PubMed Health⌕ Search

Biomedical subjects

W Pohlit

Publications and source records attributed to W Pohlit.

At least 19 recordsLinked to original sources
PubMed1996

Smoking impairs alveolar macrophage activation after inert dust exposure.

Magnetopneumography was applied to investigate intracellular phagosome motion in alveolar macrophage cells of healthy subjects (non-smokers and smokers). Ingested magnetic microparticles are inhaled and phagocytized by alveolar macrophages within hours. Thereby the particles are transferred into phagolysosomes. After magnetization the particles produce a macroscopic magnetic field of the lungs. Cellular motility causes a decay of the field (relaxation) by stochastic disorientation of the dipole particles (phagolysosomes) in the cells. Our studies have shown that the deposition of magnetite test particles induces a non-specific activation of the macrophage cells with a faster relaxation. This activation vanishes within the first day after particle deposition. This macrophage activation due to dust exposure was not present in smokers. It follows that cigarette smoking either causes a damage of the cellular defense or causes an adaptation of the macrophage cells to the permanent cigarette smoke inhalation.

Administration, Inhalation↗
PubMed1993

Reversibility of inhibition of DNA double strand break repair by 2-deoxy-D-glucose in Ehrlich ascites tumour cells.

The glycolytic inhibitor 2-deoxy-D-glucose (2-DG), a potent therapeutic adjuvant in cancer radiotherapy, was tested for the reversibility of its inhibitory action on X-ray-induced DNA double strand break (dsb) repair. Cells were exposed to 40 Gy of X-rays and allowed to repair with or without 2-DG in suspension at 37 degrees C. DNA dsb rejoining was measured by pulsed field gel electrophoresis. The fraction of 14C-thymidine activity released from the plug (FAR) during electrophoresis was used as a measure for the number of dsb present in the DNA. After certain time intervals 2-DG was withdrawn from the cells and the extent of reversal of inhibition of dsb rejoining was measured. Biphasic repair of dsb was generally observed, with a fast component extending up to about 60 min after irradiation and a much slower progression of repair thereafter. Different mathematical models are considered for a quantitative description of these two components. The experimental data strongly indicate that only one type of dsb is primarily induced by irradiation which can be repaired fast with a time constant of about 0.05 min-1 (t1/2 approximately 13 min). In competition with this repair, other DNA dsb arise which are repaired slowly with a time constant of about 0.009 min-1 (t1/2 approximately 77 min). The time constant for the transformation of fast reparable dsb into slowly repaired dsb is about 0.026 min-1. Treatment with 2-DG inhibits the fast repair and, as a consequence, more DNA dsb are transformed into the type being repaired slowly. In competition with this slow repair, DNA dsb are fixed. Treatment with 2-DG also reduces slow repair processes and as a consequence the number of lesions being fixed is increased. Cell survival and ATP content of the cells showed a reversibility to the same extent as dsb repair, indicating the close relationship of these processes in living cells.

Animals↗
PubMed1993

The RBE of negative pions in the treatment of tumors with different volumes.

For negative pions, large differences exist between experimental RBE values obtained by in vivo investigations with animals and corresponding data being used in clinical tumor therapy. Therefore, the influence of the treatment volume on the radiation quality and respectively on the RBE is examined. The RBE for euoxic mammalian cells is measured with high precision in different volumes irradiated in the spot-scan mode with the PIOTRON at the Paul Scherrer Institute. It is shown experimentally that the RBE is reduced if the radius of the irradiation volume is increased. Using a simple mathematical approximation for the spot-scan technique this relation can be understood quantitatively. The same approximation is also used to calculate dose mean values for the lineal energy yD present in different irradiated volumes. The good agreement with existing experimental data for yD indicates that the approximation used is adequate and the main physical parameters have been taken into consideration. The above mentioned differences between animal experiments and treatment of patients can be explained by changes in the effective radiation quality due to the scanning procedure used in the clinical treatments.

Animals↗
PubMed1993

Tumor response to ionizing radiation and combined 2-deoxy-D-glucose application in EATC tumor bearing mice: monitoring of tumor size and microscopic observations.

The present study deals with the changes induced by two fractionation schedules (5 x 9 Gy and 10 x 4.5 Gy; 30 MeV-electrons) of ionizing radiations and 2-deoxy-D-glucose (2-DG) application on EATC tumor bearing swiss albino mice. The monitoring of tumor response was carried out by means of caliper measurement on the macroscopic level and by histopathological examination of tumor preparations stained with hematoxiline and eosine on the microscopic level. The tumor material was assessed at suitable intervals after treatment by killing the animals. The tumor response was analysed in the histological preparations and the thickness of the tumor band was determined quantitatively by an ocular micrometric technique. Tumor damage was most extensive in the combined treated animals (5 x 9 Gy + 2-DG). Only in this group local tumor control was achievable. The histological analysis of tumor preparations revealed additional data about treatment-induced changes in the tumor compared to the measurement of the tumor volume with mechanical calipers. We also found that the treatment outcome could be predicted from the histopathological analysis. It is concluded that studies involving histopathological examinations may give some insight into the way cancer is controlled by radiotherapy and may be of value in prognosis and selection of treatment in patients.

