Nasal hyperreactivity and inflammation in allergic rhinitis

Alterations of vasoactive intestinal polypeptide receptors in allergic rhinitis

BACKGROUND

Vasoactive intestinal peptide (VIP) is one of the parasympathetic neurotransmitters involved in the regulation of airway mucus secretion. The biological functions of VIP are mediated through two receptors (vasoactive intestinal peptide receptor type 1 [VPAC1R] and type 2 [VPAC2R]). The purpose of this study was to determine the distribution of VIP receptors and to compare the level of VIP receptor expression in the nasal mucosa of patients with allergic rhinitis and normal controls.

METHODS

Inferior turbinate mucosal samples were obtained from 20 normal subjects and 20 patients with allergic rhinitis. VPAC1R and VPAC2R mRNA was extracted from the nasal mucosa, and then a reverse-transcription-polymerase chain reaction was performed. Sections were immunostained using specific antibodies for VIP receptors. Western blot analysis was used to analyze differences in the level of expression of VPAC1R and VPAC2R protein between patients with allergic rhinitis and normal controls.

RESULTS

The level of expression of VIP receptor mRNA and protein in patients with allergic rhinitis was significantly increased compared with normal nasal mucosa. VIP receptor immunoreactivity was detected on the nasal epithelium and submucosal glands in nasal specimens from both normal controls and patients with allergic rhinitis. In the epithelium from patients with allergic rhinitis, VIP receptor immunoreactivity was strong, whereas in the nasal epithelium from normal subjects it was faint.

CONCLUSION

These results suggest that an increased expression level of VIP receptors is one possible explanation for nasal hyperresponsiveness in patients with allergic rhinitis.

Effect of Oral Immunotherapy on Nasal Blockage in Experimental Allergic Rhinitis

We previously reported that when Japanese cedar pollen was prophylactically p.o. administered before a sensitization stage in a guinea-pig model of allergic rhinitis, pollen-induced nasal blockage was suppressed. In this study, we evaluated whether the oral immunotherapy is also effective when the pollen extract was administered starting from the day when the nasal blockage was clearly induced and whether the effectiveness continued after cessation of the immunotherapy. Sensitized animals were repeatedly challenged by pollen inhalation once every week. After the 7th challenge, the extract was orally administered twice a week until the 30th challenge. At the 11th challenge, the oral immunotherapy showed inhibition of the biphasic nasal blockage. The effectiveness was consistently observed during the immunotherapy until the 30th challenge. Furthermore, the increased nasal responsiveness to intranasal application of leukotriene D4 was markedly suppressed by the immunotherapy. Interestingly, even after cessation of the therapy, inhibition of the nasal blockage was sustained for more than 2 months. Nevertheless, neither sneezing nor antigen-specific IgE antibody production was substantially influenced by the immunotherapy. In conclusion, Oral immunotherapy may be clinically useful for allergic nasal blockage. Mechanisms underlying the effectiveness may be associated with the hyporesponsiveness of the nasal mucosa to released mediators.

Kinins are involved in the development of allergic nasal hyperresponsiveness in guinea pigs

We evaluated roles of kinins in allergen-induced nasal blockage and sneezing, and development of nasal hyperresponsiveness to leukotriene D4 in a Japanese cedar pollen-induced allergic rhinitis model of guinea pigs. Sensitised guinea pigs were repeatedly challenged by pollen inhalation once every week. Neither a bradykinin B1 receptor antagonist, des-Arg9-[Leu8]bradykinin nor a bradykinin B2 receptor antagonist, icatibant suppressed allergen-induced sneezing and nasal blockage. However, development of nasal hyperresponsiveness to leukotriene D4 was significantly suppressed by them. The amount of bradykinin in nasal cavity lavage fluid was immediately increased after the challenge. In non-sensitised animals, hyperresponsiveness to leukotriene D4 was developed by a bradykinin B2 receptor agonist, bradykinin, but not by a bradykinin B1 receptor agonist, des-Arg10-kallidin, while in the sensitised-challenged animal, both agonists developed hyperresponsiveness. In conclusion, the nasal hyperresponsiveness appeared to be induced by kinins produced in response to the antigen challenge through activation of not only bradykinin B2 but also B1 receptors.

No involvement of interleukin-5 or eosinophils in experimental allergic rhinitis in guinea pigs

The aim of this study is to evaluate whether nasal airway eosinophilia is a true pathogenetic component of allergic rhinitis. We investigated the effects of TRFK5, an anti-interleukin-5 antibody, not only on leukocyte mobilization from the bone marrow, but also on the development of nasal symptoms and hyperresponsiveness in a guinea pig model of allergic rhinitis. Intranasally sensitized animals were repetitively challenged by exposure to Japanese cedar pollen as antigen. TRFK5 (100 microg/kg, i.p.) given 12 h before the final antigen challenge selectively prevented the antigen-induced eosinophilia in blood and the nasal airway, and suppressed the corresponding decrease in the number of cells in bone marrow; however, it failed to inhibit the immediate development of sneezing, early and late nasal blockage responses, goblet cell degranulation and nasal hyperresponsiveness to histamine. Furthermore, TRFK5 did not significantly affect the production of thromboxane A(2) and cysteinyl leukotrienes in the nasal airway during the late response. These results strongly suggest that while interleukin-5 is essential for eosinophil migration from the bone marrow to the nasal airway, neither interleukin-5 nor eosinophils are required for the development of the nasal symptoms and nasal hyperresponsiveness of allergic rhinitis.

Involvement of nitric oxide in pollen-induced biphasic nasal blockage in sensitised guinea pigs

We have developed a reproducible allergic rhinitis model showing biphasic nasal blockage on repetitive inhalation challenge with Japanese cedar pollen in sensitised guinea pigs. The role of nitric oxide (NO) in inducing nasal blockage was evaluated with this model. N(omega)-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase (NOS) inhibitor, intravenously administered before the challenge, significantly inhibited both early and late nasal blockage by approximately 80% and 50%, respectively. When L-NAME treatment was performed after the challenge, the late response was inhibited by approximately 70%. This inhibition was completely reversed by co-administration of L-arginine. However, aminoguanidine and L-N(6)-(1-iminoethyl)lysine, selective inhibitors of inducible NOS, negligibly influenced the degree of nasal blockage. Meanwhile, the alpha-adrenergic agonist, naphazoline, strongly suppressed both early and late nasal blockage. These results indicate that NO, likely produced by constitutive rather than inducible NOS, plays a major role in the occurrence of biphasic nasal blockage, primarily by inducing vasodilatation.