Particulate matter in cigarette smoke increases ciliary axoneme beating through mechanical stimulation

Background: The lung's ability to trap and clear foreign particles via the mucociliary elevator is an important mechanism for protecting the lung against respirable irritants and microorganisms. Although cigarette smoke (CS) exposure and particulate inhalation are known to alter mucociliary clearance, little is known about how CS and nanoparticles (NPs) modify cilia beating at the cytoskeletal infrastructure, or axonemal, level. Methods: We used a cell-free model to introduce cigarette smoke extract (CSE) and NPs with variant size and surface chemistry to isolated axonemes and measured changes in ciliary motility. We hypothesized that CSE would alter cilia beating and that alterations in ciliary beat frequency (CBF) due to particulate matter would be size- and surface chemistry-dependent. Demembranated axonemes were isolated from ciliated bovine tracheas and exposed to adenosine triphosphate (ATP) to initiate motility. CBF was measured in response to 5% CSE, CSE filtrate, and carboxyl-modified (COOH), sulphate (SO ₄)-modified (sulfonated), or PEG-coated polystyrene (PS) latex NPs ranging in size from 40nm to 500 nm. Results: CSE concentrations as low as 5% resulted in rapid, significant stimulation of CBF ( p < 0.05 vs. baseline control). Filtering CSE through a 0.2-μm filter attenuated this effect. Introduction of sulphate-modified PS beads ∼300 nm in diameter resulted in a similar increase in CBF above baseline ATP levels. Uncharged, PEG-coated beads had no effect on CBF regardless of size. Similarly, COOH-coated particles less than 200nm in diameter did not alter ciliary motility. However, COOH-coated PS particles larger than 300nm increased CBF significantly and increased the number of motile points. Conclusions: These data show that NPs, including those found in CSE, mechanically stimulate axonemes in a size- and surface chemistry-dependent manner. Alterations in ciliary motility due to physicochemical properties of NPs may be important for inhalational lung injury and efficient drug delivery of respirable particles.