Urine metabolomics reveals novel physiologic functions of human aldehyde oxidase and provides biomarkers for typing xanthinuria

Classical xanthinuria is a rare inherited metabolic disorder caused by either isolated xanthine dehydrogenase (XDH) deficiency (type I) or combined XDH and aldehyde oxidase (AO) deficiency (type II). XDH and AO are evolutionary related enzymes that share a sulfurated molybdopterin cofactor. While the role of XDH in purine metabolism is well established, the physiologic functions of AO are mostly unknown. XDH and AO are important drug metabolizing enzymes. Urine metabolomic analysis by high pressure liquid chromatography and mass spectrometry of xanthinuric patients was performed to unveil physiologic functions of XDH and AO and provide biomarkers for typing xanthinuria. Novel endogenous products of AO, hydantoin propionic acid, N1-methyl-8-oxoguanine and N-(3-acetamidopropyl) pyrrolidin-2-one formed in the histidine, nucleic acid and spermidine metabolic pathways, respectively, were identified as being lowered in type II xanthinuria. Also lowered were the known AO products, N1-methyl-2-pyridone-5-carboxamide and N1-methyl-4-pyridone-5-carboxamide in the nicotinamide degradation pathway. In contrast to the KEGG annotations, the results suggest minor role of human AO in the conversion of pyridoxal to pyridoxate and gentisaldehyde to gentisate in the vitamin B6 and tyrosine metabolic pathways, respectively. The perturbations in purine degradation due to XDH deficiency radiated further from the previously known metabolites, uric acid, xanthine and hypoxanthine to guanine, methyl guanine, xanthosine and inosine. Possible pathophysiological implications of the observed metabolic perturbations are discussed. The identified biomarkers have the potential to replace the allopurinol-loading test used in the past to type xanthinuria, thus facilitating appropriate pharmacogenetic counseling and gene directed search for causative mutations.     

Deletion mutation in Drosophila ma-l homologous, putative molybdopterin cofactor sulfurase gene is associated with bovine xanthinuria type II

Defective xanthine dehydrogenase (XDH) activity in humans results in xanthinuria and xanthine calculus accumulation in kidneys. Bovine xanthinuria was demonstrated in a local herd and characterized as xanthinuria type II, similar to the Drosophila ma-l mutations, which lose activities of molybdoenzymes, XDH, and aldehyde oxidase, although sulfite oxidase activity is preserved. Linkage analysis located the disease locus at the centromeric region of bovine chromosome 24, where a ma-l homologous, putative molybdopterin cofactor sulfurase gene (MCSU) has been physically mapped. We found that a deletion mutation at tyrosine 257 in MCSU is tightly associated with bovine xanthinuria type II.     

Mutation of human molybdenum cofactor sulfurase gene is responsible for classical xanthinuria type II

Drosophila ma-l gene was suggested to encode an enzyme for sulfuration of the desulfo molybdenum cofactor for xanthine dehydrogenase (XDH) and aldehyde oxidase (AO). The human molybdenum cofactor sulfurase (HMCS) gene, the human ma-l homologue, is therefore a candidate gene responsible for classical xanthinuria type II, which involves both XDH and AO deficiencies. However, HMCS has not been identified as yet. In this study, we cloned the HMCS gene from a cDNA library prepared from liver. In two independent patients with classical xanthinuria type II, we identified a C to T base substitution at nucleotide 1255 in the HMCS gene that should cause a CGA (Arg) to TGA (Ter) nonsense substitution at codon 419. A classical xanthinuria type I patient and healthy volunteers lacked this mutation. These results indicate that a functional defect of the HMCS gene is responsible for classical xanthinuria type II, and that HMCS protein functions to provide a sulfur atom for the molybdenum cofactor of XDH and AO.     

Aryl hydrocarbon receptor (AhR)-mediated induction of xanthine oxidase/xanthine dehydrogenase activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), an environmental contaminant, induced xanthine oxidase and xanthine dehydrogenase (XO/XDH) activities, in addition to ethoxyresorufin-O-dealkylase and methoxyresorufin-O-dealkylase activities in liver of mice. When TCDD was given to mice as a single oral dose of 40 microg/kg, the activities of XO and XDH increased about threefold within 3 days and the increased levels were maintained for 4 weeks. The treatment of mice with 3-methylcholanthrene also induced XO/XDH activities, but phenobarbital and dexamethasone had no effect. The level of aldehyde oxidase, a molybdenum flavoenzyme related to XO/XDH, in mouse liver was also enhanced about 1.5-fold by TCDD treatment. The inducing effect of TCDD and 3-methylcholanthrene was not observed in null mice (AhR(-/-)), which lack the AhR gene. XO and XDH activities were induced by TCDD in heterozygous mice (AhR(+/-)). The lipid peroxidation in liver was stimulated by TCDD. The induction of XO and XDH, which produces reactive oxygen species, may contribute to the various toxicities of TCDD.     

