Beware the low urine pH--the major cause of the increased prevalence of nephrolithiasis in the patient with type 2 diabetes

Analysis of metabolic syndrome in bilateral upper urinary tract stones: A retrospective study of 3905 cases

Bilateral upper urinary tract stones are significantly related to renal function damage. However, few studies characterized the risk factors of bilateral upper urinary tract stones. We retrospectively enrolled 3905 patients with urinary tract stones from March 2019 to March 2022 at the Second Hospital of Tianjin Medical University. Patients were divided into two groups according to the location of the stones, and the related data were evaluated. In this study, 2485 unilateral and 1420 bilateral stone patients were included. Multivariate logistic regression analysis showed that BMI, gout, hyperparathyroidism, uric acid stone, urine PH, 24-h urinary calcium, blood uric acid, and metabolic syndrome (Mets) were independent risk factors for bilateral stone formation(P < 0.05). Based on these results, we construct a discrimination model. This model revealed good discrimination with an area under the receiver operating characteristic curves of 0.617, and the sensitivity and specificity were 0.592 and 0.586, respectively. Furthermore, the number of Mets components increased the risk of bilateral upper urinary tract stones. Hypertension, hyperglycemia, and low HDL level were strongly associated with bilateral upper urinary tract stones (P < 0.05). Patients with 5 components Mets had 1.89-fold higher risk of bilateral upper urinary tract stones than those with 1 component Mets (OR 3.381; 95 % CI 1.221-9.360; P = 0.013). Additionally, male patients with Mets had higher risk of bilateral upper urinary tract stones than female patients. Our analysis revealed that eight clinical factors were associated with the formation of bilateral upper urinary tract stones, namely BMI, gout, hyperparathyroidism, uric acid stone, urine PH, 24-h urinary calcium, blood uric acid, and Mets. This study could help clinicians adjust treatment strategies for high-risk patients with bilateral upper urinary tract stones.

Uric acid in health and disease: From physiological functions to pathogenic mechanisms

Owing to renal reabsorption and the loss of uricase activity, uric acid (UA) is strictly maintained at a higher physiological level in humans than in other mammals, which provides a survival advantage during evolution but increases susceptibility to certain diseases such as gout. Although monosodium urate (MSU) crystal precipitation has been detected in different tissues of patients as a trigger for disease, the pathological role of soluble UA remains controversial due to the lack of causality in the clinical setting. Abnormal elevation or reduction of UA levels has been linked to some of pathological status, also known as U-shaped association, implying that the physiological levels of UA regulated by multiple enzymes and transporters are crucial for the maintenance of health. In addition, the protective potential of UA has also been proposed in aging and some diseases. Therefore, the role of UA as a double-edged sword in humans is determined by its physiological or non-physiological levels. In this review, we summarize biosynthesis, membrane transport, and physiological functions of UA. Then, we discuss the pathological involvement of hyperuricemia and hypouricemia as well as the underlying mechanisms by which UA at abnormal levels regulates the onset and progression of diseases. Finally, pharmacological strategies for urate-lowering therapy (ULT) are introduced, and current challenges in UA study and future perspectives are also described.

Identifying diagnostic indicators for type 2 diabetes mellitus from physical examination using interpretable machine learning approach

Background

Identification of patients at risk for type 2 diabetes mellitus (T2DM) can not only prevent complications and reduce suffering but also ease the health care burden. While routine physical examination can provide useful information for diagnosis, manual exploration of routine physical examination records is not feasible due to the high prevalence of T2DM.

Objectives

We aim to build interpretable machine learning models for T2DM diagnosis and uncover important diagnostic indicators from physical examination, including age- and sex-related indicators.

Methods

In this study, we present three weighted diversity density (WDD)-based algorithms for T2DM screening that use physical examination indicators, the algorithms are highly transparent and interpretable, two of which are missing value tolerant algorithms.

Patients

Regarding the dataset, we collected 43 physical examination indicator data from 11,071 cases of T2DM patients and 126,622 healthy controls at the Affiliated Hospital of Southwest Medical University. After data processing, we used a data matrix containing 16004 EHRs and 43 clinical indicators for modelling.

