Hypocitraturia in patients with gastrointestinal malabsorption

Determinants and impact of calcium oxalate crystal deposition on renal outcomes in acute kidney injury patients

OBJECTIVES

Calcium oxalate (CaOx) crystal deposition in acute kidney injury (AKI) patients is under recognized but impacts renal outcomes. This study investigates its determinants and effects.

METHODS

We studied 814 AKI patients with native kidney biopsies from 2011 to 2020, identifying CaOx crystal deposition severity (mild: <5, moderate: 5-10, severe: >10 crystals per section). We assessed factors like urinary oxalate, citrate, urate, electrolytes, pH, tubular calcification index, and SLC26A6 expression, comparing them with creatinine-matched AKI controls without oxalosis. We analyzed how these factors relate to CaOx severity and their impact on renal recovery (eGFR < 15 mL/min/1.73 m2 at 3-month follow-up).

RESULTS

CaOx crystal deposition was found in 3.9% of the AKI cohort (32 cases), with 72% due to nephrotoxic medication-induced tubulointerstitial nephritis. Diuretic use, higher urinary oxalate-to-citrate ratio induced by hypocitraturia, and tubular calcification index were significant contributors to moderate and/or severe CaOx deposition. Poor baseline renal function, low urinary chloride, high uric acid and urea nitrogen, tubular SLC26A6 overexpression, and glomerular sclerosis were also associated with moderate-to-severe CaOx deposition. Kidney recovery was delayed, with 43.8%, 31.2%, and 18.8% of patients having eGFR < 15 mL/min/1.73 m2 at 4, 12, and 24-week post-injury. Poor outcomes were linked to high urinary α1-microglobulin-to-creatinine (α1-MG/C) ratios and active tubular injury scores. Univariate analysis showed a strong link between this ratio and poor renal outcomes, independent of oxalosis severity.

CONCLUSIONS

In AKI, CaOx deposition is common despite declining GFR. Factors worsening tubular injury, not just oxalate-to-citrate ratios, are key to understanding impaired renal recovery.

Metabolic Profile of Calcium Oxalate Stone Patients with Enteric Hyperoxaluria and Impact of Dietary Intervention

This study investigated the risk profile and the impact of dietary intervention in calcium oxalate stone formers with enteric hyperoxaluria under controlled, standardized conditions. Thirty-seven patients were included in the study. Dietary and 24-h urinary parameters were obtained on the self-selected diet and a balanced, standardized diet. Tests for [13C2]oxalate absorption, calcium- and ammonium chloride-loading were performed. Mean [13C2]oxalate absorption was 18.8%. A significant positive association was observed between urinary oxalate excretion and intestinal oxalate absorption. In addition, urinary oxalate excretion was significantly correlated with dietary oxalate intake. Mean urinary oxalate excretion decreased from 0.841 mmol/24 h on the usual diet to 0.662 mmol/24 h on the balanced diet, corresponding to a reduction of 21.3%. Besides hyperoxaluria, hypocitraturia and hypomagnesuria were the most common urinary abnormalities at baseline, being present in 83.8% and 81.1% of patients, respectively. Urinary citrate increased by 50.9% and magnesium excretion increased by 25.2% on the balanced diet. As a result, the relative supersaturation of calcium oxalate declined significantly (by 36.2%) on the balanced diet. Since 41% of patients on the balanced diet still had a urine volume of less than 2.0 L/24 h, efforts should be made to increase urine volume by increasing fluid intake and reducing intestinal fluid losses. Dietary intervention proved to be effective in reducing urinary oxalate excretion and should be a cornerstone of the treatment of patients with enteric hyperoxaluria.

Management of de novo nephrolithiasis after kidney transplantation: a comprehensive review from the European Renal Association CKD-MBD working group

The lifetime incidence of kidney stones is 6%-12% in the general population. Nephrolithiasis is a known cause of acute and chronic kidney injury, mediated via obstructive uropathy or crystal-induced nephropathy, and several modifiable and non-modifiable genetic and lifestyle causes have been described. Evidence for epidemiology and management of nephrolithiasis after kidney transplantation is limited by a low number of publications, small study sizes and short observational periods. Denervation of the kidney and ureter graft greatly reduces symptomatology of kidney stones in transplant recipients, which may contribute to a considerable underdiagnosis. Thus, reported prevalence rates of 1%-2% after kidney transplantation and the lack of adverse effects on allograft function and survival should be interpreted with caution. In this narrative review we summarize current state-of-the-art knowledge regarding epidemiology, clinical presentation, diagnosis, prevention and therapy of nephrolithiasis after kidney transplantation, including management of asymptomatic stone disease in kidney donors. Our aim is to strengthen clinical nephrologists who treat kidney transplant recipients in informed decision-making regarding management of kidney stones. Available evidence, supporting both surgical and medical treatment and prevention of kidney stones, is presented and critically discussed. The specific anatomy of the transplanted kidney and urinary tract requires deviation from established interventional approaches for nephrolithiasis in native kidneys. Also, pharmacological and lifestyle changes may need adaptation to the specific situation of kidney transplant recipients. Finally, we point out current knowledge gaps and the need for additional evidence from future studies.

Intestinal Oxalate Absorption, Enteric Hyperoxaluria, and Risk of Urinary Stone Formation in Patients with Crohn's Disease

Nephrolithiasis is a common urologic manifestation of Crohn's disease. The purpose of this study was to investigate the clinical characteristics, intestinal oxalate absorption, and risk factors for urinary stone formation in these patients. In total, 27 patients with Crohn's disease and 27 healthy subjects were included in the present study. Anthropometric, clinical, and 24 h urinary parameters were determined, and the [13C2]oxalate absorption test was performed. Among all patients, 18 had undergone ileal resection, 9 of whom had a history of urinary stones. Compared to healthy controls, the urinary excretion values of calcium, magnesium, potassium, sulfate, creatinine, and citrate were significantly lower in patients with Crohn's disease. Intestinal oxalate absorption, the fractional and 24 h urinary oxalate excretion, and the risk of calcium oxalate stone formation were significantly higher in patients with urolithiasis than in patients without urolithiasis or in healthy controls. Regardless of the group, between 83% and 96% of the [13C2]oxalate was detected in the urine within the first 12 h after ingestion. The length of ileum resection correlated significantly with the intestinal absorption and urinary excretion of oxalate. These findings suggest that enteric hyperoxaluria can be attributed to the hyperabsorption of oxalate following extensive ileal resection. Oral supplementation of calcium and magnesium, as well as alkali citrate therapy, should be considered as treatment options for urolithiasis.

Oxalate nephropathy in an elderly patient with newly diagnosed celiac disease - a case report

Oxalate nephropathy, due to secondary hyperoxaluria has widely been described in gastrointestinal diseases. However, reports of oxalate nephropathy in newly diagnosed celiac disease are rare. A 72-year-old Caucasian male presented to the hospital with abdominal discomfort and acute renal insufficiency with a creatinine of 290 µmol/L. The clinical course, laboratory results and urinalysis were suspect for tubular injury. Renal biopsy showed calcium oxalate depositions. Elevated plasma and urine oxalate levels established the diagnosis oxalate nephropathy. The abdominal complaints with steatorrhea and positive anti-tissue transglutaminase antibodies were diagnosed as celiac disease, which was confirmed after duodenal biopsies. Treatment with prednisone, and gluten-free, low oxalate and normal calcium diet, lowered the plasma oxalate levels and improved his renal function. Decreased absorption of free fatty acids can lead to increased free oxalate in the colon due to the binding of free fatty acids to calcium, preventing the formation of the less absorbable calcium oxalate in the colon. Oxalate dispositions in the kidney can lead to acute tubular injury and chronic renal insufficiency. Celiac disease is therefore one of the intestinal diseases that can lead to hyperoxaluria and oxalate nephropathy.

