Chemically induced carcinogenesis

Anisimov, V. N., Zabezhinski, M. A., Popovich, I. G., Liebcrman, A. I. and Shmidt, J. L., Prevention of spontaneous and chemically-induced carcinogenesis using activated carbon fiber adsorbent. I. Effect of the activated carbon fiber adsorbent Aqualen on spontaneous carcinogenesis and life span in mice, Cancer Lett., 1998, 126(1), 23 28. 

The data in this paper are consistent with a wealth of evidence showing that dietary Se consumed in excess of the Recommended Dietary Allowance lowers the risk of several important cancers (2, 14, 26, 27). Previous research has established a strong association between the dietary form of Se and the cancer-preventive properties of this element (5, 28). This paper extends the evidence that Se in chemical forms known to accumulate in garlic and some Brassica species is especially effective in the prevention of chemically induced carcinogenesis (14, 17). 

Figure 12.10 General aspects of chemically induced carcinogenesis.

Fat-soluble vitamins, in addition to their antioxidative effects on lipids, appear to exert a general protective effect in animals. Vitamin A and beta-carotenes protect lab animals from toxicity of citral, cyclophosphamide and some hydrocarbons (Seifter et al, (A2.) In related but independent studies, it was observed that high levels of vitamin A inhibit tumorogenesis and that low levels of vitamin A appear to enhance tumorogenesis (Baird, (1 ). vitamin E inhibited chemically-induced carcinogenesis in test systems (Shamberger, ) and also reduced the susceptibility of rats to cigarette smoke (Chow,... 

Vitamins. The laboratory evidence suggests that vitamin A itself and many of the retinoids are able to suppress chemically induced carcinogenesis. The epidemiological evidence is sufficient to suggest that foods rich in carotenes or vitamin A are associated with a reduced risk of cancer. 

The evidence for radical involvement in some types of chemically-induced carcinogenesis is now quite strong (2,12.-25J. 

There have been several epidemiological and several case reports inversely relating ascorbic acid intake from food to human cancer mortality. These studies are interesting, but may be confounded with the fact that the same ascorbic acid containing foods, namely fruits and vegetables, also contain large amounts of vitamin A and fiber. Both vitamin A and fiber have been inversely related to human cancer mortality and have been shown to inhibit several types of chemically-induced carcinogenesis in animals. Therefore, the possible anti cancer effect of ascorbic acid may be due to other factors. 

Our laboratory has completed a series of studies designed to evaluate the simultaneous effects of dietary protein and fat on 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast cancer in rats. Sprague-Dawley female rats were assigned to nine diets in a 3 x 3 factorial arrangement with protein (casein) at 8, 16, and 32% of kcals and fat (corn oil) at 12, 24, and 48% of kcals. As fat content was increased, all nutrients other than carbohydrate were adjusted to remain constant with respect to calories. Forty rats were assigned to each diet for each of three experiments (Figure 1) to examine initiation, promotion, and the combined phases of chemically-induced carcinogenesis. 

These studies indicate that palm oil exerts an inhibitory effect on the progression of chemically induced carcinogenesis. 

Figure 8. Schematic of one experimental approach designed to search for the cellular components of tissue undergoing chemically induced carcinogenesis that are essential to the carcinogenic process (e.g. Ref 85. ...

In mice topically and orally administered 2 mg of a pepper extract 3 days a week for 3 months, an increase in incidences of tumors was observed. A reduction in the increase of tumor formation was observed in rats orally and topically administered 5 or 10 mg of vitamin A pal-mitate twice weekly for 3 months during and after pepper administration. No impact on carcinogenesis was observed in mice fed diets containing 1.6% pepper (Shwaireb et al. 1990). Conversely, another study indicated that pepper inhibited chemically induced carcinogenesis in rats (Nalini 1998). 

Various organic sulfides present in Allium have been found to have anticar-cinogenic activity. For example, allyl sulfide, a constituent of garlic oil, inhibited colon cancer in mice exposed to 1,2-dimethylhydrazine, and allyl methyl trisulfide, allyl methyl disulfide, aUyl trisulfide, and allyl sulfide all inhibited benzo[a]pyrene-induced neoplasma of the forestomach and lung in female mice (55). Lam et al. (Chapter 22) investigated the ability of 2-n-butyl thiophene, a constituent of roast beef aroma, to inhibit chemically induced carcinogenesis in three different tumor systems. This compound was found to be effective in the forestomach, lung, and colon models. 

Inhibition of Chemically Induced Carcinogenesis by 2-/i-Heptylfuran and 2-7i-Butylthiophene from Roast Beef Aroma... 

Citrus limonoids are furanoid natural products found in citrus fruits. The most abundant limonoids, limonin and nomdin, have been determined to induce increased activity of GST and inhibit chemically induced carcinogenesis (6,7). These findings with furan containing natural products led to the investigation of mono and disubstituted furan and the corresponding sulfur containing thiophene compounds that are found in complex mixtures of beef aroma. 

Conjugated linoleic acid (CLA) has been shown to prevent chemically induced carcinogenesis in different animal experimental models and at different sites, including mammary gland, skin, colon and forestomach. All of the literature up to 1998 on the anticancer effect of CLA was reviewed thoroughly in the first volume of this series (1). Therefore, in this chapter, we will review mainly the developments in this field since 1999 except where reference to earher work emphasizes recent findings. 

Previous studies in rats and mice showed that limonene prevented the growth of tumors in chemical-induced carcinogenesis models. 

Effects of Retinoids on Chemically Induced Carcinogenesis and Photocarcinogenesis... 

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