Esophageal cancer prevention in zinc-deficient rats: Rapid induction of apoptosis by replenishing zinc

Background. Nutritional zinc deficiency in rats increases esophageal cell p roliferation and the incidence of N-nitroso-methylbenzylamine (NMBA)-induce d esophageal tumors. Replenishing zinc with a zinc-sufficient diet reduces these effects in zinc-deficient (ZD) rats. We investigated whether apoptosi s was involved in the reduction of NMBA-induced esophageal tumors when ZD r ats consumed a zinc-sufficient diet. Methods: Weanling rats were fed a ZD d iet (zinc at 3-4 ppm) for 5 weeks to establish esophageal. cell proliferati on, then treated once with NMBA (2 mg/kg body weight), and divided into the following five groups (47-100 per group). One ZD group was fed the ZD diet , and four zinc-replenished (ZR) groups, ZR(1), ZR(24,) ZR(72), and ZR(432, ) were fed a zinc-sufficient diet (zinc at 74-75 ppm) beginning 1, 24, 72, and 432 hours, respectively, after NMBA treatment. From 24 hours to 2 weeks after beginning a zinc-sufficient diet, esophagi from all ZR groups were a nalyzed for apoptosis and cell proliferation; ZD esophagi were the controls . Tumor incidence was determined 15 weeks after zinc replenishment. All sta tistical tests were two-sided. Results: Zinc replenishment initiated shortl y after NMBA treatment effectively reduced esophageal. tumorigenesis; 8% (t hree of 37) of ZR(1) 14% (five of 37) of ZR(24), 19% (five of 26) of ZR(72) , and 48% (19 of 40) of ZR(432) rats developed esophageal tumors compared w ith 93% (14 of 15) of ZD animals (all P < .001). Importantly, 24 and 30 hou rs after zinc replenishment, esophagi had numerous apoptotic cells (% apopt otic cells: 0 hour = 2.9%, 95% confidence interval [CI] = 2.5% to 3.3%; 24 hours = 9.4%, 95% CI = 8.2% to 10.6%), and the expression of the proapoptot ic Bax protein doubled. Within 48 hours, the ZR(1) epithelium was three to five cell layers thick compared with 10-20 layers before zinc replenishment . Conclusions: Zinc replenishment of NMBA-treated ZD rats rapidly induces a poptosis in esophageal epithelial cells and thereby substantially reduces t he development of esophageal cancer.