Mechanisms of antimutagenesis and anticarcinogenesis: role in primary prevention

Isolating antigenotoxic components and cancer cell growth suppressors from agricultural by-products

Commercial processing wastes or by-products of crops were found to be sources of antimutagens and human tumor cell growth suppressors. We developed a microplate method to measure genomic DNA damage in Chinese hamster ovary cells with a modified single cell gel electrophoresis (SCGE) assay. This allowed us to measure the repression of 2-acetoxyacetylaminofluorene (2AAAF)-induced DNA damage by very small amounts of complex mixtures, fractions or individual chemicals isolated from agricultural by-products. We previously demonstrated that PCC, an ethanol extract of a commercial soybean processing by-product, repressed induced genomic DNA damage in mammalian cells. PCC was separated into a series of chemically defined fractions and two fractions (PCC70 and PCC100) repressed mutagen-induced damage. Of the isoflavones isolated from soybean fraction PCC70, daidzein expressed antigenotoxic activity, however, genistin and genistein enhanced DNA damage. An antigenotoxic response also was observed with a fraction isolated from corn distillate solids (CDS40). We developed a microplate assay to measure the suppression of the growth rate of human cancer cells in which the cytostatic/cytotoxic status at each concentration of the test sample was quantitatively determined. Genistein, genistin, daidzein and daidzin isolated from soybean fraction PCC70 expressed a wide range of growth suppression of HT-29 human colon cancer cells. The biological assays were integrated with, and directed, the separation and analytical chemistry component of this project. Compounds were purified from biologically active fractions and the structure of individual chemicals was determined with analytical HPLC and LC-mass spectroscopy (LC-MS). This research may lead to the isolation of novel chemoprotectants from agronomic commercial processing products and by-products.

Mechanisms of N-acetylcysteine in the prevention of DNA damage and cancer, with special reference to smoking-related end-points

Although smoking cessation is the primary goal for the control of cancer and other smoking-related diseases, chemoprevention provides a complementary approach applicable to high risk individuals such as current smokers and ex-smokers. The thiol N-acetylcysteine (NAC) works per se in the extracellular environment, and is a precursor of intracellular cysteine and glutathione (GSH). Almost 40 years of experience in the prophylaxis and therapy of a variety of clinical conditions, mostly involving GSH depletion and alterations of the redox status, have established the safety of this drug, even at very high doses and for long-term treatments. A number of studies performed since 1984 have indicated that NAC has the potential to prevent cancer and other mutation-related diseases. N-Acetylcysteine has an impressive array of mechanisms and protective effects towards DNA damage and carcinogenesis, which are related to its nucleophilicity, antioxidant activity, modulation of metabolism, effects in mitochondria, decrease of the biologically effective dose of carcinogens, modulation of DNA repair, inhibition of genotoxicity and cell transformation, modulation of gene expression and signal transduction pathways, regulation of cell survival and apoptosis, anti-inflammatory activity, anti-angiogenetic activity, immunological effects, inhibition of progression to malignancy, influence on cell cycle progression, inhibition of pre-neoplastic and neoplastic lesions, inhibition of invasion and metastasis, and protection towards adverse effects of other chemopreventive agents or chemotherapeutical agents. These mechanisms are herein reviewed and commented on with special reference to smoking-related end-points, as evaluated in in vitro test systems, experimental animals and clinical trials. It is important that all protective effects of NAC were observed under a range of conditions produced by a variety of treatments or imbalances of homeostasis. However, our recent data show that, at least in mouse lung, under physiological conditions NAC does not alter per se the expression of multiple genes detected by cDNA array technology. On the whole, there is overwhelming evidence that NAC has the ability to modulate a variety of DNA damage- and cancer-related end-points.

