Study On RDP Modified Liposome Delivery Into The Brain

Curcumin is a natural phenolic antioxidants, and also commonly used as spices and food colorinig. It’s main pharmacological effects is anti-virus, anti-inflammatory, anti-tumor, anti-lipid peroxidation, anti-atherosclerosis and so on. But several characteristics as follows limit its application, such as:oxidation, photolysis, unstable hydroxyl groups in structure, poor dissolution in water, poor absorption in vivo and vulnerable metabolism in vitro.Curcumin encapsulated by liposomes can avoid above-mentioned shortcomings. Liposomes are lipid vesicles that constituted by a phospholipid bilayer, which has a similar structure with the cell membrane. It has a targeting, enhance bioavailability, reduced toxicity. After PEG modified, liposomes’surface is covered with supple and hydrophilic PEG, which forms a hydration layer on the surface of the liposome, what is called "stealth". It can reduce the interaction of plasma proteins with the liposome, and can avoid being phagocytosis of reticuloendothelial system to prolong circulation time in the body. Macromolecules and lipid presence permeability enhancement and retention in tumor tissue, which is called the EPR effect (ehanced permeablility and retention).Liposomes are accumulation in tumor tissue and "passive targeting" tumor tissue through the EPR effect.On this basis, a concept of "active targeting" is further proposed, i.e. against tumor cells or tumor angio genesis antibodies or ligands attached to the liposome surface, so that it can take the initiative to the tumor tissue, to further improve the therapeutic effect of drugs, reduce toxicity. According to the literature, the tumor cells or tumor blood vessels overexpression of certain receptors, such as EGFR, transferrin receptor, folate receptor, and these receptors are not expressed or slightly expressed in normal cells, and therefore, In the end of the PEG chain is connected targeting ligands such as folate, transferrin, antibodies anti-EGFR, etc., such that the targeting ligand and tumor cells overexpressing the receptor-specific binding, via the "ligand-receptor "specifically recognizing and binding effect, to promote cellular endocytic carrier, increase the antitumor effect of the drug, and can be directionally transport the drug to the target site.Although today some more in-depth study about targeted liposomes have been carried out, but the study of brain-targeted liposomes is few at home and abroad. Because of the blood-brain barrier (BBB) in the presence of blocking essentially 100% of macromolecules and over 98% of small molecule drug transport into the brain, so that the ordinary liposomal drugs is difficult to play a role.We therefore use PEG phospholipid liposomes to connect with a mercapto group of the RDP, which has a brain targeting.RDP (RVG-derived peptide) for rabies virus glycoprotein (rabies virus glycoprotein, RVG) derived peptides. Transforming the RVG peptides from 189 to 214 and 330 to 357 to obtain RVG-derived peptides(RDP),which have targeting to central nervous system and without immunogenicity, and such derived peptide retains the neurotropic of RVG, with exogenous macromolecular compounds transported into the brain of a potential function.This study selected polypeptide RDP which has brain targeting effect as ligands, with natural plant extracts of curcumin as a model of anti-cancer drug, prepared the brain targeted long-circulating liposomes curcumin(RDP-CUR-L), and its grain size distribution, Zeta potential, the degree of dispersion, encapsulation efficiency and stability of the physicochemical properties were characterized. The results showed that RDP-CUR-L average particle size was (98.56 ± 6.97) nm, the encapsulation efficiency was (87.68 ± 2.83)%, while the ordinary curcumin liposomes (CUR-L) average grain diameter was (81.20 ± 5.13) nm, the encapsulation efficiency was (89.12 ± 3.71)%, and it had a good reproducibility and stability.The curcumin distribution in heart, liver, spleen, lung, kidney and brain of mice was investigated by injecting curcumin suspension (CUR), curcumin liposomes (CUR-L), PEGylated liposomes modified with RDP(RDP-CUR-L)in the caudal vein of mice via HPLC assay at 0.25,0.5,1,2,6,8,12,24h. In vitro release test measured curcumin release in CUR-L and RDP-CUR-L. The results show that after injecting CUR and CUR-L in the caudal vein of mice, no curcumin was detected in the brain. Nevertheless, high concentration of curcumin was detected in it after injecting RDP-CUR-L, and it had a remarkably better long-circulating effect(more than 24h), and in various organs of the organization there has been a marked changes, showing a significant brain targeting.MTT assay of SH-SY5Y,U87 and A549 cells showed the IC50 of RDP-CUR-L was significantly lower than CUR-L. The inhibitory effect of RDP-CUR-L to nerve cells SH-SY5Y and U87 was stronger than non-neuronal cells A549, showed obvious neurotropic.In vivo imaging experiments can be seen that CUR-L in mice distributed mainly in the bladder, kidney, liver, spleen, etc., there was no distribution in the brain. The RDP-CUR-L significantly into the brain. Dissection to take the organs of mice after in vitro images showed a more obvious brain targeting effect of RDP.In summary, RDP-CUR-L was successfully prepared in this experiment, and there was a strong validation of its brain targeting and better tumor suppression effect compared to CUR and CUR-L. Although intense research on active targeting of liposomes has been applied now, because of the BBB, limiting the development of brain-targeted liposomes, and RDP as a brain targeting cell-penetrating peptide, not only mediate nucleic acids, peptides and other small molecules into the brain, but also can be applied to nano-drug system for the treatment of brain diseases.