Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

With the use of combination chemotherapy as well as a wide range of symptomatic therapies (e.g. analgesics and antiemetics) for the treatment of patients with cancer, the field of oncology practises polypharmacy to an extreme degree. The risk for a drug interaction under these conditions is high, and the pharmacological characteristics of the anti-cancer drugs, such as steep dose-response curves, low therapeutic indices and severe toxicities, suggest that even small changes in the pharmacokinetic profile of the affected drug could significantly alter its toxicity or efficacy. In this review, drug interactions which quantitatively affect the absorption, distribution, biotransformation or excretion of the commonly used anticancer drugs are described. Most of the significant drug interactions involving this class of drugs occur at the level of biotransformation and excretion. For example, the renal excretion of methotrexate by glomerular filtration and tubular secretion is affected by a number of weak organic acids, such as probenecid, salicylates and penicillin, which compete for tubular secretion, resulting in delayed clearance of methotrexate. The best described example of an interaction at the level of biotransformation is the effect of allopurinol on the catabolism of 6-mercaptopurine. By inhibiting xanthine oxidase, allopurinol blocks the first-pass metabolism of 6-mercaptopurine following its oral administration, leading to a 4- to 5-fold increase in plasma concentrations. Known drug interactions may potentially be used to enhance the antitumour activity of a drug--for instance, the administration of tetrahydrouridine (a cytidine deaminase inhibitor) with cytarabine in an attempt to block its rapid inactivation to uridine arabinoside. Overall, little information is available concerning the pharmacokinetic interactions of anticancer drugs with each other and with other classes of drugs in man, in part because the high incidence of toxicity and treatment failure, and empirical dosing methods, obscure the recognition of possible interactions. Awareness on the part of the clinician and more extensive pharmacokinetic investigation will be needed to recognise, document and avoid potentially harmful pharmacokinetic drug interactions involving this class of drugs.
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PMID:Pharmacokinetic drug interactions of commonly used anticancer drugs. 242 30

The effect of reactive oxygen species (ROS) generated by a xanthine oxidase hypoxanthine system (mainly H2O2) on proteoglycan (PG) metabolism and structure was investigated in vitro, using cell monolayers of cultured rabbit articular chondrocytes and purified resident and newly synthesized proteoglycans. It was shown that ROS generated in this system frequently stimulate (at low concentrations), and consistently inhibit (at higher concentrations), the incorporation of 35SO4 and 3H-glucosamine into PG molecules synthesized by cultured chondrocytes. The inhibition of isotopes' incorporation at higher enzyme concentrations was suppressed completely by heating xanthine oxidase and allopurinol with superoxide dismutase (SOD) and catalase. ROS at high concentration also inhibited 3H-uridine incorporation but had no effect on 35SO4 and 3H-uridine uptake by the cells. They also alter hyaluronan (HA) and PG monomers by fragmenting the core protein moiety and destroying the hyaluronic acid binding region. Altered PG monomers do not interact with HA to form complexes, but fragmented HA still retain a significant PG monomer-binding capacity. PG-HA complexes are easily and irreversibly destroyed by ROS. These results suggest that ROS may at low fluxes stimulate PG-synthesis under physiological conditions and alter cartilage metabolism and structure in conditions where they are overproduced, such as in rheumatoid arthritis, and in hemochromatosis and other iron storage diseases.
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PMID:Effect of reactive oxygen species on the biosynthesis and structure of newly synthesized proteoglycans. 800 11

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.
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PMID:Effect of TEI-6720, a xanthine oxidase inhibitor, on the nucleoside transport in the lung cancer cell line A549. 1062 41

