Identification of ABCG2 as an Exporter of Uremic Toxin Indoxyl Sulfate in Mice and as a Crucial Factor Influencing CKD Progression.

Chronic kidney disease (CKD) patients accumulate uremic toxins in the body, potentially require dialysis, and can eventually develop cardiovascular disease. CKD incidence has increased worldwide, and preventing CKD progression is one of the most important goals in clinical treatment. In this study, we conducted a series of in vitro and in vivo experiments and employed a metabolomics approach to investigate CKD. Our results demonstrated that ATP-binding cassette transporter subfamily G member 2 (ABCG2) is a major transporter of the uremic toxin indoxyl sulfate. ABCG2 regulates the pathophysiological excretion of indoxyl sulfate and strongly affects CKD survival rates. Our study is the first to report ABCG2 as a physiological exporter of indoxyl sulfate and identify ABCG2 as a crucial factor influencing CKD progression, consistent with the observed association between ABCG2 function and age of dialysis onset in humans. The above findings provided valuable knowledge on the complex regulatory mechanisms that regulate the transport of uremic toxins in our body and serve as a basis for preventive and individualized treatment of CKD.

Recurrent peritoneal inclusion cysts successfully treated with oral contraceptives: a report of two cases.

OBJECTIVE: To examine whether conservative treatment with oral contraceptives is effective in the shrinkage of a peritoneal inclusion cyst (PIC). This is a case report of two patients with a PIC that developed after gynecological surgery. CASES: Both cases were suspected of a PIC based on the medical history, laboratory data, and image findings. It was difficult in differentiate a PIC from an ovarian tumor. Surgery was chosen at first. However, PICs in both cases recurred after surgery and were treated with oral contraceptives as a conservative treatment. PICs shrank after the treatment of oral contraceptives in both cases. CONCLUSION: Due to the high rate of recurrence following surgery, conservative treatment is recommended to treat PICs. Hormone therapy using oral contraceptives seems to have some therapeutic benefit for the PICs.

Antihypertensive effect of a fixed-dose combination of losartan/hydrochlorothiazide in patients with uncontrolled hypertension: a multicenter study.

BACKGROUND: Achieving adequate blood pressure (BP) control often requires more than one antihypertensive agent. The purpose of this study was to determine whether a fixed-dose formulation of losartan (LOS) plus hydrochlorothiazide (HCTZ) (LOS/HCTZ) is effective in achieving a greater BP lowering in patients with uncontrolled hypertension. METHODS: The study was a prospective, multicenter, observational trial exploring the antihypertensive effect of a single tablet of LOS 50 mg/HCTZ 12.5 mg. A total of 228 patients whose BP had previously been treated with more than one antihypertensive agents without having achieved BP goal below 130/80 mmHg enrolled in the study. RESULTS: A significant decrease in systolic and diastolic BP was observed in both clinic and home measurement after switching from the previous treatment to LOS/HCTZ. There was a significant decrease in both B-type natriuretic peptide (BNP) and urinary albumin creatinine (Cr) excretion ratio (ACR), especially in patients with elevated values. In contrast, there was a significant increase in serum Cr concentration in conjunction with a decrease in estimated glomerular filtration rate (eGFR). Overall serum uric acid (UA) concentration increased, whereas in patients with hyperuricemia there was a significant reduction in this value. CONCLUSION: Switching to LOS/HCTZ provides a greater reduction in clinic and home BP in patients with uncontrolled hypertension. This combination therapy may lead to cardio-, reno protection and improve UA metabolism.

Identification of ABCG2 dysfunction as a major factor contributing to gout.

The ATP-binding cassette, subfamily G, member 2 gene ABCG2/BCRP locates in a gout-susceptibility locus (MIM 138900) on chromosome 4q. Recent genome-wide association studies also showed that the ABCG2 gene relates to serum uric acid levels and gout. Since ABCG2 is also known as a transporter of nucleotide analogs that are structurally similar to urate, and is an exporter that has common polymorphic reduced functionality variants, ABCG2 could be a urate secretion transporter and a gene causing gout. To find candidate mutations in ABCG2, we performed a mutation analysis of the ABCG2 gene in 90 Japanese patients with hyperuricemia and found six non-synonymous mutations. Among the variants, ATP-dependent urate transport was reduced or eliminated in five variants, and two out of the five variants (Q126X and Q141K) were frequently detected in patients. Haplotype frequency analysis revealed that there is no simultaneous presence of Q126X and Q141K in one haplotype. As Q126X and Q141K are a nonfunctional and half-functional haplotype, respectively, their genotype combinations are divided into four estimated functional groups. The association study with 161 male gout patients and 865 male controls showed that all of those who had dysfunctional ABCG2 had an increased risk of gout, and that a remarkable risk was observed in those with ≤1/4 function (OR, 25.8; 95% CI, 10.3-64.6; p = 3.39 × 10(-21)). In 2,150 Japanese individuals, the frequency of those with dysfunctional ABCG2 was more than 50%. Our function-based clinicogenetic analysis identified the combinations of dysfunctional variants of ABCG2 as a major contributing factor in Japanese patients with gout.

