Effects of oral pyridoxine upon plasma and 24-hour urinary oxalate levels in normal subjects and stone formers with idiopathic hypercalciuria

Summary The effect of pyridoxine hydrochloride, 200 mg/day (0.97 mmol/day) for 3 weeks, upon plasma and urinary oxalate has been determined in ten normal subjects and seven patients with idiopathic hypercalciuria while both groups were on low-oxalate diets. Patients had higher basal urinary oxalate levels than normal subjects. In normal subjects pyridoxine administration decreased plasma oxalate levels and raised urinary oxalate. The patients showed no change in either plasma or urinary oxalate.     

Serum,urinary and stone zinc,iron, magnesium and copper levels in idiopathic calcium oxalate stone patients

Many theories have been put forward to explain the mechanism of stone formation and growth. The aim of this study was to investigate the urinary, serum and stone levels of zinc, iron, magnesium, and copper in patients with calcium oxalate stones and to investigate urinary and serum element levels in healthy controls and to find a possible connection between the elements and calcium oxalate stone formation. A total of 104 patients with calcium oxalate stones ranging in age from 3 to 79 years (mean 44.0 ± 18.1) and 77 healthy controls ranging in age from 18 to 77 (mean 44.2 ± 17.9) were included in this study. The mean urinary iron and copper levels in stone patients were significantly higher than healthy controls (P = 0.000). The mean urinary zinc and magnesium levels in healthy controls were significantly higher than stone patients (P = 0.000). There was no significant difference in the serum levels of magnesium and copper in stone patients and healthy controls. Serum zinc and iron level were significantly high in healthy controls as compared to stone patients. Each stone had all 4 elements. Zn and Mg have inhibitory effect on calcium oxalate stone formation. Fe and Cu could be promotor of the calcium oxalate stone formation.     

Intestinal and renal handling of oxalate loads in normal individuals and stone formers

The renal handling and intestinal absorption of dietary oxalate are believed to be risk factors for calcium oxalate stone formation. In this study, we have examined the time and dose effects of soluble oxalate loads on the intestinal absorption and renal handling of oxalate in six stone formers (SF) and six normal individuals (N) who consumed diets controlled in oxalate and other nutrients. Urinary and plasma oxalate changes were monitored over 24 h after ingestion of 0, 2, 4, and 8 mmole oxalate loads, containing a mixture of ¹²C- and ¹³C₂-oxalate. There were significant time and dose dependent changes in urinary oxalate excretion and secretion after these loads. However, there were no significant differences between SF and N in both the intestinal absorption and the renal handling of oxalate loads, as measured by the urinary excretion of oxalate (P = 0.96) and the ratio of oxalate to creatinine clearance (P = 0.34). ¹³C₂-oxalate absorption studies showed three of the subjects, two SF and one N, had enhanced absorption with the 8 mmole load. A clear difference in absorption was demonstrated in these individuals during the 8–24 h interval, suggesting that in these individuals there was greater oxalate absorption in the large intestine as compared to the other subjects. This enhanced absorption of oxalate warrants further characterization. This research was supported in part by NIH grants RO1 DK62284 and MO1 RR07122.     

Calcium oxalate monohydrate binding protein: a diagnostic biomarker for calcium oxalate kidney stone formers

Urinary oxalate is a biomarker for calcium oxalate kidney stone disease; however, its assay is insensitive and nonspecific. Calcium oxalate monohydrate (COM) binding protein (45 kDa) is a promoter of calcium oxalate kidney disease, which is markedly upregulated by oxalate induced oxidative stress. The current study was carried out to evaluate whether COM binding protein can serve as a diagnostic marker for calcium oxalate kidney stone formers. COM binding protein was isolated, purified and antibody was raised against it in rabbits. Urine samples (24 h) were collected from patients suffering from various kidney diseases such as acute nephritis, chronic nephritis, nephrotic syndrome, calcium oxalate (CaOx) stone formers, uric acid stone formers, struvite stone formers and calcium phosphate stone formers. This COM binding protein was quantified by an in house ELISA method and the excretion was found to lie between 2 and 3 mg in control samples, while in CaOx stone formers it was detected between 11 and 19 mg. Urinary risk factors were assayed. We conclude that COM binding protein can serve as a diagnostic marker for CaOx stone formers.     

