Effects of Selenium and Low Levels of Lead on Mamm

Authors: G N Schrauzer

Publish Date: 2008/08/26

Volume: 125, Issue: 3, Pages: 268-

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Abstract

Selenium Se has been demonstrated in previous studies to inhibit mammary tumorigenesis in C3H mice infected with the murine mammary tumorvirus MMTV The antitumorigenic effects of Se in this animal model of breast cancer were subsequently shown to be counteracted by Seantagonistic elements Lead Pb for example was found to abolish the anticarcinogenic effects of Se at 5 ppm in the drinking water The present study was undertaken to explore the effects of Pb at just 05 ppm in the water ie at a level comparable to the concentrations of Pb that have been measured in the tap water of older homes in some communities Groups of 30 female virgin C3H/St mice infected with MMTV maintained on Torula yeastbased diets containing either 015 or 065 ppm of yeastbased organic Se and received either deionized water or water containing 05 ppm Pb as the acetate over their entire postweaning lifespan In the control group on deionized water and the 015 ppm Se feed the tumor incidence was 786 which is normal for this strain Increasing the Se content of the feed to 065 ppm lowered the tumor incidence to 30 demonstrating the antitumorigenic effect of Se In the experimental groups the Pbexposed mice on the 015 ppm Se feed developed signs of chronic Pb toxicity as evidenced by diminished weight gain that persisted up to the age of 10 months during which period the animals remained tumorfree Thereafter weight gains ensued to near the values of the controls and the tumors began to develop in rapid succession until the final tumor incidence of 737 was reached In the group of mice on the 065 ppm Se feed the toxic effects of Pb were diminished as evidenced by the normal weight gains during the first 10 months but with concomitant physiological inactivation of Se causing 826 of the mice to develop tumors with the first tumor to appear at the age of 5 months 7 months earlier than in the Pbunexposed controls In addition tumor growth rates in this group were greatly accelerated and the survival of the tumorbearing animals was significantly shortened Direct evidence for the interactions of Pb with Se were obtained by determinations of the two elements in the livers kidneys and hair of tumorfree and tumorbearing mice However the exposure of the mice to Pb in the water also altered the levels of Zn Cu Fe and Cr in the organs and tissues more so in tumorbearing than tumorfree animals The present study demonstrates the need to consider the interactions of Se with other trace elements in discussions of its mechanism of anticarcinogenic actionThis work was supported in part by funds from the US Department of Agriculture the US National Science Foundation and the University of California San Diego The experimental assistance of D Hamm L Bell R Pelton J Palmer and T Molenaar is gratefully acknowledged

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