Diet, vitamin D and vertebral mineral density in hypercalciuric calcium stone formers

Bone disease in primary hypercalciuria

Primary hypercalciuria (PH) is very often accompanied by some degree of bone demineralization. The most frequent clinical condition in which this association has been observed is calcium nephrolithiasis. In patients affected by this disorder, bone density is very frequently low, and increased susceptibility to fragility fractures is reported. The very poor definition of this bone disease from a histomorphometric point of view is a crucial aspect. At present, the most common finding seems to be a low bone turnover condition. Many factors are involved in the complex relationships between bone loss and PH. Since bone loss was mainly reported in patients with fasting hypercalciuria, a primary alteration in bone metabolism was proposed as a cause of both hypercalciuria and bone demineralization. This hypothesis was strengthened by the observation that some bone resorbing-cytokines, such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor nechrosis factor-alpha (TNF-alpha), are high in hypercalciuric patients. An excessive response to the acid load induced by dietary protein intake seems to be an additional factor explaining a primitive alteration of bone. The intestine plays a major role in the clinical course of bone disease in PH. Patients with absorptive hypercalciuria less frequently show bone disease, and a reduction in dietary calcium greatly increases the probability of bone loss in PH subjects. It has recently been reported that greater bone loss is associated with a larger increase in intestinal calcium absorption in PH patients. Considering the absence of parathyroid hormone (PTH) alterations, it was proposed that this is not a compensatory phenomenon, but probably the marker of disturbed cell calcium transport, involving both intestinal and bone tissues. While renal hypercalciuria is rather uncommon, the kidney still seems to play a role in the pathogenesis of bone loss in PH patients, possibly via the effect of mild-to-moderate urinary phosphate loss with secondary hypophosphatemia. In conclusion, bone loss is very common in PH patients. Even if most of the factors involved in this process have been identified, many aspects of this intriguing clinical condition remain to be elucidated.

Bone mineral content in calcium renal stone formers

Idiopathic renal calcium stone disease often presents with reduced bone mineral content. Investigations using non-invasive methods for the measurement of bone mineral content (single and dual-photon absorptiometry, dual-energy x-ray absorptiometry, quantitative computed tomodensitometry) show a slight decrease in skeletal mineral content of idiopathic renal stone formers (RSFs). The alterations in bone mineral content in RSFs have different explanations: prostaglandin-mediated bone resorption, subtle metabolic acidosis and 1-25 vitamin D disorders. Bone mineral content is worsened by insufficient dietary calcium leading to a negative calcium balance.

Urinary calcium is a determinant of bone mineral density in elderly men participating in the InCHIANTI study

BACKGROUND

It is generally acknowledged that calcium excretion is a determinant of bone mineral density. Since data confirming this hypothesis are not conclusive, the present study evaluates the relationship between calcium excretion and volumetric bone mineral density (vBMD) in a sample of general population mostly composed of elderly subjects.

METHODS

This relationship was studied in 595 subjects in good health (M/F 302/293), selected from the InCHIANTI population, an epidemiologic survey on aging in Tuscany (Italy). Of these subjects, 432 (72.6%) were 65 years old or older. Trabecular and cortical apparent vBMDs were measured by peripheral quantitative computed tomography at right tibia and standardized to age and body mass index (BMI) in each gender (z-score).

RESULTS

Men in the highest tertile of calcium excretion had significantly lower trabecular vBMD, and were more likely to have a trabecular z-score of -1 or less. These results were confirmed in men older than 64 years, but not in women and younger men. Sodium excretion and 25-hydroxycolecalciferol (25(OH)D) were greater in men and women in the highest tertile. No differences among tertiles were observed for cortical vBMD, circulating levels of interleukin-1beta and interleukin-6, and intake of principal nutrients and calcium. The lower levels of vBMD z-score were confirmed in men in the highest tertile of calcium excretion, standardized to creatinine clearance, sodium excretion, plasma calcium, and logarithm of circulating 25(OH)D, and resulted to be associated with calcium excretion at multiple regression analysis in men.

CONCLUSION

High calcium excretion is associated with a decreased trabecular BMD in elderly men and may predispose men to trabecular bone loss.

Analysis of bone mineral density in urolithiasis patients

BACKGROUND

The association between hypercalciuria and bone mineral density (BMD) has been already recognized. The aim of the present study is to relate BMD to age and sex and to evaluate the calcium metabolism and hypercalciuria-defined dietary or non-dietary category in patients with urolithiasis.

METHODS

The BMI of the L2-L4 lumbar vertebrae was measured in 310 renal stone patients (191 men and 119 women). Percent age matched score (%AMS), which is the percent ratio of measured BMD to the mean BMD of age-matched control subjects, was utilized for the appraisal of BMD. Low BMD groups were defined by lower than 90% of %AMS.

RESULTS

Low BMD was observed in 27.7% of urinary stone patients, which was not a significant difference to that of control subjects (23.5%) who were measured in the health examination. In male patients with urolithiasis, the frequency of patients in whom BMD had been apt to decrease since youth was high, but there was not a proven significant difference among the three age groups (20-39 years old, 40-59 years old and 60 years old or older). In contrast, for female stone patients, the frequency of low BMD markedly increased in patients aged 40 years or older, when menopause occurs. Furthermore, in female stone patients with hypercalciuria, the frequency of reduced BMD reached more than 40%. When the cause was non-dietary hypercalciuria (classified mainly on the daily amount of urinary calcium excretion after ingestion of calculus test diet), the frequency of reduced BMD reached 65% (P < 0.01).

CONCLUSIONS

In case female stone patients with non-dietary hypercalciuria become menopausal, not only the risk of recurrent lithiasis increases, but the possibility of developing osteopenia in the future also increases. Appropriate treatments for prophylactic effects on urolithiasis or osteopenia should be considered, as judged from BMD, diet, sex, urinary calcium excretion and other factors synthetically.

