## 5 Chitosan Nanocarriers in Brain Targeting
### Nanoparticles (NPs)
There was a decrease in the concentration of the NPs in the two aforementioned regions of the brain over time. No significant oxidative stress damage was observed. A significant reduction in the GFAP (Glial fibrillary acidic protein) expression, which was dose-dependent, was observed in the cerebellum after exposure to TmCS-NPs (Tween-80-modified chitosan nanoparticles), suggesting the degenerative changes in the cerebellum and activated astrocytes can induce brain damage [58]. The significant reduction in the GFAP expression in the cerebellum after exposure to TmCS-NPs indicate that a thorough investigation should be done in order to evaluate the toxicity of TmCS-NPs. Reports have revealed that TmCS-NPs has toxic effects on muscle structure and the axonal development of primary and secondary motor neurons in vivo suggesting that it must be used with caution [59]. The ionic gelation method was used to prepare rivastigmine loaded chitosan nanoparticles for enhanced bioavailability and uptake of the drug to the brain via intranasal delivery [60]. The permeation enhancing activity of chitosan played an important role in drug loaded nanoparticles uptake which was high when compared to the pure drug solution [60]. The interaction of negatively charged sites of the cell membranes and tight junctions of the mucosal epithelial cells with the positively charged amino group on chitosan stimulated the opening of the tight junctions [61]. The hydrophilic nature of the pure drug influenced the reduced permeation of the pure drug solution. The brain-blood ratio of the drug after the administration of the drug via intravenous and intranasal route formulations were 0.24 and 0.79, respectively, when compared to the drug-loaded NPs which was 1.71 after intranasal administration over a period of 30 min. The low concentration of the drug in the plasma after intranasal administration was significant when compared to the intranasal administration of the free drug. The high brain-blood ratio and low plasma concentration of the drug after intranasal administration of the drug-loaded NPs indicate a nose-to-brain transport of the formulation bypassing the BBB. The brain drug concentration achieved from intranasal administration of the drug loaded chitosan NPs was C\({}_{\text{max}}\) (966) and AUC (247,730 ng. min/mL), which was significantly higher when compared to the intravenous and intranasal administration of the drug solution. The results revealed that NPs have good brain targeting capability and they are potential therapeutics for the treatment of [PERSON]'s disease. The drug uptake into the brain from the nasal mucosa can occur via two pathways, which are the systemic pathway, in which some of the drug reaches the brain by crossing the BBB, and by the olfactory pathway, in which the drug is transported to the brain from the nasal cavity [62]. The chitosan nanoparticles loaded with olanzapine was developed for the treatment of depression [63]. Olanzapine is a drug used for the management of neurological disorders such as schizophrenia [64; 65]. It is characterized by poor bioavailability resulting from the hepatic first pass metabolism. Its low permeability results from its efflux by P-glycoprotein [66]. Olanzapine-loaded nanoparticles' mean particle size was 183 nm with zeta potential and polydispersity index of +52.1 mV and 0.122, respectively. The entrapment efficiency and drug-loading capacity of the NPs was 72% and 26%, respectively. In vitro drug release profile of the NPs was an initial burst release followed by a sustained release mechanism. In vitro toxicity studies on RPMI 2650 human nasal epithelial cell line by MTT (3-(4,5-Dimethylthiazol-2-ylyl)-2,5-diphenyltetrazololium bromide) assay revealed low toxicity when compared to the free drug. Ex vivo studies on excised goat nasal mucosa further indicated the non-toxic nature of the NPs when compared to the drug solution in which the nasal mucosa displayed detachment of some cilia from the epithelial tissues indicating toxicity [63].