Novel insights into the pathogenesis of uric acid nephrolithiasis

2022 Recommendations of the AFU Lithiasis Committee: Medical management - from diagnosis to treatment

The morphological-compositional analysis of urinary stones allows distinguishing schematically several situations: dietary, digestive, metabolic/hormonal, infectious and genetic problems. Blood and urine testing are recommended in the first instance to identify risk factors of urinary stone disease in order to avoid recurrence or progression. The other objective is to detect a potential underlying pathology associated with high risk of urinary stone disease (e.g. primary hyperparathyroidism, primary or enteric hyperoxaluria, cystinuria, distal renal tubular acidosis) that may require specific management. Lifestyle-diet measures are the basis of the management of all stone types, but pharmacological treatments may be required. METHODOLOGY: These recommendations were developed using two methods: the Clinical Practice Recommendation (CPR) method and the ADAPTE method, depending on whether the question was considered in the European Association of Urology (EAU) recommendations (https://uroweb.org/guidelines/urolithiasis) [EAU 2022] and their adaptability to the French context.

Type 4 renal tubular acidosis and uric acid nephrolithiasis: two faces of the same coin?

PURPOSE OF REVIEW

The present review summarizes findings of recent studies examining the epidemiology, pathophysiology, and treatment of type 4 renal tubular acidosis (RTA) and uric acid nephrolithiasis, two conditions characterized by an abnormally acidic urine.

RECENT FINDINGS

Both type 4 RTA and uric acid nephrolithiasis disproportionately occur in patients with type 2 diabetes and/or chronic kidney disease. Biochemically, both conditions are associated with reduced renal ammonium excretion resulting in impaired urinary buffering and low urine pH. Reduced ammoniagenesis is postulated to result from hyperkalemia in type 4 RTA and from insulin resistance and fat accumulation in the renal proximal tubule in uric acid nephrolithiasis. The typical biochemical findings of hyperkalemia and systemic acidosis of type 4 RTA are rarely reported in uric acid stone formers. Additional clinical differences between the two conditions include findings of higher urinary uric acid excretion and consequent urinary uric acid supersaturation in uric acid stone formers but not in type 4 RTA.

SUMMARY

Type 4 RTA and uric acid nephrolithiasis share several epidemiological, clinical, and biochemical features. Although both conditions may be manifestations of diabetes mellitus and thus have a large at-risk population, the means to the shared biochemical finding of overly acidic urine are different. This difference in pathophysiology may explain the dissimilarity in the prevalence of kidney stone formation.

Clinical characteristics of surgically managed patients with asymptomatic renal stones: Comparison of patients with symptomatic renal stones

PURPOSE

This study aimed to compare the characteristics of asymptomatic and symptomatic nephrolithiasis in patients who underwent surgical treatment for kidney stones.

MATERIALS AND METHODS

Between 2015 and 2019, 245 patients who underwent percutaneous nephrolithotomy or retrograde intrarenal surgery for kidney stones were included. The patients were divided into asymptomatic (n=124) and symptomatic (n=121) groups. All patients underwent blood and urine tests, preoperative non-contrast computed tomography, and postoperative stone composition analysis. We retrospectively analyzed and compared the characteristics of the patients and stones, operation time, stone-free rate, and postoperative complications between the two groups.

RESULTS

In the asymptomatic group, mean body mass index (BMI) was significantly higher (25.7±3.8 kg/m² vs. 24.3±2.8 kg/m², p=0.002) and urine pH was significantly lower (5.6±0.9 vs. 5.9±0.9, p=0.013). The ratio of calcium oxalate dihydrate stones was significantly higher in the symptomatic group (5.3% vs. 15.5%, p=0.023). No significant differences were observed in stone characteristics, postoperative outcomes, or complications. In the multivariate logistic regression analysis for predicting variables for asymptomatic renal stones, BMI (odds ratio [OR], 1.144; 95% confidence interval [CI], 1.038-1.260; p=0.007), and urine pH (OR, 0.608; 95% CI, 0.407-0.910; p=0.016) were independent predictive variables for asymptomatic renal stones.

CONCLUSIONS

This study demonstrated that thorough medical check-ups are needed for the early detection of renal stones in individuals with a high BMI or low urine pH.

Epidemiology of Kidney Stones

In the past two decades, major breakthroughs that improve our understanding of the pathophysiology and therapy of kidney stones (KS) have been lacking. The disease continues to be challenging for patients, physicians, and healthcare systems alike. In this context, epidemiological studies are striving to elucidate the worldwide changes in the patterns and the burden of the disease and identify modifiable risk factors that contribute to the development of kidney stones. Our expanding knowledge of the epidemiology of kidney stones is of paramount importance and largely upgrades the modern management of the disease. In this paper, we review the variables affecting prevalence and incidence, including age, gender, race, ethnicity, occupation, climate, geography, systemic diseases, diabetes, vascular disease, chronic kidney disease, and dietary risk factors relevant to kidney stones.

Over-the-counter alkali agents to raise urine pH and citrate excretion: a prospective crossover study in healthy adults

OBJECTIVE

To assess the effect of two over-the-counter alkalizing agents on 24-hour urinary parameters.

MATERIALS AND METHODS

Ten healthy volunteers without a history of kidney stones were recruited to complete a baseline 24-hour urinalysis with a four-day diet inventory. Participants then maintained the same diet on either LithoLyte® (20 mEq two times per day) or KSPtabs^TM (1 tablet two times per day) and submitted another 24-hour urinalysis. The process was repeated with the other supplement. Urinary alkali parameters were compared to baseline, and side effects were elicited with a questionnaire.

RESULTS

LithoLyte® intake resulted in a non-significant increase in citrate (597 to 758 mg/day, p=0.058, an increase in urine pH (6.46 to 6.66, p=0.028), and a decrease in urine ammonium (41 to 36 mmol/day, p=0.005) compared to baseline. KSPtabs^TM resulted in an increase in citrate (597 to 797 mg/day, p=0.037) and urine pH (6.46 to 6.86, p=0.037), with a non-significant decrease in ammonium (41 to 34 mmol/day, p=0.059). No significant differences were seen comparing urinary analytes between LithoLyte® and KSPtabs^TM. With Litholyte®, no side effects, mild, moderate, and severe side effects were seen in 50%, 40%, 10%, and 0%, respectively. With KSPtabs^TM, rates were 60%, 20%, 10%, and 10%, respectively.

CONCLUSIONS

In healthy participants without a history of kidney stones, LithoLyte® and KSPtabs^TM are effective over-the-counter alkali supplements, with a similar side effect profile to prescription potassium citrate.

Role of insulin resistance and the gut microbiome on urine oxalate excretion in ob/ob mice

Ob/ob mice have recently emerged as a model for obesity-related hyperoxaluria as they are obese and excrete more urine oxalate compared to wild type mice. Ob/ob mice are deficient of leptin and develop obesity with hyperphagia and hyperinsulinemia. We hypothesized that insulin resistance and the gut microbiome contribute to hyperoxaluria in ob/ob mice. We developed a new liquid chromatography-mass spectrometry assay for urine oxalate and first compared urine oxalate excretion in ob/ob mice before and after ablation of intestinal bacteria with a standard antibiotic cocktail. We then compared urine oxalate excretion in ob/ob mice before and after leptin replacement or pioglitazone treatment, two maneuvers that reduce insulin resistance in ob/ob mice. Ob/ob mice excreted more oxalate into the urine in a 24-h period compared to wild type mice, but antibiotic, leptin, or pioglitazone treatment did not change urine oxalate excretion in ob/ob mice. Unexpectedly, we found that when food intake was carefully matched between ob/ob and wild type mice, the amount of 24-h urine oxalate excretion did not differ between the two mouse strains, suggesting that ob/ob mice excrete more urine oxalate because of hyperphagia. Since the level of urine oxalate excretion in wild type mice in our study was higher than those reported in prior studies, future work will be needed to standardize the measurement of urine oxalate and to define the range of urine oxalate excretion in wild type mice so that accurate and valid comparisons can be made between wild type mice and ob/ob mice or other mouse models.

