In vitro glycation of an endothelialized and innervated tissue-engineered skin to screen anti-AGE molecules

The protective role of resveratrol in diabetic wound healing

Diabetic wounds are severe complications of diabetes mellitus (DM), which have difficulty in healing. Although diverse treatments have been used, the prognosis of diabetic wounds is not satisfactory; therefore, an effective therapy to accelerate diabetic wound healing is urgently needed. In our review, we summarized that resveratrol can promote diabetic wound healing by protecting against hyperglycemia, inflammation, oxidative stress, vascular pathology, infection, and peripheral neuropathy. To clarify it clearly, we highlighted its underlying mechanisms of protective effects of resveratrol against diabetic wounds, and high-quality studies are needed to firmly establish its clinical efficacy. Otherwise, with the development of material sciences, resveratrol can exert its therapeutic effectiveness efficiently; however, more high-quality studies are needed to confirm the clinical efficacy of resveratrol on diabetic wounds.

In vitro glycation of a tissue-engineered wound healing model to mimic diabetic ulcers

Diabetic foot ulcers are a major complication of diabetes that occurs following minor trauma. Diabetes-induced hyperglycemia is a leading factor inducing ulcer formation and manifests notably through the accumulation of advanced glycation end-products (AGEs) such as N-carboxymethyl-lysin. AGEs have a negative impact on angiogenesis, innervation, and reepithelialization causing minor wounds to evolve into chronic ulcers which increases the risks of lower limb amputation. However, the impact of AGEs on wound healing is difficult to model (both in vitro on cells, and in vivo in animals) because it involves a long-term toxic effect. We have developed a tissue-engineered wound healing model made of human keratinocytes, fibroblasts, and endothelial cells cultured in a collagen sponge biomaterial. To mimic the deleterious effects induced by glycation on skin wound healing, the model was treated with 300 µM of glyoxal for 15 days to promote AGEs formation. Glyoxal treatment induced carboxymethyl-lysin accumulation and delayed wound closure in the skin mimicking diabetic ulcers. Moreover, this effect was reversed by the addition of aminoguanidine, an inhibitor of AGEs formation. This in vitro diabetic wound healing model could be a great tool for the screening of new molecules to improve the treatment of diabetic ulcers by preventing glycation.

Cellular Pathogenesis of Chemotherapy-Induced Peripheral Neuropathy: Insights From Drosophila and Human-Engineered Skin Models

Chemotherapy-induced peripheral neuropathy (CIPN) is a highly prevalent and complex condition arising from chemotherapy cancer treatments. Currently, there are no treatment or prevention options in the clinic. CIPN accompanies pain-related sensory functions starting from the hands and feet. Studies focusing on neurons in vitro and in vivo models significantly advanced our understanding of CIPN pathological mechanisms. However, given the direct toxicity shown in both neurons and non-neuronal cells, effective in vivo or in vitro models that allow the investigation of neurons in their local environment are required. No single model can provide a complete solution for the required investigation, therefore, utilizing a multi-model approach would allow complementary advantages of different models and robustly validate findings before further translation. This review aims first to summarize approaches and insights from CIPN in vivo models utilizing small model organisms. We will focus on Drosophila melanogaster CIPN models that are genetically amenable and accessible to study neuronal interactions with the local environment in vivo. Second, we will discuss how these findings could be tested in physiologically relevant vertebrate models. We will focus on in vitro approaches using human cells and summarize the current understanding of engineering approaches that may allow the investigation of pathological changes in neurons and the skin environment.

In Vitro Sensitive Skin Models: Review of the Standard Methods and Introduction to a New Disruptive Technology

The skin is a protective organ, able to decode a wide range of tactile, thermal, or noxious stimuli. Some of the sensors belonging to the transient receptor potential (TRP) family, for example, TRPV1, can elicit capsaicin-induced heat pain or histamine-induced itching sensations. The sensory nerve fibers, whose soma is located in the trigeminal or the dorsal root ganglia, are able to carry signals from the skin’s sensory receptors toward the brain via the spinal cord. In some cases, in response to environmental factors, nerve endings might be hyper activated, leading to a sensitive skin syndrome (SSS). SSS affects about 50% of the population and is correlated with small-fiber neuropathies resulting in neuropathic pain. Thus, for cosmetical and pharmaceutical industries developing SSS treatments, the selection of relevant and predictive in vitro models is essential. In this article, we reviewed the different in vitro models developed for the assessment of skin and neuron interactions. In a second part, we presented the advantages of microfluidic devices and organ-on-chip models, with a focus on the first model we developed in this context.

