A Pilot Study of the Effect of Sodium Thiosulfate on Urinary Lithogenicity and Associated Metabolic Acid Load in Non-Stone Formers and Stone Formers with Hypercalciuria

Background and Objectives

Sodium thiosulfate (STS) reduced calcium stone formation in both humans and genetic hypercalciuric stone forming (GHS) rats. We sought to measure urine chemistry changes resulting from STS administration in people.

Design, Setting, Participants & Measurements

STS was given to healthy and hypercalciuric stone forming adults. Five normal non-stone forming adults (mean age 33 years), and 5 people with idiopathic hypercalciuria and calcium kidney stones (mean age 66 years) participated. Two baseline 24-hour urine collections were performed on days 2 and 3 of 3 days of self-selected diets. Subjects then drank STS 10 mmol twice a day for 7 days and did urine collections while repeating the self-selected diet. Results were compared by non-parametric Wilcoxon signed rank test. The primary outcome was the resulting change in urine chemistry.

Results

STS administration did not cause a significant change in urinary calcium excretion in either group. In both groups, 24 hour urinary ammonium (P = 0.005) and sulfate excretion (P = 0.007) increased, and urinary pH fell (P = 0.005); citrate excretion fell (P<0.05) in hypercalciuric participants but not in non-stone formers. Among stone formers with hypercalciuria, 3 of 5 patients had measurement of serum HCO₃ concentration after the STS period: it did not change. The net effect was an increase in supersaturation of uric acid, and no change in supersaturation of calcium oxalate or calcium phosphate.

Conclusions

The basis for studies demonstrating that STS prevented stones in rats and people was not reflected by the changes in urine chemistry reported here. Although serum HCO₃ did not change, urine tests suggested an acid load in both non-stone forming and hypercalciuric stone-forming participants. The long term safety of STS needs to be determined before the drug can be tested in humans for long-term prevention of stone recurrence.     

Difference in 24-Hour Urine Composition between Diabetic and Non-Diabetic Adults without Nephrolithiasis

Background

Diabetic patients are more likely to develop kidney stones than the general population. The underlying mechanisms for this disparity remain to be elucidated. Little is known about the relationship between urine composition and diabetes mellitus in non-stone-forming individuals. We sought to examine the differences in the 24-hour (24-h) urine composition between diabetic and non-diabetic adults who were not stone formers.

Methods

A convenience sample of 538 individuals without a history of nephrolithiasis, gout, hyperparathyroidism, or gastroenteric diseases participated in this study. The 24-h urine profiles of 115 diabetic adults were compared with those of 423 non-diabetic adults. Diabetes was defined by self-reported physician diagnosis or medication use. All participants were non-stone formers confirmed by urinary tract ultrasonography. Participants provided a fasting blood sample and a single 24-h urine collection for stone risk analysis. Student’s t-test was used to compare mean urinary values. Linear regression models were adjusted for age, gender, body mass index, hypertension, fasting serum glucose, serum total cholesterol, estimated creatinine clearance rate and urinary factors.

Results

Univariable analysis showed that the diabetic participants had significantly higher 24-h urine volumes and lower urine calcium and magnesium excretions than non-diabetic participants (all P < 0.05). After multivariate adjustment, no significant differences in 24-h urine composition were observed between diabetic and non-diabetic participants except for a slightly increased 24-h urine volume in diabetic participants (all P > 0.05). The main limitation of this study is that the convenience samples and self-reported data may have been sources of bias.

Conclusion

Our data showed that there were no differences in 24-h urine composition between diabetic and non-diabetic adults who are not stone formers. The reason for it might be the improved glycemic control in diabetic individuals in our study. Therefore, a tighter glycemic control might reduce stone formation in diabetic adults.     

