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Biomedical subjects

G Weber

Publications and source records attributed to G Weber.

At least 307 records · Page 17Linked to original sources
PubMed1992

Effects of hydrostatic pressure on a membrane-enveloped virus: high immunogenicity of the pressure-inactivated virus.

A new approach to the preparation of antiviral vaccines relying on the inactivation of the virus particle by hydrostatic pressure is described. The enveloped virus vesicular stomatitis virus was utilized as a model; a pressure of 260 MPa applied for 12 h reduced infectivity by a factor of 10(4), and the antibodies against pressurized material were as effective as those against the intact virus when measured by their neutralization titer. Fluorescence measurements indicate that application of pressure results in perturbations of the particle interactions that permit binding of specific molecular probes. Electron microscopy showed that the membrane of the pressurized virus was partially preserved, presenting the spike pattern of the membrane G protein. Unlike the icosahedral viruses, dissociation into smaller particles was not observed, but a constant change in the morphology was the presence of a bulge in the surface of the pressurized virus, indicating a displacement of the capsid subunits, retained under the lipid and protein membrane.

Animals↗
PubMed1992

Predictive testing for multiple endocrine neoplasia type 1 using DNA polymorphisms.

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominantly inherited predisposition to neoplastic lesions of the parathyroids, pancreas, and the pituitary. We have previously located the predisposing genetic defect to the long arm of chromosome 11 by genetic linkage. In this study, 124 members of six MEN1 families, including 59 affected individuals, were genotyped for restriction fragment length polymorphisms with different DNA probes, and the genetic linkage between these marker systems and MEN1 was determined. 13 marker systems (17 DNA probes) were found to be linked to MEN1. These markers are located within a region on chromosome 11 spanning 14% meiotic recombinations, with the MEN1 locus in the middle. Four of the marker systems are on the centromeric side of MEN1, and four on the telomeric side, based on meiotic crossovers. The remaining five DNA probes are closely linked to MEN1, with no crossovers in our set of families. The 13 marker systems can be used for an accurate and reliable premorbid test for MEN1. In most clinical situations it is possible to identify a haplotype of this part of chromosome 11 with the mutant MEN1 allele in the middle. The calculated predictive accuracy is greater than 99.5% if three such marker systems are informative. Therefore, genetic linkage testing can be used for informed genetic counseling in MEN1 families, and to avoid unnecessary biochemical screening programs.

Chromosome Mapping↗
PubMed1992

Antitumor activity of tiazofurin in human colon carcinoma HT-29.

Tiazofurin is effective in treating end-stage leukemic patients (Tricot et al., Cancer Res 49:3696-3701, 1989). In sensitive tumors, the active metabolite of tiazofurin, TAD, potently inhibits IMP dehydrogenase activity, resulting in reduced guanylate pools. To elucidate tiazofurin activity in human solid tumors, we examined its activity in human colon carcinoma HT-29. Tiazofurin exhibited an LC50 of 35 microM in cultured HT-29 cells. Incubation of HT-29 cells with 100 microM tiazofurin for 2 h resulted in TAD formation (9.3 nmol/g cells) and in a 64% decrease in GTP pools. For biochemical and chemotherapy studies, athymic nude mice were transplanted s.c. with HT-29 cells. Twenty-four days later, mice were injected i.p. with tiazofurin (500 mg/kg); 6 h later, tumors were removed and analyzed. These tumors formed 17 nmol/g of TAD with decreased GTP pools (56%). To study oncolytic activity, transplanted mice were treated 24 h later with tiazofurin (500 mg/kg, once a day for 10 days). To examine the effectiveness of tiazofurin in established tumors, the drug was administered to mice 14 days after tumor implantation (500 mg/kg, once a day for 5 days, course repeated 4 times with a 10-day rest). Both treatment schedules resulted in significant antitumor activity. This study illustrates the potential usefulness of tiazofurin in treating human colon carcinoma.

