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Biomedical subjects

G Tóth

Publications and source records attributed to G Tóth.

At least 73 records · Page 4Linked to original sources
PubMed1999

Synthesis and binding characteristics of [3H] H-Tyr-Ticpsi[CH2-NH] Cha-Phe-OH, a highly specific and stable delta-opioid antagonist.

Substitution of the Phe3 aromatic ring in H-Tyr-Ticpsi[CH2-NH]Phe-Phe-OH with cyclohexylalanine (Cha) has been reported to result in a compound, H-Tyr-Ticpsi[CH2-NH]Cha-Phe-OH (TICP[psi]), showing substantially increased delta-opioid antagonist potency and high delta selectivity. TICP[psi] was radiolabeled by catalytic tritiation of its precursor Tyr(3',5'-I2)1TICP[psi]. Binding characteristics of the new tritiated pseudopeptide were determined using the radioligand binding assay in rat brain membranes. On the basis of the results of saturation binding studies performed at 25 degrees C, an equilibrium dissociation constant (Kd) of 0.35 nM and a receptor density (Bmax) of 112 fmol/mg protein were calculated. This new tritiated ligand exhibits high affinity for delta-opioid receptors, whereas its binding to mu and kappa receptors is weak. A study of [H3]TICP[psi] binding displacement by various receptor-selective opioids showed the following rank order of potency: delta > kappa = mu. These receptor binding characteristics of the ligand, together with its high specific radioactivity (41.3 Ci/mmol) and stability, makes it a useful tool for labeling delta-opioid receptors, both in vitro and in vivo.

Animals↗
PubMed1999

Long-lasting antinociceptive effect of DAMGO chloromethyl ketone in rats.

Previously, the opioid peptide Tyr-D-Ala-Gly-(NMe)Phe-CH2Cl (DAMCK) has been shown to bind irreversibly to mu opioid receptors in vitro. In the present work, the antinociceptive effect of DAMCK has been evaluated. Rats treated systemically with DAMCK (1-100 pg/kg) displayed a dose-dependent increase in tail-flick analgesia that peaked by 15 min, then stayed about the same until 60 min, followed by some decrease over time. Higher doses of DAMCK (10 ng/kg-100 microg/kg) produced a near-maximal antinociceptive effect that remained stable for 4 h. Significant antinociception was still detected 8 h, but not 24 h postinjection. In comparison, the parent peptide DAMGO (Tyr-D-Ala-Gly-(NMe)Phe-Gly-ol) reached maximal effect by about 30 min, followed by a rapid cessation of its antinociceptive response. Naloxone administered before DAMCK antagonized the antinociceptive response of DAMCK, indicating that it was mediated via opioid receptors. Naloxone administered 45 min after DAMCK attenuated the tail-flick response to some extent, but a substantial part (40-60% depending on the peptide concentration and evaluation time) remained unaffected. Central administration of DAMCK also elicited time- and concentration-dependent, profound, opioid receptor mediated, apparently irreversible antinociception.

Amino Acid Chloromethyl Ketones↗
PubMed1999

Deletion patterns of dystrophin gene in Hungarian patients with Duchenne/Becker muscular dystrophies.

Deletion pattern analysis of the dystrophin gene was performed in 159 Hungarian patients with Duchenne/Becker muscular dystrophy. In 116 cases (73% of total patients), exon deletions were detected by PCR amplification. In 37 patients (31.9% of patients with a deletion) one exon was deleted, while five or more exons were missing in 40 children (34.4%). With respect to the proximal-distal distribution of the deletions, 90 children (77.6%) had deletions exclusively at the 3' end of the gene, 21 deletions (18.1%) affected only the 5' end, and in five patients (4.3%) large-scale deletions were detected, which affected both regions. Analysis of the breakpoint distribution pattern in the dystrophin gene showed that, similarly to that observed in several Western European populations, intron 44 was involved most frequently (n = 35, 15.1%) as a starting breakpoint. In the Hungarian population introns 50 and 52 were the second (n = 30, 12.9%) and third (n = 29, 12.5%) most frequently observed hot spots at the 3' end; these seem to be characteristic for the Hungarian patients. At the 5' end the breakpoint peak (n = 6, 2.58%) was in intron two. As it was proposed by previous national studies, our findings also suggest that certain intronic sequences, characteristic for a population, probably determine the development of a preferential breakpoint profile in this disease.

