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A Kyriakopoulos

Publications and source records attributed to A Kyriakopoulos.

31 records · Page 2Linked to original sources
PubMed1995

Studies on the distribution and characteristics of new mammalian selenium-containing proteins.

It has now been established that the essential effects of selenium in mammals are owing to the presence of several biologically active selenium compounds. Seleno-enzymes identified so far include several glutathione peroxidases and the type 1 iodothyronine de-iodinase. Some other selenoproteins have been sequenced and characterized. After in vivo labelling of rats with 75Se and protein separation using gel electrophoretic methods, more than 25 selenium-containing proteins or protein sub-units were detected. Some of the results of the investigations on these compounds are summarized and discussed here. By determining the pattern in a large number of tissues information on the distribution of the selenium-containing proteins was obtained. Their biological significance is not yet known but several findings indicate that some of these proteins may have important functions, especially in the brain and the endocrine and reproductive organs. More detailed information is already available on a 34 kDa-protein found in the testis and spermatozoa. Studies on the effects of dosage and chemical form of dietary selenium indicated that the tissue levels of the seleno-enzymes are homeostatically controlled and cannot be increased by additional supply. The increase in the tissue selenium observed with high selenium intake was found to be mainly caused by the non-specific incorporation of the element into a large number or proteins. The formation of most of the other selenium-containing proteins has priority over that of the cytosolic and plasma glutathione peroxidases. Thus the selenium requirement, which was calculated for optimum plasma glutathione peroxidase activity, also covers the amounts needed for normal levels of the other biologically important selenium compounds.

Animals↗
PubMed1994

Application of nuclear analytical methods in the investigation and identification of new selenoproteins.

Nuclear methods have been applied in the investigation of selenium-containing proteins in rat tissues. Selenium was determined in tissues, cells, and cellular compartments by instrumental neutron activation analysis via 77mSe or 75Se. For tracer studies, the selenium compounds were labeled in vivo by administering 75Se with a high specific activity to rats. Quantitative determination of very small amounts of the element in protein fractions was achieved by measurement of the tracer after replenishment of selenium-depleted animals with the labeled element. The application of the nuclear methods in the detection, characterization, and identification of new selenium-containing proteins is shown with the help of some examples.

Animals↗
PubMed1993

The expression of the adhesion molecules ICAM-1, VCAM-1, PECAM, and E-selectin in human atherosclerosis.

The expression of PECAM, ICAM-1, VCAM-1, and E-selectin was studied in 64 samples of human coronary arteries taken from 15 explanted hearts obtained within 5 min of transplantation. Normal artery (n = 12), predominantly fibrous plaques (n = 23), and plaques containing extracellular lipid (n = 26) and three segments showing recanalization channels were studied. All endothelial cells strongly and equally expressed PECAM; positive staining was used to check that artefactual denudation of the endothelial surface had not occurred. PECAM was also present in some lipid-filled macrophages. Normal arteries showed no VCAM-1 staining but focal segments of the endothelium were positive for ICAM-1 and E-selectin. ICAM-1 was strongly and constantly expressed by the endothelium over all types of plaques and in macrophages. E-selectin expression was confined to endothelial cells and occurred on the surface in 35 per cent of fibrous and 22 per cent of lipid-containing plaques. VCAM-1 staining of surface endothelium occurred in 39 per cent of fibrous and 20 per cent of lipid-containing plaques. A population of spindle-shaped cells of macrophage type (positive for EMB11 antigen) expressed VCAM-1 in lipid-containing plaques. Adventitial vessels adjacent to plaques showed endothelial expression of ICAM-1 and E-selectin. VCAM-1 staining of adventitial vessel endothelium was associated with local lymphoid aggregation. In conclusion, the expression of cell adhesion molecules is an important element in the inflammatory component of atherosclerosis and contributes to both monocyte and lymphocyte activation and recruitment from adventitial vessels and the arterial lumen.

Adult↗
PubMed1993

Effects of dietary selenium on the tissue concentrations of type I iodothyronine 5'-deiodinase and other selenoproteins.

