Investigation of skin permeation, ex vivo inhibition of venom-induced tissue destruction, and wound healing of African plants used against snakebites

ETHNOPHARMACOLOGICAL RELEVANCE

Snakebite envenomation causes 5000-10,000 mortalities and results in more than 5-15,000 amputations in sub-Saharan Africa alone every year. The inaccessibility of antiserum therapy is a vast problem, and only about 2.5% of the actual need for antiserum in Africa is covered. Numerous plants have shown in vitro inhibitory activity against one or more of the hydrolytic enzymes involved in snakebite-induced necrosis. However, a more thorough examination of the plant species in ex vivo and in vitro cell assay models is needed to test their ability to inhibit necrosis.

MATERIALS AND METHODS

Extracts which had previously shown in vitro inhibitory activity against necrosis enzymes, were tested in an ex vivo air-liquid-interface model, and a wound healing scratch assay as well as for their ability to permeate the skin barrier and inhibit venom induced cell death.

RESULTS

Of the 14 water extracts and 16 ethanol extracts tested at a concentration of 10 μg/mL, only the ethanol extracts of Tamarindus indica and Paullinia pinnata resulted in a small but significant increase in cell migration of around 10% compared to treatment with buffer after 24h treatment. The remaining extracts showed no effect, or they even delayed the cell migration compared to the treatment with buffer. After 48 h treatment, 10 of the tested extracts showed a decreased cell migration compared to no treatment. At a 100 μg/mL concentration all the extracts inhibited cell migration and five extracts killed some of the cells, while four extracts killed all the cells. Ten of the thirty extracts were tested in a Franz cell set-up but none of the extracts tested did permeate the skin barrier over a 48 h period, and will therefore be of very limited use topically in the initial treatment of snakebites in its present form. None of the extracts were able to directly interact with the enzyme to lower the cell toxicity of the venom. Two extracts, Dichrostachys cinerea and Grewia mollis, were tested in the ex vivo model, but none of them inhibited the tissue destruction caused by venom.

CONCLUSION

On the basis of this study, topical treatment with plant extracts for snakebite-induced tissue necrosis cannot be recommended.

Promotion of wound healing by Plantago major L. leaf extracts--ex-vivo experiments confirm experiences from traditional medicine

The wound-healing properties of Plantago major L. (plantain) were evaluated using an ex-vivo porcine wound-healing model. Ethanol- and water-based extracts were prepared from greenhouse-grown and freeze-dried leaves of P. major. Both types of extracts stimulated wound healing in porcine skin, but the ethanol-based extracts had a somewhat stronger effect. A concentration of 1.0 mg/mL (on dry weight basis) produced the best results for both types of extracts.

Epidermal tight junctions in health and disease

The skin, the largest organ of the body, is an essential barrier that under homeostatic conditions efficiently protects and/or minimizes damage from both environmental (e.g. microorganisms, physical trauma, ultraviolet radiation) and endogenous (e.g., cancers, inflammation) factors. This formidable barrier function resides mainly in the epidermis, a dynamic, highly-stratified epithelium. The epidermis has 2 major barrier structures: stratum corneum, the outmost layer and tight junctions, intercellular junctions that seal adjacent keratinocytes in the stratum granulosum, found below the stratum corneum. In recent years there have been significant advances in our understanding of tight junction function, composition and regulation. Herein we review what is known about tight junctions in healthy skin and keratinocyte culture systems and highlight the dynamic crosstalk observed between tight junctions and the cutaneous immune system. Finally we discuss the preliminary observations suggesting that tight junction function or protein expression may be relevant for the pathogenesis of a number of common cutaneous inflammatory and neoplastic conditions.

