Pressure Induced Fusion (Pif) Liposomes: A Solventless Sterilizing Method for Producing Large Phospholipid Vesicles

AbstractWe have recently described a new method to create liposomes of high captured volume we term interdigitation-fusion vesicles or IFVs (Ahl, et al. (1994) Biochim. Biophys. Acta 1195: 237–244). These vesicles arise from small (<100 nm) precursor liposomes comprised of saturated chain phospholipids which fuse upon induction to the interdigitated gel state after ethanol addition to form extensive sheets. When heated to the liquid crystalline state, these sheets vesicularize into large, predominantly unilamellar liposomes (IFVs). Here we report that a similar event occurs when hydrostatic pressures capable of causing acyl chain interdigitation are applied to small precursor vesicles of DPPC or DSPC. When DPPC small unilamellar vesicles were cycled three times between ambient pressure and 4.1 kbar (15 minute intervals) the resulting pressure induced fusion (PIF) vesicles had captured volumes of 13.1 ± 0.6 μl/μmole and were unilamellar as judged by 31P-NMR. Although three cycles yielded the maximum captur...