Biomedical subjects

K Tóth

Publications and source records attributed to K Tóth.

At least 37 records · Page 2Linked to original sources

PubMed2000

Time-lapse video reveals immediate heterogeneity and heritable damage among human ileocecal carcinoma HCT-8 cells treated with raltitrexed (ZD1694).

BACKGROUND: Cellular heterogeneity in drug response has important clinical implications, and is believed to develop over many generations during clonal evolution in human tumors. The purpose of this study was to determine the level of heterogeneity exhibited by sister cells soon after their birth. METHODS: Human ileocecal carcinoma cells (HCT-8) were followed up to 11 days in vitro after a 2-h exposure to 1 microM raltitrexed (IC(95)) in a time-lapse video system. RESULTS: Over five experiments, 414 cells were followed after exposure to raltitrexed. Immediate sterility occurred in 74% of treated cells. Only 6% of cells could produce more than two generations of offspring, and heterogeneity in drug response was seen. Comparing sister cells < 24 h old, the more proliferative sibling produced up to 73 times more offspring, with a median ratio of 9.0 (control median = 1.19). Offspring of prolific drug-treated cells had a decreased probability of division (68% compared with 92%) and an increased average interdivision time (19.0 h compared with 15.1 h). CONCLUSIONS: Short-term exposure to raltitrexed resulted in increased interdivision times and production of sterile offspring extending seven generations. Cellular heterogeneity (difference in proliferation potential comparing drug-treated sister cells) was evident without a period of clonal evolution.

Aged↗

PubMed2000

Target-specific expression of pre- and postsynaptic mechanisms.

Target-specific expression of pre- and postsynaptic mechanisms of synaptic transmission has been shown in a variety of central neurons by a number of laboratories. These data have demonstrated that synaptic transmission between single axons diverging onto distinct target neurons can behave independently, differentially influencing activity in the target neuron. Similarly, single neurons are capable of manufacturing molecularly distinct ligand-gated receptors and targeting them to synapses innervated by distinct converging afferent projections. A picture is emerging consistent with a role for both pre- and postsynaptic mechanisms in influencing the target-specific nature of transmission at numerous diverse synapses throughout the mammalian CNS. This target specificity adds another level of complexity in unravelling the roles played by individual neurons within a computational network. To begin to understand the coordinated activity of large ensembles of neurons it is becoming clear that the nature of transmission between individual pre- and postsynaptic elements within a circuit must first be understood for each and every neural element involved.

Animals↗

PubMed2000

Salt-dependent compaction of di- and trinucleosomes studied by small-angle neutron scattering.

Using small-angle neutron scattering (SANS), we have measured the salt-dependent static structure factor of di- and trinucleosomes from chicken erythrocytes and from COS-7 cells. We also determined the sedimentation coefficients of these dinucleosomes and dinucleosomes reconstituted on a 416-bp DNA containing two nucleosome positioning sequences of the 5S rDNA of Lytechinus variegatus at low and high salt concentrations. The internucleosomal distance d was calculated by simulation as well as Fourier back-transformation of the SANS curves and by hydrodynamic simulation of sedimentation coefficients. Nucleosome dimers from chicken erythrocyte chromatin show a decrease in d from approximately 220 A at 5 mM NaCl to 150 A at 100 mM NaCl. For dinucleosomes from COS-7 chromatin, d decreases from 180 A at 5 mM to 140 A at 100 mM NaCl concentration. Our measurements on trinucleosomes are compatible with a compaction through two different mechanisms, depending on the salt concentration. Between 0 and 20 mM NaCl, the internucleosomal distance between adjacent nucleosomes remains constant, whereas the angle of the DNA strands entering and leaving the central nucleosome decreases. Above 20 mM NaCl, the adjacent nucleosomes approach each other, similar to the compaction of dinucleosomes. The internucleosomal distance of 140-150 A at 100 mM NaCl is in agreement with distances measured by scanning force microscopy and electron microscopy on long chromatin filaments.

Animals↗

PubMed2000

Overexpression of Bax enhances antitumor activity of chemotherapeutic agents in human head and neck squamous cell carcinoma.

