Lauren Nielson and Dr. Merrill Christensen, Nutrition, Dietetics and Food Science
The purpose of my ORCA project was to determine the highest intake of selenomethylcysteine mice could consume without it being toxic to them. Selenium has been shown to have preventative effects on the progression of prostate cancer, so determining the optimum dosage of selenomethylcysteine (the most absorabable form of selenium) is essential for future research on this topic.
This project is important because selenium (Se) toxicity has not been systematically studied. There is no toxicity data regarding common mouse strains, and as these animals are often used as preclinical models of human disease this information would be highly valuable. Researchers using mice to study the effects of Se on human diseases need to know the maximum tolerable dosage to be physiologically relevant. We chose the C57BL/6 strain because it is a general, multi-purpose model and it is a strain frequently used to develop transgenic models of human disease. Methylselenocysteine (MSeC), a dietary relevant form of the trace element selenium, occurs in plants, and has been shown to be chemo-preventative (Wang et al, 2009). This experiment would find the maximum dosage of MSeC in the C57BL/6 that could be given while not being toxic. These findings inform all researchers of the effective dose of Se in any transgenic or knockout model derived from the C57BL/6 mouse. This information can be used to establish relevant human-subject doses and help to further the prevention of prostate cancer or other diseases on which Se may have preventive efficacy. This research is not only relevant to future research performed with transgenic mice models, but also the health of the American population.
We studied eight groups of mice. The study began immediately after the subjects had been weaned (age three weeks) and methylselenocysteine was administered to mice using a gavage technique. This technique involves pipetting the dose directly into the throat of the mouse, taking advantage of the lack of a gag reflex to mimic supplementation in humans and ensure the entire dose is administered. We used 8 animals per dietary treatment. Based on the average weight and standard deviation of C57BL/6 mice shown on the Charles River Laboratory growth chart for this strain, this sample size will be sufficient to detect a 15% difference in body weight at a statistical significance of 0.05 with 0.90 power. Doses ranged from 2 milligrams per kilogram of body weight to 20 milligrams per kilogram of body weight and were administered five times a week, at approximately the same time every day. The treatment groups were 2, 4, 6, 8, 10, 15, and 20 milligrams of Se per kilogram of body weight, as well as control group which was administered water by gavage. Past experiments demonstrated the efficacy of dosages of 2-4 milligrams per kilogram of body weight (Jiang et al, 2008; Li et al, 2007; Wang et al 2009) Our range of dosages ensured that toxicity occurred, but also provided a basis of comparison for these previous studies regarding the protective effects of MSeC. The mice were fed a low-isoflavone stock diet, since our recent studies in this lab showed that the effects Se may depend on the isoflavone content of the diet (Quiner et al, 2010). The use of weanling animals is a conservative approach as the efficacy of Se has been shown to be greater in younger mice. Young mice, where growth is most rapid, are most susceptible to the effects of Se or other forms of insult therefore results are safe for any age of mouse. Previous work manifests growth changes as early as 17 days (Li et al, 2007) but we continued the treatment to six weeks post weaning. We measured the weights of the mice daily (off of which we based each mouse’s unique dose), analyzed any changes in weight, and observed them daily for the first effects of toxicity i.e. lethargy, hunching, painful movement, and hair loss. After the period of measurement, the collected data was analyzed to determine the maximum dosage of MSeC that can be ministered to a young C57BL/6 mouse while not being toxic.
This study indicated that 4 milligrams per kilogram of body weight is the optimal dosage to be given in selenium studies. This dosage showed no statistical difference in growth rate when compared to the 0 mg/kg and 2 mg/kg dosage groups. Past experiments demonstrated the efficacy of dosages of 2 to 4 milligrams per kilogram of body weight, and our results are consistent with those previously published. As predicted, all dosages above 4 milligrams per kilogram of body weight demonstrated toxicity in the respective treatment groups.
Scholarly Sources
- Jiang W., Jeng C., Pei H., Wang L., Zhang J., Hu H., Lu J. (2008). In vivo molecular mediators of cancer growth suppression and apoptosis by selenium in mammary and prostate models: lack of involvement of gadd genes. Mol Canc Ther 2009; 8(3):682-691.
- Li G., Lee H., Wang Z., Hu H., Liao J.D., Watts J.C., Combs, G.F. Jr., Lu, J., (2007). Superior in vivo inhibitory efficacy of methylseleninic acid against human prostate cancer over selenomethionine or selenite. Carcinogenesis 2008; 29(5):1005-1012.
- Quiner T.E., Lindsay H.S., Mason B.A., Lephart E.D., Christensen M.J., (2010). Basal diet composition determines effects of supplemental selenium. FASEB 2010; 916.11.
- Wang L., Bonorden M.J.L., Li G., Lee H., Hu H., Zhang Y., Liao J.D., Cleary M.P., and Lu J., (2009). Methyl-Selenium Compounds Inhibit Prostate Carcinogenesis in the Transgenic Adenocarcinoma of Mouse Prostate Model with Survival Benefit .Cancer Prev Res 2009;2(5):484-495.