Brassica vegetables and cancer prevention. Epidemiology and mechanisms

This paper first gives an overview of the epidemiological data concerning the cancer-preventive effect of brassica vegetables, including cabbages, kale, broccoli, Brussels sprouts, and cauliflower. A protective effect of brassicas against cancer may be plausible due to their relatively high content of glucosinolates. Certain hydrolysis products of glucosinolates have shown anticarcinogenic properties. The results of six cohort studies and 74 case-control studies on the association between brassica consumption and cancer risk are summarized. The cohort studies showed inverse associations between the consumption of brassica's and risk of lung cancer, stomach cancer, all cancers taken together. Of the case-control studies 64% showed an inverse association between consumption of one or more brassica vegetables and risk of cancer at various sites. Although the measured effects might have been distorted by various types of bias, it is concluded that a high consumption of brassica vegetables is associated with a decreased risk of cancer. This association appears to be most consistent for lung, stomach, colon and rectal cancer, and least consistent for prostatic, endometrial and ovarian cancer. It is not yet possible to resolve whether associations are to be attributed to brassica vegetables per se or to vegetables in general. Further epidemiological research should separate the anticarcinogenic effect of brassica vegetables from the effect of vegetables in general. The mechanisms by which brassica vegetables might decrease the risk of cancer are reviewed in the second part of this paper. Brassicas, including all types of cabbages, broccoli, cauliflower, and Brussels sprouts, may be protective against cancer due to their glucosinolate content. Glucosinolates are usually broken down through hydrolysis catalysed by myrosinase, an enzyme that is released from damaged plant cells. Some of the hydrolysis products, viz. indoles, and isothiocyanates, are able to influence phase 1 and phase 2 biotransformation enzyme activities, thereby possibly influencing several processes related to chemical carcinogenesis, e.g. the metabolism, DNA-binding, and mutagenic activity of promutagens. Most evidence concerning anticarcinogenic effects of glucosinolate hydrolysis products and brassica vegetables has come from studies in animals. In addition, studies carried out in humans using high but still realistic human consumption levels of indoles and brassica vegetables have shown putative positive effects on health. The combination of epidemiological and experimental data provide suggestive evidence for a cancer preventive effect of a high intake of brassica vegetables.

Antimutagenic activity of chemical fractions isolated from a commercial soybean processing by-product

Commercial products of agronomic crop plants may become a reliable and inexpensive source of phytonutrients, such as antimutagenic food supplements. We previously demonstrated that PCC, an ethanol extract of a commercial soybean processing by-product, was able to repress induced genomic DNA damage, whole cell clastogenicity, and point mutation in mammalian cells. In this paper we separated PCC into a series of chemically defined fractions and determined their ability to repress induced mutagenic damage in Chinese hamster lung cells, Chinese hamster ovary cells and human lymphocytes. Fraction PCC70 (PCC 70% methanol eluate) contained the flavonoids from PCC and daidzin and genistin repressed 2-acetoxyacetylaminofluorene (2AAAF)-induced DNA damage measured with single cell gel electrophoresis. Genistein, however, enhanced the genotoxic impact of 2AAAF. Fraction PCC100 (PCC 100% methanol eluate) had the greatest level of antigenotoxic activity against 2AAAF in CHO cells and repressed the genotoxic capacity of the dietary carcinogen 2-amino-3-methylimidazo-(4,5-f)quinoline (IQ) in human lymphocytes. These data indicate that commercial soybean products and by-products may be a source of chemoprotective food additives.

Chemopreventive properties and mechanisms of N-Acetylcysteine. The experimental background

The thiol N-acetylcysteine (NAC), now under clinical trial for cancer chemoprevention both in Europe (project Euroscan) and in the US (National Cancer Institute), has been shown during the past decade to exert protective effects in a variety of experimental test systems. NAC inhibited spontaneous mutagenicity and that induced by a number of chemical compounds and complex mixtures. Moreover, NAC significantly decreased the incidence of neoplastic and preneoplastic lesions induced by several chemical carcinogens in rodents (mice, rats, hamsters), e.g., in lung, trachea, colon, liver, mammary gland, Zymbal gland, bladder and skin. Our studies provided evidence that multiple mechanisms contribute to NAC antimutagenicity and anticarcinogenicity. They include extracellular mechanisms, such as detoxification of reactive compounds due to the nucleophilic and antioxidant properties of NAC, inhibition of nitrosation products, and enhancement of thiol concentration in intestinal bacteria; trapping and enhanced detoxification of carcinogens in long-lived non-target cells, such as erythrocytes and bronchoalveolar lavage cells; mechanisms working in the cytoplasm of target cells, such as replenishment of GSH stores, modulation of metabolism of mutagens/carcinogens, blocking of electrophiles, and scavenging of reactive oxygen species; and nuclear effects, such as inhibition of DNA adduction by metabolites of carcinogens, inhibition of "spontaneous" mutations, attenuation of carcinogen-induced DNA damage, and protection of nuclear enzymes, such as poly(ADP-ribose) polymerase.(ABSTRACT TRUNCATED AT 250 WORDS)