Long-term potassium citrate therapy and bone mineral density in idiopathic calcium stone formers

Several authors have described an association between idiopathic calcium (Ca) stone disease and bone mass reduction. Hypocitraturia is a frequent feature of urolithiasis, and alkaline citrate has been recommended as one of the choice treatments in this disease. Some evidence exists as to the positive effect of potassium (K) citrate therapy on bone mass. The aim of this work was the longitudinal evaluation of bone mineral density (BMD) changes in a group of Ca oxalate stone formers treated with K citrate for two years. Enrolled patients were 120; 109 subjects completed the study (51 males and 58 females). A metabolic study and distal radius BMD measurements were conducted both at baseline (BAS) and at the end of the study (END). BMD (0.451 +/- 0.081 vs 0.490 +/- 0.080 g/cm2), T-score (-1.43 +/- 1.02 vs -0.90 +/- 1.04), net gastrointestinal alkali absorption (40.37 +/- 50.57 vs 61.26 +/- 42.26 mEq/day), urinary citrate (2.53 +/- 1.15 vs 3.10 +/- 1.44 mmol/day) and K (58.93 +/- 22.28 vs 65.45 +/- 23.97 mmol/day) excretion significantly increased from BAS to END. Urinary Ca excretion remained unchanged from BAS to END (5.16 +/- 2.74 vs 5.57 +/- 2.85 mmol/ day). Our results indicate that long-term treatment with K citrate increases forearm BMD in idiopathic Ca stone formers. It seems probable that the alkali load provided by this drug reduces bone resorption by a buffering of the endogenous acid production. K citrate appears to be a further therapeutic opportunity for the management of osteoporosis in Ca stone formers.

Primary hyperparathyroidism and neuropsychiatric alterations in a nonagenarian woman

Whether elderly patients with asymptomatic or minimally symptomatic primary hyperparathyroidism (PHPT) should be treated or not is still under debate. Several literature reports have shown improvements in terms of bone density and physical and mental well-being after surgical resolution of PHPT. Here, we present the case of a 93-year-old hypertensive woman, who had suffered for one year from cognitive impairment, accompanied during the last month by behavioral alterations (and polyuria and polydipsia), which resulted in sopor leading to hospitalization. A CT brain scan evidenced cortical atrophy and cerebrovascular disease, and biochemical analyses were remarkable for hypercalcemia (11.4-12.6 mg/dL, corrected for albumin levels) associated with increased parathormone levels (95.4-100.6 pg/mL). A diagnosis of PHPT was established. Densitometry evaluation of radius showed osteopenia. Withdrawal of psycho-therapy drugs and thiazidic, together with i.v. saline hydration and loop diuretics, significantly improved the patient's mental state and resolved behavioral alterations. As the patient and her relatives refused the surgical option, and the clinical situation improved after medical normalization of calcium levels, PHPT was managed conservatively, and calcium levels were maintained within the normal range through i.v. administration of zoledronate at 8-week intervals. Our case highlights the importance of considering hypercalcemia as the cause of onset of behavioral alterations and worsening of mental condition in elderly patients with cognitive decline. Therapy with bisphosphonates in patients with PHPT who are unfit for or refuse surgery seems advisable, but needs further study.

Idiopathic hypercalciuria in children--how valid are the existing diagnostic criteria?

Idiopathic hypercalciuria is a common metabolic abnormality in children of all ages. There is evidence of an association of idiopathic hypercalciuria with nephrolithiasis, hematuria, and osteoporosis. However, much of this evidence is anecdotal and the precise role of hypercalciuria in the pathogenesis of these conditions is far from clear. Furthermore, the precise definition of idiopathic hypercalciuria has not yet been established. The methodologies for quantitating urinary calcium excretion have also not been standardized, adding another potential confounding factor to the accurate interpretation of urinary calcium excretion. Long-term studies on the natural history of unselected children with idiopathic hypercalciuria are needed to establish the true clinical significance of this condition. The focus of this review is to critically evaluate the methods currently being used to measure urinary calcium excretion in children and to assess the validity of existing criteria for diagnosing idiopathic hypercalciuria.

Intestinal calcium absorption is associated with bone mass in stone-forming women with idiopathic hypercalciuria

BACKGROUND

Patients with idiopathic hypercalciuria are predisposed to osteoporosis despite their high enteral calcium absorption. Conversely, low calcium absorption has been reported in patients with osteoporosis. Because bone loss occurs earlier in women, this work explores the relationship between bone mineral density (BMD) and calcium absorption in premenopausal and postmenopausal hypercalciuric stone-forming women.

METHODS

BMD and intestinal calcium absorption were compared in 64 hypercalciuric and 42 normocalciuric calcium stone-forming women. Calcium absorption was assessed by using strontium as a surrogate marker for calcium. Strontium was administered to patients as an oral load, then measured in blood to calculate absorption after 60 minutes. Femoral and lumbar-spine BMD were measured by dual-energy x-ray absorptiometry.

RESULTS

Strontium absorption was significantly increased in hypercalciuric stone formers, whereas BMD z score was decreased in hypercalciuric patients at the lumbar spine, but not the femur. The increase in strontium absorption was detected in both postmenopausal (n = 29) and premenopausal (n = 35) hypercalciuric patients. The decrease in lumbar-spine BMD was confirmed in postmenopausal, but not premenopausal, hypercalciuric patients. Strontium absorption was greater in hypercalciuric patients with a lumbar-spine BMD z score of -2 or less (n = 10) than in those with a score greater than -2 (n = 54). Multiple stepwise regression showed that lumbar-spine BMD was related negatively to intestinal strontium absorption and age in hypercalciuric patients.

CONCLUSION

Results of the strontium absorption test suggest that the increase in calcium absorption is associated with a decrease in lumbar-spine BMD in hypercalciuric stone-forming women. Hypercalciuric stone-forming women with high calcium intestinal absorption denote a group of patients predisposed to loss of bone mass.