Purification and properties of milk xanthine dehydrogenase.

Milk xanthine oxidase (XO) has been prepared in a dehydrogenase form (XDH) by purifying the enzyme in the presence of 2.5 mM dithiothreitol. Unlike XO, which reacts rapidly only with oxygen and not with NAD, the XDH form of the enzyme reacts rapidly with NAD. XDH has a turnover number for the NAD-dependent conversion of xanthine to urate of 380 mol/min/mol at pH 7.5, 25 degrees C, with a Km = < or = 1 microM for xanthine and a Km = 7 microM for NAD, but has very little O2-dependent activity. There is evidence that the two forms of the enzyme have different flavin environments: XDH stabilizes the neutral form of the flavin semiquinone and XO does not. Further, XDH binds the artificial flavin 8-mercapto-FAD in its neutral form, shifting the pK of this flavin by 5 pH units, while XO binds 8-mercapto-FAD in its benzoquinoid anionic form. XDH can be converted back to the XO form by the addition of three to four equivalents of the disulfide-forming reagent 4,4'-dithiodipyridine, suggesting that, in the XDH form of the enzyme, disulfide bonds are broken; this may cause a conformational change which creates a binding site for NAD and changes the protein structure near the flavin.     

Acute inhibition of the endogenous xanthine oxidase improves renal hemodynamics in hypercholesterolemic pigs

Hypercholesterolemia (HC), a major risk factor for onset and progression of renal disease, is associated with increased oxidative stress, potentially causing endothelial dysfunction. One of the sources of superoxide anion is xanthine oxidase (XO), but its contribution to renal endothelial function in HC remains unclear. We tested the hypothesis that XO modulates renal hemodynamics and endothelial function in HC pigs. Four groups (n = 23) of female domestic pigs were studied 12 wk after either normal (n = 11) or HC diet (n = 12). Oxidative stress was assessed by plasma isoprostanes and oxidized LDL, and the XO system by plasma uric acid, urinary xanthine, and renal XO expression (by immunoblotting and immunohistochemistry). Renal hemodynamics and function were studied with electron beam-computed tomography before and after endothelium-dependent (ACh) and -independent (sodium nitroprusside) challenge, during a concurrent intrarenal infusion of either oxypurinol or saline (n = 5-6 in each group). HC showed elevated oxidative stress, higher plasma uric acid (23.8 +/- 3.8 vs. 6.2 +/- 0.8 microM/mM creatinine, P = 0.001), lower urinary xanthine, and greater renal XO expression compared with normal. Inhibition of XO in HC significantly improved the blunted responses to ACh of cortical perfusion (13.5 +/- 12.1 and 37.2 +/- 10.6%, P = 0.01 and P = not significant vs. baseline, respectively), renal blood flow, and glomerular filtration rate; restored medullary perfusion; and improved the blunted cortical perfusion response to sodium nitroprusside. This study demonstrates that the endogenous XO system is activated in swine HC. Furthermore, it suggests an important role for XO in regulation of renal hemodynamics, function, and endothelial function in experimental HC.     

从猕猴肝脏组织扩增黄嘌呤脱氢酶／氧化酶基因片段

RT-PCR扩增猕猴黄嘌呤脱氢酶／氧化酶（XDH／XO）基因片段,为进一步开展相关研究提供实验资料。方法提取猕猴新鲜肝脏组织总RNA,用RT-PCR二步法进行XDH／XO基因片段扩增,对获得的目的片段进行序列测定,与GenBank上发表的人类（Homosapiens）、小鼠（Musmusculus）、家鼠（Rattusnorvegicus）、野猪（Susscrofa）等物种XDH／XO基因进行该序列同源性比对分析,DNAMAN软件预测该段核苷酸的氨基酸序列,Inter-ProScan及SWISS-MODEL工具进行XDH／XO的编码蛋白结构域及功能预测及三维结构构建。结果RT-PCR产物电泳检测得到了与设计大小相一致的目的条带,序列测定共测到683个核苷酸,DNAMAN软件预测该段核苷酸的氨基酸序列包括了1个编码53个氨基酸的开放阅读框（ORF）,通过该软件包中Multiplealignment对目的基因片段的核苷酸序列与NCBI报道的人类、小鼠、家鼠、野猪XDH／XO基因mRNA互补的cDNA核苷酸序列同源性进行同源性比较分析,结果显示所扩增得到的目的片段与人类同源性最高,为95．6％,与小鼠、家鼠、野猪的同源性分别为85．2％、84．3％、86．1％,说明获得的基因片段是猕猴的XDH／XO基因片段,且该基因在物种间具有较高的相似性。生物信息学预测该段XDH／XO编码蛋白含有醛氧化／脱氢酶的钼喋呤结合点结构域及黄嘌呤脱氢酶结构域。结论在体外成功扩增出猕猴XDH／XO基因片段,为进一步开展高尿酸血症致病机理研究,抗高尿酸血症新药研发奠定工作基础。     

