DNA integrity under alkaline conditions: An investigation of factors affecting the comet assay

Abstract

The effect of pH on DNA integrity was assessed using a three-step approach. The comet assay was used on a whole genome level, with three different protocols: neutral (no alkaline unwinding), flash (pH 12.5 with 2.5 min unwinding), and the conventional alkaline protocol (pH>13 with 40 min unwinding). Real-time quantitative PCR (RT-qPCR) was then used to study the isolated DNA, revealing that gene amplification decreased with increasing pH, indicating DNA degradation. Specially designed molecular beacons were used to examine DNA at the molecular level, with or without alkali-labile site (ALS) insertions. At pH 12.5, fluorescence in the hairpins with ALS started to increase after 30 min, while at pH> 13, this increase was already observed after 5 min, indicating a significant increase in DNA strand breaks. Liquid chromatography analysis was also used, demonstrating that the hairpins remained intact up to pH 10, even after 1 h exposure, whereas, at pH 12.5, partial conversion into strand breaks occurred after 30 min. At pH> 13, the hairpins were almost completely degraded after 30 min. The flash protocol effectively detects DNA single- and double-strand breaks and identified these damages after 2.5 min of alkaline treatment at pH 12.5. When the hairpins were exposed to pH 12.5 for 60 min, ALS were converted to strand breaks, demonstrating the sensitivity of this approach to detect changes in DNA structure. These findings indicate that pH poses a substantial risk to DNA integrity, leading to significantly higher background levels of DNA damage compared to conditions closer to neutrality. Our study demonstrates the importance of understanding the influence of pH on DNA stability and provides insights into risks associated with alkaline environments, especially at pH> 13.

Keywords: Alkali-labile sites; Comet assay; Flash comet; Molecular beacons; RT-qPCR; UHPLC-UV.