Bone mineral density and urine calcium excretion among subjects with and without nephrolithiasis

BACKGROUND

Bone mineral density (BMD) is reduced among patients with idiopathic hypercalciuria (IH) and nephrolithiasis. To disentangle effects of diet, stone formation, and physiology upon BMD, we studied vertebral and femoral neck BMD among relatives of hypercalciuric stone formers, and contrasted those with to those without stones.

METHODS

Among 59 subjects from 11 families, vertebral and femoral neck BMD, diet calcium intake, urine excretions of calcium, sodium, ammonium, titratable acid, sulfate, urea nitrogen, and serum levels of calcitriol and markers of bone turnover were studied.

RESULTS

Stone formers (SF) consumed less calcium than non-stone formers (NSF). Spine and femoral neck BMD z-scores varied inversely with urine calcium loss and urine ammonium excretion among SF but not NSF. No correlations of BMD z-score were found for bone markers, calcitriol, or any of the other measurements.

CONCLUSION

SF consumed less calcium, presumably to prevent more stones, and displayed a bone mineral responsiveness to calcium loss and ammonium excretion not present among NSF, who ate more calcium. Lowered calcium consumption in IH, perhaps in response to stone formation, alters bone responses in a direction that can predispose to mineral loss and eventual fracture.

Bone alterations in children with idiopathic hypercalciuria at the time of diagnosis

Some children with idiopathic hypercalciuria (IH) develop bone alterations at some stage of the disease. The aims of this study were to evaluate bone mass in 88 children with IH (G1) at the time of diagnosis and to compare the findings with data for a control group of 29 normal children (G2). Kidney and bone metabolism markers were measured in both groups, and bone densitometry was performed. Serum alkaline phosphatase, intact parathyroid hormone, urinary calcium and uric acid were significantly higher in G1, whereas urinary volume and urinary citrate excretion were lower. The following densitometric parameters were significantly lower in G1: (1) lumbar spine (L(2)-L(4)) bone mineral density (BMD), bone mineral content (BMC), BMC corrected for height and for width of the vertebra, volumetric BMD (BMDvol), and Z score; (2) whole-body BMD; (3) femoral neck BMD. Lumbar spine BMDvol was reduced (osteopenia) in 35% of the patients compared with G2. N telopeptide, a urinary marker of bone resorption, was significantly higher in G1 than in G2, and was negatively correlated with lumbar spine BMD and BMDvol. Children with urinary lithiasis or idiopathic hyperuricosuria associated with IH showed no significant differences in bone metabolism compared with children without these associations. We conclude that (1) there is an altered bone metabolism in IH, with osteopenia already present at diagnosis in 35% of the patients; (2) N telopeptide is one of the most useful markers of bone alterations in IH, especially at an early stage of the disease; (3) investigation of bone metabolism is necessary in IH to prevent future serious consequences such as osteoporosis and bone fractures.

Bone alterations in patients with idiopathic hypercalciuria and calcium nephrolithiasis

OBJECTIVES

To verify whether alterations in bone density and turnover in patients with calcium nephrolithiasis and hypercalciuria are observable in various subgroups of patients divided according to the pathogenesis of the hypercalciuria.

METHODS

Seventy patients with calcium nephrolithiasis and idiopathic hypercalciuria, 19 to 64 years old, were assessed for spine and femur mineral metabolism and bone density using a Dexa evaluation system. After a low calcium diet, the subjects were classified into two groups: fasting hypercalciuria (FH, 39 patients) and absorptive hypercalciuria (AH, 31 patients).

RESULTS

Only in the patients with FH was the lumbar spine bone density lower than in the controls (P <0.001). Also, only the patients with FH had higher bone alkaline phosphatase and urinary hydroxyproline levels than the control group (P <0.005 and <0.015, respectively). The blood pH levels were lower, even though within the normal range, in the hypercalciuric patients than in the controls (P <0.01). There was a negative correlation between the urinary hydroxyproline level and lumbar spine and femoral neck density in patients with FH (P <0.001 and <0.005, respectively), and the blood pH correlated positively with the lumbar spine bone density.

CONCLUSIONS

Altered bone metabolism and overall bone loss were found only in the patients with FH. Overloading of acid valences, perhaps of dietary origin, could be the pathogenic factor responsible.

Identification and characterization of a gene with base substitutions associated with the absorptive hypercalciuria phenotype and low spinal bone density

Absorptive hypercalciuria (AH) is a kidney stone-forming condition frequently complicated by bone loss. Previously, we mapped the locus for an inherited form of AH to chromosome 1q23.3-q24. We have sequenced a putative gene (subsequently shown by others to be homologous with the rat soluble adenylate cyclase gene) in this region in 12 unrelated Caucasian AH patients. Eighteen base substitutions were identified in the soluble adenylate cyclase human homolog gene. All sequence variations were further evaluated in 3-68 additional unrelated AH patients and 19-132 normal subjects, and 1 additional base substitution was identified. Six of the identified sequence variations occurred with increased frequency in the AH population and tracked with the AH phenotype in AH families. Calculated odds ratios showed that the occurrence of any 4 of these individual base substitutions was associated with a 2.2- to 3.5-fold increase in estimated risk for AH (P < 0.02). In addition, 1 or more base changes was associated with a lower L2-L4 vertebral bone density. Sequence analysis of 3 other genes within the AH linkage interval showed no difference in the distribution of sequence variations between AH and normal populations. This is the first description of a specific gene defect associated with AH.

