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16 pages, 3151 KiB

Open AccessArticle

Analysis of Purine Metabolism to Elucidate the Pathogenesis of Acute Kidney Injury in Renal Hypouricemia

by Daisuke Miyamoto, Nana Sato, Koji Nagata, Yukinao Sakai, Hitoshi Sugihara, Yuki Ohashi, Blanka Stiburkova, Ivan Sebesta, Kimiyoshi Ichida and Ken Okamoto

Biomedicines 2022, 10(7), 1584; https://doi.org/10.3390/biomedicines10071584 - 2 Jul 2022

Cited by 9 | Viewed by 2218

Abstract

Renal hypouricemia is a disease caused by the dysfunction of renal urate transporters. This disease is known to cause exercise-induced acute kidney injury, but its mechanism has not yet been established. To analyze the mechanism by which hypouricemia causes renal failure, we conducted [...] Read more.

Renal hypouricemia is a disease caused by the dysfunction of renal urate transporters. This disease is known to cause exercise-induced acute kidney injury, but its mechanism has not yet been established. To analyze the mechanism by which hypouricemia causes renal failure, we conducted a semi-ischemic forearm exercise stress test to mimic exercise conditions in five healthy subjects, six patients with renal hypouricemia, and one patient with xanthinuria and analyzed the changes in purine metabolites. The results showed that the subjects with renal hypouricemia had significantly lower blood hypoxanthine levels and increased urinary hypoxanthine excretion after exercise than healthy subjects. Oxidative stress markers did not differ between healthy subjects and hypouricemic subjects before and after exercise, and no effect of uric acid as a radical scavenger was observed. As hypoxanthine is a precursor for adenosine triphosphate (ATP) production via the salvage pathway, loss of hypoxanthine after exercise in patients with renal hypouricemia may cause ATP loss in the renal tubules and consequent tissue damage. Full article

(This article belongs to the Special Issue Hypouricemia)

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10 pages, 903 KiB

Open AccessArticle

Renal Hypouricemia 1: Rare Disorder as Common Disease in Eastern Slovakia Roma Population

by Blanka Stiburkova, Jana Bohatá, Kateřina Pavelcová, Velibor Tasic, Dijana Plaseska-Karanfilska, Sung-Kweon Cho, Ludmila Potočnaková and Jana Šaligová

Biomedicines 2021, 9(11), 1607; https://doi.org/10.3390/biomedicines9111607 - 3 Nov 2021

Cited by 12 | Viewed by 2091

Abstract

Renal hypouricemia (RHUC) is caused by an inherited defect in the main reabsorption system of uric acid, SLC22A12 (URAT1) and SLC2A9 (GLUT9). RHUC is characterized by a decreased serum uric acid concentration and an increase in its excreted fraction. Patients suffer from hypouricemia, [...] Read more.

Renal hypouricemia (RHUC) is caused by an inherited defect in the main reabsorption system of uric acid, SLC22A12 (URAT1) and SLC2A9 (GLUT9). RHUC is characterized by a decreased serum uric acid concentration and an increase in its excreted fraction. Patients suffer from hypouricemia, hyperuricosuria, urolithiasis, and even acute kidney injury. We report clinical, biochemical, and genetic findings in a cohort recruited from the Košice region of Slovakia consisting of 27 subjects with hypouricemia and relatives from 11 families, 10 of whom were of Roma ethnicity. We amplified, directly sequenced, and analyzed all coding regions and exon–intron boundaries of the SLC22A12 and SLC2A9 genes. Sequence analysis identified dysfunctional variants c.1245_1253del and c.1400C>T in the SLC22A12 gene, but no other causal allelic variants were found. One heterozygote and one homozygote for c.1245_1253del, nine heterozygotes and one homozygote for c.1400C>T, and two compound heterozygotes for c.1400C>T and c.1245_1253del were found in a total of 14 subjects. Our result confirms the prevalence of dysfunctional URAT1 variants in Roma subjects based on analyses in Slovak, Czech, and Spanish cohorts, and for the first time in a Macedonian Roma cohort. Although RHUC1 is a rare inherited disease, the frequency of URAT1-associated variants indicates that this disease is underdiagnosed. Our findings illustrate that there are common dysfunctional URAT1 allelic variants in the general Roma population that should be routinely considered in clinical practice as part of the diagnosis of Roma patients with hypouricemia and hyperuricosuria exhibiting clinical signs such as urolithiasis, nephrolithiasis, and acute kidney injury. Full article

(This article belongs to the Special Issue Hypouricemia)

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14 pages, 4020 KiB

Open AccessArticle

Characterization of a Compound Heterozygous SLC2A9 Mutation That Causes Hypouricemia

by Jaeho Yoon, Raul Cachau, Victor A. David, Mary Thompson, Wooram Jung, Sun-Ha Jee, Ira O. Daar, Cheryl A. Winkler and Sung-Kweon Cho

Biomedicines 2021, 9(9), 1172; https://doi.org/10.3390/biomedicines9091172 - 6 Sep 2021

Cited by 3 | Viewed by 2057

Abstract

Renal hypouricemia is a rare genetic disorder. Hypouricemia can present as renal stones or exercise-induced acute renal failure, but most cases are asymptomatic. Our previous study showed that two recessive variants of SLC22A12 (p.Trp258*, pArg90His) were identified in 90% of the hypouricemia patients [...] Read more.

