Liposome-mediated calcium phosphate formation in metastable solutions

Area of Science:

• Biochemistry
• Materials Science
• Biophysics

Background:

• Liposomes are crucial in drug delivery and biomimetic studies.
• Calcium phosphate precipitation is fundamental to biomineralization processes.
• Understanding liposome-mineral interactions is key to explaining biological calcification.

Purpose of the Study:

• To investigate the impact of anionic liposomes on calcium phosphate precipitate formation.
• To determine the role of intraliposomal inorganic phosphate (PI) and membrane permeability in precipitation.
• To elucidate the mechanism of mineral deposition in relation to liposome integrity.

Main Methods:

• Anionic liposomes were prepared using phosphatidylcholine, dicetyl phosphate, and cholesterol.
• Liposomes with entrapped inorganic phosphate (PI) were incubated in calcium (Ca2+) solutions.
• Ionophore X-537A was used to induce liposome membrane permeability.
• Calcium and phosphate concentrations were monitored to assess precipitate formation.

Main Results:

• Significant Ca2+ and PI losses from the external solution occurred only when liposomes containing PI became permeable to Ca2+ via ionophore addition.
• Ca2+ loss was substantially greater when coupled with PI loss, indicating a synergistic effect on precipitation.
• Intraliposomal precipitation, previously shown to reduce internal Ca2+, appeared to seed secondary precipitation in the external metastable solution.

Conclusions:

• Anionic liposomes can modulate calcium phosphate precipitation.
• Intraliposomal precipitation, facilitated by ionophore-induced permeability, can act as a nucleation site for external mineral deposits.
• This mechanism may contribute to the formation of extravesicular mineral deposits observed in matrix vesicle calcification.