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Biomedical subjects

W Geurtsen

Publications and source records attributed to W Geurtsen.

106 records · Page 6Linked to original sources
PubMed1981

Arabinosyl nucleosides. XXXII. Mechanism of inhibition of L5178y mouse lymphoma cells by 9-beta-D-arabinofuranosylguanine.

The mechanism of the growth-inhibitory action of 9-beta-D-arabinofuranosylguanine (ara-G) on mouse lymphoma cells (L5178y) at the level of nucleic acid synthesis was studied. Ara-G inhibits the cell proliferation at an ED50 concentration of 12.3 microM. The cells die because of unbalanced growth. At cytostatic concentrations ara-G inhibits the incorporation rate of dThd into DNA to a much higher degree compared to those of the precursors into RNA or proteins. Ara-G has no effect on the induction of DNA polymerase alpha occurring at the beginning of the S-phase; this compound exerts its inhibitory activity during the S-phase. Ara-G is intracellularly phosphorylated to ara-GTP. It was demonstrated that ara-G is incorporated into DNA but not into RNA; one molecule of ara-G is incorporated per 7050 molecules of deoxyguanosine. The ara-GMP moieties, incorporated into DNA of L5178y cells are not removed during a culture period of 7.7 doubling steps; compared to the controls no reduction of the viability and growth rate was observed.

Animals↗
PubMed1981

Inhibition of DNA synthesis in permeabilized mouse P815 mast cells by arabinofuranosyladenine 5'-triphosphate.

P815 mast cells (mouse leukemic cells) have been successfully permeabilized to 9-beta-arabinofuranosyladenine 5'-triphosphate (araATP) using lysolecithin. The permeabilized cells remained viable according to the following criteria: (a) exclusion of trypan blue after replacing the lysolecithin with culture medium; (b) cell growth rate identical to control cultures, and (c) intact DNA-synthesizing complex in permeable cells. It was shown that permeabilized cells incorporate [3H]thymidine and [3H]deoxyadenosine-triphosphate (dATP) into DNA when the suspension is supplied with the appropriate substrates and cofactors. Permeable cells break down araATP to 9-beta-D-arabinofuranosyladenine 5'-diphosphate only slightly after incubation for 60 min; no further dephosphorylation to 9-beta-D-arabinofuranosyladenine 5'-monophosphate or 9-beta-D-arabinofuranosyladenine occurs. In kinetic experiments it was shown that the DNA-replicating complex of permeabilized cells is competitively inhibited by araATP with respect to dATP; Ki(araATP) was determined to be 0.6 microM and the Km(dATP), 0.9 microM.

Animals↗
PubMed1981

Stimulation of DNA polymerase beta activity in permeabilized mouse P815 mast cells after neocarzinostatin treatment.

Neocarzinostatin (NCS), which causes DNA strand scission both in vitro and in vivo, reversibly inhibits the growth of both unpermeabilized and lysolecithin-permeabilized P815 mast cells (mouse leukemic cells). Kinetic experiments with NCS-pretreated cells revealed that the permeabilized cells are more strongly affected than the unpermeabilized cells, indicating that the membrane protects the cells against the influence of NCS. The two major DNA polymerase activities (form alpha and form beta) were determined in permeabilized cells during the lag phase of growth, after NCS treatment, and an 8.5-fold higher DNA polymerase beta activity was observed in NCS-treated cells than in controls. The activity of the second enzyme, DNA polymerase alpha, was low during the period of cell proliferation.

Animals↗
PubMed1980

Age-dependent alterations of DNA synthesis. Terminal deoxynucleotidyl transferase and DNA polymerase activities in bone marrow subpopulations from mice.

The decrease of functional capacity of cellular immunity during ageing seems to be due to cellular changes of stem cells, particularly in the growth properties and the cell density in T-cell subsets. We approached this problem at the molecular biological level by quantifying the key enzymes necessary for DNA synthesis in bone marrow cells from mice: deoxynucleotidyl transferase (TdT) and DNA polymerase alpha. The bone marrow cells were fractionated on a discontinuous bovine serum albumin density gradient and the extractable enzyme activities (expressed per 10(8) nucleated cells in the respective fraction) were determined. TdT activity was found to decrease markedly during ageing. Mature animals contain only 34% and senescent animals only 13% of the activity observed in immature mice. From the density distribution analysis it was found that a shift of TdT-containing cells to the lower density occurs. The specific DNA polymerase alpha activity also decreases in bone marrow cells with age. While the overall activity amounts in immature cells to 78 enzyme units/10(8) cells, it decreases in mature cells to 57 units/10(8) cells, and in cells from senescent animals to 36 units/10(8) cells. Density distribution analysis of the cells shows that the highest activity is observed in the low-density fraction. From these experimental data we conclude that in the fractions containing precursor T-cells, a reduced number of proliferating cells is present.

Aging↗
PubMed1979

Additive effects of bleomycin and neocarzinostatin on degradation of DNA, inhibition of DNA polymerase beta, and cell growth.

The interactions of the two antitumor protein antibiotics, neocarzinostatin (NCS) and bleomycin (BLM), were studied on subcellular and cellular levels. BLM and NCS were found to remove thymine from double-stranded DNA. Combination experiments using BLM and NCS together in an assay with isolated DNA revealed an additive effect in splitting. Under limiting concentration conditions, BLM and NCS induce alkali-labile sites in DNA without a subsequent cleavage of the chain. After transfer of BLM- or NCS-treated DNA into an alkaline solution, strand scissions occur. Combination of BLM and NCS results in an additive DNA-cleaving effect, which indicates that the splitting reactions initiated by BLM or NCS are not influenced if the two antibiotics are applied in combination. The DNA polymerase beta is inhibited by BLM (at higher concentrations) and by NCS in a competitive way with respect to DNA. The inhibition constant of BLM and NCS in a combination experiment was found to be the result of the sum of the inhibition constants of BLM and NCS. Using L5178Y mouse lymphoma cells, it was found that cells incubated with both BLM and NCS show "unbalanced growth." The dose-response curves from BLM and NCS have identical slopes; they are characteristic for compounds which selectively inhibit DNA synthesis. By use of isobolograms, it could also be clearly shown that BLM and NCS interact additively.

Animals↗
PubMedDate not supplied

A 4-year retrospective clinical study of Class I and Class II composite restorations.

OBJECTIVES: The purpose of this study was to determine the longevity and quality of Class I and Class II resin composite (Herculite XR) restorations placed in private practice. METHODS: One thousand two hundred and nine Class I and Class II composite restorations with margins in enamel were evaluated clinically after periods of between 12 months and 4.5 years in clinical service by two calibrated examiners using a modified version of established criteria. RESULTS: Of the restorations investigated 94.8% were rated as 'good' (Alpha 79.3%) or 'clinically acceptable' (Bravo 15.5%). Significantly more restorations in premolar teeth were rated as Alpha (82%) than in permanent molar teeth (77%). The survival rate after 4 years was around 87%. The 50% survival-time, calculated by extrapolation according to Weibull, was approximately 9 years. CONCLUSIONS: It is concluded that the composite investigated is an appropriate material for the restoration of Class I and Class II lesions with margins located in enamel in premolar and permanent molar teeth.

Bicuspid↗