Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 8, 2002
Publication Date: September 8, 2002
Citation: Reeves, P.G., Chaney, R.L. 2002. Mineral nutrient status of the consumer affects the bioavailability of cadmium from food [abstract]. Presented at teh 2nd Conference on Molecular Mechanisms of Metal Toxicity and Carcinogenesis, Morgantown, WV, September 8-11, 2002. Technical Abstract: Grains such as rice, wheat, and maize consumed as staple foods by different population groups differ greatly in their concentrations and bioavailability of nutrients that are antagonists to cadmium (Cd) absorption. These include zinc (Zn), iron (Fe), and calcium (Ca). We hypothesized that individuals who consume these grains as a major portion of their diet will have low nutritional status for these minerals; thus, they become more susceptible to soil Cd contamination from these grains than from other foods with a higher mineral content and a higher bioavailability. Experimental design. To test this hypothesis, we used the laboratory rat as the animal model. We used polished rice and roasted sunflower kernels (SFK) to represent foods with low and high concentrations of natural minerals, respectively. A 2x2x2 factorial study was conducted with each food source. Rats were fed diets with adequate or marginal amounts of dietary Zn, Fe, or Ca. The basal diets for rice contained 40% unenriched, milled rice fortified with 0.62 mg Cd/kg (0.25 mg Cd/kg diet). The basal diets for SFK contained 20% roasted, ground SFK containing 0.9 mg endogenous Cd/kg of (0.18 mg Cd/kg diet). Rats consumed each diet for 5 weeks to allow the intestinal absorption processes to adapt to the composition of the test diets, and then were fed 1 g of a similar diet labeled with 109Cd in the rice or SFK. After 2 more weeks of consuming unlabeled test diets, whole-body (WB) retention of 109Cd was determined. Rats then were killed and organs removed for total Cd determinations. A second experiment was conducted to determine the effects of marginal mineral intake on the accumulation and turnover of Cd in the intestine and other organs. Rats were fed rice-based diets with adequate or marginal amounts of dietary Zn, Fe, or Ca for 5 wk. They were dosed with 1 g of 109Cd-labeled diets, returned to unlabeled diets, and then killed at intervals up to 64 days. Various organs, including different segments of the small intestine were removed to measure the retention of 109Cd. Results of experiment 1: Marginal diets caused mild deficiencies in the rats, but not to the extent of inhibiting growth. Rats fed rice diets with marginal concentrations of dietary Zn had slightly but significantly more WB retention of 109Cd than controls; however, rats fed marginal Fe or Ca had 3-fold higher retention of the label. Rats fed marginal amounts of all three minerals retained as much as 8 times more 109Cd than rats fed adequate minerals. Whole body retention of 109Cd was not affected when rats were fed SFK diets with marginal Zn; however, when marginal amounts of Fe or Ca, or a combination of both, were fed, the retention of the label was increased 4-fold. No effect of Zn with SFK might reflect the naturally high content of this mineral in SFK as compared to the low content of rice. When the results were compared between marginal rice diets and SFK diets, the amount of retained Cd and its label was about 3 times higher in rats fed the rice diet. The effects on Cd concentrations in liver and kidney were similar to the effects on 109Cd retention. Results of experiment 2: The intestine was divided into 5 parts from the duodenum to the jejunum. Six to 12 hr after dosing with diet containing 109Cd, the duodenum of rats eating the diet with adequate minerals contained 50 times more label than the lower part of the jejunum, but in rats eating the marginal Zn-Fe-Ca diet, the difference was 300 times. The amount of 109Cd in the duodenum of marginally fed rats was 6 times higher than in rats fed diets with an adequate supply of minerals. Disappearance of the label over a 64-day period showed that the turnover rate in the gut was similar between groups, with highest 109Cd present in the upper duodenum. 109Cd in the liver peaked at about 8 days after dosing and was about 7 times higher in the marginal rats than in the adequate rats. 109Cd in the kidney was still increasing in the marginal rats after 64 days and was about 10 times higher than that in the kidneys of adequate rats. These results support the hypothesis that populations exposed to dietary sources of Cd and subsisting on marginal mineral intakes have a greater risk of developing Cd-related disease than populations who are well-nourished but exposed to similar amounts of dietary Cd. Thus, different food crops might cause unequal Cd risk at equal Cd concentration if diets containing the food are not balanced to provide adequate concentrations of interacting minerals.