EQUIL2: a BASIC computer program for the calculation of urinary saturation

A vertical (pseudodominant) pattern of inheritance in the autosomal recessive disease primary hyperoxaluria type 1: lack of relationship between genotype, enzymic phenotype, and disease severity

Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disease caused by a deficiency of alanine:glyoxylate aminotransferase (encoded by the AGXT gene). Primary hyperoxaluria type 1 is characterized by the elevated urinary excretion of oxalate and glycolate, and the deposition of insoluble calcium oxalate in the renal parenchyma and urinary tract. In the present study, we investigated an unusual family containing four affected individuals in two different generations. Based on our genetic, enzymic, metabolic, and clinical analyses, we have come to the following conclusions. First, although the pattern of inheritance of PH1 is usually horizontal (ie, all patients in the same generation), as expected for an autosomal recessive disease, it can sometimes show a vertical (pseudodominant) pattern of inheritance (ie, patients in more than one generation) due to the segregation within a family of three, rather than two, mutant AGXT alleles. Second, affected members of such a family can manifest very different clinical phenotypes both within and between generations. Although the clinical differences between generations might be at least partly due to differences in AGXT genotype, differences can equally occur within the same generation in individuals who possess the same AGXT genotype. Finally, individuals with PH1 at the level of the AGXT genotype might remain asymptomatic and undiagnosed for many years. The consequences of these findings for the clinical management and genetic counseling of families with PH1 are profound and wide-ranging.

Risk formulas in calcium oxalate urolithiasis

In order to reflect the risk of calcium stone formation, risk formulas have been described in the literature with the objective of being able to predict the further course of the stone disease. Some of these formulas are reviewed in this paper. Various results were obtained when different risk expressions were related to the severity of the stone disease. Although a reliable prediction of the future course of the disease most certainly cannot be made by analysis of the variables included in these expressions, several of the risk formulas differed significantly between patients with and without recurrent stone formation during a reasonable follow-up period. Some risk formulas might thus be helpful, at least to some extent, in selecting those patients in whom continuous stone formation can be anticipated and in whom active therapeutic measures should be beneficial and worthwhile. With an increased understanding of the mechanisms of calcium oxalate stone formation and our possibilities of measuring the relevant risk factors, it is likely that improved risk formulas with an increased predictive power can be developed. Until this becomes a reality, in most cases we have to combine important information on the history and clinical observations of the disease with a risk formula that offers a high degree of discrimination with respect to the risk of further stone formation.

Activation of c-myc gene mediates the mitogenic effects of oxalate in LLC-PK1 cells, a line of renal epithelial cells

Recent studies on LLC-PK1 cells demonstrated that oxalate, a simple dicarboxylic acid, acts as a mitogen for these renal epithelial cells. Exposure to oxalate initiates DNA synthesis, induces the expression of one of the early growth response genes c-myc and stimulates proliferation of quiescent cultures of LLC-PK1 cells. The present studies examined the possibility that expression of the c-myc protooncogene is obligatory for this mitogenic response. Specifically we determined whether pretreatment with c-myc antisense oligonucleotides would block the proliferative effects of oxalate in LLC-PK1 cells. Quiescent cultures of LLC-PK1 cells were exposed to oxalate in the presence and absence of c-myc antisense and the effects of oxalate on c-myc protein expression (Myc), DNA synthesis and cell growth were assessed. Exposure of cells to oxalate alone increased the expression of Myc within two hours. Pretreatment with c-myc antisense abolished this response. Further, pretreatment of cells with c-myc antisense but not nonsense oligonucleotides blocked the oxalate-induced initiation of DNA synthesis. Increases in cell number in response to oxalate (measured after 72 hr exposure) were also blocked by exposure to c-myc antisense. These findings suggest that c-myc gene expression is critical for the mitogenic effects of oxalate in LLC-PK1 cells.

Comparison of the Equil2 program and other methods for estimating the ion-activity product of urinary calcium oxalate: a new simplified method is proposed

BACKGROUND

We aimed to develop a new simplified method to determine the urinary calcium-oxalate saturation.

METHODS

The ion-activity product (AP) of urinary calcium oxalate was estimated in 345 clinical urine specimens (all 2.5 hour collections) using the Equil2 computer program and several other methods, and the results were compared. A new index using 4 parameters was created using multiple regression analysis.

RESULTS

Our new simplified method (the AP(CaOx) index EQ2) provided a better approximation to the Equil2 method (r = 0.9897) than other conventional methods.

CONCLUSION

This new method requiring 4 factors (urinary calcium, magnesium, oxalate, and citrate concentrations) is simple and clinically usable.

Risk factors in urinary calcium oxalate stone formation and their relation to urinary calcium oxalate supersaturation

BACKGROUND

We studied the effect of potential risk factors of urinary calcium oxalate saturation on calcium oxalate stone formation.

METHODS

Using the Equil2 program, the DG values of calcium oxalate in 390 clinical urine specimens were estimated in 5 healthy male individuals with and without citrate therapy.

RESULTS

Critical calcium-oxalate supersaturation (DG value, > 2.8) was noted in 15 out of 390 urine specimens. Of the 15, 14 late night or morning specimens had critical calcium oxalate supersaturation, while only 1 afternoon specimen was supersaturated. Critical calcium oxalate supersaturation was often associated with hyperoxaluria and hypercalciuria, while undersaturation was often associated with hypomagnesiuria, a high Ca/Mg ratio, and hypocitraturia.

CONCLUSIONS

Hypomagnesiuria, hypocitraturia, and a high Ca/Mg ratio appear to be poor indicators of calcium-oxalate supersaturation, and it is hard to predict the level of calcium-oxalate saturation using single parameters.

