Fractional Excretion Of Urate Research Articles

Fractional Excretion of Urate is Positively Associated with Type 2 Diabetes in HUA Patients: A Cross-Sectional Study.

People with hyperuricemia (HUA) are often related to metabolic disorders such as diabetes, metabolic syndrome (MetS), and obesity. However, the correlation between excretion of uric acid and these diseases is unclear. Our study aimed to explore the relationship between uric acid excretion and type 2 diabetes (T2D). A total of 228 HUA patients from Tianjin Medical University General Hospital from 2022 to 2023 were included in this study. We collected demographic, biochemical, and anthropometric data on each subject. Urine uric acid excretion (UUAE) was calculated enzymatically from a single urine collection that lasted 24 hours. And fractional excretion of uric acid (FEUA) was calculated from serum uric acid and creatinine and uric acid and creatinine. Binary logistic regression modeling assessed the association between uric acid excretion and T2D. Of the 228 subjects, 13.4% had T2D and 48.7% had obesity. The obesity group had a lower FEUA (p<0.05) and a higher UUAE compared to the control group (p<0.05). And FEUA had a stronger correlation with the risk of T2D (p<0.001). Also, there was a negative association between BMI and FEUA and a positive link between BMI and UUAE in the outpatients. Increased FEUA levels were significantly associated with T2D in HUA patients. Therefore, routine calculating of FEUA is essential for proper diagnosis and appropriate treatment T2D of in HUA patients.

Recurrent exercise-induced acute kidney injury associated with hypouricemia: a case report and literature review

BackgroundHereditary renal hypouricemia (RHUC) is a heterogenous disorder characterized by defective uric acid (UA) reabsorption resulting in hypouricemia and increased fractional excretion of UA. RHUC is an important cause of exercise-induced acute kidney injury (EIAKI), nephrolithiasis and posterior reversible encephalopathy syndrome (PRES). We present here an unusual case of a patient with RHUC who presented with recurrent EIAKI and had two heterozygous mutations in the SLC2A9 gene.Case presentationA 43-year old man was admitted to our clinic because of bilateral loin pain, nausea and sleeplessness for 3 days after strenuous exercise. The laboratory results revealed increased levels of blood urea nitrogen (BUN) (15 mmol/l) and serum creatinine (Scr) (450 μmol/l), while the UA level was extremely low at 0.54 mg/dl, and his fractional excretion of urate (FE-UA) was 108%. The patient had an episode of acute kidney injury after playing soccer approximately 20 years ago, and on routine physical examination, his UA was less than 0.50 mg/dl. In view of the marked hypouricemia and high FE-UA, a diagnosis of RHUC was suspected, which led us to perform mutational screening of the SLC22A12 and SLC2A9 genes. DNA sequencing revealed no mutation in SLC22A12 gene, but two heterozygous mutations in the SLC2A9 gene.ConclusionsThis is a rare report of a patient with RHUC2 due to the mutation of SLC2A9. And this unique symptom of EIAKI and decreased or normal serum concentrations of UA warrant more attention as an early cue of RHUC.

Hipouricemia con hipercalciuria. Estudio longitudinal y revisión del tema

Background and objectiveThe association of hypouricemia and hypercalciuria is rare. In 1974 a new syndrome named Hypouricemia with hypercalciuria and decreased bone density was described. Afterwards, some cases with such association were published in which the fractional excretion of urate was higher than 20/100ml FGR. We have analyzed a series of children who were diagnosed with hypouricemia and hypercalciuria and who were monitored. The aim of this study was to determine whether our patients could be affected by the aforementioned syndrome or be carriers of a variant of idiopathic hypercalciuria. Patients and methodsRetrospective longitudinal study in which the medical records of eight patients (5V and 3M) diagnosed with hypouricemia and hypercalciuria in childhood. Clinical features at diagnosis, ultrasound and densitometric findings and selected biochemical variables were noted, with special emphasis on renal tubular handling of urate. Results were compared with 36 children with idiopathic hypercalciuria without hypouricemia (14V and 22M). ResultsIn the hypouricemia group baseline urate levels were 1.9 (0.3)mg/dl (range: 1.5-2) and first day urine calcium/creatinine ratio 0.27 (0.05)mg/mg (range: 0.23-0.31). In all cases fractional urate excretion was less than 20/100ml FGR. The z-DMO values were less than −1 in 4/8 cases. At the last follow-up only three cases still had an elevated calcium/creatinine ratio and in all of them the urates levels was greater than 2mg/dl. The z-DMO value had improved in five cases and worsened in three others. In relation to the group without hypouricemia, no differences were observed between the various parameters studied including the z-DMO value, with the exception of fractional excretion and tubular urate reabsorption although plasmatic uric acid levels were still significantly lower. ConclusionOur patients with hypercalciuria and hypouricemia would be affected by a variant of idiopathic hypercalciuria in which, due to an unknown cause, the proximal tubular reabsorption of urate is modestly reduced and improves over time. Hypouricemia with hypercalciuria and decreased bone density may not be a specific entity.

