Glucosinolates in Brassica: Occurrence and significance as cancer-modulating agents

Abstract

Brassica vegetables comprise all kinds of cabbages, Brussels sprouts, broccoli, cauliflower, kohlrabi, turnip and swede. Brassicas are frequently consumed by humans from both Western and Eastern cultures, as well as by animals. The typical flavor of brassicas is largely due to glucosinolate-derived volatiles. The occurrence of glucosinolates in plants for human consumption appears to be limited to cruciferous plants. The levels of total glucosinolates in plants may depend on variety, cultivation conditions, climate and agricultural practice, while the levels in a particular plant vary between the parts of the plant. In plants, glucosinolates and their hydrolysis products act as allelochemicals, which are compounds affecting behavior, health and growth of other species. Among the problems associated with the consumption of glucosinolate volatile hydrolysis products, those affecting the thyroid have been studied most extensively. In most animal studies performed in the past, goitrogenicity induced by glucosinolate breakdown products appeared to be limited to situations of iodine deficiency. In a study on human thyroid function, no effects of glucosinolates could be found (McMillan et al. 1986). It has been suggested that glucosinolate-derived products become mutagenic and carcinogenic after nitrosation. In an in-depth study, the potential of several Dutch brassicas to directly form nitrosyl mutagenic compounds in response to nitrite treatment was investigated. This potential was compared with the level of glucosinolates. The formation of the nitrosated products indole-3-acetonitrile, indole-3-carbinol and indole, and the stability of these products were studied. These studies revealed that indole compounds present in brassicas can be nitrosated and thereby become mutagenic. However, the nitrosated products are stable only in the presence of large amounts of free nitrite. Nitrosation of glucosinolates and their breakdown products does not constitute a significant health risk. On the other hand, epidemiological data indicate that consumption of cruciferous vegetables is associated with a decreased incidence in human populations. Several principal active agents were identified as glucosinolate-derived products, and it has been shown that the probably explanation of protective effects modification in the equilibrium between the activating enzymatic systems (associated with cytochromes P450) and the deactivating enzymatic systems (conjugants) favoring the deactivation of known mutagenic and carcinogenic agents.