Kinetics of selenium incorporation into tissues of female mallard ducks

Selenium toxicokinetics after oral and intravenous administration in buffalo calves

The blood levels, toxicokinetics and urinary excretion of selenium were investigated in healthy male buffalo calves after single oral and intravenous administration of selenourea at the dose rate of 0.75mg/kg (providing 0.48mg/kg selenium). The concentration of selenium in blood and urine was estimated spectrophotometrically. Following administration of the drug, the blood selenium disposition patterns exhibited two distinct peaks. The toxicokinetic parameters of selenium were determined by employing non-compartmental analysis. The values of AUC, t(1/2elm), Cl(B) and Vd(SS) were 18.46μgml(-1)h, 10.33h, 20.04mlkg(-1)h(-1)and 0.3lkg(-1), respectively, after oral administration and 23.97μgml(-1)h, 7.12h, 20.53mlkg(-1)h(-1) and 0.2lkg(-1), respectively, following intravenous injection of selenourea. The value of MRT was higher after oral dosing. The bioavailability of selenium, following oral administration of selenourea was 77%. Approximately, 22% of the total intravenous dose and 5.9% of total oral dose of selenium was excreted in urine within 24h of administration of selenourea. The data on blood Se levels may be of help in diagnosing the impeding selenium toxicosis and thus preventing mortality due to selenium toxicity.

Selenium toxicity: cause and effects in aquatic birds

There are several manners in which selenium may express its toxicity: (1) an important mechanism appears to involve the formation of CH(3)Se(minus sign) which either enters a redox cycle and generates superoxide and oxidative stress, or forms free radicals that bind to and inhibit important enzymes and proteins. (2) Excess selenium as selenocysteine results in inhibition of selenium methylation metabolism. As a consequence, concentrations of hydrogen selenide, an intermediate metabolite, accumulate in animals and are hepatotoxic, possibly causing other selenium-related adverse effects. (3) It is also possible that the presence of excess selenium analogs of sulfur-containing enzymes and structural proteins play a role in avian teratogenesis. L-selenomethionine is the most likely major dietary form of selenium encountered by aquatic birds, with lesser amounts of L-selenocysteine ingested from aquatic animal foods. The literature is suggestive that L-selenomethionine is not any more toxic to adult birds than other animals. L-Selenomethionine accumulates in tissue protein of adult birds and in the protein of egg white as would be expected to occur in animals. There is no suggestion from the literature that the levels of L-selenomethionine that would be expected to accumulate in eggs in the absence of environmental concentration of selenium pose harm to the developing embryo. For several species of aquatic birds, levels of Se as selenomethionine in the egg above 3 ppm on a wet weight basis result in reduced hatchability and deformed embryos. The toxicity of L-selenomethionine injected directly into eggs is greater than that found from the entry of L-selenomethionine into the egg from the normal adult diet. This suggests that there is unusual if not abnormal metabolism of L-selenomethionine in the embryo not seen when L-selenomethionine is present in egg white protein where it likely serves as a source of selenium for glutathione peroxidase synthesis in the developing aquatic chick.

Selenium and the brain: a review

Similar to other tissues selenium from selenomethionine is deposited in the brain at higher concentrations than selenium in other forms. Vitamin E has a greater effect than selenium in reducing lipid peroxidation in various brain regions. Selenium does not have as great effect on glutathione peroxidase (GPX) activity in the brain as in most other organs. Prolonged selenium and iodine deficiencies will compromise thyroid hormone homeostatus in the brain and this is due to changes in deiodinases activities and lipid peroxidation. Even though selenium deficiency results in reduced GPX activity and selenium content in the brain, there is no reduction in thioredoxin reductase activity or selenoprotein W levels. Selenoprotein P is taken up in greater amounts by the brain but not by other organs in selenium deficient animals, suggesting a critical function of this selenoprotein in this organ. Selenium will influence compounds with hormonal activity (and neurotransmitters) in the brain, and this is postulated to be the reason selenium affects moods in humans and behavior in animals. Even though selenium counteracts the neurotoxicity of mercury, cadmium, lead and vanadium, it causes them to accumulate in the brain, presumably in a nontoxic complex.