Decreased xanthine oxidase activities and increased urinary oxypurines in heterozygotes for hereditary xanthinuria

A ratiometric SERS sensor with one signal probe for ultrasensitive and quantitative monitoring of serum xanthine

Xanthine can be converted into uric acid, and a high concentration of xanthine in the human body can cause many diseases. Therefore, it is important to develop a sensitive, simple, and reliable approach for measuring xanthine in biological liquids. Hence, a ratiometric surface-enhanced Raman spectroscopy (SERS) sensing strategy with one signal probe was exploited for reliable, sensitive, and quantitative monitoring of serum xanthine. 3-Mercaptophenylboronic acid (3-MPBA) was used as a typical reference with a Raman peak at 996 cm-1. First, 3-MPBA was bound to gold nanoflowers@silica (GNFs@Si) through Au-S bonds. Xanthine oxidase (XOD) catalyzed the oxidation of xanthine into H2O2 on GNFs@Si. Afterward, the obtained H2O2 further reduced 3-MPBA to 3-hydroxythiophenol (3-HTP) accompanied by the emergence of a new Raman peak at 883 cm-1. Meanwhile, the Raman intensity at 996 cm-1 remained constant. Therefore, the ratio of I883/I996 increased with the increasing of xanthine concentration, thus realizing quantitative detection of xanthine. As a result, a ratiometric SERS sensor for the detection of xanthine was proposed with a detection limit of 5.7 nM for xanthine. The novel ratiometric SERS sensor provides a new direction for analyzing other biomolecules with high sensitivity and reliability.

Determination of xanthine using a ratiometric fluorescence probe based on boron-doped carbon quantum dots and gold nanoclusters

A dual-emission ratiometric fluorescent sensing system based on boron-doped carbon quantum dots (B-CQDs) and gold nanoclusters (AuNCs) has been developed for the determination of xanthine. The blue fluorescence of B-CQDs at 445 nm is then reduced by the AuNCs through the inner filter effect (IFE) under a single excitation wavelength of 370 nm. By the catalysis of xanthine oxidase (XOD), xanthine is oxidized by oxygen dissolved in the solution to produce H₂O₂. The horseradish peroxidase (HRP) catalyzes H₂O₂ to generate hydroxyl radicals, which can quench the fluorescence of AuNCs, leading to the recovery of the fluorescence of B-CQDs. Based on the relationship between the fluorescence intensity ratio (F₄₄₅/F₆₆₅) and the concentration of xanthine, the designed method exhibits a good linearity range of 1.2-500.0 μmol L ^-1 and a limit of detection of 0.37 μmol L ^-1. The ratiometric fluorescent is applied to determine xanthine in human urine samples. Good recoveries of spiked samples in the range 99.2-105.0% are obtained by the proposed assay, with relative standard deviations (RSD) ranging from 0.9 to 2.6%.

Hereditary xanthinuria in a goat

A 2-year-old mixed breed goat was presented for a 1-day history of anorexia and 1 week of weight loss. Serum biochemistry disclosed severe azotemia. Abdominal ultrasound examination showed decreased renal corticomedullary distinction, poor visualization of the renal pelves, and dilated ureters. On necropsy, the kidneys were small, the pelves were dilated, and the medulla was partially effaced by variably sized yellow nephroliths. Histologically, cortical and medullary tubules were distended by yellow-brown, multilayered crystals. Stone composition was 100% xanthine. Exonic sequencing of xanthine dehydrogenase (XDH) and molybdenum cofactor sulfurase (MOCOS) identified 2 putative pathogenic variants: a heterozygous XDH p.Leu128Pro variant and a homozygous MOCOS p.Asp303Gly variant. Variant frequencies were determined in 7 herd mates, 12 goats undergoing necropsy, and 443 goats from genome databases. The XDH variant was not present in any of these 462 goats. The MOCOS variant allele frequency was 0.03 overall, with 3 homozygotes detected. Hereditary xanthinuria is a recessive disorder in other species, but the XDH variant could be causal if the case goat is a compound heterozygote harboring a second variant in a regulatory region not analyzed or if the combination of the XDH and MOCOS variants together abolish XDH activity. Alternatively, the MOCOS variant alone could be causal despite the presence of other homozygotes, because hereditary xanthinuria in humans often is asymptomatic. Ours is the first report describing the clinical presentation and pathology associated with xanthine urolithiasis in a goat. The data support hereditary xanthinuria, but functional studies are needed to conclusively determine the causal variant(s).

