Ludger Kolbe

Corticosteroid-induced atrophy and barrier impairment measured by non-invasive methods in human skin.

Background/aims: Atrophy is a distressing side effect of potent corticosteroids. After open application of a high potency steroid, we monitored atrophogenicity by a variety of non‐invasive methods.

Usefulness of alkaline hydrogen peroxide oxidation to analyze eumelanin and pheomelanin in various tissue samples: application to chemical analysis of human hair melanins

Eumelanin and pheomelanin in tissue samples can be specifically measured as the markers pyrrole‐2,3,5‐tricarboxylic acid (PTCA) and 4‐amino‐3‐hydroxyphenylalanine after acidic permanganate oxidation and hydroiodic acid hydrolysis, respectively. Those degradation methods, although widely applied, are not easily performed in most laboratories. To overcome this difficulty, we developed alkaline H2O2 oxidation in 1 M K2CO3 that produces, in addition to the eumelanin marker PTCA, thiazole‐2,4,5‐tricarboxylic acid (TTCA) and thiazole‐4,5‐dicarboxylic acid (TDCA) as markers for pheomelanin and pyrrole‐2,3‐dicarboxylic acid (PDCA) as a marker for 5,6‐dihydroxyindole‐derived eumelanin. Those four degradation products can be easily separated by HPLC and analyzed with ultraviolet detection. The alkaline H2O2 oxidation method is simple, reproducible and applicable to all pigmented tissues. Its application to characterize eumelanin and pheomelanin in human hair shows that PTCA and TTCA serve as specific markers for eumelanin and pheomelanin, respectively, although some caution is needed regarding the artificial production of TTCA from eumelanic tissue proteins.

Anti-inflammatory efficacy of licochalcone a : correlation of clinical potency and in vitro effects

Licochalcone A (LicA), a major phenolic constituent of the licorice species Glycyrrhiza inflata, has recently been reported to have anti-inflammatory as well as anti-microbial effects. These anti-inflammatory properties might be exploited for topical applications of LicA. We conducted prospective randomized vehicle-controlled clinical trials to assess the anti-irritative efficacy of cosmetic formulations containing LicA in a post-shaving skin irritation model and on UV-induced erythema formation. The clinical trials were accompanied by a series of in vitro experiments to characterize anti-inflammatory properties of LicA on several dermatologically relevant cell types. Topical LicA causes a highly significant reduction in erythema relative to the vehicle control in both the shave- and UV-induced erythema tests, demonstrating the anti-irritative properties of LicA. Furthermore, LicA is a potent inhibitor of pro-inflammatory in vitro responses, including N-formyl-MET-LEU-PHE (fMLP)- or zymosan-induced oxidative burst of granulocytes, UVB-induced PGE2 release by keratinocytes, lipopolysaccharide (LPS)-induced PGE2 release by adult dermal fibroblasts, fMLP-induced LTB4 release by granulocytes, and LPS-induced IL-6/TNF-α secretion by monocyte-derived dendritic cells. The reported data suggest therapeutic skin care benefits from LicA when applied to sensitive or irritated skin.

The fibroblast-derived paracrine factor neuregulin-1 has a novel role in regulating the constitutive color and melanocyte function in human skin

Interactions between melanocytes and neighboring cells in the skin are important in regulating skin color in humans. We recently demonstrated that the less pigmented and thicker skin on the palms and soles is regulated by underlying fibroblasts in those areas, specifically via a secreted factor (DKK1) that modulates Wnt signaling. In this study, we tested the hypothesis that dermal fibroblasts regulate the constitutive skin color of individuals ranging from very light to very dark. We used microarray analysis to compare gene expression patterns in fibroblasts derived from lighter skin types compared to darker skin types, with a focus on secreted proteins. We identified a number of genes that differ dramatically in expression and, among the expressed proteins, neuregulin-1, which is secreted by fibroblasts derived from dark skin, effectively increases the pigmentation of melanocytes in tissue culture and in an artificial skin model and regulates their growth, suggesting that it is one of the major factors determining human skin color.

The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human skin.

The relationship between human skin pigmentation and protection from ultraviolet (UV) radiation is an important element underlying differences in skin carcinogenesis rates. The association between UV damage and the risk of skin cancer is clear, yet a strategic balance in exposure to UV needs to be met. Dark skin is protected from UV‐induced DNA damage significantly more than light skin owing to the constitutively higher pigmentation, but an as yet unresolved and important question is what photoprotective benefit, if any, is afforded by facultative pigmentation (i.e. a tan induced by UV exposure). To address that and to compare the effects of various wavelengths of UV, we repetitively exposed human skin to suberythemal doses of UVA and/or UVB over 2 weeks after which a challenge dose of UVA and UVB was given. Although visual skin pigmentation (tanning) elicited by different UV exposure protocols was similar, the melanin content and UV‐protective effects against DNA damage in UVB‐tanned skin (but not in UVA‐tanned skin) were significantly higher. UVA‐induced tans seem to result from the photooxidation of existing melanin and its precursors with some redistribution of pigment granules, while UVB stimulates melanocytes to up‐regulate melanin synthesis and increases pigmentation coverage, effects that are synergistically stimulated in UVA and UVB‐exposed skin. Thus, UVA tanning contributes essentially no photoprotection, although all types of UV‐induced tanning result in DNA and cellular damage, which can eventually lead to photocarcinogenesis.