Haptoglobin-Related Protein without Signal Peptide as Biomarker of Renal Salt Wasting in Hyponatremia, Hyponatremia-Related Diseases and as New Syndrome in Alzheimer’s Disease

The application of pathophysiologic tenets has created significant changes in our approach to hyponatremia and hyponatremia-related conditions. This new approach incorporated the determination of fractional excretion (FE) of urate before and after the correction of hyponatremia and the response to isotonic saline infusion to differentiate the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) from renal salt wasting (RSW). FEurate simplified the identification of the different causes of hyponatremia, especially the diagnosis of a reset osmostat and Addison's disease. Differentiating SIADH from RSW has been extremely difficult because both syndromes present with identical clinical parameters, which could be overcome by successfully carrying out the difficult protocol of this new approach. A study of 62 hyponatremic patients from the general medical wards of the hospital identified 17 (27%) to have SIADH, 19 (31%) with reset osmostat, and 24 (38%) with RSW with 21 of these RSW patients presenting without clinical evidence of cerebral disease to warrant changing the nomenclature from cerebral to renal salt wasting. The natriuretic activity found in the plasma of 21 and 18 patients with neurosurgical and Alzheimer's disease, respectively, was later identified as haptoglobin-related protein without signal peptide (HPRWSP). The high prevalence of RSW creates a therapeutic dilemma of deciding whether to water-restrict water-logged patients with SIADH as compared to administering saline to volume-depleted patients with RSW. Future studies will hopefully achieve the following: 1. Abandon the ineffective volume approach; 2. Develop HPRWSP as a biomarker to identify hyponatremic and a projected large number of normonatremic patients at risk of developing RSW, including Alzheimer's disease; 3. Facilitate differentiating SIADH from RSW on the first encounter and improve clinical outcomes.

New Approach to Hyponatremia: High Prevalence of Cerebral/Renal Salt Wasting, Identification of Natriuretic Protein That Causes Salt Wasting.

Our understanding of hyponatremic conditions has undergone major alterations. There is a tendency to treat all patients with hyponatremia because of common subtle symptoms that include unsteady gait that lead to increased falls and bone fractures and can progress to mental confusion, irritability, seizures, coma and even death. We describe a new approach that is superior to the ineffectual volume approach. Determination of fractional excretion (FE) of urate has simplified the diagnosis of a reset osmostat, Addison's disease, edematous causes such as congestive heart failure, cirrhosis and nephrosis, volume depletion from extrarenal salt losses with normal renal tubular function and the difficult task of differentiating the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) from cerebral/renal salt wasting (C/RSW). SIADH and C/RSW have identical clinical and laboratory parameters but have diametrically opposite therapeutic goals of water-restricting water-loaded patients with SIADH or administering salt water to dehydrated patients with C/RSW. In a study of nonedematous patients with hyponatremia, we utilized FEurate and response to isotonic saline infusions to differentiate SIADH from C/RSW. Twenty-four (38%) of 62 hyponatremic patients had C/RSW with 21 having no clinical evidence of cerebral disease to support our important proposal to change cerebral to renal salt wasting (RSW). Seventeen (27%) had SIADH and 19 (31%) had a reset osmostat. One each from hydrochlorothiazide and Addison's disease. We demonstrated natriuretic activity in the plasma of patients with neurosurgical and Alzheimer diseases (AD) in rat clearance studies and have now identified the natriuretic protein to be haptoglobin related protein without signal peptide (HPRWSP). We introduce a new syndrome of RSW in AD that needs further confirmation. Future studies intend to develop HPRWSP as a biomarker to simplify the diagnosis of RSW in hyponatremic and normonatremic patients and explore other clinical applications that can improve clinical outcomes.

Genetic polymorphisms and decreased protein expression of ABCG2 urate transporters are associated with susceptibility to gout, disease severity and renal-overload hyperuricemia

Gout is a common crystal induced disease of high personal and social burden, characterised by severe arthritis and comorbidity if untreated. Impaired function of ABCG2 transporter is causative in gout and may be responsible for renal-overload type hyperuricemia. Despite its importance, there is limited information on how clinical parameters correlate with protein expression and that with genetic changes. Urate and clinical parameters of 78 gouty patients and healthy controls were measured among standardised circumstances from a Hungarian population. ABCG2 membrane expression of red blood cells was determined by flow cytometry-based method and SNPs of this protein were analysed by TaqMan-based qPCR. The prevalence of ABCG2 functional polymorphisms in gouty and control patients were 32.1 and 13.7%, respectively. Most common SNP was Q141K while one sample with R236X, R383C and the lately described M71V were found in the gouty population. These polymorphisms showed strong linkage with decreased protein expression while the latter was also associated with higher fractional urate excretion (FUE) and urinary urate excretion (UUE). This study firstly evaluated ABCG2 protein expression in a clinically defined gouty population while also proving its associations between ABCG2 genetic changes and renal-overload hyperuricemia. The paper also highlighted relations between ABCG2 SNPs, gout susceptibility and disease severity characterised by an early onset disease with frequent flares and tophi formation.