Standardised nurse-led protocol of radiolucent renal and proximal ureteric stones using sodium bicarbonate oral dissolution therapy

Objective:

Oral dissolution therapy is a recognised treatment option for radiolucent kidney stones. A standardised nurse-led protocol was developed. Efficacy and compliance was audited and results reviewed.

Methods:

Twenty-two patients with radiolucent stones were prescribed oral sodium bicarbonate. Patients monitored their urinary pH and the Urology Nurse Practitioner checked compliance. Follow-up with non-contrast computerised tomography of the kidneys, ureters and bladder (CT KUB) was evaluated at 6 weeks.

Results:

Twenty patients with radiolucent stones completed treatment. Mean stone size was 8 mm (2–23 mm). Nine patients (45%) had complete dissolution, three (15%) had partial dissolution and eight (40%) had no visible response on follow-up CT KUB. The Hounsfield unit (HU) average was 464 (116–1285). Those patients with complete dissolution had HU of less than 605. Three patients with encrusted ureteric stents underwent complete dissolution.

Conclusions:

Utilisation of a nurse-led sodium bicarbonate dissolution therapy protocol for the treatment of radiolucent stones is effective and acceptable to patients in carefully selected cases. Orally dissolution therapy (ODT) is a suitable option in patients with multiple co-morbidities and high anaesthetic risk. In our series, ODT was also highly effective in treating radiolucent stent encrustation.

Urate Crystals; Beyond Joints

Gout is the most common inflammatory arthropathy caused by the deposition of monosodium urate (MSU) crystals. The burden of gout is substantial with increasing prevalence of gout globally. The prevalence of Gout in the United States has increased by over 7% in the last two decades. Initially, it was believed that MSU crystal deposits occur only in the joints with the involvement of the periarticular soft tissues, but recent studies have shown the presence of MSU crystal deposition in extra-articular sites as well. Human plasma becomes supersaturated with uric acid at 6.8 mg/dl, a state called hyperuricemia. Beyond this level, uric acid crystals precipitate out of the plasma and deposit in soft tissues, joints, kidneys, etc. If left untreated, hyperuricemia leads to chronic gout characterized by the deposition of tophi in soft tissues such as the joints, tendons, and bursae. With the advent of newer imaging techniques such as DECT, MSU crystals can be visualized in various extra-articular sites. Extra-articular deposition of MSU crystals is believed to be the causative factor for the development of multiple comorbidities in gout patients. Here, we review the literature on extra-articular deposition of urate crystals and the role of dual-energy computed tomography (DECT) in elucidating multi-organ involvement. DECT has emerged as an invaluable alternative for accurate and efficient MSU crystal deposition detection. Future studies using DECT can help determine the clinical consequences of extra-articular deposition of MSU in gout patients.

Ureteral calculi associated with high-altitude polycythemia: A case report

RATIONALE

High-altitude polycythemia (HAPC) is a common disease in high-altitude areas characterized by excessive erythrocyte proliferation and severe hypoxemia. Recently, the incidence of ureteral calculi has risen. However, cases of ureteral calculi associated with HAPC have not been reported.

PATIENT CONCERNS

We present the cases of 2 patients (26-year-old female, Case 1; 31-year-old male, Case 2) with HAPC who were born in the lowlands and worked in areas of high altitudes. Both patients were admitted to the hospital with acute severe pain in the ureter as the first symptom.

DIAGNOSES

Urological examinations confirmed the presence of a ureteral stone. Interestingly, the biochemical tests showed elevated serum uric acid levels, and the calculous component analysis suggested anhydrous uric acid.

INTERVENTIONS

In the first case, the patient underwent extracorporeal shock wave lithotripsy. In the second case, the patient underwent right ureteroscopy and right ureteral stenting. The patient received postoperative anti-inflammatory, hemostatic, and rehydration therapy.

OUTCOMES

Both patients recovered well with no recurrences observed upon regular re-examinations.

LESSONS

Recently, extensive research has demonstrated a significant correlation between hyperuricemia and HAPC. Therefore, we speculated that the occurrence of ureteral calculi among immigrants to the plateau might be related to hyperuricemia associated with HAPC. This case report and literature review highlights that the prevention of ureteral calculi in patients with polycythemia who immigrate to the plateaus from high-altitude areas should be considered. Additionally, the serum uric acid levels and urine pH should be monitored regularly.

Prevention and management of urinary stone

The prevalence of urolithiasis is increasing not only in South Korea but also around the world. Urolithiasis has a high recurrence rate, therefore, reducing it is very important in the quality of life for stone formers. For this purpose, dietary modifications and drug therapy can be performed through stone analysis and 24-hour urine collection. Stone analysis is recommended for all stone formers, and the 24-hour urine collection is usually recommended for recurrent stone formers or high-risk groups. A general dietary modification for all stone formers includes a sufficient fluid intake, low levels of sodium, sugar, and animal protein, a normal calcium diet, as well as a high amount of citrate intake. Drug therapy should be performed in cases such as the recurrence of stones or increase of the existing ones, even after the application of preservation therapy, such as dietary modification. The ideal drug therapy should prevent the occurrence of urolithiasis, have no side effects, and have a suitable patientsʼ compliance. Follow-up should be performed periodically, through 24-hour urine collections and imaging studies. For follow-up imaging studies, a lowdose non-enhanced computed tomography is recommended, and it can be performed once a year if the patient is in a stable state. To control various and complex metabolic abnormalities in recurrent stone formers, multiple approaches may be required through diet modifications, drug therapy, treatment of the metabolic syndrome, and lifestyle modifications.

Uric acid stone disease: lessons from recent human physiologic studies

PURPOSE OF REVIEW

An overly acidic urine resulting in supersaturation of urine with respect to uric acid is the major mechanism responsible for uric acid nephrolithiasis. The present review summarizes findings from recent human physiologic studies examining the pathophysiology and reversibility of low urine pH in uric acid stone formers.

RECENT FINDINGS

Epidemiologic and metabolic studies have confirmed an increase in the prevalence of uric acid nephrolithiasis and reported its association with several features of the metabolic syndrome including dyslipidemia, hyperglycemia, hepatic steatosis, and greater visceral adiposity. Physiologic studies in uric acid stone formers have identified diet-independent excessive net acid excretion and concomitant reduction in urinary buffering from impaired renal ammoniagenesis as the two causes underlying the greater aciduria. Administration of the insulin sensitizer pioglitazone to uric acid stone formers reduced the acid load presented to the kidney and enhanced ammoniagenesis and ammonium excretion, resulting in significantly higher urine pH.

SUMMARY

Recent human physiologic studies have identified greater acid excretion and reduced urinary buffering by ammonia as two culprits of aciduria in uric acid nephrolithiasis that can be reversed by pioglitazone, raising new questions regarding the origin of the aciduria and opening the door to pathophysiology-based treatment of uric acid stones.

