ABSTRACT
Vesicular phospholipid gels (VPGs), highly concentrated phospholipid dispersions of semisolid consistency and vesicular morphology are under investigation as potential implantable depots for sustained release of drugs and as intermediates for subsequent dilution into 'conventional' liposome dispersions. It was investigated here if VPGs can be steam sterilised. VPGs prepared from 400 mg/g egg-phosphatidylcholine by high-pressure homogenisation retained their vesicular structure but showed a slight increase in vesicle size (freeze-fracture electron microscopy). However, autoclaving slowed down both, the in vitro release of the hydrophilic marker carboxyfluorescein and vesicles from VPGs. This was assumed to be due to bigger vesicle sizes and corresponding increase in packing density of the vesicular matrix. Upon dilution into a liposome dispersion both negative staining electron microscopy and dynamic laser light scattering analysis confirmed a distinct increase in liposome size, mainly due to fusion of small (20 nm) vesicles with unfavourable curvature. This was consistent with the observed increase in encapsulation efficiency of carboxyfluorescein. Phospholipid hydrolysis during autoclaving was negligible with lysophosphatidylcholine formation of less than 2% (thin layer chromatography). Despite significant change of their morphological and functional properties during autoclaving VPGs retained their main characteristics, such as vesicular structure, sustained release and dilutability to liposome dispersions, and are, therefore, considered as autoclavable.
Subject(s)
Phospholipids/chemistry , Steam , Sterilization , Fluoresceins/chemistry , Fluorescent Dyes/chemistry , Gels , Hydrolysis , Liposomes , Particle Size , Phosphatidylcholines/chemistry , Sterilization/methodsABSTRACT
Phosphatidylcholine, when dispersed in aqueous medium in high concentrations (300 mg/g and above) by high pressure homogenisation, forms semisolid pastes of vesicular morphology. The multivesicular matrix can accommodate hydrophilic compounds in the aqueous compartments. The disintegration and release of hydrophilic marker of these dispersions were studied in vitro by using a flow-through cell. Slow release of the marker over periods of hours up to days took place via two different mechanisms: (1) erosion of the matrix with release of marker-filled liposomes and marker which had been trapped in between the liposomes and (2) diffusion of marker through the membranes. Whereas for lipid concentrations up to 300 mg/g almost spontaneous disintegration occurred, more concentrated pastes (350-400 mg/g) showed zero-order erosion kinetics for 4-6 h. Erosion was rate limiting for overall release. For 450 and 500 mg/g lipid dispersions, the release of free marker followed square root of time kinetics for 13 or 21 h, respectively, which is typical for matrix-controlled diffusion. Underlying the diffusion was a slow zero-order erosion of the matrix. The results are important for the future development of vesicular phospholipid gels as sustained release therapeutic system, e.g. as implantable depot.
Subject(s)
Fluoresceins/administration & dosage , Phosphatidylcholines/administration & dosage , Drug Carriers , Liposomes , PharmacokineticsABSTRACT
Three sera, showing only a 2-3% of the usual cholinesterase activity and belonging to two families of 800 Caucasian inhabitants of the same small town, were classified as type II silent cholinesterase genes by polyacrylamide slab gel electrophoresis, dibucaine and fluoride number and by their specific activity with acetyl- butyryl- or propionyl-thiocholine.
Subject(s)
Cholinesterases/deficiency , Isoenzymes/deficiency , White People/genetics , Blood Protein Electrophoresis , Cholinesterases/blood , Cholinesterases/genetics , Dibucaine/pharmacology , Female , Homozygote , Humans , Isoenzymes/blood , Isoenzymes/genetics , Italy , Male , Pedigree , Substrate SpecificityABSTRACT
The presence of maternal cells was determined in a blood sample of 86 rhesus D-negative newborns with a rhesus D-positive mother using the 'minor cell population technique' of Jones and Silver. Maternal cells were found in 43 percent of the samples, irrespective of ABO incompatibility. Anti-D antibodies were detected in 22.2 percent of serum samples from 53 children taken at 6-10 months after birth. There was no correlation between the presence of anti-D and the results of the minor cell population technique at birth. The results are discussed.