Regulation of Human Skin Pigmentation in situ by Repetitive UV Exposure: Molecular Characterization of Responses to UVA and/or UVB

UV radiation is a major environmental factor that affects pigmentation in human skin and can eventually result in various types of UV-induced skin cancers. The effects of various wavelengths of UV on melanocytes and other types of skin cells in culture have been studied, but little is known about gene expression patterns in situ following in situ exposure of human skin to different types of UV (UVA and/or UVB). Paracrine factors expressed by keratinocytes and/or fibroblasts that affect skin pigmentation might be regulated differently by UV, as might their corresponding receptors expressed on melanocytes. To test the hypothesis that different mechanisms are involved in the pigmentary responses of the skin to different types of UV, we used immunohistochemical and whole human genome microarray analyses to characterize human skin in situ to examine how melanocyte-specific proteins and paracrine melanogenic factors are regulated by repetitive exposure to different types of UV compared with unexposed skin as a control. The results show that gene expression patterns induced by UVA or UVB are distinct-UVB eliciting dramatic increases in a large number of genes involved in pigmentation as well as in other cellular functions, whereas UVA had little or no effect on these. The expression patterns characterize the distinct responses of the skin to UVA or UVB, and identify several potential previously unidentified factors involved in UV-induced responses of human skin.

Optical coherence tomography in dermatology

Background/alms: Optical coherence tomography is a new in vivo imaging tool originally developed to investigate the eye. We undertook a preliminary investigation of experimental and clinical dermatological applications.

4-n-butylresorcinol, a highly effective tyrosinase inhibitor for the topical treatment of hyperpigmentation

Background  Hyperpigmentary disorders like melasma, actinic and senile lentigines are a major cosmetic concern. Therefore, many topical products are available, containing various active ingredients aiming to reduce melanin production and distribution. The most prominent target for inhibitors of hyperpigmentation is tyrosinase, the key regulator of melanin production. Many inhibitors of tyrosinase are described in the literature; however, most of them lack clinical efficacy.

UVA‐induced oxidative degradation of melanins: fission of indole moiety in eumelanin and conversion to benzothiazole moiety in pheomelanin

Eumelanin is photoprotective while pheomelanin is phototoxic to pigmented tissues. Ultraviolet A (UVA)‐induced tanning seems to result from the photooxidation of pre‐existing melanin and contributes no photoprotection. However, data available for melanin biodegradation remain limited. In this study, we first examined photodegradation of eumelanin and pheomelanin in human black hairs and found that the ratio of Free (formed by peroxidation in situ) to Total (after hydrogen peroxide oxidation) pyrrole‐2,3,5‐tricarboxylic acid (PTCA) increases with hair aging, indicating fission of the dihydroxyindole moiety. In red hair, the ratio of thiazole‐2,4,5‐tricarboxylic acid (TTCA) to 4‐amino‐3‐hydroxyphenylalanine (4‐AHP) increases with aging, indicating the conversion from benzothiazine to benzothiazole moiety. These photodegradation of melanins were confirmed by UVA (not UVB) irradiation of melanins from mice and human hairs and synthetic eumelanin and pheomelanin. These results show that both eumelanin and pheomelanin degrade by UVA and that Free/Total PTCA and TTCA/4‐AHP ratios serve as sensitive indicators of photodegradation.

TRP-channel-specific cutaneous eicosanoid release patterns

Summary Specific transient receptor potential channel agonists induced a differential release pattern of LTB4 and PGE2 from skin. These might directly influence perception thresholds and neurogenic inflammatory symptoms. ABSTRACT Analyzing mechanisms and key players in peripheral nociception nonneuronal skin cells are getting more and more into focus. Herein we investigated the functional expression of TRPV1 and TRPA1 in human keratinocytes and fibroblasts and assessed proinflammatory lipid mediator release upon their stimulation as well as sensory effects after topical application, combining in vitro and in vivo approaches. In vitro, the expression of functional TRPV1 and TRPA1 channels on fibroblasts and keratinocytes was confirmed via immunofluorescence, qualitative real time (RT) polymerase chain reaction, and cellular Ca2+ influx measurements. Additionally, the agonists allyl isothiocyanate (TRPA1) and capsaicin (TRPV1) induce a differential secretion pattern of the eicosanoids PGE2 and LTB4 in human dermal fibroblasts and keratinocytes, which was also detectable in vivo, analyzing suction blister fluid at various times after short‐term topical application. Capsaicin provoked the release of LTB4 at 2 and 24 hours. In contrast, PGE2 levels were reduced upon stimulation. Allyl isothiocyanate, however, increased PGE2 levels only at 24 hours, but did not alter LTB4 levels. In parallel, heat pain thresholds were reduced by both agents after short‐term topical application, but only AITC provoked a long‐lasting local erythema. In conclusion, the agonist‐induced activation of nociceptors by TRPA1 and TRPV1 elicits painful sensations, whereas nonneuronal tissue cells respond with differential release of inflammatory mediators, thus influencing local vasodilatation and neuronal sensitization. These results have implications for the application of transient receptor potential antagonists to improve inflammatory skin conditions and pain management.