Metabolic syndrome and uric acid nephrolithiasis

Relationship between the weight-adjusted-waist index and kidney stone: a population-based study

BACKGROUND

At present, a growing number of studies have shown a positive association between obesity and kidney stone, while traditional anthropometric measures, such as body mass index (BMI) and Waist circumference (WC), have limited ability to assess the risk of kidney stone. Therefore, this study aimed to investigate the association between the weight-adjusted-waist index (WWI) and the risk of kidney stone.

METHOD

Data from the National Health and Nutrition Examination Survey (NHANES) between 2009 and 2016 were used. A total of 17,292 participants from NHANES were included in the study. Multivariate logistic regression and restricted cubic splines (RCS) were used to investigate the relationship between WWI and kidney stone. Interaction analysis was performed for subgroups to verify the results. Meanwhile, the receiver operating characteristic curve (ROC) was used to analyze the efficacy of different anthropometric indices in predicting the risk of kidney stone.

RESULTS

After adjusting for potential confounding factors, we found a positive and independent association between kidney stone and WWI. After adjusting for all covariates, a one-unit increase in WWI was associated with a 36% increase in the risk of kidney stones. Dose-response curve analysis showed that WWI was non-linear correlated with the prevalence of kidney stone. In ROC analysis, WWI showed better discrimination for kidney stone (area under the curve: 0.612; 95% CI: 0.599-0.626; optimal cutoff value: 11.063) compared with other indices.

CONCLUSION

In this study, increased WWI was strongly associated with the risk of kidney stone.

Description of Stone Morphology and Crystalluria Improve Diagnosis and Care of Kidney Stone Formers

Stone analysis by physical methods is critical to determine their chemical nature and to diagnose the underlying conditions affecting kidney stone formers. This analysis should be completed by a morphologic examination of stone surface and section, leading to the diagnosis of anatomical or metabolic disorders and of specific diseases. Crystalluria study, the analysis of urine crystals, provides complementary information and is extremely useful for both diagnosis and patient follow-up. This review describes briefly how these techniques may be used and in which conditions stone morphology and urine crystal description are particularly relevant for patients medical care.

Association between visceral adiposity index and kidney stones in American adults: A cross-sectional analysis of NHANES 2007–2018

Objective

To explore the association between Visceral Adiposity Index (VAI) and kidney stones in an American adult population.

Materials and methods

National Health and Nutrition Examination Survey (NHANES) datasets from 2007 to 2018 were used. Participants aged ≥20 years who reported kidney stone history and VAI were included. Weighted proportions, multivariable analysis, generalized additive model (GAM), and spline smoothing were used to evaluate the associations between VAI and kidney stones by adjusting gender, age, race, education, marital status, poverty income ratio, smoking, alcohol, high blood pressure, diabetes, congestive heart failure, cancer, vigorous activity, moderate activity, HEI2015 total score, and energy.

Results

Totally 13,871 American adults were included. All the participants were divided by the VAI into four groups according to the quartile: Q1 (11.96–42.89), Q2 (42.90–74.45), Q3 (74.45–131.43), and Q4 (131.45–611.34). The mean ± standard deviation of the VAI in the four groups were Q1 (29.07 ± 8.22), Q2 (57.53 ± 8.81), Q3 (99.52 ± 16.25), and Q4 (225.92 ± 95.83). In the fully adjusted multivariable model, VAI was positively correlated with urolithiasis [odds ratio (OR) = 1.001; 95% confidence interval (CI) 1.000–1.001]. Compared with the first quartile of VAI, the population in the fourth quartile of VAI had a higher prevalence of kidney stones (OR = 1.329; 95% CI 1.104–1.600). Subgroup analysis detected no significant interaction effect after adjusting for covariates.

Conclusion

The value of VAI is positively correlated with the prevalence of kidney stones, which suggest VAI can be used to assess the potential risk of the prevalence of kidney stones.

Nephrolithiasis: A Red Flag for Cardiovascular Risk

Epidemiological evidence shows that nephrolithiasis is associated with cardiovascular (CV) morbidities. The association between nephrolithiasis and CV disease is not surprising because both diseases share conditions that facilitate their development. Metabolic conditions, encompassed in the definition of metabolic syndrome (MS), and habits that promote nephrolithiasis by altering urine composition also promote clinical manifestations of CV disease. By inducing oxidative stress, these conditions cause endothelial dysfunction and increased arterial stiffness, which are both well-known predictors of CV disease. Furthermore, the subtle systemic metabolic acidosis observed in stone formers with CV disease may have a pathogenic role by increasing bone turnover and leading to reduced mineral content and osteoporosis/osteopenia. Heart valves and/or coronary artery and aortic calcifications are frequently associated with reduced mineral density. This is known as the 'calcification paradox' in osteoporosis and has also been observed in subjects with calcium nephrolithiasis. Evidence supports the hypothesis that osteoporosis/osteopenia is an independent risk factor for the development of CV calcifications. In the long term, episodes of renal stones may occur from the onset of metabolic derangements/MS to arterial stiffness/atherosclerosis and CV morbidities. These episodes should be considered a warning sign of an ongoing and silent atherosclerotic process. The evaluation of cardiometabolic risk factors and MS components should be routine in the assessment of renal stone formers. This would allow for treatment and prevention of the development of CV complications, which are much more severe for the patient and for public health.

Association between hyperlipidemia and calcium oxalate lower urinary tract uroliths in dogs

Background

Metabolic syndrome is associated with formation of calcium oxalate (CaOx) uroliths in humans.

Objectives

To investigate the association between obesity and hyperlipidemia with CaOx lower urinary tract uroliths in client‐owned dogs.

Animals

Dogs with (n = 55, U [uroliths]‐dogs) and without (n = 39, UF [uroliths‐free]‐dogs) CaOx lower urinary tract uroliths.

Methods

Case‐control study. U‐dogs were retrospectively enrolled and compared to UF‐dogs. Body condition score (BCS; 1‐9 scoring scale), serum triglyceride (TG) and total cholesterol (CH) concentrations and glycemia (after >12‐hour food withholding) were recorded in both groups.

Results

On univariate logistic regression, when excluding Miniature Schnauzers, odds of having uroliths increased by a factor of 3.32 (95% CI 1.38‐11.12) for each mmol/L of TG (P = .027), of 39 (95% CI 9.27‐293.22) for each mmol/L of glycemia (P < .0001), and of 2.43 (95% CI 1.45‐4.45) per unit of BCS (P = .002). In multivariable models, the effect of TG was retained when all breeds were included for analysis and odds of having uroliths increased by a factor of 4.34 per mmol/L of TG (95% CI 1.45‐19.99; P = .02).

Conclusions and Clinical Importance

Serum lipid screening in dogs diagnosed with CaOx uroliths might be recommended to improve their medical staging and management.