Dietary management of hypocitraturia in children with urolithiasis: results from a systematic review

PURPOSE

Hypocitraturia is a low urinary excretion of citrate and a well-known risk factor for kidney stone development in children. This systematic review aimed to evaluate the dietary management of hypocitraturia in children with urolithiasis.

METHODS

Literature search was performed on 30th September 2022 using Embase, PubMed, and Cochrane Central Controlled Register of Trials. Studies were included if children with stones and hypocitraturia were managed with diet supplements.

RESULTS

Six papers were included. Four studies evaluated the role of oral potassium citrate associated with high fluid intake on stone resolution and recurrence. Two studies assessed the impact of oral potassium citrate on long-term stone recurrence after percutaneous nephrolithotomy and shock wave lithotripsy. All studies demonstrated that the association of potassium citrate and high fluid intake was well tolerated with no side effects and restored normal urine citrate excretion, allowed a reduction in stone size, and, following definitive treatments, was associated with a lower rate of stone regrowth and recurrence compared with controls. These effects were demonstrated across all pediatric ages.

CONCLUSIONS

Our review infers that oral potassium citrate and high fluid assumption are safe and effective in restoring urine citrate excretion, treating and preventing stone recurrence with no serious adverse events, and should probably be the first-line treatment of pediatric patients with asymptomatic stones and hypocitraturia.

Risk factors for developing hyperoxaluria in children with Crohn's disease

BACKGROUND

For the purpose of a better understanding of enteric hyperoxaluria in Crohn's disease (CD) in children and adolescents, we investigated the occurrence and risk factors for development of hyperoxaluria in those patients.

METHODS

Forty-five children with CD and another 45 controls were involved in this cross-sectional study. Urine samples were collected for measurement of spot urine calcium/creatinine (Ur Ca/Cr), oxalate/creatinine (Ur Ox/Cr), and citrate/creatinine (Ur Citr/Cr) ratios. Fecal samples were also collected to detect the oxalyl-CoA decarboxylase of Oxalobacter formigenes by PCR. Patients were classified into 2 groups: group A (with hyperoxaluria) and group B (with normal urine oxalate excretion). The disease extent was assessed, and the activity index was calculated.

RESULTS

According to the activity index, 30 patients (66.7%) had mild disease and 13 patients (28.9%) had moderate disease. There was no significant difference in Ur Ox/Cr ratio regarding the disease activity index. O. formigenes was not detected in 91% of patients in group A while it was detected in all patients in group B (p < 0.001). By using logistic regression analysis, the overall model was statistically significant when compared to the null model, (χ² (7) = 52.19, p < 0.001), steatorrhea (p = 0.004), frequent stools (p = 0.009), and O. formigenes (p < 0.001).

CONCLUSION

Lack of intestinal colonization with O. formigenes, steatorrhea, and frequent stools are the main risk factors for development of enteric hyperoxaluria in CD patients. Identifying risk factors facilitates proper disease management in future studies. A higher resolution version of the Graphical abstract is available as Supplementary information.

Kidney stones are common in patients with short-bowel syndrome receiving long-term parenteral nutrition: A predictive model for urolithiasis

BACKGROUND

In short-bowel syndrome (SBS) treated with parenteral nutrition (PN), multiple complications can occur. The etiology of kidney stones may be linked to the underlying disease thrombosis, surgical complications, complications of therapy for cancer, Crohn's disease, metabolic abnormalities resulting from morphological and functional changes in the gastrointestinal tract, and to treatment used. We analyzed all these parameters in a large cohort of patients receiving home PN (HPN), to define the incidence of stones and groups of patients particularly at risk of stone formation. One of the objectiveswas to develop a predictive model of urolithiasis.

METHODS

This observational retrospective study included 459 patients with SBS recieving HPN in a single center. Patient records were evaluated for demographics, SBS etiology, and underlying disease, anatomy of the gastrointestinal tract, intestinal failure classification, nutrition regimen, and presence of urolithiasis.

RESULTS

Kidney stones were diagnosed in 24% of patients. Nodifferences in incidence were noted between the various etiologic groups. The incidence in patients with a colon in continuity and those with an end stoma was similar. The length of residual small bowel did not play a role in stone formation. There were no differences between patients according to the severity of intestinal failure. In patients treated with PN and limited oral feeding, the risk of urolithiasis was twice as high as in patients receiving PN only.

CONCLUSIONS

Patients developed urolithiasis with no relation to the SBS etiology. The risk of kidney stone formation was higher in patients recieving PN with oral feeding.

Urine metabolic risk factors and outcomes of patients with kidney transplant nephrolithiasis

Background

Nephrolithiasis in allograft kidneys is rare, but this diagnosis may lead to allograft complications and patient morbidity. Previous studies that have evaluated nephrolithiasis posttransplant have focused on surgical stone management, with limited data on urine metabolic risk factors and the presence of stones after follow-up.

Methods

We retrospectively evaluated kidney transplant recipients who were diagnosed with transplant nephrolithiasis between 2009 and 2019. Computed tomography and ultrasound imaging were used to confirm stone presence.

Results

The incidence of allograft kidney stone formation was 0.86% of 6548 kidney transplant recipients. Of the 56 cases identified, 17 (30%) had a pretransplant history of nephrolithiasis. Only four (7%) patients received a known kidney stone at the time of allograft implantation. Of the 56 cases, 34 had a 24-h supersaturation study. The urine supersaturation study showed 32 patients (94%) had a urine citrate of &lt;450 mg excreted in 24 h (median 124.5 mg/24 h, reference range &gt;500 mg/24 h), along with 22 patients (61%) having a urine oxalate excretion of ≥30 mg in 24 h (median 34.4 mg/24 h, reference range &lt;30 mg/24 h). Calcium oxalate composition was most common (91% with &gt;1 supersaturation for calcium oxalate crystals), with normal median urine calcium levels (median urine calcium 103.5 mg/24 h, reference range &lt;200 mg/24 h). After a 4-year follow-up, 50% (n = 28) required surgical intervention and 43 (77%) patients continued to have evidence of transplant nephrolithiasis on imaging.

Conclusions

This is the largest study of transplant nephrolithiasis confirming that hypocitraturia and hyperoxaluria were the most significant urine metabolic risk factors associated with allograft nephrolithiasis and that hyperoxaluria was the most prevalent driver for calcium oxalate stone composition. Our study is first to show low stone-free rates at the last follow-up and a significant proportion requiring surgical intervention.

Proton-pump inhibitors associated with decreased urinary citrate excretion

INTRODUCTION

Proton-pump inhibitors (PPIs) may increase the risk of kidney stone formation, but the mechanism has not been elucidated. There is a paucity of literature evaluating the effects of PPIs on urinary metabolites and urine pH.

METHODS

We performed a retrospective review of nephrolithiasis patients treated at our institution and compared patients who were taking PPIs to those who were not at the time of their 24-h urine collections. Hierarchical multivariate linear regression was used to evaluate the independent relationship between PPI use and urinary mineral composition.

RESULTS

We identified 301 consecutive patients, 88 (29%) of whom were taking PPIs at the time of their 24-h urine collections. Patients taking PPIs were older and more likely to have medical comorbidities associated with metabolic syndrome such as hypertension, diabetes, and dyslipidemia (p < 0.01). Controlling for these factors, patients taking PPIs were found to have 12% lower 24-h urine citrate excretion (β =  - 0.12, ΔF = 4.24, p = 0.04). There were no other differences in urinary mineral composition between the groups.

