Fluoride and Biological Mineralization II: Mechanism of Action of Fluoride to Influence the Collagen-Induced In Vitro Mineralization and Demineralization Reactions.

Fluoride had been shown to inhibit collagen-induced in vitro mineralization without affecting demineralization at its lower concentrations (> 1X10 and < 1X10 M) and stimulate mineralization in addition to inhibiting demineralization at its concentration > 1X10 M. The present studies were designed to investigate the mechanism by which fluoride acts to produce these concentration-dependent effects. The inhibition of mineralization occurring at the lower concentrations of fluoride was found to be due to the inactivation of the specific calcium binding sites of collagen involved in initiating the process of mineralization.

Fluoride and Biological Calcification I: Effect of Fluoride on Collagen-Induced In Vitro Mineralization and Demineralization Reactions.

An in vitro system employing collagen isolated from the sheep tendons to induce mineralization and demineralization reactions was used not only to study the effect of various concentrations of fluoride on the collagen-induced mineralization and demineralization reactions but also to compare their action with the inhibitors of mineralization and/or demineralization. Studies demonstrated that under physiological conditions, at lower concentrations (5 × 10 to 5 × 10 M) fluoride inhibited while at higher concentrations (> 10 M), it stimulated the collagen-induced in vitro mineralization. At higher concentrations, fluoride was also found to inhibit the demineralization of the collagen bound preformed mineral phase.

Role of a protein inhibitor isolated from human renal stone matrix in urolithiasis.

The role of biomolecule(s) from renal stone matrix in urolithiasis was investigated. The ability of a particular fraction (> 10 kDa fraction) isolated from the EDTA extract of powdered human renal stones to influence calcium oxalate monohydrate (COM) crystal growth was studied. The most potent inhibitor of COM crystal growth obtained from > 10 kDa fraction was purified by various chromatographic techniques and SDS-PAGE, etc.

Effect of nucleoside-5'-phosphates on collagen-induced in vitro mineralization.

Nucleoside triphosphates (NTPs) at 4-10 microM concentrations were found to inhibit the rates of collagen-induced in vitro mineralization and ion exchange reactions. The sequential removal of the terminal phosphate groups caused a step-wise decrease in their inhibitory potency. The results suggest that NTPs inhibit the rates of ion uptake and exchange reactions at concentrations much lower than their intracellular physiological concentrations.

Mg2+: a potent inhibitor of collagen-induced in vitro mineralization.

At physiological concentrations, Mg2+ has been found to be a potent inhibitor of collagen-induced in vitro mineralization. Mg2+ inhibits mineralization by competing with Ca2+ for specific phosphate independent Ca2+ binding sites of the catalytic matrix. Matrix bound Mg2+ subsequently reacts with HPO4(2-) to form MgHPO4 complex which can not be further converted to the matrix bound mineral phase.

Concentration of a potent calcium oxalate monohydrate crystal growth inhibitor in the urine of normal persons and kidney stone patients by ELISA-based assay system employing monoclonal antibodies.

Standardized calcium oxalate monohydrate (COM) crystal growth assay system was employed to study the ability of various test samples to influence growth rates of COM crystals. The inhibitory activity (IA) of various samples was expressed in terms of inhibitory units. Urine samples obtained from normal persons and kidney stone patients were found to have IA of 3.

Role of biomolecules from human renal stone matrix on COM crystal growth.

Human renal calculi surgically removed from kidney stone patients were obtained and chemically analysed. Stones with CaOx (calcium oxalate) as the major component were washed in 0.15 M NaCl with gentle stirring for 48 h and then pulverised to a fine powder.

Inhibitors of in vitro mineralization from rabbit aorta and their role in biomineralization.

Mineralization of aorta is known to occur late in life and appears to be a pathological phenomenon. In vitro studies revealed that the matrix prepared from the thoracic aorta pieces after their extraction with 3% Na2HPO4 and 0.1 mM CaCl2 were mineralized under physiological conditions of temperature, pH, and ionic strength of the media to form matrix-bound mineral phase resembling hydroxyapatite in nature.

Inhibitors of in vitro mineralization from flexor tendons of rabbits and their role in biological mineralization.

Studies demonstrate that flexor tendons contain loosely associated biomolecules which inhibit its mineralization under physiological conditions. Based upon their molecular weights, these inhibitory biomolecules, could be classified into two categories, having molecular weights less than and greater than 13,000 daltons. The main inhibitory biomolecule was found to be an acidic polypeptide having molecular weight of 12,400 daltons.

Calcium and oxalate uptake by the renal brush border membrane vesicles in magnesium-deficient rats.

Calcium and oxalate uptake by renal brush border membrane vesicles (BBMV) was examined in magnesium-deficient and pair-fed control rats. Uptake studies were carried out by rapid filtration technique and rate of influx of calcium and oxalate as a function of extravesicular concentration (0.1 nM--1.

Oxalate metabolism in magnesium-deficient rats.

Male weanling rats were maintained on magnesium-deficient diet for 30 d and compared with pair-fed control rats fed magnesium-supplemented diet. Magnesium deficiency led to slow growth and finally to a significant decrease in body weight (P < 0.001) accompanied by a significant hypomagnesaemia, hypomagnesuria and hyperoxaluria (P < 0.

Intestinal absorption of calcium and oxalate in magnesium-deficient rats.

To examine the contribution of exogenous calcium and oxalate in magnesium deficiency, intestinal absorption of both calcium and oxalate was studied by preparing brush border membrane vesicles (BBMV). Purity of the BBMV was ascertained biochemically by enrichment of the marker enzyme alkaline phosphatase by 14-fold with a concomitant 90 per cent decrease in the basolateral marker enzyme Na+/K(+)-ATPase in the purified membrane preparation as compared to the respective homogenate in both the groups. Uptake studies were carried out by a rapid filtration technique.

Electrical conductivity of kidney stones.

Electret behaviour of surgically removed kidney stones through thermally stimulated polarization and thermally stimulated depolarization has already been reported by the authors. To develop an understanding of the conduction mechanism of such samples, d.c.

Effect of an Ayurvedic compound preparation on the ability of rat urine to influence mineral phase formation.

Rat urine could inhibit not only the in vitro initial precipitation of calcium and phosphate/oxalate ions as mineral phase but also the subsequent growth of the preformed mineral phase. Oral administration of the aqueous extract of a commercially available Ayurvedic compound preparation to rats, was found to significantly increase the ability of the urine samples to inhibit both the initial mineral phase formation and its subsequent growth.

The electret effect of kidney stones.

Surgically removed kidney stones were powdered and samples made from them were subjected to a d.c. field of 20-50 kV/cm whilst being heated at 1 degree C/min.