The precise role of each nitric oxide (NO) synthase (NOS) isoform in the pathobiology of asthma is not well established. Our objective was to investigate the contribution of constitutive NO synthase (cNOS) and inducible NOS (iNOS) isoforms to lung mechanics and inflammatory and remodeling responses in an experimental model of chronic allergic pulmonary inflammation. Guinea pigs were submitted to seven ovalbumin exposures with increasing doses (1 approximately 5 mg/ml) for 4 wk. The animals received either chronic L-NAME (N-nitro-L-arginine methyl ester, in drinking water) or 1,400 W (iNOS-specific inhibitor, intraperitoneal) treatments. At 72 h after the seventh inhalation of ovalbumin solution, animals were anesthetized, mechanically ventilated, exhaled NO was collected, and lung mechanical responses were evaluated before and after antigen challenge. Both L-NAME and 1,400 W treatments increased baseline resistance and decreased elastance of the respiratory system in nonsensitized animals. After challenge, L-NAME increased resistance of the respiratory system and collagen deposition on airways, and decreased peribronchial edema and mononuclear cell recruitment. Administration of 1,400 W reduced resistance of the respiratory system response, eosinophilic and mononuclear cell recruitment, and collagen and elastic fibers content in airways. L-NAME treatment reduced both iNOS- and neuronal NOS-positive eosinophils, and 1,400 W diminished only the number of eosinophils expressing iNOS. In this experimental model, inhibition of NOS-derived NO by L-NAME treatment amplifies bronchoconstriction and increases collagen deposition. However, blockage of only iNOS attenuates bronchoconstriction and inflammatory and remodeling processes.

We assessed the effects of neurokinin (tachykinin) depletion by capsaicin (CAP) treatment on airway inflammation induced by repeated ovalbumin (OA) aerosol exposures (twice a week for 4 wk) in guinea pigs. The animals were then anesthetized, tracheostomized, mechanically ventilated and challenged with ovalbumin aerosol. Maximal values of respiratory system resistance and elastance after antigen challenge were significantly lower in capsaicin-treated guinea pigs than in intact animals (p < 0.001). Morphometric analysis of noncartilaginous airways revealed less intense bronchoconstriction (p < 0.001) and peribronchiolar edema (p < 0.001) in capsaicin-treated guinea pigs. Chronic antigen exposure resulted in a significant increase in lymphocytes and eosinophils both in bronchoalveolar lavage (BAL) fluid and airway wall. Immunohistochemistry with monoclonal antibodies revealed that most of the lymphocytes present in airway wall were CD4+ T cells. Capsaicin treatment resulted in values of CD4+ T cells in airway wall significantly lower than non-capsaicin-treated guinea pigs (p < 0.005). This difference was not observed in eosinophil recruitment. Our results suggest that neurokinin release by sensory nerve terminals results in an amplification of the pulmonary inflammatory changes induced by chronic antigen exposure. In addition, neurokinins play a role in T-cell recruitment induced by chronic allergen exposure.

Endogenously produced nitric oxide is a recognized regulator of physiological lung events, such as a neurotransmitter and a proinflammatory mediator. We tested the differences between chronic and acute nitric oxide inhibition by N(omega)-nitro-L-arginine methyl ester (L-NAME) treatment in lung mechanics, inflammation, and airway remodeling in an experimental asthma model in guinea pigs. Both acute and chronic L-NAME treatment reduced exhaled nitric oxide in sensitized animals (P < 0.001). Chronic L-NAME treatment increased baseline and maximal responses after antigen challenge of respiratory system resistance and reduced peribronchial edema and mononuclear cells airway infiltration (P < 0.05). Acute administration of L-NAME increased maximal values of respiratory system elastance and reduced mononuclear cells and eosinophils in airway wall (P < 0.05). Chronic ovalbumin exposure resulted in airway wall thickening due to an increase in collagen content (P < 0.005). Chronic nitric oxide inhibition increased collagen deposition in airway wall in sensitized animals (P < 0.05). These data support the hypothesis that in this model nitric oxide acts as a bronchodilator, mainly in proximal airways. Furthermore, chronic nitric oxide inhibition was effective in reducing edema and mononuclear cells in airway wall. However, airway eosinophilic inflammation was unaltered by chronic L-NAME treatment. In addition, nitric oxide inhibition upregulates collagen deposition in airway walls.

Several studies have demonstrated the importance of Rho-kinase in the modulation of smooth muscle contraction, airway hyperresponsiveness, and inflammation. However, the effects of repeated treatment with a specific inhibitor of this pathway have not been previously investigated. We evaluated the effects of repeated treatment with Y-27632, a highly selective Rho-kinase inhibitor, on airway hyperresponsiveness, oxidative stress activation, extracellular matrix remodeling, eosinophilic inflammation, and cytokine expression in an animal model of chronic airway inflammation. Guinea pigs were subjected to seven ovalbumin or saline exposures. The treatment with Y-27632 (1 mM) started at the fifth inhalation. Seventy-two hours after the seventh inhalation, the animals' pulmonary mechanics were evaluated, and exhaled nitric oxide (E(NO)) was collected. The lungs were removed, and histological analysis was performed using morphometry. Treatment with Y-27632 in sensitized animals reduced E(NO) concentrations, maximal responses of resistance, elastance of the respiratory system, eosinophil counts, collagen and elastic fiber contents, the numbers of cells positive for IL-2, IL-4, IL-5, IL-13, inducible nitric oxide synthase, matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1, transforming growth factor-β, NF-κB, IFN-γ, and 8-iso-prostaglandin F2α contents compared with the untreated group (P < 0.05). We observed positive correlations among the functional responses and inflammation, remodeling, and oxidative stress pathway activation markers evaluated. In conclusion, Rho-kinase pathway activation contributes to the potentiation of the hyperresponsiveness, inflammation, the extracellular matrix remodeling process, and oxidative stress activation. These results suggest that Rho-kinase inhibitors represent potential pharmacological tools for the control of asthma.

Although leukotriene receptor antagonist treatment reduces eosinophil accumulation induced by multiple antigen challenges, glucocorticoid treatment attenuates both eosinophil and mononuclear cell infiltration.