Effect of urine storage on urinary uric acid concentrations

Accurate determination of serum and urinary uric acid concentrations is essential for the diagnosis and classification of gout according to uric acid metabolism derangement. Urine and/or serum samples are often kept at either 4 degrees C or -20 degrees C until assayed, when a large number of samples are handled simultaneously. Our preliminary study indicated a significant decrease in urinary uric acid concentration after preservation, regardless of the storage temperature. Uric acid crystals were often observed in these cases which showed a marked decrease in urinary uric acid concentration after storage. In the present study, we sought the factor(s) that might cause this decrease in urinary uric acid concentration, as well as measures to overcome the problem. High urinary uric acid concentration and low pH proved to play major roles in the decrease in urinary uric acid concentration after storage. In contrast, dilution of the urine samples before storage resulted in no significant change in urinary uric acid concentration. Based on these results, we recommend diluting urine before storage for determination of uric acid concentration and avoiding underestimation.

Effect of branched-chain amino acids on the plasma concentration of uridine does not occur via the action of glucagon or insulin

To examine whether branched-chain amino acids affect the plasma concentration of uridine, we administered branched-chain amino acids (L-isoleucine, 2.85 g, L-leucine 5.71 g, and L-valine, 3.43 g) orally to 6 healthy subjects. Plasma uridine and glucose decreased by 44% and 12%, respectively, together with an increase in plasma isoleucine, leucine, and valine 90 minutes after administration. However, branched-chain amino acids did not affect the plasma concentration and urinary excretion of purine bases (hypoxanthine, xanthine, and uric acid) and uridine or the plasma concentration of insulin, glucagon, and cyclic adenosine monophosphate (cAMP). Since small amounts of regular insulin, which were found to decrease plasma glucose more than the amino acids, did not decrease the plasma concentration of uridine, these results suggest that plasma uridine was decreased by a direct effect of the branched-chain amino acids on the cellular uptake and/or release of uridine.

Effect of TEI-6720, a xanthine oxidase inhibitor, on the nucleoside transport in the lung cancer cell line A549

To examine the effect of 2-(3-cyano-4-isobutoxyphenyl)-4-methyl-5-thiazolecarboxylic acid (TEI-6720), an inhibitor of xanthine oxidase, on purine metabolism in the lung cancer cell line A549, the activities of adenosine deaminase, purine nucleoside phosphorylase, adenine phosphoribosyltransferase, hypoxanthine guanine phosphoribosyltransferase, xanthine oxidase, and guanase together with pyrimidine nucleoside phosphorylase were measured with or without the addition of TEI-6720, and the extracellular concentrations of hypoxanthine, xanthine, inosine, uracil, and uridine were measured after the addition of inosine or uridine to the incubation medium with or without TEI-6720. Moreover, the Na-independent nucleoside transport was determined in A549 cells with or without TEI-6720. TEI-6720 inhibited the activity of xanthine oxidase in A549 cells, but did not affect other enzymes. During incubation, TEI-6720 not only prevented a decrease in the inosine concentration in inosine-containing medium, but also a decrease in the uridine concentration in uridine-containing medium. Furthermore, the Na-independent transport of uridine was inhibited by TEI-6720 with a K(i) value of 4.1 micromol/l. These results indicate that TEI-6720 is an inhibitor of the Na-independent nucleoside transport of uridine and inosine, as well as xanthine oxidase.

Effect of amino acids on the plasma concentration and urinary excretion of uric acid and uridine

To determine the effect of amino acids on the plasma level and urinary excretion of uric acid and uridine, 200 mL 12% amino acid solution, and 2 weeks later, 100 mL physiological saline solution containing glucagon (1.2 microg/kg weight), was infused into five healthy men. Both increased the urinary excretion of uric acid and the concentration of glucagon, insulin, and glucose in plasma and pyruvic acid in blood, whereas they decreased the concentration of uridine and inorganic phosphate in plasma. However, neither the amino acid infusion nor glucagon infusion affected the concentration of purine bases (hypoxanthine, xanthine, and uric acid), cyclic adenosine monophosphate (cAMP) in plasma, or lactic acid in blood or the urinary excretion of oxypurines (hypoxanthine and xanthine), uridine, or sodium. These results suggest that glucagon may have an important role in the amino acid-induced increase in urinary excretion of uric acid and decrease in plasma uridine.

