Investigation of the Role of Liposomes in Bone Formation

Liposomes are spherical lipid vesicles that in vivo, may play a role in the formation and retention of calcium in the form of calcium phosphate. Objective: This study aims to (1) examine the effect of liposomes on calcium phosphate formation from calcifying solutions and (2) examine the ability of liposomes to encapsulate already formed calcium phosphates. We will test the hypothesis that lipids in the form of liposomes affect the formation of calcium phosphates. Method: Synthetic unilamellar and multilamellar liposomes were produced using L-á-phosphatidycholine (PC) and cholesterol by rehydration using calcifying solutions of different composition and at different pHs. The liposomes obtained were then incubated (37°C, up to 24h). The liposomes were imaged following incubation using transmission electron microscopy (TEM) and the mineralized deposits characterised using Fourier transform infrared spectroscopy (FTIR). Solution composition was analysed before and after mineralization, using inductively coupled plasma-mass spectrometry (ICP-MS). Precipitated apatite and dicalcium phosphate dihydrate were encapsulated into the liposomes. The effect on cell growth and activity was also monitored, using Mg63 and Saos-2 osteosarcoma cell lines. Results: Preliminary results showed that multilamellar liposomes promoted calcium phosphate formation in the presence of carbonate from calcifying solution and also encapsulated previously formed minerals. The type of calcium phosphate formed depended on the solution pH. In addition, the mineralized liposomes had no cytotoxic effects on the cells and were shown to increase alkaline phosphatise production.

Conclusion: Liposomes can effectively encapsulate calcium phosphate or other calcium compounds. Mineralized liposomes may have the potential for bone repair as bone graft materials or as scaffolds for bone regeneration.