A Predictive Self-Organizing Multicellular Computational Model of Infant Skin Permeability to Topically Applied Substances.

Computational models of skin permeability are typically based on assumptions of fixed geometry and homogeneity of the whole epidermis or of epidermal strata and are often limited to adult skin. Infant skin differs quantitatively from that of the adult in its structure and its functional properties, including its barrier function to permeation. To address this problem, we developed a self-organizing multicellular epidermis model of barrier formation with realistic cell morphology. By modulating the parameters relating to cell turnover reflecting those in adult or infant epidermis, we were able to generate accordingly two distinct models. Emerging properties of these models reflect the corresponding experimentally measured values of epidermal and stratum corneum thickness. Diffusion of an externally applied substance (e.g., caffeine) was simulated by a molecular exchange between the model agents, defined by the individual cells and their surrounding extracellular space. By adjusting the surface concentration and the intercellular exchange rate, the model can recapitulate experimental permeability data after topical exposure. By applying these parameters to an infant model, we were able to predict the caffeine concentration profile in infant skin, closely matching experimental results. This work paves the way for a better understanding of skin physiology and function during the first years of life.

Topical stabilized retinol treatment induces the expression of HAS genes and HA production in human skin in vitro and in vivo.

Skin Aging manifests primarily with wrinkles, dyspigmentations, texture changes, and loss of elasticity. During the skin aging process, there is a loss of moisture and elasticity in skin resulting in loss of firmness finally leading to skin sagging. The key molecule involved in skin moisture is hyaluronic acid (HA), which has a significant water-binding capacity. HA levels in skin decline with age resulting in decrease in skin moisture, which may contribute to loss of firmness. Clinical trials have shown that topically applied ROL effectively reduces wrinkles and helps retain youthful appearance. In the current study, ROL was shown to induce HA production and stimulates the gene expression of all three forms of hyaluronic acid synthases (HAS) in normal human epidermal keratinocytes monolayer cultures. Moreover, in human skin equivalent tissues and in human skin explants, topical treatment of tissues with a stabilized-ROL formulation significantly induced the gene expression of HAS mRNA concomitant with an increased HA production. Finally, in a vehicle-controlled human clinical study, histochemical analysis confirmed increased HA accumulation in the epidermis in ROL-treated human skin as compared to vehicle. These results show that ROL increases skin expression of HA, a significant contributing factor responsible for wrinkle formation and skin moisture, which decrease during aging. Taken together with the activity to increase collagen, elastin, and cell proliferation, these studies establish that retinol provides multi-functional activity for photodamaged skin.

Colloidal Oatmeal (Avena Sativa) Improves Skin Barrier Through Multi-Therapy Activity.

Oats (Avena sativa) are a centuries-old topical treatment for a variety of skin barrier conditions, including dry skin, skin rashes, and eczema; however, few studies have investigated the actual mechanism of action for the skin barrier strengthening activity of colloidal oatmeal. Four extracts of colloidal oatmeal were prepared with various solvents and tested in vitro for skin barrier related gene expression and activity. Extracts of colloidal oatmeal were found to induce the expression of genes related to epidermal differentiation, tight junctions and lipid regulation in skin, and provide pH-buffering capacity. Colloidal oatmeal boosted the expression of multiple target genes related to skin barrier, and resulted in recovery of barrier damage in an in vitro model of atopic dermatitis. In addition, an investigator-blinded study was performed with 50 healthy female subjects who exhibited bilateral moderate to severe dry skin on their lower legs. Subjects were treated with a colloidal oatmeal skin protectant lotion. Clinically, the colloidal oatmeal lotion showed significant clinical improvements in skin dryness, moisturization, and barrier. Taken together, these results demonstrate that colloidal oatmeal can provide clinically effective benefits for dry and compromised skin by strengthening skin barrier.

J Drugs Dermatol. 2016;15(6):684-690.

Anti-inflammatory activities of colloidal oatmeal (Avena sativa) contribute to the effectiveness of oats in treatment of itch associated with dry, irritated skin.

