Medical management of nephrolithiasis in Dallas: update 1987

Glycine suppresses kidney calcium oxalate crystal depositions via regulating urinary excretions of oxalate and citrate

An abnormal urine composition is a key reason for kidney stone formation, but little is known about the roles of small metabolites in the urine during kidney stone formation. Here, we found urine glycine in patients with kidney calcium oxalate (CaOx) stone was significantly lower than that in healthy people via 1 H NMR spectra detection, and investigated the role and underlying mechanism of glycine in the regulation of CaOx stone formation. Our results showed that glycine could significantly attenuate ethylene glycol-induced CaOx crystal depositions in rat kidney via decreasing urine oxalate and increasing urine citrate. Mechanism studies revealed that glycine could decrease urine oxalate through downregulating Slc26a6 expression, whereas increase urine citrate via inhibiting Nadc1 expression. Moreover, glycine decreased the protein expression of both Slc26a6 and Nadc1 via increasing the expression of miRNA-411-3p, which directly bound to the 3'-untranslated regions of Slc26a6 and Nadc1 messenger RNAs, in vitro and in vivo. Together, our results revealed a novel role of glycine in the regulation of kidney CaOx crystal formation and provided a potential target for the treatment of kidney CaOx stone.

Risk of Hypertension among First-Time Symptomatic Kidney Stone Formers

BACKGROUND AND OBJECTIVES

Prior work has suggested a higher risk of hypertension in kidney stone formers but lacked disease validation and adjustment for potential confounders. Certain types of stone formers may also be at higher risk of hypertension.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In our study, incident symptomatic stone formers in Olmsted County from 2000 to 2011 were manually validated by chart review and age and sex matched to Olmsted County controls. We followed up patients through November 20, 2015. Hypertension was also validated by manual chart review, and the risk of hypertension in stone formers compared with controls was assessed both univariately and after adjusting for comorbidities. The risk of hypertension among different subtypes of stone formers was also evaluated.

RESULTS

Among 3023 coded stone formers from 2000 to 2011, a total of 1515 were validated and matched to 1515 controls (mean age was 45 years old, and 56% were men). After excluding those with baseline hypertension (20% of stone formers and 18% of controls), 154 stone formers and 110 controls developed hypertension. Median follow-up time was 7.8 years in stone formers and 9.6 years in controls. Stone formers were found to have a higher risk of hypertension compared with controls (hazard ratio, 1.50; 95% confidence interval, 1.18 to 1.92), even after adjusting for age, sex, body mass index, serum creatinine, CKD, diabetes, gout, coronary artery disease, dyslipidemia, tobacco use, and alcohol abuse (hazard ratio, 1.58; 95% confidence interval, 1.12 to 2.21). Results were similar after excluding patients who were ever on a thiazide diuretic (hazard ratio, 1.65; 95% confidence interval, 1.16 to 2.38). Stone composition, radiographic stone burden, number of subsequent stone events, and stone removal surgeries were not associated with hypertension (P>0.05 for all).

CONCLUSIONS

The risk of hypertension was higher after the first symptomatic kidney stone event. However, kidney stone severity, type, and treatment did not associate with hypertension.

Recent advances in the pathophysiology of nephrolithiasis

Over the past 10 years, major progress has been made in the pathogenesis of uric acid and calcium stones. These advances have led to our further understanding of a pathogenetic link between uric acid nephrolithiasis and the metabolic syndrome, the role of Oxalobacter formigenes in calcium oxalate stone formation, oxalate transport in Slc26a6-null mice, the potential pathogenetic role of Randall's plaque as a precursor for calcium oxalate nephrolithiasis, and the role of renal tubular crystal retention. With these advances, we may target the development of novel drugs including (1) insulin sensitizers; (2) probiotic therapy with O. formigenes, recombinant enzymes, or engineered bacteria; (3) treatments that involve the upregulation of intestinal luminal oxalate secretion by increasing anion transporter activity (Slc26a6), luminally active nonabsorbed agents, or oxalate binders; and (4) drugs that prevent the formation of Randall's plaque and/or renal tubular crystal adhesions.