Development of Evaluation Methods for Anti-Glycation Activity and Functional Ingredients Contained in Coriander and Fennel Seeds

Spices are known to have various physiological functions. We focused on the anti-glycation effects of spices, researched anti-glycation active ingredients in coriander (Coriandrum sativum L.) and fennel (Foeniculum vulgare) seeds, and conducted experiments using human skin-derived fibroblast TIG-110 cells as a model of glycation. We isolated 11 compounds from two spice seeds and found several substances that showed anti-glycation activity. A new compound (5,5′-diallyl-2,2′-diglucopyranosyl-3,3′-dimethoxy diphenyl ether) was isolated from fennel seeds and showed high anti-glycation activity with an IC50 value of 0.08 mM, thereby indicating a high anti-glycosylation activity. In this study, we established a glyoxal (GO)-induced glycation test method for human skin cells, confirmed the anti-glycation effect of spice seeds using this glycation induction model, and found that the exposure of TIG-110 human skin-derived fibroblast cells to GO reduced cell viability. The most stable conditions for cell viability were found to be a GO concentration of 1.25 mM and a culture time of 48 h. We evaluated extracts and isolates of spice seeds using this model as a model test for glycation induction. We conducted qualitative and quantitative analyses of carboxymethyl lysine (CML), a type of AGE, to determine the relationship between cell viability and AGEs. The relationship between cell viability and the amount of CML was correlated. Establishing a glycation induction model test using skin cells makes it possible to quickly screen extracts of natural ingredients in the future. Moreover, the results of this model showed that extracts of two spice seeds and their isolates have high anti-glycation activity, and they are expected to be used as cosmetics, health foods, and pharmaceutical ingredients.

Tissue engineering strategies to bioengineer the ageing skin phenotype in vitro

Human skin ageing is a complex and heterogeneous process, which is influenced by genetically determined intrinsic factors and accelerated by cumulative exposure to extrinsic stressors. In the current world ageing demographic, there is a requirement for a bioengineered ageing skin model, to further the understanding of the intricate molecular mechanisms of skin ageing, and provide a distinct and biologically relevant platform for testing actives and formulations. There have been many recent advances in the development of skin models that recapitulate aspects of the ageing phenotype in vitro. This review encompasses the features of skin ageing, the molecular mechanisms that drive the ageing phenotype, and tissue engineering strategies that have been utilised to bioengineer ageing skin in vitro.

Determination of Chemical Irritation Potential Using a Defined Gene Signature Set on Tissue-Engineered Human Skin Equivalents

There are no physical or visual manifestations that define skin sensitivity or irritation; a subjective diagnosis is made on the basis of the evaluation of clinical presentations, including burning, prickling, erythema, and itching. Adverse skin reaction in response to topically applied products is common and can limit the use of dermatological or cosmetic products. The purpose of this study was to evaluate the use of human skin equivalents based on immortalized skin keratinocytes and evaluate the potential of a 22-gene panel in combination with multivariate analysis to discriminate between chemicals known to act as irritants and those that do not. Test compounds were applied topically to full-thickness human skin equivalent or human ex vivo skin and gene signatures determined for known irritants and nonirritants. Principle component analysis showed the discriminatory potential of the 22-gene panel. Linear discrimination analysis, performed to further refine the gene set for a more high-throughput analysis, identified a putative seven-gene panel (IL-6, PTGS2, ATF3, TRPV3, MAP3K8, HMGB2, and matrix metalloproteinase gene MMP-3) that could distinguish potential irritants from nonirritants. These data offer promise as an in vitro prediction tool, although analysis of a large chemical test set is required to further evaluate the system.