Magnesium status in idiopathic calcium urolithiasis--an orientational study in younger males

With the aim of revealing a possible magnesium (Mg) deficiency in the aetiology of idiopathic recurrent calcium urolithiasis we studied the Mg content of red blood cells, serum total, protein-bound, ionised and complexed fractions of Mg, and urinary Mg after an overnight fast. The two study groups comprised 12 male recurrent calcium urolithiasis patients and 12 healthy male controls (mean age 31 and 29 years, respectively). In recurrent calcium urolithiasis, serum albumin and Mg of erythrocytes were significantly decreased, as was serum total and protein-bound Mg, whereas serum ultrafiltrable, ionised and complexed Mg were statistically indistinguishable from values in controls. Urinary Mg (per unit creatinine) in recurrent calcium urolithiasis (mean 0.188 vs 0.209 in controls; p = 0.386) was not statistically different, whereas urinary total protein, glucose, and pH were significantly increased. The renal clearances of Mg and glucose were positively correlated (r = 0.56; p < 0.01), with a steeper slope in recurrent calcium urolithiasis than controls. Further fractionation of serum and urinary Mg into ions and complexes in recurrent calcium urolithiasis subjects with identical creatinine clearance revealed no statistical difference between 1) Mg ions and complexes filtered by renal glomeruli; 2) Mg ions and complexes excreted in urine; 3) fractional Mg excretion. Median urine supersaturation with respect to calcium oxalate was insignificantly lower (1.5 vs 2.2), with respect to hydroxyapatite insignificantly higher (3.3 vs 1.8), than in controls. It is concluded that relatively young recurrent calcium urolithiasis patients exhibit a deficiency of Mg in erythrocytes and serum total Mg, but no alteration of renal Mg handling. Thus, in recurrent calcium urolithiasis, a role of Mg deficiency in urine as a factor initiating stone formation may be ruled out, whereas a possible link between cellular Mg deficiency and the impairment of renal tubular functions involved in reabsorption of glucose and proteins, and in urine acidification, deserves further studies.

Is citrate an inhibitor of calcium oxalate crystal growth in high concentrations of urine?

The effect of citrate on calcium oxalate (CaOx) crystal growth was studied in a system in which series of samples containing [45Ca]calcium chloride were brought to different levels of supersaturation with various concentrations of oxalate. The crystallization was assessed by measuring the amount of isotope remaining in solution 30 min after the addition of CaOx seed crystals to samples containing citrate in concentrations corresponding to those in final urine. The experiments were carried out both in pure salt solutions and in solutions with dialysed urine. Increased concentrations of citrate resulted in a reduced crystallization of CaOx in both the presence and absence of dialysed urine, but with the lowest rate of crystallization in the samples containing urine. The increased concentration of 45Ca remaining in solution reflected a reduced crystallization, which could possibly be explained both by a reduced supersaturation and by an increased inhibition of CaOx crystal growth. The direct effects of citrate on CaOx crystal growth were assessed by calculating the ion-activity product of CaOx (APCaOx) at corresponding degrees of crystallization. The APCaOx recorded at a 30% reduction of the amount of isotope in solution increased with increasing concentrations of citrate between 1.0 and 1.5 mmol/l samples both with and without dialysed urine. These findings indicate that citrate has a weak direct inhibitory effect on CaOx crystal growth, which adds to the reduced growth rate brought about by urinary macromolecules and a decreased supersaturation.

Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study

PURPOSE

We define the role of urine volume as a stone risk factor in idiopathic calcium stone disease and test the actual preventive effectiveness of a high water intake.

MATERIALS AND METHODS

We studied 101 controls and 199 patients from the first idiopathic calcium stone episode. After a baseline study period the stone formers were divided by randomization into 2 groups (1 and 2) and they were followed prospectively for 5 years. Followup in group 1 only involved a high intake of water without any dietetic change, while followup in group 2 did not involve any treatment. Each year clinical, laboratory and radiological evaluation was obtained to determine urinary stone risk profile (including relative supersaturations of calcium oxalate, brushite and uric acid by Equil 2), recurrence rate and mean time to relapse.

RESULTS

The original urine volume was lower in male and female stone formers compared to controls (men with calcium oxalate stones 1,057 +/- 238 ml./24 hours versus normal men 1,401 +/- 562 ml./24 hours, p < 0.0001 and women calcium oxalate stones 990 +/- 230 ml./24 hours versus normal women 1,239 +/- 440 ml./24 hours, p < 0.001). During followup recurrences were noted within 5 years in 12 of 99 group 1 patients and in 27 of 100 group 2 patients (p = 0.008). The average interval for recurrences was 38.7 +/- 13.2 months in group 1 and 25.1 +/- 16.4 months in group 2 (p = 0.016). The relative supersaturations for calcium oxalate, brushite and uric acid were much greater in baseline urine of the stone patients in both groups compared to controls. During followup, baseline values decreased sharply only in group 1. Finally the baseline urine in patients with recurrences was characterized by a higher calcium excretion compared to urine of the patients without recurrences in both groups.

CONCLUSIONS

We conclude that urine volume is a real stone risk factor in nephrolithiasis and that a large intake of water is the initial therapy for prevention of stone recurrences. In cases of hypercalciuria it is suitable to prescribe adjuvant specific diets or drug therapy.

Oxalate toxicity in LLC-PK1 cells: role of free radicals

Oxalate, the most common constituent of kidney stones, is an end product of metabolism that is excreted by the kidney. During excretion, oxalate is transported by a variety of transport systems and accumulates in renal tubular cells. This process has been considered benign; however, recent studies on LLC-PK1 cells suggested that high concentrations of oxalate are toxic, inducing morphological alterations, increases in membrane permeability to vital dyes and loss of cells from the monolayer cultures. The present studies examined the basis for oxalate toxicity, focusing on the possibility that oxalate exposure might increase the production/availability of free radicals in LLC-PK1 cells. Free radical production was monitored in two ways, by monitoring the reduction of nitroblue tetrazolium to a blue reaction product and by following the conversion of dihydrorhodamine 123 (DHR) to its fluorescent derivative, rhodamine 123. Such studies demonstrated that oxalate induces a concentration-dependent increase in dye conversion by a process that is sensitive to free radical scavengers. Specifically, addition of catalase or superoxide dismutase blocked the oxalate-induced changes in dye fluorescence/absorbance. Addition of these free radical scavengers also prevented the oxalate-induced loss of membrane integrity in LLC-PK1 cells. Thus it seems likely that free radicals are responsible for oxalate toxicity. The levels of oxalate that induced toxicity in LLC-PK1 cells (350 microM) was only slightly higher than would be expected to occur in the renal cortex. These considerations suggest that hyperoxaluria may contribute to the progression of renal injury in several forms of renal disease.