CONCLUSION

Our findings suggest that patients who take PPIs regularly may be at risk for decreased urinary citrate excretion. The consequent decrease in urinary citrate may become clinically significant for patients with other predisposing factors for hypocitraturia.

Risk factors for urolithiasis in patients with Crohn's disease

OBJECTIVE

To study the risk factors for urolithiasis in patients with Crohn's disease.

METHODS

This retrospective study included 1071 patients with Crohn's disease who were treated at a single center. Data pertaining to the following variables were analyzed: sex; age; type of Crohn's disease; number of intestinal resections; residual small intestine length; ileostomy; history of glucocorticoid therapy; and duration of Crohn's disease treatment.

RESULTS

Of the 1071 patients, 34 (28 male and six female) had urolithiasis (urolithiasis group) and 1037 (711 male and 326 female) did not (non-urolithiasis group). The median residual small intestine length measured in the urolithiasis group (280.0 cm) was significantly shorter than that in the non-urolithiasis group (342.5 cm; P < 0.01). Significantly more patients in the urolithiasis group (14/34) received steroid medication than those in the non-urolithiasis group (213/1037; P < 0.01). On multivariate analysis, male sex (odds ratio 3.15; P < 0.05), history of glucocorticoid therapy (odds ratio 3.07; P < 0.05), and shorter residual small intestine length (odds ratio 0.99; P < 0.01) were risk factors for the development of urolithiasis in patients with Crohn's disease.

CONCLUSION

Our results suggest that male sex, history of glucocorticoid therapy, and shorter residual small intestine length are risk factors for urolithiasis in patients with Crohn's disease.

The membrane protein ANKH is crucial for bone mechanical performance by mediating cellular export of citrate and ATP

The membrane protein ANKH was known to prevent pathological mineralization of joints and was thought to export pyrophosphate (PPi) from cells. This did not explain, however, the presence of ANKH in tissues, such as brain, blood vessels and muscle. We now report that in cultured cells ANKH exports ATP, rather than PPi, and, unexpectedly, also citrate as a prominent metabolite. The extracellular ATP is rapidly converted into PPi, explaining the role of ANKH in preventing ankylosis. Mice lacking functional Ank (Ankank/ank mice) had plasma citrate concentrations that were 65% lower than those detected in wild type control animals. Consequently, citrate excretion via the urine was substantially reduced in Ankank/ank mice. Citrate was even undetectable in the urine of a human patient lacking functional ANKH. The hydroxyapatite of Ankank/ank mice contained dramatically reduced levels of both, citrate and PPi and displayed diminished strength. Our results show that ANKH is a critical contributor to extracellular citrate and PPi homeostasis and profoundly affects bone matrix composition and, consequently, bone quality.

Role of Calcium to Citrate Ratio in Predicting Stone Formation in Idiopathic Hypercalciuria Children (2-12 Years Old)

OBJECTIVE

Considering the predictive role of the relatively low urinary citrate for stone formation, especially in hypercalciuric patients, this study is aimed at comparing urine calcium to citrate (Ca/Cit) ratio in 3 groups of children, including patients with idiopathic hypercalciuria with and without renal stone as well as the healthy children.

METHODS

This study was carried out on 96 children (2 to 12 years old) referred to a pediatric nephrology clinic in the city of Ahvaz, Southwest Iran. All the children underwent renal ultrasonography, urinalysis, and measurement of random nonfasting urine Ca, Cr, and citrate. Those with secondary hypercalciuria, urinary tract malformations, and/or functional abnormalities of the gastrointestinal tract were excluded from the study.

RESULTS

The mean Ca/Cit. ratio (mg/mg) in the three groups, including children with hypercalciuric with and without renal stones and the healthy children (control group), was 0.44 ± 0.14, 0.39 ± 0.13, and 0.19 ± 0.08, respectively, which showed a significant difference (P < .001). There was also a significant difference in Ca/Cit ratio between the first and the control group by Tukey's range test (P < .001). Mean urinary Ca/Cit ratio in those with a positive family history of urolithiasis within three groups was 0.42 ± 0.17 and in those with a negative family history was 0.32 ± 0.16 (P = .013). Mean Ca/Cit. ratio (mg/mg) of 0.25 showed a sensitivity of 90.6% (confidence interval: 75.7-96.7%) and a specificity of 81.2% (confidence interval: 64.7-91.1%) to differentiate between the renal stone group and the control group.

CONCLUSION

High Ca/Cit ratio can predict stones formation in hypercalciuric patients, especially in those with a positive family history of urolithiasis. The present study found the cutoff level of 0.25 for Ca/Cit. ratio as the highest prognostic value for renal stone formation.

NMR-based metabolic profiling of urine, serum, fecal, and pancreatic tissue samples from the Ptf1a-Cre; LSL-KrasG12D transgenic mouse model of pancreatic cancer

Pancreatic cancer is the third leading cause of cancer deaths in the United States with more than 53,000 expected to be diagnosed with the disease in 2018. The median survival time after diagnosis is four to six months. The poor survival statistics are due in part to the fact that pancreatic cancer is typically asymptomatic until it reaches advanced stages of the disease. Although surgical resection provides the best chance of survival, pancreatic cancer is rarely detected when surgery is still possible due, in part, to lack of effective biomarkers for early detection. The goal of the research reported here was to determine if it was possible to identify metabolic biomarkers for detection of pre-cancerous pancreatic intraepithelial neoplasia (PanIN) that precede pancreatic adenocarcinoma. The transgenic Ptf1a-Cre; LSL-KrasG12D mouse strain was used as a model of pancreatic cancer progression. Nuclear magnetic resonance (NMR) spectroscopy was employed to compare metabolic profiles of urine, sera, fecal extracts, and pancreatic tissue extracts collected from control and study mice aged 5, 11, and 15 months, including 47 mice with tumors. We were able to identify the following potential biomarkers: decreased 3-indoxylsulfate, benzoate and citrate in urine, decreased glucose, choline, and lactate in blood, and decreased phenylalanine and benzoate and increased acetoin in fecal extracts. Potential biomarkers were validated by p-values, PLS-DA VIP scores, and accuracies based on area under ROC curve analyses. Essentially, all of the metabolic profiling changes could be explained as being associated with the consequences of bicarbonate wasting caused by a complete substitution of the normal pancreatic acinar tissue by tissue entirely composed of PanIN. Given the nature of the mouse model used here, our results indicate that it may be possible to use NMR-based metabolic profiling to identify biomarkers for detection of precancerous PanIN that immediately precede pancreatic cancer.

Metabolic and Nutritional Consequences of Urinary Diversion Using Intestinal Segments to Reconstruct the Urinary Tract

Intestinal segments in various forms have been used to reconstruct the urinary tract since the mid-1800s. Currently, many different forms of continent and incontinent diversion options exist. Incorporating bowel mucosa within the urinary tract leads to predictable metabolic and nutritional consequences. The use of ileum or colon can cause a hyperchloremic metabolic acidosis, vitamin B12 deficiency, osteoporosis, fat malabsorption, urinary calculi, and ammoniagenic encephalopathy. Due to metabolic and nutritional consequences associated with the use of jejunum and gastric segments, the use of these bowel segments is not recommended.

Urolithiasis in inflammatory bowel disease and bariatric surgery

AIM

To analyse current literature focusing on pathogenesis and therapeutic aspects of urolithiasis with inflammatory bowel disease (IBD) and following bariatric surgery.

METHODS

A systematic literature search was performed using PubMed, supplemented with additional references. Studies assessing the association of IBD or bariatric surgery with renal stones in both paediatric and adulthood were included.

RESULTS

Certain types of stones are seen more frequently with IBD. Hyperoxaluria and hypocitraturia are the main metabolic changes responsible for urolithiasis. The incidence of renal stones in malabsorptive types of bariatric surgery such as gastric bypass is high; this is not as common in modern restrictive surgical methods. Preventative methods and urine alkalinisation have been shown to be beneficial.