Overexpression of the Bax protein in human head and neck squamous cell carcinoma A253 cells was reported to result in an increased sensitivity to various chemotherapeutic agents in vitro (Guo et al., Oncol. Res., 11: 91-99, 1999). In the present study, the relationship between Bax expression and response to chemotherapy was further investigated in vitro and in vivo model systems. For in vitro study, A253, A253/Vec (pcDNA3 vector transfectant), and A253/Bax (pcDNA3/Bax transfectant, expressing 50-fold higher Bax protein than A253 and A253/Vec) cells were exposed to various concentrations of raltitrexed (a specific thymidylate synthase inhibitor) and SN-38 (a topoisomerase I inhibitor) for 2 h, and cell growth inhibition was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide clonogenic assay. Compared to A253/Vec, A253/Bax cells exhibited 9.5- and 13.5-fold increases in sensitivity to raltitrexed and SN-38, respectively. For in vivo study, A253/Vec and A253/Bax tumor xenografts were established by s.c. injection of tumor cells into nude mice. The antitumor activity and toxicity of raltitrexed (i.v. push daily for 5 days) and irinotecan (a prodrug of SN-38; i.v. push daily for 3 days) were evaluated. The maximum tolerated doses of raltitrexed and irinotecan were 30 and 100 mg/kg/day, respectively. At the maximum tolerated doses, minimal antitumor activity was observed with raltitrexed, although irinotecan was more active than raltitrexed against A253 or A253/Vec tumors. In contrast, both raltitrexed and irinotecan were significantly more active against A253/Bax xenografts than against A253/Vec xenografts; the yield for complete tumor regression (cure) was 40% and 100% with raltitrexed and irinotecan, respectively, with no significant toxicity. Furthermore, the observed increase of antitumor activity in A253/Bax tumors was associated with an enhanced induction of apoptosis in vivo. The in vivo results demonstrated a proof of the principal concept that selecting up-regulation of the proapoptosis gene Bax can provide the basis for a greater therapeutic efficacy to a variety of chemotherapeutic agents with different structures and mechanisms of action.

Animals↗

PubMed1999

Involvement of cyclin D1-cdk5 overexpression and MCM3 cleavage in bax-associated spontaneous apoptosis and differentiation in an A253 human head and neck carcinoma xenograft model.

Time-dependent ladder-type DNA fragmentation and morphological alterations consistent with apoptosis were observed among A253 human head and neck squamous cell carcinoma (HNSCC) cells in nude mice from 15 to 18 days after transplantation, without any drug treatment. No evidence of ladder-type DNA fragmentation was detected in A253 cells in vitro or in normal nude mouse tissues (skin and muscle). Our aim was to explore molecular factors associated with such spontaneous apoptosis. Bcl-2 protein expression decreased, while bax protein expression increased from day 9 after transplantation. Moreover, altered expression of bcl-2 and bax was accompanied by the increased proteolytic cleavage of poly(ADP-ribose) polymerase (PARP). Time-dependent dephosphorylation of Rb, followed by proteolytic cleavage, was also observed from day 9 after transplantation. The data indicate that the caspase-3 activation and cleavage of Rb protein may represent important steps in the regulation pathway of bax-mediated spontaneous apoptosis. Interestingly, the time-dependent activation of spontaneous apoptosis was almost simultaneous with the induction of differentiation and increased expression of several differentiation-associated regulatory proteins. An increased expression of cyclin D1 and cyclin-dependent kinase-5 (cdk5) was observed from day 9 after transplantation, whereas only slight alteration of cdk4 expression was found. The time-dependent activation of cyclin D1 and cdk5 preceded both the induction of ladder-type DNA fragmentation and increased keratin pearl formation. Furthermore, MCM3 was cleaved early in spontaneous apoptosis and differentiation. Our observations suggest the involvement of cyclin D1-cdk5 overexpression and MCM3 cleavage in bax-mediated spontaneous apoptosis and differentiation in A253 xenografts. P53 and WAF1 proteins were not expressed in the xenografts, indicating that the changes in the regulatory proteins during apoptosis and differentiation were not p53 or WAF1 dependent.

