Characterization of deposits on double J stents

We have characterized the types of encrustations that form on ureteral stents. The deposit that generates blocks is composed of hydroxyapatite/magnesium ammonium phosphate (44%). Calcium oxalate dihydrate was also detected at a high degree of encrustation (13%). Hydroxyapatite deposits, also of high degree of encrustation (13%) are generated due to their formation as a consequence of persistently high urinary pH values. The formation of large uric acid deposits (31%) must be attributed to the persistence of urinary $\mathrm{pH} < 5.5$. To avoid development of encrustations of ureteral stents, urinary calcium levels and urinary pH control should be carried out, avoiding urinary infections

Characterization of deposits on double J stents

We have characterized the types of encrustations that form on ureteral stents. The deposit that generates blocks is composed of hydroxyapatite/magnesium ammonium phosphate (44%). Calcium oxalate dihydrate was also detected at a high degree of encrustation (13%). Hydroxyapatite deposits, also of high degree of encrustation (13%) are generated due to their formation as a consequence of persistently high urinary pH values. The formation of large uric acid deposits (31%) must be attributed to the persistence of urinary $\mathrm{pH} < 5.5$. To avoid development of encrustations of ureteral stents, urinary calcium levels and urinary pH control should be carried out, avoiding urinary infections

Theobromine inhibits uric acid crystallization. A potential application in the treatment of uric acid nephrolithiasis.

To assess the capacity of methylxanthines (caffeine, theophylline, theobromine and paraxanthine) to inhibit uric acid crystallization, and to evaluate their potential application in the treatment of uric acid nephrolithiasis.The ability of methylxathines to inhibit uric acid nucleation was assayed turbidimetrically. Crystal morphology and its modification due to the effect of theobromine were evaluated by scanning electron microscopy (SEM). The ability of theobromine to inhibit uric acid crystal growth on calculi fragments resulting from extracorporeal shock wave lithotripsy (ESWL) was evaluated using a flow system.The turbidimetric assay showed that among the studied methylxanthines, theobromine could markedly inhibit uric acid nucleation. SEM images showed that the presence of theobromine resulted in thinner uric acid crystals. Furthermore, in a flow system theobromine blocked the regrowth of post-ESWL uric acid calculi fragments.Theobromine, a natural dimethylxanthine present in high amounts in cocoa, acts as an inhibitor of nucleation and crystal growth of uric acid. Therefore, theobromine may be clinically useful in the treatment of uric acid nephrolithiasis

Xanthine urolithiasis: Inhibitors of xanthine crystallization.

OBJECTIVE:To identify in vitro inhibitors of xanthine crystallization that have potential for inhibiting the formation of xanthine crystals in urine and preventing the development of the renal calculi in patients with xanthinuria. METHODS:The formation of xanthine crystals in synthetic urine and the effects of 10 potential crystallization inhibitors were assessed using a kinetic turbidimetric system with a photometer. The maximum concentration tested for each compound was: 20 mg/L for 3-methylxanthine (3-MX); 40 mg/L for 7-methylxanthine (7-MX), 1-methylxanthine (1-MX), theobromine (TB), theophylline, paraxanthine, and caffeine; 45 mg/L for 1-methyluric acid; 80 mg/L for 1,3-dimethyluric acid; and 200 mg/L for hypoxanthine. Scanning electron microscopy was used to examine the morphology of the crystals formed when inhibitory effects were observed. RESULTS:Only 7-MX, 3-MX, and 1-MX significantly inhibited xanthine crystallization at the tested concentrations. Mixtures of inhibitors had an additive effect rather than a synergistic effect on crystallization. CONCLUSION:Two of the inhibitors identified here-7-MX and 3-MX-are major metabolites of TB. In particular, after TB consumption, 20% is excreted in the urine as TB, 21.5% as 3-MX, and 36% as 7-MX. Thus, consumption of theobromine could protect patients with xanthinuria from the development of renal xanthine calculi. Clinical trials are necessary to demonstrate these effects in vivo

Diagram of the experimental flow device used to assess uric acid renal calculi regrowth.

<p>The device shown here is used to study the regrowth of post ESWL fragments of uric acid calculi. 1. Temperature-controlled chamber; 2. Chamber containing post-ESWL uric acid calculi fragments solutions; 3. Three-way T mixing chamber for solutions A and B; 4. Uric acid (B) and synthetic urine (A) solutions; 5. Temperature controller.</p

Scanning electron microscopy of uric acid crystals.

<p>After finishing the turbidimetrical assay, some of the solutions were filtered through a 45 µm filter, and uric acid crystals were observed by scanning electron microscopy. These images correspond to uric acid crystals formed at pH = 4.65, in the absence (A) and presence of 20 mg/L (B) and 40 mg/L (C) theobromine.</p

Increased relative weight of post-ESWL uric acid calculi fragments.

<p>The fragments were placed into a temperature-controlled flow chamber and incubated for 48 h. A constant flow of 400 mg/L uric acid in synthetic urine, with 0, 10 and 20 mg/L theobromine, passed through the flow chamber containing the calculus fragment. A total volume of 750 mL synthetic urine passed every 24 hours, which is approximately the volume that passes through one kidney per day. The calculi fragments were weight before and after the experiment, and the relative weight increase was calculated for each fragment. In this figure, the relative weight variation are represented as a mean ± SEM for 5 calculi fragments.</p

A Case of Randall's Plugs Associated to Calcium Oxalate Dihydrate Calculi

A case of a patient who developed multiple calcium oxalate dihydrate calculi, some of them connected to intratubular calcifications (Randall's plugs), is presented. Randall's plugs were isolated and studied. The mechanism of Randall's plug development is also suggested