Inhalation of the Rho-kinase inhibitor Y-27632 reverses allergen-induced airway hyperresponsiveness after the early and late asthmatic reaction

Abstract

Background: In guinea pigs, we have previously demonstrated that the contribution of Rho-kinase to airway responsiveness in vivo and ex vivo is enhanced after active sensitization with ovalbumin (OA). Using conscious, unrestrained OA-sensitized guina pigs, we now investigated the role of Rho-kinase in the development of airway hyperresponsiveness (AHR) after the allergen-induced early (EAR) and late asthmatic reaction (LAR) in vivo.

Methods: Histamine and PGF2alpha PC100-values (provocation concentrations causing 100% increase in pleural pressure) were assessed before OA-challenge (basal airway responsiveness) and after the OA-induced EAR (5 h after challenge) and LAR (23 h after challenge). Thirty minutes later, saline or the specific Rho-kinase inhibitor Y-27632 (5 mM, nebulizer concentration) were nebulized, after which PC100-values were reassessed.

Results: In contrast to saline, Y-27632 inhalation significantly decreased the basal responsiveness toward histamine and PGF2alpha before OA-challenge, as indicated by increased PC100 -values. Both after the allergen-induced EAR and LAR, AHR to histamine and PGF2alpha was present, which was reversed by Y-27632 inhalation. Moreover, there was an increased effectiveness of Y-27632 to reduce airway responsiveness to histamine and PGF2alpha after the EAR and LAR as compared to pre-challenge conditions. Saline inhalations did not affect histamine or PGF2alpha PC100-values at all. Interestingly, under all conditions Y-27632 was significantly more effective in reducing airway responsiveness to PGF2alpha as compared to histamine. Also, there was a clear tendency (P = 0.08) to a more pronounced degree of AHR after the EAR for PGF2alpha than for histamine.

Conclusion: The results indicate that inhalation of the Rho-kinase inhibitor Y-27632 causes a considerable bronchoprotection to both histamine and PGF2alpha. Moreover, the results are indicative of a differential involvement of Rho-kinase in the agonist-induced airway obstruction in vivo. Increased Rho-kinase activity contributes to the allergen-induced AHR to histamine and PGF2alpha after both the EAR and the LAR, which is effectively reversed by inhalation of Y-27632. Therefore, Rho-kinase can be considered as a potential pharmacotherapeutical target in allergic asthma.

Figure 1

Effects of saline (A) and Y-27632 (5 mM nebulizer concentration; B) inhalations on airway responsiveness toward histamine after the allergen-induced EAR and LAR. Data represent means ± s.e.mean of 5 animals. *P < 0.05, **P < 0.01, ***P < 0.001 compared to basal; ^#P < 0.05, ^## P < 0.01 compared to control.

Figure 2

Effects of saline (A) and Y-27632 (5 mM nebulizer concentration; B) inhalations on airway responsiveness toward PGF_2α after the allergen-induced EAR and LAR. Data represent means ± s.e.mean of 7 animals. *P < 0.05, **P < 0.01, ***P < 0.001 compared to basal; ^##P < 0.01, ^### P < 0.001 compared to control.

Figure 3

Effectiveness of saline and Y-27632 inhalations to reduce basal airway responsiveness and airway (hyper)responsiveness after the EAR and the LAR for histamine (A) and PGF_2α (B). Data are expressed as the PC₁₀₀ ratio post/pre saline or Y-27632 inhalation. Data represent means ± s.e.mean of 5 (histamine) and 7 (PGF_2α) animals. *P < 0.05 **P < 0.01 compared to basal effectiveness.