Selective induction of phase II enzymes in the urinary bladder of rats by allyl isothiocyanate, a compound derived from Brassica vegetables.

Allyl isothiocyanate (AITC) is formed from sinigrin, a glucosinolate that is present in many Brassica vegetables. In the present study, the effect of various dose levels of AITC on the activities of the phase II detoxification enzymes quinone reductase (QR) and glutathione S-transferase (GST) in rat tissues has been examined. High dose levels of AITC, given daily for 5 days, increased the activity of QR and/or GST in the liver, kidneys, lungs, spleen, urinary bladder, glandular and nonglandular stomach, duodenum, jejunum, ileum, cecum, and colon plus rectum of the animals. At low doses, however, increases in enzyme activity were observed only in the urinary bladder of the rats, with a significant effect being recorded in this tissue at a dose of AITC of only 10 micromol/kg/day. The effect of duration of exposure to AITC on enzyme levels in the urinary bladder was also investigated, with rats receiving the isothiocyanate each day for 1-21 days. In the case of QR, a plateau of activity was reached after 15 daily doses of AITC, but GST activity continued to increase with continued exposure, and no plateau was reached after 21 doses. The dose level of AITC found to be effective in rats approaches the level that could be achieved through human consumption of Brassica vegetables, suggesting that induction of phase II enzymes by food-derived isothiocyanates could contribute to the lower incidence of bladder cancer observed in individuals who regularly consume such vegetables.