The structure and function of normally mineralizing avian tendons

The leg tendons of certain avian species normally calcify. The gastrocnemius, or Achilles, tendon of the domestic turkey, Meleagris gallopavo, is one such example. Its structure and biomechanical properties have been studied to model the adaptive nature of this tendon to external forces, including the means by which mineral deposition occurs and the functional role mineralization may play in this tissue. Structurally, the distal rounded, thick gastrocnemius bifurcates into two smaller proximal segments that mineralize with time. Mineral deposition occurs at or near the bifurcation, proceeding in a distal-to-proximal direction along the segments toward caudal and medial muscle insertions of the bird hip. Mineral formation appears mediated first by extracellular matrix vesicles and later by type I collagen fibrils. Biomechanical analyses indicate lower tensile strength and moduli for the thick distal gastrocnemius compared to narrow, fan-shaped proximal segments. Tendon mineralization here appears to be strain-induced, the muscle forces causing matrix deformation leading conceptually to calcium binding through the exposure of charged groups on collagen, release of sequestered calcium by proteoglycans, and increased diffusion. Functionally, the mineralized tendons limit further tendon deformation, reduce tendon strain at a given stress, and provide greater load-bearing capacity to the tissue. They also serve as important and efficient elastic energy storage reservoirs, increasing the amount of stored elastic energy by preventing flexible type I collagen regions from stretching and preserving muscle energy during locomotion of the animals.     

Idiopathic calcium nephrolithiasis. 1. Differences in urine crystalloids,urine saturation with brushite and urine inhibitors of calcification between persons with and persons without recurrent kidney stone formation.

The propensity of urine to promote calcium stone formation was compared in 64 patients with recurrent idiopathic calcium nephrolithiasis and 30 healthy individuals without such a history. The rates of excretion of urine crystalloids, the urine saturation with brushite (CaHPO4-2H2O), the ability of the urine to calcify collagen in vitro, and the concentration of urine inhibitors of collagen calcification were measured. The patients had a reduced urine citrate excretion rate in addition to an increased urine calcium excretion rate, while the rates for urine magnesium, phosphate, uric acid and oxalate were not significantly different in the two groups of subjects. The urine concentration of magnesium, phosphate and uric acid was decreased in the patients because of the higher urine volume. The urine creatinine excretion rate correlated with the rates of excretion of urine calcium, magnesium, phosphate, uric acid and oxalate in both groups, which suggested that increased lean body mass, possibly associated with greater food intake, may be an important determinant of crystalloid excretion. The urine of the patients was significantly more saturated with brushite than the urine of the control subjects and resulted in greater collagen calcification when incubated in vitro. The urine concentration of inhibitors of collagen calcification, however, was not significantly different in the two groups. Thus, the urine of patients with recurrent idiopathic calcium nephrolithiasis is more highly saturated with brushite, largely as a result of an increased urine calcium excretion rate, and contains a lower concentration of magnesium and citrate, substances that tend to prevent the precipitation and growth of crystals in urine.     

Label-free quantitative proteomics reveals differentially regulated proteins influencing urolithiasis

Urinary proteins have been implicated as inhibitors of kidney stone formation (urolithiasis). As a proximal fluid, prefiltered by the kidneys, urine is an attractive biofluid for proteomic analysis in urologic conditions. However, it is necessary to correct for variations in urinary concentration. In our study, individual urine samples were normalized for this variation by using a total protein to creatinine ratio. Pooled urine samples were compared in two independent experiments. Differences between the urinary proteome of stone formers and nonstone-forming controls were characterized and quantified using label-free nano-ultraperformance liquid chromatography high/low collision energy switching analysis. There were 1063 proteins identified, of which 367 were unique to the stone former groups, 408 proteins were unique to the control pools, and 288 proteins were identified for comparative quantification. Proteins found to be unique in stone-formers were involved in carbohydrate metabolism pathways and associated with disease states. Thirty-four proteins demonstrated a consistent >twofold change between stone formers and controls. For ceruloplasmin, one of the proteins was shown to be more than twofold up-regulated in the stone-former pools, this observation was validated in individuals by enzyme-linked immunosorbent assay. Moreover, in vitro crystallization assays demonstrated ceruloplasmin had a dose-dependent increase on calcium oxalate crystal formation. Taken together, these results may suggest a functional role for ceruloplasmin in urolithiasis.     

