Aquasomes as a drug delivery system for proteins and peptides

Abstract

Aquasomes are nanocarrier systems consist of three distinctive layers; an inner core, a polyhydroxy carbohydrate layer and an outer layer of an API (Kossovsky et al., 1991). Aquasomes have a unique structure and ability to carry active molecules through a non-covalent bounding and provide superior stability, especially for proteins and peptides (Masatoshi and Yongning, 1998; Kim and Kim, 2002; Khopade et al., 2002). Different core and coating materials were used to prepare aquasomes under different conditions to investigate the relationship between preparation conditions and loading efficiency. In terms of loading efficiency, hydroxyapatite aquasomes, with either lactose or trehalose as a coating material, had the highest BSA loading (40%-60%) when compared to DSPA aquasomes. While DCPA aquasomes, with either lactose or trehalose as a coating material, had the lowest BSA loading (8%-16%). To investigate the interaction of the three layers of aquasomes, Surface analysis, docking and MD simulations were performed. Surface analysis performed by Discovery Studio showed that HA and trehalose interact by hydrogen bonding with the later acting as a hydrogen acceptor, while BSA displayed almost complete SAS and that there are numerous targets for trehalose attachments (no specific active site). MD simulations of BSA performed by AMBER 12 showed a stable MD simulation of BSA for 5 ns. Total energy analysis of BSA on the two conditions performed (300K and 280K) support the experimental data of lower BSA loadings of aquasomes prepared at 400C compared to those manufactured at 250C (p<0.05). This could be related to that BSA might have either started to denature/unfold or breaking up which eventually resulted in low BSA loadings obtained experimentally. The high loading efficiency highlights aquasomes as a promising carrier for the delivery of proteins and peptides. Following formulation Optimisation, two routes of delivery were investigated, pulmonary and oral routes. For pulmonary delivery of aquasomes, BSA-loaded aquasomes were successfully formulated as pMDI and DPI formulations. Both pMDI and DPI formulations were investigated to identify lung distribution of BSA-loaded aquasomes using NGI. In vitro release studies on the selected size fractions from NGI show a sustained release of BSA over a period of 6 hr. In order to complement the in vitro release data, cell culture studies were performed to demonstrate the controlled release effect of aquasomes with BEAS-2B cell lines. The release of salbutamol sulphate (model drug) from aquasomes post 2 hr started to slow gradually until it reached its highest difference at 6 hr (p<0.05) when compared to the control. For oral delivery of aquasomes, BSA-loaded aquasome tablets were successfully formulated with MCC as multifunctional excipient and talc as a lubricant. Various powder blends of varying aquasomes amounts (25, 37.5, 50, 62.5 and 75%) were prepared and compressed at increasing compression forces (0.5, 1, 2 and 3 tons). It was noticed that under high compression forces of 2 and 3 tons, BSA spreads out of BSA-loaded aquasomes as was presented with confocal microscopy images. Tablets compressed under 1 ton of compression force was therefore chosen for coating as it showed desirable tablet characteristics (hardness, disintegration etc.). Acrylic based coating was used to spray coat the tablets. The coated tablets were found to disintegrate in pH >5.5 and steadily release for 6 hr. Cell culture studies were conducted to demonstrate the controlled release effect of aquasomes using Caco-2 cell lines. The release of metronidazole (model drug) from aquasomes post 2 hr started to slow gradually until it reached its highest difference at 6 hr (p<0.05) when compared to the control.