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Supplement: WALTHAM International Science Symposium: Nature, Nurture, and the Case for Nutrition

Application of the Comet Assay for Investigation of Oxidative DNA Damage in Equine Peripheral Blood Mononuclear Cells^1,2

David J. Marlin³, Lucy Johnson, Demelza A. Kingston, Nicola C. Smith, Chris M. Deaton, Sarah Mann, Paul Heaton, Fenneke Van Vugt, Kelly Saunders^*, Julia Kydd^* and Pat A. Harris

Centers for Equine Studies and ^* Preventive Medicine, Animal Health Trust, Kentford, Newmarket, Suffolk, CB8 7UU, UK and Equine Studies Group, WALTHAM Centre for Pet Nutrition, Waltham-on-the-Wolds, Leicestershire LE14 4RT, UK

³ To whom correspondence should be addressed. E-mail: david.marlin{at}aht.org.uk.

Oxidative stress occurs when antioxidant defense mechanisms are overwhelmed by free radicals and may lead to DNA damage, which has been implicated in processes such as aging and diseases such as cancer. The two main techniques presently used to quantify DNA damage are measurement of 8-hydroxydeoxyguanosine and the Comet assay (also known as single-cell gel electrophoresis). The aim of this study was to apply the comet assay to equine peripheral blood mononuclear cells (PBMCs) and identify two conditions in which we hypothesized that oxidative DNA damage would be increased in PBMCs: aging and equine recurrent airway obstruction (RAO, a condition similar to human asthma). The images obtained were similar to those previously published for humans, cats, and dogs. The optimum concentration of H₂O₂ to estimate susceptibility to exogenous damage was 50 µM. Mean intraassay coefficients of variation were 4.7 and 9.7% for endogenous and exogenous tail-DNA quantities, respectively, and 7.3 and 8.3%, respectively, for interassay coefficients. There was no significant difference in either endogenous or exogenous percentages of tail DNA for samples collected from six ponies on three consecutive days. There was no significant difference in endogenous, exogenous, or exogenous (corrected for endogenous) oxidative DNA damage between mature and aged ponies. However, young pony foals had significantly less endogenous DNA damage than mature or aged ponies (P < 0.05). RAO-affected horses without airway inflammation (i.e., in clinical remission) had significantly greater endogenous damage compared with non-RAO–affected control animals (P = 0.009). There was a significant correlation between endogenous percentage of tail DNA in PBMCs and red blood cell hemolysate glutathione concentration (r = 0.720; P < 0.001). In conclusion, the comet assay appears to be suitable for investigating DNA damage in equine PBMCs.

KEY WORDS: • single-cell gel electrophoresis • horse • recurrent airway obstruction • aging • foals