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Biomedical subjects

J Brtko

Publications and source records attributed to J Brtko.

At least 55 records · Page 3Linked to original sources
PubMed1997

The effect of antigen stimulation on splenic transplants.

The present paper deals with the regeneration of splenic tissue after autologous transplantation. Control and transplanted rats (60 days after operation (10(6) cells per injection). The effect of a primary response was studied by a single injection, long-lasting bacteraemia was imitated by 5 injections in weekly intervals. Spleens and transplants were investigated by flow-cytometry and immunohistochemistry. Additionally, the proliferation activity and the specific antibody production against Escherichia coli proteins were tested. Flow-cytometric analysis showed altered behaviour of T-helper cells and B-cells in transplants following a primary response, whereas in the multiple injection group a difference between the splenic and transplant response was restricted to macrophages and MHC II+ cells. The results of the morphometric analysis revealed that the cellular composition of unstimulated transplants was very similar to that of the spleen with some subtle alterations. Only the marginal zone showed more striking differences concerning the homing of several cell classes. Under stimulatory conditions, these subtle alterations became more drastic so that CD5+ cells, B-cells and macrophages responded in an abnormal manner in both groups. The analysis of thymidine kinase disclosed decreased activity in the spleen after weekly antigen stimulation. The stimulation index of all transplant groups was significantly lower than that of the spleen. The specific antibody (IgG) production after a single immunization was highest in the transplant group. All groups responded after the multiple challenge. In conclusion, the results demonstrate that splenic transplants differs in several, but subtle aspects from normal splenic tissue. The main reason for most of these alterations may be a slightly misguided recirculation and/or homing of cells.

Animals↗
PubMed1996

Effects of retinoids and role of retinoic acid receptors in human thyroid carcinomas and cell lines derived therefrom.

Retinoic acids (RAs), well characterized regulators of proliferation and differentiation, partly re-differentiate follicular thyroid carcinoma cell lines (FTC-133, FTC-238, and HTC-TSHr) as well as SV40-transfected immortalized thyroid cell lines (ori3 and 7751). This is indicated by the stimulation of type I 5'-deiodinase and other differentiation markers. As demonstrated by RT-PCR, electrophoretic mobility shift, and [3H]-retinoic acid binding assays, thyroid carcinoma cell lines express RA receptor mRNAs and functional ligand- and DNA-binding receptor proteins able to mediate RA-dependent signal transduction. Together, these properties make these thyroid-derived cell lines useful in vitro models for studying the effects of an RA re-differentiation therapy of thyroid cancer.

Animals↗
PubMed1996

Selenium: metabolism and endocrines (Minireview).

Selenium occurs both in prokaryocytes and eukaryocytes as a component of selenoenzymes or selenoproteins. Approximately 80 % of selenium in animal or human body occurs in the form of seleno-L-cysteine, an amino acid encoded by one of standard termination codons. Selenium is an integral component of the active site of glutathione peroxidases which plays an important role in the antioxidant system. Iodothyronine 5-deiodinase, type I is also a selenoenzyme consisting of two identical subunits which catalyzes a reductive monodeiodination of iodothyronine residues of the phenolic ring. General characteristics of several selenoproteins and selenium binding proteins are summarized, also certain facts on the effects of selenium deficiency in man and its distribution and toxicity in higher organisms, are reviewed. Selenium status in the population from selected regions in Slovakia is reported and compared with that in other countries.

Journal Article↗
PubMed1996

[The basis for the variable effects of thyroid hormones].

Among physiological reactions of the organism, the multiplicity of action of thyroid hormones is a well known phenomenon. Thyroid hormones (TH) regulate activity of other hormones, receptors for bioactive signals, enzymes, and the function of ion channels. Until triiodothyronine has been identified as a ligand for oncoprotein c-erbA, this broad potency of actions has been mysterious. C-erbA has been recognized to be a transcription factor and an authentic thyroid hormone receptor. Important evidence comes from molecular studies, which have described isoforms of c-erbA and other members of intranuclear receptor family, their heterodimerization, thyroid hormone responsive elements in the target genes, and the existence of the cross-talk mechanism. Till present, much has been learned about TH transcription regulations in vitro. An open question remains whether this regulations are operative also in the intact organism.