Hypercalciuria

Hypercalciuria is a biological syndrome defined as excretion in the urine of more than 0.1 mmol/kg/24 hours of calcium in the absence of dietary manipulation. A number of endocrine, renal, and bone diseases can cause hypercalciuria. Urinary calcium excretion is substantially influenced by dietary intakes of calcium, sodium, protein, carbohydrates, alcohol, and potassium: a poorly balanced diet can result in hypercalciuria. Recently, there has been a burst of interest in the molecular underpinnings of rare nephrolithiasis syndromes, which have been shown to result from mutations in the CLCN5 chloride channel gene. Mutations affecting the calcium-sensing receptor (CaSR) have been identified in other forms of hypercalciuria. Idiopathic hypercalciuria is defined as hypercalciuria that persists after correction of dietary imbalances and has no detectable cause. The classification suggested by Pak ("absorptive" hypercalciuria [with three types] and "renal" hypercalciuria) is controversial and of little assistance in clinical practice. Three mechanisms can be incriminated in idiopathic hypercalciuria: increased intestinal absorption of calcium, defective reabsorption of calcium by the renal tubule, and increased bone resorption. Overexpression of the vitamin D receptor (VDR) and deficiencies in renal tubule enzymes may also be involved. Bone mineral density is moderately decreased in idiopathic hypercalciuria, particularly in the renal type. The risk of vertebral fracture seems increased, however. Overproduction of calcitriol and cytokines that stimulate bone resorption have been incriminated in the bone loss. Treatment of the cause is essential in secondary hypercalciuria (dietary advice, treatment of an underlying disease, etc.). A diet low in sodium and meat and containing no more than 800 mg of calcium per day is advocated in idiopathic hypercalciuria. Hydrochlorothiazide therapy is warranted in patients with osteopenia and an inadequate response to dietary therapy.

Plasma phospholipid arachidonic acid content and calcium metabolism in idiopathic calcium nephrolithiasis

BACKGROUND

Reports of an increase in plasma and erythrocyte phospholipid arachidonic acid content and in urinary prostaglandin E2 (PGE2) excretion in patients with idiopathic calcium nephrolithiasis suggested their crucial role in the pathogenesis of hypercalciuria, a well-known risk factor for lithogenesis.

METHODS

To confirm this hypothesis, 15 healthy subjects and 20 nephrolithiasis patients were evaluated for plasma phospholipid polyunsaturated fatty acid content and PGE2 concentration, serum parathyroid hormone, 25 hydroxyvitamin D3, 1, 25-dihydroxyvitamin D3, and bone-specific alkaline phosphatase levels, as well as urinary excretion of calcium, biochemical markers of bone resorption (hydroxyproline and crossLaps), and intestinal calcium absorption. Furthermore, the effect of a 30-day fish-oil diet supplementation on the previously mentioned parameters was investigated in the patients.

RESULTS

At baseline, patients compared with controls showed higher levels of plasma phospholipid arachidonic acid content (P = 0.002), PGE2 (P = 0.0004), serum 25-vitamin D3 (P = 0.001), and 1,25-vitamin D3 (P = 0.001), urinary excretion of calcium (P = 0.001), hydroxyproline (P = 0.007), and crossLaps (P = 0.019), as well as intestinal calcium absorption (P = 0.03 at 60 min). Fish oil supplementation induced a reduction in the plasma phospholipid arachidonic acid level (P < 0.0001), and except for serum concentrations of 25-vitamin D3, normalized baseline blood and urinary parameters, including intestinal calcium absorption. A close correlation between plasma PGE2 and serum 1,25-vitamin D3 (P = 0.004) and between phospholipid arachidonic acid and intestinal calcium absorption (P = 0.0002) and calciuria (P = 0.007) was observed, as well as between urine excretion of crossLaps and hydroxyproline (P < 0.0001), crossLaps and calcium (P < 0.0001), and hydroxyproline and calcium (P < 0.0001).

CONCLUSIONS

These findings indicate that the phospholipid arachidonic acid content anomaly could represent the primary event responsible for the mosaic of metabolic and clinical alterations that are distinctive features of renal stone formers, and suggest that a common pathogenetic mechanism might account for the several forms of hypercalciuria detected in idiopathic calcium nephrolithiasis.

Role of diet in the therapy of urolithiasis

The data reviewed in this paper indicate that there is compelling direct and indirect evidence that certain dietary modifications can limit the risk for stone formation. Fluid therapy should be a front-line approach for all stone formers, because it is safe, cheap, and effective. Restricting sodium and animal-protein consumption produces changes in the urinary environment that should benefit the majority of stone formers, including a decrease in calcium and increase in citrate excretion. Minimizing the intake of processed goods limits sodium gluttony. These dietary modifications also reduce cardiovascular risks. Indiscriminant calcium restriction should be avoided, because it could accelerate stone formation and violate skeletal integrity. Oxalate restriction should be considered for calcium oxalate stone formers, especially those with hyperoxaluria. Specific recommendations for modifying the consumption of other nutrients cannot be made at this time because of the limited available information about the resultant effects. The aforementioned goals can be achieved within the context of a nutritionally balanced diet providing adequate sources of fruits and vegetables. There is a definite need for better designed studies of the nutritional effects on stone disease. This would promote a better understanding of the interplay between the genetic and environmental components of this disorder.

Should dietary calcium and protein be restricted in patients with nephrolithiasis?

Renal stone disease is a painful condition that affects 1-20% of the general population. Therapy aimed at decreasing the incidence of recurrent stones includes dietary advice. Dietary considerations include intake of both calcium and protein. Calcium restriction in stone formers is not recommended because it can have adverse effects on bone and the incidence of stones. Although a high-protein diet can elevate urinary calcium, uric acid, and sulfate and decrease urinary citrate, which may alter the propensity to form stones, restriction of protein to less than the current RDA for the management of stone disease can not be recommended at this time.

Dietary manipulation of delta-6-desaturase modifies phospholipid arachidonic acid levels and the urinary excretion of calcium and oxalate in the rat: insight in calcium lithogenesis

An anomalous n-6 polyunsaturated fatty acid composition in plasma and erythrocyte membrane phospholipids, namely increased levels of arachidonic acid (AA), has been reported in calcium nephrolithiasis and has been proposed to play an important role in its pathogenesis. To confirm this, in rats we modified phospholipid AA levels by dietary manipulation of the delta-6-desaturase, the rate-limiting enzyme of the fatty acid biosynthetic pathway, and evaluated the effect on cellular and renal functions predisposing to lithogenesis. Increased AA levels led to conditions at risk for nephrolithiasis: higher oxalate flux and lower sodium cotransport in erythrocytes and a rise in urinary prostaglandin E2, calcium, sodium, and oxalate levels; reduced AA levels reversed these changes. In vitro, in human erythrocytes the incorporation of exogenous AA into membranes increased band 3 protein phosphorylation directly activating the Ser/Thr protein kinase CK1 and induced a parallel raise in band 3-mediated oxalate transport. These findings demonstrate the pivotal role of phospholipid AA in modulating erythrocyte and renal transport of calcium and oxalate.