Medical stone management: 35 years of advances

PURPOSE

The urological community has had a vital role in the author's 35 years of research on the medical management of urolithiasis. The goal of this article is to review the progress made from the perspective of collaborating urologists and urological journals in which the findings were reported.

MATERIALS AND METHODS

The author's work appeared in 94 articles in urological journals, including 63 in The Journal of Urology, and in 28 other journals with collaborating urologists. Progress on various aspects of medical management of stone disease was reviewed based on these articles.

RESULTS

Pathophysiological exploration was performed by elucidating metabolic-dietary etiologies of hypocitraturia, separating hypercalciuria into 3 types, and linking gouty diathesis (uric acid stones) with obesity and insulin resistance. Physicochemical consequences of hypocitraturia were delineated and semi-empirical methods were developed to assess calcium salt saturation. Potassium-rich fruit juices differed from potassium-poor fruit juices and excessive salt intake increased the stone forming risk. Vital to diagnostic separation was a comprehensive analysis of urine for stone risk factors. As an example of selective treatment, potassium citrate was shown to be useful for controlling uric acid stones by urinary alkalinization as well as calcareous stones by hypercitraturia.

CONCLUSIONS

During the last 35 years much progress has been made on the pathophysiology of stone formation, crystallization of stone forming salts, diagnostic separation and prevention of stone recurrence. The author's contribution in this effort would not have been possible without the active participation and support of the urological community.

Metabolic syndrome and uric acid nephrolithiasis

The metabolic syndrome describes a cluster of metabolic features that increases the risk for type 2 diabetes mellitus and cardiovascular disease. The prevalence of uric acid nephrolithiasis is higher among stone-forming patients with features of the metabolic syndrome such as obesity and/or type 2 diabetes mellitus. The major determinant in the development of idiopathic uric acid stones is an abnormally low urinary pH. The unduly urinary acidity in uric acid stone formers increasingly is recognized to be one of the features observed in the metabolic syndrome. Two major abnormalities have been implicated to explain this overly acidic urine: (1) increased net acid excretion, and (2) impaired buffering caused by defective urinary ammonium excretion, with the combination resulting in abnormally acidic urine. New information is emerging linking these defects to changes in insulin signaling in the kidney. This article reviews the epidemiologic and metabolic studies linking uric acid nephrolithiasis with the metabolic syndrome, and examines the potential mechanisms underlying the unduly acidic urine in these conditions.

Calcium metabolism in sarcoidosis and its clinical implications

OBJECTIVE

: To examine the clinical implications of disturbed calcium metabolism in sarcoidosis and how the pathophysiology affects management strategies.

METHODS

: The literature concerning calcium metabolism in sarcoidosis was reviewed.

RESULTS

: Dysregulated calcium metabolism is a well-recognized complication of sarcoidosis, resulting in hypercalcaemia (prevalence 5-10%), hypercalcuria (40-62%) and reduced bone density (40-55%). Extrarenal synthesis of calcitriol [1,25(OH)(2)D(3)] is central to the pathogenesis of abnormal calcium homeostasis, but alterations in parathyroid hormone (PTH) activity and the expression of PTH-related peptide have also been demonstrated. The immunosuppressive properties of calcitriol suggest that the raised levels seen in sarcoidosis could represent an adaptive response to the undefined antigen that causes sarcoidosis.

CONCLUSIONS

: The mechanisms of abnormal calcium metabolism in sarcoidosis need to be understood when treating hypercalcaemia, hypercalcuria and corticosteroid-induced osteoporosis. Studies are required to determine if the currently available therapies for osteoporosis are safe and effective in sarcoidosis.

Medical management of nephrolithiasis

About 1 out of 14 males and 1 out of 30 females are afflicted with kidney stones. In many of these patients, the disease is recurrent. Fortunately, our understanding of the disease and ability to treat renal stone disease has increased in the last decade. Parenteral NSAIDs have been shown to be as effective as narcotics in treating renal colic. Dietary and drug therapy after proper metabolic evaluation of patients with recurrent stones is beneficial in reducing the recurrence rate. New understanding of the role of diet and many organic inhibitors of crystallization in urine will further broaden the scope of management of this common disease.

