Possibility of heat sterilization of liposomes.

Abstract

Several kinds of liposomes were sterilized at 121 degrees C for 20 min. They tended to aggregate after heat sterilization (HS) in saline, while no aggregation was observed in an isotonized sugar or polyol solution. The dispersions containing egg phosphatidylcholine (EggPC) with a high peroxide value (POV) turned slightly yellowish after HS. This color change was prevented by using EggPC with a low POV, hydrogenated EggPC (H-EggPC) or dipalmitoylphosphatidylcholine (DPPC). Nitrogen gas bubbling at neutral pH also prevented the color change, but vitamin E did not. The particle size of the EggPC liposomes extruded through a 0.4 micron membrane filter did not change significantly after HS, whereas the H-EggPC or DPPC liposomes extruded through a 0.8 micron membrane filter tended to be reduced in size. On this change the type of medium had a considerable influence. The anionic 6-carboxyfluorescein leaked from the negatively charged liposomes (EggPC/cholesterol (Chol)/egg phosphatidylglycerol) during HS, while no leakage was observed from the positively charged liposomes (EggPC/Chol/stearylamine) not only during HS but also during a long period of storage. It was suggested that sterilization of liposomes by heating was practicable as well as that by filtration, if the liposomes were prepared as follows: the charged liposomes made of lipids with low POV's were dispersed in a sugar or polyol solution adjusted to nearly pH 6.5, where the amount of dissolved oxygen was minimized. An ionic water-soluble drug had to be encapsulated in the oppositely charged liposomes.

Characteristics of DNA-Tagged Liposomes Allowing Their Use in Capillary-Migration, Sandwich-Hybridization Assays

“…The fluorescence value is corrected for the increased fluorescence been noted by others as well (25). However, when intensity of free sulforhodamine B dye in methanol compared with placed in SHB, it was found that liposomes retain their SSC or SHB.…”

Archaeosomes: an excellent carrier for drug and cell delivery

“…Leakage of encapsulated CF indicated that vesicles prepared from TPL containing higher amounts of caldarchaeol lipids generally had lower amounts of CF leakage. The potential benefit of caldarchaeol lipids in preventing leakage was confirmed by the observation that the leakage from M. mazei TPL vesicles (100%archaeols) was reduced after incorporation of progressively higher proportions of TPL from T. acidophilum, which contains about 90% caldarchaeols (Kikuchi et al, 1991). The stability of M. mazei archaeosomes could alternatively be improved by incorporation of cholesterol similar to that seen with ester liposomes.…”

“…The maximum thermal stability (60 C) of vesicles made from S. solfataricus polar lipid fraction Pressurized liquid extraction (PLE) when mixed with egg Phosphatidylcholine (PC) was reported when the lipids were used at a molar ratio of 1:2, and these vesicles were more thermo-stable than those made from the PLE lipid alone (Gregoriadis, 1995). The stability of vesicles made from mixtures of TPL (consisting of natural mixtures of archaeol and caldarchaeol lipids) with egg PC demonstrated that the stability at 37 C was related to the greater content of the polar ether lipids in the mixture (Kikuchi et al, 1991). Comparative thermal stability of vesicles made from a highly purified caldarchaeol subfraction from TPL of S. acidocaldarius with those made from unsaturated palmitoyl-oleoyl phosphatidylcholine, or saturated diphytanoyl phosphatidylcholine, showed that unlike the latter two that become very permeable at 35-40 C, the caldarchaeol lipid vesicles were not sensitive to leakage up to 60 C, and at 80 C released55% of encapsulated CF marker dye.…”

Preparation, stability, and in vitro performance of vesicles made with diblock copolymers

“…These systems include archaelipids naturally designed for such purposes (Fan et al, 1995;Khan and Chong, 2000) as well as suspensions of small vesicles made with phosphocholines and containing minimal dissolved oxygen (Kikuchi et al, 1991;Zuidam et al, 1993). In the latter reference, autoclaving was explored as a means of sterilizing submicron vesicles that were too large for filtration through 0.22 m filters.…”