Cytochemical calcium distribution in secretory ameloblasts of the rat in relation to enamel mineralization

Calcium distribution in secretory ameloblasts was studied in rat incisor enamel in which mineralization was temporarily disturbed by injection of either fluoride or cobalt. Pyroantimonate precipitates of calcium were analysed morphometrically in regions of the cell membranes, mitochondria and secretory granules. The disturbances in mineralization were characterized by accumulations of unmineralized enamel matrix at the secretory regions of Tomes' process within 1 h after injection. Fluoride-induced disturbances in mineralization were not accompanied by marked changes in calcium concentration and distribution. It may be that fluoride causes alterations in the synthesis and secretion of the organic matrix which affects its ability to mineralize. Secretory ameloblasts treated with cobalt showed a broad basis for interference with calcium, in particular that which is associated with cell membranes and secretory granules. Secretory ameloblasts may be actively controlling the availability of calcium to enamel by mechanisms involving the cell membrane as well as the secretory granules.     

Effect of hydrochlorothiazide on urine saturation with brushite,in vitro collagen calcification by urine,and urinary inhibitors of collagen calcification

To clarify further the beneficial effect of thiazide diuretics on recurrent calcium nephrolithiasis, the effect of short-term hydrochlorothiazide therapy on urine saturation with brushite (CaHPO₄·2H₂O), in vitro collagen calcification by urine, and urinary inhibitors of calcification was studied.In 22 patients with idiopathic calcium oxalate/phosphate stones the urine calcium excretion decreased, the urine magnesium excretion increased and the urine magnesium/calcium ratio increased significantly (P < 0.001) during hydrochlorothiazide therapy. Supersaturation of the urine with brushite, which was present in 19 of the 22 patients, was reduced significantly (P < 0.001) in all during thiazide therapy, and to the undersaturated range in 16. The ability of urine to calcify collagen in vitro also decreased significantly (P < 0.001) during thiazide therapy, a change that correlated significantly (r = 0.4513, P < 0.05) with the decrease in brushite saturation. The concentration of urinary inhibitors of calcification, as determined with an in vitro collagen calcification system, was decreased significantly (P < 0.01) by thiazide therapy.It was concluded that, in addition to decreasing urine calcium excretion and increasing urine magnesium excretion, thiazide diuretics decrease the urinary brushite saturation and thus may prevent spontaneous nucleation or crystal growth, or both, of calcium phosphate. The ability of thiazides to decrease collagen calcification in vitro suggests that they may also prevent crystal growth on a nidus of organic matrix. Thiazides do not appear to act by increasing the excretion of urinary inhibitors of calcification.     

Urinary Excretion of Calcium and Citrate in Normal Individuals and Stone Formers with Variation in Calcium Intake

The changes which occur in both calcium and citrate excretion in normal persons, in idiopathic calcium stone formers and in persons with hyperparathyroidism have been measured at high and low levels of dietary calcium intake. The findings suggested a difference in the renal handling of calcium between normal subjects and stone formers. There was a greater increase in the urinary excretion of calcium with increased intake of calcium in individuals with renal calculi than in normals. Increasing the calcium intake shifted the mole ratio of calcium to citrate unfavourably for the chelation of calcium by citrate, and this unfavourable shift was more marked in the stone formers than in normal individuals. These findings support the concept that urinary citrate may be of importance in the prevention of calcium precipitation and hence in the pathogenesis of kidney stones.     

Risk of renal stone events in primary hyperparathyroidism before and after parathyroid surgery: controlled retrospective follow up study

