Negative electric potential induces alteration of ion gradient and lamellar body secretion in the epidermis, and accelerates skin barrier recovery after barrier disruption

Bioelectric medicine: unveiling the therapeutic potential of micro-current stimulation

Bioelectric medicine (BEM) refers to the use of electrical signals to modulate the electrical activity of cells and tissues in the body for therapeutic purposes. In this review, we particularly focused on the microcurrent stimulation (MCS), because, this can take place at the cellular level with sub-sensory application unlike other stimuli. These extremely low-level currents mimic the body's natural electrical activity and are believed to promote various physiological processes. To date, MCS has limited use in the field of BEM with applications in several therapeutic purposes. However, recent studies provide hopeful signs that MCS is more scalable and widely applicable than what has been used so far. Therefore, this review delves into the landscape of MCS, shedding light on the multifaceted applications and untapped potential of MCS in the realm of healthcare. Particularly, we summarized the hierarchical mediation from cell to whole body responses by MCS including its physiological applications. Our final objective of this review is to contribute to the growing body of literature that unveils the captivating potential of BEM, with MCS poised at the intersection of technological innovation and the intricacies of the human body.

Wound Repair and Ca2+ Signalling Interplay: The Role of Ca2+ Channels in Skin

The process of wound healing is intricate and tightly controlled, involving a number of different cellular and molecular processes. Numerous cellular functions, especially those related to wound healing, depend critically on calcium ions (Ca2+). Ca2+ channels are proteins involved in signal transduction and communication inside cells that allow calcium ions to pass through cell membranes. Key Ca2+ channel types involved in wound repair are described in this review.

Micro-Current Stimulation Suppresses Inflammatory Responses in Peptidoglycan-Treated Raw 264.7 Macrophages and Propionibacterium acnes-Induced Skin Inflammation via TLR2/NF-κB Signaling Pathway

Acne is a common inflammatory disorder of the human skin and a multifactorial disease caused by the sebaceous gland and Propionibacterium acnes (P. acnes). This study aimed to evaluate the anti-inflammatory effect of micro-current stimulation (MC) on peptidoglycan (PGN)-treated raw 264.7 macrophages and P. acnes-induced skin inflammation. To specify the intensity with anti-inflammatory effects, nitric oxide (NO) production was compared according to various levels of MC. As the lowest NO production was shown at an intensity of 50 μA, subsequent experiments used this intensity. The changes of expression of the proteins related to TLR2/NF-κB signaling were examined by immunoblotting. Also, immunofluorescence analysis was performed for observing NF-κB p65 localization. All of the expression levels of proteins regarding TLR2/NF-κB signaling were decreased by the application of MC. Moreover, the application of MC to PGN-treated raw 264.7 cells showed a significant decrease in the amount of nuclear p65-protein. In the case of animal models with P. acnes-induced skin inflammation, various pro-inflammatory cytokines and mediators significantly decreased in MC-applied mice. In particular, the concentration of IL-1β in serum decreased, and the area of acne lesions, decreased from the histological analysis. We suggest for the first time that MC can be a novel treatment for acne.

Electrical aspects of skin as a pathway to engineering skin devices

Skin is one of the indispensable organs for life. The epidermis at the outermost surface provides a permeability barrier to infectious agents, chemicals, and excessive loss of water, while the dermis and subcutaneous tissue mechanically support the structure of the skin and appendages, including hairs and secretory glands. The integrity of the integumentary system is a key for general health, and many techniques have been developed to measure and control this protective function. In contrast, the effective skin barrier is the major obstacle for transdermal delivery and detection. Changes in the electrical properties of skin, such as impedance and ionic activity, is a practical indicator that reflects the structures and functions of the skin. For example, the impedance that reflects the hydration of the skin is measured for quantitative assessment in skincare, and the current generated across a wound is used for the evaluation and control of wound healing. Furthermore, the electrically charged structure of the skin enables transdermal drug delivery and chemical extraction. This paper provides an overview of the electrical aspects of the skin and summarizes current advances in the development of devices based on these features.

Do epidermal keratinocytes have sensory and information processing systems?

