[show abstract][hide abstract] ABSTRACT: Self-assembled drug delivery systems (SADDS) were designed in the paper. They can be prepared from the amphiphilic conjugates of hydrophilic drugs and lipids through self-assembling into small-scale aggregates in aqueous media. The outstanding characteristic of SADDS is that they are nearly wholly composed of amphiphilic prodrugs. The self-assembled nanoparticles (SAN) as one of SADDS had been prepared from the lipid derivative of acyclovir (SGSA) in the previous paper. They were further studied on the properties and the in vitro/in vivo behavior in this paper. The SAN kept the physical state stable upon centrifugation or some additives including some inorganic salts, alkaline solutions, surfactants and liposomes except for HCl solution, CaCl(2) solution and animal plasma. Autoclave and bath heat for sterilization hardly influenced the SAN. However, gamma-irradiation strongly destroyed the structure of SAN and SGSA was degraded. SGSA in SAN showed good stability in weak acidic or neutral buffers although it was very sensitive to alkaline solutions and carboxylester enzymes, the half-lives (t(1/2)) of which in the buffer at pH 7.4, the alkaline solution at pH 12.0, pig liver carboxylester enzyme solution, rabbit plasma, and rabbit liver tissue homogenate were 495, 21, 4.7, 25 and 8.7 h, respectively. Compared with SGSA in a disordered state, the specific bilayer structures of SAN could protect SGSA from hydrolysis through hiding the sensitive ester bonds. The SAN showed hemolytic action because the amphiphilic SGSA could insert into rabbit erythrocyte membranes. Both the high concentration of SGSA in samples and the long incubation time improved hemolysis. No hemolysis was observed if the additional volume of the SAN was less than 10% of rabbit whole blood in spite of the high concentration of SGSA. Plasma proteins could interfere the interaction between the SAN and erythrocytes by binding the SAN. The in vitro antiviral activity of acyclovir SAN was limited possibly because of the weak hydrolysis of SGSA in Vero cells, and the SAN showed a little cell toxicity possible due to the amphiphilicity of SGSA. A macrophage cell line of QXMSC1 cells showed uptake of the SAN but not significantly. The SAN were rapidly removed from blood circulation after bolus iv administration to rabbits with the very short distribution t(1/2) (1.5 min) and the elimination t(1/2) (47 min). The SAN were mainly distributed in liver, spleen and lung after iv administration, and SGSA was eliminated slowly in these tissues (t(1/2), about 7 h). It would appear that the nanosized SAN were trapped by the mononuclear phagocyte system. SADDS including SAN combine prodrugs, molecular self-assembly with nanotechnology, and hopefully become novel drug delivery approaches.
International Journal of Pharmaceutics 03/2006; 309(1-2):199-207. · 3.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: The long-chain alkyl derivatives of a nucleoside analogue-acyclovir were prepared in the paper. One is stearyl-glycero-succinyl-acyclovir (SGSA) with a single 18-carbon length (C18) alkyl chain. Another is dioctadecyl-aspartate-succinyl-acyclovir (DASA) with double C18 alkyl chains. They were prepared by the esterification of succinyl-acyclovir with the lipids, and sodium salts of them were also prepared. Guanine moieties and alkyl moieties bring the derivatives intermolecular hydrogen bonding and hydrophobic interaction in water separately. The forces are influenced by the number of alkyl chains and the charged state, and determine the solubility and the self-assembly behavior of the derivatives. The double alkyl-chain derivatives (DASA and DASA-Na) formed rigid Langmuir monolayers on air/water surface, while the single alkyl chain derivatives (SGSA and SGSA-Na) did not. However, cholesterol (Chol) could assist SGSA to form rigid monolayers through inserting into the alkyl chains of SGSA to mimic the second alkyl chain. SGSA self-aggregates in water were prepared by the injection method with tetrahydrofuran as solvent. Cuboid-like shape and nanoscale size demonstrated that SGSA self-aggregates were self-assembled nanoparticles. Shape, particle size, zeta potential and phase transition of the nanoparticles were characterized. And they showed an average size of 83.2 nm, a negative surface charge of -31.3-mV zeta potential and a gel-liquid crystalline phase transition of 50.38 degrees C. The formation mechanism of self-assembled nanoparticles was analyzed. Hydrophobic interaction of alkyl chains improves SGSA molecules to form bilayers, and then cuboid-like nanoparticles were obtained by layer-by-layer aggregation based on inter-bilayers hydrogen bonding. However, the charged guanine moieties make SGSA-Na lose the function of hydrogen bonding so that SGSA-Na only forms vesicles in water based on hydrophobic interaction. Strong hydrophobicity and wide-open rigid double alkyl chains of DASA and DASA-Na restrict self-assembly in water media, and no homogeneous suspensions were obtained. Therefore, the molecular self-assembly behavior of the long-chain alkyl derivatives of nucleoside analogues on water surface or in water media is determined by the number of alkyl chains and the charged state.
[show abstract][hide abstract] ABSTRACT: Pyrocatechol violet (PV), a chelating agent for cupric ions was used to characterize liposomal membrane permeability. After cupric ions were added to PV liposomes, free PV turned into its chelate (PV-Cu), and encapsulated PV kept stable since liposomal membranes prevented metal ions from permeating. After the light scattering background of liposomes and the absorbance of PV were eliminated by the first-order derivative spectrophotometric method, PV-Cu i.e. free PV in liposome suspensions could be determined without separation. The released PV from liposomes could also be determined. Because PV release is relevant to liposomal membrane permeability, PV becomes a marker to characterize the membrane permeability. This new method was simple, rapid, sensitive, and was used to measure the temperature-dependent liposomal membrane permeability in this paper. Dipalmitoylphosphatidylcholine (DPPC) and soybean lecithin liposomes showed the peaks of release at 40 degrees C and 39 degrees C, respectively.
Journal of Pharmaceutical and Biomedical Analysis 03/2005; 37(2):379-82. · 2.95 Impact Factor