Animals↗
PubMed1996

Polarographic behavior of kojic acid and its derivatives, determination of potential carcinogenicity and correlation of these properties with their other attributes.

Polarographic properties of kojic acid [5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one] and 10 of their synthetic derivatives were investigated. It was shown that these compounds are reduced in anhydrous conditions, usually in one two-electron step or in two one-electron steps. The presence of some substituents may change the course of reduction process. The polarography of these compounds in the presence of alpha-lipoic acid showed the kojic acid analog-alpha-lipoic acid complex formation. The determined potential carcinogenic activity of these compounds expressed as a parameter tg alpha is not substantial.

Carcinogenicity Tests↗
PubMed1995

In vitro effects of sodium selenite on nuclear 3,5,3'-triiodothyronine (T3) receptor gene expression in rat pituitary GH4C1 cells.

The present study was undertaken in order to investigate the effects of sodium selenite on: 1. The growth of rat pituitary GH4C1 cells; 2. The nuclear T3 receptor gene expression; 3. The cytoplasmic protein phosphorylation; and 4. The prolactin secretion in rat pituitary GH4C1 cell line. Sodium selenite (up to 2.5 microM) has no inhibitory effect on GH4C1 cell proliferation as well as the prolactin secretion. On the other hand, 0.5 microM sodium selenite significantly decreases the rate of mRNA synthesis and/or degradation of both, the alpha 1 form of the T3 receptor (TR alpha 1) and the alpha 2 isoform of the T3 receptor. At 1 microM of sodium selenite, significant changes in the electrophoretic profile of low molecular mass cytoplasmic proteins were found, moreover, sodium selenite (1 microM) also considerably affects phosphorylation of a higher molecular mass proteins. The results based on the in vitro experiments suggest that sodium selenite may affect specific processes at the pretranslational level as well as it may also take part in processes of posttranslational modification of protein(s), the cell vitality and the cell growth remaining unchanged.

Animals↗
PubMed1995

Antileukemic activity of 4-pyranone derivatives.

In a search for new compounds possessing antitumor activity, we examined the effects of a group of oxygen containing heterocyclic derivatives on L1210 murine leukemia cell growth. Several 5-hydroxy-2-hydroxymethyl-4-pyranone derivatives were tested in a growth assay employing a human leukemia K562 cells line. IC50 was extrapolated from the growth inhibition curves at compound concentrations ranging from 0.1 to 100 microM. The halogen derivatives of 5-hydroxy-2-hydroxymethyl-4-pyranone inhibited L1210 cell growth in suspension culture after 96 hr incubation in the following order: 5-hydroxy-2-iodomethyl-4-pyranone (IC50 3.15 microM) > 6-bromo-2-bromomethyl-5-hydroxy-4-pyranone (IC50 3.40 microM) > 6-bromo-5-hydroxy-2-hydroxy-methyl-4-pyranone (IC50 3.75 microM) > 2-bromomethyl-5-hydroxy-4-pyranone (IC50 4.30 microM) > 5-benzyloxy-2-chloromethyl-4-pyranone (IC50 5 microM) > 6-bromo-2-chloromethyl-4-pyranone (IC50 13.50 microM) > 6-chloro-2-chloromethyl-5-hydroxy-4-pyranone (IC50 18 microM) > 2-chloromethyl-5-hydroxy-4-pyranone (IC50 20 microM). The compound, 5-hydroxy-2-hydroxymethyl-4-pyranone has no effect on L1210 cell growth. These results suggest that 5-hydroxy-2-hydroxymethyl-4-pyranone derivatives might represent a new class of compounds with antileukemic activity.

Animals↗
PubMed1994

Accurate determination and physicochemical properties of rat liver nuclear retinoic acid (RA) receptors.

