Effects of cellulose phosphate and sodium phosphate on formation product and activity product of brushite in urine

Reduced crystallization inhibition by urine from women with nephrolithiasis

BACKGROUND

Human urine is known to inhibit growth, aggregation, nucleation, and cell adhesion of calcium oxalate monohydrate (COM) crystals, the main solid phase of human kidney stones. This study tested the hypothesis that low levels of inhibition are present in women with calcium oxalate stones and, therefore, could promote stone production.

METHODS

In 17 stone-forming women and 17 normal women matched in age within five years, inhibition by dialyzed urine proteins of COM growth and aggregation was examined, as well as whole urine upper limits of metastability (ULM) for COM and calcium phosphate (CaP) in relation to the corresponding supersaturation (SS).

RESULTS

Compared to normals, patient urine showed a reduced ULM in relation to SS. In contrast to men, there was no difference in growth inhibition.

CONCLUSIONS

Reduced CaP and CaOx ULM values in relation to SS are a characteristic of female stone formers. This defect could promote stones by facilitating crystal nucleation. Abnormal inhibition may well be a very important cause of human nephrolithiasis.

Phytic acid in health and disease

Phytic acid (PA), a major phosphorus storage compound of most seeds and cereal grains, contributes about 1 to 7% of their dry weight. It may account for more than 70% of the total kernel phosphorus. PA has the strong ability to chelate multivalent metal ions, especially zinc, calcium, and iron. The binding can result in very insoluble salts that are poorly absorbed from the gastrointestinal tract, which results in poor bioavailability (BV) of minerals. Alternatively, the ability of PA to chelate minerals has been reported to have some protective effects, such as decreasing iron-mediated colon cancer risk and lowering serum cholesterol and triglycerides in experimental animals. Data from human studies are still lacking. PA is also considered to be a natural antioxidant and is suggested to have potential functions of reducing lipid peroxidation and as a preservative in foods. Finally, certain inositol phosphates, which may be derived from PA, have been noted to have a function in second messenger transduction systems. The potential nutritional significance of PA is discussed in this review.

Physicochemical effects of a new slow-release potassium phosphate preparation (UroPhos-K) in absorptive hypercalciuria

A new slow-release, neutral potassium phosphate salt (UroPhos-K) has been formulated in order to minimize gastrointestinal side effects and avoid sodium-induced calciuria. It was tested in a prospective randomized, double-blind trial in a group of 21 kidney stone patients with absorptive hypercalciuria type I (AH). Twelve patients allocated to the UroPhos-K group received four tablets twice daily with breakfast and an evening snack providing 1240 mg of phosphorus and 63.5 mEq of potassium daily. Nine patients assigned to the placebo group received placebo tablets of the same appearance containing excipient only. Subjects were studied during a 3-day period in the hospital while consuming a constant metabolic diet containing 400 mg Ca, 100 mEq Na, and 800 mg P per day before and after 3 months of treatment. Treatment with UroPhos-K did not cause any significant gastrointestinal side effects; nor did it raise fasting serum K or phosphorus, or reduce hemoglobin or creatinine clearance. It was associated with a rise in urinary K from 46 +/- 7 to 98 +/- 9 mEq per day and phosphorus from 744 +/- 185 to 1535 +/- 112 mg per day (p < 0.001 each). UroPhos-K treatment reduced urinary Ca from 288 +/- 63 to 171 +/- 49 mg/day (p < 0.001), without altering oxalate excretion. It reduced the urinary saturation of calcium oxalate without altering that of brushite. Moreover, by increasing urinary excretion of inhibitors (citrate and pyrophosphate), it reduced the propensity for spontaneous nucleation of brushite (increased formation product of brushite) and inhibited crystal agglomeration of calcium oxalate.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic and histologic investigation of the nature of nephrocalcinosis in children with hypophosphatemic rickets and in the Hyp mouse

To investigate the biochemical nature of nephrocalcinosis in children with hypophosphatemic rickets treated with orally administered phosphate and vitamin D, we studied five such patients, aged 3.7 to 12.3 years, during treatment and again 3 days after it had been discontinued. Treatment was associated with significant increases in mean serum phosphate concentration and urine phosphate/creatinine ratio, from 0.71 to 1.03 mmol/L and from 3.61 to 9.42 mmol/mmol, respectively. Significant correlation was found between urine phosphate/creatinine and oxalate/creatinine ratios (r = 0.670; p less than 0.01); however, the mean urine oxalate/creatinine ratio of 65.0 mumol/mmol while patients were taking phosphate orally was not significantly different from the ratio of 59.0 mumol/mmol when treatment was discontinued. Kidney biopsy specimens from three of the patients showed that the renal calcifications were located mainly intratubularly and were composed exclusively of calcium phosphate. In a further investigation of the nature of phosphate-induced nephrocalcinosis, six 6-week-old male Hyp mice, the murine analog of the human disease, received oral phosphate therapy with drinking water for 48 days; six others served as control animals. Mice in the experimental group excreted more phosphate (p less than 0.001) and less calcium (p less than 0.01) than control mice did, and medullary nephrocalcinosis, with a high kidney calcium content, developed (p less than 0.001). Histologic sections showed that the renal calcifications were located intratubularly and were composed of calcium phosphate. We conclude that, both in children with hypophosphatemic rickets and in the Hyp mouse, the development of nephrocalcinosis is associated with high oral phosphate intake and subsequent deposition of calcium phosphate precipitates in the kidney.