Association between metabolic syndrome and calcium oxalate stone risk in Chinese individuals: a nomogram prediction model

Objective

This retrospective study explored the association between calcium oxalate (CaOx) stones and metabolic syndrome. It also developed and validated a nomogram to aid in the prediction of CaOx stones.

Methods

This case-control study enrolled 150 patients with CaOx stones and 635 individuals without urolithiasis from October 2016 to October 2018. Student’s t-test, the chi-squared test, and logistic univariate and multivariate regression analyses were used. A nomogram for prediction of CaOx stones was established based on independent associated factors. The concordance index and calibration curves were plotted to determine nomogram accuracy.

Results

Female sex, age ≥66 years, blood pressure (systolic pressure ≥130 mmHg and/or diastolic pressure ≥85 mmHg), and blood uric acid level independently influenced the risk of CaOx stones, according to multivariate logistic regression analysis; these factors were included in the nomogram. The concordance index was 0.701 (95% confidence interval: 0.658–0.737). The standard curve showed a robust fit with the calibrated predictive curve.

Conclusions

Female sex, age ≥66 years, elevated blood pressure, and blood uric acid level independently influenced the risk of CaOx stones. Our nomogram for the prediction of CaOx stones may provide a clinical basis for the assessment of CaOx stone and facilitate early prevention efforts.

Association between metabolic syndrome components and the risk of developing nephrolithiasis: A systematic review and bayesian meta-analysis

Background: There is increasing evidence that nephrolithiasis is a systemic disease, as opposed to an isolated urinary metabolic problem, after considerable links were found between nephrolithiasis and systemic diseases such as hypertension, obesity, dyslipidemia, and insulin resistance. The interplay between these four factors defines metabolic syndrome (MetS). In this review we aim to clarify the associations of MetS and its components to kidney stone incident. Methods: Online databases of EMBASE, MEDLINE, and Google Scholar were searched from January 1998 up to October 2020 to identify observational studies examining the association between metabolic syndrome components and kidney stone incident. Bayesian random-effects meta-analysis and meta-regression were performed to observe the association. Linear dose-response analysis was conducted to shape the direction of the association. Data analysis was performed using STATA, and R statistics. Results: A total of 25 potentially relevant studies (n = 934,588 participants) were eventually identified. The pooled results suggested that metabolic syndrome was associated with an increased risk of nephrolithiasis with an odds ratio (OR) of 1.769 (95% CI: 1.386 - 2.309).  The summary OR of hypertension and dyslipidemia for developing nephrolithiasis were 1.613 (95% CI: 1.213 - 2.169) and 1.586 (95% CI: 1.007 - 2.502) respectively. The presence of diabetes mellitus and obesity had an OR of 1.552 (95% CI: 1.027 - 2.344) and 1.531 (95% CI: 1.099 - 2.109) respectively. Our results revealed that the increasing number of MetS traits will increase the risk of developing nephrolithiasis, the higher the fasting plasma glucose, and body mass index, the higher the risk of kidney stones incident. Conclusions: Our results suggest that hypertension, diabetes, obesity and dyslipidemia are associated with increased risk of developing nephrolithiasis. Linear significant association between MetS components and nephrolithiasis were revealed in our study which reinforced the notion that should be considered a systemic disorder.

Association of low urine pH as a metabolic feature with abdominal obesity

Objective

Low urine pH (LUP) is not only affected by environmental factors, but is also a feature of metabolic syndrome (MS), which is characterized by insulin resistance, abdominal obesity, dyslipidaemia and hypertension. However, it is unclear which factors contribute most to urine acidity. This study investigated factors influencing LUP and the link between LUP and metabolic traits in South Korea.

Methods

Participants were middle-aged subjects (age, 52.2 ± 8.9 years; average body mass index, 24.6 ± 3.2 kg/m²), of whom 4,626 had urine pH of 5.0 and were assigned to the LUP group and 4,185 had urine pH > 5.0 and were assigned to the control group. The association between LUP and various phenotypes, including environmental and metabolic traits, was analysed.

Results

LUP was significantly associated with MS diagnostic components and with environmental exposures such as smoking, alcohol intake and low-fibre diet. Multivariate analysis showed that the waist-to-hip ratio was the best predictor for LUP compared with other MS components (OR: 2.439).

Conclusions

LUP is an indicator of MS and is mainly related to the MS diagnostic criterion of abdominal obesity, even after adjusting for environmental influences on urine acidity.

Determining the true burden of kidney stone disease

The incidence and prevalence of kidney stones have increased over the past four decades. However, the diagnosis of 'kidney stone' can range from an incidental asymptomatic finding of limited clinical significance to multiple painful episodes of ureteral obstruction with eventual kidney failure. Some general strategies may be useful to prevent the recurrence of kidney stones. In particular, greater attention to kidney stone classification, approaches to assessing the risk of recurrence and individualized prevention strategies may improve the clinical care of stone formers. Although there have been some advances in approaches to predicting the recurrence of kidney stones, notable challenges remain. Studies of kidney stone prevalence, incidence and recurrence have reported inconsistent findings, in part because of the lack of a standardized stone classification system. A kidney stone classification system based on practical and clinically useful measures of stone disease may help to improve both the study and clinical care of stone formers. Any future kidney stone classification system should be aimed at distinguishing asymptomatic from symptomatic stones, clinically diagnosed symptomatic stone episodes from self-reported symptomatic stone episodes, symptomatic stone episodes that are confirmed from those that are suspected, symptomatic recurrence from radiographic recurrence (that is, with radiographic evidence of a new stone, stone growth or stone disappearance from presumed passage) and determine stone composition based on mutually exclusive categories.

Relationship Between Body Mass Index and Kidney Stones Based on Dose-Response Analyses Using Restricted Cubic Splines Applied to NHANES 2011-2016 Data

OBJECTIVE

The objective of the study was to estimate the dose-response relationship between body mass index (BMI) and the self-reported prevalence of kidney stones based on a restricted cubic spline (RCS) method.

METHODS

This cross-sectional study analyzed 13,223 adults aged ≥20 years who had participated in the National Health and Nutrition Examination Survey performed during 2011-2016. Kidney stones were identified using a standard questionnaire, and physical examinations were used to determine BMI. Logistic regression was used to assess the relationship between BMI and the prevalence of kidney stones, with the dose-response relationship explored using RCSs.

RESULTS

The overall prevalence of kidney stones was 9.7%: 10.6% in males and 8.9% in females. After adjusting for potential confounders, compared with those with a BMI in quartile 1, the odds ratios of kidney stones among those with BMIs in quartiles 2, 3, and 4 were 1.45, 1.60, and 2.00, respectively (95% confidence interval = 1.21-1.75, 1.33-1.92, and 1.67-2.39; all P < .001). Multivariate RCS regression revealed that BMI was related to kidney stones in a nonlinear manner (P for nonlinearity <0.001). There was a significant positive relationship, with the curves being steeper when BMI was <28 kg/m².