The present study was undertaken to establish a novel in vitro method for quantitative determination of the nuclear RA receptors in rat liver. Binding characteristics of RA receptors (free of any contaminating cytoplasmic proteins), in relation to various physicochemical conditions, were evaluated. Three different binding sites for all-trans RA were found in nuclear proteins of rat liver. One of them represents a high affinity and low capacity RA specific binding site with Ka1 0.687 +/- 0.294 x 10(9) M-1 and the Bmax1 0.644 +/- 0.397 pmol/mg protein. Others represent low affinity and high capacity RA non-specific binding sites with Ka2 2.694 x 10(6) M-1; Bmax2 225 pmol/mg protein and Ka3 0.131 x 10(6) M-1; Bmax3 1125 pmol/mg protein, respectively.

Animals↗
PubMed1994

Effect of 3,5,3'-L-triiodothyronine on hepatic ornithine decarboxylase and thymidine kinase activity in rat after partial hepatectomy.

Partial hepatectomy (60%) led to the biphasic increase (first one at 4 h and second one at 48 h) of ornithine decarboxylase activity in the remnant rat liver. Daily administration of 3,5,3'-L-triiodothyronine (T3) (10 micrograms/100 g) to rats for 7 days before partial hepatectomy had little effect on the enzyme activity. At five days, ornithine decarboxylase activity declined to control level (sham operated controls) and its activity was significantly enhanced by T3. Ornithine decarboxylase gene expression in the rat liver (examined by Northern blot analysis using poly A+ mRNA) started to increase 4 h after partial hepatectomy, remained elevated for 48 h and decreased after 5 days. Its activity was not altered by T3 treatment. The activity of thymidine kinase increased progressively after partial hepatectomy, but its peak value was delayed by T3 administration. Plasma prolactin levels increased within 5-15 min after liver resection, then declined to control values and increased 24 h after the surgery. The data demonstrate that the changes in ornithine decarboxylase activity in the rat liver after partial hepatectomy might result from the direct effect of prolactin on the activity of enzyme rather than from its induction by hormone. Triiodothyronine administration altered both ornithine decarboxylase and thymidine kinase activities suggesting that T3 appears to regulate ornithine decarboxylase activity at post-translational level.

Animals↗
PubMed1993

Relationship between antifungal activity and hydrophobicity of kojic acid derivatives.

Twenty three kojic acid derivatives were tested in the agar diffusion test against twenty five dermatophytic fungi. The inhibitory effects at equal doses (10 mg/L) were correlated with the 1-octanol-water partition coefficients of the compounds. An improvement in antifungal activity can be achieved by increasing the hydrophobicity of the compounds.

Antifungal Agents↗
PubMed1993

Inhibition of 3,5,3'-triiodothyronine binding to its receptor in rat liver by protease inhibitors and substrates.

Various protease inhibitors (e.g. phenylmethanesulfonyl fluoride (PMSF), tosyl-phenylalanine chloromethyl ketone (TosPheCH2Cl)) and substrates (e.g., tosyl-arginine methyl ester (TosArgOMe), tryptophan methyl ester (TrpOMe)) inhibit the binding of adrenal and sex steroids to their cognate receptors (Hubbard and Kalimi (1985) Mol. Cell. Biochem. 66, 101-109). Here we extend this finding to the receptor for 3,5,3'-triiodothyronine (T3) in rat liver nuclei. We find that PMSF, TosPheCH2Cl and other protease inhibitors as well as TosArgOMe, TrpOMe, tyrosine methyl ester (TyrOMe) and tyrosine ethyl ester (TyrOEt) inhibit binding of 125I-T3 to its receptor in rat liver nuclei. Inhibition by protease substrates appears to be at or close to the hormone binding domain. By analogy with the known mechanism of binding of protease inhibitors and substrates to enzymes, we suggest that the T3 receptor contains a nucleophilic site at or close to the hormone binding domain.