Child↗
PubMed1999

Decrease in serum levels of vitamin A and zeaxanthin in patients with colorectal polyp.

OBJECTIVE: Several retrospective and prospective epidemiological investigations have demonstrated that a diet rich in carotenoids could prevent the development of pre-cancerous and neoplastic lesions of the digestive tract. The aim of this examination was to analyse the correlation between colorectal polyps with different histological classifications and serum carotenoid levels. DESIGN AND METHODS: A 10 ml blood sample was taken from all of the patients after the colonoscopic diagnosis. The serum levels of vitamin A, lutein, zeaxanthin, alpha- and beta-cryptoxanthin, alpha- and beta-carotene were measured in patients with adenomatous colorectal polyp (n = 59, 35 males, 24 females) by high-pressure liquid chromatography (HPLC) and compared with those in healthy subjects (n = 20, 10 males, 10 females). The patients were separated into four groups depending on their histological findings. RESULTS: The serum levels of vitamin A and zeaxanthin were significantly lower in all patients with polyps (vitamin A: 0.913 +/- 0.112 micromol/l, zeaxanthin: 0.071 +/- 0.012 micromol/l) than in the control healthy group (vitamin A: 2.036 +/- 0.354 micromol/l, zeaxanthin: 0.138 +/- 0.048 micromol/l). The lowest levels were found in patients with focal adenocarcinoma in the polyp. There were no significant differences in the serum levels of other carotenoids. The serum levels of cholesterol, haemoglobin, total protein and albumin were normal in these patients. CONCLUSIONS: There are close and inverse correlations between the serum level of carotenoids and colorectal polyps with different histological grades. The low mean carotenoid levels in patients with adenocarcinoma in the polyp indicate that deficiency of carotenoids may be an important factor in the development of colorectal cancer.

Adenocarcinoma↗
PubMed1999

Labeled trimethyllysine load depletes unlabeled carnitine in premature infants without evidence of incorporation.

6-N-Trimethyl-[d9]-L-lysine (dTML), the labeled form of a mammalian carnitine precursor, was administered to two groups of premature infants. Although the urinary output of dTML significantly increased in the low-dose-treated group (100 micromol/day), this amount did not affect the urinary output or plasma levels of carnitine and carnitine esters. In the second group of infants, after administration of 500 micromol dTML the plasma-free carnitine concentration increased (from 9.95 +/- 0.63 to 12.9 +/- 0.87 nmol/ml, p > 0.05) with a significant increase in the urinary excretion of free carnitine on the day of dTML administration and on the posttreatment day (from 4.79 +/- 1.36 to 9.85 +/- 1.18 and to 17.5 +/- 2.31 micromol/day, respectively). Analysis of urine using fast atom bombardment mass spectrometry (FAB-MS) revealed only the presence of the dTML in the urine of the newborns; no change was detected in the relative abundance of any other carnitine precursor. Surprisingly, in the second group, which received the higher dose of dTML supplement, only the signal intensity of the unlabeled carnitine increased after dTML administration; no new peak appeared in the urine that would correspond to the de novo synthesized carnitine containing the stable isotope-labeled trimethyl group of dTML. Thus, the FAB-MS analysis clearly demonstrated that contrary to the likely prediction, the 270% extra free carnitine output was a consequence of a dose-dependent dTML-induced depletion of the free carnitine reserves from the newborns. The absence of the incorporation of the label from dTML into carnitine strongly suggests that circulating TML is not the precursor of carnitine in premature infants.

Carnitine↗
PubMed1999

A specifically radiolabeled somatostatin analog with strong antitumor activity induces apoptosis and accumulates in the cytosol and the nucleus of HT29 human colon carcinoma cells.

