Chemoprotective effects of broccoli and other Brassica vegetables

Abstract

Numerous epidemiological studies indicate that Brassica vegetables protect humans against cancer. The family Cruciferae genus Brassica consists of the species Brassica oleracea (e.g., broccoli, cabbage, cauliflower, Brussels sprouts, kale, turnips, collards), which are the most frequently consumed vegetables worldwide. Brassica vegetables are the richest sources of glucosinolates (p-thioglycoside-N-hydroxysulfates), which have considerable anticarcinogenic properties. Glucosinolates are hydrolyzed to biologically active isothiocyanates by the plant enzyme myrosinase when the cells in the plant are damaged (e.g., cut, ground or chewed). Glucoraphanin, which accounts for 35-50% of broccoli glucosinolates, is converted to sulforaphane (1-isothiocyannato-4-(methylsulfinyl)butane), a potent monofunctional phase II enzyme inducer. Several animal studies demonstrated that Brassica vegetables are protective against various classes of DNA-reactive carcinogens. They can reduce chemically induced tumor formation, attenuate the effects of polycyclic aromatic hydrocarbons and nitrosoamines and have a protective effect against heterocyclic amines. This review outlines Brassica vegetables and their metabolism, chemoprotective mechanisms of action, pharmacogenomics and adverse effects. In addition, the overview of recently conducted epidemiological studies on risk reduction of different cancers due to consumption of Brassica vegetables is provided.