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.

Variables related to urinary calcium excretion in young girls

The relations among dietary and calcium kinetic factors and 24-h urinary mineral excretion were evaluated in a group of 89 healthy girls (51 white and 38 black) aged 4.9-16.7 years. Nutrient intakes were calculated for each participant using a weighed intake of all food and beverage on the day of the 24-h urine collection study and two subsequent 24-h food records. A significant relation was noted between urinary calcium and sodium excretion (r = 0.55; p < 0.0001). No significant relations were found between urinary calcium and (a) calcium intake (r = 0.08), (b) protein intake (r = 0.14), or (c) phosphorus intake (r = 0.11). Urinary calcium was not significantly related to fractional calcium absorption (r = 0.03) or net calcium absorption (r = 0.11), but was significantly associated with the bone calcium deposition rate (r = 0.24; p < 0.03). Using a multiple regression model, both urinary sodium and the bone calcium deposition rate were independent predictors of urinary calcium excretion in this population (r = 0.57; p = 0.0001). A substantial number of the children in this population had urinary calcium excretion > 4 mg/kg/day (12%). The incidence of hypercalciuria differed between the racial groups and was markedly higher in the white than in the black children (17.6 vs. 5.3%). Over a range of usual calcium intakes, during the rapid-bone-growth period in childhood and early adolescence, urinary calcium appears relatively unaffected by calcium intake and is most strongly associated with urinary sodium levels.

Effect of medical management and residual fragments on recurrent stone formation following shock wave lithotripsy

Minimal emphasis has been placed on the clinical sequelae of residual stone fragments following shock wave lithotripsy. Moreover, there are no studies investigating the role of medical therapy on the course of stone disease in patients with residual fragments. In this retrospective, nonrandomized review, we evaluated 80 patients who had undergone shock wave lithotripsy at various institutions in Texas and were referred to our mineral metabolism clinic for metabolic evaluation and medical management of the stone disease. Of the patients 31 were determined to be stone-free following lithotripsy, while 49 had residual stone fragments. All patients were contacted an average of 43.2 months (range 9 to 79) following shock wave lithotripsy and the radiographs were reviewed. Patients were placed into 4 groups after shock wave lithotripsy: stone-free or residual fragments on or off medical therapy. In the stone-free group (19 patients), medical treatment produced a significant decrease in stone formation from a median of 0.67 to 0.0 stones per patient per year (p < 0.001). In 36 patients with residual fragments stone formation before shock wave lithotripsy was higher than in the stone-free group but there was also a significant decrease in the stone formation rate from a median of 2.47 to 0.00 stones per patient per year while on medical therapy (p < 0.001). Of the 12 stone-free patients who did not remain on medical therapy there was a slight decrease in the stone formation rate from a mean of 0.83 to 0.40 stones per patient per year, although this decrease was not significant (p = 0.07). In 13 patients with residual fragments not on medical treatment there was only a minimal decrease in the stone formation rate from a median of 1.33 to 0.77 stones per patient per year (p = 0.06). We also assessed the significance of so-called clinically insignificant residual fragments (smaller than 5 mm.) following shock wave lithotripsy in 26 of the 36 patients with residual fragments. More than half of the 26 patients with clinically insignificant fragments in the group that did not continue on medical therapy demonstrated significant stone growth during followup, suggesting that these fragments were not insignificant. Moreover, only 16% of the patients with fragments smaller than 5 mm. demonstrated an increase in fragment size while on medical therapy, again suggesting that appropriate medical treatment can decrease the risk of recurrent stone formation or growth (p < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones

BACKGROUND

A high dietary calcium intake is strongly suspected of increasing the risk of kidney stones. However, a high intake of calcium can reduce the urinary excretion of oxalate, which is thought to lower the risk. The concept that a higher dietary calcium intake increases the risk of kidney stones therefore requires examination.

