Development of numerous nerve fibers in the epidermis of hairless mice with atopic dermatitis-like pruritic skin inflammation

Intractable Itch in Atopic Dermatitis: Causes and Treatments

Itch or pruritus is the hallmark of atopic dermatitis and is defined as an unpleasant sensation that evokes the desire to scratch. It is also believed that itch is a signal of danger from various environmental factors or physiological abnormalities. Because histamine is a well-known substance inducing itch, H₁-antihistamines are the most frequently used drugs to treat pruritus. However, H₁-antihistamines are not fully effective against intractable itch in patients with atopic dermatitis. Given that intractable itch is a clinical problem that markedly decreases quality of life, its treatment in atopic dermatitis is of high importance. Histamine-independent itch may be elicited by various pruritogens, including proteases, cytokines, neuropeptides, lipids, and opioids, and their cognate receptors, such as protease-activated receptors, cytokine receptors, Mas-related G protein-coupled receptors, opioid receptors, and transient receptor potential channels. In addition, cutaneous hyperinnervation is partly involved in itch sensitization in the periphery. It is believed that dry skin is a key feature of intractable itch in atopic dermatitis. Treatment of the underlying conditions that cause itch is necessary to improve the quality of life of patients with atopic dermatitis. This review describes current insights into the pathophysiology of itch and its treatment in atopic dermatitis.

IL-33/ST2 signaling excites sensory neurons and mediates itch response in a mouse model of poison ivy contact allergy

Poison ivy-induced allergic contact dermatitis (ACD) is the most common environmental allergic condition in the United States. Case numbers of poison ivy ACD are increasing due to growing biomass and geographical expansion of poison ivy and increasing content of the allergen, urushiol, likely attributable to rising atmospheric CO₂ Severe and treatment-resistant itch is the major complaint of affected patients. However, because of limited clinical data and poorly characterized models, the pruritic mechanisms in poison ivy ACD remain unknown. Here, we aim to identify the mechanisms of itch in a mouse model of poison ivy ACD by transcriptomics, neuronal imaging, and behavioral analysis. Using transcriptome microarray analysis, we identified IL-33 as a key cytokine up-regulated in the inflamed skin of urushiol-challenged mice. We further found that the IL-33 receptor, ST2, is expressed in small to medium-sized dorsal root ganglion (DRG) neurons, including neurons that innervate the skin. IL-33 induces Ca²⁺ influx into a subset of DRG neurons through neuronal ST2. Neutralizing antibodies against IL-33 or ST2 reduced scratching behavior and skin inflammation in urushiol-challenged mice. Injection of IL-33 into urushiol-challenged skin rapidly exacerbated itch-related scratching via ST2, in a histamine-independent manner. Targeted silencing of neuronal ST2 expression by intrathecal ST2 siRNA delivery significantly attenuated pruritic responses caused by urushiol-induced ACD. These results indicate that IL-33/ST2 signaling is functionally present in primary sensory neurons and contributes to pruritus in poison ivy ACD. Blocking IL-33/ST2 signaling may represent a therapeutic approach to ameliorate itch and skin inflammation related to poison ivy ACD.

A novel mechanism for improvement of dry skin by dietary milk phospholipids: Effect on epidermal covalently bound ceramides and skin inflammation in hairless mice

BACKGROUND

Dietary milk phospholipids (MPLs) increase hydration of the stratum corneum and reduced transepidermal water loss (TEWL) in hairless mice fed a standard diet. However, the mechanism by which MPLs improve skin barrier functions has yet to be established.

OBJECTIVE

This study was designed to examine the mechanism by which MPLs may affect covalently bound ceramides and markers of skin inflammation and improve the skin barrier defect in hairless mice fed a magnesium-deficient (HR-AD) diet.

METHODS

Four-week-old female hairless mice were randomized into four groups (n=10/group), and fed a standard (control) diet, the HR-AD diet, the HR-AD diet supplemented with either 7.0 g/kg MPLs (low [L]-MPL) or 41.0 g/kg MPLs (high [H]-MPL).

RESULTS

Dietary MPLs improved the dry skin condition of hairless mice fed the HR-AD diet. MPLs significantly increased the percentage of covalently bound ω-hydroxy ceramides in the epidermis, and significantly decreased both thymus and activation-regulated chemokine (TARC) mRNA and thymic stromal lymphopoietin (TSLP) mRNA levels in skin, compared with the HR-AD diet. Furthermore, the MPL diets significantly decreased serum concentrations of immunoglobulin-E, TARC, TSLP, and soluble P-selectin versus the HR-AD diet.

CONCLUSION

Our study showed for the first time that dietary MPLs may modulate epidermal covalently bound ceramides associated with formation of lamellar structures and suppress skin inflammation, resulting in improved skin barrier function.

The effect of wasabi rhizome extract on atopic dermatitis-like symptoms in HR-1 hairless mice

We investigated the effect of wasabi rhizome extract on atopic dermatitis (AD) model mice. The wasabi extract was fed to the HR-1 hairless mice, which develop AD-like symptoms with a special diet (HR-AD diet). The extract was expected to reduce the symptoms induced. Wasabi rhizome-containing HR-AD diet (5% and 10%) reduced the scratching behavior, and the 10% wasabi rhizome HR-AD diet significantly reduced scratching behavior on days 28, 35 and 42. Plasma components (histamine, eotaxin, IgE and thymus and activation-regulated chemokine (TARC)) were decreased in the 10% wasabi rhizome HR-AD diet. In histopathological examinations (toluidine blue (T.B.), major basic protein (MBP), CD4, IL-4, IL-5, eotaxin, TARC and IgE), the wasabi rhizome-containing HR-AD diet (5% and 10%) significantly reduced the number of positive stained cells. These results suggested that the wasabi rhizome extract improved the AD-like symptoms of HR-1 hairless mice.