Results

The indicators were ranked according to their model weights, and the top 25% of indicators were found to be directly or indirectly related to T2DM. We further investigated the clinical characteristics of different age and sex groups, and found that the algorithms can detect relevant indicators specific to these groups. The algorithms performed well in T2DM screening, with the highest area under the receiver operating characteristic curve (AUC) reaching 0.9185.

Conclusion

This work utilized the interpretable WDD-based algorithms to construct T2DM diagnostic models based on physical examination indicators. By modeling data grouped by age and sex, we identified several predictive markers related to age and sex, uncovering characteristic differences among various groups of T2DM patients.

Asymptomatic hyperuricaemia in chronic kidney disease: mechanisms and clinical implications

Asymptomatic hyperuricaemia (HU) is considered a pathogenic factor in multiple disease contexts, but a causative role is only proven for the crystalline form of uric acid in gouty arthritis and urate nephropathy. Epidemiological studies document a robust association of HU with hypertension, cardiovascular disease (CVD) and CKD progression, but CKD-related impaired uric acid (UA) clearance and the use of diuretics that further impair UA clearance likely accounts for these associations. Interpreting the available trial evidence is further complicated by referring to xanthine oxidase inhibitors as urate-lowering treatment, although these drugs inhibit other substrates, so attributing their effects only to HU is problematic. In this review we provide new mechanistic insights into the biological effects of soluble and crystalline UA and discuss clinical evidence on the role of asymptomatic HU in CKD, CVD and sterile inflammation. We identify research areas with gaps in experimental and clinical evidence, specifically on infectious complications that represent the second common cause of death in CKD patients, referred to as secondary immunodeficiency related to kidney disease. In addition, we address potential therapeutic approaches on how and when to treat asymptomatic HU in patients with kidney disease and where further interventional studies are required.

The impacts of metabolic syndrome on the risk of severe urolithiasis

Metabolic syndrome (MetS) is significantly correlated with urolithiasis. However, few studies have evaluated the severity of urolithiasis. This study aimed to investigate the relationship of MetS with severe urolithiasis disease (SUD). The data of 910 patients with urolithiasis in the Department of Urology, Second Hospital of Tianjin Medical University from June 2020 to May 2021 were retrospectively collected. The patients were divided into two groups according to the severity of urolithiasis, and the relationships of MetS and its components with SUD were evaluated. The results showed 605 SUD and 272 Mets patients. Multiple regression analysis showed that middle age, male gender, and MetS increased the risk of SUD, whereas serum magnesium decreased it (P < 0.05). Further analysis revealed that the odds ratio (OR) of SUD increased with MetS grade (0-4) (1.029-2.117). Grade 4 patients had a 2.1-fold higher risk of SUD than grade 0 patients (OR 2.117; 95% CI 1.053-4.256; P = 0.035); hypertension and dyslipidemia were most strongly associated with SUD among the four MetS features (P < 0.05). Additionally, calcium oxalate was the most predominant stone component (78.7%) in the SUD(+) group, which also had stones with higher uric acid and lower calcium oxalate dihydrate levels than those of the SUD(-) group (P < 0.05). Our study concluded that SUD is more common in middle-aged men, MetS is an independent risk factor for SUD. The more severe the MetS, the higher the risk of SUD, in which hypertension and dyslipidemia play major roles.

Association of acidic urine pH with impaired renal function in primary gout patients: a Chinese population-based cross-sectional study

Background

Patients with gout frequently have low urinary pH, which is associated with the nephrolithiasis. However, the specific distribution of urinary pH and potential relationship of acidic urine pH to broader manifestations of kidney disease in gout are still poorly understood.

Methods

A 2016–2020 population-based cross-sectional study was conducted among 3565 gout patients in the dedicated gout clinic of the Affiliated Hospital of Qingdao University to investigate the association between low urinary pH and kidney disease. We studied patients that we defined to have “primary gout”, based on the absence of > stage 2 CKD. All subjects underwent 14 days of medication washout and 3-day standardized metabolic diet. We obtained general medical information, blood and urine biochemistries, and renal ultrasound examination on the day of the visit. The primary readouts were urine pH, eGFR, nephrolithiasis, renal cysts, microhematuria, and proteinuria. Patients were assigned into 5 subgroups (urine pH ≤5.0, 5.0 <pH≤ 5.5, 5.5 <pH< 6.2, 6.2 ≤pH≤ 6.9, and pH >6.9), aligning with the clinical significance of urine pH.

