Poster X14 - Size Control and Stability of Phosphatidylcholine Liposomes

Saturday, October 26, 2024

10:00 AM - 11:00 AM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Anna Fay

Undergraduate Researcher
Valparaiso University, United States
Makayla Mann

Undergraduate Researcher
Valparaiso University
Valparaiso, Indiana, United States

Last Author(s)

Lauren F. Sestito, PhD

Assistant Professor of Mechanical Engineering and Bioengineering
Valparaiso University
Valparaiso, Indiana, United States

Introduction: Liposomes are nanoscale vesicles composed of amphiphilic lipids, producing a phospholipid bilayer surrounding an aqueous interior. Liposomes have been widely employed in drug delivery applications due to their ability to encapsulate both hydrophobic drugs, which partition into the lipid bilayer, and hydrophilic drugs, which incorporate into the aqueous core. These particles provide unique advantages for lymphatic drug delivery after oral administration due to the role of intestinal enterocytes in lipid transport, their ability to promote chylomicron formation [1], and their potential to improve drug stability in the gastrointestinal tract [2]. In order to investigate the impact of liposome properties on transport and drug access to lymph after oral administration, a panel of liposomes must be created. The goal of this work is thus to characterize the impact of synthesis parameters on liposome size, enabling future size control, and to evaluate the stability of synthesized liposomes in the gastrointestinal environments experienced after oral administration.

Materials and

Methods: Liposome Synthesis: Liposomes were synthesized by the thin film method. Briefly, soy phosphatidylcholine (PC) and cholesterol (chol) were dissolved in chloroform in a 1:1 molar ratio. After solvent evaporation, the resulting thin film was rehydrated in deionized water by stirring. Liposomes were then downsized by bath sonication and filtered through 1 µm and 0.22 µm filters. Liposome size was measured using a Horiba LA-960 particle size analyzer. Size Control: The synthesis protocol was adjusted to investigate the impact of parameters like sonication time (15-220 minutes), PC:Chol molar ratio (1:1 to 2:1), and rehydration concentration (2-20 mg/ml) on resulting liposome size. Gastrointestinal Stability: Liposome stability in gastric and intestinal environments was evaluated by monitoring liposome size after incubation in test conditions for 2 hours at 37°C. The gastric condition included 2 mg/ml pepsin at pH 2, while the intestinal condition included 140 U/L pancreatic lipase and 2% m/v bile salts at pH 7.5.

Results, Conclusions, and Discussions: Impact of synthesis conditions on size: Synthesized liposomes ranged from 100 – 600nm in diameter depending on synthesis conditions (Figure 1). Liposome diameter decreased with increasing sonication time (Figure 1a), but this also resulted in increased size variability. Increasing rehydration concentration also appeared to reduce liposome diameter up to about 5 mg/ml (Figure 1b), but PC:Chol ratio had no clear effect on the resulting size (Figure 1c). Together these results suggest that liposome diameter could be minimized by increasing sonication time and rehydrating at a concentration of at least 5 mg/ml. GI Stability: Liposome diameter was additionally monitored after incubation in conditions that mimic gastric and intestinal environments (Figure 2a). Liposome size appeared to increase particularly in gastric conditions, suggesting that the particles may be aggregating. This effect may be primarily due to the reduced pH (Figure 2b). Future work will explore the impact of this size increase on drug loading and release, as well as the impact of changing liposome composition or coating on size and stability.

Acknowledgements (Optional): References
[1] Ahn, H. & Park, J. H., "Liposomal delivery systems for intestinal lymphatic drug transport," Biomater Res 20, (2016). DOI: 10.1186/s40824-016-0083-1
[2] Iwanaga, K., Ono, S., Narioka, K., Morimoto, K., Kakemi, M., Yamashita, S., Nango, M. & Oku, N., "Oral delivery of insulin by using surface coating liposomes Improvement of stability of insulin in GI tract." Int J Pharm 157, (1997).