The effect of raw and processed vegetables on colonocyte dna damage.
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 attributed mainly to their content of glucosinolates (GLS). The breakdown of GLS into their bioactive products is largely dependent on the plant enzyme myrosinase; in contrast, 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 deactivate myrosinase and ESP, thereby altering both the location and extent of GLS breakdown within the GI tract, and also the profile of breakdown products formed. This in turn may determine whether cruciferous vegetables exert beneficial or detrimental effects. A pig-feeding trial was conducted in order 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. These biomarkers included 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 blanch-frozen broccoli had no significant effect. Both broccoli diets had no significant effect on XME or the concentration of SCFA, but they did cause 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 used in order to explore whether a raw vegetable that was 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.
LYNN, A. 2011. The effect of raw and processed vegetables on colonocyte dna damage. Robert Gordon University, PhD thesis.
|Deposit Date||Aug 22, 2011|
|Publicly Available Date||Aug 22, 2011|
LYNN 2011 Effect of raw and processed vegetables
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Copyright: the author and Robert Gordon University