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The comet assay and the kiwi fruit

 The research group of Andrew Collins has played a leading role in the development and application of the comet assay over a period of almost two decades, first at the Rowett Research Institute, Aberdeen, and now at the University of Oslo.  For nearly a decade, the comet assay has been a crucial tool in the biomonitoring field (Dusinska and Collins, 2008). 

The comet assay is the method of choice for measuring DNA damage, of various sorts, in human cells.  Human-cell samples which have been obtained in the course of population-based studies of environmental and occupational exposure to different genotoxic agents, including radiation, chemicals and oxidative stress can be used in the comet assay.  The comet assay is noted for its versatility and the breadth of its possible applications. 

Here, a human intervention trial involving twenty-four men and women who consumed additional portions of the golden kiwifruit, Actinidia chinensis, were analysed biologically.  The recently available golden kiwifruit differs significantly in phytochemical make-up with 20% higher vitamin C content than the green kiwifruit (Ferguson, 2003).  Based on this and other phytochemical properties, the golden kiwifruit would be expected to show stronger protection against effects of oxidative damage in vivo.  To test this hypothesis, a human dietary intervention trial with golden kiwifruit was performed, examining potential effects on platelet function, plasma antioxidant status, DNA oxidation, base excision repair and nucleotide excision repair activity.

The comet assay was used to measure DNA strand breaks. Mononuclear cells from the patients were subjected to the comet assay and DNA loops containing breaks extended under electrophoresis to form 'comet tails'. The relative intensity of DNA in the tail indicated the DNA break frequency.  The tail intensity was assessed; 100 comets selected at random were graded according to their degree of damage.  However, this study concluded, using the comet assay, that neither DNA base excision nor nucleotide excision repair were influenced in humans by kiwifruit consumption.  Nevertheless, golden kiwifruit consumption does strengthen resistance towards endogenous oxidative damage. 

Regular intake of golden kiwifruit can protect against lymphocyte DNA oxidation as well as increase total antioxidant activity and specifically plasma vitamin C. Regular golden kiwifruit consumption can also reduce platelet aggregation, and lower plasma triglycerides. Consumption of these fruits could therefore benefit public health by countering oxidative stress factors and by reducing the risk of thrombotic events mediated by platelet activation.

This case study is based on:
Supplementation of a western diet with golden kiwifruits (Actinidia chinensis var.'Hort 16A':) effects on biomarkers of oxidation damage and antioxidant protection.
Brevik A, Gaivão I, Medin T, Jørgenesen A, Piasek A, Elilasson J, Karlsen A, Blomhoff R, Veggan T, Duttaroy AK, Collins AR. Nutr J. 2011 May 18;10:54.

Additional references:
Dusinska M, Collins AR The comet assay in human biomonitoring: gene-environment interactions.  Mutagenesis 23:3, 191–205, 2008.
Ferguson AR, Fillion L. Are kiwifruit really good for you? Acta Horticulturae. 610:131–135. 2003.