Adenine Nucleotides↗
PubMed1992

Increased deoxycytidine kinase activity in cancer cells and inhibition by difluorodeoxycytidine.

The activity of deoxycytidine kinase (EC 2.7.1.74), an important pyrimidine salvage enzyme, was elevated 5- to 30-fold in human ovarian carcinoma and OVCAR-5 cells, in human colon carcinoma and HT-29 cells, in rat hepatoma 3924A solid tumors and cells, and in rat sarcoma as compared with the respective control normal cells. There was an inverse relationship between cell doubling time and deoxycytidine kinase activity in 8 cancer cell lines, with rapidly growing HL-60 cells (20 hr) showing the highest, and slower-growing lung H69 cells (60 hr) the smallest, increase in enzyme activity. In time-sequence studies in human HL-60, OVCAR-5, PANC-1, and rat hepatoma 3924A cells, there was a significant rise in deoxycytidine kinase activity after 3-6 hr of seeding, with peak increases (3.5- to 4-fold) at 48-72 hr in the log phase in comparison with values of the respective plateau phase cells (96-144 hr). In extracts of various cancer cells, the high deoxycytidine kinase activity was competitively inhibited by difluorodeoxycytidine (DFDC), with Ki = 7 to 30 microM. The Km for deoxycytidine in various carcinoma cell lines ranged from 0.3 to 0.7 mM and addition of DFDC increased the apparent Km from 0.7 to 4 mM. Deoxycytidine kinase activity in human HL-60 cells was inhibited by the end product, dCTP, with IC50 = 3 microM; dCTP elevated the Km for deoxycytidine from 0.35 to 0.9 mM. dTTP reversed the inhibition by dCTP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Sublocalization of the multiple endocrine neoplasia type 1 gene.

Tumorigenesis in multiple endocrine neoplasia type 1 (MEN 1) involves the unmasking of a recessive mutation at the MEN 1 locus which has been mapped to chromosomal region 11q11-13. By analyzing 58 DNA markers on a panel of radiation-reduced somatic cell hybrids, the region encompassing the MEN 1 gene was divided into nine subregions. Pulsed field gel electrophoresis analysis of markers within subgroups showed that the recombination rate around the MEN 1 locus is high. Combined linkage analysis in MEN 1 families and deletion mapping in MEN 1-related tumors suggest the MEN 1 gene is located centromeric to D11S807 and telomeric to PYGM.

Animals↗
PubMed1992

Action of tiazofurin and 8-Cl-cAMP in human colon and pancreatic cancer cells.

Tiazofurin and 8-Cl-cAMP are novel chemotherapeutic agents shown to be effective against various cancer cells in vitro and in vivo. They act through distinct mechanisms that might modulate the signal transduction pathway, which causes growth inhibition, differentiation and down-regulation of c-ras and c-myc oncogene expression. We examined the effects of tiazofurin and 8-Cl-cAMP on colony formation of HT-29 human colon cancer and BxPC-3 and PANC-1 human pancreatic cancer cell lines. The IC50 of 8-Cl-cAMP was 0.1 and 0.2 microM in the pancreatic and colon cancer cell lines, respectively, and tiazofurin yielded IC50s from 4 (PANC-1) to 18 microM (HT-29). Simultaneous incubation with 8-Cl-cAMP and tiazofurin had additive effects on the inhibition of colony formation in the three examined cell lines. These results indicate possible clinical usefulness of a combination of tiazofurin and 8-Cl-cAMP in the treatment of colon and pancreatic carcinomas.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1992

Iron content in human alveolar macrophages.

