Incorporation of quercetin in respirable lipid microparticles: effect on stability and cellular uptake on A549 pulmonary alveolar epithelial cells

The aim of the present study was to develop controlled release inhalable lipid microparticles (LMs) loaded with the antioxidant flavonoid, quercetin and to investigate the interaction of these microparticles with A549 pulmonary alveolar epithelial cells. The LMs were produced using different lipidic materials and surfactants, by melt emulsification followed by a sonication step. The most efficient modulation of the in vitro release of quercetin was achieved when LMs were prepared with tristearin and hydrogenated phosphatidylcholine; which were used for subsequent studies.

These LMs exhibited a quercetin loading of 11.8±0.3%, and a volume median diameter, determined by laser diffraction, of 4.1±0.2 μm.  Moreover, their mass median aerodynamic diameter (4.82 ±0.15 μm) and fine particle fraction (27.2±3.9%), as measured by multi-stage liquid impinger, were suitable for pulmonary delivery. Quercetin was found to be highly unstable (complete decomposition within 6-h incubation) in Ham’s F-12 medium used for A549 cell culture. Degradation was markedly reduced (16.4% of the initial quercetin content still present after 24-h incubation) after encapsulation in the lipid system. 

Viability studies performed by lactate dehydrogenase assay, demonstrated that quercetin LMs showed no significant cytotoxicity on the A549 cells, over the concentration 0.1-5 μM. The uptake of quercetin by the A549 lung alveolar cells was also investigated.  After 4-h incubation, the accumulation of quercetin in the A549 cells was significantly higher (2.3-fold increase) for the microparticle entrapped flavonoid when compare to non-encapsulated quercetin. The enhanced intracellular delivery of quercetin achieved by the LMs is likely due to the flavonoid stabilization after encapsulation.