Isothiocyanates and cancer prevention

Extensive epidemiological evidence supports the contention that high fruit and vegetable consumption is associated with a reduction in the incidence of cancer. Moreover, it is well established that consumption of cruciferous vegetables is inversely associated with the risk of cancer of the lung, colon, stomach, and prostate.^1-3 In the mid-1980s, studies in rats demonstrated that isothiocyanates (ITCs) (Figure 21.1), which occur widely as conjugates in Brassica and other vegetables of the family Cruciferae (e.g., cabbage, cauliflower, Brussels sprouts, watercress, broccoli, kale) and the genus Raphanus (radishes and daikons), inhibit the metabolic activation of a variety of carcinogens that occur in tobacco products and the diet, suggesting chemopreventive effects of ITCs.^4,5 Organic ITCs (R-NCS) occur in plants as thioglycoside conjugates known as glucosinolates. Damage to plant cells, such as from cutting and chewing, releases myrosinase (β-thioglucoside glucohydrolase) that catalyzes the hydrolysis of glucosinolates and the formation of ITCs by a Lossen rearrangement (Figure 21.2). The microflora in the intestinal tract also acts as a source for the hydrolysis of glucosinolates to ITCs in humans.⁶.