Peripheral neurovascular link: an overview of interactions and in vitro models

Nerves and blood vessels (BVs) establish extensive arborized networks to innervate tissues and deliver oxygen/metabolic support. Developmental cues direct the formation of these intricate and often overlapping patterns, which reflect close interactions within the peripheral neurovascular system. Besides the mutual dependence to survive and function, nerves and BVs share several receptors and ligands, as well as principles of differentiation, growth and pathfinding. Neurovascular (NV) interactions are maintained in adult life and are essential for certain regenerative mechanisms, such as wound healing. In pathological situations (e.g., type 2 diabetes mellitus), the NV system can be severely perturbed and become dysfunctional. Unwanted neural growth and vascularization are also associated with the progression of some pathologies, such as cancer and endometriosis. In this review, we describe the fundamental NV interactions in development, highlighting the similarities between both networks and wiring mechanisms. We also describe the NV contribution to regenerative processes and potential pathological dysfunctions. Finally, we provide an overview of current in vitro models used to replicate and investigate the NV ecosystem, addressing present limitations and future perspectives.

Skin-Nerve Co-Culture Systems for Disease Modeling and Drug Discovery

Prominent clinical problems related to the skin-nerve interface include barrier dysfunction and erythema, but it is the symptoms of pain and itch that most often lead patients to seek medical treatment. Tissue-engineered innervated skin models provide an excellent solution for studying the mechanisms underlying neurocutaneous disorders for drug screening, and cutaneous device development. Innervated skin substitutes provide solutions beyond traditional monolayer cultures and have advantages that make them preferable to in vivo animal studies for certain applications, such as measuring somatosensory transduction. The tissue-engineered innervated skin models replicate the complex stratified epidermis that provides barrier function in native skin, a feature that is lacking in monolayer co-cultures, while allowing for a level of detail in measurement of nerve morphology and function that cannot be achieved in animal models. In this review, the advantages and disadvantages of different cell sources and scaffold materials will be discussed and a presentation of the current state of the field is reviewed. Impact statement A review of the current state of innervated skin substitutes and the considerations that need to be addressed when developing these models. Tissue-engineered skin substitutes are customizable and provide barrier function allowing for screening of topical drugs and for studying nerve function.

In vitro epidermis model mimicking IGF-1-specific age-related decline

Ageing is a complex multifaceted process affecting skin functionality and structure. Several 3D organotypic skin culture models have reproduced ageing by inducing replicative senescence, glycation or oxidative stress. Yet, very few models have focused on hormonal ageing and especially the insulin-like growth factor 1 (IGF-1) signalling pathway, which has been associated with longevity in animal studies and is necessary for the early stages of skin development. In this study, we built an organotypic epidermis model with targeted IGF-1 receptor knockdown to reproduce some aspects of hormonal ageing on skin. Our model displayed morphological and functional features of aged epidermis, which were mostly attributed to a loss of function of the Stratum basale. IGF-1 receptor knockdown keratinocytes depicted an extended cell cycle, reduced proliferation potential and reduced adhesion capacities and greater sensitivity to oxidative stress than control cells. Altogether, this model represents an essential tool for further investigations into the mechanisms linked to some aspects of hormonal decline or when screening for potent anti-ageing compounds.

Ultrastructural and Molecular Analysis of Ribose-Induced Glycated Reconstructed Human Skin

Aging depicts one of the major challenges in pharmacology owing to its complexity and heterogeneity. Thereby, advanced glycated end-products modify extracellular matrix proteins, but the consequences on the skin barrier function remain heavily understudied. Herein, we utilized transmission electron microscopy for the ultrastructural analysis of ribose-induced glycated reconstructed human skin (RHS). Molecular and functional insights substantiated the ultrastructural characterization and proved the relevance of glycated RHS beyond skin aging. In particular, electron microscopy mapped the accumulation and altered spatial orientation of fibrils and filaments in the dermal compartment of glycated RHS. Moreover, the epidermal basement membrane appeared thicker in glycated than in non-glycated RHS, but electron microscopy identified longitudinal clusters of the finest collagen fibrils instead of real thickening. The stratum granulosum contained more cell layers, the morphology of keratohyalin granules decidedly differed, and the stratum corneum lipid order increased in ribose-induced glycated RHS, while the skin barrier function was almost not affected. In conclusion, dermal advanced glycated end-products markedly changed the epidermal morphology, underlining the importance of matrix⁻cell interactions. The phenotype of ribose-induced glycated RHS emulated aged skin in the dermis, while the two to three times increased thickness of the stratum granulosum resembled poorer cornification.