Intracellular iron can be estimated semi-quantitatively by histochemical determination using the ferrocyanide reagent's score. Particle-induced X-ray emission (PIXE) allows accurate determination of various elements including iron in cells and biological fluids. Both techniques have been used to measure iron in alveolar macrophages gathered by bronchoalveolar lavage. The purpose of this study was to investigate the clinical usefulness of the PIXE technique in occupational respiratory medicine and in various pulmonary diseases. Using the PIXE method, we measured the iron content of alveolar macrophages in healthy subjects, with and without occupational exposure to iron dust, and in patients with pulmonary diseases (chronic obstructive pulmonary disease (COPD), lung cancer, Goodpasture's syndrome). Our results were then compared with those obtained with the ferrocyanide reagent. Intramacrophagic iron was 0.33 +/- 0.21 micrograms.10(-6) (mean +/- SD) cells in healthy non-smoking subjects without occupational exposure. Intramacrophagic iron was increased in smokers, iron-steelworkers, and in patients with COPD or lung cancer even in the absence of pulmonary haemorrhage. The two patients with Goodpasture's syndrome had high intramacrophagic iron content. About 80% of the whole bronchoalveolar lavage fluid iron content was in the cells. Mean iron content of blood monocytes, lymphocytes and neutrophils of eight healthy subjects was significantly lower than that of alveolar macrophages. A significant correlation was found between iron determination by the PIXE method and the ferrocyanide reagent's score (r = 0.89). We conclude that intramacrophagic iron may be increased in steelworkers and subjects with pulmonary haemorrhage, but also in asymptomatic smokers, in COPD and lung cancer patients without occupational exposure to iron dust.

Anti-Glomerular Basement Membrane Disease↗
PubMed1992

Updating on in-vivo and in-vitro effects of heparin and other glycosaminoglycans (mesoglycan) on arterial endothelium: a morphometrical study.

Glycosaminoglycans, which include heparin, heparansulfate and dermatansulfate, are substances that exhibit many significant biological activities. In-vitro and in-vivo experiments for studying the effects of heparin and an association of heparan-like glycosaminoglycan and dermatansolfate (mesoglycan) on aortic arterial endothelium were performed. The studies were developed by means of computerized morphometric techniques. The in-vitro tests, performed on bovine aortic endothelial cells, have revealed an increase in survival rate, enhancement of cell density at confluence, and increase of nucleus/cytoplasm ratio, after "in-vitro" administration of heparin or mesoglycan. The in-vivo tests have revealed a minor development of aortic intimal lipid deposition in mesoglycan-treated hypercholesterolaemic rabbits. Our morphometrical results confirmed by statistical tests strongly support the data collected in the literature over many years on the protective effects of mesoglycan and heparin on endothelium.

Animals↗
PubMed1992

Effect of estrogen replacement therapy on bone mineral content in girls with Turner syndrome.

Because a close relationship between estrogen deficiency and osteoporosis has been proven, it is possible that lifelong estrogen deficiency might be the cause of osteopenia in Turner syndrome. This study was done to characterize the effect of estrogen therapy on bone mineralization in girls with Turner syndrome. Radial bone mineral content values were found to be below the 95% normal confidence interval in 44 of 49 untreated patients, aged 10.82 +/- 3.45 years. An inverse correlation was found between the patients' ages and their delta bone mineral content values. The effect of beginning estrogen treatment early or late was studied in 16 girls who started the treatment before and 11 who started after age 12. Although they were still deficient compared with controls, the first group had better mineralization than the second (P = .0005). Finally, nine patients were followed prospectively during replacement therapy; their bone mineral content delta values changed significantly (P = .02) during the follow-up period (3.17 +/- 0.33 years), but the bone mineral content did not normalize. Our data show that estrogen deficiency per se does not cause osteoporosis in young girls with Turner syndrome. In fact, estrogen therapy prevented bone loss but failed to normalize the low bone mineral content values. Early treatment is preferable because it reduces the bone density deficit present in untreated patients.

Adolescent↗
PubMed1992

Azidothymidine and dipyridamole as biochemical response modifiers: synergism with methotrexate and 5-fluorouracil in human colon and pancreatic carcinoma cells.