'Pseudohypouricosuria' in alcaptonuria: homogentisic acid interference in the measurement of urinary uric acid with the uricase-peroxidase reaction

Urinary excretion of uric acid was found to be extremely low in a 58-year-old female patient with alcaptonuria. This was due to interference with the uricase-peroxidase method used, because analysis using high-performance liquid chromatography (HPLC) showed a normal urinary concentration of uric acid. In vitro experiments demonstrated that a high concentration of homogentisic acid in the patient's urine inhibited the peroxidase reaction, possibly due to inhibition of the colour development of 3-methyl-N-ethyl-N-(beta-hydroxyethyl)aniline (MEHA) and 4-aminoantipyrine, via the peroxidase reaction. A homogentisic acid concentration equivalent to that in plasma did not affect the uricase-peroxidase reaction. This result suggests that any assay based on a peroxidase method is affected by a high urinary concentration of homogentisic acid in patients with alcaptonuria.

Effect of interferon-gamma on purine catabolic and salvage enzyme activities in rats

To determine whether interferon-gamma affects rat purine catabolic and salvage enzyme activities, rats were injected with interferon-gamma (600000 U/kg, i.p.) and, similarly to a vehicle-injected control group, killed before or after injection at 6, 12, and 24 h. Organ homogenates were prepared and enzymatic reactions with substrates were carried out, after which the products were measured either chromatographically or spectrophotometrically. Western and Northern blotting also were performed. In contrast to the vehicle-injected rats, interferon-gamma-injected rats showed a significant rise in xanthine oxidoreductase activity in the liver, while enzyme activity was unchanged in the spleen, kidney, and lung. Western analysis of hepatic xanthine oxidoreductase showed an increased concentration of this protein 12 and 24 h after interferon-gamma injection. Northern analysis disclosed an enhanced mRNA expression coding for this enzyme, peaking 12 h after injection. Contrastingly, the activities of adenosine deaminase, purine nucleoside phosphorylase, hypoxanthine guanine phosphoribosyltransferase, and adenine phosphoribosyltransferase were not affected by interferon-gamma in any organ tested. While interferon-gamma causes an increased hepatic biosynthesis of xanthine oxidoreductase, the physiologic role of this enzyme induction remains undetermined.

Effects of fructose and xylitol on the urinary excretion of adenosine, uridine, and purine bases

To examine whether fructose and xylitol increase the plasma concentration and urinary excretion of adenosine, as well as uridine and purine bases (hypoxanthine, xanthine, and uric acid), we intravenously administered xylitol and, 2 weeks later, fructose, to five healthy subjects. Analyses of blood and urine samples obtained during these infusion studies demonstrated that fructose increased the urinary excretion of adenosine and uridine 11.9- and 105.5-fold, respectively, and caused only a small increase in the plasma concentrations of uridine and purine bases. It was further demonstrated that xylitol increased the urinary excretion of uridine 58.4-fold, with a marked increase in the plasma concentrations of purine bases and uridine but without an increase in the urinary excretion of adenosine. However, neither infusion increased the plasma concentration of adenosine. These results suggest that in addition to many organs, including the liver, fructose is significantly metabolized by an abrupt adenosine triphosphate (ATP) consumption in the kidney, leading to an increase in the urinary excretion of adenosine and uridine. They also suggest that xylitol is not significantly metabolized in the kidney.

Effect of glucose on the plasma concentration and urinary excretion of uridine and purine bases

To examine whether glucose increases the plasma concentration of purine bases and uridine, 75 g glucose was administered orally to eight healthy subjects and two patients with hyperuricemia. The plasma concentration of uridine increased by 21%, 25%, and 20% 30, 60, and 90 minutes after administration of glucose, respectively. However, urinary excretion of uridine was not affected, nor were the plasma concentrations and urinary excretion of purine bases (hypoxanthine, xanthine, and uric acid). These results suggest that the glucose-induced increase in plasma uridine was not concomitant with adenosine triphosphate (ATP) consumption-induced purine degradation, but instead was ascribable to a uridine diphosphate (UDP)-glucose consumption-induced pyrimidine degradation (UDP-glucose-->UDP-->uridine monophosphate [UMP]-->uridine).

Determination of adenosine and deoxyadenosine in urine by high-performance liquid chromatography with column switching

The means of measurement of adenosine and deoxyadenosine in urine was developed by separating adenosine and deoxyadenosine from other compounds using high-performance liquid chromatography with column switchings. This method is simple and convenient since no pretreatment of the urine is needed. Using this method, it could be demonstrated that urinary adenosine was higher in an adenosine deaminase (ADA) deficient patient who had a bone marrow transplant treatment (1.97 micromol/mmol creatinine) and in a heterozygote who had a markedly low erythrocyte ADA activity (1% of control ADA activity) (1.33 micromol/mmol creatinine) as compared to normal subjects (0.22+/-0.09 micromol/mmol creatinine, n=11). It was also noted that urinary deoxyadenosine was below the detection limits in the ADA-deficient bone marrow transplant patient, but it was detected in the heterozygote (3.7 micromol/mmol creatinine). Furthermore, it was also demonstrated that a fructose infusion increased the urinary concentration of adenosine from 0.21+/-0.03 to 2.66+/-1.21 micromol/mmol creatinine in five normal subjects.