Renal Transcriptional Profiles of Hyperuricemic Mouse Models Reveal Urate Dependent Alternations in Metabolic Pathways

Increased serum urate (hyperuricemia, HUA) contributes to the development of kidney stones, chronic kidney disease, cardiovascular disease, metabolic syndrome, and gout. HUA is caused by an underexcretion or an overproduction of urate. These two mechanisms result in similar serum urate levels, but critically important differences in how urate is handled in the kidney and resulting tubular urate levels. To better understand altered gene expression by divergent renal handling of urate in each subtype of HUA, we compared transcriptional profiles of kidneys of two functionally different mouse models of HUA. The underexcretion model is our well established ABCG2‐Q140K knock‐in mouse, which inserts the human pathological variant Q141K into the orthologous position of the mouse Abcg2 gene. This causes decreased secretion of urate, leading to an increase in serum urate in male mice only. The overproduction model is a novel inducible knock‐out of the urate metabolizing gene uricase (UOX‐iKO), which renders both male (M) and female (F) mice unable to metabolize urate, which increases circulating levels to a similar degree seen in HUA humans. Here, UOX‐iKO mice of both sexes were induced at 9 weeks of age, and 2 weeks later, UOX‐iKO mice had serum urate levels similar to age matched ABCG2‐Q140K M mice. These UOX‐iKO mice had increased overall urinary urate excretion (UUE), as well as increased fractional excretion of urate (FEUA) in both M and F, implying higher tubular urate, consistent with urate overproduction. In contrast, ABCG2‐Q140K mice demonstrated no change in overall UUE, with a decrease in FEUA seen in M only, implying lower tubular urate, consistent with urate underexcretion. Next, we harvested kidneys from M and F mice of both HUA models and appropriate controls, followed by RNA‐Seq. To determine pathways altered by HUA, we utilized pathway analysis (DAVID Bioinformatics Resource 6.8) on all significant differentially expressed genes (DESeq2, p &lt; 0.05, FDR &lt; 0.1). Both models showed similar alterations in gene expression, with approximately 10% of all differentially expressed genes from all 3 groups of HUA mice clustered into metabolic pathways, including genes involved in steroid and amino acid metabolism. M HUA mice of both models also shared differential expression of genes involved in glutathione and fatty acid metabolism. We hypothesize that although luminal urate differs between the two models, the intracellular urate values in the proximal tubule cells will be similarly elevated. This elevation must be influencing the observed changes in metabolism related gene expression. To begin to elucidate urate dependent metabolic regulators, we next explored which transcription factors (TFs) may be driving this differential expression (Enrichr enrichment analysis) and found 2 TFs shared by all 3 HUA groups: Gata2 and Tcf3, with 2 more TFs, Sox2 and Nanog, in both M HUA mice. In conclusion, we found that models of both classical types of HUA alter renal metabolic pathways. We have also identified 2 candidate TFs that may be directly affected by urate, which could drive transcriptional changes in response to HUA. Additional experiments are required to determine the effect of urate itself on the activity of these TFs, as well as mechanistic studies to explore the effects of altered intracellular urate levels. Further elucidation these interactions may lead to improved understanding of urate homeostasis and new insights into HUA treatment.

Urinary retinol binding protein predicts renal outcome in systemic immunoglobulin light-chain (AL) amyloidosis.

Renal risk stratification in systemic immunoglobulin light-chain (AL) amyloidosis is according to estimated glomerular filtration rate (eGFR) and urinary protein creatinine ratio (uPCR), the latter attributed to glomerular dysfunction, with proximal tubular dysfunction (PTD) little studied. Urinary retinol binding protein4 (uRBP), a low molecular weight tubular protein and highly sensitive marker of PTD, was prospectively measured in 285 newly diagnosed, untreated patients with systemic AL amyloidosis between August 2017 to August 2018. At diagnosis, the uRBP/creatinine ratio (uRBPCR) correlated with serum creatinine (r=0·618, P<0·0001), uPCR (r=0·422, P<0·0001) as well as both fractional excretion of phosphate and urate (r=0·563, P<0·0001). Log uRBPCR at diagnosis was a strong independent predictor of end-stage renal disease {hazard ratio [HR] 2·65, [95% confidence interval (CI) 1·06-6·64]; P=0·038}, particularly in patients with an eGFR >30ml/min/1.73m2 [HR 4·11, (95% CI 1·45-11·65); P=0·008] and those who failed to achieve a deep haematological response to chemotherapy within 3months of diagnosis [HR 6·72, (95% CI 1·83-24·74); P=0·004], and also predicted renal progression [HR 1·91, (95% CI 1·18-3·07); P=0·008]. Elevated uRBPCR indicates PTD and predicts renal outcomes independently of eGFR, uPCR and clonal response in systemic AL amyloidosis. The role of uRBPCR as a novel prognostic biomarker merits further study, particularly in monoclonal gammopathies of renal significance.