Determining the Depth of Injury in Bioengineered Tissue Models of Cornea and Conjunctiva for the Prediction of All Three Ocular GHS Categories

The depth of injury (DOI) is a mechanistic correlate to the ocular irritation response. Attempts to quantitatively determine the DOI in alternative tests have been limited to exvivo animal eyes by fluorescent staining for biomarkers of cell death and viability in histological cross sections. It was the purpose of this study to assess whether DOI could also be measured by means of cell viability detected by the MTT assay using 3-dimensional (3D) reconstructed models of cornea and conjunctiva. The formazan-free area of metabolically inactive cells in the tissue after topical substance application is used as the visible correlate of the DOI. Areas of metabolically active or inactive cells are quantitatively analyzed on cryosection images with ImageJ software analysis tools. By incorporating the total tissue thickness, the relative MTT-DOI (rMTT-DOI) was calculated. Using the rMTT-DOI and human reconstructed cornea equivalents, we developed a prediction model based on suitable viability cut-off values. We tested 25 chemicals that cover the whole range of eye irritation potential based on the globally harmonized system of classification and labelling of chemicals (GHS). Principally, the MTT-DOI test method allows distinguishing between the cytotoxic effects of the different chemicals in accordance with all 3 GHS categories for eye irritation. Although the prediction model is slightly over-predictive with respect to non-irritants, it promises to be highly valuable to discriminate between severe irritants (Cat. 1), and mild to moderate irritants (Cat. 2). We also tested 3D conjunctiva models with the aim to specifically address conjunctiva-damaging substances. Using the MTT-DOI method in this model delivers comparable results as the cornea model, but does not add additional information. However, the MTT-DOI method using reconstructed cornea models already provided good predictability that was superior to the already existing established invitro/exvivo methods.

Abstract 2950: Regulation of the functional interface between nucleotide excision repair and transcription by MITF modulates melanoma growth

Nucleotide excision repair (NER) is an essential instrument to maintain genomic stability in eukaryotes especially towards ultraviolet radiation (UVR). There is profound knowledge of the mechanistic execution of NER, however its regulation is not well understood. Here we provide evidence that the lineage-dependent oncogene MITF regulates the functional interface between NER and transcription through transactivation of XPG and GTF2H1, which constitute core elements of the NER and general transcription factor machineries, respectively.

For this purpose, flow cytometry and microscopy fluorescence assays were applied to evaluate the temporal repair kinetics of DNA lesions after UVR in the presence and upon depletion of MITF in human primary melanocytes and several melanoma cell lines. Moreover, ChIP and luciferase reporter assays were performed to show the in vivo occupancy and a MITF dependent transactivation of the XPG and GTF2H1 promoters. Transcriptome as well as tissue microarrays (TMA) analysis were used to demonstrate the relationship between MITF and TFIIH. Finally, in vivo experiments were performed utilizing a subcutaneous xenograft tumor model in SCID mice to confirm our hypothesis.

Our results showed that the NER/TFIIH complex is controlled by MITF in the presence and absence of UVR mediated genotoxic attack resulting in nucleotide repair deficiency and breakdown of global transcription upon MITF depletion. Importantly, in primary human melanoma the TFIIH subunit GTF2H1, which is involved in NER and RNA transcription, is linked to MITF abundance and prognostic melanoma stage. Moreover, RNA-interference mediated repression of GTF2H1 led to a significant reduction in tumor formation in a melanoma xenograft model.

Collectively, these results describe an unanticipated role of MITF in the regulation of intimately linked NER and transcription machineries in the melanocytic lineage, which is preserved upon transformation into melanoma. Through its control of the NER/TFIIH complex MITF might coordinately regulate repair and transcription processes, thereby optimizing the rapid resumption of transcriptional activity after completion of strand repair, which is vitally important for cellular survival. The very same mechanism may drive the genesis of melanoma and its progression in the context of aberrant transcriptional activity of MITF due to SUMOylation defective germline mutation or genomic amplification.

Citation Format: Marcos Seoane, Laia Pagerols Raluy, Karoline Kaufmann, Julia Strauss, Kevin Dierck, Jüergen Thomale, Johanna M. Brandner, Udo Schumacher, Peter Nollau, Peter J. Wild, Martin Zimmermann, Jinyan Du, David E. Fisher, Martin A. Horstmann. Regulation of the functional interface between nucleotide excision repair and transcription by MITF modulates melanoma growth. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2950. doi:10.1158/1538-7445.AM2014-2950

Accelerated reepithelialization by triterpenes: proof of concept in the healing of surgical skin lesions

