Clinical Chemistry Siemens Point of Care - Urinalysis
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Clinical Chemistry 51: 1493-1498, 2005. First published May 26, 2005; 10.1373/clinchem.2005.048033
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(Clinical Chemistry. 2005;51:1493-1498.)
© 2005 American Association for Clinical Chemistry, Inc.

General Clinical Chemistry

Methylated Purines in Urinary Stones

Krzysztof Safranowa and Zygmunt Machoy

1 Department of Biochemistry and Chemistry, Pomeranian Medical University, Szczecin, Poland.

aAddress correspondence to this author at: Department of Biochemistry and Chemistry, Pomeranian Medical University, Powstancow Wielkopolskich 72 70-111 Szczecin, Poland. Fax 48-91-4661516; e-mail chrissaf{at}mp.pl.

Background: The aim of the study was to measure the content of methylated purines that appear as admixtures in uric acid stones.

Methods: We analyzed urinary calculi from 48 residents of Western Pomerania who underwent surgery at the urology ward in Szczecin. Stone samples were dissolved in 0.1 mol/L NaOH. Extracts were diluted in 50 mmol/L KH2PO4 and analyzed by reversed-phase HPLC with ultraviolet detection and use of a gradient of methanol concentration and pH.

Results: Uric acid was the main component of 9 stones. All 9 showed admixtures of 9 other purine derivatives: endogenous purine breakdown products (xanthine, hypoxanthine, and 2,8-dihydroxyadenine) and exogenous methyl derivatives of uric acid and xanthine (1-, 3-, and 7-methyluric acid; 1,3-dimethyluric acid; and 3- and 7-methylxanthine). Amounts of these purine derivatives ranged from the limit of detection to 12 mg/g of stone weight and showed a strong positive correlation (Spearman rank correlation coefficients, 0.63–0.94) with the uric acid content of the samples. The main methylated purine in the stones was 1-methyluric acid.

Conclusions: Urinary purines at concentrations below their saturation limits may coprecipitate in samples supersaturated with uric acid and appear as admixtures in urinary stones. The amount of each purine depends on its average urinary excretion, similarity to the chemical structure of uric acid, and concentration of the latter in the stone. These findings suggest that purines in stones represent a substitutional solid solution with uric acid as solvent. Methylxanthines, which are ubiquitous components of the diet, drugs, and uric acid calculi, may be involved in the pathogenesis of urolithiasis.






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