BACKGROUND: Oat (Avena sativa) in colloidal form is a centuries-old topical treatment for a variety of skin conditions, including skin rashes, erythema, burns, itch, and eczema; however, few studies have investigated the exact mechanism of action for the anti-inflammatory activity of colloidal oatmeal. METHODS: Four extracts of colloidal oatmeal were made with various solvents and tested in anti-inflammatory and antioxidant assays. In addition, an investigator blind study was performed with twenty-nine healthy female subjects who exhibited bilateral mild to moderate itch with moderate to severe dry skin on their lower legs. Subjects were treated with a colloidal oatmeal skin protectant lotion. RESULTS: Extracts of colloidal oatmeal diminished pro-inflammatory cytokines in vitro and the colloidal oat skin protectant lotion showed significant clinical improvements in skin dryness, scaling, roughness, and itch intensity. CONCLUSIONS: These results demonstrate that colloidal oat extracts exhibit direct anti-oxidant and anti-inflammatory activities, which may provide the mechanisms for observed dermatological benefits while using the colloidal oatmeal skin protectant lotion.

A purified feverfew extract protects from oxidative damage by inducing DNA repair in skin cells via a PI3-kinase-dependent Nrf2/ARE pathway.

BACKGROUND: Environmental factors such as solar ultraviolet (UV) radiation and other external aggressors provide an oxidative challenge that is detrimental to skin health. The levels of endogenous antioxidants decrease with age, thus resulting in less protection and a greater potential for skin damage. The NF-E2-related factor-2 (Nrf2) - antioxidant response element (ARE) pathway is a primary defense mechanism against oxidative stress, and induces the expression of antioxidant, detoxification and repair genes. Activation of ARE-Nrf2 can help restore oxidative homeostasis of the skin and play a role in inflammatory response and DNA repair mechanisms. OBJECTIVE: To evaluate the role of a purified parthenolide-depleted Feverfew (PD-Feverfew) extract on the ARE-Nrf2 pathway and DNA repair in skin cells. METHODS: These studies were undertaken in primary human keratinocytes or KB cells using Luciferase Promoter assay, siRNA transfection studies, Western blot analyses, Immunofluorescence microscopy, comet assay and quantitative real-time PCR. RESULTS: PD-Feverfew was found to induce Nrf2 nuclear translocation and to increase ARE activity in a dose dependent manner. Furthermore, knockdown of Nrf2 resulted in suppression of PD-Feverfew-induced ARE activity. PD-Feverfew was also found to induce phosphorylation of Akt, a kinase downstream of PI3K. Inhibition of PI3K via pre-treatment with the selective pharmacological inhibitor, LY294002, abolished PD-Feverfew-induced Nrf2/ARE activation. PD-Feverfew also reduced UV-induced DNA damage in a PI3K and Nrf2-dependent manner. CONCLUSIONS: Therefore, by increasing endogenous defense mechanisms and aid in DNA repair of damaged skin cells via activation of a PI3K-dependent Nrf2/ARE pathway, PD-Feverfew may help protect the skin from numerous environmental aggressors.

Irradiation of skin with visible light induces reactive oxygen species and matrix-degrading enzymes.

Daily skin exposure to solar radiation causes cells to produce reactive oxygen species (ROS), which are a primary factor in skin damage. Although the contribution of the UV component to skin damage has been established, few studies have examined the effects of non-UV solar radiation on skin physiology. Solar radiation comprises <10% of UV, and thus the purpose of this study was to examine the physiological response of skin to visible light (400-700 nm). Irradiation of human skin equivalents with visible light induced production of ROS, proinflammatory cytokines, and matrix metalloproteinase (MMP)-1 expression. Commercially available sunscreens were found to have minimal effects on reducing visible light-induced ROS, suggesting that UVA/UVB sunscreens do not protect the skin from visible light-induced responses. Using clinical models to assess the generation of free radicals from oxidative stress, higher levels of free radical activity were found after visible light exposure. Pretreatment with a photostable UVA/UVB sunscreen containing an antioxidant combination significantly reduced the production of ROS, cytokines, and MMP expression in vitro, and decreased oxidative stress in human subjects after visible light irradiation. Taken together, these findings suggest that other portions of the solar spectrum aside from UV, particularly visible light, may also contribute to signs of premature photoaging in skin.

Galvanic zinc-copper microparticles produce electrical stimulation that reduces the inflammatory and immune responses in skin.

