Rotation Frequency of Human Bronchial and Nasal Epithelial Spheroids as an Indicator of Mucociliary Function

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Abstract
Background: We evaluated a new in vitro model for mucociliary transport function. Spheroids of human respiratory epithelium show beating cilia at their surface. When cultured in their own mucus, spheroids can rotate along their axis due to coordinated ciliary beating. Objective and Methods: To assess whether this setup yields meaningful results we measured rotation frequency (RF) of human bronchial or nasal epithelial spheroids under different temperatures and concentrations of isoproterenol. Isoproterenol was administered either as caged compound releasing active isoproterenol after illumination with UV light, or through a permeable membrane in a two-chamber system. Results: Under stable conditions, RF remained constant over 200 min. Between 27 and 35°C, there was a temperature-dependent increase: RF27°C = 0.27 ± 0.08 s–1, and RF37°C = 0.43 ± 0.10 s–1 (means ± SEM). Isoproterenol (10–5, 10–4 and 10–3 mmol/l) induced concentration-dependent increases in RF (9, 20 and 25%, respectively; medians) if applied in the two-chamber system. The experiments with caged isoproterenol did not yield conclusive results, probably because the byproducts from photolysis negatively affected ciliary function. The transport velocity at the surface of bronchial and nasal spheroids was estimated to be 2.96 and 3.62 mm/min (medians), respectively, which is in the same range as mucus transport velocity measured in vivo in humans. Conclusions: This setup can be used to study mucociliary transport function under controlled conditions in vitro, in particular as RF is likely to reflect not only ciliary beat frequency, but also the coordination of ciliary beating and the properties of the mucus.