Epidermal nerve fibers modulate keratinocyte growth via neuropeptide signaling in an innervated skin model

Atopic eczema is a chronic inflammatory skin disease characterized by cutaneous nerve fiber sprouting and epidermal hyperplasia, pointing to an involvement of the peripheral nervous system in cutaneous homeostasis. However, the interaction of sensory neurons and skin cells is poorly understood. Using an innervated skin model, we investigated the influence of sensory neurons on epidermal morphogenesis. Neurons induced the proliferation of keratinocytes, resulting in an increase in the epidermal thickness. Inhibition of calcitonin gene-related peptide (CGRP), but not substance P (SP) signaling, reversed this effect. Human CGRP enhanced keratinocyte proliferation and epidermal thickness in skin models, demonstrating a key role of CGRP in modulating epidermal morphogenesis, whereas SP had only a moderate effect. Innervated skin models composed of atopic skin cells showed increased neurite outgrowth, accompanied by elevated CGRP release. As atopic keratinocytes were sensitized to CGRP owing to higher expression levels of the CGRP receptor components, receptor activity-modifying protein 1 (RAMP1) and receptor component protein (RCP), atopic innervated skin models displayed a thicker epidermis than did healthy controls. We conclude that neural CGRP controls local keratinocyte growth. Our results show that the crosstalk of the cutaneous peripheral nervous system and skin cells significantly influences epidermal morphogenesis and homeostasis in healthy and atopic skin.

GABA blocks pathological but not acute TRPV1 pain signals

Sensitization of the capsaicin receptor TRPV1 is central to the initiation of pathological forms of pain, and multiple signaling cascades are known to enhance TRPV1 activity under inflammatory conditions. How might detrimental escalation of TRPV1 activity be counteracted? Using a genetic-proteomic approach, we identify the GABAB1 receptor subunit as bona fide inhibitor of TRPV1 sensitization in the context of diverse inflammatory settings. We find that the endogenous GABAB agonist, GABA, is released from nociceptive nerve terminals, suggesting an autocrine feedback mechanism limiting TRPV1 sensitization. The effect of GABAB on TRPV1 is independent of canonical G protein signaling and rather relies on close juxtaposition of the GABAB1 receptor subunit and TRPV1. Activating the GABAB1 receptor subunit does not attenuate normal functioning of the capsaicin receptor but exclusively reverts its sensitized state. Thus, harnessing this mechanism for anti-pain therapy may prevent adverse effects associated with currently available TRPV1 blockers.

Licochalcone A activates Nrf2 in vitro and contributes to licorice extract-induced lowered cutaneous oxidative stress in vivo

The retrochalcone licochalcone A (LicA) has previously been shown to possess antimicrobial and anti-inflammatory properties. In this study, we focused on pathways responsible for the antioxidative properties of LicA. In vitro, LicA protected from oxidative stress mediated by reactive oxygen species (ROS) by activating the expression of cytoprotective phase II enzymes. LicA induced nuclear translocation of NF-E2-related factor 2 (Nrf2) in primary human fibroblasts and elevated the expression of the cytoprotective and anti-inflammatory enzymes heme oxygenase 1 and glutamate-cysteine ligase modifier subunit. LicA-treated cells displayed a higher ratio of reduced to oxidized glutathione and decreased concentrations of ROS in UVA-irradiated human dermal fibroblasts, as well as in activated neutrophils. In vivo, ultraweak photon emission analysis of skin treated with LicA-rich licorice extract revealed a significantly lowered UVA-induced luminescence, indicative for a decrease in oxidative processes. We conclude from these data that topical application of licorice extract is a promising approach to induce Nrf2-dependent cytoprotection in human skin.

Thiamidol containing treatment regimens in facial hyperpigmentation: An international multi-centre approach consisting of a double-blind, controlled, split-face study and of an open-label, real-world study

Objective

Tyrosinase is the rate‐limiting enzyme in melanogenesis. Thiamidol is the most potent inhibitor of human tyrosinase out of 50 000 tested compounds. In clinical studies, it was shown to improve facial hyperpigmentation, post‐inflammatory hyperpigmentation and age spots significantly. To identify the optimal number of daily Thiamidol applications, we conducted a split‐face study comparing the efficacy and tolerability of four‐times with two‐times daily application. Subsequently, we evaluated the efficacy and tolerability of a typical face care regimen containing Thiamidol in a real‐world study.

