Simultaneous Determination of Genomic DNA Methylation and Uracil Misincorporation

Objective: To develop a method for the simultaneous measurement of 5-methylcytosine (5-metC) and 2'-deoxyuridine monophosphate (dU). Materials and Methods: Genomic DNA was extracted from the HepG2 cell line grown in experimental complete medium or in folate-depleted medium. Samples were treated with RNAse A and RNAse T1 to avoid any RNA contamination. High-performance liquid chromatography (HPLC)/electrospray ionization mass spectrometric (ESI-MS) method was used to separate nucleotides after enzymatic hydrolysis of DNA with nuclease P1, phosphodiesterase I and alkaline phosphatase. Results: Using this sensitive new methodology, we were able to quantify simultaneously the concentration of DNA-5-metC and DNA-uracil in DNA. The linear correlation coefficient (R 2) between the MS signal and the concentration of 5-metC in a range of 0.5-5 mu M or dU in a range of 10-100 mu M was 0.9954 and 0.9999, respectively. The coefficient of variation was 16.94 and 14.77%, respectively. The applicability of this assay is demonstrated by detection of a decrease in 5-metC% and elevation of dU/thymidylate (dT) into genomic DNA extracted from the HepG2 cell line grown in a folate-depleted medium. Conclusion: Our results confirm that the HPLC/ESI-MS method reported earlier for measuring 5-metC allows measurement of uracil misincorporation into DNA. Copyright (C) 2009 S. Karger AG, Basel