Effect of antiallergic drugs on interleukin 5-induced eosinophil infiltration of rat airways

Prostanoid DP receptor antagonists suppress symptomatic asthma-like manifestation by distinct actions from a glucocorticoid in rats

While inhaled glucocorticoids are the best treatment for the majority of chronic asthmatics, there is a small group who do not respond to these drugs or whose disease can only be controlled by high doses of oral glucocorticoids with risks of severe side effects. Therefore, a safe novel anti-asthmatic agent which has a different mechanism from that of glucocorticoids is needed for the management of asthma. We have previously shown that an orally active prostanoid DP receptor antagonist, S-5751, had potent anti-inflammatory effects in guinea pig and sheep asthma models. In this study, using a rat asthma like model, we found that lung neutrophilia and proinflammatory cytokine secretion as well as bronchial hyperresponsiveness and lung eosinophilia were induced by repeated antigen-inhalations after antigen-sensitization. These symptoms are similar to the pathogenesis of symptomatic asthma. Orally-administered prostanoid DP receptor antagonists S-5751 and pinagladin significantly suppressed not only bronchial hyperresponsiveness and lung eosinophilia but also neutrophilia and mucus secretion in the lung, while oral prednisolone inhibited only bronchial hyperresponsiveness and eosinophil infiltration. In addition, prostanoid DP receptor antagonists significantly suppressed interleukin (IL)-1β, IL-6 and CXCL1 mRNA in contrast to suppression of IL-4 and CCL11 mRNA by prednisolone. The majority of prostanoid DP receptor-expressing cells in both rat and human asthmatic lungs are infiltrative macrophages and/or monocytes. These results suggest that prostanoid DP receptor antagonists utilize different mechanisms from glucocorticoids, and that they would be a novel alternative and/or combination drug for asthma therapy.

Glucocorticoids ameliorate antigen-induced bronchial smooth muscle hyperresponsiveness by inhibiting upregulation of RhoA in rats

To determine the mechanism(s) of the inhibitory effect of glucocorticoids on airway hyperresponsiveness in allergic bronchial asthma, the effects of systemic treatment with glucocorticoids on bronchial smooth muscle hyperresponsiveness and RhoA upregulation were investigated in rats with allergic bronchial asthma. Rats were sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen. Animals were also treated with prednisolone or beclomethasone (each 10 mg/kg, i.p.) once a day during the antigen inhalation period. Repeated antigen inhalation caused a marked bronchial smooth muscle hyperresponsiveness to acetylcholine with an upregulation of RhoA. Augmented acetylcholine-induced activation of RhoA and phosphorylation of myosin light chain were observed in bronchial smooth muscles of the antigen-exposed animals. Systemic treatment with either glucocorticoid used inhibited the bronchial smooth muscle hypercontraction until the level of the sensitized control rats that received saline inhalation instead of antigen challenge. Interestingly, both glucocorticoids also inhibited the upregulation of RhoA and augmented acetylcholine-induced activation of RhoA and phosphorylation of myosin light chain. In conclusion, glucocorticoids ameliorated the augmented bronchial smooth muscle contraction by inhibiting upregulation of RhoA. These effects of glucocorticoids may account for, in part, their beneficial effects in the treatment of asthma.

Effects of triterpenoid-rich extracts of Ganoderma tsugae on airway hyperreactivity and Th2 responses in vivo

BACKGROUND

Airway inflammation and Th2 responses play central roles in allergic asthma. We have previously reported that Ganoderma tsugae supplementation could attenuate airway inflammation in the murine model. Since it remains unclear which part of the G. tsugae exerts this effect on allergic asthma in vivo, this study was meant to investigate if triterpenoid extracts have anti-inflammatory effects on airway responses and regulatory effects on Th2 responses.

METHODS

BALB/c mice sensitized intraperitoneally and challenged with ovalbumin (OVA) were treated with either triterpenoid-rich extracts (TRE) of G. tsugae or prednisolone for 2 weeks. The effects of TRE on bronchial airway hyperresponsiveness (AHR), airway inflammation, serum antigen-specific antibody levels, and cytokine secretions from splenocytes were evaluated.

RESULTS

TRE supplementation significantly decreased AHR and reduced the total infiltrating leukocytes and eosinophils, as well as the levels of inflammatory mediators, such as interleukin (IL)-4, IL-5 and eotaxin in bronchoalveolar lavage fluid when compared with those of the control group. Lung histology also showed less cell recruitment and lung damage. TRE supplements suppressed IL-5 secretions from OVA-stimulated splenocytes, but did not affect the cell number of splenocytes, which was also reduced by prednisolone. Although OVA-specific immunoglobulin E levels were not significantly different among the groups, a lower level of OVA-specific immunoglobulin G1, another Th2-related antibody, was found in TRE and prednisolone treatment.

CONCLUSIONS

TRE of G. tsugae exert anti-inflammatory effects on airway responses and attenuate Th2 responses without the overall immunosuppression effects in allergic murine models of asthma.

Recent advances in the development of anti-allergic drugs

Research over the past decade has provided information concerning the onset and treatment of allergic diseases, including bronchial asthma, allergic rhinitis and atopic dermatitis. Recent studies also indicated that allergic inflammation is the basic pathophysiology of allergic diseases and is closely associated with their progression and exacerbation. Our understanding of the mechanism of allergic inflammation with regard to therapeutic agents has improved as a result of immunological and molecular biological studies. While much effort has been paid to developing a new anti-allergic drug, allergic disease has yet to be completely conquered. More extensive research will allow the development of new therapeutics to combat allergic diseases. This article provides an overview of recent advances in the development of anti-allergic drugs.