It was long considered that the role of epidermal keratinocytes is solely to construct a water-impermeable protective membrane, the stratum corneum, at the uppermost layer of the skin. However, in the last two decades, it has been found that keratinocytes contain multiple sensory systems that detect environmental changes, including mechanical stimuli, sound, visible radiation, electric fields, magnetic fields, temperature and chemical stimuli, and also a variety of receptor molecules associated with olfactory or taste sensation. Moreover, neurotransmitters and their receptors that play crucial roles in the brain are functionally expressed in keratinocytes. Recent studies have demonstrated that excitation of keratinocytes can induce sensory perception in the brain. Here, we review the sensory and information processing capabilities of keratinocytes. We discuss the possibility that epidermal keratinocytes might represent the earliest stage in the development of the brain during the evolution of vertebrates.

Calcium Channels: Noteworthy Regulators and Therapeutic Targets in Dermatological Diseases

Dysfunctional skin barrier and impaired skin homeostasis may lead to or aggravate a series of dermatologic diseases. A large variety of biological events and bioactive molecules are involved in the process of skin wound healing and functional recovery. Calcium ions (Ca²⁺) released from intracellular stores as well as influx through plasma membrane are essential to skin function. Growing evidence suggests that calcium influx is mainly regulated by calcium-sensing receptors and channels, including voltage-gated, transient potential receptor, store-operated, and receptor-operated calcium channels, which not only maintain cellular Ca²⁺ homeostasis, but also participate in cell proliferation and skin cell homeostasis through Ca²⁺-sensitive proteins such as calmodulin (CaM). Furthermore, distinct types of Ca²⁺ channels not merely work separately, they may work concertedly to regulate cell function. In this review, we discussed different calcium-sensing receptors and channels, including voltage-gated, transient receptor potential, store-operated, and receptor-operated calcium channels, particularly focusing on their regulatory functions and inherent interactions as well as calcium channels-related reagents and drugs, which is expected to bridge basic research and clinical applications in dermatologic diseases.

Therapeutic effects of iontophoresis with gold nanoparticles in the repair of traumatic muscle injury

Studies have shown the benefits of gold nanoparticles (GNPs) in muscle and epithelial injury models. In physiotherapy, the use of the microcurrent apparatus is associated with certain drugs (Iontophoresis) to increase the topical penetration and to associate the effects of both therapies. Therefore, the objective of this study was to investigate the effects of iontophoresis along with GNPs in the skeletal muscle of rats exposed to a traumatic muscle injury. We utilised 50 Wistar rats randomly divided in to five experimental groups (n = 10): Control group (CG); Muscle injury group (MI); MI + GNPs (20 nm, 30 mg kg^-1); MI + Microcurrent (300 μA); and MI + Microcurrent + GNPs. The treatment was performed daily for 7 days, with the first session starting at 24 h after the muscle injury. The animals were sacrificed and the gastrocnemius muscle was surgically removedand stored for the proper evaluations. The group that received iontophoresis with GNPs showed significant differences in inflammation and oxidative stress parameters and in the histopathological evaluation showed preserved morphology. In addition, we observed an improvement in the locomotor response and pain symptoms of these animals. These results suggest that the association of boththerapies accelerates the inflammatory response of the injured limb.

Mild electrical stimulation with heat shock reduces inflammatory symptoms in the imiquimod-induced psoriasis mouse model

Psoriasis is a chronic skin disease caused by immune disorder. The chronic skin inflammation involves inflammatory molecules that are released from T lymphocytes and keratinocytes. Therefore, developing an anti-inflammatory therapy that is suitable for long-term treatment is needed. Electrical stimulation induces biological responses by modulating intracellular signaling pathways. Our previous studies showed that the optimized combination treatment of mild electrical stimulation (MES, 0.1-millisecond; ms, 55-pulses per second; pps) and heat shock (HS, 42°C) modulates inflammatory symptoms of metabolic disorders and chronic kidney disease in mice models and clinical trials. Here, we investigated the effect of MES+HS treatment on imiquimod-induced psoriasis mouse model. Topical application of imiquimod cream (15 mg) to mice ear induced keratinocyte hyperproliferation and psoriasis-like inflammation. In MES+HS-treated mice, imiquimod-induced skin hyperplasia was significantly decreased. MES+HS treatment reduced the protein expression of IL-17A and the infiltration of CD3-positive cells in lesioned skin. In addition, MES+HS-treated mice had decreased mRNA expression level of antimicrobial molecules (S100A8 and Reg3γ) which aggravate psoriasis. In IL-17A-stimulated HaCaT cells, MES+HS treatment significantly lowered the mRNA expression of aggravation markers (S100A8, S100A9 and β-defensin2). Taken together, our study suggested that MES+HS treatment improves the pathology of psoriasis via decreasing the expression of inflammatory molecules.