AimTo study the risk of renal stone episodes and risk factors for renal stones in primary hyperparathyroidism before and after surgery.DesignRegister based, controlled retrospective follow up study.SettingTertiary hospitals in Denmark.Participants674 consecutive patients with surgically verified primary hyperparathyroidism. Each patient was compared with three age- and sex-matched controls randomly drawn from the background population. Hospital admissions for renal stone disease were compared between patients and controls. Risk factors for renal stones among patients were assessed.ResultsRelative risk of a stone episode was 40 (95% confidence interval 31 to 53) before surgery and 16 (12 to 23) after surgery. Risk was increased 10 years before surgery, and became normal more than 10 years after surgery. Stone-free survival 20 years after surgery was 90.4% in patients and 98.7% in controls (risk difference 8.3%, 4.8% to 11.7%). Patients with preoperative stones had 27 times the risk of postoperative stone incidents than controls. Before surgery, males had more stone episodes than females and younger patients had more stone episodes than older patients. Neither parathyroid pathology, weight of removed tissue, plasma calcium levels, nor skeletal pathology (fractures) influenced the risk of renal stones. After surgery, younger age, preoperative stones and ureteral strictures were significant risk factors for stones.ConclusionsThe risk of renal stones is increased in primary hyperparathyroidism and decreases after surgery. The risk profile is normal 10 years after surgery. Preoperative stone events increase the risk of postoperative stones. Stone formers and non-stone formers had the same risk of skeletal complications.

What is already known on this topic

Patients with primary hyperparathyroidism have an increased risk of renal stone eventsThe extent to which parathyroid surgery reduces the risk of further stones is unclear

What this study adds

The risk of a new stone event was 8.3% higher in patients than in controls after surgeryIn patients with stone disease before operation the risk rate for a postoperative stone event was 27times that in controlsThe risk of a renal stone event was higher than the risk among controls until more than 10 years after surgery     

Increased Calcium Absorption in Nephrolithiasis Explained by Uptake Studies in Ileal Brush Border Membrane Vesicles

We previously showed that recurrent calcium renal stone formers have enhanced urinary excretions of calcium and oxalate resulting from malabsorption of citrate. In the present investigation, the mechanism of the citrate-induced increased calcium uptake was studied using guinea pig ileal brush border membrane vesicles. In this model, calcium is absorbed in a concentration dependent, single mechanism uptake with a K_m of 275 ± 30 umol/liter (SD) and a V_max of 4.0 ± 0.5 nmol/min · mg protein. Under conditions of maximal calcium uptake, both citrate and phosphate inhibited calcium absorption into brush border membrane vesicles (BBMVs). In contrast, when phosphate and citrate were added together, calcium absorption normalized. Citrate inhibition of calcium absorption appeared to be due to free citrate ions, and phosphate ions overcame this inhibition. Phosphate inhibition was mostly due to decreased concentrations of ionized calcium and partly to precipitation of insoluble calcium phosphate. These studies confirm that the effects of citrate in humans in enhancing calcium absorption occur in the lumen of the gut and are not related to further biochemical conversions of citrate by the gut cells, to effects of citrate on calcium-related hormones, or to the renal handling of calcium. Also, the effects of citrate on increasing calcium absorption should be increased or attenuated in patients who malabsorb citrate, and this explains the increased urinary calcium and oxalate excretions reported for recurrent calcium stone formers.     

Effect of Acetazolamide and Triple Sulfonamide on Citrate and Calcium Excretion

The administration of acetazolamide was shown to increase the excretion of calcium in both normal persons and in stone formers, while at the same time the urinary excretion of citrate was reduced. Urinary citrate is potentially of importance in chelating calcium and preventing it from precipitating. In view of the chemical similarity between acetazolamide and the sulfonamides it was considered that the latter might produce a similar effect, with potential hazard if administered to a stone former. This was shown not to be the case.     

An in vitro model of fibroplasia: simultaneous quantification of fibroblast proliferation, migration, and collagen synthesis

Previous studies of fibroblast proliferation, migration, and collagen synthesis have been limited in their ability to define the interrelationship among these events in response to various inflammatory mediators. We have now defined an in vitro tissue culture model for the synchronous quantification of these parameters of fibroplasia. Biopsies (2 mm) of chicken flexor tendons are embedded in a fibrin matrix and exposed to various factors for 5 days in tissue culture. The availability of the fibrin matrix surrounding the tendon biopsy satisfies the need for a solid support medium for fibroblast migration. Multiple measurements of tendon fibroblast proliferation, migration into the fibrin matrix, and relative collagen synthesis are then made on these preparations. Fetal calf serum stimulated tendon fibroblast proliferation and migration in a dose responsive fashion, whereas the selective expression of collagen synthesis was decreased. Platelet lysate stimulated fibroblast proliferation at low concentration, but migration only at high concentration and was without effect on relative collagen synthesis. This model now provides a means of more clearly defining the influence of various inflammatory factors on the events of fibroplasia.     

