Conjugated linoleic acid does not inhibit development of aberrant crypt foci in colons of male Sprague-Dawley rats.

Conjugated linoleic acid (CLA) is a potent inhibitor of the initiation and promotion of mammary carcinogenesis in animal models, but its role in colon carcinogenesis remains unclear. The objective of this study was to determine whether CLA inhibits the promotion of colon carcinogenesis. Forty male Sprague-Dawley rats were given a single dose of azoxymethane (20 mg/kg body wt i.p.). After 1 wk, the animals were randomized into two groups (n = 20) and fed a control AIN-93G diet or the control diet supplemented with 1% CLA at the expense of the soybean oil. After 12 wk, the animals were killed, and their colons were stained with methylene blue for aberrant crypt foci (ACF) analysis by light microscopy. The total number of ACF per animal did not differ between the control (174 +/- 11) and CLA (170 +/- 10) groups. Furthermore, CLA did not affect the average crypt multiplicity (crypts/ACF) or the average number of ACF in any size category. However, rats fed the 1% CLA diet had significantly higher serum insulin levels at the time of sacrifice than those fed the control diet. Thus it is possible that the promoting effects of elevated serum insulin on colon carcinogenesis may have counteracted an inhibitory effect of CLA.

Induction of hepatic insulin-like growth factor binding protein-1 (IGFBP-1) in rats by dietary n-6 polyunsaturated fatty acids.

The insulin-like growth factors (IGFs) are mitogenic polypeptides that have been linked to a variety of normal physiological processes as well as neoplasia. Overexpression of several components of the IGF system is associated with hepatocarcinogenesis in humans and rodents. In rat liver, diets rich in n-6 polyunsaturated fatty acid (PUFA) enhance the development of preneoplastic lesions and tumors. Therefore, the objective of this study was to determine the effect of these dietary fatty acids on the hepatic expression of the various components of the IGF system. The mRNA levels of IGF-1 and the type 1 receptor were not different in livers of rats fed a diet containing 20% corn oil (CO) compared with those fed 5% CO. Analysis of the IGF binding proteins revealed that insulin-like growth factor binding protein-1 (IGFBP-1) levels were altered by the amount and type of dietary fat. A 2.5-fold induction of IGFBP-1 mRNA occurred within 1 week after the animals were fed the 20% corn oil diet compared with those fed 5% CO and was further enhanced to over 6-fold after 1 month. Furthermore, IGFBP-1 protein was only detectable in the livers of animals fed the 20% CO diet. Induction of IGFBP-1 mRNA (4.5-fold) also occurred in rats fed a high-fat diet containing safflower (rich in n-6 PUFAs) compared with those fed a high-fat diet containing menhaden oil (rich in n-3 PUFAs). The induction of IGFBP-1 mRNA was independent of serum insulin levels and the development of insulin resistance. Since IGFBP-1 mRNA is upregulated in regenerating liver, we reasoned that the induction of IGFBP-1 mRNA may be associated with an increase in cell proliferation; however, no difference was observed in the hepatic labeling index of rats fed the 20% CO compared with the 5% CO diet. In summary, these studies show a striking induction by dietary n-6 PUFAs of hepatic IGFBP-1, a protein that has been implicated in liver cancer development.

The effect of dietary n-3 and n-6 polyunsaturated fatty acids on the expression of cyclooxygenase 1 and 2 and levels of p21ras in rat mammary glands.