Urinary oxalate excretion increases with body size and decreases with increasing dietary calcium intake among healthy adults

Increasing dietary calcium intake decreases urinary oxalate excretion by increasing intestinal precipitation of dietary oxalate as calcium oxalate. This mechanism was speculated to account for the decreased prospective incidence of kidney stones as estimated dietary calcium intake, adjusted for caloric intake, increased among men in a recent large epidemiological study. To further assess the relationship between estimated diet calcium and urinary oxalate, we studied 94 health adults, 50 women and 44 men, ages 20 to 70 years with weights ranging form 47 to 104 kg while they ate their customary diets. Each subject completed a semiquantitative food frequency questionnaire and collected three 24-hour urines preserved with HCl. The urines were collected accurately as judged by a mean intrasubject CV for creatinine excretion of 9.8% and direct relations between urinary creatinine excretion and body wt (r = 0.62; P < 0.0001), or predicted urine creatinine content for sex, age and weight using the Cockcroft and Gault formulas (r = 0.76; P < 0.0001). Estimated diet calcium intake ranged from 6.8 to 68 mmol/day (272 to 2720 mg/day) and averaged 29.5 mmol/day (1180 mg/day). Individual mean urinary oxalate excretion ranged from 0.079 go 0.332 mmol/day (7 to 29 mg/day) and averaged 0.198 mmol/day (17 mg/day). Among all subjects, daily oxalate excretion was directly related to creatinine excretion as an estimate of lean body mass (r = 0.61; P < 0.0001). Thus, oxalate excretion among men averaged 0.228 +/- 0.051 SD mmol/day, a value significantly higher than the average among women of 0.173 +/- 0.045 mmol/day (P < 0.001). Daily urine oxalate excretion/creatinine decreased curvilinearly as estimated dietary Ca intake increased (r = -0.30; P = 0.0035) and as the ratio of estimated dietary calcium to dietary oxalate increased (r = -0.39; P = 0.0001). We conclude that body size is the major determinant of urinary oxalate excretion among healthy adults, presumably reflecting variations in endogenous oxalate synthesis with lean body mass. Increasing estimated diet calcium intake, especially up to the range of 15 to 20 mmol/day (600 to 800 mg/day) has an additional effect to decrease during oxalate excretion, presumably by limiting intestinal absorption of dietary oxalate.

Stone formation in genetic hypercalciuric rats

Our genetic hypercalciuric (GH) rats have been selected and inbred for 29 generations to maximize urine calcium (UCa) excretion compared to identical gender controls (Ctl). To determine the effect of the increased UCa on urinary supersaturation and stone formation, we pair fed 15 GH and 15 Ctl rats a standard 1.2% calcium diet for 18 weeks, measured urine supersaturation every two weeks, and examined the urinary tract of 1/3 of the rats for the presence of stones every six weeks. Any stones formed were studied by SEM, X-ray and electron diffraction and X-ray microanalysis. Over the entire study UCa was increased in the GH compared to Ctl, resulting in greater supersaturation with respect to calcium hydrogen phosphate (CaHPO4) at all times and calcium oxalate (CaOx) at most times. There was a progressive increase in the incidence of stone formation in GH rats with one of five rats having stones at six weeks, three of five with stones at 12 weeks and five of five with stones at 18 weeks. There were no stones formed in Ctl rats. SEM reveals discrete stones and not nephrocalcinosis. X-ray and electron diffraction and X-ray microanalysis reveal the stones to be poorly crystalline apatite which is a solid phase of calcium and phosphate. Compared to Ctl, in the GH rats the saturation ratio for CaHPO4 increased proportionally more than that for CaOx, perhaps explaining why the rats formed apatite and not oxalate stones. This is the first description of an animal model of spontaneous nephrolithiasis.

Effects of urinary macromolecules on the nucleation of calcium oxalate in idiopathic stone formers and healthy controls

Urinary macromolecules have attracted great interest because of their possible role as both promoters and inhibitors of calcium oxalate (CaOx) crystallization and it remains unclear whether there is any difference, in their nucleating activity, between stone formers and controls. We selected 9 male idiopathic CaOx stone formers whose 24-h urines presented no evidence of common urinary stone risk factors such as hypercalciuria, hyperoxaluria, hyperuricosuria, hypocitraturia, hypomagnesiuria or low glycosaminoglycans excretion and 12 male controls (matched for age and body weight) whose 24-h urines did not differ from those of stone formers. The study of urinary CaOx nucleation was made in freshly voided overnight urines whose biochemical composition was almost identical in the two groups. In filtered (0.22 micron) and ultrafiltered (10 kDa) urine we performed an oxalate tolerance test to determine the permissible increment of oxalate, the oxalate level for nucleation and the permissible increment of CaOx relative supersaturation (CaOx RS). In filtered urine from stone formers the permissible increment of oxalate was lower than controls (30 +/- 10.2 vs. 46.7 +/- 9.7 mg/l, P = 0.001), the oxalate level for nucleation was lower (64.4 +/- 14.2 vs. 79.5 +/- 15.6 mg/l, P = 0.035) and the permissible increment of CaOx RS was also lower (9.71 +/- 2.59 vs. 13.39 +/- 3.62, P = 0.018). In ultrafiltered urine these differences disappeared because the removal of macromolecules in stone formers significantly enhanced the oxalate-tolerance values. The difference between the change of the oxalate permissible increment of filtered and ultrafiltered urine allowed a distinction to be made between stone formers and controls that was not feasible in other ways (7.6 +/- 5.3 vs. 3.3 +/- 5.9 mg/l, P < 0.0001). The study suggests that, in idiopathic CaOx stone formers free from common urinary risk factors of CaOx crystallization, there is an increased tendency for CaOx nucleation in urine, which is mediated by macromolecular components.

