Role of Nitric Oxide on Eosinophilic Lung Inflammation in Allergic Mice

Abstract

Nitric oxide (NO) is an important mediator of inflammatory reactions and may contribute to the lung inflammation in allergic pulmonary diseases. To assess the role of NO in pulmonary inflammation, we studied the effect of four nitric oxide synthase (NOS) inhibitors, N-nitro-L-arginine methyl ester (L-NAME), aminoguanidine, N(G)-monomethyl-L-arginine (NMMA) and L-N6-(1-Iminoethyl) lysine (L-NIL), on the influx of eosinophils into the bronchoalveolar lavage (BAL) fluid and lung tissue of antigen-challenged allergic mice. We also analyzed lung tissues for the presence of steady state mRNA for inducible nitric oxide synthase (iNOS) and iNOS protein. Furthermore, BAL fluid and serum were analyzed for their nitrite content. B6D2F1/J mice were sensitized to ovalbumin (OVA) and challenged with aerosolized OVA. The NOS inhibitors were given 0.5 h before and 4 h after the antigen challenge. OVA challenge induced a marked eosinophilia in the BAL fluid and lung tissue 24 h after challenge. The OVA-induced pulmonary eosinophilia was significantly reduced by L-NAME (10 and 50 mg/kg, intraperitoneally [i.p.]). The inactive isomer, D-NAME (50 mg/kg, i.p.) had no effect. When mice were treated with L-NAME (20 mg/kg, i.p.) and an excess of NOS substrate, L-arginine (200 mg/kg, i.p.), the OVA-induced pulmonary eosinophilia was restored. Treatment with aminoguanidine (0.4-50 mg/kg, i.p.) also reduced the pulmonary eosinophilia. Treatment with NMMA (2-50 mg/kg, i.p.) partially reduced the eosinophilia, but L-NIL (10-50 mg/kg, i.p.), a selective iNOS inhibitor, had no effect. L-NAME had no effect on the reduction of eosinophils in the bone marrow following OVA challenge to sensitized mice. OVA challenge to sensitized mice had no effect on iNOS protein expression or iNOS mRNA in the lungs or on the levels of nitrite in the BAL fluid. These results suggest that NO is involved in the development of pulmonary eosinophilia in allergic mice. The NO contributing to the eosinophilia is not generated through the activity of iNOS nor does NO contribute to the efflux of eosinophils from the bone marrow in response to antigen challenge. It is speculated that after antigen challenge, the localized production of NO, possibly from pulmonary vascular endothelial cells, is involved in the extravasation of eosinophils from the circulation into the lung tissue.

Collagen Deposition in a Non-Fibrotic Lung Granuloma Model after Nitric Oxide Inhibition

“…All compounds were administered at a dose of 8 mg/kg as previously described. 27,29 L-NAME is a nondiscriminating inhibitor of all three isoforms of nitric oxide synthase, whereas D-NAME is a structural enantiomer of L-NAME that lacks nitric oxide synthase inhibitory actions. 30 Aminoguanidine has been used by a number of investigators to more selectively inhibit NOS II activity.…”

“…30 Aminoguanidine has been used by a number of investigators to more selectively inhibit NOS II activity. 29,[31][32][33] Aminoguanidine has also been shown to inhibit the induction of NOS II in the endotoxin-challenged lung. 34 L-NAME and aminoguanidine were used in the present study to determine the relative contribution of all of the isoforms nitric oxide synthase (ie, NOS I, II, and III) as compared with the inducible nitric oxide synthase (ie, NOS II) on the development of extracellular matrix around PPD-bead granulomas.…”

Nitric oxide paradox in asthma

“…Also nitrite levels measured in BAL fluid were not increased. The authors conclude from these results that NO contribute to OVA-induced eosinophilia but its production is not generated through the activity of inducible NOS2 (Feder et al 1997). In contrast, Trifilieff et al (2000) using a similar approach, found that two different selective inhibitors of NOS2, EIT (S-ethylisothiourea) or AMT (2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine), administered during the challenge period, markedly reduced AHR and BAL eosinophilia.…”

“…Feder et al (1997) investigated the effect of four NOS inhibitors, N-nitro-L-arginine methyl ester (L-NAME), aminoguanidine, NG-onomethyl-L-arginine (NMMA), and L-N6-(1-Iminoethyl) lysine (L-NIL), on the influx of eosinophils into the bronchoalveolar lavage (BAL) fluid and lung tissue of sensitized and OVA-challenged mice. The authors found that treating the animals with L-NAME, aminoguanidine or NMMA significantly reduced the OVA-induced pulmonary eosinophilia.…”

“…This issue is further unsettled because several groups that investigated the role of NOS2 in the murine asthma model generated conflicting data. For instance, it has been shown that acute inhibition of NOS2 activity has no effect (Feder et al 1997), suppresses (Trifilieff et al 2000), or exacerbates airway inflammation (Blease et al 2000). Controversial data was also generated in studies using NOS2 knockout mice.…”