The effects of canagliflozin on gout in type 2 diabetes: a post-hoc analysis of the CANVAS Program

BACKGROUND

Sodium glucose co-transporter 2 inhibitors have been shown to reduce serum urate concentration. The Canagliflozin Cardiovascular Assessment Study (CANVAS) Program integrated data from two similarly designed, randomised, double-blind, placebo-controlled trials (CANVAS and CANVAS-Renal) assessing the cardiovascular and renal safety of canagliflozin compared with placebo in patients with type 2 diabetes. In this post-hoc analysis, we aimed to investigate the effect of canagliflozin compared with placebo on gout in the CANVAS Program.

METHODS

In the CANVAS Program, individuals with type 2 diabetes and an elevated risk of cardiovascular disease were randomly assigned to receive either canagliflozin (100 or 300 mg) or placebo. In this post-hoc analysis, we assessed the effects of canagliflozin versus placebo on serum urate concentration using mixed linear models and the occurrence of either an adverse event attributed to gout flare or the commencement of a drug for gout using Kaplan-Meier analysis with Cox proportional hazards models to determine a hazard ratio (HR) and 95% CIs. All analyses were done according to the principle of intention to treat, and there was no imputation for missing data.

FINDINGS

10 142 participants were included in analyses. At baseline, mean age was 63 years (SD 8), 3633 (36%) participants were female, mean serum urate concentration was 348·9 μmol/L (95·5), and 471 (5%) of participants had a history of gout. Mean follow-up was 3·6 years (SD 2·0) and mean serum urate concentration was -23·3 μmol/L (95% CI -25·4 to -21·3) lower in participants treated with canagliflozin than in those who received placebo, equating to a 6·7% reduction in serum urate (percentage difference -6·7%, 95% CI -7·3 to -6·1). During follow-up, 80 individuals reported an episode of gout flare and 147 commenced a drug for gout. The occurrence of gout flare or the need for treatment for gout was lower in participants treated with canagliflozin than in those who received placebo (HR 0·53, 95% CI 0·40-0·71; p<0·0001). The proportional reduction for gout flare adverse events (2·0 patients with an event per 1000 patient-years in the canagliflozin group vs 2·6 patients with an event per 1000 patient-years in the placebo group; 0·64, 95% CI 0·41-0·99; p=0·046) was similar in size to that for commencement of a drug for gout (3·3 vs 5·4 patients with an event per 1000 patient-years; 0·52, 0·38-0·72; p<0·0001) and hyperuricaemia (1·8 vs 2·5 patients with an event per 1000 patient-years; 0·59, 0·37-0·93; p=0·023).

INTERPRETATION

In this post-hoc analysis, compared with placebo, canagliflozin reduced serum urate concentration and also reduced events related to gout flare among patients with type 2 diabetes. A trial explicitly designed to test the effects of sodium glucose co-transporter 2 inhibition on gout is required to confirm these observations.

FUNDING

Janssen Research & Development.

Decreased Associated Risk of Gout in Diabetes Patients with Uric Acid Urolithiasis

Uric acid urolithiasis constitutes approximately 7–10% of all urinary stones. Previous studies have revealed that patients with gout do not equally have uric acid stones. Instead, the risk of gout in patients with uric acid stones remains controversial. This study aimed to investigate whether there is different associated risk of gout for diabetes mellitus (DM) and non-diabetes patients with uric acid urolithiasis. Therefore, we examined all baseline chemistries to determine any risk factors or protective factors related to developing gout in patients with uric acid stones. Ninety-nine patients from a single medical center, who had a uric acid component in their stone specimen were enrolled and their medical records were reviewed retrospectively between January 2010 and December 2016. All patients were divided into gout and non-gout groups. Gout was confirmed in 24 patients in this study (24.2%). The proportion of DM was significantly higher in the non-gout group (34.7%) than in the gout group (4.3%, p < 0.05). Renal function was decreased and serum triglyceride was higher in patients with gout. Uric acid urolithiasis patients with DM had a lower risk for gout (adjusted odds ratio: 0.08; 95% confidence interval (CI) = 0.01–0.61, p = 0.015). In 89 patients with predominant uric acid stones (>50% uric acid composition), the risk for gout was still lower in patients with diabetes than non-diabetes (adjusted odds ratio: 0.08; 95% confidence interval (CI) = 0.01–0.61, p = 0.015). These findings suggest that decreased risk of gout is found in uric acid urolithiasis patients with diabetes. Our results imply that patients with uric acid stones should have complete diabetes evaluation before the administration of uric acid controlling medication.

Method of alkalization and monitoring of urinary pH for prevention of recurrent uric acid urolithiasis: a systematic review

Uric acid (UA) urolithiasis comprises around 5-10% of all stones and can frequently recur. Due to the fact that UA stones form in acidic urine with a pH <5.5, these patients require special attention compared to other stone patients. The international guidelines suggest treatment and metaphylaxis by urinary alkalization. The objective of this review is to critically asses the available evidence concerning the method and efficacy of this treatment modality. A systematic review on the methods of metaphylactic therapy using oral alkalization of UA urolithiasis was conducted by two authors. Evidence was sought using a predefined search strategy in seven different databases. The provided evidence was critically evaluated using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Cochrane collaboration tool for assessing the risk of bias. Twelve manuscripts were included of which one was a randomised trial. They focussed on ways to alkalize urine and its effect on stone recurrence. Because of their methodology and heterogeneity, the evidence is presented in a narrative review. There were differences in medication used for alkalizing urine, ways of monitoring urine pH and evaluating its efficacy. The reported outcomes also differed between studies. There is currently a lack of clear evidence for the method of alkalization of urine and the method of pH measurement. Besides this, for an established treatment modality, there is lack of long term results for the alkalization therapy. In conclusion, urine alkalization is an established treatment modality for the metaphylaxis of UA urolithiasis despite the lack of evidence from high quality studies on the methods of alkalization and its treatment efficacy. The studies published on this topic are scarce and contain notable risks of bias which should be kept in mind when interpreting the stated results.

Net Acid Excretion and Urinary Organic Anions in Idiopathic Uric Acid Nephrolithiasis

BACKGROUND AND OBJECTIVES

Idiopathic uric acid nephrolithiasis, which is closely associated with obesity and the metabolic syndrome, is increasing in prevalence. Unduly acidic urine pH, the quintessential pathophysiologic feature of this disease, is in part explained by inadequate excretion of the principal urinary buffer ammonium. The role of net acid excretion in the pathogenesis of uric acid nephrolithiasis is incompletely understood.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We compared acid-base parameters of patients with idiopathic uric acid nephrolithiasis with matched control subjects under controlled diets in an inpatient metabolic unit. Measurements included fasting blood and 24-hour urine chemistries and 24-hour urine metabolomic analysis. Comparisons between groups included analysis of covariance models controlling for urine pH or body mass index.

RESULTS

Subjects with idiopathic uric acid nephrolithiasis had lower urine pH (5.5 versus 5.9; P<0.001) and higher net acid excretion (60 versus 43 mEq/24 h; P<0.001), with the excess H+ carried by nonammonium buffers. In all subjects, there was a positive relationship of net acid excretion with higher body mass index in spite of strictly controlled equivalent dietary acid intake. This relationship was most evident among control subjects (r=0.36; P=0.03). It was attenuated in patients with idiopathic uric acid nephrolithiasis whose net acid excretion remained fixedly high and ammonium excretion remained low relative to net acid excretion, resulting in low urine pH over a wide body mass index range. Urinary metabolomics was performed to attempt to identify excess organic acids presented to the kidney in idiopathic uric acid nephrolithiasis. Among the tricarboxylic acid cycle intermediates and amino acid and lipid metabolites analyzed, 26 organic anions with acid dissociation constants values in the range of urine pH showed greater protonation. However, protons carried by the identified organic acids did not entirely account for the higher titratable acidity seen in idiopathic uric acid nephrolithiasis.