Renal hypouricemia is a rare genetic disorder. Hypouricemia can present as renal stones or exercise-induced acute renal failure, but most cases are asymptomatic. Our previous study showed that two recessive variants of SLC22A12 (p.Trp258*, pArg90His) were identified in 90% of the hypouricemia patients from two independent cohorts: the Korean genome and epidemiology study (KoGES) and the Korean Cancer Prevention Study (KCPS-II). In this work, we investigate the genetic causes of hypouricemia in the rest of the 10% of unsolved cases. We found a novel non-synonymous mutation of SLC2A9 (voltage-sensitive uric acid transporter) in the whole-exome sequencing (WES) results. Molecular dynamics prediction suggests that the novel mutation p.Met126Val in SLCA9b (p.Met155Val in SLC2A9a) hinders uric acid transport through a defect of the outward open geometry. Molecular analysis using Xenopus oocytes confirmed that the p.Met126Val mutation significantly reduced uric acid transport but does not affect the SLC2A9 protein expression level. Our results will shed light on a better understanding of SLC2A9-mediated uric acid transport and the development of a uric acid-lowering agent. Full article

(This article belongs to the Special Issue Hypouricemia)

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13 pages, 1673 KiB

Open AccessArticle

A Proposal for Practical Diagnosis of Renal Hypouricemia: Evidenced from Genetic Studies of Nonfunctional Variants of URAT1/SLC22A12 among 30,685 Japanese Individuals

by Yusuke Kawamura, Akiyoshi Nakayama, Seiko Shimizu, Yu Toyoda, Yuichiro Nishida, Asahi Hishida, Sakurako Katsuura-Kamano, Kenichi Shibuya, Takashi Tamura, Makoto Kawaguchi, Satoko Suzuki, Satoko Iwasawa, Hiroshi Nakashima, Rie Ibusuki, Hirokazu Uemura, Megumi Hara, Kenji Takeuchi, Tappei Takada, Masashi Tsunoda, Kokichi Arisawa, Toshiro Takezaki, Keitaro Tanaka, Kimiyoshi Ichida, Kenji Wakai, Nariyoshi Shinomiya and Hirotaka Matsuo Show full author list Hide full author list

Biomedicines 2021, 9(8), 1012; https://doi.org/10.3390/biomedicines9081012 - 13 Aug 2021

Cited by 8 | Viewed by 3010

Abstract

Background: Renal hypouricemia (RHUC) is characterized by a low serum uric acid (SUA) level and high fractional excretion of uric acid (FE_UA). Further studies on FE_UA in hypouricemic individuals are needed for a more accurate diagnosis of RHUC. Methods: In [...] Read more.

Background: Renal hypouricemia (RHUC) is characterized by a low serum uric acid (SUA) level and high fractional excretion of uric acid (FE_UA). Further studies on FE_UA in hypouricemic individuals are needed for a more accurate diagnosis of RHUC. Methods: In 30,685 Japanese health-examination participants, we genotyped the two most common nonfunctional variants of URAT1 (NFV-URAT1), W258X (rs121907892) and R90H (rs121907896), in 1040 hypouricemic individuals (SUA ≤ 3.0 mg/dL) and 2240 individuals with FE_UA data. The effects of NFV-URAT1 on FE_UA and SUA were also investigated using linear and multiple regression analyses. Results: Frequency of hypouricemic individuals (SUA ≤ 3.0 mg/dL) was 0.97% (male) and 6.94% (female) among 30,685 participants. High frequencies of those having at least one allele of NFV-URAT1 were observed in 1040 hypouricemic individuals. Furthermore, NFV-URAT1 significantly increased FE_UA and decreased SUA, enabling FE_UA and SUA levels to be estimated. Conversely, FE_UA and SUA data of hypouricemic individuals are revealed to be useful to predict the number of NFV-URAT1. Conclusions: Our findings reveal that specific patterns of FE_UA and SUA data assist with predicting the number of nonfunctional variants of causative genes for RHUC, and can also be useful for practical diagnosis of RHUC even before genetic tests. Full article

(This article belongs to the Special Issue Hypouricemia)

