The characterisation of a zymosan model of inflammation

Abigail Morris, Yanira Riffo Vasquez, Ian McFadzean, Domenico Spina. King’s College London, London, United Kingdom.

Zymosan is a β-glucan which is a polyglucose structure in the cell wall of moulds, bacteria and plants and has been implicated in the pathogenesis of asthma (Rylander & Lin, Toxicology 2000; 152: 47-52). The mechanism by which zymosan induces lung inflammation, not involving signaling via toll like receptor (TLR)2, TLR4, MyD88, dectin-1 receptors or activation of complement or macrophages, remains to be established (Kelly et al. Am J Respir Cell Mol Biol 2008; 38: 227-238). Moreover, few studies have investigated the pharmacological effect of glucocorticosteroids and phosphodiesterase (PDE)4 inhibitors on lung inflammation induced by zymosan. Female Balb/c mice (18-20g) were administered (2mg/mL) intranasally (i.n) under short-acting anaesthesia and a time course was conducted. To test the anti-inflammatory compounds, mice were dosed at specified time points before zymosan administration. The doses chosen for each compound have been demonstrated to be efficacious in other murine models of lung inflammation. Budesonide, 1.5 mg/kg and 2 mg/kg, was administered subcutaneously 24 hours and 1 hour before zymosan. Roflumilast, 5 and 10 mg/kg, was administered orally 30 minutes before zymosan. In all studies, mice were culled 24 hours after the last exposure and inflammatory cells (number of cells/mL) in bronchoalveolar lavage were counted. The inflammatory response to zymosan peaked after 24 hours (number of neutrophils; saline, 0.09 ± 0.04 x105; zymosan 6.6 ± 0.3 x105; n = 8, p ≤ 0.001)). Budesonide had no significant effect on inflammatory cell counts at either dose tested (n = 4, p ≥ 0.05) whereas Roflumilast caused a dose dependent decrease in the number of neutrophils (vehicle, 5.0 ± 0.2 x105, Roflumilast 5 mg/kg, 4.2 ± 0.8 x105; 10 mg/kg, 1.2 ± 0.6 x105 ; n = 3-5, p ≤ 0.001). These results demonstrate neutrophilic inflammation induced by zymosan is refractory to the anti-inflammatory actions of glucocorticosteroids but sensitive to PDE4 inhibition. This model might be useful to study steroid insensitive inflammation observed in respiratory diseases like non-esosinophilic asthma, severe asthma and chronic obstructive pulmonary disease.