Results

Overall, the median urine pH and eGFR of all patients was 5.63 (IQR 5.37~6.09), and 98.32 (IQR 86.03~110.6), with acidic urine in 46.5% of patients. The prevalence of nephrolithiasis, microhematuria, and proteinuria were 16.9%, 49.5%, and 6.9%, respectively. By univariate analysis, eGFR was significantly associated with age, sex, duration of gout, tophus, body mass index, systolic blood pressure, diastolic blood pressure, fasting blood glucose, total cholesterol, serum utare, hypertension, diabetes, and urine pH. On multivariable analysis, eGFR was associated with age, sex, diastolic blood pressure, serum uric acid, hypertension, diabetes, and urine pH. Acidic urine pH, especially urine pH < 5.0, was significantly associated with the prevalence of kidney disease, including > stage 1 CKD, nephrolithiasis, kidney cyst, and microhematuria. Patients with 6.2 ≤ urine pH ≤ 6.9 and SU ≤ 480 μmol/L had the highest eGFR with the lowest prevalence of nephrolithiasis, microhematuria, and proteinuria.

Conclusions

Approximately half of gout subjects had acidic urine pH. Urine pH < 5.0 was associated with significantly increased nephrolithiasis, renal cyst, microhematuria, and proteinuria. The results support prospective clinical investigation of urinary alkalinization in selected gout patients with acidic urine pH.

Gender-related differences in the risk factors for repeat stone surgery

Our objective was to analyze and compare the associations between potential risk factors for nephrolithiasis and repeat stone surgery in male and female patients. We retrospectively analyzed 1970 patients who had stone surgery at our institution in the period from January 2009 to May 2017, were older than 18 years and had at least 12 months of postoperative follow-up. Our definition of surgical recurrence included repeat surgery on the same renal unit or on the opposite renal unit if the original imaging did not demonstrate significant stones on that side. Uni- and multivariate Cox regression models were built for each gender. We also explored the interactions between gender and other patient's characteristics in their effect on the risk of recurrence. Ureteroscopy was the most common treatment modality for both first (83%) and repeat (87%) procedures. Over a mean follow-up of 4.3 years (median 3.8, interquartile range 2.2-6.0), 413 (21.0%) patients had a surgical recurrence. In multivariate analyses, hypertension, diabetes, Caucasian race and younger age (less than 60 years) were significantly associated with the risk of surgical recurrence only in females. Interaction between these characteristics and gender was significant indicating a larger effect on the risk of surgical recurrence in females compared to males. Our study demonstrated a number of differences in the predictors of repeat surgery for nephrolithiasis between males and females. If confirmed by future studies these differences may be helpful for optimizing nephrolithiasis prevention efforts.

Only Hyperuricemia with Crystalluria, but not Asymptomatic Hyperuricemia, Drives Progression of Chronic Kidney Disease

BACKGROUND

The roles of asymptomatic hyperuricemia or uric acid (UA) crystals in CKD progression are unknown. Hypotheses to explain links between UA deposition and progression of CKD include that (1) asymptomatic hyperuricemia does not promote CKD progression unless UA crystallizes in the kidney; (2) UA crystal granulomas may form due to pre-existing CKD; and (3) proinflammatory granuloma-related M1-like macrophages may drive UA crystal-induced CKD progression.

METHODS

MALDI-FTICR mass spectrometry, immunohistochemistry, 3D confocal microscopy, and flow cytometry were used to characterize a novel mouse model of hyperuricemia and chronic UA crystal nephropathy with granulomatous nephritis. Interventional studies probed the role of crystal-induced inflammation and macrophages in the pathology of progressive CKD.

RESULTS

Asymptomatic hyperuricemia alone did not cause CKD or drive the progression of aristolochic acid I-induced CKD. Only hyperuricemia with UA crystalluria due to urinary acidification caused tubular obstruction, inflammation, and interstitial fibrosis. UA crystal granulomas surrounded by proinflammatory M1-like macrophages developed late in this process of chronic UA crystal nephropathy and contributed to the progression of pre-existing CKD. Suppressing M1-like macrophages with adenosine attenuated granulomatous nephritis and the progressive decline in GFR. In contrast, inhibiting the JAK/STAT inflammatory pathway with tofacitinib was not renoprotective.