Molecular characterization of glycation-associated skin ageing: an alternative skin model to study in vitro antiglycation activity of topical cosmeceutical and pharmaceutical formulations

BACKGROUND

Glycation is a nonenzymatic reaction that cross-links a sugar molecule and protein macromolecule to form advanced glycation products (AGEs) that are associated with various age-related disorders; thus glycation plays an important role in skin chronological ageing.

OBJECTIVES

To develop a novel in vitro skin glycation model as a screening tool for topical formulations with antiglycation properties and to further characterize, at the molecular level, the glycation stress-driven skin ageing mechanism.

METHODS

The glycation model was developed using human reconstituted full-thickness skin; the presence of N^ε -(carboxymethyl) lysine (CML) was used as evidence of the degree of glycation. Topical application of emulsion containing a well-known antiglycation compound (aminoguanidine) was used to verify the sensitivity and robustness of the model. Cytokine immunoassay, quantitative real-time polymerase chain reaction and histological analysis were further implemented to characterize the molecular mechanisms of skin ageing in the skin glycation model.

RESULTS

Transcriptomic and cytokine profiling analyses in the skin glycation model demonstrated multiple biological changes, including extracellular matrix catabolism, skin barrier function impairment, oxidative stress and subsequently the inflammatory response. Darkness and yellowness of skin tone observed in the in vitro skin glycation model correlated well with the degree of glycation stress.

CONCLUSIONS

The newly developed skin glycation model in this study has provided a new technological dimension in screening antiglycation properties of topical pharmaceutical or cosmeceutical formulations. This study concomitantly provides insights into skin ageing mechanisms driven by glycation stress, which could be useful in formulating skin antiageing therapy in future studies.

In vitro activation of the neuro-transduction mechanism in sensitive organotypic human skin model

Recent advances in tissue engineering have encouraged researchers to endeavor the production of fully functional three-dimensional (3D) thick human tissues in vitro. Here, we report the fabrication of a fully innervated human skin tissue in vitro that recapitulates and replicates skin sensory function. Previous attempts to innervate in vitro 3D skin models did not demonstrate an effective functionality of the nerve network. In our approach, we initially engineer functional human skin tissue based on fibroblast-generated dermis and differentiated epidermis; then, we promote rat dorsal root ganglion (DRG) neurons axon ingrowth in the de-novo developed tissue. Neurofilaments network infiltrates the entire native dermis extracellular matrix (ECM), as demonstrated by immunofluorescence and second harmonic generation (SHG) imaging. To prove sensing functionality of the tissue, we use topical applications of capsaicin, an agonist of transient receptor protein-vanilloid 1 (TRPV1) channel, and quantify calcium currents resulting from variations of Ca⁺⁺ concentration in DRG neurons innervating our model. Calcium currents generation demonstrates functional cross-talking between dermis and epidermis compartments. Moreover, through a computational fluid dynamic (CFD) analysis, we set fluid dynamic conditions for a non-planar skin equivalent growth, as proof of potential application in creating skin grafts tailored on-demand for in vivo wound shape.

[Experimental models of human skin aging]

The skin is a representative model for the study of human aging. Despite the high regenerative capacity of the skin, skin physiology changes over the course of life. Medical and cosmetic research is trying to prevent aging, to slow, to stop, or to reverse it. Effects of age-related DNA damage and of changing skin structure on pharmacological parameters are largely unknown. This review article summarizes the state of scientific knowledge in the field of experimental models of human skin aging and shows approaches to improve organotypic skin models, to develop predictive models of aging, and improve aging research.