Nanoparticles increase ciliary beat frequency in the murine trachea

Although the airway epithelium is the one of the first barriers that interacts with nanoparticles, the effects of nanoparticles on the airway epithelium are incompletely understood. We therefore examined the effects of two different nanoparticles on the epithelium of the mouse trachea.

The trachea of Balb/c mice was explanted and incubate with nanoparticles up to 24h. Carbon black (Printex90, 10µg/ml, median size 160nm in solution) and silica particles (DQ12, 1µg/ml and 10µg/ml, median size of 600nm in solution) were used. Ciliary beat frequency and particle transport capacity were investigated by video microscopy. Damage of cells was assessed by ethidium homodimer-1 staining and scanning electron microscopy. Apoptosis was detected by staining activated caspase-3. Gene expression was analysed by real time RT-PCR. Adherence of nanoparticles to the epithelium was assessed using 40nm fluorescent polystyrene beads.

Printex90 and DQ 12 increased ciliary beat frequency. In contrast to DQ12, Printex90 induced marked mucus release resulting in aggregates of particles with mucus. However, Printex90 did not increase Muc5ac mRNA expression in the airway epithelium indicating that mucus was released from submucus glands present in the upper part of the trachea of Balb/c mice. These agglomerates impaired particle transport in the upper part of the trachea. DQ12 and Printex90 did not induce cell damage. But DQ12 particles caused cell apoptosis without impairing the integrity of the epithelium as assessed by scanning electron microscopy. Neither DQ12 nor Printex90 induced expression of inflammatory cytokine mRNA. Local application of fluorescent nanoparticles resulted in staining of cilia indicating that nanoparticles can adhere directly to cilia.

Our data indicates that nanoparticles interact and directly activate ciliated cells, and increase ciliary beat frequency. Although Printex90 did not damage the epithelium, it induced mucus release.