The acceleration of wound healing is a major surgical concern. A triterpene extract from birch bark (Betulae cortex) experimentally enhances keratinocyte differentiation in vitro and accelerates wound healing ex vivo. We conducted an open, blind-evaluated, controlled, prospective, randomized (1:1) phase II clinical trial in patients requiring split-thickness skin graft transplantation at two university hospitals in Germany. Donor sites on the upper legs were covered with a moist silicone-coated dressing. Oleogel-S10 ointment containing 10% birch bark extract was randomly applied to the distal or proximal half of the wound, with the other half serving as an intraindividual control, for 14 days after the skin graft surgery. The primary efficacy variable was faster reepithelialization as determined from macrophotographs by independent, blinded experts. Twenty-four patients were randomized and completed the trial. After the 14-day test period, the planned interim analysis revealed a highly significant (p < 0.0001) superiority of Oleogel-S10 in the primary efficacy variable and the trial was terminated early due to ethical concerns. The treatment side was also better reepithelialized and more similar to normal skin after 3 months. In conclusion, Oleogel-S10 significantly accelerated reepithelialization at split-thickness skin graft donor sites. Treatment with Oleogel-S10 was safe and well tolerated.

From a traditional medicinal plant to a rational drug: understanding the clinically proven wound healing efficacy of birch bark extract

BACKGROUND

Birch bark has a long lasting history as a traditional medicinal remedy to accelerate wound healing. Recently, the efficacy of birch bark preparations has also been proven clinically. As active principle pentacyclic triterpenes are generally accepted. Here, we report a comprehensive study on the underlying molecular mechanisms of the wound healing properties of a well-defined birch bark preparation named as TE (triterpene extract) as well as the isolated single triterpenes in human primary keratinocytes and porcine ex-vivo wound healing models.

METHODOLOGY/PRINCIPAL FINDINGS

We show positive wound healing effects of TE and betulin in scratch assay experiments with primary human keratinocytes and in a porcine ex-vivo wound healing model (WHM). Mechanistical studies elucidate that TE and betulin transiently upregulate pro-inflammatory cytokines, chemokines and cyclooxygenase-2 on gene and protein level. For COX-2 and IL-6 this increase of mRNA is due to an mRNA stabilizing effect of TE and betulin, a process in which p38 MAPK and HuR are involved. TE promotes keratinocyte migration, putatively by increasing the formation of actin filopodia, lamellipodia and stress fibers. Detailed analyses show that the TE components betulin, lupeol and erythrodiol exert this effect even in nanomolar concentrations. Targeting the actin cytoskeleton is dependent on the activation of Rho GTPases.

CONCLUSION/SIGNIFICANCE

Our results provide insights to understand the molecular mechanism of the clinically proven wound healing effect of birch bark. TE and betulin address the inflammatory phase of wound healing by transient up-regulation of several pro-inflammatory mediators. Further, they enhance migration of keratinocytes, which is essential in the second phase of wound healing. Our results, together with the clinically proven efficacy, identify birch bark as the first medical plant with a high potential to improve wound healing, a field which urgently needs effective remedies.

Immunohistochemical analyses point to epidermal origin of human Merkel cells

Merkel cells, the neurosecretory cells of skin, are essential for light-touch responses and may probably fulfill additional functions. Whether these cells derive from an epidermal or a neural lineage has been a matter of dispute for a long time. In mice, recent studies have clearly demonstrated an epidermal origin of Merkel cells. Given the differences in Merkel cell distribution between human and murine skin, it is, however, unclear whether the same holds true for human Merkel cells. We therefore attempted to gain insight into the human Merkel cell lineage by co-immunodetection of the Merkel cell marker protein cytokeratin 20 (CK20) with various proteins known to be expressed either in epidermal or in neural stem cells of the skin. Neither Sox10 nor Pax3, both established markers of the neural crest lineage, exhibited any cell co-labeling with CK20. By contrast, β1 integrin, known to be enriched in epidermal stem cells, was found in nearly 70 % of interfollicular epidermal and 25 % of follicular Merkel cells. Moreover, LRIG1, also enriched in epidermal stem cells, displayed significant co-immunolabeling with CK20 as well (approximately 20 % in the interfollicular epidermis and 7 % in the hair follicle, respectively). Further epidermal markers were detected in sporadic Merkel cells. Cells co-expressing CK20 with epidermal markers may represent a transitory state between stem cells and differentiated cells. β1 integrin is probably also synthesized by a large subset of mature Merkel cells. Summarizing, our data suggest that human Merkel cells may originate from epidermal rather than neural progenitors.