Stable isotope dilution mass spectrometric assay for PRPP using enzymatic procedures.

5-Phosphoribosyl-1-pyrophosphate (PRPP) is an important regulator of de novo purine synthesis. A method for the measurement of PRPP in erythrocytes was designed, which is based on the determination of [(13)C(5)]glutamate derived from [(13)C(5)]glutamine following the utilization of PRPP by the action of amidophosphoribosyltransferase. The present study describes a gas chromatographic-mass spectrometric method for determination of [(13)C(5)]glutamate using [(13)C(2)]glutamate as an internal standard. The methods involved purification by anion-exchange chromatography using a BondElut SAX and derivatization with isobutyl chlorocarbonate in water-methanol-pyridine. Quantitation was performed by selected ion monitoring of the protonated molecular ions in the chemical ionization mode. The intra-day reproducibility in the amounts of [(13)C(5)]glutamate determined was in good agreement with the actual amounts added in erythrocytes. A linear relationship was found between the amount of PRPP added and the amount of [(13)C(5)]glutamate formed from [(13)C(5)]glutamine using amidophosphoribosyltransferase.

Two cases of nephrotic syndrome (NS)-induced acute kidney injury (AKI) associated with renal hypouricemia.

Renal hypouricemia is a clinical disorder attributed to an increased renal urate excretion rate and is well known to involve a high risk of urolithiasis and exercise-induced acute kidney injury (AKI). This report concerns two interesting cases of nephrotic syndrome (NS)-induced AKI associated with renal hypouricemia. A 64-year-old female (Case 1) and a 37-year-old male (Case 2) were hospitalized because of AKI (serum creatinine: 2.07 mg/dl and 3.3 mg/dl, respectively), oliguria and NS. They were treated with prednisolone and temporary hemodialysis. Renal function improved, but hypouricemia persisted during hospitalization. Histological findings in both cases led to a diagnosis of minimal change nephrotic syndrome and identification of the diuretic phase of tubulointerstitial damage because of findings such as acute tubular necrosis. Furthermore, distal tubules of Case 2 showed an amorphous mass, possibly a uric acid crystal. Analysis of the two cases with the URAT1 gene, encoded by SLC22A12, found a homozygous mutation in exon 4 (W258stop) of each one. Our cases show that patients with renal hypouricemia may be susceptible to AKI without involvement of exercise if they possess some facilitators. Renal hypouricemic patients should therefore be carefully examined for all complications from renal hypouricemia because of high risk of AKI.

Establishment and analysis of SLC22A12 (URAT1) knockout mouse.

In order to elucidate the mechanisms of post-exercise acute renal failure, one of the complications of hereditary renal hypouricemia, we have targeted the mouse Slc22a12 gene by the exchange of exons 1-4 with pMC1neo-polyA. The knockout mice revealed no gross anomalies. The concentration ratio of urinary urate/creatinine of the knockout mice was significantly higher than that of wildtype mice, indicating an attenuated renal reabsorption of urate. The plasma levels of urate were around 11 muM and were similar among the genotypes. Although the fractional excretion of urate of knockout mice was tend to higher than that of wildtype mice, the urate reabsorption ability remained in the kidney of knockout mice, indicating a urate reabsorptive transporter other than Urat1.

Age and origin of the G774A mutation in SLC22A12 causing renal hypouricemia in Japanese.

