The effect of raw and processed vegetables on colonocyte dna damage.
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Cruciferous vegetables and their bioactive constituents have been shown to inhibit chemically induced colon cancer (IARC, 2004). However, the results of epidemiological studies have been inconsistent (IARC, 2004). This may reflect a lack of sensitivity of such studies. One factor that is often overlooked by epidemiological studies is the effect of processing. Processing may alter the content of the bioactive compounds present in cruciferous vegetables or their bioavailability. Cruciferous vegetables contain numerous bioactive compounds, but their anticarcinogenic properties have been mainly attributed to their content of glucosinolates (GLS). The breakdown of GLS to their bioactive products is largely dependent on the plant enzyme myrosinase, whereas the profile of products formed, depends on the parent GLS, conditions of hydrolysis and the presence of a cofactor, epithiospecifier protein (ESP). Thermal processing may inactivate myrosinase and ESP thereby altering the location and extent of GLS breakdown within the GI tract and the profile of breakdown products formed. This may in turn, determine whether cruciferous vegetables exert beneficial or detrimental effects. A pig feeding trial was conducted to investigate the effect of blanch-freezing on the ability of broccoli (600 g/d; 12 d) to influence putative intermediary biomarkers of colon cancer, including DNA damage in colonocytes, the xenobiotic metabolising enzyme (XME) system, the colonic microflora and SCFA concentrations. The consumption of raw broccoli (cv. Marathon) caused a significant 27% increase in DNA strand breakage (measured by the „comet assay‟) in colonocytes (P=0.025), whereas blanched-frozen broccoli had no significant effect. Both broccoli diets had no significant effect on XME or the concentration of SCFA, but they caused an increase in the ratio of lactobacilli to coliforms of borderline significance (P=0.065). A second trial was conducted to further investigate the effect of raw broccoli consumption. Pigs were fed a different cultivar of raw broccoli (cv. Monaco) or raw carrots (cv. Nairobi). Carrots were fed to explore whether a raw vegetable high in antioxidants but devoid of GLS would influence colonocyte DNA damage. Results were similar to the first experiment, raw broccoli caused a significant 54% increase in DNA strand breakage (P<0.001), whereas raw carrots had no significant effect; both raw vegetables caused a significant increase in the ratio of lactobacilli to coliforms (P<0.001, broccoli; P=0.002, carrots), but had no effect on other measures. These studies appear to be the first to report that raw broccoli consumption causes an increase in DNA strand breakage in colonocytes. Collectively, they suggest that the consumption of high intakes of raw broccoli may not be advisable.