Dietary modulation of colon cancer risk: the roles of fat, fiber and calcium

Mutagenicity and cytotoxicity of fruits and vegetables evaluated by the Ames test and 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay / Mutagenicidad y citotoxicidad de frutas y vegetales evaluadas por el test de Ames y el ensayo del bromuro de 3-(4,5-dimetiltiazol-2-il)-2,5-difeniltetrazolio (MTT)

The mutagenic and cytotoxic activity of the aqueous (H2O) and ethanolic (EtOH) extracts of fruits and vegetables were studied by the Ames test and the MTT assay. A significant mutagenic activity was found for three H2O extracts of broccoli ( Brassica oleracea), carrot ( Dacus carota) and licorice ( Glycyrrhiza glabra) and for one EtOH extract of kiwi ( Ananas sativus ) of the nine species analyzed. The frameshift tester strain TA98 was reverted by broccoli (2.4, 4.8 and 9.6 mg/mL; p < 0.01) and carrot (9.6 mg/mL; p < 0.001) aqueous extracts and by kiwi (9.6 mg/mL; p < 0.0001) EtOH extract, whereas strain TA100 was only sensitive to the mutagens of licorice H,O extract, within the nine fruits and vegetables tested. The mutagenic response of the extracts was not altered by the presence of S9 mix. Cytotoxicity was only found for three of the nine species tested. Percentage cytotoxic ac tivities at 4.8 mg/mL in pineapple ( Actinidin diasinensis) and garlic ( Allium sativum) H,O extracts were 77 and 91 %, respectively. Licorice EtOH extract was the only one that showed a cytotoxic activity at all of the concentrations used. The percentage of cytotoxic activity of licorice extract was 63% at 0.24 mg/mL and increased with increasing concentration of licorice up to 4.8 mg/mL. Thus, licorice (EtOH) extract was the most cytotoxic of the species tested.

Cytotoxicity screening of several tomato extracts

The cytotoxic effects of extracts of the tomato variety "Racimo" have been evaluated through the use of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay at several concentrations. Three extracts-ethanol-water, petroleum ether, and in vitro digested tomato-exhibited in vitro cytotoxicity against the proliferation of the cultured cancer cell line HT-29. The concentration that caused 50% inhibition of cancer cell growth occurred (GI(50)) of the different extracts for HT-29 cells was 62.5 μg/mL for the petroleum ether extract and 87.0 μg/mL for the digested tomato extract. For the ethanol-water extract, it was not possible to determine this parameter at the assayed extract concentrations. These results clearly indicate that after the digestion process, the less polar substances, such as carotenoids and sterols, are bioavailable as active species against cancer cells. The GI(50) levels for tomato extracts are similar to those values reported for medicinal plants. The results of the MTT assay on nonmutagenic CCD-18 cells showed a lack of negative effect on cell growth, which indicates that tomato extracts act selectively on HT-29 tumor cells. (1)H-Nuclear magnetic resonance spectra confirmed the presence of known compounds with accepted cytotoxic activity against tumor lines (lycopene and β-carotene). The high cytotoxicity for HT-29 cells showed by the petroleum ether extract might be due to the simultaneous presence in the extract of both carotenoids and glyceryl esters of fatty acids. The results of this work clearly indicate the importance of carotenoid consumption on colon tumor proliferation and prevention, and also the importance of the dietary fats in carotenoid bioavailability.

Basis and consequences of primary and secondary prevention of gastrointestinal tumors

Carcinomas of the gastrointestinal tract (GI) are among the most common malignancies with regard to their incidence and mortality. Nutritional factors play an important role in the tumor development. The strength of their influence varies with the localization in the GI tract. Epidemiological studies focusing on GI cancer incidence or mortality as an endpoint necessitate large numbers of subjects to achieve significant results. Generally, a low energy and fat intake and a high intake of antioxidative vitamins (vitamin C, E, beta-carotene) and secondary plant metabolites (especially polyphenols) appear to be protective in GI carcinogenesis. Moderate drinking of alcohol and increased consumption of whole grain products, as opposed to highly refined carbohydrates, may help to reduce the risk of colon cancer. The recommended type of diet is low in fat, especially in saturated fatty acids, includes monounsaturated fatty acids, and includes moderate amounts of polyunsaturated fatty acids (no more than 10% of calories). Moderate consumption of salt and of highly salted, smoked, and barbecued foods should be encouraged. Obesity should be avoided by trying to match energy intake with expenditure while increasing physical activity levels. The mechanisms by which nutritional factors act especially on molecular events still remain to be examined. The use of molecular biomarkers will help us better understand cancer development as well as the role and significance of nutritional factors in this process.