Background – While Se intakes of Australian and New Zealand consumers are sufficient to ensure no overt signs of deficiency, the relatively low intakes may contribute the risk for some cancers. However, Se supplementation is problematic, as high Se intake can be toxic, particularly if the source is inorganic. Protein-bound Se is more bioactive and less toxic than inorganic forms of Se and there is interest in delivering Se in organic forms in food products.
Objectives – To use real time RT-PCR to determine the colonic gene expression of important selenoproteins and genes involved in development of some colon cancers in rats fed Se-enriched casein or yeast.
Design – 51 male Sprague Dawley rats were fed diets containing either control casein (0.035 ppm Se), Se-enriched casein (1 ppm Se) from cows fed Sel-Plex® (HseC) or control casein plus Se-enriched yeast (1 ppm, as Sel-Plex®) (HseY). Rats were fed diets for 5 wk prior to initial s.c. azoxymethane (AOM) injection (15 mg/kg) in the lower abdomen. A 2nd dose of AOM was given one wk later and after 9 wks rats were euthanised and colon removed.
Outcomes – There was no significant effect of dietary Se on colonic GPx expression (+840 and +164% for HSeC and HSeY respectively, P=0.19). When the HSeC was compared to the other diets there was an increase in GPx expression (+623%, P=0.078). While there was no significant effect of dietary Se on K-ras expression (-61% and - 90%, P=0.15), when both high Se diets were compared to the control diet the expression of K-ras was decreased by supplemental Se (-79%, P=0.10). There was no effect of dietary Se on expression of SelP (+31 and -50%, P=0.59).
Conclusion – These data suggest that dietary Se can influence the expression of key biomarkers of Se status and colon cancer formation, but the form of the Se may be important. Increased dietary Se either as yeast or casein reduced the expression of K-ras whereas only casein bound Se increased the expression of colonic GPx.