CONCLUSION

Both conditions are associated with renal stones. Patients’ counselling and prevention strategies are the mainstay of urolithiasis management in these patients.

Evidence for epistatic interaction between VDR and SLC13A2 genes in the pathogenesis of hypocitraturia in recurrent calcium oxalate stone formers

BACKGROUND

Genetic factors play a key role in the pathogenesis of hypocitraturia, a common risk factor for nephrolithiasis. The Na⁺-dicarboxylate cotransporter NaDC1, encoded by the sodium-dicarboxylate cotransporter (SLC13A2) gene, is a major determinant of urinary citrate excretion and its biological functions are regulated also by the vitamin D/Vitamin D receptor (VDR) biological system. The aim of this case-control study was to evaluate the possible epistatic interaction between VDR ^rs731236and SLC13A2 ^rs11567842 allelic variants in the pathogenesis of hypocitraturia.

METHODS

Recurrent calcium-oxalate stone formers (SF) with or without hypocitraturia and healthy controls (C) were genotyped. Gene-gene interactions were estimated by the 1.0 software package of multifactor dimensionality reduction (MDR).

RESULTS

The prevalence of VDR ^TT and SLC13A2 ^GG genotypes was higher in hypocitraturic SF compared to C (odds ratio [OR] 3.24, 95 % confidence interval [CI] 1.38-7.60 for VDR ^TT vs. VDR ^tt and OR 4.06, 95 % CI 1.75-9.42 for SLC13A2 ^GG vs. SLC13A2 ^AA ). MDR analysis indicated a significant interaction between VDR ^TT and SLC13A2 ^GG in hypocitraturic SF compared to C [OR 3.81 (2.11-6.88)]. These data are compatible with an epistatic interaction between the VDR ^TT and SLC13A2 ^GG genotypes with a significant impact on the magnitude of the effect (suppressive effect).

CONCLUSIONS

These results point to an epistatic interaction between the VDR and the SLC13A2 alleles in the pathogenesis of idiopathic hypocitraturia in calcium-oxalate SF.

Model-Based Assessment of Plasma Citrate Flux Into the Liver: Implications for NaCT as a Therapeutic Target

Cytoplasmic citrate serves as an important regulator of gluconeogenesis and carbon source for de novo lipogenesis in the liver. For this reason, the sodium-coupled citrate transporter (NaCT), a plasma membrane transporter that governs hepatic influx of plasma citrate in human, is being explored as a potential therapeutic target for metabolic disorders. As cytoplasmic citrate also originates from intracellular mitochondria, the relative contribution of these two pathways represents critical information necessary to underwrite confidence in this target. In this work, hepatic influx of plasma citrate was quantified via pharmacokinetic modeling of published clinical data. The influx was then compared to independent literature estimates of intracellular citrate flux in human liver. The results indicate that, under normal conditions, <10% of hepatic citrate originates from plasma. Similar estimates were determined experimentally in mice and rats. This suggests that NaCT inhibition will have a limited impact on hepatic citrate concentrations across species.

Exploratory analysis of urinary tract infection using a GC-APCI-MS platform

This study shows the first application of GC-APCI-MS in a clinical setting specifically in the context of urinary tract infection.

The Role of INDY in Metabolic Regulation

Reduced expression of the Indy (I'm Not Dead Yet) gene in D. melanogaster and C. elegans extends longevity. Indy and its mammalian homolog mINDY (Slc13a5, NaCT) are transporters of TCA cycle intermediates, mainly handling the uptake of citrate via the plasma membrane into the cytosol. Deletion of mINDY in mice leads to significant metabolic changes akin to caloric restriction, likely caused by reducing the effects of mINDY-imported citrate on fatty acid and cholesterol synthesis, glucose metabolism and ß-oxidation. This review will provide an overview on different mammalian SLC1 3 family members with a focus on mINDY (SLCl3A5) in glucose and energy metabolism and will highlight the role of mINDY as a putative therapeutic target for the treatment of obesity, non-alcoholic fatty liver disease and type 2 diabetes.

An overview of short bowel syndrome management: adherence, adaptation, and practical recommendations

Short bowel syndrome (SBS) refers to the clinical consequences resulting from loss of small bowel absorptive surface area due to surgical resection or bypass. The syndrome is characterized by maldigestion, malabsorption, and malnutrition. Survival of patients with SBS is dependent on adaptation in the remaining bowel and a combination of pharmacologic and nutrition therapies. Individual plans of care are developed based on the length and sites of remaining bowel, the degree of intestinal adaptation, and the patient's ability to adhere to the medication and dietary regimens. Antisecretory and antidiarrheal medications are prescribed to slow intestinal transit times and optimize fluid and nutrient absorption. Based on postsurgical anatomy, enteral feedings, parenteral infusions, complex diet plans, and vitamin and mineral supplementation are used in various combinations to nourish patients with SBS. In the acute care setting, registered dietitians (RDs) assist with infusion therapy, diet education, and discharge planning. Long-term, as the small intestine adapts, RDs revise the nutrition care plan and monitor for nutrient deficiencies, metabolic bone disease, and anemia. The frequent monitoring and revision of care plans, plus the appreciable benefits from proper medical nutrition therapy, make this patient population extremely challenging and rewarding for RDs to manage. This article provides a brief, case study-based overview of the medical and nutrition management of SBS.

Isaac Albeniz (1860-1909): Spanish musician who died of chronic renal disease

Isaac Albéniz was a Spanish musician and pianist who was best known in France and England. One of his last works for piano, the suite Iberia, is well-known and identifies his country of origin. He died with terminal uraemia following longstanding chronic intestinal and kidney symptoms. Suggestions as to pathology include amyloidosis complicated by kidney stones and hypertension that sometimes manifested itself in the form of hypertensive crisis, accompanied by obesity.

Determinants of urolithiasis in patients with intestinal fat malabsorption

OBJECTIVE

To investigate the determinants of urinary stone formation in patients with fat malabsorption, because, although the prevalence of urolithiasis is greater in patients with intestinal diseases, the pathogenetic mechanisms and risk factors associated with urolithiasis in this population remain partially unsolved.

MATERIALS AND METHODS

The present study retrospectively analyzed the determinants of urolithiasis in 51 patients with fat malabsorption due to different intestinal diseases. Anthropometric, clinical, blood, 24-hour urinary parameters, and dietary intake were assessed.

RESULTS

The resection rate (ie, pancreatic and/or bowel resection) differed significantly between stone formers (SF; n=10) and nonstone formers (NSF; n=41; 70% vs 29%; P=.027). Urinary citrate was lower (1.606±1.824 vs 3.156±1.968 mmol/24 h; P=.027), while oxalate excretion (0.659±0.292 vs 0.378±0.168 mmol/24 h; P=.002) and the relative supersaturation of calcium oxalate were greater in SF than NSF (8.16±4.61 vs 3.94±2.93; P=.003). Total cholesterol and low-density lipoprotein cholesterol, but also high-density lipoprotein cholesterol, plasma β-carotene, and vitamin E concentrations, were significantly diminished, whereas serum aspartate aminotransferase activity was significantly greater in SF compared with NSF. Binary logistic regression analysis revealed resection status as a major extrarenal risk factor for stone formation (odds ratio 5.639).

CONCLUSION

Increased urinary oxalate and decreased citrate excretion, probably resulting from pancreatic and/or bowel resection with mainly preserved colon, were identified as the most crucial urinary risk factors for stone formation in patients with fat malabsorption. The findings suggest that hyperoxaluria predominantly results from increased colonic permeability for oxalate due to disturbed bile acid metabolism. The impaired status of fat-soluble antioxidants β-carotene and vitamin E indicates severe malabsorptive states associated with an enhanced stone-forming propensity.

