Calcium carbonate suppresses haem toxicity markers without calcium phosphate side effects on colon carcinogenesis

Abstract

Red meat intake is associated with an increased risk of colorectal cancer. We have previously shown that haemin, Hb and red meat promote carcinogen-induced preneoplastic lesions, aberrant crypt foci (ACF), in the colon of rats. We have also shown that dietary calcium phosphate inhibits haemin-induced promotion and normalises faecal lipoperoxides and cytotoxicity. Unexpectedly, high-calcium phosphate control diet-fed rats had more preneoplastic lesions in the colon than low-Ca control diet-fed rats. The present study was designed to find a Ca supplementation with no adverse effect, by testing several doses and types of Ca salts. One in vitro study and two short-term studies in rats identified calcium carbonate as the most effective Ca salt to bind haem in vitro and to decrease faecal biomarkers previously associated with increased carcinogenesis: faecal water cytotoxicity and thiobarbituric acid-reactive substances. A long-term carcinogenesis study in dimethylhydrazine-injected rats demonstrated that a diet containing 100 μmol/g calcium carbonate did not promote ACF, in contrast with a previously tested calcium phosphate diet. The results suggest that calcium carbonate, and not calcium phosphate, should be used to reduce haem-associated colorectal cancer risk in meat eaters. They support the concept that the nature of the associated anion to a protective metal ion is important for chemoprevention.

Figure 1

Effect of diets on haem and TBARS in faecal water after the first short term study (A) Haem in faecal water. (B) TBARS (MDA equivalents) in faecal waters as marker for lipid luminal peroxidation. * Significantly different from Phos20 (P<0.01, by fisher LSD test). Data are means, bars are standard deviations (n = 5 in each group). Note: Phos20 to Phos250 are low-calcium beef diet supplemented with calcium phosphate from 20 μmol/g to 250 μmol/g. Carb250 and Gluc 250 are low-calcium beef diet supplemented respectively with calcium carbonate and calcium gluconate at 250 μmol/g.

Figure 2

Effect of calcium salts on haem solubility in vitro. Haem (0.36 mM) was incubated with six different concentrations of calcium salts (150, 125, 100, 75, 50, 25 mMol). Data are means, bars are standard deviations (n = 3). * Significantly different from other salts.

Figure 3

Effect of calcium carbonate-based diets (30 to 155 μmol/g) on faecal water values after the second short term study A. Haem concentration in faecal water (μmol/L) B. TBARS concentration in faecal water, expressed as μmol/L MDA equivalents. * Significantly different from Carb30 by fisher LSD test (P< 0.05). Data are mean, bars are standard deviation (n=5 in each group). Note: Carb33 to Carb155 are low-calcium haemoglobin diet supplemented with calcium carbonate from 33 μmol/g to 155 μmol/g.

Figure 4

Effect of calcium salts in diet on putative precancerous lesions (ACF) per rat colon 101 d after the injection of dimethylhydrazine. Hatched bars are results of this study with 100 μmol/g of calcium carbonate. Solid bars are previous results with 250 μmol/g of calcium phosphate (Pierre et al 2008 [16]). Results are expressed after normalization of the Control Diet groups to 100. * Significantly different control group (CD). Note: The Control Diet was a low-calcium haemoglobin diet supplemented with calcium carbonate at 33 μmol/g. Carb100 and CaPhos250 are low-calcium haemoglobin diet supplemented respectively with calcium carbonate (100μmol/g) and calcium gluconate ( 230 μmol/g).

Figure 5

Meta-analysis of the relation between calcium carbonate and colon cancer in carcinogen-injected rats. The common relative risk with 95% confidence was calculated from 11 studies.* * Solid black circles correspond to the study specific relative risk. The open white circle represents the common relative risk. Horizontal lines are 95% confidence intervals. References are indicated between brackets