Merkel cell polyomavirus detection in Merkel cell cancer tumors in Northern Germany using PCR and protein expression

Merkel cell carcinoma is a highly malignant skin cancer which predominantly occurs in elderly and immunocompromised persons. The identification of the Merkel cell polyomavirus (MCPyV) has inaugurated a new understanding of Merkel cell carcinoma pathogenesis. The frequent detection of the virus in Merkel cell carcinoma tissue (70-90%), its monoclonal integration in the tumor cells and the expression of viral oncogenes highly suggest that MCPyV is causally linked to the pathogenesis of the majority of Merkel cell cancer (MCC) cases. Using qualitative and quantitative PCR together with immunohistochemical staining this study aimed at characterizing the presence of MCPyV sequences and viral early gene expression in a cohort of MCC cases (n = 32) selected in Northern Germany. 40-57% of the cases were identified as MCPyV positive with 40.6% of the cases positive by immunohistochemical staining and 51.6-57.6% positive by PCR. Interestingly, in the majority (64%) of LT-Antigen positive tumors only 25-50% of tumor cells express LT-Antigen. These data are in accord with published studies describing heterogeneity in MCPyV viral loads and suggest that detection of MCPyV in Merkel cell carcinoma by PCR should be undertaken using multiple primer pairs.

TGF-β1 and TNF-α differentially regulate Twist1 mediated resistance towards BRAF/MEK inhibition in melanoma

Resistance to BRAF and MEK inhibition is a common phenomenon in melanoma. Cytokines and transcription factors have been attributed to contribute to the loss of sensitivity towards these inhibitors. Here, we show that transforming growth factor (TGF)-β1 if combined with PLX4032, a BRAF inhibitor, or GSK1120212, a MEK inhibitor, substantially increased cell death in BRAF-mutant melanoma cell lines. This increase was based on the combined regulatory decrease in Twist1, an antiapoptotic protein. Overexpression or silencing of Twist1 attenuated or aggravated induction of apoptosis through PLX4032 or GSK1120212, respectively. Exposure to tumour necrosis factor (TNF)-α, however, led to increased Twist1 levels and oppositional decrease in cell death if exposed to PLX4032 or GSK1120212. This increase in drug resistance again depended on Twist1 levels. Our studies suggest that Twist1 as a common downstream target of multiple signalling cascades plays a crucial role in mediating drug resistance to BRAF- and MEK-targeted molecular inhibitors.

Occludin is involved in adhesion, apoptosis, differentiation and Ca2+-homeostasis of human keratinocytes: implications for tumorigenesis

Tight junction (TJ) proteins are involved in a number of cellular functions, including paracellular barrier formation, cell polarization, differentiation, and proliferation. Altered expression of TJ proteins was reported in various epithelial tumors. Here, we used tissue samples of human cutaneous squamous cell carcinoma (SCC), its precursor tumors, as well as sun-exposed and non-sun-exposed skin as a model system to investigate TJ protein alteration at various stages of tumorigenesis. We identified that a broader localization of zonula occludens protein (ZO)-1 and claudin-4 (Cldn-4) as well as downregulation of Cldn-1 in deeper epidermal layers is a frequent event in all the tumor entities as well as in sun-exposed skin, suggesting that these changes result from chronic UV irradiation. In contrast, SCC could be distinguished from the precursor tumors and sun-exposed skin by a frequent complete loss of occludin (Ocln). To elucidate the impact of down-regulation of Ocln, we performed Ocln siRNA experiments in human keratinocytes and uncovered that Ocln downregulation results in decreased epithelial cell-cell adhesion and reduced susceptibility to apoptosis induction by UVB or TNF-related apoptosis-inducing ligand (TRAIL), cellular characteristics for tumorigenesis. Furthermore, an influence on epidermal differentiation was observed, while there was no change of E-cadherin and vimentin, markers for epithelial-mesenchymal transition. Ocln knock-down altered Ca²⁺-homeostasis which may contribute to alterations of cell-cell adhesion and differentiation. As downregulation of Ocln is also seen in SCC derived from other tissues, as well as in other carcinomas, we suggest this as a common principle in tumor pathogenesis, which may be used as a target for therapeutic intervention.