Genetic and Physiological Effects of Insulin on Human Urate Homeostasis.

Insulin and hyperinsulinemia reduce renal fractional excretion of urate (FeU) and play a key role in the genesis of hyperuricemia and gout, via uncharacterized mechanisms. To explore this association further we studied the effects of genetic variation in insulin-associated pathways on serum urate (SU) levels and the physiological effects of insulin on urate transporters. We found that urate-associated variants in the human insulin (INS), insulin receptor (INSR), and insulin receptor substrate-1 (IRS1) loci associate with the expression of the insulin-like growth factor 2, IRS1, INSR, and ZNF358 genes; additionally, we found genetic interaction between SLC2A9 and the three loci, most evident in women. We also found that insulin stimulates the expression of GLUT9 and increases [14C]-urate uptake in human proximal tubular cells (PTC-05) and HEK293T cells, transport activity that was effectively abrogated by uricosurics or inhibitors of protein tyrosine kinase (PTK), PI3 kinase, MEK/ERK, or p38 MAPK. Heterologous expression of individual urate transporters in Xenopus oocytes revealed that the [14C]-urate transport activities of GLUT9a, GLUT9b, OAT10, OAT3, OAT1, NPT1 and ABCG2 are directly activated by insulin signaling, through PI3 kinase (PI3K)/Akt, MEK/ERK and/or p38 MAPK. Given that the high-capacity urate transporter GLUT9a is the exclusive basolateral exit pathway for reabsorbed urate from the renal proximal tubule into the blood, that insulin stimulates both GLUT9 expression and urate transport activity more than other urate transporters, and that SLC2A9 shows genetic interaction with urate-associated insulin-signaling loci, we postulate that the anti-uricosuric effect of insulin is primarily due to the enhanced expression and activation of GLUT9.

The Combined Use of Fractional Urate and Potassium Excretion in the Diagnosis of Diuretic-Induced Hyponatremia.

IntroductionThiazide and loop-diuretics are among the most widely used drugs in the therapy of hypertension and chronic heart failure. Furthermore, hyponatremia is the most prevalent electrolyte imbalance affecting up to 25-30% of hospitalized patients while syndrome of inappropriate antidiuresis (SIAD) is involving approximately 35% of hyponatraemic inpatients. Clinical and laboratoristic algorithms support the differential diagnosis of hypotonic hyponatremia in actual guidelines of SIAD, but a potential bias is represented by the misleading clinical assessment of the extracellular volume status in diuretic-treated patients where the necessity of withdrawal of the therapy is mandatory. We investigated the role of fractional uric acid and potassium excretion (FEUA and FEK) in the differential diagnosis of hypotonic hyponatremia in SIAD and diuretic-treated patients.MethodsThirty-six SIAD, 30 thiazide-induced hyponatremia (TIH), and 32 diuretic-induced hyponatremia (DIH) patients were investigated calculating FEUA and FEK values in receiver operating characteristic (ROC) curve analysis to improve the diagnostic approach of hypotonic hyponatremia.ResultsThe combination of the two investigated markers showed different significative results generating patterns useful to discriminate among the three different hyponatremic groups.ConclusionThe fractional uric acid and potassium excretion could be considered as new markers in the diagnostic approach of hyponatremic diuretic-treated patients where classical algorithms could fail.

The Effect of Berberine, a Drug From Chinese Folk Medicine, on Serum and Urinary Uric Acid Levels in Rats With Hyperuricemia.

BackgroundThe principal manifestation of hyperuricemia is gout. Many drugs are in use nowadays to treat gout, but they are linked with multiple side effects. The present study observed berberine (from Chinese folk medicine) on serum and urinary uric acid levels in rats with potassium oxonate-induced hyperuricemia.Materials and methodsThirty-six adult healthy female Sprague Dawley rats were randomly divided into six groups of six rats each. To induce hyperuricemia, all the groups except Group A were given potassium oxonate (250 mg/kg) intraperitoneally on days 1, 3, and 7. Group A, the normal control group, was given normal saline for seven consecutive days intraperitoneally. Group C was administered allopurinol (5 mg/kg body weight) intraperitoneally, and Group D, E, and F were given berberine in doses of 0.75 mg/kg, 1.25 mg/kg, and 2.5 mg/kg body weight respectively intraperitoneally for seven consecutive days, one hour after the potassium oxonate injection. On zero, first, third, and seventh day of the experiment, blood and urine samples were taken to estimate the serum and urinary uric acid levels. On days zero and 7, serum uric acid was measured by cardiac puncture, while on days 1 and 3, it was measured by the tail prick method. The uric acid was measured by an enzymatic colorimetric method and creatinine by the Jaffe method. Fractional excretion of urate was also calculated.ResultsBerberine lowered serum uric acid levels in rats with potassium oxonate-induced hyperuricemia with highly significant results (p-value <0.001) in all three dosages. Berberine increased the urinary uric acid level and the fractional excretion of urate in a time-dependent manner in all three dosages. This effect was maximally shown by low dose berberine with a highly significant result (p-value <0.001).ConclusionBerberine successfully decreased the serum uric acid level of hyperuricemic rats by increasing the urinary uric acid level and fractional excretion of urate.

