Dietary calcium supplementation and apoptosis in murine colonic epithelium

Abstract

Introduction: Increased dietary calcium may reduce colorectal cancer risk, possibly by reducing colonic epithelial hyperproliferation although some studies have failed to demonstrate effects on cell proliferation. Little is known about possible effects of calcium on intestinal apoptosis. Aim: To quantify the effects of increasing dietary calcium on apoptosis and cell proliferation in normal murine colonic crypt epithelium. Methods: 21 day old male C57BI/6 mice were fed either control (n=10) AIN-76 semisynthetic mouse diet (0.5% calcium, 0.5% phosphate wt/wt, n=10) or the same supplemented with calcium carbonate (1.0% Ca, 0.5% PO4, n=10) for 12 weeks. Animals were weighed weekly and food intake monitored. All were injected intraperitoneaUy with 50mg/kg bromodeoxyuridine (BrdU) 1 hour before death. Colons were measured and divided into proximal and distal portions. Apoptotic cells were counted in routine formalin-fixed paraffin sections stained with haematoxylin and eosin and expressed as an apoptotic index (AI) per 100 longitudinal crypts. The BrdU labeling index (LI) was expressed as positively stained cells per 100 crypts. Differences were analyzed by Student's t-test. Results: (mean +SEM) There were no significant differences in initial or final animal weights or food intake between the groups (data not shown). In control animals A1 was significantly higher in caecum/proximal colon compared to distal colon (p = 0.004, see Table). In the calcium treated group AI in caecum/proximal colon was similar to controls (p = 0.71) but the AI in distal colon was significantly greater (p = 0.001) and raised to levels similar to those in proximal colon. There were no significant differences in the BrdU L1 between groups or between proximal and distal colonic segments in each group.