Microelements in Stones,Urine, and Hair of Stone Formers: A New Key to the Puzzle of Lithogenesis?

The role of trace elements in lithogenesis is still unclear. The aim of this study was to evaluate the levels of elements in urinary stones and in the urine and hair of stone formers to identify these elements that have synergic correlations in studied materials and may contribute to lithogenesis. A total of 219 consecutive patients with idiopathic upper urinary tract stones were prospectively enrolled in the study. Urine and hair samples were collected from all patients. The content of the stone was evaluated using atomic absorption spectrometry, spectrophotometry, and colorimetric methods. The analysis of 29 elements in stones and hair and 21 elements in urine was performed using inductively coupled plasma-atomic emission spectrometry. The strength of correlation was described with the value of Spearman’s rank correlation coefficient. The positive correlation between concentration of sodium, potassium, magnesium, barium, vanadium, zinc, silicon, phosphorus, and iodine in phosphate stones was observed. Only a few incidental correlations between the composition of stones and the distribution of elements in urine and in hair were found. There were 109 positive two-element correlations between two materials. The most common were observed for vanadium, aluminum, lead, cobalt, and molybdenum. Two-element positive correlations for all samples were established only for three elements: vanadium, lead, and aluminum. Results indicate that analysis of particular elements in hair and urine cannot predict the composition of urinary stones. This study showed, for the first time, correlations between the levels of vanadium, lead, and aluminum in the stones, urine, and hair of stone formers.     

Sulfate but Not Thiosulfate Reduces Calculated and Measured Urinary Ionized Calcium and Supersaturation: Implications for the Treatment of Calcium Renal Stones

Background

Urinary sulfate (SO₄ ²⁻) and thiosulfate (S₂O₃ ²⁻) can potentially bind with calcium and decrease kidney stone risk. We modeled the effects of these species on the concentration of ionized calcium (iCa) and on supersaturation (SS) of calcium oxalate (CaOx) and calcium phosphate (CaP), and measured their in vitro effects on iCa and the upper limit of stability (ULM) of these salts.

Methods

Urine data from 4 different types of stone patients were obtained from the Mayo Nephrology Clinic (Model 1). A second data set was obtained from healthy controls and hypercalciuric stone formers in the literature who had been treated with sodium thiosulfate (STS) (Model 2). The Joint Expert Speciation System (JESS) was used to calculate iCa and SS. In Model 1, these parameters were calculated as a function of sulfate and thiosulfate concentrations. In Model 2, data from pre- and post STS urines were analyzed. ULM and iCa were determined in human urine as a function of sulfate and thiosulfate concentrations.

Results

Calculated iCa and SS values for all calcium salts decreased with increasing sulfate concentration. Thiosulfate had no effect on these parameters. In Model 2, calculated iCa and CaOx SS increased after STS treatment, but CaP SS decreased, perhaps due to a decrease in pH after STS treatment. In confirmatory in vitro experiments supplemental sulfate, but not thiosulfate, significantly increased the calcium needed to achieve the ULM of CaP and tended to increase the oxalate needed to reach the ULM of CaOx. Sulfate also significantly decreased iCa in human urine, while thiosulfate had no effect.

Conclusion

Increasing urinary sulfate could theoretically reduce CaOx and CaP stone risk. Although STS may reduce CaP stone risk by decreasing urinary pH, it might also paradoxically increase iCa and CaOx SS. As such, STS may not be a viable treatment option for stone disease.     

A recombinant human TGF-beta1 fusion protein with collagen-binding domain promotes migration, growth, and differentiation of bone marrow mesenchymal cells.

