The lipids in the uppermost layer of the skin, the stratum corneum (SC), play an important role in the skin barrier function. The three main SC lipid classes are ceramides (CER), cholesterol and... Show moreThe lipids in the uppermost layer of the skin, the stratum corneum (SC), play an important role in the skin barrier function. The three main SC lipid classes are ceramides (CER), cholesterol and free fatty acids. In inflammatory skin diseases, such as atopic dermatitis and psoriasis, the SC lipid composition is altered compared to the healthy SC composition. The studies presented in this thesis focused on the effect of the CER subclass composition on the lipid organization, molecular arrangement and barrier function of the skin. First, the CER compositional changes were examined in the SC of seborrheic dermatitis patients, an inflammatory skin disease. A particular emphasis was paid to the ratio of two important CER subclasses, sphingosine CER (CER NS) and phytosphingosine CER (CER NP), and its correlation to the skin barrier. In the subsequent chapters lipid model systems with a simple CER subclass composition were used to study the influence of the CER NS: CER NP molar ratio on the barrier function and lipid organization. Show less
Purpose The duration of type 2 diabetes mellitus (T2DM) and blood glucose levels have a significant impact on the development of T2DM complications. However, currently known risk factors are not... Show morePurpose The duration of type 2 diabetes mellitus (T2DM) and blood glucose levels have a significant impact on the development of T2DM complications. However, currently known risk factors are not good predictors of the onset or progression of diabetic retinopathy (DR). Therefore, we aimed to investigate the differences in the serum lipid composition in patients with T2DM, without and with DR, and search for potential serological indicators associated with the development of DR. Methods A total of 622 patients with T2DM hospitalized in the Department of Endocrinology of the First Affiliated Hospital of Xi’an JiaoTong University were selected as the discovery set. One-to-one case–control matching was performed according to the traditional risk factors for DR (i.e., age, duration of diabetes, HbA1c level, and hypertension). All cases with comorbid chronic kidney disease were excluded to eliminate confounding factors. A total of 42 pairs were successfully matched. T2DM patients with DR (DR group) were the case group, and T2DM patients without DR (NDR group) served as control subjects. Ultra-performance liquid chromatography–mass spectrometry (LC–MS/MS) was used for untargeted lipidomics analysis on serum, and a partial least squares discriminant analysis (PLS-DA) model was established to screen differential lipid molecules based on variable importance in the projection (VIP)>1. An additional 531 T2DM patients were selected as the validation set. Next, 1:1 propensity score matching (PSM) was performed for the traditional risk factors for DR, and a combined 95 pairings in the NDR and DR groups were successfully matched. The screened differential lipid molecules were validated by multiple reaction monitoring (MRM) quantification based on mass spectrometry. Results The discovery set showed no differences in traditional risk factors associated with the development of DR (i.e., age, disease duration, HbA1c, blood pressure, and glomerular filtration rate). In the DR group compared Show less
Barrier function is the natural role of the skin. The lipid matrix present in the outermost layer of the skin, the stratum corneum is important for this function. Barrier impairment and altered... Show moreBarrier function is the natural role of the skin. The lipid matrix present in the outermost layer of the skin, the stratum corneum is important for this function. Barrier impairment and altered lipid composition are observed in several inflammatory skin diseases including atopic dermatitis and psoriasis. However, the relationship between the lipid properties and barrier function is not comprehended.In this project, a lipid model was prepared from synthetic lipids that closely resemble the stratum corneum lipid composition and organization. Subsequently, diseased skin models were developed to mimic various abnormalities in lipid composition observed in atopic dermatitis patients’ skin. Biophysical methods were used to monitor the changes in lipid organization in these models. Diffusion studies and trans-epidermal water loss measurements were performed to monitor the barrier function. This allowed the determination of the changes in lipid properties that were most instrumental in reducing the lipid barrier.This thesis further describes the use of simple skin lipid model membranes incorporating fewer components to provide a detailed insight into the relationship between lipid composition, lipid organization, and the skin barrier. The information gained in this project offers the opportunity to develop a new generation of formulations to treat these patients. Show less
