Human skin equivalents (HSEs) are in vitro 3D-skin models that mimic many aspects of the native human skin (NHS) and can be a valuable tool. In this thesis, several (medium based) approaches have... Show moreHuman skin equivalents (HSEs) are in vitro 3D-skin models that mimic many aspects of the native human skin (NHS) and can be a valuable tool. In this thesis, several (medium based) approaches have been investigated to improve the barrier characteristics of this HSE to mimic that of NHS. Show less
The skin is our natural barrier and lipids are a key part of this barrier. In the outer skin layer, the stratum corneum (SC), lipids form a densely organized structure dependent on the composition... Show moreThe skin is our natural barrier and lipids are a key part of this barrier. In the outer skin layer, the stratum corneum (SC), lipids form a densely organized structure dependent on the composition of these lipids. Multiple skin diseases are characterized by alterations in SC lipid composition. These alterations are related to pathological barrier defects. This thesis describes the next steps towards a treatment modifying the lipid composition and thereby restoring this barrier. We developed a novel method to quantify a key SC lipid group called ceramides. This method was applied to compare SC regeneration of skin models to healthy volunteers. Regeneration in such an ex vivo skin model proved to be a potent model for formulation development. Ensuing, a clinical study was performed to determine the mechanistic effects of a formulation on barrier repair in healthy skin. The results warranted follow up analysis of the formulation in atopic dermatitis patients. This thesis also describes a detailed analysis of the ceramide fraction that is covalently attached to the cells in the SC. It was shown that a selected group of ceramides becomes bound. Further analysis showed that this group of ceramides was also affected in atopic dermatitis patients SC. Show less
The stratum corneum is the outermost skin layer and consists of dead cells embedded in a lipid matrix. The lipid matrix, consisting of ceramides, fatty acids, and cholesterol, is crucial for a... Show moreThe stratum corneum is the outermost skin layer and consists of dead cells embedded in a lipid matrix. The lipid matrix, consisting of ceramides, fatty acids, and cholesterol, is crucial for a proper skin barrier function. In inflammatory skin diseases the lipid composition and ordering is altered contributing to the impaired skin barrier. Vernix caseosa (VC) is the cheesy, white cream that covers the skin of the human fetus. Application of an in house developed synthetic VC enhanced skin barrier repair in mice. Currently, there are no suitable skin models available to study human skin barrier repair after application of a topical formulation. This thesis describes the development of a human skin barrier repair model and evaluates VC based formulations using this model. The results demonstrate that the barrier of this repair model mimics several aspects of inflammatory skin diseases. Additionally, it was shown that the lipid properties in this model were improved when a synthetic VC-based formulation was applied. Based on the outcome, clinical studies were performed. These studies showed that application on a disrupted human skin barrier in vivo enhanced the barrier repair. However, the effects of the formulation are limited when applied on atopic dermatitis skin Show less
The stratum corneum (SC), the thin uppermost layer of the skin, consists of dead flattened skin cells (corneocytes) embedded in a lipid matrix. The lipid matrix is considered to play a crucial role... Show moreThe stratum corneum (SC), the thin uppermost layer of the skin, consists of dead flattened skin cells (corneocytes) embedded in a lipid matrix. The lipid matrix is considered to play a crucial role in the skin barrier function. It consists of ceramides (CER), cholesterol (CHOL) and free fatty acids (FFA) forming crystalline lipid lamellae. From studies with native SC and SC lipid models much information has been gained on the phase behavior of the SC lipid matrix. However, little is known about the correlation between SC lipid organization and the permeability of the SC. This is difficult to investigate using native SC, due to its complex structure. Therefore SC lipids were casted on a porous membrane, resulting in a lipid organization and lamellar orientation similar to that in SC. This lipid membrane is referred to as the stratum corneum substitute (SCS). The SCS can be used to perform diffusion studies. Therefore, when modifying the lipid composition and thus the lipid organization in the SCS, it is possible to study the relationship between lipid organization and permeability. The main objectives of this thesis are 1) to investigate the influence of lipid organization on the barrier function in the SCS and 2) to obtain insights in the molecular organization within the unit cell of the lamellar phases in SC. Show less
