Spontaneous scratching behaviour in DS-Nh mice as a possible model for pruritus in atopic dermatitis

Abstract

Itching is one of the major clinical symptoms in atopic dermatitis (AD) and complicates the management of this pathological condition. An animal model of AD-like pruritus would contribute to a better understanding of AD and could lead to the development of safe and effective antipruritic agents. DS non-hair (DS-Nh) mice raised under conventional conditions spontaneously develop pruritus, which is associated with a dermatitis similar to human AD. There is a significant positive correlation between disease severity and the period of scratching behaviour in DS-Nh mice. In the present study, we found that levels of histamine and nerve growth factor (NGF) in serum and/or skin tissue were higher in DS-Nh mice with AD-like dermatitis than in age-matched mice without dermatitis. The histopathological data indicated that nerve fibres extend into and mast cells infiltrate the surrounding area of the skin lesion. NGF production by XB-2 cells, which was derived from mouse keratinocytes, was enhanced by histamine via the H1 receptor. We also found that prolonged treatment with an H1-antagonist was effective against pruritus through depression of the production of NGF, which is thought to be generated by keratinocytes. We conclude that DS-Nh mice can serve as a suitable model for gaining a better understanding of pruritus in AD, and that prolonged treatment with an H1-antagonist may be beneficial in patients with AD-associated pruritus.

Figure 1

Clinical features of DS-Nh mice kept under conventional conditions at 20 weeks (a) and fluctuation of clinical skin condition with aging (b). Closed circles show data for conventionally housed DS-Nh mice, and open circles show data for DS-Nh mice raised under specific pathogen-free (SPF) conditions. Total clinical scores for skin conditions were determined from the severity of erythema, oedema, dry skin, erosion and excoriation (open and closed black circle indicate clinical skin score). Rubbing/scratching time was counted per 5 min (open and closed red circle indicate scratching time). Each value represents the mean and standard deviation for 10 conventionally housed DS-Nh mice or five DS-Nh mice raised under SPF conditions.

Figure 2

Serological conditions with aging and kinetic levels of nerve growth factor (NGF) and histamine in skin lesions from mice. Levels of immunoglobulin E (IgE) (a) and NGF (b) were measured in sera collected from mice kept under conventional and specific pathogen-free (SPF) conditions. Skin from a series of DS-Nh mice was collected, and histamine and NGF from skin homogenate were eluted to measure histamine (c) and NGF (d) contents using enzyme-linked immunosorbent assay (ELISA) or enzyme-based colour reaction kits. Each value represents the mean and standard deviation of 10 conventionally housed DS-Nh mice or five DS-Nh mice raised under SPF conditions.

Figure 3

Kinetic change in number of mast cells and frequency of degranulated mast cells (a) and histological features of facial skin tissue from DS-Nh conventionally housed mice at 20 weeks (b) The number of mast cells per mm² of skin area was counted using paraffin sections from conventionally and specific pathogen-free (SPF) housed DS-Nh mice.

Figure 4

Immunohistological features of facial skin tissue. Frozen sections from conventionally housed DS-Nh mice at 5, 8, 10 and 15 weeks of age were stained with anti-S100 antibodies.

Figure 5

Effect of histamine on nerve growth factor (NGF) production and inhibition by desloratadine as a H1 receptor antagonist. The XB-2 cell line was precultured with 0, 4, 20, 100 and 500 nm of loratadine, and then cultured with 100 mm of histamine for 24 hr. The cell-free culture supernatants were assayed for NGF measurement. Each value represents the mean and standard deviation.

Figure 6

Effects of rinderon V in DS-Nh mice with atopic dermatitis (AD)-like dermatitis. Changes in the pathology of skin lesions (a) and scratching times (b) in DS-Nh mice with severe dermatitis after steroid treatment are shown. Paraffin sections were stained with haematoxylin and eosin (HE) acidic toluidine for treatment blue (TB) (left) and non-treatment (right) with steroid, and frozen sections were immunostained for mouse CD4 for treatment (left) and non-treatment (right) with steroid (a). We counted scratching time in DS-Nh mice with severe dermatitis for 20-min periods after steroid or base treatment (b). Each value represents the mean and standard deviation.

Figure 7

Effects of loratadine in DS-Nh mice with atopic dermatitis (AD)-like dermatitis. Changes in the clinical features of facial skin (a), clinical severity (b), and scratching time (c) in DS-Nh mice with weak to moderate dermatitis after loratadine treatment are shown. Levels of nerve growth factor (NGF) in serum from DS-Nh mice were significantly reduced after loratadine treatment compared with those after base material treatment (d) Each value represents the mean and standard deviation or standard error (levels of NGF).