CONCLUSIONS

Higher acid load to the kidney, resulting in higher urinary net acid excretion, is an important factor in the pathogenesis of idiopathic uric acid nephrolithiasis.

Medical dissolution therapy for the treatment of uric acid nephrolithiasis

INTRODUCTION

Uric acid (UA) nephrolithiasis represents 10% of kidney stones in the US with low urine pH and high saturation of UA as the main risk factors for stone development. Dissolution therapy for UA kidney stones via urinary alkalization has been described as a treatment option. We present our experience in treating UA nephrolithiasis with medical dissolution therapy.

METHODS

A retrospective review was performed of UA stone patients referred for surgery but treated with dissolution therapy between July 2007 and July 2016. Patients were identified using ICD-9 codes. Patients were treated with potassium citrate alone or in combination with allopurinol. Serial imaging and urine pH were obtained at follow-up. Demographics, aggregate stone size, time to stone clearance, urine pH (office dip), and complications were recorded.

RESULTS OBTAINED

Twenty-four patients (14 men and 10 women) were identified that started medical dissolution therapy for UA nephrolithiasis after initial referral for surgical management. Three patients (13%) did not tolerate the initiation of dissolution therapy and discontinued this treatment. Of the 21 patients that were maintained on dissolution therapy, 14 patients (67%) showed complete resolution of nephrolithiasis and 7 patients (33%) showed partial reduction. Patients with partial response had a mean reduction in stone burden of 68%. There were 3 recorded complications (UTI, GI upset with therapy, and throat irritation) and 4 recorded stone recurrences among these 21 patients.

CONCLUSION

Based on our study population, medical dissolution therapy is a well-tolerated, non-invasive option for UA nephrolithiasis.

Increased production and reduced urinary buffering of acid in uric acid stone formers is ameliorated by pioglitazone

Idiopathic uric acid nephrolithiasis is characterized by an overly acidic urine pH caused by the combination of increased acid production and inadequate buffering of urinary protons by ammonia. A large proportion of uric acid stone formers exhibit features of the metabolic syndrome. We previously demonstrated that thiazolidinediones improved the urinary biochemical profile in an animal model of the metabolic syndrome. In this proof-of-concept study, we examined whether the thiazolidinedione pioglitazone can also ameliorate the overly acidic urine in uric acid stone formers. Thirty-six adults with idiopathic uric acid nephrolithiasis were randomized to pioglitazone 30 mg/day or matching placebo for 24 weeks. At baseline and study end, participants underwent collection of blood and 24-hour urine in an inpatient research unit while consuming a fixed metabolic diet, followed by assessment of the ammoniagenic response to an acute oral acid load. Twenty-eight participants completed the study. Pioglitazone treatment improved features of the metabolic syndrome. Pioglitazone also reduced net acid excretion and increased urine pH (5.37 to 5.59), the proportion of net acid excreted as ammonium, and ammonium excretion in response to an acute acid load, whereas these parameters were unchanged with placebo. Treatment of patients with idiopathic uric acid nephrolithiasis with pioglitazone for 24 weeks led to a reduction in the acid load presented to the kidney and a more robust ammoniagenesis and ammonium excretion, resulting in significantly higher urine pH. Future studies should consider the impact of this targeted therapy on uric acid stone formation.

Empiric therapy for kidney stones

Careful phenotyping of patients to classify those with kidney stones has a long and important history in revealing the chemical basis for stone formation. Advances in our genetic understanding of kidney stones will lead to incredible insights regarding the pathophysiology of this common disorder. At this time, both evaluation of urine chemistry and genotyping of patients are extremely useful in the setting of a university and research-based kidney stone clinic. For much of the world, in a more clinically focused setting, these techniques are neither available nor absolutely necessary. Careful implementation of an empiric prescription based on stone composition would have an important effect to reduce stone recurrence in the world's many stone formers. Increased fluid intake, generic dietary manipulations, and prescription of potassium citrate and thiazides are all appropriate empiric therapies for people with calcium and uric acid kidney stones.

Medical therapy for nephrolithiasis: State of the art

The prevalence of nephrolithiasis is increasing worldwide. Understanding and implementing medical therapies for kidney stone prevention are critical to prevent recurrences and decrease the economic burden of this condition. Dietary and pharmacologic therapies require understanding on the part of the patient and the prescribing practitioner in order to promote compliance. Insights into occupational exposures and antibiotic use may help uncover individual risk factors. Follow-up is essential to assess response to treatment and to modify treatment plans to maximize therapeutic benefit.

Hypokalemic Distal Renal Tubular Acidosis

Distal renal tubular acidosis (DRTA) is defined as hyperchloremic, non-anion gap metabolic acidosis with impaired urinary acid excretion in the presence of a normal or moderately reduced glomerular filtration rate. Failure in urinary acid excretion results from reduced H⁺ secretion by intercalated cells in the distal nephron. This results in decreased excretion of NH₄⁺ and other acids collectively referred as titratable acids while urine pH is typically above 5.5 in the face of systemic acidosis. The clinical phenotype in patients with DRTA is characterized by stunted growth with bone abnormalities in children as well as nephrocalcinosis and nephrolithiasis that develop as the consequence of hypercalciuria, hypocitraturia, and relatively alkaline urine. Hypokalemia is a striking finding that accounts for muscle weakness and requires continued treatment together with alkali-based therapies. This review will focus on the mechanisms responsible for impaired acid excretion and urinary potassium wastage, the clinical features, and diagnostic approaches of hypokalemic DRTA, both inherited and acquired.

Incomplete Distal Renal Tubular Acidosis and Kidney Stones

Renal tubular acidosis (RTA) is comprised of a diverse group of congenital or acquired diseases with the common denominator of defective renal acid excretion with protean manifestation, but in adults, recurrent kidney stones and nephrocalcinosis are mainly found in presentation. Calcium phosphate (CaP) stones and nephrocalcinosis are frequently encountered in distal hypokalemic RTA type I. Alkaline urinary pH, hypocitraturia, and, less frequently, hypercalciuria are the tripartite lithogenic factors in distal RTA (dRTA) predisposing to CaP stone formation; the latter 2 are also commonly encountered in other causes of urolithiasis. Although the full blown syndrome is easily diagnosed by conventional clinical criteria, an attenuated forme fruste called incomplete dRTA typically evades clinical testing and is only uncovered by provocative acid-loading challenges. Stone formers (SFs) that cannot acidify urine of pH < 5.3 during acid loading are considered to have incomplete dRTA. However, urinary acidification capacity is not a dichotomous but rather a continuous trait, so incomplete dRTA is not a distinct entity but may be one end of a spectrum. Recent findings suggest that incomplete dRTA can be attributed to heterozygous carriers of hypofunctional V-ATPase. The value of incomplete dRTA diagnosis by provocative testing and genotyping candidate genes is a valuable research tool, but it remains unclear at the moment whether they alter clinical practice and needs further clarification. No randomized controlled trials have been performed in SFs with dRTA or CaP stones, and until such data are available, treatment of CaP stones are centered on reversing the biochemical abnormalities encountered in the metabolic workup. SFs with type I dRTA should receive alkali therapy, preferentially in the form of K-citrate delivered judiciously to treat the chronic acid retention that drives both stone formation and bone disease.