Azidothymidine (AZT), inhibiting thymidine kinase (EC 2.7.1.21) (Weber, G. et al., Cancer Commun. 2:129-133, 1990) and dipyridamole, inhibiting nucleoside transport (Zhen, Y.-s. et al., Cancer Res. 43:1616-1619, 1983) exert blocking action on the activities of salvage pathways of nucleotide biosynthesis. Determined by clonogenic assay in human colon cancer HT-29 cells, the cell survivals for AZT, 10 microM, dipyridamole, 5 microM, and methotrexate (MTX), 0.025 microM, were 90, 82, and 62%, respectively; while the combinations of AZT + MTX, dipyridamole + MTX and AZT + dipyridamole + MTX, reduced survivals to 36, 4.3, and 0.7%. AZT or dipyridamole was synergistic with MTX, whereas AZT plus dipyridamole showed an even more marked potentiation of MTX activity. The survivals for 5-fluorouracil (5-FU), 0.5 microM, alone, AZT + 5-FU, dipyridamole + 5-FU, and AZT + dipyridamole + 5-FU were 86, 47, 29 and 5.1%, respectively. Similar results were observed in human pancreatic carcinoma BxPC-3 and PANC-1 cells. AZT markedly enhanced the inhibitory effect of dipyridamole in reversing the thymidine-hypoxanthine rescue from MTX cytotoxicity. AZT inhibited [14C]thymidine incorporation into DNA in HT-29 cells and strongly enhanced the effect of dipyridamole. The results indicate that combinations composed of AZT, dipyridamole, and antimetabolites, such as MTX and 5-FU, are potentially effective in the chemotherapy of human neoplasias.

Adenocarcinoma↗
PubMed1991

Cytotoxicity of tiazofurin and its arabinose and xylose analogues in K562 cells.

2-beta-D-Arabinofuranosylthiazole-4-carboxamide and 2-beta-D-xylofuranosyl-thiazole-4-carboxamide are sugar modified analogues of tiazofurin, a C-glycosyl nucleoside which after anabolism to the dinucleotide, TAD (thiazole-4-carboxamide adenine dinucleotide), exhibits antitumor activity. However, ara-T and xylo-T did not exhibit cytotoxicity. Compared to tiazofurin, only 12.5% of the ara-T and 8.8% of the xylo-T were metabolized to TAD derivatives by human myelogenous leukemia K562 cells. This was reflected in the finding that guanylate pools were not depressed after treatment with either tiazofurin derivative. These results provide evidence that the ribose moiety is essential for the metabolism and cytotoxicity of tiazofurin. This investigation should be helpful in the design of new analogues of tiazofurin for future clinical trials.

Adenine Nucleotides↗
PubMed1991

Determination of NAD pyrophosphorylase activity in biological samples.

A sensitive and simple method was developed for the accurate measurement of NAD pyrophosphorylase (NMN adenylyltransferase; EC 2.7.7.1) activity in biological samples. The reaction product of [4-3H]NAD was separated from the substrates [4-3H]NMN and ATP by HPLC. Under the standardized conditions of the assay, the enzyme activity in human chronic myelogenous leukemia K562 cells was found mainly in the nucleus (97%) with a sp act of 183.5 +/- 3.5 nmol/h/mg protein. The Km's for substrates NMN and ATP were 0.11 +/- 0.01 mM and 0.55 +/- 0.04 mM, respectively. This technique is highly reproducible with a 5% variation (SD) in five separate determinations. The lowest number of cells used for this enzyme assay was 41,000 with a protein content of 4 micrograms. The range of NAD produced during the assay was 2 to 200 microM. NAD pyrophosphorylase activities in the mononuclear cells of leukemic patients, human ovarian carcinoma cells, and rat liver were assayed.

Adenosine Triphosphate↗
PubMed1991

Selective up-regulation of type II inosine 5'-monophosphate dehydrogenase messenger RNA expression in human leukemias.

