Synthesis And Characterization Of Modified Chitosan As Carriers Of Drugs Treatment For Restenosis After PTCA

Blood flow through an obstructed coronary artery could be effectively restored by percutaneous transluminal coronary angioplasty (PTCA). Statistically, 30-40% of patients undergoing PTCA require additional surgical intervention because of a combination of factors including elastic recoil, thrombosis, vessel remodeling, local tissue inflammation, and neointima formation. The incidence of elastic recoil had been reduced by the postangioplasty deployment of vascular stents, which reduced the need for follow-up surgery by some 30%. However, even with stent implantation, restenosis was still a significant medical problem after PTCA. In order to improve the cure rate of restenosis after PTCA, new targeting drug carriers were the key to solve the problem, which could meet drug concentration of the treatment and time of drug release at the same time, while reducing toxicity of drugs on normal tissue. In the dissertation, the modified products of chitosan were used as biocompatible and targeting carrier in order to cure restenosis after PTCA. A series of novel chitosan modification were synthesized and characterized, including quaternized chitosan, chitosan modified by folic acid and chitosan modified by gluconic acid. In addition, the release properties of aspirin (ASA), probucol (PRO) and NO loaded in these chitosan modification carriers were investigated. The main content can be classified into five parts as follows:1. Antioxidative activity of chitosans and novel quaternized chitosans with varying molecular weights. Different types of modified chitosans were prepared and characterized. Chitosan was not only modified by quaternization on the C-2 position, but slso modification happened on C-6 position of chitosan whose functional groups of the NH2 groups were protected in advance. The hydroxyl radical, superoxide anion and DPPH radical scavenging activities of quaternized chitosans with different modification position and different molecular weight were studied, which could also provide a basis for more application.C-2 quternized chitosan was better than C-6 quternized chitosan in antioxidant capacity, which suggested C-2 hydroxy-antioxidant activity of chitosan played a relatively important role. According to the experimental results, some resistance and molecular reaction of association and other reasons were related to some facts that chitosan with the higher molecular weight had the stronger capacity in the superoxide and hydroxyl radical scavenging activities, on the contrary, chitosan with the lower molecular weight had the stronger capacity in the DPPH radical scavenging. In addition, chitosan with higher molecular weight modified by larger quaternary ammonium salt had the higher antioxidant capacity. 2. O-(2-hydroxy)propyl-3-trimethylammonium chloride chitosan (O-HTCC) was synthesized and characterized, and also BSA loaded O-HTCC nanoparticles was studied. The size and morphology changes of nanoparticles under the different formation conditions were discussed in detail. In vitro release properties of the BSA were studied, at the same time, the changes of BSA crystal in the chitosan and O-HTCC nanoparticles were first characterized.BSA encapsulation efficiency and BSA loading capacity of O-HTCC nanoparticles were much larger than that of chitosan nanoparticles. When the TPP concentration was 2mg/mL and BSA concentration was 1mg/mL, BSA encapsulation efficiency and BSA loading capacity of O-HTCC nanoparticles reached to 87.5% and 99.5%, respectively. After loaded BSA, the size of BSA loaded chitosan nanoparticles was larger than that of pure chitosan nanoparticles. By contrast, BSA loaded O-HTCC nanoparticles was smaller than that of pure O-HTCC nanoparticles, and also with the BSA concentration increasing, not only the size of BSA loaded chitosan, but the size of BSA loaded O-HTCC nanoparticles became larger. BSA concentration also had a great influence on the BSA burst release in BSA loaded O-HTCC nanoparticles, and with the BSA concentration increasing, BSA encapsulation efficiency and BSA loading capacity increased. The crystal structure of BSA had undergone great change after loaded in the chitosan and O-HTCC nanoparticles, which showed that during the process of cross-linking between cationic macromolecules and TPP, a new crystal structure of BSA occurred.3. Preparation and characterization of nanoparticles containing aspirin (ASA) and probucol (PRO) based on quant ammonium salt modified and study on quaternized chitosans'NO adducts properties. Only one drug loaded O-HTCC nanoparticles was compared with ASA and PRO combined drugs loaded O-HTCC nanoparticles at the same time, consisted of nanoparticles size and morphology and in vitro release. The results showed that: the presence states of ASA and PRO in the nanoparticles were different, hydrophilicity of the ASA was in the existence of non-state crystal, and lipophilic PRO was in the crystal state. When ASA and PRO were loaded at the same time, both drugs could affect one another in release rate, and speed up the release of their speed. In addition, the quaternary ammonium chitosan salt/NO adducts were synthesized, and the structure and properties of different quaternary ammonium chitosans/NO adducts were discussed in detail, as well as the influence of quaternary ammonium chitosan salt with different molecular weights and different site modification on the release kinetics of NO. These results showed that: Compared with HTCC, O-HTCC had the higher NO loading capacity and also had the higher release rate. As far as quaternized chitosans with the same modification and with the different molecular weight, quaternized chitosan with the higher molecular weight had the poorer NO loading capacity.4. The study of folic acid modified chitosan, CMCS and O-HTCC and their NO adducts properties. Chitosan, CMCS and O-HTCC modified by folic acid were synthesized and reacted with nitric oxide to form novel nitric oxide donors. The synthesized method was carried out: folic acid was actived by N-Hydroxysuccinimide (NHS) and 1-Ethyl-3-(3-dimethyllaminopropyl)carbodiimide hydrochloride (EDC), then reacted with the amine groups on chitosan, CMCS and O-HTCC. The chemical structures of the products were characterized by FTIR, UV spectrum, and NMR. The results showed that: folic acid modified chitosan, CMCS and O-HTCC at C2 position could be prepared by this method. The maximum NO release and half life of O-HTCC-FA-NO (molar ratio: O-HTCC/FA=2/1), CS-FA-NO (CS/FA=2/1) and CS-FA-NO (CS/FA=1/2) were 52.3nmol/mg (t1/2=0.866h), 36.72nmol/mg (t1/2=0.248h) and 84.3nmol/mg (t1/2=0.257h), respectively. The reasons of these differences were attributed to the different of degree of substitution of folic acid and the obstacle in space of folic acid.5. Gluconic acid modified chitosan and carboxymethyl chitosan and their NO adducts properties. A series of gluconic acid modified chitosan (SBC) and gluconic acid modified CMCS (SBCS) as new NO adducts were prepared and characterized, as well as NO in vitro release properties were studied. The results showed that: SBC-NO adducts obtained by chitosan modification with the smaller molecular weight had the higher loading capacity, on the contrary, with the same molecular weight, the release half-life of SBCS-NO adducts was much longer than that of SBC-NO adducts.