Frontiers in epidermal barrier homeostasis--an approach to mathematical modelling of epidermal calcium dynamics

Intact epidermal barrier function is crucial for survival and is associated with the presence of gradients of both calcium ion concentration and electric potential. Although many molecules, including ion channels and pumps, are known to contribute to maintenance of these gradients, the mechanisms involved in epidermal calcium ion dynamics have not been clarified. We have established that a variety of neurotransmitters and their receptors, originally found in the brain, are expressed in keratinocytes and are also associated with barrier homeostasis. Moreover, keratinocytes and neurons show some similarities of electrochemical behaviour. As mathematical modelling and computer simulation have been employed to understand electrochemical phenomena in brain science, we considered that a similar approach might be applicable to describe the dynamics of epidermal electrochemical phenomena associated with barrier homeostasis. Such methodology would also be potentially useful to address a number of difficult problems in clinical dermatology, such as ageing and itching. Although this work is at a very early stage, in this essay, we discuss the background to our approach and we present some preliminary results of simulation of barrier recovery.

Iontophoresis with gold nanoparticles improves mitochondrial activity and oxidative stress markers of burn wounds

The aim of this study was to analyse the effects of microcurrent and gold nanoparticles on oxidative stress parameters and the mitochondrial respiratory chain in the healing of skin wounds. Thirty 60-day old male Wistar rats (250-300 g) were divided into five groups (N=6): Control; Burn wounds; Microcurrent (MIC); Gold nanoparticle gel (GNP gel) and Microcurrent+Gold nanoparticle gel (MIC+GNP gel). The microcurrent treatment was applied for five consecutive days at a dose of 300 μA. The results demonstrate a significant decrease in the activity of complexes I, II-III and IV in the Burn Wounds group compared to the control, and the MIC+GNP gel group was able to reverse this inhibition in complexes I, III and IV. Furthermore, a significant reduction in oxidative damage parameters and a significant increase in the levels of antioxidant defence enzymes were induced in the MIC+GNP gel group compared to the Burn Wounds group. The data strongly indicate that the group receiving treatment with MIC+GNP gel had improved mitochondrial functioning and oxidative stress parameters, which contributed to tissue repair.

External negative electric potential accelerates exocytosis of lamellar bodies in human skin ex vivo

Exocytosis of lamellar bodies at the uppermost nucleated layer of the epidermis is a crucial process for epidermal permeability barrier homoeostasis. We have previously suggested that skin surface electric potential might be associated with barrier homoeostasis. Thus, we hypothesized that the potential might drive exocytosis of lamellar bodies. In this study, we tested this idea by applying negative electric potential (-0.5 V) to human skin samples ex vivo for 2 h and observing the ultrastructure of the uppermost layer. The secretion of lamellar bodies was accelerated in the potential-applied skin, compared to that in untreated control skin. Multiphoton observation indicated that extracellular lipid domains were more extensive in treated skin than in control skin. Moreover, the calcium ion gradient was greater at the uppermost layer of the epidermis of treated skin, compared to that in control skin. These results indicate that electric potential may regulate lamellar body secretion in healthy human skin.

Antioxidant nutrient intakes and corresponding biomarkers associated with the risk of atopic dermatitis in young children

BACKGROUND/OBJECTIVES

To investigate the association of antioxidant nutritional status with the risk of atopic dermatitis (AD) in young children in a case-control, population-based study.

SUBJECTS/METHODS

Identified from preschools by using the Korean version of the International Study of Asthma and Allergies in Childhood (ISAAC). Final analysis included 180 AD (mean age 5.3+/-0.9 years) and 242 non-AD (mean age 5.2+/-1.0 years) children. Diet was assessed using a validated semi-quantitative food frequency questionnaire. Fasting blood samples were used for analyses of fat-soluble vitamins (retinol, alpha-tocopherol, and beta-carotene) and vitamin C.