Plasma oxalate level in pediatric calcium stone formers with or without secondary hyperoxaluria

Plasma oxalate (POx) concentration is significantly elevated in primary hyperoxaluria, severe renal failure or ethylene glycol poisoning. In these conditions, the degree of hyperoxalemia correlates with the severity of systemic calcium oxalate (CaOx) deposition and should be therefore carefully monitored. Although secondary hyperoxaluria (secHyOx) is a common finding in pediatric patients with kidney stone disease, very little is known about POx in this condition. We therefore evaluated POx level in 59 children and adolescence with calcium urolithiasis (34 confirmed by CaOx stone analysis and 25 children with a strong clinical suspicion of this type of urolithiasis), with or without “mild” secHyOx. A control group consisted of 41 healthy sex- and age-matched children. We found that POx was significantly increased in children with calcium urolithiasis and secHyOx compared to healthy children (9.16 ± 3.60 vs. 6.42 ± 2.53 μmol/l), but that was not the case in children with calcium urolithiasis but with normal urinary oxalate excretion (7.12 ± 3.33 μmol/l). We conclude that POx may be slightly increased in some pediatric calcium stone formers with secHyOx, probably related to intestinal oxalate hyperabsorption.     

Studies on crystalluria in calcium oxalate stone formers

Summary The excretion of calcium oxalate and calcium phosphate crystals was studied in fractionated 24 h urine from 7 men with recurrent calcium oxalate stone disease, both before and during daily administration of 5 mg bendroflumethiazide. Urinary calcium, oxalate, magnesium, citrate, phosphate, pH, and inhibition of calcium oxalate crystal growth rate were analyzed in all samples. Exclusively calcium oxalate crystals were found in 30 per cent of the samples, all with a pH below 6.25, whereas calcium phosphate was the crystal type encountered in urine with a pH above 6.50. Bendroflumethiazide decreased the volume of calcium phosphate but not of calcium oxalate crystals. During the period of observation there was no correlation between calcium oxalate supersaturation and calcium oxalate crystal volume, but a relationship was demonstrated between calcium phosphate supersaturation and calcium phosphate crystal volume.     

草酸钙晶体表面结合蛋白质的研究

目的 了解草酸钙晶体表面结合蛋白质在结石形成的过程中的作用。方法 用草酸钙过饱和结晶法制备正常人和草权钙结石患者尿草酸钙晶体表面结合物质（ＣＳＢＳ）,经ＤＥＡＥ－ＳｅｐｈａｒｏｓｅＣＬ－６Ｂ柱层析分离蛋白质和葡胺聚糖,用ＳＤＳ－聚丙烯酰胺凝胶电泳（ＳＤＳ－ＰＡＧＥ）测定蛋白质组成和分子量,用氨基酸自动分析仪测定蛋白质的氨基酸,结果;正常仍ＣＳＢＳ中主要含分子量为３１０００的尿凝血酶原激活肽片段１（     

Chemical factors governing the state of saturation towards brushite and whewellite in urine of calcium stone formers

Summary Variations of urinary pH and concentrations of calcium, phosphate, oxalate, magnesium and citrate have been produced by 4 different diets given to 19 idiopathic calcium stone formers. The state of saturation towards whewellite and brushite was directly measured in the 76 urine samples by equilibration with the corresponding salts and was compared to chemical constituents by regression analyses. The state of saturation towards calcium oxalate monohydrate was significantly governed only by the urinary oxalate concentration, and a soluble oxalate fraction not contributing to calcium oxalate chelation was demonstrated. The state of saturation towards brushite was exclusively determined by urinary calcium and pH, the latter below 5.5 showing a high influence on brushite solubility.     

Reduced inhibitory activity of uronic-acid-rich protein in urine of stone formers

We recently reported that human urine contains a newly identified urinary glycoprotein acting as a potent inhibitor against calcium oxalate crystallization. This inhibitor is a uronic-acid-rich protein (UAP) with a molecular weight of approximately 35 kDa. In the present study, UAP was isolated from urine of stone formers and of subjects without a stone history, and its inhibitory activity was tested in a calcium oxalate crystallization system in vitro. Our results show a weaker inhibitory activity of UAP extracted from the urine of stone formers than that extracted from the urine of healthy subjects. Preliminary analyses of amino acid and carbohydrate content showed some differences between the two groups. The main difference was the reduction in sialic acid in UAP isolated from the urine of stone formers. We suggest that UAP contributes significantly to total urinary inhibitory activity of calcium oxalate crystallization and that the decrease in this activity in the urine of recurrent stone formers is due, in part, to the weak inhibitory activity of UAP. A structural abnormality of UAP could explain the diminution of its inhibitory activity in the urine of stone formers.     