CONCLUSION

This analysis of National Health and Nutrition Examination Survey data has demonstrated that BMI is significantly associated with the prevalence of kidney stones.

Nephrolithiasis and Elevated Urinary Ammonium: A Matched Comparative Study

OBJECTIVE

To describe the associations between elevated urinary ammonium and clinical characteristics of kidney stone formers. A 24-hour urine test is recommended in high-risk patients to identify urinary abnormalities and select interventions to reduce the recurrence risk. While elevations in urine ammonium may be seen in acidosis, diarrhea, high protein diets or due to pathogenic bacteria, the clinical characteristics of these patients have not been previously described.

METHODS

We retrospectively identified adult patients with kidney stone disease who completed a 24-hour urine at our institution between 2006 and 2017. Patients with elevated urinary ammonium were identified (n = 121) and matched 1:1 by age and sex to controls for an overall cohort of n = 242. Differences in medical and surgical history, 24-hour urine analytes and stone composition were compared.

RESULTS

Among 3625 24-hour urine studies screened, 7.1% of patients showed high urinary ammonium. In our study cohort, patients with elevated urinary ammonium also showed higher urine volume, oxalate, calcium, uric acid, sodium, chloride, and sulfate. Clinically, these patients had higher body mass index, and more often had a history of recurrent urinary tract infections, diabetes, gout, bowel resection, and urinary reconstruction history. Struvite stones tended to be more common in the elevated ammonium group vs control (n = 7 vs 1, P = .07).

CONCLUSION

Elevated urinary ammonium among kidney stone patients is relatively uncommon. However, these patients have higher rates of comorbid metabolic conditions, urinary tract infections, and bowel surgery. This finding should prompt further review of the patient's history and may help direct prevention strategies.

Obesity and stones

PURPOSE OF REVIEW

The incidence of urolithiasis has shown a prominent increase in the last two to three decades and evidence-based data have clearly indicated the certain role of obesity and overweight in both children and adults. As a certain component of metabolic syndrome, 'obesity' has been found to have a significant impact on the urinary metabolic risk factors which may be important in stone formation. In this present review article, we aimed to evaluate the possible association between obesity and urolithiasis and related risk factors. The epidemiology, pathophysiology, and management of stone disease in obese cases will be discussed in detail.

RECENT FINDINGS

The possible influence of overweight/obesity on the metabolic stone-forming risk factors has been subjected to several studies which in turn well demonstrated the increased risk of stone formation in this population. Although the exact underlying mechanisms are still to be outlined, some certain pathogenetic factors, namely, changes in urinary pH and increased excretion of some urinary stone components have been well demonstrated. Given this increased risk status, these cases require a more comprehensive workup for urolithiasis. Appropriate metabolic evaluation-based medical therapy alongside dietary recommendations will be effective in preventing stone formation.

SUMMARY

Patients suffering from obesity problem have particular risk factors for urolithiasis when compared with their normal-weight counterparts. All efforts should be taken to increase the awareness of this problem and necessary precautions with well-planned treatment plan are the main tasks for urologists.

Pharmacologic inducers of the uric acid exporter ABCG2 as potential drugs for treatment of gouty arthritis

Uric acid is the end product of purine catabolism and its plasma levels are maintained below its maximum solubility in water (6–7 mg/dl). The plasma levels are tightly regulated as the balance between the rate of production and the rate of excretion, the latter occurring in urine (kidney), bile (liver) and feces (intestinal tract). Reabsorption in kidney is also an important component of this process. Both excretion and reabsorption are mediated by specific transporters. Disruption of the balance between production and excretion leads to hyperuricemia, which increases the risk of uric acid crystallization as monosodium urate with subsequent deposition of the crystals in joints causing gouty arthritis. Loss-of-function mutations in the transporters that mediate uric acid excretion are associated with gout. The ATP-Binding Cassette exporter ABCG2 is important in uric acid excretion at all three sites: kidney (urine), liver (bile), and intestine (feces). Mutations in this transporter cause gout and these mutations occur at significant prevalence in general population. However, mutations that are most prevalent result only in partial loss of transport function. Therefore, if the expression of these partially defective transporters could be induced, the increased number of the transporter molecules would compensate for the mutation-associated decrease in transport function and hence increase uric acid excretion. As such, pharmacologic agents with ability to induce the expression of ABCG2 represent potentially a novel class of drugs for treatment of gouty arthritis.

Targeted renal knockdown of Na+/H+ exchanger regulatory factor Sip1 produces uric acid nephrolithiasis in Drosophila

Nephrolithiasis is one of the most common kidney diseases, with poorly understood pathophysiology, but experimental study has been hindered by lack of experimentally tractable models. Drosophila melanogaster is a useful model organism for renal diseases because of genetic and functional similarities of Malpighian (renal) tubules with the human kidney. Here, we demonstrated function of the sex-determining region Y protein-interacting protein-1 (Sip1) gene, an ortholog of human Na⁺/H⁺ exchanger regulatory factor (NHERF1), in Drosophila Malpighian tubules and its impact on nephrolithiasis. Abundant birefringent calculi were observed in Sip1 mutant flies, and the phenotype was also observed in renal stellate cell-specific RNA interference Sip1 knockdown in otherwise normal flies, confirming a renal etiology. This phenotype was abolished in rosy mutant flies (which model human xanthinuria) and by the xanthine oxidase inhibitor allopurinol, suggesting that the calculi were of uric acid. This was confirmed by direct biochemical assay for urate. Stones rapidly dissolved when the tubule was bathed in alkaline media, suggesting that Sip1 knockdown was acidifying the tubule. SIP1 was shown to collocate with Na⁺/H⁺ exchanger isoform 2 (NHE2) and with moesin in stellate cells. Knockdown of NHE2 specifically to the stellate cells also increased renal uric acid stone formation, and so a model was developed in which SIP1 normally regulates NHE2 activity and luminal pH, ultimately leading to uric acid stone formation. Drosophila renal tubules may thus offer a useful model for urate nephrolithiasis.

Association of Adherence to The Mediterranean Diet with Urinary Factors Favoring Renal Lithiasis: Cross-Sectional Study of Overweight Individuals with Metabolic Syndrome

Our purpose was to study the relationship of adherence to the Mediterranean diet (MedDiet) with urinary factors that favor the formation of renal calcium and uric acid stones in overweight and obese participants who had metabolic syndrome. This cross-sectional study examined 267 participants. A well-known MedDiet score (range 0–9) was calculated for each patient, and patients were then categorized has having low (≤3), medium (4–5), or high (≥6) adherence to the MedDiet. Baseline characteristics and urinary parameters were also analyzed. High calcium salt urinary crystallization risk (CaUCR) and high uric acid urinary crystallization risk (UrUCR) were calculated from urinary parameters using pre-defined criteria. More than half of patients with MedDiet scores ≤3 had high UrUCR (55.4%) and high CaUCR (53.8%). In contrast, fewer patients with high adherence (≥6) to the MedDiet had high UrUCR (41.2%) and high CaUCR (29.4%). Relative to those with low adherence, individuals with high adherence had a prevalence ratio (PR) of 0.77 for a high UrUCR (95% CI: 0.46–1.12; p for trend: 0.069) and a PR of 0.51 for a high CaUCR (95% CI: 0.26–0.87; p for trend: 0.012) after adjusting for age, sex, body mass index, type 2 diabetes, and total energy intake. Our findings indicate that greater adherence to the MedDiet was associated with a reduced CaUCR and a reduced UrUCR. This suggests that adequate dietary management using the MedDiet patterns may prevent or reduce the incidence and recurrence of calcium salt and uric acid renal stones.

