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M Löffler

Publications and source records attributed to M Löffler.

At least 91 records · Page 5Linked to original sources
PubMed1980

On the role of dihydroorotate dehydrogenase in growth cessation of Ehrlich ascites tumor cells cultured under oxygen deficiency.

In pyrimidine biosynthesis the oxidation of dihydroorotate is catalyzed by dihydroorotate dehydrogenase, which is linked to the mitochondrial electron transport chain in vertebrates. In order to elucidate the role of this oxygen-dependent anabolic process in the arrest of cell proliferation under anaerobic culture conditions, the effect of the antimetabolite dihydro-5-azaorotic acid on growth, metabolism and cell cycle distribution of Ehrlich ascites tumor cells was studied and compared with the effect of oxygen-free culture conditions. Experiments with cell homogenates confirmed that the dehydrogenation of dihydroorotate is blocked by the inhibitor. In intact cells 2 mM dihydro-5-azaorotic acid inhibited incorporation of dihydro[6-14C]orotate into nucleic acids, and no further increase in RNA and DNA content was observed in its presence for several hours. The cells remained viable; glycolytic activity was normal; respiration was reduced; growth cessation occurred within a few hours. DNA histograms obtained by flow cytometry revealed an accumulation of cells in the G1 phase, which was also observed with anaerobically cultured cells. Substitution of cultures with pyrimidine nucleosides completely sustained cell proliferation in the presence of the inhibitor but not in an anoxic atmosphere. It is concluded that in the absence of oxygen cell proliferation may be arrested by inhibition of the dihydroorotate dehydrogenase alone. However, additional impairments of cell metabolism must play an important role.

Animals↗
PubMed1979

Lipogenesis in Ehrlich ascites tumor cells under anaerobic culture conditions.

Anaerobic culture conditions (95% argon/5% CO2) caused a slightly greater increase in total lipids of Ehrlich ascites tumor cells than a gas phase of 20% O2, 75% N2, 5% CO2. Whereas the rate of [U-14C]acetate incorporation into total lipids and lipid-subclasses rose markedly in the absence of oxygen, a drastic decrease of [U-14C]pyruvate and [1-14C]octanoate incorporation as well as a 30% reduction of 3H incorporation into lipids from tritiated water were observed under these conditions. Since profound changes in the metabolic state of cells cause alterations in the specific activity of the acetyl-CoA pool but do not alter the specific activity of intracellular water, this precursor is considered to be an adequate monitor for lipogenesis under aerobic and anaerobic culture conditions. Therefore, it is concluded that Ehrlich ascites tumor cells are not able to reoxidize NADH/NADPH in the absence of oxygen by a stimulation of biosynthesis of fatty acids as is discussed to be the case in normal cells. The slight increase in total lipids of anaerobically cultured cells seems to be the result of an imbalance between normal uptake and impaired utilization of lipids from serum-supplemented culture medium.

Anaerobiosis↗
PubMed1979

Unexpectedly low incorporation of isotopic acetate into lipids of Ehrlich ascites tumor cells cultured in lipid-poor medium.

The present communication reports data on the lipid biosynthesis of Ehrlich ascites tumor cells grown in culture media supplemented with modified sera. Whereas the metabolisms of [14C]pyruvate and [14C]mevalonate are identical in all media tested, the incorporation of [14C] acetate is higher in medium with dialyzed serum than in medium with delipidized serum; it is suppressed in the absence of all lipids in culture medium. Cellular integrity is not impaired in modified media. The results indicate that acetyl-CoA synthetase of Ehrlich ascites tumor cells is not regulated by exogenous lipids as is known to be the case in nonmalignant cells.

Acetate-CoA Ligase↗
PubMed1978

Anaerobiosis and oxygen recovery: changes in cell cycle distribution of Ehrlich ascites tumor cells grown in vitro.