A continuous source of osteoblasts for normal bone maintenance, as well as remodeling and regeneration during fracture repair, is ensured by the mesenchymal osteoprogenitor stem cells of the bone marrow (BM). The differentiation and maturation of osteoprogenitor cells into osteoblasts are thought to be modulated by transforming growth factors-beta (TGF-beta1 and TGF-beta2) and TGF-beta-related bone morphogenetic proteins (BMPs). To define the responses of mesenchymal osteoprogenitor stem cells to several growth factors (GFs), we cultured Fischer 344 rat BM cells in a collagen gel medium containing 0.5% fetal bovine serum for prolonged periods of time. Under these conditions, survival of BM mesenchymal stem cells was dependent on the addition of GFs. Recombinant hTGF-beta1-F2, a fusion protein engineered to contain an auxiliary collagen binding domain, demonstrated the ability to support survival colony formation and growth of the surviving cells, whereas commercial hTGF-beta1 did not. Initially, cells were selected from a whole BM cell population and captured inside a collagen network, on the basis of their survival response to added exogenous GFs. After the 10-day selection period, the surviving cells in the rhTGF-beta1-F2 test groups proliferated rapidly in response to serum factors (10% FBS), and maximal DNA synthesis levels were observed. Upon the addition of osteoinductive factors, osteogenic differentiation in vitro was evaluated by the induction of alkaline phosphatase (ALP) expression, the production of osteocalcin (OC), and the formation of mineralized matrix. Concomitant with a down-regulation of cell proliferation, osteoinduction is marked by increased ALP expression and the formation of colonies that are competent for mineralization. During the induction period, when cells organize into nodules and mineralize, the expression of OC was significantly elevated along with the onset of extracellular matrix mineralization. Differentiation of BM mesenchymal stem cells into putative bone cells as shown by increased ALP, OC synthesis, and in vitro mineralization required the presence of specific GFs, as well as dexamethasone (dex) and beta-glycerophosphate (beta-GP). Although rhTGF-beta1-F2-selected cells exhibited the capacity to mineralize, maximal ALP activity and OC synthesis were observed in the presence of rhBMPs. We further report that a novel rhTGF-beta1-F2 fusion protein, containing a von Willebrand's factor-derived collagen binding domain combined with a type I collage matrix, is able to capture, amplify, and stimulate the differentiation of a population of cells present in rat BM. When these cells are subsequently implanted in inactivated demineralized bone matrix (iDBM) and/or diffusion chambers into older rats they are able to produce bone and cartilage. The population of progenitor cells captured by rhTGF-beta1-F2 is distinct from the committed progenitor cells captured by rhBMPs, which exhibit a considerably more differentiated phenotype.     

Effect of Cystone on urinary composition and stone formation over a one year period

Kidney stones are a common problem for which inadequate prevention exists. We recruited ten recurrent kidney stone formers with documented calcium oxalate stones into a two phased study to assess safety and effectiveness of Cystone^®, an herbal treatment for prevention of kidney stones. The first phase was a randomized double-blinded 12 week cross over study assessing the effect of Cystone^® vs. placebo on urinary supersaturation. The second phase was an open label one year study of Cystone^® to determine if renal stone burden decreased, as assessed by quantitative and subjective assessment of CT. Results revealed no statistically significant effect of Cystone^® on urinary composition short (6 weeks) or long (52 weeks) term. Average renal stone burden increased rather than decreased on Cystone^®. Therefore, this study does not support the efficacy of Cystone^® to treat calcium oxalate stone formers. Future studies will be needed to assess effects on stone passage, or on other stone types.     

The effect of in vivo treatment with EHDP and/or 1,25-DHCC on calcium uptake and release in isolated kidney mitochondria

Previous work on calcium transport (uptake and release) in isolated mitochondria, in vitro, has shown that addition of EHDP to the medium does not influence calcium uptake, but does delay calcium release. In vivo treatment of normal chicks with high doses of EHDP (10 mg P/kg body weight/day) has now also been found not to affect the in vitro calcium uptake in isolated chick kidney mitochondria, but to delay the subsequent release as compared with controls. The effect is not due to the decrease in 1,25-DHCC, since chronic administration of this metabolite did not correct the delay. In fact 1,25-DHCC in itself had a delaying effect on accumulated calcium release.     

