Complement dependent and independent liposome uptake by peritoneal macrophages: cholesterol content dependency

Area of Science:

• Biomedical Sciences
• Cell Biology
• Drug Delivery Systems

Background:

• Liposomes are widely investigated as drug delivery vehicles.
• Understanding liposome-macrophage interactions is crucial for optimizing their in vivo performance.
• Cholesterol content and liposome size are known factors influencing liposome behavior.

Purpose of the Study:

• To elucidate the uptake mechanisms of liposomes by rat peritoneal macrophages (PMs).
• To investigate the role of serum opsonization and complement system in liposome uptake.
• To determine how liposome size and cholesterol content affect these uptake pathways.

Main Methods:

• Incubation of liposomes with varying cholesterol content and sizes with rat peritoneal macrophages and fresh rat serum.
• Quantification of liposome uptake and binding.
• Calculation of the rate constant for internalization (k(int)).
• Inhibition studies using anti-C3 antibody to assess complement involvement.

Main Results:

• Serum enhanced liposome uptake and binding, with effects dependent on liposome size and cholesterol content.
• Internalization rate constants (k(int)) varied significantly with cholesterol content, suggesting multiple uptake mechanisms.
• High and medium cholesterol liposomes showed complement-dependent uptake, inhibited by anti-C3 antibody.
• Low cholesterol liposomes exhibited complement-independent uptake and serum-induced disintegration.

Conclusions:

• Rat peritoneal macrophages utilize both complement-dependent and independent mechanisms for liposome uptake.
• The specific uptake pathway is dictated by the liposome's cholesterol content.
• These findings provide critical insights into the in vivo fate and targeting of liposomal drug delivery systems.