Lung redox homeostasis: emerging concepts

This symposium was organized to present some aspects of current research pertaining to lung redox function. Focuses of the symposium were on roles of pulmonary endothelial NADPH oxidase, xanthine oxidase (XO)/xanthine dehydrogenase (XDH), heme oxygenase (HO), transplasma membrane electron transport (TPMET), and the zinc binding protein metallothionein (MT) in the propagation and/or protection of the lung or other organs from oxidative injury. The presentations were chosen to reflect the roles of both intracellular (metallothionein, XO/XDH, and HO) and plasma membrane (NADPH oxidase, XO/XDH, and unidentified TPMET) redox proteins in these processes. Although the lung endothelium was the predominant cell type under consideration, at least some of the proposed mechanisms operate in or affect other cell types and organs as well.     

Radiomodfication of xanthine oxidoreductase system in the liver of mice by phenylmethylsulfonyl fluoride and dithiothreitol

The widely distributed xanthine oxidoreductase (XOR) system has been shown to be modulated upon exposure of animals to ionizing radiation through the conversion of xanthine dehydrogenase (XDH) into xanthine oxidase (XO). In the present work, radiomodification of the XOR system by phenylmethylsulfonyl fluoride (PMSF) and dithiothreitol (DTT) was examined using female Swiss albino mice which were irradiated with gamma rays at a dose rate 0.023 Gy s(-1). PMSF, a serine protease inhibitor, and DTT, the sulfhydryl reagent, were administered intraperitoneally prior to irradiation. The specific activities of XDH and XO as well as the XDH/XO ratio and the total activity (XDH+XO) were determined in the liver of the mice. The inhibition of XO activity, restoration of XDH activity, and increase in the XDH/XO ratio upon administration of PMSF were suggestive of irreversible conversion of XDH into XO mediated through serine proteases. The biochemical events required for the conversion were probably initiated during the early phase of irradiation, as the treatment with PMSF immediately after irradiation did not have a modulatory effect. Interestingly, DTT was not effective in modulating radiation-induced changes in the XOR system or oxidative damage in the liver of mice. The DTT treatment resulted in inhibition of the release of lactate dehydrogenase. However, the protection appears to be unrelated to the formation of TBARS. On the other hand, the presence of PMSF during irradiation inhibited radiation-induced oxidative damage and radiation-induced increases in the specific activity of lactate dehydrogenase. These findings suggest that a major effect of ionizing radiation is irreversible conversion of xanthine to xanthine oxidase.     

Analysis of purines in urinary calculi by high-performance liquid chromatography

A high-pressure liquid chromatography method has been developed for the analysis in urinary calculi of six purines: uric acid, 2, 8-dihydroxyadenine, xanthine, hypoxanthine, allopurinol, and oxypurinol. Separation was conducted isocratically on a reversed-phase column, using 50 mM phosphate buffer (pH 5.5) / methanol (97/3, v/v) as mobile phase. Limits of detection, depending on compound, ranged from 7 to 28 microg/g stone weight. Hitherto, no reports have appeared on other purines present with uric acid in stones, due to lack of a sensitive and specific analytical method. We have now found that all calculi with more than 4% uric acid also contained 1-methyluric and 7-methyluric acids and trace amounts of hypoxanthine, xanthine, and 2,8-dihydroxyadenine. Accurate identification and quantitation of purines in urinary calculi are important for the diagnosis of rare metabolic diseases leading to urolithiasis (xanthinuria, dihydroxyadeninuria), as well as for prevention of iatrogenic complications during treatment with allopurinol of uric acid urolithiasis. The method may be used for reference purposes in clinical laboratories and for research on the pathogenesis of urolithiasis in disorders of purine metabolism.     