We investigated the relationship between the toxic effect of allopurinol and pyrimidine metabolism in mice. Allopurinol-induced increases in plasma transaminase levels in dinitrofluorobenzene (DNFB)-sensitized mice were not affected by uridine. In contrast, plasma creatinine and BUN tended to decrease 18 hr after the last injection of uridine. Both plasma and urinary orotidine (OD) were detected in DNFB-sensitized mice after administration of a single dose of allopurinol. In contrast, TEI-6720, a newly synthesized xanthine oxidase/xanthine dehydrogenase inhibitor, caused neither pyrimidine metabolism abnormality nor renal impairment in DNFB-sensitized mice. Also, normal mice administered high doses of allopurinol showed abnormal pyrimidine metabolism together with renal toxicity which could be ameliorated by uridine, indicating that allopurinol essentially causes pyrimidine metabolism abnormality leading to renal impairment. In DNFB-sensitized mice, allopurinol increased urinary OD excretion to an extent similar to that in normal mice administered the same dose of allopurinol. However, renal impairment by allopurinol was more striking in DNFB-sensitized mice than in normal mice. Histopathological observations showed that allopurinol induced calculus formation in the collecting tubules and papillary duct. Calculus formation was increased by DNFB and decreased by uridine. These observations indicate that the enhancement of the renal toxicity of allopurinol by DNFB-sensitization may be due to some biological interactions between DNFB and allopurinol. In humans, it is possible that there are some biological interactions which serve to enhance the toxicity of allopurinol, resulting in the development of allopurinol hypersensitivity syndrome (AHS). In contrast, TEI-6720, had no effect on pyrimidine metabolism and showed no toxic effect.
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PMID:Allopurinol induces renal toxicity by impairing pyrimidine metabolism in mice. 1082 45

Purines and pyrimidines are of interest owing to their significance in processes in living organisms. Mass spectrometry is a promising analytical tool utilized in their analysis. Two atmospheric pressure ionization (API) methods (electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)) in both negative and positive modes applied to selected purine and pyrimidine metabolites (markers of inherited metabolic disorders) were studied. APCI is less sensitive to alkali metal cations present in a sample and offers higher response than ESI for studied compounds. Both of the techniques afford quasi-molecular ions, but fragmentation also occurs to a certain extent. However, the application of collision-induced dissociation of quasi-molecular ions is essential to confirm a certain metabolite in a sample. Fragmentation of both positive and negative ions was evaluated using multi-stage mass spectrometric experiments. Typical neutral losses correspond to molecules NH(3), H(2)O, HCN, CO, H(2)NCN, HNCO and CO(2). The ion [NCO](-) arises in the negative mode. The cleavage of the glycosidic C-N bond is characteristic for relevant metabolites. Other neutral losses (CH(2)O, C(2)H(4)O(2) and C(3)H(6)O(3)) originate from fragmentation of the glycosidic part of the molecules. In addition to fragmentation, the formation of adducts of some ions with applied solvents (H(2)O, CH(3)OH) was observed. The composition of the solution infused into the ion source affects the appearance of the mass spectra. Tandem mass spectra allow one to distinguish compounds with the same molecular mass (uridine-pseudouridine and adenosine-2'-deoxyguanosine). Flow injection analysis APCI-MS/MS was tested on model samples of human urines corresponding to adenosine deaminase deficiency and xanthine oxidase deficiency. In both cases, the results showed potential diagnostic usefulness.
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PMID:Atmospheric pressure ionization mass spectrometry of purine and pyrimidine markers of inherited metabolic disorders. 1248 84

The prevalence of obesity in adults and children is rapidly increasing across the world. Several general (patho)physiological alterations associated with obesity have been described, but the specific impact of these alterations on drug metabolism and elimination and its consequences for drug dosing remains largely unknown. In order to broaden our knowledge of this area, we have reviewed and summarized clinical studies that reported clearance values of drugs in both obese and non-obese patients. Studies were classified according to their most important metabolic or elimination pathway. This resulted in a structured review of the impact of obesity on metabolic and elimination processes, including phase I metabolism, phase II metabolism, liver blood flow, glomerular filtration and tubular processes. This literature study shows that the influence of obesity on drug metabolism and elimination greatly differs per specific metabolic or elimination pathway. Clearance of cytochrome P450 (CYP) 3A4 substrates is lower in obese as compared with non-obese patients. In contrast, clearance of drugs primarily metabolized by uridine diphosphate glucuronosyltransferase (UGT), glomerular filtration and/or tubular-mediated mechanisms, xanthine oxidase, N-acetyltransferase or CYP2E1 appears higher in obese versus non-obese patients. Additionally, in obese patients, trends indicating higher clearance values were seen for drugs metabolized via CYP1A2, CYP2C9, CYP2C19 and CYP2D6, while studies on high-extraction-ratio drugs showed somewhat inconclusive results. Very limited information is available in obese children, which prevents a direct comparison between data obtained in obese children and obese adults. Future clinical studies, especially in children, adolescents and morbidly obese individuals, are needed to extend our knowledge in this clinically important area of adult and paediatric clinical pharmacology.
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PMID:Impact of obesity on drug metabolism and elimination in adults and children. 2244 19