Three-Dimensional Epidermal Model from Human Hair Follicle-Derived Keratinocytes

Type 2 Cytokine-Dependent Skin Barrier Regulation in Personalized 2-Dimensional and 3-Dimensional Skin Models of Atopic Dermatitis: A Pilot Study

Keratinocytes (KCs) from healthy donors stimulated with type 2 cytokines are often used to experimentally study atopic dermatitis (AD) inflammatory responses. Owing to potential intrinsic alterations, it seems favorable to use KCs from patients with AD. KCs isolated from hair follicles offer a noninvasive approach to investigate AD-derived KCs. To evaluate whether such AD-derived KCs are suitable to mimic AD inflammatory responses, we compared hair follicle-derived KCs from healthy donors with those from patients with AD in a type 2 cytokine environment. Stimulation of AD-derived KCs with IL-4 and IL-13 induced higher expression changes of AD-associated markers than that of healthy KCs. The combination of IL-4 and IL-13 generally induced highest expression changes, but IL-13 alone also induced significant changes of AD-specific markers. Similar to the 2-dimensional cultures, IL-4/IL-13 stimulation of 3-dimensional skin models generated with AD-derived KCs modulated the expression of several AD-relevant factors. Whole-transcriptome analysis revealed that IL-4 and IL-13 acted similarly on these 3-dimensional skin models. Histologically, IL-13 alone and in combination with IL-4 increased epidermal spongiosis, a histological hallmark of AD skin. Taken together, our pilot study suggests that hair follicle-derived KCs from patients with AD represent a useful model system to study AD-related inflammation in a personalized in vitro model.

Development of an iPSC-derived immunocompetent skin model for identification of skin sensitizing substances

The development of immunocompetent skin models marks a significant advancement in in vitro methods for detecting skin sensitizers while adhering to the 3R principles, which aim to reduce, refine, and replace animal testing. This study introduces for the first time an advanced immunocompetent skin model constructed entirely from induced pluripotent stem cell (iPSC)-derived cell types, including fibroblasts (iPSC-FB), keratinocytes (iPSC-KC), and fully integrated dendritic cells (iPSC-DC). To evaluate the skin model's capacity, the model was treated topically with a range of well-characterized skin sensitizers varying in potency. The results indicate that the iPSC-derived immunocompetent skin model successfully replicates the physiological responses of human skin, offering a robust and reliable alternative to animal models for skin sensitization testing, allowing detection of extreme and even weak sensitizers. By addressing critical aspects of immune activation and cytokine signaling, this model provides an ethical, comprehensive tool for regulatory toxicology and dermatological research.

Advancing skin model development: A focus on a self-assembled, induced pluripotent stem cell-derived, xeno-free approach

The demand for skin models as alternatives to animal testing has grown due to ethical concerns and the need for accurate substance evaluation. These alternatives, known as New Approach Methodologies (NAMs), are increasingly used for regulatory decisions. Current skin models from primary human cells often rely on bovine collagen, raising ethical issues. This study explores self-assembled skin models (SASM) as a new method, utilizing hair follicle-derived keratinocytes reprogrammed into induced pluripotent stem cells (iPSC) and differentiated into fibroblasts and keratinocytes. The model relies on the ability of fibroblasts to secrete collagen to produce a xeno-free dermal layer and on the differentiation of keratinocytes to create a functional epidermal layer. These layers exhibited confirmed metabolic activity and the capability to withstand test substances. The successful development of SASM underscores the significance of accurate alternatives in dermatological research, providing an ethical and reliable option for substance evaluation and regulatory testing.

Methodologies to Evaluate the Hair Follicle-Targeted Drug Delivery Provided by Nanoparticles

Nanotechnology has been investigated for treatments of hair follicle disorders mainly because of the natural accumulation of solid nanoparticles in the follicular openings following a topical application, which provides a drug "targeting effect". Despite the promising results regarding the therapeutic efficacy of topically applied nanoparticles, the literature has often presented controversial results regarding the targeting of hair follicle potential of nanoformulations. A closer look at the published works shows that study parameters such as the type of skin model, skin sections analyzed, employed controls, or even the extraction methodologies differ to a great extent among the studies, producing either unreliable results or precluding comparisons altogether. Hence, the present study proposes to review different skin models and methods for quantitative and qualitative analysis of follicular penetration of nano-entrapped drugs and their influence on the obtained results, as a way of providing more coherent study protocols for the intended application.