The role of zinc in life: a review.

Zinc is a common element in human and natural environments and plays an important part in many biological processes. Zinc, which is defined as an essential trace element, or a micronutrient, is essential for the normal growth and the reproduction of all higher plants and animals, and of humans. In addition, it plays a key role during physiological growth and fulfills an immune function. It is vital for the functionality of more than 300 enzymes, for the stabilization of DNA, and for gene expression. This review summarizes the role and manifestations of zinc in the environment and its importance for human health and metabolism, as well as its physiological role. Toxicity, teratogenicity, carcinogenicity, and immunological functions of zinc are outlined with particular reference to the properties of zinc as an antioxidant, and its role in cancer prevention.

Induction of cytochrome P450, generation of oxidative stress and in vitro cell-transforming and DNA-damaging activities by glucoraphanin, the bioprecursor of the chemopreventive agent sulforaphane found in broccoli.

The reduced cancer risk that appears to be linked to a diet rich in fruits and vegetables has fueled the belief that regular intake of isolated phytochemicals could potentially prevent cancer. In recent years, the glucosinolate metabolites derived from cruciferous vegetables, such as the isothiocyanate sulforaphane in broccoli, have gained much attention as potential cancer chemopreventive agents. The protective effect of sulforaphane, which is liberated from its glucosinolate precursor glucoraphanin (GRP) by myrosinase hydrolysis, is conventionally thought to involve the induction of Phase-II metabolizing enzymes. These Phase-II enzymes are implicated in the detoxication of many carcinogens and reactive oxygen species (ROS), thereby protecting cells against DNA damage and subsequent malignant transformation. While the induction of Phase-II enzymes is usually considered beneficial, in some cases these enzymes also bioactivate several hazardous chemicals. Furthermore, despite its projected benefits, the unknown effect of sulforaphane on Phase-I enzyme systems, which are involved in the bioactivation of a variety of carcinogens, should not be overlooked. Here we show that, in rat lungs, while GRP, the bioprecursor of the chemopreventive agent sulforaphane, slightly induced Phase-II detoxifying enzymes, it powerfully induced Phase-I carcinogen-activating enzymes, including activators of carcinogenic polycyclic aromatic hydrocarbons (PAHs). Concomitant with this Phase-I induction, GRP also over-generated ROS. Additionally, in a cell-transforming assay, GRP facilitated the metabolic activation of the PAH benzo[a]pyrene to reactive carcinogenic forms and in a yeast genotoxicity test it damaged DNA. This suggests that regular administration of GRP could actually increase rather than decrease cancer risk, especially in individuals exposed to environmental mutagens and carcinogens such as those found in tobacco smoke and in certain industrial settings.

Antimutagenicity of sodium selenite in Chinese hamster V79 cells exposed to azoxymethane, methylmethansulphonate and hydrogen peroxide.

In the last 10 years, there is an increasing interest in selenium (Se) because of its environmental, biological, and toxicological importance, and in particular, because of its antioxidant properties. However, inspite of extensive studies, the optimal concentration of Se to be used for its beneficial effects in not yet known. In addition, the mechanisms of Se antioxidant property require further study. We report on the effects of various mutagens/carcinogens such as azoxymethane, methylmethanesulphonate, and hydrogen peroxide on Chinese V79 hamster cells, in presence of sodium selenite in the concentration of 0.5 microM. We found that Se reduced the genotoxic effect of these mutagens/carcinogens. We also investigated enzymatic activities of glutathione peroxidase, catalase, superoxide dismutase, and glutathione S-transferase, in order to understand the Se involvement in the detoxification of free radicals. Sodium selenite increased the activities of glutathione peroxidase and catalase.