Methods

The split‐face study was double‐blind, randomized, controlled, including two Thiamidol containing products (serum and day care SPF 30). The serum was applied twice daily on one half of the face and the day care SPF30 twice‐daily on the whole face. The real‐world study was open‐label, observational, including three Thiamidol containing products (day care SPF 30 in the morning, serum and night care in the evening). In both studies, subjects with mild‐to‐moderate facial hyperpigmentation applied the products over 12 weeks. Assessments included clinical and subjective grading of hyperpigmentation, skin condition, hemi‐/modified MASI, chromameter and clinical photography.

Results

In the split‐face study (n = 34), hyperpigmentation, skin roughness and hMASI improved all significantly (P < 0.001) versus baseline, with first visible results after two weeks of twice‐daily application. The four‐times daily application led to significant improvement versus the two‐times daily application. In the real‐world study (n = 83), all evaluated parameters, including skin condition and chromametry (n = 30), improved significantly (P < 0.001) in comparison with baseline and the corresponding preceding visits. The subjects judged the cosmetic properties of the products positively. In both studies, the products were well tolerated.

Conclusion

Four‐times daily Thiamidol improves facial hyperpigmentation significantly more than two‐times daily and is well tolerated by the subjects. The real‐world study with a typical face care regimen containing Thiamidol shows improvement of facial hyperpigmentation and confirms tolerability. Furthermore, the data provide evidence for the suitability of this three‐product Thiamidol regimen for day‐to‐day life.

Effective reduction of post-inflammatory hyperpigmentation with the tyrosinase inhibitor isobutylamido-thiazolyl-resorcinol (Thiamidol)

Objective

Post‐inflammatory hyperpigmentation (PIH) is a major cosmetic concern especially in individuals with darker skin complexion. Unfortunately, treatment with anti‐inflammatory ingredients alone does not prevent the development of hyperpigmented spots. Recently, isobutylamido‐thiazolyl‐resorcinol (Thiamidol) was described as a very potent inhibitor of human tyrosinase. The objective of this research was to investigate the potential of this compound to prevent PIH induced by epidermal wounding (suction blister) and related to acne.

Methods

Suction blister‐induced PIH was treated with a formulation containing Thiamidol or a vehicle for 3 months, and the changes in hyperpigmentation were monitored by spectroscopic measurements. The effect of skin care formulations containing Thiamidol on acne‐related PIH was investigated in two studies, a vehicle‐controlled, double‐blinded, randomized clinical study and a clinical observational study. Both studies had a duration of 3 months and included assessments such as clinical photography, clinical grading and melanin index measurements.

Results

Already after 2 weeks of treatment, suction blister sites treated with Thiamidol were significantly lighter than control sites and improved throughout the treatment period. Subjects´ self‐grading demonstrated that Thiamidol significantly improved the visibility of acne‐induced hyperpigmentation compared to the vehicle treatment. A skin care regimen with Thiamidol significantly improved acne‐related PIH over 12 weeks shown by Mexameter measurements, expert grading, self‐grading and clinical photography.

Conclusion

Thiamidol represents a safe and effective ingredient for cosmetic products against post‐inflammatory hyperpigmentation.

Impaired glyoxalase activity is associated with reduced expression of neurotrophic factors and pro-inflammatory processes in diabetic skin cells

Patients suffering from type II diabetes develop several skin manifestations including cutaneous infections, diabetic dermopathy, diabetic bullae and acanthosis nigricans. Diabetic micro- and macroangiopathy as well as diabetic neuropathy are believed to play a crucial role in the development of diabetic skin disorders. A reduced cutaneous nerve fibre density was reported in diabetic subjects, which subsequently leads to impaired sensory nerve functions. Using an innervated skin model, we investigated the impact of human diabetic dermal fibroblasts and keratinocytes on porcine sensory neurons. Diabetic skin cells showed a reduced capacity to induce neurite outgrowth due to a decreased support with neurotrophic factors, such as NGF. Furthermore, diabetic keratinocytes displayed insulin resistance and increased expression of pro-inflammatory cytokines demonstrating the persistent effect of diabetes mellitus on human skin cells. Dysregulations were related to a significantly reduced glyoxalase enzyme activity in diabetic keratinocytes as experimentally reduced glyoxalase activity mimicked the increase in pro-inflammatory cytokine expression and reduction in NGF. Our results demonstrate an impaired crosstalk of diabetic skin cells and sensory neurons favouring hypo-innervation. We suggest that reduced methylglyoxal detoxification contributes to an impaired neurocutaneous interaction in diabetic skin.