Novel electrochemical xanthine biosensor based on chitosan-polypyrrole-gold nanoparticles hybrid bio-nanocomposite platform

The aim of this study was the electrochemical detection of the adenosine-3-phosphate degradation product, xanthine, using a new xanthine biosensor based on a hybrid bio-nanocomposite platform which has been successfully employed in the evaluation of meat freshness. In the design of the amperometric xanthine biosensor, chitosan-polypyrrole-gold nanoparticles fabricated by an in situ chemical synthesis method on a glassy carbon electrode surface was used to enhance electron transfer and to provide good enzyme affinity. Electrochemical studies were carried out by the modified electrode with immobilized xanthine oxidase on it, after which the biosensor was tested to ascertain the optimization parameters. The Biosensor exhibited a very good linear range of 1-200 μM, low detection limit of 0.25 μM, average response time of 8 seconds, and was not prone to significant interference from uric acid, ascorbic acid, glucose, and sodium benzoate. The resulting bio-nanocomposite xanthine biosensor was tested with fish, beef, and chicken real-sample measurements.

Significance of hepatic xanthine oxidase and uric acid in aged and dietary restricted rats

Xanthine oxidase (XOD), one of the major intracellular sources of superoxide production, is well characterized as a causative factor in ischemia/reperfusion related damage. In the present study, we investigated age-effect on the status of XOD, an enzyme interconvertible with xanthine dehydrogenase (XDH) under oxidative stress. We also examined the modulation of the enzyme using the anti-oxidative action of dietary restriction (DR). We obtained evidence showing XOD activity to be significantly increased by DR, peaking at 24 months, although no progressive, age-related changes were noticed. On the other hand, while XDH activity decreased in ad libitum fed rats with age, DR maintained higher activity levels at 18 and 24 months of age. During aging, the conversion of XDH to XOD was slightly increased, as indicated by the XOD/XDH ratio. One novel finding of the present study is DR's ability to elevate the uric acid level, which likely augments the anti-oxidative defense system, thereby buffering against oxidatively stressed conditions during aging. Based on what is known about the antioxidative abilities of DR and uric acid, we propose that the high uric acid levels we observed in DR rats may well serve as part of a defense strategy to protect redox balance.

Novel mutations in xanthine dehydrogenase/oxidase cause severe hypouricemia: biochemical and molecular genetic analysis in two Czech families with xanthinuria type I

BACKGROUND

The article describes the clinical, biochemical, enzymological and molecular genetics findings in two patients from two families with xanthinuria type I.

METHODS

Biochemical analysis using high performance liquid chromatography, allopurinol loading test and analysis of xanthine oxidase activity in plasma and of uromodulin excretion in urine were performed. Sequencing analysis of the xanthine dehydrogenase gene and the haplotype and statistical analyses of consanguinity were performed.

RESULTS

Probands showed extremely low concentrations of uric acid, on seven occasions under the limit of detection. The concentration of uric acid in 38-year-old female was 15 μmol/L in serum and 0.04 mmol/L in urine. Excretion of xanthine in urine was 170 mmol/mol creatinine. The concentration of uric acid in 25-year-old male was 0.03 mmol/L in urine. Excretion of xanthine in urine was 141 mmol/mol creatinine. The allopurinol loading test confirmed xanthinuria type I. The xanthine oxidase activities in patients were 0 and 0.4 pmol/h/mL of plasma. We found three nonsense changes: p.P214QfsX4 and unpublished p.R825X and p.R881X.

CONCLUSIONS

We found two nonconsanguineous compound heterozygotes with xanthinuria type I caused by three nonsense changes. The methods used did not confirm consanguinity in the probands, thus there might be an unconfirmed biological relationship or mutational hotspot.

Lithiases urinaires récidivantes révélant une xanthinurie héréditaire

INTRODUCTION

Hereditary xanthinuria, due to a purine metabolism disorder, is a rare cause of urinary lithiasis in children.

