Inhibition of hepatic mixed-function oxidase enzymes in mice by acute and chronic treatment with selenium

Metals and linear alkylbenzene sulphonate as inhibitors of the algae Pseudokirchneriella subcapitata acid phosphatase activity

Sewage sludge applied to soils as a fertilizer often contains metals and linear alkylbenzene sulphonate (LAS) as contaminants. These pollutants can be transported to the aquatic environment where they can alter the phosphatase activity in living organisms. The acid phosphatase of algae plays important roles in metabolism such as decomposing organic phosphate into free phosphate and autophagic digestive processes. The order of in vitro inhibition of Pseudokirchneriella subcapitata acid phosphatase at the highest concentration tested was LAS > Hg2+ = Al3+ > Se4+ = Pb2+ > Cd2+. A non-competitive inhibition mechanism was obtained for Hg2+ (Ki = 0.040 mM) and a competitive inhibition for LAS (Ki = 0.007 mM). In vivo studies with treated algae cultures showed that the inhibition of specific activity was observed in algae exposed during 7 days, in contrast to short term (24 h) treatments with both these chemicals. Our results suggest that the inhibition parameters in vitro did not markedly differ between the two chemicals. On the other hand, in vivo evaluations showed strong differences between both pollutants regarding the concentration values and the degree of response.

Chemopreventive mechanisms of selenium

The element selenium (Se) was recognized only 40 years ago as being essential in the nutrition of animals and humans. It is recognized as being an essential component of a number of enzymes in which it is present as the amino acid selenocysteine (SeCys). Selenium compounds have also been found to inhibit tumorigenesis in a variety of animal models and recent studies indicate that supplemental Se in human diets may reduce cancer risk. Anti-tumorigenic activities have been associated with Se intakes that are more than sufficient to correct nutritionally deficient status; that is, Se appears to be anti-tumorigenic at intakes that are substantially greater than those associated with maximal expression of the known SeCys-containing enzymes. Therefore, while some cancer protection may involve one or more Se-enzymes, it is probable that anti-tumorigenic functions of Se are discharged by certain Se-metabolites produced in significant amounts at relatively high Se intakes. Thus, Se supplementation of individuals with relatively low or frankly deficient natural intakes of the element can be expected to support enhanced anti-oxidant protection due to increased expression of the Se-dependent glutathione peroxidases and thioredoxin reductase. Higher levels of Se-supplementation can be expected to affect other functions related to tumorigenesis: carcinogen metabolism, immune function, cell cycle regulation and apoptosis. Thus, according to this 2-stage model of the roles of Se in cancer prevention, even individuals with nutritionally adequate Se intakes may benefit from Se-supplementation.

Effect of selenium supplementation on biological constants and antioxidant status in rats

Oxygen-derived free radicals are currently suspected to be widely involved in the aetiology of several clinical disorders. In animals as well as in man, antioxidant trials are often undertaken to prevent oxidative stress. Among antioxidant molecules selenium has been largely studied. This study shows that plasma Se level is not a good index of Se status in the organism, at least at high levels of selenium. Red blood cell Se seems to be a more reliable index of Se status and could replace plasma Se level in the supplementation trials both in animals and humans. Se supplementation did not result in a significant decrease in oxidative stress markers as evaluated by blood and tissue malondialdehyde contents in healthy animals. Furthermore, heart function was altered and plasma Alanine aminotransferase activity was significantly increased in the selenium-supplemented group, which could reflect a slight subtoxic effect of selenium supplementation at the level used here. In view of the results presented, the maximum selenium content in animal diet in selenium supplementation experiments should not be higher than 2 mg/kg.