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that decrease the formation of the lamellar lipids that also are a part of the stratum corneum. The net effect of these epidermal impairments is a reduced ability in atopic skin to
self-repair, leading to extended signaling of repair and inflammatory cascades. These signals lead to further impairment of skin functions resulting in chronic activation of immune cells which
eventually presents as atopic dermatitis and related conditions.
Figure 19: Depiction of the composition and architecture of the epidermis.
LXRs are important regulators of epidermal biology. Activation of LXRs by ligands, which are molecules that bind to the active site on
LXR, leads to stimulation of keratinocyte differentiation, epidermal lipid synthesis and an anti-inflammatory response in skin cells. LXR ligands stimulate keratinocyte differentiation by inducing the
expression of genes involved in stratum corneum formation, including involucrin, loricrin and filaggrin. Lipids such as cholesterol, ceramides and fatty acids are produced in the epidermis and are
essential for skin barrier formation and maintenance. Topical application of LXR agonists has been demonstrated to augment epidermal lipid synthesis and secretion into extracellular spaces in mouse
skin by inducing new lipid synthesis and expression of the ABC family of lipid transporters. In addition, LXR ligands have been shown to have anti-inflammatory properties. LXR agonism exerts
general inhibitory action on pro-inflammatory genes in multiple cell types. This anti-inflammatory activity is illustrated by the observed efficacy of LXR agonists in mouse models of atopic
dermatitis, irritant dermatitis and epidermal proliferation. As a result, we believe LXR activation has potential as a novel therapeutic approach because it enhances the integrity of the epidermal
barrier and simultaneously suppresses skin inflammation.
Atopic dermatitis, also known as eczema, affects both children and adults. The National Eczema Association reports that there are
approximately 31.6 million people in the United States with symptoms of eczema or eczematous conditions and, among that group, at least 17.8 million people have symptoms of atopic
dermatitis, considered a more severe form of eczema. The National Institute of Arthritis and Musculoskeletal and Skin Diseases estimates that the worldwide prevalence of atopic dermatitis in infants
and children is approximately 7-17%, approximately 60% of whom have recurrence of the disease as adults. The two most commonly used classes of topical therapies for atopic dermatitis are