CASE

We report the case of a child aged 3 and a half years, who presented recurrent urinary lithiasis that led to destruction of the right kidney. Infrared spectrophotometric analysis of the calculus concluded that it was composed of 100% xanthine. Laboratory tests showed hypouricemia and hypouricosuria with elevated urinary excretion of oxypurines. These findings led to a diagnosis of hereditary xanthinuria.

CONCLUSION

Early diagnosis of this rare disease is essential to avoid its complications. Metabolic causes must be sought in children with lithiasis.

Canine urate urolithiasis. Etiopathogenesis, diagnosis, and management

Etiopathologic factors predisposing to urate lithogenesis in Dalmatian and non-Dalmatian dogs represent diverse pathologic and/or physiologic processes involving purine nucleotide and ammonia synthesis, biodegradation, and excretion. Predisposing factors for urate urolith formation include hyperuricemia, hyperammonemia, hyperuricosuria, hyperammonuria, aciduria, and genetic predisposition. Medical therapy of dogs forming urate uroliths should be directed at modifying these predisposing factors through dietary modification, administration of allopurinol, and/or surgical correction of portovascular anomalies if present. The precise mechanisms resulting in urate urolith formation in dogs have not been determined.

Xanthine analysis in biological fluids by capillary electrophoresis

Xanthine, a precursor of uric acid, is measured here in serum, urine, and cerebrospinal fluids by capillary electrophoresis (CE) after deproteinization with acetonitrile. The migration time is about 7.5 min with a minimum detection limit of 0.4 mg/l. Different purines and pyrimidines did not interfere with the determination. The method demonstrates the suitability of the CE for determination of small molecules present in a complex matrix at levels of ca. 1mg/l. It also demonstrates that acetonitrile deproteinization is a simple and effective method for preparing samples for CE, allowing a large volume to be introduced into the capillary.

Influence of daily drinking habits on ethanol-induced hyperuricemia

We examined the influence of alcohol drinking habits on the serum uric acid level after the ingestion of a small amount of ethanol. Subjects were divided into two groups according to their alcohol drinking habits--regular drinkers, who consume more than 60 g ethanol every day, and nondrinkers/occasional drinkers, who consume less than 20 g ethanol occasionally. Drinking 0.5 g ethanol/kg increased serum uric acid levels in regular drinkers by 52.6 +/- 26.3 mumol/L (0.8 +/- 0.4 mg/dL), whereas it did not in nondrinkers/occasional drinkers. Urinary excretion of uric acid was unaltered in both groups. Hypoxanthine and xanthine in both plasma and urine and serum acetate were increased more in regular drinkers than in nondrinkers/occasional drinkers. Accelerated adenine nucleotide degradation secondary to enhanced ethanol oxidation likely explains the ethanol-induced hyperuricemia in regular drinkers.

High levels of xanthine oxidoreductase in rat endothelial, epithelial and connective tissue cells

The localization of xanthine oxidoreductase activity was investigated in unfixed cryostat sections of various rat tissues by an enzyme histochemical method which specifically demonstrates both the dehydrogenase and oxidase forms of xanthine oxidoreductase. High activity was found in epithelial cells from skin, vagina, uterus, penis, liver, oral and nasal cavities, tongue, esophagus, fore-stomach and small intestine. In addition activity was demonstrated in sinusoidal cells of liver and adrenal cortex, endothelial cells in various organs and connective tissue fibroblasts. Xanthine oxidoreductase produces urate which is a scavenger of oxygen-derived radicals. Because the enzyme is found in epithelial and endothelial cells which are subject to relatively high oxidant stress, it is postulated that in these cells xanthine oxidoreductase is involved in the antioxidant enzyme defense system. In addition, a possible role for the enzyme in proliferation and differentiation processes is discussed.

An immunoreactive xanthine oxidase protein-possessing xanthinuria and her family

The presence of immunoreactive xanthine oxidase protein was proven in a xanthinuric patient, using a polyclonal antibody against xanthine oxidase. The antibody was raised against purified human liver xanthine oxidase in a rabbit. Double immunodiffusion method demonstrated the existence of an immunologically reactive xanthine oxidase which did not possess xanthine oxidase activity. In addition, urinary excretion of oxypurines in the patient and her family was investigated. The results indicated that a brother and a sister had xanthinuria.