Individualized treatment strategies for hyperuricemia informed by a semi-mechanistic exposure-response model of uric acid dynamics

To provide insight into pharmacological treatment of hyperuricemia we developed a semi-mechanistic, dynamical model of uric acid (UA) disposition in human. Our model represents the hyperuricemic state in terms of production of UA (rate, PUA), its renal filtration (glomerular filtration rate, GFR) and proximal tubular reabsorption (fractional excretion coefficient, FE). Model parameters were estimated using data from 9 Phase I studies of xanthine oxidase inhibitors (XOI) allopurinol and febuxostat and a novel uricosuric, the selective UA reabsorption inhibitor lesinurad, approved for use in combination with a XOI. The model was qualified for prediction of the effect of patients' GFR and FE on concentration of UA in serum (sUA) and UA excretion in urine and their response to drug treatment, using data from 2 Phase I and 4 Phase III studies of lesinurad. Percent reduction in sUA from baseline by a XOI is predicted to be independent of GFR, FE or PUA. Uricosurics are more effective in underexcreters of UA or patients with normal GFR. Co-administration of a XOI and an uricosuric agent should be considered for patients with high sUA first in the treatment algorithm of gout before uptitration of XOI. The XOI dose in combination with a uricosuric can be reduced compared to XOI alone for the same target sUA to the degree dependent on patient's GFR and FE. This exposure-response model of UA can be used to rationally select the best drug treatment option to lower elevated sUA in gout patients under differing pathophysiological situations.

Impact of non-adherence on the safety and efficacy of uric acid-lowering therapies in the treatment of gout

AIMS

Dual-urate-lowering therapy (ULT) with xanthine oxidase inhibitor and uricosuric medications is a treatment option for severe gout. Uricosuric agents can cause hyperuricosuria, a risk factor for nephrolithiasis and acute uric acid nephropathy. The aims of the present study were to simulate the relationship between suboptimal drug adherence and efficacy, and to quantify the risk of hyperuricosuria in gout patients receiving mono- and dual-ULTs.

METHODS

The impact of poor medication adherence was studied using two-compartment pharmacokinetic (PK) models based on published evidence, and a semi-mechanistic four-compartment pharmacodynamic (PD) model. The PKPD model was used to simulate mono and dual-ULT in gout patients with either under-excretion (lowered clearance) or overproduction of uric acid, with suboptimal adherence modelled as either a single drug holiday of increasing duration or doses taken at random.

RESULTS

Simulation results showed a surge in urinary uric acid occurring when dosing is restarted following missed doses. For under-excreters taking a 20-day drug holiday, the addition of 200 mg (or 400 mg) lesinurad to 80 mg febuxostat increased the percentage of patients experiencing hyperuricosuria from 0% to 1.4% (or 3.1%). In overproducers, restarting ULTs following drug holidays of more than 5 days leads to over 60% of patients experiencing hyperuricosuria.

CONCLUSIONS

Suboptimal medication adherence may compromise the safety and efficacy of mono- and dual-ULTs, especially in patients with gout resulting from an overproduction of uric acid. Clinicians and pharmacists should consider counselling patients with respect to the risks associated with partial adherence, and offer interventions to improve adherence or tailor treatments, where appropriate.

Redefining the Stone Belt: Precipitation Is Associated with Increased Risk of Urinary Stone Disease

OBJECTIVES

The American Southeast has been labeled the "Stone Belt" due to its relatively high burden of urinary stone disease, presumed to be related to its higher temperatures. However, other regions with high temperatures (e.g., the Southwest) do not have the same disease prevalence as the southeast. We seek to explore the association of stone disease to other climate-associated factors beyond temperature, including precipitation and temperature variation.

METHODS

We identified all patients who underwent a surgical procedure for urinary stone disease from the California Office of Statewide Health Planning and Development (OSHPD) databases (2010-2012). Climate data obtained from the National Oceanic and Atmospheric Administration (NOAA) were compared to population adjusted county operative stone burden, controlling for patient and county demographic data as potential confounders.

RESULTS

A total of 63,994 unique patients underwent stone procedures in California between 2010 and 2012. Multivariate modeling revealed that higher precipitation (0.019 average increase in surgeries per 1000 persons per inch, p < 0.01) and higher mean temperature (0.029 average increase in surgeries per 1000 persons per degree, p < 0.01) were both independently associated with an increased operative stone disease burden. Controlling for county-level patient factors did not change these observed effects.

CONCLUSIONS

In the state of California, higher precipitation and higher mean temperature are associated with increased rates of stone surgery. Our results appear to agree with the larger trends seen throughout the United States where the areas of highest stone prevalence have warm wet climates and not warm arid climates.

Compositional analysis of various layers of upper urinary tract stones by infrared spectroscopy

The objective of the present study was to determine the composition of various layers of upper urinary stones and assess the mechanisms of stone nucleation and aggregation. A total of 40 integrated urinary tract stones with a diameter of >0.8 cm were removed from the patients. All of the stones were cut in half perpendicularly to the longitudinal axis. Samples were selected from nuclear, internal and external layers of each stone. Fourier transform infrared spectroscopy (FT-IR) was adopted for qualitative and quantitative analysis of all of the fragments and compositional differences among nuclear, internal and external layers of various types of stone were subsequently investigated. A total of 25 cases of calcium oxalate (CaOx) stones and 10 cases of calcium phosphate (CaP) stones were identified to be mixed stones, while 5 uric acid (UA) calculi were pure stones (purity, >95%). In addition, the contents of CaOx and carbapatite (CA.AP) crystals in various layers of the mixed stones were found to be variable. In CaOx stones, the content of CA.AP in nuclear layers was significantly higher than that of the outer layers (32.0 vs. 6.8%; P<0.05), while the content of CaOx was lower in the inner than in the outer layers (57.6 vs. 86.6%; P<0.05). In CaP stones, the content of CA.AP in the nuclear layers was higher than that in the outer layers (74.0 vs. 47.3%; P<0.05), while the content of CaOx was lower in the inner than in the outer layers (7.0 vs. 40.0%; P<0.05). The UA stones showed no significant differences in their composition among different layers. In conclusion, FT-IR analysis of various layers of human upper urinary tract stones revealed that CaOx and CaP stones showed differences in composition between their core and surface, while all of the UA calculi were pure stones. The composition showed a marked variation among different layers of the stones, indicating that metabolism has an important role in different phases of the evolution of stones. The present study provided novel insight into the pathogenesis of urinary tract stones and may contribute to their prevention and treatment.

Furosemide/Fludrocortisone Test and Clinical Parameters to Diagnose Incomplete Distal Renal Tubular Acidosis in Kidney Stone Formers

BACKGROUND AND OBJECTIVES

Incomplete distal renal tubular acidosis is a well known cause of calcareous nephrolithiasis but the prevalence is unknown, mostly due to lack of accepted diagnostic tests and criteria. The ammonium chloride test is considered as gold standard for the diagnosis of incomplete distal renal tubular acidosis, but the furosemide/fludrocortisone test was recently proposed as an alternative. Because of the lack of rigorous comparative studies, the validity of the furosemide/fludrocortisone test in stone formers remains unknown. In addition, the performance of conventional, nonprovocative parameters in predicting incomplete distal renal tubular acidosis has not been studied.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a prospective study in an unselected cohort of 170 stone formers that underwent sequential ammonium chloride and furosemide/fludrocortisone testing.