Clinical characteristics in urolithiasis formation according to body mass index

Although urolithiasis is considered to be strongly associated with lifestyle habits, there are numerous cases in which urolithiasis develops despite a non-obese body type or healthy lifestyle habits. However, in clinical practice, the diet therapy and lifestyle changes instructed for the prevention of recurrence of urolithiasis are almost identical in numerous cases. Therefore, the present study examined the effect of body mass index (BMI) on urolithiasis and its surrounding environment in patients, by analyzing the number of normal- and high-BMI (healthy and overweight) patients with urolithiasis. The present study analyzed 63 patients with urolithiasis for whom height and weight were measured at our hospital (Tokyo Medical University Ibaraki Medical Center). BMI <25 represents healthy body types and BMI ≥25 BMI defines overweight body types. Thus, patients were then grouped by BMI-defined body type using a threshold value of 25 accordingly. It was observed that a higher percentage of males were obese compared with females. Upon comparing the normal- and high-BMI groups, no significant difference was observed in uric acid level, urine pH or calculus number between the two groups. Liver computed tomography (CT) values were significantly lower in the high-BMI group compared with the normal-BMI group. There was no significant correlation between calculus size counts and BMI. However, a significant negative correlation was observed between BMI and the liver CT value. These results suggest that liver CT values correlated negatively with BMI, but the data indicates that other mechanisms unassociated with a fatty liver may be involved in urolithiasis in non-obese patients. The results of the present study suggest that physicians should consider the mechanism involved in preventing the recurrence of urolithiasis.

Addition of Sodium Bicarbonate to Irrigation Solution May Assist in Dissolution of Uric Acid Fragments During Ureteroscopy

INTRODUCTION

We hypothesized that adding sodium bicarbonate (bicarb) to normal saline (NS) irrigation during ureteroscopy in patients with uric acid (UA) nephrolithiasis may assist in dissolving small stone fragments produced during laser lithotripsy. In vitro testing was performed to determine whether dissolution of UA fragments could be accomplished within 1 hour.

MATERIALS AND METHODS

In total 100% UA renal calculi were fragmented, filtered, and separated by size. Fragment sizes were <0.5 mm and 0.5 to 1 mm. Similar amounts of stone material were agitated in solution at room temperature. Four solutions were tested (NS, NS +1 ampule bicarb/L, NS +2, NS +3). Both groups were filtered to remove solutions after fixed periods. Filtered specimens were dried and weighed. Fragment dissolution rates were calculated as percent removed per hour. Additional testing was performed to determine whether increasing the temperature of solution affected dissolution rates.

RESULTS

For fragments <0.5 mm, adding 2 or 3 bicarb ampules/L NS produced a dissolution rate averaging 91% ± 29% per hour. This rate averaged 226% faster than NS alone. With fragments 0.5 to 1 mm, addition of 2 or 3 bicarb ampules/L NS yielded a dissolution rate averaging 22% ± 7% per hour, which was nearly five times higher than NS alone. There was a trend for an increase in mean dissolution rate with higher temperature but this increase was not significant (p = 0.30).

CONCLUSIONS

The addition of bicarbonate to NS more than doubles the dissolution rate of UA stone fragments and fragments less than 0.5 mm can be completely dissolved within 1 hour. Addition of bicarb to NS irrigation is a simple and inexpensive approach that may assist in the dissolution of UA fragments produced during ureteroscopic laser lithotripsy. Further studies are needed to determine whether a clinical benefit exists.

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.

Meeting report of the "Symposium on kidney stones and mineral metabolism: calcium kidney stones in 2017"

A symposium on kidney stones and mineral metabolism held on December 2017 in Brussels, Belgium was the first international multidisciplinary conference of the International Collaborative Network on Kidney Stones and Mineral Metabolism. This meeting addressed epidemiology, underlying pathophysiological mechanisms, genetics, pathological, as well as clinical and research topics. The participants included clinicians and recognized experts in the field from Europe and the United States interacted closely during the symposium which promoted a chance to explore new frontiers in the field of kidney stone disease. This manuscript summarizes some of the major highlights of the meeting.

Association between blood lipid profile and urolithiasis: A systematic review and meta-analysis of observational studies

The objective of this study was to pool individual studies regarding the association of blood lipid profiles with urolithiasis to carry out a systematic review and meta-analysis. We searched MEDLINE, PubMed, Embase and Cochrane Library to identify the relevant studies up to November 2017. Studies that met all inclusion criteria were chosen, and a pooled analysis of the odds ratio between urolithiasis and dyslipidemia traits was calculated. A total of 11 observational studies (seven cross-sectional, three cohort, one case-control) with a total of 282 479 participants were examined. The overall pooled analysis of eight studies showed that high triglyceride was associated with increased estimated risk of urolithiasis (odds ratio 1.287, 95% CI 1.073-1.544; P = 0.007). Estimates of the total effect size were consistent in the sensitivity analysis. No evidence of publication bias was detected. The overall pooled analysis of nine studies showed low high-density lipoprotein was weakly associated with increased estimated risk of urolithiasis (odds ratio 1.171, 95% CI 1.010-1.358; P = 0.032). The sensitivity analysis showed conflicting results. No evidence of publication bias was detected. Three studies on the association between any dyslipidemia traits and urolithiasis showed a significant association (odds ratio 1.309, 95% CI 1.202-1.425; P < 0.001). The present meta-analysis showed that patients with higher triglyceride and lower high-density lipoprotein had an increased estimated risk of urolithiasis. A triglyceride-urolithiasis association was found to be more coherent and consistent compared with the high-density lipoprotein-urolithiasis association. Although somewhat contradictory results have been found, the meta-analysis is encouraging for evaluating urolithiasis as a systemic disorder. Further well-designed prospective randomized controlled or cohort studies are necessary to better elucidate the causal association of dyslipidemia and urolithiasis.

Obesity and metabolic stone disease

PURPOSE OF REVIEW

In this article, we aim to review the data regarding associations between obesity and nephrolithiasis to assist with workup and treatment of these intersecting disorders. As obesity has a multifactorial influence on the risk for urinary stone disease, the complicated mechanisms will be discussed to improve diagnosis and management.

