Development of pathological skin models: from conventional techniques to 3D bioprinting

Reconstructed human skin models were first developed in the 1970s. Since then, they have played a pivotal role in dermatological research, significantly advanced our understanding of skin biology, and brought huge insights into dermatological pathologies. Many conventional pathological skin models exist covering a wide range of diseases including melanomas, psoriasis, atopic dermatitis, genetic disorders, and wound healing conditions. However, conventional skin models remain limited by technical constraints which prevent complete replication of the spatial organization (heterogeneities, microenvironment) of skin diseases. Bioprinting has emerged as a powerful technology with the potential to overcome some of these limitations. By enabling precise control over the spatial organization of multiple cell types within a tailored extracellular matrix, bioprinting facilitates the creation of complex, three-dimensional skin models that closely mimic the architecture and function of human skin. This review initially explores the current landscape of conventional reconstructed pathological skin models. Bioprinting techniques, bioink considerations, and their roles in creating complex skin models are discussed. It then highlights the benefits of bioprinting for tissue microenvironment replication, architectural fidelity, and integration of multiple cell types in pathological skin models. In terms of healthy skin models, three-dimensional bioprinting is already revolutionizing personalized medicine, automating model production, and supporting translational research and therapeutic and cosmetic screening. It also represents a transformative approach for developing advanced pathological skin models despite the remaining technical and regulatory challenges

Topical prevention from high energy visible light-induced pigmentation by 2-mercaptonicotinoyl glycine, but not by ascorbic acid antioxidant: 2 randomized controlled trials

IntroductionHyperpigmentation and pigmentary disorders are major clinical consequences of sun exposure. While UV radiation is a known contributor, visible light (VL), particularly High Energy Visible (HEV) light (400–450 nm), also induces long-lasting pigmentation in melanocompetent individuals (Fitzpatrick Phototype III and above), and can worsen pigmentary disorders. Therefore, photoprotection in this wavelengths range is recommended to prevent worsening of hyperpigmentation issues. Efficient solutions rely on the use of pigments, absorbing and diffusing VL. However, tint and opacity of these products may limit their use by consumers and patients. The search for actives preventing VL-induced pigmentation is therefore of interest. This work aimed at assessing 2 non tinted biological actives to counteract HEV-induced pigmentation.Material and MethodsTwo very potent inhibitors of UV-induced pigmentation, ascorbic acid 7% (powerful antioxidant) and 2-mercaptonicotinoyl glycine (2-MNG, 0.5 or 1%, melanogenesis inhibitor), were assessed in 2 controlled randomized clinical trials (registered under the identification numbers NCT06945393 and NCT06937515 on ClinicalTrials.gov), including in total, 58 individuals with Fitzpatrick Phototype III or IV. Delineated areas on the subjects back, topically treated or not by the product, were exposed to HEV once a day for 4 days. The product was applied before, during and 5 weeks after HEV exposure. Pigmentation was assessed using chromametry and visual scoring throughout the studies.ResultsWhile ascorbic acid did not exhibit any efficacy versus its vehicle in limiting skin hyperpigmentation induced by HEV, the use of 2-MNG (0.5 or 1%) led to an early significant decrease in HEV-induced pigmentation, which was sustained until the end of the study, as evidenced by colorimetry and significantly scored by visual assessment. Moreover, a 2-MNG dose effect could be evidenced at early time points.Conclusion2-MNG represents an efficient and transparent alternative solution to pigments for the mitigation of HEV worsening of hyperpigmentation issues. This opens up perspectives for its use as a complement to UV protection afforded by sun filters