Barriers and more: functions of tight junction proteins in the skin

Although the existence of tight junction (TJ) structures (or a secondary epidermal barrier) was postulated for a long time, the first description of TJ proteins in the epidermis (occludin, ZO-1, and ZO-2) was only fairly recent. Since then, a wealth of new insights concerning TJs and TJ proteins, including their functional role in the skin, have been gathered. Of special interest is that the epidermis as a multilayered epithelium exhibits a very complex localization pattern of TJ proteins, which results in different compositions of TJ protein complexes in different layers. In this review, we summarize our current knowledge about the role of TJ proteins in the epidermis in barrier function, cell polarity, vesicle trafficking, differentiation, and proliferation. We hypothesize that TJ proteins fulfill TJ structure-dependent and structure-independent functions and that the specific function of a TJ protein may depend on the epidermal layer where it is expressed.

Tight junctions and differentiation--a chicken or the egg question?

Skin barrier function is indispensable to prevent the uncontrolled loss of water and solutes and to protect the body from external assaults. To fulfil this function, keratinocytes undergo a complex pathway of differentiation that terminates in the formation of the stratum corneum. Additionally, tight junctions (TJs), which are cell-cell junctions localized in the stratum granulosum, are involved in the barrier function of the skin. Important biological and clinical roles of TJs are strongly suggested by altered TJ protein levels and distribution in skin diseases like psoriasis, ichthyosis and atopic dermatitis. Because these skin diseases show alterations in differentiation and TJs, it was suggested that changes in TJs might simply be a consequence of altered differentiation. However, in this viewpoint, we like to argue that the situation is not as simple and depends on the specific microenvironment. We discuss three hypotheses regarding the interplay between TJs/TJ proteins and differentiation: (1) TJs/TJ proteins are influenced by differentiation, (2) differentiation is influenced by TJs/TJ proteins, and (3) TJs/TJ proteins and differentiation are independent of each other. In addition, the concept is introduced that both processes are going on at the same time, which means that while one specific TJ protein/barrier component might be influenced by differentiation, the other may influence differentiation.

Prevalidation of a human cornea construct as an alternative to animal corneas for in vitro drug absorption studies

The use of ophthalmic drugs has increased consistently over the past few decades. Currently, most research is conducted using in vivo and ex vivo animal experiments; however, they have many disadvantages, including ethical concerns, high costs, the questionable extension of animal results to humans, and poor standardization. Although several cell culture-based cornea models have been developed, none have been validated and accepted for general use. In this study, a standardized, three-dimensional model of the human cornea (Hemicornea, HC) based on immortalized human corneal cells and cultivated in serum-free conditions was developed for drug absorption studies and prevalidated using compounds with a wide range of molecular characteristics (sodium fluorescein, rhodamine B, fluorescein isothiocyanate-labeled dextran, aciclovir, bimatoprost, dexamethasone, and timolol maleate). The HC model was independently cultured in three different laboratories, and the intralaboratory and interlaboratory reproducibility was analyzed and compared with the rabbit cornea. This analysis showed that the HC has a barrier in the same range as excised animal corneas, although with a higher reproducibility and lower variability. Because of the demonstrated transferability, the HC represents a promising in vitro alternative to the use of ex vivo tissue and offers a well-defined and standardized system for drug absorption studies.