Animals↗
PubMed1992

Effect of 2-deoxy-D-glucose on DNA double strand break repair, cell survival and energy metabolism in euoxic Ehrlich ascites tumour cells.

Effects of 2-deoxy-D-glucose (2-DG) on DNA double strand break (dsb) repair, cell survival and on the energy metabolism were investigated in exponentially growing Ehrlich ascites tumour (EAT) cells. Cells in suspension were exposed to 40 Gy of X-rays and allowed to repair (up to 4 h) with or without 2-DG at 37 degrees C. DNA dsb rejoining was measured by means of clamped homogeneous electric field (CHEF), a pulsed field gel electrophoresis technique. The fraction of activity released (FAR) during electrophoresis (DNA associated 14C-thymidine) was used as a parameter to determine the number of dsb present in the DNA. Biphasic kinetics for dsb repair were observed. The presence of 2-DG significantly inhibited the slow component of dsb repair. The presence of 2-DG also enhanced radiation-induced cell killing. ATP content of cells was measured by a bioluminescence method. ATP content in exponentially growing cells was about 4 pg per cell. The level of ATP was reduced by 50% in presence of 2-DG (C2-DG/CG = 1.0).

Adenosine Triphosphate↗
PubMed1990

The RBE of euoxic and hypoxic Ehrlich ascites tumour cells irradiated with negative pions in vitro and in vivo.

Ehrlich ascites tumour cells (EAT-F5) were irradiated in vitro with the sparsely ionizing "plateau pions" and with the more densely ionizing "peak pions". From cell survival curves obtained under euoxic and hypoxic conditions, the RBE for the production of irreparable lethal and potentially lethal damage was derived. Cells of the same strain were used to produce solid tumours in the leg muscle of mice. Survival of these cells irradiated in vivo was compared with the corresponding in vitro data. It can be concluded that a large fraction of hypoxic cells is present in these tumours and that repair takes place in vivo at least as much as under the in vitro conditions. These solid tumours were irradiated with 5 dose fractions of fast protons as reference radiation, and the probability pT of tumour destruction was determined as a function of dose. Irradiation with a spot of "plateau pions" indicated the same pT as a function of dose, but side effects in the intestinal tract increased also with dose, leading to the death of the animals. The probability for avoiding these side effects in the animals, pS, was also determined. Using both values, pT and pS, the probability for local tumour control was estimated. Irradiation with "peak pions" resulted in an RBE of about 2.5 for tumour destruction corresponding to the RBE found in vitro for the production of irreparable lethal lesions in hypoxic cells. Side effects in the mouse gut showed a RBE of 2.0, corresponding to irreparable lethal lesions in euoxic in vitro cells.

Animals↗
PubMed1990

Repair inhibition in tumours irradiated with fast protons and negative pions.

Solid Ehrlich mouse tumours were irradiated in the 80 MeV proton beam of the Paul-Scherrer-Institute. The tumour volume was measured as a function of time after irradiation and two experimental endpoints were determined: local tumour control and minimal tumour volume after irradiation. The application of 2-deoxy-D-glucose (2-DG; 2 mg/kg) increased the radiation effect of protons by a factor of 1.4. The same tumour system was used with negative pions. Human tumours are usually irradiated with a mixed radiation produced by the "spot-scan-technique". This radiation quality was simulated in the mouse experiment by two successive irradiations with a spot of densely ionizing peak pions and a spot of sparsely ionizing plateau pions. Application of 2-DG raised the radiation effect due to the sparsely ionizing component again by a factor of 1.4. This indicates that clinical results in radiotherapy might be improved by application of 2-DG during the treatment.

Animals↗
PubMed1986

[Radiation biology risk of imaging procedures].

The environmental radiation burden of man in Germany is about 1 mGy (Milligray) per year. This is, of course, also valid for children. Due to diagnostical procedures this burden is increased to about 1.3 mGy. The question arises wether this can be neglected, or important consequences have to be drawn. To give a clear answer, the action of ionizing radiation in living cells and in organisms is explained in detail. Many of the radiation actions at the DNA can soon be repaired by the cell, if the radiation dose was small. Some damage, however will remain irreparable for the cell and consequently leads to cell death, to mutations or to cell transformation. The number of these lesion increases or decreases linearily with radiation dose. Therefore, it must be expected that the risk of tumour induction is increased to above the normal background even by the smallest doses. This small but not negligible risk has to be compared with other risks of civilization or with other medical risks. But also the benefit and the efficacy of diagnostic procedures have to be considered. A suitable cooperation of all medical doctors--not only of the radiologists--is recommended.