Sunscreen photoprotection and vitamin D status

Background: Global concern about vitamin D deficiency has fuelled debates on photoprotection and the importance of solar exposure to meet vitamin D requirements. Objectives: To review the published evidence to reach a consensus on the influence of photoprotection by sunscreens on vitamin D status, considering other relevant factors. Methods: An international panel of 13 experts in endocrinology, dermatology, photobiology, epidemiology and biological anthropology reviewed the literature prior to a 1-day meeting in June 2017, during which the evidence was discussed. Methods of assessment and determining factors of vitamin D status, and public health perspectives were examined and consequences of sun exposure and the effects of photoprotection were assessed. Results: A serum level of ≥ 50 nmol L−1 25(OH)D is a target for all individuals. Broad-spectrum sunscreens that prevent erythema are unlikely to compromise vitamin D status in healthy populations. Vitamin D screening should be restricted to those at risk of hypovitaminosis, such as patients with photosensitivity disorders, who require rigorous photoprotection. Screening and supplementation are advised for this group. Conclusions: Sunscreen use for daily and recreational photoprotection does not compromise vitamin D synthesis, even when applied under optimal conditions

Different Oxidative Stress Response in Keratinocytes and Fibroblasts of Reconstructed Skin Exposed to Non Extreme Daily-Ultraviolet Radiation

Experiments characterizing the biological effects of sun exposure have usually involved solar simulators. However, they addressed the worst case scenario i.e. zenithal sun, rarely found in common outdoor activities. A non-extreme ultraviolet radiation (UV) spectrum referred as “daily UV radiation” (DUVR) with a higher UVA (320–400 nm) to UVB (280–320 nm) irradiance ratio has therefore been defined. In this study, the biological impact of an acute exposure to low physiological doses of DUVR (corresponding to 10 and 20% of the dose received per day in Paris mid-April) on a 3 dimensional reconstructed skin model, was analysed. In such conditions, epidermal and dermal morphological alterations could only be detected after the highest dose of DUVR. We then focused on oxidative stress response induced by DUVR, by analyzing the modulation of mRNA level of 24 markers in parallel in fibroblasts and keratinocytes. DUVR significantly modulated mRNA levels of these markers in both cell types. A cell type differential response was noticed: it was faster in fibroblasts, with a majority of inductions and high levels of modulation in contrast to keratinocyte response. Our results thus revealed a higher sensitivity in response to oxidative stress of dermal fibroblasts although located deeper in the skin, giving new insights into the skin biological events occurring in everyday UV exposure

La peau reconstruite : modèle d'étude du keratinocyte, du fibroblaste et de leurs interactions. Effets des ultraviolets, dommages et réparation

Le rôle de protection de la peau est apporté par les deux tissus majeurs, le derme et l'épiderme. L'une des principales agressions est l'exposition aux rayonnements ultraviolets solaires, dont les conséquences à long terme sont le vieillissement photo-induit et l'apparition de cancers. La caractérisation de la réponse de la peau face aux UV est un point essentiel pour prévenir ou corriger ces effets. L'approche in vitro dite organotypique consiste à reconstruire de la peau à partir de cellules humaines en culture et d'éléments matriciels. Ainsi le modèle de peau reconstruite peut comporter un épiderme différencié, mais aussi un derme équivalent vivant contenant des fibroblastes. Les effets induits par les UVB ont pu être reproduits dans ce modèle. Ils sont localisés dans l'épiderme et sont identiques à ceux observés dans la peau humaine lors d'un coup de soleil modéré, notamment l'apparition dans les kératinocytes des lésions de l'ADN spécifiques des UVB. Des altérations caractéristiques d'exposition aux rayonnements UVA ont aussi été identifiées dans les fibroblastes et ont pu être reliées aux dommages dermiques associés au phénomène de photovieillissement. L'interaction entre les deux types cellulaires a été illustrée dans la production de la MMP-1. Les dommages occasionnés par les UV sont en général réparés par des systèmes spécialisés. Un modèle déficient dans la réparation des lésions induites par les UVB a pu être développé grace à l'utilisation de cellules de patients atteints de Xeroderma Pigmentosum, une maladie génétique de la réparation de l'ADN caractérisée par une hypersensibilité aux UV et une très forte prédisposition aux cancers cutanés sur les zones exposées. Dans ces études, des traits phénotypiques particuliers ont pu être révélés au niveau du fibroblaste XP-C suggérant des interactions stroma-épithélium impliquées dans le développement des signes cliniques. Enfin, dans un contexte de correction de certaines altérations de la peau photoendommagée, des effets bénéfiques de la vitamine C ont été identifiés, particulièrement au niveau de la jonction dermo-épidermique (JDE). Ces effets ont ensuite permis d'approfondir la participation respective des deux types cellulaires majeurs dans la morphogenèse de la JDE. L'ensemble de ces travaux apporte une vision globale et tissulaire de la réponse aux rayonnements UV dans un système in vitro et illustre l'intérêt plus large de ces outils biologiques en biologie cellulaire. L'amélioration des modèles, notamment par l'incorporation d'autres types cellulaires, devrait permettre d'affiner encore nos connaissances

