In vitro assessment of archaeosome stability for developing oral delivery systems.
The in vitro stability of archaeosomes made from the total polar lipids of Methanosarcina mazei, Methanobacterium espanolae or Thermoplasma acidophilum, was evaluated under conditions encountered in the human gastrointestinal tract. At acidic pH, multilamellar vesicles (MLV) prepared from T. acidophilum lipids were the most stable, releasing approximately 80, 20, 10 and 5% of encapsulated 14C-sucrose at pH 1.5, 2.0, 2.5 and 6.2, respectively, after 90 min at 37 degrees C. Archaeosomes from M. mazei lipids were the least stable. For each type of total polar lipid, unilamellar vesicles (ULV) were less stable than the corresponding MLV vesicles. Pancreatic lipase had relatively minor effect on the stability of archaeosomes made from either of the three types of total polar lipids, causing the release of 12-27% of the encapsulated 5(6)-carboxyfluorescein (CF) from ULV and MLV after 90 min at 37 degrees C. In simulated human bile at pH 6.2, MLV from M. mazei total polar lipids lost 100% of the encapsulated CF after 90 min at 37 degrees C, whereas those from the polar lipids of M. espanolae or T. acidophilum lost approximately 85% of the marker. Pancreatic lipase and simulated human bile had no synergistic effect on the release of carboxyfluorescein from ULV or MLV prepared from any of the total polar lipids. After 90 min in the combined presence of these two stressors at pH 6.2, the leakage of fluorescein conjugated bovine serum albumin from MLV prepared from T. acidophilum lipids was similar to that of CF, and 13% of the initially present vesicles appeared to be intact. These results indicate that archaeosomes show stability properties indicative of potential advantages in developing applications as an oral delivery system.