CONCLUSIONS

Asymptomatic hyperuricemia does not affect CKD progression unless UA crystallizes in the kidney. UA crystal granulomas develop late in chronic UA crystal nephropathy and contribute to CKD progression because UA crystals trigger M1-like macrophage-related interstitial inflammation and fibrosis. Targeting proinflammatory macrophages, but not JAK/STAT signaling, can attenuate granulomatous interstitial nephritis.

Renal biomarkers of acid excretion capacity: relationships with body fatness and blood pressure

BACKGROUND

Overweight and higher BMI are known to be related to increased blood pressure (BP) and additionally associate with lowered urine pH values even at comparable total daily acid loading. Since a reduced urine pH level at a given total acid load indicates an impaired renal net acid excretion capacity (NAEC) and renal function also relates to BP, we hypothesized that NAEC may be one mediator of the body fat-BP association.

METHODS

Ammonium, titratable acid, pH, creatinine, and urea were measured in 24-h urine samples among 9-15-year-old adolescents of the DONALD Study. NAEC was determined as residual of the body surface area-corrected net acid excretion on urine pH (NAEC1) or body surface area-corrected ammonium excretion on urine pH (NAEC2). Markers of body fatness were determined anthropometrically and systolic and diastolic BP sphygmomanometrically. Multilinear regressions were used to examine cross-sectionally the body fat-NAEC and prospectively the NAEC1-BP associations.

RESULTS

All body fat parameters were inversely associated with both NAEC1 and NAEC2 among youth (P ≤ 0.01). In a separate prospective analyses, to check for possible mediation, higher adolescent NAEC1 was significantly associated with lower systolic BP in male adults only (P = 0.04), but this association was attenuated to a trend (P = 0.07) in multivariable-adjusted models.

CONCLUSIONS

Independent of systemic acid load, NAEC, i.e., the kidney's function to eliminate acids is reduced with higher body fatness, and may also contribute as a mediator in the body fatness-BP relation.

Diabetes Mellitus Might Not Be Associated with Any Stone Component in a Local District

BACKGROUND

Type II diabetes mellitus (DM) is a risk factor for urinary stones, but the pathogenesis remains unclear. The aim of our study was to present the distribution of stone components between DM and no DM group from a local stone center in China and to help the prevention department in decision-making.

METHODS

We reviewed the records of patients with upper urinary stones attending our hospital from January 2015 to September 2018. The patients with complete information were divided into 2 groups: type II DM group (DM group) and without DM group (no DM group). The distribution of stone components was analyzed.

RESULTS

Two hundred twenty-two patients were complicated with DM, whereas 1,894 (89%) were not. Significant difference was found in the distribution of hypertension and BMI (p = 0, p = 0, respectively). Distribution of sex, age, and stone components did not differ between the 2 groups. By the binary logistic analysis, increasing age and sex seemed to be the main risk factors influencing the stone components. Only the calcium stone seemed to be free of the -impact from age and sex. Occurrence of hypertension is a single risk factor for calcium stone from our analysis. Presence of diabetes and increasing BMI was not found to be significantly associated with the risk for any stone component.

CONCLUSIONS

In a local district, DM might not be the main factor associated with an increased risk for uric acid stone formation or any stone component. We should also consider the local characteristics of the stone distribution.

Comparison of Two Dietary Supplements for Treatment of Uric Acid Renal Lithiasis: Citrate vs. Citrate + Theobromine

Background. Uric acid (UA) renal lithiasis has a high rate of recurrence and a prevalence ranging from 10% and 15%, depending on the population. The most important etiological factor is persistence of urinary pH below 5.5 and one of the most common treatments is alkalization with citrate. Recent studies demonstrated that theobromine, which is abundant in chocolate and cocoa, is a potent inhibitor of UA crystallization. Aim. The aim was to compare the efficacy of citrate versus citrate + theobromine as treatment for UA lithiasis. Methods. This randomized cross-over trial investigated the efficacy of two treatments in 47 patients with UA renal lithiasis. Urine volume, pH, UA excretion, theobromine excretion, and risk of UA crystallization (RUAC) at baseline and at the end of each intervention period were measured. Results. Each treatment significantly reduced the risk of UA crystallization compared to basal values. The RUAC after citrate + theobromine was lower than the RUAC after citrate, although this difference was not statistically significant. Conclusion. The combined consumption of citrate and theobromine may be a promising strategy for the prevention of UA kidney stones.