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24 pages, 2699 KiB

Open AccessArticle

Classical Xanthinuria in Nine Israeli Families and Two Isolated Cases from Germany: Molecular, Biochemical and Population Genetics Aspects

by Hava Peretz, Ayala Lagziel, Florian Bittner, Mustafa Kabha, Meirav Shtauber-Naamati, Vicki Zhuravel, Sali Usher, Steffen Rump, Silke Wollers, Bettina Bork, Hanna Mandel, Tzipora Falik-Zaccai, Limor Kalfon, Juergen Graessler, Avraham Zeharia, Nasser Heib, Hannah Shalev, Daniel Landau and David Levartovsky

Biomedicines 2021, 9(7), 788; https://doi.org/10.3390/biomedicines9070788 - 7 Jul 2021

Cited by 4 | Viewed by 2419

Abstract

Classical xanthinuria is a rare autosomal recessive metabolic disorder caused by variants in the XDH (type I) or MOCOS (type II) genes. Thirteen Israeli kindred (five Jewish and eight Arab) and two isolated cases from Germany were studied between the years 1997 and [...] Read more.

Classical xanthinuria is a rare autosomal recessive metabolic disorder caused by variants in the XDH (type I) or MOCOS (type II) genes. Thirteen Israeli kindred (five Jewish and eight Arab) and two isolated cases from Germany were studied between the years 1997 and 2013. Four and a branch of a fifth of these families were previously described. Here, we reported the demographic, clinical, molecular and biochemical characterizations of the remaining cases. Seven out of 20 affected individuals (35%) presented with xanthinuria-related symptoms of varied severity. Among the 10 distinct variants identified, six were novel: c.449G>T (p.(Cys150Phe)), c.1434G>A (p.(Trp478*)), c.1871C>G (p.(Ser624*)) and c.913del (p.(Leu305fs*1)) in the XDH gene and c.1046C>T (p.(Thr349Ileu)) and c.1771C>T (p.(Pro591Ser)) in the MOCOS gene. Heterologous protein expression studies revealed that the p.Cys150Phe variant within the Fe/S-I cluster-binding site impairs XDH biogenesis, the p.Thr349Ileu variant in the NifS-like domain of MOCOS affects protein stability and cysteine desulfurase activity, while the p.Pro591Ser and a previously described p.Arg776Cys variant in the C-terminal domain affect Molybdenum cofactor binding. Based on the results of haplotype analyses and historical genealogy findings, the potential dispersion of the identified variants is discussed. As far as we are aware, this is the largest cohort of xanthinuria cases described so far, substantially expanding the repertoire of pathogenic variants, characterizing structurally and functionally essential amino acid residues in the XDH and MOCOS proteins and addressing the population genetic aspects of classical xanthinuria. Full article

(This article belongs to the Special Issue Hypouricemia)

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Review

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12 pages, 669 KiB

Open AccessReview

Genetic Basis of the Epidemiological Features and Clinical Significance of Renal Hypouricemia

by Masayuki Hakoda and Kimiyoshi Ichida

Biomedicines 2022, 10(7), 1696; https://doi.org/10.3390/biomedicines10071696 - 13 Jul 2022

Cited by 10 | Viewed by 1734

Abstract

A genetic defect in urate transporter 1 (URAT1) is the major cause of renal hypouricemia (RHUC). Although RHUC is detected using a serum uric acid (UA) concentration <2.0 mg/dL, the relationship between the genetic state of URAT1 and serum UA concentration is not [...] Read more.

A genetic defect in urate transporter 1 (URAT1) is the major cause of renal hypouricemia (RHUC). Although RHUC is detected using a serum uric acid (UA) concentration <2.0 mg/dL, the relationship between the genetic state of URAT1 and serum UA concentration is not clear. Homozygosity and compound heterozygosity with respect to mutant URAT1 alleles are associated with a serum UA concentration of <1.0 mg/dL and are present at a prevalence of ~0.1% in Japan. In heterozygous individuals, the prevalence of a serum UA of 1.1–2.0 mg/dL is much higher in women than in men. The frequency of mutant URAT1 alleles is as high as 3% in the general Japanese population. The expansion of a specific mutant URAT1 allele derived from a single mutant gene that occurred in ancient times is reflected in modern Japan at a high frequency. Similar findings were reported in Roma populations in Europe. These phenomena are thought to reflect the ancient migration history of each ethnic group (founder effects). Exercise-induced acute kidney injury (EI-AKI) is mostly observed in individuals with homozygous/compound heterozygous URAT1 mutation, and laboratory experiments suggested that a high UA load on the renal tubules is a plausible mechanism for EI-AKI. Full article

(This article belongs to the Special Issue Hypouricemia)

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15 pages, 720 KiB

Open AccessReview

Hypouricemia and Urate Transporters

by Naoyuki Otani, Motoshi Ouchi, Kazuharu Misawa, Ichiro Hisatome and Naohiko Anzai

Biomedicines 2022, 10(3), 652; https://doi.org/10.3390/biomedicines10030652 - 11 Mar 2022

Cited by 18 | Viewed by 4715

Abstract

Hypouricemia is recognized as a rare disorder, defined as a serum uric acid level of 2.0 mg/dL or less. Hypouricemia is divided into an overexcretion type and an underproduction type. The former typical disease is xanthinuria, and the latter is renal hypouricemia (RHUC). [...] Read more.