RECENT FINDINGS

Obesity and metabolic syndrome interact with nephrolithiasis risk factors to produce a myriad of bodily responses that induce stone formation. For this reason, many societies recommend prompt metabolic workup to evaluate the precise causes of stone formation. Data have shown that dietary and directed medical therapies can produce an excellent therapeutic response in this patient population, although the response may be blunted compared with nonobese patients.

SUMMARY

Given the increasing number of obese and overweight patients, the urologist should be familiar with the pathophysiology, workup, and treatment of metabolic stone disease in this population, which are outlined here.

Kidney stone formers have more renal parenchymal crystals than non-stone formers, particularly in the papilla region

BACKGROUND

We investigated the renoprotective ability of healthy people against kidney stone formation. To clarify intratubular crystal kinetics and processing in human kidneys, we performed a quantitative and morphological observation of nephrectomized renal parenchyma tissues.

METHODS

Clinical data and pathological samples from 60 patients who underwent radical nephrectomy for renal cancer were collected from June 2004 to June 2010. The patients were retrospectively classified as stone formers (SFs; n = 30, kidney stones detected by preoperative computed tomography) and non-stone formers (NSFs; n = 30, no kidney stone history). The morphology of parenchymal intratubular crystals and kidney stone-related gene and protein expression levels were examined in noncancerous renal sections from both groups.

RESULTS

SFs had a higher smoking rate (P = 0.0097); lower red blood cell, hemoglobin, and hematocrit values; and higher urinary red blood cell, white blood cell, and bacterial counts than NSFs. Scanning electron microscopy revealed calcium-containing crystal deposits and crystal attachment to the renal tubular lumen in both groups. Both groups demonstrated crystal transmigration from the tubular lumen to the interstitium. The crystal diffusion analysis indicated a significantly higher crystal existing ratio in the medulla and papilla of SFs and a significantly higher number of papillary crystal deposits in SFs than NSFs. The expression analysis indicated relatively high osteopontin and CD68, low superoxide dismutase, and significantly lower Tamm-Horsfall protein expression levels in SFs. Multivariate logistic regression analysis involving the above factors found the presence of renal papillary crystals as a significant independent factor related to SFs (odds ratio 5.55, 95% confidence interval 1.08-37.18, P = 0.0395).

CONCLUSIONS

Regardless of stone formation, intratubular crystals in the renal parenchyma seem to transmigrate to the interstitium. SFs may have reduced ability to eliminate renal parenchymal crystals, particularly those in the papilla region, than NSFs with associated gene expression profiles.

The Relationship Between Nephrolithiasis Risk with Body Fat Measured by Body Composition Analyzer in Obese People

BACKGROUND

Nephrolithiasis (kidney stones) continues to be a major cause of morbidity and healthcare spending that visceral and subcutaneous adipose tissue may associate with kidney stone formation. This study aimed to investigate the relationship between nephrolithiasis with visceral fat scale in obese people in Western Iran for the first time.

MATERIALS AND METHODS

In 2017, 103 participants with BMI≥30 kg/m² were selected for the present study. The participants were divided into two groups, 52 as case group (having the kidney stone) and 58 as healthy control group (no kidney stone or history of the kidney stone or any other disease). The levels of body composition were checked by body composition analyzer (BoCA x1) based on Bio Impedance mechanism.

RESULTS

Two groups were matched in terms of sex and BMI. There was a significant difference between two groups for the visceral fat to subcutaneous fat ratio (VSR) that accordingly, the mean VSR in the case group was higher than the control group. The difference for other variables between two groups was not significant.

CONCLUSIONS

The results showed that visceral and subcutaneous fat and VSR were important risk factors for kidney stone formation (nephrolithiasis). Evaluating these fats in stone formers may facilitate a tailored metabolic evaluation and treatment plan.

The influence of serum uric acid on renal function in patients with calcium or uric acid stone: A population-based analysis

OBJECTIVES

To determine the influence of serum uric acid (UA) levels on renal impairment in patients with UA stone.

MATERIALS AND METHODS

We retrospectively analyzed 463 patients with calcium oxalate and/or calcium phosphate stones (CaOx/CaP), and 139 patients with UA stones. The subjects were divided into the serum UA-high (UA ≥ 7.0 mg/dL) or the UA-low group (UA < 7.0 mg/dL). The control group comprised 3082 community-dwelling individuals that were pair-matched according to age, sex, body mass index, comorbidities, hemoglobin, serum albumin, and serum UA using propensity score matching. We compared renal function between controls and patients with UA stone (analysis 1), and between patients with CaOx/CaP and with UA stone (analysis 2). Logistic regression analysis was used to evaluate the impact of the hyperuricemia on the development of stage 3 and 3B chronic kidney disease (CKD) (analysis 3).

RESULTS

The renal function was significantly associated with serum UA levels in the controls and patients with CaOx/CaP and UA stones. In pair-matched subgroups, patients with UA stone had significantly lower renal function than the control subjects (analysis 1) and patients with CaOx/CaP stones (analysis 2) regardless of hyperuricemia. Multivariate logistic regression analysis revealed that patients with UA stone, CaOx/CaP, hyperuricemia, presence of cardiovascular disease, higher body mass index, older age and lower hemoglobin had significantly higher risk of stage 3 and 3B CKD (analysis 3).

CONCLUSION

Patients with UA stones had significantly worse renal function than controls and CaOx/CaP patients regardless of hyperuricemia. Urolithiasis (CaOx/CaP and UA stone) and hyperuricemia had an association with impaired renal function. Our findings encourage clinicians to initiate intensive treatment and education approaches in patients with urolithiasis and/or hyperuricemia in order to prevent the progression of renal impairment.

The association of nephrolithiasis with metabolic syndrome and its components: a cross-sectional analysis

Background

Metabolic syndrome is a worldwide disorder and also the major risk factor of several systemic diseases. Evidence identifying the association between metabolic syndrome and nephrolithiasis is lacking, especially in Taiwan.

Aim

The aim of this study was to investigate the association between nephrolithiasis and metabolic syndrome and its components.

Design and setting

This was a cross-sectional study conducted in the Health Examination Department of a medical center in Changhua, Taiwan, from January 2010 to December 2010.

Methods

We reviewed the medical records of patients who had visited the Health Examination Center of Changhua Christian Hospital in 2010. A total of 3,886 individuals were enrolled. According to the exclusion criteria, those with an age <20 years and an abnormal renal function were excluded. A total of 3,793 subjects were included. All P-values are two tailed, and P<0.05 was defined as statistically significant.

Results

The results showed a correlation between nephrolithiasis and metabolic syndrome and its components. The multivariate-adjusted odds ratio (OR) (95% confidence interval [CI]) of metabolic syndrome for nephrolithiasis was 1.318 (1.083–1.604), with a P-value of 0.006. Larger waist circumference (multivariable-adjusted OR 1.338; 95% CI 1.098–1.631; P=0.004), higher blood pressure (multivariable-adjusted OR 1.333; 95% CI 1.106–1.607; P=0.003), and increased fasting glucose (multivariable-adjusted OR 1.276; 95% CI 1.054–1.546; P=0.01) were associated with nephrolithiasis.