Cell Division↗
PubMed1984

Split-dose recovery explained quantitatively by repair of potentially lethal lesions.

It is known from experimental and theoretical considerations that the shoulder in the usual dose-survival curve for mammalian cells is due to repair of potentially lethal lesions (PLL). As a consequence, reappearance of the shoulder in a split-dose experiment should also be related to repair of PLL. A procedure for calculation of cell survival curves for split-dose irradiation is described which takes into consideration repair of PLL only. The reproduction of the shoulder with increasing time interval between the two dose fractions can be seen to take place with a time constant closely related to that of repair of PLL. Other quantitative parameters such as the dose dependence of this recovery time constant can be predicted quantitatively from the calculation.

Animals↗
PubMed1982

DNA double strand breaks in Ehrlich ascites tumour cells at low doses of x-rays. II. Can cell death be attributed to double strand breaks?

The induction and repair of DNA double strand breaks (dsb) in early stationary Ehrlich ascites tumour cells by X-rays was determined using an improved sedimentation technique in neutral sucrose gradients. The disappearance of dsb was followed during post-irradiation incubation of the cells and was interpreted as dsb repair. Kinetics were approximated by exponential functions with time constants of t37 = 3.0 +/- 0.7 hours ('conditioned' medium) and t37 = 2.0 +/- 0.5 hours (growth medium). Maximal repair was reached after 24 hours and the relationship of the remaining breaks with dose was interpreted on the basis of a recombination repair model. Using these dsb data and on the assumption of one dsb being a lethal event, cell survival curves were calculated for different repair times and compared with experimental curves. It was shown that cell survival curves can be interpreted on the basis of one unrepaired dsb being a lethal event, when dsb repair continues for about 11 hours after plating the cells on nutrient agar.

Animals↗
PubMed1979

Radiobiological data for clinical dosimetry in pion tumour therapy.

Ehrlich ascites tumour cells were irradiated with negative pions at different positions in the plateau and the peak of the depth absorbed dose curve. Dose-survival curves for immediate testing of the viability of the cells are given and are compared with other types of radiations in use for therapy. From the data obtained after repair of potentially lethal damage effective survival curves for fractionated irradiation are evaluated.

Animals↗
PubMed1979

Quantitative aspects of repair of potentially lethal damage in mammalian cells.

Stationary cultures of Ehrlich ascites tumour cells have been irradiated with X-rays and then immediately or after a time interval trep plated to measure the survival. The increase in survival observed after delayed plating is interpreted as repair of potentially lethal damage. A cybernetic model is used to analyse these data. Three states of damage are assumed for the cells. In state A the cells can grow to macrocolonies, in state B the cells have suffered potentially lethal damage and can grow to macrocolonies only if they are allowed to repair the damage and in state C the cells are lethally damaged. A method of deriving the values of the parameters of the model from the experimental data is given. The dependence of the reaction rate constant of the repair of potentially lethal damage on the dose D is used to derive a possible mechanism for the production of the shoulder in the dose effect curve. Finally this model is compared with other models of radiation action on living cells.

Animals↗
PubMed1977

Growth of cells on solid culture medium. II. Cell physiological data of stationary yeast cells and the initiation of cell cycle in nutrient free buffer solution.

For precise experiments with yeast (or other) cells stationary populations are produced by growth on the surface of a solid nutrient medium. The energy supply to these cells is well known from a former publication. The oxygen supply during growth is analysed here in detail. Different types of cell populations can be produced in this way dependent on the thickness of nutrient medium. If such cells are transferred into a liquid buffer solution cell multiplication can be initiated without any nutrient flux into the cell. This new type of initiation of the cell cycle of G1-cells has to be distinguished from the usual initiation by nutrient supply and from the mechanism of meiotic cell division. The dependence of this cell growth on cell volume, pH-value, oxygen concentration and osmotic pressure is analysed and possibilities to avoid this kind of cell multiplication reaction are discussed.

Cell Cycle↗
PubMed1977

Inhibition of unscheduled DNA synthesis and repair of potentially lethal X-ray damage by 2-deoxy-D-glucose in yeast.

The effects of the glucose antimetabolite, 2-deoxy-D-glucose (2-DG), on DNA repair (assayed by unscheduled DNA synthesis) and on the repair of potentially-lethal damage (assayed by cell viability after irradiation) have been studied in X-irradiated respiratory-deficient yeast cells (auxotroph for 5'-thymidine-monophosphate). Experimental results show that: (a) both these phenomena can be inhibited by 2-DG; (b) the repair of potentially-lethal damage occurs after the unscheduled DNA synthesis is almost complete; and (c) the repair of potentially-lethal damage can be inhibited by 2-DG even after the completion of the unscheduled DNA synthesis.

Cell Survival↗