Effects of citrate on renal stone formation and osteopontin expression in a rat urolithiasis model

Previous studies have described the inhibitory effects of citrate on calcium oxalate crystallization in place of crystal growth, but the effects of citrate on matrix proteins of stones has not been studied in vivo. To examine the effect of citrate on the matrix, we investigated the effect of citrate on osteopontin (OPN) expression, which we had previously identified as an important stone matrix protein. Control rats were treated with saline while rats of the stone group were treated with ethylene glycol (EG) and vitamin D₃, and the citrate groups (low-dose and high-dose groups) were treated with a citrate reagent compound of sodium citrate and potassium citrate, in addition to EG and vitamin D₃. The rate of renal stone formation was lower in the citrate groups than in the stone group. This was associated with a low expression of OPN mRNA in citrate-treated rats relative to that in the stone group. Citrate was effective in preventing calcium oxalate stone formation and reduced OPN expression in rats. Our results suggest that citrate prevents renal stone formation by acting against not only the crystal aggregation and growth of calcium oxalate but also OPN expression. Received: 7 June 2000 / Accepted: 20 September 2000     

Effect of urinary macromolecules on aggregation of calcium oxalate in recurrent calcium stone formers and healthy

Summary The inhibitory activity of urinary macromolecules on the aggregation of calcium oxalate crystals was studied using an aggregometer originally devised to measure thrombocyte aggregation capacity by means of the optical turbidity at 660 nm. The macromolecular fraction of the urine (molecular weight above 5000) of recurrent calcium stone formers showed much less inhibitory activity than that of healthy controls (P0.05). It was speculated on the basis of the results of gel filtration that there were some proteins (molecular weight about 10000–30000) which had inhibitory activities for the aggregation of calcium oxalate. This gives support to the assumption that macromolecules are important during the phase of aggregation of calcium oxalate crystals.     

Urine composition in patients with urolithiasis during treatment with magnesium oxide

Summary Fifteen patients with recurrent renal stone formation were treated with 400 mg magnesium oxide daily. Urine composition was analyzed before the start of treatment and after 6–12 months. The urinary excretion of magnesium before and during treatment was 321±120 (mean ±SD) and 409±140 mmol per mol creatinine respectively, a difference that was not statistically significant. Urinary calcium increased from 473±186 to 662±213 mmol per mol creatinine (p<0.05). All patients who increased their excretion of magnesium also increased the urinary output of calcium and, as a result of this, the calcium/magnesium-quotients were unaffected by the treatment. No significant effect was observed on urine oxalate excretion. Serum concentrations of calcium, magnesium and urate all remained at the pre-treatment level. From the results obtained in this study, magnesium oxide in this dosage cannot be recommended for use in treatment of patients with urolithiasis.     

Effects of calcium supplementation on body weight reduction in overweight calcium stone formers

A randomized, placebo-controlled trial was conducted in overweight calcium stone-forming (CSF) patients, to evaluate the effect of calcium supplementation associated with a calorie-restricted diet on body weight (BW) and fat reduction and its potential changes upon serum and urinary parameters. Fifteen patients were placed on a hypocaloric diet for 3 months, supplemented with either calcium carbonate (CaCO₃, n = 8) or placebo (n = 7), 500 mg bid. Blood and 24-h urine samples were collected and body composition was assessed at baseline and after the intervention. At the end of the study, final BW was significantly lower vs baseline in both CaCO₃ (74 ± 14 vs. 80 ± 14 kg, P = 0.01) and placebo groups (80 ± 10 vs. 87 ± 9 kg, P = 0.02) but the mean percentage of loss of body weight and body fat did not differ between CaCO₃ and placebo (7.0 ± 2.0 vs. 8.0 ± 3.0%, P = 0.40 and 13.0 ± 7.0 vs. 13.0 ± 10.0%; P = 0.81, respectively). After CaCO₃ or placebo, no significant differences versus baseline were observed for urinary parameters in both CaCO₃ and placebo, except for a higher mean urinary citrate in placebo group. These data suggest that increasing calcium intake by calcium carbonate supplementation did not contribute to a further reduction of BW and fat in overweight CSF patients submitted to a hypocaloric diet nor altered urinary lithogenic parameters.     

