B75-02 Microvascular Actin Enhancement by Liposomal Therapeutics in Precision-cut Lung Slices

Rationale Acute Lung Injury (ALI), a major cause of mortality following lung infection, lacks a cure. Since injury to the lung microvascular barrier underlies ALI, we considered that barrier enhancement by a therapeutic strategy that stabilizes lung endothelial f-actin might protect against ALI. Hence, we evaluated the efficacy of liposome-mediated delivery of the f-actin stabilizer, jasplakinolide, to lung microvessels in precision-cut lung slices (PCLS). Methods Liposomes prepared by thin-film hydration and extrusion of FM1-43-labeled cationic lipids, were characterized for size (∼100 nm) and charge (zeta potential, 28.16 mV). The liposomes were loaded with jasplakinolide (790 nM) and calcein green-AM (59 uM), then 24h after intranasal LPS (10 mg/kg) instillation, they were given intravenously. After 1h, lungs were harvested to obtain PCLS, which were viewed by confocal microscopy to determine liposome distribution in terms of FM1-43 and calcein green fluorescence in live slices, and actin distribution in terms of phalloidin fluorescence in paraformaldehyde-fixed slices. For control, we instilled PBS. Results In live slices, lung microvessels (20 um diameter) were delineated by endothelial fluorescence of calcein green, which confirmed cell viability and successful delivery of liposomal cargo to the endothelium. For both LPS and PBS groups (n = 3 each), FM1-43 fluorescence similarly marked liposome attachment to microvascular lumens. In fixed slices of LPS instilled lungs, treatment with jasplakinolide-loaded liposomes markedly increased microvascular phalloidin fluorescence as compared with lungs that did not receive liposome treatment (p < 0.001). Results were similar for PBS-treated lungs. Conclusions Our findings indicate that intravenously injected cationic liposomes efficiently deliver bioactive molecules to lung microvessels. Liposomal delivery of jasplakinolide enhanced f-actin in microvessels of lungs exposed to LPS-induced ALI. We propose that intravenous liposomal therapy of actin enhancing agents might protect and repair the lung microvascular barrier in conditions predisposing to ALI. (Support: HL36024).