Conclusion

This is the first study in Taiwan to investigate the relationship between metabolic syndrome and nephrolithiasis. The mechanism is controversial, and several hypotheses are offered. Adequate lifestyle modification and proper treatment in metabolic syndrome management may both contribute to nephrolithiasis prevention.

Nephrolithiasis in elderly population; effect of demographic characteristics

Background

Kidney stone (nephrolithiasis) is one of the most common diseases. During the past several decades, its prevalence and incidence have increased markedly in elderly population.

Objectives

This study was conducted to evaluate the risk factors for nephrolithiasis in elderly population.

Patients and Methods

This study was based on the Amirkola Health and Ageing Project (AHAP). Elderly people with kidney stones in every size, type and number were considered to be the case group and other subjects without a history of kidney stones served as control group. Demographic and anthropometric data, smoking, diabetes and metabolic syndrome (MetS), calcium (Ca), vitamin D, parathyroid hormone (PTH), uric acid and urine pH were compared in both groups.

Results

In this study, 1390 elderly people with the mean age of 69.37 ± 7.42 years were evaluated which 202 (14.53%) cases had renal stones. The patients with nephrolithiasis were younger (P = 0.010) and had higher uric acid and body mass index (BMI) levels (P = 0.041 and P = 0.006, respectively). Age <75 years, male gender and BMI ≥30 kg/m² had a significant association with stone formation. The prevalence of diabetes, MetS and smoking in the patients with nephrolithiasis was lower than the subjects without it.

Conclusions

This study suggests that male gender, obesity and age <75 years might be independent risk factors for the development of nephrolithiasis. Hence, low animal protein intake and weight reduction should be included as part of the counseling of senior stone-formers.

A Targeted Metabolomics Assay to Measure Eight Purines in the Diet of Common Bottlenose Dolphins, Tursiops truncatus

Bottlenose dolphins managed under human care, human beings and Dalmatian dogs are prone to forming urate uroliths. Limiting dietary purine intake limits urate urolith formation in people and dogs because purines are metabolized to uric acid, which is excreted in urine. Managed dolphins develop ammonium urate nephroliths, whereas free-ranging dolphins do not. Free-ranging dolphins consume live fish, whereas managed dolphins consume different species that have been stored frozen and thawed. Differences in the purine content of fish consumed by dolphins under human care versus in the wild may be responsible for the difference in urolith prevalence. Commercially available purine assays measure only four purines, but reported changes in purines during frozen storage suggest that a wider range of metabolites should be measured when comparing fresh and stored fish. A method using high performance liquid chromatography with tandem mass spectrometry was developed to quantify eight purine metabolites in whole fish and squid commonly consumed by dolphins. The coefficient of variation within and among days was sometimes high for purines present in small amounts but was acceptable (≤ 25%) for guanine, hypoxanthine, and inosine, which were present in high concentrations. This expanded assay identified a total purine content up to 2.5 times greater than the total that would be quantified if only four purines were measured. Assuming additional purines are absorbed, these results suggest that additional purine metabolites should be measured to better understand the associated risk when fish or other purine-rich foods are consumed by people or animals prone to developing uroliths.

A Targeted Metabolomics Assay to Measure Eight Purines in the Diet of Common Bottlenose Dolphins, Tursiops truncatus

Bottlenose dolphins managed under human care, human beings and Dalmatian dogs are prone to forming urate uroliths. Limiting dietary purine intake limits urate urolith formation in people and dogs because purines are metabolized to uric acid, which is excreted in urine. Managed dolphins develop ammonium urate nephroliths, whereas free-ranging dolphins do not. Free-ranging dolphins consume live fish, whereas managed dolphins consume different species that have been stored frozen and thawed. Differences in the purine content of fish consumed by dolphins under human care versus in the wild may be responsible for the difference in urolith prevalence. Commercially available purine assays measure only four purines, but reported changes in purines during frozen storage suggest that a wider range of metabolites should be measured when comparing fresh and stored fish. A method using high performance liquid chromatography with tandem mass spectrometry was developed to quantify eight purine metabolites in whole fish and squid commonly consumed by dolphins. The coefficient of variation within and among days was sometimes high for purines present in small amounts but was acceptable (≤ 25%) for guanine, hypoxanthine, and inosine, which were present in high concentrations. This expanded assay identified a total purine content up to 2.5 times greater than the total that would be quantified if only four purines were measured. Assuming additional purines are absorbed, these results suggest that additional purine metabolites should be measured to better understand the associated risk when fish or other purine-rich foods are consumed by people or animals prone to developing uroliths.

Efficacy and safety of mini percutaneous nephrolithotomy in obese patients

Purpose

We aimed to evaluate the effect of obesity on surgical outcomes of mini percutaneous nephrolithotomy (Mini-PNL).

Methods

Hundred and eighty two Mini-PNL procedures were performed between May 2013 and January 2015 and their results were evaluated retrospectively. Patients were classified as non-obese (BMI, 18.5–30 kg/m²) and obese (≥30 kg/m²) groups. Obese and non-obese patients were compared according to pre-operative demographic values, intra-operative surgery techniques and post-operative results.

Results

BMI values of 133 patients were lower than 30 kg/m² while 49 patient’s BMI values were higher than 30 kg/m². There were no significant difference between operation time, fluoroscopy time, number of access and access sites when two groups were compared. No significant difference was found in total length of hospital stay, hemoglobin drop, and complication rates. Stone-free rates were 70.7 % in the non-obese and 71.4 % in the obese group (p = 0.9).

Conclusions

Mini-PNL procedure is a safe and effective treatment modality, which should be strongly considered for obese patients with appropriate sized stones.

Metabolic syndrome and nephrolithiasis

Problem

This review focuses on the association between the metabolic syndrome (MS) and nephrolithiasis.

Findings

Associations between nephrolithiasis and systemic diseases are recognized, including atherosclerosis, cardiovascular (CV) disease, hypertension (HNT), diabetes mellitus (DM)—composite risk factors grouped as the MS. Kidney stones incidence is increasing in this particularly high risk group. Those with stones are prone to the disease and those with the systemic disease are at risk for stone formation, with the highest incidence in persons with multiple traits of the MS. Pathophysiologic explanations for the increased stone risk related to MS are likely complex and dynamic.

Conclusions

Kidney stones disproportionately affect persons with some or all traits of MS. One unifying theory may be of a common systemic malfunction of inflammation and tissue damage as an underlying mechanism, but it is unlikely to be the only mechanistic explanation. Further research is needed to investigate this and other hypotheses that go beyond population based and urine physiochemical studies in order to elucidate the mechanisms behind the individual disease states themselves.

