Effects of chemical form of selenium on plasma biomarkers in a high-dose human supplementation trial

Selenoprotein P mRNA expression in human hepatic tissues

AIM

To investigate the expression of selenoprotein P mRNA (SePmRNA) in tissues of normal liver, liver cirrhosis and hepatocellular carcinoma (HCC), and its relationship with HCC occurrence and development.

METHODS

The expression of SePmRNA in tissues of normal liver, liver cirrhosis and HCC were detected by in situ hybridization using a cDNA probe.

RESULTS

The enzyme digesting products of PBluescript-Human Selenoprotein P were evaluated by electrophoresis. The positive expression of SePmRNA was found in the tissues of normal liver, liver cirrhosis and HCC. The expression of SeP mRNA was found in hepatic interstitial substance, especially in endothelial cells and lymphocytes of vasculature. The positive rate of SePmRNA in normal liver tissue was 84.6% (11/13) and the positive signals appeared in the nucleus and cytoplasm, mostly in the nucleolus, and the staining granules were larger in the nucleolus and around the nucleus. The positive rate of SePmRNA in liver cirrhosis tissue was 45.0% (9/20) and the positive signals were mainly in the nucleolus and cytoplasm, being less around the nucleus and inner nucleus than that in normal liver tissue. The positive rate of SePmRNA in HCC tissue was 30.0% (9/30) and the positive signals were in the cytoplasm, but less in the nucleus.

CONCLUSION

SePmRNA expression in the tissues of normal liver and HCC is significantly different (84.6% vs 30.0%, P=0.003), suggesting that SeP might play a role in the occurrence and development of HCC.

Randomised, double blind, placebo-controlled trial of selenium supplementation in adult asthma

BACKGROUND

Epidemiological evidence from observational studies has suggested that blood levels and dietary intake of selenium of adults with asthma are lower than those of controls. The only previous trial of selenium supplementation in adults with asthma found no objective evidence of benefit but involved only 24 participants.

METHODS

A randomised, double blind, placebo-controlled trial of selenium supplementation was performed in adults with asthma in London, UK, the majority of whom (75%) reported inhaled steroid use at baseline. 197 participants were randomised to receive either a high-selenium yeast preparation (100 microg daily, n=99) or placebo (yeast only, n=98) for 24 weeks. The primary outcome was asthma-related quality of life (QoL) score. Secondary outcomes included lung function, asthma symptom scores, peak flow and bronchodilator usage. Linear regression was used to analyse the change in outcome between the two treatment arms by "intention to treat".

RESULTS

There was a 48% increase in plasma selenium between baseline and end of trial in the active treatment group but no change in the placebo group. While the QoL score improved more in the active treatment group than in the placebo group, the difference in change in score between the two groups was not significant (-0.05 (95% CI -0.19 to 0.09); p=0.47). Selenium supplementation was not associated with any significant improvement in secondary outcomes compared with placebo.

CONCLUSIONS

Selenium supplementation had no clinical benefit in adults with asthma, the majority of whom were taking inhaled steroids.

Selenium and coronary heart disease: a meta-analysis

BACKGROUND

It is hypothesized that low selenium concentrations are associated with an increased risk of cardiovascular disease and that selenium supplements prevent coronary heart disease.

OBJECTIVE

The objective was to perform a meta-analysis on the association of selenium biomarkers with coronary heart disease endpoints in observational studies and on the efficacy of selenium supplements in preventing coronary heart disease endpoints in randomized trials.

DESIGN

The MEDLINE and the Cochrane Library databases were searched for studies conducted from 1966 through 2005. Relative risks were pooled by using an inverse-variance weighted random-effects model.

RESULTS

Twenty-five observational studies (14 cohort and 11 case-control studies) that measured blood or toenail selenium concentrations and 6 randomized trials that evaluated supplements containing selenium met our inclusion criteria. The pooled relative risk in a comparison of the highest with the lowest selenium concentration categories was 0.85 (95% CI: 0.74, 0.99) in cohort studies and 0.43 (0.29, 0.66) in case-control studies. In observational studies, a 50% increase in selenium concentrations was associated with a 24% (7%, 38%) reduction in coronary heart disease risk. In randomized trials, the pooled relative risk in a comparison of supplements containing selenium with placebo was 0.89 (0.68, 1.17).

CONCLUSIONS

Selenium concentrations were inversely associated with coronary heart disease risk in observational studies. Because observational studies have provided misleading evidence for other antioxidants, the validity of this association is uncertain. Few randomized trials have addressed the cardiovascular efficacy of selenium supplementation, and their findings are still inconclusive. Evidence from large ongoing trials is needed to establish low selenium concentrations as a cardiovascular disease risk factor. Currently, selenium supplements should not be recommended for cardiovascular disease prevention.

Selenium: From cancer prevention to DNA damage

Selenium (Se) is a dietary essential trace element with important biological roles. Accumulating evidence indicates that Se compounds possess anticancer properties. Se is specifically incorporated into proteins in the form of selenocysteine and non-specifically incorporated as selenomethionine in place of methionine. The effects of Se compounds on cells are strictly compositional and concentration-dependent. At supranutritional dietary levels, Se can prevent the development of many types of cancer. At higher concentrations, Se compounds can be either cytotoxic or possibly carcinogenic. The cytotoxicity of Se is suggested to be associated with oxidative stress. Accordingly, sodium selenite, an inorganic Se compound, was reported to induce DNA damage, particularly DNA strand breaks and base damage. In this review we summarize the various activities of Se compounds and focus on their relation to DNA damage and repair. We discuss the use of Saccharomyces cerevisiae for identification of the genes involved in Se toxicity and resistance.