Enteric hyperoxaluria, recurrent urolithiasis, and systemic oxalosis in patients with Crohn's disease

BACKGROUND

Prevalence of recurrent calcium-oxalate (CaOx) urolithiasis (UL) is up to fivefold higher in Crohn's disease than in the general population. Treatment options are scarce and the risk of recurrent UL or progressive renal CaOx deposition, (oxalosis) based early end-stage renal failure (ESRF), subsequent systemic oxalosis, and recurrence in the kidney graft is pronounced. We aimed to find proof that secondary hyperoxaluria is the main risk factor for the devastating course and correlates with intestinal oxalate absorption.

METHODS

24-h urines were collected and analyzed for urinary oxalate (Uox) in 27 pediatric (6-18 years) and 19 adult patients (20-62 years). In the 21 patients (8 adults and 13 children) with hyperoxaluria a [(13)C(2)]oxalate absorption test was performed under standardized dietary conditions.

RESULTS

Mean Uox was significantly higher in patients with UL or oxalosis (0.92 ± 0.57) compared with those without (0.53 ± 0.13 mmol/1.73 m(2)/24 h, p<0.05, normal < 0.5). Hyperoxaluria then significantly correlated with intestinal oxalate absorption (p< 0.05).

CONCLUSION

As UL/oxalosis has major implications for the general health in patients with Crohn's disease (ESRF and systemic oxalosis), new medication, e.g. to reduce intestinal oxalate absorption, is definitely needed.

Dietary Ascophyllum nodosum increases urinary excretion of tricarboxylic acid cycle intermediates in male Sprague-dawley rats

We used a (1)H NMR-based metabonomics approach to examine the physiological effects of the seaweed Ascophyllum nodosum in a mammalian model, assess the dosage level required to elicit a response in the urinary profile, and identify potential toxic effects. Male Sprague-Dawley rats (n = 6/group) were fed a control or 5, 10, or 15% freeze-dried, ground A. nodosum diet for 4 wk. Urine samples were collected 3 times daily (0-4, 4-8, and 8-24 h) prior to feeding experimental diets and, at the end of the study, were profiled using (1)H NMR spectroscopy. Food intake, weight gain, and serum enzyme (alanine transaminase and aspartate transaminase) levels indicated that seaweed diets were well tolerated. The spectral data and principal component analysis (PCA) revealed that rats fed 5, 10, and 15% seaweed diets had increased urinary excretion of citrate, 2-oxoglutarate, succinate, trimethylamine (TMA), TMA-N-oxide, and malonate and decreased excretion of taurine, creatinine, and acetate compared with the controls. In addition, mannitol was detected in the 8- to 24-h urine samples from seaweed-fed rats. Metabolic responses related to ingestion of seaweed polyphenolics and fiber were not observed in the spectral profiles. Increased seaweed concentration in the diet did not increase the magnitude of the rats' response as detected by (1)H NMR. Visual analysis and PCA of the spectral data for serum samples collected at the end of the study did not show diet-related clustering. The lack of toxicity at 15% seaweed incorporation allows the use of this concentration in future A. nodosum intervention studies.

Causes of hypocitraturia in recurrent calcium stone formers: focusing on urinary potassium excretion

BACKGROUND

Multiple factors associated with hypocitraturia have been identified. However, limited studies addressing the causal relationship to hypocitraturia are available. We therefore conducted this study to determine factors associated with hypocitraturia and show their causal relationship in recurrent calcium stone formers.

METHODS

Dietary review and 24-hour urine samples were obtained from all recurrent calcium stone formers referred for metabolic workup in the stone clinic. One month of oral potassium chloride supplementation was prescribed to stone formers to determine the causal relationship between urinary potassium and citrate levels.

RESULTS

Eighty-three subjects, 44 men and 39 women, were recruited to participate in this study. Hypocitraturia (citrate < 300 mg/d [<1.43 mmol/d]) was found in 50.6% of subjects. Four independent urinary variables associated with hypocitraturia were identified, including potassium level, net gastrointestinal alkaline absorption, calcium level, and titratable acid. Urinary potassium level was the strongest predictor of urinary citrate level. Hypocitraturic subjects also had lower fruit intake compared with subjects with high urinary citrate levels. Potassium chloride supplementation to a subgroup of this population (n = 58) resulted in a significant increase in urinary citrate excretion (350.73 +/- 27.25 versus 304.15 +/- 30.00 mg/d [1.67 +/- 0.13 versus 1.45 +/- 0.14 mmol/d]; P < 0.02), but no alteration in fractional excretion of citrate (19.7% +/- 2.7% versus 23.1% +/- 2.4%; P > 0.05).

CONCLUSION

Hypocitraturia was found to be a common risk factor associated with recurrent calcium stone formation and low urinary potassium level, low alkaline absorption, low urinary calcium level, and high titratable acid excretion. Hypocitraturia is predominantly of dietary origin. Estimation of fruit intake should be included in the metabolic evaluation for recurrent calcium stone formation.

METABOLIC CONSEQUENCES AND LONG-TERM COMPLICATIONS OF ENTEROCYSTOPLASTY IN CHILDREN: A REVIEW

PURPOSE

We summarize important metabolic consequences and long-term complications associated with enterocystoplasty with particular emphasis on the pediatric patient with genitourinary abnormalities.

MATERIALS AND METHODS

A directed MEDLINE literature review for metabolic and long-term complications following enterocystoplasty was performed. Information gained through the published literature and from our database was reviewed and summarized to provide the reader with a thorough review of the subject.

RESULTS

Bowel is not a perfect tissue for substitution or augmentation and its use to treat functionally and structurally compromised bladders is associated with several metabolic consequences and long-term complications. Metabolic acidosis is the most common metabolic abnormality seen. The rates and severity of these complications vary, although they may have a profound impact on patient quality of life after enterocystoplasty.

CONCLUSIONS

The metabolic consequences and long-term complications associated with enterocystoplasty are important clinical features of this intervention. Careful consideration should be given to them prior to pursuing enterocystoplasty.

Effect of high protein diet on stone-forming propensity and bone loss in rats

BACKGROUND

High protein diets are believed to cause kidney stone formation and bone loss, but the mechanisms mediating these changes are unknown. The purpose of this study was to create an animal model of animal protein excess and to evaluate the response of kidney and bone to the dietary protein load.

METHODS

Rats (12 per group) were pair-fed with a high (48%) and low (12%) casein diets that were otherwise identical in their content of sodium, potassium, calcium, phosphorus, and magnesium.

RESULTS

Compared with the low casein group, the high casein group delivered a substantial acid load during 59 days of study, since it significantly decreased urinary pH, and increased urinary ammonium, titratable acidity, and net acid excretion. Animals on high casein diet also had higher urinary volumes. On the high casein diet, urinary calcium excretion was significantly higher and urinary citrate excretion and concentration was significantly lower. On the high casein diet, urinary saturation of calcium phosphate was higher. Serum calcitriol concentration did not significantly differ between the two groups. Histomorphometric analysis of femur procured after 59 days on the diet showed marked increase in bone resorption in the high casein group. Hypocitraturia was associated with increased activity of sodium-citrate cotransporter in renal cortical brush-border membranes (BBM) in the high casein group.

CONCLUSION

Both the kidney and bone contribute to the pathogenesis of hypercalciuria during high casein diet in rats. Hypocitraturia is probably renal in origin. This rat model will be useful in elucidating the mechanisms by which high protein intake increases the risk of nephrolithiasis and bone loss in human beings.

