Effects of selenium supplementation on selenoprotein gene expression and response to influenza vaccine challenge: a randomised controlled trial

Abstract

Background: The uncertainty surrounding dietary requirements for selenium (Se) is partly due to limitations in biomarkers of Se status that are related to health outcomes. In this study we determined the effect of different doses and forms of Se on gene expression of selenoprotein S (SEPS1), selenoprotein W (SEPW1) and selenoprotein R (SEPR), and responses to an immune function challenge, influenza vaccine, were measured in order to identify functional markers of Se status.

Methods and findings: A 12 week human dietary intervention study was undertaken in 119 volunteers who received placebo, 50, 100 or 200 µg/day Se-enriched yeast (Se-yeast) or meals containing unenriched or Se-enriched onions (50 µg/day). Gene expression was quantified in RNA samples extracted from human peripheral blood mononuclear cells (PBMC's) using quantitative RT-PCR. There was a significant increase in SEPW1 mRNA in the Se-enriched onion group (50 µg/day) compared with the unenriched onion group. SEPR and SEPW1 did not change significantly over the duration of the supplementation period in the control or Se-yeast groups, except at week 10 when SEPW1 mRNA levels were significantly lower in the 200 µg/day Se-yeast group compared to the placebo group. Levels of SEPS1 mRNA increased significantly 7 days after the influenza vaccine challenge, the magnitude of the increase in SEPS1 gene expression was dose-dependent, with a significantly greater response with higher Se supplementation.

Conclusions: This novel finding provides preliminary evidence for a role of SEPS1 in the immune response, and further supports the relationship between Se status and immune function.

Trial registration: ClinicalTrials.gov [NCT00279812].

Figure 1. Plasma Se concentration over the 12 week intervention period for all groups.

Values are means ± SEM. □ Placebo (n = 20); ▪ 50 µg/day Se-yeast (n = 17); ♦ 100 µg/day Se-yeast (n = 21); ×200 µg/day Se-yeast (n = 23); ○ Unenriched onions (n = 16); • 50 µg/day Se-enriched onion meals (n = 18). ▴ denotes influenza vaccine challenge administered at week 10 of the study. Plasma Se concentration data displayed for weeks 11 and 12, one and two weeks post-vaccination, are novel data. To display the effect of Se supplementation over the duration of the intervention period and to illustrate the plasma Se concentration before and after vaccination, data from time points baseline, week 6 and 10 are reproduced with permission of Hurst et al. 2010 .

Figure 2. mRNA level in PBMCs measured over the duration of intervention period for (A) SEPW1, (B) SEPS1, (C) SEPR in the placebo and Se-yeast groups.

Values are means ± SEM relative to baseline, week 0 expression. GUSB was used as reference gene for normalisation. White bars  =  placebo group (n = 14 to 20); light grey bars  =  50 µg/day Se-yeast (n = 11 to 15); mid grey bars  =  100 µg/day Se-yeast (n = 10 to 19); black bars  =  200 µg/day Se-yeast (n = 14 to 18). The variation in sample number (n) between time points for each treatment is due to insufficient RNA at some sampling time points and missing time course sample data for some of the target genes. For the SEPS1 gene expression data set: placebo group n = 20 at all time points; 50 µg/day group n = 14 at wks 0, 6 and 12 (n = 13 at wks 10, 11); 100 µg/day group n = 19 at wks 0, 6, 10 (n = 18 at wks 11, 12); 200 µg/day group n = 18 at wks 0, 6, 12 (n = 17 wk 10, n = 15 wk 11). Data were analysed using mixed-effects models and statistically significant differences are indicated on the figure.

Figure 3. SEPS1 mRNA level in PMBCs measured over the intervention period, each time point showing the mean of all the yeast supplement groups (placebo, 50, 100 and 200 µg/day).

GUSB was used as reference gene for normalisation. Data are presented as mean ± SEM (n = 65 to 71 per time point) relative to baseline, week 0 expression.

Figure 4. SEPW1, SEPS1 and SEPR mRNA level over the duration of the intervention in the PBMC samples from the unenriched and Se-enriched onion meal groups.

SEPW1, SEPS1 and SEPR mRNA levels were quantified using real time RT-PCR and normalised to reference gene, GUSB. Data expressed are means ± SEM relative to baseline, week 0 expression. (A) SEPW1, (B) SEPS1, (C) SEPR. Values are means ± SEM. ---○--- unenriched onions, n = 14 to 16;—•— Se-enriched onions, n = 16 to 17. SEPW1 mRNA level is significantly greater in the enriched onion group compared to the unenriched onion group (p = 0.012). SEPS1 mRNA level is significantly influenced by week (p = 0.009).