Differences in the free Ca2+ in undiluted urine from stone formers and normal subjects using a new generation of ion-selective electrodes

OBJECTIVES

To measure the ionized Ca2+ in urine from normal subjects and patients with urinary tract stones.

PATIENTS AND METHODS

Urine samples were obtained from 37 normal subjects and 52 stone-formers. Ca2+ was measured using plastic dip-cast ion-selective electrodes; total Ca and other variables were measured by standard analytical techniques.

RESULTS

The ionized Ca2+ and the total Ca were greater in stone-formers' urine although the difference was more significant with the Ca2+ data, especially at a standardized pH. Absolute values of the Ca2+ were dependent on the type of reference electrode used. The Ca2+ was a function of urine pH; lower values were recorded as pH increased. Measured values of the Ca2+ did not correlate well with calculated values using a standard computer program.

CONCLUSIONS

Measurement of the Ca2+ in spot urine samples at a standard pH provides a more discriminative test than total Ca for the presence of urinary tract stones. The pH dependence of the Ca2+ may have important consequences in the formation of urinary tract stones. The poor correlation between measured and computed values of Ca2+ emphasizes the importance of accurate measurement of this variable.

Urinary calcium and oxalate excretion in children

We have established normal values for calcium/creatinine (Ca/Cr) and oxalate/creatinine (Ox/Cr) ratios in 25 infants (aged 1-7 days) and 391 children (aged 1 month to 14.5 years) and compared these with values obtained in 137 children with post-glomerular haematuria and 27 with nephrolithiasis. Oxalate was measured by ion chromatography. Nomograms of Marshall and Robertson were used to calculate urine saturation to calcium oxalate. The Ca/Cr ratio was normally distributed whereas the Ox/Cr ratio had a log-normal distribution. The molar ratio of Ca/Cr was the lowest in the first days of life and the highest between 7 month and 1.5 years (mean +/- SD = 0.39 +/- 0.28 mmol/mmol). Following a slight decrease it stabilised by the age of 6 years (0.34 +/- 0.19 mmol/mmol). The highest Ox/Cr values were measured during the 1st month of life [geometric mean 133 (range 61-280) mumol/mmol], followed by a gradual decrease until 11 years of age [mean 24 (range 6-82) mumol/mmol]. Thirty-six haematuric children had hypercalciuria (26%), 23 had absorptive hypercalciuria, 13 renal type. Children with absorptive hypercalciuria on a calcium-restricted diet had significantly higher oxalate excretion than those with renal hypercalciuria and the control group [38 (range 28-49) vs. 22 (range 16-29) and 23 (range 22-27) mumol/mol respectively, P < 0.01]. Calcium oxalate urine saturation of stone patients was higher than that of patients with haematuria and the normal population (1.18 +/- 0.05 vs. 1.06 +/- 0.03, P < 0.03 and 0.84 +/- 0.03, P < 0.001 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Results of long-term treatment with orthophosphate and pyridoxine in patients with primary hyperoxaluria

BACKGROUND

The prognosis for patients with primary hyperoxaluria has been ominous, with the expectation of renal failure, poor results with transplantation, and early death.

METHODS

We studied the long-term effects of orthophosphate and pyridoxine therapy in 25 patients with primary hyperoxaluria who were treated for an average of 10 years (range, 0.3 to 26). Their mean age at the start of treatment was 12 years (median, 6; range, 0.5 to 32). We also studied the effect of orthophosphate and pyridoxine on urinary supersaturation with calcium oxalate, crystal inhibition using a seeded growth system, and crystal formation using scanning electron microscopy in 12 patients during three-day stays in the clinical research center.

RESULTS

The mean (+/- SD) glomerular filtration rate at the start of treatment was 91 +/- 26 ml per minute per 1.73 m2. The median decline in glomerular filtration rates was 1.4 ml per minute per 1.73 m2 of body-surface area per year. The actuarial survival free of end-stage renal disease was 96, 89, 74, and 74 percent of 5, 10, 15, and 20 years, respectively. Treatment with orthophosphate and pyridoxine reduced urinary supersaturation with calcium oxalate from 8.3 +/- 3.0 to 2.1 +/- 1.7 kJ per mole at 38 degrees C (P < 0.001), increased the inhibition of calcium oxalate formation from 63 +/- 11 to 108 +/- 10 inhibitor units per 24 hours (P < 0.001), and improved the crystalluria score from 2.6 +/- 0.3 to 0.6 +/- 0.1 (P < 0.001).

CONCLUSIONS

Treatment of patients with primary hyperoxaluria with orthophosphate and pyridoxine decreases urinary calcium oxalate crystallization and appears to preserve renal function.

Evaluation of a simple test to estimate urine saturation with calcium oxalate in stone-forming patients

In 43 patients with recent-onset calcium oxalate nephrolithiasis (25 male, 18 female; age range: 17-61 yr), urine saturation with calcium oxalate (CaOx) was calculated using a computer program (Equil-AT). The results in kJ/mol (normal < or = 2.0) were compared with those obtained with a simple test consisting of the addition of increasing amounts of calcium and oxalate to 3 tubes containing 10 ml urine. Development of turbidity in tube I denotes urine supersaturation with CaOx; turbidity in tubes II or III indicates lesser degrees of saturation, while a lack of turbidity (NT: no turbidity) shows undersaturation. Both saturation estimates were performed using aliquots of 24-hour urine collections. Twenty-one samples developed turbidity in tube I, 9 in tube II, and 6 in tube III, while 7 showed NT. There were no significant differences in Equil-AT values between II and III and between III and NT (p < 0.05 for I vs II and I vs III). High computer-calculated saturation values were found in 86% of group I samples and 22% of group II samples. None of the urines exhibiting turbidity in tube III or NT had high saturation values as estimated by Equil-AT. The turbidity test was also performed using freshly voided morning urine samples from the same patients. The results agreed with those obtained using the same test on aliquots of 24-hour collections, although in 10.8% of patients the morning test indicated higher levels of saturation. It is concluded that the turbidity test is a rapid, inexpensive and accurate way of estimating urine saturation with CaOx in the outpatient clinic.