Serum calcitriol and dietary protein intake in idiopathic calcium stone patients

In kidney stone patients, high protein intake and calcitriol overproduction are factors leading to hypercalciuria, but there are conflicting reports on the effects of dietary protein on calcitriol production. To investigate the relationships between serum calcitriol, dietary protein intake, and urinary calcium excretion, 33 male idiopathic calcium stone formers (aged 20-60 years), with normal renal function and on unrestricted diet, have been studied. Dietary protein intake was estimated by the protein catabolic rate determination. Abnormally elevated calcitriol levels were found in 16 patients (48.5%) who had similar levels of serum intact parathyroid hormone and phosphate, creatinine clearance, and calcium and phosphate urinary excretion, but lower protein catabolic rate (82+/-16 vs. 97+/-20 g/day, P<0.05) than the patients with normal calcitriol levels. The calcitriol to intact parathyroid hormone ratio was higher in hypercalciuric than in normocalciuric patients (2.4+/-1.1 vs. 1.6+/-0.8, P<0.05). Calcitriol was positively correlated with plasma calcium (r=0.41, P<0.01) and inversely with protein catabolic rate (r=-0.42, P<0.01). Protein catabolic rate was positively correlated with creatinine clearance (r=0.69, P<0.001) and urinary phosphate excretion (r=0.72, P<0.001). No relationship was observed between calcitriol and creatinine clearance. These results confirm the calcitriol overproduction in calcium stone disease and that the high calcitriol to intact parathyroid hormone ratio is the main feature associated with hypercalciuria. Calcitriol serum levels appear to be unrelated to creatinine clearance, whereas there is an inverse relationship with protein catabolic rate. This suggests that low rather than high dietary protein intake may favor the increase of calcitriol synthesis in male calcium stone formers with normal renal function.

Suggestive evidence for a susceptibility gene near the vitamin D receptor locus in idiopathic calcium stone formation

Calcium is the principal crystalline constituent in up to 80% of kidney stones. Epidemiologic studies have suggested that genetic predisposition plays a major role in the etiology of this condition. This study evaluates by a candidate-gene approach whether the vitamin D receptor (VDR) locus on chromosome 12q12-14 is implicated in idiopathic hypercalciuria and calcium nephrolithiasis in a cohort of 47 French Canadian pedigrees. These comprised 54 sibships with a total of 303 pairs of siblings concordant for > or =1 stone episode. Evidence is provided for linkage to nephrolithiasis with microsatellite marker D12S339 (near the VDR locus, P = 0.01), as well as with flanking markers (D12S1663: P = 0.03 and D12S368: P = 0.01). Inclusion of unaffected sibs in the analyses also supported evidence for linkage. Quantitative trait linkage analysis of urinary calcium excretion yielded linkage to some, but not all, markers. This appears to be the first study to suggest linkage for idiopathic calcium stone formation.

Acute effects of moderate dietary protein restriction in patients with idiopathic hypercalciuria and calcium nephrolithiasis

BACKGROUND

High dietary protein intake is a potential risk factor for nephrolithiasis because of its capacity to increase urinary calcium and to facilitate lithogenesis through many other mechanisms.

OBJECTIVE

Our aim was to verify the effects of moderate protein restriction in hypercalciuric patients.

DESIGN

We studied 18 patients (10 men and 8 women aged 45.6+/-12.3 y) with idiopathic hypercalciuria and renal calculi. Before and after 15 d of a diet with 0.8 g protein x kg(-1) x d(-1) and 955 mg Ca, all patients were evaluated for the main serum and urinary measures of calcium metabolism as well as for urinary uric acid, oxalate, citrate, and prostaglandin E2.

RESULTS

Urinary excretion of urea fell after the diet (P < 0.001). Urinary calcium (P < 0.001), uric acid (P < 0.005), oxalate (P < 0.01), and hydroxyproline (P < 0.01) decreased after protein restriction, whereas urinary citrate increased (P < 0.025). Blood pH increased after the hypoproteic diet (P < 0.05). 1,25-Dihydroxycholecalciferol (calcitriol) concentration fell significantly (P < 0.025) and parathyroid hormone increased (P < 0.001). Creatinine clearance tended to decrease (106.4+/-4.8 compared with 97.5+/-5.7 mL/min) after the diet. The decrease in urinary uric acid after the diet correlated with calcitriol concentration (r = 0.57, P < 0.05) and the decrease in urinary urea correlated positively with that in hydroxyproline excretion (r = 0.58, P < 0.01).

CONCLUSIONS

In hypercalciuric patients, moderate protein restriction decreases calcium excretion, mainly through a reduction in bone resorption and renal calcium loss; both are likely due to a decreased exogenous acid load. Moreover, dietary protein restriction ameliorates the entire lithogenic profile in these patients.

Alendronate decreases urine calcium and supersaturation in genetic hypercalciuric rats

BACKGROUND

The mechanism of excess urine calcium excretion in human idiopathic hypercalciuria (IH) has not been determined but may be secondary to enhanced intestinal calcium absorption, decreased renal calcium reabsorption, and/or enhanced bone demineralization. We have developed a strain of genetic hypercalciuric stone-forming (GHS) rats as an animal model of human IH. When these GHS rats are placed on a low-calcium diet (LCD), urinary calcium (UCa) excretion exceeds dietary calcium intake, suggesting that bone may contribute to the excess UCa excretion. We used the GHS rats to test the hypothesis that bone contributes to the persistent IH when they are fed an LCD by determining if alendronate (Aln), which inhibits bone resorption, would decrease UCa excretion.