Animals↗

PubMed1999

Superhelical DNA studied by solution scattering and computer models.

We present here recent results on the structure of superhelical DNA and its changes with salt concentration between 0.01 and 1.5 M NaCl. Scattering curves of two different superhelical DNAs were determined by static light scattering. The measured radii of gyration do not change significantly with salt concentration. Small-angle neutron scattering, together with calculations from a Monte Carlo model, allows to determine the superhelix diameter. Measured and simulated scattering curves agreed almost quantitatively. Experimentally we find that the diameter decreases from 16.0 +/- 0.9 nm at 10 mM to 9.0 +/- 0.7 nm at 100 mM NaCl. The superhelix diameter from the simulated conformations decreased from 18.0 +/- 1.5 nm at 10 mM to 9.4 +/- 1.5 nm at 100 mM NaCl. At higher salt concentrations up to 1.5 M NaCl, the diameter stays constant at 9 nm.

Computer Simulation↗

PubMed1999

Persistent induction of apoptosis and suppression of mitosis as the basis for curative therapy with S-1, an oral 5-fluorouracil prodrug in a colorectal tumor model.

In an effort to improve the therapeutic selectivity of 5-fluorouracil (FUra) against colorectal cancer, S-1, a combination agent including a prodrug of FUra with two modulators, was recently developed by Taiho Pharmaceuticals Co. S-1 is a combination of tegafur (FT), 5-chloro-2,4-hydroxypyridine, and potassium oxonate in the molar ratio of 1.0:0.4:1.0, with the latter two components as inhibitors of dihydropyrimidine dehydrogenase and phosphoribosylpyrophosphate transferase, respectively. In this study, the therapeutic selectivity and efficacy of S-1 (oral) was compared with FT (oral) and FUra (i.v. infusion) in rats bearing advanced colorectal cancer by using clinically relevant schedules. The maximum tolerated doses (MTDs) of S-1, FT, and FUra were 31.5, 200, and 25 mg/kg/d for 7 days and 22.5, 150, and 12.5 mg/kg/d for 28 days, respectively. The therapeutic index of S-1 was 4- to 5-fold higher than that of either FT or FUra. S-1 achieved 100% complete tumor regression (CR) at its MTD in both 7-day and 28-day schedules. Furthermore, the high incidences of stomatitis, alopecia, and diarrhea observed with FUra and FT, were not observed with S-1. In an attempt to understand the basis for the observed superior therapeutic selectivity with S-1, we studied pharmacokinetic analysis of FUra, drug-induced apoptosis, suppression of mitosis, and inhibition of thymidylate synthase (TS) after S-1, FUra, or FT administration. The peak plasma FUra concentrations derived from FUra or S-1 (FT) at comparable MTDs were similar, but the plasma level of FUra was higher with S-1 than with FUra. Induction of high and sustained apoptosis was achieved with S-1. Although the initial level of apoptosis induced by FUra was comparable to S-1, it was not sustained. The sustained level of apoptosis appears to correlate with tumor growth inhibition. Mitotic figures were more greatly suppressed with S-1 treatment than with FUra. Studies on TS inhibition indicated that, although both S-1 and FUra caused a 4- to 6-fold induction of total TS protein, single oral administration of S-1 was superior to 24-h infusion of FUra in suppressing free TS. The data are consistent with the observation that the therapeutic efficacy of S-1 (100% cure) over FUra is associated with high and sustained levels of drug-induced apoptosis, greater suppression of mitosis, and inhibition of free TS in tumor tissues.

Animals↗

PubMed1999

Effect of transfusion on the endothelium dependent dilatation of brachial artery in patients with chronic anemia.