The cell cycle distribution of in vitro cultured Ehrlich ascites tumor (EAT) cells was analysed by pulse-cytophotometry to characterize the growth cessation observed under anaerobic conditions. DNA histograms provided evidence that in the absence of oxygen EAT cells accumulate in the G1 and early S phase of the cell cycle while in the presence of oxygen an increase in G2 was observed during 24h culture period. Cellular recovery from anaerobiosis was observed soon after transfer of the cells into fresh aerobic culture medium but occurred slowly if the cells were only resupplied with air. Cell cycle analyses as well as (14C)-thymidine incorporation suggest considerable synchronization results from the introduction of anaerobiosis.

Anaerobiosis↗
PubMedDate not supplied

[Quality standards and their assurance for study centers in the competence network malignant lymphoma].

BACKGROUND: The aim of most of the trials of the Competence Network Malignant Lymphoma is to optimize the standard treatment of lymphoma using only registered drugs in the case of medicinal therapies (quality assurance protocols). In contrast to regulatory trials, special regulations for quality assurance protocols are not given by the legislature. However, there is agreement that also for this type of studies the declaration of Helsinki and the Guidelines of the International Conference on Harmonisation (ICH) are relevant. The ICH Guidelines must be formulated to take into account the specific situation of quality assurance protocols and to ensure at the same time efficiency and transparency of these studies. This is the aim of the quality management of the study groups in the Competence Network Malignant Lymphoma. METHOD: The quality assurance measures already established in the study groups are being expanded to a comprehensive quality management concept in agreement with the ICH Guidelines and allowing for the situation of quality assurance protocols. To this end, a working group for quality management (AG-QM) has been set up to define and establish general quality standards for all aspects of planning, executing and evaluating quality assurance protocols in study centers. RESULTS: The AG-QM has developed a system of Standard Operating Procedures (SOPs) reflecting all working procedures of the study centers. Furthermore, evaluation parameters for the quality of trial execution have been identified and the harmonisation of documentation parameters has been initiated. Term definitions are collected and their harmonisation coordinated. CONCLUSIONS: Development of quality standards is the first step of quality management. To ensure the realisation of these standards in practice, the AG-QM will establish quality assurance measures including continuous reevaluation of quality criteria and actualization of quality standards if necessary.

Helsinki Declaration↗
PubMedDate not supplied

Further investigations on the p-nitrophenylphosphatase activity of intact Ehrlich ascites tumor cells.

The substrate specificity and the effects of nucleotides and SH-blocking agents on the p-nitrophenylphosphatase activity of intact Ehrlich ascites tumor cells (EAT) cells were studied. DL-beta-Glycerophosphate, o-phosphoethanolamine, cholinephosphate, glucose-6-phosphate, o-carboxyphenylphosphate,, phosphoenolpyruvate and AMP were not attacked by intact cells. ATP is greater than GTP is greater than UPT is greater than PPi is greater than pNPP were cleaved with decreasing velocity. A stimulation of the cleavage of p-NPP by the following nucleotides was observed with decreasing effectivity: ATP is greater than ADP is greater than GTP is greater than UTP; AMP was ineffective. The phosphatase activity was not affected by malate, tartrate and glutathion disulfide. The SH blocking agents diamide and thimerosal were more effective inhibitors of the pNPPase than of the ATPase activity, whereas the hydrolysis of ATP is more affected by the ATP analog adenylylimidodiphosphate. The present data are best compatible with a double headed enzyme: Both active sites interact with ATP, only one is active against p-NPP and sensitive against SH-blocking agents.

4-Nitrophenylphosphatase↗
PubMedDate not supplied

Proliferation and metabolic activities of Ehrlich ascites tumor cells in chemically defined albumin media.

Cell proliferation, viability, DNA-, RNA-, protein synthesis, amino acid transport, repiration and lactate/glucose quotient of Ehrlich ascites tumor cells grown in suspension culture in serum free medium supplemented with albumin charges of different origin were studied. Optimal cell growth was obtained in nutrient medium supplemented with 1% bovine serum albumin (Cohn-fraction V, Serva). Cell proliferation under these culture conditions was delayed to 50% as compared to controls in normal medium; the rate of synthesis of macromolecules was reduced; energy metabolism was not significantly imparied. The trend of the cells in albumin medium to attach to glass was independent from the pH of the cultures between 7.2 and 8.0; it was enhanced by fatty acid deprivation of the albumin.