METHODS

GHS rats (N = 16) and the parent strain (Ctl, N = 16) were fed 13 g/day of a normal (1.2%) calcium diet (NCD) for seven days and were then switched to a LCD (0. 02%) for seven days. Ctl and GHS rats in each group were then continued on LCD for an additional seven days, with or without injection of Aln (50 micrograms/kg/24 hrs). UCa excretion was measured daily during the last five days of each seven-day period. To determine the effects of Aln on urine supersaturation, the experiment was repeated. All relevant ions were measured, and supersaturation with respect to calcium oxalate and calcium hydrogen phosphate was determined at the end of each period.

RESULTS

UCa was greater in GHS than in Ctl on NCD (7.4 +/- 0.5 mg/24 hrs vs. 1.2 +/- 0.1, GHS vs. Ctl, P < 0.01) and on LCD (3.9 +/- 0.2 mg/24 hrs vs. 0. 7 +/- 0.1, GHS vs. Ctl, P < 0.01). LCD provides 2.6 mg of calcium/24 hrs, indicating that GHS rats are excreting more calcium than they are consuming. On LCD, Aln caused a significant decrease in UCa in GHS rats and brought GHS UCa well below calcium intake. Aln caused a marked decrease in calcium oxalate and calcium hydrogen phosphate supersaturation.

CONCLUSION

Thus, on a LCD, there is a significant contribution of bone calcium to the increased UCa in this model of IH. Aln is effective in decreasing both UCa and supersaturation. The Aln-induced decrease in urine supersaturation should be beneficial in preventing stone formation in humans, if these results, observed in a short-term study using the hypercalciuric stone-forming rat can be confirmed in longer term human studies.

Stones and bones: bone resorption and metabolism in stoneformers

Abnormalities of bone metabolism and osteopenia (which may be progressive) are features of idiopathic calcium stone disease. This abnormal bone metabolism may be mediated by increased levels of, or responsiveness to, calcitriol or cytokines, including interleukin-1. Bone resorption may be reduced experimentally with bisphosphonates, but for clinical management an appropriate adjustment of dietary calcium intake may be the method of choice to ameliorate bone loss.

Pathogenesis of idiopathic calcium nephrolithiasis: update 1997

Idiopathic calcium nephrolithiasis (ICN) is a frequent disease in Western countries. The physicochemical theory of lithogenesis, which explains stone formation by the precipitation, growth, and crystalline aggregation of lithogenic salts in the urine, has contributed greatly to the understanding of the pathogenesis of calcium urolithiasis. However, several aspects are still unexplained; the co-existence of familial occurrence, primary tubular dysfunctions with ICN, and anomalies in the systemic handling of oxalate and calcium led to the development of a cellular hypothesis of ICN. A number of cellular defects in the handling of ions has been reported that involves both anion and cation transport. These anomalies are probably the expression of a still unknown cellular defect in idiopathic calcium stone formers. We suggested that an anomaly in the cell membrane composition might be responsible for the complex array of cell ion flux abnormalities observed in ICN. Recently, a disorder in the n-6 polyunsaturated fatty acid series has been described; it is characterized by a lower linoleic acid content and a higher arachidonic acid concentration in both plasma and erythrocyte membrane phospholipids of renal calcium stone patients. This anomaly could cause an increased activity of ion carriers; furthermore, it may lead to increased prostaglandin synthesis and to secondary phenomena at the kidney, skeletal, and intestinal level. As a consequence, critical conditions for lithogenesis in the kidney may ensue. The data suggest a common pathogenesis for hypercalciuria and hyperoxaluria. The systemic defect in the phospholipid arachidonic acid level may be both of dietary or genetic origin; experimental data suggest that the increase in delta-6 desaturase activity, the limiting enzyme in the metabolic pathway of polyunsaturated fatty acids, might be relevant to the pathogenesis of lipid abnormalities observed in nephrolithiasis and to the pathogenesis of ICN and its related problems (at the kidney, intestinal, and bone level).

Fracture risk among patients with urolithiasis: a population-based cohort study

In a population-based retrospective cohort study, 624 Rochester, Minnesota residents with an initial symptomatic episode of urolithiasis in 1950 to 1974 were followed for 11,909 person-years for subsequent age-related fractures. During this period of observation, the number of patients with a first vertebral fracture was over four times the number expected on the basis of vertebral fracture incidence rates in the general population of Rochester [standardized morbidity ratio (SMR), 4.3; 95% confidence interval, 3.4 to 5.3]. The risk of vertebral fracture was elevated among men as well as women, and was associated with increasing age and with the use of corticosteroids for more than six months. However, vertebral fracture risk was increased nearly fourfold (SMR 3.9; 95% confidence interval, 3.0 to 4.9) among the urolithiasis patients without such exposure, which suggests that corticosteroids do not completely account for the association with vertebral fractures. There was no increase in the risk of hip, pelvis, proximal humerus or distal forearm fractures in this cohort of patients, and their survival was not impaired. Additional studies are needed to define the pathophysiology of vertebral fractures among patients with urolithiasis.

Markers of bone turnover in patients with nephrolithiasis

A total of 19 patients with active nephrolithiasis, 14 patients with non-active nephrolithiasis and 17 healthy subjects were examined under standardized intake of calcium, phosphorus, purine and protein. In patients with both active and non-active renal stone disease the following abnormalities were found: elevated plasma levels of PTH and osteocalcin, increased activity of the bone isozyme of alkaline phosphatase, low plasma levels of phosphate and increased urinary excretion of calcium and oxalic acid. These abnormalities were more marked in patients with active than non-active nephrolithiasis. No correlation was found between plasma PTH levels and parameters of bone turnover as well as calciuria and oxaluria. Results presented in this paper suggest that (a) Smith's criteria of active renal stone disease are of minor pathogenetic and therapeutic value and (b) patients with active nephrolithiasis differ from non-active renal stone formers by more elevated oxaluria and markers of bone turnover and more marked abnormalities in calcium-phosphate metabolism related parameters.

