Fundamental study of nanoliposomes for ocular therapy

• Main Author: Chaw, Su Yin
• Other Authors: -
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Nanotechnology; Engineering::Materials::Biomaterials
• Online Access: https://hdl.handle.net/10356/144959
• Institution: Nanyang Technological University

Delivering ocular drugs via subconjunctival administration has garnered much interest due to its ability to utilize the trans-scleral route. However, the exact distribution or fate of nano-carriers is still largely unknown. In order to achieve and maintain therapeutic drug concentrations in the eye, it is important to know the in vivo fate of the nano-carriers in the eye after administration. This research aims to study the in vivo fate of nano-carriers after sub-conjunctivally injecting them into the eyes. By focusing on liposomes, factors that affect the in vivo ocular distribution and disposition of the liposomes was studied. The factors include liposomal charge, size, incorporation of cholesterol and chain saturation. The first part of this research involves optimization of the protocol for imaging the injected liposomes in the eye. By employing the use of CellVizio® Dual Band, a real time in vivo confocal laser imaging system, ocular distribution of up to a few microns depth can be detected. A pilot study was conducted to investigate the feasibility of the CellVizio® Dual Band by following the distribution of 100nm POPC liposomes over 28 days. It was concluded that CellVizio® Dual Band was indeed a suitable imaging system for longitudinal study of distribution of liposomes in the eye and 2% Evans Blue is suitable for use as a vasculature stain. This was also the first time CellVizio® Dual Band has been used for longitudinal ocular imaging study. The effect of liposomal charge, size, cholesterol and chain saturation on the distribution in the eye was studied using the CellVizio® Dual Band system by improving on the protocol used for the pilot study. The effect of the charge and size on the distribution of liposomes in the eye was evident 3 days after injection. The liposomes were observed to be distributed to both the sclera and cornea on Day 1, probably due to clearance through blood circulation and convective fluid flow. The mobility for micro sized liposomes was much lesser as they were too big to move away from the injection site. At Day 3, most of the negatively charged liposomes have moved away from the injection site, while neutral and positively charged liposomes can still be seen in the sclera region. By day 5, the liposomes have already migrated to their preferred locations. Neutral liposome and negatively charged liposomes settled at the limbus zone (near the corneal periphery) while positively charged liposomes remained at the sclera. Both neutral and negatively charged liposomes could have left the injection site due to the repulsive interactions between the negatively-charged sclera which drove the liposomes away from the sclera. Positively charged liposomes naturally remained at the sclera due to attractive interactions with the negatively charged environment of the sclera. Liposomes with cholesterol and DPPC liposomes were distributed in a similar manner to POPC. The studies done on radiolabeled liposomes to quantify the ocular distribution of the liposomes complemented the findings from the imaging study. The radioactivity detected was highest in the eye for positively charge liposomes and micron sized liposomes while the amount detected for POPC liposomes and DPPC liposomes were similar. It can be concluded from both the qualitative and quantitative studies that the main factors that affect distribution of the liposomes in the eye were size and charge. This can greatly influence the way we design nanocarriers to the eye.