Hyponatraemia and hypernatraemia: Disorders of Water Balance in Neurosurgery.

Disorders of tonicity, hyponatraemia and hypernatraemia, are common in neurosurgical patients. Tonicity is sensed by the circumventricular organs while the volume state is sensed by the kidney and peripheral baroreceptors; these two signals are integrated in the hypothalamus. Volume is maintained through the renin-angiotensin-aldosterone axis, while tonicity is defended by arginine vasopressin (antidiuretic hormone) and the thirst response. Edelman found that plasma sodium is dependent on the exchangeable sodium, potassium and free-water in the body. Thus, changes in tonicity must be due to disproportionate flux of these species in and out of the body. Sodium concentration may be measured by flame photometry and indirect, or direct, ion-sensitive electrodes. Only the latter method is not affected by changes in plasma composition. Classification of hyponatraemia by the volume state is imprecise. We compare the tonicity of the urine, given by the sodium potassium sum, to that of the plasma to determine the renal response to the dysnatraemia. We may then assess the activity of the renin-angiotensin-aldosterone axis using urinary sodium and fractional excretion of sodium, urate or urea. Together, with clinical context, these help us determine the aetiology of the dysnatraemia. Symptomatic individuals and those with intracranial catastrophes require prompt treatment and vigilant monitoring. Otherwise, in the absence of hypovolaemia, free-water restriction and correction of any reversible causes should be the mainstay of treatment for hyponatraemia. Hypernatraemia should be corrected with free-water, and concurrent disorders of volume should be addressed. Monitoring for overcorrection of hyponatraemia is necessary to avoid osmotic demyelination.

Renal salt wasting syndrome in a patient with COVID-19; a case report and review of the literature

Introduction: Cerebral salt wasting or renal salt wasting (RSW) syndrome, may be more common than syndrome of inappropriate antidiuretic hormone secretion (SIADH) and may even occur in the absence of cerebral disease. We report a case of RSW in a Bangladeshi patient positive for COVID-19 without clinical cerebral disease. Case Presentation: A 53 years-old Bangladeshi patient presented with history of chest pain and acute MI. On examination, the patient was conscious, alert, vitally stable, chest with fine bilateral basal crepitation and heart with additional S3 sound and abdomen was lax with no organomegaly. There was no lower limbs oedema. His serum creatinine; 68 umol/L, urea; 3.4 mmol/L, K; 4.7 mmol/L, sodium; 135 mmol/L, uric acid; 141 mmol/L and phosphate was 1.3 mmol./L. Echocardiography (ECG) revealed anterior lateral wall STEMI. PCI was done for LAD. ECG revealed ejection fraction (EF) 10-15 %. Nasopharyngeal swab for COVID-19 was positive. Serum sodium decreased from 135 to 108 with signs of hypovolemia. Work up for hyponatremia revealed serum osmolality of 237 mOsm/kg, urine NA; 109 mmol/L, urine osmolality; 295 mOsm/kg, urine uric acid; 685 umol/L, and urine phosphate; 6.5 mmol/L. Additionally serum T3, T4, TSH and serum basal cortisol were normal. The patient received normal saline infusion and fludrocortisone and serum sodium increased to 134 mmol/L. Our patient had all the important clinical and laboratory characteristics of RSW in the absence of cerebral disease which include hyponatremia associated with hypovolemia, high urinary sodium excretion, increased fraction excretion of phosphate and persistent hypouricemia with increased fractional excretion of urate after correction of hyponatremia and with normal renal, adrenal and thyroid functions. Furthermore, there was a prompt response to saline replacement and fludrocortisone and steady improvement in serum sodium with negativity and improvement of COVID-19. Our diagnosis was RSW in the absence of cerebral disease and to our knowledge; this is the first case of RSW in a patient with COVID-19 in the literature. Conclusion: RSW should be considered in patients with COVID-19 with hyponatremia and absence of cerebral disease. We suggest changing cerebral salt wasting to the more appropriate term RSW.

Olsalazine Sodium Increases Renal Urate Excretion by Modulating Urate Transporters in Hyperuricemic Animals.