The new heptapeptide somatostatin analog TT-232 decreases proliferation of HT-29 human colon carcinoma cells in vitro by reducing mitotic and increasing apoptotic activity. We have synthesized and characterized a specifically tritium labeled 3H-Tyr3-TT-232 (30 Ci/mmol) to investigate the effect and the fate of this antitumor peptide on human colon tumor cells. 3H-labeled TT-232 could be detected on the cell surface, on cytoplasmic membranes and also in the nucleus of HT-29 cells, 1-6 h after the administration of 0.5 and 50 microg/mL [3H]TT-232. Binding and internalization of TT-232 to human colon tumor cells at a relatively high dose provide further evidence for the existence of low-affinity somatostatin receptors in such cells, which might mediate the apoptosis-inducing effect. Our data suggest the possible use of TT-232 in the treatment of human colon tumors.

Antineoplastic Agents↗
PubMed1999

Comparison of the endogenous heptapeptide Met-enkephalin-Arg6-Phe7 binding in amphibian and mammalian brain.

In previous communications [4, 38] we published that [3H]Met-enkephalin-Arg6-Phe7 (MERF) binds to opioid (kappa2 and delta) and sigma2 sites in frog and rat brain membrane preparations, however no binding to kappa1 sites could be established. In the present paper we compare the frog, rat and guinea pig brain membrane fractions with respect to their MERF binding data. No qualitative differences were found between the three species but specific binding of labelled MERF was maximal in frog brain and lowest in guinea pig brain, which corresponds to their kappa2 opioid receptor distribution. The naloxone resistant binding was also present in all investigated species and varied from 25% in frog and guinea pig cerebrum, to 50% in rat cerebrum and cerebellum, but no naloxone inhibition was found in guinea pig cerebellum where no kappa2 opioid receptors have been found. The presence of sigma2-like receptor was demonstrated in each investigated membrane fraction with displacement experiments using (-)N-allyl-normetazocine as competitor of tritiated MERF. It was shown that this site was responsible for 60-80% of [3H]MERF binding. The remaining part of the naloxone resistant labelled MERF binding could be displaced only with endogenous opioid peptides as met-enkephalin, dynorphin and beta-endorphin. The eventual physiological role of multiple MERF receptors is discussed.

Animals↗
PubMed1998

Effect of temperature on retention of enantiomers of beta-methyl amino acids on a teicoplanin chiral stationary phase.

The isocratic retention of enantiomers of beta-methyl amino acids (beta-methyltyrosine, beta-methylphenylalanine, beta-methyl-tryptophan and beta-methyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) was studied on a teicoplanin-containing chiral stationary phase at different temperatures and at different mobile phase compositions, using the reversed-phase mode. With variation of both mobile phase composition and temperature, almost baseline separations could be achieved for all four enantiomers of sterically hindered amino acids. The retention factors and selectivity factors for the enantiomers of all investigated compounds decreased with increasing temperature. The natural logarithms of the retention factors (ln k) of the investigated compounds depended linearly on the inverse of temperature (1/T). van 't Hoff plots afforded thermodynamic parameters, such as the apparent change in enthalpy (delta H degree), the apparent change in entropy (delta S degree) and the apparent change in Gibbs free energy (delta G degree) for the transfer of analyte from the mobile to the stationary phase. The thermodynamic constants (delta H degree, delta S degree and delta G degree) were calculated in order to promote an understanding of the thermodynamic driving forces for retention in this chromatographic system.

Amino Acids↗
PubMed1998

Side chain methyl substitution in the delta-opioid receptor antagonist TIPP has an important effect on the activity profile.

The delta-opioid antagonist H-Tyr-Tic-Phe-Phe-OH (TIPP-OH) or its C-terminal amide analogue was systematically modified topologically by substitution of each amino acid residue by all stereoisomers of the corresponding beta-methyl amino acid. The potency and selectivity (delta- vs mu- and kappa-opioid receptor) were evaluated by radioreceptor binding assays. Agonist or antagonist potency were assayed in the mouse vas deferens and in the guinea pig ileum. In the TIPP analogues containing L-beta-methyl amino acids the influence on delta-receptor affinity and on delta-antagonist potency is limited, the [(2S,3R)-beta-MePhe3]TIPP-OH analogue being among the most potent delta-antagonists reported. In the D-beta-methyl amino acid series, the [D-beta-MeTic2] analogues are delta-selective antagonists whereas [D-Tic2]TIPP-NH2 is a delta-agonist. NMR studies did not indicate any influence of the beta-methyl substituent on the conformation of the Tic residue. The [(2R,3S)-beta-MePhe3]TIPP-NH2 is a potent delta-agonist, its C-terminal carboxylic acid analogue being more delta-selective but displaying partial agonism in both the delta- and mu-bioassay. These results constitute further examples of a profound influence of beta-methyl substitution on the potency, selectivity, and signal transduction properties of a peptide.

