Search

Epidemiological studies have demonstrated clear associations between specific dietary and environmental risk factors and incidence of colorectal cancer, but the mechanisms responsible for these associations are not known. An animal model could facilitate such an understanding. Both genotoxic and nongenotoxic carcinogens induce aberrant crypt foci (ACF) in the colons of F344 rats. F344 rats were provided with diets that contained putative risk factors for CRC: low calcium and low vitamin D, high iron, high fructose, and decreased light (UV) exposure or a control diet for 14 wk. The rats were then assessed with biochemical measures and by topological examination for evidence of colon abnormalities. Circulating ionized calcium was decreased from 2.85 to 1.69 mmol/L, and ACF were increased from 0.7 to 13.6 lesions/colon (both P < 0.001). Rats exposed to the multiple environmental conditions associated with colon cancer, developed ACF similar to the heterogeneous or ill-defined ACF in the human colon. Heterogeneous ACF are the most frequently seen in humans and are also seen in rats shortly after exposure to the non-genotoxic colon carcinogen, dextransulfate sodium. The rodent model could be used to assess the pathways from diet and environment to colon cancer and to provide guidance for clinical studies.

This work describes the application of high-resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy to the study of the thermal peroxidation of beef tallow and corn oil under standardized conditions. The approach provides a rapid, quantitative method for determining the degree of oxidation of unsaturated fatty acids in animal and vegetable fats and oils by quantitating the decreasing intensities of 1H-NMR peaks for allylic and olefinic protons in unsaturated fatty acid chains of triglycerides and the increasing peak intensities of hydroperoxide and saturated and alpha, beta-unsaturated aldehydic protons in relation to the less labile protons in the triglyceride molecule. Two-dimensional correlation spectroscopy analysis of highly oxidized beef tallow (180 degrees C for 24 h) suggested that the unsaturated aldehydes that persisted were apparently associated with carboxy groups.

Thermally oxidized animal fat (beef tallow) was assessed for colon cancer-promoting and -initiating activity in F-344 rats and CF-1 mice with the use of the aberrant crypt focus (ACF) assay. In two promotion studies, extensively oxidized beef tallow (110 degrees C for 144-168 h, peroxide value approx 200 meq/kg, with80% loss of allylic and olefinic protons) had relatively little effect on the growth of ACF in F-344 rats. The multiplication constant for treatment/control of ACF size in aberrant crypts per ACF at 100 days was 1.07 (95% confidence interval = 1.01-1.14) and 0.98 (95% confidence interval = 0.91-1.06). ACF size was not affected by less extensively oxidized beef tallow or by a 10-fold reduction of dietary alpha-tocopherol during the growth of the ACF. In initiation studies, extensively oxidized beef tallow administered by gavage increased the number of animals with ACF and the number of ACF per colon (11 of 23 and 5 of 29 animals with ACF; 1.09 +/- 0.29 and 0.21 +/- 0.09 ACF/colon, respectively). Less severely oxidized beef tallow was without effect. Further studies with CF-1 mice confirmed that extensively oxidized beef tallow increased numbers of animals with ACF and average ACF per colon. The unsaturated aldehyde acrolein was without effect in the ACF assay. These data suggest that highly thermolyzed beef tallow contains an uncharacterized initiator or leads to conditions in which spontaneously initiated ACF are increased.

The putative cancer preventive agent 3,3'-diindolylmethane (DIM) is formed in the acidic environment of the stomach following consumption of indole-3-carbinol (I3C), which is present in vegetables of the Brassica genus. We have recently shown that the transcription factor Sp1 is involved in the regulation of both proliferation and de novo lipogenesis in cancer cells. Here we show that DIM inhibits the proliferation of 3 human breast cancer cell lines, MCF-7, MDA-MB-231, and SKBr-3, and concomitantly inhibits the expression of Sp1 and fatty acid synthase (FAS). There were no DIM-related effects on the proliferation or expression of Sp1 or FAS in the nontumorigenic human breast epithelial cell line MCF-10A. These results suggest that inhibition of Sp1 and/or FAS expression could contribute to the anticancer properties of the dietary indoles.

The objective of this study was to determine whether downregulation of fatty acid synthase (FAS) expression and/or inhibition of its activity by the two major CLA isomers, 10t,12c and 9c,11t CLA, could contribute to their inhibitory effect on the growth of human breast (MCF-7), colon (HT-29) and prostate (LNCaP) cancer cell lines. We first confirmed and extended the results of others showing that the inhibitory action of CLA on proliferation is dependent on the cell type as well as the structure of the isomer, the 10,12 isomer being a more potent inhibitor than the 9,11 isomer in the concentration range 25-100 microM. By Western analysis, we showed that 10,12 CLA downregulated FAS expression in all of the cell lines in a concentration-dependent manner, but the 9,11 isomer had no effect. Both isomers inhibited FAS enzyme activity, but 10,12 CLA was again more potent than the 9,11 isomer. Our results suggest that downregulation of FAS by 10,12 CLA, but not by the 9,11 isomer, as well as inhibition of FAS enzyme activity by both isomers, may contribute to growth inhibition of cancer cells but only at relatively high concentrations.

We evaluated the effect of dietary cholesterol and oxidized cholesterol on the promotion of aberrant crypt foci (ACF), which are putative precancerous lesions in the colon. Sixty female C57BL/6J mice were given four weekly injections (ip) of azoxymethane (AOM) then fed either a control AIN-76 diet or the control diet supplemented with 0.3% cholesterol or 0.3% oxidized cholesterol for 100 days. The oxidized cholesterol was prepared by heating cholesterol at 110 degrees C for 48 hours. Gas chromatographic analysis of the oxidized cholesterol showed that 96% of the cholesterol was unchanged and less than 2% of the cholesterol was oxidized. The remaining 2% impurities were unidentified and present in both the cholesterol and heated cholesterol. The number of ACF in the group fed cholesterol was significantly lower than the control group (7.9 +/- 1.0 vs. 12.5 +/- 1.2, p0.01). The number of ACF in the group fed oxidized cholesterol (10.1 +/- 1.1) was not different from the control or cholesterol groups. The size of the ACF (no. of crypts per focus) did not differ between the three dietary groups. Serum low-density lipoprotein (LDL) cholesterol was greater in the cholesterol-fed group than the control group (40.5 +/- 4.6 vs. 24.3 +/- 3.6 mg/dl, p0.05). LDL cholesterol from the animals fed oxidized cholesterol (37.7 +/- 4.7 mg/dl) was not different from the control or cholesterol-fed animals. Total and high-density lipoprotein (HDL) cholesterol did not differ between the groups. The results show that dietary cholesterol significantly inhibits the promotion of ACF in the colon. The elevated LDL cholesterol may inhibit de novo cholesterol synthesis in the preneoplastic colonic epithelial cells, thereby inhibiting DNA synthesis and cell proliferation.