Accumulating evidence indicates that ceramide (Cer) and palmitic acid (PA) possess the ability to modulate switching of macrophage phenotypes and possess anti-tumorigenic effects; however, the... Show moreAccumulating evidence indicates that ceramide (Cer) and palmitic acid (PA) possess the ability to modulate switching of macrophage phenotypes and possess anti-tumorigenic effects; however, the underlying molecular mechanisms are largely unknown. The aim of the present study was to investigate whether Cer and PA could induce switching of macrophage polarization from the tumorigenic M2- towards the pro-inflammatory M1-phenotype, and whether this consequently altered the potential of colorectal cancer cells to undergo epithelial-mesenchymal transition (EMT), a hallmark of tumor progression. Our study showed that Cer- and PA-treated macrophages increased expression of the macrophage 1 (M1)-marker CD68 and secretion of IL-12 and attenuated expression of the macrophage 2 (M2)-marker CD163 and IL-10 secretion. Moreover, Cer and PA abolished M2 macrophage-induced EMT and migration of colorectal cancer cells. At the molecular level, this coincided with inhibition of SNAI1 and vimentin expression and upregulation of E-cadherin. Furthermore, Cer and PA attenuated expression levels of IL-10 in colorectal cancer cells co-cultured with M2 macrophages and downregulated STAT3 and NF-kappa B expression. For the first time, our findings suggest the presence of an IL-10-STAT3-NF-kappa B signaling axis in colorectal cancer cells co-cultured with M2 macrophages, mimicking the tumor microenvironment. Importantly, PA and Cer were powerful inhibitors of this signaling axis and, consequently, EMT of colorectal cancer cells. These results contribute to our understanding of the immunological mechanisms that underlie the anti-tumorigenic effects of lipids for future combination with drugs in the therapy of colorectal carcinoma. Show less
Cell-based in vitro developed human skin equivalents facilitate screenings of compounds for therapeutic potential or toxicity and enable scientific research expanding knowledge on skin physiology... Show moreCell-based in vitro developed human skin equivalents facilitate screenings of compounds for therapeutic potential or toxicity and enable scientific research expanding knowledge on skin physiology and pathophysiology. Human skin equivalents resemble key features of native human skin, including the dermal and epidermal architecture. However, a limitation of human skin equivalents is the altered lipid barrier formation, which leads to a decreased barrier functionality. This could be induced by suboptimal cell culture conditions or the different cell microenvironment. The primary aim of this dissertational research was to enhance the morphogenesis and barrier formation of human skin equivalents to better mimic that of native human skin. The results indicate that modification of the dermal extracellular matrix by the biopolymer chitosan enhanced epidermal morphogenesis and barrier formation. Furthermore, by better resembling native skin conditions in vitro, primarily through a reduction in oxygen level, the epidermal morphogenesis and lipid barrier formation was improved. Finally, using a combinatory approach of optimized cell culture conditions and enhanced cell culture medium, the epidermal morphogenesis and barrier formation of human skin equivalents resembled that of native human skin more closely. Show less
Drug delivery across the skin is a challenging task because of the skin barrier. The skin barrier underlies in the outermost layer of the skin, the stratum corneum (SC). The lipids play a crucial... Show moreDrug delivery across the skin is a challenging task because of the skin barrier. The skin barrier underlies in the outermost layer of the skin, the stratum corneum (SC). The lipids play a crucial role in this barrier function. The focus of this PhD project was to elucidate the molecular structure of the lipid matrix present in the SC and to relate this structure with the barrier function. The lipid compositions selected for these studies were particularly chosen to understand the changes in barrier function in dry and diseased skin, i.e.,atopic eczema, Netherton syndrome compared to healthy skin. A variety of biophysical and analytical methods such as X-ray diffraction, neutron diffraction, infra-red spectroscopy, microscopy and LC/MS were combined to unravel the molecular structure. Diffusion studies and trans-epidermal water loss measurements were carried out to relate lipid organization with the lipid barrier. All the diffraction studies were performed in Grenoble, France at the ESRF (X-rays) and ILL (neutron). Neutron diffraction studies are in collaboration with King's College, University of London (Prof. J. Lawrence, Dr. D. Barlow). Show less