Hepatobiliary, renal and bone complications of intestinal failure

Abnormal liver function tests in patients with intestinal failure (IF) may be due to the underlying disease, IF or the treatments given (including parenteral nutrition (PN)). PN-related liver disease in children usually relates to intrahepatic cholestasis and in adults to steatosis. Steatosis may be consequent upon an excess of carbohydrate, lipid or protein, or upon a deficiency of a specific molecule. Pigment-type gallstones are common in adults and children with IF; these develop from biliary sludge that forms during periods of gallbladder stasis. Ileal disease/resection, parenteral nutrition, surgery, rapid weight loss and drugs all increase the risk of developing gallstones. Gallstone formation may be prevented by reducing gallbladder stasis (oral/enteral feeding or prokinetic agents), altering bile composition, or by means of a prophylactic cholecystectomy. Calcium oxalate renal stones are common in patients with a short bowel and retained functioning colon and are consequent upon increased absorption of dietary oxalate; they are prevented by a low-oxalate diet. An osteopathy may occur with long-term parenteral nutrition.

Urinary lithogenic and inhibitory factors in preterm neonates receiving either total parenteral nutrition or milk formula

The aim of this study was to evaluate prospectively the influence of nutrition on certain factors which may inhibit or promote nephrocalcinosis in two groups of preterm infants, receiving total parenteral nutrition (TPN) and special preterm milk formula respectively, but not furosemide. A total of 37 preterm infants, 15 on TPN and 22 fed a special preterm formula were studied at the end of the 1st, 2nd and 3rd weeks of life, at which time serum and 8 h urine specimens were collected. High ratios of urinary calcium to urinary creatinine (UCa/cr), urinary oxalate to urinary creatinine (Uox/cr) and urinary calcium to urinary citrate (UCa/cit) indicates an increased risk for nephrocalcinosis while high urinary citrate to urinary creatinine (Ucit/cr) ratio indicates protection. Uox/cr increased significantly (P<0.05) in those infants fed preterm formula, from the end of 2nd week of life and was two-fold higher than in the TPN group of preterm infants (P<0.01). Ucit/cr was higher throughout the study period in the formula fed than in the TPN preterm infants. UCa/cit was five-fold higher (P<0.01) in the TPN group, by the end of the 3rd week. Urinary calcium and magnesium was similar in both groups during the study period. Two of the infants studied (5.4%), one from each group, developed nephrocalcinosis.

CONCLUSION

In preterm neonates on total parenteral nutrition, urinary oxalate -to-creatinine ratio (a potent lithogenic factor) was lower and urinary citrate -to-creatinine ratio (a lithoprotective factor) also lower than in formula fed neonates. The type of feeding (total parenteral nutrition or special preterm milk formula) seems to affect urinary oxalate and citrate but not calcium and magnesium in non-furosemide treated preterm infants during the first 3 weeks of life.

Predictive value of kidney stone composition in the detection of metabolic abnormalities

PURPOSE

To determine if kidney stone composition can predict the underlying medical diagnosis, and vice versa.

METHODS

We studied 1392 patients with kidney stones who underwent a complete ambulatory evaluation and who submitted one or more stones for analysis. We ascertained the associations between medical diagnosis and stone composition.

RESULTS

The most common kidney stones were composed of calcium oxalate (n = 1041 patients [74.8%]), mixed calcium oxalate-calcium apatite (n = 485 [34.8%]), and calcium apatite alone (n = 146 [10.5%]). The most common medical diagnoses were hypocitraturia (n = 616 patients [44.3%]), absorptive hypercalciuria (n = 511 [36.7%]), and hyperuricosuria (n = 395 [28.4%]). Calcium apatite and mixed calcium oxalate-calcium apatite stones were associated with the diagnoses of renal tubular acidosis and primary hyperparathyroidism (odds ratios >/=2), but not with chronic diarrheal syndromes. As the phosphate content of the stone increased from calcium oxalate to mixed calcium oxalate-calcium apatite, and finally to calcium apatite, the percentage of patients with renal tubular acidosis increased from 5% (57/1041) to 39% (57/146), and those with primary hyperparathyroidism increased from 2% (26/1041) to 10% (14/146). Calcium oxalate stones were associated with chronic diarrheal syndromes, but not with renal tubular acidosis. Pure and mixed uric acid stones were strongly associated with a gouty diathesis, and vice versa. Chronic diarrheal syndromes and uric acid stones were associated with one another, and brushite stones were associated with renal tubular acidosis. As expected, there was a very strong association between infection stones and infection, and between cystine stones and cystinuria.

CONCLUSION

Stone composition has some predictive value in diagnosing medical conditions, and vice versa, especially for noncalcareous stones.

Potassium depletion in a healthy north-eastern Thai population: No association with tubulo-interstitial injury

Potassium depletion prevails among the healthy population of north-east Thailand, as well as among patients with certain metabolic disorders such as upper urinary tract stones, the sudden unexplained death syndrome, distal renal tubular acidosis and hypokalaemic periodic paralysis. However, definite proof of the relationship of potassium depletion and these metabolic disorders is lacking. We prospectively studied muscle and kidney potassium content including renal tissue pathology in three groups of healthy adult Thai subjects who died of vehicular accidents. Group 1 (n = 24) were Bangkok city dwellers; groups 2 (n = 10) and 3 (n = 22) lived in north-eastern Thailand in the metropolitan area and in the villages, respectively. The muscle potassium content of group 1 (338.5 +/- 9.6 mEq/kg dry weight (DW)) were similar to group 2 (307.9 +/- 11.9 mEq/kg DW), but was greater than group 3 (295.4 +/- 9.1 mEq/kg DW; P < 0.01). The kidney potassium content of group 1 (208.6 +/- 7.8 mEq/kg DW) was significantly higher than group 3 (175.9 +/- 6.3 mEq/kg DW, P < 0.05). In group 3, the muscle potassium correlated linearly with the kidney potassium (r = 0.455, P = 0.33). None of the group 3 patients had renal histopathological change compatible with a diagnosis of focal or diffuse interstitial nephritis. This study confirms that potassium depletion is common among healthy rural dwellers in north-east Thailand. This deficit was probably chronic. However, there was minimal renal tubulo-interstitial change.

Association between vitamin D receptor gene polymorphisms and tubular citrate handling in calcium nephrolithiasis

OBJECTIVES

Hypocitraturia is a risk factor for calcium nephrolithiasis. 1,25(OH)2D3 influences renal citrate handling and enhances citraturia. The aim of this study was to evaluate the relationship between vitamin D receptor (VDR) allelic variant and urinary citrate excretion in recurrent stone formers (SF) patients.

DESIGN

Case-control study.

SUBJECTS

A total of 220 recurrent calcium oxalate SF patients and 114 healthy control (C) subjects were enrolled for this study. Subjects with urinary tract infections, hyperparathyroidism, cystinuria >70 micromol/24 h, gouty diathesis, renal tubular acidosis, renal failure, chronic diarrhoeal states, intake of thiazide diuretics, angiotensin-converting enzyme (ACE)-inhibitors, glucocorticoids or oestrogens were excluded. A standard constant diet was given for 7 days. The 24-h urinary citrate excretion and the active tubular reabsorption of filtered citrate (Rcit) were evaluated. Hypocitraturia was defined as a urinary citrate excretion lower than 1.7 mmol day-1. Stone formers patients and C were genotyped for BsmI and TaqI VDR alleles. Contingency table chi-square tests were used to compare genotype frequencies in hypocitraturic SF patients, normocitraturic SF and C.