Hyperuricemia is mainly the result of relative underexcretion of urate. Urate is mainly eliminated by kidney and several important transporters expressed on the membrane of renal tubular cells involved in urate excretion. Olsalazine sodium was screened from 3167 authorized small compounds/drugs, targeting xanthine oxidoreductase. In previous study, we reported that olsalazine sodium significantly reduced the serum urate levels, and the anti-hyperuricemic activity linked with inhibiting urate formation by reducing the activity of xanthine oxidoreductase. The current research aimed to assess olsalazine sodium renal urate excretion and likely molecular mechanism. The results showed that administration of olsalazine sodium 5.0 mg/kg decreased the levels of serum urate in hyperuricemic rats, and noticeably improved the fractional excretion of urate and urate clearance, exhibiting an uricosuric action. Moreover, olsalazine sodium (2.5, 5.0, 10.0 mg/kg) reduced the level of blood urea nitrogen in rats. Further study showed that olsalazine sodium reduced the mRNA expression of urate reabsorptive transporter glucose transporter 9 (GLUT9), increased the mRNA expression of urate secretory transporters, organic anion transporter 1 (OAT1), OAT3 and type 1 sodium-dependent phosphate transporter (NPT1) as well as the protein expression of OAT3 in the kidney in hyperuricemic mice. In conclusion, olsalazine sodium exhibited a promotion of urate excretion in kidney by increasing the expression of OAT3.

Salt wasting syndrome in brain trauma patients: a pathophysiologic approach using sodium balance and urinary biochemical analysis

BackgroundTo explore the underlying mechanisms leading to the occurrence of hyponatremia and enhanced urinary sodium excretion in brain trauma patients using sodium balance and urinary biochemical analysis.MethodsWe conducted a retrospective analysis of a local database prospectively collected in 60 brain trauma patients without chronic renal dysfunction. Metabolic and hemodynamic parameters were averaged over three consecutive periods over the first seven days after admission. The main outcome investigated in this study was the occurrence of at least one episode of hyponatremia.ResultsOver the study period, there was a prompt decrease in sodium balance (163 ± 193 vs. -12 ± 154 mmol/day, p < 0.0001) and free water clearance (− 0.7 ± 0.7 vs. -1.8 ± 2.3 ml/min, p < 0.0001). The area under the ROC curves for sodium balance in predicting the occurrence of hyponatremia during the next period was 0.81 [95% CI: 0.64–0.97]. Variables associated with averaged urinary sodium excretion were sodium intake (R2 = 0.26, p < 0.0001) and fractional excretion of urate (R2 = 0.15, p = 0.009). Urinary sodium excretion was also higher in patients with sustained augmented renal clearance over the study period (318 ± 106 vs. 255 ± 135 mmol/day, p = 0.034).ConclusionThe decreased vascular volume resulting from a negative sodium balance is a major precipitating factor of hyponatremia in brain trauma patients. Predisposing factors for enhanced urinary sodium excretion were high sodium intake, high fractional excretion of urate and augmented renal clearance over the first seven days after ICU admission.

Deciphering genetic signatures by whole exome sequencing in a case of co-prevalence of severe renal hypouricemia and diabetes with impaired insulin secretion

BackgroundRenal hypouricemia (RHUC) is a hereditary disorder where mutations in SLC22A12 gene and SLC2A9 gene cause RHUC type 1 (RHUC1) and RHUC type 2 (RHUC2), respectively. These genes regulate renal tubular reabsorption of urates while there exist other genes counterbalancing the net excretion of urates including ABCG2 and SLC17A1. Urate metabolism is tightly interconnected with glucose metabolism, and SLC2A9 gene may be involved in insulin secretion from pancreatic β-cells. On the other hand, a myriad of genes are responsible for the impaired insulin secretion independently of urate metabolism.Case presentationWe describe a 67 year-old Japanese man who manifested severe hypouricemia (0.7 mg/dl (3.8–7.0 mg/dl), 41.6 μmol/l (226–416 μmol/l)) and diabetes with impaired insulin secretion. His high urinary fractional excretion of urate (65.5%) and low urinary C-peptide excretion (25.7 μg/day) were compatible with the diagnosis of RHUC and impaired insulin secretion, respectively. Considering the fact that metabolic pathways regulating urates and glucose are closely interconnected, we attempted to delineate the genetic basis of the hypouricemia and the insulin secretion defect observed in this patient using whole exome sequencing. Intriguingly, we found homozygous Trp258* mutations in SLC22A12 gene causing RHUC1 while concurrent mutations reported to be associated with hyperuricemia were also discovered including ABCG2 (Gln141Lys) and SLC17A1 (Thr269Ile). SLC2A9, that also facilitates glucose transport, has been implicated to enhance insulin secretion, however, the non-synonymous mutations found in SLC2A9 gene of this patient were not dysfunctional variants. Therefore, we embarked on a search for causal mutations for his impaired insulin secretion, resulting in identification of multiple mutations in HNF1A gene (MODY3) as well as other genes that play roles in pancreatic β-cells. Among them, the Leu80fs in the homeobox gene NKX6.1 was an unreported mutation.ConclusionWe found a case of RHUC1 carrying mutations in SLC22A12 gene accompanied with compensatory mutations associated with hyperuricemia, representing the first report showing coexistence of the mutations with opposed potential to regulate urate concentrations. On the other hand, independent gene mutations may be responsible for his impaired insulin secretion, which contains novel mutations in key genes in the pancreatic β-cell functions that deserve further scrutiny.

