Suppressive Activity of Adiponectin on the Development of Allergic Rhinitis in Mice

Adiponectin is accepted as playing pivotal roles in the development of allergic rhinitis (AR) through modulation of production of inflammatory mediators. Although it is also well known that neuropeptides, especially substance P (SP), function in the development and persistence of clinical conditions of AR, the influence of adiponectin on neuropeptide production is not well understood. The present study was designed to examine the influence of adiponectin on the production of SP both in vivo and in vitro.

PC-12 cells (1×10⁴ cells) were stimulated with 10.0 ng/ml nerve growth factor (NGF) for 2 h and then with 10.0 ng/ml capsaicin in the presence of different concentrations of adiponectin. After 72 h, culture supernatants were obtained, and SP levels were measured with enzyme-linked immunosorbent assay (ELISA). The influence of adiponectin on the total number of neurites developed per PC-12 cell and on the percentage of PC-12 cells with outgrowing neurites was also examined 24 and 72 h after the start of culture, respectively. In the second part of the study, BALB/c mice were sensitized intraperitoneally with 1.0 μg of ovalbumin and then challenged with intranasal ovalbumin. At 7 days following sensitization, these mice were treated with different doses of adiponectin intranasally in a volume of 5.0 μl. Nasal allergy-like symptoms, which were induced by bilateral application of 0.1 % OVA (5.0 μl), were assessed by counting sneezing and nasal rubbing behavior for 10 min immediately after nasal ovalbumin challenge. SP levels in nasal lavage fluid obtained 6 h after nasal ovalbumin challenge were examined by ELISA.

Treatment of NGF-stimulated PC-12 cells with adiponectin suppressed SP production, which was induced by capsaicin stimulation. The minimum concentration of adiponectin that caused significant suppression was 7.5 ng/ml. On the other hand, adiponectin did not affect the total number of neurites and the percentage of PC-12 cells with outgrowing neurites, even at 1,000 ng/ml. Intranasal instillation of adiponectin into ovalbumin-sensitized mice at more than 10.0 ng/ml, but not 5.0 ng/ml, significantly inhibited the appearance of SP in nasal secretions, which was increased by intranasal challenge with ovalbumin. Adiponectin also suppressed the development of nasal allergic-like symptoms, sneezing and rubbing behavior, when ovalbumin-sensitized mice were treated intranasally with adiponectin at more than 10.0 ng/ml. The present results strongly suggested that adiponectin suppresses the production of SP and results in improvement of the clinical conditions of AR.