The human body has its own innate electrical system that regulates the body's functions via communications among organs through the well-known neural system. While the effect of low-level electrical stimulation on wound repair has been reported, few studies have examined the effect of electric potential on non-wounded, intact skin. A galvanic couple comprised of elemental zinc and copper was used to determine the effects of low-level electrical stimulation on intact skin physiology using a Dermacorder device. Zn-Cu induced the electrical potential recorded on intact skin, enhanced H(2)O(2) production and activated p38 MAPK and Hsp27 in primary keratinocytes. Treatment with Zn-Cu was also found to reduce pro-inflammatory cytokines, such as IL-1α, IL-2, NO and TNF-α in multiple cell types after stimulation with PHA or Propionibacterium acnes bacteria. The Zn-Cu complex led to a dose-dependent inhibition of TNF-α-induced NF-κB levels in keratinocytes as measured by a dual-luciferase promoter assay, and prevented p65 translocation to the nucleus observed via immunofluorescence. Suppression of NF-κB activity via crosstalk with p38 MAPK might be one of the potential pathways by which Zn-Cu exerted its inflammatory effects. Topical application of Zn-Cu successfully mitigated TPA-induced dermatitis and oxazolone-induced hypersensitivity in mice models of ear edema. Anti-inflammatory activity induced by the Zn-Cu galvanic couple appears to be mediated, at least in part, by production of low level of hydrogen peroxide since this activity is reversed by the addition of Catalase enzyme. Collectively, these results show that a galvanic couple containing Zn-Cu strongly reduces the inflammatory and immune responses in intact skin, providing evidence for the role of electric stimulation in non-wounded skin.

The discovery of a Werner Helicase Interacting Protein (WHIP) association with the nuclear pore complex.

The gateway for molecular trafficking between the cytoplasm and the nucleus is the Nuclear Pore Complex (NPC). Through mass spectral analysis of the isolated Nuclear Pore Nup107-160 subcomplex, we discovered an in vivo interaction with Werner's Helicase Interacting Protein 1, (WRNIP1 or WHIP). WHIP was originally identified as a binding partner of Werner protein (WRN), which functions to maintain genome stability and is responsible for the progeria disease, Werner syndrome. We established the reciprocal isolation of Nup107 by alpha-WHIP. WHIP was found in purified Nuclear Envelope (NE) fractions treated with DNase/RNase/Heparin. We demonstrated by immunofluorescence microscopy that WHIP is located at the nuclear rim as well as punctate regions in the nuclear matrix. Ultimately, synchronized cells show a dynamic association between WHIP and the Nup107-160 subcomplex through the cell cycle without an interaction with WRN. We thus identify WHIP as a partner/component of the NE/NPC and set forth to investigate a role for the protein positioned at the NPC.

Induction of prostaglandin D2 through the p38 MAPK pathway is responsible for the antipruritic activity of sertaconazole nitrate.

Prostaglandin D(2) (PGD(2)) is known to have antipruritic activity by suppressing histamine release. However, agents that can topically induce PGD(2) for itch relief are not well established. The antimycotic sertaconazole nitrate (STZ) has been shown to exhibit anti-itch properties; however, the mechanism for this activity has not been elucidated. STZ mitigated degranulation of RBL-2H3 (rat basophilic leukemia) mast cells induced by compound 48/80, a pruritogenic agent known to promote the release of histamine, and augmented PGD(2) production in mast cells and macrophages. Addition of exogenous PGD(2) abrogated compound 48/80-induced degranulation by acting through the prostanoid D receptor 1 (DP1). STZ induced p38 mitogen-activated protein kinase (MAPK) phosphorylation in mast cells and a pharmacological inhibitor of p38 MAPK, SB203580, resulted in the attenuation of PGD(2) levels. Finally, in a murine model of pruritus, the scratching behavior induced by compound 48/80 was mitigated by topical application of STZ. This effect was reversed by the addition of the cyclooxygenase inhibitor, ibuprofen, or a DP1 receptor antagonist (MK0524). Collectively, these results suggest that STZ mediates its anti-itch effects by boosting the antipruritic agent, PGD(2), by the activation of the p38-MAPK pathway. This is the first report to demonstrate a promising approach to topically induce PGD(2) for improving pruritus.

Regulation of epithelial ion channels by Rab GTPases.

Epithelial ion channels are crucial to many of life's processes and disruption of their functions can lead to several disorders. Cystic fibrosis, an autosomal recessive disorder, is caused by defects in the biosynthesis or function of the CFTR chloride channel. Similarly, mutations in certain ENaC genes leading to increased or reduced channel activity cause diseases such as Liddle's syndrome or PHA. In order for ion channel proteins to be functional they need to be expressed on the plasma membrane. Thus, molecules that modulate the trafficking of ion channels to and from the membrane are of utmost significance. Among the numerous factors that regulate their functioning is a family of small GTPases known as Rab proteins. While Rabs have always played a pivotal role in membrane trafficking, their diversity of functions and plethora of interacting partners have lately been brought to light. Recent studies reveal that multiple Rab isoforms physically interact with and/or modulate the activity of several ion channels. Rab proteins have the ability to serve as molecular switches and many of the ion channels are regulated differentially by the GTP- or GDP-bound Rab isoforms. This review examines the role of Rab GTPases in the trafficking of ion channels, including CFTR, ENaC, TRPV5/6, and aquaporins, based on recent evidence.

