Diet, body mass index, and colonic epithelial cell proliferation in a healthy population

Rectal epithelial proliferation in persons with or without a history of adenoma and its association with diet and lifestyle habits

BACKGROUND

Rectal epithelial proliferation (REP) measurements are used as a biomarker of risk for colorectal neoplasia and response to chemoprevention. The authors evaluated REP in screenees with and without a history of adenoma and its association with demographic and adenoma characteristics, diet, and other lifestyle habits.

METHODS

Long term lifestyle habits were evaluated and proliferation assessed by in vitro bromodeoxyuridine labeling of rectal biopsies in 223 screenees, 132 of whom had adenomas removed > 3 years previously. Analyses included the total population, screenees with a previous history of adenomas and adenoma free screenees separately, and a subgroup of 55 matched adenoma cases and controls.

RESULTS

Crypt proliferation measurements were not elevated in screenees with a history of adenomas compared with adenoma free screenees (mean total labeling index [LI] of 4.8% and 4.9%, respectively). This was confirmed by the case-control analysis, in which the LI of the most superficial crypt compartment was lower in the adenoma cases (P=0.05). Moreover, their total LI correlated negatively with the number of adenomas removed previously (P < 0.01). Proliferation was more frequent in the most superficial crypt compartments of female adenoma free screenees than in female screenees with a history of adenomas (P=0.02), and in men age > 65 years compared with younger men (P=0.06). In the total population, negative Spearman rank correlations were found between total LI and long term dietary intake of calcium (correlation coefficient [r]=-0.15; P=0.02), LI of the two most superficial crypt compartments and intake of fiber (r=-0.18; P=0.01), water (r=-0.12; P=0.08), and carbohydrates (not significant). A positive correlation was found between LI of the most superficial crypt compartment and cigarette smoking (r=0.4; P=0.02).

CONCLUSIONS

REP measurements did not discriminate between screenees with a history of adenomas and adenoma free screenees. Long-term lifestyle habits, gender, and age were associated with REP levels and need to be considered when evaluating human intervention studies.

Iron supplementation does not affect cell proliferation or aberrant crypt foci development in the colon of sprague-dawley rats

It has been suggested that high iron stores enhance colon carcinogenesis. The effect of high dietary iron (Fe) on indices of iron, copper (Cu) and manganese (Mn) status, lipid peroxidation using the thiobarbituric acid reactive substances assay, superoxide dismutase, glutathione peroxidase, glutathione transferase and ceruloplasmin activities, cell proliferation and development of preneoplastic lesions known as aberrant crypt foci (ACF) in rat colon was examined using a 3 x 2 factorial design. Male weanling Sprague-Dawley rats were fed adequate (AFe; 45 mg Fe/kg diet), moderately high (MHFe; 225 mg Fe/kg diet) and high (HFe; 450 mg Fe/kg diet) dietary Fe for 2.5 wk, then treated with azoxymethane (AOM; 2 injections, 1 wk apart; total dose 30 mg/kg body weight) or saline (n = 14-15 per group). Dietary treatment continued for another 6 wk after the second AOM dose. At the time of AOM injection, colon Fe concentrations were one- and threefold higher for MHFe and HFe rats, respectively, than for AFe rats. It was proposed that high dietary Fe would adversely affect Cu and Mn status, resulting in impaired antioxidant enzyme activity. However, neither indices of Cu and Mn status nor colonic mucosal antioxidant enzyme activities were affected by dietary Fe except for plasma ceruloplasmin activity, which was slightly lower in rats fed high iron diets than in rats fed adequate iron diets (P < 0.01). Dietary Fe had no significant effect on colonic mucosal lipid peroxidation, cell proliferation or ACF development. In conclusion, our findings suggest that dietary Fe concentrations that are approximately 5 and 10 times adequate do not enhance oxidative stress, cell proliferation and ACF development in the colon of rats.

Ca2+-sensing receptors in intestinal epithelium

Expression of Ca2+-sensing receptors (CaR) was demonstrated in several human intestinal epithelial cell lines (T84, HT-29, and Caco-2) and in rat intestinal epithelium by both reverse transcriptase-polymerase chain reaction (PCR) and Northern blotting of RNA. Restriction patterns of the PCR products were of the sizes predicted by the human and rat sequences. CaR agonists (Ca2+, poly-L-arginine, protamine) mediated an increase in intracellular Ca2+ in HT-29-18-C1 cells (monitored by changes in fura 2 fluorescence), which was dependent on release from thapsigargin-sensitive stores. U-73122, an inhibitor of phosphatidylinositol-phospholipase C, eliminated the CaR agonist-mediated rise in intracellular Ca2+, whereas its inactive analog, U-73343, had no effect. Pertussis toxin pretreatment had no effect on CaR agonist-mediated modulation of intracellular Ca2+. Taken together, these studies demonstrate that CaR are expressed in intestinal epithelial cells and couple to mobilization of intracellular Ca2+. The presence of CaR in intestinal epithelial cells presents a new locus for investigations into the role(s) of extracellular Ca2+ in modulating intestinal epithelial cell differentiation and transepithelial Ca2+ transport.

Ascorbic acid and gastrointestinal cancer

A literature review was made to critically evaluate the ability of ascorbic acid to modulate the incidence of gastrointestinal cancer. A comparison of preclinical, clinical, and epidemiological studies indicated that evidence for ascorbic acid as an inhibitor of carcinogenesis is stronger with regard to gastric cancer and weaker with regard to esophageal and colon/rectal cancer. Insufficient evidence currently exists regarding the oral cavity and the use of ascorbic acid in precancerous conditions such as polyposis and leukoplakia.