Background: We wanted to investigate the relationship between the fecal levels of granulocyte marker protein (GMP) and the presence of aberrant crypt foci (ACF) and colorectal cancer in rats given injections of azoxymethane (AOM) and fed either of two different diets, a basal diet plus 20% corn oil or 20% beef suet, respectively.
Methods: The rats received intraperitoneal injections of AOM, 15 mg/kg, once weekly for 6 weeks and were killed after 22 weeks.
Results: In the group fed beef suet 17 of 19 rats developed colon cancer, whereas in the group fed corn oil 4 of 14 rats developed cancer. None of the 20 control rats fed either the beef suet or corn oil diets developed cancer or aberrant crypts, and GMP remained unchanged. Surprisingly, the numbers of ACF were significantly higher (467 versus 295; P = 0.004) in the group fed corn oil than in the group fed beef suet. On the other hand, the size (crypts/focus) of the ACF was significantly higher (P = 0.03) in the beef suet group. Furthermore, fecal GMP was significantly higher in the beef suet group than in the corn oil group after 18 weeks, and this difference increased further toward the end of the study. GMP was greatly increased in all rats with colorectal cancer.
Conclusions: Fecal GMP may have provided us with a valuable tool for further studies of the induction and progression of neoplasia in rats and, possibly, in mice, since the anti-GMP antibody cross-reacts with feces extracts from mice.