The effect of changes in the main determinants of whole blood viscosity after red blood cell transfusion on endothelium dependent dilatation of brachial artery was studied in patients treated with symptoms of chronic anemia. 10 patients were involved in the study, 8 males, 2 females, mean age 52.7+/-18.7 years. Following blood tests performed at hospital admission: hemoglobin (Hgb), red blood cell count (RBC), hematocrit (Hct), white blood cell count, platelet count, plasma total protein, fibrinogen, plasma viscosity, BUN, creatinine, cholesterol, triglycerides. Flow mediated dilatation of brachial artery (FMD) was determined by Doppler method. Blood tests and FMD study were repeated after transfusion. The main determinants of whole blood viscosity increased after transfusion. The increases of Hgb, RBC, Htc were highly significant. The central flow velocity in brachial artery decreased at rest and during hyperemia as well. FMD of brachial artery was not changed significantly after transfusion. The change in factors determining whole blood viscosity did not cause a significant change in FMD. The probable explanation for this is that the increase of whole blood viscosity is associated with a decrease of central flow velocity. These two counteracting changes can equal each other.

Adult↗

PubMed1999

Dimerization of mitochondrial Bax is associated with increased drug response in Bax-transfected A253 cells.

Human head and neck squamous cell carcinoma A253 cells, which do not express p53 and p21 proteins, were engineered to stably express about 50-fold higher level of Bax protein (A253/Bax) than the mock-transfected (A253/vec) or parental cells. Using these cell lines, studies were carried out to evaluate the role of Bax in response to anticancer drugs and to study the associated mechanisms. A253/Bax cells exhibited a significant increase in in vitro sensitivity to various anticancer drugs, including tomudex (9.5-fold), SN-38 (13.8-fold), doxorubicin (7.9-fold), taxol (3.1-fold), 5-FU (2.7-fold), and 5-FU/LV (4.5-fold). Increased level of drug-induced apoptosis was observed in A253/Bax cells in a drug concentration-dependent manner. In untreated A253/Bax cells, Bax was expressed in a monomeric state. Treatment with tomudex induced the formation of Bax dimer in a drug concentration-dependent manner. Dimerization of Bax occurred only in mitochondria, while the cytosolic Bax was retained in the monomeric state. Low level of Bax dimerization was also detected in parental A253 cells following tomudex exposure. In addition, Bax dimer formation was associated with mitochondrial cytochrome c release and activation of caspases in A253/Bax cells. The data suggest that Bax overexpression increases drug response by enhancing drug-induced apoptosis. Furthermore, dimerization of mitochondrial Bax and downstream mechanisms are associated with drug-induced apoptotic cell death and increased drug sensitivity.

Apoptosis↗

PubMed1998

[Effect of chronic anemia on the endothelium-dependent dilatation of the brachial artery].

UNLABELLED: The effect of changes in main determinants of whole blood viscosity after red blood cell transfusion on endethel dependent dilatation of brachial artery was studied in patients treated with transfusion because of symptoms of chronic anaemia. PATIENTS AND METHODS: 10 patients were involved, 8 females 2 males, mean age 50.9 +/- 16.6 years. Following blood tests were performed at hospital admission: hemoglobin, red blood cell count, heamatocrit, white blood cell count, platelet count, plasma total protein, fibrinogen, plasma viscosity, blood urea nitrogen, creatinine, cholesterol, triglicerides. Flow mediated dilatation of brachial artery was determined, too. Blood tests and flow mediated dilatation study were repeated after transfusion. RESULTS: The main determinants of whole blood viscosity increased after transfusion. The increase of hemoglobin, red blood cell count, hematocrit were highly significant. The central flow velocity in brachial artery decreased at rest and during hyperemia as well. The flow mediated dilatation of brachial artery wasn't significantly changed by transfusion. CONCLUSIONS: Change of determinants of whole blood viscosity caused by transfusion didn't change the flow mediated dilatation of brachial artery. The probable reason for this that the increase of whole blood viscosity in associated with the decrease of central flow velocity. These two counteracting changes probably equal each other.

Aged↗

PubMed1998

[Lymphoblast transformation colorimetry in the diagnosis of drug hypersensitivity].