Rab27a negatively regulates CFTR chloride channel function in colonic epithelia: involvement of the effector proteins in the regulatory mechanism.

Cystic fibrosis, an autosomal recessive disorder, is caused by the disruption of biosynthesis or function of CFTR. CFTR regulatory mechanisms include channel transport to plasma membrane and protein-protein interactions. Rab proteins are small GTPases involved in vesicle transport, docking, and fusion. The colorectal epithelial HT-29 cells natively express CFTR and respond to cAMP with an increase in CFTR-mediated currents. DPC-inhibited currents could be completely eliminated with CFTR-specific SiRNA. Over-expression of Rab27a inhibited, while isoform specific SiRNA and Rab27a antibody stimulated CFTR-mediated currents in HT-29 cells. CFTR activity is inhibited both by Rab27a (Q78L) (constitutive active GTP-bound form of Rab27a) and Rab27a (T23N) (constitutive negative form that mimics the GDP-bound form). Rab27a mediated effects could be reversed by Rab27a-binding proteins, the synaptotagmin-like protein (SLP-5) and Munc13-4 accessory protein (a putative priming factor for exocytosis). The SLP reversal of Rab27a effect was restricted to C2A/C2B domains while the SHD motif imparted little more inhibition. The CFTR-mediated currents remain unaffected by Rab3 though SLP-5 appears to weakly bind it. The immunoprecipitation experiments suggest protein-protein interactions between Rab27a and CFTR. Rab27a appears to impair CFTR appearance at the cell surface by trapping CFTR in the intracellular compartments. Munc13-4 and SLP-5, on the other hand, limit Rab27a availability to CFTR, thus minimizing its effect on channel function. These observations decisively prove that Rab27a is involved in CFTR channel regulation through protein-protein interactions involving Munc13-4 and SLP-5 effector proteins, and thus could be a potential target for cystic fibrosis therapy.

Rab4 GTP/GDP modulates amiloride-sensitive sodium channel (ENaC) function in colonic epithelia.

The sodium-selective amiloride-sensitive epithelial sodium channel (ENaC) mediates electrogenic sodium re-absorption in tight epithelia. ENaC expression at the plasma membrane requires regulated transport, processing, and macromolecular assembly of subunit proteins in a defined and highly compartmentalized manner. Ras-related Rab GTPases monitor these processes in a highly regulated sequence of events. In order to evaluate the role of Rab proteins in ENaC function, Rab4 wild-type (WT), the GTPase-deficient mutant Rab4Q67L, and the dominant negative GDP-locked mutant Rab4S22N were over-expressed in the colon cancer cell line, HT-29 and amiloride-sensitive currents were recorded. Rab4 over-expression inhibited amiloride-sensitive currents. The effect was reversed by introducing Rab4-neutralizing antibody and Rab4 specific SiRNA. The GDP-locked Rab4 mutant inhibited, while GTPase-deficient mutant moderately stimulated amiloride-sensitive currents. Active status of Rab4 was confirmed by GTP overlay assay, while its expression was verified by Western blotting. Immunoprecipitation and pull-down assay suggest protein-protein interaction between Rab4 and ENaC. In addition, the functional modulation coincides with concomitant changes in ENaC expression at the cell surface and in intracellular pool. We propose that Rab4 is a critical element that regulates ENaC function by mechanisms that include GTP-GDP status, recycling, and expression level. Our observations imply that channel expression in apical membranes of epithelial cell system incorporates RabGTPase as an essential determinant of channel function and adds an exciting paradigm to ENaC therapeutics.

Rab4GTPase modulates CFTR function by impairing channel expression at plasma membrane.

