Lignans Are Involved in the Antitumor Activity of Wheat Bran in Colon Cancer SW480 Cells,

Abstract

Wheat bran was shown to provide protection against colorectal cancer in human intervention and animal studies. Our recent study showed, however, that antitumor activities of wheat bran from various wheat cultivars differed significantly even when wheat fiber was equal in diets. We hypothesized that phytochemical lignans in wheat bran may account for the differences among wheat cultivars in cancer prevention. The concentration of a major lignan, secoisolariciresinol diglycoside, was determined by HPLC in 4 selected wheat cultivars (i.e., Madison, Ernie, Betty, and Arapahoe). The lignan concentrations and their antitumor activities, previously determined in APC-Min mice, were correlated (r = 0.73, P < 0.02). The cancer preventive mechanisms of 2 prominent lignan metabolites (enterolactone and enterodiol) were further studied in human colonic cancer SW480 cells. Treatment with enterolactone and enterodiol, alone or in combination, at 0-40 micromol/L resulted in dose- and time-dependent decreases in cell numbers. Although the cytotoxicity as measured by trypan blue staining in adherent cells was not affected, DNA flow cytometric analysis indicated that the treatments induced cell cycle arrest at the S-phase. Western blot analysis for cyclin A, a required protein for S/G2 transition, showed that the cyclin A protein levels decreased after treatment with enterodiol or the combination of enterolactone and enterodiol at 40 micromol/L for 72 h. Apoptosis analysis by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay showed an increased percentage of apoptotic cells in the floating cells after enterodiol alone or combined treatments. These results suggest for the first time that lignans may contribute, at least in part, to the cancer prevention by wheat bran observed in APC-Min mice. Inhibition of cancer cell growth by lignan metabolites seems to be mediated by cytostatic and apoptotic mechanisms.

Cytostatic inhibition of cancer cell growth by lignan secoisolariciresinol diglucoside

“…We also found that dietary SDG at 46 0.01% significantly reduced azoxymethane-induced formation of aberrant crypt foci in F344 rats 47 [10]. In addition, we have shown that enterolactone and enterodiol or both in combinations 48 inhibit human cancer cell growth through inducing S-phase cell cycle arrest and apoptosis [9]. 49…”

“…43 Many studies show that SDG has cancer preventive properties in animal models. Our 44 previous study demonstrated that SDG levels in wheat bran from various wheat cultivars were 45 correlated to antitumor activities in APC-Min mice [9]. We also found that dietary SDG at 46 0.01% significantly reduced azoxymethane-induced formation of aberrant crypt foci in F344 rats 47 [10].…”

“…DMSO was kept less than 0.2% in 73 the final treatment, which did not alter cell growth or cell cycle measurements when compared 74 with DMSO-free media (data not shown). After treatment, the cells were detached and counted 75 by hemacytometer as described by our previous publication [9]. 76…”

“…The cell viability was measured in the adherent cells by trypan blue staining [9]. The 78 viable cell numbers in the treated cells were compared with that in the vehicle controls.…”

“…The cell cycle analysis was done as previously described [9][10]. Briefly, the cells were 81 fixed in ethanol, centrifuged and then the pellet was resuspended in the phosphate buffer saline 82 solution at pH 7.4, containing 20 g/L propidium iodide and 5000 U/L of RNase (Promega) at 37 83 o C for 30 min.…”