RESULTS

Using the ammonium chloride test as gold standard, the prevalence of incomplete distal renal tubular acidosis was 8%. Sensitivity and specificity of the furosemide/fludrocortisone test were 77% and 85%, respectively, yielding a positive predictive value of 30% and a negative predictive value of 98%. Testing of several nonprovocative clinical parameters in the prediction of incomplete distal renal tubular acidosis revealed fasting morning urinary pH and plasma potassium as the most discriminative parameters. The combination of a fasting morning urinary threshold pH <5.3 with a plasma potassium threshold >3.8 mEq/L yielded a negative predictive value of 98% with a sensitivity of 85% and a specificity of 77% for the diagnosis of incomplete distal renal tubular acidosis.

CONCLUSIONS

The furosemide/fludrocortisone test can be used for incomplete distal renal tubular acidosis screening in stone formers, but an abnormal furosemide/fludrocortisone test result needs confirmation by ammonium chloride testing. Our data furthermore indicate that incomplete distal renal tubular acidosis can reliably be excluded in stone formers by use of nonprovocative clinical parameters.

The Association of Uric Acid Calculi with Obesity, Prediabetes, Type 2 Diabetes Mellitus, and Hypertension

Objectives

To disclose the link between the composition of urolithiasis, especially that of uric acid calculi, and obesity, prediabetes, type 2 diabetes mellitus, and hypertension.

Materials and Methods

Patients who had urinary calculi and underwent surgical treatment were registered in the study. The composition of urinary calculi was analyzed and correlated with clinical features and biomedical profiles of the patients before surgical intervention.

Results

A total of 666 patients with urolithiasis who underwent surgical management were registered and analyzed. In those who had uric acid calculi, there was a significant association with prediabetic (OR: 20.11, 95% CI: 7.40–54.63, P < 0.001) and diabetic states (OR: 11.55, 95% CI: 4.41–29.97, P < 0.001). It also seemed that uric acid calculi were related to obesity but there was no statistical significance (OR: 2.45, 95% CI: 0.91–6.62, P = 0.078). There was no association of uric acid calculi with hypertension (OR: 1.08, 95% CI: 0.54–2.17, P = 0.822) and concurrent urinary tract infection (OR: 0.93, 95% CI: 0.44–1.96, P = 0.841).

Conclusion

There was a remarkable association of uric acid calculi with prediabetic and diabetic states. The uric acid calculi were also seemingly associated with obesity in patients with urolithiasis undergoing surgical management.

Epidemiology, pathophysiology, and management of uric acid urolithiasis: A narrative review

An in-depth comprehension of the epidemiology as well as pathophysiology of uric acid urolithiasis is important for the identification, treatment, and prophylaxis of calculi in these patients. Persistently low urinary pH, hyperuricosuria, and low urinary volume are the most important factors in pathogenesis of uric acid urolithiasis. Other various causes of calculus formation comprises of chronic diarrhea, renal hyperuricosuria, insulin resistance, primary gout, extra purine in the diet, neoplastic syndromes, and congenital hyperuricemia. Non-contrast-enhanced computed tomography is the radiologic modality of choice for early assessment of patients with renal colic. Excluding situations where there is acute obstruction, rising blood chemistry, severe infection, or unresolved pain, the initial management ought to be medical dissolution by oral chemolysis since this method has proved to be effective in most of the cases.

Biochemical and dietary factors of uric acid stone formation

The aim of this study was to compare the clinical characteristics of "pure" uric acid renal stone formers (UA-RSFs) with that of mixed uric acid/calcium oxalate stone formers (UC-RSFs) and to identify which urinary and dietary risk factors predispose to their formation. A total of 136 UA-RSFs and 115 UC-RSFs were extracted from our database of renal stone formers. A control group of 60 subjects without history of renal stones was considered for comparison. Data from serum chemistries, 24-h urine collections and 24-h dietary recalls were considered. UA-RSFs had a significantly (p = 0.001) higher body mass index (26.3 ± 3.6 kg/m²) than UC-RSFs, whereas body mass index of UA-RSFs was higher but not significantly than in controls (24.6 ± 4.7) (p = 0.108). The mean urinary pH was significantly lower in UA-RSFs (5.57 ± 0.58) and UC-RSFs (5.71 ± 0.56) compared with controls (5.83 ± 0.29) (p = 0.007). No difference of daily urinary uric acid excretion was observed in the three groups (p = 0.902). Daily urinary calcium excretion was significantly (p = 0.018) higher in UC-RSFs (224 ± 149 mg/day) than UA-RSFs (179 ± 115) whereas no significant difference was observed with controls (181 ± 89). UA-RSFs tend to have a lower uric acid fractional excretion (0.083 ± 0.045% vs 0.107+/-0.165; p = 0.120) and had significantly higher serum uric acid (5.33 ± 1.66 vs 4.78 ± 1.44 mg/dl; p = 0.007) than UC-RSFs. The mean energy, carbohydrate and vitamin C intakes were higher in UA-SFs (1987 ± 683 kcal, 272 ± 91 g, 112 ± 72 mg) and UC-SFs (1836 ± 74 kcal, 265 ± 117, 140 ± 118) with respect to controls (1474 ± 601, 188 ± 84, 76 ± 53) (p = 0.000). UA-RSFs should be differentiated from UC-RSFs as they present lower urinary pH, lower uric acid fractional excretion and higher serum uric acid. On the contrary, patients with UC-RSFs show urinary risk factors more similar to those for calcium oxalate stones. The dietary approach in patients forming uric acid stones should be reconsidered with more attention to the quantity and quality of carbohydrate intake.

An Increase Incidence in Uric Acid Nephrolithiasis: Changing Patterns

INTRODUCTION

Nephrolithiasis is a complex disease affecting all age groups globally. As the causative factors for nephrolithiasis rises significantly, its incidence, prevalence and recurrence continues to baffle clinicians and patients.

AIM

To study the prevalence of different types of renal stones extracted by Percutaneous Nephrolithotomy (PCNL) and open surgical procedures.

MATERIALS AND METHODS

Renal stones from 50 patients were retrieved by Percutaneous Nephrolithotomy (PCNL), Ureterorenoscopy (URS) and open surgical techniques for qualitative tests for detection of calcium, oxalate, uric acid, phosphate, ammonium ion, carbonate, cystine and xanthine.

RESULTS

Three patients had stone removed by open surgery and rest had undergone PCNL. Nine of the stones were pure of calcium oxalate, 9 were of pure uric acid and 32 were mixed stones. Forty one stones had calcium. Among the mixed stones, oxalate was present in 25 samples (39 of total), uric acid was seen in 17 (25 of total stones), phosphate was present in 23 (23 of total) and carbonate was present in 4 stones (4 of total). Only 1 patient had triple phosphate stone. 12 were of staghorn appearance of which 6 were of struvite type, 6 were pure uric acid and remaining were mixed oxalate-phosphate stones.

CONCLUSION

Our study, though in a small number of hospital based patients, found much higher prevalence of uric acid stones and mixed stones than reported by previous hospital based studies in north India (oxalate stones~90%, uric acid~1% and mixed stones~3%). Biochemical analysis of renal stones is warranted in all cases.

[Effect of the body mass index on outcomes of ureterorenoscopy for renal stones]

BACKGROUND

Purpose of this work is to compare the outcome of ureterorenoscopy (URS) with regard to stone-free rates (SFR) and complication rates (CR) in patients with different body mass index (BMI) scores for the treatment of kidney stones.

MATERIALS AND METHODS

A retrospective chart review of all patients with known BMI, who underwent URS for kidney stones between 2006 and 2012 at our institution, was performed (n = 556 patients). The SFR and CR of obese patients were compared to overweight and normal weight patients.