Diagnosis of drug allergy has been considered to be a multistage procedure consisting of detailed history of previous medication, analysis of symptoms, laboratory tests and provocation with the supposed sensitizing drug. Many laboratory methods are used for demonstration drug allergy, but opinions differ with regard to their specificity, sensitivity and reproducibility. Lymphocyte transformation test (LTT) is considered to be a valuable in vitro method in the diagnosis of drug allergy. For evaluation of LTT we introduced a tetrazolium-based colorimetric assay (MTT). Comparison of MTT assay with 3H-Thymidine incorporation in evaluation of Phytohaemagglutinin induced LTT resulted no significant difference in the dose-response curve. During the past 3 years 315 patients were tested with LTT-MTT method; 736 lymphocyte transformation tests mainly with antibiotics, topical anesthetics and painkillers were evaluated by MTT resulting 280 positive results. Physicians requested skin tests were performed with drugs induced no in vitro lymphocyte transformation and only 8 topical reactions without general symptoms were observed. MTT method was found to be a sensitive laboratory test in evaluation of LTT performable even in routine laboratories. Its application can lead to a substantial decrease in the number of patients who must be subjected to the possible risk of in vivo tests for the determination of the sensitizing drug.

Colorimetry↗

PubMed1998

[Hemorheologic parameters in coronary artery disease].

Hemorheological parameters were proved to be primary risk factors in ischemic heart disease (IHD) by several studies. In the present study the relation of these parameters to the severity of coronary artery disease (CAD) was examined. The data of 109 patients (mean age: 55 +/- 9 yrs) undergoing coronary angiography and 59 healthy controls (mean age: 35 +/- 10 yrs) were analyzed. Hemorheological parameters [hematocrit, fibrinogen level, plasma viscosity (PV) and whole blood viscosity (WBV)] were measured and circulatory index (CRI) was calculated. Patients were classified into three groups according to their coronary vessel state based on the coronary angiogram: Group 1 (n = 19, mean age: 53 +/- 8 yrs) without significant CAD, Group 2 (n = 19, mean age: 51 +/- 11 yrs) with single vessel disease, Group 3 (n = 71, mean age: 57 +/- 8 yrs) with multivessel disease. All the measured hemorheological parameters of IHD patients were significantly higher than those of controls. Fibrinogen and PV was significantly elevated in Group 2 and 3 comparing to Group 1 (p < 0.05 and 0.01). Hematocrit and WBV was significantly increased in Group 3 comparing to Group 1 and 2 (p < 0.05). CRI was significantly decreased in IHD patients, and it was also lower in Group 3 than in Group 2 (p < 0.05). These results indicate that hemorheological parameters may play a role in the pathogenesis and development of CAD.

Adult↗

PubMed1998

DNA curvature in solution measured by fluorescence resonance energy transfer.

The sequence-induced curvature of DNA fragments free in solution was characterized by measurements of the end-to-end distance using fluorescence resonance energy transfer (FRET). The 31 bp oligonucleotides were labeled at their 5' ends with fluorescein as the donor and rhodamine X as the acceptor. We compared a curved oligonucleotide with three phased A6 blocks and a control containing (AT)3 instead of the A6 blocks. The increased efficiency of energy transfer of the A6-containing DNA indicates the existence of a permanent sequence-induced curvature, the magnitude of which is in good agreement with estimates from theoretical curvature predictions. Energy transfer efficiency and correspondingly curvature increases with NaCl concentration.

Circular Dichroism↗

PubMed1998

[An unusual case of morbid weight loss].

A 47 year old patient was admitted because of 20 kg weight loss and microcytic anaemia. There wasn't any important disease in his medical history. During examinations it has been found microcytic anaemia, hypoproteinaemia, low serum potassium, elevated prothrombin INR value, malabsorption and mild hepatosplenomegaly. After precluding the possibility of malignant disorders and any other chronic diseases, examinations have cleared Whipple-disease.

Anemia↗

PubMed1998

Determination of fenbendazole, praziquantel and pyrantel pamoate in dog plasma by high-performance liquid chromatography.

Simple and rapid high-performance liquid chromatographic methods were developed for the determination of fenbendazole, praziquantel and pyrantel pamoate in dog plasma. The combination of these drugs is the most powerful treatment against most types of worms. Blood plasma samples obtained in a pharmacokinetic trial were prepared using solid-phase extraction. Fenbendazole and praziquantel were analyzed simultaneously by reversed-phase high-performance liquid chromatography on an octadecyl-modified silica stationary phase employing acetonitrile-phosphate buffer (pH 3.0) eluent and ultraviolet detection at 220 nm. Pyrantel was analyzed separately on a base-deactivated reversed-phase column using methanol-tetrahydrofuran-ammonium acetate buffer (pH 4.6) eluent and ultraviolet detection at 317 nm. Average recoveries for fenbendazole, praziquantel and pyrantel pamoate were 76.8, 93.4 and 90.5%, respectively. Limits of quantitation were in the range of 15-25 ng/ml plasma.

