## 3 Results and Discussion
### Insulin Permeation across Excised Olfactory Sheep Nasal Epithelial Tissues  
The P\({}_{\text{app}}\) values for insulin across excised sheep olfactory nasal epithelial tissues after the application of the different microparticle formulations are shown in Figure 3.  
The permeation of insulin alone (control group) across the excised olfactory sheep nasal epithelial tissues showed a relatively low P\({}_{\text{app}}\) value of 0.10 \(\times\) 10\({}^{-6}\) cm/s. This low permeation was expected because insulin is a large (5.8 kDa) hydrophilic peptide molecule with poor membrane permeation properties [41, 42].  
The P\({}_{\text{app}}\) for insulin across the excised olfactory nasal epithelial tissue from E + AVP emulsion microparticle formulation was 4.10 \(\times\) 10\({}^{-6}\) cm/s, while it was 3.73 \(\times\) 10\({}^{-6}\) cm/s for the AVP emulsion microparticle formulation. The AVP ionic gelation microparticle formulation exhibited a P\({}_{\text{app}}\) value of 3.68 \(\times\) 10\({}^{-6}\) cm/s for insulin. The P\({}_{\text{app}}\) values for insulin from all the microparticle formulations were statistically significantly higher (\(p<0.05\)) across the excised olfactory nasal epithelial tissues than the P\({}_{\text{app}}\) value of the insulin control group.  
_A. vera_ polysaccharides have previously been shown to be effective permeation enhancers for oral drug absorption. It was shown in in vitro studies that _A. vera_ gel polysaccharides  
Figure 3: Apparent permeability coefficient (P\({}_{\text{app}}\)) values for insulin across excised olfactory sheep nasal epithelial tissues after application of the microparticle formulations and insulin alone (control group). AVP emulsion = insulin microparticle formulation prepared by emulsion-solvent evaporation consisting of _A. vera_ polysaccharides, E + AVP emulsion = emulsion-solvent evaporation with Eudragit® L100 and _A. vera_ polysaccharide, and AVP ionic gelation = insulin microparticle formulation prepared by ionic gelation with _A. vera_ polysaccharides. * Statistically significantly different from the control group (\(n=6\); \(p<0.05\)).  
rides have the ability to increase the paracellular intestinal epithelial membrane permeation of a small molecular weight compound (atenolol) and a large molecular weight compound (FITC-dextran, 4 kDa) by the opening of tight junctions [21,43]. In this study, the incorporation of _A. vera_ polysaccharides in the microparticle formulations significantly increased the delivery of insulin across excised olfactory nasal epithelial tissues compared to the control group. The olfactory nasal epithelial permeation results of this study provided proof of concept for the use of _A. vera_ polysaccharides in microparticles as potential delivery systems for insulin delivery into the brain from the olfactory region after intranasal administration. These microparticles may potentially be used for insulin delivery into the brain by means of intranasal administration for the treatment of neurodegenerative diseases. However, targeting the microparticles to the olfactory region during intranasal administration may present a challenge, which should be addressed before this could be applied clinically. Furthermore, follow-up in vivo studies is needed to determine if clinically significant insulin levels can be achieved in the brain after intranasal administration from the olfactory region.