Proteins in renal stones and urine of stone formers

Knowledge of the essential characteristics of macromolecules constituting the organic matrix of the nidus of urinary stones is required to understand the mechanism of urolithogenesis. The aim of this study was to isolate and characterise those stone nidus proteins. Using an extraction buffer containing SDS and β-mercaptoethanol, we were able to overcome known problems of protein isolation from urinary stone matrix. These proteins were characterised by a strong tendency to aggregate under reducing and denaturing conditions. On SDS-PAGE, their molecular weights range from ≤12 to 66 kDa. Antisera raised against stone matrix proteins showed a cross-reactivity between proteins isolated from different stones irrespective of their origin or mineral composition. Moreover, urinary proteins from stone formers also cross-reacted with these whereas there was no reaction with urinary proteins of non-stone formers. Western blotting confirmed these findings. Given the above summarised properties, it can be safely concluded that these proteins are prevalent in urines of stone formers, that they are selectively incorporated into renal stones of all aetiologies, and that they most likely have a role in nidus and, therefore, early stone formation. Received: 4 February 1998 / Accepted: 4 May 1998     

Inhibitory effect of bikunin on calcium oxalate crystallization in vitro and urinary bikunin decrease in renal stone formers

Two proteins of 17 and 24 kDa, respectively, which were immunologically related to bikunin, were purified from urine of healthy men, using in the last step a trypsin CNBr-sepharose affinity column. These proteins strongly inhibited calcium oxalate (CaOx) crystallization in two in vitro models. In the first model, the presence of 8 μg/ml protein in a medium containing 0.76 mM CaCl₂ (with ⁴⁵Ca) and 0.76 mM ammonium oxalate inhibited the crystallization process by 80%, as estimated by supernatant radioactivity after 60 min of incubation. A similar inhibition was observed in the second turbidimetric model, where the CaOx crystallization kinetics were followed for 10 min at 620 nm in a medium containing 4 mM CaCl₂ and 0.5 mM Na₂Ox. These proteins were used as standard protein for the development of an enzyme-linked immunosorbent assay (ELISA) in urine. Mean (± SEM) urinary bikunin concentration in 18 healthy subjects was 5.01 ± 0.91 μg/ml. This was a concentration range of strong inhibitory activity in vitro. Bikunin values were nearly 50% lower (2.54 ± 0.42 μg/ml, P=0.007) in 31 CaOx renal stone formers (having weddelite crystals in their first morning urine) than in the healthy volunteers. A correlation was found between urinary bikunin and alpha-1 microglobulin concentrations in the control group (y=0.73x + 1.09, r ²=0.8) while no such correlation existed in the lithiasis group. In conclusion, bikunin exerts a strong inhibitory action of CaOx crystallization in vitro. Its involvement in urinary CaOx crystallization of stone formers is highly probable, based on the significant decrease in its urinary concentration in the majority of stone formers studied. Received: 16 December 1997 / Accepted: 23 June 1998     

The effect of takusha, a kampo medicine, on renal stone formation and osteopontin expression in a rat urolithiasis model

Kampo medicine is a traditional Japanese therapeutic system which originated in China and was used to treat various diseases for hundreds of years. Kampo medicine had been also used for the cure and the prevention of urinary calculi for many years, but the effect and the mechanism of this use of kampo medicine are unclear. We examined the inhibitory effect of the kampo medicine takusha on the formation of calcium oxalate renal stones induced by ethylene glycol (EG) and vitamin D₃ in rats. We also investigated the effect of takusha on osteopontin (OPN) expression, which we previously identified as an important stone matrix protein. The control group rats were non-treated; the stone group rats were administered EG and vitamin D₃, and the takusha group was administered takusha in addition to EG and vitamin D₃. The rate of renal stone formation was lower in the takusha group than in the stone group; thus, the OPN expression in the takusha group was smaller than in the stone group. Takusha was effective in preventing oxalate calculi formation and OPN expression in rats. These findings suggest that takusha prevents stone formation including not only calcium oxalate aggregation but also proliferation. Received: 14 May 1998 / Accepted: 14 August 1998     

