DNA repair as a biomarker in human biomonitoring studies; further applications of the comet assay.

DNA repair plays a major role in maintaining genetic stability, and so measurement of individual DNA repair capacity should be a valued tool in molecular epidemiology studies. The comet assay (single cell gel electrophoresis), in different versions, is commonly used to measure the repair pathways represented by strand break rejoining, removal of 8-oxoguanine, and repair of bulky adducts or UV-induced damage. Repair enzyme activity generally does not reflect the level of gene expression; but there is evidence - albeit piecemeal - that it is affected by polymorphisms in repair genes. There are mixed reports concerning the regulation of repair by environmental factors; several nutritional supplementation trials with phytochemical-rich foods have demonstrated increases in base excision repair of oxidation damage, while others have shown no effect. Exposure to genotoxic agents has in general not been found to stimulate repair. Crucial questions concerning the factors regulating repair and the causes of individual variation are as yet unanswered.