Towards consensus in the analysis of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine as a non-invasive biomarker of oxidative stress

Of the DNA-derived biomarkers of oxidative stress, urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) is the most frequently measured. However, there is significant discrepancy between chromatographic and immunoassay approaches, and intratechnique agreement among all available chromatography-based assays and ELISAs is yet to be established. This is a significant obstacle to their use in large molecular epidemiological studies. To evaluate the accuracy of intra/intertechnique and interlaboratory measurements, samples of phosphate buffered saline and urine, spiked with different concentrations of 8-oxoG, together with a series of urine samples from healthy individuals were distributed to ESCULA members. All laboratories received identical samples, including 2 negative controls that contained no added 8-oxodG. Data were returned from 17 laboratories, representing 20 methods, broadly classified as mass spectrometric (MS), electrochemical detection (EC), or enzyme-linked immunosorbant assay (ELISA). Overall, there was good within-technique agreement, with the majority of laboratories' results lying within 1 sd of their consensus mean. However, ELISA showed more within-technique variation than did the chromatographic techniques and, for the urine samples, reported higher values. Bland-Altman plots revealed good agreement between MS and EC methods but concentration-dependent deviation for ELISA. All methods ranked urine samples according to concentration similarly. Creatinine levels are routinely used as a correction factor for urine concentration, and therefore we also conducted an interlaboratory comparison of methods for urinary creatinine determination, in which the vast majority of values lay within 1 sd of the consensus value, irrespective of the analysis procedure. This study reveals greater consensus than previously expected, although concern remains over ELISA.-ESCULA [European Standards Committee on Urinary (DNA) Lesion Analysis], Evans, M. D., Olinski, R., Loft, S., Cooke, M. S. Toward consensus in the analysis of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine as a noninvasive biomarker of oxidative stress. Some of the authors of this paper are partners in, and this work was partly supported by, ECNIS (Environmental Cancer Risk, Nutrition and Individual Susceptibility), a Network of Excellence operating within the European Union 6th Framework Program, Priority 5: Food Quality and Safety (contract 513943)