Metabolic Syndrome and Kidney Stone Disease: A Systematic Review of Literature

INTRODUCTION

Worldwide obesity has more than doubled since 1980 with more than 600 million obese patients in 2014. Metabolic syndrome (MetS) is the co-occurrence of metabolic abnormalities, including centrally distributed obesity, hypertension, dyslipidemia, and hyperglycemia. With a concurrent rise in the incidence of kidney stone disease, we wanted to conduct a systematic review focused on the association of MetS to nephrolithiasis.

MATERIALS AND METHODS

A systematic review was performed according to the Cochrane and preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines on all English language articles for the following relevant keywords: association, metabolic syndrome, metabolic syndrome traits, syndrome X, nephrolithiasis, kidney stones, and renal calculi. Our inclusion criteria were studies comparing the prevalence of kidney stone disease in patients with and without MetS.

RESULTS

The initial literature search identified 355 potentially relevant studies. After screening, 22 full text articles were reviewed and 6 (219,255 patients) were included in the final review. All studies displayed increasing odds of nephrolithiasis with increasing number of MetS traits, where patients with three or more MetS traits tended to have a higher prevalence of nephrolithiasis. Studies also showed different significant components of MetS contributing to nephrolithiasis.

CONCLUSIONS

Our review shows a definite association of MetS with kidney stone disease. Although multifactorial in etiology, lifestyle and dietary factors seem to be increasingly important in prevention of stone disease.

Assessment of Urinary Inhibitor or Promoter Activity in Uric Acid Nephrolithiasis

PURPOSE

We assessed decreased inhibitor activity or increased promoter activity in the urine of idiopathic uric acid stone formers compared to nonstone formers independent of urinary pH.

MATERIALS AND METHODS

A total of 30 idiopathic uric acid stone formers, and 9 obese and 12 lean nonstone formers collected 24-hour urine while on a metabolic diet. Three urine aliquots per subject were used to assess spontaneous nucleation (de novo crystal formation), crystal growth using a 0.1 mg/ml anhydrous uric acid seed and steady-state uric acid solubility (the maximum amount of uric acid dissolvable in urine) using a 5 mg/ml uric acid seed. All experiments were performed for 6 hours at a constant pH of 5.0. Uric acid concentration was measured in filtered aliquots at 0, 3 and 6 hours.

RESULTS

At baseline 24-hour urinary pH was significantly lower and uric acid saturation was significantly higher in idiopathic uric acid stone formers. No significant spontaneous nucleation developed and similar uric acid steady-state solubility was reached in the 3 groups. Idiopathic uric acid stone formers and lean nonstone formers showed a similar decrease in uric acid concentration during crystal growth. Obese nonstone formers started with a higher uric acid concentration and consequently demonstrated a greater decrease in the uric acid concentration for crystal growth.

CONCLUSIONS

This study suggests that there is no significant difference between idiopathic uric acid stone formers and nonstone formers in promoter or inhibitor activity in whole urine against uric acid stone formation when urine pH is maintained constant. The findings suggest that uric acid stone formation is dictated by high urinary saturation with respect to uric acid, which is driven primarily by low urine pH.

Influence of body mass index on pediatric urolithiasis

OBJECTIVE

In recent years, there has been increased incidence of urolithiasis in children. Changing nutritional patterns and sedentary lifestyles predispose to urolithiasis, as well as to the global rise in obesity. It has been established that the prevalence of high body mass index (BMI) is increasing in the pediatric population. The aim of the present study was to incorporate 24-h urine metabolic analysis results with BMI values to evaluate the tendency towards stone formation in children.

METHODS

Eighty-four children were recruited to the study, stratified into three BMI categories as low, normal, or upper. All patients were evaluated with 24-h urine analysis results. Patients with a secondary cause of stone formation such as hyperparathyroidism, cystinuria, primary hyperoxaluria, inflammatory bowel disease, cystic fibrosis, history of prematurity and/or use of drug, recurrent urinary tract infection, and urinary tract anomaly were excluded. Additionally, it was ensured that none of the patients were taking specific medication or diet that could alter their acid-base metabolism and calcium, oxalate, and uric acid levels.

RESULTS

Mean BMI of patients was 21.6 ± 2.9 kg/m(2). LBMI was found in 52 (61.9%), N-BMI in 20 (23.8%), and U-BMI in 12 (14.3%) of the patients. No significant differences were present between the three groups for stone sizes and numbers. The patients' characteristics and 24-h urine parameters for BMI groups are presented in the Table.

DISCUSSION

In the literature, several studies have focused on the relationship between obesity and pediatric urinary stone disease. However, only a few evaluated the urinary metabolic analysis in pediatric patients. We have encountered different results from mainly adult studies and some pediatric studies. Our study shows that U-BMI children are not under greater risk for urolithiasis than the other groups. An important portion of our study group was in the L-BMI group; nevertheless we cannot conclude that having a low BMI predisposes to urolithiasis based on the urinary metabolic evaluation as well as the stone sizes and numbers. The N-BMI group has increased risk factors for urolithiasis rather than the other groups, according to results of 24-h urine analysis.

CONCLUSION

The results of our study indicate that BMI itself could not be considered as a separate and definite risk factor for urolithiasis development in children. Although the mechanisms and causative factors for urinary stone formation are better defined in adults, further studies investigating these parameters in children are warranted.

The association of metabolic syndrome and urolithiasis

There has been an increasing prevalence of kidney stones over the last 2 decades worldwide. Many studies have indicated a possible association between metabolic syndrome and kidney stone disease, particularly in overweight and obese patients. Many different definitions of metabolic syndrome have been suggested by various organizations, although the definition by the International Diabetes Federation (IDF) is universally considered as the most acceptable definition. The IDF definition revolves around 4 core components: obesity, dyslipidemia, hypertension, and diabetes mellitus. Several hypotheses have been proposed to explain the pathophysiology of urolithiasis resulting from metabolic syndrome, amongst which are the insulin resistance and Randall's plaque hypothesis. Similarly the pathophysiology of calcium and uric acid stone formation has been investigated to determine a connection between the two conditions. Studies have found many factors contributing to urolithiasis in patients suffering from metabolic syndrome, out of which obesity, overweight, and sedentary lifestyles have been identified as major etiological factors. Primary and secondary prevention methods therefore tend to revolve mainly around lifestyle improvements, including dietary and other preventive measures.

The metabolic syndrome and urolithiasis: a systematic review and meta-analysis

PURPOSE

The aim of this study was to assess the association between metabolic syndrome (MetS) and urolithiasis.

BACKGROUND

Observational studies and reviews suggest an association between the incidence of urolithiasis and the prevalence of MetS. However, individual studies are needed to be gathered to come to a more reliable and precise conclusion.

METHODS

We searched the Pubmed-Medline and Embase databases up to February 2014 to identify studies related to urolithiasis and metabolic syndrome. Three authors independently extracted information on the study design, the characteristics of the study participants, exposure and outcome assessments, and the method used to control for potential confounding factors. A random-effects model was used for the risk estimates.