RESULTS

Mean age was 52.51 years and the average BMI 27.74 kg/m². Of the patients, 34.2 % had normal weight (22.59 ± 1.91 kg/m²), 39.6 % were overweight (27.30 ± 1.42 kg/m²), and 26.3 % were obese (35.09 ± 5.93 kg/m²). The mean ASA score differed significantly between normal weight (1.99 ± 0.57), overweight (2.03 ± 0.62), and obese (2.22 ± 0.63) patients (p ≤ 0.036). The mean stone size was 8.51 ± 6.84 mm and the mean number of stones per patient 1.9 ± 2.41, whereby the differences between groups was not significant. There were no differences between the groups regarding the use of preoperative (94.8 %) and postoperative ureteral stents (60.3 %), the Ho:YAG laser (33.6 %), the use of flexible (16.2 %) or semirigid/flexible URS (59.4 %), and the mean operative time (52.04 ± 34.55 min). There were no differences in the SFR for the upper (90 %), mid (94.7 %), and lower pole (90.2 %), multiple location (68.6 %) or the total SFR (86.3 %). Total SFR of 95.7, 88.4, and 73.7 % for urinary calculi < 5 mm, 5-9 mm, and ≥ 10 mm, respectively, were found and the differences between the patient groups was not significant. The CR was 10.4 % (differences between the patient groups not significant).

CONCLUSION

URS is an appropriate treatment for renal stones with high SFR and low CR regardless of patient's BMI.

Risks associated with drug treatments for kidney stones

INTRODUCTION

Renal stones are one of the most painful medical conditions patients experience. For many they are also a recurrent problem. Fortunately, there are a number of drug therapies available to treat symptoms as well as prevent future stone formation.

AREAS COVERED

Herein, we review the most common drugs used in the treatment of renal stones, explaining the mechanism of action and potential side effects. Search of the Medline databases and relevant textbooks was conducted to obtain the relevant information. Further details were sourced from drug prescribing manuals. Recent studies of drug effectiveness are included as appropriate.

EXPERT OPINION

Recent controversies include medical expulsive therapy trials and complex role of urinary citrate in stone disease. Future directions in research will involve new medical therapies for stone prevention, for example new drugs for hyperoxaluria.

Stone Composition Among First-Time Symptomatic Kidney Stone Formers in the Community

OBJECTIVE

To determine the variation in kidney stone composition and its association with risk factors and recurrence among first-time stone formers in the general population.

PATIENTS AND METHODS

Medical records were manually reviewed and validated for symptomatic kidney stone episodes among Olmsted County, Minnesota, residents from January 1, 1984, through December 31, 2012. Clinical and laboratory characteristics and the risk of symptomatic recurrence were compared between stone compositions.

RESULTS

There were 2961 validated first-time symptomatic kidney stone formers. Stone composition analysis was obtained in 1508 (51%) at the first episode. Stone formers were divided into the following mutually exclusive groups: any brushite (0.9%), any struvite (0.9%), any uric acid (4.8%), and majority calcium oxalate (76%) or majority hydroxyapatite (18%). Stone composition varied with clinical characteristics. A multivariable model had a 69% probability of correctly estimating stone composition but assuming calcium oxalate monohydrate stone was correct 65% of the time. Symptomatic recurrence at 10 years was approximately 50% for brushite, struvite, and uric acid but approximately 30% for calcium oxalate and hydroxyapatite stones (P<.001). Recurrence was similar across different proportions of calcium oxalate and hydroxyapatite (P for trend=.10). However, among calcium oxalate stones, 10-year recurrence rate ranged from 38% for 100% calcium oxalate dihydrate to 26% for 100% calcium oxalate monohydrate (P for trend=.007).

CONCLUSION

Calcium stones are more common (93.5% of stone formers) than has been previously reported. Although clinical and laboratory factors associate with the stone composition, they are of limited utility for estimating stone composition. Rarer stone compositions are more likely to recur.

Protein expression of urate transporters in renal tissue of patients with uric acid nephrolithiasis

URAT1 and GLUT9 are two primary urate transporters involved in the renal urate handling. Renal urate underexcretion was reported in uric acid stone formers (UASF) in previous clinical studies. The aim of this study was to investigate the clinical features and possible impact of protein expression of URAT1 and GLUT9 in renal tissues of patients with uric acid (UA) nephrolithiasis. 23 UASF, 27 patients with calcium oxalate (CaOx) stones, and 22 normal controls were enrolled in this study. Clinical data revealed that older age of onset, high plasma UA concentration, low urinary PH, and relative renal urate underexcretion were associated with UASF. By immunohistochemical or western blotting analysis, a significant increase in the relative expression quantity of URAT1 in renal tissue of UASF was found compared to patients with CaOx nephrolithiasis and normal controls. In conclusion, our results suggested that upregulated URAT1 protein expression might contribute to the relative urate underexcretion from the kidney of UASF.

Medical management of kidney stones: AUA guideline

PURPOSE

The purpose of this guideline is to provide a clinical framework for the diagnosis, prevention and follow-up of adult patients with kidney stones based on the best available published literature.

MATERIALS AND METHODS

The primary source of evidence for this guideline was the systematic review conducted by the Agency for Healthcare Research and Quality on recurrent nephrolithiasis in adults. To augment and broaden the body of evidence in the AHRQ report, the AUA conducted supplementary searches for articles published from 2007 through 2012 that were systematically reviewed using a methodology developed a priori. In total, these sources yielded 46 studies that were used to form evidence-based guideline statements. In the absence of sufficient evidence, additional statements were developed as Clinical Principles and Expert Opinions.

RESULTS

Guideline statements were created to inform clinicians regarding the use of a screening evaluation for first-time and recurrent stone formers, the appropriate initiation of a metabolic evaluation in select patients and recommendations for the initiation and follow-up of medication and/or dietary measures in specific patients.

CONCLUSIONS

A variety of medications and dietary measures have been evaluated with greater or less rigor for their efficacy in reducing recurrence rates in stone formers. The guideline statements offered in this document provide a simple, evidence-based approach to identify high-risk or interested stone-forming patients for whom medical and dietary therapy based on metabolic testing and close follow-up is likely to be effective in reducing stone recurrence.

[Nephrolithiasis: metabolic defects and terapeutic implications]

Over the past 10 years, major progress has been made in the knowledge of urinary lithogenesis, including the potential pathogenetic role of Randall's plaques and renal tubular crystal retention. Urine supersaturation is the driving force of this process and can be induced by some risk factors, including low urine volume, high urinary excretion of calcium oxalate and uric acid and low urinary excretion of citrate. Primary hypercalciuria can be due to intestinal overabsorption renal leak and bone reabsorption of calcium. Prophilaxis is mainly conducted with thiazides and low calcium diet which is indicated only in the intestinal form. Primary hyperoxaluria is treated with pyridoxine and may require in the severe forms simultaneous renal and liver transplantation. Enteric hyperoxaluria is secondary to fatty acids malabsorption and requires diet, oral calcium and cholestiramine. Hyperuricosuria is caused by diet endogenous overproduction, mainly due to enzymatic defects or high renal excretion of uric acid. Urine alkalinization with K or K and Mg citrate can prevent stone formation even in idiopathic uric acid nephrolithiasis, in which a defect of urine acidification is supposed to be the main abnormality, and in hypocitraturic patients. Cystinuria is a rare inherited defect with an intense clinical impact. It can be classified in three forms and urinary stone formation is the role. Increased solubility and conversion of cystine in a more soluble form are the main goals of the prophylaxis which includes K citrate and thiol agents administration. Tiopronin is preferred to D-penicillamine due to its lower side effects.

