Residue Analyses: How They Were Used to Assess the Hazards of Contaminants to Wildlife, J.O. Keith DDT, DDD, and DDE in Birds, L.J. Blus Dieldrin and Other Cyclodiene Pesticides in Wildlife, D.B. Peakall Other Organochlorine Pesticides in Birds, S.N. Wiemeyer PCBs in Aquatic Organisms, A.J. Niimi Toxicological Implications of PCB Residues in Mammals, M.A. Kamrin and R.K. Ringer PCBs and Dioxins in Birds, D.J. Hoffman, C.P. Rice, and T.J. Kubiak Dioxins: An Environmental Risk for Fish? D. Sijm and A. Opperhuizen Polycyclic Aromatic Hydrocarbons in Marine Mammals, Finfish, and Molluscs, J. Hellou Lead in Waterfowl, D.J. Pain Interpretation of Tissue Lead Residues in Birds Other Than Waterfowl, J.C. Franson Lead in Mammals, W.-C. Ma Toxicological Significance of Mercury in Freshwater Fish, J.G. Wiener and D.J. Spry Mercury in Birds and Terrestrial Mammals, D.R. Thompson Metals in Marine Mammals, R.J. Law Cadmium in Small Mammals, J.A. Cooke and M.S. Johnson Cadmium in Birds, R.W. Furness Heavy Metals in Aquatic Invertebrates, P.S. Rainbow Selenium in Aquatic Organisms, A.D. Lemly Selenium in Birds, G.H. Heinz Fluoride in Birds, W.J. Fleming Fluoride in Small Mammals, J.A. Cooke, I.C. Boulton, and M.S. Johnson

/pdf/environmental-contaminants-in-wildlife-interpreting-tissue-4yboamevo7.pdf

Environmental contaminants in wildlife: interpreting tissue concentrations

On the nature of selenium toxicity and carcinostatic activity.

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.

/pdf/selenium-and-its-relationship-to-cancer-an-update-34e4t5ugbv.pdf

Selenium and its relationship to cancer: an update.

There are several selenocompounds in tissues of plants and animals. Selenate is the major inorganic selenocompound found in both animal and plant tissues. Selenocysteine is the predominant selenoamino acid in tissues when inorganic selenium is given to animals. Selenomethionine is the major selenocompound found initially in animals given this selenoamino acid, but is converted with time afterwards to selenocysteine. Selenomethionine is the major selenocompound in cereal grains, grassland legumes and soybeans. Selenomethionine can also be the major selenocompound in selenium enriched yeast, but the amount can vary markedly depending upon the growth conditions. Se-methylselenocysteine is the major selenocompound in selenium enriched plants such as garlic, onions, broccoli florets and sprouts, and wild leeks.

Selenocompounds in Plants and Animals and their Biological Significance

Selenium is regulated in the body to maintain vital selenoproteins and to avoid toxicity. When selenium is limiting, cells utilize it to synthesize the selenoproteins most important to them, creating a selenoprotein hierarchy in the cell. The liver is the central organ for selenium regulation and produces excretory selenium forms to regulate whole-body selenium. It responds to selenium deficiency by curtailing excretion and secreting selenoprotein P (Sepp1) into the plasma at the expense of its intracellular selenoproteins. Plasma Sepp1 is distributed to tissues in relation to their expression of the Sepp1 receptor apolipoprotein E receptor-2, creating a tissue selenium hierarchy. N-terminal Sepp1 forms are taken up in the renal proximal tubule by another receptor, megalin. Thus, the regulated whole-body pool of selenium is shifted to needy cells and then to vital selenoproteins in them to supply selenium where it is needed, creating a whole-body selenoprotein hierarchy.

E.J. Novacek

Papers

Investigations on selenium in wheat