Dietary n-6 polyunsaturated fatty acids (PUFAs) promote rat mammary cancer while n-3 PUFAs are inhibitory. The purpose of this study was to determine whether the fats exert their effects by altering the expression of genes that affect cancer development. Therefore, we have examined the effect of PUFAs on the expression of the cyclooxygenase (COX) 1 and 2 genes that are involved in prostaglandin biosynthesis. We also investigated the effect of dietary PUFAs on the expression of the p21ras protein and Ha-ras mRNA. Rats were fed either low- (7%; LF) or high- (21%; HF) fat diets that were rich in either n-6 PUFAs (safflower oil, S) or n-3 PUFAs (menhaden oil, M) for 3 weeks. COX-1 mRNA levels were approximately the same in groups fed diets containing either level of menhaden oil, but were increased by approximately 30% in the LFS and HFS groups (P < 0.05). Transcripts of the inducible COX-2 gene were not detectable in the menhaden oil groups, but this gene was expressed in animals fed either level of safflower oil and in the HFS group was associated with increased levels of COX enzymatic activity and production of PGE2. Animals fed safflower oil had elevated levels of p21ras protein compared to animals fed menhaden oil. Ha-ras mRNA was increased by approximately 35% in animals fed HFS compared to the group fed HFM (P < 0.05). These results demonstrate that dietary n-6 PUFAs upregulate COX-2 and, to some extent, COX-1 expression. There was a concomitant increase in COX enzyme activity and PG synthesis in the mammary glands of rats fed high levels of n-6 PUFAs. Together with associated changes in p21ras expression, these results may explain, at least in part, the promoting effects of dietary n-6 PUFAs on mammary carcinogenesis.

Rapid quantitation of thermal oxidation products in fats and oils by 1H-NMR spectroscopy.

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 dietary fat and colon carcinogenesis in rodents.

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, with > 80% 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.

Regulation of mevalonate synthesis in rat mammary glands by dietary n-3 and n-6 polyunsaturated fatty acids.

It is well established that dietary n-6 polyunsaturated fatty acids (PU-FAs) enhance rat mammary tumor development whereas n-3 PUFAs inhibit it, yet the mechanisms are unclear. The objective of this study was to investigate a mechanism by which n-3 and n-6 PUFAs could modulate mammary carcinogenesis. Female Sprague Dawley rats were fed diets containing either menhaden (n-3) or safflower oil (n-6) in a 7% fat diet for 1 week. In comparison to the n-6 diet, the n-3 diet significantly reduced the activity and levels of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase in mammary glands, thereby suppressing the formation of mevalonate. In addition to being essential for cholesterol biosynthesis, mevalonate is also required for DNA synthesis and may be involved in malignant transformation. Serum cholesterol was lower in the n-3 group than in the n-6 group (1.91 +/- 0.18 versus 2.61 +/- 0.37 mM; P < 0.01). Extrahepatic tissues meet most of their cholesterol requirements from circulating cholesterol, and the internalized cholesterol down-regulates HMG-CoA reductase. Thus, the concomitant decrease in serum cholesterol and mammary gland HMG-CoA reductase levels suggests that changes in circulating cholesterol levels do not solely determine the activity of extrahepatic reductase. We conclude that the mevalonate pathway may be a mechanism through which different types of dietary fat modulate breast cancer development.

Analysis of the immunoadjuvant octadecyl tyrosine hydrochloride.

A simple, rapid, high performance liquid chromatographic (HPLC) method for the analysis of the immunoadjuvant octadecyl tyrosine hydrochloride is described. The HPLC procedure can be applied to the direct determination of amino acid reactants present as contaminants in the adjuvant (tyrosine, ethyl tyrosine) and from this information the content of octadecanol reactant can be estimated. Further, these same determinations provide a means of monitoring immunoadjuvant stability in any vaccine preparation.

Compounds formed by treatment of corn (Zea mays) with nitrous acid.

Nitrohexane has been identified as a major product formed following treatment of corn (Zea mays) with nitrous acid. Preliminary evidence suggests that another compound isolated from the nitrosated corn is an unsaturated nitrolic acid. As an aid to the analysis of N-nitro compounds, we have characterized the response of a chemiluminescence detector (Thermal Energy Analyzer) as a function of pyrolysis chamber temperature for several nitrosamines and for an aliphatic C-nitroso compound, an aromatic C-nitro compound, a nitramine and an alkyl nitrite. The response-temperature profiles are valuable in distinguishing among the various compounds and in optimizing the sensitivity of the detector for use in chromatography. Other tests, including photolysis and stability toward nitrite-scavenging reagents, further aid in distinguishing among the various compounds.