Differential expression of renal urate transporters in male and female mice

Elevated urate (UA) levels in the serum (hyperuricemia, HUA) can contribute to the development of many diseases, including kidney stones, chronic kidney disease, cardiovascular disease, metabolic syndrome, and gout, the most prevalent form of inflammatory arthritis. Men are 5‐fold more likely to have HUA than women, however, this risk increases in women 4‐fold after menopause. This suggests premenopausal women are protected against developing HUA, but the mechanisms have yet to be elucidated. These differences are echoed in our hyperuricemia mice models. Previously, we found insertion of the orthologous human pathological mutation Q141K (Q140K in mice) in the UA transporter ABCG2 causes significant hyperuricemia in the male mice but not in the female mice. Paradoxically, we also observed female mice have lower fractional UA excretion than males, suggesting complex differences in the renal handling between males and females. We hypothesized that these differences were likely due to either UA transporter expression or regulation. To better understand the gene expression architecture of UA transporters in the mouse kidney, we compared gene expression in male and female wild type (WT) and Q140K ABCG2 mice. RNA‐Seq was performed followed by DESeq2 analysis to determine differentially expressed genes between males and females of each genotype. Targets of interest included the 12 transporter and 3 transcription factor (TF) genes that associate with serum UA levels in humans in recent genome wide association studies. We found small (0.49 – 2.1‐fold) but statistically significant changes in all the UA associated transporter genes, except ABCG2and SLC2A9. Specifically, female mice had lower transcript expression of UA transporters SLC22A12, SLC22A6, SLC17A1, and ABCA1. These genes have variants that associated with lower UA levels in human populations, consistent with the female mice potentially more efficiently excreting surplus UA. Females also had significantly lower levels of the 3 key urate associated transcription factors HNF1A, HNF4A, and HNF4G, providing a potential mechanism of differentiation. Interestingly, the Q140K mice DESeq2 analysis reveals 486 alterations in male Q140K kidney gene expression as compared to WT, including 5 potentially compensatory SLC transporters. None of these changes were observed in female Q140K mice, indicating that changes are the result of the elevation in SUA and not due to mutant ABCG2 protein. These findings strongly suggest female sex may confer protection from developing HUA and associated conditions. Further understanding this mechanism should lead to improved understanding of UA homeostasis and new insights into HUA treatment.Support or Funding InformationNIDDK R01DK114091

Pharmacological Evaluation of Dotinurad, a Selective Urate Reabsorption Inhibitor.

The effect of dotinurad [(3,5-dichloro-4-hydroxyphenyl)(1,1-dioxo-1,2-dihydro-3H-1λ 6-1,3-benzothiazol-3-yl)methanone] was compared with that of commercially available uricosuric agents-namely, benzbromarone, lesinurad, and probenecid. Its effect on urate secretion transporters was evaluated using probe substrates for respective transporters. Dotinurad, benzbromarone, lesinurad, and probenecid inhibited urate transporter 1 (URAT1) with IC50 values of 0.0372, 0.190, 30.0, and 165 μM, respectively. Dotinurad weakly inhibited ATP-binding cassette subfamily G member 2 (ABCG2), organic anion transporter 1 (OAT1), and OAT3, with IC50 values of 4.16, 4.08, and 1.32 μM, respectively, indicating higher selectivity for URAT1. The hypouricemic effects of dotinurad and benzbromarone were evaluated in Cebus monkeys. Dotinurad, at doses of 1-30 mg/kg, concomitantly decreased plasma urate levels and increased fractional excretion of urate (FEUA) in a dose-dependent manner. On the contrary, benzbromarone, at a dose of 30 mg/kg, showed a modest effect on plasma urate levels. The inhibitory effect of dotinurad on urate secretion transporters was evaluated in Sprague-Dawley rats, with sulfasalazine and adefovir as probe substrates of ABCG2 and OAT1, respectively. Drugs, including febuxostat as a reference ABCG2 inhibitor, were administered orally before sulfasalazine or adefovir administration. Dotinurad had no effect on urate secretion transporters in vivo, whereas benzbromarone, lesinurad, probenecid, and febuxostat increased the plasma concentrations of probe substrates. These results suggested dotinurad is characterized as a selective urate reabsorption inhibitor (SURI), which is defined as a potent URAT1 inhibitor with minimal effect on urate secretion transporters, including ABCG2 and OAT1/3, because of its high efficacy in decreasing plasma urate levels compared with that of other uricosuric agents. SIGNIFICANCE STATEMENT: Our study on the inhibitory effects on urate transport showed that dotinurad had higher selectivity for urate transporter 1 (URAT1) versus ATP-binding cassette subfamily G member 2 (ABCG2) and organic anion transporter (OAT) 1/3 compared to other uricosuric agents. In Cebus monkeys, dotinurad decreased plasma urate levels and increased fractional excretion of urate in a dose-dependent manner. To determine the inhibitory effect of dotinurad on urate secretion transporters, we studied the movement of substrates of ABCG2 and OAT1 in rats. Dotinurad had no effect on these transporters, whereas the other uricosuric agents increased the plasma concentrations of the substrates. These results suggested dotinurad as a potent and selective urate reabsorption inhibitor is characterized by increased efficacy with decreasing plasma urate levels.