Since selenium was identified as the essential component of the type I iodothyronine 5'-deiodinase, it has become important to determine the selenium dose necessary for the formation of the deiodinase. In this survey the results of studies of the effects of dosage and chemical form of the element on the concentrations of this enzyme and of other selenoproteins are discussed. They show that the selenium requirement for normal deiodinase activity is lower than it is for adequate glutathione peroxidase activity. Elevated tissue selenium concentrations found after intake of higher doses of the element, especially when given in the form of selenomethionine, are due to nonspecific incorporation into other proteins. The tissue concentrations of the selenonenzymes appear to be homeostatically controlled and cannot be further increased by additional selenium supplementation.

Diet↗
PubMed1992

Type I iodothyronine deiodinase activity after high selenium intake, and relations between selenium and iodine metabolism in rats.

Type I iodothyronine deiodinase (I-D), which catalyzes the production of the thyroid hormone 3,3',5-triiodothyronine from thyroxine, has recently been identified as a selenoenzyme. It is therefore of interest to investigate the relationships between selenium and iodine metabolism. In the livers of Se-deficient rats I-D activity was inhibited; the production of 3,3',5-triiodothyronine and 3,3'-diiodothyronine from added thyroxine was decreased by greater than 95% relative to Se-adequate controls. The hepatic I-D activity was also reduced in rats fed a diet with a low iodine concentration. Unaltered glutathione peroxidase activities in liver and plasma of these rats suggest, however, that with normal Se intake this metabolic pathway of Se is not affected by iodine depletion. When rats were administered 75Se-labeled selenium at levels equal to the amounts ingested from diets with Se concentrations of 0.3 or 2 mg Se/kg, greater Se concentrations were found in the thyroid and liver of the animals receiving the higher dosage. The thyroidal 3,3',5-triiodothyronine and thyroxine concentrations, however, were comparable in rats fed diets with 0.3 mg Se/kg diet as selenite and 2 mg Se/kg as selenite or L-selenomethionine. The measurement of the hepatic I-D and glutathione peroxidase activities in these animals showed that excessive Se supply does not elevate the activities of the two enzymes but might even have the opposite effect. At high Se intake tissue Se concentration cannot therefore be used as indicator of the selenoenzyme activities.

Administration, Oral↗
PubMed1992

Sex-related effects of zinc deficiency on the selenium metabolism in rats.

The effects of a low zinc status on selenium metabolism were investigated in female and male rats which were fed diets with low and adequate zinc contents and a suboptimal selenium content. For the selenium content and glutathione peroxidase activity in the liver and plasma of the female animals no differences were found between the low zinc group and the pair-fed zinc-adequate control group. In the male rats zinc depletion resulted in testis atrophy and decreased testicular contents of selenium and glutathione peroxidase. In the pair-fed and ad libitum-fed control groups the levels of hepatic selenium and glutathione peroxidase and plasma glutathione peroxidase in the males were lower than those in the females. In the low zinc group, however, they rose to the levels of the females. The results indicate that these effects of zinc deficiency on selenium metabolism are sex-specific and suggest that they are related to changes in the sex hormone status of the male animals.

Animals↗
PubMed1991

Effects of chemical form and dosage on the incorporation of selenium into tissue proteins in rats.

We investigated the incorporation of Se into the proteins of liver and muscle, the two main Se pools, during replenishment of Se-deficient rats with normal or large doses of 75Se-labeled selenite and selenomethionine, doses equivalent to the amounts ingested from a diet with 0.2 or 2 mg Se/kg. With the higher intake, Se levels were elevated. More Se was retained from selenomethionine than from selenite. After separation of the labeled proteins, it was apparent that the higher tissue Se contents were mainly due to nonspecific incorporation into a large number of proteins. We observed no differences between the two chemical forms with regard to the formation of the specific selenoproteins. The 10-fold increase in the Se supply led to a relatively small rise in the levels of these compounds. The results indicate that after ingestion of normal amounts of selenite nearly all of the element is present in the specific selenoproteins. With increasing doses a part is also incorporated nonspecifically into numerous other proteins. In the case of selenomethionine, a part of the element follows the same metabolic pathways, but a percentage is also deposited directly and nonspecifically into proteins in place of methionine.