Propensity for spontaneous nucleation of calcium oxalate. Quantitative assessment by urinary FPR-APR discriminant score

The stone-forming urinary environment may be conducive to spontaneous nucleation of calcium salts, since it is generally characterized by a reduced limit of metastability (FPR or minimum supersaturation required for initiation of spontaneous nucleation) and an increased saturation (APR) of calcium oxalate and brushite (CaHPO4.2H2O). A discriminant analysis of the relationship between FPR and APR yielded a FPR-APR discriminant score, which gave a quantitative measure of the propensity for spontaneous nucleation. Positive scores, indicative of the "likelihood" of spontaneous nucleation, were found in the majority of patients with hypercalciuria in whom stones formed. Negative scores, representative of the "unlikelihood" of nucleation, were found in the majority of control subjects. Treatment with thiazide or sodium cellulose phosphate significantly reduced the discriminant score for both calcium oxalate and brushite, a finding which suggested that the propensity for spontaneous nucleation of calcium salts was retarded. Allopurinol lowered the score for calcium oxalate but not for brushite. Moreover, the FPR-APR discriminant score for calcium oxalate was positively correlated with the stone formation rate. It is concluded that FPR-APR discriminant scores are useful in the identification of stone-forming potential in urine, and in the assessment of response to therapy.

Clinical pharmacology of sodium cellulose phosphate

The safety and effectiveness of sodium cellulose phosphate (SCP) in the treatment of calcium urolithiasis of absorptive hypercalciuria was explored. Eighteen patients with absorptive hypercalciuria with intestinal hyperabsorption of calcium, normal or suppressed parathyroid function, and active stone disease received 10 to 15 Gm SCP daily (2.5 to 5 Gm with meals) and 2 to 3 Gm magnesium gluconate daily (1 to 1.5 Gm twice daily orally separately from SCP) for eight to 54 months, while maintained on a moderate calcium and oxalate restriction. During treatment, serum calcium, immunoreactive parathyroid hormone, and urinary cyclic AMP remained within the normal range. Serum alkaline phosphatase and bone density (measured by photon absorptiometry) did not change significantly or remained within normal limits. Serum concentrations of magnesium, copper, zinc, and iron and blood hematocrit were not significantly altered by therapy. However, urinary calcium returned toward normal, and incidence of renal stone formation markedly decreased. The results suggest that SCP is a safe and an effective drug for absorptive hypercalciuria.

Inhibitors and promoters of stone formation

The understanding of the formation of urinary stones centers around three main mechanisms: the urinary concentration of stone-forming ions, the role of promoters, and the role of inhibitors of crystal formation and crystal aggregation. With respect to the promoting activity, lately emphasis has shifted from the role of the organic matrix to that of one salt inducing by epitaxy the precipitation of another salt. Among the inhibitors, it has become necessary to distinguish between those affecting crystal formation and those affecting crystal aggregation. For measuring the inhibitory activity, the various techniques and their relevance have been reviewed. It has been found that the main inhibitors for calcium phosphate and calcium oxalate precipitation are citrate, pyrophosphate, and perhaps magnesium. Those for calcium phosphate and calcium oxalate aggregation are glycosaminoglycans, pyrophosphate, and citrate. Among the synthetic inhibitors, the diphosphonates are the most powerful for both processes. The role and the therapeutic implications of these various concepts have been discussed.

Effect of sodium cellulose phosphate therapy on crystallization of calcium oxalate in urine

Effects of oral sodium cellulose phosphate therapy (5 g three times a day with meals for 4 days) on renal excretion of oxalate and on the crystallization of calcium oxalate in urine were examined in six patients with absorptive hypercalciuria on a constant metabolic dietary regimen. During treatment, urinary oxalate increased by 9-50 mg/day. However, urinary calcium decreased by 138-225 mg/day (50%-70%). Thus, the state of saturation of urine with respect to calcium oxalate decreased or did not change significantly. There was no consistent or significant change in the formation product ratio (limit of metastability) or in the crystal growth of calcium oxalate in urine.