Renal hypouricemia is an inherited disorder characterized by impaired tubular uric acid transport. Impairment of the function of URAT1, the main transporter for the reabsorption of uric acid at the apical membrane of the renal tubules, causes renal hypouricemia. The G774A mutation in the SLC22A12 gene encoding URAT1 predominates in Japanese renal hypouricemia. From data on linkage disequilibrium between the G774 locus and the 13 markers flanking it (12 single nucleotide polymorphisms and 1 dinucleotide insertion/deletion locus), we here estimate the age of this mutation at approximately 6820 years [95% confidence interval (CI) 1860-11,760 years; median = 2460 years]. This indicates that the origin of the G774A mutation dates back from between the time when the Jomon people predominated in Japan and the time when the Yayoi people started to migrate to Japan from the Korean peninsula. These data are consistent with a recent finding that this G774A mutation was also predominant in Koreans with hypouricemia and indicate that the mutation originated on the Asian continent. Thus, this mutation found in Japanese patients was originally brought by immigrant(s) from the continent and thereafter expanded in the Japanese population either by founder effects or by genetic drift (or both).

A Turkish case with molybdenum cofactor deficiency.

Molybdenum cofactor deficiency (MIM 252150) is a rare progressive neurodegenerative disorder with about 100 cases reported worldwide. We have identified a male with molybdenum cofactor deficiency and analyzed the molybdenum cofactor synthesis (MOCS)1 gene, MOCS2 gene, MOCS3 gene and GEPH gene. We homozygously identified the CGA insertion after A666 of the MOCS1 gene which produces arginine insertion at codon 222 of MOCS1A. The parents, his brother and his sister who did not have any symptoms were heterozygous for the same mutation. This region was highly conserved in various species. The N-terminal part of MOCS1 a protein is suggested to form the central core of the protein and be composed of an incomplete [(alpha/beta)6] triosephosphate isomerase (TIM) barrel with a lateral opening that is covered by the C-terminal part of the protein. The insertion is located in the loop connecting the fifth beta strand to the sixth alpha helices of the TIM barrel structure. This arginine insertion would induce the conformation change and the lack of the activity.

Serum uric acid and renal prognosis in patients with IgA nephropathy.

BACKGROUND/AIMS: This study was designed to elucidate the clinical significance of serum uric acid (SUA) and the relationship between hyperuricemia and renal prognosis in IgA nephropathy. METHODS: The correlation between SUA and other clinical parameters were examined in 748 IgA nephropathy patients (432 males and 316 females). Among these patients, 226 (144 males and 82 females) who were followed for more than 5 years were examined for the relationship between hyperuricemia and renal prognosis. RESULTS: In IgA nephropathy, SUA correlated negatively with creatinine clearance (Ccr), and positively with urinary protein and tubulointerstitial damage. SUA was higher in patients with hypertension or diffuse proliferative glomerulonephritis. Hyperuricemia was a risk factor for renal prognosis, both in terms of serum creatinine (p = 0.0025) and Ccr (p = 0.0057). In 56 patients with normal Ccr at renal biopsy, the change of Ccr after more than 8 years was -22.3 +/- 20.8% in 13 patients with hyperuricemia, compared with +2.6 +/- 39.4% in 43 patients without hyperuricemia (p = 0.0238). Hyperuricemia was related independently to deterioration of Ccr (p = 0.0461). CONCLUSION: Hyperuricemia in IgA nephropathy is derived from both glomerular and tubulointerstitial damage, and correlated with hypertension. Hyperuricemia is a risk factor for renal prognosis in IgA nephropathy.

Mutation of human molybdenum cofactor sulfurase gene is responsible for classical xanthinuria type II.

Drosophila ma-l gene was suggested to encode an enzyme for sulfuration of the desulfo molybdenum cofactor for xanthine dehydrogenase (XDH) and aldehyde oxidase (AO). The human molybdenum cofactor sulfurase (HMCS) gene, the human ma-l homologue, is therefore a candidate gene responsible for classical xanthinuria type II, which involves both XDH and AO deficiencies. However, HMCS has not been identified as yet. In this study, we cloned the HMCS gene from a cDNA library prepared from liver. In two independent patients with classical xanthinuria type II, we identified a C to T base substitution at nucleotide 1255 in the HMCS gene that should cause a CGA (Arg) to TGA (Ter) nonsense substitution at codon 419. A classical xanthinuria type I patient and healthy volunteers lacked this mutation. These results indicate that a functional defect of the HMCS gene is responsible for classical xanthinuria type II, and that HMCS protein functions to provide a sulfur atom for the molybdenum cofactor of XDH and AO.

