Combined Cryogenic Transmission Electron Microscopy and Electron Spin Resonance Studies of Egg Phosphatidylcholine Liposomes Loaded with a Carboranyl Compound Intended for Boron Neutron Capture Therapy

Abstract

The lactosyl carborane [1,2-dicarba-closo-dodecarboran(12)-1-ylmethyl](β-d-galactopyranosyl)-(1→4)-β-gluco-pyranoside (LCOB) is an amphipilic boron-containing compound intended for boron neutron capture therapy. In this study cryogenic transmission electron microscopy was used to investigate the effects of LCOB on the structure and properties of extruded egg phosphatidylcholine liposomes. The results showed that LCOB concentrations up to at least x LCOB = 0.25 could be included in the preparations without any noticeable effects on the liposomal size or structure. Inclusion of LCOB concentrations corresponding to x LCOB = 0.44 or more gave, however, rise to significant changes in the liposome size distribution and the overall sample structure. In fresh samples no signs of phospholipid solubilization were detected until the molar fraction of LCOB reached 0.82. At this concentration the boronated compound induced, however, formation of open liposomes and threadlike micelles and, furthermore, with time the sample displayed a macroscopic phase separation. More details on the molecular interaction between LCOB and the liposome membranes were obtained by electron spin resonance spectroscopy. Two different n-doxyl stearic acid spin probes were used to measure the dynamics and the degree of order in the mixed systems. The results indicated that LCOB insertion into the phospholipid bilayer increased the packing order in the vicinity of the water/hydrocarbon interface whereas the inner hydrophobic region of the bilayer was unaffected.

Effect of the preparation procedure on the structural properties of oligonucleotide/cationic liposome complexes (lipoplexes) studied by electron spin resonance and Zeta potential

“…Samples for cryo-TEM analysis were prepared at room temperature and treated as described in previous papers [41,42].…”

Size Control of Mixed Egg Yolk Phosphatidylcholine (EggPC)/Oleate Vesicles

“…The studies on this process have contributed to size regulation of vesicles prepared by removing detergent from detergent-phospholipid mixed micelles. [1][2][3][4] Fatty acids are one kind of surfactants whose properties are different from the others, that is, the fatty acids exist as micellar form above pH 9 but they can spontaneously form vesicles in the appropriate conditions. [5][6][7][8][9] Luisi et al have made interesting reports using dynamic light scattering, freeze fracture electron microscopy and cryotransmission electron microscopy as follows: when sodium oleate micellar solution was added into suspension of preformed oleate vesicles or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles, the size of newly formed vesicles was similar to that of the preformed vesicles and preformed vesicles remarkably expedited the rate of new vesicles organization.…”

Ex Vivo and In Vivo Evaluation of Dodecaborate-Based Clusters Encapsulated in Ferumoxytol Nanoparticles

“…At a dose of 20 mg/kg, 1 @FMX localized in tissues ranging from 0 to 65 μg of B per gram of tissue, suggesting that encapsulation of dodecaborate-based compounds in a polymer matrix can potentially have favorable effects on the biodistribution results. More broadly, this work suggests the potential importance of noncovalent interaction between boron clusters and polymers stemming from nonelectrostatic interactions and points to new avenues for creating hybrid boron-cluster-based nanomaterials without covalent attachment. − …”