RESULTS

Five studies were included in the final analysis. Our meta-analysis of five cross-sectional controlled studies identified a significant association between urolithiasis and MetS, with an overall OR of 1.39 (1.14-1.70).

CONCLUSIONS

Patients with metabolic syndrome have an increased risk of having urolithiasis indicating that it should be assessed as a systemic disorder. However, these observations need to be evaluated using prospective, randomized studies.

Metabolic disorders: stones as first clinical manifestation of significant diseases

INTRODUCTION

Metabolic syndrome, type 2 diabetes, and primary hyperparathyroidism are metabolic disorders that should deserve a special focus in renal stone patients as a pathogenic link is established with some stone components. Indeed, an acidic urinary pH due to a decreased ammonium bioavailability explains the high prevalence of uric acid stones in patients with metabolic syndrome or diabetes and, primary hyperparathyroidism induced hypercalciuria increases the risk of calcium phosphate stones.

MATERIALS AND METHODS

We report here four clinical cases of renal stone patients with metabolic disorders encountered in a daily practice. Clinical and metabolic findings altogether with stone analysis components presented here, illustrate relevant pathophysiological links.

CONCLUSION

24 hours urine evaluation and stone analysis which includes both morphological typing and infrared spectroscopy, are key diagnostic steps for early recognition of metabolic disorders. Metabolic screening allows diet related stone identification, points out stone risk factors and identifies patients'comorbidity. The occurrence of nephrocalcinosis with or without chronic renal failure should require a more detailed metabolic evaluation in order to identify uncommon etiologies such as renal tubular acidosis.

Triglycerides in the human kidney cortex: relationship with body size

Obesity is associated with increased risk for kidney disease and uric acid nephrolithiasis, but the pathophysiological mechanisms underpinning these associations are incompletely understood. Animal experiments have suggested that renal lipid accumulation and lipotoxicity may play a role, but whether lipid accumulation occurs in humans with increasing body mass index (BMI) is unknown. The association between obesity and abnormal triglyceride accumulation in non-adipose tissues (steatosis) has been described in the liver, heart, skeletal muscle and pancreas, but not in the human kidney. We used a quantitative biochemical assay to quantify triglyceride in normal kidney cortex samples from 54 patients undergoing nephrectomy for localized renal cell carcinoma. In subsets of the study population we evaluated the localization of lipid droplets by Oil Red O staining and measured 16 common ceramide species by mass spectrometry. There was a positive correlation between kidney cortex trigyceride content and BMI (Spearman R = 0.27, P = 0.04). Lipid droplets detectable by optical microscopy had a sporadic distribution but were generally more prevalent in individuals with higher BMI, with predominant localization in proximal tubule cells and to a lesser extent in glomeruli. Total ceramide content was inversely correlated with triglycerides. We postulate that obesity is associated with abnormal triglyceride accumulation (steatosis) in the human kidney. In turn, steatosis and lipotoxicity may contribute to the pathogenesis of obesity-associated kidney disease and nephrolithiasis.

Use of the National Health and Nutrition Examination Survey to calculate the impact of obesity and diabetes on cost and prevalence of urolithiasis in 2030

BACKGROUND

The prevalence of urolithiasis and its risk factors such as obesity and diabetes have increased over time.

OBJECTIVE

Determine the future cost and prevalence of kidney stones using current and projected estimates for stones, obesity, diabetes, and population rates.

DESIGN, SETTING, AND PARTICIPANTS

The stone prevalence in 2000 was estimated from the National Health and Nutrition Examination Survey (NHANES) 1988-1994 and 2007-2010. The cost per percentage prevalence of stones in 2000, calculated using Urologic Diseases in America Project data, was used to estimate the annual cost of stones in 2030, adjusting for inflation and increases in population, stone prevalence, obesity and diabetes rates.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary outcome was prevalence and cost of stones in 2030. The secondary outcomes were the impact of obesity and diabetes on these values, calculated using odds ratios for stones by body mass index and diabetes status.

RESULTS AND LIMITATIONS

The annual cost of stone disease in 2000, adjusted for inflation to 2014 US dollars, was approximately $2.81 billion. After accounting for increases in population and stone prevalence from 2000, the estimated cost of stones in 2007 in 2014 US dollars was $3.79 billion. Future population growth alone would increase the cost of stone disease by $780 million in 2030. Based on projected estimates for 2030, obesity will independently increase stone prevalence by 0.36%, with an annual cost increase of $157 million. Diabetes will independently increase stone prevalence by 0.72%, associated with a cost increase of $308 million annually by 2030. NHANES data, however, capture patient self-assessment rather than medical diagnosis, which is a potential bias.

CONCLUSIONS

The rising prevalence of obesity and diabetes, together with population growth, is projected to contribute to dramatic increases in the cost of urolithiasis, with an additional $1.24 billion/yr estimated by 2030.

PATIENT SUMMARY

Obesity, diabetes, and population rates will contribute to an estimated $1.24 billion/yr increase in the cost of kidney stones by 2030.

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.

Relevance of Mediterranean diet and glucose metabolism for nephrolithiasis in obese subjects

BACKGROUND

Nephrolithiasis is more frequent and severe in obese patients from different western nations. This may be supported by higher calcium, urate, oxalate excretion in obese stone formers. Except these parameters, clinical characteristics of obese stone formers were not extensively explored.

AIMS

In the present paper we studied the relationship between obesity and its metabolic correlates and nephrolithiasis.

MATERIALS AND METHODS

We studied 478 Caucasian subjects having BMI ≥ 25 kg/m². The presence of nephrolithiasis, hypertension, diabetes mellitus and metabolic syndrome were noted. They underwent measurements of anthropometry (BMI and waist circumference, body composition), serum variables (fasting glucose, serum lipids and serum enzymes) and Mediterranean diet (MedDiet) nutritional questionnaire.

RESULTS

45 (9.4%) participants were stone formers. Subjects with high serum concentrations of triglycerides (≥ 150 mg/dl), fasting glucose (> 100 mg/dl) and AST (>30 U/I in F or >40 U/I in M) were more frequent among stone formers than non-stone formers.Multinomial logistic regression confirmed that kidney stone production was associated with high fasting glucose (OR = 2.6, 95% CI 1.2-5.2, P = 0.011), AST (OR = 4.3, 95% CI 1.1-16.7, P = 0.033) and triglycerides (OR = 2.7, 95% CI 1.3-5.7, P = 0.01). MedDiet score was not different in stone formers and non-stone formers. However, stone formers had a lower consumption frequency of olive oil and nuts, and higher consumption frequency of wine compared with non-stone formers.

CONCLUSIONS

Overweight and obese stone formers may have a defect in glucose metabolism and a potential liver damage. Some foods typical of Mediterranean diet may protect against nephrolithiasis.