RESULTS

AD was associated negatively with intakes of antioxidant-related nutrients. The adjusted odds ratio (OR) and 95% confidence interval (95% CI) were 0.44 (0.22-0.88) for the highest (vs lowest) quintile of beta-carotene. A similar association was observed for dietary vitamin E (OR=0.33, 95% CI=0.16-0.67), folic acid (OR=0.37, 95% CI=0.18-0.73), and iron (OR=0.39, 95% CI=0.19-0.79). Reduced AD risk was found with 1 s.d. increase of serum alpha-tocopherol [OR=0.64, 95% CI=0.41-0.98) and retinol (OR=0.74, 95% CI=0.58-0.96) concentrations, and marginally with that of serum beta-carotene levels (P=0.0749 for trend). There was no relationship of AD risk with dietary and plasma vitamin C as well as nutrient supplement intake regardless of nutrient type. AD was predicted better by the intake measure than the corresponding blood biomarker regarding vitamin E and beta-carotene.

CONCLUSIONS

These findings suggest that higher antioxidant nutritional status reduces the risk of AD and that such risk-reduction effects depend on nutrient type.

Acute modulations in permeability barrier function regulate epidermal cornification: role of caspase-14 and the protease-activated receptor type 2

Stratum corneum comprises corneocytes, derived from outer stratum granulosum during terminal differentiation, embedded in a lipid-enriched extracellular matrix, secreted from epidermal lamellar bodies. Permeability barrier insults stimulate rapid secretion of preformed lamellar bodies from the outer stratum granulosum, regulated through modulations in ionic gradients and serine protease (SP)/protease-activated receptor type 2 (PAR2) signaling. Because corneocytes are also required for barrier function, we hypothesized that corneocyte formation could also be regulated by barrier function. Barrier abrogation by two unrelated methods initiated a wave of cornification, assessed as TdT-mediated dUTP nick end-labeling-positive cells in stratum granulosum and newly cornified cells by electron microscopy. Because cornification was blocked by occlusion, corneocytes formed specifically in response to barrier, rather than injury or cell replacement, requirements. SP inhibitors and hyperacidification (which decreases SP activity) blocked cornification after barrier disruption. Similarly, cornification was delayed in PAR2(-/-) mice. Although classical markers of apoptosis [poly(ADP-ribose)polymerase and caspase (Casp)-3] remained unchanged, barrier disruption activated Casp-14. Moreover, the pan-Casp inhibitor Z-VAD-FMK delayed cornification, and corneocytes were structurally aberrant in Casp14(-/-) mice. Thus, permeability barrier requirements coordinately drive both the generation of the stratum corneum lipid-enriched extracellular matrix and the transformation of granular cells into corneocytes, in an SP- and Casp-14-dependent manner, signaled by PAR2.

Dynamics of Skin Barrier Repair following Topical Applications of Miconazole Nitrate

The skin barrier function (SBF) is an important aspect of skin biology, particularly in the elicitation of inflammation. The SBF recovery rate after tape stripping and surfactant challenge can be assessed by measuring the transepidermal water loss (TEWL). Previous clinical studies have shown some inflammatory effect after topical applications of miconazole. The aim of this study was to compare the effect of pastes (petrolatum and 15% zinc oxide) containing or not miconazole nitrate on controlled impaired SBF. Fifteen volunteers were enrolled. In each subject, successive cyanoacrylate skin surface strippings were harvested from 5 sites of the volar forearm until TEWL raised above 15 g/cm(2)/h on all test sites. In addition, one daily soak session with a 0.2% dishwashing liquid further damaged the SBF. Each of the test formulations was applied twice daily for 5 days at two dosages, namely 1 and 2 mg/cm(2), on randomized test sites. Another site remained untreated. TEWL was measured daily for 5 days. A fastened SBF repair was observed on all treated sites, particularly where the largest amount of the products had been applied. A faster SBF recovery rate was obtained at the site receiving the miconazole nitrate paste. We conclude that the occlusive effect of a paste helped mitigate SBF defect. The adjunction of miconazole nitrate improved the efficacy.