Animals↗
PubMed1998

In vitro binding and signaling profile of the novel mu opioid receptor agonist endomorphin 2 in rat brain membranes.

The recently discovered endogenous mu receptor selective endomorphin 2 was prepared in tritiated form by a catalytic dehalogenation method resulting in a specific radioactivity of 1.98 TBq/mmol (53.4 Ci/mmol), and used for in vitro labelling of rat brain membranes. The binding was saturable, stereospecific and of high affinity (Kd: 0.97 and 1.12 nM based on kinetic and equilibrium binding studies, respectively). The maximal number of binding sites (Bmax) was found to be 114.8 fmol/mg protein. [3H]Endomorphin 2 was displaced by mu-receptor selective specific peptides and heterocyclic compounds with high affinity, whereas kappa and delta receptor specific ligands were much less potent. The Ki values of endomorphin 1 and 2 in inhibiting [3H]naloxone binding increased by 15-fold in the presence of 100 mM NaCl which indicates the agonist property of these peptides. Endomorphins stimulated [35S]GTPgammaS binding and inhibited adenylyl cyclase activity which also provides evidence for the agonist character of endomorphins.

Analgesics, Opioid↗
PubMed1998

Different effects of an oligonucleotide uptake stimulating protein on leukemic cells in their primitive and differentiated state.

The single stranded [3H]oligonucleotide uptake by HL-60 human promyelocyte and K562 human erythroleukemia cells was stimulated 20-45-fold by DUSF (DNA uptake stimulating protein), and this effect was drastically reduced (to 1.6-13x) if the cells were induced to differentiate. The oligonucleotide uptake stimulating effect of DUSF was not altered in HL-60 and K562 cells, if the proliferation of the cells was inhibited by hydroxyurea (HU) treatment. The oligonucleotide uptake by separated granulocytes and mononuclear cells from healthy donors was not stimulated by DUSF, while the uptake of oligonucleotides by myeloid and lymphoid leukemic cells was greatly stimulated (10-15x). The uptake of oligonucleotides by differentiated mononuclear cells of healthy donors could not be stimulated by DUSF, but the oligonucleotide uptake was greatly increased (11x) by DUSF if the cells were subjected to blast transformation.

Biological Transport↗
PubMed1998

Molecular characterization of metal-binding polypeptide domains by electrospray ionization mass spectrometry and metal chelate affinity chromatography.

Metal ion-binding of synthetic peptides containing HxH and CxxC motifs was investigated by electrospray ionization mass spectrometry (ESI-MS) and metal chelate affinity chromatography. A high affinity of Ni2+ and Cu2+ to HxH containing sequences was found. Based on their natural metal ion-binding potential it was possible to include metal affinity chromatography in the purification process of two proteins without using an additional His-tag sequence: ATPase-439, a P type ATPase from Helicobacter pylori and the amyloid precursor protein (APP).

Adenosine Triphosphatases↗
PubMed1998

Transforming growth factor-beta induced protein, betaIG-H3, is present in degraded form and altered localization in lattice corneal dystrophy type I.

Lattice corneal dystrophy type I (LCDI) is an inherited autosomal dominant local amyloidosis, restricted to the corneal stroma. Comparison of electrophoretic profiles of normal and dystrophic corneas revealed a 42 kD protein, which was present only in dystrophic corneas. The N-terminal sequence of this protein showed identity to transforming growth factor-beta induced gene product (betaIG-H3). A polyclonal antiserum was raised in chicken against a synthetic peptide identical to the N-terminal portion of betaIG-H3. On immunoblots, the antiserum stained the 42 kD band, and also a 68 kD band corresponding to the reported molecular weight of the intact betaIG-H3. In normal corneas, only the 68 kD band was present. Immunohistologically, the antiserum stained corneal subepithelial regions, including subepithelial deposits, in dystrophic corneas. In normal corneas, the staining was observed only in the epithelium. These results may reflect the role of betaIG-H3 in extracellular matrix construction and/or amyloid formation.