XDH gene mutation is the underlying cause of classical xanthinuria: a second report.

BACKGROUND: Classical xanthinuria is a rare autosomal recessive disorder characterized by excessive excretion of xanthine in urine. Type I disease results from the isolated deficiency of xanthine dehydrogenase (XDH), and type II results from dual deficiency of XDH and aldehyde oxidase. The XDH gene has been cloned and localized to chromosome 2p22-23. The aim of this study was to characterize the molecular basis of classical xanthinuria in an Iranian-Jewish family. METHODS: The apparently unrelated parents originated from a community in which consanguineous marriages are common. Subtyping xanthinuria was attempted by homozygosity mapping using microsatellite markers D2S352, D2S367, and D2S2374 in the vicinity of the XDH gene. Mutation detection was accomplished by PCR-SSCP screening of all 36 exons and exon-intron junctions of the XDH gene, followed by direct sequencing and confirmation of sequence alteration by restriction analysis. RESULTS: The index case was homozygous for all three microsatellite markers analyzed. The expected frequency of this genotype in a control population was 0. 0002. These results suggested that xanthinuria in the patient is linked to the XDH gene. Consequently, a 1658insC mutation in exon 16 of the XDH gene was identified. The 1658insC mutation was not detected in 65 control DNA samples. CONCLUSION: A molecular approach to the diagnosis of classical xanthinuria type I in a female patient with profound hypouricemia is described. Linkage of xanthinuria to the XDH locus was demonstrated by homozygosity mapping, and a 1658insC mutation, predicting a truncated inactive XDH protein, was identified. These results reinforce the notion that mutations in the XDH gene are the underlying cause of classical xanthinuria type I.

Characterization of a palytoxin-induced non-selective cation channel in mouse megakaryocytes.

We used the whole-cell clamp and fura-2 techniques to study the membrane current and intracellular Ca2+ concentration ([Ca2+]i) changes of mouse megakaryocytes in response to palytoxin (PTX), a highly potent marine toxin. At a holding potential of -60 mV, PTX induced a sustained inward current in a dose-dependent manner. The reversal potentials measured in the presence of various extracellular major cations indicated that the PTX-induced channel had a non-selective permeability to alkali metal ions. Although elimination of intracellular Ca2+ had no effect on the PTX-induced current, removal of external Ca2+ inhibited the current activation. During the sustained phase of the PTX-induced current, treatment with ADP activated an additional current. Pretreatment with ouabain, an inhibitor of Na+-K+-ATPase, suppressed the PTX-induced current. During the stable phase of the PTX-induced current, challenge with NiCl2 (5 mM) or 2,4-dichlorobenzamil (DCB, 25 microM), a non-selective cation channel blocker, partially reversed the current. Simultaneous measurement of the membrane current and [Ca2+]i showed that PTX induced the current response without increasing the [Ca2+]i. Taken together, these results indicate that PTX induces a non-selective cation channel in mouse megakaryocytes. This channel is distinct from the ADP-operated channel and is sensitive to ouabain, NiCl2 and DCB.

Partial deficiency of hypoxanthine-guanine phosphoribosyltransferase manifesting as acute renal damage.

A 32-year-old man who had had frequent gouty arthritis over the past 17 years, was admitted for acute renal failure. Acute renal failure was improved rapidly after medication was resumed and the patient was sufficiently hydrated. The hypoxanthine-guanine phosphoribosyltransferase (HPRT) activity in the patient had been reduced to about 30% of the normal control. Therefore we considered that this patient suffered from a partial deficiency of HPRT. A point mutation of HPRT gene 68G (guanine) to T (thymine) was detected. This is a mutation that has not been previously reported. Familial analysis indicated that his mother and sister were heterozygotes.

Two siblings with classical xanthinuria type 1: significance of allopurinol loading test.

Two brothers with classical xanthinuria who lacked xanthine dehydrogenase activity were encountered. Their hypouricemia was caused by underproduction of uric acid. In their duodenal mucosa, no xanthine dehydrogenase (oxidase) activity was detected. The patients had no symptoms except for duodenal ulcer in one case. The conversion of allopurinol to oxipurinol during an allopurinol loading test for determining the type of classical xanthinuria revealed that the patients had classical type 1 xanthinuria, because aldehyde oxidase activity was present. Furthermore, the allopurinol loading test was conducted to determine the optimal examination times and specimens required for this test.