Mammalian xanthine oxidoreductase - mechanism of transition from xanthine dehydrogenase to xanthine oxidase

Reactive oxygen species are generated by various biological systems, including NADPH oxidases, xanthine oxidoreductase, and mitochondrial respiratory enzymes, and contribute to many physiological and pathological phenomena. Mammalian xanthine dehydrogenase (XDH) can be converted to xanthine oxidase (XO), which produces both superoxide anion and hydrogen peroxide. Recent X-ray crystallographic and site-directed mutagenesis studies have revealed a highly sophisticated mechanism of conversion from XDH to XO, suggesting that the conversion is not a simple artefact, but rather has a function in mammalian organisms. Furthermore, this transition seems to involve a thermodynamic equilibrium between XDH and XO; disulfide bond formation or proteolysis can then lock the enzyme in the XO form. In this review, we focus on recent advances in our understanding of the mechanism of conversion from XDH to XO.     

Lack of conversion of xanthine dehydrogenase to xanthine oxidase during warm renal ischemia

Irreversible transformation of xanthine dehydrogenase (XDH) to xanthine oxidase (XO) during ischemia was determined measuring XDH and total enzyme activity in kidneys before and after 60 min of clamp of the renal pedicle. Tissue levels of adenine nucleotides, xanthine and hypoxanthine were used as indicators of ischemia. After 60 min of clamping, ATP levels decreased by 72% with respect to controls whereas xanthine and hypoxanthine progressively reached tissue concentrations of 732 +/- 49 and 979 +/- 15 nmol.g tissue-1, respectively. Both total and XDH activities in ischemic kidneys (30 +/- 15 and 19 +/- 1 nmol.min-1.g tissue-1) were significantly lower than in controls when expressed on a tissue weight basis. The fraction of enzyme in the XDH form was however unchanged indicating that the reduction of the nucleotide pool is not accompanied by induction of the type-O activity of xanthine oxidase.     

Phosphorylation of xanthine dehydrogenase/oxidase in hypoxia

The enzyme xanthine oxidase (XO) has been implicated in the pathogenesis of several disease processes, such as ischemia-reperfusion injury, because of its ability to generate reactive oxygen species. The expression of XO and its precursor xanthine dehydrogenase (XDH) is regulated at pre- and posttranslational levels by agents such as lipopolysaccharide and hypoxia. Posttranslational modification of the protein, for example through thiol oxidation or proteolysis, has been shown to be important in converting XDH to XO. The possibility of posttranslational modification of XDH/XO through phosphorylation has not been adequately investigated in mammalian cells, and studies have reported conflicting results. The present report demonstrates that XDH/XO is phosphorylated in rat pulmonary microvascular endothelial cells (RPMEC) and that phosphorylation is greatly increased ( approximately 50-fold) in response to acute hypoxia (4 h). XDH/XO phosphorylation appears to be mediated, at least in part, by casein kinase II and p38 kinase as inhibitors of these kinases partially prevent XDH/XO phosphorylation. In addition, the results indicate that p38 kinase, a stress-activated kinase, becomes activated in response to hypoxia (an approximately 4-fold increase after 1 h of exposure of RPMEC to hypoxia) further supporting a role for this kinase in hypoxia-stimulated XDH/XO phosphorylation. Finally, hypoxia-induced XDH/XO phosphorylation is accompanied by a 2-fold increase in XDH/XO activity, which is prevented by inhibitors of phosphorylation. In summary, this study shows that XDH/XO is phosphorylated in hypoxic RPMEC through a mechanism involving p38 kinase and casein kinase II and that phosphorylation is necessary for hypoxia-induced enzymatic activation.     

Effect of radiation on the xanthine oxidoreductase system in the liver of mice.

The xanthine oxidoreductase system is one of the major sources of free radicals in many pathophysiological conditions. Since ionizing radiations cause cell damage and death, the xanthine oxidoreductase system may contribute to the detrimental effects in irradiated systems. Therefore, modulation of the xanthine oxidoreductase system by radiation has been examined in the present study. Female Swiss albino mice (7-8 weeks old) were irradiated with gamma rays (1-9 Gy) at a dose rate of 0.023 Gy s(-1) and the specific activities of xanthine oxidase (XO) and xanthine dehydrogenase (XDH) were determined in the liver of the animals. The mode and magnitude of change in the specific activities of XO and XDH were found to depend on radiation dose. At doses above 3 Gy, the specific activity of XO increased rapidly and continued to increase with increasing dose. However, the specific activity of XDH was decreased. These findings are suggestive of an inverse relationship between the activity of XO and XDH. The ratio of the activity of XDH to that of XO decreased with radiation dose. However, the total activity (XDH + XO) remained constant at all doses. These results indicate that XDH may be converted into XO. An intermediate form, D/O, appears to be transient in the process of conversion. The enhanced specific activity of XO may cause oxidative stress that contributes to the radiation damage and its persistence in the postirradiation period. Radiation-induced peroxidative damage determined in terms of the formation of TBARS and the change in the specific activity of lactate dehydrogenase support this possibility.     