UV radiation induces CXCL5 expression in human skin

CXCL5 has recently been identified as a mediator of UVB-induced pain in rodents. To compare and to extend previous knowledge of cutaneous CXCL5 regulation, we performed a comprehensive study on the effects of UV radiation on CXCL5 regulation in human skin. Our results show a dose-dependent increase in CXCL5 protein in human skin after UV radiation. CXCL5 can be released by different cell types in the skin. We presumed that, in addition to immune cells, non-immune skin cells also contribute to UV-induced increase in CXCL5 protein. Analysis of monocultured dermal fibroblasts and keratinocytes revealed that only fibroblasts but not keratinocytes displayed up regulated CXCL5 levels after UV stimulation. Whereas UV treatment of human skin equivalents, induced epidermal CXCL5 mRNA and protein expression. Up regulation of epidermal CXCL5 was independent of keratinocyte differentiation and keratinocyte-keratinocyte interactions in epidermal layers. Our findings provide first evidence on the release of CXCL5 in UV-radiated human skin and the essential role of fibroblast-keratinocyte interaction in the regulation of epidermal CXCL5.

Thiamidol® in moderate-to-severe melasma: 24-week, randomized, double-blind, vehicle-controlled clinical study with subsequent regression phase

Thiamidol^® was the most potent inhibitor of human tyrosinase out of 50 000 screened substances. In vivo, it was well tolerated and improved melasma significantly. This was the first 24-week, randomized, double-blind, vehicle-controlled, cosmetic clinical study to assess the efficacy and tolerability of thiamidol in moderate-to-severe melasma of phototype III-V subjects with subsequent regression phase. Females allocated to verum (n = 23), applied daily Dual Serum followed either by Day Care SPF30 in the morning or by Night Care in the evening, all containing Thiamidol. The vehicle group (25 females) followed the same skin care routine using the corresponding vehicle formulations. Subjects came back for a follow-up visit 13-20 weeks after treatment (regression phase). Assessments included clinical photography, Melasma Area and Severity Index (MASI), skin lightness, quality of life, and tolerability. Baseline demographics and hyperpigmentation were well balanced across the treatment groups. Clinical photography and MASI improved with Thiamidol significantly versus baseline (p < 0.001) and vehicle (p < 0.001-0.043) at all time points up to treatment end. At follow-up, the MASI was still significantly lower than at baseline but similar for verum and vehicle. Skin lightness and quality of life improved significantly versus baseline without significant differences between verum and vehicle. This study demonstrated that Thiamidol is well tolerated and superior in improving melasma compared to baseline and vehicle over a treatment period of 24 weeks.

A Biomimetic Combination of Actives Enhances Skin Hydration and Barrier Function via Modulation of Gene Expression: Results of Two Double-Blind, Vehicle-Controlled Clinical Studies

INTRODUCTION

Xerosis cutis is characterized by a decreased stratum corneum (SC) hydration and an impaired skin barrier function. Urea, the most prevalent natural moisturizing factor (NMF), is currently considered the gold standard. Its efficacy can further be increased by combining urea with other NMF and skin barrier lipids (SBLs).

OBJECTIVE

We set out to evaluate physiological effects of a novel functional moisturizer containing 10% urea, additional NMF components, and a combination of SBLs on skin hydration and skin barrier integrity on a cellular and phenotypic level in female volunteers suffering from xerosis.

METHODS

Two double-blind, vehicle-controlled clinical studies were conducted. In the first study, 44 female subjects having very dry body skin applied the moisturizer or its vehicle twice daily to their volar forearms. Twenty-four hours after a single product application as well as 24 h after 2 weeks of treatment, SC hydration was measured by corneometry. Skin barrier function was assessed by transepidermal water loss 24 h and 48 h after 2 weeks of regular use. Twenty-four hours after 2 weeks of application, skin tape stripping was performed, and urea content was determined in the 3rd strip by means of high-performance liquid chromatography/tandem mass spectrometry. In the second study, 22 women with self-reported very dry skin applied the moisturizer or vehicle twice daily to their volar forearms for 2 weeks. Then, suction blister samples were obtained for gene expression analysis using RT-PCR.

RESULTS

Application of the actives led to significantly improved skin hydration and barrier function at all points in time. Compared to the vehicle, application of the moisturizer for 2 weeks resulted in a significant increase in SC urea content. Relative gene expression data revealed significant upregulation of genes associated with skin barrier function, hydration, differentiation, and lipid metabolism compared to the vehicle-treated area.

CONCLUSIONS

Overall, our data demonstrate that the functional moisturizer provides an adequate bioavailability of urea and a beneficial biophysical impact on xerotic skin. Topical treatment with a combination of urea and additional NMF as well as SBL can modify mRNA expression of important epidermal genes stimulating cellular processes and functions. The well-tolerated novel functional moisturizer stimulates molecular mechanisms involved in skin hydration and barrier function and is a profoundly effective treatment option for xerosis cutis.