Amino Acid Sequence↗
PubMed1998

Two triterpene saponins from Arenaria filicaulis.

Two novel triterpenoid saponins, Snatzkein C, (3beta, 20-dihydroxylupan-28-oic acid 3-O-[beta-D-galactopyranosyl-(1-->2)-beta-D-glucopyranosyl-28- O-beta-D-glucopyranoside) and Snatzkein D, (3beta, 20-dihydroxylupan-28-oic acid 3-O-[beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl]-28-O-beta-D-++ +glucopyranoside), have been isolated from Arenaria filicaulis. Their structure and conformational behaviour were elucidated by one- and two-dimensional 1H NMR and 13C NMR spectroscopy.

Carbohydrate Conformation↗
PubMed1998

Interaction of agonist peptide [3H]Tyr-D-Ala-Phe-Phe-NH2 with mu-opioid receptor in rat brain and CHO-mu/1 cell line.

Opioid receptor binding properties of [3H]Tyr-D-Ala-Phe-Phe-NH2 (TAPP) were characterized in rat brain and Chinese hamster ovary (CHO) cells expressing the rat mu-receptor. In rat brain, [3H]TAPP labeled a single class of opioid sites with a dissociation constant (Kd) of 0.31 nM and maximal number of binding sites (Bmax) of 119 fmol/mg protein. In CHO-mu/1 cell membranes, the Kd and Bmax values were 0.78 nM and 1806 fmol/mg protein, respectively. Binding to rat brain was demonstrated to be pharmacologically identical to that obtained with CHO-mu/1 cell membranes and modulated by Na+ ions and guanine nucleotides. The high affinity and selectivity of [3H]TAPP together with its low non-specific binding make this radioligand a useful tool for labeling the native and cloned mu-opioid receptor.

Animals↗
PubMed1998

Affinity profiles of novel delta-receptor selective benzofuran derivatives of non-peptide opioids.

Highly selective heterocyclic opioid ligands with potent delta-antagonist activity have been developed on the basis of the "message-address" concept. Using this strategy, benzofuran derivatives corresponding to the non-selective opioid antagonist, naloxone, and to the mu-opioid receptor selective agonists, oxymorphone and oxycodone, were synthesized. In vitro opioid receptor binding profiles and agonist/antagonist character of these compounds were determined in rat brain membrane preparations with highly selective radioligands. All three benzofuran derivatives displayed high affinities for the delta-opioid receptor, much less potency toward the mu-binding site, and were the least effective at the kappa-site. The results indicated that the addition of the bezofuran moiety to these fused ring opioids confers delta-receptor selectivity. The Na+ indices suggested a partial agonist character for oxymorphone- and oxycodone-benzofuran, and an antagonist character for naloxone-benzofuran. These compounds were capable of irreversible inhibition of opioid binding sites in a dose-dependent.

Animals↗
PubMed1998

Direct anticancer activity of gonadotropin-releasing hormone-III.

In previous studies GnRH-III, a variant of the hypothalamic neurohormone GnRH, was isolated from the brain of the sea lamprey and structurally characterized. GnRH-III is a hypothalamic neurohormone in both female and male sea lampreys. In the present work biological activities of GnRH-III in mammalian systems were examined. In superfused rat pituitary cells, GnRH-III at 1 nM to 100 nM neither induced LH-secretion nor inhibited the LH-secretion elicited by native GnRH and elicited LH release only at 1 microM. At high dose (500 microg/day) in vivo, GnRH-III behaved as a GnRH agonist, though, it was 1000-fold less active than ovurelin. The in vitro and in vivo results were in good agreement in showing that GnRH-III is only a weak agonist of the endocrine activity of GnRH. GnRH-III specifically bound to receptors on cancer cells and recognized not only the high-, but also the low-affinity binding sites. GnRH-III significantly suppressed growth of human cancer cells which have GnRH receptors. The inhibitory effect of GnRH-III on growth of cancer cells was specific and direct since the peptide did not have endocrine activity in the concentration range found to be effective in anticancer assays. GnRH-III inhibited equally the growth of ER-positive and -negative breast and TeR-positive and negative prostate cells.

Animals↗