Mechanisms of action of malondialdehyde and 4-hydroxynonenal on xanthine oxidoreductase

Studies have been made on the possible involvement of malondialdehyde (MDA) and (E)-4-hydroxynon-2-enal (HNE), two terminal compounds of lipid peroxidation, in modifying xanthine oxidoreductase activity through interaction with the oxidase (XO) and/or dehydrogenase (XDH) forms. The effect of the two aldehydes on XO (reversible, XO(rev), and irreversible, XO(irr)) and XDH was studied using xanthine oxidase from milk and xanthine oxidoreductase partially purified from rat liver. The incubation of milk xanthine oxidase with these aldehydes resulted in the inactivation of the enzyme following pseudo-first-order kinetics: enzyme activity was completely abolished by MDA (0.5-4 mM), while residual activity (5% of the starting value) associated with an XO(irr) form was always observed when the enzyme was incubated in the presence of HNE (0.5-4 mM). The addition of glutathione to the incubation mixtures prevented enzyme inactivation by HNE. The study on the xanthine oxidoreductase partially purified from rat liver showed that MDA decreases the total enzyme activity, acting only with the XO forms. On the contrary HNE leaves the same level of total activity but causes the conversion of XDH into an XO(irr) form.     

A Mouse Model of Early-Onset Renal Failure Due to a Xanthine Dehydrogenase Nonsense Mutation

Chronic kidney disease (CKD) is characterized by renal fibrosis that can lead to end-stage renal failure, and studies have supported a strong genetic influence on the risk of developing CKD. However, investigations of the underlying molecular mechanisms are hampered by the lack of suitable hereditary models in animals. We therefore sought to establish hereditary mouse models for CKD and renal fibrosis by investigating mice treated with the chemical mutagen N-ethyl-N-nitrosourea, and identified a mouse with autosomal recessive renal failure, designated RENF. Three-week old RENF mice were smaller than their littermates, whereas at birth they had been of similar size. RENF mice, at 4-weeks of age, had elevated concentrations of plasma urea and creatinine, indicating renal failure, which was associated with small and irregularly shaped kidneys. Genetic studies using DNA from 10 affected mice and 91 single nucleotide polymorphisms mapped the Renf locus to a 5.8Mbp region on chromosome 17E1.3. DNA sequencing of the xanthine dehydrogenase (Xdh) gene revealed a nonsense mutation at codon 26 that co-segregated with affected RENF mice. The Xdh mutation resulted in loss of hepatic XDH and renal Cyclooxygenase-2 (COX-2) expression. XDH mutations in man cause xanthinuria with undetectable plasma uric acid levels and three RENF mice had plasma uric acid levels below the limit of detection. Histological analysis of RENF kidney sections revealed abnormal arrangement of glomeruli, intratubular casts, cellular infiltration in the interstitial space, and interstitial fibrosis. TUNEL analysis of RENF kidney sections showed extensive apoptosis predominantly affecting the tubules. Thus, we have established a mouse model for autosomal recessive early-onset renal failure due to a nonsense mutation in Xdh that is a model for xanthinuria in man. This mouse model could help to increase our understanding of the molecular mechanisms associated with renal fibrosis and the specific roles of XDH and uric acid.     

