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Methylene blue but not indigo carmine causes DNA damage to colonocytes in vitro and in vivo at concentrations used in clinical chromoendoscopy
  1. J Davies1,
  2. D Burke2,
  3. J R Olliver3,
  4. L J Hardie3,
  5. C P Wild3,
  6. M N Routledge3
  1. 1Molecular Epidemiology Unit, Centre for Epidemiology and Biostatistics, Leeds Institute for Genetics Health and Therapeutics, The LIGHT Laboratories, University of Leeds, Leeds, UK
  2. 2Academic Unit of Surgery, The General Infirmary at Leeds, Leeds, UK
  3. 3Molecular Epidemiology Unit, Centre for Epidemiology and Biostatistics, Leeds Institute for Genetics Health and Therapeutics, The LIGHT Laboratories, University of Leeds, Leeds, UK
  1. Correspondence to:
    M N Routledge
    Molecular Epidemiology Unit, Centre for Epidemiology and Biostatistics, Leeds Institute for Genetics Health and Therapeutics, The LIGHT Laboratories, University of Leeds, Leeds LS2 9JT, UK; medmnr{at}leeds.ac.uk

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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 …

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