Animals↗
PubMed1990

Identification of type I iodothyronine 5'-deiodinase as a selenoenzyme.

A 27.8 kDa membrane selenoprotein was previously identified in rat thyroid, liver and kidney, the tissues with the highest activities of type I iodothyronine 5'-deiodinase. This membrane enzyme catalyzes the deiodination of L-thyroxine to the biologically active thyroid hormone 3,3',5-triiodothyronine. A decrease in the activity of this enzyme, observed here in the liver of selenium-deficient rats, was found to be due to the absence of a selenium-dependent membrane-bound component. By chemical and enzymatic fragmentation of the 75Se-labeled selenoprotein and of the 27 kDa substrate binding type I 5'-deiodinase subunit, affinity-labeled with N-bromoacetyl-[125I]L-thyroxine, and comparison of the tracer distribution in the peptide fragments the identity of the two proteins was shown. The data indicate that the deiodinase subunit contains one selenium atom per molecule and suggest that a highly reactive selenocysteine is the residue essential for the catalysis of 5'-deiodination. From the results it can be concluded that type I iodothyronine 5'-deiodinase is a selenoenzyme.

Animals↗
PubMed1990

Subcellular distribution of selenoproteins in the liver of the rat.

After in vivo labeling with [75Se]selenite, the intracellular distribution of selenoproteins in the liver was investigated in selenium-adequate and selenium-deficient rats. In the subcellular fractions, which were obtained by differential centrifugation, the proteins were separated by means of SDS-PAGE and the selenium compounds were identified via their 75Se activity. In this way twelve selenium-containing proteins or protein subunits with molecular weights between 12,100 and 75,400 were found. Glutathione peroxidase was concentrated in the cytosol and in the mitochondria. With the newly detected selenoproteins, some were enriched in the cytosol, one was mainly found in the nuclear fraction and some, which were present mainly in the mitochondrial and microsomal fractions, are most probably membrane-bound. In the liver of selenium-depleted rats the selenium administered was used predominantly to restore the levels of some of the newly found selenoproteins, while in the liver of selenium-adequate animals most of the selenium retained was incorporated into the glutathione peroxidase. The differences in the distribution among the subcellular fractions and the specific incorporation of the element in selenium deficiency into certain compounds suggest that there are several metabolic pathways for selenium and that the selenoproteins are involved in several different processes of intracellular metabolism.

Animals↗
PubMedDate not supplied

Studies on 16 kDa selenium-containing proteins enriched by means of preparative electrophoresis.

By in vivo labeling with [75Se]selenite and separation of the proteins in the tissue homogenates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), several selenium-containing proteins or protein subunits were detected in rat tissues (liver, lung, spleen and prostate). Their distribution among the cell components was investigated after fractionation by means of differential centrifugation. The selenium-containing proteins in the 16 kDa range were found to be mainly membrane-bound. By two-dimensional electrophoresis they were resolved into three labeled spots, two with the same relative molecular mass and pI values of about 4.8 and 5.0 and the third with a slightly lower molecular mass and a pI of 4.8. For further investigation they were concentrated and separated from the other labeled compounds by SDS-PAGE using preparative flow-through electrophoresis.

Animals↗
PubMedDate not supplied

Combination of neutron activation analysis, tracer techniques, and biochemical methods in the investigation of selenium metabolism.

In several studies on rats, the metabolism of selenium was investigated. The quantitative determination of the element was carried out by instrumental neutron activation analysis. For in vivo tracer experiments, 75Se-labeled selenium compounds were used. In addition to these methods, procedures for the measurement of the selenoenzyme glutathione peroxidase, and for the investigation of other selenoproteins, were applied. In this way, information on the specific pools and sites of action of the element, on biologically important selenoproteins and the regulation of the selenium metabolism, was obtained.

Animals↗