The Role of Overweight and Obesity in Calcium Oxalate Stone Formation

Objective: The aim of the study was to assess the influence of overweight and obesity on the risk of calcium oxalate stone formation. Research Methods and Procedures: BMI, 24‐hour urine, and serum parameters were evaluated in idiopathic calcium oxalate stone formers (363 men and 164 women) without medical or dietetic pretreatment. Results: Overweight and obesity were present in 59.2% of the men and in 43.9% of the women in the study population. Multiple linear regression analysis revealed a significant positive relationship between BMI and urinary uric acid, sodium, ammonium, and phosphate excretion and an inverse correlation between BMI and urinary pH in both men and women, whereas BMI was associated with urinary oxalate excretion only among women and with urinary calcium excretion only among men. Serum uric acid and creatinine concentrations were correlated with BMI in both genders. Because no association was established between BMI and urinary volume, magnesium, and citrate excretion, inhibitors of calcium oxalate stone formation, the risk of stone formation increased significantly with increasing BMI among both men and women with urolithiasis (p = 0.015). The risk of calcium oxalate stone formation, median number of stone episodes, and frequency of diet‐related diseases were highest in overweight and obese men. Discussion: Overweight and obesity are strongly associated with an elevated risk of stone formation in both genders due to an increased urinary excretion of promoters but not inhibitors of calcium oxalate stone formation. Overweight and obese men are more prone to stone formation than overweight women.     

PHACOTUS LENTICULARIS (CHLAMYDOMONADALES,PHACOTACEAE) ZOOSPORES REQUIRE EXTERNAL SUPERSATURATION OF CALCIUM CARBONATE FOR CALCIFICATION IN CULTURE1,2

In nature, zoospores of the chlamydophycean genus Phacotus Perty usually have a calcified lorica. The only cultured species, Phacotus lenticularis (Ehrenberg) Stein, did not readily calcify in artificial media. To overcome this deficiency, we developed an artificial culture medium (N-HS) in which Phacotus lenticularis formed mineralized loricae, as under natural conditions. Calcification of Phacotus (strain Krienitz 91/1) was achieved in a medium containing the ionic concentrations found in natural habitats (i.e. Lake Haussee and Lake Stechlin), hard-water lakes of the Baltic Lake District (Germany). The N-HS medium contained extremely low phosphate concentrations and high calcium and magnesium concentrations compared with common culture media, but the concentrations were similar to those in the lakes. Calcium carbonate in N-HS medium was dissolved up to the saturation concentration (saturation index = 1). Supersaturation was achieved by the addition of ultra-alkaline compounds (Na₂S_iO₃ or NaOH). The medium with the highest super-saturation had a saturation index of 118 and was extremely supersaturated with respect to calcium carbonate. In that medium and in modified media with less of the sodium compounds (lower supersaturations), calcification of zoospores was observed. To determine the effects of sodium and silicon compounds on calcification, various other silicon and sodium compounds were tested but were shown to be ineffective. In conclusion, calcification of Phacotus lenticularis depends directly on the degree of calcium carbonate supersaturation of the medium, but the fundamental mineralization pattern does not. Our study shows that calcification in Phacotus lenticularis can be triggered and controlled by supersaturation of calcium carbonate.     

Plasma levels and urinary excretion of amino acids by subjects with renal calculi

Plasma levels and urinary amino acid excretions were estimated by high-performance liquid chromatography in 15 control subjects and 36 stone formers (SFs) classified according to the stone type: (1) 22 cases with calcium oxalate stones; (2) four cases with pure uric acid stones; (3) 10 cases with magnesium-ammonium phosphate stones, either pure or mixed with apatite. Some types of stones (namely oxalate and uric acid calculi) are mainly formed as a result of a metabolic deficiency that may affect the amino acid metabolism, and thus may be reflected in the urinary amino acid pattern. Data demonstrated clearly that there is a general tendency towards decreased amino acid excretions in all SFs with all types of stones. As a whole, one can observe a higher percentage of patients with calcium oxalate and phosphate calculosis, who have low urine excretions of amino acids; about 50% are the SFs with lower urine excretion of serine, glycine, taurine and i-leucine; the high percentage of patients with CaOX calculi shows lower urine excretions of tyrosine and ornithine.