Circadian variations in the risk of urinary calcium oxalate stone formation

OBJECTIVE

To evaluate the circadian fluctuations in the risk of urinary calcium oxalate stone formation with regard to critical periods of crystallization.

PATIENTS AND METHODS

Over a given time period, the Tiselius index depends on urine volume and urinary excretion of oxalate, calcium, citrate and magnesium. This crystallization potential was evaluated during three successive periods spread over 24 h for 25 recurrent stone-formers aged 16-76 years (mean 50) and 25 control subjects aged 27-71 years (mean 44).

RESULTS

There was no significant difference in the value of the Tiselius index for all equivalent time periods in both groups of patients. The minimum value was recorded in the afternoon and the circadian pattern of the index illustrated the predominant importance of urinary output in its determination. Morning urinary concentrations and excretions of citrate, and nocturnal levels of magnesium were significantly higher in the stone-formers when compared with the control subjects.

CONCLUSION

The lithogenic risk for calcium oxalate stones was maximal at the end of the night or during the early morning, when urinary output was minimal. This circadian study revealed abnormalities that are not apparent from non-fractionated 24 h urine samples, and which were potentially relevant to therapy.

Oxalate transport in a line of porcine renal epithelial cells--LLC-PK1 cells

The present studies examined oxalate handling in LLC-PK1 cells, an epithelial cell line of porcine origin. These cells appear to express transport systems for oxalate, as evidenced by the fact that uptake was saturable, time dependent and sensitive to the anion transport inhibitor DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid). Oxalate uptake in these cells was also affected by the presence of certain inorganic anions (Cl-, SO4(2-), or HCO3-) but not by organic anions (para-aminohippurate, urate, malate, phenylsuccinate, succinate). This uptake was Na independent and unaffected by changes in membrane potential but was affected by external pH, with acidic pH stimulating and alkaline pH inhibiting oxalate accumulation. These findings suggest that LLC-PK1 cells express oxalate transporters similar to those observed in the mammalian renal cortex. Further studies using these cells may prove useful in defining the conditions that govern transcellular oxalate flux in renal epithelial cells.

EQUIL93: a tool for experimental and clinical urolithiasis

An extensively updated version of the EQUIL software is described. The former version, designated EQUIL2, is widely used to study urolithiasis and related areas of biomineralization. In this report, we discuss recent enhancements which give EQUIL93 an expanded scope of application. This program has been frequently used in studies of the physicochemical processes underlying stone salt crystallization, especially crystal growth and nucleation, but it has also been employed as an aid for in vivo research and as an evaluator of therapeutic measures. We illustrate several new applications, including some outside the urologic realm, and we discuss how the enhanced software can be helpful in stone risk assessments.

Urinary calcium oxalate saturation in 'stone formers' and normal subjects: an application of the EQUIL2 program

OBJECTIVE

To produce an index of lithogenic risk which identifies patients at risk of stone recurrence and facilitates the monitoring of prophylactic treatments.

PATIENTS AND METHODS

The EQUIL2 program provides an evaluation of the state of urinary saturation, particularly of calcium oxalate, based on the pH and total concentrations (mmol/l) of sodium, potassium, calcium, magnesium, uric acid, chloride, ammonium, citrate, phosphate, sulphate, oxalate, pyrophosphate and carbon dioxide. The morning urinary calcium oxalate saturation coefficient was thus calculated for 30 stone-formers (Group 1) and 30 normal control subjects (Group 2).

RESULTS

Urine from the majority of individuals was saturated, with no significant difference between the two groups. There appeared to be a correlation between the state of saturation and the urinary calcium oxalate molar product in both stone-formers (r = 0.931) and controls (r = 0.914).

CONCLUSION

In future studies on urinary calcium oxalate saturation, it should be possible to supplement the sophisticated coefficient determined by the EQUIL2 program with the molar product, except in cases where monitoring therapies have little or no effect on urinary oxalate or urinary calcium levels.

Hot occupation and nephrolithiasis

We investigated the prevalence of stone disease and urinary stone risk factors in machinists chronically exposed to a hot environment and massive sweating, without interference of nephrotoxic metals or other lithogenic compounds. The study was performed at a glass plant and exposure to heat stress was estimated by the Wet Bulb Globe Temperature climatic index. The prevalence of nephrolithiasis on the entire population of the machinists was 8.5% (20 of 236), while the prevalence on the controls working in normal temperature was 2.4% (4 of 165) (p = 0.03). A high incidence (38.8%) of uric acid stones was present in the workers exposed to heat stress. Among the urinary stone risk indexes determined for 3 days during the 8-hour work shift on a randomly selected sample of 21 workers exposed and 21 workers not exposed to heat stress without any evidence of stone disease significant differences were found in uric acid concentration (722 +/- 195 versus 482 +/- 184 mg./l., p < 0.001), specific gravity (1,026 +/- 4 versus 1,021 +/- 6, p < 0.005) and pH (5.31 +/- 0.28 versus 5.64 +/- 0.54, p < 0.02), respectively. Thus, high uric acid relative supersaturation was present during occupation in hot temperatures (8.67 +/- 3.49) compared to occupation in normal temperatures (4.15 +/- 2.7) (p < 0.001). This study confirms that chronic dehydration represents a real lithogenic risk factor, mainly for uric acid stones, and adequate fluid intake is recommended during hot occupations.

Does fish oil benefit stone formers?

The possibility that dietary fish oil supplementation may benefit patients with hypercalciuric urolithiasis by decreasing calcium excretion and enhancing protective mechanisms has been studied in rats and humans. In experiments on rats in metabolic cages, fish oil inhibited experimental nephrocalcinosis induced by intraperitoneal calcium gluconate. There were no significant changes in urinary biochemistry. In a clinical study on 18 hypercalciuric recurrent stone patients fish oil significantly decreased urinary calcium excretion. This effect was accompanied by decreases in the excretion of magnesium and citrate. Oxalate excretion and urinary fibrinolytic activity were unchanged. Overall, fish oil had a limited impact on the risk profile for recurrent urolithiasis.