RESULTS

The prevalence of hypocitraturia in SF patients was 32.7% (72 of 200). Hypocitraturia in these patients resulted from excessive Rcit of a normal load of citrate. We found a different distribution (P < 0.05) of BsmI and TaqI VDR genotypes in hypocitraturic SF patients compared with normocitraturic SF and C. In particular, the prevalence of bb and TT VDR genotypes in hypocitraturic SF was significantly higher than in normocitraturic SF and C.

CONCLUSIONS

These results point to a genetic association between BsmI and TaqI VDR polymorphisms and idiopathic hypocitraturia in calcium-oxalate recurrent SF patients.

Urine stone risk factors in nephrolithiasis patients with and without bowel disease

BACKGROUND

The prevalence of nephrolithiasis among patients with bowel disease is higher than in the general population. We examined urine stone risk factors and clinical characteristics of these patients, contrasted with a large group of stone forming patients without systemic disease.

METHODS

A total of 180 patients with bowel disease were compared with a group of 2048 nephrolithiasis patients with calcium or uric acid stones and without systemic diseases. Bowel diseases included inflammatory bowel disease with and without bowel resections, bowel resections from cancer or trauma, and bypass procedures for obesity or hypercholesterolemia. Urine stone risk factors, stone rates, stone compositions, and creatinine clearance were measured.

RESULTS

Compared to ordinary stone forming patients, bowel patients formed stones higher in rate of recurrence and in uric acid content. Uric acid content was highest when colon surgery had occurred. Urine volumes were low among all bowel patients except those with a bypass. Average creatinine clearance values were low among all bowel patients. Urine oxalate excretion was modestly elevated after small bowel resection, but very high with bypass. Supersaturations were increased mainly by low urine volume and-for uric acid-low pH. Patients with no surgery were indistinguishable from routine stone formers.

CONCLUSIONS

Low urine volume and pH are the main stone-forming abnormalities in bowel disease patients. Hyperoxaluria is extreme after bypass, but only modest after small bowel surgery. In the absence of surgery, bowel disease patients with stones cannot be distinguished from common stone formers by comprehensive stone risk measurements.

Stones from bowel disease

Kidney stones are increased in patients with bowel disease, particularly those who have had resection of part of their gastrointestinal tract. These stones are usually CaOx, but there is a marked increase in the tendency to form uric acid stones, as well, particularly in patients with colon resection. These patients all share a tendency to chronic volume contraction due to loss of water and salt in diarrheal stool, which leads to decreased urine volumes. They also have decreased absorption, and therefore diminished urinary excretion, of citrate and magnesium, which normally act as inhibitors of CaOx crystallization. Patients with colon resection and ileostomy form uric acid stones, as loss of bicarbonate in the ileostomy effluent leads to formation of an acid urine. This, coupled with low urine volume, decreases the solubility of uric acid, causing crystallization and stone formation. Prevention of stones requires treatment with alkalinizing agents to raise urine pH to about 6.5, and attempts to increase urine volume, which increases the solubility of uric acid and prevents crystallization. Patients with small bowel resection may develop steatorrhea; if the colon is present, they are at risk of hyperoxaluria due to increased permeability of the colon to oxalate in the presence of fatty acids, and increased concentrations of free oxalate in the bowel lumen due to fatty acid binding of luminal calcium. EH leads to supersaturation of urine with respect to CaOx, in conjunction with low volume, hypocitraturia and hypomagnesuria. Therapy involves a low-fat, low-oxalate diet, attempts to increase urine volume, and agents such as calcium given to bind oxalate in the gut lumen. Correction of hypocitraturia and hypomagnesuria are also helpful.

Magnesium status of patients with renal stones and its effect on urinary citrate excretion

OBJECTIVES

To assess the magnesium status and its effect on urinary citrate excretion in patients with renal stones, as they have a low muscular magnesium content.

PATIENTS, SUBJECTS AND METHODS

Using a magnesium-tolerance test (0.1 mmol/L MgSO4/kg body weight, delivered intravenously), the magnesium status was assessed in 17 patients with renal stones from rural North-east Thailand, and in three groups of normal subjects from different environments (i.e. 17 from rural Central Thailand, 16 from urban and 14 from rural North-east Thailand). Participants with magnesium deficiency (magnesium retention > 50%) were supplemented with 300 mg chelated magnesium daily for 1 month and reassessed. Their urinary citrate excretion was also measured before and after supplementation.

RESULTS

Nine of the patients with renal stones were magnesium deficient, as were six normal subjects from the same area, whereas only one and two of the rural Central and urban North-east Thais had magnesium deficiency. The magnesium status of the 13 deficient subjects significantly improved (P = 0.003) after supplementation with chelated magnesium. The supplement also caused a significant increase in mean (sd) urinary citrate excretion, from 237.7 (173.1) to 361.3 (284.1) mg/day (P= 0.012).

CONCLUSIONS

These results indicate that magnesium deficiency is common among patients with renal stones in rural North-east Thailand, and that the probable cause is environmental. The increase in urinary citrate excretion after magnesium supplementation suggests that magnesium is important in renal stone formation, through its effect on citrate metabolism.

Risk factors for developing renal stones in inflammatory bowel disease

OBJECTIVE

To correlate renal calculi and other clinical factors with urinary biochemical analytes in patients with inflammatory bowel disease, and to investigate the relative importance of hyperoxaluria (associated with fat malabsorption) or reduced stone inhibitors in the development of calculi in these patients.

PATIENTS, SUBJECTS AND METHODS

Samples were obtained from 25 patients with Crohn's disease (CD), 15 with ulcerative colitis (UC) and 17 normal subjects (controls). Evidence for the presence of renal calculi was obtained from plain films, ultrasonography or intravenous urography. Urine oxalate and citrate were analysed using commercial enzymatic assays; magnesium was measured using atomic absorption and other analytes assayed using standard methods on automated analysers.

RESULTS

Renal calculi were found in two patients with CD and in none with UC. Hyperoxaluria was present in 36% of patients with CD but was absent in those with UC. Analysis of covariance showed an association between low urinary citrate/creatinine ratio and renal stones (P=0.02), and between a combined urinary citrate and magnesium deficit relative to calcium, as expressed in the CMC index ((citratexmagnesium)/calcium), and renal stones (P=0.017). Changes in urinary calcium, oxalate, urate, magnesium or the calcium oxalate index were not associated with the presence of stones. There was no independent relationship between any clinical factor and the presence of stones.

CONCLUSION

Lower urinary concentrations of magnesium and citrate (stone inhibitors), relative to calcium (stone promoter; the CMC index) may be more important in lithogenesis in inflammatory bowel disease than is hyperoxaluria. In patients with a functioning colon, a low CMC index may predict likely stone-formers; this requires a prospective evaluation. Avoiding low urinary levels of magnesium and citrate may aid in preventing and treating renal calculi.

Metabolic risk factors for stone formation in patients with cystic fibrosis

PURPOSE

Cystic fibrosis is characterized by chronic pulmonary disease, insufficient pancreatic and digestive function, and abnormal sweat concentrations. Patients with cystic fibrosis also have an increased incidence of nephrolithiasis. We compared the results of metabolic evaluation in patients with cystic fibrosis with and without nephrolithiasis.

MATERIALS AND METHODS

A total of 496 patients were evaluated at our center, including 98 with a mean age of 25 years who had cystic fibrosis and complete metabolic evaluation available between 1996 and 2000. Of these patients 13 (13%) had a history of nephrolithiasis. The records were reviewed for clinical characteristics and all patients underwent metabolic evaluation, including serum electrolyte measurement and 24-hour urine collection. Statistical analysis was done to compare the stone versus nonstone groups.