Defective renal calcium reabsorption in genetic hypercalciuric rats

Idiopathic hypercalciuria is a frequent cause of calcium (Ca) containing kidney stones. We have previously shown that there is increased intestinal Ca absorption in selectively inbred genetic hypercalciuric stone forming (GHS) rats; however, excess Ca excretion persists when the rats are fed a low Ca diet indicating a defect in renal Ca reabsorption and/or increased bone resorption. To determine if GHS rats have a defect in renal Ca reabsorption we performed 14C-inulin clearance studies on parathyroidectomized female GHS and control (Ctl) rats. After three baseline collections, chlorothiazide (CTZ) or furosemide (FUR) was infused and three more collections were obtained. Both GFR and filtered load of Ca did not differ among the groups; however, fractional and absolute excretion (UcaV) of Ca was three times higher in GHS rats. The increased Ca excretion was not diminished by a low Ca diet. Urine flow rate nearly tripled in all rats after either FUR or CTZ. After CTZ, UcaV was decreased to a greater extent in GHS compared to Ctl rats. After FUR, UcaV was increased to a greater extent in Ctl rats compared to GHS rats. These data indicate that GHS rats have a defect in renal Ca reabsorption, in addition to increased intestinal Ca absorption. The effect of CTZ was greater, and that of FUR was smaller, in GHS compared with Ctl rats, suggesting that the defect in renal Ca handling might be at the level of the thick ascending limb.

Nonacidotic proximal tubulopathy transmitted as autosomal dominant trait

The family of a patient with a nonacidotic and hypercalciuric proximal tubulopathy was studied. The proband showed glycosuria, aminoaciduria, tubular proteinuria, renal hypophosphatemia, and urate tubular hyporeabsorption without bicarbonate loss. He also presented increased urine calcium excretion, plasma 1,25-dihydroxyvitamin D, and enteral calcium absorption. Clinical consequences of the tubulopathy were osteopenia and calcium kidney stones. Fifteen of the proband's relatives were studied; six of them had renal hypophosphatemia, 10 presented hypercalciuria, and three showed both hypercalciuria and hypophosphatemia. No other reabsorption defects were observed. High plasma levels of 1,25-dihydroxyvitamin D were found in 13 family members; their values correlated positively with calcium excretion and negatively with tubular phosphate reabsorption. None produced stones or had reduced mineral bone density. Hypophosphatemia and hypercalciuria occurred in the two generations studied; their transmission was independent of gender, and male-to-male transmission occurred for both defects. Our findings suggest that a genetic alteration of proximal tubular function could cause multiple reabsorption defects in the proband or renal phosphate leakage in the proband's relatives. The genotypic alteration causing the proximal dysfunctions may be monogenic, with an autosomal dominant pattern of inheritance and variable expressivity. Increased calcium excretion may be due to the proximal tubular alteration; alternatively, it may be the result of a genetic background predisposing to idiopathic hypercalciuria. Phosphate and calcium loss could stimulate 1,25-dihydroxyvitamin D synthesis in proximal tubular cells.

Increased sensitivity to 1,25(OH)2D3 in bone from genetic hypercalciuric rats

As a model of human hypercalciuria, we have selectively inbred genetic hypercalciuric stone-forming (GHS) Sprague-Dawley rats whose mean urine calcium excretion is eight to nine times greater than that of controls. A large component of this excess urine calcium excretion is secondary to increased intestinal calcium absorption, which is not due to an elevation in serum 1,25(OH)2D3, but appears to result from an increased number of intestinal 1,25(OH)2D3 receptors (VDR). When GHS rats are fed a low-calcium diet, the hypercalciuria is only partially decreased and urine calcium excretion exceeds intake, suggesting that an additional mechanism contributing to the hypercalciuria is enhanced bone demineralization. To determine if GHS rat bones are more sensitive to exogenous 1,25(OH)2D3, we cultured calvariae from neonatal (2- to 3-day-old) GHS and control rats with or without 1,25(OH)2D3 or parathyroid hormone (PTH) for 48 h at 37 degrees C. There was significant stimulation of calcium efflux from GHS calvariae at 1 and 10 nM 1,25(OH)2D3, whereas control calvariae showed no significant response to 1,25(OH)2D3 at any concentration tested. In contrast, PTH induced similar bone resorption in control and GHS calvariae. Immunoblot analysis demonstrated a fourfold increase in the level of VDR in GHS calvariae compared with control calvariae, similar to the increased intestinal receptors described previously. There was no comparable change in VDR RNA levels as measured by slot blot analysis, suggesting the altered regulation of the VDR occurs posttranscriptionally. That both bone and intestine display an increased amount of VDR suggests that this may be a systemic disorder in the GHS rat and that enhanced bone resorption may be responsible, in part, for the hypercalciuria in the GHS rat.

Hypercalciuria in renal glucosuria

Primary renal glucosuria is a benign condition in which serum glucose level is normal. Idiopathic hypercalciuria is defined as increased urinary calcium excretion of more than 4 mg/kg/day in normocalcemic individuals in whom all known causes of hypercalciuria have been excluded. In this paper, we report on a case who has both renal glucosuria and hypercalciuria.

Possible role of cytokines on the bone mineral loss in idiopathic hypercalciuria

Decreased bone mass has been reported in patients with idiopathic hypercalciuria. Previous studies, using bioassays, have suggested a role of interleukin-1 (IL-1), in the decreased bone mineral density (BMD) of fasting hypercalciuria. The present study was designed to determine which IL-1 fraction (alpha or beta) correlates with bone resorption and whether other known bone resorting cytokines like interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) may play a role in this process. Cytokines production was determined by quantitative and specific analysis, enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase polymerase chain reaction (RT-PCR). Dual-energy X-ray absorptiometry and cytokine production by unstimulated and lipopolysaccharide (LPS)-stimulated peripheral blood mononuclear cells (PBMCs) were determined in a group of 29 patients with recurrent nephrolithiasis (17 hypercalciurics and 12 normocalciurics), and 12 healthy controls. The hypercalciuric subjects showed lower vertebral BMD than the normocalciuric or normal controls. There was no difference in spinal or femoral BMD between absorptive or fasting hypercalciurics. A significant negative correlation existed between urinary calcium excretion and vertebral BMD (r = -0.55, P < 0.01). Basal IL-1 alpha production correlated with vertebral BMD (r = -0.45, P < 0.02). This correlation was not seen with IL-1 beta, IL-6 or TNF-alpha production. LPS-induced IL-6 and TNF-alpha production were enhanced in the hypercalciuric patients, when compared to normocalciurics or controls. Control and normocalciuric subjects showed minimal amounts of IL-1 alpha mRNA. In contrast, hypercalciuric patients showed a significant increase of spontaneous IL-1 alpha mRNA transcription. These results suggest that different cytokines could be involved in the bone resorption process observed in hypercalciuria.

