Determining effective Selenium exposures for individuals/subgroups of differing Selenium status, has direct public health significance as it will determine whether Selenium is part of a pharmaceutical or a healthy food intervention strategy. That is, the 200 μg dose can be achieved only through the use of nutritional supplements, whereas lower exposures (e.g., 50-100 μg) may be achieved by food-based approaches, using normally consumed foods or foods enriched through such means as sourcing from high-Se soils, Se-fertilization, and Se-fortification.
A randomized, double-blind, intervention study will be conducted. Briefly, the protocol will be as follows:
Subject recruitment: Healthy men (120) and women (120) will be recruited by the Grand Forks Human Nutrition Research Center (GFHNRC) from the Grand Forks, ND, community. Each prospective volunteer, will sign an informed consent and be evaluated for eligibility on the basis of a physical examination, standard clinical chemistries, health and diet histories.
Treatment: Subjects will be assigned randomly to treatments consisting of 0, 50, 100, or 200 ug Se/day (as L-selenomethionine) administered in daily oral doses. Each subject will receive a 30 day supply of pills and must return to the Center monthly to receive a new supply.
Endpoints: Fasting blood samples and 24-hr. urine samples will be drawn one week prior to and at the beginning of the study, and at three mo. intervals for a year of supplementation. Selenium, homocysteine, vitamin B12 and folate (potential effectors of the methylation-dependent excretion of Se) and glutathione peroxidase activity will be determined in plasma. Selenium and 8-OH-deoxyguanosine will be determined in urine. Blood will be analyzed for DNA damage utilizing flow cytometric methods and the comet assay. At the beginning of the study, lymphocytes will be prepared from whole blood samples from each subject; cellular DNA will be prepared and archived for future determinations of the allelic variants of Se-dependent enzymes (e.g., glutathione peroxidases [GPX] 1 and 4), selenoprotein P and selenoprotein 15 and/or other relevant enzymes (e.g., glutathione S-transferase). Analytical results will be used to compute the relationship of final-plateau plasma (9-12 mos.) Se concentration as a function of baseline (0 mos.) Se level, Se dose (μg/d), metabolic body size (k 0.75) and urinary Se, as well as outcomes related to carcinogenesis (lymphocyte DNA damage and urinary 8-OH-deoxyguanosine). Other parameters will be tested for significance as covariants: sex; plasma homocysteine, folate and vitamin B12; and selenoprotein genotypes.
Subject Compensation: Subjects will be compensated for their participation in the supplementation study, $300/subject using a graded payment schedule.
Human Subjects Protection: The study protocol will be reviewed and approved by the University of North Dakota Human Subjects Committee, which provides that service to the GFHNRC.
Publication of Results: The results will be published in the open, peer-reviewed scientific literature. Authorship will be consistent with the policies of both agencies; it is anticipated that authorship will reflect the contributions of Drs. Combs, Davis and Milner as well as other collaborating scientists from each agency.
Addendum: In this addendum to the statement of work, the GFHNRC will conduct a short term study to examine changes in gene expression in response to selenium supplementation in individuals homozygous for the proline containing allele and individuals homozygous for the leucine containing allele at position 198 of the glutathione peroxidase gene. The money from this addendum would be used for recruitment, genotyping, subject feeding, sample collection and/or subject stipends. |