Sugar-Induced Obesity and Insulin Resistance Are Uncoupled from Shortened Survival in Drosophila

High-sugar diets cause thirst, obesity, and metabolic dysregulation, leading to diseases including type 2 diabetes and shortened lifespan. However, the impact of obesity and water imbalance on health and survival is complex and difficult to disentangle. Here, we show that high sugar induces dehydration in adult Drosophila, and water supplementation fully rescues their lifespan. Conversely, the metabolic defects are water-independent, showing uncoupling between sugar-induced obesity and insulin resistance with reduced survival in vivo. High-sugar diets promote accumulation of uric acid, an end-product of purine catabolism, and the formation of renal stones, a process aggravated by dehydration and physiological acidification. Importantly, regulating uric acid production impacts on lifespan in a water-dependent manner. Furthermore, metabolomics analysis in a human cohort reveals that dietary sugar intake strongly predicts circulating purine levels. Our model explains the pathophysiology of high-sugar diets independently of obesity and insulin resistance and highlights purine metabolism as a pro-longevity target.

A Cobalt (II) Oxide Carbon Nanotube Composite to Assay Dopamine

A cobalt (II) oxide/carboxylic acid functionalized multiwalled carbon nanotube (CoO/COOH-MWNT) composite was fabricated for the biochemical detection of dopamine (DA). CoO particles were tethered to COOH-MWNTs by sonication. The current response versus different concentration was measured using cyclic voltammetry. Various parameters, including sonication time, pH, and loading were varied for the best current response. The composite with optimum current response was formed using a 30-min sonication time, at pH 5.0 and a 0.89 µg/mm2 loading onto the glassy carbon electrode surface. Good sensitivity with a limit of detection of 0.61 ± 0.03 μM, and dynamic range of 10–100 µM for DA is shown, applicable for neuroblastoma screening. The sensor was selective against ascorbic and uric acids.

Increased body fatness adversely relates to 24-hour urine pH during childhood and adolescence: evidence of an adipo-renal axis

BACKGROUND

Reduced net acid excretion (NAE) capacity indicates a decrease in renal function. This reduction manifests as a disproportionally low 24-h urine pH in relation to the sum of actually excreted ammonium and titratable acidity by the kidney.

OBJECTIVE

The aim of this study was to test the hypothesis that higher body fatness is one determinant of kidney function impairment with a lowered urine pH even at a young age.

METHODS

NAE, pH, urea, and creatinine were measured in 24-h urine samples from 524 healthy children and adolescents (aged 6-17 y) participating in the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) Study. Body fatness was assessed anthropometrically by body mass index-standard deviation score (BMI-SDS), fat mass index (FMI), body fat % (BF%), and waist circumference (WC). Multivariable linear and mixed linear regressions were used to examine cross-sectionally (n = 524 urine samples; age groups: 6-8, 9-11, 12-14, 15-17 y) and longitudinally (n = 1999 urine samples) the associations of body fatness with 24-h urine pH as the outcome variable, respectively.

RESULTS

After adjusting for the kidneys' total net acid load (24-h urinary NAE) and further relevant covariates, FMI showed significant inverse relations with urinary pH in all 4 age groups, and BMI-SDS, BF%, and WC each in 3 out of these 4 groups (P ≤ 0.02). Longitudinal results substantiated these interindividual relations and further showed intraindividual increases in body fatness to be paralleled by urine pH decreases (P ≤ 0.0002).

CONCLUSIONS

Independent of underlying acid load, an early increase in body fatness is associated with increased free proton excretion, and thus with a decline in the kidney's acid excretion function, which could potentiate the risk of renal nephrolithiasis.

