Zn²⁺ Induced Irreversible Aggregation, Stacking, and Leakage of Choline Phosphate Liposomes

Abstract

The interaction between lipids and metal ions is important for metal sensing, cellular signal transduction, and oxidative lipid damage. While most previous work overlooked the phosphate group of lipids for metal binding, we herein highlight its importance. Phosphocholine (PC) and its headgroup inversed choline phosphate (CP) lipids were used to prepare liposomes. From dynamic light scattering (DLS), Zn causes significant aggregation or fusion of the CP liposomes, but not PC liposomes. The size change induced by Zn is not fully reversed by adding EDTA, implying liposome fusion induced by Zn. Isothermal titration calorimetry (ITC) shows that binding between Zn and CP liposomes is endothermic with a K of 110 μM Zn, suggesting an entropy driven reaction likely due to the release of bound water. In comparison, no heat was detected by titrating Zn into PC liposomes or Ca into CP liposomes. Furthermore, Zn causes a transient leakage of the CP liposomes, and further leakage is observed upon removing Zn by EDTA. Transmission electron microscopy (TEM) with negative stained samples showed multilamellar CP lipid structures attributable to Zn sandwiched between lipid bilayers, leading to a proposed reaction mechanism. This work provides an interesting system for studying metal interacting with terminal phosphate groups in liposomes, affecting the size, charge, and membrane integrity of the liposomes.

Charge and Coordination Directed Liposome Fusion onto SiO2 and TiO2 Nanoparticles

“…In addition, the p K a values of their surface hydroxyl groups (e.g., electrostatic interactions) have been focused on as the main difference between SiO 2 and TiO 2 , while their chemical interaction with lipids has not been carefully considered . Recently, studies on the binding of metal ions and metal oxides to lipids have attracted increasing attention. − In this context, we want to re-examine these two surfaces with a few more lipids. Our goal is to understand the inorganic surfaces and lipids at the same time by varying the headgroup chemistry and pH.…”

Liposome‐Boosted Peroxidase‐Mimicking Nanozymes Breaking the pH Limit

“…The calcein fluorescence was excited at 485 nm and monitored at 515 nm for 500 s, and 2 μL Fe 3 O 4 nanoparticles (50 μg mL −1 ) were added at the time of 100 s. Then, 5 μL of 10 % Triton X‐100 was added to fully rupture the liposomes. Each group was measured at least 3 times [52, 53] …”

Liposomes as models for membrane integrity

“…DLS has been employed in several studies investigating membrane integrity and stability in response to various agents. For example, Liu and Liu (2017) 61 have used DLS to show how the diameter of choline phosphate (inversed phosphocholine) liposomes increased upon exposure to Zn 2+ , suggesting swelling or fusion. DLS has been used to monitor membrane integrity in response to conjugated polyelectrolytes (CPE).…”