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Identification of mucosal abnormalities is aided by the use of dyes during colonoscopy (chromoendoscopy).1 Two dyes that have found particular favour are methylene blue and indigo carmine.2,3
Methylene blue, which, unlike indigo carmine, is taken up by cells, induces cellular DNA damage in vitro via the generation of singlet oxygen when photoexcited by white light.4 In contrast, indigo carmine appears to be photostable and to possess little potential to damage genetic material in vitro.5,6 A recent clinical study has shown that the extent of DNA damage (particularly oxidative DNA damage) in human oesophageal cells is increased after methylene blue chromoendoscopy.7 Additional iatrogenic oxidative DNA damage to epithelial cells is of particular concern in such precancerous tissue because of the association between oxidative DNA damage, mutagenesis and the development of malignancy.8 We hypothesised that indigo carmine would induce less DNA damage than methylene blue both in vitro in cultured colon cells during simulated chromoendoscopy conditions and in vivo in colonic biopsy samples collected at chromoendoscopy.
We used the alkaline comet assay …
Funding: This research was supported by a local research grant from the Leeds Teaching Hospitals NHS Trust.
Competing interests: None.
Ethical approval was given by the Harrogate Local Research Ethics Committee to collect biopsy samples from 20 patients undergoing elective sigmoidoscopic and colonoscopic examinations for a variety of clinical indications at the Endoscopy Department at The General Infirmary at Leeds (Ethics reference number 04/Q1107/16).
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