Animals↗
PubMed1993

Cross-linking of iodinated prolactin to rat liver nuclear protein.

The specific binding of prolactin (PRL) in rat liver nuclei have been examined. Following cross-linking with the use of 125I-rat prolactin and autoradiography the evidence is presented for the specific binding of PRL to a nuclear protein with low Mr of about 7000. This study shows that the PRL binder in rat liver nuclei is a small protein and probably differs from molecular form of the rat liver membrane prolactin receptor.

Animals↗
PubMed1993

Rat liver nuclear receptors for thyroid hormone: binding characteristics after stabilization and storage.

Conditions for both stabilization and storage of rat liver nuclear receptors for thyroid hormone for up to 28 days were determined using agents that might protect the receptor from spontaneous degradation. Without any protective agent a statistically significant (P < 0.05) diminution of 3,5,3'-triiodothyronine (T3) binding occurred at 0 degree C within 14 days. Dithiothreitol can maintain the initial T3 maximum binding capacity (MBC) for up to 7 days at 0 degree C. The compounds tested, including spermine, sodium molybdate, thioglycerol, and nitrogen gas, had no stabilization effect on nuclear receptors. A statistically significant (P < 0.05) stabilization for up to 28 days at 0 degree C of the initial MBC of T3 receptors was observed in the presence of 0.2 mol.l-1 phosphate anion or 20% (w/w) glycerol. The protective effect of phosphate anion was due to the phosphate ion itself rather than to the high ionic strength.

Animals↗
PubMed1992

Thyroid hormone responsiveness of the L1210 murine leukemia cell line.

The presence of saturable and high affinity 3,5,3'-triiodothyronine (T3) binding sites was demonstrated in L1210 murine leukemia cell nuclei. Scatchard analysis revealed one class of receptors for T3 with Ka = 2.187 x 10(9) l/mol and a maximum binding capacity (Bmax) of 3.96 fmol/10(6) cells. The effects of T3 on protein phosphorylation and growth rate of L1210 cells were investigated in a medium containing T3-depleted fetal calf serum. T3 was observed to be effective in enhancing protein phosphorylation (153.06% +/- 5.99 SD) compared to cells grown in the absence of T3 (81.49% +/- 13.50 SD). Moreover, in the presence of high T3 concentration (11.15 nmol/l) T3 was found to significantly increase the cell growth rate. In addition, the T3 receptor-associated alterations during the cell cycle, as measured by flow cytometry, suggest that the presence of T3 receptors becomes evident during the late G1 phase of the cell cycle, and T3 receptor numbers increase during the S phase. These results suggest that in in vitro conditions representing high T3 concentration, the number of L1210 leukemia cells may be increased by T3 via nuclear receptors. The L1210 leukemia cell line may serve as a convenient tool for in vitro studies of nuclear receptors and/or mechanism of action of T3. The binding affinity of T3 receptors is similar to that found in rat hepatocytes or human lymphocytes.

Animals↗
PubMed1992

Distribution of triiodothyronine nuclear receptors during the cell cycle in mouse leukemia cells.

The process of the appearance of thyroid hormone receptors in the cell cycle was studied in mouse leukemia cells L1210. After cell synchronization by 2 mM thymidine for 12 h followed by 80 nM Colcemid for 4 h, the specific binding of triiodothyronine (T3) to its nuclear receptors was determined 3, 6, 9 and 12 h after release from the thymidine-Colcemid block. Three h after release from the block, [125I]T3 specific binding was 11.4 +/- 2.5% of a control value measured for an asynchronous population. An upward slope in progression of T3 nuclear receptors was found 6 h (32.3% +/- 4.5%), 9 h (47.8% +/- 5.2%) and 12 h (83% +/- 4.3%) after release from thymidine-Colcemid block. The data suggest that processes involving T3 receptor promotion in cell nuclei are operative within the late G1 and S phases of the cell cycle, and thus the increase in T3 receptor concentration in the nuclei is in a positive correlation with the number of cells in the S compartment of the cell cycle.

Animals↗