Dual actions of norathyriol as a new candidate hypouricaemic agent: uricosuric effects and xanthine oxidase inhibition

Hyperuricaemia, which results from the overproduction and underexcretion of uric acid, has been linked with chronic renal dysfunction, cardiovascular diseases, diabetes and metabolic syndrome. However, available clinical drugs cannot simultaneously target the production and excretion of uric acid. Norathyriol, a natural xanthone, was expected to have the dual actions. We previously reported that norathyriol possessed potent anti-hyperuricaemic activity related to the inhibition of uric acid production. Here, we investigated the uricosuric actions in hyperuricaemic animals and explored the possible molecular mechanisms associated with renal urate transporters and xanthine oxidase (XO). The results showed that norathyriol (0.5–4.0 mg/kg) dose- and time-dependently decreased serum urate levels in uric acid-induced hyperuricaemic mice and markedly increased the fractional excretion of urate in oxonate-induced hyperuricaemic rats, demonstrating a promotion of urate excretion in the kidney. Further evidence showed that norathyriol markedly increased renal mRNA and protein expression of the secretory organic anion transporter 1 (OAT1) in hyperuricaemic mice and strengthened its transport function in vitro. Moreover, norathyriol also upregulated the mRNA expression of the secretory transporters OAT3, ATP-binding cassette transporter G2 and multidrug resistance protein 4, but not their protein expression. Changes in the expression of the reabsorptive transporters were not observed. This is the first report that norathyriol has uricosuric effects by targeting OAT1. Moreover, norathyriol significantly inhibited XO activity in an uncompetitive manner. Taken together, these findings suggest that norathyriol has the potential to be developed as a new anti-hyperuricaemic agent with dual actions that activate OAT1 and inhibit XO activity.

Gout Causing ABCG2 Mutation Results in Intestinal Net Urate Transport Defect, Hyperuricemia, &amp; Altered Metabolic Phenotype

Hyperuricemia causes gout and is implicated in metabolic syndrome, impaired glucose tolerance/type 2 diabetes, and hypertension. Individuals carrying a common loss of function variant in the dominant secretory transporter, Q141K ABCG2, have significantly increased serum urate and gout risk yet their renal fractional excretion of urate (FEUA) is largely unchanged. However, the role in ABCG2 and other urate transporters in extra‐renal secretion remains mostly unexplored. Here we sought to identify the role of ABCG2 in trans‐epithelial urate transport in the intestines and contribution of intestinal ABCG2 dysfunction to hyperuricemia and urate related phenotypes. First, we established a genetic mouse model of the human ABCG2 Q141K variant (Q140K in mouse) using CRISPR Cas9 gene editing techniques on a C57BL6 mouse background. As compared to control mice, mice possessing the Q140K Abcg2 allele were profoundly hyperuricemic, yet exhibited only modest changes in renal excretion of urate, similar to what has been reported previously in humans. To explore mechanisms, we first mapped prominent urate transporters ABCG2 and SLC2A9 along the mouse intestine and found the highest levels in the jejunum and ileum. Localization of the wild type ABCG2 protein was exclusive to the brush border (apical membrane) of the villus cells, seemingly optimized to facilitate urate secretion(JUAsm). Interestingly, we also found evidence that SLC2A9 localized predominantly to the basolateral enterocyte membrane. In Ussing chamber experiments, we functionally confirmed basolateral localization of the electrogenic SLC2A9 transporter by observing basolateral but not apical addition of 0.5 mM urate significantly stimulated Isc (24 ± 3μA/cm2) in comparison with control (10± 2.2 μA/cm2). Further, treatment of the serosal membrane with SLC2A9 inhibitors tranilast and pCMBS partially inhibited JUAsm flux of urate in an intestinal loop model. In contrast to the WT controls, Q140K mice demonstrated a significant decrease of apical ABCG2 protein abundance, with commiserate, significant loss of unidirectional urate transport (JUAsm) in jejunal loops (Q140K, 24 ± 3.38 μM/cm2/min; WT, 46 ± 1.50 μM/cm2/min), resulting in conversion of net urate secretion (−18 ± 4 μM/cm2/min) to net urate absorption (+5.99 ± 2.2 μM/cm2/min). Interestingly, these significant alterations in intestinal urate secretion in the Q140K mice correlated with evidence of altered serum insulin and non‐fasting glucose levels, not unlike what has been previously reported in mice lacking intestinal SLC2A9 strongly suggesting the establishment of SLC2A9 and ABCG2 as the intestinal urate excretion pathway.CONCLUSIONSOur findings demonstrate the pathophysiology of one of the most common hyperuricemia and gout risk variants, Q141K ABCG2, primarily affects the urate secretion in the gut, causing hyperuricemia and alterations in insulin and glucose levels with important implications for human disease.Support or Funding InformationNIDDK RO1DK114091AHA14SDG18060004This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.