Jun-ichi Yamakita

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.

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.

Determination of human plasma xanthine oxidase activity by high-performance liquid chromatography

An assay for human plasma xanthine oxidase activity was developed with pterin as the substrate and the separation of product (isoxanthopterin) by high-performance liquid chromatography with a fluorescence detector. The reaction mixture consists of 60 microliters of plasma and 240 microliters of 0.2 M Tris-HCl buffer (pH 9.0) containing 113 microM pterin. With this assay, the activity of plasma xanthine oxidase could be easily determined despite its low activity. As a result, it could be demonstrated that the intravenous administration of heparin or the oral administration of ethanol did not increase plasma xanthine oxidase activity in normal subjects, and also that plasma xanthine oxidase activity was higher in patients with hepatitis C virus infection than in healthy subjects or patients with gout. In addition, a single patient with von Gierkes disease showed a marked increase in the plasma activity of this enzyme, relative to that apparent in normal subjects.

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.

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.

Comparative localization of aldehyde oxidase and xanthine oxidoreductase activity in rat tissues

The distribution of aldehyde oxidase activity was evaluated in unfixed cryostat sections from tissues of male Wistar rats using a tissue protectant, polyvinyl alcohol, with Tetranitro BT as a final electron acceptor. The distribution of aldehyde oxidase activity was compared with that of xanthine oxidoreductase. The enzyme histochemical method demonstrated aldehyde oxidase activity in the epithelium of the tongue, renal tubules and bronchioles, as well as in the cytoplasm of liver cells. Such activity was not detected in oesophagus, stomach, spleen, adrenal glands, small or large intestine or skeletal and heart muscle fibres. In contrast, xanthine oxidoreductase activity was demonstrated in the tongue, renal tubules, bronchioles, oesophageal, gastric, small and large intestinal epithelial cells, adrenal glands, spleen and liver cytoplasm but not in skeletal and heart muscle fibres. The significance of the ubiquitous distribution of aldehyde oxidase activity, especially in surface epithelial cells from various tissues, except for the gastrointestinal tract, is unclear. However, aldehyde oxidase may possess some physiological activity other than in the metabolism of N-heterocyclics or of certain drugs.

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.

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 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.

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.