The Proposal of Molecular Mechanisms of Weak Organic Acids Intake-Induced Improvement of Insulin Resistance in Diabetes Mellitus via Elevation of Interstitial Fluid pH

Blood contains powerful pH-buffering molecules such as hemoglobin (Hb) and albumin, while interstitial fluids have little pH-buffering molecules. Thus, even under metabolic disorder conditions except severe cases, arterial blood pH is kept constant within the normal range (7.35~7.45), but the interstitial fluid pH under metabolic disorder conditions becomes lower than the normal level. Insulin resistance is one of the most important key factors in pathogenesis of diabetes mellitus, nevertheless the molecular mechanism of insulin resistance occurrence is still unclear. Our studies indicate that lowered interstitial fluid pH occurs in diabetes mellitus, causing insulin resistance via reduction of the binding affinity of insulin to its receptor. Therefore, the key point for improvement of insulin resistance occurring in diabetes mellitus is development of methods or techniques elevating the lowered interstitial fluid pH. Intake of weak organic acids is found to improve the insulin resistance by elevating the lowered interstitial fluid pH in diabetes mellitus. One of the molecular mechanisms of the pH elevation is that: (1) the carboxyl group (R-COO⁻) but not H⁺ composing weak organic acids in foods is absorbed into the body, and (2) the absorbed the carboxyl group (R-COO⁻) behaves as a pH buffer material, elevating the interstitial fluid pH. On the other hand, high salt intake has been suggested to cause diabetes mellitus; however, the molecular mechanism is unclear. A possible mechanism of high salt intake-caused diabetes mellitus is proposed from a viewpoint of regulation of the interstitial fluid pH: high salt intake lowers the interstitial fluid pH via high production of H⁺ associated with ATP synthesis required for the Na⁺,K⁺-ATPase to extrude the high leveled intracellular Na⁺ caused by high salt intake. This review article introduces the molecular mechanism causing the lowered interstitial fluid pH and insulin resistance in diabetes mellitus, the improvement of insulin resistance via intake of weak organic acid-containing foods, and a proposal mechanism of high salt intake-caused diabetes mellitus.

Metabolic syndrome and uric acid nephrolithiasis: insulin resistance in focus

Uric acid nephrolithiasis (UAN) is an increasingly common disease in ethnically diverse populations and constitutes about 10% of all kidney stones. Metabolic syndrome and diabetes mellitus are accounted among the major risk factors for UAN, together with environmental exposure, individual lifestyle habits and genetic predisposition. The development and overt manifestation of UAN appears to stem on the background of insulin resistance, which acts at the kidney level by reducing urinary pH, thus hampering the ability of the kidney to generate renal ammonium in response to an acid load. Unduly acidic urinary pH and overt UAN are both considered renal manifestations of insulin resistance. The mechanisms underlying increased endogenous acid production and/or defective ammonium excretion are yet to be completely understood. Although the development of UAN and, more in general, of kidney stones largely recognizes modifiable individual determining factors, the rising prevalence of diabetes, obesity and accompanying metabolic disorders calls for the identification of novel therapeutic approaches and intervention targets. This review aims at providing an updated picture of existing evidence on the relationship between insulin resistance and UAN in the context of metabolic syndrome and in light of the most recent advancements in our understanding of its genetic signature.

Simplified methods for the evaluation of the risk of forming renal stones and the follow-up of stone-forming propensity during the preventive treatment of stone-formation

Renal lithiasis is a complex multifactorial disease in which recurrence is common. Thus, simple and reliable procedures are needed to evaluate patients with previous kidney stones to determine the risk of recurrence. In this paper we review simple biochemical procedures that can be used to determine the risk for renal stone formation when the stone is available or unavailable for analysis. Our present knowledge of renal lithiasis indicates that renal stones form due to several well-defined factors. Analysis of the renal stone itself can provide important information about clinical factors that require further investigation. When the stone is unavailable, it is necessary to perform a general evaluation of main urinary risk factors associated to renal stone formation, but this study should be complemented considering information related to direct familial antecedents, recidivant degree, radiological images, medical history, and life style habits. Finally, tools for patient follow-up of stone-forming propensity during the preventive treatment are discussed .

