Yumiko Nasako

Purification and immunohistochemical tissue localization of human xanthine oxidase

Xanthine oxidase was purified 1600-fold from human liver cytosol. The purified enzyme was shown as a single band of 300 kDa on polyacrylamide gel electrophoresis and 150 kDa on SDS-PAGE. Using this purified enzyme, polyclonal antibody against xanthine oxidase was raised in a rabbit. On Ouchterlonys double immunodiffusion method, the raised antibody and the human liver cytosol made a precipitation line stained by activity stain and protein stain, respectively. With the raised anti-xanthine oxidase sera, the immunohistochemical localization of xanthine oxidase in human tissues was examined. Immunostaining of frozen hepatic tissue section showed that the cytoplasm of hepatocytes and endothelial lining cells were stained. In a number of other tissues, the xanthine oxidase antigen was detected only in the endothelial lining cells from heart, kidney, brain, aorta, lung and mesentery, except for the duodenal mucosa cells. A possible role for xanthine oxidase in the endothelial cells from various human tissues in the pathogenesis of reperfusion injury was suggested.

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.

In vitro oxidation of pyrazinamide and allopurinol by rat liver aldehyde oxidase

Aldehyde oxidase was purified about 120-fold from rat liver cytosol by sequential column chromatography using diethylaminoethyl (DEAE) cellulose, Benzamidine-Sepharose 6B and gel filtration. The purified enzyme was shown as a single band with M(r) of 2.7 x 10(5) on polyacrylamide gel electrophoresis (PAGE) and M(r) of 1.35 x 10(5) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Using this purified enzyme, in vitro conversion of allopurinol, pyrazinamide and pyrazinoic acid was investigated. Allopurinol and pyrazinamide were oxidized to oxypurinol and 5-hydroxy-pyrazinamide, respectively, while pyrazinoic acid, the microsomal deamidation product of pyrazinamide, was not oxidized to 5-hydroxypyrazinoic acid. The apparent Km value of the enzyme for pyrazinamide was 160 microM and that for allopurinol was 1.1 mM. On PAGE, allopurinol- or pyrazinamide-stained band was coincident with Coomassie Brilliant Blue R 250-stained band, respectively. These results suggest that aldehyde oxidase may play a role in the oxidation of allopurinol to oxypurinol and that of pyrazinamide to 5-hydroxypyrazinamide with xanthine dehydrogenase which can oxidize both allopurinol and pyrazinamide in vivo. The aldehyde oxidase may also play a major role in the oxidation of allopurinol and pyrazinamide in the subgroup of xanthinuria patients (xanthine oxidase deficiency) who can oxidize both allopurinol and pyrazinamide.

Effect of BOF-4272 on the oxidation of allopurinol and pyrazinamide in vivo: Is xanthine dehydrogenase or aldehyde oxidase more important in oxidizing both allopurinol and pyrazinamide?

Allopurinol or pyrazinamide was administered to rats treated with BOF-4272 (a potent xanthine oxidase inhibitor) to investigate to what degree xanthine dehydrogenase participates in the oxidation of these agents. BOF-4272 markedly decreased the plasma concentration and the urinary excretion of both oxypurinol and 5-hydroxypyrazinamide. It also decreased the sum of the urinary excretion of allopurinol and oxypurinol and that of pyrazinamide and its metabolites, although it did not affect the sum of the plasma concentrations of allopurinol and oxypurinol at 105 min after administration of allopurinol or the plasma concentration of pyrazinamide during the period after the administration of pyrazinamide. These results suggested that BOF-4272 almost completely inhibited the oxidation of allopurinol and pyrazinamide and had some effect on the excretion and/or the tissue incorporation of these two compounds. Since the in vitro study demonstrated that BOF-4272 did not inhibit the activity of aldehyde oxidase, which oxidized both allopurinol to oxypurinol and pyrazinamide to 5-hydroxypyrazinamide, the results suggested that xanthine dehydrogenase was the more important enzyme in converting allopurinol to oxypurinol and pyrazinamide to 5-hydroxypyrazinamide.

Effect of Lactate Infusion on Renal Transport of Purine Bases and Oxypurinol

To investigate whether or not lactic acid inhibits the renal transport of oxypurines and oxypurinol, we administered physiological saline containing 0.2 mol sodium lactate to 5 normal subjects intravenously. Lactate infusion decreased the fractional clearance of uric acid, but the fractional clearances of hypoxanthine, xanthine and oxypurinol were not affected. These results suggest that uric acid and lactic acid share the renal transport system of organic acids but hypoxanthine, xanthine and oxypurinol do not. It is further suggested that allopurinol treatment is reasonable in subjects with hyperuricemia accompanied by hyperlactatemia since only the urinary excretion of uric acid and not oxypurines (hypoxanthine and xanthine) was inhibited by lactate infusion.

'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 patients urine inhibited the peroxidase reaction, possibly due to inhibition of the colour development of 3-methyl-N-ethyl-N-(β-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.

Uric Acid Transport in Fanconi Syndrome with Marked Renal Hypouricemia: Analysis Using Pyrazinamide and Benzbromarone

Uric Acid Transport in Fanconi Syndrome with Marked Renal Hypouricemia: Analysis Using Pyrazinamide and Benzbromarone Y. Yuji Moriwaki T. Tetsuya Yamamoto S. Sumio Takahashi K. Keisai Hiroishi J.-i. Jun-ichi Yamakita Y. Yumiko Nasako Y. Yutaka Naito K. Kazuya Higashino Third Department of Internal Medicine, Hyogo College of Medicine, and Sunago Ryouikuen, Institute for Severely Handicapped, Nishinomiya, Hyogo, Japan

Atherogenic Risk Factors in Patients with Gout

In recent years, atherosclerotic diseases such as ischemic heart disease have become an important cause of death in Japanese patients with gout.1 However, since it remained undetermined whether or not hyperuricemia per se is an independent risk factor for atherosclerosis, we investigated the possible risk factors for atherosclerosis including serum lipids in patients with gout.

In Vitro and In Vivo Study on the Conversion of Allopurinol and Pyrazinamide

Allopurinol is widely used in the treatment of gout. The main metabolic pathway of allopurinol is its oxidation to oxypurinol. Pyrazinamide is an antituberculous drug. One of the main metabolic pathways of pyrazinamide is its oxidation to 5-hydroxypyrazinamide. The oxidation of allopurinol and pyrazinamide is known to be attributed to xanthine oxidase1, 2. However, it has been suggested that aldehyde oxidase also participates in the oxidation of these agents3, 4. Therefore, we investigated whether aldehyde oxidase plays a role in the oxidation of allopurinol and pyrazinamide by in vivo and in vitro studies.

Study on lipoprotein lipase and hepatic triglyceride lipase activities in patients with gout.

Hypertriglyceridemia is frequently observed in patients with gout whose first cause of death in Japan is coronary heart disease. However, its mechanism still remains undetermined. Until recently hypertriglyceridemia has not been accepted as an independent risk factor for coronary atherosclerosis, and it has often been ignored in clinical practice. However, recent epidemiological studies showed that hypertriglyceridemia might indeed be a risk factor for coronary atherosclerosis1. To clarify the etiology of hypertriglyceridemia in patients with gout, the relationship between postheparin lipolytic enzyme activity, lipoprotein lipase (LPL), hepatic triglyceride lipase (HTGL), and serum lipids was investigated.