Urinary saturation and nephrocalcinosis in preterm infants: effect of parenteral nutrition

Urinary lithogenic and inhibitory factors were studied in 27 preterm infants; 16 had total parenteral nutrition (TPN) and 11 had breastmilk with an additional glucose-sodium chloride infusion. Urines were collected for 24 hours on day 2 (period A), day 3 (B), and once between days 4 and 10 (C). Urinary calcium oxalate saturation was calculated by the computer program EQUIL 2. Renal ultrasonography was performed every second week until discharge. The calcium/creatinine ratio increased in infants on TPN (A 0.91; C 1.68 mol/mol) and was significantly higher at period C than that in infants on breastmilk/infusion (A 0.52; C 0.36). The oxalate/creatinine ratio was persistently higher with TPN (203 mmol/mol) than with breastmilk/infusion (98; 137). The citrate/creatinine remained constant with TPN (0.44 mol/mol), whereas it increased significantly with breastmilk/infusion (0.26; 0.49). Calcium/citrate rose considerably with TPN, but decreased with breastmilk/infusion to a significantly lower level than with TPN. The urinary calcium oxalate saturation increased with TPN (2.4; 4.5) and decreased with breastmilk/infusion (2.1; 1.5) to a significantly lower value than with TPN. Nephrocalcinosis developed in two infants on TPN. Mean daily calcium intake was similar in both groups, whereas protein, sodium, and phosphorus intake were significantly higher on TPN. It is concluded that the increase in urinary calcium oxalate saturation observed with TPN is due to the combined effect of an increased urinary calcium excretion and higher urinary oxalate/creatinine and calcium/citrate ratios. The changes observed are likely to be caused by TPN itself, which differs in several respects from breastmilk feeding.

Calculation of titratable acidity from urinary stone risk factors

Using urine samples and standard solutions, this study demonstrates that the existing procedure for measuring titratable acidity in the urine is not reliable and may result in overestimates of up to 25%. The accuracy is affected by loss of CO2, the presence of uric acid crystals, and the precipitation of calciumphosphate phases during the titration. A method is presented for calculating titratable acidity, using a number of routinely-measured urine components and a computer program for calculating complex equilibria in the urine. The calculated titratable acidity is shown to be more reliable then the measured one. The results are compiled in a nomogram from which the titratable acidity can be directly read. When the parameters of urine pH, PO4 content and pCO2 are used, the accuracy of the nomogram is > 96% for urine samples with a pH value above 6.0 and > 89% for urine samples with a pH value below 6.0. For all samples, the accuracy is improved to > 97% when the nomogram using uric acid and citrate content is used in additionally.

Management of primary hyperoxaluria: efficacy of oral citrate administration

The prognosis of primary hyperoxaluria (PH) is not only related to endogenous oxalate production and the response (if any) to pyridoxine (in type I), but is greatly influenced by extrarenal factors like dehydration. The earlier the diagnosis of PH, the better the chances of improving the prognosis in individual patients. Measures to enhance the solubility of calcium oxalate are important. Besides ensuring at all times a generous fluid intake (> 2 l/m2), administration of alkali citrate (0.15 g/kg), which has not been advocated so far in PH, appears very promising. We studied the effect of sodium citrate in six patients with PH. Mean urinary citrate excretion (mmol/day per 1.73 m2) without oral citrate was very low (0.57) and rose to 2.49 with citrate administration. This was accompanied by a significant decrease in the calcium oxalate saturation (calculated by equil 2) from 11.7 to 6.9 (P < 0.05). Treatment in five patients over 10-36 months resulted in improved (1) or stabilized (4) renal function and reduced passage of stones. Additional measures include restriction of salt and of oxalate-rich food. We conclude that long-term administration of alkali citrate is beneficial in patients with PH.

Crystallization kinetics of calcium oxalate in fresh, minimally diluted urine: comparison of recurrent stone formers and healthy controls in a continuous mixed suspension mixed product removal crystallizer

A reproducible method has been developed for studying calcium oxalate crystallization from fresh, minimally diluted (92%) urine with the mixed suspension mixed product removal continuous crystallization technique. All samples were adjusted to give the same starting calcium and oxalate concentrations. Twenty-one recurrent male stone formers were compared with twenty-two healthy controls. There was no difference in crystal growth rates but crystal nucleation rates were much higher in the control group (p = 0.003). Using growth rate and nucleation rate results, the amount of crystalline material in suspension was shown to be lower in the urine from stone formers, and therefore the equilibrium supersaturation in the crystallizer was lower in the control group (p = 0.001). We propose that the ability of a healthy person's urine to maintain a lower supersaturation is a crucial protective factor distinguishing non-stone formers from stone formers.

Magnesium oxide administration and prevention of calcium oxalate nephrolithiasis

We studied the effect of oral administration of magnesium oxide (MgO) on calcium oxalate (CaOx) nephrolithiasis in rats. Nephrolithiasis was induced by administration of 1.0% ethylene glycol (EG) in drinking water. Magnesium oxide was given mixed with food at 500 mg./100 g. rat chow. Dispensation of MgO resulted in a significant increase of urinary pH and a modest increase in urinary excretion of citrate. Urinary excretion of oxalate started to decline by day 14 and was significantly reduced on days 21 and 28. All rats receiving EG displayed crystalluria. From the group receiving EG only, 3 of 4 rats sacrificed on day 15 and 2 of 4 rats sacrificed on day 29 had CaOx crystal deposits in their kidneys. None of the 8 rats who received both EG and MgO had CaOx nephrolithiasis. Thus our findings indicate that dispensation of magnesium as MgO can be beneficial against calcium oxalate nephrolithiasis.

The role of citrate complexes in preventing urolithiasis

There is considerable clinical evidence that the oral administration of potassium citrate significantly reduces the incidence of calcium oxalate stone formation in the urinary tract. The effectiveness of citrate ions in preventing stone formation could be due to the reduction in the concentrations of calcium and oxalate ions caused by complex ion formation with the citrate ions and/or due to the inhibition of the crystallisation of calcium oxalate. This paper reports an experimental study aimed at elucidating the role of citrate complexes in preventing urolithiasis. An experimental method is described which allows the identification of two hitherto unknown complexes CaOx cit3- and (Ca cit2)4-. The stability constants of these complexes have been determined, respectively, as log K = 4.54 +/- 0.08 and beta 2 cit = 5.15 +/- 0.14 (25 degrees C, I = 0.16). The inclusion of these complexes in ion-equilibrium calculations led to the conclusion that the effectiveness of the citrate ion in preventing calcium oxalate stone formation is due to its inhibition of agglomeration or growth of calcium oxalate crystals rather than any significant reduction in the degree of supersaturation of urine.