Filaggrin genotype in ichthyosis vulgaris predicts abnormalities in epidermal structure and function

Although it is widely accepted that filaggrin (FLG) deficiency contributes to an abnormal barrier function in ichthyosis vulgaris and atopic dermatitis, the pathomechanism of how FLG deficiency provokes a barrier abnormality in humans is unknown. We report here that the presence of FLG mutations in Caucasians predicts dose-dependent alterations in epidermal permeability barrier function. Although FLG is an intracellular protein, the barrier abnormality occurred solely via a paracellular route in affected stratum corneum. Abnormal barrier function correlated with alterations in keratin filament organization (perinuclear retraction), impaired loading of lamellar body contents, followed by nonuniform extracellular distribution of secreted organelle contents, and abnormalities in lamellar bilayer architecture. In addition, we observed reductions in corneodesmosome density and tight junction protein expression. Thus, FLG deficiency provokes alterations in keratinocyte architecture that influence epidermal functions localizing to the extracellular matrix. These results clarify how FLG mutations impair epidermal permeability barrier function.

Connexin 43 mimetic peptide Gap27 reveals potential differences in the role of Cx43 in wound repair between diabetic and non-diabetic cells

During early wound healing (WH) events Connexin 43 (Cx43) is down-regulated at wound margins. In chronic wound margins, including diabetic wounds, Cx43 expression is enhanced suggesting that down-regulation is important for WH. We previously reported that the Cx43 mimetic peptide Gap27 blocks Cx43 mediated intercellular communication and promotes skin cell migration of infant cells in vitro. In the present work we further investigated the molecular mechanism of Gap27 action and its therapeutic potential to improve WH in skin tissue and diabetic and non-diabetic cells. Ex vivo skin, organotypic models and human keratinocytes/fibroblasts of young and old donors and of diabetic and non-diabetic origin were used to assess the impact of Gap27 on cell migration, proliferation, Cx43 expression, localization, phosphorylation and hemichannel function. Exposure of ex vivo WH models to Gap27 decreased dye spread, accelerated WH and elevated cell proliferation. In non-diabetic cell cultures Gap27 decreased dye uptake through Cx hemichannels and after scratch wounding cells showed enhanced migration and proliferation. Cells of diabetic origin were less susceptible to Gap27 during early passages. In late passages these cells showed responses comparable to non-diabetic cells. The cause of the discrepancy between diabetic and non-diabetic cells correlated with decreased Cx hemichannel activity in diabetic cells but excluded differences in Cx43 expression, localization and Ser368-phosphorylation. These data emphasize the importance of Cx43 in WH and support the concept that Gap27 could be a beneficial therapeutic to accelerate normal WH. However, its use in diabetic WH may be restricted and our results highlight differences in the role of Cx43 in skin cells of different origin.

Homo- and heterotypic cell-cell contacts in Merkel cells and Merkel cell carcinomas: heterogeneity and indications for cadherin switching

AIMS

Merkel cell carcinomas (MCCs) are rare but aggressive tumours associated recently with Merkel cell polyomavirus (MCV). As development and progression of several types of carcinomas can be promoted by changes in cell adhesion proteins, the aim of this study was to examine homo- and heterotypic cell contacts of Merkel cells and MCCs.

METHODS AND RESULTS

Merkel cells of healthy glabrous epidermis and 52 MCCs were analysed by double-label immunostaining, immunofluorescence and confocal microscopy. Merkel cells were connected to keratinocytes by E- and P-cadherin, desmoglein 2 and desmocollin 2. In contrast, the vast majority of MCCs (90%) contained N-cadherin, but only 67% and 65% contained E- and P-cadherin, respectively. Interestingly, P-cadherin was absent significantly more frequently in lymph node metastases than in primary tumours and by trend in more advanced clinical stages. Moreover, major subsets of MCCs synthesized desmoglein 2 and, surprisingly, tight junction proteins. No significant differences were observed upon stratification for MCV DNA, detected in 84% of tumours by real-time polymerase chain reaction.

CONCLUSIONS

Assuming that MCCs originate from Merkel cells, our data indicate a switch from E- and P-cadherin to N-cadherin during tumorigenesis. Whether the unexpected heterogeneity of junctional proteins can be exploited for prognostic and therapeutic purposes will need to be examined.