Expression of voltage-gated calcium channel subunit alpha1C in epidermal keratinocytes and effects of agonist and antagonists of the channel on skin barrier homeostasis

Recent studies demonstrated that skin surface electric conditions affect epidermal permeability barrier homeostasis. These results suggest the existence of voltage sensor on the keratinocytes of the epidermis. On the contrary, specific blockers of the voltage-gated calcium channel (VGCC) also affect epidermal barrier homeostasis, but the existence and function of the channel has not been determined. We demonstrated here immunohistochemically the expression of the main subunit of the L-type VGCC, alpha1C, which alone has a calcium channel function, in mouse and human epidermis. Immunostaining, RT-PCR, and Western blotting were carried out to detect the channel protein. Messenger RNA of alpha1C was also detected in mouse epidermis and human keratinocyte culture by RT-PCR. We also evaluated the function of the channel in the cultured human keratinocytes. Previously, we demonstrated that influx of calcium ion into epidermal keratinocytes delayed the barrier recovery after barrier disruption and topical application of calcium channel blocker accelerated the barrier recovery. In this study, topical application of nifedipine and R-(+)-BAY K8644 after tape stripping of hairless mice accelerated the barrier repair rate while application of S-(-)-BAY K8644 delayed the barrier recovery. These results suggest that the VGCC exists on epidermal keratinocytes and plays an important role in skin barrier homeostasis.

Drinking deep-sea water restores mineral imbalance in atopic eczema/dermatitis syndrome

OBJECTIVE

The effect of drinking deep-sea water on hair minerals was studied in patients with atopic eczema/dermatitis syndrome (AEDS). Study of hair minerals revealed an imbalance of essential minerals and an increase in toxic minerals in AEDS patients.

DESIGN

After drinking deep-sea water (Amami no Mizu) for 6 months in AEDS patients, hair minerals (essential minerals and toxic minerals), clinical evaluation of the skin symptoms were compared before drinking with after drinking.

SUBJECTS

After obtaining informed consent, 33 patients (mean age 26 y, range 1-50 y, 13 male and 20 female subjects) with mild to moderate AEDS were enrolled.

RESULTS

After drinking deep-sea water, the levels of the essential mineral, potassium (K), were significantly decreased, while the levels of selenium (Se) increased. On the other hand, drinking deep-sea water significantly decreased the levels of the toxic minerals, mercury and lead. Moreover, after drinking deep-sea water, the skin symptoms were improved in 27 out of 33 patients.

CONCLUSION

These results indicate that the mineral abnormalities/imbalance may be involved in the pathogenesis of AEDS, and that drinking deep-sea water may be useful in the treatment of AEDS.

In vitro skin irritation: facts and future. State of the art review of mechanisms and models

The skin is the main target tissue for exogenous noxes, protecting us from harmful environmental hazards, UV-irradiation and endogenous water loss. It is composed of three layers, whereas the outermost epidermis is a squamous epithelium that mainly consists of keratinocytes. These cells execute a terminal differentiation, which finally results in the assembly of the stratum corneum. This layer, consisting of cornified keratinocytes, is an effective barrier against a vast number of substances. Apart of this, keratinocytes play crucial roles in the immune surveillance and the initiation, modulation and regulation of inflammation in the epidermis. Regarding cutaneous inflammatory reactions, skin irritation is one of the most common adverse effect in humans. For reasons of human safety assessment new chemicals are still evaluated for irritant potentials by application to animals followed by visible changes such as erythema and oedema. Testing for skin irritation in animals potentially cause them pain and discomfort. Furthermore, the results are not always predictive for those found in humans. In order to replace animal testing and to improve the prediction of irritants, the cosmetic and toiletry industry, in Europe represented by Colipa, develops and uses several alternative in vitro test systems. In this respect, the use of in vitro reconstructed organotypic skin equivalents are mostly favored, because of their increasingly close resemblance to human skin. Due to ethical and scientific questions and on account of the 7th amendment of the European Council Directive 76/768/EEC, the authors see the requirement to drive the development of alternative tests for irritants. Therefore, this article centres on cosmetic ingredients and provides the readership an overview of the state of art of cellular mechanisms of skin irritation and summarizes the results of the commonly used skin equivalents to evaluate irritation in vitro.

Topical Application of Ionic Polymers Affects Skin Permeability Barrier Homeostasis

We previously demonstrated that the external electric potential affected skin barrier homeostasis. On the other hand, topical application of an ionic polymer formed a diffusion electric double layer on the surface of the skin. Thus, we evaluated effects of topical application of ionic polymers on the damaged skin barrier. Application of a nonionic polymer did not affect barrier recovery. Application of sodium salts of anionic polymers accelerated barrier recovery, while that of cationic polymers delayed it. Topical application of a sodium-exchange resin accelerated barrier recovery, but application of a calcium-exchange resin had no effect even when the resins had the same structure. Application of a chloride-exchange resin delayed barrier recovery. Topical application of ionic polymers influenced skin barrier homeostasis.

