Zanamivir Diminishes Lung Damage in Influenza A Virus-infected Mice by Inhibiting Nitric Oxide Production

Abstract

Background/aim: Severe pulmonary influenza A virus (IAV) infection causes lung inflammation and expression of inducible nitric oxide synthase (iNOS), leading to overproduction of nitric oxide (NO). We studied whether zanamivir reduces pulmonary inflammation through inhibition of NO production in mice.

Materials and methods: We treated IAV-infected mice daily with intranasal zanamivir. Controls were infected and either placebo-treated or untreated, or not infected and placebo-treated. Mice were weighed daily. After euthanasia on day 3, lungs were excised and bronchoalveolar lavage was performed and fluid nitrite concentration was determined. Lungs were analyzed microscopically. iNOS and IAV RNA levels in lungs were assessed using quantitative reverse transcription-polymerase chain reaction (RT-qPCR).

Results: Mice undergoing zanamivir treatment had less weight loss, viral replication, and lung damage, as well as significant reductions of local NO and iNOS mRNA synthesis (p<0.05).

Conclusion: Zanamivir is associated with an anti-inflammatory effect mediated through inhibition of NO production in IAV-infected mice.

Keywords: Influenza virus; lung pathology; nitric oxide; zanamivir.

Figure 1. RNA levels of viral polymerase acidic (PA) protein in lungs of treatment and control groups of mice on day 3 after influenza A virus (IAV) infection. Data are shown as mean±SEM. Significantly different at p<0.05 vs. #uninfected placebo-treated mice (n=3), *infected mice without any treatment (n=3), §infected placebotreated mice (n=3). Infected + zanamivir, n=4.

Figure 2. Histological lung sections of BALB/c mice stained with hematoxylin and eosin. Arrows indicate: (i) alveolar hemorrhage, (ii) focal leukocytic infiltration, (iii) perivascular lymphocytic infiltration, (iv) peribronchial lymphocytic infiltration, (v) bronchiolitis

Figure 3. Nitrite (NO2−) concentration in mice bronchoalveolar lavage fluids. Data are shown as mean±SEM. Significantly different at p<0.05 vs. *infected mice without any treatment (n=3), and §infected placebo-treated mice (n=3). Uninfected + placebo, n=3; infected + zanamivir, n=4.

Figure 4. Relative levels of inducible nitric oxide synthase (iNOS) mRNA in mouse lung tissues. Data are shown as mean±SEM. Significantly different at p<0.05 vs. #uninfected placebo-treated mice (n=3), *infected mice without any treatment (n=3), and §infected placebo-treated mice (n=3). Infected + zanamivir, n=4.