RESULTS

The incidence of nephrolithiasis in our study was 3%. We identified 13 patients 16 to 41 years old (mean age 27) with nephrolithiasis, of whom 62% had had multiple episodes. Flank pain was the presenting symptom in 9 of the 13 cases (69%). Renal ultrasound and computerized tomography were the most common imaging modalities. In 9 cases stones were passed without intervention, extracorporeal shock wave lithotripsy was required in 2 and ureteroscopy with stone extraction was done in 2. Calcium oxalate was the dominant stone composition in the 9 patients in whom stone analysis was performed. Metabolic evaluation of the stone versus no stone groups showed elevated urinary oxalate (45.5 versus 42.5 mg./24 hours), relative calcium oxalate supersaturation (5.3 versus 7.2) and decreased urinary citrate in the 2 groups. There was a statistical difference in citrate excretion with lower levels in stone formers (102 versus 218 mg./24 hours, p = 0.0007).

CONCLUSIONS

Patients with cystic fibrosis have an increased incidence of nephrolithiasis and are at high risk for recurrence. Metabolic evaluation is indicated in all patients with cystic fibrosis and urolithiasis since most have hyperoxaluria, urinary calcium oxalate supersaturation and decreased urinary citrate. Correcting detected stone risk factors in these cases may decrease stone recurrence.

Management of patients with a short bowel

There are two common types of adult patient with a short bowel, those with jejunum in continuity with a functioning colon and those with a jejunostomy. Both groups have potential problems of undernutrition, but this is a greater problem in those without a colon, as they do not derive energy from anaerobic bacterial fermentation of carbohydrate to short chain fatty acids in the colon. Patients with a jejunostomy have major problems of dehydration, sodium and magnesium depletion all due to a large volume of stomal output. Both types of patient have lost at least 60 cm of terminal ileum and so will become deficient of vitamin B₁₂. Both groups have a high prevalence of gallstones (45%) resulting from periods of biliary stasis. Patients with a retained colon have a 25% chance of developing calcium oxalate renal stones and they may have problems with D (-) lactic acidosis. The survival of patients with a short bowel, even if they need long-term parenteral nutrition, is good.

Chronic metabolic acidosis increases NaDC-1 mRNA and protein abundance in rat kidney

BACKGROUND

Chronic metabolic acidosis increases, while alkali feeding inhibits, proximal tubule citrate absorption. The activity of the apical membrane Na+/citrate cotransporter is increased in metabolic acidosis, but is not altered by alkali feeding.

METHODS

Renal cortical mRNA and brush border membrane protein abundances of sodium/dicarboxylate-1 (NaDC-1), the apical membrane Na+/citrate transporter, were measured.

RESULTS

By immunohistochemistry, NaDC-1 was localized to the apical membrane of the proximal tubule. Chronic metabolic acidosis caused an increase in NaDC-1 protein abundance that was maximal in the S2 segment and that increased with time. Metabolic acidosis also increased NaDC-1 mRNA abundance, but this was first seen at three hours and correlated with the severity of the metabolic acidosis. Alkali feeding had no effect on NaDC-1 protein or mRNA abundance.

CONCLUSIONS

Chronic metabolic acidosis increases renal cortical NaDC-1 mRNA abundance and apical membrane NaDC-1 protein abundance, while alkali feeding is without effect on NaDC-1.

Medical therapy and new approaches to management of urolithiasis

A simple, step-by-step approach to diagnosis and medical treatment of stone disease is described. It uses urinary stone risk profile obtained before and after dietary modification, history, and minimum diagnostic tests. For each abnormal stone risk factor, potential causes are discussed and treatment options are presented. The article concludes with diagnosis and treatment of combined disturbances.

Autoantibodies and primary Sjögren's syndrome in a hypocitraturic stone population

Primary Sjögren's syndrome may be complicated by distal renal tubular acidosis (dRTA) and hypocitraturia, which are risk factors for calcium stone formation. Approached from a different perspective, in patients with urolithiasis and dRTA, autoantibodies and various autoimmune diseases are not uncommon. In search for signs of autoimmune disease, we analysed antinuclear antibodies and total levels of serum IgG in 197 hypocitraturic stone formers (67 women and 130 men). Antinuclear antibodies were present in 1.5% of the men and in 18% of the women. An isolated increase in serum IgG was found in 9% of the men and in 3% of the women. Anti-SS-A antibodies were analysed in a subgroup of 46 women and were estimated to occur in 16% of all hypocitraturic stone forming women. Four of 4 examined women, but no men, fulfilled the criteria of definite or possible primary Sjögren's syndrome. We recommend the analysis of anti-SS-A antibodies in female hypocitraturic stone formers.

Adenosine triphosphate citrate lyase mediates hypocitraturia in rats

Chronic metabolic acidosis increases proximal tubular citrate uptake and metabolism. The present study addressed the effect of chronic metabolic acidosis on a cytosolic enzyme of citrate metabolism, ATP citrate lyase. Chronic metabolic acidosis caused hypocitraturia in rats and increased renal cortical ATP citrate lyase activity by 67% after 7 d. Renal cortical ATP citrate lyase protein abundance increased by 29% after 3 d and by 141% after 7 d of acid diet. No significant change in mRNA abundance could be detected. Hypokalemia, which causes only intracellular acidosis, caused hypocitraturia and increased renal cortical ATP citrate lyase activity by 28%. Conversely, the hypercitraturia of chronic alkali feeding was associated with no change in ATP citrate lyase activity. Inhibition of ATP citrate lyase with the competitive inhibitor, 4S-hydroxycitrate, significantly abated hypocitraturia and increased urinary citrate excretion fourfold in chronic metabolic acidosis and threefold in K+-depletion. In summary, the hypocitraturia of chronic metabolic acidosis is associated with an increase in ATP citrate lyase activity and protein abundance, and is partly reversed by inhibition of this enzyme. These results suggest an important role for ATP citrate lyase in proximal tubular citrate metabolism.

Nephrolithiasis due to primary hyperparathyroidism and enteric hyperoxaluria: a case report

Enteric hyperoxaluria and primary hyperparathyroidism have been associated with the development of nephrolithiasis. We report a case involving a patient who had hyperparathyroidism due to a parathyroid adenoma and enteric hyperoxaluria resulting from a small bowel bypass and who had severe stone-related complications. This combination of stone-generating factors has heretofore not been reported. The pathophysiology of these entities is discussed.

The importance of urinary magnesium values in patients with gut failure

OBJECTIVE

To determine whether urinary magnesium (Mg) values in patients with gut failure would be more helpful than serum Mg measurements in assessment of Mg deficiency.

DESIGN

We compared serum and urinary Mg values in 16 patients with gut failure and 16 age- and sex-matched control subjects.

MATERIAL AND METHODS

Sixteen patients with gut failure (nine women and seven men; mean age, 59 years) had serum and 24-hour urinary mg measured before Mg replacement therapy. Short bowel syndrome was present in 75%, and diffuse small bowel disease was present in 25%.

RESULTS

The median value for serum Mg was 1.7 mg/dL for patients and 2.0 mg/dL for healthy control subjects (P < 0.001). The median values for urinary Mg were 19 mg and 127 mg per 24-hour specimen in patient and control groups, respectively (P < 0.001). A strong correlation was noted between serum Mg and urinary Mg levels. All patients had low urinary Mg values even though 9 of 16 (56%) had normal serum Mg values. Two patients with normal serum Mg concentrations had urinary Mg values of 20 mg/24 h (25% of normal). Serum, but not urinary, Mg correlated significantly with the length of remaining small bowel (P = 0.03).

CONCLUSIONS

Urinary Mg declines before serum Mg and is an earlier and more reliable indicator of evolving Mg deficiency. On the basis of these observations and those showing beneficial effects of parenterally administered Mg supplements on urinary citrate excretion (and, presumably, formation of calcium oxalate stones), replacement of Mg in patients with gut failure should be targeted at normalizing urinary Mg.