The relationship between urinary stone components and visceral adipose tissue using computed tomography--based fat delineation

OBJECTIVE

To determine the relationship between body mass index (BMI), visceral adipose tissue (VAT), and stone components.

METHODS

A cross-sectional study has been done for urinary stone cohort between 2010 and 2012. Data on patient's age, gender, BMI, urinary pH, stone components, and VAT using computed tomography-based delineation were collected. Obesity was defined as BMI≥25 kg/m2 or as VAT≥100 cm2. To compare the differences between the types of stones, multinomial logistic regression analyses were conducted.

RESULTS

Of 203 cases, 49.3% patients were obese based on BMI, and 65.5% were obese using VAT criteria. Multinomial logistic regression analysis revealed that obesity defined by VAT was found to be associated with uric acid stones compared with calcium phosphate stones (odds ratio [OR] 6.544, 95% confidence interval [CI], P=.030) and mixed calcium oxalate phosphate stones (OR 5.582, 95% CI, P=.038). Similar results were observed in calcium oxalate stones over calcium phosphate stones (OR 2.984, 95% CI, P=.032) and calcium oxalate phosphate stones (OR 2.542, 95% CI, P=.041). On the contrary, obesity defined based on BMI has no correlation over all types of urinary stone components.

CONCLUSION

This result implies that VAT has a more important role in uric acid and calcium oxalate stone formation than total body fat, represented by BMI.

Metabolic syndrome and nephrolithiasis: a systematic review and meta-analysis of the scientific evidence

The metabolic syndrome is a cluster of cardiometabolic alterations at least partly dependent on reduced insulin sensitivity and hyperinsulinemia that can have several renal implications. A systematic review and meta-analysis of studies available in the international literature in English language demonstrates that the metabolic syndrome occurrence is associated with a significantly higher prevalence of nephrolithiasis (odds ratio 1.29, 95% confidence intervals: 1.11-1.51). The pathophysiological bases of this association are currently not completely understood, however. Potential pathogenetic links between the two conditions include metabolic factors that promote insulin resistance as well as stone formation in urine, environmental factors such as diet, oxidative stress and inflammation, and molecular changes impacting the transport of some analytes in urine. Metabolic syndrome-related nephrolithiasis shows peculiar clinical and biochemical characteristics and should be considered a multifactorial systemic disorder needing a multidisciplinary approach for adequate prevention and management in pediatric and adult age.

Epidemiology and clinical pathophysiology of uric acid kidney stones

There is global diversity in the prevalence of uric acid (UA) nephrolithiasis. UA nephrolithiasis comprises 8-10 % of all kidney stones in the United States. However, its prevalence is higher in patients with type 2 diabetes mellitus and those with obesity. Three significant urinary abnormalities have been described as the main etiologic factors for the development of UA nephrolithiasis; low urinary pH, hyperuricosuria and low urinary volume. However, an unduly acidic urine below the ionization constant of uric acid (pKa < 5.5) increases the urinary content of undissociated uric acid and thereby uric acid precipitation. Previous studies have shown the two major pathogenic mechanisms for unduly urinary pH are increased net acid excretion (NAE) and reduced renal ammonium (NH4 (+)), with a combination resulting in overly acidic urine. The impaired ammonium excretion has been demonstrated in a steady state in 24-hour urine and also following an oral ammonium chloride (NH4Cl) challenge to amplify ammoniogenic defects in this population. Similar abnormalities have been disclosed in normal populations and also in T2DM populations without kidney stones. To date, the underlying mechanism of increased acid production, source and nature of putative organic acid anions have not been fully elucidated. One plausible mechanism is the production of organic acid by intestinal and aerobic metabolism. This may occur in obese, diabetic and uric acid stone formers due to the differences in gut microflora.

The Study of Pyridazine Compounds on Prostanoids: Inhibitors of COX, cAMP Phosphodiesterase, and TXA2Synthase

The pyridazine moiety is an important structural feature of various pharmacological active compounds. Synthetic pyridazine compounds have been reported as effective antiprostaglandins (PGs), 5-lipoxygenase (5-LOX), and antiplatelet agents, that is, inhibitors of prostaglandin or cyclooxygenase (COX-I & COX-II) enzyme, platelet cAMP phosphodiesterase, and thromboxane A2 (TXA2) synthase. These compounds are selective and nonselective COX inhibitors and showed analgesic, anti-inflammatory, and antipyretic activity. Pyridazine compounds with antiplatelet agents inhibited TXA2enzyme. Pyridazines also exhibited antirheumatoid activity. These pyridazine compounds hold considerable interest relative to the preparation of organic intermediates and other anticipated biologically active compounds.

Mass spectrometric study of stone matrix proteins of human bladder stones

OBJECTIVE

To evaluate the mechanisms of bladder uric acid stone (BUAS) formation by analyzing BUAS stone matrix proteins, with mass spectrometry (MS).

MATERIALS AND METHODS

Stone matrix proteins were extracted from 5 pure BUASs. The obtained proteins were analyzed with reverse phase liquid chromatography-tandem MS. The acquired data were investigated against a Swiss Prot human protein database, using Matrix Science Mascot. The identified proteins were submitted to UniProtKB website for gene ontology analysis to define their correlation. They were also submitted to Metacore platform and Kyoto Encyclopedia of Genes and Genomes website for pathway analysis. MS-determined protein expressions were validated by immunoblot.

RESULTS

The liquid chromatography-tandem MS analysis identified 58-226 proteins in the 5 BUASs (450 proteins). Metacore software analysis suggests that inflammation might play an important role for BUAS formation. The analysis of endogenous metabolic pathways revealed that these proteins were categorized into glycerophospholipid or glycosphingolipid biosynthesis. Four of 5 identified proteins selected for validation, including uromodulin, S100P, Histone 4, and nucleophosmin, can be validated in the immunoblot data.

CONCLUSION

Our results suggest that inflammatory process and lipid metabolism might play a role in the formation of BUAS. Whether these inflammatory responses are the etiology of stone formation or whether they result from local damage by stone irritation is uncertain.

Kidney stones: an update on current pharmacological management and future directions

INTRODUCTION

Kidney stones are a common problem worldwide with substantial morbidities and economic costs. Medical therapy reduces stone recurrence significantly. Much progress has been made in the last several decades in improving therapy of stone disease.

AREAS COVERED

This review discusses i) the effect of medical expulsive therapy on spontaneous stone passage, ii) pharmacotherapy in the prevention of stone recurrence and iii) future directions in the treatment of kidney stone disease.

EXPERT OPINION

Fluid intake to promote urine volume of at least 2.5 L each day is essential to prevent stone formation. Dietary recommendations should be adjusted based on individual metabolic abnormalities. Properly dosed thiazide treatment is the standard therapy for calcium stone formers with idiopathic hypercalciuria. Potassium alkali therapy is considered for hypocitraturia, but caution should be taken to prevent potential risk of calcium phosphate stone formation. For absorptive hyperoxaluria, low oxalate diet and increased dietary calcium intake are recommended. Pyridoxine has been shown effective in some cases of primary hyperoxaluria type I. Allopurinol is used in calcium oxalate stone formers with hyperuricosuria. Treatment of cystine stones remains challenging. Tiopronin can be used if urinary alkalinization and adequate fluid intake are insufficient. For struvite stones, complete surgical removal coupled with appropriate antibiotic therapy is necessary.