Aspects of the influence of magnesium ions on the formation of calcium oxalate

Summary The influence of magnesium ions on the solubility and formation of calcium oxalate was studied. Both calcium oxalate mineral constituents of urinary calculi (whewellite and weddellite) were prepated in the presence of Mg²⁺-ions. For preparation, a gel growth technique and precipitation in aqueous solutions were used. The metastable weddellite formed only when Mg²⁺ concentration, reaction, temperature and precipitation velocity (see text) were combined in the proper way. It is concluded that Mg²⁺ions may induce an increase of solubility of calcium oxalate but in contrast also broaden the Ostwald-Miers range, thus favouring the formation of larger crystals.     

芭蕉芯及维生素B6对小鼠肾草酸钙结晶抑制作用的研究

目的寻找预防及控制尿路结石的方法。方法在小鼠模型上用图像分析仪研究芭蕉芯提取液与维生素Ｂ６对肾草酸钙结晶形成的作用。将３６只小鼠分为正常对照组、成石组、芭蕉芯组和维生素Ｂ６组进行实验,３周后处死动物取肾脏分别进行结晶形态定量及钙和草酸测定。结果维生素Ｂ６组和芭蕉芯组小鼠肾脏结晶的面密度及数密度明显低于成石组;湿肾组织钙含量各组之间无显著差异,草酸含量在维生素Ｂ６和芭蕉芯组低于成石组。结论维生素Ｂ６和芭蕉芯提取液都具有抑制实验性高草酸尿症小鼠肾脏草酸钙结晶形成的作用,而芭蕉芯提取液的抑制作用明显比维生素Ｂ６强     

Regulation by macromolecules of calcium oxalate crystal aggregation in stone formers

Based on the structure of kidney stones, it is likely that they form as aggregations of preformed crystals, mostly calcium oxalate monohydrate (COM). In this study, we examined the ability of a macromolecular mixture isolated from the urine of normal individuals and stone formers to inhibit aggregation of preformed COM seed crystals in a simple ionic solution using measurements of changes in the particle size distribution (PSD) of preformed COM crystal aggregates. We also examined the effect in this assay of a number of synthetic homopolymers, naturally occurring urine macromolecules, and binary mixtures thereof. The macromolecular mixtures from urine of normals and most stone formers reduced the degree of aggregation of the seed crystals, whereas 22% of stone former urine macromolecules either did not disaggregate or actually promoted further aggregation. Stone formers within one family shared this property, but a non-stone forming sibling did not. Polyanions, either synthetic or naturally occurring, induced disaggregation to an extent similar to that exhibited by normal urine macromolecules, while polycations had no effect on the PSD. However, mixing a polyanion, either poly-aspartate or osteopontin, with the polycation poly-arginine, changed their behavior from disaggregation to aggregation promotion. The disaggregating behavior of normal urinary macromolecules provides a defense against aggregation, but a minority of stone forming individuals lacks this defense, which may contribute to stone formation.     

Acute caffeine effects on urine composition and calcium kidney stone risk in calcium stone formers

PURPOSE: Caffeine increases urinary calcium (ca) excretion in nonstone formers. We designed a study to determine the effect of caffeine consumption on urinary composition in stone formers. MATERIALS AND METHODS: A total of 39 normocalcemic patients with calcium stones consumed caffeine (6 mg/kg lean body mass) after 14 hours of fasting. Urinary composition was compared 2 hours before and 2 hours after caffeine consumption. Control subjects included 9 nonstone formers studied contemporaneously with patients plus data from 39 nonstone formers from previous studies matched to each patient by level of fasting calcium/creatinine (Cr), gender and age. RESULTS: Caffeine increased urinary Ca/Cr, magnesium/Cr, citrate/Cr and sodium/Cr but not oxalate/Cr in stone formers and controls. The Tiselius stone risk index for calcium oxalate precipitation increased from 2.4 to 3.1 in stone formers and from 1.7 to 2.5 in nonstone formers. Of the 39 stone formers 32 had an increased Tiselius risk index after caffeine. Post-caffeine increases in Ca/Cr and Na/Cr were highly correlated. CONCLUSIONS: Caffeine consumption may modestly increase risk of calcium oxalate stone formation.