METHODS

We conducted a prospective study of the relation between dietary calcium intake and the risk of symptomatic kidney stones in a cohort of 45,619 men, 40 to 75 years of age, who had no history of kidney stones. Dietary calcium was measured by means of a semiquantitative food-frequency questionnaire in 1986. During four years of follow-up, 505 cases of kidney stones were documented.

RESULTS

After adjustment for age, dietary calcium intake was inversely associated with the risk of kidney stones; the relative risk of kidney stones for men in the highest as compared with the lowest quintile group for calcium intake was 0.56 (95 percent confidence interval, 0.43 to 0.73; P for trend, < 0.001). This reduction in risk decreased only slightly (relative risk, 0.66; 95 percent confidence interval, 0.49 to 0.90) after further adjustment for other potential risk factors, including alcohol consumption and dietary intake of animal protein, potassium, and fluid. Intake of animal protein was directly associated with the risk of stone formation (relative risk for men with the highest intake as compared with those with the lowest, 1.33; 95 percent confidence interval, 1.00 to 1.77); potassium intake (relative risk, 0.49; 95 percent confidence interval, 0.35 to 0.68) and fluid intake (relative risk, 0.71; 95 percent confidence interval, 0.52 to 0.97) were inversely related to the risk of kidney stones.

CONCLUSIONS

A high dietary calcium intake decreases the risk of symptomatic kidney stones.

Study of potassium citrate treatment of crystalluric nephrolithiasis

Patients with crystalluric nephrolithiasis were treated orally with aqueous potassium citrate solution three times a day with a large quantity of water. After administration of potassium citrate, citric acid (P < 0.001) and potassium (P < 0.001) excretion was significantly increased. Increase in protein (P < 0.05) and uric acid (P < 0.05) excretion in urine revealed their association with the crystallization process. Crystals were absent in 12 (71%) out of 17 patients. Calcium excretion in urine was significantly decreased (P < 0.05). A decrease of calcium ions availability to oxalate ions to form calcium oxalate crystals may result in the prevention of calcium oxalate stone formation.

Thiazide treatment for calcium urolithiasis in patients with idiopathic hypercalciuria

In a randomised trial based on a parallel design to determine the prophylactic effect of thiazide on stone formation, 210 calcium urolithiasis patients with idiopathic hypercalciuria were allocated either to treatment with trichlormethiazide (4 mg/day) or no treatment with only close follow-up; 35 patients were excluded for various reasons, including voluntary withdrawal. The background of the remaining 175 patients (82 in the thiazide group and 93 in the control group), including age and sex, was similar for both groups. In patients treated with thiazide there was a statistically significant fall in urinary calcium output. Statistical analyses also demonstrated that the stone formation rate in the thiazide group was significantly less than that in the control group. Adverse clinical reactions probably due to the drug were observed in 9 patients. These findings indicate that trichlormethiazide has a prophylactic effect on calcium urolithiasis in patients with idiopathic hypercalciuria.

Gastrointestinal citrate absorption in nephrolithiasis

Gastrointestinal absorption of citrate was measured in stone patients with idiopathic hypocitraturia to determine if citrate malabsorption could account for low urinary citrate. Citrate absorption was measured directly from recovery of orally administered potassium citrate (40 mEq.) in the intestinal lavage fluid, using an intestinal washout technique. In 7 stone patients citrate absorption, serum citrate levels, peak citrate concentration in serum and area under the curve were not significantly different from those of 7 normal subjects. Citrate absorption was rapid and efficient in both groups, with 96 to 98% absorbed within 3 hours. The absorption of citrate was less efficient from a tablet preparation of potassium citrate than from a liquid preparation, probably due to a delayed release of citrate from wax matrix. However, citrate absorption from solid potassium citrate was still high at 91%, compared to 98% for a liquid preparation. Thus, hypocitraturia is unlikely to be due to an impaired gastrointestinal absorption of citrate in stone patients without overt bowel disease.

