Esophageal cancer prevention in zinc-deficient rats: rapid induction of apoptosis by replenishing zinc.
BACKGROUND
Nutritional zinc deficiency in rats increases esophageal cell proliferation and the incidence of N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumors. Replenishing zinc with a zinc-sufficient diet reduces these effects in zinc-deficient (ZD) rats. We investigated whether apoptosis was involved in the reduction of NMBA-induced esophageal tumors when ZD rats consumed a zinc-sufficient diet.


METHODS
Weanling rats were fed a ZD diet (zinc at 3-4 ppm) for 5 weeks to establish esophageal cell proliferation, 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 analyzed for apoptosis and cell proliferation; ZD esophagi were the controls. Tumor incidence was determined 15 weeks after zinc replenishment. All statistical tests were two-sided.


RESULTS
Zinc replenishment initiated shortly after NMBA treatment effectively reduced esophageal tumorigenesis; 8% (three 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 with 93% (14 of 15) of ZD animals (all P<.001). Importantly, 24 and 30 hours after zinc replenishment, esophagi had numerous apoptotic cells (% apoptotic 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 proapoptotic 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 apoptosis in esophageal epithelial cells and thereby substantially reduces the development of esophageal cancer.
Fong
L Y
LY
Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, PA 19107-6799, USA. L_Fong@lac.jci.tju.edu
Nguyen
V T
VT
Farber
J L
JL
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002254:Carbonates / Q000008:administration & dosage; D002273:Carcinogens; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced / Q000378:metabolism; D004128:Dimethylnitrosamine / Q000031:analogs & derivatives*; D004847:Epithelial Cells / Q000187:drug effects / Q000473:pathology; D004938:Esophageal Neoplasms / Q000139:chemically induced / Q000737:chemistry / Q000473:pathology / Q000517:prevention & control*; D004947:Esophagus / Q000737:chemistry / Q000187:drug effects / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006965:Hyperplasia; D008297:Male; D009363:Neoplasm Proteins / Q000032:analysis; D010212:Papilloma / Q000139:chemically induced / Q000737:chemistry / Q000473:pathology / Q000517:prevention & control*; D011230:Precancerous Conditions / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D011518:Proto-Oncogene Proteins / Q000032:analysis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015032:Zinc / Q000172:deficiency / Q000494:pharmacology / Q000502:physiology / Q000627:therapeutic use*; D017967:Zinc Compounds / Q000008:administration & dosage; D051028:bcl-2-Associated X Protein
C494828:Bax protein, rat; D002254:Carbonates; D002273:Carcinogens; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D017967:Zinc Compounds; D051028:bcl-2-Associated X Protein; C014707:nitrosobenzylmethylamine; C036650:zinc carbonate; D015032:Zinc; D004128:Dimethylnitrosamine