Effect of bucladesine sodium on the plasma concentrations and urinary excretion of purine bases and uridine

To examine whether bucladesine sodium affects the plasma concentrations of purine bases (hypoxanthine, xanthine, and uric acid) and uridine, 100 mL of physiological saline containing bucladesine sodium (6 mg/kg weight) was administered intravenously to eight healthy subjects for 1 hour after overnight fast except for water. Blood was drawn 30 minutes before, and 30 minutes and 1 hour after the beginning of the infusion, and 1-hour urine was collected before and after the beginning of the infusion. Two weeks later, 100 mL of only physiological saline was administered under the same protocol. Bucladesine sodium decreased the plasma concentrations of hypoxanthine by 36% and by 37%, and of xanthine by 16% and 33%, and of uridine by 17% and 30%, 30 minutes and 1 hour after the beginning of the infusion, respectively, and increased the urinary excretion of hypoxanthine and uric acid by 140% and 30%, respectively, after the beginning of the infusion. However, it did not affect the plasma concentration of uric acid or the urinary excretion of xanthine, and the urinary excretion of uridine was less than 0.2 micromol/h before or after bucladesine sodium infusion. On the other hand, physiological saline alone did not affect any of the values described. These results suggest that bucladesine sodium acts on the secretory process of the renal transport of hypoxanthine, resulting in the increased urinary excretion of hypoxanthine, and further suggest that bucladesine sodium enhances the uptake of uridine in plasma to liver cells.

Effect of glucagon on the plasma concentration of uridine

To determine whether glucagon affects the plasma concentration of uridine, we administered 100 mL physiological saline containing 1 mg glucagon or 100 mL physiological saline alone intravenously over 1 hour to healthy subjects. Glucagon decreased the plasma concentration of uridine from 5.72 +/- 1.05 to 4.80 +/- 0.60 micromol/L but increased the concentrations of cyclic adenosine monophosphate (cAMP) in plasma and pyruvic acid and lactic acid in blood 59-, 1.4-, and 1.3-fold, respectively. Although glucagon increased urinary excretion of uric acid, it did not affect the plasma concentration of purine bases (hypoxanthine, xanthine, and uric acid) or urinary excretion of oxypurines and uridine, indicating that glucagon does not affect purine degradation and suggesting that glucagon does not affect adenosine triphosphate (ATP) consumption-induced pyrimidine degradation. In contrast, physiological saline did not affect any of the measured variables. These results suggest that glucagon enhanced Na+-dependent uridine uptake from the blood into the cells, since glucagon stimulates Na+-dependent uridine uptake into cells in vitro.

Xylitol-induced increase in the plasma concentration and urinary excretion of uridine and purine bases

To determine whether xylitol increases the plasma concentration and urinary excretion of uridine together with purine bases, we administered xylitol (0.6 g/kg weight) intravenously to six normal subjects using a 10% xylitol solution. Xylitol infusion increased the plasma concentration and urinary excretion of uridine, as well as purine bases, while it decreased both the concentrations of inorganic phosphate in plasma and pyruvic acid in blood and increased the blood concentration of lactic acid. These results suggest that an increase in the plasma concentration and urinary excretion of uridine is ascribable to increased pyrimidine degradation following purine degradation induced by xylitol.

Zonal distribution of allopurinol-oxidizing enzymes in rat liver

We describe an enzymatic histochemical localization of two allopurinol-oxidizing enzymes, xanthine oxidase and aldehyde oxidase in rat hepatic tissues. This method is based on the tetrazolium salt procedures by use of a tissue protectant, polyvinyl alcohol, with tetra-nitro BT as the final electron acceptor. The present study demonstrated that both oxidases are present in the cytoplasm of hepatic cells. However, the distribution of the enzymes was uneven, being seen mainly in the pericentral rather than the periportal area. When allopurinol was used as a substrate, the specific staining by xanthine oxidase was more prominent than that of aldehyde oxidase. The results suggested that xanthine oxidase is more effective in oxidizing allopurinol than aldehyde oxidase.

