sterol metabolite, produced in large amounts in squamous keratinizing epithelia. Because patients with recessive x-linked ichthyosis display not only a 10-fold increase in cholesterol sulfate, but also a 50% reduction in cholesterol, we assessed here whether cholesterol sulfate accumulation and/or cholesterol deficiency produce abnormal barrier function in recessive x-linked ichthyosis. Patients with recessive x-linked ichthyosis display both an abnormal barrier under basal conditions, and a delay in barrier recovery after acute perturbation, which correlate with minor abnormalities in membrane structure and extensive lamellar-phase separation. Moreover, both the functional and the structural abnormalities were corrected by topical cholesterol. Yet, topical cholesterol sulfate produced both a barrier abnormality in intact skin and extracellular abnormalities in isolated stratum corneum, effects largely reversed by coapplications of cholesterol. Together, these results suggest that cholesterol sulfate accumulation rather than cholesterol deficiency is responsible for the barrier abnormality. Despite the apparent importance of cholesterol sulfate-to-cholesterol processing for normal barrier homeostasis, neither steroid sulfatase activity nor mRNA levels are upregulated following acute perturbations. These results demonstrate both a potential role for cholesterol sulfate-to-cholesterol processing in normal permeability barrier homeostasis, and that basal levels of steroid sulfatase are sufficient to accommodate acute insults to the permeability barrier.

Exposure to a dry environment enhances epidermal permeability barrier function.

Previous studies have suggested that transepidermal water movement may play an important role in epidermal homeostasis and barrier repair. Here we analyzed cutaneous barrier function, epidermal morphology, and lipid content of the stratum corneum in hairless mice maintained in a high relative humidity (RH > 80%) versus low humidity (RH < 10%) environment for 2 wk. Basal transepidermal water loss was reduced by 31% in animals maintained in a dry versus humid environment. Moreover, the number of lamellar bodies in stratum granulosum cells, the extent of lamellar body exocytosis, and the number of layers of stratum corneum increased in animals kept in a dry environment. Furthermore, the dry weight of the stratum corneum and the thickness of the epidermis also increased in a dry environment. In addition, total stratum corneum lipids increased but lipid analysis revealed no significant differences in lipid distribution. Lastly, barrier recovery following either acetone treatment or tape stripping was accelerated after prolonged prior exposure to a dry environment, while conversely, it was delayed by prior exposure to a humid environment. These studies demonstrate that environmental conditions markedly influence epidermal structure and function, and suggest mechanisms by which the environment could induce or exacerbate various cutaneous disorders.

Influence of dry environment on epidermal function.

Recent studies have demonstrated that a dry environment contributes to the exacerbation of cutaneous disorders such as epidermal hyperplasia, mast cell degranulation, and cytokine secretion. The effects of a dry environment on the skin can be prevented by occlusion with water-impermeable material or topical application of a humectant. The stratum corneum, which protects internal organs from the environment, has two functions: a water-impermeable barrier function and a buffer function against a dry environment. Regulation of protease activity or ionic balance in the epidermis can accelerate barrier repair after injury. Improvement of the stratum corneum homeostasis can ameliorate skin damage induced by barrier disruption in a dry environment.

Dry condition affects desquamation of stratum corneum in vivo.

We examined whether a dry condition actually induces scaly skin in vivo. Hairless mice were kept in a high humidity condition or a low humidity condition and skin changes were examined. Scales appeared on the backs of mice kept for 3 days under the dry condition. The weight of stratum corneum (SC) was increased at this point, and these alterations were not accompanied with hyperproliferation of the nucleated cell layer of the epidermis. A decrease of desmosomal degradation was observed, though, desquamation-related enzyme activity was not altered. The regulation mechanism of desquamation is not yet clear, however, in vitro experiments suggest that the water content in SC is an important factor. The water content of SC was decreased in the dry condition. These results indicate that a dry environment perturbs desmosome degradation in intact SC by decreasing the water content of SC, and the consequent impairment of desquamation in normal skin in vivo may lead to the induction of a scaly skin surface.

