The OECD Test Guideline 489 describes the in vivo alkaline comet assay, also known as the single-cell gel electrophoresis assay, used for detecting breaks in DNA strand post exposure to a potentially genotoxic test chemical. These breaks may be found in cells or nuclei isolated from multiple tissues of animals, typically in rodents.

Under strongly alkaline conditions, the assay can detect single- and double-strand DNA breaks arising from direct interactions with DNA, alkali-labile sites, or transient strand breaks associated with DNA excision repair.

In the assay, animals are exposed to the test chemical, after which specific tissues are collected and processed to obtain single-cell or nuclei suspensions. The cells or nuclei are embedded in agar, lysed to remove cellular and nuclear membranes, and exposed to strong alkaline conditions to unwind the DNA and release relaxed DNA loops and fragments.

The exposed DNA undergoes electrophoresis, with the intact DNA largely remaining at the original nuclear position, while the fragmented DNA and relaxed DNA loops migrate towards the anode, producing the characteristic “comet” appearance. DNA migration is visualized using fluorescent staining and analysed microscopically. The percentage of DNA present in the comet tail (% tail DNA or % tail intensity) is a recommended endpoint for assessing the extent of DNA damage.

Vipragen Biosciences offers Mammalian Alkaline Comet Assay testing in accordance with OECD TG 489 as part of its in vivo genetic toxicology testing services.