Background: The role of the airway epithelium in the development of invasive aspergillosis has rarely been studied although the patients at risk have frequent epithelium damage. To study interactions between Aspergillus fumigatus and airway epithelium, we have developed an in vitro model of primary culture of human nasal epithelial cells (HNEC) in air-liquid interface. We have shown that filtrate of A. fumigatus culture specifically alters HNEC compared with Penicillium chrysogenum. a non pathogenic filamentous fungus (1).
Aim of the study: To identify the molecules produced by A. fumigatus responsible for the electrophysiological modifications. Material and methods: After chloroform extraction, the organic phase of 3-day filtrate of A. fumigatus cultures was purified using high-performance liquid chromatography. Five fractions of 10 minutes each were recovered, lyophilized, and subsequently resuspended in DMSO before challenging HNEC cultures. The transepithelial electrical properties (resistance: R, potential differences: PD) were measured. Results: Only the 20-30 min fraction mimicked the effects of the whole filtrate. As this fraction was known to contain the secondary metabolites fumagillin, acid helvolic and verruculogen, the effects of different concentrations of these molecules commercially available (Sigma) were successively tested. Only verruculogen, at 5.10– 4 µg//µl concentration, had the same effect as the whole filtrate, i.e. a specific decrease in transepithelial R and an increase of PD. Verruculogen is a toxin known as tremorgen action, with K+ channels inhibition of neuromusculary synapses . The inhibition of the verruculogen effects with charybdotoxine, specific inhibitor, suggests that the verruculogen acts through K+ channels of HNEC. Discussion-Conclusion: We have identified verruculogen as one, if not the only one, of the secondary metabolites responsible for the observed electrophysiological modifications of HNEC cultures. The precise mechanism of the action of verruculogen remains to be elucidated. These modifications, by modifying the natural clearance of the respiratory tract might help the fungus to colonize the respiratory tract.
Full conference title:
- RICAI 24th (2004)