Pyrophosphate in synovial fluid and urine and its relationship to urinary risk factors for stone disease

Inorganic pyrophosphate (PPi) measurement in urine and synovial fluid has been established using the PPi-dependent phosphorylation of fructose-6-phosphate and subsequent reduction of dihydroxyacetone phosphate by NADH. The assay is linear up to 200 mumol/L, easy to perform and gives results comparable to more complex methods. Daily urinary output of PPi was independently related to both age (P = 0.0014) and sex (P = 0.0002). Men had higher values than women and older individuals excreted greater amounts. Male stone formers, younger than 45 years, had lower values than age matched male controls (P = 0.012). Younger female stone formers also tended to have lower values. In stone formers' urine significant and independent correlations were found of PPi excretion with urine volume (P = 0.004) and with phosphate excretion (P = 0.008). Oxalate excretion and that of other urine constituents and the degree of supersaturation with common stone-forming salts were not correlated with PPi. PPi excretion was markedly elevated in the urine of two patients with hypophosphatasia. The PPi concentration in synovial fluid from painful, swollen knee joints was elevated, but unrelated to the presence or absence of PPi or urate crystals.

Pathogenesis of nephrolithiasis post-partial ileal bypass surgery: case-control study. The POSCH Group

Between 1975 and 1983, 838 patients were randomized into the Program on the Surgical Control of Hyperlipidemias (POSCH) trial: 417 to standard medical care and 421 to partial ileal bypass (PIB) surgery. During the course of the trial, an increased incidence of kidney stone formation was found in the surgery group (4%/year) as compared to the control group (0.4%/year). A matched triplet case-control study was conducted to assess the possible causes for the increased incidence of kidney stones. Three groups were studied: PIB stone-formers (S); PIB non-stone formers (N); and non-PIB, non-stone formers in the control group (C). Initially, 162 patients (54 triplets) were selected. Ten percent of the patients declined to participate which resulted in a sample size of 146 patients. The PIB patients had statistically significant (P less than 0.05) lower levels of serum vitamin D metabolites; lower urine volume, pH, citrate, magnesium, carbon dioxide, and sulfate, and higher urinary oxalate, ammonia and relative supersaturation for calcium oxalate and uric acid than the control patients. Although S and N had similar results, those S with no prior history of stones had a higher calcium oxalate supersaturation than similar N with a negative prior history of stones (P less than 0.025). Based on these results, all PIB patients appear to be at risk for kidney stone formation. The combination of reduced urinary volume and calcium oxalate precipitation inhibitor substance with increased calcium oxalate relative supersaturation produced an increase in nephrolithiasis risk in the PIB groups.

Inhibition of calcium oxalate crystallization by urinary macromolecules

The crystallization of calcium oxalate (CaOx) was determined in dialyzed urine samples collected between 0600 and 1000 hours from 18 normal men, 10 normal women and 13 men and 10 women with CaOx stone disease. Each urine samples was supersaturated by the addition of calcium chloride and sodium oxalate, and CaOx crystallization was followed by quantification of the [14C]-oxalate remaining in solution for 30 min after supersaturation of the sample. The rate of crystallization was compared with that in physiological saline. The surface area delimited by the urine and saline curves was used to express the inhibition of CaOx crystallization by urinary macromolecules (IUMM). The IUMM was significantly higher in urine from normal women than in that from stone-forming women (P less than 0.05), normal men (P less than 0.005), and stone-forming men (P less than 0.02). However, there were no significant differences between stone-forming men and stone-forming women, nor was IUMM higher in normal men than in stone-forming men. A high concentration of inhibitors might protect women from CaOx stone formation and be one factor explaining the lower stone-formation rate in women. Although low values were more predominate in normal men than in normal women, there were no significant differences between the groups when the inhibition was corrected for differences in urinary volumes.

Effect of magnesium on calcium oxalate urolithiasis

Previous studies have shown that hypomagnesuria induced by magnesium deficient diet causes calcium oxalate crystal deposition in renal tubules of hyperoxaluric rats and administration of magnesium to these rats results in prevention of calcium oxalate crystallization in their kidneys. Based on these studies magnesium was claimed to be beneficial for calcium oxalate stone patients. However, hypomagnesuria is not a common phenomenon. To better understand the role of magnesium as an inhibitor of calcium oxalate crystallization in urine, we studied the effect of magnesium on calcium oxalate urolithiasis in rats on a regular diet and a hyperoxaluric protocol. Excess magnesium was administered to male rats on regular diet and a lithogenic protocol. Magnesium administration to hyperoxaluric rats did not result in significant changes in urinary excretion of calcium or oxalate or in calcium oxalate relative supersaturation. Urinary excretion of citrate was also not significantly altered. Some animals from both groups, those on magnesium therapy and those not on magnesium therapy had crystals deposited in their renal tubules. We conclude that excess magnesium has no significant effect on calcium oxalate urolithiasis in normomagnesuric conditions.

Diet and hyperoxaluria in the syndrome of idiopathic calcium oxalate urolithiasis

Hyperoxaluria is an important risk factor in patients who form calcium oxalate stones within the urinary tract. It occurs in patients with primary hyperoxaluria, enteric hyperoxaluria, and the syndrome of idiopathic calcium oxalate urolithiasis. In the latter condition, the specific causes of the hyperoxaluria are not well defined. Diet and the availability of calcium and oxalate from the diet within the intestine are important factors in the hyperoxaluria that is present in some of these patients with idiopathic calcium oxalate urolithiasis. Other abnormalities in endogenous metabolism or transport of oxalate may play a role in the hyperoxaluria in some of these patients.