Theobromine inhibits uric acid crystallization. A potential application in the treatment of uric acid nephrolithiasis

PURPOSE

To assess the capacity of methylxanthines (caffeine, theophylline, theobromine and paraxanthine) to inhibit uric acid crystallization, and to evaluate their potential application in the treatment of uric acid nephrolithiasis.

MATERIALS AND METHODS

The ability of methylxathines to inhibit uric acid nucleation was assayed turbidimetrically. Crystal morphology and its modification due to the effect of theobromine were evaluated by scanning electron microscopy (SEM). The ability of theobromine to inhibit uric acid crystal growth on calculi fragments resulting from extracorporeal shock wave lithotripsy (ESWL) was evaluated using a flow system.

RESULTS

The turbidimetric assay showed that among the studied methylxanthines, theobromine could markedly inhibit uric acid nucleation. SEM images showed that the presence of theobromine resulted in thinner uric acid crystals. Furthermore, in a flow system theobromine blocked the regrowth of post-ESWL uric acid calculi fragments.

CONCLUSIONS

Theobromine, a natural dimethylxanthine present in high amounts in cocoa, acts as an inhibitor of nucleation and crystal growth of uric acid. Therefore, theobromine may be clinically useful in the treatment of uric acid nephrolithiasis.

The pathophysiology of hyperuricaemia and its possible relationship to cardiovascular disease, morbidity and mortality

Uric acid is the end product of purine metabolism in humans. High levels are causative in gout and urolithiasis. Hyperuricaemia has also been implicated in the pathophysiology of hypertension, chronic kidney disease (CKD), congestive heart failure (CHF), the metabolic syndrome, type 2 diabetes mellitus (T2DM), and atherosclerosis, with or without cardiovascular events. This article briefly reviews uric acid metabolism and summarizes the current literature on hyperuricaemia in cardiovascular disease and related co-morbidities, and emerging treatment options.

Update on the evaluation of repeated stone formers

Office management of stone disease is an important component of a urologist's practice. Evaluation should include analysis of stone composition, 24-hour urine studies, identification of modifiable risk factors, and targeted dietary, lifestyle, and/or medical therapy. A sizeable portion of investigated etiologies and risk factors for stone disease have centered on the complex interplay between obesity, diabetes, and other disease states that comprise the metabolic syndrome. Alternatives to traditional preventive therapy, such as probiotics and various fruit juices, are still being studied but may prove useful adjuncts to traditional preventive therapy, where the mainstays remain increased fluid intake, dietary modification, and pharmacologic therapy. Future studies on preventive therapy of urolithiasis are likely to focus on strategies to increase compliance, cost-effectiveness, and systems-based implementation.

Who makes uric acid stones and why--observations from a renal stones clinic

AIMS

Excessively acidic urine is the dominant factor in uric acid stone formation. Recent evidence implicating insulin resistance has revived interest in its causation. We reviewed data on uric acid stone formers attending a general stones clinic to find out whether this supports and adds to current concepts.

METHODS

A retrospective database study of 1504 stone formers investigated at the Southampton renal stones clinic from 1990 to March 2007. Uric acid stone formers and idiopathic calcium stone formers were compared using non-parametric tests.

RESULTS

Fifty-nine patients (3.9%; 43 men) had uric acid stones. In men the commonest associated conditions were diabetes (20%), gout (20%) and an ileostomy (15%); in women, diabetes (33%), urinary infections (27%) and hyperparathyroidism (20%). Most patients with diabetes (85% of men, 75% of women), however, produced calcium stones. Risk factors did not differ significantly between calcium and uric acid stone formers with diabetes, gout or ileostomies. The median urine pH of men with idiopathic calcium stones was 6.20, idiopathic uric acid stones 5.47, diabetes 5.68, gout 6.05, diabetes and gout 5.20 and ileostomy 5.10. Plasma urate was higher with gout and idiopathic uric acid stones. Urate excretion was increased in gout. Oxalate excretion was lower with idiopathic uric acid stones (new finding). Urine volume decreased and oxalate concentration increased with ileostomy.

CONCLUSIONS

Uric acid stones are increased in diabetes, but most patients with diabetes make calcium stones. Different mechanisms may explain low pH with diabetes, gout and idiopathic stones. Low oxalate excretion with idiopathic urate stones needs confirmation.