Amino Acids↗
PubMedDate not supplied

Cell proliferation and metabolism of Ehrlich ascites tumor cells grown in chemically defined albumin medium for several passages.

Cell proliferation, cell cycle distribution, viability, uptake of alpha-aminoisobutytic acid, cyclo leucine and 2-deoxyglucose as well as DNA, RNA and protein synthesis of Ehrlich ascites tumor cells grown in suspension culture over three passages in serum free nutrient medium supplemented with 1-2% bovine serum albumin) Cohn fraction V, Serva) were measured and compared to cells grown in medium supplemented with 15% horse serum. At the end of the fourth passage in vitro, that is the third passage in serum free albumin medium, the growth of the cells is reduced to about 10% of the controls, accumulation of the cells in G2 is delayed and the number of dead cells rises to 30%. The transport rates of alpha-aminoisobutyric acid and of 2-deoxyglucose slowly decrease while the uptake of cycloleucine shows a more complex behaviour in albumin medium. Incorporation of thymidine and leucine into the cells corresponds to the growth rate, while the incorporation of uridine in normal as well as in albumin medium exhibits different pattern. The present experiments demonstrate, that it may be possible to preserve this cells in a fairly "physiological" state during two passages in albumin medium.

Aminoisobutyric Acids↗
PubMedDate not supplied

Lipid metabolism of Ehrlich ascites tumor cells grown in chemically defined albumin medium.

Total lipids of Ehrlich ascites tumor cells grown in nutrient medium supplemented with 1% bovine serum albumin instead of 15% native horse serum and rate of incorporation of [3H] acetate into total lipids are reduced, while the cholesterol content of the cells is higher than of controls grown in normal medium. The lower lipid content of cells cultured in albumin supplemented medium is explained by a lack of exogenous lipids, which are normally taken up from the serum containing nutrient medium. A several fold increase of incorporation of labelled choline and ethanolamine into the phospholipids of the cells grown in the modified medium is observed. We suggest, that the observed stimulation of the incorporation of phospholipid precursors reflects changes in the dynamic state of the membranes produced by serum depletion.

Animals↗
PubMedDate not supplied

Energy parameters, macromolecular synthesis and cell cycle progression of in vitro grown Ehrlich ascites tumor cells after inhibition of oxidative ATP synthesis by oligomycin.

In order to elucidate the significance of oxidative ATP production for the proliferation of Ehrlich ascites tumor cells, cell cycle progression, energy metabolism and macromolecular synthesis in the presence of oligomycin were studied. In the presence of the inhibitor (20 micrograms/ml), lactate production and glucose uptake of the cells increased by about 30-35% as compared to controls; oxygen consumption was maximally inhibited by 30-45% and could not further be reduced by higher concentrations of the inhibitor. ATP/ADP ratios of the oligomycin treated cells and control cells were not significantly different. In the first passage in the presence of oligomycin proliferation of the cells is reduced to about 50% that of controls; without severely affecting viability (dye exclusion test). In the second passage with oligomycin cell proliferation completely arrests. As was shown by flow cytometric analysis and BrdU-H33258 technique of flow cytometry, cells accumulate in the early S phase; division of cells which are in the S- and G2M compartment at the beginning of oligomycin treatment accounts for the increase of cell number in the first passage in the presence of oligomycin. On recultivation in the third passage in the absence of the inhibitor cells take up proliferation again; an increase of cell number of about 60% of controls was observed within 24 h. In the presence of oligomycin incorporation of [2-14C]thymidine is reduced to about 20% of the controls within 8 h, incorporation of [U-14C]lysine begins to slow down immediately after treatment with the inhibitor, the same is true for the incorporation of [2-14C]uridine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