Hypouricemia is recognized as a rare disorder, defined as a serum uric acid level of 2.0 mg/dL or less. Hypouricemia is divided into an overexcretion type and an underproduction type. The former typical disease is xanthinuria, and the latter is renal hypouricemia (RHUC). The frequency of nephrogenic hypouricemia due to a deficiency of URAT1 is high in Japan, accounting for most asymptomatic and persistent cases of hypouricemia. RHUC results in a high risk of exercise-induced acute kidney injury and urolithiasis. It is vital to promote research on RHUC, as this will lead not only to the elucidation of its pathophysiology but also to the development of new treatments for gout and hyperuricemia. Full article

(This article belongs to the Special Issue Hypouricemia)

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10 pages, 882 KiB

Open AccessReview

Hypothetical Mechanism of Exercise-Induced Acute Kidney Injury Associated with Renal Hypouricemia

by Makoto Hosoyamada

Biomedicines 2021, 9(12), 1847; https://doi.org/10.3390/biomedicines9121847 - 6 Dec 2021

Cited by 10 | Viewed by 3049

Abstract

Renal hypouricemia (RHUC) is a hereditary disease that presents with increased renal urate clearance and hypouricemia due to genetic mutations in the urate transporter URAT1 or GLUT9 that reabsorbs urates in the renal proximal tubule. Exercise-induced acute kidney injury (EIAKI) is known to [...] Read more.

Renal hypouricemia (RHUC) is a hereditary disease that presents with increased renal urate clearance and hypouricemia due to genetic mutations in the urate transporter URAT1 or GLUT9 that reabsorbs urates in the renal proximal tubule. Exercise-induced acute kidney injury (EIAKI) is known to be a complication of renal hypouricemia. In the skeletal muscle of RHUC patients during exhaustive exercise, the decreased release of endothelial-derived hyperpolarization factor (EDHF) due to hypouricemia might cause the disturbance of exercise hyperemia, which might increase post-exercise urinary urate excretion. In the kidneys of RHUC patients after exhaustive exercise, an intraluminal high concentration of urates in the proximal straight tubule and/or thick ascending limb of Henle’s loop might stimulate the luminal Toll-like receptor 4–myeloid differentiation factor 88–phosphoinositide 3-kinase–mammalian target of rapamycin (luminal TLR4–MyD88–PI3K–mTOR) pathway to activate the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome and may release interleukin-1β (IL-1β), which might cause the symptoms of EIAKI. Full article

(This article belongs to the Special Issue Hypouricemia)

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16 pages, 30587 KiB

Open AccessReview

Association of Mutations Identified in Xanthinuria with the Function and Inhibition Mechanism of Xanthine Oxidoreductase

by Mai Sekine, Ken Okamoto and Kimiyoshi Ichida

Biomedicines 2021, 9(11), 1723; https://doi.org/10.3390/biomedicines9111723 - 20 Nov 2021

Cited by 10 | Viewed by 3654

Abstract

Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the two-step reaction from hypoxanthine to xanthine and from xanthine to uric acid in purine metabolism. XOR generally carries dehydrogenase activity (XDH) but is converted into an oxidase (XO) under various pathophysiologic conditions. The complex [...] Read more.

Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the two-step reaction from hypoxanthine to xanthine and from xanthine to uric acid in purine metabolism. XOR generally carries dehydrogenase activity (XDH) but is converted into an oxidase (XO) under various pathophysiologic conditions. The complex structure and enzymatic function of XOR have been well investigated by mutagenesis studies of mammalian XOR and structural analysis of XOR–inhibitor interactions. Three XOR inhibitors are currently used as hyperuricemia and gout therapeutics but are also expected to have potential effects other than uric acid reduction, such as suppressing XO–generating reactive oxygen species. Isolated XOR deficiency, xanthinuria type I, is a good model of the metabolic effects of XOR inhibitors. It is characterized by hypouricemia, markedly decreased uric acid excretion, and increased serum and urinary xanthine concentrations, with no clinically significant symptoms. The pathogenesis and relationship between mutations and XOR activity in xanthinuria are useful for elucidating the biological role of XOR and the details of the XOR reaction process. In this review, we aim to contribute to the basic science and clinical aspects of XOR by linking the mutations in xanthinuria to structural studies, in order to understand the function and reaction mechanism of XOR in vivo. Full article

(This article belongs to the Special Issue Hypouricemia)

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