Water content and thickness of the stratum corneum contribute to skin surface morphology.

Skin surface morphology has long been recognized as reflecting skin pathology. In the present study, we evaluated skin surface morphology using hairless mice under contrasting conditions of humidity. The skin surface microrelief was recorded with opaque quick-drying silicone rubber, and examined under a microscope. A binary image was produced by density slicing. Within 3 days of exposure to dry conditions, skin roughness was significantly increased. The skin roughness was partially mitigated by topical application of an aqueous solution of glycerol or hydration by immersion in water. A significant correlation between skin roughness and stratum corneum thickness was also observed. These results suggest that skin surface morphology is associated with both water content and thickness of the stratum corneum.

Stratum corneum lipid morphology and transepidermal water loss in normal skin and surfactant-induced scaly skin.

Stratum corneum lipid morphology was evaluated using attenuated total reflectance infrared spectroscopy (ATR-IR) in normal skin and surfactant-induced scaly skin to evaluate skin barrier function. To evaluate the degree of order of the intercellular lipid alkyl chain conformation, we measured the wavenumbers (frequency shifts) of the symmetrical and asymmetrical C-H stretching vibrations observed at approximately 2850 cm-1 and 2920 cm-1, respectively. There was a correlation between the wave-number and transepidermal water loss in normal skin. However, no difference was observed in surfactant-induced scaly skin from the baseline value in the wavenumbers of the C-H vibrations. These results suggest that in normal skin, lipid morphology plays an important role in the barrier function of the stratum corneum. However, the decline in barrier function in scaly skin is not due to conformational disorder of the lipid alkyl chain.

Loss of water from the stratum corneum induces epidermal DNA synthesis in hairless mice.

Many clinical studies have shown that low humidity has a deleterious effect on skin, but the mechanisms involved are poorly understood. To clarify the changes that occur in skin, we examined epidermal cell proliferation in mice kept in a dry (relative humidity < 10%) or a moist (relative humidity > 90%) environment. In animals exposed to low humidity, epidermal DNA synthesis started to increase within 12 h, reaching twice the original level, and the increased level was maintained for up to 5 days. The transepidermal water loss (TEWL) of mice kept for 12 h in the dry environment was the same as that of mice kept in the moist environment, but the skin conductance was lower. The increase in epidermal DNA synthesis following exposure to the dry environment was inhibited by topical application of petrolatum. It is concluded that loss of water from the stratum corneum induces epidermal cell proliferation within 12 h, and this change occurs in the absence of apparent cutaneous barrier dysfunction.

Epidermal injury stimulates prenylation in the epidermis of hairless mice.

Isoprenylation is the covalent attachment of isoprenyl groups, intermediates of the cholesterol biosynthesis pathway, to carboxyl terminal cysteine residues of proteins. Numerous proteins are isoprenylated including small GTP binding proteins, trimeric G proteins, and nuclear lamins, and these prenylated proteins regulate a variety of cell functions, including cell growth, cytokinesis, and differentiation. Here, we quantitated protein prenylation and determined which proteins are prenylated in the epidermis of hairless mice by radiolabeling with 3H-mevalonolactone following acute or chronic epidermal injury. In normal epidermis, four major radiolabeled bands, with molecular weights of 17-26, 48, 54, and 68 kDa, were observed. The levels of each of these bands increased by 24-63% 16 h following acute epidermal injury induced by topical acetone treatment or tape stripping, returning to normal by 24 h. On 2D gel electrophoresis, there were no major differences between the patterns of labeling following barrier disruption. Subacute epidermal injury induced by either acetone or tape stripping twice a day for 7 days and chronic injury induced by feeding an essential fatty acid-deficient (EFAD) diet, also resulted in a significant increase in protein prenylation. As with an acute injury, SDS-PAGE and 2D gel electrophoresis did not reveal marked differences in the pattern of protein prenylation. These results demonstrate that the prenylation of proteins in the epidermis is stimulated by injury, suggesting that one or more of these prenylated species may be important in epidermal proliferation or differentiation.