Selenium and its relationship to cancer: an update

Abstract

Selenomethionine (Semet) is the major seleno-compound in cereal grains and enriched yeast whereas Se-methylselenocysteine (SeMCYS) is the major seleno-compound in Se-accumulator plants and some plants of economic importance such as garlic and broccoli exposed to excess Se. Animals can metabolize both Semet and SeMCYS. Epidemiological studies have indicated an inverse relationship between Se intake and the incidence of certain cancers. Blood or plasma levels of Se are usually lower in patients with cancer than those without this disorder, but inconsistent results have been found with toenail-Se values and the incidence of cancer. There have been eight trials with human subjects conducted on the influence of Se on cancer incidence or biomarkers, and except for one, all have shown a positive benefit of Se on cancer reduction or biomarkers of this disorder. This is consistent with about 100 small-animal studies where Se has been shown to reduce the incidence of tumours in most of these trials. Se-enriched yeast is the major form of Se used in trials with human subjects. In the mammary-tumour model, SeMCYS has been shown to be the most effective seleno-compound identified so far in reduction of tumours. Several mechanisms have been proposed on the mechanism whereby Se reduces tumours. Even though SeMCYS was shown to be the most effective seleno-compound in the reduction of mammary tumours, it may not be the most effective seleno-compound for reduction of colon tumours.

Polymorphisms in the selenoprotein S and 15-kDa selenoprotein genes are associated with altered susceptibility to colorectal cancer

“…Selenium (Se) is a dietary micronutrient that is essential for human health [23,29]. Cancer mortality is inversely correlated with estimated Se intake [8,29].…”

“…Cancer mortality is inversely correlated with estimated Se intake [8,29]. Low Se intake or low plasma Se concentrations are associated with increased risk of colorectal cancer (CRC) [7,25] whereas in contrast, higher Se status is associated with lower risk of a recurrence of colonic tumours [15].…”

Selenite and selenate affect the fatty acid profile in in vitro incubated ovine ruminal fluid containing linseed oil

“…Analysis of the selenium (Se) concentration of the microorganisms revealed that the ruminal microbial Se abundance was enriched relative to the level of Se in the diets. This concentration of Se in the ruminal microorganisms was significantly higher than that of the diet (Lyons and Jacques, 2001;Whanger, 2004). Ruminal bacteria are also able to synthesize Se-methionine (Se-Met) and Se-cysteine (Se-Cys), and these Se-amino acids (Se-AA) are then incorporated into the microbial protein.…”

“…Ruminal bacteria are also able to synthesize Se-methionine (Se-Met) and Se-cysteine (Se-Cys), and these Se-amino acids (Se-AA) are then incorporated into the microbial protein. The predominant Se-AA was Se-Cys, when the ruminal microbes were incubated with Se IV or Se VI (Whanger, 2004). Microorganisms can reduce excessive doses of Se-compounds to unabsorbable elemental Se or selenide forms.…”

Selenium induced selenocysteine methyltransferase gene expression and antioxidant enzyme activities in Astragalus chrysochlorus

“…In addition to nutritional needs for Se, the element also has health efficacy. It is also effective in reducing the incidence of some debilitating disorders (McKenzie et al 2001, Foresta et al 2002, Beck et al 2003, Soriano-Garcia 2004 and there is some evidence that Se plays a role as a cancer preventive agent when given in certain amounts (Ip 1998, Combs and Gray 1998, Fleming et al 2001, Whanger 2004.…”