Rapid, efficient and dose-controlled delivery of liquid aerosol to pulmonary cells cultured at the air-liquid interface

Introduction: In vitro cell systems play a prominent role in preclinical pathomechanistic and therapeutic studies. Traditionally, these studies have been performed with cells cultured under submerged conditions, i.e. the cells are completely covered with cell culture medium. However, this does not resemble the physiological situation during inhalation therapy, where the aerosolized drug is deposited onto the air-exposed, apical side of the pulmonary epithelium.

Here we present a novel cell exposure system (ALICE) for dose-controlled delivery of aerosolized liquids to cell systems cultured at the air-liquid interface.

Methods: The ALICE (Air-Liquid Interface Cell Exposure system) utilizes a vibrating membrane nebulizer to convert 1–5 ml of liquid substances into a dense cloud of droplets. A unique combination of cloud motion, an effect known from cloud physics, and single particle settling allows for rapid (10–15min), yet gentle delivery of aerosolized drugs to pulmonary cells cultured at the air-liquid interface. In addition, the cell-delivered dose can be monitored in quasi-real-time with a quartz crystal microbalance (QCM). Simultaneous exposure of up to two standard multi-well plates is possible.

Results: For the recommended 1mL of sprayed liquid, a single ALICE exposure can provide 0.02–200µg/cm² of dissolved substance to the cells depending on the mass concentration of the sprayed solution (0.0012–12%). Currently, 7.2% of the invested liquid is deposited onto the cells with a well-to-well variability of 14% (CL=95%) about the mean dose. Control experiments with a pulmonary cell line (A549) showed that the ALICE exposure procedure itself does not induce adverse effects on cell viability. Applications of the ALICE include studies on the cellular uptake and trafficking of gold nanoparticles and the toxicity of zinc oxide nanoparticles.

Discussion: Both aqueous solutions and suspensions of particles with diameters less than about 1µm can be processed with the ALICE. While the delivery efficiency (7.2%) of the invested drug may seem small, it excels over all other currently available air-liquid interface cell exposure systems, if referenced to the total use of substance. The combination of an easy-to-use, yet, fast, efficient, repeatable, dosimetrically accurate and physiologically realistic exposure system for pulmonary cells, makes this a unique tool for preclinical pulmonary studies.