The discovery of isozymes (types I and II) of IMP dehydrogenase (IMPDH; EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, has attracted attention as a possible novel approach to cancer diagnosis and selective tumor cell chemotherapy. To elucidate differences in expression and regulation of the two IMPDH isozymes, we examined the steady-state levels of these mRNAs in various types of leukemic cells from patients. Northern blot analysis revealed that type II IMPDH was more active transcriptionally (1.5- to 5.1-fold) in all the leukemic cells examined than in normal lymphocytes, whereas type I expression was similar. The increased expression of type II mRNA in leukemic cells was closely linked with the increase in total IMPDH activity (r = 0.92). When leukemic cells from a patient with chronic granulocytic leukemia in blast crisis were separated into blast-rich and mature leukocyte-rich fractions, the expression of type II mRNA correlated positively with the population of immature leukemic cells, whereas type I expression was unchanged. Treatment of leukemic blasts with 12-O-tetradecanoyl-phorbol-13-acetate for 5 days resulted in a 90% decrease in the expression of type II mRNA with macrophage-like differentiation, while the expression of type I mRNA was relatively stable. These observations suggest that expression of type II IMPDH is stringently linked with immature characteristics of leukemic cells; thus, it should be a selective target for antileukemic chemotherapy.

Cell Differentiation↗
PubMed1991

Clonality and methylation status of the Epstein-Barr virus (EBV) genomes in in vivo-infected EBV-carrying chronic lymphocytic leukemia (CLL) cell lines.

Directly growing Epstein-Barr virus (EBV)-carrying cell lines were established from a chronic lymphocytic leukemia (CLL) patient (PG) on repeated occasions. The lines carried the same ring chromosome 15 as the leukemia cells in vivo and were similarly trisomic for chromosome 12. They all showed the same JH rearrangement, indicating that they had arisen from the same B-cell progenitor. They also had the same single EBV-terminal repeat (TR), indicating that they had been generated by a single EBV infection event. It may be surmised that a single CLL cell had been infected by EBV in vivo and established itself subsequently as a subclone within the CLL population. This subpopulation persists in vivo but does not appear to expand with time. After explantation, it transforms into lymphoblastoid cells and proliferates selectively as immortalized lines. The leukemia-representative CLL lines were phenotypically indistinguishable from the B95-8 virus-transformed normal diploid cells of the patient, established in parallel by in vitro infection. They grew as typical LCL clusters and expressed the same B-cell activation markers. The methylation status of EBV-DNA was different in the CLL lines and the B95-8-virus-transformed LCLs. When Hpall- and Mspl- digested DNA was probed with BamHI C, E, H and W fragments, the CLL lines showed a mixture of methylated and unmethylated restriction fragments as in certain EBV-carrying Burkitt lymphoma (BL) lines. In contrast, the EBV-DNA of B95-8 virus-transformed normal diploid cells was completely unmethylated, as in other LCLs.

Antigens, CD↗
PubMed1991

Oligomeric protein associations: transition from stochastic to deterministic equilibrium.

Transfer of electronic excitation energy (sensitized fluorescence) between donor and acceptor fluorophores separately attached to dimer or tetramer proteins is used to demonstrate the exchange of subunits among the undissociated particles. In dimers subjected to a pressure that produces half-dissociation, the exchange occurs at a rate that approaches the rate of dissociation. In the tetramers of glyceraldehydephosphate dehydrogenase and lactate dehydrogenase at 0 degrees C, the times for subunit exchange are nearly 2 orders of magnitude, and at room temperature 5-10 times longer than the time required to reach the dissociation equilibrium. By application of a novel method, pressure is shown to preferentially increase the rate of dissociation in dimers and decrease the rate of association in tetramers. From these observations, we conclude that the tetramers constitute a heterogeneous population, the members of which are dissociated by pressure according to individual molecular properties that can be retained over periods of time much longer than the time for equilibration of the dissociation. The dissociation of dimers exhibits the characteristics of the classical stochastic chemical equilibria, while those of the tetramers, like the more complex protein aggregates, must already be considered similar to the deterministic mechanical equilibria of macroscopic bodies.

Animals↗