Cystic fibrosis (CF), an autosomal recessive disorder, is caused by the disruption of biosynthesis or the function of a membrane cAMP-activated chloride channel, CFTR. CFTR regulatory mechanisms include recruitment of channel proteins to the cell surface from intracellular pools and by protein-protein interactions. Rab proteins are small GTPases involved in regulated trafficking controlling vesicle docking and fusion. Rab4 controls recycling events from endosome to the plasma membrane, fusion, and degradation. The colorectal cell line HT-29 natively expresses CFTR and responds to cAMP stimulation with an increase in CFTR-mediated currents. Rab4 over-expression in HT-29 cells inhibits both basal and cAMP-stimulated CFTR-mediated currents. GTPase-deficient Rab4Q67L and GDP locked Rab4S22N both inhibit channel activity, which appears characteristically different. Active status of Rab4 was confirmed by GTP overlay assay, while its expression was verified by Western blotting. The pull-down and immunoprecipitation experiments suggest that Rab4 physically interacts with CFTR through protein-protein interaction. Biotinylation with cell impermeant NHS-Sulfo-SS-Biotin implies that Rab4 impairs CFTR expression at cell surface. The enhanced cytosolic CFTR indicates that Rab4 expression restrains CFTR appearance at the cell membrane. The study suggests that Rab4 regulates the channel through multiple mechanisms that include protein-protein interaction, GTP/GDP exchange, and channel protein trafficking. We propose that Rab4 is a dynamic molecule with a significant role in CFTR function.

Distinct domain-dependent effect of syntaxin1A on amiloride-sensitive sodium channel (ENaC) currents in HT-29 colonic epithelial cells.

The amiloride-sensitive epithelial sodium channel (ENaC), a plasma membrane protein mediates sodium reabsorption in epithelial tissues, including the distal nephron and colon. Syntaxin1A, a trafficking protein of the t-SNARE family has been reported to inhibit ENaC in the Xenopus oocyte expression and artificial lipid bilayer systems. The present report describes the regulation of the epithelial sodium channel by syntaxin1A in a human cell line that is physiologically relevant as it expresses both components and also responds to aldosterone stimulation. In order to evaluate the physiological significance of syntaxin1A interaction with natively expressed ENaC, we over-expressed HT-29 with syntaxin1A constructs comprising various motifs. Unexpectedly, we observed the augmentation of amiloride-sensitive currents with wild-type syntaxin1A full-length construct (1-288) in this cell line. Both gammaENaC and neutralizing syntaxin1A antibodies blocked native expression as amiloride-sensitive sodium currents were inhibited while munc18-1 antibody reversed this effect. The coiled-coiled domain H3 (194-266) of syntaxin1A inhibited, however the inclusion of the transmembrane domain to this motif (194-288) augmented amiloride sensitive currents. More so, data suggest that ENaC interacts with multiple syntaxin1A domains, which differentially regulate channel function. This functional modulation is the consequence of the physical enhancement of ENaC at the cell surface in cells over-expressed with syntaxin(s). Our data further suggest that syntaxin1A up-regulates ENaC function by multiple mechanisms that include PKA, PLC, PI3 and MAP Kinase (p42/44) signaling systems. We propose that syntaxin1A possesses distinct inhibitory and stimulatory domains that interact with ENaC subunits, which critically determines the overall ENaC functionality/regulation under distinct physiological conditions.

Rab proteins regulate epithelial sodium channel activity in colonic epithelial HT-29 cells.

ENaC, the sodium-selective amiloride-sensitive epithelial channel, mediates electrogenic sodium re-absorption in tight epithelia and is deeply associated with human hypertension. The ENaC expression at plasma membrane requires the regulated transport, processing, and macromolecular assembly in a defined and highly compartmentalized manner. Ras-related Rab GTPases regulate intracellular trafficking during endocytosis, regulated exocytosis, and secretion. To evaluate the role of these proteins in regulating amiloride-sensitive sodium channel activity, multiple Rab isoforms 3, 5, 6, and Rab27a were expressed in HT-29 cells. Rab3 and Rab27a inhibited ENaC currents, while the expression of other Rab isoforms failed to elicit any statistically significant effect on amiloride-sensitive currents. The immunoprecipitation experiments suggest protein-protein interaction of Rab3 and Rab27a with epithelial sodium channel. Biotinylation studies revealed that modulation of ENaC function is due to the reduced apical expression of channel proteins. Study also indicates that Rabs do not appear to affect the steady-state level of total cellular ENaC. Alternatively, introduction of isoform-specific small inhibitory RNA (SiRNA) reversed the Rab-dependent inhibition of amiloride-sensitive currents. These observations point to the involvement of multiple Rab proteins in ENaC transport through intracellular routes like exocytosis, recycling from ER to plasma membrane or degradation and thus serve as potential target for human hypertension.