The effect of dietary folate on Apc and p53 mutations in the dimethylhydrazine rat model of colorectal cancer.

Dietary inadequacy of folate enhances and folate supplementation suppresses colorectal carcinogenesis in the dimethylhydrazine rat model. Folate is an essential factor for DNA methylation and the de novo biosynthesis of nucleotides, aberrations of which play important roles in mutagenesis. This study investigated whether the mutational hot spots of the Apc and p53 genes for human colorectal cancer are mutated in dimethylhydrazine-induced colorectal neoplasms and whether dietary folate can modulate mutations in these regions. Rats were fed diets containing 0, 2 (basal requirement), 8 or 40 mg folate/kg diet. Five weeks after diet initiation, dimethylhydrazine was injected weekly for 15 weeks. Mutations were determined by direct sequencing in 11 low and seven high grade dysplasias and 13 invasive adenocarcinomas. A total of six Apc mutations were found in four dysplastic and carcinomatous lesions: two in two low grade dysplasias, two in one high grade dysplasia and two in one adenocarcinoma. All mutations were single base substitutions, four of which were A:T-->G:C transitions. Five of the six mutations were located upstream from the region corresponding to the human APC mutation cluster region. Dietary folate had no effect on the frequency and type of Apc mutations. No mutations were detected in exons 5-9 of the p53 gene in neoplastic lesions. These data suggest that in the dimethylhydrazine rat model of colorectal cancer, the Apc gene is mutated in early stages, albeit to a lesser degree than observed in human colorectal cancer, whereas the mutational hot spot of the p53 gene for human colorectal cancer is not commonly mutated. Although the low frequency of Apc mutations and the small number of neoplasms studied in this study might have precluded our ability to observe modulatory effects of folate, dietary folate appears to have no significant effect on Apc and p53 mutations.

Dietary folate protects against the development of macroscopic colonic neoplasia in a dose responsive manner in rats.

BACKGROUND AND AIMS: Diminished folate status is associated with enhanced colorectal carcinogenesis. This study investigated the potential chemopreventive role of dietary folate in the dimethylhydrazine colorectal cancer model. SUBJECTS AND METHODS: Sprague-Dawley rats were fed diets containing either 0, 2 (daily dietary requirement), 8 or 40 mg folate/kg diet for 20 weeks. After five weeks of diet, rats were injected with dimethyl-hydrazine (44 mg/kg) weekly for 15 weeks. Fifteen weeks after the first injection of dimethylhydrazine, all rats were killed. Folate status was determined, and the entire colorectum from each rat was analysed for macroscopic and microscopic neoplasms. RESULTS: Plasma and colonic folate concentrations correlated directly with dietary folate levels (p < 0.005). The incidence of microscopic neoplasms was similar among the four groups. However, the incidence and the average number of macroscopic tumours per rat decreased progressively with increasing dietary folate levels up to 8 mg/kg diet (p < 0.05). In the strongly procarcinogenic milieu used in this study, folate supplementation at 20 times the basal requirement was associated with rates of macroscopic tumour development that were intermediate, and not statistically distinct, from rates observed at either 0 or 8 mg/kg diet. CONCLUSIONS: These data indicate that in this rat model, (a) increasing dietary folate up to four times the basal requirement leads to a progressive reduction in the evolution of macroscopic neoplasms from microscopic foci; and (b) folate supplementation beyond four times the requirement does not convey further benefit.

Atherogenic diets enhance endotoxin-stimulated interleukin-1 and tumor necrosis factor gene expression in rabbit aortae.

Cytokine-induced vascular changes may contribute to the atherogenic process. We examined the effect of atherogenic diets on the aortic expression of genes for the cytokines interleukin-1 alpha and beta and tumor necrosis factor alpha. Male New Zealand White rabbits were fed one of the following diets for 10 wk: nonpurified diet, a semipurified diet with 10% corn oil, a semipurified diet with 1% corn oil and 9% partially hydrogenated coconut oil, or the 9% coconut oil diet supplemented with either 0.1, 0.3 or 0.9% added cholesterol (n = 6/group). At 10 wk, 3 rabbits per group received lipopolysaccharide (200 micrograms/kg) intravenously. After 1.5 h the rabbits were killed and their aortae removed and analyzed. Histologic examination showed that the 0.3% and 0.9% cholesterol-fed rabbits developed appreciable aortic lesions. Diet had no major effect on the basal levels of aortic cytokine mRNA as determined by polymerase chain reaction analysis of DNAs. However, aortic tissue from rabbits fed 0.3% and 0.9% cholesterol diets showed significantly enhanced lipopolysaccharide-evoked levels of mRNA encoding interleukin-1 alpha (392 +/- 91 for saturated fat vs. 759 +/- 191 and 800 +/- 120 fmoles/reaction for 0.3% and 0.9% cholesterol), interleukin-1 beta (99 +/- 10 vs. 353 +/- 80 and 355 +/- 86) and tumor necrosis factor alpha (195 +/- 15 vs. 594 +/- 78 and 667 +/- 97). Extracts of aortae from rabbits injected with lipopolysaccharide contained interleukin-1 and tumor necrosis factor alpha activity but differences in biological activity due to diet were not detectable at the 1.5 h time point (chosen for maximal mRNA expression). Increased local cytokine gene expression in response to acute stimulus might influence the evolution of the vascular response to diets rich in cholesterol and saturated fats.