Calcium Phosphate Precipitation in Liposomal Suspensions

1989 ◽  
Vol 174 ◽  
Author(s):  
Edward D. Eanes
Keyword(s):  
Calcium Phosphate ◽  
Lipid Vesicles ◽  
Matrix Vesicles ◽  
Liposomal Membrane ◽  
Liposomal Membranes ◽  
Precipitation Reactions ◽  
Basic Features ◽  
Calcium Phosphate Precipitation

AbstractArtificial lipid vesicles (liposomes) provide an in vitro approach for microencapsulating calcium phosphate precipitation reactions in a manner similar to that which occurs in matrix vesicles, the initial loci for extracellular mineralization in many skeletal tissues. Apatitic precipitates readily form within the aqueous interiors of liposomes prepared from phosphatidylcholine, dicetylphosphate, and cholesterol when the liposomal membranes enclosing pH 7.4 buffered PO4 solutions are made permeable to external Ca2+ with ionophores. If the external Ca solution is rendered metastable with PO4, the apatitic precipitates rapidly expand to outside the liposomes as well. The present paper describes the basic features of liposomal mineralization and presents some specific examples on how compositional alterations in the liposomal membrane and external Ca solution can affect the progress of this mineralization.

Molecular Basis of Salivary Proline-rich Protein and Peptide Synthesis: Cell-free Translations and Processing of Human and Macaque Statherin mRNAs and Partial Amino Acid Sequence of their Signal Peptides

1987 ◽  
Vol 66 (2) ◽  
pp. 462-466 ◽  
Author(s):  
F.G. Oppenheim ◽  
D.I. Hay ◽  
D.J. Smith ◽  
G.D. Offner ◽  
R.F. Troxler
Keyword(s):  
Calcium Phosphate ◽  
Macaca Fascicularis ◽  
Electrophoretic Analysis ◽  
Proteolytic Processing ◽  
Oral Environment ◽  
Reticulocyte Lysate ◽  
Polyprotein Precursor ◽  
Phosphate Salts ◽  
Calcium Phosphate Precipitation

Acidic proline-rich phosphoproteins and phosphopeptides are abundant components of parotid and submandibular salivary secretions in man and in the subhuman primate, Macaca fascicularis. The major acidic proline-rich proteins and the proline-rich phosphopeptide, statherin, of man and macaques have been shown to be potent inhibitors of calcium phosphate precipitation and are thought to function in the oral environment by maintaining saliva supersaturated with respect to calcium phosphate salts. Little is known about the biosynthesis of these proline-rich phosphoproteins and peptides, and the aim of the present work was to determine the structural relationship between statherin precursors and native human and macaque statherin. RNA was isolated from human submandibular gland, and poly(A+) mRNA was selected by affinity chromatography on oligo(dT) cellulose and translated in a reticulocyte lysate. Electrophoretic analysis of the translation products revealed that this mRNA directed the synthesis of a large number of polypeptides with M,s ranging from 5000 to 70,000. Immunoprecipitates, prepared with an antiserum directed against human statherin, contained a single component with a Mr of 7800, approximately 2000 daltons larger than native statherin. Radiosequencing of the in vitro precursor of statherin in immunoprecipitates demonstrated the presence of a 19-residue signal peptide. These results suggest that statherin is derived from a unique structural gene, and does not result from proteolytic processing of a large polyprotein precursor.

The Effect of Silicic Acid on Calcium Phosphate Precipitation

1989 ◽  
Vol 68 (9) ◽  
pp. 1355-1359 ◽  
Author(s):  
J.J.M. Damen ◽  
J.M. Ten Cate
Keyword(s):  
Crystal Growth ◽  
Calcium Phosphate ◽  
Silicic Acid ◽  
Inhibitory Effect ◽  
Polysilicic Acid ◽  
Lag Period ◽  
Additional Support ◽  
Silica Suspensions ◽  
Calcium Phosphate Precipitation

