| Self-assembled polymeric nanoparticles are formed from a amphiphilic polymer, which could self-assemble (or self-aggregate) into core-shell nanoparticles with a hydrophilic outer shell and hydrophobic inner core in water through the molecular forces such as hydrophobic interaction, electrostatic interaction, hydrogen bonding and metal complexation. Amphiphilic polymeric self-assembled nanoparticles possess high thermodynamic stability and the hydrophobic inner core can be utilized as a cargo space for poorly water-soluble drugs, genes, peptides and proteins, while the hydrophilic outer shell allows a long circulation of drugs in vivo. Amphiphilic polymeric self-assembled nanoparticles have high potentials in drug delivery and receive more and more attentions by experts because after chemical modification, they can also achieve special pharmacological characteristics such as active targeting, micro-environment response (e.g. pH sensitivity, temperature sensitivity and magnetic targeting), escaping the engulfment of mononuclear phagocytic cells, improving transportation through biomembrane.In this study, water-soluble O-carboxymethyl chitosan was chosen as a framework material. Hydrophobic modification and targeting modification were completed before it was be used to construct nanoparticles for anti-cancer drug carriers. Firstly, stearic acid with hydrophobic alkyl group and lactobionic acid with liver targeting functional group were grafted onto O-carboxymethyl chitosan through the EDC-mediated amidation. The polymeric structure of the chitosan derivative was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectrometer and elementary analysis. Nanoparticles were prepared by sonication. The particle diameter of nanoparticles prepared by O-carboxymethyl chitosan-graft-stearic acid (OS) conjugates was between168and216nm and the diameter was decreased with the increase of the substitution degree of stearic acid, and then increased. OS conjugates with a substitution degree of9.8%were used to further modified with lactobionic acid and the final products of galactosylated O-carboxymethyl chitosan-graft-stearic acid (Gal-OS) with a substitution degree of13.1%lactobionic acid were obtained. The particle size of Gal-OS nanoparticles was160nm. The critical aggregation concentrations of conjugates were determined by a fluorescence probe technique. The results indicate that as the increase of stearic acid substitution, the critical aggregation concentrations of OS gradually decreased. However, the critical aggregation concentrations of Gal-OS conjugates was larger than the corresponding OS conjugates with the same stearic acid substitution. Hemolysis test results show that the hemolysis rates of OS and Gal-OS conjugates were both less than5%, indicating a good hemocompatibility and suitability for intravenous injection. The cytotoxicity experiment indicate that both the two materials prepared did not have significant cell cytotoxicity, and thus can be used in the biomedical applications. Doxorubicin (DOX) was chosen as a therapeutic drug and DOX loaded nanoparticles were then prepared. Gal-OS/DOX nanoparticles with a diameter of181.9nm had a satisfactory drug loading content of13.4%and entrapment efficiency of77.4%. TEM images show that Gal-OS/DOX nanoparticles were roughly spherical in shape without adhesion. The in-vitro release behaviors of DOX from Gal-OS/DOX and OS/DOX nanoparticles were studied by a dialysis method in a phosphate buffered saline with different pH values. The results reveal that both of two types of nanoparticles showed a sustained and pH-dependent drug release pattern. In the lower pH condition, the drug released faster.The characterization methods of DOX nanoparticles in the plasma and tissues using fluorescence spectrophotometry were established in this study. Pharmacokinetics studies in rats revealed that both Gal-OS/DOX and OS/DOX nanoparticles could prolong the circulation time of DOX in the blood and reduce the elimination rate. The AUC values of the Gal-OS/DOX and OS/DOX nanoparticles were31-and29-fold higher than the DOX solution group. Tissue distribution studies in mice indicated that the Gal-OS/DOX and OS/DOX nanoparticles increased the uptake of DOX in the liver and spleen. The DOX uptake in the liver of mice treated with the OS/DOX nanoparticles was7.3fold higher than that with the DOX solution. The drug uptake for the Gal-OS/DOX nanoparticles was9.8fold higher, revealing the Gal-OS/DOX nanoparticles exhibited higher accumulation in the liver comparing with the OS/DOX nanoparticles. In addition, the AUC of the drug-loaded nanoparticles was lower in heart, lung, and kidney than the DOX solution group, indicating that the drug-loaded nanoparticles can reduce the toxicity of DOX to heart, lung, and kidney. Particularly, the reducing of cardiotoxicity was beneficial to the clinical application of DOX. Targeting evaluation showed that two kinds of nanoparticles were both more efficient to deliver DOX to liver than the DOX solution, and the liver targeting of the Gal-OS/DOX nanoparticles was greater than that of the OS/DOX nanoparticles.This work describes the synthesis of the novel liver-targeting carrier composed of galactose, stearic acid and O-carboxymethyl chitosan and the preparation of DOX loaded and liver-targeting chitosan polymeric nanoparticles with the galactose modification using Gal-OS conjugates. This study will provide a reference and options for the clinical application of DOX and further exploration of liver-targeting drug delivery systems. |
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