Predictive value of proliferation, differentiation and apoptosis as intermediate markers for colon tumorigenesis

In order to determine the prognostic significance of proliferation,differentiation, and apoptosis as intermediate markers for colon tumordevelopment, these indices were measured during the promotion phase oftumorigenesis. Two hundred and sixty male Sprague-Dawley rats were providedwith one of two fats (corn oil and fish oil) and two fibers (pectin andcellulose) plus or minus the carcinogen azoxymethane (AOM) and killed attwo time points (18 and 36 wk) in a 2x2x2x2 factorial design. In vivo cellproliferation was measured immunohistochemically using incorporation ofbromodeoxyuridine into DNA. Differentiation was assessed by binding ofDolichos biflorus agglutinin (DBA) to colonocytes. Apoptosis was measuredby immunoperoxidase detection of digoxigenin-labeled genomic DNA.Adenocarcinoma incidence results at week 36 were 70.3% for corn oil + AOMand 56.1% for fish oil + AOM treatment (P < 0.05); no main effect offiber was observed. At week 18, AOM treatment increased the number of cellsper crypt column in the proximal colon compared with saline controls (P =0.0358) and increased the proliferative zone in the distal colon comparedwith controls (P = 0.0073). However, changes in cell proliferation at week18 did not predict the beneficial effect of fish oil versus corn oil. Incontrast, DBA binding (the marker for differentiation) was higher in fishoil versus corn oil fed animals in both the proximal and distal colon andin each portion of the crypt (P = 0.0001). There were a greater number ofapoptotic cells/crypt column in the proximal colon (P = 0.0019) and distalcolon (P = 0.0358) with fish oil compared with corn oil, and indices ofapoptosis also predicted certain fat/fiber interactions. Measurements ofdifferentiation and apoptosis had greater prognostic value to detectdietary effects on tumor incidence than did measurements of cellproliferation.