Decreased serum concentrations of 1,25(OH)2-vitamin D3 in patients with gout

We measured the serum concentrations of 1,25(OH)2-vitamin D3, 25(OH)-vitamin D3, parathyroid hormone (PTH) in 82 male patients with primary gout whose serum uric acid was significantly higher than that of 41 normal control male subjects (8.8 +/- 0.2 vs 5.6 +/- 0.2 mg/dL, p < 0.001). The serum 1,25(OH)2-vitamin D3 concentration was significantly lower in the patients with gout compared with the control subjects (39.6 +/- 1.4 vs 44.8 +/- 1.7 pg/mL, p < 0.05), while no differences were observed between the two groups in either the serum concentration of 25(OH)-vitamin D3 or PTH. The administration of uric acid lowering agent to the patients for 1 year caused a significant increase in their serum 1,25(OH)2-vitamin D3 concentration which was associated with a significant decrease in their serum uric acid concentration. In contrast, the serum concentrations of 25(OH)-vitamin D3 and PTH were not affected by these drugs. These results suggest that uric acid per se may directly decrease the serum concentration of 1,25(OH)2-vitamin D3 in patients with gout by inhibiting 1-hydroxylase activity.

Decreased serum concentrations of 1,25(OH)2-vitamin D3 in patients with gout

We measured serum concentrations of 1,25(OH)2-vitamin D3, 25(OH)-vitamin D3, parathyroid hormone (PTH), and uric acid in 114 male patients with primary gout and 51 normal male control subjects. Serum 1,25(OH)2-vitamin D3 was significantly lower in patients with gout compared with control subjects (38.4 +/- 11.9 v 44.4 +/- 11.0 pg/mL, P < .005), whereas no differences were observed between the two groups for serum 25(OH)-vitamin D3 or PTH. Serum uric acid was significantly higher in patients with gout versus control subjects (8.8 +/- 1.3 v 5.7 +/- 1.0 mg/dL, P < .0001). In addition, there was a significant negative correlation between serum uric acid and 1,25(OH)2-vitamin D3 concentrations (r = .17, P < .05). Administration of allopurinol or benzbromarone to the patients for 1 year caused a significant increase in serum 1,25(OH)2-vitamin D3, which was associated with a significant decrease in serum uric acid. In contrast, serum concentrations of 25(OH)-vitamin D3 and PTH were not affected by these drugs. These results suggest that uric acid per se may directly decrease serum 1,25(OH)2-vitamin D3 in patients with gout by inhibiting 1alpha-hydroxylase activity.

Effect of Tofu (bean curd) ingestion and on uric acid metabolism in healthy and gouty subjects

The effect of Tofu (bean curd) ingestion on uric acid metabolism was examined in 8 healthy and 10 gout subjects. Ingestion of Tofu increased plasma concentration of uric acid, together with increases in uric acid clearance and urinary excretion of uric acid. However, the increase in plasma concentration of uric acid was fairy small. Interestingly, no significant rise in the plasma, urinary and clearance of uric acid was observed in gout patients with uric acid clearance > 6.0 mL/min (lower normal limit). The results suggest that tofu is a preferable source of protein, especially in gout patients with uric acid clearance > 6.0 mL/min.

Effect of allopurinol and benzbromarone on the concentration of uridine in plasma

To investigate whether allopurinol and benzbromarone affect the concentration of uridine in plasma, allopurinol or benzbromarone were administered to patients with gout for 3 to 6 months. Allopurinol decreased the concentrations of uridine and uric acid in plasma and the urinary excretion of uric acid, but increased the plasma concentration and urinary excretion of oxypurines and orotidine. Benzbromarone decreased the concentration of uric acid in plasma and increased the excretion of uric acid in urine. However, it did not affect the plasma concentration of uridine or oxypurines or the urinary excretion of oxypurines or orotidine. These results suggest that orotidilytic decarboxylase was inhibited by allopurinol and oxypurinol ribonucleotides and/or that phosphoribosyl pyrophosphate (PRPP) was consumed by conversion from hypoxanthine, allopurinol, and oxypurinol to the respective ribonucleotides, resulting in a decrease in the de novo synthesis of pyrimidine leading to the decreased concentration of uridine in plasma. Furthermore, it was suggested that benzbromarone did not affect the de novo synthesis of pyrimidine or purine.

Effect of muscular exercise on the concentration of uridine and purine bases in plasma--adenosine triphosphate consumption-induced pyrimidine degradation

To identify whether muscular exercise increases the plasma concentration of uridine and of purine bases, the effect of rigorous muscular exercise was determined in five healthy men with a bicycle ergometer. Twenty-five-minute muscular exercise at 65% maximum O2 consumption increased the concentration of uridine, purine bases, and inorganicphosphate in plasma and of NH3 and lactic acid in blood. These results suggest that exercise-induced excessive adenosine triphosphate (ATP) consumption enhanced not only purine degradation but also pyrimidine degradation (uridine triphosphate [UTP]-->uridine diphosphate [UDP]-->uridine monophosphate [UMP]-->uridine) in exercising muscles.

