Toxicity testing of sildenafil base-loaded liposomes in in vitro and ex vivo models for pulmonary application

The aim of this study was to formulate sildenafil base-loaded liposomes using a solvent-free method, followed by the investigation of the potential cytotoxicity of the prepared liposomes in in vitro and ex vivo cell culture models. The liposomes were manufactured by dispersing 5% w/v phospholipid in aqueous phase at RT. The prepared dispersion was then homogenized using an Avestin extruder. The particle size of the prepared liposomes was between 100 and 110nm and was stable up to 6 months. For in vitro models, human alveolar epithelial cell line (A549) and mouse heart endothelium cell line (MHEC5-T) were used. For ex vivo models, rat precision cut lung slices (PCLS) and rat heart slices (PCHS) were used. All the models were treated with liposomes loaded with or without sildenafil in a concentration range of 0-2500 mu g/mL of phospholipid. The toxicity was assessed in vitro and ex vivo using MTT assay. Median lethal dose (LD50) values for A549 cells and PCLS were found between 800 and 1800 mu g/mL while for MHEC5-T cells and PCHS they were found between 1000 and 1200 mu g/mL. PCHS demonstrated higher LD50 values as compared to PCLS. Considering the high LD50 values, sildenafil-loaded liposomes may have the potential for the treatment of pulmonary hypertension via inhalation route.