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Modulation of calcium phosphate formation by phosphatidate-containing anionic liposomes

journal contribution
posted on 2023-05-18, 14:13 authored by Eanes, ED, Hailer, AW, Heywood, BR
Liposomes prepared from 7∶2∶1 molar mixtures of phosphatidylcholine, dicetyl phosphate, and cholesterol to which 1–20 mole % dioleoylphosphatidic acid (DOPA) was added were used to examine the effect of membrane-bound monoester phosphatidate phosphate anions on calcium phosphate formation in aqueous solutions at 22°C, pH 7.4, and 240 mOsm. Results showed that up to 20 mole % DOPA in the liposomal envelope did not initiate mineralization in solutions made meta-stable with 2.25 mM CaCl2 and 1.50 mM KH2PO4. Results also revealed that precipitation induced in metastable solutions by the seeding action of intraliposomally formed mineral was measurably reduced with as little as 1 mole % DOPA and completely suppressed with 5 mole % DOPA. In contrast, 10 mole % concentrations of diester phosphate lipids either had no effect on extraliposomal precipitation (e.g., phosphatidylglycerol and phosphatidylinositol) or, as reported previously for phosphatidylserine, only partially reduced the amount of precipitate formed. Transmission electron microscopical analysis suggests that DOPA-containing lipid bilayers adhering to the seed crystals inhibited extraliposomal mineralization by encapsulating the crystals within the liposomes and/or by blocking potential growth sites on the crystal faces. The polar head group of DOPA, being more negatively charged and sterically less encumbered than diester phosphate ligands, most probably was responsible for this adherence of the lipid bilayers to the crystal surfaces.

History

Publication title

Calcified Tissue International

Volume

43

Issue

4

Pagination

226-234

ISSN

0171-967X

Publisher

Springer-Verlag

Place of publication

175 Fifth Ave, New York, USA, Ny, 10010

Rights statement

?Copyright 1988 Springer-Verlag New York Inc.

Repository Status

  • Restricted

Socio-economic Objectives

Clinical health not elsewhere classified

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