Imidazopurinones are markers of physiological genomic damage linked to DNA instability and glyoxalase 1-associated tumour multidrug resistance.

Glyoxal and methylglyoxal are reactive dicarbonyl metabolites formed and metabolized in physiological systems. Increased exposure to these dicarbonyls is linked to mutagenesis and cytotoxicity and enhanced dicarbonyl metabolism by overexpression of glyoxalase 1 is linked to tumour multidrug resistance in cancer chemotherapy. We report herein that glycation of DNA by glyoxal and methylglyoxal produces a quantitatively important class of nucleotide adduct in physiological systems-imidazopurinones. The adduct derived from methylglyoxal-3-(2'-deoxyribosyl)-6,7-dihydro-6,7-dihydroxy-6/7-methylimidazo-[2,3-b]purine-9(8)one isomers-was the major quantitative adduct detected in mononuclear leukocytes in vivo and tumour cell lines in vitro. It was linked to frequency of DNA strand breaks and increased markedly during apoptosis induced by a cell permeable glyoxalase 1 inhibitor. Unexpectedly, the DNA content of methylglyoxal-derived imidazopurinone and oxidative marker 7,8-dihydro-8-oxo-2'-deoxyguanosine were increased moderately in glyoxalase 1-linked multidrug resistant tumour cell lines. Together these findings suggest that imidazopurinones are a major type of endogenous DNA damage and glyoxalase 1 overexpression in tumour cells strives to counter increased imidazopurinone formation in tumour cells likely linked to their high glycolytic activity.

Simultaneous electrochemical monitoring of metabolites related to the xanthine oxidase pathway using a grinded carbon electrode.

Using a mechanically grinded pyrolytic graphite electrode in edge orientation, a sensitive electrochemical method was developed for simultaneous determination of uric acid (UA), xanthine (XAN), hypoxanthine (HYP) (products of purine catabolism in human), allopurinol (ALO), and oxypurinol (OXY) (a drug used in treatment of purine catabolism disorders and its metabolite, respectively). It is demonstrated that differential pulse voltammetry in connection with this electrode can serve as a simple and efficient tool for monitoring transformation of purine catabolites (HYP --> XAN --> UA) catalyzed by xanthine oxidase (XO) as well as inhibition of this pathway by ALO being enzymatically converted to OXY. Our protocol is based on direct electrochemical measurement of oxidation peaks for each of the substances during in vitro reactions in a single detection step by the same electrode system. In addition, we show that the proposed electrochemical technique can be applied to parallel detection of metabolites involved in the XO pathway excreted in urine without any pretreatment of the clinical samples.

[Ischemia and reperfusion: the production and release of malondialdehyde, oxypurines and nucleosides in the isolated rat heart]. / Ischemia e riperfusione: produzione e rilascio di malondialdeide, ossipurine e nucleosidi nel cuore isolato di ratto.

Ischemia and reperfusion damage has been evaluated by determining the sum of adenine nucleotides, nucleosides, oxypurines and the concentration of malondialdehyde, ascorbic acid, lactate and pyruvate in the isolated rat heart subjected to global normothermic ischemia and subsequent reperfusion. In addition, the sum of oxypurines and nucleosides, and the concentration of malondialdehyde has been determined in the perfusate collected during the reperfusion. Data indicate that ischemia and reperfusion induce an oxidative stress to myocardial tissue (increase of tissue malondialdehyde and decrease of ascorbic acid, and release of malondialdehyde during reperfusion) that, due to the output of relevant amount of oxypurines (congruent to 6.7 mumol/g dry weight) and of nucleosides (congruent to 7.0 mumol/30/min/g dry weight), it is not even able to restore its energy metabolism after reperfusion.

Direct injection/h.p.l.c. methods for the analysis of drugs in biological samples.

1. Direct injection h.p.l.c. methods for zaprinast, and pantoprazole and its sulphone metabolite were developed. 2. Optimal recovery of pantoprazole and its sulphone metabolite was effected by the absence of transfer losses and the effective adjustment of sample pH on-line. 3. Acetonitrile reduced the recovery of pantoprazole and its sulphone metabolite at acetonitrile concentrations greater than 5% in serum. 4. Direct injection h.p.l.c. methods minimize sample handling losses, reduce human contact with biological samples and are sufficiently accurate and reproducible to be used to support pharmacodynamic and toxicokinetic studies.

Simultaneous determination of inosine, hypoxanthine, xanthine, and uric acid and the effect of metal chelators.

We describe a sensitive, reproducible method for the simultaneous determination of the ATP catabolites inosine, hypoxanthine, xanthine, and uric acid in biological samples and organ perfusate using reverse-phase chromatography and multiwavelength detection at 254, 270, and 292 nm. Sample preparation includes precipitating proteins with perchloric acid, neutralizing the sample, passing the supernatant over a polyethyleneimine column, and analyzing the collected fractions by high-performance liquid chromatography. Addition of metal chelators to the perchloric acid resulted in increased values for xanthine, hypoxanthine, and uric acid. The method was sensitive (limit of detection, 0.08 nmol on column; S/N = 4) and linear over the range 0.5-30 microM. Precision and accuracy of the method were evaluated for lung tissue and lung perfusate. Coefficients of variation ranged from 2.8 to 6.1% for perfusate and from 1.7 to 12.6% for tissue. Recoveries for all compounds exceeded 90%. We applied this method to rat lung tissue, lung perfusate, and rat and human blood. Advantages of this method are simultaneous quantitation with excellent sensitivity of all compounds, simplified peak identification by using multiwavelength detection, and improved accuracy by preventing loss of compounds with metal chelators.