The connexin mimetic peptide Gap27 increases human dermal fibroblast migration in hyperglycemic and hyperinsulinemic conditions in vitro

Significant increases in skin wound healing rates occur by reducing connexin-mediated communication (CMC). Gap27, a connexin (Cx) mimetic peptide targeted to the second extracellular loop of Cx43, which inhibits CMC, increases migration of human keratinocytes and dermal fibroblasts. To examine the efficacy of Gap27 in a hyperglycemic and hyperinsulinemic in vitro environment, cell migration, gap junction, and Cx hemichannel functionality and cell-substrate adhesion assays were performed on human dermal fibroblasts and diabetic fibroblast and keratinocytes. To investigate fibroblast genes involved in these processes, extra-cellular matrix (ECM) and adhesion gene expression was determined with a PCR array. Gap27 increased fibroblast migration in both euglycemia/euinsulinemia and hyperglycemia/hyperinsulinemia, and influenced migration in diabetic keratinocytes. Hyperglycemia/hyperinsulinemia reduced gap junction coupling in fibroblasts and Gap27 reduced CMC and cell adhesion to substrata in fibroblasts cultured in high glucose. Migrating dermal fibroblast ECM and cell adhesion genes were found to be differentially regulated by Gap27 in euglycemia and hyperglycemia. The PCR array showed that Gap27 upregulated 34 genes and downregulated 1 gene in euglycemic migrating fibroblasts. By contrast in hyperglycemia, Gap27 upregulated 1 gene and downregulated 9 genes. In euglycemic conditions, Gap27 induced upregulation of genes associated with ECM remodeling, whereas in hyperglycemia, ECM component genes were downregulated by Gap27. Thus, Gap27 improves cell migration during scrape-wound repair in hyperglycemia/hyperinsulinemia conditions in vitro, although migration of diabetic cells is less influenced. Our results suggest that this increase in motility may occur by decreasing gap junction and hemichannel activity and altering gene expression in the adhesion and ECM pathway.

Somatostatin regulates tight junction function and composition in human keratinocytes

Somatostatin (SST) is a regulatory peptide hormone that acts through five different G protein-coupled receptors (SSTR1-5). Whereas expression of all five SSTR subtypes in epidermis has been shown, the biological relevance of the SST/SSTR system in the skin is completely unknown. We show here that SST is expressed in human skin and is present in a subset of Merkel cells and dendritic cells as well as in keratinocytes. We focused further on the somatostatin receptor subtype 3 (SSTR3) and its interacting protein MUPP1, as both were found to be localized at cellular junctions in epidermal keratinocytes. MUPP1 is a component of tight junctions (TJs); these cell-cell junctions contribute to barrier function of the paracellular pathway in cultured keratinocytes. We provide evidence that SSTR3 and MUPP1 interact in primary cultured human keratinocytes at high Ca(2+) conditions. Interestingly, SST, presumably via SSTR3/MUPP1, regulates TJ permeability in cultured keratinocytes. During long-term treatment of human keratinocytes, SST also affects the expression of distinct TJ proteins such as claudin-4. Our data are the first example of a peptide hormone regulating TJ functionality and composition in human keratinocytes, suggesting that control via peptide hormones provides the possibility to regulate the TJ barrier characteristics of the skin.

Caffeine improves barrier function in male skin

The influence of androgens, especially testosterone and its effector dihydrotestosterone, results in a constitutive disadvantage for male skin, e.g. reduced viability of hair at the scalp and reduced epidermal permeability barrier repair capacity. Dihydrotestosterone can act, among others, as an adenyl cyclase inhibitor. Caffeine on the other hand is an inexpensive and (in regular doses) harmless substance used in various cosmetic products, which can act as a phosphodiesterase inhibitor. To prove the hypothesis that caffeine as a phosphodiesterase inhibitor is able to override testosterone-induced effects on barrier function, we performed a double-blind placebo controlled study with healthy volunteers. In this study, 0.5% caffeine in a hydroxyethylcellulose gel preparation (HEC) was applied on one forearm, HEC without caffeine on the other forearm of male and female volunteers for 7 days and transepidermal water loss (TEWL) was measured before and at the end of the treatment period. Basal TEWL did not differ significantly between male and female subjects but the application of caffeine significantly reduced TEWL in male skin compared with female skin. We conclude that caffeine is beneficial for barrier function in male skin.