Successive Alteration and Recovery of Epidermal Differentiation and Morphogenesis after Specific UVB-Damages in Skin Reconstructedin Vitro

AbstractThe sequence of events affecting skin morphogenesis occurring after a single exposure to UVB was investigated on a model of human skin reconstructedin vitro.The biologically efficient dose (BED) able to induce the early UVB-DNA damages such as pyrimidine dimers, sunburn cells, and apoptotic keratinocytes was determined as 50 mJ/cm2. The subsequent changes induced during a period of 14 days following irradiation were analyzed. Up to Day 3, an epidermal disorganization led to a parakeratotic epidermis characterized by nucleated horny layers, as well as the down regulation of major markers of keratinocyte differentiation such as keratin 10, loricrin, filaggrin, and the keratinocyte transglutaminase (type I). On the contrary, the expression of involucrin and spr1 seemed to be unaffected, indicating distinct responses to UVB of proteins involved in keratinocyte differentiation. A progressive regeneration of normal epidermal morphogenesis begins from Day 4 leading to the normalization of keratinocyte differentiation at Day 10 to 14. In parallel, epidermal proliferation was increased. Taken together, these findings show that in skin reconstructedin vitro,UVB exposure leads to major epidermal developmental changes characterized by (i) an early apoptotic process, (ii) a subsequent down-regulation of specific keratinocyte differentiation markers, and (iii) the recovery of both the early and delayed effects resulting in normal epidermal morphogenesis

Delayed Onset of Epidermal Differentiation in Psoriasis

In normal epidermis, as previously reported, the first signs of differentiation occur within the basal layer in a subpopulation of keratinocytes that start to express K1 and K10 “suprabasal” keratin transcripts (20-30% of the basal cells) and proteins (5-10% of the basal cells). We found that in psoriatic lesions, the basal layer was devoid of cells expressing these early differentiation markers. This was already the case at the periphery of the lesions, where epidermis, although slightly acanthotic, still completes the keratinization process. In the center of the lesions, not only the basal layer, but also several rows of suprabasal cells, were negative for keratin K10 transcripts or protein. Moreover, the upper nucleated layers of involved epidermis were also devoid of K10 keratin transcripts or proteins. In normal epidermis, as previously reported, transcripts for the “basal” K5 keratin were mainly restricted to the basal layer, whereas the protein persisted in a few suprabasal layers. We found that in psoriatic epidermis, K5 keratin transcripts persisted in several suprabasal layers up to the level where K10 keratin transcripts appeared. These data, although not contradictory with previous reports showing a reduction of K1-K10 keratins and other differentiation markers in psoriasis, demonstrate that these quantitative changes are in fact the result of major qualitative differences in the distribution of these markers in psoriatic versus normal skin. Our results indicating that the onset of differentiation is delayed in psoriasis show that, contrary to conclusions accepted so far, not only the suprabasal compartment, but also the basal one, is abnormal in psoriatic epidermis