## 5 Chitosan Nanocarriers in Brain Targeting
### Nanoparticles (NPs)
Docetaxel-loaded D-\(\alpha\)-tocopherol polyethylene glycol 1000 succinate conjugated chitosan nanoparticles were prepared with the presence or absence of transferrin on the surface [78]. The particle size of the nanoparticles was in the size range of 130-300 nm. The incorporation of docetaxel into the NPs with targeting ligand and the presence of transferrin on the surface of NPs increased the particle size. The zeta potential of the chitosan nanoparticles was significantly positive. However, the incorporation of TPGS into the nanoparticles increased the negative charge resulting from the non-ionic nature of TPGS. The transferrin served as a receptor for specific drug delivery. The entrapment efficiency of the nanoparticles was 75%. The drug release profile of the formulation was pH-dependent, resulting from the protonation of the chitosan's amino groups at a low pH value. Increased electrostatic repulsion effect also induced drug diffusion from nanoparticles. The high drug release was significant at pH 5.5 and sustained at the pH of 7.4. The in vitro cytotoxicity evaluation on C6 glioma cell lines indicated that the IC\({}_{50}\) values of the non-targeted and targeted drug-loaded NPs were 2.21 and 0.41 \(\upmu\)g/mL, respectively, which was lower when compared to DocelTM with IC\({}_{50}\) of 60.98 \(\upmu\)g/mL. The conjugation of chitosan together with transferrin in the NPs resulted in a synergistic effect. In vivo pharmacokinetics studies further showed that the nanoparticles with transferrin exhibited a high AUC with a prolonged circulation in blood when compared to DocelTM. The NPs is a potential treatment approach for TfR overexpressingcancer cells [78]. Methotrexate-loaded chitosan or glycol chitosan nanoparticles was coated with a layer of Tween 80 for brain delivery. Tween(tm) 80 coating layer of NPs is useful for brain delivery because the surfactant adsorbs apolipoproteins E and B from the blood which are useful in promoting receptor-mediated endocytosis of the NPs by the endothelial cells of the BBB [79]. The NPs were cytotoxic against C6 glioma cells line and were able to overcome the MDCKII-MDR1 (Multi-drug Resistance gene-1-Madin-Darby Canine Kidney) cell barrier. The glycol chitosan nanoparticles were the most cytotoxic NPs. A low concentration of Tween 80 of 0.1% v/v was adequate for enhanced transportation of methotrexate from the NPs across the BBB [80]. The transportation of the NPs across the MDCKII-MDR1 monolayer is believed to occur as a result of the disruption of BBB resulting in the uptake of the NPs by enhanced permeation retention effect while an adsorptive-mediated transcytosis occurred across the intact BBB. The latter transport mechanism is influenced by the electrostatic interaction between the positively charged NPs and the negatively charged membrane of the monolayer [80; 81]. Nanoparticles used for the incorporation of drugs for brain targeting resulted in a high brain uptake in vivo. The high brain uptake of the drug suggests that incorporating the drugs onto the nanoparticles results in the drug's capability to cross the BBB. Some factors such as the particle size, surface properties, and positive charge of the nanoparticles are important in the uptake of the incorporated drug into the brain. The positive charge on the surface of the nanoparticles due to chitosan induced an interaction with the negatively charged sites on the cell membranes and tight junctions of the mucosal epithelial cells, thereby opening the tight junctions. The BBB is a system of vascular cellular structures composed of tight junctions between endothelial cells, receptors, transporters, and efflux pumps of the multidrug resistance (MDR) pathway, etc., which regulate the transport of molecules into the brain. The permeability of drug to the brain is enhanced by the loosening of tight junctions between the endothelial cells [82].