Predictors of hip fractures in elderly men

To assess the influence on the risk of hip fractures in men of medical conditions associated with secondary osteoporosis or with an increased likelihood of falling, we conducted a population-based nested case-control study among the 232 Rochester, Minnesota, men with an initial hip fracture due to moderate trauma in 1965-1989 and an equal number of age-matched control men from the general population. Information on selected medical and surgical conditions and certain behavioral risk factors prior to fracture (or comparable index date for controls) was obtained from inpatient and outpatient medical records in the community that averaged over 36 years in duration. After adjusting for age, obesity, and inactivity, disorders linked with secondary osteoporosis were associated with a 2-fold increase in the risk of hip fracture in men (odds ratio [OR] 2.3; 95% confidence interval [CI] 1.3-4.3), while conditions linked with an increased risk of falling were associated with almost a 7-fold increase in risk (OR 6.9; 95% CI 3.3-14.8). These factors together appeared to account for about 72% of the hip fractures in men. Increased attention must be paid to these conditions which, in aggregate, are very common in elderly men and lead to a substantial increase in the risk of hip fracture with its devastating sequelae of death, disability and cost.

Low bone mass in idiopathic renal stone formers: magnitude and significance

To assess bone mineral density (BMD) in idiopathic calcium nephrolithiasis, dual-energy x-ray absorptiometry was performed at lumbar spine, upper femur (femoral neck, Ward's triangle, and total area), distal tibial diaphysis, and distal tibial epiphysis in 110 male idiopathic calcium stone formers (ICSF); 49 with and 61 without hypercalciuria on free-choice diet). Results were compared with those obtained in 234 healthy male controls, using (1) noncorrected BMD, (2) BMD corrected for age, height, and BMI, and (3) a skeletal score based on a tercile distribution of BMD values at following four sites: lumbar spine, Ward's triangle, tibial diaphysis, and tibial epiphysis. After correction, BMD--and therefore also skeletal score--tended to be lower in the stone formers than in controls at five of the six measurement sites, that is, lumbar spine, upper femur, Ward's triangle, tibial diaphysis, and tibial epiphysis, limit of significance being reached for the last two sites without difference between hypercalciuric (HCSF) and normocalciuric stone formers (NCSF). Estimated current daily calcium intake was significantly lower in patients (616 +/- 499 mg/24 h, mean +/- SEM) than in controls (773 +/- 532, p = 0.02). Of 17 patients who in the past had received a low-calcium diet for at least 1 year, 10 had a low skeletal score (4-6) whereas only 1 had a high score (10-12; p = 0.037). Of the 12 stone formers in the study with skeletal score 4 (i.e., the lowest), 8 had experienced in the past one or more fractures of any kind versus only 19 of the remaining 77 patients with skeletal score 5-12 (p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

An increasing number of calcium oxalate stone events worsens treatment outcome

Current practice recommends metabolic evaluation of patients who have formed multiple renal stones, but not those with one stone or temporally remote stones. This presumes that recentness and recurrence imply greater risk of new future stones. We hypothesize that number of stones reflects how long patients are permitted to form stones untreated, and that forming more stones, itself, raises risk of future stones despite treatment. Our report is a retrospective analysis of 371 male patients selected from a comprehensive clinical and laboratory data base containing 2,527 patients with nephrolithiasis. Before treatment, number of stone events rises with time of observation, and rate of stone event occurrence is constant or falls. During treatment, relapse is correlated with number of pretreatment stones. Life table analysis showed increasing relapse for patients grouped into those with one, two, and three or more stones. Even though number of stones seems controlled by the interval of observation before treatment, more stones predict higher relapse during treatment. Perhaps by leaving nuclei of crystals as residues, stones appear to promote new stones, and the practice of waiting while patients declare themselves multiple stone formers may not always be the best.

Reduced vertebral bone density in hypercalciuric nephrolithiasis

Dual-energy x-ray absorptiometry and single-photon absorptiometry were used to determine bone density at the lumbar spine and radial shaft in 62 patients with absorptive hypercalciuria, 27 patients with fasting hypercalciuria, and 31 nonhypercalciuric stone formers. Lumbar bone density was significantly lower in patients with absorptive (-10%) as well as in those with fasting hypercalciuria (-12%), with 74 and 92% of patients displaying values below the normal mean, whereas only 48% of the nonhypercalciuric stone formers had bone density values below the normal mean. In contrast, radial bone density was similar in all three groups of renal stone formers investigated. The comparison of urinary chemistry in patients with absorptive hypercalciuria and low normal bone density compared to those with high normal bone density showed a significantly increased 24 h urinary calcium excretion on random diet and a trend toward a higher 24 h urinary uric acid excretion and a higher body mass index in patients with low normal bone density. Moreover, among the patients with absorptive hypercalciuria we found a statistically significant correlation between the spinal bone density and the 24 h sodium and sulfate excretion and the urinary pH. These results gave evidence for an additional role of environmental factors (sodium and animal proteins) in the pathogenesis of bone loss in absorptive hypercalciuria. In conclusion, our data suggest an osteopenia of trabecular-rich bone tissues in patients with fasting and absorptive hypercalciurias.