Wednesday, March 16, 2011

Does selenium prevent cancer?

Public release date: 16-Mar-2011

Does selenium prevent cancer?

It may depend on which form people take
Scientists are reporting that the controversy surrounding whether selenium can fight cancer in humans might come down to which form of the essential micronutrient people take. It turns out that not all "seleniums" are the same — the researchers found that one type of selenium supplement may produce a possible cancer-preventing substance more efficiently than another form of selenium in human cancer cells.

Their study appears in the ACS' journal Biochemistry.
Hugh Harris and colleagues note that although the Nutritional Prevention of Cancer clinical trial showed that selenium reduced the risk of cancer, a later study called the Selenium and Vitamin E Cancer Prevention Trial did not show a benefit. A major difference between the trials was the form of selenium that was used. To find out whether different types of selenium have different chemopreventive properties, the researchers studied how two forms—SeMet and MeSeCys—are processed in human lung cancer cells.

The researchers found that MeSeCys killed more lung cancer cells than SeMet did. Also, lung cancer cells treated with MeSeCys processed the selenium differently than than cells treated with SeMet. They say that these findings could explain why studies on the health benefits of selenium sometimes have conflicting results.

The authors acknowledge funding from the Australian Research Council.

Biochemistry. 2011 Mar 15;50(10):1641-50.
Epub 2011 Feb 20.

Uptake, Distribution, and Speciation of Selenoamino
Acids by Human Cancer Cells: X-ray Absorption and Fluorescence Methods.

Weekley CM, Aitken JB, Vogt S, Finney LA, Paterson DJ, de Jonge MD, Howard DL, Musgrave IF, Harris HH.

School of Chemistry and Physics, The University of Adelaide, Adelaide, SA 5005, Australia.

Selenium compounds exhibit chemopreventative properties at supranutritional doses, but the efficacy of selenium supplementation in cancer prevention is dependent on the chemical speciation of the selenium supplement and its metabolites. The uptake, speciation, and distribution of the common selenoamino acid supplements, selenomethionine (SeMet) and Se-methylselenocysteine (MeSeCys), in A549 human lung cancer cells were investigated using X-ray absorption and fluorescence spectroscopies. X-ray absorption spectroscopy of bulk cell pellets treated with the selenoamino acids for 24 h showed that while selenium was found exclusively in carbon-bound forms in SeMet-treated cells, a diselenide component was identified in MeSeCys-treated cells in addition to the carbon-bound selenium species. X-ray fluorescence microscopy of single cells showed that selenium accumulated with sulfur in the perinuclear region of SeMet-treated cells after 24 h, but microprobe selenium X-ray absorption near-edge spectroscopy in this region indicated that selenium was carbon-bound rather than sulfur-bound. X-ray absorption and X-ray fluorescence studies both showed that the selenium content of MeSeCys-treated cells was much lower than that of SeMet-treated cells. Selenium was distributed homogeneously throughout the MeSeCys-treated cells.
PMID: 21261286 [PubMed - in process]

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