Animals↗

PubMed1998

Target-specific expression of presynaptic mossy fiber plasticity.

Mossy fiber synaptic transmission at hippocampal CA3 pyramidal cells and interneurons was compared in rat brain slices to determine whether mossy terminals are functionally equivalent. Tetanic stimulation of mossy fibers induced long-term potentiation in pyramidal neurons but was either without effect or it induced depression at synapses onto interneurons. Unlike transmission onto pyramidal neurons, transmission onto interneurons was not potentiated after adenosine 3',5'-monophosphate (cAMP) activation. Furthermore, metabotropic glutamate receptor depression of transmission onto interneurons did not involve cAMP-dependent pathways. Thus, synaptic terminals arising from a common afferent pathway do not function as a single compartment but are specialized, depending on their postsynaptic target.

Afferent Pathways↗

PubMed1998

Salt-dependent DNA superhelix diameter studied by small angle neutron scattering measurements and Monte Carlo simulations.

Using small angle neutron scattering we have measured the static form factor of two different superhelical DNAs, p1868 (1868 bp) and pUC18 (2686 bp), in dilute aqueous solution at salt concentrations between 0 and 1.5 M Na+ in 10 mM Tris at 0% and 100% D2O. For both DNA molecules, the theoretical static form factor was also calculated from an ensemble of Monte Carlo configurations generated by a previously described model. Simulated and measured form factors of both DNAs showed the same behavior between 10 and 100 mM salt concentration: An undulation in the scattering curve at a momentum transfer q = 0.5 nm-1 present at lower concentration disappears above 100 mM. The position of the undulation corresponds to a distance of approximately 10-20 nm. This indicated a change in the DNA superhelix diameter, as the undulation is not present in the scattering curve of the relaxed DNA. From the measured scattering curves of superhelical DNA we estimated the superhelix diameter as a function of Na+ concentration by a quantitative comparison with the scattering curve of relaxed DNA. The ratio of the scattering curves of superhelical and relaxed DNA is very similar to the form factor of a pair of point scatterers. We concluded that the distance of this pair corresponds to the interstrand separation in the superhelix. The computed superhelix diameter of 16.0 +/- 0.9 nm at 10 mM decreased to 9.0 +/- 0.7 nm at 100 mM salt concentration. Measured and simulated scattering curves agreed almost quantitatively, therefore we also calculated the superhelix diameter from the simulated conformations. It decreased from 18.0 +/- 1.5 nm at 10 mM to 9.4 +/- 1.5 nm at 100 mM salt concentration. This value did not significantly change to lower values at higher Na+ concentration, in agreement with results obtained by electron microscopy, scanning force microscopy imaging in aqueous solution, and recent MC simulations, but in contrast to the observation of a lateral collapse of the DNA superhelix as indicated by cryo-electron microscopy studies.

Biophysical Phenomena↗

PubMed1998

Afferent-specific innervation of two distinct AMPA receptor subtypes on single hippocampal interneurons.

Using the polyamine toxin philanthotoxin, which selectively blocks calcium-permeable AMPA receptors, we show that synaptic transmission onto single hippocampal interneurons occurs by afferent-specific activation of philanthotoxin-sensitive and -insensitive AMPA receptors. Calcium-permeable AMPA receptors are found exclusively at synapses from mossy fibers. In contrast, synaptic responses evoked by stimulation of CA3 pyramidal neurons are mediated by calcium-impermeable AMPA receptors. Both pathways converge onto single interneurons and can be discriminated with Group II mGluR agonists. Thus, single interneurons target AMPA receptors of different subunit composition to specific postsynaptic sites, providing a mechanism to increase the synapse-specific computational properties of hippocampal interneurons.

Afferent Pathways↗