Close correlation between visceral fat accumulation and uric acid metabolism in healthy men

We evaluated the effect of accumulation of intraabdominal visceral fat on the metabolism of uric acid in 50 healthy male subjects to elucidate any relationship between such obesity and hyperuricemia. The area of abdominal fat (visceral fat and subcutaneous fat) was measured at the level of the umbilicus by abdominal computed tomographic scanning. Serum and urinary concentrations of uric acid and creatinine were determined with an autoanalyzer. Uric acid clearance and the ratio of urinary uric acid to creatinine excreted in urine were calculated. Univariate and multivariate analyses were used to evaluate the relationship between uric acid metabolism and body fat. The size of the area of visceral fat was significantly correlated with the serum concentration of uric acid (r = .37, P < .01), uric acid clearance (r = -.34, P < .05), and the urinary uric acid to creatinine ratio (r = .65, P < .0001). The size of the area of subcutaneous fat was significantly correlated only with the urinary uric acid to creatinine ratio (r = .38, P < .01). Multivariate analyses, including body mass index (BMI), showed that the size of the visceral fat area was the strongest contributor to an elevated serum concentration of uric acid, a decrease in uric acid clearance, and an increase in the urinary uric acid to creatinine ratio. These results suggest that accumulation of visceral fat may have a greater adverse effect on the metabolism of uric acid than BMI or accumulation of subcutaneous fat. Clearly, patients with hyperuricemia should lose weight to reduce excessive visceral fat stores, to help avoid attacks of gout.

Is the plasma uridine level a marker of the overproduction of uric acid?

To determine whether the plasma level of uridine can be used to identify patients with gout, the plasma concentration of uridine was determined in patients with gout and normal subjects. Plasma uridine was significantly higher in patients with gout than in normal subjects. It was also significantly higher in patients with gout of the overexcretion (of uric acid) type than in those with gout of the underexcretion type. Plasma uridine was used to classify gout patients into underexcretion and overexcretion types, with a diagnostic accuracy of 92.5%. Results indicate that the plasma uridine concentration may be a marker of uric acid production and can be used to separate hyperuricemia into the overexcretion and underexcretion types.

Effect of ethanol and fructose on plasma uridine and purine bases

To determine whether both ethanol and fructose increase the plasma concentration of uridine, we administered ethanol (0.6 g/kg) or fructose (1.0 g/kg) to seven normal subjects. Both ethanol and fructose increased the plasma concentration of uridine together with an increase in the plasma concentration of oxypurines, whereas fructose also increased the plasma concentration of uric acid, but ethanol did not. In ethanol ingestion and fructose infusion, an increase in the plasma concentration of purine bases correlated with that of uridine. These results strongly suggest that an increase in the plasma concentration of uridine is ascribable to increased pyrimidine degradation following purine degradation increased by ethanol and fructose.

Effect of glucagon on renal excretion of oxypurinol and purine bases

OBJECTIVE

To investigate whether glucagon increases the urinary excretion of oxypurinol and purine bases.

METHODS

We administered 1 mg glucagon intravenously to 5 healthy subjects taking 300 mg allopurinol orally, and determined plasma concentrations and urinary excretion of oxypurinol and purine bases.

RESULTS

Glucagon increased the urinary excretion and fractional clearances of uric acid, xanthine, and oxypurinol, together with an increase in creatinine clearance, while it decreased plasma concentrations of xanthine and hypoxanthine.

CONCLUSION

Glucagon-induced increases in urinary excretion of uric acid, xanthine, and oxypurinol were attributable to increases in the fractional clearances of uric acid, xanthine, and oxypurinol in addition to an increase in glomerular filtration rate. It is suggested that glucagon affects the renal common transport pathway of uric acid, xanthine, and oxypurinol by stimulating the release of a liver derived renal vasodilator.

[Gout and atherosclerosis]

Recently atherosclerotic diseases, such as coronary heart disease and cerebrovascular disease have been considered as an important complication of hyperuricemia and gout. However, it is still controversial whether or not hyperuricemia is an independent risk factor of atherosclerotic diseases. On the other hand, several risk factors for coronary heart disease, for example hyperlipidemia and hypertension, are frequently observed in the patients with gout. Atherosclerosis in relation to hyperuricemia was discussed in view of definite and probable risk factors.