Modulation of radiation-induced changes in the xanthine oxidoreductase system in the livers of mice by its inhibitors

The xanthine oxidoreductase (XOD) system, which consists of xanthine dehydrogenase (XDH) and xanthine oxidase (XO), is one of the major sources of free radicals in biological systems. The XOD system is present predominantly in the normal tissues as XDH. In damaged tissues, XDH is converted into XO, the form that generates free radicals. Therefore, the XO form of the XOD system is expected to be found mainly in radiolytically damaged tissue. In this case, XO may catalyze the generation of free radicals and potentiate the effect of radiation. Inhibition of the XOD system is likely to attenuate the detrimental effects of ionizing radiation. We have examined this possibility using allopurinol and folic acid, which are known inhibitors of the XOD system. Swiss albino mice (7-8 weeks old) were given single doses of allopurinol and folic acid (12.5-50 mg/kg) intraperitoneally and irradiated with different doses of gamma radiation at a dose rate of 0.023 Gy/s. The XO and XDH activities as well as peroxidative damage and lactate dehydrogenase (LDH) were determined in the liver. An enhancement of the activity of XO and a simultaneous decrease in the activity of XDH were observed at doses above 3 Gy. The decrease in the ratio XDH/XO and the unchanged total activity (XDH + XO) suggested the conversion of XDH into XO. The enhanced activity of XO may potentiate radiation damage. The increased levels of peroxidative damage and the specific activity of LDH in the livers of irradiated mice supported this possibility. Allopurinol and folic acid inhibited the activities of XDH and XO, decreased their ratio (XDH/XO), and lowered the levels of peroxidative damage and the specific activity of LDH. These results suggested that allopurinol and folic acid have the ability to inhibit the radiation-induced changes in the activities of XDH and XO and to attenuate the detrimental effect of this conversion, as is evident from the diminished levels of peroxidative damage and the decreased activity of LDH.     

Identification of a new point mutation in the human xanthine dehydrogenase gene responsible for a case of classical type I xanthinuria

A 60-year-old Japanese man was diagnosed as having hypouricemia at an annual health check-up. The routine laboratory data was not remarkable except that the patient's hypouricemia and plasma levels of xanthine and hypoxanthine were much higher than those of normal subjects. Furthermore, the patient's daily urinary excretion of xanthine and hypoxanthine was markedly increased compared with reference values. The xanthine dehyrogenase activity of the duodenal mucosa was below the limits of detection. Nevertheless, allopurinol was metabolized to oxypurinol in vivo. Based on these findings, a subtype of classical xanthinuria (type I) was diagnosed. The xanthine dehyrogenase protein was detected by Western blotting analysis. Sequencing of the cDNA of the xanthine dehyrogenase obtained from the duodenal mucosa revealed that a point mutation of C to T had occurred in nucleotide 445. This changed codon 149 from CGC (Arg) to TGC (Cys), a finding that has not been previously reported in patients with classical xanthinuria type I.     

Xanthine Oxidase Inhibition by 1,3-dipropyl-8-sulfophenyl-xanthine (DPSPX), an Antagonist of Adenosine Receptors

Xanthine oxidase (XO), an enzyme involved in purine metabolism, is a source of either oxidants (superoxide radical) or antioxidants (uric acid). Interference with XO activity can lead to oxidative stress, thus contributing to the pathogenesis of cardiovascular diseases. The adenosine receptors antagonist, 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), induces hypertension and cardiovascular injury in rats. Since DPSPX is a xanthine, we aimed at evaluating DPSPX's influence on XO activity to ascertain its contribution to DPSPX-induced hypertension. The activity of isolated XO in the presence of DPSPX was evaluated spectrophotometrically. Serum and urinary uric acid levels of DPSPX-treated rats were measured using a commercial kit. DPSPX inhibited XO activity in a concentration-dependent manner and reduced rat serum and urinary uric acid levels. It can be concluded that: DPSPX is an inhibitor of XO; decreased generation of uric acid may lead to oxidative stress, thus contributing to endothelial dysfunction and vascular morphological changes in DPSPX-treated rats.     

Xanthine oxidase inhibition by 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), an antagonist of adenosine receptors

Xanthine oxidase (XO), an enzyme involved in purine metabolism, is a source of either oxidants (superoxide radical) or antioxidants (uric acid). Interference with XO activity can lead to oxidative stress, thus contributing to the pathogenesis of cardiovascular diseases. The adenosine receptors antagonist, 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), induces hypertension and cardiovascular injury in rats. Since DPSPX is a xanthine, we aimed at evaluating DPSPX's influence on XO activity to ascertain its contribution to DPSPX-induced hypertension. The activity of isolated XO in the presence of DPSPX was evaluated spectrophotometrically. Serum and urinary uric acid levels of DPSPX-treated rats were measured using a commercial kit. DPSPX inhibited XO activity in a concentration-dependent manner and reduced rat serum and urinary uric acid levels. It can be concluded that: DPSPX is an inhibitor of XO; decreased generation of uric acid may lead to oxidative stress, thus contributing to endothelial dysfunction and vascular morphological changes in DPSPX-treated rats.