Biomedical subjects

G Röpke

Publications and source records attributed to G Röpke.

At least 19 recordsLinked to original sources

PubMed2001

Dynamic structure factor for a two-component model plasma.

Analytical results for the structure factor of a two-component model plasma that describe an electron-ion plasma with modified interaction are derived from a Green function approach in different approximations. The random-phase approximation is improved by including the dynamic collision frequency, and results for the long-wavelength limit are extended to arbitrary wave numbers using the Mermin ansatz. After taking the classical limit of the resulting expressions, they are compared with molecular dynamics simulation results for the classical two-component model plasma.

Journal Article↗

PubMed2001

Alpha cluster condensation in 12C and 16O.

A new alpha-cluster wave function is proposed which is of the alpha-particle condensate type. Applications to 12C and 16O show that states of low density close to the 3 and 4 alpha-particle thresholds in both nuclei are possibly of this kind. It is conjectured that all self-conjugate 4n nuclei may show similar features.

Journal Article↗

PubMed2001

Isentropes and Hugoniot curves for dense hydrogen and deuterium.

Multiple-shock experiments with fluid hydrogen have shown that a transition from semiconducting behavior to metal-like conductivity occurs at pressures (p) of about 140 GPa and temperatures (T) near 3000 K. We model the p-T pathway by Hugoniot curves (initial shock) and isentropes (subsequent shocks). For the calculation of these curves we apply an expression for the free energy developed recently for dense hydrogen and deuterium plasma in the regions of partial dissociation and partial ionization. Furthermore, we discuss the relations between Hugoniot curves, isentropes and the coexistence line of the plasma phase transition.

Journal Article↗

PubMed2001

Short-time dynamics with initial correlations.

The short-time dynamics of correlated systems is strongly influenced by initial correlations, giving rise to an additional collision integral in the non-Markovian kinetic equation. Exact cancellation of the two integrals is found if the initial state is thermal equilibrium, which is an important consistency criterion. Analytical results are given for the time evolution of the correlation energy, which are confirmed by comparisons with molecular dynamics simulations.

Journal Article↗

PubMed2000

Efficient gene transfer into lymphoma cells using adenoviral vectors combined with lipofection.

Tumor cells, such as lymphoma cells, are possible targets for gene therapy. In general, gene therapeutic approaches require efficient gene transfer to host cells and sufficient transgene expression. However, lymphoma cells previously have been demonstrated to be resistant to most of the currently available gene transfer methods. The aim of this study was to analyze various methods for transfection of lymphoma cells and to improve the efficiency of gene delivery. In accordance with previously published reports, lymphoma cells were demonstrated to be resistant to lipofection and electroporation. In contrast, we present an improved adenoviral protocol leading to highly efficient gene transfer to lymphoma cell lines derived from B cells as well as primary lymphoma cells being achieved with an adenoviral vector system encoding the beta-galactosidase protein. At a multiplicity of infection of 200, up to 100% of Daudi cells and Raji cells and 70% of OCI-Ly8-LAM53 cells could be transfected. Even at high adenoviral concentrations, no marked toxicity was observed, and the growth characteristics of the lymphoma cell lines were not impaired. The transfection rates in primary cells derived from six patients with non-Hodgkin's lymphoma were 30-65%, respectively. Transfection efficiency could be further increased by addition of cationic liposomes to adenoviral gene transfer. Furthermore, we examined the expression of the Coxsackie-adenoviral receptor (CAR) and the integrin receptors on the lymphoma cell surface. Flow cytometric analysis showed that 88% of Daudi cells, 69% of Raji cells, and 6% of OCI-Ly8-LAM53 cells expressed CAR on the cell surface. According to our data, adenoviral infection of lymphoma cells seems to be mediated by CAR. In contrast, integrin receptors are unlikely to play a major role, because lymphoma cells were negative for alphavbeta3-integrins and negative for alphavbeta5-integrins. In conclusion, this study demonstrates that B-lymphoma cell lines and primary lymphoma cells can be efficiently transfected using an adenoviral vector system. By adding cationic liposomes, the efficiency of adenoviral gene transfer to primary tumor cells could be further improved. This protocol may have an impact on the use of lymphoma cells in cancer gene therapy.

Adenoviridae↗

PubMed2000

Increase in proliferation rate and normalization of TNF-alpha secretion by blockage of gene transfer-induced apoptosis in lymphocytes using low-dose cyclosporine A.

Efficient gene transfer of lymphocytes is extremely difficult. We have shown previously that induction of apoptosis may play a role in the gene transfer resistance of lymphocytes. Anti-CD3 antibody can be used as a surrogate for receptor-mediated gene transfer in T lymphocytes. However, anti-CD3 antibody has been shown to be the causative agent of apoptosis in receptor-mediated gene transfer. In this study, we show that blockage of apoptosis by addition of low-dose cyclosporine A can lead to normalization of elevated TNF-alpha secretion and to a significant increase in the proliferation rate of transfected lymphocytes. In contrast, this had no negative effect on cytotoxic activity of immunologic effector cells called cytokine-induced killer cells. Therefore, blockage of apoptosis should have an impact on the use of lymphocytes transfected with cytokine genes as immunologic effector cells in cancer gene therapy protocols.

Apoptosis↗

PubMed1999

Response function including collisions for an interacting fermion gas.

The response function of an interacting fermion gas is considered in the entire (k-->,omega) space. Applying a generalized linear response theory, it is expressed in terms of determinants of equilibrium correlation functions, which allow for a systematic perturbative treatment. The relation to dynamical local-field factors is given. As a special case, the dielectric function is evaluated for two-component (hydrogen) plasmas at arbitrary degeneracies. Collisions are treated in Born approximation leading to a (k-->,omega)-dependent collision integral. The link to the dynamical conductivity is given in the long-wavelength limit. Sum rules are discussed.

Journal Article↗

PubMed1999

TNF-alpha secretion and apoptosis of lymphocytes mediated by gene transfer.

Efficient gene transfer of lymphocytes is extremely difficult. Apoptosis may play a role in this gene transfer resistance of lymphocytes. Here we show that transfection of lymphocytes via non-viral vectors leads to induction of apoptosis in a significant proportion of cells. Since apoptosis may be mediated via tumor necrosis factor d (TNF-alpha) and the TNF-alpha receptor pathway, we studied the amount of TNF-alpha secreted by lymphocytes transfected without gene insert. TNF-alpha secretion was dependent on the gene transfer method used. High amounts were detected using receptor-mediated gene transfer and lipofection. In contrast, only low amounts of TNF-alpha were detected after electroporation and retroviral gene transfer. In receptor-mediated gene transfer, TNF-alpha secretion was due to the use of anti-CD3 antibody. Transfection of lymphocytes led to selective decrease in CD120b/TNF-alpha receptor II (TNFR-2)-positive cells. Induction of apoptosis and necrosis mediated by TNF-alpha via TNFR-2 (p80) was partially blocked using a neutralizing anti-TNF-alpha antibody. Blockage of apoptosis and necrosis could be further increased by adding anti-Fas-ligand (FasL) antibody, suggesting that induction of apoptosis via FasL and Fas receptor (Apo-1/CD95) may also play a role. This blockage led to a significant increase in the proliferation rate of lymphocytes transfected with cytokine genes. In conclusion, various gene transfer techniques led to TNF-alpha secretion, apoptosis and necrosis of lymphocytes. Apoptosis and necrosis could be partially blocked using a neutralizing anti-TNF-alpha antibody.

Antibodies, Monoclonal↗

PubMed1996