Strong inference in mechanistic urolithiasis: a tribute to Birdwell Finlayson's biophysical contributions

The career of Birdwell Finlayson was distinguished by his continual efforts at casting problems he encountered in urolithiasis in terms of relevant physical theory. His extensive background in biophysics qualified him uniquely for this task. He employed a process called "strong inference" as much as possible; this process was derived from a 1964 essay by John R. Platt, and it appears repeatedly as a guiding principle in Finlayson's research.

Studies on the crystallization of magnesium ammonium phosphate in urine

The crystallization of magnesium ammonium phosphate (MAP) was studied in salt solutions and dialysed urine at similar levels of MAP supersaturation. At pH levels of 7.1 or higher crystallization occurred to the same extent in solutions with and without urinary macromolecules. Whereas crystals in the size range 3.5-5 microns were observed in the salt solution at pH 7.0, this was not so in dialysed urine. When the crystal size distribution was determined after 30 min larger crystals were observed in dialysed urine, indicating a promoting effect by urinary macromolecules on the formation of MAP crystals. A modified AP(MAP) index was formulated based on calculations with the EQUIL 2 programme in order to improve the relationship between this simplified estimate and the ion-activity product of MAP (APMAP). This index had the following form: [formula: see text] for 24-h values of magnesium (Mg), ammonium (NH4), phosphate (P), pH and urine volume (V). The APMAP required for the formation of 2,000 crystals in the size range 3.5-5 microns varied between 226 x 10(-15) and 293 x 10(-15) (mmol/l)2 in dialysed urine. An experimental system was designed based on the measurement of pH during the addition of NH4OH. At the point assumed to correspond to the start of crystallization, AP(MAP) index values between 409 and 903 were recorded. Such a test might provide useful information on the crystallization properties in urine.

Cell injury associated calcium oxalate crystalluria

Renal tubular cell damage, resulting in membranuria, was induced by the administration of subcutaneous gentamicin to male Sprague-Dawley rats. One group of rats received gentamicin only, while a second group was given gentamicin plus ethylene glycol in drinking water at a concentration which increased urine oxalate but alone did not cause calcium oxalate crystalluria. Crystalluria occurred early in the combined treatment groups and persisted for the duration of the experiment. Crystalluria was not present in animals receiving gentamicin or ethylene glycol only. These results suggest that cellular fragments can serve as heterogeneous foci for the nucleation of calcium oxalate crystals.

Effects of urinary macromolecules on the crystallization of calcium oxalate

The macromolecular fraction of urine with a molecular weight above 3,000 was isolated by dialysis. In the dialysed urine the rate of calcium oxalate (CaOx) crystallization was reduced both in the presence and absence of CaOx seed crystals. There was a clear relationship between crystallization and the relative concentration of the dialysed urine, with the highest crystallization propensity at the lowest concentration of macromolecules. Dilution of dialysed urine also affected crystal size distribution, with a predominance of small (2.8-4.5 microns) crystals in 100% dialysed urine and of large (5.6-14.0 microns) crystals in 5% dialysed urine. This is consistent with a macromolecular inhibition of both crystal growth and aggregation. Analysis of the crystal size distribution 120 min after supersaturation of whole urine to a level at which approximately 100 crystals in the size interval 3.5-5 microns were detected in a Coulter counter surprisingly disclosed a higher mean crystal volume in urine samples from normal subjects than from stone formers. This gives support to the assumptions that macromolecules might be of importance during the initial phase of CaOx crystallization and that urine from stone formers and normal subjects might be different in this respect.

Calcium oxalate crystallisation kinetics and the effects of calcium and gamma-carboxyglutamic acid

gamma-carboxyglutamic acid (GLA) is an amino acid with a high affinity for calcium. It is found in urine both as the free amino acid and incorporated into proteins such as osteocalcin. Free and bound GLA have been reported to be found at higher concentrations in the urine of stone formers than controls. We have investigated the effect of GLA and calcium, at physiological levels, on the crystallisation of calcium oxalate using a mixed suspension mixed product removal continuous crystalliser. GLA caused very significant changes in the crystallisation kinetics, but the effect was dependent on the calcium concentration. At 4 mM calcium, GLA decreased the growth rate and increased the nucleation rate; at 12 mM the reverse occurred. At all concentrations of calcium tested, GLA caused a significantly increased crystal mass to be produced. Our evidence supports the hypothesis that GLA modifies calcium oxalate crystallisation and could be a promoter of stone formation in vivo, particularly at moderately elevated levels of calcium excretion.

Rapid method of measuring the inhibition of calcium-oxalate monohydrate growth in urine

In order to have a rapid method of measuring the inhibition of calcium-oxalate monohydrate growth in freshly voided whole urine, a test system by Meyer and Smith that has originally been developed for diluted urine was modified. The crystallization processes were monitored by an ion-selective calcium electrode, which allowed determination of the half-life value of the decrease in calcium within 25 min. Even given the high inhibitory activity of whole urine, the test gave reliable results when a high seed concentration was used. Inhibition was expressed as the ratio between the half-lives of the calcium decrease obtained in the presence and in the absence of inhibitors. This approach allowed kinetic studies of individual inhibitors in model solutions. Furthermore, the measurements of inhibitors in urine could be performed before the chemical composition was determined.

Laxative abuse as a cause for ammonium urate renal calculi

Nine women with laxative abuse and predominantly ammonium urate renal calculi underwent metabolic studies to identify common chemical abnormalities and determine pathophysiology. The 24-hour urine studies demonstrated marked decreases in volume (902 cm.3), sodium (28 mEq.), citrate (116 mg.) and potassium (21 mEq.). A significant elevation in ammonium urate supersaturation was found compared to control subjects when studied by the computer model EQUIL 2. Of the patients 7 had 1 or more urine specimens positive for phenolphthalein. Gastrointestinal loss of fluid and electrolytes allowed for chronic extracellular volume depletion. Intracellular acidosis was present as judged by low urinary citrate and potassium. The fact that the ion product for ammonium urate is increased significantly compared to controls reflects the stated pathophysiological changes. Laxative abuse should be suspected whenever a woman has an ammonium urate renal calculus in sterile urine.