Barium sulphate with a negative zeta potential accelerates skin permeability barrier recovery and prevents epidermal hyperplasia induced by barrier disruption

BACKGROUND

Barium sulphate, a stable inorganic material, has been used in contrast media and cosmetic products because of its stability. As a negative external electric potential accelerates the skin barrier repair after barrier disruption, we hypothesized that topical application of barium sulphate may affect the skin barrier recovery rate depending on its zeta potential.

OBJECTIVES

To investigate whether barium sulphate particles in aqueous solution have different zeta potentials depending on their surface structure, and to investigate the possible relation between zeta potential and skin barrier recovery rate.

METHODS

Mice were subjected to tape stripping to disrupt barrier function, or were treated with acetone and kept in a dry environment to induce epidermal hyperplasia. They were then treated with different forms of barium sulphate, and barrier recovery was monitored by measurements of transepidermal water loss.

RESULTS

There was a significant correlation between the barrier recovery rate and zeta potential of barium sulphate applied topically. Barium sulphate with a negative zeta potential significantly accelerated barrier recovery, but barium sulphate with a positive zeta potential did not accelerate or even delayed barrier repair. Barium sulphate with a negative zeta potential had an X-ray diffraction pattern different from that with a positive potential. The distribution of calcium in the epidermis was also influenced by the polarity of zeta potential.

CONCLUSIONS

These findings suggest a new pharmacological approach towards altering barrier function or epidermal hyperplasia with inorganic particles in healthy and diseased skin.

Influx of calcium and chloride ions into epidermal keratinocytes regulates exocytosis of epidermal lamellar bodies and skin permeability barrier homeostasis

In the nervous system, influx of calcium and chloride ions into neurons regulates the signaling system by excitation and inhibition, respectively. In this study, we demonstrated the effects of the ion influx into epidermal keratinocytes in the permeability barrier repair process of the skin after damage. Topical application of the neurotransmitters glutamate and nicotine, which activate the calcium channel in neurons, delayed the barrier repair after tape stripping. In contrast, the neurotransmitters GABA and glycine, which activate the chloride channel in neurons, accelerated barrier repair. Topical application of the calcium ionophore ionomycin delayed barrier recovery and chloride ionophore 1 accelerated barrier repair after barrier disruption by tape stripping and acetone treatment. Ionomycin increased the intracellular calcium concentration in cultured keratinocytes whereas the chloride ionophore 1 increased the intracellular chloride ion concentration. In vivo light microscopy and electron microscopy observation showed acceleration of the exocytosis of lipid-containing lamellar bodies by the chloride ionophore and delay of the exocytosis by the calcium ionophore. These results suggest that, like the nervous system, influx of calcium and chloride ions into epidermal keratinocytes through ionotropic receptors plays a crucial role in cutaneous barrier homeostasis.

NMDA-type glutamate receptor is associated with cutaneous barrier homeostasis

Glutamate receptors play an important role in the excitatory synaptic action of the central nervous system. In this study, effects of glutamate receptor agonists and antagonists on skin barrier homeostasis were studied using hairless mouse. Topical application of L-glutamic acid, L-aspartic acid (non-specific glutamate receptor agonists) and N-methyl-D-aspartate (NMDA, NMDA type receptor agonist) delayed the barrier recovery rate after barrier disruption with tape stripping. On the other hand, topical application of D-glutamic acid (non-specific antagonist of glutamate receptor), MK 801 and D-AP5, (NMDA-type receptor antagonists) accelerated the barrier repair. The non-NMDA type receptor agonist, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), did not affect the barrier recovery. Topical application of MK-801 also promoted the healing of epidermal hyperplasia induced by acetone treatment under low environmental humidity. Immediately after barrier disruption on skin organ culture, secretion of glutamic acid from skin was significantly increased. Immunohistochemistry, reverse transcription polymearse chain reaction (RT-PCR) and in situ hybridization showed an expression of NMDA-type receptor-like protein on hairless mouse epidermis. NMDA increased intercellular calcium in cultured human keratinocytes and the increase was blocked by MK 801. These results suggest that glutamate plays an important role as a signal of cutaneous barrier homeostasis and epidermal hyperplasia induced by barrier disruption.

