High intake of fruits and vegetables is linked to a reduced risk of some cancer such as colon cancer. Colon cancer is the third most common cancer in the United States. Colon cancer is only for 10% caused by genetic factors and for 90% by environmental factors, including diet. Phytochemicals, including flavonoids are mainly responsible for this protective action.
Quercetin belongs to this group of flavonoids and is found in many plants and fruits, including apples, onions, tea and red wine. Many studies have already confirmed that quercetin may have a protective action against breast, lung, liver, ovarian and colon cancer.
The purpose of this study was to investigate the influence of quercetin on the proteome of the SW480 human colon adenocarcinoma cell line. The cells were incubated in a medium containing 20 microMol quercetin. The change in molecular structure of proteins were determined after treatment of the cells with quercetin. The identification of the proteins was carried out with two-dimensional gel electrophoresis and final identification of trypsin digested protein with mass spectrometry.
The investigators found that quercetin decreased the expression of three proteins and increased the expression of one protein. Two of the proteins, which were decreased, were identified as type II cytoskeletal 8 keratin and NADH dehydrogenase Fe-S protein 3. The protein that showed and increased expression was an annexin protein. The down regulation of keratin in cells by quercetin could be interpreted as cells becoming less tumorigenic. The levels of NADH dehydrogenase Fe-S protein 3 are normally increased in tumor cells. A reduction NADH dehydrogenase Fe-S protein 3 by quercetin suggest that quercetin is associated with decreased tumorigenicity.
The increase of the annexin protein level could also indicate that quercetin has anti-tumor properties, because annexin is higher in normal cells than in tumor cells.
The investigators concluded that the expression of several proteins were influenced by quercetin and that these changes could explain the chemo-protective action of quecetin towards colon cancer.
Source: Michel F Mouat, Kumar Kolli, Ronal Orlando, James L. Hargrove and Arthur Grider. The Effect of Quercetin on SW480 Human Colon Carcinoma Cells: a Proteomic Study. Nutritional Journal 2005, 4:11