Citrate and recurrent idiopathic calcium urolithiasis. A longitudinal pilot study on the metabolic effects of oral potassium citrate administered over the short-, medium- and long-term medication of male stone patients

In idiopathic recurrent calcium urolithiasis (RCU) in men (n = 37) the metabolic effects of oral tripotassium citrate (PC) were investigated in a longitudinal field study. The patients were either normo- (n = 22) or hypocitraturic (n = 15). Laboratory examinations were performed before, and after 3, 6, and more than 12 months of medication. Acceptance of PC was poor, mainly because of the salty taste of the tablet preparation chosen, and a number of participants dropped out of the study. In the remaining participants, compliance was acceptable when evaluated on the basis of urinary potassium and undesired side effects did not occur. In the short term (up to 3 months), PC evoked compensated metabolic alkalosis (pH and citrate in urine increased; blood gases remained normal), a drop in urinary calcium, together with increasing oxaluria, hydroxyapatite supersaturation, and calcium phosphate crystalluria. In the long term (greater than 12 months) PC urinary pH and citrate "dissociated", in that pH returned to pretreatment baseline values, whereas citrate stayed at high levels. In normocitraturics but not in hypocitraturics, urinary urea and sodium increased with PC. Hypocitraturics appeared to be less sensitive to the effects of PC, as reflected by the relatively small rise in urinary pH and citrate, and they maintained higher mean levels of indicators of bone metabolism (osteocalcin, alkaline phosphatase, hydroxyproline) despite continuous administration of PC. It was concluded that although the PC tablet preparation was effective it may not be an ideal anti-stone drug treatment in the long term and that, especially in hypocitraturics, the intrinsic metabolic defect of RCU may not be sufficiently well controlled.

Etiology and treatment of urolithiasis

Nephrolithiasis is a heterogeneous disorder, with varying chemical composition and pathophysiologic background. Although kidney stones are generally composed of calcium oxalate or calcium phosphate, they may also consist of uric acid, magnesium-ammonium phosphate, or cystine. Stones develop from a wide variety of metabolic or environmental disturbances, including varying forms of hypercalciuria, hypocitraturia, undue urinary acidity, hyperuricosuria, hyperoxaluria, infection with urease-producing organisms, and cystinuria. The cause of stone formation may be ascertained in most patients using the reliable diagnostic protocols that are available for the identification of these disturbances. Effective medical treatments, capable of correcting underlying derangements, have been formulated. They include sodium cellulose phosphate, thiazide, and orthophosphate for hypercalciuric nephrolithiasis; potassium citrate for hypocitraturic calcium nephrolithiasis; acetohydroxamic acid for infection stones; and D-penicillamine and alpha-mercaptopropionylglycine for cystinuria. Using these treatments, new stone formation can now be prevented in most patients.

Citrate and renal calculi: new insights and future directions

Citrate is pathogenetically important in stone formation, because it retards the crystallization of stone-forming calcium salts and because its level in urine is low in many patients with nephrolithiasis. Potassium citrate is useful therapeutically, because it can often restore normal urinary citrate. Hypocitraturia often results from dietary aberrations, including sodium excess, and exaggerated intake of animal proteins. Hypocitraturia is frequently accompanied by a low net gastrointestinal absorption of alkali. New drugs are under development as improvements or refinements of currently available potassium citrate. They are potassium citrate 10-mEq-tablet preparation, effervescent calcium citrate, and potassium-magnesium citrate.

Prevention and treatment of kidney stones. Role of medical prevention

Despite dramatic advances in stone removal brought by extracorporeal shock wave lithotripsy, there is a continuing need for medical diagnosis and prevention. Justifications for the medical approach include prevention of recurrence (medical treatment could prevent further stone formation, unlike a surgical approach), efficacy of prophylactic program (recurrent stone formation may be inhibited in most patients using a variety of treatment programs), inhibition of spontaneous passage (by medical treatment, although not amenable to surgical treatment), potential avoidance of renal colic (occurring before stone removal avoided by preventing recurrence), reduced need for stone removal (achieved by successful medical treatment), correction of extrarenal manifestations (deleterious extrarenal manifestations of a stone-forming condition, such as bone disease in distal renal tubular acidosis, may be corrected by appropriate medical treatment) and cost-effectiveness. The cost of medical care is estimated to be half to a fourth that of surgical care. The need and type of medical treatment should be appraised continually to accommodate advances in techniques of stone removal.