P2X purinergic receptor antagonist accelerates skin barrier repair and prevents epidermal hyperplasia induced by skin barrier disruption

The effects of ATP receptor agonists/antagonists on skin barrier recovery rate were evaluated in hairless mice. Topical application of ATP and alpha,beta-methylene ATP (agonist of P2X receptor) delayed barrier recovery. Topical application of suramin (nonspecific ATP receptor antagonist), pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) (P2X receptor antagonist), and 2',3'-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate (TNP-ATP) (P2X1, P2X3, P2X2/3 antagonist) after barrier disruption accelerated the barrier repair. The P2Y type receptor antagonist Reactive Blue 2 did not affect the barrier repair process. Moreover, topical application of TNP-ATP prevented epidermal hyperplasia induced by barrier insult under low environmental humidity. ATP was secreted immediately after tape stripping on skin in organ culture. alpha,beta-Methylene ATP increased intercellular calcium in cultured keratinocytes and the increase was blocked by TNP-ATP. Both reverse transcription polymerase chain reaction assay and immunohistochemical study showed the existence of protein that had a structure similar to P2X3 on hairless mouse epidermis. These results suggest that cutaneous barrier homeostasis can be regulated by cation flux through a P2X3-like ATP receptor.

New strategies to improve skin barrier homeostasis

The uppermost thin layer, stratum corneum, plays a crucial role as a water impermeable barrier. After acute damage, it recovers automatically, but with aging or psychological stress, the recovery is delayed. Frequent damage, or damage under a dry environment, induces epidermal hyperplasia or inflammation. A specific protease inhibitor, histamine antagonist, and some magnesium salts have been demonstrated to accelerate the barrier recovery. These treatments also mitigated the epidermal hyperplasia induced by repeated barrier disruption or the damage under a dry condition. For the delay of the barrier repair induced by psychological stress, a glucocorticoid receptor antagonist or reduction of the stress by some specific odorant was significantly effective. Recently, the ion flux in the epidermis was found to be crucial for the barrier homeostasis. An external negative electric field accelerated the skin barrier recovery. These new methods to improve skin barrier homeostasis could be useful strategies to solve skin problems.

gamma-Aminobutyric acid (A) receptor agonists accelerate cutaneous barrier recovery and prevent epidermal hyperplasia induced by barrier disruption

gamma-Aminobutyric acid, is an amino acid transmitter, which mediates rapid inhibition in the central nervous system. gamma-Aminobutyric acid (A) receptor is a ligand-gated chloride ion channel playing an important part in polarizing the cell membrane and reducing neuronal excitability in the neuron. In this study, we demonstrated the effects of gamma-aminobutyric acid (A) receptor agonists on the cutaneous barrier repair process after the barrier disruption of hairless mice. Topical application of gamma-aminobutyric acid and gamma-aminobutyric acid (A) receptor-specific agonists, musimol and isoguvacine, after barrier disruption accelerated the barrier recovery. The gamma-aminobutyric acid (B)-specific agonist, baclofen, did not affect the barrier recovery rate. The effect of gamma-aminobutyric acid on the barrier recovery was blocked by the gamma-aminobutyric acid (A)-receptor antagonist, bicuculline methobromide, but gamma-aminobutyric acid (B) receptor antagonist, saclofen, did not affect the effect of gamma-aminobutyric acid. Topical application of gamma-aminobutyric acid also prevented epidermal hyperplasia, which was induced by the barrier insults under low environmental humidity and bicuculline methobromide blocked the effect of gamma-aminobutyric acid on the epidermal hyperplasia. Immunoreactivity against gamma-aminobutyric acid (A) polyclonal antibody was observed in hairless mouse epidermis. The fluorescent probe of gamma-aminobutyric acid (A) receptor, TXR-musimol showed the localization of gamma-aminobutyric acid (A) receptor in the epidermis of the hairless mice. Elevation of intracellular chloride ion was induced by gamma-aminobutyric acid in cultured human keratinocytes and it was blocked by bicuculline methobromide. These results suggest that the gamma-aminobutyric acid (A)-like receptor is associated with skin barrier homeostasis and regulation of the receptor clinically effective for barrier dysfunctional or epidermal hyperproliferative diseases.