So that a possible involvement in the mineralization of dental plaque could be investigated, the effects of silicic acid on calcium phosphate precipitation were assessed in vitro. By measuring the decrease in Ca2+ concentration (by means of ion-selective electrodes), we determined both spontaneous precipitation and seeded crystal growth from solutions that contained 1 mmol/L calcium, 7.5 mmol/L phosphate, 50 mmol/L Hepes pH 7.2, and various amounts of silicic acid. Polymerized silicic acid, but not its monomer, was found both to cause a 60% reduction in the lag period that precedes spontaneous precipitation and to enhance the growth rate of seeded hydroxyapatite crystals. Silica suspensions showed effects similar to those of polysilicic acid. In all cases, the precipitated material was found to be hydroxyapatite. Whereas seeded brushite crystals grew slowly without silicic acid, hydroxyapatite was the only mineral detected after crystal growth in the presence of silicic acid. Apparently, polysilicic acid acted as a substrate for hydroxyapatite nucleation, inducing secondary nuclei on both hydroxyapatite and brushite crystals. The finding that polysilicic acid could overcome part of the inhibitory effect of a phosphoprotein on calcium phosphate precipitation gave additional support for the idea that polysilicic acid and silica may promote the formation of dental calculus.

scholarly journals Stimulation of precipitation of calcium phosphate by matrix vesicles

1978 ◽  
Vol 170 (3) ◽  
pp. 681-691 ◽  
Author(s):  
R Felix ◽  
W Herrmann ◽  
H Fleisch
Keyword(s):  
Calcium Phosphate ◽  
Matrix Vesicles ◽  
Crystal Formation ◽  
Freezing And Thawing ◽  
Minimum Concentration ◽  
Vesicle Preparation ◽  
Before And After ◽  
Stimulation Of

The ability of matrix vesicles isolated from the epiphysial growth plate of 6-week-old chicks to facilitate the precipitation of calcium phosphate was studied in vitro. The vesicles lowered the minimum concentration product [ca2+]X[p1] needed to induce crystal formation, thereby showing the vesicles are nucleators of crystallization. After freezing and thawing the vesicles at pH6.0, part but not all of this ability to nucleate disappeared. Freezing and thawing markedly decreased the Ca and Pi content of the vesicles, suggesting that part of the nucleating activity may have been due to mineral already present. After removal of the mineral the residual nucleating activity could be destroyed by extracting the vesicles with lipid solvents or by treatment with enzymes such as phosphoilipase C, neuraminidase or proteinase. Matrix vesicles obtained from chicks treated with 1-hydroxyethane-1, 1-diphosphonate, a compound that inhibits calcification in vivo, showed impaired nucleating activity, both before and after treatment at pH6.0. The vesicle preparation bound some diphosphonate in vitro, probably to the mineral present in the preparation, since no binding could be detected in vesicles preincubated at pH6.0. No difference was found in the nucleating activity of vesicles isolated from rachitic chicks which had or had not received cholacalciferol 48 h before death. These results suggest that matrix vesicles possess intrinsic nucleating activity that may be important in biological calcification.

Isolation from urine of pyrophosphate, a calcification inhibitor

1962 ◽  
Vol 203 (4) ◽  
pp. 671-675 ◽  
Author(s):  
Herbert Fleisch ◽  
Sylvia Bisaz
Keyword(s):  
Calcium Phosphate ◽  
Inorganic Pyrophosphate ◽  
Minimum Value ◽  
Phosphate Compound ◽  
Apatite Crystals ◽  
Urinary Inhibitors ◽  
The Mean ◽  
Calcium Phosphate Precipitation

The minimum value of the product, Ca X P, necessary for calcium phosphate precipitation to occur, was determined in vitro. The addition of 2.2% urine to the solutions raised the mean product from 53 to 105 (mg/100 ml)2, which shows that the urine contains inhibitors to hydroxyapatite precipitation. One of these was isolated and purified. Its characteristics are those of inorganic pyrophosphate. The mean level of urinary pyrophosphate was 2.24 mg P/liter, sufficient to inhibit precipitation of hydroxyapatite. Pyrophosphate is one of the substances permitting urine to be supersaturated with calcium and phosphate; other urinary inhibitors are still to be identified. It is suggested that the phosphate compound present in the plasma which inhibits hydroxyapatite precipitation is pyrophosphate. In bone, pyrophosphatase would act by locally destroying this calcification inhibitor, thus allowing the apatite crystals to form.

scholarly journals Laminin Coating Promotes Calcium Phosphate Precipitation on Titanium Discs in vitro

2011 ◽  
Vol 2 (4) ◽  
Author(s):  
Kostas Bougas ◽  
Victoria Franke Stenport ◽  
Pentti Tengvall ◽  
Fredrik Currie
Keyword(s):  
Calcium Phosphate ◽  
Calcium Phosphate Precipitation
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